Hyaluronic acid

Hyaluronic acid (HA) is a polysaccharide polymer that is one of the main building blocks of connective tissue in the body. It forms a slippery jelly-like material surrounding cells in the extracellular matrix and is also found throughout the body in the skin, joints, eyes, and neural tissues. As a major component of synovial fluid, HA provides lubrication to joints to help them move smoothly by preventing friction between bones and absorbing shock from movement. It has chain-like molecular properties that allow it to bind to and retain water, and can hold up to one thousand times its weight. The structure of HA also allows skin to be flexible and gives it properties to heal quickly since half of all of the body’s HA is found in skin cells.

HA is produced naturally by cells. The average-sized person has about 15 grams of HA in their body, with about 5 grams of it being replaced each day. However, as a person ages, levels of HA decrease, therefore the protection HA provides decreases. Scientists, who refer to HA by its technical name as hyaluronan, can create it in a laboratory using animal sources or bacteria. Laboratory-created HA is used as a dietary supplement, inhalant, injection, eye drops, or topically as a skin care product.

Background

The name hyaluronic acid comes from the Greek word, hyalos, which means vitreous or glass-like, and uronic acid, which is a type of sugar acid. The reason that it was given this name is that the substance was first identified by German biochemists Karl Meyer and John Palmer in 1934 from the transparent vitreous humor of a cow’s eye. They also saw that the newly isolated substance contained uronic acid. It is commonly referred to as hyaluronan by scientists because it is a polysaccharide. Sodium hyaluronate is a conjugate base of HA, which is a substance that is able to absorb or gain a proton in a chemical reaction. It is sometimes called an ester or physiological salt of hyaluronic acid, or listed on skin products as hyaluronic acid (as sodium hyaluronate).

HA is naturally made in the body in the plasma membrane of a cell, but it was first developed and created in the laboratory as a biomedical product in the 1970s called Healon. Healon was first used in eye surgery for procedures such as cataract removal, corneal transplants, intraocular lens implantation, glaucoma correction, and repairing retinal detachment. Manufacturers have worked with biochemists to extend the stability and viability of HA using various techniques. One such way was to extend the length of the chain by using protein-based cross-links to make a hydrogel, while another involved adding sorbitol molecules to scavenge free radicals. These practices are common in HA products to significantly extend the shelf life.

The potential of HA was also seen in skin products to fight dryness, wrinkles, sagging, and other signs of aging. Eva Friederichs, a California esthetician, began investigating the use of sodium hyaluronate topically on skin after reading research about its properties and benefits in eye surgery. She created one of the first facial serums used in the skincare industry in the late 1970s. By the 2000s, it started to become popular to replace collagen as a dermal filler in cosmetic subdermal skin injections. The American Society of Plastic Surgeons (ASAPS) reported that it was the most popular wrinkle filler by 2013 and accounted for 85 percent of injections other than Botox Botulinum toxin injections.

Overview

As a polymer, HA is a long and complex chain-like molecule with places for other chemical compounds to join the chain. This structure acts as a scaffold to allow for the growth and regeneration of damaged tissue, allowing wounds to heal faster and better and reducing inflammation by redirecting blood flow to heal tissue damage. This chain-like property is also how HA molecules absorb and retain water, for example, a quarter of a teaspoon of HA is able to hold about a gallon and a half of water. It is also able to use this latching-on property to transport other molecules and attach itself to cells. In the skin, it can bind to collagen on one side of the chain and water on the other, providing hydration and plumpness. Biochemists are researching ways of using hyaluronic acid to deliver medications to targeted body tissues.

HA can be made by fermenting bacteria or removing it from rooster combs. As an over-the-counter dietary supplement in liquid, powder, or pill form, HA has been reported to reduce pain from arthritis by improving the concentration of HA in the synovial fluid to improve skin integrity and fight the natural decline of HA levels that comes with aging. It also improves skin dryness, plumps wrinkles, and promotes healing when applied topically in a serum, lotion, or gel, but some studies have suggested that much of the HA molecules found in skin care products are too large to pass through the outer layers of skin. Since HA acts as a gentle lubricant, it is also found in eye drops to reduce irritation and is used in personal lubricant gels and creams. It has been found to be especially beneficial for women experiencing vaginal dryness during menopause.

Prescription HA can be used for various medical treatments in addition to its initial use during eye surgery. It is can be used as a vehicle with intravenous (IV) medication given in a healthcare setting. It can also be directly injected into joints to provide lubrication and relief from arthritis pain or injected under the skin as a dermal filler to treat damage from acne or to add volume to the skin. As a nasal inhalant, it can help mucus membranes better absorb medication or treat respiratory conditions, such as asthma. Since HA is a naturally occurring substance in the body, there are very few risks or side effects associated with its medical use. Any adverse effects, such as pain, bruising, or swelling, are generally associated with the route of delivery through injection.

Bibliography

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