GPLD1 and Alzheimer disease: Additionally, the liver generates a large number of factors such as glycosylphosphatidylinositol (GPI)-specific phospholipase D1 (Gpld1) and S-adenosylmethionine (SAM) that are important for metabolism and neuroinflammation and can cross BBB affecting brain function in transgenic murine AD models, revealing a liver–brain axis [22, 29–31].