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.

Aquaporins are proteins that reside in the cellular membrane. In response to osmotic forces, they control the passage of specific materials into and out of the cell. As reported previously in Cosmetics & Toiletries magazine,¹ one type of aquaporin in human skin is aquaporin-3 (AQP3), a pore by which water, glycerin and certain other moisturizing agents gain access to the interior of epidermal cells. The importance of moisturization for skin health and appearance means that personal care companies have a reason to be interested in the activity or presence (expression) of aquaporins, especially AQP3. As reported in the technical literature, four personal care companies have studied the world of biochemicals to discover AQP3 stimulators from three different sources: vitamins, steroids and sugar alcohols.

Vitamins
A vitamin is an organic compound that an animal, plant or other organism needs but cannot synthesize for itself, so it must be obtained from the diet. Thus, the term is conditional both on the circumstances and the particular organism. For example, ascorbic acid functions as vitamin C for some animals but not others, and vitamins D and K are required in the human diet only in certain circumstances, such as liver or kidney disorders in the case of vitamin D and intestinal damage in the case of vitamin K.²

Vitamins serve diverse biochemical functions. For example, vitamin D acts as a hormone. Vitamin E is an antioxidant. Vitamin A regulates cell and tissue growth and differentiation.²

Vitamin B₃, also known as niacin, in the form of niacinamide plays a role in AQP3 stimulation and has been investigated at the upstream research division of Procter & Gamble (P&G) Beauty. A 2007 US patent application3 from P&G discloses personal care compositions comprised of at least one ingredient from each of two ingredient groups in a dermatologically acceptable carrier. One group consists of niacinamide, glycerin and mixtures thereof. The other group consists of aquaporin-stimulating compounds—of which 40 are named—and their mixtures. Some of the aquaporin-stimulating compounds mentioned in that patent are well-established cosmetic ingredients, such as caffeine, green tea, menthol, tea tree oil and kinetin. Others, such as Ajuga turkestanica extracts and various ginsenoside compounds (components of ginseng extract), also were disclosed. This work from P&G Beauty was described previously.⁴

Vitamin A, or retinoic acid, has been studied at Johnson & Johnson Consumer France SAS.⁵ Researchers there investigated the in vitro and ex vivo effects of all-trans retinoic acid (ATRA) on AQP3 expression and function. An ATRA treatment was found to provoke a rapid accumulation of AQP3 transcripts in cultured normal human epidermal keratinocytes (NHEK). This increase was observed as long as 24 hr after application of ATRA. The induction of AQP3 gene was accompanied by an augmentation of immunoreactivity. Incubation of NHEK in ATRA for 24, 48 and 72 hr stimulated glycerol influx, suggesting that the increase in AQP3 gene and protein expression was followed by an enhancement of biological activity. Topical application of ATRA for 24 hr on skin explants induced significant epidermal expression of AQP3 and strong immunoreactivity in the epidermal basal layers. According to the authors, these results show that ATRA increased AQP3 expression and enhanced biological activity in human skin.