Metabolites Mandelic Acid Research Articles

Ethylbenzene and styrene exposure in the United States based on urinary mandelic acid and phenylglyoxylic acid: NHANES 2005–2006 and 2011–2012

Ethylbenzene and styrene are air toxicants with widespread nonoccupational exposure sources, including tobacco smoke and diet. Ethylbenzene and styrene (EB/S) exposure was quantified from their common metabolites measured in spot urine samples obtained from participants (≥6 years old) in the 2005–2006 and 2011–2012 cycles of the National Health and Nutrition Examination Survey (NHANES; N = 4690). EB/S metabolites mandelic acid (MA) and phenylglyoxylic acid (PGA) were measured using ultra-high performance liquid chromatography coupled with electrospray ionization tandem mass spectrometry (UPLC-ESI-MS/MS). MA and PGA were detected in 98.9% and 90.6% of tested urine specimens, respectively. Exclusive smokers had 2-fold and 1.6-fold higher median urinary MA and PGA, respectively, compared with non-users. Sampleweighted regression analysis among exclusive smokers showed that smoking 0.5 pack cigarettes per day significantly increased MA (+97.9 μg/L) and PGA (+69.3 μg/L), controlling for potential confounders. In comparison, exposure from the median daily dietary intake of grain products increased MA by 1.95 μg/L and was not associated with statistically significant changes in urinary PGA levels. Conversely, consuming vegetables and fruit was associated with decreased MA and PGA. These results confirm tobacco smoke as a major source of ethylbenzene and styrene exposure for the general U.S. population.

Biomarkers of early genotoxicity and oxidative stress for occupational risk assessment of exposure to styrene in the fibreglass reinforced plastic industry

This study aimed to identify sensitive and not-invasive biomarkers of early genotoxic/oxidative effect for exposure to styrene in the fibreglass reinforced plastic manufacture. We studied 11 workers of a plastic manufacture using open molding process (A), 16 workers of a manufacture using closed process (B) and 12 controls. We evaluated geno/cytotoxic effects on buccal cells by Buccal Micronucleus Cytome (BMCyt) assay and genotoxic/oxidative effects on lymphocytes by Fpg-comet test. On A workers we also evaluated urinary 8oxoGua, 8oxodGuo and 8oxoGuo to investigate oxidative stress. Personal inhalation exposure to styrene was monitored by passive air sampling and GC/MS. Biological monitoring included urinary metabolites mandelic acid (MA) and phenylglyoxylic acid (PGA). The findings show higher styrene exposure, urinary MA + PGA levels and micronucleus frequency in manufacture A. Higher buccal karyolytic cell frequency vs controls were found in both exposed populations. We found in exposed workers, no induction of direct DNA damage but oxidative DNA damage. Fpg-comet assay and urinary oxidized guanine seem to be sensitive biomarkers of oxidative stress and BMCyt assay a good-not invasive biomarker of cyto-genotoxicity at target organ. The study, although limited by the small number of studied subjects, shows the usefulness of used biomarkers in risk assessment of styrene-exposed workers.

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.

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

Here we evaluate the influence of individual genetic polymorphisms of drug-metabolizing enzymes as well as body mass index (BMI) and lifestyle (smoking, alcohol consumption) on urinary metabolites after occupational exposure to styrene. Seventy-three workers exposed to styrene in a reinforced-plastics workplace were studied. The personal styrene exposure in the air and the urinary styrene metabolites mandelic acid and phenylglyoxylic acid were measured. The subjects’ genetic polymorphisms in the genes that encode the styrene-metabolizing enzymes CYP2E1, CYP2B6, EPHX1, GSTM1, GSTT1 and GSTP1 were determined. Neither genotype nor lifestyle significantly affected urinary metabolites. There was, however, an interaction between the CYP2E1 genotype and smoking. Among non-smokers, urinary styrene metabolites were significantly decreased in subjects with c1/c1 alleles of CYP2E1 as compared with those with the c1/c2 genotype. There was no significant difference in urinary metabolites among smokers. When the combined influence of the CYP2B6 genotype and the predicted activity of EPHX1 were examined, urinary metabolites in subjects with low enzyme activity were lower than in those with medium or high activity after high styrene exposure (≥50 ppm). The results suggest that genetic susceptibility and lifestyle should be considered in biological monitoring of exposure to styrene.

Stereochemical metabolism of styrene in volunteers.

To study the stereochemistry of styrene metabolism in volunteers, and its interindividual variability. Twenty healthy male volunteers (aged 18-37 years) were exposed to 360 mg/m3 styrene for 1 h while they performed 50 W physical exercise. Venous blood was drawn during and for up to 2 h after exposure. Urine was collected at time-intervals up to 24 h after exposure. The following parameters were determined: styrene, free and conjugated styrene glycol (SG) in blood, and conjugated SG, mandelic acid (MA) and phenylglyoxylic acid (PGA) in urine. Average pulmonary retention of styrene was 62%. Excretion of the acidic metabolites MA and PGA accounted for 58% of the pulmonary uptake. The average maximum concentration (Cmax) and area under the curve (AUC) of free (R)-SG in blood were 1.3 and 1.7 times higher than those of (S)-SG respectively; the half-life of (R)-SG was longer (82 vs 62 min, P < 0.005). Cmax and AUC of the conjugated SG enantiomers in blood did not differ, but again half-life for (R)-SG was longer (72 vs 64 min, P < 0.05). Cumulative excretion and renal clearance of conjugated (S)-SG in urine were three and four times higher, respectively, than that of (R)-SG. Cumulative excretion of (S)-MA was 1.6 times higher than (R)-MA. Interindividual differences in the kinetic parameters of the metabolites were two- to threefold. The enantiomeric excess found was different for each metabolite under study, implying different enantioselectivity and/or enantiospecificity of the enzymes and carrier-proteins involved in the biotransformation and excretion. The use of these metabolites as biological indicators for prediction of the enantiomeric excess of the toxic metabolite styrene-7,8-oxide (SO) is therefore not justified. Interindividual differences in the stereochemical metabolism of styrene are moderate.

Intervention study on acquired color vision deficiencies in styrene-exposed workers.

The main aim of the study was to examine the possible effects of occupational exposure to styrene on color vision function and the course after reduction of exposure. Color vision function was examined in 22 styrene-exposed laminators and 11 control subjects at a boat manufacturing plant. The Lanthony D-15 desaturated panel was used to test acquired dyschromatopsia. In all, six examinations were performed: Monday morning and Thursday afternoon of the same week, before and immediately after a vacation of 4 weeks (altogether, phase 1), and approximately 10 months later (phase 2), after the exposure level of styrene had been reduced. Styrene uptake was objectified by biological monitoring measuring the metabolites mandelic acid and phenylglyoxcylic acid in urine samples taken on Thursday afternoon. In both Thursday examinations, styrene-exposed workers had higher color confusion index (CCI) values compared with controls, which indicated quantitative color vision loss. After an exposure-free period of 4 weeks, a significant decrease of CCI values to normal range was found in laminators. Reexamination 10 months later showed also lower CCI values in exposed workers, indicating a dose-effect relationship. Abnormal CCI values occurred primarily in subjects with an excretion of approximately 500 to 600 mg mandelic acid plus phenylglyoxcylic acid per gram creatinine or more. We concluded that styrene-induced color vision dysfunction is reversible after an exposure-free interval of 4 weeks. The current Biological Tolerance Value of 600 mg mandelic acid plus phenylglyoxcylic acid per gram creatinine, as used in Germany, protects styrene-exposed workers from this subclinical effect.

Biological monitoring of standardized exposure to ethylbenzene: evaluation of a biological tolerance (BAT) value.

The results of standardized 8 h lasting exposures of n = 18 volunteers to ethylbenzene (EthBz) at levels of 25 and 100% of the maximum allowable concentrations at the workplace (MAK) value of 100 ppm as well as the results of field studies are considered to evaluate a biological tolerance (BAT) value for EthBz. On the basis of the relationship between the external and internal exposure a BAT value of 1.5 mg/l has been set for the EthBz concentration in blood as the most sensitive and specific parameter of exposure to this aromatic hydrocarbon. The interpretation of EthBz blood values has to take into account the short half-life of t1/2 = 0.5 +/- 0.08 h in the first hour after the end of exposure in which this aromatic hydrocarbon is eliminated from the blood. The additional determination of the EthBz metabolites mandelic acid (MA) and phenylglyoxylic acid (PGA), respectively, excreted in post shift urine as well as in urine samples at the beginning of the next shift shows good correlations with the external exposure. The biological half-life of MA was calculated to t1/2 = 5.3 +/- 1.1 h. Because the time of sampling can vary the relationship between the levels of MA to PGA the total concentration of the excreted metabolites depends less on this influence and is therefore better suited for monitoring exposed persons. On the basis of the standardized experiments a BAT value has been proposed of 2 g MA plus PGA corrected per gram creatinine. Both BAT values are adjusted to data which result from earlier standardized exposures during 30 min to EthBz under physical activity of 50 watt on a bicycle ergometer.

Environmental and Biological Monitoring of Styrene Exposure: Urinary Excretion of D‐Glucaric Acid Compared with Exposure Indices

Environmental and Biological Monitoring of Styrene Exposure: Urinary Excretion of D‐Glucaric Acid Compared with Exposure Indices: M.L. Scapellato, et al. Istituto di Medicina del Lavoro, University degli Studi di Padova—Styrene, oxidized by liver microsomal enzymes, can determine a liver enzyme induction. Urinary excretion of D‐glucaric acid (DGA), which is believed to estimate this effect, was measured in 27 workers exposed to styrene in a fiberglass plant and in 27 control subjects in order to make a comparison with environmental and biological exposure indices. In exposed workers, airborne concentrations (8‐h TWA) of styrene varied between 9 and 415 mg/m3, with styrene metabolites [sum of mandelic acid (MA) + phenylglyoxylic acid (PGA)] ranging from 93 to 2130 mg/g Cr in endshift urine samples collected on a Thursday, and from 45 to 792 mg/g Cr in samples taken before work the following morning. The correlation coefficient (r) between 8‐h TWAs and sum of urinary metabolites MA + PGA was 0.92 (y=4.06x‐36.05; p&lt;0.001) for Thursday endshift (ES) samples, and 0.84 (y=1.46x + 46.82; p&lt;0.001) for Friday morning samples (beginning of shift: BS). Urinary excretion of MA correlated better with exposure than that of PGA (MA: ES r=0.91; BS r=0.86. PGA: ES r=0.80; BS r=0.76). ES and BS levels of DGA in exposed subjects (equal to 4.41 ± 1.57 and 4.01 ±1.18 mmol/mol Cr respectively) were both significantly higher than the 2.93 ± 0.88 observed in 27 control subjects (Mann‐Whitney test; p&lt;0.001). No significant correlation was found between individual exposure to styrene evaluated by the environmental concentration or by urinary metabolites and urinary excretion of DGA. Furthermore, both ES and BS urinary DGA levels increased across three classes of styrene exposure (&lt;100, 101‐200, and &gt;200 mg/m3, respectively, including 10, 7 and 10 workers). The DGA difference between the most exposed and the not exposed subjects was significant (ES‐DGA: z=4.03 and p &lt;0.05; BS‐DGA: z=3.16 and p&lt;0.05; Kruskall‐Wallis test), but individual pairwise comparisons among all other groups were not. In spite of the above results, no significant correlation was found between individual exposure to styrene and urinary excretion of DGA, so that this biomarker cannot be used to monitor the exposure effects on an individual basis.