Coloured X-ray of the knees of an 87-year old male patient with severe osteoarthritis DR P. MARAZZI/SCIENCE PHOTO LIBRARY
Painful arthritic knees could be treated by injections of a lubricating fluid that mimics a natural version found in joints. The fluid allows the damaged joints to repair themselves and has been shown to boost cartilage regeneration in rats.
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Osteoarthritis, a result of wear and tear as people get older, involves damage to cartilage, a rubbery tissue that caps the ends of bones. Scans of arthritic knees can show bits of cartilage inside the joint that have broken off from the main cartilage tissue.
This increases friction inside the joint, leading to a feedback loop that accelerates the damage, says Chuanbin Mao at the University of Oklahoma in Norman.
People can have surgery to remove the debris and smooth remaining cartilage, but this doesn’t work very well. Some experimental approaches involve injecting stem cells, often taken from the person’s blood or fat.
Mao and his team focused instead on synovial fluid, the liquid inside joints. Healthy joint fluid contains a large molecule called a lubrication complex, comprised of a backbone of hyaluronic acid that bears feathery subunits called lubricin, as well as lipid subunits.
The feathery subunits bind to water molecules, while the entire lubrication complex binds to cartilage. This creates a watery layer on top of the cartilage, which reduces friction during joint movement.
Mao and his colleagues created an artificial version of the lubrication complex by binding another feathery molecule called PAMPS and a lipid substitute to the same hyaluronic acid backbone. When applied to pieces of human cartilage, this reduced friction in lab tests.
The researchers also injected the substance into rats with early arthritis in their leg joints. After eight weeks, the rats’ joints looked close to normal when viewed under the microscope, as gauged by a commonly used arthritis-grading scale. The cartilage seemed to have regrown, says Mao. “We found that lubrication can help tissue regeneration – that’s something new.”
Next, the team will try out the artificial fluid on larger animals with joints that are more similar to those of people.
Journal reference: Nature Biomedical Engineering, DOI: 10.1038/s41551-021-00785-y
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