Harders, Gerald E.

Introduction: As importantly underscored by the SPRINT Trial, innovative blood pressure (BP) lowering and multiorgan protective drugs are needed for treating hypertension (HTN). We engineered a Mayo Clinic designer atrial natriuretic peptide (ANP)-based drug, ZD100, which possesses a unique 12 amino acid (AA) carboxy-terminus (CT) extension while maintaining the N-terminus (NT) of ANP. ZD100 is more potent than ANP in reducing BP, inducing natriuresis and inhibiting aldosterone via pGC-A and its second messenger cGMP. To date, the in vivo actions of ZD100 in a model of essential HTN are undefined. Further, in attempt to enhance and/or minimize pGC-A activation, the importance of specific AAs in the CT and NT of ZD100 is unknown and is critical to define. Hypothesis: We hypothesize that ZD100 is a potent anti-HTN drug activating pGC-A/cGMP system and that specific AA variations in the CT and/or NT of ZD100 will modify the ability of activating pGC-A. Methods: Spontaneously hypertensive rats (SHRs) received intravenous (IV) ZD100 or vehicle and BP, plasma and urinary cGMP and the natriuretic effects were determined. We then engineered 15 strategic ZD100 variants (Vs) consisting of mutated peptides in the CT or NT or both. We stimulated HEK293 cells overexpressing pGC-A with ZD100 and the 15 Vs (10-8 M) and measured intracellular cGMP generation. Results: In SHRs, acute IV ZD100 reduced BP, increased plasma and urinary cGMP generation and induced natriuresis demonstrating efficacy in HTN. In vitro, we found two more potent pGC-A activators (+100% cGMP activation) only among the CT-only mutated ZD100 Vs. Importantly, key mutations of either the CT or NT resulted in 6 loss-of-function Vs identifying importance of peptide-receptor dependency. Conclusions: We demonstrate for the first time in a genetic model of HTN that ZD100 reduces BP, activates systemic and renal pGC-A/cGMP and induces natriuresis. Enhanced or reduced pGC-A activation with targeted AA mutations in the CT and NT of ZD100 provides key structure function insights into ZD100 which may lead to next generation ZD100 therapeutic peptides. These findings support ZD100 as a novel peptide therapeutic strategy for HTN and will help guide the selection of best-in-class ZD100 analogues.

Background: C-type natriuretic peptide (CNP) is of endothelial cell origin and represents the most potent anti-fibrotic peptide of the natriuretic peptide family and is important for extracellular matrix homeostasis including mediating bone growth in the young. Cardiorenal aging is associated with altered cardiac and renal structure and function that may contribute to the development of heart and kidney failure, particularly in the elderly. The impact of aging on circulating CNP and associated changes in cardiorenal structure and function are undefined. Hypothesis: We hypothesized that a decrease in endogenous plasma CNP occurs with aging and is associated with an increase in cardiorenal fibrosis and altered left ventricular (LV) and renal structure and function. Methods: Studies were performed in 2, 11 and 20 month old male Fischer rats (n = 8 –10/group). Echo was used to assess LV structure and function. Blood pressure (BP), urinary protein excretion, plasma B-type natriuretic peptide (BNP) and CNP were measured. Kidneys and LV were harvested for gross and histology analysis. Mean±SE, *p<0.05. Results: Aging from 2 to 20 months was associated with progressive reductions in plasma CNP (30±3 to 21±1* to 9±1*pg/ml). Significant and progressive cardiac and renal fibrosis were observed with aging (LV: 9±0.3 to 15±0.7* to 21±1*% and kidney: 1±0.3 to 8±2* to 17±1* %). In contrast to CNP, plasma BNP was modestly increased from the 2 to 20 month old group (21±2 to 26±1*pg/ml). The reduction in CNP and increase in BNP, the latter a biomarker for LV dysfunction, were associated with decreased EF (88±1 to 80±1*%) and increased LVEDd (6.61±0.09 to 7.48±0.09*mm). BP and urinary protein excretion were mildly elevated with aging (91±1 to 101±3* mmHg and 8±0.3 to 20±3* mg/day, respectively). Conclusion: We report for the first time that aging is associated with a progressive decline in circulating CNP and progressive cardiorenal fibrosis, systolic dysfunction and proteinuria. Further studies are warranted to explore the hypothesis that a mechanism of cardiorenal aging with altered cardiorenal structure and function may include a decrease in the bioavailability of CNP.

Introduction: Fibrosis is a hallmark of cardiorenal diseases, including heart failure, for which there are few effective therapies. C-type natriuretic peptide (CNP) is a cardiorenal-derived peptide whose mature active form, CNP-22, possesses potent anti-fibrotic actions through the activation of guanylyl cyclase receptor B (GC-B) and its second messenger, cGMP. However, CNP-22’s therapeutic potential is limited due to its short half-life. We recently identified a 53 amino acid (AA) peptide, CNP-53, whose structure consists of CNP-22 with an additional 31 AA on the N-terminus. Herein, we investigated the cGMP generating actions of CNP-53 (compared to CNP-22) in vivo and in vitro, with the goal of advancing a potential anti-fibrotic strategy for cardiorenal disease. Hypotheses: We hypothesized that CNP-53 would elevate circulating CNP levels as well as have greater cGMP activating actions compared to CNP-22 in vivo. We also hypothesized that CNP-53 would stimulate GC-B specific cGMP production in vitro. Methods: In vivo, two groups of anesthetized normal rats (n=8) received a 75-minute intravenous infusion of an equimolar dose of CNP-53 or CNP-22. Mean arterial pressure (MAP), plasma CNP and plasma and urinary cGMP were assessed. In vitro, HEK 293 cells over-expressing GC-A and GC-B and human fibroblasts (hFs), where GC-B is abundant, were stimulated with CNP-53 or CNP-22 for 10 minutes at a dose of (10-8M). Data are mean ± SE, *p<0.05. Results: In vivo, plasma CNP (CNP-53: 311±66, CNP-22: 153±16 pg/ml*) and cGMP (CNP-53: 21±2, CNP-22: 11±1 pmol/ml*) and urinary cGMP excretion (CNP-53: 75±4, CNP-22: 38±1 pmol/min*) were greater with CNP-53 infusion than CNP-22. MAP was similar between the 2 groups (CNP-53: 85±2, CNP-22: 88±4 mmHg). In vitro, both CNP-53 and CNP-22 activated cGMP in GC-B HEK cells and in hFs, with no activation of cGMP in GC-A HEK cells. Conclusions: These findings demonstrate that CNP-53 is superior to CNP-22 in activating cGMP in vivo, without inducing hypotension. Additionally, CNP-53 is a GC-B specific cGMP activating peptide that potently increases cGMP in hFs. Thus, CNP-53 may represent a novel first in class GC-B agonist with therapeutic potential targeting fibrosis and preventing the progression of cardiorenal disease.

Introduction: Heart failure (HF) is a major health burden in which renal impairment worsens prognosis. Targeting the vicious cycle between heart and kidney may be a more optimal therapeutic strategy for HF. The cardiac natriuretic peptides have cardiorenal protective effects through their receptor GC-A and GC-B. We sought to determine the actions of chronic administration of the dual GC-A/GC-B agonist cenderitide (CD-NP) upon cardiorenal function in experimental HF. Hypothesis: Chronic cenderitide therapy will improve cardiorenal function in HF. Methods: Experimental canine HF was induced by rapid right ventricular pacing at 240 bpm for 10 days which mimics advanced overt HF in humans. Canines (n=5 of each group) were treated with or without cenderitide (Capricor Therapeutics) subcutaneous injection (SQ) twice per day (SQ-BID, 10 ug/kg/day), cenderitide continuous SQ pump (SQ-pump, 5 ng/kg/min), or oral enalapril (ACEi, 0.5 mg/kg/day) for 10 days from the beginning of pacing. We defined hemodynamics, echo parameters, circulating neurohumoral factors at day 11, and global gene profiles using RT-PCR microarrays related to the NP system, fibrosis, growth factors, and inflammation in left atrium which undergoes early remodeling in this model. Results: The SQ-pump group showed significantly less atrial and renal weights, higher cardiac output, glomerular filtration rate, and % ejection fraction, and lower systemic vascular resistance and plasma renin activity (all p<0.05) without lowering mean arterial pressure (MAP), whereas SQ-BID and ACEi lacked these effects together with lowering MAP compared to untreated canines. Gene profile analyses showed gene related to inflammatory cytokines such as TNF-alpha, IL-1 beta, and ROCK-2, and apoptosis such as caspase 7, Fas ligand, C-Myc and TP53 were suppressed (all p<0.05) in SQ-pump but not SQ-BID or ACEi compare to un-treated group. Conclusions: Continuous SQ administration of cenderitide demonstrated superior beneficial effects on cardiorenal function and remodeling together with inhibition of circulating renin and tissue inflammatory and apoptosis pathways. Our studies suggest that continuous administration of cenderitide may provide cardiorenal protection in the setting of advanced HF.

Background : Studies in human myocardial infarction (MI) suggest that even in the absence of heart failure (HF) alterations in renal function may occur and contribute to poor outcomes. After MI a decline in renal function may be seen acutely by mechanisms which are unclear. The long term consequences of MI upon renal function and structure remain poorly defined. We hypothesized that even without pre-existing renal disease, renal functional and structural changes would be present following MI. Methods : Cardiorenal function and structure were assessed in Wistar rats, Sham (S; n=10) and MI groups (n=9) 3 weeks after MI. GFR was determined by inulin clearance. Blood was obtained for PRA and aldosterone. Hearts and kidneys were harvested for histological analysis. Cardiac function was assessed by echo. Genome-wide microarray analysis was performed on kidney cortex (KC) and medulla (KM) (Affymetrix GeneChip® Rat Genome 230 2.0). Results : EF decreased after MI (S:62.8±2.3, MI:42.8±6.5 %, p<0.01) and LVEDd increased (p<0.005) PRA and aldosterone activation were absent. Blood pressure (BP) was not different between groups. There was no HF as sodium and water excretion was maintained. GFR tended to decrease (S:2.9±0.3, MI:2.4±0.2 ml/min, NS). Picrosirius Red staining for collagen in the KC and KM after MI showed greater fibrosis especially in the RM (KC S:1.1±0.2, MI:3.5±0.6 %, p<0.001 and KM S:1±0.2, MI:18.8±6 %, p<0.005). Microarray analysis revealed that 303 genes significantly changed in KM and 407 genes in the KC after MI (1.5 fold, P<0.05). Gene dysregulation was related to cell proliferation, metabolic processes and cell communication (Z value>2). Conclusion : We conclude that experimental MI results in renal structural remodeling characterized by renal cortical and medullary fibrosis with a mild reduction in GFR and extensive modulation of molecular pathways related to renal growth and metabolism. This investigation provides evidence for a heart-kidney connection after MI by mechanisms which remain to be defined. We also conclude that therapies for MI targeting the heart also should be evaluated for properties of renoprotection.

Background: Decreased renal function is associated with increased cardiovascular morbidity and mortality by mechanisms that remain unclear. We hypothesized that even mild renal insufficiency produced by unilateral nephrectomy results in changes in ventricular structure and gene expression in the absence of hypertension or volume overload underscoring a kidney-heart connection in the control of myocardial structure. Methods: Cardiorenal function and structure were assessed in Wistar rats [sham (S; n=10) and unilateral nephrectomized (UNX; n=9)] 4 weeks after UNX. GFR was determined by inulin clearance and renal blood flow (RBF) by PAH. Blood was obtained for BNP, PRA, and aldosterone. Hearts and kidneys were harvested for histological analysis. Cardiac function was assessed by echo. Genome-wide microarray analysis was performed on left ventricular myocardium (Affymetrix GeneChip® Rat Genome 230 2.0). Results: Glomerular hypertrophy was observed in UNX (S:1±0.04, Nx:1.6±0.1 u3x106, p<0.001). GFR tended to decrease with a reduction in RBF (S:8±1, Nx:5±1 ml/min, p<0.005). Sodium and water excretions were not different between groups with no activation of PRA, aldosterone or BNP. LVEF and LV end-systolic and end-diastolic diameters were normal. Blood pressure (BP) was not different between groups. Importantly, Picrosirius Red staining in the ventricular myocardium of UNX compared to S revealed greater fibrosis (S:2.4±0.1, Nx:4.2±0.4 %, p<0.001). Further, microarray analysis of ventricular myocardium revealed that 278 genes significantly changed with UNX (1.5 fold, P<0.05) compared to S in genes related to cell growth, bone remodeling and muscle contraction (Z value>2). Conclusion: We conclude that even mild renal insufficiency produced by unilateral nephrectomy initiates myocardial gene responses and fibrosis independent of alterations in the circulating RAAS, BNP, BP, volume overload or systolic dysfunction. These studies support a kidney - heart connection in early renal dysfunction resulting in molecular ventricular remodeling and fibrosis. These studies in experimental mild renal dysfunction produced by removal of one kidney reveal a renal mediated mechanism for myocardial remodeling.

Introduction: The incidence of post-myocardial infarction (MI) heart failure (HF) is increasing in the elderly. Studies have demonstrated that B-type natriuretic peptide (BNP) mediates critical cardiorenal compensatory and protective actions through guanylyl cyclase receptor A and cGMP activation. Such actions include natriuresis, diuresis and suppression of adverse cardiorenal remodelling. Hypothesis: While the mechanism of this increased risk may be multifactorial, we hypothesized that an impairment of the compensatory protective BNP/cGMP axis in both the aged kidney and heart contributes to post-MI HF. Methods: 20 month old Fischer rats were randomized into two groups: Sham-operated (S) and MI(produced by left coronary artery ligation). Cardiorenal structure and function were assessed at 4 weeks and included mean arterial pressure(MAP), LV EF, LV chamber dimension, proteinuria, sodium (Na) excretion and fibrosis by picrosirius red staining. Plasma BNP and cGMP levels were assessed by RIA. Data presented as mean±SE,*P<0.05. Results: LV EF (S:78±2, MI:46±3 %*) was significantly reduced in aged MI rats, despite no difference in LV fibrosis in the remote region and no change in MAP compared to aged sham rats. Post-MI HF was evident and characterized by a significant reduction in Na excretion (S:0.20±0.03, MI:0.13±0.01 mEq/day*) as well as significant increases in LV dilatation (S:7.2±0.1, MI:8.3±0.2 mm*) and cardiac hypertrophy (S:2.78±0.06, MI:3.25±0.16 mg/g*) in aged MI rats. Notably, plasma BNP (S:9±1, MI:11±2 pg/ml) failed to increase and plasma cGMP (S:44±6, MI:27±3 mm*) was significantly reduced in the MI group. Importantly, MI in the aged rat resulted in a significant loss in total renal mass (S:2739±83, MI:2351±68 mg*), consistent with renal atrophy, while no changes in proteinuria or renal fibrosis were observed. Conclusions: Post-MI dysfunction of the protective BNP/cGMP axis in the aged rat was associated with various cardiorenal abnormalities including renal atrophy, which may contribute to the pathophysiology of HF. This pre-clinical model provides new insights into post-MI HF and may be used to examine therapeutic strategies using natriuretic peptides to protect the heart and kidney in the elderly post-MI population.

Decreased renal function is associated with increased CV morbidity and mortality. The changes mild renal impairment may cause structurally/molecularly in the heart remain unclear. We hypothesized that mild renal dysfunction produced by unilateral nephrectomy(UNX)results in changes in ventricular structure and gene expression in the absence of hypertension or vol overload. Wistar rats were used[sham (S; n=10) and UNX; n=9]. At 4 weeks, GFR was determined by inulin clearance and RBF by PAH. Hearts and kidneys were harvested for histological analysis. Cardiac function assessed by echo. Genomewide microarray analysis was performed on LV myocardium (Affymetrix). Glomerular hypertrophy was observed in UNX. GFR tended to decrease with a reduction in RBF (S:8±1, Nx:5±1 ml/min, p<0.005). Blood pressure (BP), Na and water excretions were maintained without activation of PRA, aldo or BNP. LVEF and LV diameters were normal. Microarray analysis of LV revealed that 278 genes changed with UNX (1.5 fold, P<0.05) related to cell growth, bone remodeling and muscle contraction (Z value>2). Importantly, Pic Red staining in the LV of UNX revealed greater fibrosis (S:2±0.1, Nx:4±0.4 %, p<0.001). We conclude that mild renal insufficiency initiates myocardial gene responses and fibrosis independent of alterations in the circulating RAAS, BNP, BP, vol overload or systolic dysfunction.

Studies in human myocardial infarction (MI) suggest that even in the absence of heart failure (HF) alterations in renal function may occur and contribute to poor outcomes. We hypothesized that even without preexisting renal disease, renal functional, structural and molecular changes would be present following MI. Wistar rats were used, Sham(S;n=10) and MI(n=9). 3 weeks after MI, GFR was determined by inulin clearance. Blood was obtained for PRA and aldosterone. Cardiac function was assessed by echo. Genomewide microarray analysis was performed on kidney cortex (KC) and medulla (KM) (Affymetrix). EF decreased after MI (S:63±2, MI:43±6%, p<0.01) and LVEDd increased. PRA, aldosterone and blood pressure (BP) did not change. There was no HF as Na and water excretion was maintained. GFR tended to decrease. Pic Red staining in the KC and KM after MI showed greater fibrosis (KC S:1±0.2, MI:3±0.6%, p<0.001 and KM S:1±0.2, MI:19±6%, p<0.005). Microarray analysis showed that 303 genes changed in KM and 407 genes in KC after MI (1.5 fold, P<0.05) related to structure morphogenesis and metabolic processes(Z value>2). We conclude that experimental MI results in renal structural remodeling characterized by cortical and medullary fibrosis with a mild reduction in GFR and extensive modulation of molecular pathways related to renal growth and morphogenesis underscoring a heart‐kidney connection after MI.

Decreased renal function is associated with increased CV morbidity and mortality. However, the impact of mild renal dysfunction upon the heart remains to be fully elucidated. It is thought that a mild reduction in renal mass is not deleterious to the heart, yet exploration of the impact of unilateral nephrectomy (Nx) on myocardial gene responses is undefined. We hypothesized that even when ventricular function and structure are grossly preserved after Nx, such a reduction in renal mass and function would result in significant alterations in the cardiac genome. Wistar rats, Sham(S)(n=10), Nx(n=9). 4 weeks after Nx we assessed proteinuria, UNaV, UcGMP and BNP. Cardiac function was assessed by echo. GFR was determined by inulin clearance and renal blood flow (RBF) by PAH. Blood was obtained for BNP, aldosterone and cGMP. Kidneys and hearts were harvested. Gene microarrays were conducted of left ventricle (LV) myocardium (Affymetrix GeneChip® Rat Genome 230 2.0). GFR strongly tended to decrease and RBF was decreased in Nx (S:8±1, Nx:5±1 ml/min, p<0.005). Glomerular volume was increased in Nx (S:1±0.04, Nx:1.6±0.1 u 3 ×10 6 , p<0.001) while UNaV and volume were not different. There was no proteinuria in Nx. EF, LV end systolic and diastolic diameters were normal. Blood pressure (BP) was unchanged. There was no activation of the systemic RAAS or BNP. Importantly, 278 cardiac genes changed their expression after Nx (1.5 fold, P<0.05). 11% were increased and 89% decreased. Pathways involved included cell adhesion, growth and proliferation. We conclude that Nx, independently of alterations in circulating RAAS or BNP, BP or myocardial structure and function, results in widespread changes in myocardial gene expression. Further long‐term studies are needed to define the impact of these early gene responses to myocardial structure and function.