CaOx Kidney Stones Research Articles

Reactive oxygen species, inflammation and calcium oxalate nephrolithiasis.

Calcium oxalate (CaOx) kidney stones are formed attached to Randall’s plaques (RPs) or Randall’s plugs. Mechanisms involved in the formation and growth are poorly understood. It is our hypothesis that stone formation is a form of pathological biomineralization or ectopic calcification. Pathological calcification and plaque formation in the body is triggered by reactive oxygen species (ROS) and the development of oxidative stress (OS). This review explores clinical and experimental data in support of ROS involvement in the formation of CaOx kidney stones. Under normal conditions the production of ROS is tightly controlled, increasing when and where needed. Results of clinical and experimental studies show that renal epithelial exposure to high oxalate and crystals of CaOx/calcium phosphate (CaP) generates excess ROS, causing injury and inflammation. Major markers of OS and inflammation are detectable in urine of stone patients as well as rats with experimentally induced CaOx nephrolithiasis. Antioxidant treatments reduce crystal and oxalate induced injury in tissue culture and animal models. Significantly lower serum levels of antioxidants, alpha-carotene, beta-carotene and beta-cryptoxanthine have been found in individuals with a history of kidney stones. A diet rich in antioxidants has been shown to reduce stone episodes. ROS regulate crystal formation, growth and retention through the timely production of crystallization modulators. In the presence of abnormal calcium, citrate, oxalate, and/or phosphate, however, there is an overproduction of ROS and a decrease in the antioxidant capacity resulting in OS, renal injury and inflammation. Cellular degradation products in the urine promote crystallization in the tubular lumen at a faster rate thus blocking the tubule and plugging the tubular openings at the papillary tips forming Randall’s plugs. Renal epithelial cells lining the loops of Henle/collecting ducts may become osteogenic, producing membrane vesicles at the basal side. In addition endothelial cells lining the blood vessels may also become osteogenic producing membrane vesicles. Calcification of the vesicles gives rise to RPs. The growth of the RP’s is sustained by mineralization of collagen laid down as result of inflammation and fibrosis.

Genetically engineered Lactobacillus plantarum WCFS1 constitutively secreting heterologous oxalate decarboxylase and degrading oxalate under in vitro.

Hyperoxaluria is a major risk factor for urinary stone disease, where calcium oxalate (CaOx) is the most prevalent type of kidney stones. Systemic treatments of CaOx kidney stone patients are limited and comprise drawbacks including recurrence of stone formation and kidney damages. In the present work Lactobacillus plantarum (L. plantarum) was engineered to constitutively secrete oxalate decarboxylase (OxdC) for the degradation of intestinal oxalate. The homologous promoter PldhL and signal peptide Lp_0373 of L. plantarum were used for constructing recombinant vector pLdhl0373OxdC. Results showed that homologous promoter PldhL and signal peptide Lp_0373 facilitated the production, secretion, and functional expression of OxdC protein in L. plantarum. SDS-PAGE analysis revealed that 44kDa protein OxdC was seen exceptionally in the culture supernatant of recombinant L. plantarum (WCFS1OxdC) harboring the plasmid pLdhl0373OxdC.The culture supernatant of L. plantarum WCFS1OxdC showed OxdC activity of 0.06U/mg of protein, whereas no enzyme activity was observed in the supernatant of the wild type WCFS1 and the recombinant NC8OxdC strains. The purified recombinant OxdC from the WCFS1OxdC strain showed an activity of 19.1U/mg protein. The recombinant L. plantarum strain secreted 25% of OxdC protein in the supernatant. The recombinant strain degraded more than 70% of soluble oxalate in the culture supernatant. Plasmid segregation analysis revealed that the recombinant strain lost almost 70-89% of plasmid in 42nd and 84th generation, respectively. In conclusion, recombinant L. plantarum strain containing plasmid pLdhl0373OxdC showed constitutive secretion of bioactive OxdC and also capable of degrading externally available oxalate under in vitro conditions.

A new era in the treatment of calcium oxalate stones?

Calcium oxalate (CaOx) is the most prevalent type of kidney stone. The amount of oxalate excreted in the urine is a major risk factor for CaOx stone formation. The study by Siener et al. makes a substantial contribution to our understanding of how Oxalobacter formigenes affects oxalate metabolism and excretion in humans and hence influences the risk of developing CaOx kidney stones.

Controlled Metabolic Diet Reduces Calcium Oxalate Supersaturation but Not Oxalate Excretion After Bariatric Surgery

To identify the effect of a controlled metabolic diet on reducing urinary calcium oxalate (CaOx) supersaturation in subjects with hyperoxaluric nephrolithiasis after potentially malabsorptive forms of bariatric surgery. Subjects with a history of CaOx kidney stones and mild hyperoxaluria after bariatric surgery (n = 9) collected baseline 24-hour urine samples while consuming a free choice diet. They were then instructed to consume a controlled diet low in oxalate (70-80 mg/d), normal in calcium (1000 mg/d), and moderate in protein before 2 final 24-hour urine collections. Overall, the urinary CaOx supersaturation decreased from 1.97 ± 0.49 delta Gibbs (DG) with the free choice diet to 1.13 ± 0.75 DG with the controlled diet (P < .01). This occurred in the absence of a significant change in urinary oxalate excretion (0.69 ± 0.29 mmol/d with the free choice diet compared with 0.66 ± 0.38 mmol/d with the controlled diet). Urinary volume, citrate, and pH all increased, although not significantly (P > .05), contributing to the significant CaOx supersaturation change. A controlled metabolic diet normal in calcium, moderate in protein, and reduced in oxalate can positively affect urinary CaOx supersaturation after bariatric surgery. However, this diet did not appear to decrease urinary oxalate excretion. Therefore, restriction of dietary oxalate alone might not be enough to reduce urinary oxalate excretion to normal levels in this group of patients with known enteric hyperoxaluria. Additional strategies could be necessary, such as the use of oral calcium supplements as oxalate binders and a lower fat diet.

The Effects of the Hydroalcohol Extract of Rosa canina L. Fruit on Experimentally Nephrolithiasic Wistar Rats

This research evaluated the possible therapeutic potential of Rosa canina (RC) as a preventive agent in experimentally induced calcium oxalate (CaOx) nephrolithiasis with ethylene glycol (1% EG) in rats. In this experiment, 50 Wistar rats were divided randomly into five groups (n = 10). These groups received tap drinking water (group I), 1% EG (group II), 250 mg/kg RC + 1% EG (group III), 500 mg/kg RC + 1% EG (group IV), or 2.5 g/kg potassium citrate + 1% EG (group V) for a period of 30 days. Blood and urine were collected for biochemical analysis, and the liver and kidneys were prepared for total lipid peroxides, calcium content and histological evaluation. The extract was analysed for total phenolics, flavonoids, ascorbic acid, citric acid and radical scavenger activity. The supplementation of the hydromethanol RC extract contributed to reducing the kidney and liver lipid peroxides to optimum levels in rats that had been treated with EG-induced CaOx lithiasis. The extract also decreased renal and urinary calcium contents, decreased the size and number of CaOx calculi in the kidneys, and significantly increased citrate excretion without changing the volume, pH, or urinary concentrations of oxalate in comparison with the control group. According to these results, RC can be useful as a preventive agent against the formation of CaOx kidney stones.

Calcium oxalate crystal deposition in metabolic syndrome model rat kidneys

Although an epidemiological link between the metabolic syndrome and kidney stone formation has been reported, the mechanism by which metabolic syndrome promotes kidney stone formation has yet to be elucidated. We investigated calcium oxalate (CaOx) kidney stone formation in a rat metabolic syndrome model. We induced hyperoxaluria in 8-week-old male Otsuka Long-Evans Tokushima fatty (OLETF) rats, and a control strain, Long-Evans Tokushima Otsuka (LETO) rats, by administering 1.0% ethylene glycol (EG) as their drinking water for 2 weeks. Rats were divided into four groups: LETO-C (control, n = 7); LETO-SF (stone forming, n = 8); OLETF-C (n = 7); and OLETF-SF (n = 8). Urine and blood samples were collected for biochemistry testing, and the kidneys were harvested for estimation of crystal deposition and determinations of the expression of osteopontin (OPN) and monocyte chemoattractant protein-1 (MCP-1). Administration of EG induced hyperoxaluria to the same degree in both strains. The OLETF-SF group showed a higher grade of renal crystal deposition and significantly higher renal calcium content than the LETO-SF group. Although the OLETF-C group excreted significantly higher amounts of uric acid and more acidic urine than the LETO-C group, similar differences were not observed in rats given EG. Significant upregulation of both OPN and MCP-1 was seen in the kidneys of hyperoxaluric rats, with higher levels of expression in the OLETF-SF group than the LETO-SF group. The present results show for the first time that OLETF rats form more renal CaOx crystal deposits compared with control rats under EG-induced hyperoxaluric conditions. The model described here should be useful for investigating the mechanisms by which the metabolic syndrome promotes CaOx kidney stone formation.

Identification of human urinary trefoil factor 1 as a novel calcium oxalate crystal growth inhibitor

Previous research on proteins that inhibit kidney stone formation has identified a relatively small number of well-characterized inhibitors. Identification of additional stone inhibitors would increase understanding of the pathogenesis and pathophysiology of nephrolithiasis. We have combined conventional biochemical methods with recent advances in mass spectrometry (MS) to identify a novel calcium oxalate (CaOx) crystal growth inhibitor in normal human urine. Anionic proteins were isolated by DEAE adsorption and separated by HiLoad 16/60 Superdex 75 gel filtration. A fraction with potent inhibitory activity against CaOx crystal growth was isolated and purified by anion exchange chromatography. The protein in 2 subfractions that retained inhibitory activity was identified by matrix-assisted laser desorption/ionization-time-of-flight MS and electrospray ionization-quadrupole-time-of-flight tandem MS as human trefoil factor 1 (TFF1). Western blot analysis confirmed the mass spectrometric protein identification. Functional studies of urinary TFF1 demonstrated that its inhibitory potency was similar to that of nephrocalcin. The inhibitory activity of urinary TFF1 was dose dependent and was inhibited by TFF1 antisera. Anti-C-terminal antibody was particularly effective, consistent with our proposed model in which the 4 C-terminal glutamic residues of TFF1 interact with calcium ions to prevent CaOx crystal growth. Concentrations and relative amounts of TFF1 in the urine of patients with idiopathic CaOx kidney stone were significantly less (2.5-fold for the concentrations and 5- to 22-fold for the relative amounts) than those found in controls. These data indicate that TFF1 is a novel potent CaOx crystal growth inhibitor with a potential pathophysiological role in nephrolithiasis.

Thiazides Reduce Brushite, but not Calcium Oxalate, Supersaturation, and Stone Formation in Genetic Hypercalciuric Stone–Forming Rats

Over 59 generations, a strain of rats has been inbred to maximize urine calcium excretion. The rats now excrete eight to 10 times as much calcium as controls. These rats uniformly form calcium phosphate (apatite) kidney stones and have been termed genetic hypercalciuric stone-forming (GHS) rats. The addition of a common amino acid and oxalate precursor, hydroxyproline, to the diet of the GHS rats leads to formation of calcium oxalate (CaOx) kidney stones. Hydroxyproline-supplemented GHS rats were used to test the hypothesis that the thiazide diuretic chlorthalidone would decrease urine calcium excretion, supersaturation, and perhaps stone formation. All GHS rats received a fixed amount of a standard 1.2% calcium diet with 5% trans-4-hydroxy-l-proline (hydroxyproline) so that the rats would exclusively form CaOx stones. Half of the rats had chlorthalidone (Thz; 4 to 5 mg/kg per d) added to their diets. Urine was collected weekly, and at the conclusion of the study, the kidneys, ureters, and bladders were radiographed for the presence of stones. Compared with control, the addition of Thz led to a significant reduction of urine calcium and phosphorus excretion, whereas urine oxalate excretion increased. Supersaturation with respect to the calcium hydrogen phosphate fell, whereas supersaturation with respect to CaOx was unchanged. Rats that were fed Thz had fewer stones. As calcium phosphate seems to be the preferred initial solid phase in patients with CaOx kidney stones, the reduction in supersaturation with respect to the calcium phosphate solid phase may be the mechanism by which thiazides reduce CaOx stone formation.

Soybean and Soyfood Consumption Increase Oxalate Excretion

Eight healthy adults with no prior history of kidney stones participated in eight oxalate (Ox) load tests, seven foods, and an Ox solution control. After correction for endogenous Ox synthesis, increases in urinary Ox excretion during the 8 hours after eating one meal of the two soybean lines and five soyfoods tested ranged from 19.6 ± 23.3 to 124 ± 156 mmol (1.7 ± 2.1 to 10.9 ± 13.8 mg). Thus, frequent consumption of soybeans and soy products (TVP, soynuts, soy beverage, and tofu) may be a risk factor for CaOx kidney stone formation in susceptible individuals, such as those with a prior history of Ca stones, high normal urinary Ox concentrations, or intestinal disease.

Effects of inter-α-inhibitor and several of its derivatives on calcium oxalate crystallization in vitro

The bikunin peptide chain of the protease inhibitor inter-alpha-inhibitor (IalphaI) has been reported to be an inhibitor of calcium oxalate (CaOx) crystallization, and hence has been proposed as having a role in CaOx kidney stone formation. However, further experimental evidence is required to assess if fragments of IalphaI other than bikunin may play a role in the regulation of crystallization events in stone formation. The aim of the present study was to assess the effects of IalphaI and several of its derivatives on CaOx crystallization in a seeded inorganic system and to compare these effects with those of a known inhibitor of crystallization, prothrombin. IalphaI was purified from a preparation of human plasma and fragmented by alkaline hydrolysis, and two of its peptide chains, bikunin and heavy chain 1 (H1), were purified further by HPLC. Their purity was confirmed by SDS/PAGE. Using Coulter counter and [(14)C]oxalate analysis and scanning electron microscopy, IalphaI, its H1 chain and bikunin from urine and from plasma were shown to be relatively weak inhibitors of CaOx crystallization in vitro at expected physiological concentrations. It was concluded that members of the IalphaI family may not be as important in kidney stone formation as has been generally proposed, although further studies are required before a possible role for IalphaI and its fragments in stone formation can be unambiguously discounted.