Octavio Jiménez-Garza

CYP2E1 epigenetic regulation in chronic, low-level toluene exposure: Relationship with oxidative stress and smoking habit.

BACKGROUND CYP2E1 is a versatile phase I drug-metabolizing enzyme responsible for the biotransformation of most volatile organic compounds, including toluene. Human toluene exposure increases CYP2E1 mRNA and modifies its activity in leucocytes; however, epigenetic implications of this interaction have not been investigated. GOAL To determine promoter methylation of CYP2E1 and other genes known to be affected by toluene exposure. METHODS We obtained venous blood from 24 tannery workers exposed to toluene (mean levels: 10.86+/-7mg/m(3)) and 24 administrative workers (reference group, mean levels 0.21+/-0.02mg/m(3)) all of them from the city of León, Guanajuato, México. After DNA extraction and bisulfite treatment, we performed PCR-pyrosequencing in order to measure methylation levels at promoter region of 13 genes. RESULTS In exposed group we found significant correlations between toluene airborne levels and CYP2E1 promoter methylation (r=-.36, p<0.05), as well as for IL6 promoter methylation levels (r=.44, p<0.05). Moreover, CYP2E1 promoter methylation levels where higher in toluene-exposed smokers compared to nonsmokers (p=0.009). We also observed significant correlations for CYP2E1 promoter methylation with GSTP1 and SOD1 promoter methylation levels (r=-.37, p<0.05 and r=-.34, p<0.05 respectively). CONCLUSION These results highlight the importance of considering CYP2E1 epigenetic modifications, as well as its interactions with other genes, as key factors for unraveling the sub cellular mechanisms of toxicity exerted by oxidative stress, which can initiate disease process in chronic, low-level toluene exposure. People co-exposed to toluene and tobacco smoke are in higher risk due to a possible CYP2E1 repression.

CYP2E1 phenotype in Mexican workers occupationally exposed to low levels of toluene

UNLABELLED CYP2E1, an inducible enzyme present in different human tissues, metabolizes several potentially toxic substances including many volatile organic compounds (VOCs). One indirect way to monitor exposure to VOCs may be, therefore, the assessment of CYP2E1 activity in vivo using the chlorzoxazone (CHZ) test. GOAL To compare CYP2E1 activity in two groups of workers: one with a known occupational exposure to VOCs (exposed group) and the other employed in administrative tasks at two universities (control group) from the city of León, Guanajuato, México. MATERIAL AND METHODS (1) Passive diffusion monitors were used to evaluate individual levels of exposure to toluene, benzene and ethylbenzene in 48 persons (24 tannery workers and 24 administrative controls) during a 8h work shift; (2) after 12h fasting 500mg CHZ, a selective probe for assessing CYP2E1 activity, was orally administered and, after 2h, a venous blood sample was collected for HPLC plasmatic quantitative determination of CHZ and its mean metabolite 6-hydroxychlorzoxazone. RESULTS Toluene mean exposure levels were higher in the exposed group (2.86±2ppm vs. 0.05±0.005ppm; p<0.001). Also, in this group CYP2E1 activity was lower (p<0.05) and it decreased as the accumulated months of labor exposure increased (negative correlation, p<0.05). These results are in line with previous findings obtained from shoemakers exposed to various solvents but, interestingly, they are partly in contrast with those of another study in printers. CONCLUSION In spite of the relatively low levels of toluene exposure found for tannery workers, an effect on CYP2E1 activity was evident. Although the mechanism of this interaction is still unknown, the decrease in CYP2E1 activity per se might represent a health risk, considering that these workers may be less protected against other CYP2E1 substrates present in the labor setting or derived from an intentional exposure.

Aberrant promoter methylation in genes related to hematopoietic malignancy in workers exposed to a VOC mixture

&NA; Occupational exposure to volatile organic compounds (VOCs) may cause hematopoietic malignancy, either by single exposure to benzene or possibly due to a concomitant exposure to several VOCs. Since oxidative stress, inflammation and DNA repair pathways are closely involved in cancer development, the effect of VOC exposure on expression of proteins involved in these pathways has been studied, but epigenetic changes have not been well described. Here, DNA methylation status following occupational exposure to a VOC mixture was assessed by bisulfite sequencing of the promoter regions of seven genes involved in the mentioned pathways. Peripheral blood samples and individual‐level VOC exposure data were obtained from healthy leather shoe factory workers (LS, n = 40) and gas station attendants (GS, n = 36), as well as a reference group of university employees (C, n = 66). Exposure levels for acetone, ethylbenzene, methyl ethyl ketone, n‐hexane, toluene and xylene were higher in LS (p < 0.001); benzene and methyl acetate levels were higher in GS (p < 0.001). TOP2A, SOD1, and TNF‐&agr; promoter methylation status was increased in LS (p < 0.05). In LS, we also found significant correlations between GSTP1 promoter methylation and both iNOS (r = 0.37, p = 0.008) and COX‐2 (r = − 0.38, p = 0.007) methylation. In exposed groups, ethylbenzene exposure levels showed a significant correlation with TOP2A methylation (&bgr; = 0.33). Our results show early, toxic effects at the epigenetic level caused by occupational exposure to high levels of a VOC mixture. These subcellular modifications may represent the initial mechanism of toxicity leading to hematopoietic malignancy, possibly due to a synergistic, hematotoxic effect of VOC mixtures. HighlightsWe analyzed promoter methylation in 7 genes from Mexican workers exposed to solvents.Workers from a shoe factory (LS) were exposed to the highest levels of ethylbenzene.SOD1, TNF‐&agr; and TOP2A methylation levels were higher in LS compared to controls.Ethylbenzene levels showed a positive correlation with TOP2A methylation status in LS.Epigenetic changes represent early, toxic mechanisms in VOC‐induced cancer.

Environmental Epigenetic Changes, as Risk Factors for the Development of Diseases in Children: A Systematic Review

Background: Children are susceptible to environmental contaminants and are at risk of developing diseases, more so if the exposure begins at an early age. Epidemiological studies have postulated the hypothesis of the fetal origin of disease, which is mediated by epigenetic changes. Epigenetic marks are inheritable; they modulate the gene expression and can affect human health due to the presence of environmental factors. Objective: This review focuses on DNA-methylation and its association with environmental-related diseases in children. Methods: A search for studies related to DNA-methylation in children by pre- or post-natal environmental exposures was conducted, and those studies with appropriate designs and statistical analyses and evaluations of the exposure were selected. Findings: Prenatal and early life environmental factors, from diet to exposure to pollutants, have been associated with epigenetic changes, specifically DNA-methylation. Thus, maternal nutrition and smoking and exposure to air particulate matter, polycyclic aromatic hydrocarbons, arsenic, heavy metals, persistent organic pollutants, and some endocrine disrupters during pregnancy have been associated with genomic and gene-specific newborns’ DNA-methylation changes that have shown in some cases sex-specific patterns. In addition, these maternal factors may deregulate the placental DNA-methylation balance and could induce a fetal reprogramming and later-in-life diseases. Conclusions: Exposure to environmental pollutants during prenatal and early life can trigger epigenetic imbalances and eventually the development of diseases in children. The integration of epigenetic data should be considered in future risk assessments.

0226 Affection in the auditory brainstem pathway associated with occupational, low-level exposure to ethylbenzene

Introduction Hearing loss in occupational exposure to a solvent mixture has been already reported; however, mixture in those reports did not contain ethylbenzene, a compound showing peripheral ototoxicity in animals exposed to high levels. In this work, we evaluated the auditory brainstem pathway in two samples of workers exposed to different levels of a solvent mixture where ethylbenzene was present, compared to a reference group. Material and methods Individual exposure levels for up to seven compounds were obtained in two groups: Exposed (n=21 gas station attendants, GS, and leather shoe factory workers, LS) and Non-exposed (n=21, administrative workers) all of them from the city of León Guanajuato, México. The click-evoked auditory brainstem response test was performed in both groups. Results Toluene, n-hexane, acetone, ethylbenzene, xylene and methyl ethyl ketone exposure levels were higher in LS (p<0.001). Only n-hexane exposure levels were above the permissible levels, while mean ethylbenzene exposure levels ranged 0.4–14.58 mg/m3. Wave V latency at four different points of stimulation for both ears was delayed in the exposed group, as well as the I-V and I-III interwave latencies at 70 dB (p<0.05). LS workers showed a delayed I-III interpeak interval compared to non-exposed group. Also in LS, ethylbenzene exposure levels showed a significant correlation with wave V latency at 40 dB (r=0.8, p=0.008). Conclusion Our results point out to a central affection in the auditory system caused by ethylbenzene in a dose response manner. Workers exposed to ethylbenzene levels far below the permissible exposure limit should be closely monitored for early ototoxicity effects.

0234 Occupational exposure to n-hexane is associated with reduced fsh levels and also with prolonged menstrual cycles in mexican workers of reproductive age

Introduction Former studies in rodents and cell lines have demonstrated ovarian toxicity caused by n-hexane and/or 2,5-hexanedione (2,5HD). In women occupationally exposed to solvents, variables ”menstrual cycle period” and ”time for getting pregnant” have been longer compared with controls, without identifying a compound responsible for those effects. Material and methods We studied a group of Mexican women labouring in a shoe Factory (n=32). Individual environmental levels for seven compounds, included n-hexane, were measured. Also, urinary 2,5HD and seric FSH and anti-Müllerian hormone (AMH) as potential biomarkers of ovarian toxicity, in addition to a gyneco-obstetric history were obtained. We performed all tests and questionnaires in a reference group as well (n=32). Results Mean exposure levels to n-hexane (49.2±39.6 mg/m3) and toluene (30.8±24.5 mg/m3) were the highest observed. There were no significant differences in serum FSH and AMH concentrations between groups (p>0.05). Exposed group showed prolonged menstrual cycles (p=0.007) and augmented time for getting pregnant compared with controls (p=0.007). Also in the exposed group, signifcant correlations were observed between FSH levels and n-hexane (r=−0.34, p=0.028) as well as FSH and 2,5HD (r=−0.33, p=0.029). Conclusions n-hexane exposure may be responsible for a prolonged menstrual cycle. As judged by the correlations between FSH with n-hexane and 2,5HD this affection could be in the endocrine pathway rather than in the ovary itself. n-hexane could act as endocrine disruptor in women of reproductive age.

Affection in the auditory brainstem pathway associated with occupational, low-level exposure to ethylbenzene

Introduction Hearing loss in occupational exposure to a solvent mixture has been already reported; however, mixture in those reports did not contain ethylbenzene, a compound showing peripheral ototoxicity in animals exposed to high levels. In this work, we evaluated the auditory brainstem pathway in two samples of workers exposed to different levels of a solvent mixture where ethylbenzene was present, compared to a reference group. Material and methods Individual exposure levels for up to seven compounds were obtained in two groups: Exposed (n=21 gas station attendants, GS, and leather shoe factory workers, LS) and Non-exposed (n=21, administrative workers) all of them from the city of León Guanajuato, México. The click-evoked auditory brainstem response test was performed in both groups. Results Toluene, n-hexane, acetone, ethylbenzene, xylene and methyl ethyl ketone exposure levels were higher in LS (p<0.001). Only n-hexane exposure levels were above the permissible levels, while mean ethylbenzene exposure levels ranged 0.4–14.58 mg/m3. Wave V latency at four different points of stimulation for both ears was delayed in the exposed group, as well as the I-V and I-III interwave latencies at 70 dB (p<0.05). LS workers showed a delayed I-III interpeak interval compared to non-exposed group. Also in LS, ethylbenzene exposure levels showed a significant correlation with wave V latency at 40 dB (r=0.8, p=0.008). Conclusion Our results point out to a central affection in the auditory system caused by ethylbenzene in a dose response manner. Workers exposed to ethylbenzene levels far below the permissible exposure limit should be closely monitored for early ototoxicity effects.