Enhancement of human neutrophil function by platelets: effects of indomethacin

N-Benzyl-2-chloroindole-3-carboxylic acids as potential anti-inflammatory agents. Synthesis and screening for the effects on human neutrophil functions and on COX1/COX2 activity

The synthesis of N-benzyl-2-chloroindole-3-carboxylic acids related to indomethacin is reported. These compounds were tested on in vitro human neutrophil activation. Some of them, more soluble in water, were tested to define the influence on prostaglandin biosynthesis via inhibition of cyclooxygenases (COX1 and COX2) by a chemiluminescent method suitable for fast screening. Several derivatives showed inhibitory effects and in some cases were more active than the parent compound.

Selectin blockade reduces neutrophil interaction with platelets at the site of deep arterial injury by angioplasty in pigs

The adhesion of neutrophils to damaged arterial surfaces is increased in the presence of platelets by a mechanism implicating platelet P-selectin. Such interactions may enhance thrombus formation and the vascular response to injury. In this study, we investigated the effects of a selectin blocker (CY-1503), an analogue of sialyl Lewisx, on platelet and neutrophil interactions after arterial injury produced by angioplasty in pigs.51Cr-platelet deposition and 111In-neutrophil adhesion were quantified on intact, mildly and deeply injured carotid arterial segments, produced by balloon dilation, in control (saline, n=8) and treated (CY-1503, 15 mg/kg IV, n=7) pigs. The hematological parameters, the aggregation of whole blood in response to adenosine diphosphate, and the activating clotting time, as well as the heart rate and mean arterial blood pressure, were similar among groups and were not influenced significantly by CY-1503. The level of platelet and neutrophil adhesion increased significantly with the severity of arterial injury but was not influenced by CY-1503 on intact and mildly injured arterial segments. However, at the site of deep arterial injury, CY-1503 treatment was associated with a 58% reduction (P<0.01) in neutrophil adhesion, from 446.7+/-72.6x10(3) neutrophils/cm2 in the control group to 186.8+/-38.7x10(3) neutrophils/cm2 in the CY-1503-treated group, whereas platelet deposition remained unchanged (43.4+/-15.6x10(6) platelets/cm2 versus 50.1+/-12.2x10(6) platelets/cm2 in the control group). In in vitro adhesion experiments, using isolated platelet and neutrophil suspensions, we found that CY-1503 interfered with the adhesion of neutrophils to damaged arterial surfaces only in the presence of platelets. In contact with thrombogenic arterial surfaces, adherent and activated platelets supports neutrophil adhesion at the site of deep injury by an adhesive interaction involving neutrophil sialyl Lewisx. The inhibitory effect of CY-1503 on neutrophil interaction with adherent platelets may be clinically relevant in patients undergoing percutaneous transluminal coronary angioplasty where platelet and neutrophil interactions may enhance the acute and chronic arterial response to injury.

Importance of platelets in neutrophil adhesion and vasoconstriction after deep carotid arterial injury by angioplasty in pigs

In previous studies we have shown that platelets can support neutrophil adhesion to the injured vessel wall in vitro and that neutrophils contribute to vascular tone regulation after arterial injury in vivo. In this study, we investigated the implication of platelets in neutrophil adhesion and the vasomotor response to arterial injury in vivo. 111In-labeled neutrophil adhesion and angiographic vasoconstriction were quantified after deep carotid arterial injury by balloon angioplasty in normal (n = 8), thrombocytopenic (n = 7), and aspirin-treated (2 mg/kg IV, n = 7) pigs. Thrombocytopenia was produced by a polyclonal antiplatelet serum that depleted circulating platelet count by 84% without influencing neutrophil count. In the control animals, neutrophil adhesion (x 10(4)/cm2) at the site of deep arterial injury averaged 26.8 +/- 4.0 and decreased significantly to 11.5 +/- 2.3 and 11.2 +/- 2.4 in the thrombocytopenic and aspirin groups, respectively. The degree of vasconstriction was also reduced significantly, from 55.5 +/- 3.8% in the control group to 31.4 +/- 6.2% after platelet depletion and to 23.6 +/- 4.5% in the aspirin-treated group. Neutrophil adhesion to intact noninjured adjacent arterial segments was low in all groups and was not affected by the antiplatelet serum or by aspirin. In in vitro superfusion flow chambers, neutrophil adhesion to damaged arterial segments increased in the presence of platelets in a concentration-dependent manner and was not influenced by the antiplatelet serum. This study demonstrates that platelets can modulate neutrophil adhesion to the deeply injured arterial wall and that both elements may influence the degree of postangioplasty vasoconstriction in vivo.

Bisaramil and antiarrhythmics as inhibitors of free radical generation

The aim of this study was to investigate the effect of bisaramil--an antiarrhythmic drug under clinical trials-on free radical generation of isolated polymorph neutrophil granulocytes (PMN) and furthermore to compare its activity to that of well-known antiarrhythmics which have different modes of action. PMNs were isolated from healthy beagle dogs, and superoxide radical generation was induced by phorbol-myristate-acetate. Stimulated free radical generation capacity of PMNs and the time lag necessary for the initiation of free radical production were measured. All compounds were used at the concentrations of 10, 25, 50, 75, 100 micrograms ml-1. None of the antiarrhythmics stimulated by itself the free radical generation. Bisaramil exerted concentration dependent inhibitory effect on PMA-stimulated free radical generation and prolonged the time lag concentration dependently. At the investigated concentration range of antiarrhythmics only propafenon, mexiletine and diltiazem showed similar activity to bisaramil, but clear concentration dependency could not be seen in any of the cases. According to the results of this study inhibition of the stimulated free radical production of isolated PMNs cannot be closely connected merely to either membrane stabilizing or Ca-antagonistic activity of drugs. In vitro and earlier measured in vivo inhibitory action of bisaramil on free radical generation indicate a possible cardioprotective effect existing independently from its antiarrhythmic one. This observation may be important in outlining of the clinical indication field of bisaramil, and may be useful in the treatment of reperfusional damage.

Granulocyte activation in restenosis after percutaneous transluminal coronary angioplasty

To examine whether or not granulocyte activation is involved in restenosis after percutaneous transluminal coronary angioplasty (PTCA), we prospectively followed the time course of the plasma level of granulocyte elastase, which is an index of granulocyte activation, before and after successful angioplasty in 43 consecutive patients. Restenosis was defined as a more than 50% loss of the initial gain in the coronary diameter achieved by PTCA with more than a 50% resultant stenosis in the follow-up coronary arteriography performed 3 months after PTCA. There was no difference in the level of granulocyte elastase between the 2 groups with (n = 15) and without (n = 28) restenosis before, the day after and 1 month after PTCA. However, 3 months after PTCA, the level of granulocyte elastase was significantly higher in the group with restenosis than in that without restenosis (171 +/- 13 vs 147 +/- 6 mg/l, P < 0.05). The level of granulocyte elastase at 3 months after PTCA also correlated significantly with the percent luminal stenosis at the angioplasty site (P < 0.05). These results suggest that granulocyte activation may be involved in restenosis after PTCA.

Effects of aspirin on platelet-neutrophil interactions. Role of nitric oxide and endothelin-1

BACKGROUND

In recent studies, the hypothesis has been raised that the mechanisms by which aspirin acts as a protective anti-ischemic agent exceed the inhibition of platelet thromboxane A2 synthesis. Recently, new data have been obtained disclosing a platelet-antiaggregating effect by neutrophils, which occurs through a nitric oxide (NO)/cGMP-dependent pathway.

METHODS AND RESULTS

The present study, using platelets and neutrophils from normal subjects, was undertaken to assess the putative effect of aspirin on the neutrophil-mediated, platelet-inactivating effect. Aspirin facilitated the inhibitory effect of neutrophils on platelet activation by thrombin, ADP, or epinephrine. This effect was equally evident in vitro and in blood samples of normal individuals taking aspirin. A significant stimulation of NO-mediated mechanisms in the presence of aspirin was disclosed by different methods, as follows: (1) the increased metabolism of arginine to citrulline, (2) the increase of cGMP in the platelet/neutrophil system, and (3) the inhibitory action of the L-arginine (L-Arg)-competitive analogue L-NMMA, which was reversed by L-Arg. The effect of aspirin appeared to be related to cyclooxygenase inhibition, since it was reproduced by using indomethacin. The vasoconstricting peptide endothelin-1 (ET-1) reversed the effect of aspirin through the endogenous production of platelet-activating factor (PAF) by neutrophils, as judged by the marked inhibitory effect of the PAF antagonist BN-52021.

CONCLUSIONS

Our results show that a significant part of the effect of aspirin on platelet activation involves a neutrophil-mediated, NO/cGMP-dependent mechanism. The presence of ET-1 counterbalances these effects of neutrophils on platelet activation, therefore acting as an indirect proactivating agent. These results add new elements for interpreting the effects of aspirin on the interactions between blood cells, with special reference to high endothelin states (for example, ischemia/reperfusion processes).

Increase of neutrophil adhesion and vasoconstriction with platelet deposition after deep arterial injury by angioplasty

Physiopathologic events after arterial injury are largely influenced by blood element reactions with the injured surface. To determine acute arterial reactivity to injury, simultaneous chromium 51-labeled platelet deposition and indium 111-labeled neutrophil adhesion were quantified at the site of different degrees of carotid arterial injury by balloon dilatation in 21 normal pigs. The degree of vasoconstriction distally to the dilated areas was also quantified angiographically. Arteries were classified histologically as (1) uninjured with intact endothelium; (2) mildly injured with endothelial desquamation; or (3) deeply injured with lesions extending beyond internal elastic lamina, exposing the media. We found that, compared to mild injury, deep injury was associated with greater platelet deposition (38.2 +/- 5.7 x 10(6)/cm2 vs 7.8 +/- 0.9 x 10(6)/cm2; p < 0.05), neutrophil adhesion (30.6 +/- 4.1 x 10(4)/cm2 vs 10.2 +/- 2.9 x 10(4)/cm2; p < 0.05), and vasoconstrictive response (45.5% +/- 3.2% vs 26.7% +/- 2.8%; p < 0.05). Although distally to both types of injuries, noninjured arterial segments with intact endothelium were thromboresistant to platelet deposition, neutrophil adhesion to intact endothelium was much higher after deep injury (2.2 +/- 0.4 x 10(4)/cm2) compared to mild injury (0.36 +/- 0.1 x 10(4)/cm2; p < 0.05). Like platelet deposition, neutrophil adhesion is influenced by the severity of arterial injury; both may therefore be implicated in thrombogenesis and vascular responsiveness after arterial injury in vivo.

Adhesion between neutrophils and platelets: a modulator of thrombotic and inflammatory events?

Recent studies have demonstrated that neutrophilic granulocytes and platelets have the capability to interact with each other. Either type of cell may release soluble factors, which either activate the other or increase its response to separate stimulating agents. Direct contact between the two types of cell generally increases the response, and it may be predicted that neutrophil-platelet adhesion will augment the potential for biochemical interaction in vivo. Adhesion may also promote immobilisation of neutrophils or platelets in thrombotic or inflamed tissue, while circulation aggregates could cause vascular blockage. Adhesion between neutrophils and platelets is dependent on P-selectin on activated platelets and sialyated carbohydrate moieties on the neutrophil, although other molecular mechanisms could stabilise the interaction. The adhesive interaction is strong enough to allow flowing neutrophils to adhere to immobilised platelets, and induce formation of aggregates in vivo. Thus, inhibition of neutrophil-platelet adhesion and modulation of their biochemical interactions could be a novel approach to treatment of thrombotic, ischaemic or inflammatory disorders.

Effects of thrombocytopenia and shear rate on neutrophil and platelet deposition on endothelial and medial arterial surfaces

Both platelets and neutrophils interact with the injured vessel wall and may contribute to thrombosis and vasospasm. The effect of platelets on neutrophil interactions with the vessel wall was studied in normal and thrombocytopenic pigs. 51Cr-labeled platelet deposition (x10(6)) and 111In-labeled neutrophil deposition (x10(3)) on undamaged aortic strips with intact endothelium or damaged aortic strips with exposed media were quantified in superfusion flow chambers before and after platelet depletion by specific rabbit antisera. Arterial blood was drawn at a constant flow rate through the superfusion chambers at 37 degrees C. Under basal conditions, platelets did not adhere to the uninjured vessel wall with intact endothelium, whereas neutrophil interaction with the endothelium was low and constant at shear rates of 427, 853, and 1280 s-1 and did not change significantly after thrombocytopenia. On exposed aortic media simulating deep arterial injury, platelet deposition increased over these shear rates from 14.0 +/- 3.4 to 37.5 +/- 12.0 (P < .05) to 68.0 +/- 9.0, respectively (P < .05). Similarly, neutrophil deposition on the media increased from 48.7 +/- 8.7 to 73.7 +/- 14.3 (P < .05) to 118.3 +/- 22.9, respectively (P < .05). Platelet deposition on the media did not occur after thrombocytopenia (80% reduction in platelet count); however, neutrophil deposition persisted, but was less intense and was now independent of shear rates (23.3 +/- 5.2 at 427 s-1, 18.7 +/- 3.2 at 853 s-1, and 24.1 +/- 3.9 at 1280 s-1; not significant).(ABSTRACT TRUNCATED AT 250 WORDS)

Enhancement of platelet 12-HETE production in the presence of polymorphonuclear leukocytes during calcium ionophore stimulation

This study investigates the effect of platelet/neutrophil interactions on eicosanoid production. Human platelets and polymorphonuclear leukocytes (PMNs) were stimulated alone and in combination, with calcium ionophore A23187 and the resulting eicosanoids 12S-hydroxy-(5Z,8Z,10E,14Z)-eicosatetraenoic acid (12-HETE), 12S-heptadecatrienoic acid (HHT), 5S,12R-dihydroxy-(6Z,8E,10E,14Z)-eicosatetraenoi c acid (LTB4) and 5S-hydroxy-(6E,8Z,11Z,14Z)-eicosatetraenoic acid (5-HETE) were measured by HPLC. The addition of PMNs to platelet suspensions caused a 104% increase in 12-HETE, a product of 12-lipoxygenase activity, but had only a modest effect on the cyclooxygenase product HHT (increase of 18%). By using PMNs labelled with [14C]arachidonic acid it was shown that the increases in these platelet eicosanoids could be accounted for by translocation of released arachidonic acid from PMNs to platelets and its subsequent metabolism. The observation that 12-lipoxygenase was about five times more efficient than cyclooxygenase at utilising exogenous arachidonic acid during the platelet/PMN interactions was confirmed in experiments in which platelets were stimulated with A23187 in the presence of [14C]arachidonic acid. Stimulations of platelets with thrombin in the presence of PMNs resulted in a decrease in 12-HETE and HHT levels of 40% and 26%, respectively. The presence of platelets caused a small increase in neutrophil LTB4 output but resulted in a decrease in 5-HETE production of 43% during stimulation with A23187. This study demonstrates complex biochemical interactions between platelets and PMNs during eicosanoid production and provides evidence of a mechanism to explain the large enhancement in 12-HETE production.

Endothelial, platelet and leukocyte interactions in ischemic heart disease: insights into potential mechanisms and their clinical relevance

Recent investigations of the complex interactions among vascular endothelium, platelets and leukocytes have relevance to the pathogenesis of atherosclerosis and ischemic heart disease. Perturbations in the hemodynamic equilibrium maintained by these cellular elements may lead to vasospasm, in vivo thrombosis and a reduction in blood flow. Recent advances in the understanding of these interactions in health and disease states are summarized. The effect of pharmacologic agents on these cell-cell interactions are discussed to provide the reader with a general understanding of the relevance of these interactions in cardiovascular disease.

Increased neutrophil elastase release in unstable angina pectoris and acute myocardial infarction

Neutrophils, a source of proteolytic enzymes and oxygen free radicals, have been shown to participate in animal models of myocardial ischemic injury. To characterize neutrophil activation in human ischemic heart disease, a specific neutrophil elastase-derived fibrinopeptide in plasma was measured in 25 patients with stable angina pectoris, 29 patients with unstable angina pectoris, 17 patients with acute myocardial infarction and 22 control subjects. Mean plasma levels (+/- standard error) of a neutrophil elastase-derived fibrinopeptide (B beta 30-43) measured by a specific radioimmunoassay were fivefold higher in patients with acute myocardial infarction (877 +/- 337 pmol/liter, p less than 0.02) and 13-fold higher in patients with unstable angina (2,277 +/- 613 pmol/liter, p less than 0.006) as compared with control subjects (172 +/- 74 pmol/liter). Mean plasma levels of peptide B beta 30-43 in patients with stable angina (676 +/- 334 pmol/liter), although higher than in control subjects, were not significantly increased (p = 0.64). Total leukocyte counts were 11.0 +/- 0.6 x 10(6)/ml in those with acute myocardial infarction, 9.2 +/- 0.7 x 10(6)/ml in those with unstable angina, 7.1 +/- 0.3 x 10(6)/ml in those with stable angina and 7.7 +/- 0.4 x 10(6)/ml in control subjects. Although total leukocyte counts in patients with unstable angina pectoris and acute myocardial infarction were higher (p less than 0.01) than in patients with stable angina or in control subjects, elevations in peptide B beta 30-43 levels were independent of the differences in both leukocyte count and absolute neutrophil count as well as in history of smoking, hypertension, diabetes mellitus or treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Neutrophil function in ischemic heart disease

Neutrophils contribute to the healing of and scar formation in myocardium after ischemic injury. Many recent studies indicate that neutrophils may be involved in the genesis and propagation of myocardial ischemia. To characterize neutrophil function in ischemic heart disease, neutrophil chemotaxis, leukotriene B4 (LTB4) generation, and elastase release in plasma were measured in 20 patients with stable angina, 17 patients with unstable angina or acute myocardial infarction (AMI), and 20 age-matched control subjects. Neutrophils from patients with stable angina exhibited markedly increased chemotactic activity and LTB4 generation as compared with the age-matched control subjects (p less than 0.01). Neutrophils of nine of 17 patients with unstable angina or AMI clumped spontaneously ex vivo and exhibited marked pseudopod formation and granule extrusion on electron microscopy. Subsequent chemotactic activity and LTB4 generation by neutrophils from these patients was less than in patients with stable angina, suggesting previous in vivo activation. Plasma levels of peptide B beta, a product of fibrin degradation by human neutrophil elastase, were approximately 15-fold higher (p less than 0.001) in patients with unstable angina or AMI (588 +/- 171 pmol/l, mean +/- SEM) compared with those in patients with stable angina (37 +/- 25 pmol/l) or control subjects (40 +/- 22 pmol/l), confirming intense in vivo neutrophil activation. Our study shows enhanced neutrophil function in patients with ischemic heart disease. The increased neutrophil chemotactic activity and LTB4 generation may be markers of stable angina pectoris. Intense neutrophil activation in unstable angina or AMI, as manifested by morphologic changes in neutrophils and elastase release, may relate to ongoing in vivo cellular activation.

Modulation of human neutrophil superoxide production by selective thromboxane synthetase inhibitor U63,557A

Prostaglandin I2 and prostaglandins of E series have been known to inhibit human neutrophil superoxide production. To examine the effects of selective thromboxane synthetase inhibition on human neutrophil superoxide production (with or without platelets), neutrophils were incubated with U63,557A and stimulated with f-MLP, serum-activated zymosan or calcium ionophore A23187. U63,557A had no significant direct inhibitory effect on neutrophil superoxide production. On the other hand, in the presence of platelets in neutrophil suspension, U63,557A significantly reduced neutrophil superoxide production and increased prostaglandin I2 release. These data suggest that selective thromboxane synthetase inhibition may reduce neutrophil superoxide generation, most likely via increase in prostaglandin I2.