Extracts of pine needles (Pinus densiflora Sieb. et Zucc.) have been used in traditional medicine for the treatment of certain disease in eastern Asia, but little is known about their precise effects and mechanisms of action. In the present study, we investigated the pathway of the induction of apoptotic cell death by water extract of pine needles (WEPN) in human leukemic U937 cells. It was found that WEPN could inhibit the cell viability and induce the apoptotic cell death in a dose-dependent manner as measured by MTT assay, fluorescent microscope, flow cytometry analysis and agarose gel electrophoresis. Apoptosis of U937 cells by WEPN was associated with an up-regulation of pro-apoptotic Bax and down-regulation of inhibitor of apoptosis proteins (IAPs) expression. WEPN treatment induced the proteolytic activation of caspase-3, -8 and -9, and a concomitant degradation of poly(ADP-ribose) polymerase (PARP) protein. Additionally, DNA fragmentation by WEPN was connected with the activation of inhibitor of caspase-activated DNase/DNA fragmentation factor 45 (ICAD/DFF45) protein expression. Taken together, these results indicated that the inhibitory effect of WEPN in U937 cells was associated with the induction of apoptotic cell death through regulation of several major growth regulatory gene products such as Bcl-2 family expression and caspase protease activity. Though further studies will be needed to identify the activity compounds that confer the anti-cancer activity of WEPN, the present findings provide important new insights into the possible molecular mechanisms of the anti-cancer activity of pine needles. (Cancer Prev Res 12, 21-29, 2007)

Keywords: Pine needles, U937, Apoptosis, Bcl-2, Caspase