A protein found in blood cells could be the key to treating or preventing two of the commonest causes of blindness, scientists in the United States believe.

In mice that simulate the processes of age-related macular degeneration (AMD) and diabetic retinopathy, damage was prevented by drugs that activate a protein called Robo4, they report in Nature Medicine.

The protein stopped the growth of abnormal blood vessels and stabilised existing ones, according to Professor Dean Li and colleagues from the University of Utah in Salt Lake City.

Abnormal blood vessel growth and leakage are two primary factors in AMD and diabetic retinopathy.

“Many diseases are caused by injury or inflammation destabilising blood vessels and causing them to leak fluid into adjacent tissues” Professor Li said.

“We found a natural pathway – the Robo4 pathway – that counter-attacks by stabilising blood vessels.”

New treatments are needed for both conditions. AMD is the commonest cause of loss of sight in the elderly and diabetic retinopathy is the commonest cause in people of working age.

Treatments for one form of AMD do exist, but the best drugs are extremely expensive and at best slow down the disease. Many patients with AMD have been denied treatment with Lucentis on the NHS, at least until they have lost the sight of one eye.

The implications of the finding may go even farther because there are other diseases, such as severe acute respiratory syndrome, in which blood vessel stability is lost, allowing fluids to leak into the lungs.

Tumours hijack blood vessel growth to feed on nutrients. Although this study did not prove Robo4 would treat those diseases, Professor Li believes it merits investigation.

Scientists from the University of Bristol said last week that they were ready to launch clinical trials of a drug to treat AMD and diabetic retinopathy. Professor Dave Bates and Dr Steve Harper have identified a naturally occurring form of vascular endothelial growth factor (VEGF) that inhibits the formation of new blood vessels. Professor Bates said: “We discovered the potential of VEGF165b in 2001 and have spent the last six years proving its efficacy. We plan to demonstrate clinical proof of concept of the drug in diabetic retinopathy and wet AMD patients by mid2009 so this is a very exciting time for us.”

The drug technology, which has been developed with the help of the charity Fight for Sight, is being licensed to a biopharmaceutical company, PhiloGene Inc.

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