Genetic variation of Cytochrome P450 1B1 (CYP1B1) and risk of breast cancer among Polish women

Four single nucleotide polymorphisms (SNPs) in CYP1B1 (Ex2 + 143 C > G, Ex2 + 356 G > T, Ex3 + 251 G > C, Ex3 + 315 A > G) cause amino acid changes (R48G, A119S, L432V and N453S, respectively) and are associated with increased formation of catechol estrogens; however, epidemiologic evidence only weakly supports an association between these variants and breast cancer risk. Because genetic variability conferring increased susceptibility could exist beyond these putative functional variants, we comprehensively examined the common genetic variability within CYP1B1. A total of eight haplotype-tagging (ht)SNPs (including Ex3 + 315 A > G), in addition to two putatively functional SNPs (Ex2 + 143 C > G and Ex3 + 251 G > C), were selected and genotyped in a large case-control study of Polish women (1995 cases and 2296 controls). Haplotypes were estimated using the expectation-maximization algorithm, and overall differences in the haplotype distribution between cases and controls were assessed using a global score test. We also evaluated levels of tumor CYP1B1 protein expression in a subset of 841 cases by immunohistochemistry, and their association with genetic variants. In the Polish population, we observed two linkage disequilibrium (LD)-defined blocks. Neither haplotypes (global P-value of 0.99 and 0.67 for each block of LD, respectively), nor individual SNPs (including three putatively functional SNPs) were associated with breast cancer risk. CYP1B1 was expressed in most tumor tissues (98%), and the level of expression was not related to the studied genetic variants. We found little evidence for modification of the estimated effect of haplotypes or individual SNPs by age, family history of breast cancer, or tumor hormone receptor status. The present study provides strong evidence against the existence of a substantial overall association between common genetic variation in CYP1B1 and breast cancer risk.     

Catechol-O-methyltransferase (COMT) genetic polymorphism in a Turkish population

Catechol-O-methyltransferase (COMT) inactivates neurotransmitters, catechol hormones and drugs such as levodopa and methyldopa. A low activity allele has been demonstrated at codon 108/158 of the soluble and membrane-bound COMT, respectively, whereby a G to A transition results in a valine to methionine substitution. Ethnic and inter-individual differences in red blood cell COMT activity have been observed in the different populations studied so far. Since, no information is available on inter-individual variability of COMT genotype in Turkish population, we genotyped 217 healthy, unrelated Turkish individuals. The allelic frequencies of COMT gene in the Turkish population were found to be the same as has been observed in Caucasians, but different from Orientals.     

Cytochrome P450 (CYP) in fish

Cytochrome P450 (CYP) enzymes are members of the hemoprotein superfamily, and are involved in the mono-oxygenation reactions of a wide range of endogenous and exogenous compounds in mammals and plants. Characterization of CYP genes in fish has been carried out intensively over the last 20 years. In Japanese pufferfish (Takifugu rubripes), 54 genes encoding P450s have been identified. Across all species of fish, 137 genes encoding P450s have been identified. These genes are classified into 18 CYP families: namely, CYP1, CYP2, CYP3, CYP4, CYP5, CYP7, CYP8, CYP11, CYP17, CYP19, CYP20, CYP21, CYP24, CYP26, CYP27, CYP39, CYP46 and CYP51.We pinpointed eight CYP families: namely, CYP1, CYP2, CYP3, CYP4, CYP11, CYP17, CYP19 and CYP26 in this review because these CYP families are studied in detail. Studies of fish P450s have provided insights into the regulation of P450 genes by environmental stresses including water pollution. In this review, we present an overview of the CYP families in fish.     

Cytochrome P450 3A: genetic polymorphisms and inter-ethnic differences

Ethnicity is a demographic variable that plays an important role in interindividual variability of drug metabolism and response. The genetic variations of drug-metabolizing enzymes exhibiting interindividual differences of drug metabolism also show differences between populations. The reason for this is that the frequency of a polymorphism is found to differ between populations. The other reason is that different variants are seen in different populations. Most drugs are biotransformed in the body by cytochrome P450. The CYP3A isozymes are responsible for the metabolism of 50-60% of all currently prescribed drugs. Studies have shown that there is variability in CYP3A activity and also inter-ethnic differences in CYP3A-mediated drug metabolism. The purpose of this review is to focus on the genetic polymorphism and ethnic variations in CYP3A-mediated oxidative drug metabolism.     

Cytochrome P450 interactions in human cancers: new aspects considering CYP1B1

Molecular epidemiological studies are now a powerful tool to determine differential genetic susceptibilities to cancer-causing agents, and to obtain information on potential mechanisms. Cytochrome P450 (CYP) allelic variants are considered biomarkers of susceptibility to cancer. Such variants have an influence on the bioactivation and thereby on the potency of chemical carcinogens. This is very much straight forward for tobacco smoke-related human cancers. A new aspect is the implication of CYP1B1 in tobacco smoke-related cancers at several organ sites. On this basis, the present review is focused on lung, breast, urinary bladder and head and neck cancer. The CYP profile of the human lung includes CYP1A1, -1B1, -2A6, -2A13, -2B6, -2C18, -2E1, -2F1, -3A5 and -4B1. Polycyclic aromatic hydrocarbons (PAHs) and nitrosamines, as active components of tobacco smoke, appear as primary chemical factors for lung malignancies. For human mammary cancer, the use of hormone replacement therapy (HRT) has been shown to be associated with an increase of breast cancer risk, and there seems to be a link between risks caused by HRT use and modifying polymorphisms of drug/xenobiotic enzymes. Specifically, an association of the CYP1B1*3/*3 genotype with increased breast cancer risks has been postulated. Cigarette smoking is a major cause of human urinary bladder cancer. Arylamines, PAHs and nitrosamines are locally activated within the urothelium. Important CYPs in the bladder epithelium of experimental animals and man are CYP1B1 and -4B1. Alcohol consumption and tobacco smoking are known as the major causes of head and neck cancers. Recently, it appears that a polymorphic variant CYP1B1*3/*3 relates significantly to the individual susceptibility of smokers to head and neck cancer, supporting the view that PAH are metabolically activated through CYP1B1. It appears that CYP1B1 plays a key role for the activation of carcinogens at several organ targets, with a likelihood of complex gene-environment interactions implying Phase II enzymes.     

Cytochrome P450 CYP1B1 protein expression: a novel mechanism of anticancer drug resistance

The overexpression of human cytochrome P450 CYP1B1 has been observed in a wide variety of malignant tumours, but the protein is undetectable in normal tissues. A number of cytochrome P450 enzymes are known to metabolise a variety of anticancer drugs, and the consequence of cytochrome P450 metabolism is usually detoxification of the drug, although bioactivation occurs in some cases. In this study, a Chinese hamster ovary cell line expressing human cytochrome P450 CYP1B1 was used to evaluate the cytotoxic profile of several anticancer drugs (docetaxel, paclitaxel, cyclophosphamide, doxorubicin, 5-fluorouracil, cisplatin, and carboplatin) commonly used clinically in the treatment of cancer. The MTT (3-[4,5-dimethylthiazol-2yl]-2,5-diphenyltetrazolium bromide) assay was used to determine the levels of cytotoxicity. The key finding of this study was that on exposure to docetaxel, a significant decrease in sensitivity towards the cytotoxic effects of docetaxel was observed in the cell line expressing CYP1B1 compared to the parental cell line (P = 0.03). Moreover, this difference in cytotoxicity was reversed by co-incubation of the cells with both docetaxel and the cytochrome P450 CYP1 inhibitor alpha-naphthoflavone. This study is the first to indicate that the presence of CYP1B1 in cells decreases their sensitivity to the cytotoxic effects of a specific anticancer drug.     

Cytochrome P450 2B (CYP2B)-mediated activation of methyl-parathion in rat brain extracts.

The role of cytochrome P450 (CYP) and the CYP isoform involved in the activation of the widely used pesticide methyl-parathion (MePA) were investigated in rat brain extracts by measuring the effect of different CYP inhibitors on acetylcholinesterase (AChE) inhibition by MePA. Brain extracts provide a useful tool to study the activation mechanisms of organophosphorus compounds (OP) since they contain both the activating enzyme(s) and the molecular target for OP toxicity. As expected, in incubations of rat brain extract supplemented with NADPH, AChE activity was non-competitively inhibited by the presence of MePA, indicating that MePA was activated to its reactive metabolite methyl-paraoxon (MePO). Indeed, Vmax(app) decreased from 13.4 to 8.7 micromol thionitrobenzoic acid (TNB)/min per mg protein. MePA activation by rat brain extracts, as measured by the AChE inhibition produced by the presence of the pesticide in the incubation, was fully prevented by previously bubbling the incubation mix with CO, by the presence of monoclonal anti-rat CYP2B1/2B2 antibodies and by the addition of phenobarbital (PB), a CYP2B substrate. Interestingly, MePA showed a greater affinity for CYP2B than PB. CYP1A1 antibodies showed no effect on MePA activation. The presence of cytochrome P450 2B (CYP2B) in the rat brain extracts was confirmed by immunoblotting. These results demonstrate indisputably the responsibility of CYP2B in MePA activation in the rat brain in vitro, suggesting that metabolic activation of OP compounds in situ might be crucial for their organ specific toxicity to the central nervous system also in vivo.     

GSTM家族基因多态性与乳腺癌遗传易感性

乳腺癌是复杂性多基因疾病.低外显率基因谷胱甘肽-S-转移酶(GST)基因在乳腺癌遗传易感性中的作用逐渐受到重视.GST基因家族成员之一的GSTM基因的多态性与某些癌症的发生相关联,尽管GSTM基因多态性与乳腺癌遗传易感性的研究尚未获得一致的结论,但相关研究及其进展值得关注.     

Cytochrome P450 (CYP) expression in human myeloblastic and lymphoid cell lines

To explore the physiological roles of cytochrome P450 (CYP) in peripheral blood cells, we examined which isoforms of CYP families were expressed in human myeloid leukemia cell lines (U937, HL-60 and K562) and lymphoid cell lines (BALL-1, MOLT-4 and Jurkat) by RT-PCR. We observed relatively high expression of CYP1A1, CYP1B1, CYP2A6, CYP2A7, CYP2D6, and CYP2E1 in all cell types, but CYP2A13 and CYP2C9 expression was not detected. Expressions of aryl hydrocarbon (Ah) receptor and Ah receptor nuclear translocator (ARNT), which mediate induction of the CYP1 family, were also detected in all cell types. Cell-type specific expression of CYP3A4 and CYP3A5 was observed in MOLT-4 and K562 cells. Weak, but significant, expression of CYP3A7 was detected in K562 cells. The profile of CYP expression in the culture cells reported here provides information that furthers our understanding of the physiological roles of CYP enzymes in human blood cells.     

CYP1B1、NQO1基因多态性与肺癌易感性关系的研究

目的研究内蒙古地区蒙古族与汉族人群的CYP1B1和NQO1基因多态性及吸烟状况与肺癌易感性的关系。方法采用PCR-RFLP技术对CYP1B1基因L432V位点和NQO1基因C609T位点多态性进行检测。结果 (1)CYP1B1基因L432V位点基因型分布频率在蒙古族和汉族健康人群中差异无统计学意义(χ2=1.220,P> 0.05);NQO1基因C609T位点基因型分布频率在蒙古族和汉族健康人群中差异无统计学意义(χ2=0.221,P> 0.05)。(2)在蒙古族和汉族人群中,NQO1 C/T和T/T基因型有明显增加患肺癌风险性的作用(汉族人群OR:1.461,2.278,P <0.05;蒙古族人群OR:1.493,2.040,P <0.05),而CYP1B1 C/G和G/G基因型无明显增加患肺癌风险性的作用(汉族人群OR:1.271,1.614,P> 0.05;蒙古族人群OR:0.970,1.758,P> 0.05)。(3)在汉族人群中,携带CYP1B1 C/G+G/G基因型的吸烟者患肺癌的危险性高于携带C/C的非吸烟者(OR:2.152,P <0.05);携带NQO1 C/C、C/T+T/T基因型的吸烟者患肺癌的危险性高于携带C/C的非吸烟者(OR:2.172,2.613,P <0.05)。在蒙古族人群中,携带CYP1B1 C/C、C/G+G/G基因型的吸烟者患肺癌的危险性高于携带C/C的非吸烟者(OR:1.409,1.765,P <0.05);携带NQO1 C/C、C/T+T/T基因型的吸烟者患肺癌的危险性高于携带C/C的非吸烟者(OR:2.479,2.729,P <0.05)。结论 (1)CYP1B1基因L432V位点基因型以及NQO1基因C609T位点基因型在内蒙古地区蒙古族和汉族健康人群中的分布不具有种族差异。(2)NQO1 C/T和T/T基因型显著增加内蒙古地区蒙古族和汉族患肺癌的易感性。(3)在蒙古族和汉族人群中,CYP1B1 C/G+G/G基因型以及NQO1 C/T+T/T基因型显著增加吸烟者患肺癌的易感性。     

Cytochrome P450 1B1 determines susceptibility to dibenzo[a,l]pyrene-induced tumor formation

Metabolic activation, DNA binding, and tumorigenicity of the carcinogenic polycyclic aromatic hydrocarbon dibenzo[a,l]pyrene (DB[a,l]P) catalyzed by murine cytochrome P450 (P450) enzymes were investigated. DNA binding of DB[a,l]P in human mammary carcinoma MCF-7 and human P450-expressing Chinese hamster V79 cell lines was previously shown to occur preferentially with metabolically generated fjord region DB[a,l]P-11,12-dihydrodiol 13,14-epoxides (DB[a,l]PDE). To elucidate different capabilities of murine P450 1A1 and 1B1 for metabolic activation of DB[a,l]P, V79 cell cultures stably expressing P450s 1A1 or 1B1 from mice were exposed to 10 or 100 nM DB[a,l]P. Both cell lines transformed DB[a,l]P to DNA binding intermediates. As with V79 cells expressing the corresponding human P450 enzyme [Luch et al. (1998) Chem. Res. Toxicol. 11, 686-695], murine P450 1B1-catalyzed metabolism and DNA binding proceeded exclusively through generation of fjord region DB[a,l]PDE. In addition, only DB[a,l]PDE-derived DNA adducts were found in V79 cells expressing P450 1A1 from mice. This is in contrast to our recent findings with V79 cells expressing P450 1A1 from humans or rats which catalyzed the formation of both highly polar DNA adducts as well as nonpolar DB[a,l]PDE-DNA adducts. To establish the role of P450 1B1 in DB[a,l]P-induced tumor formation in vivo, we treated P450 1B1-null and wild-type mice intragastrically and monitored survival rates and appearance of neoplasias in various organs. All wild-type mice (n = 17) used in this study developed at least one tumor at one site (tumor rate of 100%). In contrast, 5 of 13 P450 1B1-null mice were observed to be free from any tumor (tumor rate of 62%). The organ sites of tumor formation and the dignity of tumors were different between wild-type and P450 1B1-null mice. Wild-type mice were diagnosed with both benign and malignant tumors of the ovaries, lymphoid tissues, as well as with skin and endometrial hyperplasias, whereas P450 1B1-null mice developed only lung adenomas and endometrial hyperplasias. DNA binding studies using embryonic fibroblasts isolated from these animals provided further evidence that P450 1B1-catalyzed formation of fjord region DB[a,l]PDE-DNA adducts is the critical step in DB[a,l]P-mediated carcinogenesis in mice, and probably also in man.     

Expression and Regulation of Xenobiotic-Metabolizing Cytochrome P450 (CYP) Enzymes in Human Lung

Pathogenesis of lung diseases, such as lung cancer and chronic obstructive pulmonary disease, is tightly linked to exposure to environmental chemicals, most notably tobacco smoke. Many of the compounds associated with these diseases require an enzymatic activation to exert their deleterious effects on pulmonary cells. These activation reactions are mostly catalyzed by cytochrome P450 (CYP) enzymes. Interindividual differences in the in situ activation and inactivation of chemical toxicants may contribute to the risk of developing lung diseases associated with these compounds. This review summarizes in detail the expression of individual CYP forms in human pulmonary tissue and gives a view on the significance of the pulmonary expression of CYP enzymes. The localization of individual CYP enzymes in various cell types of human lung and the emerging field of regulation of human pulmonary CYP enzymes are discussed. At least CYP1A1 (in smokers), CYP1B1, CYP2B6, CYP2E1, CYP2J2, and CYP3A5 proteins are expressed in human lung, and also other CYP forms are likely to be expressed. Xenobiotic-metabolizing CYP enzymes are mostly expressed in bronchial and bronchiolar epithelium, Clara cells, type II pneumocytes, and alveolar macrophages in human lung, although individual CYP forms have different patterns of localization in pulmonary tissues. Problems in animal to human lung toxicity extrapolation and several specific aspects requiring more detailed assessment are identified.     

Distribution of the major cytochrome P450 (CYP) 2C9 genetic variants in a Saudi population

Cytochrome P450 (CYP) 2C9 is responsible for the metabolism of a number of widely used drugs such as oral anticoagulants, oral antidiabetics and non-steroidal anti-inflammatory drugs. The CYP2C9 is a genetically polymorphic enzyme. The most common allele is CYP2C9*1, while CYP2C9*2 and CYP2C9*3 are the less-frequent variants. The activity of the enzyme encoded by either CYP2C9 *2 or *3 variant is lower compared with that of the CYP2C9*1. The metabolism of most of the CYP2C9 substrates decreases in varying degrees in subjects carrying the CYP2C9 *2 or *3 allele. The aim of this study was to investigate the frequencies of the major variants of the CYP2C9 in Saudi Arabians.     

Cytochrome P450 (CYP) inhibition screening: comparison of three tests.

There are several different experimental systems for screening of in vitro inhibitory potency of drugs under development. In this study we compared three different types of cytochrome P450 (CYP) inhibition tests: the traditional single substrate assays, the fluorescent probe method with recombinant human CYPs, and a novel n-in-one technique. All major hepatic drug-metabolizing CYPs were included (1A2, 2A6, 2B6, 2C8, 2C9, 2C19, 2D6, 2E1, 3A4). Six compounds (sotalol, propranolol, citalopram, fluoxetine, oxazepam and diazepam) were selected for detailed comparisons. The IC50 values of each of these compounds were measured using the three assay types. The inhibitory potencies of these model drugs were generally within the same order of magnitude and followed similar inhibition profiles in all the assay types. Clinically observed inhibitory interactions, or lack thereof, were predictable with all three assays. Comparison of potencies of 'diagnostic' inhibitors revealed also some notable differences between the assays, especially regarding CYP2E1. The potency of inhibitors towards CYP3A4 was dependent on the substrate and reaction measured. Generally all three assays gave reasonably comparable results, although some unexplained differences were also noted.     

Progesterone metabolism in recombinant yeast simultaneously expressing bovine cytochromes P450c17 (CYP17A1) and P450c21 (CYP21B1) and yeast NADPH-P450 oxidoreductase.

Simultaneous expression plasmids were constructed for bovine adrenal cytochromes P450c17 and P450c21 (pA gamma alpha) and for both P450s together with NADPH-cytochrome P450 reductase (pAR gamma alpha). On introduction of each of the plasmids into Saccharomyces cerevisiae AH22 cells, the transformed yeast strains AH22/pA gamma alpha and AH22/pAR gamma alpha produced about 10(5) molecules per cell of P450c17 and 2 x 10(3) molecules per cell of P450c21. The expression levels of NADPH-cytochrome P450 reductase was about 3 x 10(4) and 6 x 10(5) molecules per cell in the strains AH22/pA gamma alpha and AH22/pAR gamma alpha, respectively. When progesterone was added to growing cell cultures of the transformed yeast strains, the substrate was metabolized more rapidly in the AH22/pAR gamma alpha cells than AH22/pA gamma alpha cells, probably due to overproduction of the reductase. In the AH22/pAR gamma alpha cells, progesterone was first converted into 17 alpha-hydroxyprogesterone to the extent of 82% by the catalysis of P450c17. 17 alpha-hydroxyprogesterone was further converted into 11-deoxycortisol by P450c21 to the extent of 60% of the added substrate. The conversion of progesterone into androstenedione through 17 alpha-hydroxyprogesterone was estimated to be less than 3%, suggesting very low C17,20-lyase activity of P450c17, although other hydroxylation products were detected. Androstenedione was further converted into testosterone by an unknown pathway present in S. cerevisiae cells.     

Cytochrome P450-mediated metabolism and cytotoxicity of aflatoxin B(1) in bovine hepatocytes.

Aflatoxin B(1) (AFB(1)) biotransformation comprises cytochrome P450-mediated reactions resulting in hydroxylated and demethylated metabolites as well as AFB(1) epoxides. As the latter are highly nucleophilic, the species-specific rate of epoxidation and the ability for rapid conjugation to glutathione by glutathione S-transferase determines the individual susceptibility to AFB(1). Here we show the time- and dose-dependent rate of AFB(1)-metabolism in bovine hepatocytes. Aflatoxin M(1) (AFM(1)) is the most prominent metabolite formed within the first 2-8 hr of incubation, whereas AFB(1)-dhd is detectable in medium mainly after a prolonged incubation period. The delayed formation of AFB(1)-dhd corresponds to the cytotoxicity demonstrated by the MTT assay. alpha-Naphthoflavone and ketoconazole, inhibitors of CYP1A and CYP3A, respectively in humans, were used to evaluate the contribution of specific P450 isoenzymes in bovine biotransformation of AFB(1). Initial experiments confirmed that alpha-naphthoflavone and ketoconazole inhibited ethoxyresorufin O-deethylation and testosterone 6beta-hydroxylation also in bovine hepatocytes. Both inhibitors reduced AFM(1) and AFB(1)-dhd formation concentration dependently, suggesting that both enzyme groups contribute to the formation of these metabolites. However, the formation of AFM(1) was less inhibited by both compounds than the formation of AFB(1)-dhd.     

细胞色素P450 1B1在上皮性卵巢癌组织中的表达

目的：检测卵巢癌组织、卵巢良性上皮性肿瘤及正常卵巢组织中细胞色素P4501B1（cytochrome P4501B1，CYP1B1）的表达，为以CYP1B1为靶点进行卵巢癌治疗提供理论基础。方法：采用免疫组化SP法检测53例上皮性卵巢癌、30例卵巢良性上皮性肿瘤及19例正常卵巢组织中CYP1B1的表达。结果：53例卵巢癌中CYP1B1阳性率92．45％，明显高于卵巢良性肿瘤组织（13．33％），差异有统计学意义（P〈0．01）。正常卵巢组织CYP1B1呈阴性表达。14例同时收集的卵巢癌转移灶组织有13例CYP1B1阳性表达，阳性率为92．86％。结论：CYP1B1可作为一个抗癌药开发及逆转化疗药耐药的新靶点。