Regulation Of Xenobiotic Metabolizing Enzymes Research Articles

Regulation of Xenobiotic-Metabolizing Enzymes by 5-Demethylnobiletin and Nobiletin to Mitigate Benzo[a]pyrene-Induced DNA Damage In Vitro and In Vivo.

Benzo[a]pyrene (B[a]P) is a genotoxic polycyclic aromatic hydrocarbon that is metabolized by cytochrome P450 family 1 enzymes (CYP 1s) and can bind to DNA to form DNA adducts, leading to DNA damage and increased colorectal cancer risk. Previous studies have shown polymethoxyflavones to have a high potential for anticancer effects by regulating CYP 1s, especially nobiletin (NBT) and 5-demethylnobiletin (5-DMNB). However, the effects of NBT and 5-DMNB on B[a]P metabolism remain unclear. Therefore, this study aimed to clarify the effects of NBT and 5-DMNB on B[a]P-induced DNA damage in vitro and in vivo. In NCM460 cells, 5-DMNB and NBT appeared to reduce the metabolic conversion of B[a]P by regulating the aryl hydrocarbon receptor (AhR)/CYP 1s signaling pathway. This process protected NCM460 cells from B[a]P's cytotoxic effects by decreasing DNA damage and suppressing B[a]P diol-epoxide-DNA adduct formation. In BALB/c mice, 5-DMNB and NBT also protected against B[a]P-induced DNA damage. Altogether, these findings indicate that 5-DMNB and NBT attenuate B[a]P-induced DNA damage by modulating biotransformation, highlighting their chemopreventive potential against B[a]P-induced carcinogenesis. Therefore, 5-DMNB and NBT are promising agents for colorectal cancer chemoprevention in the future.

Protein phosphatase 2A regulates cytotoxicity and drug resistance by dephosphorylating AHR and MDR1

Protein phosphatase 2A (PP2A) is a serine/threonine dephosphorylating enzyme complex that plays numerous roles in biological processes, including cell growth and metabolism. However, its specific actions in many of these critical pathways are unclear. To explore mechanisms underlying metabolic enzyme regulation in the liver, we investigated the key pathways involved in regulation of xenobiotic-metabolizing enzymes in a mouse model with hepatocyte-specific deletion of Ppp2r1a, encoding the Aα subunit of PP2A. We performed transcriptome and phosphoproteome analysis in mouse livers at the age of 3 months and identified 2695 differentially expressed genes and 549 upregulated phosphoproteins in homozygous knockout mouse livers compared with WT littermates. In particular, the expression of metabolic enzymes Cyp2e1, Cyp1a1, Cyp1a2, Mdr1a, and Abcg2 was dramatically altered in homozygous knockout mouse livers. We also demonstrated that activation of PP2A reversed the decline of metabolic enzyme expression in primary mouse hepatocytes. We found that specific PP2A holoenzymes were involved in metabolic enzyme induction through dephosphorylation of transcription factors, nuclear receptors, or the target enzymes themselves, leading to dysregulation of xenobiotic metabolism or drug-induced hepatotoxicity. Notably, we confirmed that a regulatory axis, PP2A B56α–aryl hydrocarbon receptor–Cyp1a1, was involved in benzo(a)pyrene-induced cytotoxicity through dephosphorylation of the metabolic nuclear receptor, aryl hydrocarbon receptor, at serine 36. In addition, we showed that PP2A B56δ complexes directly dephosphorylated the multidrug efflux pump MDR1 (encoded by multi-drug resistance gene 1), contributing to drug resistance against the chemotherapeutic 5-fluorouracil. Taken together, these novel findings demonstrate the involvement of PP2A in the regulation of liver metabolism.

Butyrate interacts with benzo[a]pyrene to alter expression and activities of xenobiotic metabolizing enzymes involved in metabolism of carcinogens within colon epithelial cell models

Butyrate helps to maintain colon homeostasis and exhibits chemopreventive effects in colon epithelium. We examined the interactive effects of butyrate and benzo[a]pyrene (BaP), dietary carcinogen, in regulation of expression of a panel of phase I and II xenobiotic metabolizing enzymes (XMEs) in human colon cells. In human colon carcinoma HCT-116 and HT-29 cell lines, butyrate alone increased mRNA levels of some enzymes, such as N-acetyltransferases (in particular NAT2). In combination with BaP, butyrate potentiated induction of cytochrome P450 family 1 enzymes (CYP1A1), aldo-keto reductases (AKR1C1) or UDP-glucuronosyltransferases (UGT1A1). There were some notable differences between cell lines, as butyrate potentiated induction of NAD(P)H:quinone oxidoreductase 1 (NQO1) and UGT1A4 only in HCT-116 cells, and it even repressed AKR1C3 induction in HT-29 cells. Butyrate also promoted induction of CYP1, NQO1, NAT2, UGT1A1 or UGT1A4 in human colon Caco-2 cells, in a differentiation-dependent manner. Differentiated Caco-2 cells exhibited a higher inducibility of selected XME genes than undifferentiated cells. Butyrate increased induction of enzymatic activities of NATs, NQO1 and UGTs by BaP in HCT-116 and HT29 cells, whereas in differentiated Caco-2 cells it helped to increase only enzymatic activity of NQO1 and UGTs. Together, the present data suggest that butyrate may modulate expression/activities of several enzymes involved in metabolism of carcinogens in colon. In some cases (NAT2, UGT1 A1), this was linked to inhibition of histone deacetylases (HDAC), as confirmed by using HDAC inhibitor trichostatin A. These results may have implications for our understanding of the role of butyrate in regulation of XMEs and carcinogen metabolism in colon.