LINKING THE MECHANICS OF HA TO KNEE CARTILAGE BIOLOGY (Orthopedics This Week)

A new, important study out of Dr. Lawrence Bonassar’s lab at Cornell University has tackled one of the central but more difficult questions surrounding viscosupplementation, namely the link between hyaluronic acid’s (HA) lubrication function and the complex biologic processes operating on the arthritic knee.

The study, which was presented at the annual meeting of the Orthopaedic Research Society (ORS) between March 10-13, 2018, is titled “Articular Cartilage Lubrication by HYADD® 4 Reduces Tissue Strains, Chondrocyte Death and Apoptosis.”
As the investigators stated in the introduction to their study: “It remains unclear how the lubricating properties of HA mediate biologic changes in cartilage tissue. Recently, our lab developed methods to measure cellular changes in response to cyclic sliding motion. The objective of this study was to examine the relationship between the lubricating properties of HYADD®4, an HA viscosupplement and chondrocyte health after sliding articular cartilage in HYADD®4.”
To understand the importance of the work coming out of Bonassar’s lab, it’s helpful to understand the originalintended purpose of viscosupplementation. Hint: It’s not pain relief.

A Short History of Viscosupplementation
Viscosupplementation, which was first used as a therapy in the 1970s (trade name of Healon®) for ophthalmic use and veterinary use (Hylartil-Vet®), is a standard of care within the continuum of care for symptomatic osteoarthritic knees.
The intended purpose of viscosupplements is to replenish the naturally occurring synovial fluid with a substance as close to normal, healthy synovial fluid as possible. Healthy synovial fluid, in addition to providing nourishment to the cartilage cells, also lubricates the articulating structures of the joint during low impact movement and shock absorption during high impact activities.
Many studies have shown that the early onset of osteoarthritis causes a deterioration of synovial fluid’s properties—specifically elasticity and viscosity. There are various disease processes at work in an arthritic knee including production of certain enzymes and “toxic” precursors. The result is a diseased synovial fluid which cannot perform the functions of lubrication or shock absorption.
At every stage of the osteoarthritic disease process, the deteriorating ability of the synovial fluid can be experienced by the patient as pain, stiffness and reduced function of the joint.
The principal of viscosupplementation, as originally presented to the FDA[1], is to break the cycle of synovial fluid deterioration. In fact, HA viscosupplement products are not registered as drugs but rather as medical devices, like liquid bioprosthesis.
Viscosupplementation helps an osteoarthritic joint by forming a protective layer around the inflamed articulating structures, covering micro-fractures and defects helping to restore the lubrication and protection that healthy synovial fluid offers.
So, physicians and researchers have long assumed that these mechanical functions of HA affected the biology of a deteriorating arthritic knee.
But how?
Enter Bonassar’s lab at Cornell University.

Dr. Bonassar’s Methodology

Dr. Bonassar, who is Professor at the Meinig School of Biomedical Engineering at Cornell University, and his team developed a way to test living cartilage under stress in both an HA bath and in a phosphate buffered saline (PBS) bath and then measured the deleterious or beneficial effect on living cartilage.
The team started with cartilage explants from the femoral condyles of seven neonatal cows.
They subjected the samples to articulation against a glass barrier under 15% normal strain for 30 cycles at 1 mm/s for 1 hour while bathed in either HYADD4 or PBS. Dr. Bonassar’s team then measured the friction coefficients.
Following the stress of articulation against glass, the team cultured the stressed yet lubricated samples for 24 hours in DMEM and then bisected and stained the samples with calcein AM and ethidium homodimer (for live and dead cells, respectively) or caspase 3/7.
They were looking for apoptotic cells.
And they took pictures—with a confocal microscope.
The team counted the living and the dead cells and did so as a function of depth from the cartilage surface using custom code written in MATLAB. In parallel, the team also bisected cartilage samples, fluorescently stained them and then mounted them onto tissue deformation stage.
They bathed those samples in either PBS or HYADD®4 and articulated them against glass at speeds ranging from 0.1 to 1 mm/s. They tracked the depth dependent shear deformations by analyzing displacements of photobleached lines which were oriented perpendicular to the articular surfaces throughout the depth of the sample.
They calculated local shear strains.
Finally, using a two-way ANOVA and Tukey HSD to compare strain between lubricants and Pearson’s correlation coefficient, they described and quantified the link between the mechanical strain of being articulated against glass and cell death.

Here Is What They Learned
First, no surprise, there is a connection between the mechanical function of HA and the biologic processes of the knee.
Second, lubrication reduces cell death.
In the study, HYADD®4-lubricated samples had a seven-fold decrease in friction coefficient compared to the PBS-lubricated samples. This form of HA cut friction from 0.36 +/- 0.001 (PBS sample) to 0.05 +/- 0.001 for the HYADD®4 samples. That increase in lubrication cut shear strain from 53.7% to 17.5%.
The HYADD®4-lubricated cartilage samples also showed lower cell death and fewer caspase-activated cells throughout the depth of the cartilage tissues versus the lesser (PBS) lubricated samples.
Better lubrication lowers cartilage cell apoptosis.

Dr. Bonassar’s Conclusions and Discussion
The study, said Bonassar, demonstrated that HYADD®4 lowers friction, tissue surface strains, chondrocyte death and apoptosis in cartilage (in a test which subjected living cartilage explants to sliding stresses at 1 mm/s for 1 hour).
Cell death, which occurred in both samples, was significantly lower in the HA-lubricated cartilage than in the PBS lubricated sample.
There is a positive correlation between cell death and strain.
Bottom line, said Bonassar, was that “the current study is consistent with the idea that hyaluronic acid therapies for arthritis may act in part through a mechanical pathway that preserves viability of chondrocytes at the cartilage surface.”
 

The HA Used in This Study

The HA used in this study, HYADD®4, is also the key component in HYMOVIS®, an HA-based hydrogel viscosupplement manufactured by Fidia Farmaceutici (Italy) and sold by its wholly owned U.S. subsidiary, Fidia Pharma USA Inc.
Fidia, which was one of the original pioneering companies in the HA viscosupplement market, is the sponsor of the Bonassar study.
HYMOVIS® is a highly viscoelastic non-crosslinked hydrogel which has been bioengineered in a way which increases lubrication and shock absorption. The result, says Fidia and as noted in the HYMOVIS® labeling, is a natural hyaluronan which is similar to the hyaluronan found in the synovial fluid present in human joints.

Latest Data on Arthritis
In 2012 the estimated prevalence of osteoarthritis among adults in the United States, the number of individuals who had ever been told by a doctor that they had the condition was approximately 52.5 million cases (source: Centers for Disease Control and Prevention; National Statistics: National Health Interview Survey [NHIS] Arthritis Surveillance). Prevalence rates vary by the joint involved and the method of diagnosis (clinical vs. radiographic). Symptomatically, the knee is the most frequently affected joint. The prevalence of osteoarthritis of the knee is increasing rapidly because of shifting population demographics. The primary risk factors for osteoarthritis of the knee are aging, obesity, prior injury, repetitive use and female gender.
The prevalence of symptomatic knee osteoarthritis may reach 50% by the age of 75. From 2002 to 2012 the number of individuals in the U.S. with a total knee replacement doubled from some 2 million to approximately 4 million. (Source: Systematic Review for Effectiveness of Hyaluronic Acid in the Treatment of Severe Degenerative Joint Disease of the Knee; Agency for Healthcare Research and Quality [AHRQ] Department of Health and Human Services; U.S. Government).
Osteoarthritis of the knee is usually diagnosed clinically based on pain. Radiographic evidence of osteoarthritis may precede symptomatic osteoarthritis but it correlates weakly with symptom severity.
The goals of treatment for osteoarthritis of the knee include pain relief, reduced inflammation, slowing the progression of the disease and improved mobility and function as well as health-related quality of life.
Treatment options for osteoarthritis of the knee include oral or topical analgesics, injected corticosteroids, physical therapy and exercise, weight loss, viscosupplementation using natural joint lubricants (most commonly hyaluronic acid [HA]), and partial or total arthroplasty.

[1] J Rheumatol Suppl. 1993 Aug;39:3-9. Viscosupplementation: a new concept in the treatment of osteoarthritis. Balazs EA1, Denlinger JL.