Age- and brain region-specific effects of dietary vitamin K on myelin sulfatides.

Dysregulation of myelin sulfatides is a risk factor for cognitive decline with age. Vitamin K is present in high concentrations in the brain and has been implicated in the regulation of sulfatide metabolism. Our objective was to investigate the age-related interrelation between dietary vitamin K and sulfatides in myelin fractions isolated from the brain regions of Fischer 344 male rats fed one of two dietary forms of vitamin K: phylloquinone or its hydrogenated form, 2',3'-dihydrophylloquinone (dK), for 28 days. Both dietary forms of vitamin K were converted to menaquinone-4 (MK-4) in the brain. The efficiency of dietary dK conversion to MK-4 compared to dietary phylloquinone was lower in the striatum and cortex, and was similar to that in the hippocampus. There were significant positive correlations between sulfatides and MK-4 in the hippocampus (phylloquinone-supplemented diet, 12 and 24 months; dK-supplemented diet, 12 months) and cortex (phylloquinone-supplemented diet, 12 and 24 months). No significant correlations were observed in the striatum. Furthermore, sulfatides in the hippocampus were significantly positively correlated with MK-4 in serum. This is the first attempt to establish and characterize a novel animal model that exploits the inability of dietary dK to convert to brain MK-4 to study the dietary effects of vitamin K on brain sulfatide in brain regions controlling motor and cognitive functions. Our findings suggest that this animal model may be useful for investigation of the effect of the dietary vitamin K on sulfatide metabolism, myelin structure and behavior functions.

Cognitive impairment in folate-deficient rats corresponds to depleted brain phosphatidylcholine and is prevented by dietary methionine without lowering plasma homocysteine.

Poor folate status is associated with cognitive decline and dementia in older adults. Although impaired brain methylation activity and homocysteine toxicity are widely thought to account for this association, how folate deficiency impairs cognition is uncertain. To better define the role of folate deficiency in cognitive dysfunction, we fed rats folate-deficient diets (0 mg FA/kg diet) with or without supplemental L-methionine for 10 wk, followed by cognitive testing and tissue collection for hematological and biochemical analysis. Folate deficiency with normal methionine impaired spatial memory and learning; however, this impairment was prevented when the folate-deficient diet was supplemented with methionine. Under conditions of folate deficiency, brain membrane content of the methylated phospholipid phosphatidylcholine was significantly depleted, which was reversed with supplemental methionine. In contrast, neither elevated plasma homocysteine nor brain S-adenosylmethionine and S-adenosylhomocysteine concentrations predicted cognitive impairment and its prevention by methionine. The correspondence of cognitive outcomes to changes in brain membrane phosphatidylcholine content suggests that altered phosphatidylcholine and possibly choline metabolism might contribute to the manifestation of folate deficiency-related cognitive dysfunction.