Isolation and Characterization of Neuroprotective Components from Citrus Peel and Their Application as Functional Food.

The elderly experience numerous physiological alterations. In the brain, aging causes degeneration or loss of distinct populations of neurons, resulting in declining cognitive function, locomotor capability, etc. The pathogenic factors of such neurodegeneration are oxidative stress, mitochondrial dysfunction, inflammation, reduced energy homeostatis, decreased levels of neurotrophic factor, etc. On the other hand, numerous studies have investigated various biologically active substances in fruit and vegetables. We focused on the peel of citrus fruit to search for neuroprotective components and found that: 1) 3,5,6,7,8,3',4'-heptamethoxyflavone (HMF) and auraptene (AUR) in the peel of Kawachi Bankan (Citrus kawachiensis) exert neuroprotective effects; 2) both HMF and AUR can pass through the blood-brain barrier, suggesting that they act directly in the brain; 3) the content of AUR in the peel of K. Bankan was exceptionally high, and consequently the oral administration of the dried peel powder of K. Bankan exerts neuroprotective effects; and 4) intake of K. Bankan juice, which was enriched in AUR by adding peel paste to the raw juice, contributed to the prevention of cognitive dysfunction in aged healthy volunteers. This review summarizes our studies in terms of the isolation/characterization of HMF and AUR in K. Bankan peel, analysis of their actions in the brain, mechanisms of their actions, and trials to develop food that retains their functions.

Auraptene/Naringin-Rich Fruit Juice of Citrus kawachiensis (Kawachi Bankan) Prevents Ischemia-Induced Neuronal Cell Death in Mouse Brain through Anti-Inflammatory Responses.

Cerebral ischemia/reperfusion leads to delayed neuronal cell death, resulting in brain damage. Auraptene (AUR) and naringin (NGIN), which exert neuroprotective effects in ischemic brain, are abundant in the peel of Citrus kawachiensis. Although parts of AUR/NGIN are transited from the peel to the juice during the squeezing of this fruit, these amounts in juice might be too low to exert effects. We thus prepared the AUR/NGIN-rich fruit juice of C. kawachiensis by addition of peel paste to the raw juice. The present study revealed that orally administration of the dried powder of this AUR/NGIN-rich fruit juice (2.5 g/kg/d) for 7 d to ischemic mice significantly suppressed the ischemia-induced neuronal cell death in the hippocampus, which was coincidently with the reduction of hyperactivation of microglia and astrocytes. These results suggest that AUR/NGIN-rich juice of C. kawachiensis may possess therapeutic potential for the prevention of neurodegenerative diseases via inhibition of inflammatory processes.