Recurrence of Hyperoxaluria and Kidney Disease after Combined Intestine-Kidney Transplantation for Enteric Hyperoxaluria.

BACKGROUND: Enteric hyperoxaluria (EH) occurs with a rate of 5-24% in patients with inflammatory bowel disease, ileal resection and modern bariatric surgery. The excessive absorption of calcium oxalate causes chronic kidney disease (CKD) in patients with EH. In the literature, a single experience was reported in combined intestine-kidney transplantation (CIKTx) in patients with CKD due to EH. METHODS: After a report of 2 successful cases of CIKTx in patients with EH and CKD, one was performed at our center in a 59-year-old Caucasian female who developed intestinal failure with total parenteral nutrition (TPN) dependence after a complication post-bariatric surgery. Before CIKTx, she underwent kidney transplantation alone (KTA) twice, which failed due to oxalate nephropathy. RESULTS: In July 2014, the patient underwent CIKTx and bilateral allograft nephrectomy to avoid EH and oxalate stone burden. The postoperative course was complicated with acute tubular necrosis due to the use of high pressors related to perioperative bleeding. The patient was discharged 79 days after CIKTx with a serum creatinine (sCr) of 1.2 mg/dl and free of TPN. Her sCr increased at 7 months and a renal biopsy showed oxalate nephropathy. SLC26A6 (oxalate transporter) staining was significantly diminished in native duodenum/rectum as well as in intestinal allograft compared to control. CONCLUSIONS: KTA in patients with CKD secondary to EH should not be recommended due to high risk of recurrence. Although other centers showed good long-term outcomes in CIKTx, our patient experienced recurrence of EH due to oxalate transporter defect, early kidney allograft dysfunction and prolonged antibiotic use.

Oxalate: effect on calcium absorbability.

Absorption of calcium from intrinsically labeled Ca oxalate was measured in 18 normal women and compared with absorption of Ca from milk in these same subjects, both when the test substances were ingested in separate meals and when ingested together. Fractional Ca absorption from oxalate averaged 0.100 +/- 0.043 when ingested alone and 0.140 +/- 0.063 when ingested together with milk. Absorption was, as expected, substantially lower than absorption from milk (0.358 +/- 0.113). Nevertheless Ca oxalate absorbability in these women was higher than we had previously found for spinach Ca. When milk and Ca oxalate were ingested together, there was no interference of oxalate in milk Ca absorption and no evidence of tracer exchange between the two labeled Ca species.

Urinary Tamm-Horsfall protein increased after potassium citrate therapy in calcium stone formers.

OBJECTIVES: To evaluate the effect of oral potassium citrate therapy on urinary excretion rates of citrate. Tamm-Horsfall protein (THP), and on calcium oxalate monohydrate crystal agglomeration inhibition [tm], in patients with recurrent calcium stone formation. METHODS: To evaluate the effect of oral therapy with potassium citrate on urinary citrate, THP, and [tm], 24-hour urine samples were collected before and at least 2 months after initiation of oral potassium citrate therapy in 33 calcium stone-forming patients who had no dietary restrictions. The citrate concentration was measured by an adaptation of a citrate lyase method. Urinary disaggregated THP concentration was determined with a quantitative enzyme-linked immunosorbent assay. The [tm] was determined by observing the effects of patients' urine, before and after oral potassium citrate therapy, on the uptake of 45Ca2+ onto the surfaces of added preformed calcium oxalate crystals in a supersaturated solution of calcium oxalate, using the in vitro kinetic method described by other investigators. RESULTS: We observed an increased urinary excretion rate of citrate from a mean of 1.9 mmol/24 h prealkali to 2.6 mmol/24 h postalkali (P < 0.0004) and of THP from a mean of 94.0 mg/24 h prealkali to 199.3 mg/24 h postalkali (P < 0.0016). A corresponding increase in [tm] from a mean of 177.1 minutes prealkali to 221.0 minutes postalkali (P < 0.024) was also observed. CONCLUSIONS: To our knowledge this is the first report correlating increased urinary citrate with THP excretion rate following oral alkalinization with potassium citrate in calcium stone formers. Of clinical importance is the corresponding increase in [tm], which was previously shown to be inversely related to stone-forming activity. Moreover, urinary citrate and THP are known to have a synergistic effect on [tm]. Our data suggest that the effectiveness of potassium citrate therapy in calcium stone-forming patients may, at least in part, be due to increased levels of THP.

Calcium oxalate and iron accumulation in sarcoidosis.

BACKGROUND: In many patients with sarcoidosis, the granulomas contain inclusion bodies within giant cells. Many giant cells contain crystalline oxalate that chemically coordinates iron on the surface of the crystal. If this iron is incompletely coordinated and capable of redox cycling, then oxalate might contribute to granuloma formation in the lung. METHODS: Using human tissues, isolated alveolar macrophages and respiratory epithelial cells, we measured the ability of calcium oxalate to sequester iron, stimulate cytokine release and cause granuloma formation. We then studied the effects of in vivo oxalate instillation on pulmonary granuloma formation over 3 to 6 months in rats. RESULTS: Calcium oxalate present in human sarcoid granulomas sequesters significant amounts of iron and ferritin. In alveolar macrophage cultures, oxalate accumulates iron and stimulates ferritin production and giant cell formation. In cultured respiratory epithelial cells, calcium oxalate increases the release of two interleukins (IL), IL-8 and IL-6, involved in granuloma formation by 8 to 10 fold within 24 hours. Intratracheal instillation of calcium oxalate crystals into the lungs of rats is associated with pulmonary iron and ferritin accumulation and organic carbonyl formation consistent with sustained oxidative stress. These exposures were accompanied by influx of alveolar macrophages, giant cell formation, and a granulomatous response in the lung. CONCLUSIONS: These results support an association between calcium oxalate deposition in the lung, iron mediated oxidative stress and formation of some of the granulomas of sarcoidosis.

Mechanisms involved in calcium oxalate endocytosis by Madin-Darby canine kidney cells.

Calcium oxalate (CaOx) crystals adhere to and are internalized by tubular renal cells and it seems that this interaction is related (positively or negatively) to the appearance of urinary calculi. The present study analyzes a series of mechanisms possibly involved in CaOx uptake by Madin-Darby canine kidney (MDCK) cells. CaOx crystals were added to MDCK cell cultures and endocytosis was evaluated by polarized light microscopy. This process was inhibited by an increase in intracellular calcium by means of ionomycin (100 nM; N = 6; 43.9% inhibition; P<0.001) or thapsigargin (1 microM; N = 6; 33. 3% inhibition; P<0.005) administration, and via blockade of cytoskeleton assembly by the addition of colchicine (10 microM; N = 8; 46.1% inhibition; P<0.001) or cytochalasin B (10 microM; N = 8; 34.2% inhibition; P<0.001). Furthermore, CaOx uptake was reduced when the activity of protein kinase C was inhibited by staurosporine (10 nM; N = 6; 44% inhibition; P<0.01), or that of cyclo-oxygenase by indomethacin (3 microM; N = 12; 17.2% inhibition; P<0.05); however, the uptake was unaffected by modulation of potassium channel activity with glibenclamide (3 microM; N = 6), tetraethylammonium (1 mM; N = 6) or cromakalim (1 microM; N = 6). Taken together, these data indicate that the process of CaOx internalization by renal tubular cells is similar to the endocytosis reported for other systems. These findings may be relevant to cellular phenomena involved in early stages of the formation of renal stones.

The bioavailability of calcium in spinach and calcium-oxalate to calcium-deficient rats.

We estimated the utilization of calcium in spinach and calcium-oxalate to calcium-deficient rats, and the effect of oxalic acid on absorption of dietary calcium by using calcium-deficient rats. The body weight gain of the calcium-deficient rats for 8 days receiving a calcium-deficient diet supplemented with raw-powdered spinach (R-sp), boiled-powdered spinach (B-sp), or calcium-oxalate (Ca-ox), and a control diet supplemented with oxalic acid (OX-C) were 4.8, 2.8, 4.9, and 5.1 g, respectively. The calcium content in the liver and kidney of the rats receiving R-sp, B-sp, Ca-ox, and OX-C diets significantly increased as compared with the calcium-deficient rats. Significant differences in the liver calcium levels were not observed among the rats receiving various additional diets, though the content in the kidneys of the rats receiving R-sp, B-sp, Ca-ox, and OX-C diets were 28.0, 21.5, 0.11, and 0.59 mg, respectively. An especially large amount of calcium was accumulated in the kidneys of the rats receiving R-sp and B-sp diets. The calcium concentration in the serum of the rats receiving Ca-ox and OX-C diets was higher than the calcium concentration in the serum of the R-sp, B-sp, and calcium-deficient rats. The calcium content in the left tibiae of the rats receiving Ca-ox and OX-C diets was higher than that of the rats receiving R-sp and B-sp diets. The breaking force of the right tibiae of the rats was highest in the OX-C group, and higher in the R-sp and Ca-ox groups than the breaking force of the right tibiae of the rats fed on B-sp diet. The alkaline phosphatase activity in the small intestines of the rats rose in the order of the R-sp, B-sp, and Ca-ox groups, although significant differences of the activity were not observed between the Ca-ox and the OX-C groups. The calcium retention of the rats receiving the calcium-deficient, R-sp, B-sp, Ca-ox, and OX-C diets was -18.5, 35.2, 25.6, 41.6, and 45.8%, respectively. About 35% of the calcium in the spinach was absorbed by the calcium-deficient rats, and oxalic acid depressed the calcium absorption in the rats.

Experience with the [13C2]oxalate absorption test.

Hyperoxaluria is the most important risk factor for a formation of calcium oxalate-urinary stones. Usually, the bulk of oxalate will be formed in the human body, but in many patients the oxalate from food plays the decisive role. Conventionally, in urine the endogenous oxalate can not be distinguished from food derived oxalate. We have developed a standardized oxalate-absorption test, applying a physiological dose (50 mg disodium salt of [13C2]oxalic acid) of labelled oxalate. The assay has been published. Now we report on the first extensive applications of this test in 86 volunteers and 135 patients from different groups with calcium oxalate stones or an increased risk of the formation of such stones. In one-third of the patients with calcium oxalate-urinary stones an oxalate hyperabsorption was diagnosed. For these patients, a dietetic stone prophylaxis and/or therapy is indicated.

[Oxalate influx rate in red blood cells in calcium oxalate nephrolithiasis].

We established a method of human red blood cell oxalate influx rate under the condition of steady state exchange. Using this method we measured the influx rate in 10 patients with recurrent calcium oxalate nephrolithiasis and in 18 controls. DIDS inhibited oxalate flux across the human red blood cell membrane. This result suggested that band 3 protein mediates oxalate transport. Oxalate influx rate depended on reaction temperature and pH of reaction buffer. Although the oxalate influx rate in 4 degrees C could not be determined under an initial condition rate, the measurable condition was in 0 degrees C of reaction temperature. Consequently we measured the oxalate influx rate under the condition of 0 degrees C reaction temperature and 20 ml volume of washing buffer. The mean oxalate influx rate was significantly higher in patients with nephrolithiasis than in controls (-1.00 +/- 0.19 vs. -0.78 +/- 0.14).

Oxalate and sucralose absorption in idiopathic calcium oxalate stone formers.

OBJECTIVES: To better understand intestinal oxalate transport by correlating oxalate and sucralose absorption in idiopathic calcium oxalate stone formers. Oxalate has been hypothesized to undergo absorption in the large and small intestine by both paracellular and transepithelial transport. Sucralose is a chlorinated sugar that is absorbed by paracellular mechanisms. METHODS: Idiopathic calcium oxalate stone formers were recruited to provide urine specimens on both a self-selected diet and after a meal containing 90 mg of (13)C(2-)oxalate and 5 g of sucralose, and a stool sample for determination of Oxalobacter formigenes colonization. The 24-hour urine collections were fractionated into the first 6 hours and the subsequent 18 hours. Sucralose and oxalate excretion were measured during these periods and used to estimate absorption. RESULTS: Thirty-eight subjects were evaluated. The majority of both the (13)C(2-)oxalate and sucralose absorption occurred within the 0-6-hour collection. The (13)C(2-)oxalate and sucralose absorptions were significantly correlated at the 0-6 hour, the 6-24 hour, and the total 24-hour time periods (P <.04). All 5 oxalate hyperabsorbers(>15% absorption) also absorbed significantly more sucralose during the 0-6 hour and whole 24-hour time points (P <.04). Oxalobacter formigenes colonization did not significantly alter oxalate absorption. CONCLUSIONS: The results suggest that most oxalate is absorbed in the proximal portion of the gastrointestinal tract and that paracellular transport is involved. Augmented paracellular transport, as evidenced by increased sucralose absorption, may also influence oxalate absorption.

Dietary oxalate and calcium oxalate nephrolithiasis.

PURPOSE: Patients with calcium oxalate kidney stones are advised to decrease the consumption of foods that contain oxalate. We hypothesized that a cutback in dietary oxalate would lead to a decrease in the urinary excretion of oxalate and decreased stone recurrence. We tested the hypothesis in an animal model of calcium oxalate nephrolithiasis. MATERIALS AND METHODS: Hydroxy-L-proline (5%), a precursor of oxalate found in collagenous foods, was given with rat chow to male Sprague-Dawley rats. After 42 days rats in group 1 continued on hydroxy-L-proline, while those in group 2 were given chow without added hydroxy-L-proline for the next 21 days. Food and water consumption as well as weight were monitored regularly. Once weekly urine was collected and analyzed for creatinine, calcium, oxalate, lactate dehydrogenase, 8-isoprostane and H(2)O(2). Urinary pH and crystalluria were monitored. Rats were sacrificed at 28, 42 and 63 days, respectively. Renal tissue was examined for crystal deposition by light microscopy. RESULTS: Rats receiving hydroxy-L-proline showed hyperoxaluria, calcium oxalate crystalluria and nephrolithiasis, and by day 42 all contained renal calcium oxalate crystal deposits. Urinary excretion of lactate dehydrogenase, 8-isoprostane and H(2)O(2) increased significantly. After hydroxy-L-proline was discontinued in group 2 there was a significant decrease in urinary oxalate, 8-isoprostane and H(2)O(2). Half of the group 2 rats appeared to be crystal-free. CONCLUSIONS: Dietary sources of oxalate can induce hyperoxaluria and crystal deposition in the kidneys with associated degradation in renal biology. Eliminating oxalate from the diet decreases not only urinary oxalate, but also calcium oxalate crystal deposits in the kidneys and improves their function.

Pathophysiological correlates of two unique renal tubule lesions in rats with intestinal resection.

Rats with small bowel resection fed a high-oxalate diet develop extensive deposition of calcium oxalate (CaOx) and calcium phosphate crystals in the kidney after 4 mo. To explore the earliest sites of renal crystal deposition, rats received either small bowel resection or transection and were then fed either standard chow or a high-oxalate diet; perfusion-fixed renal tissue from five rats in each group was examined by light microscopy at 2, 4, 8, and 12 wk. Rats fed the high-oxalate diet developed birefringent microcrystals at the brush border of proximal tubule cells, with or without cell damage; the lesion was most common in rats with both resection and a high-oxalate diet (10/19 with the lesion) and was significantly correlated with urine oxalate excretion (P < 0.001). Rats with bowel resection fed normal chow had mild hyperoxaluria but high urine CaOx supersaturation; four of these rats developed birefringent crystal deposition with tubule plugging in inner medullary collecting ducts (IMCD). Two rats fed a high-oxalate diet also developed this lesion, which was correlated with CaOx supersaturation, but not oxalate excretion. Tissue was examined under oil immersion, and tiny birefringent crystals were noted on the apical surface of IMCD cells only in animals with IMCD crystal plugging. In one animal, IMCD crystals were both birefringent and nonbirefringent, suggesting a mix of CaOx and calcium phosphate. Overall, these animals demonstrate two distinct sites and mechanisms of renal crystal deposition and may help elucidate renal lesions seen in humans with enteric hyperoxaluria and stones.

Importance of magnesium in absorption and excretion of oxalate.

INTRODUCTION: Magnesium treatment for calcium oxalate urolithiasis is discussed controversially. The aim of this study was to investigate the influence of magnesium supplementation on the oxalate absorption. MATERIALS AND METHODS: The [13C2]oxalate absorption test was always performed three times in 6 healthy volunteers under standardized conditions, with one 10-mmol magnesium supplement together with the labeled oxalate and with two 10-mmol magnesium supplements given in 12-hour intervals. RESULTS: The mean intestinal oxalate absorption under standard conditions was 8.6 +/- 2.83%. The oxalate absorption with one 10-mmol magnesium supplement was 5.2 +/- 1.40% and with two supplements 5.5 +/- 1.62%. Both decreases were statistically significant relative to the standard test, however, not significantly different from each other. CONCLUSIONS: The results show that magnesium administration decreases the oxalate absorption, when magnesium is taken together with oxalate. However, magnesium administration does not decrease the oxalate absorption, when magnesium and oxalate intake differ by 12 h.

Kinetic factors influencing the dissolution behavior of calcium oxalate renal stones: a constant composition study.

A constant composition method has been used to examine the dissolution kinetics of calcium oxalate renal stones over a wide range of undersaturation in vitro. Demineralization experiments have been carried out with the concentrations of calcium and oxalate ions and ionic strength (hence the solution undersaturation) held constant by the potentiometrically controlled addition of medium electrolyte solution as diluent, triggered by a calcium ion electrode. Kinetic data for renal stones have been compared with results obtained for synthetic calcium oxalate. In addition, constant composition results have been directly compared with results obtained using conventional dissolution methods for both calculi and synthetic calcium oxalate. Overall, calcium oxalate renal stones exhibited markedly different kinetic dissolution behavior as compared with synthetic controls. The renal stone samples dissolved more slowly at all undersaturations, exhibited increased kinetic orders of reaction, and showed reduced sensitivity to solution hydrodynamics. Stones composed of mixed hydrates of calcium oxalate (mono- and di-) came to dihydrate equilibrium in conventional experiments and underwent net dissolution in solutions supersaturated to monohydrate under constant composition conditions. No conversion of di- to monohydrate was observed under these experimental conditions. These results indicate that stone dissolution is strongly influenced by adsorbed inhibitors, presumably including matrix components, which may complicate efforts to develop systemic and/or irrigation measures effective for in situ solubilization.

Surface interaction between glycosaminoglycans and calcium oxalate.

Molecules and macromolecules are known to alter the process of crystallization, either through inhibition or promotion of nucleation, growth, and/or aggregation. One particular group of macromolecules, glycosaminoglycans (GAGs), has been of interest in our laboratory. The GAGs chondroitin A, chondroitin C, heparan sulfate, dermatan sulfate, hyaluronic acid, and keratan sulfate have all been shown to be inhibitors of calcium oxalate crystallization. Heparin, the only GAG which is not naturally present in urine, is the most potent inhibitor of all GAGs. Using the method of Langmuir isotherm adsorption, we studied the adsorption of certain GAGs onto calcium oxalate crystals. Under standardized conditions, heparin, chondroitin C, hyaluronic acid, and pentosan polysulfate (a synthetic polyanionic molecule similar to, but a weaker inhibitor than, heparin) were adsorbed onto calcium oxalate. The total amount of GAG required to maximally cover the crystal surface, as well as the equilibrium concentration at which surface was half-covered with GAG (inversely related to the desorption energy) were measured. Chondroitin C was adsorbed in the greatest amount, followed by heparin, pentosan polysulfate, and finally hyaluronic acid. Using the method of fiducial limits, the only insignificant difference was between heparin and chondroitin C, and between hyaluronic acid and pentosan polysulfate. Pentosan polysulfate required significantly higher equilibrium concentration than heparin and hyaluronic acid to cover half of the surface of the calcium oxalate crystals. The principle of Langmuir isotherm adsorption can be useful in predicting the effects of macromolecules on crystallization. Weaker inhibitors bind with less affinity than do stronger inhibitors. Further work is underway to characterize other inhibitors and promoters.

Influence of ionic strength on crystal adsorption and inhibitory activity of macromolecules.

We investigated the influence of ionic strength on both the binding ability of macromolecules onto calcium oxalate crystals and the inhibitory activity of macromolecules related to calcium oxalate crystal growth and aggregation in vitro. The amount of heparin sodium salt adsorbed onto calcium oxalate crystals was studied in both a seed and a non-seed crystal system at various ionic strengths with the aid of radiolabelled heparin. In both adsorption models, adsorption of heparin was greater in the buffered solutions of lower ionic strength, and significantly so in the range of physiological ionic strength. The inhibitory activity of heparin in the non-seed crystal system, which was determined using a Coulter Multisizer, increased as the adsorbed dose increased. The naturally existing urinary macromolecules showed a similar change in their inhibitory activity on calcium oxalate crystal growth and/or aggregation in accordance with changes in ionic strength. These results indicate that macromolecular inhibitory activity seems to be enhanced in urine of lower ionic strength as a result of an increased adsorption of macromolecules on the surface of calcium oxalate crystals.

Absorption of calcium oxalate does not require dissociation in rats.

Calcium absorption is thought to occur only if calcium is in a soluble or dissociated form, although experimental evidence is lacking. The intestinal absorption of calcium oxalate, a small, neutral and virtually insoluble calcium salt, was elucidated in the whole body of awake rats. Suspensions of 45Ca ascorbate, 14C-oxalic acid and doubly labeled 45Ca-[14C]-oxalate were given by gavage to separate groups of rats. Following dosing, blood samples were drawn for up to 240 min through a previously inserted intravenous catheter. Serum was assayed for radioactive tracers, and data were then plotted as fraction of dose over time. Calcium absorption was 15% [with a loading of 0.3 mmol (15 mg) calcium], oxalic acid absorption was 22% and Ca-oxalate absorption was <2%. Appearance of 45Ca from calcium ascorbate and 14C from oxalic acid differed, whereas 45Ca and 14C from doubly labeled Ca-oxalate had identical serum appearance profiles. Therefore, we conclude that calcium oxalate was absorbed intact. Addition of excess, unlabeled calcium to the doubly-labeled calcium oxalate did not alter the relationship of the serum level of the two tracers, confirming absorption of calcium oxalate as the intact salt. Thus, calcium bound as a small, neutral, calcium salt such as calcium oxalate does not have to be dissociated prior to absorption. Possibly other small compounds would be similarly absorbed. These results alter our current understanding of calcium bioavailability from foods and therapeutic agents.

Surface studies of calcium oxalate dihydrate single crystals during dissolution in the presence of stone-formers' urine.

Dissolution of calcium oxalate dihydrate (COD) single crystals was studied at different pH levels and in different dilutions of stone formers' (SF) urine. The Fourier descriptors of the contour were determined during dissolution of COD using a quantitative morphological technique. The surface ruggedness of COD single crystals was determined from fractal analysis. The results obtained were compared with COD single crystals behavior in different dilutions of normal urine previously reported. The shape parameters and surface geometry of the dissolving COD crystals were significantly different in normal and SF urine. The data suggest that the shape descriptors and fractal geometry is likely to be a potential factor in identifying the urine of stone formers.

Reference range for gastrointestinal oxalate absorption measured with a standardized [13C2]oxalate absorption test.

PURPOSE: Hyperoxaluria is a prominent risk factor for calcium oxalate urinary stones. Oxalate in urine is synthesized in the body or absorbed from food in the gastrointestinal tract. The amount of oxalate absorbed by patients with calcium oxalate stones may vary from a few percent to 50% of the dietary intake. Reference values for oxalate absorption measured under a standardized diet have never been attained in sufficient numbers from healthy individuals. Therefore, to our knowledge we collected for the first time the values required to interpret test results in patients with recurrent urinary stones. MATERIALS AND METHODS: A total of 120 healthy volunteers, including 60 females and 60 males, received an identical standard diet on 2 consecutive days. On the morning of day 2 a capsule containing 0.37 mmol. sodium [13C2]oxalate (not radioactive) was ingested with water. Urinary oxalate was measured by gas chromatography-mass spectrometry. Absorption at a fixed 800 mg. daily Ca input is expressed as a percent of the labeled oxalate dose. RESULTS: For the standardized [13C2]oxalate absorption test the reference range in 95% of the 120 volunteers was 2.2% to 18.5% (mean +/- SD 7.9% +/- 4.0%). The repeatability of the standardized test was determined in 26 of the 120 volunteers by repeating the test twice. The mean intra-individual SD was 3.39% +/- 1.68%. CONCLUSIONS: We assessed reference values of intestinal oxalate absorption using a standardized diet. Interindividual and intra-individual variance was high.