'Viagra principle' harnessed

The chemical reaction which makes Viagra such a successful drug is being harnessed to tackle other illnesses.

Viagra can help men with erectile dysfunction, but one expert in the field, Dr Joseph Beavo, believes that one day soon we will have the equivalent of Viagra for the mind, eyes and lungs.

Certainly, progress on similar drugs to tackle asthma and chronic obstructive pulmonary disease (COPD) has advanced.

Addressing a meeting of the American Association for the Advancement of Science annual meeting in San Francisco, Dr Beavo said there was potential for drugs as effective as Viagra in several areas of disease.

Viagra works by stopping the work of a body chemical called phosphodiesterase which affects only the smooth muscle of the penis.

However, there are many different types of phosphodiesterases (PDEs) in different types of cell around the body.

There are certainly some which in theory affect areas such as insulin production, vision and memory.

Finding a drug which could inhibit the work of these without affecting any of the others is the goal of many teams of scientists around the world.

Dr Beavo said: "The challenge has been for the drug companies to find agents that are selective for specific phosphodiesterases without causing toxic side effects."

So far, Viagra has generated more than $1bn in sales - a successful anti-asthma drug would rival that.

Professor Fan Chung, a professor of respiratory medicine from Imperial College in London, is working on drugs to control two PDEs, which, if successful, would have an impact on the disease.

The first targets and inhibits inflammatory immune cells such as neutrophils, T-cells and macrophages, stopping them from releasing the body chemicals, or cytokines, which cause the airway restrictions characterising an asthma attack.

The other may work on the smooth muscle lining the airways in a similar way to Viagra's effect on smooth muscle elsewhere.

He said: "The problem has been finding a compound which isn't too toxic. But in the last few years we have been getting closer."