The inhibitory effect of tannic acid on cytochrome P450 enzymes and NADPH-CYP reductase in rat and human liver microsomes.

Tannic acid has been shown to decrease mutagenicity and/or carcinogenicity of several amine derivatives and polycyclic aromatic hydrocarbons in rodents. The purpose of this study was to evaluate the effect of tannic acid on cytochrome P450 (CYP)-catalyzed oxidations using rat liver microsomes (RLM) and human liver microsomes (HLM) as the enzyme sources. In RLM, tannic acid showed a non-selective inhibitory effect on 7-methoxyresorufin O-demethylation (MROD), 7-ethoxyresorufin O-deethylation (EROD), tolbutamide hydroxylation, p-nitrophenol hydroxylation and testosterone 6beta-hydroxylation activities with IC(50) values ranged from 14.9 to 27.4 microM. In HLM, tannic acid inhibited EROD, MROD and phenacetin O-deethylation activities with IC(50) values ranged from 5.1 to 7.5 microM, and diclofenac 4-hydroxylation, dextromethorphan O-demethylation, chlorzoxazone 6-hydroxylation and testosterone 6beta-hydroxylation with IC(50) values ranged from 20 to 77 microM. In baculovirus-insect cell-expressed human CYP 1A1 and 1A2, the IC(50) values of tannic acid for CYP 1A1- and 1A2-catalyzed EROD activities were 23.1 and 2.3 microM, respectively, indicating that tannic acid preferably inhibited the activity of CYP1A2. Tannic acid inhibited human CYP1A2 non-competitively with a Ki value of 4.8 microM. Tannic acid was also found to inhibit NADPH-CYP reductase in RLM and HLM with IC(50) values of 11.8 and 17.4 microM, respectively. These results suggested that the inhibition of CYP enzyme activities by tannic acid may be partially attributed to its inhibition of NADPH-CYP reductase activity.

Biotransformation of 6-methoxy-3-(3',4',5'-trimethoxy-benzoyl)-1H-indole (BPR0L075), a novel antimicrotubule agent, by mouse, rat, dog, and human liver microsomes.

6-Methoxy-3-(3',4',5'-trimethoxy-benzoyl)-1H-indole (BPR0L075) is a novel synthetic indole compound with microtubule binding activity. Incubation of BPR0L075 with mouse, rat, dog, and human liver microsomes in the presence of NADPH resulted in the formation of six metabolites. Liquid chromatography-tandem mass spectrometry and comparison with the synthetic reference standards identified two metabolites (M1 and M5) as the products derived from hydroxylation on the indole moiety of the molecule. M3 was also identified as a product derived from hydroxylation, but the structure of this metabolite was not identified because of the lack of a reference standard. M2, M4, and M6 were identified as the products derived from O-demethylation. M2, 6-desmethyl-BPR0L075, was the major metabolite formed by the liver microsomes of the four species. No qualitative species difference in the metabolism of BPR0L075 was observed. There was quantitative species difference in the metabolism of BPR0L075 among the four species. Whereas mouse and rat liver microsomes metabolized BPR0L075 predominantly via O-demethylation, dog liver microsomes metabolized BPR0L075 by O-demethylation and hydroxylation to about the same extent. The rank order of intrinsic clearance rates for the conversion of BPR0L075 to 6-desmethyl-BPR0L075 was mouse > rat > human > dog. Incubation of BPR0L075 with baculovirus-insect cell-expressed human cytochrome P450 (P450) isozymes showed that CYP1A2, 2C9, 2C19, 2D6, 2E1, and 3A4 all catalyzed the O-demethylation and hydroxylation of BPR0L075 but to a different degree. Among the six P450 isozymes tested, CYP1A2 and 2D6 were most active on catalyzing the metabolism of BPR0L075. CYP1A2 catalyzed mainly the formation of M1, M2, and M3. M2 was the predominant metabolite formed by CYP2D6.

Development and validation of a liquid chromatography-tandem mass spectrometry for the determination of BPR0L075, a novel antimicrotuble agent, in rat plasma: application to a pharmacokinetic study.

A rapid and sensitive liquid chromatography-tandem mass spectrometric method (LC-MS/MS) had been developed and validated to determine the concentrations of BPR0L075 in rat plasma. After a simple protein precipitation of plasma samples by acetonitrile, BPR0L075 was analyzed on a C(8) column at a flow rate of 0.5 mL/min. The mobile phase consisted of a mixture of 10 mM ammonium acetate containing 0.1% formic acid and acetonitrile (20:80, v/v). Both BPR0L075 (analyte) and the internal standard (BPR0L092) were determined using electro-spray ionization and the MS data acquisition was via multiple reactions monitoring (MRM) in positive scanning model. The MS/MS ion transitions monitored are m/z 342.2/195.2 and 312.5/165.2 for BPR0L075 and BPR0L092, respectively. The low limit of quantitation was 0.5 ng/mL. Each plasma sample was chromatographed within 5 min. The method was validated with respect to linearity, accuracy, precision, recovery, and stability. A good linear relationship was observed over the concentration range of 0.5-1000 ng/mL (r>0.9994). Absolute recoveries ranged from 63.45 to 68.34% in plasma at the concentrations of 2, 40, 400, and 800 ng/mL. The intra- and inter-day accuracy ranged from 92.04 to 111.80%. Intra- and inter-day relative standard deviations were 1.08-3.29% and 1.96-5.46%, respectively. This developed and validated assay method had been successfully applied to a pharmacokinetic study after intravenous injection of BPR0L075 in rats at a dose of 5mg/kg.

The inhibitory effect of polyunsaturated fatty acids on human CYP enzymes.

The inhibitory effect of saturated fatty acids (SFAs): palmitic acid (PA), stearic acid (SA) and polyunsaturated fatty acids (PUFAs): linoleic acid (LA), linolenic acid (LN), arachidonic acid (AA), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) on six human drug-metabolizing enzymes (CYP1A2, 2C9, 2C19, 2D6, 2E1 and 3A4) was studied. Supersomes from baculovirus-expressing single isoforms were used as the enzyme source. Phenacetin O-deethylation (CYP1A2), diclofenac 4-hydroxylation (CYP2C9), mephenytoin 4-hydroxylation (CYP2C19), dextromethorphan O-demethylation (CYP2D6), chlorzoxazone 6-hydroxylation (CYP2E1) and midazolam 1-hydroxylation (CYP3A4) were used as the probes. Results show that all the five examined PUFAs competitively inhibited CYP2C9- and CYP2C19-catalyzed metabolic reactions, with Ki values ranging from 1.7 to 4.7 microM and 2.3 to 7.4 microM, respectively. Among these, AA, EPA and DHA tended to have greater inhibitory potencies (lower IC(50) and Ki values) than LA and LN. In addition, these five PUFAs also competitively inhibited the metabolic reactions catalyzed by CYP1A2, 2E1 and 3A4 to a lesser extent (Ki values>10 microM). On the other hand, palmitic and stearic acids, the saturated fatty acids, had no inhibitory effect on the activities of six human CYP isozymes at concentrations up to 200 microM. Incubation of PUFAs with CYP2C9 or CYP2C19 in the presence of NADPH resulted in the decrease of PUFA concentrations in the incubation mixtures. These results indicate that the PUFAs are potent inhibitors as well as the substrates of CYP2C9 and CYP2C19.

Novel indole-based peroxisome proliferator-activated receptor agonists: design, SAR, structural biology, and biological activities.

The synthesis and structure-activity relationship studies of novel indole derivatives as peroxisome proliferator-activated receptor (PPAR) agonists are reported. Indole, a drug-like scaffold, was studied as a core skeleton for the acidic head part of PPAR agonists. The structural features (acidic head, substitution on indole, and linker) were optimized first, by keeping benzisoxazole as the tail part, based on binding and functional activity at PPARgamma protein. The variations in the tail part, by introducing various heteroaromatic ring systems, were then studied. In vitro evaluation led to identification of a novel series of indole compounds with a benzisoxazole tail as potent PPAR agonists with the lead compound 14 (BPR1H036) displaying an excellent pharmacokinetic profile in BALB/c mice and an efficacious glucose lowering activity in KKA(y) mice. Structural biology studies of 14 showed that the indole ring contributes strong hydrophobic interactions with PPARgamma and could be an important moiety for the binding to the protein.

Multiple pathways are involved in the oral absorption of BMS-262084, a tryptase inhibitor, in rats: role of paracellular transport, binding to trypsin, and P-glycoprotein efflux.

BMS-262084 is a potent and selective beta-lactam tryptase inhibitor with therapeutic potential for treating asthma. The oral bioavailability of BMS-262084 was low in rats (4% at a dose of 0.5 mg/kg) due to poor absorption. BMS-262084 was excreted mainly unchanged in the urine, suggesting minimal metabolism in rats. The objective of this study was to investigate the mechanisms of oral absorption of BMS-262084 in rats. Modulation of intestinal tight junctions, binding to trypsin, and involvement of the intestinal dipeptide transport system and P-glycoprotein (P-gp) in the absorption of BMS-262084 were examined. Coadministration of BMS-262084 with SQ-29852, a substrate of the intestinal dipeptide transport system, did not change the oral absorption of BMS-262084. An increase in the dose of BMS-262084 from 0.5 to 50 mg/kg resulted in a 3.7-fold increase in its oral absorption. Inulin absorption was enhanced upon coadministration with BMS-262084, suggesting the opening of tight junctions in the intestinal epithelium. Coadministration of aprotinin, a trypsin inhibitor, increased the oral absorption of BMS-262084 several fold. In vitro, using Caco-2 cells, BMS-262084 appeared to be a P-gp substrate, with an efflux ratio of 14. These results suggest that absorption of BMS-262084 is mediated by several concurrent mechanisms. At higher doses of BMS-262084, increased absorption may be primarily due to opening of tight junctions in the intestinal epithelium and consequent absorption via the paracellular pathway, while at lower doses, binding to trypsin may contribute to limiting its absorption. P-gp efflux may also play a role in influencing the absorption of BMS-262084. The intestinal dipeptide transporter system does not appear to be involved in the absorption of BMS-262084.

Dual angiotensin II and endothelin A receptor antagonists: synthesis of 2'-substituted N-3-isoxazolyl biphenylsulfonamides with improved potency and pharmacokinetics.

In a previous report we demonstrated that merging together key structural elements present in an AT(1) receptor antagonist (1, irbesartan) with key structural elements in a biphenylsulfonamide ET(A) receptor antagonist (2) followed by additional optimization provided compound 3 as a dual-action receptor antagonist (DARA), which potently blocked both AT(1) and ET(A) receptors. Described herein are our efforts directed toward improving both the pharmacokinetic profile as well as the AT(1) and ET(A) receptor potency of 3. Our efforts centered on modifying the 2'-side chain of 3 and examining the isoxazolylsulfonamide moiety in 3. This effort resulted in the discovery of 7 as a highly potent second-generation DARA. Compound 7 also showed substantially improved pharmacokinetic properties compared to 3. In rats, DARA 7 reduced blood pressure elevations caused by intravenous infusion of Ang II or big ET-1 to a greater extent and with longer duration than DARA 3 or AT(1) or ET(A) receptor antagonists alone. Compound 7 clearly demonstrated superiority over irbesartan (an AT(1) receptor antagonist) in the normal SHR model of hypertension in a dose-dependent manner, demonstrating the synergy of AT(1) and ET(A) receptor blockade in a single molecule.