Endothelin in nondiabetic chronic kidney disease: preclinical and clinical studies

Liraglutide Improves the Kidney Function in a Murine Model of Chronic Kidney Disease

BACKGROUND

Chronic kidney disease (CKD) is a global health burden, and the current treatment options only slow down the disease progression. GLP-1 receptor agonists (GLP-1 RA) have shown a renal protective effect in models of CKD; however, the mechanism behind the beneficial effect is not understood. In this study, we investigate the effect of the GLP-1 RA liraglutide in the nephrotoxic serum nephritis (NTN) CKD model. Moreover, we compare the gene expression pattern of liraglutide-treated mice to the gene expression pattern of mice treated with the angiotensin converting enzyme inhibitor, enalapril.

METHODS

The effect of liraglutide was tested in the NTN model by evaluating the glomerular filtration rate (GFR), albuminuria, mesangial expansion, renal fibrosis, and renal inflammation. Furthermore, the regulation of selected genes involved in CKD and in glomerular, cortical tubulointerstitial, and whole kidney structures was analyzed using a gene expression array on samples following laser capture microdissection.

RESULTS

Treatment with liraglutide improved CKD hallmarks including GFR, albuminuria, mesangial expansion, renal inflammation, and renal fibrosis. The gene expression revealed that both liraglutide and enalapril reversed the regulation of several fibrosis and inflammation associated genes, which are also regulated in human CKD patients. Furthermore, liraglutide and enalapril both regulated genes in the kidney involved in blood pressure control.

CONCLUSIONS

Treatment with liraglutide improved the kidney function and diminished renal lesions in NTN-induced mice. Both liraglutide and enalapril reversed the regulation of genes involved in CKD and regulated genes involved in blood pressure control.

The Role of Endothelin and Endothelin Antagonists in Chronic Kidney Disease

Background

Endothelins (ET) are a family of peptides that act as potent vasoconstrictors and pro-fibrotic growth factors. ET-1 is integral to renal and cardiovascular pathophysiology and exerts effects via autocrine, paracrine and endocrine signaling pathways tied to regulation of aldosterone, catecholamines, and angiotensin. In the kidney, ET-1 is critical to maintaining renal perfusion and controls glomerular arteriole tone and hemodynamics. It is hypothesized that ET-1 influences the progression of chronic kidney disease (CKD), and the objective of this review is to discuss the pathophysiology, and role of ET and endothelin receptor antagonists (ERAs) in CKD.

Summary

The use of ERAs in hypertensive nephropathy has the potential to decrease proteinuria, and in diabetic nephropathy has the potential to restore glycocalyx thickness, also decreasing proteinuria. Focal segmental glomerular sclerosis has no specific Food and Drug Administration-approved therapy currently, however, ERAs show promise in decreasing proteinuria and slowing tissue damage. ET-1 is a potential biomarker for autosomal dominant polycystic kidney disease progression and so it is thought that ERAs may be of some therapeutic benefit.

Key Messages

Multiple studies have shown the utility of ERAs in CKD. These agents have shown to reduce blood pressure, proteinuria, and arterial stiffness. However, more clinical trials are needed, and the results of active or recently concluded studies are eagerly awaited.

Renoprotection Provided by Additional Diuretic Treatment in Partially Nephrectomized Ren-2 Transgenic Rats Subjected to the Combined RAS and ETA Blockade

Objective

Our previous study in heterozygous Ren-2 transgenic rats (TGR) demonstrated that long-term treatment with endothelin receptor A (ET_A) blocker atrasentan added to the renin-angiotensin system (RAS) blockade had renoprotective effects in a model of chronic kidney disease (CKD) induced by partial nephrectomy. Since ET_A blockade is known to cause edema, we were interested whether diuretic treatment added to this therapy would be beneficial.

Design and Methods

Partial nephrectomy (NX) was performed at the age of 3 months in TGR rats which were subjected to: (i) RAS blockade alone (angiotensin receptor blocker losartan and angiotensin converting enzyme inhibitor trandolapril), (ii) combined RAS (losartan and trandolapril) and ET_A receptor blockade (atrasentan), or (iii) diuretic (hydrochlorothiazide) added to the combined RAS + ET_A blockade for 50 weeks following NX.

Results

At the end of the study systolic blood pressure and cardiac hypertrophy were similarly decreased in all treated groups. Survival was significantly improved by ET_A receptor blockade added to RAS blockade with no further effects of diuretic treatment. However, additional diuretic treatment combined with RAS + ET_A blockade decreased body weight and had beneficial renoprotective effects - reductions of both kidney weight and kidney damage markers. Proteinuria gradually increased in rats treated with RAS blockade alone, while it was substantially lowered by additional ET_A blockade. In rats treated with additional diuretic, proteinuria was progressively reduced throughout the experiment.

Conclusion

A diuretic added to the combined RAS and ET_A blockade has late renoprotective effects in CKD induced by partial nephrectomy in Ren-2 transgenic rats. The diuretic improved: renal function (evaluated as proteinuria and creatinine clearance), renal morphology (kidney mass, glomerular volume), and histological markers of kidney damage (glomerulosclerosis index, tubulointerstitial injury).

Renoprotective effects of ET(A) receptor antagonists therapy in experimental non-diabetic chronic kidney disease: Is there still hope for the future?

Chronic kidney disease (CKD) is a life-threatening disease arising as a frequent complication of diabetes, obesity and hypertension. Since it is typically undetected for long periods, it often progresses to end-stage renal disease. CKD is characterized by the development of progressive glomerulosclerosis, interstitial fibrosis and tubular atrophy along with a decreased glomerular filtration rate. This is associated with podocyte injury and a progressive rise in proteinuria. As endothelin-1 (ET-1) through the activation of endothelin receptor type A (ET(A)) promotes renal cell injury, inflammation, and fibrosis which finally lead to proteinuria, it is not surprising that ET(A) receptors antagonists have been proven to have beneficial renoprotective effects in both experimental and clinical studies in diabetic and non-diabetic CKD. Unfortunately, fluid retention encountered in large clinical trials in diabetic CKD led to the termination of these studies. Therefore, several advances, including the synthesis of new antagonists with enhanced pharmacological activity, the use of lower doses of ET antagonists, the addition of diuretics, plus simply searching for distinct pathological states to be treated, are promising targets for future experimental studies. In support of these approaches, our group demonstrated in adult subtotally nephrectomized Ren-2 transgenic rats that the addition of a diuretic on top of renin-angiotensin and ET(A) blockade led to a further decrease of proteinuria. This effect was independent of blood pressure which was normalized in all treated groups. Recent data in non-diabetic CKD, therefore, indicate a new potential for ET(A) antagonists, at least under certain pathological conditions.

Establishment of a model to predict the prognosis of pregnancy-related acute kidney injury

BACKGROUND

Our aim was to investigate the prognostic factors of pregnancy related acute kidney injury (PR-AKI), establish the prognosis prediction model and evaluate predictability with the model.

METHODS

Serum creatinine (SCr), placental growth factor (PLGF), endothelin-1 (ET-1), urinary kidney injury molecule-1 (KIM-1), and β2-microglobulin (β2-MG) levels in 122 patients with PR-AKI were measured at 1 month, 3 months, 6 months, and 1 year after delivery and the logistic backward stepwise regression method was used to screen the factors associated with the prognosis, establish the model to predict the prognosis of patients 1 year after delivery, and evaluate predictability with the model.

RESULTS

1) At 1 month, 3 months, 6 months, and 1 year after delivery, SCr was not significantly different in the poor prognosis group (P˃0.05); ET-1, KIM-1 and β2-MG were decreased significantly, and PLGF was significantly increased (P˂0.05); all testing indicators in the good prognosis group were significantly different and returned to normal within 1 year (P˂0.05). By comparing the two groups, there were no significant differences in SCr, PLGF and β2-MG levels at 1 month after delivery (P˃0.05), while there were significant differences in the remaining testing indicators at each time point (P˂0.05). 2) Logistic backward stepwise regression analysis showed that SCr, KIM-1, ET-1, and time were related to the prognosis of patients with PR-AKI, and the above screening indicators were used to fit the model Logit.

CONCLUSIONS

The logistic regression model fitting-effect was good, its accuracy of predicting renal injury prognosis was high. SCr, KIM-1, and ET-1 can be used for PR-AKI screening and are important for monitoring the disease condition of patients, intervention, and evaluation of prognosis.

Nephron Prorenin Receptor Deficiency Alters Renal Medullary Endothelin-1 and Endothelin Receptor Expression

The endothelin (ET) and prorenin/renin/prorenin receptor (PRR) systems have opposing physiological effects on collecting duct (CD) salt and water reabsorption. It is unknown if the CD ET and renin/PRR systems interact, hence we examined the effects of deleting CD renin or nephron PRR on CD ET system components. PRR knockout (KO) mice were polyuric and had markedly increased urinary ET-1 and inner medullary CD (IMCD) ET-1 mRNA. PRR KO mice had greatly increased IMCD ETA receptor mRNA and protein, while ETB mRNA and protein were decreased. Water loaded wild-type mice with similar polyuria as PRR KO mice had modestly increased urinary ET-1 excretion and inner medullary ET-1 mRNA, while inner medullary ETA and ETB mRNA or protein expression were unaffected. In contrast to PRR KO, CD prorenin/renin KO did not alter ET system components. Taken together, these results suggest that the nephron PRR is involved in regulating CD ET system expression, but this effect may be independent of CD-derived renin.

Cardiovascular dysfunction in sepsis at the dawn of emerging mediators

Subcellular dysfunction and impaired metabolism derived from the complex interaction of cytokines and mediators with cellular involvement are on the basis of the cardiovascular response to sepsis. The lethal consequences of an infection are intimately related to its ability to spread to other organ sites and the immune system of the host. About one century ago, William Osler (1849-1919), a Canadian physician, remarkably defined the sequelae of the host response in sepsis: "except on few occasions, the patient appears to die from the body's response to infection rather than from it." Cardiac dysfunction has received considerable attention to explain the heart failure in patients progressing from infection to sepsis, but our understanding of the processes remains limited. In fact, most concepts are linked to a mechanical concept of the sarcomeric structure, and physiological data seems to be often disconnected. Cytokines, prostanoids, and nitric oxide release are high direct impact factors, but coronary circulation and cardiomyocyte physiology also play a prominent role in modulating the effects of monocyte adhesion and infiltration. Damage-associated molecular patterns (DAMPs) and pathogen-associated molecular patterns (PAMPs) are involved in the host response. The identification of microRNAs, as well as the cyclic activation of the inflammatory cascade, has further added complexity to the scene. In this review, we delineate the current concepts of cellular dysfunction of the cardiomyocyte in the setting of sepsis and consider potential therapeutic strategies.

Endothelial dysfunction and vascular disease - a 30th anniversary update

The endothelium can evoke relaxations of the underlying vascular smooth muscle, by releasing vasodilator substances. The best-characterized endothelium-derived relaxing factor (EDRF) is nitric oxide (NO) which activates soluble guanylyl cyclase in the vascular smooth muscle cells, with the production of cyclic guanosine monophosphate (cGMP) initiating relaxation. The endothelial cells also evoke hyperpolarization of the cell membrane of vascular smooth muscle (endothelium-dependent hyperpolarizations, EDH-mediated responses). As regards the latter, hydrogen peroxide (H₂ O₂ ) now appears to play a dominant role. Endothelium-dependent relaxations involve both pertussis toxin-sensitive G_i (e.g. responses to α₂ -adrenergic agonists, serotonin, and thrombin) and pertussis toxin-insensitive G_q (e.g. adenosine diphosphate and bradykinin) coupling proteins. New stimulators (e.g. insulin, adiponectin) of the release of EDRFs have emerged. In recent years, evidence has also accumulated, confirming that the release of NO by the endothelial cell can chronically be upregulated (e.g. by oestrogens, exercise and dietary factors) and downregulated (e.g. oxidative stress, smoking, pollution and oxidized low-density lipoproteins) and that it is reduced with ageing and in the course of vascular disease (e.g. diabetes and hypertension). Arteries covered with regenerated endothelium (e.g. following angioplasty) selectively lose the pertussis toxin-sensitive pathway for NO release which favours vasospasm, thrombosis, penetration of macrophages, cellular growth and the inflammatory reaction leading to atherosclerosis. In addition to the release of NO (and EDH, in particular those due to H₂ O₂ ), endothelial cells also can evoke contraction of the underlying vascular smooth muscle cells by releasing endothelium-derived contracting factors. Recent evidence confirms that most endothelium-dependent acute increases in contractile force are due to the formation of vasoconstrictor prostanoids (endoperoxides and prostacyclin) which activate TP receptors of the vascular smooth muscle cells and that prostacyclin plays a key role in such responses. Endothelium-dependent contractions are exacerbated when the production of nitric oxide is impaired (e.g. by oxidative stress, ageing, spontaneous hypertension and diabetes). They contribute to the blunting of endothelium-dependent vasodilatations in aged subjects and essential hypertensive and diabetic patients. In addition, recent data confirm that the release of endothelin-1 can contribute to endothelial dysfunction and that the peptide appears to be an important contributor to vascular dysfunction. Finally, it has become clear that nitric oxide itself, under certain conditions (e.g. hypoxia), can cause biased activation of soluble guanylyl cyclase leading to the production of cyclic inosine monophosphate (cIMP) rather than cGMP and hence causes contraction rather than relaxation of the underlying vascular smooth muscle.

Emerging therapeutics for the treatment of diabetic nephropathy

Diabetic nephropathy (DN) is the most common pathology contributing to the development of chronic kidney disease (CKD). DN caused by hypertension and unmitigated inflammation in diabetics, renders the kidneys unable to perform normally, and leads to renal fibrosis and organ failure. The increasing global prevalence of DN has been directly attributed to rising incidences of Type II diabetes, and is now the largest non-communicable cause of death worldwide. Despite the high morbidity, successful new treatments for DN are lacking. This review seeks to provide new insight on emerging clinical candidates under investigation for the treatment of DN.

Endothelin

The endothelins comprise three structurally similar 21-amino acid peptides. Endothelin-1 and -2 activate two G-protein coupled receptors, ETA and ETB, with equal affinity, whereas endothelin-3 has a lower affinity for the ETA subtype. Genes encoding the peptides are present only among vertebrates. The ligand-receptor signaling pathway is a vertebrate innovation and may reflect the evolution of endothelin-1 as the most potent vasoconstrictor in the human cardiovascular system with remarkably long lasting action. Highly selective peptide ETA and ETB antagonists and ETB agonists together with radiolabeled analogs have accurately delineated endothelin pharmacology in humans and animal models, although surprisingly no ETA agonist has been discovered. ET antagonists (bosentan, ambrisentan) have revolutionized the treatment of pulmonary arterial hypertension, with the next generation of antagonists exhibiting improved efficacy (macitentan). Clinical trials continue to explore new applications, particularly in renal failure and for reducing proteinuria in diabetic nephropathy. Translational studies suggest a potential benefit of ETB agonists in chemotherapy and neuroprotection. However, demonstrating clinical efficacy of combined inhibitors of the endothelin converting enzyme and neutral endopeptidase has proved elusive. Over 28 genetic modifications have been made to the ET system in mice through global or cell-specific knockouts, knock ins, or alterations in gene expression of endothelin ligands or their target receptors. These studies have identified key roles for the endothelin isoforms and new therapeutic targets in development, fluid-electrolyte homeostasis, and cardiovascular and neuronal function. For the future, novel pharmacological strategies are emerging via small molecule epigenetic modulators, biologicals such as ETB monoclonal antibodies and the potential of signaling pathway biased agonists and antagonists.