Human superoxide dismutase 1 attenuates quinoneimine metabolite formation from mefenamic acid.

Mefenamic acid (MFA), one of the nonsteroidal anti-inflammatory drugs (NSAIDs), sometimes causes liver injury. Quinoneimines formed by cytochrome P450 (CYP)-mediated oxidation of MFA are considered to be causal metabolites of the toxicity and are detoxified by glutathione conjugation. A previous study reported that NAD(P)H:quinone oxidoreductase 1 (NQO1) can reduce the quinoneimines, but NQO1 is scarcely expressed in the human liver. The purpose is to identify enzyme(s) responsible for the decrease in MFA-quinoneimine formation in the human liver. The formation of MFA-quinoneimine by recombinant CYP1A2 and CYP2C9 was significantly decreased by the addition of human liver cytosol, and the extent of the decrease in the metabolite formed by CYP1A2 was larger than that by CYP2C9. By column chromatography, superoxide dismutase 1 (SOD1) was identified from the human liver cytosol as an enzyme decreasing MFA-quinoneimine formation. Addition of recombinant SOD1 into the reaction mixture decreased the formation of MFA-quinoneimine from MFA by recombinant CYP1A2. By a structure-activity relationship study, we found that SOD1 decreased the formation of quinoneimines from flufenamic acid and tolfenamic acid, but did not affect those produced from acetaminophen, amodiaquine, diclofenac, and lapatinib. Thus, SOD1 may selectively decrease the quinoneimine formation from fenamate-class NSAIDs. To examine whether SOD1 can attenuate cytotoxicity caused by MFA, siRNA for SOD1 was transfected into CYP1A2-overexpressed HepG2 cells. The leakage of lactate dehydrogenase caused by MFA treatment was significantly increased by knockdown of SOD1. In conclusion, we found that SOD1 can serve as a detoxification enzyme for quinoneimines to protect from drug-induced toxicity.

Comprehensive metabolic profiling of Alismatis Rhizoma triterpenes in rats based on characteristic ions and a triterpene database / 药物分析学报

Alismatis Rhizoma(AR)is widely used in Chinese medicine,and its major bioactive components,tri-terpenes,reportedly possess various pharmacological activities.Therefore,it is very important to study the metabolism of triterpenes in vivo.However,the metabolism of AR triterpene extract has not been comprehensively elucidated due to its complex chemical components and metabolic pathways.In this study,an ultra-performance liquid chromatography quadrupole time-of-flight mass spectrometry method,which was based on the characteristic ions from an established database of known triterpenes,was used to analyze the major metabolites in rats following the oral administration of Alismatis Rhizoma extracts(ARE).As a result,a total of 233 constituents,with 85 prototype compounds and 148 metabo-lites,were identified for the first time.Hydrogenation,oxidation,sulfate and glucuronidation conjugation were the major metabolic pathways for triterpenes in AR.In addition,the mutual in vivo transformation of known ARE triterpenes was discovered and confirmed for the first time.Those results provide comprehensive insights into the metabolism of AR in vivo,which will be useful for future studies on its pharmacodynamics and pharmacokinetics.Moreover,this established strategy may be useful in meta-bolic studies of similar compounds.