Osteoarthritis (OA), often called "wear and tear" arthritis, is the most common form of arthritis in the U.S. Approximately 27 million adults have reported being diagnosed with OA by their physicians.

Nearly 1 in 2 Americans develop symptomatic knee OA by age 85, and a study earlier this year showed that the first symptoms in the knee often occur when climbing the stairs. In fact, patients usually are in pain by the time their physicians diagnose osteoarthritis.

However, a big challenge in properly assessing OA is that radiographic X-rays do not indicate the level of pain or allow physicians to directly see the amount of cartilage loss. A major hurdle in OA research has been the lack of effective detection and monitoring methods, but there is optimism on the horizon.

In a recent study at Tufts University School of Medicine (TUSM), researchers found that a fluorescent probe tracked the development of OA in male mice, brightening as the disease progressed.

The researchers hypothesized that proteases, such as matrix metalloproteinases (MMPs), were up-regulated in the early stages of OA development. The purpose of the study was to investigate whether a near-infrared (NIR) fluorescent probe activated by MMPs could visualize in vivo progression beginning in the early stages of the disease.

The right knees of 54 mice affected by injury-induced OA served as the experimental group. The healthy left knees of the mice served as the control group. Over a two-month period, the researchers took images of each knee every two weeks to determine if the fluorescent probe emitted a signal.

The signal became brighter in the injured right knee through the early to moderate stages of OA at every examined time point. The probe emitted a lower signal in the healthy left knee and did not increase significantly over time.

According to the researchers, the fluorescent probe made it easy to see the activities that lead to cartilage breakdown in the initial and moderate stages of OA, which is necessary for early detection and adequate monitoring of the disease.

Senior author Li Zeng, Ph.D., an associate professor in the Department of Integrative Physiology and Pathobiology at TUSM, reported that the next step is to monitor the fluorescent probe over a longer period of time to determine whether the same results are produced during the late stages of OA.

This study is the first to demonstrate that near-infrared fluorescence can be used to detect OA changes over time. Imaging of the MMP activity in a mouse model provided sensitive and consistent visualization of OA progression, beginning in the early stages of OA, perhaps providing an approach with the possibility of future potential use in humans.