Formation of photoproducts and cytotoxicity of bilirubin irradiated with turquoise and blue phototherapy light.
OBJECTIVE
To compare a new turquoise ("green") fluorescent phototherapy lamp (490 nm) with a conventional blue phototherapy lamp (450 nm) with respect to cytotoxicity and photochemical effects of bilirubin.


METHODS
Mouse lymphoma cells (L5178Y-R) in the presence of bilirubin solutions were exposed to phototherapy light. Occurrence of necrosis and apoptosis, reduction of mitotic index and inhibited cell growth was assayed by appropriate methods. The presence of bilirubin and its photoisomers was measured by high-pressure liquid chromatography analysis and absorption spectroscopy.


RESULTS
At constant and equal light irradiances, the cytotoxic effects in the presence of bilirubin bound to human serum albumin showed that the green lamp caused significantly less necrosis (n = 4, p < 0.05) and less inhibition of cell multiplication (n = 3, p < 0.05) than the blue lamp. A slightly lower apoptotic fraction, although not statistically significant, was observed in cells exposed to the blue lamp. Photo-oxidation of bilirubin was more prominent with blue light irradiation. The photoequilibria between geometric isomers of bilirubin were different for the two lamps; more geometric photoisomers were formed by blue irradiation (n = 6, p < 0.05). The amounts of the most water-soluble isomers (presumably mainly lumirubin) were rather similar for the two lamps.


CONCLUSIONS
The two lamps were similar in the formation of therapeutically relevant photoproducts, but the blue lamp showed potential in forming more photo-oxidation products and in causing more severe cellular damage in the presence of bilirubin.
Roll
Ellen Bruzell
EB
Norwegian Radiation Protection Authority, Østerås, Norway.
Christensen
Terje
T
D000818:Animals; D017209:Apoptosis / Q000528:radiation effects; D001663:Bilirubin; D016923:Cell Death / Q000528:radiation effects*; D002851:Chromatography, High Pressure Liquid; D003116:Color; D051379:Mice; D018462:Photobiology; D017319:Photosensitizing Agents / Q000494:pharmacology; D010789:Phototherapy / Q000295:instrumentation* / Q000379:methods; D011336:Probability; D012680:Sensitivity and Specificity; D014407:Tumor Cells, Cultured
D017319:Photosensitizing Agents; D001663:Bilirubin