Differential effects of homocysteine on porcine endothelial and vascular smooth muscle cells

Abstract

High concentrations of homocysteine damage endothelial cells and lower concentrations increase vascular smooth muscle cell (VSNIC) growth. This study investigated the effects of various concentrations of homocysteinc on endothelial cells (VECs) and VSMCs in terms of cell survival, proliferation, and function. VECs and VSMCs from porcine thoracic aorta were studied. These cells were exposed to homocysteine in concentrations of 20 muM, 400 muM, and 1 mM every 8 h for 24 h, and its effect on cell survival, proliferation, and function were studied using methylthiazoletetrazolium assay, [H-3]-thymidine incorporation test, and 6-keto-prostaglandin F-1alpha enzymelinked immunosorbent assay for VECs, and platelet-derived growth factor (PDGF) enzyme-linked immunosorbent assay for VSMCs, respectively. In VECs, 20 muM of homocysteine reduced the viable cell count to 95 31%, 400 muM reduced it to 89 +/- 35%, 1,000 muM reduced it to *58 +/- 29% (control = 100 +/- 30%, n = 18, *p < 0.05). In VSMCs, 20 muM of homocysteine slightly increased the viable cell count to 106 30%, but there was no statistical significance; 400 muM of homocysteine reduced the viable cell count to *74 +/- 29%, 1,000 muM to *50 +/- 24% (control = 100 +/- 28%, n = 18, *p < 0.05). In VECs, 20 muM of homocysteine reduced [H-3]-thymidine uptake by 98 +/- 14%, 400 muM reduced it by *82 +/- 17%, 1,000 muM reduced it by *66 +/- 17% (control = 100 +/- 12, n = 6, *p < 0.05), respectively. But in VSMCs, 20 muM of homocysteine significantly increased [3 H]-thymidine uptake (*131 +/- 16%), and thereafter, homocysteine decreased VSMCs [3 H]-thymidine uptake, 400 muM by *24 +/- 7%, 1,000 muM by *29 +/- 10% (control = 100 16, n = 6, *p < 0.05), respectively. Homocysteine decreased VEC prostacyclin secretion in a dose-dependent manner, 20 muM by 105 +/- 0.65 pg/100 mul, 400 muM by *100 +/- 2.37 pgl100 mu1, 1,000 muM by *93 +/- 2.54 pg/100 mul (control = 107 +/- 1.26 pg/100 mul, n = 6, *p = 0.007). In VSMCs, 20 muM of homocysteine slightly increased PDGF secretion by 62.2 +/- 20.7 pg/100 mul, but there was little statistical significance (p = 0.13); 400 muM of homocysteine reduced PDGF secretion by *28.9 +/- 10.7 pg/100 mul, and 1,000 muM reduced it by *21.3 +/- 4.7 pg/100 mul (control = 54.5 +/- 9.3 pg/100 mul, n = 6, *p < 0.05). High concentrations of homocysteine damaged both VECs and VSMCs with respect to cell survival, proliferation, and function. By increasing exposure to homocysteine, it was shown that physiologic high concentrations of homocysteine enhanced VSMC proliferation. Key Words: Endothelial cell-Homocysteine-Platelet-derived growth factor-Prostacyclin-Vascular smooth muscle cell.