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Bilirubin photoisomerization in premature neonates under low- and high-dose phototherapy
Insights
High-dose phototherapy for infant jaundice significantly increases lumirubin, a structural isomer of bilirubin. This finding helps explain the dose-dependent effects of phototherapy in treating neonatal jaundice.
Area of Science:
- Neonatal Medicine
- Photochemistry
- Biochemistry
Background:
- Physiologic jaundice in premature infants is common.
- Phototherapy is a standard treatment for neonatal jaundice.
- Bilirubin undergoes photoisomerization during treatment.
Purpose of the Study:
- To investigate the effect of low-dose versus high-dose phototherapy on bilirubin photoisomerization in premature infants.
- To compare the production of configurational isomers (Z,E-bilirubin) and structural isomers (lumirubin) under different phototherapy doses.
Main Methods:
- Prospective study of 20 premature infants with physiologic jaundice.
- Comparison of low-dose (6 microW/cm2/nm) and high-dose (12 microW/cm2/nm) white light phototherapy.
- Analysis of serum bilirubin photoisomers using high-pressure liquid chromatography at various time points.
Main Results:
- Both low- and high-dose phototherapy increased configurational and structural isomers of bilirubin.
- No significant difference in configurational isomers between low- and high-dose groups.
- High-dose phototherapy significantly increased the proportion of lumirubin after four hours (1.3% vs 0.7%).
Conclusions:
- Phototherapy effectively induces both configurational and structural isomerization of bilirubin in vivo.
- The increased production of lumirubin under high-dose phototherapy may explain its "dose" effect in treating jaundice.
Abstract:
Photoisomerization of native bilirubin to more polar configurational isomers (Z,E-bilirubin) and structural isomers (lumirubin) was studied in 20 premature infants with physiologic jaundice to determine the effect of low-dose (6 microW/cm2/nm) v high-dose (12 microW/cm2/nm) phototherapy. Patients were assigned prospectively to receive either low- or high-dose treatment. Study groups were comparable with regard to birth weight, gestational age, and total bilirubin prior to the initiation of phototherapy. Treatment was administered with white light produced by a commercially available halogen-tungsten lamp. Dose was measured periodically during the study to ensure a uniform distribution of irradiance and constant exposure. Sera for photoisomers were obtained before initiation of treatment and at two, four, and eight hours. Photoisomers expressed as a percent of total bilirubin were determined using high-pressure liquid chromatography. Serum proportion of both configurational and structural isomers increased with the duration of phototherapy in both treatment groups. There was no significant difference between the percent of configurational isomers in low- and high-dose phototherapy groups. However, high-dose treatment produced a significantly higher proportion of the structural isomer lumirubin after four hours (0.7% low dose v 1.3% high dose, P less than .05). These data confirm that phototherapy results in both configurational and structural isomerization of bilirubin in vivo. Furthermore, the previously described "dose" effect of phototherapy may be attributed to the production of the structural isomer, lumirubin.