Cytotoxicity of monocrotaline in isolated rat hepatocytes: effects of dithiothreitol and fructose.
ABSTRACT Monocrotaline (MCT) is a pyrrolizidine alkaloid present in plants of the Crotalaria species that causes cytotoxicity and genotoxicity, including hepatotoxicity in animals and humans. It is metabolized by cytochrome P-450 in the liver to the alkylating agent dehydromonocrotaline (DHM). In previous studies using isolated rat liver mitochondria, we observed that DHM, but not MCT, inhibited the activity of respiratory chain complex I and stimulated the mitochondrial permeability transition with the consequent release of cytochrome c. In this study, we evaluated the effects of MCT and DHM on isolated rat hepatocytes. DHM, but not MCT, caused inhibition of the NADH-linked mitochondrial respiration. When hepatocytes of rats pre-treated with dexamethasone were incubated with MCT (5 mM), they showed ALT leakage, impaired ATP production and decreased levels of intracellular reduced glutathione and protein thiols. In addition, MCT caused cellular death by apoptosis. The addition of fructose or dithiotreitol to the isolated rat hepatocyte suspension containing MCT prevented the ATP depletion and/or glutathione or thiol oxidation and decreased the ALT leakage and apoptosis. These results suggest that the toxic effect of MCT on hepatocytes may be caused by metabolite-induced mitochondrial energetic impairment, together with a decrease of cellular glutathione and protein thiols.
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ABSTRACT: A method for measurement of both oxidized (GSSG) and reduced (GSH) glutathione has been developed, with use of o-phthalaldehyde (OPT) as a fluorescent reagent. The method takes advantage of the reaction of GSH with OPT at pH 8 and of GSSG with OPT at pH 12; GSH can be complexed to N-ethylmaleimide to prevent interference of GSH with measurement of GSSG. The method gave “recoveries” of 91 to 110% for both GSH and GSSG and was quite specific for glutathione; and none of the manipulations appeared to influence the amount of glutathione present in the tissue. Results for GSH levels agreed well with earlier reports but levels of GSSG estimated here were higher than earlier reported values. The reasons for the apparently higher levels of GSSG are discussed.Analytical Biochemistry 08/1976; 74(1):214-26. · 2.58 Impact Factor
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- Pharmacological Reviews 01/1971; 22(4):429-83. · 22.35 Impact Factor