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Quantum yield and skin filtering effects on the formation rate of lumirubin
G Agati1, F Fusi, G P Donzelli
1Istituto di Elettronica Quantistica, Consiglio, Nazionale delle Ricerche, Firenze, Italy.
Insights
Phototherapy for jaundiced infants uses blue-green light to convert bilirubin to lumirubin. Optimizing light wavelengths between 490-510 nm can significantly improve bilirubin elimination and phototherapy effectiveness.
Area of Science:
- Biophysics
- Photochemistry
- Neonatal Medicine
Background:
- Infant jaundice is treated with phototherapy, primarily involving bilirubin photodegradation.
- Bilirubin converts to lumirubin via photocyclization, a key elimination pathway.
- Previous phototherapy models did not fully account for wavelength-dependent quantum yields.
Purpose of the Study:
- To model bilirubin photochemistry in vivo, optimizing phototherapy efficacy.
- To investigate the impact of wavelength-specific quantum yields on lumirubin formation rate.
- To identify optimal light emission spectra for enhanced bilirubin elimination.
Main Methods:
- Utilized a simplified skin optical model based on Kubelka-Munk theory.
- Incorporated recently measured, wavelength-dependent quantum yields for bilirubin-lumirubin photoreaction (phi LR) and photoisomerization (phi ZE).
- Calculated lumirubin formation rate (kappa LR) for a four-layer skin model under various light sources.
Main Results:
- Quantum yield for lumirubin formation (phi LR) peaks around 520 nm.
- Quantum yield for photoisomerization (phi ZE) decreases at longer wavelengths.
- Combined effects of optical properties and quantum yields shift optimal lumirubin formation to the 490-510 nm range.
Conclusions:
- Wavelength optimization is crucial for effective bilirubin phototherapy.
- Current phototherapy may not be optimally tuned to maximize lumirubin formation.
- New lamps emitting in the 490-510 nm range could significantly improve phototherapy outcomes for jaundiced infants.
Abstract:
Photocyclization of bilirubin to lumirubin in the skin of jaundiced infants exposed to blue-green light irradiation is considered to be the most important process for bilirubin elimination from the organism. The quantum yield phi LR of the bilirubin-->lumirubin photoreaction has been recently measured and found to vary with the excitation wavelength, with a peak at about 520 nm. The quantum yield phi ZE for the strongly competing reversible configurational photoisomerization of bilirubin has also been recently shown to be wavelength dependent and to decrease significantly in the long-wavelength part of the absorption band of bilirubin. These new data are taken into account to model the bilirubin photochemistry in vivo by using a simplified skin optical model based on the Kubelka-Munk theory. The rate kappa LR of formation of lumirubin has been evaluated for the case of a four-layer skin and for monochromatic and narrow-band coloured fluorescent lamps. The effects of long-wavelength increase in phi LR, decrease in phi ZE and skin optical losses all combine to shift significantly the optimal rate of formation of lumirubin towards the green. These results suggest that a significant improvement in phototherapy might be obtained with the introduction of new lamps emitting in the blue-green spectral region between 490 and 510 nm.