Scientists Study Smokers' Bones

Can Quitting For A Short Time Lead To Faster Bone Healing?

(AP) 
While the link between smoking and bone harm is clear, no one knows why it occurs, says Dr. Thomas Einhorn, chairman of orthopedic surgery at Boston University. Nicotine may not play the only role; there are lots of toxins in cigarette smoke.

But the Rochester team's theory is plausible, he says. And it's crucial to pursue because if they're right, using nicotine patches or gum immediately after a bone injury would likely be as bad as continuing to smoke.

Stem cells are building blocks for tissue, and the first step toward bone healing is for mesenchymal stem cells to transform into cartilage-forming cells. They build a scaffolding over the fracture, which gradually fills in and hardens into bone. It takes about three months. Stress a healing fracture before then and the still soft cartilage can break again easily, causing lasting pain.

Put nicotine onto those stem cells and they go into overdrive, making an enormous amount of cartilage, Zuscik discovered in tests with mice.

"Too much of a good thing is a bad thing," he explains. "What you end up with, we hypothesize, is a situation where the healing process ends up taking longer."

Nicotine seems to do that by parking in receptors on the stem cells' surface that are intended for acetylcholine, a chemical that helps nerve cells communicate. If the stem cells turn into nerve cells, they'll need those receptors. If they turn into cartilage-forming chondrocytes, the receptors quickly disappear.

Zuscik's preliminary data suggests they're gone in a week.

So the nicotine has only a short time to jump into those cellular docking sites. Hence Zuscik's theory that this is a window during which smokers should heal more like nonsmokers if only they could abstain.

It will take a few years of additional animal research before that theory can be tested in smokers, he says, although there's no down side to people trying to kick the habit in hopes it will help heal their bones.

Indeed, there's some indirect evidence that quitting helps: In 2000, Kentucky researchers reviewed the medical records of 357 spinal fusion patients. About three-quarters of both nonsmokers and those who kicked the habit while healing recovered well enough to return to work, compared with just half of the smokers.