Vascular cell adhesion molecule--1 expression is obligatory for endotoxin-induced myocardial neutrophil accumulation and contractile dysfunction

CARDIOMYOCYTE REPROGRAMMING IN ANIMAL MODELS OF SEPTIC SHOCK

ABSTRACT

Cardiomyocyte reprogramming plays a pivotal role in sepsis-induced cardiomyopathy through the induction or overexpression of several factors and enzymes, ultimately leading to the characteristic decrease in cardiac contractility. The initial trigger is the binding of LPS to TLR-2, -3, -4, and -9 and of proinflammatory cytokines, such as TNF, IL-1, and IL-6, to their respective receptors. This induces the nuclear translocation of nuclear factors, such as NF-κB, via activation of MyD88, TRIF, IRAK, and MAPKs. Among the latter, ROS- and estrogen-dependent p38 and ERK 1/2 are proinflammatory, whereas JNK may play antagonistic, anti-inflammatory roles. Nuclear factors induce the synthesis of cytokines, which can amplify the inflammatory signal in a paracrine fashion, and of several effector enzymes, such as NOS-2, NOX-1, and others, which are ultimately responsible for the degradation of cardiomyocyte contractility. In parallel, the downregulation of enzymes involved in oxidative phosphorylation causes metabolic reprogramming, followed by a decrease in ATP production and the release of fragmented mitochondrial DNA, which may augment the process in a positive feedback loop. Other mediators, such as NO, ROS, the enzymes PI3K and Akt, and adrenergic stimulation may play regulatory roles, but not all signaling pathways that mediate cardiac dysfunction of sepsis do that by regulating reprogramming. Transcription may be globally modulated by miRs, which exert protective or amplifying effects. For all these mechanisms, differentiating between modulation of cardiomyocyte reprogramming versus systemic inflammation has been an ongoing but worthwhile experimental challenge.

HepaticIschemia/Reperfusion Injuryinvolves functional tryptase/PAR-2 signaling in liver sinusoidal endothelial cell population

Mast cells (MCs) are tissue-resident effector cells that could be the earliest responder to release a unique, stimulus-specific set of mediators in hepatic ischemia-reperfusion (IR) injury However, how MCs function in the hepatic IR has remained a formidable challenge due to the substantial redundancy and functional diverse of these mediators. Tryptase is the main protease for degranulation of MCs and its receptor-protease-activated receptor 2 (PAR-2) is widely expressed in endothelial cells. It is unclear whether and how tryptase/PAR-2 axis participates in hepatic IR. We employed an experimental warm 70% liver IR model in mice and found that tryptase was accumulated in the circulation during hepatic IR and positively correlated with liver injury. Tryptase inhibition by protamine can significantly down-regulate the expression of adhesion molecules and reduce neutrophil infiltration within the liver. The level of inflammatory factors and chemokines were also consistent with the pathological change of the liver. In addition, the treatment with exogeneous tryptase in MC-deficient mice can induce the damage observed in wild type mice in the context of liver IR. In vitro, neutrophil infiltration and inflammatory factor secretion were regulated by Tryptase/PAR-2, involving the adhesion molecule expression to regulate neutrophil adhesion dependent on NF-κB pathway. Conclusion: tryptase/PAR-2 participates in liver injury through the activation of LSECs in the early phase of liver IR.

Sepsis-induced cardiac dysfunction: a review of pathophysiology

It is well known that cardiac dysfunction in sepsis is associated with significantly increased mortality. The pathophysiology of sepsis-induced cardiac dysfunction can be summarized as involving impaired myocardial circulation, direct myocardial depression, and mitochondrial dysfunction. Impaired blood flow to the myocardium is associated with microvascular dysfunction, impaired endothelium, and ventriculo-arterial uncoupling. The mechanisms behind direct myocardial depression consist of downregulation of β-adrenoceptors and several myocardial suppressants (such as cytokine and nitric oxide). Recent research has highlighted that mitochondrial dysfunction, which results in energy depletion, is a major factor in sepsis-induced cardiac dysfunction. Therefore, the authors summarize the pathophysiological process of cardiac dysfunction in sepsis based on the results of recent studies.

Sepsis-Induced Cardiomyopathy: Mechanisms and Treatments

Sepsis is a lethal syndrome with a high incidence and a weighty economy burden. The pathophysiology of sepsis includes inflammation, immune dysfunction, and dysfunction of coagulation, while sepsis-induced cardiomyopathy (SIC), defined as a global but reversible dysfunction of both sides of the heart induced by sepsis, plays a significant role in all of the aspects above in the pathogenesis of sepsis. The complex pathogenesis of SIC involves a combination of dysregulation of inflammatory mediators, mitochondrial dysfunction, oxidative stress, disorder of calcium regulation, autonomic nervous system dysregulation, and endothelial dysfunction. The treatments for SIC include the signal pathway intervention, Chinese traditional medicine, and other specific therapy. Here, we reviewed the latest literatures on the mechanisms and treatments of SIC and hope to provide further insights to researchers and create a new road for the therapy of sepsis.

NOX2 in lung inflammation: quantum dot based in situ imaging of NOX2-mediated expression of vascular cell adhesion molecule-1

Quantum dot (QD) imaging is a powerful tool for studying signaling pathways as they occur. Here we employ this tool to study adhesion molecule expression with lung inflammation in vivo. A key event in pulmonary inflammation is the regulation of vascular endothelial cell adhesion molecule-1 (VCAM), which drives activated immune cell adherence. The induction of VCAM expression is known to be associated with reactive oxygen species (ROS) production, but the exact mechanism or the cellular source of ROS that regulates VCAM in inflamed lungs is not known. NADPH oxidase 2 (NOX2) has been reported to be a major source of ROS with pulmonary inflammation. NOX2 is expressed by both endothelial and immune cells. Here we use VCAM-targeted QDs in a mouse model to show that NOX2, specifically endothelial NOX2, induces VCAM expression with lung inflammation in vivo.

HDL Mimetic Peptide Administration Improves Left Ventricular Filling and Cardiac output in Lipopolysaccharide-Treated Rats

AIMS: Cardiac dysfunction is a complication of sepsis and contributes to morbidity and mortality. Since raising plasma apolipoprotein (apo) A-I and high density lipoprotein (HDL) concentration reduces sepsis complications, we tested the hypothesis that the apoA-I mimetic peptide 4F confers similar protective effects in rats treated with lipopolysaccharide (LPS). METHODS AND RESULTS: Male Sprague-Dawley (SD) rats were randomized to receive saline vehicle (n=13), LPS (10 mg/kg: n=16) or LPS plus 4F (10 mg/kg each: n=13) by intraperitoneal injection. Plasma cytokine and chemokine levels were significantly elevated 24 hrs after LPS administration. Echocardiographic studies revealed changes in cardiac dimensions that resulted in a reduction in left ventricular end-diastolic volume (LVEDV), stroke volume (SV) and cardiac output (CO) 24 hrs after LPS administration. 4F treatment reduced plasma levels of inflammatory mediators and increased LV filling, resulting in improved cardiac performance. Chromatographic separation of lipoproteins from plasma of vehicle, LPS and LPS+4F rats revealed similar profiles. Further analyses showed that LPS treatment reduced the agarose electrophoretic mobility of isolated HDL fractions. HDL-associated proteins were characterized by SDSPAGE and mass spectrometry. ApoA-I and apoA-IV were reduced while apoE content was increased in LPStreated rats. 4F treatment in vivo attenuated changes in HDL-associated apolipoproteins and increased the electrophoretic mobility of the particle. CONCLUSIONS: The ability of 4F to reduce inflammation and improve cardiac performance in LPS-treated rats may be due to its capacity to neutralize endotoxin and prevent adverse changes in HDL composition and function.

The relative efficacy of aminoguanidine and pentoxifylline in modulating endotoxin-induced cardiac stress

This study investigates the effect of aminoguanidine (AG), a selective inducible nitric oxide synthase (iNOS) inhibitor, and pentoxifylline (PTX), a tumour necrosis factor-alpha (TNF-α) inhibitor, on lipopolysaccharide (LPS)-induced cardiac stress. Rats were divided into four groups: group I served as a control, group II (LPS) received a single intraperitoneal injection of LPS (10 mg·kg(-1) ), group III (LPS+AG) and group IV (LPS+PTX) were injected with either AG (100 mg·kg(-1) ) or PTX (150 mg·kg(-1) ) intraperitoneally 10 days prior to LPS administration. Normalization of cardiac levels of nitrite/nitrate (NO(X) ), malondialdehyde (MDA), glutathione (GSH), heme oxygenase-1 (HO-1), glutathione peroxidase (GPx) and Na(+) , K(+) -ATPase activities was evident in the AG group. Both AG and PTX decreased the elevated serum TNF-α levels, the activities of lactate dehydrogenase (LDH), creatine kinase (CK) and cardiac myeloperoxidase (MPO). The levels of adenosine triphosphate (ATP), adenosine diphosphate (ADP) and phosphocreatine (PCr) were enhanced following AG and PTX pretreatments. Calcium (Ca(2+) ) levels were altered, and the histopathological observations supported the described results. Conclusively, the study highlights the cardioprotective potential of AG and PTX with superior results from AG. These findings reveal the relative contribution of nitric oxide and TNF-α to oxidative stress and energy failure during endotoxemia.

Early myocardial dysfunction is not caused by mitochondrial abnormalities in a rat model of peritonitis

BACKGROUND

Patients with complicated intra-abdominal infections are prone to develop multiple organ failure, including myocardial dysfunction. We hypothesized that early dysfunction during sepsis is associated with inflammation, mitochondrial injury, impaired mitochondrial function, and activation of mitochondrial biogenesis.

MATERIALS AND METHODS

Rats received lipopolysaccharide (LPS, n = 11) intraperitoneally. Healthy rats (n = 6) served as controls. Myocardial function was measured ex vivo in an isolated Langendorff-perfused heart set-up. Myocardial vascular cell adhesion molecule-1 (VCAM-1) expression was determined by immunofluorescence microscopy. Cytochrome c release and cytochrome c oxidase (COX IV) activity were measured by immunohistochemistry and enzyme histochemistry, respectively. Protein expression of tumor necrosis factor-α (TNF-α), B-cell lymphoma (Bcl)-2, peroxisome proliferator activated receptor γ cofactor 1α (PGC-1α), and mitochondrial transcription factor A (TFAM) were analyzed by Western blot technique. Mitochondria were studied by electron microscopy.

RESULTS

Two hours after LPS injection, developed pressure had decreased and after 4 h myocardial contractility (+dP/dt) and relaxation (-dP/dt) also had decreased. TNF-α protein expression was increased after 2 h and returned to normal at 4 h, whereas after 4 h VCAM-1 expression was higher in LPS-treated animals. At 2 h a substrate-dependent increase in COXIV-activity was seen, but no mitochondrial damage occurred as cytochrome c release, COX IV activity and Bcl-2, PGC-1α or TFAM expression were not changed. Electron microscopy did not reveal differences in myocardial mitochondrial characteristics between LPS-treated and control rats.

CONCLUSIONS

Early myocardial dysfunction in sepsis is associated with myocardial inflammation but not with mitochondrial injury, impaired mitochondrial function, or activated mitochondrial biogenesis.

Innate immunity signaling pathways: links between immunonutrition and responses to sepsis

Septic infections in patients treated in intensive care units show the highest mortality rates. Despite advances in treatment methods, there is still no therapy available to efficiently reduce the excessive inflammatory response, which can increase the risk of multiple organ failure. One of the ways to discover new, more efficient treatment methods involves regulating the mechanisms of inflammatory response to a massive infection. Toll-like receptors (TLRs) that recognize pathogen-associated molecular patterns play a significant role in innate antibacterial and inflammatory responses. The regulatory impact of immunonutrition on TLR expression in septic patients seems to be a promising research direction. This paper presents the main mechanisms for the innate immune response to lipopolysaccharide, based on the research results for both TLR-dependent and independent signaling pathways. Special emphasis was put on the research results for the TLR-dependent immune response and the anti-bacterial/anti-inflammatory response after applying immunonutrition with increased concentrations of glutamine and unsaturated fatty acids.

Effects of caffeic acid phenethyl ester on endotoxin-induced cardiac stress in rats: a possible mechanism of protection

Endotoxins (lipopolysaccharides; LPS) are known to cause multiple organ failure, including myocardial dysfunction. The present study aimed to investigate the mechanism of caffeic acid phenethyl ester (CAPE) protection against LPS-induced cardiac stress. Rats were allocated into three groups; group 1 served as a normal control group, group 2 (LPS) received a single intraperitoneal injection of LPS (10 mg/kg), group 3 (LPS + CAPE) was injected intraperitoneally with CAPE (10 mg/kg/day; solubilized in saline containing 20% tween 20) throughout a period of 10 days prior to LPS injection. Rats were maintained 4 h before sacrifice. Caffeic acid phenethyl ester pretreatment normalized LPS-enhanced activities of serum creatine kinase (CK) and lactate dehydrogenase (LDH) as well as glutathione peroxidase (GPx), and myeloperoxidase (MPO) in cardiac tissue. A significant reduction of the elevated levels of serum tumor necrosis factor-alpha (TNF-α) as well as serum and cardiac nitrite/nitrate (NOx) ) was achieved after CAPE pretreatment. CAPE also restored malondialdelyde (MDA), reduced glutathione (GSH), and cytosolic calcium (Ca2+ ) levels in the heart. A marked induction of cardiac heme oxygenase-1 (HO-1) protein level was detected in CAPE-pretreated group. Whereas, LPS-induced reduction of adenosine triphosphate (ATP) and phosphocreatine (PCr) levels was insignificantly changed. Conclusively, the early treatment with CAPE maintained antioxidant defences, reduced oxidative injury, cytokine damage, and inflammation but did not markedly improve energy status in cardiac tissue. The beneficial effect of CAPE might be mediated, at least in part, by the superinduction of HO-1.

Cardiomyocyte Toll-like receptor 4 is involved in heart dysfunction following septic shock or myocardial ischemia

Toll-like receptors are expressed in immune cells and cardiac muscle. We examined whether the cardiac Toll-like receptor 4 (TLR4) is involved in the acute myocardial dysfunction caused by septic shock and myocardial ischemia (MI). We used wild type mice (WT), TLR4 deficient (TLR4-ko) mice and chimeras that underwent myeloablative bone marrow transplantation to dissociate between TLR4 expression in the heart (TLR4-ko/WT) and the immunohematopoietic system (WT/TLR4-ko). Mice were injected with lipopolysaccharide (LPS) (septic shock model) or subjected to coronary artery ligation (MI model) and tested in vivo and ex vivo, for function, histopathology proinflammatory cytokine and TLR4 expression. WT mice challenged with LPS or MI displayed reduced cardiac function, increased myocardial levels of IL-1 beta and TNF-alpha and upregulation of mRNA encoding TLR4 prior to myocardial leukocyte infiltration. TLR4 deficient mice sustained significantly smaller infarctions as compared to control mice at comparable areas at risk. The cardiac function of TLR4-ko mice was not affected by LPS and demonstrated reduced suppression by MI compared to WT. Chimeras deficient in myocardial TLR4 were resistant to suppression induced by LPS and the heart function was less depressed, compared to the TLR4-ko, following MI in the acute phase (4h). In contrast, hearts of chimeras deficient in immunohematopoietic TLR4 expression were suppressed both by LPS and MI, exhibiting increased myocardial cytokine levels, similar to WT mice. We concluded that cardiac function of TLR4-ko mice and chimeric mice expressing TLR4 in the immunohematopoietic system, but not in the heart, revealed resistance to LPS and reduced cardiac depression following MI, suggesting that TLR4 expressed by the cardiomyocytes themselves plays a key role in this acute phenomenon.

Sepsis and the heart

Sepsis is generally viewed as a disease aggravated by an inappropriate immune response encountered in the afflicted individual. As an important organ system frequently compromised by sepsis and always affected by septic shock, the cardiovascular system and its dysfunction during sepsis have been studied in clinical and basic research for more than 5 decades. Although a number of mediators and pathways have been shown to be associated with myocardial depression in sepsis, the precise cause remains unclear to date. There is currently no evidence supporting global ischemia as an underlying cause of myocardial dysfunction in sepsis; however, in septic patients with coexistent and possibly undiagnosed coronary artery disease, regional myocardial ischemia or infarction secondary to coronary artery disease may certainly occur. A circulating myocardial depressant factor in septic shock has long been proposed, and potential candidates for a myocardial depressant factor include cytokines, prostanoids, and nitric oxide, among others. Endothelial activation and induction of the coagulatory system also contribute to the pathophysiology in sepsis. Prompt and adequate antibiotic therapy accompanied by surgical removal of the infectious focus, if indicated and feasible, is the mainstay and also the only strictly causal line of therapy. In the presence of severe sepsis and septic shock, supportive treatment in addition to causal therapy is mandatory. The purpose of this review is to delineate some characteristics of septic myocardial dysfunction, to assess the most commonly cited and reported underlying mechanisms of cardiac dysfunction in sepsis, and to briefly outline current therapeutic strategies and possible future approaches.

The role of ICAM-1 in endotoxin-induced acute renal failure

The pathogenesis of acute renal failure (ARF) occurring during the course of sepsis is incompletely understood. Intercellular adhesion molecule-1 (ICAM-1) is a key cell adhesion molecule upregulated by LPS, which binds to the integrins CD11a/CD18 and CD11b/CD18 present on the surface of leukocytes. We hypothesized that ICAM-1 facilitates renal injury in LPS-induced ARF. To test this, three groups of mice (n = 8 per group) were injected intraperitoneally with 6 mg/kg LPS: 1) normal C57BL/6 mice, 2) mice with a targeted deficiency of ICAM-1 (ICAM-1(-/-)), and 3) mice expressing very low levels of CD18 (CD18-def). ICAM-1(-/-) mice were significantly resistant to LPS-mediated ARF, as opposed to CD18-def mice, which developed severe ARF, as did wild-type controls (48 h blood urea nitrogen 143 +/- 31.5, 70.8 +/- 24.4, and 185 +/- 16.6 mg/dl in wild-type, ICAM-1(-/-), and CD18-def mice, respectively, P < 0.05). At death, ICAM-1(-/-) mice had significantly less renal neutrophil infiltration than the other two groups, as well as less histological tubular injury. Depletion of neutrophils with mAb Gr-1 led to a profound exaggeration of tumor necrosis factor (TNF) release and high mortality, but neutrophil-depleted mice receiving 10-fold less LPS were protected against ARF despite TNF release similar to what is normally associated with LPS-induced ARF. LPS caused a significant increase in renal expression of chemokines; however, this increase was significantly exaggerated in CD18-def mice, which may account for their lack of protection. In conclusion, these data show that ICAM-1 plays a key role in LPS-induced ARF.

Complement-related molecular events in sepsis leading to heart failure

Despite intensive ongoing research efforts, the mortality of patients with sepsis remains unacceptably high. A significant number of clinical trials have failed to produce sufficient therapeutic strategies despite showing promising results in animal models. So far, many studies have focused on deterioration of the humoral and cellular components of the immune system, the main cause of death in septic patients being multi-organ failure. However, not much is known about the effects of the complement system on parenchymal cells of organs such as the heart. Recently, septic cardiomyopathy has been recognized as one of the major complications during sepsis, often determining the clinical outcome. In this review, we describe molecular events which are thought to be related to cardiac dysfunction during sepsis. A special emphasis will be placed on the complement system, which generates powerful anaphylatoxins (such as C5a) and which has recently been associated with septic cardiomyopathy. Together with the impact on cardiac function of various cytokines we will provide a synopsis of the current knowledge regarding the pathophysiology underlying cardiac failure during sepsis with a special emphasis on C5a and C5aR.

Toll-like receptor modulation in cardiovascular disease: a target for intervention?

Toll-like receptors (TLRs) form a family of pattern recognition receptors that have emerged as key mediators of innate immunity. These receptors sense invading microbes and initiate the immune response. TLR-mediated inflammation is an important pathogenic link between innate immunity and a diverse panel of clinical disorders. Among the processes in which TLRs play a role are cardiovascular disorders such as cardiac ischaemia, coronary artery disease, ventricular remodelling, cancer angiogenesis or transplant rejection. From these, many important opportunities for disease modification through TLR signalling manipulation can be imagined. Their role as potential targets for therapeutic intervention is just beginning to be appreciated and this article reviews the current status of these treatment strategies for cardiovascular disease.

Is there a role for cardiomyocyte toll-like receptor 4 in endotoxemia?

Lipopolysaccharide (LPS) is thought to be an important molecule in myocardial depression in sepsis. Toll-like receptor 4 (TLR4), the lipopolysaccharide receptor, is known to underlie these responses. Because TLR4 is expressed on both cardiac myocytes and immune cells, it is unclear as to which cell type is responsible for myocyte depression. In this article, we present evidence that the early response is likely related to TLR4 on immune cells and most likely macrophages, whereas the more delayed response may involve various immune cells as well as myocytes.

Cellular and molecular mechanisms underlying LPS-associated myocyte impairment

Recently we reported that Toll-like receptor 4 (TLR4)-positive immune cells of unknown identity were responsible for the LPS-induced depression of cardiac myocyte shortening. The aim of this study is to identify the TLR4-positive cell type that is responsible for the LPS-induced cardiac dysfunction. Neither neutrophil depletion alone nor mast cell deficiency had any impact on the impairment of myocyte shortening during LPS treatment. In contrast, LPS-treated, macrophage-deficient mice demonstrated a partial reduction in shortening compared with saline-treated, macrophage-deficient mice. Because the removal of macrophages could only partially restore myocyte shortening, we also investigated the effects of removing both neutrophils and macrophages on myocyte shortening. Interestingly, endotoxemic, neutrophil-depleted, and macrophage-deficient mice had completely restored myocyte shortening. Because both macrophages and neutrophils can produce nitric oxide (NO) and TNF-α, we examined LPS-treated inducible NO synthase knockout (iNOSKO) mice and TNF receptor (TNFR)-deficient mice. Eliminating both TNFR1 and TNFR2 was required to restore myocyte shortening during LPS treatment, whereas iNOS deficiency had no effect. These data suggest that macrophages and to a lesser degree neutrophils cause cardiac impairment, presumably via TNF-α.

Endotoxin-induced heart dysfunction in rats: assessment of myocardial perfusion and permeability and the role of fluid resuscitation

OBJECTIVE

The pathophysiology of sepsis-induced myocardial dysfunction is still controversial. Whether microcirculatory hypoperfusion together with capillary leakage can occur in the heart wall also remains a matter of debate. The objective was to evaluate the impact of fluid resuscitation on endotoxin-induced myocardial dysfunction.

DESIGN

Adult rats were given intraperitoneal injection of endotoxin (lipopolysaccharide, Escherichia coli, 10 mg/kg) or phosphate-buffered solution, followed up by echocardiography and acetate micro-positron emission tomography scan imaging, together with final hemodynamic, biochemical, and pathologic evaluations up to 48 hrs.

SETTING

University laboratory.

SUBJECTS

Pathogen-free male Wistar rats (350 g).

INTERVENTIONS

Influence of isovolumic fluid infusion type (saline vs. pentastarch) on these variables was assessed in 11 groups of six animals including an unchallenged control one.

MEASUREMENTS AND MAIN RESULTS

Endotoxin injection induced a) myocardial dysfunction (decrease of approximately 15-20% in left ventricular ejection fraction); b) ventricular enlargement (approximately 1.5- to 1.7-fold increase in left ventricular systolic volume); c) cardiac output increase (10-15%); d) myocardial hypoperfusion ( approximately 1.5- to 2-fold decrease in acetate k1 constant rate); e) increased oxygen consumption (k2); and f) interstitial wall increase. Endotoxin injection also enhanced levels of arterial lactates and troponin I. Colloid (pentastarch) over crystalloid (saline) fluid resuscitation significantly reversed echocardiographic changes, some positron emission tomography imaging alterations, and lactate and troponin I levels without further enhancing interstitial spaces.

CONCLUSION

Endotoxin can induce reversible myocardial alterations with evidence of coronary hypoperfusion and heart wall enlargement/damage, some of which can be prevented by fluid resuscitation. The use of crystalloids is less beneficial than pentastarch.

Human serum from patients with septic shock activates transcription factors STAT1, IRF1, and NF-kappaB and induces apoptosis in human cardiac myocytes

Proinflammatory cytokines have been linked to depression of myocardial contractility in vivo in patients with acute septic shock and in vitro models employing isolated myocytes exposed to serum from such patients. The key pathways involved in mediating this septic organ dysfunction (cell adhesion molecule expression, inducible nitric-oxide synthase induction, and apoptosis) are known to be regulated by transcription factors STAT1, IRF1, and NF-kappaB. Utilizing a model that mimics human disease, we have demonstrated activation of the transcription factors STAT1, IRF1, and NF-kappaB in human fetal myocytes exposed to human septic serum. Both reporter and electrophoretic mobility shift assays demonstrated a 5-19-fold increase in activation of transcription factors STAT1, IRF1, and NF-kappaB in response to incubation with human septic serum. The addition of human septic serum to human fetal myocytes induced apoptosis in human fetal myocytes and activation of the mitogen-activated protein kinase c-Jun NH -terminal kinase and caspase 1 as measured by Western blot. These data suggest that transcription factor activation and early myocyte apoptosis play a mechanistic role in septic myocardial depression and sepsis-induced organ dysfunction.

Sepsis and myocardial depression in a young woman

Severe sepsis may be associated with depression of myocardial function, attributed to various inflammatory mediators. Myocardial dysfunction in sepsis is characterized by biventricular failure and complicates usual therapy with high-volume fluid resuscitation and vasopressors. However, in patients who survive septic shock, myocardial dysfunction can improve rapidly. We describe a young woman with septic shock due to Streptococcus pneumoniae, complicated by severe but reversible biventricular dysfunction.

Endotoxin-induced myocardial dysfunction: effects of macrophage migration inhibitory factor neutralization

The pathophysiology of sepsis-induced myocardial dysfunction still remains controversial. Macrophage migration inhibitory factor (MIF) has recently been identified as a cardiac-derived myocardial depressant factor in septic shock. Putative mechanisms by which MIF affects cardiac function are unknown. In an investigation of possible mechanisms of action, a rat model of endotoxin toxicity was designed using intraperitoneal (I/P) injection of lipopolysaccharides (LPS) with or without coinfusion of neutralizing anti-MIF or isotypic-matched antibodies. Echocardiographic evaluation revealed that MIF neutralization reversed endotoxin-induced myocardial dysfunction at 24 hours after injection. RNase protection assay (RPA) and Western blot established that MIF neutralization prevented LPS-induced mRNA expression and production of heart-derived inflammatory paracrine and autocrine cytokines such as IL-1s and IL-6. Moreover, MIF immunoneutralization increased heart Bcl-2/Bax protein ratio and suppressed endotoxin-induced release of mitochondrial cytochrome-c, as demonstrated by Western blotting. Inhibition of mitochondrial loss of cytochrome-c decreased in heart caspase-3 activity at 6 and 24 hours after injection. MIF neutralization also restored the LPS-induced deficient nuclear translocation of phospho-Akt and consequently the expression of the heart survival nuclear factor GATA-4. The restoration of the translocation/expression of survival factors by MIF inhibition resulted in lowered endotoxin-induced DNA fragmentation at 24 hours, a hallmark of downstream cardiomyocyte apoptosis. Our data indicate that early inactivation of MIF significantly reverses the imbalance of proapoptotic to prosurvival pathways and reduces acute inflammation of the heart thereby improving myocardial dysfunction induced by endotoxin.

Molecular mechanisms in endothelial regulation of cardiac function

Endothelium is now recognized as a massive, regionally specific, multifunctional organ. Given its strategic anatomic location between the circulating blood components and the vascular smooth muscle or the cardiac muscle, it is a biologically significant interface whose dysfunction can be a critical factor in various pathological conditions. Two types of endothelial cells are recognized in the heart, the endocardial endothelial (EE) cells and the microvascular endothelial cells (MVE). Both produce common autacoids and share similar roles in signal transduction induced by neurotransmitters, hormones or mechanical stimuli. They are however two distinct cell populations with dissimilar embryological origin, cytoskeletal organization, receptor mediated functions and electrophysiological properties. Both the MVE and EE are modulators of cardiac performance. Myocardial contraction may be modulated by cardioactive agents such as nitric oxide, prostanoids, endothelin, natriuretic peptides, angiotensin II, kinins, reactive oxygen species and adenyl purines released from the cardiac endothelium. Two mechanisms have been proposed for the signal transduction from EE to the underlying myocytes: stimulus-secretion-contraction coupling and blood-heart barrier. Nitric oxide, bradykinin and myofilament desensitizing agent are probably important in short-term regulation of myocardial functions. Endothelin and Angiotensin II are probably involved in long-term regulation. Besides its sensory function and paracrine modulation of myocardial performance, EE as a blood-heart barrier could be of significance for the ionic homeostasis of the cardiac interstitium. In cardiac diseases, the damage to EE or MVE leading to failure of the endothelial cells to perform its regulatory and modulator functions may have serious consequences. A better understanding of the endothelial signaling pathways in cardiac physiology and pathophysiology may lead to the development of novel therapeutic strategies.

Immune cell Toll-like receptor 4 is required for cardiac myocyte impairment during endotoxemia

The aim of this study was to investigate the importance of Toll-like receptor 4 (TLR4) signaling on cardiac myocytes versus immune cells in lipopolysaccharide (LPS)-induced cardiac dysfunction. Cardiac myocytes isolated from LPS-treated C57Bl/6 mice showed reduced shortening and calcium transients as compared with myocytes from untreated mice. In addition, LPS-treated C57Bl/6 mice showed impaired cardiac mitochondrial function, including reduced respiration and reduced time of induction of permeability transition. All of the aforementioned cardiac dysfunction was dependent on TLR4, because LPS-treated TLR4-deficient mice did not have reduced myocyte shortening or mitochondrial dysfunction. To evaluate the role of cardiac myocyte versus leukocyte TLR4, LPS was injected into chimeric mice with TLR4-positive leukocytes and TLR4-deficient myocytes. These mice showed reduced myocyte shortening in response to LPS. Myocytes from chimeric mice with TLR4-deficient leukocytes and TLR4-positive myocytes had no response to LPS. In addition, isolated myocytes from C57Bl/6 mice subsequently treated with LPS and serum for various times did not have reduced shortening, despite the presence of TLR4 mRNA and protein, as determined by reverse-transcription polymerase chain reaction and fluorescent-activated cell sorting. In fact, cardiac myocytes had equivalent amounts of TLR4 as endothelium; however, only the latter is responsive to LPS. Furthermore, signaling pathways downstream of TLR4 were not activated during direct LPS treatment of myocytes. In conclusion, TLR4 on leukocytes, and not on cardiac myocytes, is important for cardiac myocyte impairment during endotoxemia.

C5a causes limited, polymorphonuclear cell-independent, mesenteric ischemia/reperfusion-induced injury

C5 is critical in the development of local mucosal damage and inflammation as well as in the development of remote organ injury after mesenteric ischemia/reperfusion (IR). To define the role of C5a in tissue injury, we treated wild-type mice with a cyclic hexapeptide C5a receptor antagonist (C5aRa) and administered recombinant C5a to C5 deficient (C5(-/-)) mice subjected to mesenteric IR. We demonstrate that at 2-h postreperfusion, C5a administered to C5-/- mice during IR induces limited intestinal mucosal injury but failed to cause remote lung injury despite the fact that it upregulated adhesion molecule expression. C5aRa treatment of C5+/+ mice undergoing IR limited local injury and prevented distant organ injury. We conclude that although C5a can trigger certain components of the IR induced injury, other mediators such as C5b-9 and local factors are needed for the complete expression of IR tissue damage.

Interleukin-6-deficient mice resist development of autoimmune myocarditis associated with impaired upregulation of complement C3

BACKGROUND

Interleukin (IL)-6 regulates various aspects of the immune response. In the context of heart diseases, it has been recognized as a prognostic factor for dilated cardiomyopathy, which often results from myocarditis.

METHODS AND RESULTS

Using IL-6-deficient mice, we studied the role of IL-6 in a model of autoimmune myocarditis resulting from immunization with a peptide derived from cardiac alpha-myosin. Prevalence and severity of myocarditis were markedly reduced in the absence of IL-6. CD4+ T cells from immunized IL-6-deficient mice proliferated poorly on restimulation with specific antigen in vitro and did not mediate disease on adoptive transfer into IL-6-competent RAG-2-deficient mice, which otherwise lack B cells and T cells. Production of complement C3, a crucial factor for the development of myocarditis, was strongly upregulated in IL-6+/+ but not in IL-6-deficient mice after immunization.

CONCLUSIONS

Our results demonstrate that IL-6 is required for the expansion of autoimmune CD4+ T cells and the pathogenesis of autoimmune myocarditis, possibly by upregulation of complement C3.

Dietary modification of inflammation with lipids

The n-3 polyunsaturated fatty acids (PUFA) eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are found in high proportions in oily fish and fish oils. The n-3 PUFA are structurally and functionally distinct from the n-6 PUFA. Typically, human inflammatory cells contain high proportions of the n-6 PUFA arachidonic acid and low proportions of n-3 PUFA. The significance of this difference is that arachidonic acid is the precursor of 2-series prostaglandins and 4-series leukotrienes, which are highly-active mediators of inflammation. Feeding fish oil results in partial replacement of arachidonic acid in inflammatory cell membranes by EPA. This change leads to decreased production of arachidonic acid-derived mediators. This response alone is a potentially beneficial anti-inflammatory effect of n-3 PUFA. However, n-3 PUFA have a number of other effects which might occur downstream of altered eicosanoid production or might be independent of this activity. For example, animal and human studies have shown that dietary fish oil results in suppressed production of pro-inflammatory cytokines and can decrease adhesion molecule expression. These effects occur at the level of altered gene expression. This action might come about through antagonism of the effects of arachidonic acid-derived mediators or through more direct actions on the intracellular signalling pathways which lead to activation of transcription factors such as nuclear factor kappa B (NFB). Recent studies have shown that n-3 PUFA can down regulate the activity of the nuclear transcription factor NFB. Fish oil feeding has been shown to ameliorate the symptoms in some animal models of chronic inflammatory disease and to protect against the effects of endotoxin and similar inflammatory challenges. Clinical studies have reported that oral fish oil supplementation has beneficial effects in rheumatoid arthritis and among some patients with asthma, supporting the idea that the n-3 PUFA in fish oil are anti-inflammatory. There are indications that inclusion of n-3 PUFA in enteral and parenteral formulas might be beneficial to patients in intensive care or post-surgery.

Neutralization of IL-18 attenuates lipopolysaccharide-induced myocardial dysfunction

Tumor necrosis factor-alpha (TNF-alpha) and interleukin-1beta (IL-1beta) have been implicated in cardiac dysfunction during endotoxemia. Because IL-18 is a proinflammatory cytokine known to mediate the production of TNF-alpha and IL-1beta and to induce the expression of intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1), we hypothesized that neutralization of IL-18 would attenuate lipopolysaccharide (LPS)-induced cardiac dysfunction. Mice (C57BL/6) were injected with LPS (0.5 mg/kg ip) or vehicle (normal saline), and left ventricular developed pressure (LVDP) was determined by the Langendorff technique. LVDP was depressed by 38% at 6 h after LPS. LPS-induced myocardial dysfunction was associated with increased myocardial levels of TNF-alpha and IL-1beta as well as increased expression of ICAM-1/VCAM-1. Pretreatment with neutralizing anti-mouse IL-18 antibody attenuated LPS-induced myocardial dysfunction (by 92%) and was associated with reduced myocardial IL-1beta production (65% reduction) and ICAM-1/VCAM-1 expression (50% and 35% reduction, respectively). However, myocardial TNF-alpha levels were not influenced by neutralization of IL-18. In conclusion, neutralization of IL-18 protects against LPS-induced myocardial dysfunction. IL-18 may mediate endotoxemic myocardial dysfunction through induction of and/or synergy with IL-1beta, ICAM-1, and VCAM-1.

ICAM-1 and VCAM-1 mediate endotoxemic myocardial dysfunction independent of neutrophil accumulation

Both intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) have been implicated in neutrophil-mediated lung and liver injury during sepsis. However, the role of these adhesion molecules as well as the contribution of neutrophils in myocardial dysfunction during sepsis remains to be determined. The purpose of this study was to examine the role of ICAM-1, VCAM-1, and neutrophils in lipopolysaccharide (LPS)-induced myocardial dysfunction. Mice were subjected to LPS (0.5 mg/kg ip) or vehicle (normal saline), and left ventricular developed pressure (LVDP) was determined by the Langendorff technique. LVDP was depressed by nearly 40% at 6 h after LPS. Immunofluorescent staining revealed a temporal increase in myocardial ICAM-1/VCAM-1 expression and neutrophils after LPS. Antibody blockade of VCAM-1 reduced myocardial neutrophil accumulation and abrogated LPS-induced cardiac dysfunction. Antibody blockade or absence of ICAM-1 (gene knockout) also abrogated LPS-induced cardiac dysfunction but did not reduce neutrophil accumulation. Neutrophil depletion (vinblastine or antibody) did not protect from LPS-induced myocardial dysfunction. Our results suggest that although endotoxemic myocardial dysfunction requires both ICAM-1 and VCAM-1, it occurs independent of neutrophil accumulation.