REN and early-onset autosomal dominant Alzheimer disease: The crosstalk between the LPS/TLR4 signal transduction pathway and other metabolic pathways such as primary bile acid biosynthesis and secretion, peroxisome, renin–angiotensin system, glutathione metabolism, arachidonic acid, and Alzheimer’s disease pathways demonstrates that LPS plays a key role in chronic inflammation and carcinogenesis.