Glutathione peroxidase, catalase, superoxide dismutase and aldose reductase: mRNA levels and enzyme activity in diabetic rat lenses

Purpose: Oxidative stress is known to play a key role in diabetic as well as senile cataracts. In the current study we have followed the mRNA levels of defense enzymes by RT-PCR in lenses of diabetic rats undergoing cataractogenesis. Methods: Streptozotocin-induced diabetic and control rats were sacrificed on days 4, 8, 12, 16, 20, 40, 60 and 80 and lenses used for extraction of total RNA, digital image analysis and enzyme activity determination. Enzyme activity was determined for superoxide dismutase (SOD), glutathione reductase (GR), glutathione peroxidase (GPX), catalase (CA) and aldose reductase (AR). Total RNA was reverse transcribed and the cDNA generated was used for PCR amplification of CA, SOD, GPX and AR messages. PCR product was quantified by autoradiography. Levels of the messages were normalized against cyclophilin which was amplified under identical conditions. Results: Diabetes elicited appreciable increase in mRNA levels of all the enzymes by day 20. However, elevation of SOD and AR mRNA was fairly short lived peaking on day 20 and dropping to normal within the next 20 days. In contrast, catalase and GPx mRNA induction lasted significantly longer, with levels touching baseline by day 80. Enzyme activity of the above enzymes appeared to follow a pattern similar to that displayed by their mRNA. although the degree of activation was significantly higher. Withing the time frame of the study, light transmittance had declined to 40% of the control. Conclusion: During diabetes, defense enzymes are induced to cope with the oxidative stress and maintain the oxidant/antioxidant capacity.