Genetic polymorphism of human cytochrome P450 2E1

Effect of Betanin, the Major Pigment of Red Beetroot (Beta vulgaris L.), on the Activity of Recombinant Human Cytochrome P450 Enzymes

Most of the currently available drugs are derived from natural sources, but they are used only after extensive chemical modifications to improve their safety and efficacy. Natural products are used in health supplements and cosmetic preparations and have been used as auxiliary drugs or alternative medicines. When used in combination with conventional drugs, these herbal products are known to alter their pharmacokinetics and pharmacodynamics, reducing their therapeutic effects. Moreover, herb-drug interactions (HDIs) may have serious side effects, which is one of the major concerns in health practice. It is postulated that HDIs affect the pathways regulating cytochrome P450 enzymes (CYPs). Betanin, the chief pigment of red beetroot (Beta vulgaris L.), has various types of pharmacological activity, such as anti-inflammatory, antioxidant, and anticancer effects. However, the potential risk of HDIs for betanin has not yet been studied. Thus, we aimed to predict more specific HDIs by evaluating the effects of betanin on CYPs (CYP1A2, CYP2B6, CYP2C9, CYP2C19, CYP2D6, and CYP3A4), the major phase I metabolic enzymes, using fluorescence-/luminescence-based assays. Our results showed that betanin inhibited CYP3A4 activity in a dose-dependent manner (IC50 = 20.97 µΜ). Moreover, betanin acted as a competitive inhibitor of CYP3A4, as confirmed by evaluating Lineweaver-Burk plots (Ki value = 19.48 µΜ). However, no significant inhibitory effects were observed on other CYPs. Furthermore, betanin had no significant effect on CYP1A2, CYP2B6, or CYP2C9 induction in HepG2 cells. In conclusion, betanin acted as a competitive inhibitor of CYP3A4, and thus it should be used cautiously with other drugs that require metabolic enzymes as substrates. Additional in vivo studies and clinical trials are needed to further elucidate the HDIs of betanin.

Association of alcohol-metabolizing genes with alcoholism in a Mexican Indian (Otomi) population

Association studies provide a powerful approach to link DNA variants and genetic predisposition to complex diseases. In this study, we determined the genotype and allelic frequencies of genes encoding enzymes involved in alcohol metabolism in alcoholic and nonalcoholic subjects of related ethnicity. A total of 118 individuals of Otomi Mexican Indian ancestry were included. Fifty-nine were chronic alcoholics according to WHO criteria and alcohol dependents according to the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM IV) criteria. They were compared to 59 teetotalers or alcohol consumers of <10 g per day. The restriction fragment length polymorphisms analyzed were ADH1B/MaeIII, ALDH2/MboII, CYP2E1/DraI, CYP2E1/RsaI, and CYP2E1/TaqI. Of the studied polymorphisms, a significant difference between alcoholic and nonalcoholic Otomies was observed only in the CYP2E1/TaqI. The common genotype in alcoholics was A1/A2 (54%), and in nonalcoholics the homozygous A2/A2 (63%) (odds ratio [OR]: 0.28; 95% confidence interval [CI]: 0.13-0.60; P=.002). The frequency of the mutant allele A1 was significantly higher in alcoholics than in nonalcoholics (41 vs. 21%; OR: 2.4; 95% CI: 1.3-4.3; P=.003). This documents the presence of a polymorphism of CYP2E1 that is overexpressed in alcoholic Otomies, in which the variant allele (A1 of CYP2E1/TaqI) is associated with increased susceptibility to alcoholism. The appreciation that this finding may be an additional factor contributing to the high frequency of liver cirrhosis in Otomies requires further investigation.

Cytochrome P450 gene polymorphisms and risk of low birth weight

This study investigated the association between polymorphisms in cytochrome P450 genes (CYP1A1MspI, CYP1A1HincII, and CYP2E1) and low birth weight. Between July 1999 and June 2002, we conducted a study using infant-parents triads in Anqing, China. The analyses included the families of 248 normal birth weight, full-term infants, and 248 low-birth-weight infants. Genotyping was performed for the polymorphisms of cytochrome P450 genes using standard techniques. We used log-linear modeling to analyze the association of CYP1A1 and CYP2E1 gene polymorphisms with the risk of low birth weight. In the analysis of children's genotypes, the relative risk was 1.92 (95% confidence interval: 1.05, 3.52, p=0.034) for CYP1A1MspI C/C6235 compared with CYP1A1 MspI T/T6235. In the analysis of mothers' genotypes, an association was also seen for maternal CYP1A1MspI C/C6235 compared with CYP1A1MspI T/T6235 (relative risk: 1.68, 95% confidence interval: 1.06, 2.68, p=0.029). We did not observe a joint effect between mother's and children's genotypes. Analysis of control triads suggests Mendelian transmissions of the variant alleles of CYP1A1MspI, CYP1A1HincII, and CYP2E1. In conclusion, both infant and maternal CYP1A1MspI C/C6235 genotypes were associated with increased risk of low birth weight in our study population. This suggests a possible role for human cytochrome P450 variability in the etiology of low birth weight.

GYKI-47261, a new AMPA [2-amino-3-(3-hydroxymethylisoxazole-4-yl)propionic acid] antagonist, is a CYP2E1 inducer

CYP2E1-inducing capacity of xenobiotics was determined in cultured hepatocytes on the basis of enzyme activities (chlorzoxazone 6-hydroxylation and 7-ethoxycoumarin O-dealkylation) and protein levels. Hepatocytes in culture showed rapid loss of CYP2E1 enzyme during 72 h. CYP2E1 inducers (ethanol, dimethyl sulfoxide, acetone, isopropanol, pyrazole, and imidazole) were able to prevent the fast decrease of the activities and protein levels of CYP2E1 enzyme. Imidazole was found to be the most effective inducer in rat hepatocytes, and it was selected as a reference in subsequent experiments. The effect of GYKI-47261 [6-(4-aminophenyl)-8-chloro-2-methyl-11H-imidazo[1,2c] [2,3]benzodiazepine], a new AMPA [2-amino-3-(3-hydroxymethylisoxazole-4-yl)propionic acid] antagonist drug-candidate, was also tested in the in vitro system. On the basis of enzyme activities and CYP2E1 protein content of rat hepatocytes, GYKI-47261 was considered as a potent CYP2E1 inducer. Furthermore, it was more effective than imidazole, since 10 microM GYKI-47261 produced the maximal induction, whereas 500 microM imidazole brought about the maximal response. Human hepatocytes were more sensitive to GYKI-47261 than were rat cells. In rat hepatocytes, 10 microM caused maximal increase, whereas 0.01 microM produced the highest induction in human cells. Elevation of CYP2E1 gene transcription as the mechanism of induction caused by GYKI-47261 can be excluded. It seems to act mainly on stabilization of CYP2E1 enzyme protein, whereas the role of stabilization of CYP2E1 mRNA can be considered negligible. Although the imidazole part of GYKI-47261 can explain its CYP2E1-inducing capacity, the other part of the molecule must contribute to the final inducing potency.

The ADH3*2 and CYP2E1 c2 alleles increase the risk of alcoholism in Mexican American men

To identify the association between the polymorphisms of genes encoding alcohol metabolizing enzymes and alcoholism, the alcohol dehydrogenase 2 (ADH2), alcohol dehydrogenase 3 (ADH3), aldehyde dehydrogenase 2 (ALDH2), and cytochrome P450 2E1 (CYP2E1) genes were studied in 101 male Mexican American alcoholics. One hundred and four Mexican American nonalcoholic males served as controls. The allele frequency of ADH2*2 (4.3%) and ALDH2*2 (0%), which are considered as protective alleles against alcohol drinking, is very low in Mexican Americans and no association is found between these alleles and alcohol dependence. A strong association was found between ADH3 genotype and alcoholism; the percentage of subjects who carry the ADH3*2 allele was significantly higher in alcoholics (64.4%) than controls (50%). Association was also found between the CYP2E1 RsaI c2 allele and alcohol dependence; the percentage of subjects who carry the RsaI c2 allele was significantly higher in alcoholics (34.7%) than in nonalcoholics (22.1%). The subjects whose alcohol drinking onset age is younger than 25 have much higher CYP2E1 c2 allele frequency than those whose alcohol drinking onset age is older than 25 (22.1% vs 15.7%). Among 101 alcoholics, only 18 subjects carry neither ADH3*2 nor CYP2E1 c2 alleles. For those subjects who have an ADH*1/*1 background, a strong association is found between CYP2E1 RsaI/DraI genotype and alcoholism; the CYP2E1 RsaI c2 and DraI C allele frequencies are much higher in alcoholics than in nonalcoholics (26.4% vs 9.6% for c2 and 27.8% vs 13.5% for C allele). Taken together, ADH3*2 and CYP2E1 c2/C alleles might independently contribute to the development of alcoholism in Mexican American men.

A High Throughput Screening Assay to Screen for CYP2E1 Metabolism and Inhibition Using a Fluorogenic Vivid® P450 Substrate

Large-scale screening of multiple compound libraries and combinatorial libraries for pharmacological activity is one of the novel approaches of the modern drug discovery process. The application of isozyme-specific high-throughput screening (HTS) assays for characterizing the interactions of potential drug candidates with major human drug-metabolizing cytochrome p450 enzymes (p450s) is newly becoming an essential part of this process. Fluorescence-based HTS assays have been successfully employed for in vitro assessment of drug-drug interactions and enzyme inhibition with several p450 isoforms, including CYP3A4, CYP2D6, CYP2C9, and CYP2C19. Here we describe a fluorescence-based HTS assay for detecting drug metabolism and inhibition with human CYP2E1. CYP2E1 plays an important role in the metabolism of several drugs, many solvents, and toxins and therefore has been repeatedly linked to numerous pathologies, including cancer, liver and kidney toxicity, diabetes, and alcoholism. The assay is based on the ability of a drug to compete with the fluorogenic Vivid CYP2E1 Blue Substrate for CYP2E1 metabolism and thus enables rapid screening of lead molecules for their inhibitory potential. We have used this assay to screen a panel of drugs and compounds for their effects on CYP2E1 metabolism and inhibition. Our results demonstrate the assay's usefulness in identifying CYP2E1 substrates and inhibitors and in enabling in-depth characterization of their interactions with the CYP2E1 isozyme. We also present detailed characteristics of the assay, including its dynamic range and Z'-factor values, which indicate that this robust assay is well suited for kinetic and inhibition studies in HTS formats.

Genetic polymorphisms and metabolism of endocrine disruptors in cancer susceptibility

Epidemiological studies have estimated that approximately 80% of all cancers are related to environmental factors. Individual cancer susceptibility can be the result of several host factors, including differences in metabolism, DNA repair, altered expression of tumor suppressor genes and proto-oncogenes, and nutritional status. Xenobiotic metabolism is the principal mechanism for maintaining homeostasis during the body's exposure to xenobiotics. The balance of xenobiotic absorption and elimination rates in metabolism can be important in the prevention of DNA damage by chemical carcinogens. Thus the ability to metabolize and eliminate xenobiotics can be considered one of the body's first protective mechanisms. Variability in individual metabolism has been related to the enzymatic polymorphisms involved in activation and detoxification of chemical carcinogens. This paper is a contemporary literature review on genetic polymorphisms involved in the metabolism of endocrine disruptors potentially related to cancer development.

Study of polymorphisms in the CYP2E1 gene in patients with alcoholic pancreatitis

Cytochrome P450IIEI (CYP2E1) is an ethanol-inducible enzyme. Recently, several novel polymorphisms in the CYP2E1 gene have been identified. A polymorphism at position -35 [G(-35)T] appears to be of functional significance in transcription assays. The aim of this study was to investigate if this and other polymorphisms, at position -1019 [C(-1019)T], 4808 [G(4808)A], and 7668 [T(7668)A] of the CYP2E1 gene are associated with alcoholic pancreatitis. DNA was extracted from peripheral blood of 38 patients with alcoholic chronic pancreatitis (CP), 19 patients with alcoholic acute pancreatitis (AP), 46 alcoholic controls (AC), and 155 normal controls (NC). The polymorphisms were examined by digestion with the corresponding restriction endonucleases following PCR amplification. The results have shown that the frequencies of the rare alleles of these polymorphisms were not significantly different between the CP, AP, and AC groups and NC. Therefore, our study results suggest to us that the polymorphisms investigated in the CYP2E1 gene are unlikely to be involved in the susceptibility and pathogenesis of alcoholic pancreatitis.

The effects of the ALDH2*1/2, CYP2E1 C1/C2 and C/D genotypes on blood ethanol elimination

The effects of CYP2E1 genotypes on the blood ethanol and acetaldehyde levels were investigated in a pair of Japanese volunteers whose ADH2, ADH3 and ALDH2 genotypes were identical but whose CYP2E1 genotypes were different. In the same way, the effects of ALDH2 and ADH2 on the ethanol elimination kinetics were also studied. The predicting 95% confidence bounds determined on regression analysis of the data suggested that after venous injection of ethanol, the blood ethanol and acetaldehyde concentrations in a volunteer normal homozygous for ALDH2 (ALDH2*1/1) were lower than in a heterozygous one (ALDH2*1/2). Also, the blood ethanol and acetaldehyde concentrations in a volunteer with the c2 and C alleles of CYP2E1 (c1/c2 and C/D) were lower than in one without the c2 and C alleles (c1/c1 and D/D). However, there were no significant differences in the blood ethanol and acetaldehyde concentrations between volunteers with ADH2*1 (ADH2*1/1) and without ADH2*1 (ADH2*1/2).

Expression of cytochrome P450RAI (CYP26) in human fetal hepatic and cephalic tissues

PCR amplifications with two sets of degenerate primers that were targeted to CYP26-specific regions were performed with cDNAs from human fetal liver and brain as templates. PCR products were purified, cloned, sequenced and analyzed with the BLAST program. Our results revealed expression of CYP26 in both human fetal liver and brain. Furthermore, human fetal CYP26 cDNA exhibited 99.2%-100% nucleotide sequence identity to its adult counterpart. Novel isoforms, that would have indicated additional CYP26 genes, were not found. A Northern blot containing poly(A+)RNAs from 43 human adult and 7 human fetal tissues was tested for CYP26 expression. We were able to detect CYP26 message in most tissues but hybridization signals varied in intensity. Highest levels of transcription were in adult liver, heart, pituitary gland, adrenal gland, placenta and regions of the brain. CYP26 expression in fetal tissues was strongest in the brain and comparable with message levels in adult tissues.

Evolution of the cytochrome P450 superfamily: sequence alignments and pharmacogenetics

The evolution of the cytochrome P450 (CYP) superfamily is described, with particular reference to major events in the development of biological forms during geological time. It is noted that the currently accepted timescale for the elaboration of the P450 phylogenetic tree exhibits close parallels with the evolution of terrestrial biota. Indeed, the present human P450 complement of xenobiotic-metabolizing enzymes may have originated from coevolutionary 'warfare' between plants and animals during the Devonian period about 400 million years ago. A number of key correspondences between the evolution of P450 system and the course of biological development over time, point to a mechanistic molecular biology of evolution which is consistent with a steady increase in atmospheric oxygenation beginning over 2000 million years ago, whereas dietary changes during more recent geological time may provide one possible explanation for certain species differences in metabolism. Alignment between P450 protein sequences within the same family or subfamily, together with across-family comparisons, aid the rationalization of drug metabolism specificities for different P450 isoforms, and can assist in an understanding of genetic polymorphisms in P450-mediated oxidations at the molecular level. Moreover, the variation in P450 regulatory mechanisms and inducibilities between different mammalian species are likely to have important implications for current procedures of chemical safety evaluation, which rely on pure genetic strains of laboratory bred rodents for the testing of compounds destined for human exposure.

Cytochrome P4502E1 inducibility and hydroxyethyl radical formation among alcoholics

BACKGROUND/AIMS

Animal studies have shown that the induction of cytochrome P4502E1 (CYP2E1) modulates oxidative damage induced by ethanol. Since CYP2E1 activity varies substantially in humans, we have investigated whether differences in CYP2E1 activity might influence the formation of hydroxyethyl free radicals and the stimulation of lipid peroxidation among alcohol abusers.

METHODS

Chlorzoxazone oxidation, an index of CYP2E1 activity, and the levels of antibodies reacting with hydroxyethyl radical and malonyldialdehyde protein adducts were investigated in 51 alcoholic patients.

RESULTS

We observed that in 40 out of 51 (78%) alcoholics, chlorzoxazone oxidation was increased over the control levels, consistently with CYP2E1 induction by ethanol. However, in the remaining 22% of the patients, in spite of a similar alcohol intake, chlorzoxazone oxidation was within the control range, indicating a lack of CYP2E1 inducibility. IgG reacting with hydroxyethyl free radical-protein adducts were absent in subjects without CYP2E1 induction, while they were significantly increased in alcoholics with induced CYP2E1 activity. IgG against malonyldialdehyde protein-adducts were increased in all patients, irrespective of CYP2E1 inducibility. Moreover, chlorzoxazone oxidation was significantly lower in alcoholics without clinical and biochemical signs of liver disease as compared to patients with alcoholic liver disease.

CONCLUSIONS

These results indicate that CYP2E1 activity greatly influences the formation of hydroxyethyl radicals in humans, and suggest a possible role of CYP2E1 in the development of alcoholic liver disease.