RELATIONSHIP BETWEEN ANTIOXIDANT SYSTEMS, INTRACELLULAR THIOLS AND DNA-PLOIDY IN LIVER OF RATS DURING EXPERIMENTAL CIRRHOGENESIS

Hyperplastic nodular cirrhosis was induced in rats by long-term (6 mon th) i.p. administration of thioacetamide at doses of 2.66 mmol/kg body wt, three times per week. The survival rate of animals at the end of the treatment was 90%. To follow the temporal changes samples at 0, 7, 15, 30, 45, 60, 90, 150 and 180 days from rats during thioacetamide i ntoxication and from chronological controls were obtained. The cirrhog enic ability of this treatment was assessed on the basis of morphologi cal changes: the development of macronodular cirrhosis and the appeara nce of fibrous septa of collagen through portal spaces. Parameters of liver injury and cholestasis were obtained by assaying the serum activ ities of isocitrate dehydrogenase and gamma-glutamyltransferase. Enzym es and metabolites related to glutathione redox systems, as well as ot her antioxidant enzymes, were tested. Catalase and glutathione peroxid ase, the two enzymes involved in the elimination of peroxides, and glu tathione reductase decreased significantly at the end of the 6 months of intoxication, while Cu-Zn and Mn superoxide dismutases increased pr ogressively during the long-term thioacetamide treatment. Protein thio l levels profile showed a biphasic change increasing from the 7th day and were insensitive to the 30% depletion of intracellular glutathione (GSH). To study the relationship of the intracellular thiols on the m echanisms of cell proliferation and differentiation during the cirrhog enic process, DNA content was assayed by flow cytometry in isolated he patocytes, and DNA ploidy and distribution between G(0)-G(1), S and G( 2) + M phases were determined. Remarkable changes in relation to a sha rp increase in diploid population from 7 to 180 days (24.5% --> 85.5%) , a pronounced decrease in polyploid populations (tetraploid + octoplo id) in the same period (73.7% --> 12.3%), and elevations in the popula tions in S phase (S-1 + S-2) were observed in thioacetamide-treated ob tained indicate that hepatocytes thioacetamide-treated rats showed a m arked tendency to diploidy, an enhancement in DNA replication parallel to the hepatic content of protein sulphydryl groups and a significant decline in antioxidant enzyme activities. The increase in protein thi ols was independent of GSH level and of the thiol redox state.