The content of free amino acids in the stratum corneum is increased in senile xerosis

Xerosis is one of the characteristics of aged skin. Xerosis may be caused by a decrease in the stratum corneum free amino acids which are natural moisturizing factors derived from filaggrin. In aged skin, filaggrin is immunohistochemically decreased compared with the levels in young skin. However, the differences in stratum corneum amino acids between aged and young skin have not been analyzed quantitatively. Therefore, in this study we determined the stratum corneum amino acids per 1000 stratum corneum cells in aged and young skin by high-performance liquid chromatography. The amount of filaggrin mRNA in the epidermis was also compared between aged and young skin using RT-PCR. The total amount of amino acids in the stratum corneum was larger in aged senile xerosis skin than in young skin. Only a few amino acids were found in the stratum corneum of ichthyosis vulgaris patients (control skin). The expression of filaggrin mRNA in aged skin was, however, similar to that in young skin. These findings suggest that the immunohistochemical decrease in filaggrin in aged skin may be caused by promotion of filaggrin proteolysis in the upper layers of the stratum spinulosum.