Glyco-oxidative mechanisms in glucose toxicity: biochemical changes of matrix collagen in diabetic rats

The aim of the present work was to study changes in mechanical properties and biochemical indices of rat tail tendon collagen under conditions of streptozotocin-induced diabetes in a 32-week experiment. Tail tendon mechanical strength characterized by breaking time in concentrated urea was significantly enhanced for diabetic animals when compared with those of age-matched controls. Pepsin digests of tail tendons from diabetic rats were found to contain elevated amounts of material, reacting rapidly with p-dimethylaminobenzaldehyde (Ehrlich's reagent) to give an adduct with an absorbance spectrum characteristic of the Ehrlich chromogen of pyrrolic nature determined in ageing collagens. Characteristic glyco-fluorophore with excitation and emission maxima of 365 nm and 416 urn, respectively, was elevated in collagen obtained from tail tendons of diabetic animals. The glycation inhibitor aminoguanidine significantly inhibited changes of all three parameters evaluated. Treatment of diabetic animals with the pyridoindole antioxidant agent stobadine resulted in a significant decrease of tendon breaking time values, while glycation-related fluorescence and Ehrlich chromogen absorbance remained unaffected. The results suggest that apart from advanced glycation additional mechanisms may participate in collagen cross-linking in diabetic connective tissues, namely hyperglyceamia-induced oxidative processes.