Document 2Nj9N2mpD6aLwENO5XZQ1ryqg

EFFECTS of ETHANOL PRBIREATMEHT OH MORPHINE DISTRIBUTION IN RATS. D.R. Steup and R.B. fnmrv. Department of Phzimecology and Toxicology. Indiana Dniveraity School of Medicine, Indianapolia, IN Previoue atudies have indicated that ethanol can alter the phanaacokinecica of morphine intravenoualy admimatered to rata. This study vaa undertaken to determine whether this change reaulted from an altered distribution of morphine to the brain, the primary site of action, or the Uver, the primary site of metabolism. Naive, male Sprague-Dawley rata (193-213 g) were administered a single iv dose of morphine sulfate (2.5 mg/kg) one hour after an oral gavage of either ethanol (3 g/kg) or an equivalent volume of saline. After ten minutes, blood was collected by orbital sinus puncture, the animals were sacrificed, and the forebrain, hindbrain, and liver were removed and frocan in liquid nitrogen. Blood and tissue homogenates were then assayed for free (unmetabolized) morphine. The data indicate a statistically significant (P<0.025) increase in the liver to blood ratio of free morphine in the ethanol-treated (0.36 0.07) vs control (0.20 0.03) rats. No changes were seen in either brain morphine levels or brain to blood ratios for the same anisials. The observed changes may represent either an enhanced distribution of morphine to the liver or a higher level ot free morphine secondary to inhibition of hepatic metabolism. 944 PHYSIOLOGICALLY-BASED PHARMACOKINETIC MODEL FOR VINYLIDINE CHLORIDE, R.W. D'Souza and M.E. Andersen, Miami Valley Laboratories, Procter & Gamble Co., Cincinnati, OH and *AAMRL/TH, Wright Patterson AFB, OH. Sponsor: G.P. Daston, A physiologically-based pharmacokinetic (PBPK) model has been developed for vinylldlne chloride (VDC). Simulations generated by the model offer insight into the behavior of VDC that would not be detected with compartmental modeling. Because of its low blood:air parti tion coefficient and saturable metabolism, the fraction of VDC dose that is metabolized or exhaled unchanged Is dependent both on exposure dose and rate of absorption. Intravenous bolus studies cannot be used to elucidate the pharmacokinetics/metabollsm of VDC as a major portion of VDC dose will be exhaled unchanged within a few minutes. Blood VDC half-life is not repre sentative of metabolism, but is due to redistri bution from fat to blood. A glutathione (GSH) depletion model is written as part of the PB-PK description and can be used to estimate the amount of intermediate epoxide that conjugates with GSH or binds to macromolecules. Simula tions generated by the PB-PK model are consis tent with literature data and have also been validated with appropriate experimental obser vations. 943 ABSORPTION STUDY OF DIMAC WITH SILVER SULFADIA7 ZINE AS COMPARED TO SILVADENE CREAM IN THE RAB BIT. Kln-Kal Hwang. Jan Battor, David Drees. Joe Lacz. Marlon Laboratories, Kansas City, MO. The purpose of this study was to determine blood levels of silver and sulfadiazine when silver sulfadiazine (AgSD) is applied to artificial wounds using SILVADENE cream or DIMAC patches as vehicles. Twenty-five young, healthy, male adult rabbits were used for this study. A 2x3 inch epi dermal layer was surgically removed from the back of each rabbit. Two grams of cream (IX AgSD) or a 4x3 inch DIMAC patch (0J.1X.2X and 5X AgSD) was applied directly to the wound once a day for 3 days. Blood samples were taken and assayed for Ag and SD content at 48 and 72 hour periods. The results show that samples from 2 of 5 rabbits treated with 52 DIMAC patches have an Ag blood level of 0. 1360 + 0.018 and 0. 1572 + 0.024 ug/tnl at 48 and 72 hour intervals, respectively. Values obtained from the lower doses were below the lower sensitivity of 0.100 ug of silver/ml of whole blood. Assays of plasma samples at 48 and 72 hour time points demonstrated a linear rela tionship between the patches and their sulfadia zine content. A maximum plasma concentration of 0.4714 + 0,227 and 0.4212 + 0.128 ug/ml of sulfa diazine for 52 DIMAC treated groups was observed at 48 and 72 hours; whereas, 0.1548 + 0.075 and 0.2502 + 0.064 ug/ml of sulfadiazine for IX DIMAC was found. Sulfadiazine blood levels obtained from animals treated with 1% cream were similar to those treated with IX DIMAC. 945 PHARMACOKINETIC MODELS FOR INDIRECT CARCINO GENS. R.H. Reitz, R.B. Conolly and M.E. AnderseTT The Dow Chemical Company, Midland, Ml; Northrop Services Inc., Dayton, OH; AAMRL/TH, Wright Patterson AFB, OH. A number of "animal carcinogens" apparently act through indirect (nongenotoxic) mechanisms. Chemically-induced cell death followed by compensatory cellular regeneration (CCR) may be involved in the activity of these agents. To better understand this process, we have com bined a two-stage carcinogenesis model (Moolgavkar and Knudson, JNCI 66:1037, [1981] with a physiologically-based pharmacokinetic (PB-PK) model for chemical disposition (Ramsey and Andersen, TAP 73:159 [1984]. The model describes the uptake, distribution, and metabolic activation of chemical(s). Depletion of a hepatic macromolecule (MM) is correlated with bioactivation, and depletion of MM increases the probability of cell death. The population of liver cells is described dynamically, with spontaneous and chemicallyinduced rates of cell death and CCR. Simula tion indicates that the population of cells with two mutations increases disproportionately with increasing chemical exposure and time. This work suggests that PB-PK models may be useful in exploring the relationship between chemical exposure, cytotoxicity, and tumor development. SJj 061722 236 PHYSIOLOGICALLY-BASED PHARMACOKINETIC MODEL FOR VINYLIDINE CHLORIDE R. W. D'Souza and *M. E. Andersen Miami Valley Laboratories Procter & Gamble Company Cincinnati, OH and *AAMRL/TH, WHght Patterson AFB, OH Sponsor. G. P. Daston SL 061723 ABSTRACT A physiologically-based pharmacokinetic (PB-PK) model has been developed for vinylidine chloride (VDC). Simulations generated by the model offer insight into the behavior of VDC that would not be detected with compartmental modeling. Because of its low blood.air partition coefficient and saturable metabolism, the fraction of VDC dose that is metabolized or exhaled unchanged is dependent both on exposure dose and rate of absorption. Intravenous bolus studies cannot be used to elucidate the pharmacokinetics/metabolism of VDC as a major portion of VDC dose will be exhaled unchanged within a few minutes. Blood VDC half-life is not representative of metabolism, but is due to redistribution from fat to blood. A glutathi one (GSH) depletion model is written as part of the PB-PK description and can be used to estimate the amount of intermediate epoxide that conjugates with GSH or binds to macromolecules. Simulations generated by the PB-PK model are consistent with literature data and have also been validated with appropriate experimental observations. SL 061724 INTRODUCTION VDC is a large volume chemical used extensively as a solvent and as an intermediate in the manufacture of plastics. VDC has been shown to be hepatotoxic and possibly carcinogenic in laboratory animals. Studies in the literature have demonstrated that VDC is rapidly metabolized, and it is the metabolite(s) and not parent VDC that is responsible for its toxicity and possible carcinogenicity. The metabolite(s) is detoxified by gluthathione (GSH), and therefore liver GSH status is an important determinant in VDC's toxicity. OBJECTIVES To develop a physiologically-based pharmacokinetic (PB-PK) model for VDC, for extrapolation of metabolism and toxicity data between different dose levels, dosing vehicles and routes-of-exposure. SL 061725 METHODS For modeling purposes a lumped compartment approach was used for distribution of VDC. Organs were grouped together based on their blood flow and ability to slowly accumulate VDC. The well-perfused compartment represented such organs as kidney and spleen and the perfused compartment included muscle and skin. The liver was con sidered the only metabolising organ. Parameters used in constructing the PB-PK model were: Partition Coefficientswere determined in vitro by a modification of the method of Sato and Nakajima (1979). Metabolism Rate Constants were estimated in vivo by Gas Uptake Measurements as described by Gargas et al., (1986). A Glutathione Depletion ModeMD'Souza et al., 1986) was included as part of the modeling description of VDC in order to predict liver GSH status and therefore VDC toxicity. Physiologic Parameters like blood flow and organ volume were obtained from the literature. SL 061726 GUT SL 061727 Parameters Used in PB-PK Model Partition Coefficients Metabolism Rate Constants Phi = 1.1 Pi = 1.1 Pr = 1.1 Ps = 0.6 Pi = 18.4 Pb = 5.0 Vmax -- 7.5 mg hr 'kg" Km = 0.25 mg LT'kg'1 Kgsm -- 0.1 hr 'kg ' Kfee -- 300 hr'1 kg'1 Kco2 -- 0.2 hr''kg'' Kmac = 0.8 hr'1 kg 1 SL 061728 Modeling for VDC Metabolism Inhaled VDC Oral Vma,Km Epoxjde K*"W Intermediate VDC L.GSH Kco2 / N^mac Kgsrn Detoxified Products r co2 MMaaccKroXml olecular Binding SL 061729 Modeling for GSH Depletion Precursors Breakdown Kip/9roducts Ki, GSH Synthetase Ko Kgsm K, Breakdown Products VDC Epoxide Detoxified Products SL 06173q Predicted (------ ) and observed (symbols) VDC concentrations in dif ferent tissues of the rat following a single 50 mg/kg intravenous dose. Predicted VDC concentrations for blood, liver, lung and brain are shown as a single curve, as the tissue:blood partition coefficients for these "well-perfused" tissues is approximately one. Time (hour) SL 061731 Predicted and observed liver glutathione concentrations following inhalation and oral exposures to VDC. Glutathione is depleted due to conjugation with VDC epoxide. Since only that amount of metabolite that is not detoxified by glutathione has toxic potential, therefore, by predicting the amount of glutathione depletion the PB-PK model can be used to predict toxic potential as a function of dose and route-of-exposure. 6-Hour Inhalation Exposures at Different Concentrations1 4-Hour Inhalation Exposure at 200 ppm Concentration2 200 mg/kg Oral Exposure in Corn Oil Vehicle 1 Data Source: Mckenna et al., 1977 2 Data Source: Reynolds et al., 1980 Simulations below show that because of the low blood:air partition coefficient on VDC and its saturable metabolism, the rate of VDC absorption can have profound effects on the potential for VDC to be metabolized or exhaled unchanged. At very rapid absorption Rates (intravenous bolus) almost all of the VDC dose is rapidly exhaled in the breath. Changes in metabolism, therefore, cannot be differen tiated from studying blood VDC kinetics after this route of exposure. As the absorption rate is decreased more VDC is metabolized and changes in Vmax result in changes in VDC blood kinetics. The change in blood kinetics becomes evident with an absorption rate constant (ka) of 5.0 (typically seen with water as a dosing vehicle) and is even more pronounced when ka is decreased to 1.0 (typically seen with corn oil as the dosing vehicle). SL 061733 Predicted (------) and observed (symbols) blood VDC concentrations in rats of different body weights. These Sprague Dawley rats were allowed free access to food and gained weight rapidly. The approxi mate age of the animals were 6 weeks (180 g), 8 weeks (300 g) and 14 weeks (600 g) with fat content of 7,12 and 20% respectively. Because of the small age difference between these groups of rats, large differ ences in metabolizing enzymes are not expected among these anim als. The computer predictions were accomplished by changing only one parameter in th PB-PK model, that is, the amount of fat in the animal. SL 061734 PB-PK model simulations describing the effect of oral dose level on the percent of VDC dose that will be exhaled unchanged, exhaled as C02, bind to macromolecules and conjugate with glutathione. Sym bols shown are experimentally observed data reported in the litera ture for VDC (circles) and CO2 (squares) exhalation. o VDC exhaled at 1 and 50 mg/kg oral dose (McKenna et al., 1977) VDC exhaled at 350 mg/kg oral dose (Jones and Hathway. 1978) C02 exhaled at 1 and 50 mg/kg oral dose (McKenna et at., 1977) VDC exhaled at 350 mg/kg oral dose (Jones and Hathway, 1978) SL O6I735 PB-PK model simulations describing the effect of inhalation dose level (6-hour exposures) on the body-burden and the amounts of dose that will be exhaled as C02 or will bind to macromolecules. Data from the literature1 for body-burden and amount of C02 exhaled following inhalation doses of 10 and 200 ppm are also shown. Inhalation Concentration (ppm) 1 Data source: McKenna et al., 1978 SL 061736 CONCLUSIONS A PB-PK model for VDC has been developed and validated. The model demonstrates the complex interrelationship between absorp tion, saturable metabolism and glutathione status in determining the toxic potential of VDC. Effects of dose level, absorption rate, and route-of-exposure on the toxic potential of VDC has been demonstrated by model simulations. Where possible, these simulations have been validated by experimen tal data from this laboratory or from data reported in the literature. fffF NOMENCLATURE First-order rate constant for oral absorption First-order rate constant for C02 formation First-order rate constant for non-GSH route First-order rate constant for GSH conjugation Michaelis-Menten constant for VDC oxidation Kmac First-order rate constant for macromolecular binding potential Ko Zero-order GSH formation Kp First-order rate constant for GSH loss Kio GSH synthetase formation Kip First-order rate constant for GSH synthetase loss Pb Blood:air partition coefficient Pf Fat:blood partition coefficient Pi Liver.blood partition coefficient Piu Lung.blood partition coefficient Pr Richly-perfused: Blood partition coefficient Ps Slowly-perfused: Blood partition coefficient Qc Cardiac output Qf Fat blood flow Qi Liver blood flow Qr Richly-perfused blood flow Qs Slowly-perfused blood flow Vmax Maximum velocity of VDC oxidation SL 061738 REFERENCES D'Souza, R. W., Francis, W. R., and Andersen, M. E. (1986). Mathemati cal model for glutathione depletion and increased resynthesis follow ing ethylene dichloride exposure. Pharmaceutical Research. 3(5), 137. Gargas, M. L., Ctewell, H. J., and Andersen, M. E. (1986). Metabolism of inhaled dihalomethanes in vivo: differentiation of kinetic constants for two different pathways. Toxicol. Appl. Pharmacol. 82,211-223. Jones, B. K. and Hathway, D. E. (1978). The biological fate of vinylidine chloride in the rat. Chem. Biol. Interactions. 20,27-41. McKenna, M. J., Watanabe, P. G., and Gehring, P. J. (1977). Pharma cokinetics of vinylidine chloride in the rat. Environ. Health Perspec. 21, 99-105. McKenna, M. J., Zempel, J. A., Madrid, E. O., Braun, W. H., and Gehring, P. J. (1978). Metabolism and pharmacokinetic profile of vinylidine chloride in rats following oral administration. Toxicol. Appl. Pharmacol. 45,821-835. Reynolds, E. S., Moslen, M. T., Boor, P. J., and Jeager, R. J. (1980). 1,1-dichloroethylene hepatotoxicity. Am. J. Pathol. 101(2), 331-342. Sato, A. and Nakajima, T. (1979). Partition Coefficients of some aro matic hydrocarbons and ketones in water, blood and oil. Brit. J. Ind. Med. 36. 231-234. SL 061739