Interference-free sample preparation for the determination of plasma oxalate analyzed by HPLC-ER: preliminary results from calcium oxalate stone-formers and non-stone-formers

Simultaneous colorimetric detection of nephrolithiasis biomarkers using a microfluidic paper-based analytical device

A microfluidic paper-based analytical device (μPAD) coupled with colorimetric detection was developed for simultaneous determination of urinary oxalate, citrate and uric acid (UA) which are important biomarkers of nephrolithiasis or kidney stones. The colorimetric detections were based on enzymatic reactions using oxalate oxidase and uricase for oxalate and UA, respectively, while an indicator displacement assay (IDA) using a copper murexide complex was applied for citrate detection. The developed μPAD was successfully applied for simultaneous determination of the three biomarkers in urine within 25 min, with linear ranges of 2-40, 5-150, and 5-45 mg L^-1 and detection limits of 0.6, 2.9 and 3.1 mg L^-1 for oxalate, UA, and citrate, respectively. The values of the percent relative standard deviation (% RSD) were lower than 6.4% for inter-day and intraday measurements of oxalate, citrate and UA standards spiked in urine samples with recovery percentages in the range of 81.0-109.8%, indicating acceptable accuracy and precision of the developed method for determination of the three biomarkers in urine samples. Accordingly, the developed μPAD holds great promise to be a simple, fast, inexpensive, low-sample and reagent volume, reliable and portable tool for simultaneous determination of oxalate, citrate and UA in urine, especially for on-site analysis.

Calcium Oxalate Differentiates Human Monocytes Into Inflammatory M1 Macrophages

Purpose

A number of hyperoxaluric states have been associated with calcium oxalate (CaOx) deposits in the kidneys. In animal models of stone disease, these crystals interact with circulating monocytes that have migrated into the kidney as part of innate immunity. Similarly, macrophages surround CaOx crystals in kidneys of patients excreting high levels of oxalate. We investigate the effect of this exposure and subsequent human immunological response in vitro.

Materials and methods

Primary human monocytes were collected from healthy donors and exposed to CaOx, potassium oxalate, and zinc oxalate (ZnOx). Cytokine production was measured with a multiplex ELISA. Quantitative reverse transcription-polymerase chain reaction was done to validate the mRNA profile expression. M1 macrophage phenotype was confirmed with immunofluorescence microscopy.

Results

Both primary monocytes and THP-1 cells, a human monocytic cell line, respond strongly to CaOx crystals in a dose-dependent manner producing TNF-α, IL-1β, IL-8, and IL-10 transcripts. Exposure to CaOx followed by 1 h with LPS had an additive effect for cytokine production compared to LPS alone, however, LPS followed by CaOx led to significant decrease in cytokine production. Supernatants taken from monocytes were previously exposed to CaOx crystals enhance M2 macrophage crystal phagocytosis. CaOx, but not potassium or ZnOx, promotes monocyte differentiation into inflammatory M1-like macrophages.

Conclusion

In our in vitro experiment, human monocytes were activated by CaOx and produced inflammatory cytokines. Monocytes recognized CaOx crystals through a specific mechanism that can enhance or decrease the innate immune response to LPS. CaOx promoted M1 macrophage development. These results suggest that monocytes have an important role promoting CaOx-induced inflammation.

Gut microbiota and oxalate homeostasis

This perspective focuses on how the gut microbiota can impact urinary oxalate excretion in the context of hyperoxaluria, a major risk factor in kidney stone disease. In the genetic disease of Primary Hyperoxaluria Type 1 (PH1), an increased endogenous production of oxalate, due to a deficiency of the liver enzyme alanine-glyoxylate aminotransferase (AGT), results in hyperoxaluria and oxalate kidney stones. The constant elevation in urinary oxalate in PH1 patients ultimately leads to tissue deposition of oxalate, renal failure and death and the only known cure for PH1 is a liver or liver-kidney transplant. The potential impact of a probiotic/therapeutic approach may be clinically significant in PH1 and could also extend to a much larger population of idiopathic oxalate stone formers who comprise ~12% of Americans, individuals with enteric hyperoxaluria, and an emerging population of hyperoxaluric patients who have undergone bariatric surgery and develop kidney stone disease as a consequence.

Secondary hyperoxaluria: a risk factor for kidney stone formation and renal failure in native kidneys and renal grafts

Secondary hyperoxaluria is a multifactorial disease affecting several organs and tissues, among which stand native and transplanted kidneys. Nephrocalcinosis and nephrolithiasis may lead to renal insufficiency. Patients suffering from secondary hyperoxaluria, should be promptly identified and appropriately treated, so that less renal damage occurs. The aim of this review is to underline the causes of hyperoxaluria and the related pathophysiologic mechanisms, which are involved, along with the description of seven cases of irreversible renal graft injury due to secondary hyperoxaluria.

Dietary hyperoxaluria is not reduced by treatment with lactic acid bacteria

Background

Secondary hyperoxaluria either based on increased intestinal absorption of oxalate (enteric), or high oxalate intake (dietary), is a major risk factor of calcium oxalate urolithiasis. Oxalate-degrading bacteria might have beneficial effects on urinary oxalate excretion resulting from decreased intestinal oxalate concentration and absorption.

Methods

Twenty healthy subjects were studied initially while consuming a diet normal in oxalate. Study participants were then placed on a controlled oxalate-rich diet for a period of 6 weeks. Starting with week 2 of the oxalate-rich diet, participants received 2.6 g/day of a lactic acid bacteria preparation for 5 weeks. Finally, subjects were examined 4 weeks after treatment while consuming again a normal-oxalate diet. Participants provided weekly 24-hour urine specimens. Analyses of blood samples were performed before and at the end of treatment.

Results

Urinary oxalate excretion increased significantly from 0.354 ± 0.097 at baseline to 0.542 ± 0.163 mmol/24 h under the oxalate-rich diet and remained elevated until the end of treatment, as did relative supersaturation of calcium oxalate. Plasma oxalate concentration was significantly higher after 5 weeks of treatment compared to baseline. Four weeks after treatment, urinary oxalate excretion and relative supersaturation of calcium oxalate fell to reach initial values.

Conclusions

Persistent dietary hyperoxaluria and increased plasma oxalate concentration can already be induced in healthy subjects without disorders of oxalate metabolism. The study preparation neither reduced urinary oxalate excretion nor plasma oxalate concentration. The preparation may be altered to select for lactic acid bacteria strains with the highest oxalate-degrading activity.

The role of Oxalobacter formigenes colonization in calcium oxalate stone disease

About 75% of urinary stones contain oxalate. As Oxalobacter formigenes is a Gram-negative anaerobic bacterium that degrades oxalate in the intestinal tract, we assessed the role of O. formigenes in oxalate metabolism by evaluating its intestinal absorption, plasma concentration, and urinary excretion. Of 37 calcium oxalate stone formers, 26 tested negative for O. formigenes and were compared with the 11 patients who tested positive. Patients provided 24-h urine samples on both a self-selected and a standardized diet. Urinary oxalate excretion did not differ significantly on the self-selected diet, but was significantly lower in O. formigenes-positive than in O. formigenes-negative patients under controlled, standardized conditions. Intestinal oxalate absorption, measured using [(13)C₂]oxalate, was similar in the patients with or without O. formigenes. Plasma oxalate concentrations were significantly higher in noncolonized (5.79 μmol/l) than in colonized stone formers (1.70 μmol/l). Colonization with O. formigenes was significantly inversely associated with the number of stone episodes. Our findings suggest that O. formigenes lowers the intestinal concentration of oxalate available for absorption at constant rates, resulting in decreased urinary oxalate excretion. Thus, dietary factors have an important role in urinary oxalate excretion. The data indicate that O. formigenes colonization may reduce the risk of stone recurrence.

Liquid chromatography-tandem mass spectrometry method for routine measurement of oxalic acid in human plasma

A solid phase extraction (SPE)-LC-MSMS method for the routine determination of oxalic acid (OX) in plasma, a diagnostic marker of primary hyperoxaluria (PH), was developed and validated. The normal range of OX was found to be 3-11 micromol/L (n=67), with no differences attributable to gender or age. The effect of pre-analytical factors on the in vitro production of OX was investigated, and plasma was found to be stable for 1-2 h at room temperature, less after ingestion of vitamin C; the process was not completely stopped by preservation at either -20 or -70 degrees C.

Early postoperative substitution procedure of the antioxidant ascorbic acid

BACKGROUND

Postoperatively reduced concentration of ascorbic acid (AA) in plasma (< or =45.5 micromol/l (< or =800 microg/dl)) is commonly interpreted as increased metabolic requirements, but it is not shown yet that the patient benefits from a substitution toward normal levels of AA. This is due to the missing knowledge on how to substitute AA effectively to normal plasma values in postoperative patients. Therefore, a postoperative AA substitution procedure "overnight" to normal values in plasma was investigated on a postoperative intensive care unit (ICU) in a university hospital.

MATERIAL AND METHODS

Fifty-seven operated patients were randomly assigned to a control- or intervention group (CG and IG, respectively). In all patients, the AA plasma concentration was analysed preoperatively and on the first three postoperative days. Patients of the IG received AA intravenously up to four times within 12 h depending upon the initial AA concentration (<34.1 micromol/l (4x500 mg AA); < or =56.8 micromol/l (2x500 mg AA); < or =68.2 micromol/l (1x500 mg AA)).

RESULTS

The preoperative and early postoperative AA values did not differ between the groups. On the first postoperative day in both groups the plasma concentration was lowered (< or =45.5 micromol/l) in 23 of all patients (CG: 85.18%; IG: 82.14%). In the IG, the dosage regime increased the AA plasma concentration to > or =45.5 micromol/l in 26 of 28 (92.86%) patients overnight.

CONCLUSION

The investigated substitution procedure is sufficient to increase AA plasma concentration overnight to normal or high normal values in postoperative ICU patients.

Application of immobilized enzyme reactor in on-line high performance liquid chromatography: A review

This review summarizes all the research efforts in the last decade (1994-2003) that have been spent to the various application of immobilized enzyme reactor (IMER) in on-line high performance liquid chromatography (HPLC). All immobilization procedures including supports, kind of assembly into chromatographic system and methods are described. The effect of immobilization on enzymatic properties and stability of biocatalysts is considered. A brief survey of the main applications of IMER both as pre-column, post-column or column in the chemical, pharmaceutical, clinical and commodities fields is also reported.

Combination of a new sample preparation strategy with an accelerated high-performance liquid chromatography assay with photodiode array and mass spectrometric detection for the determination of destruxins from Metarhizium anisopliae culture broth

A method is presented allowing the qualitative and quantitative analysis of destruxins (dtxs) in fungal culture broth. Sample preparation was carried out by ultrafiltration over a commercially available acetylated cellulose (CTA) membrane with a Mr 10000 cut-off. The developed high-performance liquid chromatography assay with diode array detection (HPLC-DAD) cuts down the analysis time by 50% compared to most of the currently applied methods (retention times: dtx A = 8.3 min, dtx B = 8.9 min, dtx E= 7.5 min) and enables dtx detection down to sub-ppm range (limits of detection: dtx A = 0.19 mg/l, dtx B = 0.41 mg/l, dtx E = 0.10 mg/l). Stability of dtx E in filtrated culture broth was found to be much lower than anticipated (half-life time = 64.5 +/- 1.7 h). Thus, the detoxification of this metabolite is an abiotic process. Coupling of the HPLC-DAD system to an ion trap mass spectrometer with an electrospray ionization source operating in the positive mode allowed identification of most dtxs encountered by utilizing multiple stage MS-MS experiments and retention time rules.

Serum oxalate in human beings and rats as determined with the use of ion chromatography

Previous enzymatic determinations have suggested that serum oxalate concentrations in normal rats, the main animal model used in urolithiasis research, to be 3 to 5 times greater than those in healthy human subjects. In this report we validated this observation using a different method (ion chromatography) on serum samples from healthy rats and human subjects that were prepared and handled similarly. Oxalate recoveries during sample preparation for ion chromatography were strongly and variably affected by ultrafiltration devices employed for sample deproteinization and after Cl(-) removal by means of ion exchange. When oxalate recoveries were accounted for, we found significant differences in serum oxalate (6 human samples, 1.47 +/- 0.15 micromol/L; and 15 rat samples, 9.88 +/- 0.91 micromol/L). We conclude that ion-chromatographic techniques confirm the differences in serum oxalate concentrations between rats and human beings measured enzymatically and that failure to account for oxalate losses during sample preparation for ion chromatography can lead to significant underestimation of serum oxalate in both species.

Determination of lactate or oxalate using injected lactate oxidase and peroxidase by capillary electrophoresis with UV detection

Two reactions, catalyzed by lactate oxidase (LO) and peroxidase, are initiated by a single injection of the enzymes and the substrate 2,2'-azino-bis(3-ethylene-thiazoline-6-sulfonic acid) (ABTS) into the capillary previously filled with the sample (lactate or lactate-oxalate mixture) and the run buffer containing NADH. The oxidized ABTS product upon reaction with NADH is converted to NAD(+) which is separated and detected in less than 2 min at 266 nm with a sample throughput of 7 min (including wash steps between samples). Simplex trade mark software is used to optimize the enzyme concentrations and reaction temperature. Consumption of the more expensive LO enzyme is only 1.4 x 10(-3) U per assay assuming 27 nL per injection. Linearity is established within the range from 0.0025 to 1 mM with R(2) of 0.9982. Recoveries of lactate from five spiked serum samples averaged 101%. Application of this method for the determination of oxalate as an inhibitor of LO is demonstrated.