Long-Range Optogenetic Control of Axon Guidance Overcomes Developmental Boundaries and Defects.

Axons connect neurons together, establishing the wiring architecture of neuronal networks. Axonal connectivity is largely built during embryonic development through highly constrained processes of axon guidance, which have been extensively studied. However, the inability to control axon guidance, and thus neuronal network architecture, has limited investigation of how axonal connections influence subsequent development and function of neuronal networks. Here, we use zebrafish motor neurons expressing a photoactivatable Rac1 to co-opt endogenous growth cone guidance machinery to precisely and non-invasively direct axon growth using light. Axons can be guided over large distances, within complex environments of living organisms, overriding competing endogenous signals and redirecting axons across potent repulsive barriers to construct novel circuitry. Notably, genetic axon guidance defects can be rescued, restoring functional connectivity. These data demonstrate that intrinsic growth cone guidance machinery can be co-opted to non-invasively build new connectivity, allowing investigation of neural network dynamics in intact living organisms.

Interaction Between Sacubitril and Valsartan in Preventing Heart Failure Induced by Aortic Valve Insufficiency in Rats.

BACKGROUND: Synergistic interactions between neprilysin inhibition (NEPi) with sacubitril and angiotensin receptor type1 blockade (ARB) with valsartan have been implicated in improvement of left ventricular (LV) contractility, relaxation, exercise tolerance, and fibrosis in preexisting heart failure (HF) induced by aortic valve insufficiency (AVI). It is not known whether this pharmacologic synergy can prevent cardiovascular pathology in a similar AVI model. Our aim was to investigate the pharmacology of sacubitril/valsartan in an experimental setting with therapy beginning immediately after creation of AVI. METHODS: HF was induced through partial disruption of the aortic valve in rats. Therapy began 3 hours after valve disruption and lasted 8 weeks. Sacubitril/valsartan (68 mg/kg), valsartan (31 mg/kg), sacubitril (31 mg/kg), or vehicle were administered daily via oral gavage (N=8 in each group). Hemodynamic assessments were conducted using Millar technology, and an exercise tolerance test was conducted using a rodent treadmill. RESULTS: Only sacubitril/valsartan increased total arterial compliance and ejection fraction (EF). Therapies with sacubitril/valsartan and valsartan similarly improved load-dependent (dP/dtmax) and load independent indices (Ees) of LV contractility, and exercise tolerance, whereas sacubitril did not. None of the therapies improved LV relaxation (dP/dtmin), whereas all reduced myocardial fibrosis. CONCLUSIONS: 1) The synergistic interaction between NEPi and ARB in early therapy with sacubitril/valsartan leads to increased total arterial compliance and EF. 2) Improvement in indices of LV contractility, and exercise tolerance with sacubitril/valsartan is likely because of ARB effect of valsartan. 3) All three therapies provided antifibrotic effects, suggesting both ARB and NEPi are capable of reducing myocardial fibrosis.

Synergy between sacubitril and valsartan leads to hemodynamic, antifibrotic, and exercise tolerance benefits in rats with preexisting heart failure.

Simultaneous neprilysin inhibition (NEPi) and angiotensin receptor blockade (ARB) with sacubitril/valsartan improves cardiac function and exercise tolerance in patients with heart failure. However, it is not known whether these therapeutic benefits are primarily due to NEPi with sacubitril or ARB with valsartan or their combination. Therefore, the aim of the present study was to investigate the potential contribution of sacubitril and valsartan to the benefits of the combination therapy on left ventricular (LV) function and exercise tolerance. Heart failure was induced by volume overload via partial disruption of the aortic valve in rats. Therapy began 4 wk after valve disruption and lasted through 8 wk. Drugs were administered daily via oral gavage [sacubitril/valsartan (68 mg/kg), valsartan (31 mg/kg), and sacubitril (31 mg/kg)]. Hemodynamic assessments were conducted using Millar technology, and an exercise tolerance test was conducted using a rodent treadmill. Therapy with sacubitril/valsartan improved load-dependent indexes of LV contractility (dP/d tmax) and relaxation (dP/d tmin), exercise tolerance, and mitigated myocardial fibrosis, whereas monotherapies with valsartan, or sacubitril did not. Both sacubitril/valsartan and valsartan similarly improved a load-independent index of contractility [slope of the end-systolic pressure-volume relationship ( Ees)]. Sacubitril did not improve Ees. First, synergy of NEPi with sacubitril and ARB with valsartan leads to the improvement of load-dependent LV contractility and relaxation, exercise tolerance, and reduction of myocardial collagen content. Second, the improvement in load-independent LV contractility with sacubitril/valsartan appears to be solely due to ARB with valsartan constituent. NEW & NOTEWORTHY Our data suggest the following explanation for the effects of sacubitril/valsartan: 1) synergy of sacubitril and valsartan leads to the improvement of load-dependent left ventricular contractility and relaxation, exercise tolerance, and reduction of myocardial fibrosis and 2) improvement in load-independent left ventricular contractility is solely due to the valsartan constituent. The findings offer a better understanding of the outcomes observed in clinical studies and might facilitate the continuing development of the next generations of angiotensin receptor neprilysin inhibitors.

A Novel Paradigm for Sacubitril/Valsartan: Beta-Endorphin Elevation as a Contributor to Exercise Tolerance Improvement in Rats With Preexisting Heart Failure Induced by Pressure Overload.

BACKGROUND: Simultaneous angiotensin receptor (AT1) blockade and neprilysin inhibition with the use of sacubitril/valsartan has been recently approved to treat patients with heart failure (HF). Therapeutic benefits of this therapy have been attributed to natriuretic peptide elevation and AT1 receptor blockade. However, that pharmacologic picture may not be complete. The aims of this study were to investigate the pharmacology of sacubitril/valsartan compared with sacubitril and valsartan alone and to examine their impact on peptides up-regulated by neprilysin inhibition, such as beta-endorphin. METHODS AND RESULTS: An HF model was induced by pressure overload via constriction of the suprarenal abdominal aorta in rats. Sacubitril/valsartan (68 mg/kg), valsartan (31 mg/kg), sacubitril (31 mg/kg), or placebo was administered by daily oral gavage (starting 4 weeks after pressure overload onset and continued for 4 additional weeks; n = 8 in each group). Exercise tolerance testing was conducted using a rodent treadmill and hemodynamic assessments were conducted under anesthesia with the use of Millar left ventricular (LV) conductance technology. Pressure overload led to exercise intolerance by 4 weeks and to hypertension and LV dysfunction and remodeling by 8 weeks. Both sacubitril/valsartan and sacubitril elevated beta-endorphin levels, by 40% and 54%, respectively, and improved exercise tolerance, by 93% and 112%, whereas valsartan did not. Indices of LV dysfunction persisted with the use of sacubitril/valsartan and valsartan therapies and even deteriorated in sacubitril group. CONCLUSIONS: When added to valsartan, sacubitril increases beta-endorphin concentrations and improves exercise tolerance. These data suggest beta-endorphin elevation as a potential mechanism of action leading to improvement in exercise tolerance that is seen with sacubitril/valsartan. This therapeutic benefit is potentially independent from LV function.

Delivery of drugs, growth factors, genes and stem cells via intrapericardial, epicardial and intramyocardial routes for sustained local targeted therapy of myocardial disease.

INTRODUCTION: Local myocardial delivery (LMD) of therapeutic agents is a promising strategy that aims to treat various myocardial pathologies. It is designed to deliver agents directly to the myocardium and minimize their extracardiac concentrations and side effects. LMD aims to enhance outcomes of existing therapies by broadening their therapeutic window and to utilize new agents that could not be otherwise be implemented systemically. Areas covered: This article provides a historical overview of six decades LMD evolution in terms of the approaches, including intrapericardial, epicardial, and intramyocardial delivery, and the wide array of classes of agents used to treat myocardial pathologies. We examines delivery of pharmaceutical compounds, targeted gene transfection and cell implantation techniques to produce therapeutic effects locally. We outline therapeutic indications, successes and failures as well as technical approaches for LMD. Expert opinion: While LMD is more complicated than conventional oral or intravenous administration, given recent advances in interventional cardiology, it is safe and may provide better therapeutic outcomes. LMD is complex as many factors impact pharmacokinetics and biologic result. The choice between routes of LMD is largely driven not only by the myocardial pathology but also by the nature and physicochemical properties of the therapeutic agents.