CONFIGURATIONAL PHOTOISOMERIZATION OF BILIRUBIN IN VITRO–II. A COMPARATIVE STUDY OF PHOTOTHERAPY FLUORESCENT LAMPS AND LASERS

Abstract— A comparative investigation of configurational photoisomerization of bilirubin (Z.Z-BR) bound to human serum albumin (HSA) in vitro produced by fluorescent lamps currently employed in phototherapy of neonatal jaundice has been carried out by using a fast absorbance technique. Photoequilibrium Z, E-BR concentrations and rise-times are reported. Similar measurements effected with monochromatic laser lines in the blue-green spectral region are presented for comparison purposes.
Narrow-spectrum fluorescent lamps (violet, special-blue, filtered-green) produce Z,E-BR concentrations at photoequilibrium almost equal to those obtained with monochromatic lines. The photoequilibrium rise-times, however, strongly depend on the spectral bandwidth of the excitation light. Special-blue, daylight and green lamps produce Z,E-BR concentrations = 34,31, and 12%, respectively. For green lamps, the intense UV-blue-Hg lines are responsible for more than 50% of Z,E-BR concentration. Green light is found to be quite ineffective in forming Z,E isomers and very efficient in causing Z,E-BR to revert to native Z.Z-BR. Moreover, simultaneous irradiation of BR solution with special-blue and green fluorescent lamps produces almost complete inhibition of the Z→E reaction at suitable green/blue intensity ratio.
On the basis of these results a possible mechanism is presented to explain the clinical success of fluorescent green lamp phototherapy and the greater production of structural BR isomers recently reported for green than that for white lamps.