Plumbing 101

or

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 ventilation

Cinh = 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 flow

Cvt = venous blood concentrationPt = tissue blood partition coefficientVt = volume of tissue

At = amount of chemical in tissue

QtCart QtCvt

Vt; 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

Ven

ou

s C

on

cen

trati

on

– m

g/l

ier

blo

od

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

Sty

ren

e C

on

cen

trati

on

(m

g/l

) 10

1.0

0.1

0.010 0.4 0.8 1.2 1.6 2.0 2.4

Hours

Oral

Sty

ren

e C

on

cen

trati

on

(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 Extrapolation

Rat - 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

Sty

ren

e C

on

cen

trati

on

(m

g/l

)

Blood

80 ppm

Exhaled Air

0 8 16 24 32 40 48

0.00001

0.0001

0.001

0.01

0.1

1.0

10

Hours

Sty

ren

e C

on

cen

trati

on

(m

g/l

)

Getting Constants for Modeling Metabolism and Closed Chamber

StainlessSteel

BellowsPump

~ 2.0L/min

CO2

Scrubber

ParticulateFilter

O2 Monitor

PressureGauge

InjectionPort

Ice Filled Pan forH2O Condensation

Desiccator JarChamber

~ 100 mL/min

INTEGRATOR

Gas Chromatograph

5 mL GasSampling Loop

Time (hours)

PP

M

CH2FCl

Time (hours)

PP

M

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 Constants

Tissue Solubility

Tissue Volumes

Blood and Air Flows

Experimental System

Model Equations

X

X

X

X

X

XX X

Tis

sue C

on

centr

ati

on

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

Collect

Data

Select

ModelFit Model to

Data

Ct = A e –kaxt + B e-kbxt

X

X

X

X

X

XX X

Tis

su

e C

on

cen

trati

on

time

k12k21

koutKOA1

A2

X

X

Tis

su

e C

on

cen

trati

on

time

XX X

X

XX