Murine models of uremic cardiomyopathy as a necessary tool to unravel mechanisms involved in cardiorenal syndrome.

Chronic kidney disease (CKD) and cardiovascular disease frequently run in parallel. Herein, Soppert et al. provide an interesting meta-analysis of the effects of CKD on cardiac remodeling and/or function in mice based on the model, strain, and duration. The authors sought to determine the most appropriate experimental model to unravel the specific underlying pathologic mechanisms involved in cardiac damage in CKD (single hit) or to investigate new strategies to prevent CKD-induced cardiovascular disease (multifactorial hits representing cardiovascular comorbidities of patients with CKD).

Amlexanox Exhibits Cardioprotective Effects in 5/6 Nephrectomized Rats

Abstract Cardiorenal syndrome is a life-threatening condition. The aim of the current study was to determine the cardioprotective effects of amlexanox in 5/6 nephrectomized rats. Rats were randomly assigned to three groups: sham, 5/6 nephrectomized rats, and amlexanox-treated 5/6 nephrectomized group. Amlexanox (25 mg/kg/day, i.p.) administration was started just after surgery and continued for 10 weeks. After treatment, kidney function (serum creatinine and urea) and blood pressure (systolic and diastolic) were measured. Heart weight (normalized to tibial length) and fibrosis area percentage were measured. Serum brain natriuretic peptide (BNP, heart failure marker) and cardiac levels of ß1-adrenergic receptor (ß1AR), ß-arrestin-2, phosphatidylinositol-4,5-bisphosphate (PIP2), diacylglycerol (DAG), pS473 Akt (a survival marker), and caspase-3 activity (an apoptosis marker) were also measured. The 5/6 nephrectomy caused renal impairment, cardiac fibrosis, apoptosis, and heart failure indicated by down- regulation of cardiac ß1AR down-stream signals compared with those in the sham group. Interestingly, amlexanox significantly reduced all cardiopathological changes induced after 10 weeks of 5/6 nephrectomy. Amlexanox showed potent cardiac antifibrotic and antiapoptotic effects in 5/6 nephrectomized rats, which were associated with reduced heart failure. To our knowledge, this is the first study that addresses the potent in vivo cardioprotective effects of amlexanox

Mitochondrial Dysfunction in Cardiorenal Syndrome 3: Renocardiac Effect of Vitamin C.

Cardiorenal syndrome (CRS) is a pathological link between the kidneys and heart, in which an insult in a kidney or heart leads the other organ to incur damage. CRS is classified into five subtypes, and type 3 (CRS3) is characterized by acute kidney injury as a precursor to subsequent cardiovascular changes. Mitochondrial dysfunction and oxidative and nitrosative stress have been reported in the pathophysiology of CRS3. It is known that vitamin C, an antioxidant, has proven protective capacity for cardiac, renal, and vascular endothelial tissues. Therefore, the present study aimed to assess whether vitamin C provides protection to heart and the kidneys in an in vivo CRS3 model. The unilateral renal ischemia and reperfusion (IR) protocol was performed for 60 min in the left kidney of adult mice, with and without vitamin C treatment, immediately after IR or 15 days after IR. Kidneys and hearts were subsequently collected, and the following analyses were conducted: renal morphometric evaluation, serum urea and creatinine levels, high-resolution respirometry, amperometry technique for NO measurement, gene expression of mitochondrial dynamic markers, and NOS. The analyses showed that the left kidney weight was reduced, urea and creatinine levels were increased, mitochondrial oxygen consumption was reduced, NO levels were elevated, and Mfn2 expression was reduced after 15 days of IR compared to the sham group. Oxygen consumption and NO levels in the heart were also reduced. The treatment with vitamin C preserved the left kidney weight, restored renal function, reduced NO levels, decreased iNOS expression, elevated constitutive NOS isoforms, and improved oxygen consumption. In the heart, oxygen consumption and NO levels were improved after vitamin C treatment, whereas the three NOS isoforms were overexpressed. These data indicate that vitamin C provides protection to the kidneys and some beneficial effects to the heart after IR, indicating it may be a preventive approach against cardiorenal insults.

Entresto protected the cardiomyocytes and preserved heart function in cardiorenal syndrome rat fed with high-protein diet through regulating the oxidative stress and Mfn2-mediated mitochondrial functional integrity.

This study tested the hypothesis that Entresto (En) therapy protected the cardiomyocytes and heart function in cardiorenal syndrome (CRS) rats fed with high-protein diet (HPD) through regulating the oxidative-stress and Mfn2-mediated mitochondrial functional integrity. En (12.5 µM for the in-vitro study) protected the H9C2-cells against H2O2-induced cell apoptosis, whereas stepwise-increased H2O2 concentrations induced a significant increase in protein expressions of Mfn2/phosphorylated (p)-DRP1/mitochondrial-Bax in H9C2-cells. En downregulated H2O2-induced mitochondrial fission/upregulated mitochondrial fusion and deletion of Mfn2 gene (i.e., shMfn2) to significantly reduce H2O2-induced ROS production. En significantly suppressed and shMfn2 further significantly suppressed both H2O2-reduced mitochondrial-membrane potential and H2O2-induced ROS production/cell apoptosis/mitochondrial damage/mitochondrial-Bax released from mitochondria in H9C2 cells. En significantly reduced protein expressions of Mfn2 and p-DRP1. Additionally, En significantly suppressed and shMfn2 further significantly suppressed the protein expressions of mitochondrial-damaged (DRP1)/oxidative-stress (NOX-1/NOX-2)/apoptosis (mitochondrial-Bax/caspase-3/PARP)/autophagic (LC3B-II/LC3B-I) biomarkers (all p < 0.01). Rats were categorized into group 1 [sham-control + high-protein-diet (HPD)], group 2 (CRS + HPD) and group 3 (CRS+ HPD + En/100 mg/kg/day). By day 63 after CRS induction, the LVEF was significantly lower in group 3 and more significantly lower in group 2 than in group 1, whereas the protein expressions of oxidative-stress (NOX-1/NOX-2/p22phox/oxidized protein)/apoptotic (mitochondrial-Bax/caspase-3/PARP), fibrotic (Smad-3/TGF-ß), autophagic (Beclin-1/Atg5/ratio of LC3B-II/LC3B-I) and mitochondrial-damaged (DRP1/cyclophilin-D/cytosolic-cytochrome-C) biomarkers exhibited an opposite pattern of LVEF among the groups. Downregulation of Mfn2 by En or shMfn2 in cardiomyocytes avoided H2O2 damage and En improved the cardiac function in HPD-feeding CRS rat via adjusting Mfn2-mediated mitochondrial functional integrity.

Apela inhibits systemic and renal inflammatory reactions in mice with type I cardiorenal syndrome.

This study investigated the effect of apela on renal function and anti-inflammatory effect on whole body and kidney tissue in mice with type I cardiorenal syndrome (CRS). The murine type I CRS model was established and apela was subcutaneously infused for two weeks. Cardiac and renal functions were evaluated by echocardiography and blood biochemistry, respectively. The systemic and renal inflammatory responses were examined with molecular biological and histological methods. Human renal glomerular endothelial cells (RGECs) were used to evaluate the adhesion effect of monocytes in vitro. Compared to mice from the control group (CRS + vehicle), the plasma levels of N-terminal pro-brain natriuretic peptide, blood urea nitrogen and creatinine were significantly decreased, while the mean left ventricular ejection fraction was increased in apela-treated CRS mice at the 4th week. The expression of monocyte chemoattractant protein-1 (MCP-1) and tumor necrosis factor-α (TNF-α) in the circulation and kidney was decreased in apela-treated mice compared with control mice, and apela improved cardio-renal pathology in mice with type I CRS. Additionally, Apela significantly suppressed the expression of MCP-1, TNF-α, intercellular adhesion molecule-1 and vascular intercellular adhesion molecule-1 in RGECs induced by angiotensin II (Ang II), and inhibited the promoting effect of Ang II on the adhesion of THP-1 cells to RGECs. Western blot results showed that the expression of phosphorylated nuclear factor kappa B (phospho-NFκB) in CRS mice was increased, but the expression of phospho-NFκB was down-regulated after apela treatment. Furthermore, apela significantly inhibited the Ang II-mediated increase in phospho-NFκB expression in RGECs in vitro, but the administration of an apelin peptide jejunum receptor (APJ) inhibitor blocked the inhibitory effect of apela. This study revealed that apela improves cardiorenal function and reduces systemic and renal inflammatory response in type I CRS mice and the apela/APJ system may alleviate renal inflammatory responses by inhibiting the NFκB signalling pathway.

Urine peptidome analysis in cardiorenal syndrome reflects molecular processes.

The cardiorenal syndrome (CRS) is defined as the confluence of heart-kidney dysfunction. This study investigates the molecular differences at the level of the urinary peptidome between CRS patients and controls and their association to disease pathophysiology. The urinary peptidome of CRS patients (n = 353) was matched for age and sex with controls (n = 356) at a 1:1 ratio. Changes in the CRS peptidome versus controls were identified after applying the Mann-Whitney test, followed by correction for multiple testing. Proteasix tool was applied to investigate predicted proteases involved in CRS-associated peptide generation. Overall, 559 differentially excreted urinary peptides were associated with CRS patients. Of these, 193 peptides were specifically found in CRS when comparing with heart failure and chronic kidney disease urinary peptide profiles. Proteasix predicted 18 proteases involved in > 1% of proteolytic cleavage events including multiple forms of MMPs, proprotein convertases, cathepsins and kallikrein 4. Forty-four percent of the cleavage events were produced by 3 proteases including MMP13, MMP9 and MMP2. Pathway enrichment analysis supported that ECM-related pathways, fibrosis and inflammation were represented. Collectively, our study describes the changes in urinary peptides of CRS patients and potential proteases involved in their generation, laying the basis for further validation.

Fibrosis, the Bad Actor in Cardiorenal Syndromes: Mechanisms Involved.

Cardiorenal syndrome is a term that defines the complex bidirectional nature of the interaction between cardiac and renal disease. It is well established that patients with kidney disease have higher incidence of cardiovascular comorbidities and that renal dysfunction is a significant threat to the prognosis of patients with cardiac disease. Fibrosis is a common characteristic of organ injury progression that has been proposed not only as a marker but also as an important driver of the pathophysiology of cardiorenal syndromes. Due to the relevance of fibrosis, its study might give insight into the mechanisms and targets that could potentially be modulated to prevent fibrosis development. The aim of this review was to summarize some of the pathophysiological pathways involved in the fibrotic damage seen in cardiorenal syndromes, such as inflammation, oxidative stress and endoplasmic reticulum stress, which are known to be triggers and mediators of fibrosis.

Telmisartan ameliorates cardiac fibrosis and diastolic function in cardiorenal heart failure with preserved ejection fraction.

Chronic kidney disease (CKD) is a major contributor to the development of heart failure with preserved ejection fraction (HFpEF), whereas the underlying mechanism of cardiorenal HFpEF is still elusive. The aim of this study was to investigate the role of cardiac fibrosis in a rat model of cardiorenal HFpEF and explore whether treatment with Telmisartan, an inhibitor of renin-angiotensin-aldosterone system (RAAS), can ameliorate cardiac fibrosis and preserve diastolic function in cardiorenal HFpEF. Male rats were subjected to 5/6 subtotal nephrectomy (SNX) or sham operation (Sham), and rats were allowed four weeks to recover and form a stable condition of CKD. Telmisartan or vehicle was then administered p.o. (8 mg/kg/d) for 12 weeks. Blood pressure, brain natriuretic peptide (BNP), echocardiography, and cardiac magnetic resonance imaging were acquired to evaluate cardiac structural and functional alterations. Histopathological staining, real-time polymerase chain reaction (PCR) and western blot were performed to evaluate cardiac remodeling. SNX rats showed an HFpEF phenotype with increased BNP, decreased early to late diastolic transmitral flow velocity (E/A) ratio, increased left ventricular (LV) hypertrophy and preserved ejection fraction (EF). Pathology revealed increased cardiac fibrosis in cardiorenal HFpEF rats compared with the Sham group, while chronic treatment with Telmisartan significantly decreased cardiac fibrosis, accompanied by reduced markers of fibrosis (collagen I and collagen III) and profibrotic cytokines (α-smooth muscle actin, transforming growth factor-ß1, and connective tissue growth factor). In addition, myocardial inflammation was decreased after Telmisartan treatment, which was in a linear correlation with cardiac fibrosis. Telmisartan also reversed LV hypertrophy and E/A ratio, indicating that Telmisartan can improve LV remodeling and diastolic function in cardiorenal HFpEF. In conclusion, cardiac fibrosis is central to the pathology of cardiorenal HFpEF, and RAAS modulation with Telmisartan is capable of alleviating cardiac fibrosis and preserving diastolic dysfunction in this rat model.

HE4 Predicts Progressive Fibrosis and Cardiovascular Events in Patients With Dilated Cardiomyopathy.

Background Cardiac fibrosis plays a crucial role in the pathogenesis of dilated cardiomyopathy (DCM). HE4 (human epididymis protein 4) is a secretory protein expressed in activated fibroblasts that exacerbates tissue fibrosis. In the present study, we investigated the clinical utility of HE4 measurement in patients with DCM and its pathophysiological role in preclinical experiments in vivo and in vitro. Methods and Results We measured serum HE4 levels of 87 patients with DCM. Endomyocardial biopsy expressed severe fibrosis only in the high HE4 group (P<0.0001). Echocardiography showed that left ventricular end-diastolic diameter tends to decrease over time (58±7.3 to 51±6.6 mm; P<0.0001) in the low HE4 group (<59.65 pmol/L [median value]). HE4 was significantly associated with risk reduction of mortality and cardiovascular hospitalization in multivariate Cox model. In vivo, HE4 was highly expressed in kidney and lung tissue of mouse, and scarcely expressed in heart. In genetically induced DCM mouse model, HE4 expression increased in kidney but not in heart and lung. In vitro, supernatant from HE4-transfected human embryonic kidney 293T cells enhanced transdifferentiation of rat neonatal fibroblasts and increased expression of fibrosis-related genes, and this was accompanied by the activation of extracellular signal-regulated kinase signaling in cardiac fibroblasts. Treatment with an inhibitor of upstream signal of extracellular signal-regulated kinase or a neutralizing HE4 antibody canceled the profibrotic properties of HE4. Conclusions HE4 functions as a secretory factor, activating cardiac fibroblasts, thereby inducing cardiac interstitial fibrosis. HE4 could be a promising biomarker for assessing ongoing fibrosis and a novel therapeutic target in DCM. Registration URL: https://upload.umin.ac.jp/cgi-open-bin/ctr; Unique identifier: UMIN000043062.

Renal protective effects and mechanisms of the angiotensin receptor-neprilysin inhibitor LCZ696 in mice with cardiorenal syndrome.

AIMS: This study investigated the renal protective effects and mechanisms of angiotensin receptor-neprilysin inhibitor LCZ696 in mice with cardiorenal syndrome. MATERIALS AND METHODS: Mice were divided into abdominal aortic ligation alone, or treatment with LCZ696 or valsartan, whilst those undergoing sham surgery served as controls. Rat proximal renal tubular epithelial cells from the NRK-52E line were treated with control solution, LCZ696 or valsartan, in the presence or absence of Ang II for 24 h. KEY FINDINGS: Compared to controls, abdominal aortic ligation significantly increased plasma NT-proBNP and urine neutrophil gelatinase-associated lipocalin (NGAL), which were associated with reduced renal length and velocity time integral on ultrasonography. Histology revealed wrinkling of the glomerular capillary wall and sclerosis of the glomerulus, dilatation of the Bowman's capsule, accompanied by diffuse renal tubular atrophy and fibrosis, accompanied by lower kidney index and higher percentage area of fibrosis. Increases in NGAL and decreased ANP protein and mRNA expression levels were observed. These abnormalities were significantly prevented by LCZ696 and to a lesser extent by valsartan. Cellular experiments demonstrated a central role of Ang II/transforming growth factor-ß1/Smad2/3/connective tissue growth factor-dependent signaling leading to type IV collagen deposition. This upregulation was reversed by LCZ696 in a greater extent than valsartan treatment alone, accompanied by a significant improvement in NGAL. SIGNIFICANCE: LCZ696 can reduce kidney injury to a level beyond valsartan therapy alone in mice with cardiorenal syndrome, which can be speculated by effects on epithelial-mesenchymal transition and fibrosis through downregulating the TGF-ß1/Smad2/3/CTGF/Collagen IV pathway.

TWEAK-Fn14 as a common pathway in the heart and the kidneys in cardiorenal syndrome.

There is a complex relationship between cardiac and renal disease, often referred to as the cardiorenal syndrome. Heart failure adversely affects kidney function, and both acute and chronic kidney disease are associated with structural and functional changes to the myocardium. The pathological mechanisms and contributing interactions that surround this relationship remain poorly understood, limiting the opportunities for therapeutic intervention. The cytokine tumor necrosis factor-like weak inducer of apoptosis (TWEAK) and its receptor, fibroblast growth factor-inducible 14 (Fn14), are abundantly expressed in injured kidneys and heart. The TWEAK-Fn14 axis promotes responses that drive tissue injury such as inflammation, proliferation, fibrosis, and apoptosis, while restraining the expression of tissue protective factors such as the anti-aging factor Klotho and the master regulator of mitochondrial biogenesis peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α). High levels of TWEAK induce cardiac remodeling, and promote inflammation, tubular and podocyte injury and death, fibroblast proliferation, and, ultimately, renal fibrosis. Accordingly, targeting the TWEAK-Fn14 axis is protective in experimental kidney and heart disease. TWEAK has also emerged as a biomarker of kidney damage and cardiovascular outcomes and has been successfully targeted in clinical trials. In this review, we update our current knowledge of the roles of the TWEAK-Fn14 axis in cardiovascular and kidney disease and its potential contribution to the cardiorenal syndrome. © 2021 The Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Excessive fibroblast growth factor 23 promotes renal fibrosis in mice with type 2 cardiorenal syndrome.

Cardiorenal syndrome (CRS) has a high mortality, but its pathogenesis remains elusive. Fibroblast growth factor 23 (FGF23) is increased in both renal dysfunction and cardiac dysfunction, and FGF receptor 4 (FGFR4) has been identified as a receptor for FGF23. Deficiency of FGF23 causes growth retardation and shortens the lifespan, but it is unclear whether excess FGF23 is detrimental in CRS. This study sought to investigate whether FGF23 plays an important role in CRS-induced renal fibrosis. A mouse model of CRS was created by surgical myocardial infarction for 12 weeks. CRS mice showed a significant increase of circulatory and renal FGF23 protein levels, as well as an upregulation of p-GSK, active-ß-catenin, TGF-ß, collagen I and vimentin, a downregulation of renal Klotho expression and induction of cardiorenal dysfunction and cardiorenal fibrosis. These changes were enhanced by cardiac overexpression of FGF23 and attenuated by FGF receptor blocker PD173074 or ß-catenin blocker IGC001. In fibroblasts (NRK-49F), expression of FGFR4 rather than Klotho was detected. Recombinant FGF23 upregulated the expression of p-GSK, active-ß-catenin, TGF-ß, collagen I and vimentin proteins. These changes were attenuated by FGFR4 blockade with BLU9931 or ß-catenin blockade with IGC001. We concluded that FGF23 promotes CRS-induced renal fibrosis mediated by partly activating FGFR4/ß-catenin signaling pathway.

Uremic Toxins and Vascular Calcification-Missing the Forest for All the Trees.

The cardiorenal syndrome relates to the detrimental interplay between the vascular system and the kidney. The uremic milieu induced by reduced kidney function alters the phenotype of vascular smooth muscle cells (VSMC) and promotes vascular calcification, a condition which is strongly linked to cardiovascular morbidity and mortality. Biological mechanisms involved include generation of reactive oxygen species, inflammation and accelerated senescence. A better understanding of the vasotoxic effects of uremic retention molecules may reveal novel avenues to reduce vascular calcification in CKD. The present review aims to present a state of the art on the role of uremic toxins in pathogenesis of vascular calcification. Evidence, so far, is fragmentary and limited with only a few uremic toxins being investigated, often by a single group of investigators. Experimental heterogeneity furthermore hampers comparison. There is a clear need for a concerted action harmonizing and standardizing experimental protocols and combining efforts of basic and clinical researchers to solve the complex puzzle of uremic vascular calcification.

IRF1-mediated downregulation of PGC1α contributes to cardiorenal syndrome type 4.

Cardiorenal syndrome type 4 (CRS4) is a common complication of chronic kidney disease (CKD), but the pathogenic mechanisms remain elusive. Here we report that morphological and functional changes in myocardial mitochondria are observed in CKD mice, especially decreases in oxidative phosphorylation and fatty acid metabolism. High phosphate (HP), a hallmark of CKD, contributes to myocardial energy metabolism dysfunction by downregulating peroxisome proliferator-activated receptor gamma coactivator 1 alpha (PGC1α). Furthermore, the transcriptional factor interferon regulatory factor 1 (IRF1) is revealed as the key molecule upregulated by HP through histone H3K9 acetylation, and responsible for the HP-mediated transcriptional inhibition of PGC1α by directly binding to its promoter region. Conversely, restoration of PGC1α expression or genetic knockdown of IRF1 significantly attenuates HP-induced alterations in vitro and in vivo. These findings demonstrate that IRF1-PGC1α axis-mediated myocardial energy metabolism remodeling plays a crucial role in the pathogenesis of CRS4.

Cardiac Remodeling in Chronic Kidney Disease.

Cardiac remodeling occurs frequently in chronic kidney disease patients and affects quality of life and survival. Current treatment options are highly inadequate. As kidney function declines, numerous metabolic pathways are disturbed. Kidney and heart functions are highly connected by organ crosstalk. Among others, altered volume and pressure status, ischemia, accelerated atherosclerosis and arteriosclerosis, disturbed mineral metabolism, renal anemia, activation of the renin-angiotensin system, uremic toxins, oxidative stress and upregulation of cytokines stress the sensitive interplay between different cardiac cell types. The fatal consequences are left-ventricular hypertrophy, fibrosis and capillary rarefaction, which lead to systolic and/or diastolic left-ventricular failure. Furthermore, fibrosis triggers electric instability and sudden cardiac death. This review focuses on established and potential pathophysiological cardiorenal crosstalk mechanisms that drive uremia-induced senescence and disease progression, including potential known targets and animal models that might help us to better understand the disease and to identify novel therapeutics.

Higenamine Improves Cardiac and Renal Fibrosis in Rats With Cardiorenal Syndrome via ASK1 Signaling Pathway.

The pathogenesis of cardiorenal syndrome (CRS) is very complex, and currently there is no effective treatment for CRS. Higenamine (HI) has been shown to improve cardiac function in rats with heart failure. However, the role of higenamine in CRS remains unknown. Here, in vitro, higenamine treatment markedly reduced neonatal rat cardiac fibroblast collagen synthesis and inhibited neonatal rat cardiac myocyte hypertrophy. In our study, a rat model of type 2 CRS was induced by left anterior descending coronary artery ligation combined with 5/6 subtotal nephrectomy (STNx). Higenamine treatment decreased serum creatinine (Scr), blood urea nitrogen, and brain natriuretic peptide levels and was capable of improving left ventricular remodeling and systolic function in CRS rats, accompanied with decreased expression of transforming growth factor-ß1 (TGF-ß1), α-smooth muscle actin (α-SMA) and collagen I (Col1A1). Moreover, higenamine significantly inhibited the protein expression of phosphorylated apoptosis signal-regulated kinase 1 (p-ASK1) and downstream mitogen-activated protein kinases (MAPK) (ERK, P38)/NF-κB in cardiorenal tissues of CRS rats and neonatal rat cardiac fibroblast/neonatal rat cardiac myocyte cells. Our study demonstrated that higenamine improved cardiorenal function in CRS rats and attenuated heart and kidney fibrosis possibly via targeting ASK1/MAPK (ERK, P38)/NF-κB signaling pathway. This finding extends our knowledge on the role of higenamine in cardiorenal fibrosis, providing a potential target to prevent the progression of CRS.

Melatonin fine-tunes intracellular calcium signals and eliminates myocardial damage through the IP3R/MCU pathways in cardiorenal syndrome type 3.

Cardiorenal syndrome type-3 (CRS-3) is characterized by acute cardiac injury induced by acute kidney injury. Here, we investigated the causes of CRS-3 by analyzing cardiac function after renal ischemia-reperfusion injury (IRI) using echocardiography and evaluation of pro-inflammatory markers, calcium balance, mitochondrial function, and cardiomyocyte death. Our results show that renal IRI reduces cardiac diastolic function associated with cardiomyocyte death and inflammatory responses. Renal IRI also disrupts cardiomyocyte energy metabolism, induces calcium overload, and impairs mitochondrial function, as evidenced by reduced mitochondrial membrane potential and increased mitochondrial fission. Further, renal IRI induces phosphorylation of inositol 1,4,5-trisphosphate receptor (IP3R) and expression of mitochondrial calcium uniporter (MCU), resulting in cytoplasmic calcium overload and mitochondrial calcium accumulation. Pretreatment with melatonin attenuates renal IRI-mediated cardiac damage by maintaining myocardial diastolic function and reducing cardiomyocyte death. Melatonin also inhibits IP3R phosphorylation and MCU expression, thereby alleviating cytoplasmic and mitochondrial calcium overload. Blockade of IP3R has similar cardioprotective effects, whereas MCU activation abrogates the melatonin-mediated cardioprotection. These results show that the negative effects of renal IRI on myocardial viability and cardiac function are caused by induced IP3R phosphorylation, MCU upregulation, and calcium overload. Melatonin protects cardiac function against CRS-3 by suppressing IP3R-MCU signaling.

The guanylate cyclase C agonist linaclotide ameliorates the gut-cardio-renal axis in an adenine-induced mouse model of chronic kidney disease.

BACKGROUND: Cardiorenal syndrome is a major cause of mortality in patients with chronic kidney disease (CKD). However, the involvement of detrimental humoral mediators in the pathogenesis of cardiorenal syndrome is still controversial. Trimethylamine-N-oxide (TMAO), a hepatic metabolic product of trimethylamine generated from dietary phosphatidylcholine or carnitine derived by the gut microbiota, has been linked directly with progression of cardiovascular disease and renal dysfunction. Thus, targeting TMAO may be a novel strategy for the prevention of cardiovascular disease and chronic kidney disease. METHODS: Linaclotide, a guanylate cyclase C agonist, was administered to adenine-induced renal failure (RF) mice and changes in renal function and levels of gut-derived uremic toxins, as well as the gut microbiota community, were analyzed using metabolomic and metagenomic methods to reveal its cardiorenal effect. RESULTS: Linaclotide decreased the plasma levels of TMAO at a clinically used low dose of 10 µg/kg in the adenine-induced RF mouse model. At a high concentration of 100 µg/kg, linaclotide clearly improved renal function and reduced the levels of various uremic toxins. A reduction in TMAO levels following linaclotide treatment was also observed in a choline-fed pro-atherosclerotic model. Linaclotide ameliorated renal inflammation and fibrosis and cardiac fibrosis, as well as decreased the expression of collagen I, transforming growth factor-ß, galectin-3 (Gal-3) and ST2 genes. Plasma levels of Gal-3 and ST2 were also reduced. Because exposure of cardiomyocytes to TMAO increased fibronectin expression, these data suggest that linaclotide reduced the levels of TMAO and various uremic toxins and may result in not only renal, but also cardiac, fibrosis. F4/80-positive macrophages were abundant in small intestinal crypts in RF mice, and this increased expression was decreased by linaclotide. Reduced colonic claudin-1 levels were also restored by linaclotide, suggesting that linaclotide ameliorated the 'leaky gut' in RF mice. Metagenomic analysis revealed that the microbial order Clostridiales could be responsible for the change in TMAO levels. CONCLUSION: Linaclotide reduced TMAO and uremic toxin levels and could be a powerful tool for the prevention and control of the cardiorenal syndrome by modification of the gut-cardio-renal axis.

The acute kidney injury to chronic kidney disease transition in a mouse model of acute cardiorenal syndrome emphasizes the role of inflammation.

Acute cardiorenal syndrome is a common complication of acute cardiovascular disease. Studies of acute kidney injury (AKI) to chronic kidney disease (CKD) transition, including patients suffering acute cardiovascular disease, report high rates of CKD development. Therefore, acute cardiorenal syndrome associates with CKD, but no study has established causation. To define this we used a murine cardiac arrest (CA) and cardiopulmonary resuscitation (CPR) model or sham procedure on male mice. CA was induced with potassium chloride while CPR consisted of chest compressions and epinephrine eight minutes later. Two weeks after AKI was induced by CA/CPR, the measured glomerular filtration rate (GFR) was not different from sham. However, after seven weeks the mice developed CKD, recapitulating clinical observations. One day, and one, two, and seven weeks after CA/CPR, the GFR was measured, and renal tissue sections were evaluated for various indices of injury and inflammation. One day after CA/CPR, acute cardiorenal syndrome was indicated by a significant reduction of the mean GFR (649 in sham, vs. 25 µL/min/100g in CA/CPR animals), KIM-1 positive tubules, and acute tubular necrosis. Renal inflammation developed, with F4/80 positive and CD3-positive cells infiltrating the kidney one day and one week after CA/CPR, respectively. Although there was functional recovery with normalization of GFR two weeks after CA/CPR, deposition of tubulointerstitial matrix proteins α-smooth muscle actin and fibrillin-1 progressed, along with a significantly reduced mean GFR (623 in sham vs. 409 µL/min/100g in CA/CPR animals), proteinuria, increased tissue transforming growth factor-ß, and fibrosis establishing the development of CKD seven weeks after CA/CPR. Thus, murine CA/CPR, a model of acute cardiorenal syndrome, causes an AKI-CKD transition likely due to prolonged renal inflammation.