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      The AN69 Hemofiltration Membrane Has a Decreasing Effect on the Intracellular Diadenosine Pentaphosphate Concentration of Platelets

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          Background/Aim: The biocompatibility of hemodialysis membranes has a substantial impact on the mortality of patients with end-stage renal failure. In the present study, the effects of hemodialysis on the intracellular amount of diadenosine pentaphosphate (Ap<sub>5</sub>A), a hydrophilic, anionic substance with a low molecular weight, was investigated. Methods: The intracellular Ap<sub>5</sub>A concentrations were measured before and after hemodialysis using either polyacrylonitrile (AN69; n = 10) or polysulfone (n = 23) membranes. Ap<sub>5</sub>A was isolated from platelets using affinity chromatography and reversed-phase chromatography methods. Results: The Ap<sub>5</sub>A concentrations were quantified by ultraviolet absorption at 254 nm. The Ap<sub>5</sub>A concentrations were significantly higher in platelets from the patients with end-stage renal failure as compared with the 21 healthy control subjects (136 ± 50 vs. 9 ± 6 fg/platelet; mean ± SEM, p < 0.01). Before hemodialysis, the intracellular Ap<sub>5</sub>A concentrations in platelets from 10 patients with end-stage renal failure using an AN69 membrane were not significantly different from those in platelets from 23 patients using a polysulfone membrane (93 ± 39 vs. 155 ± 70 fg/platelet). However, after a hemodialysis session, the intracellular Ap<sub>5</sub>A concentrations in platelets from patients with end-stage renal failure using an AN69 membrane were significantly lower as compared with those in platelets before hemodialysis (51 ± 18 vs. 93 ± 39 fg/platelet, p < 0.05) as well as compared with those in platelets from patients using a polysulfone membrane (51 ± 18 vs. 250 ± 59 fg/platelet, p < 0.05). Conclusions: It was found that hemofiltration by using an AN69 membrane has a direct effect on the intracellular amount of Ap<sub>5</sub>A and that changes of intracellular hydrophilic substances are dependent on the hemodialysis membrane used.

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          Diadenosine phosphates and the physiological control of blood pressure.

          Our understanding of the regulation of vascular tone has been extended since the identification of vasoactive agents such as the atrial natriuretic peptides, endothelial-derived relaxing factor and endothelin. Unidentified vasopressive agents have been found in platelets. Here we isolate these vasopressors and identify them as diadenosine pentaphosphate (AP5A) and diadenosine hexaphosphate (AP6A) by chromatography, mass spectrometry, ultraviolet spectroscopy and enzymatic cleavage. In the vasculature of isolated perfused rat kidney, both diadenosine phosphates were active at a concentration of 10(-9) M; in aortic rings, contractions were elicited at 10(-8) M. Intra-aortic injection in the rat caused a prolonged increase in blood pressure. We conclude that AP5A and AP6A may play a part in local vasoregulation and possibly in the regulation of blood pressure.
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            Increased vascular growth in hemodialysis patients induced by platelet-derived diadenosine polyphosphates.

            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. 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. 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]. The increased amount of dinucleoside polyphosphate in platelets from hemodialysis patients may be an important additional atherogenic factor.
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              Diadenosine polyphosphates as extracellular signal molecules


                Author and article information

                Kidney Blood Press Res
                Kidney and Blood Pressure Research
                S. Karger AG
                24 April 2003
                : 26
                : 1
                : 50-54
                Medizinische Klinik IV, Universitätsklinikum Benjamin Franklin, Freie Universität, Berlin, Germany
                69765 Kidney Blood Press Res 2003;26:50–54
                © 2003 S. Karger AG, Basel

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                Figures: 2, Tables: 2, References: 12, Pages: 5
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