Inhibitory effects of lycopene on the induction of NO, cytokines, and mitogen-activated protein kinase expression by lipopolysaccharide in primary cultured microglia

Microglia are activated in response to brain injury and release neurotoxic factors including nitric oxide (NO) and proinflammatory cytokines such as tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β). Lycopene, a potent antioxidant, is known to inhibit brain injury. In this study, we found that lycopene (5-20 μM) significantly inhibited lipopolysaccharide (LPS)-induced NO release in primary cultured microglia. Lycopene (5-20 μM) also concentration-dependently diminished the LPS-induced production of proinflammatory cytokines such as TNF-α and IL-1β in microglia. Further study of the molecular mechanisms revealed that lycopene markedly inhibited extracellular signal-regulated kinase (ERK1/2) but not c-Jun N-terminal kinase (JNK1/2) or p38 mitogen-activated protein kinase (MAPK) phosphorylation stimulated by LPS in microglia. These results suggest that microglial inactivation by lycopene is at least partially due to activation of ERK1/2 phosphorylation Therefore, inhibition of NO and proinflammatory cytokine production in activated microglia by lycopene may represent a powerful and potential therapeutic strategy for various neurodegenerative diseases including ischemia-reperfusion cerebral infarction.