Sandberg, Sharon M.

Although angiotensin II (Ang II) has been implicated in the pathophysiology of congestive heart failure, its temporal and regional changes during the development and progression of the disease are poorly defined. Our objective was to assess circulating, renal, cardiac, and vascular Ang II in a canine model of rapid ventricular pacing–induced heart failure that evolves from early left ventricular dysfunction to overt congestive heart failure. Ang II was measured by radioimmunoassay with low cross-reactivity to other angiotensins. Control, early left ventricular dysfunction, and overt congestive heart failure dogs were studied. Early left ventricular dysfunction was characterized by impaired cardiac function, cardiac enlargement, preserved renal perfusion pressure, maintained urinary sodium excretion, and normal plasma renin activity. Overt congestive heart failure was characterized by further impaired cardiac function and cardiac enlargement, reduced renal perfusion pressure, urinary sodium retention, and increased plasma renin activity and plasma Ang II. In early left ventricular dysfunction dogs, renal cortical, renal medullary, ventricular, and aortic Ang II were unchanged, and atrial Ang II was decreased. In overt congestive heart failure dogs, Ang II was increased in the kidney and heart compared with normal dogs and in all tissues compared with early left ventricular dysfunction dogs. The greatest increase in tissue Ang II occurred in the renal medulla. We conclude that early increases in local renal, myocardial, and vascular Ang II do not occur in this model of early left ventricular dysfunction and may even be suppressed. In contrast, increased myocardial and particularly renal Ang II in association with increased circulating Ang II are hallmarks of overt experimental congestive heart failure. These studies provide new insights into the temporal and regional alterations in Ang II during the progression of experimental congestive heart failure.

Background —Endothelin-converting enzyme-1 (ECE-1) processes big endothelin-1 (ET-1) to ET-1, a peptide implicated in atheroma formation. ECE-1 exists in 2 isoforms (ECE-1α and ECE-1β), the result of alternative splicing of a common gene. Neutral endopeptidase (NEP) is a genetically distinct metallopeptidase that degrades the natriuretic peptides. These peptides mediate antiproliferative and vasodilating actions. We sought to demonstrate the distribution of the 2 ECE-1 isoforms in experimental atherosclerosis, to determine the effects of chronic NEP-I on plasma cGMP concentrations, vascular wall ECE-1 activity, and ET-1 concentration, and to correlate these actions with atheroma formation. Our hypothesis was that chronic NEP-I, in association with augmented cGMP, would inhibit ECE-1 conversion of big ET-1 to active ET-1, thus reducing tissue ET-1 concentrations and associated atheroma formation. Methods and Results —Cholesterol-fed New Zealand White rabbits (n=8, 1% cholesterol diet) and NEP-I–treated cholesterol-fed New Zealand White rabbits (n=8; candoxatril, 30 mg/kg per day, Pfizer) were euthanized after 8 weeks of feeding. ECE-1α and ECE-1β immunoreactivity was present in the aortas of both groups. Compared with control values, plasma cGMP concentrations were increased (2.8±0.6 versus 8.4±1.2 pmol/mL, P <0.05), ECE-1 activity was attenuated (68±3% versus 32±8%, P <0.05), aortic tissue ET-1 concentrations were reduced (4.6±0.5 versus 3.2±0.3 pg/mg protein, P <0.05), and atheroma formation was attenuated (62±6% versus 34±5%, P <0.01) by NEP-I. Conclusions —These studies suggest that ECE-1 is present and functionally active in the vascular wall in atherosclerosis. Inhibition of ECE-1 by NEP-I represents a novel approach to interruption of the endothelin system in this cardiovascular disease state.

BACKGROUND Cardiac glycosides have traditionally been used as inotropic agents in the treatment of congestive heart failure (CHF). The renal actions of cardiac glycosides independent of inotropic effects are not characterized. The presence of endogenous digitalis-like factors (EDLFs) with characteristic Na+,K(+)-ATPase activity has been postulated in volume-expanded states such as CHF, and recent studies have demonstrated that at least one EDLF shares structural homology with ouabain. This study was undertaken to evaluate the renal actions of ouabain in normal dogs and those with CHF. METHODS AND RESULTS After surgical preparation, normal dogs (n = 6) and dogs in pacing-induced CHF (n = 6) received intrarenal ouabain in sequential doses of 0.167 micrograms/kg/min, 0.334 micrograms/kg/min, and 0.668 micrograms/kg/min. Hemodynamics and renal function were evaluated during the infusion. There was no change in heart rate or mean arterial pressure during the infusion compared with baseline in both groups. Sodium excretion and urine volume significantly increased in both groups. Plasma renin activity, activated by the onset of pacing in the CHF group, was inhibited by the administration of intrarenal ouabain in this group only. CONCLUSIONS These studies demonstrate that ouabain has diuretic and natriuretic actions independent of cardiac hemodynamics that are preserved in CHF. Furthermore, intrarenal ouabain suppresses activation of renin in CHF.

BACKGROUNDB-type natriuretic peptide (BNP), which is activated in heart failure (HF), is processed to an active form by corin. The corin gene is expressed in the human heart and kidney, but corin protein expression in the heart, kidney, and circulation, along with whether proBNP is processed by circulating corin, remains unknown.METHODSWe examined corin protein expression by immunostaining and Western blot in human heart and kidney, and we assessed the circulating corin concentration by ELISA. We examined histidine-tagged (His-tag) proBNP1–108 processing in serum and plasma by immunoprecipitation and Western blot and sequenced the processed form.RESULTSNormal human heart and kidney displayed the presence of corin, especially in cells around the vasculature. Both corin and proBNP1–108 were present in the plasma of healthy human subjects, with circulating corin significantly higher in men than women (P &lt; 0.0001) and a positive correlation of corin to age (P = 0.0497, r = 0.27). In fresh normal plasma and serum, His-tag proBNP1–108 was processed to a lower molecular weight form confirmed to be BNP. Processed BNP was higher in men than women (P = 0.041) and was positively correlated to plasma corin concentrations (P = 0.041, r = 0.65).CONCLUSIONSOur results support the concept that proBNP1–108 may be processed outside of the heart in the circulation where the proprotein convertase is present. Moreover, sex may impact this process, since corin concentrations are higher in men. These findings may have important physiologic and pathophysiologic implications for the proBNP/corin system in the human.

Recent studies support the speculation that different molecular forms of the cardiac hormone BNP with differential biological activity may circulate in heart failure and be detected by conventional assays. In the current study we determined the ability of 3 widely used conventional assays to detect these different forms thought to circulate in heart failure. We also evaluated the ability of pro-BNP (1-108), N-terminal peptide (NT)–pro-BNP (1-76), and BNP 3-32, the latter a cleavage product of BNP 1-32 by dipeptidyl peptidase IV, on an equimolar basis to activate cGMP in cultured cardiac fibroblasts and cardiomyocytes compared with the biologically active mature BNP 1-32. Specifically, we observed that the Roche NT–pro-BNP assay detected both NT–pro-BNP 1-76 and pro-BNP 1-108 and that Biosite Triage and Shionogi detected both mature BNP 1-32 and the shortened BNP 3-32. Moreover, in cultured cardiac fibroblasts and cardiomyocytes, BNP 1-32 (10 −6 mol/L) activated cGMP. BNP 3-32 demonstrated a similar cGMP activating property in both cardiac cell types. In contrast, the cGMP response to pro-BNP 1-108 and NT–pro-BNP 1-76 was not significantly greater than no treatment alone. We conclude that widely used commercial assays for NT–pro-BNP 1-76 and BNP 1-32 cannot differentiate among pro-, processed, or degraded forms and, thus, may not thoroughly identify circulating BNP forms in heart failure patients. These findings also demonstrate differential cGMP activating properties of BNP forms and, importantly, that pro-BNP 1-108 and NT–pro-BNP 1-76 have reduced cGMP activity in vitro that may have biological relevance to human 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.