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Protein glycation by hexoses has been implicated in the pathophysiology of a number of diseases as well as the aging process. Studies of ADP-ribose polymer metabolism have shown that free ADP-ribose is generated at high rates in the cell nucleus following DNA damage. Protein glycation by ADP-ribose has been reported although the chemistry is not understood. Described here is the synthesis and characterization of model conjugates for protein glycation of lysine residues by ADP-ribose. Two stable conjugates derived from ADP-ribose and n-butylamine were isolated and characterized. Both conjugates were shown to be ketoamines derived from a Schiff base by an Amadori rearrangement. The chemical stability of the ketamines allowed them to be differentiated from all classes of enzymic protein modification by ADP-ribose. Further, their chemical properties suggest that a previous report of histone H1 modification in carcinogen treated cells was due to glycation by ADP-ribose.

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Sensitized production of reactive oxygen species after photo-excitation of endogenous chromophores is thought to contribute to skin photo-oxidative stress. Here we present experimental evidence in support of a potential role of extracellular matrix proteins as skin photosensitizers. Human and bovine type I collagen and elastin sensitized of hydrogen peroxide generation upon irradiation with solar simulated light or ultraviolet A. Induction of intracellular oxidative stress by extracellular matrix-protein sensitization was demonstrated by flow cytometric analysis of fibroblasts preloaded with the intracellular redox dye dihydrorhodamine 123 and exposed to pre-irradiated type I collagen. Pre-irradiated collagen and elastin induced pronounced inhibition of proliferation in cultured keratinocytes and fibroblasts, which was reversed by antioxidant or catalase treatment and reproduced by exposure to concentrations of H2O2 formed during extracellular matrix-protein irradiation. In fibroblasts, chromosomal DNA damage as a consequence of collagen-sensitized H2O2 formation was demonstrated using a single cell electrophoresis assay. The enzymatic cross-links pyridinoline and desmosine were examined as candidate sensitizer chromophores contained in collagen and elastin, respectively. Pyridinoline, but not desmosine, sensitized light-driven H2O2 production and inhibition of fibroblast proliferation. Our results support the hypothesis that extracellular matrix proteins play a functional role in skin photoaging and carcinogenesis by sensitization of photo-oxidative damage.