Dapagliflozin, administered to patients in once-daily oral doses, is a sodium-glucose cotransporter 2 (SGLT2) inhibitor that blocks the reabsorption of glucose from urine into the blood. This 14-day study randomized patients with type 2 diabetes mellitus (T2DM) to four treatment groups receiving daily oral doses of 5-, 25-, or 100-mg doses of dapagliflozin or placebo, in order to evaluate glucosuria and glycemic parameters. Significant reductions in fasting serum glucose (FSG) were observed on day 2 with 100 mg dapagliflozin (-9.3%, P < 0.001), and dose-dependent reductions were observed on day 13 with the 5-mg (-11.7%; P < 0.05), 25-mg (-13.3%; P < 0.05), and 100-mg (-21.8%; P < 0.0001) doses as compared with placebo. Significant improvements in oral glucose tolerance test (OGTT) were observed with all doses on days 2 and 13 (P < 0.001 as compared with placebo). On day 14, urine glucose values were 36.6, 70.1, and 69.9 g/day for the 5-, 25-, and 100-mg doses (as compared with no change for placebo), which were slightly lower than those on day 1. This was attributed to the decrease in filtered glucose load following improved glycemic control. Dapagliflozin produced dose-dependent increases in glucosuria and clinically meaningful changes in glycemic parameters in T2DM patients.

Dapagliflozin selectively inhibits renal glucose reabsorption by inhibiting sodium-glucose cotransporter-2 (SGLT2). It was developed as an insulin-independent treatment approach for type 2 diabetes mellitus (T2DM). The safety, tolerability, pharmacokinetics, and pharmacodynamics of the drug were evaluated in single-ascending-dose (SAD; 2.5-500 mg) and multiple-ascending-dose (MAD; 2.5-100 mg daily for 14 days) studies in healthy subjects. Dapagliflozin exhibited dose-proportional plasma concentrations with a half-life of approximately 17 h. The amount of glucosuria was also dose-dependent. Cumulative amounts of glucose excreted on day 1, relating to doses from 2.5-100 mg (MAD), ranged from 18 to 62 g; day 14 values were comparable to day 1 values, with no apparent changes in glycemic parameters. Doses of approximately 20-50 mg provided close-to-maximal SGLT2 inhibition for at least 24 h. Dapagliflozin demonstrates pharmacokinetic (PK) characteristics and dose-dependent glucosuria that are sustained over 24 h, which indicates that it is suitable for administration in once-daily doses and suggests that further investigation of its efficacy in T2DM patients is warranted.

Sister of P-glycoprotein (SPGP) is the major hepatic bile salt export pump (BSEP). BSEP/SPGP expression varies dramatically among human livers. The potency and hierarchy of bile acids as ligands for the farnesyl/ bile acid receptor (FXR/BAR) paralleled their ability to induce BSEP in human hepatocyte cultures. FXR:RXR heterodimers bound to IR1 elements and enhanced bile acid transcriptional activation of the mouse and human BSEP/SPGP promoters. In FXR/BAR nullizygous mice, which have dramatically reduced BSEP/SPGP levels, hepatic CYP3A11 and CYP2B10 were strongly but unexpectedly induced. Notably, the rank order of bile acids as CYP3A4 inducers and activators of pregnane X receptor/steroid and xenobiotic receptor (PXR/SXR) closely paralleled each other but was markedly different from their hierarchy and potency as inducers of BSEP in human hepatocytes. Moreover, the hepatoprotective bile acid ursodeoxycholic acid, which reverses hydrophobic bile acid hepatotoxicity, activates PXR and efficaciously induces CYP3A4 (a bile-metabolizing enzyme) in primary human hepatocytes thus providing one mechanism for its hepatoprotection. Because serum and urinary bile acids increased in FXR/BAR ؊/؊ mice, we evaluated hepatic transporters for compensatory changes that might circumvent the profound decrease in BSEP/SPGP. We found weak MRP3 up-regulation. In contrast, MRP4 was substantially increased in the FXR/ BAR nullizygous mice and was further elevated by cholic acid. Thus, enhanced hepatocellular concentrations of bile acids, due to the down-regulation of BSEP/SPGPmediated efflux in FXR nullizygous mice, result in an alternate but apparent compensatory up-regulation of CYP3A, CYP2B, and some ABC transporters that is consistent with activation of PXR/SXR by bile acids.

ABSTRACT:(2S,3R,4R,5S,6R)-2-(3-(4-Ethoxybenzyl)-4-chlorophenyl)-6-hydroxymethyl-tetrahydro-2H-pyran-3,4,5-triol (dapagliflozin; BMS-512148) is a potent sodium-glucose cotransporter type II inhibitor in animals and humans and is currently under development for the treatment of type 2 diabetes. The preclinical characterization of dapagliflozin, to allow compound selection and prediction of pharmacological and dispositional behavior in the clinic, involved Caco-2 cell permeability studies, cytochrome P450 (P450) inhibition and induction studies, P450 reaction phenotyping, metabolite identification in hepatocytes, and pharmacokinetics in rats, dogs, and monkeys. Dapagliflozin was found to have good permeability across Caco-2 cell membranes. It was found to be a substrate for P-glycoprotein (P-gp) but not a significant P-gp inhibitor. Dapagliflozin was not found to be an inhibitor or an inducer of human P450 enzymes. The in vitro metabolic profiles of dapagliflozin after incubation with hepatocytes from mice, rats, dogs, monkeys, and humans were qualitatively similar. Rat hepatocyte incubations showed the highest turnover, and dapagliflozin was most stable in human hepatocytes. Prominent in vitro metabolic pathways observed were glucuronidation, hydroxylation, and O-deethylation. Pharmacokinetic parameters for dapagliflozin in preclinical species revealed a compound with adequate oral exposure, clearance, and elimination half-life, consistent with the potential for single daily dosing in humans. The pharmacokinetics in humans after a single dose of 50 mg of [ 14 C]dapagliflozin showed good exposure, low clearance, adequate half-life, and no metabolites with significant pharmacological activity or toxicological concern.

ABSTRACT:St. John's wort extract (SJW) (Hypericum perforatum L.) is among the most commonly used herbal medications in the United States. The predominance of clinical reports indicates that SJW increases the activity of cytochrome P450 3A4 (CYP3A4) enzyme and reduces plasma concentrations of certain drugs. Although the inductive effect of SJW on CYP3A4 is clear, other reports indicate that SJW constituents may have, to a small degree, some enzyme inhibitory effects. Therefore, we sought to study the induction and inhibition effects of the constituents of SJW on CYP3A4 in the human hepatocyte model. Moreover, most research has focused on the induction of CYP3A4 by SJW with little attention paid to other prominent drug-metabolizing enzymes such as CYP1A2, CYP2C9, and CYP2D6. To examine the effects of SJW on CYP1A2, CYP2C9, CYP2D6, as well as CYP3A4, hepatocytes were exposed to hyperforin and hypericin, the primary constituents of SJW extract. Hepatocytes treated with hypericin or hyperforin were exposed to probe substrates to determine enzyme activity and protein and RNA harvested. Hyperforin treatment resulted in significant increases in mRNA, protein, and activity of CYP3A4 and CYP2C9, but had no effect on CYP1A2 or CYP2D6. Acute administration of hyperforin at 5 and 10 M 1 h before and along with probe substrate inhibited CYP3A4 activity. Hypericin had no effect on any of the enzymes tested. These results demonstrate that with chronic exposure, the inductive effect of SJW on drug-metabolizing enzymes predominates, and human hepatocyte cultures are a versatile in vitro tool for screening the effect of herbal products on cytochrome P450 enzymes.In 2002, sales of botanical supplements in the United States reached nearly $293 million dollars. St. John's wort accounted for 15 million U.S. dollars in sales, making it the fourth highest grossing botanical supplement (Blumenthal, 2003). Several clinical studies have demonstrated the effectiveness of St. John's wort compared with conventional therapy in the treatment of mild to moderate depression (Linde et al., 1996;Wheatley, 1997).Marketed St. John's wort, an extract of the flowering portion of the plant Hypericum perforatum L., is a mixture of a number of biologically active, complex compounds. At 0.3 mg per capsule, the naphthodianthrone hypericin is used as a means of standardization of the marketed product. The phloroglucinol hyperforin, the most plentiful lipophilic compound in the extract, is a potent reuptake inhibitor of serotonin, norepinephrine, and dopamine (Muller et al., 1998).Several recent reports have documented decreased blood/plasma levels of cytochrome P450 3A4 (CYP3A4) substrates, such as indinavir and cyclosporin A, in patients concomitantly taking St. John's wort (Piscitelli et al., 2000;Ahmed et al., 2001). Similar observations have been documented for digoxin, a substrate of the intestinal transporter P-glycoprotein (P-gp 4 ). Additional in vivo evidence has demonstrated that St. John's wort increased CYP3A4 and P-gp protein levels in rats (Dur...

No abstract

ABSTRACT:The effects of green tea compounds on the metabolism of irinotecan have never been investigated. We aimed to study whether catechins [ (ECG), and 44% (EGC) of the hepatocyte preparations. Phenobarbital increased the formation of SN-38G in 100% of the same hepatocyte preparations. In Hep G2 cells, no increase in SN-38G formation was observed. With the exception of ECG in one liver, catechins did not increase UGT1A1 mRNA levels. NPC production was also significantly increased in 40% of the hepatocyte preparations for each catechin. However, the production of 6␤-hydroxytestosterone remained unaffected in other hepatocyte preparations. At pharmacologically relevant concentrations, catechins are unlikely to inhibit the formation of irinotecan inactive metabolites when administered concomitantly. The induction effect of catechins on UGT1A1 seems to be modest and highly variable. Catechins do not induce CYP3A4 activity. The effect of acute and prolonged use of green tea on the pharmacokinetics of irinotecan in patients remains to be evaluated.

Background and Purpose: St. John's wort is a commonly used herbal medication that increases cytochrome P450 3A (CYP3A) activity. Because docetaxel is inactivated by CYP3A, we studied the effects of the St. John's wort constituent hyperforin on docetaxel metabolism in a human hepatocyte model. Experimental Design: Hepatocytes, isolated from three donor livers, were exposed to hyperforin (0.1, 0.5, or 1.5 Amol/L) or rifampin (10 Amol/L) for 48 hours. After 48 hours, hyperforin-or rifampin-containing medium was replaced with medium containing 100 Amol/L docetaxel. After 1 hour, docetaxel metabolism was characterized by liquid chromatography-tandem mass spectrometry. Subsequent incubations characterized the specific cytochrome P450s that produced the docetaxel metabolites observed in hepatocyte incubations. Results: Rifampin induced docetaxel metabolism 6.8-to 32-fold above docetaxel metabolism in control cultures. Hyperforin induced docetaxel metabolism in all three hepatocyte preparations. Hyperforin induction was dose-dependent and, at maximum, was 2.6-to 7-fold greater than that in controls. Docetaxel metabolites identified in rifampin-and hyperforin-treated hepatocyte preparations included the previously described tert-butyl^hydroxylated metabolite and two previously unidentified metabolites involving hydroxylation on the baccatin ring. CYP3A4 produced the tert-butyl^hydroxylated metabolite and the two ring-hydroxylated metabolites. CYP2C8 produced one of the newly described ring-hydroxylated metabolites. Conclusions: Exposure to the St. John's wort constituent hyperforin induces docetaxel metabolism in vitro.This implies that subtherapeutic docetaxel concentrations may result when docetaxel is administered to patients using St. John's wort on a chronic basis. The results also show induction of previously undescribed metabolic pathways for docetaxel, one of which may be analogous to the known 6-a-hydroxylation of paclitaxel by CYP2C8.