Kiyoko Simizu

Dose-dependent study of the effects of acute lindane administration on rat liver superoxide anion production, antiooidant enzyme activities and lipid peroxidation

The administration of single i.p. doses of lindane (20, 40, 60 and 80 mg/kg) to rats produced a progressive increase in the liver microsomal content of cytochrome P-450 and in the rate of superoxide anion generation, as measured by adrenochrome formation. A dose-dependent increase in lipid peroxidation of liver homogenates, assessed by measuring thiobarbituric acid reactants, was also found. Lindane treatment did not alter the activity of liver glucose-6-phosphate dehydrogenase, glutathione reductase or glutathione peroxidase, while that of superoxide dismutase and catalase was significantly reduced. These changes were accompanied by a progressive liver steatosis. The collected metabolic data were interpreted in terms of a causal relationship between an increase in superoxide radical generation, secondary to cytochrome P-450 induction and a resulting increase in lipid peroxidation. The decrease in superoxide dismutase and catalase activities is likely to contribute to the increased levels of lipid peroxidation in view of their antioxidant properties.

Lindane-Induced Oxidative Stress. I. Time Course of Changes in Hepatic Microsomal Parameters, Antioxidant Enzymes, Lipid Peroxidative Indices and Morphological Characteristics

1. Lindane (60 mg/kg) administered orally to rats increased liver cytochrome P-450 content and superoxide radical (O2-.) generation 24 h after treatment, while formation of thiobarbituric acid reactants and NADPH/ADP-supported microsomal chemiluminescence were significantly increased 4 h after treatment. 2. Hepatic superoxide dismutase (SOD) and catalase decreased 6 h after lindane treatment and SOD/O2-. ratio progressively decreased during 4 to 24 h after lindane treatment. 3. Morphological evidence of hepatic cell injury after lindane treatment was seen at all times studied, and appeared to increase with time. 4. Lindane administration results in time-dependent oxidative stress in liver which involves an early component (4-6 h) related to the reductive metabolism of lindane, and a late component (24 h) associated with the induction of cytochrome P-450; the biochemical changes correlated with the observed morphological lesions.

Lindane-Induced Oxidative Stress. II. Time Course of Changes in Hepatic Glutathione Status

1. Four hours after treatment of rats with lindane (60 mg/kg), hepatic GSH content was decreased (22%) and GSSG was increased (20%), while biliary concentration and excretion of both GSH and GSSG and bile flow were diminished. These changes coincide with the onset of hepatic lipid peroxidation. 2. The changes induced by lindane at 4 h disappeared at 6 h after treatment, but liver GSSG content (91%), biliary GSSG excretion (133%) and bile flow (42%) were enhanced at 24 h. 3. The data indicate that lindane treatment elicits marked changes in hepatocyte glutathione status, with a decrease in the GSH/GSSG ratio at early (2-4 h) and late (24 h) periods of poisoning.

Liver lipid peroxidation-related parameters after short-term administration of hexachlorocyclohexane isomers to rats

Rats treated with diets containing 20 ppm of alpha- or gamma-hexachlorocyclohexane (HCH) for 15 or 30 days showed increased levels of liver cytochrome P-450 followed by increased production of both thiobarbituric acid reactants by liver homogenates and microsomes and superoxide anion production by liver microsomes. In these animals superoxide dismutase (SOD) activity was also increased. In consequence, the ratio between SOD activity and microsomal superoxide radical (O2-.) production showed a slight increase after 15 days of treatment. However, after 30 days, there was a tendency for this ratio to decrease. Other parameters studied were liver glucose-6-phosphate dehydrogenase, glutathione peroxidase, glutathione reductase and catalase (CAT) activities. Among them, only CAT activity showed a 26% and 38% increase after 15 or 30 days of treatment with the alpha-isomer. It is suggested that when lipid peroxidation is involved in the mechanism of toxicity of a xenobiotic, this parameter can be used to determine the no-observed-effect level.

Prooxidant and antioxidant hepatic factors in rats chronically fed an ethanol regimen and treated with an acute dose of lindane

While acute lindane treatment and chronic ethanol feeding to rats have been associated with hepatic oxidative stress, the possible roles of these stresses in the pathogenesis of hepatic lesions reported in acute lindane intoxication and in those observed in some models of chronic alcoholism have not been established. Our previous studies in rats chronically fed ethanol regimens and then treated with a single intraperitoneal (i.p.) dose of lindane (20 mg/kg) showed that while lindane per se was invariably associated with hepatic oxidative stress, chronic ethanol feeding only produced this stress when the dietary level of vitamin E was relatively low. Chronic ethanol pretreatment did not significantly affect the lindane-associated oxidative stress, and neither chronic ethanol feeding nor acute lindane, single or in combination, produced any histologic and biochemical evidence of liver damage. In the present experiment, the acute dose of lindane was increased to 40 mg/kg, and we have studied a larger number of prooxidant and antioxidant hepatic factors. Male Wistar rats (115.5 +/- 5.4 g) were fed ad lib for 11 weeks a calorically well-balanced and nutritionally adequate basal diet, or the same basal diet plus a 32% ethanol/25% sucrose solution, also ad lib, and were then injected i.p. with a single dose of lindane or with equivalent amounts of corn oil. The results indicated that acute lindane treatment to naive rats increased practically all the prooxidant hepatic factors examined (cytochromes P450 and b5, NADPH cytochrome c reductase, NADPH oxidase), as well as the generation of microsomal superoxide radical and thiobarbituric acid reactive substances of liver homogenates, but did not modify any of the antioxidant hepatic factors studied. Conversely, the chronic administration of ethanol alone did not significantly affect the prooxidant hepatic factors but reduced some of the antioxidants (i.e., the activities of GSH-Px and the contents of alpha-tocopherol and ubiquinols 9 and 10). Although chronic ethanol pretreatment further increased the superoxide generation induced by lindane per se, it did not increase but generally reduced the effects of lindane per se on the other prooxidant factors studied. Furthermore, although acute lindane administration to ethanol-pretreated rats was associated with decreases in GSH and catalase (not affected by ethanol or lindane treatment alone), it did not substantially modify the reducing effects of ethanol feeding per se on GSH-Px, alpha-tocopherol, and ubiquinols. Once again, neither chronic ethanol feeding nor lindane treatment, single or in combination, was associated with any evidence of liver damage.

Mechanisms of lindane-induced hepatotoxicity : alterations of respiratory activity and sinusoidal glutathione efflux in the isolated perfused rat liver

1. Lindane (25-60 mg/kg) at 24 h after dosage induced a dose-dependent increase in oxygen consumption by perfused rat livers, an effect not observed at early times (2-6 h) after administration. About 60% of the increase in liver oxygen uptake is suppressed by the antioxidant, desferrioxamine, indicating enhanced free radical activity induced by the insecticide. 2. The hepatic content of total GSH equivalents (GSH + 2GSSG) decreased 4 h after lindane treatment (60 mg/kg), together with significant diminution in net and fractional rates of sinusoidal GSH efflux, that returned to control values 24 h after treatment. 3. These data indicate that lindane resulted in marked changes in hepatic oxidative capacity and glutathione metabolism, which condition the production of oxidative stress in the liver at different times of intoxication.

Effect of phenobarbital and 3-methylcholanthrene on the early oxidative stress component induced by lindane in rat liver

1. Lindane administered to untreated rats or rats pretreated with phenobarbital (PB) or 3-methylcholanthrene (MC) increased liver lipid peroxidation, of the same magnitude in all groups. 2. PB pretreatment produced a 50% increase in lipid peroxidation (TBAR) by liver homogenates and microsomes, an effect accompanied by increases in cytochrome P-450, NADPH-cytochrome P-450 reductase, NADPH oxidase and microsomal superoxide anion production, MC pretreatment resulted in increases in liver cytochrome P-450 and NADPH oxidase only. 3. Pretreatment of rats with PB, but not MC or lindane, gave increases in glutathione peroxidase and reductase. 4. Pretreatment with PB, but not MC, increased liver GSH. Lindane decreased liver GSH to the same extent as PB plus lindane. 5. Biliary GSH, GSSG and bile flow were decreased by lindane to similar extents in all groups. 6. Lindane induced periportal necrosis with haemorrhagic foci in all groups. 7. Data presented indicate that the early lipid peroxidative response of liver to lindane was unchanged by PB- or MC-stimulated hepatic microsomal enzyme induction.

Turnover of hepatic glutathione after acute lindane intoxication

The administration of lindane (60 mg/kg) to fed rats diminished the content of hepatic glutathione (GSH) 4 h after treatment, which was recovered at 24 h. At these experimental times, the activities of glutathione peroxidase, glutathione reductase, glutathione-S-transferases and gamma-glutamyltransferase in the liver of lindane-treated rats and control animals were comparable. Liver GSH turnover, measured after a pulse of [35S]cysteine, was enhanced by 69% (P < 0.05) in lindane-treated rats 24 h after intoxication compared to controls, with a 63% (P < 0.05) increase in the estimated rate of GSH synthesis. It is concluded that lindane enhances GSH synthesis in rat liver 24 h after treatment as a consequence of the decrement in its content observed at early times of intoxication (4 h), thus allowing the recovery of the normal level of hepatic GSH.