Breast cancer resistance protein (BCRP) and sulfotransferases contribute significantly to the disposition of genistein in mouse intestine

The ABC membrane transporter ABCG2 prevents access of FAAH inhibitor URB937 to the central nervous system

The O-arylcarbamate URB937 is a potent inhibitor of fatty-acid amide hydrolase (FAAH), an intracellular serine hydrolase responsible for the deactivation of the endocannabinoid anandamide. URB937 is unique among FAAH inhibitors in that is actively extruded from the central nervous system (CNS), and therefore increases anandamide levels exclusively in peripheral tissues. Despite its limited distribution, URB937 exhibits marked analgesic properties in rodent models of pain. Pharmacological evidence suggests that the extrusion of URB937 from the CNS may be mediated by the ABC membrane transporter ABCG2 (also called Breast cancer resistance protein, BCRP). In the present study, we show that URB937 is a substrate for both mouse and human orthologues of ABCG2. The relative transport ratios for URB937 in Madin-Darby canine kidney (MDCKII) cells monolayers over-expressing either mouse Abcg2 or human ABCG2 were significantly higher compared to parental monolayers (13.6 and 13.1 vs. 1.5, respectively). Accumulation of the compound in the luminal/apical side was prevented by co-administration of the selective ABCG2 inhibitor, Ko-143. In vivo studies in mice showed that URB937 (25 mg kg(-1)) readily entered the brain and spinal cord of Abcg2-deficient mice following intraperitoneal administration, whereas the same dose of drug remained restricted to peripheral tissues in wild-type mice. By identifying ABCG2 as a transport mechanism responsible for the extrusion of URB937 from the CNS, the present results should facilitate the rational design of novel peripherally restricted FAAH inhibitors.

First-pass metabolism via UDP-glucuronosyltransferase: a barrier to oral bioavailability of phenolics

Glucuronidation mediated by UDP-glucuronosyltransferases (UGTs) is a significant metabolic pathway that facilitates efficient elimination of numerous endobiotics 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.

Validated LC-MS/MS method for the determination of maackiain and its sulfate and glucuronide in blood: application to pharmacokinetic and disposition studies

The purpose of this study was to develop a simultaneous, sensitive and reproducible UPLC-MS/MS method to quantify maackiain and its phase II metabolites, maackiain-sulfate (M-7-S) and maackiain-glucuronide (M-7-G). A Waters BEH C18 column was used with acetonitrile/water as mobile phases. Analysis was performed under negative ionization electrospray mass spectrometer via the multiple reaction monitoring (MRM). The one-step protein precipitation by methanol was used to extract the analytes from plasma. The results showed that the linear response range was 5000-9.75 nM for maackiain, M-7-S, and M-7-G. The lower limit of detection (LLOD) was 4.88 nM for these three analytes. The intra-day variance is less than 12.4% and accuracy is in 85.7-102.0%. The inter-day variance is less than 11.2% and accuracy is in 89.6-122.2%. The analysis was done within 4.0 min. Only 20 μl of blood is needed for the analysis due to the high sensitivity of this method. The validated method was used for pharmacokinetic study in A/J mouse, maackiain Caco-2 cell culture model experiment, and maackiain glucuronidation/sulfation metabolism studies. The applications revealed that this method can be used for maackiain, M-7-S, and M-7-G analysis in both bioequivalent buffer and in blood.