Assessment of DNA damage and plasma catalase activity in healthy term hyperbilirubinemic infants receiving phototherapy

Phototherapy (PT) is the most widely used form of treatment for unconjugated hyperbilirubinemia. One possible harmful consequence of PT is of a genetic nature. High levels of bilirubin may lead to oxidative damage in newborns: photochemical reactions may produce toxic photoproducts, probably peroxides. In order to investigate this hypothesis further under in vivo conditions, DNA strand-break frequency was examined by means of the comet assay in peripheral lymphocytes of icteric newborns undergoing PT treatment, and the levels of catalase, an antioxidant enzyme, were determined.We analyzed 20 term non-hemolitic hyperbilirubinemic jaundiced neonates before PT (‘before PT’ group) and just prior to ending PT (‘after PT’ group) and compared comet scores of these patients with those of 20 healthy term neonates who all had bilirubin levels in the physiological range. Comet scores (tail length, tail moment and %DNA in tail) of the group ‘before phototherapy’ were 23.5 ± 16.3, 7.41 (0.97–40.7), 33.0 ± 12.1, respectively and scores of after phototherapy group were 3.2 ± 1.8, 0.29 (0.3–3.2), 10.7 ± 3.7, respectively. Comet scores of the control group were 3.0 ± 2.9, 0.25 (0.03–3.22), 10.9 ± 4.5, respectively. Comet scores and plasma catalase activities in hyperbilirubinemic newborns were significantly higher before phototherapy, compared with the values after phototherapy and in the control groups (p < 0.001). There was no statistical difference between the ‘after phototherapy’ group and the controls (p > 0.05).These results indicate that high serum bilirubin level has genotoxic effects as is evident from the high rate of DNA strand-breaks in jaundiced newborns. Also PT does not cause an increase in DNA oxidation or induce the genotoxic effects of bilirubin. The counteracting effect of higher catalase activities in hyperbilirubinemic newborns may be responsible for the inactivating toxic and DNA-damaging effects of PT.