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U.VA. RESEARCHERS FIND NEW TOOLS IN REPAIR OF CARTILAGE DAMAGE IN KNEE INJURIES, QUESTION CURRENT METHOD

It is estimated that five million Americans suffer knee injuries each year, many with associated cartilage damage that can lead to osteoarthritis if untreated.  Now researchers at the University of Virginia Health System are using gel culture and gene therapy to deliver and trace cells necessary to repair knee cartilage defects. The research, featured in the September issue of the Journal of Bone and Joint Surgery, also questions the effectiveness of the chondrocyte autotransplantation procedure currently being used.

In the study, U.Va. researchers studied what effect growing cartilage cells (chondrocytes) within a gel culture had on their ability to emit the proteins necessary for cartilage development, and whether gel culture was a useful vehicle to deliver chondrocytes into knee defects.  The researchers used gene therapy to label the cells with enhanced green fluorescent protein (EGFP), which glows green under a fluorescent microscope, in order to track the cells while in culture and after being placed into the knee. 

Researchers preconditioned the chondrocytes by suspending them within gel culture beads (calcium alginate) two weeks prior to placing them in knee defects and found the cells produced the proteins, type II collagen and aggrecan.  These proteins create a type of scaffolding around the chondrocytes essential to forming normal cartilage. 

The team, headed by Dr. David Diduch, associate professor of orthopaedics at the University of Virginia Health System and principal investigator of the study, created additional beads with EGFP labeled chondrocytes the day of surgery, and along with the preconditioned beads, placed them into cartilage defects that penetrated the bone below in the knees of six rabbits.  The researchers examined the defects over a four-week period and found the cell numbers remained at 100 percent after the first week, but dropped to 75 percent the second and third week and had diminished to 15 percent by the fourth week.  Researchers found the repair tissue that formed within the defect after the beads were inserted did not come from the transplanted chondrocytes, but from the surrounding cells migrating from the bone into the defect and creating scar tissue.

“We found the preconditioning of cells had no effect on the cells ability to survive once transplanted into the knee,” Diduch said.  “However, we did find that calcium alginate, because it is similar to the cells natural environment within cartilage, promotes the expression of cartilage-specific genes and is a useful vehicle for delivery of chondrocytes because it can be pressed into articular cartilage defects.”

Diduch also said the use of gene therapy to genetically mark cells may improve our understanding in tissue repair and regeneration, and will critically test the usefulness of cell-based approaches for joint resurfacing in the future. 

“By using gene therapy, researchers will be better able to scientifically prove the cells are producing the desired effects.  More importantly, it may enable researchers to administer growth factors to specific areas, influencing the body’s own repair process,” Diduch said.

He believes this research calls into question what role, if any, transplanted chondrocytes play in the repair of cartilage defects using the chondrocyte autotransplantation procedure.

According to Diduch, chondrocyte autotransplantation is a costly, two-step procedure, which involves harvesting cartilage from the knee, removing the chondrocytes from within the cartilage and culturing them fifteen-fold in a single-layer culture.  A flap of tissue (periosteum) is then scraped from the shinbone and sewn over the defect.  The cultured cells are then injected under the flap to repair the defect. Diduch says because clinical studies on chondrocyte autotransplantation are based on outcome and do not address the biomechanical and biochemical properties of the repair tissue, it remains unclear whether the transplanted cells are responsible for the repair of the defects or whether they even persist at the site of injury for any length of time.   

“We know from other work that cells in a certain layer of the periosteum can create scar tissue and fill a defect the same way,” he said.  “Our research has shown that chondrocytes cultured in a single layer become less specialized and no longer produce the type II collagen protein necessary for cartilage development.  So, the question is, are these cells that are so expensive actually doing anything?  Our research suggests no.”

September 30, 2003