Genetic polymorphism in cytochrome P450 7A1 and risk of colorectal cancer: the Fukuoka Colorectal Cancer Study

Cholesterol in colorectal cancer: an essential but tumorigenic precursor?

Colorectal cancer (CRC) is one of the most lethal human malignancies, and with the growth of societies and lifestyle changes, the rate of people suffering from it increases yearly. Important factors such as genetics, family history, nutrition, lifestyle, smoking, and alcohol can play a significant role in increasing susceptibility to this cancer. On the other hand, the metabolism of several macromolecules is also involved in the fate of tumors and immune cells. The evidence discloses that cholesterol and its metabolism can play a role in the pathogenesis of several cancers because there appears to be an association between cholesterol levels and CRC, and cholesterol-lowering drugs may reduce the risk. Furthermore, changes or mutations of some involved genes in cholesterol metabolism, such as CYP7A1 as well as signaling pathways, such as mitogen-activated protein kinase (MAPK), can play a role in CRC pathogenesis. This review summarized and discussed the role of cholesterol in the pathogenesis of CRC as well as available cholesterol-related therapeutic approaches in CRC.

Pathogenic role of 25-hydroxycholesterol in cancer development and progression

Cholesterol is an essential lipid that serves several important functions, including maintaining the homeostasis of cells, acting as a precursor to bile acid and steroid hormones and preserving the stability of membrane lipid rafts. 25-hydroxycholesterol (25-HC) is a cholesterol derivative that may be formed from cholesterol. 25-HC is a crucial component in various biological activities, including cholesterol metabolism. In recent years, growing evidence has shown that 25-HC performs a critical function in the etiology of cancer, infectious diseases and autoimmune disorders. This review will summarize the latest findings regarding 25-HC, including its biogenesis, immunomodulatory properties and role in innate/adaptive immunity, inflammation and the development of various types of cancer.

Association of CYP7A1 and CYP2E1 Polymorphisms with Type 2 Diabetes in the Chinese Han Populations

Background

Type 2 diabetes mellitus (T2DM) is caused by diverse environmental and genetic risk factors. Previous studies have reported that cytochrome P450 (CYP) is a promising gene for T2DM. Therefore, we aimed to determine the effects of CYP7A1 and CYP2E1 polymorphisms on T2DM susceptibility among the Chinese Han population.

Methods

A case-control study was conducted to assess the potential relationship of four polymorphisms (rs8192879, rs12542233, rs2070672 and rs2515641) with T2DM susceptibility in the Chinese population, involving 512 T2DM patients and 515 age- and gender-matched healthy individuals. We used the Agena MassARRAY platform to detect CYP7A1 and CYP2E1 polymorphisms. The relationship between genetic polymorphisms and T2DM risk was evaluated using odds ratios (ORs) and 95% confidence intervals (CIs) in various genetic models.

Results

After adjusting for age and gender, rs12542233 in the CYP7A1 gene was significantly associated with decreased T2DM risk (recessive: OR = 0.67, 95% CI = 0.49–0.91, p = 0.012; after FDR correction, p = 0.048). The CYP7A1 rs12542233 was associated with a reduced risk of T2DM in people over 59 years of age (p = 0.010). In the population with BMI ≤ 24 kg/m², CYP7A1 rs12542233 was associated with an increased risk of T2DM (p < 0.05). In the population with BMI > 24 kg/m², CYP2E1 rs2515641 can significantly reduce the risk of T2DM (p < 0.05). And rs8192879, rs2070672 and rs2515641 could significantly increase the risk of diabetes retinopathy in T2DM patients (p < 0.05). Furthermore, the T_rs8192879C_rs12542233 haplotype was significantly associated with T2DM (p = 0.019).

Conclusion

CYP7A1 and CYP2E1 polymorphisms may contribute to T2DM susceptibility in the Chinese Han population, especially in stratified analysis.

Association of cholesterol 7α-hydroxylase (CYP7A1) promoter polymorphism (rs3808607) and cholesterol 24S-hydroxylase (CYP46A1) intron 2 polymorphism (rs754203) with serum lipids, vitamin D levels, and multiple sclerosis risk in the Turkish population

BACKGROUND

Patients with multiple sclerosis (MS) have significantly lower vitamin D levels. Cholesterol is known to be the precursor for vitamin D synthesis, and cholesterol removal is regulated by cholesterol 7α-hydroxylase (CYP7A1) in the liver and cholesterol 24S-hydroxylase (CYP46A1) in the brain. In this study, single nucleotide polymorphisms (SNPs) within the genes CYP7A1 (rs3808607) and CYP46A1 (rs754203) were investigated for their effects on serum lipid profiles, vitamin D levels, and the risk of developing MS.

METHODS

Patients with MS (n = 191) and controls (n = 100) were tested using the PCR-RFLP method to determine their genotypes for rs3808607 and rs754203 SNPs.

RESULTS

The minor (C) allele frequency for CYP7A1 rs3808607 variation was 0.380 in patients with MS and 0.305 in control subjects (P = .074). For CYP46A1 rs754203, the frequencies of the minor (C) allele were 0.272 and 0.250 in patients and control subjects, respectively (P = .563). Serum vitamin D (25(OH)D3) concentrations were significantly lower in patients than in control subjects (P = .002). The CYP46A1 rs754203 SNP was associated with total cholesterol levels in patients, whereas the CYP7A1 rs3808607 variant was not associated with serum lipid parameters or vitamin D levels in patients or control subjects.

CONCLUSION

CYP7A1 rs3808607 and CYP46A1 rs754203 variations are not likely to confer an independent risk for MS development in the Turkish population. To the best of our knowledge, this is the first study to investigate the association between CYP46A1 rs754203 and MS risk.

Oxysterols and Gastrointestinal Cancers Around the Clock

This review focuses on the role of oxidized sterols in three major gastrointestinal cancers (hepatocellular carcinoma, pancreatic, and colon cancer) and how the circadian clock affects the carcinogenesis by regulating the lipid metabolism and beyond. While each field of research (cancer, oxysterols, and circadian clock) is well-studied within their specialty, little is known about the intertwining mechanisms and how these influence the disease etiology in each cancer type. Oxysterols are involved in pathology of these cancers, but final conclusions about their protective or damaging effects are elusive, since the effect depends on the type of oxysterol, concentration, and the cell type. Oxysterol concentrations, the expression of key regulators liver X receptors (LXR), farnesoid X receptor (FXR), and oxysterol-binding proteins (OSBP) family are modulated in tumors and plasma of cancer patients, exposing these proteins and selected oxysterols as new potential biomarkers and drug targets. Evidence about how cholesterol/oxysterol pathways are intertwined with circadian clock is building. Identified key contact points are different forms of retinoic acid receptor related orphan receptors (ROR) and LXRs. RORs and LXRs are both regulated by sterols/oxysterols and the circadian clock and in return also regulate the same pathways, representing a complex interplay between sterol metabolism and the clock. With this in mind, in addition to classical therapies to modulate cholesterol in gastrointestinal cancers, such as the statin therapy, the time is ripe also for therapies where time and duration of the drug application is taken as an important factor for successful therapies. The final goal is the personalized approach with chronotherapy for disease management and treatment in order to increase the positive drug effects.

Interactions Between Regulatory Variants in CYP7A1 (Cholesterol 7α-Hydroxylase) Promoter and Enhancer Regions Regulate CYP7A1 Expression

BACKGROUND

CYP7A1 (cholesterol 7α-hydroxylase) catalyzes the rate-limiting step in bile acid biosynthesis from cholesterol-a main pathway for cholesterol removal from the body. CYP7A1 single-nucleotide polymorphisms (SNPs) are associated with total cholesterol and LDL (low-density lipoprotein) levels, risk of cardiovascular diseases, and other phenotypes; however, results are inconsistent, and causative variants remain uncertain, except for a frequent promoter SNP (rs3808607).

METHODS

We used chromatin conformation capture (4C assay), chromatin immunoprecipitation qPCR assay in hepatocytes, and CRISPR (clustered regularly interspaced short palindromic repeats)-mediated genome editing in hepatocellular carcinoma cell line cells to identify regulatory regions for CYP7A1. We then screened for SNPs located in regulatory regions, testing effects on reporter gene assays and on hepatic CYP7A1 expression by measuring allelic mRNA expression imbalance.

RESULTS

4C assays showed several regions interacting with CYP7A1 promoter. CRISPR-mediated genome editing in hepatocellular carcinoma cell line cells revealed a novel CYP7A1 enhancer and a repressor region, located >10 kb downstream of the CYP7A1 promoter. SNP screening with an allelic mRNA expression imbalance in human livers and reporter gene assays identified a frequent functional SNP (rs9297994) located in the downstream CYP7A1 enhancer region. SNP rs9297994 is in high linkage disequilibrium with promoter SNP rs3808607 but has opposite effects on CYP7A1 mRNA expression. Their combined effects using a 2-SNP model robustly associate with hepatic CYP7A1 mRNA expression, ranging >2 orders of magnitude. Moreover, only the 2-SNP model, but not each SNP alone, is significantly associated with LDL levels, risk of coronary artery disease, statin response, and diabetes mellitus in several clinical cohorts, including CATHGEN (Catheterization Genetics) and Framingham.

CONCLUSIONS

Two interacting regulatory SNPs modulate CYP7A1 expression and are associated with risk of coronary artery disease and diabetes mellitus.

Current immunogenetic predisposition to tuberculosis in the Moroccan population

Tuberculosis (TB) is a serious infectious disease that kills approximately two million people per year, particularly in low- and middle-income countries. Numerous genetic epidemiology studies have been conducted of many ethnic groups worldwide and have highlighted the critical impact of the genetic environment on TB distribution. Many candidate genes associated with resistance or susceptibility to TB have been identified. In Morocco, where TB is still a major public health problem, various observations of clinical, microbiological and incidence distribution are heavily affected by genetic background and external environment. Morocco has almost the same clinical profile as do other North African countries, mainly the increase in more extrapulmonary than pulmonary forms of the diseases, when compared to European, Asian or American populations. In addition, a linkage analysis study that examined Moroccan TB patients identified a unique chromosome region that had a strong association with the risk of contracting TB. Other genes in the Moroccan population that were found to be associated seem to be involved predominantly in modulating the innate immunity. In this review, we appraise the major candidate genes that have been reported in Moroccan immunogenetic studies and discuss their updated role in TB, particularly during the first phase of the immune response to Mycobacterium tuberculosis (Mtb) infection.

CYP7A1 gene polymorphism located in the 5' upstream region modifies the risk of coronary artery disease

Background. 7-Alpha cholesterol hydroxylase (CYP7A1), the first enzyme of classic conversion pathway leading from cholesterol to bile acids synthesis, is encoded by CYP7A1 gene. Its single nucleotide polymorphisms (SNPs) influence serum lipid levels and may be related to impaired lipid profile leading to coronary artery disease (CAD). The aim of the present study was to analyze the possible association between the rs7833904 CYP7A1 polymorphism and premature CAD. Material and Methods. Serum lipid levels and rs7833904 SNP were determined in 419 subjects: 200 patients with premature CAD and 219 age and sex matched controls. Results. The A allele carrier state was associated with CAD (OR = 1.76, 95% CI; 1.14–2.71, P = 0.014). The effect was even stronger in the male subgroups (OR = 2.16, 95% CI; 1.28–3.65, P = 0.003). There was no effect in the females. Risk factors of CAD and clinical phenotype of atherosclerosis were not associated with genotype variants of the rs7833904 SNP. Lipid profiles also did not differ significantly between individual genotypes. Conclusion. The CYP7A1 rs7833904 polymorphism may modify the risk of CAD. This effect is especially strong in male subjects. The studied polymorphism does not significantly influence serum lipid levels, in the present study.

The CYP7A1 gene rs3808607 variant is associated with susceptibility of tuberculosis in Moroccan population

Introduction

Despite the medical progress in treatment. Tuberculosis (TB) continues to be a serious global health problem. A genome-wide linkage study identified a major susceptibility locus on chromosomal region 8q12-q13 in Moroccan TB patients. The CYP7A1 gene is located in this region and codes for cholesterol 7a-hydroxylase, an enzyme involved in cholesterol catabolism.

Methods

We selected three SNPs (rs3808607, rs8192875 and rs8192879) and studied their genotype and allele frequencies distribution in patients with pulmonary (PTB) or pleural TB (pTB), and compared them to Healthy Controls (HC). Genotyping of rs8192875 and rs8192879 SNPs was carried out using the Taq Man SNP genotyping Assay while rs3808607 was investigated by PCR-RFLP.

Results

We reported here for the first time a statistically significant increase in the AA homozygote genotype frequency of rs3808607 in PTB patients compared to HC (p = 0.02, OR = 1.93, 95% CI: 1.93 (1.07;3.49). The increased risk of developing TB was maintained when we combined the groups of patients (PTB-pTB) (p = 0.01, OR= 1.91, 95% CI = (1.07 - 3.42). In contrast, no genetic association was observed between the rs8192875 or rs8192879 polymorphisms and TB.

Conclusion

Our investigations suggest that rs3808607 may play a role in susceptibility to TB in a Moroccan population.

Impaired 8-hydroxyguanine repair activity of MUTYH variant p.Arg109Trp found in a Japanese patient with early-onset colorectal cancer

PURPOSE

The biallelic inactivation of the 8-hydroxyguanine repair gene MUTYH leads to MUTYH-associated polyposis (MAP), which is characterized by colorectal multiple polyps and carcinoma(s). However, only limited information regarding MAP in the Japanese population is presently available. Since early-onset colorectal cancer (CRC) is a characteristic of MAP and might be caused by the inactivation of another 8-hydroxyguanine repair gene, OGG1, we investigated whether germline MUTYH and OGG1 mutations are involved in early-onset CRC in Japanese patients.

METHODS

Thirty-four Japanese patients with early-onset CRC were examined for germline MUTYH and OGG1 mutations using sequencing.

RESULTS

Biallelic pathogenic mutations were not found in any of the patients; however, a heterozygous p.Arg19∗  MUTYH variant and a heterozygous p.Arg109Trp MUTYH variant were detected in one patient each. The p.Arg19∗ and p.Arg109Trp corresponded to p.Arg5∗ and p.Arg81Trp, respectively, in the type 2 nuclear-form protein. The defective DNA repair activity of p.Arg5∗ is apparent, while that of p.Arg81Trp has been demonstrated using DNA cleavage and supF forward mutation assays.

CONCLUSION

These results suggest that biallelic MUTYH or OGG1 pathogenic mutations are rare in Japanese patients with early-onset CRC; however, the p.Arg19∗ and p.Arg109Trp MUTYH variants are associated with functional impairments.

Cholesterol metabolism and colorectal cancers

Colorectal cancer (CRC) is primarily a lifestyle disease of the western world. As such it can be likened to cardiovascular disease and indeed it shares many of the same risk factors. It is therefore perhaps unsurprising that cholesterol metabolism and colorectal cancer are also intricately linked. Many of the initial studies suggesting a link between dietary cholesterol, blood cholesterol levels and cholesterol lowering drugs were performed more than a decade ago. The most recent insights in this field are the result of meta-analyses, advances in pharmacogenetics and the new field of molecular pathological epidemiology. This review summarises the current evidence linking cholesterol metabolism with colorectal cancer including the suggested underlying molecular causes and the implications for colorectal cancer prevention.

Microsomal epoxide hydrolase polymorphisms, cigarette smoking, and risk of colorectal cancer: the Fukuoka Colorectal Cancer Study

Microsomal epoxide hydrolase (EPHX1) plays an important role in the activation and detoxification of polycyclic aromatic hydrocarbons, carcinogens found in cigarette smoke. Polymorphisms in exon 3 (Y113H) and exon 4 (H139R) of the EPHX1 have been associated with enzyme activity. We investigated the risk of colorectal cancer in relation to the EPHX1 Y113H and H139R polymorphisms and assessed effect modifications of cigarette smoking and the other covariates. The interaction between the EPHX1 polymorphisms and selected genetic polymorphisms was also examined. We used data from Fukuoka Colorectal Cancer Study, a community-based case-control study, including 685 cases and 778 controls. In-person interviews were conducted to assess lifestyle factors. The EPHX1 Y113H and H139R polymorphisms were determined by the TaqMan assay and the polymerase chain reaction-restriction fragment length polymorphism, respectively. Neither of the two polymorphisms nor the imputed EPHX1 phenotype was associated with colorectal cancer risk. Cigarette smoking and alcohol intake showed no effect modification on the association with the EPHX1 polymorphisms or the imputed EPHX1 phenotype. Increased risks of colorectal cancer associated with the 113Y allele and imputed EPHX1 phenotype were observed among individuals with high body mass index (BMI; ≥25.0 kg/m(2)), but not among those with low BMI (<25.0 kg/m(2)). The risk decreased with an increasing number of the 139R allele in the null genotypes of GSTM1/GSTT1. It is unlikely that the EPHX1 polymorphisms play an important role in colorectal carcinogenesis. The observed interactions of the EPHX1 polymorphisms with BMI and the GSTM1/GSTT1 genotypes warrant further investigation.

Risk modification of colorectal adenoma by CYP7A1 polymorphisms and the role of bile acid metabolism in carcinogenesis

Cholesterol 7α-hydroxylase (CYP7A1), the rate-limiting enzyme in the conversion of cholesterol to bile acids, is a postulated gene modifier of colorectal cancer risk and target for the therapeutic bile acid, ursodeoxycholic acid (UDCA). We investigated associations between CYP7A1 polymorphisms and fecal bile acids, colorectal adenoma (CRA), and UDCA efficacy for CRA prevention. Seven tagging, single-nucleotide polymorphisms (SNP) in CYP7A1 were measured in 703 (355 UDCA, 348 placebo) participants of a phase III chemoprevention trial, of which 495 had known baseline fecal bile acid concentrations. In the placebo arm, participants with two minor G(rs8192871) alleles (tag for a low activity promoter polymorphism at -204) had lower odds of high secondary bile acids (OR = 0.26, 95% CI: 0.10-0.69), and CRA at 3 years' follow-up (OR = 0.41, 95% CI: 0.19-0.89), than AA carriers. Haplotype construction from the six polymorphic SNPs showed participants with the third most common haplotype (C(rs10957057)C(rs8192879)G(rs8192877)T(rs11786580)A(rs8192871)G(rs13251096)) had higher odds of high primary bile acids (OR = 2.34, 95% CI: 1.12-4.89) and CRA (OR = 1.89, 95% CI: 1.00-3.57) than those with the most common CTACAG haplotype. Furthermore, three SNPs (rs8192877, rs8192871, and rs13251096) each modified UDCA efficacy for CRA prevention, and CCGTAG-haplotype carriers experienced 71% lower odds of CRA recurrence with UDCA treatment, an effect not present for other haplotypes (test for UDCA-haplotype interaction, P = 0.020). Our findings support CYP7A1 polymorphisms as determinants of fecal bile acids and risk factors for CRA. Furthermore, UDCA efficacy for CRA prevention may be modified by genetic variation in CYP7A1, limiting treatment benefit to a subgroup of the population.

Cytochrome P450s in the synthesis of cholesterol and bile acids--from mouse models to human diseases

The present review describes the transgenic mouse models that have been designed to evaluate the functions of the cytochrome P450s involved in cholesterol and bile acid synthesis, as well as their link with disease. The knockout of cholesterogenic Cyp51 is embrionally lethal, with symptoms of Antley-Bixler syndrome occurring in mice, whereas the evidence for this association is conflicting in humans. Disruption of Cyp7a1 from classic bile acid synthesis in mice leads to either increased postnatal death or a milder phenotype with elevated serum cholesterol. The latter is similar to the case in humans, where CYP7A1 mutations associate with high plasma low-density lipoprotein and hepatic cholesterol content, as well as deficient bile acid excretion. Disruption of Cyp8b1 from an alternative bile acid pathway results in the absence of cholic acid and a reduced absorption of dietary lipids; however, the human CYP8B1 polymorphism fails to explain differences in bile acid composition. Unexpectedly, apparently normal Cyp27a1(-/-) mice still synthesize bile acids that originate from the compensatory pathway. In humans, CYP27A1 mutations cause cerebrotendinous xanthomatosis, suggesting that only mice can compensate for the loss of alternative bile acid synthesis. In line with this, Cyp7b1 knockouts are also apparently normal, whereas human CYP7B1 mutations lead to a congenital bile acid synthesis defect in children or spastic paraplegia in adults. Mouse knockouts of the brain-specific Cyp46a1 have reduced brain cholesterol excretion, whereas, in humans, CYP46A1 polymorphisms associate with cognitive impairment. At present, cytochrome P450 family 39 is poorly characterized. Despite important physiological differences between humans and mice, mouse models prove to be an invaluable tool for understanding the multifactorial facets of cholesterol and bile acid-related disorders.

Cigarette smoking, genetic polymorphisms and colorectal cancer risk: the Fukuoka Colorectal Cancer Study

Background

It is uncertain whether smoking is related to colorectal cancer risk. Cytochrome P-450 CYP1A1, glutathione-S-transferase (GST) and NAD(P)H:quinone oxidoreductase 1 (NQO1) are important enzymes in the metabolism of tobacco carcinogens, and functional genetic polymorphisms are known for these enzymes. We investigated the relation of cigarette smoking and related genetic polymorphisms to colorectal cancer risk, with special reference to the interaction between smoking and genetic polymorphism.

Methods

We used data from the Fukuoka Colorectal Cancer Study, a population-based case-control study, including 685 cases and 778 controls who gave informed consent to genetic analysis. Interview was conducted to assess lifestyle factors, and DNA was extracted from buffy coat.

Results

In comparison with lifelong nonsmokers, the odds ratios (OR) of colorectal cancer for <400, 400-799 and ≥800 cigarette-years were 0.65 (95% confidence interval [CI], 0.45-0.89), 1.16 (0.83-1.62) and 1.14 (0.73-1.77), respectively. A decreased risk associated with light smoking was observed only for colon cancer, and rectal cancer showed an increased risk among those with ≥400 cigarette-years (OR 1.60, 95% CI 1.04-2.45). None of the polymorphisms under study was singly associated with colorectal cancer risk. Of the gene-gene interactions studied, the composite genotype of CYP1A1*2A or CYP1A1*2C and GSTT1 polymorphisms was associated with a decreased risk of colorectal cancer, showing a nearly statistically significant (P_interaction = 0.06) or significant interaction (P_interaction = 0.02). The composite genotypes of these two polymorphisms, however, showed no measurable interaction with cigarette smoking in relation to colorectal cancer risk.

Conclusions

Cigarette smoking may be associated with increased risk of rectal cancer, but not of colon cancer. The observed interactions between CYP1A1 and GSTT1 polymorphisms warrant further confirmation.

Association of CYP7A1 -278A>C polymorphism and the response of plasma triglyceride after dietary intervention in dyslipidemic patients

We investigated the effect of the -278A>C polymorphism in the CYP7A1 gene on the response of plasma lipids to a reduced-fat diet for 6 to 8 weeks in a group of 82 dyslipidemic males with a mean age of 46.0 +/- 11.7 years. Individuals who presented at least one high alteration in total cholesterol, low-density lipoprotein cholesterol or triglyceride values were considered to be dyslipidemic. Exclusion criteria were secondary dyslipidemia due to diabetes mellitus, renal, liver, or thyroid disease. None of the subjects were using lipid-lowering medication. Baseline and follow-up lipid concentrations were measured. The genotypes were determined by the digestion of PCR products with the BsaI restriction endonuclease. There were statistically significant reductions in plasma total cholesterol, low-density lipoprotein cholesterol and triglyceride concentrations after dietary intervention. The minor allele C has a frequency of 43%. Carriers of the C allele had significantly lower triglyceride concentrations (P = 0.02) than AA homozygotes. After adjustment of covariates, subjects with the AC and CC genotypes showed a greater reduction in triglyceride concentrations compared to subjects with the AA genotype. Multiple linear regression analyses showed that the AC and CC CYP7A1 genotypes accounted for 5.2 and 6.2% of triglyceride concentration during follow-up and adjusted percent of change of triglyceride concentration, respectively. The present study provides evidence that -278A>C polymorphism in the CYP7A1 gene can modify triglyceride concentrations in response to a reduced fat diet in a dyslipidemic male population. This gene represents a potential locus for a nutrigenetic directed approach.

Transcriptional toxicity of the Yangtze River source water on mouse (Mus musculus) detected by cDNA microarray

In order to assess the potential health effects of source water from the Yangtze River at Nanjing section, China, hepatic transcriptional profiles of male mice (Mus musculus) exposed to source water for 90 days were measured with Affymetrix Mouse Genome 430A 2.0 Array. A total of 585 gene expressions were significantly altered (1.5-fold, P < or = 0.05), including 298 up-regulated genes and 287 down-regulated genes. Among the identified genes, potentially important genes that may be implicated in the liver cancer were found, including VCAM 1, Dusp1, Cyp7a1, Egfr and Fhit. The source water exposure also resulted in significant aberration of gene expressions and biological pathways linking to xenobiotic metabolism, signal transduction, cell growth and death, immune/inflammation response and oxidative stress response. The results provide excellent insights into early toxic effects of the Yangtze River source water on human and environmental health.

Genetic polymorphisms of CYP2E1 and risk of colorectal cancer: the Fukuoka Colorectal Cancer Study

Cytochrome P450 2E1 (CYP2E1) is involved in the metabolic activation of a wide variety of potential carcinogens, and functional polymorphisms in the CYP2E1 gene have been investigated in relation to colorectal cancer. We examined the relation of the CYP2E1 RsaI and 96-bp insertion polymorphisms to colorectal cancer risk and the interaction between these polymorphisms and some lifestyle risk factors. Subjects were 685 incident cases of colorectal cancer and 778 community controls. Statistical adjustment was made for alcohol use, body mass index, physical activity, and other factors. The RsaI c2 allele was associated with a decreased risk of rectal cancer [adjusted odds ratio for at least one c2 allele, 0.71; 95% confidence interval (95% CI), 0.53-0.95], and an increased risk of rectal cancer was observed among individuals having one or two 96-bp insertion alleles (adjusted odds ratio, 1.40; 95% CI, 1.06-1.85). Individuals with two 96-bp insertion alleles showed a 2.28-fold increase in colon cancer risk (95% CI, 1.29-4.01). The two polymorphisms were in almost complete linkage disequilibrium (D' = 0.94). A positive association between alcohol intake and colorectal cancer was observed only in individuals without RsaI c2 allele (P(trend) = 0.03) or in those without 96-bp insertion allele (P(trend) = 0.009). Colon cancer risk was increased in relation to red meat intake only in individuals having one or two 96-bp insertion alleles (P(interaction) = 0.03). The present study suggests that variation in activity and inducibility of CYP2E1, in relation to alcohol or red meat intake, contributes to the development of colorectal cancer.

Prospective weight change and colon cancer risk in male US health professionals

Epidemiological studies are remarkably consistent, especially among men, in showing that overweight and obesity [body mass index (BMI) >25] are associated with increased risk of colon cancer. However, no prospective studies address the influence of weight change in adulthood on subsequent colon cancer risk. In this study, we investigated whether weight change influences colon cancer risk utilizing prospectively collected weight data. We included 46,349 men aged 40-75 participating in the Health Professionals Follow-Up Study. Questionnaires including items on weight were completed every second year during follow-up from 1986 to 2004. Updated weight change between consecutive questionnaires during follow-up and recalled weight gain since age 21 was evaluated. All eligible men were cancer-free at baseline. Proportional hazard and restricted spline regression models were implemented. Over an 18-year period, we documented 765 cases of colon cancer. Cumulative mean BMI >22.5 was associated with significantly increased risk of colon cancer. The short-term weight change in the prior 2 to 4 years was positively and significantly associated with risk [HR = 1.14 (95% confidence interval, 1.00-1.29) for 4.54 kg (10 pounds) increment, p = 0.04 for overall trend]. Weight gain per 10 years since age 21 was associated with significantly increased risk [HR = 1.33 (1.12-1.58) for 4.54 kg increase per 10 years, p = 0.001]. We estimated that 29.5% of all colon cancer cases was attributable to BMI above 22.5. Our results add support that overweight and obesity are modifiable risk factors for colon cancer among men and suggest that weight has an important influence on colon cancer risk even in later life.

Role of genetic variant A-204C of cholesterol 7alpha-hydroxylase (CYP7A1) in susceptibility to gallbladder cancer

Gallbladder carcinoma (GBC) usually arises in the background of gallstone disease. Cholesterol 7alpha-hydroxylase (CYP7A1) is a rate-limiting enzyme for cholesterol catabolism and bile acid synthesis. A-204C genetic polymorphism in CYP7A1 may influence gene expression and thus affect the risk of gallstone disease and GBC. We aimed to study the association of A-204C variation of CYP7A1 gene promoter polymorphism in GBC patients, gallstone patients and healthy subjects. The study included 141 histopathologically proven GBC patients, ultrasonographically proven 185 symptomatic gallstone patients and 200 gallstone-free healthy subjects. Genotyping was done by PCR-RFLP method. CYP7A1 A-204C genotypes in control population were in Hardy-Weinberg equilibrium. The CC genotype conferred marginally significant risk for gallstone disease (p=0.051; OR=1.54; 95% CI=0.9-3.4). In GBC patients, the CYP7A1 A-204C polymorphism conferred high risk for GBC at genotype (p=0.005; OR=2.78; 95% CI: 1.3-5.6) as well as allele levels (p=0.008; OR=1.58 and 95% CI: 1.1-2.2). After stratification of GBC patients on the basis of presence or absence of gallstones, CC genotype imparted higher risk for GBC without stones (p=0.002; OR=4.44: 95% CI=1.7-11.3). The association of the polymorphism with GBC was more pronounced in female GBC patients, and also in cancer patients who developed GBC at advanced age. The CC genotype of CYP7A1 is an independent genetic risk factor for GBC but plays a modest role in susceptibility to gallstone disease. The GBC pathogenesis by CYP7A1 polymorphism appears to be independent of gallstone pathway and probably involves genotoxicity due to lipid peroxidation mechanisms.

Association between genetic polymorphisms of the base excision repair gene MUTYH and increased colorectal cancer risk in a Japanese population

The MUTYH gene encodes a DNA glycosylase that can initiate the base excision repair pathway and prevent G:C > T:A transversion by excising adenine mispaired with 8-hydroxyguanine. Biallelic germline mutations of MUTYH have been shown to predict familial and sporadic multiple colorectal adenomas and carcinomas, however, whether there is an association between single nucleotide polymorphisms (SNPs) of MUTYH and sporadic colorectal cancer (CRC) risk has remained unclear. In this study we investigated four MUTYH SNPs, IVS1+11C > T, IVS6+35G > A, IVS10-2A > G, and 972G > C (Gln324His), for an association with increased CRC risk in a population-based series of 685 CRC patients and 778 control subjects from Kyushu, Japan. A statistically significant association was demonstrated between IVS1+11T and increased CRC risk (odds ratio [OR]: 1.43; 95% confidence interval [CI]: 1.012-2.030; P = 0.042) and one of the five haplotypes based on the four SNPs, the IVS1+11T - IVS6+35G - IVS10-2A - 972C (TGAC) haplotype containing IVS1+11T, was demonstrated to be associated with increased CRC risk (OR, 1.43; 95% CI, 1.005-2.029; P = 0.046). Subsite-specific analysis showed that the TGAC haplotype was statistically significantly (P = 0.013) associated with an increased risk of distal colon, but not proximal colon or rectal cancer. Furthermore, IVS1+11C > T was found to be in complete linkage disequilibrium with -280G > A and 1389G > C (Thr463Thr). The results indicated that Japanese individuals with - 280A/IVS1+11T/1389C genotypes or the TGAC haplotype are susceptible to CRC.

Mendelian randomization: Using genes as instruments for making causal inferences in epidemiology

Observational epidemiological studies suffer from many potential biases, from confounding and from reverse causation, and this limits their ability to robustly identify causal associations. Several high-profile situations exist in which randomized controlled trials of precisely the same intervention that has been examined in observational studies have produced markedly different findings. In other observational sciences, the use of instrumental variable (IV) approaches has been one approach to strengthening causal inferences in non-experimental situations. The use of germline genetic variants that proxy for environmentally modifiable exposures as instruments for these exposures is one form of IV analysis that can be implemented within observational epidemiological studies. The method has been referred to as 'Mendelian randomization', and can be considered as analogous to randomized controlled trials. This paper outlines Mendelian randomization, draws parallels with IV methods, provides examples of implementation of the approach and discusses limitations of the approach and some methods for dealing with these.

Overexpression of CYP2A6 in human colorectal tumors

CYP2A6 metabolizes various nitrosamines, such as those in the diet and in tobacco smoke, which have been implicated as risk factors for colorectal tumors. To determine whether changes in expression levels could contribute to their progression, we carried out immunohistochemistry for CYP2A6 in human colon tumors. Colon specimens (n = 53) were diagnosed as adenoma (n = 16), adenocarcinoma (n = 30) or carcinoma in or with adenoma (n = 7). Colon tumor cells showed cytoplasmic granular immunoreactivity for CYP2A6. Adenocarcinomas and adjacent mucosa showed similar highly elevated degrees of CYP2A6 expression, whereas carcinomas in or with adenoma and adenomas showed lesser increases. To further determine whether CYP2A6 mRNA was expressed at the same level as the CYP2A6 protein, we carried out in situ hybridization of CYP2A6 in two cases of adenocarcinoma. In situ hybridization for CYP2A6 revealed mRNA expression in adenocarcinoma cells. The data indicate that CYP2A6 may have important roles in human colorectal tumorigenesis and progression, so that it could be a candidate therapeutic and chemopreventive target for colorectal cancers.

Alcohol dehydrogenase and aldehyde dehydrogenase polymorphisms and colorectal cancer: the Fukuoka Colorectal Cancer Study

Alcohol dehydrogenase and aldehyde dehydrogenase are key enzymes in alcohol metabolism and therefore may be of importance to colorectal cancer development. The present case-control study was conducted to determine the influence of ADH2, ADH3 and ALDH2 polymorphisms in Fukuoka, Japan, with 685 incident cases of histologically confirmed colorectal adenocarcinomas and 778 community controls selected randomly from the study area. Alcohol use was ascertained by in-person interview. Statistical adjustment was made for sex, age class, area, and alcohol use. Individuals with the allele 47Arg of the ADH2 polymorphism (slow metabolizers) had a statistically significant increase in risk, with an adjusted OR of 1.32 (95% CI = 1.07-1.63), compared with those having the ADH2*47His/His genotype. This association was not affected by the level of alcohol consumption. The ADH3 polymorphism showed no measurable association with the risk of colorectal cancer on either overall analysis or stratified analysis with alcohol use. The heterozygous ALDH2*487Glu/Lys genotype was not associated with an increase in the risk of colorectal cancer (adjusted OR 0.89, 95% CI = 0.71-1.13) compared with the ALDH2*487Glu/Glu genotype. Rather unexpectedly, the homozygous ALDH2*487Lys/Lys genotype was related to a statistically significantly decreased risk of colorectal cancer (adjusted OR 0.55, 95% CI = 0.33-0.93). It is unlikely that acetaldehyde metabolism determined by ALDH2 polymorphism contributes to the risk of colorectal cancer, whereas the role of ADH2 polymorphism deserves further investigation.

Phase I and Phase II Enzyme Polymorphisms and Childhood Cancer

Childhood cancers continue to be challenging clinical entities whose etiology, demographic characteristics, clinical progression, treatment efficacy, and outcomes remain incompletely understood. Research suggests that multiple environmental and genetic factors may play crucial roles in the pathophysiology of many of these malignancies. Recent attention has been directed to the role of carcinogen metabolizing enzymes in the etiology and progression of cancer in both adults and children due to their multitude of polymorphic variants and their intimate interaction with environmental factors. In particular, xenobiotic metabolizing enzymes (XME), which are intimately involved in the activation and deactivation of many environmental carcinogens, have become an area of significant interest. Traditionally, these enzymes have been classified into either phase I or phase II enzymes depending on their substrates, activity, and occasionally based on their sequence in the metabolic pathways, and have been demonstrated to have numerous polymorphic variants. Phase I enzymes predominantly consist of cytochrome enzymes responsible for mixed function oxidase activity, whereas phase II enzymes are frequently conjugation reactions necessary for drug metabolism or the further metabolism of phase I enzyme products. Current research has discovered numerous interactions between polymorphisms in these enzymes and changes in cancer susceptibility, treatment efficacy, and clinical outcomes in childhood cancer. Furthermore, studies of polymorphisms in these enzymes have demonstrated to have synergistic/antagonistic interactions with other XME polymorphisms and demonstrate variable influences on disease pathophysiology depending on the patient's ethnic background and environmental milieu. Continuing research on the role of polymorphisms in phase I and phase II enzymes will likely further elucidate the intimate role of these polymorphisms with environmental factors in the etiology of childhood cancer.

Single-Step analysis of individual conjugated bile acids in human bile using 1H NMR spectroscopy

1H and 13C NMR spectra of intact human bile were assigned using one-dimensional (1H and 13C) and two-dimensional (1H-1H and 1H-13C) experiments. Individual conjugated bile acids--glycocholic acid, glycodeoxycholic acid, glycochenodeoxycholic acid, taurocholic acid, taurodeoxycholic acid, and taurochenodeoxycholic acid--were identified. The bile acids were quantified accurately and individually in a single step by using distinct and characteristic amide signals. Making use of 13C NMR, the study also suggests a way to analyze unconjugated bile acids separately, if present. Chemical shift assignments and rapid single-step analysis of individual conjugated bile acids from intact bile presented herein may have immense utility in the study of bile acid metabolism and deeper understanding of hepatobiliary diseases.

Linkage disequilibrium blocks, haplotype structure, and htSNPs of human CYP7A1 gene

Background

Cholesterol 7-alpha-hydroxylase (CYP7A1) is the rate limiting enzyme for converting cholesterol into bile acids. Genetic variations in the CYP7A1 gene have been associated with metabolic disorders of cholesterol and bile acids, including hypercholesterolemia, hypertriglyceridemia, arteriosclerosis, and gallstone disease. Current genetic studies are focused mainly on analysis of a single nucleotide polymorphism (SNP) at A-278C in the promoter region of the CYP7A1 gene. Here we report a genetic approach for an extensive analysis on linkage disequilibrium (LD) blocks and haplotype structures of the entire CYP7A1 gene and its surrounding sequences in Africans, Caucasians, Asians, Mexican-Americans, and African-Americans.

Result

The LD patterns and haplotype blocks of CYP7A1 gene were defined in Africans, Caucasians, and Asians using genotyping data downloaded from the HapMap database to select a set of haplotype-tagging SNPs (htSNP). A low cost, microarray-based platform on thin-film biosensor chips was then developed for high-throughput genotyping to study transferability of the HapMap htSNPs to Mexican-American and African-American populations. Comparative LD patterns and haplotype block structure was defined across all test populations.

Conclusion

A constant genetic structure in CYP7A1 gene and its surrounding sequences was found that may lead to a better design for association studies of genetic variations in CYP7A1 gene with cholesterol and bile acid metabolism.

Genetic polymorphism of cholesterol 7alpha-hydroxylase (CYP7A1) and colorectal adenomas: Self Defense Forces Health Study

Bile acids have long been implicated in colorectal carcinogenesis, but epidemiological evidence is limited. Cholesterol 7alpha-hydroxylase (CYP7A1) is the rate-limiting enzyme producing bile acids from cholesterol. A recent case-control study showed a decreased risk of proximal colon cancer associated with the CC genotype of the CYP7A1 A-203C polymorphism. The present study examined the relationship between the CYP7A1 A-203C polymorphism and colorectal adenoma, which is a well-established precursor lesion of colorectal cancer. The study subjects comprised 446 cases of colorectal adenomas and 914 controls of normal total colonoscopy among men receiving a preretirement health examination at two hospitals of the Self Defense Forces (SDF). The CYP7A1 genotype was determined by the polymerase chain reaction-restriction fragment length polymorphism method. Statistical adjustment was made for age, hospital, rank in the SDF, smoking, alcohol use, body mass index, physical activity and parental history of colorectal cancer. The CYP7A1 polymorphism was not measurably related to the overall risk of colorectal adenomas. However, the CC genotype was associated with a decreased risk of proximal colon adenomas, but not of distal colon and rectal adenomas. Adjusted odds ratios of proximal colon adenomas (95% confidence intervals) for the AC and CC genotype versus AA genotype were 0.82 (0.54-1.24) and 0.56 (0.34-0.95), respectively. The findings add to evidence for the role of bile acids in colorectal carcinogenesis. The CC genotype of the CYP7A1 A-203C polymorphism probably renders lower activity of the enzyme synthesizing bile acids.