Effect of megadoses of ascorbic acid on serum and urinary oxalate

Vitamin C overload may contribute to systemic oxalosis in children receiving dialysis

BACKGROUND

Malnutrition and anorexia are common in children with chronic kidney disease (CKD) and gastrostomy tubes (GT) as well as nasogastric tubes (NGT) have been recommended to maximize nutritional support. The optimal requirement of vitamin C in children with CKD remains to be defined but oxalate is a breakdown product of vitamin C. Elevated vitamin C intake and bone oxalate were identified in two formula-fed dialyzed children with negative genetic testing for primary hyperoxaluria.

METHODS

We evaluated the impact of nutritional support on serum ascorbic acid and plasma oxalate levels in 13 dialyzed infants and young children.

RESULTS

All patients were fed by GT or NGT since the first months of life; overall patients were receiving between 145 and 847% of the age-specific DRI for vitamin C. Mean serum ascorbic acid and plasma oxalate levels were elevated (244.7 ± 139.7 μM/L and 44.3 ± 23.1 μM/L, respectively), and values did not differ according to the degree of residual kidney function. Ascorbic acid levels did not correlate with oxalate levels (r = 0.44, p = 0.13).

CONCLUSIONS

Excessive vitamin C intake may contribute to oxalate accumulation in dialyzed children.

Reductive Stress in Inflammation-Associated Diseases and the Pro-Oxidant Effect of Antioxidant Agents

Abstract: Reductive stress (RS) is the counterpart oxidative stress (OS), and can occur in response to conditions that shift the redox balance of important biological redox couples, such as the NAD⁺/NADH, NADP⁺/NADPH, and GSH/GSSG, to a more reducing state. Overexpression of antioxidant enzymatic systems leads to excess reducing equivalents that can deplete reactive oxidative species, driving the cells to RS. A feedback regulation is established in which chronic RS induces OS, which in turn, stimulates again RS. Excess reducing equivalents may regulate cellular signaling pathways, modify transcriptional activity, induce alterations in the formation of disulfide bonds in proteins, reduce mitochondrial function, decrease cellular metabolism, and thus, contribute to the development of some diseases in which NF-κB, a redox-sensitive transcription factor, participates. Here, we described the diseases in which an inflammatory condition is associated to RS, and where delayed folding, disordered transport, failed oxidation, and aggregation are found. Some of these diseases are aggregation protein cardiomyopathy, hypertrophic cardiomyopathy, muscular dystrophy, pulmonary hypertension, rheumatoid arthritis, Alzheimer's disease, and metabolic syndrome, among others. Moreover, chronic consumption of antioxidant supplements, such as vitamins and/or flavonoids, may have pro-oxidant effects that may alter the redox cellular equilibrium and contribute to RS, even diminishing life expectancy.

Hyperoxaluria: a gut-kidney axis?

Hyperoxaluria leads to urinary calcium oxalate (CaOx) supersaturation, resulting in the formation and retention of CaOx crystals in renal tissue. CaOx crystals may contribute to the formation of diffuse renal calcifications (nephrocalcinosis) or stones (nephrolithiasis). When the innate renal defense mechanisms are suppressed, injury and progressive inflammation caused by these CaOx crystals, together with secondary complications such as tubular obstruction, may lead to decreased renal function and in severe cases to end-stage renal failure. For decades, research on nephrocalcinosis and nephrolithiasis mainly focused on both the physicochemistry of crystal formation and the cell biology of crystal retention. Although both have been characterized quite well, the mechanisms involved in establishing urinary supersaturation in vivo are insufficiently understood, particularly with respect to oxalate. Therefore, current therapeutic strategies often fail in their compliance or effectiveness, and CaOx stone recurrence is still common. As the etiology of hyperoxaluria is diverse, a good understanding of how oxalate is absorbed and transported throughout the body, together with a better insight in the regulatory mechanisms, is crucial in the setting of future treatment strategies of this disorder. In this review, the currently known mechanisms of oxalate handling in relevant organs will be discussed in relation to the different etiologies of hyperoxaluria. Furthermore, future directions in the treatment of hyperoxaluria will be covered.

Evaluation of the kidney stone patient

Kidney stones are one of the most common chronic disorders in industrialized countries. In patients with kidney stones, the goal of medical therapy is to prevent the formation of new kidney stones and to reduce growth of existing stones. The evaluation of the patient with kidney stones should identify dietary, environmental, and genetic factors that contribute to stone risk. Radiologic studies are required to identify the stone burden at the time of the initial evaluation and to follow up the patient over time to monitor success of the treatment program. For patients with a single stone an abbreviated laboratory evaluation to identify systemic disorders usually is sufficient. For patients with multiple kidney stones 24-hour urine chemistries need to be measured to identify abnormalities that predispose to kidney stones, which guides dietary and pharmacologic therapy to prevent future stone events.

A review of dietary supplement-induced renal dysfunction

Complementary and alternative medicine (CAM) is a multibillion-dollar industry. Almost half of the American population uses some form of CAM, with many using them in addition to prescription medications. Most patients fail to inform their health care providers of their CAM use, and physicians rarely inquire. Annually, thousands of dietary supplement-induced adverse events are reported to Poison Control Centers nationwide. CAM manufacturers are not responsible for proving safety and efficacy, because the Food and Drug Administration does not regulate them. However, concern exists surrounding the safety of CAM. A literature search using MEDLINE and EMBASE was undertaken to explore the impact of CAM on renal function. English-language studies and case reports were selected for inclusion but were limited to those that consisted of human subjects, both adult and pediatric. This review provides details on dietary supplements that have been associated with renal dysfunction and focuses on 17 dietary supplements that have been associated with direct renal injury, CAM-induced immune-mediated nephrotoxicity, nephrolithiasis, rhabdomyolysis with acute renal injury, and hepatorenal syndrome. It is concluded that it is imperative that use of dietary supplements be monitored closely in all patients. Health care practitioners must take an active role in identifying patients who are using CAM and provide appropriate patient education.

Metabolic clearance of the antioxidant ascorbic acid in surgical patients

BACKGROUND

A reduction of plasma ascorbic acid concentration in the post-operative period has been well documented and is associated with an increase in post-operative complications. The underlying reason for the decreased concentration of ascorbic acid in the plasma is not clear. However, only an increased post-operative requirement for ascorbic acid would justify a substitution. Therefore, we investigated the pre-operative and post-operative metabolic clearance of ascorbic acid.

MATERIALS AND METHODS

We calculated the metabolic clearance subsequent to intravenous bolus injection of 6 mg ascorbic acid/kg body weight in 15 patients before and after they underwent major maxillofacial surgery. Blood samples were taken before and 5, 15, 30, 45, 60, 90, 120, and 240 min after administration of ascorbic acid before and after the operation. Urine was collected. Ascorbic acid in plasma and urine was analyzed using a high performance liquid chromatographic technique.

RESULTS

The pre-operative metabolic clearance was 7.6 +/- 2.22 l/h (mean +/- SD), increasing significantly to 12.1 +/- 4.87 l/h on the first post-operative day (P < 0.001). Doses of approximately 1150 mg ascorbic acid would be necessary to compensate for the observed loss and to raise plasma ascorbic acid to high normal values.

CONCLUSIONS

There is a significantly increased post-operative metabolic clearance of ascorbic acid that might be considered when framing future dose recommendations in post-operative patients.

Intestinal transport of an obdurate anion: oxalate

In this review, we focus on the role of gastrointestinal transport of oxalate primarily from a contemporary physiological standpoint with an emphasis on those aspects that we believe may be most important in efforts to mitigate the untoward effects of oxalate. Included in this review is a general discussion of intestinal solute transport as it relates to oxalate, considering cellular and paracellular avenues, the transport mechanisms, and the molecular identities of oxalate transporters. In addition, we review the role of the intestine in oxalate disease states and various factors affecting oxalate absorption.

Effect of ascorbic acid consumption on urinary stone risk factors

PURPOSE

Ascorbic acid (AA) has been implicated as a risk factor for calcium oxalate stones due to its conversion to oxalate and potential acidifying properties. We evaluated the effect of AA consumption on urinary saturation of calcium oxalate (CaOx) and urinary pH.

MATERIALS AND METHODS

A total of 12 normal subjects (NS) and 12 CaOx stone formers (SF) underwent 2, 6-day phases of study while maintained on a controlled metabolic diet. In each phase subjects ingested 1 gm AA or an identical appearing placebo twice daily. On the last 2 days of each phase 2, 24-hour urine collections were analyzed for pH and stone risk factors, and blood specimens were submitted for serum chemistry studies.

RESULTS

No difference in urinary pH was found between placebo and AA phases in NS (6.02 versus 6.02) and SF (6.0 versus 6.0). However, urinary oxalate was statistically significantly higher in the AA versus placebo phase for NS (34.7 versus 28.5 mg, p = 0.008) and SF (41.0 versus 30.5 mg, p <0.001). Likewise, the CaOx relative saturation ratio was significantly higher in the AA versus placebo phase for both groups.

CONCLUSIONS

Ingestion of 2 gm AA daily results in no change in urinary pH but a moderate though statistically significant increase in urinary oxalate in NS (20%) and SF (33%). Stone formers respond no differently to AA than normal subjects. We recommend limiting AA use to less than 2 gm daily in CaOx stone formers.

Effect of vitamin C supplements on urinary oxalate and pH in calcium stone-forming patients

BACKGROUND

The contribution of ascorbate to urinary oxalate is controversial. The present study aimed to determine whether urinary oxalate and pH may be affected by vitamin C supplementation in calcium stone-forming patients.

METHODS

Forty-seven adult calcium stone-forming patients received either 1 g (N=23) or 2 g (N=24) of vitamin C supplement for 3 days and 20 healthy subjects received 1 g. A 24-hour urine sample was obtained both before and after vitamin C for calcium, oxalate, magnesium, citrate, sodium, potassium, and creatinine determination. The Tiselius index was used as a calcium oxalate crystallization index. A spot fasting morning urine sample was also obtained to determine the urinary pH before and after vitamin C.

RESULTS

Fasting urinary pH did not change after 1 g (5.8 +/- 0.6 vs. 5.8 +/- 0.7) or 2 g vitamin C (5.8 +/- 0.8 vs. 5.8 +/- 0.7). A significant increase in mean urinary oxalate was observed in calcium stone-forming patients receiving either 1 g (50 +/- 16 vs. 31 +/- 12 mg/24 hours) or 2 g (48 +/- 21 vs. 34 +/- 12 mg/24 hours) of vitamin C and in healthy subjects (25 +/- 12 vs. 39 +/- 13 mg/24 hours). A significant increase in mean Tiselius index was observed in calcium stone-forming patients after 1 g (1.43 +/- 0.70 vs. 0.92 +/- 0.65) or 2 g vitamin C (1.61 +/- 1.05 vs. 0.99 +/- 0.55) and in healthy subjects (1.50 +/- 0.69 vs. 0.91 +/- 0.46). Ancillary analyses of spot urine obtained after vitamin C were performed in 15 control subjects in vessels with or without ethylenediaminetetraacetic acid (EDTA) with no difference in urinary oxalate between them (28 +/- 23 vs. 26 +/- 21 mg/L), suggesting that the in vitro conversion of ascorbate to oxalate did not occur.

CONCLUSION

These data suggest that vitamin C supplementation may increase urinary oxalate excretion and the risk of calcium oxalate crystallization in calcium stone-forming patients.

Medical evaluation of nephrolithiasis

A careful and individualized evaluation of risk factors is a fundamental part of the management of patients with urinary tract stone disease. Identification and correction of important abnormalities provide the basis for designing an efficient and rational treatment program, aiming at an arrest or at least reduction of recurrent stone formation. It is beyond doubt that appropriate therapeutic steps in this regard are of great benefit for the patient. It needs to be emphasized, however, that no success will be obtained unless the patient is willing and able to follow the ensuing dietary recommendations and medical advice.

Hyperoxaluric calcium nephrolithiasis

Hyperoxaluria leads to increased calcium oxalate supersaturation and calcium oxalate stone formation. Excess oxalate can arise from endogenous overproduction as in primary hyperoxaluria or from dietary sources. In the last 15 years great strides have been made in the diagnosis and treatment of primary hyperoxaluria. However options still seem limited in treating the mild hyperoxaluria found in many stone formers. Inadequate knowledge of food oxalate content, the effect of dietary oxalate precursors on oxalate excretion, and the factors affecting handling of oxalate by the intestine prevent development of rational therapies for treatment of hyperoxaluria. Recent studies of oxalate degrading bacteria and renewed interest in the role of diet calcium in oxalate absorption may lead to better therapeutic strategies for hyperoxaluric calcium nephrolithiasis.

Acute renal failure, oxalosis, and vitamin C supplementation: a case report and review of the literature

With the increased use of nonprescription vitamin supplementation, physicians involved in critical care must be aware of the potential complications of these medications. We report the case of a 31-year-old African-American man presenting to the emergency department with acute renal failure. He had previously been well and initially denied the use of any drugs except for vitamin C tablets obtained at a local health food store. This case report and review of the literature is utilized to illustrate the importance of historical data in patients presenting with acute renal failure to a critical care service.

Relative hyperoxaluria, crystalluria and haematuria after megadose ingestion of vitamin C

BACKGROUND

Long-term or high-dosage consumption of vitamin C may play a role in calcium oxalate kidney stone formation. The present study was undertaken to determine the biochemical and physicochemical risk factors in a male subject who developed haematuria and calcium oxalate crystalluria after ingestion of large doses of ascorbic acid for 8 consecutive days.

METHODS

Twenty-four-hour urine samples were collected before and during the ascorbic acid ingestion period as well as after the detection of haematuria. A special procedure was implemented for urine collections to allow for oxalate, ascorbate and other urinalysis. Oxalate was determined in the presence of EDTA to prevent in vitro conversion to ascorbic acid, whereas ascorbate itself was determined by manual titration in a redox method using the dye dichlorophenolindophenol. Urinalysis data were used to compute calcium oxalate relative supersaturations and Tiselius risk indices, whereas scanning electron microscopy was used to examine urinary deposits.

RESULTS

Oxalate excretion increased by about 350% during ascorbate ingestion before haematuria. Ascorbate concentrations also increased dramatically but appeared to reach a plateau maximum. Increasing calcium excretion was accompanied by decreasing potassium and phosphate values. The calcium oxalate relative supersaturation and Tiselius risk index increased during vitamin C ingestion and large aggregates of calcium oxalate dihydrate crystals were observed by scanning electron microscopy immediately after the detection of haematuria.

CONCLUSION

High percentage metabolic conversion of ascorbate to oxalate in this subject caused relative hyperoxaluria and crystalluria, the latter manifesting itself as haematuria. Clinicians need to be alerted to the potential dangers of large dose ingestion of vitamin C in some individuals.

The effect of ascorbic acid ingestion on the biochemical and physicochemical risk factors associated with calcium oxalate kidney stone formation

The present study was undertaken to determine the effect of ingestion of large doses of vitamin C on urinary oxalate excretion and on a number of other biochemical and physicochemical risk factors associated with calcium oxalate urolithiasis. A further objective was to determine urinary ascorbate excretion and to relate it qualitatively to ingested levels of the vitamin and oxalate excretion. Ten healthy males participated in a protocol in which 4 g ascorbic acid was ingested for 5 days. Urines (24 h) were collected prior to, during and after the protocol. The urine collection procedure was designed to allow for the analysis of oxalate in the presence and absence of an EDTA preservative and for the analysis of ascorbic acid by manual titration using 2,6 dichlorophenolindophenol. Physicochemical risk factors such as the calcium oxalate relative supersaturation and Tiselius risk index were calculated from urine composition. The results showed that erroneously high analytical oxalate levels occur in the asence of preservative. In the preserved samples there was no significant increase in oxalate excretion at any stage of the protocol. Ascorbate excretion increased when vitamin C ingestion commenced but levelled out after 24 hours suggesting that saturation of the metabolic pool is reached within 24 hours after which ingested ascorbic acid is excreted unmetabolized in the urine. While transient statistically significant changes occurred in some of the biochemical risk factors, they were not regarded as being clinically significant. There were no changes in either the calcium oxalate relative supersaturation or Tiselius risk index. It is concluded that ingestion of large doses of ascorbic acid does not affect the principal risk factors associated with calcium oxalate kidney stone formation.

Applications of antioxidants in physiologically functional foods: safety aspects

Intense public and scientific debate exists over whether the intake of some nutrients above the recommended dietary allowances may provide benefits beyond their traditional functions. However, excessive intakes of nutrients are well documented to cause adverse effects. This review focuses on methods that may be useful for identifying chronic intakes that result in adverse effects and for identifying intakes that provide a reasonable margin of safety from these effects. Groups responsible for nutrition and health policy must establish effective criteria for establishing safety limits, for validating end points, and determination of data acceptability. These criteria are needed to minimize toxicity while maximizing potential health benefits of exaggerated nutrient intake.

Effect of high dose vitamin C on urinary oxalate levels

The effect of high dose ascorbate on urinary oxalate levels in healthy adults was investigated using a modified ion chromatography method. Subjects ingested 1, 5 and 10 gm. supplemental ascorbate per day for 5 days, separated by 5 days of no supplementation. Urine ascorbate levels demonstrated variable increases with ascorbate supplementation. Ascorbate added directly to urine in vitro resulted in statistically significant but modest increases in measured oxalate. Addition of 5.68 mmol./l. ascorbate increased measured urinary oxalate by 36 mumol./l., implying conversion of ascorbate to oxalate during analysis. Measurement of 24-hour urinary oxalate levels with 5 and 10 gm. ascorbate per day showed similar, modest increases, which could be entirely accounted for by oxalate production during analytical procedures. Thus, no genuine increase in urinary oxalate was demonstrable despite a greatly increased ascorbate intake.

Effects of ascorbic acid and pyridoxine supplementation on oxalate metabolism in peritoneal dialysis patients

We studied the effect of vitamin C and B6 supplementation on oxalate metabolism in seven patients receiving chronic peritoneal dialysis therapy. The study was divided into three phases, each lasting 4 weeks. Plasma oxalate, total ascorbic acid, and pyridoxal-5'-phosphate (PLP) were measured at the end of each phase. Twenty-four-hour urinary excretion and dialysate removal rates of oxalate were also obtained. At the end of phase I (supplement-free period), plasma oxalate levels were markedly elevated at 47.6 +/- 7.1 mumol/L (437 +/- 66 micrograms/dL) (normal, 3.4 +/- 0.4 mumol/L [30.3 +/- 1.6 micrograms/dL]). Plasma total ascorbic acid levels were 62 +/- 6 mumol/L (1.0 +/- 0.1 mg/dL) (normal, 45 to 57 mumol/L [0.8 to 1.0 mg/dL]), while plasma PLP levels were markedly reduced to 24 +/- 5 nmol/L (normal, 40 to 80 nmol/L). Daily supplements of 0.57 mmol (100 mg) ascorbic acid orally (phase II) resulted in a 19% increase in the plasma oxalate levels to 57.8 +/- 6.1 mumol/L (520 +/- 55 micrograms/dL) (P less than 0.03), with a concomitant 60% increase in the plasma ascorbate levels (91 +/- 6 mumol/L [1.6 +/- 0.1 mg/dL], P less than 0.01). Plasma PLP values remained low. Finally, during phase III (0.57 mmol or 100 mg ascorbic acid plus 59.6 mumol or 10 mg pyridoxine HCI orally daily), plasma oxalate levels declined by 17% to 47.9 +/- 5.2 mumol/L (431 +/- 47 micrograms/dL) (P greater than 0.05 v phase II).(ABSTRACT TRUNCATED AT 250 WORDS)

Diet and renal stones in 72 areas in England and Wales

Geographical differences in emergency admission rates for renal stones and colic in England and Wales have been shown to correlate with the incidence of renal stones determined from case registers. The rates in 72 areas were related to per capita consumption of different foods, measured from household food purchases. There was an inverse relation with consumption of dietary fibre and all cereal foods. Differences in adult diet are not, however, the major determinants of the geographical variations in renal stone incidence within Britain.

A case-control study of dietary intake of renal stone patients. I. Preliminary analysis

The average daily dietary intake of 88 idiopathic renal stone cases and 88 age and sex matched controls was assessed by history using a standardised questionnaire. Statistical analysis was undertaken on the whole group and on male and female subgroups, to establish if there were any significant differences between cases and controls. There were statistically significant differences in dietary intake between the whole group, the female cases and the control group. Male cases showed only a significantly lower intake of thiamine compared to controls. There was little difference between cases and controls intake of iron or multivitamin supplements but vitamin C supplements (greater than 1 g/day) were taken more than twice as frequently by cases than controls. These results suggest that control dietary studies of renal stone patients without regard to their sex may conceal many differences in dietary intake between cases and controls.

Kidney stones. Medical management and newer options for stone 'removal'

Patients with recurrent kidney stone disease or stone formers at increased risk of recurrence deserve a thorough metabolic workup. This should be based on a careful history and include urinalysis, serum chemistry studies, and analysis of 24-hour urine collections. Measures to prevent recurrent stone formation are aimed at correcting the metabolic imbalances detected in the workup. A variety of drugs are available that target one or more of the metabolic abnormalities that may be involved. For "surgically active" renal and ureteral stone disease, newer techniques make surgery unnecessary in most cases. Extracorporeal shock wave lithotripsy is becoming the preferred technique for disintegration of upper urinary tract stones. Percutaneous ultrasonic lithotripsy and electrohydraulic disintegration also are widely used. For lower urinary tract stones, the ureteroscope permits either extraction under visualization or ultrasonic disintegration.

Oxalate removal by hemodialysis in end-stage renal disease

Because of mounting evidence of precipitation of calcium oxalate in the soft tissues of patients with end-stage renal disease (ESRD) on maintenance hemodialysis, the plasma oxalate concentrations and calculated dialysis removal of oxalate were studied in seven patients without evidence of either primary or absorption hyperoxaluria prior to ESRD. A reversed-phase high-pressure liquid chromatographic method was developed to quantitate serum oxalate. Mean value +/- SE in four healthy controls was 28 +/- 5 mumol/L, and in the seven patients it was 187 +/- 15 mumol/L predialysis and 89 +/- 11 mumol/L postdialysis. Oxalate deposition in the soft tissues of ESRD patients is the consequence of sustained hyperoxalemia. Oxalate removal by dialysis was calculated from the four-hour oxalate clearance. Since the ionic radii of phosphate and oxalate are similar, total oxalate clearance was calculated midpoint of dialysis. Mean oxalate removal/dialysis was 3.01 +/- 0.283 mmol. On a daily basis this value was 1.645 +/- 0.155 mmol, which is about threefold the normal oxalate excretion rate. It is not significantly different from the excretion rate in absorption oxalurias but is less than that in primary hyperoxaluria. Therefore, it is concluded that hyperoxalemia in ESRD results from loss of renal excretion, failure of hemodialysis to remove enough oxalate to maintain a normal serum concentration, and increased intestinal absorption of oxalate and/or increased endogenous production.

The effects of vegetable and animal protein diets on calcium, urate and oxalate excretion

A group of 30 meat eating normal subjects were compared with a second group of vegetarians matched for age and sex. Their diets and urinary excretion patterns were compared by statistical analysis. A link between protein intake, particularly animal protein, and urinary calcium excretion was demonstrated and also that dietary calcium was inversely related to urinary oxalate excretion. Urinary oxalate increases with the vegetable protein content of the diet, but within the limits of these diets, animal protein does not affect oxalate excretion though it does affect excretion of urinary urate.

A control study of dietary factors in renal stone formation

Fifty-one first admission renal stone patients and an equal number of controls were interviewed and a dietary history of the average weekly intake was collected from each participant. A comparison of the dietary intake per kilogram body weight in each group was made using standard statistical procedures. None of the nutrient intakes showed a significant difference, but dietary fibre intake and the percentage of energy provided by carbohydrate were consistently higher in the control group, whereas the percentage of energy provided by fat was consistently higher in the renal stone group.