Simulation of urine levels of 1- hydroxypyrene with a generic PBTK- - PowerPoint PPT Presentation

AIRMON 2011, Loen Simulation of urine levels of 1- hydroxypyrene with a generic PBTK- model in situations with inhalation and/or dermal exposure Frans Jongeneelen, IndusTox Consult, Nijmegen, NL Wil ten Berge, Santoxar, Westervoort, NL

Overview of the PBTK- Exposure scenario  Three routes of uptake: model IndusChemFate  Inhalation - concentration  Dermal – dose rate  Oral - dose  Duration of exposure  Personal Protective Equipment  Physical activity level (rest/ light) Compound data  Physical-chemical properties:  Density  Molecular weight  Vapour pressure PBTK-model  Log(K ow ) at pH 5.5 and 7.4  Water Solubility  Biochemical parameters :  Metabolism (k M and V max )  Renal tubulair resorption Pyrene and metabolites (Venous Blood) 4,50E-04  Enterohepatic circulation ratio 4,00E-04 3,50E-04 3,00E-04 2,50E-04 VenBl C0 µmol/l 2,00E-04 VenBl C1 µmol/l VenBl C2 µmol/l 1,50E-04 1,00E-04 5,00E-05 0,00E+00 2 0,000 10,000 20,000 30,000 40,000 50,000 60,000 70,000 80,000 Hours

What is a PBTK-model?  PBTK-model = Physiologically Based ToxicoKinetic model  A PBTK-model is a mathematical description for absorption, distribution, metabolism and excretion (ADME) of a chemical in the body of experimental animals or humans  Compartments corresponds to predefined organs or tissues, with interconnections corresponding to blood  A system of differential equations is used to estimate the concentration of a chemical in each compartment  Such a model can predict the time-course of concentrations in blood and/or urine after inhalation (or dermal exposure) 3

Scheme of the physiology of the PBTK-model Parent compound Inhalation Exhalation Lungs Cyclus of 1st metabolite Heart Exhalation Brain Lungs Dermal Evaporation load Heart Dermis Brain A V R E Adipose N T Dermis E O V A Muscle U R R E Adipose I S N T Bone A O E Muscle R U L Bone marrow S I Bone Oral A intake L Bone marrow Stomach + intestine o 2 nd T Stomach + B B intestine metabolite L L B B cyclus Liver L O L O Liver O O O O O O Kidney D D Kidney D D Excretion of Excretion of 1 st metabolite parent compound in urine in urine 4

Routing of chemicals and metabolites in the PBTK-model – Absorption – Inhalation – Oral uptake – Dermal uptake – Distribution over the body – QSPR algorithm for estimate of blood:air partitioning – QSPR algorithm for estimate of tissue:blood partitioning – Metabolism – Saturable metabolism according to Michaelis-Menten kinetics – Metabolism in all tissues, only liver is default – Excretion – Urine – Exhaled air 5

Dermal absorption module of the model As liquid and/or solid As vapour/gas = New model of Vapour of AIHA-EASC substance Deposition named Evaporation IH SKINPERM Stagnant air layer Substance Stratum corneum Absorption Skin Viable epidermis To systemic circulation 6

Distribution over compartments in the body – Blood:air partition coefficient • QSPR Algorithm for estimation of blood:air partitioning based on Henry coefficient and K oa – Blood:tissue partition coefficient • QSPR Algorithm for estimation of blood:tissue partitioning taken from De Jong et al (1997), based on lipid content and K ow 7

The PBTK-model is build as application in MS-Excel, called IndusChemFate • The differential equations of the PBTK-model are written in speadsheet syntax (visual basic) • The file IndusChemFate contains 4 sheets: 1. Tutorial with instructions in short 2. Worksheet – For data entry (exposure scenario, properties of chemical under study) – For numerical output 3. Database of phys-chemical and biochemical properties of various chemicals 4. Graphical output sheet 8

Simulation experiment 1 Operator creosote impregnating plant • 1-hydroxypyrene was measured in urine of an operator of a creosote impregnating plant during 7-days • Creosote oil = a timber protective agent that contains PAH • Pyrene is metabolised to 1-hydroxypyrene Figure 3-1A . Excretion of 1OHP in urine of a creosote impregnating worker (Jongeneelen et al, 1988) 9

Metabolism of pyrene 10

Human metabolism kinetics of pyrene Step Tissue Parameter and value ref V max = 180 µ mol/hr/kg Pyrene Hepatic 9000*g Jongeneelen to fraction of 12 tissue (1987) 1-OH-pyrene individuals K M = 4.4 µ M V max = 6,900 µ mol/hr/kg 1-OH-Pyrene Hepatic microsomal Luukkanen to fraction of 3 tissue et al (2001) 1-OH-pyrene- gluc individuals K M = 7.7 µ M 11

Simulation experiment 1 Enter data  Enter phys-chemical properties and biochemical parameters of parent compound and metabolites under study  Enter exposure scenario  Inhalation: concentration and duration  Dermal: dose rate and duration  Oral: bolus dose 12

Simulation experiment 1 Pyrene Entering properties of pyrene and 1-OH-Pyrene metabolite 1-OH-Pyrene-glucuronide 13

Simulation experiment 1 Entering exposure scenario of the creosote plant operator Airborne exposure scenario Dermal exposure scenario Oral intake scenario 14

Simulation experiment 1 Run program - Results as table with levels and amounts in fluids and tissues

pyrene and metabolites (Alveolar Air) Simulation experiment 1 3,00E-10 Figure 1: Alveolair air 2,50E-10 Run program- 2,00E-10 1,50E-10 AlvAir C0 µMol/l Results as graphs AlvAir C1 µMol/l 1,00E-10 AlvAir C2 µMol/l 5,00E-11 0,00E+00 0,000 20,000 40,000 60,000 80,000 100,000 120,000 140,000 160,000 180,000 -5,00E-11 Hours pyrene and metabolites (Urine) 4,00E-01 Figure 3: Urine 3,50E-01 3,00E-01 pyrene and metabolites (Venous Blood) 2,50E-01 9,00E-04 Figure 2: Blood 2,00E-01 UrinConc C0 µMol/l 8,00E-04 UrinConc C1 µMol/l 7,00E-04 1,50E-01 UrinConc C2 µMol/l 6,00E-04 1,00E-01 5,00E-04 VenBl C0 µMol/l 5,00E-02 4,00E-04 VenBl C1 µMol/l VenBl C2 µMol/l 3,00E-04 0,00E+00 2,00E-04 0,000 20,000 40,000 60,000 80,000 100,000 120,000 140,000 160,000 180,000 -5,00E-02 1,00E-04 Hours 0,00E+00 0,000 20,000 40,000 60,000 80,000 100,000 120,000 140,000 160,000 180,000 -1,00E-04 Hours 16

Pyrene (C0) and free 1-OH-pyrene (C1) in urine Simulation 0,000003 0,0000025 Experiment 1 0,000002 Results: levels 0,0000015 UrinConc C0 µmol/l 0,000001 UrinConc C1 µmol/l in urine 0,0000005 0 24 48 72 96 120 144 168 Hours Pyrene and metabolites (Urine) 0,500 0,475 0,450 0,425 0,400 0,375 0,350 0,325 0,300 0,275 UrinConc C0 µmol/l 0,250 0,225 0,200 UrinConc C1 µmol/l 0,175 0,150 UrinConc C2 µmol/l 0,125 0,100 0,075 0,050 0,025 0,000 24 48 72 96 120 144 168 17 Hours

Simulation experiment 1 Comparison of measured and PBTK-model predicted level of 1-OH-pyrene in urine of operator Level is expressed as sum of free 1-OHP and 1-OHP-glucuronide 18

Other comparisons of experiments/field measurements with simulations Reference Nr. Type of study Exposure Exposure route scenario Walter & Bitumen fume Dermal 8h exposure to 20 2 Knecht mg/m 3 of bitumen fume exposed volunteers 2007 = 0.65 µ g/m 3 pyrene with RPE (n=10) Bentsen et Intervention study with Inhalation Two weeks 5 shifts*8h 3 al, 1998 exposure to 2.75 µ g/m 3 RPE of electrode paste plant workers (n=18) pyrene Quinlan et Individual differences Inhalation 4 shift*12h at work 4 al, 1995 with 1.3 µ g/m 3 pyrene. among coal and dermal liquefaction workers + (n=5) 96h off work. 19

Results experiment 2: Dermal uptake of bitumen fume among volunteers (Walter & Knecht, 2007) • Non-smoking volunteers with only shorts • Volunteers used RPE to prevent inhalation • 8h exposure to 20 mg/m 3 bitumen fume = 0.65 µ g/m 3 pyrene exposure --- = sum of free 1-OHP and 1-OHP-glucuronide 20

Experiment 3: Reduction of exposure after extra respiratory protection Nr. Type of study Exposure Exposure scenario Reference route 8h to 20 mg/m 3 bitumen Walter & Bitumen fume exposed Dermal 2 Knecht volunteers with RPE fume = 2007 0.65 µ g/m 3 pyrene (n=10) Bentsen et Intervention study with Inhalation Two weeks 5 shifts*8h 3 al, 1998 exposure to 2.75 µ g/m 3 RPE of electrode paste plant workers pyrene (n=18) Quinlan et Individual differences Inhalation 4 shift*12h at work with 4 al, 1995 1.3 µ g /m 3 pyrene. among coal liquefaction and dermal workers + (n=5) 96h off work. 21

Results experiment 3: Reduction of exposure after extra respiratory protection (Bentsen et al, 1998) • Pre- and postshift urine samples during 5-days working week • Regular RPE (red lines) and week with extra RPE (black lines) • Measured (contineous lines) and predicted (broken lines) Dermal exposure was not measured and set at zero in simulation ! 22

Experiment 4: Average level versus boundaries of interindividual differences Nr. Type of study Exposure Exposure scenario Reference route 8h to 20 mg/m 3 bitumen Walter & Bitumen fume exposed Dermal 2 Knecht volunteers with RPE fume = 2007 0.65 µ g/m 3 pyrene (n=10) Bentsen et Intervention study with Inhalation Two weeks 5 shifts*8h 3 al, 1998 exposure to 2.75 µ g/m 3 RPE of electrode paste plant workers pyrene (n=18) Quinlan et Individual differences Inhalation 4 shift*12h at work with 4 al, 1995 1.3 µ g/m 3 pyrene. among coal and liquefaction workers dermal + (n=5) 96h off work. 23