According to the Washington University School of Medicine, osteoarthritis affects at least 27 million people in the United States and about 12 percent of these cases are a result of a previous injury to a joint. While anti-inflammatory medicines help reduce pain, they do nothing to halt the ongoing cartilage destruction that increases the level of pain.
Researchers at the university led by Christine Pham, MD, have shown in mice that they can inject nanoparticles into an injured joint and suppress inflammation immediately following an injury, reducing the destruction of cartilage. Their study was published in the Proceedings of the National Academy of Sciences.
“I see a lot of patients with osteoarthritis, and there’s really no treatment,” said senior author Christine Pham, MD, an associate professor of medicine told Jim Dryden of Washington University in St. Louis.
“We try to treat their symptoms, but even when we inject steroids into an arthritic joint, the drug only remains for up to a few hours, and then it’s cleared. These nanoparticles remain in the joint longer and help prevent cartilage degeneration.”
Osteoarthritis sufferers often have suffered an earlier injury — an injury in the knee, a fall, car accident or other trauma. The body’s natural response to the injury to the joints is with significant inflammation.
The typical treatment for pain is over-the-counter pain medications and with more severe pain, steroid injections are often used. Both treatments are short-lived, which is why the findings from the study are most interesting.
According to the university, “The nanoparticles were injected shortly after an injury, and within 24 hours, the nanoparticles were reducing inflammation in the joint. Unlike steroid injections that are quickly cleared, the particles remained in cartilage cells in the joints for weeks.”
The nanoparticles carry a peptide derived from a natural protein called melittin that was modified to enable it to bind to a molecule called small interfering RNA (siRNA). The melittin delivers siRNA to the damaged joint, interfering with inflammation in cells.
The peptide-based nanoparticle was designed by study co-investigators Hua Pan, PhD, an assistant professor of medicine, and Samuel Wickline, MD, the James R. Hornsby Family Professor of Biomedical Sciences.
“The nanoparticles are injected directly into the joint, and due to their size, they easily penetrate into the cartilage to enter the injured cells,” Wickline said. “Previously, we’ve delivered nanoparticles through the bloodstream and shown that they inhibit inflammation in a model of rheumatoid arthritis. In this study, they were injected locally into the joint and given a chance to penetrate into the injured cartilage.”
It’s unknown if this approach to treating or preventing osteoarthritis will pan out over time. These early findings do, however, suggest that treatment soon after injury may maintain cartilage strength and possibly prevent the disease.
“The inflammatory molecule that we’re targeting not only causes problems after an injury, but it’s also responsible for a great deal of inflammation in advanced cases of osteoarthritis,” said Linda J. Sandell, the Mildred B. Simon Research Professor of Orthopaedic Surgery and director of Washington University’s Center for Musculoskeletal Research. “So we think these nanoparticles may be helpful in patients who already have arthritis, and we’re working to develop experiments to test that idea.”