Differential scanning calorimetry, biochemical, and biomechanical analysis of human skin from individuals with diabetes mellitus.

The aim of this work was to compare biochemical, two-dimensional biomechanical and calorimetric parameters of diabetic skin vs. control skin. Skin specimens taken from the palms and backs of the hands of aged persons with non-insulin-dependent diabetes mellitus (NIDDM) and of controls (CO) were compared (age range 68-85 years). Only skin specimens from individuals with diabetes mellitus (DM) showed an increased fluorescence specific for the formation of advanced glycation end-products (AGEs) and the presence of tissue AGEs, such as N(e)-(Carboxymethyl)lysine (CML). Differential scanning calorimetry (DSC) revealed an elevation of the heat flow per unit mass during collagen denaturation in diabetic skin samples. However, the temperatures of the heat flow maximum and the onset of the phase transformation were not uniformly altered. Young's moduli were found to be increased in diabetic skin and correlated with AGE-fluorescence and tissue AGEs. The ratio between the Young's moduli, which defines a measure for the degree of anisotropy, was higher for dorsal skins from hands. In dorsal skin specimens from diabetic subjects the degree of anisotropy was more pronounced than in healthy controls. In general, neither of the measured parameters showed any correlation with age. However, E(1) moduli were clearly associated with the duration of diabetes.

Alterations of biochemical and two-dimensional biomechanical properties of human skin in diabetes mellitus as compared to effects of in vitro non-enzymatic glycation.

OBJECTIVE: The aim of this study was to evaluate whether multiaxial analysis of diabetes-specific biomechanical changes generated in vitro by non-enzymatic glycation of human skin samples from healthy subjects reflect the changes seen in skin from subjects with diabetes mellitus. DESIGN: Descriptive study. BACKGROUND: Non-enzymatic glycation of skin in vitro causes an increased stiffness comparable to in vivo changes seen in diabetic patients. These changes are probably due to increased cross-linking of collagen molecules. METHODS: Skin specimens from 7 subjects with diabetes mellitus and 7 controls (age range: 74-90) were analyzed for biomechanical changes using a multiaxial tensile testing device. Control skins from healthy individuals in the age range of 50-65 yr were artificially glycated. One part of these samples was coincubated with the glycation inhibitor aminoguanidine. Glycation of tissues was determined by measuring fluorescence of solubilized samples. Multiaxial biomechanical analysis allows the determination of maximum (a(I)) and minimum elastic modulus (a(II)). These parameters describe the amplitude of the elastic stress response, which is exponentially related to strain. RESULTS: Principal stresses, both maximum and minimum, were increased in skins from diabetic subjects as compared to controls. The increases of the principal stresses were comparable to those obtained by in vitro glycation of normal skins. CONCLUSION: These results, which can be detected unequivocally with the multiaxial test mode, show that our in vitro model closely reflects changes in skin samples from individuals with diabetes mellitus. Aminoguanidine partially inhibited these as well as biochemical changes. RELEVANCE: Multiaxial testing of in vitro glycated skin samples can be used as a model for in vivo changes caused by diabetes mellitus. In addition, therapeutical effects of aminoguanidine, an inhibitor of non-enzymatic glycation, can be monitored in this model.

Comparison of palmar aponeuroses from individuals with diabetes mellitus and Dupuytren's contracture.

It is well known that Dupuytren's contracture is often associated with diabetes mellitus. Palmar fascia from individuals with diabetes mellitus and/or Dupuytren's contracture as well as controls were subjected to differential scanning calorimetry, biomechanical and biochemical analysis. The collagen denaturation temperature of the palmar aponeurosis from individuals with diabetes mellitus in the presence (71.0 degrees C) or absence of Dupuytren's contracture (70. 6 degrees C) was increased as compared with controls (68.5 degrees C), while this parameter was significantly reduced (about 3.5 degrees C) in contracture bands of Dupuytren's contracture. Stress relaxation experiments revealed that the viscous fraction was slightly reduced in diabetes mellitus (6.5%) vs. controls (8.3%), whereas in Dupuytren's contracture, irrespective of additional diabetes mellitus, a pronounced increase of this parameter was seen (36.5% vs. 24.5%) in the presence of diabetes mellitus. The time constants were significantly elevated by both disorders, this increase being more pronounced in Dupuytren's contracture. Taken together, these changes can be explained by increased cross-linking in diabetes mellitus, while in Dupuytren's contracture other structural changes, such as increased collagen type III content and loss of fascicular organization, play an additional role besides the finding of reduced cross linking.

Comparison of normal and in vitro aging by non-enzymatic glycation as verified by differential scanning calorimetry.

The biomechanical parameters of rat tail tendons (RTTs) from 35-, 64-, 180- and 900-day-old animals, corresponding to the early maturation phase, the mature and the senescent state were determined. The increase of maximum stiffness, ultimate stress and the elastic fraction of stress was most pronounced in the maturation phase. Differential scanning calorimetry (DSC) experiments were performed showing an almost linear increase of the collagen denaturation temperature in the age range 35-139 days. After 14 days incubation in glucose, we observed a marked increase of the biomechanical parameters in the young, an increase of maximum stiffness in mature, and only slight alterations of the biomechanical behavior in senescent RTTs. Both glucose incorporation and formation of advanced glycation end products were most prominent in 35-day-old RTTs. These biochemical findings were in excellent agreement with the enhancement of the collagen denaturation temperature after the incubation phase. Results suggest that the validity of the term 'accelerated aging' depends on the experimental approach, i.e. biomechanical tests, thermal isometric contraction or DSC.