iloprost and Hypercholesterolemia

We have analyzed the extent of endothelial dysfunction in cardiac resistance vessels of hyperlipidaemic apoE-/- mice and explored whether NO and/or prostacyclin dependent pathways are involved.. Coronary resistance was measured in isolated perfused hearts from WT and apoE-/- mice. To discriminate between NO and PGI(2)-dependent flow responses, we made use of the finding that acetylcholine (ACh) predominantly activates the prostaglandin pathway whereas bradykinin (Bk) mainly acts via NO in murine cardiac resistance vessels.. Basal coronary flow as well as the ACh induced vasodilation (0.1-1 microM) were not different between WT and apoE-/- hearts (flow increase+100%). Similarly, vasodilation in response to the prostacyclin mimetic iloprost reached the same levels. In contrast, the Bk-stimulated [3.3 microM Bk] coronary flow was reduced from 31.6+/-4.2 in WT to 19.2+/-2.7 ml min(-1) g(-1) in apoE-/- hearts. NOS inhibition by ethylisothiourea (ETU, 10 microM) reduced basal as well as Bk-stimulated coronary flow in WT and apoE-/- hearts to the same extent. RT-PCR and Western analysis demonstrated that neither eNOS expression nor protein levels were reduced. Similarly, the flow response to the NO donor SNAP (0.3-33 microM) was not altered suggesting that soluble guanylyl cyclase was not affected. Intracoronary application of superoxide dismutase augmented the Bk-induced vasodilation of apoE-/- hearts almost back to WT levels (26.6+/-3.3 ml min(-1) g(-1)). In line with this finding the NADPH induced O(2)(-) formation was enhanced in cardiac extracts from apoE-/- hearts.. apoE-/- hearts develop a hemodynamically relevant endothelial dysfunction at the level of coronary resistance vessels most likely via inactivation of bioavailable NO by superoxide anions. The function of the prostacyclin system is not altered.

Topics: Acetylcholine; Adenosine; Analysis of Variance; Animals; Apolipoproteins E; Bradykinin; Cholesterol, LDL; Coronary Vessels; Cyclooxygenase Inhibitors; Diclofenac; Dose-Response Relationship, Drug; Endothelium, Vascular; Enzyme Inhibitors; Epoprostenol; Hypercholesterolemia; Iloprost; Mice; Mice, Inbred C57BL; Mice, Mutant Strains; Nitric Oxide; Nitric Oxide Synthase; omega-N-Methylarginine; Perfusion; Superoxide Dismutase; Vascular Resistance; Vasodilator Agents

This study determines the antiplatelet effects of oral ticlopidine (100 mg/kg x day) in experimental hypercholesterolemia. Rabbits were fed either a standard diet or a cholesterol-enriched diet (0.5% for 3 months, 1% for 1 month). In normocholesterolemic controls ADP-, but not collagen-induced platelet aggregation was inhibited by ticlopidine treatment. This was accompanied by a significantly enhanced inhibition of ADP-induced platelet aggregation and stimulation of cyclic AMP accumulation by iloprost. Hypercholesterolemia considerably attenuated the inhibition of ADP-induced aggregation by ticlopidine but did not change its effect on the iloprost-induced inhibition of platelet function and cyclic AMP formation. ADP-induced platelet-derived thromboxane formation was considerably greater in hypercholesterolemic rabbits and not reduced by ticlopidine. Ticlopidine did also not significantly influence the extent and severity of atherosclerotic plaque formation although a tendency for improvement was observed in a subgroup of animals. The data suggest that hypercholesterolemia attenuates the inhibitory effect of ticlopidine on ADP-induced platelet aggregation. This might be related to the stimulation of thromboxane formation by ADP in hypercholesterolemia. The maintained protection from ADP-induced inhibition of cAMP accumulation suggests a minor role of this mechanism in the progression of hypercholesterolemia-induced vessel disease in this model.

Topics: Adenosine Diphosphate; Animals; Aortic Diseases; Arteriosclerosis; Biotransformation; Cholesterol, Dietary; Collagen; Cyclic AMP; Hypercholesterolemia; Iloprost; Indomethacin; Liver; Male; Platelet Aggregation; Rabbits; Signal Transduction; Thromboxane B2; Ticlopidine

Among other mediators, platelet-derived serotonin (5-HT) may contribute to thromboembolic complications of atherosclerosis. We determined whether long-term oral treatment with the 5-HT2 antagonist naftidrofuryl (NAF, 50 mg/kg daily for 12 weeks) alters platelet function in cholesterol-fed (1%) rabbits. Hypercholesterolemia resulted in marked platelet hyperreactivity to collagen and ADP. This included increased aggregation, ATP secretion, and thromboxane formation; e.g., collagen-induced (1.2 micrograms/ml) platelet aggregation was stimulated to 210 +/- 10 mm/30 s in cholesterol-fed rabbits as compared with 108 +/- 9 mm/30 s in rabbits fed a standard diet (p < 0.05). Inhibition of ADP-stimulated platelet activation by the prostacyclin mimetic iloprost was significantly reduced. NAF did not reduce plasma cholesterol in hypercholesterolemia, but prevented enhanced platelet aggregation, thromboxane formation, and ATP secretion. NAF treatment significantly reduced collagen-induced (1.2 micrograms/ml) aggregation to 81 +/- 20 mm/30 s in these animals (p < 0.05). NAF also inhibited functional desensitization of platelets to iloprost, but did not alter the impaired binding of [3H]iloprost to platelet membranes in hypercholesterolemic animals. NAF also did not change any of these parameters in normocholesterolemic rabbits. These data suggest beneficial effects of NAF on platelet hyperreactivity in experimental hypercholesterolemia which may also be relevant for its clinical use.

Topics: Adenosine Diphosphate; Adenosine Triphosphate; Animals; Blood Platelets; Cholesterol; Collagen; Diet; Epoprostenol; Humans; Hypercholesterolemia; Iloprost; In Vitro Techniques; Male; Nafronyl; Platelet Aggregation; Platelet Aggregation Inhibitors; Rabbits; Thromboxanes

Platelets from type IIa hypercholesterolemic subjects have been previously shown to be less sensitive than normal platelets to the antiaggregatory effect of PGI2. We demonstrate here that these platelets display a reduced response to iloprost, a chemically stable analogue of PGI2, as well. In fact, the concentration of iloprost yielding 50% inhibition of PRP aggregation was higher in type IIa patients (0.77 +/- 0.08 nM) than in controls (0.51 +/- 0.06 nM, P less than 0.01). In addition, an inverse relationship existed between the threshold aggregatory concentration for collagen and the concentration of iloprost yielding 50% inhibition of PRP aggregation, both in type IIa and normal individuals. In order to elucidate the mechanism of the different sensitivity of platelets to prostacyclin and its analogue, we characterized the binding of 3H-iloprost to platelet rich plasma from single individuals. The binding was rapid, reversible, inhibited by iloprost, PGI2 and PGE1 (Kd = 50.7; 346.2 and 7500 nM, respectively); no heterogeneity of sites could be demonstrated in the PRP from a single individual. When binding studies were carried out in PRP of type IIa patients and controls, it appeared that the amount of 3H-iloprost bound at a fixed (300 nM) concentration was significantly lower in platelets from type IIa individuals (0.94 +/- 0.17 vs. 1.77 +/- 0.27 fmol/10(6) platelets, for patients and controls, respectively). It is concluded that such difference in binding might represent the mechanism underlying the reduced response to PGI2 and iloprost observed in platelets from type IIa patients.

Topics: Adult; Binding Sites; Blood Platelets; Epoprostenol; Female; Humans; Hypercholesterolemia; Iloprost; Male; Middle Aged; Platelet Aggregation