RESUMO
The inhibitory effects of flavonoids on the human cytochrome P450 1A2 (CYP1A2) were examined. Among flavonoids tested, galangin, kaempferol, chrysin, and apigenin were potent inhibitors. Although apigenin belonging to flavones and genistein belonging to isoflavones are similar in the chemical structures, the inhibitory potencies for CYP1A2 were distinguished markedly between these two flavonoids. In computer-docking simulation, apigenin interacted with the same mode of cocrystallized alpha-naphthoflavone in the active site of CYP1A2, and then the B ring of apigenin was placed close to the heme iron of the enzyme with a single orientation. In contrast, the docked genistein conformation showed two different binding modes, and the A ring of genistein was oriented to the heme iron of CYP1A2. Furthermore, the binding free energy of apigenin was lower than that of genistein. These results demonstrate a possible mechanism that causes the differential inhibitory potencies of apigenin and genistein for CYP1A2.
Assuntos
Apigenina/química , Inibidores do Citocromo P-450 CYP1A2 , Citocromo P-450 CYP1A2/química , Genisteína/química , Modelos Moleculares , Anticarcinógenos/farmacologia , Apigenina/farmacologia , Citocromo P-450 CYP1A2/metabolismo , Inibidores Enzimáticos/farmacologia , Genisteína/farmacologia , Humanos , Estrutura Terciária de ProteínaRESUMO
The inhibitory effects of diesel exhaust components and flavonoids on 20alpha-hydroxysteroid dehydrogenase (20alpha-HSD) activity were examined in cytosolic fractions from the liver, kidney and lung of male mice. 9,10-Phenanthrenequinone (9,10-PQ) and 1,2-naphthoquinone (1,2-NQ), which are contained in diesel exhaust particles (DEPs), potently inhibited 20alpha-HSD activity in liver cytosol. 9,10-PQ also inhibited the enzyme activity in lung cytosol. However, 20alpha-HSD activity in kidney cytosol was little inhibited by 9,10-PQ or 1,2-NQ. Flavonoids such as quercetin, fisetin and kaempferol exhibited high inhibitory potencies for 20alpha-HSD activity in liver cytosol, whereas these flavonoids were poor inhibitors for the enzyme activity in kidney cytosol. It is likely that several diesel exhaust components and flavonoids augment the signaling of progesterone in the liver cells, by potently inhibiting 20alpha-HSD activity in mouse liver cytosol. The possibility that there are distinct enzymes catalyzing 20alpha-HSD activity in the non-reproductive tissues of male mice is also discussed.
Assuntos
20-alfa-Hidroxiesteroide Desidrogenase/química , Citosol/enzimologia , Flavonoides/química , Fígado/enzimologia , Emissões de Veículos , 20-alfa-Hidroxiesteroide Desidrogenase/metabolismo , Animais , Inibidores Enzimáticos/química , Flavonoides/farmacologia , Flavonóis , Concentração de Íons de Hidrogênio , Quempferóis/farmacologia , Masculino , Camundongos , Modelos Químicos , Quercetina/farmacologia , Distribuição TecidualRESUMO
The effects of flavonoids and quinones on NADPH- and NADH-dependent 20alpha-hydroxysteroid dehydrogenase (20alpha-HSD) activities were examined in cytosolic fractions from the liver and kidney of mice. Judging from the data for the inhibition of NADPH- and NADH-dependent 20alpha-HSD activities by flavonoids and quinones, enzyme catalyzing renal NADPH-dependent 20alpha-HSD activity was found to be distinct from enzyme(s) catalyzing hepatic NADPH- and NADH-dependent 20alpha-HSD activities. Sulfobromophthalein (SBP) had little ability to inhibit hepatic NADPH-dependent 20alpha-HSD activity and bromophenol blue (BPB) exhibited a weak activation against the enzyme activity, whereas SBP and BPB were potent and moderate inhibitors, respectively, of hepatic NADH-dependent 20alpha-HSD activity. Thus, enzyme catalyzing hepatic NADPH-dependent 20alpha-HSD activity appeared to be distinct from enzyme catalyzing hepatic NADH-dependent 20alpha-HSD activity. The data for the pH profiles of hepatic NADPH- and NADH-dependent 20alpha-HSD activities also led us to the conclusion. Based on these results, we propose the possibility that several distinct enzymes catalyze NADPH- and NADH-dependent 20alpha-HSD activities in cytosolic fractions from the liver and kidney of mice.
