Asymmetric dimethylarginine (ADMA) induces chronic kidney disease through a mechanism involving collagen and TGF-β1 synthesis

Metabolic reprogramming and renal fibrosis: what role might Chinese medicine play?

Metabolic reprogramming is a pivotal biological process in which cellular metabolic patterns change to meet the energy demands of increased cell growth and proliferation. In this review, we explore metabolic reprogramming and its impact on fibrotic diseases, providing a detailed overview of the key processes involved in the metabolic reprogramming of renal fibrosis, including fatty acid decomposition and synthesis, glycolysis, and amino acid catabolism. In addition, we report that Chinese medicine ameliorates renal inflammation, oxidative stress, and apoptosis in chronic kidney disease by regulating metabolic processes, thereby inhibiting renal fibrosis. Furthermore, we reveal that multiple targets and signaling pathways contribute to the metabolic regulatory effects of Chinese medicine. In summary, this review aims to elucidate the mechanisms by which Chinese medicine inhibits renal fibrosis through the remodeling of renal cell metabolic processes, with the goal of discovering new therapeutic drugs for treating renal fibrosis.

An account of the current status of point-of-care lateral flow tests for kidney biomarker detection

Globally, the primary causes of mortality and morbidity related to kidney ailments can be classified as Acute Kidney Injury (AKI) and Chronic Kidney Disease (CKD). Biomarker detection can have great potential to improve survival, lower mortality, and reduce the cost of treatment of kidney diseases. Considering the chronic nature of CKD, non-invasive identification and monitoring have proven to be useful. Biosensors and more specifically lateral flow test strips (LFTs) are regarded as the most desirable point-of-care instruments which have shown promise in elevating the healthcare industry to a new level. The major aspects of an ideal point-of-care (POC) lateral flow test include its cost effectiveness, high sensitivity and specificity, ease of use, quick result delivery, and quality control. This review provides a detailed account of recent developments, challenges, and opportunities in renal biomarker detection using LFTs including various approaches for sensitivity enhancement along with potential future advancements in POC and LFT kits.

Revealing novel biomarkers for diagnosing chronic kidney disease in pediatric patients

Pediatric chronic kidney disease (CKD) is a clinical condition characterized by progressive renal function deterioration. CKD diagnosis is based on glomerular filtration rate, but its reliability is limited, especially at the early stages. New potential biomarkers (citrulline (CIT), symmetric dimethylarginine (SDMA), S-adenosylmethionine (SAM), n-butyrylcarnitine (nC4), cis-4-decenoylcarnitine, sphingosine-1-phosphate and bilirubin) in addition to creatinine (CNN) have been proposed for early diagnosis. To verify the clinical value of these biomarkers we performed a comprehensive targeted metabolomics study on a representative cohort of CKD and healthy pediatric patients. Sixty-seven children with CKD and forty-five healthy children have been enrolled in the study. Targeted metabolomics based on liquid chromatography-triple quadrupole mass spectrometry has been used for serum and plasma samples analysis. Univariate data analysis showed statistically significant differences (p < 0.05) in the concentration of CNN, CIT, SDMA, and nC4 among healthy and CKD pediatric patients. The predictive ability of the proposed biomarkers was also confirmed through specificity and sensitivity expressed in Receiver Operating Characteristic curves (AUC = 0.909). In the group of early CKD pediatric patients, AUC of 0.831 was obtained, improving the diagnostic reliability of CNN alone. Moreover, the models built on combined CIT, nC4, SDMA, and CNN allowed to distinguish CKD patients from healthy control regardless of blood matrix type (serum or plasma). Our data demonstrate potential biomarkers in the diagnosis of early CKD stages.

A systematic review of metabolomic findings in adult and pediatric renal disease

Chronic kidney disease (CKD) affects over 0.5 billion people worldwide across their lifetimes. Despite a growingly ageing world population, an increase in all-age prevalence of kidney disease persists. Adult-onset forms of kidney disease often result from lifestyle-modifiable metabolic illnesses such as type 2 diabetes. Pediatric and adolescent forms of renal disease are primarily caused by morphological abnormalities of the kidney, as well as immunological, infectious and inherited metabolic disorders. Alterations in energy metabolism are observed in CKD of varying causes, albeit the molecular mechanisms underlying pathology are unclear. A systematic indexing of metabolites identified in plasma and urine of patients with kidney disease alongside disease enrichment analysis uncovered inborn errors of metabolism as a framework that links features of adult and pediatric kidney disease. The relationship of genetics and metabolism in kidney disease could be classified into three distinct landscapes: (i) Normal genotypes that develop renal damage because of lifestyle and / or comorbidities; (ii) Heterozygous genetic variants and polymorphisms that result in unique metabotypes that may predispose to the development of kidney disease via synergistic heterozygosity, and (iii) Homozygous genetic variants that cause renal impairment by perturbing metabolism, as found in children with monogenic inborn errors of metabolism. Interest in the identification of early biomarkers of onset and progression of CKD has grown steadily in the last years, though it has not translated into clinical routine yet. This systematic review indexes findings of differential concentration of metabolites and energy pathway dysregulation in kidney disease and appraises their potential use as biomarkers.

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

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

Metabolomic markers mediate erythrocyte anisocytosis in older adults: Results from three independent aging cohorts

BACKGROUND

Anisocytosis reflects unequal-sized red blood cells and is quantified using red blood cell distribution width (RDW). RDW increases with age and has been consistently associated with adverse health outcomes, such as cardiovascular disease and mortality. Why RDW increases with age is not understood. We aimed to identify plasma metabolomic markers mediating anisocytosis with aging.

METHODS

We performed mediation analyses of plasma metabolomics on the association between age and RDW using resampling techniques after covariate adjustment. We analyzed data from adults aged 70 or older from the main discovery cohort of the Baltimore Longitudinal Study of Aging (BLSA, n = 477, 46% women) and validation cohorts of the Health, Aging and Body Composition Study (Health ABC, n = 620, 52% women) and Invecchiare in Chianti, Aging in the Chianti Area (InCHIANTI) study (n = 735, 57% women). Plasma metabolomics was assayed using the Biocrates MxP Quant 500 kit in BLSA and Health ABC and liquid chromatography with tandem mass spectrometry in InCHIANTI.

RESULTS

In all three cohorts, symmetric dimethylarginine (SDMA) significantly mediated the association between age and RDW. Asymmetric dimethylarginine (ADMA) and 1-methylhistidine were also significant mediators in the discovery cohort and one validation cohort. In the discovery cohort, we also found choline, homoarginine, and several long-chain triglycerides significantly mediated the association between age and RDW.

CONCLUSIONS AND RELEVANCE

This metabolomics study of three independent aging cohorts identified a specific set of metabolites mediating anisocytosis with aging. Whether SDMA, ADMA, and 1-methylhistidine are released by the damaged erythrocytes with high RDW or they affect the physiology of erythrocytes causing high RDW should be further investigated.

LncRNA DANCR deficiency promotes high glucose-induced endothelial to mesenchymal transition in cardiac microvascular cells via the FoxO1/DDAH1/ADMA signaling pathway

Cardiac fibrosis is the main pathological basis of diabetic cardiomyopathy (DCM), and endothelial-to-meschenymal transition (EndMT) is a key driver to cardiac fibrosis and plays an important role in the pathogenesis of DCM. Asymmetric dimethylarginine (ADMA), a crucial pathologic factor in diabetes mellitus, is involved in organ fibrosis. This study aims to evaluate underlying mechanisms of ADMA in DCM especially for EndMT under diabetic conditions. A diabetic rat model was induced by streptozotocin (STZ) injection, and human cardiac microvascular endothelial cells (HCMECs) were stimulated with high glucose to induce EndMT. Subsequently, the role of ADMA in EndMT was detected either by exogenous ADMA or by over-expressing dimethylarginine dimethylaminohydrolase 1 (DDAH1, degradation enzyme for ADMA) before high glucose stimulation. Furthermore, the relationships among forkhead box protein O1 (FoxO1), DDAH1 and ADMA were evaluated by FoxO1 over-expression or FoxO1 siRNA. Finally, we examined the roles of LncRNA DANCR in FoxO1/DDAH1/ADMA pathway and EndMT of HCMECs. Here, we found that EndMT in HCMECs was induced by high glucose, as evidenced by down-regulated expression of CD31 and up-regulated expression of FSP-1 and collagen Ⅰ. Importantly, ADMA induced EndMT in HCMECs, and over-expressing DDAH1 protected from developing EndMT by high glucose. Furthermore, we demonstrated that over-expression of FoxO1-ADA with mutant phosphorylation sites of T24A, S256D, and S316A induced EndMT of HCMECs by down-regulating of DDAH1 and elevating ADMA, and that EndMT of HCMECs induced by high glucose was reversed by FoxO1 siRNA. We also found that LncRNA DANCR siRNA induced EndMT of HCMECs, activated FoxO1, and inhibited DDAH1 expression. Moreover, over-expression of LncRNA DANCR could markedly attenuated high glucose-mediated EndMT of HCMECs by inhibiting the activation of FoxO1 and increasing the expression of DDAH1. Collectively, our results indicate that LncRNA DANCR deficiency promotes high glucose-induced EndMT in HCMECs by regulating FoxO1/DDAH1/ADMA pathway.

Molecular hydrogen promotes wound healing by inducing early epidermal stem cell proliferation and extracellular matrix deposition

BACKGROUND

Despite progress in developing wound care strategies, there is currently no treatment that promotes the self-tissue repair capabilities. H₂ has been shown to effectively protect cells and tissues from oxidative and inflammatory damage. While comprehensive effects and how H₂ functions in wound healing remains unknown, especially for the link between H₂ and extracellular matrix (ECM) deposition and epidermal stem cells (EpSCs) activation.

METHODS

Here, we established a cutaneous aseptic wound model and applied a high concentration of H₂ (66% H₂) in a treatment chamber. Molecular mechanisms and the effects of healing were evaluated by gene functional enrichment analysis, digital spatial profiler analysis, blood perfusion/oxygen detection assay, in vitro tube formation assay, enzyme-linked immunosorbent assay, immunofluorescent staining, non-targeted metabonomic analysis, flow cytometry, transmission electron microscope, and live-cell imaging.

RESULTS

We revealed that a high concentration of H₂ (66% H₂) greatly increased the healing rate (3 times higher than the control group) on day 11 post-wounding. The effect was not dependent on O₂ or anti-reactive oxygen species functions. Histological and cellular experiments proved the fast re-epithelialization in the H₂ group. ECM components early (3 days post-wounding) deposition were found in the H₂ group of the proximal wound, especially for the dermal col-I, epidermal col-III, and dermis-epidermis-junction col-XVII. H₂ accelerated early autologous EpSCs proliferation (1-2 days in advance) and then differentiation into myoepithelial cells. These epidermal myoepithelial cells could further contribute to ECM deposition. Other beneficial outcomes include sustained moist healing, greater vascularization, less T-helper-1 and T-helper-17 cell-related systemic inflammation, and better tissue remodelling.

CONCLUSION

We have discovered a novel pattern of wound healing induced by molecular hydrogen treatment. This is the first time to reveal the direct link between H₂ and ECM deposition and EpSCs activation. These H₂-induced multiple advantages in healing may be related to the enhancement of cell viability in various cells and the maintenance of mitochondrial functions at a basic level in the biological processes of life.

Associations of serum amino acids related to urea cycle with risk of chronic kidney disease in Chinese with type 2 diabetes

OBJECTIVE

Serum levels of amino acids related to urea cycle are associated with risk of type 2 diabetes mellitus (T2DM). Our study aimed to explore whether serum levels of amino acids related to urea cycle, i.e., arginine, citrulline, and ornithine, are also associated with increased risk of chronic kidney disease (CKD) in T2DM.

METHODS

We extracted medical records of 1032 consecutive patients with T2DM from the Electronic Administrative System of Liaoning Medical University First Affiliated Hospital (LMUFAH) system from May 2015 to August 2016. Of them, 855 patients with completed data available were used in the analysis. CKD was defined as estimated glomerular filtration rate (eGFR) <60 mL/min/1.73 m². Serum amino acids were measured by mass spectrometry (MS) technology. Binary logistic regression was performed to obtain odds ratios (ORs) and their 95% confidence intervals (CIs).

RESULTS

52.3% of the 855 T2DM patients were male, and 143 had CKD. In univariable analysis, high serum citrulline, high ratio of arginine to ornithine, and low ratio of ornithine to citrulline were associated with markedly increased risk of CKD (OR of top vs. bottom tertile: 2.87, 95%CI, 1.79-4.62 & 1.98, 95%CI,1.25-3.14 & 2.56, 95%CI, 1.61-4.07, respectively). In multivariable analysis, the ORs of citrulline and ornithine/citrulline ratio for CKD remained significant (OR of top vs. bottom tertile: 2.22, 95%CI, 1.29-3.82 & 2.24, 1.29-3.87, respectively).

CONCLUSIONS

In Chinese patients with T2DM, high citrulline and low ornithine/citrulline ratio were associated with increased risk of CKD.

Role of ADMA in the pathogenesis of microvascular complications in type 2 diabetes mellitus

Diabetic microangiopathy is a typical and severe problem in diabetics, including diabetic retinopathy, diabetic nephropathy, diabetic neuropathy, and diabetic cardiomyopathy. Patients with type 2 diabetes and diabetic microvascular complications have significantly elevated levels of Asymmetric dimethylarginine (ADMA), which is an endogenous inhibitor of nitric oxide synthase (NOS). ADMA facilitates the occurrence and progression of microvascular complications in type 2 diabetes through its effects on endothelial cell function, oxidative stress damage, inflammation, and fibrosis. This paper reviews the association between ADMA and microvascular complications of diabetes and elucidates the underlying mechanisms by which ADMA contributes to these complications. It provides a new idea and method for the prevention and treatment of microvascular complications in type 2 diabetes.

Glomerular filtration rate abnormalities in sickle cell disease

Sickle cell disease (SCD) is a group of inherited blood disorders affecting the β-globin gene, resulting in the polymerization of hemoglobin and subsequent sickling of the red blood cell. Renal disease, the most common complication in SCD, begins in childhood with glomerular hyperfiltration and then progresses into albuminuria, a fast decline of glomerular filtration, and renal failure in adults. This mini-review focuses on glomerular filtration abnormalities and the mechanisms of hyperfiltration, explores genetic modifiers and methods of estimating glomerular filtration rates, and examines novel biomarkers of glomerular filtration in SCD.

Predictive markers in chronic kidney disease

Chronic kidney disease (CKD) is defined by gradual deterioration of the renal parenchyma and decline of functioning nephrons. CKD is now recognized as a distinct risk factor for cardiovascular disease (CVD). This risk rises in tandem with the decline in kidney function and peaks at the end-stage. It is important to identify individuals with CKD who are at a higher risk of advancing to end-stage renal disease (ESRD) and the beginning of CVD. This will enhance the clinical benefits and so that evidence-based therapy may be started at the initial stages for those individuals. A promising biomarker must represent tissue damage, and be easy to detect using non-invasive methods. Current CKD progression indicators have difficulties in reaching this aim. Hence this review presents an update on markers studied in the last decade, which help in the prediction of CKD progression such as neutrophil gelatinase-associated lipocalin, kidney injury molecule-1, urinary liver-type fatty acid-binding protein, cystatin-C, asymmetric dimethylarginine, symmetric dimethylarginine, endotrophin, methylglyoxal, sclerostin, uric acid, and miRNA-196a. Additional research is needed to determine the predictive usefulness of these indicators in clinical samples for disease development. Their utility as surrogate markers need to be explored further for the early identification of CKD progression.

A Recombinant Dimethylarginine Dimethylaminohydrolase-1-Based Biotherapeutics to Pharmacologically Lower Asymmetric Dimethyl Arginine, thus Improving Postischemic Cardiac Function and Cardiomyocyte Mitochondrial Activity

High serum levels of asymmetric dimethyl arginine (ADMA) are associated with cardiovascular disease and mortality. Pharmacological agents to specifically lower ADMA and their potential impact on cardiovascular complications are not known. In this study, we aimed to investigate the effect of specific lowering of ADMA on myocardial response to ischemia-reperfusion injury (I/R) and direct effects on cardiomyocyte function. Effects of recombinant dimethylarginine dimethylaminohydrolase (rDDAH)-1 on I/R injury were determined using isolated mouse heart preparation. Respiration capacity and mitochondrial reactive oxygen species (ROS) generation were determined on mouse cardiomyocytes. Our results show that lowering ADMA by rDDAH-1 treatment resulted in improved recovery of cardiac function and reduction in myocardial infarct size in mouse heart response to I/R injury (control 22.24 ±4.60% versus rDDAH-1 15.90 ±4.23%, P < 0.01). In mouse cardiomyocytes, rDDAH-1 treatment improved ADMA-induced dysregulation of respiration capacity and decreased mitochondrial ROS. Furthermore, in human induced pluripotent stem cell (hiPSC)-derived cardiomyocytes with impaired contractility under hypoxia and high ADMA, rDDAH-1 treatment improved recovery and beating frequency (P < 0.05). rDDAH-1 treatment selectively modified I/R-induced myocardial cytokine expression, resulting in reduction in proinflammatory cytokine IL-17A (P < 0.001) and increased expression of anti-inflammatory cytokines IL-10 and IL-13 (P < 0.01). Further in vitro studies showed that IL-17A was the predominant and common cytokine modulated by ADMA-DDAH pathway in heart, cardiomyocytes, and endothelial cells. These studies show that lowering ADMA by pharmacological treatment with rDDAH-1 reduced I/R injury, improved cardiac function, and ameliorated cardiomyocyte bioenergetics and beating activity. These effects may be attributable to ADMA lowering in cardiomyocytes and preservation of cardiomyocyte mitochondrial function. SIGNIFICANCE STATEMENT: The pathological role of asymmetric dimethyl arginine (ADMA) has been demonstrated by its association with cardiovascular disease and mortality. Currently, pharmacological drugs to specifically lower ADMA are not available. The present study provides the first evidence that lowering of ADMA by recombinant recombinant dimethylarginine dimethylaminohydrolase (rDDAH)-1 improved postischemic cardiac function and cardiomyocyte bioenergetics and beating activity. Our studies suggest that lowering of ADMA by pharmacologic treatment offers opportunity to develop new therapies for the treatment of cardiovascular and renal disease.

Protective Effect of Nebivolol against Oxidative Stress Induced by Aristolochic Acids in Endothelial Cells

Aristolochic acids (AAs) are powerful nephrotoxins that cause severe tubulointerstitial fibrosis. The biopsy-proven peritubular capillary rarefaction may worsen the progression of renal lesions via tissue hypoxia. As we previously observed the overproduction of reactive oxygen species (ROS) by cultured endothelial cells exposed to AA, we here investigated in vitro AA-induced metabolic changes by 1H-NMR spectroscopy on intracellular medium and cell extracts. We also tested the effects of nebivolol (NEB), a β-blocker agent exhibiting antioxidant properties. After 24 h of AA exposure, significantly reduced cell viability and intracellular ROS overproduction were observed in EAhy926 cells; both effects were counteracted by NEB pretreatment. After 48 h of exposure to AA, the most prominent metabolite changes were significant decreases in arginine, glutamate, glutamine and glutathione levels, along with a significant increase in the aspartate, glycerophosphocholine and UDP-N-acetylglucosamine contents. NEB pretreatment slightly inhibited the changes in glutathione and glycerophosphocholine. In the supernatants from exposed cells, a decrease in lactate and glutamate levels, together with an increase in glucose concentration, was found. The AA-induced reduction in glutamate was significantly inhibited by NEB. These findings confirm the involvement of oxidative stress in AA toxicity for endothelial cells and the potential benefit of NEB in preventing endothelial injury.

The role of oxidative stress markers in Indonesian chronic kidney disease patients: a cross sectional study

Background: Several aspects of chronic kidney disease (CKD) such as the incidence rate and mortality rate are concerning. Oxidative stress contributes to progression and mortality in patients with CKD; however, a specific correlation between several markers of oxidative stress and the estimated glomerular filtration rate (eGFR) and albumin-creatinine ratio (ACR) in the Indonesian population has not been sufficiently described yet. Methods: This study was an analytic observational study with a sample of 56 patients with CKD in Universitas Airlangga Hospital, Surabaya, Indonesia, from December 2019 – March 2020. The markers for oxidative stress investigated were urinary 8-hydroxy-2 deoxyguanosine (8-OHdG), serum symmetric dimethylarginine (SDMA) and asymmetric dimethylarginine (ADMA). The correlations between each variable of oxidative stress and CKD were analyzed using Pearson analysis. Results: There was a positive correlation between 8-OHdG and eGFR (p=0.00, r=0.51); however, there was a negative correlation between 8-OHdG and ACR (p=0.025, r=-0.30). SDMA and eGFR showed a negative correlation (p=0.00, r=-0.648), while SDMA and ACR showed a positive correlation (p=0.03, r=0.349). ADMA showed a negative correlation with eGFR (p=0.00, r=-0.476). There were significantly decreased 8-OHdG but increased ADMA and SDMA as the CKD stage progressed (p=0.001, p=0.00, and p = 0.00, respectively). Higher urine 8-OHdG was detected in patients without history of hemodialysis, whereas ADMA and SDMA showed higher value in patients with hemodialysis (p=0.00, p=0.00, and p=0.004, respectively), patients with history of diabetes mellitus (DM) had higher mean 8-OHdG (p 0.000) yet lower serum ADMA and SDMA (p=0.004 and p=0.003, respectively). Conclusions: In patients with CKD in Indonesia, the markers for oxidative stress 8-OHdG, SDMA, and ADMA are correlated with eGFR and ACR levels. There were also significant difference in 8-OHdG, SDMA, and ADMA levels among CKD stages, between dialysis vs non dialysis, and DM vs non DM patients.

Nonatherosclerotic Vascular Abnormalities Associated with Chronic Kidney Disease

Nonatherosclerotic vascular diseases are manifested by endothelial dysfunction, hypertension, vascular calcification, coronary microvascular dysfunction, and calciphylaxis. Unfortunately, there are no definitive treatments for many of these disorders other than hypertension. In addition, although hypertension is more difficult to treat in the chronic kidney disease population, it is necessary to try and target a blood pressure of less than 130/80 mm Hg through the use of aggressive angiotensin-converting enzyme inhibitors/angiotensin receptor blockers, diuretics, and other antihypertensive medications. New therapies are being actively investigated in an attempt to treat nonatherosclerotic vascular diseases in the chronic kidney disease population.

Maternal resveratrol therapy protected adult rat offspring against hypertension programmed by combined exposures to asymmetric dimethylarginine and trimethylamine-N-oxide

Resveratrol, a phytochemical, has shown antioxidant properties and potential benefits in hypertension. Asymmetric dimethylarginine (ADMA)-related nitric oxide deficiency and gut microbiota-derived metabolite trimethylamine-N-oxide (TMAO) have been linked to hypertension. We aimed to test whether maternal resveratrol therapy would protect adult offspring against hypertension programmed by prenatal exposure to ADMA and TMAO. Pregnant Sprague-Dawley rats received ADMA 10 mg/kg/day (A), TMAO 0.65 mg/hr (T), ADMA+TMAO (AT), or vesicle (CV). One group of ADMA+TMAO-exposed rats received 50 mg/L of resveratrol in drinking water during pregnancy and lactation periods (ATR). Male offspring (n = 8/group) were assigned to five groups: CV, A, T, AT, and ATR. Rats were killed at 12 weeks of age. ADMA exposure caused the elevation of blood pressure in 12-week-old male offspring, which was exacerbated by TMAO exposure. Treatment with resveratrol rescued hypertension programmed by combined ADMA and TMAO exposure. This was accompanied by alterations in the compositions of gut microbiota and increased fecal butyrate levels. Both the abundance of the butyrate-producing genera Lachnospiraceae and Ruminococcaceae were augmented by resveratrol. Meanwhile, resveratrol therapy significantly increased the abundance of the Cyanobiaceae and Erysipelotrichaceae families. Moreover, the protective effects of resveratrol were related to the mediation of the renin-angiotensin system . Our data provide new insights into the protective mechanisms of resveratrol against hypertension programmed by ADMA and TMAO, including regulation of gut microbiota and their metabolites, the renin-angiotensin system, and nitric oxide pathway. Resveratrol might be a potential reprogramming strategy to protect against the hypertension of developmental origins.

Uremic Toxins in the Progression of Chronic Kidney Disease and Cardiovascular Disease: Mechanisms and Therapeutic Targets

Chronic kidney disease (CKD) is a progressive loss of renal function. The gradual decline in kidney function leads to an accumulation of toxins normally cleared by the kidneys, resulting in uremia. Uremic toxins are classified into three categories: free water-soluble low-molecular-weight solutes, protein-bound solutes, and middle molecules. CKD patients have increased risk of developing cardiovascular disease (CVD), due to an assortment of CKD-specific risk factors. The accumulation of uremic toxins in the circulation and in tissues is associated with the progression of CKD and its co-morbidities, including CVD. Although numerous uremic toxins have been identified to date and many of them are believed to play a role in the progression of CKD and CVD, very few toxins have been extensively studied. The pathophysiological mechanisms of uremic toxins must be investigated further for a better understanding of their roles in disease progression and to develop therapeutic interventions against uremic toxicity. This review discusses the renal and cardiovascular toxicity of uremic toxins indoxyl sulfate, p-cresyl sulfate, hippuric acid, TMAO, ADMA, TNF-α, and IL-6. A focus is also placed on potential therapeutic targets against uremic toxicity.

Specific Lowering of Asymmetric Dimethylarginine by Pharmacological Dimethylarginine Dimethylaminohydrolase Improves Endothelial Function, Reduces Blood Pressure and Ischemia-Reperfusion Injury

Multiple clinical and preclinical studies have demonstrated that plasma levels of asymmetric dimethylarginine (ADMA) are strongly associated with hypertension, diabetes, and cardiovascular and renal disease. Genetic studies in rodents have provided evidence that ADMA metabolizing dimethylarginine dimethylaminohydrolase (DDAH)-1 plays a role in hypertension and cardiovascular disease. However, it remains to be established whether ADMA is a bystander, biomarker, or sufficient contributor to the pathogenesis of hypertension and cardiovascular and renal disease. The goal of the present investigation was to develop a pharmacological molecule to specifically lower ADMA and determine the physiologic consequences of ADMA lowering in animal models. Further, we sought to determine whether ADMA lowering will produce therapeutic benefits in vascular disease in which high ADMA levels are produced. A novel long-acting recombinant DDAH (M-DDAH) was produced by post-translational modification, which effectively lowered ADMA in vitro and in vivo. Treatment with M-DDAH improved endothelial function as measured by increase in cGMP and in vitro angiogenesis. In a rat model of hypertension, M-DDAH significantly reduced blood pressure (vehicle: 187 ± 19 mm Hg vs. M-DDAH: 157 ± 23 mm Hg; P < 0.05). Similarly, in a rat model of ischemia-reperfusion injury, M-DDAH significantly improved renal function as measured by reduction in serum creatinine (vehicle: 3.14 ± 0.74 mg/dl vs. M-DDAH: 1.1 ± 0.75 mg/dl; P < 0.01), inflammation, and injured tubules (vehicle: 73.1 ± 11.1% vs. M-DDAH: 22.1 ± 18.4%; P < 0.001). These pharmacological studies have provided direct evidence for a pathologic role of ADMA and the therapeutic benefits of ADMA lowering in preclinical models of endothelial dysfunction, hypertension, and ischemia-reperfusion injury. SIGNIFICANCE STATEMENT: High levels of ADMA occur in patients with cardiovascular and renal disease. A novel modified dimethylarginine dimethylaminohydrolase by PEGylation effectively lowers ADMA, improves endothelial function, reduces blood pressure and protects from ischemia-reperfusion renal injury.

Asymmetric dimethylarginine (ADMA) accelerates renal cell fibrosis under high glucose condition through NOX4/ROS/ERK signaling pathway

We previously reported that the circulatory level of Asymmetric dimethylarginine (ADMA), an endogenous competitive inhibitor of nitric oxide synthase, was increased in diabetic kidney disease patients. However, the mechanism and the role of ADMA in diabetic kidney injury remain unclear. Hence, our principal aim is to investigate the causal role of ADMA in the progression of renal cell fibrosis under high glucose (HG) treatment and to delineate its signaling alterations in kidney cell injury. High Glucose/ADMA significantly increased fibrotic events including cell migration, invasion and proliferation along with fibrotic markers in the renal cells; whereas ADMA inhibition reversed the renal cell fibrosis. To delineate the central role of ADMA induced fibrotic signaling pathway and its downstream signaling, we analysed the expression levels of fibrotic markers, NOX4, ROS and ERK activity by using specific inhibitors and genetic manipulation techniques. ADMA stimulated the ROS generation along with a significant increase in NOX4 and ERK activity. Further, we observed that ADMA activated NOX-4 and ERK are involved in the extracellular matrix proteins accumulation. Also, we observed that ADMA induced ERK1/2 phosphorylation was decreased after NOX4 silencing. Our study mechanistically demonstrates that ADMA is involved in the progression of kidney cell injury under high glucose condition by targeting coordinated complex mechanisms involving the NOX4- ROS-ERK pathway.

Renal asymmetric dimethylarginine inhibits fibrosis

Chronic kidney disease (CKD) is a worldwide public health problem that is caused by repeated injuries to the glomerulus or renal tubules. Renal fibrosis commonly accompanies CKD, and it is histologically characterized by excessive deposition of extracellular matrix proteins, such as fibronectin and collagen I, in interstitial areas. Indirect in vivo experimental data suggest that renal asymmetric dimethylarginine (ADMA) exerts antifibrotic activity in CKD. In this study, we aimed to demonstrate that renal ADMA has a direct effect on fibrosis in vivo. Normal saline, ADMA, nonsense control siRNA, Ddah1 siRNA or Ddah2 siRNA was administered into the kidney through the left ureter in a mouse model of unilateral ureteral obstruction (UUO). UUO kidneys were harvested at day 1 or 7. Western blotting was performed to assess the expression of ADMA, DDAH1 and DDAH2 and the expression of fibrotic markers, such as fibronectin, collagen I, α-smooth muscle actin, phosphorylation of Smad3 and connective tissue growth factor. Masson's trichrome staining was used to further evaluate renal fibrosis. We observed that intrarenal administration of ADMA increased the renal accumulation of ADMA and attenuated renal fibrosis at days 1 and 7. Knockdown of Ddah1 or Ddah2 increased the amount of ADMA in UUO kidneys and inhibited the expression of fibrotic proteins at days 1 and 7, which was further confirmed by Masson's staining. Thus, our in vivo data suggest that renal ADMA exerts direct antifibrotic effects in a mouse model of UUO.

Hypoxia and Endothelial Dysfunction in Autosomal-Dominant Polycystic Kidney Disease

Autosomal-dominant polycystic kidney disease (ADPKD) is the most prevalent inherited kidney disease, characterized by growth of bilateral renal cysts, hypertension, and multiple extrarenal complications that eventually can lead to renal failure. It is caused by mutations in PKD1 or PKD2 genes encoding the proteins polycystin-1 and polycystin-2, respectively. Over the past few years, studies investigating the role of primary cilia and polycystins, present not only on the surface of renal tubular cells but also on vascular endothelial cells, have advanced our understanding of the pathogenesis of ADPKD and have shown that mechanisms other than cyst formation also contribute to renal functional decline in this disease. Among them, increased oxidative stress, endothelial dysfunction, and hypoxia may play central roles because they occur early in the disease process and precede the onset of hypertension and renal functional decline. Endothelial dysfunction is linked to higher asymmetric dimethylarginine levels and reduced nitric oxide bioavailability, which would cause regional vasoconstriction and impaired renal blood flow. The resulting hypoxia would increase the levels of hypoxia-inducible-transcription factor 1α and other angiogenetic factors, which, in turn, may drive cyst growth. In this review, we summarize the existing evidence for roles of endothelial dysfunction, oxidative stress, and hypoxia in the pathogenesis of ADPKD.

Urinary metabolites associate with the rate of kidney function decline in patients with autosomal dominant polycystic kidney disease

Background

The variable course of autosomal dominant polycystic kidney disease (ADPKD), and the advent of renoprotective treatment require early risk stratification. We applied urinary metabolomics to explore differences associated with estimated glomerular filtration rate (eGFR; CKD-EPI equation) and future eGFR decline.

Methods

Targeted, quantitative metabolic profiling (¹H NMR-spectroscopy) was performed on baseline spot urine samples obtained from 501 patients with ADPKD. The discovery cohort consisted of 338 patients (56% female, median values for age 46 [IQR 38 to 52] years, eGFR 62 [IQR 45 to 85] ml/min/1.73m², follow-up time 2.5 [range 1 to 3] years, and annual eGFR slope –3.3 [IQR –5.3 to –1.3] ml/min/1.73m²/year). An independent cohort (n = 163) was used for validation. Multivariate modelling and linear regression were used to analyze the associations between urinary metabolites and eGFR, and eGFR decline over time.

Results

Twenty-nine known urinary metabolites were quantified from the spectra using a semi-automatic quantification routine. The model optimization routine resulted in four metabolites that most strongly associated with actual eGFR in the discovery cohort (F = 128.9, P = 7×10⁻⁵⁴, R² = 0.724). A model using the ratio of two other metabolites, urinary alanine/citrate, showed the best association with future annual change in eGFR (F = 51.07, P = 7.26×10⁻¹², R² = 0.150). This association remained significant after adjustment for clinical risk markers including height-adjusted total kidney volume (htTKV). Results were confirmed in the validation cohort.

Conclusions

Quantitative NMR profiling identified urinary metabolic markers that associated with actual eGFR and future rate of eGFR decline. The urinary alanine/citrate ratio showed additional value beyond conventional risk markers.

Asymmetric (ADMA) and Symmetric (SDMA) Dimethylarginines in Chronic Kidney Disease: A Clinical Approach

Asymmetric dimethylarginine (ADMA) and its enantiomer, Symmetric dimethylarginine (SDMA), are naturally occurring amino acids that were first isolated and characterized in human urine in 1970. ADMA is the most potent endogenous inhibitor of nitric oxide synthase (NOS), with higher levels in patients with end-stage renal disease (ESRD). ADMA has shown to be a significant predictor of cardiovascular outcome and mortality among dialysis patients. On the other hand, although initially SDMA was thought to be an innocuous molecule, we now know that it is an outstanding marker of renal function both in human and in animal models, with ESRD patients on dialysis showing the highest SDMA levels. Today, we know that ADMA and SDMA are not only uremic toxins but also independent risk markers for mortality and cardiovascular disease (CVD). In this review, we summarize the role of both ADMA and SDMA in chronic kidney disease along with other cardiovascular risk factors.

An update of urine and blood metabolomics in chronic kidney disease

Chronic kidney disease is considered as a serious obstacle in global health, with increasing incidence and prevalence. In spite of numerous attempts by using recent omics technologies, specially metabolomics, for understanding pathophysiology, molecular mechanism and identification reliable consensus biomarkers for diagnosis and prognosis of this complex disease, the current biomarkers are still insensitive and many questions about its pathomechanism are still to be unanswered. This review is focused on recent findings about urine and serum/plasma metabolite biomarkers and changes in the pathways that occurs in the disease conditions. The urine and blood metabolome content in the normal and disease state is investigated based on the current metabolomics studies and well known metabolite candidate biomarkers for chronic kidney disease are discussed.

Asymmetric dimethylarginine: An crucial regulator in tissue fibrosis

Fibrosis is a reparative process with very few therapeutic options to prevent its progression to organ dysfunction. Chronic fibrotic diseases contribute to an estimated 45% of all death in the industrialized world. Asymmetric dimethylarginine (ADMA), an endothelial nitric oxide synthase inhibitor, plays a crucial role in the pathogenesis of various cardiovascular diseases associated with endothelial dysfunction. Recent reports have focused on ADMA in the pathogenesis of tissue fibrosis. This review discusses the current knowledge about ADMA biology, its association with risk factors of established fibrotic diseases and the potential pathophysiological mechanisms implicating ADMA in the process of tissue fibrosis.

Biopolymer-delivered vascular endothelial growth factor improves renal outcomes following revascularization

Renal angioplasty and stenting (PTRAs) resolves renal artery stenosis, but inconsistently improves renal function, possibly due to persistent parenchymal damage. We developed a bioengineered fusion of a drug delivery vector (elastin-like polypeptide, ELP) with vascular endothelial growth factor (VEGF), and showed its therapeutic efficacy. We tested the hypothesis that combined ELP-VEGF therapy with PTRAs improves renal recovery more efficiently than PTRAs alone, by protecting the stenotic renal parenchyma. Unilateral renovascular disease (RVD) was induced by renal artery stenosis in 14 pigs. Six weeks later, stenotic kidney blood flow (RBF) and glomerular filtration rate (GFR) were quantified in vivo using multidetector CT. Blood and urine were collected during in vivo studies. All pigs underwent PTRAs and then were randomized into single intrarenal ELP-VEGF administration or placebo (n = 7 each) groups. Pigs were observed for four additional weeks, in vivo CT studies were repeated, and then pigs were euthanized for ex vivo studies to quantify renal microvascular (MV) density, angiogenic factor expression, and morphometric analysis. Renal hemodynamics were similarly blunted in all RVD pigs. PTRAs resolved stenosis but modestly improved RBF and GFR. However, combined PTRAs+ ELP-VEGF improved RBF, GFR, regional perfusion, plasma creatinine, asymmetric dimethlyarginine (ADMA), and albuminuria compared with PTRAs alone, accompanied by improved angiogenic signaling, MV density, and renal fibrosis. Greater improvement of renal function via coadjuvant ELP-VEGF therapy may be driven by enhanced MV proliferation and repair, which ameliorates MV rarefaction and fibrogenic activity that PTRAs alone cannot offset. Thus, our study supports a novel strategy to boost renal recovery in RVD after PTRAs.

Reduced asymmetric dimethylarginine accumulation through inhibition of the type I protein arginine methyltransferases promotes renal fibrosis in obstructed kidneys

The role of asymmetric dimethylarginine (ADMA) in chronic kidney disease (CKD) is unclear. Through inhibition of type I protein arginine methyltransferases (PRMTs), a novel strategy, we aimed to determine the effect of ADMA on renal fibrosis and explore its underlying working mechanisms. After sham or unilateral ureter ligation (UUO) operation, 20-25 g male c57 mice were treated with vehicle or PT1001B, an inhibitor of type I PRMTs, for 13 d. Moreover, human kidney 2 (HK2) and normal rat kidney 49F (NRK-49F) cells were treated with various concentrations of PT1001B or ADMA in the presence of 2.5 ng/ml TGF-β. We found that treatment with PT1001B increased the deposition of extracellular matrix proteins, the expression of α smooth muscle actin, and connective tissue growth factor in UUO-induced fibrotic kidneys, which is correlated with reduced expression of PRMT1, reduced the production of ADMA, and increased expression of uromodulin. In TGF-β-stimulated HK2 and NRK-49F cells, PT1001B dose-dependently inhibited ADMA production, increased NO concentrations, and enhanced the expression of profibrotic proteins. Exogenous addition of ADMA inhibited the expression of profibrotic proteins dose-dependently and attenuated the profibrotic effect of PT1001B. Moreover, ADMA reduced the NO concentration in PT1001B-treated HK2 cells. Finally, we conclude that ADMA has an antifibrotic effect in obstructed kidneys, and future application of type I PRMT inhibitor should be done cautiously for patients with CKD.-Wu, M., Lin, P., Li, L., Chen, D., Yang, X., Xu, L., Zhou, B., Wang, C., Zhang, Y., Luo, C., Ye, C. Reduced asymmetric dimethylarginine accumulation through inhibition of the type I protein arginine methyltransferases promotes renal fibrosis in obstructed kidneys.

Symmetric dimethylarginine is a stronger predictor of mortality risk than asymmetric dimethylarginine among older people with kidney disease

BACKGROUND

Circulating asymmetric dimethylarginine and symmetric dimethylarginine are increased in patients with kidney disease. Symmetric dimethylarginine is considered a good marker of glomerular filtration rate, while asymmetric dimethylarginine is a marker of cardiovascular risk. However, a link between symmetric dimethylarginine and all-cause mortality has been reported. In the present study, we evaluated both dimethylarginines as risk and glomerular filtration rate markers in a cohort of elderly white individuals, both with and without chronic kidney disease.

METHODS

Glomerular filtration rate was measured in 394 individuals aged >74 years using an iohexol clearance method. Plasma asymmetric dimethylarginine, symmetric dimethylarginine and iohexol were measured simultaneously using isotope dilution tandem mass spectrometry.

RESULTS

Plasma asymmetric dimethylarginine concentrations were increased ( P < 0.01) in people with glomerular filtration rate <60 mL/min/1.73 m² compared with those with glomerular filtration rate ≥60 mL/min/1.73 m², but did not differ ( P > 0.05) between those with glomerular filtration rate 30-59 mL/min/1.73 m² and <30 mL/min/1.73 m². Plasma symmetric dimethylarginine increased consistently across declining glomerular filtration rate categories ( P < 0.0001). Glomerular filtration rate had an independent effect on plasma asymmetric dimethylarginine concentration, while glomerular filtration rate, gender, body mass index and haemoglobin had independent effects on plasma symmetric dimethylarginine concentration. Participants were followed up for a median of 33 months. There were 65 deaths. High plasma asymmetric dimethylarginine ( P = 0.0412) and symmetric dimethylarginine ( P < 0.0001) concentrations were independently associated with reduced survival.

CONCLUSIONS

Among elderly white individuals with a range of kidney function, symmetric dimethylarginine was a better marker of glomerular filtration rate and a stronger predictor of outcome than asymmetric dimethylarginine. Future studies should further evaluate the role of symmetric dimethylarginine as a marker of outcome and assess its potential value as a marker of glomerular filtration rate.

Relationship between Serum Asymmetric Dimethylarginine Level and Microvascular Complications in Diabetes Mellitus: A Meta-Analysis

Objective

The purpose of the meta-analysis was to evaluate the relationship between serum asymmetric dimethylarginine (ADMA) level and microvascular complications in diabetes mellitus (DM) including diabetic retinopathy (DR), diabetic neuropathy (DN), and diabetic nephropathy.

Methods

Studies were comprehensively identified by searching Web of Science, Embase, and PubMed databases up to August 30, 2018. The meta-analysis was carried out to compare the difference of serum ADMA concentrations of DR, DN, and diabetic nephropathy patients with healthy controls. The Newcastle-Ottawa Scale and the Agency for Healthcare Research and Quality were applied to assess the methodological quality. Chi-squared Q test and I² statistics were applied to evaluate statistical heterogeneity. Subgroup analyses were conducted and publication bias was assessed by Egger's test.

Result

Ten studies were finally entered in the meta-analysis. Statistically significant heterogeneity was observed across these studies (I ² = 77.0%, p < 0.001). Compared with DM without microvascular complications, circulating level of ADMA was significantly higher in DM with microvascular complications (all p < 0.05). Sensitivity analysis suggested that the results of this meta-analysis were shown to be stable. There was no significant publication bias (P=0.823).

Conclusion

Elevated ADMA levels correlate with diabetic microangiopathies such as DR and diabetic nephropathy. ADMA may play an important role in the pathobiology of microvascular complications of diabetes.

Clinical and metabolomic risk factors associated with rapid renal function decline in sickle cell disease

Sickle cell disease (SCD) nephropathy and lower estimated glomerular filtration rate (eGFR) are risk factors for early mortality. Furthermore, rate of eGFR decline predicts progression to end-stage renal disease in many clinical settings. However, factors predicting renal function decline in SCD are poorly documented. Using clinical, laboratory, genetic, and metabolomic data, we evaluated predictors of renal function decline in a longitudinal cohort of 288 adults (mean age 33.0 years). In 193 subjects with 5-year follow-up data, mean rate of eGFR decline was 2.35 mL/min/1.73 m² /year, nearly twice that of African American adults overall. Hyperfiltration was prevalent at baseline (61.1%), and 36.8% of subjects experienced rapid eGFR decline (≥3 mL/min/1.73 m² /year). Severe Hb genotype; proteinuria; higher platelet and reticulocyte counts, and systolic BP; and lower Hb level and BMI were associated with rapid decline. A risk scoring system was created using these 7 variables and was highly predictive of rapid eGFR decline, with odds of rapid decline increasing 1.635-fold for every point increment (P < 0.0001). Rapid eGFR decline was also associated with higher organ system severity score and peak creatinine. Additionally, two metabolites (asymmetric dimethylarginine and quinolinic acid) were associated with rapid decline. Further investigation into longitudinal SCD nephropathy (SCDN) trajectory, early markers of SCDN, and tools for risk stratification should inform interventional studies targeted to slowing GFR decline and improving SCD outcomes.

The Renal Safety of L-Carnitine, L-Arginine, and Glutamine in Athletes and Bodybuilders

One of the major concerns about taking amino acid supplements is their potential adverse effects on the kidney as a major organ involved in the metabolism and excretion of exogenous substances. The aim of this study is to review available data about renal safety of the most prominent amino acid supplements including L-arginine, glutamine and also L-carnitine as well as creatine (as amino acid derivatives) in athletes and bodybuilders. The literature was searched by keywords such as "L-carnitine", "L-arginine", "glutamine", and "kidney injury" in databases such as Scopus, Medline, Embase, and ISI Web of Knowledge. Articles published from 1950 to December 2017 were included. Among 3171, 5740, and 1608 records after primary search in the relevant databases, 8, 7, and 5 studies have been finally included, respectively, for L-carnitine, L-arginine, and glutamine in this review. Arginine appears to have both beneficial and detrimental effects on kidney function. However, adverse effects are unlikely to occur with the routine doses (from 3 to >100 g/day). The risks and benefits of L-carnitine on the athletes' and bodybuilders' kidney have not been evaluated yet. However, L-carnitine up to 6000 mg/day is generally considered to be a safe supplement at least in healthy adults. Both short-term (20-30 g within a few hours) and long-term (0.1 g/kg four times daily for 2 weeks) glutamine supplementation in healthy athletes were associated with no significant adverse effects, but it can cause glomerulosclerosis and serum creatinine level elevation in the setting of diabetic nephropathy. Creatine supplementation (ranged from 5 to 30 g/day) also appears to have no detrimental effects on kidney function of individuals without underlying renal diseases. More clinical data are warranted to determine the optimal daily dose and intake duration of common supplemental amino acids associated with the lowest renal adverse effects in sportsmen and sports women.

Kidney Mass Reduction Leads to l-Arginine Metabolism-Dependent Blood Pressure Increase in Mice

Background

Uninephrectomy (UNX) is performed for various reasons, including kidney cancer or donation. Kidneys being the main site of l‐arginine production in the body, we tested whether UNX mediated kidney mass reduction impacts l‐arginine metabolism and thereby nitric oxide production and blood pressure regulation in mice.

Methods and Results

In a first series of experiments, we observed a significant increase in arterial blood pressure 8 days post‐UNX in female and not in male mice. Further experimental series were performed in female mice, and the blood pressure increase was confirmed by telemetry. l‐citrulline, that is used in the kidney to produce l‐arginine, was elevated post‐UNX as was also asymmetric dimethylarginine, an inhibitor of nitric oxide synthase that competes with l‐arginine and is a marker for renal failure. Interestingly, the UNX‐induced blood pressure increase was prevented by supplementation of the diet with 5% of the l‐arginine precursor, l‐citrulline. Because l‐arginine is metabolized in the kidney and other peripheral tissues by arginase‐2, we tested whether the lack of this metabolic pathway also compensates for decreased l‐arginine production in the kidney and/or for local nitric oxide synthase inhibition and consecutive blood pressure increase. Indeed, upon uninephrectomy, arginase‐2 knockout mice (Arg‐2^−/−) neither displayed an increase in asymmetric dimethylarginine and l‐citrulline plasma levels nor a significant increase in blood pressure.

Conclusions

UNX leads to a small increase in blood pressure that is prevented by l‐citrulline supplementation or arginase deficiency, 2 measures that appear to compensate for the impact of kidney mass reduction on l‐arginine metabolism.

Dimethylarginine Dimethylaminohydrolase 1 Deficiency Induces the Epithelial to Mesenchymal Transition in Renal Proximal Tubular Epithelial Cells and Exacerbates Kidney Damage in Aged and Diabetic Mice

AIMS

Asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthase, is mainly degraded by dimethylarginine dimethylaminohydrolase (DDAH). Emerging evidence suggests that plasma ADMA accumulation and DDAH1 activity/expression reduction are linked to chronic kidney disease (CKD) pathology, but the mechanisms remain largely unknown. Here, we examined the role of ADMA/DDAH1 in the epithelial-mesenchymal transition (EMT) of tubular epithelial cells (TECs), an important mechanism for the pathogenesis of renal fibrosis.

RESULTS

In HK-2 cells, DDAH1 expression was reduced by aldosterone treatment, and overexpression of DDAH1 significantly attenuated aldosterone-induced EMT. More interestingly, DDAH1 deficiency resulted in EMT-related changes in primary TECs via increasing oxidative stress, impairing adenosine monophosphate-activated kinase (AMPK) signaling, and downregulating of peroxiredoxin 5 (Prdx5). However, those effects could not be mimicked by increasing the ADMA concentration. After regular feeding for 24 months or inducing type 2 diabetes, Ddah1^-/- mice had higher serum creatinine levels than wild-type (WT) mice. In the kidneys of the aged or diabetic mice, loss of DDAH1 resulted in more interstitial fibrosis, more collagen deposition, and greater induction of EMT-related changes and oxidative stress than in the WT kidneys. Innovation and Conclusion: Our results provide the first direct evidence that the DDAH1 has a marked effect on kidney fibrosis and oxidative stress induced by aging or diabetes. Our findings suggest that strategies to increase DDAH1 activity in TECs may provide a novel approach to attenuate CKD development. Antioxid. Redox Signal. 27, 1347-1360.

Role of DDAH/ADMA pathway in TGF-β1-mediated activation of hepatic stellate cells

Asymmetric dimethylarginine (ADMA) is catalyzed by the enzyme dimethylarginine dimethylaminohydrolase (DDAH) in humans, and the role for ADMA has been associated with hepatic fibrogenesis. Transforming growth factor‑β (TGF‑β) has been shown to mediate the myofibroblastic transformation of quiescent hepatic stellate cells (HSCs), a pivotal step in liver fibrogenesis. However, the underlying molecular mechanisms are not well understood. Accumulation of ADMA due to low activity of DDAH has been reported to be associated with liver damage and hepatic fibrosis. In this study, the role of the DDAH/ADMA pathway in the TGF‑β1‑induced HSC activation was assessed. Freshly harvested primary HSCs from rat liver were used in this study. It was demonstrated that TGF‑β1 treatment significantly suppressed the DDAH protein expression and activity, and increased levels of ADMA in the culture medium of rat primary HSCs. Notably, the TGF‑β1‑mediated effects on DDAH/ADMA were significantly abrogated by the p38 mitogen activated protein kinase specific inhibitor, SB203580. Furthermore, it was demonstrated that excessive ADMA led to an increase in the number of TGF‑β1‑positive HSCs and induced the expression of α‑smooth muscle actin and collagen type I in rat primary HSCs. In addition, rat primary HSCs exposed to excessive ADMA showed a significant increase in the expressions of α‑SMA and collagen type I. Finally, it was revealed that ADMA treatment promoted the proliferation of rat primary HSCs. In conclusion, the results obtained from the study suggest a potentially novel role for the ADMA/DDAH1 signaling pathway in TGF‑β1‑induced HSC activation, and along with the studies of others, suppression of the ADMA/DDAH1 pathway may be an alterative approach for the treatment of liver fibrosis.

Plasma biomarker discovery for early chronic kidney disease diagnosis based on chemometric approaches using LC-QTOF targeted metabolomics data

Chronic kidney disease (CKD) is a progressive pathological condition in which renal function deteriorates in time. The first diagnosis of CKD is often carried out in general care attention by general practitioners by means of serum creatinine (CNN) levels. However, it lacks sensitivity and thus, there is a need for new robust biomarkers to allow the detection of kidney damage particularly in early stages. Multivariate data analysis of plasma concentrations obtained from LC-QTOF targeted metabolomics method may reveal metabolites suspicious of being either up-regulated or down-regulated from urea cycle, arginine methylation and arginine-creatine metabolic pathways in CKD pediatrics and controls. The results show that citrulline (CIT), symmetric dimethylarginine (SDMA) and S-adenosylmethionine (SAM) are interesting biomarkers to support diagnosis by CNN: early CKD samples and controls were classified with an increase in classification accuracy of 18% when using these 4 metabolites compared to CNN alone. These metabolites together allow classification of the samples into a definite stage of the disease with an accuracy of 74%, being the 90% of the misclassifications one level above or below the CKD stage set by the nephrologists. Finally, sex-related, age-related and treatment-related effects were studied, to evaluate whether changes in metabolite concentration could be attributable to these factors, and to correct them in case a new equation is developed with these potential biomarkers for the diagnosis and monitoring of pediatric CKD.

Restored nitric oxide bioavailability reduces the severity of acute-to-chronic transition in a mouse model of aristolochic acid nephropathy

Aristolochic Acid (AA) nephropathy (AAN) is a progressive tubulointerstitial nephritis characterized by an early phase of acute kidney injury (AKI) leading to chronic kidney disease (CKD). The reduced nitric oxide (NO) bioavailability reported in AAN might contribute to renal function impairment and progression of the disease. We previously demonstrated that L-arginine (L-Arg) supplementation is protective in AA-induced AKI. Since the severity of AKI may be considered a strong predictor of progression to CKD, the present study aims to assess the potential benefit of L-Arg supplementation during the transition from the acute phase to the chronic phase of AAN. C57BL/6J male mice were randomly subjected to daily i.p. injections of vehicle or AA for 4 days. To determine whether renal AA-induced injuries were linked to reduced NO production, L-Arg was added to drinking water from 7 days before starting i.p. injections, until the end of the protocol. Mice were euthanized 5, 10 and 20 days after vehicle or AA administration. AA-treated mice displayed marked renal injury and reduced NO bioavailability, while histopathological features of AAN were reproduced, including interstitial cell infiltration and tubulointerstitial fibrosis. L-Arg treatment restored renal NO bioavailability and reduced the severity of AA-induced injury, inflammation and fibrosis. We concluded that reduced renal NO bioavailability contributes to the processes underlying AAN. Furthermore, L-Arg shows nephroprotective effects by decreasing the severity of acute-to-chronic transition in experimental AAN and might represent a potential therapeutic tool in the future.

Kidney dysfunction in patients with pulmonary arterial hypertension

Pulmonary arterial hypertension (PH) and chronic kidney disease (CKD) both profoundly impact patient outcomes, whether as primary disease states or as co-morbid conditions. PH is a common co-morbidity in CKD and vice versa. A growing body of literature describes the epidemiology of PH secondary to chronic kidney disease and end-stage renal disease (ESRD) (WHO group 5 PH). But, there are only limited data on the epidemiology of kidney disease in group 1 PH (pulmonary arterial hypertension [PAH]). The purpose of this review is to summarize the current data on epidemiology and discuss potential disease mechanisms and management implications of kidney dysfunction in PAH. Kidney dysfunction, determined by serum creatinine or estimated glomerular filtration rate, is a frequent co-morbidity in PAH and impaired kidney function is a strong and independent predictor of mortality. Potential mechanisms of PAH affecting the kidneys are increased venous congestion, decreased cardiac output, and neurohormonal activation. On a molecular level, increased TGF-β signaling and increased levels of circulating cytokines could have the potential to worsen kidney function. Nephrotoxicity does not seem to be a common side effect of PAH-targeted therapy. Treatment implications for kidney disease in PAH include glycemic control, lifestyle modification, and potentially Renin-Angiotensin-Aldosterone System (RAAS) blockade.

ADMA predicts major adverse renal events in patients with mild renal impairment and/or diabetes mellitus undergoing coronary angiography

Asymmetric dimethylarginine (ADMA) is a competitive inhibitor of the nitric oxide (NO)-synthase and a biomarker of endothelial dysfunction (ED). ED plays an important role in the pathogenesis of contrast-induced nephropathy (CIN). The aim of our study was to evaluate serum ADMA concentration as a biomarker of an acute renal damage during the follow-up of 90 days after contrast medium (CM) application.Blood samples were obtained from 330 consecutive patients with diabetes mellitus or mild renal impairment immediately before, 24 and 48 hours after the CM application for coronary angiography. The patients were followed for 90 days. The composite endpoints were major adverse renal events (MARE) defined as occurrence of death, initiation of dialysis, or a doubling of serum creatinine concentration.Overall, ADMA concentration in plasma increased after CM application, although, there was no differences between ADMA levels in patients with and without CIN. ADMA concentration 24 hours after the CM application was predictive for dialysis with a specificity of 0.889 and sensitivity of 0.653 at values higher than 0.71 μmol/L (area under the curve: 0.854, 95% confidential interval: 0.767-0.941, P < 0.001). This association remained significant in multivariate Cox regression models adjusted for relevant factors of long-term renal outcome. 24 hours after the CM application, ADMA concentration in plasma was predictive for MARE with a specificity of 0.833 and sensitivity of 0.636 at a value of more than 0.70 μmol/L (area under the curve: 0.750, 95% confidence interval: 0.602-0.897, P = 0.004). Multivariate logistic regression analysis confirmed that ADMA and anemia were significant predictors of MARE. Further analysis revealed that increased ADMA concentration in plasma was highly significant predictor of MARE in patients with CIN. Moreover, patients with CIN and MARE had the highest plasma ADMA levels 24 hours after CM exposure in our study cohort. The impact of ADMA on MARE was independent of such known CIN risk factors as anemia, pre-existing renal failure, pre-existing heart failure, and diabetes.ADMA concentration in plasma is a promising novel biomarker of major contrast-induced nephropathy-associated events 90 days after contrast media exposure.

Asymmetric Dimethylarginine and Its Relation As a Biomarker in Nephrologic Diseases

It is encouraging to observe that a search for publications on "asymmetric dimethylarginine (ADMA)" in PubMed, as updated on June 2016, yielded >2500 items, 24 years after a splendid paper published by Vallance et al in which the authors proposed that ADMA accumulation could be a cardiovascular risk factor in chronic kidney diseases. ADMA is the endogenous inhibitor of nitric oxide synthase and is related to endothelial dysfunction, which plays an important role in vascular damage elicited by various cardiometabolic risk factors. Although current knowledge suggests that ADMA has critical central roles in renal diseases, there are still unexplained details. The present article aims to provide a review on ADMA and its relation as a biomarker in nephrologic diseases. We aimed to systematize articles in which ADMA levels were assessed in order to clarify its role in many diseases and establish its reference values in different populations.

The Association of Helicobacter pylori Eradication with the Occurrences of Chronic Kidney Diseases in Patients with Peptic Ulcer Diseases

The association of Helicobacter pylori eradication with the occurrence of renal dysfunction in patients with peptic ulcer diseases is still unclear. This study aimed to clarify the relevance of H. pylori eradication to the occurrence of chronic kidney diseases in patients with peptic ulcer diseases. Data that were available from 2000–2011 were extracted from the National Health Insurance Research Database in Taiwan, and all patients with peptic ulcer diseases (n = 208 196) were screened for eligibility. We divided randomly selected patients into an H. pylori eradication cohort (cohort A, n = 3593) and matched them by age and sex to a without H. pylori eradication cohort (cohort B, n = 3593). Subgroup analysis was further performed for H. pylori eradication within ≤ 90 days of the diagnosis date (early eradication, n = 2837) and within 91–365 days (non-early eradication, n = 756). Cox proportional hazards regression analysis was used to estimate the association of H. pylori eradication with the risk of developing chronic kidney diseases and mortality. We observed that there were more patients suffering from chronic kidney disease in cohort B than in the early eradication subgroup of cohort A (8.49% vs. 6.70%, respectively, p = 0.0075); the mortality rate was also higher in cohort B (4.76% vs. 3.70%, respectively, p = 0.0376). Old age, pulmonary disease, connective tissue disorders, and diabetes were risk factors for chronic kidney diseases but early H. pylori eradication was a protective factor against chronic kidney diseases (hazard ratio: 0.68, 95% confidence interval: 0.52–0.88, p = 0.0030), and death (hazard ratio: 0.69, 95% confidence interval: 0.49–0.96, p = 0.0297). In conclusion, our findings have important implications suggesting that early H. pylori eradication is mandatory since it is associated with a protective role against the occurrence of chronic kidney diseases.

Serum nitric oxide is associated with the risk of chronic kidney disease in women: Tehran lipid and glucose study

Background and aim This study was conducted to investigate the association between serum nitric oxide metabolites (NOx) and the risk of chronic kidney disease (CKD). Methods We recruited 3462 and 2504 participants of the Tehran Lipid and Glucose Study (TLGS), for a cross-sectional and prospective analysis, respectively. Serum NOx concentrations were measured at baseline (2006-2008), and demographics, anthropometrics and biochemical variables were evaluated at baseline and again after 3 years (2009-2011). Estimated glomerular filtration rate (eGFR) and CKD were defined. Association between serum NOx and CKD in the cross-sectional phase and the predictability of NOx in CKD occurrence were assessed using multivariable logistic regression models with adjustment for confounders. Results Mean age of participants was 45.0 ± 15.9 years at baseline and 40.5% were male. The prevalence of CKD was 17.9% (13.4% in men, 21.0% in women) at baseline, at which point, marginally significant odds of CKD in the highest tertile of serum NOx in men (OR = 1.53, 95% CI = 0.96-2.45, p for trend = 0.047) and a significant odds of CKD in women (OR = 2.48, 95% CI = 1.76-3.49, p for trend = 0.001) were observed. After a 3-year follow-up, in women, risk of CKD was higher in the highest compared to the lowest NOx tertiles (OR = 1.86, 95% CI = 1.10-3.14, p for trend = 0.032) but no significant association was observed in men. Conclusion Serum NOx level was found to be an independent predictor of CKD in women; it could be a valuable surrogate for prediction of renal dysfunction in women and help to identify high-risk subjects.

Hemodynamic and biologic determinates of arteriovenous fistula outcomes in renal failure patients

The outcome of patients with end-stage renal disease on hemodialysis depends on a functioning vascular access. Although a variety of access options are available, the arteriovenous fistula remains the best vascular access. Unfortunately the success rate of mature fistula use remains poor. The creation of an arteriovenous fistula is followed by altered hemodynamic and biological changes that may result in neointimal hyperplasia and eventual venous stenosis. This review provides an overview of these changes and the needed research to provide a long lasting vascular access and hence improve outcomes for patients with end-stage renal disease.

Elevated Levels of Asymmetric Dimethylarginine (ADMA) in the Pericardial Fluid of Cardiac Patients Correlate with Cardiac Hypertrophy

Background

Pericardial fluid (PF) contains several biologically active substances, which may provide information regarding the cardiac conditions. Nitric oxide (NO) has been implicated in cardiac remodeling. We hypothesized that L-arginine (L-Arg) precursor of NO-synthase (NOS) and asymmetric dimethylarginine (ADMA), an inhibitor of NOS, are present in PF of cardiac patients and their altered levels may contribute to altered cardiac morphology.

Methods

L-Arg and ADMA concentrations in plasma and PF, and echocardiographic parameters of patients undergoing coronary artery bypass graft (CABG, n = 28) or valve replacement (VR, n = 25) were determined.

Results

We have found LV hypertrophy in 35.7% of CABG, and 80% of VR patients. In all groups, plasma and PF L-Arg levels were higher than that of ADMA. Plasma L-Arg level was higher in CABG than VR (75.7±4.6 μmol/L vs. 58.1±4.9 μmol/L, p = 0.011), whereas PF ADMA level was higher in VR than CABG (0.9±0.0 μmol/L vs. 0.7±0.0 μmol/L, p = 0.009). L-Arg/ADMA ratio was lower in the VR than CABG (VR_plasma: 76.1±6.6 vs. CABG_plasma: 125.4±10.7, p = 0.004; VR_PF: 81.7±4.8 vs. CABG_PF: 110.4±7.2, p = 0.009). There was a positive correlation between plasma L-Arg and ADMA in CABG (r = 0.539, p = 0.015); and plasma and PF L-Arg in CABG (r = 0.357, p = 0.031); and plasma and PF ADMA in VR (r = 0.529, p = 0.003); and PF L-Arg and ADMA in both CABG and VR (CABG: r = 0.468, p = 0.006; VR: r = 0.371, p = 0.034). The following echocardiographic parameters were higher in VR compared to CABG: interventricular septum (14.7±0.5 mm vs. 11.9±0.4 mm, p = 0.000); posterior wall thickness (12.6±0.3 mm vs. 11.5±0.2 mm, p = 0.000); left ventricular (LV) mass (318.6±23.5 g vs. 234.6±12.3 g, p = 0.007); right ventricular (RV) (33.9±0.9 cm² vs. 29.7±0.7 cm², p = 0.004); right atrial (18.6±1.0 cm² vs. 15.4±0.6 cm², p = 0.020); left atrial (19.8±1.0 cm² vs. 16.9±0.6 cm², p = 0.033) areas. There was a positive correlation between plasma ADMA and RV area (r = 0.453, p = 0.011); PF ADMA and end-diastolic (r = 0.434, p = 0.015) and systolic diameter of LV (r = 0.487, p = 0.007); and negative correlation between PF ADMA and LV ejection fraction (r = -0.445, p = 0.013) in VR.

Conclusion

We suggest that elevated levels of ADMA in the PF of patients indicate upregulated RAS and reduced bioavailability of NO, which can contribute to the development of cardiac hypertrophy and remodeling.

Plasma ADMA associates with all-cause mortality in renal transplant recipients

Asymmetric dimethylarginine (ADMA) is a key endogenous inhibitor of endothelial NO synthase that affects endothelial function, blood pressure and vascular remodeling. Increased plasma levels of ADMA are associated with worse outcome from cardiovascular disease. Due to endothelial dysfunction before and after kidney transplantation, renal transplant recipients (RTR) are at high risk for the alleged deleterious effects of ADMA. We investigated the associations of ADMA levels with all-cause mortality and graft failure in RTR. Plasma ADMA levels were determined in 686 stable outpatient RTR (57 % male, 53 ± 13 years), with a functioning graft for ≥1 year. Determinants of ADMA were evaluated with multivariate linear regression models. Associations between ADMA and mortality were assessed using multivariable Cox regression analyses. The strongest associations with plasma ADMA in the multivariable analyses were male gender, donor age, parathyroid hormone, NT-pro-BNP and use of calcium supplements. During a median follow-up of 3.1 [2.7–3.9] years, 79 (12 %) patients died and 45 (7 %) patients developed graft failure. ADMA was associated with increased all-cause mortality [HR 1.52 (95 % CI 1.26–1.83] per SD increase, P < 0.001], whereby associations remained upon adjustment for confounders. ADMA was associated with graft failure [HR 1.41 (1.08–1.83) per SD increase, P = 0.01]; however, upon addition of eGFR significance was lost. High levels of plasma ADMA are associated with increased mortality in RTR. Our findings connect disturbed NO metabolism with patient survival after kidney transplantation.