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4-Oct-2008 : A Chinese herbal remedy known as "horny goat weed" may indeed live up to its name as a natural version of Viagra.

Italian researchers report that laboratory studies show that the compound has the potential to treat erectile dysfunction, and possibly with fewer side effects than its pharmaceutical cousin.


"No in-vivo studies in an animal model have been performed at this regard, so a lot of work must be done. We would like to test in vivo [with animals] the molecule to understand if it really works in humans," said study lead author Mario Dell'Agli, of the University of Milan's laboratory of pharmacognosy. "At this stage of the research, we cannot say if the molecule we have synthesized possesses less side effects with respect to Viagra. However, this derivative seems to be in vitro [in lab tests] more selective than Viagra, because it targets [an enzyme involved in blood flow to the penis] more precisely."


The study was expected to be published in the Oct. 24 issue of the Journal of Natural Products, a publication of the American Chemical Society.


Viagra (sildenafil) is one of several prescription medications available and widely prescribed for erectile dysfunction, a condition that affects an estimated 18 million men in the United States. Viagra and other drugs like it can cause side effects such as headache, stomach problems and visual disturbances.


Horny goat weed, hailing primarily from southern China, has a long history as an aphrodisiac.


As part of a new screening program to find natural alternatives to Viagra, the study authors analyzed a number of herbal extracts long used for male impotence, including Ferula hermonis or Lebanese Viagra; Cinnamomum cassia or Chinese cinnamon; as well as Epimedium brevicornum aka horny goat weed. All three extracts are reputed to improve sexual performance.


The main active component of each extract was tested against an enzyme known as phosphodiesterase-5A1 (PDE5A1), which regulates blood supply to the penis. Inhibition of this enzyme results in more blood flow to the penis, resulting in an erection.


Icariin, the active ingredient of horny goat weed, inhibited PDE5A1 to a greater degree than the other compounds tested.


"The novelty of this work is the new molecule we have synthesized by icariin," Dell'Agli said. "It is derived by chemical modifications of the structure of icariin, which is the active ingredient purified from E. brevicornum (horny goat weed). The mechanism by which the molecule we have found might work in humans is the inhibition of phosphodiesterase 5 (PDE 5) in the corpus cavernosum [erectile tissue in the penis], which is the mechanism by which Viagra works. This is an in vitro study. It can be considered a pre-clinical study."