Toshihiro Tsuruda

Brain Natriuretic Peptide Is Produced in Cardiac Fibroblasts and Induces Matrix Metalloproteinases

Abstract— Cardiac fibroblasts (CFs) produce extracellular matrix proteins and participate in the remodeling of the heart. It is unknown if brain natriuretic peptide (BNP) is synthesized by CFs and if BNP participates in the regulation of extracellular matrix turnover. In this study, we examined the production of BNP in adult canine CFs and the role of BNP and its signaling system on collagen synthesis and on the activation of matrix metalloproteinases (MMPs). BNP mRNA was detected in CFs, and a specific radioimmunoassay demonstrated that BNP1-32 was secreted into the media at a rate of 11.2±1.0 pg/105 cells per 48 hours (mean±SEM). The amount of BNP secretion was significantly (P <0.01) augmented by 10−7 mol/L tumor necrosis factor-&agr; in a time-dependent manner. BNP significantly (P <0.01) inhibited de novo collagen synthesis as assessed by [3H]proline incorporation, whereas zymographic MMP-2 (gelatinase) abundance was significantly (P <0.05) stimulated by BNP between 10−7 and 10−6 mol/L. In addition, protein expression of MMP-1, -2, and -3 and membranous type-1 MMP was significantly increased by 10−6 mol/L BNP. The cGMP analogue 8-bromo-cGMP (10−4 mol/L) mimicked the BNP effect, whereas inhibition of protein kinase G by KT5823 (10−6 mol/L) significantly (P <0.05) attenuated BNP-induced zymographic MMP-2 abundance. In summary, this study reports that BNP is present in cultured CFs and that BNP decreases collagen synthesis and increases MMPs via cGMP–protein kinase G signaling. These in vitro findings support a role for BNP as a regulator of myocardial structure via control of cardiac fibroblast function.

Matrix metalloproteinases: pathways of induction by bioactive molecules.

Regulation of the extracellular matrix (ECM) is an important therapeutic target that can potentially attenuate the adverse ventricular remodeling seen in the progression of heart failure. Matrix metalloproteinases (MMPs) degrade numerous ECM proteins. Importantly, the activation of MMPs and their endogenous inhibitors (TIMPs) are associated with ventricular remodeling. Bioactive-molecules (vasoactive peptides) become activated in proportion to the magnitude of heart failure and have been demonstrated to affect directly collagen degradation as well as collagen synthesis in the myocardium. Pro-fibrotic factors such as norepinephrine, angiotensin II, and endothelin-1 stimulate fibrosis by modulating collagen synthesis and MMP/TIMP activity. Antagonism of these bioactive-molecules has produced improved hemodynamic performance concomitant with modulation of MMP/TIMP activity and in association with reverse remodeling. The natriuretic peptides and nitric oxide, both of which function via the second messenger cGMP, demonstrate anti-fibrotic actions by inhibiting collagen synthesis and by stimulating MMP activity. Furthermore, bioactive-molecules along with certain cytokines are reported to amplify MMP activity, suggesting that different signaling systems work together to modulate ECM turnover. Taken together, the evidence supports an important functional role for bioactive-molecules in the regulation of ECM turnover and suggests that pharmacological intervention at the level of such bioactive molecules may provide potential therapeutic strategies for attenuation of the adverse ventricular remodeling associated with the progression of heart failure.

Cardiorenal and humoral properties of a novel direct soluble guanylate cyclase stimulator BAY 41-2272 in experimental congestive heart failure.

Background—BAY 41-2272 is a recently introduced novel orally available agent that directly stimulates soluble guanylate cyclase (sGC) and sensitizes it to its physiological stimulator, nitric oxide. To date, its therapeutic actions in congestive heart failure (CHF) remain undefined. We characterized the cardiorenal actions of intravenous BAY 41-2272 in a canine model of CHF and compared it to nitroglycerin (NTG). Methods and Results—CHF was induced by rapid ventricular pacing for 10 days. Cardiorenal and humoral function were assessed at baseline and with administration of 2 doses of BAY 41-2272 (2 and 10 &mgr;g · kg−1 · min−1; n=8) or NTG (1 and 5 &mgr;g · kg−1 · min−1; n=6). Administration of 10 &mgr;g · kg−1 · min−1 BAY 41-2272 reduced mean arterial pressure (113±8 to 94±6 mm Hg;P <0.05), pulmonary artery pressure (29±2 to 25±2 mm Hg;P <0.05), and pulmonary capillary wedge pressure (25±2 to 20±2 mm Hg;P <0.05). Cardiac output (2.1±0.2 to 2.3±0.2 L/min;P <0.05) and renal blood flow (131±17 to 162±18 mL/min;P <0.05) increased. Glomerular filtration rate was maintained. There were no changes in plasma renin activity, angiotensin II, or aldosterone. NTG mediated similar hemodynamic changes and additionally decreased right atrial pressure and pulmonary vascular resistance. Conclusion—The new sGC stimulator BAY 41-2272 potently unloaded the heart, increased cardiac output, and preserved glomerular filtration rate without activation of the renin-angiotensin-aldosterone system in experimental CHF. These beneficial properties make direct sGC stimulation with BAY 41-2272 a promising new strategy for the treatment of cardiovascular diseases such as CHF.

Brain natriuretic peptide enhances renal actions of furosemide and suppresses furosemide-induced aldosterone activation in experimental heart failure.

Background—The renal actions of brain natriuretic peptide (BNP) in congestive heart failure (CHF) are associated with increased diuresis and natriuresis, preserved glomerular filtration rate (GFR), and lack of activation of the renin-angiotensin-aldosterone system (RAAS). In contrast, diuretic-induced natriuresis may be associated with reduced GFR and RAAS activation. The objective of this study was to test the hypothesis that exogenous BNP enhances the renal diuretic and natriuretic actions of furosemide (Fs) and retards the activation of aldosterone in a model of CHF. Methods and Results—CHF was produced in 2 groups of dogs by ventricular pacing. One group received continuous (90-minute) intravenous Fs (1 mg · kg−1 · h−1). A second group (Fs+BNP) received 45-minute intravenous coinfusion of Fs (1 mg · kg−1 · h−1) and low-dose (2 pmol · kg−1 · min−1) BNP followed by 45-minute coinfusion of Fs (1 mg · kg−1 · h−1) and high-dose (10 pmol · kg−1 · min−1) BNP. Fs increased urinary flow, but the effect of Fs+BNP was greater. Similarly, urinary sodium excretion was higher in the Fs+BNP group. Although GFR tended to decrease in the Fs group, it increased in the Fs+BNP group (35±3 to 56±4*) (* indicates P <0.05 versus baseline) (P <0.0001 between groups). Plasma aldosterone increased with Fs (41±10 to 100±11* ng/dL) but was attenuated in the Fs+BNP group (44±11 to 54±9 ng/dL low-dose and to 47±7 ng/dL high-dose) (P =0.0007 between groups). Conclusions—Fs+BNP has more profound diuretic and natriuretic responses than Fs alone and also increases GFR without activation of aldosterone. Coadministration of BNP and loop diuretic is effective in maximizing natriuresis and diuresis while preserving renal function and inhibiting activation of aldosterone.

Adrenomedullin: An Autocrine/Paracrine Factor for Cardiorenal Protection

Since 1993, with the discovery of adrenomedullin (AM) by Kitamura and coworkers,1 we have gained many insights into the biology of this new peptide. Although AM was originally found in human pheochromocytoma, preproAM gene expression and its immunoreactivity are widely distributed in humans and rodents and found in cardiovascular tissues, kidney, digestive organs, nervous system, and tumor cells.2–4⇓⇓ While this ubiquitous AM distribution has prompted many investigators to clarify the role of AM, we advance the concept that the role of endogenous AM is especially important in cardiovascular and renal homeostasis. We now know that AM circulates in plasma and is present in organs and tissues with increases in AM activity in heart failure, hypertension, and renal dysfunction.5,6⇓ Although AM synthesis may be mainly regulated by lipopolysaccharide (LPS) and cytokines, it has been reported that hormones, as well as physical stimuli, stimulate AM synthesis in smooth muscle cells (SMCs), endothelial cells (ECs), and cardiomyocytes.7–12⇓⇓⇓⇓⇓ It is also accepted that AM has multiple functional properties linked to intracellular cyclic adenosine monophosphate (cAMP) elevation. Indeed, exogenous AM administration induces vasodilation and natriuresis with cAMP elevation, resulting in beneficial cardiorenal response in humans with heart failure.13 Although AM was originally found by monitoring cAMP elevation in platelets,1 supporting a key role for cAMP, it has been reported that the nitric oxide (NO)-cGMP pathway also contributes to actions of …

Ventricular adrenomedullin is associated with myocyte hypertrophy in human transplanted heart

Adrenomedullin (ADM) is a vasoactive and natriuretic peptide. While it is known that ADM is increased in failing human ventricles, the expression of ADM in human ventricular allografts remains unknown. The present study was designed to investigate tissue localization and intensity of ADM expression in ventricular biopsy specimens and to characterize ventricular ADM in human cardiac allografts. Thirty-three post-transplant endomyocardial biopsy specimens were examined immunohistochemically. The average score (range: 0-4) of ADM immunoreactivity (IR) was 2.4+/-0.9 (mean+/-standard deviation). Right ventricular (RV) systolic pressure was significantly increased with high ADM-IR (p=0.048) and the ADM-IR positively associated with myocyte size (r(2)=0.23, p=0.010). In contrast, ADM-IR was not associated with systemic blood pressure, serum creatinine, cyclosporine concentration, cardiac fibrosis, or allograft rejection. The present study shows that ADM-IR is present in human ventricular endomyocardium after transplantation, and ADM-IR is associated with the magnitude of RV pressure and myocyte size, suggesting an important role for ventricular ADM in the counteraction against overload as well as in the progress of myocyte hypertrophy after heart transplantation.