Collagen in its fibrillar state is protected from glycation

To assess the impact collagen structures may have on glycation, the effects of glucose upon bovine serum albumin, guinea pig skin collagen, rat tail tendon and monomeric collagen were compared under near physiological conditions. Proteins were incubated with or without 50 mM glucose for 64 d in pH 7.4 50 mM phosphate buffer, followed by reduction, acid/alkaline hydrolysis, and analysis. Yields of non-reducible fructose-lysine, in the form of the acid-degradation products furosine and pyridosine, were significantly higher from skin collagen when compared to albumin. Yields of reducible fructose-lysine, in the form of glucitol- and mannitol-lysine, were conversely much greater for albumin, while tail tendon reported intermediate values. Fructose-lysine and unmodified lysine within collagen fibres prior to incubation was therefore protected by the tight packing of the collagen helices, where milling of tail tendon to increase the surface area exposed much of it to reduction protocols. Together with an analysis of pentosidine formation and other products, these results have shown that the interior of the tightly packed skin collagen fibres is protected from both glycation and reduction, and that glycation products differ depending on the protein incubated. Amino acid analysis then showed that our glycated skin collagen was similar to human diabetic skin collagen. Significant quantities of glucose-independent unknowns form in control incubations; their composition again being protein-dependent. The four compound Ks as previously reported were found to be unique to glycated rat tail tendon and soluble collagen, while another glycation product detected in collagen but not albumin may be attributable to carboxymethyl-arginine.