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Antioxidant activities of volatile extracts isolated from thyme, basil, rosemary, chamomile, lavender, and cinnamon were evaluated by two independent assays: the aldehyde/carboxylic acid assay and the conjugated diene assay. The volatile extracts were prepared from dried herbs and spices using liquid-liquid continuous extraction following steam distillation under reduced pressure (55 degrees C and 95 mmHg). The antioxidant activities of the extracts decreased in the following order in both of the lipophilic assay systems: thyme > basil > rosemary > chamomile > lavender and cinnamon. Thyme and basil extracts inhibited the oxidation of hexanal for 40 days at the levels of 10 microg/mL and 50 microg/mL, respectively. The extracts of thyme and basil were effective in retarding methyl linoleate deterioration at 40 degrees C, with activity increasing with concentration in the range 10-200 microg/mL. At a concentration of 50 microg/mL, thyme extract was similar in antioxidant activity to BHT and alpha-tocopherol in the conjugated diene assay. The antioxidant potentials of the volatile extracts used in this study were accurately measured by the lipophilic systems, such as the aldehyde/carboxylic acid assay and the conjugated diene assay.

Beta-amyloid (betaA)-induced oxidative toxicity on neuronal cells is a principal route in Alzheimer's disease (AD), and its toxicity occurs after fibril formation. Inhibitory or promoting effects of naturally occurring compounds on betaA fibril formation were evaluated. Among 214 tested compounds, curcuminoids, flavone type flavonoids, and naphthoquinones were shown to be potent inhibitors of betaA fibrilization. The addition of the curcuminoids, curcumin, demethoxycurcumin, and bisdemethoxycurcumin strongly inhibited betaA fibril formation. Flavonoids such as quercetin, rhamnetin, and fisetin strongly inhibited betaA fibril formation. Limonoids, cinnamic acids, and catechins enhanced fibril formation in vitro. Anthothecol possessed the most enhancing activity on fibril formation of the compounds tested. On the other hand, it was found that curcuminoids showed cytotoxicity with the 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide assay and did not protect HT22 murine neuroblastoma cells from betaA(25-35) insult. Two flavone type flavonoids, morin and quercetin, exhibited no cytotoxicity and strongly protected HT22 murine neuroblastoma cells from betaA(25-35) oxidative attack. Conclusively, morin or quercetin could be a key molecule for the development of therapeutics for AD.