Neutrophil-independent myocardial dysfunction during an early stage of global ischemia and reperfusion of isolated hearts

Do cardiomyocytes mount an immune response to Group A Streptococcus?

Some patients with Group A Streptococcal toxic shock syndrome (StrepTSS) develop a unique form of cardiomyopathy characterized by global hypokinesia and reduced cardiac index. Here we investigated the immune responses of cardiomyocytes to Group A Streptococcus both in vivo and in vitro. Our data demonstrate that cardiomyocyte-derived cytokines are produced following both direct GAS stimulation and after exposure to GAS-activated inflammatory cells. These locally produced, cardiomyocyte-derived cytokines may mediate cardiac contractile dysfunction observed in patients with StrepTSS-associated cardiomyopathy and may hold the key to our ability to attenuate this severe complication.

Intracoronary formation and retention of micro aggregates of leukocytes and platelets contribute to postischemic myocardial dysfunction

OBJECTIVE

Cardiac pump function and coronary regulation can be impaired after short-term ischemia. Recent studies with platelets (P) and neutrophils (PMN) yielded contradicting results about the "cellular" contribution to reperfusion injury.

METHODS

Isolated guinea pig hearts performing pressure-volume work were employed, external heart work (EHW), aortic flow (AF), coronary flow (CF) and heart rate (HR) serving as parameters of cardiac function. After global ischemia, human blood cells were given as bolus (1 min) during reperfusion (intracoronary hematocrit 7%). Expression of specific adhesion molecules (P: CD62P, CD41; PMN: integrin CD11b) was measured on cells before and after coronary passage (FACS analysis).

RESULTS

Postischemic recovery of pump function was significantly reduced in hearts with blood cell application (EHW: -cells 54 +/- 14%, +cells 41 +/-12%, p <0.05). Coronary response to bradykinin and reactive hyperemia were not effected. The blood-cell dependent functional loss was partly reduced by blocking CD18 (anti-CD 18) and completely abrogated by blockage of CD41 (lamifiban). The expression of CD11b on PMN and monocytes (M) and CD62P on platelets was significantly reduced in the coronary effluent and a significant decrease of CD41 on leukocytes occurred during coronary passage after ischemia. Increases in CD41 on PMN in the presence of lamifiban demasked intracoronary formation of micro aggregates (P/PMN). These micro aggregates were visualized by light microscopy. Electron microscopy revealed no significant microvascular plugging.

CONCLUSION

1) A specifically blood-cell induced loss of myocardial pump function has been demonstrated after short-term ischemia. 2) CD41 (= GpIIbIIIa) on P is responsible for this cardiac reperfusion damage. 3) The effect is causally linked to the formation of micro aggregates between PMN and P, but seems attenuated in the presence of erythrocytes as compared to effects reported from experiments in which PMN and P were applied singly or co-perfused. 4) Intracoronary retention of PMN, M and platelet-leukocyte micro aggregates seems to be transient, as adherence was not confirmed by electron microscopy.

Antithrombotic controversies in off-pump coronary bypass

The purpose of this article is to evaluate the use of perioperative antithrombotics in patients undergoing surgical revascularization of the coronary vessels. Although there is a general agreement about the use of anticoagulation during off-pump coronary revascularization (OPCAB), the degree of the required anticoagulation varies from one center to another. The review is divided into four major sections. The first section describes the pathophysiology of the coagulation system in cardiac surgery with and without the use of cardiopulmonary bypass. In this section, we also discuss the interactions between the coagulation system and the inflammatory response to cardiac surgery. The second section examines the role of prophylactic antithrombosis in patients referred to surgical revascularization, and their role in bleeding complications associated with surgery. Heparinization and neutralizing its anticoagulative effects during coronary surgery are discussed in the third section. The fourth section examines the evidence that the inflammatory response contributes to adverse peri-operative events, in particular organ dysfunction, and potential therapeutic strategies to control this response. The review concludes with a summary of potential future research directions and key deficiencies in our knowledge regarding the use of anticoagulants in cardiac surgery.

Brief hypoxia conditions monocytes to protect reperfused cardiocytes against cell death via the CD11b receptor

BACKGROUND

Traditionally leukocytes have been viewed as the mediators and effectors of cell injury after tissue ischemia and reperfusion through the indiscriminate release of toxic cytokines and oxygen free radicals. This can be detrimental to functioning of the transplanted heart when reperfused after implantation. Paradoxically, evidence now suggests that certain cytotoxic cytokines and even oxygen free radicals can be cytoprotective in smaller concentrations. This study sought to determine whether cultured human monocytes can be pre-conditioned by brief hypoxia to protect cardiomyocytes from cell death after hypoxia and re-oxygenation.

METHODS

Cultured human monocytes were exposed to transient hypoxia (10 minutes), after which we determined CD11b expression using flow cytometry. The 3 control groups comprised immunoglobulin G-negative controls, fMLP-positive controls, and virgin monocyte (VM) controls. We studied chick embryonic ventricular myocytes in a flow-through chamber while controlling flow rate, pH, O(2), and CO2 tension. We quantified cardiomyocyte viability using propidium iodide (5 micromol/liter). Cell systems of cardiomyocytes alone, cardiomyocytes and VM, human monocytes exposed to transient hypoxia before coculture with cardiomyocytes (PCHM-cardiomyocyte), and PCHM cocultured with anti-CD11b antibodies for 30 minutes before coculture with cardiomyocytes (CDHM-cardiomyocyte) were subjected to 1 hour of hypoxia and 3 hours of re-oxygenation, and cell death was determined. The experiment was repeated and the cell systems fixed, stained, and examined for monocytes adhering to cardiomyocytes.

RESULTS

CD11b expression increased significantly with both transient hypoxia and fMLP (18.39% +/- 4.116%, n = 5, and 37.04% +/- 7.783%, n = 5, respectively, p < 0.05 vs VM 100%, n = 5). Coculture of cardiomyocytes with VM had no effects on cardiocyte death (40.6% +/- 6.1%, n = 6) compared with controls (46.5% +/- 4.0%, n = 10). The PCHM cocultured with cardiomyocytes significantly decreased cardiomyocyte death (25.2% +/- 4.7%, n = 6, p < 0.05). This protection was abrogated by the addition of CD11b-blocking antibodies to PCHM before coculture with cardiomyocytes (51.0% +/- 6.1%, n = 6, p < 0.05). The PCHM showed increased adhesion to cardiomyocytes (5.4 +/- 0.38/high-power [HP] field vs 0.67 +/- 0.24/HP field in VM, p < 0.05). The increased adhesion was abolished by CD11b-blocking antibody (0.78 +/- 0.28 vs 0.67 +/- 0.24 cells/HP field, p < 0.05).

CONCLUSIONS

These results suggest that monocytes activated by transient hypoxia protect cardiomyocytes during hypoxia and re-oxygenation through expression of CD11b receptors. These cells seem to adhere to myocytes through this receptor to achieve this effect. The exact mechanism is unclear and requires further study. Autologous recipient monocytes may be pre-conditioned to protect the donor heart during reperfusion.

Induction of nuclear factor kappaB but not kappaB-responsive cytokine expression during myocardial reperfusion injury after neutropenia

Neutrophils may contribute to myocardial ischemia/reperfusion (I/R) injury by generating reactive oxygen intermediates (ROIs). ROIs activate nuclear factor (NF)-kappaB, which regulates genes for cytokines with negative inotropic effects (interleukin [IL]-1beta, IL-6, and tumor necrosis factor [TNF]-alpha). We investigated the impact of neutrophil depletion on NF-kappaB DNA binding activity, and expression of these cytokines during myocardial I/R injury. Male WKY rats (n = 28) received a single dose of antineutrophil antiserum (i/v). Twenty two hours later, when the peripheral blood neutrophil counts were profoundly decreased (94% reduction), the animals underwent 15 min of left anterior descending coronary artery ligation followed by reperfusion for 0.25, 0.5, 1, 2, 3, and 6 h (n = 4/group). Saline-treated animals underwent a similar protocol, and served as controls (n = 28, 4/group). Neutrophil accumulation, defined by myeloperoxidase activity, was present in controls, but not in anti-PMN antisera-treated animals (at least p <0.05 at 1, 2, 3, and 6 h R). Despite this difference, in both saline- and antiserum-treated animals, the GSH levels were very similar and fell significantly (p < 0.0001) at 15 min R; the levels increased gradually over time. In contrast, GSSG levels rose at 15 and 30 min R (p < 0.05), and declined thereafter. NF-kappaB DNA binding activity increased in both groups at 15 min and again at 3 h of R. Both NF-kappaBp50 and p65 subunits were detected by supershift assay. In saline-injected controls both mRNA and protein for IL-1beta, IL-6, and TNF-alpha were detected at 1 h R; levels remained high until 3 h, then fell (except IL-6, which was elevated at 6 h). In neutropenic animals, however, a significant decrease in mRNA (at least 1.7-fold, p < 0.05) as well as protein levels (at least 2. 3-fold, p < 0.01) for all three cytokines was observed. Thus, while neutrophils had minimal effects on oxidative stress (GSH/GSSG) and oxidative stress-responsive NF-kappaB activity, they contributed significantly to myocardial cytokine expression.

Activated macrophages decrease rat cardiac myocyte contractility: importance of ICAM-1-dependent adhesion

Macrophages are found in the heart as part of the inflammatory response. To determine whether macrophages could contribute to myocardial dysfunction, rat ventricular myocytes were isolated and cocultured with elicited peritoneal macrophages in media containing tumor necrosis factor-alpha (TNF-alpha), interleukin (IL)-1beta, or endotoxin for 4 h. Cardiac myocytes were electrically stimulated, and fractional shortening was determined using videomicroscopy. When myocytes alone or myocytes in coculture with macrophages separated by a membrane were challenged with TNF-alpha, lipopolysaccharide, or IL-1, fractional shortening did not decrease. When macrophages were allowed to contact myocytes, fractional shortening decreased from 20. 1 +/- 0.9% in unchallenged macrophage-myocyte cocultures to 15.5 +/- 0.9, 16.3 +/- 0.8, and 15.8 +/- 0.6% when challenged for 4 h with TNF-alpha, endotoxin, or IL-1beta, respectively (P < 0.05). Myocytes had a mean adherence of 4.2 +/- 0.2 macrophages after TNF-alpha challenge compared with 2.6 +/- 0.3 for controls (P < 0.05). The number of adherent macrophages was associated with the decrease in fractional shortening. Anti-intercellular adhesion molecule-1 (ICAM-1) reduced macrophage adherence and prevented the decrease in fractional shortening. This decrease was also prevented by desferoxamine, superoxide dismutase, and nitro-L-arginine methyl ester. This suggests that activated macrophages adhere to myocytes via ICAM-1, and adherent macrophages decrease their contractile function via TNF-alpha, oxygen free radicals, and nitric oxide.