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In this study we compared, simultaneously, the growth-inhibitory effect of Hypericum perforatum L. extracts, containing various amounts of hyperforin (A 3.25%; B 2.21%; C 0.21% w/w) and flavonoids (A and B 5.3%; C 10% w/w), but closely same amounts of naphthodiantrones (0.3%) on two leukaemic cell lines K562 and U937 in the WST-1 assay. The GI50 (concentration of extracts which caused 50% of cell growth inhibition) for H. perforatum extracts analysed and characterized by HPLC for their biologically active constituents was 248.3-621.3 microg mL(-1) in K562 and 378.2-911.7 microg mL(-1) in U937 cells. The corresponding values of the three main groups were 1.6-3.9 microM naphthodianthrones, 1.0-40.7 microM phloroglucinols and 30.5-68.5 microM flavonoids. The results of this study supported the hypothesis that, apart from hyperforin and flavonoids, other components of the extract could be involved in its growth-inhibitory effect that it exerts without light activation.

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