Novel pharmacological approach to medicinal effects of Allium vegetables: The interactions of organosulfur and flavonoid constituents with membrane lipids
Allium vegetables, especially garlic (A. sativum L.) and onion (A. cepa L.), have been used as common foods and for the prevention and treatment of various diseases including cancer, cardiovascular and infectious disease. As a novel pharmacological approach, we studied the interactions of their bioactive constituents with membrane lipids to modify the membrane fluidity. Liposomal cell model membranes  were treated with garlic and onion preparations, followed by measuring membrane fluidity changes . Allyl (20–500µM) and quercetin derivatives (2.5–10µM) rigidified tumor cell and platelet membranes with the potency being diallyl trisulfide > diallyl disulfide >> diallyl sulfide and quercetin dimers > quercetin >> quercetin-4'-O-glucoside. They (100–500µM) were effective in rigidifying candida cell membranes with ergosterol (the potency being diallyl disulfide > diallyl trisulfide > diallyl sulfide) but not in bacterial cell membranes without ergosterol. Both relative intensity and selectivity in membrane effects of allyl and quercetin derivatives correlated with their antiproliferative, antiplatelet and antimicrobial activities . Membrane-active diallyl trisulfide and disulfide (20–500µM) and quercetin dimers (10–100µM) inhibited the growth of tumor cells cultured for 1–48h, together with rigidifying cell membranes. Membrane-rigidifying quercetin derivatives showed inhibitory effects on human platelet aggregation induced by collagen and ADP. However, membrane-inactive compounds were not effective on tumor cells and platelets. The membrane lipid interactions of organosulfur and flavonoid constituents are referred to as one of possible mechanisms underlying the medicinal effects of Allium vegetables.
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