Differential effects of low-dose sacubitril and/or valsartan on renal disease in salt-sensitive hypertension

Potential renoprotective effects and possible underlying mechanisms of angiotensin receptor-neprilysin inhibitors in cardiorenal syndrome

Angiotensin receptor-neprilysin inhibitors (ARNIs) represent a novel class of medications characterized by their dual action on major cardiorenal regulators, specifically the renin-angiotensin system (RAS) and the natriuretic peptide (NP) system. Sacubitril/valsartan, a pioneering ARNI, has demonstrated strong antihypertensive effect as well as superior efficacy in preserving renal function compared to RAS inhibitors in heart failure patients with reduced ejection fraction. Here, we gathered evidence on the impact of sacubitril/valsartan on the preservation of kidney function in patients with cardiorenal syndrome (CRS). In particular, we present a comprehensive summary of the latest advancements and findings from clinical trials, studies, and meta-analyses on the impact of ARNIs in maintaining or improving renal function. We also discussed the pre-clinical evidence supporting the use of sacubitril/valsartan for improving renal function, along with the underlying molecular mechanisms in animal models mimicking various clinical scenarios. Altogether, the analysis of published data from both pre-clinical and clinical studies provides substantial support for the usefulness of ARNIs in enhancing renal protection in subjects with CRS.

Sacubitril/valsartan: research progress of multi-channel therapy for cardiorenal syndrome

Cardiorenal syndrome (CRS) results from complex interaction between heart and kidneys, inducing simultaneous acute or chronic dysfunction of these organs. Although its incidence rate is increasing with higher mortality in patients, effective clinical treatment drugs are currently not available. The literature suggests that renin-angiotensin-aldosterone system (RAAS) and diuretic natriuretic peptide (NP) system run through CRS. Drugs only targeting the RAAS and NPs systems are not effective. Sacubitril/valsartan contains two agents (sacubitril and valsartan) that can regulate RAAS and NPs simultaneously. In the 2017 American College of Cardiology/American Heart Association/American Heart Failure (HF) ssociation (ACC/AHA/HFSA) guideline, sacubitril/valsartan was recommended as standard therapy for HF patients. The latest research shows that Combined levosimendan and Sacubitril/Valsartan markets are protected the heart and kidney against cardiovascular syndrome in rat. However, fewer studies have reported its therapeutic efficacy in CRS treatment, and their results are inconclusive. Therefore, based on RAAS and NPs as CRS biomarkers, this paper summarizes possible pathophysiological mechanisms and preliminary clinical application effects of sacubitril/valsartan in the prevention and treatment of CRS. This will provide a pharmacological justification for expanding sacubitril/valsartan use to the treatment of CRS.

Formononetin ameliorates ferroptosis-associated fibrosis in renal tubular epithelial cells and in mice with chronic kidney disease by suppressing the Smad3/ATF3/SLC7A11 signaling

AIMS

Chronic kidney disease (CKD) is characterized by interstitial fibrosis, while limited treatment drugs are available. Ferroptosis is a newly identified process that can trigger tubular atrophy and fibrosis. The aim of this study is to investigate the effects of formononetin (FN), a bioflavonoid, on ferroptosis and renal fibrosis.

MAIN METHODS

In vivo experiments, unilateral ureteral obstruction (UUO)- and folic acid (FA, 250 mg/kg)-induced CKD models were constructed in C57BL/6 mice of 6-8 weeks old, followed by the administration with 40 mg/kg/day FN by gavage. For in vitro experiments, ferroptosis was induced with RSL3 or erastin in primary mouse renal tubular epithelial cells (TECs), followed by the addition of indicated concentrations of FN. Then, the levels of ferroptosis and fibrosis were analyzed. The translocation of Smad3, ATF3, and Nrf2 from the cytoplasm to the nucleus was checked by western blotting. The interaction of Smad3 and ATF3 was detected by Co-immunoprecipitation.

KEY FINDINGS

FN dramatically ameliorated tubular injury along with reduced expression of the profibrotic genes including α-SMA, Col1a1, and fibronectin in both two CKD mouse models and RSL3/erastin-treated TECs. Furthermore, FN administration also significantly suppressed ferroptosis, as evidenced by increased expression of SLC7A11 and GPX4, and decreased levels of 4-HNE. In mechanism, FN disrupted the interaction between Smad3 and ATF3, resulting in the blocking of their translocation from the cytoplasm to the nucleus. In addition, FN also promoted the separation of the Nrf2/Keap1 complex and enhanced Nrf2 nuclear accumulation.

SIGNIFICANCE

FN alleviates CKD by impeding ferroptosis-associated fibrosis by suppressing the Smad3/ATF3/SLC7A11 signaling and could serve as a candidate therapeutic drug for CKD.

Protective effect of sacubitril/valsartan (Entresto) on kidney function and filtration barrier injury in a porcine model of partial nephrectomy

Kidney surgery often includes organ ischaemia with a risk of acute kidney injury. The present study tested if treatment with the combined angiotensin II-angiotensin II receptor type 1 and neprilysin blocker Entresto (LCZ696, sacubitril/valsartan) protects filtration barrier and kidney function after ischaemia and partial nephrectomy (PN) in pigs. Single kidney glomerular filtration rate (GFR) by technetium-99m diethylene-triamine-pentaacetate clearance was validated (n = 6). Next, four groups of pigs were followed for 15 days (n = 24) after PN (one-third right kidney, 60 min ischaemia) + Entresto (49/51 mg/day; n = 8), PN + vehicle (n = 8), sham + Entresto (49/51 mg/day; n = 4) and sham + vehicle (n = 4). GFR, diuresis and urinary albumin were measured at baseline and from each kidney after 15 days. The sum of single-kidney GFR (right 25 ± 6 mL/min, left 31 ± 7 mL/min) accounted for the total GFR (56 ± 14 mL/min). Entresto had no effect on baseline blood pressure, p-creatinine, mid-regional pro-atrial natriuretic peptide (MR-proANP), heart rate and diuresis. After 15 days, Entresto increased GFR in the uninjured kidney (+23 ± 6 mL/min, P < .05) and reduced albuminuria from both kidneys. In the sham group, plasma MR-proANP was not altered by Entresto; it increased to similar levels 2 h after surgery with and without Entresto. Fractional sodium excretion increased with Entresto. Kidney histology and kidney injury molecule-1 in cortex tissue were not different. In conclusion, Entresto protects the filtration barrier and increases the functional adaptive response of the uninjured kidney.

Knockout of the Circadian Clock Protein PER1 (Period1) Exacerbates Hypertension and Increases Kidney Injury in Dahl Salt-Sensitive Rats

BACKGROUND

Circadian rhythms play an essential role in physiological function. The molecular clock that underlies circadian physiological function consists of a core group of transcription factors, including the protein PER1 (Period1). Studies in mice show that PER1 plays a role in the regulation of blood pressure and renal sodium handling; however, the results are dependent on the strain being studied. Using male Dahl salt-sensitive (SS) rats with global knockout of PER1 (SSPer1-/-), we aim to test the hypothesis that PER1 plays a key role in the regulation of salt-sensitive blood pressure.

METHODS

The model was generated using CRISPR/Cas9 and was characterized using radiotelemetry and measures of renal function and circadian rhythm.

RESULTS

SSPer1-/- rats had similar mean arterial pressure when fed a normal 0.4% NaCl diet but developed augmented hypertension after three weeks on a high-salt (4% NaCl) diet. Despite being maintained on a normal 12:12 light:dark cycle, SSPer1-/- rats exhibited desynchrony mean arterial pressure rhythms on a high-salt diet, as evidenced by increased variability in the time of peak mean arterial pressure. SSPer1-/- rats excrete less sodium after three weeks on the high-salt diet. Furthermore, SSPer1-/- rats exhibited decreased creatinine clearance, a measurement of renal function, as well as increased signs of kidney tissue damage. SSPer1-/- rats also exhibited higher plasma aldosterone levels.

CONCLUSIONS

Altogether, our findings demonstrate that loss of PER1 in Dahl SS rats causes an array of deleterious effects, including exacerbation of the development of salt-sensitive hypertension and renal damage.

Pathophysiology and genetics of salt-sensitive hypertension

Most hypertensive cases are primary and heavily associated with modifiable risk factors like salt intake. Evidence suggests that even small reductions in salt consumption reduce blood pressure in all age groups. In that regard, the ACC/AHA described a distinct set of individuals who exhibit salt-sensitivity, regardless of their hypertensive status. Data has shown that salt-sensitivity is an independent risk factor for cardiovascular events and mortality. However, despite extensive research, the pathogenesis of salt-sensitive hypertension is still unclear and tremendously challenged by its multifactorial etiology, complicated genetic influences, and the unavailability of a diagnostic tool. So far, the important roles of the renin-angiotensin-aldosterone system, sympathetic nervous system, and immune system in the pathogenesis of salt-sensitive hypertension have been studied. In the first part of this review, we focus on how the systems mentioned above are aberrantly regulated in salt-sensitive hypertension. We follow this with an emphasis on genetic variants in those systems that are associated with and/or increase predisposition to salt-sensitivity in humans.

Modulation of blood pressure regulatory genes in the Agtrap-Plod1 locus associated with a deletion in Clcn6

The AGTRAP-PLOD1 locus is a conserved gene cluster containing several blood pressure regulatory genes, including CLCN6, MTHFR, NPPA, and NPPB. Previous work revealed that knockout of Clcn6 on the Dahl Salt-Sensitive (SS) rat background (SS-Clcn6) resulted in lower diastolic blood pressure compared to SS-WT rats. Additionally, a recent study found sickle cell anemia patients with mutations in CLCN6 had improved survival and reduced stroke risk. We investigated whether loss of Clcn6 would delay the mortality of Dahl SS rats on an 8% NaCl (HS) diet. No significant difference in survival was found. The ability of Clcn6 to affect mRNA expression of nearby Mthfr, Nppa, and Nppb genes was also tested. On normal salt (0.4% NaCl, NS) diets, renal Mthfr mRNA and protein expression were significantly increased in the SS-Clcn6 rats. MTHFR reduces homocysteine to methionine, but no differences in circulating homocysteine levels were detected. Nppa mRNA levels in cardiac tissue from SS-Clcn6 rat in both normotensive and hypertensive conditions were significantly reduced compared to SS-WT. Nppb mRNA expression in SS-Clcn6 rats on a NS diet was also substantially decreased. Heightened Mthfr expression would be predicted to be protective; however, diminished Nppa and Nppb expression could be deleterious and by preventing or blunting vasodilation, natriuresis, and diuresis that ought to normally occur to offset blood pressure increases. The conserved nature of this genetic locus in humans and rats suggests more studies are warranted to understand how mutations in and around these genes may be influencing the expression of their neighbors.

Effects of elevation of ANP and its deficiency on cardiorenal function

Atrial natriuretic peptide (ANP), encoded by Nppa, is a vasodilatory hormone that promotes salt excretion. Genome-wide association studies identified Nppa as a causative factor of blood pressure development, and in humans, ANP levels were suggested as an indicator of salt sensitivity. This study aimed to provide insights into the effects of ANP on cardiorenal function in salt-sensitive hypertension. To address this question, hypertension was induced in SSNPPA-/- (knockout of Nppa in the Dahl Salt-Sensitive (SS) rat background) or SSWT (wild type Dahl SS) rats by a high salt diet challenge (HS, 4% NaCl for 21 days). Chronic infusion of ANP in SSWT rats attenuated the increase in blood pressure and cardiorenal damage. Overall, SSNPPA-/- strain demonstrated higher blood pressure and intensified cardiac fibrosis (with no changes in ejection fraction) compared to SSWT rats. Furthermore, SSNPPA-/- rats exhibited kidney hypertrophy and higher glomerular injury scores, reduced diuresis, and lower sodium and chloride excretion than SSWT when fed a HS diet. Additionally, the activity of epithelial Na+ channel (ENaC) was found to be increased in the collecting ducts of the SSNPPA-/- rats. Taken together, these data show promise for the therapeutic benefits of ANP and ANP-increasing drugs for treating salt-sensitive hypertension.

Potential effects and application prospect of angiotensin receptor-neprilysin inhibitor in diabetic kidney disease

Diabetic kidney disease (DKD) is one of the main causes of end-stage renal disease (ESRD) and all-cause mortality in diabetic patients, despite the extensive use of angiotensin-converting enzyme inhibitor (ACEI) and angiotensin II receptor blocker (ARB). Angiotensin receptor-neprilysin inhibitor (ARNI), combining ARB and neutral endopeptidase inhibitor (NEPI), is likely to have potential favorable effects in DKD. This review summarizes existing preclinical and clinical studies on mechanism of ARNI and its potential effects on DKD. In preclinical studies, ARNI manifested its renoprotective effects by improving natriuresis, ameliorating inflammation, oxidative stress and renal dysfunction, and slowing down glomerulosclerosis and tubulointerstitial injury of kidney, but its effect on proteinuria is still controversial. Beneficial effects of ARNI on blood glucose regulation and glycometabolism have also been reported. There are no clinical studies of ARNI that specifically focus on DKD patients so far. ARNI has application potential in DKD, but there still need clinical studies that focus on DKD patients to determine its effectiveness, safety and underlying mechanism.

Sacubitril/valsartan treatment has differential effects in modulating diabetic kidney disease in db/db mice and KKAy mice compared with valsartan treatment

Although renin-angiotensin blockade has shown beneficial outcomes in patients with diabetes, renal injury progresses in most of these patients. Therefore, there remains a need for new therapeutic targets in diabetic kidney disease. Enhancement of vasoactive peptides, such as natriuretic peptides, via neprilysin inhibition, has been a new approach. A first-in-class drug, sacubitril/valsartan (Sac/Val), a combination of the angiotensin II receptor blocker Val and neprilysin inhibitor prodrug Sac, has been shown to be more effective than renin-angiotensin blockade alone in the treatment of heart failure with reduced ejection fraction. In this study, we tested the effects of Sac/Val in diabetic kidney disease. We administered Sac/Val or Val to two type 2 diabetes mouse models, db/db mice or KKAy mice. After 3 mo of treatment, Sac/Val attenuated the progression of proteinuria, glomerulosclerosis, and podocyte loss in both models of diabetic mice. Val shared a similar improvement but to a lesser degree in some parameters compared with Sac/Val. Sac/Val but not Val decreased the blood glucose level in KKAy mice. Sac/Val exerted renal protection through coordinated effects on antioxidative stress and anti-inflammation. In both diabetic models, we revealed a new mechanism to cause inflammation, self-DNA-activated cGMP-AMP synthase-stimulator of interferon genes (cGAS-STING) signaling, which was activated in diabetic kidneys and prevented by Sac/Val or Val treatment. The present data suggest that Sac/Val has sufficient therapeutical potential to counter the pathophysiological effects of diabetic kidney disease, and its effectiveness could be better than Val alone.NEW & NOTEWORTHY The first-in-class drug sacubitril/valsartan, a combination of the angiotensin II receptor blocker valsartan and neprilysin inhibitor sacubitril, was tested for its effects in diabetic kidney disease using db/db mice and KKAy mice. We found that Sac/Val has sufficient therapeutical potential to counter the pathophysiological effects of diabetic kidney disease. We further revealed a new mechanism to cause inflammation, self-DNA-activated cGAS-STING signaling, which was activated in diabetic kidneys and prevented by sacubitril/valsartan or valsartan treatment.

Protection of kidney function and tissue integrity by pharmacologic use of natriuretic peptides and neprilysin inhibitors

With variable potencies atrial-, brain-type and c-type natriuretic peptides (NP)s, best documented for ANP and its analogues, promote sodium and water excretion, renal blood flow, lipolysis, lower blood pressure, and suppress renin and aldosterone secretion through interaction predominantly with cGMP-coupled NPR-A receptor. Infusion of especially ANP and its analogues up to 50 ng/kg/min in patients with high risk of acute kidney injury (cardiac vascular bypass surgery, intraabdominal surgery, direct kidney surgery) protects kidney function (GFR, plasma flow, medullary flow, albuminuria, renal replacement therapy, tissue injury) at short term and also long term and likely additively with the diuretic furosemide. This documents a pharmacologic potential for the pathway. Neprilysin (NEP, neutral endopeptidase) degrades NPs, in particular ANP, and angiotensin II. The drug LCZ696, a mixture of the neprilysin inhibitor sacubitril and the ANGII-AT1 receptor blocker valsartan, was FDA approved in 2015 and marketed as Entresto®. In preclinical studies of kidney injury, LCZ696 and NPs lowered plasma creatinine, countered hypoxia and oxidative stress, suppressed proinflammatory cytokines, and inhibited fibrosis. Few randomized clinical studies exist and were designed with primary cardiac outcomes. The studies showed that LCZ696/entresto stabilized and improved glomerular filtration rate in patients with chronic kidney disease. LCZ696 is safe to use concerning kidney function and stabilizes or increases GFR. In perspective, combined AT1 and neprilysin inhibition is a promising approach for long-term renal protection in addition to AT1 receptor blockers in acute kidney injury and chronic kidney disease.

Inhibition of neprilysin with sacubitril without RAS blockage aggravates renal disease in Dahl SS rats

Salt-sensitive (SS) hypertension is accompanied with severe cardiorenal complications. In this condition, elevated blood pressure (BP) resulting from salt retention is associated with counterintuitively lower levels of atrial natriuretic peptide (ANP). In plasma, ANP is degraded by the neprilysin; therefore, pharmacological inhibition of this metalloprotease (i.e., with sacubitril) can be employed to increase ANP level. We have shown earlier that sacubitril in combination with valsartan (75 μg/day each) had beneficial effects on renal function in Dahl SS rats. The goal of this study was to evaluate the effects of a higher dose of sacubitril on renal damage in this model. To induce hypertension, male Dahl SS rats were fed a 4% NaCl diet (HS) for 21 days, and were administered sacubitril (125 μg/day) or vehicle via s.c. osmotic pumps. At the end of the HS challenge, both groups exhibited similar outcomes for GFR, heart weight, plasma electrolytes, BUN, and creatinine. Sacubitril exacerbated kidney hypertrophy, but did not affect levels of renal fibrosis. We also observed aggravated glomerular lesions and increased formation of protein casts in the sacubitril-treated animals compared to controls. Thus, in Dahl SS rats, administration of sacubitril without renin-angiotensin-system blockage had adverse effects on renal disease progression, particularly in regards to glomerular damage and protein cast formation. We can speculate that while ANP levels are increased because of neprilysin inhibition, there are off-target effects of sacubitril, which are detrimental to renal function in the SS hypertensive state.

NOX4-dependent regulation of ENaC in hypertension and diabetic kidney disease

NADPH oxidase 4 (NOX4) is the most abundant NOX isoform in the kidney; however, its importance for renal function has only recently emerged. The NOX4-dependent pathway regulates many factors essential for proper sodium handling in the distal nephron. However, the functional significance of this pathway in the control of sodium reabsorption during the initiation of chronic kidney disease is not established. The goal of this study was to test Nox4-dependent ENaC regulation in two models: SS hypertension and STZ-induced type 1 diabetes. First, we showed that genetic ablation of Nox4 in Dahl salt-sensitive (SS) rat attenuated a high-salt (HS)-induced increase in epithelial Na⁺ channel (ENaC) activity in the cortical collecting duct. We also found that H₂ O₂ upregulated ENaC activity, and H₂ O₂ production was reduced in both the renal cortex and medulla in SS^Nox4-/- rats fed an HS diet. Second, in the streptozotocin model of hyperglycemia-induced renal injury ENaC activity in hyperglycemic animals was elevated in SS but not SS^Nox4-/- rats. NaCl cotransporter (NCC) expression was increased compared to healthy controls, while expression values between SS and SS^Nox4-/- groups were similar. These data emphasize a critical contribution of the NOX4-mediated pathway in maladaptive upregulation of ENaC-mediated sodium reabsorption in the distal nephron in the conditions of HS- and hyperglycemia-induced kidney injury.