Differential effects of isoflurane and ketamine/inactin anesthesia on cAMP and cardiac function in FVB/N mice during basal state and beta-adrenergic stimulation

α7 nicotinic receptors play a role in regulation of cardiac hemodynamics

The α7 nicotinic receptors (NR) have been confirmed in the heart but their role in cardiac functions has been contradictory. To address these contradictory findings, we analyzed cardiac functions in α7 NR knockout mice (α7-/-) in vivo and ex vivo in isolated hearts. A standard limb leads electrocardiogram was used, and the pressure curves were recorded in vivo, in Arteria carotis and in the left ventricle, or ex vivo, in the left ventricle of the spontaneously beating isolated hearts perfused following Langedorff's method. Experiments were performed under basic conditions, hypercholinergic conditions, and adrenergic stress. The relative expression levels of α and β NR subunits, muscarinic receptors, β1 adrenergic receptors, and acetylcholine life cycle markers were determined using RT-qPCR. Our results revealed a prolonged QT interval in α7-/- mice. All in vivo hemodynamic parameters were preserved under all studied conditions. The only difference in ex vivo heart rate between genotypes was the loss of bradycardia in prolonged incubation of isoproterenol-pretreated hearts with high doses of acetylcholine. In contrast, left ventricular systolic pressure was lower under basal conditions and showed a significantly higher increase during adrenergic stimulation. No changes in mRNA expression were observed. In conclusion, α7 NR has no major effect on heart rate, except when stressed hearts are exposed to a prolonged hypercholinergic state, suggesting a role in acetylcholine spillover control. In the absence of extracardiac regulatory mechanisms, left ventricular systolic impairment is revealed.

Application of a combination of echocardiographic techniques in an experimental model of epirubicin-induced cardiotoxicity

This study compared the potential ability of multinomial echocardiographic parameters in early detection, prediction and combined diagnosis of antineoplastic-related cardiotoxicity. Male Balb/c mice were repeatedly administered with low doses of epirubicin (6 × 3 mg/kg; n = 20) to induce cardiac injury or with placebo as control (n = 10). Conventional and strain parameters as well as myocardial performance index (MPI) were analyzed at baseline, 1 day after the second, fourth and sixth cycle, and 12 days after completion of chemotherapy (as follow-up) by a high-resolution rodent ultrasound machine. After the experiment, serum cTnI levels were measured, and myocardial injury was evaluated by histological analyses. Thirteen mice developed cardiotoxicity after epirubicin exposure. Global longitudinal (GLS), radial strain (GRS) and longitudinal strain rate (LSR) were markedly decreased (all P ≤ 0.01) and MPI was increased (P ≤ 0.05) at the completion of treatment compared with baseline values. GLS expressed the best correlations with myocardial pathological injury, especially with collagen content (ρ = - 0.68, P < 0.01). Additionally, GLS and MPI were associated with serum cTnI levels. A > 9.5% decrease in GLS from baseline to the fourth cycle of chemotherapy could predict future cardiotoxicity (odds ratio = 0.331, P < 0.05). GLS (cutoff value, - 15.16%) combined with MPI (cutoff value, 0.64) could improve the accuracy of diagnosing cardiotoxicity (sensitivity, 92%; specificity, 87%). GLS was the only predictor of cardiotoxicity. GLS combined with MPI may provide a noninvasive and accurate method for the early detection of cardiotoxicity.

Visualizing Viral Infection In Vivo by Multi-Photon Intravital Microscopy

Viral pathogens have adapted to the host organism to exploit the cellular machinery for virus replication and to modulate the host cells for efficient systemic dissemination and immune evasion. Much of our knowledge of the effects that virus infections have on cells originates from in vitro imaging studies using experimental culture systems consisting of cell lines and primary cells. Recently, intravital microscopy using multi-photon excitation of fluorophores has been applied to observe virus dissemination and pathogenesis in real-time under physiological conditions in living organisms. Critical steps during viral infection and pathogenesis could be studied by direct visualization of fluorescent virus particles, virus-infected cells, and the immune response to viral infection. In this review, I summarize the latest research on in vivo studies of viral infections using multi-photon intravital microscopy (MP-IVM). Initially, the underlying principle of multi-photon microscopy is introduced and experimental challenges during microsurgical animal preparation and fluorescent labeling strategies for intravital imaging are discussed. I will further highlight recent studies that combine MP-IVM with optogenetic tools and transcriptional analysis as a powerful approach to extend the significance of in vivo imaging studies of viral pathogens.

Carbon monoxide modulates cytochrome oxidase activity and oxidative stress in the developing murine brain during isoflurane exposure

Commonly used anesthetics induce widespread neuronal degeneration in the developing mammalian brain via the oxidative-stress-associated mitochondrial apoptosis pathway. Dysregulation of cytochrome oxidase (CcOX), the terminal oxidase of the electron transport chain, can result in reactive oxygen species (ROS) formation. Isoflurane has previously been shown to activate this enzyme. Carbon monoxide (CO), as a modulator of CcOX, is of interest because infants and children are routinely exposed to CO during low-flow anesthesia. We have recently demonstrated that low concentrations of CO limit and prevent isoflurane-induced neurotoxicity in the forebrains of newborn mice in a dose-dependent manner. However, the effect of CO on CcOX in the context of anesthetic-induced oxidative stress is unknown. Seven-day-old male CD-1 mice underwent 1h exposure to 0 (air), 5, or 100ppm CO in air with or without isoflurane. Exposure to isoflurane or CO independently increased CcOX kinetic activity and increased ROS within forebrain mitochondria. However, exposure to CO combined with isoflurane paradoxically limited CcOX activation and oxidative stress. There were no changes seen in steady-state levels of CcOX I protein, indicating post-translational modification of CcOX as an etiology for changes in enzyme activity. CO exposure led to differential effects on CcOX subunit I tyrosine phosphorylation depending on concentration, while combined exposure to isoflurane with CO markedly increased the enzyme phosphorylation state. Phosphorylation of tyrosine 304 of CcOX subunit I has been shown to result in strong enzyme inhibition, and the relative reduction in CcOX kinetics following exposure to CO combined with isoflurane may have been due, in part, to such phosphorylation. Taken together, the data suggest that CO modulates CcOX in the developing brain during isoflurane exposure, thereby limiting oxidative stress. These CO-mediated effects could have implications for the development of low-flow anesthesia in infants and children to prevent anesthesia-induced oxidative stress.

Cardioprotective effects of isoflurane in a rat model of stress-induced cardiomyopathy (takotsubo)

BACKGROUND

Stress-induced cardiomyopathy (SIC) is a common syndrome with substantial morbidity and mortality. SIC is common in intensive care units' patients. No therapeutic intervention for SIC has been evaluated in randomized clinical trial so far. Our aim was to investigate whether isoflurane is cardioprotective in an experimental SIC model.

METHODS

We induced SIC-like cardiac dysfunction in rats with intraperitoneal injection of isoprenaline (50 mg/kg) and performed this study in two parts. First, we pre-treated rats with isoflurane (1.5%, n=12), pentobarbital (50 mg/kg, n=12) and ketamine (80 mg/kg, n=12) and compared to controls (n=12). We used glyburide, an ATP-dependent potassium channel blocker (n=6), to test whether isoflurane-protection is mediated through KATPm. In a second set of experiments, we treated rats with two different doses of isoflurane i.e. 0.75% (n=12) and 1.5% (n=12) before induction of SIC and compared to controls. We assessed left ventricular function and morphology in all rats by transthoracic echocardiography. We also measured peak body temperature, blood gases, acid-base homeostasis, blood pressure and heart rate.

RESULTS

The extent of apical akinesia was lowest and cardiac function was best in the isoflurane treated rats. The protective effects were not attenuated by glibenclamide. Higher dose of isoflurane was more cardioprotective than the lower dose. This was persistent after the adjustment for changes in hemodynamics and blood biochemistry induced by anesthesia.

CONCLUSIONS

Isoflurane prevented SIC-like cardiac dysfunction in rats. This protection was not mediated via KATPm. Our study provides an experimental foundation for future clinical trials in SIC.

A Novel Transgenic Mouse Model of Cardiac Hypertrophy and Atrial Fibrillation

Cardiac hypertrophy is a major risk factor for the development of atrial fibrillation (AF). However, there are few animal models of AF associated with cardiac hypertrophy. In this study, we describe the in vivo electrophysiological characteristics and histopathology of a mouse model of cardiac hypertrophy that develops AF. Myostatin is a well-known negative regulator of skeletal muscle growth that was recently found to additionally regulate cardiac muscle growth. Using cardiac-specific expression of the inhibitory myostatin pro-peptide, we generated transgenic (TG) mice with dominant-negative regulation of MSTN (DN-MSTN). One line (DN-MSTN TG13) displayed ventricular hypertrophy, as well as spontaneous AF on the surface electrocardiogram (ECG), and was further evaluated. DN-MSTN TG13 had normal systolic function, but displayed atrial enlargement on cardiac MRI, as well as atrial fibrosis histologically. Baseline ECG revealed an increased P wave duration and QRS interval compared with wild-type littermate (WT) mice. Seven of 19 DN-MSTN TG13 mice had spontaneous or inducible AF, while none of the WT mice had atrial arrhythmias (p<0.05). Connexin40 (Cx40) was decreased in DN-MSTN TG13 mice, even in the absence of AF or significant atrial fibrosis, raising the possibility that MSTN signaling may play a role in Cx40 down-regulation and the development of AF in this mouse model. In conclusion, DN-MSTN TG13 mice represent a novel model of AF, in which molecular changes including an initial loss of Cx40 are noted prior to fibrosis and the development of atrial arrhythmias.

Arterial Pressure Monitoring in Mice

The use of mice for the evaluation and study of cardiovascular pathophysiology is growing rapidly, primarily due to the relative ease for developing genetically engineered mouse models. Arterial pressure monitoring is central to the evaluation of the phenotypic changes associated with cardiovascular pathology and interventions in these transgenic and knockout models. There are four major techniques for measuring arterial pressure in the mouse: tail cuff system, implanted fluid filled catheters, Millar catheters and implanted telemetry systems. Here we provide protocols for their use and discuss the advantages and limitations for each of these techniques .

Echocardiographic assessment of global left ventricular function in mice

Doppler-echocardiographic assessment of cardiovascular structure and function in murine models has developed into one of the most commonly used non-invasive techniques during the last decades. Recent technical improvements even expanded the possibilities. In this review, we summarize the current options to assess global left ventricular (LV) function in mice using echocardiographic techniques. In detail, standard techniques as structural and functional assessment of the cardiovascular phenotype using one-dimensional M-mode echocardiography, two-dimensional B-mode echocardiography and spectral Doppler signals from mitral inflow respective aortal outflow are presented. Further pros and contras of recently implemented techniques as three-dimensional echocardiography and strain and strain rate measurements are discussed. Deduced measures of LV function as the myocardial performance index according to Tei, estimation of the mean velocity of circumferential fibre shortening, LV wall stress and different algorithms to estimate the LV mass are described in detail. Last but not least, specific features and limitations of murine echocardiography are presented. Future perspectives in respect to new examination techniques like targeted molecular imaging with advanced ultrasound contrast bubbles or improvement of equipment like new generation matrix transducers for murine echocardiography are discussed.

Expression of Slow Skeletal Troponin I in Adult Mouse Heart Helps to Maintain the Left Ventricular Systolic Function During Respiratory Hypercapnia

Compared with the adult, neonatal heart muscle is less sensitive to deactivation by acidic pH. We hypothesized that expression of slow skeletal troponin I (ssTnI), the embryonic isoform, in adult heart would help maintain left ventricular (LV) systolic function during respiratory hypercapnia. We assessed LV function by transthoracic 2D-targeted M-mode and pulsed Doppler echocardiography in transgenic (TG) mice in which cardiac TnI was replaced with ssTnI and in nontransgenic (NTG) littermates. Anesthetized mice were ventilated with either 100% oxygen or 35% CO 2 balanced with oxygen. Arterial blood pH with 35% CO 2 decreased to the same levels in both groups of animals. In the absence of propranolol, the LV fractional shortening was higher in TG compared with NTG mice throughout most of the experimental protocol. LV diastolic function was impaired in TG compared with NTG mice both at 100% oxygen and 35% CO 2 because E-to-A wave ratio of mitral flow was significantly lower, and E-wave deceleration time and LV isovolumic relaxation time were longer in TG compared with NTG mice. When compensatory mechanisms that occur through stimulation of β-adrenergic receptors during hypercapnia were blocked by continuous perfusion with propranolol, we found that NTG mice died within 3 to 4 minutes after switching to 35% CO 2 , whereas TG mice survived. Our experiments demonstrate the first evidence that specific replacement of cardiac TnI with ssTnI has a protective effect on the LV systolic function during hypercapnic acidosis in situ.