Natriuretic peptides as therapeutic targets

Venom natriuretic peptides guide the design of heart failure therapeutics

Heart failure (HF) affects over 26 million people world-wide. It is a syndrome triggered by loss of normal cardiac function due to many acute (eg myocardial infarction) and/or chronic (eg hypertension) causes and characterized by mixed beneficial and deleterious activation of a complex of multifaceted neurohormonal systems the net effect of which frequently is further adverse disruption of pressure-volume homeostasis. Unlike the situation in chronic heart failure, current strategies for treatment of acute heart failure are empirical and lack a strong evidence base. Management includes any of a combination of vasodilators, diuretics and ionotropic agents depending on the hemodynamic profile of the patient. Despite the improvement in the options available to improve outcomes in patients with chronic HF, for several decades little gain has been made in the treatment of the acute decompensated state. Morbidity and mortality rates remain high necessitating new therapeutic agents. The cardiac natriuretic peptides (NPs) are key hormones in pressure-volume homoeostasis. There are three isoforms of mammalian NPs, namely ANP, BNP and CNP. These peptides bind to membrane-bound NP receptors (NPRs) on the heart, vasculature and kidney to lower blood pressure and circulating volume. Intravenous infusion of NPs in HF patients improves hemodynamic status but is associated with occasional severe hypotension. Apart from mammalian NPs, snake venom NPs are an excellent source of pharmacologically distinct ligands that offer the possibility of engineering NPs for therapeutic purposes. Venom NPs have long half-lives, differential NPR activation profiles and varied NPR specificity. The scaffolds of venom NPs encode the molecular information for designing NPs with longer half-lives and improved and differential vascular and renal functions. This review focuses on the structure-function paradigm of mammalian and venom NPs and the different peptide engineering strategies that have been utilized in the design of clinically relevant new NP-analogues.

Expression patterns of natriuretic peptides in pre-hibernating and hibernating Anatolian ground squirrel (Spermophilus xanthoprymnus) kidney

Hibernation is characterized by marked suppression of renal function. Natriuretic peptides (NPs) are involved in the regulation of renal function. However, the role of NPs in the renal function during hibernation remains unclear. We aimed to investigate the distribution patterns of atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP) and C-type natriuretic peptide (CNP) in Anatolian ground squirrel (Spermophilus xanthoprymnus) kidneys during pre-hibernation and hibernation periods. Cortical proximal tubules showed weak ANP immunoreactivity, with moderate staining on the brush border during the pre-hibernation period. In the hibernation period, moderate ANP immunoreactivity was seen in cortical proximal tubules, with very weak reaction in hibernating cortical distal tubules, medullary proximal and collecting tubules. Cortical proximal and distal tubules of both periods had strong and weak BNP immunoreactivity, respectively. Medullary proximal, distal and Henle's loop segments showed very weak BNP immunoreactivity during pre-hibernation. Medullary distal, proximal and collecting tubules and Henle's loop segments had moderate staining during hibernation. In both periods, cortical proximal tubules displayed strong immunoreactivity to CNP. Distal tubules had moderate CNP staining during pre-hibernation, albeit weak staining during hibernation. Medullary proximal tubules exhibited moderate to strong immunoreactivity during pre-hibernation. Medullary distal and proximal tubules had weak and moderate CNP staining, respectively, during pre-hibernation. In both periods, Henle's loop segments displayed moderate CNP immunoreactivity. Glomeruli had similar weak ANP, BNP and CNP staining in both periods. These results suggest that heterothermic conditions differently affected the expression of NPs in the squirrel kidney. This different expression of NPs may contribute to the renal adaptation during hibernation.

Decoding the molecular switches of natriuretic peptides which differentiate its vascular and renal functions

Heart failure (HF) is associated with high morbidity and mortality. Dysfunction of blood pressure and/or volume homeostatic processes result in lower perfusion and/or congestion. Treatment strategies exerting differential effects on pressure and volume mechanisms are critical in handling patients with HF. Atrial natriuretic peptides (ANPs) are a key hormone in maintaining circulation. It binds to NP receptor-A (NPR-A) on vasculature, kidneys and nervous system to lowers blood pressure and volume. It exerts a concentration-dependent pharmacological activity, and only increased renal excretion of water and sodium at low doses and vasodilation along with renal effects at slightly higher doses. Recently, we showed that K-Ring (conserved ring of krait venom NP) elicited only vasodilatory properties despite its ability to evoke NPR-A. Through systematic analysis of the structure-function relationships of K-Ring, we have delineated the molecular switches that control vasodilatory and diuretic properties of NPs in anesthetized rats. In the process, we have identified residues that - (a) differentiate vascular and renal functions, (b) affect heart rate and pulse pressure, (c) exhibit sustained effect on vasodilatory function and (d) forceful diuresis switches. Furthermore, we have shown these residues to have equivalent effects on ANP scaffold, thereby introducing modularity in designing function-based ANP analogs. By comparing the ability of designed NPs to evoke cGMP levels, we propose a hypothetical mechanism for the observed tissue-specific effects. The present study opens new avenues in the development of suitable therapeutic agents for personalized care for HF patients.

Effect of exercise training on cardiac oxytocin and natriuretic peptide systems in ovariectomized rats

Exercise training results in cardiovascular and metabolic adaptations that may be beneficial in menopausal women by reducing blood pressure, insulin resistance, and cholesterol level. The adaptation of the cardiac hormonal systems oxytocin (OT), natriuretic peptides (NPs), and nitric oxide synthase (NOS) in response to exercise training was investigated in intact and ovariectomized (OVX) rats. Ovariectomy significantly augmented body weight (BW), left ventricle (LV) mass, and intra-abdominal fat pad weight and decreased the expression of oxytocin receptor (OTR), atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP), and guanylyl cyclase-A (GC-A), in the right atrium (RA) and LV, indicating estrogenic control of these genes. These effects of ovariectomy were counteracted by 8-wk-long exercise training which decreased fat pad weight (33.4 +/- 2.3 to 23.4 +/- 3.1 g, n = 8, P < 0.05), plasma free fatty acids (0.124 +/- 0.033 to 0.057 +/- 0.010 mM, n = 8, P < 0.01), and plasma triacylglycerol (0.978 +/- 0.174 to 0.588 +/- 0.115 mM, n = 8, P < 0.05). Chronic exercise tended to decrease BW and stimulated ANP (4- to 5-fold) and OTR gene expression in the LV and RA and BNP and inducible NOS (iNOS) mRNA in the LV. In sham-operated rats, exercise augmented ANP expression in the RA, downregulated GC-A mRNA in the LV and RA, but increased its expression threefold in the RA of OVX animals. Endothelial NOS and iNOS expression was enhanced in the left atrium of sham-operated rats. Altogether, these data indicate that in OVX animals, chronic exercise significantly enhances cardiac OT, NPs, and NOS, thus implicating all three hormonal systems in the beneficial effects of exercise training.