To maintain a youthful and attractive appearance, skin must be flexible, soft, smooth and wrinkle-free. All of these attributes are directly associated with moisturization. Water is vital for the normal functioning of the skin and its cells; an absence or shortage of water leads to a dry, flaky and scaly appearance, or even xerosis.² Thus, water levels need to be carefully regulated, a task mainly dependent on the nature of the skin’s most external layer, known as stratum corneum (SC). The SC is a selectively permeable, heterogeneous, composite epidermal stratum that is the primary barrier and is therefore constantly exposed to major desiccation stress and damaging agents like wind and heat. But environmental elements aren’t the only factors that alter water levels; there are other agents involved in water availability such as certain proteins implicated in transport and the aging process itself. Skin dehydration can be naturally aggravated with aging, as there are fewer interactions between water and the surrounding molecules.

Natural Barrier Against Water Loss
The water content of viable epidermis is particularly high (70%) but it drops drastically when approaching the skin surface and the SC, where its content is much lower (10-30%).^3,4 In this superficial layer, the epidermis developed a barrier function system formed by macromolecular components and cells that provide the required structure to diminish skin water loss and maintain an adequate water level.³ This barrier is mainly formed by the migrated keratinocytes from the epidermal basal layer to the SC (called corneocytes) and the inter-corneocyte lipids (mainly ceramides) surrounding them. It can be described as a brick wall-like structure where “bricks” represent the terminally differentiated corneocytes and the “cement” corresponds to the highly specialized intercellular lipids.

Corneocytes constitute the physical barrier of the SC due to their direct contact with environmental factors. They contain keratin filaments, filaggrin (protein surrounding keratin filaments) and the natural moisturizing factor (NMF), elements that confer flexibility and mechanical resilience to the SC. Surrounding these anuclear cells, the lipid multilamellar organization is vital to the mechanical and cohesive properties of this external layer, enabling it to function as an effective water barrier. Therefore, the hydrophilic nature of corneocytes together with the hydrophobic environment found in the extracellular domains of the lower SC is the main reason to impede free water diffusion.⁴ Adding that the water flux within the skin layers is constant and abundant, it is clear that the proper functioning and organization of both elements is needed to assure skin hydration and integrity.

Inner Hydration & Water Transport
Apart from this first barrier, other inner elements contribute to protect from dehydration by managing transport of water molecules. Among these agents, aquaporins are a family of hydrophobic and small integral membrane proteins that act as water selective pores, facilitating water transport along a favorable osmotic gradient.⁵ One of these 13 homologous protein types found in mammals acts like a water channel, conducting water molecules inside and outside the cell, while another type known as aquaglyceroporins can transport other molecules exceptionally as well.⁵

Aquaporin 3 (AQP3) is the most abundant aquaglyceroporin in human epidermis, being responsible for facilitating the transportation of water, glycerol and other solutes like urea through membranes. This aquaglyceroporin provides a short water circuit between the base of the epidermis and the SC, maintains constant water content and prevents the formation of a continuous water gradient across the epidermis below the SC. Unfortunately, aging and sun exposure reduce AQP3 expression.^5,6 Thus, increasing the levels of this protein would help to regulate water transport and maintain appropriate water levels within the skin.

Topicals & Ingestibles
The use of dietary supplements for a cosmetic benefit provides an opportunity to ameliorate skin appearance and health from the inside, complementing traditional topical agents. The combination of both types of ingredients results in a superior benefit for the skin, as the problem is attacked from opposing flanks. To improve skin hydration, nutrition experts selected a mixture of hydrating and barrier function enhancing compounds to create Inhydrate; these capsules contain evening primrose oil, wheat seed extract and vitamin E.

Evening primrose seed oil has substantial levels of linoleic acid, gamma-linolenic acid, alpha-linolenic acid and ceramides, which improve essential fatty acids levels and skin barrier function, normalize excessive transepidermal water loss (TEWL), smooth the skin and modulate inflammatory reactions.^1,4,7,8 Wheat extract presented restructuring, hydrating, anti-free radicals and anti-elastase activities, being able to increase skin hydration and reduce TEWL, desquamation, roughness and itching.^1-4 Finally, vitamin E is one of the natural endogenous antioxidants of the skin but diet is the only source. As the SC is a major oxidative target due to the adverse factors that result from free radicals and reactive species formation, large quantities of vitamin E are needed in the SC9. In fact, its topical pre-treatment was found to be photoprotective and reduced erythema, lipid peroxidation and sunburn cell formation, while its oral intake reduced TEWL and enhanced skin barrier function.^10-11 Thus, this mixture of compounds improves skin barrier function, diminishes TEWL and increases skin moisturization.

As a topical hydrating ingredient, Diffuporine (INCI name: Acetyl hexapeptide-37) protects against dehydration by activating the human AQP3 promoter and inducing its protein transcription, which improves the water flux to the SC. Additionally, it induces type I collagen synthesis and keratinocytes proliferation, which provide skin resiliency, strength, compactness and firmness. This peptide presents immediate and long-lasting hydrating effects, which help to rejuvenate the appearance of the skin. Therefore, Lipotec proposes combining the oral and topical treatment to observe the hydrating benefits for the skin.

Improving Skin Moisturization  
In order to confirm the efficacy of the oral and topical ingredients in ameliorating the alterations induced by a lack of water, several studies were carried out. An increase of TEWL implies barrier function irregularities, so a mixture containing the components of the oral ingredient (evening primrose oil, wheat seed extract and vitamin E acetate) was evaluated on skin discs to observe their possible effect on TEWL reduction. Using a diffusion Franz cell, TEWL values were measured after the product application (active or placebo). Compared to placebo, the active combination improved TEWL values by 26.5%, 38.0% and 36.7% after 1, 2 and 24 hours, respectively, highly diminishing water loss (see Figure 1).

Additionally, the separate ingredients of this mixture were applied on human keratinocytes to observe their protecting effects when these cells were exposed to a severe desiccation. After incubating cells, the medium alone or with the active mixture was added to the plates, one of which was desiccated for 40 minutes. Pictures of the cells were taken before and after the stress, determining their viability by the Neutral Red Uptake method and measuring the optical density at 540 nm with a spectrophotometer. Vitamin E acetate, evening primrose oil and wheat seed extract offered clear statistically significant protection from dehydration, raising cell viability by 28.8%, 29.0% and 54.3%, respectively. The images of different cells showed that, despite cell tendency to shrink after being exposed to stress, the cells treated with the oral ingredients maintained the same area size as before the stress, versus 28% reduction in non-treated cells.

Regarding the topical ingredient, it increased the in vitro AQP3 promoter activity (up to 96%), AQP3 transcription (up to 131%), cellular viability after a dehydration stress (up to 35% more protection and up to 22% more recovery) and type I collagen synthesis (up to 61%). Furthermore, 20 female volunteers with dry skin applied a cream with 2% of a solution with the peptide twice a day for 56 days on half-face and a placebo on the other half, so its in v ivo efficacy could be evaluated by corneometry.

A significant increase in the mean basal hydration was detected in the areas that applied the active cream after 2 hours (37.6%), 8 hours (107.6%) and 56 days (130.9%) versus the placebo effects. Thus, the peptide provided immediate and long-lasting skin hydration (see Figure 2).

A Superior Approach
Once the benefits of the oral and topical ingredient were proved separately, it made sense to combine the two to boost hydration even more. Thus, an in vivo study was carried out in 20 female volunteers (30-50 years old) with dry skin. Volunteers applied a cream containing 2% of a solution with the peptide on one side of the face and a placebo on the other, twice a day for 56 days. During this period, volunteers also took two capsules containing the oral ingredient once a day.

After measuring skin hydration before and after the treatment using a corneometer, the active cream alone had a higher effect (by 131%) than the placebo cream alone. However, the combination of the topical application and the oral ingestion significantly raised skin hydration by 152% after 56 days versus the active capsules alone (see Figure 3).

Conclusions
Hydration is paramount to maintaining healthy and youthful skin, so the natural mechanisms that retain water and manage its transport are crucial to avoid evident alterations. The SC is the first barrier to control water loss and protect it from environmental factors, as its corneocytes and lipids are responsible for avoiding free water diffusion. Other inner elements also contribute to maintain water levels and hydration, such as the aquaporin family that facilitates the transport of water molecules and its flux, avoiding water shortage in needed zones.

In order to prevent skin dehydration, reduce water loss and maintain attractive skin, a combination of an inside and outside treatment is proposed. While topical cosmetics are widely demonstrated to act on skin conditions and beauty, nutricosmetics are a recent category of products that work from the inside with the capacity to complement the topical treatment.

Inhydrate capsules contain a mixture of ingredients that help the skin remain hydrated by keeping its water molecules, avoiding its loss and protecting from dehydration. Topically, Diffuporine promotes AQP3 presence and protects from dehydration as well, complementing the oral hydrating efficacy. The combination of the intake of the oral capsules containing the active compounds and the regular application of a topical product containing the peptide noticeably improves hydration.

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References

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