Relationship between vessel wall 13-HODE synthesis and vessel wall thrombogenicity following injury: influence of salicylate and dipyridamole treatment

Reduced cognitive function, increased blood-brain-barrier transport and inflammatory responses, and altered brain metabolites in LDLr -/-and C57BL/6 mice fed a western diet

Recent work suggests that diet affects brain metabolism thereby impacting cognitive function. Our objective was to determine if a western diet altered brain metabolism, increased blood-brain barrier (BBB) transport and inflammation, and induced cognitive impairment in C57BL/6 (WT) mice and low-density lipoprotein receptor null (LDLr -/-) mice, a model of hyperlipidemia and cognitive decline. We show that a western diet and LDLr -/- moderately influence cognitive processes as assessed by Y-maze and radial arm water maze. Also, western diet significantly increased BBB transport, as well as microvessel factor VIII in LDLr -/- and microglia IBA1 staining in WT, both indicators of activation and neuroinflammation. Interestingly, LDLr -/- mice had a significant increase in ¹⁸F- fluorodeoxyglucose uptake irrespective of diet and brain ¹H-magnetic resonance spectroscopy showed increased lactate and lipid moieties. Metabolic assessments of whole mouse brain by GC/MS and LC/MS/MS showed that a western diet altered brain TCA cycle and β-oxidation intermediates, levels of amino acids, and complex lipid levels and elevated proinflammatory lipid mediators. Our study reveals that the western diet has multiple impacts on brain metabolism, physiology, and altered cognitive function that likely manifest via multiple cellular pathways.

Anti-platelet therapy: phosphodiesterase inhibitors

Inhibition of platelet aggregation can be achieved either by the blockade of membrane receptors or by interaction with intracellular signalling pathways. Cyclic adenosine 3',5'-monophosphate (cAMP) and cyclic guanosine 3',5'-monophosphate (cGMP) are two critical intracellular second messengers provided with strong inhibitory activity on fundamental platelet functions. Phosphodiesterases (PDEs), by catalysing the hydrolysis of cAMP and cGMP, limit the intracellular levels of cyclic nucleotides, thus regulating platelet function. The inhibition of PDEs may therefore exert a strong platelet inhibitory effect. Platelets possess three PDE isoforms (PDE2, PDE3 and PDE5), with different selectivity for cAMP and cGMP. Several nonselective or isoenzyme-selective PDE inhibitors have been developed, and some of them have entered clinical use as antiplatelet agents. This review focuses on the effect of PDE2, PDE3 and PDE5 inhibitors on platelet function and on the evidence for an antithrombotic action of some of them, and in particular of dipyridamole and cilostazol.

Hydroxyoctadecadienoic acids: novel regulators of macrophage differentiation and atherogenesis

Hydroxyoctadecadienoic acids (HODEs) are stable oxidation products of linoleic acid, the generation of which is increased where oxidative stress is increased, such as in diabetes. In early atherosclerosis, 13-HODE is generated in macrophages by 15-lipoxygenase-1. This enhances protective mechanisms through peroxisome proliferator-activated receptor (PPAR)-g activation leading to increased clearance of lipid and lipid-laden cells from the arterial wall. In later atherosclerosis, both 9-HODE and 13-HODE are generated nonenzymatically. At this stage, early protective mechanisms are overwhelmed and pro-inflammatory effects of 9-HODE, acting through the receptor GPR132, and increased apoptosis predominate leading to a fragile, acellular plaque. Increased HODE levels thus contribute to atherosclerosis progression and the risk of clinical events such as myocardial infarction or stroke. Better understanding of the role of HODEs may lead to new pharmacologic approaches to modulate their production or action, and therefore lessen the burden of atherosclerotic disease in high-risk patients.

Antithrombotic drugs for secondary stroke prophylaxis

Stroke is the third most common cause of adult mortality in the United States. Antithrombotic agents form the mainstay of stroke prevention. Aspirin produces a modest reduction in the risk of second stroke and is widely recommended for initial therapy. The thienopyridines ticlopidine and clopidogrel are alternatives for secondary prevention in patients who do not respond to or cannot take aspirin. They are no more effective than aspirin and have been associated with thrombotic thrombocytopenic purpura. The combination of aspirin and extended-release dipyridamole has several mechanisms of action and an additive effect on reducing stroke risk compared with either agent alone. A 2-fold increase in risk reduction and favorable safety profile suggest that the combination can serve as first-line prophylaxis against a second stroke.

Dipyridamole inhibits PDGF- and bFGF-induced vascular smooth muscle cell proliferation

Dipyridamole is the only pharmacologic agent demonstrated to reduce polytetrafluoroethylene (PTFE) graft occlusion in hemodialysis patients. However, the mechanism of action of dipyridamole in preventing graft occlusion is unknown. The purpose of this study was to examine the direct effects of dipyridamole on both platelet-derived growth factor (PDGF) and basic fibroblast growth factor (bFGF)-induced vascular smooth muscle cell (VSMC) proliferation. Human aortic smooth muscle cells were grown to confluence in 96 well plates. A total of 5 x 10(-6) molar dipyridamole, PDGF 10 ng/ml, or bFGF 10 ng/ml were added to appropriate wells at the start of each experiment. Cell proliferation at 48 hours was determined using tritiated thymidine uptake. Intracellular cyclic AMP (cAMP) was measured using a competitive enzyme immunoassay. Treatment of VSMC with 5 microM dipyridamole dramatically reduced basal proliferation rates compared to controls [5229 +/- 1131 counts per minute (CPM) versus 387 +/- 68 CPM, P < 0.001]. Treatment with dipyridamole also reduced PDGF-stimulated VSMC proliferation (7311 +/- 1655 CPM vs. 593 +/- 110 CPM, P < 0.001) as well as the response to bFGF (5632 +/- 1270 CPM vs. 310 +/- 31 CPM, P < 0.001). Treatment of VSMC with either 5 or 20 microM dipyridamole did not change intracellular cAMP levels. Furthermore, the addition of dibutyryl cAMP to VSMC demonstrated only a modest inhibitory effect on proliferation. We conclude that dipyridamole inhibits both PDGF- and bFGF-stimulated VSMC proliferation. The effects of dipyridamole on VSMC proliferation do not appear to be entirely mediated by changes in intracellular cAMP concentrations. The direct effect of dipyridamole on VSMC proliferation may account for its efficacy in reducing PTFE graft thrombosis in hemodialysis patients.

Mechanisms involved in the early interaction between HeLa cells, platelets and endothelial cells in vitro under the influence of thrombin. Effects of acetylsalicylic acid and Na-salicylate

The aim of the study was to obtain more information about the mechanisms involved in the initial adhesion of tumour cells to endothelial cell during metastasis. In a previous paper, we found that addition of both platelets and thrombin increased the adhesion of tumour cells to cultured endothelial cells within 15 min, compared to when either one or both of the ingredients were absent. In the present study, HeLa cells, prelabelled with radioactive 51Cr, human platelets, and thrombin, were added to the medium in dishes of endothelial cells. The dishes were then shaken for 15 min at 37 degrees C. Scanning and transmission electron micrographs showed HeLa cells adhering to the endothelium either together with platelets or without them. In other experiments, the endothelium was pretreated for 30 min with either of the following: 0.5 mM or 0.1 mM acetylsalicylic acid (ASA); 0.5 mM or 0.1 mM Na-salicylate (NaS). Pretreatment of the endothelium with 0.5 mM ASA significantly increased the percentage of adherent tumour cells, while 0.1 mM ASA and the two concentrations of NaS caused only minor changes. In addition, the ASA-treatment caused more HeLa cells to adhere without platelets while NaS-treatment caused more HeLa cells to adhere together with platelets. Release of 51Cr from HeLa cells during the experimental period was also measured; the addition of thrombin and platelets did not change the 51Cr release significantly. In separate experiments, HeLa cells and platelets were mixed without the presence of endothelial cells. Transmission electron micrographs showed that in the absence of thrombin, mixed HeLa cells and platelets did not react with each other; when thrombin was added they formed co-aggregates. In conclusion, we show that in our experimental model HeLa cells adhere to the endothelium in two ways, both with and without platelets. The production of prostacyclin in the endothelial cells has an inhibitory effect on tumour cell adhesion. Without thrombin, the HeLa cells are not capable of activating platelets.

Aspirin enhances platelet-derived growth factor-induced vascular smooth muscle cell proliferation

PURPOSE

Aspirin is frequently used after vascular reconstruction to pharmacologically prevent graft occlusion and to suppress the development of myointimal hyperplasia in vascular surgery, but its efficacy is controversial. The purpose of this study was to examine the direct effects of aspirin on platelet-derived growth factor (PDGF)-induced vascular smooth muscle cell (SMC) proliferation.

METHODS

Human aortic SMCs were grown to confluence in 96 well plates. 3 x 10(-5) mol/L aspirin was added 24 hours previously and PDGF 10 ng/ml at the beginning of each experiment. Cell proliferation at 48 hours was determined using tritiated thymidine uptake. Supernatant 12-L-hydroxy 5,8,10,14-eicosatetraenoic acid (12-HETE) and prostaglandin E2 (PGE2) were measured by competitive enzyme immunoassay.

RESULTS

Aspirin did not change vascular SMC proliferation rates relative to controls (4665 +/- 181 counts per minute [CPM] vs 4749 +/- 155 CPM). However, aspirin pretreatment of PDGF-stimulated vascular SMCs increased proliferation (9408 +/- 237 CPM vs 7283 +/- 283 CPM; p < 0.001). 5,8,10,14-eicosatriynoic acid, a 12-lipoxygenase inhibitor, decreased basal (2037 +/- 181 CPM vs 2306 +/- 158 CPM; p < 0.05) and PDGF-stimulated vascular SMC proliferation (4909 +/- 1089 CPM vs 4310 +/- 1022 CPM; p < 0.001). Aspirin increased supernatant 12-HETE levels and decreased PGE2 levels in both basal and PDGF-stimulated cell cultures.

CONCLUSIONS

Aspirin enhances PDGF-stimulated vascular SMC proliferation. The effects of aspirin on vascular SMC proliferation may be mediated by changes in vascular SMC arachidonic acid metabolism.

Anti-platelet therapy in graft thrombosis: results of a prospective, randomized, double-blind study

Hemodialysis (HD) vascular access thrombosis remains a major cause of morbidity, accounting for 17.4% of all HD patient hospital admissions in 1986. We initiated this prospective, randomized, double-blind, placebo-controlled, parallel group study to examine if dipyridamole and/or aspirin decreased the rate of thrombosis of expanded polytetrafluoroethylene (ePTFE) grafts in HD patients. Two patient groups were studied: Type I--with a new ePTFE graft; and Type II--with thrombectomy and/or revision of a previously placed ePTFE graft. One hundred and seven patients were followed for 18 months or until the first thrombotic episode. Actuarial analysis of Type I patients showed cumulative thrombosis rates (mean +/- SEM) of 21 +/- 9% on dipyridamole alone, compared with 25 +/- 11% on dipyridamole and aspirin combination, 42 +/- 13% on placebo, and 80 +/- 12% on aspirin alone. The relative risk of thrombosis with dipyridamole was 0.35 (P = 0.02) and that for aspirin was 1.99 (P = 0.18). In Type II patients, the rate of thrombosis was high in all study drug and placebo groups (overall 78% thrombosis) and actuarial analysis was not carried out because of the small number of patients enrolled. We conclude that dipyridamole is beneficial in patients with new ePTFE grafts and that aspirin does not improve the risk of thrombosis in ePTFE grafts. Neither dipyridamole nor aspirin has any beneficial effect in patients with prior thrombosis of ePTFE grafts.

Interleukin 1-induced cancer cell/endothelial cell adhesion in vitro and its relationship to metastasis in vivo: role of vessel wall 13-HODE synthesis and integrin expression

Previously, we have demonstrated that stimulation of endothelial cells (ECs) with interleukin-1 alpha (IL-1 alpha) enhances the synthesis and expression of the vitronectin receptor (VnR), promotes VnR-dependent adhesion of human A549 adenocarcinoma cells to ECs, and is associated with decreased EC 13-hydroxyoctadecadienoic acid (13-HODE) synthesis in vitro. To determine whether these observations are relevant in vivo, we examined the acute retention and subsequent metastasis of intravenously-injected B16F10 melanoma cells in murine lungs, in relation to vessel wall 13-HODE. In C57BL/6 mice pretreated with IL-1 alpha, vessel wall 13-HODE was decreased and B16F10 lung entrapment and metastasis were increased. The latter two events were blocked by pretreating the animals with the GRGDS peptide. These data suggest a relationship between vessel wall 13-HODE synthesis, adhesion molecule expression, and adhesion of B16F10 cells to the endothelium.

Formation of prostanoids and hydroxy fatty acids by stimulated peritoneal mast cells: role of the dietary fat type in rat

To study the influence of membrane fatty acid composition on the formation of prostanoids and hydroxy fatty acids by rat peritoneal mast cells (MC), animals were fed three different types of fatty acids: mackerel oil (MO), abundant in n-3 fatty acids; sunflower seed oil (SO), rich in linoleic acid; and hydrogenated coconut oil (HCO), mainly containing saturated fatty acids. The presence of n-3 fatty acids in the diet resulted in the incorporation of 20:5(n-3), 22:5(n-3) and 22:6(n-3) in MC phospholipids. A decrease of arachidonic acid, 20:4(n-6), was observed in MC-phospholipids of the MO-fed animals. Furthermore, increasing the relative amounts of 18:2(n-6) in the diet (SO group) led to an increased incorporation of linoleic acid, 18:2(n-6) in MC phospholipids when compared to both other dietary groups. The changes in MC phospholipid fatty acid composition were (partly) reflected in the formation of prostanoids and hydroxy fatty acids upon stimulation with the calcium ionophore A23187. The decrease in arachidonic acid content in MC phospholipids of MO-fed rats resulted in a decreased formation of PGD2 when compared to both other groups. Also, the increased amounts of 18:2(n-6) in MC phospholipids of SO-fed rats resulted in an increased formation of 9- and 13-HODE upon stimulation. The results show that modifications in the fatty acid composition of the diet influences MC membrane fatty acid composition which ultimately results in changes in prostanoid and hydroxy fatty acid synthesis by MC upon stimulation with the calcium ionophore A23187.

1-Deamino-8 D-arginine vasopressin decreases the production of 13-hydroxyoctadecadienoic acid by endothelial cells

1-Deamino-8 D-arginine vasopressin (DDAVP) has been used effectively to normalize the bleeding time in various hemostatic disorders. In von Willebrand disease the reduction in bleeding time is due to the preferential release of large multimers of von Willebrand factor from endothelial cells. However, since the bleeding time correction in patients with uremia and liver disease is independent of the release of von Willebrand antigen and activity, other mechanisms of action of DDAVP need to be considered. Endothelial cells generate several thromborepellant factors including 13-hydroxyoctadecadienoic acid (13-HODE), an inhibitor of platelet adhesion to subendothelium. Using cultured fetal bovine aortic endothelial cells (FBAECs), we have investigated whether DDAVP modulates the production of 13-HODE. We have demonstrated that 14C-linoleic acid labeled FBAECs release several oxygenated derivatives of linoleic acid following a 120 min incubation in the presence of serum. One of these products was identified by chromatographic procedures as 13-HODE. The production of 13-HODE was decreased significantly by DDAVP (1-100 ng/ml) with maximal reduction (approx. 25%) seen at 1 ng/ml of DDAVP. While vehicle treated control FBAECs generated 6780 +/- 690 cpm of 13-HODE per 10(6) cells (mean +/- SE, n = 8), DDAVP treated FBAECs produced 4950 +/- 310 (P < 0.01), 5390 +/- 390 (P < 0.01), and 5720 +/- 410 cpm (P < 0.05) of 13-HODE at 1, 10, and 100 ng/ml DDAVP respectively. Our findings of a decrease in 13-HODE would explain the previously observed morphologic changes of increased platelet adhesion to subendothelium following DDAVP infusion and contributes to our understanding of the mode of action of this therapeutic agent in hemostatic disorders.

Dipyridamole induces changes in the thrombogenic properties of extracellular matrix generated by endothelial cells in culture

Dipyridamole (DIP) is a drug widely used as an antiplatelet agent, which also has effects on endothelial cells. In this study, the effects of treating confluent endothelial cell monolayers (EC) with DIP on EC viability (trypan blue exclusion test) and metabolic activity (3H-thymidine incorporation) were examined. Platelet reactivity of the extracellular matrix (ECM) produced by untreated and DIP-treated ECs was determined morphometrically by a perfusion technique. Levels of ECM-associated von Willebrand factor (vWF) and fibronectin (FN) were also quantified (ELISA). The present results indicate that treatment of EC with 10 microM DIP did not reduce EC viability but that the incorporation of labelled nucleotides was significantly decreased (p less than 0.01). Platelet deposition onto the ECM generated by DIP-treated cells, perfused at a shear rate of 1300 sec-1, differed significantly with respect to controls (p less than 0.05), and platelet adhesion was also reduced (25% less, p less than 0.05). This effect was shear rate dependent, as no differences were noted when the ECMs were perfused at 300 sec-1 shear rate. Levels of VWF and FN associated with ECM remained unchanged with respect to controls. These results suggest that treatment with DIP alters EC metabolic activity, which in turn, influences the reactivity of the ECM generated by treated cells.

Dipyridamole--evaluation of an established antithrombotic drug in view of modern concepts of blood cell-vessel wall interactions

The effect of dipyridamole on the local antithrombotic activities of endothelium has been evaluated. Human whole blood was allowed to flow over an endothelial cell-derived extracellular matrix partially covered by human endothelial cells. Half-maximal suppression of platelet aggregate formation occurred with approximately 5 microM dipyridamole. Similarly, a pronounced inhibition of thrombus formation was observed by in vivo microscopy and computer-assisted morphometric analysis, after oral treatment of non-anesthetized hamsters with dipyridamole, 5 mg/kg. This strong suppression of thrombus formation was maintained in animals on a long-term cholesterol-supplemented diet. The antithrombotic potential of dipyridamole has been clearly demonstrated, both in vitro and in vivo using these more complex approaches employing quantitative microscopy.