gms | German Medical Science

The extent of aspartic acid racemization of corneal proteins describes ageing processes of the cornea. These are important for transplant quality. Under physiological conditions aspartic acid accumulates age related in proteins of the stroma. As we have shown in previous studies exogenious factors can influence the extent of racemization and consequently the degradation of corneal proteins. In our cornea bank there are many donors having suffered from diabetes mellitus. These donors often reveal high concentrations of glucose in aqueous humour. So the question arises if glycosylation processes may have an impact on corneal proteins.

The extent of aspartic acid racemization in corneal proteins of donors with known diabetes mellitus and without was evaluated by measurement of D- and L-aspartic acid concentrations using HPLC. Furthermore in vitro-experiments were performed: glucose was added to culture medium in concentrations as it can be found in patients with diabetes. During cultivation endothelium morphology and the extent of aspartic acid racemization in stromal proteins were examined.

In donors with known diabetes the extent of aspartic acid racemization was significantly reduced (p<0.05). In vitro-experiments could show that reduction of endothelial cells in coincidence with cell polymorphism was dependent on glucose concentration. The extent of aspartic acid racemization was lower in those media with added glucose than in routine culture medium.

The evaluation of aspartic acid racemization shows that in diabetes there is diminished corneal protein ageing / degradation. Obviously high glucose concentrations lead to a slower ageing of structure proteins, whereas cellular structures may be damaged.