Kegg Pathway: Metabolism of xenobiotics by cytochrome P450

Int Urol Nephrol. 2008 Aug 9;
Altayli E, Gunes S, Yilmaz AF, Goktas S, Bek Y

Genetic differences in the Metabolism of xenobiotics have recently been suggested as modifiers of individual susceptibility to bladder cancer (BC). The objective of this study was to investigate the relationship between bladder tumor and variants of cytochrome P450 1A2 (CYP1A2) 734 C --> A, cytochrome P450 2D6 (CYP2D6) 1934 G --> A, glutathione S-transferase M1, (GSTM1 null), glutathione S-transferase T1 (GSTT1 null), and glutathione S-transferase P1 (GSTP1) I105 V. We investigated the distribution of these polymorphisms in 135 BC patients and in 128 age and sex-matched cancer-free controls. The polymorphisms were analyzed using polymerase chain reaction (PCR)-restriction fragment length polymorphism (RFLP) assay and the multiplex PCR method. Genotype and allele frequencies and their associations with BC risk, demographic factors, smoking status, and tumor stage were investigated. The prevalence of GSTT1 null genotype in cases was 23%, compared with 7% in the control group (OR = 3.94, 95% CI = 1.70-9.38, P = 0.001). There was no association between the studied polymorphisms of CYP1A2, CYP2D6, GSTM1, and GSTP1 genes and BC. There was an association between smoking status and BC. These data seem to indicate that GSTT1 gene polymorphism may be associated with BC in the Turkish population studied. Further studies will be needed to clarify the role of such variation in determining susceptibility to BC.

J Pharmacol Exp Ther. 2008 Aug 5;
Gonzalez FJ, Cheung C

cytochrome P450s (P450s) are important enzymes involved in the Metabolism of xenobiotics, particularly clinically used drugs, and are also responsible for metabolic activation of chemical carcinogens and toxins. Many xenobiotics can activate nuclear receptors that in turn induce the expression of genes encoding xenobiotic metabolizing enzymes and drug transporters. Marked species differences in the expression and regulation of cytochromes P450 and xenobiotic nuclear receptors exist. Thus obtaining reliable rodent models to accurately reflect human drug and carcinogen Metabolism is severely limited. Humanized transgenic mice were developed in an effort to create more reliable in vivo systems to study and predict human responses to xenobiotics. Human P450s or human xenobiotic-activated nuclear receptors were introduced directly or replaced the corresponding mouse gene, thus creating "humanized" transgenic mice. Mice expressing human CYP1A1/CYP1A2, CYP2E1, CYP2D6, CYP3A4, CY3A7, PXR, PPARalpha were generated and characterized. These humanized mouse models offers a broad utility in the evaluation and prediction of toxicological risk that may aid in the development of safer drugs.

Eur Arch Otorhinolaryngol. 2008 Jul 22;
Kleinsasser NH, Harréus UA, Gamarra F, Driemel O, Hagen R, Buehrlen M

Three dimensional mini organ cultures (MOCs) of human nasal turbinate epithelia have been shown to be a relevant tool in genotoxicology studies. MOCs allow repetitive or chronic exposure of cells in an organ specific mucosal architecture for an extended period of time and monitoring of possible adverse effects with, e.g., the comet assay. It is the aim to demonstrate whether the proteins of key enzymes of xenobiotic Metabolism, represented by cytochrome P450 2A6 (CYP2A6), remain on a stable level for a culture period that allows repetitive or chronic exposure to xenobiotics. Culture of mini organs was performed by cutting pieces of 1 mm(3) from fresh specimens of human nasal turbinates. MOCs of five tissue donors were incubated on multi-well plates with BEBM, on days 0, 4, 7, 9, and 11 aliquots were transmitted to flow cytometric quantification of the CYP2A6 protein. The CYP2A6 protein could be demonstrated on all days of culture investigated. Interindividual differences were more pronounced on day 0 than at later stages of culture. Although there appeared to be a slight decrease over the culture period, flow cytometric analysis did not reveal a significant loss of the signals up to day 11. The present data could show a pre-requisite of metabolic competence of MOCs that is in contrast to single cell cultures. Thus, this type of organ culture provides an in vitro model suitable for the assessment of genotoxic effects of environmental pollutants mimicking the in vivo situation with target cells of carcinogens in their functional organ specific architecture.

Acta Pol Pharm. 2008 May-Jun; 65(3): 319-29
Tomaszewski P, Kubiak-Tomaszewska G, Łukaszkiewicz J, Pachecka J

In the human genome 684 alleles of CYP genes, and additionally 30 complete CYP pseudogenes, have been identified. So far 388 isoforms of 58 human CYP isoenzymes have been described at the phenotypic level. The molecular forms of many CYP isoenzymes responsible for drug biotransformation show a differentiated degree of specific catalytic activity - from increased, through normal and decreased to various extent, to trace or even absent. Depending on the homo- or heterozygous genotype, a broad palette of phenotypic forms may be present, differentiated in respect to biotransformation dynamics of specific drugs. The progress of molecular biology with particular consideration of genotyping and DNA microarray technologies has created a basis for the dynamic progress of pharmacogenetics, allowing fast and sensitive determination of the individual pharmacogenetic profile, encompassing a large set of CYP alleles extended by allelic variants of genes encoding other enzymes participating in drug Metabolism. The possibility to evaluate the pharmacogenetic profile of patients together with the increasing knowledge about the mechanisms of inhibition, repression and also induction of enzymes participating in biotransformation of xenobiotics and endogenous compounds create increasing possibilities of elaborating optimal individualized pharmacotherapeutic strategies.

Acta Pol Pharm. 2008 May-Jun; 65(3): 307-18
Tomaszewski P, Kubiak-Tomaszewska G, Pachecka J

In the human organism 58 cytochrome P450 (CYP) isoenzymes belonging to 18 families have been described. These hemoproteins, with enzymatic activity characteristic for monooxygenases, show a broad affinity for chemically differentiated endo- or exogenous compounds, including drugs. CYP isoenzymes participate in metabolic pathways important for proper physiological functioning of the human organism, i.e.: cholesterol, bile acid and oxysterol biosynthesis; Metabolism of fatty acids, prostaglandins, prostacyclins, leukotrienes, steroid hormones, ketone bodies, vitamines A and D. CYP isoenzymes participate in the Metabolism of over 80% of drugs and other xenobiotic substances which can be present in the human organism. Differences in molecular structure and kinetics of conformational changes of particular isoenzymes of CYP superfamily monooxygenases on the one hand determine their affinity direction for chemically differentiated groups of compounds susceptible to oxidation, on the other hand determine the mechanism and position of the oxidative change of their molecules. Drugs and their metabolites and other endogenous and xenobiotic compounds may be acting not only as substrates, but also as competitive and non- competitive inhibitors, suicide inhibitors and inducers of CYP isoenzymes as well as repressors of CYP genes. These relationships are the metabolic basis of numerous multidirectional interactions between drugs, drug metabolites, food components, stimulants, environmental toxins and metabolites of these xenobiotics.

Comp Biochem Physiol C Toxicol Pharmacol. 2008 Sep; 148(3): 230-7
Jones BR, El-Merhibi A, Ngo SN, Stupans I, McKinnon RA

cytochromes P450 (CYPs) are critically important in the oxidative Metabolism of a diverse array of xenobiotics and endogenous substrates. We have previously reported that the obligate Eucalyptus feeder koala (Phascolarctos cinereus) exhibits a higher hepatic CYP2C activity as compared to non-Eucalyptus feeders human or rat, with stimulation of CYP2C activity by cineole. In the present study, we examine CYP2C expression by immunohistochemistry and describe the identification and cloning of koala CYP2Cs. Utilising anti-rat CYP2C6 antibody, the expression of CYP2C was found to be uniform across the hepatic sections, being consistent with that observed in human and rat. Two 1647 and 1638 bp koala liver CYP2C complete cDNAs, designated CYP2C47 and CYP2C48 respectively, were cloned by cDNA library screening. The koala CYP2C cDNAs encode a protein of 495 amino acids. Three additional partial CYP2C sequences were also identified from the koala, indicating the multiplicity of the CYP2C subfamily in this unique marsupial species. The results of this study demonstrate the presence of koala hepatic CYP2Cs that share several common features with other published CYP2Cs; however CYP2C47 and CYP2C48 contain four extra amino acid residues at the NH2-terminal, a transmembrane anchor which was reported being a fundamentally conserved structure core of all eukaryote CYP enzymes.

J Pediatr Gastroenterol Nutr. 2008 Jul; 47(1): 3-10
Johnson TN, Thomson M

The presence of cytochrome P450 enzymes in the small bowel results in the reduced bioavailability of several drugs. Recently, there has been much research on the interplay between these enzymes and transporter proteins such as P-glycoprotein. Intestinal drug Metabolism not only has an effect on drug disposition but also may have a role in protecting the host from xenobiotics. Although there is some information on how both the enzymes and transporters develop in the small bowel with age, there is little information regarding the clinical effects of these changes. In addition to developmental changes, the influence of gastrointestinal disease and nutrition are additional covariates in the intestinal Metabolism of drugs.

Toxicol Appl Pharmacol. 2008 Jun 17;
Arpiainen S, Järvenpää SM, Manninen A, Viitala P, Lang MA, Pelkonen O, Hakkola J

The nutritional state of organisms and energy balance related diseases such as diabetes regulate the Metabolism of xenobiotics such as drugs, toxins and carcinogens. However, the mechanisms behind this regulation are mostly unknown. The xenobiotic-metabolizing cytochrome P450 (CYP) 2A5 enzyme has been shown to be induced by fasting and by glucagon and cyclic AMP (cAMP), which mediate numerous fasting responses. Peroxisome proliferator-activated receptor gamma coactivator (PGC)-1alpha triggers many of the important hepatic fasting effects in response to elevated cAMP levels. In the present study, we were able to show that cAMP causes a coordinated induction of PGC-1alpha and CYP2A5 mRNAs in murine primary hepatocytes. Furthermore, the elevation of the PGC-1alpha expression level by adenovirus mediated gene transfer increased CYP2A5 transcription. Co-transfection of Cyp2a5 5' promoter constructs with the PGC-1alpha expression vector demonstrated that PGC-1alpha is able to activate Cyp2a5 transcription through the hepatocyte nuclear factor (HNF)-4alpha response element in the proximal promoter of the Cyp2a5 gene. Chromatin immunoprecipitation assays showed that PGC-1alpha binds, together with HNF-4alpha, to the same region at the Cyp2a5 proximal promoter. In conclusion, PGC-1alpha mediates the expression of Cyp2a5 induced by cAMP in mouse hepatocytes through coactivation of transcription factor HNF-4alpha. This strongly suggests that PGC-1alpha is the major factor mediating the fasting response of CYP2A5.

BMC Med Genet. 2008; 9: 61
Siraj AK, Ibrahim M, Al-Rasheed M, Abubaker J, Bu R, Siddiqui SU, Al-Dayel F, Al-Sanea O, Al-Nuaim A, Uddin S, Al-Kuraya K

BACKGROUND: The xenobiotic enzyme system that enables us to detoxify carcinogens exhibits identifiable genetic polymorphisms that are highly race specific. We hypothesized that polymorphisms of these genes may be associated with risk of thyroid cancer. To evaluate the role of genetic polymorphisms of xenobiotic genes in thyroid cancer, we conducted a hospital-based case-control study in Saudi population. METHODS: 223 incident papillary thyroid cancer cases and 513 controls recruited from Saudi Arabian population were analyzed for the association between polymorphisms in genes encoding folic acid metabolizing enzymes MTHFR and six xenobiotics-metabolizing enzymes including CYP1A1 T3801C, C4887A, GSTP1 A1578G, C2293T, GSTM1, GSTT1, NAT2 G590A, NQO*1 C609T, using PCR-RELP. RESULTS: Among selected genes, CYP1A1 C4887A genotypes CA, AA and variant allele A demonstrated significant differences and greater risk of developing thyroid cancer comparing to wild type genotype CC (CA vs. CC; p < 0.0001, OR = 1.91, 95% CI = 1.36-2.70, AA vs. CC; p < 0.001, OR = 3.48, 95% CI = 1.74-6.96 and CA+AA vs. CC; p < 0.0001, OR = 2.07, 95% CI = 1.49-2.88). GSTT1 null showed 3.48 times higher risk of developing thyroid cancer (p < 0.0001, 95% CI = 2.48-4.88) while GSTM1 null showed protective effect (p < 0.05, OR = 0.72, 95% CI = 0.52-0.99). Remaining loci demonstrated no significance with risk. CONCLUSION: Of the 9 polymorphisms screened, we identified GST, GSTM1 and CYP1A1 C4887A, may be of importance to disease process and may be associated with papillary thyroid cancer risk in Saudi Arabian population.

Drug Metab Pharmacokinet. 2008; 23(3): 149
Yamada H

J Toxicol Environ Health A. 2008; 71(13-14): 969-75
Plottner S, Borza A, Wolf A, Bolt HM, Kuhlmann J, Follmann W

Exposure to tobacco smoke is an established cause of cancer in humans and cigarette smoking is a risk factor for urinary bladder cancer development. Aromatic amines are believed responsible for the bladder-specific carcinogenic effect, but polycyclic aromatic hydrocarbons (PAHs) are also of potential relevance. Urothelial cells contain a number of xenobiotic-metabolizing enzymes, which enable them to convert pro-carcinogens into reactive intermediates. In a preceding study, it was demonstrated using cultured porcine urinary bladder epithelial cells (PUBEC) that CYP1A1 mRNA is induced in a potent manner by treatment with benzo[a]pyrene (BaP). In the present study, the time dependence of these effects was evaluated and whether PUBEC cultures derived from individual donors respond differently to BaP treatment was determined. CYP1A1 induction was analyzed by quantitative reverse-transcription polymerase chain reaction (RT-PCR), and genotoxic effects were studied using the Comet assay. Incubation of PUBEC with BaP increased CYP1A1 expression and induction of DNA strand breaks in a time-dependent manner. Interindividual differences were found between PUBEC cultures derived from several donor animals with respect to the response to BaP, such that the extent of CYP1A1 induction and magnitude of DNA damage was interrelated. Hence, individual differences in metabolic capacities and responsiveness to xenobiotics of urothelial cells from individual donors may be factors in susceptibility to genotoxic effects induced by PAHs.

Oncol Res. 2008; 17(2): 75-85
Vidjaya Letchoumy P, Chandra Mohan KV, Stegeman JJ, Gelboin HV, Hara Y, Nagini S

The objective of this study was to evaluate the chemopreventive potential of the black tea polyphenols Polyphenon-B and BTF-35 during the preinitiation phase of 7,12-dimethylbenz[a]anthracene (DMBA)-induced hamster buccal pouch (HBP) carcinogenesis. Hamsters were divided into six groups. Animals in groups 2 and 3 received diet containing Polyphenon-B and BTF-35, respectively, 4 weeks before carcinogen administration when they were 6 weeks of age and continued until the final exposure to carcinogen. At 10 weeks of age, animals in groups 1, 2, and 3 were painted with 0.5% DMBA three times a week for 14 weeks. Animals in groups 4 and 5 were given Polyphenon-B and BTF-35 alone, respectively, as in groups 2 and 3. Animals in group 6 served as control. All the animals were sacrificed after an experimental period of 18 weeks. Phase I and phase II xenobiotic-metabolizing enzymes and 8-hydroxy-deoxyguanosine (8-OH-dG) in the buccal pouch and liver were used as biomarkers of chemoprevention. Hamsters painted with DMBA showed increased expression of 8-OH-dG and enhanced activities of phase I (CYP450; total as well as CYP1A1, 1A2, and 2B isoforms and cytochrome b5) and phase II (GST and quinone reductase) xenobiotic-metabolizing enzymes with increased immunohistochemical expression of CYP1A1, and CYP1B1 isoforms in the buccal pouch. This was accompanied by increased phase I and decreased phase II enzyme activities in the liver. Administration of Polyphenon-B and BTF-35 significantly decreased tumor incidence, oxidative DNA damage, phase I enzyme activities as well as expression of CYP1A1 and CYP1B1 isoforms, while enhancing phase II enzyme activities in the buccal pouch and liver. Our results provide a mechanistic basis for the chemopreventive potential of black tea polyphenols. Furthermore, the greater efficacy of BTF-35 in chemoprevention of HBP carcinomas via inhibition of oxidative DNA damage and modulation of xenobiotic-metabolizing enzymes may have a major impact in human oral cancer prevention.

Curr Drug Metab. 2008 Jun; 9(5): 363-73
Ekins S, Iyer M, Krasowski MD, Kharasch ED

CYP2B6 has not been as fully characterized at the molecular level as other members of the human cytochrome P450 family. As more widely used in vitro probes for characterizing the involvement of this enzyme in the Metabolism of xenobiotics have become available, the number of molecules identified as CYP2B6 substrates has increased. In this study we have analyzed the available kinetic data generated by multiple laboratories with human recombinant expressed CYP2B6 and along with calculated molecular properties derived from the ChemSpider database, we have determined the molecular features that appear to be important for CYP2B6 substrates. In addition we have applied 2D and 3D QSAR methods to generate predictive pharmacophore and 2D models. For 28 molecules with K(m) data, the molecular weight (mean +/- SD) is 253.78+/-74.03, ACD/logP is 2.68+/-1.51, LogD(pH 5.5) is 1.51+/-1.43, LogD(pH 7.4) is 2.02+/-1.25, hydrogen bond donor (HBD) count is 0.57 +/-0.57, hydrogen bond acceptor (HBA) count is 2.57+/-1.37, rotatable bonds is 3.50+/-2.71 and total polar surface area (TPSA) is 27.63+/-19.42. A second set of 15 molecules without K(m) data possessed similar mean molecular property values. These properties are comparable to those of a set of 21 molecules used in a previous pharmacophore modeling study (Ekins et al., J Pharmacol Exp Ther 288 (1), 21-29, 1999). Only the LogD and HBD values were statistically significantly different between these different datasets. We have shown that CYP2B6 substrates are generally small hydrophobic molecules that are frequently central nervous system active, which may be important for drug discovery research.

Anal Bioanal Chem. 2008 Jun 8;
Neve EP, Ingelman-Sundberg M

The cytochrome P450 (P450) enzymes are mainly localized to the endoplasmic reticulum (ER), where they function within catalytic complexes metabolizing xenobiotics and some endogenous substrates. However, certain members of families 1-3 were also found in other subcellular compartments, such as mitochondria, plasma membrane, and lysosomes. The physiological function of these enzymes in non-ER locations is not known, although plasma-membrane-associated P450s have been described to be catalytically active and to participate in immune-mediated reactions with autoantibody formation that can trigger drug-induced hepatitis. Several retention/retrieval mechanisms are active in the ER retention of the P450s and inverse integration of the translated P450 into the ER membrane appears to be responsible for transport to the plasma membrane. Furthermore, hydrophilic motifs in the NH(2)-terminal part have been suggested to be important for mitochondrial import. Phosphorylation of P450s has been described to be important for increased rate of degradation as well as for targeting into mitochondria. It was also suggested that the mitochondria-targeted P450s from families 1-3 could be active in drug Metabolism using an alternative electron transport chain. In this review we present an update of the field emphasizing studies concerning localization, posttranslational modification, such as phosphorylation, and intracellular transport of microsomal P450s.

Breast Cancer Res Treat. 2008 Jun 3;
Justenhoven C, Hamann U, Pierl CB, Baisch C, Harth V, Rabstein S, Spickenheuer A, Pesch B, Brüning T, Winter S, Ko YD, Brauch H

cytochrome P450 2C19 (CYP2C19) plays an important role in the Metabolism of xenobiotics and drugs and contributes to the catabolism of endogenous substrates like estradiol. Genetic variability impacts expression and activity of CYP2C19 and therefore can influence catabolism of estrogens. In the present study we analyzed the association of three polymorphisms of CYP2C19 namely CYP2C19*2 (CYP2C19_681_G>A, rs4244285), CYP2C19*3 (CYP2C19_636_G>A, rs57081121) and CYP2C19*17 (CYP2C19_-806_C>T, rs12248560), with breast cancer susceptibility. We genotyped 1,015 breast cancer cases and 1,021 age-matched, population-based controls of the German GENICA study by matrix assisted laser desorption/ionization time-of-flight mass spectrometry. Risk estimates were calculated by logistic regression. All tests were two-sided. We observed a decreased breast cancer risk for carriers of the CYP2C19*17 allele (OR 0.77, 95% CI: 0.65-0.93; P = 0.005). In subgroup analysis we observed a significant decreased breast cancer risk for women using hormone therapy for ten years or longer who were carriers of the CYP2C19*17 allele (OR 0.57, 95% CI: 0.39-0.83; P = 0.003). Since CYP2C19*17 defines an ultra rapid metabolizer phenotype we suggest that an increased catabolism of estrogens by CYP2C19 may lead to decreased estrogen levels and therefore reduces breast cancer risk. This protective effect seems to be stronger in combination with long-term intake of supplemental estrogens during hormone therapy.

Anticancer Res. 2008 Mar-Apr; 28(2A): 1023-8
Losi-Guembarovski R, Cólus IM, De Menezes RP, Poliseli F, Chaves VN, Kuasne H, Leichsenring A, Guembarovski AL, Oliveira BW, Ramos G, Cavalcanti TC, Mizuno LT, Cavalli IJ, Ribeiro EM

BACKGROUND: A case control association study was carried out to investigate polymorphisms in genes CYP1A1 (3801T > C), GSTM1, and GSTT1 (null genotypes) and oral squamous cell carcinoma (OSCC), including a correlation with some histopathological findings (tumor size, lymph node invasion and degree of tumor differentiation). PATIENTS AND METHODS: The patients (n = 91) and the controls (n = 81) were matched by age, sex, ethnicity and smoking habits. The molecular analysis was carried out using Polymerase Chain Reaction-Restrict Length Polymorphisms PCR-RFLP (CYP1A1) and Multiplex-PCR (GSTM1/GSTT1). RESULTS: No association was found for any of the studied genes: CYP1A1 (odds ratio (OR) = 1.24; 95% Confidence Interval (CI) = 0.67-2.31), GSTM1 (OR = 0.61; CI 95% = 0.33-1.11), and GSTT1 (OR = 1.24; CI 95% = 0.65-2.38). The analysis of combining genotypes also showed lack of association. Comparison with the histopathological findings did not, in general, detect any statistically significant differences. CONCLUSION: CYP1A1, GSTM1 and GSTT1 polymorphisms do not appear to influence the genetic susceptibility to OSCC or the progression to more advanced stages.

Biochem Pharmacol. 2008 Jul 1; 76(1): 139-45
Yoshinari K, Ueda R, Kusano K, Yoshimura T, Nagata K, Yamazoe Y

Omeprazole induces human CYP1A1 and CYP1A2 in human hepatoma cells and human liver. Aryl hydrocarbon receptor (AHR) is shown to be involved in this induction. However, its precise molecular mechanism remains unknown because the chemical activates AHR without its direct binding in contrast to typical AHR ligands such as 3-methylcholanthrene (3MC) and beta-naphthoflavone (BNF). Human CYP1A1 and CYP1A2 genes are located in a head-to-head orientation sharing about 23 kb 5'-flanking region. Recently, we succeeded to measure CYP1A1 and CYP1A2 transcriptional activities simultaneously using dual reporter gene constructs containing the 23 kb sequence. I