Cyclobilirubin formation by in vitro photoirradiation with neonatal phototherapy light.

Abstract

BACKGROUND:

The main mechanism of phototherapy for neonatal hyperbilirubinemia is the production and excretion of (EZ)- and (EE)-cyclobilirubin (4E,15Z- and 4E,15E-cyclobilirubin). Thus, the clinical efficacy of the light source for phototherapy must be evaluated by cyclobilirubin formation from (ZZ)-bilirubin in in vitro photoirradiation.

METHODS:

In the present study, we investigated the in vitro production pattern of bilirubin photoisomers by phototherapy light from the bilirubin-human serum albumin complex.

RESULTS:

No clear difference was found in the curves relative to (ZZ)-bilirubin and its photoisomers under aerobic and anaerobic conditions. The ratio of (EZ)-cyclobilirubin to (ZZ)-bilirubin increased proportionately to the dose of irradiating light and no photoequilibrium state was observed analogous to that found in configurational photoisomerization. The concentration of (EZ)- and (EE)-cyclobilirubin increased proportionately with the grade of the percentage decrease in A(460 nm) from 0 to 23%. With a percentage decrease in A(460 nm) of 23% or more, the cyclobilirubin concentrations reached a steady state. The reason for this appears to be that the concentration of (ZZ)-bilirubin, a substrate for photoisomers, dropped below 1 mg/100 mL. Biliverdin was produced only in trace amounts. However, the absorption at 520--700 nm increased after a percentage decrease in A(460 nm) of more than 23%.

CONCLUSIONS:

The results of the present study show that little bilirubin photooxidation occurred with in vitro aerobic photoirradiation. Before the concentration of cyclobilirubin reaches a steady state, it is theoretically valid to use the percentage decrease in A(460 nm) for the evaluation of the clinical efficacy of the light source.

• Authors: S Yasuda, S Itoh, T Imai, K Isobe, S Onishi
• Journal: Pediatrics international : official journal of the Japan Pediatric Society (Pediatr Int) Vol. 43 Issue 3 Pg. 270-5 (Jun 2001) ISSN: 1328-8067 [Print] Australia
• PMID: 11380923 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• cyclobilirubin
• Bilirubin

Topics

• Bilirubin (analogs & derivatives, biosynthesis)
• Dose-Response Relationship, Radiation
• Humans
• In Vitro Techniques
• Infant, Newborn
• Phototherapy