Metabolic activation of the tricyclic antidepressant amineptine--II. Protective role of glutathione against in vitro and in vivo covalent binding

Designing around Structural Alerts in Drug Discovery

Cumulative research over several decades has implicated the involvement of reactive metabolites in many idiosyncratic adverse drug reactions (IADRs). Consequently, "avoidance" strategies have been inserted into drug discovery paradigms, which include the exclusion of structural alerts and possible termination of reactive metabolite-positive compounds. Several noteworthy examples where reactive metabolite-related liabilities have been resolved through structure-metabolism studies are presented herein. Considerable progress has also been made in addressing the limitations of the avoidance strategy and further refining the process of managing reactive metabolite issues in drug development. These efforts primarily stemmed from the observation that numerous drugs, which contain structural alerts and/or form reactive metabolites, are devoid of ADRs. The Perspective also dwells into an analysis of the structural alert/reactive metabolite concept with a discussion of risk mitigation tactics to support the progression of reactive metabolite-positive drug candidates.

Selective Extraction and Antioxidant Properties of Thiol-Containing Peptides in Soy Glycinine Hydrolysates

A highly selective procedure to extract thiol-containing peptides (TCPs) from complicated soy glycinin hydrolysates (SGHs) was described. This procedure included the reduction of disulfide bonds by 1,4-dithiothreitol (DTT) and enrichment of TCPs through Thiopropyl-Sephrose 6B covalent chromatography. TCPs were confirmed using a strategy based on mass shift after differential alkylation of sulfhydryl groups with iodoacetamide and N-ethylmaleimide by matrix-assisted laser desorption ionization mass spectrometry (MALDI-TOF-MS). The antioxidant activities of TCPs were evaluated using chemical assays. DTT reduction increased the concentration of sulfhydryl groups from 1.8 μmol/g to 113.8 μmol/g. The efficiency of the extraction was improved by optimizing the loading of sample, extraction and desorption time and the content of desorption reagent. Both of the adsorption and desorption process were found to fit a pseudo-second order model. MALDI-TOF-MS showed that 36 of the 45 extracted peptides were TCPs. The EC50 of TCPs for DPPH, hydroxyl radical, and superoxide anion radical was 0.1, 1.49 and 0.084 mg/mL, respectively. The reducing power of TCPs (0.2 mg/mL) was of 0.375. These results suggest that the combination of DTT reduction and Thiopropyl-Sepharose 6B covalent chromatograph was a successful pathway to extract TCPs from SGHs and the TCPs could be used as potential antioxidants.

Predicting toxicities of reactive metabolite-positive drug candidates

Because of the inability to predict and quantify the risk of idiosyncratic adverse drug reactions (IADRs) and because reactive metabolites (RMs) are thought to be responsible for the pathogenesis of some IADRs, the potential for RM formation within new chemical entities is routinely examined with the ultimate goal of eliminating or reducing the liability through iterative design. Likewise, avoidance of structural alerts is almost a standard practice in drug design. However, the perceived safety concerns associated with the use of structural alerts and/or RM screening tools as standalone predictors of toxicity risks may be overexaggerated. Numerous marketed drugs form RMs but do not cause idiosyncratic toxicity. In this review article, we present a critique of the structural alert/RM concept as applied in drug discovery and evaluate the evidence linking structural alerts and RMs to observed toxic effects. Pragmatic risk mitigation strategies to aid the advancement of drug candidates that carry a RM liability are also discussed.

Protective effects of a novel sea buckthorn wine on oxidative stress and hypercholesterolemia

We developed a novel sea buckthorn wine containing significant in vitro free radical-scavenging activity. High-performance liquid chromatographic analysis of the sea buckthorn wine revealed that it contains high rutin, myricetin and quercetin levels compared to Cabernet Shiraz wine. In this study, we evaluated the protective effects of sea buckthorn wine against phorone-induced oxidative stress and high-cholesterol diet induced hypercholesterolemia in male LACA mice. Oral administration of sea buckthorn wine increased the redox ratio accompanied by reduction of oxidized glutathione levels leading to attenuation of phorone-induced oxidative stress. Furthermore, the sea buckthorn wine supplementation reduced hepatic lipid peroxidation and increased the superoxide dismutase activity indicating improved resistance to oxidative stress. In addition, high-cholesterol-fed mice administered with sea buckthorn wine exhibited a 197% increase in the HDL-C/LDL-C ratio compared to high-cholesterol diet treated mice. These studies provide important evidence that sea buckthorn wine exerts protective effects against oxidative stress and hypercholesterolemia.

Structural alert/reactive metabolite concept as applied in medicinal chemistry to mitigate the risk of idiosyncratic drug toxicity: a perspective based on the critical examination of trends in the top 200 drugs marketed in the United States

Because of a preconceived notion that eliminating reactive metabolite (RM) formation with new drug candidates could mitigate the risk of idiosyncratic drug toxicity, the potential for RM formation is routinely examined as part of lead optimization efforts in drug discovery. Likewise, avoidance of "structural alerts" is almost a norm in drug design. However, there is a growing concern that the perceived safety hazards associated with structural alerts and/or RM screening tools as standalone predictors of toxicity risks may be over exaggerated. In addition, the multifactorial nature of idiosyncratic toxicity is now well recognized based upon observations that mechanisms other than RM formation (e.g., mitochondrial toxicity and inhibition of bile salt export pump (BSEP)) also can account for certain target organ toxicities. Hence, fundamental questions arise such as: When is a molecule that contains a structural alert (RM positive or negative) a cause for concern? Could the molecule in its parent form exert toxicity? Can a low dose drug candidate truly mitigate metabolism-dependent and -independent idiosyncratic toxicity risks? In an effort to address these questions, we have retrospectively examined 68 drugs (recalled or associated with a black box warning due to idiosyncratic toxicity) and the top 200 drugs (prescription and sales) in the United States in 2009 for trends in physiochemical characteristics, daily doses, presence of structural alerts, evidence for RM formation as well as toxicity mechanism(s) potentially mediated by parent drugs. Collectively, our analysis revealed that a significant proportion (∼78-86%) of drugs associated with toxicity contained structural alerts and evidence indicating that RM formation as a causative factor for toxicity has been presented in 62-69% of these molecules. In several cases, mitochondrial toxicity and BSEP inhibition mediated by parent drugs were also noted as potential causative factors. Most drugs were administered at daily doses exceeding several hundred milligrams. There was no obvious link between idiosyncratic toxicity and physicochemical properties such as molecular weight, lipophilicity, etc. Approximately half of the top 200 drugs for 2009 (prescription and sales) also contained one or more alerts in their chemical architecture, and many were found to be RM-positive. Several instances of BSEP and mitochondrial liabilities were also noted with agents in the top 200 category. However, with relatively few exceptions, the vast majority of these drugs are rarely associated with idiosyncratic toxicity, despite years of patient use. The major differentiating factor appeared to be the daily dose; most of the drugs in the top 200 list are administered at low daily doses. In addition, competing detoxication pathways and/or alternate nonmetabolic clearance routes provided suitable justifications for the safety records of RM-positive drugs in the top 200 category. Thus, while RM elimination may be a useful and pragmatic starting point in mitigating idiosyncratic toxicity risks, our analysis suggests a need for a more integrated screening paradigm for chemical hazard identification in drug discovery. Thus, in addition to a detailed assessment of RM formation potential (in relationship to the overall elimination mechanisms of the compound(s)) for lead compounds, effects on cellular health (e.g., cytotoxicity assays), BSEP inhibition, and mitochondrial toxicity are the recommended suite of assays to characterize compound liabilities. However, the prospective use of such data in compound selection will require further validation of the cellular assays using marketed agents. Until we gain a better understanding of the pathophysiological mechanisms associated with idiosyncratic toxicities, improving pharmacokinetics and intrinsic potency as means of decreasing the dose size and the associated "body burden" of the parent drug and its metabolites will remain an overarching goal in drug discovery.

Drug bioactivation, covalent binding to target proteins and toxicity relevance

A number of therapeutic drugs with different structures and mechanisms of action have been reported to undergo metabolic activation by Phase I or Phase II drug-metabolizing enzymes. The bioactivation gives rise to reactive metabolites/intermediates, which readily confer covalent binding to various target proteins by nucleophilic substitution and/or Schiff's base mechanism. These drugs include analgesics (e.g., acetaminophen), antibacterial agents (e.g., sulfonamides and macrolide antibiotics), anticancer drugs (e.g., irinotecan), antiepileptic drugs (e.g., carbamazepine), anti-HIV agents (e.g., ritonavir), antipsychotics (e.g., clozapine), cardiovascular drugs (e.g., procainamide and hydralazine), immunosupressants (e.g., cyclosporine A), inhalational anesthetics (e.g., halothane), nonsteroidal anti-inflammatory drugs (NSAIDSs) (e.g., diclofenac), and steroids and their receptor modulators (e.g., estrogens and tamoxifen). Some herbal and dietary constituents are also bioactivated to reactive metabolites capable of binding covalently and inactivating cytochrome P450s (CYPs). A number of important target proteins of drugs have been identified by mass spectrometric techniques and proteomic approaches. The covalent binding and formation of drug-protein adducts are generally considered to be related to drug toxicity, and selective protein covalent binding by drug metabolites may lead to selective organ toxicity. However, the mechanisms involved in the protein adduct-induced toxicity are largely undefined, although it has been suggested that drug-protein adducts may cause toxicity either through impairing physiological functions of the modified proteins or through immune-mediated mechanisms. In addition, mechanism-based inhibition of CYPs may result in toxic drug-drug interactions. The clinical consequences of drug bioactivation and covalent binding to proteins are unpredictable, depending on many factors that are associated with the administered drugs and patients. Further studies using proteomic and genomic approaches with high throughput capacity are needed to identify the protein targets of reactive drug metabolites, and to elucidate the structure-activity relationships of drug's covalent binding to proteins and their clinical outcomes.

The role of reactive drug metabolites in immune-mediated adverse drug reactions

OBJECTIVE

To highlight recent advances in the understanding of adverse drug reactions (ADRs), with a focus on models outlining interactions between drug metabolism, disease processes, and immunity. Specific mechanisms that identify the metabolic pathways responsible for drug bioactivation to reactive drug metabolites (RDMs) involved in the initiation and propagation of specific immune-mediated hypersensitivity reactions are discussed. Drug classes well known to be associated with immune-mediated ADRs are reviewed and the clinical implications of current research are discussed.

DATA SOURCES

Original experimental research and immunologic review articles relevant to ADR diagnosis and etiology.

DATA EXTRACTION

Results of relevant in vitro experiments and clinical reactions to drug therapy were compiled and reviewed. Critical discoveries concerning the identification of RDMs involved in ADRs were highlighted, with respect to RDM involvement in the production of an immune response to drug haptens.

DATA SYNTHESIS

Drug adverse effects are classified according to clinical characteristics, immune interactions, and mechanistic similarities. Cytochrome P450 bioactivation of drug molecules to RDMs is a prerequisite to many ADRs. An electrophilic metabolite may react with cellular macromolecules (i.e., lipids, proteins, nucleic acids), resulting in direct cellular damage and organ toxicity. Covalent binding of an RDM to cellular macromolecules may also result in the formation of a hapten that is capable of eliciting a cellular or humoral immune response against drug or protein epitopes, culminating in the characteristic symptoms of hypersensitivity reactions. Mechanistic details concerning the identification of stable protein-metabolite conjugates and their interaction with the immune system remain unclear. Genetic imbalance between bioactivation and detoxification pathways, as well as reduced cellular defense against RDMs due to disease or concomitant drug therapy, act as risk factors to the onset and severity of ADRs.

CONCLUSIONS

Adverse reactions to drug therapy cause significant morbidity and mortality. Identification of the pathways involved in drug bioactivation and detoxification may elucidate the potential of chemical agents to induce immune-mediated ADRs. Understanding the mechanisms of ADRs to current xenobiotics is helpful in the prevention and management of ADRs, and may prove useful in the design of novel therapeutic agents with reduced incidence of severe adverse events.

Genetic predisposition to drug-induced hepatotoxicity

Drug-induced hepatitis is uncommon and generally unpredictable. Hepatotoxicity may be related to the drug itself, or to chemically reactive metabolites which can bind covalently to hepatic macromolecules and may lead to either idiosyncratic, toxic hepatitis or to immunoallergic hepatitis. There is now evidence indicating that genetic variations in systems of biotransformation or detoxication may modulate either the toxic or sensitizing effects of some drugs. Thus, the genetic deficiency in a particular hepatic cytochrome P 450 isozyme (CYP 2D6) is involved in per-hexiline liver injury. The deficiency in CYP 2C19 might also contribute to Atrium hepatotoxicity. Slow acetylation related to N-acetyltransferase 2 deficiency contributes to sulfonamide hepatitis. The genetic deficiency in glutathione synthetase may increase the susceptibility to several drugs including acetaminophen. A constitutional deficiency in another cell defense mechanism, still not characterized, seems to increase significantly the risk of hepatotoxicity with halothane, phenytoin, carbamazepine, phenobarbital, sulfamides and amineptine.

Idiosyncratic reactions to antidepressants: a review of the possible mechanisms and predisposing factors

Antidepressants, a widely used group of drugs, are associated with a range of idiosyncratic reactions affecting in particular the liver, skin and both the hematological and central nervous systems. These reactions seem to be mediated by chemically reactive metabolites formed by the cytochrome P450 enzyme system, the toxicity occurring either directly or indirectly via an immune mechanism. Individual susceptibility is determined by factors, both genetic and environmental, which result in inadequate detoxication of the chemically reactive metabolite. Prevention of such reactions will depend on either the development of new compounds which are not converted to toxic metabolites or by prediction of individual susceptibility prior to drug administration.

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.

Metabolic activation of the antidepressant tianeptine. II. In vivo covalent binding and toxicological studies at sublethal doses

Administration of [14C]tianeptine (0.5 mmol/kg i.p.) to non-pretreated hamsters resulted in the in vivo covalent binding of [14C]tianeptine metabolites to liver, lung and kidney proteins; this very high dose (360-fold the human therapeutic dose) depleted hepatic glutathione by 60%, and increased SGPT activity 5-fold. Lower doses (0.25 and 0.125 mmol/kg) depleted hepatic glutathione to a lesser extent and did not increase SGPT activity. Pretreatment of hamsters with piperonyl butoxide decreased in vivo covalent binding to liver proteins, and prevented the increase in SGPT activity after administration of tianeptine (0.5 mmol/kg i.p.). In contrast, pretreatment of hamsters with dexamethasone increased in vivo covalent binding to liver proteins, and increased SGPT activity after administration of tianeptine (0.5 mmol/kg i.p.). Nevertheless, liver cell necrosis was histologically absent 24 hr after the administration of tianeptine (0.5 mmol/kg i.p.) to non-pretreated or dexamethasone-pretreated hamsters. In vivo covalent binding to liver proteins also occurred in mice and rats, being increased by 100% in dexamethasone-pretreated animals. In vivo covalent binding to liver proteins was similar in untreated female Dark Agouti rats and in female Sprague-Dawley rats. These results show that tianeptine is transformed in vivo by cytochrome P-450, including glucocorticoid-inducible isoenzymes, into chemically reactive metabolites that covalently bind to tissue proteins. The metabolites, however, exhibit no direct hepatotoxic potential in hamsters below the sublethal dose of 0.5 mmol/kg i.p. The predictive value of this study regarding possible idiosyncratic and immunoallergic reactions in humans remains unknown.

Metabolic activation of the antidepressant tianeptine. I. Cytochrome P-450-mediated in vitro covalent binding

Incubation under air of [14C]tianeptine (0.5 mM) with a NADPH-generating system and hamster, mouse or rat liver microsomes resulted in the in vitro covalent binding of [14C]tianeptine metabolites to microsomal proteins. Covalent binding to hamster liver microsomes required NADPH and oxygen; it was decreased in the presence of the cytochrome P-450 inhibitors, carbon monoxide, piperonyl butoxide (4 mM), and SKF 525-A (4 mM) or in the presence of the nucleophile, glutathione (1 or 4 mM). In vitro covalent binding to hamster liver microsomes was not decreased in the presence of quinidine (1 microM), and was similar with microsomes from either female Dark Agouti, or female Sprague-Dawley rats. In contrast, in vitro covalent binding to hamster liver microsomes was decreased in the presence of troleandomycin (0.25 mM), while covalent binding was increased with microsomes from either hamsters, mice or rats pretreated with dexamethasone. Preincubation with IgG antibodies directed against rabbit liver glucocorticoid-inducible cytochrome P-450 3c(P-450 IIIA4) decreased in vitro covalent binding by 53 and 89%, respectively, with microsomes from control hamsters and dexamethasone-pretreated hamsters, and by 60 and 81%, respectively, with microsomes from control and dexamethasone-pretreated rats. We conclude that tianeptine is activated by hamster, mouse and rat liver cytochrome P-450 into a reactive metabolite. Metabolic activation is mediated in part by glucocorticoid-inducible isoenzymes but not by the isoenzyme metabolizing debrisoquine. In vivo studies are reported in the accompanying paper.

Genetic predisposition to drug hepatotoxicity: role in hepatitis caused by amineptine, a tricyclic antidepressant

Amineptine-induced immunoallergic hepatitis is unpredictable. It may be related to its oxidation into a reactive metabolite acting as hapten. We have looked for a possible genetic predisposition involving drug oxidation capacity and/or cell defense mechanisms in nine patients with previous amineptine hepatitis. Drug oxidation capacity was assessed using dextromethorphan, a test compound recently proposed as a substitute for debrisoquine. The eight patients tested had the extensive metabolizer phenotype. The susceptibility to amineptine metabolites was studied by an in vitro test assessing the destruction of the patients' lymphocytes by reactive metabolites generated from amineptine by a standardized oxidation microsomal system. Lymphocyte death increased with the dose of amineptine (1 to 2.5 mM); it was increased by preincubation with trichloropropene oxide, but was absent when amineptine was omitted or when the oxidation system was not operating. Mean lymphocyte death was twice higher in the nine patients with amineptine hepatitis than in 17 healthy controls. In contrast, when the test was performed with acetaminophen (3 to 10 mM), lymphocyte death was similar in controls and in patients. Basal epoxide hydrolase activity toward benzo[a]pyrene-4,5-oxide and glutathione concentration was similar in lymphocytes from controls and patients. Family studies showed an increased susceptibility to amineptine metabolites in lymphocytes from several first-degree relatives of two patients. These results show that amineptine hepatitis occurs in patients with extensive dextromethorphan oxidation capacity but with an increased susceptibility to amineptine reactive metabolites, probably related to a genetic deficiency in a cell defense mechanism.

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)

A comparative study of the formation of chemically reactive drug metabolites by human liver microsomes

1. The metabolism of amodiaquine (A), ethinyloestradiol (E), mianserin (M), phenytoin (Ph), sulphanilamide (S) and paracetamol (Pa) to both stable and chemically reactive, i.e. irreversibly protein bound, metabolites was investigated using microsomes prepared from histologically normal human liver obtained from eight kidney donors. 2. All drugs, except amodiaquine, were metabolized by NADPH-dependent microsomal enzymes to chemically reactive metabolites. The degree of NADPH-dependent binding varied between drugs (E, 11.5 +/- 5.8% incubated drug; M, 3.0 +/- 1.9%; Ph, 0.10 +/- 0.09%; S, 0.57 +/- 0.38%; Pa, 1.2 +/- 1.2%; mean of eight livers +/- s.d.). 3. Inclusion of glutathione (1 mM) or ascorbic acid (1 mM) in the incubation reduced the NADPH-dependent binding for all substrates, indicating the involvement of electrophilic oxidation products. 4. Binding of M and Pa correlated with each other (Spearman's r = 0.86) and with total cytochrome P-450 content (r = 0.76 and 0.78 respectively). E binding also correlated with the binding of M (r = 0.79) and Pa (r = 0.81) but not with cytochrome P-450. Binding of Ph and S did not correlate with any of the other measured metabolic parameters.

Acute and chronic drug-induced hepatitis

Adverse drug reactions may mimic almost any kind of liver disease. Acute hepatitis is often due to the formation of reactive metabolites in the liver. Despite several protective mechanisms (epoxide hydrolases, conjugation with glutathione), this formation may lead to predictable toxic hepatitis after hugh overdoses (e.g. paracetamol), or to idiosyncratic toxic hepatitis after therapeutic doses (e.g. isoniazid). Both genetic factors (e.g. constitutive levels of cytochrome P-450 isoenzymes, or defects in protective mechanisms) and acquired factors (e.g. malnutrition, or chronic intake of alcohol or other microsomal enzyme inducers) may explain the unique susceptibility of some patients. Formation of chemically reactive metabolites may also lead to allergic hepatitis, probably through immunization against plasma membrane protein epitopes modified by the covalent binding of the reactive metabolites. This may be the mechanism for acute hepatitis produced by many drugs (e.g. amineptine, erythromycin derivatives, halothane, imipramine, isaxonine, alpha-methyldopa, tienilic acid, etc.). Genetic defects in several protective mechanisms (e.g. epoxide hydrolase, acetylation) may explain the unique susceptibility of some patients, possibly by increasing exposure to allergenic, metabolite-altered plasma membrane protein epitopes. Like toxic idiosyncratic hepatitis, allergic hepatitis occurs in a few patients only. Unlike toxic hepatitis, allergic hepatitis is frequently associated with fever, rash or other hypersensitivity manifestations; it may be hepatocellular, mixed or cholestatic; it promptly recurs after inadvertent drug rechallenge. Lysosomal phospholipidosis occurs frequently with three antianginal drugs (diethylaminoethoxyhexestrol, amiodarone and perhexiline). These cationic, amphiphilic drugs may form phospholipid-drug complexes within lysosomes. Such complexes resist phospholipases and accumulate within enlarged lysosomes, forming myeloid figures. This phospholipidosis has little clinical importance. In a few patients, however, it is associated with alcoholic-like liver lesions leading to overt liver disease and, at times, cirrhosis. Subjects with a deficiency in a particular isoenzyme of cytochrome P-450 poorly metabolize perhexiline and are at higher risk of developing liver lesions. Prolonged, drug-induced liver-cell necrosis may also lead to subacute hepatitis, chronic hepatitis or even cirrhosis. This usually occurs when the drug administration is continued, either because the liver disease remains undetected or because its drug aetiology is overlooked. Several autoantibodies may be present.(ABSTRACT TRUNCATED AT 400 WORDS)

Ornithine decarboxylase induction and polyamine biosynthesis by phorone (diisopropylidene acetone), a glutathione depletor, in rats

The administration of Phorone (diisopropylidene acetone, 250 mg/kg, ip.), a glutathione (GSH) depletor, markedly induced (400-fold of the control at 12 hr) ornithine decarboxylase (ODC) in the liver of rats. Parallel to ODC induction there was a marked increase in hepatic putrescine content. Phorone also produced an increase in spermidine content and a decrease in spermine content. The effects of phorone on ODC and putrescine content occurred dose-dependently with more than a 1000-fold increase in ODC activity over the controls at a dose of 500 mg/kg. Pretreatment of rats with buthionine sulfoximine, a GSH depletor by inhibition of biosynthesis, failed to inhibit phorone-mediated induction of ODC. In contrast, pretreatment with GSH, but not post-treatment, blocked the induction of ODC by phorone.

Metabolic activation of the tricyclic antidepressant amineptine--I. Cytochrome P-450-mediated in vitro covalent binding

Incubation of [14C]amineptine (1 mM) with hamster liver microsomes resulted in the irreversible binding of an amineptine metabolite to microsomal proteins. Covalent binding measured in the presence of various concentrations of amineptine (0.0625-1 mM) followed Michaelis-Menten kinetics. Pretreatment with phenobarbital increased not only the Vmax, but also the Km, for this binding. Covalent binding required NADPH and molecular oxygen and was decreased when the incubation was made in the presence of inhibitors of cytochrome P-450 such as piperonyl butoxide (4 mM), SKF 525-A (4 mM) or carbon monoxide (80:20 CO-O2 atmosphere). In contrast, binding was increased when microsomes from untreated hamsters were incubated in the presence of 0.5 mM 1,1,1-trichloropropene 2,3-oxide, an inhibitor of epoxide hydrolase. Metabolic activation also occurred in kidney microsomes. In vitro covalent binding to kidney microsomal proteins required NADPH and was decreased by piperonyl butoxide (4 mM) but was not increased by pretreatment with phenobarbital. We conclude that amineptine is activated by hamster liver and kidney microsomes into a chemically reactive metabolite that covalently binds to microsomal proteins.