Inhibitory effects of glycolipids fraction from spinach on mammalian DNA polymerase activity and human cancer cell proliferation

We succeeded in purifying the fraction containing the major glycolipids in monogalactosyl diacylglycerol, digalactosyl diacylglycerol and sulfoquinovosyl diacylglycerol (SQDG) from dried vegetables. This glycolipids fraction was an inhibitor of DNA polymerase alpha (pol alpha) in vitro and also the proliferation of human cancer cells. In this study, eight common vegetables were investigated in terms of the glycolipids fraction, the amounts of major glycolipids, mammalian DNA polymerase inhibitory activity and antiproliferative activity toward human cancer cells. Green tea possessed the largest amount of glycolipids overall. Spinach contained the largest amount of SQDG, followed by parsley, green onion, chive, sweet pepper, green tea, carrot and garlic. Spinach had the strongest inhibitory effect on pol alpha activity and human cancer cell proliferation. A significant correlation was found between SQDG content and inhibition of DNA polymerase. Therefore, the inhibition of pol alpha activity by SQDG may lead to cell growth suppression. Of the six subspecies of spinach (Spinacia oleracea) tested, "Anna" had the largest amount of SQDG, strongest inhibitory activity toward DNA polymerase and greatest effect on human cancer cell proliferation. Based on these results, the glycolipids fraction from spinach is potentially a source of food material for a novel anticancer activity.