Non-enzymatic glycosylation of keratin from the stratum corneum of the diabetic foot

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Abstract
Non-enzymatic glycosylation of keratin from the stratum corneum of the sole of the foot was measured by the thiobarbituric acid technique in thirty diabetic and thirty control subjects. A significant increase in the level of glycosylation was demonstrated in the diabetic subjects (P < 0.001). HbA1 levels were measured in a further eighteen subjects at the same time as keratin was removed, and in this group a significant association between non-enzymatic glycosylation of that protein and diabetic control was demonstrated (P < 0.01). In vitro incubation of keratin in the presence of free glucose produced increased non-enzymatic glycosylation (P < 0.01) and this effect was blocked by incubation in the presence of increasing concentrations of aspirin (P < 0.01). Measurement of non-enzymatic glycosylation of keratin in a further group of twenty diabetics with neuropathic ulceration showed a significant increase in levels when compared with a group of diabetics without ulcers (P < 0.05). As keratin is the principle structural protein of the stratum corneum of the sole of the foot, it is possible that changes in this protein associated with non-enzymatic glycosylation may contribute to abnormalities seen in the skin of the feet of diabetics.