A near-infrared fluorescent probe may make it easier to diagnose and monitor osteoarthritis. Tested in mice, the probe detected the activity leading to cartilage loss in joints. As the osteoarthritis progressed, the probes’ brightness levels increased. This was the first study to demonstrate that NIR fluorescence can be used to detect osteoarthritis changes, according to a research team led by Tufts University School of Medicine. “The fluorescent probe made it easy to see the activities that lead to cartilage breakdown in the initial and moderate stages of osteoarthritis,” said Shadi Esfahani, a postdoctoral fellow at Massachusetts General Hospital and Harvard Medical School. An x-ray image of osteoarthritic knees. Courtesy of the National Institute of Arthritis and Musculoskeletal and Skin Diseases. X-ray imaging tests used today for patients with osteoarthritis don’t indicate the level of pain or visualize amount of cartilage loss, the researchers said. For the two-month study, the researchers created injury-induced osteoarthritis in the right knees of 54 mice. The left knees of the mice served as the control group. The mice received pain medication. The fluorescent probes are activated by matrix metalloproteinases (MMPs), enzymes associated with the beginning stages of osteoarthritis. They were injected into both knees of each mouse. Researchers took images of each knee every two weeks to determine if the fluorescent probes emitted a signal. At each examination, the signals became brighter in the injured right knees throughout the early to moderate stages of osteoarthritis. The probes emitted lower signals in the healthy left knees and did not increase significantly throughout the study. The next step will be to monitor the fluorescent probe over a longer period of time to determine whether the same results are produced during the late stages of osteoarthritis, the researchers said. Professor Dr. Li Zeng said she hopes to use the probes to help develop treatments for animals, as certain breeds of dogs are prone to osteoarthritis. If the technology can be applied to humans, the researcher said, it may allow for earlier treatment, including helping to analyze the effectiveness of osteoarthritis drugs and treatment methods. Osteoarthritis affects 27 million Americans and is most often detected in its late stages, according to the Centers for Disease Control and Prevention. The research was published in Arthritis & Rheumatology (doi: 10.1002/art.38957). For more information, visit www.tufts.edu.