Serum Free Indoxyl Sulfate Associated with In-stent Restenosis After Coronary Artery Stentings

The Gut Microbiota (Microbiome) in Cardiovascular Disease and Its Therapeutic Regulation

In the last two decades, considerable interest has been shown in understanding the development of the gut microbiota and its internal and external effects on the intestine, as well as the risk factors for cardiovascular diseases (CVDs) such as metabolic syndrome. The intestinal microbiota plays a pivotal role in human health and disease. Recent studies revealed that the gut microbiota can affect the host body. CVDs are a leading cause of morbidity and mortality, and patients favor death over chronic kidney disease. For the function of gut microbiota in the host, molecules have to penetrate the intestinal epithelium or the surface cells of the host. Gut microbiota can utilize trimethylamine, N-oxide, short-chain fatty acids, and primary and secondary bile acid pathways. By affecting these living cells, the gut microbiota can cause heart failure, atherosclerosis, hypertension, myocardial fibrosis, myocardial infarction, and coronary artery disease. Previous studies of the gut microbiota and its relation to stroke pathogenesis and its consequences can provide new therapeutic prospects. This review highlights the interplay between the microbiota and its metabolites and addresses related interventions for the treatment of CVDs.

Diet-mediated metaorganismal relay biotransformation: health effects and pathways

In recent years, the concept of metaorganism expands our insight into how diet-microbe-host interactions contribute to human health and diseases. We realized that many biological metabolic processes in the host can be summarized into metaorganismal relay pathways, in which metabolites such as trimethylamine-N‑oxide, short-chain fatty acids and bile acids act as double-edged swords (beneficial or harmful effects) in the initiation and progression of diseases. Pleiotropic effects of metabolites are derived from several influencing factors including dose level, targeted organ of effect, action duration and species of these metabolites. Based on the pleiotropic effects of metabolites, personalized therapeutic approaches including microecological agents, enzymatic regulators and changes in dietary habits to govern related metabolite production may provide a new insight in promoting human health. In this review, we summarize our current knowledge of metaorganismal relay pathways and elaborate on the pleiotropic effects of metabolites in these pathways, with special emphasis on related therapeutic nutritional interventions.

Plasma Metabolic Profiling Analysis of Gout Party on Acute Gout Arthritis Rats Based on UHPLC-Q-TOF/MS Combined with Multivariate Statistical Analysis

Gout Party is a Chinese medicine prescription composed of Aconiti Lateralis Radix Praeparaia, Aconiti Radix Cocta, Cremastrae Pseudobulbus Pleiones Pseudobulbus, Smilacis Glabrae Rhizoma, Rehmanniae Radix, and Glycyrrhizae Radix et Rhizoma, which can relieve joint pain caused by gouty arthritis (GA) and rheumatoid, and has a therapeutic effect on acute gouty arthritis (AGA). However, little information is available on the molecular biological basis and therapeutic mechanism of Gout Party for the treatment of AGA. AGA model was established by injecting sodium urate, and colchicine served as a positive control drug. We established a metabolomic method based on ultra-high-performance liquid chromatography–tandem quadrupole/time-of-flight mass spectrometry (UHPLC–Q–TOF/MS) to analyze the plasma samples of model group rats and blank group rats. Multiple statistical analyses, including principal component analysis (PCA) and partial least square discrimination analysis (PLS-DA), were used to examine metabolite profile changes in plasma samples. Finally, we identified 2–ketobutyric acid, 3–hexenedioic acid, but–2–enoic acid, and so on; 22 endogenous metabolites associated with AGA. After successful molding, we found that 2–ketobutyric acid, 3–hexenedioic acid, but–2–enoic acid, argininic acid, galactonic acid, lactic acid, equol 4′–O–glucuronide, deoxycholic acid glycine conjugate, glycocholic acid, sphinganine 1–phosphate, LPE (0:0/20:3), LPE (0:0/16:0), LPC (15:0) decreased significantly (p < 0.05 or p < 0.01), alanine, erythrulose, 3–dehydrocarnitine, m–methylhippuric acid, 3–hydroxyoctanoic acid, p–cresol sulfate, estriol 3–sulfate 16–glucuronide, 10–hydroxy–9–(phosphonooxy)octadecenoate, docosahexaenoic acid increased significantly (p < 0.05 or p < 0.01). After Gout Party treatment, 14 biomarkers had a tendency to normal conditions. These above biomarkers were mainly involved in fatty acid metabolism, bile acid metabolism, amino acid metabolism, and energy metabolism pathways. These results suggested that Gout Party exerted therapeutic effects of treating AGA by improving energy metabolism disorder and amino acid metabolism dysfunction, and attenuating fatty acid metabolism abnormal and inflammation. The results of this experiment provided a reference for revealing the metabolic mechanism produced by Gout Party in the treatment of AGA, but the subsequent studies need to be further improved and supported by relevant cell experiments and clinical experiments.

Indoxyl sulfate-induced calcification of vascular smooth muscle cells via the PI3K/Akt/NF-κB signaling pathway

Vascular calcification (VC) is highly prevalent in patients with chronic kidney disease (CKD) and contributes to their high rate of cardiovascular mortality. Indoxyl sulfate (IS) is a representative protein-bound uremic toxin in CKD patients, which has been recognized as a major risk factor for VC. Recent studies have demonstrated that nuclear factor-kappa B (NK-κB) is highly activated in the chronic inflammation conditions of CKD patients and participated in the pathogenesis of VC. However, whether NK-κB is involved in the progression of IS-induced VC remains without elucidation. Here, we showed that NK-κB activity was increased in the IS-induced calcification of human aortic smooth muscle cells (HASMCs). Blocking the NK-κB with a selective inhibitor (Bay-11-7082) significantly relieved the osteogenic transdifferentiation of HASMCs, characterized by the downregulation of early osteogenic-specific marker, core-binding factor alpha subunit 1 (Cbfα1), and upregulation of smooth muscle α-actin (α-SMA), a specific vascular smooth muscle cell marker. Besides, IS stimulated the activation of PI3K/Akt signaling. Furthermore, LY294002, a specific inhibitor of PI3K/Akt pathway, attenuated the activation of NK-κB and osteogenic differentiation of HASMCs. Together, these results suggest that PI3K/Akt/NK-κB signaling plays an important role in the pathogenesis of osteogenic transdifferentiation induced by IS.

Unique aspects of peripheral artery disease in patients with chronic kidney disease

Peripheral artery disease (PAD) represents a major health care burden. Despite the advent of screening and interventional procedures, the long-term clinical outcomes remain suboptimal, especially in patients with chronic kidney disease (CKD). While CKD and PAD share common predisposing factors, emerging studies indicate that their co-existence is not merely an association; instead, CKD represents a strong, independent risk factor for PAD. These findings implicate CKD-specific mediators of PAD that remain incompletely understood. Moreover, there is a need to understand the mechanisms underlying poor outcomes after interventions for PAD in CKD. This review discusses unique clinical aspects of PAD in patients with CKD, including high prevalence and worse outcomes after vascular interventions and the influence of renal allograft transplantation. In doing so, it also highlights underappreciated aspects of PAD in patients with CKD, such as disparities in revascularization and higher peri-procedural mortality. While previous reviews have discussed general mechanisms of PAD pathogenesis, focusing on PAD in CKD, this review underscores a need to probe for CKD-specific pathogenic pathways that may unravel novel biomarkers and therapeutic targets in PAD and ultimately improve the risk stratification and management of patients with CKD and PAD.

Measuring serum total and free indoxyl sulfate and p-cresyl sulfate in chronic kidney disease using UPLC-MS/MS

Chronic kidney disease (CKD) is a complex disorder that affects multiple organs and increases the risk of cardiovascular complications. CKD affects approximately 12% of the population in Taiwan. Loss of kidney function leads to accumulation of potentially toxic compounds such as indoxyl sulfate (IS) and p-cresyl sulfate (pCS), two protein-bound uremic solutes that can stimulate the progression of CKD. The aim of this study was to assess whether IS and pCS levels were correlated with CKD stage. We developed and validated a method for quantitating total and free IS and pCS in serum by ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). Serum samples were pretreated using protein precipitation with acetonitrile containing stable isotope-labeled IS and pCS as internal standards. After centrifugation, the supernatant was diluted and injected into a UPLC-MS/MS system. Analyte concentrations were calculated from the calibration curve and ion ratios between the analyte and the internal standard. The calibration curves were linear with a correlation coefficient of >0.999; the analytical measurement range was 0.05–5 mg/L. The limit of quantitation of this assay was 0.05 mg/L for both analytes. The reference interval was ≤0.05–1.15 mg/L for total-form IS, ≤0.05 −5.33 mg/L for total-form pCS, ≤0.05 mg/L for free-form IS, and ≤0.12 mg/L for free-form pCS. A positive correlation was observed between analyte concentration and CKD stage. Our sensitive UPLC-MS/MS method for quantifying total and free-form IS and pCS in serum can be used to monitor the progression of CKD in clinical settings, identify patients at risk, and facilitate development of further therapies for this devastating disease.

Prognostic Significance of Serum Indoxyl Sulfate and Albumin for Patients with Cardiovascular Disease

The progression of renal dysfunction reduces serum albumin and deteriorates the binding capacity of protein-bound uremic toxins. We evaluated the prognostic implications of serum indoxyl sulfate (IS) and albumin levels in patients with cardiovascular disease.We prospectively enrolled 351 consecutive patients undergoing percutaneous revascularization for coronary artery disease or peripheral artery disease. The primary endpoint was all-cause mortality. Patients were assigned to four groups according to the median levels of serum IS (0.1 mg/dL) and albumin (3.9 g/dL).During the median follow-up time of 575 days, 16 patients died. The IS level was significantly higher in nonsurvivors (0.33 versus 0.85 mg/dL, P < 0.05). On the Kaplan-Meier curve, the high IS/low albumin group presented the highest mortality rate (log-rank test, P < 0.01). Cox proportional hazard analysis revealed that high IS/low albumin (hazard ratio (HR): 5.33; 95% confidence interval (CI): 1.71-16.5; P < 0.01), diastolic pressure (HR: 0.94; 95% CI: 0.91-0.98; P < 0.01), prior stroke (HR: 4.54; 95% CI: 1.33-15.4; P = 0.01), and left ventricular ejection fraction (LVEF) (HR: 0.92; 95% CI: 0.88-0.96; P < 0.001) were associated with increased mortality. Furthermore, the combination of IS and albumin levels significantly conferred an additive value to LVEF for predicting mortality (C-statistic: 0.69 versus 0.80; P < 0.001; net reclassification improvement: 0.83; P < 0.001; integrated discrimination improvement: 0.02; P = 0.02).A lower albumin level adds potentiating effects on IS as a prognostic factor for cardiovascular disease.

Generation, clearance, toxicity, and monitoring possibilities of unaccounted uremic toxins for improved dialysis prescriptions

Current dialysis-dosing calculations provide an incomplete assessment of blood purification. They exclude clearances of protein-bound uremic toxins (PB-UTs), such as polyamines, p-cresol sulfate, and indoxyl sulfate, relying solely on the clearance of urea as a surrogate for all molecules accumulating in patients with end-stage renal disease (ESRD). PB-UTs clear differently in dialysis but also during normal renal function. The kidney clears PB toxins via the process of secretion, whereas it clears urea through filtration. Herein, we review the clearance, accumulation, and toxicity of various UTs. We also suggest possible methods for their monitoring toward the ultimate goal of a more comprehensive dialysis prescription. A more inclusive dialysis prescription would retain the kidney-filtration surrogate, urea, and consider at least one PB toxin as a surrogate for UTs cleared through cellular secretion. A more comprehensive assessment of UTs that includes both secretion and filtration is expected to result in a better understanding of ESRD toxicity and consequently, to reduce ESRD mortality.

Gut Microbiota and Cardiovascular Uremic Toxicities

Cardiovascular disease (CVD) remains a major cause of high morbidity and mortality in patients with chronic kidney disease (CKD). Numerous CVD risk factors in CKD patients have been described, but these do not fully explain the high pervasiveness of CVD or increased mortality rates in CKD patients. In CKD the loss of urinary excretory function results in the retention of various substances referred to as "uremic retention solutes". Many of these molecules have been found to exert toxicity on virtually all organ systems of the human body, leading to the clinical syndrome of uremia. In recent years, an increasing body of evidence has been accumulated that suggests that uremic toxins may contribute to an increased cardiovascular disease (CVD) burden associated with CKD. This review examined the evidence from several clinical and experimental studies showing an association between uremic toxins and CVD. Special emphasis is addressed on emerging data linking gut microbiota with the production of uremic toxins and the development of CKD and CVD. The biological toxicity of some uremic toxins on the myocardium and the vasculature and their possible contribution to cardiovascular injury in uremia are also discussed. Finally, various therapeutic interventions that have been applied to effectively reduce uremic toxins in patients with CKD, including dietary modifications, use of prebiotics and/or probiotics, an oral intestinal sorbent that adsorbs uremic toxins and precursors, and innovative dialysis therapies targeting the protein-bound uremic toxins are also highlighted. Future studies are needed to determine whether these novel therapies to reduce or remove uremic toxins will reduce CVD and related cardiovascular events in the long-term in patients with chronic renal failure.

Uremic Toxin Clearance and Cardiovascular Toxicities

Uremic solutes contribute to cardiovascular disease in renal insufficiency. In this review we describe the clearance of selected uremic solutes, which have been associated with cardiovascular disease. These solutes—indoxyl sulfate (IS), p-cresol sulfate (PCS), phenylacetylglutamine (PAG), trimethylamine-n-oxide (TMAO), and kynurenine—exemplify different mechanisms of clearance. IS and PCS are protein-bound solutes efficiently cleared by the native kidney through tubular secretion. PAG and TMAO are not protein-bound but are also cleared by the native kidney through tubular secretion, while kynurenine is not normally cleared by the kidney. Increases in the plasma levels of the normally secreted solutes IS, PCS, TMAO, and PAG in chronic kidney disease (CKD) are attributable to a reduction in their renal clearances. Levels of each of these potential toxins are even higher in patients on dialysis than in those with advanced chronic kidney disease, which can be accounted for in part by a low ratio of dialytic to native kidney clearance. The rise in plasma kynurenine in CKD and dialysis patients, by contrast, remains to be explained. Our ability to detect lower levels of the potential uremic cardiovascular toxins with renal replacement therapy may be limited by the intermittency of treatment, by increases in solute production, and by the presence of non-renal clearance. Reduction in the levels of uremic cardiovascular toxins may in the future be achieved more effectively by inhibiting their production.

Uremic Toxin Clearance and Cardiovascular Toxicities

Uremic solutes contribute to cardiovascular disease in renal insufficiency. In this review we describe the clearance of selected uremic solutes, which have been associated with cardiovascular disease. These solutes-indoxyl sulfate (IS), p-cresol sulfate (PCS), phenylacetylglutamine (PAG), trimethylamine-n-oxide (TMAO), and kynurenine-exemplify different mechanisms of clearance. IS and PCS are protein-bound solutes efficiently cleared by the native kidney through tubular secretion. PAG and TMAO are not protein-bound but are also cleared by the native kidney through tubular secretion, while kynurenine is not normally cleared by the kidney. Increases in the plasma levels of the normally secreted solutes IS, PCS, TMAO, and PAG in chronic kidney disease (CKD) are attributable to a reduction in their renal clearances. Levels of each of these potential toxins are even higher in patients on dialysis than in those with advanced chronic kidney disease, which can be accounted for in part by a low ratio of dialytic to native kidney clearance. The rise in plasma kynurenine in CKD and dialysis patients, by contrast, remains to be explained. Our ability to detect lower levels of the potential uremic cardiovascular toxins with renal replacement therapy may be limited by the intermittency of treatment, by increases in solute production, and by the presence of non-renal clearance. Reduction in the levels of uremic cardiovascular toxins may in the future be achieved more effectively by inhibiting their production.

Role of Uremic Toxins for Kidney, Cardiovascular, and Bone Dysfunction

With decreasing kidney function, cardiovascular disease (CVD) and mineral bone disorders frequently emerge in patients with chronic kidney disease (CKD). For these patients, in addition to the traditional risk factors, non-traditional CKD-specific risk factors are also associated with such diseases and conditions. One of these non-traditional risk factors is the accumulation of uremic toxins (UTs). In addition, the accumulation of UTs further deteriorates kidney function. Recently, a huge number of UTs have been identified. Although many experimental and clinical studies have reported associations between UTs and the progression of CKD, CVD, and bone disease, these relationships are very complex and have not been fully elucidated. Among the UTs, indoxyl sulfate, asymmetric dimethylarginine, and p-cresylsulfate have been of particular focus, up until now. In this review, we summarize the pathophysiological influences of these UTs on the kidney, cardiovascular system, and bone, and discuss the clinical data regarding the harmful effects of these UTs on diseases and conditions.

Role of uremic toxin indoxyl sulfate in the progression of cardiovascular disease

The prevalence of cardiovascular disease (CVD) among patients with chronic kidney disease (CKD) is relatively high. Deterioration of renal function in CKD leads to accumulation of indoxyl sulfate, a tryptophan metabolite produced by gut microbiota. It is acknowledged that indoxyl sulfate is capable to stimulate oxidative stress, which in turn contributes to the progression of vascular disorders and its resultant coronary artery disease. Recent research have demonstrated the adverse effects of indoxyl sulfate on the heart, together with the acceleration of vascular dysfunction, suggesting that indoxyl sulfate might contribute to high prevalence of CVD in CKD. The present mini review has focused on the potential mechanisms by which indoxyl sulfate exerts this pro-oxidant effects on the cardiovascular system. The action of indoxyl sulfate are related to multiple NADPH oxidase-mediated redox signaling pathways, which have been implicated in the pathophysiology of different forms of CVD, including chronic heart failure, arrhythmia, atherosclerotic vascular disease and coronary calcification. Future therapeutic options are discussed, including modulating gut microbial flora and blocking responsible pathophysiologic pathways.

Vasculopathy in the setting of cardiorenal syndrome: roles of protein-bound uremic toxins

Chronic kidney disease (CKD) often leads to and accelerates the progression of cardiovascular disease (CVD), while CVD also causes kidney dysfunction. This bidirectional interaction leads to the development of a complex syndrome known as cardiorenal syndrome (CRS). CRS not only involves both the heart and the kidney but also the vascular system through a vast array of contributing factors. In addition to hemodynamic, neurohormonal, mechanical, and biochemical factors, nondialyzable protein-bound uremic toxins (PBUTs) are also key contributing factors that have been demonstrated through in vitro, in vivo, and clinical observations. PBUTs are ineffectively removed by hemodialysis because their complexes with albumins are larger than the pores of the dialysis membranes. PBUTs such as indoxyl sulfate and p-cresyl sulfate are key determinate and predictive factors for the progression of CVD in CKD patients. In CRS, both vascular smooth muscle cells (VSMCs) and endothelial cells (ECs) exhibit significant dysfunction that is associated with the progression of CVD. PBUTs influence proliferation, calcification, senescence, migration, inflammation, and oxidative stress in VSMCs and ECs through various mechanisms. These pathological changes lead to arterial remodeling, stiffness, and atherosclerosis and thus reduce heart perfusion and impair left ventricular function, aggravating CRS. There is limited literature about the effect of PBUT on the vascular system and their contribution to CRS. This review summarizes current knowledge on how PBUTs influence vasculature, clarifies the relationship between uremic toxin-related vascular disease and CRS, and highlights the potential therapeutic strategies of uremic vasculopathy in the setting of CRS.

Indoxyl Sulfate-Review of Toxicity and Therapeutic Strategies

Indoxyl sulfate is an extensively studied uremic solute. It is a small molecule that is more than 90% bound to plasma proteins. Indoxyl sulfate is derived from the breakdown of tryptophan by colon microbes. The kidneys achieve high clearances of indoxyl sulfate by tubular secretion, a function not replicated by hemodialysis. Clearance by hemodialysis is limited by protein binding since only the free, unbound solute can diffuse across the membrane. Since the dialytic clearance is much lower than the kidney clearance, indoxyl sulfate accumulates to relatively high plasma levels in hemodialysis patients. Indoxyl sulfate has been most frequently implicated as a contributor to renal disease progression and vascular disease. Studies have suggested that indoxyl sulfate also has adverse effects on bones and the central nervous system. The majority of studies have assessed toxicity in cultured cells and animal models. The toxicity in humans has not yet been proven, as most data have been from association studies. Such toxicity data, albeit inconclusive, have prompted efforts to lower the plasma levels of indoxyl sulfate through dialytic and non-dialytic means. The largest randomized trial showed no benefit in renal disease progression with AST-120. No trials have yet tested cardiovascular or mortality benefit. Without such trials, the toxicity of indoxyl sulfate cannot be firmly established.