Therapeutic options of Angiotensin Receptor Neprilysin inhibitors (ARNis) in chronic heart failure with reduced ejection fraction: Beyond RAAS and sympathetic nervous system inhibition

Elimination of endogenous high molecular weight FGF2 prevents pressure-overload-induced systolic dysfunction, linked to increased FGFR1 activity and NR1D1 expression

Fibroblast growth factor 2 (FGF2), produced as high (Hi-) and low (Lo-) molecular weight isoforms, is implicated in cardiac response to injury. The role of endogenous FGF2 isoforms during chronic stress is not well defined. We investigated the effects of endogenous Hi-FGF2 in a mouse model of simulated pressure-overload stress achieved by transverse aortic constriction (TAC) surgery. Hi-FGF2 knockout mice, expressing only Lo-FGF2, FGF2(Lo), and wild-type mice, FGF2(WT), expressing both Hi-FGF2 and Lo-FGF2, were used. By echocardiography, a decline in systolic function was observed in FGF2(WT) but not FGF2(Lo) mice compared to corresponding sham-operated animals at 4-8 weeks post-TAC surgery. TAC surgery increased markers of myocardial stress/damage including B-type natriuretic peptide (BNP) and the pro-cell death protein BCL2/adenovirus E1B 19 kDa protein-interacting protein-3 (Bnip3) in FGF2(WT) but not FGF2(Lo) mice. In FGF2(Lo) mice, cardiac levels of activated FGF receptor 1 (FGFR1), and downstream signals, including phosphorylated mTOR and p70S6 kinase, were elevated post-TAC. Finally, NR1D1 (nuclear receptor subfamily 1 group D member 1), implicated in cardioprotection from pressure-overload stress, was downregulated or upregulated in the presence or absence, respectively, of Hi-FGF2 expression, post-TAC surgery. In wild-type cardiomyocyte cultures, endothelin-1 (added to simulate pressure-overload signals) caused NR1D1 downregulation and BNP upregulation, similar to the effect of TAC surgery on the FGF2(WT) mice. The NR1D1 agonist SR9009 prevented BNP upregulation, simulating post-TAC findings in FGF2(Lo) mice. We propose that elimination of Hi-FGF2 is cardioprotective during pressure-overload by increasing FGFR1-associated signaling and NR1D1 expression.

Neprilysin Inhibitors: Filling a Gap in Heart Failure Management, Albeit Amidst Controversy and at a Significant Cost

Dual angiotensin and neprilysin inhibition using the combination drug sacubitril-valsartan has ushered in a new era in the treatment of heart failure (HF). The randomized controlled PARADIGM-HF trial, which randomized 8399 patients with HF to enalapril or sacubitril-valsartan, showed a 20% reduction in mortality and HF hospitalization with the new drug. This has been heralded as a step toward filling a crucial gap in HF management by providing strong evidence that combined inhibition of the angiotensin receptor and neprilysin is superior to inhibition of the renin-angiotensin system alone in stable patients with chronic HF as it negates the deleterious effects of angiotensin while concomitantly augmenting the beneficial effects of the endogenous natriuretic peptide system. This new therapy is costly, and other confirmatory studies have been lacking for over 2 years since its approval by major regulatory authorities. As such, controversy and heated discussions have amassed, as has detailed information from a plethora of secondary analyses of this pivotal trial about the pros and cons of this promising new therapeutic strategy in HF management. The aim of this review was to provide a critical assessment of all these aspects.

Neprilysin inhibition in heart failure: mechanisms and substrates beyond modulating natriuretic peptides

The autonomic nervous system, the renin-angiotensin-aldosterone system, and the natriuretic peptide system represent critical regulatory pathways in heart failure and as such have been the major targets of pharmacological development. The introduction and approval of angiotensin receptor neprilysin inhibitors (ARNi) have broadened the available drug treatments of patients with chronic heart failure with reduced ejection fraction. Neprilysin catalyses the degradation of a number of vasodilator peptides, including the natriuretic peptides, bradykinin, substance P, and adrenomedullin, as well as vasoconstrictor peptides, including endothelin-1 and angiotensin I and II. We review the multiple, potentially competing, substrates for neprilysin inhibition, and the resultant composite clinical effects of ARNi therapy. A mechanistic understanding of this novel therapeutic class may provide important insights into the expected on-target and off-target effects when this agent is more widely prescribed.