Barry Campbell

Synergism Between Platelets and Neutrophils in Provoking Cardiac Dysfunction After Ischemia and Reperfusion Role of Selectins

BACKGROUND Neutrophils (PMNs) are known to contribute to both cardiac dysfunction and myocardial necrosis after reperfusion of an ischemic heart. Moreover, platelets are also important blood cells that can aggravate myocardial ischemic injury. This study was designed to test the effects of PMNs and platelets separately and together in provoking cardiac dysfunction in isolated perfused rat hearts after ischemia and reperfusion. METHODS AND RESULTS Control rat hearts not subjected to ischemia were perfused without blood cells for 80 minutes. Additional control rat hearts were perfused with 75x106 PMNs, with 100x106 platelets, or with 75x106 PMNs+100x106 platelets over a 5-minute perfusion followed by a 75-minute observation period. No significant reduction in coronary flow, left ventricular developed pressure (LVDP), or the first derivative of LVDP (dP/dtmax) was observed at the end of the observation period in any nonischemic group. Similarly, global ischemia (I) for 20 minutes followed by 45 minutes of reperfusion (R) produced no sustained effects on the final recovery of any of these parameters in any group of hearts perfused in the absence of blood cells. However, I/R hearts perfused with either PMNs or platelets alone exhibited decreases in these variables of 10% to 12% (P<0.05 from control). Furthermore, I/R hearts perfused with both PMNs and platelets exhibited decreases of 50% to 60% in all measurements of cardiac function (P<0.001). These dual-cell-perfused I/R hearts also exhibited marked increases in cardiac myeloperoxidase (MPO) activity, indicating a significant PMN infiltration, and enhanced P-selectin expression on the coronary microvascular endothelium. All cardiodynamic effects as well as MPO accumulation and PMN infiltration were markedly attenuated by a sialyl LewisX-oligosaccharide or a recombinant soluble P-selectin ligand, which inhibits selectin-mediated cell adhesion. CONCLUSIONS These results provide evidence that platelets and neutrophils act synergistically in provoking postreperfusion cardiac dysfunction and that this may be largely due to cell-to-cell interactions mediated by P-selectin. These findings may help explain the reperfusion injury phenomenon.

Recombinant soluble P-selectin glycoprotein ligand-1 protects against myocardial ischemic reperfusion injury in cats

OBJECTIVE Neutrophils (PMNs) contribute importantly to the tissue injury associated with ischemia and subsequent reperfusion of a vascular bed. The effects of a recombinant soluble human form of P-selectin glycoprotein ligand-1 (rsPSGL.Ig) on PMN-endothelial cell interactions were investigated in a well established model of feline myocardial-ischemia reperfusion injury. METHODS Cats were subjected to 90 min of myocardial ischemia followed by 270 min of reperfusion. RESULTS Administration of rsPSGL.Ig (1 mg/kg) just prior to reperfusion resulted in a significant reduction in myocardial necrosis compared to that in cats administered a low affinity mutant form of rsPSGL.Ig (1 mg/kg) (16 +/- 3 vs. 42 +/- 7% of area-at-risk, P < 0.01). Cardioprotective effects were confirmed by significant (P < 0.05) reductions in plasma creatine kinase activity in cats treated with rsPSGL.Ig. Inhibition of PMN-endothelial cell interactions was evidenced by a significant attenuation in cardiac myeloperoxidase activity (P < 0.01) and reduced PMN adherence to ischemic-reperfused coronary endothelium (P < 0.001). In addition, rsPSGL.Ig treatment significantly (P < 0.01) preserved endothelium-dependent vasorelaxation in ischemic-reperfused coronary arteries. CONCLUSION These results demonstrate that the administration of a recombinant soluble PSGL-1 reduces myocardial reperfusion injury and preserves vascular endothelial function, which is largely the result of reduced PMN-endothelial cell interactions.

Time course of endothelial dysfunction and neutrophil adherence and infiltration during murine traumatic shock

Traumatic shock in rats has been shown to induce endothelial dysfunction, and to increase intestinal myeloperoxidase activity (MPO) indicative of neutrophil infiltration. To examine the time course of endothelial dysfunction and neutrophil adherence and infiltration, pentobarbital anesthetized rats, subjected to Noble-Collip drum trauma, were studied prior to and 15, 30, 60, 90, 120, 150, and 180 min following drum trauma. Superior mesenteric artery rings obtained from traumatized rats were tested for responsiveness to acetylcholine (ACh), a receptor-mediated endothelium-dependent vasodilator, and to NaNO2 an endothelium-independent vasodilator. ACh-induced relaxation was not impaired immediately after the induction of trauma (time 0). However, 15–30 min after trauma, responses to ACh were significantly depressed (p < .05) and were further reduced (p < .01) 90–180 min after trauma. No significant changes occurred in response to the direct vasodilator NaNO2 at any of the times studied, indicating no vascular smooth muscle injury. Moreover, the adherence of polymorphonuclear leukocytes (PMNs) to the post-traumatic mesenteric vascular endothelium also showed an increase that peaked 30 min post-trauma. Intestinal MPO activity, indicative of neutrophil infiltration, was characterized by a continuous and sustained increase from 30–180 min. Our findings suggest that endothelial dysfunction resulting in reduced NO release occurs in the early phase of murine traumatic shock, and that this phenomenon is followed by a time-dependent increase in adhesivity of neutrophils to the vascular endothelium leading to a progressive accumulation of PMNs in injured tissues (e.g., intestine).

Beneficial effects of C1 esterase inhibitor in murine traumatic shock.

Activation of the complement system is an integral part of the initiation and maintenance of the inflammatory process such as that occurring in traumatic shock, and is considered responsible for much of the trauma-induced microvascular injury. We investigated the effects of early complement blockade induced by a C1 esterase inhibitor (C1 INH) in a rat model of traumatic shock. Pentobarbital-anesthetized rats subjected to Noble-Collip drum trauma developed a shock state characterized by marked hypotension and a 83.3% mortality rate with a mean survival time of 157.5 ± 26 min. Accompanying these effects were significant endothelial dysfunction and elevated intestinal myeloperoxidase activity. Treatment with C1 INH 15 mg/kg administered intravenously 10 min post-trauma, increased survival rate to 66.7% (p < .05), and prolonged survival time to 248 ± 27 min (p < .05). C1 INH significantly preserved the endothelium-dependent relaxation to acetylcholine and attenuated the increases in myeloperoxidase activity in C1 INH-treated rats compared with untreated trauma rats (p < .05). Our results suggest that complement activation plays an important role in tissue injury associated with trauma, and that its inhibition at an early step in the complement cascade through a C1 esterase inhibitor is beneficial in rats experiencing traumatic shock. The mechanisms of the protective effect of C1 INH involves preservation of vascular endothelial function and diminished neutrophil accumulation leading to reduced neutrophil-mediated tissue injury.

Beneficial effects of N,N,N-trimethylsphingosine following ischemia and reperfusion in the isolated perfused rat heart

OBJECTIVE Ischemia followed by reperfusion in the presence of polymorphonuclear leukocytes (PMNs) results in cardiac contractile dysfunction as well as myocardial injury. These deleterious effects are due in large part to endothelial dysfunction leading to an upregulation of cell adhesion molecules and subsequent neutrophil-induced cardiac injury. At physiologically relevant concentrations, N,N,N-trimethylsphingosine (TMS), a synthetic N-methylated sphingosine derivative, has been shown to attenuate leukocyte-endothelial cell interactions. We wanted to test the effects of TMS on neutrophil-mediated cardiac dysfunction in ischemia/reperfusion. METHODS This study examines the effects of TMS in a neutrophil-dependent isolated perfused rat heart model of ischemia (I) (20 min) and reperfusion (R) (45 min) injury. RESULTS Administration of TMS (20 micrograms/kg) to I/R hearts perfused with PMNs improved coronary flow and preserved left ventricular developed pressure as an index of cardiac contractile function (95 +/- 5%) in comparison to those I/R hearts receiving only vehicle (60 +/- 7%) (P < 0.001). In addition, TMS significantly reduced PMN accumulation in the ischemic myocardium, as evidenced by an attenuation in cardiac myeloperoxidase activity from 1.12 +/- 0.04 in untreated hearts to 0.01 +/- 0.02 in treated hearts (P < 0.001). However, TMS did not directly stimulate nitric oxide (NO) release from rat vascular endothelium. CONCLUSION These results provide evidence that TMS is a potent and effective cardioprotective agent that inhibits leukocyte-endothelial cell interactions and preserves cardiac contractile function and coronary perfusion following myocardial ischemia and reperfusion.

Vascular endothelial growth factor attenuates trauma-induced injury in rats.

Endothelial dysfunction and loss of nitric oxide (NO) is an integral part of the initiation and maintenance of the inflammatory process such as that occurring in traumatic shock, and is considered responsible for much of the trauma induced microvascular injury. We investigated the effects of a vascular endothelial growth factor (VEGF) in a rat model of traumatic shock. Pentobarbital‐anaesthetized rats subjected to Noble‐Collip drum trauma developed a shock state characterized by marked hypotension and a 93% mortality rate with a mean survival time of 108±10 min in 14 rats. Accompanying these effects was a significant degree of endothelial dysfunction and a markedly elevated intestinal myeloperoxidase (MPO) activity. Treatment with 125 μg kg−1 VEGF administered intravenously 18 h pre‐trauma, increased survival rate to 67% (P<0.01), and prolonged survival time to 252±24 min in 12 rats (P<0.01). VEGF also significantly preserved the endothelium‐dependent relaxation to ACh indicating a preservation of endothelium‐derived NO. Our results indicate that endothelial dysfunction with its accompanying loss of NO plays an important role in tissue injury associated with trauma, and that preservation of NO is beneficial in traumatic shock. The mechanisms of the protective effect of VEGF in trauma involves preservation of eNOS function and diminished neutrophil accumulation resulting in reduced neutrophil‐mediated tissue injury.