Effect Of Panretinal Laser Photocoagulation On The Concentration Of Enzymatic Antioxidants In The Serum Of Diabetic Patients Single Vs Multiple Sittings.

摘要

The present study was carried on 60 eyes of 60 patients who attended the “Retina Centre” of Institute of Ophthalmology Aligarh Muslim University. The patients included in the study were divided into two groups; one group (Group A) comprised of 30 patients who received panretinal laser photocoagulation (PRP) in single sitting and the other group (Group B) also comprised of 30 patients who received PRP in four sittings. Informed consent was obtained from all the participants of the study and the protocol was approved by the ethical committee of the centre. Estimation of enzyme levels of superoxide dismutuse, catalase and glutathione peroxidase was done in serum prior to laser photocoagulation, 24 hours after photocoagulation and 6 weeks after the last sitting of laser photocoagulation. In our study the mean enzyme level 24 hours after each sitting of laser photocoagulation in both the groups were significantly higher than the pre laser levels. This increase in the mean antioxidant enzyme level could be due to tissue response to increase in reactive oxygen species. The increase in mean enzyme level decreases after each sitting of laser photocoagulation in Group B corroborates with the fact that the defense mechanism against oxidative stress gradually becomes more efficacious after each laser sitting. The increase in mean level of enzymatic antioxidants remained significant even after 6 weeks of laser photocoagulation, may help to explain the mechanism where local laser treatment causes clinical improvement through out the retina and also explains why successful panretinal photocoagulation often prevents further retinal microvascular change despite the continued metabolic derangement. In the present study the mean serum change in the levels of catalase, superoxide dismutase and glutathione peroxidase after 24 hours was greater in Group A as compared to mean of the enzyme changes in all the sittings of laser photocoagulation in Group B. This difference in the change in antioxidant level between Group A and Group B was statistically significant at 24 hours after laser photocoagulation. At 6 weeks after the last laser sitting the mean change in serum catalase, superoxide dismutase and glutathione peroxidase levels in Group A were higher than the levels of these enzymes in Group B. This difference in the level of enzymatic antioxidants was statistically significant (p value < 0.05). The fact that the change in mean of enzymatic antioxidants is greater in Group A as compared to the change in the mean of the enzyme levels in all the laser sittings in Group B as well as, at 6 weeks could be due to inducement of antioxidant enzymes at each laser sitting there by producing lesser changes in subsequent laser sittings. Therefore, it can be concluded that the oxidative stress produced by panretinal photocoagulation in single sitting is greater than that produced in multiple sittings. Introduction Oxidative stress is the disturbance in the equilibrium status of pro-oxidant and antioxidant systems in intact cells. In tissues where glucose uptake is independent of insulin, including retina exposure to elevated glucose levels causes an increase in intracellular sorbitol and fructose levels due to increased activity of aldose reductase and sorbitol dehydrogenase1. These two enzymes constitute the polyol pathway. Increased substrate flux through the polyol pathway not only increases cellular levels of sorbitol and fructose but also decreases the ratio of NADPH to NADP+ and increases the cytosolic NADH to NAD+ ratio. The depletion of NADPH cell stores by aldose reductase may inhibit the activity of other NADPH – requiring enzymes2.An increased production of malondialdehyde has been found in erythrocyte membranes of diabetic patients, together with a depressed erythrocyte content of reduced glutathione3.Studies carried by Nishigaki et al4., (1991) and Altomore5 (1992) showed that the melondialdehyde is also higher in plasma of diabetic subjects as co