A differential scanning calorimetry analysis of the age-related changes in the thermal stability of rat skin collagen.

Differential scanning calorimetry (DSC) has been applied to the study of connective tissue to evaluate the denaturation process of collagen. We have applied this technique to the study of the ageing of rat skin. We have tried to correlate the variations of the parameters measured by DSC and the modifications of collagen crosslinks with ageing. The thermograms obtained are composed of one main peak located between two shoulders. The relative size of each peak varies with time: the first peak diminishes regularly from 2 to 20 months whilst, at the same time, the third peak increases; the recovery temperature increases with age (+ 16 degrees C between 2 and 20 months); the total denaturation enthalpy does not vary: the main value obtained is 5.9 X 10(-2) J/mg collagen. On the other hand, the assay of reducible collagen crosslinks in rat skin, over the same age range, shows a decrease of heat-labile aldimine crosslink (essentially hydroxylysinonorleucine). These results and the study of thermograms obtained with altered rat skin (animals treated with beta-aminopropionitrile or skin reduced with NaBH4) allow us to conclude that heat-labile and heat-stable crosslinks account for a collagen thermal stabilization which can explain the delay of denaturation characterized by the third peak of DSC thermograms.

Study of the thermal stability of skin collagen by differential calorimetry. Influence of a cosmetic treatment.

Synopsis Collagen being the main structural protein of the skin, the influence of a face cream containing this molecule was studied in the dermis using differential scanning calorimetry. This method, using samples of rat dermis, gives curves from which the denaturation temperature and enthalpy change of the collagen fibre network can be followed. The present study was made using two groups of rats which were treated by the cream (or placebo) during 4 months (5 days a week), and were aged 5 and 9 months at.

Influence of collagen denaturation on the chemorheological properties of skin, assessed by differential scanning calorimetry and hydrothermal isometric tension measurement.

The curves obtained for skin samples of different ages and species by hydrothermal isometric tension ("HIT") measurement are compared to those obtained by differential scanning calorimetry (DSC) under the same thermal conditions (for a rise in temperature at a rate of 1.0 degrees C/min). Collagen denaturation, observed by DSC, directly affects the kinetics of the tension variations in the first part of the "HIT" curves, including the early peak due to the presence and destruction of the heat-labile cross-links in the collagen network. The presence of cross-links is in term shown to delay collagen denaturation to an extent which depends in part on their heat-stability. The final part of the "HIT" curves reflecting the effects of heat in the stable polymeric collagen network is no longer affected by collagen denaturation. Thus, both "HIT" and DSC are useful methods to evaluate collagen reticulation in connective tissues.

Composition, cross-linking and thermal stability of bone and skin collagens in patients with osteogenesis imperfecta.

The composition, cross-linking, and thermal stability of the collagens were determined in bone and skin biopsies from 4 patients with moderate to severe forms of osteogenesis imperfecta (OI). The major modification observed with respect to control subjects was an overhydroxylation of lysine in type I bone collagen (hydroxylysine content doubled in three patients and increased by 50% in the last patient). This overhydroxylation is confirmed by a similar increase in the dihydroxylated cross-link of bone collagen: the dehydrodihydroxylysinonorleucine. The type II collagen from cartilage and the pepsin-soluble collagens from the skin of these patients contained the normal amount of hydroxylysine. A small amount of type III collagen has been found in three patients, while only in one patient a slight increase in the type III/type I collagen ratio was observed in skin. In all patients the thermal stability of the collagen triple helix, measured by differential scanning calorimetry, was normal in both bone and skin. Although in at least three patients the clinical features allowed us to classify our patients into two different groups (Sillence et al., 1979 classification--groups I and III), the biochemical results are similar, suggesting that the overhydroxylation of the lysine in type I bone collagen is a common feature of severe forms of osteogenesis imperfecta.