Mechanisms of tissue factor induction by the uremic toxin indole-3 acetic acid through aryl hydrocarbon receptor/nuclear factor-kappa B signaling pathway in human endothelial cells

Gut microbiota-derived metabolites: Potential targets for cardiorenal syndrome

The characteristic of cardiorenal syndrome (CRS) is simultaneous damage to both the heart and kidneys. CRS has caused a heavy burden of mortality and incidence rates worldwide. The regulation of host microbiota metabolism that triggers heart and kidney damage is an emerging research field that promotes a new perspective on cardiovascular risk. We summarize current studies from bench to bedside of gut microbiota-derived metabolites to better understand CRS in the context of gut microbiota-derived metabolites. We focused on the involvement of gut microbiota-derived metabolites in the pathophysiology of CRS, including lipid and cholesterol metabolism disorders, coagulation abnormalities and platelet aggregation, oxidative stress, endothelial dysfunction, inflammation, mitochondrial damage and energy metabolism disorders, vascular calcification and renal fibrosis, as well as emerging therapeutic approaches targeting CRS metabolism in gut microbiota-derived metabolites which provides an innovative treatment approach for CRS to improve patient prognosis and overall quality of life.

Oxidative Score and Microvesicle Profile Suggest Cardiovascular Risk in Chronic Kidney Disease

Chronic kidney disease (CKD) is associated with a high incidence of cardiovascular disease (CVD) due to the accumulation of uremic toxins, altered redox state, and chronic systemic inflammation. This study aimed to analyze the relationship between the redox status of patients with CKD and the phenotype of microvesicles (MVs) subtypes, and cardiovascular events. The oxidative stress level of each participant was determined using an individualized OXY-SCORE. The relationship between pro-oxidant and antioxidant parameters and the expression of membrane markers in endothelial-derived microvesicles (EMVs) and platelet-derived microvesicles (PMVs) was established. Patients with advanced CKD (ACKD) and hemodialysis (HD) had a higher OXY-SCORE than healthy subjects (HS), whereas peritoneal dialysis (PD) patients had similar scores to HS. PD patients showed elevated PMVs and CD41 expression, whereas HD patients had higher EMVs and CD31 expression. Patients with ACKD had higher tissue factor (TF) expression in the PMVs and EMVs. TF expression was correlated with xanthine oxidase (XO) activity and was negatively correlated with antioxidant parameters. Patients with cardiovascular events show elevated TF. In conclusion, microvesicles and oxidative stress may serve as markers of cardiovascular risk in CKD, with TF expression in PMVs and EMVs being potential predictive and prognostic biomarkers of CVD.

Protein-bound uremic toxins as therapeutic targets for cardiovascular, kidney, and metabolic disorders

Cardiovascular-kidney-metabolic (CKM) syndrome is a systemic clinical condition characterized by pathological and physiological interactions among metabolic abnormalities, chronic kidney disease, and cardiovascular diseases, leading to multi-organ dysfunction and a higher incidence of cardiovascular endpoints. Traditional approaches to managing CKM syndrome risk are inadequate in these patients, necessitating strategies targeting specific CKM syndrome risk factors. Increasing evidence suggests that addressing uremic toxins and/or pathways induced by uremic toxins may reduce CKM syndrome risk and treat the disease. This review explores the interactions among heart, kidney, and metabolic pathways in the context of uremic toxins and underscores the significant role of uremic toxins as potential therapeutic targets in the pathophysiology of these diseases. Strategies aimed at regulating these uremic toxins offer potential avenues for reversing and managing CKM syndrome, providing new insights for its clinical diagnosis and treatment.

Advances in the mechanisms of vascular calcification in chronic kidney disease

Vascular calcification (VC) is common in patients with advanced chronic kidney disease (CKD).A series of factors, such as calcium and phosphorus metabolism disorders, uremic toxin accumulation, inflammation and oxidative stress and cellular senescence, cause osteoblast-like differentiation of vascular smooth muscle cells, secretion of extracellular vesicles, and imbalance of calcium regulatory factors, which together promote the development of VC in CKD. Recent advances in epigenetics have provided better tools for the investigation of VC etiology and new approaches for finding more accurate biomarkers. These advances have not only deepened our understanding of the pathophysiological mechanisms of VC in CKD, but also provided valuable clues for the optimization of clinical predictors and the exploration of potential therapeutic targets. The aim of this article is to provide a comprehensive overview of the pathogenesis of CKD VC, especially the new advances made in recent years, including the various key factors mentioned above. Through the comprehensive analysis, we expect to provide a solid theoretical foundation and research direction for future studies targeting the specific mechanisms of CKD VC, the establishment of clinical predictive indicators and the development of potential therapeutic strategies.

Gut microbiota regulates oxidative stress and inflammation: a double-edged sword in renal fibrosis

Gut microbiota is a complex and dynamic system that plays critical roles in human health and various disease. Progressive chronic kidney disease (CKD) suggests that patients irreversibly progress to end-stage kidney disease and need renal replacement treatments, including dialysis and transplantation. Ample evidence indicates that local oxidative stress and inflammation play pivotal roles in the pathogenesis and progression of CKD and dysbiosis of gut microbiota. CKD is always accompanied by intestinal inflammation and oxidative stress, which lead to rapid systemic translocation of bacterial-derived uraemic toxins, including indoxyl sulphate, phenyl sulphate and indole-3-acetic acid, and the consequent development and aggravation of renal fibrosis. Although inflammation and oxidative stress have been extensively discussed, there is a paucity of reports on the effects of gut microbiota on renal fibrosis and gut microbiota mediation of oxidative stress and inflammation. This review provides an overview of gut microbiota on inflammation and oxidative stress in renal fibrosis, briefly discusses regulation of the gut flora using microecological preparations and natural products, such as resveratrol, curcumin and emodin as treatments for CKD, and provides a clear pathophysiological rationale for the design of promising therapeutic strategies.

Acute kidney disease in mice is associated with early cardiovascular dysfunction

Acute kidney injury (AKI) and chronic kidney disease (CKD) are major health concerns due to their increasing incidence and high mortality. They are interconnected syndromes; AKI without recovery evolves into acute kidney disease (AKD), which can indicate an AKI-to-CKD transition. Both AKI and CKD are associated with a risk of long-term cardiovascular complications, but whether vascular and cardiac dysfunctions can occur as early as the AKD period has not been studied extensively. In a mouse model of kidney injury (KI) with non-recovery, we performed vasoreactivity and echocardiography analyses on days 15 (D15) and 45 (D45) after KI. We determined the concentrations of two major gut-derived protein-bound uremic toxins known to induce cardiovascular toxicity-indoxyl sulfate (IS) and para-cresyl sulfate (PCS)-and the levels of inflammation and contraction markers on D7, D15, and D45. Mice with KI showed acute tubular and interstitial kidney lesions on D7 and D15 and chronic glomerulosclerosis on D45. They showed significant impairment of aorta relaxation and systolic-diastolic heart function, both on D15 and D45. Such dysfunction was associated with downregulation of the expression of two contractile proteins, αSMA and SERCA2a, with a more pronounced effect on D15 than on D45. KI was also followed by a rapid increase in IS and PCS serum concentrations and the expression induction of pro-inflammatory cytokines and endothelial adhesion molecules in serum and cardiovascular tissues. Therefore, these results highlight that AKD leads to early cardiac and vascular dysfunctions. How these dysfunctions could be managed to prevent cardiovascular events deserves further study.

Role of Uremic Toxins in Vascular Inflammation Associated with Chronic Kidney Disease

Cardiovascular disease (CVD) is a major complication of chronic kidney disease (CKD), despite improvements in patient care. Vascular inflammation is a crucial process in the pathogenesis of CVD and a critical factor in the cardiovascular complications in CKD patients. CKD promotes a pro-inflammatory environment that impacts the vascular wall, leading to endothelial dysfunction, increased oxidative stress, and vascular remodeling. The uremic toxins that accumulate as kidney function declines are key contributors to vascular inflammatory processes. Our review will examine how CKD leads to vascular inflammation, paving the way to CVD. We will provide an overview of the mechanisms of vascular inflammation induced by uremic toxins, with a particular focus on those derived from tryptophan metabolism. These toxins, along with their receptor, the aryl hydrocarbon receptor (AHR), have emerged as key players linking inflammation and thrombosis. A deeper understanding of the mechanisms underlying inflammation in CKD, particularly those driven by uremic toxins, could reveal valuable therapeutic targets to alleviate the burden of CVD in CKD patients.

Indole-3-acetic acid exposure leads to cardiovascular inflammation and fibrosis in chronic kidney disease rat model

Indole-3-acetic acid (IAA), a protein-bound uremic toxin, has been linked to cardiovascular morbidity and mortality in chronic kidney disease (CKD) patients. This study explores the influence of IAA (125 mg/kg) on cardiovascular changes in adenine sulfate-induced CKD rats. HPLC analysis revealed that IAA-exposed CKD rats had lower excretion and increased circulation of IAA compared to both CKD and IAA control groups. Moreover, echocardiography indicated that CKD rats exposed to IAA exhibited heart enlargement, thickening of the myocardium, and cardiac hypertrophy in contrast to CKD or IAA control group. Biochemical analyses supported the finding that IAA-induced CKD rats had elevated serum levels of c-Tn-I, CK-MB, and LDH; there was also evidence of oxidative stress in cardiac tissues, with a significant decrease in SOD and CAT levels, as well as an increase in MDA levels. The gene expression analysis found significant increases in ANP, BNP, β-MHC, TNF-α, IL-1β, and NF-κB levels in IAA-exposed CKD groups in contrast to the CKD or IAA control group. In addition, higher cardiac fibrosis markers, including Col-I and Col-III. The findings of this study indicate that IAA could trigger cardiovascular inflammation and fibrosis in CKD conditions.

Indole-3-Acetic Acid Protects Against Lipopolysaccharide-induced Endothelial Cell Dysfunction and Lung Injury through the Activation of USP40

Lung microvascular endothelial cell (EC) dysfunction is the pathological hallmark of acute respiratory distress syndrome. Heat shock protein 90 (HSP90) is a key regulator in control of endothelial barrier disruption and inflammation. Our recent study has demonstrated that ubiquitin-specific peptidase 40 (USP40) preserves endothelial integrity by targeting HSP90β for its deubiquitination and inactivation. Indole-3-acetic acid (IAA), a plant hormone of the auxin class, can also be catabolized from dietary tryptophan by the intestinal microbiota. Accumulating evidence suggests that IAA reduces oxidative stress and inflammation and promotes intestinal barrier function. However, little is known about the role of IAA in endothelial cells and acute lung injury. In this study, we investigated the role of IAA in lung endothelial cell function in the context of acute lung injury. IAA exhibited EC barrier protection against LPS-induced reduction in transendothelial electrical resistance and inflammatory responses. The underlying mechanism of IAA on EC protective effects was investigated by examining the influence of IAA on degrees of HSP90 ubiquitination and USP40 activity. We identified that IAA, acting as a potential activator of USP40, reduces HSP90 ubiquitination, thereby protecting against LPS-induced inflammation in human lung microvascular endothelial cells as well as alleviating experimental lung injury. Furthermore, the EC protective effects of IAA against LPS-induced EC dysfunction and lung injury were abolished in USP40-deficient human lung microvascular endothelial cell and lungs of USP40 EC-specific knockout (USP40cdh5-ECKO) mice. Taken together, this study reveals that IAA protects against LPS-induced EC dysfunction and lung injury through the activation of USP40.

Barleriside A, an aryl hydrocarbon receptor antagonist, ameliorates podocyte injury through inhibiting oxidative stress and inflammation

INTRODUCTION

Increasing evidence shows that hyperactive aryl hydrocarbon receptor (AHR) signalling is involved in renal disease. However, no currently available intervention strategy is effective in halting disease progression by targeting the AHR signalling. Our previous study showed that barleriside A (BSA), a major component of Plantaginis semen, exhibits renoprotective effects.

METHODS

In this study, we determined the effects of BSA on AHR expression in 5/6 nephrectomized (NX) rats. We further determined the effect of BSA on AHR, nuclear factor kappa B (NF-ƙB), and the nuclear factor erythroid 2-related factor 2 (Nrf2) signalling cascade in zymosan-activated serum (ZAS)-stimulated MPC5 cells.

RESULTS

BSA treatment improved renal function and inhibited intrarenal nuclear AHR protein expression in NX-treated rats. BSA mitigated podocyte lesions and suppressed AHR mRNA and protein expression in ZAS-stimulated MPC5 cells. BSA inhibited inflammation by improving the NF-ƙB and Nrf2 pathways in ZAS-stimulated MPC5 cells. However, BSA did not markedly upregulate the expression of podocyte-specific proteins in the ZAS-mediated MPC5 cells treated with CH223191 or AHR siRNA compared to untreated ZAS-induced MPC5 cells. Similarly, the inhibitory effects of BSA on nuclear NF-ƙB p65, Nrf2, and AHR, as well as cytoplasmic cyclooxygenase-2, heme oxygenase-1, and AHR, were partially abolished in ZAS-induced MPC5 cells treated with CH223191 or AHRsiRNA compared with untreated ZAS-induced MPC5 cells. These results indicated that BSA attenuated the inflammatory response, partly by inhibiting AHR signalling.

DISCUSSION

Both pharmacological and siNRA findings suggested that BSA mitigated podocyte lesions by improving the NF-ƙB and Nrf2 pathways via inhibiting AHR signalling. Therefore, BSA is a high-affinity AHR antagonist that abolishes oxidative stress and inflammation.

Indole-3-acetic acid induced cardiogenesis impairment in in-vivo zebrafish via oxidative stress and downregulation of cardiac morphogenic factors

Plant growth regulators (PGRs) are increasingly used to promote sustainable agriculture, but their unregulated use raises concerns about potential environmental risks. Indole-3-acetic acid (IAA), a commonly used PGR, has been the subject of research on its developmental toxicity in the in-vivo zebrafish model. IAA exposure to zebrafish embryos caused oxidative stress, lipid peroxidation, and cellular apoptosis. The study also revealed that critical antioxidant genes including sod, cat, and bcl2 were downregulated, while pro-apoptotic genes such as bax and p53 were upregulated. IAA exposure also hampered normal cardiogenesis by downregulating myl7, amhc, and vmhc genes and potentially influencing zebrafish neurobehavior. The accumulation of IAA was confirmed by HPLC analysis of IAA-exposed zebrafish tissues. These findings underscore the need for further study on the potential ecological consequences of IAA use and the need for sustainable agricultural practices.

Natural antagonistic flavones for AhR inhibit indoxyl sulfate-induced inflammatory gene expression in vitro and renal pathological damages in vivo

Background

Uremic toxin indoxyl sulfate (IS) induces vascular inflammation, a crucial event in renal failure, and vascular complications in patients with chronic kidney disease (CKD). In endothelial cells, IS increases the production of inflammatory cytokines partially via the activation of the aryl hydrocarbon receptor (AhR), and several food flavonoids have been reported to act as antagonists of AhR.

Objective

This study aimed to investigate whether antagonistic flavonoids can attenuate IS-induced inflammatory responses in vascular endothelial cells in vitro and renal failure in vivo.

Design

Human umbilical vein endothelial cells (HUVECs) pretreated with the flavones apigenin, chrysin, or luteolin were stimulated with IS. Expression levels of genes involved in AhR signaling, inflammatory cytokine production, and reactive oxygen species (ROS) production were analyzed. Uninephrectomized mice were orally administered chrysin and received daily intraperitoneal injections of IS for 4 weeks.

Results

In HUVECs, IS upregulated the mRNA expression of AhR-targeted genes (CYP1A1 and AhRR), and genes involved in inflammation (NOX4, MCP-1, IL-6, and COX2) and monocyte invasion/adhesion (ICAM1). All three flavones attenuated the IS-induced increase in the expression of these mRNAs. They also suppressed the IS-induced nuclear translocation of AhR and intracellular ROS production. Furthermore, IS-induced phosphorylation of the signal transducer and activator of transcription 3 (STAT3) was inhibited by treatment with these flavones. The results of in-vivo experiments showed that administration with chrysin attenuated the elevation of blood urea nitrogen levels and AhR-target gene expression and the pathological impairment of renal tissues in mice, regardless of higher serum levels of IS.

Conclusions

Natural food flavones antagonizing AhR exerted protective effects against IS-induced inflammation through the inhibition of the AhR-STAT3 pathway in HUVECs. Moreover, chrysin ameliorated IS-induced renal dysfunction in a mouse model of CKD. These flavonoids could be a therapeutic strategy for vascular inflammation in CKD.

Interleukin-6 as a Director of Immunological Events and Tissue Regenerative Capacity in Hemodialyzed Diabetes Patients

Hemodialyzed patients have innate immunity activation and adaptive immunity senescence. Diabetes mellitus is a frequent cause for chronic kidney disease and systemic inflammation. We studied the immunological pattern (innate and acquired immunity) and the tissular regeneration capacity in two groups of hemodialyzed patients: one comprised of diabetics and the other of non-diabetics. For inflammation, the following serum markers were determined: interleukin 6 (IL-6), interleukin 1β (IL-1β), tumoral necrosis factor α (TNF-α), IL-6 soluble receptor (sIL-6R), NGAL (human neutrophil gelatinase-associated lipocalin), and interleukin 10 (IL-10). Serum tumoral necrosis factor β (TNF-β) was determined as a cellular immune response marker. Tissue regeneration capacity was studied using neurotrophin-3 (NT-3) and vascular endothelial growth factor β (VEGF-β) serum levels. The results showed important IL-6 and sIL-6R increases in both groups, especially in the diabetic patient group. IL-6 generates trans-signaling at the cellular level through sIL-6R, with proinflammatory and anti-regenerative effects, confirmed through a significant reduction in NT-3 and VEGF-β. Our results suggest that the high serum level of IL-6 significantly influences IL-1β, TNF-β, NT-3, VEGF-β, and IL-10 behavior. Our study is the first that we know of that investigates NT-3 in this patient category. Moreover, we investigated VEGF-β and TNF-β serum behavior, whereas most of the existing data cover only VEGF-α and TNF-α in hemodialyzed patients.

Production of Toxins by the Gut Microbiota: The Role of Dietary Protein

PURPOSE OF REVIEW

This narrative review will discuss how the intake of specific protein sources (animal and vegetable) providing specific amino acids can modulate the gut microbiota composition and generate toxins. A better understanding of these interactions could lead to more appropriate dietary recommendations to improve gut health and mitigate the risk of complications promoted by the toxic metabolites formed by the gut microbiota.

RECENT FINDINGS

Gut microbiota is vital in maintaining human health by influencing immune function and key metabolic pathways. Under unfavorable conditions, the gut microbiota can produce excess toxins, which contribute to inflammation and the breakdown of the integrity of the intestinal barrier. Genetic and environmental factors influence gut microbiota diversity, with diet playing a crucial role. Emerging evidence indicates that the gut microbiota significantly metabolizes amino acids from dietary proteins, producing various metabolites with beneficial and harmful effects. Amino acids such as choline, betaine, l-carnitine, tyrosine, phenylalanine, and tryptophan can increase the production of uremic toxins when metabolized by intestinal bacteria. The type of food source that provides these amino acids affects the production of toxins. Plant-based diets and dietary fiber are associated with lower toxin formation than animal-based diets due to the high amino acid precursors in animal proteins.

Indole-3 acetic acid induced cardiac hypertrophy in Wistar albino rats

Indole-3-acetic acid (IAA) is the most widely utilized plant growth regulator. Despite its extensive usage, IAA is often overlooked as an environmental pollutant. Due to its protein-binding nature, it also functions as a uremic toxin, contributing to its association with chronic kidney disease (CKD). While in vitro and epidemiological research have demonstrated this association, the precise impact of IAA on cardiovascular disease in animal models is unknown. The main objective of this study is to conduct a mechanistic analysis of the cardiotoxic effects caused by IAA using male Wistar albino rats as the experimental model. Three different concentrations of IAA (125, 250, 500 mg/kg) were administered for 28 days. The circulating IAA concentration mimicked previously observed levels in CKD patients. The administration of IAA led to a notable augmentation in heart size and heart-to-body weight ratio, indicating cardiac hypertrophy. Echocardiographic assessments supported these observations, revealing myocardial thickening. Biochemical and gene expression analyses further corroborated the cardiotoxic effects of IAA. Dyslipidemia, increased serum c-Troponin-I levels, decreased SOD and CAT levels, and elevated lipid peroxidation in cardiac tissue were identified. Moreover, increased expression of cardiac inflammatory biomarkers, including ANP, BNP, β-MHC, Col-III, TNF-α, and NF-κB, was also found in the IAA-treated animals. Histopathological analysis confirmed the cardiotoxic nature of IAA, providing additional evidence of its adverse effects on cardiovascular health. These results offer insights into the potential negative impact of IAA on cardiovascular function, and elucidating the underlying mechanisms of its cardiotoxicity.

Uremic toxins mediate kidney diseases: the role of aryl hydrocarbon receptor

Aryl hydrocarbon receptor (AhR) was originally identified as an environmental sensor that responds to pollutants. Subsequent research has revealed that AhR recognizes multiple exogenous and endogenous molecules, including uremic toxins retained in the body due to the decline in renal function. Therefore, AhR is also considered to be a uremic toxin receptor. As a ligand-activated transcriptional factor, the activation of AhR is involved in cell differentiation and senescence, lipid metabolism and fibrogenesis. The accumulation of uremic toxins in the body is hazardous to all tissues and organs. The identification of the endogenous uremic toxin receptor opens the door to investigating the precise role and molecular mechanism of tissue and organ damage induced by uremic toxins. This review focuses on summarizing recent findings on the role of AhR activation induced by uremic toxins in chronic kidney disease, diabetic nephropathy and acute kidney injury. Furthermore, potential clinical approaches to mitigate the effects of uremic toxins are explored herein, such as enhancing uremic toxin clearance through dialysis, reducing uremic toxin production through dietary interventions or microbial manipulation, and manipulating metabolic pathways induced by uremic toxins through controlling AhR signaling. This information may also shed light on the mechanism of uremic toxin-induced injury to other organs, and provide insights into clinical approaches to manipulate the accumulated uremic toxins.

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.

The complexity of nicotinamide adenine dinucleotide (NAD), hypoxic, and aryl hydrocarbon receptor cell signaling in chronic kidney disease

Early-stage detection of chronic kidney diseases (CKD) is important to treatment that may slow and occasionally halt CKD progression. CKD of diverse etiologies share similar histologic patterns of glomerulosclerosis, tubular atrophy, and interstitial fibrosis. Macro-vascular disease and micro-vascular disease promote tissue ischemia, contributing to injury. Tissue ischemia promotes hypoxia, and this in turn activates the hypoxia-inducible transcription factors (HIFs). HIF-1α and HIF-2α, share a dimer partner, HIF-1β, with the aryl hydrocarbon receptor (AHR) and are each activated in CKD and associated with kidney cellular nicotinamide adenine dinucleotide (NAD) depletion. The Preiss-Handler, salvage, and de novo pathways regulate NAD biosynthesis and gap-junctions regulate NAD cellular retention. In the Preiss-Handler pathway, niacin forms NAD. Niacin also exhibits crosstalk with HIF and AHR cell signals in the regulation of insulin sensitivity, which is a complication in CKD. Dysregulated enzyme activity in the NAD de novo pathway increases the levels of circulating tryptophan metabolites that activate AHR, resulting in poly-ADP ribose polymerase activation, thrombosis, endothelial dysfunction, and immunosuppression. Therapeutically, metabolites from the NAD salvage pathway increase NAD production and subsequent sirtuin deacetylase activity, resulting in reduced activation of retinoic acid-inducible gene I, p53, NF-κB and SMAD2 but increased activation of FOXO1, PGC-1α, and DNA methyltransferase-1. These post-translational responses may also be initiated through non-coding RNAs (ncRNAs), which are additionally altered in CKD. Nanoparticles traverse biological systems and can penetrate almost all tissues as disease biomarkers and drug delivery carriers. Targeted delivery of non-coding RNAs or NAD metabolites with nanoparticles may enable the development of more effective diagnostics and therapies to treat CKD.

Oxidative stress and inflammation are mediated via aryl hydrocarbon receptor signalling in idiopathic membranous nephropathy

Membranous nephropathy (MN) patients are diagnosed by the presence of phospholipase A2 receptor (PLA2R) before they progress to renal failure. However, the subepithelium-like immunocomplex deposit-mediated downstream molecular pathways are poorly understood. The aryl hydrocarbon receptor (AHR), NF-ƙB and Nrf2 pathways play central roles in the pathogenesis and progression of chronic kidney disease. However, their mutual effects on MN require further examination. Thus, we investigated the effect of AHR signalling on the NF-ƙB and Nrf2 pathways in IMN patients, cationic bovine serum albumin (CBSA)-injected rats and zymosan activation serum (ZAS)-treated podocytes. IMN patients show significantly decreased serum total protein and albumin levels, increased urine protein levels and intrarenal IgG4 and PLA2R protein expression in glomeruli compared with controls. IMN patients exhibited increased mRNA expression of intrarenal AHR and its target genes, including CYP1A1, CYP1A2, CYP1B1 and COX-2. This increase was accompanied by significantly upregulated protein expression of CD3, NF-ƙB p65 and COX-2 and significantly downregulated Nrf2 and HO-1 expression. Similarly, CBSA-induced rats showed severe proteinuria and activated intrarenal AHR signalling. This was accompanied by significantly upregulated protein expression of intrarenal p-IκBα, NF-κB p65 and its gene products, including COX-2, MCP-1, iNOS, 12-LOX, p47phox and p67phox, and significantly downregulated protein expression of Nrf2 and its gene products, including HO-1, catalase, GCLC, GCLM, MnSOD and NQO1. These results were further verified in ZAS-induced podocytes. Treatment with the AHR antagonist CH223191 and AHRsiRNA significantly preserved podocyte-specific protein expression and improved the NF-ƙB and Nrf2 pathways in ZAS-induced podocytes. In contrast, similar results were obtained in ZAS-induced podocytes treated with the NF-ƙB inhibitor BAY 11-7082 and NF-κBp65 siRNA. However, neither method had a significant effect on AHR signalling. Collectively, these results indicate that the NF-ƙB pathway is a downstream target of AHR signalling. Our findings suggest that blocking AHR signalling inhibits oxidative stress and inflammation, thereby improving proteinuria and renal injury.

Platelets in Renal Disease

Kidney disease is a major global health concern, affecting millions of people. Nephrologists have shown interest in platelets because of coagulation disorders caused by renal diseases. With a better understanding of platelets, it has been found that these anucleate and abundant blood cells not only play a role in hemostasis, but also have important functions in inflammation and immunity. Platelets are not only affected by kidney disease, but may also contribute to kidney disease progression by mediating inflammation and immune effects. This review summarizes the current evidence regarding platelet abnormalities in renal disease, and the multiple effects of platelets on kidney disease progression. The relationship between platelets and kidney disease is still being explored, and further research can provide mechanistic insights into the relationship between thrombosis, bleeding, and inflammation related to kidney disease, and elucidate targeted therapies for patients with kidney disease.

Moshen granule ameliorates membranous nephropathy by regulating NF-ƙB/Nrf2 pathways via aryl hydrocarbon receptor signalling

Considerable achievements were realized in illuminating underlying pathological mechanisms of patients with idiopathic membranous nephropathy (IMN). Although IMN patients are well diagnosed before they reach renal failure, no currently available drug intervention is effective in halting IMN progression. In this study, we assess Moshen granule (MSG) effect on IMN patients and cationic bovine serum albumin (CBSA)-induced rats. Increasing studies has indicated that activation of aryl hydrocarbon receptor (AHR) was related to oxidative stress and inflammation. We further determine MSG effect on AHR, nuclear factor ƙB (NF-ƙB) and nuclear factor erythroid 2-related factor 2 (Nrf2) in the CBSA-induced rats. MSG markedly reduces proteinuria and improves kidney function in both IMN patients and rats induced by CBSA. MSG markedly inhibits increased mRNA expressions of intrarenal AHR and its four downstream target genes including CYP1A1, CYP1A2, CYP1B1 and COX-2 compared with untreated CBSA-induced rats. This is accompanied by markedly downregulated protein expressions of p-IƙBα and NF-ƙB p65 and its downstream gene products including MCP-1, COX-2, 12-LOX, iNOS, p47phox and p67phox, while markedly preserves protein expressions of Nrf2 and its downstream gene products including catalase, HO-1, GCLM, GCLC, MnSOD and NQO1 in the kidney tissues. These data suggests MSG blunts podocyte damage through inhibiting activation of NF-ƙB/Nrf2 pathway via AHR signaling. This finding may provide a promising therapy for treatment of IMN through oxidative stress and inflammation.

Emergence of an Auxin Sensing Domain in Plant-Associated Bacteria

Bacteria have evolved a sophisticated array of signal transduction systems that allow them to adapt their physiology and metabolism to changing environmental conditions. Typically, these systems recognize signals through dedicated ligand binding domains (LBDs) to ultimately trigger a diversity of physiological responses. Nonetheless, an increasing number of reports reveal that signal transduction receptors also bind antagonists to inhibit responses mediated by agonists. The mechanisms by which antagonists block the downstream signaling cascade remain largely unknown. To advance our knowledge in this field, we used the LysR-type transcriptional regulator AdmX as a model. AdmX activates the expression of an antibiotic biosynthetic cluster in the rhizobacterium Serratia plymuthica. AdmX specifically recognizes the auxin phytohormone indole-3-acetic acid (IAA) and its biosynthetic intermediate indole-3-pyruvic acid (IPA) as signals. However, only IAA, but not IPA, was shown to regulate antibiotic production in S. plymuthica. Here, we report the high-resolution structures of the LBD of AdmX in complex with IAA and IPA. We found that IAA and IPA compete for binding to AdmX. Although IAA and IPA binding does not alter the oligomeric state of AdmX, IPA binding causes a higher degree of compactness in the protein structure. Molecular dynamics simulations revealed significant differences in the binding modes of IAA and IPA by AdmX, and the inspection of the three-dimensional structures evidenced differential agonist- and antagonist-mediated structural changes. Key residues for auxin binding were identified and an auxin recognition motif defined. Phylogenetic clustering supports the recent evolutionary emergence of this motif specifically in plant-associated enterobacteria. IMPORTANCE Although antagonists were found to bind different bacterial signal transduction receptors, we are still at the early stages of understanding the molecular details by which these molecules exert their inhibitory effects. Here, we provide insight into the structural changes resulting from the binding of an agonist and an antagonist to a sensor protein. Our data indicate that agonist and antagonist recognition is characterized by small conformational differences in the LBDs that can be efficiently transmitted to the output domain to modulate the final response. LBDs are subject to strong selective pressures and are rapidly evolving domains. An increasing number of reports support the idea that environmental factors drive the evolution of sensor domains. Given the recent evolutionary history of AdmX homologs, as well as their narrow phyletic distribution within plant-associated bacteria, our results are in accordance with a plant-mediated evolutionary process that resulted in the emergence of receptor proteins that specifically sense auxin phytohormones.

Tissue Factor, Thrombosis, and Chronic Kidney Disease

Coagulation abnormalities are common in chronic kidney disease (CKD). Tissue factor (TF, factor III) is a master regulator of the extrinsic coagulation system, activating downstream coagulation proteases, such as factor Xa and thrombin, and promoting fibrin formation. TF and coagulation proteases also activate protease-activated receptors (PARs) and are implicated in various organ injuries. Recent studies have shown the mechanisms by which thrombotic tendency is increased under CKD-specific conditions. Uremic toxins, such as indoxyl sulfate and kynurenine, are accumulated in CKD and activate TF and coagulation; in addition, the TF-coagulation protease-PAR pathway enhances inflammation and fibrosis, thereby exacerbating renal injury. Herein, we review the recent research studies to understand the role of TF in increasing the thrombotic risk and CKD progression.

A bacterial chemoreceptor that mediates chemotaxis to two different plant hormones

Indole-3-acetic acid (IAA) is the main naturally occurring auxin and is produced by organisms of all kingdoms of life. In addition to the regulation of plant growth and development, IAA plays an important role in the interaction between plants and growth-promoting and phytopathogenic bacteria by regulating bacterial gene expression and physiology. We show here that an IAA metabolizing plant-associated Pseudomonas putida isolate exhibits chemotaxis to IAA that is independent of auxin metabolism. We found that IAA chemotaxis is based on the activity of the PcpI chemoreceptor and heterologous expression of pcpI conferred IAA taxis to different environmental and human pathogenic isolates of the Pseudomonas genus. Using ligand screening, microcalorimetry and quantitative chemotaxis assays, we found that PcpI failed to bind IAA directly, but recognized and mediated chemoattractions to various aromatic compounds, including the phytohormone salicylic acid. The expression of pcpI and its role in the interactions with plants was also investigated. PcpI extends the range of central signal molecules recognized by chemoreceptors. To our knowledge, this is the first report on a bacterial receptor that responds to two different phytohormones. Our study reinforces the multifunctional role of IAA and salicylic acid as intra- and inter-kingdom signal molecules.

Immune System Dysfunction and Inflammation in Hemodialysis Patients: Two Sides of the Same Coin

Biocompatibility in hemodialysis (HD) has considerably improved in recent decades, but remains an open issue to be solved, appearing essential to reduce systemic inflammation and enhance patients’ clinical outcomes. Clotting prevention, reduction in complement and leukocyte activation, and improvement of antioxidant effect represent the main goals. This review aims to analyze the different pathways involved in HD patients, leading to immune system dysfunction and inflammation. In particular, we mostly review the evidence about thrombogenicity, which probably represents the most important characteristic of bio-incompatibility. Platelet activation is one of the first steps occurring in HD patients, determining several events causing chronic sub-clinical inflammation and immune dysfunction involvement. Moreover, oxidative stress processes, resulting from a loss of balance between pro-oxidant factors and antioxidant mechanisms, have been described, highlighting the link with inflammation. We updated both innate and acquired immune system dysfunctions and their close link with uremic toxins occurring in HD patients, with several consequences leading to increased mortality. The elucidation of the role of immune dysfunction and inflammation in HD patients would enhance not only the understanding of disease physiopathology, but also has the potential to provide new insights into the development of therapeutic strategies.

Gut microbiota and diabetic kidney diseases: Pathogenesis and therapeutic perspectives

Diabetic kidney disease (DKD) is one of the major chronic complications of diabetes mellitus (DM), as well as a main cause of end-stage renal disease. Over the last few years, substantial research studies have revealed a contributory role of gut microbiota in the process of DM and DKD. Metabolites of gut microbiota like lipopolysaccharide, short-chain fatty acids, and trimethylamine N-oxide are key mediators of microbial–host crosstalk. However, the underlying mechanisms of how gut microbiota influences the onset and progression of DKD are relatively unknown. Besides, strategies to remodel the composition of gut microbiota or to reduce the metabolites of microbiota have been found recently, representing a new potential remedial target for DKD. In this mini-review, we will address the possible contribution of the gut microbiota in the pathogenesis of DKD and its role as a therapeutic target.

What If Not All Metabolites from the Uremic Toxin Generating Pathways Are Toxic? A Hypothesis

The topic of uremic toxicity has received broad attention from the nephrological community over the past few decades. An aspect that is much less often considered is the possibility that the metabolic pathways that generate uremic toxins also may produce molecules that benefit body functions. Here, we discuss this dualism based on the example of tryptophan-derived metabolites, which comprise elements that are mainly toxic, such as indoxyl sulfate, kynurenine and kynurenic acid, but also beneficial compounds, such as indole, melatonin and indole-3-propionic acid, and ambivalent (beneficial for some aspects and harmful for others) compounds such as serotonin. This dualism can also be perceived at the level of the main receptor of the tryptophan-derived metabolites, the aryl hydrocarbon receptor (AHR), which has also been linked to both harm and benefit. We hypothesize that these beneficial effects are the reason why uremic toxin generation remained preserved throughout evolution. This duality is also not unique for the tryptophan-derived metabolites, and in this broader context we discuss the remote sensing and signaling theory (RSST). The RSST proposes that transporters (e.g., organic anion transporter 1—OAT1; ATP-binding cassette transporter G—ABCG2) and drug metabolizing enzymes form a large network of proteins interacting to promote small molecule remote communication at the inter-organ (e.g., gut–liver–heart–brain–kidney) and inter-organismal (e.g., gut microbe–host) levels. These small molecules include gut microbe-derived uremic toxins as well as beneficial molecules such as those discussed here. We emphasize that this positive side of uremic metabolite production needs more attention, and that this dualism especially needs to be considered when assessing and conceiving of therapeutic interventions. These homeostatic considerations are central to the RSST and suggest that interventions be aimed at preserving or restoring the balance between positive and negative components rather than eliminating them all without distinction.

Tryptophan Metabolites Regulate Neuropentraxin 1 Expression in Endothelial Cells

In patients with chronic kidney disease (CKD) and in animal models of CKD, the transcription factor Aryl Hydrocabon Receptor (AhR) is overactivated. In addition to the canonical AhR targets constituting the AhR signature, numerous other genes are regulated by this factor. We identified neuronal pentraxin 1 (NPTX1) as a new AhR target. Belonging to the inflammatory protein family, NPTX1 seems of prime interest regarding the inflammatory state observed in CKD. Endothelial cells were exposed to tryptophan-derived toxins, indoxyl sulfate (IS) and indole-3-acetic acid (IAA). The adenine mouse model of CKD was used to analyze NPTX1 expression in the burden of uremia. NPTX1 expression was quantified by RT-PCR and western blot. AhR involvement was analyzed using silencing RNA. We found that IS and IAA upregulated NPTX1 expression in an AhR-dependent way. Furthermore, this effect was not restricted to uremic indolic toxins since the dioxin 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) and the tryptophan photoproduct 6-formylindolo[3,2-b]carbazole (FICZ) do the same. In CKD mice, NPTX1 expression was increased in the aorta. Therefore, NPTX1 is a new target of AhR and further work is necessary to elucidate its exact role during CKD.

Zebrafish Model-Based Assessment of Indoxyl Sulfate-Induced Oxidative Stress and Its Impact on Renal and Cardiac Development

Kidney disease patients may have concurrent chronic kidney disease-associated mineral bone disorder and hypertension. Cardiovascular disease (CVD) and neuropathy occur due to kidney failure-induced accumulation of uremic toxins in the body. Indoxyl sulfate (IS), a product of indole metabolism in the liver, is produced from tryptophan by the intestinal flora and is ultimately excreted through the kidneys. Hemodialysis helps renal failure patients eliminate many nephrotoxins, except for IS, which leads to a poor prognosis. Although the impacts of IS on cardiac and renal development have been well documented using mouse and rat models, other model organisms, such as zebrafish, have rarely been studied. The zebrafish genome shares at least 70% similarity with the human genome; therefore, zebrafish are ideal model organisms for studying vertebrate development, including renal development. In this study, we aimed to investigate the impact of IS on the development of zebrafish embryos, especially cardiac and renal development. At 24 h postfertilization (hpf), zebrafish were exposed to IS at concentrations ranging from 2.5 to 10 mM. IS reduced survival and the hatching rate, caused cardiac edema, increased mortality, and shortened the body length of zebrafish embryos. In addition, IS decreased heart rates and renal function. IS affected zebrafish development via the ROS and MAPK pathways, which subsequently led to inflammation in the embryos. The results suggest that IS interferes with cardiac and renal development in zebrafish embryos, providing new evidence about the toxicity of IS to aquatic organisms and new insights for the assessment of human health risks. Accordingly, we suggest that zebrafish studies can ideally complement mouse model studies to allow the simultaneous and comprehensive investigation of the physiological impacts of uremic endotheliotoxins, such as IS, on cardiac and renal development.

Aryl Hydrocarbon Receptor Mechanisms Affecting Chronic Kidney Disease

The aryl hydrocarbon receptor (AHR) is a basic helix-loop-helix transcription factor that binds diverse endogenous and xenobiotic ligands, which regulate AHR stability, transcriptional activity, and cell signaling. AHR activity is strongly implicated throughout the course of chronic kidney disease (CKD). Many diverse organic molecules bind and activate AHR and these ligands are reported to either promote glomerular and tubular damage or protect against kidney injury. AHR crosstalk with estrogen, peroxisome proliferator-activated receptor-γ, and NF-κB pathways may contribute to the diversity of AHR responses during the various forms and stages of CKD. The roles of AHR in kidney fibrosis, metabolism and the renin angiotensin system are described to offer insight into CKD pathogenesis and therapies.

Platelet Abnormalities in CKD and Their Implications for Antiplatelet Therapy

Patients with CKD display a significantly higher risk of cardiovascular and thromboembolic complications, with around half of patients with advanced CKD ultimately dying of cardiovascular disease. Paradoxically, these patients also have a higher risk of hemorrhages, greatly complicating patient therapy. Platelets are central to hemostasis, and altered platelet function resulting in either platelet hyper- or hyporeactivity may contribute to thrombotic or hemorrhagic complications. Different molecular changes have been identified that may underlie altered platelet activity and hemostasis in CKD. In this study, we summarize the knowledge on CKD-induced aberrations in hemostasis, with a special focus on platelet abnormalities. We also discuss how prominent alterations in vascular integrity, coagulation, and red blood cell count in CKD may contribute to altered hemostasis in these patients who are high risk. Furthermore, with patients with CKD commonly receiving antiplatelet therapy to prevent secondary atherothrombotic complications, we discuss antiplatelet treatment strategies and their risk versus benefit in terms of thrombosis prevention, bleeding, and clinical outcome depending on CKD stage. This reveals a careful consideration of benefits versus risks of antiplatelet therapy in patients with CKD, balancing thrombotic versus bleeding risk. Nonetheless, despite antiplatelet therapy, patients with CKD remain at high cardiovascular risk. Thus, deep insights into altered platelet activity in CKD and underlying mechanisms are important for the optimization and development of current and novel antiplatelet treatment strategies, specifically tailored to these patients who are high risk. Ultimately, this review underlines the importance of a closer investigation of altered platelet function, hemostasis, and antiplatelet therapy in patients with CKD.

Consequences of oral antithrombotic use in patients with chronic kidney disease

We assessed the risks of bleeding, acute kidney injury (AKI), and kidney failure associated with the prescription of antithrombotic agents (oral anticoagulants and/or antiplatelet agents) in patients with moderate-to-advanced chronic kidney disease (CKD). CKD-REIN is a prospective cohort of 3022 nephrology outpatients with CKD stages 2-5 at baseline. We used cause-specific Cox proportional hazard models to estimate hazard ratios (HRs) for bleeding (identified through hospitalizations), AKI, and kidney failure. Prescriptions of oral antithrombotics were treated as time-dependent variables. At baseline, 339 (11%) patients (65% men; 69 [60-76] years) were prescribed oral anticoagulants only, 1095 (36%) antiplatelets only, and 101 (3%) both type of oral antithrombotics. Over a median (interquartile range [IQR]) follow-up period of 3.0 (IQR, 2.8-3.1) years, 152 patients experienced a bleeding event, 414 patients experienced an episode of AKI, and 270 experienced kidney failure. The adjusted HRs (95% confidence interval [95% CI]) for bleeding associated with prescriptions of antiplatelets only, oral anticoagulants only, and antiplatelet + oral anticoagulant were, respectively, 0.74 (95% CI, 0.46-1.19), 2.38 (95% CI, 1.45-3.89), and 3.96 (95% CI, 2.20-7.12). An increased risk of AKI risk was associated with the prescription of oral anticoagulants (adjusted HR, 1.90, 95% CI, 1.47-2.45) but not the prescription of antiplatelets (HR, 1.24, 95% CI, 0.98-1.56). Kidney failure was not associated with the prescription of oral antithrombotics of any type. This study confirms the high risk of AKI associated with oral anticoagulants prescription in patients with CKD and also highlights the potential aggravating effect of combining vitamin K antagonist (VKA) and antiplatelets on the risk of bleeding.

Myeloid cell-derived coagulation tissue factor is associated with renal tubular damage in mice fed an adenine diet

Patients with chronic kidney disease (CKD) commonly exhibit hypercoagulability. Increased levels of uremic toxins cause thrombogenicity by increasing tissue factor (TF) expression and activating the extrinsic coagulation cascade. TF is induced in monocytes and macrophages under pathological conditions, such as inflammatory diseases. However, the role of monocyte myeloid cell TF in CKD progression remains unclear. We aimed to clarify this issue, and the present study found that patients with CKD had elevated levels of D-dimer, a marker of fibrin degradation, which was associated with decreased estimated glomerular filtration rate and increased serum levels of uremic toxins, such as indoxyl sulfate. In vitro studies showed that several uremic toxins increased cellular TF levels in monocytic THP-1 cells. Mice with TF specifically deleted in myeloid cells were fed an adenine diet to cause uremic kidney injury. Myeloid TF deletion reduced tubular injury and pro-inflammatory gene expression in the kidneys of adenine-induced CKD but did not improve renal function as measured by plasma creatinine or blood urea nitrogen. Collectively, our findings suggest a novel concept of pathogenesis of coagulation-mediated kidney injury, in which elevated TF levels in monocytes under uremic conditions is partly involved in the development of CKD.

The therapeutic potential of diet on immune-related diseases: based on the regulation on tryptophan metabolism

Tryptophan (TRP), as an essential amino acid, plays crucial roles in maintaining immune homeostasis due to its complex metabolism pathway, including the microbial metabolism, 5-hydroxytryptamine and kynurenine pathways (KP). Metabolites from these pathways can act antioxidant and endogenous ligand of aryl hydrocarbon receptor (including microbiota metabolites: indole, indole aldehyde, indole acetic acid, indole acrylic acid, indole lactate, indole pyruvate acid, indole propionic acid, skatole, tryptamine, and indoxyl sulfate; and KP metabolites: kynurenine, kynurenic acid, 3-hydroxyanthranilic acid, xanthurenic acid, and cinnabarinic acid) for regulating immune response. In immune-related diseases, the production of pro-inflammatory cytokine activates indoleamine-2,3-dioxygenase, a rate-limiting enzyme of KP, leading to abnormal TRP metabolism in vivo. Many recent studies found that TRP metabolism could be regulated by diet, and the diet regulation on TRP metabolism could therapy related diseases. Accordingly, this review provides a critical overview of the relationships among diet, TRP metabolism and immunity with the aim to seek a treatment opportunity for immune-related diseases.

Uremic Toxins: An Alarming Danger Concerning the Cardiovascular System

The kidneys and heart share functions with the common goal of maintaining homeostasis. When kidney injury occurs, many compounds, the so-called "uremic retention solutes" or "uremic toxins," accumulate in the circulation targeting other tissues. The accumulation of uremic toxins such as p-cresyl sulfate, indoxyl sulfate and inorganic phosphate leads to a loss of a substantial number of body functions. Although the concept of uremic toxins is dated to the 1960s, the molecular mechanisms capable of leading to renal and cardiovascular injuries are not yet known. Besides, the greatest toxic effects appear to be induced by compounds that are difficult to remove by dialysis. Considering the close relationship between renal and cardiovascular functions, an understanding of the mechanisms involved in the production, clearance and overall impact of uremic toxins is extremely relevant for the understanding of pathologies of the cardiovascular system. Thus, the present study has as main focus to present an extensive review on the impact of uremic toxins in the cardiovascular system, bringing the state of the art on the subject as well as clinical implications related to patient's therapy affected by chronic kidney disease, which represents high mortality of patients with cardiac comorbidities.

Thrombolome and Its Emerging Role in Chronic Kidney Diseases

Patients with chronic kidney disease (CKD) are at an increased risk of thromboembolic complications, including myocardial infarction, stroke, deep vein thrombosis, and pulmonary embolism. These complications lead to increased mortality. Evidence points to the key role of CKD-associated dysbiosis and its effect via the generation of gut microbial metabolites in inducing the prothrombotic phenotype. This phenomenon is known as thrombolome, a panel of intestinal bacteria-derived uremic toxins that enhance thrombosis via increased tissue factor expression, platelet hyperactivity, microparticles release, and endothelial dysfunction. This review discusses the role of uremic toxins derived from gut-microbiota metabolism of dietary tryptophan (indoxyl sulfate (IS), indole-3-acetic acid (IAA), kynurenine (KYN)), phenylalanine/tyrosine (p-cresol sulfate (PCS), p-cresol glucuronide (PCG), phenylacetylglutamine (PAGln)) and choline/phosphatidylcholine (trimethylamine N-oxide (TMAO)) in spontaneously induced thrombosis. The increase in the generation of gut microbial uremic toxins, the activation of aryl hydrocarbon (AhRs) and platelet adrenergic (ARs) receptors, and the nuclear factor kappa B (NF-κB) signaling pathway can serve as potential targets during the prevention of thromboembolic events. They can also help create a new therapeutic approach in the CKD population.

Gut microbiota-derived tryptophan metabolism mediates renal fibrosis by aryl hydrocarbon receptor signaling activation

The gut microbiota has a crucial effect on regulating the intestinal mucosal immunity and maintaining intestinal homeostasis both in health and in disease state. Many effects are mediated by gut microbiota-derived metabolites and tryptophan, an essential aromatic amino acid, is considered important among many metabolites in the crosstalk between gut microbiota and the host. Kynurenine, serotonin, and indole derivatives are derived from the three major tryptophan metabolism pathways modulated by gut microbiota directly or indirectly. Aryl hydrocarbon receptor (AHR) is a cytoplasmic ligand-activated transcription factor involved in multiple cellular processes. Tryptophan metabolites as ligands can activate AHR signaling in various diseases such as inflammation, oxidative stress injury, cancer, aging-related diseases, cardiovascular diseases (CVD), and chronic kidney diseases (CKD). Accumulated uremic toxins in the body fluids of CKD patients activate AHR and affect disease progression. In this review, we will elucidate the relationship between gut microbiota-derived uremic toxins by tryptophan metabolism and AHR activation in CKD and its complications. This review will provide therapeutic avenues for targeting CKD and concurrently present challenges and opportunities for designing new therapeutic strategies against renal fibrosis.

Microbiota-Mediated Immune Regulation in Atherosclerosis

There is a high level of interest in identifying metabolites of endogenously produced or dietary compounds generated by the gastrointestinal (GI) tract microbiota, and determining the functions of these metabolites in health and disease. There is a wealth of compelling evidence that the microbiota is linked with many complex chronic inflammatory diseases, including atherosclerosis. Macrophages are key target immune cells in atherosclerosis. A hallmark of atherosclerosis is the accumulation of pro-inflammatory macrophages in coronary arteries that respond to pro-atherogenic stimuli and failure of digesting lipids that contribute to foam cell formation in atherosclerotic plaques. This review illustrates the role of tryptophan-derived microbiota metabolites as an aryl hydrocarbon receptor (AhR) ligand that has immunomodulatory properties. Also, microbiota-dependent trimethylamine-N-oxide (TMAO) metabolite production is associated with a deleterious effect that promotes atherosclerosis, and metabolite indoxyl sulfate has been shown to exacerbate atherosclerosis. Our objective in this review is to discuss the role of microbiota-derived metabolites in atherosclerosis, specifically the consequences of microbiota-induced effects of innate immunity in response to atherogenic stimuli, and how specific beneficial/detrimental metabolites impact the development of atherosclerosis by regulating chronic endotoxemic and lipotoxic inflammation.

The Aryl Hydrocarbon Receptor in Chronic Kidney Disease: Friend or Foe?

The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor that promotes cell responses to small molecules derived from the diet, microorganisms, metabolism and pollutants. The AhR signal regulates many basic cellular processes, including cell cycle progression, adhesion, migration, apoptosis and cell proliferation. Many studies have shown that AhR is associated with chronic kidney disease (CKD) and its complications. This article reviews the current knowledge about the role of AhR in CKD, showing that AhR mediates CKD complications, including cardiovascular disease, anemia, bone disorders, cognitive dysfunction and malnutrition, and that it influences drug metabolism in individuals with CKD. AhR enhances the intestinal barrier function to reduce the harmful effects of uremic toxins. Therefore, understanding the complex roles of AhR during CKD is important to be able to target this transcription factor safely and effectively for CKD prevention and treatment.

Resveratrol Rescue Indoxyl Sulfate-Induced Deterioration of Osteoblastogenesis via the Aryl Hydrocarbon Receptor /MAPK Pathway

Indoxyl sulfate (IS), a uremic toxin derived from dietary tryptophan metabolism by the gut microbiota, is an endogenous aryl hydrocarbon receptor (AhR) agonist and a key player in bone remodeling. Resveratrol (RSV), an AhR antagonist, plays a protective role in shielding against AhR ligands. Our study explored the impact of IS on osteoblast differentiation and examined the possible mechanism of IS in controlling the expression of osteoblastogenesis markers through an in-depth investigation of AhR signaling. In vivo, we found histological architectural disruption of the femoral bones in 5/6 nephrectomies of young adult IS exposed mice, including reduced Runx2 antigen expression. RSV improved the diaphysis architecture, Runx2 expression, and trabecular quality. In vitro data suggest that IS at 500 and 1000 μM disturbed osteoblastogenesis through suppression of the ERK and p38 mitogen-activated protein kinase (MAPK) pathways, which were found to be downstream of AhR. RSV proved to ameliorate the anti-osteoblastogenic effects of IS through the inhibition of AhR and downstream signaling. Taken together, we demonstrated that the IS/AhR/MAPK signaling pathway plays a crucial role in the inhibition of osteoblastogenesis, and RSV has a potential therapeutic role in reversing the IS-induced decline in osteoblast development and suppressing abnormal bone turnover in chronic kidney disease patients.

Endogenous Indole Pyruvate Pathway for Tryptophan Metabolism Mediated by IL4I1

l-tryptophan (Trp) is widely used in food and feed enforcement to play an important role in biological processes. Various metabolites of Trp perform its potent function. The indole pyruvate pathway is one of the main pathways of Trp metabolism in the gut microbiota, providing numerous indole-derivatives, which can modulate intestinal homeostasis and mucosal immunity by activating the aryl hydrocarbon receptor (AHR) signaling pathway. In this study, we constructed an IL4I1-overexpressed 293T cell line and found that IL4I1 can catalyze Trp to produce indole-3-acetic acid (IAA) and indole-3-carboxaldehyde (IAld). Moreover, both IAA and IAld are accumulated in dendritic cells (DCs) and can stimulate the expression of CYP1A1. Our results demonstrate the existence of the indole pyruvate pathway in host cells with IL4I1 as the key enzyme. The IL4I1-mediated Trp metabolism implies the role of dietary impact on immunity.

Molecular Mechanisms Underlying the Cardiovascular Toxicity of Specific Uremic Solutes

Mounting evidence strongly suggests a causal link between chronic kidney disease (CKD) and cardiovascular disease (CVD). Compared with non-CKD patients, patients with CKD suffer disproportionately from CVD and derive suboptimal benefits from interventions targeting conventional CVD risk factors. Uremic toxins (UTs), whose plasma levels rapidly rise as CKD progresses, represent a unique risk factor in CKD, which has protean manifestations on CVD. Among the known UTs, tryptophan metabolites and trimethylamine N-oxide are well-established cardiovascular toxins. Their molecular mechanisms of effect warrant special consideration to draw translational value. This review surveys current knowledge on the effects of specific UTs on different pathways and cell functions that influence the integrity of cardiovascular health, with implication for CVD progression. The effect of UTs on cardiovascular health is an example of a paradigm in which a cascade of molecular and metabolic events induced by pathology in one organ in turn induces dysfunction in another organ. Deciphering the molecular mechanisms underlying such cross-organ pathologies will help uncover therapeutic targets to improve the management of CVD in patients with CKD.

How do Uremic Toxins Affect the Endothelium?

Uremic toxins can induce endothelial dysfunction in patients with chronic kidney disease (CKD). Indeed, the structure of the endothelial monolayer is damaged in CKD, and studies have shown that the uremic toxins contribute to the loss of cell–cell junctions, increasing permeability. Membrane proteins, such as transporters and receptors, can mediate the interaction between uremic toxins and endothelial cells. In these cells, uremic toxins induce oxidative stress and activation of signaling pathways, including the aryl hydrocarbon receptor (AhR), nuclear factor kappa B (NF-κB), and mitogen-activated protein kinase (MAPK) pathways. The activation of these pathways leads to overexpression of proinflammatory (e.g., monocyte chemoattractant protein-1, E-selectin) and prothrombotic (e.g., tissue factor) proteins. Uremic toxins also induce the formation of endothelial microparticles (EMPs), which can lead to the activation and dysfunction of other cells, and modulate the expression of microRNAs that have an important role in the regulation of cellular processes. The resulting endothelial dysfunction contributes to the pathogenesis of cardiovascular diseases, such as atherosclerosis and thrombotic events. Therefore, uremic toxins as well as the pathways they modulated may be potential targets for therapies in order to improve treatment for patients with CKD.

Endothelial Damage, Inflammation and Immunity in Chronic Kidney Disease

Chronic kidney disease (CKD) patients have an accelerated atherosclerosis, increased risk of thrombotic-ischemic complications, and excessive mortality rates when compared with the general population. There is also evidence of an endothelial damage in which the proinflammatory state, the enhanced oxidative stress, or the accumulation of toxins due to their reduced renal clearance in uremia play a role. Further, there is evidence that uremic endothelial cells are both involved in and victims of the activation of the innate immunity. Uremic endothelial cells produce danger associated molecular patterns (DAMPS), which by binding to specific pattern recognition receptors expressed in multiple cells, including endothelial cells, induce the expression of adhesion molecules, the production of proinflammatory cytokines and an enhanced production of reactive oxygen species in endothelial cells, which constitute a link between immunity and inflammation. The connection between endothelial damage, inflammation and defective immunity in uremia will be reviewed here.

Assessment of Thrombotic and Bleeding Tendency in Two Mouse Models of Chronic Kidney Disease: Adenine-Diet and 5/6th Nephrectomy

The coexistence of bleeding and thrombosis in patients with chronic kidney disease (CKD) is frequent and poorly understood. Mouse models are essential to understand complications of CKD and to develop new therapeutic approaches improving the health of patients. We evaluated the hemostasis in two models of renal insufficiency: adenine-diet and 5/6th nephrectomy (5/6Nx). Compared with 5/6Nx mice, mice fed with 0.25% adenine had more severe renal insufficiency and so higher levels of prothrombotic uremic toxins like indoxyl sulfate. More severe renal inflammation and fibrosis were observed in the adenine group, as demonstrated by histological and reverse transcription quantitative polymerase chain reaction experiments. Liver fibrinogen γ chain expression and level of plasma fibrinogen were increased only in adenine mice. In both CKD mouse models, tissue factor (TF) expression was increased in kidney and aorta extracts. Immunochemistry analysis of kidney sections showed that TF is localized in the vascular walls. Thrombin–antithrombin complexes were significantly increased in plasma from both adenine and 5/6Nx mice. Tail bleeding time increased significantly only in adenine mice, whereas platelet count was not significant altered. Finally, results obtained by intravital microscopy after laser-induced endothelial injury showed impaired platelet function in adenine mice and an increase in fibrin generation in 5/6Nx mice. To summarize, adenine diet causes a more severe renal insufficiency compared with 5/6Nx. The TF upregulation and the hypercoagulable state were observed in both CKD models. Bleeding tendency was observed only in the adenine model of CKD that recapitulates the whole spectrum of hemostasis abnormalities observed in advanced human CKD.

Female AhR Knockout Mice Develop a Minor Renal Insufficiency in an Adenine-Diet Model of Chronic Kidney Disease

Cardiovascular complications observed in chronic kidney disease (CKD) are associated with aryl hydrocarbon receptor (AhR) activation by tryptophan-derived uremic toxins-mainly indoxyl sulfate (IS). AhR is a ligand-activated transcription factor originally characterized as a receptor of xenobiotics involved in detoxification. The aim of this study was to determine the role of AhR in a CKD mouse model based on an adenine diet. Wild-type (WT) and AhR^-/- mice were fed by alternating an adenine-enriched diet and a regular diet for 6 weeks. Our results showed an increased mortality rate of AhR^-/- males. AhR^-/- females survived and developed a less severe renal insufficiency that WT mice, reflected by urea, creatinine, and IS measurement in serum. The protective effect was related to a decrease of pro-inflammatory and pro-fibrotic gene expression, an attenuation of tubular injury, and a decrease of 2,8-dihydroxyadenine crystal deposition in the kidneys of AhR^-/- mice. These mice expressed low levels of xanthine dehydrogenase, which oxidizes adenine into 2,8-dihydroxyadenine, and low levels of the IS metabolism enzymes. In conclusion, the CKD model of adenine diet is not suitable for AhR knockout mice when studying the role of this transcription factor in cardiovascular complications, as observed in human CKD.

Aryl Hydrocarbon Receptor Activation and Tissue Factor Induction by Fluid Shear Stress and Indoxyl Sulfate in Endothelial Cells

Endogenous agonists of the transcription factor aryl hydrocarbon receptor (AHR) such as the indolic uremic toxin, indoxyl sulfate (IS), accumulate in patients with chronic kidney disease. AHR activation by indolic toxins has prothrombotic effects on the endothelium, especially via tissue factor (TF) induction. In contrast, physiological AHR activation by laminar shear stress (SS) is atheroprotective. We studied the activation of AHR and the regulation of TF by IS in cultured human umbilical vein endothelial cells subjected to laminar fluid SS (5 dynes/cm2). SS and IS markedly increased the expression of AHR target genes PTGS2 (encoding for COX2), AHRR, CYP1A1, and CYP1B1, as well as F3 (encoding for TF), in an AHR-dependent way. IS amplified SS-induced TF mRNA and protein expression and upregulation of AHR target genes. Interestingly, tyrosine kinase inhibition by genistein decreased SS- but not IS-induced TF expression. Finally, the increase in TF expression induced by laminar SS was not associated with increased TF activity. In contrast, IS increased TF activity, even under antithrombotic SS conditions. In conclusion, IS and SS induce AHR activation and AHR-dependent TF upregulation by different mechanisms. Impairment of the antithrombotic properties of shear stressed endothelium by toxic AHR agonists could favor cardiovascular diseases in CKD.

Chronodisruption: A Poorly Recognized Feature of CKD

Multiple physiological variables change over time in a predictable and repetitive manner, guided by molecular clocks that respond to external and internal clues and are coordinated by a central clock. The kidney is the site of one of the most active peripheral clocks. Biological rhythms, of which the best known are circadian rhythms, are required for normal physiology of the kidneys and other organs. Chronodisruption refers to the chronic disruption of circadian rhythms leading to disease. While there is evidence that circadian rhythms may be altered in kidney disease and that altered circadian rhythms may accelerate chronic kidney disease (CKD) progression, there is no comprehensive review on chronodisruption and chronodisruptors in CKD and its manifestations. Indeed, the term chronodisruption has been rarely applied to CKD despite chronodisruptors being potential therapeutic targets in CKD patients. We now discuss evidence for chronodisruption in CKD and the impact of chronodisruption on CKD manifestations, identify potential chronodisruptors, some of them uremic toxins, and their therapeutic implications, and discuss current unanswered questions on this topic.

Uraemic toxin-induced inflammation and oxidative stress in human endothelial cells: protective effect of polyphenol-rich extract from açaí

NEW FINDINGS

What is the central question of this study? Does a polyphenol-rich extract from açaí have a potential role in preventing uraemic toxin-induced endothelial cell dysfunction? What is the main finding and its importance? Polyphenols from açaí prevented cell death, restored migratory capacity, protected from inflammation and contributed to the restoration of the antioxidant response in endothelial cells exposed to uraemic toxins. The protective role of açaí against toxic effects exerted by uraemic toxins presents a potential new therapeutic target in endothelial cells.

ABSTRACT

In chronic kidney disease (CKD), progressive loss of kidney function results in the accumulation of protein-bound uraemic toxins such as p-cresyl sulfate (pCS) and indoxyl sulfate (IS). Among strategies to ameliorate the harmful actions of uraemic toxins, phenolic compounds have been extensively studied. The main goal of this work was to evaluate the antioxidant and anti-inflammatory actions of phenolic-rich açaí seed extract (ASE) in response to endothelial dysfunction induced by IS and pCS, in human umbilical vein endothelial cells (HUVECs). Cells were treated with ASE (10 µg ml^-1 ) in the presence or absence of IS (61 µg ml^-1 ) and pCS (40 µg ml^-1 ). Cell viability, cell death, cell migratory capacity and inflammatory biomarker expression were evaluated. Cellular antioxidant response was measured through the activity and expression of antioxidant enzymes, and oxidative damage was evaluated. IS and pCS lowered cell viability, triggered cell death and lowered the migratory capacity in endothelial cells (P < 0.05). ASE prevented cell death and restored the migratory capacity in cells exposed to IS. Both toxins up-regulated pro-inflammatory cytokine expression, and ASE was able to beneficially counteract this effect. Tumour necrosis factor-α secretion was greater in uraemic toxin-treated cells and ASE reversed this phenomenon in cells treated with both toxins concomitantly (P < 0.05). With regard to the antioxidant response, superoxide dismutase expression was strikingly lower in cells treated with both toxins, and ASE inhibited this harmful effect (P < 0.05). From the results, we conclude that ASE exerted protective effects on inflammation and oxidative stress caused by uraemic toxins (particularly by IS) in human endothelial cells.