Qi-activating quercetin alleviates mitochondrial dysfunction and neuroinflammation in vivo and in vitro

Parkinson's disease (PD) is a multifactorial neurodegenerative disease manifesting mitochondrial damages and neuroinflammation. Qi is defined as a natural power that can regulate the energy flow in Oriental medicine, whereas mitochondria generate energy power in Western medicine. We investigated whether Qi-enhancing component in Oriental herb medicines could activate mitochondrial activities. Quercetin was found as a major bioactive compound in most Qi-activating Oriental herb medicines through online search for active compounds in several Oriental Medicine databases. We then investigated if quercetin could reverse 1-methyl-4-phenylpyridinium (MPP⁺)-induced mitochondrial dysfunction and lipopolysaccharide (LPS)-induced neuroinflammation. Mitochondrial activities were monitored based on complex 1 NADH dehydrogenase activities, ATP contents, mitochondrial membrane potential, cellular/mitochondrial reactive oxygen species, and oxygen consumption rate in SH-SY5Y cells. Quercetin at concentration up to 20 µg/ml was not cytotoxic to SH-SY5Y cells. Pre-treatment with quercetin significantly protected mitochondrial damages in 1 mM MPP⁺- or 100 ng/ml LPS-treated cells. Quercetin increased expression levels of tyrosine hydroxylase and mitochondria controlling proteins. When in vivo effects of quercetin were assessed by immunohistochemical staining of tissue sections from LPS-injected mice brains, quercetin reduced the activation of microglia and astrocytes in the hippocampus and substantia nigra of LPS-injected mice. Our data suggest that Qi-activating quercetin might be therapeutically effective for neuroinflammation-mediated neurodegeneration by alleviating mitochondrial damages.