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P Lettéron

Publications and source records attributed to P Lettéron.

At least 19 recordsLinked to original sources
PubMed2001

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.

Adenosine Triphosphate↗
PubMed2001

Prolonged, but not acute, glutathione depletion promotes Fas-mediated mitochondrial permeability transition and apoptosis in mice.

Glutathione depletion either decreased or increased death-receptor-mediated apoptosis in previous studies. Comparison of the durations of glutathione depletion before death-receptor stimulation in these studies might suggest a different effect of prolonged versus acute thiol depletion. We compared the effects of the prolonged glutathione depletion caused by a sulfur amino acid-deficient (SAA(-)) diet and the acute depletion caused by a single dose of phorone on hepatic apoptosis triggered by the administration of an agonistic anti-Fas antibody. The chronic SAA(-) diet did not affect hepatic Fas or Bcl-XL, but increased p53 and Bax, and exacerbated Fas-mediated mitochondrial membrane depolarization, electron-microscopy-proven outer mitochondrial membrane rupture, cytochrome c translocation to the cytosol, and caspase 3 activation. These effects were prevented by cyclosporin A, an inhibitor of mitochondrial permeability transition. The SAA(-) diet increased internucleosomal DNA fragmentation, the percentage of apoptotic hepatocytes, serum alanine transaminase (ALT) activity, and mortality after Fas stimulation. Despite a similar decrease in hepatic glutathione, administration of a single dose of phorone 1 hour before the anti-Fas antibody did not change p53 or Bax, and did not enhance Fas-induced mitochondrial permeability transition and toxicity. However, 4 repeated doses of phorone (causing more prolonged glutathione depletion) increased Bax and Fas-mediated toxicity. In conclusion, a chronic SAA(-) diet, but not acute phorone administration, increases p53 and Bax, and enhances Fas-induced mitochondrial permeability transition and apoptosis. Thiol depletion could cause oxidative stress that requires several hours to increase p53; the latter induces Bax, which translocates to mitochondria after Fas stimulation.

Amino Acids↗
PubMed2001

Effect of stavudine on mitochondrial genome and fatty acid oxidation in lean and obese mice.

Like other antihuman immunodeficiency virus dideoxynucleosides, stavudine may occasionally induce lactic acidosis and perhaps lipodystrophy in metabolically or genetically susceptible patients. We studied the effects of stavudine on mitochondrial DNA (mtDNA), fatty acid oxidation, and blood metabolites in lean and genetically obese (ob/ob) mice. In lean mice, mtDNA was depleted in liver and skeletal muscle, but not heart and brain, after 6 weeks of stavudine treatment (500 mg/kg/day). With 100 mg/kg/day, mtDNA transiently decreased in liver, but was unchanged at 6 weeks in all organs, including white adipose tissue (WAT). Despite unchanged mtDNA levels, lack of significant oxidative mtDNA lesions (as assessed by long polymerase chain reaction experiments), and normal blood lactate/pyruvate ratios, lean mice treated with stavudine for 6 weeks had increased fasting blood ketone bodies, due to both increased hepatic fatty acid beta-oxidation and decreased peripheral ketolysis. In obese mice, basal WAT mtDNA was low and was further decreased by stavudine. In conclusion, stavudine can decrease hepatic and muscle mtDNA in lean mice and can also cause ketoacidosis during fasting without altering mtDNA. Stavudine depletes WAT mtDNA only in obese mice. Fasting and ketoacidosis could trigger decompensation in patients with incipient lactic acidosis, whereas WAT mtDNA depletion could cause lipodystrophy in genetically susceptible patients.

Animals↗
PubMed2000

Cytochrome P450-generated reactive metabolites cause mitochondrial permeability transition, caspase activation, and apoptosis in rat hepatocytes.

Although cytochrome P-450 (CYP)-generated reactive metabolites can cause hepatocyte apoptosis, the mechanism of this effect is incompletely understood. In the present study, we assessed the hepatotoxicity of skullcap, a diterpenoid-containing herbal remedy. Male rat hepatocytes were incubated for 2 hours with skullcap diterpenoids (100 microg/mL). This treatment decreased cell glutathione and protein thiols and increased cell [Ca(2+)]. This activated Ca(2+)-dependent tissue transglutaminase, forming a cross-linked protein scaffold, and also opened the mitochondrial permeability transition pore, causing outer mitochondrial membrane rupture, increased cytosolic cytochrome c, activation of procaspase 3, internucleosomal DNA fragmentation, and ultrastructural features of apoptosis. Cell death was increased by a CYP3A inducer (dexamethasone) or a sulfur amino acid-deficient diet increasing glutathione depletion. In contrast, cell death was prevented by decreasing CYP3A activity (with troleandomycin), preventing glutathione depletion (with cysteine or cystine), blocking Ca(2+)-modulated events (with calmidazolium), preventing mitochondrial permeability transition (with cyclosporin A), or inhibiting caspase 3 (with acetyl-Asp-G u-Va-Asp-a dehyde). Both calmidazolium and cyclosporin A also prevented the increase in cytosolic cytochrome c and procaspase 3 activation. In conclusion, CYP3A activates skullcap diterpenoids into reactive metabolites that deplete cellular thiols and increase cell [Ca(2+)]. This activates Ca(2+)-dependent transglutaminase and also opens the mitochondrial permeability transition pore, causing outer mitochondrial membrane rupture, cytochrome c release, and caspase activation. Preventing mitochondrial permeability transition pore opening and/or caspase activity blocks apoptosis, showing the fundamental role of these final events in metabolite-mediated hepatotoxicity.

Animals↗
PubMed1999

Decrease in hepatic cytochrome P450 after interleukin-2 immunotherapy.

Interleukin-2 (IL-2) has been shown to decrease cytochrome P450 (CYP) mRNAs and proteins in cultured rat hepatocytes, and IL-2 administration decreases CYPs in rats. Although high doses of IL-2 are administered to cancer patients, the effect on human CYPs has not yet been determined. Patients with hepatic metastases from colon or rectum carcinomas were randomly allocated to various daily doses of human recombinant IL-2 (from 0 to 12.10(6) units/m(2)). IL-2 was infused from day 7 to day 3 before hepatectomy and the conservation of a non-tumorous liver fragment in liquid nitrogen. Hepatic CYPs and monooxygenase activities were not significantly decreased in 5 patients receiving daily doses of 3 or 6 10(6) IL-2 units/m2, compared to 7 patients who did not receive IL-2. In contrast, in 6 patients receiving daily doses of 9 or 12 x 10(6) IL-2 units/m2, the mean values for immunoreactive CYP1A2, CYP2C, CYP2E1, and CYP3A4 were 37, 45, 60 and 39%, respectively, of those in controls; total CYP was significantly decreased by 34%, methoxyresorufin O-demethylation by 62%, and erythromycin N-demethylation by 50%. These observations suggest that high doses of IL-2 may decrease total CYP and monooxygenase activities in man.

Adenocarcinoma↗
PubMed1999

An alcoholic binge causes massive degradation of hepatic mitochondrial DNA in mice.

BACKGROUND & AIMS: Ethanol causes oxidative stress in the hepatic mitochondria of experimental animals and mitochondrial DNA deletions in alcoholics. We postulated that ethanol intoxication may cause mitochondrial DNA strand breaks. METHODS: Effects of an intragastric dose of ethanol (5 g/kg) on hepatic mitochondrial DNA levels, structure, and synthesis were determined by slot blot hybridization, Southern blot hybridization, and in vivo [3H]thymidine incorporation, respectively. RESULTS: Two hours after ethanol administration, ethane exhalation (an index of lipid peroxidation) increased by 133%, although hepatic lipids were unchanged. Mitochondrial DNA was depleted by 51%. Its supercoiled form disappeared, whereas linearized forms increased. Long polymerase chain reaction evidenced lesions blocking polymerase progress on the mitochondrial genome. Mitochondrial transcripts decreased. Subsequently, [3H]thymidine incorporation into mitochondrial DNA increased, and mitochondrial DNA levels were restored. In contrast, nuclear DNA was not fragmented and its [3H]thymidine incorporation was unchanged. Liver ultrastructure only showed inconstant mitochondrial lesions. Ethanol-induced mitochondrial DNA depletion was prevented by 4-methylpyrazole, an inhibitor of ethanol metabolism, and attenuated by melatonin, an antioxidant. CONCLUSIONS: After an alcoholic binge, ethanol metabolism causes oxidative stress and hepatic mitochondrial DNA degradation in mice. DNA strand breaks may be involved in the development of mitochondrial DNA deletions in alcoholics.

Alcohol Drinking↗
PubMed1998

Steatohepatitis-inducing drugs cause mitochondrial dysfunction and lipid peroxidation in rat hepatocytes.

BACKGROUND & AIMS: 4,4'-Diethylaminoethoxyhexestrol (DEAEH), amiodarone, and perhexiline cause steatohepatitis in humans. The mechanisms of these effects are unknown for DEAEH and have not been completely elucidated for amiodarone and perhexiline. The aim of this study was to determine these mechanisms. METHODS: Rat liver mitochondria, cultured rat hepatocytes, or rats were treated with these drugs, and the effects on mitochondrial respiration, beta-oxidation, reactive oxygen species formation, and lipid peroxidation were determined. RESULTS: DEAEH accumulated in mitochondria and inhibited carnitine palmitoyl transferase I and acyl-coenzyme A dehydrogenases; it decreased beta-oxidation and caused lipid deposits in hepatocytes. DEAEH also inhibited mitochondrial respiration and decreased adenosine triphosphate (ATP) levels in hepatocytes. DEAEH, amiodarone, and perhexiline augmented the mitochondrial formation of reactive oxygen species and caused lipid peroxidation in rats. CONCLUSIONS: Like amiodarone and perhexiline, DEAEH accumulates in mitochondria, where it inhibits both beta-oxidation (causing steatosis) and respiration. Inhibition of respiration decreases ATP and also increases the mitochondrial formation of reactive oxygen species. The latter oxidize fat deposits, causing lipid peroxidation. We suggest that ATP depletion and lipid peroxidation may cause cell death and that lipid peroxidation products may account, in part, for other steatohepatitis lesions.

Animals↗
PubMed1997

Premature oxidative aging of hepatic mitochondrial DNA in Wilson's disease.

BACKGROUND & AIMS: Aging is associated with and may be caused by acquired somatic mutations of the mitochondrial genome. In Wilson's disease, inherited mutations of a nuclear gene encoding a copper transporter cause accumulation of copper in the liver, particularly within mitochondria. Because copper has prooxidant properties and the mitochondrial genome is particularly susceptible to oxidative damage, we hypothesized that Wilson's disease may cause premature oxidative aging of mitochondrial DNA. METHODS: Hepatic DNA was screened for large mitochondrial DNA deletion(s) in 16 patients with Wilson's disease and 67 control subjects. Deleted mitochondrial DNA copies were amplified by polymerase chain reaction and were sequenced. RESULTS: Although 15 of the 16 patients with Wilson's disease were 30 years old or younger, 8 of them (50%), including the 6 patients with cirrhosis (100%), had diverse mitochondrial DNA deletions, whereas only 2 controls (3%), aged 39 and 45 years, showed a mitochondrial DNA deletion. CONCLUSIONS: Wilson's disease is associated with frequent, diverse, and early deletions of mitochondrial DNA. Accumulation of prooxidant copper within hepatic mitochondria may cause this premature oxidative aging of mitochondrial DNA. Thus, inherited mutations of a nuclear gene may cause somatic mutations of the mitochondrial genome in this condition.

Adolescent↗
PubMed1997

In vivo assessment of lipid peroxidation in experimental edematous and necrotizing rat pancreatitis.

Lipid peroxidation, which may be involved in the pathogenesis of acute pancreatitis, is usually assessed in vitro or indirectly using antioxidants or free radical scavengers. We assessed lipid peroxidation in an in vivo model by measuring ethane exhalation in two models of acute pancreatitis. Edematous acute pancreatitis was induced by a supramaximal intraperitoneal injection of cerulein. Necrotizing acute pancreatitis was induced by retrograde infusion of sodium taurocholate into the pancreaticobiliary duct. Rats were placed in closed chambers and ethane exhalation was measured in aliquots. Ethane exhalation was significantly increased (p < 0.002) in cerulein (n = 12)- but not in taurocholate (n = 6)-induced pancreatitis compared to controls (n = 12 and 6, respectively). Our results suggest that free radicals may play a role in the pathogenesis of edematous pancreatitis but do not play an important role in the progression to necrotizing pancreatitis.

Acute Disease↗
PubMed1997

Glucocorticoids inhibit mitochondrial matrix acyl-CoA dehydrogenases and fatty acid beta-oxidation.

Glucocorticoid administration may produce fatty liver in humans. We investigated the effects of dexamethasone on hepatic mitochondria and lipid metabolism in mice. Dexamethasone 21-phosphate (20 microM) did not inhibit the mitochondrial inner membrane-bound very-long-chain acyl-CoA dehydrogenase but inhibited the matrixlocated long-, medium-, and short-chain dehydrogenases. Dexamethasone 21-phosphate (20 microM) inhibited the first beta-oxidation cycle of [1-(14C)]butyric acid and [1-(14C)]octanoic acid but not that of [1-(14C)]palmitic acid. Administration of dexamethasone 21-phosphate (100 mg/kg) decreased the in vivo oxidation of [1-(14C)]butyric acid and [1-(14C)]octanoic acid into [14C]CO2 but not that of [1-(14C)]palmitic acid and decreased the hepatic secretion of triglycerides. After 5 days of treatment (100 mg/kg daily), hepatic triglycerides were increased and both microvesicular steatosis and ultrastructural mitochondrial lesions were present. In conclusion, glucocorticoids inhibit medium- and short-chain acyl-CoA dehydrogenation and hepatic lipid secretion in mice. These effects may account for their steatogenic effects in humans.

Acyl-CoA Dehydrogenases↗
PubMed1996

Uncoupling of rat and human mitochondria: a possible explanation for tacrine-induced liver dysfunction.

BACKGROUND & AIMS: Tacrine administration (1-3 mg/kg) may lead to sinusoidal concentrations in the micromolar range and produce liver dysfunction in 50% of recipients. The aim of this study was to determine the cellular effects of tacrine that account for liver dysfunction. METHODS: The effects of tacrine on mitochondrial function were determined in isolated rat liver mitochondria, cultured rat hepatocytes, and isolated human lymphocytes. RESULTS: In vitro, tacrine was taken up by rat liver mitochondria, decreased their membrane potential, and stimulated their respiration. Ex vivo, respiration was increased in rat mitochondria isolated 30 minutes after the administration of 2 mg of tacrine per kilogram. After 7 days of culture, tacrine (2.5 mumol/L) decreased rat hepatocyte adenosine triphosphate levels. Ten micromolar decreased 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium reduction and neutral red uptake without modifying cell glutathione, the morphology of the endoplasmic reticulum, or protein synthesis. Tacrine (1.25 mumol/L) decreased levels of adenosine triphosphate in human lymphocytes. CONCLUSIONS: The weak base tacrine exerts a protonophoric effect in mitochondria that wastes energy and decreases levels of adenosine triphosphate in rat and human cells. These effects are visible after clinically relevant doses of tacrine and might be involved in tacrine-induced liver dysfunction.

Animals↗
PubMed1995

Comparison of erythrocyte transketolase activity with thiamine and thiamine phosphate ester levels in chronic alcoholic patients.

The effect of chronic alcoholism on biochemical evaluation of thiamine status was studied by the concomitant determination of erythrocyte transketolase (ETK) activity, its relative increase by in vitro addition of thiamine diphosphate (TDP effect) and the direct measurement of thiamine and its phosphate esters by high performance liquid chromatography. Thirty-eight percent of alcoholic subjects showed a thiamine deficiency with decreased thiamine diphosphate concentrations compared with healthy subjects (90.8 +/- 25.7 nmol/l vs. 176 +/- 28.0 nmol/l, respectively, mean +/- S.D., P < 0.001). Thiamine diphosphate concentrations were highly correlated with total thiamine concentrations and TDP effect (respectively r = 0.99 and 0.79, n = 85, P < 0.001). No abnormality in thiamine phosphorylation related to chronic alcoholism was noted. Finally, 47% of these deficient alcoholic patients had normal ETK activity. We concluded that, if indirect evaluation of thiamine status is to be chosen, the determination of ETK activity should be associated with TDP effect since the latter has been shown to be highly linked to total thiamine and thiamine diphosphate in erythrocytes. Furthermore, the direct measurement of thiamine and its phosphate esters was a more sensitive and specific index of thiamine nutrition.

Adult↗
PubMed1993

Increased ethane exhalation, an in vivo index of lipid peroxidation, in alcohol-abusers.

Ethane exhalation was measured in 42 control subjects, 52 patients with various non-alcoholic liver diseases, and 89 alcohol abusers who had been admitted to hospital for alcohol withdrawal and assessment of liver disease (six with normal liver tests, 10 with steatosis with or without fibrosis, six with alcoholic hepatitis, 29 with cirrhosis, 34 with both cirrhosis and alcoholic hepatitis, and four with both cirrhosis and a hepatocellular carcinoma). Ethane exhalation was similar in control subjects and in patients with non-alcoholic liver diseases, but was five times higher in alcohol abusers. Ethane exhalation in alcohol abusers was significantly, but very weakly, correlated with the daily ethanol intake before hospital admission, and the histological score for steatosis, but not with the inflammation or alcoholic hepatitis scores. Ethane exhalation was inversely correlated with the duration of abstinence before the test. In nine alcoholic patients, the exhalation of ethane was measured repeatedly, and showed slow improvement during abstinence. Ethane exhalation was significantly but weakly correlated with the Pugh's score in patients with alcoholic cirrhosis. It is concluded that the mean ethane exhalation is increased in alcohol abusers. One of the possible mechanisms may be the presence of oxidizable fat in the liver. The weak correlation with the Pugh's score is consistent with the contribution of many other factors in the progression to severe liver disease.

Adult↗
PubMed1990

Metabolic activation of the new tricyclic antidepressant tianeptine by human liver cytochrome P450.

Incubation of [14C]tianeptine (0.5 mM) with human liver microsomes and a NADPH-generating system resulted in the in vitro covalent binding of a tianeptine metabolite to microsomal proteins. This covalent binding required oxygen and NADPH. It was decreased by piperonyl butoxide (4 mM) by 81%, and SKF 525-A (4 mM) by 87%, two relatively non-specific inhibitors of cytochrome P450, and by glutathione (4 mM) by 70%, a nucleophile. Covalent binding was decreased by 54% in the presence of troleandomycin (0.1 mM), a specific inhibitor of the glucocorticoid-inducible cytochrome P450 IIIA3, but remained unchanged in the presence of quinidine (0.1 mM) or dextromethorphan (0.1 mM), two inhibitors of cytochrome P450 IID6. Preincubation with IgG antibodies directed against cytochrome P450 IIIA3 decreased covalent binding by 65% whereas either preimmune IgG or IgG antibodies directed against P450 IA1, an isoenzyme inducible by polycyclic aromatic compounds, exhibited no significant inhibitory effect. We conclude that tianeptine is activated by human liver cytochrome P450 into a reactive metabolite. This activation is mediated in part by glucocorticoid-inducible isoenzymes but not by P450 IID6 (the isoenzyme which oxidizes debrisoquine) nor by P450 IA1 (an isoenzyme inducible by polycyclic aromatic compounds). The predictive value of this study regarding possible idiosyncratic and immunoallergic reactions in humans remains unknown.

Antidepressive Agents, Tricyclic↗
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↗
PubMed1989

Presence of covalently bound metabolites on rat hepatocyte plasma membrane proteins after administration of isaxonine, a drug leading to immunoallergic hepatitis in man.

Isaxonine and several other drugs transformed by cytochrome P-450 into reactive metabolites apparently lead to immunoallergic hepatitis in man. Protein epitopes modified by the covalent binding of the metabolites have been proposed as possible targets for the immune response. The purpose of this work was to determine whether covalently bound metabolites are indeed present on hepatocyte plasma membrane proteins. In a first series of experiments, rats were killed 15 or 60 min after administration of [2-14C]isaxonine (0.2 mmol.kg-1 i.p.), and various fractions were prepared from isolated hepatocytes; microsomal contamination of the plasma membrane fraction was 1.2% or less. At 60 min, the amount of isaxonine metabolite covalently bound per mg of protein was similar in plasma membranes (0.42 nmole metabolite.mg protein-1) and in microsomes (0.38); both values were decreased by about 70% in rats pretreated with piperonyl butoxide, an inhibitor of cytochrome P-450. At 15 min, however, covalent binding to plasma membrane proteins (0.06 nmole metabolite.mg protein-1) was only half of that to microsomal proteins (0.12). In a second series of experiments, [2-14C] isaxonine (0.1 mM) was incubated with NADPH, hepatic microsomes and plasma membranes. The reactive isaxonine metabolite became bound extensively to microsomal proteins, but not to plasma membrane proteins. These results show that administration of isaxonine leads to the presence of isaxonine adducts on the proteins of the hepatocyte plasma membrane.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗