Grape Seed Extract Acting on Astrocytes Reveals Neuronal Protection Against Oxidative Stress via Interleukin-6-mediated Mechanisms

Grape polyphenols are known to protect neurons against oxidative stress. We used grape seed extract (GSE) from Koshu grapes (Vitis vinifera) containing a variety of polyphenols, and performed transcriptome analysis to determine the effects of GSE on primary cultures of astrocytes in the hippocampus. GSE upregulated various mRNAs for cytokines, among which interleukin-6 (IL-6) showed the biggest increase after treatment with GSE. The GSE-evoked increase in IL-6 mRNAs was confirmed by quantitative RT-PCR. We also detected IL-6 proteins by ELISA in the supernatant of GSE-treated astrocytes. We made an oxidative stress-induced neuronal cell death model in vitro using a neuron rich culture of the hippocampus. Treatment of the neurons with H2O2 caused neuronal cell death in a time- and concentration-dependent manner. Exogenously applied IL-6 protected against the H2O2-induced neuronal cell death, which was mimicked by endogenous IL-6 produced by GSE-treated astrocytes. Taken together, GSE acting on astrocytes increased IL-6 production, which functions as a neuroprotective paracrine, could protect neuronal cells from death by oxidative stress.