Polyphenol fractions from twenty-three honey samples of various floral origins were extracted with an Amberlite XAD-2 column, and total polyphenol content and antioxidant properties were determined. The Folin-Ciocalteu method was used to determine total polyphenol content, and antioxidant activity was evaluated using the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging assay. Total polyphenol content per 100 g of honey ranged from 17.5 mg (Japanese prickly-ash) to 132.8 mg (peppermint). Peppermint honey had the highest flavonoid content (48.3 mg/100 g) and exhibited the highest antioxidant activity of all samples. A positive linear correlation was observed between honey color and DPPH radical scavenging activity. p-Coumaric acid and kaempferol were isolated and identified as antioxidants from peppermint honey. Additionally, quantification of these compounds in other honey samples was carried out. Peppermint honey contained a large amount of p-coumaric acid (705 μg/100 g) and kaempferol (471 μg/100 g). The potent antioxidant activity of peppermint honey is attributable to the quantities of these compounds, especially kaempferol.
We found that azurocidin, a secretory protein in neutrophils, binds to calreticulin, a multifunctional chaperone of the endoplasmic reticulum. Azurocidin is known to induce cytokine production in monocytes, but the mechanism of monocyte activation by azurocidin remains unknown. On the other hand, an antibacterial peptide, KLKLLLLLKLK-NH(2) (L5), is known to bind to cell surface calreticulin of human neutrophils, resulting in their activation to produce O(2)(-). Therefore, we examined whether cell surface calreticulin is involved in the activation of human monocytes by azurocidin to produce IL-6. We found that carlreticulin is in fact located on the surface of monocytes and that the IL-6 production stimulated by an azurucidin is inhibited by anti-calreticulin antibody. Possibly, binding between cell surface calreticulin and azurocidin is prerequisite for the activation of monocytes by azurocidin to produce IL-6.
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