Role of soluble guanylyl cyclase in renal afferent and efferent arterioles

Combined Inhibition of Phosphodiesterase-5 and -9 in Experimental Heart Failure

BACKGROUND

Intracellular second messenger cyclic guanosine monophosphate (cGMP) mediates bioactivity of the natriuretic peptides and nitric oxide, and is key to circulatory homeostasis and protection against cardiovascular disease. Inhibition of cGMP-degrading phosphodiesterases (PDEs) PDE5 and PDE9 are emerging as pharmacological targets in heart failure (HF).

OBJECTIVES

The present study investigated dual enhancement of cGMP in experimental HF by combining inhibition of PDE-5 (P5-I) and PDE-9 (P9-I).

METHODS

Eight sheep with pacing-induced HF received on separate days intravenous P5-I (sildenafil), P9-I (PF-04749982), P5-I+P9-I, and vehicle control, in counterbalanced order.

RESULTS

Compared with control, separate P5-I and P9-I significantly increased circulating cGMP concentrations in association with reductions in mean arterial pressure (MAP), left atrial pressure (LAP), and pulmonary arterial pressure (PAP), with effects of P5-I on cGMP, MAP, and PAP greater than those of P9-I. Only P5-I decreased pulmonary vascular resistance. Combination P5-I+P9-I further reduced MAP, LAP, and PAP relative to inhibition of either phosphodiesterase alone. P9-I and, especially, P5-I elevated urinary cGMP levels relative to control. However, whereas inhibition of either enzyme increased urine creatinine excretion and clearance, only P9-I induced a significant diuresis and natriuresis. Combined P5-I+P9-I further elevated urine cGMP with concomitant increases in urine volume, sodium and creatinine excretion, and clearance similar to P9-I alone, despite the greater MAP reductions induced by combination treatment.

CONCLUSIONS

Combined P5-I+P9-I amalgamated the superior renal effects of P9-I and pulmonary effects of P5-1, while concurrently further reducing cardiac preload and afterload. These findings support combination P5-I+P9-I as a therapeutic strategy in HF.

Sildenafil and Kidney Function in Heart Failure with Preserved Ejection Fraction

Key Points

Sildenafil induced an acute effect on eGFR without change in the overall eGFR slope after 24 weeks in a heart failure with preserved ejection fraction (HFpEF) cohort. N -terminal pro–brain natriuretic peptide levels and baseline diuretic use were most strongly associated with eGFR decline in this HFpEF cohort. Long-term studies are required to determine sildenafil's influence on kidney function and outcomes in HFpEF.

Background

CKD worsens the prognosis for people with heart failure with preserved ejection fraction (HFpEF). In the Phosphodiesterase-5 Inhibition to Improve Clinical Status and Exercise Capacity in Diastolic HFpEF (RELAX) trial, sildenafil decreased eGFR compared with placebo despite favorable kidney effects in preclinical models. Since acute eGFR decline precedes long-term kidney benefits for select medications, we assessed the influence of sildenafil on acute and chronic eGFR slopes.

Methods

The RELAX trial randomized 216 participants to placebo or sildenafil and assessed 24-week changes in cardiopulmonary exercise testing, cardiovascular imaging, and laboratory data. We applied linear mixed modeling to calculate the total, acute (0–12 weeks), and chronic (3–24 weeks) eGFR slopes by treatment. Using regression modeling, we assessed respective associations between eGFR slope and baseline data and clinical end points. We repeated the analyses using a binary outcome on the basis of a substantial (≥20%) decline in eGFR.

Results

The mean baseline eGFR was 60.8 ml/min per 1.73 m2, and the mean eGFR slope during follow-up was −3.21 ml/min per 1.73 m2 per year. Sildenafil did not alter total eGFR slope compared with placebo (difference +0.47 ml/min per 1.73 m2 per year, 95% confidence interval [CI], −6.63 to 7.57 ml/min per 1.73 m2 per year). Sildenafil users tended to experience a more negative acute eGFR slope (difference −3.15 ml/min per 1.73 m2 per year) and more positive chronic slope (+2.06 ml/min per 1.73 m2 per year) compared with placebo, but neither difference reached statistical significance. Baseline N -terminal pro–B-type natriuretic peptide and loop diuretic use were associated with worse eGFR trajectory regardless of treatment. Substantial eGFR decline was associated with increase in endothelin-1 and a greater risk of hospitalization or death (HR, 2.34, 95% CI, 1.21 to 4.53, P =0.01).

Conclusions

Sildenafil induced an acute effect on eGFR without change in the overall eGFR slope after 24 weeks in an HFpEF cohort, suggesting lack of long-term risk related to early reduction in eGFR after initiating treatment. Long-term studies are needed to determine the effect of sildenafil on kidney function in HFpEF.

Nitric Oxide Signalling in Descending Vasa Recta after Hypoxia/Re-Oxygenation

Reduced renal medullary oxygen supply is a key factor in the pathogenesis of acute kidney injury (AKI). As the medulla exclusively receives blood through descending vasa recta (DVR), dilating these microvessels after AKI may help in renoprotection by restoring renal medullary blood flow. We stimulated the NO-sGC-cGMP signalling pathway in DVR at three different levels before and after hypoxia/re-oxygenation (H/R). Rat DVR were isolated and perfused under isobaric conditions. The phosphodiesterase 5 (PDE5) inhibitor sildenafil (10⁻⁶ mol/L) impaired cGMP degradation and dilated DVR pre-constricted with angiotensin II (Ang II, 10⁻⁶ mol/L). Dilations by the soluble guanylyl cyclase (sGC) activator BAY 60-2770 as well as the nitric oxide donor sodium nitroprusside (SNP, 10⁻³ mol/L) were equally effective. Hypoxia (0.1% O₂) augmented DVR constriction by Ang II, thus potentially aggravating tissue hypoxia. H/R left DVR unresponsive to sildenafil, yet sGC activation by BAY 60-2770 effectively dilated DVR. Dilation to SNP under H/R is delayed. In conclusion, H/R renders PDE5 inhibition ineffective in dilating the crucial vessels supplying the area at risk for hypoxic damage. Stimulating sGC appears to be the most effective in restoring renal medullary blood flow after H/R and may prove to be the best target for maintaining oxygenation to this vulnerable area of the kidney.

Age Impairs Soluble Guanylyl Cyclase Function in Mouse Mesenteric Arteries

Endothelial dysfunction (ED) comes with age, even without overt vessel damage such as that which occurs in atherosclerosis and diabetic vasculopathy. We hypothesized that aging would affect the downstream signalling of the endothelial nitric oxide (NO) system in the vascular smooth muscle (VSM). With this in mind, resistance mesenteric arteries were isolated from 13-week (juvenile) and 40-week-old (aged) mice and tested under isometric conditions using wire myography. Acetylcholine (ACh)-induced relaxation was reduced in aged as compared to juvenile vessels. Pretreatment with L-NAME, which inhibits nitrix oxide synthases (NOS), decreased ACh-mediated vasorelaxation, whereby differences in vasorelaxation between groups disappeared. Endothelium-independent vasorelaxation by the NO donor sodium nitroprusside (SNP) was similar in both groups; however, SNP bolus application (10⁻⁶ mol L⁻¹) as well as soluble guanylyl cyclase (sGC) activation by runcaciguat (10⁻⁶ mol L⁻¹) caused faster responses in juvenile vessels. This was accompanied by higher cGMP concentrations and a stronger response to the PDE5 inhibitor sildenafil in juvenile vessels. Mesenteric arteries and aortas did not reveal apparent histological differences between groups (van Gieson staining). The mRNA expression of the α1 and α2 subunits of sGC was lower in aged animals, as was PDE5 mRNA expression. In conclusion, vasorelaxation is compromised at an early age in mice even in the absence of histopathological alterations. Vascular smooth muscle sGC is a key element in aged vessel dysfunction.

Redox regulation of hemodynamics response to diadenosine tetraphosphate an agonist of P2 receptors and renal function in diet-induced hypercholesterolemic rats

Hypercholesterolemia and oxidative stress may lead to disturbances in the renal microvasculature in response to vasoactive agents, including P2 receptors (P2R) agonists. We investigated the renal microvascular response to diadenosine tetraphosphate (Ap₄A), an agonist of P2R, in diet‐induced hypercholesteremic rats over 28 days, supplemented in the last 10 days with tempol (2 mM) or DL‐buthionine‐(S,R)‐sulfoximine (BSO, 20 mM) in the drinking water. Using laser Doppler flowmetry, renal blood perfusion in the cortex and medulla (CBP, MBP) was measured during the infusion of Ap₄A. This induced a biphasic response in the CBP: a phase of rapid decrease was followed by one of rapid increase extended for 30 min in both the normocholesterolemic and hypercholesterolemic rats. The phase of decreased CBP was not affected by tempol or BSO in either group. Early and extended increases in CBP were prevented by tempol in the hypercholesterolemia rats, while, in the normocholesterolemic rats, only the extended increase in CBP was affected by tempol; BSO prevented extended increase in CBP in normocholesterolemic rats. MBP response is not affected by hypercholesterolemia. The hypercholesterolemic rats were characterized by increased urinary albumin and 8‐isoPGF_2α excretion. Moreover, BSO increased the urinary excretion of nephrin in the hypercholesterolemic rats but, similar to tempol, did not affect the excretion of albumin in their urine. The results suggest the important role of redox balance in the extracellular nucleotide regulation of the renal vasculature and glomerular injury in hypercholesterolemia.