The Impact of Uremic Toxins on Vascular Smooth Muscle Cell Function

Research on cognitive impairment and potential risk factors in peritoneal dialysis patients: An observational study

The objective of this study is to investigate the associated risk factors and their effects on cognitive impairment (CI) in patients undergoing peritoneal dialysis. A retrospective analysis was conducted on the basic information of 268 patients who underwent continuous ambulatory peritoneal dialysis (CAPD) at our hospital from January 2020 to September 2023. Cognitive function was assessed using the Montreal Cognitive Assessment Scale during their subsequent dialysis visits. Participants were categorized into a CI group and a cognitively normal group. Blood and other biological samples were collected for relevant biomarker analysis. Subsequently, we analyzed and compared the factors influencing CI between the 2 groups. The prevalence of CI among CAPD patients was 58.2%. Compared to the cognitively normal group, the CI group had a higher prevalence of alcohol consumption, lower levels of education, and reduced serum uric acid levels (P < .05). There was also a higher incidence of autoimmune diseases such as systemic lupus erythematosus in the CI group (P < .05). In terms of dialysis efficacy, the residual kidney Kt/V and residual kidney Ccr were significantly lower in the CI group compared to the cognitively normal group. In blood parameters, the CI group showed elevated total cholesterol levels and lower serum calcium concentrations (P < .05). Logistic regression analysis identified male gender, older age, lower educational attainment, hypercholesterolemia, and elevated high-sensitivity C-reactive protein levels as independent risk factors for CI in CAPD patients (P < .05). Additionally, in this patient cohort, dialysis duration and residual renal function were protective factors against CI (P < .05). CI is prevalent among PD patients. Elevated high-sensitivity C-reactive protein levels, male gender, older age, lower educational attainment, and hypercholesterolemia constitute an independent risk factor for CI in CAPD patients, whereas residual renal function acts as a protective element.

Zic family member 3 attenuates oxidative stress-induced vascular smooth muscle cell apoptosis in patients with chronic kidney disease

Neointimal hyperplasia is reportedly essential for arteriovenous fistulas (AVF) in patients undergoing hemodialysis. Oxidative stress is vital in the progression of uremic venous intimal hyperplasia. Studies have suggested that zinc ions obstruct vascular calcification in patients with chronic kidney disease (CKD). Recent studies have shown that the zinc finger protein, Zic family member 3 (ZIC3), is crucial for the earliest cardiovascular progenitors. ZIC3 mutations are associated with congenital heart disease. However, the mechanism of action of ZIC3 in vascular intimal hyperplasia in CKD remains unelucidated. Venous specimens were collected during primary AVF surgery and traumatic amputation, and serum samples were collected from patients with CKD and healthy controls. Mouse vascular smooth muscle cells (VSMCs) were treated with hydrogen peroxide (H2O2) to clarify the role of ZIC3 in CKD. ZIC3 expression was reduced in the veins of patients with uremia and the serum of those with CKD. Zic3 and Bcl2 levels were significantly decreased in mouse VSMCs treated with H2O2·H2O2 inhibited mouse VSMC activity, upregulated Bax, and cleaved caspase 3 expression. Following Zic3 overexpression, Bcl2 expression level and cell viability were elevated, whereas Bax and cleaved caspase 3 expression levels were downregulated. In contrast, Zic3 knockdown yielded the opposite results. Therefore, ZIC3 could be a new therapeutic target in venous neointimal hyperplasia of CKD.

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

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

Association of Smoking, Diabetes, and Dialysis with the Presence of Popliteal Lesions in Femoropopliteal Artery Disease

AIM

Although recent advances in endovascular devices have markedly improved clinical outcomes of femoropopliteal endovascular therapy, lesions located in the popliteal artery are still a major challenge. This study aimed to determine the association of cardiovascular risk factors, including smoking, diabetes mellitus, and dialysis-dependent renal failure, with the location of atherosclerotic lesions in femoropopliteal artery disease.

METHODS

We used a multicenter prospective study database registering patients with symptomatic femoropopliteal artery disease undergoing drug-coated balloon treatment. The analysis included 1912 patients with de novo femoropopliteal lesions. The association of clinical characteristics with popliteal lesions was investigated using the logistic regression model. In addition, the femoropopliteal artery was divided into six segments (the proximal, middle, and distal portions of the superficial femoral artery and P1, P2, and P3 segments of the popliteal artery), and the association of clinical characteristics with the presence of atherosclerotic lesions in the respective arterial segments was investigated.

RESULTS

Smoking and dialysis-dependent renal failure showed a statistically significant inverse and positive association with the presence of popliteal lesions, respectively (adjusted odds ratio, 0.66 [95% confidence interval, 0.51-0.85] and 2.01 [1.62-2.49]; P=0.001 and P＜0.001), whereas diabetes mellitus did not (P=0.17). The subsequent per-segment analysis presented similar results.

CONCLUSIONS

Smoking was inversely associated with popliteal lesions, whereas renal failure on dialysis was positively associated in patients with symptomatic femoropopliteal artery disease who underwent drug-coated balloon treatment. Diabetes mellitus was not significantly associated.

The effect of chronic kidney disease on tissue formation of in situ tissue-engineered vascular grafts

Vascular in situ tissue engineering encompasses a single-step approach with a wide adaptive potential and true off-the-shelf availability for vascular grafts. However, a synchronized balance between breakdown of the scaffold material and neo-tissue formation is essential. Chronic kidney disease (CKD) may influence this balance, lowering the usability of these grafts for vascular access in end-stage CKD patients on dialysis. We aimed to investigate the effects of CKD on in vivo scaffold breakdown and tissue formation in grafts made of electrospun, modular, supramolecular polycarbonate with ureido-pyrimidinone moieties (PC-UPy). We implanted PC-UPy aortic interposition grafts (n = 40) in a rat 5/6th nephrectomy model that mimics systemic conditions in human CKD patients. We studied patency, mechanical stability, extracellular matrix (ECM) components, total cellularity, vascular tissue formation, and vascular calcification in CKD and healthy rats at 2, 4, 8, and 12 weeks post-implantation. Our study shows successful in vivo application of a slow-degrading small-diameter vascular graft that supports adequate in situ vascular tissue formation. Despite systemic inflammation associated with CKD, no influence of CKD on patency (Sham: 95% vs CKD: 100%), mechanical stability, ECM formation (Sirius red⁺, Sham 16.5% vs CKD 25.0%-p:0.83), tissue composition, and immune cell infiltration was found. We did find a limited increase in vascular calcification at 12 weeks (Sham 0.08% vs CKD 0.80%-p:0.02) in grafts implanted in CKD animals. However, this was not associated with increased stiffness in the explants. Our findings suggest that disease-specific graft design may not be necessary for use in CKD patients on dialysis.

Preliminary study of the interactive effects of coronary heart disease and lacunar infarction on renal function in patients with type 2 diabetes mellitus by gender

BACKGROUND

Coronary heart disease (CHD) and lacunar infarction (LI) are the most common cardio- cerebrovascular complications of type 2 diabetes mellitus (T2DM) and a recognized risk factor for renal injury. Although a unidirectional association of CHD or LI with T2DM or the kidney has been demonstrated, however, it remains unknown whether there is an interactive effect of the coexistence of CHD and LI on renal function in T2DM patients. The aim of our study was to investigate the interaction between CHD and LI on renal function in gender-specific patients with T2DM and the association between cardio-cerebrovascular disease-related conventional serum markers and the estimated glomerular filtration rate (eGFR).

METHODS

We conducted a cross-sectional study in Beijing and Tianjin from April 2019 to August 2021. Participants with T2DM aged ≥18 years were asked to complete a one-to-one questionnaire and physical examination.

RESULTS

In this study, 389 eligible patients with T2DM were included, with a mean age of 63.04 ± 9.41 years, of whom 200 (51.41 %) were male. The proportions of patients with CHD, LI, and both CHD and LI were 28.53 %, 24.42 %, and 11.05 %, respectively. Compared to T2DM patients without either CHD or LI, those with both CHD and LI were found to have a significantly greater risk of reduced eGFR (OR: 12.82, 95 % CI 5.06-32.52, P < 0.001) than those with CHD alone (OR: 2.42, 95 % CI 1.37-3.00, P = 0.004) or LI alone (OR: 1.15, 95 % CI 0.61-2.18, P = 0.664). The combined presence of CHD and LI is associated with a significantly greater risk of decreased eGFR in female T2DM patients compared to their male counterparts. We found both multiplicative and additive effects in all T2DM patients; however, when stratified by sex, only multiplicative effects were observed. After controlling for interference from CHD, LI, and age, we found that total cholesterol (TC) was negatively correlated with eGFR in females (r = -0.156, P = 0.034), and low-density lipoprotein cholesterol (LDL-C) was negatively correlated with eGFR in males (r = -0.229, P = 0.001).

CONCLUSION

This study provides novel evidence that the synergistic effect of CHD and LI on renal injury in patients with T2DM is significantly greater than their individual effects. Women with T2DM who have both CHD and LI are at a 4.85-fold higher risk of decreased eGFR than men. Therefore, increased clinical attention should be given to preventing and treating vascular complications in T2DM patients, as well as aggressively reducing lipid levels, particularly TC and LDL-C, to delay or prevent renal dysfunction in T2DM patients.

Role of the Microbiome in Gut-Heart-Kidney Cross Talk

Homeostasis is a prerequisite for health. When homeostasis becomes disrupted, dysfunction occurs. This is especially the case for the gut microbiota, which under normal conditions lives in symbiosis with the host. As there are as many microbial cells in and on our body as human cells, it is unlikely they would not contribute to health or disease. The gut bacterial metabolism generates numerous beneficial metabolites but also uremic toxins and their precursors, which are transported into the circulation. Barrier function in the intestine, the heart, and the kidneys regulates metabolite transport and concentration and plays a role in inter-organ and inter-organism communication via small molecules. This communication is analyzed from the perspective of the remote sensing and signaling theory, which emphasizes the role of a large network of multispecific, oligospecific, and monospecific transporters and enzymes in regulating small-molecule homeostasis. The theory provides a systems biology framework for understanding organ cross talk and microbe-host communication involving metabolites, signaling molecules, nutrients, antioxidants, and uremic toxins. This remote small-molecule communication is critical for maintenance of homeostasis along the gut-heart-kidney axis and for responding to homeostatic perturbations. Chronic kidney disease is characterized by gut dysbiosis and accumulation of toxic metabolites. This slowly impacts the body, affecting the cardiovascular system and contributing to the progression of kidney dysfunction, which in its turn influences the gut microbiota. Preserving gut homeostasis and barrier functions or restoring gut dysbiosis and dysfunction could be a minimally invasive way to improve patient outcomes and quality of life in many diseases, including cardiovascular and kidney disease.

Involvement of lysyl oxidase in the pathogenesis of arterial stiffness in chronic kidney disease

Patients with chronic kidney disease (CKD) are at increased risk for adverse cardiovascular events. CKD is associated with increases in arterial stiffness, whereas improvements in arterial stiffness correlate with better survival. However, arterial stiffness is increased early in CKD, suggesting that there might be additional factors, unique to kidney disease, that increase arterial stiffness. Lysyl oxidase (LOX) is a key mediator of collagen cross linking and matrix remodeling. LOX is predominantly expressed in the cardiovascular system, and its upregulation has been associated with increased tissue stiffening and extracellular matrix remodeling. Thus, this study was designed to evaluate the role of increased LOX activity in inducing aortic stiffness in CKD and whether β-aminopropionitrile (BAPN), a LOX inhibitor, could prevent aortic stiffness by reducing collagen cross linking. Eight-week-old male C57BL/6 mice were subjected to 5/6 nephrectomy (Nx) or sham surgery. Two weeks after surgery, mice were randomized to BAPN (300 mg/kg/day in water) or vehicle treatment for 4 wk. Aortic stiffness was assessed by pulse wave velocity (PWV) using Doppler ultrasound. Aortic levels of LOX were assessed by ELISA, and cross-linked total collagen levels were analyzed by mass spectrometry and Sircol assay. Nx mice showed increased PWV and aortic wall remodeling compared with control mice. Collagen cross linking was increased in parallel with the increases in total collagen in the aorta of Nx mice. In contrast, Nx mice that received BAPN treatment showed decreased cross-linked collagens and PWV compared with that received vehicle treatment. Our results indicated that LOX might be an early and key mediator of aortic stiffness in CKD.NEW & NOTEWORTHY Arterial stiffness in CKD is associated with adverse cardiovascular outcomes. However, the mechanisms underlying increased aortic stiffness in CKD are unclear. Herein, we demonstrated that 1) increased aortic stiffness in CKD is independent of hypertension and calcification and 2) LOX-mediated changes in extracellular matrix are at least in part responsible for increased aortic stiffness in CKD. Prevention of excess LOX may have therapeutic potential in alleviating increased aortic stiffness and improving cardiovascular disease in CKD.

Biomechanical Properties of the Aortic Wall: Changes during Vascular Calcification

Medial vascular calcification (MAC) is characterized by the deposition of hydroxyapatite (HAP) in the medial layer of the vessel wall, leading to disruption of vessel integrity and vascular stiffness. Because currently no direct therapeutic interventions for MAC are available, studying the MAC pathogenesis is of high research interest. Several methods exist to measure and describe the pathophysiological processes in the vessel wall, such as histological staining and gene expression. However, no method describing the physiological properties of the arterial wall is currently available. This study aims to close that gap and validate a method to measure the biomechanical properties of the arterial wall during vascular calcification. Therefore, a stress-stretch curve is monitored using small-vessel-myography upon ex vivo calcification of rat aortic tissue. The measurement of biomechanical properties could help to gain further insights into vessel integrity during calcification progression.

Aorta- and liver-generated TMAO enhances trained immunity for increased inflammation via ER stress/mitochondrial ROS/glycolysis pathways

We determined whether gut microbiota-produced trimethylamine (TMA) is oxidized into trimethylamine N-oxide (TMAO) in nonliver tissues and whether TMAO promotes inflammation via trained immunity (TI). We found that endoplasmic reticulum (ER) stress genes were coupregulated with MitoCarta genes in chronic kidney diseases (CKD); TMAO upregulated 190 genes in human aortic endothelial cells (HAECs); TMAO synthesis enzyme flavin-containing monooxygenase 3 (FMO3) was expressed in human and mouse aortas; TMAO transdifferentiated HAECs into innate immune cells; TMAO phosphorylated 12 kinases in cytosol via its receptor PERK and CREB, and integrated with PERK pathways; and PERK inhibitors suppressed TMAO-induced ICAM-1. TMAO upregulated 3 mitochondrial genes, downregulated inflammation inhibitor DARS2, and induced mitoROS, and mitoTEMPO inhibited TMAO-induced ICAM-1. β-Glucan priming, followed by TMAO restimulation, upregulated TNF-α by inducing metabolic reprogramming, and glycolysis inhibitor suppressed TMAO-induced ICAM-1. Our results have provided potentially novel insights regarding TMAO roles in inducing EC activation and innate immune transdifferentiation and inducing metabolic reprogramming and TI for enhanced vascular inflammation, and they have provided new therapeutic targets for treating cardiovascular diseases (CVD), CKD-promoted CVD, inflammation, transplantation, aging, and cancer.

The Molecular Basis of the Anti-Inflammatory Property of Astragaloside IV for the Treatment of Diabetes and Its Complications

Astragali Radix is a significant traditional Chinese medication, and has a long history of clinical application in the treatment of diabetes mellitus (DM) and its complications. AS-IV is an active saponin isolated from it. Modern pharmacological study shows that AS-IV has anti-inflammatory, anti-oxidant and immunomodulatory activities. The popular inflammatory etiology of diabetes suggests that DM is a natural immune and low-grade inflammatory disease. Pharmacological intervention of the inflammatory response may provide promising and alternative approaches for the prevention and treatment of DM and its complications. Therefore, this article focuses on the potential of AS-IV in the treatment of DM from the perspective of an anti-inflammatory molecular basis. AS-IV plays a role by regulating a variety of anti-inflammatory pathways in multiple organs, tissues and target cells throughout the body. The blockade of the NF-κB inflammatory signaling pathway may be the central link of AS-IV's anti-inflammatory effect, resulting in a reduction in the tissue structure and function damage stimulated by inflammatory factors. In addition, AS-IV can delay the onset of DM and its complications by inhibiting inflammation-related oxidative stress, fibrosis and apoptosis signals. In conclusion, AS-IV has therapeutic prospects from the perspective of reducing the inflammation of DM and its complications. An in-depth study on the anti-inflammatory mechanism of AS-IV is of great significance for the effective use of Chinese herbal medicine and the promotion of its status and influence on the world.

Indoxyl sulfate impairs in vitro erythropoiesis by triggering apoptosis and senescence

Anemia is a major complication in over 50% of chronic kidney disease (CKD) patients. One of the main causes of anemia in CKD is the reduction of erythropoietin (EPO) synthesis from renal tubular cells. Therefore, first-line treatment of CKD is EPO administration; however, EPO unresponsiveness in several patients is frequently found. More undefined causes of anemia in CKD are under interest, especially uremic toxins, which are a group of solutes accumulated in CKD patients. The highly detectable protein-bound uremic toxin, indoxyl sulfate (IS) was investigated for its effects on in vitro erythropoiesis in this study. CD34+ hematopoietic stem cells were isolated from human umbilical cord blood and differentiated toward erythrocyte lineage for 14 days in various concentrations of IS (12.5, 25, 50, and 100 µg/mL). The effects of IS on cell proliferation, differentiation, apoptosis, and senescence were determined. Cell proliferation was investigated by manual cell counting. Cell surface marker expression was analyzed by flow cytometry. Wright's staining was performed to evaluate cell differentiation capacity. Apoptosis and senescence marker expression was measured using reverse transcription polymerase chain reaction (RT-PCR). TUNEL assay was performed to detect apoptotic DNA fragmentation. Our results demonstrated that IS reduced cell proliferation and impaired erythrocyte differentiation capacity. In addition, this study confirmed the effects of IS on cell apoptosis and senescence during erythropoietic differentiation. Therefore, the promotion of apoptosis and senescence might be one of the possible mechanisms caused by uremic toxin accumulation leading to anemia in CKD patients.

The direct effect of fibroblast growth factor 23 on vascular smooth muscle cell phenotype and function

BACKGROUND

In chronic kidney disease (CKD) patients, increased levels of fibroblast growth factor 23 (FGF23) are associated with cardiovascular mortality. The relationship between FGF23 and heart hypertrophy has been documented, however, it is not known whether FGF23 has an effect on vasculature. Vascular smooth muscle cells VSMCs may exhibit different phenotypes; our hypothesis is that FGF23 favours a switch from a contractile to synthetic phenotype that may cause vascular dysfunction. Our objective was to determine whether FGF23 may directly control a change in VSMC phenotype.

METHODS

This study includes in vitro, in vivo and ex vivo experiments and evaluation of patients with CKD stages 2-3 studying a relationship between FGF23 and vascular dysfunction.

RESULTS

In vitro studies show that high levels of FGF23, by acting on its specific receptor FGFR1 and Erk1/2, causes a change in the phenotype of VSMCs from contractile to synthetic. This change is mediated by a downregulation of miR-221/222, which augments the expression of MAP3K2 and PAK1. miR-221/222 transfections recovered the contractile phenotype of VSMCs. Infusion of recombinant FGF23 to rats increased vascular wall thickness, with VSMCs showing a synthetic phenotype with a reduction of miR-221 expression. Ex-vivo studies on aortic rings demonstrate also that high FGF23 increases arterial stiffening. In CKD 2-3 patients, elevation of FGF23 was associated with increased pulse wave velocity and reduced plasma levels of miR-221/222.

CONCLUSION

In VSMCs, high levels of FGF23, through the downregulation of miR-221/222, causes a change to a synthetic phenotype. This change in VSMCs increases arterial stiffening and impairs vascular function, which might ultimately worsen cardiovascular disease.

The Role of Sirtuins in Osteogenic Differentiation of Vascular Smooth Muscle Cells and Vascular Calcification

Vascular calcification (VC) is a common pathological change in many chronic diseases, such as diabetes and chronic kidney disease. It is mainly deposited in the intima and media of vessels in the form of hydroxyapatite. Recently, a lot of research has been performed to show that VC is associated with various cellular stresses, such as hyperphosphate, hyperglycemia and oxidative stress. Unfortunately, our understanding of the pathogenesis of calcification is far from comprehensive. Sirtuins belong to a family of class III highly conserved deacetylases that are involved in the regulation of biological and cellular processes including mitochondrial biogenesis, metabolism, oxidative stress, inflammatory response, DNA repair, etc. Numerous studies have shown that sirtuins might play protective roles in VC, and restoring the activity of sirtuins may be a potentially effective treatment for VC. However, the exact mechanism of their vascular protection remains unclear. Here, we reviewed the roles of sirtuins in the osteogenic transformation of vascular smooth muscle cells and the development of VC. We also elucidated the applications of sirtuins agonists for the treatment of VC.

Translational Medicine in Uremic Vascular Calcification: Scavenging ROS Attenuates p-Cresyl Sulfate-Activated Caspase-1, NLRP3 Inflammasome and Eicosanoid Inflammation in Human Arterial Smooth Muscle Cells

We formerly proved that uremic vascular calcification (UVC) correlates tightly with oxidative elastic lamina (EL) injury and two cell fates (apoptosis and osteocytic conversion) in smooth muscle cells (SMC) of chronic kidney disease (CKD) patients and eliminating p-cresyl sulfate (PCS)-activated intracellular ROS ameliorates the MAPK signaling pathway in a human arterial SMC (HASMC) model. Nonetheless, whether ROS scavenger attenuates PCS-triggered inflammasome activation and eicosanoid inflammation in the UVC process remains unknown. Patients with lower extremity amputation were categorized into CKD and normal control group according to renal function. We used immunohistochemistry stain to analyze UVC in arterial specimens, including oxidative injury (8-hydroxy-2′-deoxyguanosine (8-OHdG) and internal EL disruption), cytosolic phospholipase A2 (cPLA2), cyclooxygenase 2 (COX2), interleukin-1 beta (IL-1β), caspase-1 and NLRP3. To simulate the patho-mechanism of human UVC, the therapeutic effects of ROS scavenger on PCS-triggered inflammatory pathways was explored in a HASMC model. We found CKD patients had higher circulating levels of PCS and an increase in medial arterial calcification than the control group. In CKD arteries, the severity of UVC corresponded with expressions of oxidative EL disruption and 8-OHdG. Furthermore, coupling expressions of cPLA2 and COX2 were accentuated in CKD arteries, indicative of eicosanoid inflammation. Notably, tissue expressions of IL-1β, caspase-1 and NLRP3 were enhanced in parallel with UVC severity, indicative of inflammasome activation. From bedside to bench, ROS scavenger attenuates PCS-activated expressions of cPLA2/COX2, pro-caspase-1 and NLRP3 in the HASMC model. UVC as an inevitable outcome is predictive of death in CKD patients. Nonetheless, UVC remain pharmacoresistant despite the evolution of treatment for mineral-parathyroid hormone-vitamin D axis. Beyond the mineral dysregulation, the stimulation of pro-oxidant PCS alone results in eicosanoid inflammation and inflammasome activation. Concerning the key role of Caspase-1 in pyroptosis, cell fates of HASMC in uremic milieu are not limited to apoptosis and osteogenesis. In view of this, reducing ROS and PCS may act as a therapeutic strategy for UVC-related cardiovascular events in CKD patients.

Atorvastatin can delay arterial stiffness progression in hemodialysis patients

Purpose

Arterial stiffness is one of the vascular pathologies in hemodialysis (HD) patients with increased cardiovascular mortality and morbidity. Few approaches have been tested to reduce arterial stiffness in patients with chronic kidney disease (CKD). We aimed to assess effects of atorvastatin on arterial stiffness in hemodialysis patients.

Methods

This research is a double-blinded, placebo-controlled, randomized clinical trial which included 50 patients maintained on regular HD. Patients were allocated to receive 10 mg atorvastatin or placebo for 24 weeks. Aortic pulse wave velocity (PWV) as an index of large artery stiffness and augmentation index (AIx) as an index of wave reflections were assessed at baseline and after 6 months in both groups.

Results

In atorvastatin group at study end, there was no significant difference from baseline findings in aortic PWV (7.86 ± 2.5 vs 7.88 ± 2.6 m/sec; p = 0.136), AIx (26.04 ± 8.5 vs 26.0 ± 8.6%; p = 0.714) and central pulse pressure (PP) (p = 1.0). On the other hand, in placebo group after 24 weeks, aortic PWV (7.80 ± 2.16 vs 7.63 ± 2.1 m/sec; p < 0.001), AIx (25.88 ± 9.4 vs 25.04 ± 9.4%; p < 0.001) increased significantly from baseline measurements but central pulse pressure (PP) (p = 0.870) did not. Also, the change (Δ) in aortic PWV and AIx was significantly higher than the change in the atorvastatin group with p value of < 0.001 and < 0.001, respectively.

Conclusions

Arterial stiffness parameters remained stable in atorvastatin group but increased significantly in placebo-treated patients suggesting a potential role for atorvastatin to delay arterial stiffness progression in HD patients. Larger randomized clinical trials are needed to confirm these findings.

Clinical Trials registration

ClinicalTrials.gov NCT04472637.

Uremic toxin indoxyl sulfate induces dysfunction of vascular smooth muscle cells via integrin-β1/ERK signaling pathway

BACKGROUND

Protein-bound uremic toxins (PBUTs) are reported to be one of the major culprits in chronic kidney disease-cardiovascular disease (CKD-CVD) development, yet its mechanism is not fully clear. Our previous study confirmed elevated expression of integrin-β1 (ITGβ1) in vascular smooth muscle cells of uremic patients. Thus, this study aimed to explore the relationship between PBUTs and ITGβ1 in uremic vasculature injury.

METHODS

Human umbilical vein smooth muscle cells (HUVSMCs) and endothelial cells (HUVECs) were treated with two representative PUBTs, indoxyl sulfate (IS) and p-cresyl sulfate (PC). Both cells were measured for the expression of ITGβ1 and downstream signaling pathways and assayed for proliferation, migration, adhesion and apoptosis.

RESULTS

The IS treatments were observed with significantly up-regulated ITGβ1 in HUVSMCs but not in HUVECs, while PC did not induce ITGβ1 alteration in either HUVSMCs or HUVECs. Furthermore, overexpression of ITGβ1 revealed activated downstream signal-regulated kinase (ERK) signaling pathway with promoted focal adhesion, migration, proliferation but no apoptosis in HUVSMCs by IS. These functional and pathway alterations could be significantly suppressed by RNA interference of ITGβ1. More importantly, the application of ERK1/2 inhibitor significantly suppressed the focal adhesion, migration and proliferation of HUVSMCs.

CONCLUSION

We first demonstrated that ITGβ1/ERK signaling pathway mediated abnormal focal adhesion, migration and proliferation of vascular smooth muscle cells stimulated by IS. ITGβ1/ERK signaling may serve as a novel therapeutic target for CKD-CVD.

Relationships between advanced glycation end products (AGEs), vasoactive substances, and vascular function

Vascular smooth muscle cells (VSMCs) and endothelial cells (ECs) are major cell types that control vascular function, and hence dysfunction of these cells plays a key role in the development and progression of vasculopathies. Abnormal vascular responsiveness to vasoactive substances including vasoconstrictors and vasodilators has been observed in various arteries in diseases including diabetes, hypertension, chronic kidney diseases, and atherosclerosis. Several substances derived from ECs tightly control vascular function, such as endothelium-derived relaxing and contracting factors, and it is known that abnormal vascular signaling of these endothelium-derived substances is often observed in various diseases. Derangement of signaling in VSMCs and altered function influence vascular reactivity to vasoactive substances and tone, which are important determinants of vascular resistance and blood pressure. However, understanding the molecular mechanisms underlying abnormalities of vascular functions in pathological states is difficult because multiple substances interact in the development of these processes. Advanced glycation end products (AGEs), a heterogeneous group of bioactive compounds, are thought to contribute to vascular dysfunction, which in turn cause the development of several diseases including diabetes, hypertension, stroke, and atherosclerosis. A growing body of evidence suggests that AGEs could affect these cells and modulate vascular function. This study is focused on the link between AGEs and functions of ECs and VSMCs, particularly the modulative effects of AGEs on vascular reactivities to vasoactive substances.

Relationship of abdominal aortic calcification with lumbar vertebral volumetric bone mineral density assessed by quantitative computed tomography in maintenance hemodialysis patients

INTRODUCTION

This cross-sectional study aimed to investigate the relationship between abdominal aortic calcification (AAC), which is a marker of vascular calcification, and volumetric bone mineral density (vBMD) by quantitative computed tomography (QCT) in maintenance hemodialysis (MHD) patients.

METHODS

All participants underwent lumbar vertebral vBMD measurement by QCT. Eight cross-sections were extracted sequentially and analyzed by ImageJ software to obtain the ratio of the calcified area to the abdominal aortic area (the calcification ratio). The AAC score was determined by the sum of the calcification ratios. The relationship between AAC and vBMD was analyzed using multivariate logistic regression.

RESULTS

Ninety MHD patients (58.89% male) with a mean age of 63.43 (standard deviation [SD] = 13.20) years were included in the study. AAC was present (AAC score > 0) in 93.33% of the patients. The 75th percentile of the AAC score corresponding to 119 was used as the cutoff point between the mild and severe groups. After full adjustment in the logistic model, AAC was found to be inversely associated with vBMD (odds ratio [OR], 0.970; 95% confidence interval [CI], 0.944 to 0.996; P = 0.025), and patients with osteoporosis had a significantly higher risk of severe AAC than those with normal bone mass (OR, 14.498; 95% CI, 1.507 to 139.486; P = 0.021). The independent inverse association was still stable after adjusting for variables measured at different time periods and using different cutoff points of the AAC score.

CONCLUSION

There was an independent inverse association between AAC and vBMD, and osteoporosis was significantly associated with severe AAC in patients with MHD.

[Relationship between gut microbiota-derived substances and vascular function: focus on indoxyl sulfate and trimethylamine-N-oxide]

Emerging evidences suggest that gut microbiota-derived substances play a pivotal role in the regulation of host homeostasis including vascular function. Actually, these substances and/or their metabolites can be presented in circulation and local tissue and their levels are often abnormal in the pathophysiological states. Therefore, to determine the role of them in physiological function is important in human health. On the other hand, vascular dysfunction is a key event in the initiation and progression of systematic complications of cardiovascular, kidney and metabolic diseases including hypertension, dyslipidemia, diabetes, and atherosclerosis. Although abnormalities in endothelial and vascular smooth muscle cells play an important role on vascular dysfunction, emerging evidences has suggested that gut microbiota-derived substances can directly or indirectly affect these cellular functions. The present review will focus on the relationship between vascular function and indoxyl sulfate or trimethylamine-N-oxide (TMAO).

Iron-based phosphorus chelator: Risk of iron deposition and action on bone metabolism in uremic rats

Phosphate chelators are frequently used in patients with chronic kidney disease (CKD). New iron-based chelators remain understudied and offer a promising therapeutic option for the control of bone and mineral disorders of chronic kidney disease (BMD-CKD). We assessed the effect of the phosphorus chelator, chitosan-iron III (CH-FeCl), compared to calcium carbonate (CaCO₃) in BMD-CKD and the potential iron overload in uremic rats. Thirty-two animals were divided into four groups, namely the control, CKD, CKD/CH-FeCl, and CKD/CaCO₃ groups. CKD was induced by adding 0.75% (4 weeks) and 0.1% (3 weeks) adenine to the diet. The chelators were administered from week 3 through week 7. The renal function, BMD-CKD markers, and histomorphometry of the femur were assessed at week 7. The CKD group showed a significant increase in creatinine (83.9 ± 18.6 vs. 41.5 ± 22.1 µmol/L; P = 0.001), phosphate (3.5 ± 0.8 vs. 2.2 ± 0.2 mmol/L; P = 0.001), fractional excretion of phosphorus (FEP) (0.71 ± 0.2 vs. 0.2 ± 0.17; P = 0.0001), and FGF23 (81.36 ± 37.16 pg/mL vs. 7.42 ± 1.96; P = 0.011) compared to the control group. There was no accumulation of serum or bone iron after the use of CH-FeCl. The use of chelators reduced the FEP (control: 0.71 ± 0.20; CKD/CH-FeCl: 0.40 ± 0.16; CKD/CaCO₃ 0.34 ± 0.15; P = 0.001), without changes in the serum FGF23 and parathyroid hormone levels. Histomorphometry revealed the presence of bone disease with high remodeling in the uremic animals without changes with the use of chelators. The CH-FeCl chelator was efficient in reducing the FEP without iron accumulation, thereby paving the way for the use of this class of chelators in clinical settings in the future.

Expanded Hemodialysis Therapy Ameliorates Uremia-Induced Systemic Microinflammation and Endothelial Dysfunction by Modulating VEGF, TNF-α and AP-1 Signaling

Abstract

Systemic chronic microinflammation and altered cytokine signaling, with adjunct cardiovascular disease (CVD), endothelial maladaptation and dysfunction is common in dialysis patients suffering from end-stage renal disease and associated with increased morbidity and mortality. New hemodialysis filters might offer improvements. We here studied the impact of novel improved molecular cut-off hemodialysis filters on systemic microinflammation, uremia and endothelial dysfunction. Human endothelial cells (ECs) were incubated with uremic serum obtained from patients treated with two different hemodialysis regimens in the Permeability Enhancement to Reduce Chronic Inflammation (PERCI-II) crossover clinical trial, comparing High-Flux (HF) and Medium Cut-Off (MCO) membranes, and then assessed for their vascular endothelial growth factor (VEGF) production and angiogenesis. Compared to HF membranes, dialysis with MCO membranes lead to a reduction in proinflammatory mediators and reduced endothelial VEGF production and angiogenesis. Cytokine multiplex screening identified tumor necrosis factor (TNF) superfamily members as promising targets. The influence of TNF-α and its soluble receptors (sTNF-R1 and sTNF-R2) on endothelial VEGF promoter activation, protein release, and the involved signaling pathways was analyzed, revealing that this detrimental signaling was indeed induced by TNF-α and mediated by AP-1/c-FOS signaling. In conclusion, uremic toxins, in particular TNF-signaling, promote endothelial maladaptation, VEGF expression and aberrant angiogenesis, which can be positively modulated by dialysis with novel MCO membranes.

Translational Perspective and Graphical Abstract

Systemic microinflammation, altered cytokine signaling, cardiovascular disease, and endothelial maladaptation/dysfunction are common clinical complications in dialysis patients suffering from end-stage renal disease. We studied the impact of novel improved medium-cut-off hemodialysis filters on uremia and endothelial dysfunction. We can show that uremic toxins, especially TNF-signaling, promote endothelial maladaptation, VEGF expression and aberrant angiogenesis, which can be positively modulated by dialysis with novel improved medium-cut-off membranes.

Immuno-regenerative biomaterials for in situ cardiovascular tissue engineering - Do patient characteristics warrant precision engineering?

In situ tissue engineering using bioresorbable material implants - or scaffolds - that harness the patient's immune response while guiding neotissue formation at the site of implantation is emerging as a novel therapy to regenerate human tissues. For the cardiovascular system, the use of such implants, like blood vessels and heart valves, is gradually entering the stage of clinical translation. This opens up the question if and to what extent patient characteristics influence tissue outcomes, necessitating the precision engineering of scaffolds to guide patient-specific neo-tissue formation. Because of the current scarcity of human in vivo data, herein we review and evaluate in vitro and preclinical investigations to predict the potential role of patient-specific parameters like sex, age, ethnicity, hemodynamics, and a multifactorial disease profile, with special emphasis on their contribution to the inflammation-driven processes of in situ tissue engineering. We conclude that patient-specific conditions have a strong impact on key aspects of in situ cardiovascular tissue engineering, including inflammation, hemodynamic conditions, scaffold resorption, and tissue remodeling capacity, suggesting that a tailored approach may be required to engineer immuno-regenerative biomaterials for safe and predictive clinical applicability.

Gut Microbiota and Atherosclerosis-Focusing on the Plaque Stability

Cardiovascular diseases (CVDs) are major causes of mortality and morbidity in the modern society. The rupture of atherosclerotic plaque can induce thrombus formation, which is the main cause of acute cardiovascular events. Recently, many studies have demonstrated that there are some relationships between microbiota and atherosclerosis. In this review, we will focus on the effect of the microbiota and the microbe-derived metabolites, including trimethylamine-N-oxide (TMAO), short-chain fatty acids (SCFAs), and lipopolysaccharide (LPS), on the stability of atherosclerotic plaque. Finally, we will conclude with some therapies based on the microbiota and its metabolites.

The Putative Role of Methylglyoxal in Arterial Stiffening: A Review

BACKGROUND

Arterial stiffening is a hallmark of vascular ageing and a consequence of many diseases including diabetes mellitus. Methylglyoxal (MGO), a highly reactive α-dicarbonyl mainly formed during glycolysis, has emerged as a potential contributor to the development of arterial stiffness. MGO reacts with arginine and lysine residues in proteins to form stable advanced glycation endproducts (AGEs). AGEs may contribute to arterial stiffening by increased cross-linking of collagen within the extracellular matrix (ECM), by altering the vascular structure, and by triggering inflammatory and oxidative pathways. Although arterial stiffness is mainly determined by ECM and vascular smooth muscle cell function, the effects of MGO and MGO-derived AGEs on these structures have not been thoroughly reviewed to date.

METHODS AND RESULTS

We conducted a PubMed search without filtering for publication date which resulted in 16 experimental and 22 clinical studies eligible for inclusion. Remarkably, none of the experimental and only three of the clinical studies specifically mentioned MGO-derived AGEs. Almost all studies reported an association between arterial stiffness and AGE accumulation in the arterial wall or increased plasma AGEs. Other studies report reduced arterial stiffness in experimental models upon administration of AGE-breakers.

CONCLUSIONS

No papers published to date directly show an association between MGO or MGO-derived AGEs and arterial stiffening. The relevance of the various underlying mechanisms is not yet clear, which is particularly due to methodological challenges in the detection of MGO and MGO-derived AGEs at the molecular, intra- and pericellular, and structural levels, as well as in challenges in the assessment of intrinsic arterial wall properties at ECM- and tissue levels.

Uremic Toxins and Cardiovascular System

When chronic kidney disease develops, the capacity of the kidneys to clear metabolic waste products from the body is gradually lost. This process results in the retention of a large array of compounds affecting biochemical and biological functions (uremic toxins), of which several can cause cardiovascular damage. This article reviews the main cardiotoxic mechanisms related to uremic toxin retention (endothelial dysfunction, vascular smooth muscle cell alterations, inflammation, mineral bone disorder, insulin resistance, and thrombogenicity) and the main responsible retention compounds. Therapeutic options are reviewed, such as influencing solute generation by intestinal microbiota.

Circulating p-Cresyl Sulfate, Non-Hepatic Alkaline Phosphatase and Risk of Bone Fracture Events in Chronic Kidney Disease-Mineral Bone Disease

Patients with chronic kidney disease (CKD), especially those undergoing hemodialysis, are at a considerably high risk of bone fracture events. Experimental data indicate that uremic toxins intricately involved in bone-related proteins exert multi-faced toxicity on bone cells and tissues, leading to chronic kidney disease–mineral and bone disorder (CKD-MBD). Nonetheless, information regarding the association between p-cresyl sulfate (PCS), non-hepatic alkaline phosphatase (NHALP) and skeletal events remains elusive. We aim to explore the association between PCS, NHALP and risk of bone fracture (BF) in patients with hemodialysis. Plasma concentrations of PCS and NHALP were ascertained at study entry. Cox proportional hazard regression analyses were used to determine unadjusted and adjusted hazard ratios (aHRs) of PCS for BF risk. In multivariable analysis, NHALP was associated with incremental risks of BFs [aHR: 1.06 (95% CI: 1.01–1.11)]. The association between the highest PCS tertile and BF risk remained robust [aHR: 2.87 (95% CI: 1.02–8.09)]. With respect to BF events, the interaction between NHALP and PCS was statistically significant (p value for the interaction term < 0.05). In addition to mineral dysregulation and hyperparathyroidism in hemodialysis patients, higher circulating levels of PCS and NHALP are intricately associated with incremental risk of BF events, indicating that a joint evaluation is more comprehensive than single marker. In light of the extremely high prevalence of CKD-MBD in the hemodialysis population, PCS may act as a pro-osteoporotic toxin and serve as a potential surrogate marker for skeletal events.

Advanced glycation end-products, measured as skin autofluorescence, associate with vascular stiffness in diabetic, pre-diabetic and normoglycemic individuals: a cross-sectional study

Background

Advanced glycation end-products are proteins that become glycated after contact with sugars and are implicated in endothelial dysfunction and arterial stiffening. We aimed to investigate the relationships between advanced glycation end-products, measured as skin autofluorescence, and vascular stiffness in various glycemic strata.

Methods

We performed a cross-sectional analysis within the European Prospective Investigation into Cancer and Nutrition (EPIC)-Potsdam cohort, comprising n = 3535 participants (median age 67 years, 60% women). Advanced glycation end-products were measured as skin autofluorescence with AGE-Reader™, vascular stiffness was measured as pulse wave velocity, augmentation index and ankle-brachial index with Vascular Explorer™. A subset of 1348 participants underwent an oral glucose tolerance test. Participants were sub-phenotyped into normoglycemic, prediabetes and diabetes groups. Associations between skin autofluorescence and various indices of vascular stiffness were assessed by multivariable regression analyses and were adjusted for age, sex, measures of adiposity and lifestyle, blood pressure, prevalent conditions, medication use and blood biomarkers.

Results

Skin autofluorescence associated with pulse wave velocity, augmentation index and ankle-brachial index, adjusted beta coefficients (95% CI) per unit skin autofluorescence increase: 0.38 (0.21; 0.55) for carotid-femoral pulse wave velocity, 0.25 (0.14; 0.37) for aortic pulse wave velocity, 1.00 (0.29; 1.70) for aortic augmentation index, 4.12 (2.24; 6.00) for brachial augmentation index and − 0.04 (− 0.05; − 0.02) for ankle-brachial index. The associations were strongest in men, younger individuals and were consistent across all glycemic strata: for carotid-femoral pulse wave velocity 0.36 (0.12; 0.60) in normoglycemic, 0.33 (− 0.01; 0.67) in prediabetes and 0.45 (0.09; 0.80) in diabetes groups; with similar estimates for aortic pulse wave velocity. Augmentation index was associated with skin autofluorescence only in normoglycemic and diabetes groups. Ankle-brachial index inversely associated with skin autofluorescence across all sex, age and glycemic strata.

Conclusions

Our findings indicate that advanced glycation end-products measured as skin autofluorescence might be involved in vascular stiffening independent of age and other cardiometabolic risk factors not only in individuals with diabetes but also in normoglycemic and prediabetic conditions. Skin autofluorescence might prove as a rapid and non-invasive method for assessment of macrovascular disease progression across all glycemic strata.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12933-021-01296-5.

Uraemic solutes as therapeutic targets in CKD-associated cardiovascular disease

Chronic kidney disease (CKD) is characterized by the retention of a myriad of solutes termed uraemic (or uremic) toxins, which inflict damage to several organs, including the cardiovascular system. Uraemic toxins can induce hallmarks of cardiovascular disease (CVD), such as atherothrombosis, heart failure, dysrhythmias, vessel calcification and dysregulated angiogenesis. CVD is an important driver of mortality in patients with CKD; however, reliance on conventional approaches to managing CVD risk is insufficient in these patients, underscoring a need to target risk factors that are specific to CKD. Mounting evidence suggests that targeting uraemic toxins and/or pathways induced by uraemic toxins, including tryptophan metabolites and trimethylamine N-oxide (TMAO), can lower the risk of CVD in patients with CKD. Although tangible therapies resulting from our growing knowledge of uraemic toxicity are yet to materialize, a number of pharmacological and non-pharmacological approaches have the potential to abrogate the effects of uraemic toxins, for example, by decreasing the production of uraemic toxins, by modifying metabolic pathways induced by uraemic toxins such as those controlled by aryl hydrocarbon receptor signalling and by augmenting the clearance of uraemic toxins.

MMP-9 Deletion Attenuates Arteriovenous Fistula Neointima through Reduced Perioperative Vascular Inflammation

Matrix metalloproteinase 9 (MMP-9) expression is upregulated in vascular inflammation and participates in vascular remodeling, including aneurysm dilatation and arterial neointima development. Neointima at the arteriovenous (AV) fistula anastomosis site primarily causes AV fistula stenosis and failure; however, the effects of MMP-9 on perioperative AV fistula remodeling remain unknown. Therefore, we created AV fistulas (end-to-side anastomosis) in wild-type (WT) and MMP-9 knockout mice with chronic kidney disease to further clarify this. Neointima progressively developed in the AV fistula venous segment of WT mice during the four-week postoperative course, and MMP-9 knockout increased the lumen area and attenuated neointima size by reducing smooth muscle cell and collagen components. Early perioperative AV fistula mRNA sequencing data revealed that inflammation-related gene sets were negatively enriched in AV fistula of MMP-9 knockout mice compared to that in WT mice. qPCR results also showed that inflammatory genes, including tumor necrosis factor-α (TNF-α), monocyte chemoattractant protein-1 (MCP-1), interleukin-6 (IL-6), intercellular adhesion molecule-1 (ICAM-1), and vascular cell adhesion molecule-1 (VCAM-1), were downregulated. In addition, Western blot results showed that MMP-9 knockout reduced CD44 and RAC-alpha serine/threonine-protein kinase (Akt) and extracellular signal-regulated kinases (ERK) phosphorylation. In vitro, MMP-9 addition enhanced IL-6 and MCP-1 expression in vascular smooth muscle cells, as well as cell migration, which was reversed by an MMP-9 inhibitor. In conclusion, MMP-9 knockout attenuated AV fistula stenosis by reducing perioperative vascular inflammation.

Long-Term Treatment of Azathioprine in Rats Induces Vessel Mineralization

Medial vascular calcification (mVC) is closely related to cardiovascular disease, especially in patients suffering from chronic kidney disease (CKD). Even after successful kidney transplantation, cardiovascular mortality remains increased. There is evidence that immunosuppressive drugs might influence pathophysiological mechanisms in the vessel wall. Previously, we have shown in vitro that mVC is induced in vascular smooth muscle cells (VSMCs) upon treatment with azathioprine (AZA). This effect was confirmed in the current study in an in vivo rat model treated with AZA for 24 weeks. The calcium content increased in the aortic tissue upon AZA treatment. The pathophysiologic mechanisms involve AZA catabolism to 6-thiouracil via xanthine oxidase (XO) with subsequent induction of oxidative stress. Proinflammatory cytokines, such as interleukin (IL)-1ß and IL-6, increase upon AZA treatment, both systemically and in the aortic tissue. Further, VSMCs show an increased expression of core-binding factor α-1, alkaline phosphatase and osteopontin. As the AZA effect could be decreased in NLRP3^−/− aortic rings in an ex vivo experiment, the signaling pathway might be, at least in part, dependent on the NLRP3 inflammasome. Although human studies are necessary to confirm the harmful effects of AZA on vascular stiffening, these results provide further evidence of induction of VSMC calcification under AZA treatment and its effects on vessel structure.

Mitochondrial Damage-Induced Innate Immune Activation in Vascular Smooth Muscle Cells Promotes Chronic Kidney Disease-Associated Plaque Vulnerability

Chronic kidney disease (CKD) is associated with accelerated atherosclerosis progression and high incidence of cardiovascular events, hinting that atherosclerotic plaques in CKD may be vulnerable. However, its cause and mechanism remain obscure. Here, it is shown that apolipoprotein E-deficient (ApoE-/-) mouse with CKD (CKD/ApoE-/- mouse) is a useful model for investigating the pathogenesis of plaque vulnerability, and premature senescence and phenotypic switching of vascular smooth muscle cells (VSMCs) contributes to CKD-associated plaque vulnerability. Subsequently, VSMC phenotypes in patients with CKD and CKD/ApoE-/- mice are comprehensively investigated. Using multi-omics analysis and targeted and VSMC-specific gene knockout mice, VSMCs are identified as both type-I-interferon (IFN-I)-responsive and IFN-I-productive cells. Mechanistically, mitochondrial damage resulting from CKD-induced oxidative stress primes the cyclic GMP-AMP synthase-stimulator of interferon genes (cGAS-STING) pathway to trigger IFN-I response in VSMCs. Enhanced IFN-I response then induces VSMC premature senescence and phenotypic switching in an autocrine/paracrine manner, resulting in the loss of fibrous cap VSMCs and fibrous cap thinning. Conversely, blocking IFN-I response remarkably attenuates CKD-associated plaque vulnerability. These findings reveal that IFN-I response in VSMCs through immune sensing of mitochondrial damage is essential for the pathogenesis of CKD-associated plaque vulnerability. Mitigating IFN-I response may hold promise for the treatment of CKD-associated cardiovascular diseases.

Metformin inhibits chronic kidney disease-induced DNA damage and senescence of mesenchymal stem cells

Mesenchymal stem cells (MSCs) are promising source of cell‐based regenerative therapy. In consideration of the risk of allosensitization, autologous MSC‐based therapy is preferred over allogenic transplantation in patients with chronic kidney disease (CKD). However, it remains uncertain whether adequate cell functionality is maintained under uremic conditions. As chronic inflammation and oxidative stress in CKD may lead to the accumulation of senescent cells, we investigated cellular senescence of CKD MSCs and determined the effects of metformin on CKD‐associated cellular senescence in bone marrow MSCs from sham‐operated and subtotal nephrectomized mice and further explored in adipose tissue‐derived MSCs from healthy kidney donors and patients with CKD. CKD MSCs showed reduced proliferation, accelerated senescence, and increased DNA damage as compared to control MSCs. These changes were significantly attenuated following metformin treatment. Lipopolysaccharide and transforming growth factor β1‐treated HK2 cells showed lower tubular expression of proinflammatory and fibrogenesis markers upon co‐culture with metformin‐treated CKD MSCs than with untreated CKD MSCs, suggestive of enhanced paracrine action of CKD MSCs mediated by metformin. In unilateral ureteral obstruction kidneys, metformin‐treated CKD MSCs more effectively attenuated inflammation and fibrosis as compared to untreated CKD MSCs. Thus, metformin preconditioning may exhibit a therapeutic benefit by targeting accelerated senescence of CKD MSCs.

Role of crosstalk between endothelial cells and smooth muscle cells in vascular calcification in chronic kidney disease

Chronic kidney disease (CKD) is a severe health problem worldwide, and vascular calcification (VC) contributes substantially to the cardiovascular morbidity and high mortality of CKD. CKD is often accompanied by a variety of pathophysiological states, such as inflammation, oxidative stress, hyperglycaemia, hyperparathyroidism and haemodynamic derangement, that can cause injuries to smooth muscle cells (SMCs) and endothelial cells (ECs) to promote VC. Similar to SMCs, whose role has been widely explored in VC, ECs may contribute to VC via osteochondral transdifferentiation, apoptosis, etc. In addition, given their location in the innermost layer of the blood vessel lumen and preferential reception of various pro‐calcification stimuli, ECs can pass messages to vascular wall cells and communicate with them. Crosstalk between ECs and SMCs via cytokines through a paracrine mechanism, extracellular vesicles, miRNAs and myoendothelial gap junctions also plays a role in VC. In this review, we emphasize the role of intercellular crosstalk between ECs and SMCs in VC associated with CKD.

Pro-Inflammatory Effects of Indoxyl Sulfate in Mice: Impairment of Intestinal Homeostasis and Immune Response

The intestines are recognized as the main source of chronic inflammation in chronic kidney disease (CKD) and, among other cells, macrophages are involved in modulating this process as well as in the impaired immune response which also occurs in CKD patients. In this study, we evaluated the effect of Indoxyl Sulfate (IS), a protein bound uremic toxin poorly eliminated by hemodialysis, on inflammatory, oxidative stress and pro-apoptotic parameters, at the intestinal level in mice, on intestinal epithelial cells (IEC-6) and on primary murine peritoneal macrophages. C57BL/6J mice were treated with IS (800 mg/kg i.p.) for 3 or 6 h and histopathological analysis showed that IS induced intestinal inflammation and increased cyclooxygenase-2 (COX-2), nitrotyrosine and Bax expression in intestinal tissue. In IEC-6 cells, IS (125–1000 µM) increased tumor necrosis factor-α levels, COX-2 and inducible nitric oxide synthase expression and nitrotyrosine formation. Moreover, IS increased pro-oxidant, pro-inflammatory and pro-apoptotic parameters in peritoneal macrophages from IS-treated mice. Also, the serum concentration of IS and pro-inflammatory levels of cytokines resulted increased in IS-treated mice. Our results indicate that IS significantly contributes to affect intestinal homeostasis, immune response, and to induce a systemic pro-inflammatory state thus highlighting its potential role as therapeutic target in CKD patients.

Uraemic toxins impair skeletal muscle regeneration by inhibiting myoblast proliferation, reducing myogenic differentiation, and promoting muscular fibrosis

Uraemic toxins increase in serum parallel to a decline in the glomerular filtration rate and the development of sarcopenia in patients with chronic kidney disease (CKD). This study analyses the role of uraemic toxins in sarcopenia at different stages of CKD, evaluating changes in the muscular regeneration process. Cultured C₂C₁₂ cells were incubated with a combination of indoxyl sulphate and p-cresol at high doses (100 µg/mL) or low doses (25 µg/mL and 10 µg/mL) resembling late or early CKD stages, respectively. Cell proliferation (analysed by scratch assays and flow cytometry) was inhibited only by high doses of uraemic toxins, which inactivated the cdc2-cyclin B complex, inhibiting mitosis and inducing apoptosis (analysed by annexin V staining). By contrast, low doses of uraemic toxins did not affect proliferation, but reduced myogenic differentiation, primed with 2% horse serum, by inhibiting myogenin expression and promoting fibro-adipogenic differentiation. Finally, to assess the in vivo relevance of these results, studies were performed in gastrocnemii from uraemic rats, which showed higher collagen expression and lower myosin heavy chain expression than those from healthy rats. In conclusion, uraemic toxins impair the skeletal muscular regeneration process, even at low concentrations, suggesting that sarcopenia can progress from the early stages of CKD.

Role of gut microbiota-derived metabolites on vascular calcification in CKD

The interaction between gut microbiota and the host has gained widespread concern. Gut microbiota not only provides nutrients from the ingested food but also generates bioactive metabolites and signalling molecules to impact host physiology, especially in chronic kidney disease (CKD). The development of CKD, accompanied by changed diet and medication, alters the gut flora and causes the effect in distant organs, leading to clinical complications. Vascular calcification (VC) is an actively regulated process and a high prevalence of VC in CKD has also been linked to an imbalance in gut microbiota and altered metabolites. In this review, we focused on gut microbiota-derived metabolites involved in VC in CKD and explained how these metabolites influence the calcification process. Correcting the imbalance of gut microbiota and regulating microbiota-derived metabolites by dietary modification and probiotics are new targets for the improvement of the gut-kidney axis, which indicate innovative treatment options of VC in CKD.

Effects of Chronic Kidney Disease and Uremic Toxins on Extracellular Vesicle Biology

Vascular calcification (VC) is a cardiovascular complication associated with a high mortality rate, especially in patients with diabetes, atherosclerosis or chronic kidney disease (CKD). In CKD patients, VC is associated with the accumulation of uremic toxins, such as indoxyl sulphate or inorganic phosphate, which can have a major impact in vascular remodeling. During VC, vascular smooth muscle cells (VSMCs) undergo an osteogenic switch and secrete extracellular vesicles (EVs) that are heterogeneous in terms of their origin and composition. Under physiological conditions, EVs are involved in cell-cell communication and the maintenance of cellular homeostasis. They contain high levels of calcification inhibitors, such as fetuin-A and matrix Gla protein. Under pathological conditions (and particularly in the presence of uremic toxins), the secreted EVs acquire a pro-calcifying profile and thereby act as nucleating foci for the crystallization of hydroxyapatite and the propagation of calcification. Here, we review the most recent findings on the EVs’ pathophysiological role in VC, the impact of uremic toxins on EV biogenesis and functions, the use of EVs as diagnostic biomarkers and the EVs’ therapeutic potential in CKD.

Uremic Vascular Calcification: The Pathogenic Roles and Gastrointestinal Decontamination of Uremic Toxins

Uremic vascular calcification (VC) commonly occurs during advanced chronic kidney disease (CKD) and significantly increases cardiovascular morbidity and mortality. Uremic toxins are integral within VC pathogenesis, as they exhibit adverse vascular influences ranging from atherosclerosis, vascular inflammation, to VC. Experimental removal of these toxins, including small molecular (phosphate, trimethylamine-N-oxide), large molecular (fibroblast growth factor-23, cytokines), and protein-bound ones (indoxyl sulfate, p-cresyl sulfate), ameliorates VC. As most uremic toxins share a gut origin, interventions through gastrointestinal tract are expected to demonstrate particular efficacy. The “gastrointestinal decontamination” through the removal of toxin in situ or impediment of toxin absorption within the gastrointestinal tract is a practical and potential strategy to reduce uremic toxins. First and foremost, the modulation of gut microbiota through optimizing dietary composition, the use of prebiotics or probiotics, can be implemented. Other promising strategies such as reducing calcium load, minimizing intestinal phosphate absorption through the optimization of phosphate binders and the inhibition of gut luminal phosphate transporters, the administration of magnesium, and the use of oral toxin adsorbent for protein-bound uremic toxins may potentially counteract uremic VC. Novel agents such as tenapanor have been actively tested in clinical trials for their potential vascular benefits. Further advanced studies are still warranted to validate the beneficial effects of gastrointestinal decontamination in the retardation and treatment of uremic VC.

CSE/H2S system alleviates uremic accelerated atherosclerosis by regulating TGF-β/Smad3 pathway in 5/6 nephrectomy ApoE-/- mice

Background

Hydrogen sulfide (H₂S) has been shown to inhibit the atherosclerosis development and progression. It is produced by cystathionine γ-lyase (CSE) in the cardiovascular system. In our previous study, it has been shown that CSE/H₂S system plays a significant role in the changes of uremic accelerated atherosclerosis (UAAS), but the mechanism is not known clearly.

Methods

In this study, we explored the antagonism of CSE/H₂S system in UAAS and identified its possible signaling molecules in ApoE^−/− mice with 5/6 nephrectomy and fed with atherogenic diet. Mice were divided into sham operation group (sham group), UAAS group, sodium hydrosulfide group (UAAS+NaHS group) and propargylglycine group (UAAS+PPG group). Serum creatinine, urea nitrogen, lipid levels and lesion size of atherosclerotic plaque in the aortic roots were analyzed. Meanwhile, the expression of CSE, TGF-β and phosphorylation of Smad3 were detected.

Results

Compared with sham group, the aortic root of ApoE^−/− mice in the UAAS group developed early atherosclerosis, the levels of total cholesterol, triglyceride, low-density lipoprotein-cholesterol, serum creatinine and urea nitrogen were also higher than that in the sham group. NaHS administration can inhibit the development of atherosclerosis, but PPG administration can accelerate the atherosclerosis development. Meanwhile, the protein expression levels of CSE and TGF-β and phosphorylation of Smad3 significantly decreased in the UAAS mice. Treatment of UAAS mice with NaHS inhibited TGF-β protein expression and Smad3 phosphorylation decrease, but PPG treatment had the opposite effect.

Conclusions

The CSE/H₂S system is of great importance for treating atherosclerosis in patients with chronic kidney disease, and it may protect the vascular from atherosclerosis through the TGF-β/Smad pathway.

Albuminuria rather than glomerular filtration rate is associated with vascular endothelial function in patients with type 2 diabetes

AIMS

Albuminuria and reduced glomerular filtration rate (GFR) are manifestations of diabetic kidney disease and are both shown to be associated with cardiovascular outcomes. However, the differential association of albuminuria and reduced GFR with endothelial dysfunction, an early feature of atherosclerotic vascular damage, remains unclear. In this study, we investigated the association between albuminuria or estimated GFR (eGFR) and flow-mediated dilatation (FMD), a marker of endothelial function, in patients with type 2 diabetes.

METHODS

This study included 633 patients with type 2 diabetes. The FMD of the brachial artery was measured by ultrasonography. Albuminuria was evaluated by urinary albumin-to-creatinine ratio (ACR).

RESULTS

The mean FMD and eGFR, and the median value of ACR were 6.7%, 66.5 mL/min/1.73m² and 12.5 mg/g creatinine, respectively. Impaired FMD was found in patients with advanced stages of chronic kidney disease based on both GFR and albuminuria categories. Multivariate analysis after adjusting for potential confounders revealed that ACR, but not eGFR, was significantly and inversely associated with FMD.

CONCLUSIONS

Albuminuria is associated with FMD, independently of traditional cardiovascular risk factors in patients with type 2 diabetes. This study suggests a close relationship between albuminuria, rather than reduced GFR, and endothelial dysfunction in type 2 diabetes.

CREB/ATF3 signaling mediates indoxyl sulfate-induced vascular smooth muscle cell proliferation and neointimal formation in uremia

BACKGROUND AND AIMS

Uremic patients are characterized by an increased risk of atherosclerotic cardiovascular diseases. Vascular smooth muscle cell (VSMC) proliferation contributes to neointimal formation, a main pathological feature in atherosclerosis. Activation of CREB/ATF3 signaling is pivotal in VSMC proliferation, yet its role in uremic atherosclerosis is unknown. This study aimed to explore whether CREB/ATF3 signaling is involved in the molecular mechanism underlying neointimal formation in uremia.

METHODS AND RESULTS

Treatment of VSMCs with uremic toxin (indoxyl sulfate [IS]) activated cAMP/CREB/ATF3/cyclin D signaling, which was reflected by increased VSMC proliferation. Blocking cAMP/PKA/CREB/ATF3 signaling attenuated the promoting effect of IS on cyclin D1 expression and VSMC proliferation. Loss-of-function and time-dependent experiments showed that ATF3 lies downstream of the CREB signaling. Mutational analysis of cyclin D1 promoter along with chromatin immunoprecipitation assays showed that CREB/ATF3 signaling participated in IS-induced cyclin D transcription. In vivo, phosphorylated CREB (an active form of CREB) and ATF3 were prominently upregulated in the neointima of experimental uremic rats, the atherosclerotic plaques of uremic ApoE^-/- mice, and the iliac arteries of uremic patients. Notably, the use of lentivirus to knock down ATF3 in the neointima of balloon-injured arteries could suppress the effect of uremia in vivo, including neointimal formation and cyclin D expression.

CONCLUSIONS

In this study, we demonstrated that CREB/ATF3-related signaling may be involved in IS-induced VSMC proliferation and the pathogenesis of neointimal formation during uremia.

LncRNA-modulated autophagy in plaque cells: a new paradigm of gene regulation in atherosclerosis?

The development of atherosclerosis is accompanied by the functional deterioration of plaque cells, which leads to the escalation of endothelial inflammation, abnormal vascular smooth muscle cell phenotype switching and the accumulation of lipid-laden macrophages within vascular walls. Autophagy, a highly conserved homeostatic mechanism, is critical for the delivery of cytoplasmic substrates to lysosomes for degradation. Moderate levels of autophagy prevent atherosclerosis by safeguarding plaque cells against apoptosis, preventing inflammation, and limiting the lipid burden, whereas excessive autophagy exacerbates cell damage and inflammation and thereby accelerates the formation of atherosclerotic plaques. Increasing lines of evidence suggest that long noncoding RNAs can be either beneficial or detrimental to atherosclerosis development by regulating the autophagy level. This review summarizes the research progress related to 1) the significant role of autophagy in atherosclerosis and 2) the effects of the lncRNA-mediated modulation of autophagy on the plaque cell fate, inflammation levels, proliferative capacity, and cholesterol metabolism and subsequently on atherogenesis.

Uremic Toxins and Vascular Calcification-Missing the Forest for All the Trees

The cardiorenal syndrome relates to the detrimental interplay between the vascular system and the kidney. The uremic milieu induced by reduced kidney function alters the phenotype of vascular smooth muscle cells (VSMC) and promotes vascular calcification, a condition which is strongly linked to cardiovascular morbidity and mortality. Biological mechanisms involved include generation of reactive oxygen species, inflammation and accelerated senescence. A better understanding of the vasotoxic effects of uremic retention molecules may reveal novel avenues to reduce vascular calcification in CKD. The present review aims to present a state of the art on the role of uremic toxins in pathogenesis of vascular calcification. Evidence, so far, is fragmentary and limited with only a few uremic toxins being investigated, often by a single group of investigators. Experimental heterogeneity furthermore hampers comparison. There is a clear need for a concerted action harmonizing and standardizing experimental protocols and combining efforts of basic and clinical researchers to solve the complex puzzle of uremic vascular calcification.

miR-381-3p inhibits high glucose-induced vascular smooth muscle cell proliferation and migration by targeting HMGB1

BACKGROUND

Hyperglycemia increases the risk of many cardiovascular diseases (CVD), and the dysregulation of proliferation and migration in vascular smooth muscle cells (VSMCs) also participates in the pathogenesis of CVD. miR-381-3p is known to suppress the proliferation and migration of multiple human cell types. Nevertheless, the function of miR-381-3p in VSMCs remains largely indistinct.

METHODS

A quantitative real-time polymerase chain reaction (qRT-PCR) was employed to investigate miR-381-3p expression in high-glucose-induced VSMCs. Inflammatory cytokines tumor necrosis factor-α, interleukin-1β and interleukin-6, as well as oxidative stress markers SOD and MDA, were determined by an enzyme-linked immunosorbent assay. Reactive oxygen species generation was examined using a 2,7'-dichlorofluorescein kit. The proliferation, migration and apoptosis of VSMCs were monitored by 3-(4,5-dimethylthiazl2-yl)-2,5-diphenyltetazolium bromide (MTT), transwell and terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) assays. The TargetScan database (http://www.targetscan.org) was employed to seek the potential target gene of miR-381-3p. Interaction between miR-381-3p and HMGB1 was determined by a qRT-PCR, western blotting and a luciferase reporter assay.

RESULTS

miR-381-3p expression was significantly reduced in a VSMCs dysfunction model induced by high-glucose in a dose- and time-dependent manner. Transfection of miR-381-3p mimics suppressed the inflammation, oxidative stress, proliferation and migration of VSMCs, whereas apoptosis of VSMCs was promoted, and the transfection of miR-381-3p inhibitors had the opposite effect. Mechanistically, HMGB1, an important factor in inflammation response, was confirmed as a target gene of miR-381-3p.

CONCLUSIONS

miR-381-3p targets HMGB1 to suppress the inflammation, oxidative stress, proliferation and migration of high-glucose-induced VSMCs by targeting HMGB1.

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.

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.

The pathogenesis of CKD complications; Attack of dysregulated iron and phosphate metabolism

Chronic kidney disease (CKD) patients have a tremendously higher risk of developing cardiovascular disease (CVD) and infection than the non-CKD population, which could be caused by intertwining actions of hyperphosphatemia and CKD associated misdistribution of iron. CVD is often associated with vascular calcification, which has been attributed to hyperphosphatemia, and could be initiated in mitochondria, inducing apoptosis, and accelerated by reactive oxygen species (ROS). The production of ROS is principally linked to intracellular ferrous iron. For infection, the virulence and pathogenicity of a pathogen is directly related to its capacity to acquire iron for proliferation and to escape or subvert the host's immune response. Iron administration for renal anemia can sometimes be overdosed, which could decrease host immune mechanisms through its direct effect on neutrophils, macrophages and T cell function. Hyperphosphatemia has been demonstrated to be associated with an increased incidence of infection. We hypothesized two possible mechanisms: 1) fibroblast growth factor-23 levels are increased in parallel with serum phosphate levels and directly impair leukocyte recruitment and host defense mechanisms, and 2) circulating non-transferrin-bound iron (NTBI) is increased due to decreased iron binding capacity of the carrier protein transferrin in high-phosphate conditions. From these observations, maintaining an adequate serum range of phosphate levels and minimizing intracellular iron accumulation could attenuate the development of CKD complications.

Scavenging Intracellular ROS Attenuates p-Cresyl Sulfate-Triggered Osteogenesis through MAPK Signaling Pathway and NF-κB Activation in Human Arterial Smooth Muscle Cells

Osteogenesis in human arterial smooth muscle cell (HASMC) is a key feature of uremic vascular calcification (UVC). Concerning pro-oxidant properties of p-cresyl sulfate (PCS), the therapeutic effect of reactive oxygen species (ROS) scavenger on PCS triggered inflammatory signaling transduction in osteogenesis was investigated in this translational research. Based on severity level of chronic kidney disease (CKD), arterial specimens with immunohistochemistry stain were quantitatively analyzed for UVC, oxidative injury and osteogenesis along with PCS concentrations. To mimic human UVC, HASMC model was used to explore whether PCS-induced ROS could trigger mitogen-activated protein kinase (MAPK) pathways with nuclear factor-κB (NF-κB) translocation that drive context-specific gene/protein expression, including Runt-related transcription factor 2 (Runx2) and alkaline phosphatase (ALP). In parallel with PCS accumulation, CKD arteries corresponded with UVC severity, oxidative DNA damage (8-hydroxy-2′-deoxyguanosine), Runx2 and ALP. PCS directly phosphorylated extracellular signal-regulated kinase (ERK)/c-Jun N-terminal kinase (JNK)/P38 (pERK/pJNK/pP38) and modulated NF-κB translocation to promote expressions of Runx2 and ALP in HASMC. Notably, intracellular ROS scavenger attenuated pERK signaling cascade and downstream osteogenic differentiation. Collectively, our data demonstrate PCS induces osteogenesis through triggering intracellular ROS, pERK/pJNK/pP38 MAPK pathways and NF-κB translocation to drive Runx2 and ALP expressions, culminating in UVC. Beyond mineral dysregulation, osteocytic conversion in HASMC could be the stimulation of PCS. Thus PCS may act as a pro-osteogenic and pro-calcific toxin. From the perspective of translational medicine, PCS and intracellular ROS could serve as potential therapeutic targets for UVC in CKD patients.