The effects of the Maillard reaction on the physical properties and cell interactions of collagen.

The non-enzymic glycation of collagen occurs as its turnover decreases during maturation, with complex carbohydrates accumulating slowly and the end-products of these reactions being permanent. The nature of these advanced glycation end-reaction products (AGEs) can be categorised as: 1) cross-linking: intermolecular cross-linking may occur between two adjacent molecules and involve lysine to lysine or lysine to arginine residues. Several compounds have been characterised. They are believed to be located between the triple helical domains of adjacent molecules in the fibre resulting in major changes of the physical properties, primarily, fibre stiffness, thermal denaturation temperature and enzyme resistance, all of which increase slowly with age but the rate is accelerated in diabetes mellitus due to high glucose levels: 2) side-chain modifications: these changes alter the charge profile of the molecule affecting the interactions within the fibre and if they occur at specific sites can affect the cell-collagen interaction. Modification of arginine within the sites RGD and GFOGER recognised by the two specific integrins (alpha1beta2 and alpha2beta1) for collagen reduce cell interactions during turnover and for platelet interactions (alpha1beta2). These changes can ultimately affect repair of, for example, vascular damage and dermal wound healing in diabetes mellitus. Both types of modification are deleterious to the optimal properties of collagen as a supporting framework structure and as a controlling factor in cell matrix interactions. Glycation during ageing and diabetes is therefore responsible for malfunctioning of the diverse collagenous tissues throughout the body.