Immune-stimulated antitumor effect of different molecular weight polysaccharides from Monascus purpureus on human leukemic U937 cells

Since polysaccharides from many fungi have been shown to exhibit immunomodulating activity, the present study was aimed at isolating polysaccharides from Monascus purpureus and examining their effects on human leukemic U937 cells with or without immunomodulating stimulation by blood mononuclear cells (MNCs). The 50-100 kDa polysaccharide fraction (MP3) obtained from ultrafiltration showed the highest antitumor activity by 42.2 ± 2.1% growth inhibition. This polysaccharide fraction was further resolved by anion exchanger resin into three peaks. Among them, the second peak (MP3B) exerted the most potent inhibitory action, and even at 1 -g/mL, it was able to activate MNCs to produce a conditioned medium that inhibited the growth of U937 by 73.43 ± 1.4%. In contrast, when U937 cells were directly cultured in the presence of MP3B, the cell growth was not retarded even at the concentrations of MP3B as high as 100 -g/mL.