What is hyaluronic acid and hyaluronidase?
Both hyaluronidase and hyaluronic acid naturally occur in the body. Hyaluronic acid is a constituent of our connective tissue, skin, and nerve tissues. The average 70kg person has approximately 15 grams of hyaluronic acid. This molecule is a polysaccharide (carbohydrate) chain and is very water-loving or hydrophilic. It is this property that helps to make our skin soft and gives our joints fluidity. Conversely, hyaluronidases are the enzymes that help break down hyaluronic acid. One-third of our body’s hyaluronic acid is turned over daily. This means that hyaluronic acid is synthesized and then broken down by hyaluronidase constantly. Interestingly, hyaluronidase is found in high concentrations in sperm. Sperm use hyaluronidase to break through the corona radiata, a barrier surrounding the egg made from hyaluronic acid, to reach the egg prior to fertilisation. The main sources of commercially available hyaluronidase are sourced from ovine (sheep) or bovine (cow) testicular tissue. Recombinant human hyaluronidase is available, but not currently in Australia.
Hyaluronic acid is also the main constituent of many commonly used dermal fillers. In dermal fillers, hyaluronic acid chains are bound by with cross-links, giving it a gel-like consistency. Cross-linking between hyaluronic acid chains found in dermal fillers provides resistance to the body’s naturally occurring hyaluronidase and increased longevity. Unlike the body’s own hyaluronic acid, cross-linked hyaluronic acid dermal fillers persist for months or years in the body. Hyaluronic acid dermal fillers are commonly used for the treatment of lines, folds, and wrinkles, and for the enhancement or volumisation of cheeks, lips, chins, and noses. Left alone, they are normally metabolised by the body over the period of 3 to 24 months (on average). To remove filler, hyaluronidase can be injected to dissolve the hyaluronic acid in dermal fillers.
What is hyaluronidase used for?
Hyaluronidase is often combined with local anaesthetic to increase the diffusion of local anaesthetic. By catalysing the breakdown of the hyaluronic acid in the tissues, the local anaesthetic is able to diffuse more effectively. Because of the relatively fast turnover of hyaluronic acid in the body, it rebuilds in approximately 48 hours. Hyaluronidase is often combined with local anaesthetic when performing retrobulbar nerve blocks which help to anaesthetise the eye for surgery such as cataract surgery. This increases the effectiveness of the local anaesthetic by helping it to reach the nerve.
In cosmetic medicine, hyaluronidase is used to dissolve hyaluronic acid based dermal fillers that have been placed incorrectly, excessively, or unevenly. It is also used in emergency situations where dermal filler has been inadvertently injected into an artery causing occlusion of the blood supply. It is injected into the vicinity of the dermal filler that needs to be dissolved. The action of hyaluronidase is very quick and starts to work immediately on the dermal fillers. The fillers are permanently dissolved and metabolised. The body’s own hyaluronic acid is also dissolved, but is replaced quickly due to its natural rapid turnover rate. Note that hyaluronidase does not work on dermal fillers made from substances other than hyaluronic acid.
An example of hyaluronidase use is to dissolve dermal filler placed around orbital (eye) region. The skin here is particularly thin, and overtreatment with dermal fillers is easily visible. Hyaluronidase is used to reduce any excess filler or lumps here, allowing for reinjection of the filler with proper placement or volume.
Having hyaluronidase on hand during hyaluronic acid filler treatment may help to prevent adverse outcomes as a result of intra-arterial injection of fillers. Intra-arterial injection of dermal fillers can cause serious complications including death of the skin (causing scarring), and blindness. Hyaluronidase can be quickly injected into the area of occlusion to re-establish blood supply to help avoid complications.
What are the possible side effects of hyaluronidase?
Injection-related side effects including swelling and bruising are the most common side effects from hyaluronidase.
Allergy, including anaphylaxis, is an uncommon side effect of hyaluronidase injections. It is more prevalent in those who are allergic to bee-stings!
The most difficult aspect of using hyaluronidase is judging the amount required to dissolve a certain amount of filler. It is quite easy to over or under-dissolve. Therefore, a second or third visit may be required to add more filler if over dissolved or to retreat with more hyaluronidase if under-dissolved.