Cyclobilirubin formation by in vitro photoirradiation with neonatal phototherapy light.
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.
Yasuda
S
S
Department of Pediatrics, Kagawa Medical University, Kagawa, Japan.
Itoh
S
S
Imai
T
T
Isobe
K
K
Onishi
S
S
D001663:Bilirubin / Q000031:analogs & derivatives* / Q000096:biosynthesis*; D004307:Dose-Response Relationship, Radiation; D006801:Humans; D066298:In Vitro Techniques; D007231:Infant, Newborn; D010789:Phototherapy
C041079:cyclobilirubin; D001663:Bilirubin