Glycative Stress and the progression of Alzheimer-type Dementia: From the Perspective of Amyloid-beta Clearance

Glycative stress is a conception of a state that causes an excess of carbohydrate-derived or fatty acid-derived short-chain aldehydes in the body. Short-chain aldehydes, which are highly reactive, undergo a carbonylation process with lysine and arginine residues in proteins and form advanced glycation endproducts (AGEs). When postprandial hyperglycemia occurs, open-ring glucose with exposed aldehyde groups (-CHO) increases and various carbohydrate-derived aldehydes are formed simultaneously (this phenomenon is named “aldehyde sparks”). Glyceraldehyde 3-phosphate dehydrogenase (GAPDH) is an enzyme abundant intracellularly as the keystone of defense against glycative stress and plays a role in metabolizing highly toxic glyceraldehyde, however, under diabetic conditions, the enzyme activity is markedly reduced by forming S-(2-succinyl) cysteine-GAPDH. We also found that a high-fat diet reduced GAPDH activity and increased glyceraldehyde and methylglyoxal. High animal fat diets in particular require caution because they increase preference dependence on animal fat. In the lipid-rich brain, they promotes the formation of lipid-derived AGEs formed by methylglyoxal and acrolein providing evidence of their close association with amyloid cascade, ultimately leading to the onset of Alzheimer-type dementia. Through the process of amylod beta (Aβ) glycation modification and cross-linking, Aβ polymerization is promoted and deposited in the brain. Thus, neurotoxicity is aggravated. Furthermore, Aβ progresses toward being persistent and Aβ clearance is reduced. Tau proteins similarly undergo glycation modification and trigger polymerization. methylglyoxal or acrolein-derived glycated Aβ clearance by primary microglia cultured cells reduced significantly compared to the unglycated Aβ provides evidence of the reduced clearance upon glycation. It was also shown that melatonin, which promotes glycolytic cross-linking degradation, may promote microglial Aβ phagocytosis. We next plan to examine the potential of plant extracts that promote glycation cross-linking degradation to improve Aβ phagocytosis. Advanced Alzheimer-type dementia with a disoriented neural network hardly recovers with treatment. In this review article, we discussed possible future therapeutic strategies for Alzheimer-type dementia by increasing Aβ clearance from the early stage such as the prevention of Aβ-glycation and the promotion of glycated-Aβ degradation, which may be a paradigm shift.