Acute Exposure to Indoxyl Sulfate Impairs Endothelium-Dependent Vasorelaxation in Rat Aorta

Donor-Derived Engineered Microvessels for Cardiovascular Risk Stratification of Patients with Kidney Failure

Cardiovascular disease is the cause of death in ≈50% of hemodialysis patients. Accumulation of uremic solutes in systemic circulation is thought to be a key driver of the endothelial dysfunction that underlies elevated cardiovascular events. A challenge in understanding the mechanisms relating chronic kidney disease to cardiovascular disease is the lack of in vitro models that allow screening of the effects of the uremic environment on the endothelium. Here, a method is described for microfabrication of human blood vessels from donor cells and perfused with donor serum. The resulting donor-derived microvessels are used to quantify vascular permeability, a hallmark of endothelial dysfunction, in response to serum spiked with pathophysiological levels of indoxyl sulfate, and in response to serum from patients with chronic kidney disease and from uremic pigs. The uremic environment has pronounced effects on microvascular integrity as demonstrated by irregular cell-cell junctions and increased permeability in comparison to cell culture media and healthy serum. Moreover, the engineered microvessels demonstrate an increase in sensitivity compared to traditional 2D assays. Thus, the devices and the methods presented here have the potential to be utilized to risk stratify and to direct personalized treatments for patients with chronic kidney disease.

Alteration of Plasma Indoles in Polycystic Ovary Syndrome

Polycystic ovary syndrome (PCOS) is one of the most common endocrinopathies in reproductive-aged women. The occurrence of PCOS was reported to be associated with the alteration of gut microbiota. Microbiota-derived indoles may possibly play a key role in glycemic control. The purpose of this work is to reveal the alteration of plasma indoles in PCOS patients and to investigate the correlation between indoles levels and glucose metabolism. Sixty-five patients with PCOS and twenty-eight age-matched women were enrolled in this work. The concentrations of plasma indoles, including indoxyl sulfate (IS), indole-3-acetic acid (IAA), indole-3-propionate (IPA), indole (IND), and 3-methylindole (3-MI), were measured by HPLC with the fluorescence detection. The plasma levels of IS, IAA, and IND were significantly elevated in patients with PCOS compared to those in the control group (p < 0.05). Furthermore, the plasma levels of IS, IAA, and IND were positively correlated with fasting glucose, fasting insulin, and the homeostatic model of insulin resistance index (HOMA-IR) (p < 0.05). Besides, the 3-MI level in the plasma was positively correlated with the fasting glucose level, whereas plasma levels of IS, IAA, IND, and 3-MI were negatively correlated with glucagon-like peptide 1 (p < 0.05). Moreover, IS and IND were considered to be risk factors for PCOS after age, BMI, T, LH, and HOMA-IR adjustment. The area under the receiver-operating characteristic curve of the combined index of five indoles was 0.867 for PCOS diagnosis. Additionally, plasma indoles altered in PCOS, which was closely associated with the glucose metabolism.

The AKI-to-CKD Transition: The Role of Uremic Toxins

After acute kidney injury (AKI), renal function continues to deteriorate in some patients. In a pro-inflammatory and profibrotic environment, the proximal tubules are subject to maladaptive repair. In the AKI-to-CKD transition, impaired recovery from AKI reduces tubular and glomerular filtration and leads to chronic kidney disease (CKD). Reduced kidney secretion capacity is characterized by the plasma accumulation of biologically active molecules, referred to as uremic toxins (UTs). These toxins have a role in the development of neurological, cardiovascular, bone, and renal complications of CKD. However, UTs might also cause CKD as well as be the consequence. Recent studies have shown that these molecules accumulate early in AKI and contribute to the establishment of this pro-inflammatory and profibrotic environment in the kidney. The objective of the present work was to review the mechanisms of UT toxicity that potentially contribute to the AKI-to-CKD transition in each renal compartment.

Indoxyl sulfate in atherosclerosis

Atherosclerosis (AS), a chronic vascular inflammatory disease, has become a main focus of attention worldwide for its chronic progressing disease course and serious complications in the later period. Nevertheless, explanations for the exact molecular mechanisms of AS initiation and development remain to be an unsolved problem. The classic pathogenesis theories, such as lipid percolation and deposition, endothelium injury, inflammation and immune damage, provide the foundation for discovering the new key molecules or signaling mechanisms. Recently, indoxyl sulfate (IS), one of non-free uremia toxins, has been noticeable for its multiple atherogenic effects. IS exists at high concentration in plasma for its great albumin binding rate. Patients with uremia have markedly elevated serum levels of IS due both to the deterioration of renal function and to the high binding affinity of IS to albumin. Nowadays, elevated incidence of circulatory disease among patients with renal dysfunction indicates correlation of uremic toxins with cardiovascular damage. In this review, the atherogenic effects of IS and the underlying mechanisms are summarized with emphasis on several key pathological events associated with AS developments, such as vascular endothelium dysfunction, arterial medial lesions, vascular oxidative stress, excessive inflammatory responses, calcification, thrombosis and foam cell formation. Although recent studies have proved the great correlation between IS and AS, deciphering cellular and pathophysiological signaling by confirming key factors involved in IS-mediated atherosclerosis development may enable identification of novel therapeutic targets.

The Role of Palmitic Acid in the Co-Toxicity of Bacterial Metabolites to Endothelial Cells

Introduction

Metabolic endotoxemia most often results from obesity and is accompanied by an increase in the permeability of the intestinal epithelial barrier, allowing co-absorption of bacterial metabolites and diet-derived fatty acids into the bloodstream. A high-fat diet (HFD) leading to obesity is a significant extrinsic factor in developing vascular atherosclerosis. In this study, we evaluated the effects of palmitic acid (PA) as a representative of long-chain saturated fatty acids (LCSFA) commonly present in HFDs, along with endotoxin (LPS; lipopolysaccharide) and uremic toxin indoxyl sulfate (IS), on human vascular endothelial cells (HUVECs).

Methods

HUVECs viability was measured based on tetrazolium salt metabolism, and cell morphology was assessed with fluorescein-phalloidin staining of cells' actin cytoskeleton. The effects of simultaneous treatment of endothelial cells with PA, LPS, and IS on nitro-oxidative stress in vascular cells were evaluated quantitatively with fluorescent probes. The expression of vascular cell adhesion molecule VCAM-1, E-selectin, and occludin, an essential tight junction protein, in HUVECs treated with these metabolites was evaluated in Western blot.

Results

PA, combined with LPS and IS, did not influence HUVECs viability but induced stress on actin fibers and focal adhesion complexes. Moreover, PA combined with LPS significantly enhanced reactive oxygen species (ROS) production in HUVECs but decreased nitric oxide (NO) generation. PA also considerably increased the expression of VCAM-1 and E-selectin in HUVECs treated with LPS or IS but decreased occludin expression.

Conclusion

Palmitic acid enhances the toxic effect of metabolic endotoxemia on the vascular endothelium.

Activation of aryl hydrocarbon receptor (AhR) in Alzheimer's disease: role of tryptophan metabolites generated by gut host-microbiota

Gut microbiota in interaction with intestinal host tissues influences many brain functions and microbial dysbiosis has been linked with brain disorders, such as neuropsychiatric conditions and Alzheimer's disease (AD). L-tryptophan metabolites and short-chained fatty acids (SCFA) are major messengers in the microbiota-brain axis. Aryl hydrocarbon receptors (AhR) are main targets of tryptophan metabolites in brain microvessels which possess an enriched expression of AhR protein. The Ah receptor is an evolutionarily conserved, ligand-activated transcription factor which is not only a sensor of xenobiotic toxins but also a pleiotropic regulator of both developmental processes and age-related tissue degeneration. Major microbiota-produced tryptophan metabolites involve indole derivatives, e.g., indole 3-pyruvic acid, indole 3-acetaldehyde, and indoxyl sulfate, whereas indoleamine and tryptophan 2,3-dioxygenases (IDO/TDO) of intestine host cells activate the kynurenine (KYN) pathway generating KYN metabolites, many of which are activators of AhR signaling. Chronic kidney disease (CKD) increases the serum level of indoxyl sulfate which promotes AD pathogenesis, e.g., it disrupts integrity of blood-brain barrier (BBB) and impairs cognitive functions. Activation of AhR signaling disturbs vascular homeostasis in brain; (i) it controls blood flow via the renin-angiotensin system, (ii) it inactivates endothelial nitric oxide synthase (eNOS), thus impairing NO production and vasodilatation, and (iii) it induces oxidative stress, stimulates inflammation, promotes cellular senescence, and enhances calcification of vascular walls. All these alterations are evident in cerebral amyloid angiopathy (CAA) in AD pathology. Moreover, AhR signaling can disturb circadian regulation and probably affect glymphatic flow. It seems plausible that dysbiosis of gut microbiota impairs the integrity of BBB via the activation of AhR signaling and thus aggravates AD pathology. KEY MESSAGES: Dysbiosis of gut microbiota is associated with dementia and Alzheimer's disease. Tryptophan metabolites are major messengers from the gut host-microbiota to brain. Tryptophan metabolites activate aryl hydrocarbon receptor (AhR) signaling in brain. The expression of AhR protein is enriched in brain microvessels and blood-brain barrier. Tryptophan metabolites disturb brain vascular integrity via AhR signaling. Dysbiosis of gut microbiota promotes inflammation and AD pathology via AhR signaling.

Endogenous humoral determinants of vascular endothelial dysfunction as triggers of acute poisoning complications

The vascular endothelium is not only the semipermeable membrane that separates tissue from blood but also an organ that regulates inflammation, vascular tone, blood clotting, angiogenesis and synthesis of connective tissue proteins. It is susceptible to the direct cytotoxic action of numerous xenobiotics and to the acute hypoxia that accompanies acute poisoning. This damage is superimposed on the preformed state of the vascular endothelium, which, in turn, depends on many humoral factors. The probability that an exogenous toxicant will cause life-threatening dysfunction of the vascular endothelium, thereby complicating the course of acute poisoning, increases with an increase in the content of endogenous substances in the blood that disrupt endothelial function. These include ammonia, bacterial endotoxin, indoxyl sulfate, para-cresyl sulfate, trimethylamine N-oxide, asymmetric dimethylarginine, glucose, homocysteine, low-density and very-low-density lipoproteins, free fatty acids and products of intravascular haemolysis. Some other endogenous substances (albumin, haptoglobin, haemopexin, biliverdin, bilirubin, tetrahydrobiopterin) or food-derived compounds (ascorbic acid, rutin, omega-3 polyunsaturated fatty acids, etc.) reduce the risk of lethal vascular endothelial dysfunction. The individual variability of the content of these substances in the blood contributes to the stochasticity of the complications of acute poisoning and is a promising target for the risk reduction measures. Another feasible option may be the repositioning of drugs that affect the function of the vascular endothelium while being currently used for other indications.

Gut Barrier in Critical States of the Body

The intestinal barrier (IB) is a system of diffusion barriers separating the intestinal chyme and blood. The aim of the review is to identify the role of IB dysfunction in the formation of critical states of the body and to substantiate ways to prevent these states. Toxic substances produced by normal intestinal microflora are characterized. The involvement of endotoxin and ammonia in the pathogenesis of sepsis, acute circulatory disorders, secondary acute pulmonary lesions, and acute cerebral insufficiency is shown. Approaches to protect the IB in critical states of the body are proposed.

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.

MicroRNA-mediated vascular intercellular communication is altered in chronic kidney disease

AIMS

Chronic kidney disease (CKD) is an independent risk factor for the development of coronary artery disease (CAD). For both, CKD and CAD, the intercellular transfer of microRNAs (miRs) through extracellular vesicles (EVs) is an important factor of disease development. Whether the combination of CAD and CKD affects endothelial function through cellular crosstalk of EV-incorporated miRs is still unknown.

METHODS AND RESULTS

Out of 172 screened CAD patients, 31 patients with CAD + CKD were identified and matched with 31 CAD patients without CKD. Additionally, 13 controls without CAD and CKD were included. Large EVs from CAD + CKD patients contained significantly lower levels of the vasculo-protective miR-130a-3p and miR-126-3p compared to CAD patients and controls. Flow cytometric analysis of plasma-derived EVs revealed significantly higher numbers of endothelial cell-derived EVs in CAD and CAD + CKD patients compared to controls. EVs from CAD + CKD patients impaired target human coronary artery endothelial cell (HCAEC) proliferation upon incubation in vitro. Consistent with the clinical data, treatment with the uraemia toxin indoxyl sulfate (IS)-reduced miR-130a-3p levels in HCAEC-derived EVs. EVs from IS-treated donor HCAECs-reduced proliferation and re-endothelialization in EV-recipient cells and induced an anti-angiogenic gene expression profile. In a mouse-experiment, intravenous treatment with EVs from IS-treated endothelial cells significantly impaired endothelial regeneration. On the molecular level, we found that IS leads to an up-regulation of the heterogenous nuclear ribonucleoprotein U (hnRNPU), which retains miR-130a-3p in the cell leading to reduced vesicular miR-130a-3p export and impaired EV-recipient cell proliferation.

CONCLUSION

Our findings suggest that EV-miR-mediated vascular intercellular communication is altered in patients with CAD and CKD, promoting CKD-induced endothelial dysfunction.

Indoxyl sulfate enhances endothelin-1-induced contraction via impairment of NO/cGMP signaling in rat aorta

The microbiome-derived tryptophan metabolite, indoxyl sulfate, is considered a harmful vascular toxin. Here, we examined the effects of indoxyl sulfate on endothelin-1 (ET-1)-induced contraction in rat thoracic aortas. Indoxyl sulfate (10-3 M, 60 min) increased ET-1-induced contraction but did not affect isotonic high-K+-induced contraction. The ET-1-induced contraction was enhanced by endothelial denudation in both control and indoxyl sulfate-treated groups. BQ123 (10-6 M), an ETA receptor antagonist, reduced the ET-1-induced contraction in both control and indoxyl sulfate groups. BQ788 (10-6 M), an ETB receptor antagonist, increased the contraction in the control group but had no effect on the indoxyl sulfate group. Conversely, indoxyl sulfate inhibited relaxation induced by IRL1620, an ETB receptor agonist. L-NNA, an NO synthase (NOS) inhibitor, increased the ET-1-induced contractions in both the control and indoxyl sulfate groups, whereas L-NPA (10-6 M), a specific neuronal NOS inhibitor, did not affect the ET-1-induced contraction in both groups. However, ODQ, an inhibitor of soluble guanylyl cyclase, increased the ET-1-induced contraction in both groups. Organic anion transporter (OAT) inhibitor probenecid (10-3 M) and antioxidant N-acetyl-L-cysteine (NAC; 5 × 10-3 M) inhibited the effects of indoxyl sulfate. A cell-permeant superoxide scavenger reduced the ET-1-induced contraction in the indoxyl sulfate group. The aortic activity of SOD was reduced by indoxyl sulfate. The present study revealed that indoxyl sulfate augments ET-1-induced contraction in rat aortae. This enhancement may be due to the impairment of NO/cGMP signaling and may be attributed to impairment of the antioxidant systems via cellular uptake through OATs.

Indoxyl-Sulfate-Induced Redox Imbalance in Chronic Kidney Disease

The accumulation of the uremic toxin indoxyl sulfate (IS) induces target organ damage in chronic kidney disease (CKD) patients, and causes complications including cardiovascular diseases, renal osteodystrophy, muscle wasting, and anemia. IS stimulates reactive oxygen species (ROS) production in CKD, which impairs glomerular filtration by a direct cytotoxic effect on the mesangial cells. IS further reduces antioxidant capacity in renal proximal tubular cells and contributes to tubulointerstitial injury. IS-induced ROS formation triggers the switching of vascular smooth muscular cells to the osteoblastic phenotype, which induces cardiovascular risk. Low-turnover bone disease seen in early CKD relies on the inhibitory effects of IS on osteoblast viability and differentiation, and osteoblastic signaling via the parathyroid hormone. Excessive ROS and inflammatory cytokine releases caused by IS directly inhibit myocyte growth in muscle wasting via myokines’ effects. Moreover, IS triggers eryptosis via ROS-mediated oxidative stress, and elevates hepcidin levels in order to prevent iron flux in circulation in renal anemia. Thus, IS-induced oxidative stress underlies the mechanisms in CKD-related complications. This review summarizes the underlying mechanisms of how IS mediates oxidative stress in the pathogenesis of CKD’s complications. Furthermore, we also discuss the potential role of oral AST-120 in attenuating IS-mediated oxidative stress after gastrointestinal adsorption of the IS precursor indole.

Apoptosis signal-regulating kinase 1 inhibition reverses deleterious indoxyl sulfate-mediated endothelial effects

AIMS

Indoxyl sulfate (IS), a protein-bound uremic toxin, is implicated in endothelial dysfunction, which contributes to adverse cardiovascular events in chronic kidney disease. Apoptosis signal regulating kinase 1 (ASK1) is a reactive oxygen species-driven kinase involved in IS-mediated adverse effects. This study assessed the therapeutic potential of ASK1 inhibition in alleviating endothelial effects induced by IS.

MAIN METHODS

IS, in the presence and absence of a selective ASK1 inhibitor (GSK2261818A), was assessed for its effect on vascular reactivity in rat aortic rings, and cultured human aortic endothelial cells where we evaluated phenotypic and mechanistic changes.

KEY FINDINGS

IS directly impairs endothelium-dependent vasorelaxation and endothelial cell migration. Mechanistic studies revealed increased production of reactive oxygen species-related markers, reduction of endothelial nitric oxide synthase and increased protein expression of tissue inhibitor of matrix metalloproteinase 1 (TIMP1). IS also increases angiopoietin-2 and tumour necrosis factor α gene expression and promotes transforming growth factor β receptor abundance. Inhibition of ASK1 ameliorated the increase in oxidative stress markers, promoted autocrine interleukin 8 pro-angiogenic signalling and decreased anti-angiogenic responses at least in part via reducing TIMP1 protein expression.

SIGNIFICANCE

ASK1 inhibition attenuated vasorelaxation and endothelial cell migration impaired by IS. Therefore, ASK1 is a viable intracellular target to alleviate uremic toxin-induced impairment in the vasculature.

Plasma Metabolomic Profiles of Glycemic Index, Glycemic Load, and Carbohydrate Quality Index in the PREDIMED Study

BACKGROUND

The quality of carbohydrate consumed, assessed by the glycemic index (GI), glycemic load (GL), or carbohydrate quality index (CQI), affects the postprandial glycemic and insulinemic responses, which have been implicated in the etiology of several chronic diseases. However, it is unclear whether plasma metabolites involved in different biological pathways could provide functional insights into the role of carbohydrate quality indices in health.

OBJECTIVES

We aimed to identify plasma metabolomic profiles associated with dietary GI, GL, and CQI.

METHODS

The present study is a cross-sectional analysis of 1833 participants with overweight/obesity (mean age = 67 y) from 2 case-cohort studies nested within the PREDIMED (Prevención con Dieta Mediterránea) trial. Data extracted from validated FFQs were used to estimate the GI, GL, and CQI. Plasma concentrations of 385 metabolites were profiled with LC coupled to MS and associations of these metabolites with those indices were assessed with elastic net regression analyses.

RESULTS

A total of 58, 18, and 57 metabolites were selected for GI, GL, and CQI, respectively. Choline, cotinine, γ-butyrobetaine, and 36:3 phosphatidylserine plasmalogen were positively associated with GI and GL, whereas they were negatively associated with CQI. Fructose-glucose-galactose was negatively and positively associated with GI/GL and CQI, respectively. Consistent associations of 21 metabolites with both GI and CQI were found but in opposite directions. Negative associations of kynurenic acid, 22:1 sphingomyelin, and 38:6 phosphatidylethanolamine, as well as positive associations of 32:1 phosphatidylcholine with GI and GL were also observed. Pearson correlation coefficients between GI, GL, and CQI and the metabolomic profiles were 0.30, 0.22, and 0.27, respectively.

CONCLUSIONS

The GI, GL, and CQI were associated with specific metabolomic profiles in a Mediterranean population at high cardiovascular disease risk. Our findings may help in understanding the role of dietary carbohydrate indices in the development of cardiometabolic disorders. This trial was registered at isrctn.com as ISRCTN35739639.

Indoxyl sulfate induces ROS production via the aryl hydrocarbon receptor-NADPH oxidase pathway and inactivates NO in vascular tissues

AIMS

The uremic toxin indoxyl sulfate (IS) was reported to be the cause of cardiovascular disease associated with chronic kidney disease. Therefore, we evaluated the direct influences of IS on vascular function, focusing on the superoxide anion (O₂^-) and nitric oxide (NO)/soluble guanylate cyclase (sGC) pathways.

MAIN METHODS

Isolated rat thoracic aortas with and without vascular endothelium were incubated with IS for 4 h in a physiological solution. In some experiments, several inhibitors were treated 30 min before the addition of IS. O₂^- production was measured by the chemiluminescence method, and the vascular reactivity to different vasorelaxants was examined using organ chamber technique.

KEY FINDINGS

1) Experiments using endothelium-intact vascular rings: IS significantly increased O₂^- production. The increase was suppressed by addition of the NADPH oxidase inhibitor apocynin, the antioxidant ascorbic acid and the aryl hydrocarbon receptor (AhR) inhibitor CH223191. Furthermore, IS attenuated the acetylcholine (ACh)-induced vasorelaxantion, which was suppressed by addition of the above drugs. 2) Experiments using endothelium-denuded vascular rings: IS significantly increased O₂^- production and also attenuated sodium nitroprusside (SNP)-induced vasorelaxation. These influences of IS were normalized only by ascorbic acid addition. On the other hand, IS did not affect the vasorelaxation by the sGC stimulator BAY 41-2272.

SIGNIFICANCE

This study suggested that IS causes O₂^- production in vascular tissues, thereby attenuating ACh- and SNP-induced vasorelaxation, probably through NO inactivation. Furthermore, it is reasonable to consider that IS-promoted O₂^- production in the presence of vascular endothelium is through binding to AhR and the activation of NADPH oxidase.

Trimethylamine-N-oxide Specifically Impairs Endothelium-Derived Hyperpolarizing Factor-Type Relaxation in Rat Femoral Artery

Although substantial evidence suggests that an increase in the level of trimethylamine-N-oxide (TMAO) is associated with the risk of cardiovascular diseases, including atherosclerosis, chronic kidney diseases, and hypertension, the direct effect of TMAO on vascular endothelial function remains unclear. Therefore, we investigated the acute effects of TMAO on endothelium-dependent relaxation induced by acetylcholine (ACh) in the superior mesenteric arteries and femoral arteries of rat. In endothelium-intact preparations, it was observed that TMAO (300 µmol/L for 60 min) did not affect ACh-induced relaxation in either of the two arteries. In endothelium-derived hyperpolarizing factor (EDHF)-mediated relaxation under nitric oxide synthase (NOS) and cyclooxygenase (COX) inhibitions by N^ω-nitro-L-arginine (L-NNA) and indomethacin, respectively, TMAO specifically impairs the relaxation in femoral arteries but not in the superior mesenteric arteries. Under the inhibitory actions of NOS and as well as blockade of intermediate-conductance calcium-activated potassium channel (IK_Ca) (by TRAM-34) and small-conductance calcium-activated potassium channel (SK_Ca) (by apamin), which are putative sources of EDHF, ACh-induced relaxation was low, and there were no differences between the control and TMAO-treated groups with respect to both arteries. In femoral arteries, TMAO slightly reduces ACh-induced relaxation in the presence of indomethacin (preserved NO and EDHF signals) but does not affect ACh-induced NO-mediated relaxation under the combined presence of indomethacin, TRAM-34, and apamin. These results suggest that acute treatment with TMAO specifically impairs EDHF-mediated relaxation in the femoral arteries but not in the superior mesenteric arteries. These novel observations show that TMAO is a causative factor in the development of peripheral arterial disease.

Role of S-Equol, Indoxyl Sulfate, and Trimethylamine N-Oxide on Vascular Function

Gut microbiota have been emerging as important contributors to the regulation of host homeostasis. Accordingly, several substances converted by gut microbiota can have beneficial or adverse effects on human health. Among them, S-equol, which is produced from the isoflavone daidzein in the human and animal gut by certain microbiota, exerts estrogenic and antioxidant activities. Indoxyl sulfate, which is metabolized in the liver from indole converted from dietary tryptophan by bacterial tryptophanases in the colon, is known as a protein-bound uremic toxin. Trimethylamine N-oxide, which is generated via the oxidization of gut microbiota-derived trimethylamine by hepatic flavin monooxygenases, is known as an accelerator of atherosclerosis. The aforementioned gut-derived substances could be potential regulators of systematic tissue/organ function, including the vascular system. Macro- and microvascular complications of cardiovascular and metabolic diseases, including atherosclerosis, hypertension, and diabetes, occur systemically and represent the principal cause of morbidity and mortality. Vascular endothelial and smooth muscle dysfunction play pivotal roles in the development and progression of vasculopathies. We herein review the link between the aforementioned gut-derived substances and endothelial and vascular smooth muscle cell function. This information will provide a conceptual framework that would allow the development of novel preventive and/or therapeutic approaches against vasculopathies.

Direct Impairment of the Endothelial Function by Acute Indoxyl Sulfate through Declined Nitric Oxide and Not Endothelium-Derived Hyperpolarizing Factor or Vasodilator Prostaglandins in the Rat Superior Mesenteric Artery

Upon stimulation, endothelial cells release various factors to regulate the vascular tone. In particular, vasorelaxing factors, called endothelium-derived relaxing factors (EDRFs), are altered in the production and/or release, as well as their signaling every vessel and under pathophysiological states, including cardiovascular, kidney, and metabolic diseases. Although indoxyl sulfate is known as a protein-bound uremic toxin and circulating levels are elevated in the impaired kidney functions, direct impact on the vascular function, especially EDRF's signaling, remains unclear. In this study, we hypothesize that acute exposure to indoxyl sulfate could alter vascular relaxation in the rat superior mesenteric artery. Accordingly, we measured acetylcholine (ACh)-induced endothelium-dependent relaxation in the absence and presence of several inhibitors to divide into each EDRF, including nitric oxide (NO), vasodilator prostaglandins (PGs), and endothelium-derived hyperpolarizing factor (EDHF). Indoxyl sulfate reduced the sensitivity to ACh but not sodium nitroprusside. Under cyclooxygenase (COX) inhibition or inhibitions of COX plus source of EDHF, such as small (SK_Ca)- and intermediate (IK_Ca)-conductance calcium-activated K⁺ channels, the decreased sensitivity to ACh in indoxyl sulfate exposed vessel was still preserved. However, under inhibition of NO synthase (NOS) or inhibitions of NOS and COX, the difference of sensitivity to ACh between vehicle and indoxyl sulfate was eliminated. These findings indicated that acute exposure of indoxyl sulfate in the rat superior mesenteric artery specifically explicitly impaired NO signaling but not EDHF or vasodilator PGs.

Mechanisms of Vascular Calcification in Kidney Disease

The increase in prevalence and severity of vascular calcification in chronic kidney disease is a result of complex interactions between changes in the vascular bed, mineral metabolites, and other uremic factors. Vascular calcification can occur in the intima and the media of arterial wall. Under permissive conditions, vascular smooth muscle cells (VSMCs) can transform to osteoblast-like phenotype. The membrane-bound vesicles released from transformed VSMCs and the apoptotic bodies derived from dying VSMCs serve as nucleating structures for calcium crystal formation. Alterations in the quality and the quantity of endogenous calcification inhibitors also give rise to an environment that potentiates calcification.

The gut microbiota and its relationship with chronic kidney disease

Chronic kidney disease (CKD) is a worldwide health problem, because it is one of the most common complications of metabolic diseases including obesity and type 2 diabetes. Patients with CKD also develop other comorbidities, such as hypertension, hyperlipidemias, liver and cardiovascular diseases, gastrointestinal problems, and cognitive deterioration, which worsens their health. Therapy includes reducing comorbidities or using replacement therapy, such as peritoneal dialysis, hemodialysis, and organ transplant. Health care systems are searching for alternative treatments for CKD patients to mitigate or retard their progression. One new topic is the study of uremic toxins (UT), which are excessively produced during CKD as products of food metabolism or as a result of the loss of renal function that have a negative impact on the kidneys and other organs. High urea concentrations significantly modify the microbiota in the gut also, cause a decrease in bacterial strains that produce anti-inflammatory and fuel molecules and an increase in bacterial strains that can metabolize urea, but also produce UT, including indoxyl sulfate and p-cresol sulfate. UT activates several cellular processes that induce oxidative environments, inflammation, proliferation, fibrosis development, and apoptosis; these processes mainly occur in the gut, heart, and kidney. The study of the microbiota during CKD allowed for the implementation of therapy schemes to try to reduce the circulating concentrations of UT and reduce the damage. The objective of this review is to show an overview to know the main UT produced in end-stage renal disease patients, and how prebiotics and probiotics intervention acts as a helpful tool in CKD treatment.

Polyamines and microbiota in bicuspid and tricuspid aortic valve aortopathy

Polyamines are small aliphatic cationic molecules synthesized via a highly regulated pathway and involved in general molecular and cellular phenomena. Both mammalian cells and microorganisms synthesize polyamines, and both sources may contribute to the presence of polyamines in the circulation. The dominant location for microorganisms within the body is the gut. Accordingly, the gut microbiota probably synthesizes most of the polyamines in the circulation in addition to those produced by the mammalian host cells. Polyamines are mandatory for cellular growth and proliferation. Established evidence suggests that the polyamine spermidine prolongs lifespan and improves cardiovascular health in animal models and humans through both local mechanisms, involving improved cardiomyocyte function, and systemic mechanisms, including increased NO bioavailability and reduced systemic inflammation. Higher levels of polyamines have been detected in non-dilated aorta of patients affected by bicuspid aortic valve congenital malformation, an aortopathy associated with an increased risk for thoracic ascending aorta aneurysm. In this review, we discuss metabolism of polyamines and their potential effects on vascular smooth muscle and endothelial cell function in vascular pathology of the thoracic ascending aorta associated with bicuspid or tricuspid aortic valve.