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Hyaluronic acid is a linear polysaccharide (long chained sugar) composed of small chain sugars containing N-acetylglucosamine and glucuronic acid. It is found naturally in the body where it is found in the highest concentrations in the connective tissues like the fluid around the joints, the skin, and vitreous body. It is also found in some specialized tissues like the umbilical cord and rooster combs.
HA is made by the cell membrane by adding simple sugar molecules or monosaccharides onto the reducing end of the chain eventually creating a polysaccharide. The polysaccharide grows out of the cell surface and its production is under the influence of various factors, such as growth hormone, inflammatory mediators, etc. The enzyme that is responsible for the production of HA is a phosphoprotein called hyaluronan synthase. When many cells, like fibroblasts in the skin, produce large amounts of HA they eventually become suspended in a gel or matrix of hyaluronic acid called the cell matrix. One of the characteristics of this cell matrix is its ability to bind to water molecules, and it is this ability of HA that makes it important for skin tone and hydration. As we get older, the production of HA decreases due to decreased production of HA. A naturally occurring enzyme present in the skin called hyaluronidase breaks down HA, this causes the skin to dehydrate and lose its “plumpness” promoting the formation of wrinkles. Other factors responsible for skin aging like damage secondary to long term exposure to UV radiation and environmental pollutants can hasten the loss of HA from the cell matrix resulting in wrinkles.
The question now remains, are there products on the market, other than the aforementioned fillers, that can replace the lost HA. One might think we can simply add some HA filler to a skin cream and let it absorb to reduce wrinkles, but it is not that easy. The problem being that HA comes in two forms, the linear or straight chain molecule and the reticulated or so-called cross-linked molecule. Fillers are composed of the later and are more resistant to the action of hyaluronidase than the straight chain molecule. This increased resistance to enzymatic breakdown is the reason that injectable fillers last for six to nine months. However, being a more complex molecule they are not easily absorbed by the skin and hence not a good option as an ingredient for a skin cream. Another problem with trying to use cross-linked HA is that it is irritating to the skin. Contrary to those who say HA is not absorbed by the skin, I refer them to an article by Brown TJ, Alcorn D, Fraser JR in the Journal of Investigative Dermatology whose findings established that hyaluronic acid is absorbed from the surface of the skin and passes rapidly through the epidermis to the deeper layers of the dermis. Their finding suggests that passage through the epidermis does not rely on passive diffusion alone but may be facilitated by active transport. The dilemma we have in creating a cream using the linear HA is that it is very sensitive to enzymatic breakdown by hyaluronidase. This breakdown can occur in twenty- four to forty-eight hours and therefore may be of little benefit.
There is, however, a newer version of topical HA found some European skincare products that is a combination of eighty percent linear HA with twenty percent cross-linked HA. This allows the linear molecule to drag some of the cross-linked molecule with it deep into the dermis resulting in an anti-wrinkle product that is both absorbable and longer lasting.
It is clear that we will never be able to completely eliminate wrinkles, but there is hope in reducing and hiding them. In my opinion, the consumer should search out a product that is natural, contains this next generation hyaluronic acid and has significant antioxidant activity to protect the skin from the aging effects caused by UV radiation as well as the damage due to environmental pollutants.