Hyaluronic acid (acid hyaluronique in french) is a substance naturally found in numerous tissues and organs of the human body: epidermis, connective tissue, cartilage, synovial fluid, eyes, etc. One of its most important properties is its ability to attract and retain water, which keeps these tissues in good condition.
It happens, however, that in the aging process its presence in the organism decreases progressively and, as a consequence, the skin loses hydration and, therefore, elasticity and firmness, becoming more flaccid and opening the door to the appearance of wrinkles. The same happens in the joints so that the cartilage becomes more rigid and can break and cause pain with every movement due to the friction between the bones. It should be noted that at the age of 50 only half of the body’s hyaluronic acid remains in the body.
But it precisely can attract and retain water that has made it one of the star products of cosmetics, aesthetic medicine, although it must be said that it has also generated its use in different treatments and therapies of regenerative and trauma medicine and other areas of medical science.
In 1934, the German pharmacist Karl Meyer and his colleague John Palmer, PhDs at Columbia University (New York), succeeded in isolating a previously unknown substance from the vitreous body of cows’ eyes in the university’s ophthalmology laboratory4. They discovered that this substance contained two sugar macromolecules, one of which was glucuronic acid. As a result, they decided to name it hyaluronic acid from the words hyaloid” (vitreous) and uronic acid. The substance, which helped the eye to retain its shape, was extremely vicious, which led Meyer to suspect that it might have some therapeutic use. However, its extraction from the eyes of cows was not commercially feasible.4
Hyaluronic acid was first used commercially in 1942 when Hungarian scientist Endre Balazs used Meyer’s techniques to synthesize acid from rooster combs, which remains one of the most profitable sources of hyaluronic acid today.4 Interested in the compound, he patented the first use of this acid as an egg white substitute in baked goods. Balazs has made most of the discoveries about hyaluronic acid over the past fifty years and has been honored for his career on numerous occasions, including having his name attached to the awards of the International Society for Eye Research.5
Hyaluronic acid (HA) is made up of complex carbohydrate chains, specifically about 50,000 disaccharides of N-acetylglucosamine and glucuronic acid per molecule6, and is derived from the union of amino sugars and uronic acids. This chain is positioned in spirals with an average molecular weight of 2 to 4 million. They have the property of retaining large amounts of water and adopting an extended conformation in solution, making them useful for cushioning or lubricating. These properties are achieved thanks to the large number of OH groups and negative charges of this molecule, which, by the establishment of repulsive forces, allows the carbohydrate chains to remain relatively separated from each other.
In cells, hyaluronic acid is produced by the action of enzymes called hyaluronic acid synthetases, which are found on the inner surface of the cell membrane. The hyaluronic acid is then extruded through pores. Three types of these enzymes have been described in mammals: HAS-1, HAS-2, and HAS-3.1
Types of hyaluronic acid
Many of the cosmetic products currently on the market contain hyaluronic acid obtained by synthesis. Its function is to penetrate the skin, mix with natural hyaluronic acid and thus promote the production of more of this substance, in addition to promoting the formation of collagen.
However, the one to be taken into account the most is the one used in aesthetic medicine or the treatment of certain joint pathologies. It is an injectable product that comes in the form of a gel and is injected into the areas to be treated. There are two types:
- Cross-linked: it is presented in gel form (dense), which allows it to maintain stability for a longer period (6 to 9 months).
- Non-cross-linked: it is liquid and retains its stability for a shorter period (approximately 3 months).
Aesthetic uses of hyaluronic acid
The function of cosmetics, apart from other theoretical effects, is basically to maintain good hydration of the skin, even in its deepest layers, so that the thickness, volume, and smoothness of the skin is maintained. It can be used to prevent or delay the appearance of wrinkles or also to treat them when they are in their most incipient stage of appearance.
However, in the field of aesthetic medicine, it has been a true revolution in the treatment of wrinkles, to the point of replacing botulinum toxin (Botox) in many cases. It has been clinically demonstrated that when applied by intradermal injection hyaluronic acid stimulates and activates fibroblasts even in elderly people, which means that in addition to providing greater volume to the skin also stimulates the formation of collagen. This is why this treatment is currently being used to eliminate certain wrinkles:
- The nasolabial folds, those that start from the nose towards the sides of the mouth).
- The periorbital folds and the corners of the mouth, in the lip contour line.
- Those between the eyebrows.
- Crow’s feet.
- Those of the forehead.
Medical uses of hyaluronic acid
The particular properties of hyaluronic acid have opened up an increasingly wide field of applications in the treatment of different pathologies. The first of these concerns the treatment of degenerative joint diseases such as osteoarthritis. In this case, infiltrations of this substance are becoming more and more frequent with a double purpose: to reduce pain and to achieve an appreciable regeneration of the cartilage.
It is also used to replace the synovial fluid lost during arthroscopic surgery. Likewise, in elite sports, it is used to recover more quickly from joint injuries (ankle, knee, etc.).
In dentistry, it is used to improve healing and regenerate gums and oral mucosa, as well as in the surgical treatment of temporomandibular joint dysfunction. Another incipient use is for the treatment of interstitial cystitis, through its introduction into the bladder. It is also suggested that it may be useful in the treatment of skin problems such as lipodystrophy, either caused by therapies with excess steroids or by antiretroviral treatment of HIV-infected persons.
See also: Fountain of youth