Injections of hyaluronic acid (HA) are a common treatment of pain in osteoarthritis of the knee – a condition that affects 27 million Americans according to the Centers for Disease Control and Prevention. The injections replace natural HA that has depleted from one’s joints, which can cause pain and stiffness due to the lack of lubrication between bones moving against each other.
There are eight different HA products sold in the U.S. with annual sales approaching $1 billion. And while all of these products are approved by the FDA, studies have produced mixed results on their effectiveness, leading researchers and doctors to question how HA actually functions in the body.
A research group led by Lawrence Bonassar, professor of biomedical engineering, and graduate student Edward Bonnevie has discovered that another molecule, lubricin, helps anchor HA at the tissue surface, which, in turn, helps to move cartilage into a low-friction regime. “The implication of this finding is that the efficacy of HA treatment might depend on how much lubricin is in the joint at the time of injection, which could explain why clinical trials of HA have such variable outcomes and may also suggest new formulations of HA that might be even more effective in the clinic,” said Bonassar.
The study, published in the journal PLOS ONE, examined how multiple formulations of HA lubricated cartilage and found that they all worked by a similar mechanism, “one that is very similar to how a car hydroplanes on a wet road,” said Bonassar. Essentially, the viscous HA solutions form pressurized films that lower the friction coefficient of cartilage, particularly at higher sliding speeds. “For many years, people doubted that this mechanism could happen in cartilage because the tissue is both flexible and porous. In this paper, we show definitively that cartilage can move to this low-friction domain in the presence of highly viscous HA solutions,” said Bonassar.
Scientists from Fidia Farmaceutici S.p.A. co-authored the study and used the results to bioengineer a new derivative of natural HA. This new HA derivative, known as HYADD4, has been approved by the FDA for clinical use in the U.S. and will be marketed under the name Hymovis starting in March.