Biomedical subjects

B Fromenty

Publications and source records attributed to B Fromenty.

43 records · Page 3Linked to original sources

PubMed1991

Generation of free radicals during the reductive metabolism of the nitroaromatic compound, nilutamide.

Incubation of the antiandrogen nilutamide with rat liver microsomes and NADPH, under anaerobic conditions, led to the formation of the nitro anion free radical, as indicated by electron spin resonance spectroscopy. The steady-state concentration of the nitro anion free radical was not decreased by SKF 525-A, carbon monoxide or metyrapone (3 inhibitors of cytochrome P-450) but was decreased by NADP+ or p-chloromercuribenzoate (2 inhibitors of NADPH-cytochrome P-450 reductase). Under aerobic conditions, the nitro anion free radical was reoxidized by oxygen, and the electron spin resonance signal was not detected. This redox cycle was associated with NADPH oxidation, consumption of oxygen, and formation of superoxide anion, hydrogen peroxide and glutathione disulfide. Under anaerobic conditions, nilutamide was further reduced to chemically reactive metabolites. Anaerobic incubation of [3H]nilutamide (0.1 mM) with rat liver microsomes and a NADPH-generating system resulted in the in vitro covalent binding of [3H]nilutamide metabolites to microsomal proteins; covalent binding required NADPH; it was decreased in the presence of NADPH-cytochrome P-450 reductase inhibitors (methylene blue, 2'-adenosine monophosphate) or in the presence of the nucleophile glutathione, but was unaffected by cytochrome P-450 inhibitors (SKF 525-A, CO). Covalent binding was decreased markedly under aerobic conditions. We conclude that nilutamide is reduced by microsomal NADPH-cytochrome P-450 reductase into a nitro anion free radical. In the presence of oxygen, this nitro anion free radical undergoes redox cycling with oxygen, and forms reactive oxygen species. In anaerobiosis, it is reduced further to covalent binding species.

Androgen Antagonists↗

PubMed1991

Inhibition by salicylic acid of the activation and thus oxidation of long chain fatty acids. Possible role in the development of Reye's syndrome.

Administration of either aspirin or salicylic acid (3 mmol.kg-1 b.wt. i.p.) decreased by 50 and 65%, respectively, the in vivo oxidation of [U-14C]palmitic acid to [14C]CO2 in mice; after salicylic acid administration, exhalation of [14C]CO2 from [1-14C]palmitic acid, [1-14C]octanoic acid or [1-14C]butyric acid was decreased by 87, 33 and 38%, respectively. Inhibition lasted 9 hr. It was associated with markedly decreased blood glucose concentrations and increased plasma ketone bodies. Repeated administration of salicylic acid (2 mmol.kg-1 i.p. every 8 hr) tripled hepatic triglycerides and produced mild microvesicular steatosis of the liver at 22 hr in fasted mice. In vitro, salicylic acid (1.5 mM) had no or little effect on the formation of beta-oxidation products from [1-14C]octanoic or [1-14C]palmitoyl-L-carnitine, in the presence of ATP, carnitine (40 microM) and coenzyme A (40 microM), but decreased by 51% that from [1-14C]palmitic acid. In the latter system, increasing the concentrations of coenzyme A and carnitine to 200 microM suppressed the inhibitory effect of salicylic acid. Salicylic acid (1.5 mM) decreased by 80% the in vitro mitochondrial formation of palmitoyl-coenzyme A from [1-14C]palmitic acid and 10 microM coenzyme A; again, increasing the concentration of coenzyme A prevented inhibition. We conclude that salicylic acid decreases the mitochondrial activation and thus beta-oxidation of long chain fatty acids, presumably by sequestering extramitochondrial coenzyme A and possibly carnitine.

Adenosine Triphosphate↗

PubMed1990

Mechanism for the protective effects of silymarin against carbon tetrachloride-induced lipid peroxidation and hepatotoxicity in mice. Evidence that silymarin acts both as an inhibitor of metabolic activation and as a chain-breaking antioxidant.

Administration of silymarin (800 mg/kg i.p.) 30 min before carbon tetrachloride (18 microL/kg i.p.) did not modify total hepatic levels of CCl4 and metabolites in mice, but decreased by 40% the in vivo covalent binding of CCl4 metabolites to hepatic lipids at 2 hr. This pretreatment decreased by 60% the exhalation of ethane during the first hour after CCl4, and decreased by 50% the incidence of liver cell necrosis. In vitro, silymarin (800 micrograms/mL) decreased by 50 to 70% various monooxygenase activities, and decreased by 20% the covalent binding of CCl4 metabolites to microsomal proteins. Silymarin (800 micrograms/mL) decreased by 70% in vitro lipid peroxidation mediated by CCl4 metabolites, and decreased by 90% peroxidation mediated by NADPH alone. Silibinin, one of the three isomers composing silymarin, also decreased carbon tetrachloride-induced lipid peroxidation; this effect, however, was less than that of silymarin in vitro, and was more transient in vivo. Pretreatment with silibinin (800 mg/kg i.p.) 30 min before CCl4 (18 microL/kg i.p.) did not improve SGPT activity or liver histology at 24 hr. We conclude that silymarin prevents carbon tetrachloride-induced lipid peroxidation and hepatotoxicity in mice, firstly, by decreasing the metabolic activation of CCl4, and, secondly, by acting as a chain-breaking antioxidant.

7-Alkoxycoumarin O-Dealkylase↗

PubMed1990

Dual effect of amiodarone on mitochondrial respiration. Initial protonophoric uncoupling effect followed by inhibition of the respiratory chain at the levels of complex I and complex II.

The effects of amiodarone on the respiration of isolated mouse liver mitochondria have been determined. Amiodarone (200 microM) had a biphasic effect on state 4 respiration supported by either glutamate plus malate or succinate. Initially, the respiratory rate was increased. This stimulatory effect was not prevented by oligomycin (an inhibitor of ATP synthase). It was associated with marked accumulation of amiodarone in the mitochondria, and with collapse of the mitochondrial membrane potential. This initial uncoupling effect was followed by a progressive decrease in the state 4 respiration rate, leading eventually to marked inhibition. Preincubation for 5 min with amiodarone (200 microM) also decreased markedly ADP-stimulated (state 3) respiration, ATP production and dinitrophenol-stimulated (uncoupled) respiration supported by glutamate plus malate (which donate electrons to complex I), and respiration supported by succinate (which donate electrons to complex II), but did not affect respiration supported by duroquinol (donating electrons to complex III) or by ascorbate plus N,N,N',N'-tetramethyl-p-phenylenediamine (donating electrons to cytochrome c). Preincubation with amiodarone (150-200 microM) decreased markedly respiration mediated by fatty acids of various chain length and respiration mediated by citrate, a tricarboxylic acid cycle substrate. We conclude that amiodarone has a dual effect on mitochondrial respiration. The initial uncoupling effect is probably due to the entry of protonated amiodarone, releasing a proton in the matrix. Accumulation of amiodarone soon leads to inhibition of the respiratory chain at the levels of complex I and complex II and to decreased ATP formation.

Adenosine Diphosphate↗

PubMed1990

Stereoselective and nonstereoselective effects of ibuprofen enantiomers on mitochondrial beta-oxidation of fatty acids.

The effects of the R-(-) and S-(+)ibuprofen enantiomers were first studied in vitro with mouse liver mitochondria incubated in the presence of various concentrations of exogenous coenzyme A. In the presence of a low concentration of coenzyme A (2.5 microM), the R-(-)enantiomer (which forms an acylcoenzyme A) inhibited stereoselectively the beta oxidation of [1-14C]palmitic acid but not that of [1-14C]palmitoyl-L-carnitine (which can directly enter the mitochondria). In the presence, however, of a concentration of coenzyme A (50 microM) reproducing that present in liver cell cytosol, both enantiomers (2 mM) slightly inhibited the beta oxidation of [1-14C]palmitic acid and markedly inhibited the beta oxidation of [1-14C]octanoic acid and [1-14C]butyric acid. In vivo, both enantiomers (1 mmol.kg-1) similarly inhibited the formation of [14C]CO2 from [1-14C]fatty acids. Both enantiomers similarly decreased plasma ketone bodies. Both similarly increased hepatic triglycerides, and both produced mild microvesicular steatosis of the liver. We conclude that both ibuprofen enantiomers inhibit beta oxidation of fatty acids in vitro and in vivo. In addition, the R-(-)enantiomer may stereoselectively sequester coenzyme A; at low concentrations of coenzyme A in vitro, this may stereoselectively inhibit the mitochondrial uptake and beta oxidation of long chain fatty acids.

Animals↗

PubMed1990

Amiodarone inhibits the mitochondrial beta-oxidation of fatty acids and produces microvesicular steatosis of the liver in mice.

Amiodarone has been shown to produce microvesicular steatosis of the liver in some recipients. We have determined the effects of amiodarone on the mitochondrial oxidation of fatty acids in mice. In vitro, the formation of 14C-acid-soluble beta-oxidation products from [U-14C]palmitic acid by mouse liver mitochondria was decreased by 92% in the presence of 125 microM amiodarone and by 94% in the presence of 125 microM N-desethylamiodarone. Inhibition due to 100 or 150 microM amiodarone persisted in the presence of 5 mM acetoacetate, whereas acetoacetate totally relieved inhibition due to 15 microM rotenone. In vivo, exhalation of [14C]CO2 from [U-14C]palmitic acid was decreased by 31, 40, 58 and 78%, respectively, in mice receiving 19, 25, 50 and 100 mg.kg-1 of amiodarone hydrochloride 1 hr before the administration of [U-14C]palmitic acid. One hour after 100 mg.kg-1, the exhalation of [14C]CO2 from [1-14C]palmitic acid, [1-14C]octanoic acid or [1-14C]butyric acid was decreased by 78, 72 and 53%, respectively. Exhalation of [14C]CO2 from [1-14C]palmitic acid was normal between 6 and 9 hr after administration of 100 mg.kg-1 of amiodarone hydrochloride, but was still inhibited by 71 and 37%, 24 and 48 hr after 600 mg.kg-1. Twenty four hours after the latter dose of amiodarone, hepatic triglycerides were increased by 150%, and there was microvesicular steatosis of the liver. We conclude that amiodarone inhibits the mitochondrial beta-oxidation of fatty acids and produces microvesicular steatosis of the liver in mice.

Amiodarone↗

PubMed1989

Tianeptine, a new tricyclic antidepressant metabolized by beta-oxidation of its heptanoic side chain, inhibits the mitochondrial oxidation of medium and short chain fatty acids in mice.

Tianeptine is a new tricyclic antidepressant which is metabolized mainly by beta-oxidation of its heptanoic side chain. We determined the effects of tianeptine on the mitochondrial oxidation of natural fatty acids in mice. In vitro, tianeptine (0.5 mM) inhibited by only 32% the formation of beta-oxidation products from [1-14C]palmitic acid by hepatic mitochondria, but inhibited by 71% that from [1-14C]octanoic acid and by 51% that from [1-14C]butyric acid. The activity of the tricarboxylic acid cycle, assessed as the in vitro formation of [14C]CO2 from [1-14C]acetylcoenzyme A was decreased by 51% in the presence of tianeptine (0.5 mM). The inhibition of both beta-oxidation and the tricarboxylic acid cycle appeared reversible in mitochondria from mice exposed to tianeptine in vivo but incubated in vitro without tianeptine. In vivo, administration of tianeptine (0.0625 mmol/kg i.p.), decreased by 53 and 58%, respectively, the formation of [14C]CO2 from [1-14C]octanoic acid and [1-14C]butyric acid, but did not significantly decrease that from [1-14C]palmitic acid. After administration of high doses of tianeptine, however, formation of [14C]CO2 from [1-14C]palmitic acid became inhibited as well, transiently after 0.25 mmol/kg and durably (greater than 24 hr) after 0.75 mmol/kg i.p. Hepatic triglycerides were increased 24 hr after administration of 0.75 mmol/kg i.p. of tianeptine, but not after 0.25 mmol/kg i.p. Microvesicular steatosis of the liver was observed in some mice after 0.75 mmol/kg i.p., but not after 0.5 mmol/kg i.p. We conclude that tianeptine inhibits the oxidation of medium- and short-chain fatty acids in mice. Microvesicular steatosis, however, requires very large doses in mice (0.75 mmol/kg i.p., i.e. 600-times the oral dose in humans), and is therefore unlikely to occur in humans.

Animals↗