Citrate in urine determined with a new citrate lyase method

An enzyme-spectrophotometric method to determine citrate in biological fluids is proposed, based on citrate lyase-catalyzed and phenylhydrazine reactions. The enzyme converts citrate into oxaloacetate, which, in the presence of phenylhydrazine, is transformed into the corresponding phenylhydrazone. The ultraviolet-absorbing product is determined by absorbance measurement at 330 nm. The method is more precise and twice as sensitive as the traditional citrate lyase method and, because it does not require the use of additional enzymes and coenzymes, is cheaper and simpler. Mean analytical recovery of citrate averaged 100.7% +/- 2.2%, imprecision (CV) of the assay for citrate at 0.96 mmol/L (urine) was 2.0%, and the lower limit of quantification was 0.08 mmol/L. Results correlated well with those by both ion-chromatographic and traditional citrate lyase methods.

Citrate in urine determined with a new citrate lyase method

An enzyme-spectrophotometric method to determine citrate in biological fluids is proposed, based on citrate lyase-catalyzed and phenylhydrazine reactions. The enzyme converts citrate into oxaloacetate, which, in the presence of phenylhydrazine, is transformed into the corresponding phenylhydrazone. The ultraviolet-absorbing product is determined by absorbance measurement at 330 nm. The method is more precise and twice as sensitive as the traditional citrate lyase method and, because it does not require the use of additional enzymes and coenzymes, is cheaper and simpler. Mean analytical recovery of citrate averaged 100.7% +/- 2.2%, imprecision (CV) of the assay for citrate at 0.96 mmol/L (urine) was 2.0%, and the lower limit of quantification was 0.08 mmol/L. Results correlated well with those by both ion-chromatographic and traditional citrate lyase methods.

Bony content of oxalate in patients with primary hyperoxaluria or oxalosis-unrelated renal failure

Oxalate retention occurs in end-stage renal failure. Regular dialysis treatment does not prevent progressive accumulation of oxalate in cases of ESRF due to primary hyperoxaluria (PH), whereas such accumulation seldom seems to occur in oxalosis-unrelated ESRF. To elucidate this issue we have measured the bony content of oxalate on biopsies of the iliac crest taken from 32 uremic patients, 7 of them with ESRF associated with PH1 (6 cases) or PH2 (1 case). Ten subjects with normal renal function and no evidence of metabolic bone disease were taken as controls. Only trace amounts levels of oxalate were detected in normal subjects and oxalate to phosphate ratio was below 3:10,000. Non-PH dialyzed patients exhibited fivefold increases in oxalate levels, which rose to 5.1 +/- 3.6 mumol/g bony tissue. Calcium oxalate was estimated to represent 0.18% of the hydroxyapatite content of bone. Oxalate amounts were neither related to pre-dialysis plasma levels of oxalate, nor with duration of dialysis treatment, suggesting that accumulation was not progressive disorder. Oxalate levels were slightly higher in patients with a low turnover osteodystrophy compared to those with a high turnover pattern. Dialyzed patients with PH had remarkable increases in oxalate levels, which ranged between 14.8 and 907 mumol/g bony tissue. Oxalate deposition appeared to be progressive in that oxalate levels were significantly related to time on dialysis. In three patients calcium oxalate was a significant fraction of the mineralized bone. The occurrence of calcium oxalate crystals affected the histomorphometric patterns, that were featured by an increase in resorptive areas and a decrease in bone formation rate.(ABSTRACT TRUNCATED AT 250 WORDS)

Assay of plasma oxalate with soluble oxalate oxidase

We use oxalate oxidase from barley seedlings for the colorimetric determination of oxalate in plasma. The oxalate is converted to hydrogen peroxide, which, in the presence of peroxidase, is detected by a Trinder-like chromogenic system. Optimization of the assay, including deproteinization and elimination of interferences from reducing substrates, is described. Ascorbate additions (200 mumol/L) did not affect oxalate concentration in plasma, even after long frozen storage. Mean analytical recovery of oxalate averaged 102% +/- 6.9%, imprecision (CV) at 2.0 mumol/L was 7.2%, and the lower limit of quantification (CV = 20%) was 0.6 mumol/L. Results correlated well with those by chromatography (r = 0.999, Sy/x = 0.29 mumol/L, n = 32, range for x, y = 0-140 mumol/L). Plasma oxalate concentrations measured in 32 healthy subjects ranged from 0.6 to 2.9 mumol/L (mean 1.28, SD 0.71 mumol/L), which agrees with those measurable by using indirect radioisotopic dilution methods. Patients with primary hyperoxaluria and chronic renal failure exhibited markedly greater plasma concentrations of oxalate.

Assay of plasma oxalate with soluble oxalate oxidase

We use oxalate oxidase from barley seedlings for the colorimetric determination of oxalate in plasma. The oxalate is converted to hydrogen peroxide, which, in the presence of peroxidase, is detected by a Trinder-like chromogenic system. Optimization of the assay, including deproteinization and elimination of interferences from reducing substrates, is described. Ascorbate additions (200 mumol/L) did not affect oxalate concentration in plasma, even after long frozen storage. Mean analytical recovery of oxalate averaged 102% +/- 6.9%, imprecision (CV) at 2.0 mumol/L was 7.2%, and the lower limit of quantification (CV = 20%) was 0.6 mumol/L. Results correlated well with those by chromatography (r = 0.999, Sy/x = 0.29 mumol/L, n = 32, range for x, y = 0-140 mumol/L). Plasma oxalate concentrations measured in 32 healthy subjects ranged from 0.6 to 2.9 mumol/L (mean 1.28, SD 0.71 mumol/L), which agrees with those measurable by using indirect radioisotopic dilution methods. Patients with primary hyperoxaluria and chronic renal failure exhibited markedly greater plasma concentrations of oxalate.

Ion-chromatographic determination of plasma oxalate reexamined

This new procedure for determining oxalic acid in plasma is based on sample deproteinization with hydrochloric acid and acetonitrile and subsequent ion-chromatographic assay of the neutralized supernate. Sample pretreatment produces very clean samples, which ensures long column life. Mean analytical recovery of oxalate (5.0-10.0 mumol/L) added to plasma samples averaged 98.6 +/- 6.2%; imprecision (CV) was 5.2% (at 2.2 mumol/L) and the detection limit was 0.5 mumol/L at a signal-to-noise ratio of 5:1. Ascorbate to oxalate conversion was < 0.2%, indicating that the procedure is free from ascorbate interference. Plasma oxalate concentrations, measured in samples from 31 healthy persons, ranged from 0.8 to 3.4 mumol/L (mean 1.89, SD 0.75 mumol/L), which agrees with results from indirect radioisotopic dilution methods.