Mechanisms of heparinoid-induced skin moisturizing effect: Influence on bound water and lamellar structures in stratum corneum

Abstract

Water in the stratum corneum exists as both bound and free water. Bound water is subdivided into primary and secondary bound water. Particularly, it is well known that secondary bound water is quickly bound to extracellular lipids formulating the lamellar structures in the stratum corneum. This implies the importance of secondary bound water on the hydration state in the stratum corneum. Hirudoid® cream or lotion containing a heparinoid as an active ingredient has been widely utilized as a skin moisturizer for patients with senile xerosis. However, the mechanisms of its moisturizing effect remain unclear. We investigated the effect of the heparinoid on bound water and intercellular lamellar structures in vitro and in vivo. The bound water content in artificial lamellar structures consisting of water and egg yolk lecithin was measured using differential scanning calorimetry (DSC) in vitro. Heparinoid increased bound water in the lamellar structures in accordance with the amount of added water. Dry skin was experimentally induced in guinea pigs treated with 3%(w/v) sodium lauryl sulfate solution once daily for 4 days. After ascertaining skin dryness, Hirudoid® Lotion was applied to the skin once daily for 5 days. The bound water content in the stratum corneum was measured using DSC. Furthermore, changes in differential thermal analysis (DTA) vaporization curves and thermogravimetry (TG) of the stratum corneum were analyzed using TG/DTA systems. The ultrastructures of the intercellular lamellar structure were investigated using electron microscopy. Results showed that the heparinoid caused significant increases in bound water and normalization of the DTA vaporization peak pattern and the lamellar structure. These results suggest that the mechanisms of the Heparinoid-induced skin moisturizing effect are based on increases of both secondary bound water and the restoration of the lamellar structure.