Walnut extract modulates activation of microglia through alteration in intracellular calcium concentration

Diets supplemented with walnuts have shown to protect brain against oxidative and inflammatory cytotoxicity and promote protective cellular and cognitive function. The current study was undertaken to test the hypothesize that whole walnut extract (WNE) inhibits lipopolysaccharide (LPS)-induced microglial activation by regulating calmodulin (CaM) expression through [Ca²⁺]_i. To test this hypothesis, we used an in vitro model the highly aggressively proliferating immortalized cells, a rat microglial cell line, treated with various concentrations of WNEs. Treatment with WNE (1.5%, 3%, or 6%) induced a slow rise in intracellular calcium in a concentration- and time-dependent manner, and this rise became exaggerated when cells were depolarized with potassium chloride (100 mmol/L). Cells treated with WNE (1%, 3%, or 6%) upregulated CaM protein levels, with 1 hour posttreatment being the peak time, regardless of WNE concentration. Interestingly, this WNE-induced upregulation of CaM was blocked by pretreatment with thapsigargin. Additionally, treatment with WNE (1%, 3%, or 6%) 1 hour prior to LPS treatment was found to be effective in preventing LPS-induced upregulation of inducible nitric oxide synthase expression, upregulation of ionized Ca²⁺-binding adaptor-1, and downregulation of CaM. These findings suggest that bioactive compounds in walnut are capable of modulating microglial activation through regulation of intracellular calcium and CaM expression. Nutritional interventions using walnuts may be effective in the amelioration of chronic inflammation and neurodegeneration.