Distribution of cytochrome P450 2C, 2E1, 3A4, and 3A5 in human colon mucosa

BACKGROUND: Despite the fact that the alimentary tract is part of the body's first line of defense against orally ingested xenobiotica, little is known about the distribution and expression of cytochrome P450 (CYP) enzymes in human colon. Therefore, expression and protein levels of four representative CYPs (CYP2C(8), CYP2E1, CYP3A4, and CYP3A5) were determined in human colon mucosa biopsies obtained from ascending, descending and sigmoid colon. METHODS: Expression of CYP2C, CYP2E1, CYP3A4, and CYP3A5 mRNA in colon mucosa was determined by RT-PCR. Protein concentration of CYPs was determined using Western blot methods. RESULTS: Extensive interindividual variability was found for the expression of most of the genes. However, expression of CYP2C mRNA levels were significantly higher in the ascending colon than in the sigmoid colon. In contrast, mRNA levels of CYP2E1 and CYP3A5 were significantly lower in the ascending colon in comparison to the descending and sigmoid colon. In sigmoid colon protein levels of CYP2C8 were significantly higher by ~73% than in the descending colon. In contrast, protein concentration of CYP2E1 was significantly lower by ~81% in the sigmoid colon in comparison to the descending colon. CONCLUSION: The current data suggest that the expression of CYP2C, CYP2E1, and CYP3A5 varies in different parts of the colon

CYP3A4 and CYP3A5 genotyping by Pyrosequencing

BACKGROUND: Human cytochrome P450 3A enzymes, particularly CYP3A4 and CYP3A5, play an important role in drug metabolism. CYP3A expression exhibits substantial interindividual variation, much of which may result from genetic variation. This study describes Pyrosequencing assays for key SNPs in CYP3A4 (CYP3A4*1B, CYP3A4*2, and CYP3A4*3) and CYP3A5 (CYP3A5*3C and CYP3A5*6). METHODS: Genotyping of 95 healthy European and 95 healthy African volunteers was performed using Pyrosequencing. Linkage disequilibrium, haplotype inference, Hardy-Weinberg equilibrium, and tag SNPs were also determined for these samples. RESULTS: CYP3A4*1B allele frequencies were 4% in Europeans and 82% in Africans. The CYP3A4*2 allele was found in neither population sample. CYP3A4*3 had an allele frequency of 2% in Europeans and 0% in Africans. The frequency of CYP3A5*3C was 94% in Europeans and 12% in Africans. No CYP3A5*6 variants were found in the European samples, but this allele had a frequency of 16% in the African samples. Allele frequencies and haplotypes show interethnic variation, highlighting the need to analyze clinically relevant SNPs and haplotypes in a variety of ethnic groups. CONCLUSION: Pyrosequencing is a versatile technique that could improve the efficiency of SNP analysis for pharmacogenomic research with the ultimate goal of pre-screening patients for individual therapy selection

Combined transcriptomic-(1)H NMR metabonomic study reveals yhat monoethylhexyl phthalate stimulates adipogenesis and glyceroneogenesis in human adipocytes

Adipose tissue is a major storage site for lipophilic environmental contaminants. The environmental metabolic disruptor hypothesis postulates that some pollutants can promote obesity or metabolic disorders by activating nuclear receptors involved in the control of energetic homeostasis. In this context, monoethylhexyl phthalate (MEHP) is of particular concern since it was shown to activate the peroxisome proliferator-activated receptor γ (PPARγ) in 3T3-L1 murine preadipocytes. In the present work, we used an untargeted, combined transcriptomic-(1)H NMR-based metabonomic approach to describe the overall effect of MEHP on primary cultures of human subcutaneous adipocytes differentiated in vitro. MEHP stimulated rapidly and selectively the expression of genes involved in glyceroneogenesis, enhanced the expression of the cytosolic phosphoenolpyruvate carboxykinase, and reduced fatty acid release. These results demonstrate that MEHP increased glyceroneogenesis and fatty acid reesterification in human adipocytes. A longer treatment with MEHP induced the expression of genes involved in triglycerides uptake, synthesis, and storage; decreased intracellular lactate, glutamine, and other amino acids; increased aspartate and NAD, and resulted in a global increase in triglycerides. Altogether, these results indicate that MEHP promoted the differentiation of human preadipocytes to adipocytes. These mechanisms might contribute to the suspected obesogenic effect of MEHP

Inter-individual variability in the oxidation of 1,2-dibromoethane: use of heterologously expressed human cytochrome P450 and human liver microsomes.

1,2-Dibromoethane (1,2-DBE) is mainly used as an additive in leaded gasoline and as a soil fumigant and it is a suspected carcinogen in humans. In this study, the oxidative bioactivation of 1,2-DBE to 2-bromoacetaldehyde (2-BA) was studied using heterologously expressed human cytochrome P450 (P450) isoenzymes and human liver microsomes. Out of ten heterologously expressed human P450 isoenzymes (CYP1A1, CYP1A2, CYP2A6, CYP2B6, CYP2E1, CYP2C8, CYP2C9, CYP2C18, CYP3A4 and CYP3A5), only human CYP2A6, CYP2B6 and CYP2E1 metabolized 1,2-DBE, albeit with strongly differing catalytic efficiencies. The apparent K(m) and V(max) values were 3.3 mM and 0.17 pmol/min per pmol P450 for CYP2A6, 9.7 mM and 3.18 pmol/min per pmol P450 for CYP2B6 and 42 μM and 1.3 pmol/min per pmol P450 for CYP2E1, respectively. In all of 21 human liver samples studied, 1,2-DBE was oxidized with activities ranging from 22.2 to 1027.6 pmol/min per mg protein, thus showing a 46-fold inter-individual variability. The kinetics of the oxidative metabolism of 1,2-DBE to 2-BA in human liver microsomes were linear, indicating the involvement of primarily one single P450 isoenzyme. There was a tendency towards a positive correlation between the oxidative metabolism of 1,2-DBE in the human liver microsomes and the 6-hydroxylation of chlorzoxazone, a selective substrate for CYPE1. Furthermore, the oxidative metabolism of 1,2-DBE was inhibited by the specific CYP2E1 inhibitors disulfiram (DS) and diethyldithiocarbamate (DDC). In contrast, a poor correlation was found between the immunochemically quantified amount of CYP2E1 and the microsomal chlorzoxazone 6-hydroxylation or the 1,2-DBE oxidation. The results indicate that CYP2E1 is probably the major P450 isoenzyme involved in the oxidative hepatic metabolism of 1,2-DBE in humans. The inter-individual variability in the oxidative bioactivation of 1,2-DBE in humans, largely due to inter-individual variability in the catalytic activity of hepatic CYP2E1, may have important consequences for the risk assessment for human exposure to 1,2-DBE

Human CYP2B6: expression, inducibility and catalytic activities

Human cytochrome (CYP)2B6 cDNA was cloned and expressed in bacteria and in yeast. Its expression in Saccharomyces cerevisiae enabled us to obtain, at a high level, an active yeast-expressed CYP2B6 protein, so as to assess its role in the metabolism of ethoxyresorufin, pentoxyresorufin, benzyloxyresorufin, ethoxycoumarin, testosterone and cyclophosphamide. Kinetic analysis showed that human CYP2B6 preferentially metabolized benzyloxyresorufin and pentoxyresorufin, although other CYPs also metabolized these substrates in human liver microsomes. CYP2B6 also manifested a strong 4-hydroxycyclophosphamide activity. Its expression in Escherichia coli enabled us to produce a very specific anti-human CYP2B6 antibody. No cross reactivity of this antibody was observed with CYPs1A1, 1A2, 3A4, 3A5, 2C8, 2C9, 2C18, 2C19, 2D6 or 2E1. This antibody enabled us to study the hepatic and extrahepatic expression of CYP2B6 in man, as well as its expression and inducibility in primary cultured human hepatocytes and in different human cell lines. Immunoblot analysis revealed that the CYP2B6 protein was expressed in 43 of the 48 human liver samples tested, with levels ranging from 0.4 to 8 pmol/mg of microsomal protein with a mean of 1.7 pmol/mg protein. CYP2B was also expressed in human brain, intestine and kidney, and at a lower level in the lung. CYP2B mRNA was detected in human liver, kidney, lung, trachea and intestine. We also found that CYP2B6 is induced at protein and mRNA levels by phenobarbital (2 mM) and cyclophosphamide (1 mM), an anticancer drug known to be metabolized by CYP2B6. No expression or inducibility of CYP2B6 was observed in any of the human cell lines tested