Role of heme oxygenase and bilirubin in oxidative stress in preterm infants

In a previous study, it was found that the decrease in the total plasma bilirubin level (Btot) in preterm infants was associated with the decrease in oxidative stress. We hypothesized that this occurs as a result of a pro-oxidant effect of heme oxygenase (HO), which outcompetes with the antioxidant properties of bilirubin. In this study we studied 12 preterm infants in whom the plasma levels of Btot, total hydroperoxide (TH), protein SH groups, HO activity, non-transferrin-bound iron (NTBI), and erythrocyte CuZn superoxide dismutase (CuZn SOD) activity were concurrently measured when the Btot was >220 microM and after a Btot drop of >34 microM. The Btot decrease was concurrent with the TH decrease, protein SH groups increase, and the HO and CuZn SOD activity increase and was not associated with an NTBI increase. We concluded that 1) Btot does not exert a meaningful antioxidant effect in vivo; 2) HO does not exert a pro-oxidant effect involving an NTBI increase and that, on the contrary, it could exert an antioxidant effect; and 3) the concurrent HO and CuZn SOD activity increase could indicate a synergic antioxidant effect of the two enzymes.