Non-enzymatic glycation of epidermal proteins of the stratum corneum in diabetic patients

Abstract

A selected group of diabetic patients showed a statistically significant increase in levels of glycated proteins in the stratum corneum compared with a control group. The values of glycated proteins correlated with those of glycohaemoglobin (GHb), and in diabetic patients also with serum glucose concentrations. The values of glycated proteins (and GHb) exhibited a positive correlation with age both in a control group and in diabetic patients. The average values of glycated proteins (and GHb) were slightly higher in women than in men. Determination of glycated proteins levels of the stratum corneum can serve as a stable parameter for long-term monitoring of the course of non-enzymatic glycation in structural and connective tissues and thus also for the prognosis of the development of dermatological complications related to diabetes mellitus. In vitro incubation of stratum corneum proteins and keratin with glucose resulted in an increase of their glycation. The values of glycated proteins and glycated keratin increased proportionally to the glucose concentration and duration of incubation. Glucose binding to keratin and proteins of the insoluble stratum corneum fraction appeared to occur at practically the same rate, and it is a first-order reaction with regard to the glucose concentration. Water-soluble proteins of the stratum corneum undergo non-enzymatic glycation preferentially (on average, 83.4% of the total amount of glycated proteins is present in the soluble fraction), regardless of the initial content of glycated proteins in the sample. The content of glycated soluble proteins of a higher molecular weight significantly increased after 4 weeks of incubation with glucose.

Keratin intrinsic fluorescence as a mechanism for non-invasive monitoring of its glycation

“…Diabetic patients showed increased levels of glycated keratin in the stratum corneum in the sole of the foot [12], and in hair [10], and in both cases this was detected using the thiobarbituric acid technique. Increased levels of glycated keratin have also been found in fingernails [15][16][17], using techniques other than fluorescence spectroscopy, which are discussed below. Moreover, a higher concentration of glycated keratins was found in patients exhibiting complications such as diabetic retinopathy, nephropathy [16], and diabetic ulcers [12], compared to those with diabetes who were not experiencing these complications.…”

“…Previous studies have used several methods to determine the amount of glycated keratin in human tissues. For example, colorimetric analysis has been used to determine glycated keratin in the stratum corneum of the skin in vitro [15], near-infrared reflectance spectroscopy [17], ATR-FTIR spectroscopy [18] and chemical analysis using techniques such as borate affinity chromatography followed by gel electrophoresis [16] has been used to determine the levels of glycated keratin in nail clippings.…”