Hyaluronic acid

Hyaluronic acid is a polysaccharide found everywhere in the body, more precisely a glycosaminoglycan. This consists of repeating disaccharide units of uronic acid, is linear and exhibits acidic properties. Hyaluronic acid is a main component of the extracellular matrix of vertebrates, especially of the connective tissue, which is located between the skin cells and fills and supports them. Up to 50,000 disaccharides can follow each other and thus form large charged structures with a high molecular mass. They are charged and thus have a very high polarity, which enables them to absorb large amounts of water as well as to be volumizing. These properties significantly influence biochemical functions in the body.

They are also used for cosmetic and therapeutic purposes.

Applications and indications

In cosmetics, hyaluronic acid is an indispensable component, especially in beauty products such as creams, because, among other things, it gives the skin its resistance and contributes to the maintenance of structural and tissue tension. In some creams, it also serves to slightly reduce wrinkles, but not to permanently smooth them, as it only reaches the uppermost layers of the skin and cannot penetrate further to the deeper ones. As it can bind large quantities of water molecules, it provides the skin with moisture and thus has a moisturizing effect, which is why it is also frequently used in moisturizing creams. By binding large amounts of water, it swells and thus additionally tightens the skin.

In addition to creams, hyaluronic acid tips are also used in aesthetic medicine to shape breasts or lips.

Furthermore, hyaluronic acid is commercially available in many dosage forms such as ampoules, gels, eye drops or capsules for oral administration as a dietary supplement.

Hyaluronic acid is also used in a variety of medical preparations and drugs. For example, some nasal sprays and eye drops contain hyaluronic acid, in which it prevents the nasal mucosa and eye from drying out. In cleaning and care solutions for contact lenses, it forms a lasting tear film on the eye after insertion without impairing vision.

Therapeutically, hyaluronic acid is used as a sodium salt (sodium hyaluronate) in the form of injection solutions for the treatment of arthrosis (wear and tear of the joint). This is a degenerative joint disease in which damage to the articular cartilage occurs. The articular cartilage, which exists as a protective and elastic layer on the ends of bones, wears away until, in the course of the disease, bone rubs on bone, causing pain and immobility of the affected person.

Using injectable solutions, hyaluronic acid is injected directly into the spaces between joints to take over the function of worn joint cartilage and act as a shock absorber. It also protects the articular cartilage from further degradation and relieves pain by forming a protective layer.

The syringe with the injection solution (e.g. Hyalarat®) is injected into the affected joint once a week as prescribed by a doctor.

History

Hyaluronic acid was first isolated from the fluid of bovine eyes by the physicians Karl Meyer and John Palmer in 1934 at Columbia University in New York, and from that time on it was studied in detail. This fluid, unknown at that time, was transparent but glassy. In addition, they were able to identify uronic acid as a component of this solution in the early days, giving it the name "hyaluronic acid", which translated from the Greek is composed of glass (hyalos) and urone (an abbreviation for hyaluronic acid).

Initially, the substance could only be obtained from animal sources. Only in the 2000s was it possible to synthesize it from bacteria, which greatly reduced the risk of side effects and made it possible to use hyaluronic acid in cosmetics.

Pharmacodynamics/mechanism of action

Hyaluronic acid is a natural compound found in the body and accordingly has many different properties, mainly due to its structure. Thus, it has water-binding, smoothing, volumizing and wound-healing properties and thus versatile physiological functions.

It is mainly found in the connective tissue in the synovial fluid (synovia), where it leads to frictionless joint movement by acting as a lubricant. Due to its viscosity, it adheres to the cartilage and can adapt to the different mechanical effects. In the skin, as well as in the vitreous humour of the eye, its ability to bind large amounts of water makes it responsible not only for moisture retention, but also for pressure resistance, since water is incompressible.

Hyaluronic acid can occur in different sizes depending on how many disaccharide units follow each other. The natural form in the body is long-chain and has a high molecular mass (high-molecular-weight hyaluronic acids).

For cosmetic purposes, however, short-chain compounds with a lower molecular mass are synthesized, so-called low-molecular hyaluronic acids, which can penetrate better and deeper into the skin and thus trigger better effects.

With age, the natural hyaluronic acid in the body declines, which is why people then resort to a wide variety of formulations and dietary supplements.

Pharmacokinetics

Hyaluronic acid is broken down in the body by hyaluronidases; the resulting metabolites are then either recycled or excreted via the kidneys.

Orally ingested hyaluronic acid is poorly absorbed due to its high molecular weight.

Interactions

Interactions are not known.

Contraindications & precautions

• In case of hypersensitivity to hyaluronic acid or any other ingredient of the formulation, the injection solution should not be used.
• One should not combine Hyalarat® with other active ingredients which are applied intra-articularly (into the joint cavity), as there are not sufficient experience reports on this.

Side effects

Pain, a feeling of heat, redness or swelling may occur during or after the injection of Hyalarat®. Possibly, puncture-worthy effusions may also occur in the area of the treated joint, which are clear to yellowish cloudy. These occur primarily in patients who already have a knee joint effusion. Treatment discontinuation could then occur.

In very rare cases, general allergic reactions such as fever, chills, edema, shortness of breath, heart palpitations, drop in blood pressure and even circulatory collapse or anaphylactic shock are possible. In such cases Hyalarat® must be discontinued immediately!

Otherwise, side effects are largely unknown, since the substance also occurs naturally in the human body and should therefore be well tolerated.

Pregnancy and lactation

Not enough studies have been carried out on pregnant or breastfeeding women.