Photo by Jeff Gray
Retinitis pigmentosa is a group of degenerative eye diseases caused by genetic mutations that lead to severe vision loss and blindness. Worldwide, more than one person in 4,000 is affected. Current experimental gene therapy involves injecting healthy copies of the culprit gene into patients' eyes. Although early clinical trials are promising, this approach is expensive and challenging, with more than 45 genetic mutations identified.
Recently, NEI-funded researchers found that curcumin, the active ingredient in the spice turmeric, may successfully treat some forms of retinitis pigmentosa. A study led by Dr. Radha Ayyagari, associate professor of ophthalmology at the University of California, San Diego, showed that curcumin prevented the abnormal and damaging protein build-up usually caused by a mutant gene.
The researchers investigated the P23H gene governing the protein rhodopsin, which eye rod cells need to detect light. With this mutation, the protein accumulates and eventually kills the cells. Previous research showed that curcumin inhibits build-up of the protein amyloid beta, thought to contribute to neuron destruction in Alzheimer’s disease.
Photo by Chris de Bode/WHO
India and China suffer the highest numbers of blindness.
The National Eye Institute supports collaborations,
partnerships and training programs with these countries
and several others in research to prevent blindness.
"Coming from India I have a lot of faith in curcumin," Ayyagari said, explaining the compound has long been used to treat wounds and inflammation.
The team found curcumin prevented mutant P23H rhodopsin from abnormally clustering in laboratory-cultured cells, so they fed the compound to rats genetically engineered to have the mutation. These rats, unlike control animals, showed reduced protein accumulation, which in turn preserved the number of retinal rods and cones and increased the light-induced electrical response in the rats' eyes.
Another benefit of curcumin is that unlike many drugs, it crosses the blood-retinal barrier, a protective meshwork of cells surrounding the retina. The researchers found curcumin had reached the rats' retinas after only two days of feeding. This suggests that patients with retinitis pigmentosa could simply take curcumin pills or include turmeric in their diet, rather than have a drug or a gene surgically injected into their eyes.
Unusual protein clustering may also be linked to eye diseases that affect other cells in the retina. The results reported by Ayyagari and her colleagues suggest that curcumin could treat all of these cases. But further work is needed to back up these preliminary findings and test which curcumin dosages are most effective.
Articles in the Focus on the National Eye Institute at NIH section were produced by Cathy Kristiansen, with contributions from Christopher G. Thomas, Tom Hoglund and Richard S. Fisher.