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Toxicity of the antiandrogen flutamide in isolated rat hepatocytes
1Institut National de la Santé et de la Recherche Médicale Unité 24 (INSERM U-24), Hôpital Beaujon, Clichy, France.
Abstract:
The hepatotoxicity of flutamide, an antiandrogen that produces hepatitis in some human recipients, was studied in isolated rat hepatocytes. Flutamide (1 mM) led to the covalent binding of reactive electrophilic metabolites to male rat hepatocyte proteins. It decreased the reduced glutathione (GSH)/glutathione disulfide ratio and total protein thiols. This was associated with an early increase in phosphorylase a activity (a Ca(++)-dependent enzyme) and a decrease in cytoskeleton-associated protein thiols, the formation of plasma membrane blebs, the release of lactate dehydrogenase (LDH) and a loss of cell viability. Both covalent binding and LDH release were decreased by piperonyl butoxide (an inhibitor of cytochrome P450) and increased by dexamethasone pretreatment (which induces cytochrome P450 3A). The toxicity was increased by beta-naphthoflavone (which induces cytochrome P450 1A). Hepatocytes from female rats (which lack cytochrome P450 3A2) exhibited lower covalent binding and lower LDH release. The addition of cystine (a GSH precursor) increased hepatocellular GSH and decreased LDH release in male hepatocytes. The administration of a diet deficient in sulfur-containing amino acids had the opposite effects; it produced toxicity with 100 microM flutamide. Flutamide (50 microM) markedly inhibited respiration (mainly at the level of complex I) in isolated male rat liver mitochondria and flutamide (1 mM) decreased ATP levels in isolated male rat hepatocytes. It was concluded that flutamide is toxic to rat hepatocytes as a result of the cytochrome P450 (3A and also 1A)-mediated formation of electrophilic metabolites, whose damaging effects are further aggravated by the inhibitory effect of flutamide on mitochondrial respiration and ATP formation.
Insights
Flutamide causes liver damage by forming toxic metabolites via cytochrome P450 enzymes. This antiandrogen also impairs mitochondrial function and reduces cellular energy, leading to hepatotoxicity.
Area of Science:
- Hepatology
- Toxicology
- Biochemistry
Background:
- Flutamide is an antiandrogen known to cause hepatitis in humans.
- Understanding the mechanisms of flutamide-induced hepatotoxicity is crucial for patient safety.
Purpose of the Study:
- To investigate the mechanisms underlying flutamide-induced hepatotoxicity in isolated rat hepatocytes.
- To identify the role of cytochrome P450 enzymes and cellular energy metabolism in flutamide toxicity.
Main Methods:
- Isolated rat hepatocytes and liver mitochondria were used to study flutamide's effects.
- Assays included covalent binding, glutathione levels, enzyme activity, lactate dehydrogenase release, mitochondrial respiration, and ATP levels.
Main Results:
- Flutamide induced covalent binding of reactive metabolites to proteins, depleted glutathione, and inhibited mitochondrial respiration (Complex I).
- Toxicity was mediated by cytochrome P450 (CYP) isoforms 3A and 1A, with reduced toxicity in female rats lacking CYP3A2.
- Cystine supplementation reduced toxicity, while sulfur-deficient diets exacerbated it.
Conclusions:
- Flutamide hepatotoxicity results from CYP-mediated formation of electrophilic metabolites.
- Flutamide's inhibition of mitochondrial respiration and ATP production exacerbates cellular damage.
- Metabolic activation by CYP enzymes and cellular defense mechanisms (glutathione) are key factors in flutamide toxicity.