Effects of Bioactive Substances from Citrus on the Central Nervous System and Utilization as Food Material

Abstract

We have recently shown that 3,5,6,7,8,3',4'-heptamethoxyflavone (HMF) and auraptene (AUR) have neuroprotective effects on the central nervous system. HMF, a citrus flavonoid, altered NMDA-type glutamate receptor antagonist MK-801-induced memory dysfunction and schizophrenia-positive symptom-like behavior. HMF also showed a protective effect against ischemia-induced short-term memory dysfunction. In the ischemic brain, HMF induced the following protective effects against brain dysfunction: 1) rescue of neuronal cell death in the hippocampus; 2) increased production of brain-derived neurotrophic factor; 3) stimulation of neurogenesis in the dentate gyrus subgranular zone; 4) activation of the autophosphorylation of calcium-calmodulin-dependent protein kinase II; and 5) suppression of microglial activation. On the other hand, AUR, a citrus coumarin, ameliorated lipopolysaccharide-induced inflammation in the brain as shown by inhibition of microglial activation and inhibition of cyclooxygenase (COX)-2 expression in the hippocampus. AUR also showed antiinflammatory effects on the ischemic brain by inhibiting microglial activation, COX-2 expression, and neuronal cell death in the hippocampus. The peel of kawachibankan (Citrus kawachiensis), a noted citrus product of Ehime prefecture, Japan, contains AUR, HMF, naringin, and narirutin. The dried powder of both the peel and juice had antiinflammatory effects in the mouse hippocampus, suggesting that citrus compounds may be beneficial as neuroprotective agents in the treatment of neurological disorders.