Modulation of interleukin-1β mediated inflammatory response in human astrocytes by flavonoids: Implications in neuroprotection

The proinflammatory cytokine interleukin-1β (IL-1β) contributes to inflammation and neuronal death in CNS injuries and neurodegenerative pathologies, and astrocytes have been implicated as the primary mediators of IL-1β induced neuronal death. As astrocytes play an important role in supporting the survival and functions of neurons, we investigated the effect of plant flavonoids quercetin and luteolin, with known anti-inflammatory properties in modulating the response of human astrocytes to IL-1β for therapeutic intervention. Flavonoids significantly decreased the release of reactive oxygen species (ROS) from astrocytes stimulated with IL-1β. This decrease was accompanied by an increase in expression of superoxide dismutase (SOD-1) and thioredoxin (TRX1)—mediators associated with protection against oxidative stress. Flavonoids not only modulated the expression of astrocytes specific molecules such as glial fibrillary acidic protein (GFAP), glutamine synthetase (GS), and ceruloplasmin (CP) both in the presence and absence of IL-1β but also decreased the elevated levels of proinflammatory cytokine interleukin-6 (IL-6) and chemokines interleukin-8 (IL-8), interferon-inducible protein (IP-10), monocyte-chemoattractant protein-1 (MCP-1), and RANTES from IL-1β activated astrocytes. Significant decrease in neuronal apoptosis was observed in neurons cultured in conditioned medium obtained from astrocytes treated with a combination of IL-1β and flavonoids as compared to that treated with IL-1β alone. Our result suggests that by (i) enhancing the potential of activated astrocytes to detoxify free radical, (ii) reducing the expression of proinflammatory cytokines and chemokines, and (iii) modulating expression of mediators associated with enhanced physiological activity of astrocyte in response to injury, flavonoids confer (iv) protection against IL-1β induced astrocyte mediated neuronal damage.