Synovial Fluid's Effect on Stem Cells

For years horse owners have turned to traditional joint therapies to help manage their animals' painful joint diseases, such as arthritis, so they might remain comfortable and usable despite their medical conditions. Today, some owners are exploring a relatively new type of joint therapy: intra-articular stem cell injections. While many initial anecdotal reports indicate this method has been successful, some questions still remain. For example, how do the stem cells interact with the synovial fluid that fills joints? A University of Georgia College of Veterinary Medicine (UGACVM) researcher recently completed a study on the topic.

Lindsey Helms-Boone, DVM, a surgical resident and PhD candidate at UGACVM set out to better understand how bone marrow-derived stem cells (BMSCs) interact within the synovial fluid environment, and to see if increasing concentrations of synovial fluid effected the BMSCs proliferation (growth) and viability (survival).

"I wanted to prove to myself when I first started this experiment that when I injected, say, 10-20 million BMSCs into a horse's joint that they would be able to survive in synovial fluid without substantial loss in viable cells before adhering to the synovial membrane," she explained.

"Synovial fluid in vivo (in the live horse) has a concentration of 100% (i.e., the synovial fluid in the horse's joints isn't mixed with anything; it's 100% synovial fluid)," Helms-Boone noted. "In an in vivo setting the nutrients available to the cells are constantly changing, but when you place this in an in vitro (in the laboratory) setting the nutrients in the synovial fluid do not change.

"We were concerned that the cells would exhaust the nutrients in the synovial fluid and not be able to survive in 100% synovial fluid for the allotted culture time," she explained. "So we were worried that if there was a decrease in viability when cells were in 100% synovial fluid that it might be just exhaustion of the available nutrients rather than due to the synovial fluid itself." It was for this reason the team elected to perform the in vitro study.

Helms-Boone and colleagues used BMSCs harvested from 11 healthy horses with no known articular ailments for their in vitro study. The team placed the BMSCs into 96 well plates (a petri dish-like apparatus commonly used in labs) in concentrations of either 3,000 cells per well or 6,000 cells per well. Each well contained complete media (a liquid that contains water, glucose, growth factors, and essentially all the things cells need to grow and divide) with increasing concentrations (0%, 5%, 10%, 25%, 50%, 75%, and 100%) of synovial fluid collected from healthy horses.

After 48 hours the team removed the media and synovial fluid from the wells and replaced them with fresh media. The team observed the well plates at 48, 72, and 96 hours.

"The plates were read for a colorimetric change in a dye called Alamar blue (which was added to the cell plates after the fresh media was added), which measures cellular metabolism through oxidation-reduction mechanisms," Helms-Boone explained.

Upon conclusion of the study, the team found that "the degree of sensitivity (the cells that showed more sensitivity had a greater degree of change in their viability and/or proliferation) of the BMSCs to the synovial fluid was unique to each horse. For example, some cells from some horses seemed to be refractory to the synovial fluid while others were altered in either a stimulatory or inhibitory manner," Helms-Boone explained.

Simply put, the synovial fluid caused little reaction in some horses' stem cells, yet stimulated or inhibited proliferation of the cells from others. The concentration of synovial fluid in the media didn't seem to play a role in the cells' reactions, the team noted.

"These preliminary results suggest that other unknown BMSC factors, unique to each horse, might influence their response to the synovial fluid environment," Helms-Boone concluded. "The next step is to carry this research into the in vivo setting. We are currently carrying out a study evaluating the systemic and local effects of intra-articular injection of allogeneic (those collected from one horse and injected into another) stem cells.

"Horse owners should realize that there are new and exciting options for regenerative medicine, but the intra-articular use of stem cells is still in its infancy," she added. "There is a lot that we do not know about the appropriate dose, appropriate time in the disease course for implantation, and the appropriate vehicle."

Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.

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