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Hyperarousal symptoms in generalized anxiety disorder (GAD) are often incongruent with the observed physiological state, suggesting that abnormal processing of interoceptive signals is a characteristic feature of the disorder. To examine the neural mechanisms underlying interoceptive dysfunction in GAD, we evaluated whether adrenergic modulation of cardiovascular signaling differentially affects the heartbeat-evoked potential (HEP), an electrophysiological marker of cardiac interoception, during concurrent electroencephalogram and functional magnetic resonance imaging (EEG-fMRI) scanning. Intravenous infusions of the peripheral adrenergic agonist isoproterenol (0.5 and 2.0 micrograms, μg) were administered in a randomized, double-blinded and placebo-controlled fashion to dynamically perturb the cardiovascular system while recording the associated EEG-fMRI responses. During the 0.5 μg isoproterenol infusion, the GAD group (n = 24) exhibited significantly larger changes in HEP amplitude in an opposite direction than the healthy comparison (HC) group (n = 24). In addition, the GAD group showed significantly larger absolute HEP amplitudes than the HC group during saline infusions, when cardiovascular tone did not increase. No significant group differences in HEP amplitude were identified during the 2.0 μg isoproterenol infusion. Using analyzable blood oxygenation level-dependent fMRI data from participants with concurrent EEG-fMRI data (21 GAD and 21 HC), we found that the aforementioned HEP effects were uncorrelated with fMRI signals in the insula, ventromedial prefrontal cortex, dorsal anterior cingulate cortex, amygdala, and somatosensory cortex, brain regions implicated in cardiac signal processing in prior fMRI studies. These findings provide additional evidence of dysfunctional cardiac interoception in GAD and identify neural processes at the electrophysiological level that may be independent from blood oxygen level-dependent responses during peripheral adrenergic stimulation.

Palpitations and dyspnea are fundamental to the human experience of panic anxiety, but it remains unclear how the brain dynamically represents changes in these interoceptive sensations. We used isoproterenol, a rapidly acting peripheral beta-adrenergic agonist similar to adrenaline, to induce sensations of palpitation and dyspnea in healthy individuals (n=23) during arterial spin labeling functional magnetic resonance imaging (fMRI). We hypothesized that the right mid-insular cortex, a central recipient of viscerosensory input, would preferentially respond during the peak period of cardiorespiratory stimulation. Bolus infusions of saline and isoproterenol (1 or 2 μg) were administered in a blinded manner while participants continuously rated the intensity of their cardiorespiratory sensation using a dial. Isoproterenol elicited dose-dependent increases in cardiorespiratory sensation, with all participants reporting palpitations and dyspnea at the 2 μg dose. Consistent with our hypothesis, the right mid-insula was maximally responsive during the peak period of sympathetic arousal, heart rate increase, and cardiorespiratory sensation. Furthermore, a shift in insula activity occurred during the recovery period, after the heart rate had largely returned to baseline levels, with an expansion of activation into anterior and posterior sectors of the right insula, as well as bilateral regions of the mid-insula. These results confirm the right mid-insula is a key node in the interoceptive network, and inform computational models proposing specific processing roles for insula subregions during homeostatic inference. The combination of isoproterenol and fMRI offers a powerful approach for evaluating insula function, and could be a useful probe for examining interoceptive dysfunction in psychiatric disorders.

Cardiac tissues generated from human induced pluripotent stem cells (iPSCs) can serve as platforms for patient-specific studies of physiology and disease 1 – 6 . However, the predictive power of these models is presently limited by the immature state of the cells 1 , 2 , 5 , 6 . Here we show that this fundamental limitation can be overcome if cardiac tissues are formed from early-stage iPSC-derived cardiomyocytes soon after the initiation of spontaneous contractions and are subjected to physical conditioning with increasing intensity over time. After only four weeks of culture, for all iPSC lines studied, such tissues displayed adult-like gene expression profiles, remarkably organized ultrastructure, physiological sarcomere length (2.2 µm) and density of mitochondria (30%), the presence of transverse tubules, oxidative metabolism, a positive force–frequency relationship and functional calcium handling. Electromechanical properties developed more slowly and did not achieve the stage of maturity seen in adult human myocardium. Tissue maturity was necessary for achieving physiological responses to isoproterenol and recapitulating pathological hypertrophy, supporting the utility of this tissue model for studies of cardiac development and disease. A tissue culture system that provides an increasing intensity of electromechanical stimulation over time enables an in vitro model of cardiac tissue derived from human induced pluripotent stem cells to develop many of the characteristics of adult cardiac tissue.

The study was conducted to evaluate the cardio-protective activity of combination (COMB) of syringic acid (SA) and resveratrol (RV) against isoproterenol (ISO) induced cardio-toxicity in rats. Rats were pre-treated orally with SA (50 mg/kg), RV (50 mg/kg) and combination of SA (25 mg/kg) and RV (25 mg/kg) along with positive control gallic acid (50 mg/kg) for 30 days. The effects of ISO on cardiac markers, lipid profile and lipid peroxidation marker, anti-oxidant enzymes and m-RNA expression of nuclear factor-kappa B (NF-kB) and tumor necrosis factor-α (TNF-α) were observed along with histopathological observations of simple and transmission electron microscopes (TEM). Serum creatine kinase-MB (CK-MB), lactate dehydrogenase (LDH) and alkaline phosphatase were significantly increased while cardiac tissue CK-MB, LDH, superoxide dismutase and catalase were significantly decreased in ISO administered rats, which also exhibited a significant increase in total cholesterol, triglycerides, low density lipoprotein cholesterol, very low density lipoprotein cholesterol and thiobarbutyric acid reactive substances and significant decrease in high density lipoprotein cholesterol in serum and heart. The m-RNA levels of inflammatory markers NF-kB and TNF-α were significantly increased in ISO treated rats. COMB Pre-treatment significantly reversed the ISO actions. Histopathological studies of simple and TEM were also co-related with the above biochemical parameters. Docking studies with NF-kB were also performed. Evidence has shown for the first time in this approach that COMB pre-treatment ameliorated ISO induced cardio-toxicity in rats and revealed cardio-protection.

Pathological cardiac hypertrophy is ultimately accompanied by cardiomyocyte apoptosis. Apoptosis mainly related to calpain-1-mediated apoptotic pathways. Studies had proved that taurine can maintain heart health through antioxidation and antiapoptotic functions, but the effect of taurine on cardiac hypertrophy is still unclear. This study aimed to determine whether taurine could inhibit calpain-1-mediated mitochondria-dependent apoptotic pathways in isoproterenol (ISO)-induced hypertrophic cardiomyocytes. We found that taurine could inhibit the increase in cell surface area and reduce the protein expression levels of the hypertrophic markers atrial natriuretic peptide, brain natriuretic polypeptide, and β-myosin heavy chain. Taurine also reduced ROS, intracellular Ca2+ overload and mitochondrial membrane potential. Moreover, taurine inhibited cardiomyocyte apoptosis by decreasing the protein expression of calpain-1, Bax, t-Bid, cytosolic cytochrome c, Apaf-1, cleaved caspase-9 and cleaved caspase-3 and by enhancing calpastatin and Bcl-2 protein expression. Calpain-1 small interfering RNA transfection results showed similar antiapoptotic effects as the taurine prevention group. However, compared with the two treatments, taurine inhibited the expression of cleaved caspase-9 more significantly. Therefore, we believe that taurine prevents ISO-induced H9c2 cardiomyocyte hypertrophy by inhibiting oxidative stress, intracellular Ca2+ overload, the calpain-1-mediated mitochondria-dependent apoptotic pathway and cleaved caspase-9 levels.Graphic abstract

Heart failure (HF) modeling requires standardized protocols to ensure translational relevance. Despite the widespread use of isoproterenol (ISO)—a β-adrenergic agonist—in HF modeling, methodological inconsistencies in dosing and administration routes limit reproducibility. This study evaluated the effects of subcutaneous (SC) and intraperitoneal (IP) administration of ISO at two literature-established doses (5 and 60 mg/kg/day for 14 days) on cardiac remodeling in C57BL/6J mice, aiming to identify the optimal protocol for HF modeling. Using a factorial design, male C57BL/6J mice aged 6–8 weeks were divided into six cohorts: (1) SC saline control, (2) IP saline control, (3) SC 5 mg/kg ISO, (4) IP 5 mg/kg ISO, (5) SC 60 mg/kg ISO, and (6) IP 60 mg/kg ISO, with daily administration for 14 days. High-dose ISO (60 mg/kg/day) induced a 25% mortality rate in both SC and IP cohorts, yet IP administration exhibited marked inter-individual variability, undermining model reliability. Echocardiography revealed SC 5 mg/kg group induced stable systolic dysfunction accompanied by left ventricular dilation, while maintaining 100% survival. This cohort also displayed significantly elevated hypertrophy indices. Histopathological quantification suggested that SC 60 mg/kg induced extensive fibrosis. All ISO-treated groups showed upregulated myocardial hypertrophy markers and approximately 2-fold elevation in serum NT-proBNP levels. In summary, SC 5 mg/kg/day regimen not only ensures reliable phenotype induction but also reduces animal attrition, offering a robust platform for investigating CHF mechanisms and accelerating therapeutic development.

β-Adrenoceptors (β-ARs) regulate cardiac function during sympathetic nerve stimulation. β-ARs are present in both the cardiac T-tubule (TTM) and outer surface membrane (OSM), but how their location impacts their function is unknown. Here, we developed a technology based on size exclusion to explore the function of β-ARs located in the OSM. We synthesized a PEG-Iso molecule by covalently linking isoprenaline (Iso) to a 5000 Da PolyEthylene-Glycol (PEG) chain to increase the size of the β-AR agonist and prevent it from accessing the T-tubule network. The affinity of PEG-Iso and Iso on β 1 - and β 2 -ARs was measured using radioligand binding. Molecular dynamics simulation was used to assess PEG-Iso conformation and visualize the accessibility of the Iso moiety to water. Using confocal microscopy, we show that PEGylation constrains molecules outside the T-tubule network of adult rat ventricular myocytes (ARVMs) due to the presence of the extracellular glycocalyx. β-AR activation in OSM with PEG-Iso produced a lower stimulation of [cAMP] i than Iso but a larger stimulation of cytosolic PKA at equivalent levels of [cAMP] I and similar effects on excitation–contraction coupling parameters. However, PEG-Iso produced a much lower stimulation of nuclear cAMP and PKA than Iso. Thus, OSM β-ARs in ARVMs control mainly cytosolic cAMP/PKA pathway and contractility, while TTM β-ARs control mainly nuclear cAMP, PKA, and consequent nuclear protein phosphorylation. Size exclusion strategy using ligand PEGylation provides a unique approach to evaluate the respective contribution of T-tubule vs. OSM proteins in cardiac cells.

Uncoupling protein 1 (UCP1) was found exclusively in the inner membranes of the mitochondria of brown adipose tissue (BAT). We found that UCP1 was also expressed in heart tissue and significantly upregulated in isoproterenol (ISO)-induced acute myocardial ischemia (AMI) rat model. The present study is to determine the underlying mechanism involved in the UCP1 upregulation in ISO-induced AMI rat model. The Ucp1−/− rats were generated by CRISPR-Cas9 system and presented decreased BAT volume. 2-months old Sprague Dawley (SD) wild-type (WT) and Ucp1−/− rats were treated with ISO intraperitoneally 30 mg/kg once a day for 3 consecutive days to establish AMI model. In saline group, the echocardiographic parameters, serum markers of myocardial injury cardiac troponin I (cTnI), creatine kinase isoenzyme MB (CK-MB), oxidant malondialdehyde (MDA), antioxidant superoxide dismutase (SOD) or fibrosis were comparable between WT and Ucp1−/− rats. ISO treatment induced worse left ventricle (LV) hypertrophy, myocardial fibrosis, increased higher cTnI, CK-MB and MDA and decreased lower SOD level in Ucp1−/− rats compared with that of WT rats. Ucp1−/− rats also presented lower myocardial phosphocreatine (PCr)/ATP-ratio, which demonstrated worse cardiac energy regulation defect. ISO treatment induced the phosphorylation of AMP-activated protein kinase (AMPK) activation, subsequently the phosphorylation of mammalian target of rapamycin (mTOR) inhibition and peroxisome proliferators-activated receptor α (PPARα) activation in WT rats, whereas activation of AMPK/mTOR/PPARα pathways significantly inhibited in Ucp1−/− rats. To sum up, UCP1 knockout aggravated ISO-induced AMI by inhibiting AMPK/mTOR/PPARα pathways in rats. Increasing UCP1 expression in heart tissue may be a cytoprotective therapeutic strategy for AMI.

Here, by developing a high-affinity camelid antibody fragment that stabilizes the active state of the β 2 -adrenoceptor, the X-ray crystal structures of the receptor in complex with three agonists, including adrenaline, were determined. Structure of the activated β 2 -adrenoceptor This study reports three structures of fully active human β 2 adrenergic receptor (β 2 AR) in complex with diverse agonists: BI167107, hydroxybenzyl isoproterenol, and the endogenous agonist adrenaline. β 2 AR is a G-protein-coupled receptor (GPCR), ubiquitous membrane proteins that are targeted by many clinically used drugs. The molecular processes by which they bind to their endogenous agonists and activate effector proteins remain poorly understood. Despite the chemical diversity of the three agonists examined, all three stabilize highly similar active states in the receptor. Subtle structural differences provide insight into how a single GPCR is activated by multiple agonists, a phenomenon that is critically important to drug development. G-protein-coupled receptors (GPCRs) are integral membrane proteins that have an essential role in human physiology, yet the molecular processes through which they bind to their endogenous agonists and activate effector proteins remain poorly understood. So far, it has not been possible to capture an active-state GPCR bound to its native neurotransmitter. Crystal structures of agonist-bound GPCRs have relied on the use of either exceptionally high-affinity agonists 1 , 2 or receptor stabilization by mutagenesis 3 , 4 , 5 . Many natural agonists such as adrenaline, which activates the β 2 -adrenoceptor (β 2 AR), bind with relatively low affinity, and they are often chemically unstable. Using directed evolution, we engineered a high-affinity camelid antibody fragment that stabilizes the active state of the β 2 AR, and used this to obtain crystal structures of the activated receptor bound to multiple ligands. Here we present structures of the active-state human β 2 AR bound to three chemically distinct agonists: the ultrahigh-affinity agonist BI167107, the high-affinity catecholamine agonist hydroxybenzyl isoproterenol, and the low-affinity endogenous agonist adrenaline. The crystal structures reveal a highly conserved overall ligand recognition and activation mode despite diverse ligand chemical structures and affinities that range from 100 nM to ∼80 pM. Overall, the adrenaline-bound receptor structure is similar to the others, but it has substantial rearrangements in extracellular loop three and the extracellular tip of transmembrane helix 6. These structures also reveal a water-mediated hydrogen bond between two conserved tyrosines, which appears to stabilize the active state of the β 2 AR and related GPCRs.

Myocardial infarction (MI) continues to be an important issue in healthcare systems worldwide, leading to high rates of morbidity and mortality. Despite ongoing efforts towards the development of preventive measures and treatments, addressing the challenges posed by MI remains difficult both in developed and developing countries. However, researchers recently investigated the potential cardioprotective effects of taraxerol utilizing an isoproterenol (ISO)-induced cardiotoxicity model among Sprague Dawley rats. Specifically, subcutaneous tissue injections consisting of 5.25 mg/kg or 8.5 mg/kg ISO were administered over two consecutive days as stimuli to induce cardiac injury. To investigate the possibility of preventing damage caused by ISO-induced cardiotoxicity by taraxerol treatment, five groups were formed: a normal control group (1% Tween 80), an ISO control group, an amlodipine group administered 5 mg/kg/day, and various doses of taraxerol. The study results showed that treatment significantly reduced cardiac marker enzymes. Additionally, pretreatment with taraxerol increased myocardial activity in SOD and GPx, leading to significant reductions in serum CK-MB levels along with MDA, TNF-α, and IL-6. Further histopathological analysis supported these observations, as treated animals had less cellular infiltration compared to untreated ones. These multifaceted findings suggest that oral administration of taraxerol could potentially protect hearts from ISO-caused damage by increasing endogenous antioxidant concentrations while decreasing pro-inflammatory cytokines.