José M. Ladero

Prevalence of CYP2D6 gene duplication and its repercussion on the oxidative phenotype in a white population

The occurrence of multiple copies of the CYP2D6 gene was investigated in 217 white healthy Spaniards by the combined use of Xba I and Eco RI restriction fragment length polymorphism (RFLP) analyses. About 3.5% of the alleles yielded an 12.1 kb Eco RI‐RFLP product in combination with the 42 kb Xba I‐RFLP product, which is indicative of multiple CYP2D6. The prevalence of subjects carrying multiple CYP2D6 was 7%. The 12.1 kb Eco RI‐RFLP product was highly associated (60%) with the presence of the genotype 29wt/42wt, as characterized by mutation‐specific polymerase chain reaction and Xba I‐RFLP analyses. Six subjects who had multiple CYP2D6 had other genotypes, namely, 44wt/42wt (four subjects), 29C/42wt (one subject), and one subject had a 12.1 kb product plus the CYP2D6C mutation associated with the 44 kb/42 kb genotype. All subjects identified as carrying multiple CYP2D6 had only two CYP2D6 copies in the same chromosome and were classified as carriers of the (CYP2D6L)2 allelic variant. Phenotyping with debrisoquin indicated an increase in the oxidative capacity as a function of the number of functional CYP2D6 genes. The metabolic ratio and the 95% confidence limits were as follows: subjects lacking functional genes, 48.8 (95% confidence limits, 14.4 to 79.3); subjects with one functional gene, 2.14 (95% confidence limits, 0.61 to 3.67); subjects with two functional genes, 1.5 (95% confidence limits, 0.88 to 2.14); and subjects with three functional genes, 0.33 (95% confidence limits, 0.22 to 0.45). Our findings indicate that the prevalence of subjects who are carriers of (CYP2D6L)2 is at least as frequent as the prevalence of poor metabolizers in the population studied. This may have clinical relevance because the duplicated CYP2D6 gene encodes an active enzyme, and its presence significantly (p < 0.002) accelerates the oxidative metabolism in the population studied.

Interethnic and Intraethnic Variability of CYP2C8 and CYP2C9 Polymorphisms in Healthy Individuals

Cytochrome P450 (CYP) superfamily members CYP2C8 and CYP2C9 are polymorphically expressed enzymes that are involved in the metabolic inactivation of several drugs, including, among others, antiepileptics, NSAIDs, oral hypoglycemics, and anticoagulants. Many of these drugs have a narrow therapeutic index, and growing evidence indicates a prominent role of CYP2C8 and CYP2C9 polymorphisms in the therapeutic efficacy and in the development of adverse effects among patients treated with drugs that are CYP2C8 or CYP2C9 substrates.In this review, we summarize present knowledge on human variability in the frequency of variant CYP2C8 and CYP2C9 alleles. Besides an expected interethnic variability in allele frequencies, a large intraethnic variability exists. Among Asian subjects, for example, statistically significant differences (p < 0.0001) in CYP2C9*3 allele frequencies between Chinese and Japanese individuals have been reported. In addition, individuals from East Asia present different allele frequencies for CYP2C9*2 and CYP2C9*3 compared with South Asian subjects (p < 0.0001). Among Caucasian Europeans, statistically significant differences for the frequency of CYP2C8*3, CYP2C9*2, and CYP2C9*3 exist (p < 0.0001). This indicates that Asian individuals or Caucasian European individuals cannot be considered as homogeneous groups regarding CYP2C8 or CYP2C9 allele frequencies. Caucasian American subjects also show a large variability in allele frequencies, which is likely to be related to ethnic ancestry. A higher frequency of variant CYP2C8 and CYP2C9 alleles is expected among Caucasian Americans with South European ancestry than in individuals with North European ancestry.The findings summarized in this review suggest that among individuals with Asian or European ancestry, intraethnic differences in the risk of developing adverse effects with drugs that are CYP2C8 or CYP2C9 substrates are to be expected. In addition, the observed intraethnic variability reinforces the need for proper selection of control subjects and points against the use of surrogate control groups for studies involving association of CYP2C8 or CYP2C9 alleles with adverse drug reactions or spontaneous diseases.

Genetic predisposition to acute gastrointestinal bleeding after NSAIDs use

Impaired drug metabolism is a major cause of adverse drug reactions, and it is often caused by mutations at genes coding for drug‐metabolising enzymes. Two amino‐acid polymorphisms of cytochrome P4502C9 (CYP2C9), an enzyme involved in the metabolism of several nonsteroidal anti‐inflammatory drugs (NSAIDs), were studied in 94 individuals with acute bleeding after NSAIDs use and 124 individuals receiving NSAIDs with no adverse effects. The frequency of CYP2C9 variant alleles was increased in overall bleeding patients, with a significant trend to higher risk with increasing number of variant alleles (P=0.02). The odds ratio for bleeding patients receiving CYP2C9 substrates (n=33) was 2.5 for heterozygous and 3.7 for homozygous carriers of mutations (P<0.015), suggesting that the inherited impairment of CYP2C9 activity increases the risk for severe adverse drug reactions after NSAIDs use.

High frequency of mutations related to impaired CYP2C9 metabolism in a Caucasian population.

Abstract. Objective: To search for ethnic variability in the impact of cytochrome P450 2C9 (CYP2C9) polymorphism. Methods: CYP2C9 allelic variants related to impaired CYP2C9 metabolism were analysed in genomic DNA from 157 Spanish healthy subjects using amplification–restriction and sequencing procedures. Results: The frequency for CYP2C9 mutated alleles is higher among the Spanish subjects analysed than that reported for other Caucasian individuals: CYP2C9*2, 0.143 and CYP2C9*3, 0.162 (P=0.0001). Nearly 10% of the individuals studied are expected to metabolise deficiently CYP2C9 substrates. Conclusion: In some Caucasian populations the impact of the CYP2C9 polymorphism may be much higher than that estimated from genotyping studies published to date.

Refinement of the basis and impact of common 11q23.1 variation to the risk of developing colorectal cancer

The common single-nucleotide polymorphism (SNP) rs3802842 at 11q23.1 has recently been reported to be associated with risk of colorectal cancer (CRC). To examine this association in detail we genotyped rs3802842 in eight independent case-control series comprising a total of 10 638 cases and 10 457 healthy individuals. A significant association between the C allele of rs3802842 and CRC risk was found (per allele OR = 1.17; 95% confidence interval [CI]: 1.12-1.22; P = 1.08 x 10(-12)) with the risk allele more frequent in rectal than colonic disease (P = 0.02). In combination with 8q21, 8q24, 10p14, 11q, 15q13.3 and 18q21 variants, the risk of CRC increases with an increasing numbers of variant alleles for the six loci (OR(per allele) = 1.19; 95% CI: 1.15-1.23; P(trend) = 7.4 x 10(-24)). Using the data from our genome-wide association study of CRC, LD mapping and imputation, we were able to refine the location of the causal locus to a 60 kb region and screened for coding changes. The absence of exonic mutations in any of the transcripts (FLJ45803, LOC120376, C11orf53 and POU2AF1) mapping to this region makes the association likely to be a consequence of non-coding effects on gene expression.

Polymorphisms of the glutathione S-transferases mu-1 (GSTM1) and theta-1 (GSTT1) and the risk of advanced alcoholic liver disease.

Objective. The aim of this study was to determine whether null genotypes for glutathione transferase mu-1 (GSTM1) and theta-1 (GSTT1) influence the risk of development of advanced alcoholic liver disease. Material and methods. GSTM1 and GSTT1 genotypes were identified on DNA through multiple analysis with polymerase chain reaction in 153 subjects diagnosed with advanced alcoholic liver disease and in 241 healthy controls. Results. The frequency of the GSTM1 null genotype was not different between patients and controls (36.6% versus 41.1%, non-significant). The GSTT1 null genotype was more frequently found in patients than in controls (32% versus 22%, odds ratio 1.67, 95% CI 1.03–2.71, p=0.027). Moreover, patients were more likely to be simultaneous carriers of both GSTM1 and GSTT1 null genotypes (odds ratio 4.30, 95% CI 1.89–9.97, p=0.0003). Conclusions. The GSTT1 null genotype is more frequent among patients with advanced alcoholic liver disease than in controls. The coincidence of this genotype with the GSTM1 null genotype is four times more likely in patients. We suggest that polymorphisms affecting the activity of the glutathione S-transferase isoforms M1 and T1 may be associated with the risk of developing chronic severe ethanol liver damage.

Debrisoquin oxidation genotype and susceptibility to lung cancer

The association between the polymorphism of the cytochrome P450 debrisoquin hydroxylase (CYP2D6) and lung cancer is controversial. Previous reports suggested a link between CYP2D6 phenotype and lung cancer, with poor metabolizers having reduced susceptibility. Nevertheless, negative findings have also been published. By using allele‐specific amplification, we have studied the frequency of four CYP2D6 (wild type and mutant) alleles in 89 patients with histologically proved bronchogenic carcinoma and in 98 healthy volunteers. Our findings confirm that poor metabolizers are underpresented among patients with lung cancer because of a different genetic background. Our findings also reveal that the rare CYP2D6(C) mutant allele is sixfold more frequent among patients with lung cancer (p < 0.0005). This suggests that the CYP2D6(C) allele could be considered as an additional risk factor because carriers could have higher susceptibility to the development of lung cancer.

Genetic basis for differences in debrisoquin polymorphism between a spanish and other white populations

The debrisoquin hydroxylation polymorphism is an autosomic recessive trait of the cytochrome P450IID6, an enzyme involved in drug metabolism, that affects 5% to 10% of white subjects. The genetic basis of this polymorphism was studied in 258 unrelated Spanish white subjects. The results revealed that about 5% of the subjects were homozygous for mutant alleles and that about 1% of the subjects carried alleles that suggested CYP2D6 gene duplication. The extensive metabolizers who were homozygous for the wild‐type allele had higher metabolic ratio than the heterozygous extensive metabolizers, indicating a gene‐dose effect for the wild type allele. The CYP2D6 allele frequencies indicate a reduced frequency for the CYP2D6(B) allele and a higher frequency for the wild‐type allele compared with other white populations. This is also reflected in an increased frequency of the subjects who were homozygous for the wild‐type allele among extensive metabolizers. We conclude that the same CTP2D6 mutations are present in Spaniards and other white subjects. Nevertheless, the frequencies of such mutations are different in our population. This implies that a high number of Spanish subjects may behave differently than other white subjects in the effect of drugs metabolized by the CYP2D6 enzyme.

Relation of IL28B gene polymorphism with biochemical and histological features in hepatitis C virus-induced liver disease.

Background/Aims Polymorphism at the IL28B gene may modify the course of hepatitis C virus (HCV) chronic infection. Our aim was to study the influence of IL28B rs12979860 gene polymorphism on the biochemistry and pathology of HCV-induced disease in the clinical course from mild chronic hepatitis C to hepatocellular carcinoma. Methods We have determined the rs12979860 single nucleotide polymorphism (SNP) upstream IL28B gene in two groups of patients with HCV-induced chronic liver disease: 1) 268 patients (159 men) with biopsy-proven chronic hepatitis C, to analyse its relation with biochemical, virological and histological features; and 2) 134 patients (97 men) with HCV-related hepatocellular carcinoma. The distribution of the analysed SNP in hepatocellular carcinoma patients was compared with that found in untreated chronic hepatitis C patients. All patients were white and most were Spaniards. Results In multivariate analysis ALT values were higher (P = 0.001) and GGT values were lower (P<0.001) in chronic hepatitis C patients homozygotes for the major rs12979860C allele as compared with carriers of the mutated rs12979860T allele. Steatosis was more frequent (Odds ratio = 1.764, 95% C.I. 1.053–2.955) and severe (P = 0.026) in carriers of the rs12979860T allele. No relation was found between the analysed SNP and METAVIR scores for necroinflammation and fibrosis, and there were no differences in the distribution of the analysed SNP between hepatocellular carcinoma and untreated chronic hepatitis C patients. Conclusion The IL28B rs12979860 polymorphism correlates with the biochemical activity and the presence and severity of liver steatosis in chronic hepatitis C.

Polymorphism of the TLR4 Gene Reduces the Risk of Hepatitis C Virus-Induced Hepatocellular Carcinoma

Objective: Toll-like receptor 4 (TLR4) signalling participates in the innate immune response against hepatitis C virus (HCV) infection. TLR4 gene polymorphisms may influence the risk of HCV-induced hepatocellular carcinoma (HCC). This is a single-centre-based study designed to analyse the distribution of several TLR4 gene single nucleotide polymorphisms in healthy controls and in patients chronically infected with HCV, with and without HCC. Methods: We have determined three single nucleotide polymorphisms (rs2149356, rs4986791 and rs5030719) at the TLR4 gene in 155 patients with HCV-related HCC, 153 patients with chronic hepatitis C and 390 healthy controls. All were white and most were Spaniards. Results:(1) rs5030719 was monomorphic and was not further analysed; (2) the rs2149356 T allele carrier state was significantly less frequent in patients with HCC than in healthy controls (OR 0.421, 95% CI 0.285–0.625) and in patients with chronic hepatitis C (OR 0.426, 95% CI 0.236–0.767); (3) the proportion of rs2149356 T allele carriers progressively diminished with increasing clinical stage of HCC; (4) no significant differences were observed for the rs4986791 T allele. Conclusion: The TLR4 rs2148356 T allele is associated with a reduced risk of HCC and could slow down its clinical progression in HCV-induced chronic liver disease.