Urocanic acid photoconversion in relation to erythematogenicity of radiation from different types of phototherapy equipment.
The photoisomerization characteristics of urocanic acid (UCA) were studied by using both a narrow-band monochromator and 4 broad-band phototherapy devices. The latter included 2 ultraviolet B (UVB) irradiators with different emission spectra, a black-light UVA source and a long-range UVA emitter. The experiments were performed by irradiating trans-UCA in quartz cuvettes or in petri dishes at a pH and area concentration corresponding to human skin conditions and measuring the generated amount of cis-UCA by liquid chromatography. The exposure time for 50% trans-->cis isomerization was in the range of typical clinical in vivo exposure times for 2 UVB sources and for the black-light UVA irradiator, but for the long-wave UVA emitter the time for 50% isomerization greatly exceeded any typical in vivo exposure time. The wavelength at which maximal UCA photoisomerization took place varied from one radiation source to another, being 296 nm, 312, nm, 320 nm and 342 nm in the different cases. When an isomerization action spectrum derived from the narrow-band irradiation was integrated with the CIE standard action spectrum for human skin erythema, it was found that, in relation to erythemal effectiveness, the wavelengths between 310 and 340 nm isomerized UCA most efficiently.
Laihia
J K
JK
Department of Physiology, University of Turku, Finland.
Jansén
C T
CT
D002851:Chromatography, High Pressure Liquid; D004890:Erythema / Q000209:etiology; D006801:Humans; D007536:Isomerism; D010789:Phototherapy / Q000295:instrumentation; D012867:Skin / Q000528:radiation effects; D013053:Spectrophotometry; D014466:Ultraviolet Rays; D014560:Urocanic Acid / Q000528:radiation effects*
D014560:Urocanic Acid