Reevaluation of lung cancer risk in the acrylonitrile cohort study of the National Cancer Institute and the National Institute for Occupational Safety and Health

A reevaluation of selected mortality risks in the updated NCI/NIOSH acrylonitrile cohort study

Objectives

The study aimed to determine whether the National Cancer Institute's (NCI) recent suggestion of associations between acrylonitrile (AN) exposure and mortality in lung and bladder cancer and pneumonitis is robust to alternative methods of data analysis.

Materials and methods

We used the Richardson method to indirectly adjust risk ratios (RRs) in relation to AN exposure for potential confounding by smoking and asbestos. We repeated key analyses omitting workers from Plant 4 to account for possible local, historical shipyard-related asbestos exposures.

Results

The adjustment of lung cancer RRs for confounding by both smoking and asbestos and omitting Plant 4 workers yielded mostly decreased RRs and much less evidence of a positive association with cumulative AN exposure.

Conclusion

Overall, our reanalysis provided little evidence to support NCI's suggestion of associations between AN exposure and mortality in lung and bladder cancer and pneumonitis.

Differences in exposure to toxic and/or carcinogenic volatile organic compounds between Black and White cigarette smokers

OBJECTIVE

It is unclear why Black smokers in the United States have elevated risk of some tobacco-related diseases compared to White smokers. One possible causal mechanism is differential intake of tobacco toxicants, but results across studies are inconsistent. Thus, we examined racial differences in biomarkers of toxic volatile organic compounds (VOCs) present in tobacco smoke.

METHOD

We analyzed baseline data collected from 182 Black and 184 White adult smokers who participated in a randomized clinical trial in 2013-2014 at 10 sites across the United States. We examined differences in urinary levels of ten VOC metabolites, total nicotine equivalents (TNE), and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL), controlling for covariates such as cigarettes per day (CPD), as well as differences in VOCs per TNE to assess the extent to which tobacco exposure, and not metabolic factors, accounted for racial differences.

RESULTS

Concentration of metabolites of acrolein, acrylonitrile, ethylene oxide, and methylating agents were significantly higher in Blacks compared to Whites when controlled for covariates. Other than the metabolite of methylating agents, VOCs per TNE did not differ between Blacks and Whites. Concentrations of TNE/CPD and VOCs/CPD were significantly higher in Blacks. Menthol did not contribute to racial differences in VOC levels.

CONCLUSIONS

For a given level of CPD, Black smokers likely take in higher levels of acrolein, acrylonitrile, and ethylene oxide than White smokers. Our findings are consistent with Blacks taking in more nicotine and toxicants per cigarette smoked, which may explain their elevated disease risk relative to other racial groups.

Mortality Patterns Among Industrial Workers Exposed to Chloroprene and Other Substances: Extended Follow-Up

OBJECTIVES

To update the U.S. portion of an historical cohort mortality study of workers with potential exposure to chloroprene (CD) and vinyl chloride (VC) with focus on lung and liver cancer.

METHODS

Subjects were 6864 workers from two sites with vital status determined through 2017 for 99% of subjects and cause of death for 97.2% of deaths. Historical exposures to CD and VC were estimated quantitatively. We performed external and internal mortality comparisons.

RESULTS

External comparisons revealed mostly deficits in deaths; internal comparisons revealed no consistent evidence of exposure-response relationships with CD or VC.

CONCLUSIONS

Our update continues to support the conclusion that the risk of death from lung or liver cancer is unrelated to exposure to CD or VC at levels experienced by workers in the two U.S. sites.

Report of an independent peer review of an acrylonitrile risk assessment

A peer review panel made up of experts in toxicology, epidemiology, cancer mode of action (MOA), cancer mechanisms, carcinogenicity, genotoxicity, dose–response, US Environmental Protection Agency (EPA) cancer and noncancer methods, pharmacokinetic modeling and acrylonitrile, met on 22–23 September 2003 in Cincinnati, OH. The purpose of the meeting was to provide an independent review of a risk assessment of acrylonitrile that had been prepared by the Acrylonitrile Group (AN Group). Toxicology Excellence for Risk Assessment (TERA) organized the peer review and selected the panel. The panel discussed the toxicity and epidemiology literature of acrylonitrile and MOA information, and reached conclusions regarding its MOA, weight of evidence (WOE) for carcinogenicity, preferred approach for dose-response assessment and risk values. This paper summarizes the discussion and conclusions of the panel regarding the acrylonitrile assessment. Subsequent to the peer review, the authors of the acrylonitrile assessment revised their report and the panel reviewed the revised report. A manuscript of the revised assessment is being published in Regulatory Toxicology and Pharmacology.

Acrylonitrile and cancer: a review of the epidemiology

Several retrospective cohort epidemiology studies evaluated a number of health outcomes in workers exposed to acrylonitrile (AN). The epidemiology studies included in this review have been published since 1970 and were identified through Ovid and MEDLINE retrieval services using search words "acrylonitrile and cancer". We identified 26 studies which examined mortality and/or incidence rates among persons with AN exposure. Where cohorts have been updated the most recent data were relied upon but descriptions of the earlier publications are provided for background and rationale. Results are provided for all causes of death and all cancers. Detailed results and discussions are provided for the cancers which have received the most attention and for which some positive results have been reported. These include lung, bladder, prostate, and central nervous system cancers. In this review the four most informative cohort studies are evaluated and it is apparent that the results do not support a causal relationship between AN and all cancers or any specific type of cancer. IARC actually downgraded acrylonitrile from "probably carcinogenic" to "possibly carcinogenic to humans" finding that "the earlier indications of an increased risk among workers exposed to acrylonitrile were not confirmed by the recent, more informative studies". This was one of few downgrades of classification by IARC. Our review of the epidemiology data is consistent with the conclusions of the earlier IARC review which found no consistent findings of increased cancer risk across studies.

Aspartame: a safety evaluation based on current use levels, regulations, and toxicological and epidemiological studies

Aspartame is a methyl ester of a dipeptide used as a synthetic nonnutritive sweetener in over 90 countries worldwide in over 6000 products. The purpose of this investigation was to review the scientific literature on the absorption and metabolism, the current consumption levels worldwide, the toxicology, and recent epidemiological studies on aspartame. Current use levels of aspartame, even by high users in special subgroups, remains well below the U.S. Food and Drug Administration and European Food Safety Authority established acceptable daily intake levels of 50 and 40 mg/kg bw/day, respectively. Consumption of large doses of aspartame in a single bolus dose will have an effect on some biochemical parameters, including plasma amino acid levels and brain neurotransmitter levels. The rise in plasma levels of phenylalanine and aspartic acid following administration of aspartame at doses less than or equal to 50 mg/kg bw do not exceed those observed postprandially. Acute, subacute and chronic toxicity studies with aspartame, and its decomposition products, conducted in mice, rats, hamsters and dogs have consistently found no adverse effect of aspartame with doses up to at least 4000 mg/kg bw/day. Critical review of all carcinogenicity studies conducted on aspartame found no credible evidence that aspartame is carcinogenic. The data from the extensive investigations into the possibility of neurotoxic effects of aspartame, in general, do not support the hypothesis that aspartame in the human diet will affect nervous system function, learning or behavior. Epidemiological studies on aspartame include several case-control studies and one well-conducted prospective epidemiological study with a large cohort, in which the consumption of aspartame was measured. The studies provide no evidence to support an association between aspartame and cancer in any tissue. The weight of existing evidence is that aspartame is safe at current levels of consumption as a nonnutritive sweetener.

Nested case-control study of occupational chemical exposures and prostate cancer in aerospace and radiation workers

BACKGROUND

To date, little is known about the potential contributions of occupational exposure to chemicals to the etiology of prostate cancer. Previous studies examining associations suffered from limitations including the reliance on mortality data and inadequate exposure assessment.

METHODS

We conducted a nested case-control study of 362 cases and 1,805 matched controls to examine the association between occupational chemical exposures and prostate cancer incidence. Workers were employed between 1950 and 1992 at a nuclear energy and rocket engine-testing facility in Southern California. We obtained cancer-incidence data from the California Cancer Registry and seven other state cancer registries. Data from company records were used to construct a job exposure matrix (JEM) for occupational exposures to hydrazine, trichloroethylene (TCE), polycyclic aromatic hydrocarbons (PAHs), benzene and mineral oil. Associations between chemical exposures and prostate cancer incidence were assessed in conditional logistic regression models.

RESULTS

With adjustment for occupational confounders, including socioeconomic status, occupational physical activity, and exposure to the other chemicals evaluated, the odds ratio for low/moderate TCE exposure was 1.3; 95%CI = 0.8 to 2.1, and for high TCE exposure was 2.1; 95%CI = 1.2 to 3.9. Furthermore, we noted a positive trend between increasing levels of TCE exposure and prostate cancer (P-value for trend = 0.02).

CONCLUSION

Our results suggest that high levels of TCE exposure are associated with prostate cancer among workers in our study population.

Mortality patterns among industrial workers exposed to chloroprene and other substances

As part of an historical cohort study to investigate the mortality experience of industrial workers exposed to chloroprene (CD) and other substances, including vinyl chloride monomer (VC), we analyzed mortality from all cancers combined, respiratory system (RSC) and liver cancer in relation to CD and VC exposures. Subjects were 12,430 workers ever employed at one of two U.S. sites (Louisville, KY (n=5507) and Pontchartrain, LA (n=1357)) or two European sites (Maydown, Northern Ireland (n=4849) and Grenoble, France (n=717)). Historical exposures for individual workers were estimated quantitatively for CD and VC. For sites L, M, P and G, respectively, average intensity of CD exposures (median value of exposed workers in ppm) were 5.23, 0.16, 0.028 and 0.149 and median cumulative exposures (ppm years) were 18.35, 0.084, 0.133 and 1.01. For sites L and M, respectively, average intensity of VC exposures (median value of exposed workers in ppm) was 1.54 and 0.03 and median cumulative exposures (ppm years) were 1.54 and 0.094. We performed relative risk (RR) regression modeling to investigate the dependence of the internal cohort rates for all cancers combined, RSC and liver cancer on combinations of the categorical CD or VC exposure measures with adjustment for potential confounding factors. We categorized exposure measures into approximate quartiles based on the distribution of deaths from all cancers combined. We also considered 5- and 15-year lagged exposure measures and adjusted some RR models for worker pay type (white/blue collar) as a rough surrogate for lifetime smoking history. All modeling was site-specific to account for exposure heterogeneity. We also computed exposure category-specific standardized mortality ratios (SMRs) to assess absolute mortality rates. With the exception of a one statistically significant association with duration of exposure to CD and all cancers combined in plant M, we observed no evidence of a positive association with all cancers, RSC or liver cancer and exposure to CD and/or VC using both the unlagged and lagged exposure measures: duration, average intensity or cumulative exposure to CD or VC; time since first CD or VC exposure; and duration of CD exposure or time since first CD exposure in presence or absence of VC exposure. We observed elevated and statistically significantly elevated RRs for some analysis subgroups, but these were due to inordinately low death rates in the baseline categories. With the possible exception of all cancer mortality in plant G, our additional adjustment of RRs for pay type revealed no evidence of positive confounding by smoking. We conclude that exposures to CD or VC at the levels encountered in the four study sites do not elevate mortality risks from all cancers, RSC or liver cancer. This conclusion is corroborated by our analysis of general mortality patterns among the CD cohort reported in our companion paper [G. Marsh, A. Youk, J. Buchanich, M. Cunningham, N. Esmen, T. Hall, M. Phillips, Mortality patterns among industrial workers exposed to chloroprene and other substances. I. General mortality patterns, Chem.-Biol. Interact., submitted for publication].

A graphical method to evaluate exposure-response relationships in epidemiologic studies using standardized mortality or morbidity ratios

In occupational epidemiology, exposure-response analyses play an important role in the evaluation of the etiologic relevance of chemical and physical exposures. The standardized mortality or morbidity ratio (SMR) has been commonly used in occupational cohort studies. Statistical approaches to evaluate exposure-response patterns using SMRs have mostly been limited to analyses in which the exposure under investigation is categorized. Here, a graphical method for evaluating exposure-response patterns is presented based on SMR estimates across moving exposure windows. This method is demonstrated using the results of two hypothetical cohort studies. The proposed approach may be useful for graphical exploration of exposure-response trends in situations where the number of observed cases is small.

Occupational acrylonitrile exposure and lung cancer: a meta-analysis

The present work summarizes the currently available published studies on lung cancer and occupational acrylonitrile exposure. Meta-analytic methods were used to estimate the overall risk. To adjust for the healthy worker effect, rate ratio estimates based on regression analyses and ratios of standard mortality ratios were aggregated. Overall effect estimates were 0.95 (95% CI 0.86 to 1.06) and 1.25 (95% CI 1.10 to 1.43) before and after adjustment for the healthy worker effect, respectively. Therefore, a 25% increase in lung cancer risk attributable to occupational acrylonitrile exposure is suggested. Possible contribution of smoking confounding the increased risk cannot be fully excluded.

Acrylonitrile-induced extracellular signal-regulated kinase (ERK) activation via protein kinase C (PKC) in SK-N-SH neuroblastoma cells

Acrylonitrile (ACN) is classified by IARC as a probable carcinogen. Chronic exposure to ACN increases the incidence of tumors in various organs of test animals, including the brain and lung. ERK1/2 activation plays crucial roles in cell proliferation and is involved in many steps of tumor progression. Therefore, this study examined whether ACN altered the activation state of ERK1/2 in human neuroblastoma SK-N-SH cells. Treatment of these cells with ACN greatly increased phosphorylation of ERK1/2 in dose- and time-dependent manners. This effect was inhibited by PD 98059 and U 0126, specific inhibitors of MEK, indicating that MEK, an upstream activator of ERK1/2, was directly involved in ACN-induced ERK1/2 activation. Furthermore, the activation of ERK1/2 by ACN was attenuated by inhibition of PKC with GF 109203X, rottlerin and prolonged incubation with PMA (phorbol 12-myristate 13-acetate). This demonstrated the participation of PKC in the ACN-stimulated activation of ERK1/2. Taken together, our results indicate that ACN-induced ERK1/2 activation involves PKC through a MEK-dependent pathway.

Cancer dose–response assessment for acrylonitrile based upon rodent brain tumor incidence: Use of epidemiologic, mechanistic, and pharmacokinetic support for nonlinearity

A cancer dose-response assessment was conducted for acrylonitrile (AN) using updated information on mechanism of action, epidemiology, toxicity, and pharmacokinetics. Although more than 10 chronic bioassays indicate that AN produces multiple tumors in rats and mice, a number of large, well-conducted epidemiology studies provide no evidence of a causal association between AN exposure and cancer mortality of any type. The epidemiological data include early industry exposures that are far higher than occur today and that approach or exceed levels found to be tumorigenic in animals. Despite the absence of positive findings in the epidemiology data, a dose-response assessment was conducted for AN based on brain tumors in rats. Mechanistic studies implicate the involvement of oxidative stress in rat brain due to a metabolite (2-cyanoethylene oxide or CEO, cyanide), but do not conclusively rule out a potential role for the direct genotoxicity of CEO. A PBPK model was used to predict internal doses (peak CEO in brain) for 12 data sets, which were pooled together to provide a consistent characterization of the dose-response relationship for brain tumor incidence in the rat. The internal dose corresponding to a 5% increase in extra risk (ED 05=0.017 mg/L brain) and its lower confidence limit (LED 05=0.014 mg/L brain) was used as the point of departure. The weight-of-evidence supports the use of a nonlinear extrapolation for the cancer dose-response assessment. A quantitative comparison of the epidemiology exposure-response data (lung and brain cancer mortality) to the rat brain tumor data in terms of internal dose adds to the confidence in the nonlinear extrapolation. Uncertainty factors of 200 and 220 (for the oral and inhalation routes, respectively) were applied to the LED 05 to account for interspecies variation, intraspecies variation, and the severity of the response measure. Accordingly, oral doses below 0.009 mg/kg-day and air concentrations below 0.1mg/m(3) are not expected to pose an appreciable risk to human populations exposed to AN.

Reevaluation of mortality risks from nasopharyngeal cancer in the formaldehyde cohort study of the National Cancer Institute

OBJECTIVE

To determine whether the National Cancer Institute's (NCI) recent suggestion of a causal association between formaldehyde exposure and mortality from nasopharyngeal cancer (NPC) is robust with respect to alternative methods of data analysis and alternative categorizations of formaldehyde exposure.

METHODS

The original authors provided the cohort data. We computed U.S. and local county (regional) rate-based standardized mortality ratios (SMRs) and internal cohort rate-based relative risks (RR) by categories of four formaldehyde exposure metrics (highest peak, average intensity, cumulative, and duration of exposure), using both NCI categories and an alternative categorization based on tertiles of all NPC deaths among exposed subjects. We computed SMRs and RRs for each of 10 study plants and by plant group (Plant 1 (n = 4261) vs. Plants 2-10 (n = 21,358)).

RESULTS

Six of 10 NPC deaths observed in the NCI study occurred in only one plant (Plant 1) and the remaining four cases occurred individually in four of the other nine plants studied. A large, statistically significant, regional rate-based NPC SMR of 10.32 (95% CI = 3.79-22.47) among formaldehyde-exposed workers in Plant 1 contrasted sharply with a 35% deficit in NPC deaths (SMR = .65, 95% CI = .08-2.33) among exposed workers in Plants 2-10 combined. The statistically significant exposure-response relationship with formaldehyde and NPC reported in the NCI study for highest peak exposure was driven entirely by a large, statistically significant excess NPC risk in Plant 1 for the highest peak exposure category (4+ ppm). For the remaining nine plants, RRs for all non-baseline highest peak exposure categories were less than 1.0, and we observed no evidence of an exposure-response relationship. Most of the observed NPC excesses for the non-baseline categories of the other exposure metrics (average intensity, cumulative, and duration of formaldehyde exposure) were concentrated in Plant 1, and by contrast to the NCI findings, none of the corresponding exposure-response relationships was statistically significant.

CONCLUSIONS

Overall, our reanalysis provided little evidence to support NCI's suggestion of a causal association between formaldehyde exposure and mortality from NPC. NCI's conclusion of a possible causal association was driven heavily by anomalous findings in one study plant (Plant 1). An independent and larger study of Plant 1 by the current authors concluded the NPC excess was not associated with formaldehyde exposure. Our findings cast considerable additional uncertainty regarding the validity of NCI's suggested causal association.

Reevaluation of mortality risks from leukemia in the formaldehyde cohort study of the National Cancer Institute

OBJECTIVE

To determine whether the National Cancer Institute's (NCI) recent suggestion of a causal association between formaldehyde exposure and mortality from leukemia and myeloid leukemia (ML) is robust with respect to alternative characterizations and categorizations of formaldehyde exposure and to alternative methods of data analysis.

METHODS

The original authors provided the cohort data. We computed US and local county rate-based standardized mortality ratios (SMRs) and internal cohort rate-based relative risks (RR) by categories of four formaldehyde exposure metrics (highest peak, average intensity (AIE), cumulative, and duration), using both NCI categories and an alternative categorization based on tertiles of deaths from all leukemia among exposed subjects. For highest peak exposure, we computed RRs by the duration of time worked in the highest peak category and the time since highest peak exposure. For AIE, we computed RRs by the duration of exposure and the time since first exposure.

RESULTS

Our external comparisons revealed that the elevated leukemia and ML RRs and associated trends reported by NCI for highest peak and AIE occurred because null (or slight) to moderate mortality excesses were compared with statistically significant baseline category deficits in deaths. Our alternative categorization of AIE yielded leukemia and ML SMRs close to 1.0 in the highest exposure category, and revealed weaker evidence of a trend in RRs for leukemia and ML. We corroborated NCI's finding of no association for cumulative and duration of formaldehyde exposure. We found no consistent evidence that leukemia or ML risks increased with increasing duration of time spent in a given highest peak exposure (or for AIE, duration of exposure in a given AIE category). We also found no consistent evidence that leukemia or ML risks were greater in the more relevant shorter (less than 20 years) versus longer (20+ years) periods of time from the first highest peak exposure (or for AIE, first exposure).

CONCLUSIONS

Our reanalysis provided little evidence to support NCI's suggestion of a causal association between formaldehyde exposure and mortality from leukemia and ML. NCI's key findings for highest peak exposure and AIE do not adequately account for the inordinately large deficits in deaths in the categories used as the baselines for internal rate-based RRs. The NCI findings also do not adequately account for the duration of time subjects spent in the highest peak category (or for AIE, duration of exposure) or the time since their first peak exposure (or for AIE, time since first exposure). Our finding that NCI's suggestion of a causal association is not robust with respect to alternative categorizations of formaldehyde exposure and methods of data analysis casts considerable additional uncertainty regarding the validity of this suggested association.

Mortality update of workers exposed to acrylonitrile in The Netherlands

To study the possible carcinogenic effects of acrylonitrile, we updated the follow up of a cohort of 2842 acrylonitrile workers. The comparison group consisted of 3961 workers from a nitrogen fixation plant. Industrial hygiene assessments quantified past exposure to acrylonitrile, 8-hour averages as well as peak exposure, the use of personal protective equipment, and exposure to other potential carcinogenic agents. Standardized mortality ratios were calculated to adjust for the effect of age distribution, length of follow up, and temporal changes in background mortality rates. Cumulative dose-effect relations were determined for 3 exposure categories and 3 latency periods. The results show that no cancer excess seems related to exposure to acrylonitrile. This additional follow up of a cohort of 2842 workers exposed to acrylonitrile further supports the notion that occupational exposures to acrylonitrile that have occurred in the past have not noticeably increased workers' cancer mortality rates.

A risk assessment for occupational acrylonitrile exposure using epidemiology data

The extensive data from the Blair et al.((1)) epidemiology study of occupational acrylonitrile exposure among 25460 workers in eight plants in the United States provide an excellent opportunity to update quantitative risk assessments for this widely used commodity chemical. We employ the semiparametric Cox relative risk (RR) regression model with a cumulative exposure metric to model cause-specific mortality from lung cancer and all other causes. The separately estimated cause-specific cumulative hazards are then combined to provide an overall estimate of age-specific mortality risk. Age-specific estimates of the additional risk of lung cancer mortality associated with several plausible occupational exposure scenarios are obtained. For age 70, these estimates are all markedly lower than those generated with the cancer potency estimate provided in the USEPA acrylonitrile risk assessment.((2)) This result is consistent with the failure of recent occupational studies to confirm elevated lung cancer mortality among acrylonitrile-exposed workers as was originally reported by O'Berg,((3)) and it calls attention to the importance of using high-quality epidemiology data in the risk assessment process.

Cytochrome P450 2E1 (CYP2E1) is essential for acrylonitrile metabolism to cyanide: comparative studies using CYP2E1-null and wild-type mice

Acrylonitrile (AN) is a rodent carcinogen and suspected human carcinogen. Metabolism of AN proceeds via conjugation with glutathione or epoxidation via cytochrome P4502E1 (CYP2E1) to cyanoethylene oxide (CEO). It was hypothesized that CEO metabolism via epoxide hydrolase (EH) is the primary pathway for cyanide formation. The objective of this work is to assess the enzymatic basis of metabolism to cyanide. Male wild-type and CYP2E1-null mice received 0, 2.5, 10, 20, or 40 mg of AN/kg by gavage, and cyanide was measured in blood and tissues. CYP2E1 and EH expression were assessed using Western blot analyses. Present results demonstrated that cyanide concentrations in blood and tissues of AN-treated wild-type mice were higher at 1 versus 3 h, increased in a dose-dependent manner, and were significantly higher in AN-treated versus vehicle-treated mice. In contrast, cyanide concentrations in the blood and tissues of AN-treated CYP2E1-null mice were not statistically different from those of vehicle-treated mice. Furthermore, this work showed that EH is expressed in CYP2E1-null and wild-type mice. In conclusion, under the current experimental conditions using CYP2E1-null mice, current work demonstrated for the first time that CYP2E1-mediated oxidation is a prerequisite for AN metabolism to cyanide. Since earlier studies showed that CYP2E1 is the only enzyme responsible for AN epoxidation, it is concluded that AN metabolism to CEO is a prerequisite for cyanide formation, and this pathway is exclusively catalyzed by CYP2E1. Finally, this work confirmed that cyanide plays an essential role in the causation of the acute toxicity/mortality of AN.

Acrylonitrile exposure: the effect on p53 and p21(WAF1) protein levels in the blood plasma of occupationally exposed workers and in vitro in human diploid lung fibroblasts

Acrylonitrile (ACN) is a compound widely used in the synthesis of a variety of organic products. It has been found that ACN is carcinogenic in rats, and some epidemiological studies also suggest a possible carcinogenic effect of ACN in humans. The aim of the present study was to assess the effect of ACN exposure on the expression of p53 and p21(WAF1) proteins in vitro as well as in vivo. In vitro ACN exposure of human lung fibroblasts resulted in the induction of both p53 and p21(WAF1) proteins. To evaluate the effect of ACN on the levels of p53 and p21(WAF1) proteins in the blood plasma of ACN-exposed workers, samples from 49 subjects (average age 44 years, 88% males, 12% females) exposed to ACN in the petrochemical industry (ACN concentration ranged from 0.05 to 0.3mg/m(3)) were analyzed. Subjects living in the same area (N=24, average age 43 years, 92% males, 8% females), but not working in the petrochemical industry were used as controls. No significant differences in either p53, or p21(WAF1) levels between the exposed and control groups were found. The expression of p53 was significantly higher in exposed non-smokers as compared with smokers (P=0.02). No effect of GSTM1 and GSTT1 genotypes on the expression of either protein was observed. Subjects with an EPHX high activity genotype had significantly higher p21(WAF1) expression as compared with genotypes with low or medium EPHX activity. We conclude that plasma levels of both proteins are not relevant biomarkers for occupational ACN exposure.