Dimethylarginine dimethylaminohydrolase prevents progression of renal dysfunction by inhibiting loss of peritubular capillaries and tubulointerstitial fibrosis in a rat model of chronic kidney disease

Antihypertensive treatment with hydrochlorothiazide-hydralazine combination aggravates medial vascular calcification in CKD rats with mineral bone disorder

Background

Arterial stiffness and medial vascular calcification, leading to isolated systolic blood pressure (BP), are major cardiovascular risk factors in patients with chronic kidney disease (CKD) and mineral bone disorders (MBD). The impact of BP on MBD-induced medial vascular calcification in CKD remains uncertain. We investigated whether BP reduction improves arterial stiffness and medial vascular calcification in a rat model of CKD-MBD.

Methods

CKD was induced in Wistar rats by subtotal nephrectomy. Then, MBD was generated by a Ca/P-rich diet with calcitriol supplementation to induce medial vascular calcification. Two antihypertensive treatments were evaluated: (1) the angiotensin AT1 receptor antagonist losartan, and (2) the combination of the thiazide diuretic hydrochlorothiazide and the direct vasodilator hydralazine (HCTZ/HY). After 5 weeks, mean BP (MBP), pulse pressure (PP), and pulse wave velocity (PWV) were determined. Vascular calcification was assessed in the thoracic aorta.

Results

While MBP was similar in CKD-MBD and control CKD rats, PP and PWV were increased in CKD-MBD rats. The heightened arterial stiffness in CKD-MBD rats was associated with diffused medial calcification along the thoracic aorta. Although both losartan and HCTZ/HY reduced MBP in CKD-MBD rats, losartan did not affect PP and PWV nor medial vascular calcification, whereas HCTZ/HY, unexpectedly, further increased arterial stiffness and medial vascular calcification.

Conclusion

In the rat model of CKD-MBD, antihypertensive treatment with losartan did not affect arterial stiffness or medial vascular calcification. However, HCTZ/HY treatment aggravated arterial stiffness and vascular calcification despite a similar reduction of MBP, suggesting a blood pressure-independent mechanism for vascular calcification.

Pro- and anti-fibrotic effects of vascular endothelial growth factor in chronic kidney diseases

Renal fibrosis is the inevitable common end-point of all progressive chronic kidney diseases. The underlying mechanisms of renal fibrosis are complex, and currently there is no effective therapy against renal fibrosis. Renal microvascular rarefaction contributes to the progression of renal fibrosis; however, an imbalance between proangiogenic and antiangiogenic factors leads to the loss of renal microvasculature. Vascular endothelial growth factor (VEGF) is the most important pro-angiogenic factor. Recent studies have unraveled the involvement of VEGF in the regulation of renal microvascular rarefaction and fibrosis via various mechanisms; however, it is not clear whether it has anti-fibrotic or pro-fibrotic effect. This paper reviews the available evidence pertaining to the function of VEGF in the fibrotic process and explores the associated underlying mechanisms. Our synthesis will help identify the future research priorities for developing specialized treatments for alleviating or preventing renal fibrosis. Abbreviation: VEGF: vascular endothelial growth factor; CKD: chronic kidney disease; ESKD: end-stage kidney disease; ER: endoplasmic reticulum; VEGFR: vascular endothelial growth factor receptor; AKI: acute kidney injury; EMT: epithelial-to-mesenchymal transition; HIF: hypoxia-inducible factor; α-SMA: α smooth muscle actin; UUO: unilateral ureteral obstruction; TGF-β: transforming growth factor-β; PMT: pericyte-myofibroblast transition; NO: nitric oxide; NOS: nitric oxide synthase; nNOS: neuronal nitric oxide synthase; iNOS: inducible nitric oxide synthase; eNOS: endothelial nitric oxide synthase; sGC: soluble guanylate cyclase; PKG: soluble guanylate cyclase dependent protein kinases; UP R: unfolded protein response

Toward Human Models of Cardiorenal Syndrome in vitro

Heart and kidney diseases cause high morbidity and mortality. Heart and kidneys have vital functions in the human body and, interestingly, reciprocally influence each other’s behavior: pathological changes in one organ can damage the other. Cardiorenal syndrome (CRS) is a group of disorders in which there is combined dysfunction of both heart and kidney, but its underlying biological mechanisms are not fully understood. This is because complex, multifactorial, and dynamic mechanisms are likely involved. Effective treatments are currently unavailable, but this may be resolved if more was known about how the disease develops and progresses. To date, CRS has actually only been modeled in mice and rats in vivo. Even though these models can capture cardiorenal interaction, they are difficult to manipulate and control. Moreover, interspecies differences may limit extrapolation to patients. The questions we address here are what would it take to model CRS in vitro and how far are we? There are already multiple independent in vitro (human) models of heart and kidney, but none have so far captured their dynamic organ-organ crosstalk. Advanced in vitro human models can provide an insight in disease mechanisms and offer a platform for therapy development. CRS represents an exemplary disease illustrating the need to develop more complex models to study organ-organ interaction in-a-dish. Human induced pluripotent stem cells in combination with microfluidic chips are one powerful tool with potential to recapitulate the characteristics of CRS in vitro. In this review, we provide an overview of the existing in vivo and in vitro models to study CRS, their limitations and new perspectives on how heart-kidney physiological and pathological interaction could be investigated in vitro for future applications.

Comparison of the Surgical Resection and Infarct 5/6 Nephrectomy Rat Models of Chronic Kidney Disease

The 5/6 nephrectomy rat remnant kidney model is commonly employed to study chronic kidney disease (CKD). This model requires removal of one whole kidney and two-thirds of the other. The two most common ways of producing the remnant kidney are surgical resection of poles, known as the polectomy (Pol) model, or ligation of upper and lower renal arterial branches, resulting in pole infarction (Inf). These models have much in common, but also major phenotypic differences, and thus respectively model unique aspects of human CKD. The purpose of this review is to summarize phenotypic similarities and differences between these two models and their relation to human CKD, while emphasizing their vascular phenotype. In this article we review studies that have evaluated arterial blood pressure, the renin-angiotensin-aldosterone-system (RAAS), autoregulation, nitric oxide, single nephron physiology, angiogenic and anti-angiogenic factors, and capillary rarefaction in these two models. Phenotypic similarities: both models spontaneously develop hallmarks of human CKD including uremia, fibrosis, capillary rarefaction, and progressive renal function decline. They both undergo whole-organ hypertrophy, hyperfiltration of functional nephrons, reduced renal expression of angiogenic factor VEGF, increased renal expression of the anti-angiogenic thrombospondin-1, impaired renal autoregulation, and abnormal vascular nitric oxide physiology. Key phenotypic differences: the Inf model develops rapid-onset, moderate-to-severe systemic hypertension, and the Pol model early normotension followed by mild-to-moderate hypertension. The Inf rat has a markedly more active renin-angiotensin-aldosterone-system. Comparison of these two models facilitates understanding of how they can be utilized for studying CKD pathophysiology (e.g., RAAS dependent or independent pathology).

α-Klotho, Plasma Asymmetric Dimethylarginine, and Kidney Disease Progression

Rationale & Objective

We aimed to explore the associated factors of endothelial injury in chronic kidney disease (CKD) and the relationship between endothelial dysfunction and CKD prognosis.

Study Design

A prospective observational cohort study.

Setting & Participants

77 adults with CKD stages 1-5 were enrolled January 2010 to December 2010 and followed up until December 2015.

Exposure

Serum asymmetric dimethylarginine (ADMA) level at baseline, α-klotho, sodium-phosphorus synergistic transporter, and dimethylarginine-dimethylamine hydrolase expression in kidney biopsy samples.

Outcome

Initiation of kidney replacement therapy (KRT).

Analytical Approach

Kaplan-Meier analysis was used for evaluation of the incidence rate of KRT. All tests were 2 tailed, and statistical significance was defined as P < 0.05.

Results

Mean serum ADMA level of 77 patients was 64.3 ± 34.6 ng/mL. ADMA level increased with CKD stages (P = 0.06) and declining kidney function (r = −0.267; P = 0.02). The expression of α-klotho in kidney biopsy specimens also decreased. Median follow-up time was 56 (interquartile range, 50.5-62) months. Kaplan-Meier analyses showed that during a total follow-up of 6 years, the incidence of KRT initiation in the high-ADMA group was significantly higher than that in the low group (35.9% vs 13.2%; P = 0.03). ADMA level was negatively correlated with α-klotho (r = −0.233; P = 0.04) and positively correlated with phosphorus level (r = 0.243; P = 0.04). The expression of sodium-phosphorus synergistic transporter in kidney tubules, which promoted phosphorus reabsorption, and the expression of dimethylarginine-dimethylamine hydrolase isoform 1, which regulated ADMA, were decreased. Correlation analysis also showed that ADMA level decreased while age increased at baseline (r = −0.292; P = 0.01).

Limitations

Small sample size with limited longer-term follow-up.

Conclusions

Serum ADMA levels increased as kidney function declined, and high serum ADMA level was associated with incident kidney failure. Low tissue α-klotho and high levels of plasma phosphorus or tissue expression of type II sodium/phosphate cotransporter in the kidney are associated with higher circulating ADMA levels, suggesting that they may be involved in the pathogenesis of endothelial dysfunction in patients with CKD.

Triple combination therapy with telmisartan, amlodipine, and hydrochlorothiazide ameliorates albuminuria in a normotensive rat remnant kidney model

Background

Some types of antihypertensive drugs may have pleiotropic effects in patients with chronic kidney disease (CKD). However, whether triple combination therapy with angiotensin II receptor blockers (ARBs), calcium channel blockers (CCBs), and thiazide diuretics (TZD) confer renoprotective effects in normotensive CKD remains unknown. Thus, we explored this issue using a normotensive rat remnant kidney model.

Methods

Sprague-Dawley rats were randomly allocated into four groups: sham (n = 10), 5/6 nephrectomy (NTx) (n = 9), NTx treated with telmisartan and amlodipine (dual) (n = 8), and NTx treated with telmisartan, amlodipine, and hydrochlorothiazide (triple) (n = 7), and followed for 4 weeks. Blood pressure (BP), blood chemistry including renal function, urinary albumin excretion (UAE), and renal pathology were evaluated in all groups.

Results

There was no significant change in systolic BP among the four groups during the study period. Serum blood urea nitrogen (BUN) was significantly higher, and 24-h creatinine clearance (Ccr) was lower in all NTx groups (p < 0.001). Dual therapy further increased the glomerular diameter in NTx rats (p < 0.001), which was significantly ameliorated by triple therapy (p < 0.001). Triple therapy, but not dual therapy, significantly reduced NTx-induced UAE levels (p < 0.05), whereas BUN, 24-h Ccr, and tubulointerstitial injury scores were comparable among all the NTx groups.

Conclusions

Our results suggest that triple combination therapy with telmisartan, amlodipine, and hydrochlorothiazide could ameliorate glomerular hypertrophy and albuminuria in normotensive CKD rats in a BP-lowering independent manner.

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.

Treatment of atherosclerosis through transplantation of endothelial progenitor cells overexpressing dimethylarginine dimethylaminohydrolase (DDAH) in rabbits

BACKGROUND

Endothelial dysfunction is a key event in the development of vascular diseases, including atherosclerosis. Endothelial progenitor cells (EPCs) play an important role in vascular repair. Decreased dimethylarginine dimethylaminohydrolase (DDAH) activity is observed in several pathological conditions, and it is associated with an increased risk of vascular disease. We hypothesized that bone marrow-derived EPCs and combination therapy with DDAH2-EPCs could reduce plaque size and ameliorate endothelial dysfunction in an atherosclerosis rabbit model.

METHOD

Four groups of rabbits (n = 8 per group) were subjected to a hyperlipidemic diet for a month. After establishing the atherosclerosis model, rabbits received 4 × 10⁶ EPC, EPCs expressing DDAH2, through femoral vein injection, or saline (the control group with basic food and the untreated group). One month after transplantation, plaque thickness, endothelial function, oxidative stress, and inflammatory mRNAs, DDAH, and eNOS function were assessed.

RESULTS

DDAH2-EPCs transplantation (p < 0.05) and EPCs transplantation (p < 0.05) were both associated with a reduction in plaque size compared to the control saline injection. The antiproliferative and antiatherogenic effects of EPCs were further enhanced by the overexpression of DDAH2 (p < 0.05, DDAH2-EPCs vs. EPCs). Furthermore, DDAH2-EPCs transplantation significantly increased endothelium integrity compared to the EPCs transplantation.

CONCLUSION

Transplantation of EPCs overexpressing DDAH2 may enhance the repair of injured endothelium by reducing inflammation and restoring endothelial function. Therefore, pCMV6-mediated DDAH2 gene-transfected EPCs are a potentially valuable tool for the treatment of atherosclerosis.

Association of advanced glycation end products with sarcopenia and frailty in chronic kidney disease

Prevalence of sarcopenia is high in patients with chronic kidney disease (CKD), especially in those with dialysis. Various pathological conditions related to CKD, such as chronic inflammation, insulin resistance, and endothelial dysfunction, are thought to be associated with the development and progression of sarcopenia. Advanced glycation end products (AGE), one of the representative uremic toxins, have been shown to contribute to various CKD-associated complications. This study investigated the role of AGE in frailty and sarcopenia in patients and animals with CKD, respectively. In patients undergoing dialysis, serum AGE levels were significantly increased according to the frailty status and inversely associated with physical performance and activity. AGE accumulated in the gastrocnemius muscle of 5/6 nephrectomy mice in association with morphological abnormalities, capillary rarefaction, and mitochondrial dysfunction, all of which were completely inhibited by DNA-aptamer raised against AGE. Our present findings may suggest the pathological role of AGE in sarcopenia and frailty in CKD.

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.

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.

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.

The role of protein arginine methyltransferases in kidney diseases

The methylation of arginine residues by protein arginine methyltransferases (PRMTs) is a crucial post-translational modification for many biological processes, including DNA repair, RNA processing, and transduction of intra- and extracellular signaling. Previous studies have reported that PRMTs are extensively involved in various pathologic states, including cancer, inflammation, and oxidative stress reaction. However, the role of PRMTs has not been well described in kidney diseases. Recent studies have shown that aberrant function of PRMTs and its metabolic products-symmetric dimethylarginine (SDMA) and asymmetric dimethylarginine (ADMA)-are involved in several renal pathological processes, including renal fibrosis, acute kidney injury (AKI), diabetic nephropathy (DN), hypertension, graft rejection and renal tumors. We aim in this review to elucidate the possible roles of PRMTs in normal renal function and various kidney diseases.

Enhancing kidney DDAH-1 expression by adenovirus delivery reduces ADMA and ameliorates diabetic nephropathy

Endothelial dysfunction, characterized by reduced bioavailability of nitric oxide and increased oxidative stress, is a hallmark characteristic in diabetes and diabetic nephropathy (DN). High levels of asymmetric dimethylarginine (ADMA) are observed in several diseases including DN and are a strong prognostic marker for cardiovascular events in patients with diabetes and end-stage renal disease. ADMA, an endogenous endothelial nitric oxide synthase (NOS3) inhibitor, is selectively metabolized by dimethylarginine dimethylaminohydrolase (DDAH). Low DDAH levels have been associated with cardiac and renal dysfunction, but its effects on DN are unknown. We hypothesized that enhanced renal DDAH-1 expression would improve DN by reducing ADMA and restoring NOS3 levels. DBA/2J mice injected with multiple low doses of vehicle or streptozotocin were subsequently injected intrarenally with adenovirus expressing DDAH-1 (Ad-h-DDAH-1) or vector control [Ad-green fluorescent protein (GFP)], and mice were followed for 6 wk. Diabetes was associated with increased kidney ADMA and reduced kidney DDAH activity and DDAH-1 expression but had no effect on kidney DDAH-2 expression. Ad-GFP-treated diabetic mice showed significant increases in albuminuria, histological changes, glomerular macrophage recruitment, inflammatory cytokine and fibrotic markers, kidney ADMA levels, and urinary thiobarbituric acid reactive substances excretion as an indicator of oxidative stress, along with a significant reduction in kidney DDAH activity and kidney NOS3 mRNA compared with normal mice. In contrast, Ad-h-DDAH-1 treatment of diabetic mice reversed these effects. These data indicate, for the first time, that DDAH-1 mediates renal tissue protection in DN via the ADMA-NOS3-interaction. Enhanced renal DDAH-1 activity could be a novel therapeutic tool for treating patients with diabetes.

Inhibition of lysyl oxidase ameliorates renal injury by inhibiting CD44-mediated pericyte detachment and loss of peritubular capillaries

Renal fibrosis is a common pathological manifestation of almost all forms of kidney disease irrespective of the etiological cause. Microvascular rarefaction represents itself as an important phenomenon associated with renal fibrosis and shows strong correlation with decline in renal functions. Lysyl oxidase (LOX) catalyzes crosslinking of extracellular matrix (ECM) proteins including collagens, plays an important role in stabilization of degradation resistant matrix. Since, there seems to be a causal link between deposition of excessive ECM and microvascular rarefaction, we investigated the effects of reduction in renal fibrosis on microvascular rarefaction in acute as well as end stage kidney. We used a well-established unilateral ureteral obstruction (UUO)-induced renal fibrosis model to produce renal fibrosis in animals. We treated animals with a LOX inhibitor, β-aminopropionitrile (BAPN, 100 mg/kg, i.p.) and investigated effects on renal fibrosis and microvascular rarefaction. We observed that LOX inhibition was associated with reduction in collagen deposition in UUO-induced renal fibrosis animal model. Further, ECM normalization by LOX inhibition decreased the loss of peritubular capillaries (PTCs) in fibrotic kidney in acute study while the LOX inhibition failed to inhibit PTCs loss in end stage kidney. The results of present study suggested that inhibition of LOX reduces collagen deposition and renal fibrosis. Further, the reduction in fibrosis fails to protect from PTCs loss in chronic study suggesting the absence of strong link between reduction in fibrosis and improvement in PTCs in an end stage kidney.

Uremic Toxin-Targeting as a Therapeutic Strategy for Preventing Cardiorenal Syndrome

Chronic kidney disease (CKD) is a global health problem. CKD patients are at high risk of developing cardiovascular disease (CVD), including coronary artery disease, heart failure and stroke. Several factors invoke a vicious cycle of CKD and CVD, which is referred as to "cardiorenal syndrome". Among these factors, the compounds retained through loss of renal excretion play a pathological role in causing atherosclerosis and CVD. These compounds have been broadly classified as uremic toxins because of their accumulation with declining renal function and cytotoxicity. The major uremic toxins contributing to CVD are asymmetric dimethylarginine (ADMA), advanced glycation endproducts (AGE), and trimethyl amine N-oxide (TMAO). ADMA is linked to CVD through regulation of nitric oxide, reactive oxygen species, and renal anemia. AGE not only directly accumulates in the heart and kidney, but interacts with the receptor for AGE (RAGE), leading to cell damage in CVD. TMAO correlates with a high prevalence of CVD and promotes organ fibrosis by itself. The levels of these and other uremic toxins rise with worsening CKD, inducing multiplicative damage in the heart and kidney. Therefore, a better understanding of uremic toxins has great clinical importance for preventing cardiorenal syndrome. This review highlights the molecular mechanism by which these uremic toxins are implicated in CVD and suggests the possible mutual relationship between them.

Gene therapy research for kidney diseases

A resurgence in the development of newer gene therapy systems has led to recent successes in the treatment of B cell cancers, retinal degeneration and neuromuscular atrophy. Gene therapy offers the ability to treat the patient at the root cause of their malady by restoring normal gene function and arresting the pathological progression of their genetic disease. The current standard of care for most genetic diseases is based upon the symptomatic treatment with polypharmacy while minimizing any potential adverse effects attributed to the off-target and drug-drug interactions on the target or other organs. In the kidney, however, the development of gene therapy modifications to specific renal cells has lagged far behind those in other organ systems. Some positive strides in the past few years provide continued enthusiasm to invest the time and effort in the development of new gene therapy vectors for medical intervention to treat kidney diseases. This mini-review will systematically describe the pros and cons of the most commonly tested gene therapy vector systems derived from adenovirus, retrovirus, and adeno-associated virus and provide insight about their potential utility as a therapy for various types of genetic diseases in the kidney.

Reduced Estimated GFR and Cardiac Remodeling: A Population-Based Autopsy Study

RATIONALE & OBJECTIVE

Evidence suggests that cardiac remodeling, including left ventricular hypertrophy and myocardial fibrosis, develops with progression of kidney disease. Few studies have examined cardiac pathology across a range of estimated glomerular filtration rates (eGFRs), which was the objective of this investigation.

STUDY DESIGN

Population-based cross-sectional study of deceased patients undergoing autopsy.

SETTING & PARTICIPANTS

334 of 694 consecutive deceased patients undergoing autopsy with available cardiac tissue, with a prior health examination within 6 years and without a prior diagnosis of heart disease.

EXPOSURE

eGFR.

OUTCOMES

The thickness of the left ventricular wall, sizes of cardiac cells, and percentages of fibrosis, estimated from pathology examination of autopsy samples.

ANALYTICAL APPROACH

Generalized estimating equations.

RESULTS

Lower eGFRs were associated with greater left ventricular wall thickness. Deceased patients with eGFRs≥60, 45 to 59, 30 to 44, and <30mL/min/1.73m² had left ventricular wall thicknesses of 9.1, 9.5, 9.8, and 10.3mm, respectively (P for trend<0.05). Lower eGFRs were also significantly associated with greater mean values of cardiac cell size in the left ventricular wall after adjusting for confounders: 15.3, 16.1, 16.4, and 17.4μm for eGFRs≥60, 45 to 59, 30 to 44, and <30mL/min/1.73m² (P for trend<0.01). Patients with lower eGFRs had significantly higher multivariable-adjusted geometric mean values for fibrosis percentage in the left ventricular wall: 3.22%, 4.33%, 3.83%, and 6.14% for eGFRs≥60, 45 to 59, 30 to 44, and <30mL/min/1.73m² (P for trend<0.001). The negative association of eGFR with multivariable-adjusted mean values of cardiac cell width was stronger among patients with than those without anemia.

LIMITATIONS

Cross-sectional study with a high proportion of elderly patients, no available information for severity or duration of hypertension and other cardiovascular risk factors, no information for medication use.

CONCLUSIONS

These findings suggest that reduced eGFR is associated with cardiac hypertrophy and fibrosis of the left ventricle, cardiac cell enlargement, and cardiac fibrosis.

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.

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.

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.

Role of Uremic Toxins for Kidney, Cardiovascular, and Bone Dysfunction

With decreasing kidney function, cardiovascular disease (CVD) and mineral bone disorders frequently emerge in patients with chronic kidney disease (CKD). For these patients, in addition to the traditional risk factors, non-traditional CKD-specific risk factors are also associated with such diseases and conditions. One of these non-traditional risk factors is the accumulation of uremic toxins (UTs). In addition, the accumulation of UTs further deteriorates kidney function. Recently, a huge number of UTs have been identified. Although many experimental and clinical studies have reported associations between UTs and the progression of CKD, CVD, and bone disease, these relationships are very complex and have not been fully elucidated. Among the UTs, indoxyl sulfate, asymmetric dimethylarginine, and p-cresylsulfate have been of particular focus, up until now. In this review, we summarize the pathophysiological influences of these UTs on the kidney, cardiovascular system, and bone, and discuss the clinical data regarding the harmful effects of these UTs on diseases and conditions.

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.

Coronary flow reserve is predictive of the risk of cardiovascular death regardless of chronic kidney disease stage

Microvascular rarefaction is found in experimental uremia, but data from patients with chronic kidney disease (CKD) are limited. We therefore quantified absolute myocardial blood flow and coronary flow reserve (the ratio of peak to resting flow) from myocardial perfusion positron emission tomography scans at a single institution. Individuals were classified into standard CKD categories based on the estimated glomerular filtration rate. Associations of coronary flow reserve with CKD stage and cardiovascular mortality were analyzed in models adjusted for cardiovascular risk factors. The coronary flow reserve was significantly associated with CKD stage, declining in early CKD, but it did not differ significantly among individuals with stage 4, 5, and dialysis-dependent CKD. Flow reserve with preserved kidney function was 2.01, 2.06 in stage 1 CKD, 1.91 in stage 2, 1.68 in stage 3, 1.54 in stage 4, 1.66 in stage 5, and 1.55 in dialysis-dependent CKD. Coronary flow reserve was significantly associated with cardiovascular mortality in adjusted models (hazard ratio 0.76, 95% confidence interval: 0.63-0.92 per tertile of coronary flow reserve) without evidence of effect modification by CKD. Thus, coronary flow reserve is strongly associated with cardiovascular risk regardless of CKD severity and is low in early stage CKD without further decrement in stage 5 or dialysis-dependent CKD. This suggests that CKD physiology rather than the effects of dialysis is the primary driver of microvascular disease. Our findings highlight the potential contribution of microvascular dysfunction to cardiovascular risk in CKD and the need to define mechanisms linking low coronary flow reserve to mortality.

Arrhythmia and Sudden Death in Hemodialysis Patients: Protocol and Baseline Characteristics of the Monitoring in Dialysis Study

BACKGROUND

Dialysis patients have high rates of cardiovascular morbidity and mortality, but data on arrhythmia burden, arrhythmia type, arrhythmia triggers, and the identity of terminal arrhythmias have historically been limited by an inability to monitor heart rhythm for prolonged periods.

OBJECTIVES

To investigate arrhythmia and its association with sudden death in dialysis-dependent ESRD, describe the potential for implantable devices to advance study of dialysis physiology, review the ethical implications of using implantable devices in clinical studies, and report on the protocol and baseline results of the Monitoring in Dialysis Study (MiD).

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

In this multicenter, interventional-observational, prospective cohort study, we placed implantable loop recorders in patients undergoing long-term hemodialysis. The proportion of patients experiencing clinically significant arrhythmias was the primary endpoint. For 6 months, we captured detailed data on the primary endpoint, symptomatic arrhythmias, other electrocardiographic variables, dialysis prescription, electrolytes, dialysis-related variables, and vital signs. We collected additional electrocardiographic data for up to 1 year.

RESULTS

Overall, 66 patients underwent implantation in sites in the United States and India. Diabetes was present in 63.6% of patients, 12.1% were age ≥70 years, 69.7% were men, and 53.0% were black. Primary and secondary endpoint data are expected in 2016.

CONCLUSIONS

Cardiac arrhythmia is an important contributor to cardiovascular morbidity and mortality in dialysis patients, but available technology has previously limited the ability to estimate its true burden and triggers and to define terminal rhythms in sudden death. Use of implantable technology in observational studies raises complex issues but may greatly expand understanding of dialysis physiology. The use of implantable loop recorders in MiD is among the first examples of such a trial, and the results are expected to provide novel insights into the nature of arrhythmia in hemodialysis patients.

MicroRNA21 promotes interstitial fibrosis via targeting DDAH1: a potential role in renal fibrosis

Scarring of the kidney directly promotes loss of kidney function. A thorough understanding of renal fibrosis at the molecular level is urgently needed. One prominent microRNA, miR-21, was previously reported to be up-regulated in renal fibrosis, but its mechanism is unclear. In the present study, an unbiased search for downstream messenger RNA targets of miR-21 using the HK-2 human tubular epithelial cell line was performed. Effects of the target gene in renal fibrosis and underlying mechanism were explored. Results show that forced expression of miR-21 significantly increased cell apoptosis, interstitial deposition, and decreased E-cadherin level of the HK-2 cells. Conversely, inhibition of miR-21 promoted the opposite effects. We identified that miR-21 directly interacted with the 3'-untranslated region of the suppressor of dimethylarginine dimethylaminohydrolase 1 (DDAH1) by dual-luciferase assay. Moreover, pcDNA3.1-DDAH1 pretreatment could effectively reduce α-SMA, collagen I, fibronectin expression, and promoted E-cadherin expression, as well as inhibiting HK-2 cell apoptosis, while all those effects can be attenuated by pretreatment with the Wnt/β-catenin signaling activator Licl. Taken together, our results suggest that miR-21 may regulate renal fibrosis by the Wnt pathway via directly targeting DDAH1. Therefore, this study may provide novel strategies for the development of renal fibrosis therapy.

Asymmetric dimethylarginine, a biomarker of cardiovascular complications in diabetes mellitus

Cardiovascular (CV) complications are an essential causal element of prospect in diabetes mellitus (DM), with carotid atherosclerosis being a common risk factor for prospective crisis of coronary artery diseases and/or cerebral infarction in DM subjects. From another point of view, asymmetric dimethylarginine (ADMA) has been established as an inhibitor of endogenous nitric oxide synthesis and the relationship between ADMA and arteriosclerosis has been reported. In our study with 87 type 2 DM (T2DM) patients, we have examined whether ADMA and other CV risk factors are the useful predictors of DMCV complications. After the measurement of the respective CV risk factors, we have followed the enrolled T2DM patients for 5 years. We have finally analyzed 77 patients. DMCV complications developed in 15 cases newly within 5 years, and 4 cases recurred. The concentrations of ADMA in plasma were markedly more elevated in 19 DM patients with CV complications than in 58 DM patients without CV complications. Urinary albumin (U-Alb), mean intimal-medial thickness (IMT) and ankle brachial index (ABI) were also higher in patients with CV complications. Multiple regression analyses showed that U-Alb had an influence on the high level of ADMA (standardized β = 6.59, P = 0.00014) independently of age, systolic BP, fibrinogen, mean IMT, plaque score, and ABI. The review indicates what is presently known regarding plasma ADMA that might be a new and meaningful biomarker of CV complications in DM subjects.

Reduced Renal Methylarginine Metabolism Protects against Progressive Kidney Damage

Nitric oxide (NO) production is diminished in many patients with cardiovascular and renal disease. Asymmetric dimethylarginine (ADMA) is an endogenous inhibitor of NO synthesis, and elevated plasma levels of ADMA are associated with poor outcomes. Dimethylarginine dimethylaminohydrolase-1 (DDAH1) is a methylarginine-metabolizing enzyme that reduces ADMA levels. We reported previously that a DDAH1 gene variant associated with increased renal DDAH1 mRNA transcription and lower plasma ADMA levels, but counterintuitively, a steeper rate of renal function decline. Here, we test the hypothesis that reduced renal-specific ADMA metabolism protects against progressive renal damage. Renal DDAH1 is expressed predominately within the proximal tubule. A novel proximal tubule-specific Ddah1 knockout (Ddah1(PT-/-)) mouse demonstrated tubular cell accumulation of ADMA and lower NO concentrations, but unaltered plasma ADMA concentrations. Ddah1(PT-/-) mice were protected from reduced kidney tissue mass, collagen deposition, and profibrotic cytokine expression in two independent renal injury models: folate nephropathy and unilateral ureteric obstruction. Furthermore, a study of two independent kidney transplant cohorts revealed higher levels of human renal allograft methylarginine-metabolizing enzyme gene expression associated with steeper function decline. We also report an association among DDAH1 expression, NO activity, and uromodulin expression supported by data from both animal and human studies, raising the possibility that kidney DDAH1 expression exacerbates renal injury through uromodulin-related mechanisms. Together, these data demonstrate that reduced renal tubular ADMA metabolism protects against progressive kidney function decline. Thus, circulating ADMA may be an imprecise marker of renal methylarginine metabolism, and therapeutic ADMA reduction may even be deleterious to kidney function.

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.

Chronic kidney disease (CKD) as a systemic disease: whole body autoregulation and inter-organ cross-talk

The inter-organ cross-talk and the functional integration of organ systems is an exceedingly complex process which until now has been investigated with a reductionist approach. CKD perturbs the inter-organ cross-talk and demands central resetting of autonomic (nervous) control of organ systems. Due to limitations inherent to the reductionist approach, we currently identify CKD-related pseudo-syndromes and largely fail at describing the complex systemic inter-relationships set into motion by renal damage and renal dysfunction. A mature technology for a system-analysis approach to physiology and pathophysiology of CKD now exists. System biology will allow in depth understanding of complex diseases like CKD and will set the stage for predictive, preventive and personalized medicine, a long-standing dream of doctors and patients alike.

Remnant nephron physiology and the progression of chronic kidney disease

In chronic kidney disease, ongoing failure of individual nephrons leads to the progressive loss of renal function. This process results in part from a cellular and molecular response to injury that represents an attempt to maintain homeostasis but instead initiates a program that damages the nephron. As nephrons are lost, compensation by the remaining nephrons exacerbates glomerular pathophysiology. The delivery of excessive amounts of biologically active molecules to the distal nephron and tubulointerstitium generates inflammation and cellular dedifferentiation. Energy requirements of hyperfunctioning nephrons exceed the metabolic substrate available to the renal tubule, and inadequacy of the local vascular supply promotes hypoxia/ischemia and consequent acidosis and reactive oxygen species generation. In this way, mechanisms activated to maintain biological balance ultimately lead to demise of the nephron.

The inhibitory effect of quercetin on asymmetric dimethylarginine-induced apoptosis is mediated by the endoplasmic reticulum stress pathway in glomerular endothelial cells

Asymmetric dimethylarginine (ADMA) is considered an independent mortality and cardiovascular risk factor in chronic kidney disease (CKD) patients, and contributes to the development of renal fibrosis. Quercetin (QC), a natural component of foods, protects against renal injury. Here, we explored the possible mechanisms that are responsible for ADMA-induced renal fibrosis and the protective effect of QC. We found that ADMA treatment activated the endoplasmic reticulum (ER) stress sensor proteins phosphorylated protein kinase RNA-activated-like ER kinase (PERK) and inositol requiring-1α (IRE1), which correspondingly induced C/EBP homologous protein (CHOP) expression and phosphorylated c-Jun N-terminal kinase (JNK) phosphorylation in glomerular endothelial cells (GEnCs). Following this, ADMA promoted ER stress-induced apoptosis and resulted in transforming growth factor β (TGF-β) expression in GEnCs. SP600125, an inhibitor of JNK, and CHOP siRNA protected against ADMA-induced cell apoptosis and TGF-β expression. QC prevented ADMA-induced PERK and IRE1 apoptotic ER stress pathway activation. Also, ADMA-induced GEnCs apoptosis and TGF-β expression was reduced by QC. Overexpression of CHOP blocked QC-mediated protection from apoptosis in ER stressed cells. Overall, these observations indicate that ADMA may induce GEnCs apoptosis and TGF-β expression by targeting the PERK-CHOP and IRE1-JNK pathway. In addition, drugs such as QC targeting ER stress may hold great promise for the development of novel therapies against ADMA-induced renal fibrosis.

Protective role of JAK/STAT signaling against renal fibrosis in mice with unilateral ureteral obstruction

Inflammation is involved in renal fibrosis, a final common pathway for kidney diseases. To clarify how JAK/STAT/SOCS system was involved in renal fibrosis, UUO was induced in BALB/c or SOCS3(+/-) mice in the presence or absence of JAK inhibitor-incorporated nanoparticle (pyridine6-PGLA). UUO increased pSTAT3 and subsequently elevated SOCS3 levels in the obstructed kidneys. pSTAT3 levels were further increased in SOCS3(+/-) mice. UUO-induced renal fibrosis was markedly suppressed in SOCS3(+/-) mice, while it was aggravated by pre-treatment with pyridine6-PGLA. Although there were no differences in renal mRNA levels of TGF-β and collagens between wild and SOCS3(+/-) mice, MMP-2 activity was enhanced in SOCS3(+/-) UUO mice. Activated MMP-2 was completely suppressed by pyridine6-PGLA-pre-treatment. TNF-α one of JAK/STAT activators, increased pSTAT3 levels and subsequently induced MMP-2 activation in proximal tubular cells. These results suggest that JAK/STAT3 signaling may play a role in repair process of renal fibrosis in UUO partly via MMP-2 activation.

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.

The role of dimethylarginine dimethylaminohydrolase (DDAH) in pulmonary fibrosis

Pulmonary fibrosis is a devastating and progressive parenchymal lung disease with an extremely poor prognosis. Patients suffering from idiopathic pulmonary fibrosis (IPF) display a compromised lung function alongside pathophysiological features such as highly increased production of extracellular matrix, alveolar epithelial cell dysfunction, and disordered fibroproliferation - features that are due to a dysregulated response to alveolar injury. Under pathophysiological conditions of IPF, abnormally high concentrations of nitric oxide (NO) are found, likely a result of increased activity of the inducible nitric oxide synthase (NOS2), giving rise to products that contribute to fibrosis development. It is known that pharmacological inhibition or knockdown of NOS2 reduces pulmonary fibrosis, suggesting a role for NOS inhibitors in the treatment of fibrosis. Recent reports identified a critical enzyme, dimethylarginine dimethylaminohydrolase (DDAH), which is exceedingly active in patients suffering from IPF and in mice treated with bleomycin. An up-regulation of DDAH was observed in primary alveolar epithelial type II (ATII) cells from mice and patients with pulmonary fibrosis, where it co-localizes with NOS2. DDAH is a key enzyme that breaks down an endogenous inhibitor of NOS, asymmetric dimethylarginine (ADMA), by metabolizing it to l-citrulline and dimethylamine. DDAH was shown to modulate key fibrotic signalling cascades, and inhibition of this enzyme attenuated many features of the disease in in vivo experiments, suggesting a possible new therapeutic strategy for the treatment of patients suffering from IPF.

The mechanism of long-term low-dose asymmetric dimethylarginine inducing transforming growth factor-β expression in endothelial cells

Asymmetric dimethylarginine (ADMA), an endogenous nitric oxide synthase (NOS) inhibitor, accumulates in plasma during chronic kidney disease (CKD). High plasma levels of ADMA can increase transforming growth factor-β (TGF-β) expression, related to renal fibrosis, but the precise molecular mechanism is not explicit. The present study was designed to determine the mechanism through which long-term low-dose ADMA induces TGF-β expression in endothelial cells and to investigate the molecular mechanism of its action. Human umbilical vein endothelial cells (HUVECs) were exposed to low-dose ADMA (5 and 10 µmol/l) for 7 passages and TGF-β expression was determined. Human renal glomerular endothelial cells (HRGECs) were exposed to high-dose ADMA (100 µmol/l) which were used to clarify the molecular mechanism. The results showed that long-term low-dose ADMA (5 and 10 µmol/l) increases TGF-β production in both mRNA and protein levels in HUVECs in a time-dependent manner. We confirmed that exogenous ADMA (100 µmol/l) significantly enhanced stress fiber formation in HRGECs and upregulated TGF-β expression. Such effects of ADMA in HRGECs were inhibited by pre-treatment with actin depolymerizing agent, actin stabilizing agent, p38 MAPK inhibitor and NADPH oxidase inhibitor. In addition, we demonstrated that ADMA (100 µmol/l) significantly activated nuclear factor-κB (NF-κB) in HRGECs, which was markedly attenuated by actin depolymerizing agent, actin stabilizing agent, p38 MAPK inhibitor and NADPH oxidase inhibitor. In brief, the present study demonstrated that long-term low-dose ADMA induces TGF-β expression in endothelial cells at both the gene and protein levels. The actin cytoskeleton may be involved in modulation of ADMA-induced NF-κB activation and the ensuing TGF-β expression in HRGECs.

Dimethylarginine dimethylaminohydrolase1 is an organ-specific mediator of end organ damage in a murine model of hypertension

BACKGROUND

The endogenous nitric oxide synthase inhibitor asymmetric dimethylarginine (ADMA) is an independent predictor of cardiovascular and overall mortality. Moreover, elevated ADMA plasma concentrations are associated with the extent of hypertension. However, data from small-sized clinical trials and experimental approaches using murine transgenic models have revealed conflicting results regarding the impact of ADMA and its metabolizing enzyme dimethylarginine dimethylaminohydrolase (DDAH) in the pathogenesis of hypertension.

METHODOLOGY/PRINCIPAL FINDINGS

Therefore, we investigated the role of ADMA and DDAH1 in hypertension-induced end organ damage using the uninephrectomized, deoxycorticosterone actetate salt, and angiotensin II-induced hypertension model in human DDAH1 (hDDAH1) overexpressing and wild-type (WT) mice. ADMA plasma concentrations differed significantly between hDDAH1 and WT mice at baseline, but did not significantly change during the induction of hypertension. hDDAH1 overexpression did not protect against hypertension-induced cardiac fibrosis and hypertrophy. In addition, the hypertension-induced impairment of the endothelium-dependent vasorelaxation of aortic segments ex vivo was not significantly attenuated by hDDAH1 overexpression. However, hDDAH1 mice displayed an attenuated hypertensive inflammatory response in renal tissue, resulting in less hypertensive renal injury.

CONCLUSION/SIGNIFICANCE

Our data reveal that hDDAH1 organ-specifically modulates the inflammatory response in this murine model of hypertension. The lack of protection in cardiac and aortic tissues may be due to DDAH1 tissue selectivity and/or the extent of hypertension by the used combined model. However, our study underlines the potency of hDDAH1 overexpression in modulating inflammatory processes as a crucial step in the pathogenesis of hypertension, which needs further experimental and clinical investigation.

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.

Biomarkers in hemodialysis patients

Patients with chronic kidney disease (CKD) are, compared to the general population, at higher risk of cardiovascular disease (CVD), including sudden death, coronary artery disease (CAD), congestive heart failure (HF), stroke, and peripheral artery disease. The presence of CVD is independently associated with kidney function decline. Renal insufficiency is a strong and independent predictor of mortality in patients with different CKD stages. The interplay of traditional and nontraditional risk factors is complex such that risk factor profiles are different in CKD patients. Seemingly, paradoxical associations between traditional risk factors and cardiovascular outcome complicate efforts to identify real cardiovascular etiology in these patients. Additional tools are often required to aid clinical assessment of cardiovascular risk. Recently, a number of cardiovascular biomarkers were identified as predictors of outcome in CVD. These may be used to guide early diagnosis and therapy for CVD or may predict outcome in CKD. This review focuses on the potential diagnostic and prognostic use of some important new biomarkers including brain natriuretic peptide (BNP), cardiac troponins (cTns), inflammatory markers, adhesion molecules, and asymmetric dimethylarginine (ADMA) in CKD as well as those patients with end-stage renal failure.

Proteinuria elevates asymmetric dimethylarginine levels via protein arginine methyltransferase-1 overexpression in a rat model of nephrotic syndrome

AIMS

Proteinuria is an independent risk factor for cardiovascular disease (CVD) in patients with chronic kidney disease (CKD). Asymmetric dimethylarginine (ADMA) is a mediator of endothelial dysfunction and is associated with proteinuria in CKD patients. Thus, ADMA can partially account for the increased risk of CVD in CKD patients presenting proteinuria. However, a causal relationship between proteinuria and ADMA remains to be demonstrated.

MAIN METHODS

We first investigated whether and how proteinuria might increase ADMA levels in adriamycin (ADR)-treated rats. Next, we examined the effects of human serum albumin (HSA) on ADMA production by human renal proximal tubular epithelial cells (RPTECs) cultured in vitro.

KEY FINDINGS

Proteinuria was associated with ADMA levels in ADR treated rats. Although ADR treatment did not affect the expression levels of the dimethylarginine dimethylaminohydrolase (DDAH)-1 or -2 enzymes that degrade ADMA, it significantly increased the expression levels of protein arginine methyltransferase-1 (PRMT-1) that facilitates the production of ADMA. HSA increased the generation of reactive oxygen species in RPTECs, which was blocked by the anti-oxidant N-acetylcysteine (NAC) or an inhibitor of NADPH oxidase. Furthermore, HSA increased ADMA generation by RPTECs in a dose- and time-dependent manner and induced gene expression of PRMT-1 but not DDAHs, which were also suppressed by NAC.

SIGNIFICANCE

Our data suggest that proteinuria might enhance ADMA generation in tubular cells, at least in part via the overexpression of PRMT-1 triggered by oxidative stress. Our findings thereby propose a mechanistic link between proteinuria and ADMA levels in CKD patients.

Treatment of 5/6 nephrectomy rats with sulodexide: a novel therapy for chronic renal failure

AIM

Sulodexide, a glycosaminoglycan, could reduce albuminuria in diabetic patients. The aim of this study was to determine whether sulodexide could be used to treat chronic kidney failure in rats.

METHODS

Sixty Wistar rats undergone 5/6 nephrectomy, then were randomly divided into 4 groups: the model group, sulodexide group (sulodexide 5 mg/kg per day, im), irbesartan group irbesartan (20 mg/kg per day, ig) and sulodexide plus irbesartan group. Another 12 rats were enrolled into the sham operation group. After the treatments for 4, 8 and 12 weeks, urinary protein and serum creatinine levels were measured. After 12 weeks, serum cholesterin and triglycerides levels were measured, and the degrees of glomerular sclerosis and renal tubulointerstitial fibrosis were scored. The expression of aminopeptidase P (JG-12) in the renal tissue was examined using immunohistochemical staining. The renal expressions of endothelial nitric oxide synthase (eNOS) and tissue type plasminogen activator (tPA) were detected with RT-PCR and Western blot.

RESULTS

Proteinuria was markedly attenuated in the sulodexide-treated groups. After 4 and 8 weeks only the sulodexide-treated groups showed significant reduction in serum creatinine; while after 12 weeks all the three treatment groups showed significant reduction in serum creatinine. Furthermore, all the three treatment groups showed significant reduction in the scores of glomerular sclerosis and tubulointerstitial fibrosis. The glomerular expression of JG-12 was increased in both the sulodexide group and the sulodexide plus irbesartan group, but not in the irbesartan group. The eNOS mRNA and protein expression was decreased and the tPA mRNA and protein expression was significantly increased in the model group compared with Sham group. Sulodexide, irbesartan, and their combination reversed the decrease of eNOS expression but increased the tPA expression much more compared with model group.

CONCLUSION

Sulodexide was similar to irbesartan that can decrease proteinuria and attenuate renal lesions in 5/6 nephrectomy rats. The renal protection by sulodexide might be achieved via its impact on renal vascular endothelial cells.

[Methylarginies-induced endothelial dysfunction in chronic kidney disease]

Chronic kidney disease (CKD), defined as low glomerular filtration rates and/or the presence of albuminuria, is considered a risk factor for cardiovascular disease (CVD). In recent years, increasing emphasis has been placed on endothelial dysfunction as a key element underlying the relationship between CKD and CVD. Endothelial cells play a pivotal role in many aspects of vascular function by generating nitric oxide (NO). However, NO production is reduced in CKD patients, partially due to decreased endothelial NO production. One possible cause of NO deficiency is increased levels of endogenous NO synthase inhibitors, in particular asymmetric dimethylarginine (ADMA). Elevated plasma levels of ADMA are consequence of increased synthesis and reduced degradation. Accumulation of ADMA and inhibition of NO production might contribute to endothelial dysfunction, hypertension, initiation of atherosclerosis, and incidence of CVD. Clinical studies revealed that ADMA plasma concentration is increased in populations with renal disease, vascular diseases, and high cardiovascular risks. In this regard, ADMA is increasingly recognized as a biomarker of CKD and CVD. This review discusses ADMA-mediated endothelial dysfunction in CKD, especially focusing on the link between CKD and CVD.