Simultaneous GC-ECNICI-MS measurement of nitrite, nitrate and creatinine in human urine and plasma in clinical settings

Comprehensive GC-MS Measurement of Amino Acids, Metabolites, and Malondialdehyde in Metformin-Associated Lactic Acidosis at Admission and during Renal Replacement Treatment

Metformin is the most widely used drug in type 2 diabetes. Regular metformin use has been associated with changes in concentrations of amino acids. In the present study, we used valid stable-isotope labeled GC-MS methods to measure amino acids and metabolites, including creatinine as well as malondialdehyde (MDA), as an oxidative stress biomarker in plasma, urine, and dialysate samples in a patient at admission to the intensive care unit and during renal replacement treatment because of metformin-associated lactic acidosis (MALA, 21 mM lactate, 175 µM metformin). GC-MS revealed lower concentrations of amino acids in plasma, normal concentrations of the nitric oxide (NO) metabolites nitrite and nitrate, and normal concentrations of MDA. Renal tubular reabsorption rates were altered on admission. The patient received renal replacement therapy over 50 to 70 h of normalized plasma amino acid concentrations and their tubular reabsorption, as well as the tubular reabsorption of nitrite and nitrate. This study indicates that GC-MS is a versatile analytical tool to measure different classes of physiological inorganic and organic substances in complex biological samples in clinical settings such as MALA.

Advancements in Preprocessing and Analysis of Nitrite and Nitrate since 2010 in Biological Samples: A Review

As a substance present in organisms, nitrite is a metabolite of nitric oxide and can also be ingested. Nitrate is the metabolite of nitrite. Therefore, it is necessary to measure it quickly, easily and accurately to evaluate the health status of humans. Although there have been several reviews on analytical methods for non-biological samples, there have been no reviews focused on both sample preparation and analytical methods for biological samples. First, rapid and accurate nitrite measurement has significant effects on human health. Second, the detection of nitrite in biological samples is problematic due to its very low concentration and matrix interferences. Therefore, the pretreatment plus measuring methods for nitrite and nitrate obtained from biological samples since 2010 are summarized in the present review, and their prospects for the future are proposed. The treatment methods include liquid-liquid microextraction, various derivatization reactions, liquid-liquid extraction, protein precipitation, solid phase extraction, and cloud point extraction. Analytical methods include spectroscopic methods, paper-based analytical devices, ion chromatography, liquid chromatography, gas chromatography-mass spectrometry, electrochemical methods, liquid chromatography-mass spectrometry and capillary electrophoresis. Derivatization reagents with rapid quantitative reactions and advanced extraction methods with high enrichment efficiency are also included. Nitrate and nitrate should be determined at the same time by the same analytical method. In addition, much exploration has been performed on formulating fast testing through microfluidic technology. In this review, the newest developments in nitrite and nitrate processing are a focus in addition to novel techniques employed in such analyses.

Impaired Nitric Oxide Synthetase Activity in Primary Ciliary Dyskinesia-Data-Driven Hypothesis

Low nasal nitric oxide (nNO) is a typical feature of Primary Ciliary Dyskinesia (PCD). nNO is part of the PCD diagnostic algorithm due to its discriminative power against other lung diseases, such as cystic fibrosis (CF). However, the underlying pathomechanisms are elusive. To better understand NO dysregulation in PCD, the L-arginine/NO (Arg/NO) pathway in patients with PCD (pwPCD) and CF (pwCF) and in healthy control (HC) subjects was investigated. In a prospective, controlled study, we measured in 24 pwPCD, 25 age-matched pwCF, and 14 HC the concentrations of the NO precursors Arg and homoarginine (hArg), the arginase metabolite ornithine (Orn), the NO inhibitor asymmetric dimethylarginine (ADMA), and the major NO metabolites (nitrate, nitrite) in sputum, plasma, and urine using validated methods. In comparison to HC, the sputum contents (in µmol/mg) of L-Arg (PCD 18.43 vs. CF 329.46 vs. HC 9.86, p < 0.001) and of ADMA (PCD 0.055 vs. CF 0.015 vs. HC 0.010, p < 0.001) were higher. In contrast, the sputum contents (in µmol/mg) of nitrate and nitrite were lower in PCD compared to HC (nitrite 4.54 vs. 9.26, p = 0.023; nitrate 12.86 vs. 40.33, p = 0.008), but higher in CF (nitrite 16.28, p < 0.001; nitrate 56.83, p = 0.002). The metabolite concentrations in urine and plasma were similar in all groups. The results of our study indicate that PCD, unlike CF, is associated with impaired NO synthesis in the lung, presumably due to mechano-chemical uncoupling.

l-Arginine/nitric oxide pathway and oxidative stress in adults with ADHD: Effects of methylphenidate treatment

INTRODUCTION

Attention deficit hyperactivity disorder (ADHD) is a mental disorder that was once thought to occur only in children. Meanwhile, it is known that adults can also be affected. The first-line drug in children and adults to treat symptoms of inattention, impulsivity, lack of self-regulation, and hyperactivity is methylphenidate (MPH). Known adverse effects of MPH include cardiovascular problems, such as elevated blood pressure and heart rate. Therefore, biomarkers to monitor potential cardiovascular side effects of MPH are needed. The l-Arginine/Nitric oxide (Arg/NO) pathway is involved in noradrenaline and dopamine release as well as in normal cardiovascular functioning and is therefore a prime candidate for the search of biomarkers. The aim of the present study was to investigate the Arg/NO pathway as well as oxidative stress in adult ADHD patients in plasma and urine and the potential influence of MPH medication.

METHODS

In plasma and urine samples of 29 adults with ADHD (39.2 ± 10.9 years) and 32 healthy adults serving as controls (CO) (38.0 ± 11.6 years) the major NO metabolites nitrite and nitrate, Arg, the NO synthesis inhibitor asymmetric dimethylarginine (ADMA) and its major urinary metabolite dimethylamine (DMA) as well as malondialdehyde (MDA) were measured by gas chromatography-mass spectrometry.

RESULTS

Of the 29 patients with ADHD 14 were currently without MPH treatment (-MPH) and 15 were treated with MPH (+MPH). Plasma nitrate concentrations were significantly higher in patients not treated with MPH vs. CO (-MPH 60.3 μM [46.2-76.0] vs. CO 44.4 μM [35.0-52.7]; p = 0.002), while plasma nitrite tended to be higher in -MPH patients (2.77 μM [2.26-3.27]) vs. CO (2.13 μM [1.50-2.93]; p = 0.053). Additionally, plasma creatinine concentrations were significantly different, with -MPH showing significantly higher concentrations than the other two groups (-MPH 141 μM [128-159]; +MPH 96.2 μM [70.2-140]; Co 75.9 μM [62.0-94.7]; p < 0.001). Urinary creatinine excretion tended to be lowest in -MPH group vs. +MPH and CO (-MPH 11.4 ± 8.88 mM; +MPH 20.7 ± 9.82 mM; 16.6 ± 7.82 mM; p = 0.076). None of the other metabolites, including MDA, a marker of oxidative stress, showed a difference between the groups.

CONCLUSION

Adult patients with ADHD, who are not treated with MPH (-MPH), showed varied Arg/NO pathway, but Arg bioavailability seemed to be consistent over the groups. Our findings imply that urinary reabsorption may be increase and/or excretion of nitrite and nitrate may be decreased in ADHD, resulting in an increase in the plasma concentration of nitrite. MPH seems to partially reverse these effects by not yet known mechanisms, and does not affect oxidative stress.

Pentafluoropropionic Anhydride Derivatization and GC-MS Analysis of Histamine, Agmatine, Putrescine, and Spermidine: Effects of Solvents and Starting Column Temperature

Gas chromatography-mass spectrometry (GC-MS) is useful for the quantitative determination of the polyamines spermidine (SPD) and putrescine (PUT) and of the biogenic amine agmatine (AGM) in biological samples after derivatization. This GC-MS method involves a two-step extraction with n-butanol and hydrochloric acid, derivatization with pentafluoropropionic anhydride (PFPA) in ethyl acetate, and extraction of the pentafluoropropionic (PFP) derivatives by toluene of SPD, PUT, and AGM. We wanted to extend this GC-MS method for the biogenic amine histamine (HA), but we faced serious problems that did not allow reliable quantitative analysis of HA. In the present work, we addressed this issue and investigated the derivatization of HA and the effects of toluene and ethyl acetate, two commonly used water-insoluble organic solvents in GC-MS, and oven temperature program. Derivatization of unlabelled HA (d₀-HA) and deuterium-labelled HA (d₄-HA) with PFPA in ethyl acetate (PFPA-EA, 1:4, v/v; 30 min, 65 °C) resulted in the formation of d₀-HA-(PFP)₂ and d₄-HA-(PFP)₂ derivatives. d₄-HA and ¹³C₄-SPD were used as internal standards for the amines after standardization. Considerable quantitative effects of toluene and ethyl acetate were observed. The starting GC column temperature was also found to influence considerably the GC-MS analysis of HA. Our study shows the simultaneous quantitative analysis of HA as HA-(PFP)₂, AGM as AGM-(PFP)₃, PUT as PUT-(PFP)₂, and SPD as SPD-(PFP)₃ derivatives requires the use of ethyl acetate for their extraction and injection into the GC-MS apparatus and a starting GC column temperature of 40 °C instead of 70 °C. The PFP derivatives of HA, AGM, PUT, and SPD were found to be stable in ethyl acetate for several hours at room temperature. Analytically satisfactory linearity, precision, and accuracy were observed for HA, AGM, PUT, and SPD in biologically relevant ranges (0 to 700 pmol). The limits of detection of AGM, PUT, and SPD were about two times lower in ethyl acetate compared to toluene (range, 1-22 fmol). The limits of detection were 1670 fmol for d₀-HA and 557 fmol for d₄-HA. Despite the improvements achieved in the study for HA, its analysis by GC-MS as a PFP derivative is challenging and less efficient than that of PUT, AGM, and SPD.

Determining Underlying Mechanisms of Early Vascular Ageing by Clustered Analysis: The African-PREDICT Study

OBJECTIVE

Identifying individuals at increased risk of early vascular ageing (EVA) is paramount to inform intervention and prevention strategies and curb the increasing burden of cardiovascular disease.

METHODS

We stratified and phenotyped pre-screened young apparently healthy South African adults (20-30 yrs) (n=1,041) into vascular ageing profile groups based on carotid femoral pulse wave velocity (cfPWV) percentiles (healthy vascular ageing [HVA]; average vascular ageing [AVA] and EVA). We further compared various anthropometric, cardiovascular (CV), oxidative stress and lifestyle risk factors and determined factor scores to explore associations between CV measures and factor clusters to explore associations in those at risk of EVA.

RESULTS

Young adults in the EVA group displayed marked phenotypic characteristics in terms of anthropometry, CV, and lifestyle risk factors, even though cfPWV were within healthy ranges. Blood pressure (brachial and central) and cfPWV were all incrementally higher across all three vascular ageing groups (p-trend ≤0.011). Hypertension, lifestyle risk factors such as self-reported smoking and alcohol consumption were all highest in the EVA group (p-trend ≤0.046). Additionally, in the EVA group only, cfPWV (adj. R²=0.028; β=0.171; p=0.042) associated positively with Factor 2 (oxidative stress and antioxidant capacity). No associations existed between Factor 1 (basic lipids) and any anthropometric or CV measures (p>0.050).

CONCLUSION

Young adults with higher cfPWV presented with a less favourable vascular profile and more unhealthy lifestyle behaviours compared to groups with lower cfPWV. In the EVA group, cfPWV positively associated with a cluster of oxidative stress and antioxidant capacity. Early lifestyle behaviours may have the ability to modify the balance between oxidants and antioxidants, potentially contributing to early onset arterial stiffness.

Short-Term Supplementation of Sodium Nitrate vs. Sodium Chloride Increases Homoarginine Synthesis in Young Men Independent of Exercise

The aim of the study was to investigate the effects of short-term oral administration of inorganic nitrate (NaNO3; n = 8) or placebo (NaCl; n = 9) (each 0.1 mmol/kg body weight/d for 9 days) on plasma amino acids, creatinine, and oxidative stress in healthy young men. At baseline, the plasma concentrations of amino acids did not differ between the groups. At the end of the study, the plasma concentrations of homoarginine (hArg; by 24%, p = 0.0001), citrulline and ornithine (Cit/Orn; by 16%, p = 0.015), and glutamine/glutamate (Gln/Glu; by 6%, p = 0.0003) were higher in the NaNO3 group compared to the NaCl group. The plasma concentrations of sarcosine (Sarc; by 28%, p < 0.0001), tyrosine (by 14%, p = 0.0051), phenylalanine (by 8%, p = 0.0026), and tryptophan (by 8%, p = 0.0047) were lower in the NaNO3 group compared to the NaCl group. These results suggest that nitrate administration affects amino-acid metabolism. The arginine/glycine amidinotransferase (AGAT) catalyzes two reactions: (1) the formation of l-homoarginine (hArg) and l-ornithine (Orn) from l-arginine (Arg) and l-lysine (Lys): Arg + Lys <−> hArg + Orn, with equilibrium constant Kharg; (2) the formation of guanidinoacetate (GAA) and Orn from Arg and glycine (Gly): Arg + Gly <−> GAA + Orn, with equilibrium constant Kgaa. The plasma Kgaa/KhArg ratio was lower in the NaNO3 group compared to the NaCl group (1.57 vs. 2.02, p = 0.0034). Our study suggests that supplementation of inorganic nitrate increases the AGAT-catalyzed synthesis of hArg and decreases the N-methyltransferase-catalyzed synthesis of GAA, the precursor of creatine. To our knowledge, this is the first study to demonstrate elevation of hArg synthesis by inorganic nitrate supplementation. Remarkably, an increase of 24% corresponds to the synthesis capacity of one kidney in healthy humans. Differences in the association between plasma concentrations of amino acids in the NaNO3 and NaCl groups suggest changes in amino-acid homeostasis. Plasma concentrations of the oxidative stress marker malondialdehyde (MDA) did not change after supplementation of NaNO3 or NaCl over the whole exercise time range. Plasma nitrite concentration turned out to be a more discriminant marker of NaNO3 ingestion than plasma nitrate (area under the receiver operating characteristic curve: 0.951 vs. 0.866, p < 0.0001 each).

Stable-Isotope Dilution GC-MS Measurement of Metformin in Human Serum and Urine after Derivatization with Pentafluoropropionic Anhydride and Its Application in Becker Muscular Dystrophy Patients Administered with Metformin, l-Citrulline, or Their Combination

Metformin (N,N-dimethylguanylguanidine) is one of the most prescribed drugs with pleiotropic, exerted in part by not fully elucidated mechanisms of action. We developed and validated a gas chromatography-mass spectrometry (GC-MS) method for the quantitative analysis of metformin (metformin-d₀) in 10-µL aliquots of human serum and urine using N,N-[dimethylo-²H₆]guanylguanidine (metformin-d₆) as the internal standard. The method involves evaporation of the samples to dryness, derivatization with pentafluoropropionic (PFP) anhydride in ethyl acetate (30 min, 65 °C), and extraction into toluene. The negative-ion chemical ionization GC-MS spectra of the PFP derivatives contain a single intense ion with mass-to-charge (m/z) ratios of m/z 383 for metformin-d₀ and m/z 389 for metformin-d₆. Our results suggest that all amine/imine groups of metformin-d₀ and metformin-d₆ are converted to their N,N,N-tripentafluoropropionyl derivatives, which cyclize to form a symmetric triazine derivative, of which the non-ring amine group is amidated. Quantification was performed by selected-ion monitoring (SIM) of m/z 383 and m/z 389. Upon validation, the method was applied to determine serum and urine metformin concentrations in 19 patients with Becker muscular dystrophy (BMD). Serum and urine samples were collected at baseline (Visit I), after six weeks of supplementation (Visit II) with metformin (3 × 500 mg/d; metformin group; n = 10) or l-citrulline (3 × 1500 mg/d; citrulline group; n = 9) followed by a six-week supplementation with 3 × 500 mg/d of metformin plus 3 × 1500 mg/d l-citrulline. At Visit I, the metformin concentration in the serum and urine was very low in both groups. The metformin concentrations in the serum and urine of the patients who first took metformin (MET group) were higher at Visit II and Visit III. The metformin concentration in the serum and urine samples of the patients who first took l-citrulline (CITR group) were higher at Visit III. The serum and urine concentrations of metformin were insignificantly lower in the CITR group at Visit III. The mean fractional excretion (FE) rate of metformin was 307% (Visit II) and 322% (Visit III) in the MET group, and 290% in the CITR group (Visit III). This observation suggests the accumulation of metformin in the kidney and its secretion in the urine. The GC-MS is suitable to measure reliably circulating and excretory metformin in clinical settings.

Nitric oxide and long-term outcomes after kidney transplantation: Results of the TransplantLines cohort study

Impaired endogenous nitric oxide (NO) production may contribute to graft failure and premature mortality in kidney transplant recipients (KTR). We investigated potential associations of 24-h urinary NOx (NO₃^- + NO₂^-) excretion (uNOx) with long-term outcomes. uNOx was determined by HPLC and GC-MS in 698 KTR and in 132 kidney donors before and after donation. Additionally, we measured urinary nitroso species (RXNO) by gas-phase chemiluminescence. Median uNOx was lower in KTR compared to kidney donors (688 [393-1076] vs. 1301 [868-1863] before donation and 1312 [982-1853] μmol/24h after donation, P < 0.001). During median follow-up of 5.4 [4.8-6.1] years, 150 KTR died (61 due to cardiovascular disease) and 83 experienced graft failure. uNOx was inversely associated with all-cause mortality (HR per doubling of uNOx: 0.84 [95% CI 0.75-0.93], P < 0.001) and cardiovascular mortality (HR 0.78 [95% CI 0.67-0.92], P = 0.002). The association of uNOx with graft failure was lost when adjusted for renal function (HR per doubling of uNOx: 0.89 [95% CI 0.76-1.05], P = 0.17). There were no significant associations of urinary RXNO with outcomes. Our study suggests that KTR have lower NO production than healthy subjects and that lower uNOx is associated with a higher risk of all-cause and cardiovascular mortality.

Characterization of the L-Arginine/Nitric Oxide Pathway and Oxidative Stress in Pediatric Patients with Atopic Diseases

Introduction: L-Arginine (Arg) is a semi-essential amino acid. Constitutive and inducible nitric oxide synthase (NOS) isoforms convert Arg to nitric oxide (NO), a potent vaso- and bronchodilator with multiple biological functions. Atopic dermatitis (AD) and bronchial asthma (BA) are atopic diseases affecting many children globally. Several studies analyzed NO in airways, yet the systemic synthesis of NO in AD and BA in children with BA, AD or both is elusive. Methods: In a multicenter study, blood and urine were obtained from 130 of 302 participating children for the measurement of metabolites of the Arg/NO pathway (BA 31.5%; AD 5.4%; AD + BA 36.1%; attention deficit hyperactivity disorder (ADHD) 12.3%). In plasma and urine amino acids Arg and homoarginine (hArg), both substrates of NOS, asymmetric dimethylarginine (ADMA) and symmetric dimethylarginine (SDMA), both inhibitors of NOS, dimethylamine (DMA), and nitrite and nitrate, were measured by gas chromatography–mass spectrometry. Malondialdehyde (MDA) was measured in plasma and urine samples to evaluate possible effects of oxidative stress. Results: There were no differences in the Arg/NO pathway between the groups of children with different atopic diseases. In comparison to children with ADHD, children with AD, BA or AD and BA had higher plasma nitrite (p < 0.001) and nitrate (p < 0.001) concentrations, suggesting higher systemic NO synthesis in AD and BA. Urinary excretion of DMA was also higher (p = 0.028) in AD and BA compared to patients with ADHD, suggesting elevated ADMA metabolization. Discussion/Conclusion: The Arg/NO pathway is activated in atopic diseases independent of severity. Systemic NO synthesis is increased in children with an atopic disease. Plasma and urinary MDA levels did not differ between the groups, suggesting no effect of oxidative stress on the Arg/NO pathway in atopic diseases.

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.

Arginine metabolism and nitric oxide turnover in the ZSF1 animal model for heart failure with preserved ejection fraction

Endothelial dysfunction and altered nitric oxide (NO) metabolism are considered causal factors in heart failure with preserved ejection fraction (HFpEF). NO synthase activity depends on the availability of arginine and its derivatives. Thus, we analyzed arginine, associated metabolites, arginine-metabolizing enzymes and NO turnover in 20-week-old female healthy lean (L-ZSF1) and obese ZSF1 rats (O-ZSF1) with HFpEF. Serum, urine and lysates of liver, kidney and heart were analyzed. There were significantly lower lysine (− 28%), arginine (− 31%), homoarginine (− 72%) and nitrite (− 32%) levels in serum of O-ZSF1 rats. Ornithine (+ 60%) and citrulline (+ 20%) levels were higher. Similar results were found in the heart. Expression of arginine consuming enzymes in liver and kidney was unchanged. Instead, we observed a 5.8-fold higher arginase 1 expression, presumably of granulocyte origin, in serum and > fourfold increased cardiac macrophage invasion in O-ZSF1. We conclude that inflammatory cells in blood and heart consume arginine and probably homoarginine via arginase 1 and inducible NO synthase and release ornithine and citrulline. In combination with evidence for decreased NO turnover in O-ZSF1 rats, we assume lower arginine bioavailability to endothelial NO synthase.

Local and Systemic Alterations of the L-Arginine/Nitric Oxide Pathway in Sputum, Blood, and Urine of Pediatric Cystic Fibrosis Patients and Effects of Antibiotic Treatment

Alterations in the L-arginine (Arg)/nitric oxide (NO) pathway have been reported in cystic fibrosis (CF; OMIM 219700) as the result of various factors including systemic and local inflammatory activity in the airways. The aim of the present study was to evaluate the Arg/NO metabolism in pediatric CF patients with special emphasis on lung impairment and antibiotic treatment. Seventy CF patients and 78 healthy controls were included in the study. CF patients (43% male, median age 11.8 years) showed moderately impaired lung functions (FEV1 90.5 ± 19.1% (mean ± SD); 21 (30%) had a chronic Pseudomonas aeruginosa (PSA) infection, and 24 (33%) had an acute exacerbation). Plasma, urinary, and sputum concentrations of the main Arg/NO metabolites, nitrate, nitrite, Arg, homoarginine (hArg), and asymmetric dimethylarginine (ADMA) were determined in pediatric CF patients and in healthy age-matched controls. Clinical parameters in CF patients included lung function and infection with PSA. Additionally, the Arg/NO pathway in sputum samples of five CF patients was analyzed before and after routine antibiotic therapy. CF patients with low fractionally exhaled NO (FENO) showed lower plasma Arg and nitrate concentrations. During acute exacerbation, sputum Arg and hArg levels were high and dropped after antibiotic treatment: Arg: pre-antibiotics: 4.14 nmol/25 mg sputum vs. post-antibiotics: 2.33 nmol/25 mg sputum, p = 0.008; hArg: pre-antibiotics: 0.042 nmol/25 mg sputum vs. post-antibiotics: 0.029 nmol/25 mg sputum, p = 0.035. The activated Arg/NO metabolism in stable CF patients may be a result of chronic inflammation. PSA infection did not play a major role regarding these differences. Exacerbation increased and antibiotic therapy decreased sputum Arg concentrations.

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.

Activated L-Arginine/Nitric Oxide Pathway in Pediatric Cystic Fibrosis and Its Association with Pancreatic Insufficiency, Liver Involvement and Nourishment: An Overview and New Results

Cystic fibrosis (CF; OMIM 219700) is a rare genetic disorder caused by a chloride channel defect, resulting in lung disease, pancreas insufficiency and liver impairment. Altered L-arginine (Arg)/nitric oxide (NO) metabolism has been observed in CF patients’ lungs and in connection with malnutrition. The aim of the present study was to investigate markers of the Arg/NO pathway in the plasma and urine of CF patients and to identify possible risk factors, especially associated with malnutrition. We measured the major NO metabolites nitrite and nitrate, Arg, a semi-essential amino acid and NO precursor, the NO synthesis inhibitor asymmetric dimethylarginine (ADMA) and its major urinary metabolite dimethylamine (DMA) in plasma and urine samples of 70 pediatric CF patients and 78 age-matched healthy controls. Biomarkers were determined by gas chromatography–mass spectrometry and high-performance liquid chromatography. We observed higher plasma Arg (90.3 vs. 75.6 µM, p < 0.0001), ADMA (0.62 vs. 0.57 µM, p = 0.03), Arg/ADMA ratio (148 vs. 135, p = 0.01), nitrite (2.07 vs. 1.95 µM, p = 0.03) and nitrate (43.3 vs. 33.1 µM, p < 0.001) concentrations, as well as higher urinary DMA (57.9 vs. 40.7 µM/mM creatinine, p < 0.001) and nitrate (159 vs. 115 µM/mM creatinine, p = 0.001) excretion rates in the CF patients compared to healthy controls. CF patients with pancreatic sufficiency showed plasma concentrations of the biomarkers comparable to those of healthy controls. Malnourished CF patients had lower Arg/ADMA ratios (p = 0.02), indicating a higher NO synthesis capacity in sufficiently nourished CF patients. We conclude that NO production, protein-arginine dimethylation, and ADMA metabolism is increased in pediatric CF patients. Pancreas and liver function influence Arg/NO metabolism. Good nutritional status is associated with higher NO synthesis capacity and lower protein-arginine dimethylation.

Nitric oxide-related markers link inversely to blood pressure in black boys and men: the ASOS and African-PREDICT studies

Nitric oxide plays an important role in maintaining endothelial function, while increased oxidative stress may lead to nitric oxide inactivation and cardiovascular disease. If nitric oxide biosynthesis/bioavailability is already suppressed early in life, it may potentially predispose an individual to the early development of cardiovascular disease. We therefore aimed to identify differences in nitric oxide-related markers (urinary nitrate, nitrite and the nitrate-to-nitrite ratio (U_NOxR)) between young black and white individuals, and whether these markers are associated with blood pressure and carotid intima media thickness. We included black and white healthy boys (n = 80; aged 6-8 years) and men (n = 510; 20-30 years) and measured blood pressure and carotid intima media thickness, along with urinary biochemical markers including nitrate and nitrite. The black boys and men had lower nitrate and U_NOxR (all p ≤ 0.003) than their white counterparts. In single and multiple regression analyses, we found an inverse association of diastolic blood pressure in the black boys (adj. R² = 0.27; β = -0.32; p = 0.030), and systolic blood pressure in black men (adj. R² = 0.07; β = -0.13; p = 0.036) with nitrate. Carotid intima media thickness associated inversely with U_NOxR in the black men (adj. R² = 0.02; β = -0.14; p = 0.023), but not in the boys. Lower urinary nitrate in black boys and young men was associated negatively with blood pressure, suggesting that potentially lower nitric oxide bioavailability in young black individuals may contribute to hypertension development in later life.

Enhanced Nitric Oxide (NO) and Decreased ADMA Synthesis in Pediatric ADHD and Selective Potentiation of NO Synthesis by Methylphenidate

Attention deficit hyperactivity disorder (ADHD) is a common pediatric psychiatric disorder, frequently treated with methylphenidate (MPH). Recently, MPH’s cardiovascular safety has been questioned by observational studies describing an increased cardiovascular risk in adults and blood pressure alterations in children. We considered members of the L-arginine (Arg)/nitric oxide (NO) pathway as possible early cardiovascular risk factors in pediatric ADHD children. They include the NO metabolites, nitrite and nitrate, the NO precursor Arg, and asymmetric dimethylarginine (ADMA), an endogenous NO synthase (NOS) inhibitor and a cardiovascular risk factor in adults. We conducted a prospective clinical trial with 42 ADHD children (aged 6–16 years) with (n = 19) and without (n = 23) MPH treatment. Age-matched children without ADHD (n = 43) served as controls. All plasma and urine metabolites were determined by gas chromatography-mass spectrometry. We observed higher plasma nitrite and lower plasma ADMA concentrations in the ADHD children. MPH-treated ADHD children had higher plasma nitrite concentrations than MPH-untreated ADHD children. As NOS activity is basally inhibited by ADMA, MPH treatment seems to have decreased the inhibitory potency of ADMA. Percentiles of systolic blood pressure were higher in MPH-treated ADHD children. The underlying mechanisms and their implications in the MPH therapy of pediatric ADHD with MPH remain to be elucidated in larger cohorts.

Advances in the Detection, Mechanism and Therapy of Chronic Kidney Disease

Chronic Kidney Disease (CKD) is characterized by the gradual loss of renal mass and functions. It has become a global health problem, with hundreds of millions of people being affected. Both its incidence and prevalence are increasing over time. More than $20,000 are spent on each patient per year. The economic burden on the patients, as well as the society, is heavy and their life quality worsen over time. However, there are still limited effective therapeutic strategies for CKD. Patients mainly rely on dialysis and renal transplantation, which cannot prevent all the complications of CKD. Great efforts are needed in understanding the nature of CKD progression as well as developing effective therapeutic methods, including pharmacological agents. This paper reviews three aspects in the research of CKD that may show great interests to those who devote to bioanalysis, biomedicine and drug development, including important endogenous biomarkers quantification, mechanisms underlying CKD progression and current status of CKD therapy.

Exercise-Induced Oxidative Stress, Nitric Oxide and Plasma Amino Acid Profile in Recreational Runners with Vegetarian and Non-Vegetarian Dietary Patterns

This study investigated the exercise-induced changes in oxidative stress, nitric oxide (NO) metabolism and amino acid profile in plasma of omnivorous (OMN, n = 25), lacto-ovo-vegetarian (LOV, n = 25) and vegan (VEG, n = 23) recreational runners. Oxidative stress was measured as malondialdehyde (MDA), NO as nitrite and nitrate, and various amino acids, including homoarginine and guanidinoacetate, the precursor of creatine. All analytes were measured by validated stable-isotope dilution gas chromatographic-mass spectrometric methods. Pre-exercise, VEG had the highest MDA and nitrate concentrations, whereas nitrite concentration was highest in LOV. Amino acid profiles differed between the groups, with guanidinoacetate being highest in OMN. Upon acute exercise, MDA increased in the LOV and VEG group, whereas nitrate, nitrite and creatinine did not change. Amino acid profiles changed post-exercise in all groups, with the greatest changes being observed for alanine (+28% in OMN, +21% in LOV and +28% in VEG). Pre-exercise, OMN, LOV and VEG recreational runners differ with respect to oxidative stress, NO metabolism and amino acid profiles, in part due to their different dietary pattern. Exercise elicited different changes in oxidative stress with no changes in NO metabolism and closely comparable elevations in alanine. Guanidinoacetate seems to be differently utilized in OMN, LOV and VEG, pre- and post-exercise.

Nitrogen-doped-carbon-coated hexagonal cobalt oxyhydroxide/reduced graphene oxide nanocomposite for sensitive and selective detection of nitrite in human hepatoma cells

Selective and sensitive determination of nitrite is of great importance in practical application. In the present work, a novel nitrite sensing platform was built based on the fabrication of nitrogen-doped-carbon-coated hexagonal cobalt oxyhydroxide (CN@CoOOH) on reduced graphene oxide (RGO) using zeolitic imidazolate framework (ZIF)-67 as a precursor. The CN@CoOOH/RGO nanocomposite was confirmed by UV-visible spectroscopy, Fourier transform infrared spectroscopy, x-ray photoelectron spectrum, transmission electron microscopy, scanning electron microscopy, and x-ray diffraction. We applied the nanocomposite to detect nitrite selectively and sensitively through amperometry for the first time. The anodic current values increased with the addition of nitrite. Therefore, the concentrations of nitrite were quantitatively detected using a CN@CoOOH/RGO based sensor. A wider linear range of 0.1 to 7000 μM was obtained with a lower detection limit of 10 nM (S/N = 3). The proposed method was also applied to detect nitrite released from normal liver cells and human hepatoma cells.

Long-term effects of NO3- on the relationship between oxygen uptake and power after three weeks of supplemented HIHVT

The aim of this study was to investigate the later effects of daily NO3- supplementation over 3 wk of training on the relationship between O₂ uptake and power at different intensities with an incremental test (IT), a double-wingate test (WT), and an endurance capacity test at 80% W_max (ECT) before and after the supplementation period. Seventeen male recreational athletes participated in this double-blind placebo (PL)-controlled study. Subjects participated in a 3-wk intermittent high-intensity, high-volume training period with 45 intervals of W_max - 10 W and an active recovery period of 10 W in between with dietary NO3- (NaNO₃) or placebo supplementation (NaCl) (both 8.5 mg·kg^-1·day^-1) on a cycle ergometer. During a training session, plasma [ NO3- ] ( P < 0.001) and plasma [ NO2- ] ( P < 0.01) were higher in nitrate (N), whereas in pre- and posttests mean plasma [ NO3- ] and [ NO2- ] were not different between groups. In the WT [48 h after cessation of supplementation (C)], the ratio between V̇o₂ and power decreased in N ( P < 0.01) with no changes in PL. Endurance capacity (4-5 days after C) similarly increased in both groups ( P < 0.01). However, the total oxygen consumption decreased by 5% ( P < 0.01) in N, with no change in PL. The slope of V̇o₂·W^-1 in IT (5-7 days after C) decreased in N ( P < 0.01), whereas no changes were found in PL. During low- and moderate-intensity workloads, no changes and differences in V̇o₂ could be detected. We conclude that nitrate supplementation causes a sustaining reduction of the oxygen cost per watt during exercise with a large recruitment of type II muscle fibers without affecting endurance capacity. NEW & NOTEWORTHY Because most studies focused on the acute effects of NO3- supplementation on exercise performance during a supplementation period, the sustainability of the effects of the NO3- supplementation remain unknown. We followed the development of V̇o₂/W at different intensities during the first week after cessation of daily NO3- supplementation over 3 wk. The results indicate that NO3- supplementation has a long-term effect for at least 7 days after cessation during heavy all-out workloads without affecting endurance capacity.

Effects of single and combined metformin and L-citrulline supplementation on L-arginine-related pathways in Becker muscular dystrophy patients: possible biochemical and clinical implications

The L-arginine/nitric oxide synthase (NOS) pathway is considered to be altered in muscular dystrophy such as Becker muscular dystrophy (BMD). We investigated two pharmacological options aimed to increase nitric oxide (NO) synthesis in 20 male BMD patients (age range 21-44 years): (1) supplementation with L-citrulline (3 × 5 g/d), the precursor of L-arginine which is the substrate of neuronal NO synthase (nNOS); and (2) treatment with the antidiabetic drug metformin (3 × 500 mg/d) which activates nNOS in human skeletal muscle. We also investigated the combined use of L-citrulline (3 × 5 g/d) and metformin (3 × 500 mg/d). Before and after treatment, we measured in serum and urine samples the concentration of amino acids and metabolites of L-arginine-related pathways and the oxidative stress biomarker malondialdehyde (MDA). Compared to healthy subjects, BMD patients have altered NOS, arginine:glycine amidinotransferase (AGAT) and guanidinoacetate methyltransferase (GAMT) pathways. Metformin treatment resulted in concentration decrease of arginine and MDA in serum, and of homoarginine (hArg) and guanidinoacetate (GAA) in serum and urine. L-Citrulline supplementation resulted in considerable increase of the concentrations of amino acids and creatinine in the serum, and in their urinary excretion rates. Combined use of metformin and L-citrulline attenuated the effects obtained from their single administrations. Metformin, L-citrulline or their combination did not alter serum nitrite and nitrate concentrations and their urinary excretion rates. In conclusion, metformin or L-citrulline supplementation to BMD patients results in remarkable antidromic changes of the AGAT and GAMT pathways. In combination, metformin and L-citrulline at the doses used in the present study seem to abolish the biochemical effects of the single drugs in slight favor of L-citrulline.

Results, meta-analysis and a first evaluation of UNOxR, the urinary nitrate-to-nitrite molar ratio, as a measure of nitrite reabsorption in experimental and clinical settings

We recently found that renal carbonic anhydrase (CA) is involved in the reabsorption of inorganic nitrite (NO₂^-), an abundant reservoir of nitric oxide (NO) in tissues and cells. Impaired NO synthesis in the endothelium and decreased NO bioavailability in the circulation are considered major contributors to the development and progression of renal and cardiovascular diseases in different conditions including diabetes. Isolated human and bovine erythrocytic CAII and CAIV can convert nitrite to nitrous acid (HONO) and its anhydride N₂O₃ which, in the presence of thiols (RSH), are further converted to S-nitrosothiols (RSNO) and NO. Thus, CA may be responsible both for the homeostasis of nitrite and for its bioactivation to RSNO/NO. We hypothesized that enhanced excretion of nitrite in the urine may contribute to NO-related dysfunctions in the renal and cardiovascular systems, and proposed the urinary nitrate-to-nitrite molar ratio, i.e., U_NOxR, as a measure of renal CA-dependent excretion of nitrite. Based on results from clinical and experimental animal studies, here, we report on a first evaluation of U_NOxR. We determined U_NOxR values in preterm neonates, healthy children, and adults, in children suffering from type 1 diabetes mellitus (T1DM) or Duchenne muscular dystrophy (DMD), in elderly subjects suffering from chronic rheumatic diseases, type 2 diabetes mellitus (T2DM), coronary artery disease (CAD), or peripheral arterial occlusive disease (PAOD). We also determined U_NOxR values in healthy young men who ingested isosorbide dinitrate (ISDN), pentaerythrityl tetranitrate (PETN), or inorganic nitrate. In addition, we tested the utility of U_NOxR in two animal models, i.e., the LEW.1AR1-iddm rat, an animal model of human T1DM, and the APOE*3-Leiden.CETP mice, a model of human dyslipidemia. Mean U_NOxR values were lower in adult patients with rheumatic diseases (187) and in T2DM patients of the DALI study (74) as compared to healthy elderly adults (660) and healthy young men (1500). The intra- and inter-variabilities of U_NOxR were of the order of 50% in young and elderly healthy subjects. U_NOxR values were lower in black compared to white boys (314 vs. 483, P = 0.007), which is in line with reported lower NO bioavailability in black ethnicity. Mean U_NOxR values were lower in DMD (424) compared to healthy (730) children, but they were higher in T1DM children (1192). ISDN (3 × 30 mg) decreased stronger U_NOxR compared to PETN (3 × 80 mg) after 1 day (P = 0.046) and after 5 days (P = 0.0016) of oral administration of therapeutically equivalent doses. In healthy young men who ingested NaNO₃ (0.1 mmol/kg/d), U_NOxR was higher than in those who ingested the same dose of NaCl (1709 vs. 369). In LEW.1AR1-iddm rats, mean U_NOxR values were lower than in healthy rats (198 vs. 308) and comparable to those in APOE*3-Leiden.CETP mice (151).

The role of L-arginine/L-homoarginine/nitric oxide pathway for aortic distensibility and intima-media thickness in stroke patients

Asymmetric dimethylarginine (ADMA) and L-homoarginine (hArg) are L-arginine (Arg) metabolites derived from different pathways. Protein arginine N-methyltransferase (PRMT) and subsequent proteolysis of proteins containing methylarginine residues release ADMA. Arginine:glycine amidinotransferase (AGAT) converts Arg to hArg and guanidinoacetate (GAA). While high concentrations of ADMA and low concentrations of hArg in the blood have been established as cardiovascular risk markers, the cardiovascular relevance of GAA is still unexplored. Arg and hArg are substrates and ADMA is an inhibitor of nitric oxide (NO) synthase (NOS). The cardiovascular effects of ADMA and hArg have been related to NO, a potent endogenous vasodilator. ADMA and hArg are considered to exert additional, not yet explored, presumably NO-unrelated effects and to act antagonistically in the renal and cardiovascular systems. Although the physiological role of Arg, ADMA, hArg and NO for endothelial function in small- and medium-sized arteries has been intensively studied in the past, the clinical relevance of aortic wall remodeling still remains unclear. Here, we evaluated potential relation between aortic distensibility (AD) or aortic intima-media thickness (aIMT) and circulating ADMA, hArg, GAA, and the NO metabolites nitrite and nitrate in the plasma of 78 patients (24 females, 54 males; aged 59 ± 14 years) with recent ischemic stroke or transient ischemic attack (TIA). All biochemical parameters were determined by stable-isotope dilution gas chromatography-mass spectrometry. AD and aIMT were measured by transesophageal echocardiography. Arg, hArg, ADMA and GAA median plasma concentrations (µM) were determined to be 61, 1.43, 0.50 and 2.16, respectively. hArg, ADMA and GAA correlated closely with Arg. Nitrite, nitrate and creatinine median plasma concentrations (µM) were 2.49, 48.7, and 84.1, respectively. Neither AD (2.61 vs. 1.85 10^-6 × cm² × dyn^-1, P = 0.064) nor aIMT (1.25 vs. 1.13 mm, P = 0.596) differed between females and males. The hArg/ADMA molar ratio (r = -0.351, P = 0.009), nitrate (r = 0.364, P = 0.007) and nitrite (r = 0.329, P = 0.015) correlated with aIMT but not with AD. Arg, hArg, ADMA and GAA correlated with aIMT but not with AD. The results demonstrate a strong relation between the Arg/NO pathway and aortic atherosclerosis but not with AD suggesting different mechanisms underlying the two aspects of aortic wall remodeling.

Pentafluorobenzyl bromide-A versatile derivatization agent in chromatography and mass spectrometry: I. Analysis of inorganic anions and organophosphates

Pentafluorobenzyl bromide (PFB-Br) is a versatile derivatization agent. It is widely used in chromatography and mass spectrometry since several decades. The bromide atom is largely the single leaving group of PFB-Br. It is substituted by wide a spectrum of nucleophiles in aqueous and non-aqueous systems to form electrically neutral, in most organic solvents soluble, generally thermally stable, volatile, strongly electron-capturing and ultraviolet light-absorbing derivatives. Because of these greatly favoured physicochemical properties, PFB-Br emerged an ideal derivatization agent for highly sensitive analysis of endogenous and exogenous substances including various inorganic and organic anions by electron capture detection or after electron-capture negative-ion chemical ionization in GC-MS. The present article attempts an appraisal of the utility of PFB-Br in analytical chemistry. It reviews and discusses papers dealing with the use of PFB-Br as the derivatization reagent in the qualitative and quantitative analysis of endogenous and exogenous inorganic anions in various biological samples, notably plasma, urine and saliva. These analytes include nitrite, nitrate, cyanide and dialkyl organophosphates. Special emphasis is given to mass spectrometry-based approaches and stable-isotope dilution techniques.

Simultaneous pentafluorobenzyl derivatization and GC-ECNICI-MS measurement of nitrite and malondialdehyde in human urine: Close positive correlation between these disparate oxidative stress biomarkers

Urinary nitrite and malondialdehyde (MDA) are biomarkers of nitrosative and oxidative stress, respectively. At physiological pH values of urine and plasma, nitrite and MDA exist almost entirely in their dissociated forms, i.e., as ONO^- (ONOH, pK_a=3.4) and ^-CH(CHO)₂ (CH₂(CHO)₂, pK_a=4.5). Previously, we reported that nitrite and MDA react with pentafluorobenzyl (PFB) bromide (PFB-Br) in aqueous acetone. Here, we report on the simultaneous derivatization of nitrite and MDA and their stable-isotope labeled analogs O¹⁵NO^- (4μM) and CH₂(CDO)₂ (1μM or 10μM) with PFB-Br (10μL) to PFBNO₂, PFB¹⁵NO₂, C(PFB)₂(CHO)₂), C(PFB)₂(CDO)₂ by heating acetonic urine (urine-acetone, 100:400μL) for 60min at 50°C. After acetone evaporation under a stream of nitrogen, derivatives were extracted with ethyl acetate (1mL). A 1-μL aliquot of the ethyl acetate phase dried over anhydrous Na₂SO₄ was injected in the splitless mode for simultaneous GC-MS analysis in the electron capture negative-ion chemical ionization mode. Quantification was performed by selected-ion monitoring (SIM) the anions [M-PFB]^-m/z 46 for ONO^-, m/z 47 for O¹⁵NO^-, m/z 251 for ^-C(PFB)(CHO)₂, and m/z 253 for ^-C(PFB)(CDO)₂. The retention times were 3.18min for PFB-ONO₂/PFB-O¹⁵NO₂, and 7.13min for ^-C(PFB)(CHO)₂/^-C(PFB)(CDO)₂. Use of CH₂(CDO)₂ at 1μM but not at 10μM was associated with an unknown interference with the C(PFB)₂(CDO)₂ peak. Endogenous MDA can be quantified using O¹⁵NO^- (4μM) and CH₂(CDO)₂ (10μM) as the internal standards. The method is also useful for the measurement of nitrate and creatinine in addition to nitrite and MDA. Nitrite and MDA were measured by this method in urine of elderly healthy subjects (10 females, 9 males; age, 60-70 years; BMI, 25-30kg/m²). Creatinine-corrected excretion rates did not differ between males and females for MDA (62.6 [24-137] vs 80.2 [52-118]nmol/mmol, P=0.448) and for nitrite (102 [71-174] vs. 278 [110-721]nmol/mmol P=0.053). We report for the first time a close correlation (r=0.819, P<0.0001) between MDA and nitrite in human urine. This correlation is assumed to be due to involvement of myeloperoxidase which catalyzes the formation of hypochlorite (^-OCl) from chloride and hydrogen peroxide. In turn, hypochlorite reacts both with nitrite and with polyunsaturated fatty acids such as arachidonic acid, with the later reaction generating MDA. The proposed mechanisms are supported by the literature but remain to be fully explored.