Genetic polymorphisms of glutathione S-transferases M1 and T1 associated with susceptibility to aflatoxin-related hepatocarcinogenesis among chronic hepatitis B carriers: a nested case-control study in Taiwan

Glutathione S-transferase M1 and T1 genetic polymorphisms are not related to the risk of hepatocellular carcinoma: a study in the Spanish population

Glutathione S-transferases constitute a superfamily of enzymes that catalyse the inactivating conjugation of endogenous and environmental substrates involved in the pathogenesis of hepatocellular carcinoma (HCC) and glutathione. Genes encoding either glutathione S-transferase Mu-1 or Theta-1 (GSTM1 and GSTT1, respectively) isoforms are polymorphic. Homozygotes for the mutated inactive alleles of each gene are devoid of any specific enzymatic activity (null genotypes). Our aim was to investigate whether individuals with null GST genotypes have a higher risk of developing HCC. A total of 184 Caucasian Spanish patients with a diagnosis of HCC and 329 healthy controls of the same ethnic origin were included. Polymorphisms in GSTM1 and GSTT1 genes were identified through multiplex polymerase chain reactions, and the dihydrofolate reductase (DHFR) gene was used as internal control. No differences were found between the frequencies of GSTM1 (47.8% versus 45.3%) and GSTT1 (28.8% versus 23.1%) null genotypes in cases and controls, respectively, nor in the proportion of carriers of two, one or no active genotypes. Gender, age at diagnosis, tobacco use, chronic infection with hepatitis B or C virus and alcohol abuse did not influence these results. In conclusion, polymorphisms in GSTM1 and GSTT1 genes are not related to the incidence of HCC in a high-risk Spanish population.

Alterations of liver function test indices of filling station workers with respect of genetic polymorphisms of GSTM1 and GSTT1

To determine the health effects of gasoline exposure on liver function test indices of filling station workers the present study was done. This case-control study was conducted in Shiraz on 56 male gasoline workers and 56 age- and sex-matched control subjects with no occupational exposure to gasoline. To elucidate the role of hepatic detoxifying enzymes, the genotypes of glutathione-S-transferases (GST) M1 and T1 were determined. Data analysis was done by multiple linear regression analysis and non-parametric Kruskal-Wallis test. The present study showed that all measurements were in normal range, although sub-clinical changes were detected in some indices. In liver function tests, exposure was associated with lower serum albumin (t=-3.88, P<0.001) and total proteins (t=-3.016, P=0.003) but higher alanine aminotransferase (t=2.856, P=0.005) and aspartate aminotransferase (t=2.11, P=0.038) levels in workers comparing to controls. Other investigators reported that GSTs involved in detoxification of several toxins including some of the compounds present in gasoline. Therefore, the possible influence of GSTT1 and GSTM1 genetic polymorphisms on alteration of liver function tests indices was investigated. The present findings showed that the genotype combinations of GSTM1 and GSTT1 did not alter the effects of exposure to gasoline in workers except for serum albumin. Serum albumin significantly decreased in workers with both active GST enzymes who had more than 5 years of employments (P=0.01). It is suggested that GSTM1 and GSTT1 are not involved in detoxification of toxicants present in gasoline which are hazardous to liver. Overall, due to detection of sub-clinical changes in hepatic test in gasoline station workers, exposure limitation and administrating safety device are recommended.

Smoking attributable mortality for Taiwan and its projection to 2020 under different smoking scenarios

OBJECTIVES

To estimate smoking attributable mortality (SAM) in Taiwan for the years 2001 through 2020 under scenarios of reductions in smoking rates by 0%, 2%, 4%, and 10% per year.

METHOD

The smoking attributable fraction (SAF) was used to calculate SAM from the risk experience in following up a large cohort (86 580 people) in Taiwan. Smoking rates were based on the 2001 National Health Interview Survey and other national surveys. An average 10 year lag was assumed between smoking rates and subsequent mortality.

RESULTS

In 2001, 18 803 deaths, or 1 out of 4 deaths (27%), in middle aged men (35-69 years old) were attributable to smoking. SAM has been increasing and will continue to increase if smoking rates remain constant or even if reduced annually by 2%. SAM would begin to decrease only if rates were to be reduced by at least 4% a year.

CONCLUSIONS

The projected SAM in this study illustrates the seriousness of smoking caused mortality. Current efforts in tobacco control would lead to a progressive increase in SAM, unless efforts were doubled and smoking rates reduced by more than 4% a year. The urgency in requiring stronger tobacco control programmes to attenuate the staggering death tolls is compelling.

Uncovering the relation between betel quid chewing and cigarette smoking in Taiwan

OBJECTIVE

To describe the characteristics of betel quid chewers and to investigate the behavioural and mortality relations between betel quid chewing and cigarette smoking.

METHOD

Prevalence and mortality risks of betel quid chewers by smoking status were calculated, based on the National Health Interview Survey in 2001 and a community based cohort, respectively. Cox's proportional hazards model was used to adjust mortality risks for age, alcohol use, and education.

RESULTS

Almost all betel quid chewers were smokers, and most started chewing after smoking. Chewers were predominantly male, mostly in their 30s and 40s, more likely being among the lowest educational or income group, and residing in the eastern regions of Taiwan. On average, betel quid chewers who smoked consumed 18 pieces of betel quid a day, and smoked more cigarettes per day. Far more smokers use betel quid than non-smokers (27.5% v 2.5%), but ex-smokers quit betel quid more than smokers (15.1% v 6.8%). The significantly increased mortality of betel quid users who also smoked, for all causes, all cancer, oral cancer, and cancer of the nasopharynx, lung, and liver, was the result of the combined effects of chewing and smoking. Smokers who chewed betel quid nearly tripled their oral cancer risks from a relative risk of 2.1 to 5.9. Increasing the number of cigarettes smoked among betel quid chewers was associated with a synergistic effect, reflective of the significant interaction between the two.

CONCLUSION

To a large extent, the serious health consequences suffered by betel quid chewers were the result of the combined effects of smoking and chewing. Betel quid chewing should not be considered as an isolated issue, but should be viewed conjointly with cigarette smoking. Reducing cigarette smoking serves as an important first step in reducing betel quid chewing, and incorporating betel quid control into tobacco control may provide a new paradigm to attenuate the explosive increase in betel quid use in Taiwan.

Hepatocellular carcinoma and polymorphisms in carcinogen-metabolizing and DNA repair enzymes in a population with aflatoxin exposure and hepatitis B virus endemicity

High rates of hepatocellular carcinoma (HCC) in The Gambia, West Africa, are primarily due to a high prevalence of chronic hepatitis B virus infection and heavy aflatoxin exposure via groundnut consumption. We investigated genetic polymorphisms in carcinogen-metabolizing (GSTM1, GSTT1, HYL1*2) and DNA repair (XRCC1) enzymes in a hospital-based case-control study. Incident HCC cases (n = 216) were compared with frequency-matched controls (n = 408) with no clinically apparent liver disease. Although the prevalence of variant genotypes was generally low, in multivariable analysis (adjusting for demographic factors, hepatitis B virus, hepatitis C virus, and TP53 status), the GSTM1-null genotype [odds ratio (OR), 2.45; 95% confidence interval (95% CI), 1.21-4.95] and the heterozygote XRCC1-399 AG genotype (OR, 3.18; 95% CI, 1.35-7.51) were significantly associated with HCC. A weak association of the HYL1*2 polymorphism with HCC was observed but did not reach statistical significance. GSTT1 was not associated with HCC. The risk for HCC with null GSTM1 was most prominent among those with the highest groundnut consumption (OR, 4.67; 95% CI, 1.45-15.1) and was not evident among those with less than the mean groundnut intake (OR, 0.64; 95% CI, 0.20-2.02). Among participants who had all three suspected aflatoxin-related high-risk genotypes [GSTM1 null, HLY1*2 (HY/HH), and XRCC1 (AG/GG)], a significant 15-fold increased risk of HCC was observed albeit with imprecise estimates (OR, 14.7; 95% CI, 1.27-169). Our findings suggest that genetic modulation of carcinogen metabolism and DNA repair can alter susceptibility to HCC and that these effects may be modified by environmental factors.

Homozygosity for Pro of p53 Arg72Pro as a potential risk factor for hepatocellular carcinoma in Chinese population

AIM: Codon 72 exon 4 polymorphism (Arg72Pro) of the p53 gene has been implicated in cancer risk. Our objective was to investigate the possible association between p53 Arg72Pro polymorphism and susceptibility to hepatocellular carcinoma (HCC) among Chinese population.

METHODS: The p53 Arg72Pro genotypes were determined by PCR-based restriction fragment length polymorphism (RFLP) analysis in 507 HCC cases and 541 controls. Odds ratios (ORs) for HCC and 95% confidence intervals (CIs) from unconditional logistic regression models were used to evaluate relative risks. Potential risk factors were included in the logistic regression models as covariates in the multivariate analyses on genotype and HCC.

RESULTS: The frequencies for Pro and Arg alleles were 44.5%, 55.5% in HCC cases, and 40.3% and 59.7% in controls, respectively. The Pro allele was significantly associated with the presence of HCC (P = 0.05) and had a higher risk for HCC (OR = 1.19, 95% CI 1.00-1.41) as compared with the Arg allele. After adjusted for potential risk factors, Arg/Pro heterozygotes had an 1.21-fold increased risk (95% CI 0.82-1.78, P = 0.34) of HCC compared with Arg homozygotes, whereas the risk for Pro homozygotes was 1.79 (95% CI 1.06-3.01, P = 0.03) times higher than that for Arg homozygotes. Pro-allele carriers had a higher relative risk of HCC than the Arg-only carriers (adjusted OR = 1.33, 95% CI 0.92-1.92, P = 0.13), although the difference was not statistically significant.

CONCLUSION: Homozygosity for Pro of p53 Arg72Pro is potentially one of the genetic risk factors for HCC in Chinese population. The p53 Arg72Pro polymorphism may be used as a stratification marker in screening individuals at a high risk of HCC.

Molecular Epidemiology of Physical Activity and Cancer

As in other areas of epidemiology, researchers studying physical activity and cancer have begun to include laboratory analyses of biological specimens in their studies. The incorporation of these “biomarkers” into epidemiology has been termed molecular epidemiology and is an approach primarily developed to study chemical carcinogens. Thus far, there has been no discussion in the field on how the established molecular epidemiologic framework might be adapted for research into physical activity, what methodologic needs exist, what the goals of such an approach might be, and what limitations exist. This article relates the literature on molecular epidemiology to the needs of physical activity research and tries to set research priorities for the field as it moves in this new direction. Although this approach will be very useful for investigating the mechanisms through which physical activity exerts effects, there are several challenges for physical activity epidemiologists in adapting molecular epidemiologic approaches. Primarily, there are currently no available biomarkers that might be considered measures of exposure or biologically effective dose. In addition, most available biomarkers of intermediate effects have been tested in training studies at activity levels much higher than those seen in population-based epidemiologic studies. Thus, it is not clear whether these biomarkers are valid at lower activity levels. Furthermore, the nature of the relationship between activity and many available biomarkers depends very much on the context of the activity. Addressing these issues should be a priority if we are to develop a molecular epidemiologic paradigm for studying physical activity.

N-Acetyltransferase-2, glutathione S-transferase M1 andT1 genetic polymorphisms, cigarette smoking and hepatocellular carcinoma: A case-control study

Our aim was to evaluate the role of N-acetyltransferase (NAT2) and glutathione S-transferase M1 and T1 (GSTM1 and GSTT1) polymorphisms in hepatocellular carcinoma (HCC) according to cigarette smoking, taking into account hepatitis B (HBV) and C (HCV) viral infection as well as alcohol consumption. A hospital-based case-control study was conducted in 2 areas of north Italy. Cases (n = 200) were patients hospitalized for HCC, and controls (n = 400) were patients admitted for reasons other than liver disease, neoplasms and tobacco- and alcohol-related diseases. Genotypes were determined using PCR and the PCR/restriction fragment length polymorphism-based method. The putative risk genotypes NAT2 slow acetylator, GSTM1 null and GSTT1 null were not associated with HCC (OR = 1.3, 95% CI 0.8-2.0; OR = 1.0, 95% CI 0.6-1.5; OR = 0.8, 95% CI 0.4-1.4, respectively). Although not statistically significant, an increase in HCC risk was observed among light smokers (1-20 pack-years) carrying GSTT1 null (OR = 1.7, 95% CI 0.6-4.7) and NAT2 slow acetylator (OR = 1.3, 95% CI 0.6-3.0) genotypes. In conclusion, there was no evidence for a gene-environment interaction in HCC risk for GSTM1, GSTT1 and NAT2 genotypes.

The mortality risks of smokers in Taiwan: Part I: cause-specific mortality

BACKGROUND

Few studies of adverse health effects from smoking have been conducted in southeastern Asian populations which may exhibit racial, cultural, and smoking behavioral differences that could affect mortality patterns. This study aims to quantify cause-specific mortality risks among cigarette smokers in Taiwan.

METHODS

The study population for this investigation was derived from two existing prospective study cohorts: a community-based cohort and a cohort composed of civil servants and teachers. Smoking data were obtained by face-to-face interview in the community cohort and by self-administered questionnaire in the civil servant/teacher cohort. The mortality risks of current smokers, adjusted for age, were compared to those of nonsmokers using Cox's proportional hazards model and dose-response relationships were examined by variables of smoking intensity and duration.

RESULTS

Male smokers had significantly higher all-cause mortality than nonsmokers. Cigarette smoking was also significantly associated with increased risks of dying from cancer, cardiovascular disease, respiratory disease, chronic bronchitis, diabetes, peptic ulcer, liver cirrhosis, and kidney disease. In addition, smokers had an increase in risk of fatal injuries from motor vehicle accidents and nonmotor vehicle accidents, as well as cancers of the oral cavity nasopharynx, esophagus, stomach, rectum, liver, and lungs. Risks for women smokers were generally higher than those for men, although this is based on small numbers of smokers. In women, deaths from all causes, all cancers, and cancers of the cervix, liver, and lung, cardiovascular disease, and respiratory disease were also significantly increased. The mean age at death for smokers who died before age 65 from smoking-related diseases was 57.4 years, which represented a loss of 22 years of life expectancy.

CONCLUSIONS

The pervasive and serious impact of cigarette smoking on the health of Taiwanese cannot be underestimated.

Synergistic interaction between aflatoxin B1 and hepatitis B virus in hepatocarcinogenesis

Chronic hepatitis B virus (HBV) infection and dietary exposure to aflatoxin B1 (AFB1), two of the major risk factors in the multifactorial aetiology of hepatocellular carcinoma (HCC), co-exist in those countries with the highest incidences of and the youngest patients with this tumour, raising the possibility of a synergistic carcinogenic interaction between the two agents. Experimental studies in HBV-transgenic mice and woodchucks infected with woodchuck hepatitis virus were the first to show a synergistic hepatocarcinogenic effect between hepadnaviral infection and AFB1 exposure. With the availability of urinary and serum biomarkers that more accurately reflect dietary exposure to AFB1 than did the initially used food sampling and dietary questionnaires, cohort studies of patients with HCC in China and Taiwan have provided compelling evidence for a multiplicative or sub-multiplicative interaction between HBV and AFB1 in the genesis of human HCC. A number of possible mechanisms for the interaction have been suggested. Chronic HBV infection may induce the cytochrome P450s that metabolise inactive AFB1 to the mutagenic AFB1-8,9-epoxide. Hepatocyte necrosis and regeneration and the generation of oxygen and nitrogen reactive species resulting from chronic HBV infection increase the likelihood of the AFB1-induced p53 249ser and other mutations and the subsequent clonal expansion of cells containing these mutations. Nuclear excision repair, which is normally responsible for removing AFB1-DNA adducts, is inhibited by HBV x protein, favouring the persistence of existing mutations. This protein also increases the overall frequency of DNA mutations, including the p53 249ser mutation, and may contribute to uncontrolled cell cycling when p53 is non-functional.

Relationship between xenobiotic-metabolizing enzyme gene polymorphisms and genetic susceptibility of gastric cancer

AIM

To investigate the relationship between genetic polymorphisms of CYP4502E1 and GSTT1 and gastric cancer.

METHODS

Fifty six patients with histologically confirmed gastric adenocarcinoma (GC case group) and 56 healthy persons (control group), matched by age, sex, smoking, dietary habits and family history of cancer were studied. Genomic DNA samples were assayed for restriction fragment length polymorphisms in the CYP2E1 by PCR amplification followed by digestion with endonuclease PstI, and GSTT1 genes were detected by multiplex PCR.

RESULTS

The frequency of CYP2E1 C1/ C1 genotype was 69.6 % in GC group and 46.4 % in control group, with a statistically significant difference (x²=6.27; P <0.05, OR=1.915, 95 % CI=1.051-3.489). The frequency of GSTT1 null genotype was higher in GC group (60.7%) than in control group (46.4 %), but the difference was not statistically significant (x²=2.30; 0.1<P<0.25,P =1.783,95 % CI=0.842-3.777). Furthermore, a joint effect of the CYP2E1 and GSTT1 genotypes on cancer risk was observed. GSTT1 non-null genotype/C₁/C₂ or C₂/C₂ genotype was lower than that in GC group (x²=6.23; 0.01<P<0.025, P =0.302,95 % CI=0.114-0.796). The GSTT1 null genotype/C₁/C₁ genotype in GC group was significantly higher than that in the other groups (x²=3.98; P <0.05, P =2.250, 95 % CI=1.007-5.026).

CONCLUSION

CYP2E1 C₁/C₁ genotype is associated with gastric cancer and individuals who carrry the C₁ allele have a higher risk of developing GC than those with the C₁/C₂ or C₂/C₂ genotype. GSTT1 null genotype does not increase the risk of GC. Combined analysis of polymorphisms has shown that GSTT1 non-null genotype/C₁/C₂ or C₂/C₂ genotype is protective factor of GC and GSTT1 null genotype/C₁/C₁ genotype is a risk factor of GC. That is, individuals with both GSTT1 null genotype and CYP2E1 C₁/C₁ genotype have a greater risk of GC.

Susceptibility and biomarker knowledge for improvement of environmental health

At the international level, environmental health problems are usually most serious in countries that have the least resources to deal with the problems. Therefore, international efforts have been initiated to achieve equitable environmental health globally. One approach is to conduct international collaborative studies. This approach has been successful in the building of scientific infrastructure in these countries so that they can address their own environmental health concerns and to sustain the environmental health programs. Using liver and oral cancers as models for discussion, examples of success in the identification of etiology and the mechanisms for the diseases are provided. For example, biomarkers are used to provide early warning signals for the disease. In addition, the application of the collected information for developing disease prevention and intervention programs is presented. Expertise in genetic susceptibility is used to provide a more precise understanding of the cancer process. With the precise knowledge, the information can potentially be used to screen for high-risk individuals and to develop "designer" intervention procedures against specific biochemical defects. Success in disease prevention is dependent upon multidisciplinary collaborations at the local and international levels.

Prevention of liver cancer

Hepatocellular carcinoma (HCC) is among the most prevalent and deadly cancers worldwide. Prominent risk factors for HCC include viral hepatitis infection; dietary exposure to hepatotoxic contaminants such as aflatoxins; alcoholism; smoking; and male gender. This review highlights ongoing efforts in HCC prevention. Strategies include vaccination against, and treatment of, viral hepatitis infection. In addition to interferon alpha, an acyclic retinoid (all-trans-3,7,11, 15-tetramethyl-2,4,6,10,14-hexadecapentanoic acid), glycyrrhizin and ginseng are currently under clinical investigation for HCC prevention in Japanese hepatitis C patients. Several recent clinical studies in a Chinese region of pervasive aflatoxin contamination also support the approach of favorably altering aflatoxin metabolism and excretion using the chemopreventive agents oltipraz or chlorophyllin. Agents exhibiting chemopreventive efficacy in preclinical HCC models include vitamins A, D, and E, herbal extracts, a 5alpha-reductase inhibitor, green tea, and D-limonene. Efforts to elucidate the molecular lesions and processes underlying HCC development have identified several putative molecular targets for preventive interventions. These include genes and gene products controlling viral replication, carcinogen metabolism, signal transduction, cell-cycle arrest, apoptosis, proliferation, and oxidative stress.

Determinants of formation of aflatoxin-albumin adducts: a seven-township study in Taiwan

Dietary exposure to aflatoxins is one of the major risk factors for hepatocellular carcinoma. Individual susceptibility to aflatoxin-induced hepatocarcinogenesis may be modulated by both genetic and environmental factors affecting metabolism. A cross-sectional study was performed to evaluate determinants of the formation of aflatoxin covalently bound to albumin (AFB1-albumin adducts). A total of 474 subjects who were free of liver cancer and cirrhosis and were initially selected as controls for previous case-control studies of aflatoxin-induced hepatocarcinogenesis in Taiwan, were employed in this study. Aflatoxin-albumin adducts were determined by competitive enzyme-linked immunosorbent assay, hepatitis B surface antigen and antibodies to hepatitis C virus by enzyme immunoassay, as well as genotypes of glutathione S-transferase M1-1 and T1-1 by polymerase chain reaction. The detection rate of AFB1-albumin adducts was significantly higher in males (42.5%) than in females (21.6%) (multivariate-adjusted odds ratio=2.6, 95% confidence interval=1.4-5.0). The formation of detectable albumin adducts was moderately higher in hepatitis B surface antigen carriers (42.8%) than in non-carriers (36.6%) (multivariate-adjusted odds ratio=1.4, 95% confidence interval=1.0-2.1). In addition, the detection rate of AFB1-albumin adducts tended to increase with the increasing number of null genotypes of glutathione S-transferase M1-1 and glutathione S-transferase T1-1. In conclusion, this cross-sectional study has assessed the relative contributions of environmental exposure and host susceptibility factors in the formation of AFB1-albumin adducts in a well characterised Chinese adult population. This study further emphasises the necessity to reduce aflatoxin exposure in people living in an area endemic for chronic hepatitis B virus infection.