Early mitochondrial disfunction in bromobenzene treated mice: a possible factor of liver injury

Brodifacoum induces early hemoglobinuria and late hematuria in rats: novel rapid biomarkers of poisoning

INTRODUCTION

Brodifacoum (BDF) is a superwarfarin that is used primarily as a rodenticide. There have been increasing numbers of reports of human cases of accidental or intentional BDF ingestion with high mortality rate. Its broad availability and high lethality suggest that BDF should be considered a potential chemical threat. Currently, there is no biomarker for early detection of BDF ingestion in humans; patients typically present with severe coagulopathy. Since we demonstrated earlier that warfarin can induce acute kidney injury with hematuria, we tested whether BDF would also lead to change in urinary biomarkers.

MATERIAL AND METHODS

BDF was administered to Sprague Dawley rats via oral gavage. N-acetylcysteine (NAC) was given per os in drinking water 24 h prior to BDF. Urinalysis was performed at different times after BDF administration. Anticoagulation and serum creatinine levels were analyzed in the blood.

RESULTS

We observed that within a few hours the animals developed BDF-dose-dependent transient hemoglobinuria, which ceased within 24 h. This was accompanied by a transient decrease in hematocrit, gross hemolysis and an increase in free hemoglobin in the serum. At later times, animals developed true hematuria with red blood cells in the urine, which was associated with BDF anticoagulation. NAC prevented early hemoglobinuria, but not late hematuria associated with BDF.

CONCLUSIONS

We propose that transient early hemoglobinuria (associated with oxidative stress) with consecutive late hematuria (associated with anticoagulation) are novel biomarkers of BDF poisoning, and they can be used in clinical setting or in mass casualty with BDF to identify poisoned patients.

Role of reactive metabolites in drug-induced hepatotoxicity

Drugs are generally converted to biologically inactive forms and eliminated from the body, principally by hepatic metabolism. However, certain drugs undergo biotransformation to metabolites that can interfere with cellular functions through their intrinsic chemical reactivity towards glutathione, leading to thiol depletion, and functionally critical macromolecules, resulting in reversible modification, irreversible adduct formation, and irreversible loss of activity. There is now a great deal of evidence which shows that reactive metabolites are formed from drugs known to cause hepatotoxicity, such as acetaminophen, tamoxifen, isoniazid, and amodiaquine. The main theme of this article is to review the evidence for chemically reactive metabolites being initiating factors for the multiple downstream biological events culminating in toxicity. The major objectives are to understand those idiosyncratic hepatotoxicities thought to be caused by chemically reactive metabolites and to define the role of toxic metabolites.

Energy intake affects the biotransformation rate, scope for induction, and metabolite profile of benzo[a]pyrene in rainbow trout

The metabolic conversion of benzo[a]pyrene (B[a]P) by rainbow trout (Oncorhynchus mykiss) hepatocytes was not significantly different between any group of fed fish (fed one of three isoenergetic diets that varied in protein and lipid content at full satiation levels or half rations), however at 12 weeks, fasted fish exhibited significantly reduced B[a]P biotransformation rates (by 58%). Alterations in metabolite profiles were also seen: fasted fish produced significantly more Phase I metabolites, higher levels of both glucuronide and sulphate conjugates, and lower levels of presumptive glutathione conjugates, compared to fed fish. When fish were fasted, higher proportions of phenols were produced, with lower proportions of quinones, triols and tetrols. Inducing metabolism (using beta-naphthoflavone) increased metabolic scope for B[a]P by 2-fold, regardless of each diet's baseline metabolic rate. However, the balance between Phase I and II reactions was altered with induction and fasting: higher proportions of Phase I metabolites were found, with lower glutathione conjugates and higher proportions of triols/tetrols. Fasting-mediated reductions in glutathione conjugation, and increased induction of oxidation vs. conjugating enzymes, can explain altered metabolite profiles. These results suggest that in contaminated habitats, where pollution-induced reductions in food quantity or quality are combined with the presence of toxic compounds and inducers, detoxification rates can be diminished.

Chlorinated methanes and liver injury: highlights of the past 50 years

The chlorinated methanes, particularly carbon tetrachloride and chloroform, are classic models of liver injury and have developed into important experimental hepatoxicants over the past 50 years. Hepatocellular steatosis and necrosis are features of the acute lesion. Mitochondria and the endoplasmic reticulum as target sites are discussed. The sympathetic nervous system, hepatic hemodynamic alterations, and role of free radicals and biotransformation are considered. With carbon tetrachloride, lipid peroxidation and covalent binding to hepatic constituents have been dominant themes over the years. Potentiation of chlorinated methane-induced liver injury by alcohols, aliphatic ketones, ketogenic compounds, and the pesticide chlordecone is discussed. A search for explanations for the potentiation phenomenon has led to the discovery of the role of tissue repair in the overall outcome of liver injury. Some final thoughts about future research are also presented.

The role of mitochondrial injury in bromobenzene and furosemide induced hepatotoxicity

Bromobenzene (BB) and furosemide (FS) are two hepatotoxicants whose bioactivation to reactive intermediates is crucial to the development of liver injury. However, the events which lead to hepatocellular toxicity following metabolite formation and covalent binding to cellular macromolecules remain unknown. The present study was undertaken to investigate the effect of administered BB and FS on mitochondrial total glutathione (GSH+GSSG, henceforth referred to as glutathione) content and respiratory function as potential initiating mechanisms of the hepatotoxicity of these compounds in the mouse. Bromobenzene (2 g/kg i.p.) significantly decreased mitochondrial glutathione to 48% of control at 3 h post administration, and to 41% at 4 h. This decrease in mitochondrial glutathione was subsequent to a significant decrease in cytosolic glutathione to 64 and 28% of control at 1 and 2 h, respectively. Oxygen consumption supported by complex I (glutamate-supported) of the respiratory chain was not inhibited by BB until 4 h, where state 3 (active) respiration was reduced to 16% of control. This resulted in a decreased respiratory control ratio (RCR) for complex I-supported respiration. Complex II (succinate)-supported state 3 and state 4 respiration were unaffected by BB until 4 h, at which time they were reduced to 57 and 48% of control, respectively. However, the similar reductions in state 3 and state 4 respiratory rates did not alter the corresponding RCR for complex II. Overt hepatic injury was detected at 4 h, with plasma alanine aminotransferase (ALT) activity increasing significantly at this time point. In contrast to the effects of BB, FS administration (400 mg/kg i.p.) did not alter mitochondrial or cytosolic glutathione, and had no effect on respiration supported by complex I or II for up to 5 h following dosing. However, ALT activity was significantly increased 5 h following FS administration. These results suggest that inhibition of mitochondrial respiratory function coinciding with a decrease in mitochondrial glutathione content may be crucial to the initiation of BB-induced hepatotoxicity, while such events are not required for the initiation of FS-induced hepatotoxicity.

Increased oxidation and decreased conjugation of drugs in the liver caused by starvation. Altered metabolism of certain aromatic compounds and acetone

Starvation causes several changes in the various processes of biotransformation. The focus of this review is on biotransformation of various aromatic and other compounds whose metabolism is catalyzed in phase I by isozymes belonging to the CYP2E1 gene subfamily, while in phase II phenol-UDPGT or conjugation with GSH play a dominant role. The other ways of conjugation are beyond the scope of this review. The reason why this aspect has been chosen is that the capacity of these reactions is profoundly altered by nutritional conditions. There is a balance between the two phases of biotransformation. Therefore, under standard circumstances in a well-fed state the intermediate formed in the course of phase I is converted to a conjugated compound rapidly, as a result of phase II. However, in starvation the pattern of drug metabolism is altered and the balance between the two phases is changed. This alteration of drug metabolism upon starvation is partly connected to the changes of cofactor supplies due to the metabolic state.

Lipid hydroperoxide induced mitochondrial dysfunction following acute ethanol intoxication in rats. The critical role for mitochondrial reduced glutathione

It has been found that acute ethanol (EtOH) intoxication of rats caused depletion of mitochondrial reduced glutathione (GSH) of approximately 40%. A GSH reduction of similar extent was also observed after the administration to rats of buthionine sulphoximine (BSO), a specific inhibitor of GSH synthesis. Combined treatment with BSO plus EtOH further decreased mitochondrial GSH up to 70% in comparison to control. Normal functional efficiency was encountered in BSO-treated mitochondria, as evaluated by membrane potential measurements during a complete cycle of phosphorylation. In contrast a partial loss of coupled functions occurred in mitochondria from EtOH- and BSO plus EtOH-treated rats. The presence in the incubation system of either GSH methyl monoester (GSH-EE), which normalizes GSH levels, or of EGTA, which chelates the available Ca2+, partially restores the mitochondrial phosphorylative efficiency. Following EtOH and BSO plus EtOH intoxication, the presence of fatty-acid-conjugated diene hydroperoxides, such as octadecadienoic acid hydroperoxide (HPODE), was detected in the mitochondrial membrane. Exogenous HPODE, when added to BSO-treated mitochondria, induced, in a concentration-dependent system, membrane potential derangement. The presence of either GSH-EE or EGTA fully prevented a drop in membrane potential. The results obtained suggest that fatty acid hydroperoxides, endogenously formed during EtOH metabolism, brought about non-specific permeability changes in the mitochondrial inner membrane whose extent was strictly dependent on the level of mitochondrial GSH.

Effect of various non-hepatotoxic compounds on urinary and liver taurine levels in rats

Administration of compounds which alter protein synthesis or sulphur amino acid metabolism in rats results in changes in the excretion of urinary taurine. Treatment with diethylmaleate (DEM) or phorone, which will deplete glutathione (GSH), reduces taurine excretion, whereas treatment with buthionine sulphoximine (BSO), which will inhibit glutathione synthesis, increases taurine excretion. Treatment with cycloheximide, an inhibitor of protein synthesis, increases taurine excretion, whereas pretreatment with phenobarbital, which will increase protein synthesis, decreases taurine excretion. Administration of agents which damage organs other than the liver such as the kidney, heart and testes, does not increase urinary taurine.

Effects of phenolic compounds on bromobenzene-mediated hepatotoxicity in mice

1. The hepatic protective effects of the phenolic compounds 7,8-dihydroxyflavone, morin, silymarin, caffeic acid and chlorogenic acid on bromobenzene-induced toxicity in mice were studied. 2. Morin, caffeic acid and chlorogenic acid at an oral dose of 200 mg/kg failed to influence hepatotoxicity in vivo, while 7,8-dihydroxyflavone exhibited efficacy and potency higher than those of the reference compound silymarin. 3. 7,8-Dihydroxyflavone, an antioxidant and hepatoprotective agent in vitro, decreased serum glutamate-pyruvate transaminase levels (SGPT) in a dose-related manner, and at 200 mg/kg inhibited bromobenzene-induced glutathione depletion in liver.

Glutathione depletion, lipid peroxidation, DNA double-strand breaks and the cytotoxicity of 2-bromo-3-(N-acetylcystein-S-yl)hydroquinone in rat renal cortical cells

The mechanisms involved in the cytotoxicity of 2-bromo-3-(N-acetylcystein-S-yl)hydroquinone, a model compound for hydroquinone derived mercapturic acids, were investigated in rat renal proximal tubule cells. 2-Bromo-3-(N-acetylcystein-S-yl)hydroquinone induced a time- and concentration-dependent decrease in cell viability and in the levels of cellular glutathione. Antioxidants such as N,N'-diphenyl-p-phenylene diamine and ascorbic acid and the iron chelator desferrioxamine very efficiently protected the cells from 2-bromo-3-(N-acetylcystein-S-yl)hydroquinone without influencing glutathione depletion. The acetoxymethyl ester of the Ca2+ chelator Quin-2, the inhibitor of the Ca(2+)- and Mg(2+)-dependent endonucleases, aurintricarboxylic acid and the poly(ADP-ribose)-polymerase inhibitor 3-aminobenzamide also ameliorated 2-bromo-3-(N-acetylcystein-S-yl)hydroquinone cytotoxicity. Moreover, 2-bromo-3-(N-acetylcystein-S-yl)hydroquinone depleted Ca2+ from isolated kidney mitochondria, increased the amount of malondialdehyde in rat kidney cells and induced DNA double-strand breaks in renal cells in culture. These results suggest that renal cells oxidize 2-bromo-3-(N-acetylcystein-S-yl)hydroquinone to the corresponding quinone; this soft electrophile reacts rapidly with glutathione, thus depleting cellular glutathione concentrations as indicated by the tentative identification of a 2-bromo-3-(N-acetylcystein-S-yl)hydroquinone thioether in the incubation medium of renal cells treated with the mercapturate. As a result of the massive glutathione depletion, peroxidative mechanisms then cause an elevation of the cytosolic concentrations of ionized calcium; impairment of the ability of the mitochondria to sequester Ca2+ plays an important role in the elevation of the Ca2+ concentration. Finally, activation of Ca(2+)- and Mg(2+)-dependent endonucleases results in DNA damage and cell death.

Mitochondrial bioenergetics as affected by DDT

The organochloride insecticide DDT (2,2-bis(p-chlorophenyl)-1,1-trichloroethane) depresses the phosphorylation efficiency of mitochondria as inferred from the decrease of respiratory control ratio (RCR) and P/O ratio, perturbations of transmembrane potential (delta psi) fluctuations associated with mitochondrial energization and phosphorylative cycle induced by ADP. DDT depresses the delta psi developed by energized mitochondria and prevents complete repolarization, that is delayed and resumed at a lower rate. The inhibitory action of DDT on phosphorylation efficiency may result from: (1) a direct effect on the ubiquinol-cytochrome c segment of the redox chain; (2) direct action on the ATP-synthetase complex; (3) partial inhibition of the phosphate transporter. DDT preferentially interacts with phosphorylation process in relation to respiration. High concentrations of DDT induce destruction of the structural integrity of mitochondria.