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)
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.
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