Formation of 1,2:3,4-diepoxybutane-specific hemoglobin adducts in 1,3-butadiene exposed workers

1,3-Butadiene (BD) is an important industrial chemical that is classified as a human carcinogen. BD carcinogenicity has been attributed to its metabolism to several reactive epoxide metabolites and formation of the highly mutagenic 1,2:3,4-diepoxybutane (DEB) has been hypothesized to drive mutagenesis and carcinogenesis at exposures experienced in humans. We report herein the formation of DEB-specific N,N-(2,3-dihydroxy-1,4-butadiyl)valine (pyr-Val) in BD-exposed workers as a biomarker of DEB formation. pyr-Val was determined in BD monomer and polymer plant workers that had been previously analyzed for several other biomarkers of exposure and effect. pyr-Val was detected in 68 of 81 (84%) samples ranging from 0.08 to 0.86 pmol/g globin. Surprisingly, pyr-Val was observed in 19 of 23 administrative control subjects not known to be exposed to BD, suggesting exposure from environmental sources of BD. The mean ± SD amounts of pyr-Val were 0.11 ± 0.07, 0.16 ± 0.12, and 0.29 ± 0.20 pmol/g globin in the controls, monomer, and polymer workers, respectively, clearly demonstrating formation of DEB in humans. The amounts of pyr-Val found in this study suggest that humans are much less efficient in the formation of DEB than mice or rats at similar exposures. Formation of pyr-Val was more than 50-fold lower than has been associated with increased mutagenesis in rodents. The results further suggest that formation of DEB relative to other epoxides is significantly different in the highest exposed polymer workers compared with controls and BD monomer workers. Whether this is due to saturation of metabolic formation or increased GST-mediated detoxification could not be determined.     

Lack of genotoxic effect in workers exposed to very low doses of 1,3-butadiene

1,3-butadiene (BD), a probable carcinogen to humans, has been shown to have an ill-defined genotoxicity in occupationally exposed workers. In the present study, the influence of exposure to very low doses of BD and to cigarette smoking was investigated on some cytogenetic endpoints, namely, sister chromatid exchanges (SCE), chromosomal aberrations (CA) and cells with a high frequency of SCE (HFC), in peripheral blood lymphocytes. Twenty-seven male workers employed in a petrochemical plant and 26 matched controls were included in the study. As regards the airborne BD values, there was a significant difference between exposed (median BD value 1.5, min–max 0.2–69.0 μg/m³) and non-exposed workers (median BD value 0.4, min–max <0.1–3.8 μg/m³). Genotoxic biomarkers were not able to distinguish between the two groups. The frequency of SCE was higher in smokers than in non-smokers (p=0.001), with a positive correlation between the number of cigarettes smoked per day and both SCE (r=0.4; p=0.004) and HFC frequency (r=0.3; p=0.04). Multiple regression analysis confirmed the influence of cigarette smoking on the level of SCE and HFC, while these parameters were not affected by personal exposure to BD. Overall, the biomarkers of genotoxic effect investigated in our study were not able to discriminate between workers with a very low exposure to BD and controls, while it was possible to distinguish between smokers and non-smokers on the basis of SCE.Piero Lovreglio and Nenad Bukvic have contributed equally to this study     

Immunological monitoring in workers occupationally exposed to asbestos

Occupational exposure to asbestos is strongly associated with pulmonary diseases, cancer and immunotoxic effects. Both systemic and local immunity may play an important role in the pathogenesis of these events. Immune cells appear to be influenced by asbestos exposure, either through direct effects or as a result of the host's protective response to exposure. In this study several immune system parameters were assessed in workers (n = 61) with at least 5 years' exposure to asbestos at an industrial plant. Workers exposed to asbestos fibres had significantly increased levels of immunoglobulin E and concentrations of interleukin-6 and -8 in comparison with two sets of controls (in-plant and town control groups). The levels of soluble adhesion molecule ICAM-1 were higher in the exposed group compared to the town control group. Significantly increased levels of IgA were found in asbestos-exposed group in comparison to the town control. Evaluation of the expression of adhesion molecules on lymphocytes, monocytes and granulocytes by flow cytometry showed significant increases in the class of selectins CD62L on monocytes and granulocytes. Moreover, significantly increased expression of markers CD69 and CD66b on eosinophils was found among workers exposed to asbestos. In conclusion, exposure to asbestos fibres was found to have several effects on immune system. Alterations of these immune parameters may indicate hypersensitivity (increased levels of IgE, increased expression of activation markers CD66b and CD69 on eosinophils) and an elevated inflammatory status (increased levels of interleukins--IL-6, IL-8) in exposed workers.     

Persistence and repair of bifunctional DNA adducts in tissues of laboratory animals exposed to 1,3-butadiene by inhalation

1,3-Butadiene (BD) is an important industrial and environmental chemical classified as a human carcinogen. The mechanism of BD-mediated cancer is of significant interest because of the widespread exposure of humans to BD from cigarette smoke and urban air. BD is metabolically activated to 1,2,3,4-diepoxybutane (DEB), which is a highly genotoxic and mutagenic bis-alkylating agent believed to be the ultimate carcinogenic species of BD. We have previously identified several types of DEB-specific DNA adducts, including bis-N7-guanine cross-links (bis-N7-BD), N(6)-adenine-N7-guanine cross-links (N(6)A-N7G-BD), and 1,N(6)-dA exocyclic adducts. These lesions were detected in tissues of laboratory rodents exposed to BD by inhalation ( Goggin et al. (2009) Cancer Res. 69 , 2479 -2486 ). In the present work, persistence and repair of bifunctional DEB-DNA adducts in tissues of mice and rats exposed to BD by inhalation were investigated. The half-lives of the most abundant cross-links, bis-N7G-BD, in mouse liver, kidney, and lungs were 2.3-2.4 days, 4.6-5.7 days, and 4.9 days, respectively. The in vitro half-lives of bis-N7G-BD were 3.5 days (S,S isomer) and 4.0 days (meso isomer) due to their spontaneous depurination. In contrast, tissue concentrations of the minor DEB adducts, N7G-N1A-BD and 1,N(6)-HMHP-dA, remained essentially unchanged during the course of the experiment, with an estimated t(1/2) of 36-42 days. No differences were observed between DEB-DNA adduct levels in BD-treated wild type mice and the corresponding animals deficient in methyl purine glycosylase or the Xpa gene. Our results indicate that DEB-induced N7G-N1A-BD and 1,N(6)-HMHP-dA adducts persist in vivo, potentially contributing to mutations and cancer observed as a result of BD exposure.     

DNA damage in workers occupationally exposed to pesticide mixtures

Pesticides are used in agriculture to protect crops but represent at the same time a potential risk to farmers and environment. The aim of this work is the evaluation of 54 subjects occupationally exposed to pesticides and 30 subjects as a control group using the quantification of DNA damage level by means of the alkaline Comet assay and the evaluation of repair processes. Damage index Comet assay (DICA) and damage index repair assay (DIRA) were studied in 27 pesticide applicator workers, 27 non-pesticide applicators and controls. Our results show that both exposed groups revealed significant increase in DICA when compared with controls (P < 0.0001), as well as in DIRA (P < 0.0001). However, the spraying group exhibited a marginally significant difference in DICA (P = 0.05) when years of exposure are considered and a significant difference (P < 0.05) when the personal protective equipment used by individuals was taken as a comparison factor. The influence of confounding factors on the genotoxic effects of occupational exposure to pesticides was investigated and no significant differences were observed considering age, gender, smoking and alcohol consumption in relation to DICA and DIRA. Since DNA damage is an important step in events leading from carcinogen exposure to cancer disease, our study highlights the potential health risk associated with agrochemical exposure in developing countries with vast cultivated areas, such as Argentina.     

Anesthetic gases and occupationally exposed workers

The aim of this study is to estimate whether the occupational exposure to low dose anesthetic gases could cause alterations of blood parameters in health care workers. 119 exposed subjects and 184 not exposed controls were included in the study. Each worker underwent the complete blood count test (CBC), proteinaemia, leukocyte count, serum lipids, liver and kidney blood markers.The liver blood markers show statistically significant differences in health care workers compared with controls (p < 0.05), a statistically significant decrease in neutrophils and an increase of lymphocytes in health care workers compared with controls (p < 0.05). The prevalence of values outside the range for GPT, GGT, total bilirubin, lymphocytes and neutrophils was statistically significant in health care workers compared with controls (p < 0.05). The results suggest that occupational exposure to low dose anesthetic gases could influence some haematochemical hepatic and hematopoietic parameters in exposed health care workers.     

Serum succinyltrialanine p-nitroanilide-hydrolytic activity in workers occupationally exposed to lead

The relationship between blood lead concentration and serum succinyltrialanine p-nitroanilide-hydrolytic (STN) activity was investigated in 74 workers occupationally exposed to lead and in 28 non-exposed workers. Exposure to lead was observed during transfer-printing processes in which paints or paint powders containing 20-50% lead were used. The mean lead concentration was 0.49 mg/m3 (0.12-1.43 mg/m3) in the working environment and 1.42 mg/m3 (0.21-4.34 mg/m3) in workers involved in printing processes. Serum STN activity became lower with increasing concentrations of blood lead (PbB) in non-exposed workers (controls). In lead-exposed workers, the activity decreased with increasing concentrations of PbB of 2.0 mumol/l and more, but increased when less than 1.9 mumol/l. Among lead-exposed workers with high PbB concentrations and/or with hepatic dysfunction, the STN/PbB ratio was distributed above the regression line obtained from the controls. The present investigation suggests that serum STN activity decreases in those highly exposed to lead. Enzymes such as elastase, which hydrolyzes succinyltrialanine p-nitroanilide and additionally is not inhibited by lead, may possibly be induced among lead workers when liver function is impaired.     

Urinary N3 adenine DNA adducts in humans occupationally exposed to styrene

Urine samples from humans occupationally exposed to styrene, with mandelic acid levels ranging from 400 to 1145 mg/g creatinine and from 68 to 400 mg/g creatinine for high and low exposure group, respectively, were analysed for N3 adenine DNA adducts, namely, 3-(2-hydroxy-1-phenylethyl)adenine (N3αA) and 3-(2-hydroxy-2-phenylethyl)adenine (N3βA). A sensitive LC-ESI–MSMS method was developed with the limit of quantification of 1 pg/mL for both analytes. Peaks corresponding to N3αA and/or N3βA were found in seven of nine end-of-shift samples of the high exposure group and in six of 19 end-of-shift samples of the low exposure group. Concentration of N3αA + N3βA amounted to 2.8 ± 1.6 pg/mL (mean ± S.D.; n = 9) and 1.8 ± 1.3 pg/mL (mean ± S.D.; n = 19) in the high and low exposure group, respectively. Of other 10 samples taken the next morning after exposure, two contained low but quantifiable concentrations of N3αA and none contained N3βA. However, interfering peaks were detected also in some control urine samples. Out of 22 controls, six and two samples contained peaks co-eluting with N3αA and N3βA, respectively. Therefore, the method used was found insufficiently specific to be applicable for biological monitoring. Comparing the excretion of N3αA + N3βA to that reported previously in mice it can be estimated that at the same absorbed dose, humans excreted not more than 1/30 of the amount of adenine adducts excreted by mice. As a consequence, the damage to DNA caused by styrene 7,8-oxide (SO), a reactive metabolite of styrene, appears to be much lower in humans than in mice.     

The concentration of protoporphyrin IX in workers occupationally exposed to lead

In the study a relationship was undertaken between the concentration of erythrocyte protoporphyrin IX and concentrations of lead and hemoglobin in blood as well as iron serum concentration in men workers exposed to lead. The test group were 54 men, 28-56 years of age, occupationally exposed to lead for a period of 9-33 years. The control were 40 men not exposed to lead, between 25-60 years of age. The test group was divided into 3 subgroups according to exposure duration. As regards the concentrations of protoporphyrin and other parameters examined, the study revealed no significant differences between the subgroups. Those concentrations were also found to be similar in respective control groups. Significantly increased level of protoporphyrin IX concentration was noted in 17 men out of the whole test group. However as compared with other groups results, all the remaining parameters showed no difference. As regards the concentrations of iron in serum and hemoglobin in blood, they fell within the range of physiological values, in all the groups studied.     

Formaldehyde risk assessment for occupationally exposed workers

Formaldehyde has been shown to be carcinogenic in animals and should be considered potentially carcinogenic in humans. The mechanism of action is unknown but formaldehyde is weakly genotoxic and also may act as a late stage carcinogen or promoter. An estimated 1.3 million workers are potentially exposed to formaldehyde through their occupation. Of those exposed workers, about 3.5% were found to be exposed to formaldehyde air concentrations greater than the 3 ppm set by OSHA as a permissible exposure level. Fewer than 12% were exposed to concentrations greater than 1 ppm, but over 88% were exposed to concentrations of 0.5 ppm or more. A quantitative risk assessment, using the multistage low-dose extrapolation model, found the (maximum likelihood) estimate of lifetime risk for excess cancers to be 620 per 100,000 at the OSHA permissible exposure level. The estimated risk is 23 per 100,000 at 1 ppm and 2.8 per 100,000 at 0.5 ppm. Reduction of the OSHA permissible exposure level to 1 ppm would significantly decrease risk with minor economic disruption for most industries involved. However, reduction of risk to levels which have been generally regarded by other regulatory agencies as acceptable, i.e., 10(-5) to 10(-6), would require increased control by all the industries reviewed.     

Metabolism of 1,3-butadiene by lung and liver microsomes of rats and mice repeatedly exposed by inhalation to 1,3-butadiene

1,3-Butadiene, a colorless gas widely used as an intermediate in the production of synthetic rubber, is carcinogenic in rats and mice. Species differences exist in the sensitivity to inhaled 1,3-butadiene and the target tissue specificity for tumor formation. We examined whether repeated inhalation exposure of rats and mice to 1,3-butadiene would affect the rate of metabolism of 1,3-butadiene by lung and liver microsomes in these species. Male Sprague-Dawley rats and B6C3F1 mice were exposed nose-only to air (control) or 7600 +/- 170 ppm 1,3-butadiene (13,600 +/- 300 micrograms/l) and 740 +/- 10 ppm 1,3-butadiene (1300 +/- 20 micrograms/l), respectively, for 6 h/day for 5 days. After the last exposure, nasal tissue (rats only), lungs and livers were removed from the animals and microsomes were prepared. Microsomes from the different tissues were incubated with 6 mumol 1,3-butadiene and 10 mumol NADPH for 30 min and the rate of disappearance of 1,3-butadiene from the reaction flasks was quantitated. There was a statistically significant (P less than 0.05) depression in the rate of 1,3-butadiene metabolism (50%) in microsomes from lungs of both rats and mice that were exposed repeatedly to 1,3-butadiene compared to control animals. There was no effect of repeated 1,3-butadiene exposure on liver or nasal tissue (rats only) metabolism of 1,3-butadiene in rats or mice. The data from these studies indicate that it is unlikely that species differences in sensitivity or tissue susceptibility are due to an inductive or inhibitory effect of 1,3-butadiene on its own metabolism in the tissues examined.     

Alterations of serum hormone levels in male workers occupationally exposed to cadmium

In order to investigate the influence of occupational exposure to cadmium (Cd) on the levels of serum hormone, a cross-sectional study was undertaken in male workers. Creatinine-adjusted urinary cadmium (UCd) was used as the indicator of cadmium body burden in workers. The levels of serum testosterone (T), follicle-stimulating hormone (FSH), and luteinizing hormone (LH) were determined by radioimmunoassay and enzyme immunoassay, respectively. The results showed that with cadmium exposure, the levels of serum testosterone and LH were significantly increased after controlling for confounding factors such as age, smoking habits, and alcohol consumption. However, no significant cadmium-associated changes in the levels of serum FSH were found. At the same time, a significant negative correlation of serum testosterone levels with age was detected. In contrast, the levels of serum FSH and LH were significantly elevated with increasing age. When taking the marital status into consideration, only significantly elevated FSH levels were noted in married workers after controlling for confounding factors. These results indicate that occupational cadmium exposure and other factors such as age and marital status may independently contribute to alterations in the levels of serum sex hormones in males.     

Evaluation of DNA damage in jewellery workers occupationally exposed to nitric oxide

Nitric oxide is a metastable radical, reacts with oxygen to produce toxic nitrogen oxides (N(2)O(3), ONOO(-)) which damage DNA. Occupational exposure to nitric oxide leads to increased frequency of chromosomal aberrations in humans. In the present study the DNA damage among the jewellery workers occupationally exposed to nitric oxide was analyzed using buccal cell comet assay. The result of this study shows increased levels of DNA damage among jewellery workers. The habit of cigarette smoking among the jewellery workers has a synergistic effect on inducing DNA damage.     

Biological monitoring of bidi industry workers occupationally exposed to tobacco.

Ambient and biological monitoring was undertaken among tobacco processors who are chronically exposed to tobacco particulates via nasopharyngeal and cutaneous routes. Ambient monitoring revealed that the inspirable dust concentration was 150-fold higher in the tobacco factory than in the control environment, and was associated with chronic bronchitis in workers. Increased systemic exposure to tobacco constituents was evident from the high levels of cotinine, thioethers, promutagens and direct acting mutagens in workers' urine. The mean glutathione level and glutathione S-transferase activity were significantly lower in the peripheral blood lymphocytes of workers; however, the frequency of the GSTM1 null allele was similar to that in controls. A significant increase in chromosomal damage was noted in target and non-target cells of tobacco processors. In view of the association between tobacco use and several non-communicable diseases, the findings of the present study indicate an urgent need to minimize tobacco exposure among the processors.     

Hearing impairment among workers occupationally exposed to excessive levels of noise

Pure tone audiometry screening and ear examinations were conducted among 138 males working as machine and equipment operators occupationally exposed to intermittent noise of 85 to 105 dBA. Hearing loss up to 30 dB (preserved socially adequate hearing) was found in 25 workers. The hearing impairment was confirmed by distortion products of otoacoustic emissions measurements. A sharp increase in the frequency of cases can be found among the workers with service length over 10 years. While the frequency of the cases among workers with service length below 10 years is 5.45%, it is 26.5% among the subjects with service length over 10 years, with a gradual increase as a result of the increase in exposure duration. A positive correlation (p < 0.05) was found between the frequency of hearing impairment among the workers and the years of exposure to excessive noise levels. Some measures for preventing occupational noise-induced hearing loss were suggested.     

Persistence of N7-(2,3,4-trihydroxybutyl)guanine adducts in the livers of mice and rats exposed to 1,3-butadiene

Liquid chromatography (LC) in combination with tandem mass spectrometry (MS/MS) and stable isotope methodology was employed for the analysis of the N7-guanine (Gua) adducts derived from 1,2:3, 4-diepoxybutane (BDO2) a reactive metabolite of 1,3-butadiene (BD). Two diastereomeric forms of N7-(2,3,4-trihydroxybutyl)guanine (THBG) were identified in the livers of both mice and rats. One of the diastereomers [(+/-)-THBG] was formed by reaction of DNA with (+/-)-BDO2, and the other diastereomer (meso-THBG) was formed by reaction of DNA with meso-BDO2. There was significantly more (+/-)-THBG and meso-THBG in the liver DNA of the mice when compared with those of the rats during the 10 days of exposure to BD and the 6 days of postexposure that were monitored. There was a 2-fold excess of (+/-)-THBG over meso-THBG in the rat liver at all the time points. In the mouse liver after 10 days of exposure to BD, the (+/-)-THBG (3.9 adducts/10(6) normal bases) was also present in an almost 2-fold excess over meso-THBG (2.2 adducts/10(6) normal bases). However, 6-days after exposure to BD, (+/-)-THBG (1.2 adducts/10(6) normal bases) and meso-THBG (1.0 adduct/10(6) normal bases) were present in almost equal amounts in the mouse liver. Furthermore, there was an almost 5-fold excess of the two THBG diastereomers in the mouse liver DNA 6 days after exposure to BD when compared with rat liver DNA. The half-lives of (+/-)-THBG and meso-THBG appeared to be slightly longer in mouse liver (4.1 and 5.5 days, respectively) than in rat liver (3.6 and 4.0 days, respectively). The apparent persistence of these adducts in the mouse may contribute to the increased susceptibility of this species to BD-induced carcinogenesis. It is possible that (+/-)-THBG and meso-THBG could have also been derived from the reaction of DNA with the hydrolysis product of BDO2, 1,2-dihydroxy-3,4-epoxybutane (DHEB). Surprisingly, a vast majority of the studies in which the mutagenic and carcinogenic potential of BDO2 have been examined have only employed the commercially available (+/-)-BDO2. In light of the present findings, additional studies will be required to determine the potency of meso-BDO2 and the DHEB that is the precursor to meso-THBG as mutagens and carcinogens.     

Chromosomal damage in workers occupationally exposed to chronic low level ionizing radiation

Chromosomal aberrations were evaluated in cultures of peripheral lymphocytes from subjects working in diagnostic X-ray and nuclear medicine areas, exposed to electromagnetic ionizing radiation and particulate ionizing emissions, respectively. A 4-fold increase in the level of chromosomal aberrations was found between the exposed and control groups without qualitative or quantitative cytogenetic differences between X-rays and nuclear medicine-exposed workers. Results are discussed in view of the early damage detection from chronic exposures particularly related to biological controls, hygienic improvements and overwork in a developing country.     

Effects of lead on neutrophil functions in occupationally exposed workers

Chemotactic and intracellular killing activity of neutrophils were examined in 25 male lead-exposed workers from storage-battery plants and compared to 25 healthy males with no history of lead exposure. Lead exposure was assessed using blood lead levels measured by atomic absorption spectrophotometry and zinc protoporphyrin levels assayed by hematofluorometry. Chemotaxis was carried out in Boyden chambers using zymosan activated serum as chemotactic stimulus. Intracellular killing activity of neutrophils was measured using nitroblue tetrazolium reduction test, measured of 515 nm in spectrophotometry. In lead-exposed workers a significant decrease in chemotaxis and random migration of neutrophils (p<0.001) was observed compared to controls. Intracellular killing activity of polymorphonuclear leukocytes have also seemed to be slightly but not significantly reduced. These results suggest that human chronic exposure to lead may diminish neutrophil function in man.     

Impaired endothelial function assessed by flow-mediated vasodilatation in workers occupationally exposed to lead

The aim of the study was to examine endothelial function in workers occupationally exposed to lead by means of FMD (flow-mediated dilatation). 44 men professionally exposed to lead, smelters and refiners, employees working at copper smelter and control group of 41 healthy men were enrolled into the study. Within the group of men occupationally exposed to lead the absolute increase in diameter after ischaemia (BAD, brachial artery diameter) and flow-mediated dilation were statistically less significant when compared to those of the control group. There was a negative linear correlation between FMD and lead concentration in copper smelters (r=-0.64). Multivariate backward step-wise regression analysis showed that blood lead concentration in copper smelters independently influenced the impairment of endothelial function expressed as decreased FMD value. In conclusion, results of our study suggest that endothelial function assessed by flow-mediated dilatation was impaired in workers occupationally exposed to lead.