Serum Total Bilirubin and Oxidative Stress Status in Diabetic Retinopathy – A Hospital-Based Observational Study

Abstract

Diabetic retinopathy (DR) is one of the common microvascular complications of Type 2 Diabetes Mellitus (T2DM). As an antioxidant, the serum total bilirubin is associated with vaso-occlusive disorders. Oxidative stress parameters such as Erythrocyte Glutathione (GSH) as an antioxidant and Malondialdehyde (MDA) as an oxidant are critical in the pathogenesis of diabetic complications. This study aimed to explore the possibilities of the endogenous protective role of serum total bilirubin on the retinal vasculature in DR patients by estimating and correlating the levels of serum total bilirubin, GSH, and MDA in DR cases. In this hospital-based case-control study, 288 participants were selected from R.L. Jalappa Hospital and Research Centre, Kolar, divided into three groups with 96 subjects per group. Group I: Controls, Group II: T2DM, and Group III: DR subjects. The fasting blood sugar, glycated hemoglobin, liver function test, and lipid profiles were estimated by standard methods. Oxidative stress parameters viz, GSH and MDA were assayed by chromogen 5,5'- di thiobis 2-nitrobenzoic acid (DTNB) and thiobarbituric acid reactive substances (TBARS) methods, respectively. The prevalence of DR was significantly lower among subjects with the highest bilirubin quartile than those with the lowest. There was a significant mean difference with p<0.001 between the groups for total bilirubin, FBS, HbA1c, GGT, TC, TG, LDL, GSH, and MDA. A Negative correlation of serum total bilirubin with FBS (r = - 0.375), HbA1c (r = -0.351), and MDA(r=-0.323), and a positive correlation with GSH (r = 0.335) was observed in DR group with a significant p-value. T2DM subjects with higher levels of bilirubin within biological reference intervals were less likely to develop retinopathy. The severity of DR was inversely proportional to the total bilirubin levels. Therefore, serum total bilirubin levels could be a biomarker to predict the risk of developing retinopathy in people with T2DM.