Evaluation of oxidant and antioxidant status in term neonates: a plausible protective role of bilirubin.

In vitro studies have shown unequivocally that bilirubin is an antioxidant. We hypothesized that bilirubin serves a physiological role of an antioxidant in vivo. To investigate the probable protective role of bilirubin in vivo, term babies with clinical jaundice were grouped into four categories-serum total bilirubin (STB) <160 mg/l, 160-200 mg/l, >200 mg/l, and kernicterus. Serum bilirubin, serum albumin, plasma glucose-6-phosphate dehydrogenase (G6PD), lipid peroxidation in blood cells, and reduced glutathione (GSH) content in whole blood were investigated. We also measured superoxide dismutase (SOD) and catalase in hemolysate and total plasma antioxidant capacity (TAC). Lipid peroxidation and antioxidant enzymes were significantly lower in babies with STB <200 mg/l compared to controls. TAC had a positive and MDA had a negative correlation with STB till 200 mg/l. However, TAC had a negative and MDA had a positive correlation with bilirubin >200 mg/l and in babies with bilirubin encephalopathy. Elevated levels of MDA, SOD, and catalase and significantly decreased levels of reduced glutathione and total antioxidant capacity were observed in STB >200 mg/l group. Antioxidant enzymes were also significantly inhibited in bilirubin encephalopathy babies. Post phototherapy, MDA production and antioxidant levels were significantly increased whilst total antioxidant capacity and reduced glutathione were significantly decreased compared to pre-phototherapy values. Exchange transfusion resulted in reduced oxidative stress in subjects with encephalopathy, whereas no significant difference was observed in other babies with STB >200 mg/l. Taken together, the present study propounds that bilirubin acts as a physiological antioxidant till 200 mg/l concentration in full-term normal neonates. It is conjectured that beyond 200 mg/l, it can no longer be considered physiologic. However, the cause of pathological jaundice needs to be identified and treated. The present data documents that phototherapy also induces oxidative stress.