Blueberries and insulin protect microglial cells against high glucose-induced inflammation and restore GLUT-1

BACKGROUND: Growing evidence suggests that hyperglycemia could be harmful for cognitive function. That insulin (INS) has a neuro-modulatory role is supported by various findings, but its effect on microglia, the innate immune cells in the brain, is largely unknown. Blueberries have been shown to reduce neuro-inflammation. OBJECTIVE: We hypothesized that high glucose stimulated an inflammation in microglia and that BB and INS were able to reduce it and both might act through GLUT-1 transporter. METHODS: We examined the effects of low (5 mM), medium (25 mM), or high (50 mM) glucose, stimulated or not with lipopolysaccharide (LPS; 100 nM) with either BB extract (2 mg/ml) and/or INS, on inflammatory responses in a microglia cell line. Nitric oxide (NO) production and the expression levels of iNOS, TNF-α, NOX4 and glucose transporter protein-1 (GLUT1) were assessed. RESULTS: We observed that treatment with BB, similarly to INS treatments, reduced the high glucose concentration-induced response on oxidative stress and inflammation, and that this protective effect is more important with LPS added to glucose media. Interestingly, both BB and INS attenuated the LPS-induced inflammatory response on GLUT1. CONCLUSION: Increasing glucose concentration triggers inflammation by microglia. BB as well as INS protected microglia from high glucose levels, by reducing inflammation and altering glucose transport in microglia. These preliminary data compared for the first time BB to Insulin on microglia. Blueberries are promising dietary intervention to prevent diabetic neuropathy. Our preliminary results suggest a possible new mechanism involving GLUT-1 by which BB has insulin-like effects.