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      Sildenafil ameliorates left ventricular T-tubule remodeling in a pressure overload-induced murine heart failure model

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          Abstract

          Aim:

          Sildenafil, a phosphodiesterase 5 (PDE5) inhibitor, has been shown to exert beneficial effects in heart failure. The purpose of this study was to test whether sildenafil suppressed transverse-tubule (T-tubule) remodeling in left ventricular (LV) failure and thereby providing the therapeutic benefits.

          Methods:

          A pressure overload-induced murine heart failure model was established in mice by thoracic aortic banding (TAB). One day after TAB, the mice received sildenafil (100 mg·kg −1·d −1, sc) or saline for 5 weeks. At the end of treatment, echocardiography was used to examine LV function. Then the intact hearts were dissected out and placed in Langendorff-perfusion chamber for in situ confocal imaging of T-tubule ultrastructure from epicardial myocytes.

          Results:

          TAB surgery resulted in heart failure accompanied by remarkable T-tubule remodeling. Sildenafil treatment significantly attenuated TAB-induced cardiac hypertrophy and congestive heart failure, improved LV contractile function, and preserved T-tubule integrity in LV cardiomyocytes. But sildenafil treatment did not significantly affect the chamber dilation. The integrity of LV T-tubule structure was correlated with cardiac hypertrophy ( R 2=0.74, P<0.01) and global LV function ( R 2=0.47, P<0.01).

          Conclusion:

          Sildenafil effectively ameliorates LV T-tubule remodeling in TAB mice, revealing a novel mechanism underlying the therapeutic benefits of sildenafil in heart failure.

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          Effect of phosphodiesterase-5 inhibition on exercise capacity and clinical status in heart failure with preserved ejection fraction: a randomized clinical trial.

          Margaret M. Redfield, Horng Chen, Barry Borlaug … (2013)
          Studies in experimental and human heart failure suggest that phosphodiesterase-5 inhibitors may enhance cardiovascular function and thus exercise capacity in heart failure with preserved ejection fraction (HFPEF). To determine the effect of the phosphodiesterase-5 inhibitor sildenafil compared with placebo on exercise capacity and clinical status in HFPEF. Multicenter, double-blind, placebo-controlled, parallel-group, randomized clinical trial of 216 stable outpatients with HF, ejection fraction ≥50%, elevated N-terminal brain-type natriuretic peptide or elevated invasively measured filling pressures, and reduced exercise capacity. Participants were randomized from October 2008 through February 2012 at 26 centers in North America. Follow-up was through August 30, 2012. Sildenafil (n = 113) or placebo (n = 103) administered orally at 20 mg, 3 times daily for 12 weeks, followed by 60 mg, 3 times daily for 12 weeks. Primary end point was change in peak oxygen consumption after 24 weeks of therapy. Secondary end points included change in 6-minute walk distance and a hierarchical composite clinical status score (range, 1-n, a higher value indicates better status; expected value with no treatment effect, 95) based on time to death, time to cardiovascular or cardiorenal hospitalization, and change in quality of life for participants without cardiovascular or cardiorenal hospitalization at 24 weeks. Median age was 69 years, and 48% of patients were women. At baseline, median peak oxygen consumption (11.7 mL/kg/min) and 6-minute walk distance (308 m) were reduced. The median E/e' (16), left atrial volume index (44 mL/m2), and pulmonary artery systolic pressure (41 mm Hg) were consistent with chronically elevated left ventricular filling pressures. At 24 weeks, median (IQR) changes in peak oxygen consumption (mL/kg/min) in patients who received placebo (-0.20 [IQR, -0.70 to 1.00]) or sildenafil (-0.20 [IQR, -1.70 to 1.11]) were not significantly different (P = .90) in analyses in which patients with missing week-24 data were excluded, and in sensitivity analysis based on intention to treat with multiple imputation for missing values (mean between-group difference, 0.01 mL/kg/min, [95% CI, -0.60 to 0.61]). The mean clinical status rank score was not significantly different at 24 weeks between placebo (95.8) and sildenafil (94.2) (P = .85). Changes in 6-minute walk distance at 24 weeks in patients who received placebo (15.0 m [IQR, -26.0 to 45.0]) or sildenafil (5.0 m [IQR, -37.0 to 55.0]; P = .92) were also not significantly different. Adverse events occurred in 78 placebo patients (76%) and 90 sildenafil patients (80%). Serious adverse events occurred in 16 placebo patients (16%) and 25 sildenafil patients (22%). Among patients with HFPEF, phosphodiesterase-5 inhibition with administration of sildenafil for 24 weeks, compared with placebo, did not result in significant improvement in exercise capacity or clinical status. clinicaltrials.gov Identifier: NCT00763867.
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            Loss of T-tubules and other changes to surface topography in ventricular myocytes from failing human and rat heart.

            Yanjun Zhang, Gaelle Kikonda-Kanda, Calum Lyon … (2009)
            T-tubular invaginations of the sarcolemma of ventricular cardiomyocytes contain junctional structures functionally coupling L-type calcium channels to the sarcoplasmic reticulum calcium-release channels (the ryanodine receptors), and therefore their configuration controls the gain of calcium-induced calcium release (CICR). Studies primarily in rodent myocardium have shown the importance of T-tubular structures for calcium transient kinetics and have linked T-tubule disruption to delayed CICR. However, there is disagreement as to the nature of T-tubule changes in human heart failure. We studied isolated ventricular myocytes from patients with ischemic heart disease, idiopathic dilated cardiomyopathy, and hypertrophic obstructive cardiomyopathy and determined T-tubule structure with either the fluorescent membrane dye di-8-ANNEPs or the scanning ion conductance microscope (SICM). The SICM uses a scanning pipette to produce a topographic representation of the surface of the live cell by a non-optical method. We have also compared ventricular myocytes from a rat model of chronic heart failure after myocardial infarction. T-tubule loss, shown by both ANNEPs staining and SICM imaging, was pronounced in human myocytes from all etiologies of disease. SICM imaging showed additional changes in surface structure, with flattening and loss of Z-groove definition common to all etiologies. Rat myocytes from the chronic heart failure model also showed both T-tubule and Z-groove loss, as well as increased spark frequency and greater spark amplitude. This study confirms the loss of T-tubules as part of the phenotypic change in the failing human myocyte, but it also shows that this is part of a wider spectrum of alterations in surface morphology.
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              Amphiphysin 2 (Bin1) and T-tubule biogenesis in muscle.

              Khashayar Farsad, Harris Weisz, M Marcucci … (2002)
              In striated muscle, the plasma membrane forms tubular invaginations (transverse tubules or T-tubules) that function in depolarization-contraction coupling. Caveolin-3 and amphiphysin were implicated in their biogenesis. Amphiphysin isoforms have a putative role in membrane deformation at endocytic sites. An isoform of amphiphysin 2 concentrated at T-tubules induced tubular plasma membrane invaginations when expressed in nonmuscle cells. This property required exon 10, a phosphoinositide-binding module. In developing myotubes, amphiphysin 2 and caveolin-3 segregated in tubular and vesicular portions of the T-tubule system, respectively. These findings support a role of the bilayer-deforming properties of amphiphysin at T-tubules and, more generally, a physiological role of amphiphysin in membrane deformation.
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                Author and article information

                Journal
                Journal ID (nlm-ta): Acta Pharmacol Sin
                Journal ID (iso-abbrev): Acta Pharmacol. Sin
                Title: Acta Pharmacologica Sinica
                Publisher: Nature Publishing Group
                ISSN (Print): 1671-4083
                ISSN (Electronic): 1745-7254
                Publication date (Print): April 2016
                Publication date (Electronic): 14 March 2016
                Volume: 37
                Issue: 4
                Pages: 473-482
                Affiliations
                [1 ]Shanghai General Hospital, Shanghai Jiao Tong University School of Medicine , Shanghai 200080, China
                [2 ]Division of Cardiovascular Medicine, Department of Internal Medicine, University of Iowa, Carver College of Medicine , Iowa City, IA 52242, USA
                [3 ]Department of Veterans Affairs Medical Center , Iowa City, IA 52242, USA
                Author notes
                Article
                Publisher Item ID: aps201613
                DOI: 10.1038/aps.2016.13
                PMC ID: 4820805
                PubMed ID: 26972492
                SO-VID: 389e4873-e13e-4362-9e44-a1a4a2fda28e
                Copyright © Copyright © 2016 CPS and SIMM
                History
                Date received : 31 October 2015
                Date accepted : 06 February 2016
                Categories
                Subject: Original Article

                ScienceOpen disciplines: Pharmacology & Pharmaceutical medicine
                Keywords: sildenafil,pde5 inhibitor,t-tubule,pressure overload,left ventricular remodeling,left heart failure
                Data availability:
                ScienceOpen disciplines: Pharmacology & Pharmaceutical medicine
                Keywords: sildenafil, pde5 inhibitor, t-tubule, pressure overload, left ventricular remodeling, left heart failure

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