Background: Enhanced vascular smooth muscle cell (VSMC) growth is one hallmark of atherosclerosis. One mechanism responsible for stimulating arterial smooth muscle cell growth is the release of growth factors from platelets aggregating at endothelial lesions. Since in end-stage renal failure (ESRF) atherogenesis is markedly accelerated, the release of VSMC growth factors on aggregation of platelets from hemodialysis patients, ESRF patients in the predialysis stage, and healthy subjects was examined.
Methods: Platelets were activated by thrombin, and the supernatant was tested for growth stimulation in VSMCs from rat aorta. The cell proliferation rate was determined by [(3)H]-thymidine incorporation in VSMCs. The diadenosine polyphosphate (Ap(n)A with N = 3 to 6) content in the supernatant and in intact platelets was determined using a chromatographic assay established on the basis of affinity- and reversed-phase chromatographic methods.
Results: The thrombin-activated platelet supernatant from hemodialysis patients (N = 15) increased the [(3)H]-thymidine incorporation rate in VSMC s in comparison to the supernatant of healthy control subjects (N = 17, counts/supernatant of 10(6) stimulated platelets +/- SEM, 604 +/- 71 vs. 364 +/- 45, P < 0.05). The addition of the selective P2-receptor blocker pyridoxal-phosphate-6-azophenyl-2,4-disulfonic acid to supernatants inhibited the stimulatory effects of Ap(n)A on the growth of vascular smooth muscle cells (219 +/- 53 vs. 156 +/- 71 counts/supernatant of 106 stimulated platelets +/- SEM). The Ap(n)A (N = 3 to 6) amount of thrombin-activated platelet supernatants from hemodialysis patients was significantly higher than in platelets from 10 healthy control subjects (Ap(3)A, 119 +/- 32 vs. 12 +/- 3; Ap(4)A, 154 +/- 59 vs. 43 +/- 20; Ap(5)A, 39 +/- 14 vs. 13 +/- 6; Ap(6)A, 42 +/- 19 vs. 2 +/- 1 fg/platelet +/- SEM, each P < 0.05, N = 10). The intracellular Ap(n)A (N = 3 to 6) amount of intact platelets from hemodialysis patients (N = 61) was significantly higher than that from healthy control subjects [N = 30, Ap(n)A amount (fg/platelet +/- SEM): Ap(3)A, 366 +/- 68 vs. 14.7 +/- 1; Ap(4)A, 336 +/- 48 vs. 19 +/- 2; Ap(5)A, 227 +/- 35 vs. 10 +/- 1; Ap(6)A, 141 +/- 45 vs. 4 +/- 1; each P < 0.01].
Conclusions: The increased amount of dinucleoside polyphosphate in platelets from hemodialysis patients may be an important additional atherogenic factor.