Effects of vinyl chloride in man: a cytogenetic follow-up study

Association between frequency of chromosomal aberrations and cancer risk is not influenced by genetic polymorphisms in GSTM1 and GSTT1

BACKGROUND

The frequency of chromosomal aberrations (CA) in peripheral blood lymphocytes of healthy individuals has been associated with cancer risk. It is presently unclear whether this association is influenced by individual susceptibility factors such as genetic polymorphisms of xenobiotic-metabolizing enzymes.

OBJECTIVES

To evaluate the role of polymorphisms in glutathione S-transferase (GST) M1 (GSTM1) and theta 1 (GSTT1) as effect modifiers of the association between CA and cancer risk.

METHODS

A case-control study was performed pooling data from cytogenetic studies carried out in 1974-1995 in three laboratories in Italy, Norway, and Denmark. A total of 107 cancer cases were retrieved from national registries and matched to 291 controls. The subjects were classified as low, medium, and high by tertile of CA frequency. The data were analyzed by setting up a Bayesian model that included prior information about cancer risk by CA frequency.

RESULTS

The association between CA frequency and cancer risk was confirmed [OR(medium) (odds ratio)(medium) = 1.5, 95% credibility interval (CrI), 0.9-2.5; OR(high) = 2.8, 95% CrI, 1.6-4.6], whereas no effect of the genetic polymorphism was observed. A much stronger association was seen in the Italian subset (OR(high)= 9.4, 95% CrI, 2.6-28.0), which was characterized by a lower technical variability of the cytogenetic analysis. CA level was particularly associated with cancer of the respiratory tract (OR(high)= 6.2, 95% CrI, 1.5-20.0), the genitourinary tract (OR(high) = 4.0, 95% CrI, 1.4-10.0), and the digestive tract (OR(high) = 2.8, 95% CrI, 1.2-5.8).

CONCLUSIONS

Despite the small size of the study groups, our results substantiate the cancer risk predictivity of CA frequency, ruling against a strong modifying effect of GSTM1 and GSTT1 polymorphisms.

Influence of DNA repair gene polymorphisms of hOGG1, XRCC1, XRCC3, ERCC2 and the folate metabolism gene MTHFR on chromosomal aberration frequencies

We have studied the effect of genetic polymorphisms in the DNA repair genes hOGG1, XRCC1, XRCC3, ERCC2 and the MTHFR gene in the folate metabolism on the frequencies of cells with chromosomal aberrations (CA), chromosome-type aberrations (CSA), chromatid-type aberrations (CTA), chromatid breaks (CTB) and chromatid gaps (CTG) scored in peripheral blood lymphocytes from 651 Norwegian subjects of Caucasian descendant. DNA was extracted from fixed cell suspensions. The log-linear Poisson regression model was used for the combined data which included age, smoking, occupational exposure and genotype for 449 subjects. Our results suggest that individuals carrying the hOGG1 326Cys or the XRCC1 399Gln allele have an increased risk of chromosomal damage, while individuals carrying the XRCC1 194Trp or the ERCC2 751Gln allele have a reduced risk regardless of smoking habits and age. Individuals carrying the XRCC1 280His allele had an increased risk of CSA which was only apparent in non-smokers. This was independent of age. A protective effect of the XRCC3 241Met allele was only found in the older age group in non-smokers for CA, CSA and CTA, and in smokers for CSA. In the youngest age group, the opposite effect was found, with an increased risk for CA, CTA and CTG in smokers. Carrying the MTHFR 222Val allele gave an increased risk for chromosome and chromatid-type aberrations for both non-smokers and smokers, especially for individuals in the older age group, and with variable results in the youngest age group. The variables included in the different regression models accounted, however, for only 4-10% of the variation. The frequency ratio for CTG was significantly higher than for CTA and CTB for only 7 of the 43 comparisons performed. Some of the gap frequencies diverge from the trend in the CA, CSA, CTA and CTB results.

Frequency of HPRT mutants in humans exposed to vinyl chloride via an environmental accident

The mutant frequency (MF) in the hypoxanthine-guanine-phosphoribosyl-transferase (HPRT) locus of peripheral blood T-lymphocytes was measured in a population environmentally exposed to vinyl chloride - a toxic and carcinogenic substance through an accidental release into the atmosphere. It was compared to MF in a control group of unexposed individuals. Both groups were re-investigated in a follow-up study, 2 years later. No significant difference could be observed in MF between exposed and controls either at the accident nor in the follow-up study. Approximately the same mean HPRT mutant frequencies were observed for both groups in T-lymphocytes from blood samples obtained shortly after the accident and from the follow-up blood samples. Both groups showed a higher mean MF in the re-investigation samples which is most probably due to the significantly lower average cloning efficiency (CE) under non-selective conditions and because of the inverse relationship between CE and MF. The exposed population showed a higher mean T-cell CE at the initial blood sampling as compared to the control group. The concurrent cytogenetic analyses of peripheral lymphocytes showed a significant increase in cells with aberrations in the exposed population. Clastogenic but not mutagenic activity of vinyl chloride was observed in our study.

Genetic toxicology of vinyl chloride--a review

Vinyl chloride (VC) is a colorless gas with a mild, sweet odor. It is extensively used in the production of vinyl chloride polymer, copolymer resin, packaging materials, wire and cable coatings as well as in industrial and laboratory intermediates. It is toxic and also carcinogenic in experimental animals. The wide human exposure to this compound in different industries throughout the world causes great concern for human health. In the present review an attempt has been made to evaluate and update the genotoxic effects of vinyl chloride based on the available literature.

Assessment of cytogenetic changes in human populations at risk in Egypt

Humans are exposed to numerous environmental agents that can increase the probability of mutagenicity and carcinogenicity. Most of environmental exposures involve concurrent or sequential exposure to several agents in air, water, and food. Interactive effects in carcinogenesis have been described for a certain number of combinations of agents. They are described in terms of enhancement or inhibition of carcinogenesis. Risk assessment of exposure to environmental agents can start either from laboratory studies after exposure to different agents or from epidemiological studies in relation to actual exposure. The use of genotoxicity testing is essential for assessment of potential human toxicity so that hazards can be prevented. Cytogenetic monitoring of human populations exposed to environmental agents has proved to be a useful tool for detecting their mutagenic effects. Cytogenetic analysis of human chromosomes in peripheral lymphocytes allows direct detection of mutation in somatic cells. Various methods can be used for chromosomal analysis (conventional chromosomal analysis, sister chromatid exchange, micronucleus frequency detection). Micronucleus frequency can be detected either in peripheral blood lymphocytes or in exfoliated cells. Different examples of human population studies are presented in this review. Several problems which are found in biomonitoring studies are discussed.

Sister chromatid exchanges, proliferating rate index, and micronuclei in biomonitoring of internal exposure to vinyl chloride monomer in plastic industry workers

The frequency of micronuclei (MN), sister chromatid exchange (SCEs), and the proliferating rate index in peripheral blood lymphocytes from 93 individuals were measured. Fifty-two of the individuals were workers in the plastics industry where they were exposed to vinyl chloride monomer while the remaining 41 individuals served as a control group. In our results, an increase of SCEs and MN, as well as inhibited cell kinetics, was observed in the group of exposed workers. Of the tests used, SCE was found to be the most sensitive endpoint for indicating a biological response. However, since methods for restricting the MN analysis to only cells at risk (i.e., second generation interphase cells) were not used, this statement requires verification.

Mutagenicity of vinyl chloride in man: comparison of chromosome aberrations with micronucleus and sister-chromatid exchange frequencies

The mutagenic effects of vinyl chloride monomer in man were studied in the lymphocyte culture with 3 methods: the chromosome aberration assay, the micronucleus assay and the sister-chromatid exchange method. Compared with control, values obtained by these tests are increased in workers occupationally exposed to vinyl chloride. In relation to non-smokers, smokers exposed to vinyl chloride show significant increases in sister-chromatid exchange frequencies. The problem of correlating the results of the chromosome aberration assay with micronucleus and sister-chromatid exchange frequencies is discussed.

Structural chromosome aberrations in lymphocytes from children previously treated for Wilms' tumor or Hodgkin's disease

Nineteen children treated for Wilms' tumor (thirteen cases) or Hodgkin's disease (six cases) with cytostatic agents and/or radiotherapy were studied cytogenetically on lymphocytes cultivated from blood samples drawn after at least 1 year of complete remission after end of therapy. A reference group of children was matched for age, sex, and residence. The frequencies of sister chromatid exchange (5.4 versus 5.6 SCE/cell), and chromosome damage type gaps (6.6 versus 7.1%) and breaks (1.9 versus 1.9%) were not different in the two groups, but exchange type aberrations were more frequent in the patients (0.9 versus 0.06%). Fifty karyotypes were analyzed in all but two cases of Hodgkin's disease. The overall frequency of stable (3.1 versus 3.8%) and unstable (1.7 versus 1.4%) structural chromosome changes such as translocations, deletions, chromatid exchanges, and dicentrics were not different in the patient and the control groups. If the chromosome data reflect a general cancer risk, this risk cannot be considerably higher among the cancer-treated children.

Chromosomal aberrations and sister-chromatid exchanges in lymphocytes from coke oven workers

To test whether coke oven workers, an occupational group known to be at increased cancer risk, manifest increased peripheral blood chromosomal aberration frequencies, we obtained samples from a group of 30 steelworker volunteers, who had worked several years at coke oven jobs. Exposure estimates were made using measurements of work place atmospheric coal tar pitch volatiles and work histories. No statistically significant positive regression of chromosomal aberrations on exposure estimates was found. The data from the coke oven workers were also compared with the obtained concurrently and employing precisely the same laboratory protocol from a group of male Brookhaven National Laboratory employees. The coke oven workers as a group were found to have statistically significantly elevated frequencies of chromatid aberrations and of sister-chromatid exchanges.

The application of clinical toxicology

The objective of this review is to assess the role of clinical toxicology as it is practiced today and its possible future development. This includes the legal and ethical aspects of the subject and their application to man. The following issues are considered: extrapolation from animal to man; the logical sequence of the implementation of the stages that constitute good clinical practice; examples of the main invasive and noninvasive techniques employed in the clinical studies; the monitoring of the health of the employee in his working environment; chemically induced chronic disease states; and a retrospective consideration of specific examples of chemical hazards.

The calculation and use of carcinogenic potency: a review

Six methods of estimating carcinogenic potency now in use to some extent by regulatory agencies are examined. It is concluded that none of these methods is adequate for regulatory decision making when used alone, as is usually the case, but that all are useful as a contribution to the whole risk assessment process. The needs for further development and improvement of these methods, where appropriate to human risk, are identified and discussed in view of the growing use of potency estimates in regulatory decision making.

Fetal loss and work in a waste water treatment plant

We investigated pregnancy outcomes in 101 wives of workers employed in a waste water treatment plant (WWTP), and verified fetal losses by hospital records. Paternal work histories were compiled and each of the 210 pregnancies was assigned a paternal exposure category. The relative risk of fetal loss was increased when paternal exposure to the WWTP occurred around the time of conception.

Diet policies of PKU clinics in the United States

About two-thirds of 90 clinics treating phenylketonuria (PKU) now recommend indefinite continuation of a low phenylalanine diet as compared to 1978 when fewer than one-fourth had this policy. The percentage of children maintained on diet has increased markedly for six to eight year-olds. Greater conservatism in clinic diet recommendations likely reflects reports of adverse consequences following diet discontinuation and negative individual clinic experiences.

Carcinogenicity and epidemiological profile analysis of vinyl chloride and polyvinyl chloride

The carcinogenicity of vinyl chloride and polyvinyl chloride (VC/PVC) is reviewed with specific attention to the gaps in knowledge for risk estimation and epidemiological presentation of the available data. Although experimental studies have demonstrated the carcinogenicity and mutagenicity of VC/PVC in general, the epidemiologic studies available for review do not include an assessment of carcinogenic risk among humans exposed to these chemicals. This conclusion is based on the observation that the majority of cohort studies reviewed lacked sufficient statistical power because of small sample sizes. Further, in epidemiological studies, individuals were not followed over an adequate period of time during which cancer could become clinically manifest.

The SCE test as a tool for cytogenetic monitoring of human exposure to occupational and environmental mutagens

The sister chromatid exchange (SCE) test system using human peripheral lymphocytes is proposed as a valuable tool for the cytogenetic monitoring of exposure to potential chemical mutagens in the occupational environment. We examined the SCE frequencies in organic solvent-exposed workers and reviewed the effects of occupational and environmental chemicals on SCE frequencies. The results obtained in these exposed populations are rather contradictory, which may be related to confounding factors, such as personal life style (smoking, drinking, and drugs) of the examinees, tissue culture conditions and the number of subjects examined. We discussed some practical problems for exposure estimation and sample size determination and are led to the following conclusions. 1) The possible combined effects of potential mutagens and cigarette smoking should be taken into consideration when using the SCE test system. 2) Cell cycle kinetic analysis by differential chromatid staining would provide valuable information as a biological indicator for the monitoring of the workers exposed to xenobiotics. 3) By appropriately setting the number of examinees, monitoring would become more efficient in detecting an increased SCE frequency in the exposed populations. Further studies are also required to enhance the sensitivity of the SCE test system for monitoring purposes.

Activity of vinyl chloride monomer in the mouse micronucleus assay

C57Bl/6J mice of both sexes were exposed to 50 000 ppm vinyl chloride monomer (VCM) for 6 h. Animals were killed 24 and 48 h after cessation of exposure and examined for the presence of micronuclei in bone marrow cells. At 24 h the control incidences of micronuclei per 1000 polychromatic erythrocytes (PCEs) were 2.6 (male) and 1.2 (female), while in animals exposed to VCM the incidences were 24.6 (male) and 25.0 (female). At 48 h the control incidences were 2.2 (male) and 1.6 (female) and in the VCM exposed animals 7.2 (male) and 4.4 (female).

Evaluation of the association between birth defects and exposure to ambient vinyl chloride

Birth defects incidence for infants born to residents of Shawinigan, Canada in 1966-1979 were significantly higher than in three comparison communities. Since there has been a vinyl chloride polymerization plant in this town since 1943 from which ten cases of angiosarcoma of the liver have been identified, this study explores the possible association between exposure to vinyl chloride monomer (VCM) in ambient air and the occurrence of birth defects in the community. The excess of birth defects fluctuated seasonally in a way that corresponded to changes in VCM concentration in the environment. Mothers who gave birth to malformed children were younger on average in Shawinigan than in the comparison communities. However, there was no excess of still-births in Shawinigan. The excess in birth defects involved most organ systems, and variation in birth-defect rates among school districts could not be accounted for by estimates of VCM in the atmosphere. The occupational and residential histories of parents who gave birth to malformed infants were compared with those of parents of normal infants. The two groups did not differ in occupational exposure or closeness of residence to the vinyl chloride polymerization plant. Some descriptive data from this study raised the hypothesis of an association between VCM in the air and birth defects in the exposed community, but as a whole, within the sample size available, such an association could not be substantiated.

Clastogenic chromosomal aberrations in 26 individuals accidentally exposed to ortho dichlorobenzene vapors in the National Medical Center in Mexico City

Chromosome studies were done in 8 males and 18 females who were accidentally exposed for 4 work days (i.e., 8 hr/day) to vapors of ortho dichlorobenzene. The clinical symptoms in 10 individuals included headache, general malaise, dizziness, and nausea. All persons had variable degrees of mucosal irritations. Of the 1345 cells studied, 120 disclosed chromosomal aberrations (mean = 8.92%), whereas a control group of 11 healthy individuals revealed 19 cells with aberrations in 942 cells examined (mean = 2.02%). The main chromosomal alterations were 84 single breaks (6.25%) and 86 double breaks (6.39%). In the control group there were 2 single breaks (0.92%) and 10 double breaks (1.06%), with significant statistic values of P less than .001 for the exposed group. Other chromosomal aberrations were poliploidy and ring formation but these were not statistically significant. Chromosome studies conducted 6 months later in 15 persons of the exposed group disclosed a significant reduction of chromosomal aberrations, but these were still present as compared with the control group. Although definite chromosomal changes occurred, these alterations seemed to be reversible after several months, at least with an original 4-day exposure to the clastogen chemical.

Cytogenetic effects of epoxy, phenolformaldehyde and polyvinylchloride resins in man

The cytogenetic analysis of persons occupationally exposed to synthetic resins has revealed a true increase in the average frequency of cells with chromosome aberrations: 5.5% for epoxy resin (146 persons), 6.1% for polyvinylchloride (52 persons), and 5.0% for phenolformaldehyde (31 persons). An incidence of 2.4% was observed in the control (74 persons). The average frequency of aberrant chromosomes per cell for all the synthetic resins (0.054-0.065) differed from the control. The average frequency of chromosome breaks per chromosome did not differ significantly from the control. Acentric fragments (single and paired) was the prevalent type of aberration.

Malignant tumors after chronic exposure to vinyl chloride

Correlations between exposure to vinyl chloride and the development of malignant tumors in the liver have been know since 1974 and have been confirmed by many an experimental investigation. Based on the evaluation of mortality statistics from nine different countries an increased incidence of malignant tumors of the lung, the gastrointestinal tract, and the central nervous system (CNS), and of malignant lymphomas is documented in connection with exposure to vinyl chloride. Statistically significant increases, however, are only found in the incidence of malignant liver tumors. Metabolism and toxicology of vinyl chloride are discussed in detail.

Acrylonitrile: in vivo cytogenetic studies in mice and rats

Acrylonitrile (VCN), a suspect human carcinogen, does not produce significant increases in cytogenetic aberrations in the mouse-bone marrow when given orally for 4, 15 or 30 days at doses equal to 7, 14 and 21 mg/kg/day resp. or by i.p. for the same time periods at doses of 10, 15 and 20 mg/kg/day. Rats treated orally with 16 daily doses of VCN (40 mg/kg/day) or potassium cyanide (KCN) (5 mg/kg/day) showed no increase of aberrant metaphases in the bone marrow over controls.

Chromosomal analyses in vinyl chloride exposed workers. Results from analysis 18 and 42 months after an initial sampling

In a previous study (Purchase et al., Mutation Res., 57 (1978) 325-334) it was reported that 57 workers occupationally exposed to vinyl chloride had an increase in the incidence of chromosomal abnormalities in their lymphocytes by comparison with 24 control workers. Since that time (July 1974) threshold limit values for vinyl chloride and plant exposure levels have been reduced. In the present study, 2 further samples from the same population of workers have been analysed for chromosomal aberrations 18 and 42 months after the initial sampling. At 18 months, 21 VC workers and 6 on-site controls were investigated as were 23 workers and 8 on-site controls at 42 months. In the second sampling there was a tendency to an increase in chromosomal abnormalities of VC-exposed workers except in those people who had changed occupation. By the third sampling, however, there was a decrease by comparison with previous samplings and the levels of abnormalities had returned to values similar to those of the controls. Thus, reduction in exposure to vinyl chloride is accompanied by a reduction in the chromosomal abnormalities to levels indistinguishabe from those of controls.

Vinyl chloride: an example for evaluating mutagenic effects in mammals in vivo after exposure to inhalation

As part of a programme of investigations on the mutagenic effects in mammals in vivo after inhalation of environmental chemicals, the effects of the industrial compound vinyl chloride (VC) was analysed. Chinese hamsters were exposed to 1.25%, 2.5% or 5% (v/v) VC in air for 6, 12 or 24 hr. Bone marrow chromosomes were analysed for induced chromosome aberrations and sister-chromatid exchanges (SCEs) 26 h after beginning of exposure. The frequency of VC-induced chromosome aberrations and SCEs both depend on dose and length of exposure. The highest measured effects were 33.25 SCEs/ cell after an exposure to 2.5% VC for 24 h and 25.7% metaphases with aberrations, when exposed to 5% VC for 24 h.

Monitoring the occupational exposure to mutagens by the cytogenetic analysis of human peripheral lymphocytes in vivo

Cytogenetic analysis of peripheral lymphocytes of workers occupationally exposed to mutagens appears to be a routinely acceptable technique to recommend as a biological indicator of genetic damage to somatic cells due to an overexposure to chemicals in the workplace. A scheme is suggested of genetic risk estimates in workers on the background of cytogenetically detected levels of aberrant cells.