EPIGALLOCATECHIN-3 GALLATE, SELECTIVELY INHIBITS THE PLATELET-DERIVED GROWTH FACTOR-BB-INDUCED SIGNALING TRANSDUCTION PATHWAYS IN VASCULAR SMOOTH MUSCLE CELLS

다국어 초록 (Multilingual Abstract)

Vascular smooth muscle cells(VSMCs) proliferation may participate in the pathophysiology of cardiovascular diseases. Platelet-derived growth factor-BB(PDGF-BB) is a potent mitogenic factor for VSMCs. Epigallocatechin gallate(EGCG) is the main compound of green tea and is believed to be the active component in tea for the prevention against several diseases. We investigated the effect of EGCG on the PDGF-BB-induced proliferation of VSMCs. VSMCs were preincubated in serum-free medium for 24 h(quiescent VSMCs) before EGCG was added to the medium. Following 24 h incubation with EGCG per se, VSMCs were trypsinized and cell counts were determined using CASY-1 system based on the coulter counter principle(Scharfe). Treatment of the cells with 0μM, 20μM, 50μM and 100μM EGCG resulted in a decrease of cell counts from 1.49×10^(6) ± 1.2×10^(5)(0μM) to 9.7×10^(5) ± 1.1×10⁴, 5.3×10^(5) ± 6.3×10⁴, 3.8×10^(5) ± 2.5×10⁴ counts/ml(mean±SD, n=3), respectively. Stimulation of quiescent cells with 50 ng/ml PDGF-BB for 24 h resulted in a 35% increase in cell counts. In the presence of 50μM EGCG, the effect of PDGF-BB on cell counts was abrogated. Activation of the 42 and 44 kDa mitogen-activated protein kinase(MAP) kinases(p44^(mapk)/p42^(mapk)) was deteced by chemiluminescence western blotting method using primary antibodies which recognizes the Tyr204-phosphorylated active isoforms. Stimulation of quiescent VSMCs with 50 ng/ml PDGF-BB caused at 5 min an 8-fold increase of the the p44^(mapk)/p42^(mapk) phosphorylation above control levels. Pretreatment of cells for 24 h with 50㎍/ml EGCG resulted in 70% inhibition of the p44^(mapk)/p42^(mapk) phosphorylation. Stimulation of the cells with PDGF-BB caused a maximal increase in [Ca^(2+)]_(i) from 40±10(basal value) to 145±15nM(mean±SD, n=4) at 25 sec(determined by the fura-2 method). Preincubation of VSMCs for 24 h with EGCG resulted in a complete inhibition of the PDGF-BB-induced increase in [Ca^(2+)]_(i). These results demonstrate that EGCG may exert its anti-proliferative effects via inhibition of the PDGF-BB-induced intracellular signaling events like stimulation of the p44^(mapk)/p42^(mapk) and elevation of [Ca^(2+)]_(i).