AST-120, an Adsorbent of Uremic Toxins, Improves the Pathophysiology of Heart Failure in Conscious Dogs

Heart Failure: a Punch from the Gut

PURPOSE OF REVIEW

This article seeks to elucidate the mechanisms underlying the bidirectional relationship between the gut and the heart, focusing on the pathophysiology of heart failure. We have previously demonstrated that Heart failure (HF) has significant effects on splanchnic vasculature and leads to key alterations in the gut microbiome, portending greater comorbidity with HF.

RECENT FINDINGS

A growing field of research is focused on the effects of a "leaky gut" in the development of disease across organ systems. The leaky gut hypothesis centers on intestinal epithelial barrier dysfunction causing increased permeability of the gut and subsequent alterations to gut composition by endotoxins and microbial metabolites. Changes in the quantities of metabolites including short-chain fatty acids, trimethylamine N-oxide and other amino acid metabolites, and various bile acid species have been shown to result in gut dysbiosis and worsening HF. The gut plays a highly significant role in HF prognosis and requires greater attention for future therapeutic interventions. Treatments targeting gut composition could have very beneficial effects on HF prognosis.

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.

AST-120 to Target Protein-Bound Uremic Toxins Improves Cardiac Output and Kidney Oxygenation in Experimental Chronic Kidney Disease

INTRODUCTION

Chronic kidney disease (CKD) is a global health problem with increasing incidence which is closely associated with cardiac dysfunction. In CKD, uremic toxins accumulate as kidney function declines. Additionally, high salt intake is a growing health issue worldwide which can exacerbate kidney disease. In this study, we investigated the effect of reducing plasma levels of protein-bound uremic toxins in a rat model of CKD, challenged with high salt intake and compared the effects to those of conventional treatment using an angiotensin-converting enzyme inhibitor (ACEI).

METHODS

In rats, the right kidney and 2/3 of the left kidney were surgically removed (5/6 nephrectomy). Animals were fed a normal-salt diet and randomized to either no treatment (control) or chronic treatment with either the oral absorbent AST-120 to reduce plasma levels of protein-bound uremic toxins or the ACEI enalapril to inhibit angiotensin II signaling for 5 weeks. Following treatment, kidney function was measured before and after a week of high salt intake. Cardiac output and markers of oxidative stress were measured at the end of the study period.

RESULTS

Treatment with AST-120 resulted in decreased levels of the uremic toxin indoxyl sulfate, improved cardiac output (mL/min: AST-120 44.9 ± 5.4 compared to control 26.6 ± 2.0; p < 0.05), and decreased urinary oxidative stress. ACEI reduced oxidative stress in kidney tissue and improved the glomerular filtration rate in response to high salt intake (mL/min: ACEI 1.5 ± 0.1; compared to control 1.1 ± 0.1; p < 0.05). Both interventions improved intrarenal oxygen availability (mm Hg: AST-120 42.8 ± 0.8; ACEI 43.2 ± 1.9; compared to control 33.4 ± 1.3; p < 0.05).

CONCLUSION

AST-120 administered to reduce plasma levels of uremic toxins, such as indoxyl sulfate, has potential beneficial effects on both cardiac and kidney function. Targeting uremic toxins and angiotensin II signaling simultaneously could be an efficient strategy to target both cardiac and kidney dysfunction in CKD, to further slow progression of disease in patients with CKD.

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.

The Role of Intestinal Flora and Its Metabolites in Heart Failure

Intestinal flora is a complex collection of microbial communities that participate in the physiological and pathological activities of the human body through various pathways. In recent years, numerous studies have reported that intestinal flora are involved in the occurrence and development of heart failure (HF) and its metabolic products could play an important role in this progression, suggesting a great value in the clinical treatment of this condition. This study reported the interaction between intestinal flora and HF, and with intestinal flora metabolites, such as short-chain fatty acids, trimethylamine N-oxide and bile acids and urotoxins, considered as the starting point, the mechanism of the roles in HF was summarized. Additionally, the current research status and the development prospects of applying flora and metabolites to the clinical therapeutic decision of HF were discussed.

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.

Research progress on the relationship between IS and kidney disease and its complications

Indoxyl sulphate (IS) a representative uraemic toxin in the blood of patients with chronic kidney disease (CKD). Its accumulation may be closely related to CKD and the increasing morbidity and mortality of the disease's related complications. Timely and effective detection of the IS level and efficient clearance of IS may effectively prevent the progression of CKD and its related complications. Therefore, this article summarizes the research progress of IS related, including IS in CKD and its associated complications including chronic kidney disease, chronic kidney disease with cardiovascular disease, renal anemia, bone mineral metabolic disease and neuropsychiatric disorders, looking for IS accurate rapid detection methods, and explore the efficient treatment to reduce blood levels of indole phenol sulphate.

The effect of dihydroceramide desaturase 1 inhibition on endothelial impairment induced by indoxyl sulfate

Protein-bound uremic toxins (PBUTs) have adverse effects on vascular function, which is imperative in the progression of cardiovascular and renal diseases. The role of sphingolipids in PBUT-mediated vasculo-endothelial pathophysiology is unclear. This study assessed the therapeutic potential of dihydroceramide desaturase 1 (Des1) inhibition, the last enzyme involved in de novo ceramide synthesis, to mitigate the vascular effects of the PBUT indoxyl sulfate (IS). Rat aortic rings were isolated and vascular reactivity was assessed in organ bath experiments followed by immunohistochemical analyses. Furthermore, cultured human aortic endothelial cells were assessed for phenotypic and mechanistic changes. Inhibition of Des1 by a selective inhibitor CIN038 (0.1 to 0.3 μM) improved IS-induced impairment of vasorelaxation and modulated immunoreactivity of oxidative stress markers. Des1 inhibition also reversed IS-induced reduction in endothelial cell migration (1.0 μM) by promoting the expression of angiogenic cytokines and reducing inflammatory and oxidative stress markers. These effects were associated with a reduction of TIMP1 and the restoration of Akt phosphorylation. In conclusion, Des1 inhibition improved vascular relaxation and endothelial cell migration impaired by IS overload. Therefore, Des1 may be a suitable intracellular target to mitigate PBUT-induced adverse vascular effects.

Plasma indoxyl sulfate levels predict cardiovascular events in patients with mild chronic heart failure

Indoxyl sulfate (IS) is associated with either chronic kidney disease or renal failure, which may predict cardiovascular events via cardiorenal syndrome. The present study aimed to elucidate whether the plasma levels of IS can predict the occurrence of cardiovascular events in patients with chronic heart failure (CHF) and investigate which causes of CHF leading to cardiovascular events are highly influenced by plasma IS levels. We measured the plasma IS levels in 165 patients with CHF [valvular disease: 78, dilated cardiomyopathy: 29, hypertrophic cardiomyopathy (HCM): 25 and others: 33] admitted to our hospital in 2012, and we followed up these patients for more than 5 years (the median follow-up period: 5.3 years). We measured the plasma IS level in 165 patients with CHF, and Kaplan–Meier analyses showed that high plasma IS levels (≥ 0.79 µg/mL, the median value) could predict the occurrence of cardiovascular events, i.e., cardiovascular death or rehospitalization due to the worsening of CHF. The sub-analyses showed that the high IS level could predict cardiovascular events in patients with CHF due to HCM and that the plasma IS levels were closely associated with left ventricular (LV) dimension, LV systolic dysfunction, and plasma B-type natriuretic peptide levels, rather than LV diastolic dysfunction. Plasma IS level predicts cardiovascular events in patients with CHF, especially those with HCM along with cardiac dysfunction. Besides, IS may become a proper biomarker to predict cardiovascular events in patients with CHF.

Uremic Toxins and Atrial Fibrillation: Mechanisms and Therapeutic Implications

Atrial fibrillation (AF) is the most prevalent arrhythmia in the general population. There is a close association between chronic kidney disease (CKD) and AF. In recent years, attention has been focused on the relationship between AF and uremic toxins, including indoxyl sulfate (IS). Several animal studies have shown that IS promotes the development and progression of AF. IS has been shown to cause fibrosis and inflammation in the myocardium and exacerbate AF by causing oxidative stress and reducing antioxidative defense. Administration of AST-120, an absorbent of uremic toxins, decreases uremic toxin-induced AF in rodents. We have recently reported that patients with a higher serum IS level exhibit a higher rate of AF recurrence after catheter ablation, with serum IS being a significant predictor of AF recurrence. In this review, we discuss the possible mechanisms behind the AF-promoting effects of uremic toxins and summarize the reported clinical studies of uremic toxin-induced AF.