Chemical and Enzymatic Transformations of Nimesulide to GSH Conjugates through Reductive and Oxidative Mechanisms

Nimesulide (NIM) is a nonsteroidal anti-inflammatory drug, and clinical treatment with NIM has been associated with severe hepatotoxicity. The bioactivation of nitro-reduced NIM (NIM-NH₂), a major NIM metabolite, has been thought to be responsible for the hepatotoxicity of NIM. However, we found that NIM-NH₂ did not induce toxic effects in primary rat hepatocytes. This study aimed to investigate other bioactivation pathways of NIM and evaluate their association with hepatotoxicity. After incubating NIM with NADPH- and GSH-supplemented human or rat liver microsomes, we identified two types of GSH conjugates: one was derived from the attachment of GSH to NIM-NH₂ (NIM-NH₂-GSH) and the other one was derived from a quinone-imine intermediate (NIM-OH-GSH). NIM-NH₂-GSH was generated not only by the oxidative activation of NIM-NH₂ but also from the reductive activation of NIM. Both NADPH and GSH could act as reducing agents. Moreover, aldehyde oxidase also participated in the reductive activation of NIM. NIM-OH-GSH was generated mainly from NIM via epoxidation with CYP1A2 as the main catalyzing enzyme. NIM was toxic to both primary human and rat hepatocytes, with IC₅₀ values of 213 and 40 μM, respectively. Inhibition of the oxidative and reductive activation of NIM by the nonspecific CYP inhibitor 1-aminobenzotriazole and selective aldehyde oxidase inhibitor estradiol did not protect the cells from NIM-mediated toxicity. Moreover, pretreating cells with l-buthionine-sulfoximine (a GSH depletor) did not affect the cytotoxicity of NIM. These results suggested that oxidative and reductive activation of NIM did not cause the hepatotoxicity and that the parent drug concentration was associated with the cytotoxicity

Pulmonary Toxicity and Metabolic Activation of Tetrandrine in CD-1 Mice

Tetrandrine, a bisbenzylisoquinoline alkaloid, has demonstrated promising pharmacologic activities. The alkaloid has a great potential for clinical use, so a careful, thorough toxicity evaluation of the alkaloid is required. In the present study, 24 h acute toxicity of tetrandrine was evaluated in CD-1 mice. Single intraperitoneal doses of tetrandrine at 150 mg (0.24 mmol)/kg were found to cause alveolar hemorrhage and over 3-fold elevation of lactate dehydrogenase activity in bronchoalveolar lavage fluids. Ethidium-based staining showed loss of membrane integrity in significant numbers of cells in the lungs of the animals treated with the same doses of tetrandrine. As much as 60% reduction in cell viability was observed after 24 h of exposure to tetrandrine at 40 μM in human lung cell lines NL-20 and WI-38. Ketoconazole, an inhibitor of P450 3A, showed a protective effect on the pulmonary injury in mice given tetrandrine. A glutathione (GSH) conjugate derived from <i>O</i>-demethylated tetrandrine was detected in incubations of tetrandrine with NADPH- and GSH-supplemented human liver and mouse lung microsomes. The electrophilic metabolite trapped by GSH is considered to be a quinone methide derivative. The formation of the metabolite reactive to GSH was found to require the presence of NADPH. The coincubation of ketoconazole suppressed the generation of the GSH conjugate. Tetrandrine was incubated with a selection of recombinant human cytochrome P450 enzymes, and only P450s 3A4 and 3A5 were responsible for the production of the reactive metabolite. The results implicate a possible correlation between the formation of the quinone methide metabolite of tetrandrine and the pulmonary toxicity induced by tetrandrine

Impact of curcumin on the pharmacokinetics of rosuvastatin in rats and dogs based on the conjugated metabolites

<p>1. Plasma concentrations of curcumin-O-glucuronide (COG) and curcumin-O-sulfate (COS) significantly increased after Sprague-Dawley rats dealt with the Oatp inhibitor rifampicin, with the <i>C</i>_max ascending 2.9 and 6.7 times, and the AUC_0–∞ ascending 4.4 and 10.8 times, respectively. When pretreated with the Oat inhibitor probenecid, the <i>C</i>_max increased 4.4 and 20 times, and the AUC_0–∞ increased 3.2 and 13.9 times, respectively. The results suggested that COG and COS may be the substrates of Oatp and Oat.</p> <p>2. The accumulation of curcumin significantly increased in organic anion transporting polypeptide (OATP)- and organic anion transporter (OAT)-transfected human embryonic kidney (HEK) 293 systems, which suggested that curcumin was a substrate of OATP1B1, OATP1B3, OATP2B1, OAT1, and OAT3; and COG was a substrate of OATP1B1, OATP1B3, and OAT3.</p> <p>3. Inhibition study using rosuvastatin as the substrate in OATP1B1- and OATP1B3-transfected cells indicated that curcumin was an OATP1B1 and 1B3 inhibitor, with IC₅₀ at 5.19 ± 0.05 and 3.68 ± 0.05 μM, respectively; the data for COG were 1.04 ± 0.01 and 1.08 ± 0.02 μM, respectively. COS was speculated to be an inhibitor of hepatic OATP1B1 as calculated using the ADMET Predictor.</p> <p>4. COG and COS are substrates and inhibitors of OATP/Oatp. Co-administration of curcumin significantly increased rosuvastatin concentration in rat and dog plasma.</p

Aldehyde Oxidase Mediated Metabolism in Drug-like Molecules: A Combined Computational and Experimental Study

Aldehyde oxidase (AOX) is an important drug-metabolizing enzyme. However, the current in vitro models for evaluating AOX metabolism are sometimes misleading, and preclinical animal models generally fail to predict human AOX-mediated metabolism. In this study, we report a combined computational and experimental investigation of drug-like molecules that are potential aldehyde oxidase substrates, of which multiple sites of metabolism (SOMs) mediated by AOX and their preferences for the reaction can be unambiguously identified. In addition, the proposed strategy was used to evaluate the metabolism of newly designed c-Met inhibitors, and a success switch-off of AOX metabolism was observed. Overall, this study provide useful information to guide lead optimization and drug discovery based on AOX-mediated metabolism