University of Michigan researchers say they have built a better rat model for repairing and, perhaps even replacing, damaged human hearts.

The team is growing muscle patches and structures that eventually might be able to do the trick. Patient use is still years away, but the advance achieved in experiments using rats' heart muscle cells is considered a major step in the right direction, the investigators reported in the online edition of the Journal of Biomedical Materials Research Part A.

Their so-called rapid 3-D cell-growth technique produces pulsing, organized tissue in the lab that contracts and reacts almost identically to a nature-made heart muscle. The ultimate goal is to be able to turn a cluster of cardiac cells into replacement parts for a heart in need of a fix -- or even to create a brand-new blood-pumping muscle.

The crew was able to refine and rush the process of growing three-dimensional bioengineered heart muscle by using a novel fibrin gel to support the rat cells before the fibrin splits up as cells collate into tissue.

"Many different approaches to growing heart muscle tissue from cells are being tried around the world, and we're pursuing several avenues in our laboratory," said team leader Ravi Birla of the Artificial Heart Laboratory in the cardiac surgery section and cardiovascular center.

"But from these results we can say that utilizing a fibrin hydrogel yields a product that is ready within a few days, that spontaneously organizes and begins to contract with a significant and measurable force and that responds appropriately to external factors such as calcium."

In contrast to other scientists, who tend to explore one approach at a time, the UM investigators said they can test multiple techniques simultaneously.

"Fundamentally, we're interested in creating models of the different components of the heart one by one," Birla said. "It's like building a house: you need to build the separate pieces first, and, once we understand how these models can be built in the lab, then we can work toward building a bioengineered heart."

Working out can work away some of the hazardous consequences of smoking -- but not nearly to the degree that can be achieved by kicking the health-harming habit altogether, researchers report in Cancer Epidemiology Biomarkers and Prevention.

Their study of more than 36,000 women showed high levels of physical activity could turn down smokers' relative risk of developing lung cancer by as much as 28 percent, while moderate exercise could cut it by up to 35 percent.

"The most important thing a smoker can do to reduce risk is to quit smoking," stressed lead study author Kathryn Schmitz, assistant professor at the University of Pennsylvania.

"That said, exercising and being active can offer a marginal change in risk," she added. "Smokers who exercise are at a 35 percent lower risk of developing lung cancer relative to smokers who don't exercise, but if you smoke at all, your risk of developing lung cancer is 10- to 11- fold higher than if you didn't smoke."

While they are uncertain as to the exact reason for the life-saving difference exercise can make, scientists speculated it might have something to do with better pulmonary function, which might reduce the concentration in the airway and deposit in the lungs of the cancer-causing particles given off during smoking. In addition, being active may boost the disease-fighting immune system and buckle down the cancer-promoting inflammatory responses, researchers conjectured.

Another study of smokers, led by scientists at Washington University School of Medicine and published in Cancer Epidemiology Biomarkers and Prevention, bespeaks the difficulty these addicts have in breaking the hazardous habit.

Of 154 smokers who had gone under the knife to remove early-stage lung cancer, nearly half fell off the cigarette-free wagon within 12 months and more than one-third had relapsed a year after their surgery. Of the latter, 60 percent had abstained from tobacco for no more than two months post-operatively.

"These patients are all addicted, so you cannot assume they will easily change their behavior simply because they have dodged this particular bullet," said lead study author Mark Walker, clinical psychologist and assistant professor of medicine. "Their choices are driven by insidious cravings for nicotine."

Those who smoked until the last minute -- as late as the very day of their operation -- and who equated smoking with pleasure were the first to take a post-op puff, the researchers found.

"The results suggest that patients who wait until cancer surgery to quit smoking need assistance from the medical community to help them stay away from cigarettes, and that this intervention should begin as soon as possible after treatment," Walker said, noting no such programs currently are offered to patients undergoing lung-cancer surgery.

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