Oxalate transport and calcium oxalate renal stone disease

Hyperoxaluria is considered to play a crucial role in calcium oxalate (CaOx) renal stone disease. The amount of oxalate excreted into the urine depends on intestinal absorption, endogenous production, renal clearance and renal tubular transport. Since a primary disorder has not been found so far in most CaOx stone formers and since oxalate is freely filtered at the glomerulus, most studies are presently focussed on alterations in epithelial oxalate transport pathways. Oxalate can be transported across an epithelium by the paracellular (passive) and transcellular (active) pathway. Oxalate transport across cellular membranes is mediated by anion-exchange transport proteins. A defect in the structure of these transport proteins could explain augmented transcellular oxalate transport. Little is known about the physiological regulation of oxalate transport. In this review cellular transport systems for oxalate will be summarized with special attention for the progress that has been made to study oxalate transport in a model of cultured renal tubule cells. Better understanding of the physiological processes that are involved in oxalate transport could yield information on the basis of which it might be possible to design new approaches for an effective treatment of CaOx stone disease.     

Physicochemical metabolic characteristics for calcium oxalate stone formation in patients with gouty diathesis

PURPOSE: We determined why calcium oxalate stones instead of uric acid stones form in some patients with gouty diathesis. MATERIALS AND METHODS: Gouty diathesis was diagnosed from absence of secondary causes of uric acid stones or low urinary pH, and reduced fractional excretion of urate with discriminant score of the relationship between urinary pH and fractional excretion of urate less than 80. From the stone registry 163 patients with gouty diathesis were identified, including 62 with uric acid stones (GD + UA) and 101 patients with calcium oxalate stones (GD + Ca). Metabolic data and 24-hour urinary chemistry study were compared between the 2 groups. RESULTS: Compared with GD + UA, GD + Ca had significantly greater urinary calcium (196 +/- 96 mg per day vs 162 +/- 82 mg per day, p <0.05) and significantly lower urinary citrate (430 +/- 228 vs 519 +/- 288 mg per day, p <0.05), resulting in higher urinary saturation of calcium oxalate. Both groups had low urinary pH (less than 5.5) and high urinary undissociated uric acid (greater than 100 mg/dl). Urinary calcium post-oral calcium load was significantly higher in GD + Ca than in GD + UA (0.227 vs 0.168 mg/dl glomerular filtrate, p <0.001). CONCLUSIONS: Calcium oxalate stones may form in some patients with gouty diathesis due to increased urinary excretion of calcium and reduced excretion of citrate. Relative hypercalciuria in GD + Ca may be due to intestinal hyperabsorption of calcium.     

Mechanism of calcium oxalate renal stone formation and renal tubular cell injury

Abstract:   Formation of calcium oxalate stones tends to increase with age and begins from the attachment of a crystal formed in the cavity of renal tubules to the surface of renal tubular epithelial cells. Though most of the crystals formed in the cavity of renal tubules are discharged as is in the urine, in healthy people, crystals that attach to the surface of renal tubular epithelial cells are thought to be digested by macrophages and/or lysosomes inside of cells. However, in individuals with hyperoxaluria or crystal urine, renal tubular cells are injured and crystals easily become attached to them. Various factors are thought to be involved in renal tubular cell injury. Crystals attached to the surface of renal tubular cells are taken into the cells ( crystal–cell interaction ). And then the crystal and crystal aggregates grow, and finally a stone is formed.     

Comparison of urinary tract infection in calcium oxalate and calcium phosphate stone formers

To compare the frequency of urine infection in calcium oxalate and calcium phosphate stone formers, we reviewed charts from patients whose last renal stone submitted for analysis was predominantly composed of calcium phosphate in 118 and of calcium oxalate in 223. Positive cultures were commoner, but not significantly, in the phosphate than the oxalate stone formers, both in men (17 vs. 7.6%) and women (22 vs. 15%). Bacteria frequently producing urease were found in only 4% of the phosphate group. Urine leucocytes were slightly more frequent in the oxalate group for men and significantly so for women. The results do not support the concept that calcium phosphate stones are mainly due to infection with urease-producing or other bacteria.     

The spectrum of metabolic abnormalities in patients with cystine nephrolithiasis

To elucidate the pathophysiology of mixed stone formation in cystinuria, 27 patients with documented cystine nephrolithiasis underwent an inpatient evaluation under a constant dietary regimen. All patients had homozygous cystinuria, since the daily urinary cystine excretion exceeded 250 mg. per gm. creatinine. Hypercalciuria was noted in 5 patients (18.5 per cent), 4 of whom had fasting hypercalciuria. Hyperuricosuria was found in 6 patients (22.2 per cent) and it was not caused by a consumption of a diet rich in animal proteins, since urinary pH was higher and urinary sulfate lower than in control subjects. Serum uric acid was slightly lower and uric acid clearance was higher in hyperuricosuric patients than in control subjects. Hypocitraturia was found in 12 patients (44.4 per cent) and it was associated with defective renal acidification in 4 of 5 patients in whom it was tested. Thus, hypercalciuria, hyperuricosuria and hypocitraturia frequently accompany cystinuria in patients with cystine nephrolithiasis. These conditions might be renal in origin, rather than a result of dietary or environmental aberrations. They may contribute to the formation of calcium and uric acid stones, which sometimes complicate cystine nephrolithiasis.     

Plasma oxalate concentration in calcium oxalate stone formers

A sensitive, simplified method for plasma oxalate determination by gas chromatography is described. After deproteinizing the plasma with 3N HC1 and 20% sulfosalicylic acid, the oxalate was methylated, extracted and analysed by gas chromatography. This method has three advantages i.e., smaller sample size (plasma 5.0 ml), rapidity (takes less than 3 hours) and accuracy. The recovery rate of oxalate added to plasma was 91.42 +/- 11.31% (SD) and the coefficient of variation of replicate determinations was 4.18%. The minimum detectable concentration of oxalate was 0.3 micrograms/ml (oxalate peak was higher than 5 mm). The mean oxalate concentration under fasting conditions from 16 healthy subjects was 1.37 +/- 0.39 micrograms/ml (SD), while that from 31 calcium oxalate stone formers was 1.45 +/- 0.39 micrograms/ml (SD). There was no significant difference in plasma oxalate concentration between the two groups. The dietary influence of oxalate on plasma and urinary oxalate was investigated in 5 healthy subjects and 5 calcium oxalate stone formers. When 100 g spinach (total oxalate 545.5 mg, soluble oxalate 381.5 mg) was given, the increase of plasma oxalate concentration was more prominent in stone formers; in stone formers it increased to 142% of control value at 2 hours (p less than 0.05) after spinach loading, to 163% at 4 hour (p less than 0.01) and to 232% at 6 hours (p less than 0.01); while in healthy subjects increased to 119% at 2 hours (ns) after loading, to 144% at 4 hours (p less than 0.05) and only to 167% at 6 hours (p less than 0.01). Urinary oxalate excretion increased promptly between 1 and 2 hours after loading in both groups, reaching peak levels between 2 and 4 hours after loading in healthy subjects and between 4 and 6 hours or later in stone formers. The mean renal clearance of oxalate was 18.0 ml/min in 6 healthy subjects and 19.0 ml/min in 4 calcium oxalate stone formers. There was no significant difference in oxalate clearance between the two groups. The mean ratio of oxalate/creatinine clearance was 0.22 for stone formers, which was equal to that for healthy subjects.     

Intestinal oxalate and calcium absorption in recurrent renal stone formers and healthy subjects

The fractional intestinal absorption of oxalate and calcium was investigated by isotope techniques in 20 normal subjects and in 12 idiopathic calcium oxalate stone formers. The greatest amount of 14C-oxalate was excreted during the first six hour period in controls as well as in stone formers. The stone formers had a greater intestinal uptake of oxalate (11 +/- 5.1%) than the controls (6.2 +/- 3.7%; p less than 0.01). There was no significant relationship between the fractional absorption of oxalate and the total urinary oxalate excretion. The stone formers also had a higher fractional uptake of calcium compared to the controls (55 +/- 11% vs. 47 +/- 9.1%; p less than 0.05). There was a positive relationship (r = 0.47) between the urinary excretions of calcium and oxalate in the stone formers. During these conditions no correlation could be demonstrated between the fractional absorptions of oxalate and calcium, neither in the stone formers nor in the controls. In conclusion, patients with recurrent formation of calcium oxalate containing stones appear to have an enhanced intestinal uptake of both oxalate and calcium. This disturbance could be of primary pathogenic importance for their stone forming propensity.     

Urinary excretion of urate in patients with calcium oxalate stone disease

Summary The diurnal variation in excretion and concentration of urinary urate was studied in 31 patients with calcium oxalate stone disease. Urate excretion was highest during the day-time, decreased in the evening and was low during the night. Meal-related peaks were observed. The concentration of urate reached the highest levels during the morning hours and, attributable to a low pH in morning urine, most samples were at this time super-saturated with respect to uric acid. In addition, many urines appeared to be at high risk of exceeding the uric acid formation product. Concerning the ion-activity product of sodium urate, supersaturated samples were frequently found, but the risk of exceeding the formation product for sodium urate at a normal urate excretion was apparently low.     

Staghorn cystine stone in a 72-year-old recurrent calcium stone former

This case deals with the first diagnosis of Type B cystinuria with cystine nephrolithiasis in a 72-year-old male. Cystinuria is an inherited disease that consists of congenital abnormalities of renal and intestinal transport of dibasic amino acids. It often leads to frequent recurrent stone formation. Cystine stones most frequently occur in the 1st through 3rd decades of life with a decreased incidence in old age. This case shows that the first diagnosis of cystinuria may be made even in the 8th decade, without any family history, and in a patient with a history of recurrent calcium stone disease. Therefore, the chance of cystinuria must be always considered, even in older calcium stone formers.     

Aggregation of freshly precipitated calcium oxalate crystals in urine of calcium stone patients and controls

Aggregation (AGN) of freshly precipitated calcium oxalate crystals was photometrically studied in urine of 30 calcium stone patients and 30 controls, in solutions containing urinary macromolecules (UMS) and in an inhibitor free control solution (CS). Crystals were produced by oxalate titration and crystallization was monitored measuring optical density (OD). Tests were repeated adding hydroxyapatite (HAP) to urine and UMS and adding citrate and pyrophosphate (PPi) to UMS of the controls. AGN was recognized as a rapid OD decrease being at least three times faster than sedimentation of single crystals (p < 0.001) and used to calculate an extent of AGN (EA%). The time between the end of titration and the beginning of AGN was determined as suspension stability (SS). The main effect of urinary inhibitors was retardation of AGN without changing EA, SS being higher in urine than UMS (p < 0.001) and in UMS than CS (p < 0.001). In urine of 63% of controls but only in 33% of patients, no AGN was recorded (p < 0.05). The high inhibitory activity of urine could not be reproduced in UMS even in combination with 3.5 mM citrate or 0.05 mM PPi. 0.05 mg/mL HAP reduced SS in all urine samples to low values and increased the rate of rapid OD decrease, being a measure for the size of aggregates. Retarding AGN of crystals during their passage through the kidney seems to be an important mechanism to prevent stone formation during crystalluria. The promotion of AGN by HAP reveals a new role of Randall’s plaques in nephrolithiasis.     

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-einberg 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.     

4种大鼠肾草酸钙结石模型的比较

目的筛选简便、快捷、成石效果好的SD大鼠肾草酸钙结石的造模方法。方法分别采用目前普遍使用的2种大鼠肾草酸钙结石的模型复制方法和2种改良的造模方法进行造模,并设立空白对照组,造模结束后采集每组大鼠24h尿量及血清,比较大鼠24h尿量、尿Ca2＋、尿Mg2＋、尿pH、尿草酸（0x）及血尿素氮（BUN）、肌酐（cr）、P、Ca2＋、Mg2＋,肾脏病理切片HE染色后光学显微镜下观察和比较各组大鼠肾脏病理改变及草酸钙结晶的沉积情况。结果E组[1％乙二醇＋2％氯化铵＋10％葡萄糖（48d）]在光学显微镜下草酸钙结晶沉积较传统组C组明显增多（P〈0．05）,但有30％大鼠死亡,血肌酐在5组大鼠中最高。D组[1％乙二醇＋2％氯化铵＋10％葡萄糖（28d）]较传统组C组草酸钙结晶沉积明显增多（P〈0．05）,并且造模时间短,大鼠存活率高（80％）,E组与D组相比结晶形成量无统计学意义（P〉0．05）,B组[1％乙二醇（28d）3肾脏中无肾结晶形成,仅有轻微的肾脏病理学改变,大鼠无死亡,肌酐不高。空白对照组无结晶形成,无病理改变。结论用1％乙二醇＋2％氯化铵＋10％葡萄糖诱导28天复制肾草酸钙结石模型的效果好,并且花费时间短,大鼠存活率高,建议选用。     

Relationship between supersaturation and calcium oxalate crystallization in normals and idiopathic calcium oxalate stone formers

BACKGROUND: In an earlier study on recurrent CaOx stone formers with no detectable abnormalities, we found that the urine of these subjects had a lower tolerance to oxalate load than controls and that the removal of urinary macromolecules with a molecular weight greater than 10,000 D improved their tolerance to oxalate. METHODS: The effects on CaOx crystallization of reduced urinary supersaturation of calcium oxalate (CaOx), induced by night water load, were studied in 12 normal males and in 15 male OxCa stone formers who were free from urinary metabolic abnormalities. The effect of the macromolecules, purified and retrieved from the natural and diluted urine, were analyzed in a metastable solution of CaOx. RESULTS: The water load caused an increase in urine volume (from 307 +/- 111 to 572 +/- 322 ml/8 hr, P = 0.014 in normal subjects, and from 266 +/- 92 to 518 +/- 208 ml/8 hr, P = 0.001 in the stone formers) and a concomitant reduction of the relative CaOx supersaturation (from 8.7 +/- 2.5 to 5.1 +/- 2.5 ml/8 hr, P = 0.001 in normal subjects, and from 10.4 +/- 3.5 to 5.0 +/- 2.7 ml/8 hr, P = 0.001 in the stone formers). The decrease in CaOx supersaturation was accompanied by an increase of the permissible increment in oxalate, both in normal subjects (from 43.8 +/- 10.1 to 67.2 +/- 30. 3 mg/liter, P = 0.018) and in the stone formers (from 25.7 +/- 9.4 to 43.7 +/- 17.1 mg/liter, P = 0.0001), without any significant variations of the upper limit of metastability for CaOx (from 21.6 +/- 5.3 to 20.5 +/- 4.2 mg/liter in normal subjects, and from 18.7 +/- 4.5 to 17.1 +/- 3.7 mg/liter in the stone formers). The inhibitory effect of urinary macromolecules with molecular weight greater than 10,000 Daltons did not undergo any change when the latter were recovered from concentrated or diluted urine, either in normal subjects or in the stone formers. CONCLUSIONS: Reduced CaOx supersaturation by means of water load has a protective effect with regards to CaOx crystallization in subjects who do not present any of the common urinary stone risk factors.     

草酸钙晶体表面结合蛋白质的研究

目的 了解草酸钙晶体表面结合蛋白质在结石形成的过程中的作用。方法 用草酸钙过饱和结晶法制备正常人和草权钙结石患者尿草酸钙晶体表面结合物质（ＣＳＢＳ）,经ＤＥＡＥ－ＳｅｐｈａｒｏｓｅＣＬ－６Ｂ柱层析分离蛋白质和葡胺聚糖,用ＳＤＳ－聚丙烯酰胺凝胶电泳（ＳＤＳ－ＰＡＧＥ）测定蛋白质组成和分子量,用氨基酸自动分析仪测定蛋白质的氨基酸,结果;正常仍ＣＳＢＳ中主要含分子量为３１０００的尿凝血酶原激活肽片段１（     

N-乙酰半胱氨酸抑制大鼠肾草酸钙结石形成机制的研究

目的：探讨N一乙酰半胱氨酸（NAc）对大鼠肾草酸钙结石形成的影响及机制,为临床预防尿路结石提供理论依据。方法：将30只健康清洁成年雄性Wistar大鼠先在相同环境下适应性喂养1周,然后随机分为3组：A组（空白对照组）、B组（单纯诱石组）、C组（诱石＋NAC干预组）。A组饮去离子水,B组饮1％乙二醇的去离子水,C组饮1％乙二醇去离子水,并给予NAC100mg／（kg·d）灌胃。第4周处死大鼠,取出双肾,左肾纵向剖开,用10％甲醛固定,HE染色石蜡切片,在100、400倍光镜下观察肾组织草酸钙结晶沉积情况,并进行分级及评分。右肾皮质制成10％的匀浆,检测丙二醛（MDA）及超氧化物歧化酶（SOD）。全部实验数据通过SPSS17．0统计软件分析处理。结果：①肾脏结晶沉积情况分级及评分结果：与B组相比,C组的肾脏结晶沉积评分明显降低（P〈0．05）。②MDA检测结果：与B组相比,C组的MDA含量降低,差异有统计学意义（P〈0．05）。③SOD检测结果：与B组相比,C组的SOD含量增高,差异有统计学意义（P〈0．05）。④A、B、C三组肾组织结晶等级评分与s0D含量的相关系数为-0．499（P〈0．01）,结晶评分与MDA含量的相关系数为0．592（P〈0．01）。结论：NAc可以通过其抗氧化作用抑制大鼠肾草酸钙结石的形成。     

草酸钙结石患者肾乳头Randall斑的超微结构特点

目的 探讨草酸钙结石患者肾乳头Randall斑与草酸钙结石形成的关系. 方法经结石化学成分分析确诊为草酸钙肾结石患者12例.于经皮肾镜取石术中直视卜获取肾乳头Randall斑活检标本,分别行HE染色和锇酸固定,光镜和透射电镜下观察其组织病理和超微结构特点.结果 12例患者共检查肾乳头72处,肾乳头表面有Randall斑形成63处(87.5%),7例部分肾乳头表面有小结石附着.12例Randall斑活检标本光镜下肾乳头组织内见成团钙盐样沉积.2例电镜下肾乳头结缔组织中散在分布大小不均簇状草酸盐团聚体,典型结晶体呈针状,晶体轮廓周边电子密度高,晶体中央呈电子透亮区. 结论草酸钙结石患者肾乳头Randall斑主要是草酸盐结晶沉积,在Randall斑基础上草酸盐结晶进一步沉积可能促使草酸钙结石的形成.     

Studies of dietary influence on urinary oxalate in calcium oxalate stone formers

In order to examine the effect of diet on the urinary excretion of oxalate, a spinach loading and milk loading experiment was performed in normal subjects and patients with single calcium oxalate stones and recurrent calcium oxalate stones after a rat experiment. When spinach (100 g, total oxalate 642.57 mg, insoluble oxalate 282.21 mg, taken oxalate 444.57 mg) was given with a low calcium diet to the patients, the increase of urinary oxalate was more prominent in those with recurrent stones; the mean urinary oxalate increased from 39.84 to 84.18 mg/day (P less than 0.01) in the group with recurrent stones, from 36.95 to 55.12 mg/day (P less than 0.05) in the group with single stones and from 33.99 to 42.78 mg/day in the control group. These increases in oxalate excretion could be ameliorated by the concurrent oral administration of milk (calcium 343 mg). Moreover, diurnal variation in oxalate excretion was observed. It was more evident under spinach load in the group with recurrent stones than in the control group. Urinary oxalate increased promptly, reaching peak levels between 4 and 6 hours after loading in the group with recurrent stones and single stones, and between 2 and 4 hours in the control group. The influence of the spinach load disappeared within 24 hours.     

Studies on crystalluria in calcium oxalate stone formers

Summary The excretion of calcium oxalate and calcium phosphate crystals was studied in fractionated 24 h urine from 7 men with recurrent calcium oxalate stone disease, both before and during daily administration of 5 mg bendroflumethiazide. Urinary calcium, oxalate, magnesium, citrate, phosphate, pH, and inhibition of calcium oxalate crystal growth rate were analyzed in all samples. Exclusively calcium oxalate crystals were found in 30 per cent of the samples, all with a pH below 6.25, whereas calcium phosphate was the crystal type encountered in urine with a pH above 6.50. Bendroflumethiazide decreased the volume of calcium phosphate but not of calcium oxalate crystals. During the period of observation there was no correlation between calcium oxalate supersaturation and calcium oxalate crystal volume, but a relationship was demonstrated between calcium phosphate supersaturation and calcium phosphate crystal volume.