Researchers here provide evidence for injections of adenosine into damaged joint tissue to provoke meaningful degrees of cartilage regrowth in an animal model of degenerative joint disease. Finding ways to force the regrowth of tissues, such as cartilage, that normally exhibit little regenerative capacity is an important goal for the research community. Many varied approaches are presently under development; this one has the merit of being comparatively simple when compared to the more logistically challenging cell therapy and tissue engineering strategies.
Previous research had shown that maintaining supplies of adenosine, known to nourish the chondrocyte cells that make cartilage, also prevented osteoarthritis in similar animal models of the disease. In a new study, researchers injected adenosine into the joints of rodents whose limbs had been damaged by inflammation resulting from either traumatic injury, such as a torn ligament, or from massive weight gain placing pressure on joints. The biological damage in these cases is similar to that sustained in human osteoarthritis. The study rodents received eight weekly injections of adenosine, which prompted regrowth rates of cartilage tissue between 50 percent and 35 percent as measured by standard laboratory scores.
Among the study's other key findings was that a cell-signaling pathway, known as transforming growth factor beta (TGF-beta) and involved in many forms of tissue growth, death, and differentiation, was highly active in cartilage tissue damaged by osteoarthritis, as well as in cartilage tissue undergoing repair after being treated with adenosine. Additional testing in lab-grown chondrocytes from people with osteoarthritis showed different chemical profiles of TGF-beta signaling during breakdown than during growth, providing the first evidence that the pathway switched function in the presence of adenosine, from assisting in cartilage breakdown to encouraging its repair.