Maki Kaneko

Glycylglycine decreases the size of conspicuous facial pores: Single-blinded half areas of face-applied study

Dear Editor, Enlarged, or dilated facial pores are one of the most frequently encountered skin problems in women of all ages. From our international survey, it has been revealed that more than half of women in their twenties and thirties complain of conspicuous pores. Because so little had been known about their anatomical structure, facial pores were investigated. The results indicated that pores were shown to form a cone-shaped hollow, which was rich in nucleated cells, an indication of parakeratosis. An investigation of the relationship between the degree of conspicuous pores and the condition of the skin indicated that women with abundant noticeably large pores showed high transepidermal water loss (TEWL) values, and high sebum content with significant amounts of unsaturated free fatty acids. A similar result of the relationship between the degree of visible pores and the amount of sebum has also been reported. Moreover, experimental application of oleic acid, an unsaturated fatty acid and the main component of human sebum, to the human skin promoted parakeratosis and increased TEWL values. Therefore, it was suggested that unsaturated fatty acids such as oleic acid may be responsible for the appearance of conspicuously enlarged pores. We then examined the effects of oleic acid on human keratinocytes to search for a substance that could inhibit such effects, and hopefully provide a way of improving the appearance of facial pores. When oleic acid was added to keratinocytes, it was found that the concentration of intracellular calcium ions increased. Various kinds of antagonists were applied before the addition of oleic acid, and N-methyl D-aspartate (NMDA)-type glutamate receptor antagonists such as MK801 were found to specifically inhibit the buildup of calcium ions. Concentrations of inflammatory cytokines such as interleukin (IL)-1α were increased by the addition of oleic acid, and MK801 inhibited the elevation of cytokine levels as such. These results suggested that oleic acid might cause parakeratosis around the pores with subsequent enlargement of the hollow, possibly via an NMDA receptor functioning in the corneocytes. We believed that the suppression of these effects would lead to the improvement of the appearance of facial pores. In addition to NMDA receptor antagonists, we screened for glycine-type receptor agonists, because glycine receptors are known to induce a chloride ion influx which should help cancel out the excess positive charge of the calcium ions in the cell. We detected that glycylglycine was one of the most effective compounds capable of suppressing increase of the TEWL value in human skin. Furthermore, glycylglycine was found to partially suppress the elevation of IL-1α levels induced by oleic acid. In this study we applied solutions containing 15% (w/w) ethanol with or without 1.6% (w/w) glycylglycine (Sigma-Aldrich, St Louis, MO, USA) to half areas of human cheeks of Japanese volunteers three times a day. We analyzed the areas corresponding to the hollow using replicas to establish whether or not glycylglycine can reduce the pore size and in turn improve the appearance of conspicuous pores. At first, 21 Japanese healthy men aged 20–50 years who had relatively conspicuous pores participated in April–May 2004, and application was performed for 1 month. Informed consent was obtained. Replicas with silicone rubber (Silflo, Flexico, Potters Bar, UK) were analyzed using a confocal microscope (HD100D; Lasertec, Yokohama, Japan). Pores were examined in areas of 3.3 × 3.3 mm of replicas by 3-D image analysis and the total areas of cross-section