Nitric oxide-cGMP pathway is involved in endotoxin-induced contractile dysfunction in rat hearts

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.

Distinct Myocardial Mechanisms Underlie Cardiac Dysfunction in Endotoxemic Male and Female Mice

In male mice, sepsis-induced cardiomyopathy develops as a result of dysregulation of myocardial calcium (Ca) handling, leading to depressed cellular Ca transients (ΔCai). ΔCai depression is partially due to inhibition of sarcoplasmic reticulum Ca ATP-ase (SERCA) via oxidative modifications, which are partially opposed by cGMP generated by the enzyme soluble guanylyl cyclase (sGC). Whether similar mechanisms underlie sepsis-induced cardiomyopathy in female mice is unknown.Male and female C57Bl/6J mice (WT), and mice deficient in the sGC α1 subunit activity (sGCα1), were challenged with lipopolysaccharide (LPS, ip). LPS induced mouse death and cardiomyopathy (manifested as the depression of left ventricular ejection fraction by echocardiography) to a similar degree in WT male, WT female, and sGCα1 male mice, but significantly less in sGCα1 female mice. We measured sarcomere shortening and ΔCai in isolated, externally paced cardiomyocytes, at 37°C. LPS depressed sarcomere shortening in both WT male and female mice. Consistent with previous findings, in male mice, LPS induced a decrease in ΔCai (to 30 ± 2% of baseline) and SERCA inhibition (manifested as the prolongation of the time constant of Ca decay, τCa, to 150 ± 5% of baseline). In contrast, in female mice, the depression of sarcomere shortening induced by LPS occurred in the absence of any change in ΔCai, or SERCA activity. This suggested that, in female mice, the causative mechanism lies downstream of the Ca transients, such as a decrease in myofilament sensitivity for Ca. The depression of sarcomere shortening shortening after LPS was less severe in female sGCα1 mice than in WT female mice, indicating that cGMP partially mediates cardiomyocyte dysfunction.These results suggest, therefore, that LPS-induced cardiomyopathy develops through distinct sex-specific myocardial mechanisms. While in males LPS induces sGC-independent decrease in ΔCai, in female mice LPS acts downstream of ΔCai, possibly via sGC-dependent myofilament dysfunction.

Cardiovascular and pharmacological implications of haem-deficient NO-unresponsive soluble guanylate cyclase knock-in mice

Oxidative stress, a central mediator of cardiovascular disease, results in loss of the prosthetic haem group of soluble guanylate cyclase (sGC), preventing its activation by nitric oxide (NO). Here we introduce Apo-sGC mice expressing haem-free sGC. Apo-sGC mice are viable and develop hypertension. The haemodynamic effects of NO are abolished, but those of the sGC activator cinaciguat are enhanced in apo-sGC mice, suggesting that the effects of NO on smooth muscle relaxation, blood pressure regulation and inhibition of platelet aggregation require sGC activation by NO. Tumour necrosis factor (TNF)-induced hypotension and mortality are preserved in apo-sGC mice, indicating that pathways other than sGC signalling mediate the cardiovascular collapse in shock. Apo-sGC mice allow for differentiation between sGC-dependent and -independent NO effects and between haem-dependent and -independent sGC effects. Apo-sGC mice represent a unique experimental platform to study the in vivo consequences of sGC oxidation and the therapeutic potential of sGC activators.

Haem-free, NO-insensitive soluble guanylate cyclase (apo-sGC) generated during oxidative stress contributes to cardiovascular pathology. By generating and characterizing apo-sGC knock-in mice, Thoonen et al. provide a scientific ground for the therapeutic concept of sGC activators, and dissect the relevance of the NO-sGC axis.

SERCA Cys674 sulphonylation and inhibition of L-type Ca2+ influx contribute to cardiac dysfunction in endotoxemic mice, independent of cGMP synthesis

The goal of this study was to identify the cellular mechanisms responsible for cardiac dysfunction in endotoxemic mice. We aimed to differentiate the roles of cGMP [produced by soluble guanylyl cyclase (sGC)] versus oxidative posttranslational modifications of Ca(2+) transporters. C57BL/6 mice [wild-type (WT) mice] were administered lipopolysaccharide (LPS; 25 μg/g ip) and euthanized 12 h later. Cardiomyocyte sarcomere shortening and Ca(2+) transients (ΔCai) were depressed in LPS-challenged mice versus baseline. The time constant of Ca(2+) decay (τCa) was prolonged, and sarcoplasmic reticulum Ca(2+) load (CaSR) was depressed in LPS-challenged mice (vs. baseline), indicating decreased activity of sarco(endo)plasmic Ca(2+)-ATPase (SERCA). L-type Ca(2+) channel current (ICa,L) was also decreased after LPS challenge, whereas Na(+)/Ca(2+) exchange activity, ryanodine receptors leak flux, or myofilament sensitivity for Ca(2+) were unchanged. All Ca(2+)-handling abnormalities induced by LPS (the decrease in sarcomere shortening, ΔCai, CaSR, ICa,L, and τCa prolongation) were more pronounced in mice deficient in the sGC main isoform (sGCα1(-/-) mice) versus WT mice. LPS did not alter the protein expression of SERCA and phospholamban in either genotype. After LPS, phospholamban phosphorylation at Ser(16) and Thr(17) was unchanged in WT mice and was increased in sGCα1(-/-) mice. LPS caused sulphonylation of SERCA Cys(674) (as measured immunohistochemically and supported by iodoacetamide labeling), which was greater in sGCα1(-/-) versus WT mice. Taken together, these results suggest that cardiac Ca(2+) dysregulation in endotoxemic mice is mediated by a decrease in L-type Ca(2+) channel function and oxidative posttranslational modifications of SERCA Cys(674), with the latter (at least) being opposed by sGC-released cGMP.

The negative inotropic effects of gaseous sulfur dioxide and its derivatives in the isolated perfused rat heart

Epidemiological investigations have revealed that sulfur dioxide (SO(2) ) exposure is linked to cardiovascular diseases. The present study was designed to investigate the negative inotropic effects of gaseous SO(2) and its derivatives in the isolated perfused rat heart and the possible mechanisms involved in their effects. The results showed that both SO(2) and SO(2) derivatives elicited a negative inotropic effect in a dose-dependent manner, and SO(2) produced a higher negative effect than SO(2) derivatives. The mechanism of SO(2) -induced negative inotropic effects at low concentrations was different from that at high concentrations. At low concentrations, the mechanism of SO(2) -induced negative inotropic effects might occur through promoting the activities of protein kinase C (PKC), cycloxygenase, and cGMP, while the mechanism of SO(2) derivatives-induced effects might be related to the opening of ATP-sensitive K(+) (K(ATP) ) channel and the inhibition of Ca(2+) influx via L-type calcium-channel. At high concentrations, the mechanisms of SO(2) and SO(2) derivatives-induced negative inotropic effects were similar, which might be related to the K(ATP) channel and L-type calcium-channel as well as the possible alterations in PKC, cycloxygenase, and cGMP. Further work is needed to determine the relative contribution of each pathway in SO(2) -mediated inotropic effect.

Mesenchymal stem cells attenuate myocardial functional depression and reduce systemic and myocardial inflammation during endotoxemia

BACKGROUND

Endotoxemia is associated with depressed cardiac function during sepsis. Mesenchymal stem cells (MSCs) possess an ability to modulate the inflammatory response during sepsis, but it is unknown whether MSCs possess the ability to reduce endotoxemia-induced myocardial injury and dysfunction.

METHODS

Endotoxemia was induced in rats via injection of lipopolysaccharide (LPS). Animals were divided into the following groups: (1) saline + saline; (2) LPS + saline; (3) LPS + MSCs; and (4) LPS + LLC-PK1 renal epithelial cells (differentiated control). At 6 hours, animals were anesthetized, serum was collected, and hearts were extracted and perfused via the isolated heart system. Hearts and serum were analyzed for tumor necrosis factor (TNF)-alpha, interleukin (IL)-1beta, IL-6, and IL-10.

RESULTS

The administration of LPS depressed myocardial function. Treatment with MSCs ameliorated this depression. Serum TNF-alpha, IL-1beta, and IL-6 were elevated in LPS-treated groups. Treatment with MSCs was associated with reduced levels of these cytokines. A trend toward reduced myocardial TNF-alpha and significant reductions in myocardial IL-1beta and IL-6 were observed in the MSC-treated group. IL-10 levels were increased after the LPS administration in both serum and myocardium. Serum levels were increased further after treatment with MSCs.

CONCLUSION

Treatment with MSCs during endotoxemia reduces systemic and myocardial inflammation and is associated with a reduction in LPS-induced myocardial functional depression.

sGC(alpha)1(beta)1 attenuates cardiac dysfunction and mortality in murine inflammatory shock models

Altered cGMP signaling has been implicated in myocardial depression, morbidity, and mortality associated with sepsis. Previous studies, using inhibitors of soluble guanylate cyclase (sGC), suggested that cGMP generated by sGC contributed to the cardiac dysfunction and mortality associated with sepsis. We used sGC(alpha)(1)-deficient (sGC(alpha)(1)(-/-)) mice to unequivocally determine the role of sGC(alpha)(1)beta(1) in the development of cardiac dysfunction and death associated with two models of inflammatory shock: endotoxin- and TNF-induced shock. At baseline, echocardiographic assessment and invasive hemodynamic measurements of left ventricular (LV) dimensions and function did not differ between wild-type (WT) mice and sGC(alpha)(1)(-/-) mice on the C57BL/6 background (sGC(alpha)(1)(-/-B6) mice). At 14 h after endotoxin challenge, cardiac dysfunction was more pronounced in sGC(alpha)(1)(-/-B6) than WT mice, as assessed using echocardiographic and hemodynamic indexes of LV function. Similarly, Ca(2+) handling and cell shortening were impaired to a greater extent in cardiomyocytes isolated from sGC(alpha)(1)(-/-B6) than WT mice after endotoxin challenge. Importantly, morbidity and mortality associated with inflammatory shock induced by endotoxin or TNF were increased in sGC(alpha)(1)(-/-B6) compared with WT mice. Together, these findings suggest that cGMP generated by sGC(alpha)(1)beta(1) protects against cardiac dysfunction and mortality in murine inflammatory shock models.

Platelet-derived exosomes from septic shock patients induce myocardial dysfunction

Introduction

Mechanisms underlying inotropic failure in septic shock are incompletely understood. We previously identified the presence of exosomes in the plasma of septic shock patients. These exosomes are released mainly by platelets, produce superoxide, and induce apoptosis in vascular cells by a redox-dependent pathway. We hypothesized that circulating platelet-derived exosomes could contribute to inotropic dysfunction of sepsis.

Methods

We collected blood samples from 55 patients with septic shock and 12 healthy volunteers for exosome separation. Exosomes from septic patients and healthy individuals were investigated concerning their myocardial depressant effect in isolated heart and papillary muscle preparations.

Results

Exosomes from the plasma of septic patients significantly decreased positive and negative derivatives of left ventricular pressure in isolated rabbit hearts or developed tension and its first positive derivative in papillary muscles. Exosomes from healthy individuals decreased these variables non-significantly. In hearts from rabbits previously exposed to endotoxin, septic exosomes decreased positive and negative derivatives of ventricular pressure. This negative inotropic effect was fully reversible upon withdrawal of exosomes. Nitric oxide (NO) production from exosomes derived from septic shock patients was demonstrated by fluorescence. Also, there was an increase in myocardial nitrate content after exposure to septic exosomes.

Conclusion

Circulating platelet-derived exosomes from septic patients induced myocardial dysfunction in isolated heart and papillary muscle preparations, a phenomenon enhanced by previous in vivo exposure to lipopolysaccharide. The generation of NO by septic exosomes and the increased myocardial nitrate content after incubation with exosomes from septic patients suggest an NO-dependent mechanism that may contribute to myocardial dysfunction of sepsis.

Lysozyme, a mediator of sepsis that produces vasodilation by hydrogen peroxide signaling in an arterial preparation

In septic shock, systemic vasodilation and myocardial depression contribute to the systemic hypotension observed. Both components can be attributed to the effects of mediators that are released as part of the inflammatory response. We previously found that lysozyme (Lzm-S), released from leukocytes, contributed to the myocardial depression that develops in a canine model of septic shock. Lzm-S binds to the endocardial endothelium, resulting in the production of nitric oxide (NO), which, in turn, activates the myocardial soluble guanylate cyclase (sGC) pathway. In the present study, we determined whether Lzm-S might also play a role in the systemic vasodilation that occurs in septic shock. In a phenylephrine-contracted canine carotid artery ring preparation, we found that both canine and human Lzm-S, at concentrations similar to those found in sepsis, produced vasorelaxation. This decrease in force could not be prevented by inhibitors of NO synthase, prostaglandin synthesis, or potassium channel inhibitors and was not dependent on the presence of the vascular endothelium. However, inhibitors of the sGC pathway prevented the vasodilatory activity of Lzm-S. In addition, Aspergillus niger catalase, which breaks down H(2)O(2), as well as hydroxyl radical scavengers, which included hydroquinone and mannitol, prevented the effect of Lzm-S. Electrochemical sensors corroborated that Lzm-S caused H(2)O(2) release from the carotid artery preparation. In conclusion, these results support the notion that when Lzm-S interacts with the arterial vasculature, this interaction results in the formation of H(2)O(2), which, in turn, activates the sGC pathway to cause relaxation. Lzm-S may contribute to the vasodilation that occurs in septic shock.

Lysozyme, a mediator of sepsis, impairs the cardiac neural adrenergic response by nonendothelial release of NO and inhibitory G protein signaling

We previously showed that lysozyme (Lzm-S), derived from leukocytes, caused myocardial depression in canine sepsis by binding to the endocardial endothelium to release nitric oxide (NO). NO then diffuses to adjacent myocytes to activate the cGMP pathway. In a canine right ventricular trabecular (RVT) preparation, Lzm-S also decreased the inotropic response to field stimulation (FSR) during which the sympathetic and parasympathetic nerves were simulated to measure the adrenergic response. In the present study, we determined whether the pathway by which Lzm-S decreased FSR was different from the pathway by which Lzm-S reduced steady-state (SS) contraction. Furthermore, we determined whether the decrease in FSR was due to a decrease in sympathetic stimulation or enhanced parasympathetic signaling. In the RVT preparation, we found that the inhibitory effect of Lzm-S on FSR was prevented by NO synthase (NOS) inhibitors. A cGMP inhibitor also blocked the depressant activity of Lzm-S. However, in contrast to the Lzm-S-induced decline in SS contraction, chemical removal of the endocardial endothelium by Triton X-100 to eliminate endothelial NO release did not prevent the decrease in FSR. An inhibitory G protein was involved in the effect of Lzm-S, since FSR could be restored by treatment with pertussis toxin. Atropine prevented the Lzm-S-induced decline in FSR, whereas beta(1)- and beta(2)-adrenoceptor function was not impaired by Lzm-S. These results indicate that the Lzm-S-induced decrease in FSR results from a nonendothelial release of NO. NO then acts through inhibitory G protein to enhance parasympathetic signaling.

Ischemia/Reperfusion of the Liver Induces Heart Injury in Rats

OBJECTIVE

We evaluated the cardiovascular injury induced by ischemia and reperfusion (I/R) of the liver by measuring changes in blood levels of cardiac troponin I (cTNI), an index of cardiovascular injury, as well as levels of selected indicators of an inflammatory response.

MATERIALS AND METHODS

Ischemia was induced in the rat liver by clamping the common hepatic artery and portal vein for 40 minutes, after which flow was restored, and the liver reperfused for 90 minutes. Blood samples were collected prior to ischemia and after reperfusion. cTNI as well as levels of tumor necrosis factor alpha (TNFalpha), hydroxyl radical (.OH), nitric oxide (NO), and alanine transferase (ALT) were measured.

RESULTS

I/R of the liver induced a significant increase in ALT (P<.001). Increased cTNI levels (P<.05) were associated with inflammatory responses, such as elevated levels of TNFalpha (P<.001), . OH (P<.001), and NO (P<.001). After administration of 3-aminobenzamide, a poly(ADP-ribose) polymerase (PARP) inhibitor, liver and heart injuries were significantly attenuated (P<.05).

CONCLUSIONS

I/R-induced liver injury was associated with cardiovascular injury, perhaps resulting from inflammatory responses triggered by elevated levels of reactive radical species of nitric oxide, superoxide, and peroxynitrite, by which PARP was activated. 3-Aminobenzamide, significantly attenuated I/R-induced liver and heart injuries.

Transforming growth factor-beta1 blocks in vitro cardiac myocyte depression induced by tumor necrosis factor-alpha, interleukin-1beta, and human septic shock serum

OBJECTIVE

Serum from patients with septic shock induces depression of myocyte contractility in vitro that is proportional the reduction of ejection fraction in vivo. This effect is mediated, in part, by tumor necrosis factor (TNF)-alpha and interleukin (IL)-1beta. Transforming growth factor (TGF)-beta is an immunomodulatory cytokine with a broad range of anti-inflammatory effects. Using an in vitro assay, this study sought to determine the effect of TGF-beta1 on myocyte depression induced by TNF-alpha, IL-1beta, and serum with known depressant activity from patients with septic shock.

DESIGN

The maximum extent of shortening of electrically paced rat cardiac myocytes in tissue culture was quantified by a closed-loop video tracking system. Myocytes were exposed to different combinations of TNF-alpha, IL-1beta, septic serum, and TGF-beta1.

SETTING

Basic research laboratory.

MEASUREMENTS AND MAIN RESULTS

Increasing concentrations of TNF-alpha and IL-1beta each caused significant depression of maximum extent of myocyte shortening in vitro over 30 mins (p<.0001). Similarly, a synergistic combination of TNF-alpha and IL-1beta as well as serum with known depressant activity from five patients with acute septic shock induced significant depression of cardiac myocyte contraction (p<.01). Increasing concentrations of TGF-beta1 alone had no effect on maximum extent of cardiac myocyte contraction. However, myocytes that were co-incubated with increasing concentrations of TGF-beta1 demonstrated dose-dependent reversal of depression induced by TNF-alpha or IL-1beta (p<.0001). Similarly, depressant effects caused by synergistic concentrations of TNF-alpha and IL-1beta and serum from all five patients with septic shock were prevented by co-incubation with TGF-beta1.

CONCLUSIONS

These data demonstrate that depression of in vitro cardiac myocyte contraction induced by proinflammatory cytokines and septic serum can be blocked by TGF-beta1. TGF-beta1 may have potential as therapy for sepsis-associated myocardial depression in humans.

Ischaemia or reperfusion: which is a main trigger for changes in nitric oxide mRNA synthases expression?

OBJECTIVE

To investigate alterations in endothelial nitric oxide synthase and inducible nitric oxide synthase mRNA expressions and nitric oxide release in the myocardium during ischaemia/reperfusion and determine whether these changes are ischaemic and/or reperfusion dependent.

MATERIALS AND METHODS

Isolated rat hearts were perfused by a modified Langendorff system. Following 1 h of global cardioplegic ischaemia, left ventricle haemodynamic parameters were recorded at baseline and during 30 min of reperfusion. Levels of endothelial, inducible nitric oxide synthases mRNA expression and nitric oxide release were measured at baseline, after ischaemia and at 30 min of reperfusion.

RESULTS

Global cardioplegic ischaemia caused a significant depression of left ventricular function and a decrease of coronary flow. Postischaemic intensities of the endothelial nitric oxide synthase mRNA bands were significantly lower than at baseline (P < 0.01). There were no significant differences in endothelial nitric oxide synthase mRNA band intensities immediately after ischaemia compared to the end of reperfusion, nor between the intensities of inducible nitric oxide synthase mRNA bands at baseline, at end of ischaemia and at end of reperfusion. Nitric oxide in the myocardial effluent was below detectable levels at all measured points.

CONCLUSION

Ischaemic injury causes down-regulation of endothelial nitric oxide synthase mRNA expression, which is then associated with reduction of coronary flow during reperfusion, representing one possible mechanism of ischaemia/reperfusion injury. We did not find expected elevations of inducible nitric oxide synthase mRNA expression during ischaemia or reperfusion and we suggest that ischaemia/reperfusion injury is not associated with nitric oxide overproduction.

Effect of lipopolysaccharide on diarrhea and gastrointestinal transit in mice: Roles of nitric oxide and prostaglandin E2

AIM: To investigate the effect of lipopolysaccharide (LPS) on the diarrheogenic activity, gastrointestinal transit (GIT), and intestinal fluid content and the possible role of nitric oxide (NO) and prostaglandin E₂ (PGE₂) in gastrointestinal functions of endotoxin-treated mice.

METHODS: Diarrheogic activity, GIT, and intestinal fluid content as well as nitric oxide and PGE₂ products were measured after intraperitoneal administration of LPS in mice.

RESULTS: LPS dose-dependently accumulated abundant fluid into the small intestine, induced diarrhea, but decreased the GIT. Both nitric oxide and PGE₂ were found to increase in LPS-treated mice. Western blot analysis indicated that LPS significantly induced the protein expression of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 in mice intestines. Pretreatment with N^G-nitro-L-arginine-methyl ester (L-NAME, a non-selective NOS inhibitor) or indomethacin (an inhibitor of prostaglandin synthesis) significantly attenuated the effects of LPS on the diarrheogenic activity and intestine content, but reversed the GIT.

CONCLUSION: The present study suggests that the pathogenesis of LPS treatment may mediate the stimulatory effect of LPS on nitric oxide and PGE2 production and NO/prostaglandin pathway may play an important role on gastrointestinal function.