Plumbing 101or

How a good boy went bad

Mel AndersenMcKim Conference

QSAR and Aquatic Toxicology & Risk AssessmentJune 27-29, 2006

You and me, fish, and rats are:• Collections of organs organized in parallel or series

with a continuous blood flow

• There are differences in the function of organs, their arrangement with respect to the circulation and each other, and biological content.

• Differences correlate with the evolutionary pressures and environments in which the organisms first developed and now live.

PhD - 1971

An Almost Post-Doc – 1972-1974

After such a promising start:Joined the mammalian toxicology world with an interest in pharmacokinetics and pharmacodynamics of toxic compounds in rats and mice and extrapolation from rodents to human populations.

The Plumbing and Delivery System(Tissue Dose, not simply Applied Dose)

Qc

Cvl

Cvf

Cvr

Cvs

Qc

Ca

QL

Qf

Qr

Qs

Ci Cx

Qp

Lung

Liver

Fat

Rapidly perfused (brain, kidney, etc.)

Slowly perfused (muscle, bone, etc.)

Describing the Individual Pieces Quantitatively

Dead Space

Lung Ventilation

Capillary Blood

InspiredAir

ExpiredAir

From: Hagaard (1924)

Body Tissue

Pulmonary Blood

Countercurrent Exchange

Problem: Estimate amount taken up in first few breaths.

QpCinhQpCexh

Cexh

QcCart

Cart

QcCven

Qc = cardiac output Qp = alveolar ventilationCinh = inhaled concentration Cexh = exhaled concentration Cart = arterial concentration Cven = venous concentration Pb = blood/air partition

coeffecient

Terms:

Uptake = Qc Cart = Pb Qc Qp Cinh /(Pb Qc + Qp)

Linking the Units in Parallel

Lung

Fat

Body

Muscle

Kety (1951)

Describing a Single Tissue

(venous equilibration assumption)

Qt = tissue blood flowCvt = venous blood concentrationPt = tissue blood partition coefficientVt = volume of tissueAt = amount of chemical in tissue

QtCart QtCvtVt; At; Pt

Tissue

Cvt = Ct/Pt

Terms

mass-balance equation: dAt = Vt dCt = QtCart - QtCvt

dt dt

Blood Flow Characteristics in Animals & Digital Computation

LUNG

Liver

Right heart

Kidney

Trunk

Lowerextremity

Largeintestine

Spleen

Upper body

Small intestine

Left heart

Bischoff and Brown (1961)

An application in toxicology....

Ramsey and Andersen (1984)

Alveolar Space

Lung Blood

Fat Tissue Group

Muscle TissueGroup

Richly PerfusedTissue Group

LiverMetabolizingTissue Group( )

MetabolitesVmax

Km

Cart

Ql

Cart

Qr

Cart

Qm

Cart

Qt

Cart

Qc

Calv (Cart/Pb)

QalvQalv

Cinh

Qc

Cven

Cvt

Cvm

Cvr

Cvl

2520151050

100

10

1

0.1

0.01

0.001

TIME - hours

Veno

us C

once

ntra

tion

– m

g/lie

r bl

ood

Conc = 80 ppm

Conc = 1200 ppmConc = 600 ppm

Extrapolations – Across Doses

Alveolar Space

Lung Blood

Fat Tissue Group

Muscle TissueGroup

Richly PerfusedTissue Group

LiverMetabolizingTissue Group( )

MetabolitesVmax

Km

Cart

Ql

Cart

Qr

Cart

Qm

Cart

Qt

Cart

Qc

Calv (Cart/Pb)

QalvQalv

Cinh

Qc

Cven

Cvt

Cvm

Cvr

Cvl

What do we need to add/change in the models to incorporate another dose

route – iv or oral?

IV

Oral

Styrene - Dose Route Extrapolation

100

10

1.0

0.1

0.010 0.6 1.2 1.8 2.4 3.0 3.6

Hours

IV

Styr

ene

Conc

entr

atio

n (m

g/l) 10

1.0

0.1

0.010 0.4 0.8 1.2 1.6 2.0 2.4

Hours

Oral

Styr

ene

Conc

entr

atio

n (m

g/l)

2.8

Alveolar Space

Lung Blood

Fat Tissue Group

Muscle TissueGroup

Richly PerfusedTissue Group

LiverMetabolizingTissue Group( )

MetabolitesVmax

Km

Cart

Ql

Cart

Qr

Cart

Qm

Cart

Qt

Cart

Qc

Calv (Cart/Pb)

QalvQalv

Cinh

Qc

Cven

Cvt

Cvm

Cvr

Cvl

What do we need to add/change in the models to describe another animal

species?

SizesFlowsMetabolic Constants

Styrene - Interspecies ExtrapolationRat - Human

51

376

216

0.1

0.01

0.001

0.00010 1.5 3.0 4.5 6.0 7.5 9.0

Hours

Styr

ene

Conc

entr

atio

n (m

g/l)

Blood80 ppm

Exhaled Air

0 8 16 24 32 40 480.00001

0.0001

0.001

0.01

0.1

1.0

10

Hours

Styr

ene

Conc

entr

atio

n (m

g/l)

Getting Constants for Modeling Metabolism and Closed Chamber

StainlessSteel

BellowsPump

~ 2.0L/min

CO2Scrubber

ParticulateFilter

O2 Monitor

PressureGauge

InjectionPort

Ice Filled Pan forH2O Condensation

Desiccator JarChamber

~ 100 mL/min

INTEGRATOR

Gas Chromatograph

5 mL GasSampling Loop

Time (hours)

PPM

CH2FCl

Time (hours)

PPM

CH2Cl2

Dihalomethane:Closed Chamber Gas Uptake Studies

Rapid estimation of Vmax, Km for a data base to support SAR/QSAR

Then along came Jim:

Jim shows up in Dayton:

Physiologically Based Pharmacokinetic (PBPK) Modeling

Define Realistic Model

Collect NeededData

Refine Model Structure

Make Predictions

Metabolic ConstantsTissue SolubilityTissue Volumes

Blood and Air FlowsExperimental System

Model EquationsX

X

X

X

XX

X X

Tiss

ue C

once

ntra

tion

Time

Liver

Fat

Body

Lung/Gill

Air/Water

• Establish role of partition coefficients and provide emphasis on establishing appropriate metabolic parameters in vitro

• Generate data bases suitable for SAR and QSAR modeling of PCs, Vmax, Km

• Organizing physiological and anatomical information to support modeling needs and show value of approach broadly across animal species – mammals, fish, birds, etc.- for estimating tissue dose (as concentration of parent, metabolites, area under curves, etc.)

PBPK Modeling – Getting the right data

Thank you• Some collaborators

Jim McKim John Nichols Mike Gargas Harvey Clewell John Ramsey

Compartments in Physiological Model

for Methotrexate

T T T

Plasma

Liver G.I. Tract

r1 r2 r3

Kidney

Muscle

QK

QL - QG

QG

QM

Gut Lumen

Gutabsorption

C1 C2 C3 C4 Feces

Bischoff et al. (1971)

Compartmental PK Modeling

CollectData

Select Model

Fit Model to Data

Ct = A e –kaxt + B e-kbxt

X

X

X

X

XX

X X

Tiss

ue C

once

ntra

tion

time

k12k21

koutKO A1

A2

X

X

Tiss

ue C

once

ntra

tion

time

XX X

X

XX