Effects of long-term vitamin K (phylloquinone) intake on retina aging

Emerging evidence suggests neuroprotective functions of vitamin K and/or vitamin K-dependent proteins. We investigated the effect of dietary vitamin K on retina aging (thinning). Female Sprague-Dawley rats were maintained from weaning on low (80 microg kg(-1) diet), adequate (500 microg kg(-1) diet) or high (2000 microg kg(-1) diet) levels of vitamin K1 (phylloquinone). Relative concentrations of brain vitamin K associated with these diets were 1: 3.3: 25 (K1) and 1: 2.7: 9.0 (menaquinone-4). Histomorphometry of old (21 month) rats revealed positive associations between vitamin K and thickness of retina layers, especially in the equatorial/peripheral retina. No association of diet and retina thickness was detected among young (6 month) animals. The sparing effect of vitamin K in the retina was most evident in the inner plexiform layer and in the photoreceptor inner and outer segments. Surprisingly, we observed no effect of vitamin K on the age-dependent loss of photoreceptor cells, interneurons or ganglion cells. These data suggest a role for vitamin K in maintaining the aging retina and suggest that the sparing effect of vitamin K does not reflect the survival-promoting (anti-apoptotic) activities of vitamin K-dependent proteins.