1

Nanxi ZhaDavid

Zhitomirsky

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Overview1.

What is DiabetesTypes I/II/IIIPhysiology and PathologyStatistics

2.

Glucose B

iosensors–

Associated Mechanisms

–

Types of Biosensors–

Future

3.

Drug Delivery–

Insulin and Insulin Analogues

–

Present drug delivery methods–

Future drug delivery methods

4.

Synthesis

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Diabetes Mellitus

3 Distinct TypesType I: Pancreas cell death required for insulin production (children)Type II: Body does not make proper use of insulin as well as reduced insulin production (adults)Gestational Diabetes: pregnancy related

•

Disease–

High blood sugar level

–

Weakness due to poor glucose metabolism–

May cause blindness, heart disease, kidney problems and nerve damage.

–

246 million are affected

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PathologyLow Insulin Production in Pancreas

Islets of Langerhans: Hormone producing regions of pancreasβ Cell death (immunological attack)

Insulin Transport to Muscle

Insulin allows cells to take up Glucose and use it to form ATP

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Pathology

Desensitization of cells to insulin (Type II)Reduced glucose intakeHigher glucose retention in the bloodCell not able to produce ATP

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Physiology

•

Blood vessel damage due to glucose uptake (insulin independent)

•

Increased blood vessel fat levels and risk of heart attack

•

High filtration requirements in kidneys, increased likelihood of kidney failure, dehydration

•

Blindness due to blood vessel damage associated with the eye

Various other complications, such as nerve and muscular tissue damage.

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Statistics and Concerns•

Diabetes is prevalent on a global scale, particularly in the Americas, Middle East and parts of Africa

•

Rapid growth in aging populations, especially in poorly developed countries

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Glucose Biosensors• Monitoring of glucose levels

− Ensuring correct balance of glucose in the blood−

Normal levels are 6.1

mmol/L when fasting (>4

hours), 7.8

mmol/L after a meal (within a period of 1-2 hours)− Indicator if administration of insulin is required

• Rely on electrochemical basis− Devices often rely on electrode substrates−Chemical basis involves immobilization of oxidative enzymes

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Glucose Biosensors• Early Models

− Not electrochemical in nature−

Relied on reflected light to

measure glucose content−Expensive and heavy (1 kg)−Mostly for hospital use

• Current Models− Rely on electrochemical principles− Inexpensive, reproducible, appropriate sensitivity− Allowed for commercialization and home use

Ames Reflectance Meter (1968)

OneTouch

Meter

Precision

Xtra

(weighs 42g)

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Associated Mechanisms• Enzyme Electrode

−

in 1962, Clark and Lyons developed the first glucose enzyme electrode−

A very similar mechanism is still

in use todayLeland C. Clark

GlucoseGlucose

OxidaseEnzyme

Gluconic

AcidReduced (inactivated) Enzyme

Hydrogen Peroxide

Oxygen

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Associated Mechanisms• Reaction Equation

Clark Type Oxygen Electrode:

Electrode for measuring partial pressure of oxygen determined

ampermotrically

YSI Probe:Set-up for measuring glucose metabolism based on detection of hydrogen peroxide

-0.6 V +0.68 V

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Associated Mechanisms

• Several problems− dependence on stable oxygen supply

−

Oxygen availability posed reproducibility issues

−

Oxygen reduction occurs at voltages allowing other species to be

electroactive

–

leads to errors in

amperometric

measurement

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Associated Mechanisms• Solutions

−

measure current due to electron transfer from enzyme active site

−

Use mediators to transfer electrons from enzyme to electrode directly. Also possible to modify electrode with salts for direct electron transfer.

−

circumvents dependence on oxygen and operation at high voltages

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Associated MechanismsFirst Generation: Hydrogen Peroxide

Second Generation: Mediators

Third Generation: Direct Transfer

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Associated Mechanisms• Glucose Meter Unit

− Applies a potential between two electrodes− Measures resultant current over a period of time−

Converts current measurement to concentration

reading

(F: Faraday constant, VA: reaction rate, A: area of electrode, n: # of electrons transferred)i is proportional to VA and VA is proportional to [glucose]

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Associated Mechanisms• Strips

─ essence of the device─

Contain layers of (1) electrodes (2) Enzyme (3) Potassium

Ferricyanide

(mediator). Fabrication via screen printing.─

Allow blood to enter device via capillary action

17 –

Reaction Site 14 –

W.E.

15 –

R.E.

11, 12, 13 –

Metal Contacts

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Glucose Meter Operation1

3

2

Lancing1.Pricking

of finger2.Squeezing of blood drop onto surface of skin

Sample Administration1.Obtain unexpired strip compatible with meter2.Place blood sample in designated region

Sample Analysis1.In

sert strip into meter2.Meter beeps (in 5-10s) and displays reading

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Biosensor Types• FreeStyle

Blood Glucose Monitoring System─

Smallest volume of blood required (3

micolitres)─

Several sites of lancing (fingertips, forearm, upper arm, thigh and calf)─ Uses GDH and charge measurement

• Test times are between 5 –

20 s

•

Implantable Glucose Sensor (Guardian by

MiniMed)

─ Continuous monitoring─ Few Products on the Market─ Prescription is required

• GlucoWatch

(Cygnus)─

Continuous monitoring using

ionophoresis

(drawing glucose from skin)─ Low accuracy, cannot replace standard meters

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Biosensor Types

• No Coding Technology─

With every new box of strips, most meters require calibration due to difference in batch fabrications─

No Coding allows for immediate auto-

calibration so human error is reduced

• Ascensia

Elite─

“Sip-in-Sampling”

obtains the exact volume of blood necessary

• Integrated Insulin Delivery System─

combination of technologies to measure blood glucose and deliver insulin─

Discontinued due to error in units, potentially leading to overdosing

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Biosensor Types•

Reading speed -

most up to date devices on the market required 5s

•

Cost

–

most systems cost anywhere from $30-$80, with strips costing about $20-$30 (50 pc)

•

Lancing locations –

some areas of body are less comfortable to lance

•

Blood sample size –

influences amount of pain, but most sensors require almost the same amount

• Data Features

–

storage of results and trends over time

• Accuracy

–

continuous operation over time with minimal error

Considerations

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Future Biosensors• Breath Analysis

─

Detection of glucose in a person’s breath via gas chromatography-mass spectrometry

• Optical

Analysis of Eye─ Spectral analysis of the vitreous

humour

• Impedance Spectroscopy─ electrodes on surface of skin─

frequency variation and analysis may relate to glucose concentration detection

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Insulin Drug Delivery

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Endogenous Insulin Secretion

Releases insulin at the basal and bolus level.Basal insulin released at 0.5-1.0U/h every day.Bolus component secretes insulin in two phases:

First phase: burst of insulin during a 2- to 5- minutes time period. Inhibits endogenous gluconeogenesiswithin the liver, assists in disposal of carbohydrates received at meals.Second phase: slow increase of insulin for 5- to 52 minutes.

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Insulin Derivation Timeline1922: Banting & Best derivation from bovine pancreas.1923: Eli Lilly purified bovine insulin in commercial amounts.1978: Genentech synthesized insulin analogue in E. coli. 2000 – Present: New synthetic insulin developed.

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Issues

Allergic Reactions due to animal-derived insulin Regular human insulin is not used because its onset time is too slow upon injection. Also, it cannot provide a continuous baseline insulin level.Addition of zinc into the insulin molecule is important to stabolize the molecule, but also make it difficult to break down in the blood stream.

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Solution

Insulin analogues derived using recombinant DNA.Bacteria used: nonpathogenic E. coliInsulin analogues allow for a wide range of onset and duration times, to better prevent hypoglycemia.

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Insulin AnaloguesInsulin Analogues

Classified by the absorption rate and duration time.Two different types:

Bolus level insulinBasal level insulin

Insulin analogues can be premixed to allow customized, optimum drug delivery.

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Insulin Analogues

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Insulin Analogues

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Insulin Analogues

Name Onset Peak Time Duration

Insulin Gluisine, Lispro,

Aspart

Less than 15min

60-90min 3-5 hours

NPH 30min 2-3 hours 6.5 hours

Insulin Glargine,

Determir

90min No peaking 24 hours

Human Insulin

30min 30min 2-3 hours

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Methods of Delivery

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Syringes & Insulin Pens

Mechanism: Piston pump that consists of a plunger fitted into a cylinder. The piston can be pulled back then pushed forward to allow the insulin to be expelled into the subcutaneous skin layer. Advantages: Disposable, economical, allows the patient to customize mixings of insulin (syringe only).Disadvantages: The patient must self-administer the insulin daily as well as regulate glucose level closely, needle discomfort.

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Jet Injectors

Mechanism: Utilizes pressure to force a stream of insulin through the skin. Pulsed microjet injectors avoids the problem of insulin splashback. Advantages: Eliminates the need for structural support of the injection – less pain.Disadvantages: Splashback on older models, need to monitor glucose level closely

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Insulin PumpsMechanism: A pump holds a reservoir of insulin. It is attached to a disposable infusion fitted with a cannula for subcutaneous insertions (e.g., at the abdomen, hip)

Advantages: Efficiency equivalent to multiple insulin injections (daily), better flexibility with prondial controls.

Disadvantages: Frequent blood glucose monitoring is needed to ensure machine dysfunction, insertion site needs to be changed every three days to reduce site infections, discomfort of carrying pump constantly

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Intravenous Delivery

Mechanism: Insulin delivered directly into the bloodstream. Typically used for patients that do not respond well to subcutaneous insulinAdvantages: Glucose uptake increases from 12.7 to 22.4umol/kg/min over 4 week period.Disadvantages: Not feasible for long term, inconvenience to the patient.

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Oral Delivery

Mechanism: Insulin taken in the form of a capsule, passing through the GI tract to be absorbed into the portal circulation system.Advantages: Does not pass through the peripheral circulation (as subcutaneous insulin does), mimics endogenous insulin secretion, reduces hyperinsulinemia.Disadvantages: Must not degrade in the GI tract, currently in research phase.

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Inhalation Delivery

Mechanism: Inhaler with dry powder insulin that is delivered orally to the lungs.Advantages: Absorbs more rapidly than subcutaneous injections (peak concentration reached at 60minutes), no pain during administration. Disadvantages: Efficiency decreased –only 20-30% of the insulin reaches the peripheral of the lungs, currently commercially unavailable in Canada.

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Transdermal

Delivery

Mechanism: Utilizes low frequency ultrasonic signals to dilates the epidermal pores for better absorption.Iontophoresis – small electric current to increase permeation of insulinAdvantages: Portable device, virtually painless delivery.Disadvantages: currently in research phase.

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Synthesis: Creating the Artificial Pancreas

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Overview

Two types of diabetes treatments:Open loop: separate glucose sensor and insulin delivery system.Closed loop: glucose sensor linked with the insulin delivery system, along with an algorithm for insulin calculation.

Closed loop treatment currently in the research stage.

Glucose Biosensor

Insulin Calculation Algorithm

Insulin Delivery System

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Current Research Case Study

G.M. Steil et. al. at UCLA, 2006.Type 1 Diabetes Closed Loop trial.10 patients affected with Type 1 D.M., 7 healthy controls.Individuals followed strict meal routines.Medtronic 511 Paradigm pump, and two subcutaneous glucose biosensors capable of real-time transmission.

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Insulin Delivery Algorithm

Automated Closed Loop insulin delivery was initiated from 7am to 11am (group 1) and to 1pm (group 2).“Proportional-integral-derivative” model used.

P(n) = KP

[SG(n) –

target]

I(n) = I(n-1) + K1

/T1

* [SG(n) –

target]

D(n) = KP

* TD

* dSGdt(n)

PID(n) = P(n) + I(n) + D(n)

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Insulin Delivery Algorithm

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Results

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Results

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Future Developments

Present results indicate feasibility of a Closed Loop insulin delivery system.Improve upon meal-time bolus insulin to reduce postprandial hyperglycemia.Accommodate a flexible meal routine.Non-invasive Closed Loop insulin delivery system.Reduce equipment costs for patients.

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Thank you…

…Questions?

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References[1] M. Chaplin. “Amperometric Biosensors”. London South Bank University. Available at:http://www.lsbu.ac.uk/biology/enztech/amperometric.html. 2004.

[2] “Diabetes Technology”. Diabetes Mall at Diabetes.net. Available at: http://www.diabetesnet.com/diabetes_technology/blood_glucose_meters.php. 2008.

[3] “Diabetes and Heart Disease”. University of Virginia Health System. Available at: http://www.healthsystem.virginia.edu/uvahealth/adult_diabetes/heart.cfm. 2007.

[4] “What is Diabetes”. Canadian Diabetes Association. Available at: http://www.diabetes.ca/about-diabetes/what/. 2008.

[5] J.D. Newman, A.P.F. Turner. “Home Blood Glucose Biosensors: a commercial perspective”. Review. Biosensors and Bioelectronics, 2005. 20 pp. 2435-2453.

[6] P. A. Fiorito and S. I. Córdoba de Torresi. Glucose Amperometric Biosensor Based on the Co-immobilization of Glucose Oxidase (GOx) and Ferrocene in Poly(pyrrole) Generated from Ethanol / Water Mixtures. J. Braz. Chem. Soc., Vol. 12, No. 6, 729-733, 2001.

[7] M. Sherman. “How do blood glucose meters work?”. Ursuline Academy. December 2006. Chem News 13 pp. 5-6.

[8] J. Wang. “Glucose Biosensors: 40 Years of Advances and Challenges”. Review. Electroanalysis 2001, 13, No. 12. pp. 983-988.

[9] “Prevalence of Diabetes”. World Health Organization. Available at http://www.who.int/diabetes/actionnow/en/mapdiabprev.pdf. 2008.

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References[10] S.K. Garg, H. Ulrich. “Achieving Goal Glycosylated Hemoglobin Levels in Type 2 Diabetes Mellitus: Practical Strategies for Success with Insulin Therapy”. Insulin, 2006. 7 pp. 109-121.

[11] T. Flood. “Advances in Insulin Delivery Systems and Devices: Beyond the Vial and Syringe”. Review. Insulin, 2006. 7 pp. 99-108.

[11] M.A. Magnotti, E.J. Rayfield. “An Update on Insulin Injection Devices”. Review. Insulin, 2007. 6 pp. 173-181.

[12] Z. Vajo, J. Fawcett, W.C. Duckworth. “Recombinant DNA Technology in the Treatment of Diabetes: Insulin Analogs”. Endocrine Reviews, 2001. 22 pp. 706-717.

[13] G.M. Steil, K. Rebrin, C. Darwin. “Feasibility of Automating Insulin Delivery for the Treatment of Type 1 Diabetes”. Diabetes, 2006. 55 pp. 3344-3350.

[14] ”Insulin”. How Products are Made. Available at: http://www.madehow.com/Volume-7/Insulin.html

[15] ”Diabetes”. Human Diseases and Conditions. Available at: http://www.humanillnesses.com/original/Conj-Dys/Diabetes.html