20 July 2006
Antioxidants Key To Beating Vision Loss
Vitamin E, alpha-lipoic acid and other antioxidant chemicals have been used to successfully stop the advance of retinal degeneration in mice with a form of retinitis pigmentosa (RP). "Much more work needs to be done to determine if what we did in mice will work in humans," said Johns Hopkins researcher Peter Campochiaro. "But these findings have helped to solve a mystery."
The eye contains two sorts of light-sensitive receptors - rods and cones. Cones are needed to see colors and make vision possible in bright light, whereas the far more numerous rods permit sight in low light. Campochiaro explained that in patients with RP, rod photoreceptors in the eye die from a mutation, but it has not been known why cone photoreceptors die. After rods die, the level of oxygen in the retina goes up, and this study shows that it is the high oxygen that gradually kills the cones. Oxygen damage is also called "oxidative damage" and can be reduced by antioxidants. The study, appearing in the Proceedings of the National Academy of Sciences, is the first to identify a treatment target in patients with RP.
The Hopkins scientists had previously established that high levels of oxygen in the retina killed both rods and cones. "This was the clue that the high oxygen levels that occur naturally in the retina after rods die was the suspect regarding cone cell death. To test this, we used antioxidants, which protect cells from oxygen damage, and since they allowed many more cones to survive, it proves that the suspect is guilty," said Campochiaro.
Campochiaro and his team used vitamin E, vitamin C and alpha-lipoic acid (an antioxidant similar to superoxide dismutase) in their experiments. In the mice that received vitamin E or alpha-lipoic acid, 40 percent of the cones survived, about twice as many as in the control group or the groups treated with the other antioxidants, which had no identifiable effect. "What's clear is the link between oxygen and photoreceptor damage, as well as the potential of antioxidant treatment," Campochiaro said. "These experiments suggest that an optimized regimen of antioxidants may help to protect patients with retinitis pigmentosa."
Source: The Johns Hopkins University School of Medicine