By Pat Anson, Editor

An experimental animal study suggest that sildenafil, an erectile dysfunction drug commonly known by the brand name Viagra, may be effective in relieving symptoms of peripheral neuropathy in men with long-term diabetes. The study is published online in PLOS ONE.

Diabetic peripheral neuropathy causes nerves to send out abnormal signals. Patients feel pain, tingling or burning sensation in their toes, feet, legs, hands or arms. Nearly 26 million people in the U.S. have diabetes and about half have some form of neuropathy, according to the American Diabetes Association. 

In previous animal studies, researchers at Henry Ford Hospital in Detroit found that sildenafil improved blood supply to the sciatic nerve and relieved symptoms of neuropathy. However, it was not known if this therapeutic effect held true for long-term peripheral neuropathy, because the diabetic mice used in the previous experiments were relatively young - 16 weeks old.

"Generally, young diabetic animals with an early stage of peripheral neuropathy are used to investigate various drug treatments," said Lei Wang, MD, the Henry Ford neuroscientist who led the research. "But patients with diabetes who are enrolled in clinical trials often are older and have advanced peripheral neuropathy.

To mimic clinical trials in which diabetes patients have advanced peripheral neuropathy, Wang and his colleagues chose male mice with type II diabetes that were 36 weeks old, roughly equivalent to middle age in humans.

In one group, 15 diabetic mice were treated with an oral dose of sildenafil/Viagra every day for eight weeks. A control group of 15 age-matched diabetic mice were treated daily with the same amount of saline.

Researchers found after a battery of nerve and function tests on both groups of mice that sildenafil markedly improved sensory function after six weeks of treatment.

“Treatment of diabetic mice at age 36 weeks with sildenafil significantly increased functional blood vessels and regional blood flow in the sciatic nerve,” said Wang. “Functional analysis showed that the sildenafil treatment considerably improved motor and sensory conduction velocities in the sciatic nerve and peripheral thermal stimulus sensitivity compared with the saline treatment.

“These findings provide new insights into mechanisms underlying the neurological dysfunction of long term diabetic peripheral neuropathy and may lead to the development of a sildenafil therapy for long term diabetic peripheral neuropathy.”

Since becoming available in 1998, Viagra has been found to relieve several other conditions beside erectile dysfunction, such as jet lag and altitude sickness. Some professional athletes also believe that Viagra enhances their performance by opening their blood vessels and increasing oxygen supply to their muscles.