Glycosaminoglycans and other sulphated polysaccharides in calculogenesis of urinary stones

Cell Protection and Crystal Endocytosis Inhibition by Sulfated Laminaria Polysaccharides Against Nano-COM-Induced Oxidative Damage in Renal Epithelial Cells

Background: The damage to renal tubular epithelial cells is closely related to the formation of kidney stones. At present, research on drugs that can protect cells from damage remains limited. Methods: This study aims to explore the protective effects of four different sulfate groups (-OSO₃ ^-) of Laminaria polysaccharides (SLPs) on human kidney proximal tubular epithelial (HK-2) cells and determine the difference in the endocytosis of nano-sized calcium oxalate monohydrate (COM) crystals before and after protection. COM with a size of 230 ± 80 nm was used to damage HK-2 cells to establish a damage model. The protection capability of SLPs (LP0, SLP1, SLP2, and SLP3) with -OSO₃ ^- contents of 0.73, 15, 23, and 31%, respectively, against COM crystal damage and the effect of SLPs on the endocytosis of COM crystals were studied. Results: Compared with that of the SLP-unprotected COM-injured group, the cell viability of the SLP-protected group was improved, healing capability was enhanced, cell morphology was restored, production of reactive oxygen species was reduced, mitochondrial membrane potential and lysosome integrity were increased, intracellular Ca²⁺ level and autophagy were decreased, cell mortality was reduced, and internalized COM crystals were lessened. The capability of SLPs to protect cells from damage and inhibit the endocytosis of crystals in cells enhanced with an increase in the -OSO₃ ^- content of SLPs. Conclusions: SLPs with a high -OSO₃ ^- content may become a potential green drug for preventing the formation of kidney stones.

Seeking consistency for the role of urinary macromolecules and glycosaminoglycans in calcium oxalate crystallization processes pertaining to the risk of renal stone formation using a multi-faceted basic science approach

BACKGROUND

The roles of urinary macromolecules (UMMs) in calcium oxalate (CaOx) renal stone formation have not been consistently established.

AIM

To unravel these roles using a multi-faceted, multi-technique approach employing a wide range of experimental variables on a rotational basis in strategically chosen combinations.

METHODS

Endogenous urinary glycosaminoglycans (GAGs) were investigated in fractions obtained after ultrafiltration of pooled human urine (HU). Exogenous GAGs (chondroitin sulphate, CS, and hyaluronic acid, HA) were studied in artificial (AU) and in individual HUs. Experiments were conducted in a batch crystallizer and in a mixed suspension, mixed product removal flow system. Crystallization was quantitatively followed using Coulter multisizer and flow cytometer techniques. Crystal aggregation in the presence and absence of exogenous CS and HA was measured by Zeta potential and crystal sedimentation.

RESULTS

Total UMMs (endogenous) and individual GAGs (exogenous) consistently promoted CaOx crystallization and disaggregation. Evidence of UMM-UMM and UMM-solution synergistic effects was consistently observed for achieving modulation of crystallization processes.

CONCLUSIONS

Total UMMs, the main modulatory component of which is GAGs, are promoters of CaOx crystal nucleation and inhibitors of CaOx crystal aggregation. These results allow researchers to disregard alternative roles that have been advocated in such studies.

Antioxidant Activities and Repair Effects on Oxidatively Damaged HK-2 Cells of Tea Polysaccharides with Different Molecular Weights

This study aims at investigating the antioxidant activity and repair effect of green tea polysaccharide (TPS) with different molecular weights (Mw) on damaged human kidney proximal tubular epithelial cells (HK-2). Scavenging activities on hydroxyl radical (·OH) and ABTS radical and reducing power of four kinds of TPS with Mw of 10.88 (TPS0), 8.16 (TPS1), 4.82 (TPS2), and 2.31 kDa (TPS3) were detected. A damaged cell model was established using 2.6 mmol/L oxalate to injure HK-2 cells. Then, different concentrations of TPSs were used to repair the damaged cells. Index changes of subcellular organelles of HK-2 cells were detected before and after repair. The four kinds of TPSs possessed radical scavenging activity and reducing power, wherein TPS2 with moderate Mw presented the strongest antioxidant activity. After repair by TPSs, cell morphology of damaged HK-2 cells was gradually restored to normal conditions. Reactive oxygen species production decreased, and mitochondrial membrane potential (Δψm) of repaired cells increased. Cells of G1 phase arrest were inhibited, and cell proportion in the S phase increased. Lysosome integrity improved, and cell apoptotic rates significantly reduced in the repaired group. The four kinds of TPSs with varying Mw displayed antioxidant activity and repair effect on the mitochondria, lysosomes, and intracellular DNA. TPS2, with moderate Mw, showed the strongest antioxidant activity and repair effect; it may become a potential drug for prevention and treatment of kidney stones.

Repair Effect of Seaweed Polysaccharides with Different Contents of Sulfate Group and Molecular Weights on Damaged HK-2 Cells

The structure⁻activity relationships and repair mechanism of six low-molecular-weight seaweed polysaccharides (SPSs) on oxalate-induced damaged human kidney proximal tubular epithelial cells (HK-2) were investigated. These SPSs included Laminaria japonica polysaccharide, degraded Porphyra yezoensis polysaccharide, degraded Gracilaria lemaneiformis polysaccharide, degraded Sargassum fusiforme polysaccharide, Eucheuma gelatinae polysaccharide, and degraded Undaria pinnatifida polysaccharide. These SPSs have a narrow difference of molecular weight (from 1968 to 4020 Da) after degradation by controlling H₂O₂ concentration. The sulfate group (⁻SO₃H) content of the six SPSs was 21.7%, 17.9%, 13.3%, 8.2%, 7.0%, and 5.5%, respectively, and the ⁻COOH contents varied between 1.0% to 1.7%. After degradation, no significant difference was observed in the contents of characteristic ⁻SO₃H and ⁻COOH groups of polysaccharides. The repair effect of polysaccharides was determined using cell-viability test by CCK-8 assay and cell-morphology test by hematoxylin-eosin staining. The results revealed that these SPSs within 0.1⁻100 μg/mL did not express cytotoxicity in HK-2 cells, and each polysaccharide had a repair effect on oxalate-induced damaged HK-2 cells. Simultaneously, the content of polysaccharide ⁻SO₃H was positively correlated with repair ability. Furthermore, the low-molecular-weight degraded polysaccharides showed better repair activity on damaged HK-2 cells than their undegraded counterpart. Our results can provide reference for inhibiting the formation of kidney stones and for developing original anti-stone polysaccharide drugs.

Is there a role for pentosan polysulfate in the prevention of calcium oxalate stones?

The clinical role for pentosan polysulfate (PPS) in the prevention of calcium oxalate urolithiasis is not known. Crystallization and aggregation are important steps in calcium oxalate stone formation, and PPS has been shown to inhibit these steps, both in vitro and in vivo. In addition, PPS has a role in repairing injured urothelium and inhibiting adhesion to epithelial defects. A randomized double-blind placebo-controlled study appears warranted to assess the utility of PPS in the prevention of recurrent calcium oxalate stones.

Kidney stone inhibitors in patients with renal stones and endemic renal tubular acidosis in northeast Thailand

Distal renal tubular acidosis (dRTA) is generally associated with hypercalciuria, hypocitraturia, and nephrolithiasis. Our intention was to study glycosaminoglycans (GAGS) and nephrocalcin (NC), two well-known crystal growth inhibitors, in a population with endemic dRTA and nephrolithiasis in northeast (NE) Thailand. We studied 13 patients, six with dRTA and seven with nephrolithiasis with normal or undefined acidification function. Six healthy adults living in the same area as the patients and another six from the Bangkok (BKK) area were used as controls. We measured urinary pH, ammonia, calcium, citrate, magnesium, oxalate, potassium, sodium and uric acid. GAGS were determined by an Alcian blue precipitation method and were qualitated by agarose gel electrophoresis after being isolated using 5% cetyltrimethylammonium bromide at pH 6.0. NC isoforms were isolated as previously described by Nakagawa et al. Citrate was higher in BKK controls ( p<0.04). There was a striking difference among GAGS from BKK when compared with other groups (103.85+/-10.70 vs. 23.52+/-8.11 for dRTA, 22.36+/-14.98 for kidney stone patients and 14.73+/-2.87 mg/ml in controls from the NE region, ( p<0.0001). dRTA and stone-forming patients excrete proportionally more (C+D) than (A+B) NC isoforms ( p<0.05). Also, their NC showed a 100-fold weaker binding capacity of calcium oxalate monohydrate crystals. The ratio of chondroitin sulfate/heparin sulfate in GAGS was approximately 9/1. In addition to the traditional risk factors for nephrolithiasis in dRTA, GAGS and NC might play an important role in the pathogenesis of stone formation in this population.

A model to quantify encrustation on ureteric stents, urethral catheters and polymers intended for urological use

OBJECTIVE

To validate an encrustation model and to quantify encrustation on currently used urological devices and polymers intended for urological use. Materials and methods An encrustation model was validated: (i) to measure the amount of calcium leaching from the glass model and from the polymer used; (ii) to determine whether the use of a single-source or pooled urine produced similar results; (iii) to determine in vitro encrustation; and (iv) to compare the results of in vivo implantation of the same materials into the bladders of rodents with the in vitro results. A test polymer (a ureteric stent, a urethral catheter or a biomaterial) and a control silicone polymer were housed separately but received human urine from the same reservoir and under the same conditions (pH 6.0 and 37 degrees C) for 5 days. The amount of calcium encrustation on each polymer was measured using atomic absorption spectroscopy. Each experiment was repeated at least four times and the results expressed as an encrustation index, defined as the ratio of encrustation of the test and reference polymers.

RESULTS

The amount of calcium leaching from the glass model and polymers tested was insignificant. The use of a single-source or pooled urine gave the same results in the encrustation model. The in vitro results correlated with in vivo implantation of disks into the bladders of rats. Among the commonly used ureteric stents tested, the Cook C-Flex ureteric stents encrusted least. Hydrogel-coated ureteric stents encrusted more than uncoated stents. The Bard polytetrafluoroethylene short-term urethral catheter encrusted more than the Bard hydrogel-coated long-term catheter. A plasma-activated surface modification of a synthetic biomaterial with hyaluronic acid encrusted less than silicone, a long-term biomaterial widely regarded as the 'gold standard'.

CONCLUSION

This validated encrustation model is the first to quantify encrustation on currently available ureteric stents and urethral catheters. A novel coating for a biomaterial was identified using the encrustation model, and which encrusted less than silicone.

Effect of urinary stone disease and extracorporeal shockwave lithotripsy on excretion of glycosaminoglycans

BACKGROUND AND PURPOSE

The effect of glycosaminoglycans (GAGs) in urinary crystal inhibition has been shown in vitro, but their inhibitor role in vivo has not been precisely determined in stone-forming patients. The aim of this study was to compare the levels of total GAGs and their components in primary stone-forming patients and a healthy control group and to investigate the impact of shockwave lithotripsy (SWL).

PATIENTS AND METHODS

Thirty-eight patients with primary kidney stones and 31 healthy controls were included in this prospective study. Total urinary GAG concentrations were determined by the dimethylene blue assay (DMB), and GAG fractions (chondroitin sulfate, heparan sulfate, and dermatan sulfate) were studied by cellulose acetate electrophoresis. Analysis was repeated after SWL in the stone patients.

RESULTS

Chondroitin sulfate was the major component secreted in the urine of the control subjects. Heparan sulfate was the major component in the urine of the stone patients with less chondroitin sulfate and dermatan sulfate (48%, 35%, 16.5%, respectively). Our study showed a significant increase in total urinary GAGs (4.75 v. 7.43 microg/mg of creatinine; P<0.0001) after SWL. Dermatan sulfate was the main component in this group (P<0.0001). The total urinary GAG concentrations remained high for at least 2 days after SWL.

CONCLUSION

The elevation in total GAGs after SWL indicates the presence of tissue injury, which also renders dermatan sulfate the principal excreted component. Studies with longer follow-up periods are needed to determine whether these changes in the excretion of GAG components persist.

Sodium pentosan polysulphate--a novel inhibitor of urinary risk factors and enzymes in experimental urolithiatic rats

Sodium pentosan polysulphate (SPP) has been shown to inhibit calcium oxalate crystallization in vitro. Here, the effect of SPP was studied on in vivo crystallization. Ammonium oxalate was used as the inducer of calcium oxalate crystallization in rats and the effect of SPP on in vivo crystallization factor is reported. The increased excretions of stone forming constituents associated with urinary marker enzymes are the salient features observed in experimental rats. Sodium pentosan polysulphate administration brought about a significant reduction in urinary stone forming constituents. It also decreased the extent of renal tubular damage as evidenced from the reduced level of marker enzymes in urine. These observations highlight the inhibitory capacity of SPP against in vivo calcium oxalate crystallization.

Changes in the surface conditioning of calcium-salt crystals treated with physiological and alkaline urine

OBJECTIVE

To study, using an in vitro model, the early phases of deposition of urinary components onto the surface of calcium-salt crystals treated with physiological and alkaline urine.

MATERIALS AND METHODS

Calcium carbonate, oxalate and phosphate crystals were incubated in either freshly collected 'physiological' urine (pH 5.5) or with urine at pH 8.0. The surface conditioning was characterized using sodium-dodecyl sulphate-polyacrylamide gel electrophoresis immunoblot profiles of the adsorbed proteins and by Fourier transform infrared spectroscopy. Crystal morphology and aggregation were assessed using scanning electron microscopy.

RESULTS

The patterns of protein adsorption from physiological urine showed the ubiquitous adsorption of bands within 51-86 kDa, while Tamm-Horsfall protein (THP) and alpha 1-microglobulin were found only in calcium oxalate crystals. Less aggregation was detected in calcium oxalate and phosphate crystals treated in urine at pH 5.5, while a new crystalline phase was deposited on calcium carbonate surfaces. Incubation in alkaline urine led to changes in the protein electrophoretic profiles, with a significant variation in the morphology of the inorganic phase only in calcium phosphate crystals.

CONCLUSIONS

The binding of urinary proteins onto crystals depends on the chemistry of the surface and on the physicochemical composition of the urine. THP, albumin, alpha 1-microglobulin and a 20 kDa protein were able to bind calcium crystals under different circumstances. Except for THP, there was no clear relationship between the adsorption of proteins on crystals and the re-arrangement of the inorganic phase.

Extracorporeal shock wave lithotripsy and glycosaminoglycans in urine

In 50 calcium oxalate stone-forming patients, the total excretion of glycosaminoglycans (GAGs) and of four of its subgroups [chondroitin-4-sulfate (CS-A), chondroitin-6-sulfate (CS-C), dermatan sulfate (DS), and hyaluronic acid (HY)] were investigated before ESWL and on the following 5 days. The standard value was determined by reference to a group of healthy test subjects. The excretion of GAGs was significantly higher in healthy test persons than in stone-forming patients. Twenty-four hours after ESWL, GAG excretion increased significantly but returned to normal values in the course of three days. ESWL had no influence on the proportional composition of GAG subgroups CS-A, CS-C, DS and HY. The increase in GAG excretion after ESWL indicates a transient injury of renal tissue and of the mucous layer lining the urothelium, respectively. This lesion, however, can be regarded as temporary with restitutio ad integrum later.

Extracorporeal Shock Wave Lithotripsy and Glycosaminoglycans in Urine

In 50 calcium-oxalate stone-forming patients, the total excretion of glycosaminoglycans (GAGs) and four of its subgroups [chondroitin-4-sulfate (CS-A), chondroitin-6-sulfate (CS-C), dermatan sulfate (DS), and hyaluronic acid (HY)] was investigated before ESWL and in the following 5 days. The standard value was determined by reference to a group of healthy test subjects. The excretion of GAGs was significantly higher in healthy test persons than in stone-forming patients. Twenty-four hours after ESWL administration, GAG excretion enhanced significantly but returned to normal values in the course of three days. ESWL had no influence on the proportional composition of GAG subgroups CS-A, CS-C, DS and HY. The increase in GAG excretion after ESWL indicates a transient injury of renal tissue, i.e. of the mucus layer lining the urothelium. This lesion, however, can be regarded as temporary with later restitutio ad integrum.

Glycosaminoglycans in urine and extracorporeal shock wave lithotripsy

In 50 calcium oxalate stone-forming patients, the total excretion of glycosaminoglycans (GAGs) and of four subgroups [chondroitin-4-sulfate (CS-A), chondroitin-6-sulfate (CS-C), dermatan sulfate (DS) and hyaluronic acid (HY)] were investigated before extracorporeal shock wave lithotripsy (ESWL) and during the subsequent 5 days. The standard value was determined by reference to a group of healthy test subjects. The excretion of GAGs was significantly higher in healthy test persons than in stone-forming patients. Twenty-four hours after ESWL administration, GAG excretion was enhanced significantly but returned to normal values over the course of 3 days. ESWL had no influence on the proportional composition of GAG subgroups CS-A, CS-C, DS and HY. The increase in GAG excretion after ESWL indicates a transient injury of renal tissue or of the mucus layer lining the urothelium. This lesion, however, can be regarded as temporary with later restitutio ad integrum.

Calcium oxalate crystal interaction with renal tubular epithelium, mechanism of crystal adhesion and its impact on stone development

The interaction between renal epithelial cells and calcium oxalate (CaOx) crystals and/or oxalate ions plays a critical role in the formation of urinary stones. Epithelial cells respond to hyperoxaluria and the presence of CaOx crystals in the kidneys by increased enzymuria and internalization of the crystals. Crystal cell interaction results in movement of crystals from the luminal to the basolateral side between the cells and the basement membrane. Once beneath the epithelium, crystals adhere to the basement membrane and become anchored inside the kidneys. Crystals anchored to basement membrane of the peripheral collecting duct aggregate with other crystals and move through an eroding epithelium to the papillary surface, furnishing an encrustation platform or a nidus for future development of a kidney stone. Thus interaction between renal epithelial cells and CaOx crystals and/or oxalate ions is an essential element in the development of urinary stone disease.