Critical parameters for the analysis of anionic oligosaccharides by desorption electrospray ionization mass spectrometry

Sulfated oligosaccharides derived from glycosaminoglycans (GAGs) are fragile compounds, highly polar and anionic. We report here on the rare but successful application of desorption electrospray ionization (DESI) - LTQ-Orbitrap mass spectrometry (MS) to the high-resolution analysis of anionic and sulfated oligosaccharides derived from the GAGs hyaluronic acid and heparin. For that purpose, key parameters affecting DESI performance, comprising the geometric parameters of the DESI source, the probed surface and the spraying conditions, applied spray voltage, flow rates and solvent composition were investigated. Under suitable conditions, the DESI technique allows the preservation of the structural integrity of such fragile compounds. DESI enabled the sensitive detection of anionic hyaluronic acid and heparin oligosaccharides with a limit of detection (LOD) down to 5 fmol (≈10 pg) for the hyaluronic acid decasaccharide. Detection of hyaluronic acid oligosaccharides in urine sample was also successfully achieved with LOD values inferior to the ng range. Multistage tandem mass spectrometry (MS(n) ) through the combination of the DESI source with a hybrid linear ion trap-orbitrap mass spectrometer allowed the discrimination of isomeric sulfated oligosaccharides and the sequence determination of a hyaluronic acid decasaccharide. These results open promising ways in glycomic and glycobiology fields where structure-activity relationships of bioactive carbohydrates are currently questioned.

Effect of urine pH changed by dietary intervention on uric acid clearance mechanism of pH-dependent excretion of urinary uric acid

BACKGROUND

The finding reported in a previous paper - alkalization of urine facilitates uric acid excretion - is contradictory to what one might expect to occur: because food materials for the alkalization of urine contain fewer purine bodies than those for acidification, less uric acid in alkaline urine should have been excreted than in acid urine. To make clear what component of uric acid excretion mechanisms is responsible for this unexpected finding, we simultaneously collected data for the concentration of both creatinine and uric acid in serum as well as in urine, in order to calculate both uric acid and creatinine clearances.

METHODS

Within the framework of the Japanese government's health promotion program, we made recipes which consisted of protein-rich and less vegetable-fruit food materials for H + -load (acidic diet) and others composed of less protein and more vegetable-fruit rich food materials (alkaline diet). This is a crossover study within some limitations. Healthy female students, who had no medical problems at the regular physical examination provided by the university, were enrolled in this consecutive 5-day study for each test. From whole-day collected urine, total volume, pH, organic acid, creatinine, uric acid, titratable acid and all cations (Na+,K+,Ca2+,Mg2+,NH4+) and anions (Cl-,SO42-,PO4-) necessary for the estimation of acid-base balance were measured. In the early morning before breakfast of the 1st, 3rd and 5th experimental day, we sampled 5 mL of blood to estimate the creatinine and uric acid concentration in serum.

RESULTS AND DISCUSSION

Urine pH reached a steady state 3 days after switching from ordinary daily diets to specified regimens. The amount of acid generated ([SO42-] + organic acid - gut alkali)was linearly related with the excretion of acid (titratable acid + [NH4+] - [HCO3-]), indicating that H + in urine is generated by the metabolic degradation of food materials. Uric acid and excreted urine pH retained a linear relationship, as reported previously. Among the five factors which are associated with calculating clearances for both uric acid and creatinine, we identified a conspicuous difference between acidic and alkaline diets in the uric acid concentration in serum as well as in urine; uric acid in the serum was higher in the acidic group than in the alkaline group, while uric acid in the urine in the acidic group was lower than that in the alkaline group. These changes of uric acid in acidic urine and in serum were reflected in the reduction of its clearance. From these observations, it is considered that uric acid may be reabsorbed more actively in acidic urine than in alkaline urine.

CONCLUSION

We conclude that alkalization of urine by eating nutritionally well-designed alkaline -prone food is effective for removing uric acid from the body.

[A new technique for urinary oxalate ion determination]

The authors propose a technique for the determination of urinary oxalate ions by high performance liquid chromatography, which may be used for clinical and scientific purposes.

Effects of plant food potassium salts (citrate, galacturonate or tartrate) on acid–base status and digestive fermentations in rats

Potassium (K) organic anion salts, such as potassium citrate or potassium malate in plant foods, may counteract low-grade metabolic acidosis induced by western diets, but little is known about the effect of other minor plant anions. Effects of K salts (chloride, citrate, galacturonate or tartrate) were thus studied on the mineral balance and digestive fermentations in groups of 6-week-old rats adapted to an acidogenic/5 % inulin diet. In all diet groups, substantial amounts of lactate and succinate were present in the caecum, besides SCFA. SCFA were poorly affected by K salts conditions. The KCl-supplemented diet elicited an accumulation of lactate in the caecum; whereas the lactate caecal pool was low in rats fed the potassium tartrate-supplemented (K TAR) diet. A fraction of tartrate (around 50 %) was recovered in urine of rats fed the K TAR diet. Potassium citrate and potassium galacturonate diets exerted a marked alkalinizing effect on urine pH and promoted a notable citraturia (around 0·5 μmol/24 h). All the K organic anion salts counteracted Ca and Mg hyperexcretion in urine, especially potassium tartrate as to magnesuria. The present findings indicate that K salts of unabsorbed organic anions exert alkalinizing effects when metabolizable in the large intestine, even if K and finally available anions (likely SCFA) are not simultaneously bioavailable. Whether this observation is also relevant for a fraction of SCFA arising from dietary fibre breakdown (which represents the major organic anions absorbed in the digestive tract in man) deserves further investigation.

High-sensitivity capillary electrophoresis determination of inorganic anions in serum and urine using on-line preconcentration by transient isotachophoresis

Concentrations of inorganic anions, both as individual species and biotransformation products, in physiological fluids are of strong concern in clinical studies. To date, analytical methodologies have either required different analytical procedures to determine these analytes in plasma and urine, or extensive sample preparation, or unconventional and often expensive detection schemes, or both. A simple and sensitive capillary electrophoresis (CE) method with direct UV detection was developed for the simultaneous determination of iodide, bromide and nitrate in human plasma and urine, with a special focus on reliable quantification of the trace serum iodide. With the latter objective, the method incorporates a transient isotachophoresis (tITP) procedure enabling an efficient on-line preconcentration of iodide (limit of detection, 1.4 microg l(-1)) as well as other moderately mobile analytes that fall into the tITP range. The analyses of both types of biofluids were performed using an acidic electrolyte system composed of 0.25 mol l(-1) sodium chloride and 7.5 mmol l(-1) cetyltrimethylammonium chloride at pH 2.2 and 0.5 mol l(-1) 2-(N-morpholino)ethanesulfonate (pH 6.0) as terminating electrolyte. Relative standard deviations (R.S.D.) below 3.0% and 9.2% were obtained for within-day and between-day precision, respectively. Resolution and quantification of oxalic acid was also feasible under optimized tITP-CE conditions. Sample preparation required only ultrafiltration (serum) and dilution (urine). A number of plasma and urine samples were evaluated with this assay and the iodide, bromide and nitrate concentrations were in the expected clinical concentration ranges.

Altered renal elimination of organic anions in rats with chronic renal failure

The progress of chronic renal failure (CRF) is characterized by the development of glomerular and tubular lesions. However, little is known about the expression of organic anions renal transporters. The objective of this work was to study, in rats with experimental CRF (5/6 nephrectomy), the expression of the organic anion transporter 1 (OAT1) and organic anion transporter 3 (OAT3) and their contribution to the pharmacokinetics and renal excretion of p-aminohippurate (PAH). Two groups of animals were used: Sham and CRF. Six months after surgery, systolic blood pressure and plasma creatinine concentrations were significantly higher in CRF groups. CRF rats showed a diminution in: the filtered, secreted and excreted load of PAH; the systemic clearance of PAH; the renal OAT1 expression; and the renal Na-K-ATPase activity. No remarkable modifications were observed in the OAT3 expression from CRF kidneys. The diminution in the systemic depuration and renal excretion of PAH may be explained by the decrease in its filtered and secreted load. The lower OAT1 expression in remnant renal mass of CRF rats or/and the lower activity of Na-K-ATPase might justify, at least in part, the diminished secreted load of this organic anion.

Citric acid or citrates in urine: which should we focus on in the prevention of calcium oxalate crystals and stones?

In order to distinguish between normocitraturia and hypocitraturia, the 24 h urine excretion value of citric acid is evaluated in relation to the established limit value of 2.5 mmol/day. We propose changing this widely-used excretion value to a "minimum contribution" of citric acid to the total urine's ionic strength, since the inhibitory effect of citric acid on crystallization depends on citrate anions being available to complex calcium ions or to associate with the crystal surface. A total of 71424 h-urine samples, taken from 74 healthy persons and 58 calcium stone formers, were investigated for pH, citric acid concentration ([CA]), and related relative calcium oxalate supersaturation (RS). Based on the Henderson-Hasselbalch-equation, the individual concentrations of the differently charged citrate anion species in each of the urines were calculated from the urinary pH and [CA]. From the anion concentrations determined, the contribution of the urine's citric acid to the total urine's ionic strength, ISCA, was calculated. Referring to the limit value of 2.5 mmol/day and assuming an average urine volume of 1.5 l/day, a hypothetical concentration limit of 1.67 mmol/l can be obtained. Grouping the samples into "stone-formers" and "non-stone-formers" as well as into three different ranges of RS revealed: (1). that the groups' median [CA]-values were below 1.67 mmol/l, and (2). that [CA] was not inversely associated with the risk of stone formation. Within the pH-range of 5 and 7, the ISCA-values which are related to, for example, [CA]=1.67 mmol/l, vary considerably by a factor of nearly three between 2.48 mmol/l and 6.64 mmol/l. The use of a fixed citric acid excretion level for the distinction of normocitraturia from hypocitraturia does not take into account the different citrate species which actually modify the urine's crystallization behaviour. The proposed ISCA approach takes this fact into consideration. From this parameter, a desirable "minimum impact of citric acid" can be derived. In a first approach, a potential ISCA-limit value, which currently distinguishes between urines indicated by a "normo-protective" impact and those indicated by a "hypo-protective" impact with respect to calcium oxalate precipitation, may be set at 2.48 mmol/l.

Plasma and urine electrolyte and mineral concentrations in Thoroughbred horses with recurrent exertional rhabdomyolysis after consumption of diets varying in cation-anion balance

OBJECTIVE

To determine whether plasma, urine, and fecal electrolyte and mineral concentrations differ between clinically normal horses and Thoroughbreds with recurrent exertional rhabdomyolysis (RER) after consumption of diets varying in cation-anion balance.

ANIMALS

5 Thoroughbred mares with RER and 6 clinically normal mixed-breed mares.

PROCEDURE

Each of 3 isocaloric diets designated as low, medium, and high on the basis of dietary cation-anion balance (DCAB) values of 85, 190, and 380, respectively, were fed to horses for 14 days. During the last 72 hours, 3 horses with RER and 3 control horses had daily urine and fecal samples obtained by total 24-hour collection. Remaining horses had urine samples collected daily by single catheterization.

RESULTS

For each diet, no differences existed between horses with RER and control horses in plasma pH, electrolyte concentrations, and creatine kinase activity or in urine pH and renal fractional excretion (FE) values. Plasma pH, strong ion difference, bicarbonate and total carbon dioxide concentrations, and base excess decreased and plasma chloride and ionized calcium concentrations increased with decreasing DCAB. Urine pH decreased with decreasing DCAB. The FE of chloride and phosphorus were greatest for horses fed the low diet. The FE values for all electrolytes exept magnesium did not differ between urine samples obtained by single catheterization and total 24-hour collection. Daily balance of calcium, phosphorus, sodium, chloride, and potassium did not differ significantly among horses fed the various diets.

CONCLUSIONS

In clinically normal horses and in horses with RER, the DCAB strongly affects plasma and urine pH and the FE of sodium, potassium, chloride, and phosphorus.

Capillary ion electrophoresis of endogenous anions and anionic adulterants in human urine

Normal human urine contains many anions and cations. Ionic concentrations in urine have classically been determined by spectrophotometry of color reactions, flame emission spectrophotometry, atomic absorption spectrophotometry, high performance liquid chromatography, or potentiometry with ion-specific electrodes. Capillary ion electrophoresis (CIE) is a form of capillary electrophoresis which uses the differential electrophoretic mobility of ions to perform a separation of an ionic mixture. Various salts can be added to urine specimens to abnormally elevate ionic concentrations and interfere with either immunoassay urine drug screening procedures or gas chromatographic/mass spectrometric confirmation techniques. Application of CIE for the direct detection of endogenous anions and anionic adulterants in human urine specimens was the purpose of this investigation. CIE was performed using a Waters Quanta 4000 Capillary Electrophoresis System with either direct or indirect ultraviolet absorption detection at 254 nm. CIE of 30 random normal urine specimens and 21 urine specimens suspected of adulteration was performed. Duplicate aliquots were assayed by CIE and by colorimetric technique for nitrite. Sixteen specimens had elevated concentrations of nitrite and/or nitrate. The correlation coefficient between nitrite CIE and colorimetric results was 0.9895. Three specimens had detectable concentrations of chromate and were suspected of being adulterated with "Urine Luck," an adulterant found to contain chromate. Two specimens suspected of being adulterated with bleach were found to only contain chloride, sulfate, and phosphate. CIE is applicable to forensic analysis of urine anion concentrations. CIE can easily quantitate numerous endogenous anions and offers a method to detect and/or confirm anion adulteration of urine specimens.

Determination of inorganic anions in biological fluids with direct sample injection by electrostatic ion chromatography using zwitterionic micelles in both stationary and mobile phases

A new ion chromatographic (IC) system, which uses zwitterionic (e.g., Zwittergent 3-14) micelles as both stationary and mobile phases, highly useful for the analysis of inorganic anions in biological samples, was developed. The zwitterionic micellar stationary phase (which is obtained by immobilizing the zwitterionic surfactant on surfaces of the reversed-phase ODS) showed high ability to confine the elution bands of the large amount of SO4(2-) and Cl- to narrow zones. As a result, a base-line separation of NO2-, Br- and NO3- from SO4(2-) and Cl- is always achieved. The zwitterionic micellar mobile phase, (which is obtained by dissolving the zwitterionic surfactant with a suppressive electrolytic solution, e.g., aqueous NaHCO3 solution), on the other hand, showed high ability for rapid elution of proteins. The separation column is therefore always being cleaned up even after the protein-containing sample is directly injected. The zwitterionic micelles are also insensitive to conductivity detection, therefore either the suppressed or the non-suppressed conductivity detection method is applicable for detection of the analyte ions. Urine and serum were chosen as the model real samples and were analysed with direct sample injection; the results of successful determination of a number of inorganic anions (SO4(2-), Cl-, NO2-, Br- and NO3-) in both samples have demonstrated the usefulness of this new IC system.

Oxalate, citrate, and sulfate concentration in human milk compared with formula preparations: influence on urinary anion excretion

BACKGROUND

Nephrocalcinosis is not uncommon in preterm infants, and elevated urinary oxalate excretion is known to be one of the main risk factors. When oxalate excretion was found to be higher in formula-fed than in human milk-fed infants, the formulas' oxalate content was thought to be responsible.

METHODS

The oxalate concentration in human milk (21 samples obtained during lactogenesis; 17 samples obtained during established lactation) and of 16 formula preparations was examined. Citrate and sulfate concentrations were also measured, because both anions influence urinary saturation.

RESULTS

The mean (+/- SE) oxalate content of human milk increased approximately 27% from early lactogenesis (70.4 +/- 6.4 micromol/1) to established lactation (96.4 +/- 9.5 micromol/l; p < 0.05). The latter was not different from the mean oxalate concentration of formula (98.2 +/- 11.4 micromol/l), however a fourfold range of measurements was recorded in both groups. The mean citrate content of human milk increased only slightly after early lactogenesis (2.66 +/- 0.22 mmol/l), but remained significantly lower than in formula (3.34 +/- 0.23 mmol/l; p < 0.05). The mean sulfate concentration did not increase and was 13 times lower in human milk (52.1 +/- 9.5 micromol/l) than in formula (688.7 +/- 95.4 micromol/l; p < 0.0001).

CONCLUSIONS

The higher oxalate excretion in formula-fed infants is not because of the milk's oxalate concentration. Urinary citrate and sulfate excretion may be influenced by their higher concentrations in formula preparations, which may be of clinical importance in the population that is at risk for development of nephrocalcinosis.

Soy protein modification of rat polycystic kidney disease

We undertook a study to determine whether soy protein feeding would ameliorate renal injury in the Han:SPRD-cy rat model of polycystic kidney disease (PKD). Male offspring of Han:SPRD-cy heterozygotes received isocaloric diets based on 20% casein or 20% heat-treated soy protein at weaning ad libitum for 8 wk. Soy-fed animals demonstrated lower serum creatinine (66 vs. 125 mumol/l; P = 0.002), lower urinary ammonium excretion (0.080 vs. 0.173 mmol/kg; P = 0.01), reduced renal cysts (0.98 vs. 4.92 ml/kg body wt, P < 0.0001), renal fibrosis (0.79 vs. 1.4 ml/kg; P = 0.016), macrophage infiltration, renal tubular cell proliferation, and apoptosis. Proton nuclear magnetic resonance (1H-NMR) studies of urine demonstrated that soy diet was associated with increased losses of citric acid cycle organic anions. 1H-NMR of perchloric acid-extracted tissue found that levels of succinate were not depleted in soy-fed animals, despite increased urinary losses. Soy-fed animals had marked elevation of tissue betaine (P < 0.001), with reduced taurine and cholines, compared with casein-fed animals (P < 0.001). Soy feeding dramatically reduces both tubular and interstitial pathology in the Han:SPRD-cy rat model of PKD, through mechanisms that remain to be determined.

What is the impact of potassium excretion on the intracellular fluid volume: importance of urine anions

Hyponatremia is a common electrolyte abnormality that causes symptoms as a result of swelling of brain cells. We evaluated the impact of a negative balance for sodium (Na) and potassium (K) salts on the intracellular fluid (ICF) volume, emphasizing the role of anions excreted with K. Rats (N = 10) were deprived of food and water for 24 hours. They received half-isotonic saline to expand their extracellular fluid (ECF) volume by 20%; a long acting antidiuretic hormone (DDAVP) preparation was given to prevent the excretion of electrolyte-free water. The concentration of Na in plasma fell from 139 +/- 1 mM to 120 +/- 2 mM 24 hours after the infusion of hypotonic saline (P < 0.01). Since these rats had a small negative balance for water (4 +/- 1 ml), hyponatremia was due to their negative balances for Na (2.2 +/- 0.3 mmol) and K (2.2 +/- 0.1). There were negative balances for Cl (2.4 +/- 0.2 mmol) and phosphate (0.7 +/- 0.05 mmol). Despite the negative balance for NaCl, the ECF volume as assessed by 3H-inulin space was not contracted. In this model for acute hyponatremia, its basis was electrolyte loss, but the ECF volume was not contracted, suggesting that water shifted from the ICF to the ECF. Hyponatremia is associated with cell swelling only if its cause is positive water balance and/or is loss of Na from the ECF. It is critical to examine the urine anions to determine the compartment of origin of particles excreted with K and thereby whether hyponatremia will result in overall expansion or contraction of the ICF volume.

Urinary organic anion excretion in response to dietary acid and base loading

Animals eating a base-loaded or base-forming diet excrete urine containing large amounts of organic anions (OA). Although citrate is the only OA previously identified as being excreted in appreciable amounts during base loading, citrate excretion accounts for only part of total OA excretion. The objectives of this study were to identify other OA excreted by rats and to see how their excretion changed in response to moderate (8 micro Eq/g per day) and heavy (30 micro Eq/g per day) loads of NaHCO3 and NH4Cl. Urinary OA were identified by high-performance liquid chromatography and were measured by enzymatic techniques as well. It was found that, in addition to citrate, significant quantities of alpha-ketoglutarate (alpha-KG) were excreted by base-loaded rats and that the excretion of citrate, alpha-KG, and succinate increased with base loading and decreased with acid loading. Citrate plus alpha-KG excretion rates were, respectively, two-thirds and one-third the rate of HCO3- excretion in rats given moderate and heavy base loads. The excretion of creatinine, glutamine, and hippurate showed no clear pattern in response to acid or base loading. It was concluded that, especially in animals experiencing moderate base loads, increases in the excretion of citrate and alpha-KG represent a much more significant component of base excretion than has been recognized previously.

Analysis of anion constituents of urine by inorganic capillary electrophoresis

Inorganic capillary electrophoresis (ICE) is a new separations technology which melds the technique of classical electrophoresis with the separations approach of ion chromatography. Matrices which have been difficult to deal with using ion chromatography have proven amenable to analysis by ICE. The simultaneous analysis of weak acid anions, oxalate and citrate and inorganic anions, chloride, sulfate, nitrate, phosphate and carbonate in diluted urine was achieved using ICE. The determination of the oxyanions of arsenic (i.e. arsenite and arsenate) in urine was also performed.

Simultaneous determination of chloride, sulphate, orthophosphate and organic anions in human urine by capillary isotachophoresis

The principle of isotachophoresis has been used to develop a simple, specific and sensitive analytical method for the determination of anions in untreated urine. Isotachophoretic separation of anions in the presence of complex-forming counter ions (e.g. Cd2+) enables the quantitative separation and determination of chloride, sulphate and orthophosphate in the same sample and the less accurate measurement of the concentrations of citrate, formate, acetate, hippurate, benzoate and glucuronate. The mean deviation from 100% recovery of chloride, sulphate and orthophosphate added to urine samples is 3.1%. The proposed method shows good agreement with chemical (routine) methods.

The urine anion gap: the critical clue to resolve a diagnostic dilemma in a patient with ketoacidosis

Usually, ketoacidosis presents few if any diagnostic or therapeutic problems; in this article, we report a case where ketoacidosis was clinically occult and biochemically obscure. The patient presented with acute pancreatitis associated with a modest antecedent alcohol intake. Metabolic acidosis with a normal anion gap (10 meq/L) was observed together with moderate hyperglycemia and a 2 + (but not 4 +) test for serum ketones. None of the usual causes of metabolic acidosis with a normal anion gap was identified nor was there an obvious explanation for a reduction in unmeasured anion gap (e.g., hypoalbuminemia, dysproteinemia, or the presence of abnormal halides). Despite the initial normal anion gap, ketoacidosis was suspected clinically and this was confirmed by the elevated serum B-hydroxybutyrate of 8 mmol/L. We deduced that the serum unmeasured anions, which should have been increased by at least 8 meq/L, were being underestimated because of the effect of hypertriglyceridemia on the serum chloride determination. When the serum chloride was reestimated by a method not influenced by hyperlipidemia, the value was 102 mmol/L not 112 mmol/L and, when reevaluated, the anion gap was indeed appropriately elevated. In addition, the urine anion gap (Na + K - Cl) was 103 meq/L in the absence of renal disease. This indicated that the expected large quantity of urinary ammonium must have been masked by an even greater quantity of unmeasured anion; in this case proven by direct measurement to be B-hydroxybutyrate. Finally, metabolism of the alcohol ingested, which yields hepatic NADH, could explain, in part, the modest hyperglycemia and the absence of a 4 + test for serum ketones.(ABSTRACT TRUNCATED AT 250 WORDS)

Some acid-base balance-dependent urinary parameters and calcium-binding anions in stone formers

Urinary organic acids were determined by gradual titration of portioned urine samples of moderately and severely recurrent stone patients and compared to those found in healthy controls. An essential deficit of organic acids was found in patients with a high recurrence rate. According to the results, the lack of organic acids in the urine of urolithiasis patients, accompanied by a reduced inhibition of the calcium-oxalate and calcium-phosphate crystallization might be causatively involved in the stone formation.