Anti-Platelet and Membrane-Rigidifying Flavonoids in Brownish Scale of Onion

Abstract

The bio-activity of the brownish scale of onion (Allium cepa) was studied together with identifying the active components and addressing the mode of action. A crude MeOH extract (0.5-1.0 mg/ml) showed the inhibitory effects on human platelet aggregation induced by collagen, adenosine 5′-diphosphate (ADP), thrombin and epinephrine. The anti-platelet extract (1.0 µg/ml) rigidified liposomal membranes by acting on the hydrocarbon core more intensively than the surface of membrane lipid bilayers. Serial solvent extractions and chromatographic purifications provided four isolates which were structurally identified as different quercetin dimers (1 and 2), quercetin (3) and quercetin-4′-glucoside (4). The flavonoidal components 1, 3, 2 and 4 (0.5-2 mM) inhibited collagen-induced platelet aggregation in increasing order of intensity. More active 1 and 3 (2 mM) also dissociated the aggregates produced by ADP. The anti-platelet flavonoids (0.25-10 µM) acted on liposomes of the lipid composition resembling human platelets to cause membrane rigidification which was greatest in the order of 1, 2, 3 and 4. The interaction with membrane lipids to modify membrane fluidity appears to be partly responsible for the anti-aggregatory and disaggregatory effects on human platelets. Although the inedible scale of onion is usually regarded as waste, it has the possibility to be a medicinal resource.

Antioxidant Activity of Hydroxyflavonoids

“…A synthetic flavonol (23) which has 3′,4′-dihydroxyl groups similar to 19-22 also showed the strong activities. In the previous paper, 9) we described that quercetin (19) rapidly react with DPPH radical to afford two dimers The dimerization was initiated by pulling off of hydrogen at C3-OH by DPPH radical. It could then be suggested that 20, 22 and 23 scavenged DPPH radical by same manners as quercetin (Fig.…”

Kinetic modelling for polyphenol extraction from onion (Allium cepa) solid wastes using acidified water/ethanol mixture

“…Most of these substances do not occur in the edible part of the onion bulb, but they represent oxidation products of quercetin and its glucosides. Some of these phenolics have been shown to possess antiplatelet properties (FURUSAWA et al, 2003).…”

Cell Growth Inhibition by Membrane-Active Components in Brownish Scale of Onion

“…Onion Scale Components ---Flavonoidal components were isolated as reported previously. 18,19) In brief, the brownish scale of onion obtained from commercial outlets was air-dried, powdered and extracted with methanol, followed by three-step chromatographic purifications. Based on spectral data, the finally obtained isolates were identified as Q, quercetin-4′-O-glucoside (QG) and two isomeric quercetin dimers (QD-1 and QD-2) (Fig.…”

“…19) Membrane perturbation is also known to be responsible for not only platelet aggregation inhibition 20,21) but cell growth inhibition by drugs and food components. 5,15) In the present study, we aimed to clarify the antiproliferative activity of the brownish scale of onion by determining the cell growth-inhibitory effects of flavonoidal components associated with membrane fluidity changes.…”