2-Hydroxy-3-methylanthraquinone from Hedyotis diffusa Willd induces apoptosis in human leukemic U937 cells through modulation of MAPK pathways

The herb of Hedyotis diffusa Willd (H. diffusa Willd), an annual herb distributed in northeastern Asia, has been known as a traditional oriental medicine for the treatment of cancer. Recently, Chinese researchers have discovered that two anthraquinones isolated from a water extract of H. diffusa Willd showed apoptosis-inducing effects against cancer cells. However, the cellular and molecular mechanisms responsible for this phenomenon are poorly understood. The current study determines the role of mitogen-activated protein kinases (MAPK) in human leukemic U937 cells apoptosis induced by 2-hydroxy-3-methylanthraquinone from H. diffusa. Our results showed that 2-hydroxy-3-methylanthraquinone decreased phosphorylation-ERK1/2 (p-ERK1/2), and increased p-p38MAPK, but did not affect expressions of p-JNK1/2 in U937 cells. Moreover, treatment of U937 cells with 2-hydroxy-3-methylanthraquinone resulted in activation of caspase-3. Furthermore, PD98059 (ERK1/2 inhibitor) significantly enhanced 2-hydroxy-3-methylanthraquinone-induced apoptosis in U937 cells, whereas caspase-3 inhibitor or SB203580 (p-p38MAPK inhibitor), decreased apoptosis in U937 cells. Taken together, our study for the first time suggests that 2-hydroxy-3-methylanthraquinone is able to enhance apoptosis of U937 cells, at least in part, through activation of p-p38MAPK and downregulation of p-ERK1/2. Moreover, the triggering of caspase-3 activation mediated apoptotic induction.