Distinct actions of intermittent and sustained β-adrenoceptor stimulation on cardiac remodeling

Isoproterenol induced cardiac hypertrophy: A comparison of three doses and two delivery methods in C57BL/6J mice

Heart Failure (HF) continues to be a complex public health issue with increasing world population prevalence. Although overall mortality has decreased for HF and hypertrophic cardiomyopathy (HCM), a precursor for HF, their prevalence continues to increase annually. Because the etiology of HF and HCM is heterogeneous, it has been difficult to identify novel therapies to combat these diseases. Isoproterenol (ISP), a non-selective β-adrenoreceptor agonist, is commonly used to induce cardiotoxicity and cause acute and chronic HCM and HF in mice. However, the variability in dose and duration of ISP treatment used in studies has made it difficult to determine the optimal combination of ISP dose and delivery method to develop a reliable ISP-induced mouse model for disease. Here we examined cardiac effects induced by ISP via subcutaneous (SQ) and SQ-minipump (SMP) infusions across 3 doses (2, 4, and 10mg/kg/day) over 2 weeks to determine whether SQ and SMP ISP delivery induced comparable disease severity in C57BL/6J mice. To assess disease, we measured body and heart weight, surface electrocardiogram (ECG), and echocardiography recordings. We found all 3 ISP doses comparably increase heart weight, but these increases are more pronounced when ISP was administered via SMP. We also found that the combination of ISP treatment and delivery method induces contrasting heart rate, RR interval, and R and S amplitudes that may place SMP treated mice at higher risk for sustained disease burden. Mice treated via SMP also had increased heart wall thickness and LV Mass, but mice treated via SQ showed greater increase in gene markers for hypertrophy and fibrosis. Overall, these data suggest that at 2 weeks, mice treated with 2, 4, or 10mg/kg/day ISP via SQ and SMP routes cause similar pathological heart phenotypes but highlight the importance of drug delivery method to induce differing disease pathways.

Puerarin attenuates isoproterenol‑induced myocardial hypertrophy via inhibition of the Wnt/β‑catenin signaling pathway

Myocardial hypertrophy (MH) is an independent risk factor for cardiovascular disease, which in turn lead to arrhythmia or heart failure. Therefore, attention must be paid to formulation of therapeutic strategies for MH. Puerarin is a key bioactive ingredient isolated from Pueraria genera of plants that is beneficial for the treatment of MH. However, its molecular mechanism of action has not been fully determined. In the present study, 40 µM puerarin was demonstrated to be a safe dose for human AC16 cells using Cell Counting Kit‑8 assay. The protective effects of puerarin against MH were demonstrated in AC16 cells stimulated with isoproterenol (ISO). These effects were characterized by a significant decrease in surface area of cells (assessed using fluorescence staining) and mRNA and protein expression levels of MH‑associated biomarkers, including atrial and brain natriuretic peptide, assessed using reverse transcription‑quantitative PCR and western blotting, as well as β‑myosin heavy chain mRNA expression levels. Mechanistically, western blotting demonstrated that puerarin inhibited activation of the Wnt signaling pathway. Puerarin also significantly decreased phosphorylation of p65; this was mediated via crosstalk between the Wnt and NF‑κB signaling pathways. An inhibitor (Dickkopf‑1) and activator (IM‑12) of the Wnt signaling pathway were used to demonstrate that puerarin‑mediated effects alleviated ISO‑induced MH via the Wnt signaling pathway. The results of the present study demonstrated that puerarin pre‑treatment may be a potential therapeutic strategy for preventing ISO‑induced MH and managing MH in the future.

Vidarabine, an anti-herpes agent, prevents occlusal-disharmony-induced cardiac dysfunction in mice

We recently reported a positive relationship between occlusal disharmony and cardiovascular disease via activation of β-adrenergic signaling in mice. Furthermore, inhibition of type 5 adenylyl cyclase (AC5), a major cardiac subtype in adults, protects the heart against oxidative stress. Here, we examined the role of AC5 in the development of occlusal-disharmony-induced cardiovascular disease in bite-opening (BO) mice, prepared by cementing a suitable appliance onto the mandibular incisor. We first examined the effects of BO treatment on cardiac function in mice treated or not treated for 2 weeks with vidarabine, which we previously identified as an inhibitor of cardiac AC. Cardiac function was significantly decreased in the BO group compared to the control group, but vidarabine ameliorated the dysfunction. Cardiac fibrosis, myocyte apoptosis and myocyte oxidative DNA damage were significantly increased in the BO group, but vidarabine blocked these changes. The BO-induced cardiac dysfunction was associated with increased phospholamban phosphorylation at threonine-17 and serine-16, as well as increased activation of the Ca2+-calmodulin-dependent protein kinase II/receptor-interacting protein 3 signaling pathway. These data suggest that AC5 inhibition with vidarabine might be a new therapeutic approach for the treatment of cardiovascular disease associated with occlusal disharmony.

Atorvastatin treatment ameliorates cardiac function and remodeling induced by isoproterenol attack through mitigation of ferroptosis

Ferroptosis has been identified as an important role in damaged heart. Meanwhile, statin therapy has been reported to be beneficial for the treatment of heart failure(HF) under different conditions. However, the beneficial effects of statin treatment on regulation of ferroptosis in failing heart is unveiled. The aim of this study is to explore the protective efficacy of atorvastatin against the ferroptosis related signaling pathway in isoproterenol(ISO)-induced HF. We found that ATV and ferrostatin-1(Fer-1,as a positive control) significantly improved ISO-decreased cell viability and cell survival by reducing oxidative stress and Fe²⁺-dependent lipid peroxidation in H9C2 cells. Additionally, ISO triggered marked ferritinophagy accompanied by up-regulating protein levels of LC3BII,NCOA4 and Beclin1 and down-regulating protein levels of P62 and FTH1 in damaged cells, which nevertheless was significantly blocked by administration of ATV and these results were in parallel with the results obtained after 3-methyadenine(3-MA) treatment. Consistently, C57BL/6J mice were used in used in this study and administered 5 mg/kg/day ISO for 2 weeks to simulate cardiac injury. 20 mg/kg/day ATV treatment for 2 weeks simultaneously markedly improved cardiac dysfunction and remodeling induced by ISO attack. ATV showed significantly protective effects through suppressing the activation of ferroptosis related signaling, as evidenced by decreasing the mRNA levels of PTGS2(a marker of ferroptosis), contents of malonaldehyde and protein levels of NOX4 and increasing the contents of glutathione(GSH), the ratio of GSH/GSSG and protein levels of GPX4 and SLC7A11. Moreover, ISO evidently triggered degradation of FTH1 in failing heart. However, ATV significantly prevented these changes in damaged heart. Overall, these results reveal atorvastatin suppresses ferroptosis and exhibits protective effect on failing myocardium of mice after ISO insult though inhibiting ferritinophagy-mediated ferroptosis, which might be a potential therapeutic strategy in the prevention of ISO-associated cardiomyopathy.

Ellagic Acid Prevents Ca2+ Dysregulation and Improves Functional Abnormalities of Ventricular Myocytes via Attenuation of Oxidative Stress in Pathological Cardiac Hypertrophy

The aim of this study was to investigate whether ellagic acid (EA) treatment can prevent changes in contractile function and Ca2+ regulation of cardiomyocytes in pathologic cardiac hypertrophy. Groups were assigned as Con group; an ISO group in which the rats received isoproterenol alone (5 mg/kg/day); and an ISO + EA group in which the rats received isoproterenol and EA (20 mg/kg/day) for 4 weeks. Subsequently, fractional shortening, intracellular Ca2+ signals, and L-type Ca2+ currents of isolated ventricular myocytes were recorded. Protein expression levels were also determined by the Western blotting method. The survival rate was increased, and the upregulated cardiac hypertrophy markers were significantly attenuated with the EA treatment. The fractional shortening and relaxation rate of myocytes was decreased in the ISO group, whereas EA significantly improved these changes. Ventricular myocytes of the ISO + EA rats displayed lower diastolic Ca2+ levels, higher Ca2+ transients, shorter Ca2+ decay, and higher L-type Ca2+ currents than those of ISO rats. Protein expression analyses indicated that the upregulated p-PLB and p-CaMKII expressions were restored by EA treatment, suggesting improved calcium handling in the ISO + EA rat heart. Moreover, ISO rats displayed significantly increased expression of p-22phox and p47phox subunits of NOX2 protein. Expression of the p22phox subunit was reduced with EA administration, while the decrease in p47phox did not reach a significant level. The increased ROS impairs Ca2+ homeostasis and contractile activity of cardiac myocytes, whereas chronic EA administration prevents Ca2+ dysregulation and functional abnormalities associated with pathological cardiac hypertrophy via the diminution of oxidative stress.

Adaptive versus maladaptive cardiac remodelling in response to sustained β-adrenergic stimulation in a new 'ISO on/off model'

On the one hand, sustained β-adrenergic stress is a hallmark of heart failure (HF) and exerts maladaptive cardiac remodelling. On the other hand, acute β-adrenergic stimulation maintains cardiac function under physiological stress. However, it is still incompletely understood to what extent the adaptive component of β-adrenergic signaling contributes to the maintenance of cardiac function during chronic β-adrenergic stress. We developed an experimental catecholamine-based protocol to distinguish adaptive from maladaptive effects. Mice were for 28 days infused with 30 mg/kg body weight/day isoproterenol (ISO) by subcutaneously implanted osmotic minipumps ('ISO on'). In a second and third group, ISO infusion was stopped after 26 days and the mice were observed for additional two or seven days without further ISO infusion ('ISO off short', 'ISO off long'). In this setup, 'ISO on' led to cardiac hypertrophy and slightly improved cardiac contractility. In stark contrast, 'ISO off' mice displayed progressive worsening of left ventricular ejection fraction that dropped down below 40%. While fetal and pathological gene expression (increase in Nppa, decrease in Myh6/Myh7 ratios, increase in Xirp2) was not induced in 'ISO on', it was activated in 'ISO off' mice. After ISO withdrawal, phosphorylation of phospholamban (PLN) at the protein kinase A (PKA) phosphorylation site Ser-16 dropped down to 20% as compared to only 50% at the Ca2+/Calmodulin-dependent kinase II (CaMKII) phosphorylation site Thr-17 in 'ISO off' mice. PKA-dependent cardioprotective production of the N-terminal proteolytic product of histone deacetylase 4 (HDAC4-NT) was reduced in 'ISO off' as compared to 'ISO on'. Taken together, these data indicate that chronic ISO infusion induces besides maladaptive remodelling also adaptive PKA signalling to maintain cardiac function. The use of the 'ISO on/off' model will further enable the separation of the underlying adaptive from maladaptive components of β-adrenergic signalling and may help to better define and test therapeutic targets downstream of β-adrenergic receptors.

Segmental analysis by speckle-tracking echocardiography of the left ventricle response to isoproterenol in male and female mice

We studied by conventional and speckle-tracking echocardiography, the response of the left ventricle (LV) to a three-week continuous infusion of isoproterenol (Iso), a non-specific beta-adrenergic receptor agonist in male and female C57Bl6/J mice. Before and after Iso (30 mg/kg/day), we characterized LV morphology and function as well as global and segmental strain. We observed that Iso reduced LV ejection in both male (−8.7%) and female (−14.7%) mice. Several diastolic function parameters were negatively regulated in males and females such as E/A, E/E′, isovolumetric relaxation time. Global longitudinal (GLS) and circumferential (GCS) strains were reduced by Iso in both sexes, GLS by 31% and GCS by about 20%. For the segmental LV analysis, we measured strain, strain rate, reverse strain rate, peak speckle displacement and peak speckle velocity in the parasternal long axis. We observed that radial strain of the LV posterior segments were more severely modulated by Iso than those of the anterior wall in males. In females, on the other hand, both posterior and anterior wall segments were negatively impacted by Iso. Longitudinal strain showed similar results to the radial strain for both sexes. Strain rate, on the other hand, was only moderately changed by Iso. Reverse strain rate measurements (an index of diastolic function) showed that posterior LV segments were negatively regulated by Iso. We then studied the animals 5 and 17 weeks after Iso treatment. Compared to control mice, LV dilation was still present in males. Ejection fraction was decreased in mice of both sex compared to control animals. Diastolic function parameters, on the other hand, were back to normal. Taken together, our study indicates that segmental strain analysis can identify LV regions that are more negatively affected by a cardiotoxic agent such as Iso. In addition, cessation of Iso was not accompanied with a complete restoration of cardiac function after four months.

Inhibition of ATGL in adipose tissue ameliorates isoproterenol-induced cardiac remodeling by reducing adipose tissue inflammation

Following cardiac injury, increased adrenergic drive plays an important role in compensating for reduced cardiac function. However, chronic excess adrenergic stimulation can be detrimental to cardiac pathophysiology and can also affect other organs including adipose tissue, leading to increased lipolysis. Interestingly, inhibition of adipose triglyceride lipase (ATGL), a rate-limiting enzyme in lipolysis, in adipocytes ameliorates cardiac dysfunction in a heart failure model. Thus, we investigated whether inhibition of adipocyte ATGL can mitigate the adverse cardiac effects of chronic adrenergic stimulation and explored the underlying mechanisms. To do this, isoproterenol (ISO) was continuously administered to C57Bl/6N mice for 2 wk with or without an ATGL inhibitor (Atglistatin). We found that Atglistatin alleviated ISO-induced cardiac remodeling and reduced ISO-induced upregulation of galectin-3, a marker of activated macrophages and a potent inducer of fibrosis, in white adipose tissue (WAT), heart, and the circulation. To test whether the beneficial effects of Atglistatin occur via inhibition of adipocyte ATGL, adipocyte-specific ATGL knockout (atATGL-KO) mice were utilized for similar experiments. Subsequently, the same cardioprotective effects of atATGL-KO following ISO administration were observed. Furthermore, Atglistatin and atATGL-KO abolished ISO-induced galectin-3 secretion from excised WAT. We further demonstrated that activation of cardiac fibroblasts by the conditioned media of ISO-stimulated WAT is galectin-3-dependent. In conclusion, the inhibition of adipocyte ATGL ameliorated ISO-induced cardiac remodeling possibly by reducing galectin-3 secretion from adipose tissue. Thus, inhibition of adipocyte ATGL might be a potential target to prevent some of the adverse effects of chronic excess adrenergic drive.NEW & NOTEWORTHY The reduction of lipolysis by adipocyte ATGL inhibition ameliorates cardiac remodeling induced by chronic β-adrenergic stimulation likely via reducing galectin-3 secretion from adipose tissue. Our findings highlight that suppressing lipolysis in adipocytes may be a potential therapeutic target for patients with heart failure whose sympathetic nervous system is activated. Furthermore, galectin-3 might be involved in the mechanisms by which excessive lipolysis in adipose tissues influences remote cardiac pathologies and thus warrants further investigation.

A novel mechanism of protection against isoproterenol-induced cardiac inflammation via regulation of the SIRT1/NRF2 signaling pathway with a natural SIRT1 agonist

Stress-induced cardiomyopathy (SIC) is associated with high mortality rates, potentially due to a lack of available therapies. To facilitate the identification of therapeutic targets for SIC, we explored the detailed mechanisms of disease onset and progression using a mouse model. Over-activation of the β-adrenergic receptor (β-AR) upon stress leads to inflammasome activation, cytokine cascades, macrophage infiltration, and pathological cardiac remodeling in mice, mimicking SIC. However, the detailed mechanisms by which acute β-AR stimulation induces cardiac inflammation remain elusive. We found that resveratrol (RSV) could attenuate isoproterenol-induced cardiac inflammation in mice, suggesting that RSV might be a promising therapeutic option in SIC. Mechanistically, we revealed that the SIRT1/NRF2 signaling pathway is the bona fide target of RSV and plays a significant role in the RSV-induced protective effect in cardiac inflammation.

Effect of Triptolide on Temporal Expression of Cell Cycle Regulators During Cardiac Hypertrophy

Adult mammalian cardiomyocytes may reenter the cell cycle and cause cardiac hypertrophy. Triptolide (TP) can regulate the expressions of various cell cycle regulators in cancer cells. However, its effects on cell cycle regulators during myocardial hypertrophy and mechanism are unclear. This study was designed to explore the profile of cell cycle of cardiomyocytes and the temporal expression of their regulators during cardiac hypertrophy, as well as the effects of TP. The hypertrophy models employed were neonatal rat ventricular myocytes (NRVMs) stimulated with angiotensin II (Ang II) for scheduled times (from 5 min to 48 h) in vitro and mice treated with isoprenaline (Iso) for from 1 to 21 days, respectively. TP was used in vitro at 1 μg/L and in vivo at 10 μg/kg. NRVMs were analyzed using flow cytometry to detect the cell cycle, and the expression levels of mRNA and protein of various cell cycle regulators were determined using real-time PCR and Western blot. It was found NRVM numbers in phases S and G₂ increased, while that in the G₁ phase decreased significantly after Ang II stimulation. The mRNA expression levels of p21 and p27 increased soon after stimulation, and thereafter, mRNA expression levels of all cell cycle factors showed a decreasing trend and reached their lowest levels in 1–3 h, except for cyclin-dependent kinase 1 (CDK1) and CDK4 mRNA. The mRNA expression levels of CDK1, p21, and p27 increased markedly after stimulation with Ang II for 24–48 h. In myocardium tissue, CDK and cyclin expression levels peaked in 3–7 days, followed by a decreasing trend, while those of p21 and p27 mRNA remained at a high level on day 21. Expression levels of all protein were consistent with the results of mRNA in NRVMs or mice. The influence of Ang II or Iso on protein expression was more obvious than that on mRNA. TP treatment effectively prevented the imbalance in the expression of cell cycle regulators in the hypertrophy model group. In Conclusion, an imbalance in the expression of cell cycle regulators occurs during cardiac hypertrophy, and triptolide corrects these abnormal expression levels and attenuates cardiac hypertrophy.

TBX5 R264K acts as a modifier to develop dilated cardiomyopathy in mice independently of T-box pathway

Background

TBX5 is a transcription factor that has an important role in development of heart. TBX5 variants in the region encoding the T-box domain have been shown to cause cardiac defects, such as atrial septal defect or ventricular septal defect, while TBX5 variants have also been identified in a few cardiomyopathy patients and considered causative. We identified a TBX5 variant (c.791G>A, p.Arg264Lys), that is over-represented in cardiomyopathy patients. This variant is located outside of the T-box domain, and its pathogenicity has not been confirmed by functional analyses.

Objective

To investigate whether the TBX5 R264K is deleterious and could contribute to the pathogenesis of cardiomyopathy.

Methods and results

We developed mice expressing Tbx5 R264K. Mice homozygous for this variant displayed compensated dilated cardiomyopathy; mild decreased fractional shortening, dilatation of the left ventricle, left ventricular wall thinning and increased heart weight without major heart structural disorders. There was no difference in activation of the ANF promotor, a transcriptional target of Tbx5, compared to wild-type. However, analysis of RNA isolated from left ventricular samples showed significant increases in the expression of Acta1 in left ventricle with concomitant increases in the protein level of ACTA1.

Conclusions

Mice homozygous for Tbx5 R264K showed compensated dilated cardiomyopathy. Thus, TBX5 R264K may have a significant pathogenic role in some cardiomyopathy patients independently of T-box domain pathway.

Protective role of berberine in isoprenaline-induced cardiac fibrosis in rats

BACKGROUND

Cardiac fibrosis is a crucial aspect of cardiac remodeling that can severely affect cardiac function. Cardiac fibroblasts surely influence this process. Besides, macrophage plays an essential role in cardiac remodeling after heart injury. However, whether macrophage influence fibroblasts remain a question worth exploring. This study aimed to define the role of berberine (BBR) on isoprenaline (ISO)-induced cardiac fibrosis in an in vivo rat model and try to figure out the mechanism in vitro study.

METHODS

The Sprague-Dawley rats were divided into five groups: control group, ISO-treated group, and ISO + BBR (10 mg/kg/d, 30 mg/kg/d, and 60 mg/kg/d orally)-pretreatment groups. Fibrosis was induced by ISO administration (5 mg/kg/d subcutaneously) for 10 days. One day after the last injection, all of the rats were sacrificed. Using picrosirius red (PSR) straining, immunohistochemistry, immunofluorescence, flow cytometry, western blot, RT-qPCR and cell co-culture, we explored the influence of pretreatment by BBR on ISO-induced cardiac fibrosis.

RESULTS

Our results showed that BBR pretreatment greatly limited ISO-induced cardiac fibrosis and dysfunction. Moreover, BBR administration reduced macrophage infiltration into the myocardium of ISO-treated rats and inhibited transforming growth factor (TGF)-β1/smads signaling pathways in comparison to that seen in the ISO group. Besides, in vitro study showed that BBR-pretreatment reduced ISO-induced TGF-β1 mRNA expression in macrophages and ISO stimulation of macrophages significantly increased the expression of fibrotic markers in fibroblasts, but BBR-pretreatment blocked this increase.

CONCLUSION

Our results showed that BBR may have a protective role to cardiac injury via reducing of macrophage infiltration and forbidding fibroblasts transdifferent into an 'activated' secretory phenotype, myofibroblasts.

Preliminary evidence that hydrostatic edema may contribute to the formation of diffuse alveolar damage in a Holstein calf model

Background: Two notable findings of clinically healthy feedlot cattle suggest they may have pulmonary hydrostatic edema during the finishing phase of production: increased pulmonary arterial wedge pressures and pulmonary venous hypertrophy. The goal of this study was to determine if increased pulmonary arterial wedge pressure (PAWP) in a Holstein calf could lead to diffuse alveolar damage consistent with the early, exudative phase of acute interstitial pneumonia of feedlot cattle.

Methods: Six male Holstein dairy calves were given daily subcutaneous injections of the nonspecific ß-adrenergic agonist isoprenaline (10 mg/kg/d), to induce left ventricular diastolic dysfunction, or sterile water for 14 days. On Day 14, pulmonary arterial pressures and wedge pressures were measured, echocardiography performed, and the ratio of mitral valve flow velocity (E) to septal lengthening velocity (e’) calculated. Calves were euthanized on Day 15 and lung lesions semi-quantitatively scored.

Results: Mean PAWP was 12 ± 1 mm Hg in calves that received isoprenaline and 7 ± 1 mm Hg in controls ( P = 0.01). Calves that received isoprenaline tended to have greater relative wall thickness than control calves ( P = 0.15) and greater E/e’ ratios ( P = 0.16), suggestive of concentric hypertrophy and diastolic dysfunction, respectively. Calves that received isoprenaline also tended to have a left ventricle and interventricular septum that was 29 ± 10 g heavier than control calves ( P = 0.10) when controlling for body mass. Hyaline membranes, the hallmark feature of diffuse alveolar damage, were evident in lung sections from all calves that received isoprenaline but none of the controls.

Conclusions: Consistent with prior pathological and physiological studies of feedlot cattle, this study provides preliminary evidence that cattle presenting with clinical signs and pathology consistent with early stage acute interstitial pneumonia could be attributable to hydrostatic edema associated with left ventricular failure.

Analyzing gene expression profiles with preliminary validations in cardiac hypertrophy induced by pressure overload

The aim of this study was to identify the key genes involved in the cardiac hypertrophy (CH) induced by pressure overload. mRNA microarray data sets GSE5500 and GSE18801 were downloaded from the Gene Expression Omnibus database, and differentially expressed genes (DEGs) were screened using the Limma package; then, functional and pathway enrichment analysis were performed for common DEGs using the Database for Annotation, Visualization and Integrated Discovery database. Furthermore, the top DEGs were further validated using quantitative PCR in the hypertrophic heart tissue induced by isoprenaline. A total of 113 common DEGs with absolute fold change > 0.5, including 60 significantly upregulated DEGs and 53 downregulated DEGs, were obtained. Gene ontology term enrichment analysis suggested that common upregulated DEG were mainly enriched in neutrophil chemotaxis, extracellular fibril organization, and cell proliferation; and the common downregulated genes were significantly enriched in ion transport, endoplasmic reticulum, and dendritic spine. Kyoto Encyclopedia of Genes and Genomes pathway analysis found that the common DEGs were mainly enriched in extracellular matrix receptor interaction, phagosome, and focal adhesion. Additionally, the expression of Mfap4, Ltbp2, Aspn, Serpina3n, and Cnksr1 were upregulated in the model of CH, while the expression of Anp32a was downregulated. The current study identified the key deregulated genes and pathways involved in the CH, which could shed new light to understand the mechanism of CH.

Age-, Gender-, and in Vivo Different Doses of Isoproterenol Modify in Vitro Aortic Vasoreactivity and Circulating VCAM-1

Different human-like cardiomyopathies associated to β-adrenergic stimulation are experimentally modeled in animals through variations in dose, route, and duration of administration of different cardiotoxic drugs. However, associated changes in the vasculature and their relation to systemic inflammation, and the influence of cardiovascular diseases risk factors (gender and age) upon them are seldom analyzed. Here we studied the effect of age and gender on the vasoreactivity of aortas from mice subjected to in vivo repeated β-adrenergic stimulation with different doses of isoproterenol (ISO) in association with circulating inflammatory cytokines. Young (2 months) and old (18 months) male and female mice received 0 (control), 5, 40, 80 or 160 μg/g/d of ISO (7 days, s.c.). IL-1α, IL-4 and vascular cell adhesion molecule-1 (VCAM-1) were quantified in plasma. In vitro, norepinephrine-induced vasoconstriction and acetylcholine-induced relaxation were measured in aortas. No differences in contraction, relaxation, IL-1α, and IL-4 were found between control young males and females. Age decreased contraction in males and relaxation was lower in females and abolished in males. VCAM-1 was higher in young males than in females and increased in old mice. Vasoconstriction in ISO-treated mice results as a bell-shaped curve on contraction in young and old males, with lower values in the latter. In females, ISO-160 increased contraction in young females but decreased it in old females. Vasorelaxation was reduced in ISO-treated young males and females. ISO-80 and 160 reduced vasorelaxation in old females, and intermediate doses relaxed aortas from old males. VCAM-1 was higher in young and old males with ISO-80 and 160; while VCAM-1 was higher only with ISO-160 in old females. Our results demonstrate that repeated β-adrenergic stimulation modifies vascular reactivity depending on gender, age, and dose. Females were less sensitive to alterations in vasoreactivity, and young females required a higher amount of the adrenergic stimuli than old females to show vascular alterations. Changes were independent of IL-1α and IL-4. VCAM-1 only changed in old females stimulated with ISO 160. Our results highlight the relevance of considering and comparing in the same study females and aged organisms to improve the accuracy of applications to clinical studies.

Triptolide Upregulates Myocardial Forkhead Helix Transcription Factor p3 Expression and Attenuates Cardiac Hypertrophy

The forkhead/winged helix transcription factor (Fox) p3 can regulate the expression of various genes, and it has been reported that the transfer of Foxp3-positive T cells could ameliorate cardiac hypertrophy and fibrosis. Triptolide (TP) can elevate the expression of Foxp3, but its effects on cardiac hypertrophy remain unclear. In the present study, neonatal rat ventricular myocytes (NRVM) were isolated and stimulated with angiotensin II (1 μmol/L) to induce hypertrophic response. The expression of Foxp3 in NRVM was observed by using immunofluorescence assay. Fifty mice were randomly divided into five groups and received vehicle (control), isoproterenol (Iso, 5 mg/kg, s.c.), one of three doses of TP (10, 30, or 90 μg/kg, i.p.) for 14 days, respectively. The pathological morphology changes were observed after Hematoxylin and eosin, lectin and Masson's trichrome staining. The levels of serum brain natriuretic peptide (BNP) and troponin I were determined by enzyme-linked immunosorbent assay and chemiluminescence, respectively. The mRNA and protein expressions of α- myosin heavy chain (MHC), β-MHC and Foxp3 were determined using real-time PCR and immunohistochemistry, respectively. It was shown that TP (1, 3, 10 μg/L) treatment significantly decreased cell size, mRNA and protein expression of β-MHC, and upregulated Foxp3 expression in NRVM. TP also decreased heart weight index, left ventricular weight index and, improved myocardial injury and fibrosis; and decreased the cross-scetional area of the myocardium, serum cardiac troponin and BNP. Additionally, TP markedly reduced the mRNA and protein expression of myocardial β-MHC and elevated the mRNA and protein expression of α-MHC and Foxp3 in a dose-dependent manner. In conclusion, TP can effectively ameliorate myocardial damage and inhibit cardiac hypertrophy, which is at least partly related to the elevation of Foxp3 expression in cardiomyocytes.

Impaired heart rate regulation and depression of cardiac chronotropic and dromotropic function in polymicrobial sepsis

The scope of cardiac pathophysiology in sepsis has not been fully defined. Accordingly, we evaluated the effects of sepsis on heart rate (HR), HR variability, and conduction parameters in a murine model of sepsis. Electrocardiograms were recorded noninvasively from conscious mice before and after cecal ligation and puncture (CLP) or sham surgery. Responses of isolated atria to tyramine and isoproterenol were quantified to assess the functional state of sympathetic nerves and postjunctional sensitivity to adrenergic stimulation. Cecal ligation and puncture mice had lower HR compared with sham at 16 to 18 h postsurgery (sham, 741 ± 7 beats/min; CLP, 557 ± 31 beats/min; n = 6/group; P < 0.001), and there was significant prolongation of the PR, QRS, and QTc intervals. Slowing of HR and conduction developed within 4 to 6 h after CLP and were preceded by a decrease in HR variability. Treatment of CLP mice with isoproterenol (5 mg/kg, intraperitoneally) at 25 h after surgery failed to increase HR or decrease conduction intervals. The lack of in vivo response to isoproterenol cannot be attributed to hypothermia because robust chronotropic and inotropic responses to isoproterenol were evoked from isolated atria at 25 °C and 30 °C. These findings demonstrate that impaired regulation of HR (i.e., reduced HR variability) develops before the onset of overt cardiac rate and conduction changes in septic mice. Subsequent time-dependent decreases in HR and cardiac conduction can be attributed to hypothermia and would contribute to decreased cardiac output and organ perfusion. Because isolated atria from septic mice showed normal responsiveness to adrenergic stimulation, we conclude that impaired effectiveness of isoproterenol in vivo can be attributed to reversible effects of systemic factors on adrenergic receptors and/or postreceptor signaling.

A systematic review concerning the relation between the sympathetic nervous system and heart failure with preserved left ventricular ejection fraction

BACKGROUND

Heart failure with preserved left ventricular ejection fraction (HFPEF) affects about half of all patients diagnosed with heart failure. The pathophysiological aspect of this complex disease state has been extensively explored, yet it is still not fully understood. Since the sympathetic nervous system is related to the development of systolic HF, we hypothesized that an increased sympathetic nerve activation (SNA) is also related to the development of HFPEF. This review summarizes the available literature regarding the relation between HFPEF and SNA.

METHODS AND RESULTS

Electronic databases and reference lists through April 2014 were searched resulting in 7722 unique articles. Three authors independently evaluated citation titles and abstracts, resulting in 77 articles reporting about the role of the sympathetic nervous system and HFPEF. Of these 77 articles, 15 were included for critical appraisal: 6 animal and 9 human studies. Based on the critical appraisal, we selected 9 articles (3 animal, 6 human) for further analysis. In all the animal studies, isoproterenol was administered to mimic an increased sympathetic activity. In human studies, different modalities for assessment of sympathetic activity were used. The studies selected for further evaluation reported a clear relation between HFPEF and SNA.

CONCLUSION

Current literature confirms a relation between increased SNA and HFPEF. However, current literature is not able to distinguish whether enhanced SNA results in HFPEF, or HFPEF results in enhanced SNA. The most likely setting is a vicious circle in which HFPEF and SNA sustain each other.

Murine models of diastolic dysfunction and heart failure with preserved ejection fraction

Left ventricular diastolic dysfunction leads to heart failure with preserved ejection fraction, an increasingly prevalent condition largely driven by modern day lifestyle risk factors. As heart failure with preserved ejection fraction accounts for almost one-half of all patients with heart failure, appropriate nonhuman animal models are required to improve our understanding of the pathophysiology of this syndrome and to provide a platform for preclinical investigation of potential therapies. Hypertension, obesity, and diabetes are major risk factors for diastolic dysfunction and heart failure with preserved ejection fraction. This review focuses on murine models reflecting this disease continuum driven by the aforementioned common risk factors. We describe various models of diastolic dysfunction and highlight models of heart failure with preserved ejection fraction reported in the literature. Strengths and weaknesses of the different models are discussed to provide an aid to translational scientists when selecting an appropriate model. We also bring attention to the fact that heart failure with preserved ejection fraction is difficult to diagnose in animal models and that, therefore, there is a paucity of well described animal models of this increasingly important condition.

Echocardiographic assessment of β-adrenoceptor stimulation-induced heart failure with reduced heart rate in mice

1. Chronic injection with the β-adrenoceptor (β-AR) agonist isoproterenol (ISO) has been commonly used as an animal model of β-AR-induced cardiac remodelling and heart failure. This ISO-treated model usually exhibits significantly decreased conscious heart rate (HR). However, the HR in treatment groups is usually adjusted to the same levels by anaesthesia to assess cardiac geometry and function. In the present study, we report a method of echocardiographic assessment that represents the true cardiac geometry and function under conditions of ISO withdrawal. 2. Briefly, C57BL/6 mice were treated with 5 mg/kg per day ISO for 12 weeks. Cardiac geometry and function were assessed by high-resolution echocardiography in vehicle (saline) - and ISO-treated mice that were either conscious or anaesthetized using different concentrations of isoflurane. 3. The cardiac β-AR response was decreased in ISO-treated mice, as evidenced by markedly decreased conscious HR. Vehicle- and ISO-treated mice did not differ in terms of cardiac geometry or function when HR was adjusted to the same level (400 b.p.m.) in both treatment groups, but cardiac geometry and function did differ when a low (1%) rather than high (1.5% or 2%) isoflurane concentration was used to adjust HR. Furthermore, 3 day ISO withdrawal eliminated the difference in conscious HR between the two groups. In addition, the groups differed in cardiac geometry and function regardless of the isoflurane concentration used. 4. In conclusion, using isoflurane to decrease the HR of treated groups to the same level may mask left ventricular dysfunction in ISO-treated mice. Withdrawal of ISO eliminated the difference in basal HR between the ISO-treated and control groups on echocardiography, allowing a more accurate assessment of cardiac pathological and functional changes.