UV excitable fluorescence of lumirubin

The effect of light wavelength on in vitro bilirubin photodegradation and photoisomer production

BACKGROUND

The action spectrum for bilirubin photodegradation has been intensively studied. However, questions still remain regarding which light wavelength most efficiently photodegrades bilirubin. In this study, we determined the in vitro effects of different irradiation wavelength ranges on bilirubin photodegradation.

METHODS

In our in vitro method, normalized absolute irradiance levels of 4.2 × 10¹⁵ photons/cm²/s from light-emitting diodes (ranging from 390-530 nm) and 10-nm band-pass filters were used to irradiate bilirubin solutions (25 mg/dL in 4% human serum albumin). Bilirubin and its major photoisomer concentrations were determined; the half-life time of bilirubin (t_1/2) was calculated for each wavelength range, and the spectral characteristics for bilirubin photodegradation products were obtained for key wavelengths.

RESULTS

The in vitro photodegradation of bilirubin at 37 °C decreased linearly as the wavelength was increased from 390 to 500 nm with t_1/2 decreasing from 63 to 17 min, respectively. At 460 ± 10 nm, a significantly lower rate of photodegradation and thus higher t_1/2 (31 min) than that at 500 nm (17 min) was demonstrated.

CONCLUSION

In our system, the optimum bilirubin photodegradation and lumirubin production rates occurred between 490 and 500 nm. Spectra shapes were remarkably similar, suggesting that lumirubin production was the major process of bilirubin photodegradation.

Effect of processing methods on colouration of human serum albumin preparations

Human serum albumin is a well tolerated therapeutic for the treatment of hypovolemia. Despite all commercial human albumin preparations being derived from plasma, these products can have a highly variable colour. Albumin samples derived from ethanol precipitation and chromatographic fractionation procedures were evaluated for bilirubin and biliverdin levels and by spectrophotometry. It was shown that albumin derived from a chromatographic process, which had a bilirubin:albumin ratio similar to that observed in plasma, had a vibrant yellow appearance. The albumin derived from ethanol precipitation had undetectable levels of bilirubin, and the amber colour of this product was attributed mainly to residual haem. The presence of bilirubin during pasteurisation led to oxidation to biliverdin, with a resultant colour change from yellow to yellow/green. Given that the antioxidant properties of bilirubin are well established, it is possible that bilirubin helps protect albumin from oxidation during the pasteurisation step.

Thematic workshop on fluorescence compensation settings in multicolor flow cytometry

In his program of thematic one-day workshops, the French Association of Cytometry had organized a workshop dedicated to the fluorescence compensation settings in multicolor flow cytometry. This special day was in honor of our past President Jean Luc D'Hautcourt who has been involved in the quality of the use of flow cytometry in its clinical and research purposes. Review on fluorescence phenomena, compensation rules, settings, and few observed confounding situations were presented.