To grow new knee cartilage, look to the nose

Cartilage-making cells in the nose seem to produce a worthy stand-in for the cartilage lost at the tips of bones in damaged knee joints, a study in goats suggests.

Patches of cartilage grown from snippets of nasal tissue worked so well when implanted into the goats that a small group of people with knee injuries have now undergone the treatment with their own nasal cartilage, researchers report August 27 in Science Translational Medicine. While full results aren’t yet available, “the patients are doing extremely well,” says study coauthor Ivan Martin, a bioengineer at the University Hospital Basel in Switzerland.

Replacing the glossy cartilage that coats the ends of bones called hyaline cartilage has been an elusive goal with a long learning curve. The trick is to get cartilage-making cells called chondrocytes to grow replacement patches. Cartilage generated from joint chondrocytes in labs (or just the chondrocytes themselves) have produced mixed results when implanted into injured knees. Similarly inconsistent results have been found with a common surgery called microfracture, in which a surgeon drills tiny holes into the ends of the bones where cartilage has been worn off or lost to injury. Marrow cells that leak out have stem cell–like properties that can form cartilage caps, but the cartilage is inferior to the glassy hyaline cartilage that normally caps the ends of bones (SN: 8/11/12, p. 22).

The nasal passages also contain hyaline cartilage. So Martin and colleagues removed chondrocyte-containing cartilage from goats’ noses, grew it in dishes for four weeks, then used the newly grown patches to repair knee cartilage damage at the ends of the animals’ femurs. Six months later, the nasal-origin patches held up better than others grown from joint chondrocytes.

The nasal chondrocytes formed higher-quality patches than the joint chondrocytes. The scientists noted that a family of genes called Hox, which are important in development, behave differently in the nasal chondrocytes than in the joints. Martin says the research team plans further tests to determine whether this unusual Hox profile has a direct role in the performance of the nasal chondrocytes.

Triggering tissue growth can be useful, but too much cell growth would be a concern. In the goats, Martin says, the injury defects were “sufficiently filled but never overfilled” by the cartilage patches, with no signs of aberrant growth.

Ming Pei, a cell biologist who studies cartilage regrowth at West Virginia University in Morgantown, calls the series of tests described in the study impressive.  It’s key that the nasal chondrocytes could grow well and produce cartilage, he says. “These nasal chondrocytes look like stem cells,” Pei says. “They’re a promising source for cartilage regeneration.”

The patches also seem to bind well to existing cartilage tissue at the edge of the injury sites being patched, Martin says. Magnetic resonance images of the human patients show no clear difference between the new and old cartilage, suggesting that hyaline cartilage derived from different parts of the body can integrate, he says.

The researchers will soon treat their tenth patient and assess the group’s knee health in a year. The researchers also plan to investigate the technique in animals with injuries that have degenerated into inflammatory osteoarthritis in the joint, he says, a model for millions of people headed for artificial knees.