Glucose-mediated cross-linking of collagen in rat tendon and skin.

BACKGROUND Cross-linking of macromolecules like collagen plays an important role in the development of complications in diabetes and ageing. One of the underlying mechanisms of this cross-linking is the formation of advanced glycation endproducts (AGEs). METHODS In this study, we assessed the use of differential scanning calorimetry (DSC) for the determination of these cross-links and the effects of an AGE inhibitor and breaker. RESULTS Treatment with N-phenacylthiazolium bromide (ALT-711) of diabetic rats with 2 months duration of diabetes normalized large artery stiffness, assessed by characteristic input impedance and systemic arterial compliance, but with the use of DSC, no statistical difference in cross-linking between control and treated animals could be measured. In addition, we performed in vitro incubation of collagen preparations with ribose and glucose to assess the DSC method as well as the influence of AGE breakers and inhibitors. Incubation of rat tail tendon (RTT) with 100 mmol/l glucose showed an increase in collagen cross-linking expressed as an increase in shrinkage temperature (T(s)). Addition of aminoguanidine (AG), an inhibitor of AGE formation, prior to glucose incubation showed a slower increase of the amount of glucose-derived cross-linking. Replacing glucose with ribose showed a quicker increase in cross-linking and less effect on cross-linking by adding aminoguanidine, demonstrating the higher reactivity of pentoses above hexoses. Similar experiments with rat skin samples (RSS) showed that RSS (type III collagen) are less susceptible to glucose-mediated cross-linking than RTT (type I collagen). We observed no effect of addition of ALT-711, a breaker of glucose-derived cross-links, on the extent of collagen cross-linking in both RTT and RSS. CONCLUSION Overall, DSC is considered a useful method for assessing glucose-mediated cross-linking in vitro with nonphysiological glucose concentrations. The in vivo use in biological samples is limited due to the lack of sensitivity. However, DSC remains a quick and well-quantitated method in comparison with other methods, like enzymatic digestibility.