Effects of avocado and soya bean lipidic non‐saponifiables on the components of skin connective tissue after topical application in the hairless rat: biophysical and biomechanical determination

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Abstract
The non-saponifiable lipidic fractions of avocado and soybean applied percutaneously to hairless rats for 15 days produced biochemical modifications of dermal connective tissue components: increases of soluble collagen and of the ratio soluble collagen/insoluble collagen. Whether these biochemical modifications could be confirmed by biophysical analytical methods and could affect the biochemical properties of the skin was investigated. The experiments was carried out on 3 groups of rats treated by application to the dorsal skin, either with 0.9% NaCl (control), or sweet almond oil (vehicle), or with a mixture of 2/3 soybean and 1/3 avocado in solution at 5% of sweet almond oil (treated group). After 15 days treatment, the rats were killed and the skin of the treated area dissected. X-ray diffraction diagrams were recorded by varying the position of previously dried samples in controlled conditions. The vehicle decreased the orientation degree of collagen fibers, acting on their reticulation. The addition of the non-saponifiable fraction did not significantly add to the vehicle effect. A study of thermostability of the cutaneous collagen by differential scanning calorimetry showed that non-saponifiables increased the slope of the rise of temperature of denaturation. The quantity of heat absorbed during the denaturation (enthalpy variation) reached around 0.04 J mg-1 of collagen in the control groups and did not exceed 0.03 J mg-1 of collagen in the treated ones. Taken in conjunction with previous work, it is probable that the non-saponifiables increase the proportion of soluble collagen. The elasticity of whole skin, determined by a static method using an Instron extensiometer was significantly modified by treatment with non-saponifiables. They produced a decrease of the elasticity module. These results correspond to a decrease of collagen reticulation degree.