APOE (apolipoprotein E) is a plasma protein implicated in lipid metabolism. It is produced predominantly by hepatocytes, macrophages, and neural cells. In the CNS, APOE is the major
extracellular lipid carrier and plays a key role in neuronal protection/repair after injury. APOE is polymorphic, with three major alleles: APOE2 (cys112, cys158), APOE3 (cys112, arg158), and APOE4 (arg112, arg158). APOE2 plays a protective role against both Alzheimer's (AD) and heart disease. APOE4 confers a higher risk for atherosclerosis and Alzheimer's disease. Analysis of cerebrospinal fluid (CSF) and plasma APOE protein levels in AD patients had been performed to examine its association with AD pathology. In old age, high plasma APOE levels precede an increase of circulating CRP and strongly associates with cardiovascular mortality.