The photosensitiser xanthurenic acid is not present in normal human lenses

UV light has often been investigated as a risk factor for the most common cause of blindness, human age-related cataract. One mechanism whereby UV light could induce cataract is via the action of photosensitisers. In this regard, xanthurenic acid has recently been highlighted since it has been reported to be present in the human lens and, in model studies, it markedly enhances the photo-oxidation of proteins by wavelengths of light that penetrate the cornea. In this study we used HPLC and mass spectrometry to examine whether xanthurenic acid is indeed present in human lenses and, if so, the effect of age on its lenticular concentration. Xanthurenic acid could be formed artefactually by incubation of 3-hydroxykynurenine (3OHKyn) yellow, a known autoxidation product of the lenticular UV filter, 3OHKyn, in the presence of air and light, however, it could not be detected in any human lenses studied. Therefore, it appears unlikely that xanthurenic acid plays a role in lens aging or human cataract.