Latest researchers were able to restore sexual function to rabbits with damaged penises by growing new penile tissue in the lab and implanting it, a new study reports.
Though a human application is a ways off, researchers say the technique could one day be used to treat severe erectile dysfunction in men.
"We were able to show the tissue was able to integrate and function in the long term, which means we can start planning clinical applications [in humans]," said Dr. Anthony Atala, director of the Institute for Regenerative Medicine at Wake Forest University Baptist Medical Center and senior author of the study. "Our hope is to be able to treat patients with many conditions, including congenital abnormalities of the penis, traumatic injuries, penile cancer and severe cases of erectile dysfunction that don't benefit from drug treatments."The study is published in the Nov. 9 online edition of the Proceedings of the National Academy of Sciences.
The penis is a complex organ, with nerve, muscle and vascular cells all needing to work together to achieve and maintain an erection. During an erection, smooth muscle tissue relaxes, allowing blood to flow into the penis. Endothelial cells, which line blood vessels, trigger the process by releasing nitric oxide.
In the study, the researchers extracted smooth muscle cells and endothelial cells from the animals' penises. The cells were then separated and grown in the laboratory on rod-shaped collagen scaffolds for support. The scaffold was placed in an incubator and nourished by fluids to mimic conditions inside the body, Atala said. After the cells had matured, the scaffolding and the newly formed penile spongy tissue, called corpora cavernosa, was surgically implanted into the rabbits' penises. About a month later, the tissue began to reconstitute itself, forming new blood vessel structures necessary for proper functioning, while nerves from the existing penile tissue integrated into the new tissue. In time, Atala said, the collagen structure was reabsorbed, and the cells built their own collagen structure.
In the treated rabbits, tests showed that pressure inside the penis, a key component of an erection, was normal. Other tests showed that blood flow, response to nitric oxide, drainage of the blood after the erection and presence of sperm in the female vagina were also normal. The tissue engineering worked so well that four of 12 females were impregnated by the repaired rabbits, according to the study.
Dr. Andrew McCullough, director of male sexual health, fertility and microsurgery at NYU Langone Medical Center, said the results are promising.
"It has a long way to go, but the researchers have basically shown they can take cells from an organ, culture them, put them back in and have them be functional," McCullough said. "This is especially impressive because the penis is an organ that's a very sensitive hydraulic pump, so to speak. During an erection, blood has to flow into the organ. The organ then has to expand and then shut down the drainage so the blood doesn't flow back out. And all of these things are very 
interrelated."
Better treatments for erectile dysfunction are badly needed, McCullough added. About 35 percent of men don't respond to impotence drugs, including Viagra, Cialis and Levitra. As men age, diabetes, high cholesterol and hypertension -- all conditions that can affect male sexual function -- can worsen, making the drugs less effective.
In previous research, the Wake Forest researchers engineered human bladders in the lab. In clinical trials, about 30 children and adults with congenital bladder abnormalities or bladder injuries who were treated with the engineered tissue showed normal or improved bladder function for nearly 10 years, Atala said. Other researchers have shown some success in clinical trials with transplanting windpipe tissue.
