Introduction to Human Cytochrome P450 Superfamily
Shufeng Zhou in Cytochrome P450 2D6, 2018
Many CYP1A1 substrates are inhibitors of this enzyme. AA significantly inhibits CYP1A1- and 1A2-dependent 7-ethoxycoumarin O-deethylation (Yamazaki and Shimada 1999). Retinol, RA, and cholecalciferol are all inhibitors of CYP1A1 (Yamazaki and Shimada 1999). Caffeine, paraxanthine, propranolol, and theophylline similarly inhibit CYP1A1- and 1A2-catalyzed phenacetin O-deethylation (Tassaneeyakul et al. 1993). α-Naphthoflavone (ANF), a common inhibitor used for CYP1A1 with a Ki of 0.01 µM, is more effective against CYP1A2 (Bourrie et al. 1996; Tassaneeyakul et al. 1993). ANF and 7-ethoxycoumarin are approximately 10-fold more potent as inhibitors of CYP1A2 than CYP1A1 (Tassaneeyakul et al. 1993). Mollugin originally isolated from Rubia cordifolia inhibits CYP1A2 with an IC50 of 3.55 µM (Kim et al. 2013). Moreover, the dietary flavonoids including acacetin, diosme-tin, eupatorin, and chrysin are inhibitors of CYP1A1 and 1A2 (Androutsopoulos et al. 2011). Quercetin and kaempferol are also inhibitors of CYP1A2 (Savai et al. 2015).
Ovotoxic Environmental Chemicals: Indirect Endocrine Disruptors
Rajesh K. Naz in Endocrine Disruptors, 2004
As regards bioactivation, BaP is metabolized initially by microsomal cytochrome P450 enzymes to arene oxides,[126] which may then spontaneously form phenols and subsequently be converted to the trans-dihydrodiol by epoxide hydrolase. The diol epoxide, 7,8-dihydrodiol-9,10-epoxide, displays the greatest degree of mutagenicity, carcinogenicity, and ovotoxicity.[65] Mattison and Nightingale[66] showed that B6 mice were more susceptible to BaP than D2 mice, whereas both strains were equally susceptible to the arene oxide metabolite.[127] Furthermore, inhibition of PAH metabolism with α-naphthoflavone prevented PAH-induced oocyte destruction observed in mice.[62,65] Detoxification of the diol epoxide involves further hydrolysis to the tetrol or conjugation to glucuronides, sulfate, or glutathione. Other PAHs, DMBA and 3-MC, follow similar metabolic pathways.[126] Sub-chronic low-dose exposures of mice and rats to BAP, DMBA, and 3-MC, however, caused reductions in different follicle populations for each of these chemicals,[63] suggesting that differences in metabolism or follicle susceptibility may exist.
Cytochrome P450 Enzymes for the Synthesis of Novel and Known Drugs and Drug Metabolites
Peter Grunwald in Pharmaceutical Biocatalysis, 2019
Other than human CYP enzymes, engineering mammalian CYP enzymes has been successfully developed over a broad range of species. For example, CYP1A9, a piscine CYP enzyme originally from Japanese eel (Anguilla japonica), was engineered using site-directed mutagenesis approach. Mutant F263A showed higher α-naphthoflavone (ANF) and 7-ethoxycoumarin hydroxylase activities than wild-type CYP1A9. Mutant F263A, V387, and I391A showed higher catalytic activities of progesterone than wild-type CYP1A9. In this study, engineering of CYP1A9 enhanced the catalytic activity, introduced hydroxyl groups into the steroid ring of progesterone, which would further increase the water solubility of the steroid molecule (Uno et al., 2015). In a recent study, CYP2B from the desert woodrat (Neotoma lepida) was engineered for site-directed mutagenesis. Desert woodrats are exposed to a number of toxins with their regular diet. Thus, the CYPs they develop have the capability to detoxify a variety of toxic materials, which makes them highly useful in toxicity studies. CYP enzymes involved in mammalian detoxification generally metabolize a broad range of substrates. Engineering of CYP2B35 changed the enzyme specificity and presented novel catalytic activity, which were not present in the wild-type enzyme. The mutant of CYP2B35 showed maximal activity with 7-butoxycoumarin, which is opposed to the wild-type enzyme. A CYP2B35 mutant I104V/I114V/M209I/A3631/A367V/I477F presented a hybrid activity profile of CYP2B35 and CYP2B37, metabolizing both short-chain and long chain 7-alkoxycoumarins (Huo et al., 2017). In addition, engineered porcine CYP3A46 has also been developed recently. Site-directed mutagenesis was performed on residues Phe-108, Ser-119, Phe-215, Phe-304, and Thr-309 of porcine CYP3A46. They found that porcine CYP3A46 can convert Aflatoxin B1 to a highly reactive epoxide intermediate AFB1-8, 9-epoxide (AFBO), exhibiting similar catalytic procedure as human CYP3A4. The product AFBO can cause hepatotoxicity and hepatocarcinoma in human. The engineered CYP3A46 demonstrated that residues Phe-108, Ser-119, Phe-215, Phe-304, and Thr-309 play important roles in AFB1-8, 9-epoxidation. These results suggested that engineered CYP3A46 can be used for toxicity evaluation studies for industrial use (Jiang et al., 2018). Summary of the engineered CYP enzymes being used in the synthesis of drugs and drug metabolites is presented in Table 14.2.
Evaluation of the effect of Bovis Calculus Artifactus on eight rat liver cytochrome P450 isozymes using LC-MS/MS and cocktail approach
Published in Xenobiotica, 2021
Yun-Jing Zhang, Wen-Li Zhou, Fei Yu, Qian Wang, Can Peng, Jia-Yi Kan
BCA, bupropion, chlorzoxazone, midazolam and acetaminophen were purchased from National Institutes for Food and Drug Control (Beijing, China). Rat liver microsomes were purchased from Guangzhou Nuojia Biological Technology Co., Ltd (Guangzhou, China). Phenacetin and tolbutamide were obtained from Dr. Ehrenstorfer GmbH (Augsburg, Germany); amodiaquine, (S)-mephenytoin and dextromethorphan were purchased from Toronto Research Chemicals (Toronto, Canada); hydroxy-bupropion was purchased from Shanghai Zzbio Co., Ltd (Shanghai, China); n-deethyl-amodiaquine, 4-hydroxy-tolbutamide, 4′-hydroxy-mephenytoin, dextrorphan and 6-hydroxy-chlorzoxazone were purchased from Toronto Research Chemicals (Toronto, Canada); 1′-hydroxy-midazolam was purchased from Cayman Chemical Co., Ltd (Shanghai, China). Positive control inhibitors, thiotepa was purchased from Toronto Research Chemicals (Toronto, Canada); α-naphthoflavone was purchased from Extrasynthese (France). Sulfaphenazole, ticlopidine and ketoconazole were purchased from Sigma-Aldrich (St Louis, MO); quercetin and 4-methylpyrazole were purchased from Shanghai Yuanye Biotechnology Co., Ltd (Shanghai, China); quinidine was purchased from J&K Scientific Co., Ltd (Beijing, China). Internal standard (glibenclamide) and NADPH were purchased from Aladdin Biochemical Technology Co., Ltd (Shanghai, China). All other chemicals and solvents were of analytical grade.
Allosteric activation of cytochrome P450 3A4 by efavirenz facilitates midazolam binding
Published in Xenobiotica, 2018
Tomohiko Ichikawa, Hirofumi Tsujino, Takahiro Miki, Masaya Kobayashi, Chiaki Matsubara, Sara Miyata, Taku Yamashita, Kohei Takeshita, Yasushige Yonezawa, Tadayuki Uno
We further examined the binding of ketoconazole and α-naphthoflavone to CYP3A4 in order to evaluate our spectroscopic method. Ketoconazole is a widely used antifungal drug and is known as a CYP3A4 inhibitor. Previous studies have shown that the binding of ketoconazole to CYP3A4 results in a type II spectral change, with ligation of an azole nitrogen to the haem; the coordination is supported by the reported crystal structure of ketoconazole-bound CYP3A4 (Ekroos & Sjogren, 2006). Ketoconazole binding was measured per the procedure described for midazolam, resulting in a type II spectral change as previously reported (Figure 2B). The spectral changes were analysed, and the Kd value was determined to be 6.4 ± 2.0 μM (Figure 2F). α-Naphthoflavone is a synthetic flavin derivative that is reportedly a CYP1A inhibitor and activator for some CYP3A4-mediated metabolic reactions (Wang et al., 2000; Zanger & Schwab, 2013). In addition, previous work has shown that α-naphthoflavone binding results in a type I spectral change (Hosea et al., 2000), suggesting an increase in the fraction of a high-spin and five-coordinated haem, as mentioned for midazolam. Here, spectral changes resulting from the addition of α-naphthoflavone to CYP3A4 were monitored, and the change is plotted against the concentration of α-naphthoflavone (Figure 2C and G). α-Naphthoflavone binding was characterised as type I binding, and a fitted curve with the Hill equation to the plots resulted in a KS and n-value of 21 ± 0.57 μM and 1.8 ± 0.19, respectively. These values are comparable with those obtained previously (KS = 5.3–5.7 μM and n = 1.7) (Hosea et al., 2000; Roberts & Atkins, 2007; Tsalkova et al., 2007).
The aryl hydrocarbon receptor as a mediator of host-microbiota interplay
Published in Gut Microbes, 2020
A different story emerges from studies designed to examine the influence of AHR activation in the liver on obesity. Transgenic mouse models that express a constitutively activated AHR in the liver have revealed that elevated expression of the CD36/fatty acid translocase results in a fatty liver phenotype through the increased uptake of fatty acids.124 The administration of 3-methyl cholanthrene, a potent AHR ligand, in C57BL6/J mice results in an increase in both liver triglycerides and CD36 expression.125 This would suggest that high-level AHR activation can lead to fatty liver. Another possible mechanism is the ability of CYP1B1 enzyme to influence fatty acid metabolism and prevent obesity, supported by results obtained in Cyp1b1−/- mice.126 The loss of Cyp1b1 expression in mice is correlated with suppression of high-fat diet (HFD)-induced obesity via decreased expression of stearoyl-CoA desaturase 1 (SCD1),127 the rate-limiting enzyme synthesizing monounsaturated fatty acids from saturated fatty acids.128 Moreover, expression of PPARγ and target genes regulated by PPARα are also reduced in Cyp1b1 knockout mouse.129 Activation of PPARγ promotes induction of adipocytes from preadipocytes and storage of triglyceride, while genes stimulated by PPARα plays a critical role in fatty acid transport and mitochondrial fatty acid β-oxidation.130 Taken together, these results suggest the involvement of AHR in regulation of CYP1B1 expression, which promotes fatty acid synthesis, and inhibition of CYP1B1 could be a potential target for clinic treatment of obesity. Indeed, dietary exposure to AHR antagonist α-naphthoflavone is capable of inhibiting fatty liver and obesity in mice fed a western diet.131,132
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