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Volume 34, Issue 12, Page 16 (December 2003)
Hyaluronic acid is the most abundant glycosaminoglycan found in human dermis. It was discovered in 1934 by Karl Meyer and John Palmer, who isolated it from bovine vitreous humor (J. Biol. Chem. 107:629-34, 1934).
The name reflects its glassy appearance (the Greek word for glass is hyalos) and the presence of a sugar known as uronic acid. Hyaluronic acid (HA), also known as hyaluronan, is important in cell growth, membrane receptor function, and adhesion.
Its primary biologic function in connective tissue is to stabilize the intercellular structures and form the elastoviscous fluid matrix in which collagen and elastin fibers are embedded. Its structure is identical in bacterial cultures, animals, and humans. HA appears freely in the dermis and is more concentrated in areas where cells are less closely packed.
In young skin, HA is found at the periphery and interfaces of collagen and elastin fibers. It is thought to help hold together collagen and elastin in the proper configuration. Studies have shown that these connections with HA are absent in aged skin, which may help explain the disorganization of collagen and elastin fibers (Int. J. Dermatol. 33:119-22, 1994).
Hyaluronan can bind water up to 1,000 times its weight. It is postulated that some of the wrinkles and lack of plumpness seen in aged skin are due to a lack of HA.
Obviously, there are many reasons why HA is a popular ingredient in injectable dermal fillers and skin care products.
Recent interest in HA has occurred because of the development and promotion of several dermal fillers, including Hylaform, Restylane, and Juvederm.
HA was developed as a dermal filler by Endre Balazs and coworkers in the late 1980s because of its biocompatibility and lack of immunogenicity. It has a large molecular weight and is made of repeating dimers of glucuronic acid and N-acetyl glucosamine assembled into long chains. These chains form highly hydrated random coils that entangle and interpenetrate, producing highly elastoviscous solutions.
Unmodified, natural-state hyaluronan is rapidly broken down by hyaluronidase; in fact, the half-life is no longer than 1 day. In order to produce a viscoelastic material with an increased residence time, hyaluronan is modified, or cross-linked.
Several cross-linked HA products are currently marketed as dermal fillers. Each has a unique method of cross-linking that causes it to have different properties than its competitors.
Unmodified HA consists of chains of HA that have not been cross-linked. This is the form of HA found in cosmeceutical products. Because of its water-binding ability, HA is a superior humectant and so is often included in cosmetic products as a moisturizing ingredient.
Even though HA has the ability to pull moisture from the atmosphere and trap it on the surface of the skin, it can't penetrate the stratum corneum and enter the epidermis (Cosmetics Toiletries 113:35-42, 1998).
Recently, topical products have been launched that intend to capitalize on the popularity of the new HA-containing dermal fillers (Hylaform and Restylane), which could be on the market by early next year. It is important for dermatologists to know that “Rest-a-Line” and other skin care products that claim to have HA have no proven benefit beyond that of moisturization. These products are just another attempt of companies to take advantage of naive buyers of skin care products.
Wasn't the “Better Than Botox” campaign bad enough?
Dr. Leslie S. Baumann is director of cosmetic dermatology at the University of Miami. To respond to this column, or to suggest topics for future columns, write to Dr. Baumann at our editorial offices via e-mail at email@example.com.
© 2003 International Medical News Group. Published by Elsevier Inc. All rights reserved.