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Styrene oxide (SO), a labile metabolite of styrene, is generally accepted as being responsible for any genotoxicity associated with styrene. To better define the hazard associated with styrene, the activity of the enzymes involved in the formation (monooxygenase) and destruction of SO (epoxide hydrolase and glutathione-S-transferase) were measured in the liver and lungs from naive and styrene-exposed male Sprague-Dawley rats and B6C3F1 mice (three daily 6-h inhalation exposures at up to 600 ppm styrene) and Fischer 344 rats (four daily 6-h inhalation exposures at up to 1000 ppm styrene), and in samples of human liver tissue. Additionally, the time course of styrene and SO in the blood was measured following oral administration of 500 mg styrene/kg body weight to naive Fischer rats and rats previously exposed to 1000 ppm styrene. The affinity of hepatic monooxygenase for styrene, as measured by the Michaelis constant (Km), was similar in the rat, mouse, and human. Based on the Vmax for monooxygenase activity and the relative liver and body size, the mouse had the greatest capacity and humans the lowest capacity to form SO from styrene. In contrast, human epoxide hydrolase and a greater affinity (i.e., lower Km) for SO than epoxide hydrolase from rats or mice while the apparent Vmax for epoxide hydrolase was similar in the rat, mouse, and human liver. However, the activity of epoxide hydrolase relative to monooxygenase activity was much greater in the human than in the rodent liver. Hepatic glutathione-S-transferase activity, as indicated by the Vmax, was 6- to 33-fold higher than epoxide hydrolase activity. However, the significance of the high glutathione-S-transferase activity is unknown because hydrolysis, rather than conjugation, is the primary pathway for SO detoxification in vivo. Human hepatic glutathione-S-transferase activity was extremely variable between individual human livers and much lower than in rat or mouse liver. Prior exposure to styrene had no effect on monooxygenase activity or on blood styrene levels in rats given a large oral dose of styrene. In contrast, prior exposure to styrene increased hepatic epoxide hydrolase activity 1.6-fold and resulted in lower (0.1 > P > 0.05) blood SO levels in rats given a large oral dose of styrene. Qualitatively, these data indicate that the mouse has the greatest capacity and the human the lowest capacity to form SO. In addition, human liver should be more effective than rodent liver in hydrolyzing low levels of SO.(ABSTRACT TRUNCATED AT 400 WORDS)

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A rapid and selective method for the determination of styrene-7,8-oxide (SO) in whole blood has been developed. Blood samples as small as 0.1 ml are extracted once with benzene containing phenyl propylene oxide as an internal standard. The extracts are analyzed by gas chromatography-mass spectrometry using an automated cold on-column injection system to avoid thermal rearrangement of SO to phenylacetaldehyde. The overall mean recovery (+/- 2 sigma) of SO from fortified blood samples was 92 +/- 21% and the detection limit was 10 ng/g. Results of experiments examining the half-life of SO in whole rat blood are presented. The method was also used to analyze sequential blood samples from rats administered SO orally.

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The absorption, distribution, metabolism and excretion of [14C]-atrazine was studied in male Fischer 344 rats administered a 30 mg [14C]-atrazine/kg of body weight oral dose with or without pretreatment with a non-radiolabeled oral dose of 60 mg tridiphane/kg of body weight. The objective of this study was to determine whether tridiphane had any meaningful effect on the pharmacokinetics and/or metabolism of atrazine in the rat. The 14C plasma time-course exhibited a mono-exponential decrease with an absorption and elimination half-life of approximately 3 h and 11 h, respectively for both treatment groups. In addition, at 72 h after the administration of [14C]-atrazine, approximately 93% of the administered radioactivity was recovered and the primary route of excretion was via the urine (67%) for both treatment groups. The feces accounted for approximately 18% of the dose, and less than 10% remained in the carcass, skin, and red blood cells (RBCs). The urine excreted in the first 24 h post-dosing contained approximately 57% of the administered radioactivity for both treatment groups. There were no appreciable differences in the metabolite distribution between treatment groups, and the major urinary metabolite of atrazine was found to be 2-chloro-4,6-diamino-1,3,5-triazine (II; 64-67%). Additionally, S-(2-amino-4-methylethylamino-1,3,5-triazin-6-yl)-mercapturi c acid (V; 13-14%), and S-(2,4-diamino-1,3,5-triazin-6-yl)-mercapturic acid (III; 9%) were tentatively identified based upon similar HPLC retention times as seen with synthesized standards. These data indicate that there are no meaningful differences in the absorption, distribution, metabolism, and excretion between rats administered only [14C]-atrazine and those administered both tridiphane and [14C]-atrazine. Therefore, it can be concluded that tridiphane has no meaningful effect on the pharmacokinetics and/or metabolism of atrazine in the rat.

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Ethylene carbonate (EC) has a toxicity profile which resembles that of ethylene glycol (EG). To determine whether the toxicity of EC could be explained on the basis of its metabolism to EG, male Fischer 344 rats were given 200 mg/kg of uniformly labeled [14C]EC in water by gavage and the disposition of the radiolabel was then followed for 72 hr. EC was rapidly metabolized, with approximately 57 and 27% of the administered dose eliminated in the expired air as 14CO2 and in the urine, respectively; the remainder was found in the carcass. Separation of the urinary metabolites using liquid chromatography revealed a single radioactive peak. This metabolite was unequivocally identified as ethylene glycol via gas chromatography-mass spectrometry with the aid of 13C enrichment of the EC dose. Measurement of whole blood levels of EC and EG in rats given 200 mg/kg of EC by gavage revealed blood levels of EG approximately 100-fold higher than the levels of EC in these same animals, with a half-life of EG in blood of 2 hr, indicating rapid conversion of EC to EG. In a separate group of animals administered an equimolar dose of [14C]EG (141 mg/kg), approximately 37% of the dose was expired as 14CO2 and 42% was excreted in the urine as parent compound. When expressed on the basis of the ethanediol moiety, the disposition of EC was identical to that of EG. In view of the rapid and extensive biotransformation of EC to EG and the similarity of the existing (though limited) toxicity data base of EC compared to EG, utilization of the extensive EG systemic toxicity data base for assessing the safety of EC appears justified.

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Male Fischer 344 rats were given a single po dose of approximately 1 or 8.7 mmol/kg of radiolabelled propylene glycol monomethyl ether (PGME) beta isomer (2-methoxy-1-propanol). After dosing, expired air, excreta, and tissues were analyzed for 14C activity and metabolites in urine were isolated and identified. Approximately 70 to 80% of the 14C was excreted in urine while about 10 to 20% was eliminated as 14CO2 within 48 hr after dosing. The major urinary metabolite was 2-methoxypropionic acid, which accounted for approximately 93 and 79% of the radioactivity in urine from high- and low-dose animals, respectively. A glucuronide conjugate of the PGME beta isomer was also identified in urine; this metabolite accounted for approximately 3 to 4% of the radioactivity in the urine at both dosages. These results indicate that the PGME beta isomer is metabolized via different routes to different types of metabolites in comparison to the PGME alpha isomer. While the two isomers are biotransformed differently, there is a substantial toxicological data base which clearly shows that the commercial grade PGME mixture (2 to 5% beta isomer) has a low degree of biological activity.

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Methyl chloride (MeCl) metabolism and pharmacokinetics were studied in male Fischer 344 rats and male beagle dogs. Apparent steady-state blood MeCl concentrations were proportionate to exposure concentration in rats and dogs exposed to 50 and 1000 ppm. Furthermore, blood MeCl concentrations were similar in both species when they were exposed to the same concentration. A linear two-compartment open model described the blood MeCl data: alpha and beta phase elimination half-times corresponded to approximately 4 and 15 min, respectively, in rats, and 8 and 40 min in dogs. Rats exposed for 6 hr to 0, 50, 225, 600, or 1000 [14C]MeCl were evaluated for tissue nonprotein sulfhydryl (NPSH), total 14C activity, nonextractable tissue 14C activity, and urinary metabolites. MeCl-induced NPSH depletion was dose-related and was greatest in liver. Total 14C in liver and kidney was approximately proportionate to exposure concentrations. Relative concentrations of nonextractable 14C decreased at 600 to 1000 ppm MeCl suggesting a dose-dependent metabolic pathway for MeCl in the rat. Metabolites in urine included N-acetyl-S-methylcysteine, methylthioacetic acid sulfoxide, and N-(methylthioacetyl)glycine. These metabolites are likely to be products of a reaction between MeCl and glutathione. A nonradiometric analysis of a putative MeCl metabolite (S-methylcysteine) was performed in dogs exposed to MeCl; this method was not a sensitive indicator of MeCl exposure.

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Male Fischer 344 rats were given a single po dose of approximately 1 or 8.7 mmol/kg of [14C]EGME (ethylene glycol monomethyl ether) or [14C]PGME (propylene glycol monomethyl ether). After dosing, expired air, excreta, and tissues were analyzed for 14C; metabolites in urine were isolated and identified. There were pronounced differences in the metabolism and disposition of [14C]EGME and [14C]PGME. Approximately 50 to 60% of the administered 14C was excreted in urine, and about 12% was eliminated as 14CO2 within 48 hr after a single po dose of [14C]EGME. For PGME, only 10 to 20% of the administered 14C was excreted in urine, while 50 to 60% was eliminated as 14CO2 within 48 hr. Methoxyacetic acid was identified as the primary urinary metabolite of EGME, accounting for 80 to 90% of the total 14C in urine. PGME, propylene glycol(1,2-propanediol), and the sulfate and glucuronide conjugates of PGME were identified in urine of rats given PGME. Since methoxyacetic acid causes the same spectrum of toxicity as EGME in male rats, it is likely that the adverse effects of EGME are the result of its in vivo bioactivation to methoxyacetic acid. Hence, differences in routes of metabolism and types of metabolites appear to be the underlying basis for the remarkably different toxicologic properties of EGME and PGME, respectively.

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The stereochemistry of the metabolism of vic-dihaloalkanes to alkenes has been studied. This glutathione-dependent biotransformation may occur by two mechanism. The first mechanism involves the nucleophilic attack of glutathione on the substrate resulting in S-(beta-haloalkyl)glutathione formation; subsequent attack of a second thiol on the sulfur atom of the conjugate yields glutathione disulfide, ethylene, and halide ion. Alternatively, glutathione may abstract a halide ion from the substrate and form ethylene, halide ion, and glutathione sulfenyl halide. These pathways were distinguished by determining the stereoisomeric alkenes formed in the metabolism of meso- and racemic 2,3-dibromobutane, erythro- and threo-2-bromo-3-chlorobutane, and meso-1,2-dideutero-1,2-dichloroethane. The stereochemical configurations of the 2-butenes and 1,2-dideuteroethylene were determined by gas chromatography and by Fourier-transform infrared spectroscopy, respectively. When incubated with glutathione and rat liver cytosol, meso- and racemic 2,3-dibromogutane were converted exclusively to (E)- and (Z)-2-butene, respectively. On the other hand, erytho- and threo-2-bromo-3-chlorobutane were converted to a mixture of (E)- and (Z)-2-butene. meso-1,2-Dideutero-1,2-dichloroethane was converted exclusively to (Z)-1,2-dideuteroethylene. These results suggest that the 2,3-dibromobutanes are metabolized to 2-butenes by a direct E2 elimination, whereas 2-bromo-3-chlorobutanes undergo metabolism to 2-butenes by both an E2 elimination and a substitution-elimination sequence. However, 1,2-dihaloethane metabolism to ethylene proceeds only by the substitution-elimination mechanism; this result is consisent with the formation of ethylene-S-glutathionylepisulfonium ion, a possible reactive species involved in 1,2-dihaloethane mutagenicity.

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The metabolism of acrylonitrile (AN) in rats was studied in conjunction with toxicological and pharmacokinetic studies to help assess the potential hazard of exposure to AN in the workplace. Rats were administered 30 mg/kg [1-14C] AN or [2,3-14C] AN orally. Radiolabeled metabolites excreted in the urine during the first 16 h were separated by ion-exclusion liquid chromatography and identified (after derivatization) by gas chromatography-infrared spectroscopy and/or gas chromatography-mass spectrometry. Two major urinary metabolites were identified as thiocyanate and N-acetyl-S-(2-cyanoethyl)cysteine. A third was tentatively identified as 4-acetyl-3-carboxy-5-cyanotetrahydro-1,4-2H-thiazine. AN was not detected in the urine. One possible scheme for the AN metabolic pathways is proposed.

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A gas chromatographic procedure is described which is capable of measuring both polar and non-polar organic solvents present simultaneously in the work environment at concentrations between 1/100 and 1 times the Threshold Limit Values (TLV). Airborne organics are collected on a single activated charcoal tube for periods of 3 to 6 hours and desorbed with a two-phase (water/carbon disulfide) desorption mixture. Organic and aqueous phases are analyzed separately on the same gas chromatographic column packed with Oronite NIW on Carbopack B. Recoveries were determined for fifteen common solvents. Most recoveries were greater than 90% with all coefficients of variation being less than +/- 10%. Breakthrough was observed only when solvents were present at very high concentrations. Examples of field sampling are also presented. This procedure is generally applicable for monitoring complex mixtures of volatile organic compounds in air. Advantages include excellent recoveries for polar solvents such as acetone and ethanol, utilization of common analytical instrumentation under a single set of operating conditions and compatibility with TWA personnel monitoring methodology.

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