The health benefits of carotenoids antioxidants found in brightly colored fruits and vegetables are widely known: they can stem the progression of eye diseases like age-related macular degeneration and even protect against certain cancers.
But exactly how one particular kind of carotenoid that humans don't usually eat winds up in the part of the eye responsible for sharp, central vision has been a mystery until now. Researchers at the John A. Moran Eye Center at the University of Utah have tracked down how meso-zeaxanthin whose only known dietary sources are shrimp shells, turtle fat, and fish skin is made in the human eye.
In a paper published in Proceedings of the National Academy of Sciences (PNAS), Moran's Paul S. Bernstein, MD, PhD, reveals that the protein RPE65, already known to be a key enzyme for vitamin A metabolism in the human eye, is also responsible for converting lutein, a common carotenoid consumed in fruits and vegetables, into meso-zeaxanthin.
"This new research solves a unique phenomenon in nature," said Bernstein, "and it's a significant development that adds to our knowledge of how the eye works. Since the retina has high concentrations of meso-zeaxanthin in the macula, we believe it's there to protect vision. Further studies can show us its exact role."
Funded by the National Eye Institute, a Ruth L. Kirschstein National Institutes of Health training grant, and Research to Prevent Blindness, the research also represents another significant discovery related to RPE65 for Bernstein. He developed the first assays for RPE65's vitamin A enzymatic activity as part of his PhD thesis work also reported in PNAS 30 years ago.