A drug already approved to heal bone loss from osteoporosis may also help to prevent and reverse the damage to cartilage that leads to osteoarthritis.

In early animal tests, the drug teriparatide (Forteo), appears to be the first agent not merely to stop cartilage loss, but to reverse it.

Currently, there are no drugs to treat cartilage loss in osteoarthritis, a condition that’s expected to affect some 50 million Americans by 2020. Patients can only take steroids and anti-inflammatories to reduce the pain.

Osteoarthritis is caused when cartilage – the spongy, shock absorbing tissue that cushions joints – deteriorates, causing joint inflammation and pain.

Parathyroid hormone, which is sold as the prescription drug teriparatide (Forteo), is FDA approved to maintain and heal bone, and earlier studies have suggested that it also affects cartilage cells.

In a study presented in 2009 at the annual meeting of the American Society for Bone and Mineral Research in Denver, scientists say that, in mice, teriparatide prevents cartilage loss from osteoarthritis following a joint injury and regenerates cartilage.

Researchers at the University of Rochester Medical Center in New York gave teriparatide to random groups of mice with cartilage and ligament injuries for 12 weeks.

Another group of mice with joint injuries was given the treatment eight weeks after injury. Doctors say this was intended to mimic the typical conditions of human injuries, since a lot of time often passes after an old injury before patients seek treatment. 

Researchers report that the group given 12 weeks of teriparatide treatment, had approximately 27 percent more joint cartilage compared to the control group. And in the group that received delayed teriparatide treatment, the amount of cartilage was even greater – 35 percent higher than the group receiving saline. Doctors say that indicates the medicine is actually helping to regenerate lost cartilage.

“We’re pretty excited about it,” says Randy Rosier, MD, PhD, a professor in the Department of Orthopaedics and Rehabilitation at the University of Rochester Medical Center in Rochester, NY.

“We have a lot more work to do to nail this down. But there have been no drugs that systemically can improve cartilage or increase the amount of cartilage after some is lost. If we can confirm that’s true, it would be the first time that may have been found and that could have a usefulness to a huge number of patients.”

Though the study was in mice, researchers say the model is very similar to the human osteoarthritis that develops after knee injuries. But they caution, it is still very early in the scientific process.

“We don’t think this is necessarily a cure for arthritis, but it is an existing drug that could provide a novel therapy to ameliorate the disease. Or maybe you could treat someone who developed early arthritis and reverse it. We don’t know the answers to a lot of those questions yet,” Dr. Rosier says.

Brian Cole, MD, a professor in the Department of Orthopaedics at Rush University Medical Center in Chicago and section head of the Cartilage Restoration Center at Rush agrees.

“Forteo is an injectable drug, but it’s still better than surgery. It suggests that there may be a non-surgical option to manage arthritis or cartilage loss. That’s why it’s significant,” Dr. Cole says. “But it’s a mouse. So it’s certainly a good place to start, with an animal model, and obviously they probably recognize they have a lot of research ahead of them. But it’s significant if it’s a non surgical option.”

Researchers don’t know the proper dosage yet, so they will conduct more animal studies to determine that. They also say the drug is expensive, so they will seek funding from the National Institutes of Health for a clinical trial on humans – perhaps as soon as late 2010. They say the drug has been used for about a decade to heal bone, with minimal side effects.

“We’re cautiously optimistic that it may be one more bullet in the fight against osteoarthritis,” Dr. Rosier says.