Erythrocyte transmembrane flux and renal clearance of oxalate in idiopathic calcium nephrolithiasis

Oxalate Flux Across the Intestine: Contributions from Membrane Transporters

Epithelial oxalate transport is fundamental to the role occupied by the gastrointestinal (GI) tract in oxalate homeostasis. The absorption of dietary oxalate, together with its secretion into the intestine, and degradation by the gut microbiota, can all influence the excretion of this nonfunctional terminal metabolite in the urine. Knowledge of the transport mechanisms is relevant to understanding the pathophysiology of hyperoxaluria, a risk factor in kidney stone formation, for which the intestine also offers a potential means of treatment. The following discussion presents an expansive review of intestinal oxalate transport. We begin with an overview of the fate of oxalate, focusing on the sources, rates, and locations of absorption and secretion along the GI tract. We then consider the mechanisms and pathways of transport across the epithelial barrier, discussing the transcellular, and paracellular components. There is an emphasis on the membrane-bound anion transporters, in particular, those belonging to the large multifunctional Slc26 gene family, many of which are expressed throughout the GI tract, and we summarize what is currently known about their participation in oxalate transport. In the final section, we examine the physiological stimuli proposed to be involved in regulating some of these pathways, encompassing intestinal adaptations in response to chronic kidney disease, metabolic acid-base disorders, obesity, and following gastric bypass surgery. There is also an update on research into the probiotic, Oxalobacter formigenes, and the basis of its unique interaction with the gut epithelium. © 2021 American Physiological Society. Compr Physiol 11:1-41, 2021.

The Efficacy of Polyunsaturated Fatty Acids as Protectors against Calcium Oxalate Renal Stone Formation: A Review

In the pathogenesis of hypercalciuria and hyperoxaluria, n-6 polyunsaturated fatty acids (PUFAs) have been implicated by virtue of their metabolic links with arachidonic acid (AA) and prostaglandin PGE₂. Studies have also shown that n-3 PUFAs, particularly those in fish oil—eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA)—can serve as competitive substrates for AA in the n-6 series and can be incorporated into cell membrane phospholipids in the latter’s place, thereby reducing urinary excretions of calcium and oxalate. The present review interrogates several different types of study which address the question of the potential roles played by dietary PUFAs in modulating stone formation. Included among these are human trials that have investigated the effects of dietary PUFA interventions. We identified 16 such trials. Besides fish oil (EPA+DHA), other supplements such as evening primrose oil containing n-6 FAs linoleic acid (LA) and γ-linolenic acid (GLA) were tested. Urinary excretion of calcium or oxalate or both decreased in most trials. However, these decreases were most prominent in the fish oil trials. We recommend the administration of fish oil containing EPA and DHA in the management of calcium oxalate urolithiasis.

Urinary Oxalate Excretion Increases in Home Parenteral Nutrition Patients on a Higher Intravenous Ascorbic Acid Dose

BACKGROUND

Vitamin C can be metabolized to oxalate. Case reports have suggested an association between IV vitamin C and urinary oxalate excretion. Recently, the US Food and Drug Administration required the dose of vitamin C in IV multivitamin preparations to be increased from 100 mg to 200 mg/d. We compared the urinary oxalate excretion level in stable home total parenteral nutrition (TPN) patients receiving both doses of vitamin C.

METHODS

Each participant provided a 24-hour urine sample for oxalate determination on the vitamin C dose (100 mg/d), and again after at least 1 month on the increased vitamin C dose (200 mg/d). A 2-day diet diary was completed covering the day before and the day of the urine collection and was analyzed for oxalate and vitamin C content. Comparisons were made using Student paired t test and Wilcoxon signed rank.

RESULTS

Thirteen patients (7 males/6 females) aged 63.1 +/- 12.2 years who had no history of nephrolithiasis and had received TPN for 55.9 +/- 78.8 months were enrolled. The most common indication for TPN was short bowel syndrome (38.5%). Eight patients had an intact colon. Urinary oxalate excretion increased on the 200-mg vitamin C dose, from 0.34 +/- 0.13 to 0.44 +/- 0.17 mmol/d (mean increase = 0.10 mmol/d; p = .04; 95% confidence interval 0.004 to 0.19 mmol/d). Oral intake of vitamin C and oxalate did not differ between the 2 collection periods.

CONCLUSIONS

In therapeutically used doses, IV vitamin C increases urinary oxalate excretion, potentially predisposing susceptible individuals to nephrolithiasis. This factor should be considered in patients receiving home TPN.

Importance of erythrocyte band III anion transporter (SLC4A1) on oxalate clearance of calcium oxalate monohydrate stone-formering patients vs. normal controls

OBJECTIVES

To examine erythrocyte band III transport protein (SLC4A1), erythrocyte oxalate flux, and plasmatic, cellular, and urine oxalate concentrations and blood gas analyses in calcium oxalate monohydrate stone-forming patients (COM) in comparison with normal controls (NC).

METHODS

Isolated red cells from 51 NC and 25 COM cases were divided for cellular oxalate measurement and for measurement of transcellular erythrocyte oxalate flux (pH 7.48-8.24). SLC4A1 protein levels were determined by Western blot analyses. Plasmatic and urinary oxalate levels and the venous blood gas analysis were measured simultaneously.

RESULTS

SLC4A1 protein levels were significantly higher in COM (8.76 ± 2.12) than in NC (4.17 ± 0.61; P < .02). Cellular oxalate and venous HCO(3)(-) were significantly lower in COM (2.35 ± 0.26 μmol/L) and (24.06 ± 0.24 mmo/l) than in NC (4.03 ± 0.49 μmol/L; P < .05) and (24.93 ± 0.17 mmol/L; P < .01). Urinary oxalate was significantly higher in COM (0.31 ± 0.02 mmol/L) than in NC (0.25 ± 0.01 mmol/L; P < .04). The erythrocyte transmembrane oxalate flux correlated with the pH value and with the urinary oxalate in both groups (r = .25-.55; P = .01). With increased pH values, the oxalate flux showed inverse effects in both groups.

CONCLUSIONS

SLC4A1 associated changes of HCO(3)(-) and pH levels influenced the cellular oxalate levels and urinary oxalate clearance. Under normal conditions (pH 7.55) the oxalate efflux in COM was comparable with the acid stimulated oxalate efflux in NC. The addition of HCO(3)(-) compensated the flux of COM stone formers to the levels of normal controls.

Oxalate-mediated oxidant–antioxidant imbalance in erythrocytes: role of N-acetylcysteine

The present in-vivo study was to observe the effect of N-acetylcysteine (NAC) on oxalate-induced oxidative stress on rat erythrocytes. A total of 15 Wistar rats were divided into three groups. The control group received normal saline by single intraperitoneal injection. Hyperoxaluria was induced by single intraperitoneal (i.p.) dose of sodium oxalate (70 mg/kg body weight in 0.5 mL saline) to a second group. The third group was administered single i.p. dose of NAC according to 200 mg/kg body weight dissolved in 0.5 mL saline, half an hour after oxalate dose. NAC administration normalized antioxidant enzyme activities (superoxide dismutase and catalase) and reduced malondialdehyde content (indicator of lipid peroxidation) in hyperoxaluric rat’s red blood cell (RBC) lysate. NAC administration also resulted in a significant improvement of thiol content in RBC lysate via increasing reduced glutathione content and maintaining its redox status. Oxalate-caused alteration of cholesterol/phospholipid ratio (determining membrane fluidity) was also rebalanced by NAC administration. Further, after NAC administration, electron microscopy showed improved cell morphology presenting its prophylactic properties. Above results indicate that NAC treatment is associated with an increase in plasma antioxidant capacity and a reduction in the susceptibility of erythrocyte membranes to oxidation. Thus, the study presents positive pharmacological implications of NAC against oxalate-mediated impairment of erythrocytes.

Lithiasis and Risk Factors

Nephrolithiasis is a worldwide disease with high clinical and economic costs. The increasing incidence in industrialized countries seems to be related to several risk factors, which are partly inherited and partly acquired. Although risk factors in urolithiasis are still under discussion, their identification would provide a notable gain for the patient in terms of stone episodes, and for the health service in terms of costs. This article presents an easy classification of risk factors based on clinical background.

Nephrolithiasis: why doesn't our "learning" progress?

OBJECTIVE

Stone research is stagnant with minor clinical fall-out. We wonder whether this, in the ESWL era, depends only on ESWL and the consequent change in our clinical management habits, or is rather due to mistakes made by investigators. We feel that indeed we did and do make some: (1) the patients we are investigating may not be appropriate; and (2) we are missing to properly recognise disease heterogeneity.

CONCLUSIONS

From the public health side most likely we are not investigating the right patients, and we probably need to address the large part of the problem, i.e. the rarely relapsing stone formers demanding 80% of all urological interventions. Although there is a consensus that urolithiasis is very heterogeneous, this position is presently under reconsideration. It is necessary to investigate the single or "occasional" stone former, and go back to the epidemiology and clinics with multicentre, prospective studies. Being a multifactorial disease, we will need to evaluate as many aspects as possible contemporaneously in the same patient. It is also necessary to "revisit" the disease in an unbiased manner, because its relationship with relevant aspects could be different than previously thought due to our incomplete knowledge of its pathogenesis and pathophysiology.

Early changes of oxalate and calcium urine excretion in those with calcium oxalate stone formation after extracorporeal shock wave lithotripsy

OBJECTIVES

To determine the extent of transient changes of tubular function in idiopathic calcium-oxalate (CaOx) stone-bearing patients after extracorporeal shock wave lithotripsy (ESWL), calcium and oxalate excretion were measured before and after ESWL.

METHODS

In 22 patients with renal CaOx stones, the plasma values and urine excretion of creatinine, calcium, oxalate, magnesium, and citrate were measured before and on days 1 and 2 after ESWL under conditions of a standardized diet. Overnight urine collection for an 8-hour period was used to measure the urine excretion, and the values were extrapolated to a 24-hour period. For calculation of the urine ion activity, the AP(CaOx) index EQ(s) and the CaOx risk index were used.

RESULTS

After ESWL, hyperoxaluria was noted in 10 patients compared with 2 before ESWL. Hypercalciuria was seen in 11 patients after ESWL compared with 3 before. Combined hyperoxaluria and hypercalciuria was found in 7 patients after ESWL compared with 1 before. Both the oxalate/creatinine and calcium/creatinine ratios were significantly increased after ESWL. The AP(CaOx) index EQ(s) and the CaOx risk index were significantly increased after ESWL in patients with increased post-ESWL calcium and/or oxalate excretion.

CONCLUSIONS

Increased calcium and/or oxalate excretion can be seen in patients with CaOx stones early after ESWL. This increased excretion of lithogenic substances represents an increased risk of fragment apposition after ESWL for the group with a significantly increased AP(CaOx) index EQ(s) and CaOx risk index. Therefore, prophylactic measures in patients at risk early after ESWL might be warranted to prevent possible recurrent stone formation.

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.

Effects of an oxalate load on urinary oxalate excretion in calcium stone formers

OBJECTIVE

To investigate the oxalate intake and the effect of an oxalate load on urinary oxalate excretion in calcium stone-forming (CSF) patients.

DESIGN

Prospective study.

SETTING

University-affiliated outpatient Renal Lithiasis Unit.

PATIENTS AND CONTROLS

Seventy (70) CSF and 41 healthy subjects (HS) collected a 24-hour urine sample and were submitted to a 3-day dietary record to determine mean oxalate (Ox), calcium (Ca) and vitamin C intake. Fifty-eight (58) CSF patients were randomly selected to receive milk (N = 28) or dark (N = 30) chocolate as an oxalate load.

INTERVENTION

Administration of either milk (94 mg Ox + 430 mg Ca) or dark chocolate (94 mg Ox + 26 mg Ca) for 3 days. A 24-hour urine sample was obtained before and after the load to determine calcium, oxalate, sodium, potassium, urea, and creatinine.

MAIN OUTCOME MEASURE

Oxalate intake and excretion.

RESULTS

CSF patients presented mean Ox intake of 98 +/- 137 mg/d, similar to that of HS (108 +/- 139 mg/d). Mean Ox and vitamin C intake was directly correlated with Ox excretion only in CSF. The consumption of dark chocolate induced a significant increase in mean urinary Ox (36 +/- 14 versus 30 +/- 10 mg/24 hr) not observed in the milk chocolate group. Thus, a 2-fold increase in Ox intake in this population of CSF patients produced a significant 20% increase in oxaluria, not observed when Ca was consumed simultaneously.

CONCLUSION

The present study suggests that even small increases in Ox intake affect oxalate excretion and the mitigation of urinary oxalate increase by Ca consumption reinforces that Ca and Ox intakes for CSF patients should be in balance. Further studies are necessary to assess whether or not a 20% increase in oxaluria will lead to a higher risk of stone formation.

(L)-2-oxothiazolidine-4-carboxylate in the treatment of primary hyperoxaluria type 1

OBJECTIVE

To evaluate the short-term efficacy of (l)-2-oxothiaolidine-4-carboxylate (OTZ, which reduces urinary oxalate excretion in normal subjects) in the treatment of primary hyperoxaluria type 1 (PH1) in a phase II study.

PATIENTS AND METHODS

Two patients with PH1 received intravenous infusions of OTZ (100 mg/kg body weight for 2 h) given every 8 h for four doses. One patient also received a placebo treatment. Urine samples (24-h collections) were obtained before and during OTZ treatment and assayed for oxalate, citrate, creatinine, sulphate and pH. Daily blood samples were assayed for plasma oxalate and serum creatinine.

RESULTS

Urinary oxalate excretion was unaffected by OTZ treatment. Plasma oxalate declined in both individuals with OTZ treatment, but the effect was small. Plasma cysteine was normal in one patient, rising from a mean (sd) of 36 (3.7) micromol/L before treatment to a peak of 141 micromol/L after OTZ, but was not detected in samples from the other patient. The ratio of oxalate to creatinine clearances was high in both patients, with mean values of 3.1 and 3.8.

CONCLUSIONS

Treatment with OTZ did not lead to clinically significant changes in urinary oxalate excretion. The high clearance of oxalate in these patients suggests a substantial renal secretion of oxalate.

Contribution of dietary oxalate to urinary oxalate excretion

BACKGROUND

The amount of oxalate excreted in urine has a significant impact on calcium oxalate supersaturation and stone formation. Dietary oxalate is believed to make only a minor (10 to 20%) contribution to the amount of oxalate excreted in urine, but the validity of the experimental observations that support this conclusion can be questioned. An understanding of the actual contribution of dietary oxalate to urinary oxalate excretion is important, as it is potentially modifiable.

METHODS

We varied the amount of dietary oxalate consumed by a group of adult individuals using formula diets and controlled, solid-food diets with a known oxalate content, determined by a recently developed analytical procedure. Controlled solid-food diets were consumed containing 10, 50, and 250 mg of oxalate/2500 kcal, as well as formula diets containing 0 and 180 mg oxalate/2500 kcal. Changes in the content of oxalate and other ions were assessed in 24-hour urine collections.

RESULTS

Urinary oxalate excretion increased as dietary oxalate intake increased. With oxalate-containing diets, the mean contribution of dietary oxalate to urinary oxalate excretion ranged from 24.4 +/- 15.5% on the 10 mg/2500 kcal/day diet to 41.5 +/- 9.1% on the 250 mg/2500 kcal/day diet, much higher than previously estimated. When the calcium content of a diet containing 250 mg of oxalate was reduced from 1002 mg to 391 mg, urinary oxalate excretion increased by a mean of 28.2 +/- 4.8%, and the mean dietary contribution increased to 52.6 +/- 8.6%.

CONCLUSIONS

These results suggest that dietary oxalate makes a much greater contribution to urinary oxalate excretion than previously recognized, that dietary calcium influences the bioavailability of ingested oxalate, and that the absorption of dietary oxalate may be an important factor in calcium oxalate stone formation.

Dietary manipulation of delta-6-desaturase modifies phospholipid arachidonic acid levels and the urinary excretion of calcium and oxalate in the rat: insight in calcium lithogenesis

An anomalous n-6 polyunsaturated fatty acid composition in plasma and erythrocyte membrane phospholipids, namely increased levels of arachidonic acid (AA), has been reported in calcium nephrolithiasis and has been proposed to play an important role in its pathogenesis. To confirm this, in rats we modified phospholipid AA levels by dietary manipulation of the delta-6-desaturase, the rate-limiting enzyme of the fatty acid biosynthetic pathway, and evaluated the effect on cellular and renal functions predisposing to lithogenesis. Increased AA levels led to conditions at risk for nephrolithiasis: higher oxalate flux and lower sodium cotransport in erythrocytes and a rise in urinary prostaglandin E2, calcium, sodium, and oxalate levels; reduced AA levels reversed these changes. In vitro, in human erythrocytes the incorporation of exogenous AA into membranes increased band 3 protein phosphorylation directly activating the Ser/Thr protein kinase CK1 and induced a parallel raise in band 3-mediated oxalate transport. These findings demonstrate the pivotal role of phospholipid AA in modulating erythrocyte and renal transport of calcium and oxalate.

Molecular basis of inherited renal lithiasis

Idiopathic calcium oxalate stone formation results from an interaction between genetic and environmental factors. Clearly identifiable risk factors for the disease that have a significant genetic influence are the excretions of calcium, oxalate and citrate. Candidate genes that may be responsible for these effects have been proposed. With the large-scale sequencing of the human genome and the identification of genetic polymorphisms, it is only a matter of time before these genes and the sequence differences within them that are associated with susceptibility to the disease are conclusively identified.

Nephrolithiasis: acute management and prevention

The primary care physician has a responsibility not only to recognize and treat acute stone passage but to ensure that the patient with recurrent stones has metabolic evaluation and appropriate preventive care. Renal colic is typically severe, radiates to the groin, is associated with hematuria, and may cause ileus. About 90% of stones that cause renal colic pass spontaneously. The patient with acute renal colic should be treated with fluids and analgesics and should strain the urine to recover stone for analysis. Highgrade obstruction or failure of oral analgesics to relieve pain may require hospitalization; a urinary tract infection in the setting of an obstruction is a urologic emergency requiring immediate drainage, usually with a ureteral stent. Several approaches are available when stones do not pass spontaneously, including extracorporeal shock wave lithotripsy, percutaneous lithotripsy, and ureteroscopic laser lithotripsy. Calcium stone disease has a lifetime prevalence of 10% in men and causes significant morbidity. Renal failure is unusual. Stone types include calcium oxalate, uric acid, struvite, and cystine. Stone analysis is particularly important when a noncalcareous constituent is identified. The majority of patients with nephrolithiasis will have recurrence, so prevention is a high priority. High fluid intake is a mainstay of prevention. Metabolic evaluation will indicate other appropriate preventive measures, which may include dietary salt and protein restriction, and use of thiazide diuretics, neutral phosphate, potassium citrate, allopurinol, and magnesium salts. Dietary calcium restriction may worsen oxaluria and negative calcium balance (osteoporosis).

Pathogenesis of idiopathic calcium nephrolithiasis: update 1997

Idiopathic calcium nephrolithiasis (ICN) is a frequent disease in Western countries. The physicochemical theory of lithogenesis, which explains stone formation by the precipitation, growth, and crystalline aggregation of lithogenic salts in the urine, has contributed greatly to the understanding of the pathogenesis of calcium urolithiasis. However, several aspects are still unexplained; the co-existence of familial occurrence, primary tubular dysfunctions with ICN, and anomalies in the systemic handling of oxalate and calcium led to the development of a cellular hypothesis of ICN. A number of cellular defects in the handling of ions has been reported that involves both anion and cation transport. These anomalies are probably the expression of a still unknown cellular defect in idiopathic calcium stone formers. We suggested that an anomaly in the cell membrane composition might be responsible for the complex array of cell ion flux abnormalities observed in ICN. Recently, a disorder in the n-6 polyunsaturated fatty acid series has been described; it is characterized by a lower linoleic acid content and a higher arachidonic acid concentration in both plasma and erythrocyte membrane phospholipids of renal calcium stone patients. This anomaly could cause an increased activity of ion carriers; furthermore, it may lead to increased prostaglandin synthesis and to secondary phenomena at the kidney, skeletal, and intestinal level. As a consequence, critical conditions for lithogenesis in the kidney may ensue. The data suggest a common pathogenesis for hypercalciuria and hyperoxaluria. The systemic defect in the phospholipid arachidonic acid level may be both of dietary or genetic origin; experimental data suggest that the increase in delta-6 desaturase activity, the limiting enzyme in the metabolic pathway of polyunsaturated fatty acids, might be relevant to the pathogenesis of lipid abnormalities observed in nephrolithiasis and to the pathogenesis of ICN and its related problems (at the kidney, intestinal, and bone level).

Genes in idiopathic calcium oxalate stone disease

An examination of the urinary excretions of 101 normal subjects indicated that the major genetic influence on calcium excretion is a codominant pair of alleles giving rise to three phenotypes, low, intermediate and high (hypercalciuric) excretors. This inference was based on variance, Hardy-Weinberg and segregation analyses. Similar independent gene pairs also appear to influence oxalate and citrate excretion, A 3-locus Hardy-Weinberg table using estimates of gene frequencies derived from the study of normals suggests that only 3 or 4 leading genes are involved in oxalate stone disease. Strong candidate genes identified from molecular and physiological studies cannot be proposed at present, but it is assumed that they influence the transport of these ions in either the intestine, kidney or both organs. The identification of the genes involved should be facilitated by the reduction of dietary influences on urinary excretions through the use of formula diets.

Cell cultures and nephrolithiasis

While the physical chemistry of stone formation has been intensively studied during the last decade, it has become clear that the pathophysiology of renal stone disease cannot be explained by crystallization processes only. In recent years, evidence has emerged that the cells lining the renal tubules can have an active role in creating the conditions under which stones may develop. Since it is difficult to study these mechanisms in vivo, cultured renal tubular cells have become increasingly popular for the study of physiological and cell biological processes that are possibly linked to stone disease. In this paper, we discuss the possible contribution of cellular processes such as transepithelial oxalate transport and crystal--cell interaction to the formation of renal stones. Experimental studies that have been performed with cultured renal cells to elucidate the mechanisms involved in these processes will be summarized.