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M. F. Simpanya, R. R. Ansari, V. Leverenz, F. J. Giblin; Measurement of Lens Protein Aggregation in vivo Using Dynamic Light Scattering in a Guinea Pig/UVA Model for Nuclear Cataract. Invest. Ophthalmol. Vis. Sci. 2008;49(13):2272. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
The possible role of UVA radiation in the formation of human nuclear cataract is not well understood. Our previous work showed increases in lens nuclear light scattering and protein disulfide in guinea pigs exposed to a chronic low level of UVA light (Giblin et al., 2002). Here we have investigated lens protein aggregation in vivo in the guinea pig/UVA model using dynamic light scattering (DLS).
Guinea pigs (initially 17 months old) were exposed to UVA light (0.5mW/cm2, 340-410nm, 365nm peak) for up to 5 months. Control animals were housed under normal lighting conditions. Crystallin aggregation was investigated in vivo with the use of DLS between 3 and 5 months of UVA exposure. DLS measurements for control (n=6) and experimental (n=8) animals were conducted at one location each in the lens anterior cortex and nucleus. Proteins were divided into small and large diameter groups, classified as <50 and >50 arbitrary units, respectively.
In UVA-irradiated lenses, DLS size distribution analysis conducted at the same location in the lens nucleus for each of the animals showed a 26% reduction in intensity of small diameter proteins compared to controls (P<0.05). In addition, large diameter proteins increased five fold in intensity compared to controls (P<0.05). The increase in apparent size of nuclear small diameter protein aggregates was three fold compared to controls (P<0.01), and the size of large diameter aggregates was more than four fold compared to controls. The average diameter of crystallin aggregates at the one location in the UVA-irradiated lens nucleus was estimated to be 350nm, a size able to scatter light (Tanaka et al., 1975). No significant changes in intensity or apparent diameter for small or large diameter proteins were detected in the anterior cortex of UVA-irradiated lenses, compared to controls.
Exposure of guinea pigs to a physiologically relevant level of UVA light for up to 5 months produced an increase in intensity and size of large diameter proteins in the nucleus, but not in the anterior cortex. It is presumed that the presence of a UVA chromophore in the guinea pig lens (NADPH bound to zeta crystallin), as well as traces of oxygen, contributed to UVA-induced crystallin aggregation. The finding indicates a potentially harmful role for UVA light in the lens nucleus, and merits further investigation regarding a possible role for UVA irradiation in human nuclear cataract.
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