Costello‐Boerrigter, Lisa C.

Background: Water and sodium (Na) retention are hallmarks of congestive heart failure (CHF). While widely employed, conventional diuretics may adversely affect renal function. Therefore, physiological strategies that enhance water and Na excretion while maintaining renal function are a high priority. Arginine vasopressin (AVP) increases water reabsorption after binding to the V2 receptor in the collecting duct (CD). In contrast, B-type natriuretic peptide (BNP) decreases Na reabsorption via activation of the NPR-A receptor also in the CD and at higher doses also in the proximal tubule. We hypothesized that coadministration of the V2-receptor antagonist tolvaptan (TLV) and BNP would mediate a potent diuresis and natriuresis without adversely affecting renal hemodynamics in experimental CHF. We also assessed plasma and urinary excretion of AVP. Methods: Severe CHF was induced in 2 groups of dogs by tachypacing. On day 11 cardiorenal function was assessed. One group received TLV alone (0.1 mg/kg IV bolus; n=6), whereas the other group received infusion of BNP (50 ng/kg/min) in addition to TLV (n=5). Results: Renal hemodynamics were preserved in both groups. TLV alone increased urine flow from 0.07±0.01 to 0.48±0.09 mL/min, while urinary Na excretion (UNaV) remained unchanged. TLV+BNP-50 increased urine flow from 0.17±0.07 to 2.58±0.47 mL/min and UNaV from 1±1 to 77±23 uEq/min while decreasing proximal fractional Na reabsorption (all p<0.05 vs. TLV alone). TLV alone increased plasma aldosterone and distal fractional Na reabsorption, both of which were prevented with BNP-50. In addition, while plasma AVP did not change with TLV or TLV+BNP, urinary AVP excretion markedly increased with TLV+BNP (from 16±5 to 694±196 pg/min) as compared to TLV alone (from 1±1 to 69±23 pg/min). Conclusions: TLV and BNP coadministration enhances aquaresis and natriuresis through proximal and distal tubular actions without changing renal hemodynamics. Further, TLV with BNP uniquely enhances urinary elimination of AVP warranting further study. We conclude from these findings in experimental CHF that simultaneously antagonizing the V2 receptor by TLV and activating the NPR-A receptor with BNP may be a novel and physiologic diuretic and natriuretic strategy in overt CHF.

Background: B-type natriuretic peptide (BNP) signals via particulate guanylyl cyclase (pGC) and cyclic guanosine monophosphate (cGMP). In heart failure (HF), BNP reduces cardiac filling pressures and in selected patients augments sodium excretion and glomerular filtration rate (GFR). Studies have established that pGC and soluble guanylyl cyclase (sGC), the main target of nitric oxide (NO), can be compartmentalized with both enzymes affecting distinct intracellular cGMP pools, resulting in different biological actions. Importantly, sGC may be oxidized in disease states like HF making it unresponsive to NO and nitrovasodilators. BAY 58 –2667 (BAY) is a novel NO and heme independent sGC activator that preferentially stimulates oxidized sGC. We hypothesized that adding direct sGC stimulation with BAY to pGC activation with BNP in HF would enhance vasodilation and cardiac unloading without attenuating the distinct renal actions of BNP. Methods: Severe HF was induced by tachypacing in 13 dogs. On day 11, cardiorenal function was assessed in an acute study under anesthesia at baseline and with intravenous BNP (50 ng/kg/min) alone or in combination with BAY (0.3 ug/kg/min). Results: BNP significantly increased urine flow (UV), urinary sodium excretion (UNaV), GFR, renal blood flow (RBF) and systemic vascular resistance (SVR) and decreased cardiac output (CO), mean arterial pressure (MAP), right atrial pressure (RAP) and pulmonary capillary wedge pressure (PCWP). Despite a greater decrease in MAP compared to BNP, BAY+BNP resulted in similar increases in UNaV, UV and GFR. Dual pGC and sGC stimulation resulted in greater decreases in SVR, RAP and PCWP together with an augmentation of CO compared to BNP alone. Conclusion: Particulate GC activation with BNP in experimental HF enhances renal function and leads to renal but not systemic vasodilation. Addition of the sGC stimulator BAY provides systemic vasodilation, greater cardiac unloading, and augmented CO. Despite a larger decrease in MAP, additional sGC stimulation does not impair the renal actions observed with pGC stimulation alone. These findings support coactivation of sGC with BAY and pGC with BNP as a novel and beneficial therapeutic strategy in HF to optimize activation of distinct GC enzymes and cGMP.

Background: Renal dysfunction has emerged as an important independent prognostic factor in patients with heart failure (HF). Cardiac resynchronization therapy (CRT) improves functional status and left ventricular (LV) function in HF patients with ventricular dyssynchrony. We hypothesized that CRT would also improve glomerular filtration rate as estimated by the abbreviated MDRD equation (eGFR) in patients with reduced eGFR. Methods: This is a retrospective analysis of the Multicenter InSync Randomized Clinical Evaluation (MIRACLE) study, which evaluated CRT in HF patients with NYHA class III–IV, ejection fraction ≤35%, QRS ≥130 ms, and stable medical regimen. Patients were evaluated before implantation and 6 months after randomization to control (CRT device OFF, n=225) or CRT (n=228). Patients were categorized according to their baseline eGFR: ≥90 (category A), 60≤eGFR<90 (category B), and 30≤eGFR<60 (category C) mL/min per 1.73m 2 . Changes in eGFR were also correlated with changes in other parameters in univariate analysis. Results: At baseline, reduced eGFR was associated with ischemic etiology, increased age, mitral regurgitation, and neurohumoral activation. CRT increased LV ejection fraction and decreased LV volumes and mitral regurgitation in all categories. Importantly, CRT improved eGFR (p=0.003) and reduced blood urea nitrogen (p=0.008) compared to control in category C, but not A (p=0.75/p=0.41) and B (p=0.43/p=0.89). In addition, only in category C did atrial natriuretic peptide decrease, suggesting reduced atrial distention and filling pressures with CRT in this group with impaired eGFR. In univariate analysis, changes in eGFR correlated weakly but significantly with changes in aldosterone (r=−0.22), plasma renin activity (r=−0.19, norepinephrine (r=−0.16), and mean blood pressure (r=+0.14), a pattern consistent with reduced neurohumoral activation due to increased systemic and renal perfusion pressure. Conclusions: CRT increased eGFR and reduced blood urea nitrogen in HF patients with reduced baseline eGFR. By improving cardiac function, CRT can indirectly improve renal function, underscoring the importance of cardiorenal interaction and providing another mechanism for the beneficial effects of CRT.

Background— Hemodynamic and neurohumoral function can affect the efficacy of diuretic therapy in congestive heart failure. Arginine vasopressin increases water reabsorption through the V 2 receptor in the collecting duct, whereas B-type natriuretic peptide (BNP) decreases sodium reabsorption in the collecting duct. We hypothesized that combining BNP to the V 2 -receptor antagonist tolvaptan (TLV) would enhance renal excretory function by augmenting sodium excretion together with aquaresis without adversely affecting renal hemodynamics in experimental congestive heart failure. Methods and Results— Congestive heart failure was induced in 3 groups (n=6 per group) of dogs by tachypacing. A acute experiment was done after 10 days. After baseline measurements, study groups received a 0.1 mg/kg IV bolus of TLV alone (TLV), TLV in combination with BNP (TLV+BNP; 50 ng/[kg · min]), or BNP alone (BNP). Mean arterial pressure increased with TLV, remained unchanged with TLV+BNP, and decreased with BNP (+5±1mm Hg versus −1±1 mm Hg versus −15±1 mm Hg; P <0.05). Renal blood flow and glomerular filtration rate were preserved with all regimens. Urine flow increased in all 3 groups but significantly more so with TLV+BNP (TLV: +0.4±0.1 mL/min versus TLV+BNP: +2.4±0.5 mL/min versus BNP: +0.8±0.3 mL/min; P <0.05). Only TLV+BNP and BNP were natriuretic ( P <0.05), whereas only TLV and TLV+BNP increased electrolyte-free water excretion ( P <0.05). Compared with TLV alone, TLV+BNP prevented an increase in aldosterone ( P <0.05). Conclusions— Coadministration of TLV and BNP in experimental HF resulted in a beneficial profile of renal, neurohumoral, and hemodynamic actions, specifically potent diuresis with natriuresis, neutral effect on mean arterial pressure, and lack of aldosterone activation.

Background— We previously reported the feasibility of an acute, orally delivered, newly developed, conjugated form of human B-type natriuretic peptide (hBNP) in normal animals. The objective of the present study was to extend our findings and to define the chronic actions of an advanced oral conjugated hBNP (hBNP-054) administered for 6 days on sodium excretion and blood pressure. We also sought to establish the ability of this new conjugate to acutely activate cGMP and to reduce blood pressure in an experimental model of angiotensin II (ANG II) –mediated hypertension. Methods and Results— First, we developed additional novel conjugated forms of oral hBNP that were superior to our previously reported hBNP-021 in reducing blood pressure in 6 normal dogs. We then tested the new conjugate, hBNP-054, chronically in 2 normal dogs to assess its biological actions as a blood pressure–lowering agent and as a natriuretic factor. Second, we investigated the effects of acute oral hBNP-054 or vehicle in 6 dogs that received continuous infusion of ANG II to induce hypertension. After baseline determination of mean blood pressure (MAP) and blood collection for plasma hBNP and cGMP, all dogs received continuous ANG II infusion (20 ng · kg −1 · min −1 , 1 mL/min) for 4 hours. After 30 minutes of ANG II, dogs received oral hBNP-054 (400 μg/kg) or vehicle in a random crossover fashion with a 1-week interval between dosing. Blood sampling and MAP measurements were repeated 30 minutes after ANG II administration and 10, 30, 60, 120, 180, and 240 minutes after oral administration of hBNP-054 or vehicle. In the chronic study in normal dogs, oral hBNP-054 effectively reduced MAP for 6 days and induced a significant increase in 24-hour sodium excretion. hBNP was not present in the plasma at baseline in any dogs, and it was not detected at any time in the vehicle group. However, hBNP was detected throughout the duration of the study after oral hBNP-054, with a peak concentration at 30 minutes of 1060±818 pg/mL. In the acute study, after ANG II administration, plasma cGMP was not activated after vehicle, whereas it was significantly increased after oral hBNP-054 ( P =0.01 between the 2 groups). Importantly, MAP was significantly increased after ANG II throughout the acute study protocol. However, although no changes occurred in MAP after vehicle administration, oral hBNP-054 reduced MAP for >2 hours (from 138±1 mm Hg after ANG II to 124±2 mm Hg at 30 minutes, 124±2 mm Hg at 1 hour, and 130±5 mm Hg at 2 hours after oral hBNP-054; P <0.001). Conclusions— This study reports for the first time that a novel conjugated oral hBNP possesses blood pressure–lowering and natriuretic actions over a 6-day period in normal dogs. Furthermore, hBNP-054 activates cGMP and reduces MAP in a model of acute hypertension. These findings advance the concept that orally administered chronic BNP is a potential therapeutic strategy for cardiovascular diseases such as hypertension.

Unlike healthy subjects, overt congestive heart failure cannot “escape” the sodium- and water-retaining actions of mineralocorticoid excess. It is undefined whether escape occurs in asymptomatic left ventricular dysfunction (ALVD), which is characterized by preserved sodium homeostasis, natriuretic peptide activation, and normal circulating aldosterone. We hypothesized that, in ALVD, mineralocorticoid excess with exogenous deoxycorticosterone acetate (DOCA) would overwhelm renal compensatory mechanisms, resulting in sodium and water retention, and promote renal and cardiac collagen deposition. ALVD was induced in 2 groups (N=5 each) of dogs by tachypacing at 180 bpm. Urine was collected daily and blood drawn at baseline and days 2, 5, 8, and 11. One group served as control (ALVD), and the other received DOCA (ALVD+DOCA) starting at day 2 of pacing. Urine flow and sodium excretion were unchanged in the ALVD group. In ALVD+DOCA, urine flow and sodium excretion decreased on the first 2 days DOCA was given but normalized starting day 4. Urine flow and urinary cGMP excretion increased in ALVD+DOCA after DOCA escape. Plasma atrial natriuretic peptide, B-type natriuretic peptide, and cGMP increased equally in both groups. There were no differences in cardiorenal and hemodynamic parameters in an acute study on day 11. Although renal collagen area fraction was similar, left ventricular collagen area fraction in ALVD+DOCA was significantly higher than in ALVD (3.3±0.4% versus 2.0±0.2%; P =0.012). We conclude that ALVD can escape the sodium- and water-retaining effects of mineralocorticoid excess. Despite renal escape, increased left ventricular collagen deposition suggests that the heart but not the kidney failed to escape the tissue effects of DOCA.

Soluble guanylate cyclase is a heterodimeric enzyme with a prosthetic heme group that, on binding of its main ligand, NO, generates the second messenger cGMP. Unlike conventional nitrovasodilators, the novel direct NO- and heme-independent soluble guanylate cyclase activator BAY 58-2667 is devoid of non-cGMP actions, lacks tolerance development, and preferentially activates NO-insensitive heme-free or oxidized soluble guanylate cyclase. BAY 58-2667, therefore, represents a novel therapeutic advance in mediating vasodilation. To date, its cardiorenal actions in congestive heart failure (CHF) are undefined. We, therefore, hypothesized that BAY 58-2667 would have beneficial preload- and afterload-reducing actions in experimental severe CHF together with renal vasodilating properties. We assessed the cardiorenal actions of intravenous administration of 2 doses of BAY 58-2667 (0.1 and 0.3 μg/kg per minute, respectively) in a model of tachypacing-induced severe CHF. In CHF, BAY 58-2667 dose-dependently reduced mean arterial, right atrial, pulmonary artery, and pulmonary capillary wedge pressure (from baseline 19±1 to 12±2 mm Hg). Cardiac output (2.4±0.3 to 3.2±0.4 L/min) and renal blood flow increased. Glomerular filtration rate and sodium and water excretion were maintained. Consistent with cardiac unloading, atrial and B-type natriuretic peptide decreased. Plasma renin activity ( P =0.31) and aldosterone remained unchanged ( P =0.19). In summary, BAY 58-2667 in experimental CHF potently unloaded the heart, increased cardiac output and renal blood flow, and preserved glomerular filtration rate and sodium and water excretion without further neurohumoral activation. These beneficial properties make direct soluble guanylate cyclase stimulation with BAY 58-2667 a promising new therapeutic strategy for cardiovascular diseases, such as heart failure.

Background— The objective of this study was to address the feasibility and the biological activity of orally administered human brain natriuretic peptide (hBNP). Proprietary technology has been developed in which short, amphiphilic oligomers are covalently attached to peptides. The conjugated peptides are intended to have an improved pharmacokinetic profile and to enable oral administration. We hypothesized that novel oral conjugated hBNP (CONJ-hBNP) increases plasma hBNP, activates cGMP, and reduces mean arterial pressure (MAP). Methods and Results— This randomized crossover-designed study tested the biological activity of oral CONJ-hBNP compared with oral native hBNP in normal conscious dogs. Measurements of MAP, plasma hBNP, and cGMP were made at baseline (BL) and repeated at 10, 30, 60, 120, 180, and 240 minutes after oral administration. Plasma hBNP was not detectable in dogs at BL. Plasma hBNP was detected after native hBNP and CONJ-HBNP administration. However, plasma hBNP concentration was significantly higher after CONJ-hBNP than after native hBNP administration ( P =0.0374 between groups). Plasma cGMP increased after CONJ-hBNP for 60 minutes (from 10.8±3 to 36.8±26 pmol/mL; P <0.05), whereas it did not change after native hBNP ( P =0.001 between groups). MAP decreased at 10 minutes and remained decreased for 60 minutes after CONJ-hBNP (from 113±8 to 101±12 mm Hg after 10 minutes to 97.5±10 mm Hg after 30 minutes to 99±13 mm Hg after 60 minutes) while remaining unchanged after native hBNP ( P =0.0387 between groups). Conclusions— This study reports for the first time that novel conjugated oral BNP activates cGMP and significantly reduces MAP, thus implying an efficacious coupling of CONJ-hBNP to the natriuretic receptor-A. These data advance a new concept of orally administered chronic BNP therapy for cardiovascular diseases.

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.