ANTIPROLIFERATIVE EFFECT IN RAT VASCULAR SMOOTH-MUSCLE CELLS BY OSTHOLE, ISOLATED FROM ANGELICA-PUBESCENS

The antiproliferative effect of osthole on rat vascular smooth muscle cells was examined in this study. A number of mitogenic agents, e.g., foetal-calf serum (10%, v/v) and platelet-derived growth factor (20 ng /ml), and pharmacological agents, e.g., serotonin (10 mu M), ionomycin (3 nM), phorbol 12,13-dibutyrate (20 nM) and phorbol myristate acetat e (200 nM), were used to induce DNA synthesis in rat vascular smooth m uscle cells; these effects were concentration dependently inhibited by osthole and the half-maximal inhibition (IC50) occurred at 13.6 +/- 1 .8, 11.8 +/- 1.3, 7.9 +/- 0.9, 7.1 +/- 0.2, 7.8 +/- 0.2 and 8.6 +/- 0. 4 mu M, respectively. Osthole itself increased the cyclic AMP and cycl ic GMP formations in a concentration-dependent manner, it synergistica lly increased cyclic AMP and cyclic GMP levels induced by forskolin an d sodium nitroprusside, respectively. After 48 h deprivation of serum, cells were re-stimulated with serum and the cell cycle was observed b y flow cytometry; treatment of cells with osthole (100 mu M) caused a block of serum-inducible cell cycle progression at a point before the G(1)-S boundary. The addition of osthole (100 mu M) at various times a fter serum addition to serum-deprived cells showed full inhibition of DNA synthesis even when added 6 h after serum. The cell cycle progress ion block was gradually lost as the delay from serum to osthole applic ation was increased from 6 to 18 h. The effect of osthole on serum-sti mulated [H-3]thymidine incorporation into endothelial cells was examin ed and the IC50 value (158.7 +/- 2.7 mu M, n = 6) was obtained; it exh ibited greater potency (12-fold) for vascular smooth muscle cells as c ompared with endothelial cells as an antiproliferative agent. These re sults suggest that osthole is a selective antiproliferative agent in v ascular smooth muscle cells. The antiproliferative effect occurs at th e early G(1) phase of the cell cycle and is due to the increase in cyc lic AMP and cyclic GMP contents.