TNF and Alzheimer disease: Previous studies have confirmed that disturbance of the intestinal microbiota in AD patients leads to increased permeability of the intestinal epithelial barrier, and some proinflammatory neurotoxins such as lipopolysaccharide (LPS) and TNF-α may reach the CNS through the vagus nerve or systemic circulation, promoting microglial cell activation and neuroinflammation [53].