The Role of Oxidative Stress as a Mechanism in the Pathogenesis of Acute Heart Failure in Acute Kidney Injury

Despite a large amount of research on synchronous and mutually induced kidney and heart damage, the basis of the disease is still not fully clarified. Healthy mitochondria are essential for normal kidney and heart function. Mitochondrial dysfunction occurs when the clearance or process of generation and fragmentation of mitochondria is disturbed. The kidney is the second organ after the heart in terms of the number of mitochondria. Kidney tubules are rich in mitochondria due to the high energy requirements for absorption of large amounts of ultrafiltrate and dissolved substances. The place of action of oxidative stress is the influence on the balance in the production and breakdown of the mitochondrial reactive oxygen species. A more precise determination of the place and role of key factors that play a role in the onset of the disease is necessary for understanding the nature of the onset of the disease and the creation of therapy in the future. This underscores the urgent need for further research. The narrative review integrates results found in previously performed studies that have evaluated oxidative stress participation in cardiorenal syndrome type 3.

Biomarkers in cardiorenal syndrome, a potential use in precision medicine

Cardiorenal syndrome refers to the interrelated dysfunction of the heart or kidney resulting in a cascade of feedback mechanisms, hemodynamic, neurohormonal, and immunological and/or biochemical feedback pathways causing damage in the other organ. Cardiorenal syndrome is categorized into five clinical subtypes depending on the perceived primary precipitant of organ injury and is associated with high morbidity and mortality. Therefore, the development of tools for the earliest identification of cardiorenal syndrome in hospitalized patients is of extremely high significance to ameliorate the prognosis and outcome of these patients. There is increasing interest in identifying molecules serving as biomarkers, reflecting hemodynamic changes, heart and kidney damage and/or dysfunction and oxidative stress-induced cell damage or changes in the extracellular matrix of both the heart and kidneys. Biomarkers provide important insights into the pathophysiology of cardiorenal syndrome and are invaluable tools to predict the decrease in renal function during cardiac dysfunction and vice versa. Based on the pathophysiological mechanisms of cardiorenal syndrome, we reviewed and evaluated the available literature on serum and urinary biomarkers as predictors of kidney and/or heart injury. In addition, heart- and kidney-specific biomarkers were also evaluated based on their reference to kidney and cardiac (dys)function respectively, and whether they would provide any prediction and prognostication of cardiorenal syndrome. In this article, we discuss the current knowledge on the pathophysiology of different types of cardiorenal syndrome, examine the clinical utility of candidate biomarkers in the early diagnosis of cardiorenal syndrome, and guide treatment by evaluating the respective roles of the involved pathophysiological pathways.

Cardiorenal Syndrome Type 3 Review

The management of patients with complex comorbidity involving several organ systems can use an approach focused on each organ system independently or can use an approach trying to integrate various injuries and dysfunction into a single syndrome. Cardiorenal syndromes can develop with an initial injury to either the heart or kidney and then sequential involvement of the second organ. This can occur acutely or chronically. Cardiorenal syndrome type 3 is defined by acute renal injury with subsequent cardiac injury and/or dysfunction. Studies on these patients must use strict inclusion criteria. Pavan reported information on 100 patients with acute kidney injury in India to determine the frequency of cardiorenal syndrome type 3. He excluded patients with significant prior comorbidity. The most frequent causes of acute kidney injury in these patients were drug toxicity, gastroenteritis with volume contraction, and obstetrical complications. This study included 100 patients with acute kidney injury, and 29 developed cardiorenal syndrome type 3. Important outcomes included frequent mortality and chronic renal failure. Other studies have reported that cardiorenal syndrome type 3 occurs relatively infrequently. The analysis of large data bases has demonstrated that the development of acute kidney injury in hospitalized patients has important consequences, including the development of heart failure and increased mortality, but the complexity of these cohorts makes it difficult to determine the time course for the development of multisystem disorders. The pathogenesis of cardiorenal syndrome type 3 involves mitochondrial dysfunction, immune dysregulation, and ischemia-reperfusion. Cardiac events occur secondary to fluid overload, electrolyte disorders, and uremic toxins. These patients need increased attention during hospitalization and outpatient management in an effort to slow the progression of the primary disorder and treat complications.

New Insight in Cardiorenal Syndrome: From Biomarkers to Therapy

Cardiorenal syndrome consists in the coexistence of acute or chronic dysfunction of heart and kidneys resulting in a cascade of feedback mechanisms and causing damage to both organs associated with high morbidity and mortality. In the last few years, different biomarkers have been investigated with the aim to achieve an early and accurate diagnosis of cardiorenal syndrome, to provide a prognostic role and to guide the development of targeted pharmacological and non-pharmacological therapies. In such a context, sodium-glucose cotransporter 2 (SGLT2) inhibitors, recommended as the first-line choice in the management of heart failure, might represent a promising strategy in the management of cardiorenal syndrome due to their efficacy in reducing both cardiac and renal outcomes. In this review, we will discuss the current knowledge on the pathophysiology of cardiorenal syndrome in adults, as well as the utility of biomarkers in cardiac and kidney dysfunction and potential insights into novel therapeutics.

Beyond the Cardiorenal Syndrome: Pathophysiological Approaches and Biomarkers for Renal and Cardiac Crosstalk

Cardiorenal syndrome encompasses complex multifactorial facets and carries significant morbidity and mortality worldwide. The bi-directional relationship between the heart and kidneys, where dysfunction in one organ worsens the function of the other, has been the leading motor for research in the last few years. In the pathophysiological process, small noncoding RNAs, epigenetics, vascular growth factors, oxidative stress, hemodynamic factors, and biomarkers play a pivotal role in the development of cardiorenal syndrome. It is therefore important to elucidate all the mechanisms in order to provide diagnostic and treatments tools. This review summarizes the hemodynamic and non-hemodynamic pathways along with biomarkers that could be the next target for diagnosis, treatment, and prognosis in cardiorenal syndrome.

Mitochondrial Dysfunction: An Emerging Link in the Pathophysiology of Cardiorenal Syndrome

The crosstalk between the heart and kidney is carried out through various bidirectional pathways. Cardiorenal syndrome (CRS) is a pathological condition in which acute or chronic dysfunction in the heart or kidneys induces acute or chronic dysfunction of the other organ. Complex hemodynamic factors and biochemical and hormonal pathways contribute to the development of CRS. In addition to playing a critical role in generating metabolic energy in eukaryotic cells and serving as signaling hubs during several vital processes, mitochondria rapidly sense and respond to a wide range of stress stimuli in the external environment. Impaired adaptive responses ultimately lead to mitochondrial dysfunction, inducing cell death and tissue damage. Subsequently, these changes result in organ failure and trigger a vicious cycle. In vitro and animal studies have identified an important role of mitochondrial dysfunction in heart failure (HF) and chronic kidney disease (CKD). Maintaining mitochondrial homeostasis may be a promising therapeutic strategy to interrupt the vicious cycle between HF and acute kidney injury (AKI)/CKD. In this review, we hypothesize that mitochondrial dysfunction may also play a central role in the development and progression of CRS. We first focus on the role of mitochondrial dysfunction in the pathophysiology of HF and AKI/CKD, then discuss the current research evidence supporting that mitochondrial dysfunction is involved in various types of CRS.

Catalytic iron mediated renal stress responses during experimental cardiorenal syndrome 1 ("CRS-1")

Cardiorenal syndrome I (CRS-1) denotes a state in which acute kidney injury occurs in the setting of acute heart failure (AHF). Isoproterenol (Iso) administration is widly used as an AHF model by transiently inducing extreme tachycardia, hypotension, and myocyte apoptosis and/or necrosis. To gain potential insights into renal manifestations of CRS-1, mice were subjected to the Iso-AHF model (50 mg Iso/kg), followed by renal functional and renal cortical assessments over 4 hours Iso induced acute azotemia (doubling of BUN, plasma creatinine) and significantly reduced renal plasma flow (prolonged plasma para-amino-hippurate clearance). Although no morphologic tubular injury was identified, marked increases in renal cortical 'stress markers' (NGAL, HO-1, IL-6, MCP-1 mRNAs) and oxidant stress (decreased glutathione, increased malondialdehyde) were observed. These changes were catalytic Fe dependent, given that the iron chelator desferrioxamine (DFO) significantly blunted, or completely reversed, these renal cortical abnormalities. Despite these acute changes, no lasting renal injury was observed (assessed over 3 days). To determine whether Iso directly impacts tubular cell integrity, cultured proximal tubule (HK-2) cells were exposed to Iso. Substantial Fe dependent cell injury (decreased MTT uptake), and Fe independent increases in HO-1/IL-6 mRNA expression were observed. We conclude that Iso-induced AHF is a useful reversible model of CRS-1. Despite its largely hemodynamic ('pre-renal') nature, Fe-mediated oxidative stress and pro-inflammatory reactions are induced. These arise, at least in part, from direct Iso- induced tubular cell toxicity, rather than simply being secondary to Iso-mediated hemodynamic events. Finally, Iso-triggered renal cytokine production can potentially contribute to 'organ cross talk' and a systemic pro-inflammatory state.

Cardiorenal Syndrome

Cardiorenal syndrome (CRS) describes a specific acute and chronic clinical picture in which the heart or the kidney are primarily dysfunctioning and secondarily affect each other. CRS is divided into five classes: acute and chronic CRS, acute and chronic renocardiac syndromes, and secondary dysfunction of heart and kidneys. This article specifically details the classification and the epidemiology, some risk factors, and the pathophysiology of CRS. Some emerging aspects of CRS are also discussed, such as CRS in patients with end-stage heart failure, with mechanical ventricular assistance, and after heart transplantation. Finally, some aspects of pediatric CRS are detailed.

Expression of miRNAs-122, -192 and -499 in end stage renal disease associated with acute myocardial infarction

INTRODUCTION

New diagnostic tools are needed to accurately detect acute myocardial infarction (AMI) in patients with end stage renal disease (ESRD) presenting with ischemic chest pain. We aimed in this study to investigate circulating miR-122, -192 and -499 expression levels in patients with AMI on top of ESRD and evaluate the potential of these miRNAs as blood-based biomarkers for AMI in patients with ESRD.

MATERIAL AND METHODS

The study included 80 ESRD patients without AMI, 80 patients with ESRD associated with AMI and 60 healthy subjects. Assessment of microRNAs was done using SYBR Green based real-time PCR.

RESULTS

Levels of miR-122 were 28-fold and 20-fold higher in controls than in ESRD patients with or without AMI respectively (p < 0.001), while no differences were detected between the two patient groups (p = 0.9). Levels of miR-192 showed a marked increase in ESRD patients with and without AMI compared to the control group (> 500-fold, > 8000-fold respectively, p ≤ 0.001). Patients who developed AMI had lower expression than ESRD patients without AMI (p < 0.001). Non-significant miR-499 elevation was found in ESRD patients without cardiac disease compared to the control group, while highly significant elevation of miR- 499 was demonstrated in ESRD patients who developed AMI compared to other ESRD patients and the control group (> 100-fold, > 350-fold respectively, p = 0.001).

CONCLUSIONS

Altered expression of miR-122 and -192 may contribute in pathogenesis of ESRD. MiR-192 and -499 may serve as potential biomarkers for AMI in ESRD. Further studies are needed to correlate these miRNAs with disease progression and outcome.

Preeclampsia: a gestational cardiorenal syndrome

It is generally accepted today that there are two different types of preeclampsia: an early-onset or placental type and a late-onset or maternal type. In the latent phase, the first one presents with a low output/high resistance circulation eventually leading in the late second or early third trimester to an intense and acutely aggravating systemic disorder with an important impact on maternal and neonatal mortality and morbidity; the other type presents initially as a high volume/low resistance circulation, gradually evolving to a state of circulatory decompensation usually in the later stages of pregnancy, with a less severe impact on maternal and neonatal outcome. For both processes, numerous dysfunctions of the heart, kidneys, arteries, veins and interconnecting systems are reported, most of them presenting earlier and more severely in early- than in late-onset preeclampsia; however, some very specific dysfunctions exist for either type. Experimental, clinical and epidemiological observations before, during and after pregnancy are consistent with gestation-induced worsening of subclinical pre-existing chronic cardiovascular dysfunction in early-onset preeclampsia, and thus sharing the pathophysiology of cardiorenal syndrome type II, and with acute volume overload decompensation of the maternal circulation in late-onset preeclampsia, thus sharing the pathophysiology of cardiorenal syndrome type 1. Cardiorenal syndrome type V is consistent with the process of preeclampsia superimposed upon clinical cardiovascular and/or renal disease, alone or as part of a systemic disorder. This review focuses on the specific differences in haemodynamic dysfunctions between the two types of preeclampsia, with special emphasis on the interorgan interactions between heart and kidneys, introducing the theoretical concept that the pathophysiological processes of preeclampsia can be regarded as the gestational manifestations of cardiorenal syndromes.

Neurohormonal, Endocrine, and Immune Dysregulation and Inflammation in Cardiorenal Syndrome

“Organ crosstalk” is the complex physiological communication between different body systems, and it is necessary for the optimal equilibrium and functioning of the organism. In particular, heart and kidney function is tightly connected, and interplay between these two organs occurs through a vast array of dynamic and bidirectional mechanisms. The term cardiorenal syndrome (CRS) indicates an interaction between the heart and kidneys in acute and chronic disease settings. In all types of CRS, multiple pathophysiological processes are implicated in the initiation and progression of organ injury. In addition to hemodynamic parameters, endothelial injury, immunological imbalance, cell death, inflammatory cascades, oxidative stress, neutrophil migration, leukocyte trafficking, caspase-mediated apoptosis, extracellular vesicles, small noncoding RNAs, and epigenetics play pivotal roles in the development of CRS. In this review, we will focus on neurohormonal, endocrine, and immune dysregulation and inflammation as mechanisms involved in the pathogenesis of CRS.

Multi-Omics Approach: New Potential Key Mechanisms Implicated in Cardiorenal Syndromes

Cardiorenal syndromes (CRS) include a scenario of clinical interactions characterized by the heart and kidney dysfunction. The crosstalk between cardiac and renal systems is clearly evidenced but not completely understood. Multi-factorial mechanisms leading to CRS do not involve only hemodynamic parameters. In fact, in recent works on organ crosstalk endothelial injury, the alteration of normal immunologic balance, cell death, inflammatory cascades, cell adhesion molecules, cytokine and chemokine overexpression, neutrophil migration, leukocyte trafficking, caspase-mediated induction of apoptotic mechanisms and oxidative stress has been demonstrated to induce distant organ dysfunction. Furthermore, new alternative mechanisms using the multi-omics approach may be implicated in the pathogenesis of cardiorenal crosstalk. The study of “omics” modifications in the setting of cardiovascular and renal disease represents an emerging area of research. Over the last years, indeed, many studies have elucidated the exact mechanisms involved in gene expression and regulation, cellular communication and organ crosstalk. In this review, we analyze epigenetics, gene expression, small non-coding RNAs, extracellular vesicles, proteomics, and metabolomics in the setting of CRS.

Heart-kidney interactions: mechanistic insights from animal models

Pathological changes in the heart or kidney can instigate the release of a cascade of cardiorenal mediators that promote injury in the other organ. Combined dysfunction of heart and kidney is referred to as cardiorenal syndrome (CRS) and has gained considerable attention. CRS has been classified into five distinct entities, each with different major pathophysiological changes. Despite the magnitude of the public health problem of CRS, the underlying mechanisms are incompletely understood, and effective intervention is unavailable. Animal models have allowed us to discover pathogenic molecular changes to clarify the pathophysiological mechanisms responsible for heart-kidney interactions and to enable more accurate risk stratification and effective intervention. Here, this article focuses on the use of currently available animal models to elucidate mechanistic insights in the clinical cardiorenal phenotype arising from primary cardiac injury, primary renal disease with special emphasis of chronic kidney disease-specific risk factors, and simultaneous cardiorenal/renocardiac dysfunction. The development of novel animal models that recapitulate more closely the cardiorenal phenotype in a clinical scenario and discover the molecular basis of this condition will be of great benefit.

Levels of Proinflammatory Cytokines, Oxidative Stress, and Tissue Damage Markers in Patients with Acute Heart Failure with and without Cardiorenal Syndrome Type 1

BACKGROUND

Cardiorenal syndrome type 1 (CRS type 1) is characterized by a rapid worsening of cardiac function leading to acute kidney injury (AKI). Inflammation and oxidative stress seem to play a pivotal role in its pathophysiology. In this in vivo study, we examined the putative role of inflammation and humoral markers in the pathogenesis of the CRS type 1.

METHODS

We enrolled 53 patients with acute heart failure (AHF); 17 of them developed AKI (CRS type 1). The cause of AKI was presumed to be related to cardiac dysfunction after having excluded other causes. We assessed the plasma levels of proinflammatory cytokines (TNF-α, IL-6, IL-18, sICAM, RANTES, GMCSF), oxidative stress marker (myeloperoxidase, MPO), brain natriuretic peptide (BNP), and neutrophil gelatinase-associated lipocalin (NGAL) in AHF and CRS type 1 patients.

RESULTS

We observed a significant increase in IL-6, IL-18, and MPO levels in CRS type 1 group compared to AHF (p < 0.001). We found higher NGAL at admission in the CRS type 1 group compared to the AHF group (p = 0.008) and a positive correlation between NGAL and IL-6 (Spearman's rho = 0.45, p = 0.003) and between IL-6 and BNP (Spearman's rho = 0.43, p = 0.004). We observed lower hemoglobin levels in CRS type 1 patients compared to AHF patients (p < 0.05) and inverse correlation between hemoglobin and cytokines (IL-6: Spearman's rho = -0.38, p = 0.005; IL-18: Spearman's rho = -0.32, p = 0.02).

CONCLUSION

Patients affected by CRS type 1 present increased levels of proinflammatory cytokines and oxidative stress markers, increased levels of tissue damage markers, and lower hemoglobin levels. All these factors may be implicated in the pathophysiology of CRS type 1 syndrome.

Cardiorenal Syndrome: An Overview

It is well established that a large number of patients with acute decompensated heart failure present with various degrees of heart and kidney dysfunction usually primary disease of heart or kidney often involve dysfunction or injury to the other. The term cardiorenal syndrome increasingly had been used without a consistent or well-accepted definition. To include the vast array of interrelated derangements and to stress the bidirectional nature of heart-kidney interactions, a new classification of the cardiorenal syndrome with 5 subtypes that reflect the pathophysiology, the time frame, and the nature of concomitant cardiac and renal dysfunction was proposed. Cardiorenal syndrome can generally be defined as a pathophysiological disorder of the heart and kidneys, in which acute or chronic dysfunction of one organ may induce acute or chronic dysfunction to the other. Although cardiorenal syndrome was usually referred to as acute kidney dysfunction following acute cardiac disease, it is now clearly established that impaired kidney function can have an adverse impact on cardiac function.

Determinants of Monocyte Apoptosis in Cardiorenal Syndrome Type 1

BACKGROUND

Cardiorenal syndrome type 1 (CRS type 1) is characterized by a rapid worsening of cardiac function leading to acute kidney injury (AKI). Its pathophysiology is complex and not completely understood. In this study, we examined the role of apoptosis and the caspase pathways involved.

MATERIAL AND METHODS

We enrolled 40 acute heart failure (AHF) patients, 11 of whom developed AKI characterizing CRS type 1. We exposed the human cell line U937 to plasma from the CRS type 1 and AHF groups and then we evaluated apoptotic activity by annexin-V evaluation, determination of caspase-3, -8 and -9 levels, and BAX, BAD, and FAS gene expression.

RESULTS

We observed significant upregulation of apoptosis in monocytes exposed to CRS type 1 plasma compared to AHF, with increased levels of caspase-3 (p < 0.01), caspase-9 (p < 0.01), and caspase-8 (p < 0.03) showing activation of both intrinsic and extrinsic pathways. Furthermore, monocytes exposed to CRS type 1 plasma had increased gene expression of BAX and BAD (intrinsic pathways) (p = 0.010 for both). Furthermore, strong significant correlations between the caspase-9 levels and BAD and BAX gene expression were observed (Spearman ρ = - 0.76, p = 0.011, and ρ = - 0.72, p = 0.011).

CONCLUSION

CRS type 1 induces dual apoptotic pathway activation in monocytes; the two pathways converged on caspase-3. Many factors may induce activation of both intrinsic and extrinsic apoptotic pathways in CRS type 1 patients, such as upregulation of proinflammatory cytokines and hypoxia/ischemia. Further investigations are necessary to corroborate the present findings, and to better understand the pathophysiological mechanism and consequent therapeutic and prognostic implications for CRS type 1.

A Call to Action to Develop Integrated Curricula in Cardiorenal Medicine

With the adoption of the new definition and classification of cardiorenal syndrome (CRS) and its relevant subtypes, much attention has been placed on elucidating the mechanisms of heart and kidney interactions. Of great interest are the pathophysiological pathways by which acute heart failure may result in acute kidney injury (AKI; type 1), chronic heart failure accelerating the progression of chronic kidney disease (CKD; type 2), AKI provoking cardiac events (type 3), and CKD increasing the risk and severity of cardiovascular disease (type 4). A remarkable interest has also been placed on the acute and chronic systemic conditions, such as sepsis and diabetes, which simultaneously affect heart and kidney function (type 5). Furthermore, the physiology of acute and chronic heart-kidney cross talk is drawing attention to hemodynamics (fluids, pressures, flows, resistances, perfusion), physiochemical (electrolytes, pH, and toxins), and biological (inflammation, immune system activation, neurohormonal signals) processes. Common clinical scenarios call for recognition, knowledge, and skill in managing CRS. There is a clear need for medical and surgical specialists that are well versed in the pathophysiology and the clinical manifestations that arise in the setting of CRS. With this editorial, we are making a call to action to stimulate universities, medical schools, and teaching hospitals to create a core curriculum for cardiorenal medicine to better equip the physicians of the future for these common, serious, and frequently fatal syndromes.

Elevated Phosphate Levels Trigger Autophagy-Mediated Cellular Apoptosis in H9c2 Cardiomyoblasts

BACKGROUND/AIM

In chronic kidney disease (CKD), kidneys fail to maintain phosphorus homeostasis in serum. Elevated phosphorus levels in serum have been associated with cardiovascular diseases in CKD patients and in normal individuals. In this study, we evaluated the level of autophagy- and apoptosis-related markers under different concentrations of hyperphosphate in myocardial cells.

METHODS

Modulation inflicted on the levels of various survival-, autophagy-, and apoptosis-related markers were determined by Western blotting analysis using total protein extract. FITC-annexin V staining was performed to quantify the apoptotic cells in all groups.

RESULTS

Hyperphosphate treatments showed to induce autophagy-related proteins beclin-1, ATG7, and LC3 II through the pAMPK-ULK1 pathway in Western blotting analysis. Further, apoptosis-associated proteins such as Bax, Bid, cytochrome c, and c-caspase-9 were also upregulated with hyperphosphate treatment. 3-Methyladenine, an autophagy inhibitor, inhibited apoptosis significantly in FITC-annexin V staining, and the inhibition of Bax, cytochrome c, and c-caspase-3 was shown by Western blotting.

CONCLUSION

The results suggest that hyperphosphate in H9c2 cardiomyoblasts would lead to cellular apoptosis via autophagy, which is mediated by the pAMPK signaling pathway. Our findings revealed the possible mechanism responsible for the heart damage under hyperphosphatemia.

Epigenetics: a potential key mechanism involved in the pathogenesis of cardiorenal syndromes

Epigenetics is defined as the heritable changes in gene expression patterns which are not directly encoded by modifications in the nucleotide DNA sequence of the genome, including higher order chromatin organization, DNA methylation, cytosine modifications, covalent histone tail modifications, and short non-coding RNA molecules. Recently, much attention has been paid to the role and the function of epigenetics and epimutations in the cellular and subcellular pathways and in the regulation of genes in the setting of both kidney and cardiovascular disease. Indeed, deregulation of histone alterations has been highlighted in a large spectrum of renal and cardiac disease, including chronic and acute renal injury, renal and cardiac fibrosis, cardiac hypertrophy and failure, kidney congenital anomalies, renal hypoxia, and diabetic renal complications. Nevertheless, the role of epigenetics in the pathogenesis and pathophysiology of cardiorenal syndromes is currently underexplored. Given the significant clinical relevance of heart-kidney crosstalk, efforts in the research for new action mechanisms concurrently operating in both pathologies are thus of maximum interest. This review focuses on epigenetic mechanisms involved in heart and kidney disease, and their possible role in the setting of cardiorenal syndromes.