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Inhibition of mitochondrial function in isolated rate liver mitochondria by azole antifungals
1Department of Pharmacology/Toxicology, University of Texas at Austin 78712-1074, USA.
Abstract:
Ketoconazole is an imidazole oral antifungal agent with a broad spectrum of activity. Ketoconazole has been reported to cause liver damage, but the mechanism is unknown. However, ketoconazole and a related rug, miconazole, have been shown to have inhibitory effects on oxidative phosphorylation in fungi. Fluconazole, another orally administered antifungal azole, has also been reported to cause liver damage despite its supposedly low toxicity profile. The primary objective of this study was to evaluate the metabolic integrity of adult rat liver mitochondria after exposure to ketoconazole, miconazole, fluconazole, and the deacetylated metabolite of ketoconazole by measuring ADP-dependent oxygen uptake polarographically and succinate dehydrogenase activity spectrophotometrically. Ketoconazole, N-deacetyl ketoconazole, and miconazole inhibited glutamate-malate oxidation in a dose-dependent manner such that the 50% inhibitory concentration (I50) was 32,300, and 110 microM, respectively. In addition, the effect of ketoconazole, miconazole, and fluconazole on phosphorylation coupled to the oxidation of pyruvate/malate, ornithine/malate, arginine/malate, and succinate was evaluated. The results demonstrated that ketoconazole and miconazole produced a dose-dependent inhibition of NADH oxidase in which ketoconazole was the most potent inhibitor. Fluconazole had minimal inhibitory effects on NADH oxidase and succinate dehydrogenase, whereas higher concentrations of ketoconazole were required to inhibit the activity of succinate dehydrogenase. N-deacetylated ketoconazole inhibited succinate dehydrogenase with an I50 of 350 microM. In addition, the reduction of ferricyanide by succinate catalyzed by succinate dehydrogenase demonstrated that ketoconazole caused a dose-dependent inhibition of succinate activity (I50 of 74 microM). In summary, ketoconazole appears to be the more potent mitochondrial inhibitor of the azoles studied; complex I of the respiratory chain is the apparent target of the drug's action.
Insights
Ketoconazole and miconazole, antifungal azoles, inhibit mitochondrial respiration, particularly Complex I. This study investigated their impact on liver mitochondria, revealing ketoconazole as a potent inhibitor.
Area of Science:
- Biochemistry
- Pharmacology
- Toxicology
Background:
- Antifungal azoles like ketoconazole can cause liver damage through unknown mechanisms.
- Previous research suggests ketoconazole and miconazole inhibit fungal oxidative phosphorylation.
- Fluconazole, another azole, also shows potential for hepatotoxicity despite a low toxicity profile.
Purpose of the Study:
- To assess the impact of ketoconazole, miconazole, fluconazole, and a ketoconazole metabolite on adult rat liver mitochondrial function.
- To investigate the inhibitory effects of these azoles on oxidative phosphorylation and enzyme activity.
Main Methods:
- Mitochondrial metabolic integrity was evaluated using polarographic measurement of ADP-dependent oxygen uptake.
- Succinate dehydrogenase activity was assessed spectrophotometrically.
- Inhibition kinetics (I50 values) were determined for various substrates and enzyme activities.
Main Results:
- Ketoconazole, N-deacetyl ketoconazole, and miconazole dose-dependently inhibited glutamate-malate oxidation.
- Ketoconazole and miconazole significantly inhibited NADH oxidase, with ketoconazole being more potent.
- Fluconazole exhibited minimal effects on NADH oxidase and succinate dehydrogenase, unlike ketoconazole.
Conclusions:
- Ketoconazole is a potent inhibitor of mitochondrial respiration, primarily targeting Complex I of the respiratory chain.
- The study elucidates a potential mechanism for ketoconazole-induced liver damage via mitochondrial dysfunction.
- Understanding these mechanisms is crucial for evaluating the safety of antifungal azoles.