Asymmetric dimethylarginine: a cardiovascular risk factor and a uremic toxin coming of age?

Asymmetric and symmetric dimethylarginine as markers of endothelial dysfunction in cerebrovascular disease: A prospective study

BACKGROUND AND AIM

Asymmetric dimethylarginine (ADMA) and symmetric dimethylarginine (SDMA) have been proposed as mediators of endothelial dysfunction. In this study, we aimed to investigate the diagnostic and prognostic role of ADMA and SDMA in acute cerebrovascular disease.

METHODS AND RESULTS

A prospective case-control study was performed, enrolling 48 patients affected by ischemic stroke with no cardioembolic origin, 20 patients affected by TIA, 40 subjects at high cardiovascular risk and 68 healthy subjects. ADMA levels were significantly lower in high-risk subjects (18.85 [11.78-22.83] μmol/L) than in patients with brain ischemic event, both transient (25.70 [13.15-40.20] μmol/L; p = 0.032) and permanent (24.50 [18.0-41.33] μmol/L; p = 0.001). SDMA levels were different not only between high-risk subjects and ischemic patients, but also between TIA and stroke patients, reaching higher levels in TIA group and lower levels in stroke group (1.15 [0.90-2.0] vs 0.68 [0.30-1.07] μmol/L; p < 0.001). SDMA was also correlated with short-term prognosis, with lower levels in case of adverse clinical course, evaluated by type of discharge (p = 0.009) and need of prolonged rehabilitation (p = 0.042).

CONCLUSIONS

The present study highlights the relationship between l-arginine, ADMA, SDMA and acute cerebrovascular events. Therefore, our results suggested a potential role of SDMA as a specific marker of transient ischemic damage and as a short-term positive prognostic marker.

Plasma levels of arginines at term pregnancy in relation to mode of onset of labor and mode of childbirth

PROBLEM

The exact biochemical mechanisms that initiate labor are not yet fully understood. Nitric oxide is a potent relaxant of uterine smooth muscles until labor starts, and its precursor is L-arginine. Asymmetric (ADMA) and symmetric (SDMA) dimethylarginines, are potent NO-inhibitors. However, arginines (dimethylarginines and L-arginine) are scarcely studied in relation to labor and childbirth. We aimed to investigate arginines in women with spontaneous (SLVB) and induced (ILVB) term labor with vaginal birth and in women undergoing elective caesarean section (ECS).

METHOD OF STUDY

Women at gestational week 16-18 were recruited to the population-based prospective cohort study BASIC at the Uppsala University Hospital, Sweden. Plasma samples taken at start of labor were analyzed for arginines, from SLVB (n = 45), ILVB (n = 45), and ECS (n = 45), using Ultra-High Performance Liquid Chromatography. Between-group differences were assessed using Kruskal-Wallis and Mann-Whitney U-test.

RESULTS

Women with SLVB and ILVB had higher levels of ADMA (p < .0001), SDMA (p < .05) and lower L-arginines (p < .01), L-arginine/ADMA (p < .0001), and L-arginine/SDMA (p < .01, respectively <.001) compared to ECS. However, ILVB had higher ADMA (p < .0001) and lower L-arginine (p < .01), L-arginine/ADMA (p < .0001), and L-arginine/SDMA (p < .01) compared to SLVB. Results are adjusted for gestational length at birth and cervical dilatation at sampling.

CONCLUSION

Our novel findings of higher levels of dimethylarginines in term vaginal births compared to ECS give insights into the biochemical mechanisms of labor. These findings might also serve as a basis for further studies of arginines in complicated pregnancies and labor.

Role of antidiabetic agents in type 2 diabetes patients with chronic kidney disease

Insulin resistance is a condition in which the target tissues have a decreased response to insulin signaling, resulting in glucose uptake defect, and an increased blood sugar level. Pancreatic beta cells thus enhance insulin production to compensate. This situation may cause further beta cell dysfunction and failure, which can lead diabetes mellitus (DM). Insulin resistance is thus an important cause of the development of type 2 DM. Insulin resistance has also been found to have a strong relationship with cardiovascular disease and is common in chronic kidney disease (CKD) patients. The mechanisms of insulin resistance in CKD are complex and multifactorial. They include physical inactivity, inflammation and oxidative stress, metabolic acidosis, vitamin D deficiency, adipose tissue dysfunction, uremic toxins, and renin-angiotensin-aldosterone system activation. Currently, available anti-diabetic agents, such as biguanides, sulfonylureas, thiazolidinediones, alfa-glucosidase inhibitors, glucagon-like peptide-1-based agents, and sodium-glucose co-transporter-2 inhibitors, have different effects on insulin resistance. In this short review, we describe the potential mechanisms of insulin resistance in CKD patients. We also review the interaction of currently available anti-diabetic medications with insulin resistance.

Diabetes acts on mortality in hemodialysis patients predicted by asymmetric dimethylarginine and inflammation

BACKGROUND

The mortality rate of diabetic patients on dialysis is higher than that of non-diabetic patients. Asymmetric dimethylarginine and inflammation are strong predictors of death in hemodialysis. This study aimed to evaluate asymmetric dimethylarginine and C-reactive protein interaction in predicting mortality in hemodialysis according to the presence or absence of diabetes.

METHODS

Asymmetric dimethylarginine and C-reactive protein were measured in 202 patients in maintenance hemodialysis assembled from 2011 to 2012 and followed for four years. Effect modification of C-reactive protein on the relationship between asymmetric dimethylarginine and all-cause mortality was investigated dividing the population into four categories according to the median of asymmetric dimethylarginine and C-reactive protein.

RESULTS

Asymmetric dimethylarginine and C-reactive protein levels were similar between diabetics and non-diabetics. Asymmetric dimethylarginine - median IQR μM - (1.95 1.75-2.54 versus 1.03 0.81-1.55 P=0.000) differed in non-diabetics with or without evolution to death (HR 2379 CI 1.36-3.68 P=0.000) and was similar in diabetics without or with evolution to death. Among non-diabetics, the category with higher asymmetric dimethylarginine and C-reactive protein levels exhibited the highest mortality (69.0% P=0.000). No differences in mortality were seen in diabetics. A joint effect was found between asymmetric dimethylarginine and C-reactive protein, explaining all-cause mortality (HR 15.21 CI 3.50-66.12 P=0.000).

CONCLUSIONS

Asymmetric dimethylarginine is an independent predictor of all-cause mortality in non-diabetic patients in hemodialysis. Other risk factors may overlap asymmetric dimethylarginine in people with diabetes. Inflammation dramatically increases the risk of death associated with high plasma asymmetric dimethylarginine in hemodialysis.

Diabetes acts on mortality in hemodialysis patients predicted by asymmetric dimethylarginine and inflammation

BACKGROUND

The mortality rate of diabetic patients on dialysis is higher than that of non-diabetic patients. Asymmetric dimethylarginine and inflammation are strong predictors of death in hemodialysis. This study aimed to evaluate asymmetric dimethylarginine and C-reactive protein interaction in predicting mortality in hemodialysis according to the presence or absence of diabetes.

METHODS

Asymmetric dimethylarginine and C-reactive protein were measured in 202 patients in maintenance hemodialysis assembled from 2011 to 2012 and followed for four years. Effect modification of C-reactive protein on the relationship between asymmetric dimethylarginine and all-cause mortality was investigated dividing the population into four categories according to the median of asymmetric dimethylarginine and C-reactive protein.

RESULTS

Asymmetric dimethylarginine and C-reactive protein levels were similar between diabetics and non-diabetics. Asymmetric dimethylarginine - median IQR μM - (1.95 1.75-2.54 versus 1.03 0.81-1.55 P=0.000) differed in non-diabetics with or without evolution to death (HR 2379 CI 1.36-3.68 P=0.000) and was similar in diabetics without or with evolution to death. Among non-diabetics, the category with higher asymmetric dimethylarginine and C-reactive protein levels exhibited the highest mortality (69.0% P=0.000). No differences in mortality were seen in diabetics. A joint effect was found between asymmetric dimethylarginine and C-reactive protein, explaining all-cause mortality (HR 15.21 CI 3.50-66.12 P=0.000).

CONCLUSIONS

Asymmetric dimethylarginine is an independent predictor of all-cause mortality in non-diabetic patients in hemodialysis. Other risk factors may overlap asymmetric dimethylarginine in people with diabetes. Inflammation dramatically increases the risk of death associated with high plasma asymmetric dimethylarginine in hemodialysis.

Associations among total p-cresylsulfate, indoxyl sulfate and hippuric acid levels with hemodialysis quality indicators in maintenance hemodialysis patients

BACKGROUND

Total p-cresylsulfate (PCS), indoxyl sulfate (IS) and hippuric acid (HA) are harmful uremic toxins known to be elevated in patients with uremia. Serum total PCS, IS and HA levels have been associated with coronary atherosclerosis, left ventricular hypertrophy, metabolic acidosis, neurological symptoms, and accelerated renal damage associated with chronic kidney disease; however, no study has examined the effect of total PCS, IS and HA on hemodialysis (HD) quality indicators. The aim of this study was to examine associations among total PCS, IS and HA with HD quality indicators in patients undergoing HD treatment.

METHODS

This study included 264 consecutive patients at a single HD center who assessed using previously demonstrated HD quality indicators including anemia, bone-mineral metabolism, dialysis dose, cardiovascular risk, and middle molecule removal area. Serum HA was measured using a capillary electrophoresis method. Serum total PCS and IS concentrations were measured using an Ultra Performance LC System.

RESULTS

Multiple regression analysis showed that sex, potassium, systolic blood pressure (SBP), average BP, β2-microglobulin, and creatinine were independently positively associated with IS level, and that age, total cholesterol, and estimated glomerular filtration rate (eGFR) was independently negatively associated with IS level. In addition, β2-microglobulin was independently positively associated with total PCS. Moreover, potassium, diastolic blood pressure, average BP, β2-microglobulin, dialysis vintage, and albumin were independently positively associated with HA level, and age, transferrin saturation, fasting glucose, and eGFR were independently negatively associated with HA level. When the patients were stratified by age and sex, serum IS and HA levels were still independently associated with some hemodialysis quality indicators. In addition, canonical correlation analysis also confirmed the relationship between uremic toxins (IS and HA) and HD quality indicators (potassium, β2-microglobulin, average BP, creatinine, and eGFR).

CONCLUSION

This study demonstrated that uremic toxins (IS and HA) and HD quality indicators (potassium, β2-microglobulin, average BP, creatinine, and eGFR) constructs were correlated with each other, and that there were sex and age differences in these associations among maintenance HD patients.

Dimethylarginines correlate to common carotid artery wall layer dimensions and cardiovascular risk factors in pregnant women with/without preeclampsia: A group comparative study

OBJECTIVES

Asymmetric- and symmetric dimethylarginines (ADMA, SDMA) are elevated in cardiovascular disease (CVD). Preeclampsia is a pregnancy-specific syndrome and is an independent risk factor for subsequent CVD. Aims were to investigate whether ADMA, SDMA levels and l-arginine/ADMA and l-arginine/SDMA ratios during pregnancy and their changes from pregnancy to postpartum are associated to arterial wall layer dimensions and cardiovascular risk factors in women with and without preeclampsia.

STUDY DESIGN

Dimethylarginines were analyzed by LC-MS, and the common-carotid-artery (CCA) intima and media thicknesses were estimated using 22-MHz non-invasive ultrasonography in women with preeclampsia (cases = 48) and normal pregnancies (controls = 58) in similar gestational age, with reassessment one-year postpartum. A thick intima, thin media and high intima/media ratio (I/M) indicates a less healthy arterial wall.

RESULTS

The median age of cases and controls was 30 years. During pregnancy, women with preeclampsia had higher plasma ADMA, SDMA and lower l-arginine/ADMA and l-arginine/SDMA (all p < 0.01) than women with normal pregnancies. Further, ADMA, SDMA, l-arginine/ADMA and l-arginine/SDMA correlated to intima thickness (r_s = 0.33/0.33/-0.33/-0.35 and p < 0.01), I/M (r_s = 0.26/0.28/-0.22/-0.26 and p < 0.05) and mean arterial pressure (MAP) (r_s = 0.43/0.42/-0.39/-0.40 and p < 0.0001). Changes in ADMA, SDMA and l-arginine/SDMA from pregnancy to postpartum correlated to changes in intima thickness (r_s = 0.22/0.32/-0.21 and p < 0.05/<0.01/<0.05), I/M (r_s = 0.22/0.31/0.08 and p < 0.05/<0.01/=0.43) and MAP (r_s = 0.31/0.53/-0.25 and p < 0.01/<0.001/<0.05). No correlations were found for conventional CCA intima-media-thickness.

CONCLUSIONS

Dimethylarginines were associated to signs of adverse effects on arterial wall layer dimensions and cardiovascular risk factors in women with and without preeclampsia, during pregnancy and to their changes from pregnancy up to one-year postpartum.

The Role of Prognostic and Predictive Biomarkers for Assessing Cardiovascular Risk in Chronic Kidney Disease Patients

Chronic kidney disease (CKD) is currently defined as the presence of proteinuria and/or an eGFR < 60 mL/min/1.73m² on the basis of the renal diagnosis. The global dimension of CKD is relevant, since its prevalence and incidence have doubled in the past three decades worldwide. A major complication that occurs in CKD patients is the development of cardiovascular (CV) disease, being the incidence rate of fatal/nonfatal CV events similar to the rate of ESKD in CKD. Moreover, CKD is a multifactorial disease where multiple mechanisms contribute to the individual prognosis. The correct development of novel biomarkers of CV risk may help clinicians to ameliorate the management of CKD patients. Biomarkers of CV risk in CKD patients are classifiable as prognostic, which help to improve CV risk prediction regardless of treatment, and predictive, which allow the selection of individuals who are likely to respond to a specific treatment. Several prognostic (cystatin C, cardiac troponins, markers of inflammation, and fibrosis) and predictive (genes, metalloproteinases, and complex classifiers) biomarkers have been developed. Despite previous biomarkers providing information on the pathophysiological mechanisms of CV risk in CKD beyond proteinuria and eGFR, only a minority have been adopted in clinical use. This mainly depends on heterogeneous results and lack of validation of biomarkers. The purpose of this review is to present an update on the already assessed biomarkers of CV risk in CKD and examine the strategies for a correct development of biomarkers in clinical practice. Development of both predictive and prognostic biomarkers is an important task for nephrologists. Predictive biomarkers are useful for designing novel clinical trials (enrichment design) and for better understanding of the variability in response to the current available treatments for CV risk. Prognostic biomarkers could help to improve risk stratification and anticipate diagnosis of CV disease, such as heart failure and coronary heart disease.

Nutraceuticals as a potential adjunct therapy toward improving vascular health in CKD

Chronic kidney disease (CKD) is a major public health epidemic and increases risk for developing cardiovascular disease (CVD). Vascular dysfunction is a major independent risk factor toward increased risk for CVD in CKD. Several mechanisms have been postulated to result in vascular dysfunction in CKD, including oxidative stress-mediated inflammation by redox imbalance and reduced nitric oxide (NO) bioavailability and synthesis. Therefore, strategies that decrease oxidative stress and/or increase NO bioactivity may have major clinical implications toward improving vascular health and reducing the burden of CVD in CKD. Nutraceutical therapy in the form of polyphenols, dietary nitrates, or selective mitochondria-targeting therapies has recently been shown to improve vascular function by reducing oxidative stress and/or increasing NO bioavailability and synthesis. This review, therefore, highlights these three emerging nutraceuticals recently implicated in pathophysiological improvement of vascular function in CKD. This review also describes those pathophysiological mechanisms thought to be responsible for the beneficial effects on the vasculature and possible experimental considerations that may exist within human CKD populations. It is clear throughout this review that human-based mechanistic preclinical and health-related clinical studies are lacking regarding whether nutraceuticals do indeed improve vascular function in patients with CKD. As such, a comprehensive, detailed, and fully integrated understanding of nutraceuticals and vasculature function is necessary in patients with CKD. Many opportunities exist for original mechanistic and therapeutic discoveries and investigations on select nutraceuticals and their impact on vascular outcomes in patients with CKD, and these will remain exciting avenues of research in the future.

Atherosclerosis in Chronic Kidney Disease: More, Less, or Just Different?

Patients with chronic kidney disease (CKD) are at an increased risk of premature mortality, mainly from cardiovascular causes. The association between CKD on hemodialysis and accelerated atherosclerosis was described >40 years ago. However, more recently, it has been suggested that the increase in atherosclerosis risk is actually observed in early CKD stages, remaining stable thereafter. In this regard, interventions targeting the pathogenesis of atherosclerosis, such as statins, successful in the general population, have failed to benefit patients with very advanced CKD. This raises the issue of the relative contribution of atherosclerosis versus other forms of cardiovascular injury such as arteriosclerosis or myocardial injury to the increased cardiovascular risk in CKD. In this review, the pathophysiogical contributors to atherosclerosis in CKD that are shared with the general population, or specific to CKD, are discussed. The NEFRONA study (Observatorio Nacional de Atherosclerosis en NEFrologia) prospectively assessed the prevalence and progression of subclinical atherosclerosis (plaque in vascular ultrasound), confirming an increased prevalence of atherosclerosis in patients with moderate CKD. However, the adjusted odds ratio for subclinical atherosclerosis increased with CKD stage, suggesting a contribution of CKD itself to subclinical atherosclerosis. Progression of atherosclerosis was closely related to CKD progression as well as to the baseline presence of atheroma plaque, and to higher phosphate, uric acid, and ferritin and lower 25(OH) vitamin D levels. These insights may help design future clinical trials of stratified personalized medicine targeting atherosclerosis in patients with CKD. Future primary prevention trials should enroll patients with evidence of subclinical atherosclerosis and should provide a comprehensive control of all known risk factors in addition to testing any additional intervention or placebo.

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.

A Systems-Level View of Renal Metabolomics

The measurement of select circulating metabolites such as creatinine, glucose, and cholesterol are integral to clinical medicine, with implications for diagnosis, prognosis, and treatment. Metabolomics studies in nephrology research seek to build on this paradigm, with the goal to identify novel markers and causal participants in the pathogenesis of kidney disease and its complications. This article reviews three themes pertinent to this goal. Each is rooted in long-established principles of human physiology, with recent updates enabled by metabolomics and other tools. First, the kidney has a broad and heterogeneous impact on circulating metabolites, with progressive loss of kidney function resulting in a multitude of small molecule alterations. Second, an increasing number of circulating metabolites have been shown to possess functional roles, in some cases acting as ligands for specific G-protein-coupled receptors. Third, circulating metabolites traffic through varied, and sometimes complex, interorgan circuits. Taken together, these themes emphasize the importance of viewing renal metabolomics at the systems level, recognizing the diverse origins and physiologic effects of blood metabolites. However, how to synthesize these themes and how to establish clinical relevance remain uncertain and will require further investigation.

Structural analysis of a Petri net model of oxidative stress in atherosclerosis

Atherosclerosis is a complex process of gathering sub-endothelial plaques decreasing lumen of the blood vessels. This disorder affects people of all ages, but its progression is asymptomatic for many years. It is regulated by many typical and atypical factors including the immune system response, a chronic kidney disease, a diet rich in lipids, a local inflammatory process and a local oxidative stress that is here one of the key factors. In this study, a Petri net model of atherosclerosis regulation is presented. This model includes also some information about stoichiometric relationships between its components and covers all mentioned factors. For the model, a structural analysis based on invariants was made and biological conclusions are presented. Since the model contains inhibitor arcs, a heuristic method for analysis of such cases is presented. This method can be used to extend the concept of feasible t-invariants.

Do we still need cross-sectional studies in Nephrology? Yes we do!

Cross-sectional studies represent the second line of evidence (after case reports) in the ladder of evidence aimed at defining disease aetiology. This study design is used to generate hypotheses about the determinants of a given disease but also to investigate the accuracy of diagnostic tests and to assess the burden of a given disease in a population. The intrinsic limitation of cross-sectional studies, when applied to generate aetiological hypotheses, is that both the exposure under investigation and the disease of interest are measured at the same point in time. For this reason, generally the cross-sectional design does not provide definitive proofs about cause-and-effect relationships. An advantage of cross-sectional studies in aetiological and diagnostic research is that they allow researchers to consider many different putative risk factors/diagnostic markers at the same time. For example, in a hypothetical study aimed at generating hypotheses about the risk factors for left ventricular hypertrophy (LVH) in patients with chronic kidney disease, investigators could look at several risk factors as potential determinants of LVH (age, gender, cholesterol, blood pressure, inflammation, etc.) with minimal or no additional costs. In this article, we make examples derived from the nephrology literature to show the usefulness of cross-sectional studies in clinical and epidemiological research.

Serum Asymmetric and Symmetric Dimethylarginine and Morbidity and Mortality in Hemodialysis Patients

BACKGROUND

Asymmetric (ADMA) and symmetric dimethylarginine (SDMA) are putative uremic toxins that may exert toxicity by a number of mechanisms, including impaired nitric oxide synthesis and generation of reactive oxygen species. The study goal was to determine the association between these metabolites and cardiovascular outcomes in hemodialysis patients.

STUDY DESIGN

Post hoc analysis of the Hemodialysis (HEMO) Study.

SETTING & PARTICIPANTS

1,276 prevalent hemodialysis patients with available samples 3 to 6 months after randomization.

PREDICTOR

ADMA and SDMA measured in stored specimens.

OUTCOMES

Cardiac death, sudden cardiac death, first cardiovascular event, and any-cause death. Association with predictors analyzed using Cox regression adjusted for potential confounders (including demographics, clinical characteristics, comorbid conditions, albumin level, and residual kidney function).

RESULTS

Mean age of patients was 57±14 (SD) years, 63% were black, and 57% were women. Mean ADMA (0.9±0.2μmol/L) and SDMA levels (4.3±1.4μmol/L) were moderately correlated (r=0.418). Higher dialysis dose or longer session length were not associated with lower predialysis ADMA or SDMA concentrations. In fully adjusted models, each doubling of ADMA level was associated with higher risk (HR per 2-fold higher concentration; 95% CI) of cardiac death (1.83; 1.29-2.58), sudden cardiac death (1.79; 1.19-2.69), first cardiovascular event (1.50; 1.20-1.87), and any-cause death (1.44; 1.13-1.83). Compared to the lowest ADMA quintile (<0.745 μmol/L), the highest ADMA quintile (≥1.07μmol/L) was associated with higher risk (HR; 95% CI) of cardiac death (2.10; 1.44-3.05), sudden cardiac death (2.06; 1.46-2.90), first cardiovascular event (1.75; 1.35-2.27), and any-cause death (1.56; 1.21-2.00). SDMA level was associated with higher risk for cardiac death (HR, 1.40; 95% CI, 1.03-1.92), but this was no longer statistically significant after adjusting for ADMA level (HR, 1.20; 95% CI, 0.86-1.68).

LIMITATIONS

Single time-point measurement of ADMA and SDMA.

CONCLUSIONS

ADMA and, to a lesser extent, SDMA levels are associated with cardiovascular outcomes in hemodialysis patients.

Association of peripheral arterial disease with all-cause and cardiovascular mortality in hemodialysis patients: a meta-analysis

Background

Recent studies have shown an association between peripheral arterial disease (PAD) and increased risk of mortality in hemodialysis (HD) patients; however, the estimates vary widely and are inconsistent. It is necessary to elucidate the degree of mortality risk for PAD patients in HD population.

Methods

PubMed, EMBASE, Web of Science and Cochrane Library (from inception to September 4th, 2016) were systematically searched for cohort studies assessing the association between PAD and mortality in HD patients. We calculated the pooled risk ratios (RRs) with 95% confidence intervals (CI) of all-cause and cardiovascular (CV) mortality using random effects models. Subgroup analyses were conducted to explore the source of heterogeneity.

Results

The search identified 2,973 potentially eligible records and 10 studies (n = 32,864) were included. Our meta-analysis revealed that PAD significantly increased the risk of all-cause mortality (RR 2.15, 95 % CI 1.67–2.77, n = 32,864) and CV mortality (RR 2.99, 95 % CI 1.66-5.38, n = 31,794) in HD patients after multivariate adjustment. Subgroup analyses showed the study design and follow-up time might be two sources of heterogeneity.

Conclusion

PAD may be a prognostic marker of all-cause and CV mortality in HD patients. More attention should be paid to diagnosis and management of PAD in HD patients.

Electronic supplementary material

The online version of this article (doi:10.1186/s12882-016-0397-1) contains supplementary material, which is available to authorized users.

Parasympathetic innervation of vertebrobasilar arteries: is this a potential clinical target?

This review aims to summarise the contemporary evidence for the presence and function of the parasympathetic innervation of the cerebral circulation with emphasis on the vertebral and basilar arteries (the posterior cerebral circulation). We consider whether the parasympathetic innervation of blood vessels could be used as a means to increase cerebral blood flow. This may have clinical implications for pathologies associated with cerebral hypoperfusion such as stroke, dementia and hypertension. Relative to the anterior cerebral circulation little is known of the origins and neurochemical phenotypes of the parasympathetic innervation of the vertebrobasilar arteries. These vessels normally provide blood flow to the brainstem and cerebellum but can, via the Circle of Willis upon stenosis of the internal carotid arteries, supply blood to the anterior cerebral circulation too. We review the multiple types of parasympathetic fibres and their distinct transmitter mechanisms and how these vary with age, disease and species. We highlight the importance of parasympathetic fibres for mediating the vasodilatory response to sympathetic activation. Current trials are investigating the possibility of electrically stimulating the postganglionic parasympathetic ganglia to improve cerebal blood flow to reduce the penumbra following stroke. We conclude that although there are substantial gaps in our understanding of the origins of parasympathetic innervation of the vertebrobasilar arteries, activation of this system under some conditions might bring therapeutic benefits.

Asymmetric Dimethylarginine (ADMA) Levels Are Lower in Hemodialysis Patients Treated With Paricalcitol

Introduction

Chronic kidney disease is a major public health problem. In the last decade, it has been shown that the early stages of chronic kidney disease are associated with an inflammatory condition involving an increased risk of cardiovascular morbidity and long-term mortality. In patients with chronic kidney disease and more specifically those on hemodialysis, cardiovascular events are the most common cause of death. Asymmetric dimethylarginine (ADMA) is an endogenous inhibitor of nitric oxide synthase and may be an independent risk factor for endothelial dysfunction and cardiovascular disease.

Methods

We performed a cross-sectional analysis to identify factors that were associated with ADMA such as certain medications related to cardiovascular disease in dialysis patients.

Results

Patients who were treated with paricalcitol had significantly lower levels of ADMA (0.21 ± 0.19 μmol/l) compared with those not treated with paricalcitol (0.42 ± 0.35 μmol/l) (P = 0.00027). Dividing ADMA levels by quartiles, patients treated with paricalcitol were less likely to have very high level ADMA (P = 0.014), whereas there were no significant differences with other medications. Higher dose of paricalcitol was also related to lower levels of ADMA noting an inverse correlation (r = –0.36, P = 0.013).

Discussion

Hemodialysis patients treated with paricalcitol presented significantly decreased ADMA levels compared with those who did not receive this treatment. Possible beneficial effects in terms of cardiovascular morbidity and mortality by paricalcitol and its association with ADMA and nitric oxide synthesis are unknown. Studies to confirm this effect and determine the underlying pathophysiological mechanism are necessary.

Liver plays a central role in asymmetric dimethylarginine-mediated organ injury

Asymmetric-dimethylarginine (ADMA) competes with L-arginine for each of the three isoforms of nitric oxide synthase: endothelial; neuronal; inducible. ADMA is synthesized by protein methyltransferases followed by proteolytic degradation. ADMA is metabolized to citrulline and dimethylamine, by dimethylarginine dimethylaminohydrolase (DDAH) and enters cells through cationic amino-acid transporters extensively expressed in the liver. The liver plays a crucial role in ADMA metabolism by DDAH-1 and, as has been recently demonstrated, it is also responsible for ADMA biliary excretion. A correlation has been demonstrated between plasma ADMA levels and the degree of hepatic dysfunction in patients suffering from liver diseases with varying aetiologies: plasma ADMA levels are increased in patients with liver cirrhosis, alcoholic hepatitis and acute liver failure. The mechanism by which liver dysfunction results in raised ADMA concentrations is probably due to impaired activity of DDAH due to severe inflammation, oxidative stress, and direct damage to DDAH. High plasma ADMA levels are also relevant as they are associated with the onset of multi-organ failure (MOF). Increased plasma concentration of ADMA was identified as an independent risk factor for MOF in critically-ill patients causing enhanced Intensive Care Unit mortality: a significant reduction in nitric oxide synthesis, leading to malperfusion in various organs, eventually culminating in multi organs dysfunction.

Asymmetric Dimethylarginine and Augmentation Index in Newly Diagnosed Patients With Hypertension

Pulse wave velocity (PWV), augmentation index (Aix), and central aortic pressure (CAP) are arterial stiffness markers of endothelial dysfunction (ED). We investigated the relationship between arterial stiffness parameters and asymmetric dimethylarginine (ADMA; a marker of ED), in newly diagnosed patients with hypertension (n = 101; 61 females). These patients were investigated in accordance with the recommendations of hypertension guidelines. Arterial stiffness was measured, and serum ADMA and C-reactive protein (CRP; a marker of inflammation) levels were determined. In both women and men, there was no difference in terms of age, body mass index, systolic and diastolic blood pressures, PWV, CAP and the levels of ADMA, while Aix and CRP levels were significantly higher in women ( P = .004, P = .046, respectively). In the whole group, ADMA levels correlated with Aix (Pearson r = .237, P = .024). Our findings provide further evidence of a link between arterial stiffness and ED in newly diagnosed patients with hypertension.

Association of angiopoietin-2 with renal outcome in chronic kidney disease

Background

The pathophysiological mechanisms of renal function progression in chronic kidney disease (CKD) have still not been completely explored. In addition to well-known traditional risk factors, non-traditional risk factors, such as endothelial dysfunction, have gradually attracted physicians' attention. Angiopoietin-2 (Ang-2) impairs endothelial function through preventing angiopoietin-1 from binding to Tie2 receptor. Whether Ang-2 is associated with renal function progression in CKD is unknown.

Methods

This study enrolled 621 patients with stages 3–5 CKD to assess the association of circulating Ang-2 with commencing dialysis, doubling creatinine and rapid decline in renal function (the slope of estimated glomerular filtration rate (eGFR) greater than 5 ml/min per 1.73 m²/y) over follow-up of more than 3 years.

Results

Of all patients, 224 patients (36.1%) progressed to commencing dialysis and 165 (26.6%) reached doubling creatinine. 85 subjects (13.9%) had rapid decline in renal function. Ang-2 quartile was divided at 1494.1, 1948.8, and 2593.1 pg/ml. The adjusted HR of composite outcomes, either commencing dialysis or doubling creatinine was 1.53 (95% CI: 1.06–2.23) for subjects of quartile 4 compared with those of quartile 1. The adjusted OR for rapid decline in renal function was 2.96 (95% CI: 1.13–7.76) for subjects of quartile 4 compared with those of quartile 1. The linear mixed-effects model shows a more rapid decrease in eGFR over time in patients with quartile 3 or more of Ang-2 than those with the lowest quartile of Ang-2.

Conclusions

Ang-2 is an independent predictor of adverse renal outcome in CKD. Further study is needed to identify the pathogenic role of Ang-2 in CKD progression.

Changes in ADMA/DDAH pathway after hepatic ischemia/reperfusion injury in rats: the role of bile

We investigated the effects of hepatic ischemia/reperfusion (I/R) injury on asymmetric dimethylarginine (ADMA, a nitric oxide synthase inhibitor), protein methyltransferase (PRMT) and dimethylarginine dimethylaminohydrolase (DDAH) (involved, resp., in ADMA synthesis and degradation), and the cationic transporter (CAT). Male Wistar rats were subjected to 30 or 60 min hepatic ischemia followed by 60 min reperfusion. ADMA levels in serum and bile were determined. Tissue ADMA, DDAH activity, DDAH-1 and CAT-2 protein, DDAH-1 and PRMT-1 mRNA expression, GSH/GSSG, ROS production, and lipid peroxidation were detected. ADMA was found in bile. I/R increased serum and bile ADMA levels while an intracellular decrease was detected after 60 min ischemia. Decreased DDAH activity, mRNA, and protein expression were observed at the end of reperfusion. No significant difference was observed in GSH/GSSG, ROS, lipid peroxidation, and CAT-2; a decrease in PRMT-1 mRNA expression was found after I/R. Liver is responsible for the biliary excretion of ADMA, as documented here for the first time, and I/R injury is associated with an oxidative stress-independent alteration in DDAH activity. These data are a step forward in the understanding of the pathways that regulate serum, tissue, and biliary levels of ADMA in which DDAH enzyme plays a crucial role.

Increased serum levels of GDF-15 associated with mortality and subclinical atherosclerosis in patients on maintenance hemodialysis

BACKGROUND/AIMS

Increased carotid intima-media thickness (CIMT) was shown to be an independent predictor of cardiovascular (CV) mortality in dialysis patients and the general population. Growth differentiation factor 15 (GDF-15), a member of the transforming growth factor superfamily, is produced by cardiomyocytes and atherosclerotic lesions under stress conditions such as inflammation. We assessed associations between serum concentrations of GDF-15, mortality, and CIMT for subclinical atherosclerosis in hemodialysis (HD) patients.

METHODS

A total of 87 patients on maintenance hemodialysis and 45 sex- and age-matched healthy controls were included in this prospective study. Serum GDF-15 levels were measured by ELISA. CIMT was assessed by Doppler ultrasonography. The association between serum GDF-15 levels and mortality was assessed using Cox regression analysis with serum levels categorized into two groups according to the median value (328.18 pg/ml). Patients were followed for 2 years and cause-specific and all-cause mortality were determined.

RESULTS

The median level of serum GDF-15 was significantly higher in HD patients than controls [328 (198-522) vs. 176 (101-289) pg/ml, p < 0.01, respectively]. Serum GDF-15 levels were correlated to CIMT (r = 0.607, p < 0.001), C-reactive protein (CRP; r = 0.250, p = 0.010), HD duration (r = 0.376, p = 0.004), and serum albumin (r = - 0.156, p = 0.030). The multivariate analysis revealed that GDF-15 was found to be an independent variable of CIMT in HD patients. In the study, the serum GDF-15 level was an independent marker of all-cause of mortality when adjusted for age, CRP, and history of diabetes mellitus.

CONCLUSION

The relationship between serum GDF-15, mortality, and carotid artery thickening suggests that GDF-15 may be a novel marker of atherosclerosis, inflammation, and malnutrition in HD patients.

Gender differences in oxidative and nitrosative stress parameters in kidney transplant patients on tacrolimus-based immunosuppression

BACKGROUND

Cardiovascular (CV) morbidity and mortality rates are still higher after kidney transplantation than in general population. It is known that oxidative and nitrosative stress may contribute to the progress of CV disease in a post-transplant period, but still gender aspect has not been elucidated completely. The aim of this study was to analyze the gender differences in the oxidative and nitrosative stress parameters, as well as asymmetric dimethylarginine (ADMA) and symmetric dimethylarginine (SDMA) levels among kidney transplant patients on tacrolimus-based immunosuppression.

METHODS

Our research included 35 patients (20 men and 15 women) with renal transplant and 25 healthy volunteers. Patients were on chronic immunosuppressive regimen, which included tacrolimus, mycophenolate mofetil and prednisone. In order to estimate oxidative and nitrosative stress, we determined plasma levels of thiobarbituric acid-reactive substances (TBARS), activity of catalase (CAT), levels of total (protein and non-protein) sulfhydryl (SH) groups, advanced oxidation protein products (AOPP), ADMA and SDMA, as well as nitrite/nitrate (NOx) ratio.

RESULTS

TBARS, CAT and SH in plasma were significantly higher in male patients than in female patients (p < 0.05, p < 0.01 and p < 0.05, respectively). There were no gender-dependent differences in AOPP, ADMA, SDMA and NOx in kidney transplant patients. Correlation analysis, Pearson and Spearman, showed significant correlations between tested oxidative and nitrosative stress parameters in male kidney transplant patients. Alternatively, in female patients, there were no significant correlations between tested parameters.

CONCLUSION

Our findings show that men might be more prone to oxidative damage than women. ADMA, the proven marker of CV morbidity and mortality, may be more significant in male kidney transplant patients concerning oxidative stress control of its level and function.

Chronic kidney disease and cardiovascular risk: epidemiology, mechanisms, and prevention

Since the first description of the association between chronic kidney disease and heart disease, many epidemiological studies have confirmed and extended this finding. As chronic kidney disease progresses, kidney-specific risk factors for cardiovascular events and disease come into play. As a result, the risk for cardiovascular disease is notably increased in individuals with chronic kidney disease. When adjusted for traditional cardiovascular risk factors, impaired kidney function and raised concentrations of albumin in urine increase the risk of cardiovascular disease by two to four times. Yet, cardiovascular disease is frequently underdiagnosed and undertreated in patients with chronic kidney disease. This group of patients should, therefore, be acknowledged as having high cardiovascular risk that needs particular medical attention at an individual level. This view should be incorporated in the development of guidelines and when defining research priorities. Here, we discuss the epidemiology and pathophysiological mechanisms of cardiovascular risk in patients with chronic kidney disease, and discuss methods of prevention.

Angiopoietin-2 is associated with albuminuria and microinflammation in chronic kidney disease

Although cardiovascular disease (CVD) is the leading cause of mortality in patients with chronic kidney disease (CKD), the pathophysiology is not thoroughly understood. Given that elevated albuminuria or circulating angiopoietin-2 associates with CVD and mortality in CKD patients, we were intrigued by the relationship between albuminuria and angiopoietin-2. A total of 416 patients with CKD stages 3 to 5 were stratified by urine albumin-creatinine ratio as normoalbuminuria (<30 mg/g), microalbuminuria (30–300 mg/g), or macroalbuminuria (>300 mg/g). The levels of plasma angiopoietin-2 and vascular endothelial growth factor (VEGF) increased, and soluble Tie-2 decreased in the subgroups of albuminuria; whereas angiopoietin-1 did not change. Linear regression showed a positive correlation between urine albumin-creatinine ratio (ACR) and plasma angiopoietin-2 (correlation coefficient r = 0.301, 95% confidence interval 0.211–0.386, P<0.0001), but not between ACR and VEGF or soluble Tie-2. Multivariate linear regression analysis showed that plasma angiopoietin-2 was independently associated with ACR (P = 0.025). Furthermore, plasma angiopoietin-2 was positively correlated with high sensitive C-reactive protein (r = 0.114, 95% confidence interval 0.018–0.208, P = 0.020). In conclusion, plasma angiopoietin-2 was associated with albuminuria and markers of systemic microinflammation in CKD patients. Although previous evidence has shown that angiopoietin-2 destabilizes vasculature and induces inflammation in different scenarios, further study will be required to delineate the role of angiopoietin-2 in albuminuria and microinflammation in CKD patients.

Effect of enzyme replacement therapy on serum asymmetric dimethylarginine levels, coronary flow reserve and left ventricular hypertrophy in patients with Fabry disease

Background

Fabry disease (FD) is a rare disorder and one of the causes of progressive renal and cardiac dysfunction. FD results from an X-linked recessive lysosomal storage disorder caused by a defect in the gene encoding lysosomal α-galactosidase A. Although accumulation of globotriaosylceramide leads to renal and cardiac manifestations, the precise mechanisms remain unclear. Coronary microvascular dysfunction may be one of the causes of cardiac complications in FD. We aimed to assess coronary flow reserve (CFR) and the effect of enzyme replacement therapy (ERT) on coronary microvascular dysfunction.

Methods

Four FD patients who had never received ERT were included. The serum asymmetric dimethylarginine (ADMA) level, as a marker of endothelial dysfunction, was measured. Two-dimensional guided M-mode echocardiography was performed to measure left ventricular wall mass. Adenosine-triphosphate stress transthoracic Doppler echocardiography was used to measure CFR before starting ERT and at 3, 6 and 12 months.

Results

All the patients tolerated ERT without any side effects. At the baseline, two patients had impaired CFR, increased left ventricular mass index (LVMI) and elevated serum ADMA levels. Twelve months after starting ERT, CFR was increased in all patients, and LVMI and serum ADMA levels decreased in two patients. Furthermore, serum ADMA levels significantly correlated with CFR (r = −0.576, P < 0.05) and LVMI (r = 0.874, P < 0.0001).

Conclusions

The results suggest that ERT prevented the progression of cardiac abnormalities, possibly by improving coronary microvascular dysfunction. ADMA may be a useful surrogate marker in FD.

Arginine-based inhibitors of nitric oxide synthase: therapeutic potential and challenges

In the past three decades, nitric oxide has been well established as an important bioactive molecule implicated in regulation of cardiovascular, nervous, and immune systems. Therefore, it is not surprising that much effort has been made to find specific inhibitors of nitric oxide synthases (NOS), the enzymes responsible for production of nitric oxide. Among the many NOS inhibitors developed to date, inhibitors based on derivatives and analogues of arginine are of special interest, as this category includes a relatively high number of compounds with good potential for experimental as well as clinical application. Though this group of inhibitors covers early nonspecific compounds, modern drug design strategies such as biochemical screening and computer-aided drug design have provided NOS-isoform-specific inhibitors. With an emphasis on major advances in this field, a comprehensive list of inhibitors based on their structural characteristics is discussed in this paper. We provide a summary of their biochemical properties as well as their observed effects both in vitro and in vivo. Furthermore, we focus in particular on their pharmacology and use in recent clinical studies. The potential of newly designed specific NOS inhibitors developed by means of modern drug development strategies is highlighted.

Immune and inflammatory pathways are involved in inherent bone marrow ossification

BACKGROUND

Bone marrow plays a key role in bone formation and healing. Although a subset of marrow explants ossifies in vitro without excipient osteoinductive factors, some explants do not undergo ossification. The disparity of outcome suggests a significant heterogeneity in marrow tissue in terms of its capacity to undergo osteogenesis.

QUESTIONS/PURPOSES

We sought to identify: (1) proteins and signaling pathways associated with osteogenesis by contrasting the proteomes of ossified and poorly ossified marrow explants; and (2) temporal changes in proteome and signaling pathways of marrow ossification in the early and late phases of bone formation.

METHODS

Explants of marrow were cultured. Media conditioned by ossified (n = 4) and poorly ossified (n = 4) subsets were collected and proteins unique to each group were identified by proteomic analysis. Proteomic data were processed to assess proteins specific to the early phase (Days 1-14) and late phase (Days 15-28) of the culture period. Pathways involved in bone marrow ossification were identified through bioinformatics.

RESULTS

Twenty-eight proteins were unique to ossified samples and eight were unique to poorly ossified ones. Twelve proteins were expressed during the early phase and 15 proteins were specific to the late phase. Several identified pathways corroborated those reported for bone formation in the literature. Immune and inflammatory pathways were specific to ossified samples.

CONCLUSIONS

The marrow explant model indicates the inflammatory and immune pathways to be an integral part of the osteogenesis process.

Insulin resistance in patients with chronic kidney disease

Metabolic syndrome and its components are associated with chronic kidney disease (CKD) development. Insulin resistance (IR) plays a central role in the metabolic syndrome and is associated with increased risk for CKD in nondiabetic patients. IR is common in patients with mild-to-moderate stage CKD, even when the glomerular filtration rate is within the normal range. IR, along with oxidative stress and inflammation, also promotes kidney disease. In patients with end stage renal disease, IR is an independent predictor of cardiovascular disease and is linked to protein energy wasting and malnutrition. Systemic inflammation, oxidative stress, elevated serum adipokines and fetuin-A, metabolic acidosis, vitamin D deficiency, depressed serum erythropoietin, endoplasmic reticulum stress, and suppressors of cytokine signaling all cause IR by suppressing insulin receptor-PI3K-Akt pathways in CKD. In addition to adequate renal replacement therapy and correction of uremia-associated factors, thiazolidinedione, ghrelin, protein restriction, and keto-acid supplementation are therapeutic options. Weight control, reduced daily prednisolone dosage, and the use of cyclosporin decrease the risk of developing new-onset diabetes after kidney transplantation. Improved understanding of the pathogenic mechanisms underlying IR in CKD may lead to more effective therapeutic strategies to reduce uremia-associated morbidity and mortality.

Evaluation of arterial structure and function in pediatric patients with end-stage renal disease on dialysis and after renal transplantation

CVD is a major cause of morbidity and mortality in pediatric patients with CKD. It is unclear whether vascular abnormalities in these patients are reversible, and if transplantation portends salutary effects on arterial function. We compared FMD, PWV, AI75, and CIMT in 15 dialysis (D), 14 transplant patients (T), and 15 controls (C), and their associations with cardiovascular risk factors. There was stepwise lower FMD (p < 0.001), higher AI75 (p < 0.001), higher PWV (p = 0.01), and higher CIMT SDS for age (p = 0.03) and height (p = 0.006) in the D group than T and C groups. FMD, PWV, and CIMT were unrelated to dialysis duration or time from transplantation. On multivariate analysis, group status was independently associated with FMD (β = 3.15, p = 0.002), AI75 (β = -5.95, p = 0.01), PWV (β = -0.57, p = 0.07) and CIMT (β = -0.02, p = 0.04) and CIMT SDS for height (β = -0.541, p = 0.009). FMD is lower and AI75, PWV and CIMT are higher in pediatric patients maintained on D than T/C. T patients have similar AI75, PWV and CIMT to C although FMD remains reduced. These findings suggest that transplantation stabilizes or improves CKD associated arteriopathy.

Nitric oxide (NO) and asymmetric dimethylarginine (ADMA): their pathophysiological role and involvement in intracerebral hemorrhage

OBJECTIVE

Nitric oxide (NO) has a variety of functions in physiological systems, particularly in the vasculature and the central nervous system. Currently, the imbalance of the pathway involving nitric oxide, nitric oxide synthase, and asymmetric dimethylarginine (NO-NOS-ADMA) is increasingly discussed in connection with endothelial dysfunction. Knowledge about the role of this pathway in intracerebral hemorrhage (ICH), which represents the most devastating stroke subtype, is increasing but still sparse. This article aims to review the current knowledge about the role and metabolism of NO and ADMA. It will also address the role of the NO-NOS-ADMA pathway in ICH and delineate some questions that should be addressed by future studies.

METHODS

A literature search regarding the data about NO, NOS, and ADMA and its role in ICH was conducted in PubMed.

RESULTS

Experimental data from cell culture and animal models indicate that, after the occurrence of ICH, neuronal and inducible nitric oxide synthases (nNOS and iNOS) are both overexpressed and uncoupled through the induction of blood compound metabolites, including thrombin and inflammatory mediators. ADMA, the most potent endogenous inhibitor of NOS, is also overproduced following dysregulation of its metabolizing enzymes. Dysfunction of the NO-NOS-ADMA pathway results in cell death, blood-brain barrier (BBB) disruption, and brain edema via different pathological mechanisms. However, the available data from clinical studies are still rare and partially contradictory.

CONCLUSION

Experimental data suggest an important role for the NO-NOS-ADMA pathway for secondary injury after ICH. Since the literature shows contradictory results, further studies are needed to address current confusion.

Chronic kidney disease, insulin resistance, and incident diabetes in older adults

BACKGROUND AND OBJECTIVES

Insulin resistance is a complication of advanced CKD. Insulin resistance is less well characterized in earlier stages of CKD. The response of the pancreatic β cell, effects on glucose tolerance, and risk of diabetes are not clear.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

The Cardiovascular Health Study included 4680 adults without baseline diabetes. The Chronic Kidney Disease Epidemiology Collaboration creatinine equation was used to obtain the estimated GFR (eGFR). Insulin resistance was evaluated as fasting insulin concentration. The insulin sensitivity index, β cell function, and glucose tolerance were assessed by oral glucose tolerance testing. Incident diabetes was defined as fasting glucose ≥126 mg/dl, nonfasting glucose ≥200 mg/dl, or use of glucose-lowering medications.

RESULTS

Mean age was 72.5 years (range, 65-98 years). Mean eGFR was 72.2 (SD 17.1) ml/min per 1.73 m(2). After adjustment, each 10 ml/min per 1.73 m(2) lower eGFR was associated with a 2.2% higher fasting insulin concentration (95% confidence interval [CI], 1.4%, 2.9%; P<0.001) and a 1.1% lower insulin sensitivity index (95% CI, 0.03%, 2.2%; P=0.04). Surprisingly, eGFR was associated with an augmented β cell function index (P<0.001), lower 2-hour glucose concentration (P=0.002), and decreased risk of glucose intolerance (P=0.006). Over a median 12 years' follow-up, 437 participants (9.3%) developed diabetes. eGFR was not associated with the risk of incident diabetes.

CONCLUSIONS

Among older adults, lower eGFR was associated with insulin resistance. However, with lower eGFR, β cell function was appropriately augmented and risks of impaired glucose tolerance and incident diabetes were not increased.

Role of the human erythrocyte in generation and storage of asymmetric dimethylarginine

Proteolytic activity in whole blood may lead to release of the endogenous nitric oxide synthase inhibitor asymmetric dimethylarginine (ADMA). We investigated the role of the human erythrocyte in storage and generation of ADMA in healthy controls (n = 36) and critically ill patients (n = 38). Both free and total (sum of free and protein-incorporated) ADMA were measured. Upon incubation of intact erythrocytes with extracellular ADMA (0 to 40 μmol/l), equilibrium between intra- and extracellular ADMA was reached within 3 h. Compared with controls, patients had significantly higher basal concentrations of ADMA in plasma (0.88 ± 0.75 vs. 0.41 ± 0.07 μmol/l) and erythrocytes (1.28 ± 0.55 vs. 0.57 ± 0.14 μmol/l). Intracellular and plasma ADMA were significantly correlated in the patient group only (r = 0.834). Upon lysis, followed by incubation at 37°C for 2 h, free ADMA increased sevenfold (to 8.60 ± 3.61 μmol/l in patients and 3.90 ± 0.78 μmol/l in controls). In lysates of controls, free ADMA increased further to 9.85 ± 1.35 μmol/l after 18 h. Total ADMA was 15.43 ± 2.44 μmol/l and did not change during incubation. The increase of free ADMA during incubation corresponded to substantial release of ADMA from the erythrocytic protein-incorporated pool (21.9 ± 4.6% at 2 h and 60.8 ± 7.6% at 18 h). ADMA was released from proteins other than hemoglobin, which only occurred after complete lysis and was blocked by combined inhibition of proteasomal and protease activity. Neither intact nor lysed erythrocytes mediated degradation of free ADMA. We conclude that intact erythrocytes play an important role in storage of ADMA, whereas upon erythrocyte lysis large amounts of free ADMA are generated by proteolysis of methylated proteins, which may affect plasma levels in hemolysis-associated diseases.

Measurement of insulin resistance in chronic kidney disease

PURPOSE OF REVIEW

Insulin resistance is a known complication of end-stage renal disease that also appears to be present in earlier stages of chronic kidney disease (CKD). It is a risk factor for cardiovascular disease and an important potential therapeutic target in this population. Measurement of insulin resistance is reviewed in the context of known pathophysiologic abnormalities in CKD.

RECENT FINDINGS

Insulin resistance in CKD is due to a high prevalence of known risk factors (e.g. obesity) and to unique metabolic abnormalities. The site of insulin resistance in CKD is localized to skeletal muscle. Estimates based on fasting insulin concentration may not adequately capture insulin resistance in CKD because they largely reflect hepatic defects and because CKD impairs insulin catabolism. A variety of dynamic tests are available to directly measure insulin-mediated glucose uptake.

SUMMARY

Insulin resistance may be an important therapeutic target in CKD. Complementary methods are available to assess insulin resistance, and each method has unique advantages, disadvantages, and levels of complexity. These characteristics, and the likelihood that CKD alters the performance of some insulin resistance measurements, must be considered when designing and interpreting clinical studies.

Asymmetric dimethylarginine may mediate increased heat pain threshold in experimental chronic kidney disease

BACKGROUND

Thermal sensitivity in uraemia is decreased. Non-selective synthetic nitric oxide synthase (NOS) inhibitors significantly attenuate thermal hyperalgesia in preclinical models. The aim of our study was to evaluate the effect of experimental uraemia, which is associated with an increase of the endogenous NOS inhibitor asymmetric dimethylarginine (ADMA), on thermal sensitivity in rats. Furthermore, we intended to study the effect of chronic ADMA infusion alone on thermal sensitivity.

METHODS

Male Sprague-Dawley rats (n = 54), 10 weeks old, weight 370-430 g, were randomly assigned to three groups receiving either (i) isotonic saline or (ii) ADMA via osmotic mini pumps or (iii) underwent 5/6 nephrectomy (Nx). After 14 days, 50% of all animals from all groups underwent thermal sensitivity testing and terminal blood draw. After 28 days, the remaining animals underwent the same procedures. Thermal sensitivity examination was performed by the hot-plate test, measuring time from heat exposition to first paw licking or jumping of the animal.

RESULTS

While the median [interquartile range] latency time between heat exposition to first paw licking or jumping of the animal in the NaCl infusion group remained unchanged between Day 14 (8.4 [6.75-11.50] s) and Day 28 (7.35 [6.10-7.90] s) both, ADMA infusion and 5/6 nephrectomy tended to increase the thermal pain threshold at Day 14 (9.25 [6.55-12.18] s) and (9.50 [5.8 ± 11.0] s), respectively, compared to NaCl on Day 14 (8.4 [6.75-11.50] s). This difference became statistical significant at Day 28 where the median latency time in the ADMA group (13.10 [11.85-15.95] s) and in the 5/6 Nx group (13.50 [10.85-17.55] s) were significantly higher than in the NaCl group (7.35 [6.10-7.90] s).

CONCLUSIONS

Induction of progressive renal failure in rats by 5/6 nephrectomy, which is accompanied by a marked increase of the serum levels of the endogenous NOS inhibitor ADMA, leads to a significantly increased heat pain threshold at 28 days. The sole infusion of ADMA into healthy rats leads to the same increase in heat pain threshold.

Sympathetic nerve traffic and asymmetric dimethylarginine in chronic kidney disease

BACKGROUND AND OBJECTIVES

Sympathetic overactivity and high levels of the endogenous inhibitor of NO synthase asymmetric dimethylarginine (ADMA) are prevalent risk factors in chronic kidney disease (CKD).

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

In 48 stage 2 to 4 CKD patients, we investigated the relationship between efferent postganglionic muscle sympathetic nerve traffic (microneurography) and circulating ADMA and analyzed the links between these risk factors and estimated GFR (eGFR), proteinuria, and different parameters of left ventricular (LV) geometry.

RESULTS

CKD patients characterized by sympathetic nerve traffic values in the third tertile showed the highest ADMA levels, and this association was paralleled by a continuous, positive relationship between these two risk factors (r = 0.32, P = 0.03) independent of other confounders. Both sympathetic nerve traffic and ADMA were inversely related to eGFR and directly to proteinuria and LV geometry. Remarkably, the variance of eGFR, proteinuria, and LV geometry explained by sympathetic nerve traffic and ADMA largely overlapped because sympathetic nerve traffic but not ADMA was retained as a significant correlate of the eGFR (P < 0.001) and of the relative wall thickness or the left ventricular mass index/LV volume ratio (P = 0.05) in models including both risk factors. ADMA, but not sympathetic nerve traffic, emerged as an independent correlate of proteinuria (P = 0.003) in a model including the same covariates.

CONCLUSIONS

Sympathetic activity and ADMA may share a pathway leading to renal disease progression, proteinuria, and LV concentric remodeling in CKD patients.