The identification of phenolics from various cultivars of fresh sweet and sour cherries and their protective effects on neuronal cells were comparatively evaluated in this study. Phenolics in cherries of four sweet and four sour cultivars were extracted and analyzed for total phenolics, total anthocyanins, and their antineurodegenerative activities. Total phenolics in sweet and sour cherries per 100 g ranged from 92.1 to 146.8 and from 146.1 to 312.4 mg gallic acid equivalents, respectively. Total anthocyanins of sweet and sour cherries ranged from 30.2 to 76.6 and from 49.1 to 109.2 mg cyanidin 3-glucoside equivalents, respectively. High-performance liquid chromatography (HPLC) analysis revealed that anthocyanins such as cyanidin and peonidin derivatives were prevalent phenolics. Hydroxycinnamic acids consisted of neochlorogenic acid, chlorogenic acid, and p-coumaric acid derivatives. Glycosides of quercetin, kaempferol, and isorhamnetin were also found. Generally, sour cherries had higher concentrations of total phenolics than sweet cherries, due to a higher concentration of anthocyanins and hydroxycinnamic acids. A positive linear correlation (r2 = 0.985) was revealed between the total anthocyanins measured by summation of individual peaks from HPLC analysis and the total anthocyanins measured by the pH differential method, indicating that there was in a close agreement with two quantifying methods for measuring anthocyanin contents. Cherry phenolics protected neuronal cells (PC 12) from cell-damaging oxidative stress in a dose-dependent manner mainly due to anthocyanins. Overall results showed that cherries are rich in phenolics, especially in anthocyanins, with a strong antineurodegenerative activity and that they can serve as a good source of biofunctional phytochemicals in our diet.

Clinical trials of several neurodegenerative diseases have increasingly targeted the evaluation of various antioxidants' effectiveness. The human diet contains several thousand phytochemicals, many of which have significant bioactivities. Vitamin C, a naturally occurring antioxidant, is known to reduce the risk of neurodegenerative disorders such as Alzheimer's disease. Quercetin, one of the major flavonoids in some fruits and vegetables, has much stronger antioxidative and anticarcinogenic activities than vitamin C. Therefore, we investigated the protective effects of quercetin on hydroxy peroxide-induced neurodegeneration. To determine the protective effects, PC12 cells were preincubated with quercetin and vitamin C before H(2)O(2) treatment for 2 h. Results showed that cell viability was clearly improved with quercetin, and quercetin showed a higher protective effect than vitamin C. Because oxidative stress is known to increase neuronal cell membrane breakdown, we further investigated lactate dehydrogenase and trypan blue exclusion assays. We observed that quercetin decreased oxidative stress-induced neuronal cell membrane damage more than vitamin C. These results suggest that quercetin, in addition to many other biological benefits, contributes significantly to the protective effects of neuronal cells from oxidative stress-induced neurotoxicity, such as Alzheimer disease.

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Because strawberries are known to contain higher concentrations of phytochemicals and have higher antioxidant capacity among common fruits, their neuroprotective activity was tested in vitro on PC12 cells treated with H2O2. Their protective effect and antioxidant capacity were also compared with those of banana and orange, which are the fresh fruits consumed at highest levels in the United States. The cell viability test using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) reduction assay showed that strawberry phenolics significantly reduced oxidative stress-induced neurotoxicity. Because oxidative stress is also known to increase neuronal cell membrane breakdown, lactate dehydrogenase (LDH) and trypan blue exclusion assays were also performed. Strawberry showed the highest cell protective effects among the samples. The overall relative neuronal cell protective activity of three fruits by three tests followed the decreasing order strawberry > banana > orange. The protective effects appeared to be due to the higher phenolic contents including anthocyanins, and anthocyanins in strawberries seemed to be the major contributors.

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Amyloid beta protein (Abeta)-induced free radical-mediated neurotoxicity is known as a leading hypothesis for a cause of Alzheimer's disease. Abeta increased free radical production and lipid peroxidation in PC12 nerve cells, resulting in apoptosis and cell death. The protective effect of naringenin, a major flavanone constituent isolated from Citrus junos, against Abeta-induced neurotoxicity was investigated using PC12 cells. Pretreatment with isolated naringenin and vitamin C prevented the generation of the Abeta-induced reactive oxygen species. Naringenin resulted in the decrease of Abeta toxicity in a manner of concentration dependence, which was assessed by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. However, treatment with these antioxidants inhibited the Abeta-induced neurotoxic effect. The antiamnestic activity of naringenin in vivo was also evaluated using ICR mice with amnesia induced by scopolamine (1 mg/kg body weight). Naringenin, when administered to ICR mice at 4.5 mg/kg body weight, significantly ameliorated scopolamine-induced amnesia as measured in the passive avoidance test. Therefore, these results indicate that micromolecular Abeta-induced in vitro oxidative cell stress is reduced by naringenin and naringenin may be a useful chemopreventive agent against a neurodegenerative disease such as Alzheimer's disease.

This study was performed to identify safe and more effective acetylcholinesterase (AChE) inhibitors in the treatment of Alzheimer’s disease. The total methanol extract of Citrus junos had a significant inhibitory effect on AChE in vitro. By sequential fractionation of C. junos, the active component was finally identified as naringenin. Naringenin inhibited AChE activity in a dose-dependent manner. In this study, we also evaluated the anti-amnesic activity of naringenin, a major flavanone constituent isolated from C. junos, in vivo using ICR mice with amnesia induced by scopolamine (1 mg/kg body weight). Naringenin, when administered to mice at 4.5 mg/kg body weight, significantly ameliorated scopolamine-induced amnesia as measured in both the passive avoidance and the Y-maze test. These results suggest that naringenin may be a useful chemopreventive agent against Alzheimer’s disease.