Neuroinflammation in Alzheimer's Disease: The Preventive and Therapeutic Potential of Polyphenolic Nutraceuticals

Brain inflammation, characterized by increased microglia and astrocyte activation, increases during aging and is a key feature of neurodegenerative diseases, such as Alzheimer's disease (AD). In AD, neuronal death and synaptic impairment, induced by amyloid-beta (A beta) peptide, are at least in part mediated by microglia and astrocyte activation. Glial activation results in the sustained production of proinflammatory cytokines and reactive oxygen species, giving rise to a chronic inflammatory process. Astrocytes are the most abundant glial cells in the central nervous system and are involved in the neuroinflammation. Astrocytes can be activated by numerous factors, including free saturated fatty acids, pathogens, lipopolysaccharide, and oxidative stress. Activation of astrocytes produces inflammatory cytokines and the enzyme cyclooxygenase-2, enhancing the production of A beta. Furthermore, the role of the receptor for advanced glycation end products/nuclear factor-kappa B (NF-kappa B) axis in neuroinflammation is in line with the nonenzymatic glycosylation theory of aging, suggesting a central role of the advanced glycation end products in the age-related cognitive and a possible role of nutraceuticals in the prevention of neuroinflammation and AD. However, modulation of P-glycoprotein, rather than antioxidant and anti-inflammatory effects, could be the major mechanism of polyphenolic compounds, including flavonoids. Curcumin, resvertrol, piperine, and other polyphenols have been explored as novel therapeutic and preventive agents for AD. The aim of this review is to critically analyze and discuss the mechanisms involved in neuroinflammation and the possible role of nutraceuticals in the prevention and therapy of AD by targeting neuroinflammation.