Aquaporins: Stimulation by Vitamins, Steroids and Sugar Alcohols

By: Bud Brewster, C&T magazine

Posted: October 30, 2008, from the November 2008 issue of Cosmetics & Toiletries.

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Nicotinamide is yet another name for vitamin B3. Chinese researchers have shown6 that while ATRA upregulates AQP3 expression in cultured human skin keratinocytes (HaCaT cells), nicotinamide attenuates the effect of ATRA in a concentration-dependent manner. This study provides insight into the molecular mechanism through which nicotinamide reverses the side effects of dryness in human skin after treatment with ATRA.

Steroids
A steroid is a terpenoid lipid characterized by a carbon skeleton with four fused rings, generally arranged in a 6-6-6-5 fashion. Steroids vary by the functional groups attached to these rings and the oxidation state of the rings. Hundreds of distinct steroids are found in plants, animals and fungi. Among the many steroids are the hormones estrogen, progesterone and testosterone.

All steroids are made in cells either from the sterol lanosterol (animals and fungi) or the sterol cycloartenol (plants). Both sterols are derived from the cyclization of the triterpene squalene, the natural compound that, when hydrogenated, is called squalane, a common ingredient in personal care formulations.

In a 2003 dissertation,⁷ a Swedish researcher addressed the question of whether there might be factors in the skin that could influence the rate and direction of water transport through perinatal skin. His investigation focused on aspects of water transport through developing skin, first by determining TEWL in a group of extremely preterm infants. Further, in an experimental rat model, he analyzed the expression and distribution of AQP in the perinatal skin in relation to biophysical parameters of the skin barrier such as TEWL, skin surface hydration and the water content of the skin. The investigation included an analysis of developmental aspects as well as the effects of a clinically relevant form of pharmacological treatment, namely antenatal corticosteroids. He found that antenatal corticosteroid treatment induces functional changes in the skin of preterm rat pups, resulting in a lower TEWL, lower skin surface hydration, and a lower water content of the skin. These changes occur in parallel with an upregulation of AQP3 in the epidermis.

For more than a decade, ecdysteroids have interested researchers at LVMH Recherche-Parfums et Cosmétiques. A 1997 patent⁸ issued to LVMH described the use of an ecdysteroid for the preparation of cosmetic or dermatological compositions intended specifically for strengthening the water barrier function of human skin. Ecdysteroids are hormones that regulate keratinocyte differentiation in humans. This differentiation manifests itself at the epidermal level in greater cellular cohesion; in the regulation of keratinocyte transformation into corneocytes, through loss of the nucleus and increase in cellular cornification; and in an increase in the number of layers of corneocytes forming the cornified layer.