Predicting physiologically-relevant oxygen concentrations in precision-cut liver slices using mathematical modelling.

Precision cut liver slices represent an encouraging ex vivo method to understand the pathogenesis of liver disease alongside drug induced liver injury. Despite being more physiologically relevant compared to in vitro models, precision cut liver slices are limited by the availability of healthy human tissue and experimental variability. Internal oxygen concentration and media composition govern the longevity and viability of the slices during the culture period and as such, a variety of approaches have been taken to maximise the appropriateness of the internal oxygen concentrations across the slice. The aim of this study was to predict whether it is possible to generate a physiologically relevant oxygen gradient of 35-65mmHg across a precision cut liver slice using mathematical modelling. Simulations explore how the internal oxygen concentration changes as a function of the diameter of the slice, the position inside the well and the external incubator oxygen concentration. The model predicts that the desired oxygen gradient may be achieved using a 5mm diameter slice at atmospheric oxygen concentrations, provided that the slice is positioned at a certain height within the well of a 12-well plate.

Is point of care testing in Irish hospitals ready for the laboratory modernisation process? An audit against the current national Irish guidelines.

BACKGROUND: The Laboratory modernisation process in Ireland will include point of care testing (POCT) as one of its central tenets. However, a previous baseline survey showed that POCT was under-resourced particularly with respect to information technology (IT) and staffing. AIMS: An audit was undertaken to see if POCT services had improved since the publication of National Guidelines and if such services were ready for the major changes in laboratory medicine as envisaged by the Health Service Executive. METHODS: The 15 recommendations of the 2007 Guidelines were used as a template for a questionnaire, which was distributed by the Irish External Quality Assessment Scheme. RESULTS: Thirty-nine of a possible 45 acute hospitals replied. Only a quarter of respondent hospitals had POCT committees, however, allocation of staff to POCT had doubled since the first baseline survey. Poor IT infrastructure, the use of unapproved devices, and low levels of adverse incident reporting were still major issues. CONCLUSIONS: Point of care testing remains under-resourced, despite the roll out of such devices throughout the health service including primary care. The present high standards of laboratory medicine may not be maintained if the quality and cost-effectiveness of POCT is not controlled. Adherence to national Guidelines and adequate resourcing is essential to ensure patient safety.

A survey of point of care testing in Irish hospitals: room for improvement.

BACKGROUND: "Guidelines for safe and effective management and use of point of care testing" have been recently launched in Ireland. AIMS: To survey point of care testing (POCT) services in the Republic of Ireland. METHODS: A questionnaire covering accreditation status, existence of POCT committees, quality management systems, and staff resources was distributed by the Irish External Quality Assessment Scheme (IEQAS). RESULTS: Of those that returned completed questionnaires, 56% had assigned specific POCT responsibilities to designated staff. Most support was for blood gases and glucose analysis. Compared with other published studies, Irish laboratories gave similar support for blood gases, less for glucose and much less for urinalysis. CONCLUSIONS: This survey demonstrated poor IT support for POCT. The majority of the respondents (78%) were dissatisfied with the quality of the POCT service in their institution.

Gene therapy progress and prospects: therapeutic angiogenesis for ischemic cardiovascular disease.

During the past decade, both in vitro and in vivo studies have provided new insights into the cellular and molecular mechanisms that govern angiogenesis and arteriogenesis. However, therapeutic angiogenesis clinical trials using recombinant protein or gene therapy formulations of single angiogenic growth factors have yielded at best only modest success to date. Among the second generation of angiogenic agents are therapeutic transgenes that enhance expression of two or more proangiogenic cytokines. These include synthetic constructs that mimic that activity of endogenous transcriptional regulators and other upstream, regulatory factors that have the potential to induce formation of morphologically and physiologically functional vessels. These agents are now beginning to be evaluated in clinical trials for patients with advanced ischemic cardiac and peripheral vascular disease.

Retinoic acid attenuates inducible nitric oxide synthase (NOS2) activation in cultured rat cardiac myocytes and microvascular endothelial cells.

S. Grosjean, Y. Devaux, C. Seguin, C. Meistelman, F. Zannad, P.-M. Mertes, R. A. Kelly and D. Ungureanu-Longrois. Retinoic Acid Attenuates Inducible Nitric Oxide Synthase (NOS2) Activation in Cultured Rat Cardiac Myocytes and Microvascular Endothelial Cells. Journal of Molecular and Cellular Cardiology (2001) 33, 933-945. The inducible NO synthase (NOS2) in cardiac tissue contributes to myocardial and coronary inflammation and dysfunction. Several natural (endogenous) hormones such as retinoic acid, the active metabolite of vitamin A, have the ability to attenuate NOS2 activation in inflammatory cells. The aim of this study was to investigate the effect of RA on NOS2 activation in cultured cardiac microvascular endothelial cells (CMEC) and adult rat ventricular myocytes (ARVM). CMEC were stimulated either with a combination of 10 microg/ml lipopolysaccharide (LPS) and 50 IU/ml interferon- gamma (IFN- gamma) or with a combination of 1 ng/ml interleukin-1 beta (IL-1 beta)+IFN- gamma whereas ARVM were stimulated with 1 ng/ml IL-1 beta and 50 IU/ml IFN- gamma in the absence or presence of all-trans retinoic acid (atRA). Activation of the NOS2 pathway was estimated by measurement of mRNA (Northern blot) and protein (Western blot) expression, enzyme activity by conversion of [(3)H]L -arginine to [(3)H]L -citrulline, and nitrite accumulation. NOS2 mRNA half-life was studied in CMEC and ARVM in the presence of actinomycin D. In CMEC and ARVM stimulated with a combination of LPS and/or cytokines, atRA (10(-6), 10(-5)M) significantly (P<0.05) attenuated NOS2 mRNA and protein expression, enzymatic activity and reduced supernatant nitrite concentration. Upon stimulation with LPS/IFN- gamma, atRA significantly decreased NOS2 mRNA half-life. This was not seen after stimulation with IL-1 beta/IFN- gamma. These results document for the first time an effect of RA on NOS2 activation in cardiac cells. They may contribute to the characterization of the immunomodulatory effects of retinoids in myocardial and coronary inflammatory disorders.

Activation of cardiac c-Jun NH(2)-terminal kinases and p38-mitogen-activated protein kinases with abrupt changes in hemodynamic load.

The role of mitogen-activated protein kinase (MAPK) pathways as signal transduction intermediates of hemodynamic stress leading to cardiac hypertrophy in the adult heart is not fully established. In a rat model of pressure-overload hypertrophy, we examined whether activation of MAPK pathways, namely, the extracellular signal-regulated protein kinase (ERK), c-Jun NH(2)-terminal kinase (JNK), and the p38-MAPK pathways, occurs during rapid changes in hemodynamic load in vivo. A slight activation of ERK2 and marked increases in JNK1 and p38-MAPK activities were observed 30 minutes after aortic banding. The increase in p38-MAPK activity was accompanied by an increase in the phosphorylation of the p38 substrate MAPK-activated protein kinases 2 and 3. Activation of these kinases was coincident with an increase in phosphorylation of c-Jun and activating transcription factor-2 (ATF-2) and enhanced DNA binding of activator protein-1 factors. Thus, hemodynamic stress of the adult rat heart in vivo results in rapid activation of several parallel MAPK kinase cascades, particularly stress-activated MAPK and p38-MAPK and their target transcription factors c-Jun and ATF-2.

Regulation of cardiomyocyte mechanotransduction by the cardiac cycle.

BACKGROUND: Overloading the left ventricle in systole (pressure overload) is associated with a distinct morphological response compared with overload in diastole (volume overload). METHODS AND RESULTS: We designed a novel computer-controlled experimental system that interfaces biaxially uniform strain with electrical pacing, so that cellular deformation can be imposed during a specified phase of the cardiac cycle. Cardiomyocytes were exposed to strain (4%) during either the first third (systolic phase) or last third (diastolic phase) of the cardiac cycle. Strain imposed during the systolic phase selectively activated p44/42 mitogen-activated protein kinase (MAPK) and MAPK/extracellular signal-regulated protein kinase kinase (MEK1/2, an activator of p44/42 MAPK) compared with strain imposed during the diastolic phase. In contrast, there was no difference in activation of p38 and c-Jun NH(2)-terminal kinases induced by strain imposed during the systolic phase (5.8- and 3.3-fold versus control, n=4) compared with the diastolic phase (5.5- and 3.1-fold). Induction of both brain natriuretic peptide (5.8-fold versus control, P:<0.05, n=3) and tenascin-C (7.0-fold, P:<0.02) mRNA expression by strain imposed during the systolic phase was greater than during the diastolic phase (3.9- and 3.6-fold, respectively). [(3)H]leucine incorporation induced by strain imposed during the systolic phase (4.0-fold versus control) was greater than during the diastolic phase (2.7-fold, P:<0.02, n=4); a selective inhibitor of MEK1/2 inhibited this difference. CONCLUSIONS: Mechanical activation of p44/42 MAPK and MEK1/2, gene expression, and protein synthesis is regulated by the cardiac cycle, suggesting that mechanotransduction at the cellular level may underlie differences between pressure and volume overload of the heart.

Role of TLR-2 in the activation of nuclear factor kappaB by oxidative stress in cardiac myocytes.

Growing evidence from patients with heart failure and from experimental animal models implicates effectors of innate immunity in the pathogenesis of this syndrome. The expression of the innate immunity signaling protein, Toll-like receptor 4 (TLR4), is increased in cardiac myocytes in situ and in failing myocardium, but the mechanism by which TLRs may be activated in the failing heart remains unclear. We report that TLR2, which is expressed in cardiac myocytes, participates in the response of these cells to oxidative stress, a major contributor to the pathogenesis of cardiac dysfunction. Hydrogen peroxide increased nuclear factor kappaB (NF-kappaB) activation in Chinese hamster ovary fibroblasts that overexpress TLR2 but not in normal or TLR4-overexpressing Chinese hamster ovary cells, an effect that was abrogated by an alpha-TLR2 antibody. In neonatal rat ventricular myocytes, the alpha-TLR2 antibody inhibited hydrogen peroxide-induced nuclear translocation of NF-kappaB and activator protein-1 (AP-1). Inhibition of TLR2 had no effect on tumor necrosis factor alpha-induced NF-kappaB or AP-1 activation, on the DNA binding of the basal transcription factor Oct-1, or on hydrogen peroxide-induced phosphorylation of p38 MAP kinase. Importantly, oxidative stress-induced cytotoxicity was enhanced by blocking TLR2. Given the importance of cytotoxicity and apoptosis to the pathology of the ischemic heart, an anti-apoptotic effect of TLR2 in cardiac myocytes exposed to elevated levels of ROS may limit further cardiac dysfunction.

In vivo electrophysiologic studies in endothelial nitric oxide synthase (eNOS)-deficient mice.

INTRODUCTION: Endothelial nitric oxide synthase (eNOS) mediates attenuation of the L-type calcium channel and modulates myocyte contractility. Arrhythmogenic afterdepolarizations are seen in vitro in ouabain-treated isolated myocytes from eNOS-deficient mice. The aim of these studies was to characterize the baseline electrophysiologic (EP) phenotype of eNOS-deficient mice and their potential susceptibility to cardiac conduction abnormalities and inducible arrhythmias. METHODS AND RESULTS: Surface ECG and in vivo intracardiac EP studies were performed in 27 mice lacking the eNOS gene and 21 wild-type littermate control mice. Baseline studies were performed in 10 eNOS-deficient mice and 10 wild-type controls. Subsequently, 17 eNOS-deficient mice and 11 wild-type controls were pretreated with digoxin, and ECG and EP testing were repeated. Data analysis revealed no significant differences in ECG intervals or cardiac conduction parameters, except sinus cycle length was higher in eNOS-deficient mice than wild-type mice (P < 0.01). After digoxin pretreatment, 7 of 17 eNOS-deficient mice had inducible ventricular tachycardia and 2 others had frequent ventricular premature beats, compared with only 3 of 11 wild-type mice with inducible ventricular tachycardia. In addition, 2 digoxin-treated eNOS-deficient mice and 1 wild-type mouse had inducible nonsustained atrial fibrillation. CONCLUSION: Mice with a homozygous targeted disruption of the eNOS gene have slower heart rates but no other distinguishable EP characteristics under basal sedated conditions. Partial inhibition of the Na+/K+ ATPase pump with digoxin administration increases ventricular ectopic activity in eNOS-/- mice, a phenotype analogous to afterdepolarizations seen in vitro in this eNOS-deficient mouse model.

Coronary microvascular endothelial cells cosecrete angiotensin II and endothelin-1 via a regulated pathway.

Although endothelial cells produce angiotensin II (ANG II) and endothelin-1 (ET-1), it is not clear whether a single cell produces both peptides, with cosecretion in response to stimulation, or whether different subpopulations of endothelial cells secrete one or the other peptide, with secretion in response to different stimuli. Exposure of cultured coronary microvascular endothelial cells to cycloheximide for 60 min had no effect on ANG II or ET-1 secretion. This result suggested the existence of a preformed intracellular pool of ANG II and ET-1, which is a precondition for regulated secretion. Exposure of endothelial cells to isoproterenol, high extracellular potassium, or cadmium, all of which stimulate peptide secretion via different signaling pathways, significantly (P > 0.001) increased the secretion of both ANG II and ET-1 in a cell size-dependent manner. Sodium nitroprusside and S-nitroso-N-acetyl penicillamine significantly (P > 0.001) decreased ANG II and ET-1 secretion, whereas N(omega)-nitro-L-arginine-methyl ester enhanced it. The similar regulation of ANG II and ET-1 secretion and the presence of both peptides around individual endothelial cells indicate that the autocrine/paracrine regulation of cardiovascular function by endothelial cells is accomplished via cosecretion of ANG II and ET-1.

Dynamin mediates caveolar sequestration of muscarinic cholinergic receptors and alteration in NO signaling.

In cardiac myocytes, agonist binding to muscarinic acetylcholine receptors (mAchRs) leads to the targeting of stimulated receptors to plasmalemmal microdomains termed caveolae. Here, we examined whether this translocation leads to mAchR internalization and alteration in downstream NO signaling. Differential binding of membrane-permeant and -impermeant mAchR radioligands on caveolae-enriched membranes revealed that carbachol stimulation of cardiac myocytes induces sequestration of mAchRs through caveolae fission. GTP but not its non-hydrolyzable analog GTP gamma S drove the further detachment of caveolae from myocyte sarcolemma. Also, incubation of extracts of carbachol-stimulated myocytes with recombinant GTPase dynamin induced mAchR sequestration in budded caveolae, while dominant-negative K44A dynamin inhibited it. These data were confirmed by immunofluorescence microscopy on m2 mAchR-expressing COS cells. Finally, repeated carbachol stimulations of mAchRs co-expressed in COS cells with endothelial nitric oxide synthase (eNOS) and wild-type, but not mutant, dynamin led to a progressive increase in mAchR sequestration and a concurrent stabilization of the inhibitory eNOS-caveolin complex. These findings emphasize the role of caveolae in mAchR trafficking and NO signaling, and suggest that caveolae fission may contribute to G-protein-coupled receptor desensitization.

Targeted deletion of matrix metalloproteinase-9 attenuates left ventricular enlargement and collagen accumulation after experimental myocardial infarction.

Matrix metalloproteinase-9 (MMP-9) is prominently overexpressed after myocardial infarction (MI). We tested the hypothesis that mice with targeted deletion of MMP9 have less left ventricular (LV) dilation after experimental MI than do sibling wild-type (WT) mice. Animals that survived ligation of the left coronary artery underwent echocardiographic studies after MI; all analyses were performed without knowledge of mouse genotype. By day 8, MMP9 knockout (KO) mice had significantly smaller increases in end-diastolic and end-systolic ventricular dimensions at both midpapillary and apical levels, compared with infarcted WT mice; these differences persisted at 15 days after MI. MMP-9 KO mice had less collagen accumulation in the infarcted area than did WT mice, and they showed enhanced expression of MMP-2, MMP-13, and TIMP-1 and a reduced number of macrophages. We conclude that targeted deletion of the MMP9 gene attenuates LV dilation after experimental MI in mice. The decrease in collagen accumulation and the enhanced expression of other MMPs suggest that MMP-9 plays a prominent role in extracellular matrix remodeling after MI.

Increased susceptibility to development of triggered activity in myocytes from mice with targeted disruption of endothelial nitric oxide synthase.

Nitric oxide generated by cardiac myocytes or delivered by drugs has been shown to regulate cardiac contractile function and has been implicated in suppressing some cardiac arrhythmias, although this remains controversial. We examined the ability of the soluble cardiac glycoside, ouabain, to trigger arrhythmic contractions in ventricular myocytes isolated from mice lacking a functional endothelial nitric oxide synthase gene (eNOS(null)). Arrhythmic activity, defined as aftercontractions, was induced with ouabain (50 micromol/L) and recorded using a video-motion detector in isolated, electrically driven single ventricular myocytes from adult eNOS(null)or from their wild-type (WT) littermates. The rate of ouabain-induced arrhythmic contractions was significantly higher in eNOS(null)myocytes than in WT myocytes. Application of the NO donor S-nitroso-acetylcysteine (SNAC) significantly diminished the frequency of arrhythmic contractions in eNOS(null)myocytes. The antiarrhythmic effect of NO, whether generated by eNOS in WT cells or by SNAC, could be partially reversed by 1H-[1,2,4]oxadiazolo-[4, 3-a]- quinoxalin-1-one (ODQ), a specific soluble guanylyl cyclase inhibitor. Ouabain significantly increased intracellular cGMP in WT but not eNOS(null)hearts, and this cGMP response was blocked by ODQ. Since cardiac glycoside- induced aftercontractions are activated by the transient inward current (I(ti)), the role of NO in ouabain (100 micromol/L)- induced I(ti)was examined using the nystatin-perforated patch-clamp technique. The frequency of ouabain-induced I(ti)was significantly higher in eNOS(null)myocytes than in WT myocytes, and this could be suppressed by SNAC. These data demonstrate that NO derived from myocyte eNOS activation suppresses ouabain-induced arrhythmic contractions by a mechanism that might involve activation of guanylyl cyclase and elevation of cGMP.

NRG-1-induced cardiomyocyte hypertrophy. Role of PI-3-kinase, p70(S6K), and MEK-MAPK-RSK.

Neuregulins are a family of growth-promoting peptides known to be important in neural and mesenchymal tissue development. Targeted disruption of neuregulin (NRG)-1 or one of two of its cognate receptors, ErbB2 or ErbB4, results in embryonic lethality because of failure of the heart to develop. Although expression of NRGs and their receptors declines after midembryogenesis, both ErbB2 and ErbB4 are present in cardiac myocytes, and NRG-1 expression remains inducible in primary cultures of coronary microvascular endothelial cells from adult rat ventricular muscle. In neonatal rat ventricular myocytes, a soluble NRG-1, recombinant human glial growth factor-2, increased [(3)H]phenylalanine uptake and induced expression of atrial natriuretic factor (ANF) and sarcomeric F-actin polymerization. The effect of NRG-1 on [(3)H]phenylalanine uptake and sarcomeric F-actin polymerization was maximal at 20 ng/ml but declined at higher concentrations. NRG-1 activated p42/p44 mitogen-activated protein kinase (MAPK) [extracellular signal-regulated kinase (ERK)-2/ERK1] and ribosomal S6 kinase (RSK)-2 (90-kDa ribosomal S6 kinase), both of which could be inhibited by the MAPK/ERK kinase-1 antagonist PD-098059. NRG-1 also activated 70-kDa ribosomal S6 kinase, which was inhibited by either rapamycin or wortmannin. Activation of these pathways exhibited the same "biphasic" response to increasing NRG-1 concentrations. Wortmannin and LY-294002 blocked sarcomeric F-actin polymerization but not [(3)H]phenylalanine uptake or ANF expression, whereas PD-098059 consistently blocked both [(3)H]phenylalanine uptake and ANF expression but not actin polymerization. In contrast, rapamycin inhibited [(3)H]phenylalanine uptake and F-actin polymerization but not ANF expression. Thus NRG-ErbB signaling triggers multiple nonredundant pathways in postnatal ventricular myocytes.

Cytokine-mediated apoptosis in cardiac myocytes: the role of inducible nitric oxide synthase induction and peroxynitrite generation.

Increased production of nitric oxide (NO) after induction of the cytokine-inducible isoform of nitric oxide synthase (iNOS or NOS2) in cardiac myocytes and other parenchymal cells within the heart may in addition to contributing to myocyte contractile dysfunction also contribute to the induction of programmed cell death (apoptosis). To investigate the mechanism(s) by which increased NO production leads to apoptosis, we examined the role of NO in primary cultures of neonatal rat ventricular myocytes (NRVMs) after induction by the cytokines interleukin-1beta (IL-1beta) and interferon gamma (IFNgamma) or exposure to the exogenous NO donor S-nitroso-N-acetylcysteine (SNAC) or peroxynitrite (ONOO(-)). Both SNAC (1 mmol/L) and ONOO(-) (100 micromol/L), but not their respective controls (ie, N-acetylcysteine and pH-inactivated ONOO(-)), induced apoptosis in confluent, serum-starved NRVMs at 48 hours. Similarly, incubation of NRVMs with IL-1beta and IFNgamma for 48 hours resulted in an increase in iNOS expression, nitrite production, and programmed cell death. Both the cytokine-induced nitrite accumulation and myocyte apoptosis could be completely prevented by the nonselective NOS inhibitor L-nitroarginine (3 mmol/L) or the specific iNOS inhibitor 2-amino-5, 6-dihydro-6-methyl-4H-1,3-thiazine (AMT, 100 micromol/L). NO-mediated myocyte apoptosis was not attenuated by the inhibition of soluble guanylyl cyclase with ODQ, nor could apoptosis be induced by the incubation of NRVMs with 1 mmol/L 8-bromo-cGMP, a cell-permeant cGMP analogue. However, NO-mediated apoptosis was significantly attenuated by the superoxide dismutase mimetic and ONOO(-) scavenger Mn(III)tetrakis (4-benzoic acid) porphyrin (MnTBAP, 100 micromol/L). NO/ONOO(-)-mediated apoptosis was associated with increased expression of Bax with no change in Bcl-2 mRNA abundance. Furthermore, apoptotic cell death was also confirmed in adult rat ventricular myocytes (ARVMs) when grown in heteroculture with IL-1beta- and IFNgamma-treated rat cardiac microvascular endothelial cells. Therefore, cytokine-induced apoptosis in NRVMs and ARVMs is mediated by iNOS induction, ONOO(-), and associated with an increase in Bax levels.

Expression and regulation of the sodium-calcium exchanger in cardiac microvascular endothelial cells.

1. The sodium-calcium exchanger (NCX) plays an important role in Ca2+ homeostasis. In the heart, NCX participates in the control of contraction and relaxation and in large vessel endothelial cells some data suggest that NCX could influence nitric oxide (NO) generation. In this context, the cardiac microvasculature has received considerable attention as a mediator of myocardial performance, via the release of paracrine acting factors such as NO. Therefore, the aim of the current study was to characterize NCX expression and regulation in cardiac microvascular endothelial cells (CMEC). The NCX expression was also examined in neonatal ventricular cardiomyocytes where aspects of its function and regulation have been well characterized. 2. The presence of functional NCX in CMEC was confirmed by the presence of a consistent rise in intracellular Ca2+ concentration ([Ca2+]i) in response to removal of extracellular Na+. Furthermore, NCX mRNA expression was readily detectable in CMEC. 3. In order to examine the role of possible physiological regulators of NCX expression, the effect of intracellular Ca2+ loading, caused by 24 h exposure to 10 mumol/L ouabain, was investigated. In Ca(2+)-loaded CMEC, there was a substantially greater rise in [Ca2+]i during exposure to Na(+)-free buffer: 33 +/- 6 versus 124 +/- 25 nmol/L% (P < 0.05), consistent with increased protein expression. Consistent with these findings, northern blot analysis confirmed the presence of a two-fold increase in NCX mRNA in these cells. 4. These data indicate the presence of functional NCX in CMEC and identify [Ca2+]i as a potential physiological regulator of expression.

Inducible nitric oxide synthase and tumor necrosis factor in animal models of myocardial necrosis induced by coronary artery ligation or isoproterenol injection.

BACKGROUND: Increased expression of inducible nitric oxide synthase (iNOS) has been described in humans with cardiomyopathies. Most animal models of ischemia-induced heart failure use the surgical ligation of coronary arteries. However, studies of iNOS expression in these models may be confounded by a robust immune response because of the surgical procedure itself leading to iNOS expression in the heart, as well as in other tissues. METHODS AND RESULTS: iNOS expression was studied in adult male rats injected subcutaneously with either 250 mg/kg of isoproterenol (ISO) or vehicle on 2 consecutive days. This approach induces diffuse myocardial necrosis and leads to the development of a dilated cardiomyopathy. Hearts from ISO-injected animals harvested at 6 weeks had evidence of apical and subendocardial scarring. These hearts showed a 9.6-fold (left ventricle [LV], P = .004) and an 11.9-fold (right ventricle, P = .002) increase in the expression of tumor necrosis factor (TNF), and a 6.8-fold increase (LV, P = .0183) in iNOS messenger RNA compared with vehicle-injected controls. iNOS protein also was detectable by immmunoprecipitation in left ventricular muscle from ISO-injected animals, as well as by immunohistochemical analysis. CONCLUSION: Expression of TNF and iNOS in the heart is increased in an experimental model of dilated cardiomyopathy that minimizes the confounding effects of surgery, supporting a role for the activation of innate immunity signaling pathways in the pathogenesis of heart failure.

Toll4 (TLR4) expression in cardiac myocytes in normal and failing myocardium.

Expression of innate immune response proteins, including IL-1beta, TNF, and the cytokine-inducible isoform of nitric oxide synthase (iNOS), have been documented in the hearts of humans and experimental animals with heart failure regardless of etiology, although the proximal events leading to their expression are unknown. Noting that expression of a human homologue of Drosophila Toll, a proximal innate immunity transmembrane signaling protein in the fly, now termed human Toll-like receptor 4 (hTLR4), appeared to be relatively high in the heart, we examined TLR4 mRNA and protein abundance in isolated cellular constituents of cardiac muscle and in normal and abnormal murine, rat, and human myocardium. TLR4 expression levels in cardiac myocytes and in coronary microvascular endothelial cells could be enhanced by either LPS or IL-1beta, an effect inhibited by the oxygen radical scavenger PDTC. Transfection of a constitutively active TLR4 construct, CD4/hTLR4, resulted in activation of a nuclear factor-kappaB reporter construct, but not of an AP-1 or an iNOS reporter construct, in cardiac myocytes. In normal murine, rat, and human myocardium, TLR4 expression was diffuse, and presumably cytoplasmic, in cardiac myocytes. However, in remodeling murine myocardium remote from sites of ischemic injury and in heart tissue from patients with idiopathic dilated cardiomyopathy, focal areas of intense TLR4 staining were observed in juxtaposed regions of 2 or more adjacent myocytes; this staining was not observed in control myocardium. Increased expression and signaling by TLR4, and perhaps other Toll homologues, may contribute to the activation of innate immunity in injured myocardium.