Intravenous Infusion of the Novel HNO Donor BMS-986231 Is Associated With Beneficial Inotropic, Lusitropic, and Vasodilatory Properties in 2 Canine Models of Heart Failure.

The effects of the nitroxyl donor BMS-986231 on hemodynamics, left ventricular (LV) function, and pro-arrhythmic potential were assessed using canine heart failure models. BMS-986231 significantly (p < 0.05) increased LV end-systolic elastance, pre-load-recruitable stroke work, ejection fraction, stroke volume, cardiac output, ratio of early-to-late filling time integrals, and early mitral valve inflow velocity deceleration time. BMS-986231 significantly decreased LV filling pressures, end-diastolic stiffness, the time-constant of relaxation, end-diastolic wall stress, systemic vascular resistance, and myocardial oxygen consumption. BMS-986231 had little effect on heart rate and did not induce de novo arrhythmias. Thus, BMS-986231 has beneficial inotropic, lusitropic, and vasodilatory effects.

CXL-1020, a Novel Nitroxyl (HNO) Prodrug, Is More Effective than Milrinone in Models of Diastolic Dysfunction-A Cardiovascular Therapeutic: An Efficacy and Safety Study in the Rat.

The nitroxyl (HNO) prodrug, CXL-1020, induces vasorelaxation and improves cardiac function in canine models and patients with systolic heart failure (HF). HNO's unique mechanism of action may be applicable to a broader subset of cardiac patients. This study investigated the load-independent safety and efficacy of CXL-1020 in two rodent (rat) models of diastolic heart failure and explored potential drug interactions with common HF background therapies. In vivo left-ventricular hemodynamics/pressure-volume relationships assessed before/during a 30 min IV infusion of CXL-1020 demonstrated acute load-independent positive inotropic, lusitropic, and vasodilatory effects in normal rats. In rats with only diastolic dysfunction due to bilateral renal wrapping (RW) or pronounced diastolic and mild systolic dysfunction due to 4 weeks of chronic isoproterenol exposure (ISO), CXL-1020 attenuated the elevated LV filling pressures, improved the end diastolic pressure volume relationship, and accelerated relaxation. CXL-1020 facilitated Ca2+ re-uptake and enhanced myocyte relaxation in isolated cardiomyocytes from ISO rats. Compared to milrinone, CXL-1020 more effectively improved Ca2+ reuptake in ISO rats without concomitant chronotropy, and did not enhance Ca2+ entry via L-type Ca2+ channels nor increase myocardial arrhythmias/ectopic activity. Acute-therapy with CXL-1020 improved ventricular relaxation and Ca2+ cycling, in the setting of chronic induced diastolic dysfunction. CXL-1020's lusitropic effects were greater than those seen with the cAMP-dependent agent milrinone, and unlike milrinone it did not produce chronotropy or increased ectopy. HNO is a promising new potential therapy for both systolic and diastolic heart failure.

Darusentan is a potent inhibitor of endothelin signaling and function in both large and small arteries.

Endothelin is a potent vasoconstrictor often up-regulated in hypertension. Endothelin vasoconstriction is mediated via the G-protein coupled endothelin A (ETA) receptor present on vascular smooth muscle. Endothelin receptor antagonists (ERAs) have been shown to antagonize ET-induced vasoconstriction. We describe the primary pharmacology of darusentan, a propanoic acid based ERA currently in phase 3 clinical trials for resistant hypertension. Darusentan was tested in membrane-, cell-, and tissue-based assays to determine its biochemical and functional potency. Rat aortic vascular smooth muscle cells (RAVSMs) were characterized using flow cytometry. RAVSM membrane fractions tested in saturation experiments exhibited moderate endothelin receptor density. Receptor counting revealed that >95% of the endothelin receptors in these fractions were the ETA subtype. (S)-Darusentan competed for radiolabeled endothelin binding in RAVSM membranes with single-site kinetics, exhibiting a Ki = 13 nmol/L. (R)-Darusentan exhibited no binding activity. In cultured RAVSMs, endothelin induced increases in inositol phosphate and Ca2+ signaling, both of which were attenuated by (S)-darusentan in a concentration-dependent manner. In isolated endothelium-denuded rat aortic rings, (S)-darusentan inhibited endothelin-induced vascular contractility with a pA2 = 8.1 +/- 0.14 (n = 4 animals; mean +/- SD). (R)-Darusentan had no effect. The vasorelaxant potency of (S)-darusentan did not change when determined in isolated denuded rat mesenteric arterioles, suggesting a similar mode of action in both conductance and resistance arteries. In vascular smooth muscle, (S)-darusentan is an ERA with high affinity for the ET receptor, which in this preparation is predominantly ETA receptors. (S)-Darusentan inhibits endothelin-induced signaling related to pro-contractile activity and is a potent inhibitor of vasoconstriction in large and small arteries.

Evaluation of the endothelin receptor antagonists ambrisentan, darusentan, bosentan, and sitaxsentan as substrates and inhibitors of hepatobiliary transporters in sandwich-cultured human hepatocytes.

To evaluate potential mechanisms of clinical hepatotoxicity, 4 endothelin receptor antagonists (ERAs) were examined for substrate activity and inhibition of hepatic uptake and efflux transporters in sandwich-cultured human hepatocytes. The 4 transporters studied were sodium-dependent taurocholate cotransporter (NTCP), organic anion transporter (OATP), bile salt export pump (BSEP), and multidrug resistance-associated protein 2 (MRP2). ERA transporter inhibition was examined using the substrates taurocholate (for NTCP and BSEP), [(3)H]estradiol-17beta-D-glucuronide (for OATP), and [2-D-penicillamine, 5-D-penicillamine]enkephalin (for MRP2). ERA substrate activity was evaluated using probe inhibitors ritonavir (OATP and BSEP), bromosulfalein (OATP), erythromycin (P-glycoprotein), probenecid (MRP2 and OATP), and cyclosporin (NTCP). ERAs were tested at 2, 20, and 100 micromol*L-1 for inhibition and at 2 micromol*L-1 as substrates. OATP, NTCP, or BSEP transport activity was not reduced by ambrisentan or darusentan. Bosentan and sitaxsentan attenuated NTCP transport at higher concentrations. Only sitaxsentan decreased OATP transport (52%), and only bosentan reduced BSEP transport (78%). MRP2 transport activity was unaltered. OATP inhibitors decreased influx of all ERAs. Darusentan influx was least affected (84%-100% of control), whereas bosentan was most affected (32%-58% of control). NTCP did not contribute to influx of ERAs. Only bosentan and darusentan were shown as substrates for both BSEP and P-glycoprotein efflux. All ERAs tested were substrates for at least one hepatic transporter. Bosentan and sitaxsentan, but not ambrisentan and darusentan, inhibited human hepatic transporters, which provides a potential mechanism for the increased hepatotoxicity observed for these agents in the clinical setting.

Resuscitation with a novel hemoglobin-based oxygen carrier in a Swine model of uncontrolled perioperative hemorrhage.

BACKGROUND: Systemic and pulmonary hypertension, possibly related to nitric oxide scavenging by free hemoglobin (Hb), is often seen during resuscitation with hemoglobin-based oxygen carriers (HBOCs). Recently, a second-generation HBOC, rHb2.0 for Injection (rHb), has been developed using recombinant human Hb that has reduced reactivity with nitric oxide. The current study evaluates the efficacy of this novel compound for resuscitation in a swine model of uncontrolled perioperative hemorrhage. METHODS: After instrumentation, animals underwent splenectomy and rapid hemorrhage to a systolic blood pressure of 35 mm Hg and isoelectric electroencephalography. 15 minutes of shock was followed by resuscitation over 30 minutes. In phase I, 18 animals were randomized into three resuscitation groups: (1) lactated Ringer's (LR) equal to three times the shed blood, the negative control group; (2) heterologous blood (BL) equal to Hb 2 g/kg, the positive control group; and (3) rHb equal to 2 g/kg, the treatment group. In phase II, six animals underwent the same experiment with a first-generation HBOC, diaspirin cross-linked Hb (DCLHb) equal to 2 g/kg, an additional control group. On day 0 after 2 hours of observation, spontaneously breathing animals were returned to their cages. Surviving animals were redosed on days 1, 2, and 3 (rHb/DCLHb 1 g/kg; LR/BL-LR 500 mL). Survivors were killed on day 5 and organs harvested for histologic examination. Group comparisons were performed using Student's t test, repeated-measures analysis of variance, and chi2 test. Significance was set at 95% confidence intervals. RESULTS: After resuscitation, systemic mean arterial pressure (MAP) (baseline = 107 +/- 15 mm Hg) was 128 +/- 34 and 108 +/- 15 mm Hg in rHb and BL animals, respectively, and remained stable. In LR and DCLHb animals, after normalization, MAP declined to 67 +/- 13 and 84 +/- 34 mm Hg, respectively. The rHb group maintained higher MAP than the LR and BL groups (p < 0.05 vs. both). With resuscitation, mean pulmonary arterial pressure (PAP) (baseline = 25 +/- 5 mm Hg) increased in rHb (40 +/- 4 mm Hg), BL (34 +/- 3 mm Hg), and DCLHb (40 +/- 3 mm Hg) groups, but stayed elevated only in the DCLHb group (36 +/- 3 mm Hg). PAP in the rHb group was similar to the BL group (p > 0.05), and both rHb and BL groups showed a higher PAP than the LR group (p < 0.05 vs. both). PAP was highest in the DCLHb group (p < 0.05 vs. rHb). Cardiac output of rHb and BL groups was similar (p > 0.05) throughout the observation period. Arterial lactate increased to 5.6 +/- 2.5 mmol/L with shock and then normalized to < 2.0 mmol/L in the rHb, BL, and LR groups within 30 minutes of resuscitation. It remained elevated to > 3.5 mmol/L and showed a delayed increase in the DCLHb group (p < 0.05). Causes and number of deaths were as follows: rHb, zero of six; BL-transfusion reaction, one of six; LR-irreversible shock, four of six; and DCLHb-ventricular failure, six of six. There was no significant increase in plasma methemoglobin (rHb) and no difference in liver or cardiac enzymes (rHb vs. BL). No histologic abnormalities were seen in the rHb group except for cytoplasmic vacuolation, a process thought to be related to metabolism of the test article. CONCLUSION: rHb2.0 for Injection, a second-generation recombinant human HBOC, performs as well as heterologous blood for resuscitation after perioperative blood loss, does not cause sustained pulmonary hypertension, maintains adequate cardiac output and oxygen delivery, and is superior to either LR or DCLHb.