Effects of endotoxin on neutrophil-mediated I/R injury in isolated perfused rat hearts

Animal models of myocardial infarction: Mainstay in clinical translation

Preclinical models with high prognostic power are a prerequisite for translational research. The closer the similarity of a model to myocardial infarction (MI), the higher is the prognostic value for clinical trials. An ideal MI model should present cardinal signs and pathology that resemble the human disease. The increasing understanding of MI stratification and etiology, however, complicates the choice of animal model for preclinical studies. An ultimate animal model, relevant to address all MI related pathophysiology is yet to be developed. However, many of the existing MI models comprising small and large animals are useful in answering specific questions. An appropriate MI model should be selected after considering both the context of the research question and the model properties. This review addresses the strengths, and limitations of current MI models for translational research.

Toll-like receptors as potential therapeutic targets in cardiac dysfunction

INTRODUCTION

The innate immune system can detect the highly conserved, relatively invariant structural motifs of pathogens. The most important innate immune receptors, Toll-like receptors (TLRs), represent a first line of defense against infectious pathogens, and play a pivotal role in initiating and shaping innate and adaptive immune responses. TLRs are not only expressed in immune cells, but also in cardiovascular cells. In addition to their role in response to microbial infections, evidence suggests that TLRs can also recognize endogenous ligands and may play a role in mediating cardiomyocyte cell death and survival after non-infectious injury.

AREAS COVERED

TLRs could be a link between cardiovascular diseases and the immune system. Experimentally, there is good evidence that TLR activation contributes to development and progression of both acute cardiac injury and chronic heart failure. The role of TLRs in myocardial ischemia-reperfusion, remodeling, septic cardiomyoparthy, autoimmune- and viral myocarditis, anthracycline-induced cardiomyopathy and cardiac hypertrophy, in basic as well as clinical science are discussed.

EXPERT OPINION

Evidence, mainly from animal experiments, indicates that TLRs contribute to all of the myocardial disease states reviewed in this paper. However, the relevance of TLRs as therapeutic targets remains to be defined as clinical data is sparse.

Toll-like receptor signaling: a critical modulator of cell survival and ischemic injury in the heart

Toll-like receptors (TLRs) represent the first line of host defense against microbial infection and play a pivotal role in both innate and adaptive immunity. TLRs recognize invading pathogens through molecular pattern recognition, transduce signals via distinct intracellular pathways involving a unique set of adaptor proteins and kinases, and ultimately lead to the activation of transcription factors and inflammatory responses. Among 10 TLRs identified in humans, at least two exist in the heart, i.e., TLR2 and TLR4. In addition to the critical role of these in mediating cardiac dysfunction in septic conditions, emerging evidence suggests that the TLRs can also recognize endogenous ligands and may play an important role in modulating cardiomyocyte survival and in ischemic myocardial injury. In animal models of ischemia-reperfusion injury or in hypoxic cardiomyocytes in vitro, the administration of a sublethal dose of lipopolysaccharide, which signals through TLR4, reduces subsequent myocardial infarction, improves cardiac functions, and attenuates cardiomyocyte apoptosis. By contrast, a systemic deficiency of TLR2, TLR4, or myeloid differentiation primary-response gene 88, an adaptor critical for all TLR signaling, except TLR3, leads to an attenuated myocardial inflammation, a smaller infarction size, a better preserved ventricular function, and a reduced ventricular remodeling after ischemic injury. These loss-of-function studies suggest that both TLRs contribute to myocardial inflammation and ischemic injury in the heart although the exact contribution of cardiac (vs. circulatory cell) TLRs remains to be defined. These recent studies demonstrate an emerging role for TLRs as a critical modulator in both cell survival and tissue injury in the heart.

Endotoxin preconditioning in pancreatic ischemia/reperfusion injury

OBJECTIVES

Prospective organ donors are exposed to various stress types. The effect of endotoxin pretreatment (ETX) on pancreatic ischemia/reperfusion injury (IRI) is unclear. We investigated, using a rat model of pancreatic IRI of an in situ isolated pancreatic tail segment, the effect of ETX on postischemic microcirculation and organ damage.

METHODS

Twenty-four hours before pancreatic dissection, either intraperitoneal application of ETX (1 mg/kg in 0.9% NaCl) or saline only (control) was performed. Two-hour normothermic ischemia of the pancreatic tail was induced by clamping the splenic vessels and was followed by a reperfusion period of 2 hours. Microcirculatory parameters were measured by intravital epifluorescence microscopy [functional capillary density (FCD), adherent leukocytes (ALs), and histology]. The presented data represent the mean +/- SEM/SD as appropriate.

RESULTS

ETX pretreatment caused a significantly greater decrease in FCD (497 +/- 6 cm/cm2 baseline versus 326 +/- 15 cm/cm2 2 hours of reperfusion) compared with controls (498 +/- 8 versus 258 +/- 15 cm/cm2) 2 hours after reperfusion (P < 0.01). Two hours after reperfusion, ALs were significantly decreased in ETX animals compared with controls (ETX: 141 +/- 37 versus 273 +/- 36 cells/mm2, P < 0.05). Histologic damage was less in ETX (6.4 score points +/- 0.32 versus 8.8 +/- 0.33 control, P < 0.05).

CONCLUSION

ETX preconditioning decreases microcirculatory deterioration caused by IRI by means of less loss of nutritive tissue perfusion, decrease in ALs, and less histologic damage. This indicates a protective effect of ETX preconditioning in pancreatic IRI.

Targeted deletion of A(3) adenosine receptors improves tolerance to ischemia-reperfusion injury in mouse myocardium

A(3) adenosine receptors (A(3)ARs) have been implicated in regulating mast cell function and in cardioprotection during ischemia-reperfusion injury. The physiological role of A(3)ARs is unclear due to the lack of widely available selective antagonists. Therefore, we examined mice with targeted gene deletion of the A(3)AR together with pharmacological studies to determine the role of A(3)ARs in myocardial ischemia-reperfusion injury. We evaluated the functional response to 15-min global ischemia and 30-min reperfusion in isovolumic Langendorff hearts from A(3)AR(-/-) and wild-type (A(3)AR(+/+)) mice. Loss of contractile function during ischemia was unchanged, but recovery of developed pressure in hearts after reperfusion was improved in A(3)AR(-/-) compared with wild-type hearts (80 +/- 3 vs. 51 +/- 3% at 30 min). Tissue viability assessed by efflux of lactate dehydrogenase was also improved in A(3)AR(-/-) hearts (4.5 +/- 1 vs. 7.5 +/- 1 U/g). The adenosine receptor antagonist BW-A1433 (50 microM) decreased functional recovery following ischemia in A(3)AR(-/-) but not in wild-type hearts. We also examined myocardial infarct size using an intact model with 30-min left anterior descending coronary artery occlusion and 24-h reperfusion. Infarct size was reduced by over 60% in A(3)AR(-/-) hearts. In summary, targeted deletion of the A(3)AR improved functional recovery and tissue viability during reperfusion following ischemia. These data suggest that activation of A(3)ARs contributes to myocardial injury in this setting in the rodent. Since A(3)ARs are thought to be present on resident mast cells in the rodent myocardium, we speculate that A(3)ARs may have proinflammatory actions that mediate the deleterious effects of A(3)AR activation during ischemia-reperfusion injury.