Grantee Research Project Results
Final Report: Molecular Biomarker of Carcinogen Exposure: 'Patched' Gene Mosaicism as a Basis for Differences in Skin Cancer Susceptibility
EPA Grant Number: R825361Title: Molecular Biomarker of Carcinogen Exposure: 'Patched' Gene Mosaicism as a Basis for Differences in Skin Cancer Susceptibility
Investigators: Brandt-Rauf, Paul
Institution: Columbia University in the City of New York
EPA Project Officer: Aja, Hayley
Project Period: November 8, 1996 through November 7, 1999
Project Amount: $335,507
RFA: Exploratory Research - Human Health (1996) RFA Text | Recipients Lists
Research Category: Human Health
Objective:
The objective of this research was to develop a molecular biomarker for exposure to the carcinogen vinyl chloride (VC) based on the detection in serum of a particular mutant form of the ras oncogene-encoded p21 protein (Asp13p21ras).EPA to clean up abandoned hazardous waste sites. The Comprehensive Environmental Response, Compensation and Liability Act (CERCLA) required the EPA to establish criteria to prioritize sites based on risks to health, environment, and welfare. Welfare was interpreted to mean impacts associated with health and the environment, not economic and social impacts (Greenberg and Schneider, 1995). Consequently, the real effect of hazardous waste sites on property values has often been neglected in cost-benefit analyses. Incorporating losses in property values in the analyses may yield a different conclusion about the effectiveness of remedial actions.
The rationale for this research was based on the fact that VC is known to produce a specific mutation (G to A transition at the second base of codon 13 of the K-ras gene) in a high percentage (83%) of the angiosarcomas of the liver (ASL) that develop in VC-exposed workers. This mutation is known to be capable of converting the gene into an actively transforming oncogene in model systems, and thus may be causally related to the carcinogenic process. It also would result in the substitution of an aspartic acid for the normally occurring glycine at amino acid residue 13 in the encoded p21 protein. The altered Asp13p21 protein can be distinguished from normal p21 and other mutant p21s immunologically by immunoblotting with a mouse monoclonal antibody that is specific for this mutant protein. Finally, the mutant p21 protein can be detected by immunoblotting in the cell-free supernatant of cells in culture known to contain the respective mutation, so similarly it was likely that the protein would be detectable in extracellular fluids, such as serum, in individuals who have been exposed to VC and have had the mutation induced in their target tissue.
This research is intended to demonstrate the ability of the Asp13p21 protein as a serum biomarker for the mutagenic effects of VC exposure by accomplishing the following specific aims: (1) examining the serum expression of Asp13p21 in cases of ASL in VC-exposed workers to confirm the correlation between the biomarker in serum and tissue; and (2) determining the serum expression of Asp13p21 in VC-exposed workers without tumors stratified by degree of VC exposure and matched unexposed controls to confirm the relationship between VC exposure and biomarker expression.
Summary/Accomplishments (Outputs/Outcomes):
Serum samples were analyzed for five workers with ASL in whom the mutational status of their tumor was known. Four of the five were positive for the mutation, as well as for the serum biomarker with perfect agreement between them. In addition, for one case of ASL, seven separate serum samples were collected over time during the course of therapy, and levels of the Asp13p21 protein in the serum appeared to parallel the clinical state of the disease and the tumor burden during therapy. This suggests that the detection in serum of the Asp13p21 protein accurately reflects changes at the target tissue level. To determine the relationship between VC exposure and the Asp13p21 protein biomarker, serum samples from a cohort of 225 French VC workers and 111 age-sex-race-smoking-drinking matched, unexposed controls were examined. Stratifying the exposed workers by degree of estimated cumulative VC exposure in ppm-years by quartiles yielded a highly statistically significant trend of increasing odds ratio of seropositivity for the Asp13p21 protein with increasing exposure (p<0.0001). These results suggest that this serum biomarker is indeed related to VC exposure, and may be an early indicator of carcinogenic risk in exposed individuals.The prevalence of the biomarker in the subgroup of individuals who were exposed to VC only at levels below the currently permissible workplace exposure limit of 1 ppm (i.e., below a cumulative VC exposure of 40 ppm-years or 1 ppm for 40 working years) was also examined. The adjusted odds ratio of seropositivity for this subgroup compared to the unexposed controls was also statistically significant (OR = 17.89, 95% CI = 3.34?95.67). These results suggest that this workplace exposure limit may not be adequately protective to prevent the occurrence of known cancer-related, VC-induced mutations in exposed individuals, and that the risk assessment for VC might have to be re-evaluated to consider the use of this biomarker.
Finally, the relationship of this Asp13p21 protein biomarker to another cancer-related, VC-induced biomarker, namely mutant p53 tumor suppressor gene protein, was examined. The same cohort of VC workers was also examined for this mutant p53 biomarker, and similar results were observed. The same stratification of the exposed workers by quartile of cumulative VC exposure in ppm-years yielded a highly statistically significant trend for increasing odds ratio of seropositivity with increasing exposure (p<0.0001). The adjusted odds ratio for seropositivity of the mutant p53 biomarker in the subgroup exposed only below the current permissible workplace exposure limit was also statistically significant (OR = 4.16, 95% CI = 1.01?17.18). In addition, when the two biomarkers (Asp13p21 and mutant p53) were analyzed in combination, there was a highly statistically significant increasing likelihood of seropositivity for one or both of the biomarkers with increasing exposure (p<0.0001). The occurrence of both biomarkers together in the same individual remained statistically significant for some of the workers exposed below the current permissible exposure limit (those with 10?40 ppm-years; p<0.05), but not for those with the very lowest exposures (<10 ppm-years; p>0.05), suggesting that there may be an adequately protective level of exposure at approximately one quarter of the present permissible level.
Conclusions:
In conclusion, this study suggests that serum Asp13p21 protein is a useful biomarker of the effect of VC exposure. It appears to accurately reflect genetic changes that occur in the target tissue following VC exposure, and it appears to correlate in a highly statistically significant way with estimated cumulative VC exposure and other biomarkers of VC effect. Its detection in individuals exposed below the present permissible workplace exposure levels at a statistically significant rate suggests that the current risk assessment for VC may need to be re-evaluated to consider the use of such biomarkers.Journal Articles on this Report : 2 Displayed | Download in RIS Format
| Other project views: | All 4 publications | 4 publications in selected types | All 2 journal articles |
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Li YL, Marion MJ, Asherova M, Coulibaly D, Smith SJ, Do T, Carney WP, Brandt-Rauf PW. Mutant p21ras in vinyl chloride-exposed workers. Biomarkers 1998;3(6):433-439. |
R825361 (1998) R825361 (Final) |
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Smith SJ, Li Y, Whitley R, Marion M-J, Partilo S, Carney WP, Brandt-Rauf PW. Molecular epidemiology of p53 protein mutations in workers exposed to vinyl chloride. American Journal of Epidemiology 1998;147(3):302-308. |
R825361 (Final) |
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Supplemental Keywords:
property values, environmental damage, stigma., RFA, Scientific Discipline, Health, Air, air toxics, Genetics, Risk Assessments, Environmental Microbiology, Molecular Biology/Genetics, cancer risk, patched gene mosaicism, risk, risk assessment, risk factors, tumor supressor genes, intracellular expression, stratospheric ozone, permissible exposure levels, dose response, cancer, carcinogens, human exposure, cancer risk assessment, molecular biology, Vinyl chloride, oncogenesProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.