Palo Azul Prevents Dryness-Induced Decrease in Filaggrin and Amino Acids

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Natural moisturizing factor (NMF), which is mainly composed of free amino acids and their derivatives, aids the retention of water in the stratum corneum (SC), preventing skin dryness caused by various environmental stimuli. Low levels of amino acids have been reported to be associated with a low hydration state in the SC of dry skin, but the mechanism underlying the decrease in amino acids is not well understood. The protein filaggrin is the major source of amino acids in the SC. We exposed cultured human keratinocytes to air by removing their medium and recognized a decrease in mRNA and protein expression of profilaggrin, a precursor of filaggrin. We employed the result to search for active ingredients to prevent the decrease and discovered that the extract of a Mexican plant, Palo Azul, effectively prevented the decrease in profilaggrin mRNA. We also confirmed that lotion containing the extract increased the hydration state and amino acid content in the SC of human SDS-induced dry skin. These findings suggest that air exposure of cultured human keratinocytes might be a useful model of human dry skin, and could be used for screening active ingredients to treat dry skin. In addition, it appears that dryness itself might lower profilaggrin mRNA expression, resulting in a decrease in amino acid content in the SC.
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