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Erectile dysfunction is a disorder that affects over 150 million males worldwide.

Penile erection is a complicated process, involving multiple stages from sexual stimulation to a cascade of chemical messengers, which eventually result in vascular relaxation and erection. One current therapy, sildenafil (Viagra), involves inhibiting an enzyme that degrades cGMP (cyclic guanosine monophosphate), a second messenger produced in the cascade.  This then allows the erection to be maintained for a longer time.

However, sildenafil cannot stimulate or produce an erection by itself, a problem for those who have neurological dysfunctions, such as those suffering from ED after a radical prostatectomy–Researchers at ETH Zurich have created a potential new therapy that can initiate and maintain an erection in male rats. Tongue-in-cheekly named EROS (erectile optogenetic stimulator, or, you know, the Greek god of love), the intervention enables erection simply by shining blue light onto the penis. The drug, a naked vector of DNA, consists of a blue light sensor domain BLUF (blue-light-using FAD) that activates the adjacent catalytic guanylate cyclase domain. When activated, the EROS system converts GTP into cGMP, which then reduces intracellular calcium and causes vascular relaxation and erection.

The scientists injected the vector into the corpus cavernosum (erectile tissue) in rats, and exposed them to blue light.  The rats then developed different levels of erections in under a minute, with some rats even reaching ejaculation. When combined with sildenafil, the rats displayed increased blue-light induced EROS-triggered vascular relaxation.

While this proof of concept shows promising results, gene therapy is still a hot area of research, with many studies to be conducted on its long-term and systemic effects. The authors argue that the penis, with reduced blood flow during the flaccid state, is a prime target for the administration of such gene therapy, as it limits the distribution into the systemic circulation.


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