Association of GST Genes Polymorphisms with Asthma in Tunisian Children

The association between glutathione S-transferase (GST) activity as measured by 1-chloro-2,4-dinitrobenzene (CDNB) conjugation and genotype at exon 5 and exon 6 of the human GSTP1 gene was investigated in normal lung tissue obtained from 34 surgical patients. These samples were genotyped for previously identified polymorphisms in exon 5 (Ile105Val) and exon 6 (Ala114Val) by PCR-RFLP and direct sequencing. GST enzyme activity was significantly lower among individuals with the 105 Val allele. Homozygous Ile/Ile samples (n = 18) had a mean cytosolic CDNB conjugating activity of 74.9 +/- 3.8 nmol/mg per min; heterozygotes (n = 13) had a mean specific activity of 62.1 +/- 4.2 nmol/mg per min and homozygous Val/Val (n = 3) had a mean specific activity of 52.5 +/- 4.5 nmol/mg per min. The CDNB conjugating activity measured for the Ile/Ile genotype group was significantly different from that observed in the Ile/Val group (P = 0.03), and from Ile/Val and Val/Val genotypes combined (P = 0.009). Mean GST activity values were consistently lower in individuals with genotypes containing the 105 valine allele, regardless of smoking exposure. Genotypes at codon 114 were also assessed but the mean GST activity was not significantly lower in individuals with the 114 valine allele. A new haplotype, present in two samples who were homozygous 105Ile and had a 114Val, was identified and proposed as GSTP1*D. Frequencies of the exon 5 and exon 6 polymorphisms were determined in samples obtained from European-Americans, African-Americans and Taiwanese. The differences observed were highly significant suggesting the possibility of GSTP1 genotype-associated, ethnic differences in cancer susceptibility and chemotherapeutic response.

The mu (GSTM1 and theta (GSTT1) members of the glutathione S-transferase multigene family are candidate cancer susceptibility genes because of their ability to regulate the conjugation of carcinogenic compounds to excretable hydrophilic metabolites. Deletion variants that are associated with a lack of enzyme function exist at both these loci. Individuals who are carriers of homozygous deletions in the GSTM1 of GSTT1 genes may have an impaired ability to metabolically eliminate carcinogenic compounds and may therefore be at increased cancer risk. Molecular epidemiological studies have provided three pieces of information about the relationship of GSTM1 and GSTT1 with cancer susceptibility. First, the frequencies of homozygous GSTM1 and GSTT1 deletion carriers is very high (i.e., 20-50%) in most populations studied to date. Second, GSTM1 and, possibly, GSTT1 may be involved in the etiology of cancer at more than one site. Third, the risk conferred to individuals who carry homozygous deletions in GSTM1 and GSTT1 appears to be small in magnitude. (e.g., odds ration of < 2). However, the magnitude of risk is larger (e.g., odds ratio of 3-5) when interactions of GSTM1 of GSTT1 with other factors (e.g., cigarette smoking) are considered. These findings have implications for studies of GSTM1 and GSTT1 in cancer susceptibility and for future applications of these biomarkers in cancer prevention of control strategies. First, molecular epidemiological studies should consider both the common frequency of deletion genotypes and the relatively low cancer risk these deletion genotypes may impart. For example, the common frequency of deletion variants may improve statistical power in some molecular epidemiological studies, but large samples may still be required to detect relatively small effect sizes or important interaction effects. Second, the fact that deletion genotypes are common implies that the proportion of cancer attributable to these variants may be large in the general population. However, these genotypes may be less suited for individual cancer risk assessment because of their relatively small contribution to the absolute risk of cancer.

Numerous studies have associated bladder cancer with exposure to carcinogens present in tobacco smoke and other environmental or occupational exposures. Approximately 50% of all humans inherit two deleted copies of the GSTM1 gene which encodes for the carcinogen-detoxification enzyme glutathione S-transferase M1. Recent findings suggest that the GSTM1 gene may modulate the internal dose of environmental carcinogens and thereby affect the risk of developing bladder cancer. We investigated whether the absence of the GSTM1 gene affects bladder cancer risk and whether there are racial differences in GSTM1 genotype frequency. Using a polymerase chain reaction (PCR)-based method, we examined the frequency of the homozygous deleted genotype (GSTM1 0/0) in 229 patients with transitional cell carcinoma of the bladder and 211 control subjects who were enrolled from the Urology Clinics at Duke University Medical Center and the University of North Carolina Hospitals. Control subjects were urology clinic patients who primarily presented with benign prostatic hypertrophy or impotence, who had no history of any cancer other than nonmelanoma skin cancer, and who were frequency matched to case patients on race, sex, and age (10-year age intervals). In order to explore racial differences in GSTM1 gene frequency, genotype was also determined in a community-based sample of 466 paid, healthy, unrelated volunteers from Durham and Chapel Hill, N.C. The presence or absence of the GSTM1 gene locus was determined by using a differential PCR, a semiquantitative technique in which multiple genes are coamplified. Overall, the GSTM1 0/0 genotype conferred a 70% increased risk of bladder cancer (odds ratio [OR] = 1.7; 95% confidence interval [CI] = 1.2-2.5; P = .004). Absence of the GSTM1 gene encoding the glutathione S-transferase M1 enzyme significantly increased risk to persons with exposure to the carcinogens in tobacco smoke (OR = 1.8; 95% CI = 1.2-3.0; P = .01) but poses little increased risk to persons without such exposure. Persons with smoking exposure of more than 50 pack-years who had the GSTM1 0/0 genotype had a sixfold greater risk relative to persons in the lowest risk group (i.e., nonsmokers who were GSTM1 +/+ or +/0). In the pooled clinic control and community sample groups (677 individuals), the GSTM1 0/0 genotype occurred less frequently among Blacks (35%) than among Whites (49%, P < .001). These findings support a protective role for the GSTM1 gene in bladder cancer. From these findings, it is estimated that 25% of all bladder cancer may be attributable to the at-risk GSTM1 0/0 genotype.