Laser Investigation of Bilirubin-Photobilirubin Photoconversion

Abstract

The reversibility of the configurational photoisomerization process of bilirubin (BR) with laser lines in the blue-green spectral region is investigated. Photoisomerization efficiency of BR is found to depend strongly on wavelength, and to decrease when the excitation wavelength is increased from blue to green. Reversion of BR photoisomers (identical to photobilirubin, PBR) back to native BR is demonstrated for several laser lines by irradiating PBR/BR mixtures with wavelengths greater than the excitation wavelengths. Green lines turn out to be very efficient for PBR----BR reversion. The PBR concentrations at photoequilibrium, obtained from the spectrophotometric data, are in close agreement with the corresponding values measured with the high performance liquid chromatography technique in the case of 10 nm bandwidth filtered light reported in the literature. The 457 nm blue laser line produces 32% PBR concentration at photoequilibrium; only 14, 7, and 3% PBR concentrations are produced by the blue-green lines at 488, 501, 514 nm, respectively. The effect on the photostationary PBR/BR mixture of successive irradiations with different wavelengths, and the influence of the wavelength sequence are reported. In the case of blue lines our results support the assumption of the first-order kinetics for the BR in equilibrium PBR photoreaction. Departures are observed with green-lines (501, 514 nm). The present results, together with the i) good clinical efficiency reported for fluorescent green lamps; and ii) slow elimination of configurational photoisomers in infants, tend to confirm the lumirubin-pathway as the main mechanism for phototherapy, and call for clinical investigation of narrow-spectrum lamps with peak emission wavelength in the (biologically safer) 480 divided by 530 nm range.

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

“…Earlier studies suggested that the increased bilirubin photodegradation at the higher wavelengths is mainly due to an increase in lumirubin formation, [24][25][26] which was found to be more rapidly excreted in vivo 6,7,27,28 in contrast to the geometric E,Zand Z,E-isomers that could be converted back to the Z,Z-isomer. 29 Since the E,Zand Z,E-configurational isomers are also diazopositive, 10 our determination of the amount of remaining bilirubin after light exposure use of the diazo method mainly reflects the conversion of bilirubin to lumirubin, which is diazo-negative.…”

Wavelength-dependence of the relative rate constants for the main geometric and structural photoisomerization of bilirubin IX α bound to human serum albumin. Demonstration of green light at 510 nm as the most effective wavelength in photochemical changes from (ZZ)-bilirubin IX α to (EZ)-cyclobilirubin IX α via (EZ)-bilirubin

“…However, recent studies in vitro showing that light of wavelengths between 350 and 450 nm is mutagenic for prokaryotic and eukaryotic cells, and therefore potentially carcinogenic, have caused concern because all commonly-used phototherapy lamps emit radiation in this region. Furthermore, a greater efficacy of green lamps compared with white fluxorescent lamps has been reported (Vecchi et al, 1982;Pratesi, 1983;Pratesi et al, 1985). As a possible cause for this Donzelli et al (I1984) suggest that the green light penetrates deeper into the skin, and the best spectral range for efficient photodegradation of bilirubin may be the result of a balance between bilirubin absorption and skin penetration.…”

“…Symbols: 0, (EZ)-bilirubin; *, sible for the rapid biliary and urinary clearance ofbilirubin during phototherapy (Onishi et al, 1980b, 198 1a;Castarino et al, 1985;McDonagh & Lightner, 1985). (EZ)-Cyclobilirubin, as photoreversible structural isomers of bilirubin (Isobe & Onishi, 1981), though many authors have described it as 'non-reversible' (Castarino et al, 1985;Knox et al, 1985;Pratesi et al, 1985), attains much lower serum concentrations, but is more rapidly excreted. Thus structural isomerization, i.e.…”

“…Moreover, studies in vitro demonstrating that wavelengths from 350 to 450 nm are mutagenic for prokaryotic and eukaryotic cells, and therefore potentially carcinogenic and teratogenic, have caused some concern with regard to the long-term safety of phototherapy (Speck & Rosenkranz, 1975;Parshad et al, 1978Parshad et al, , 1981Bradley et al, 1978;Burki & Lam, 1978;Sideris et al, 1981). This concern has led to a recommendation that green light be used (Vecchi et al, 1982;Pratesi et al, 1985). At present, the precise relative contribution of geometric and structural photoisomers to the net effect of phototherapy is unknown, but in the Gunn rat the geometric photoisomers (Onishi et al, 1984b) and in humans the structural photoisomers are the main contributors (Onishi et al, 1980b(Onishi et al, , 1984a.…”

Phototherapy for Neonatal Jaundice

“…Because the isomers have overlapping absorption spectra, a photoequilibrium state is achieved when bilirubin is irradiated under anaerobic conditions. When bilirubin is bound to human albumin, there is a marked wavelength dependence for the equilibrium between native bilirubin and the 4Z,15E-isomer (Ennever et al, 1983;Pratesi et al, 1984aPratesi et al, , 1985Onishi et al, 1986a;Itoh et al, 1987). Pratesi et al (1984a) have fit experimental data on the isomer composition at photoequilibrium to a simple kinetic model which assumes a common twisted intermediate between 42,152 and 4Z,15E (Greene et al,198l), to determine the relative quantum yield for the two reactions.…”