Early biochemical alterations in liver mitochondria from carbon tetrachloride poisoned rats

Nifurtimox nitroreductase activity in different cellular fractions from male rat pancreas. Biochemical and ultrastructural alterations

Nifurtimox (Nfx) is a nitroheterocyclic drug used in the treatment of Chagas' disease. It has serious side effects which frequently force to interrupt the treatment. Nfx toxicity has been linked to its nitroreduction to a nitroanion radical with a subsequent redox cycling which generate reactive oxygen species. We analyzed the ability of Sprague Dawley male rat pancreas to nitroreduce Nfx and whether this drug may cause deleterious effects in this organ. The microsomal fraction exhibited Nfx nitroreductase activity in the presence of NADPH under anaerobic atmosphere, which was fully inhibited under air but not altered when N2 was replaced by pure CO. The cytosol nitroreduced Nfx in the presence of hypoxanthine under N2; it was inhibited by allopurinol and negligible in aerobiosis. Nfx reached pancreatic tissue at 1, 3 or 6 h after intragastric administration (100 mg/kg). Six hours after drug administration, a significant increase in t-buthylhydroperoxide promoted chemiluminiscence was detected. Pancreatic protein sulfhydryl content significantly decreased at either 1, 3 or 6 h after Nfx administration. No changes in either protein carbonyl or in lipid hydroperoxides were observable. Ultrastructural alterations were observed in the endoplasmic reticulum and nuclei from acinar cells and in the insulin-containing granules from the pancreas. However, the seric amylase levels were not changed, but the blood glucose levels were slightly but significantly increased 24 h after Nfx administration. These studies might suggest that Nfx treatment could impose an increased risk to patients exposed to other insults provoking oxidative stress or having preexisting pathologies in the pancreas.

Nifurtimox biotransformation to reactive metabolites or nitrite in liver subcellular fractions and model systems

Liver microsomal (mic); nuclei (N) and mitochondria (mit) anaerobically nitroreduce Nifurtimox (Nfx) in the presence of NADPH generating system. Simultaneous formation of small amounts of nitrite was observed in microsomes and nuclei but not in mitochondria. The microsomal nitroreductase activity was enhanced by the presence of flavine-adenine-dinucleotide disodium salt (FAD), was not inhibited by CO and was significantly inhibited by diphenyleneiodonium (DPI). In the microsomal NADPH-dependent fraction nitrite formation was null in the presence of FAD, DPI and under air and was partially inhibited by pure CO. Pure human cytochrome P450 reductase in the presence of NADPH significantly nitroreduced Nfx and produced small amounts of nitrite. The nitroreductive process was significantly enhanced by FAD but the nitrite formation became null. FAD itself was able to chemically nitroreduce Nfx without production of nitrite. NADPH generating system enhanced the FAD nitroreductive effect and led to small production of nitrite. Formation of reactive metabolites and nitric oxide during Nfx metabolism might contribute to its toxicity.

Effects of dietary polyunsaturated fatty acids and nucleotides on tissue fatty acid profiles of rats with carbon tetrachloride-induced liver damage

The deficiency of polyunsaturated fatty acids (PUFA) that occurs in plasma of patients with liver cirrhosis has been assessed in rats with severe steatosis and mild liver necrosis induced by repeated administration of low doses of carbon tetrachloride (CCl(4)). The contribution of both dietary (n-3) long-chain PUFA and nucleotides to the recovery of the altered fatty acid profiles of tissue lipids of these rats has also been studied. Two groups of rats were used. The first was intraperitoneally injected 0.15 ml of a 10% (v/v) CCl(4)solution in paraffin per 100 g of body weight, three times a week for 9 weeks; the second received paraffin alone. After the treatment, six rats of each group were killed. Afterwards, the remaining controls were fed a semipurified diet (SPD) for 3 weeks, and the remaining rats in the CCl(4)group were divided into three new groups: the first was fed the SP diet; the second was fed the SP diet supplemented with 1% (n-3) polyunsaturated fatty acids (PUFA diet); and the third was fed the SP diet supplemented with 250 mg nucleotides per 100 g diet (NT diet). Fatty acids of plasma, erythrocyte membranes and liver microsomes were analyzed. Decreases in linoleic and arachidonic acids in both total plasma lipids and liver microsomal phospholipids were the main findings due to CCl(4)treatment. The rats that received CCl(4)and the PUFA diet showed the lowest levels of (n-6) PUFA and the highest levels of (n-3) PUFA in liver microsomal phospholipids, as well as a significant increase of (n-3) PUFAs in total plasma lipids. The animals that received the NT diet showed no signs of fatty infiltration and exhibited the highest levels of (n-6) PUFAs in liver microsomal phospholipids. These results show that CCl(4)affects fatty acid metabolism which is accordingly reflected in altered tissue fatty acid profiles, and that balanced diets containing PUFA and nucleotides are important for the recovery of the damaged liver in rats.

Cholesterol interaction with free radicals produced from carbon tetrachloride or bromotrichloromethane by either catalytic decomposition or via liver microsomal activation

The reaction between cholesterol (Ch) and trichloromethyl or trichloromethyl peroxyl radicals was studied. The latter were generated from CCl4 either by benzoyl peroxide (BP) catalysis or via thermal activation or by liver microsomal NADPH-dependent biotransformation of CBrCl3. The structure of the products formed was elucidated by gas chromatography-mass spectrometry (GC/MS). Under aerobic conditions and using thermal activation of CCl4, the formation of 6 products was observed. Two (I and II) were dehydrated Ch derivatives (one also having a third double bond) (I). Another product was a delta(5)-3 ketone derivative of Ch (III). Two additional reaction products were determined as ketocholesterols (IV and V). One chloro Ch was also formed (VI). At low concentrations of BP, reaction was more extensive than under thermal activation, and the formation of peaks I to IV was also observed. When the reaction was conducted anaerobically and using thermal activation of CCl4 to generate radicals, only products I and II were formed in low yield. Under anaerobic conditions, but using catalyst, compounds I and III were produced plus two new isomeric ketocholesterol derivatives (VIII and IX) and also a compound having an extra hydroxyl group on the Ch structure (X). In order to check whether similar reactions are observable under biological experimental conditions, we used activation of CBrCl3 by liver microsomes. The incubation using only microsomes (without CBrCl3 or NADPH) showed two ketocholesterol peaks (A and B). In the presence of CBrCl3 we could detect peak B and hydroxycholesterol (C) and two others, ketocholesterols (D and E). D was the only peak showing close similarity (spectrum and retention time) to one of those observed in the chemical reaction system (V). The reaction of CBrCl3 in the presence of NADPH showed peaks B, C, D and E, in low abundance and a 7-ketocholesterol (F). If some of the reaction products reported here were formed during the intoxication with these haloalkanes, significant biological consequences might be expected.

Tyrosine attack by free radicals derived from catalytic decomposition of carbon tetrachloride

The interaction between free radicals derived from the catalytic decomposition of carbon tetrachloride and tyrosine (the N-acetyl tyrosine ethyl ester, ATEE) under anaerobic and aerobic conditions was studied. The structure of the reaction products formed was deciphered by the GLC/MS analysis of their trimethylsilyl derivatives. Under anaerobic conditions the formation of the following products was found: (1) an unsaturated derivative of the amino acid; (2) the trimethylsilyl derivative of N-acetyl chloro tyrosine ethyl ester; (3) a hydroxyl adduct of ATEE; (4) an ATEE adduct having a chlorine and a CCl3 group in the molecule (it is suggested that CCl3 is attached to the benzyl carbon and the chlorine located in the benzene ring); (5) an ATEE adduct having only a CCl3 group tentatively assigned to be located on the benzyl carbon; and (6) and (7) were found to be two isomers of an ATEE having one CCl3 on the aromatic ring. Under aerobic conditions the following reaction products were identified: Two products which were similar to those numbered (1) and (2) and formed anaerobically; (8) and (11) two isomeric dichlorinated adducts of ATEE; (9) and (10) two isomeric dichlorinated monohydroxylated derivatives of ATEE. Concerning the potential relevance of these findings, we consider that if similar interactions to those here reported occurred during CCl4 poisoning, the activity of enzymes having tyrosine in their active center might result in impairment. Further, enzymes operating on tyrosine moieties in proteins might be perturbed in their action tyrosine groups were attacked by the free radicals arising from catalytic decomposition of CCl4 evidenced here.

Decreased incorporation of 14C-leucine in different liver nuclear protein fractions at early stages of carbon tetrachloride poisoning in the rat

Administration of CCl4 to 12-14 h starved Sprague Dawley male rats (220-240 g) at a dose of 5 ml of a 20% (v/v) olive oil solution/kg i.p. decreased the incorporation of 14C-leucine into microsomal and nuclear proteins at 1 or 2 h after the hepatotoxin. Decreased amino acid incorporation capacity in nuclear but not in microsomal proteins returned to control values at 4 h after poisoning. Cycloheximide given i.p. at a dose of 1 mg/kg in saline either alone or before CCl4 also decreased to a similar or greater extent the incorporation of 14C-leucine into both, microsomal and nuclear proteins at 1 h. The CCl4-induced decrease in amino acid incorporation was observable and significant even 1 h after CCl4 and involved histone and different non-histone nuclear protein fractions. Results suggest that decreased protein synthesis at the endoplasmic reticulum occurring in the very early stages of CCl4 poisoning might provoke temporary deficiencies in protein supplies to nuclei with as yet unknown consequences. However, some of the proteins involved have major regulatory properties in DNA expression.

Free radical-induced liver injury. II. Effects of intraperitoneally administered 2,2'-azobis(2-amidinopropane) dihydrochloride on the fatty acid profiles of hepatic triacylglycerol and phospholipids

Liver injury induced by the radical initiator, 2,2'-azobis(2-amidinopropane) dihydrochloride (AAPH) and carbon tetrachloride (CCI4) was examined by the analysis of lipids in the liver of rats. Increased triacylglycerol (TAG) was found in the liver within 24 hr following injection of these drugs. In AAPH-treated and CCI4-treated rats, it was 2.1 and 1.8 times that in the controls, respectively. TAG-palmitate and -oleate were found at particularly increased levels, while polyunsaturated fatty acid profiles of hepatic phospholipids were essentially the same for the treated and untreated rats. It is evident from these findings that radical initiators cause no decrease in polyunsaturated fatty acids in hepatic lipids, but accumulate TAG in the liver. Such a condition is the equivalent of liver injury in the rats in whose diets vitamin E has long been deficient.

Protection against carbon-tetrachloride-induced lymphoid organotoxicity in rats by protein A

In a previous study we described protection of rats from carbon tetrachloride (CCl4)-induced hepatotoxicity by protein A (PA). In the present report we described protection against CCl4-induced lymphoid organotoxicity in rats by PA. Our data indicate that CCl4 administration produced a significant increase in the number of total leukocytes and polymorphs in blood, a significant decrease in leukocyte count in bone marrow, and a significant loss in weight of spleen and adrenals. In the animals receiving PA prior to and after CCl4, these values were found to be near those of controls. Histological examination revealed thymocyte depletion in thymic lobe and degenerative changes of tissue in spleen of CCl4-exposed animals. PA treatment to CCl4-exposed animals exhibited improvement and recovery from the damage caused by CCl4. These observations throw a new light on the field of CCl4 toxicity to lymphoid organs and their protection by PA.

Further studies on the late preventive effects of the anticalmodulin trifluoperazine on carbon tetrachloride-induced liver necrosis

Trifluoperazine (TFP) (50 mg/kg ip) administration to rats 6 or 10 hr after CCl4 (1 ml/kg ip in olive oil) significantly prevented liver necrosis but not fatty liver caused by the hepatotoxin at 24 hr as evidenced by either histology or electron microscopy. TFP given 6 hr after CCl4 significantly decreased the CCl4-induced increases in liver calcium content. TFP raised four to five times the liver glycogen content in control rats but was unable to modify decreased glycogen content of CCl4 poisoned animals. TFP administration increased phospholipid and protein synthesis as evidenced by studies on 32P incorporation into microsomal phospholipid and by experiments on [14C]leucine incorporation in microsomal protein fractions from control rat livers. No significant changes were observed in microsomal phospholipid degradation as studied by decay of label from 32P-prelabeled microsomal lipids or in increased protein degradation as evidenced by decay of label from [14C-guanidino]arginine-prelabeled microsomal proteins found in livers of control rats after TFP treatment. Electron microscopy observations of liver from control animals treated with TFP evidenced accumulation of glycogen in areas close to smooth endoplasmic reticulum (SER); large Golgi areas with an abundant number of lysosomes, and minor dilatation effects on the rough endoplasmic reticulum (RER) and nuclear membrane. Results suggest that TFP preventive effects might be due to the anticalmodulin actions of this drug.