Sildenafil and B-Type Natriuretic Peptide Acutely Phosphorylate Titin and Improve Diastolic Distensibility In Vivo

Abstract

Background In vitro studies suggest that phosphorylation of titin reduces myocyte/myofiber stiffness. Titin can be phosphorylated by cGMP activated protein kinase (PKG). Intracellular cGMP production is stimulated by B-type natriuretic peptide (BNP) and degraded by phosphodiesterases (PDE) including PDE-5A. We hypothesized that a PDE-5A inhibitor (sildenafil) alone or in combination with BNP would increase left ventricular (LV) diastolic distensibility by phosphorylating titin. Methods and Results 8 elderly dogs with experimental hypertension (OH) and 4 young normal (YN) dogs underwent measurement of the end-diastolic pressure (EDP) volume (EDV) relationship (EDPVR) during caval occlusion at baseline, after sildenafil and after BNP infusion. To assess diastolic distensibility independent of load/extrinsic forces, the EDV at a common EDP on the sequential EDPVRs was measured (LV capacitance). In a separate group of dogs (n=7 OH and 7 YN), serial full thickness LV biopsies were harvested from the beating heart during identical infusions to measure myofilament protein phosphorylation. Plasma cGMP increased with sildenafil and further with BNP (7.31±2.37 to 26.9±10.3 to 70.3±8.1 pmol/ml, P<0.001). LV diastolic capacitance increased with sildenafil and further with BNP (51.4±16.9 to 53.7±16.8 to 60.0±19.4 ml, P<0.001). Changes were similar in OH and YN dogs. There were no effects on phosphorylation of troponin I, troponin T, phospholamban, or myosin light chains −1 or −2. Titin phosphorylation increased with sildenafil and BNP, whereas titin-based cardiomyocyte stiffness decreased. Conclusion Acute cGMP enhancing treatment with sildenafil and BNP improves LV diastolic distensibility in vivo, in part, by phosphorylating titin.

Pulmonary Hypertension in Heart Failure Preserved Ejection Fraction

“…62 The multiple effects of sildenafil in our group's study 40 were consistent with findings in a rat aortic banding model of LV pressure overload leading to HFpEF 30 in which PDE5 inhibitors showed beneficial effects on lung endothelial function, pulmonary vascular remodeling, as well as on LVH. Consistently, capillaries and small size arteries showed some degrees of vascular wall thickness that were inversely related to cGMP levels.…”

A change of heart: oxidative stress in governing muscle function?

“…In contrast, a decreased N2BA/N2B ratio was observed in a study of endomyocardial biopsies from HFpEF patients versus HFrEF patients (van Heerebeek et al 2006). Similarly, a modest decrease in the proportion of N2BA titin was seen in an old dog model of hypertrophy-associated early HFpEF (Bishu et al 2011, Hamdani et al 2013a. This model shows signs of diastolic dysfunction similar to those frequently seen in elderly HFpEF patients: impaired LV relaxation, unaltered coefficient of LV diastolic stiffness and reduced diastolic capacitance, together with elevated natriuretic peptides, normal LV volume but increased LV mass and moderated myocardial fibrosis.…”

“…The technique of cellular membrane removal used in these studies abolished the effect of Ca 2+ handling on passive stiffness, allowing the role of the giant myofilament protein titin in passive stiffness to be demonstrated (Borbély et al 2009b;Bishu et al 2011;Hamdani et al 2013aHamdani et al , 2014Linke and Hamdani 2014). Titin functions as a bidirectional spring, exhibiting a stiffness constant that can be tuned by either isoform switching or post-translational modifications Linke and Krüger 2010).…”

Gigantic Business

“…Feasibility of this concept was demonstrated when young healthy or old hypertensive HFpEF dogs were exposed to acute cGMP-enhancing treatment with phosphodiesterase-5A inhibitor sildenafil, followed by B-type natriuretic peptide. 150 Sildenafil rapidly increased cardiac titin phosphorylation and lowered cardiomyocyte passive tension, and this was maintained with B-type natriuretic peptide, thus explaining the better diastolic distensibility observed in living dog hearts after the treatment. 150 In summary, reducing titin stiffness through cGMP-enhancing therapy seems to be a reasonable strategy to correct the pathologically high diastolic stiffness characteristic of patients with HFpEF.…”