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Mukoma F. Simpanya, Catherine E. Fick, Li R. Lin, Victor R. Leverenz, Frank J. Giblin; Lens Nuclear Fluorescence Induced By Ultraviolet-A Irradiation Of Rabbit Eyes In Vivo. Invest. Ophthalmol. Vis. Sci. 2011;52(14):1553.
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The possible role of ultraviolet-A (UVA) light in the formation of human nuclear cataract is not well understood. Fluorescence of the lens is known to increase with age, and may be a precursor to nuclear cataract. Here, we investigated UVA-induced fluorescence in the rabbit lens, which normally contains a high level of the UVA chromophore NADH, existing both free and bound to -crystallin.
Rabbit eyes were irradiated with UVA light in vivo (100mW/cm2) for 1 hr using a monochromatic source of 365nm light. The rabbits were euthanized, and control and irradiated lenses were isolated and photographed under 365nm light. Lenses were dissected into cortex and nucleus for HPLC (280nm and 570nm detection) and SDS-PAGE analysis. NADH levels in lenses and HPLC fractions were measured using a cycling assay.
Eyes irradiated in vivo initially showed a blue fluorescence, but this changed to a yellow fluorescence after about 30 min. Isolated, previously irradiated lenses showed a yellow fluorescence originating from the lens nucleus when observed under 365nm light, but exhibited a normal blue fluorescence arising from the equatorial cortex. Analysis of lens soluble proteins by HPLC showed no effect of the irradiation on protein elution profiles. Two yellow fluorescent peaks (Peak 1: α-crystallin and Peak 2: -crystallin) were observed, surprisingly, in both the control and experimental cortex and nucleus. Peak 2 of the nucleus, but not the cortex, was two-fold higher in the UVA-irradiated fraction, compared to the control. The 1 hr in vivo UVA treatment decreased the level of total NADH (free plus bound) in the lens nucleus by 53%, but by only 13% in the anterior cortex. The level of NADH in the nuclear Peak 2 was 3-fold higher in the experimental fraction, compared to the control, but NADH was not detectable in Peak 1.
UVA-induced loss of free NADH (which fluoresces blue) in the nucleus may have allowed the yellow fluorescence of -crystallin to be visible. However, why the experimental nuclear Peak 2 fluorescence was higher than the control, as well as the identity of the protein-bound UVA chromophore associated with Peak 1, are not yet known. The results demonstrate the greater susceptibility of the lens nucleus to UVA-induced stress, and may relate to the formation of human nuclear cataract.
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