At least 27 million people in the United States are affected by osteoarthritis and  at least 12 percent of osteoarthritis cases arises from earlier injuries. Over-the-counter (OTC) painkillers, like anti-inflammatory drugs, help reduce pain but do not cease unrelenting cartilage destruction. Hence, pain associated with the condition only gets worse.

The researchers at Washington University School of Medicine in St. Louis have revealed in mice that they can inject nanoparticles into an injured joint and conquer inflammation soon after an injury, lowering the destruction of cartilage. These findings are described online in the Proceedings of the National Academy of Sciences.

According to senior author Christine Pham, MD, an associate professor of medicine,"I see a lot of patients with osteoarthritis, and there's really no treatment. 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."

An osteoarthritis patient has persistently suffered an earlier injury - a torn meniscus or ACL injury in the knee, a fall, car accident or other trauma. Inflammation is followed after such injuries as a result of body's natural response. Some commonly used drugs like acetaminophen and ibuprofen, and injections of steroids (worst cases of pain) also can provide pain relief to the patients, although their effects are short-lived.

The nanoparticles were injected shortly after an injury, and within 24 hours in the study mentioned here. The nanoparticles were at work taming inflammation in the joint. The  particles remained in cartilage cells in the joints for weeks unlike steroid injections that are quickly removed.

These nanoparticles penetrate deeply into the tissues as they are more than 10 times smaller than a red blood cell. The particles carry a peptide derived from a natural protein- melittin. It has been altered to enable it to bind to a molecule called small interfering RNA (siRNA). The melittin transfers siRNA to the damaged joint, obstructing with inflammation in cells. The  co-investigators Hua Pan, PhD, an assistant professor of medicine, and Samuel Wickline, MD, the James R. Hornsby Family Professor of Biomedical Sciences formulated the peptide-based nanoparticle.

As per Wickline," The nanoparticles are injected directly into the joint, and due to their size, they easily penetrate into the cartilage to enter the injured cells. 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."

To avert the cartilage breakdown after injury, the nanoparticles were injected immediately. Whether such a technique will work years after an injury, when osteoarthritis is initiated and there is severe cartilage loss, still needs to be estimated. But the results point out that the nanoparticles, if given soon after joint injuries occur, could assist in maintaining cartilage viability and hinder the progression to osteoarthritis.

Linda J. Sandell, PhD, the Mildred B. Simon Research Professor of Orthopaedic Surgery and director of Washington University's Center for Musculoskeletal Research said that

"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. 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."