Relationships between glycation and oxidation related fluorescences in rat collagen during aging: an in vivo and in vitro study

An increase of all fluorescence intensities was observed in rat collagen during aging: the glycation-related ones (y(370/440) = 28.3 e(0.08x), r = 0.808, p < 0.01; y(335/385) = 66.7 e(0.06x), r = 0.798, p < 0.01) and the hydroxynonenal adduct-related (y(356/460) = 44.3 e(0.06x), r = 0.810, p < 0.01) were exponential, whereas that derived from MDA-adduct was almost linear (y(320/460) = 17.7 + 4.1x, r = 0.661, p < 0.01). A different accumulation rate might explain this result. Significant correlation coefficients were found within the age-adjusted fluorescence intensities of both reactions, suggesting a close relationship between glycation and oxidation, besides a mutual influence due to the broad spectrum area. The in vitro study confirmed a good specificity of collagen fluorescence after incubation with a reducing sugar (ribose 0.5 M for 6 hours) for protein glycation, and after incubation with malondialdehyde (0.1 mM for 3 hours) for lipoperoxidation adducts; surprisingly enough hydroxynonenal (0.5 mM for 3 hours) significantly increased the fluorescence related to pentosidine-like products (335 nm excitation/385 nm emission) suggesting that this compound might be the precursor of products with a fluorescence similar to pentosidine or of pentosidine itself. The in vivo results of this study confirm that nonenzymatic reactions, glycation and oxidation, significantly modify collagen fluorescence during aging and can play a role in tissue damage related to age. The close relationships among fluorescences may be due to a reciprocal interconnection rather than to a parallel increase of both reactions during aging; this hypothesis is supported by the in vitro findings of this study.