The metabolism and disposition of hexachloro-1:3-butadiene in the rat and its relevance to nephrotoxicity

Following po administration of a nephrotoxic dose (200 mg/kg) of hexachloro-1:3-butadiene (HCBD) to male rats, the principal route of excretion was biliary, 17-20% of the dose being eliminated on each of the first 2 days. Fecal excretion over this period was less than 5% of the dose per day, suggesting enterohepatic recirculation of biliary metabolites. Urinary excretion was small, not exceeding 3.5% of the dose during any 24-hr period. The major biliary metabolite was a direct conjugate between glutathione and HCBD itself. The cysteinylglycine conjugate of HCBD has also been found in bile. Evidence was obtained to show that biliary metabolites of HCBD are reabsorbed and excreted via the kidneys. The glutathione conjugate, its mercapturic acid derivative, and bile containing HCBD metabolites were all nephrotoxic when dosed orally to rats. In common with HCBD, these metabolites caused localized damage to the kidney with minimal effects in the liver. Rats fitted with a biliary cannula were completely protected from kidney damage when dosed with HCBD, demonstrating that hepatic metabolites were solely responsible for the nephrotoxicity of this compound. It is proposed that the hepatic glutathione conjugate of HCBD was degraded to its equivalent cysteine conjugate which was cleaved by the renal cytosolic enzyme beta-lyase to give a toxic thiol which caused localized kidney damage. A urinary sulphenic acid metabolite of HCBD has been identified which is consistent with this hypothesis. The mode of activation of HCBD conjugates in the kidney is believed to be analogous to that proposed for S-(1,2-dichlorovinyl)-L-cysteine.

Species differences in the disposition of inhaled butadiene

Recent chronic inhalation carcinogenicity studies of butadiene indicated that B6C3F1 mice are more sensitive to the tumorigenic effects of inhaled butadiene than are Sprague-Dawley rats. Tumors in mice included lymphomas, hemangiosarcomas, alveolar/bronchiolar adenomas and carcinomas, and hepatocellular adenomas and carcinomas whereas in rats tumors included mammary tumors, thyroid follicular cell adenomas, uterine tumors, and exocrine pancreatic adenomas. The purpose of this investigation was to determine if there were differences in the uptake and disposition of inhaled butadiene between rats and mice and if these differences were consistent with the differences in the species susceptibility to inhaled butadiene. Male Sprague-Dawley rats and B6C3F1 mice were exposed nose only to concentrations in the range of 0.14 to 13,000 micrograms [14C]butadiene/liter air (0.08 to 7100 ppm; 25 degrees C, 620 torr) for 6 hr. Blood samples were taken during exposure and urine, feces, and expired air were collected for up to 65 hr after exposure. In both rats and mice there was a significant (p less than 0.001) concentration-related decrease in the percentage of butadiene retained at the cessation of a 6-hr exposure with increasing butadiene exposure concentration, suggesting saturable metabolism of this chemical. At all concentrations of butadiene tested, mice retained about 4 to 7 times the amount (mumol/kg body wt) of butadiene and metabolites than did rats. In both species and at all butadiene concentrations tested, urine and exhaled air were the major routes of excretion of 14C, together accounting for 75 to 85% of the total 14C eliminated. In mice, for all concentrations tested, elimination of 14C in urine, feces, and exhaled air increased with increasing butadiene exposure concentration, although the increase was not proportional to exposure concentration. However, exposure of rats to 13,000 micrograms butadiene/liter air resulted in a leveling off in the amount of 14C that was eliminated in urine and a concomitant increase in exhalation of 14CO2. Analysis of blood samples taken during exposure indicated that the blood of mice contained 2 to 5 times the concentration of 1,2-epoxy-3-butene than did the blood of rats. The data from this study indicate that species differences exist in the amount retained and metabolism of inhaled butadiene.

Biomarkers of exposure to 1,3-butadiene as a basis for cancer risk assessment

1,3-Butadiene (BD) is carcinogenic in mice and rats, with mice being considerably more sensitive than rats. Urine metabolites are 1, 2-dihydroxybutyl mercapturic acid (DHBMA) and a mixture of monohydroxy-3-butenyl mercapturic acids (MHBMA). The reactive metabolite 1,2-epoxy-3-butene forms 1- and 2-hydroxy-3-butenyl valine adducts in hemoglobin (MHBVal). The objectives of the study were (1) to compare the suitability of MHBMA, DHBMA, and MHBVal as biomarkers for low levels of exposure to BD, and (2) to explore relative pathways of metabolism of BD in humans for comparison with mice and rats, which is important in relation to cancer risk assessment in man. Analytical methods of measuring MHBMA, DHBMA, and MHBVal were modified and applied in 2 studies to workers engaged in the manufacture and use of BD. Airborne BD concentrations were assessed by personal air monitoring. MHBMA in urine was more sensitive for monitoring recent exposures to BD when compared to DHBMA and could measure 8-h time weighted average exposures as low as 0.13 ppm. Relatively high natural background levels in urine restricted the sensitivity of DHBMA. The origin of this background is currently unknown. The measurement of MHBVal adducts in hemoglobin was a sensitive method for monitoring cumulative exposures to BD at or above 0.35 ppm. Statistically significant relationships were found between urinary MHBMA and DHBMA concentrations, between either of these variables and 8-h airborne BD levels and between MHBVal adducts and average airborne BD levels over 60 days. The data on biomarkers demonstrated a much higher rate of hydrolytic metabolism of 1,2-epoxy-3-butene in humans compared to mice and rats, which was reflected in a much higher DHBMA/(DHBMA + MHBMA) ratio and in much lower levels of MHBVal in humans. Assuming a genotoxic mechanism, the data of this study, coupled with other published data on DNA and hemoglobin binding in mice and rats, suggest that the cancer risk for man from exposure to BD is expected to be less than for the rat and much less than for the mouse.

Species differences in urinary butadiene metabolites; identification of 1,2-dihydroxy-4-(N-acetylcysteinyl)butane, a novel metabolite of butadiene

1,3-Butadiene (BD) is used in the manufacture of styrene-BD and polybutadiene rubber. Differences seen in chronic toxicity studies in the susceptibility of B6C3F1 mice and Sprague-Dawley rats to BD raise the question of how to use the rodent toxicology data to predict the health risk of BD in humans. The purpose of this study was to determine if there are species differences in the metabolism of BD to urinary metabolites that might help to explain the differences in the toxicity of BD. The major urinary metabolites of BD in F344/N rats, Sprague-Dawley rats, B6C3F1 mice, Syrian hamsters, and cynomolgus monkeys were identified as 1,2-dihydroxy-4-(N-acetylcysteinyl)-butane (I) and the N-acetylcysteine conjugate of BD monoxide [1-hydroxy-2-(N-acetylcysteinyl)-3-butene] (II). These mercapturic acids are formed by addition of glutathione at either the double bond (I) or the epoxide (II) respectively. When exposed to approximately 8000 p.p.m. of BD for 2 h, the mice excreted 3-4 times as much metabolite II as I, the hamster and the rats produced approximately 1.5 times as much metabolite II as I, while the monkeys produced primarily metabolite I. The ratio of formation of metabolite I to the total formation of the two mercapturic acids correlated well with the known hepatic epoxide hydrolase activity in the different species. These data suggest that (i) the availability of the monoepoxide for conjugation with glutathione is highest in the mouse, followed by the hamster and the rat, and is lowest in the monkey; and (ii) the epoxide availability is inversely related to the hepatic activity of epoxide hydrolase, the enzyme that removes the epoxide by hydrolysis. The ratio of the two mercapturic acids in human urine following BD exposure may indicate the pathways of BD metabolism in humans and may aid in the determination of the most appropriate animal model for BD toxicity.

hprt mutant lymphocyte frequencies in workers at a 1,3-butadiene production plant

1,3-Butadiene is a major industrial chemical that has been shown to be a carcinogen at multiple sites in mice and rats at concentrations as low as 6.25 ppm. Occupational exposures have been reduced in response to these findings, but it may not be possible to determine by using traditional epidemiological methods, whether current exposure levels are adequate for protection of worker health. However, it is possible to evaluate the biological significance of exposure to genotoxic chemicals at the time of exposure by measuring levels of genetic damage in exposed populations. We have conducted a pilot study to evaluate the effects of butadiene exposure on the frequencies of lymphocytes containing mutations at the hypoxanthine-guanine phosphoribosyl transferase (hprt) locus in workers in a butadiene production plant. At the same time, urine specimens from the same individuals were collected and evaluated for the presence of butadiene-specific metabolites. Eight workers from areas of the plant where the highest exposures to butadiene occur were compared to five workers from plant areas where butadiene exposures were low. In addition, six subjects with no occupational exposure to butadiene were also studied as outside controls. All of the subjects were nonsmokers. An air sampling survey conducted for 6 months, and ending about 3 months before the study, indicated that average butadiene levels in the air of the high-exposure areas were about 3.5 +/- 7.5 ppm. They were 0.03 +/- 0.03 ppm in the low-exposure areas. Peripheral blood lymphocytes from the subjects were assayed using an autoradiographic test for hprt mutations.(ABSTRACT TRUNCATED AT 250 WORDS)

Quantitative and qualitative differences in the metabolism of 14C-1,3-butadiene in rats and mice: relevance to cancer susceptibility

1,3-Butadiene (butadiene) is a potent carcinogen in mice, but not in rats. Metabolic studies may provide an explanation of these species differences and their relevance to humans. Male Sprague-Dawley rats and B6C3F1 mice were exposed for 6 h to 200 ppm [2,3-14C]-butadiene (specific radioactivity [sa] 20 mCi/mmol) in a Cannon nose-only system. Radioactivity in urine, feces, exhaled volatiles and 14C-CO2 were measured during and up to 42 h after exposure. The total uptake of butadiene by rats and mice under these experimental conditions was 0.19 and 0.38 mmol (equivalent to 3.8 and 7.5 mCi) per kg body weight, respectively. In the rat, 40% of the recovered radioactivity was exhaled as 14C-CO2, 70% of which was trapped during the 6-h exposure period. In contrast, only 6% was exhaled as 14C-CO2 by mice, 3% during the 6-h exposure and 97% in the 42 h following cessation of exposure. The formation of 14C-CO2 from [2,3-14C]-labeled butadiene indicated a ready biodegradability of butadiene. Radioactivity excreted in urine accounted for 42% of the recovered radioactivity from rats and 71% from mice. Small amounts of radioactivity were recovered in feces, exhaled volatiles and carcasses. Although there was a large measure of commonality, the exposure to butadiene also led to the formation of different metabolites in rats and mice. These metabolites were not found after administration of [4-14C]-1,2-epoxy-3-butene to animals by i.p. injection. The results show that the species differences in the metabolism of butadiene are not simply confined to the quantitative formation of epoxides, but also reflect a species-dependent selection of metabolic pathways. No metabolites other than those formed via an epoxide intermediate were identified in the urine of rats or mice after exposure to 14C-butadiene. These findings may have relevance for the prediction of butadiene toxicity and provide a basis for a revision of the existing physiologically based pharmacokinetic models.

Disposition and nephrotoxicity of hexachloro-1,3-butadiene

Hexachloro-1,3-butadiene (HCBD) administration to rats results in impaired kidney function. The time course of nephrotoxicity and disposition of HCBD were examined. Within 4 h after HCBD (300 mg/kg, i.p.) compromised kidney function was found as decreased urine osmolality, glomerular filtration rate (GFR) and drug excretion. At 24 h elevated blood urea nitrogen (BUN) was found. However, no definitive signs of hepatotoxicity were observed up to 48 h after HCBD. Control ralts excreted 40% of tracer dose (0.1 mg/kg, i.p.) of [14C]HCBD in feces and 30% in urine in 48 h. Rats with HCBD-induced nephrotoxicity excreted much less, 7% in feces and 6% in urine. Aliquots of these samples were extracted with hexane. All of 14C in bile and 87% of that in urine was water soluble, indicating that HCBD was biotransformed into polar metabolites.

Biotransformation, excretion and nephrotoxicity of haloalkene-derived cysteine S-conjugates

The formation of cysteine S-conjugates is thought to play an important role in the nephrotoxicity of haloalkenes such as trichloroethene, tetrachloroethene and hexachlorobutadiene. Glutathione S-conjugates formed from these haloalkenes in the liver are processed to the corresponding cysteine S-conjugates, which may be N-acetylated to mercapturic acids and may be accumulated in the kidney. Haloalkene-derived cysteine S-conjugates are also substrates for cysteine conjugate beta-lyases and reactive intermediates are formed in this reaction. The equilibrium between cysteine S-conjugate and mercapturic acid thus influences the extent of beta-lyase dependent bioactivation and subsequently the nephrotoxicity of S-conjugates. In this study, we compared the rates of N-acetylation in vitro and the biotransformation, excretion and nephrotoxicity of S-(1,2-dichlorovinyl)-L-cysteine (1,2-DCVC), S-(2,2-dichlorovinyl)-L-cysteine (2,2-DCVC), S-(1,2,2-trichlorovinyl)-L-cysteine (TCVC) and S-(1,2,3,4,4-pentachlorobutadienyl)-L-cysteine (PCBC) in rats after i.v. injection (40 micromoles/kg). Marked differences in the extent of enzymatic N-acetylation were observed; N-acetylation was most efficient with 2,2-DCVC and least efficient with 1,2-DCVC. In urine, within 48 h, most of the given 2,2-DCVC (77% of the recovered dose) and 1,2-DCVC (92%) were recovered as the corresponding mercapturic acids. In contrast, a higher percentage of cysteine S-conjugate and less of the mercapturic acid were recovered in urine after administration of PCBC and TCVC (50 and 23% of dose as mercapturic acid), respectively. Histopathological examination of the kidneys and urine clinical chemistry showed marked differences in the extent of renal damage. Necroses of the proximal tubules were found after TCVC, PCBC and 1,2-DCVC administration in male, but not in female rats. These differences in nephrotoxicity do not correlate with the balance of acetylation/deacetylation. The higher toxicity observed in male rats may indicate the involvement of other parameters such as uptake mechanisms.

Comparison of breath, blood and urine concentrations in the biomonitoring of environmental exposure to 1,3-butadiene, 2,5-dimethylfuran, and benzene

OBJECTIVES

To investigate and compare alveolar, blood, and urine concentrations of 1,3-butadiene, 2,5 dimethylfuran, and benzene, in non-occupational exposure to these products.

METHODS

Benzene, 2,5-dimethylfuran and 1,3-butadiene were measured in the breath, blood, and urine samples of 61 subjects living in small mountain villages. All 61 were regularly employed as forestry workers. Sampling was done during the long winter-season non-working period. Samples were collected after overnight rest and analysed by headspace and GC-mass spectrometry methods.

RESULTS

The median 1,3-butadiene level was 1.2 ng/l (range: <0.8-13.2 ng/l) in alveolar air, 2.2 ng/l (range: <0.5-50.2 ng/l) in blood, and 1.1 ng/l (range: <1-8.9 ng/l) in urine. The median benzene level was 5.7 ng/l (range: <1-24.9 ng/l) in alveolar air, 62.3 ng/l (range: 33.5-487.2 ng/l) in blood, and 63.4 ng/l (range: 25.8-1099.1 ng/l) in urine. The median 2,5-dimethylfuran level was 0.5 ng/l (range: <1-12.5 ng/l) in alveolar air, 2.5 ng/l (range: <5-372.9 ng/l) in blood, and 51.8 ng/l (range: <5-524.9 ng/l) in urine. In several cases, 2,5-dimethylfuran levels were below the detection limit in alveolar air and blood, especially in non-smokers. 1,3-Butadiene, 2,5-dimethylfuran and benzene levels were significantly higher in smokers than non-smokers in all biological media.

CONCLUSIONS

1,3-Butadiene and benzene, as ubiquitous pollutants, are detectable and quantifiable in human alveolar air, blood and urine. 2,5-Dimethylfuran, which is not a usual environmental pollutant, is almost always detectable in biological media, but only in smokers.

Influence of smoking charcoal filter tipped cigarettes on various biomarkers of exposure

Charcoal (CC) filters of cigarettes are known to significantly reduce a series of volatile constituents in mainstream smoke, including reactive alpha,beta-unsaturated aldehydes such as acrolein and crotonaldehyde. We performed a randomized, crossover, 2-wk brand-switching study with 39 smokers. Twenty of the subjects smoked cellulose acetate (CA) filter tipped cigarettes during wk 1 of the study; the remaining 19 subjects smoked CC filter tipped cigarettes during wk 1. In wk 2, the subjects switched to the corresponding brand with the other filter type, with similar smoking machine-derived tar and nicotine yields. Daily cigarette consumption, carbon monoxide in exhaled breath, salivary cotinine, and urinary nicotine equivalents (molar sum of nicotine plus five major metabolites) did not change significantly when switching to the cigarettes with the other filter type. Urinary excretion rates of 3-hydroxy-1-methylpropylmercapturic acid (metabolite of crotonaldehyde), monohydroxybutenylmercapturic acid (metabolite of 1,3-butadiene), and S-phenylmercapturic acid (metabolite of benzene) were significantly lower when smoking CC compared to CA filter tipped cigarettes. The reduction in amount of 3-hydroxypropylmercapturic acid (metabolite of acrolein) was of borderline significance. Other mercapturic acids and thioethers (the latter is a summary parameter that indicates the exposure to electrophilic compounds) were not or were only slightly reduced upon smoking CC filter tipped cigarettes. We conclude that smoking CC filter tipped cigarettes does not change the uptake of carbon monoxide and nicotine when compared to CA filter tipped cigarettes with similar tar and nicotine yields, but significantly reduces the exposure to toxicologically relevant smoke constituents such as acrolein, crotonaldehyde, 1,3-butadiene, and benzene.

Excretion pattern and metabolism of hexachlorobutadiene in rats. Evidence for metabolic activation by conjugation reactions

Excretion, covalent binding and metabolism of hexachloro-1,3-butadiene (HCBD), a nephrotoxic and nephrocarcinogenic compound, have been studied in female rats. Seventy-two hours after administration of a single oral dose of 1 mg/kg [14C]HCBD, 5.3% of the dose were exhaled as unchanged HCBD and 76.3% were metabolized and excreted in urine and feces or exhaled as 14CO2. After a 50 mg/kg dose of [14C]HCBD, the amount of exhaled parent compound was nearly unchanged at 5.4%. At the higher dose the gastro-intestinal absorption of HCBD appeared to be saturated with the result that unchanged HCBD constituted the major portion of the 69% radioactivity eliminated. Covalent binding to proteins in kidney and liver agreed well with the organ-specific toxicity of HCBD: binding was higher in the kidney, independent of the dose. It increased significantly when the rats were pretreated with phenobarbital, an inducer of monooxygenases; it decreased when the inhibitor piperonyl butoxide was given. Urinary radioactivity in 24 hr urine was separated by column chromatography into four fractions. High performance liquid chromatography, radio gas chromatography and gas chromatography/mass spectrometry were used for further separation and identification. Two major metabolites were identified as pentachlorobutadiene methylthio ether and pentachlorobutadiene carboxymethylthio ether. Their formation is plausibly explained via glutathione conjugation, which appears to be the first step in HCBD metabolism. The mechanism of the conjugation at the olefinic double bond of HCBD is explained by an addition-elimination reaction. This pathway, which appears to lead to a destabilization of the HCBD molecule, could explain the distinct nephrotoxic effects of HCBD.

Urinary metabolites and haemoglobin adducts as biomarkers of exposure to 1,3-butadiene: a basis for 1,3-butadiene cancer risk assessment

Since 1,3-butadiene (BD) is a suspected human carcinogen, exposure to BD should be minimised and controlled. This study aimed at comparing the suitability of biomarkers for low levels of exposure to BD, and at exploration of the relative pathways of human metabolism of BD for comparison with experimental animals. Potentially sensitive biomarkers for BD are its urinary metabolites 1,2-dihydroxybutyl mercapturic acid (DHBMA, also referred to as MI) and 1- and 2-monohydroxy-3-butenyl mercapturic acid (MHBMA, also referred to as MII) and its haemoglobin (Hb) adducts 1- and 2-hydroxy-3-butenyl valine (MHBVal). In two field studies in BD-workers, airborne BD, MHBMA, DHBMA and MHBVal were determined. MHBMA proved more sensitive than DHBMA for monitoring recent exposures to BD and could measure 8-h time weighted average exposures as low as 0.13 ppm (0.29 mg/m(3)). The sensitivity of DHBMA was restricted by relatively high natural background levels in urine, of which the origin is currently unknown. MHBVal proved a sensitive method for monitoring cumulative exposures to BD at or above 0.35 ppm (0.77 mg/m(3)). Statistically significant relationships were found between either MHBMA or DHBMA and 8-h airborne BD levels, and between MHBVal adducts and average airborne BD levels over 60 days. The data showed a much higher rate of hydrolytic metabolism of BD in humans compared to animals, which was reflected in a much higher DHBMA/(MHBMA+DHBMA) ratio, and in much lower levels of MHBVal in humans, confirming in vitro results. Assuming a genotoxic mechanism, the data of this study coupled with our recent data on DNA and Hb binding in rodents, suggest that the cancer risk for humans from exposure to BD will be less than for the rat, and much less than for the mouse.

Urinary biomarkers of 1,3-butadiene in environmental settings using liquid chromatography isotope dilution tandem mass spectrometry

Although, 1,3-butadiene is a known human carcinogen emitted from mobile sources, little is known about traffic-related human exposure to this toxicant. This pilot study was designed to characterize traffic-related environmental exposure to 1,3-butadiene and evaluate its urinary mercapturic acids as biomarkers of exposure in these settings. Personal air samples and multiple urine samples were collected on two separate occasions from three groups of individuals that differed by spatial proximity as well as intensity of traffic: (i) toll collectors, (ii) urban-weekday and (iii) suburban-weekend group. Air samples were analyzed using thermal desorption followed by GC/MS and urine samples were analyzed using isotope dilution liquid chromatography tandem mass spectrometry (ID-LC-MS/MS) for two mercapturic acids of 1,3-butadiene: monohydroxy-3-butenyl mercapturic acid (MHBMA) and 1,2-dihydroxybutyl mercapturic acid (DHBMA). Exposure differed between groups (p<0.05) with median values of 2.38, 1.62 and 0.88 microg/m(3) for toll collectors, the urban-weekday group and the suburban-weekend group, respectively. A refined ID-LC-MS/MS method enabled detection of MHBMA, previously detected only in occupational settings, with high frequency. MHBMA and DHBMA were detected in 95 and 100% of urine samples at levels (mean+/-S.D.) of 9.7+/-9.5, 6.0+/-4.3 and 6.8+/-2.6 ng/mL for MHBMA and 378+/-196, 258+/-133 and 306+/-242 ng/mL for DHBMA for the three different groups, respectively. Mean biomarker levels were higher among the toll collectors compared to the other two groups, however, the differences were not statistically significant (p>0.05). This study is the first to evaluate 1,3-butadiene biomarkers for subtle differences in environmental exposures. However, additional research will be required to ascertain whether the lack of statistical association observed here is real or attributable to unexpectedly small differences in exposure between groups (<1 microg/m(3)), non-specificity of the biomarker at low exposure, and/or small sample size.

High throughput HPLC-ESI(-)-MS/MS methodology for mercapturic acid metabolites of 1,3-butadiene: Biomarkers of exposure and bioactivation

1,3-Butadiene (BD) is an important industrial and environmental carcinogen present in cigarette smoke, automobile exhaust, and urban air. The major urinary metabolites of BD in humans are 2-(N-acetyl-L-cystein-S-yl)-1-hydroxybut-3-ene/1-(N-acetyl-L-cystein-S-yl)-2-hydroxybut-3-ene (MHBMA), 4-(N-acetyl-L-cystein-S-yl)-1,2-dihydroxybutane (DHBMA), and 4-(N-acetyl-L-cystein-S-yl)-1,2,3-trihydroxybutyl mercapturic acid (THBMA), which are formed from the electrophilic metabolites of BD, 3,4-epoxy-1-butene (EB), hydroxymethyl vinyl ketone (HMVK), and 3,4-epoxy-1,2-diol (EBD), respectively. In the present work, a sensitive high-throughput HPLC-ESI(-)-MS/MS method was developed for simultaneous quantification of MHBMA and DHBMA in small volumes of human urine (200 μl). The method employs a 96 well Oasis HLB SPE enrichment step, followed by isotope dilution HPLC-ESI(-)-MS/MS analysis on a triple quadrupole mass spectrometer. The validated method was used to quantify MHBMA and DHBMA in urine of workers from a BD monomer and styrene-butadiene rubber production facility (40 controls and 32 occupationally exposed to BD). Urinary THBMA concentrations were also determined in the same samples. The concentrations of all three BD-mercapturic acids and the metabolic ratio (MHBMA/(MHBMA+DHBMA+THBMA)) were significantly higher in the occupationally exposed group as compared to controls and correlated with BD exposure, with each other, and with BD-hemoglobin biomarkers. This improved high throughput methodology for MHBMA and DHBMA will be useful for future epidemiological studies in smokers and occupationally exposed workers.

Binding of hexachlorobutadiene to alpha 2u-globulin and its role in nephrotoxicity in rats

Hexachlorobutadiene (HCBD) is nephrotoxic in rats causing damage to the proximal tubules. Renal toxicity is presumed to be due to bioactivation by glutathione S-conjugate formation and further processing by the enzymes of the mercapturic acid pathway to reactive intermediates. Recent studies revealed major sex-dependent differences in the pattern of urinary metabolites and gave evidence for the excretion of unmetabolized HCBD in the urine of male, but not female, rats. The objective of this study was to investigate the basis for the excretion of unchanged HCBD in the urine. We administered [14C]-HCBD (200 mg/kg bw, po) to male and female Sprague-Dawley (SD) and NCI Black-Reiter rats (NBR), an alpha 2u-globulin-deficient strain. No major differences in the disposition and in the rates of excretion of [14C]-derived radioactivity were observed between animals of both strains. Previously observed sex-specific differences in the formation of urinary metabolites in Wistar rats were now confirmed in SD rats and were also found in NBR rats. In contrast to male SD rats, however, NBR rats did not excrete unmetabolized HCBD with urine. [14C]-HCBD (10% of total urinary metabolites) was only present in the urine of male SD rats. Anion-exchange HPLC showed radioactivity associated with the alpha 2u-globulin fraction in urine and renal cytosol of male SD rats; the radioactive compound was identified as HCBD bound to the protein. The results indicate that the male-specific urinary excretion of HCBD is associated with its binding to alpha 2u-globulin. Light microscopic examination revealed the formation of hyaline droplets indicative of the accumulation of alpha 2u-globulin in the kidney of male SD rats after staining with Lee's methylene blue basic fuchsin. H&E staining additionally confirmed the finding of more pronounced necrotic changes in renal tubules of male SD rats than in females as previously described for Wistar rats. Binding of HCBD to alpha 2u-globulin may contribute to the pronounced nephrotoxicity in male rats.

Health risk evaluation in a population exposed to chemical releases from a petrochemical complex in Thailand

Emissions from petrochemical industries may contain toxic and carcinogenic compounds that can pose health risk to human populations. The scenario may be worse in developing countries where management of such exposure-health problems is typically not well-implemented and the public may not be well-informed about such health risk. In Thailand, increasing incidences of respiratory diseases and cancers have been reported for the population around a major petrochemical complex, the Map Ta Phut Industrial Estate (MTPIE). This study aimed to systematically investigate an exposure-health risk among these populations. One-hundred and twelve healthy residents living nearby MTPIE and 50 controls located approximately 40km from MTPIE were recruited. Both external and internal exposure doses to benzene and 1,3-butadiene, known to be associated with the types of cancer that are of concern, were measured because they represent exposure to industrial and/or traffic-related emissions. Health risk was assessed using the biomarkers of early biological effects for cancer and inflammatory responses, as well as biomarkers of exposure for benzene and 1,3-butadiene. The exposure levels of benzene and 1,3-butadiene were similar for both the exposed and control groups. This was confirmed by a non-significant difference in the levels of specific urinary metabolites for benzene (trans,trans-muconic acid, t,t-MA) and 1,3-butadiene (monohydroxy-butyl mercapturic acid, MHBMA). Levels of 8-hydroxydeoxyguanosine (8-OHdG) and DNA strand breaks between the two groups were not statistically significantly different. However, functional biomarkers, interleukin-8 (IL-8) expression was significantly higher (p<0.01) and DNA repair capacity was lower (p<0.05) in the exposed residents compared to the control subjects. This suggests that the exposed residents may have a higher risk for development of diseases such as cancer compared to controls. However, the increased expression of IL-8 and lower DNA repair capacity were not associated with recent and excessive exposure to benzene and 1,3-butadiene, which were at the similar levels as those in the controls. The data would indicate that previous exposure to the two chemicals together with exposure to other toxic chemicals from the MTPIE may be responsible for the elevated functional biomarkers and health risk. Further studies are required to determine which other pollutants from the industrial complex could be causing these functional abnormalities.

Partial contribution of biliary metabolites to nephrotoxicity, renal content and excretion of [14C]hexachloro-1,3-butadiene in rats

Male Sprague Dawley rats with cannulated bile duct (BDC rats) received 100 or 200 mg kg-1 labelled hexachloro-1,3-butadiene ([14C]HCBD) by gavage 1 h (BDC1 rats) or 24 h (BDC24 rats) after surgical cannula implantation. Twenty-four hours after treatment with HCBD, rats were examined histochemically and biochemically for kidney damage. Urine, faeces, liver and kidney radioactivities were also measured in 24-h samples. Results were compared with those obtained from non-cannulated (NC) rats. Bile-duct cannulation did not completely protect against HCBD-induced kidney damage. The 24-h [14C] urinary excretion and tissue content was 30-50% lower in BDC rats compared to NC rats and correlated well with the toxicity findings. BDC1 rats appeared to be much more resistant to HCBD treatment than BDC24 rats. Since faecal [14C] radioactivity extractable by diethyl ether at neutral pH in BDC1 rats was twice that measured in BDC24 rats, the greater resistance was attributed to a higher deficiency in the gastrointestinal absorption of unchanged HCBD. The present results reveal that the biliary metabolites of HCBD are not solely responsible for kidney toxicity as previously assumed. They suggest a sinusoidal efflux of the HCBD conjugates from the liver.

Metabolic distribution of radioactivity in Sprague-Dawley rats and B6C3F1 mice exposed to 1,3-[2,3-14C]-butadiene by whole body exposure

The uptake of 1,3-[2,3-(14)C]-butadiene and its disposition, measured as radioactivity in urine, faeces, exhaled volatiles and CO(2) during and following 6 h whole body exposure to 20 ppm butadiene has been investigated in male Sprague-Dawley rats and B6C3F1 mice. Whilst there were similarities between the two species, the uptake and metabolic distribution of butadiene were somewhat different for rats and mice. The major differences observed were in the urinary excretion of radioactivity and in the exhalation of 14C-CO(2). After 42 h from the start of exposure, 51.1% of radioactivity was eliminated in rat urine compared with 39.5% for mouse urine. 34.9% of the recovered radioactivity was exhaled by rats as 14C-CO(2), compared with 48.7% by mice. Excretion of radioactivity in faeces was similar for both species (3.8% for rats and 3.4% for mice). The tissue concentrations of 14C-butadiene equivalents measured in liver, testes, lung and blood of exposed mice were 0.493, 0460, 0.457, and 1.626 nmol/g tissue, respectively. The values for the corresponding rat tissues were 0.869, 0.329, 0.457, and 1.626 nmol butadiene equivalents/g tissue, respectively. For rats, 6.2% of recovered radioactivity (0.288 nmol butadiene equivalents/g tissue) was retained in carcasses whereas for mice the amount was 3.6% (0.334 nmol butadiene equivalents/g tissue). There were also some significant differences between the metabolic conversion of 1,3-[2,3-(14)C]-butadiene and excretion by mice following the 20 ppm whole body exposure compared to previously reported data for nose-only exposure to 200 ppm butadiene [Richardson et al., Toxicol. Sci. 49 (1999) 186]. The main difference between the high- and low-exposure studies was in the exhalation of 14C-CO(2). At the 200 ppm exposure, 40% of the radioactivity was exhaled as 14C-CO(2) by rats whereas 6% was measured by this route for mice. The proportional conversion of butadiene to CO(2) by mice was significantly greater at the low exposure concentration compared with that reported for the higher concentration. This shift was not observed for rats. The difference between species could be caused by a saturation of metabolism in mice between 20 and 200 ppm for the pathways leading to CO(2). Restraint or error in collection of CO(2) in the 200 ppm study could also be factors.

Biomarkers in Czech workers exposed to 1,3-butadiene: a transitional epidemiologic study

A multiinstitutional, transitional epidemiologic study was conducted with a worker population in the Czech Republic to evaluate the utility of a continuum of non-disease biological responses as biomarkers of exposure to 1,3-butadiene (BD)* in an industrial setting. The study site included two BD facilities in the Czech Republic. Institutions that collaborated in the study were the University of Vermont (Burlington, Vermont, USA); the Laboratory of Genetic Ecotoxicology (Prague, the Czech Republic); Shell International Chemicals, BV (Amsterdam, The Netherlands); the University of North Carolina at Chapel Hill (Chapel Hill, North Carolina, USA); University of Texas Medical Branch at Galveston (Galveston, Texas, USA); Leiden University (Leiden, The Netherlands); and the Health and Safety Laboratory (Sheffield, United Kingdom). Male volunteer workers (83) participated in the study: 24 were engaged in BD monomer production, 34 in polymerization activities, and 25 plant administrative workers served as unexposed control subjects. The BD concentrations experienced by each exposed worker were measured by personal monitor on approximately ten separate occasions for 8-hour workshifts over a 60-day exposure assessment period before biological samples were collected. Coexposures to styrene, benzene, and toluene were also measured. The administrative control workers were considered to be a homogeneous, unexposed group for whom a series of 28 random BD measurements were taken during the exposure assessment period. Questionnaires were administered in Czech to all participants. At the end of the exposure assessment period, blood and urine samples were collected at the plant; samples were. fractionated, cryopreserved, and kept frozen in Prague until they were shipped to the appropriate laboratories for specific biomarker analysis. The following biomarkers were analyzed: * polymorphisms in genes involved in BD metabolism (Prague and Burlington); * urinary concentrations of 1-hydroxy-2-(N-acetylcysteinyl)-3-butene and 2-hydroxy-1-(N-acetylcysteinyl)-3-butene (M2 [refers to an isomeric mixture of both forms]) (Amsterdam); * urinary concentrations of 1,2-dihydroxy-4-(N-acetylcysteinyl)-butane (M1) (Amsterdam); * concentrations of the hemoglobin (Hb) adducts N-(1-[hydroxymethyl]-2-propenyl)valine and N-(2-hydroxy-3-butenyl)valine (HBVal [refers to an isomeric mixture of both forms]) (Amsterdam); * concentrations of the Hb adduct N-(2,3,4-trihydroxybutyl)valine (THBVal) (Chapel Hill); * T cell mutations in the hypoxanthine phosphoribosyltransferase (HPRT) gene (autoradiographic assay in Galveston with slide review in Burlington; cloning assay in Leiden with mutational spectra determined in Burlington); and * chromosomal aberrations by the conventional method and by fluorescence in situ hybridization [FISH]), and cytogenetic changes (sister chromatid exchanges [SCEs] (Prague). All assay analysts were blinded to worker and sample identity and remained so until all work in that laboratory had been completed and reported. Assay results were sent to the Biometry Facility in Burlington for statistical analyses. Analysis of questionnaire data revealed that the three exposure groups were balanced with respect to age and years of residence in the district, but the control group had significantly more education than the other two groups and included fewer smokers. Group average BD exposures were 0.023 mg/m3 (0.010 ppm) for the control group, 0.642 mg/m3 (0.290 ppm) for the monomer group, and 1.794 mg/m3 (0.812 ppm) for the polymer group; exposure levels showed considerable variability between and within individuals. Styrene exposures were significantly higher in the polymer group than in the other two groups. We found no statistically significant differences in the distributions of metabolic genotypes over the three exposure groups; genotype frequencies were consistent with those previously reported for this ethnic and national population. Although some specific genotypes were associated with quantitative differences in urinary metabolite concentrations or Hb adduct dose-response characteristics, none indicated a heightened susceptibility to BD. Concentrations of both the M2 and M1 urinary metabolites and both the HBVal and THBVal Hb adducts were significantly correlated with group and individual mean BD exposure levels; the Hb adducts were more strongly correlated than the urinary metabolites. By contrast, no significant relations were observed between BD exposures and HPRT gene mutations (whether determined by the auto-radiographic or the cloning method) or any of the cytogenetic biomarkers (whether determined by the conventional method or FISH analysis). Neither the mutational nor the cytogenetic responses showed any association with genotypes. The molecular spectrum of HPRT mutations in BD-exposed workers showed a high frequency of deletions; but the same result was found in the unexposed control subjects, which suggests that these were not due to BD exposure. This lack of association between BD exposures and genetic effects persisted even when control subjects were excluded from the analyses or when we conducted regression analyses of individual workers exposed to different levels of BD.

Synthesis and characterization of the trans- and cis-isomers of N-acetyl-S-(4-hydroxy-2-buten-1-yl)-L-cysteine and their attempted detection in human urine

1,3-Butadiene (BD) is a carcinogenic air pollutant. N-acetyl-S-(4-hydroxy-2-buten-1-yl)-L-cysteine (MHBMA3 or 4HBeMA), an urinary BD metabolite with unspecified configuration, is considered the most sensitive BD biomarker and has been used in routine biomonitoring since 2012. However, two issues remain unaddressed: why its concentrations are unusually high relative to other urinary BD biomarkers and why some authors reported no detection of the biomarker whereas other authors readily quantitated it. To address the issues, we synthesized and structurally characterized the authentic trans- and cis-isomers of MHBMA3 (designated NE and NZ, respectively), developed an isotope-dilution LC-MS/MS method for their quantification, and examined 67 urine samples from barbecue restaurant personnel (n = 47) and hotel administrative staff (n = 20). The restaurant personnel were exposed to barbecue fumes, which contain relatively high concentrations of BD. The results showed that NE and NZ had highly similar NMR spectra, and were difficult to be well separated chromatographically. The NMR data showed that the MHBMA3 isomer investigated in most previous studies was NE. We did not detect NE and NZ in any samples; however, an interfering peak with varying heights was observed in most samples. Notably, under the chromatographic conditions used in the literature, the peak exhibited indistinguishable retention time from that of NE. Thus, it is highly likely that the interfering peak has been mis-identified as NE in previous studies, providing a reasonable explanation for the high MHBMA3 concentration in urine. The contradiction in the presence of MHBMA3 in urine was also caused by the mis-identification, because the researchers who reported the absence of MHBMA3 were actually detecting NZ. Thus, we clarified the confusion on MHBMA3 in previous studies through correctly identifying the two MHBMA3 isomers. The presence of NE and NZ in human urine warrants further investigations.

Measurement and modeling of exposure to selected air toxics for health effects studies and verification by biomarkers

The overall aim of our investigation was to quantify the magnitude and range of individual personal exposures to a variety of air toxics and to develop models for exposure prediction on the basis of time-activity diaries. The specific research goals were (1) to use personal monitoring of non-smokers at a range of residential locations and exposures to non-traffic sources to assess daily exposures to a range of air toxics, especially volatile organic compounds (VOCs) including 1,3-butadiene and particulate polycyclic aromatic hydrocarbons (PAHs); (2) to determine microenvironmental concentrations of the same air toxics, taking account of spatial and temporal variations and hot spots; (3) to optimize a model of personal exposure using microenvironmental concentration data and time-activity diaries and to compare modeled exposures with exposures independently estimated from personal monitoring data; (4) to determine the relationships of urinary biomarkers with the environmental exposures to the corresponding air toxic. Personal exposure measurements were made using an actively pumped personal sampler enclosed in a briefcase. Five 24-hour integrated personal samples were collected from 100 volunteers with a range of exposure patterns for analysis of VOCs and 1,3-butadiene concentrations of ambient air. One 24-hour integrated PAH personal exposure sample was collected by each subject concurrently with 24 hours of the personal sampling for VOCs. During the period when personal exposures were being measured, workplace and home concentrations of the same air toxics were being measured simultaneously, as were seasonal levels in other microenvironments that the subjects visit during their daily activities, including street microenvironments, transport microenvironments, indoor environments, and other home environments. Information about subjects' lifestyles and daily activities were recorded by means of questionnaires and activity diaries. VOCs were collected in tubes packed with the adsorbent resins Tenax GR and Carbotrap, and separate tubes for the collection of 1,3-butadiene were packed with Carbopack B and Carbosieve S-III. After sampling, the tubes were analyzed by means of a thermal desorber interfaced with a gas chromatograph-mass spectrometer (GC-MS). Particle-phase PAHs collected onto a quartz-fiber filter were extracted with solvent, purified, and concentrated before being analyzed with a GC-MS. Urinary biomarkers were analyzed by liquid chromatography-tandem mass spectrometry (LC-MS-MS). Both the environmental concentrations and personal exposure concentrations measured in this study are lower than those in the majority of earlier published work, which is consistent with the reported application of abatement measures to the control of air toxics emissions. The environmental concentration data clearly demonstrate the influence of traffic sources and meteorologic conditions leading to higher air toxics concentrations in the winter and during peak-traffic hours. The seasonal effect was also observed in indoor environments, where indoor sources add to the effects of the previously identified outdoor sources. The variability of personal exposure concentrations of VOCs and PAHs mainly reflects the range of activities the subjects engaged in during the five-day period of sampling. A number of generic factors have been identified to influence personal exposure concentrations to VOCs, such as the presence of an integral garage (attached to the home), exposure to environmental tobacco smoke (ETS), use of solvents, and commuting. In the case of the medium- and high-molecular-weight PAHs, traffic and ETS are important contributions to personal exposure. Personal exposure concentrations generally exceed home indoor concentrations, which in turn exceed outdoor concentrations. The home microenvironment is the dominant individual contributor to personal exposure. However, for those subjects with particularly high personal exposures, activities within the home and exposure to ETS play a major role in determining exposure. Correlation analysis and principal components analysis (PCA) have been performed to identify groups of compounds that share common sources, common chemistry, or common transport or meteorologic patterns. We used these methods to identify four main factors determining the makeup of personal exposures: fossil fuel combustion, use of solvents, ETS exposure, and use of consumer products. Concurrent with sampling of the selected air toxics, a total of 500 urine samples were collected, one for each of the 100 subjects on the day after each of the five days on which the briefcases were carried for personal exposure data collection. From the 500 samples, 100 were selected to be analyzed for PAHs and ETS-related urinary biomarkers. Results showed that urinary biomarkers of ETS exposure correlated strongly with the gas-phase markers of ETS and 1,3-butadiene. The urinary ETS biomarkers also correlated strongly with high-molecular-weight PAHs in the personal exposure samples. Five different approaches have been taken to model personal exposure to VOCs and PAHs, using 75% of the measured personal exposure data set to develop the models and 25% as an independent check on the model performance. The best personal exposure model, based on measured microenvironmental concentrations and lifestyle factors, is able to account for about 50% of the variance in measured personal exposure to benzene and a higher proportion of the variance for some other compounds (e.g., 75% of the variance in 3-ethenylpyridine exposure). In the case of the PAHs, the best model for benzo[a]pyrene is able to account for about 35% of the variance among exposures, with a similar result for the rest of the PAH compounds. The models developed were validated by the independent data set for almost all the VOC compounds. The models developed for PAHs explain some of the variance in the independent data set and are good indicators of the sources affecting PAH concentrations but could not be validated statistically, with the exception of the model for pyrene. A proposal for categorizing personal exposures as low or high is also presented, according to exposure thresholds. For both VOCs and PAHs, low exposures are correctly classified for the concentrations predicted by the proposed models, but higher exposures were less successfully classified.

Identification of urinary metabolites of isoprene in rats and comparison with mouse urinary metabolites

Isoprene, a major commodity chemical used in production of polyisoprene elastomers, has been shown to be carcinogenic in rodents. Similar to findings for the structurally related compound butadiene, mice are more susceptible than rats to isoprene-induced toxicity and carcinogenicity. Although differences in uptake, and disposition of isoprene in rats and mice have been described, its in vivo biotransformation products have not been characterized in either species. The purpose of these studies was to identify the urinary metabolites of isoprene in Fischer 344 rats and compare these metabolites with those formed in male B6C3F1 mice. After i.p. administration of 64 mg [14C]isoprene/kg to rats and mice, isoprene was excreted unchanged in breath ( approximately 50%) or as urinary metabolites ( approximately 32%). In rats isoprene was primarily excreted in urine as 2-hydroxy-2-methyl-3-butenoic acid (53%), 2-methyl-3-buten-1,2-diol (23%), and the C-1 glucuronide conjugate of 2-methyl-3-buten-1,2-diol (13%). These metabolites are consistent with preferential oxidation of isoprene's methyl-substituted vinyl group. No oxidation of the unsubstituted vinyl group was observed. In addition to the isoprene metabolites found in rat urine, mouse urine contained numerous other isoprene metabolites with a larger percentage (25%) of total urinary radioactivity associated with an unidentified, polar fraction than in the rat (7%). Unlike butadiene, there was no evidence that glutathione conjugation played a significant role in the metabolism of isoprene in rats. Because of the unidentified metabolites in mouse urine, involvement of glutathione in the metabolism of isoprene in mice cannot be delineated.

Metabolism of 3-butene-1,2-diol in B6C3F1 mice. Evidence for involvement of alcohol dehydrogenase and cytochrome p450

3-Butene-1,2-diol (BDD), a metabolite of 1,3-butadiene, is rapidly metabolized by B6C3F1 mice at doses ranging from 10 to 250 mg/kg. Calculation of plasma clearance suggested that the kinetics of BDD metabolism were dose-dependent. Clearance varied 5-fold in this dose range. Urinary excretion of BDD was also dose-dependent but did not exceed 5% of the administered dose. A small fraction of the dose (<1%) was excreted as glucuronide or sulfate conjugates. Benzylimidazole, a cytochrome P450 inhibitor, decreased the clearance of BDD (25 mg/kg) by 44%, whereas 4-methylpyrazole, an alcohol dehydrogenase and cytochrome P450 inhibitor, decreased BDD clearance by 82%. BDD administration (250 mg/kg) resulted in depletion of hepatic and renal nonprotein thiols, by 48 and 22%, respectively. Pretreatment of mice with 4-methylpyrazole provided partial protection against depletion of nonprotein thiols, whereas pretreatment with benzylimidazole was ineffective. Incubation of BDD with NADPH and mouse liver microsomes resulted in time-dependent inactivation of p-nitrophenol hydroxylase (PNPH) activity, a marker for cytochrome P450. Inclusion of glutathione, with or without glutathione peroxidase, did not attenuate the inactivation of PNPH, whereas deferoxamine, superoxide dismutase, catalase, and mannitol provided modest protection. These results are consistent with suicide inhibition of PNPH by BDD, with a minor role for reactive oxygen species in the loss of PNPH. Treatment of mice with BDD (250 mg/kg) inactivated hepatic microsomal PNPH activity by 50% after 60 min. These results suggest that BDD is extensively and rapidly metabolized in mice, and they provide evidence for the formation of reactive intermediates that could play a role in the toxicity of 1, 3-butadiene.