In vivo metabolic fates of sinensetin, 5-demethylsinensetin and their metabolites under diverse conditions
Creators: name: Wang, Xiaoqi
Publisher: name: No Publisher Supplied
Year: 2022

description: Citrus polymethoxyflavones (PMFs) have attracted great research interest since the recent decade. However, the existed investigations mainly focused on the potential bioactivities of those PMFs, and paid little attention to the in vivo metabolic fates of them. Nevertheless, it was indicated by former research that the bioefficacy generated from parent compounds may contribute by their in vivo metabolites. Therefore, to explore the basic metabolic patterns of PMF compounds could in turn broaden our understanding towards the inherent mechanism of the health-beneficial roles of those PMFs.One nonnegligible pitfall of the former studies regarding the metabolism of citrus PMFs lies in that, only the demethylation reactions happened on B ring and the C-5 positions are evaluated; probably due to the difficulties in achieving A-ring metabolites (except for the 5-demethylated ones) via chemical synthesis, as well as the high numbers of methoxy groups on A ring of the most frequently investigated PMFs, nobiletin and tangeretin. In this way, sinensetin (Sin), another major citrus PMF, was selected in this study to fulfill our goal. With relatively balanced methoxy groups on both A and B rings, Sin can be treated as an excellent model compound to identify all its mono-demethylated metabolites.In the first part of this study, the two B-ring metabolites of Sin were chemically synthesized via a simplified 3-step pathway, and the 5-demethylsinensetin (5-OH Sin) was achieved via a single-step selected acidic reaction. Considering the difficulties in yielding other A-ring metabolites, the [6-D₃] Sin was synthesized as a replacement of 6-demethylsinensetin, and 6-demethylsinensetin was successfully identified in rats’ urine after the in vivo metabolism of [6-D₃] Sin. In addition, via matching parent and daughter ions with that of 5-OH Sin, the 7-demethylsinensetin was also determined by LC-MS/MS detection using MRM mode.Then, the metabolic fates of these analytes were quantitatively evaluated in urine, feces and plasma of rats after one-time oral administration of Sin at 100 mg/(kg.bw) within 48 hours. Results demonstrated that, Sin could be readily absorbed in the small intestine, and was extensively biotransformed to its metabolites in liver and gut. Besides, the 4′-demethylsinensetin, 6-demethylsinensetin and 3′-demethylsinensetin are identified as the three dominant in vivo metabolites of Sin in the three biological samples. Interestingly, only 5-OH Sin showed a synchronously higher content in feces than in urine with Sin. Moreover, the variation trends of the dynamic concentrations of Sin and 5-OH Sin in rats’ plasma also resembled each other closely, which aroused our interest towards this compound.Being the least biotransformed metabolite from Sin in urine and plasma, 5-OH Sin possessed ultra low polarity. Whereas intriguingly, superior bioactivities of the 5-demethylated PMFs to their parent counterparts has been reported by former researches. In order to uncover this mystery from the aspect of metabolism, the in vivo biotransformation of 5-OH Sin was quantitatively discovered in the second part of this study.5,3′-Didemethylsinensetin and 5,4′-didemethylsinensetin, being speculated as the two major metabolites of 5-OH Sin, were chemically synthesized as standards via a modified 4-step synthetic method. Then, pharmacokinetic and excretion studies were conducted on rats after one-time oral gavage of 5-OH Sin. Results showed that 5-OH Sin was mostly detected in feces, indicating its poor absorption in small intestine. In addition, 5,3′-didemethylsinensetin and 5,4′-didemethylsinensetin were identified as the two major metabolites of 5-OH Sin, and the C-3′ position of 5-OH Sin was more facile to be demethylated in the systemic circulation. Moreover, other than demethylation reactions, the methylation metabolism of 5-OH Sin and its metabolites were also observed in this study, suggesting the bidirectional biotransformation between 5-OH Sin and its parent compound, Sin, under in vivo conditions.Based on these findings, the significantly accumulated 5-OH Sin in gut inspired us that, 5-OH Sin may possess better colon-protective effect than Sin. In addition, the metabolic patterns of PMF compounds in experimental animals with colonic inflammation are still lacking exploration. Therefore, in the third part of this study, we evaluated the basic anti-acute colitis effects of Sin and 5-OH Sin in C57BL/6 mice, as well as their long-time metabolic fates before and during colitis after consecutive oral administration. Results indicated that the shortened colon length of mice brought from DSS-induced colitis was significantly restored by 5-OH Sin at 80 mg/(kg.bw), whereas Sin did not exhibit certain alleviating effect. Besides, the demethylation capability of gut microbiota at the C-3′ positions of PMFs declined in both Sin-treated and 5-OH Sin-treated groups after colitis modeling, suggesting the altered gut microbial structure during colonic inflammation. Interestingly, comparing to Sin-treated group, the average ratios of fewer compounds were significantly changed in 5-OH Sin-treated group after DSS treatment, implying that 5-OH Sin could probably reshape gut microbiota composition in mice with acute colitis. Furthermore, the different biotransformation pathways from parent compounds Sin and 5-OH Sin to 5,3′,4′-tridemethylsinensetin were also elucidated in this study, in detail.