AST-120 Improves Cardiac Dysfunction in Acute Kidney Injury Mice via Suppression of Apoptosis and Proinflammatory NF-κB/ICAM-1 Signaling

Role of mitochondria in reno-cardiac diseases: A study of bioenergetics, biogenesis, and GSH signaling in disease transition

Acute kidney injury (AKI) and chronic kidney disease (CKD) are global health burdens with rising prevalence. Their bidirectional relationship with cardiovascular dysfunction, manifesting as cardio-renal syndromes (CRS) types 3 and 4, underscores the interconnectedness and interdependence of these vital organ systems. Both the kidney and the heart are critically reliant on mitochondrial function. This organelle is currently recognized as a hub in signaling pathways, with emphasis on the redox regulation mediated by glutathione (GSH). Mitochondrial dysfunction, including impaired bioenergetics, redox, and biogenesis pathways, are central to the progression of AKI to CKD and the development of CRS type 3 and 4. This review delves into the metabolic reprogramming and mitochondrial redox signaling and biogenesis alterations in AKI, CKD, and CRS. We examine the pathophysiological mechanisms involving GSH redox signaling and the AMP-activated protein kinase (AMPK)-sirtuin (SIRT)1/3-peroxisome proliferator-activated receptor-gamma coactivator (PGC-1α) axis in these conditions. Additionally, we explore the therapeutic potential of GSH synthesis inducers in mitigating these mitochondrial dysfunctions, as well as their effects on inflammation and the progression of CKD and CRS types 3 and 4.

AST-120 alleviates renal ischemia-reperfusion injury by inhibiting HK2-mediated glycolysis

OBJECTIVE

Renal ischemia/reperfusion injury (IRI) is a major cause of acute kidney injury (AKI), which is associated with high incidence and mortality. AST-120 is an oral carbonaceous adsorbent that can alleviate kidney damage. This study aimed to explore the effects of AST-120 on renal IRI and the molecular mechanism.

METHODS

A renal IRI mouse model was established and administrated AST-120, and differentially expressed genes were screened using RNA sequencing. Renal function and pathology were analyzed in mice. Hypoxia/reoxygenation (H/R) cell model was generated, and glycolysis was evaluated by detecting lactate levels and Seahorse analysis. Histone lactylation was analyzed by western blotting, and its relationship with hexokinase 2 (HK2) was assessed using chromatin immunoprecipitation.

RESULTS

The results showed that HK2 expression was increased after IRI, and AST-120 decreased HK2 expression. Knockout of HK2 attenuated renal IRI and inhibits glycolysis. AST-120 inhibited renal IRI in the presence of HK2 rather than HK2 absence. In proximal tubular cells, knockdown of HK2 suppressed glycolysis and H3K18 lactylation caused by H/R. H3K18 lactylation was enriched in HK2 promoter and upregulated HK2 levels. Rescue experiments revealed that lactate reversed IRI that suppressed by HK2 knockdown.

CONCLUSIONS

In conclusion, AST-120 alleviates renal IRI via suppressing HK2-mediated glycolysis, which suppresses H3K18 lactylation and further reduces HK2 levels. This study proposes a novel mechanism by which AST-120 alleviates IRI.

Predictive value of protein-bound uremic toxins for heart failure in patients with chronic kidney disease

AIMS

This retrospective cohort study aimed to be the first to evaluate the association between plasma protein-bound uremic toxins (PBUTs) concentrations, echocardiographic parameters of heart failure (HF), and incident HF events in patients with chronic kidney disease (CKD) not on dialysis.

METHODS AND RESULTS

Retrospective, single-centre, cohort study at the Ghent University Hospital, Belgium. Adults with CKD stages G1-G5, not on dialysis, could be included. Exclusion criteria were ongoing pregnancy, age <18 years, active acute infection, active malignancy, history of transplantation, or a cardiovascular event within 3 months prior to inclusion. Free and total concentrations of five PBUTs were quantified at baseline: indoxyl sulfate (IxS), p-cresyl sulfate (pCS), p-cresyl glucuronide (pCG), indole-3 acetic acid (IAA), and hippuric acid (HA). Patients were grouped into three echocardiographic categories: normal left ventricular ejection fraction (LVEF) and normal left ventricular end-diastolic pressure (LVEDP), normal LVEF and increased LVEDP, and reduced LVEF, based on available echocardiographic data in a time interval of ±6 months around the plasma sample collection. A total of 523 patients were included between January 2011 and January 2014. Echocardiographic data within the predefined timeframe were available for 210 patients (40% of patients). Levels of pCG and pCS were significantly higher in patients with reduced (<50%) versus normal LVEF (P < 0.05). After a median follow-up 5.5 years, 43 (8.4%) patients reached the composite endpoint of hospitalization or mortality due to HF. Free fractions of IxS, pCS, and pCG showed the strongest association with clinical outcome: free IxS: HR 1.71 (95% CI 1.11-2.63; P = 0.015), free pCS: HR 1.82 (95% CI 1.11-3.01; P = 0.019), and free pCG: HR 1.67 (95% CI 1.08-2.58; P = 0.020), and these results were independent of age, gender, body mass index, diabetes, and systolic blood pressure. In models that were also adjusted for serum creatinine, the free fractions of these PBUTs remained significant.

CONCLUSIONS

Elevated free concentrations of IxS, pCG, and pCS were independently associated with an increased risk of HF events in non-dialysed CKD patients. Further research is necessary to confirm these findings and investigate the potential impact of PBUT-lowering interventions on HF events in this patient group.

The Dietary Fiber Inulin Slows Progression of Chronic Kidney Disease-Mineral Bone Disorder (CKD-MBD) in a Rat Model of CKD

Chronic kidney disease (CKD)-mineral bone disorder (CKD-MBD) leads to fractures and cardiovascular disease. Observational studies suggest beneficial effects of dietary fiber on both bone and cardiovascular outcomes, but the effect of fiber on CKD-MBD is unknown. To determine the effect of fiber on CKD-MBD, we fed the Cy/+ rat with progressive CKD a casein-based diet of 0.7% phosphate with 10% inulin (fermentable fiber) or cellulose (non-fermentable fiber) from 22 weeks to either 30 or 32 weeks of age (~30% and ~15% of normal kidney function; CKD 4 and 5). We assessed CKD-MBD end points of biochemistry, bone quantity and quality, cardiovascular health, and cecal microbiota and serum gut-derived uremic toxins. Results were analyzed by two-way analysis of variance (ANOVA) to evaluate the main effects of CKD stage and inulin, and their interaction. The results showed that in CKD animals, inulin did not alter kidney function but reduced the increase from stage 4 to 5 in serum levels of phosphate and parathyroid hormone, but not fibroblast growth factor-23 (FGF23). Bone turnover and cortical bone parameters were similarly improved but mechanical properties were not altered. Inulin slowed progression of aorta and cardiac calcification, left ventricular mass index, and fibrosis. To understand the mechanism, we assessed intestinal microbiota and found changes in alpha and beta diversity and significant changes in several taxa with inulin, together with a reduction in circulating gut derived uremic toxins such as indoxyl sulfate and short-chain fatty acids. In conclusion, the addition of the fermentable fiber inulin to the diet of CKD rats led to a slowed progression of CKD-MBD without affecting kidney function, likely mediated by changes in the gut microbiota composition and lowered gut-derived uremic toxins. © 2023 The Authors. JBMR Plus published by Wiley Periodicals LLC. on behalf of American Society for Bone and Mineral Research.

Acute kidney disease: an overview of the epidemiology, pathophysiology, and management

Acute kidney injury (AKI) increases the risk of chronic kidney disease (CKD), and AKI and CKD are seen as interconnected syndromes. Acute kidney disease (AKD) is defined as subacute damage and/or loss of kidney function occurring 7 to 90 days after AKI, during which period key interventions may be initiated to hinder the development of CKD. While AKD is usually under-recognized, it is associated with high morbidity and mortality globally. This review article aims to summarize the current knowledge concerning the epidemiology, pathophysiology, and management of AKD with the aim to develop monitoring strategies and therapeutic agents of AKD. Generally, AKD tends to occur more frequently in the elderly and those with chronic diseases, such as hypertension, diabetes mellitus, and metabolic syndrome. In addition, the severity, duration, and frequency of AKI are independent risk factors for AKD. Investigations of several mechanisms of AKD, such as renal tubular epithelium cell-cycle arrest, epigenetic change, chronic inflammation, mitochondria dysfunction, failed regeneration of tubular cells, metabolic reprogramming, and renin-angiotensin system (RAS) activation, have identified additional potential pharmacotherapy targets. Management of AKD includes prevention of repeated AKI, early and regular follow-up by a nephrologist, resumption and adjustment of essential medication, optimization of blood pressure control and nutrition management, and development of new pharmaceutical agents including RAS inhibitors. Finally, we outline a care bundle for AKD patients based on important lessons learned from studies and registries and identify the need for clinical trials of RAS inhibitors or other novel agents to impede ensuing CKD development.

Gut microbiota and neonatal acute kidney injury biomarkers

One of the most frequent issues in newborns is acute kidney injury (AKI), which can lengthen their hospital stay or potentially raise their chance of dying. The gut-kidney axis establishes a bidirectional interplay between gut microbiota and kidney illness, particularly AKI, and demonstrates the importance of gut microbiota to host health. Since the ability to predict neonatal AKI using blood creatinine and urine output as evaluation parameters is somewhat constrained, a number of interesting biomarkers have been developed. There are few in-depth studies on the relationships between these neonatal AKI indicators and gut microbiota. In order to gain fresh insights into the gut-kidney axis of neonatal AKI, this review is based on the gut-kidney axis and describes relationships between gut microbiota and neonatal AKI biomarkers.

Novel Approaches in Chronic Renal Failure without Renal Replacement Therapy: A Review

Chronic kidney disease (CKD) is characterized by renal parenchymal damage leading to a reduction in the glomerular filtration rate. The inflammatory response plays a pivotal role in the tissue damage contributing to renal failure. Current therapeutic options encompass dietary control, mineral salt regulation, and management of blood pressure, blood glucose, and fatty acid levels. However, they do not effectively halt the progression of renal damage. This review critically examines novel therapeutic avenues aimed at ameliorating inflammation, mitigating extracellular matrix accumulation, and fostering renal tissue regeneration in the context of CKD. Understanding the mechanisms sustaining a proinflammatory and profibrotic state may offer the potential for targeted pharmacological interventions. This, in turn, could pave the way for combination therapies capable of reversing renal damage in CKD. The non-replacement phase of CKD currently faces a dearth of efficacious therapeutic options. Future directions encompass exploring vaptans as diuretics to inhibit water absorption, investigating antifibrotic agents, antioxidants, and exploring regenerative treatment modalities, such as stem cell therapy and novel probiotics. Moreover, this review identifies pharmaceutical agents capable of mitigating renal parenchymal damage attributed to CKD, targeting molecular-level signaling pathways (TGF-β, Smad, and Nrf2) that predominate in the inflammatory processes of renal fibrogenic cells.

The Dietary Fermentable Fiber Inulin Alters the Intestinal Microbiome and Improves Chronic Kidney Disease Mineral-Bone Disorder in a Rat Model of CKD

Background

Dietary fiber is important for a healthy diet, but intake is low in CKD patients and the impact this has on the manifestations of CKD-Mineral Bone Disorder (MBD) is unknown.

Methods

The Cy/+ rat with progressive CKD was fed a casein-based diet of 0.7% phosphate with 10% inulin (fermentable fiber) or cellulose (non-fermentable fiber) from 22 weeks to either 30 or 32 weeks of age (~30 and ~15 % of normal kidney function). We assessed CKD-MBD, cecal microbiota, and serum gut-derived uremic toxins. Two-way ANOVA was used to evaluate the effect of age and inulin diet, and their interaction.

Results

In CKD animals, dietary inulin led to changes in microbiota alpha and beta diversity at 30 and 32 weeks, with higher relative abundance of several taxa, including Bifidobacterium and Bacteroides , and lower Lactobacillus . Inulin reduced serum levels of gut-derived uremic toxins, phosphate, and parathyroid hormone, but not fibroblast growth factor-23. Dietary inulin decreased aorta and cardiac calcification and reduced left ventricular mass index and cardiac fibrosis. Bone turnover and cortical bone parameters were improved with inulin; however, bone mechanical properties were not altered.

Conclusions

The addition of the fermentable fiber inulin to the diet of CKD rats led to changes in the gut microbiota composition, lowered gut-derived uremic toxins, and improved most parameters of CKD-MBD. Future studies should assess this fiber as an additive therapy to other pharmacologic and diet interventions in CKD.

Significance Statement

Dietary fiber has well established beneficial health effects. However, the impact of fermentable dietary fiber on the intestinal microbiome and CKD-MBD is poorly understood. We used an animal model of progressive CKD and demonstrated that the addition of 10% of the fermentable fiber inulin to the diet altered the intestinal microbiota and lowered circulating gut-derived uremic toxins, phosphorus, and parathyroid hormone. These changes were associated with improved cortical bone parameters, lower vascular calcification, and reduced cardiac hypertrophy, fibrosis and calcification. Taken together, dietary fermentable fiber may be a novel additive intervention to traditional therapies of CKD-MBD.

Uremic toxins in chronic kidney disease highlight a fundamental gap in understanding their detrimental effects on cardiac electrophysiology and arrhythmogenesis

Chronic kidney disease (CKD) and cardiovascular disease (CVD) have an estimated 700-800 and 523 million cases worldwide, respectively, with CVD being the leading cause of death in CKD patients. The pathophysiological interplay between the heart and kidneys is defined as the cardiorenal syndrome (CRS), in which worsening of kidney function is represented by increased plasma concentrations of uremic toxins (UTs), culminating in dialysis patients. As there is a high incidence of CVD in CKD patients, accompanied by arrhythmias and sudden cardiac death, knowledge on electrophysiological remodeling would be instrumental for understanding the CRS. While the interplay between both organs is clearly of importance in CRS, the involvement of UTs in pro-arrhythmic remodeling is only poorly investigated, especially regarding the mechanistic background. Currently, the clinical approach against potential arrhythmic events is mainly restricted to symptom treatment, stressing the need for fundamental research on UT in relation to electrophysiology. This review addresses the existing knowledge of UTs and cardiac electrophysiology, and the experimental research gap between fundamental research and clinical research of the CRS. Clinically, mainly absorbents like ibuprofen and AST-120 are studied, which show limited safe and efficient usability. Experimental research shows disturbances in cardiac electrical activation and conduction after inducing CKD or exposure to UTs, but are scarcely present or focus solely on already well-investigated UTs. Based on UTs data derived from CKD patient cohort studies, a clinically relevant overview of physiological and pathological UTs concentrations is created. Using this, future experimental research is stimulated to involve electrophysiologically translatable animals, such as rabbits, or in vitro engineered heart tissues.

The Role of Gut-Derived, Protein-Bound Uremic Toxins in the Cardiovascular Complications of Acute Kidney Injury

Acute kidney injury (AKI) is a frequent disease encountered in the hospital, with a higher incidence in intensive care units. Despite progress in renal replacement therapy, AKI is still associated with early and late complications, especially cardiovascular events and mortality. The role of gut-derived protein-bound uremic toxins (PBUTs) in vascular and cardiac dysfunction has been extensively studied during chronic kidney disease (CKD), in particular, that of indoxyl sulfate (IS), para-cresyl sulfate (PCS), and indole-3-acetic acid (IAA), resulting in both experimental and clinical evidence. PBUTs, which accumulate when the excretory function of the kidneys is impaired, have a deleterious effect on and cause damage to cardiovascular tissues. However, the link between PBUTs and the cardiovascular complications of AKI and the pathophysiological mechanisms potentially involved are unclear. This review aims to summarize available data concerning the participation of PBUTs in the early and late cardiovascular complications of AKI.

The Intestinal Microbiota and Metabolites in the Gut-Kidney-Heart Axis of Chronic Kidney Disease

Emerging evidences demonstrate the involvement of gut microbiota in the progression of chronic kidney disease (CKD) and CKD-associated complications including cardiovascular disease (CVD) and intestinal dysfunction. In this review, we discuss the interactions between the gut, kidney and heart in CKD state, and elucidate the significant role of intestinal microbiota in the gut-kidney-heart axis hypothesis for the pathophysiological mechanisms of these diseases, during which process mitochondria may serve as a potential therapeutic target. Dysregulation of this axis will lead to a vicious circle, contributing to CKD progression. Recent studies suggest novel therapies targeting gut microbiota in the gut-kidney-heart axis, including dietary intervention, probiotics, prebiotics, genetically engineered bacteria, fecal microbiota transplantation, bacterial metabolites modulation, antibiotics, conventional drugs and traditional Chinese medicine. Further, the identification of specific microbial communities and their corresponding pathophysiological metabolites and the illumination of the gut-kidney-heart axis may contribute to innovative basic research, clinical trials and therapeutic strategies against CKD progression and uremic complications in CKD patients.

Roxadustat (FG-4592) Facilitates Recovery From Renal Damage by Ameliorating Mitochondrial Dysfunction Induced by Folic Acid

Incomplete recovery from acute kidney injury induced by folic acid is a major risk factor for progression to chronic kidney disease. Mitochondrial dysfunction has been considered a crucial contributor to maladaptive repair in acute kidney injury. Treatment with FG-4592, an inhibitor of hypoxia inducible factor prolyl-hydroxylase, is emerging as a new approach to attenuate renal damage; however, the underlying mechanism has not been fully elucidated. The current research demonstrated the protective effect of FG-4592 against renal dysfunction and histopathological damage on the 7th day after FA administration. FG-4592 accelerated tubular repair by promoting tubular cell regeneration, as indicated by increased proliferation of cell nuclear antigen-positive tubular cells, and facilitated structural integrity, as reflected by up-regulation of the epithelial inter-cellular tight junction molecule occludin-1 and the adherens junction molecule E-cadherin. Furthermore, FG-4592 ameliorated tubular functional recovery by restoring the function-related proteins aquaporin1, aquaporin2, and sodium chloride cotransporter. Specifically, FG-4592 pretreatment inhibited hypoxia inducible factor-1α activation on the 7th day after folic acid injection, which ameliorated ultrastructural abnormalities, promoted ATP production, and attenuated excessive reactive oxygen species production both in renal tissue and mitochondria. This was mainly mediated by balancing of mitochondrial dynamics, as indicated by down-regulation of mitochondrial fission 1 and dynamin-related protein 1 as well as up-regulation of mitofusin 1 and optic atrophy 1. Moreover, FG-4592 pretreatment attenuated renal tubular epithelial cell death, kidney inflammation, and subsequent interstitial fibrosis. In vitro, TNF-α-induced HK-2 cells injury could be ameliorated by FG-4592 pretreatment. In summary, our findings support the protective effect of FG-4592 against folic acid-induced mitochondrial dysfunction; therefore, FG-4592 treatment can be used as a useful strategy to facilitate tubular repair and mitigate acute kidney injury progression.

Vascular Endothelial Dysfunction in the Thoracic Aorta of Rats with Ischemic Acute Kidney Injury: Contribution of Indoxyl Sulfate

Chronic kidney disease (CKD) and cardiovascular disease are known to be linked, and the involvement of indoxyl sulfate (IS), a type of uremic toxin, has been suggested as one of the causes. It is known that IS induces vascular dysfunction through overproduction of reactive oxygen species (ROS). On the other hand, the involvement of IS in the vascular dysfunction associated with acute kidney injury (AKI) is not fully understood. Therefore, we investigated this issue using the thoracic aorta of rats with ischemic AKI. Ischemic AKI was induced by occlusion of the left renal artery and vein for 45 min, followed by reperfusion 2 weeks after contralateral nephrectomy. One day after reperfusion, there was marked deterioration in renal function evidenced by an increase in plasma creatinine. Furthermore, blood IS levels increased markedly due to worsening renal function. Seven days and 28 days after reperfusion, blood IS levels decreased with the improvement in renal function. Of note, acetylcholine-induced vasorelaxation deteriorated over time after reperfusion, contradicting the recovery of renal function. In addition, 28 days after reperfusion, we observed a significant increase in ROS production in the vascular tissue. Next, we administered AST-120, a spherical adsorbent charcoal, after reperfusion to assess whether the vascular endothelial dysfunction associated with the ischemic AKI was due to a temporary increase in blood IS levels. AST-120 reduced the temporary increase in blood IS levels after reperfusion without influencing renal function, but did not restore the impaired vascular reactivity. Thus, in ischemic AKI, we confirmed that the vascular endothelial function of the thoracic aorta is impaired even after the recovery of kidney injury, probably with excessive ROS production. IS, which increases from ischemia to early after reperfusion, may not be a major contributor to the vascular dysfunction associated with ischemic AKI.

Uremic Toxins and Protein-Bound Therapeutics in AKI and CKD: Up-to-Date Evidence

Uremic toxins are defined as harmful metabolites that accumulate in the human body of patients whose renal function declines, especially chronic kidney disease (CKD) patients. Growing evidence demonstrates the deteriorating effect of uremic toxins on CKD progression and CKD-related complications, and removing uremic toxins in CKD has become the conventional treatment in the clinic. However, studies rarely pay attention to uremic toxin clearance in the early stage of acute kidney injury (AKI) to prevent progression to CKD despite increasing reports demonstrating that uremic toxins are correlated with the severity of injury or mortality. This review highlights the current evidence of uremic toxin accumulation in AKI and the therapeutic value to prevent CKD progression specific to protein-bound uremic toxins (PBUTs).