The roles of Rev-erbα and circadian clock in colonic inflammation remain unclarified. Here we show colon clock genes (including Rev-erbα) are dysregulated in mice with DSS-induced colitis. In turn, disruption of the circadian clock exacerbates experimental colitis. Rev-erbα-deficient mice are more sensitive to DSS-induced colitis, supporting a critical role of Rev-erbα in disease development. Further, Rev-erbα ablation causes activation of Nlrp3 inflammasome in mice. Cell-based experiments reveal Rev-erbα inactivates Nlrp3 inflammasome mainly at the priming stage. Rev-erbα directly represses Nlrp3 transcription through specific binding to the promoter region. Additionally, Rev-erbα represses p65 transcription and indirectly repressed Nlrp3 via the NF-κB pathway. Interestingly, Rev-erbα activation in wild-type mice by SR9009 attenuates DSS-induced colitis, whereas the protective effects are lost in Nlrp3−/− and Rev-erbα−/− mice. Taken together, Rev-erbα regulates experimental colitis through its repressive action on the NF-κB/Nlrp3 axis. Targeting Rev-erbα may represent a promising approach for prevention and management of colitis.

Glucuronidation mediated by UDP-glucuronosyltransferases (UGTs) is a significant metabolic pathway that facilitates efficient elimination of numerous endo- and xenobiotics including phenolics. UGT genetic deficiency and polymorphisms or inhibition of glucuronidation by concomitant use of drugs are associated with inherited physiological disorders or drug induced toxicities. Moreover, extensive glucuronidation can be a barrier to oral bioavailability as the first-pass glucuronidation (or premature clearance by UGTs) of orally administered agents usually results in the poor oral bioavailability and lack of efficacies. This review focused on the first-pass glucuronidation of phenolics including natural polyphenols and pharmaceuticals. The complexity of UGT-mediated metabolism of phenolics is highlighted with species-, gender-, organ- and isoform-dependent specificity, as well as functional compensation between UGT1A and 2B subfamily. In addition, recent advances are discussed with respect to the mechanisms of enzymatic actions including the important properties such as binding pocket size and phosphorylation requirements.

Active transport of glucuronide out of cells is a critical process in elimination of drugs via the glucuronidation pathway. Here, HeLa cells were stably transfected with UGT1A1 and the contributions of BCRP and MRP family transporters to the cellular efflux of chrysin glucuronide (CG) were determined. The cDNA of UGT1A1 was introduced into HeLa cells using the lentiviral transfection method. The modified cells were functional in generation of the glucuronide from chrysin. Ko143 at 10-20 mM (a dual inhibitor of BCRP and UGT1A1) caused a marked decrease (51.3%-59.7%, P < 0.01) in the excretion rate and efflux clearance of CG. Likewise, MK-571 at 5-20 mM (an inhibitor of MRPs but an activator of UGT1A1) resulted in a significant reduction in the excretion rate (18.2%-64.0%, P < 0.01) and efflux clearance (37.0%-90.2%, P < 0.001). By contrast, dipyridamole and leukotriene C4 showed no inhibitory effects on CG excretion. The chemical inhibition indicated that excretion of CG was contributed by the MRP family transporters, whereas the role of BCRP was unclear. Furthermore, short hairpin RNA-mediated silencing of a target transporter led to a marked reduction in the excretion rate of CG (38.6% for BCRP, 39.3% for MRP1, 36.4% for MRP3, and 28.7% for MRP4; P < 0.01). Transporter silencing also led to substantial decreases in the efflux clearance (44.7% for BCRP, 60.4% for MRP1, 36.7% for MRP3, and 28.7% for MRP4; P < 0.01). The gene silencing results suggested that BCRP, MRP1, MRP3, and MRP4 were significant contributors to excretion of CG.

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The present study aims to predict the regiospecific glucuronidation of three dihydroxyflavones and seven mono-hydroxyflavones in human liver and intestinal microsomes using recombinant UGT isoforms. Seven mono-hydroxyflavones (or HFs), 2′-, 3′-, 4′-, 3-, 5-, 6-, and 7-hydroxyflavone, and three di-hydroxyflavones (or diHFs), 3,7-dihydroxyflavone (3,7-diHF), 3,5-dihydroxyflavone (3,5-diHF) and 3,4′-dihydroxyflavone (3,4′-diHF) were chosen and rates were measured at 2.5, 10 and 35 μM. The results indicated that the position of glucuronidation of three diHFs could be determined by using the UV spectra of relevant HFs. The results also indicated that UGT1A1, UGT1A7, UGT1A8, UGT1A9, UGT1A10 and UGT2B7 are the most important six UGT isoforms for metabolizing the chosen flavones. Regardless of isoforms used, 3-HF was always metabolized the fastest whereas 5-HF was usually metabolized the slowest, probably due to the formation of an intra-molecular hydrogen bond between 4-carbonyl and 5-OH group. Relevant UGT isoformspecific metabolism rates generally correlated well with the rates of glucuronidation in human intestinal and liver microsomes at each of the three tested concentrations. In conclusion, the glucuronidation "fingerprint" of seven selected mono-hydroxyflavones was affected by UGT isoforms used, positions of the −OH group, and the substrate concentrations, and the rates of glucuronidation by important recombinant UGTs correlated well with those obtained using human liver and intestinal microsomes.