Effects of phytoestrogens on DNA synthesis and creatine kinase activity in vascular cells

Background: The aim of this study was to assess the effect of phytoestrogens on the human vascular wall in vitro. Methods: We compared the effects of E₂ to those of genistein (G), daidzein (D), biochanin A (BA), equol (EQ), and quecertin (Qu) on ³[H] thymidine incorporation and creatine phosphokinase (CK) activity in human vascular smooth muscle cells (VSMC) and in a human endothelial cell line (E304). Results: In VSMC, E₂, the estrogen antagonist raloxifene (RAL), G, and D stimulated DNA synthesis at low concentrations and suppressed ³[H] thymidine incorporation at higher concentrations. In contrast, BA and EQ had a monophasic stimulatory effect on ³[H] thymidine incorporation (87% ± 9% and 54% ± 17%, respectively) whereas Qu had only an inhibitory effect (-36 ± 16% at 30 nmol/L). In E304 cells, all phytoestrogens stimulated DNA synthesis in a dose-related manner. In both cell types E₂, RAL as well as all phytoestrogens increased CK specific activity. The administration of phytoestrogens to immature female rats resulted in increased CK in the aorta (Ao) (60% to 220%) and in the left ventricle of the heart (Lv) (45% to 160%). Similar increases in Ao and Lv CK were also induced by E₂ and all five phytoestrogens in ovariectomized (OVX) female rats. RAL antagonized phytoestrogen-induced CK activity in human vascular cells and in the rat Ao and Lv tissue but did not block phytoestrogen effects on DNA synthesis in human VSMC. Conclusions: Although phytoestrogens have estrogen-mimetic effects on cell growth and CK in cultured human vascular cells and on CK in rat vascular tissues in vivo, the effects on human VSMC replication are highly dependent on the concentration and the particular phytoestrogen under investigation.