REVIEW Toxicological considerations of clinically applicable nanoparticlesucaptt0/toxicology-nanoparticles... · 2011. 12. 7. · Nanoparticles have a large surface area to volume

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Nano Today (2011) 6, 585—607

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REVIEW

Toxicological considerations of clinically applicablenanoparticles

Lara Yildirimera, Nguyen T.K. Thanhb,c,∗, Marilena Loizidoua,Alexander M. Seifaliana,d

a Centre for Nanotechnology & Regenerative Medicine, UCL Division of Surgery & Interventional Science, University CollegeLondon, London, UKb Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UKc The Davy Faraday Research Laboratory, The Royal Institution of Great Britain, 21 Albemarle Street, London W1S 4BS, UKd Royal Free Hampstead NHS Trust Hospital, London, UK

Received 24 July 2011; received in revised form 9 September 2011; accepted 21 October 2011

KEYWORDSNanoparticles;Toxicity;Polymeric;Carbon nanotubes;Silica;Silver;Gold;Quantum dots;Superparamagneticiron oxide;Route ofadministration;Administered dose;Pulmonary;Oral;Transdermal;Intravenous;Lung;Skin

Summary In recent years, nanoparticles (NPs) have increasingly found practical applicationsin technology, research and medicine. The small particle size coupled to their unique chemicaland physical properties is thought to underlie their exploitable biomedical activities. Here, wereview current toxicity studies of NPs with clinical potential. Mechanisms of cytotoxicity arediscussed and the problem of extrapolating knowledge gained from cell-based studies into ahuman scenario is highlighted. The so-called ‘proof-of-principle’ approach, whereby ultra-highNP concentrations are used to ensure cytotoxicity, is evaluated on the basis of two consider-ations; firstly, from a scientific perspective, the concentrations used are in no way related tothe actual doses required which, in many instances, discourages further vital investigations.Secondly, these inaccurate results cast doubt on the science of nanomedicine and thus, quitedangerously, encourage unnecessary alarm in the public. In this context, the discrepanciesbetween in vitro and in vivo results are described along with the need for a unifying protocolfor reliable and realistic toxicity reports.© 2011 Elsevier Ltd. All rights reserved.

∗ Corresponding author at: Department of Physics and Astronomy, University College London, Gower Street, London, WC1E 6BT, UK.Tel.: +44 2074916509.

E-mail address: [email protected] (N.T.K. Thanh).

1748-0132/$ — see front matter © 2011 Elsevier Ltd. All rights reserved.doi:10.1016/j.nantod.2011.10.001


586 L. Yildirimer et al.

Introduction

Nanoparticles have a large surface area to volume ratiowhich leads to an alteration in biological activity comparedto the parent bulk materials. In the past two decades,the use of nanoparticles (NPs) in experimental and clinicalsettings has risen exponentially due to their wide rangeof biomedical applications, for example in drug delivery,imaging and cell tracking [1—4]. This highlights the need toconsider not only the usefulness of NPs but also the poten-tially unpredictable and adverse consequences of humanexposure thereto. In this context, NP toxicity refers tothe ability of the particles to adversely affect the nor-mal physiology as well as to directly interrupt the normalstructure of organs and tissues of humans and animals. Itis widely accepted that toxicity depends on physiochemi-cal parameters such as particle size, shape, surface chargeand chemistry, composition, and subsequent NPs stability.The exact underlying mechanism is as yet unknown, how-ever, recent literature suggests cytotoxicity to be relatedto oxidative stress and pro-inflammatory gene activation[5—7]. Further to particle-related factors, the administereddose, route of administration and extent of tissue dis-tribution seem important parameters in nano-cytotoxicity.Typically, cell-based toxicity studies use increasing doses ofthe NP in order to observe dose-related cellular or tissu-lar toxicity. Such dose—response correlations are the basisfor determining safe limits of particle concentrations forin vivo administration. Despite the theoretically brilliantlogic, animal and human studies have taught us differentlyand highlighted the issue of the feasibility of correlatingorgan toxicity with the pre-determined dose; there existsa widely acknowledged problem of extrapolating in vitroconcentrations into in vivo scenarios which can be subdi-vided into two points; firstly, it has yet to be determinedhow efficiently any administered NP dose is reaching the tar-get tissue and secondly, NPs can induce biochemical changesin vivo which may have gone unnoticed in isolated cell-based studies. With the potentially disastrous consequencesin mind, new ways of predicting as yet unpredictable, non-dosage-dependent actions of NPs in vivo must be sought.Apart from the dosing issue, another, so far underexposedarea of nanotoxicity relates to the route of particle adminis-tration which may also, quite independently from the dose,influence toxicity in an adverse fashion. It is sensible toassume that biodistribution, accumulation, metabolism andexcretion of NPs will differ depending on the route of admin-istration as will its toxicity. So far, no reviews have focusedon the association between different routes of administra-tion and NP toxicity.

Substances may enter the body via oral ingestion,inhalation, dermal penetration and intravascular injectionand subsequently distribute to any organ system. Fig. 1summarizes the advantages and disadvantages of each ofthe routes. Pulmonary drug delivery shows tremendouspotential but concerns regarding local and systemic toxicitycurrently curb enthusiasm [8]. NP aggregation and subse-quent tissue inflammatory reactions have been postulatedto be the underlying mechanism [9—11]. Topically applicablesubstances such as sunscreen preparations and cosmeticsalready rely on the use of nano-formulations of titanium-and zinc-dioxide by exploiting their ultraviolet radiation

blocking ability. In the future, the penetrative capacity ofcertain NPs could be exploited for transdermal drug delivery.Therefore, the mechanistics of transition and potential der-mal or systemic toxicity need to be evaluated. Intravenousand oral NP administrations inherently have a more rapidsystemic effect compared to transdermal administrationand once within the circulation, most substances aresubject to first-pass metabolism within the liver where theymay accumulate or distribute via the vasculature to endorgans including the brain. Despite its innate protectionby the blood—brain-barrier (BBB) against external chemicalinsults, the potential for nanoparticulate matter to perco-late through tight junctions renders the brain vulnerableto potential particle-mediated toxicity. Reliable data on NPtoxicity is therefore necessary to avoid detrimental adverseeffects.

In this review, we aim to identify clinically relevantNPs and critically appraise organ-based toxicological studieswhich have been carried out on a cellular and pre-clinicallevel as well as on human volunteers. Furthermore, empha-sis will be placed upon the importance of particle size andthe route of administration with respect to toxicity as theauthors believe that the latter has not received adequateevaluation despite its fundamental importance with respectto the clinical setting.

Types of nanoparticles for clinical applications

NPs have a vast potential in the medical arena as drugand gene delivery vehicles, fluorescent labels and contrastagents [1,12]. For a particle to qualify as a ‘‘true’’ NP, atleast one of its material dimensions must lie within the sizerange of 1—100 nm. The use of NPs as carrier systems fordrugs, particularly chemotherapeutic drugs, is gaining inpopularity due to the ability to specifically target cancercells, enhance efficacy and reduce systemic toxicity. GoldNPs (AuNP) show several advantageous properties includinga non-toxic and biocompatible metal core making them anideal starting point for nanocarrier systems [13]. Further-more, AuNP can undergo multiple surface functionalizationscombining different moieties such as drugs and targetingagents which renders them a highly versatile tool for target-ing [14] (Fig. 3). Other drug nano-vehicles which are alreadyin clinical use include lipid-based [15], polymer-based [16]and biological NPs [17]. Quantum dots (QDs), or semiconduc-tor nanocrystals, are another type of NPs which enjoy a widerange of potential clinical applications including cell label-ing, in vivo imaging and diagnostics [18]. Due to the QD’sexceptional photophysical properties such as broad absorp-tion spectra coupled to a narrow emission spectrum, QDsof different emission colors may be simultaneously excitedby a single wavelength, thus enabling multiplexed detec-tion of molecular targets [19]. Other fluorescent labels usedin medical research include magnetic NPs such as super-paramagnetic iron oxide nanoparticles (SPIONs) [20]. SPIONsare one of the few clinically approved metal oxide NPs andfind ubiquitous applications in the biomedical field such asmagnetic resonance imaging (MRI) [21], drug [22] and genedelivery [23] and hyperthermic destruction of tumor tissue[22]. Their superparamagnetism confers several advantages:firstly, the ability to be guided by means of an externalmagnetic field may be exploited in targeted imaging or


Toxicological considerations of clinically applicable nanoparticles 587

Figure 1 Routes of administration of nanoparticles and their advantages and disadvantages.

drug delivery systems; secondly, the production of cytotoxicheat when subjected to alternating magnetic fields couldbe utilized in cancer treatments [24]. A different modalityof exposure to metal oxide NPs comprises that of topi-cally applicable formulations such as creams and sunscreenlotions containing titanium dioxide and zinc oxide NPs [25].Here, it is important to determine whether NPs can pen-etrate deeper into skin layers and possibly be absorbedinto the systemic circulation and accumulate in tissues.Nanoscaled silver (AgNP) became popular for its markedantimicrobial effect which is successfully exploited in medi-cal applications such as silver-impregnated wound dressings,contraceptive devices, surgical instruments and bone pros-theses [26—29]. Carbon nanotubes are made from rolled upsheets of graphene and are classified as single-walled (SWC-NTs) or multi-walled carbon nanotubes (MWCNTs) dependingon the constituent numbers of graphene layers. Due to theirunique size and shape, much effort has been dedicated toanalyzing biomedical applications of CNTs. Such extensivepotential requires the meticulous evaluation of toxicity.

This widespread use of different types of NPs in thebiomedical field raises concerns over their increasing access

to tissues and organs of the human body and, consequently,the potential toxic effects. Various studies evaluatingin vitro and in vivo absorption, distribution and biocom-patibility of NPs have been reviewed and are criticallyappraised in this article. Fig. 2 shows a summary ofbiologically important nanoparticles and their possibleroutes of administration (adapted from reference [30]).

Toxicological profiling in cell based targets,animal targets and human volunteers

Due to their small size and physical resemblance to physio-logical molecules such as proteins, NPs possess the capacityto revolutionise medical imaging, diagnostics, therapeuticsas well as carry out functional biological processes. Butthese features may underlie their toxicity. Also, depend-ing on the mode of administration and sites of deposition,toxicity may vary in severity. Therefore, to maintain clini-cal relevance, information on toxicity is presented using asystem-based approach focusing on experimental lung, der-mal, liver and brain targets (see Table 1).



Tabl

e1

Sum

mar

yof

invi

tro

and

invi

voev

alua

tion

sof

nano

part

icle

toxi

city

.

Targ

etN

anop

arti

cle

Conj

ugat

ion

Conc

entr

atio

n(t

ime/

size

)/ro

ute

ofad

min

istr

atio

n

Cellu

lar

targ

etAn

imal

targ

etM

ajor

outc

omes

Ref.

Lung

PLG

AN

PCh

itos

an30

0-50

00�

g/m

L(4

h)A5

49hu

man

lung

canc

erce

lls

Non

-tox

icev

enat

high

est

conc

entr

atio

ns.

[31]

Solid

lipid

NP

500

�g/

mL

(24

h)A5

49hu

man

lung

canc

erce

lls

No

infl

amm

ator

ych

ange

sin

lung

pare

nchy

ma

atth

ecr

itic

alco

ncen

trat

ion

of50

0�

g/m

L.Co

ncen

trat

ions

low

erth

an20

0�

g/m

Lar

eth

ough

tto

besa

fe.

[32]

SWCN

T1.

56-8

00�

g/m

L(2

4h)

A549

hum

anlu

ngca

ncer

cells

Low

acut

ecy

toto

xici

tyw

asfu

rthe

rre

duce

dby

disp

ersi

onof

SWCN

Tsin

seru

m.

[33]

SWCN

T1

or5

mg/

kg(2

4h,

1w

eek,

1m

onth

,3

mon

ths)

Intr

atra

chea

lin

still

atio

n

Spra

gue-

Daw

ley

rats

Mor

talit

yin

15%

ofan

imal

saf

ter

24h

expo

sure

tohi

ghes

tdo

sedu

eto

phys

ical

bloc

kage

ofai

rway

sra

ther

than

acut

ein

flam

mat

ion.

Mul

tifo

cal

gran

ulom

atou

sch

ange

onhi

stol

ogy

-ap

pare

ntly

nore

lati

onto

dose

orti

me.

No

infl

amm

ator

ych

ange

.

[10]

SWCN

T1.

5m

g/kg

(30

days

)In

trat

rach

eal

inst

illat

ion

C57B

l/6

mic

eSi

gnifi

cant

redu

ctio

nin

infl

amm

ator

yan

dfib

roti

cch

ange

saf

ter

expo

sure

ofse

rum

-dis

pers

edpa

rtic

les

rela

tive

toth

eno

n-di

sper

sed

pend

ent.

Toxi

city

isat

trib

utab

leto

part

icle

aggr

egat

ion

rath

erth

anph

ysio

chem

ical

prop

erty

ofin

divi

dual

nano

tube

.

[9]

SWCN

TPE

G47

mg

onda

ys0

and

7(f

ollo

w-u

p:4

mon

ths)

Intr

aven

ous

infu

sion

Nud

em

ice

No

sign

ifica

ntin

flam

mat

ory

chan

ges

wer

eob

serv

ed,

how

ever

,pa

rtic

lede

posi

tion

inliv

erm

acro

phag

esw

asob

serv

ed.

[34]


Toxicological considerations of clinically applicable nanoparticles 589Ta

ble

1(C

onti

nued

)

Targ

etN

anop

arti

cle

Conj

ugat

ion

Conc

entr

atio

n(t

ime/

size

)/ro

ute

ofad

min

istr

atio

n

Cellu

lar

targ

etAn

imal

targ

etM

ajor

outc

omes

Ref.

MW

CNT

0.5,

2or

5m

g/an

imal

(3an

d15

days

)In

trat

rach

eal

inst

illat

ion

Spra

gue-

Daw

ley

rats

Dos

e-de

pend

ent

incr

ease

inin

flam

mat

ory

mar

kers

post

-BAL

.D

ose-

depe

nden

tfib

roti

cch

ange

and

inte

rsti

tial

gran

ulom

afo

rmat

ion.

[11]

MW

CNT

0.2,

0.5

or2.

7m

g/kg

(7,

14da

ys)

Inha

lati

on

C57B

L/6

mic

eU

nifo

rmpa

rtic

leup

take

bypu

lmon

ary

mac

roph

ages

.N

oin

flam

mat

ory

orfib

roti

cch

ange

sw

ere

obse

rved

.

[35]

Silic

aN

P10

-100

�g/

mL

(24

h,48

han

d72

h)A5

49hu

man

lung

canc

erce

lls

Dos

e-an

dti

me-

depe

nden

tde

crea

sein

cell

viab

ility

:up

to50

%re

duct

ion

athi

ghes

tdo

sage

afte

r72

h.O

xida

tive

stre

ssin

dica

ted

asm

echa

nism

ofcy

toto

xici

ty.

[36]

Silic

aN

P5,

10,

20,

50or

100

�g/

mL

(24

h)Pr

imar

ym

ouse

embr

yofib

robl

asts

(BAL

B/3T

3)

Dos

e-de

pend

ent

redu

ctio

nin

cell

viab

ility

.Ex

cess

ive

ROS

gene

rati

onan

dG

SHde

plet

ion

sugg

est

oxid

ativ

ece

llda

mag

eas

the

unde

rlyi

ngm

echa

nism

ofcy

toto

xici

ty.

[37]

Silic

aN

P25

�g/

mL

(24

h)A5

49hu

man

lung

canc

erce

llsH

epG

2ce

llsRP

MI2

650

hum

anna

sal

sept

alep

ithe

lialc

ells

N2a

mou

sene

urob

last

cells

Nuc

lear

prot

ein

aggr

egat

ion

and

subs

eque

ntin

terf

eren

cew

ith

gene

expr

essi

onre

sult

ing

inin

hibi

tion

ofre

plic

atio

n,tr

ansc

ript

ion

and

cell

prol

ifer

atio

n.

[38]

Silic

aN

P0-

185

�g/

mL

(24

h)A5

49hu

man

lung

canc

erce

llsEA

HY9

26en

doth

elia

lce

llsJ7

74m

onoc

yte

mac

roph

ages

Dos

e-de

pend

ent

incr

ease

incy

toto

xici

ty.

[39]


590 L. Yildirimer et al.Ta

ble

1(C

onti

nued

)

Targ

etN

anop

arti

cle

Conj

ugat

ion

Conc

entr

atio

n(t

ime/

size

)/ro

ute

ofad

min

istr

atio

n

Cellu

lar

targ

etAn

imal

targ

etM

ajor

outc

omes

Ref.

Silic

aN

P33

-47

�g/

cm2

(sm

all

NP)

,89

-254

�g/

cm2

(lar

ger

NP)

(24

h)

EAH

Y926

endo

thel

ial

cells

Size

-dep

ende

ntre

duct

ion

invi

abili

tyw

ith

smal

ler

part

icle

sin

the

nano

scal

eex

hibi

ting

high

erto

xici

tyco

mpa

red

topa

rtic

les

>100

nm.

[40]

Silic

aN

P20

mg/

anim

al(1

or2

mon

ths)

Intr

atra

chea

lin

still

atio

n

Wis

tar

rats

Nan

o-si

zed

silic

apa

rtic

les

prod

uced

rela

tive

lylo

wer

pulm

onar

yfib

rosi

sco

mpa

red

tom

icro

-siz

edsi

lica

part

icle

s.Th

isis

thou

ght

tobe

due

toth

etr

ansl

ocat

ion

oful

trafi

nena

nosi

lica

away

from

the

lung

pare

nchy

ma.

[41]

Silv

erN

P75

0�

g/m

3(4

hfo

r2

wee

ks)

Inha

lati

on

Spra

gue-

Daw

ley

rats

No

sign

ifica

ntch

ange

sin

lung

func

tion

and

body

wei

ght

inex

pose

dgr

oups

com

pare

dto

fres

hai

rco

ntro

ls.

[42]

Silv

erN

P61

�g/

m3

(6h/

day,

5da

ys/w

eek

for

4w

eeks

)In

hala

tion

Spra

gue-

Daw

ley

rats

No

sign

ifica

ntcl

inic

alch

ange

sor

chan

ges

inha

emat

olog

yan

dbl

ood

bioc

hem

ical

valu

es.

[43]

Silv

erN

P51

5�

g/m

3(6

h/da

y,5

days

/wee

kfo

r13

wee

ks)

Inha

lati

on

Spra

gue-

Daw

ley

rats

Dos

e-an

dti

me-

depe

nden

tin

crea

sein

bloo

dAg

nano

part

icle

conc

entr

atio

nw

asob

serv

edal

ong

wit

hco

rrel

atin

gin

crea

ses

inal

veol

arin

flam

mat

ion

and

smal

lgra

nulo

mat

ous

lesi

ons.

[44]

Der

mal

Silv

erN

P50

and

100

�g/

mL

(24

h)N

IH3T

3(m

ouse

fibro

blas

ts)

Mit

ocho

ndri

a-de

pend

ent

cellu

lar

apop

tosi

sas

soci

ated

wit

hRO

Sat

aco

ncen

trat

ion

of≥5

0�

g/m

L.

[45]

Silv

erN

P0.

76-5

0�

g/m

L(2

4h)

A431

(hum

ansk

inca

rcin

oma)

No

evid

ence

for

cellu

lar

dam

age

upto

aco

ncen

trat

ion

of6.

25�

g/m

L.M

orph

olog

ical

chan

ges

atco

ncen

trat

ions

betw

een

6.25

and

50�

g/m

Lw

ith

conc

omit

ant

rise

inG

SH,

SOD

and

lipid

pero

xida

tion

.D

NA

frag

men

tati

onsu

gges

tsce

llde

ath

byap

opto

sis.

[46]



ble

1(C

onti

nued

)

Targ

etN

anop

arti

cle

Conj

ugat

ion

Conc

entr

atio

n(t

ime/

size

)/ro

ute

ofad

min

istr

atio

n

Cellu

lar

targ

etAn

imal

targ

etM

ajor

outc

omes

Ref.

Silv

erN

P0-

1.7

�g/

mL

(24

h)H

EKce

llsSi

gnifi

cant

dose

-dep

ende

ntde

crea

sein

cell

viab

ility

ata

crit

ical

conc

entr

atio

nof

1.7

�g/

mL

wit

hco

ncom

itan

tri

sein

infl

amm

ator

ycy

toki

nes

(IL-

1�,

IL-6

,IL

-8,

and

TNF-

�).

[47]

0.34

-34.

0�

g/m

L(1

4co

nsec

utiv

eda

ys)

Porc

ine

skin

No

gros

sir

rita

tion

sm

acro

scop

ical

ly.

Ult

rast

ruct

ural

obse

rvat

ions

reve

aled

area

sof

foca

lin

flam

mat

ion

and

loca

lizat

ion

ofAg

NPs

inst

ratu

mco

rneu

mof

the

skin

.Si

lver

NP

Silv

er-c

oate

dw

ound

dres

sing

‘Act

icoa

t’(1

wee

k)

Hum

anbu

rns

pati

ent

Reve

rsib

lehe

pato

toxi

city

and

argy

ria-

like

disc

olor

atio

nof

trea

ted

area

ofsk

in,

elev

ated

plas

ma

and

urin

esi

lver

conc

entr

atio

nsan

din

crea

sed

liver

enzy

mes

.

[48]

TiO

2N

P15

�g/

cm2

(24

h)H

aCaT

(ker

atin

ocyt

ece

lllin

e),

hum

ande

rmal

fibro

blas

ts,

hum

anim

mor

taliz

edse

bace

ous

glan

dce

lllin

e(S

Z95)

Cyto

toxi

city

was

obse

rved

affe

ctin

gce

llula

rfu

ncti

ons

such

asce

llpr

olif

erat

ion,

diff

eren

tiat

ion

and

mob

ility

resu

ltin

gin

apop

tosi

s.

[49]

TiO

2N

P2

mg/

cm2

suns

cree

nap

plie

dto

vola

rfo

rear

m5×

onda

ys1,

2an

d3;

1×on

day

4(t

ape

stri

ppin

g1

hpo

stre

peti

tive

appl

icat

ion

ofsu

nscr

een)

Hum

anvo

lunt

eers

Tape

-str

ippi

ngre

veal

edno

nano

part

icle

sin

the

deep

erla

yers

ofth

est

ratu

mco

rneu

m.

Smal

lam

ount

sof

NP

(<1%

ofto

tala

mou

ntof

suns

cree

nap

plie

d)co

uld

only

beid

enti

fied

wit

hin

pilo

seba

ceou

sor

ifice

s.

[50]



Tabl

e1

(Con

tinu

ed)

Targ

etN

anop

arti

cle

Conj

ugat

ion

Conc

entr

atio

n(t

ime/

size

)/ro

ute

ofad

min

istr

atio

n

Cellu

lar

targ

etAn

imal

targ

etM

ajor

outc

omes

Ref.

TiO

2N

PN

Pco

ntai

ning

suns

cree

nH

uman

volu

ntee

rsIn

crea

sed

skin

perm

eati

onof

NP

whe

nsu

nscr

een

was

appl

ied

atha

iry

skin

ofhu

man

volu

ntee

red.

[51]

TiO

2N

P2

mg/

cm2

suns

cree

nap

plie

dto

exte

rnal

surf

ace

ofup

per

arm

(tap

est

ripp

ing

5h

post

appl

icat

ion

ofsu

nscr

een)

Hum

anvo

lunt

eers

>90%

ofsu

nscr

een

reco

vere

din

first

15ta

pest

ripp

ings

.Re

mai

ning

10%

did

not

pene

trat

ein

tovi

able

tiss

ue.

[52]

Silic

aN

P70

,30

0an

d10

00nm

insi

zeXS

52(m

urin

eLa

nger

hans

cells

)

Size

-rel

ated

toxi

city

wit

hfa

ster

cellu

lar

upta

keof

smal

ler

part

icle

san

dco

ncom

itan

thi

gher

toxi

city

.

[53]

Silic

aN

P30

-300

�g/

mL

(48

h)CH

K(h

uman

kera

tino

cyte

s)Re

duce

dce

llvi

abili

ty.

[54]

500

�g/

mL

(5or

18h)

HSE

MN

oir

rita

tion

at50

0�

g/m

L.50

0�

g/m

L(2

4an

d72

h)In

vivo

rabb

itm

odel

(Dra

ize

skin

irri

tati

onte

st)

No

eryt

hem

aor

oede

ma

form

atio

nob

serv

ed-

even

onta

pe-u

ntre

ated

anim

als.

Gol

dN

P95

,14

2an

d19

0�

g/m

L(1

3nm

)13

,20

and

26�

g/m

L(4

5nm

)(3

or6

days

)

CF-3

1(h

uman

derm

alfib

robl

asts

)

Cyto

toxi

city

was

size

-an

ddo

se-d

epen

dent

.La

rger

part

icle

s(4

5nm

)ex

hibi

ted

grea

ter

toxi

city

atsm

alle

rdo

ses

(10

�g/

mL)

com

pare

dto

smal

ler

ones

(13

nm)

whi

chon

lyex

hibi

ted

cyto

toxi

city

ata

conc

entr

atio

nof

75�

g/m

L.

[55]

Gol

dN

P0.

8-15

nmin

size

(48

h)SK

-Mel

-28

(mel

anom

ace

lls),

L929

mou

sefib

robl

asts

Max

imum

cyto

toxi

city

wit

hsm

alle

rN

P(1

.4nm

)ch

arac

teri

zed

byap

opto

sis

and

necr

osis

.

[56]

Gol

dN

PCi

trat

e0-

0.8

�g/

mL

(14

nmin

size

)(2

,4

or6

days

)H

uman

derm

alfib

robl

asts

Dos

e-de

pend

ent

redu

ctio

nin

cell

prol

ifer

atio

n.[5

7]



ble

1(C

onti

nued

)

Targ

etN

anop

arti

cle

Conj

ugat

ion

Conc

entr

atio

n(t

ime/

size

)/ro

ute

ofad

min

istr

atio

n

Cellu

lar

targ

etAn

imal

targ

etM

ajor

outc

omes

Ref.

Gol

dN

P15

,10

2an

d19

8nm

insi

zeEx

cise

dab

dom

inal

skin

ofW

ista

rra

ts

Size

-dep

ende

ntpe

rmea

tion

thro

ugh

rat

skin

wit

hsm

alle

stN

Pha

ving

deep

erti

ssue

pene

trat

ion

[58]

Live

rG

old

NP

Imm

unog

enic

pept

ides

:•

pFM

DV

•pH

5N1

8m

g/kg

/wee

k(3

-100

nmin

size

)(4

wee

ks)

Intr

aper

iton

eal

BALB

/Cm

ice

Nak

edN

P:se

vere

adve

rse

effe

cts

wit

hre

sult

ant

deat

hw

ith

part

icle

sra

ngin

gfr

om8

to37

nmin

diam

eter

.M

icro

scop

ical

ly,

Kupf

fer

cell

acti

vati

onin

the

liver

and

lung

pare

nchy

mal

dest

ruct

ion

was

obse

rved

.Su

rfac

em

odifi

edN

P:el

icit

edin

crea

sed

host

imm

une

resp

onse

and

impr

oved

cyto

com

pati

bilit

y.

[59]

Gol

dN

PPE

G0.

17,

0.85

and

4.26

mg/

kgbo

dyw

eigh

t(1

3nm

insi

ze)

(30

min

afte

rin

ject

ion

for

7da

ys)

Intr

aven

ous

BALB

/Cm

ice

NPs

wer

efo

und

toac

cum

ulat

ein

liver

and

sple

en.

Sign

ifica

ntup

regu

lati

onof

infl

amm

ator

ycy

toki

nes

(IL-

1,6,

10an

dTN

F-�

)w

ith

subs

eque

ntap

opto

sis

ofhe

pato

cyte

sat

high

est

conc

entr

atio

ns(4

.26

mg/

kg).

No

sign

ifica

ntch

ange

sin

the

liver

atlo

wer

dose

s.

[60]

Gol

dN

PPE

G4.

26m

g/kg

(4an

d10

0nm

insi

ze)

(30

min

)In

trav

enou

s

BALB

/Cm

ice

Both

4an

d10

0nm

size

dgo

ldN

Pup

regu

late

dge

nes

resp

onsi

ble

for

infl

amm

atio

n,ap

opto

sis

and

cell

cycl

e.

[61]

Gol

dN

P0.

14-2

.2m

g/kg

(13.

5nm

insi

ze)

(14-

28da

ys)

Per

oral

,in

trap

erit

onea

lor

intr

aven

ous

Hig

hest

toxi

city

was

foun

dw

ith

oral

and

i.p.

adm

inis

trat

ion

whe

reas

low

est

toxi

city

was

seen

wit

hta

ilve

inin

ject

ion.

[62]

Silv

erN

P30

or12

0�

g/m

Ldi

sper

sed

infis

hta

nk(2

4h)

Zebr

afish

Oxi

dati

vest

ress

-med

iate

dto

xici

tydu

eto

free

Ag+

liber

atio

n.In

duct

ion

ofpr

o-ap

opto

tic

sign

als

inliv

erti

ssue

s.

[63]

Silv

erN

P23

.8,

26.4

or27

.6�

g/m

Lsi

ngle

orre

peat

edad

min

istr

atio

n(2

0,80

and

110

nm,

resp

ecti

vely

),on

ceda

ilyfo

r5

cons

ecut

ive

days

(1,

3,5

days

)In

trav

enou

s

Wis

tar

rats

Size

-rel

ated

tiss

ueup

take

wit

hsm

alle

rN

P(2

0nm

)sh

owin

ghi

gher

conc

entr

atio

nsin

orga

nsth

anla

rger

ones

.Ac

cum

ulat

ion

ofN

Paf

ter

repe

ated

adm

inis

trat

ion

has

impl

icat

ions

for

tiss

ueto

xici

ty.

[64]



Tabl

e1

(Con

tinu

ed)

Targ

etN

anop

arti

cle

Conj

ugat

ion

Conc

entr

atio

n(t

ime/

size

)/ro

ute

ofad

min

istr

atio

n

Cellu

lar

targ

etAn

imal

targ

etM

ajor

outc

omes

Ref.

Silv

erN

P6.

25-1

00�

g/m

Lfo

rpr

imar

yfib

robl

asts

and

12.5

-200

�g/

mL

for

prim

ary

liver

cells

(7-2

0nm

size

dsp

here

s)(2

4h)

Prim

ary

mou

sefib

robl

asts

,pr

imar

yhe

pato

cyte

s

NP

ente

rce

llsw

hich

resu

lts

inth

epr

oduc

tion

ofm

edia

tors

ofox

idat

ive-

stre

ss.

How

ever

,pr

otec

tive

mec

hani

sms

coul

dbe

obse

rved

whi

chin

crea

seG

SHpr

oduc

tion

toav

oid

oxid

ativ

eda

mag

e.

[65]

Silic

aN

P0.

001

�g/

mL

(1,

3,7,

15,

and

30da

ys)

Intr

aven

ous

ICR

mic

ePr

inci

ple

end-

orga

nsfo

rN

Pac

cum

ulat

ion

wer

eliv

er,

sple

enan

dlu

ngs.

Mon

onuc

lear

cell

infil

trat

ion

athe

pati

cpo

rtal

area

and

hepa

tocy

tene

cros

isw

ere

obse

rved

.

[66]

Silic

aN

P50

mg/

kg(5

0,10

0or

200

nmin

size

)(1

2,24

,48

and

72h,

7da

ys)

Intr

aven

ous

BALB

/Cm

ice

Size

-dep

ende

nthe

pati

cto

xici

tyw

ith

infl

amm

ator

yce

llin

filtr

ates

.M

acro

phag

e-m

edia

ted

frus

trat

edph

agoc

ytos

isof

larg

erN

P(1

00an

d20

0nm

)re

sult

edin

rele

ase

ofpr

o-in

flam

mat

ory

cyto

kine

san

dce

llin

filtr

ates

wit

hin

hepa

tic

pare

nchy

ma.

[67]

Silic

aN

PPE

G2

mg/

kg(2

0-25

nmin

size

)(2

4h)

Intr

aven

ous

Nud

em

ice

Gre

ates

tac

cum

ulat

ion

ofN

Pin

liver

,sp

leen

and

inte

stin

esbu

tno

path

olog

ical

chan

ges

wer

eob

serv

edw

ith

smal

lNP

(<25

nm).

Nea

r-to

tal

excr

etio

nof

NP

via

the

hepa

tobi

liary

syst

em.

[68]

Silic

aN

P10

-100

mg/

kg(7

0,30

0or

1000

nmin

size

)In

trav

enou

s

BALB

/Cm

ice

Sign

ifica

nthe

pato

toxi

city

(deg

ener

ativ

ene

cros

isof

hepa

tocy

tes)

was

obse

rved

wit

hsm

alle

rN

P(<

100

nm)

whe

reas

nopa

thol

ogic

alch

ange

sw

ere

seen

wit

hla

rger

part

icle

s(3

00or

1000

nm),

even

atre

lati

vely

high

erco

ncen

trat

ions

ofN

P(1

00m

g/kg

).

[69]

CdSe

QD

±ZnS

shel

l62

.5,

250

and

1000

�g/

mL

(24

h)Pr

imar

yra

the

pato

cyte

sCy

toto

xici

tyw

asth

ough

tto

bedu

eto

the

rele

ase

offr

eeca

dmiu

mio

nsw

hich

coul

dno

tbe

fully

elim

inat

edby

ZnS

coat

ing

ofth

eO

Dco

re.

[70]



ble

1(C

onti

nued

)

Targ

etN

anop

arti

cle

Conj

ugat

ion

Conc

entr

atio

n(t

ime/

size

)/ro

ute

ofad

min

istr

atio

n

Cellu

lar

targ

etAn

imal

targ

etM

ajor

outc

omes

Ref.

CdSe

TeO

DZn

Ssh

ell

PEG

40pm

ol(1

8.5

nmin

size

)(1

,4

and

24h;

3,7,

14an

d28

days

)In

trav

enou

s

ICR

mic

eEx

trav

asat

ion

ofsm

allQ

D(<

20nm

)vi

ahe

pati

cca

pilla

ryfe

nest

rae

(∼10

0nm

)an

dde

posi

tion

wit

hin

liver

pare

nchy

ma.

[71]

CdSe

QD

ZnS

shel

l62

.5,

100

and

250

�g/

mL

(24,

48or

72h)

Hep

G2

cells

Dos

e-de

pend

ent

cyto

toxi

city

.In

extr

eme

cond

itio

ns(2

50�

g/m

Lfo

r72

h)a

redu

ctio

nin

cell

viab

ility

ofal

mos

t40

%w

asob

serv

edw

hich

corr

elat

edw

ith

anin

crea

sein

free

cadm

ium

ion

conc

entr

atio

nof

1.51

ppm

.

[72]

CdTe

/CdS

eQ

DZn

Ssh

ell+

eith

erof

the

follo

win

g:•

orga

nic

coat

ing

•CO

OH

•N

H2

•PE

G

20,

40or

80nM

(2,

4,24

and

48h)

J774

.A1

(mur

ine

‘mac

roph

age-

like’

cells

)

Rega

rdle

ssof

coat

ing,

allQ

Din

duce

dsi

gnifi

cant

cyto

toxi

city

afte

r48

has

mea

sure

dby

cell

viab

ility

and

LDH

rele

ase.

[73]

Brai

nG

old

NP

0.8-

50�

g/m

L(3

,5,

7,10

,30

and

60nm

)(2

4h)

rBM

EC(p

rim

ary

rat

brai

nm

icro

vess

elen

doth

elia

lce

lls)

No

mor

phol

ogic

alch

ange

sco

uld

bede

tect

edaf

ter

24h

sugg

esti

ngcy

toco

mpa

tibi

lity

ofth

eN

Pte

sted

.O

nly

the

smal

lest

NP

test

ed(3

nm)

indu

ced

mild

sign

sof

cellu

lar

toxi

city

.

[74]

Gol

dN

P(1

2.5

nmin

size

)(4

0,20

0or

400

�g/

kg/d

ayfo

r8

days

)In

trap

erit

onea

l

C57/

BL6

mic

eSm

alla

mou

nts

ofN

Pw

ere

able

tocr

oss

the

BBB

but

did

not

indu

ceev

iden

tne

urot

oxic

ity.

[75]

Silv

erN

P6.

25-5

0�

g/m

L(2

5,40

or80

nmin

size

)(2

4h)

rBM

EC(p

rim

ary

rat

brai

nm

icro

vess

elen

doth

elia

lce

lls)

Tim

e-an

ddo

se-d

epen

dent

incr

ease

inpr

o-in

flam

mat

ory

cyto

kine

rele

ase

and

corr

elat

ing

incr

ease

sin

perm

eabi

lity

and

cyto

toxi

city

ofce

lls.

[76]

Silv

erN

P10

,25

or50

�g/

mL

(1h)

Wis

tar

rat

tiss

uean

dho

mog

enat

es

Invi

tro

acti

viti

esof

mit

ocho

ndri

alre

spir

ator

ych

ain

com

plex

esI,

II,III

,an

dIV

wer

ede

crea

sed

inth

ebr

ain

and

othe

rti

ssue

sth

usin

crea

sing

the

pote

ntia

lfor

oxid

ativ

est

ress

-ind

uced

cell

dam

age.

[77]



Tabl

e1

(Con

tinu

ed)

Targ

etN

anop

arti

cle

Conj

ugat

ion

Conc

entr

atio

n(t

ime/

size

)/ro

ute

ofad

min

istr

atio

n

Cellu

lar

targ

etAn

imal

targ

etM

ajor

outc

omes

Ref.

Silv

erN

P30

,30

0or

1000

mg/

kg/d

ayfo

r28

days

(60

nmin

size

)Pe

ror

al

Spra

gue-

Daw

ley

rats

Dos

e-de

pend

ent

accu

mul

atio

nof

NP

was

obse

rved

inth

ebr

ain

and

othe

ror

gans

sugg

esti

ngsy

stem

icdi

stri

buti

onaf

ter

oral

adm

inis

trat

ion.

ALP

and

chol

este

roli

ncre

ased

sign

ifica

ntly

inhi

gh-d

ose

grou

p(1

000

mg/

kg/d

ay)

indi

cati

nghe

pato

toxi

city

.

[78]

Silv

erN

P0.

03,

0.1

or0.

3�

M(4

hpf

-5da

yspf

)Ze

brafi

shem

bryo

sN

euro

beha

viou

rala

bnor

mal

itie

sw

ere

obse

rved

inad

ult

zebr

afish

wit

hin

crea

sed

DA

and

5HT

turn

over

inpr

evio

usly

expo

sed

embr

yos

seco

ndar

yto

alte

red

syna

ptic

func

tion

ing.

[79]

(U)S

PIO

N20

8or

1042

�g/

mL

of:

•Fe

rum

oxtr

an-1

0(2

0-50

nm)

•Fe

rum

oxyt

ol(2

0-50

nm)

•Fe

rum

oxid

e(6

0-18

5nm

)(3

mon

ths)

Intr

acer

ebra

lin

ocul

atio

nor

Intr

a-ar

teri

alaf

ter

BBB

disr

upti

on

Long

Evan

sra

tsD

irec

tin

ocul

atio

nof

all3

SPIO

Nag

ents

resu

lted

inth

eup

take

into

the

CNS

pare

nchy

ma.

No

path

olog

ical

chan

ges

wer

ede

tect

ed.

[80]

CdSe

QD

ZnS

shel

lCa

ptop

ril(

cap)

conj

ugat

ion

0.68

mg

cont

aini

ng50

nmol

Cd(1

3.5

nmin

size

)(6

h)In

trap

erit

onea

l

ICR

mic

eRe

lati

vely

high

amou

nts

ofCd

ions

foun

din

brai

nti

ssue

but

nosi

gns

ofin

flam

mat

ion

orpa

renc

hym

alda

mag

ew

ere

obse

rved

.

[81]

Key:

5-H

T,se

roto

nin;

Ag/A

g+,

silv

er/s

ilver

ion;

ALP,

alka

line

phos

phat

ase;

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Lung targets

The lung is an attractive target for drug delivery due to thenon-invasive nature of inhalation therapy, the lung’s largesurface area, localization/accumulation of drugs within thepulmonary tissue and avoidance of first-pass metabolism,thus reducing systemic side effects [82,83]. Nanocarrier sys-tems for pulmonary drug delivery have several advantageswhich can be exploited for therapeutic reasons and, thus,are intensively studied.

Polymeric nanoparticlesPolymeric NPs are biocompatible, surface modifiable and arecapable of sustained drug release. They show potential forapplications in the treatment of various pulmonary condi-tions such as asthma, chronic obstructive pulmonary disease(COPD), tuberculosis (TB) and lung cancer as well as extra-pulmonary conditions such as diabetes [84—89]. Already,there is a multitude of organic nano-polymers including col-lagen, gelatin, chitosan, alginate and bovine serum albumin(BSA). Furthermore, the last three decades has seen a risein the development of synthetic polymers such as the bio-compatible and biodegradable poly(lactic-co-glycolic acid)(PLGA) for use as drug carrier devices [90,91].

While such drug loaded nano-configurations demon-strate promising alternatives to current cancer treatment,cytotoxicity needs to be evaluated. PLGA NP successfullyimprove therapeutic outcome and reduce adverse effectsvia sustained and targeted drug delivery. Additionally, theuse of biological capping materials such as chitosan or BSA

further reduce toxicity while their biocompatibility andbiodegradative capacity making them an intuitive choice fornanoparticulate surface modification. Romero et al. demon-strated a reduction in cytotoxicity of PLGA NPs stabilizedwith BSA compared to synthetic coating materials in cul-tured lung cancer cells [90]. Albumin, the most abundantserum protein, was found to be highly biocompatible mak-ing it a useful stabilizer for drug delivery vehicles. Similarly,chitosan-stabilization resulted in near-total cellular preser-vation and improved pulmonary mucoadhesion in an in vivolung cancer model [31].

Biological capping materials reduce cytotoxicity by mim-icking the physiological environment, thus ‘hiding’ fromthe immune system. However, the possibility of enzymaticdegradation due to biophysical resemblance needs furtherinvestigation.

Carbon nanotubes (CNTs)CNTs are frequently used for in vivo inhalation models andcan be subdivided into SWCNTs and MWCNTs with the formerbeing considered more cytotoxic. This difference in toxicityhas been attributed to the larger surface area of SWCNTscompared to the multi-layered alternative [92]. CNTs showbiomedical potential in areas such as drug delivery, photo-dynamic therapy (PDT) and as tissue engineering scaffolds[93—95]. Previous studies have highlighted the toxic poten-tial of both SWCNTs and MWCNTs; after murine intra-trachealinstillation of CNTs, pulmonary epitheloid granulomas andinterstitial inflammation with subsequent fibrotic changeswere observed [10,11,96]. Cytotoxicity is thought to be



Figure 3 Schematic representation of functionalization potential of gold nanoparticles [120].

mediated by the up-regulation of inflammatory cytokinessuch as TNF-�. However, a recent study by Mutlu et al. postu-lates that toxicity after murine intra-tracheal instillation ofSWCNTs arises due to nanotubular aggregation rather thanthe large aspect ratio of the individual nanotube [9]. Thishas led to the development of several methods to achieveimproved nanotube dispersion [8]. Exposure of animals toMWCNTs results in contradictory reports with some authorsappending toxicities in the range of asbestos poisoningwhereas other studies found MWCNTs to be biocompati-ble and far from cytotoxic [35,96]. Such discrepancies maybe explained by subtle variations in nanotube compositionand ways of administration (intratracheal instillation versuswhole-body inhalation) and warrants further investigation.

Silica (SiO2) nanoparticlesSilica NPs are already in wide-spread use in the non-medicalfield as additives to chemical polishing, cosmetics, varnishesand food stuffs [36,97]. Relatively recently, such particleshave been introduced into the biomedical field as biomark-ers [98], cancer therapeutics [99] and drug delivery vehicles[100]. Silica NPs are considered ‘safe’ in moderate dosage(<20 �g/mL) as opposed to their crystalline pendants whichare classed as class 1 carcinogens [36,37,101]. However, at adose of 25 �g/mL silica NPs exhibited agglomerative poten-tial in vitro and dose-dependent cytotoxicity at a criticalconcentration of 50 �g/mL as demonstrated on A549 cells[38,39]. Cell death was mediated by reactive oxygen species(ROS) induction and membrane lipid peroxidation. Apartfrom concentration dependence, silica NPs further exhib-ited particle size-dependent cellular toxicity with smallerdiameters causing more harm than bigger ones as shown byNapierska et al. [40]. Paradoxical results have been obtainedin animal studies focusing on the exposure of lungs tosilica NPs. Previous studies on the pulmonary toxicity afterintra-tracheal exposure of silica NPs have revealed profound

acute pulmonary inflammation and neutrophil infiltration oflung tissue with the development of chronic granulomatouschanges after 14 weeks in a dose-dependent manner [102].However, subsequent longer-term studies utilizing the sameNPs showed the induction of anti-inflammatory mediatorsand the reversibility of inflammatory and fibrotic changesto levels close to the control [103,104]. Fibrogenic media-tors (IL-4, IL-10 and IL-13) were upregulated shortly afterexposure to silica NPs and contributed to fibrotic changes[104]. These were counteracted by the overexpression ofmatrix-metalloproteinases (MMP), particularly MMP-2 andinterferon gamma (INF-�). Further to the expression of anti-fibrotic mediators, eventual recovery of lung tissue may beassociated with the time-dependent reduction of NP con-centration in the alveoli. Some studies suspect diffusion andtranslocation of NPs away from the lung tissue via the sys-temic circulation and deposition in extra-pulmonary organs[41,105,106]. The above suggests that it is theoretically fea-sible and within acceptable safety limits to use moderatedoses of silica NPs; however high-dose toxicity profiles war-rant further investigations.

Silver nanoparticlesThe most common route of pulmonary exposure to silverNPs (AgNP) is via the occupational inhalation of airborneparticles during manufacturing [107]. Oberdorster et al.have shown in a rat model that inhaled NPs can translocatefrom their original site of deposition (e.g. lungs) to othertissues [105]. The current American Conference of Govern-mental Industrial Hygienist’s (ACGIH) limit for silver dustexposure is 100 �g/m3. In order to evaluate potentiallyacute and delayed adverse pulmonary effects of AgNP, Sunget al. have carried out a series of inhalation studies focusingon the acute, subacute (28 days) and subchronic (90 days)toxicity of AgNP in rats [42,43,108]. In the acute setting,rats were exposed to different particle concentrations in a



whole-body inhalation chamber for 4 consecutive hours andwere subsequently observed for a further 2 weeks. At thehighest concentration used (750 �g/m3; 7.5 times higherthan the limit), no significant body weight changes or clinicalchanges were observed. Furthermore, lung function testsrevealed no statistical differences between exposed andcontrol groups. Repeated administration of AgNP for 4 weeksshowed similar results. In contrast, subchronic inhalationfor 13 weeks at a maximum concentration of 515 �g/m3

(5 times the limit) revealed time- and dose-dependentalveolar inflammatory and granulomatous changes as wellas decreased lung function [44]. Such results suggest thatwhile high-dose chronic exposure to AgNP has the potentialto cause harm, under current guidelines and limits suchexcessive particle inhalation would seem unrealistic.

Dermal targets

The skin is the largest organ of the body and functions asthe first-line barrier between the external environment andthe internal organs of the human body. Consequently, it isexposed to a plethora of non-specific environmental assaultswithin the air as well as to distinct and potentially toxic sub-stances within creams, sprays or clothing. Topically appliedNPs can potentially penetrate the skin and access the sys-temic circulation and exert adverse effects on a systemicscale.

Silver nanoparticlesAg is one of the most consistently studied NPs in termsof toxicity. This arises from the fact that AgNP possessproven anti-microbial effects which are currently used inmany products ranging from wound dressings to clothing.However, the specificity of AgNP toxicity towards micro-organisms must be elucidated in order to exclude potentiallyadverse effects mediated by such particles on other exposedcell types within the body. Ag ingestion and topical appli-cation can induce the benign condition known as argyria,a grey—blue discoloration of the skin and liver caused bydeposition of Ag particles in the basal laminae of such tissues[109]. This has prompted a limitation on the recommendeddaily dosage of Ag. Furthermore, numerous toxicity stud-ies focusing on AgNP have been carried out on cell linesincluding mouse fibroblast, rat liver, human hepatocellularcarcinoma and human skin carcinoma cells [5,45,46,110].All observed a rise in ROS and oxidative-stress mediatedcell death and apoptosis (concentrations between 2.5 and200 �g/mL). The degree of toxicity was concentration-dependent and varied with surface coatings. Samberg et al.reported significant toxicity of uncoated AgNP on human epi-dermal keratinocytes in contrast to carbon-coated particles[47]. The exact mechanism of AgNP toxicity is unknown butROS generation and oxidative stress are two likely routes.Once excessive ROS production outstrips the anti-oxidativecapacity of the cell, oxidative stress is induced with subse-quent production of inflammatory mediators, DNA damageand apoptosis [111]. Dermal penetration studies are ideallycarried out on porcine skin due to its resemblance to that ofhumans in terms of thickness and rate of absorption [112].Samberg et al. demonstrated porcine dermal biocompatibil-ity after daily topical application of AgNP-containing cream

over a period of 14 consecutive days (0.34—34 �g/mL). How-ever, microscopically, dose-dependent oedema formationand hyperplasia were observed with particle deposition insuperficial layers of the stratum corneum only. Trop et al.observed reversible silver toxicity in a human burns patientwho was treated with a AgNP-coated dressing [48]. Theseresults suggest reversible toxicity of AgNP and a transientdiscoloration of exposed skin.

Titanium dioxide (TiO2) nanoparticlesTiO2 NPs have several properties which make them anadvantageous ingredient for commercial sunscreens and cos-metics. They exhibit UV-light blocking properties and conferbetter transparency and aesthetics to creams. In vitrostudies demonstrated cell type-dependent TiO2 toxicityaffecting cellular functions such as cell proliferation, dif-ferentiation, mobility and apoptosis [49,113]. Such adverseeffects, however, could not be replicated in vivo. In orderto assess penetrative capacities, dermal infiltration studieshave been carried out on human volunteers using differ-ent investigative techniques. Lademan et al. investigatedthe penetrative effect of repeated administration of TiO2-containing sunscreen on the skin of volunteers [50]. Tapestripping and histological appraisal of skin biopsies revealedthat TiO2 penetrated into the open part of a hair follicle asopposed to the viable layers of the epidermis or dermis. Fur-thermore, the titanium amount in any given follicle was lessthan 1% of the applied total amount of sunscreen. Surfacepenetration via hair follicles or pores was also suggestedby a study conducted by Bennat and Muller-Goymann whereskin permeation was greater when sunscreen was applied torelatively hairy skins [51]. Mavon et al. demonstrated neartotal recovery of sunscreen after 15 tape strippings with noTiO2 deposition in hair follicles or skin layers [52]. It couldbe argued that different degrees of permeation and toxic-ity correlate with surface coatings and functionalizations ofTiO2 NPs as well as with the number of follicular pores withinthe skin facilitating particle uptake.

Silica nanoparticlesSilica NPs are frequently incorporated in drug additivesand cosmetics as well as being used as nano-vehicles fordrug delivery [114,115]. However, sparse literature on itscutaneous toxicity is available. Cell-based toxicity studiesrevealed a size-related increase in cytotoxicity when murineepidermal Langerhans cells were exposed to silica particlesof diameters 70, 300 and 1000 nm [53]. Cellular uptake wasmore efficient for smaller particles (<100 nm) which corre-lated with an increased cytotoxicity. Park et al. evaluatedtoxicity of differently sized silica NPs on cultured human ker-atinocytes (CHK) and compared results with a human skinequivalent model (HSEM) as well as with an in vivo rabbitmodel [54]. Silica NPs exhibited significant dose-dependenttoxicity on human keratinocytes with a statisticallysignificant reduction in cell viability at a concentration of50 �g/mL. A size-dependent increase in toxicity, as sug-gested by Jiang et al. could, however, not be confirmed[116]. Exposure of NPs to HSEM showed no inflammatorychanges even at a maximum concentration of 500 �g/mL.Such low acute toxicity was confirmed with the in vivo rabbitskin model. These results highlight the superiority of HSEM



compared to culture-based systems in terms of evaluatingrelative dermal toxicities of NPs and emphasize the discrep-ancies encountered if one tries to extrapolate results gainedfrom cell-based studies into human scenarios.

Gold nanoparticlesDue to facile means of synthesis and the potential for bio-functionalization, gold NPs (AuNP) are being investigated forclinical applications including dermal drug-delivery [117].Sonavane et al. demonstrated size-dependent permeationon excised rat skin after topical application of differentlysized AuNP (15, 102 and 198 nm) [58]. Smaller NPs pene-trated deeper into the tissue than larger ones which weremainly accumulated in the more superficial epidermis anddermis. These findings may have important implications withregards to efficient NP-based dermal drug delivery. Au com-pounds are generally considered safe and have been inroutine clinical use for many years, e.g. in the treatmentof rheumatoid arthritis [118]. However, once reduced tonanometer scale, particles are known to undergo profoundchanges in terms of their biochemical properties whichnecessitates renewed investigations into their cytotoxic pro-file. Despite the relative wealth of toxicity studies focusingon AuNP, contradictory results remain the main obstacleto transition into the clinical setting. Several studies havedemonstrated cellular uptake of AuNP to be a function oftime, particle size and concentration. In a study by Miron-ava et al., human dermal fibroblasts were exposed to AuNPfor a period of up to 6 days [55]. Three sets of NP concentra-tions were obtained for each of two different sizes. Largerparticles, 45 nm, exhibited marked cytotoxicity at a concen-tration of 10 �g/mL compared to smaller particles, 13 nmin size, which only displayed cytotoxic signs at the muchhigher concentration of 75 �g/mL. These results conflictwith those obtained by Pan et al. who reported maximumtoxicity for a particle size of 1.4 nm [56]. Such differencesmay be explained by the distribution pattern of particleswithin cells and require more research.

Liver targets

Being the site for first-pass metabolism, the liver is partic-ularly vulnerable to NP toxicity and has consistently beenshown to accumulate administered substances, even longafter cessation of exposure. Thorough evaluation of NP-mediated hepatocellular toxicity thus remains of prevailingimportance.

Gold nanoparticlesAuNP play an interesting role in biomedicine and have mul-tiple possible applications in the fields of imaging, drug andgene delivery [14,119]. A study conducted by Chen et al.revealed size-associated toxicity and lethality of AuNP [59].Mice were exposed to intraperitoneal injection with nakedAuNP ranging from 3 to 100 nm in size at a concentrationof 8 mg/kg/week for 4 weeks. Particles sized 3, 5, 50 and100 nm did not induce significant toxicity. However, particlesranging from 8 to 37 nm induced severe systemic adverseside effects in the test subjects such as fatigue, loss ofappetite, weight loss and fur color changes. Death ratesof mice exposed to that particular size range were near

total. Histological examination of organs indicated Kupf-fer cell activation in the liver, splenic white pulp diffusionand structural deformities in lung parenchyma which wereconsistently associated with gold deposition at these sites.Toxicity was improved by surface modification of parti-cles with a highly immunogenic peptide which induced anincreased antibody response in the host. Despite improvedcytocompatibility conferred by biological surface coatings,the primary mechanism of liver toxicity is thought to arisefrom acute inflammatory changes and subsequent apopto-sis [60,61]. Increasingly, evidence shows that AuNP toxicitydepends not only on the conventionally listed propertiesincluding surface functionalization but also on the route ofadministration [62,120]. It has been shown that intraperi-toneal administration of particles is related to a significantlyhigher incidence of adverse effects than comparable intra-venously delivered ones [62]. Despite the fact that thesefindings may have implications for clinical uses of such par-ticles, caution should be exercised when stating that oneroute of administration gives a higher incidence of adverseeffects than another, especially when based on toxicityresults from different studies.

Silver nanoparticlesWell known for their anti-microbial effects, AgNP may gainaccess into the circulation via various routes. Once withinthe systemic circulation, first-pass metabolism via the liveris likely, if not probable, thus potentially rendering hep-atocytes vulnerable to toxic insults. Many studies haveindicated the propensity for AgNP to accumulate within theliver and induce oxidative stress-related toxicity [63]. Cer-tain parameters influencing the degree of toxicity includeparticle concentration [121], size [64], shape [65] and theability to deplete cells of anti-oxidants [122]. Teodoroet al. demonstrated significant toxicity exerted by AgNP onBRL3A rat liver cells by measuring a significant reduction inmitochondrial function, a concomitant rise in lactate dehy-drogenase (LDH) leakage from cells, significantly depletedlevels of the antioxidant glutathione (GSH) as well as a rise inROS concentrations [122]. Oxidative stress-dependent cyto-toxicity was also confirmed by Kim et al. who were able tosignificantly improve viability of rat hepatoma cells exposedto AgNP after pre-treating cells with the naturally occurringanti-oxidant N-acetylcysteine [121].

Silica nanoparticlesBiomedical applications for silica NPs are widespread andinclude diagnosis and drug delivery [123,124]. Despite suchpromising uses in the medical arena, a thorough evaluationof cytotoxicity is still lacking. Few studies have been car-ried out and contradictory results regarding toxicity furthernecessitate systematic research. Xie et al. demonstratedthe hepatotoxic potential of silica NPs causing mononu-clear inflammatory cell infiltrates at the portal area withconcomitant hepatocyte necrosis [66]. Such inflammatorychanges are postulated to relate to frustrated phagocytosisof larger silica NPs (>100 nm) with subsequent stimulation ofpro-inflammatory cytokine release [67]. A size relationshiphas also been reported by Kumar et al. who found smallsilica NPs (<25 nm) to be biocompatible and non-toxic tomurine liver parenchyma [68]. In contrast to these findings,



Nishimori et al. suggests acute toxicity related to small sil-ica NPs (<100 nm) [69]. Several factors may lead to theseapparently inconsistent results; the presence or absenceand type of coating is one of the major parameters indetermining interactions between the NPs and physiologicalenvironment as is the particle’s size. However, contradic-tory results in terms of size-dependent toxicity warrantfurther investigations into the role of different routes ofparticle administration. The results for silica NPs suggestthat less invasive means of administration (e.g. oral) reduceorgan-specific toxicity compared to intravenously dispensedparticles. Building on this theory, intravenously given largerNPs (>100 nm) may prove less cytotoxic due to impairedextravasation through minute capillary fenestrae and thus,little organ-specific deposition, as postulated by Nishimoriet al. [69].

Quantum dotsSemiconductor nanocrystals, or QDs may be used in avariety of biomedical applications. The general structureof QDs comprises an inorganic core—shell and an organiccoating to which biomolecules may be conjugated to enabletargeting to specific areas within the body. Such close prox-imity and interaction with the physiological environmentnecessitates toxicological evaluation of these particles. Cellbased studies focusing on QD-induced adverse effects foundtoxicity most likely arises from the liberation of metalions released from the heavy metal core [70]. Oxidativeenvironments further promote degradation and metal ionleaching. The liver is of particular importance with regardsto bio-toxicity because of first-pass metabolism and poten-tial accumulation and deposition within the organ, as shownby Yang et al. [125]. QD size was also postulated to be amajor parameter in organ-specific deposition with smallerparticles (<20 nm) extravasating through capillary fenestraethat are large enough in the liver (∼100 nm in size) [71].The long half-life clearly has implications for organ toxicity,particularly in view of the liver’s untoward propensity toheavy metal ion poisoning which makes exposure to QDspotentially very hazardous. Surface coating to protect thecore from degradation has been shown to reduce toxicity[126]. Conventionally, QDs are coated with a layer of zincsulphide (ZnS) or mercaptoacetic acid. However, evidenceof continued cellular toxicity after prolonged periods oftime suggests either inadequate core coverage or the needfor a different type of coating material [72]. Clift et al.carried out a series of experiments assessing additionalsurface coatings for their respective cytotoxicities [73].CdTe/CdSe cored QDs with a ZnS shell were additionallycovered with organic, carboxylated (COOH), amino (NH2)or poly(ethylene glycol) (PEG) coatings. Cytotoxicity wastested on exposure to each type separately by measurementof macrophage cell viability and LDH release. All QDs wereshown to induce significant cytotoxicity after 48 h and coat-ing materials as well as liberated Cd ions were suggestedto be the causative agents. It is likely that a breakdown ofphysically labile surface material resulted in ion liberationand subsequent toxicity. Recently, Seifalian and colleagueshave demonstrated that the novel synthetic nanomaterialpolymeric oligohedral silsesquioxane (POSS), when incor-porated onto CdTe cored QDs, shows significantly enhanced

cytocompatibility than conventionally used materials, evenwithout ZnS shelling (unpublished data). POSS was shown tobe non-toxic by preventing ion leakage from the core. Theseresults underline the importance of the type of coatingmaterial used and suggest that the most important factorinfluencing QD toxicity remains heavy metal ion leakagefrom the core due to inadequate surface coverage.

Brain targets

The brain, unlike the liver, has very limited regenerativecapacity and must therefore be particularly protected fromexogenous insults. This is achieved by the protective BBBwhich separates the cerebrospinal fluid (CSF) surroundingthe brain from the systemic blood circulation via tight junc-tions around the capillaries and is of undoubted benefitin preventing blood-borne pathogens from gaining entryand causing potentially irreversible damage while allowingthe diffusion of smaller lipophilic molecules such as oxy-gen. However, bypassing the BBB may be beneficial andpotentially life-saving in the management of acute condi-tions such as cerebral meningitis as well as chronic illnesseslike dementia or Parkinson’s disease. Targeted drug deliveryallows the use of smaller drug doses and hence reduces sys-temic adverse effects. Nevertheless, the fate of NPs aftertranslocation into the structures of the central nervous sys-tem (CNS) requires toxicological analyses. External insult tothe BBB could potentially activate cerebral epithelial cellsthus inducing oxidative stress-mediated injury. Additionally,the integrity and biostability of the particle’s coating mate-rials require rigorous assessment [127].

Recently, Oberdorster et al. demonstrated the uptake ofNPs by sensory nerve endings within the pulmonary epithe-lium and subsequent axonal translocation into the CNS whichpresents a further route of exposure to potentially harmfulNPs [127].

Gold nanoparticlesAuNP are valuable imaging modalities for in vitro andin vivo cell tracking. Studies suggesting AuNP as imagingagents of the CNS are manifold and could prove to be use-ful in the diagnoses and therapeutics of CNS pathologies[128—130]. However, such enthusiasm is dampened by therelative paucity of data on the interactive capabilities ofAuNP with the cells of the CNS. Primary brain microvascu-lar endothelial cells (BMECs) are frequently used to provideinformation on BBB transport characteristics and molec-ular mechanisms and offer an opportunity to investigateinto the interactions between NPs and the surface of theBBB [131—133]. It has been postulated that the releaseof pro-inflammatory cytokines (e.g. TNF-�, IL-� and IL-2) induces an increase in permeability and toxicity in ratbrain microvessel endothelial cells (BMECs) exposed toAgNP which seemed both size- and time-dependent [76].In contrast, a similar study utilizing AuNP of comparabledimensions did not evoke increased secretion of inflam-matory markers nor was enhanced cellular permeabilitydetectable [74]. These findings are supported by a studycarried out on RAW264.7 macrophage cells which demon-strated no pro-inflammatory cytokine release in response toAuNP exposure [75]. However, mild toxicity was observed



with smaller AuNP (3 nm) compared to larger ones (5 nm).Such size-dependent toxicity has previously been observedin various cell lines [134,135] and in vivo models [136,137].Ultra-small NPs were found to be widely distributed toalmost all tissues including the brain whereas larger oneswere barred access to cerebral tissues. This could be dueto either the physical hindrance provided by the BBB or thefaster and more efficient removal of larger particles fromthe circulation compared with smaller ones. Consequently, alower particle concentration would reach and subsequentlybe absorbed by the BBB. The BBB’s regulatory function aswell as the removal-theory were further demonstrated ina different study where, even after repeated administra-tion of relatively large AuNP (12.5 nm), the amount in thebrain was significantly lower than that in the liver, spleenand kidneys [138].

Silver nanoparticlesIn contrast to Au, AgNP have been shown to exhibit neu-rodegenerative abilities [139,140]. Recent research focusingon the interaction between AgNP and BBB has revealedfunctional disruption of the BBB and subsequent brainoedema formation [139]. In support of these findings, Tanget al. demonstrated AgNP-induced BBB destruction, astro-cyte swelling and neuronal degeneration in a rat model[140,141]. The pattern of distribution and degree of toxic-ity was found to be concentration- and size-dependent [64].A study conducted by Costa et al. suggests mitochondrialdysfunction and impaired energy production as the possibleunderlying mechanism of neurodegeneration [77]. Repeatedadministration resulted in significant accumulation in organswith smaller AgNP (<100 nm) being predominantly picked upby the liver while larger particles (>100 nm) mainly accu-mulated in the spleen. This pattern of particle uptake isregulated by the pore size of capillary fenestrae (∼100 nm).Dose-dependent accumulation has previously been observedin rats following repeated oral doses of AgNP [78]. Humansubjects demonstrated a greyish hyperpigmentation of theirskin following oral ingestion of AgNP [142,143]. These resultssuggest the capacity for gastrointestinal absorption of AgNPwith subsequent systemic distribution and accumulation invarious tissues.

This apparent potential for AgNP to accumulate andcause harm requires further investigation with particularattention assigned to the influence of NP size on thedistribution and toxicity. Powers et al. demonstrated thepotential for AgNP to behave as a developmental neurotoxinin zebrafish embryos and cause long-term changes in synap-tic functioning [79]. Exposure to ionized silver (Ag+)resulted in a marked increase in turnover of the neuro-transmitters dopamine (DA) and serotonin (5-HT) which arekey components in the reward, anxiety and sensorimotorpathways. Ag+-induced neurotransmitter hyperactivityresulted in behavioural changes consistent with a loweranxiety-threshold.

Superparamagnetic nanoparticlesSPIONs and ultra-small SPIO nanoparticles (USPIONs) consistof an iron oxide core and a variable carbohydrate coatingwhich determines cellular uptake and biological half life.The degree of surface coverage has been postulated to be

the main parameter in cellular uptake as incomplete sur-face coverage was shown to promote opsonization and rapidendocytosis whereas fully coated SPION escaped opsoniza-tion which, as a result, prolonged plasma half-life [144].However, more recently, particle size as opposed to coat-ing degree has been suggested to exert chief influence onthe rates of uptake by macrophages [145]. Being one ofthe few FDA approved NPs for the use in MRI, SPION mostcommonly find applications in the imaging of the vascula-ture and lymph nodes [146—149]. However, recent reportsfrom both animal models and human subjects have showntheir efficacy in visualizing intracerebral malignancies andneurological lesions within the CNS [150,151]. Despite suchroutine use of SPION, the long-term effects and potentialneurotoxicity have, as yet, not been evaluated extensively.

The unique physio-chemical properties shared by all NPs,such as nanometer size and a large surface area to volumeratio, makes SPION particularly valuable for novel therapeu-tic and diagnostic applications. However, such dimensionalreductions may potentially induce cytotoxicity and inter-fere with the normal components and functions of the cell[152,153]. Previous in vitro studies have shown the capac-ity for SPION to induce ROS generation, impair mitochondrialfunction and cause leakage of LDH — all of which could inciteneurotoxicity as well as potentially aggravate pre-existingneuronal damage [154—156]. Furthermore, toxicity reportsdemonstrated an association between particle size, typeof surface coating and breakdown products, concentrationand the degree of opsonization and cytotoxicity in culturedcells [157—159]. For example, Berry et al. utilized fibro-blast cultures to demonstrate the ability to tune particletoxicity according to particle coating. They compared thein vitro toxicity of plain, uncoated magnetic iron oxide NPs(P particles) with either dextran derivatized (DD) or albu-min derivatized (AD) NPs. P particles as well as DD particlesexhibited similar toxicities, whereas AD particles managedto induce cell proliferation [157].

In a study by Muldoon et al., the distribution, cellularuptake and toxicity of three FDA approved SPION of dif-ferent sizes and surface coatings were compared to eachother and to a laboratory reagent [80]. Firstly, inoculationof ferumoxtran-10 (USPION: 20—50 nm in size, complete sur-face coverage with native dextran), ferumoxytol (USPION:20—50 nm in size, complete surface coverage with semisyn-thetic carbohydrate) and ferumoxide (SPION: 60—185 nmin size, incompletely coated with dextran) as well asthe lab reagent MION-46 into tumor-bearing rat brainsdemonstrated direct uptake of ferumoxtran-10 into tumortissue and long-term retention within the cancerous lesion(5 days). However, uptake seemed NP dependent. Feru-moxide inoculation did not yield tumor enhancement whichsuggests size and surface coverage dependence. The sec-ond step involving osmotic BBB disruption to evaluatetransvascular SPION delivery and neurotoxicity displayedno evidence of gross pathology implying the feasibility ofintracerebral injection of clinical USPION into humans.

Quantum dotsQDs may be functionalized to serve both diagnosticand therapeutic purposes. Presently, QDs find invaluableexperimental applications in visualizing neural stem andprogenitor cells in developing mouse embryos in vivo [160],



act as nano-vehicles for brain-targeted drug delivery [161]and demarcate brain malignancies for precise tumor resec-tion [162]. Previously, it has been suggested that NPs canbypass the BBB and reach the brain via the olfactory epithe-lium or trigeminal nerve to potentially cause harm [163].In order to investigate the potential to reach the structuresof the CNS, Kato et al. intraperitoneally injected CdSe/ZnS-core/shell-typed QDs functionalized with captopril with adiameter of 13.5 nm into mice [81]. Six hours post-injection,organs were harvested and brains were dissected into sev-eral areas including the olfactory bulb, cerebral cortex,hippocampus, thalamus and brainstem. Despite the detec-tion of unexpectedly high amounts of Cd within the braintissues, no signs of inflammation, neuronal loss or functionaldisorders were present. Several possible routes of entryinto the brain have been suggested. Small QDs may transferthrough minute gaps (<20 nm) between astrocytic foot pro-cesses which constitute the BBB out of the capillary bed intothe brain parenchyma. Alternatively, interaction betweenQD-cap and the receptors located at the BBB may lead to theuptake of QDs via phagocytosis or pinocytosis [164]. How-ever, no evidence for the presence of captopril receptorsat the BBB has been published making receptor-mediateduptake unlikely. Another postulated route of entry into thebrain is the retrograde axonal transport from gut neuronesvia peripheral nerves into the tissues of the CNS. However,according to the published report, no QD-cap was found inperipheral nerves. These results suggest that for clinical ortherapeutic purposes, the route across the BBB may showpromise in the future management of CNS pathologies. How-ever, the combination of scarce clinical data on the toxiceffects with the lack of long-term in vivo toxicity studiescalls for the need for considerable attention to the system-atic evaluation of QDs intended for brain-specific purposes.

Conclusion

NPs have certain unique characteristics which can be andhave been exploited in many biomedical applications. How-ever, these unique features are postulated to be the groundsfor NP-induced biotoxicity which arises from the complexinterplay between particle characteristics (e.g. size, shape,surface chemistry and charge), administered dose and hostimmunological integrity. Recently, more emphasis has beenplaced onto understanding the role of the route of particleadministration as a potential source for toxicity. Currentresearch focuses on elucidating the mechanistics underlyingNP toxicity which are postulated to range from inflammatorycell infiltration and cellular necrosis to ROS-induced apo-ptosis. Despite the wealth of toxicity studies available, theauthors have identified several points of criticism which cur-rently hinder the progression into clinical settings. Firstly,the application of the so-called ‘proof of principle’ approachwhere cell cultures or experimental animals are exposed toultra-high NP concentrations to ensure cytotoxicity leads tounrealistic results which cannot be extrapolated into thehuman scenario since diagnostic and therapeutic interven-tions usually only require the administration of minimalconcentrations. Thus, not only are we faced with scientifi-cally unreliable data, such practices may, quite dangerouslycause unnecessary alarm in the public. Additionally, theauthors have identified two further limitations of current

toxicity studies; firstly, the chronicity of NPs exposure in thecase of therapeutic applications needs more thorough long-term evaluation; secondly, different studies apply differentparticle formulations leading to conflicting and unreliableresults. Consequently and for the future, more emphasisshould be placed on defining the dose of NPs in relationto the route of administration. As mentioned at the begin-ning, end-organ accumulation and distribution as well asmetabolism and excretion are variable depending on theroutes of administration, such that intravenous NP adminis-tration may have more implications with regards to systemicadverse effects than dermal application of NPs. However,one must treat and compare toxicity results from differ-ent studies with caution, as current toxicity protocols lackuniformity with respect to NP formulations and applicationprotocols. It has become apparent that a unifying protocolfor the toxicological profiling of NPs may be required in orderto achieve reliable outcomes that have realistic implicationsfor the human usage of NPs. In summary, current difficultiesin evaluating NP toxicity originate in the inherent discrepan-cies found amongst toxicity study protocols such that is hasbecome apparent that a unifying protocol for the toxico-logical profiling of NPs may be required in order to achievereliable outcomes that have realistic implications for thehuman usage of NPs. Not only is there a pressing need forlong-term studies, the future of nanotoxicology must alsomore heavily rely on realistic particle dosages and compo-sition principles as well as differentiating more carefullybetween various routes of administrations if nanotechnologyis to fully unfold its clinical potential.

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Lara Yildirimer is a medical student at Uni-versity College London (UCL, London, UK) whois currently suspending her medical degreein order to pursue a PhD in Nanotechnologyand Regenerative Medicine at UCL under thesupervision of Professor Alexander Seifalian.She is the recipient of the MBPhD scholarshipawarded at UCL. She received an interca-lated Honors BSc in Surgical Sciences fromUCL in 2010. Her research interests coverareas of nanotoxicology and the utilization of

nanoparticles for regenerative purposes as well as their clinicalapplications. Lara is particularly focused on developing clini-cally viable and biologically intelligent scaffolds for dermal tissueregeneration. Using a scaffold based on the nanocomposite mate-rial POSS-PCL, a tissue engineering approach is used to engrafthuman adipose-derived stem cells onto the scaffold — achievingboth biocompatibility and controlled biodegradation. Additionally,an anti-bacterial surface coating based on silver nanoparticles willbe applied onto the dermal scaffold to reduce contamination andpost-operative infection.

Marilena Loizidou is a senior lecturer in Phar-macology at University College London. Hermajor research focus is on experimental can-cer therapeutics, with a special interest inbowel cancer. She is leading the researchgroup targeting cancer treatment using nano-

technology and recently has been looking atthe toxicology of nanoparticles.

Nguyen T.K. Thanh, FRSC, CChem, CSci, MRIis the UCL-RI Reader (Associate Professor)in Nanotechnology, Royal Society Univer-sity Research Fellow at The Davy FaradayResearch Laboratory, The Royal Institution ofGreat Britain and Department of Physics andAstronomy, University College London (UCL),UK.

She received the award for top academic achievement in Chem-istry and was selected to study at the University of Amsterdam forher MSc in 1992. In 1994—1998, she read Biochemistry/Toxicology inLondon for PhD, her thesis was on: Renal Lipid Changes In ResponseTo Chemical Insults. She developed a method to analyze differenttypes of lipids in rat kidney and urine to study the renal toxic-ity of N-phenyl anthranilic acid, an agent inducing renal papillarynecrosis and mefenamic acid, a nonsteroidal anti-inflammatory andanalgesic drug.

In 1999, she undertook postdoctoral work in medicinal chemistryat Aston University, UK. In 2001, she moved to the United Statesto take advantage of pioneering work in nanotechnology. In 2003,she joined the Liverpool Centre for Nanoscale Science. In 2005, shewas awarded a prestigious Royal Society University Research Fellow-ship and University of Liverpool Lectureship. In January 2009, shewas appointed a UCL-RI Readership in Nanotechnology and basedat The Davy Faraday Research Laboratory, The Royal Institution ofGreat Britain, the oldest independent scientific research body inthe world. There she leads a very dynamic research team focusedon the design, synthesis and study of the physical properties ofnanomaterials as well as their applications in biomedicine.

She has been an invited speaker at over 60 institutes and scien-tific meetings. Furthermore she was a guest editor of The RoyalSociety Philosophical Transactions A on ‘‘Nanoparticles’’ themeissue published in September 2010. She is the editor of the book:Magnetic Nanoparticles: From Fabrication to Clinical Applications tobe published with CRC Press/Taylor and Francis Group in December2011. Currently she is a member of Editorial Board of Advancesin Natural Sciences: Nanoscience and Nanotechnology, also a com-mittee member of Royal Society of Chemistry Colloid & InterfaceScience Group and Society of Chemical Industry Colloid & SurfaceChemistry Group. She has organised many conferences and hasbeen given the responsibility to organize the ‘Functional Nanopar-ticles for Biomedical Applications’ Symposium at the 244th ACSmeeting in Philadelphia, Pennsylvania, in 2012. She has also beenselected to serve as the chair of the scientific committee of afuture prestigious RSC Faraday discussion on the same theme in2014.

Alexander M. Seifalian is a Professor of Nano-technology and Regenerative Medicine andthe Director of Centre for Nanotechnology& Regenerative Medicine at University Col-lege London. He is based within the Divisionof Surgery & Interventional Sciences. He hascompleted his education at University of Lon-don and University College London MedicalSchool. He is a Fellow of the Institute of Nano-technology (FIoN) and has published over 325peer-reviewed research papers, 31 bookchapters and 4 families of patents.



During his career, he has led and managed many large projectswith multidisciplinary teams with very successful outcomes in termsof commercialisation and translation to patients, including thedevelopment and commercialisation of a bypass graft for vascularaccess for haemodialysis; laser activated vascular sealants, regen-eration of lacrimal ducts in man with Swiss eye surgeon Dr KarlaChaloupka using nanomaterials and stem cells and recently, thedevelopment of the first synthetic trachea based on a nanocompos-ite polymer and stem cells which has been implanted into a patientat the Karolinska Institute, Sweden.

His current projects include the development of nanomaterialswith bioactive molecules, which include nitric oxide for cardio-vascular implants, development of nanoparticles for stem cellstracking, the development of skin, nerve regeneration and a rangeof tissue engineered organs with a current grant sum of £5.2 million.

He has been awarded the top prize in the field of developmentof nanomaterials and technologies for the development of cardio-vascular implants in 2007 by Medical Future Innovation and in 2009received a Business Innovation Award from the UK Trade & Invest-ment (UKTI) in the Life Sciences and Healthcare category.

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REVIEW Toxicological considerations of clinically applicable nanoparticlesucaptt0/toxicology-nanoparticles... · 2011. 12. 7. · Nanoparticles have a large surface area to volume