In the study, adult male rabbits with severely damaged penises received a graft of specially engineered penile tissue. The animals then re-grew full penises that functioned normally — even to the point of successfully impregnating females.
"This is very exciting — the researchers have been working on this for a long time in a variety of different organs. It’s not yet clinically available, but if it works and proves safe and effective, it would be a tremendous advance," said Dr. Ira Sharlip, a spokesman for the American Urological Association and a clinical professor of urology at the University of California, San Francisco.
Sharlip was not involved in the study, which was led by Dr. Anthony Atala, director of the Institute for Regenerative Medicine at Wake Forest University in Winston-Salem, N.C. His team reported its findings Tuesday at the American Urological Association annual meeting, in Atlanta.
Drugs like Cialis, Levitra and Viagra have revolutionized the treatment of impotence for millions of men over the past decade. However, some forms of erectile dysfunction remain very difficult to treat.
A condition called "corporal fibrosis" — where the tubes of penile "spongy tissue" that maintain erection are gradually replaced by inactive, fibrous scar tissue — remains largely untreatable. The disorder occurs when the penis’ sensitive spongy-tissue cells don’t get the oxygen they need to survive, usually because of a chronic reduction in blood flow.
"It’s relatively common in men with diabetes and various forms of vascular disease, or men who’ve previously had infections — usually infections of a penile prosthesis," Sharlip said. "There are men who have such severe fibrosis that nothing can be done to restore their natural erection function, other than to implant a surgical prosthesis," he added.
However, advances in biotechnology have spurred research into replacing dead tissues with new, living tissues grown in a laboratory using the patient’s own cells. According to Sharlip, Atala has long been a pioneer in this field, working not just with penile tissues but with tissues from other organs.
In their latest study, the Wake Forest researchers first used standard biopsy techniques to harvest smooth-muscle and blood-vessel cells from the penises of healthy adult male rabbits. In the lab, the researchers used these cells to "seed" a special nutrient-rich collagen matrix. Over time, the cells multiplied within this framework to grow into new penile tissue.
Next, the team surgically removed all of the natural spongy tissue from the penises of the donor rabbits. They then grafted in the engineered tissue.
Atala’s group tracked the rabbits’ penile growth and function over the next one, three and six months.
The researchers found that the new penises were similar in structure to natural rabbit penises. The "artificial penis" also achieved and maintained erectile pressures equal to those of normal rabbit penises.
Next came the real test, as the rabbits that had received the new penises were presented with sexually mature females.
Things proceeded just as nature intended, the researchers said.
"Mating activity in the animals with the engineered [penis] resumed by 1 month after implantation," they reported. "Presence of sperm was confirmed in the vaginal vault of the female partners, and all females conceived and delivered healthy pups."
Sharlip cautioned this is a preliminary study involving animals. But he said that "rabbit tissue is fairly similar to human tissue. If it can be done in rabbits, it probably can be done in humans."
Doctors who treated men with corporal fibrosis in this way would still face another hurdle, however: Treating the underlying cause of the fibrosis itself.
"There’s the question of how you restore that needed blood supply," Sharlip said. "You may be able to restore the natural spongy tissue of these erection chambers, but in a patient with severe corporal fibrosis you also have to get the blood supply to come back into the new, restored tissue." Without that steady source of oxygen, any implant might meet the same fate as the tissue it had replaced, he said.
Still, the advance does mark one of the few breakthroughs against the disorder in years, Sharlip said. And he added that success in tissue engineering has implications "not only for the treatment of erectile dysfunction but in the world of medicine in general."
"If we could re-grow and replace worn-out tissue [in other body parts], that would have tremendous implications," Sharlip said.