Plasma oxalate concentration and secondary oxalosis in patients with chronic renal failure.

To examine the association between hyperoxalaemia and secondary oxalosis, measurement of plasma oxalate concentration was combined with a search for tissue deposition of calcium oxalate crystals in patients with chronic renal disease. Two groups of patients were studied. In the first, samples of the inferior epigastric artery were taken from 35 patients at the time of renal transplantation. In the second, sections taken at necropsy from 23 patients with chronic renal failure in whom plasma oxalate had been measured before death were examined. Though plasma oxalate concentrations ranged between 6 and 116 mumol/l (four to 78 times greater than the upper limit of the reference range), no extrarenal deposits of oxalate were found in either study. Renal deposition of oxalate was associated with a plasma oxalate concentration of greater than 20 mumol/l. This study gives no support to the suggestion that hyperoxalaemia of the degree seen in patients with the type of chronic renal failure that is not due to primary hyperoxaluria confers an appreciable risk of extrarenal oxalosis.

Correction of subclinical ascorbate deficiency in patients receiving dialysis: effects on plasma oxalate, serum cholesterol, and capillary fragility.

Whole blood ascorbate, plasma oxalate, serum cholesterol, and capillary fragility were measured at monthly intervals for 3 mth in 7 patients receiving continuous ambulatory peritoneal dialysis and 4 receiving haemodialysis, to whom ascorbate supplements had not been prescribed for at least 12 mth. Ascorbate supplements, 25 mg/day, were prescribed for the first month and 50 mg/day for the second month; in the final month patients received no supplements. Whole blood ascorbate was below normal in 6/11 patients at the start of the study but was normal in 10/11 patients when taking ascorbate 50 mg/day. No significant changes in plasma oxalate were observed with these doses of ascorbate, and correction of ascorbate deficiency had no effect on serum cholesterol, mean cell volume, or the results of capillary fragility tests. In a supplementary study, ascorbic acid 500 mg/day was administered for 3 wk to 11 patients. This resulted in a significant rise in mean plasma oxalate from 30.3 (SEM 3.5) to 48.4 (SEM 20.3) mumol/l.

The determination of plasma oxalate concentrations using an enzyme/bioluminescent assay. 2. Co-immobilisation of bioluminescent enzymes and studies of in vitro oxalogenesis.

An inexpensive, continuous flow assay for the determination of oxalate in plasma is described. The assay is based on the bioluminescent determination of NADH, a product of the degradation of oxalate by oxalate decarboxylase and formate dehydrogenase, using bioluminescent enzymes immobilized on cyanogen bromide-activated sepharose. The detection limit of the assay is 0.8 mumol/l. Intra-batch CV values of 5.2 and 3.8% were obtained at oxalate concentrations of 18 and 60 mumol/l. Recovery of added oxalate averaged 100.7%. Plasma oxalate ranged from less than 0.8 to 2 mumol/l in 14 healthy subjects, and from 6 to 134 mumol/l in 125 patients with renal disease treated by continuous ambulatory peritoneal dialysis. Ascorbic and dehydroascorbic acid did not directly interfere in the assay. In vitro oxalogenesis was observed in blood from 12 healthy subjects, but only after samples had stood at room temperature for more than 6 h. No significant oxalate generation occurred in blood from 24 patients with impaired renal function, even after standing at room temperature for 24 h. Oxalate generation was inhibited by the addition of oxalate to plasma, but the addition of urea and creatinine was without effect.

Oxalate retention in chronic renal failure: tubular vs glomerular diseases.

Plasma oxalate concentration was measured using an enzyme/bioluminescent assay in 289 patients (178 males, 111 females) with chronic renal failure (plasma creatinine greater than 200 mumol/l), age (SD) 55.5 (13.8) years. Plasma oxalate ranged between less than 0.8 and 48 mumol/l and showed a positive correlation with plasma creatinine (r = 0.57, p less than 0.0001). The slope of the regression line in 55 patients with glomerulonephritis (GN) was significantly lower than in patients with tubulointerstitial disease (TI); however the intercept was significantly higher in GN than in TI. Analysis of covariance showed no relationship between plasma oxalate concentration and age, duration of renal impairment, or administration of diuretics, vitamin D analogues, or phosphate binders. Longitudinal analysis of plasma oxalate measured 3-monthly in selected patients showed marked variability of oxalate/creatinine and oxalate/urea ratios.

Aluminum in the dialysis fluid.

The major source of aluminum in patients with chronic renal failure treated by hemodialysis is the hemodialysis fluid. The aluminum is derived from both the water and the chemical concentrate used in the preparation of the hemodialysis fluid. Due to the complex physico-chemistry of aluminum in water and dialysis fluid, both the total aluminum concentration and the proportion of aluminum species able to cross the hemodialysis membrane may vary from water supply to water supply and from day to day within a supply. A "safe" level of aluminum in dialysis fluid, which will prevent aluminum transfer from dialysis fluid to blood, and promotes aluminum removal from blood, has yet to be determined.

Affinity of the aluminium binding protein.

The affinity for aluminium of the binding protein (transferrin) in serum was studied by in vitro ultrafiltration and equilibrium dialysis. It was found that the binding of aluminium to transferrin is very tight and cannot be dissociated by prolonged dialysis or desferrioxamine (DFO). The tight binding of aluminium to transferrin may play a role in the development of microcytic hypochromic anaemia in aluminium intoxicated patients despite the presence of adequate iron.

Plasma oxalate concentration, oxalate clearance and cardiac function in patients receiving haemodialysis.

Pre-dialysis plasma oxalate concentration was measured in a cross-sectional study of 75 patients receiving maintenance haemodialysis. The aims of this study were to enable formulation of hypotheses regarding the determinants of plasma oxalate concentration and to allow preliminary examination of the possibility that hyperoxalaemia confers an increased risk of cardiac and vascular disease even in the absence of primary hyperoxaluria. Plasma oxalate concentration ranged between 7 and 76 mumol/l, mean (SD) 34.6 (18.1) mumol/l (normal range less than 0.8-2.0 mumol/l). Significant correlations were found between plasma oxalate concentration and plasma creatinine, duration of dialysis, current dose of ascorbic acid, and serum phosphate, and each of these variables retained significance on multiple linear regression. Oxalate clearance across a 1 m2 hollow-fibre Cuprophan dialyser, at 500 ml/min dialysate flow and blood flow between 175 and 225 ml/min, was measured 1 h after commencement of dialysis (n = 19). Mean (SD) clearance was 96.5 (27.0) ml/min. No significant association was found between self-reported maximum walking distance or the occurrence of symptoms of cardiac failure and plasma oxalate concentration. No relationship was found between plasma oxalate concentration and electrocardiographic conduction disturbances (n = 8) 'major' ST/T wave changes (n = 22), 'minor' ST/T wave changes (n = 49). Plasma oxalate was significantly greater in patients with radiologically detectable calcification of medium-sized arteries than in those without calcification, but duration of dialysis was also significantly longer in these patients. Routine haemodialysis results in marked hyperoxalaemia, which may be exacerbated by ascorbate supplementation. Oxalate clearance is similar to that of other small molecules such as creatinine and phosphate.(ABSTRACT TRUNCATED AT 250 WORDS)

Ammonium chloride-induced acidosis increases protein breakdown and amino acid oxidation in humans.

The effect of acidosis on whole body protein turnover was determined from the kinetics of infused L-[1-13C]leucine. Seven healthy subjects were studied before (basal) and after (acid) the induction of acidosis with 5 days oral ammonium chloride (basal pH 7.42 +/- 0.01, acid pH 7.35 +/- 0.03). Bicarbonate recovery, measured from the kinetics of infused NaH13CO3, was increased in the acidotic state (basal 72.9 +/- 1.2 vs. acid 77.6 +/- 1.6%; P = 0.06). Leucine appearance from body protein (PD), leucine disappearance into body protein (PS), and leucine oxidation (O) increased significantly (PD: basal 120.5 +/- 5.6 vs. acid 153.9 +/- 6.2, P < 0.01; PS: basal 98.8 +/- 5.6 vs. acid 127.0 +/- 4.7, P < 0.01; O: basal 21.6 +/- 1.1 vs. acid 26.9 +/- 2.3 mumol.kg-1.h-1, P < 0.01). Plasma levels of the amino acids threonine, serine, asparagine, citrulline, valine, leucine, ornithine, lysine, histidine, arginine, and hydroxyproline increased significantly with the induction of acidosis. These results confirm that acidosis in humans is a catabolic factor stimulating protein degradation and amino acid oxidation.

Ascorbate-induced hyperoxalaemia has no significant effect on lactate generation or erythrocyte 2,3,diphosphoglycerate in dialysis patients.

To examine the possible effects of hyperoxalaemia on anaerobic metabolism and erythrocyte pyruvate kinase activity, we induced a rise in plasma oxalate in 11 dialysis patients by the oral administration of ascorbic acid, 500 mg day-1 for 3 weeks. Blood samples were taken from the same antecubital vein before and after the supplementation period, without venous stasis, after an overnight fast. This protocol allowed patients to be used as their own controls. Five healthy subjects underwent an identical protocol to exclude any effect of ascorbate per se. Mean (SEM) plasma oxalate (mumol l-1) rose from 30.3 (3.5) to 48.4 (6.1) in patients and from 1.4 (0.2) to 6.8 (0.9) in healthy subjects. Whole blood ascorbate (mg l-1) rose from 7.0 (0.7) to 26.6 (2.5) in patients and from 9.3 (1.2) to 17.8 (1.8) in healthy subjects (reference range 7.5-20.0 mg l-1). No changes were observed in either group in plasma creatinine, bicarbonate, haemoglobin, or erythrocyte 2,3,diphosphoglycerate (2,3 DPG) after the 3 week supplementation period. Before supplementation lactate generation (area under curve, mmol min l-1) in the 5 min following a 60 s period of standardized ischaemic forearm exercise was significantly (P = 0.026) greater in patients [69.1 (4.7)] than in healthy subjects [46.9 (6.7)]; no significant change in lactate generation occurred in either group after ascorbate-induced hyperoxalaemia. We conclude that changes in plasma oxalate of the order of 20 mumol l-1 have no significant effect on lactate generation or 2,3,DPG levels in uraemic subjects.

Correction of acidosis in hemodialysis decreases whole-body protein degradation.

Correction of acidosis in hemodialysis (HD) decreases protein degradation. The effect of the correction of chronic metabolic acidosis in chronic renal failure patients treated with HD was determined from the kinetics of infused L-[1-(13)C]leucine. Six HD patients were studied before (acid) and after (bicarbonate) correction of acidosis (pH: acid 7.36 +/- 0.01, bicarbonate 7.40 +/- 0.01, P < 0.005). Leucine appearance from body protein (PD) and leucine disappearance into body protein (PS) decreased significantly with correction of acidosis (PD: acid 180.6 +/- 7.3, bicarbonate 130.9 +/- 7.2 mumol.kg-1.h-1, P < 0.005; PS: acid 172.3 +/- 6.8, bicarbonate 122.0 +/- 6.8 mumol.kg-1.h-1, P < 0.005). There was no significant change in leucine oxidation or plasma amino acid concentrations. These results demonstrate that optimal correction of acidosis in HD is beneficial in terms of protein turnover and may improve long-term nutritional status in HD.

Methods for studying the binding of aluminum by serum protein.

We describe methods for studying the binding of Al by protein in serum: ultrafiltration, gel filtration, and immuno-affinity chromatography. For ultrafiltration we used an Amicon YM10 cellophane membrane with a nominal cutoff of 10 000 Da to separate ultrafiltrable and non-ultrafiltrable Al. For gel filtration we used Sephacryl S-300, and for immuno-affinity chromatography we used anti-transferrin coupled to CNBr-activated Sepharose to identify the Al-binding protein. For 30 normal subjects 54% of the total Al in serum was non-ultrafiltrable; for 30 patients with chronic renal failure being treated by hemodialysis 67% was non-ultrafiltrable. In both groups transferrin was identified as the major Al-binding protein in the serum. Results of gel-filtration studies should be interpreted with caution: some gel media adsorb "free" Al, which can be subsequently taken up by transferrin or desferrioxamine passing through the column. We find affinity chromatography to be a specific and reliable method, suitable for use in quantitative studies.

Raised serum nickel concentrations in chronic renal failure.

We have measured serum nickel concentrations using flameless atomic absorption spectrophotometry. In 71 normals the median concentration was 1.0 micrograms/L, range less than 0.6-3.0 micrograms/L. Increased concentrations (p less than 0.05) were found in patients with chronic renal failure (CRF) treated conservatively (median 1.6 micrograms/L, range less than 0.6-3.6 micrograms/L). Significantly increased concentrations (p less than 0.001) were found in patients treated by continuous ambulatory peritoneal dialysis (CAPD) (median 8.6 micrograms/L, range 5.4-11.4 micrograms/L) and haemodialysis. In patients on haemodialysis, post-dialysis concentrations (median 8.8 micrograms/L, range 3.0-21.4 micrograms/L) were significantly higher (p less than 0.001) than pre-dialysis values (median 8.6 micrograms/L, range 0.6-16.6 micrograms/L).

Protein binding of aluminium in normal subjects and in patients with chronic renal failure.

Ultrafiltration of serum through YM10 membranes showed that 46 per cent of the aluminium in normal subjects and 33 per cent of the aluminium in patients with chronic renal failure is ultrafiltrable, suggesting that the majority of the aluminium is bound to some serum component(s) having molecular weight greater than 10,000 daltons. After desferrioxamine infusion, both the ultrafiltrable and protein-bound aluminium increases significantly, probably due to mobilisation of aluminium from body tissues. Gel filtration on Sephacryl S-300 and affinity chromatography have shown that transferrin is the major aluminium binding protein.

Insulin-mediated changes in PD and glucose uptake after correction of acidosis in humans with CRF.

To test the hypothesis that acidosis contributes to the insulin resistance of chronic renal failure (CRF) and impairs the action of insulin to decrease protein degradation, eight CRF patients were studied using the combined L-[1-13C]leucine-euglycemic clamp technique before (acid) and after (NaHCO3) 4 wk treatment with NaHCO3 (pH: acid 7.29 +/- 0.01 vs. NaHCO3 7.36 +/- 0.01, P < 0.001). Protein degradation (PD) was estimated sequentially from the kinetics of a primed continuous infusion of L-[1-13C]leucine in the basal state and during a hyperinsulinemic euglycemic clamp. Insulin sensitivity was measured during the clamp. The correction of acidosis significantly increased the glucose infusion rate necessary to maintain euglycemia (acid 6.44 +/- 0.89 vs. bicarbonate 7.38 +/- 0.90 mg.kg-1.min-1, P < 0.01) and significantly decreased PD in the basal state (acid 126.4 +/- 8.1 vs. bicarbonate 100.1 +/- 6.9 mumol.kg-1.h-1, P < 0.001). Hyperinsulinemia decreased PD in both studies (acid basal 126.4 +/- 8.1 vs. clamp 96.5 +/- 7.7, P < 0.001; bicarbonate basal 100.1 +/- 6.9 vs. clamp 88.2 +/- 5.5 mumol.kg-1.h-1, P = 0.06), its effect being unaltered by acidosis, with a reduction of 24% before and 12% after the correction of acidosis. In conclusion, acidosis contributes to the insulin resistance of CRF but does not affect the action of insulin on PD.

Correction of acidosis in humans with CRF decreases protein degradation and amino acid oxidation.

The effect of correction of acidosis in chronic renal failure (CRF) was determined from the kinetics of infused L-[1-13C]leucine. Nine CRF patients were studied before (acid) and after two 4-wk treatment periods of sodium bicarbonate (NaHCO3) and sodium chloride (NaCl) (pH: acid 7.31 +/- 0.01, NaHCO3 7.38 +/- 0.01, NaCl 7.30 +/- 0.01). Leucine appearance from body protein (PD), leucine disappearance into body protein (PS) and leucine oxidation (O) decreased significantly with correction of acidosis (PD: acid 122.4 +/- 6.1, NaHCO3 88.3 +/- 6.9, NaCl 116.2 +/- 9.1 mumol.kg-1.h-1, acid vs. NaHCO3 P < 0.01, NaHCO3 vs. NaCl P < 0.01, acid vs. NaCl NS; PS: acid 109.4 +/- 5.6, NaHCO3 79.0 +/- 6.3, NaCl 101.3 +/- 7.7 mumol.kg-1.h-1, acid vs. NaHCO3 P < 0.01, NaHCO3 vs. NaCl P < 0.01, acid vs. NaCl NS; O: acid 13.0 +/- 1.2, NaHCO3 9.2 +/- 0.9, NaCl 15.0 +/- 1.9 mumol.kg-1.h-1, acid vs. NaHCO3 P < 0.05, NaHCO3 vs. NaCl P < 0.01, acid vs. NaCl NS). There were no significant changes in plasma amino acid concentrations. These results confirm that correction of acidosis in chronic renal failure removes a potential catabolic factor.

Effect of pyridoxine supplementation on plasma oxalate concentrations in patients receiving dialysis.

Plasma oxalate and erythrocyte glutamic oxaloacetate transaminase activity (EGOT) (an indicator of nutritional status with respect to pyridoxine) were measured in 21 patients maintained on regular continuous ambulatory peritoneal dialysis or haemodialysis before and after a 4-month period of supplementation with pyridoxine, 100 mg day-1. Prior to supplementation 10/21 patients showed subnormal EGOT activity, although the increment in activity on addition of pyridoxal-5-phosphate in vitro was within the normal range in all cases. Mean plasma oxalate was 31.5 mumol l-1 (SEM 2.9) prior to supplementation and did not change significantly with supplementation, despite normalization of EGOT activity in all but 2/21 patients. We conclude that pyridoxine deficiency does not contribute significantly to hyperoxalaemia in patients receiving dialysis and that 100 mg of pyridoxine daily is insufficient to reduce oxalate generation by a pharmacological action on glycine transamination.

Correction of acidosis in CAPD decreases whole body protein degradation.

Correction of acidosis in CAPD decreases protein degradation and synthesis but has no effect on leucine oxidation. The effect of the correction of metabolic acidosis in CRF patients treated with CAPD was determined from the kinetics of infused L-[1-13C]leucine. Seven CAPD patients were studied before (acid) and after correction of acidosis (bicarbonate) (pH:acid 7.39 +/- 0.01, bicarbonate 7.41 +/- 0.01, P = 0.005). Leucine appearance from body protein (PD) [corrected] and leucine disappearance into body protein (PS) [corrected] decreased significantly with correction of acidosis. (PS: acid 211.7 +/- 9.8, bicarbonate 142.3 +/- 4.2 micromol x kg-1 x hr-1, P < 0.001; PD: acid 200.6 +/- 8.5, bicarbonate 132.4 +/- 3.7 micromol x kg-1 x hr-1, P < 0.001). There was no significant change in leucine oxidation or plasma amino acid concentrations. These results demonstrate that optimal correction of acidosis in CAPD is beneficial in terms of protein turnover.

Plasma oxalate in patients receiving continuous ambulatory peritoneal dialysis.

Plasma oxalate has been measured in 125 patients maintained on continuous ambulatory peritoneal dialysis using an enzyme/bioluminescent assay. Values ranged between 6 and 134 mumol/l, with a positively skewed distribution. Multiple linear regression analysis with plasma oxalate as the dependent variable showed highly significant associations with the dose of ascorbic acid, dose of alfacalcidol, and plasma creatinine, and weaker associations with serum phosphate, serum calcium, and body weight. When the presence of other potential risk factors was taken into account, no significant relationship could be found between the presence of clinically evident cardiac or vascular disease and plasma oxalate.