Daniel Fau

Hepatotoxicity of germander in mice

BACKGROUND/AIMS An epidemic of hepatitis due to germander teas or capsules recently occurred in France. The aim of the present study was to show the hepatotoxicity of germander and determine its mechanism in mice. METHODS A germander tea lyophilisate and a fraction that isolated and concentrated 10-fold the furano neo-clerodane diterpenoids of the lyophilisate were prepared. RESULTS (1) Intragastric administration of the lyophilisate (1.25 g/kg) or the furano neo-clerodane diterpenoid fraction (0.125 mg/kg) produced similar midzonal liver cell necrosis at 24 hours in mice. (2) Toxicity was prevented by pretreatment with a single dose of troleandomycin (a specific inhibitor of cytochromes P4503A) and enhanced by pretreatment with dexamethasone or clotrimazole (two inducers of cytochromes P4503A). (3) Toxicity was attenuated by pretreatment with butylated hydroxyanisole or clofibrate (two inducers of microsomal epoxide hydrolase) and markedly increased by phorone-induced glutathione depletion. CONCLUSIONS We conclude that germander constituents (probably its furano neo-clerodane diterpenoids) are transformed by cytochromes P450 (particularly P4503A) into hepatotoxic metabolites. The metabolites (probably epoxides) are partly inactivated by glutathione and probably epoxide hydrolase.

Mechanisms for experimental buprenorphine hepatotoxicity: major role of mitochondrial dysfunction versus metabolic activation

BACKGROUND/AIMS Although sublingual buprenorphine is safely used as a substitution drug in heroin addicts, large overdoses or intravenous misuse may cause hepatitis. Buprenorphine is N-dealkylated to norbuprenorphine by CYP3A. METHODS We investigated the mitochondrial effects and metabolic activation of buprenorphine in isolated rat liver mitochondria and microsomes, and its toxicity in isolated rat hepatocytes and treated mice. RESULTS Whereas norbuprenorphine had few mitochondrial effects, buprenorphine (25-200 microM) concentrated in mitochondria, collapsed the membrane potential, inhibited beta-oxidation, and both uncoupled and inhibited respiration in rat liver mitochondria. Both buprenorphine and norbuprenorphine (200 microM) underwent CYP3A-mediated covalent binding to rat liver microsomal proteins and both caused moderate glutathione depletion and increased cell calcium in isolated rat hepatocytes, but only buprenorphine also depleted cell adenosine triphosphate (ATP) and caused necrotic cell death. Four hours after buprenorphine administration to mice (100 nmol/g body weight), hepatic glutathione was unchanged, while ATP was decreased and serum transaminase increased. This transaminase increase was attenuated by a CYP3A inducer and aggravated by a CYP3A inhibitor. CONCLUSIONS Both buprenorphine and norbuprenorphine undergo metabolic activation, but only buprenorphine impairs mitochondrial respiration and ATP formation. The hepatotoxicity of high concentrations or doses of buprenorphine is mainly related to its mitochondrial effects.

Generation of free radicals during the reductive metabolism of nilutamide by lung microsomes: possible role in the development of lung lesions in patients treated with this anti-androgen.

The pulmonary metabolism of nilutamide, a nitroaromatic anti-androgen drug leading to pulmonary lesions in a few recipients, has been investigated in rats. Incubation of nilutamide (1 mM) with rat lung microsomes and NADPH under anaerobic conditions led to the formation of the nitro anion free radical, as indicated by ESR spectroscopy. The steady state concentration of this radical was not decreased by CO or SKF 525-A (two inhibitors of cytochrome P450), but was decreased by NADP+ (10 mM) or p-chloromercuribenzoate (0.47 mM) (two inhibitors of NADPH-cytochrome P450 reductase activity). Anaerobic incubations of [3H]nilutamide (0.1 mM) with rat lung microsomes and a NADPH-generating system resulted in the in vivo covalent binding of [3H]nilutamide metabolites to microsomal proteins; covalent binding required NADPH; it was decreased in the presence of NADP+ (10 mM), or in the presence of the nucleophile glutathione (10 mM), but was unchanged in the presence of carbon monoxide. Under aerobic conditions, in contrast, the nitro anion free radical was reoxidized by oxygen, and its ESR signal was not detected. Covalent binding was essentially suppressed. Instead, there was consumption of NADPH and oxygen, and production of superoxide anion and hydogen peroxide. We conclude that nilutamide is reduced by rat lung microsomes NADPH-cytochrome P450 reductase into a nitro anion free radical. In anaerobiosis, the radical is reduced further to covalent binding species. In the presence of oxygen, in contrast, this nitro anion free radical undergoes redox cycling, with the generation of reactive oxygen species.

Effects of chronic absorption of dietary supplements of methionine and cystine on arterial morphology in the rat

Male Wistar rats were fed diets containing supplements of either methionine or cystine from 10 weeks of age and compared to rats fed a control diet or a high protein diet kept under identical conditions. At 11-16 months of age, the aorta and the renal, iliac and caudal arteries of all rats were fixed and examined by light and electron microscopy. Cystine-fed rats showed arterial morphology similar to that of control rats and of those having received a high protein diet. Methionine-fed rats showed marked thickening of the arterial wall which was due, on the one hand, to massive intimal thickening, as a result of accumulation of granular material in the subendothelial region and, on the other hand, to marked thickening of the media as a result of increased extracellular material around smooth muscle cells. Zones of early phases of chondroid metaplasia were also observed in the media. Thus cystine and methionine, despite their interrelated metabolism, have very different effects on the morphology of the arterial wall. However, cystine and methionine both inhibited the spontaneous rupture of the internal elastic lamina in the renal artery. This latter result is discussed in the light of the similarities between spontaneous rupture of the internal elastic lamina and beta-aminopropionitrile-induced aortic aneurysm and rupture.