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Secret ingredient. Adding adult stem cells (inset) to penis grafts improves healing and sexual function in rats.

Jean-Etienne Minh-Duy Poirrier; L. Ma et al., PNAS Early Edition (2012) (inset)

Stem Cells Build a Better Rat Penis

Men in need of penis reconstruction could soon enjoy the benefits of a special ingredient: stem cells. A new study in rats shows that lacing a penis graft with adult stem cells yields better healing and sexual function than using the graft alone. The finding may point the way to improved treatments for a variety of human penile impairments.

Men with penis injuries, deformities, or severe Peyronie's disease—which causes excessive scarring that can curve or shrink the penis—sometimes need surgery to reconstruct their genitalia and restore their sexual function. Many receive a graft made of their own tissue, cadaver tissue, or pig intestines, but the surgery can cause complications, including erectile dysfunction.

Wayne Hellstrom, a urologic surgeon at Tulane University School of Medicine in New Orleans, Louisiana, who regularly treats men with Peyronie's disease and other penile problems, wanted to offer his patients a surgical intervention with fewer side effects. So he teamed up with colleagues in California and China to build a better penis graft.

The team seeded pig intestine grafts with adult stem cells taken from fat tissue in rats. Because rats don't develop Peyronie's disease, the researchers had to induce scarring by making incisions in the rodent penises. They then operated on the scarred rats, removing part of the scar tissue and supplanting it with a graft, as is done in patients with severe Peyronie's disease. Eight rats received the stem cell-laced grafts; another eight got the grafts sans stem cells. A third group had a "sham" surgery that didn't involve a graft, and a control group didn't undergo surgery at all.

Eight weeks later, when the rats had recovered from surgery, the researchers examined the rodents' penises. They found that rats with stem cell-laden grafts had less scarring and better erectile responses, as measured by the animals' reactions to electric stimulation, than did those with stem cell-free grafts. The rodents' erections were comparable in rigidity, blood flow, and response time to those in the "sham" and control rats. Cells from the penises with stem cell-laced grafts contained more neuronal and endothelial NOS, enzymes that help trigger and maintain erections. They also had more VEGF, a growth factor whose functions include stimulating new blood vessel development.

The results, published online today in the Proceedings of the National Academy of Sciences, suggest that lacing the grafts with stem cells enhances blood flow and boosts the production of molecules that make and maintain erections, all of which makes for a better penis reconstruction.

"We were really excited and surprised that stem cells can create this much improvement," says Tulane urologist Asim Abdel-Mageed, a co-author of the study.

"This is an excellent study, with lots of clinical implications," says Trinity Bivalacqua, a urologist at the Johns Hopkins Medical Institutions in Baltimore, Maryland. But he notes that the method applies only to reconstructions, not to cases where a surgeon may need to build a new penis from scratch. And although the technique works well in rats, "this doesn't always translate to humans," Bivalacqua says.

Hellstrom and colleagues plan to test the method in primates next and then eventually in people. "Peyronie's affects 3% to 9% of adult males and causes a lot of psychological distress," Hellstrom says. "If we can improve what we have now, it seems like the logical thing to do."