Oral Administration of Alpha Linoleic Acid Rescues A beta-Induced Glia-Mediated Neuroinflammation and Cognitive Dysfunction in C57BL/6N Mice

Abstract

In this work, we evaluated the effects of alpha linoleic acid (ALA), an omega-3 polyunsaturated fatty acid, on amyloid-beta-induced glial-cell-mediated neuroinflammation, amyloidogenesis, and cognitive dysfunction in mice. After an infusion of A beta(1-42) (A beta(1-42), 5 mu L/5 min/mouse, intracerebroventricular injection (i.c.v), and respective treatments of ALA (60 mg/kg per oral for six weeks), neuroinflammation, apoptotic markers, and synaptic markers were evaluated by Western blot and immunofluorescence analyses. According to our findings, the infusion of A beta(1-42) activated Toll-like receptor 4 (TLR4), glial fibrillary acidic protein (GFAP), and ionized calcium adaptor molecule 1 (Iba-1) in the frontal cortices and hippocampi of the A beta(1-42)-injected mice to a greater extent than the A beta(1-42) + ALA-cotreated mice. Similarly, there was an elevated expression of phospho-c-Jun-N-terminal kinase (p-JNK), phospho-nuclear factor-kB p65 (p-NF-kB p65 (Ser536)), and tissue necrosis factor (TNF) in the A beta(1-42) infused mouse brains; interestingly, these markers were significantly reduced in the A beta + ALA-cotreated group. The elevated expression of pro-apoptotic markers was observed during apoptotic cell death in the A beta(1-42)-treated mouse brains, whereas these markers were markedly reduced in the A beta + ALA-cotreated group. Moreover, A beta(1-42) infusion significantly increased amyloidogenesis, as assessed by the enhanced expression of the amyloid precursor proteins (APP) beta-amyloid cleaving enzyme-1 (BACE-1) and amyloid-beta (A beta(1-42)) in the mouse brains, whereas these proteins were markedly reduced in the A beta + ALA-cotreated group. We also checked the effects of ALA against A beta-triggered synaptic dysfunction and memory dysfunction, showing that ALA significantly improved memory and synaptic functions in A beta-treated mouse brains. These results indicated that ALA could be an applicable intervention in neuroinflammation, apoptotic cell loss, amyloidogenesis, and memory dysfunction via the inhibition of TLR4 and its downstream targets in A beta + ALA-cotreated mouse brains.