Tumor necrosis factor alpha up-regulates Gi alpha and G beta proteins and adenylyl cyclase responsiveness in rat cardiomyocytes

MECHANISMS OF CARDIAC DYSFUNCTION IN SEPSIS

ABSTRACT

Studies in animal models of sepsis have elucidated an intricate network of signaling pathways that lead to the dysregulation of myocardial Ca 2+ handling and subsequently to a decrease in cardiac contractile force, in a sex- and model-dependent manner. After challenge with a lethal dose of LPS, male animals show a decrease in cellular Ca 2+ transients (ΔCa i ), with intact myofilament function, whereas female animals show myofilament dysfunction, with intact ΔCa i . Male mice challenged with a low, nonlethal dose of LPS also develop myofilament desensitization, with intact ΔCa i . In the cecal ligation and puncture (CLP) model, the causative mechanisms seem similar to those in the LPS model in male mice and are unknown in female subjects. ΔCa i decrease in male mice is primarily due to redox-dependent inhibition of sarco/endoplasmic reticulum Ca 2+ ATP-ase (SERCA). Reactive oxygen species (ROS) are overproduced by dysregulated mitochondria and the enzymes NADPH/NADH oxidase, cyclooxygenase, and xanthine oxidase. In addition to inhibiting SERCA, ROS amplify cardiomyocyte cytokine production and mitochondrial dysfunction, making the process self-propagating. In contrast, female animals may exhibit a natural redox resilience. Myofilament dysfunction is due to hyperphosphorylation of troponin I, troponin T cleavage by caspase-3, and overproduction of cGMP by NO-activated soluble guanylate cyclase. Depleted, dysfunctional, or uncoupled mitochondria likely synthesize less ATP in both sexes, but the role of energy deficit is not clear. NO produced by NO synthase (NOS)-3 and mitochondrial NOSs, protein kinases and phosphatases, the processes of autophagy and sarco/endoplasmic reticulum stress, and β-adrenergic insensitivity may also play currently uncertain roles.

Proinflammatory Cytokines Mediate GPCR Dysfunction

Proinflammatory reaction by the body occurs acutely in response to injury that is considered primarily beneficial. However, sustained proinflammatory cytokines observed with chronic pathologies such as metabolic syndrome, cancer, and arthritis are detrimental and in many cases is a major cardiovascular risk factor. Proinflammatory cytokines such as interleukin-1, interleukin-6, and tumor necrosis factor α (TNFα) have long been implicated in cardiovascular risk and considered to be a major underlying cause for heart failure (HF). The failure of the anti-TNFα therapy for HF indicates our elusive understanding on the dichotomous role of proinflammatory cytokines on acutely beneficial effects versus long-term deleterious effects. Despite these well-described observations, less is known about the mechanistic underpinnings of proinflammatory cytokines especially TNFα in pathogenesis of HF. Increasing evidence suggests the existence of an active cross-talk between the TNFα receptor signaling and G-protein-coupled receptors such as β-adrenergic receptor (βAR). Given that βARs are the key regulators of cardiac function, the review will discuss the current state of understanding on the role of proinflammatory cytokine TNFα in regulating βAR function.

Proinflammatory switch from Gαs to Gαi signaling by Glucagon-like peptide-1 receptor in murine splenic monocyte following burn injury

OBJECTIVE

Glucagon-like peptide-1 (GLP-1)-based therapy via G protein-coupled receptor (GPCR) GLP-1R, to attenuate hyperglycemia in critical care has attracted great attention. However, the exaggerated inflammation by GLP-1R agonist, Exendin-4, in a mouse model of burn injury was quite unexpected. Recent studies found that GPCR might elicit proinflammatory effects by switching from Gαs to Gαi signaling in the immune system. Thus, we aimed to investigate the possible Gαs to Gαi switch in GLP-1R signaling in monocyte following burn injury.

MATERIALS AND METHODS

Splenic monocytes from sham and burn mice 24 h following burn injury were treated with consecutive doses of Exendin-4 alone or in combination with an inhibitor of Gαi signaling (pertussis toxin, PTX), or a blocker of protein kinase A (H89). Cell viability was assessed by CCK-8, and the supernatant was collected for cytokine measurement by ELISA. Intracellular cAMP level, phosphorylated PKA activity, and nuclear NF-κB p65 were determined by ELISA, ERK1/2 activation was analyzed by Western blot. The expression of GLP-1R downstream molecules, Gαs, Gαi and G-protein coupled receptor kinase 2 (GRK2) were examined by immunofluorescence staining and Western blot.

RESULTS

Exendin-4 could inhibit the viability of monocyte from sham rather than burn mice. Unexpectedly, it could also reduce TNF-α secretion from sham monocyte while increase it from burn monocyte. The increased secretion of TNF-α by Exendin-4 from burn monocyte could be reversed by pretreatment of PTX or H89. Accordingly, Exendin-4 could stimulates cAMP production dose dependently from sham instead of burn monocyte. However, the blunt cAMP production from burn monocyte was further suppressed by pretreatment of PTX or H89 after 6-h incubation. Nevertheless, phosphorylated PKA activity was significantly increased by low dose of Exendin-4 in sham monocyte, by contrast, it was enhanced by high dose of Exendin-4 in burn monocyte after 1-h incubation. Following Exendin-4 treatment for 2 h ex vivo, total nuclear NF-κB and phosphorylated NF-κB activity, as well as cytoplasmic pERK1/2 expressions were reduced in sham monocyte, however, only pERK1/2 was increased by Exendin-4 in burn monocytes. Moreover, reduced expressions of GLP-1R, GRK-2 and Gαs in contrast with increased expression of Gαi were identified in burn monocyte relative to sham monocyte.

CONCLUSIONS

This study presents an unexpected proinflammatory switch from Gαs to Gαi signaling in burn monocyte, which promotes ERK1/2 and NF-κB activation and the downstream TNF-α secretion. This phenomenon is most probably responsible for proinflammatory response evoked by Gαs agonist Exendin-4 following burn injury.

Role of cytokines in myocardial ischemia and reperfusion

Mediators of myocardial inflammation, predominantly cytokines, have for many years been implicated in the healing processes after infarction. In recent years, however, more attention has been paid to the possibility that the inflammation may result in deleterious complications for myocardial infarction. The proinflammatory cytokines may mediate myocardial dysfunction associated with myocardial infarction, severe congestive heart failure, and sepsis. A growing body of literature suggests that inflammatory mediators could play a crucial role in ischemia–reperfusion injury. Furthermore, ischemia–reperfusion not only results in the local transcriptional and translational upregulation of cytokines but also leads to tissue infiltration by inflammatory cells. These inflammatory cells are a ready source of a variety of cytokines which could be lethal for the cardiomyocytes. At the cellular level it has been shown that hypoxia causes a series of well documented changes in cardiomyocytes that includes loss of contractility, changes in lipid metabolism and subsequent irreversible cell membrane damage leading to cell death. For instance, hypoxic cardiomyocytes produce interleukin-6 (IL-6) which could contribute to the myocardial dysfunction observed in ischemia reperfusion injury. Ischemia followed by reperfusion induces a number of other multi-potent cytokines, such as IL-1, IL-8, tumor necrosis factor-α (TNF-α), transforming growth factor-β1 (TGF-β1) as well as an angiogenic cytokine/ growth factor, vascular endothelial growth factor (VEGF), in the heart. Intrestingly, these multipotent cytokines (e.g. TNF-α) may induce an adaptive cytoprotective response in the reperfused myocardium. In this review, we have included a number of cytokines that may contribute to ventricular dysfunction and/or to the cytoprotective and adaptive changes in the reperfused heart.

Airway smooth muscle in asthma: just a target for bronchodilation?

Airway smooth muscle (ASM) has long been recognized as the main cell type responsible for bronchial hyperresponsiveness. It has, thus, been considered as a target for bronchodilation. In asthma, however, there is a complex relationship between ASM and inflammatory cells, such as mast cells and T lymphocytes. Moreover, the increased ASM mass in asthmatic airways is one of the key features of airway remodeling. This article aims to review the main concepts about the 3 possible roles of ASM in asthma: (1) contractile tone, (2) inflammatory response, and (3) remodeling.

Low level laser therapy partially restores trachea muscle relaxation response in rats with tumor necrosis factor alpha-mediated smooth airway muscle dysfunction

BACKGROUND AND OBJECTIVE

It is unknown if the decreased ability to relax airway smooth muscles in asthma and other inflammatory airways disorders can be influenced by low level laser therapy (LLLT) irradiation. To investigate if LLLT could reduce impairment in inflamed trachea smooth muscles (TSM) in rats.

STUDY DESIGN/MATERIALS AND METHODS

Controlled rat study where trachea was dissected and mounted in an organ bath apparatus with or without a TNF-alpha solution.

RESULTS

Low level laser therapy administered perpendicularly to a point in the middle of the dissected trachea with a wavelength of 655 nm and a dose of 2.6 J/cm(2), partially restored TSM relaxation response to isoproterenol. Tension reduction was 47.0 % (+/-2.85) in the laser-irradiated group compared to 22.0% (+/-2.21) in the control group (P < 0.01). Accumulation of cAMP was almost normalized after LLLT at 22.3 pmol/mg (+/-2.1) compared to 17.6 pmol/mg (+/-2.1) in the non-irradiated control group (P < 0.01).

CONCLUSION

Low level laser therapy partially restores the normal relaxation response in inflamed TSM and normalizes accumulation of cAMP in the presence of isoproterenol.

Lipopolysaccharide-induced sensitization of adenylyl cyclase activity in murine macrophages

LPS is known to modulate macrophage responses during sepsis, including cytokine release, phagocytosis, and proliferation. Although agents that elevate cAMP reverse LPS-induced macrophage functions, whether LPS itself modulates cAMP and whether LPS-induced decreases in proliferation are modulated via a cAMP-dependent pathway are not known. Murine macrophages (RAW264.7 cells) were treated with LPS in the presence or absence of inhibitors of prostaglandin signaling, protein kinases, CaM, Giproteins, and NF-κB translocation or transcription/translation. LPS effects on CaMKII phosphorylation and the expression of relevant adenylyl cyclase (AC) isoforms were measured. LPS caused a significant dose (5–10,000 ng/ml)- and time (1–8 h)-dependent increase in forskolin-stimulated AC activity that was abrogated by pretreatment with SN50 (an NF-κB inhibitor), actinomycin D, or cycloheximide, indicating that the effect is mediated via NF-κB-dependent transcription and new protein synthesis. Furthermore, LPS decreased the phosphorylation state of CaMKII, and pretreatment with a CaM antagonist attenuated the LPS-induced sensitization of AC. LPS, cAMP, or PKA activation each independently decreased macrophage proliferation. However, inhibition of NF-κB had no effect on LPS-induced decreased proliferation, indicating that LPS-induced decreased macrophage proliferation can proceed via PKA-independent signaling pathways. Taken together, these findings indicate that LPS induces sensitization of AC activity by augmenting the stimulatory effect of CaM and attenuating the inhibitory effect of CaMKII on isoforms of AC that are CaMK sensitive.

Amitriptyline administration transforms tumor necrosis factor-alpha regulation of norepinephrine release in the brain

The present study demonstrates that the mixed action antidepressant drug amitriptyline enhances norepinephrine (NE) release by transforming the nature of the response of neurons to both tumor necrosis factor-alpha (TNF) as well as to an alpha(2)-adrenergic agonist in an area of the central nervous system (CNS) rich in adrenergic neurons. Administration of the antidepressant drug amitriptyline for 1 day or 14 days to rats significantly increases TNF bioactivity in total homogenates of the locus coeruleus (LC) and the hippocampus as assessed by the WEHI-13VAR bioassay. Superfusion and electrical field stimulation of rat hippocampal brain slices were used to study the regulation of NE release. Exposure to TNF, as well as activation of the alpha(2)-adrenergic autoreceptor inhibits stimulation-evoked norepinephrine (NE) release from adrenergic neurons of the CNS from naïve rats. Superfusion of hippocampal slices isolated from rats chronically (14 days) administered amitriptyline demonstrates that TNF inhibition of NE release is transformed, such that TNF facilitates NE release, dependent upon alpha(2)-adrenergic activation. Furthermore, chronic administration of amitriptyline increases stimulation-evoked NE release and decreases alpha(2)-adrenergic autoreceptor inhibition of NE release, an effect not observed with acute drug administration. These data support the hypothesis that chronic antidepressant drug administration, through regulation of TNF expression, transforms alpha(2)-adrenergic receptors such that they function to facilitate NE release, suggesting a mechanism of action of antidepressant drugs.

Cytokine-Induced Modulation of Cardiac Function

Cytokines act in an autocrine and/or paracrine fashion to induce a diverse variety of biological responses. Several cardiac diseases are associated with cytokine activation, and such activation significantly influences several physiologic parameters, including cardiac mechanical function. This review summarizes the current concepts regarding the modulation of myocardial function by cytokines and provides rationale for the sometimes-conflicting results in the literature regarding underlying mechanisms and patterns of dysfunction. Although traditionally considered cardiodepressant mediators, contractile responses are complex and bimodal, with an early response (within minutes) of variable direction, stimulatory or depressant, depending on the ambient physiologic milieu and relative contributions of the underlying signaling pathways that are activated. These pathways include sphingomyelinase-, nitric oxide (NO)-, and phospholipase A2-dependent signaling with resultant combined effects on contraction and the Ca2+ transient. This is subsequently followed by a profoundly cardiodepressant late response lasting hours to days, depending on the production of secondary mediators and the combined influence of NO generated from inducible NO synthase, reactive oxygen species, and alterations in beta-adrenergic receptor signaling. The interrelationships between these pathways and the time-dependence of their activation are important considerations in the evaluation of cytokine-dependent dysfunction during both acute cardiac injury and chronic cardiac pathologies.

Interleukin-1beta mediates endotoxin- and tumor necrosis factor alpha-induced RGS16 protein expression in cultured cardiac myocytes

Endotoxin (LPS)-induced cardiac failure is associated with an up-regulation of RGS16 protein expression and repression of phospholipase C activity in vivo. Since the release of pro-inflammatory cytokines plays an important role in mediating LPS-induced myocardial dysfunction, we examined the effect of recombinant cytokines on the expression of RGS16 protein in neonatal cardiac myocytes. Myocytes in culture were treated with 50 ng/ml recombinant tumor necrosis factor alpha (TNFalpha), 2 ng/ml interleukin 1beta (IL-1beta), interleukin 6 (IL-6), interferon gamma (IFNgamma) or diluent (NaCl) for 24 h. Before stimulation with LPS (4 micro g/ml for 24 h) cells were treated with 200 ng/ml interleukin 1-receptor antagonist (IL-1ra), 500 ng/ml soluble TNF receptor (sTNFr), or NaCl for 1 h. Isolated membrane proteins were used for Western blot analysis. Cell-associated and secreted IL-1beta and TNFalpha protein content were determined in myocyte protein homogenates and cell culture supernatants by ELISA immunoblotting 3, 6, 24, 48 and 72 h after treatment with LPS. IL-1beta (1.75-fold) and TNFalpha (1.62-fold) but not IL-6 and IFNgamma induced RGS16 protein expression. LPS stimulated intracellular IL-1beta expression within 6 h (847.1+/-172.9 pg/3x10(6) cells) followed by an increase in extracellular secretion up to 70.8+/-8.1 pg/3x10(6) cells after 48 h. In contrast, intracellular protein concentrations of TNFalpha were almost not detectable (0.03+/-0.01 pg/3x10(6) cells), but extracellular secretion was induced by LPS with a maximum at 6 h (653.9+/-36.3 pg/3x10(6) cells). The LPS-induced increase in RGS16 (1.6-fold) was blunted by IL-1ra but not by TNFalpha scavenging. Interestingly, both, the IL-1beta- and TNFalpha-effect could be blocked by IL-1ra, indicating that also the TNFalpha-induced RGS16 expression is mediated by IL-1. We therefore conclude that LPS induces RGS16 protein expression by activation of the cytokine IL-1beta in cardiac myocytes. Our data substantiate the role of IL-1beta as an important mediator in LPS-induced cardiac failure.

Involvement of G(i) proteins and Src tyrosine kinase in TNFalpha production induced by lipopolysaccharide, group B Streptococci and Staphylococcus aureus

Previous studies have suggested that heterotrimeric G(i) proteins, Src tyrosine kinase and phosphatidylinositol-3 kinase (PI3 Kinase) are involved in signaling events induced by lipopolysaccharide (LPS) leading to pro-inflammatory cytokines gene expression. To investigate the involvement of these mediators in Gram-positive bacteria induced pro-inflammatory cytokine expression, LPS (10 ng/ml), heat killed group B Streptococci (GBS 1 microg/ml) and Staphylococcus aureus (SA 10 microg/ml) were used to induce TNFalpha production in the murine J774A.1 macrophage (MØ) cell line and human promonocytic THP-1 cell line. Pertussis toxin (PTx, 1 microg/ml), an inhibitor of G(i) protein; pyrazolopyrimidine-2 (PP2, 1 or 25 microM), a Src tyrosine kinase inhibitor; and LY294002 (100 nM), an inhibitor of PI3 Kinase were used to examine the involvement of G(i), Src tyrosine kinase and PI3 Kinase, respectively, in TNFalpha production. In J774A.1 cells, pretreatment with PTx and PP2 attenuated TNFalpha production induced by LPS (60+/-9% and 81+/-11% inhibition, n=3, p<0.05, respectively), GBS (95+/-1% and 80+/-6% inhibition, n=3, p<0.05, respectively) and SA (51+/-18% and 68+/-16% inhibition, n=4, p<0.05, respectively). However, pretreatment with LY 294002 inhibited LPS induced TNFalpha production (82+/-13% inhibition, n=3, p<0.05), but did not inhibit GBS or SA induced TNFalpha production. In THP-1 cells, pretreatment with PTx, PP2 and LY 294002 inhibited TNFalpha production induced by LPS (84+/-3%, 59+/-12% and 84+/-4% inhibition, n=3, p<0.05, respectively) and SA (56+/-7%, 87+/-1% and 35+/-6% inhibition, n=3, p<0.05, respectively). These data support our hypothesis that G(i)-coupled and Src tyrosine kinase-coupled signaling pathways are involved in both Gram-negative and Gram-positive bacteria induced pro-inflammatory cytokine expression. However, unlike LPS, involvement of PI3 Kinase in Gram-positive bacteria induced signaling pathways are species dependent.

TNF-alpha increases transcription of Galpha(i-2) in human airway smooth muscle cells

Tumor necrosis factor-alpha (TNF-alpha) is a proinflammatory cytokine that has an important role in the regulation of airway smooth muscle tone and reactivity. We have shown previously that TNF-alpha upregulates the expression of Galpha(i-2) protein without significantly increasing G(s)alpha protein and enhances adenylyl cyclase inhibition by carbachol in cultured human airway smooth muscle cells (Hotta K, Emala CW, and Hirshman CA. Am J Physiol Lung Cell Mol Physiol 276: L405-L411, 1999). The present study was designed to investigate the molecular mechanisms by which TNF-alpha upregulates Galpha(i-2) protein in these cells. TNF-alpha pretreatment for 48 h increased the expression of Galpha(i-2) protein without significantly altering the Galpha(i-2) protein half-life (41.0 +/- 8.2 h for control and 46.8 +/- 5.2 h for TNF-alpha-treated cells). Inhibition of new protein synthesis by cycloheximide blocked the increase in Galpha(i-2) protein induced by TNF-alpha. Furthermore, TNF-alpha treatment for 12-24 h increased the steady-state level of Galpha(i-2) mRNA without significantly altering Galpha(i-2) mRNA half-life (9.0 +/- 0.75 h for control and 8.9 +/- 1.1 h for TNF-alpha-treated cells). The transcription inhibitor actinomycin D blocked the increase in Galpha(i-2) mRNA induced by TNF-alpha. These observations indicate that the increase in Galpha(i-2) protein induced by TNF-alpha is due to an increased rate of Galpha(i-2) protein synthesis, most likely as a consequence of the transcriptional increase in the steady-state levels of its mRNA.

Tumor necrosis factor-alpha is expressed in donor heart and predicts right ventricular failure after human heart transplantation

BACKGROUND-Myocardial failure is an important problem after heart transplantation. Right ventricular (RV) failure is most common, although its mechanisms remain poorly understood. Inflammatory cytokines play an important role in heart failure. We studied the expression of tumor necrosis factor (TNF)-alpha and other cytokines in donor myocardium and their relationship to the subsequent development of RV failure early after transplantation. METHODS AND RESULTS-Clinical details were obtained, and ventricular function was assessed by transesophageal echocardiography in 26 donors before heart retrieval. A donor RV biopsy was obtained immediately before transplantation, and each recipient was followed for the development of RV failure. Reverse transcriptase-polymerase chain reaction was performed to detect TNF-alpha, interleukin-2, interferon-gamma, and inducible nitric oxide synthase expression. Eight of 26 recipients (30.8%) developed RV failure. Seven of these 8 (87.5%) expressed TNF-alpha, but only 4 of the 18 (22.2%) who did not develop RV failure expressed TNF-alpha (P<0.005). As a predictor of RV failure, TNF-alpha mRNA had a sensitivity of 87.5%, a specificity of 83.3%, a positive predictive value of 70%, and a negative predictive value of 93.7%. Western blotting demonstrated more TNF-alpha protein in the myocardium of donor hearts that developed RV failure (658+/-60 versus 470+/-57 optical density units, P<0.05). Immunocytochemistry localized TNF-alpha expression to cardiac myocytes. Reverse transcriptase-polymerase chain reaction detected interferon-gamma in 2 (7.7%), interleukin-2 in 1 (3.8%), and inducible nitric oxide synthase mRNA in 1 (3.8%) of the 26 donor hearts, none of which developed RV failure. CONCLUSIONS-TNF-alpha expression in donor heart cardiac myocytes seems to predict the development of RV failure in patients early after heart transplantation.

Tumor necrosis factor-alpha at acute myocardial infarction in rats and effects on cardiac fibroblasts

Tumor necrosis factor-alpha (TNF-alpha) biosynthesis by the myocardium in response to several diseases has not been solely associated with activation of the immune system but may also serve as a stress response in the context of neurohumoral gene activation. In this regard, beneficial as well as adverse effects of the cytokine on injured myocardium have been reported. TNF-alpha has been suggested to modulate myocyte and fibroblast cell growth and function. Now, in a rat model of acute myocardial infarction TNF-alpha expression and effects on cardiac fibroblast were determined. TNF-alpha was detected in rat hearts with acute myocardial infarction, parallel to the presence of proliferating fibroblasts, at the border zone of the infarct region, to a lesser degree in the infarct zone and was still present in the surviving myocardium. Similarly, the TNF-alpha mRNA level was, compared to sham-operated heart, higher in the infarct area. In the remote myocardium, a trend to an elevated TNF-alpha mRNA level was observed. TNF-alpha stimulated proliferation and expression of fibronectin in fibroblasts isolated from the infarct, non-infarct-region and sham-operated hearts. Angiotensin II is mitogenic for fibroblasts post-myocardial infarction and effects might be mediated indirectly by TNF-alpha. Addition of a neutralising anti-TNF-alpha antibody inhibited angiotensin II stimulated proliferation of fibroblasts only from the infarcted myocardium. The regional differences in TNF-alpha protein and mRNA levels, parallel to proliferating fibroblasts and proliferative effects may foster the reparative, reactive and adverse post-infarct remodeling of the heart.

Sequential changes in autonomic regulation of cardiac myocytes after in vivo endotoxin injection in rat

We report that in vivo injection of endotoxin (EDTX, 6 mg. kg(-)(1)) induces cardiovascular alterations in rats that closely mimic the clinical situation, as assessed by in vivo hemodynamic measurements in anesthetized and conscious, chronically instrumented animals. The patch-clamp technique was used to characterize the L-type calcium current (I(Ca)) and its autonomic regulation in isolated cardiac myocytes. The density of I(Ca) progressively decreased at 12 and 36 h after EDTX injection. However, the dihydropyridine (+/-)Bay K 8644 (100 nM) enhanced I(Ca) to levels similar to those in control and EDTX-treated myocytes. In addition, the net stimulatory effect of a beta-adrenergic agonist (isoproterenol) on I(Ca) was increased 12 h after EDTX injection. This change in the beta-adrenergic effect declined 24 h later. The potentiation in the beta-adrenergic stimulation of I(Ca) was mimicked by L858051 (10 microM), a direct activator of adenylyl cyclase, but not by IBMX (200 microM), a phosphodiesterase inhibitor. Besides, the antiadrenergic effect of acetylcholine on I(Ca) was unchanged 12 h after EDTX injection, but increased 36 h after EDTX injection. These results support the hypothesis that time-dependent changes in the adenylyl cyclase pathway in cardiac myocytes may contribute, via the autonomic regulation of I(Ca), to the severity of myocardial dysfunction during sepsis.

Tumor necrosis factor alpha stimulates lipolysis in adipocytes by decreasing Gi protein concentrations

Prolonged treatment (12-24 h) of adipocytes with tumor necrosis factor alpha (TNFalpha) stimulates lipolysis. We have investigated the hypothesis that TNFalpha stimulates lipolysis by blocking the action of endogenous adenosine. Adipocytes were incubated for 48 h with TNFalpha, and lipolysis was measured in the absence or presence of adenosine deaminase. Without adenosine deaminase, the rate of glycerol release was 2-3-fold higher in the TNFalpha-treated cells, but with adenosine deaminase lipolysis increased in the controls to approximately that in the TNFalpha-treated cells. This suggests that TNFalpha blocks adenosine release or prevents its antilipolytic effect. Both N6-phenylisopropyl adenosine and nicotinic acid were less potent and efficacious inhibitors of lipolysis in treated cells. A decrease in the concentration of alpha-subunits of all three Gi subtypes was detected by Western blotting without a change in Gs proteins or beta-subunits. Gi2alpha was about 50% of control, whereas Gi1alpha and Gi3alpha were about 20 and 40% of control values, respectively. The time course of Gi down-regulation correlated with the stimulation of lipolysis. Furthermore, down-regulation of Gi by an alternative approach (prolonged incubation with N6-phenylisopropyl adenosine) stimulated lipolysis. These findings indicate that TNFalpha stimulates lipolysis by blunting endogenous inhibition of lipolysis. The mechanism appears to be a Gi protein down-regulation.

TNF-alpha upregulates Gialpha and Gqalpha protein expression and function in human airway smooth muscle cells

Chronic inflammation is a characteristic feature of asthma. Multiple inflammatory mediators are released within the asthmatic lung, some of which may have detrimental effects on signal transduction pathways in airway smooth muscle. The effects of tumor necrosis factor (TNF)-alpha on the expression and function of muscarinic receptors and guanine nucleotide-binding protein (G protein) alpha-subunits were examined in human airway smooth muscle cells. Cultured human airway smooth muscle cells were incubated in serum-free culture medium for 72 h in the presence and absence of 10 ng/ml of TNF-alpha, after which the cells were lysed and subjected to electrophoresis and Galphai-2, Gqalpha, and Gsalpha protein subunits were detected by immunoblot analysis with specific antisera. TNF-alpha treatment for 72 h significantly increased the expression of Galphai-2 and Gqalpha proteins and enhanced carbachol (10(-7) M)-mediated inhibition of adenylyl cyclase activity and inositol phosphate synthesis. These data provide new evidence demonstrating that TNF-alpha not only increases expression of Galphai-2 and Gqalpha proteins but also augments the associated signal transduction pathways that would facilitate increased tone of airway smooth muscle.

Cytokines induce airway smooth muscle cell hyperresponsiveness to contractile agonists

The important pathophysiological features of the airways in asthma include exaggerated narrowing to bronchoconstrictor agonists and attenuated relaxation to beta adrenoceptor stimulation. These physiological perturbations are associated with inflammation and remodelling of the airways, the latter including an increase in airway smooth muscle cell mass, disruption of the airway epithelium, and changes in the airway tissue extracellular matrix. Recent evidence suggests that cytokines, important molecules modulating airway inflammation, also directly decrease airway smooth muscle responsiveness to beta adrenergic agents, stimulate cytokine secretion, inhibit or promote airway smooth muscle proliferation, and "prime" airway smooth muscle to become hyperresponsive to bronchoconstrictors. Characterisation of the cellular and biochemical events that are involved in activation of airway smooth muscle is likely to be the major consideration in the design of future therapies for asthma. Because calcium is an essential regulatory element for cell growth and cell contraction, it is likely that alterations in calcium mobilisation may, in part, play a role in creating an airway smooth muscle phenotype that is hyperresponsive to contractile agonists. Further studies will be required to determine the precise mechanisms involved in cytokine modulation of calcium homeostasis in airway smooth muscle.

Mechanisms underlying TNF-alpha effects on agonist-mediated calcium homeostasis in human airway smooth muscle cells

We have previously shown that tumor necrosis factor (TNF)-alpha, a cytokine involved in asthma, enhances Ca2+ responsiveness to bronchoconstrictor agents in cultured human airway smooth muscle (ASM) cells. In the present study, we investigated the potential mechanism(s) by which TNF-alpha modulates ASM cell responsiveness to such agents. In human ASM cells loaded with fura 2, TNF-alpha and interleukin (IL)-1 beta significantly enhanced thrombin- and bradykinin-evoked elevations of intracellular Ca2+. In TNF-alpha-treated cells. Ca2+ responses to thrombin and bradykinin were 350 +/- 14 and 573 +/- 93 nM vs. 130 +/- 17 and 247 +/- 48 nM in nontreated cells, respectively (P < 0.0001). In IL-1 beta-treated cells, the Ca2+ response to bradykinin was 350 +/- 21 vs. 127 +/- 12 nM in nontreated cells (P < 0.0001). The time course for TNF-alpha potentiation of agonist-induced Ca2+ responses requires a minimum of 6 h and was maximum after 12 h of incubation. In addition, cycloheximide, a protein synthesis inhibitor, completely blocked the potentiating effect of TNF-alpha on Ca2+ signals. We also found that TNF-alpha significantly enhanced increases in phosphoinositide (PI) accumulation induced by bradykinin. The percentage of change in PI accumulation over control was 115 +/- 8 to 210 +/- 15% in control cells vs. 128 +/- 10 to 437 +/- 92% in TNF-alpha-treated cells for 3 x 10(-9) to 3 x 10(-6) M bradykinin. The PI turnover to 10 mM NaF, a direct activator of G proteins, was also found to be enhanced by TNF-alpha. The percentage of change in PI accumulation over control increased from 280 +/- 35% in control cells to 437 +/- 92% in TNF-alpha-treated cells. Taken together, these results show that TNF-alpha can potently regulate G protein-mediated signal transduction in ASM cells by activating pathways dependent on protein synthesis. Our study demonstrates one potential mechanism underlying the enhanced Ca2+ response to bronchoconstrictor agents induced by cytokines in human ASM cells.

Dilated cardiomyopathy in transgenic mice with cardiac-specific overexpression of tumor necrosis factor-alpha

The failing human heart expresses tumor necrosis factor-alpha (TNF-alpha). However, its pathophysiological significance is not clear. We previously reported that robust overexpression of TNF-alpha in the murine heart causes lethal myocarditis. In this study, we modified the transgene to reduce the production of TNF-alpha by preserving the destabilizing sequence in TNF-alpha cDNA. Expression was driven by the murine alpha-myosin heavy chain promoter. Use of this modified construct allowed to the establish a mutine transgenic line (TG). TG offspring were examined at 6, 12, and 24 weeks. All showed a significantly higher heart weight-to-body weight ratio. Northern blot analysis confirmed the expression of transgene in the heart, and enzyme-linked immunosorbent assay demonstrated the presence of TNF-alpha protein. The TG heart demonstrated a mild, diffuse, lymphohistiocytic interstitial inflammatory infiltrate. Cardiomyocyte necrosis and apoptosis were present but not abundant. Magnetic resonance imaging showed that the TG heart was significantly dilated with reduced ejection fraction. Although the left ventricular dP/dtmax was not different at baseline, its responsiveness to isoproterenol was significantly blunted in TG. Atrial natriuretic factor was expressed in the TG ventricle. A group of TG died spontaneously, and subsequent autopsies revealed exceptional dilation of the heart, increased lung weight, and pleural effusion, suggesting that they died of congestive heart failure. The cumulative mortality rate at 6 months was 23%. In conclusion, the mouse overexpressing TNF-alpha recapitulated the phenotype of congestive heart failure. This provides a novel model to elucidate the role of this cytokine in the development of congestive heart failure.

[Cytokines and heart diseases. Attempt at an update]

Acute septic cardiomyopathy is-to our present knowledge-the heart disease most strongly interrelated with cytokines. Myocardial depression by cytokines is characterized by their pleiotropic actions mediating not only impairment of one, but several inotropic cascades. Information concerning the relevance of cytokines in non-septic heart diseases is-at present-scarce: Concepts emerge in cases of myocarditis, heart failure and cardiomyopathies, acute coronary syndromes, systemic inflammatory response due to cardiopulmonary bypass, heart transplant rejection and Kawasaki disease.

CONCLUSION

Cytokines are involved in heart diseases.

Cytokines and nitric oxide synthase inhibitor as mediators of adrenergic refractoriness in cardiac myocytes

We have previously proposed that pro-inflammatory cytokines and nitric oxide (NO) contributed to reversible myocardial depression in patients with sepsis and congestive heart failure. Sepsis and heart failure are also associated with refractoriness to beta-adrenoceptor agonists. Therefore, the chronotropic effects of cytokines and the NO synthase inhibitor, NG-methyl-L-arginine (NMA), on beta-adrenoceptor stimulation of neonatal cardiac myocytes were studied. Tumor necrosis factor alpha, interleukin-1 beta and interleukin-6 but not interleukin-4 or interleukin-5 significantly enhanced spontaneous beating rates compared to untreated myocytes in serum-free media for 48 h (P < 0.01; n = 12 for each). NMA also significantly enhanced spontaneous beating rates (P < 0.01; n = 12 for each). Only interleukin-1 beta treatment resulted in significant nitrite production, immunohistochemical staining for inducible nitric oxide synthase and detection of inducible NO synthase messenger RNA by reverse transcriptase-polymerase chain reaction (RT-PCR). However, tumor necrosis factor alpha, interleukin-1 beta, interleukin-6, and NMA each completely blocked the positive chronotropic effects of the beta-adrenoceptor agonist, isoproterenol (P < 0.01; n = 12 for each). These findings are most consistent with an inducible NO synthase-independent effect of cytokines and NMA on the chronotropic responses of neonatal cardiac myocytes to beta-adrenoceptor stimulation. This effect of cytokines and NMA on adrenergic signaling may involve a myocardial constitutive NO synthase or an NO-independent mechanism.

Elucidating molecular mechanisms of septic cardiomyopathy--the cardiomyocyte model

In the multiple organ dysfunction syndrome of sepsis and septic shock the heart is one of the organs subject to failure. Many new insights into the mechanisms underlying septic cardiomyopathy were gained in the last years. Experimental work with neonatal and adult cardiomyocytes considerably contributed to this progress, facilitating the documentation of direct attenuation of the contractions of the heart muscle cell by toxins and mediators, as well as investigating the underlying cellular mechanisms. With this respect, contractile-depressant effects have been found in cardiomyocytes for many toxins and sepsis mediators, with endotoxin, Pseudomonas exotoxin A, tumor necrosis factor alpha, interleukin-1 and nitric oxide being the most relevant ones identified. These substances interfere at clinically relevant concentrations with several main inotropic axes, not only with the beta-adrenoceptor/adenylyl cyclase and with the NO-cGMP-system-on which most of the interest is focused at present-but also with the alpha 1-adrenoceptor/phosphoinositide pathway and the Ca2+ homeostasis of the cardiomyocyte, the latter representing the common final inotropic pathway. Not a single cardiodepressant factor, but more likely a total bunch of toxins and mediators with different attack mechanisms seem to contribute to the picture of septic cardiomyopathy.

Alterations in inotropy, nitric oxide and cyclic GMP synthesis, protein phosphorylation and ADP-ribosylation in the endotoxin-treated rat myocardium and cardiomyocytes

To evaluate the effects of the in vivo endotoxin treatment of the rat on (1) the contractile responses in the subsequently isolated papillary muscle to adrenergic and cholinergic agonists and (2) the biochemical parameters (cyclic GMP, nitric oxide synthesis, protein phosphorylation and ADP-ribosyslation) in the subsequently isolated cardiomyocytes. Following the in vivo endotoxin treatment (4 mg/kg i.p., 18 h), contractile responses to increasing amounts of isoprenaline or to increasing amounts of oxotremorine in the presence of a fixed amount of isoprenaline were determined in isolated papillary strips. Activities of nitric oxide synthase, guanylyl cyclase, as well as phosphorylation of phospholamban and troponin-inhibitory subunit, and pertussis toxin-catalyzed and endogenous ADP-ribosylations were determined in the intact cardiomyocytes and subcellular fractions. The increase in the force of contraction by isoprenaline was reduced, while its inhibition by oxotremorine was greater in the endotoxin-treated papillary strips. The activities of both nitric oxide synthase, primarily of the inducible form of the enzyme, and cytosolic guanylyl cyclase were higher while the phosphorylations of both phospholamban and troponin-inhibitory subunit were of lesser magnitude in the cardiomyocytes following the in vivo endotoxin treatment. Pertussis toxin-catalyzed ADP-ribosylation of the 41 kDa polypeptide, which is the alpha subunit of Gi, was also decreased. The results of the present study support the postulate that alterations in both the cyclic AMP and cyclic GMP signalling cascade contribute to the myocardial dysfunction caused by endotoxin and cytokines.

Cytoprotective mechanisms in cultured cardiomyocytes

Tumor necrosis factor-alpha (TNF-alpha), a potent cytokine mainly secreted by macrophages exerts pleiotropic effects on different cell types. However, the intracellular mediators of its action are not yet well characterized. To get an insight into endogenous cytoprotective mechanisms, we developed an in vitro model based on cultured cardiomyocytes treated with TNF-alpha at which we examined gene expression of heat shock proteins (HSP-27, HSP-70 and ubiquitin). Cardiomyocytes were isolated from the hearts of 18 day old fetal mice by enzymatic dissociation and grown in minimum essential medium containing 10% fetal calf serum. Spontaneously contractile cells were serum deprived for 24 h and treated with TNF-alpha (25 ng/ml) for 1, 2, 4, 6, 8, 12, and 24 h After each incubation, cells were processed to extract total proteins for Western and total RNA for Northern blot analyses. TNF-alpha induced arrhythmias and cessation of spontaneous contractions in a concentration and time dependent manner. Steady state (ubiquitin) or undetectable mRNA levels (HSP-27, HSP-70) were drastically induced (> 4 fold for all three genes vs untreated control cells) by TNF-alpha, reaching maximal values between 6-8 h of stimulation. Thereafter, the expression of these stress genes declined but remained elevated as compared to control. By Western blot analysis, we found increased multiple bands of ubiquitin protein conjugates in TNF-alpha treated cells whereas no significant change in HSP-27 protein accumulation until 12 h was observed as compared to control. 24 h of TNF-alpha incubation resulted in partial cellular necrosis. Our results indicate that TNF-alpha induces in cardiomyocytes transiently gene expression for cytoprotective molecules like HSP-27, HSP-70 and ubiquitin, suggesting these stress proteins to participate in subsequent defense mechanisms, for example in postischemic myocardial recovery.

Effect of endurance physical training on rat liver adenylyl cyclase system

The adaptive response to endurance exercise of the catecholamine- and glucagon-sensitive adenylyl cyclase system was studied in rat liver plasma membranes. Endurance exercise enhanced adenylyl cyclase system activation by cellular agonists (glucagon, isoproterenol), by stimulators of the enzyme catalytic subunit (forskolin, Mn2+), and by Gs-protein activators (GppNHp, fluoride). In addition, endurance exercise increased the levels of G50, Gi alpha, and G beta subunits. These results show that the adenylyl cyclase system becomes sensitized in response to physical training.

Temporal regulation by adrenergic receptor stimulation of macrophage (M phi)-derived tumor necrosis factor (TNF) production post-LPS challenge

Macrophage (M phi) responsiveness can be regulated by various mediators, including those which emanate from, and mimic, the sympathetic nervous system. Whereas beta-adrenergic agonists suppress, alpha 2-adrenergic agonists augment lipopolysaccharide (LPS)-stimulated tumor necrosis factor (TNF) production and gene expressed. The susceptibility of M phi s to regulation of LPS-induced TNF production and mRNA accumulation was examined following beta-adrenergic and alpha 2-adrenergic receptor activation at specific time points post-LPS challenge. Complete Freund's adjuvant-elicited murine M phi s were incubated with LPS (30 ng/ml) in the presence or absence of adrenergic agonists or antagonists. We assessed the susceptibility of immunologically-activated M phi s to adrenergic receptor regulation: a) during the 1 h delay in the production of TNF after LPS-stimulation, and b) during the rapid increase in TNF production which follows. Disparate responsiveness of M phi s to adrenergic drugs was observed during this time course of TNF production and TNF mRNA accumulation. In particular, while the concomitant addition of an alpha 2-adrenergic antagonist and LPS resulted in 45% suppression of TNF production, this selective blockade of alpha 2-adrenergic receptors on M phi s was equally effective throughout the first 45 min post-LPS challenge. After this initial period, the alpha 2-adrenergic receptor became progressively less responsive as demonstrated by the delayed addition of yohimbine (10(-5) M) post-LPS challenge. The addition of the selective alpha 2-adrenergic agonist UK-14304 (10(-7) M) to LPS-activated M phi s augmented TNF mRNA accumulation. However, this augmentation was even greater when the addition of the alpha 2-adrenergic agonist was delayed post-LPS challenge. It was also shown that the beta-adrenergic agonist isoproterenol (10(-6) M) produced maximum suppression of TNF production within the first 1.5 h post-LPS challenge. Suppression by isoproterenol (10(-6) M) of TNF mRNA accumulation occurred throughout the 2-h period assessed post-LPS stimulation of M phi s. The decline in isoproterenol-induced regulation was accompanied by an elevation in beta 2-adrenergic receptor mRNA accumulation. Furthermore, suppression of TNF production induced by a maximum concentration of isoproterenol was observed at various LPS concentrations (0.001-1000 ng/ml), although this was not as pronounced a suppression as demonstrated for dibutyrl cAMP. These results demonstrate that the susceptibility of M phi s to adrenergic receptor regulation changes throughout the time period necessary for gene activation and ultimate release of TNF. Thus, the production of TNF during LPS-dependent disease states may be regulated by adrenergic mediators throughout different temporal windows, better explaining the role played by the nervous system.

Subchronic exposure of cardiomyocytes to low concentrations of tumor necrosis factor alpha attenuates the positive inotropic response not only to catecholamines but also to cardiac glycosides and high calcium concentrations

The main purpose of this study was to determine the subchronic effects of low concentrations of tumor necrosis factor alpha (TNF alpha) on the inotropic response and on the cellular level of high energy phosphates of cardiomyocytes. Therefore, the inotropic response of cultured neonatal rat heart cells to 10(-5) M isoproterenol-, 10(-6) M ouabain-, 10(-5) M forskolin- and 2,4 mM calcium-perfusion was studied 24 h after exposure to TNF alpha (0.01/0.1/1/10/100 U/ml). In parallel experiments high energy phosphates (CP, ATP, ADP, AMP) were determined by high performance liquid chromatography. Furthermore, the reversibility of TNF alpha-induced changes was studied after washout of TNF alpha or after administration of anti-TNF alpha-antibody. Whereas control cells showed an increase of cell wall motion to 150 +/- 5% of baseline value during 10(-5) M isoproterenol-perfusion respectively 180 +/- 7% during 2,4 mM calcium-perfusion, 24 h exposure of the cells to 1 U/ml up to 100 U/ml TNF alpha resulted in an inhibition of the inotropic response. Almost complete inhibition was observed 12 h after exposure to TNF alpha and was reversible 12 h after administration of the anti-TNF alpha-antibody. If the cells were perfused with 10(-6) M ouabain or 10(-5) M forskolin, a similar inhibition of the inotropic response was observed 24 h after TNF alpha-exposure. Determination of high energy phosphates showed that 24 h TNF alpha-exposure resulted in a reversible decrease of ATP, ADP, AMP and CP by 30-40% (p < 0.05). However, a similar reduction of cellular high energy phosphate levels using a TNF alpha independent mechanism (2,5 mM 2-deoxy-D-glucose) did not inhibit the inotropic response of the cardiomyocytes. From our results we conclude that subchronic exposure to low concentrations of TNF alpha resulted in an almost complete but reversible inhibition of the response of cardiomyocytes to different inotropic agents suggesting that a common final step of the inotropic cascade might be altered by TNF alpha. Though energy metabolism of TNF alpha exposed cells was affected also, reduction of high energy phosphate levels alone did not explain the observed inhibition of the inotropic response of the cardiomyocytes.

Increase of myocardial inhibitory G-proteins in catecholamine-refractory septic shock or in septic multiorgan failure

PURPOSE

The aim of the study was to investigate the mechanisms of myocardial catecholamine refractoriness in septic shock.

METHODS

The inhibitory guanine nucleotide-binding proteins (Gi alpha) were studied with pertussis toxin labeling and radioimmunologically in myocardium from patients who died while in catecholamine-refractory septic shock and from patients who died of noncardiac disease.

RESULTS

An increase by 62% (immunological Gi alpha) and 221% (pertussis toxin substrate) of myocardial Gi alpha was observed in patients with catecholamine-refractory shock compared with controls. The increases of Gi alpha were greater than those found in chronic heart failure reported earlier.

CONCLUSIONS

An increase in the expression of Gi alpha could also be important in conditions other than chronic heart failure, eg, septic shock. An increase of Gi alpha could play a pathophysiologically relevant role in catecholamine refractoriness in septic shock and could provide a target for pharmacologic treatment in this condition.

Tumor necrosis factor alpha decreases inositol phosphate formation and phosphatidylinositol-bisphosphate (PIP2) synthesis in rat cardiomyocytes

Treatment of neonatal rat cardiomyocytes for 72 h in the presence of tumor necrosis factor alpha (TNF alpha) (10 U/ml) lead to a decrease in basal and alpha 1-adrenoceptor-induced formation of the calcium-mobilizing second messenger inositol trisphosphate (IP3) and its metabolites, IP2 and IP1, by 35 and 26%, respectively. The synthesis of phosphatidylinositol bisphosphate (PIP2), the substrate of PI-specific phospholipase C, was decreased by 45% following the TNF alpha (10 U/ml) exposure. Time courses of TNF alpha (10 U/ml)-induced alterations in rat cardiomyocytes showed a parallel decline of basal inositol phosphate formation and PIP2 synthesis suggesting that the decrease in inositol phosphate formation was due to the reduction in PIP2 synthesis. As the TNF alpha-induced decrease of PIP2 synthesis was associated with a decreased synthesis of the phospholipid phosphatidylinositol (PI), the precursor of PIP2, by 33%, the decreased availability of PIP2 is apparently, at least in part, the result of the decreased synthesis of PI. As an apparent functional consequence of the decrease in IP3 formation following the TNF alpha exposure, the alpha 1-adrenoceptor-mediated induction of arrhythmias by 100 mumol/l noradrenaline + 10 mumol/l timolol was abolished in TNF alpha-pretreated rat cardiomyocytes. To investigate one of the possible mechanisms of the TNF alpha-induced decrease of PIP2 formation, the effect of TNF alpha pretreatment on glycerol-3-phosphate dehydrogenase (GDH), a key enzyme of lipogenesis, was studied: Exposure of the rat cardiomyocytes for 72 h to TNF alpha induced a concentration-dependent decrease in GDH activity by maximally 55%.(ABSTRACT TRUNCATED AT 250 WORDS)

Application of high resolution two-dimensional polyacrylamide gel electrophoresis of polypeptides from cultured neonatal rat cardiomyocytes: regulation of protein synthesis by catecholamines

High resolution two-dimensional polyacrylamide gel electrophoresis (2-D PAGE) was applied to cultured neonatal rat heart muscle cells, incubated for 72 h at 37 degrees C in serum-free medium, either in the absence or in the presence of 0.1 microM norepinephrine. After silver staining, about 340 and 550 protein spots could be seen in cardiomyocytes, cultured either in the absence or presence of norepinephrine. Of these spots, 141 could be further characterized according to isoelectric point and molecular weight, with 71 protein spots being present under both conditions. In cells cultivated in presence of norepinephrine, 58 new protein spots appeared, whereas 12 spots disappeared, and 22 spots increased (whereas 3 spots decreased) in intensity. In comparison with 2-D PAGE of rat cardiomyocytes, the protein pattern of the intact heart of neonatal rats is incongruent. 2-D PAGE of polypeptides of cultured neonatal rat cardiomyocytes may be a suitable tool to study the regulation of protein synthesis by various stimuli with relevance to cardiac growth adaptation, inotropy and heart failure.

Cytokines induce stress protein formation in cultured cardiac myocytes

Diseases accompanied by severe cardiac impairment like sepsis and chronic uremia are frequently linked to an increase in cytokine release. In order to investigate possible toxic effects of the immune mediators on myocardial cells, we studied the contractility of cardiac myocytes and the de novo formation of stress proteins in cultured heart cells under cytokine exposition. All cytokines investigated induce, concentration-dependently, arrhythmias and cessation of spontaneous contractions. Interleukin(IL)-2, IL-3, IL-6, and tumor necrosis factor (TNF) stimulate the synthesis of a 30 kD stress protein in heart cells, whereas IL-1 additionally evokes two proteins of the 70 kD family. These findings confirm a direct interference of the interleukins and TNF with myocytes and, especially, myocardial protein formation. As the induction of stress proteins makes cells more resistant towards a subsequent challenge, the cytokines are possibly involved in the activation of cell protecting mechanisms in cardiac myocytes.

Mechanisms in acute septic cardiomyopathy: evidence from isolated myocytes

Although often not considered, the heart is one of the targets of multiple organ failure in sepsis and septic shock, with myocardial depression being a prominent component of this "acute septic cardiomyopathy". Hypotheses concerning the etiology of this depression are increasingly elucidated on a cellular level, including dysfunction of the beta-adrenoceptor/G protein/adenylate cyclase system, calcium channel blockade by cardiodepressant factor, contractile impairment by activated leucocytes, as well as inhibition of protein synthesis by Pseudomonas exotoxin A. In the search for "mechanisms of myocardial depression in sepsis", isolated cardiomyocytes may play a role as research tools with respect to: a) discrimination between direct and indirect cardiodepressant effects; b) identifying not only the acute, but also chronic toxin- and mediator-induced cardiodepression; c) clarification of the mechanism of action of cardiodepressant bacterial toxins and sepsis mediators; d) establishment of in vitro models of leucocyte-mediated cardiodepression in sepsis.