Plumbing 101 or How a good boy went bad Mel Andersen McKim Conference QSAR and Aquatic Toxicology & Risk Assessment June 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 An Almost Post-Doc – 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) QcQc C vl C vf C vr C vs QcQc CaCa QLQL QfQf QrQr QsQs CiCi CxCx QpQp Lung Liver Fat Rapidly perfused (brain, kidney, etc.) Slowly perfused (muscle, bone, etc.)

Describing the Individual Pieces Quantitatively Dead Space Lung Ventilation Capillary Blood Inspired Air Expired Air From: Hagaard (1924) Body Tissue Pulmonary Blood

Countercurrent Exchange Problem: Estimate amount taken up in first few breaths. Q p C inh Q p C exh C exh Q c C art C art Q c C ven Q c = cardiac output Q p = alveolar ventilation C inh = inhaled concentration C exh = exhaled concentration C art = arterial concentration C ven = venous concentration P b = 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) Q t = tissue blood flow C vt = venous blood concentration P t = tissue blood partition coefficient V t = volume of tissue A t = amount of chemical in tissue Q t C art Q t C vt V t ; A t ; P t Tissue C vt = C t /P t Terms mass-balance equation: dA t = V t dC t = Q t C art - Q t C vt dt

Blood Flow Characteristics in Animals & Digital Computation LUNG Liver Right heart Kidney Trunk Lower extremity Large intestine 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 Tissue Group Richly Perfused Tissue Group Liver Metabolizing Tissue Group () Metabolites V max KmKm C art QlQl QrQr QmQm QtQt QcQc C alv (C art /Pb) Q alv C inh QcQc C ven C vt C vm C vr C vl

TIME - hours Venous Concentration – mg/lier blood Conc = 80 ppm Conc = 1200 ppm Conc = 600 ppm Extrapolations – Across Doses

Alveolar Space Lung Blood Fat Tissue Group Muscle Tissue Group Richly Perfused Tissue Group Liver Metabolizing Tissue Group () Metabolites V max KmKm C art QlQl QrQr QmQm QtQt QcQc C alv (C art /Pb) Q alv C inh QcQc C ven C vt C vm C vr C vl What do we need to add/change in the models to incorporate another dose route – iv or oral? IV Oral

Styrene - Dose Route Extrapolation Hours IV Styrene Concentration (mg/l) Hours Oral Styrene Concentration (mg/l) 2.8

Alveolar Space Lung Blood Fat Tissue Group Muscle Tissue Group Richly Perfused Tissue Group Liver Metabolizing Tissue Group () Metabolites V max KmKm C art QlQl QrQr QmQm QtQt QcQc C alv (C art /Pb) Q alv C inh QcQc C ven C vt C vm C vr C vl What do we need to add/change in the models to describe another animal species? Sizes Flows Metabolic Constants

Styrene - Interspecies Extrapolation Rat - Human Hours Styrene Concentration (mg/l)

Getting Constants for Modeling Metabolism and Closed Chamber Stainless Steel Bellows Pump ~ 2.0 L/min CO 2 Scrubber Particulate Filter O 2 Monitor Pressure Gauge Injection Port Ice Filled Pan for H 2 O Condensation Desiccator Jar Chamber ~ 100 mL/min INTEGRATOR Gas Chromatograph 5 mL Gas Sampling Loop

Time (hours) PPM CH 2 FCl Time (hours) PPM CH 2 Cl 2 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 Needed Data Refine Model Structure Make Predictions Metabolic Constants Tissue Solubility Tissue Volumes Blood and Air Flows Experimental System Model Equations X X X X X X X X Tissue Concentration 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 TTT Plasma LiverG.I. Tract r1r1 r2r2 r3r3 Kidney Muscle QKQK Q L - Q G QGQG QMQM Gut Lumen Gut absorption C1C1 C2C2 C3C3 C4C4 Feces Bischoff et al. (1971)

Compartmental PK Modeling Collect Data Select Model Fit Model to Data C t = A e –kaxt + B e -kbxt X X X X X X X X Tissue Concentration time k 12 k 21 k out KO A1 A2 X X Tissue Concentration time X X X X X X