Liquid chromatography-tandem mass spectrometry method for the analysis of asymmetric dimethylarginine in human plasma

High-throughput quantitation of serological dimethylarginines by LC/MS/MS: Potential cardiovascular biomarkers for rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic autoimmune disorder characterized by systemic inflammation of the joints and extra-articular tissues. The incidence of cardiovascular disease (CVD) remains the main cause of morbidity and mortality in patients with RA. Despite the development of new therapeutics targeting the articular manifestations, the relief of the cardiovascular burden is still an unmet medical need during the management of RA. So, the early prognosis of RA-associated CVD plays a crucial role in improving the clinical outcomes of RA patients. Recently, circulating dimethylarginines have gained attention as potential biomarkers for CVDs. Here, we present the development and validation of a high-throughput liquid chromatography-tandem mass spectrometric (LC/MS/MS) method for simultaneous quantification of creatinine, arginine, and dimethylarginines in human serum within 2 mins by isotope dilution mass spectrometry. This method employed a protein precipitation method for rapid sample preparation, trichloroacetic acid (TCA)-based ion pairing chromatography for fast analyte separation, and multiple reaction monitoring (MRM) with stable isotope-labeled internal standards (ISs) for simultaneous quantitation. To assure the quality, our method was validated against the FDA guidelines for lower limit of quantitation (0.2 µM), linearity (square of coefficient correlation>0.99), precision (intra-&inter-assay imprecision < 10 %), accuracy (intra-&inter-assay inaccuracy < 10 %), sample preparation recovery (recovery ≥ 90 %), stability (instability < 10 %), matrix effect (signal suppression < 55 %), and carryover ( < 0.01 %). Afterward, we applied the validated method to a retrospective cross-sectional study. We aimed to evaluate the utility of serological dimethylarginines as potential cardiovascular biomarkers in the development of RA-associated CVD. Our results revealed that the serological ratio of asymmetric dimethylarginine (ADMA) and symmetric dimethylarginine (SDMA), an indicator of physiological arginine methylation status, was significantly elevated in patients with RA. This finding might provide value in detecting CVD to improve clinical outcomes in RA management.

Comparison between one and two-dimensional liquid chromatographic approaches for the determination of plasmatic stroke biomarkers by isotope dilution and tandem mass spectrometry

This work presents the evaluation of one- and two-dimensional liquid chromatography for the quantification of three stroke outcome predictors in plasma. Isotopically labelled analogues of L-arginine (L-Arg), asymmetric dimethylarginine (ADMA) and symmetric dimethylarginine (SDMA) are used to quantify the three analytes by isotope dilution and tandem mass spectrometry. Chromatographic isotope effects were not observed between natural L-Arg and its ¹⁵N-labelled analogue but they were observed between natural ADMA and SDMA and their multiple deuterated analogues. Under these conditions, bidimensional chromatography through the use of an automated multiple heart cutting mode provided unsatisfactory results for ADMA and SDMA due to the different amounts of natural and labelled compounds transferred from the first to the second chromatographic dimension. In contrast, using one dimensional liquid chromatography after a derivatization step to esterify carboxylic groups, chromatographic isotope effects did not alter the initial mass balance as full coelution of natural and labelled analogues or baseline resolution between the analytes was not required. This method was successfully validated following the Clinical & Laboratory Standards Institute guidelines and applied to the analysis of plasma samples from patients who had suffered from an intraparenchymal haemorrhagic stroke.

Short-Term Effects of Supplemental L-Arginine, Diosmin, Troxerutin, and Hesperidin in Diabetic Patients: A Pilot Study

Background and Aims

Inflammatory, oxidative stress, and endothelial dysfunction play a key role in the pathogenesis of long-term cardiovascular complications in patients with diabetes. The present observational prospective study is aimed at evaluating the effects of micronutrients and phytochemicals contained in the dietary supplement Flebotrofine® (AMNOL Chimica Biologica) on biochemical markers of inflammation, endothelial dysfunction, and glycemic control in patients with diabetes.

Methods

105 type 1 or type 2 diabetes patients regularly took a daily dose of the dietary supplement Flebotrofine® for three consecutive months, and haematological and biochemical parameters were checked at baseline, after three months of treatment, and one month after its suspension. Statistical comparison of the laboratory parameters was performed using the two-tailed ANOVA test for repeated samples with a statistical significance level set at p < 0.05.

Results

The daily use of Flebotrofine® did not change the glycemic metabolic compensation of enrolled patients. After three months of regular Flebotrofine® intake, the plasma levels of the antioxidant β-carotene and of arginine were significantly higher compared with the baseline values, with a decrease in the ADMA/arginine ratio. In contrast, apolipoprotein B, ApoB/ApoA1 ratio, and platelet and leukocyte counts significantly dropped.

Conclusion

The daily use of Flebotrofine® might be a valid supplement of arginine, the precursor of NO, and essential in the prevention of endothelial dysfunction. The regular intake of arginine and phytochemicals also improved the antioxidant and antithrombotic profile of enrolled patients. Therefore, Flebotrofine® could be a useful dietary supplement to prevent long-term complications in patients with diabetes.

Developing a robust, fast and reliable measurement method for the analysis of methylarginine derivatives and related metabolites

Background

Nitric oxide (NO) plays an important role in endothelial homeostasis. Asymmetric dimethyl arginine (ADMA), L-N monomethyl arginine (L-NMMA) and symmetric dimethyl arginine (SDMA), which are derivatives of methylarginine, directly or indirectly reduce NO production. Therefore, these metabolites are an important risk factor for various diseases, including cardiovascular diseases. Numerous methods have been developed for the measurement of methylarginine derivatives, but various difficulties have been encountered. This study aimed to develop a reliable, fast and cost-effective method for the analysis and measurement of methylarginine derivatives (ADMA, SDMA, L-NMMA) and related metabolites (arginine, citrulline, homoarginine, ornithine), and to validate this method according to Clinical and Laboratory Standards Institute (CLSI) protocols.

Methods

For the analysis of ADMA, SDMA, L-NMMA, arginine, homoarginine, citrulline, ornithine, 200 Âµl of serum were precipitated with methanol, and subsequently derivatized with a butanol solution containing 5% acetyl chloride. Butyl derivatives were separated using a C18 reverse phase column with a 5 min run time. Detection of analytes was achieved by utilising the specific fragmentation patterns identified through tandem mass spectrometry.

Results

The method was linear for ADMA, SDMA, L-NMMA, ornithine, arginine, homoarginine and citrulline in the ranges of 0.023–6.0, 0.021–5.5, 0.019–5.0, 0.015–250, 0.015–250, 0.019–5 and 0.015–250 µM, respectively. The inter-assay CV% values for all analytes was less than 9.8%.

Conclusions

Data obtained from method validation studies shows that the developed method is highly sensitive, precise and accurate. Short analysis time, cost-effectiveness, and multiplexed analysis of these metabolites, with the same pretreatment steps, are the main advantages of the method.

Central systolic blood pressure relates inversely to nitric oxide synthesis in young black adults: the African-PREDICT study

Lower nitric oxide (NO) bioavailabilty associates with hypertension in patients and elderly populations. With hypertension known to develop earlier in black populations, we compared both plasma and urinary NO-related markers and their associations with central systolic blood pressure (cSBP) and arterial stiffness in healthy young black and white adults. We included healthy black and white men and women (n = 1110; 20-30 years) and measured cSBP and pulse wave velocity (PWV), along with both plasma and urinary arginine, homoarginine, asymmetric dimethylarginine (ADMA), symmetric dimethylarginine (SDMA), as well as urinary ornithine/citrulline, nitrite and nitrate. In addition, the urinary nitrate-to-nitrite ratio (U_NOxR) was calculated. The black men and women had higher cSBP and higher plasma arginine and ADMA, but lower urinary nitrate and U_NOxR (all p ≤ 0.003) than their white counterparts. In single and forward stepwise multiple regression analyses, we found an inverse association of cSBP (adj. R² = 0.124; β = -0.134; p = 0.006) and plasma homoarginine in black men. Central SBP associated inversely with U_NOxR in black women only (adj. R² = 0.171; β = -0.130; p = 0.029). In the white women, cSBP associated positively with urinary ADMA (adj. R² = 0.372; β = 0.162; p = 0.015). PWV associated inversely with plasma ADMA (adj. R² = 0.253; β = -0.163; p = 0.024) in the white women only. The lower NO synthesis and the higher cSBP in our black cohort support the notion of a potential increased risk for future large artery stiffness and hypertension development in later life.

Associations of circulating dimethylarginines with the metabolic syndrome in the Framingham Offspring study

Background

Circulating levels of the endogenous inhibitor of nitric oxide synthase, asymmetric dimethylarginine (ADMA), are positively associated with the prevalence of metabolic syndrome (MetS) in cross-sectional investigations. It is unclear if circulating ADMA and other methylarginines are associated with incident MetS prospectively.

Methods

We related circulating ADMA, symmetric dimethylarginine (SDMA), L-arginine (ARG) concentrations (measured with a validated tandem mass spectrometry assay) and the ARG/ADMA ratio to MetS and its components in 2914 (cross-sectional analysis, logistic regression; mean age 58 years, 55% women) and 1656 (prospective analysis, Cox regression; mean age 56 years, 59% women) individuals from the Framingham Offspring Study who attended a routine examination.

Results

Adjusting for age, sex, smoking, and eGFR, we observed significant associations of ADMA (direct) and ARG/ADMA (inverse) with odds of MetS (N = 1461 prevalent cases; Odds Ratio [OR] per SD increment 1.13, 95%CI 1.04–1.22; and 0.89, 95%CI 0.82–0.97 for ADMA and ARG/ADMA, respectively). Upon further adjustment for waist circumference, systolic and diastolic blood pressure, glucose, high-density lipoprotein cholesterol, and triglycerides, we observed a positive relation between SDMA and MetS (OR per SD increment 1.15, 95% CI 1.01–1.30) but the other associations were rendered statistically non-significant. We did not observe statistically significant associations between any of the methylarginines and the risk of new-onset MetS (752 incident events) over a median follow-up of 11 years.

Conclusion

It is unclear whether dimethylarginines play an important role in the incidence of cardiometabolic risk in the community, notwithstanding cross-sectional associations. Further studies of larger samples are needed to replicate our findings.

Serum L-arginine and endogenous methylarginine concentrations predict irritable bowel syndrome in adults: A nested case-control study

BACKGROUND & AIMS: Nitric oxide, a major inhibitory nonadrenergic, noncholinergic neurotransmitter that relaxes smooth muscle, may be implicated in the pathophysiology of visceral hypersensitivity in irritable bowel syndrome (IBS). Impaired bioavailability of the nitric oxide precursor molecule L-arginine and higher concentrations of methylarginines (endogenous inhibitors of nitric oxide synthesis) are known to impair nitric oxide synthesis in numerous gastrointestinal cell types. We therefore examined serum concentrations of L-arginine and the methylarginines in a nested case-control study, to assess whether these factors are associated with adult IBS.

METHODS

Data on clinical characteristics, methylarginines, and L-arginine (measured using LC-MS/MS) were collected from a random population-based cohort of Australian adults (median age = 64 years; IQR = 60-70). Cases of IBS, defined according to Rome III criteria (N = 156), and controls (N = 332) were identified from within the cohort at the 5-year follow-up.

RESULTS

In adjusted logistic regression analyses, L-arginine, asymmetric dimethylarginine, symmetric dimethylarginine, L-arginine/asymmetric dimethylarginine ratio, and Kessler-10 psychological distress scores were significantly associated with IBS (p < 0.05). [Correction added on 18 September 2021, after first online publication: In the preceding sentence, the value (p > 0.05) has been changed to (p < 0.05)]. Similar results were found for IBS subtypes. Higher serum L-arginine concentration had the strongest association with IBS diagnosis, with an odds ratio of 9.03 for those with serum L-arginine at the 75th (84 μmol/L) versus 25th (46 μmol/L) percentile (95% CI: 5.99-13.62). L-arginine had the best discriminative ability with a bias-adjusted area under the receiver operator characteristic curve of 0.859.

CONCLUSIONS

Higher serum concentrations of L-arginine and endogenous methylarginines are strongly associated with IBS in adults.

Sequence Variation in the DDAH1 Gene Predisposes for Delayed Cerebral Ischemia in Subarachnoidal Hemorrhage

Delayed cerebral ischemia (DCI) often causes poor long-term neurological outcome after subarachnoidal hemorrhage (SAH). Asymmetric dimethylarginine (ADMA) inhibits nitric oxide synthase (NOS) and is associated with DCI after SAH. We studied single nucleotide polymorphisms (SNPs) in the NOS3, DDAH1, DDAH2, PRMT1, and AGXT2 genes that are part of the L-arginine–ADMA–NO pathway, and their association with DCI. We measured L-arginine, ADMA and symmetric dimethylarginine (SDMA) in plasma and cerebrospinal fluid (CSF) of 51 SAH patients at admission; follow-up was until 30 days post-discharge. The primary outcome was the incidence of DCI, defined as new infarctions on cranial computed tomography, which occurred in 18 of 51 patients. Clinical scores did not significantly differ in patients with or without DCI. However, DCI patients had higher plasma ADMA and SDMA levels and higher CSF SDMA levels at admission. DDAH1 SNPs were associated with plasma ADMA, whilst AGXT2 SNPs were associated with plasma SDMA. Carriers of the minor allele of DDAH1 rs233112 had a significantly increased relative risk of DCI (Relative Risk = 2.61 (1.25–5.43), p = 0.002). We conclude that the DDAH1 gene is associated with ADMA concentration and the incidence of DCI in SAH patients, suggesting a pathophysiological link between gene, biomarker, and clinical outcome in patients with SAH.

LC-MS/MS quantification of asymmetric dimethyl arginine and symmetric dimethyl arginine in plasma using surrogate matrix and derivatization with fluorescamine

Aim: A novel LC-MS/MS method using a surrogate matrix and derivatization with fluorescamine was developed and validated for simultaneous quantification of asymmetric dimethyl arginine and symmetric dimethyl arginine. Methods & results: Asymmetric dimethyl arginine, symmetric dimethyl arginine and corresponding internal standards were extracted using protein precipitation and derivatization with fluorescamine followed by SPE. Derivatives were analyzed by turbo ion spray LC-MS/MS in the positive ion mode. Methodology was successfully transferred across multiple preclinical species and utilized in the support of several investigative studies. Conclusion: A new LC-MS/MS analytical methodology that utilizes a surrogate matrix and derivatization with fluorescamine was successfully developed and validated.

Circulating asymmetric dimethylarginine and cognitive decline: A 4-year follow-up study of the 1936 Aberdeen Birth Cohort

BACKGROUND

The underlying mechanisms leading to dementia and Alzheimer's disease (AD) are unclear. Asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthase, may be associated with cognitive decline, but population-based evidence is lacking.

METHODS

Change in cognitive performance was assessed in participants of the Aberdeen Birth Cohort of 1936 using longitudinal Raven's progressive matrices (RPM) between 2000 and 2004. Multiple linear regression was used to estimate the association between ADMA concentrations in 2000 and change in cognitive performance after adjustment for potential confounders.

RESULTS

A total of 93 participants had complete information on cognitive performance between 2000 and 2004. Mean plasma ADMA concentrations were approximately 0.4 μmol/L lower in those participants with stable or improved RPM scores over follow-up compared with participants whose cognitive performance worsened. In confounder-adjusted analysis, one SD (0.06 μmol/L) increase in ADMA at 63 years of age was associated with an average reduction in RPM of 1.26 points (95% CI 0.14-2.26) after 4 years.

CONCLUSION

Raised plasma ADMA concentrations predicted worsening cognitive performance after approximately 4 years in this cohort of adults in late-middle age. These findings have implications for future research, including presymptomatic diagnosis or novel therapeutic targets for dementia and AD.

Urinary albumin-to-creatinine ratio is inversely related to nitric oxide synthesis in young black adults: the African-PREDICT study

Hypertension is common in black populations and is known to be associated with low nitric oxide (NO) bioavailability. We compared plasma and urinary NO-related markers and plasma creatine kinase (CK) levels between young healthy black and white adults along with the associations of these markers with the urinary albumin-to-creatinine ratio (uACR), which is a surrogate marker of endothelial and kidney function. We included 1105 participants (20-30 years). We measured the uACR, plasma CK, plasma and urinary arginine, homoarginine, asymmetric (ADMA) and symmetric dimethylarginine (SDMA), urinary ornithine/citrulline, nitrate and nitrite, and malondialdehyde (MDA). In addition, the urinary nitrate-to-nitrite ratio (U_NOxR) was calculated and used as a measure of circulating NO bioavailability. The uACR was comparable between the groups, yet the black group had lower urinary nitrate (by -15%) and U_NOxR values (by -18%) (both p ≤ 0.001), higher plasma (by +9.6%) and urinary (by +5.9%) arginine (both p ≤ 0.004), higher plasma (by +13%) and urinary (by +3.7%) ADMA (both p ≤ 0.033), and higher CK (by +9.5%) and MDA (by +19%) (both p < 0.001) compared with white adults. Plasma and urinary homoarginine were similar between the groups. In the multiple regression analysis, we confirmed the inverse associations of the uACR with both plasma (adj. R² = 0.066; β = -0.209; p = 0.005) and urinary (adj. R² = 0.066; β = -0.149; p = 0.010) homoarginine and with the U_NOxR (adj. R² = 0.060; β = -0.122; p = 0.031) in the black group only. The overall less favorable NO profile and higher CK and MDA levels in the black cohort along with the adverse associations with the uACR may reflect the vulnerability of this cohort to the early development of hypertension.

Myeloperoxidase and related biomarkers are suggestive footprints of endothelial microvascular inflammation in HFpEF patients

Aims

In heart failure (HF) with preserved ejection fraction (HFpEF), microvascular inflammation is proposed as an underlying mechanism. Myeloperoxidase (MPO) is associated with vascular dysfunction and prognosis in congestive HF.

Methods and results

MPO, MPO‐related biomarkers, and echocardiography were assessed in 86 patients, 4–8 weeks after presentation with acute HF (EF ≥ 45%), and in 46 healthy controls. Patients were followed up for median 579 days (Q1;Q3 276;1178) regarding the composite endpoint all‐cause mortality or HF hospitalization. Patients were 73 years old, 51% were female, EF was 64% (Q1;Q3 58;68), E/e′ was ratio 10.8 (8.3;14.0), and left atrial volume index (LAVI) was 43 mL/m² (38;52). Controls were 60 (57;62) years old (vs. patients; P < 0.001), 24% were female (P = 0.005), and left ventricular EF was 63% (59;66; P = 0.790). MPO was increased in HFpEF compared with controls, 101 (81;132) vs. 86 (74;101 ng/mL, P = 0.015), as was uric acid 369 (314;439) vs. 289 (252;328 μmol/L, P < 0.001), calprotectin, asymmetric dimethyl arginine (ADMA), and symmetric dimethyl arginine (SDMA), while arginine was decreased. MPO correlated with uric acid (r = 0.26; P = 0.016). In patients with E/e′ > 14, uric acid and SDMA were elevated (421 vs. 344 μM, P = 0.012; 0.54 vs. 0.47 μM, P = 0.039, respectively), and MPO was 121 vs. 98 ng/mL (P = 0.090). The ratios of arginine/ADMA (112 vs. 162; P < 0.001) and ADMA/SDMA (1.36 vs. 1.17; P = 0.002) were decreased in HFpEF patients, suggesting reduced NO availability and increased enzymatic clearance of ADMA, respectively. Uric acid independently predicted the endpoint [hazard ratio (HR) 3.76 (95% CI 1.19–11.85; P = 0.024)] but not MPO [HR 1.48 (95% CI 0.70–3.14; P = 0.304)] or the other biomarkers.

Conclusions

In HFpEF, MPO‐dependent oxidative stress reflected by uric acid and calprotectin is increased, and SDMA is associated with diastolic dysfunction and uric acid with outcome. This suggests microvascular neutrophil involvement mirroring endothelial dysfunction, a central component of the HFpEF syndrome and a potential treatment target.

Obtainment of an enriched fraction of Inga edulis: identification using UPLC-DAD-MS/MS and photochemopreventive screening

Inga edulis is a fruit tree native from Central and South America. Different species of Inga have demonstrated high polyphenolic content and high antioxidant capacity. The oxidative stress significantly contributes to the development of several chronicle diseases, particularly age-related diseases. Therefore, photochemoprevention is an emerging interest in the use of naturally occurring antioxidants for their therapeutic use. A partial purification of the extract was carried out onto macroporous resin and the main components of I. edulis leaf extract and fraction were identified using UPLC-DAD-MS/MS as epicatechin, apigenin C-di-hexoside, myricetin-O-hexose-deoxyhexose, myricetin-O-deoxyhexose and vicenin-2, which was identified for the first time in I. edulis. Both extract and fraction presented high antioxidant capacity, the fraction exhibiting higher polyphenol and flavonoid contents and higher content of vicenin-2, suggesting that the fractioning process effectively resulted in the partial purification of the extract. The cytotoxicity and photostability were assessed in L929 fibroblast cells to evaluate whether I. edulis extract and fraction were suitable for topical application. The UVA and UVB irradiated extract and fraction did not decrease the antioxidant capacity and cell viability of L929 fibroblasts, demonstrating the photostability of the samples. The fractioning process successfully purified and enriched I. edulis extract, and both the extract and fraction are potential candidates to be safely incorporated in topical photochemopreventive formulations.

The protective effect of dronedarone on the structure and mechanical properties of the aorta in hypertensive rats by decreasing the concentration of symmetric dimethylarginine (SDMA)

BACKGROUND AND AIMS

Dronedarone is a new multichannel-blocking antiarrhythmic for the treatment of patients with atrial fibrillation. Our group has demonstrated that dronedarone produces regression of cardiac remodeling; however, its effect on the remodeling of the elastic arteries has not yet been reported. We aim to assess the effects of dronedarone on the regression of thoracic aortic remodeling in spontaneously hypertensive rats (SHRs).

METHOD

Ten-month-old male SHRs were randomly assigned to an intervention group (SHR-D), where the animals received dronedarone treatment (100 mg/kg), to a control group (SHR) where rats were given vehicle, or to a group (SHR-A) where they were given amiodarone. A fourth group of normotensive control rats (Wistar-Kyoto rats, WKY) was also added. After two weeks of treatment, we studied the structure, the elastic fiber content of the thoracic aorta using histological techniques and confocal microscopy, and the vascular mechanical properties using an organ bath and isometric tension analysis. A mass spectrometric determination of symmetric dimethylarginine (SDMA) concentrations was performed.

RESULTS

SHR group developed the classic remodeling expected from the experimental model: outward hypertrophic remodeling, increased elastic fiber content and wall stiffness. However, the SHR-D group showed statistically significantly lower values for aortic tunica media thickness, wall to lumen ratio, external diameter, cross-sectional area, volume density of the elastic fibers, wall stiffness, and aortic SDMA concentration when compared to the SHR group. These parameters were similar in the SHR and SHR-A groups. Interestingly, the values for tunica media thickness, volume density of the elastic fibers, wall stiffness, and SDMA concentration obtained from the SHR-D group were similar to those measured in the WKY group.

CONCLUSION

These results suggest that dronedarone improves the structure and passive mechanical properties of the thoracic aorta in hypertensive rats, and that this protective effect could be associated with a reduction in the concentration of aortic SDMA.

Dronedarone induces regression of coronary artery remodeling related to better global antioxidant status

Our group previously demonstrated that dronedarone induces regression of left ventricular hypertrophy in spontaneously hypertensive rats (SHRs). We assessed changes in vascular remodeling and oxidative stress following short-term use of this agent. The coronary artery was isolated from 10-month-old male SHRs treated with 100 mg kg^-1 dronedarone once daily for 14 days (SHR-D group), and age-matched untreated SHRs were used as hypertensive controls. We analyzed the geometry and composition of the artery and constructed dose-response curves for acetylcholine and serotonin (5-HT). We calculated a global score (OXY-SCORE) from plasma biomarkers of oxidative status: carbonyl levels, thiol levels, reduced glutathione levels, total antioxidant capacity, and superoxide anion scavenging activity. Finally, we analyzed asymmetric dimethylarginine (ADMA) concentrations in plasma. Dronedarone significantly decreased wall thickness (medial and adventitial layer thickness and cell count) and the cross-sectional area of the artery. Dronedarone significantly improved endothelium-dependent relaxation and reduced the contraction induced by 5-HT. The OXY-SCORE was negative in the SHR model group (suggesting an enhanced oxidative status) and was positive in the SHR-D group (suggesting enhanced antioxidant defense). Dronedarone significantly decreased the concentrations of ADMA. We conclude that dronedarone improves coronary artery remodeling in SHRs. The better global antioxidant status after treatment with dronedarone and decreased plasma ADMA levels could contribute to the cardiovascular protective effect of dronedarone.

Increased Aqueous Humor Symmetric Dimethylarginine Level in Patients with Primary Open Angle Glaucoma

Purpose: To evaluate the asymmetric dimethylarginine (ADMA), symmetric dimethylarginine (SDMA) and L-arginine (L-Arg) levels both in plasma and aqueous humor of primary open angle glaucoma (POAG) patients and matched controls. Patients and Methods: 25 primary open angle glaucoma patients and 42 control cases with senile cataract were included in the study. Plasma and aqueous humor ADMA, SDMA and L-Arg levels of the participants were measured by using liquid chromatography-tandem mass spectrometry. Results: A significant increase in aqueous humor SDMA level was detected in POAG patients compared with controls (p = 0.0115). No significant difference was detected in plasma and aqueous humor ADMA, L-Arg levels. Conclusion: The aqueous humor levels of SDMA are found to be associated with POAG. The result of this current study supports the role of nitric oxide pathway in glaucoma.

Quantitative Analysis of l-Arginine, Dimethylated Arginine Derivatives, l-Citrulline, and Dimethylamine in Human Serum Using Liquid Chromatography-Mass Spectrometric Method

ABSTRACT

Nitric oxide (NO) is a small molecule involved in the regulation of many physiological processes. It plays a crucial role in the regulation of nervous system, immune and inflammatory responses, and blood flow. NO is synthesized by nitric oxide synthase (NOS) during two-step oxidation of l-arginine to l-citrulline. Intermediates and derivatives of NO metabolism, such as l-arginine, l-citrulline, asymmetrical dimethylarginine (ADMA), symmetrical dimethylarginine (SDMA), and dimethylamine (DMA), are investigated as potential biomarkers. In this article, we present a novel analytical method that allowed for simultaneous analysis of l-arginine, ADMA, SDMA, l-citrulline, and DMA, in a single-step extraction and derivatization using benzoyl chloride. In brief, aliquots of serum were mixed with internal standard solution mixture (50 µM D6-DMA, 20 µM D7-ADMA, and 100 µM D7-arginine) and 0.025 M borate buffer, pH 9.2 (10:1:5). The derivatization process was performed at 25 °C for 5 min using 10% benzoyl chloride. A reverse phase column was used for chromatographic separation. Quantitation was performed using following ions (m/z): 279.1457, 286.1749, 307.1717, 314.2076, 280.1297, 150.0919, and 156.1113 for l-arginine, D7-arginine, ADMA, SDMA, D7-ADMA, l-citrulline, DMA, and D6-DMA, respectively. The method was validated, and its assay linearity, accuracy and precision, recovery, and limits of detection (1.7 µM l-arginine, 0.03 µM ADMA, 0.02 µM SDMA, 0.36 µM l-citrulline, 0.06 µM DMA) and quantification (3.2 µM l-arginine, 0.08 µM ADMA, 0.05 µM SDMA, 1.08 µM l-citrulline, 0.19 µM DMA) were determined. The method is sensitive, reliable, repeatable, and reproducible. It can be applied in the routine clinical/diagnostic laboratory.

GRAPHICAL ABSTRACT

Serum Methylarginines and Hearing Loss in a Population-based Cohort of Older Adults

OBJECTIVE

Age-related hearing loss is associated with endothelial dysfunction and increased cardiovascular risk, suggesting a vascular etiology. Methylarginines are endogenous nitric oxide synthase inhibitors that cause endothelial dysfunction and increase cardiovascular disease risk. This study is the first to examine the hypothesis that higher serum concentrations of methylarginines are associated with greater hearing loss prevalence.

STUDY DESIGN/PATIENTS

Cross-sectional audiometric data on hearing levels, and serum methylarginines were collected from a population-based sample of 630 older community-dwelling adults.

RESULTS

Linear regression analysis showed a statistically significant association between higher serum concentrations of asymmetric dimethylarginine (ADMA) and L-arginine and greater degrees of hearing loss for males, particularly over 75 years. Higher body mass index and previous history of stroke were also associated with hearing loss. For females, ADMA concentration was not associated with hearing loss, but higher serum L-arginine concentrations were associated with reduced hearing loss prevalence in older females. Antihypertensive medication use was also associated with reduced hearing loss prevalence. LDL cholesterol and previous myocardial infarction were associated with greater hearing loss.

CONCLUSION

This study showed a significant association between serum concentrations of ADMA and hearing loss for males, consistent with the association between endothelial dysfunction and hearing loss. The opposite effect of L-arginine on hearing loss in males versus females might reflect a different role of this precursor toward nitric oxide versus methylated arginines synthesis. These findings are potentially clinically significant if the association between ADMA and hearing loss is causal, as serum methylarginine levels are modifiable through pharmacotherapeutic/lifestyle interventions.

Comparison of Three Sample Preparation Procedures for the Quantification of L-Arginine, Asymmetric Dimethylarginine, and Symmetric Dimethylarginine in Human Plasma Using HPLC-FLD

Increased asymmetric dimethylarginine (ADMA) in human plasma has been associated with reduced generation of nitric oxide, leading to atherosclerotic diseases. ADMA may therefore be an important biomarker for cardiovascular disease. In the present study, three sample preparation techniques were compared regarding the quantification of L-arginine and ADMA in human plasma: (A) protein precipitation (PP) based on aqueous trichloroacetic acid (TCA), (B) PP using a mixture of ammonia and acetonitrile, and (C) solid-phase extraction (SPE). The samples were analysed by using high-performance liquid chromatography with fluorescence detection (HPLC-FLD). The analytical performance of (A) was comparable with that of (C), demonstrating recoveries of >90%, coefficient of variations (CVs, %) of <8, and a resolution (R_s ) between ADMA and symmetric dimethylarginine (SDMA) of 1.2. (B) was disregarded due to recoveries below 75%. (A) was validated with good results regarding linearity (>0.994), precision (<5%), and sensitivity (lower limit of quantification (LLOQ)) of 0.14 µM and 12 nM for L-arginine and ADMA, respectively. Due to the simplicity and speed of procedure (A), this approach may serve as preferred sample preparation of human plasma samples before HPLC-FLD in providing important information regarding elevated ADMA concentrations.

Human dimethylarginine dimethylaminohydrolase 1 inhibition by proton pump inhibitors and the cardiovascular risk marker asymmetric dimethylarginine: in vitro and in vivo significance

Proton pump inhibitor (PPI)-induced inhibition of dimethylarginine dimethylaminohydrolase 1 (DDAH1), with consequent accumulation of the nitric oxide synthase inhibitor asymmetric dimethylarginine (ADMA), might explain the increased cardiovascular risk with PPI use. However, uncertainty exists regarding whether clinical PPI concentrations significantly inhibit DDAH1 under linear initial rate conditions, and whether PPI-induced DDAH1 inhibition significantly increases ADMA in humans. DDAH1 inhibition by esomeprazole, omeprazole, pantoprazole, lansoprazole and rabeprazole was determined by quantifying DDAH1-mediated L-citrulline formation in vitro. Plasma ADMA was measured in PPI users (n = 134) and non-users (n = 489) in the Hunter Community Study (HCS). At clinical PPI concentrations (0.1–10 μmol/L), DDAH1 retained >80% activity vs. baseline. A significant, reversible, time-dependent inhibition was observed with lansoprazole (66% activity at 240 min, P = 0.034) and rabeprazole (25% activity at 240 min, P < 0.001). In regression analysis, PPI use was not associated with ADMA in HCS participants (beta 0.012, 95% CI −0.001 to 0.025, P = 0.077). Furthermore, there were no differences in ADMA between specific PPIs (P = 0.748). At clinical concentrations, PPIs are weak, reversible, DDAH1 inhibitors in vitro. The lack of significant associations between PPIs and ADMA in HCS participants questions the significance of DDAH1 inhibition as a mechanism explaining the increased cardiovascular risk reported with PPI use.

Arginine/Asymmetric Dimethylarginine Ratio in Colorectal Surgery

BACKGROUND

Asymmetric dimethylarginine (ADMA) is a naturally occurring amino acid that inhibits the effects of nitric oxide synthetases, producing considerable effects on the vascular system. Recent studies have suggested that increased ADMA is a major contributor to endothelial dysfunction, resulting in significant effects on cardiovascular and renal function.

METHODS

The study sample consisted of five male and 11 female patients scheduled for elective laparoscopic colorectal surgery; patients were between 41 and 77 years of age. Venous whole blood (8 - 10 mL) was collected from patients prior to colorectal surgery, as well as on postoperative day 1 and 2. Arginine, citrulline, ADMA, and symmetric dimethylarginine levels were measured in collected blood using liquid chromatography coupled to mass spectrometry.

RESULTS

Data from the amino-acid blood analysis demonstrated that the levels of L-citrulline and L-arginine decreased on postoperative days 1, coinciding with an increase of ADMA levels. The overall result of these changes was a decrease in the arginine to ADMA ratio by 21% from the preoperative period to postoperative day 2 (P = 0.02).

CONCLUSIONS

The data collected through this study demonstrate a significant increase in systemic ADMA levels following major laparoscopic colorectal surgery.

Long-Term Intermittent Exposure to High Altitude Elevates Asymmetric Dimethylarginine in First Exposed Young Adults

Lüneburg, Nicole, Patricia Siques, Julio Brito, Juan José De La Cruz, Fabiola León-Velarde, Juliane Hannemann, Cristian Ibanez, and Rainer Böger. Long-term intermittent exposure to high altitude elevates asymmetric dimethylarginine in first exposed young adults. High Alt Med Biol. 18:226–233, 2017.—Hypoxia-induced dysregulation of pulmonary and cerebral circulation may be related to an impaired nitric oxide (NO) pathway. We investigated the effect of chronic intermittent hypobaric hypoxia (CIH) on metabolites of the NO pathway. We measured asymmetric and symmetric dimethylarginine (ADMA and SDMA) and monomethyl-L-arginine (L-NMMA) and assessed their associations with acclimatization in male draftees (n = 72) undergoing CIH shifts at altitude (3550 m) during 3 months. Sixteen Andean natives living at altitude (3675 m) (chronic hypobaric hypoxia [CH]) were included for comparison. In CIH, ADMA and L-NMMA plasma concentrations increased from 1.14 ± 0.04 to 1.95 ± 0.09 μmol/L (mean ± SE) and from 0.22 ± 0.07 to 0.39 ± 0.03 μmol/L, respectively, (p < 0.001 for both) after 3 months, whereas SDMA did not change. The concentrations of ADMA and L-NMMA were higher in CH (3.48 ± 0.07, 0.53 ± 0.08 μmol/L; p < 0.001) as compared with CIH. In both CIH and CH, ADMA correlated with hematocrit (r² = 0.07, p < 0.05; r² = 0.26; p < 0.01). In CIH, an association of ADMA levels with poor acclimatization status was observed. We conclude that the endogenous NO synthase inhibitors, ADMA and L-NMMA, are elevated in hypoxia. This may contribute to impaired NO production at altitude and may also be predictive of altitude-associated health impairment.

Fluorometric enzymatic assay of l-arginine

The enzymes of l-arginine (further - Arg) metabolism are promising tools for elaboration of selective methods for quantitative Arg analysis. In our study we propose an enzymatic method for Arg assay based on fluorometric monitoring of ammonia, a final product of Arg splitting by human liver arginase I (further - arginase), isolated from the recombinant yeast strain, and commercial urease. The selective analysis of ammonia (at 415nm under excitation at 360nm) is based on reaction with o-phthalaldehyde (OPA) in the presence of sulfite in alkali medium: these conditions permit to avoid the reaction of OPA with any amino acid. A linearity range of the fluorometric arginase-urease-OPA method is from 100nM to 6μМ with a limit of detection of 34nM Arg. The method was used for the quantitative determination of Arg in the pooled sample of blood serum. The obtained results proved to be in a good correlation with the reference enzymatic method and literature data. The proposed arginase-urease-OPA method being sensitive, economical, selective and suitable for both routine and micro-volume formats, can be used in clinical diagnostics for the simultaneous determination of Arg as well as urea and ammonia in serum samples.

Early regression of coronary artery remodeling with esmolol and DDAH/ADMA pathway in hypertensive rats

Our preclinical study demonstrated that esmolol produces early regression of left ventricular hypertrophy in arterial hypertension. The aim of this study was to assess the effects of short-term esmolol therapy on the regression of left anterior descending artery remodeling in spontaneously hypertensive rats (SHRs), and to determine whether the asymmetric dimethylarginine (ADMA)/dimethylarginine dimethylaminohydrolase (DDAH) pathway, a regulator of nitric oxide (NO) bioavailability, accounted for this regression. Fourteen-month-old male SHRs were treated intravenously with vehicle (SHR, n=15) or esmolol (SHR-E, n=20) (300 μg kg^-1 min^-1). Age-matched, vehicle-treated male Wistar-Kyoto rats (WKY, n=15) served as controls. SHRs were also treated with nitroglycerin (SHR-N, n=5). After 48 h, the left anterior descending artery structure and morphology were assessed, and dose-response curves for 5-hydroxytryptamine (5-HT, 10^-9-3 × 10^-5 mol l^-1) were constructed. ADMA concentrations in plasma and left ventricle and DDAH activity in tissue were analyzed. Wall thickness and cross-sectional area were significantly lower after treatment with esmolol in SHR-E than in SHR. Media thickness and smooth muscle cell count were lower in SHR-E than in SHR. Esmolol induced a significant reduction in adventitial cell count in SHR-E. The area under the concentration-response curves was significantly higher in SHR than in SHR-E, as were the esmolol normalized coronary artery contracting responses to 5-HT. We found significantly lower ADMA levels and significantly higher DDAH activity in the ventricle in SHR-E than in SHR. The protective effect of esmolol on the regression of left anterior descending artery remodeling may be related to the reduction in ADMA levels.

Long-Term Chronic Intermittent Hypobaric Hypoxia in Rats Causes an Imbalance in the Asymmetric Dimethylarginine/Nitric Oxide Pathway and ROS Activity: A Possible Synergistic Mechanism for Altitude Pulmonary Hypertension?

Chronic intermittent hypoxia (CIH) and chronic hypoxia (CH) are associated with high-altitude pulmonary hypertension (HAPH). Asymmetric dimethylarginine (ADMA), a NO synthase (NOS) inhibitor, may contribute to HAPH. This study assessed changes in the ADMA/NO pathway and the underlying mechanisms in rat lungs following exposure to CIH or CH simulated in a hypobaric chamber at 428 Torr. Twenty-four adult Wistar rats were randomly assigned to three groups: CIH2x2 (2 days of hypoxia/2 days of normoxia), CH, and NX (permanent normoxia), for 30 days. All analyses were performed in whole lung tissue. L-Arginine and ADMA were analyzed using LC-MS/MS. Under both hypoxic conditions right ventricular hypertrophy was observed (p < 0.01) and endothelial NOS mRNA increased (p < 0.001), but the phosphorylated/nonphosphorylated vasodilator-stimulated phosphoprotein (VASP) ratio was unchanged. ADMA increased (p < 0.001), whereas dimethylarginine dimethylaminohydrolase (DDAH) activity decreased only under CH (p < 0.05). Although arginase activity increased (p < 0.001) and L-arginine exhibited no changes, the L-arginine/ADMA ratio decreased significantly (p < 0.001). Moreover, NOX4 expression increased only under CH (p < 0.01), but malondialdehyde (MDA) increased (up to 2-fold) equally in CIH2x2 and CH (p < 0.001). Our results suggest that ADMA and oxidative stress likely reduce NO bioavailability under altitude hypoxia, which implies greater pulmonary vascular reactivity and tone, despite the more subdued effects observed under CIH.

The relationship of nitric oxide synthesis capacity, oxidative stress, and albumin-to-creatinine ratio in black and white men: the SABPA study

Inadequate substrate availability and increased nitric oxide synthase inhibitor levels attenuate nitric oxide (NO) synthesis, whereas increased vascular oxidative stress may lead to inactivation of NO. We compared markers of NO synthesis capacity and oxidative stress in a bi-ethnic male population. Inter-relationships of ambulatory blood pressure and urinary albumin-to-creatinine ratio with NO synthesis capacity and oxidative stress markers were investigated. NO synthesis capacity markers (L-arginine, asymmetric dimethylarginine (ADMA), and symmetric dimethylarginine (SDMA)) and oxidative stress markers (serum peroxides, total glutathione, glutathione peroxidase (GPx), glutathione reductase (GR), superoxide dismutase (SOD), and catalase) were measured. Black men displayed higher blood pressure and albumin-to-creatinine ratio (all p < 0.001), while NO synthesis capacity was more favorable (higher L-arginine and lower ADMA (p ≤ 0.003)). Antioxidant enzyme activities were similar except for the redox status markers (GR activity and GR/GPx ratio), which were upregulated in black men (p < 0.001). In black men, ADMA was inversely related to GPx activity (R (2) = 0.15; β = -0.20; p = 0.050) and GPx/SOD ratio (R (2) = 0.24; β = -0.37; p < 0.001), but none of these markers related to blood pressure or albumin-to-creatinine ratio. In white men, albumin-to-creatinine ratio was positively associated with ADMA (R (2) = 0.18; β = 0.39; p < 0.001) while ADMA was inversely related to GR activity (R (2) = 0.26; β = -0.29; p = 0.002) and GR/GPx ratio (R (2) = 0.25; β = -0.28; p = 0.003). Black men with elevated blood pressure and albumin-to-creatinine ratio displayed a favorable NO synthesis capacity. This may be counteracted by increased inactivation of NO, although it was not linked to vascular or renal phenotypes. In white men, reduced NO synthesis capacity may lower NO bio-availability, thereby influencing the albumin-to-creatinine ratio.

Impaired Coronary and Renal Vascular Function in Spontaneously Type 2 Diabetic Leptin-Deficient Mice

BACKGROUND

Type 2 diabetes is associated with macro- and microvascular complications in man. Microvascular dysfunction affects both cardiac and renal function and is now recognized as a main driver of cardiovascular mortality and morbidity. However, progression of microvascular dysfunction in experimental models is often obscured by macrovascular pathology and consequently demanding to study. The obese type 2 diabetic leptin-deficient (ob/ob) mouse lacks macrovascular complications, i.e. occlusive atherosclerotic disease, and may therefore be a potential model for microvascular dysfunction. The present study aimed to test the hypothesis that these mice with an insulin resistant phenotype might display microvascular dysfunction in both coronary and renal vascular beds.

METHODS AND RESULTS

In this study we used non-invasive Doppler ultrasound imaging to characterize microvascular dysfunction during the progression of diabetes in ob/ob mice. Impaired coronary flow velocity reserve was observed in the ob/ob mice at 16 and 21 weeks of age compared to lean controls. In addition, renal resistivity index as well as pulsatility index was higher in the ob/ob mice at 21 weeks compared to lean controls. Moreover, plasma L-arginine was lower in ob/ob mice, while asymmetric dimethylarginine was unaltered. Furthermore, a decrease in renal vascular density was observed in the ob/ob mice.

CONCLUSION

In parallel to previously described metabolic disturbances, the leptin-deficient ob/ob mice also display cardiac and renal microvascular dysfunction. This model may therefore be suitable for translational, mechanistic and interventional studies to improve the understanding of microvascular complications in type 2 diabetes.

LC–MS/MS for the simultaneous determination of polar endogenous ADMA and CML in plasma and urine from diabetics

Background: Asymmetric dimethylarginine (ADMA) and ε-N-carboxymethyl-l-lysine (CML) are microvascular risk factors and potential biomarkers of diabetic microvascular complication. Results: Sample preparation was achieved using acetonitrile for protein precipitation step. ADMA, CML and IS CML-d2 were separated with gradient on a Welch Ultimate® XB- NH2 column. The assays were validated according to current bioanalytical guidelines with respect to specificity, linearity (20–1000 ng/ml for ADMA in human plasma, 50–2000 ng/ml in urine, 10–500 ng/ml for CML in human plasma and urine), accuracy and precision, extraction recovery, matrix effect and stability. Conclusion: The LC–MS/MS method was successfully applied to quantification of ADMA and CML in plasma and urine samples from healthy individuals and patients with diabetic nephropathy.

Overexpression of dimethylarginine dimethylaminohydrolase 1 attenuates airway inflammation in a mouse model of asthma

Levels of asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthase, are increased in lung, sputum, exhaled breath condensate and plasma samples from asthma patients. ADMA is metabolized primarily by dimethylarginine dimethylaminohydrolase 1 (DDAH1) and DDAH2. We determined the effect of DDAH1 overexpression on development of allergic inflammation in a mouse model of asthma. The expression of DDAH1 and DDAH2 in mouse lungs was determined by RT-quantitative PCR (qPCR). ADMA levels in bronchoalveolar lavage fluid (BALF) and serum samples were determined by mass spectrometry. Wild type and DDAH1-transgenic mice were intratracheally challenged with PBS or house dust mite (HDM). Airway inflammation was assessed by bronchoalveolar lavage (BAL) total and differential cell counts. The levels of IgE and IgG1 in BALF and serum samples were determined by ELISA. Gene expression in lungs was determined by RNA-Seq and RT-qPCR. Our data showed that the expression of DDAH1 and DDAH2 was decreased in the lungs of mice following HDM exposure, which correlated with increased ADMA levels in BALF and serum. Transgenic overexpression of DDAH1 resulted in decreased BAL total cell and eosinophil numbers following HDM exposure. Total IgE levels in BALF and serum were decreased in HDM-exposed DDAH1-transgenic mice compared to HDM-exposed wild type mice. RNA-Seq results showed downregulation of genes in the inducible nitric oxide synthase (iNOS) signaling pathway in PBS-treated DDAH1-transgenic mice versus PBS-treated wild type mice and downregulation of genes in IL-13/FOXA2 signaling pathway in HDM-treated DDAH1-transgenic mice versus HDM-treated wild type mice. Our findings suggest that decreased expression of DDAH1 and DDAH2 in the lungs may contribute to allergic asthma and overexpression of DDAH1 attenuates allergen-induced airway inflammation through modulation of Th2 responses.

Measurement of arginine metabolites: regulators of nitric oxide metabolism

Arginine is the substrate for nitric oxide synthases (NOS), and arginine availability regulates the production of nitric oxide. Through the activity of methyltransferases, arginine can be methylated to form monomethylarginine (NMMA), asymmetrical dimethylarginine (ADMA), and symmetrical dimethylarginine (SDMA). NMMA and ADMA directly inhibit NOS, whereas SDMA inhibits the cellular import of arginine through the cationic amino acid transporter. Increased levels of methylarginine compounds have been associated with many diseases including atherosclerosis, renal failure, pulmonary hypertension, and preeclampsia. Previous HPLC methods to measure these molecules rely on derivatization with ortho-phthalaldehyde, which is unstable and requires immediate pre- or post-column reactions. We have identified a new fluorometric agent that is stable for at least 1 week and provides chromatographic properties that facilitate separation of these chemically similar compounds by reverse phase chromatography.

Effects of acute and chronic stress on the L-arginine nitric oxide pathway in black and white South Africans: the sympathetic activity and ambulatory blood pressure in Africans study

OBJECTIVE

This study investigated the impact of stress on effectors of the L-arginine/nitric oxide (NO) system including the endogenous inhibitor asymmetric dimethylarginine (ADMA).

METHODS

Black (n = 168) and white (n = 206) South African teachers were exposed to a mental and a physical stressor for 1 minute, respectively. Serum samples for determination of l-arginine, NO metabolites, ADMA, and symmetric dimethylarginine (SDMA) were obtained at rest and during stress exposure. Perception of task stressfulness was assessed on a 7-point Likert scale, and psychological distress was estimated by the General Health Questionnaire.

RESULTS

Black South Africans exhibited higher resting levels of NO metabolites (adjusted mean [standard error of the mean] = 11.3 [1.3] versus 3.9 [1.1] μmol/l, p < .001) but lower circulating ADMA (0.62 [0.02] versus 0.70 [0.02] μmol/l, p = .004) and SDMA (0.41 [0.01] versus 0.53 [0.01] μmol/l, p < .001) than did white South Africans. Ethnicity-by-psychological distress interaction was observed for resting levels of ADMA (p = .002), SDMA (p = .038), and L-arginine (p = .048). Ethnic differences in responses to experimental stress were evident for NO metabolites (blacks versus whites: 5.94 [1.55] versus -0.74 [1.25] μmol/l, p = .004) and SDMA (blacks versus whites: -0.02 [0.01] versus 0.02 [0.01] μmol/l, p = .004). Ethnicity-by-psychological distress interaction for stress responses was found for l-arginine/ADMA ratio (p = .027).

CONCLUSIONS

The l-arginine/NO system is affected by psychosocial distress with higher susceptibility in black South Africans. This interaction may contribute to the higher cardiovascular disease risk in black South Africans.

Methylated arginines and nitric oxide in end-stage renal disease: impact of inflammation, oxidative stress and haemodialysis

OBJECTIVES

To determine whether inflammation (C-reactive protein, CRP), oxidative stress (malondialdehyde, MDA) or haemodialysis (HD) affect associations between asymmetric (ADMA), symmetric (SDMA) dimethylarginine, NG-monomethyl-L-arginine (L-NMMA) and nitrite/nitrate (NOx) in end-stage renal disease (ESRD).

METHOD

Metabolites were measured pre-HD, after 1 hour and end-HD in 40 ESRD patients (age 63 ± 14 years).

RESULTS

Positive associations between NOx and ADMA (p = 0.04), SDMA (p < 0.001) and L-NMMA (p = 0.04) were observed pre-HD. Associations weakened during HD but were not significantly influenced by CRP or MDA.

CONCLUSIONS

HD, oxidative stress or inflammation did not significantly affect the positive associations between methylated arginines and NOx in ESRD.

A comparison of the association between glomerular filtration and L-arginine status in HIV-infected and uninfected African men: the SAfrEIC study

Hypertension, a major risk factor for cardiovascular disease worldwide, is increasing significantly in urbanised South Africans. Impaired glomerular filtration is a potential contributor to hypertension. Although HIV infection is widespread, little is known regarding its contribution to diminished estimated glomerular filtration rate (eGFR) and, in turn, hypertension in Africans. We compared eGFRs and cardiovascular profiles of newly identified HIV infected African men (N=53) not yet undergoing anti-retroviral therapy, and uninfected African men of similar age and anthropometry. The aim of the study was to determine whether eGFR is diminished in treatment naive HIV infected individuals and whether eGFR is associated with a potential modulator of hypertension, namely serum L-arginine. Cardiovascular risk factor profiles of HIV infected and uninfected men were similar. In men with healthy eGFRs >90 ml min(-1) per 1.73 m(2), eGFR was significantly lower with HIV infection (114 (90; 147)) compared with that in uninfected men: (120 (91; 168)), P=0.043. Despite the absence of clinically-diagnosed renal dysfunction, eGFR associated significantly with serum L-arginine only in HIV infected men (R(2)=0.277, β=-0.299, P=0.034), whereas L-arginine did not stay in the model for uninfected men. This difference suggests that the fate of L-arginine as a substrate for nitric oxide generation may be altered in HIV infected individuals. Subsequently this is likely to escalate endothelial dysfunction, contributing to later hypertension and cardiovascular disease. Our findings show that while glomerular filtration rate is not associated with L-arginine in uninfected men, it is diminished and significantly negatively associated with serum L-arginine in HIV infected men.

Transsulfuration pathway thiols and methylated arginines: the Hunter Community Study

Background

Serum homocysteine, when studied singly, has been reported to be positively associated both with the endogenous nitric oxide synthase inhibitor asymmetric dimethylarginine [ADMA, via inhibition of dimethylarginine dimethylaminohydrolase (DDAH) activity] and with symmetric dimethylarginine (SDMA). We investigated combined associations between transsulfuration pathway thiols, including homocysteine, and serum ADMA and SDMA concentrations at population level.

Methods

Data on clinical and demographic characteristics, medication exposure, C-reactive protein, serum ADMA and SDMA (LC-MS/MS), and thiols (homocysteine, cysteine, taurine, glutamylcysteine, total glutathione, and cysteinylglycine; capillary electrophoresis) were collected from a sample of the Hunter Community Study on human ageing [n = 498, median age (IQR) = 64 (60–70) years].

Results

Regression analysis showed that: a) age (P = 0.001), gender (P = 0.03), lower estimated glomerular filtration rate (eGFR, P = 0.08), body mass index (P = 0.008), treatment with beta-blockers (P = 0.03), homocysteine (P = 0.02), and glutamylcysteine (P = 0.003) were independently associated with higher ADMA concentrations; and b) age (P = 0.001), absence of diabetes (P = 0.001), lower body mass index (P = 0.01), lower eGFR (P<0.001), cysteine (P = 0.007), and glutamylcysteine (P<0.001) were independently associated with higher SDMA concentrations. No significant associations were observed between methylated arginines and either glutathione or taurine concentrations.

Conclusions

After adjusting for clinical, demographic, biochemical, and pharmacological confounders the combined assessment of transsulfuration pathway thiols shows that glutamylcysteine has the strongest and positive independent associations with ADMA and SDMA. Whether this reflects a direct effect of glutamylcysteine on DDAH activity (for ADMA) and/or cationic amino acid transport requires further investigations.

Quantification of arginine and dimethylated arginines in human plasma by field-amplified sample injection capillary electrophoresis UV detection

We report a capillary electrophoresis method by field-amplified sample injection (FASI) for the separation and detection of free plasma arginine and dimethylated arginines. Protein elimination from plasma was performed by acetonitrile/ammonia precipitation. Supernatants were dried, reswollen in water, and directly injected on capillary without complex cleanup by solid-phase extraction and/or tedious sample derivatization procedures. Analytes were baseline-separated within 22 min by using 50 mmol/L Tris phosphate pH 2.3 as running buffer. Due to the stacking effects of electrokinetic injection, it is possible to perform a considerable on-line preconcentration of the analytes before running the electrophoresis. This procedure allows to reach a detection limit in real sample of 10 nmol/L for dimethylated arginines and 20 nmol/L for arginine. Recovery of plasma ADMA was 99-104 % and inter-day CV was less than 3 %.

Asymmetric and symmetric dimethylarginine and risk of secondary cardiovascular disease events and mortality in patients with stable coronary heart disease: the KAROLA follow-up study

BACKGROUND

Asymmetric dimethylarginine (ADMA) is an endogenous nitric oxide synthase inhibitor, which has been associated with total and cardiovascular mortality in various clinical settings. Studies on its structural isomer, symmetric dimethylarginine (SDMA), are scarce. This study aimed to determine the associations of both ADMA and SDMA levels with secondary cardiovascular disease events and all-cause mortality in patients with stable coronary heart disease (CHD).

METHODS

In the observational prospective cohort study KAROLA, 1,148 CHD patients were followed for a median of 8.1 years. ADMA and SDMA were determined by liquid chromatography-tandem mass spectrometry. Baseline ADMA and SDMA levels were categorized in quartiles or standardized by their respective standard deviation, and appropriate hazard ratios and 95 % confidence intervals (HR [95 % CI]) were estimated in Cox proportional hazards models.

RESULTS

150 patients experienced secondary cardiovascular disease events (CVD) and 121 patients died. After adjustment for confounders, ADMA was not associated with the risk of secondary CVD events (HR per standard deviation increase: 1.02 [95 %CI: 0.86-1.21]), whereas an association was suggested for SDMA (HR 1.17 [1.00-1.37]). Higher hazard ratios were observed in all-cause mortality models (ADMA: HR 1.15 [0.95-1.37]; SDMA: HR 1.29 [1.09-1.52]).

CONCLUSIONS

Our results suggest that especially SDMA might possibly have potential as a risk marker for all-cause mortality and to a lesser extent for secondary cardiovascular events. Future studies are needed to quantify these associations more precisely and should, in particular, further address the possibility of residual confounding by impaired kidney function.

Online trapping and enrichment ultra performance liquid chromatography-tandem mass spectrometry method for sensitive measurement of "arginine-asymmetric dimethylarginine cycle" biomarkers in human exhaled breath condensate

BACKGROUND

Exhaled breath condensate (EBC) is a biofluid collected non invasively that, enabling the measurement of several biomarkers, has proven useful in the study of airway inflammatory diseases, including asthma, COPD and cystic fibrosis. To the best of our knowledge, there is no previous report of any analytical method to detect ADMA in EBC.

OBJECTIVES

Aim of this work was to develop an online sample trapping and enrichment system, coupled with an UPLC-MS/MS method, for simultaneous quantification of seven metabolites related to "Arginine-ADMA cycle", using the isotopic dilution.

METHODS

Butylated EBC samples were trapped in an online cartridge, washed before and after each injection with cleanup solution to remove matrix components and switched inline into the high pressure analytical column. Multiple reaction monitoring in positive mode was used for analyte quantification by tandem mass spectrometry.

RESULTS

Validation studies were performed in EBC to examine accuracy, precision and robustness of the method. For each compound, the calibration curves showed a coefficient of correlation (r(2)) greater than 0.992. Accuracy (%Bias) was <3% except for NMMA and H-Arg (<20%), intra- and inter-assay precision (expressed as CV%) were within ±20% and recovery ranged from 97.1 to 102.8% for all analytes. Inter-day variability analysis on 20 EBC of adult subjects did not demonstrate any significant variation of quantitative data for each metabolite. ADMA and SDMA mean concentrations (μmolL(-1)), measured in EBC samples of asthmatic adolescents are significantly increased (p<0.0001) than in normal controls (0.0040±0.0021 vs. 0.0012±0.0005 and 0.0020±0.0015 vs. 0.0002±0.0001, respectively), as well the ADMA/Tyr (0.34±0.09 vs. 0.12±0.02, p<0.0001) and the SDMA/Tyr ratio (0.10±0.04 vs. 0.015±0.004, p<0.0001).

CONCLUSIONS

The proposed method features simple specimen preparation, maintenance of an excellent peak shape of all metabolites and reduced matrix effects as well mass spectrometer noise. Moreover, the possibility to perform different cycles of enrichment, using large injection volumes, compensated for the low concentration of analytes contained in EBC, leading to a good analytical sensitivity. Preliminary data obtained from asthmatic and healthy adolescents, demonstrated that the analytical method applied to EBC seems suitable not only for research purposes, but also for clinical routinely analysis.

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.

Relationship between DDAH gene variants and serum ADMA level in individuals with type 1 diabetes

Asymmetric dimethylarginine (ADMA) levels are elevated in diabetes and likely contribute to diabetic complications such as retinopathy and nephropathy. The DDAH enzymes are primarily responsible for ADMA metabolism. Polymorphisms in the dimethylarginine dimethylaminohydrolase (DDAH) 1 and 2 genes have been previously associated with serum ADMA levels in type 2 diabetes (T2DM). We sought to determine whether they are also associated with ADMA levels in individuals with type 1 diabetes (T1DM). Serum ADMA concentrations were measured in 196 individuals with T1DM. Twenty-six tag SNPs in the DDAH1 gene and 10 in the DDAH2 gene were genotyped. One SNP in the DDAH1 gene (rs3738111) and one in the DDAH2 gene (rs805293) showed a correlation with serum ADMA levels; however, neither survived correction for multiple testing. We found limited evidence that genetic polymorphisms in DDAH genes influence serum ADMA levels in individuals with T1DM. This differs to findings in T2DM and may be due to underlying differences in the cohorts or to fundamental differences in the pathogenesis of the two types of diabetes.

Severely decreased activity of placental dimethylarginine dimethylaminohydrolase in pre-eclampsia

OBJECTIVES

Asymmetric dimethylarginine (ADMA) is a key regulator of nitric oxide production. Elevations of ADMA have previously been associated with endothelial dysfunction in pre-eclamptic women. ADMA is degraded mainly by dimethylarginine dimethylaminohydrolase (DDAH), which is also expressed in placental tissue. Therefore, we measured placental DDAH expression and activity in pre-eclampsia and normal pregnancies in order to determine whether impairment of this enzyme in the pre-eclamptic placenta could contribute to elevations of ADMA levels in these women.

STUDY DESIGN

ADMA plasma levels were measured by LC-MS/MS in 18 pre-eclamptic patients and 28 controls. Placental DDAH activity was determined by measuring the degradation of [(2)H(6)]-labeled ADMA in tissue homogenates from placental biopsies in 15 women with pre-eclampsia and 16 controls. Placental mRNA expression of DDAH 1, DDAH 2, endothelial nitric oxide synthase (eNOS), inducible nitric oxide synthase (iNOS) and protein-arginine methyltransferase 1 (PRMT1) was determined in tissue biopsies by RT-PCR.

RESULTS

Placental DDAH activity was almost undetectable in pre-eclampsia, and it was significantly higher in controls. ADMA plasma levels were higher in pre-eclampsia as compared to normal pregnancies (0.51±0.15μmol/l vs. 0.42±0.07μmol/l; p=0.005), and the difference between maternal and fetal ADMA levels (feto-maternal ADMA gradient) was lower in pre-eclampsia (0.63±0.20μmol/l vs. 0.80±0.18μmol/l; p=0.02). Furthermore, mRNA expression levels of DDAH 2 were significantly lower in pre-eclamptic women (p=0.04), while PRMT1 expression levels were the same. In pre-eclampsia, we found only weak correlations between maternal ADMA levels and DDAH 1 (r=-0.41; p=0.22) and DDAH 2 expressions (r=-0.45; p=0.17) but a slightly stronger correlation between DDAH 2 expression and feto-maternal ADMA gradient (r=0.60; p=0.07).

CONCLUSION

Decreased DDAH activity in the pre-eclamptic placenta might contribute to elevated ADMA levels in these patients.

Reference intervals for plasma L-arginine and the L-arginine:asymmetric dimethylarginine ratio in the Framingham Offspring Cohort

L-arginine, as a precursor of NO synthesis, has attracted much scientific attention in recent years. Experimental mouse models suggest that L-arginine supplementation can retard, halt, or even reverse atherogenesis. In human studies, supplementation with L-arginine improved endothelium-dependent vasodilation. However, L-arginine levels are best interpreted in the context of levels of asymmetric dimethylarginine (ADMA), a competitive inhibitor of NO synthase. Thus, reference limits for circulating L-arginine and the L-arginine:ADMA ratio may help to determine the nutritional state of individuals at high cardiovascular risk in light of increased ADMA levels. We defined reference limits for plasma L-arginine in 1141 people and for the L-arginine:ADMA ratio in 1138 relatively healthy individuals from the Framingham Offspring Cohort. Plasma L-arginine and ADMA concentrations were determined by using a stable isotope-based LC-MS/MS method. The reference limits (2.5th and 97.5th percentiles) for plasma L-arginine were 41.0 μmol/L (95% CI = 39.5-42.5 μmol/L) and 114 μmol/L (95% CI = 112-115 μmol/L), whereas corresponding reference limits (2.5th and 97.5th percentiles) for the L-arginine:ADMA ratio were 74.3 μmol/L (95% CI = 71.1-77.3 μmol/L) and 225 μmol/L (95% CI = 222-228 μmol/L). Plasma L-arginine was positively associated with the estimated glomerular filtration rate (eGFR) and blood glucose levels, whereas the L-arginine:ADMA ratio was positively associated with eGFR and diastolic blood pressure but inversely associated with homocysteine and (log)C-reactive protein. We report reference levels for plasma L-arginine and for the L-arginine:ADMA ratio that may be helpful for evaluation of the effects of L-arginine supplementation in participants with an impaired L-arginine/NO pathway.