Oral Administration of Ethanolamine Glycerophospholipid Containing a High Level of Plasmalogen Improves Memory Impairment in Amyloid β-Infused Rats

Ethanolamine plasmalogen (PlsEtn), a major phospholipid in neuronal membranes [60–90 mol% of ethanolamine glycerophospholipid (EtnGpl)], is specifically decreased in brains from patients with Alzheimer’s disease (AD). The present study investigated how PlsEtn administration affects cognitive deficits and lipid composition in an animal model of AD. AD model rats were infused with amyloid-β (Aβ) into the cerebral ventricle and divided into three groups. Control, Egg, and Ascidian groups were then orally administered vehicle, egg yolk EtnGpl (260 μmol as EtnGpl/kg BW/day; 10 μmol as PlsEtn/kg BW/day), or ascidian viscera EtnGpl (260 μmol as EtnGpl/kg BW/day; 209 μmol as PlsEtn/kg BW/day), respectively. After 4 weeks of dosing, Aβ-infused rats were tested for learning ability in an 8-arm radial maze. The administration of ascidian viscera EtnGpl improved both reference and working memory-related learning abilities. In lipid analysis, the Ascidian group showed higher levels of PlsEtn species in the plasma, erythrocytes, and liver when compared to other groups. In addition, although there were no differences at levels of total plasmalogen including choline plasmalogen, the Ascidian group had significantly higher levels of 18:0ol/22:6-PlsEtn in the cerebral cortex. These levels of 18:0ol/22:6-PlsEtn in the cerebral cortex were correlated with working memory-related learning ability. Moreover, 18:0ol/22:6-PlsEtn levels in the cerebral cortex showed positive correlations with those in the erythrocytes and liver. In summary, dietary PlsEtn, especially that with 22:6n-3 (docosahexaenoic acid, DHA), may ameliorate learning deficiencies in AD by altering lipid composition in the brain.