Possible role for chondroitin sulfate in urolithiasis: in vivo studies in an experimental model

Age-Specific Excretion of Calcium, Oxalate, Citrate, and Glycosaminoglycans and Their Ratios in Healthy Children and Children with Urolithiasis

We analyzed children with urolithiasis with age- and gender-matched healthy children. Calcium (mmol/mmol creatinine) and the calcium/citrate ratio (mol/mmol) are the only variables that differentiate children before puberty from healthy children (ROC analysis confirmed only calcium/citrate as a significant variable with cut-off value > 0.84). Peri-pubertal children are distinguished from age- and gender-matched healthy children by the following variables: citrate (mmol/mol creatinine), calcium/citrate (mol/mmol), oxalate/glycosaminoglycans (mmol/g), oxalate/citrate ratios (mmol/mmol) and oxalate/(citrate × glycosaminoglycans) (mol oxalate × mol creatinine)/(mol citrate × g glycosaminoglycans). All variables were confirmed by ROC analysis with cut-off values ≤ 327.87, >1.02, >11.24, >0.12 and >0.03, respectively. These results indicate a different risk of urinary stones development before puberty vs. pubertal/postpubertal children and increasing importance (deficiency) of citrate and glycosaminoglycans in such children. J48 classifier confirmed the importance of the oxalate/(citrate × glycosaminoglycans) and the calcium/citrate ratios (Ox/Cit × GAG 0.22 and Cit/GAG 0.612) with the practically applicable classification tree for distinguishing between pubertal/postpubertal children with urolithiasis with age- and gender-matched healthy children.

Inhibition of Spiral Growth and Dissolution at the Brushite (010) Interface by Chondroitin 4-Sulfate

Modulation of mineralization and demineralization of calcium phosphates (Ca-Ps) with organic macromolecules is a critical process which prevents human kidney stone disease. As a long unbranched polysaccharide of urinary glycosaminoglycans, chondroitin 4-sulfate (Ch4S) has been shown to play an essential role in inhibiting the formation of kidney stones. However, the mechanism of the role of Ch4S remains poorly understood. Here, we used in situ atomic force microscopy to observe the growth and dissolution of spirals on brushite (CaHPO₄·2H₂O) (010) surfaces. The results show that Ch4S preferentially inhibits the [101]_Cc step growth/dissolution by step pinning. This step-specific effect appears to be related to specific binding of Ch4S to Ca sites, as the observed inhibition is not seen in other crystallographic directions where there are fewer Ca terminations. Moreover, Ch4S promotes an increase in the terrace width of [101̅]_Cc by the modification of the interfacial energies of the step edge. These in vitro direct observations of Ch4S modulating brushite mineralization and demineralization reveal a dual control of both step kinetics and interfacial energy.

Inhibition of urinary macromolecule heparin on aggregation of nano-COM and nano-COD crystals

Purpose: This research aims to study the influences of heparin (HP) on the aggregation of nano calcium oxalate monohydrate (COM) and nano calcium oxalate dihydrate (COD) with mean diameter of about 50 nm. Method: The influences of different concentrations of HP on the mean diameter and Zeta potential of nano COM and nano COD were investigated using a nanoparticle size Zeta potential analyzer. Results: HP could be adsorbed on the surface of nano COM and nano COD crystals, leading to an increase in the absolute value of Zeta potential on the crystals and an increase in the electrostatic repulsion force between crystals. Consequently, the aggregation of the crystals is reduced and the stability of the system is improved. The strong adsorption ability of HP was closely related to the -OSO₃⁻ and -COO⁻ groups contained in the HP molecules. X-ray photoelectron spectroscopy confirmed the coordination of HP with Ca²⁺ ions of COM and COD crystals. Conclusion: HP could inhibit the aggregation of nano COM and nano COD crystals and increase their stability in aqueous solution, which is conducive in inhibiting the formation of calcium oxalate stones.

Studies on the in vitro and in vivo antiurolithic activity of Holarrhena antidysenterica

Holarrhena antidysenterica has a traditional use in the treatment of urolithiasis, therefore, its crude extract has been investigated for possible antiurolithic effect. The crude aqueous-methanolic extract of Holarrhena antidysenterica (Ha.Cr) was studied using the in vitro and in vivo methods. In the in vitro experiments, Ha.Cr demonstrated a concentration-dependent (0.25-4 mg/ml) inhibitory effect on the slope of aggregation. It decreased the size of crystals and transformed the calcium oxalate monohydrate (COM) to calcium oxalate dehydrate (COD) crystals, in calcium oxalate metastable solutions. It also showed concentration-dependent antioxidant effect against 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radicals and lipid peroxidation induced in rat kidney tissue homogenate. Ha.Cr (0.3 mg/ml) reduced (p < 0.05) the cell toxicity and LDH release in renal epithelial cells (MDCK) exposed to oxalate (0.5 mM) and COM (66 μg/cm(2)) crystals. In male Wistar rats, receiving 0.75 % ethylene glycol (EG) for 21 days along with 1 % ammonium chloride (AC) in drinking water, Ha.Cr treatment (30-100 mg/kg) prevented the toxic changes caused by lithogenic agents; EG and AC, like loss of body weight, polyurea, oxaluria, raised serum urea and creatinine levels and crystal deposition in kidneys compared to their respective controls. These data indicate that Holarrhena antidysenterica possesses antiurolithic activity, possibly mediated through the inhibition of CaOx crystal aggregation, antioxidant and renal epithelial cell protective activities and may provide base for designing future studies to establish its efficacy and safety for clinical use.

Characterization of glycosaminoglycans in tubular epithelial cells: calcium oxalate and oxalate ions effects

BACKGROUND

The interaction between tubular epithelial cells and calcium oxalate crystals or oxalate ions is a very precarious event in the lithogenesis. Urine contains ions, glycoproteins and glycosaminoglycans that inhibit the crystallization process and may protect the kidney against lithogenesis. We examined the effect of oxalate ions and calcium oxalate crystals upon the synthesis of glycosaminoglycans in distal [Madin-Darby canine kidney (MDCK)] and proximal (LLC-PK1) tubular cell lines.

METHODS

Glycosaminoglycan synthesis was analyzed by metabolic labeling with (35)S-sulfate and enzymatic digestion with specific mucopolysaccharidases. Cell death was assessed by fluorescent dyes and crystal endocytosis was analised by flow cytometry.

RESULTS

The main glycosaminoglycans synthesized by both cells were chondroitin sulfate and heparan sulfate most of them secreted to the culture medium or present at cellular surface. Exposition of MDCK cells to oxalate ions increased apoptosis rate and the incorporation of (35)S-sulfate in chondroitin sulfate and heparan sulfate, while calcium oxalate crystals were endocyted by LLC-PK1, induced necrotic cell death, and increased (35)S-sulfate incorporation in glycosaminoglycans. These effects seem to be specific and due to increased biosynthesis, since hydroxyapatite and other carboxylic acid did not induced cellular death or glycosaminoglycan synthesis and no changes in sulfation degree or molecular weight of glycosaminoglycans could be detected. Thapsigargin inhibited the glycosaminoglycan synthesis induced by calcium oxalate in LLC-PK1, suggesting that this effect was sensitive to the increase in cytosolic calcium.

CONCLUSION

Tubular cells may increase the synthesis of glycosaminoglycans to protect from the toxic insult of calcium oxalate crystals and oxalate ions, what could partially limit the lithogenesis.

Reduced urinary excretion of sulfated polysaccharides in diabetic rats

The aim of the present study was to further understand the changes in renal filtration that occur in the early stages of diabetes mellitus. Diabetes was induced in male Wistar rats by a single injection of streptozotocin. Glycemia, body weight, 24-h urine volume and urinary excretion of creatinine, protein and glycosaminoglycans were measured 10 and 30 days after diabetes induction. All the diabetic animals used in the present study were hyperglycemic, did not gain weight, and presented proteinuria and creatinine hyperfiltration. In contrast, the glycosaminoglycan excretion decreased. Dextran sulfates of different molecular weights (6.0 to 11.5 kDa) were administered to the diabetic rats, and to age-matched, sham-treated controls. Most of the dextran sulfate was excreted during the first 24 h, and the amounts excreted in the urine were inversely proportional to the dextran sulfate molecular weight for all groups. Nevertheless, diabetic rats excreted less and accumulated more dextran sulfate in kidney and liver, as compared to controls. These differences, which were observed only for the dextran sulfates of higher molecular weights (>7 kDa), increased with the duration of diabetes. Our findings suggest differential renal processing mechanisms for proteins and sulfated polysaccharides, with the possible involvement of kidney cells.

Changes in cat urinary glycosaminoglycans with age and in feline urologic syndrome

The aim of the present study was to characterize the urinary excretion of glycosaminoglycans in kittens and adult healthy cats, as well as in cats with a low urinary tract disease, the feline urologic syndrome (FUS). The main urinary glycosaminoglycan in cats was found to be chondroitin sulfate, with smaller amounts of dermatan sulfate and heparan sulfate. There was no difference in the urinary glycosaminoglycan concentration with sex, but a marked decrease occurred with age, due to chondroitin sulfate. Trace amounts of keratan sulfate were also detected in the urine of kittens, but not of healthy adult cats. Dermatan sulfate and heparan sulfate were the only glycosaminoglycans found in the urinary tract and kidney, and chondroitin sulfate was the only glycosaminoglycan found in the plasma. These data suggest that the main urinary glycosaminoglycan chondroitin sulfate is of systemic origin and filtered in the kidney, while the minor components dermatan sulfate and heparan sulfate may come from the urinary tract. The urinary glycosaminoglycan concentration was greatly decreased in animals with FUS, as compared to normal adults. We hypothesize that these low glycosaminoglycan levels reflect a damage to the bladder surface, resulting in absorption and/or degradation of the endogenous urinary glycosaminoglycans.

Low-molecular-weight dextran sulfate prevents experimental urolithiasis in rats

BACKGROUND

Low-molecular-weight dextran sulfate was tested on an experimental model of urolithiasis induced in rats.

METHODS

Male Wistar rats weighing 250 g had a 15-mg calcium oxalate stone surgically placed into the bladder. A group was sham operated, another group was treated by daily intraperitoneal injection of low-molecular-weight dextran sulfate and the other by daily intraperitoneal saline injection.

RESULTS

This treatment prevents the growth of exogenous calcium oxalate stone introduced into the bladder and also avoided the formation of secondary stones in the animals. In addition, low-molecular-weight dextran sulfate prevented the aggregation of other ions, such as ammonium, phosphate and magnesium to the calcium oxalate stone placed in the bladder. These effects of the low-molecular-weight dextran sulfate are associated with the presence of the sulfated polysaccharide in the urine. However, the polysaccharide did not adhere to the bladder stone. Possibly, dextran sulfate forms soluble complex with calcium ions dissolved in the urine and therefore prevented calcium salt crystallization.

CONCLUSION

Dextran sulfate, 8000 Da, led to a decrease in calculi glycosaminoglycans in animals treated with dextran, and there was an inhibition in bladder-implanted stones growth.

Tamm-Horsfall glycoprotein: biology and clinical relevance

Tamm-Horsfall glycoprotein (THP) is the most abundant urinary protein in mammals. Urinary excretion occurs by proteolytic cleavage of the large ectodomain of the glycosyl phosphatidylinositol-anchored counterpart exposed at the luminal cell surface of the thick ascending limb of Henle's loop. We describe the physical-chemical structure of human THP and its biosynthesis and interaction with other proteins and leukocytes. The clinical relevance of THP reported here includes: (1) involvement in the pathogenesis of cast nephropathy, urolithiasis, and tubulointerstitial nephritis; (2) abnormalities in urinary excretion in renal diseases; and (3) the recent finding that familial juvenile hyperuricemic nephropathy and autosomal dominant medullary cystic kidney disease 2 arise from mutations of the THP gene. We critically examine the literature on the physiological role and mechanism(s) that promote urinary excretion of THP. Some lines of research deal with the in vitro immunoregulatory activity of THP, termed uromodulin when isolated from urine of pregnant women. However, an immunoregulatory function in vivo has not yet been established. In the most recent literature, there is renewed interest in the capacity of urinary THP to compete efficiently with urothelial cell receptors, such as uroplakins, in adhering to type 1 fimbriated Escherichia coli. This property supports the notion that abundant THP excretion in urine is promoted in the host by selective pressure to obtain an efficient defense against urinary tract infections caused by uropathogenic bacteria.

The effect of Phyllanthus niruri on urinary inhibitors of calcium oxalate crystallization and other factors associated with renal stone formation

OBJECTIVE

To evaluate the effect of an aqueous extract of Phyllanthus niruri (Pn), a plant used in folk medicine to treat lithiasis, on the urinary excretion of endogenous inhibitors of lithogenesis, citrate, magnesium and glycosaminoglycans (GAGs).

MATERIALS AND METHODS

The effect of chronic (42 days) administration of Pn (1.25 mg/mL/day, orally) was evaluated in a rat model of urolithiasis induced by the introduction of a calcium oxalate (CaOx) seed into the bladder of adult male Wistar rats. The animals were divided into four groups: a sham control (16 rats); a control+Pn (six); CaOx+water instead of Pn (14); and CaOx+Pn (22). Plasma and urine were collected after 42 days of treatment for biochemical analysis and the determination of urinary excretion of citrate, magnesium and GAGs. The animals were then killed and the calculi analysed.

RESULTS

The creatinine clearance or urinary and plasma concentrations of Na+, K+, Ca2+, oxalate, phosphate and uric acid were unaffected by Pn or the induction of lithiasis. Treatment with Pn strongly inhibited the growth of the matrix calculus and reduced the number of stone satellites compared with the group receiving water. The calculi were eliminated or dissolved in some treated animals (three of 22). The urinary excretion of citrate and magnesium was unaffected by Pn treatment. However, the mean (sd) urinary concentration of GAGs was significantly lower in rats treated with CaOx+Pn, at 5.64 (0.86) mg/g creatinine, than when treated with CaOx + water, at 11.78 (2.21) mg/g creatinine. In contrast, the content of GAGs in the calculi was higher in the CaOx + Pn rats, at 48.0 (10.4) g/g calculus, than in the CaOx + water group, at 16.6 (9.6) g/g calculus.

CONCLUSION

These results show that Pn has an inhibitory effect on crystal growth, which is independent of changes in the urinary excretion of citrate and Mg, but might be related to the higher incorporation of GAGs into the calculi.

Control of calcium oxalate crystal structure and cell adherence by urinary macromolecules

Crystal polymorphism is exhibited by calcium oxalates in nephrolithiasis, and we have proposed that a shift in the preferred crystalline form of calcium oxalate (CaOx) from monohydrate (COM) to dihydrate (COD) induced by urinary macromolecules reduces crystal attachment to epithelial cell surfaces, thus potentially inhibiting a critical step in the genesis of kidney stones. We have tested the validity of this hypothesis by studying both the binding of monohydrate and dihydrate crystals to renal tubule cells and the effect of macromolecular urinary solutes on crystal structure. Renal tubule cells grown in culture bound 50% more CaOx monohydrate than dihydrate crystals of comparable size. The effects of macromolecules on the spontaneous nucleation of CaOx were examined in HEPES-buffered saline solutions containing Ca2+ and C2O4(2-) at physiologic concentrations and supersaturation. Many naturally occurring macromolecules known to be inhibitors of crystallization, specifically osteopontin, nephrocalcin and urinary prothrombin fragment 1, were found to favor the formation of calcium oxalate dihydrate in this in vitro system, while other polymers did not affect CaOx crystal structure. Thus, the natural defense against nephrolithiasis may include impeding crystal attachment by an effect of macromolecular inhibitors on the preferred CaOx crystal structure that forms in urine.

Urinary glycosaminoglycan excretion in healthy and stone-forming children

Both in vivo and in vitro studies suggest that macromolecules excreted in the urine, e.g. glycosaminoglycans (GAGs) may be inhibitors of kidney stone formation. We evaluated urinary GAG excretion in 22 children with calcium oxalate stones [8 with absorptive hypercalciuria, 6 with renal hypercalciuria (RH), 8 with normocalciuria], and in 20 age-matched controls. There was no significant difference between the two groups in the total urinary GAG level. In terms of the various GAG fractions, patients with RH excreted considerably less keratan sulphate and considerably more dermatan sulphate than the other patients and healthy controls. There was no difference between the two groups in condroitin sulphate, heparan sulphate and hyaluronic acid excretion. We conclude that there is no significant correlation between the formation of calcium oxalate stones and urinary GAG excretion.

Glycosaminoglycans, proteins, and stone formation: adult themes and child's play

The relative infrequency of renal stones in children is probably the main reason for the paucity of literature devoted to the study of urolithiasis in pediatric patients. Nonetheless, when pediatricians do address the issue, the contents of their papers reflect those prevalent in the adult literature; with one notable exception. Papers dealing with the potential role of urinary macromolecules in pediatric stone disease are very scarce indeed; to my knowledge, only four have been published in the English literature in the last 15 years. One of these is to be found in this issue and, like the remaining three, it compares the urinary excretion of glycosaminoglycans in healthy children and those with stones. This article briefly reviews the history of the association of urinary macromolecules, particularly glycosaminoglycans and proteins, with calcium oxalate urolithiasis, and discusses in more detail the published experimental evidence for their fulfilling a determinant role in stone formation.

Glycosaminoglycans and other sulphated polysaccharides in calculogenesis of urinary stones

Naturally occurring glycosaminoglycans (GAGs) and other, semisynthetic, sulphated polysaccharides are thought to play an important role in urolithiasis. Processes involved in urinary stone formation are crystallization and crystal retention. Oxalate transport and renal tubular cell injury are determining factors in these processes. In this article experimental results concerning the possible mechanisms of action of GAGs and other sulphated polysaccharides are reviewed. GAGs are inhibitors of crystal growth and agglomeration and possibly also of nucleation. They can prevent crystal adherence, correct an abnormal oxalate flux and prevent renal tubular cell damage.