Protective Effect of Lupeol Against Lipopolysaccharide-Induced Neuroinflammation via the p38/c-Jun N-Terminal Kinase Pathway in the Adult Mouse Brain

Recent studies have demonstrated a close interaction between neuroinflammatory responses, increased production of inflammatory mediators, and neurodegeneration. Pathological findings in neurological diseases such as Alzheimer's disease, Parkinson's disease, and Huntington's disease have shown common signs of neuroinflammation and neurodegeneration. Lupeol, a natural pentacyclic triterpene, has revealed a number of pharmacological properties including an anti-inflammatory activity. This study aimed to evaluate the effect of lupeol against lipopolysaccharide (LPS)-induced neuroinflammation in the cortex and hippocampus of adult mice. Our results showed that systemic administration of LPS induced glial cell production of proinflammatory cytokines, tumor necrosis factor (TNF)-alpha, inducible nitric oxide synthase (iNOS), and interleukin (IL)-1 beta, while co-treatment with lupeol significantly inhibited the LPS-induced activation of microglia and astrocytes, and decreased the LPS-induced generation of TNF-alpha, iNOS, and IL-1 beta. The intracellular mechanism involved in the LPS-induced activation of inflammatory responses includes phosphorylation of P38 mitogen-activated protein kinase (MAPK) and c-Jun N-terminal kinase (JNK), which was significantly inhibited by lupeol. We further elucidated that lupeol inhibited the LPS-induced activation of the mitochondrial apoptotic pathway and reversed the LPS-induced expression of apoptotic markers such as Bax, cytochrome C, caspase-9, and caspase-3. Taken together; our results suggest that lupeol inhibits LPS-induced microglial neuroinflammation via the P38-MAPK and JNK pathways and has therapeutic potential to treat various neuroinflammatory disorders.