A Novel and Highly Potent Urotensin II Receptor Antagonist Inhibits Urotensin II-Induced Pressure Response in Mice.

This study was designed to characterize the pharmacological profile of DS37001789, which is a structurally novel piperazine derivative that acts as urotensin II (U-II) receptor antagonist. DS37001789 inhibited [I]-U-II binding to human GPR14, U-II receptor, with an IC50 value 0.9 nM. Its potency was superior to that of ACT-058362, a nonpeptide U-II receptor antagonist whose IC50 was 120 nM. Human U-II-induced vascular contraction was blocked by DS37001789. The dose-response curve of DS37001789 in rats and monkeys did not show species differences, and it shifted to the right without any effects on the maximum vascular response. Moreover, orally administered DS37001789 dose-dependently prevented human U-II-induced blood pressure elevation in mice, and this effect was significant at dose and higher dose (30 and 100 mg/kg), and its potency was superior to that of ACT-058362 (100 mg/kg). These results suggest that DS37001789 is a highly potent U-II receptor antagonist both in vitro and in vivo, with no marked species difference. DS37001789 would be a useful tool to clarify the physiological roles of U-II/GPR14 system. In addition, it can serve as a novel therapeutic agent for diseases in which the U-II/GPR14 system is upregulated, such as hypertension, heart failure, renal dysfunction, and diabetes.

Pharmacokinetic and Pharmacodynamic Profiles of Glyco-Modified Atrial Natriuretic Peptide Derivatives Synthesized Using Chemo-enzymatic Synthesis Approaches.

Atrial natriuretic peptide (ANP) exerts beneficial pharmacological effects in the treatment of various cardiovascular disorders, such as acute congestive heart failure (ADHF). However, the clinical use of ANP is limited to the continuous intravenous infusion owing to its short half-life (2.4 ± 0.7 min). In the present study, we conjugated the glyco-modified ANP with a monoclonal antibody (mAb) or an Fc via chemo-enzymatic glyco-engineering using EndoS D233Q/Q303L. The most potent derivative SG-ANP-Fc conjugate extended the half-life to 14.9 d and the duration of blood pressure lowering effect to over 28 d. This new biologic modality provides an opportunity to develop outpatient therapy after ADHF.

Sustained Activation of Guanylate Cyclase-A with TDT, a Natriuretic Peptide Derivative, Exhibits Cardiorenal Protection in Dahl Salt-Sensitive Hypertensive Rats.

Heart failure often presents with prognosis-relevant impaired renal function. To investigate whether the chronic activation of guanylate cyclase-A (GC-A) protects both heart and kidney, we examined the effects of TDT, a neprilysin (NEP)-resistant natriuretic peptide (NP) derivative, on cardiac and renal dysfunction in Dahl salt-sensitive hypertensive (DS) rats. Pretreatment with NEP or NEP inhibitor did not influence GC-A activation by TDT both in vitro and in vivo, resulting in a long-acting profile of TDT compared with native human atrial NP (hANP). The repeated administration of TDT to DS rats suppressed the progress of cardiac hypertrophy, systolic/diastolic dysfunction, and proteinuria in a dose-dependent manner. Compared with vehicle and hANP, salt diet-induced podocyte injury was reduced by TDT, as analyzed by urinary podocalyxin concentration, renal expression of nephrin mRNA, and glomerular expression of desmin protein. Since glomerular TRPC6 plays detrimental roles in podocyte homeostasis, we examined the renal expression of TRPC6 in DS rats and found that salt diet upregulated the expression of TRPC6. Importantly, TRPC6 induction was significantly decreased in TDT-treated rats, compared with vehicle and hANP. Consistently, in primary-culture podocytes from DS rats, TDT inhibited ATP-induced calcium influx, similar to TRPC inhibitor SKF96365. Finally, TDT-mediated protection of podocytes was abolished by protein kinase G inhibitor KT5823. In conclusion, TDT treatment attenuated heart and kidney dysfunction, accompanied by podocyte protection through inhibition of TRPC6. Thus, long-acting NPs could be a new avenue for treatment of heart failure.

Discovery and SAR of a novel series of Natriuretic Peptide Receptor-A (NPR-A) agonists.

Novel thienopyrimidine compounds 2 and 3 were discovered from high-throughput screening as Natriuretic Peptide Receptor A (NPR-A) agonists. Scaffold hopping of a thienopyrimidine ring to a quinazoline ring, introduction of the basic functional group and optimization of the substituent on the 6-position of the benzene ring of quinazoline led to improved agonistic activity. We discovered compound 48, which showed potent agonistic activity for NPR-A with an EC50 value of 0.073µM, indicating 350-fold potency compared to the hit compound 3.

Three classical Cepheid variable stars in the nuclear bulge of the Milky Way.

The nuclear bulge is a region with a radius of about 200 parsecs around the centre of the Milky Way. It contains stars with ages ranging from a few million years to over a billion years, yet its star-formation history and the triggering process for star formation remain to be resolved. Recently, episodic star formation, powered by changes in the gas content, has been suggested. Classical Cepheid variable stars have pulsation periods that decrease with increasing age, so it is possible to probe the star-formation history on the basis of the distribution of their periods. Here we report the presence of three classical Cepheids in the nuclear bulge with pulsation periods of approximately 20 days, within 40 parsecs (projected distance) of the central black hole. No Cepheids with longer or shorter periods were found. We infer that there was a period about 25 million years ago, and possibly lasting until recently, in which star formation increased relative to the period of 30-70 million years ago.

Pathological cardiac hypertrophy alters intracellular targeting of phosphodiesterase type 5 from nitric oxide synthase-3 to natriuretic peptide signaling.

BACKGROUND: In the normal heart, phosphodiesterase type 5 (PDE5) hydrolyzes cGMP coupled to nitric oxide- (specifically from nitric oxide synthase 3) but not natriuretic peptide (NP)-stimulated guanylyl cyclase. PDE5 is upregulated in hypertrophied and failing hearts and is thought to contribute to their pathophysiology. Because nitric oxide signaling declines whereas NP-derived cGMP rises in such diseases, we hypothesized that PDE5 substrate selectivity is retargeted to blunt NP-derived signaling. METHODS AND RESULTS: Mice with cardiac myocyte inducible PDE5 overexpression (P5(+)) were crossed to those lacking nitric oxide synthase 3 (N3(-)), and each model, the double cross, and controls were subjected to transaortic constriction. P5(+) mice developed worse dysfunction and hypertrophy and enhanced NP stimulation, whereas N3(-) mice were protected. However, P5(+)/N3(-) mice behaved similarly to P5(+) mice despite the lack of nitric oxide synthase 3-coupled cGMP generation, with protein kinase G activity suppressed in both models. PDE5 inhibition did not alter atrial natriuretic peptide-stimulated cGMP in the resting heart but augmented it in the transaortic constriction heart. This functional retargeting was associated with PDE5 translocation from sarcomeres to a dispersed distribution. P5(+) hearts exhibited higher oxidative stress, whereas P5(+)/N3(-) hearts had low levels (likely owing to the absence of nitric oxide synthase 3 uncoupling). This highlights the importance of myocyte protein kinase G activity as a protection for pathological remodeling. CONCLUSIONS: These data provide the first evidence for functional retargeting of PDE5 from one compartment to another, revealing a role for natriuretic peptide-derived cGMP hydrolysis by this esterase in diseased heart myocardium. Retargeting likely affects the pathophysiological consequence and the therapeutic impact of PDE5 modulation in heart disease.

Synthesis and optimization of novel (3S,5R)-5-(2,2-dimethyl-5-oxo-4-phenylpiperazin-1-yl)piperidine-3-carboxamides as orally active renin inhibitors.

We report synthesis and optimization of a series of (3S,5R)-5-(2,2-dimethyl-5-oxo-4-phenylpiperazin-1-yl)piperidine-3-carboxamides as renin inhibitors. Chemical modification of P1', P2' and P3 portions led to a promising 3,5-disubstituted piperidine 32o showing high renin inhibitory activity and favorable oral exposure in both rats and cynomolgus monkeys with acceptable CYP and hERG current inhibition. Compound 32o exhibited a significant blood pressure lowering effect by oral administration in two hypertensive animal models, double transgenic rats and furosemide pretreated cynomolgus monkeys.

Lead optimization of 5-amino-6-(2,2-dimethyl-5-oxo-4-phenylpiperazin-1-yl)-4-hydroxyhexanamides to reduce a cardiac safety issue: discovery of DS-8108b, an orally active renin inhibitor.

With the aim to address an undesired cardiac issue observed with our related compound in the recently disclosed novel series of renin inhibitors, further chemical modifications of this series were performed. Extensive structure-activity relationships studies as well as in vivo cardiac studies using the electrophysiology rat model led to the discovery of clinical candidate trans-adamantan-1-ol analogue 56 (DS-8108b) as a potent renin inhibitor with reduced potential cardiac risk. Oral administration of single doses of 3 and 10 mg/kg of 56 in cynomolgus monkeys pre-treated with furosemide led to significant reduction of mean arterial blood pressure for more than 12 h.

Regulator of G protein signaling 2 mediates cardiac compensation to pressure overload and antihypertrophic effects of PDE5 inhibition in mice.

The heart initially compensates for hypertension-mediated pressure overload by enhancing its contractile force and developing hypertrophy without dilation. Gq protein-coupled receptor pathways become activated and can depress function, leading to cardiac failure. Initial adaptation mechanisms to reduce cardiac damage during such stimulation remain largely unknown. Here we have shown that this initial adaptation requires regulator of G protein signaling 2 (RGS2). Mice lacking RGS2 had a normal basal cardiac phenotype, yet responded rapidly to pressure overload, with increased myocardial Gq signaling, marked cardiac hypertrophy and failure, and early mortality. Swimming exercise, which is not accompanied by Gq activation, induced a normal cardiac response, while Rgs2 deletion in Galphaq-overexpressing hearts exacerbated hypertrophy and dilation. In vascular smooth muscle, RGS2 is activated by cGMP-dependent protein kinase (PKG), suppressing Gq-stimulated vascular contraction. In normal mice, but not Rgs2-/- mice, PKG activation by the chronic inhibition of cGMP-selective phosphodiesterase 5 (PDE5) suppressed maladaptive cardiac hypertrophy, inhibiting Gq-coupled stimuli. Importantly, PKG was similarly activated by PDE5 inhibition in myocardium from both genotypes, but PKG plasma membrane translocation was more transient in Rgs2-/- myocytes than in controls and was unaffected by PDE5 inhibition. Thus, RGS2 is required for early myocardial compensation to pressure overload and mediates the initial antihypertrophic and cardioprotective effects of PDE5 inhibitors.

Monoamine oxidase A-mediated enhanced catabolism of norepinephrine contributes to adverse remodeling and pump failure in hearts with pressure overload.

RATIONALE: Monoamine oxidases (MAOs) are mitochondrial enzymes that catabolize prohypertrophic neurotransmitters, such as norepinephrine and serotonin, generating hydrogen peroxide. Because excess reactive oxygen species and catecholamines are major contributors to the pathophysiology of congestive heart failure, MAOs could play an important role in this process. OBJECTIVE: Here, we investigated the role of MAO-A in maladaptive hypertrophy and heart failure. METHODS AND RESULTS: We report that MAO-A activity is triggered in isolated neonatal and adult myocytes on stimulation with norepinephrine, followed by increase in cell size, reactive oxygen species production, and signs of maladaptive hypertrophy. All of these in vitro changes occur, in part, independently from alpha- and beta-adrenergic receptor-operated signaling and are inhibited by the specific MAO-A inhibitor clorgyline. In mice with left ventricular dilation and pump failure attributable to pressure overload, norepinephrine catabolism by MAO-A is increased accompanied by exacerbated oxidative stress. MAO-A inhibition prevents these changes, and also reverses fetal gene reprogramming, metalloproteinase and caspase-3 activation, as well as myocardial apoptosis. The specific role of MAO-A was further tested in mice expressing a dominant-negative MAO-A (MAO-A(neo)), which were more protected against pressure overload than their wild-type littermates. CONCLUSIONS: In addition to adrenergic receptor-dependent mechanisms, enhanced MAO-A activity coupled with increased intramyocardial norepinephrine availability results in augmented reactive oxygen species generation, contributing to maladaptive remodeling and left ventricular dysfunction in hearts subjected to chronic stress.

Design and optimization of novel (2S,4S,5S)-5-amino-6-(2,2-dimethyl-5-oxo-4-phenylpiperazin-1-yl)-4-hydroxy-2-isopropylhexanamides as renin inhibitors.

Introduction of the 2,2-dimethyl-4-phenylpiperazin-5-one scaffold into the P(3)-P(1) portion of the (2S,4S,5S)-5-amino-6-dialkylamino-4-hydroxy-2-isopropylhexanamide backbone dramatically increased the renin inhibitory activity without using the interaction to the S(3)(sp) pocket. Compound 31 exhibited >10,000-fold selectivity over other human proteases, and 18.5% oral bioavailability in monkey.

Design and discovery of new (3S,5R)-5-[4-(2-chlorophenyl)-2,2-dimethyl-5-oxopiperazin-1-yl]piperidine-3-carboxamides as potent renin inhibitors.

Utilizing X-ray crystal structure analysis, (3S,5R)-5-[4-(2-chlorophenyl)-2,2-dimethyl-5-oxopiperazin-1-yl]piperidine-3-carboxamides were designed and identified as renin inhibitors. The most potent compound 15 demonstrated favorable pharmacokinetic and pharmacodynamic profiles in rat.

A novel sphingosine-1-phosphate receptor 1 antagonist prevents the proliferation and relaxation of vascular endothelial cells by sphingosine-1-phosphate.

A sphingosine-1-phosphate receptor 1 (S1P1) antagonist is expected to be an anti-angiogenic compound; however, there are few reports that demonstrated that a S1P1 inhibitor improved the disease state in an angiogenic animal model. Since we determined that a prototype S1P1 antagonist was an in vivo angiogenesis inhibitor, we developed the derivatives to acquire more effective compounds. In this report, we show the S1P1 antagonistic activity of some representatives, especially compound 5 {sodium 4-[(4-butoxyphenyl)thio]-2'-[{4-[(heptylthio)methyl]-2-hydroxyphenyl}(hydroxy)methyl]biphenyl-3-sulfonate}. The IC50 values calculated from an intracellular cyclic AMP measurement assay and a [33P]sphingosine-1-phosphate (Sph-1-P)/S1P1 binding assay were 38 and 200 nM, respectively. A subtype specificity test for the other Sph-1-P receptors showed that compound 5 was the S1P1-directional antagonist. It also inhibited the proliferation, migration, and tube formation of human umbilical vein endothelial cells stimulated by Sph-1-P with the IC50 values of 18, 650, and 230 nM, respectively. A cytotoxicity assay concurrently performed with a tube formation assay supported the hypothesis that these biological effects were not due to its cytotoxicity. Furthermore, administration (10 mg/kg, intravenously) to anesthetized Sprague-Dawley rats inhibited Sph-1-P-induced hypotension by 100-90% for 30 min. This is presumably through the inhibition of Sph-1-P-induced vasorelaxation, mainly by the blocking of S1P1 and/or S1P3. Taken together, these results show that compound 5 is an inhibitor of in vitro and in vivo Sph-1-P signaling, and that it will be useful to elucidate the in vivo effect of Sph-1-P on vascular endothelial cells.

The urotensin II receptor antagonist DS37001789 ameliorates mortality in pressure-overload mice with heart failure.

This study was designed to evaluate the effects of DS37001789, a novel and highly potent urotensin II (U-II) receptor (GPR14) antagonist, against mortality, hypertrophy, and cardiac dysfunction in pressure-overload hypertrophy by transverse aortic constriction (TAC) in mice. In addition, we analyzed the phenotype of GPR14 knockout (KO) mice after TAC induction to confirm the contribution of the U-II/GPR14 system. The oral administration of 0.2% DS37001789 to TAC mice for 12 weeks significantly ameliorated the mortality rate and 0.2% DS37001789 for 4 weeks significantly improved cardiac function by pressure-volume analysis. GPR14 expression was significantly upregulated in the left ventricle in the TAC mice treated with 0.2% DS37001789. Moreover, we confirmed that the significant amelioration of mortality was accomplished by the inhibition of cardiac enlargement and the improvement of cardiac function in GPR14 KO mice after TAC surgery. These results suggest that the U-II/GPR14 system contributes to the progression of heart failure and its blockade ameliorates the mortality via improved cardiac function. The U-II/GPR14 system may thus be an attractive target for treating heart failure with pathological cardiac hypertrophy and DS37001789 may be a novel therapeutic agent for heart failure in patients with pressure-overload conditions such as hypertension and aortic valve stenosis.

Identification of novel Urotensin-II receptor antagonists with potent inhibition of U-II induced pressor response in mice.

Urotensin II (U-II) has been found to be one of the most potent vasoconstrictor (Ames et al., 1999; Bohm et al., 2002) reported till date. U-II exerts its response via activation of a G-protein coupled receptor, Urotensin II receptor(UT). Binding of U-II to UT leads to an instant increase in the inositol phosphate turnover and intracellular Ca2+. Such an instant Ca2+ release and potent vasoconstriction exerted by U-II is expected to have an important role in the progression of cardiac diseases. We have previously shown that UT antagonist DS37001789 prevents U-II induced blood pressure elevation in mice (Nishi et al., 2019) in a dose dependent manner, with potent efficacy at 30 and 100 mg/kg. Further to this, we have also shown that DS37001789 ameliorates mortality in pressure-overload mice with heart failure (Nishi et al., 2020). We therefore conducted an extensive structure-activity relationship studies to identify molecules with superior efficacy. In the present manuscript, we report the identification of two potent, non-peptide small molecule antagonists of Urotensin II receptor (UT), RCI-0879 and RCI-0298 which blocked the action of U-II, both in vitro and in vivo. These molecules were found to be very potent in in vitro Ca2+ and radioligand binding assays using human and mouse UT over-expressing CHO cells. RCI-0879 and RCI-0298 also exhibited superior efficacy in in vivo mouse pressor response model using C57BL/6 mice, compared to our initial molecules (Nishi et al., 2019) and demonstrated ED50 values of 3.2 mg/kg and 6.8 mg/kg respectively. Our findings reported herewith, further strengthen our concept and belief in UT antagonization as a potential therapeutic approach for the management of chronic heart failure.

Pressure-overload magnitude-dependence of the anti-hypertrophic efficacy of PDE5A inhibition.

Increased myocardial cGMP, achieved by enhancing cyclase activity or impeding cGMP hydrolysis by phosphodiesterase type-5 (PDE5A), suppresses cellular and whole organ hypertrophy. The efficacy of the latter also requires cyclase stimulation and may depend upon co-activation of maladaptive signaling suppressible by cGMP-stimulated kinase (cGK-1). Thus, PDE5A inhibitors could paradoxically be more effective against higher than lower magnitudes of pressure-overload stress. To test this, mice were subjected to severe or moderate trans-aortic constriction (sTAC, mTAC) for 6 wks +/-co-treatment with oral sildenafil (SIL 200 mg/kg/d). LV mass (LVM) rose 130% after 3-wks sTAC and SIL blunted this by 50%. With mTAC, LVM rose 56% at 3 wks but was unaffected by SIL, whereas a 90% increase in LVM after 6 wks was suppressed by SIL. SIL minimally altered LV function and remodeling with mTAC until later stages that stimulated more hypertrophy and remodeling. SIL stimulated cGK-1 activity similarly at 3 and 6 wks of mTAC. However, pathologic stress signaling (e.g. calcineurin, ERK-MAPkinase) was little activated after 3-wk mTAC, unlike sTAC or later stage mTAC when activity increased and SIL suppressed it. With modest hypertrophy (3-wk mTAC), GSK3beta and Akt phosphorylation were unaltered but SIL enhanced it. However, with more severe hypertrophy (6-wk mTAC and 3-wk sTAC), both kinases were highly phosphorylated and SIL treatment reduced it. Thus, PDE5A-inhibition counters cardiac pressure-overload stress remodeling more effectively at higher than lower magnitude stress, coupled to pathologic signaling activation targetable by cGK-1 stimulation. Such regulation could impact responses of varying disease models to PDE5A inhibitors.

Mice lacking fat storage-inducing transmembrane protein 2 show improved profiles upon pressure overload-induced heart failure.

Fat storage-inducing transmembrane proteins 1 and 2 (FITM1 and FITM2, respectively) are transmembrane endoplasmic/sarcoplasmic reticulum proteins involved in lipid droplet formation. The physiological functions of FITM1 have only been reported in skeletal muscle, while those of FITM2 were analyzed using genetically engineered mice. However, their roles in the heart have not been characterized. To examine their cardiac functions, we analyzed Fitm1- or Fitm2-knockout mice. Neither constitutive Fitm1 (-/-) aged nor heart failure model mice showed significant differences in heart size or function. Fitm2 (-/-) mice exhibited embryonic death, and aged Fitm2 (+/-) mice had shortened left ventricular end-diastolic dimension, and shortened left ventricular end-systolic dimension. However, body weight and ejection fraction of Fitm2 (+/-) mice were similar to those of wild-type littermates. In the chronic heart failure models, Fitm2 (+/-) mice showed significant suppression of increased left ventricular end-diastolic dimension and reduced ejection fraction. These results suggest the involvement of Fitm2 in chronic heart failure, whereas Fitm1 have a minor effect in this context in mice.

Control of in vivo left ventricular [correction] contraction/relaxation kinetics by myosin binding protein C: protein kinase A phosphorylation dependent and independent regulation.

BACKGROUND: Cardiac myosin binding protein-C (cMyBP-C) is a thick-filament protein whose presence and phosphorylation by protein kinase A (PKA) regulates cross-bridge formation and kinetics in isolated myocardium. We tested the influence of cMyBP-C and its PKA-phosphorylation on contraction/relaxation kinetics in intact hearts and revealed its essential role in several classic properties of cardiac function. METHODS AND RESULTS: Comprehensive in situ cardiac pressure-volume analysis was performed in mice harboring a truncation mutation of cMyBP-C (cMyBP-C(t/t)) that resulted in nondetectable protein versus hearts re-expressing solely wild-type (cMyBP-C(WT:(t/t))) or mutated protein in which known PKA-phosphorylation sites were constitutively suppressed (cMyBP-C(AllP-:(t/t))). Hearts lacking cMyBP-C had faster early systolic activation, which then terminated prematurely, limiting ejection. Systole remained short at faster heart rates; thus, cMyBP-C(t/t) hearts displayed minimal rate-dependent decline in diastolic time and cardiac preload. Furthermore, prolongation of pressure relaxation by afterload was markedly blunted in cMyBP-C(t/t) hearts. All 3 properties were similarly restored to normal in cMyBP-C(WT:(t/t)) and cMyBP-C(AllP-:(t/t)) hearts, which supports independence of PKA-phosphorylation. However, the dependence of peak rate of pressure rise on preload was specifically depressed in cMyBP-C(AllP-:(t/t)) hearts, whereas cMyBP-C(t/t) and cMyBP-C(AllP-:(t/t)) hearts had similar blunted adrenergic and rate-dependent contractile reserve, which supports linkage of these behaviors to PKA-cMyBP-C modification. CONCLUSIONS: cMyBP-C is essential for major properties of cardiac function, including sustaining systole during ejection, the heart-rate dependence of the diastolic time period, and relaxation delay from increased arterial afterload. These are independent of its phosphorylation by PKA, which more specifically modulates early pressure rise rate and adrenergic/heart rate reserve.

Sustained soluble guanylate cyclase stimulation offsets nitric-oxide synthase inhibition to restore acute cardiac modulation by sildenafil.

Phosphodiesterase type 5 (PDE5) inhibitors are used to treat erectile dysfunction, and growing evidence supports potential cardiovascular utility. Their efficacy declines with reduced nitric-oxide synthase (NOS) activity common to various diseases. We tested whether direct soluble guanylate cyclase (sGC) stimulation restores in vivo cardiovascular modulation by PDE5 inhibition despite acute or chronically suppressed NOS activity. Mice (C57/Bl6; n = 62) were studied by in vivo pressure-volume analysis to assess acute modulation by the PDE5 inhibitor sildenafil (SIL; 100 microg/kg/min) of the cardiac response to isoproterenol (ISO) with or without NOS inhibition [N(omega)-nitro-L-arginine methyl ester (L-NAME)] and cotreatment by the sGC stimulator 2-[1-(2-fluorobenzyl)-1H-pyrazolo[3,4-b]pyridin-3-yl]-5-(4-morpholinyl)pyrimidine-4,6-diamine (BAY 41-8543). SIL induced mild vasodilation but no basal cardiac effects and markedly blunted ISO-stimulated contractility. Acute BAY 41-8543 at a dose lacking cardiovascular effects did not alter ISO responses. However, after acute L-NAME, SIL ceased to influence cardiovascular function, but adding BAY 41-8543 fully restored SIL effects. After 1 week of L-NAME, neither SIL nor SIL + BAY 41-8543 acutely induced vasodilation or blunted ISO responses. However, sustained BAY 41-8543 despite concurrent NOS inhibition restored the cardiovascular efficacy of SIL. The disparity between acute and chronic NOS inhibition related to diffusion of PDE5 away from myocyte z-bands coupled with reduced protein kinase G activation. Both were restored by sustained sGC costimulation. Thus, PDE5 regulation of adrenergic reserve and systemic vasodilation depends upon NOS-induced cGMP/protein kinase G and can be enhanced by sustained low-level stimulation of sGC. This may prove beneficial for enhancing the efficacy of PDE5 inhibitors in conditions with chronically reduced NOS activity.

Phosphodiesterase regulation of nitric oxide signaling.

Nitric oxide regulation of the cardiovascular system involves both cGMP-dependent and independent mechanisms. The former directly interacts with the family of catabolic phosphodiesterases (PDEs) that control cGMP levels and thus distal effects such as protein kinase G stimulation. Growing evidence supports an important role of several PDEs, including PDE1, PDE2, and PDE5, in the regulation of cGMP in both vascular smooth muscle and cardiac myocytes. These PDEs have relatively little impact on resting function, but they can potently modulate acute contractile tone in cells stimulated by external agonists such as angiotensin or catecholamines. Regulation by PDEs is compartmentalized, with selective interactions occurring between a given source of cGMP and PDE hydrolysis. PDE1 and/or PDE5 are also reportedly up-regulated in chronic disease conditions such as atherosclerosis or cardiac pressure-load stress and heart failure as well as in response to long-term exposure to nitrates. Such up-regulation is thought to contribute to vascular and cardiac pathophysiology and to drug tolerance. Recent studies utilizing selective PDE5 inhibitors support significant cross-signaling with NO-cGMP synthetic pathways that may be particularly helpful in treating certain disease states.