Influence of genetic polymorphisms of styrene-metabolizing enzymes and smoking habits on levels of urinary metabolites after occupational exposure to styrene

The genotoxicity of an organic solvent mixture: A human biomonitoring study and translation of a real-scenario exposure to in vitro

This study aimed to evaluate occupational exposure to a styrene and xylene mixture through environmental exposure assessment and identify the potential genotoxic effects through biological monitoring. Secondly, we also exposed human peripheral blood cells in vitro to both xylene and styrene either alone or in mixture at concentrations found in occupational settings in order to understand their mechanism of action. The results obtained by air monitoring were below the occupational exposure limits for both substances. All biomarkers of effect, except for nucleoplasmic bridges, had higher mean values in workers (N = 17) compared to the corresponding controls (N = 17). There were statistically significant associations between exposed individuals and the presence of nuclear buds and oxidative damage. As for in vitro results, there was no significant influence on primary DNA damage in blood cells as evaluated by the comet assay. On the contrary, we did observe a significant increase of micronuclei and nuclear buds, but not nucleoplasmic bridges upon in vitro exposure. Taken together, both styrene and xylene have the potential to induce genomic instability either alone or in combination, showing higher effects when combined. The obtained data suggested that thresholds for individual chemicals might be insufficient for ensuring the protection of human health.

Stereoselective glucuronidation metabolism, pharmacokinetics, anti-amnesic pharmacodynamics, and toxic properties of vasicine enantiomers in vitro and in vivo

Vasicine (VAS) is a potential natural cholinesterase inhibitor for treatment of Alzheimer's disease. Due to one chiral centre (C-3) presenting in molecule, VAS has two enantiomers, d-vasicine (d-VAS) and l-vasicine (l-VAS). The study was undertaken to investigate the stereoselective glucuronidation metabolism, pharmacokinetics, anti-amnesic effect and acute toxicity of VAS enantiomers. In results, the glucuronidation metabolic rate of l-VAS was faster than d-VAS in human liver microsomes and isoenzymes tests, and it was proved that the UDP-glucuronosyltransferase (UGT) 1A9 and UGT2B15 were the major metabolic enzymes for glucuronidation of l-VAS, while only UGT1A9 for d-VAS, which take responsibility of the significantly less metabolic affinity of d-VAS than l-VAS in HLM and rhUGT1A9. The plasma exposure of d-VAS in rats was 1.3-fold and 1.6-fold higher than that of l-VAS after intravenous and oral administration of d-VAS and l-VAS, respectively. And the plasma exposure of the major glucuronidation metabolite d-VASG was one of tenth of l-VASG or more less, no matter by intravenous or oral administration. Both d-VAS and l-VAS were exhibited promising acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) inhibitory activities, and the BChE inhibitory activity of d-VAS with IC₅₀ of 0.03 ± 0.001 μM was significantly stronger than that of l-VAS with IC₅₀ of 0.98 ± 0.19 μM. The molecular docking results indicated that d-VAS and l-VAS could bind to the catalytic active site (CAS position) either of human AChE and BChE, and the BChE combing ability of d-VAS (the score of GBI/WAS dG -7.398) was stronger than that of l-VAS (the score of GBI/WAS dG -7.135). Both d-VAS and l-VAS could improving the learning and memory on scopolamine-induced memory deficits in mice. The content of acetylcholine (ACh) after oral administration d-VAS increased more than that of l-VAS in mice cortex, through inhibiting cholinesterase (ChE) and increasing choline acetyltransferase (ChAT). In addition, the LD₅₀ value of d-VAS (282.51 mg·kg^-1) was slight lower than l-VAS (319.75 mg·kg^-1). These results indicated that VAS enantiomers displayed significantly stereoselective metabolic, pharmacokinetics, anti-amnesic effect and toxic properties in vitro and in vivo. The d-VAS might be the dominant configuration for treating Alzheimer's disease.

Effects of Styrene-metabolizing Enzyme Polymorphisms and Lifestyle Behaviors on Blood Styrene and Urinary Metabolite Levels in Workers Chronically Exposed to Styrene

The aim of this study was to investigate whether genetic polymorphisms of CYP2E1, GSTM1, and GSTT1 and lifestyle habits (smoking, drinking, and exercise) modulate the levels of urinary styrene metabolites such as mandelic acid (MA) and phenylglyoxylic acid (PGA) after occupational exposure to styrene. We recruited 79 male workers who had received chronic exposure in styrene fiberglass-reinforced plastic manufacturing factories. We found that serum albumin was significantly correlated with blood styrene/ambient styrene (BS/AS), urinary styrene (US)/AS, and US/BS ratios as well as urinary metabolites, that total protein correlated with US/MA and US/PGA ratios, and that low density lipoprotein (LDL)-cholesterol significantly correlated with US/BS, US/MA, and US/PGA ratios. Multiple logistic regression analyses using styrene-metabolizing enzyme genotypes and lifestyle habits as dependent variables and blood and urine styrene concentrations and urine styrene metabolite levels as independent variables revealed that CYP2E1*5 was associated with the MA/US ratio and GSTM1 with US/BS, that a smoking habit was associated with US/AS and MA/US ratios and MA and PGA levels, and that regular exercise was correlated with PGA/US. In conclusion, the results suggested that genetic polymorphisms of styrene-metabolizing enzymes, lifestyle behaviors, and albumin and LDL-cholesterol serving as homeostasis factors together are involved in styrene metabolism.

Influence of genetic polymorphisms of styrene-metabolizing enzymes on the levels of urinary biomarkers of styrene exposure

Styrene exposure is still present in different occupational settings including manufacture of synthetic rubber, resins, polyesters and plastic. The aim of this work was to investigate the effects of polymorphic genes CYP2E1, EPHX1, GSTT1, and GSTM1 on the urinary concentrations of the styrene metabolites mandelic acid (MA), phenylglyoxylic acid (PGA) and on the concentration ratios between (MA+PGA) and urinary styrene (U-Sty) and airborne styrene (A-Sty), in 30 workers from two fiberglass-reinforced plastic manufacturing plants and 26 unexposed controls. Personal air sampling and biological monitoring results revealed that sometimes exposure levels exceeded both the threshold limit value (TLV) and the biological exposure index (BEI) suggested by the American Conference of Governmental Industrial Hygienists. A significantly reduced excretion of styrene metabolites (MA+PGA) in individuals carrying the CYP2E1*5B and CYP2E1*6 heterozygote alleles, with respect to the homozygote wild type, was observed only in the exposed group. A reduction was also detected, in the same group, in subjects carrying the slow allele EPHX1 (codon 113), through the lowering of (MA+PGA)/urinary styrene concentration ratio. In addition, the ratio between MA+PGA and the personal airborne styrene concentration appeared to be modulated by the predicted mEH activity, in the exposed group, as evidenced by univariate linear regression analysis. Our results confirm some previous hypotheses about the role of the polymorphism of genes coding for enzymes involved in the styrene detoxification pathway: this may significantly reduce the levels of excreted metabolites and therefore it must be taken into account in the interpretation of the biological monitoring results for occupational exposure.

Microwave-Assisted Synthesis of(±)-Mandelic Acid-d5, Optical Resolution, and Absolute Configuration Determination

An efficient microwave-assisted synthesis of(±)-mandelic acid-d5was developed. The racemic mixture was resolved by diastereomeric salt formation using 1-phenylethylamine enantiomers as resolving agents. At each step, the resolution process was checked by determining mandelic acid-d5enantiomer ee values directly on fractional crystallized diastereomeric salts by chiral capillary electrophoresis analysis. Highly enriched (−)- and (+)-mandelic acid-d5(95% and 90% ee, resp.) were obtained and their absolute configurations—RandS, respectively—were determined by correlation of the (−)-mandelic acid-d5circular dichroism spectrum to the (R)-mandelic acid one.

Contributions of human enzymes in carcinogen metabolism

Considerable support exists for the roles of metabolism in modulating the carcinogenic properties of chemicals. In particular, many of these compounds are pro-carcinogens that require activation to electrophilic forms to exert genotoxic effects. We systematically analyzed the existing literature on the metabolism of carcinogens by human enzymes, which has been developed largely in the past 25 years. The metabolism and especially bioactivation of carcinogens are dominated by cytochrome P450 enzymes (66% of bioactivations). Within this group, six P450s--1A1, 1A2, 1B1, 2A6, 2E1, and 3A4--accounted for 77% of the P450 activation reactions. The roles of these P450s can be compared with those estimated for drug metabolism and should be considered in issues involving enzyme induction, chemoprevention, molecular epidemiology, interindividual variations, and risk assessment.

EPHX1 gene polymorphisms in alcohol dependence and their distribution among the Indian populations

BACKGROUND

The microsomal epoxide hydrolase is a phase II enzyme of the biotransformation. The human epoxide hydrolase 1 (EPHX1) gene lies in the chromosomal region 1q42.1 and exhibits polymorphism. Two single nucleotide polymorphisms (SNPs) have been described in the coding region of the EPHX1 gene that produces two protein variants.

SUBJECTS AND METHODS

A total of 604 samples belonging to 13 Indian populations were included in this study. Based on the DSM-IV criteria, 184 individuals from Kota population were classified into alcoholism cases (100) and controls (84). Genotypes of Tyr113His and His139Arg polymorphisms in the EPHX1 gene were determined using PCR and sequencing. Associations were tested using Pearson's χ(2) test and haplotype analyses.

RESULTS

We found significant association between EPHX1 gene Tyr113His polymorphism and alcoholism in the Kota population (T vs. C: OR = .615, 95% CI = .399-.949, p = .027; TT vs. CC + CT: OR = .536, 95% CI = .297-.969, p = .038). The very slow activity haplotype CA (113His-139His) was also found to be associated with alcohol dependence (p = .048). Analysis of additional populations demonstrated that the Tyr113His polymorphism significantly deviated from Hardy-Weinberg equilibrium in four populations but only one population deviated for the His139Arg locus. All populations shared the four possible two-site haplotypes. Linkage disequilibrium between these two loci was not significant in any of the population studied.

CONCLUSION

EPHX1 gene polymorphisms and haplotypes are associated with an increased risk for alcoholism in the Kota population. This is the first report from India that will serve as a template for future investigations of the prevalence of EPHX1 alleles in association with various clinical entities.

Study on the metabolic mechanism of chiral inversion of S-mandelic acid in vitro

Mandelic acid (MA) is generally used as a biological indicator of occupational exposure to styrene, which is classified as a class of hazardous environmental pollutants. It was found to undergo one-directional chiral inversion (S-MA to R-MA) in Wistar and Sprague-Dawley rats in vivo. This study was aimed to explore the metabolic mechanism of chiral inversion of S-MA in vitro. S-MA was converted to R-MA in rat hepatocytes, whereas MA enantiomers remained unchanged in acidic and neutral phosphate buffers, HepG2 cells, and intestinal flora. In addition, the synthesized S-MA-CoA thioester was rapidly racemized and hydrolyzed to R-MA by rat liver homogenate and S9, cytosolic and mitochondrial fractions. The data suggest that chiral inversion of S-MA may involve the hydrolysis of S-MA-CoA, and its metabolic mechanism could be the same as that of 2-arylpropionic acid (2-APA) drugs.

Changes in oxidative stress biomarker and gene expression levels in workers exposed to volatile organic compounds

Exposure to volatile organic compounds (VOCs) was known to result in immunologic, respiratory, carcinogenic, reproductive, neurologic, and cardiovascular effects. However, the mechanisms by which VOCs induce these adverse health effects are not well understood. To evaluate the change of oxidative stress biomarker and gene expression levels in workers exposed to VOCs, we obtained urine and blood samples from 21 subjects before and after occupational exposure to VOCs. We measured levels of muconic acid (MuA), hippuric acid (HA), mandelic acid (MaA), and methyl hippuric acid (MHA) as urinary exposure biomarkers for benzene, toluene, ethylbenzene, and xylene (collectively BTEX), and malondialdehyde (MDA) and 8-hydroxydeoxyguanine (8-OHdG) as oxidative stress biomarkers in all subjects. We also evaluated BTEX-mediated RNA expression using cDNA microarray in 14 subjects. HA and MHA levels were higher following occupational exposure to VOCs (p < 0.01). In the linear regression analysis, HA ratios of after- and before-exposure were found to be significantly associated with increase of MDA ratios of after- and before-exposure after controlling for age, body mass index, and smoking (β = 0.06, p = 0.031). Evaluation of the gene expressions by HA showed that 23 gene expressions were found to be significantly associated with HA levels after adjusting for age, body mass index, and smoking (p < 0.001). In particular, expressions of ENO3 and CDNA FLJ39461 fis among the 23 genes were significantly associated with the change in MDA level (p < 0.05). Our study results suggest that exposure to VOCs, specifically toluene, induces oxidative stress and various gene expression change of which some may be responsible for oxidative stress.

Reduced production of anti-inflammatory soluble HLA-G molecules in styrene exposed workers

HLA-G antigens are non-classical HLA-class I anti-inflammatory molecules. Since styrene exposure has been suggested to induce immune alteration, we analyzed plasma levels and "in vitro" peripheral blood mononuclear cell (PBMC) production of soluble HLA-G (sHLA-G) and interleukin-10 (IL-10) molecules after lipopolysaccharide (LPS) stimulation, in styrene exposed workers and healthy subjects. Exposed workers showed reduced plasma levels of sHLA-G and IL-10 in comparison to healthy controls. Similarly, lower levels of sHLA-G and IL-10 molecules were observed in PBMC culture supernatants after LPS activation. These data propose styrene exposure as a mediator of impaired sHLA-G production.

Styrene Metabolism, Genotoxicity, and Potential Carcinogenicity

This report reviews styrene biotransformation, including minor metabolic routes, and relates metabolism to the genotoxic effects and possible styrene-related carcinogenicity. Styrene is shown to require metabolic activation in order to become notably genotoxic and styrene 7,8-oxide is shown to contribute quantitatively by far the most (in humans more than 95%) to the genotoxicity of styrene, while minor ring oxidation products are also shown to contribute to local toxicities, especially in the respiratory system. Individual susceptibility depending on metabolism polymorphisms and individual DNA repair capacity as well as the dependence of the nonlinearity of the dose-response relationships in the species in question and the consequences for risk evaluation are analyzd.

Critical appraisal of the expression of cytochrome P450 enzymes in human lung and evaluation of the possibility that such expression provides evidence of potential styrene tumorigenicity in humans

Styrene is widely used with significant human exposure, particularly in the reinforced plastics industry. In mice it is both hepatotoxic and pneumotoxic, and this toxicity is generally thought to be associated with its metabolism to styrene oxide. Styrene causes lung tumors in mice but not in rats. The question is how the tumorigenic effect in mouse lung may relate to the human. This review examines the comparison of the metabolic activation rates (1) between the liver and lung and (2) for the lung, between the rodent and human. Emphasis is placed on the specific cytochromes P450 present in the lungs of humans and what role they might play in the bioactivation of styrene and other compounds. In general, pulmonary metabolism is very slow compared to hepatic metabolism. Furthermore, metabolic rates in humans are slow compared to those in rats and mice. There is a wide difference in what specific cytochromes P450 investigators have reported as being present in human lung which makes comparisons, both inter-species and inter-organ, difficult. The general low activity for cytochrome P450 activity in the lung, especially for CYP2F1, the human homolog for CYP2F2 which has been identified in mice as being primarily responsible for styrene metabolism, argues against the hypothesis that human lung would produce enough styrene oxide to damage pulmonary epithelial cells leading to cell death, increased cell replication and ultimately tumorigenicity, the presumed mode of action for styrene in the production of the mouse lung tumors.

CYP2E1 Rsa I polymorphism impacts on risk of colorectal cancer association with smoking and alcohol drinking

AIM: To investigate associations between the Rsa I polymorphism of CYP2E1 and risk of colorectal cancer.

METHODS: A case-control study was conducted with 315 colorectal cancer cases (105 colon, 210 rectal) and 439 population-based controls in Jiangsu Province of China. Genomic DNA samples were assayed for restriction fragment length polymorphisms in CYP2E1 by PCR amplification followed by digestion with Rsa I. Information on smoking and alcohol drinking was collected using a questionnaire. Odds ratios (ORs) were estimated with an unconditional logistic model.

RESULTS: The proportional distribution of the CYP2E1 Rsa I c1/c1, c1/c2 and c2/c2 genotypes were 61.4%, 35.6% and 3.0% in controls, 60.6%, 33.7% and 5.8% in colon cancer cases, and 58.4%, 34.0% and 7.7% in rectal cancer cases, respectively. A significant difference was noted between controls and rectal cancer cases (P = 0.029), the c2/c2 genotype being associated with elevated OR (adjusted age, sex and status of the smoking and alcohol drinking) for rectal cancer (1.64, 95% CI, 1.12-2.41, vs c1 allele carriers), but not for colon cancer. In interaction analysis between the CYP2E1 Rsa I genotype and smoking and drinking habits, we found a significant cooperative action between the c2/c2 genotype and alcohol drinking in the sex-, age-adjusted ORs for both colon (4.74, 95% CI, 1.10-20.40) and rectal (5.75, 95% CI, 1.65-20.05) cancers. Among non-smokers, the CYP2E1 Rsa I c2/c2 genotype was also associated with elevated ORs in the two sites (1.95, 95% CI, 0.99-3.86 and 2.30, 95% CI, 1.32-3.99).

CONCLUSION: The results of the present study suggest that the CYP2E1 c2/c2 genotype increases susceptibility to rectal cancer and the gene-environmental interactions between the CYP2E1 polymorphism and smoking or alcohol drinking exist for colorectal neoplasia in general.

The importance of cytochrome P450 2B6 in the human metabolism of environmental chemicals

Cytochrome P450 (CYP) 2B6 (CYP2B6) is a human CYP isoform found in variable amounts in the liver and other organs. It is known to be inducible and polymorphic and has a wide range of xenobiotic substrates. Studies of CYP2B6 to date have concentrated heavily on clinical drugs. In the present communication, however, we concentrate on its role in the metabolism of environmental xenobiotics. The term environment is used, in its broadest sense, to include natural ecosystems and agroecosystems as well as the industrial and indoor domestic environments. In essence, this excludes only clinical drugs and drugs of abuse. Many of these chemicals, including agrochemicals and industrial chemicals, can serve as substrates, inhibitors and/or inducers of CYP2B6, these activities being often modified by the existence of polymorphic variants. Metabolism-based interactions between environmental chemicals are discussed, as well as the emerging possibility of metabolic interactions between environmental chemicals and clinical drugs.

Maternal smoking during pregnancy and genetic polymorphisms in the Ah receptor, CYP1A1 and GSTM1 affect infant birth size in Japanese subjects

Genetic susceptibility to tobacco smoke might have relation to adverse pregnancy outcomes. To estimate the effects of maternal smoking and genetic polymorphisms on infant birth weight and length, we conducted a prospective cohort study of 293 women who delivered singleton live births in Sapporo, Japan. Birth weight and length were significantly lower among infants born to continuously smoking women having the aryl hydrocarbon receptor (AhR) wild type genotype (Arg/Arg; 211 g +/- 76 g; 1.2 cm +/- 0.4 cm, p < 0.01 and p < 0.01, respectively), the CYP1A1 variant genotype (m1/m2 + m2/m2; 170 g +/- 64 g, 0.8 cm +/- 0.3 cm, p < 0.01 and p < 0.05, respectively), or the GSTM1 null genotype (171 g +/- 58 g, 0.6 cm +/- 0.3 cm, p < 0.01 and p < 0.05, respectively). When combinations of these genotypes were considered, birth weight and length were significantly lower for infants of continuously smoking women in the AhR wild type + CYP1A1 variant group (315 g +/- 116 g; 1.7 cm +/- 0.6 cm, p < 0.01 and p < 0.01, respectively) and in the CYP1A1 variant + GSTM1 null group (237 g +/- 92 g; 1.3 cm +/- 0.5 cm, p < 0.05 and p < 0.01, respectively). These genotypes did not confer adverse effects among women who had never smoked; therefore, maternal smoking in combination with maternal AhR, CYP1A1 and GSTM1 genetic polymorphisms may adversely affect infant birth size.