The role of speckle tracking echocardiography in assessment of lipopolysaccharide-induced myocardial dysfunction in mice

Cardiomyocyte-specific disruption of soluble epoxide hydrolase limits inflammation to preserve cardiac function

Endotoxemia elicits a multiorgan inflammatory response that results in cardiac dysfunction and often leads to death. Inflammation-induced metabolism of endogenous N-3 and N-6 polyunsaturated fatty acids generates numerous lipid mediators, such as epoxy fatty acids (EpFAs), which protect the heart. However, EpFAs are hydrolyzed by soluble epoxide hydrolase (sEH), which attenuates their cardioprotective actions. Global genetic disruption of sEH preserves EpFA levels and attenuates cardiac dysfunction in mice following acute lipopolysaccharide (LPS)-induced inflammatory injury. In leukocytes, EpFAs modulate the innate immune system through the NOD-like receptor family pyrin domain-containing 3 (NLRP3) inflammasome. However, the mechanisms by which both EpFAs and sEH inhibition exert their protective effects in the cardiomyocyte are still elusive. This study investigated whether cardiomyocyte-specific sEH disruption attenuates inflammation and cardiac dysfunction in acute LPS inflammatory injury via modulation of the NLRP3 inflammasome. We use tamoxifen-inducible CreER recombinase technology to target sEH genetic disruption to the cardiomyocyte. Primary cardiomyocyte studies provide mechanistic insight into inflammasome signaling. For the first time, we demonstrate that cardiomyocyte-specific sEH disruption preserves cardiac function and attenuates inflammatory responses by limiting local cardiac inflammation and activation of the systemic immune response. Mechanistically, inhibition of cardiomyocyte-specific sEH activity or exogenous EpFA treatment do not prevent upregulation of NLRP3 inflammasome machinery in neonatal rat cardiomyocytes. Rather, they limit downstream activation of the pathway leading to release of fewer chemoattractant factors and recruitment of immune cells to the heart. These data emphasize that cardiomyocyte sEH is vital for mediating detrimental systemic inflammation.NEW & NOTEWORTHY The cardioprotective effects of genetic disruption and pharmacological inhibition of sEH have been demonstrated in a variety of cardiac disease models, including acute LPS inflammatory injury. For the first time, it has been demonstrated that sEH genetic disruption limited to the cardiomyocyte profoundly preserves cardiac function and limits local and systemic inflammation following acute LPS exposure. Hence, cardiomyocytes serve a critical role in the innate immune response that can be modulated to protect the heart.

Effect of thymoquinone on sepsis-induced cardiac damage via anti-inflammatory and anti-apoptotic mechanisms

Objective

Sepsis is a systemic and deleterious host reaction to severe infection. Cardiac dysfunction is an established serious outcome of multiorgan failure associated with this condition. Therefore, it is important to develop drugs targeting sepsis-induced cardiac damage and inflammation. Thymoquinone (TQ) has anti-inflammatory, anti-oxidant, anti-fibrotic, anti-tumor, and anti-apoptotic effects. This study examined the effects of thymoquinone on sepsis-induced cardiac damage.

Methods

Male BALB/c mice were randomly segregated into four groups: control, TQ, cecal ligation and puncture (CLP), and CLP + TQ groups. CLP was performed after gavaging the mice with TQ for 2 weeks. After 48 hours, we estimated the histopathological changes in the cardiac tissue and the serum levels of cardiac troponin-T. We evaluated the expression of factors associated with inflammation, apoptosis, oxidative stress, and the PI3K/AKT pathway.

Results

TQ significantly reduced intestinal histological alterations and inhibited the upregulation of interleukin-6, tumor necrosis factor-α, Bax, NOX4, p-PI3K, and p-AKT. TQ also increased Bcl-2, HO-1, and NRF2 expression.

Conclusion

These results suggest that TQ effectively modulates pro-inflammatory, apoptotic, oxidative stress, and PI3K/AKT pathways, making it indispensable in the treatment of sepsis-induced cardiac damage.

Circulating cardiomyocyte-derived extracellular vesicles reflect cardiac injury during systemic inflammatory response syndrome in mice

The release of extracellular vesicles (EVs) is increased under cellular stress and cardiomyocyte damaging conditions. However, whether the cardiomyocyte-derived EVs eventually reach the systemic circulation and whether their number in the bloodstream reflects cardiac injury, remains unknown. Wild type C57B/6 and conditional transgenic mice expressing green fluorescent protein (GFP) by cardiomyocytes were studied in lipopolysaccharide (LPS)-induced systemic inflammatory response syndrome (SIRS). EVs were separated both from platelet-free plasma and from the conditioned medium of isolated cardiomyocytes of the left ventricular wall. Size distribution and concentration of the released particles were determined by Nanoparticle Tracking Analysis. The presence of GFP + cardiomyocyte-derived circulating EVs was monitored by flow cytometry and cardiac function was assessed by echocardiography. In LPS-treated mice, systemic inflammation and the consequent cardiomyopathy were verified by elevated plasma levels of TNFα, GDF-15, and cardiac troponin I, and by a decrease in the ejection fraction. Furthermore, we demonstrated elevated levels of circulating small- and medium-sized EVs in the LPS-injected mice. Importantly, we detected GFP+ cardiomyocyte-derived EVs in the circulation of control mice, and the number of these circulating GFP+ vesicles increased significantly upon intraperitoneal LPS administration (P = 0.029). The cardiomyocyte-derived GFP+ EVs were also positive for intravesicular troponin I (cTnI) and muscle-associated glycogen phosphorylase (PYGM). This is the first direct demonstration that cardiomyocyte-derived EVs are present in the circulation and that the increased number of cardiac-derived EVs in the blood reflects cardiac injury in LPS-induced systemic inflammation (SIRS).

Role of Thymoquinone in Cardiac Damage Caused by Sepsis from BALB/c Mice

Sepsis is a major health complication causing patient mortality and increased healthcare costs. Cardiac dysfunction, an important consequence of sepsis, affects mortality. We previously reported that thymoquinone (TQ) protected against hyperlipidemia and doxorubicin-induced cardiac damage. This study investigated the possible protective effects of TQ against cardiac damage in septic BALB/c mice. Eight-week-old male BALB/c mice were divided into four groups: control, TQ, cecal ligation and puncture (CLP), and TQ + CLP. CLP was performed after 2-week TQ gavage. After 48 h, we measured the histopathological alterations of the cardiac tissue and the plasma levels of troponin-T (cTnT) and ATP. We evaluated autophagy (p62 and beclin 1), pyroptosis (NLRP3, caspase-1, interleukin [IL]-1β, and IL-18) at the gene and protein levels and IL-6 and tumor necrosis factor-α (TNF-α) at the gene level. Our results demonstrated that TQ administration significantly reduced intestinal histological alterations. TQ inhibited plasma cTnT levels; improved ATP; significantly inhibited p62, NLRP3, caspase-1, IL-1β, IL-18, IL-6, TNF-α, and MCP-1expressions; and increased beclin 1 and IL-10 level. The phosphatidylinositide 3-kinase level was significantly decreased in the TQ + CLP group versus the CLP group. These results suggest that TQ effectively modulates autophagy, pyroptosis, and pro-inflammatory, making it important in the treatment of sepsis-induced cardiac damage.

Circumferential strain rate to detect lipopolysaccharide-induced cardiac dysfunction: a speckle tracking echocardiography study

Background

Lipopolysaccharide (LPS)-induced myocardial dysfunction is a widely used indicator to study septic cardiomyopathy (SC). This study investigated the efficiency of strain rate imaging (SRI) in detecting LPS-induced myocardial dysfunction.

Methods

A total of 30 mice were randomly assigned to saline group (n=10), 10 mg/kg LPS group (n=10) and 20 mg/kg LPS group (n=10). Then at baseline, 6 and 20 h after LPS injection, 2-D and M-mode echocardiography were conducted with GE Vivid 7 ultrasound (il3L linear probe, 10.0-14.0 MHz) and Echopac PC software. Ejection fraction (EF) and fractional shortening (FS) were measured with M-mode tracings. Serum biochemical examination was then performed to evaluate sepsis-induced myocardial injury.

Results

In LPS 20 mg/kg group, at 6 h after LPS injection, SRI found significantly decreased early diastolic strain rate (SRe, 1.76±1.05 vs. 3.18±0.83 unit/s, P<0.05), but M-mode echo found no change in EF and FS. In 10 mg/kg LPS group, compared with those at 6 h after LPS injection, SRI found a decline in SRe (1.57±0.75 vs. 3.18±0.83 unit/s, P<0.05), and M-mode tracings found an elevation in EF (71.31%±11.68% vs. 55.36%±7.42%, P<0.05) and FS (35.67%±8.79% vs. 25.43%±4.32%, P<0.05) at 20 h. Furthermore, LPS elevated the levels of serum creatine kinase-MB (CK-MB) and cardiac troponin-T (cTnT) at 20 h.

Conclusions

SRI is useful to early assess LPS-induced cardiac deformation in mice. circumferential strain rate (SRcirc) is a sensitive indicator for LPS-induced myocardial injury in severe sepsis.

Age-dependent cardiac function during experimental sepsis: effect of pharmacological activation of AMP-activated protein kinase by AICAR

Age represents a major risk factor for multiple organ failure, including cardiac dysfunction, in patients with sepsis. AMP-activated protein kinase (AMPK) is a crucial regulator of energy homeostasis that controls mitochondrial biogenesis by activation of peroxisome proliferator-activated receptor-γ coactivator-1α and disposal of defective organelles by autophagy. We investigated whether AMPK dysregulation contributes to age-dependent cardiac injury in young (2-3 mo) and mature adult (11-13 mo) male mice subjected to sepsis by cecal ligation and puncture and whether AMPK activation by 5-amino-4-imidazole carboxamide riboside affords cardioprotective effects. Plasma proinflammatory cytokines and myokine follistatin were similarly elevated in vehicle-treated young and mature adult mice at 18 h after sepsis. However, despite equivalent troponin I and T levels compared with similarly treated young mice, vehicle-treated mature adult mice exhibited more severe cardiac damage by light and electron microscopy analyses with more marked intercellular edema, inflammatory cell infiltration, and mitochondrial derangement. Echocardiography revealed that vehicle-treated young mice exhibited left ventricular dysfunction after sepsis, whereas mature adult mice exhibited a reduction in stroke volume without apparent changes in load-dependent indexes of cardiac function. At molecular analysis, phosphorylation of the catalytic subunits AMPK-α₁/α₂ was associated with nuclear translocation of peroxisome proliferator-activated receptor-γ coactivator-1α in vehicle-treated young but not mature adult mice. Treatment with 5-amino-4-imidazole carboxamide riboside ameliorated cardiac architecture derangement in mice of both ages. These cardioprotective effects were associated with attenuation of the systemic inflammatory response and amelioration of cardiac dysfunction in young mice only, not in mature adult animals. NEW & NOTEWORTHY Our data suggest that sepsis-induced cardiac dysfunction manifests with age-dependent characteristics, which are associated with a distinct regulation of AMP-activated protein kinase-dependent metabolic pathways. Consistent with this age-related deterioration, pharmacological activation of AMP-activated protein kinase may afford cardioprotective effects allowing a partial recovery of cardiac function in young but not mature age.

Lipopolysaccharide acutely suppresses right-ventricular strain in rats with pulmonary artery hypertension

Worsening right ventricular (RV) dysfunction in the presence of pulmonary artery hypertension (PAH) increases morbidity and mortality in this patient population. Transthoracic echocardiography (TTE) is a non-invasive modality to evaluate RV function over time. Using a monocrotaline-induced PAH rat model, we evaluated the effect of acute inflammation on RV function. In this study, both PAH and control rats were injected with Escherichia coli lipopolysaccharide (LPS) to induce an acute inflammatory state. We evaluated survival curves, TTE parameters, and inflammatory markers to better understand the mechanism and impact of acute inflammation on RV function in the presence of PAH. The survival curve of the PAH rats dropped sharply within 9 h after LPS treatment. Several echocardiographic parameters including left ventricular (LV) stroke volume, RV tricuspid annular plane systolic excursion, RV longitudinal peak systolic strain, and strain rate decreased significantly in PAH rats before LPS injection and 2 h after LPS injection. The expression of phospholamban (PLB) and tumor necrosis factor-α (TNF-α) significantly increased and the expression of SERCA2a significantly decreased in PAH rats after LPS administration. LPS suppressed the RV longitudinal peak systolic strain and strain rate and cardiac function deteriorated in PAH rats. These effects may be associated with the signal pathway activity of SERCA2a/PLB.

Escherichia coli outer membrane vesicles can contribute to sepsis induced cardiac dysfunction

Sepsis induced cardiac dysfunction (SIC) is a severe complication to sepsis which significantly worsens patient outcomes. It is known that bacteria have the capacity to release outer membrane vesicles (OMVs), which are nano-sized bilayered vesicles composed of lipids and proteins, that can induce a fatal inflammatory response. The aim of this study was to determine whether OMVs from a uropathogenic Escherichia coli strain can induce cardiac dysfunction, and to elucidate any mechanisms involved. OMVs induced irregular Ca²⁺ oscillations with a decreased frequency in cardiomyocytes through recordings of intracellular Ca²⁺ dynamics. Mice were intraperitoneally injected with bacteria-free OMVs, which resulted in increased concentration of pro-inflammatory cytokine levels in blood. Cytokines were increased in heart lysates, and OMVs could be detected in the heart after OMVs injection. Troponin T was significantly increased in blood, and echocardiography showed increased heart wall thickness as well as increased heart rate. This study shows that E. coli OMVs induce cardiac injury in vitro and in vivo, in the absence of bacteria, and may be a causative microbial signal in SIC. The role of OMVs in clinical disease warrant further studies, as bacterial OMVs in addition to live bacteria may be good therapeutic targets to control sepsis.

Inhibition of miR-155 Protects Against LPS-induced Cardiac Dysfunction and Apoptosis in Mice

Sepsis-induced myocardial dysfunction represents a major cause of death in intensive care units. Dysregulated microRNAs (miR)-155 has been implicated in multiple cardiovascular diseases and miR-155 can be induced by lipopolysaccharide (LPS). However, the role of miR-155 in LPS-induced cardiac dysfunction is unclear. Septic cardiac dysfunction in mice was induced by intraperitoneal injection of LPS (5 mg/kg) and miR-155 was found to be significantly increased in heart challenged with LPS. Pharmacological inhibition of miR-155 using antagomiR improved cardiac function and suppressed cardiac apoptosis induced by LPS in mice as determined by echocardiography, terminal deoxynucleotidyl transferase nick-end labeling (TUNEL) assay, and Western blot for Bax and Bcl-2, while overexpression of miR-155 using agomiR had inverse effects. Pea15a was identified as a target gene of miR-155, mediating its effects in controlling apoptosis of cardiomyocytes as evidenced by luciferase reporter assays, quantitative real time-polymerase chain reaction, Western blot, and TUNEL staining. Noteworthy, miR-155 was also found to be upregulated in the plasma of patients with septic cardiac dysfunction compared to sepsis patients without cardiac dysfunction, indicating a potential clinical relevance of miR-155. The receiver-operator characteristic curve indicated that plasma miR-155 might be a biomarker for sepsis patients developing cardiac dysfunction. Therefore, inhibition of miR-155 represents a novel therapy for septic myocardial dysfunction.