1 氯乙烯聚合工人之易感性標記研究
Study on the Susceptibility Biomarkers in Polyvinyl Chloride Workers 計畫編號：NSC87-2314-B-002-247 執行期限：自民國 86 年 8 月 1 日起至民國 87 年 7 月 31 日止 主持人：鄭尊仁 執行機構及單位名稱：國立台灣大學公共衛生學院職業醫學與工業衛生研究所 中文摘要 研究顯示氯乙烯單體暴露可引起 肝功能異常，但是代謝基因與微量營 養素，在氯乙烯工人所引起的肝臟危 害所扮演之角色並未徹底地被探討。 動 物 實 驗 指 出 氯 乙 烯 可 能 被 CYP2E1、ADH、ALDH 和 GSTs 酵素 所代謝。先前我們已經證實了氯乙烯 工人的 CYP2E1 和 GSTT1 基因型與其 肝功能異常有關，在這個研究中，我 們收集了更多的樣本來進一步探討代 謝基因型、微量營養素與氯乙烯聚合 工人的肝功能異常之相關，在五家氯 乙烯製造工廠中，共收集了 287 名男 性工人，並依其職務名稱與空氣濃度 區分為高暴露組（TWA＞1 ppm）和低 暴露組（TWA＜1 ppm）。藉由問卷收 集其抽煙、飲酒、職業史與疾病史資 料 ， 並 且 以 血 清 中 ALT （ Alanine aminotransferase）濃度來當作肝功能指 標；此外，B 型 及 C 型肝炎病毒感染 標記也一併分析。CYP2E1，ADH2， ALDH2，GSTM1 和 GSTT1 基因型是 以 PCR/RFLP 來測定。微量營養素則 包括維生素 A、維生素 E、α-胡蘿蔔 素和β-胡蘿蔔素是以 HPLC 來測定。 結果顯示 CYP2E1，GSTT1 和 ALDH2 基因型與氯乙烯聚合工人的 ALT 異常 有關，但是本研究並未顯示去氧化劑 與氯乙烯工人肝功能異常有關。 關 鍵 字 ： 氯 乙 烯 、 CYP2E1 、 GSTT1、ALDH2 基因型、微量元素 Abstr act
The role of inherited metabolic traits and micronutrients on liver damage in VCM workers has not been thoroughly investigated. In this study, 287 male workers from five PVC factories were classified into high (time weight average, TWA>1 ppm), and low VCM exposure (TWA<1 ppm). Questionnaires were administered to obtain detailed infor-mation. The activity of serum alanine aminotransferase (ALT) was used as a marker of liver damage. Markers of hepatitis B and C virus infection were also analyzed. CYP2E1, ADH2, ALDH2, GSTM1 and GSTT1 genotypes were identified using the polymerase chain reaction. Vitamin A, vitamin E, α-carotene, β-carotene, were measured by HPLC. The results showed that CYP2E1 c2c2, GSTT1 null, ALDH2 1-2/2-2 genotypes were associated with increased ALT abnormality. Whereas, antioxidants were not associated VCM-induced liver damage.
Key Word: vinyl chloride, CYP2E1, GSTT1, ALDH2, ADH2, micronutrient
2 Introduction
Studies have shown that vinyl chloride monomer (VCM) exposure can cause liver damage (1,2). Alanine amino-transferase (ALT) is one of most sensitive and specific biomakers for liver damage.
In liver, VCM may be metabolized by CYP2E1, ADH2, ALDH2 and GSTs (3,4,5). These metabolic enzymes have been reported to be associated with carcinogenesis induced by various chemicals (6). However, the role of inherited metabolic traits on liver damage in VCM workers has not been thoroughly investigated.
Additionally, there is compelling evidence that diet rich in fresh fruit and vegetables, may lower the risk of cancers and coronary heart diseases (7). Antioxidants including vitamin A, vitamin E and carotene may be res-ponsible for this effect. In this study, the role of micronutrients on the elevation of liver enzymes was also investigated.
Mater ials and methods
Study Subjects: A total of 287 male
workers, with greater than six months of VCM exposure from five plants, were included for analysis. Detailed information was collected from interviewer administered questionnaires, after informed consent was obtained. Alcohol drinking was defined as alcoholic consumption at least one time and more than 80 grams of alcohol weekly. In this study, subjects were
divided into high (TWA>1 ppm) and low VCM (TWA<1 ppm) exposure groups.
Liver F unction Tests: Alanine
amino-transferase (ALT) was used as a marker of liver damage, while HBsAg and anti-HCV were also assayed.
Metabolic Genetic Polymorphism
Genetic polymorphisms for CYP2E1, ALDH2 and ADH2 were determined by PCR/RFLP. GSTM1 and GSTT1 genotypes were determined by the presence of these genes after PCR.
Deter mination of plasma micro-nutr ients levels: Micromicro-nutrients levels including vitamin A, vitamin E, α-carotene, β-carotene, were measured by high-performance liquid chromatogra-phy.
Statistical Analysis
Odds ratios (OR) and their 95% confidence intervals (C.I.) were computed to examine the association of liver damage with various variables. Logistic regression was used to estimate ORs after adjusting covariates.
Results
287 male subjects were included in the analysis. Individuals of high VCM exposure had higher ALT level than those with low exposure. Univariate analysis showed those with low β-carotene level (less than or equal to 0.19
3 µg/ml) had lower proportion on ALT
abnormality than those with high β-carotene level (P=0.09). Subsequent analysis on the association of abnormal ALT level with genotypes in high and low VCM exposure groups was performed after adjusting the effects of hepatitis infection, BMI, and alcohol drinking. CYP2E1 c2c2 genotypes in high VCM exposure had the highest proportion of abnormal ALT than other combination of CYP2E1 genotype with VCM exposure (OR=3.5, 95% C.I.=2.5~19.8). In addition, GSTT1 null-type had higher proportion of ALT abnormality than GSTT1 non-null type in high VCM exposure. However, GSTT1 null-type had significantly lower proportion of abnormal ALT than GSTT1 non-null type in low exposure (OR=0.2, 95% C.I.=0.0~1.1). In high VCM exposure group, ALDH2 1-2/2-2 had higher abnormality of ALT than ALDH2 1-1. However, this did not reach a statistical significance. Similarly, ADH2 1-2/2-2 had high abnormality of ALT than ADH2 1-1 in high exposure group. Again this did not reach a significance. In contrast, vitamin A, vitamin E, α-carotene and β-carotene levels were not associated with ALT abnormality.
Further analysis was performed to test the effect of combination of CYP2E1 and ALDH2 after the adjustment of VCM exposure, hepatitis infection, alcohol drinking, and BMI. When individuals with both CYP2E1
c1c1/c1c2 genotypes and ALDH2 1-1 genotype were used as the reference, OR was 8.3 (95% C.I.=1.9~42.9) for those with both CYP2E1 c2c2 genotypes and ALDH2 1-2/2-2 genotypes, OR was 1.9 (95% C.I.=0.5~ 7.9) for those with both CYP2E1 c2c2 genotype and ALDH2 1-1 genotype, and 1.4 (95% C.I.=0.9~3.7) for those with both ALDH2 1-2/2-2 genotypes and CYP2E1 c1c1 genotype.
Discussion
In this study, CYP2E1 c2c2, GSTT1 null as well as ALDH2 1-1/2-2 were associated with increased abnormality of liver enzymes. Previous work has shown that those with ALDH22 allele have lower enzyme activity (8), thus these susceptible workers tend to accumulate more reactive intermediates which lead to higher liver enzymes. The role of ALDH2 in the health outcomes of VCM workers need further investigation, because one half of Chinese do not have adequate activity for this enzyme (9). Interestingly, susceptible ALDH2 and CYP2E1 had more than additive effect for liver damage. This indicates that VCM is metabolized by CYP2E1 and ALDH2 on the same metabolic pathway. The association of antioxidant and VCM- related abnormal liver enzyme is not shown in this study. Further work to look into the potential chemopreventive agents is indicated.
Reference
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