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PubMed1994

Exposure of workers to a mixture of toluene and xylenes. I. Metabolism.

The urinary excretion of hippuric acid and methylhippuric acid was studied in workers (233 subjects; 122 men and 111 women) exposed to toluene and xylenes in combination and in non-exposed controls (281 subjects; 141 men and 140 women) recruited from the same factories or factories of the same regions. Smoking and drinking habits of the subjects were obtained by medical interviews. From each worker, one urine sample was collected at the end of a shift and analysed for hippuric and methylhippuric acids by high performance liquid chromatography. Air samples for the estimation of toluene and xylenes were collected with diffusive personal samplers. There was a linear correlation between the time weighted average exposure either to toluene or xylene isomers and the concentrations of hippuric acid or methylhippuric acid isomers in urine. Essentially no difference was found in the correlation between quantitative exposure and excretion in the three xylene isomers. Comparison of the slopes of regression lines indicated the absence of metabolic interaction between toluene and xylenes at the measured concentrations. The metabolism of toluene and xylenes was significantly reduced among smokers or drinkers compared with non-smokers and non-drinkers.

Adult↗
PubMed1996

Human cytochrome P450 isoform specificity in the regioselective metabolism of toluene and o-, m- and p-xylene.

The conversion of toluene and o-, m- and p-xylene to their respective side-chain and ring monohydroxylated metabolites by human liver microsomes was investigated. Methyl hydroxylation, to form a benzylalcohol, was the major metabolic pathway for all four methylbenzenes. With the exception of 2,4-dimethylphenol formation from m-xylene, ring hydroxylation accounted for < 5% of total metabolite formation. However, regioselectivity of ring hydroxylation was apparent, with hydroxylation occurring only at positions ortho and/or para to a methyl substituent. Toluene and each xylene isomer exhibited biphasic methylhydroxylation kinetics in human liver microsomes. The high-affinity component of each methylhydroxylation was selectively inhibited by diethyldithiocarbamate and correlated significantly with cytochrome P-4502E1 (CYP2E1) content and activities in a panel of human liver microsomes. cDNA-expressed CYP2E1 was shown to catalyze the formation of each benzylalcohol, with apparent Km values similar to those of the high affinity microsomal reactions. In contrast, the conversion of m-xylene to 2,4-dimethylphenol followed single enzyme Michaelis-Menten kinetics, was inhibited selectively by furafylline, and correlated significantly with known CYP1A2 catalyzed reactions. cDNA-expressed CYP1A2 converted m-xylene to 2,4-dimethylphenol, with an apparent Km similar to that of the microsomal reaction. Although CYP1A2 appears to be responsible for the formation of the minor (phenolic) metabolites of toluene and the xylene isomers, CYP2E1 catalyzed methylhydroxylation will be the major determinant of the clearance of these compounds in humans.

Cytochrome P-450 Enzyme System↗
PubMed1980

The combined toxicity of technical grade xylene and ethanol in the rat.

1. Inhalation exposure to xylene of technical grade (300 p.p.m. in air, 6 h a day, 5 days a week, up to 18 weeks) enhanced the overall mono-oxygenation reactions (7-ethoxycoumarin O-deethylase and 2,5-diphenyloxazole hydroxylase( as well as the UDP-glucuronyltransferase activity in rat liver microsomes. 2. The simultaneous ingestion of aqueous 15-20% ethanol as drinking fluid increased the cytochrome P-450 concn. and the mono-oxygenation activity even more than the xylene exposure alone. 3. Xylene-ethanol treatment resulted in additive or less than additive effects on the measured hepatic enzyme activities. 4. Renal ethoxycoumarin deethylase activity was enhanced both by ethanol ingestion and by xylene inhalation, and the response was additive after the combined exposure. 5. Liver histology revealed that even though the xylene exposure alone did not produce detectable liver damage, the xylene-ethanol treatment produced more severe liver damage than did ethanol ingestion alone.

Animals↗
PubMed1978

Exposure to xylene and ethylbenzene. I. Uptake, distribution and elimination in man.

Industrial xylene is a mixture of xylene and ethylbenzene. Twelve male subjects were exposed to industrial xylene in inspired air, six subjects in series I to 870 mg/m3 at rest (30 min) and light exercise on a bicycle ergometer (90 min) and six subjects in series II to 435 mg/m3 at rest (30 min) and during exercise of increasing work loads (90 min). The measurements of xylene uptake were performed continuously with the Douglas bag technique. In both series, about 60% of the amount of xylene supplied to the lungs was taken up. In both series, the concentration in alveolar air was relatively low throughout the entire exposure. The relative concentration in alveolar air displayed a linear correlation to the percentage uptake in the lungs. The ratio between the concentration in arterial blood (mg/kg) and alveolar air (mg/l) amounted to 30--40 at the different work loads. The total amount of xylene expired after the exposure was estimated from the alveolar concentration and alveolar ventilation. In series I, with a total uptake of 1.4 g, the subjects expired about 70 mg, i.e., about 5%. The corresponding value in series II was 40 mg of a total uptake of 1.0 g, i.e., about 4%.

Adult↗
PubMed1999

Effect of benzene, toluene, xylene on the semen quality of exposed workers.

OBJECTIVE: To examine the effects on semen and sperm quality of workers after a short and long term exposure to benzene, toluene, and xylene. METHODS: The semen and blood of 24 married workers exposed to benzene, toluene, and xylene from shoemaking, spray painting, or paint manufacturing factories were collected. The concentration of benzene, toluene, and xylene in the blood and semen was determined by using headspace chromatographic method. Routine sperm test was carried out and acrosin activity detected. RESULTS: The results showed that benzene, toluene, and xylene were found in the blood and semen of some ex-workers in a working environment where the air concentration of benzene, toluene, and xylene exceeded the maximum allowable concentration (MAC). This result was not found in workers of the control group. There were also some effects on the quality of semen in the exposed workers. For example, the percentage of semen with liquefaction time exceeding 30 minutes increased. The sperm vitality, motility and acrosin activity decreased. At the same time, there were a positive correlation between liquefaction time and the level of toluene in semen, and a negative correlation between sperm vitality, sperm activity or acrosin activity and working history. CONCLUSIONS: The results suggested that the mixture could affect the quality of semen and sperm, which might be the main reason of the abnormal pregnancy outcome among the wives of workers exposed to benzene, toluene, and xylene. Further studies are, however, required to confirm these findings.

Acrosin↗
PubMedDate not supplied

Antioxidative properties of coenzyme Q10 and vitamin E in exposure to xylene and gasoline and their mixture with methanol.

Exposure to a mixture of solvents in industry is still a problem particularly in industrial laboratories. In the paint and laquer industry the employees are exposed to xylene (Rx) and gasoline (Rg). The influence of xylene and gasoline or their mixture with methanol on lipid peroxidation was evaluated in the presented paper. Antioxidative properties of CoQ10 or vitamin E were also tested. It was observed that xylene caused an increase of lipid peroxidation measured as a MDA level in all used concentrations, but gasoline only in very high doses. The mixture of xylene with methanol increased significantly MDA level, whereas gasoline with methanol did not influence lipid peroxidation. The character of interaction depends on hydrocarbons dose. CoQ10 and vitamin E are effective antioxidants lowering the increased MDA level caused by xylene, gasoline or their mixture with methanol, however the dose of CoQ10 should be adjusted to the strength of oxidative stress in order to avoid disadvantageous effect. CoQ10 is a more effective antioxidant in exposure to xylene rather than gasoline, but vitamin E acts better in exposure to gasoline decreasing the MDA level.

Adult↗
PubMed1990

[Stimulation of microsomal lipid peroxidation as the effect of combined action of xylene and ethanol].

The aim of the study was to evaluate if in the case of combined exposure of rats to xylene and ethanol stimulation of lipid peroxidation in the liver microsomes (an index of interaction with lipids and derangements of integrity/fluidity of membranes) might occur. Experiments were carried out on male Wistar rats in the conditions of prolonged, inhalatory preexposure to m-xylene at concentration of 4000 mg/m3 for 6 and 12 weeks, and next joint 5-fold treatment with ethanol (2.5 g/kg oral doses in 12 hours intervals for 3 days). The degree of lipid peroxidation was assessed both in vivo and in vitro under chemical stimulation: enzymatically (NADPH, Fe2+) and nonenzymatically (ascorbic acid, Fe2+). The chemical stimulation permits to measure multiplied biological effects of chemicals acting in vivo. As a results of performed studies it was found that the highest increase of lipid peroxidation appeared in the case of prolonged, 12 weeks exposure to m-xylene (4000 mg/m3) and successively under subacute ethanol treatment and 6-week m-xylene exposure. Thus, it was evidenced that stimulation of lipid peroxidation depends on the duration of exposure to m-xylene. Stimulation of lipid peroxidation, revealed here, may arise from the processes of biotransformation of xylene in cyt. P-450 monooxygenase system where generated oxygen free radicals may attack the lipid components of microsomal membrane as well as from the mechanisms leading to decrease of antioxidant ability of the organism (decrease of glutathione-SH and vitamins E and C levels).

Animals↗
PubMed1989

Excretion of methylbenzoic acid in urine as a result of single and combined exposure to m-xylene.

Influence of combined exposure to solvent vapours on the metabolism of m-xylene and the kinetics of excretion of methylbenzoic acid (MBA) in urine was investigated. The volunteers were exposed in groups of four or five. Each experiment consisted of two parts. During the first part, the same test group was exposed to m-xylene for a period of 4 hours, whereas during the second part, the group was exposed to m-xylene in combination with other solvents. No significant differences in the excretion of MBA in urine were observed after exposure to m-xylene in concentrations of about 45 and 70 ppm and exposure to m-xylene together with n-hexane, toluene, methyl isobutyl ketone or n-butyl alcohol in combined concentrations of about 90 and 140 ppm. Only in the case of combined exposure to m-xylene and n-butyl acetate was a significant increase in the excretion of MBA in urine found. For both the single and combined exposure to kinetics of excretion of MBA was similar with t1/2 values in the first phase of excretion ranging between 1-1.3 h.

Acetates↗
PubMed1994

Toxic effects of subchronic combined exposure to n-butyl alcohol and m-xylene in rats.

Effects of combined exposure to m-xylene and n-butyl alcohol in the conditions of subchronic inhalation experiment in rats were examined. Rats were exposed to vapours of individual solvents at concentrations of 50 and 100 ppm and their 1:1 mixture at concentrations of 50 + 50 ppm and 100 + 100 ppm, 6 h/day, 5 days/week for 3 months. No significant changes in body weight gain, in absolute and relative organ weights and clinical biochemistry parameters were observed. The motor coordination disturbances caused by mixture of m-xylene and n-butyl alcohol at concentrations of 100 + 100 ppm were identical as those caused by n-butyl alcohol at concentration of 100 ppm. Thus, in condition of combined exposure, the toxic effect of m-xylene was not added to the effect of n-butyl alcohol. Significant increase in sensitivity to pain in animals exposed to m-xylene at both concentrations, and parallel lack of changes in the pain sensitivity in animals exposed to n-butyl alcohol and to the solvent mixtures was observed. n-Butyl alcohol provoked the increase of lipid peroxidation in hepatic microsomes without any induction of cytochrome P-450 monooxygenases, m-Xylene did not affect the activity of monooxygenase and lipid peroxidation rate in hepatic microsomes and moreover, in the case of combined exposure it abolished the effect on n-butyl alcohol. Results obtained in condition of acute and subchronic inhalation exposure interpreted jointly, indicate the less than additive toxic effect of combined exposure to m-xylene and n-butyl alcohol.

1-Butanol↗
PubMed1994

Effect of xylene clearance of mesenteric fat on harvest of lymph nodes after colonic resection.

OBJECTIVE: To find out if clearance of surgical colectomy specimens with xylene gave a higher yield of lymph nodes and more accurate staging than the traditional step-sectioning technique. DESIGN: Consecutive open study. SETTING: Private hospital, United States. MATERIAL: 84 specimens from colonic resections, 4 of which were total colectomies and the remaining 80 segmental resections. INTERVENTIONS: The first 41 (2 colectomies and 39 segmental resections) were cleared by step-sectioning alone (to establish baseline values). The remainder (n = 2 and 41, respectively) were step-sectioned, the lymph nodes were removed, and then the residual tissue was cleared with xylene. MAIN OUTCOME MEASURES: The number of lymph nodes found, and if the diagnosis was changed by the finding of additional nodes. RESULTS: The baseline values in the two total colectomy specimens were 76 and 101, and the mean (range) after segmental colectomy was 21 (1-98). The values after total colectomy in the second group were 33 and 73, and after xylene clearance an additional 12 and 17 nodes were found. After segmental colectomy a mean (range) of 13 (0-43) was found, and an additional 4 (0-12) were found after xylene clearance. No additional nodes containing metastases were found in total colectomy specimens after xylene clearance, and only 6 additional nodes after segmental resection contained metastases. These changed the histological stage of the disease in only 2 patients. CONCLUSIONS: Xylene clearance offers little advantage over careful traditional step-sectioning of specimens, but may be of value if the histopathologist does not do routine meticulous step-sectioning.

Case-Control Studies↗
PubMed1994

TOL plasmid-specified xylene oxygenase is a wide substrate range monooxygenase capable of olefin epoxidation.

Xylene oxygenase, which is encoded on the TOL plasmid pWWO of Pseudomonas putida mt-2, is a key enzyme system in the degradation of toluene and xylenes by this organism. It was expressed in an Escherichia coli recombinant strain carrying the xylMA structural genes. This recombinant, which expressed xylene oxygenase from the heat-shock induced lambda PL promoter, was analyzed for its potential as a biocatalytic tool so as to effect the oxidation of side chains of aromatic hydrocarbons to the corresponding alcohols. Compounds that were tested as potential substrates carried different substituents on the aromatic ring at ortho, meta, and para positions, relative to the methyl moiety. Products that accumulated after administration of the aromatic hydrocarbons to concentrated suspensions of the recombinant were identified by gas chromatography and mass spectrometry. Toluene derivatives with ortho substituents could not serve as substrates for the biocatalyst, whereas a number of meta- or para- substituted analogs were efficiently oxidized to the corresponding benzylalcohols. Bioconversion of the substrates by resting cells varied from 3 mumol min-1 g-1 cell dry weight for 1,3,5-trimethylbenzene to 18 mumol min-1 g-1 cell dry weight for meta-xylene. Whole cells that expressed xylene oxygenase did catalyze the oxidation of the methyl substituent attached to a benzene ring, but no conversion of n-alkylbenzene derivatives with longer side chains was observed. Although the ethyl group of ethylbenzene could not be converted by the biocatalyst, cells containing xylene oxygenase were capable of oxidizing the ethylene side group of styrene to produce styrene epoxide.

Alkenes↗
PubMed1999

Identification of the Pseudomonas stutzeri OX1 toluene-o-xylene monooxygenase regulatory gene (touR) and of its cognate promoter.

Toluene-o-xylene monooxygenase is an enzymatic complex, encoded by the touABCDEF genes, responsible for the early stages of toluene and o-xylene degradation in Pseudomonas stutzeri OX1. In order to identify the loci involved in the transcriptional regulation of the tou gene cluster, deletion analysis and complementation studies were carried out with Pseudomonas putida PaW340 as a heterologous host harboring pFB1112, a plasmid that allowed regulated expression, inducible by toluene and o-xylene and their corresponding phenols, of the toluene-o-xylene monooxygenase. A locus encoding a positive regulator, designated touR, was mapped downstream from the tou gene cluster. TouR was found to be similar to transcriptional activators of aromatic compound catabolic pathways belonging to the NtrC family and, in particular, to DmpR (83% similarity), which controls phenol catabolism. By using a touA-C2,3O fusion reporter system and by primer extension analysis, a TouR cognate promoter (P(ToMO)) was mapped, which showed the typical -24 TGGC, -12 TTGC sequences characteristic of sigma(54)-dependent promoters and putative upstream activating sequences. By using the reporter system described, we found that TouR responds to mono- and dimethylphenols, but not the corresponding methylbenzenes. In this respect, the regulation of the P. stutzeri system differs from that of other toluene or xylene catabolic systems, in which the hydrocarbons themselves function as effectors. Northern analyses indicated low transcription levels of tou structural genes in the absence of inducers. Basal toluene-o-xylene monooxygenase activity may thus transform these compounds to phenols, which then trigger the TouR-mediated response.

Base Sequence↗
PubMed1998

Associations between several sites of cancer and occupational exposure to benzene, toluene, xylene, and styrene: results of a case-control study in Montreal.

BACKGROUND: Except for the leukemogenic effects of benzene, there is inadequate or sparse evidence on the carcinogenicity of the most common monocyclic aromatic hydrocarbons. The purpose of this study was to generate hypotheses on associations between exposure to benzene, toluene, xylene, and styrene and various common types of cancer. METHODS: In the context of a population-based case-control study carried out in Montreal, 3,730 cancer patients (15 types of cancers, not including leukemia) and 533 population controls were interviewed, and their job histories were translated by a team of experts into occupational exposures, including benzene, toluene, xylene, and styrene. In the present analysis, exposure to these substances was compared between each case series and a control group pooling selected cancer patients and population controls, using logistic regression analysis. RESULTS: Exposure levels were low for most exposed subjects, and there was a high correlation between exposure to benzene, toluene and xylene. For most sites of cancer there was no evidence of excess risk due to these substances. However, limited evidence of increased risk was found for the following associations: esophagus-toluene, colon-xylene, rectum-toluene, rectum-xylene and rectum-styrene. CONCLUSIONS: These latter observations warrant further investigation.

Adult↗
PubMed1982

Toxicology updates. Xylene.

Like most organic solvents, xylene has irritating effects on the skin, mucous membranes and respiratory tract. It has a narcotic effect on the nervous system, variable effects on the liver and kidneys, and questionable effects on the cardiovascular system and female reproductive system. Xylene was thought to be deleterious to the hemopoietic system, but more recent studies concluded that such effects were due to benzene contamination or inflammation response to xylene injection. The latest evidence indicates that xylenes are not co-carcinogenic, carcinogenic or teratogenic. If maternal toxicity is avoided, xylenes do not have embryotoxic effects.

Abnormalities, Drug-Induced↗
PubMed1982

Short-term exposure of human subjects to m-xylene and 1,1,1-trichloroethane.

Inhalation exposure of male volunteers to m-xylene (8.2 mumol/l, 200 ppm) and 1,1,1-trichloroethane (TCE) (8.2 and 16.4 mumol/l, 200 and 400 ppm), as well as to a combination of TCE (16.4 mumol/l) and xylene (8.2 mumol/l), induced only slight changes in psychophysiological functions such as body sway and reaction time. Exposure to the 8.2 mumol/l concentration of xylene or TCE tended to improve the performances, whereas TCE exposure at 16.4 mumol/l alone or in combination with xylene tended to have an opposite effect. The results thus suggest a biphasic acute effect of TCE on the central nervous system (CNS) and reveal that xylene and TCE together exhibit neither kinetic interaction nor synergistic nor antagonistic acute effects on the CNS functions studied.

Adult↗
PubMed1986

Quantitative analysis of urinary glycine conjugates by high performance liquid chromatography: excretion of hippuric acid and methylhippuric acids in the urine of subjects exposed to vapours of toluene and xylenes.

A new method for the direct determination of hippuric acid (HA) and o-, m- and p-methylhippuric acids (MHAs) in the urine, metabolites of toluene and o-, m- and p-xylenes by high performance liquid chromatography (HPLC) is described. A stainless-steel column packed with silica gel having dinitrophenyl residue and a mixed solution of methanol/water/acetic acid (80/20/0.2) containing tetra-n-butylammonium bromide (0.2% w/v) as mobile phase was used. Concentrations of HA and MHAs were estimated from their peak height at a wave length of 225 nm. Urine can be analyzed directly without solvent extraction or pretreatment to obtain complete separation of HA and o-, m- and p-MHAs. Urine samples from male workers exposed to toluene or xylenes were analyzed for HA or MHAs. The urinary levels of HA and MHAs increased by exposure to toluene and xylenes in proportion to the environmental concentrations of the solvents, although there is a considerable variation in metabolite concentrations. The slope of regression line between toluene and HA and that between m-xylene and m-MHA were similar. The urinary concentrations of HA and MHAs corresponding to 100 ppm (TLV) of toluene was 2.35 g/g creatinine and that of m-MHA corresponding to 100 ppm (TLV) of m-xylene was 2.05 g/g creatinine. The warning levels of the urinary metabolite concentrations of a group of workers and that of an individual worker corresponding to TLV of organic solvent concentration is discussed.

Adult↗
PubMed1993

Acute effects of m-xylene inhalation on body sway, reaction times, and sleep in man.

Nine male volunteers were exposed to either a constant or a fluctuating exposure pattern of m-xylene with a time-weighted average exposure concentration of 200 ppm in both cases. The subjects remained sedentary throughout the exposure, or the exercised at 100 W for 10 min at the beginning of the morning and the afternoon sessions. In another experiment, 12 sedentary male volunteers were exposed to a fixed 200 ppm of m-xylene. The effects of m-xylene on body sway, reaction time performance, and overnight sleep were measured. Body balance was stabilized after exposure to the peaks of 400 ppm of m-xylene in both sedentary and exercising subjects. Simple visual reaction times were prolonged after the peak exposures at rest whereas auditive choice reaction times were prolonged after peaks combined with exercise. Exposure to m-xylene at a constant level of 200 ppm did not affect the ratio of "active" to "quiet" sleep in the volunteers as measured with the static charge sensitive bed recording, but decreased slightly the number of body movements in bed. On the next morning no changes were found in body sway and reaction time performance as compared to the morning before exposure.

Adult↗
PubMed1991

Effect of simultaneous exposure to toluene and xylene on their respective biological exposure indices in humans.

Studies that specifically address the influence of controlled human exposure to a combination of solvents on the biological monitoring of exposure are limited in number. The present study was undertaken to investigate whether simultaneous exposure of human volunteers to toluene and xylene could modify the respective metabolic disposition of these solvents. Five adult Caucasian men were exposed for 7 consecutive h/day over 3 consecutive days to 50 ppm toluene and 40 ppm xylene either separately or in combination in a dynamic, controlled exposure chamber (low-level exposure). The experiment was repeated three times at intervals of 2 weeks. In another experiment, three subjects were exposed to 95 ppm toluene and 80 ppm xylene or a combination of both for 4 h (high-level exposure). The concentration of unchanged solvents in blood (B) and in end-exhaled air (EA) as well as the urinary excretion of hippuric acid (HA) and methylhippuric acids (MHAs) were determined. Simultaneous exposure to the lowest level of solvents did not alter the concentration of unchanged solvents in blood or in exhaled air (average of 3-weekly means; single vs mixed exposure at 6.5 h exposure): B-toluene, 77.1 vs 78.1 micrograms/100 ml; B-xylene, 67.6 vs 77.8 micrograms/100 ml; EA-toluene, 9.9 vs 9.5 ppm; EA-xylene, 5.3 vs 4.8 ppm. Similarly, mixed exposure did not modify the excretion of urinary metabolites during the 3- to 7-h exposure period: HA, 1.11 vs 1.11 g/g creatinine: MHAs, 0.9 vs 0.87 g/g creatinine.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗