AGE-DEPENDENT MODIFICATIONS IN RAT HEPATOCYTE ANTIOXIDANT DEFENSE SYSTEMS

Background/Aims: Age-dependent changes in the hepatic antioxidant syst ems were studied in hepatocytes from newly weaned (21 days) to 30-mont h-old rats. Results: Biphasic changes were observed in superoxide dism utase (SOD), glucose-6-phosphate dehydrogenase (G6PDH) and malic enzym e (ME), in which noticeable decreases were detected in hepatocytes fro m newly weaned to 6-month-old rats: Cu-Zn SOD decreased to 46% (p<0.00 1), Mn SOD to 41% (p<0.001), G6PDH to 71% and ME to 19% (p<0.001), and significant increases were observed from 6 to 30 months. In hepatocyt es from 6- to 36-month-old rats the enzymes involved in antioxidant de fense underwent increases in their activities as well in their mRNA: C u-Zn SOD (142%, p<0.001), catalase (182%, p<0.001) and glutathione per oxidase (325%, p<0.001). However, chronological decreases were observe d in the levels of reduced glutathione (69%, p<0.001), in the GSH/GSSG ratio (78%) and in protein thiol groups (55%, p<0.001), with concomit ant increases in peroxides (155%, p<0.001.) and malondialdehyde (142%, p<0.001) levels. DNA ploidy was also assayed by flow cytometry; a sha rp increase in tetraploid (2.5-40.1%;p<0.001) and octoploid (0.1-16.1% ; p<0.001) populations, and a noticeable decrease in diploid hepatocyt es (92.9-34.3%; p<0.001), were observed. Populations involved in 2C--> 4C DNA synthesis decreased from 3.6 to 0.9% (p<0.001), while those inv olved in 4C-->8C increased from 0.9% to 5.2% (p<0.001). A hypodiploid population (apoptotic cells) was detected from 12 months, increasing t hereafter. Conclusions: These results show that the antioxidant cell d efense system increases with age but the rate of reactive oxygen speci es generation exceeds the induced antioxidant ability, generating a si tuation that favors oxidative stress and peroxidation. The progressive polyploidization is accompanied by changes in the proliferative poten tial that decreases from 2C to 4C and increased from 4C to 8C. The rel ationship between the modifications of the oxidant/antioxidant system and increased polyploidy is not clear and may be interpreted as two in dependent manifestations of the aging process.