Biomedical subjects
Publications and source records attributed to C S Cierniewski.
The cytotoxicity of anti-PAI-5 hexadecanucleotides (phosphodiesters and phosphorothioates) and their conjugates with lipophilic alcohols was tested in EA.hy 926 hybrid endothelial cells. Some cytotoxicity was found for cholesteryl and bornyl conjugates at concentrations higher than those used for antisense inhibition experiments.
Parameters of fibrinogen binding with blood platelets (number of receptors and their affinity) have been studied in patients with ischemic stroke. Due to the increased platelet ability to aggregate in the ischemic diseases such studies seem helpful. The studies involved 13 patients with ischemic stroke. Blood platelets collected from younger patients (under 50 years) possessed significantly higher number of receptors binding fibrinogen than blood platelets of healthy individuals (p less than 0.02). These receptors significantly more strongly bound ligand than those in the control group (p less than 0.05), and in the group of older patients with stroke (less than 0.05). Fibrinogen binding to blood platelets in patients over 50 years of age did not differ significantly from that in the control group. These results may indicate, that the increased platelet aggregation might be a significant pathogenic factor of the stroke in younger patients.
Recently we have described a dependence of platelet disability in thrombosis upon the progression in renal failure and an elevated level of RGDS-containing degradation products in uremic plasma, which is also correlated with progression in renal failure. Based on fluorescence techniques, our present investigations concerned possible changes in platelet membrane fluidity and intraplatelet calcium homeostasis in uremic platelets. Washed platelets loaded with DPH or with Fura-2 were examined with LS-50 luminescence spectrometer. Light anisotropy of DPH measured at 37 degrees C was significantly higher in control platelet membranes than in uremic ones. It can be considered as more fluidic membranes of uremic platelets. No difference between the basal intraplatelet calcium level was found for uremic and control platelets, but in the presence of 5 mM EGTA, the basal level was reduced significantly deeper in uremic platelets. Activation of platelets by both ADP (12.5 microM) and thrombin (0.1 U/ml) resulted in rapid increase in the intraplatelet calcium level in the examined platelets, but this increase was significantly higher for control platelets. The results indicate an abnormal intracellular calcium homeostasis in uremic platelets, which is associated with an increased fluidity of platelet membranes in uremia.
Verapamil is widely used in the treatment of patients with coronary artery disease. The effect of verapamil on vascular smooth muscle cells is well documented. This effect is mediated by the inhibition of calcium fluxes across plasma membranes. Some data suggest that verapamil may affect platelet functions in thrombosis, but those observations were made for much higher verapamil concentration than could be achieved in vivo. Our current investigations are focused on an influence of low doses of verapamil (0.1-1.0 microM) on platelet response to ADP. We have found that verapamil at concentration of 0.1 microM can inhibit platelet aggregation (by 10%) evoked in PRP by 1.0-1.5 microM ADP. Moreover, the inhibitory effect is potentiated by prolonged time of platelet preincubation with verapamil. On the other hand, we have found a significant reduction in the number of fibrinogen receptors exposed on the platelet surface of patients (n = 21) treated with therapeutic doses (240 mg/day) of verapamil during two weeks of drug administration. The mean number of exposed receptors was reduced from 75,000 to 40,000 per platelet, with significance p < 0.0001. In vitro platelet preincubation with verapamil, even in much higher concentrations, did not affect fibrinogen binding to ADP activated platelets. It suggests, that in vitro exposure of platelets to verapamil for a short time has no effect on the expression of fibrinogen receptors on platelets, but prolonged in vivo interaction of this drug with platelets results in reduction of the fibrinogen receptor exposition. Thus, observed inhibition of platelet aggregation does not relay on a simple reduction of the number of exposed receptors, but intraplatelet signalling has to be affected. In fact, we have observed, in platelets pretreated with low doses of verapamil, significantly reduced release of calcium ions upon activation by ADP, whereas the calcium influx under such conditions does not seem to be affected.