Specific inhibitory effects of myricetin on human proton-coupled folate transporter: Comparison with its effects on rat proton-coupled folate transporter and human riboflavin transporter 3

Preclinical pharmacokinetics of M10 after intragastrical administration of M10-H and M10-Na in Wistar rats

As a myricetin derivative, M10 is a potent agent of anti-chronic colonic inflammation. It has better activity than myricetin in preventing azoxymethane/dextran sulfate sodium - induced ulcerative colitis. Here, we introduce a sensitive quantification method based on ultra performance liquid chromatography-tandem mass spectrometry for the determination of M10-H and M10-Na in Wistar rat plasma. Samples were treated with L - ascorbic acid and phosphate buffer solution to maintain stability and with acetonitrile to remove the proteins in the plasma. The supernatant was separated with BEH C18 column and eluted with ultrapure water and acetonitrile both containing 0.1% formic acid. The detection was performed by a triple quadrupole mass spectrometer with positive electrospray ionization mode in multiple reactive monitoring. This method was validated for the carryover effect, selectivity, accuracy, precision, matrix effect, stability, and recovery. A linear correlation was established between concentration and response by the calibration curves over 10-2000 ng·mL^-1 (r > 0.99). This method was applied to a pharmacokinetic study of intragastrical administration of M10-H and M10-Na in Wistar rats. In addition, the relative bioavailability of M10-H to M10-Na in Wistar rats was 60 ± 19%, calculated by the ratio of area under concentration (AUC) of M10-H to M10-Na after intragastrical administration of a single dose (100 mg·kg^-1 for M10-H and M10-Na, respectively) in Wistar rats.

Identification of the amino acid residue responsible for the myricetin sensitivity of human proton-coupled folate transporter

Human proton-coupled folate transporter (hPCFT/SLC46A1) has recently been found to be inhibited by myricetin by a sustained mechanism, raising a concern that the inhibition might lead to malabsorption of folates in the intestine, where hPCFT works for their epithelial uptake. However, rat PCFT (rPCFT) has more recently been found not to be inhibited by myricetin. Prompted by this finding, we attempted to determine the amino acid residue involved in that by analyses comparing between hPCFT and rPCFT. In the initial analysis, chimeric constructs prepared from hPCFT and rPCFT were examined for myricetin sensitivity to determine the hPCFT segment involved in the sensitivity. Focusing on the thereby determined segment from 83rd to 186th amino acid residue, hPCFT mutants having a designated amino acid residue replaced with its counterpart in rPCFT were prepared for the subsequent analysis. Among them, only G158N-substituted hPCFT was found to be transformed to be insensitive to myricetin and, accordingly, oppositely N158G-substituted rPCFT was transformed to be sensitive to myricetin. These results indicate the critical role of Gly¹⁵⁸ in the myricetin sensitivity of hPCFT. This finding would help advance the elucidation of the mechanism of the myricetin-induced inhibition of hPCFT and manage the potential risk arising from that.