Oral Absorbent AST-120 Is Associated with Compositional and Functional Adaptations of Gut Microbiota and Modification of Serum Short and Medium-Chain Fatty Acids in Advanced CKD Patients

Machine-learning assisted discovery unveils novel interplay between gut microbiota and host metabolic disturbance in diabetic kidney disease

Diabetic kidney disease (DKD) is a serious healthcare dilemma. Nonetheless, the interplay between the functional capacity of gut microbiota and their host remains elusive for DKD. This study aims to elucidate the functional capability of gut microbiota to affect kidney function of DKD patients. A total of 990 subjects were enrolled consisting of a control group (n = 455), a type 2 diabetes mellitus group (DM, n = 204), a DKD group (n = 182) and a chronic kidney disease group (CKD, n = 149). Full-length sequencing of 16S rRNA genes from stool DNA was conducted. Three findings are pinpointed. Firstly, new types of microbiota biomarkers have been created using a machine-learning (ML) method, namely relative abundance of a microbe, presence or absence of a microbe, and the hierarchy ratio between two different taxonomies. Four different panels of features were selected to be analyzed: (i) DM vs. Control, (ii) DKD vs. DM, (iii) DKD vs. CKD, and (iv) CKD vs. Control. These had accuracy rates between 0.72 and 0.78 and areas under curve between 0.79 and 0.86. Secondly, 13 gut microbiota biomarkers, which are strongly correlated with anthropometric, metabolic and/or renal indexes, concomitantly identified by the ML algorithm and the differential abundance method were highly discriminatory. Finally, the predicted functional capability of a DKD-specific biomarker, Gemmiger spp. is enriched in carbohydrate metabolism and branched-chain amino acid (BCAA) biosynthesis. Coincidentally, the circulating levels of various BCAAs (L-valine, L-leucine and L-isoleucine) and their precursor, L-glutamate, are significantly increased in DM and DKD patients, which suggests that, when hyperglycemia is present, there has been alterations in various interconnected pathways associated with glycolysis, pyruvate fermentation and BCAA biosynthesis. Our findings demonstrate that there is a link involving the gut-kidney axis in DKD patients. Furthermore, our findings highlight specific gut bacteria that can acts as useful biomarkers; these could have mechanistic and diagnostic implications.

Gut microbiota-targeted therapies in pediatric chronic kidney disease: gaps and opportunities

Given the complex relationship between the gut microbiome and chronic kidney disease (CKD), exploring the potential role and scope of microbiota-targeted therapies in pediatric CKD is highly relevant. We aim to provide an overview of gut-targeted therapeutic strategies, including nutritional interventions (fiber, phytochemicals, fermented foods, and traditional Chinese medicines), probiotics, synbiotics, oral absorbents, and fecal microbial transplantation. Enhancing physical activity and preventing constipation are additional strategies that may promote gut microbiome health. In a uremic environment, gut microbiota-targeted therapies could potentially rebalance the gut microbiota, improve gut barrier function, decrease uremic toxin concentrations, enhance the production of short-chain fatty acids (SCFA), and reduce inflammation. While research in adult CKD patients has provided insights into these approaches, there are limited data in children with CKD. This review aims to summarize potential targeted therapies for restoring a balanced gut microbiota, emphasizing the need for studies that evaluate their effects on clinical outcomes in pediatric CKD.

A high-throughput liquid chromatography-tandem mass spectrometry assay for the simultaneous quantification of p-cresol sulfate, p-cresol glucuronide, indoxyl sulfate, and indoxyl glucuronide in HepaRG culture medium and the demonstration of mefenamic acid as a potent and selective detoxifying agent

BACKGROUND

p-cresol and indole are uremic compounds which undergo sulfonation to generate the highly toxic p-cresol sulfate (pCS) and indoxyl sulfate (IxS). They are also subjected to glucuronidation to produce the less toxic p-cresol glucuronide (pCG) and indoxyl glucuronide (IG). We developed and validated an assay to quantify these metabolites in HepaRG cells. We also tested the effects of mefenamic acid on their in-situ formations in relation to the development of cellular necrosis.

RESEARCH DESIGN AND METHODS

HepaRG cells were exposed to p-cresol or indole (0-1 mM) with mefenamic acid (0-3000 nM) for 24 hours to generate uremic metabolites. Cells were also exposed to 0.5 mM p-cresol or indole with/without 30 nM mefenamic acid to characterize lactate dehydrogenase (LDH) release.

RESULTS

The assay exhibited high sensitivity and wide calibration ranges covering human concentrations. HepaRG cells also generated physiologically-relevant concentrations of each metabolite. Mefenamic acid inhibited pCS formation in a concentration-dependent manner without affecting pCG, IxS, or IG. Mefenamic acid also reduced LDH release from p-cresol (by 50.12±5.86%) or indole (56.26±3.58%).

CONCLUSIONS

This novel assay is capable of quantifying these metabolites in HepaRG cells. Our novel findings suggest that mefenamic acid can be potentially utilized therapeutically to attenuate pCS-associated toxicities.

The Ability of AST-120 to Lower the Serum Indoxyl Sulfate Level Improves Renal Outcomes and the Lipid Profile in Diabetic and Nondiabetic Animal Models of Chronic Kidney Disease: A Meta-Analysis

The therapeutic benefit of the oral adsorbent drug AST-120 in chronic kidney disease (CKD) is related to an indoxyl sulfate (IS)-lowering action. Diabetes and dyslipidemia might worsen kidney damage in CKD. However, it is not known whether AST-120 influences lipid abnormalities as well as renal function in patients with CKD and diabetes. The objective of the present meta-analysis was to evaluate the efficacy of AST-120 treatment in CKD using data from preclinical studies. Mixed-effect or random-effect models were used to estimate the standardized mean difference (SMD) and the 95% confidence interval (CI). Publication bias was assessed with a funnel plot and Egger's test. The potential influence of some variables (the dose and duration of AST-120 treatment, the animal species, and the CKD model's diabetic status) was evaluated in subgroup analyses. Treatment with AST-120 was associated with a significantly lower IS level in animals with CKD (SMD = -1.75; 95% CI = -2.00, -1.49; p < 0.001). Significant improvements in markers of renal function and the lipid profile were also observed. In subgroup analyses of the cholesterol level, the diabetic status, the AST-120 dose, and the animal species were found to be influential factors. AST-120 lowered serum IS and triglyceride levels and improved renal function in animal models of CKD independent of diabetes status. However, AST-120's ability to lower the total cholesterol level was more prominent in animals with diabetic CKD.

Gut Dysbiosis and Its Role in the Anemia of Chronic Kidney Disease

The gut dysbiosis present in chronic kidney disease (CKD) has been associated with anemia. Factors such as the accumulation of gut-derived uremic toxins, increased gut barrier permeability-induced inflammation, and a reduced intestinal production of short-chain fatty acids (SCFAs), all associated with changes in the intestinal microbiota composition in CKD, may lead to the development or worsening of anemia in renal patients. Understanding and addressing these mechanisms related to gut dysbiosis in CKD patients can help to delay the development of anemia and improve its control in this population. One approach is to avoid or reduce the use of drugs linked to gut dysbiosis in CKD, such as phosphate binders, oral iron supplementation, antibiotics, and others, unless they are indispensable. Another approach involves introducing dietary changes that promote a healthier microbiota and/or using prebiotics, probiotics, or symbiotics to improve gut dysbiosis in this setting. These measures can increase the presence of SCFA-producing saccharolytic bacteria and reduce proteolytic bacteria, thereby lowering the production of gut-derived uremic toxins and inflammation. By ameliorating CKD-related gut dysbiosis, these strategies can also improve the control of renal anemia and enhance the response to erythropoiesis-stimulating agents (ESAs) in ESA-resistant patients. In this review, we have explored the relationship between gut dysbiosis in CKD and renal anemia and propose feasible solutions, both those already known and potential future treatments.

Pathogenesis of Sarcopenia in Chronic Kidney Disease-The Role of Inflammation, Metabolic Dysregulation, Gut Dysbiosis, and microRNA

Chronic kidney disease (CKD) is a progressive disorder associated with a decline in kidney function. Consequently, patients with advanced stages of CKD require renal replacement therapies, such as dialysis and kidney transplantation. Various conditions lead to the development of CKD, including diabetes mellitus, hypertension, and glomerulonephritis, among others. The disease is associated with metabolic and hormonal dysregulation, including uraemia and hyperparathyroidism, as well as with low-grade systemic inflammation. Altered homeostasis increases the risk of developing severe comorbidities, such as cardiovascular diseases or sarcopenia, which increase mortality. Sarcopenia is defined as a progressive decline in muscle mass and function. However, the precise mechanisms that link CKD and the development of sarcopenia are poorly understood. Knowledge about these linking mechanisms might lead to the introduction of precise treatment strategies that could prevent muscle wasting. This review discusses inflammatory mediators, metabolic and hormonal dysregulation, gut microbiota dysbiosis, and non-coding RNA alterations that could link CKD and sarcopenia.

Liquid Chromatography-Mass Spectrometry Analytical Methods for the Quantitation of p-Cresol Sulfate and Indoxyl Sulfate in Human Matrices: Biological Applications and Diagnostic Potentials

Indoxyl sulfate (IxS) and p-cresyl sulfate (pCS) are toxic uremic compounds with documented pathological outcomes. This review critically and comprehensively analyzes the available liquid chromatography-mass spectrometry methods quantifying IxS and pCS in human matrices and the biological applications of these validated assays. Embase, Medline, PubMed, Scopus, and Web of Science were searched until December 2023 to identify assays with complete analytical and validation data (N = 23). Subsequently, citation analysis with PubMed and Scopus was utilized to identify the biological applications for these assays (N = 45). The extraction methods, mobile phase compositions, chromatography, and ionization methods were evaluated with respect to overall assay performance (e.g., sensitivity, separation, interference). Most of the assays focused on human serum/plasma, utilizing acetonitrile or methanol (with ammonium acetate/formate or formic/acetic acid), liquid-liquid extraction, reverse phase (e.g., C18) chromatography, and gradient elution for analyte separation. Mass spectrometry conditions were also consistent in the identified papers, with negative electrospray ionization, select multiple reaction monitoring transitions and deuterated internal standards being the most common approaches. The validated biological applications indicated IxS and/or pCS were correlated with renal disease progression and cardiovascular outcomes, with limited data on central nervous system disorders. Methods for reducing IxS and/or pCS concentrations were also identified (e.g., drugs, natural products, diet, dialysis, transplantation) where inconsistent findings have been reported. The clinical monitoring of IxS and pCS is gaining significant interest, and this review will serve as a useful compendium for scientists and clinicians.

Exploring Microbial Metabolite Receptors in Inflammatory Bowel Disease: An In Silico Analysis of Their Potential Role in Inflammation and Fibrosis

Metabolites produced by dysbiotic intestinal microbiota can influence disease pathophysiology by participating in ligand-receptor interactions. Our aim was to investigate the differential expression of metabolite receptor (MR) genes between inflammatory bowel disease (IBD), healthy individuals (HIs), and disease controls in order to identify possible interactions with inflammatory and fibrotic pathways in the intestine. RNA-sequencing datasets containing 643 Crohn's disease (CD) patients, 467 ulcerative colitis (UC) patients and 295 HIs, and 4 Campylobacter jejuni-infected individuals were retrieved from the Sequence Read Archive, and differential expression was performed using the RaNA-seq online platform. The identified differentially expressed MR genes were used for correlation analysis with up- and downregulated genes in IBD, as well as functional enrichment analysis using a R based pipeline. Overall, 15 MR genes exhibited dysregulated expression in IBD. In inflamed CD, the hydroxycarboxylic acid receptors 2 and 3 (HCAR2, HCAR3) were upregulated and were associated with the recruitment of innate immune cells, while, in the non-inflamed CD ileum, the cannabinoid receptor 1 (CNR1) and the sphingosine-1-phospate receptor 4 (S1PR4) were downregulated and were involved in the regulation of B-cell activation. In inflamed UC, the upregulated receptors HCAR2 and HCAR3 were more closely associated with the process of TH-17 cell differentiation, while the pregnane X receptor (NR1I2) and the transient receptor potential vanilloid 1 (TRPV1) were downregulated and were involved in epithelial barrier maintenance. Our results elucidate the landscape of metabolite receptor expression in IBD, highlighting associations with disease-related functions that could guide the development of new targeted therapies.

Gut microbial metabolites SCFAs and chronic kidney disease

The global incidence of Chronic Kidney Disease (CKD) is steadily escalating, with discernible linkage to the intricate terrain of intestinal microecology. The intestinal microbiota orchestrates a dynamic equilibrium in the organism, metabolizing dietary-derived compounds, a process which profoundly impacts human health. Among these compounds, short-chain fatty acids (SCFAs), which result from microbial metabolic processes, play a versatile role in influencing host energy homeostasis, immune function, and intermicrobial signaling, etc. SCFAs emerge as pivotal risk factors influencing CKD's development and prognosis. This paper review elucidates the impact of gut microbial metabolites, specifically SCFAs, on CKD, highlighting their role in modulating host inflammatory responses, oxidative stress, cellular autophagy, the immune milieu, and signaling cascades. An in-depth comprehension of the interplay between SCFAs and kidney disease pathogenesis may pave the way for their utilization as biomarkers for CKD progression and prognosis or as novel adjunctive therapeutic strategies.

Inhibition of Indoxyl Sulfate-Induced Reactive Oxygen Species-Related Ferroptosis Alleviates Renal Cell Injury In Vitro and Chronic Kidney Disease Progression In Vivo

The accumulation of the uremic toxin indoxyl sulfate (IS) is a key pathological feature of chronic kidney disease (CKD). The effect of IS on ferroptosis and the role of IS-related ferroptosis in CKD are not well understood. We used a renal tubular cell model and an adenine-induced CKD mouse model to explore whether IS induces ferroptosis and injury and affects iron metabolism in the renal cells and the kidneys. Our results showed that exposure to IS induced several characteristics for ferroptosis, including iron accumulation, an impaired antioxidant system, elevated reactive oxygen species (ROS) levels, and lipid peroxidation. Exposure to IS triggered intracellular iron accumulation by upregulating transferrin and transferrin receptors, which are involved in cellular iron uptake. We also observed increased levels of the iron storage protein ferritin. The effects of IS-induced ROS generation, lipid peroxidation, ferroptosis, senescence, ER stress, and injury/fibrosis were effectively alleviated by treatments with an iron chelator deferoxamine (DFO) in vitro and the adsorbent charcoal AST-120 (scavenging the IS precursor) in vivo. Our findings suggest that IS triggers intracellular iron accumulation and ROS generation, leading to the induction of ferroptosis, senescence, ER stress, and injury/fibrosis in CKD kidneys. AST-120 administration may serve as a potential therapeutic strategy.

Gut Microbiota Interventions to Retain Residual Kidney Function

Residual kidney function for patients with chronic kidney disease (CKD) is associated with better quality of life and outcome; thus, strategies should be implemented to preserve kidney function. Among the multiple causes that promote kidney damage, gut dysbiosis due to increased uremic toxin production and endotoxemia need attention. Several strategies have been proposed to modulate the gut microbiota in these patients, and diet has gained increasing attention in recent years since it is the primary driver of gut dysbiosis. In addition, medications and faecal transplantation may be valid strategies. Modifying gut microbiota composition may mitigate chronic kidney damage and preserve residual kidney function. Although various studies have shown the influential role of diet in modulating gut microbiota composition, the effects of this modulation on residual kidney function remain limited. This review discusses the role of gut microbiota metabolism on residual kidney function and vice versa and how we could preserve the residual kidney function by modulating the gut microbiota balance.