Inhibition of eNOS phosphorylation mediates endothelial dysfunction in renal failure: new effect of asymmetric dimethylarginine. Kidney Int. 2012;81:762-768. [PMID: 22297680 DOI: 10.1038/ki.2011.476]

Crosstalk between autophagy and ferroptosis mediate injury in ischemic stroke by generating reactive oxygen species

Stroke represents a significant threat to global human health, characterized by high rates of morbidity, disability, and mortality. Predominantly, strokes are ischemic in nature. Ischemic stroke (IS) is influenced by various cell death pathways, notably autophagy and ferroptosis. Recent studies have increasingly highlighted the interplay between autophagy and ferroptosis, a process likely driven by the accumulation of reactive oxygen species (ROS). Post-IS, either the inhibition of autophagy or its excessive activation can escalate ROS levels. Concurrently, the interaction between ROS and lipids during ferroptosis further augments ROS accumulation. Elevated ROS levels can provoke endoplasmic reticulum stress-induced autophagy and, in conjunction with free iron (Fe2+), can trigger ferroptosis. Moreover, ROS contribute to protein and lipid oxidation, endothelial dysfunction, and an inflammatory response, all of which mediate secondary brain injury following IS. This review succinctly explores the mechanisms of ROS-mediated crosstalk between autophagy and ferroptosis and the detrimental impact of increased ROS on IS. It also offers novel perspectives for IS treatment strategies.

Mitigation of aircraft noise-induced vascular dysfunction and oxidative stress by exercise, fasting, and pharmacological α1AMPK activation: molecular proof of a protective key role of endothelial α1AMPK against environmental noise exposure

AIMS

Environmental stressors such as traffic noise represent a global threat, accounting for 1.6 million healthy life years lost annually in Western Europe. Therefore, the noise-associated health side effects must be effectively prevented or mitigated. Non-pharmacological interventions such as physical activity or a balanced healthy diet are effective due to the activation of the adenosine monophosphate-activated protein kinase (α1AMPK). Here, we investigated for the first time in a murine model of aircraft noise-induced vascular dysfunction the potential protective role of α1AMPK activated via exercise, intermittent fasting, and pharmacological treatment.

METHODS AND RESULTS

Wild-type (B6.Cg-Tg(Cdh5-cre)7Mlia/J) mice were exposed to aircraft noise [maximum sound pressure level of 85 dB(A), average sound pressure level of 72 dB(A)] for the last 4 days. The α1AMPK was stimulated by different protocols, including 5-aminoimidazole-4-carboxamide riboside application, voluntary exercise, and intermittent fasting. Four days of aircraft noise exposure produced significant endothelial dysfunction in wild-type mice aorta, mesenteric arteries, and retinal arterioles. This was associated with increased vascular oxidative stress and asymmetric dimethylarginine formation. The α1AMPK activation with all three approaches prevented endothelial dysfunction and vascular oxidative stress development, which was supported by RNA sequencing data. Endothelium-specific α1AMPK knockout markedly aggravated noise-induced vascular damage and caused a loss of mitigation effects by exercise or intermittent fasting.

CONCLUSION

Our results demonstrate that endothelial-specific α1AMPK activation by pharmacological stimulation, exercise, and intermittent fasting effectively mitigates noise-induced cardiovascular damage. Future population-based studies need to clinically prove the concept of exercise/fasting-mediated mitigation of transportation noise-associated disease.

Asymmetric and Symmetric Dimethylarginines as Renal Function Parameters in Paediatric Kidney Diseases: A Literature Review from 2003 to 2022

Asymmetric dimethylarginine (ADMA) and symmetric dimethylarginine (SDMA), inhibitors of nitric oxide synthase, play important roles in many processes in the body. Most data in the literature concern their importance in adult chronic kidney disease (CKD). According to them, SDMA well reflects the glomerular filtration rate (GFR), and higher ADMA concentrations are associated with hypertension and higher mortality. In addition, both substances are recognised cardiovascular risk factors in CKD. The purpose of this review was to summarise the studies on dimethylarginines in renal diseases in children, about which we have much fewer data. The review focuses specifically on dimethylarginine's relation to routinely used renal function parameters. Finally, we analysed 21 of the 55 articles published between 2003 and 2022 on dimethylarginines in kidney diseases in children (from birth to 18 years of age), obtained by searching PubMed/MEDLINE (search terms: "dimethylarginine" and "kidney").

Cystatin C-based eGFR predicts cardiovascular disease in patients with overweight/obesity and hyperglycemia

Background

Although many clinical parameters have been identified as predictors for cardiovascular disease (CVD) development in the general population, the accurate predictor for CVD in patients with obesity is still unknown.

Objective

The study aimed to explore an additional risk factor and predictor for CVD in patients with overweight/obesity considering the interaction of obesity-related pathophysiology.

Methods

The Japan Obesity and Metabolic Syndrome study, a multicenter prospective study, enrolled 787 outpatients, of which 318 eligible patients were analyzed. Patients with fasting plasma glucose (FPG) levels ≥6.11 and < 6.11 mmol/L were considered to have high FPG (HFPG) and normal FPG (NFPG), respectively. Thirty-six patients who developed CVD during the 5 years follow-up were assigned to the CVD group.

Results

Cox's proportional hazards model revealed no significant association between CVD and cystatin C-based estimated glomerular filtration rate (eGFRcys) or creatinine-based eGFR (eGFRcr) in the NFPG group. In the HFPG group, lower eGFRcys, but not eGFRcr, was significantly associated with CVD development. A generalized linear mixed model demonstrated greater reduction in eGFRcys levels over time with HFPG than with NFPG. Although the CVD group showed gradual reduction in eGFRcys levels, the non-CVD group-matched using propensity scores-did not show a decline in eGFRcys levels.

Conclusions

Lower eGFRcys levels may be more accurate than eGFRcr in predicting CVD development in patients with overweight/obesity and hyperglycemia. Furthermore, eGFRcys reduction over time is associated with CVD development.

Clinical Trial Registry Number

UMIN000000559.

The Interplay between Uremic Toxins and Albumin, Membrane Transporters and Drug Interaction

Uremic toxins are a heterogeneous group of molecules that accumulate in the body due to the progression of chronic kidney disease (CKD). These toxins are associated with kidney dysfunction and the development of comorbidities in patients with CKD, being only partially eliminated by dialysis therapies. Importantly, drugs used in clinical treatments may affect the levels of uremic toxins, their tissue disposition, and even their elimination through the interaction of both with proteins such as albumin and cell membrane transporters. In this context, protein-bound uremic toxins (PBUTs) are highlighted for their high affinity for albumin, the most abundant serum protein with multiple binding sites and an ability to interact with drugs. Membrane transporters mediate the cellular influx and efflux of various uremic toxins, which may also compete with drugs as substrates, and both may alter transporter activity or expression. Therefore, this review explores the interaction mechanisms between uremic toxins and albumin, as well as membrane transporters, considering their potential relationship with drugs used in clinical practice.

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.

Most exposed: the endothelium in chronic kidney disease

Accumulating evidence indicates that the pathological changes of the endothelium may contribute to the development of cardiovascular complications in chronic kidney disease (CKD). Non-traditional risk factors related to CKD are associated with the incidence of cardiovascular disease, but their role in uraemic endothelial dysfunction has often been disregarded. In this context, soluble α-Klotho and vitamin D are of importance to maintain endothelial integrity, but their concentrations decline in CKD, thereby contributing to the dysfunction of the endothelial lining. These hormonal disturbances are accompanied by an increment of circulating fibroblast growth factor-23 and phosphate, both exacerbating endothelial toxicities. Furthermore, impaired renal function leads to an increment of inflammatory mediators, reactive oxygen species and uraemic toxins that further aggravate the endothelial abnormalities and in turn also inhibit the regeneration of disrupted endothelial lining. Here, we highlight the distinct endothelial alterations mediated by the abovementioned non-traditional risk factors as demonstrated in experimental studies and connect these to pathological changes in CKD patients, which are driven by endothelial disturbances, other than atherosclerosis. In addition, we describe therapeutic strategies that may promote restoration of endothelial abnormalities by modulating imbalanced mineral homoeostasis and attenuate the impact of uraemic retention molecules, inflammatory mediators and reactive oxygen species. A clinical perspective on endothelial dysfunction in CKD may translate into reduced structural and functional abnormalities of the vessel wall in CKD, and ultimately improved cardiovascular disease.

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

AIMS

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

MAIN METHODS

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

KEY FINDINGS

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

SIGNIFICANCE

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

Raised Plasma Levels of Asymmetric Dimethylarginine Are Associated with Pathological Type and Predict the Therapeutic Effect in Lupus Nephritis Patients Treated with Cyclophosphamide

Background

Lupus nephritis (LN) is one of the most serious complications of systemic lupus erythematosus (SLE). Asymmetric dimethylarginine (ADMA) has been associated with cardiovascular events in SLE patients and is a strong predictor of the progression of chronic kidney disease. However, whether ADMA can provide a predictive value for the diagnosis and treatment of LN patients remains unclear. This study evaluated the clinical significance of ADMA in LN patients.

Methods

Blood samples of 114 patients with LN, 52 patients with primary glomerular disease, and 20 healthy people were collected. Plasma ADMA was measured via enzyme-linked immunosorbent assay. The relationship between plasma ADMA levels and pathological types and renal function and efficacy in LN patients were further analyzed.

Results

There was no significant difference in plasma ADMA levels between LN and primary glomerular disease, but both were significantly higher than the values in healthy people (p < 0.05). Plasma ADMA levels in LN patients were negatively correlated with baseline estimated glomerular filtration rate (eGFR) and serum superoxide dismutase and positively correlated with serum cystatin C and serum β₂-microglobulin (p < 0.05). The plasma ADMA levels of diffuse proliferative LN patients were significantly higher than those of other histopathological classes of LN. High plasma ADMA levels in LN patients (OR = 1.012; 95% CI 1.003-1.022; p = 0.010) is a risk factor for diffuse proliferative LN. The area under the receiver operating characteristic (ROC) curve of diagnosing diffuse proliferative LN by plasma ADMA was 0.707 (95% CI 0.610-0.805). The area under the ROC curve of combination with plasma ADMA, serum complement C3, and eGFR for diffuse proliferative LN was 0.796 (95% CI 0.713-0.879), which was significantly higher than that of ADMA, complement C3, and eGFR for diffuse proliferative LN alone, respectively (p < 0.05). Low plasma ADMA is an independent protective factor for proliferative LN patients achieving complete remission with cyclophosphamide as induction therapy (OR = 0.978; 95% CI 0.961-0.996; p < 0.05).

Conclusion

High plasma ADMA levels in combination with eGFR and complement C3 may be useful to diagnose diffuse proliferative LN. Low plasma ADMA may help to predict complete remission in proliferative LN patients treated with cyclophosphamide as induction therapy. Plasma ADMA may be a new biomarker to determine the pathological type of LN and predict the therapeutic effect.

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.

Asymmetric dimethylarginine exacerbates cognitive dysfunction associated with cerebrovascular pathology

Asymmetric dimethylarginine (ADMA), an endogenous inhibitor and uncoupler of nitric oxide synthase, has gained attention as a risk factor for cardiac disease, metabolic syndrome, and cerebrovascular disease. In this study, we investigated the role of systemic ADMA overburden in cerebromicrovascular pathology associated with cognitive dysfunction using APPSwDI transgenic mice expressing human β-amyloid precursor protein Swedish (Tg-SwDI), a model of cerebrovascular β-amyloidosis. To induce systemic overburden of ADMA, Tg-SwDI mice were treated with a daily dose of exogenous ADMA. ADMA treatment resulted in elevated ADMA levels in the blood and brain of Tg-SwDI mice. ADMA treatment induced the brain nitrosative stress and inflammation as well as enhanced the brain Aβ deposition and cognitive impairment in Tg-SwDI mice. However, ADMA treatment had no such effects on wild type mice. ADMA treatment also exacerbated brain microvascular pathology in Tg-SwDI mice as observed by increased blood-brain barrier dysfunction, loss of tight junction proteins, increased endothelial stress fibers, and decreased microvessel density in the brain. In addition, similar observations were made in cultured human brain microvessel endothelial cells, where ADMA in the presence of VEGF-induced endothelial cell signaling for F-actin stress fiber inducing endothelial barrier dysfunction. Overall, these data document the potential role of ADMA in the cognitive pathology under conditions of cerebrovascular β-amyloidosis.

Renal dysfunction is associated with lower incidence of positive fractional flow reserve values in patients with severe hypertension

BACKGROUND

Renal dysfunction, an important predictor of cardiovascular mortality, is paradoxically associated with a lower incidence of positive coronary fractional flow reserve (FFR) values, possibly due to renal disease-associated myocardial microvascular dysfunction. It is unknown if this relationship is influenced by arterial hypertension, a condition strongly associated with renal- and microvascular dysfunction.

METHODS

The incidence of positive (<0.81) FFR values was retrospectively evaluated in consecutive patients with intermediate severity coronary artery lesions that were either associating or not associating renal dysfunction (creatinine clearance, CrCl <90 mL/min/1.73 m2), and had mild/moderate or severe arterial hypertension (treated by <3 or ≥3 different drugs).

RESULTS

Positive FFR values were found in 49.5% of the 109 included patients, with a significantly lower incidence in those with renal dysfunction: 23 vs. 31 cases (39.7% vs. 60.8%, P=0.03). However, uni- and multivariate subpopulation analysis evidenced that renal dysfunction was a significant independent predictor of fewer positive FFR results only in severely hypertensive patients (univariate P values for mild/moderate and severe hypertension: 0.80 and <0.01, respectively; multivariate P in severely hypertensive patients: 0.04). This categorization significantly restricted the number of borderline FFR results (0.75-0.80) where measurement interpretation could be challenging because of renal dysfunction (from 13.8% to 4.6% of the whole study population, P=0.03).

CONCLUSIONS

In the current study renal dysfunction was independently associated with a significantly higher incidence of negative FFR results in patients with intermediate severity coronary artery lesions only in the presence of severe arterial hypertension. This observation should be confirmed by large-scale prospective clinical trials.

Racial disparities in cardiovascular disease risk: mechanisms of vascular dysfunction

Cardiovascular disease (CVD) accounts for a third of all deaths in the United States making it the leading cause of morbidity and mortality. Although CVD affects individuals of all races/ethnicities, the prevalence of CVD is highest in non-Hispanic black (BL) individuals relative to other populations. The mechanism(s) responsible for elevated CVD risk in the BL population remains incompletely understood. However, impaired vascular vasodilator capacity and exaggerated vascular vasoconstrictor responsiveness are likely contributing factors, both of which are present even in young, otherwise healthy BL individuals. Within this review, we highlight some historical and recent data, collected from our laboratories, of impaired vascular function, in terms of reduced vasodilator capacity and heightened vasoconstrictor responsiveness, in the peripheral and cerebral circulations in BL individuals. We provide data that such impairments may be related to elevated oxidative stress and subsequent reduction in nitric oxide bioavailability. In addition, divergent mechanisms of impaired vasodilatory capacity between BL men and women are discussed. Finally, we propose several directions where future research is needed to fill in knowledge gaps, which will allow for better understanding of the mechanisms contributing to impaired vascular function in this population. Ultimately, this information will allow for better lifestyle and therapeutic approaches to be implemented in an effort to minimize the increased CVD burden in the BL population.

Reduced endothelial nitric oxide synthase activation contributes to cardiovascular injury during chronic kidney disease progression

Major cardiovascular events are a common complication in patients with chronic kidney disease (CKD). Endothelial dysfunction can contribute to the cardiovascular injury observed in CKD. Here, we used a rat model of acute kidney injury to CKD transition to investigate heart alterations in the pathway activating endothelial nitric oxide synthase (eNOS) and its impact on the cardiac injury observed during CKD progression. Fifty male Wistar rats were subjected to sham surgery ( n = 25) or bilateral renal ischemia-reperfusion (IR-CKD) for 45 min ( n = 25). Rats were studied on a monthly basis up to 5 mo ( n = 5). In another set of sham and IR-CKD rats, l-arginine was administered starting on the third month after renal ischemia. CKD development and cardiac alterations were monitored in all groups. CKD was characterized by a progressive increase in proteinuria and renal dysfunction that was evident after the fifth month of followup. Heart hypertrophy was observed starting on the fourth month after ischemia-reperfusion. There was a significant increase in brain natriuretic peptide levels. In the heart, IR-CKD rats had increased eNOS phosphorylation at threonine 495 and reduced eNOS-heat shock protein-90α interactions. l-Arginine administration prevented the heart alterations observed during CKD and increased eNOS coupling/dimerization and activation. In summary, CKD progression is accompanied by cardiac hypertrophy, fibrosis, oxidative stress, and increased brain natriuretic peptide levels. These alterations were associated with limited eNOS activation in the heart, which may result in reduced nitric oxide bioavailability and contribute to cardiac injury during CKD.

Metabolites of the Nitric Oxide (NO) Pathway Are Altered and Indicative of Reduced NO and Arginine Bioavailability in Patients with Cardiometabolic Diseases Complicated with Chronic Wounds of Lower Extremities: Targeted Metabolomics Approach (LC-MS/MS)

OBJECTIVE

The status of metabolites of the nitric oxide (NO) pathway in patients with chronic wounds in the course of cardiometabolic diseases is largely unknown. Yet arginine supplementation and citrulline supplementation as novel therapeutic modalities aimed at increasing NO are tested.

MATERIAL AND METHODS

Targeted metabolomics approach (LC-MS/MS) was applied to determine the concentrations of L-arginine, L-citrulline, asymmetric and symmetric dimethylarginines (ADMA and SDMA), and arginine/ADMA and arginine/SDMA ratios as surrogate markers of NO and arginine availability in ulnar and femoral veins, representing systemic and local levels of metabolites, in patients with chronic wounds in the course of cardiometabolic diseases (n = 59) as compared to patients without chronic wounds but with similar cardiometabolic burden (n = 55) and healthy individuals (n = 88).

RESULTS

Patients with chronic wounds had significantly lower systemic L-citrulline and higher ADMA and SDMA concentrations and lower L-arginine/ADMA and L-arginine/SDMA as compared to healthy controls. The presence of chronic wounds in patients with cardiometabolic diseases was associated with decreased L-arginine but with increased L-citrulline, ADMA, and SDMA concentrations and decreased L-arginine/ADMA and L-arginine/SDMA. Serum obtained from the ulnar and femoral veins of patients with chronic wounds differed by L-arginine concentrations and L-arginine/SDMA ratio, both lower in the femoral vein. Wound etiology affected L-citrulline and SDMA concentrations, lower and higher, respectively, in patients with venous stasis, and the L-arginine/SDMA ratio-lower in venous stasis. The wound type affected L-arginine/ADMA and citrulline-lower in patients with ulcerations or gangrene. IL-6 was an independent predictor of L-arginine/ADMA, VEGF-A of ADMA, G-CSF of L-arginine/SDMA, and GM-CSF of L-citrulline and SDMA.

CONCLUSION

Chronic wounds in the course of cardiometabolic diseases are associated with reduced NO and arginine availability due to ADMA and SDMA accumulation rather than arginine deficiency, not supporting its supplementation. Wound character seems to affect NO bioavailability and wound etiology-arginine bioavailability. Arginine concentration and its availability are more markedly reduced at the local level than the systemic level.

Oxidative stress in chronic kidney disease

Oxidative stress (OS), defined as disturbances in the pro-/antioxidant balance, is harmful to cells due to the excessive generation of highly reactive oxygen (ROS) and nitrogen (RNS) species. When the balance is not disturbed, OS has a role in physiological adaptations and signal transduction. However, an excessive amount of ROS and RNS results in the oxidation of biological molecules such as lipids, proteins, and DNA. Oxidative stress has been reported in kidney disease, due to both antioxidant depletions as well as increased ROS production. The kidney is a highly metabolic organ, rich in oxidation reactions in mitochondria, which makes it vulnerable to damage caused by OS, and several studies have shown that OS can accelerate kidney disease progression. Also, in patients at advanced stages of chronic kidney disease (CKD), increased OS is associated with complications such as hypertension, atherosclerosis, inflammation, and anemia. In this review, we aim to describe OS and its influence on CKD progression and its complications. We also discuss the potential role of various antioxidants and pharmacological agents, which may represent potential therapeutic targets to reduce OS in both pediatric and adult CKD patients.

Research progress on signaling pathways in cirrhotic portal hypertension

Portal hypertension (PHT) is an important consequence of liver cirrhosis, which can lead to complications that adversely affect a patient’s quality of life and survival, such as upper gastrointestinal bleeding, ascites, and portosystemic encephalopathy. In recent years, advances in molecular biology have led to major discoveries in the pathological processes of PHT, including the signaling pathways that may be involved: PI3K-AKT-mTOR, RhoA/Rho-kinase, JAK2/STAT3, and farnesoid X receptor. However, the pathogenesis of PHT is complex and there are numerous pathways involved. Therefore, the targeting of signaling pathways for medical management is lagging. This article summarizes the progress that has been made in understanding the signaling pathways in PHT, and provides ideas for treatment of the disorder.

Cellular and molecular mechanisms of kidney fibrosis

Renal fibrosis is the final pathological process common to any ongoing, chronic kidney injury or maladaptive repair. It is considered as the underlying pathological process of chronic kidney disease (CKD), which affects more than 10% of world population and for which treatment options are limited. Renal fibrosis is defined by excessive deposition of extracellular matrix, which disrupts and replaces the functional parenchyma that leads to organ failure. Kidney's histological structure can be divided into three main compartments, all of which can be affected by fibrosis, specifically termed glomerulosclerosis in glomeruli, interstitial fibrosis in tubulointerstitium and arteriosclerosis and perivascular fibrosis in vasculature. In this review, we summarized the different appearance, cellular origin and major emerging processes and mediators of fibrosis in each compartment. We also depicted and discussed the challenges in translation of anti-fibrotic treatment to clinical practice and discuss possible solutions and future directions.

Novel Biomarkers in the Diagnosis of Chronic Kidney Disease and the Prediction of Its Outcome

In its early stages, symptoms of chronic kidney disease (CKD) are usually not apparent. Significant reduction of the kidney function is the first obvious sign of disease. If diagnosed early (stages 1 to 3), the progression of CKD can be altered and complications reduced. In stages 4 and 5 extensive kidney damage is observed, which usually results in end-stage renal failure. Currently, the diagnosis of CKD is made usually on the levels of blood urea and serum creatinine (sCr), however, sCr has been shown to be lacking high predictive value. Due to the development of genomics, epigenetics, transcriptomics, proteomics, and metabolomics, the introduction of novel techniques will allow for the identification of novel biomarkers in renal diseases. This review presents some new possible biomarkers in the diagnosis of CKD and in the prediction of outcome, including asymmetric dimethylarginine (ADMA), symmetric dimethylarginine (SDMA), uromodulin, kidney injury molecule-1 (KIM-1), neutrophil gelatinase-associated lipocalin (NGAL), miRNA, ncRNA, and lincRNA biomarkers and proteomic and metabolomic biomarkers. Complicated pathomechanisms of CKD development and progression require not a single marker but their combination in order to mirror all types of alterations occurring in the course of this disease. It seems that in the not so distant future, conventional markers may be exchanged for new ones, however, confirmation of their efficacy, sensitivity and specificity as well as the reduction of analysis costs are required.

Asymmetric Dimethylarginine Contributes to the Impaired Response to Erythropoietin in CKD-Anemia

Erythropoietin-resistant anemia is associated with adverse cardiovascular events in patients with ESRD, but the underlying mechanism remains unclear. Here, we evaluated the role of the endogenous nitric oxide synthase inhibitor asymmetric dimethylarginine (ADMA). In 54 patients with advanced CKD, erythrocyte but not plasma ADMA levels independently associated with low hemoglobin values, although levels of both types of ADMA were elevated compared with those in healthy volunteers. Furthermore, erythrocyte ADMA level associated with the erythropoietin resistance index in patients receiving a weekly injected dose of erythropoiesis-stimulating agents standardized for hemoglobin levels and body weight, whereas it correlated with the erythropoietin demand index (plasma erythropoietin units divided by the hemoglobin value) in patients not receiving erythropoiesis-stimulating agents. Compared with sham-operated controls, wild-type mice with 5/6 subtotal nephrectomy (Nx), a remnant kidney model with advanced CKD, had decreased hemoglobin, hematocrit, and mean corpuscular volume values but increased erythrocyte and plasma ADMA and plasma erythropoietin levels. In comparison, dimethylarginine dimethlaminohydrolase-1 transgenic (DDAH-1 Tg) mice, which efficiently metabolized ADMA, had significant improvements in all of the values except those for erythropoietin after 5/6 Nx. Additionally, wild-type Nx mice, but not DDAH-1 Tg Nx mice, had reduced splenic gene expression of erythropoietin receptor and erythroferrone, which regulates iron metabolism in response to erythropoietin. This study suggests that erythrocyte ADMA accumulation contributes to impaired response to erythropoietin in predialysis patients and advanced CKD mice via suppression of erythropoietin receptor expression.

Indoxyl sulfate potentiates endothelial dysfunction via reciprocal role for reactive oxygen species and RhoA/ROCK signaling in 5/6 nephrectomized rats

Accumulative indoxyl sulfate (IS) retained in chronic kidney disease (CKD) can potentiate vascular endothelial dysfunction, and herein, we aim at elucidating the underlying mechanisms from the perspective of possible association between reactive oxygen species (ROS) and RhoA/ROCK pathway. IS-treated nephrectomized rats are administered with antioxidants including NADPH oxidase inhibitor apocynin, SOD analog tempol, and mitochondrion-targeted SOD mimetic mito-TEMPO to scavenge ROS, or ROCK inhibitor fasudil to obstruct RhoA/ROCK pathway. First, we find in response to IS stimulation, antioxidants treatments suppress increased aortic ROCK activity and expression levels. Additionally, ROCK blockade prevent IS-induced increased NADPH oxidase expression (mainly p22phox and p47phox), mitochondrial and intracellular ROS (superoxide and hydrogen peroxide) generation, and decreased Cu/Zn-SOD expression in thoracic aortas. Apocynin, mito-TEMPO, and tempol also reverse these markers of oxidative stress. These results suggest that IS induces excessive ROS production and ROCK activation involving a circuitous relationship in which ROS activate ROCK and ROCK promotes ROS overproduction. Finally, ROS and ROCK depletion attenuate IS-induced decrease in nitric oxide (NO) production and eNOS expression levels, and alleviate impaired vasomotor responses including increased vasocontraction to phenylephrine and decreased vasorelaxation to acetylcholine, thereby preventing cardiovascular complications accompanied by CKD. Taken together, excessive ROS derived from NADPH oxidase and mitochondria coordinate with RhoA/ROCK activation in a form of positive reciprocal relationship to induce endothelial dysfunction through disturbing endothelium-dependent NO signaling upon IS stimulation in CKD status.

Homocysteine deteriorates intrahepatic derangement and portal-systemic collaterals in cirrhotic rats

In liver cirrhosis, the altered levels of vasoactive substances, especially endothelin-1 (ET-1) and nitric oxide (NO) lead to elevated intrahepatic resistance, increased portal-systemic collaterals and abnormal intra- and extra-hepatic vascular responsiveness. These derangements aggravate portal hypertension-related complications such as gastro-oesophageal variceal bleeding. Homocysteine, a substance implicated in cardiovascular diseases, has been found with influences on vasoresponsiveness and angiogenesis. However, their relevant effects in liver cirrhosis have not been investigated. In the present study, liver cirrhosis was induced by common bile duct ligation (BDL) in Sprague–Dawley rats. In acute study, the results showed that homocysteine enhanced hepatic vasoconstriction to ET-1 but decreased portal-systemic collateral vasocontractility to arginine vasopressin (AVP). Homocysteine down-regulated hepatic phosphorylated endothelial NO synthase (p-eNOS) and p-Akt protein expressions. Inducible NOS (iNOS) and cyclooxygenase (COX)-2 expressions were up-regulated by homocysteine in splenorenal shunt (SRS), the most prominent intra-abdominal collateral vessel. In chronic study, BDL or thioacetamide (TAA) rats received homocysteine or vehicle for 14 days. The results revealed that homocysteine increased hepatic collagen fibre deposition and fibrotic factors expressions in both BDL- and TAA-induced liver fibrotic rats. Portal-systemic shunting and expressions of mesenteric angiogenetic factors [vascular endothelial growth factor (VEGF), platelet-derived growth factor (PDGF), PDGF receptor β (PDGFRβ) and p-eNOS] were also increased in BDL rats. In conclusion, homocysteine is harmful to vascular derangements and liver fibrosis in cirrhosis.

L-Arginine Derivatives Are Associated with the Hyperthyroid State in the General Population

BACKGROUND

Arginine (ARG) derivatives and thyroid function independently influence atherosclerotic processes. Since thyroid hormones may mediate the association between ARG derivatives and atherosclerosis, this study investigated whether asymmetric and symmetric dimethylarginines (ADMA and SDMA, respectively) as well as homoarginine (hARG) are associated with parameters of thyroid function in the general population.

METHODS

Cross-sectional data from 3689 individuals aged 20-81 years from the population-based Study of Health in Pomerania (SHIP-0) were analyzed. Thyroid function was defined according to serum concentrations of thyrotropin (TSH), free triiodothyronine (fT3), and free thyroxine (fT4). Low and high serum TSH were defined by the cutoffs 0.3 mIU/L and 3 mIU/L, respectively. Serum concentrations of ARG, ADMA, SDMA, and hARG were measured using liquid chromatography-tandem mass spectrometry. ARG, ADMA, SDMA, and hARG were associated with serum concentrations of TSH, fT3, and fT4 by median regression and with categorized TSH values by multinomial logistic regression adjusted for age, sex, smoking status, physical activity, body mass index, and estimated glomerular filtration rate.

RESULTS

Levels of ADMA (relative risk [RR] = 5.40 [confidence interval (CI) 1.96-14.86]) and SDMA (RR = 3.55 [CI 1.01-12.70]) were associated with low TSH. In addition, ADMA (β = 0.38 [CI 0.23-0.45]) was positively associated with fT3, while both ADMA (β = 0.98 [CI 0.43-1.54]) and SDMA (β = 1.19 [CI 0.50-1.88]) were positively associated with fT4. No consistent associations of ARG and hARG with thyroid function were detected.

CONCLUSIONS

The positive associations of ADMA and SDMA with low TSH, fT3, and fT4 argue for a relationship of arginine derivatives with increased thyroid function. This suggests that the atherogenic properties of ADMA and SDMA may be partially mediated by thyroid function.

Apolipoprotein E polymorphism modulation of asymmetric dimethylarginine in hypertensive patients is determined by renal function

Background

Endothelial dysfunction is considered an early step of atherosclerotic vascular disease. Asymmetric dimethylarginine (ADMA), the main endogenous inhibitor of nitric oxide synthase (NOS), plays a critical role in the process of atherosclerosis in a uremic environment. Increased plasma ADMA not only works as a cardiovascular morbidity biomarker but it is also involved in the genesis of atherosclerosis in renal disease. Considering the relationships of apolipoprotein E(ApoE) polymorphism with LDL cholesterol (LDL-C) levels and coronary risk, it is possible that it brings on susceptibility to endothelial dysfunction and atherogenesis seen on uremia.

Methods

Six hundred twenty patients were stratified according to glomerular filtration rate (GFR) estimated by Chronic Kidney Disease Epidemiology Collaboration (CKDEPI) formula: group I > 60 mL/min, group II ≤ 60 mL/min and > 15 mL/min, and group III ≤ 15 mL/min or in hemodialysis. Polymorphic ApoE analysis was performed by polymerase chain reaction amplification (PCR). Plasma ADMA levels were measured by high performance liquid chromatography (HPLC). Groups were compared on clinical and laboratory characteristics as well as allele and genotype distribution towards.

Results

The ε2 allele of ApoE was present in 62 (10.3 %) patients, ε3 allele in 581 (96.2 %), and ε4 allele in 114 (18.9 %). Their distribution among the 3 groups was uniform. Such uniformity was not observed when we considered endothelial function measured by asymmetric dimethylarginine. In group III, the frequency of ε4 allele was significantly lower in the third tertile compared with the first tertile (14.7 versus 53.3 %, P = 0.000; Pearson chi-square). In groups I and II, there was no difference in allele frequency according to ADMA levels. This association remained significant even after confouding factors corrections (OR 0.329, 95 % CI 0.155 - 0.699, P = 0.004).

Conclusions

The results of this study shows that the frequency of ε4 allele of ApoE is significantly lower among hypertensive patients on hemodialysis with the highest levels of ADMA. Uremia is capable of determining lower plasma ADMA levels in hypertensive ε4 allele carriers.

Changes in serum asymmetric dimethylarginine and endothelial markers levels with varying periods of hemodialysis

Asymmetric dimethylarginine (ADMA) as a uremia toxin is accumulated in end-stage renal disease (ESRD) patients. Elevated ADMA level has been shown to be predictive of cardiovascular diseases (CVDs) and all-cause mortality in ESRD. Therefore, we investigated the effect of prolonged hemodialysis (HD) treatment on the levels of serum ADMA, arginine, nitric oxide (NO), soluble intercellular adhesion molecule-1 (sICAM-1) and soluble vascular cell adhesion molecule-1 (sVCAM-1). Seventy-five patients (M/F = 40/35) with chronic renal failure (CRF) and who were on HD were divided into five groups with differing treatment periods of HD; from 6 to 24 months to 97-120 months. Fifteen apparently healthy subjects acted as controls. The serum levels of ADMA, sICAM-1 and sVCAM-1 were increased in all patient groups compared to the control group. No significant difference was observed when the patient groups were compared in terms of HD treatment periods. Nitric oxide levels were lower in the three groups who were treated for periods of 49-72, 73-96, 97-120 months compared to the control group. The L-arginine to ADMA ratio was decreased in all patient groups compared to controls. Consequently, our investigations have shown that in HD continued for more than 4 years NO levels began to decrease significantly and the levels of serum ADMA, sICAM-1 and sVCAM-1 levels increased although this increase was not affected by the period in which hemodialysis treatment was applied.

The role of klotho on vascular calcification and endothelial function in chronic kidney disease

Recent insights into novel roles of klotho in vascular biology make this primarily kidney-derived protein a possible candidate to form a link between chronic kidney disease and cardiovascular morbidity and mortality. Typical features of vascular dysfunction or structural abnormalities in the arterial wall are exacerbated in klotho-deficient states. Reported klotho functions include inhibition of local phosphate transport in vascular cells, phenotypic switches of vascular cellular elements into bone-forming cells, attenuation of matrix mineralization and calcification, and also preservation of endothelial functional properties and viability. To a large extent these insights rely on animal models of kidney or cardiovascular diseases. In this review the current state of knowledge on these issues is summarized, and we aim to provide a possible new perspective on cardiovascular disease in chronic kidney disease.

L-Arginine and its metabolites in kidney and cardiovascular disease

L-Arginine is a semi essential amino acid synthesised from glutamine, glutamate and proline via the intestinal-renal axis in humans and most mammals. L-Arginine degradation occurs via multiple pathways initiated by arginase, nitric-oxide synthase, Arg: glycine amidinotransferase, and Arg decarboxylase. These pathways produce nitric oxide, polyamines, proline, glutamate, creatine and agmatine with each having enormous biological importance. Several disease are associated to an L-arginine impaired levels and/or to its metabolites: in particular various L-arginine metabolites may participate in pathogenesis of kidney and cardiovascular disease. L-Arginine and its metabolites may constitute both a marker of pathology progression both the rationale for manipulating L-arginine metabolism as a strategy to ameliorate these disease. A large number of studies have been performed in experimental models of kidney disease with sometimes conflicting results, which underlie the complexity of Arg metabolism and our incomplete knowledge of all the mechanisms involved. Moreover several lines of evidence demonstrate the role of L-arg metabolites in cardiovascular disease and that L-arg administration role in reversing endothelial dysfunction, which is the leading cause of cardiovascular diseases, such as hypertension and atherosclerosis. This review will discuss the implication of the mains L-arginine metabolites and L-arginine-derived guanidine compounds in kidney and cardiovascular disease considering the more recent literature in the field.

Role of kidney biomarkers of chronic kidney disease: An update

Chronic kidney disease (CKD) is a progressive pathological condition marked by deteriorating renal function over time. Diagnostic of kidney disease depend on serum creatinine level and glomerular filtration rate which is detectable when kidney function become half. The detection of kidney damage in an early stage needs robust biomarkers. Biomarkers allow monitoring the disease progression at initial stages of disease. On the onset of impairment in cellular organization there is perturbation in signaling molecules which are either up-regulated or down-regulated and act as an indicator or biomarker of diseased stage. This review compiled the cell signaling of different kidney biomarkers associated with the onset of chronic kidney diseases. Delay in diagnosis of CKD will cause deterioration of nephron function which leads to End stage renal disease and at that point patients require dialysis or kidney transplant. Detailed information on the complex network in signaling pathway leading to a coordinated pattern of gene expression and regulation in CKD will undoubtedly provide important clues to develop novel prognostic and therapeutic strategies for CKD.

BMP type I receptor inhibition attenuates endothelial dysfunction in mice with chronic kidney disease

The molecular mechanisms of endothelial dysfunction and vascular calcification have been considered independently and potential links are currently unknown in chronic kidney disease (CKD). Bone morphogenetic protein (BMP) receptor signaling mediates calcification of atherosclerotic plaques. Here we tested whether BMP receptor signaling contributes to endothelial dysfunction, as well as to osteogenic differentiation of vascular smooth muscle cells (VSMCs), in a model of short-term CKD. In C57BL/6 mice, subtotal nephrectomy activated BMP receptor and increased phosphatase-and-tensin homolog (PTEN) protein in the endothelial cells and medial VSMCs without vascular remodeling in the aorta. In the endothelial cells, PTEN induction led to inhibition of the Akt-endothelial nitric oxide synthase (eNOS) pathway and endothelial dysfunction. In VSMCs, the PTEN increase induced early osteogenic differentiation. CKD-induced inhibition of eNOS phosphorylation and the resultant endothelial dysfunction were inhibited in mice with endothelial cell-specific PTEN ablation. Knockout of the BMP type I receptor abolished endothelial dysfunction, the inhibition of eNOS phosphorylation, and VSMC osteogenic differentiation in mice with CKD. A small molecule inhibitor of BMP type I receptor, LDN-193189, prevented endothelial dysfunction and osteogenic differentiation in CKD mice. Thus, BMP receptor activation is a mechanism for endothelial dysfunction in addition to vascular osteogenic differentiation in a short-term CKD model. PTEN may be key in linking BMP receptor activation and endothelial dysfunction in CKD.

Obeticholic acid, a farnesoid X receptor agonist, improves portal hypertension by two distinct pathways in cirrhotic rats

The farnesoid X receptor (FXR) is a nuclear bile acid receptor involved in bile acid homeostasis, hepatic and intestinal inflammation, liver fibrosis, and cardiovascular disease. We studied the effect of short-term treatment with obeticholic acid (INT-747), a potent selective FXR agonist, on intrahepatic hemodynamic dysfunction and signaling pathways in different rat models of cirrhotic portal hypertension (PHT). For this, thioacetamide (TAA)-intoxicated and bile-duct-ligated (BDL) rats were used as models. After gavage of two doses of 30 mg/kg of INT-747 or vehicle within 24 hours, in vivo hemodynamics were assessed. Additionally, we evaluated the direct effect of INT-747 on total intrahepatic vascular resistance (IHVR) and intrahepatic vascular tone (endothelial dysfunction and hyperresponsiveness to methoxamine) by means of an in situ liver perfusion system and on hepatic stellate cell contraction in vitro. FXR expression and involved intrahepatic vasoactive pathways (e.g., endothelial nitric oxide synthase [eNOS], Rho-kinase, and dimethylarginine dimethylaminohydrolase [DDAH]) were analyzed by immunohistochemistry, reverse-transcriptase polymerase chain reaction, or western blotting. In both cirrhotic models, FXR expression was decreased. Treatment with INT-747 in TAA and BDL reactivated the FXR downstream signaling pathway and decreased portal pressure by lowering total IHVR without deleterious systemic hypotension. In the perfused TAA and BDL cirrhotic liver, INT-747 improved endothelial vasorelaxation capacity, but not hyperresponsiveness. In both groups, this was associated with an increased eNOS activity, which, in TAA, related to down-regulation of Rho-kinase and in BDL to up-regulation of DDAH-2.

CONCLUSION

FXR agonist INT-747 improves PHT in two different rat models of cirrhosis by decreasing IHVR. This hemodynamic effect relates to increased intrahepatic eNOS activity by pathways that differ depending on the etiology of cirrhosis.

Effect of lowering asymmetric dimethylarginine (ADMA) on vascular pathology in atherosclerotic ApoE-deficient mice with reduced renal mass

The purpose of the work was to study the impact of the endogenous nitric oxide synthase (NOS) inhibitor asymmetric dimethylarginine (ADMA) and its degrading enzyme, dimethylarginine dimethylaminohydrolase (DDAH1), on atherosclerosis in subtotally nephrectomized (SNX) ApoE-deficient mice. Male DDAH1 transgenic mice (TG, n = 39) and C57Bl/6J wild-type littermates (WT, n = 27) with or without the deletion of the ApoE gene underwent SNX at the age of eight weeks. Animals were sacrificed at 12 months of age, and blood chemistry, as well as the extent of atherosclerosis within the entire aorta were analyzed. Sham treated (no renal mass reduction) ApoE-competent DDAH1 transgenic and wild-type littermates (n = 11) served as a control group. Overexpression of DDAH1 was associated with significantly lower ADMA levels in all treatment groups. Surprisingly, SNX mice did not exhibit higher ADMA levels compared to sham treated control mice. Furthermore, the degree of atherosclerosis in ApoE-deficient mice with SNX was similar in mice with or without overexpression of DDAH1. Overexpression of the ADMA degrading enzyme, DDAH1, did not ameliorate atherosclerosis in ApoE-deficient SNX mice. Furthermore, SNX in mice had no impact on ADMA levels, suggesting a minor role of this molecule in chronic kidney disease (CKD) in this mouse model.

Peritubular capillary rarefaction: a new therapeutic target in chronic kidney disease

Chronic kidney disease (CKD) has reached worldwide epidemic proportions and desperately needs new therapies. Peritubular capillary (PTC) rarefaction, together with interstitial fibrosis and tubular atrophy, is one of the major hallmarks of CKD and predicts renal outcome in patients with CKD. PTC endothelial cells (ECs) undergo apoptosis during CKD, leading to capillary loss, tissue hypoxia, and oxidative stress. Although the mechanisms of PTC rarefaction are not well understood, the process of PTC rarefaction depends on multiple events that occur during CKD. These events, which lead to an antiangiogenic environment, include deprivation of EC survival factors, increased production of vascular growth inhibitors, malfunction of ECs, dysfunction of endothelial progenitor cells, and loss of EC integrity via pericyte detachment from the vasculature. In this review, we focus on major factors regulating angiogenesis and EC survival and describe the roles of these factors in PTC rarefaction during CKD and possible therapeutic applications.

Asymmetric dimethylarginine and critical illness

PURPOSE OF REVIEW

Asymmetric dimethylarginine (ADMA) is an analog of arginine and functions as an endogenous inhibitor of the nitric oxide synthase, which forms nitric oxide. Nitric oxide is crucial for perfusion of vital organs and is an important signaling agent in the development of critical illness. The role of ADMA in the pathophysiological mechanisms underlying critical illness is widely studied in the last decades, and recently it has become clear that ADMA should not be overlooked by clinicians working at the ICU. The aim of this review is to describe new insights into the role of ADMA in critical illness and its clinical relevance.

RECENT FINDINGS

High levels of ADMA are found in critically ill patients, because of higher levels of protein methylation, increased rate of protein turnover, decreased activity of dimethylamine dimethylaminohydrolase, and impaired renal and hepatic clearance capacity. These high levels are an independent risk factor for cardiac dysfunction, organ failure, and ICU mortality. The arginine : ADMA ratio in particular is of clinical importance and the restoration of this ratio is expedient to restore several functions that are disturbed during critical illness.

SUMMARY

Elevated ADMA levels occur in critically ill patients, which is detrimental for morbidity and mortality. The arginine : ADMA ratio should be restored to maintain nitric oxide production and therewith improve the clinical outcome of the patient.

Predictors of high sensitivity cardiac troponin T in chronic kidney disease patients: a cross-sectional study in the chronic renal insufficiency cohort (CRIC)

Background

Cardiac troponin T is independently associated with cardiovascular events and mortality in patients with chronic kidney disease (CKD). Serum levels of high sensitivity cardiac troponin T (hs-TnT) reflect subclinical myocardial injury in ambulatory patients. We sought to determine the distribution and predictors of hs-TnT in CKD patients without overt cardiovascular disease (CVD).

Methods

We studied 2464 participants within the multi-ethnic Chronic Renal Insufficiency Cohort (CRIC) who did not have self-reported CVD. We considered renal and non-renal factors as potential determinants of hs-TnT, including demographics, comorbidities, left ventricular (LV) mass, serologic factors, estimated glomerular filtration rate (eGFR) and albumin to creatinine ratio.

Results

Hs-TnT was detectable in 81% of subjects, and the median (IQR) hs-TnT was 9.4 pg/ml (4.3-18.3). Analysis was performed using Tobit regression, adjusting for renal and non-renal factors. After adjustment, lower eGFR was associated with higher expected hs-TnT; participants with eGFR < 30 ml/min/1.73 m² had 3-fold higher expected hs-TnT compared to subjects with eGFR > 60. Older age, male gender, black race, LV mass, diabetes and higher blood pressure all had strong, independent associations with higher expected hs-TnT.

Conclusions

Knowledge of the determinants of hs-TnT in this cohort may guide further research on the pathology of heart disease in patients with CKD and help to stratify sub-groups of CKD patients at higher cardiovascular risk.

Suppressed soluble Fms-like tyrosine kinase-1 production aggravates atherosclerosis in chronic kidney disease

Patients with chronic kidney disease (CKD) die of cardiovascular diseases for unknown reasons. Blood vessel formation in plaques and its relationship with plaque stability could be involved with signaling through the Flt-1 receptor and its ligands, vascular endothelial growth factor, and the closely related placental growth factor (PlGF). Flt-1 also exists as a circulating regulatory splice variant short-inhibitory form (sFlt-1) that serves as a decoy receptor, thereby inactivating PlGF. Heparin releases sFlt-1 by displacing the sFlt-1 heparin-binding site from heparin sulfate proteoglycans. Heparin could provide diagnostic inference or could also induce an antiangiogenic state. In the present study, postheparin sFlt-1 levels were lower in CKD patients than in control subjects. More importantly, sFlt-1 levels were inversely related to atherosclerosis in CKD patients, and this correlation was more robust after heparin injection, as verified by subsequent cardiovascular events. Knockout of apolipoprotein E (ApoE) and/or sFlt-1 showed that the absence of sFlt-1 worsened atherogenesis in ApoE-deficient mice. Thus, the relationship between atherosclerosis and PlGF signaling, as regulated by sFlt-1, underscores the underappreciated role of heparin in sFlt-1 release. These clinical and experimental data suggest that novel avenues into CKD-dependent atherosclerosis and its detection are warranted.

Endothelial cell transfusion ameliorates endothelial dysfunction in 5/6 nephrectomized rats

Endothelial dysfunction is prevalent in chronic kidney disease. This study tested the hypothesis that transfusion of rat aortic endothelial cells (ECs) ameliorates endothelial dysfunction in a rat model of chronic kidney disease. Male Sprague-Dawley rats underwent sham surgery or 5/6 nephrectomy (Nx). Five weeks after Nx, EC (1.5 × 10(6) cells/rat) or vehicle were transfused intravenously. One week later, vascular reactivity of mesenteric artery was assessed on a wire myograph. Sensitivity of endothelium-dependent relaxation to acetylcholine and maximum vasodilation were impaired by Nx and improved by EC transfusion. Using selective pharmacological nitric oxide synthase isoform inhibitors, we demonstrated that the negative effect of Nx on endothelial function and rescue by EC transfusion are, at least in part, endothelial nitric oxide synthase mediated. Plasma asymmetric dimethylarginine was increased by Nx and decreased by EC transfusion, whereas mRNA expression of dimethylarginine dimethylaminohydrolases 1 (DDAH1) was decreased by Nx and restored by EC transfusion. Immunohistochemical staining confirmed that local expression of DDAH1 is decreased by Nx and increased by EC transfusion. In conclusion, EC transfusion attenuates Nx-induced endothelium-dependent vascular dysfunction by regulating DDAH1 expression and enhancing endothelial nitric oxide synthase activity. These results suggest that EC-based therapy could provide a novel therapeutic strategy to improve vascular function in chronic kidney disease.

FTY720 prevents progression of renal fibrosis by inhibiting renal microvasculature endothelial dysfunction in a rat model of chronic kidney disease

Recent studies have shown that chronic endothelial dysfunction can impair multiple aspects of renal physiology and, in turn, contribute to renal fibrosis. Sphingosine 1-phosphate (S1P) has been highlighted as an endothelial barrier-stabilizing mediator. The aim of our study was to investigate the effect of FTY720, an S1P analog, on the progression of renal fibrosis by inhibiting renal microvasculature endothelial dysfunction in a rat model of chronic kidney disease. Thirty male Sprague-Dawley rats were used in this study. Seven days after surgery, we placed the animals into three groups: sham surgery; 5/6 nephrectomized (Nx) rats; and 5/6Nx + FTY720 (1 mg/kg/day). All of the animals were sacrificed 12 weeks after surgery. We obtained and analyzed blood and kidney tissue samples from all of the groups. Glomerular capillary density and peritubular capillary (PTC) density were determined by CD31 immunostaining. The expression of transforming growth factor beta 1 (TGF-β1), collagen IV, fibronectin, endothelial nitric oxide synthase (eNOS) and vascular endothelial growth factor (VEGF) were analyzed by immunohistochemistry, reverse transcription-polymerase chain reaction and western blotting. The 5/6Nx group exhibited increased blood urea nitrogen and serum creatinine, visible renal histological changes, pro-fibrotic molecule (TGF-β1) and production of extracellular matrix proteins such as collagen IV and fibronectin and decreased glomerular and PTC density, compared to the sham controls (P < 0.01). We observed that treatment with FTY720 reduced these abnormalities. Furthermore, the level of NO, the expression levels of eNOS and VEGF were downregulated in the kidney tissue in 5/6Nx rats, FTY720 treatment significantly attenuated this decrease. FTY720 prevents the progression of renal fibrosis by inhibiting renal microvasculature endothelial dysfunction in a rat model of chronic kidney disease.

High levels of asymmetric dimethylarginine are strongly associated with low HDL in patients with acute myocardial infarction

Objectives

Low levels of high-density lipoprotein (HDL) cholesterol are associated with an increased risk of acute myocardial infarction possibly through impaired endothelial atheroprotection and decreased nitric oxide (NO) bioavailability. Asymmetric dimethylarginine (ADMA) mediates endothelial function by inhibiting nitric oxide synthase activity. In patients with acute myocardial infarction, we investigated the relationship between serum levels of HDL and ADMA.

Approach and Results

Blood samples from 612 consecutive patients hospitalized for acute MI <24 hours after symptom onset were taken on admission. Serum levels of ADMA, its stereoisomer, symmetric dimethylarginine (SDMA) and L-arginine were determined using high-performance liquid chromatography. Patients with low HDL (<40 mg/dL for men and <50 mg/dL for women) were compared with patients with higher HDL. Most patients (59%) had low HDL levels. Median ADMA levels were markedly higher in the low HDL group (0.69 vs. 0.50 µmole/L, p<0.001). In contrast, SDMA and L-arginine levels were similar for the two groups (p = 0.120 and p = 0.064). Notably, ADMA, but not SDMA or L-arginine, was inversely correlated with HDL (r = −0.311, p<0.001). In stratified analysis, this relationship was only found for low HDL levels (r = −0.265, p<0.001), but not when HDL levels were higher (r = −0.077, p = 0.225). By multivariate logistic regression analysis, ADMA level was strongly associated with low HDL levels (OR(95%CI):6.06(3.48–10.53), p<0.001), beyond traditional confounding factors.

Conclusions

Our large population-based study showed for the first time a strong inverse relationship between HDL and ADMA in myocardial infarction patients, suggesting a functional interaction between HDL and endothelium, beyond metabolic conditions associated with low HDL levels.

Role of asymmetrical dimethylarginine in the progression of renal disease

Asymmetric dimethylarginine (ADMA) is a naturally occurring amino acid found in tissues and cells that circulates in plasma and is excreted in urine. It inhibits nitric oxide synthases (NOs) and produces considerable cardiovascular biological effects. Several studies have suggested that plasma concentrations of ADMA provide a marker of risk for endothelial dysfunction and cardiovascular disease. In animal and in population studies ADMA has been associated with progression of CKD. Several mechanisms may be involved in this association, such as compromise of the integrity of the glomerular filtration barrier and development of renal fibrosis. This review summarizes the existing literature on the biology and physiology of ADMA focusing on its role in the progression of renal disease.

Inhibition of ATP-induced calcium influx by homocysteine in human umbilical vein endothelial cells

Mechanisms involved in the association between hyperhomocysteinemia and vascular occlusive diseases remain unclear. Homocysteine (Hcy) may disturb calcium (Ca(2+) ) cytosolic regulation in endothelial cells, a process that can directly affect the synthesis of vasoactive substances, such as nitric oxide (NO). We have investigated the effect of acute and chronic incubation with high concentrations of Hcy (100 and 500 μmol/L) on the changes in the intracellular Ca(2+) concentration ([Ca(2+) ]i ) induced by ATP, using primary cultures of human umbilical vein endothelial cells (HUVEC). The changes in [Ca(2+) ]i , expressed as ΔFt /Fb , were measured using the microspectrofluorimetric technique with Fluo-3 as Ca(2+) indicator. HUVEC acutely exposed to Hcy did not produce significant effects on any of the parameters studied. However, chronic exposition (24 h) caused a significant decrease in the speed of store-mediated Ca(2+) entry, expressed as (ΔFt /Fb )/t (s(-1) ). Exposure of HUVEC to 100 and 500 µmol/L Hcy gave significantly lower values (0.019 ± 0.002 s(-1) , n = 5 and 0.021 ± 0.004 s(-1) , n = 6, respectively) compared to the controls (0.046 ± 0.004 s(-1) , n = 8, P < 0.003). This was detected only when the sustained phase of the ATP-induced [Ca(+2) ]i increase was isolated. These results demonstrate that high concentrations of Hcy can affect the mechanisms involved in [Ca(2+) ]i regulation of HUVEC, and that alteration occurs specifically in the sustained phase, which has been directly associated with NO synthesis.

Vaspin increases nitric oxide bioavailability through the reduction of asymmetric dimethylarginine in vascular endothelial cells

Vaspin is an adipocytokine recently identified in the visceral adipose tissue of diabetic rats and having anti-diabetic effects. We have recently shown that vaspin has anti-atherogenic effect through Akt-mediated inhibition of endothelial cell apoptosis. Decreased activity of endothelial nitric oxide synthase (eNOS) plays an important role in the pathogenesis of atherosclerosis. Asymmetric dimethylarginine (ADMA) is a well-known endogenous competitive inhibitor of eNOS and risk factor of cardiovascular diseases. The aim of this study was to examine whether vaspin might protect against atherosclerosis through its beneficial effects on the ADMA-eNOS system. Treatment of vaspin significantly increased NO secretion from endothelial cells and isolated aorta from Sprague-Dawley (SD) rats. Furthermore, treatment of vaspin prevented fatty acid-induced decrease in endothelium-dependent vasorelaxation in isolated aorta of SD rat. For the mechanism of vaspin-induced NO biosynthesis, vaspin activated the STAT3 signaling pathway and stimulated eNOS phosphorylation (Ser 1177), a marker of eNOS activation, through STAT3-dependent mechanism. Furthermore, vaspin treatment increased the expression of dimethylarginine dimethylaminohydrolase (DDAH) II, the responsible enzyme for the degradation of ADMA, leading to a reduction in ADMA levels. Vaspin-induced increase in DDAH II gene expression was through STAT3-mediated stimulation of DDAH II promoter activity. These results suggest that vaspin increases eNOS activity by reducing ADMA level through STAT3-mediated regulation of DDAH II expression. Our findings provide a novel molecular mechanism of antiatherogenic actions of vaspin.

Protection of DDAH2 overexpression against homocysteine-induced impairments of DDAH/ADMA/NOS/NO pathway in endothelial cells

BACKGROUND/AIMS

Homocysteine-induced endothelial dysfunction favors the development of cardiovascular diseases through accumulation of endogenous nitric oxide (NO) synthase (NOS) inhibitor asymmetric dimethylarginine (ADMA). Dimethylarginine dimethylaminohydrolase 2 (DDAH2) is the major enzyme for the degradation of ADMA in endothelial cells. The purpose of this study was to determine whether suppressed DDAH2 expression contributed to impairments of DDAH/ADMA/NOS/NO pathway induced by homocysteine in endothelial cells and whether DDAH2 overexpression could prevent endothelial cell dysfunction caused by homocysteine.

METHODS

Liposome-mediated transfection of endothelial cells was performed to establish the cell line of DDAH2 overexpression. After treatment of cells with 1 mmol/L homocysteine for 24 h, the transcription and expression of DDAH1 and DDAH2, DDAH and NOS activities as well as ADMA and NO concentrations were measured.

RESULTS

Treatment of endothelial cells with homocysteine significantly suppressed the transcription and expression of DDAH2 but not DDAH1. This suppression was associated with the declined DDAH activity, increased ADMA accumulation, inhibited NOS activity and decreased NO production in endothelial cells. DDAH2 overexpression not only resisted homocysteine-induced decline of DDAH activity, but also decreased the accumulation of endogenous ADMA, subsequently attenuated the reductions of NOS activity and NO production induced by homocysteine.

CONCLUSIONS

These results indicate that suppression of DDAH2 expression is a culprit for homocysteine-induced impairments of DDAH/ADMA/NOS/NO pathway in endothelial cells, and therapeutic manipulation of DDAH2 expression may be a promising strategy for preventing endothelial dysfunction and cardiovascular diseases associated with hyperhomocysteinemia.

Asymmetric dimethylarginine, endothelial dysfunction and renal disease

l-Arginine (Arg) is oxidized to l-citrulline and nitric oxide (NO) by the action of endothelial nitric oxide synthase (NOS). In contrast, protein-incorporated Arg residues can be methylated with subsequent proteolysis giving rise to methylarginine compounds, such as asymmetric dimethylarginine (ADMA) that competes with Arg for binding to NOS. Most ADMA is degraded by dimethylarginine dimethyaminohydrolase (DDAH), distributed widely throughout the body and regulates ADMA levels and, therefore, NO synthesis. In recent years, several studies have suggested that increased ADMA levels are a marker of atherosclerotic change, and can be used to assess cardiovascular risk, consistent with ADMA being predominantly absorbed by endothelial cells. NO is an important messenger molecule involved in numerous biological processes, and its activity is essential to understand both pathogenic and therapeutic mechanisms in kidney disease and renal transplantation. NO production is reduced in renal patients because of their elevated ADMA levels with associated reduced DDAH activity. These factors contribute to endothelial dysfunction, oxidative stress and the progression of renal damage, but there are treatments that may effectively reduce ADMA levels in patients with kidney disease. Available data on ADMA levels in controls and renal patients, both in adults and children, also are summarized in this review.

ADMA and NOS regulation in chronic renal disease: beyond the old rivalry for l-arginine

Chronic kidney disease is associated with increased levels of assymetric N(G),N(G)-dimethylarginine (ADMA), which is predictive of increased mortality and cardiovascular disease. ADMA induces endothelial dysfunction through competitive inhibition of the endothelial nitric oxide (eNOS) substrate L-arginine. Kajimoto et al. show that ADMA may also reduce nitric oxide production via decreased eNOS phosphorylation; this effect is mediated by the MAPK pathway and can be reversed in vivo by increased catabolism of ADMA through dimethylarginine dimethylaminohydrolase-1 overexpression.

Selective gene expression analysis of muscular and vascular components in hearts using laser microdissection method

Background. The heart consists of various kinds of cell components. However, it has not been feasible to separately analyze the gene expression of individual components. The laser microdissection (LMD) method, a new technology to collect target cells from the microscopic regions, has been used for malignancies. We sought to establish a method to selectively collect the muscular and vascular regions from the heart sections and to compare the marker gene expressions with this method. Methods and Results. Frozen left ventricle sections were obtained from Wistar-Kyoto rats (WKY) and stroke-prone spontaneously hypertensive rats (SHR-SP) at 24 weeks of age. Using the LMD method, the muscular and vascular regions were selectively collected under microscopic guidance. Real-time RT-PCR analysis showed that brain-type natriuretic peptide (BNP), a marker of cardiac myocytes, was expressed in the muscular samples, but not in the vascular samples, whereas α-smooth muscle actin, a marker of smooth muscle cells, was detected only in the vascular samples. Moreover, SHR-SP had significantly greater BNP upregulation than WKY (P < 0.05) in the muscular samples. Conclusions. The LMD method enabled us to separately collect the muscular and vascular samples from myocardial sections and to selectively evaluate mRNA expressions of the individual tissue component.