Glycosaminoglycans and semisynthetic sulfated polysaccharides: an overview of their potential application in treatment of patients with urolithiasis

Influence of nutrition on feline calcium oxalate urolithiasis with emphasis on endogenous oxalate synthesis

The prevalence of calcium oxalate (CaOx) uroliths detected in cats with lower urinary tract disease has shown a sharp increase over the last decades with a concomitant reciprocal decrease in the occurrence of struvite (magnesium ammonium phosphate) uroliths. CaOx stone-preventative diets are available nowadays, but seem to be marginally effective, as CaOx urolith recurrence occurs in patients fed these diets. In order to improve the preventative measures against CaOx urolithiasis, it is important to understand its aetiopathogenesis. The main research focus in CaOx formation in cats has been on the role of Ca, whereas little research effort has been directed towards the role and origin of urinary oxalates. As in man, the exogenous origin of urinary oxalates in cats is thought to be of minor importance, although the precise contribution of dietary oxalates remains unclear. The generally accepted dietary risk factors for CaOx urolithiasis in cats are discussed and a model for the biosynthetic pathways of oxalate in feline liver is provided. Alanine:glyoxylate aminotransferase 1 (AGT1) in endogenous oxalate metabolism is a liver-specific enzyme targeted in the mitochondria in cats, and allows for efficient conversion of glyoxylate to glycine when fed a carnivorous diet. The low peroxisomal activity of AGT1 in cat liver is compatible with the view that felids utilised a low-carbohydrate diet throughout evolution. Future research should focus on understanding de novo biosynthesis of oxalate in cats and their adaptation(s) in oxalate metabolism, and on dietary oxalate intake and absorption by cats.

Urinary glycosaminoglycans as biomarker for urothelial injury: is it possible to discriminate damage from recovery?

OBJECTIVES

The glycosaminoglycan (GAG) layer is referred to as a bladder protective factor. We reproduced an experimental model of urothelial damage to assess GAG metabolism in the process of injury and recovery of the urothelium.

METHODS

Wistar female rats were bladder catheterized and instilled with either protamine sulfate (PS groups) or sterile saline (control groups). At different days after the procedure, 24-hour urine samples were obtained. The urinary levels of hyaluronic acid (HA) and sulfated glycosaminoglycan were determined in all groups and in nonmanipulated rats (day 0). Additionally, sulfated-GAG synthesis was assessed by the incorporation of [(35)S]-inorganic sulfate. The bladders were analyzed by histochemical staining for HA and immunofluorescence for heparin sulfate and syndecan-4.

RESULTS

Urinary HA and sulfated-GAG were elevated after PS injection (P <0.05). A greater concentration of [(35)S]-labeled GAG in the PS group animals on the fifth day and, especially, on the seventh day represented increased GAG synthesis at these periods (P <0.05). Bladder sections from the PS group animals on day 1 showed a greater amount of HA in the urothelium. PS instillation damaged the urothelium layer of heparin sulfate and syndecan-4 seen in the control animals. On day 5, patchy areas of a restored layer were seen, and, on day 7, this layer had completely regenerated.

CONCLUSIONS

Urinary GAG cannot differentiate urothelial damage from recovery. Elevated levels of urinary GAG can result from either desquamation of the surface cell GAG layer or increased GAG synthesis to regenerate the damaged urothelium.

Effects of low-molecular-weight polyguluronate sulfate on experimental urolithiasis in rats

Urinary macromolecules, especially glycosaminoglycans (GAGs), have attracted great interest as promising inhibitors of urinary stone formation. As an analogue of GAGs, low-molecular-weight polyguluronate sulfate (LPGS) with strong polyanionic nature was prepared by chemical modification of brown algae extract. The effects of LPGS both on ethylene glycol-induced nephrolithiasis and Zinc disc implant-induced urinary bladder stone formation in Wistar rats were evaluated, and its acute toxicity in Kunming mice and Wistar rats were also investigated. The contents of renal oxalate and calcium in ethylene glycol-induced nephrolithiasic rats were decreased significantly from 5.01 +/- 0.96 to 3.26 +/- 1.31 mumol/g kidney (P < 0.01) and 20.11 +/- 4.60 to 11.83 +/- 3.54 mumol/g kidney (P < 0.01), respectively, after oral administration of LPGS at dose-level of 100 mg/kg. The renal crystal depositions and histopathological changes were reduced also. The formation of zinc disc implant-induced urinary bladder stones in rats was inhibited considerably after oral administration of LPGS at dose-levels of 50 mg/kg (P < 0.05) and 100 mg/kg (P < 0.01). The intravenous LD(50) and the oral maximum tolerance value of LPGS in mice are 6.29 and 25 g/kg, and in rats are 2.25 and 10 g/kg, respectively. These data show that LPGS has significant prevention effects both on nephrolithiasis and urinary bladder stone formation in rats, and negligible oral toxicity both in mice and rats. LPGS is a safe and promising drug candidate for the prevention of urolithiasis.

Physico-chemical alterations of urine in experimental hyperoxaluria: a biochemical approach with fucoidan

Urinary supersaturation-induced crystal formation has been attributed as one of the key factor for the pathogenesis/progression of lithogenesis. This study was aimed at investigating whether fucoidan, a naturally occurring sulfated glycosaminoglycan, could ameliorate the biochemical changes in urine induced by stone formation. Two groups of male albino Wistar rats (120+/-20 g) received 0.75% ethylene glycol (EG) for 28 days to induce hyperoxaluria, and one of them received sulfated polysaccharides (fucoidan from Fucus vesiculosus, 5 mg kg(-1), s.c.), commencing from the 8(th) day of the experimental period. One group was maintained as normal control group and another group served as drug control, which received sulfated polysaccharides. The urine collected from all the groups was analysed for changes in pH, volume, oxalate, calcium, phosphorus, uric acid, magnesium, citric acid and glycosaminoglycans. Urinary crystals were analysed with a light microscope. Renal tissues were studied under polarized light for deposition of crystals and also analysed for their oxalate and calcium content. The changes in extracellular matrix on crystal deposition were also evaluated. The urinary pH and volume were altered in rats treated with EG along with an increase in weight of the kidney. Further, administration of EG to rats increased the supersaturation of urine by escalating the levels of the stone-forming constituents, such as oxalate, calcium, phosphorus and uric acid, which was completely restored by fucoidan treatment. The decrease in the inhibitors, like citrate, magnesium and glycosaminoglycans, in urine was prevented by the co-treatment with fucoidan. In hyperoxaluric rats, there was an increased excretion of calcium oxalate monohydrate crystals in urine along with crystal deposition in renal tissues; this was prevented by fucoidan treatment. Fucoidan administration reversed even the tissue levels of calcium and oxalate. The increased accumulation of collagen and expression of transforming growth factor-beta(1) in hyperoxaluria was normalized on fucoidan administration. These results suggest that the physico-chemical alterations in urine produced during hyperoxaluria can be reversed by fucoidan administration.

Encrustation of biomaterials in the urinary tract

This review considers the problem of the encrustation of biomaterials used for urinary prostheses. After a general discussion of the problem it deals with exciting new developments which may prove to be clinically applicable in preventing this costly and resource consuming complication. The widespread use of use of in vitro models which accurately simulate the conditions found in the human urinary tract will allow appropriate preliminary studies. Perhaps then clinical evaluation will be warranted.

Urinary glycosaminoglycans as risk factors for uric acid nephrolithiasis: case control study in a Sardinian genetic isolate

OBJECTIVES

To assess the clinical association between glycosaminoglycan (GAG) excretion and uric acid (UA) nephrolithiasis by measuring urinary GAG levels in a case-control study conducted in a Sardinian genetic isolate. Inhibitors of crystallization such as GAGs seem to be involved in kidney stone formation.

METHODS

Overnight (12-hour) urinary excretion of GAGs, calcium, oxalate, and UA were measured in urine samples from 60 patients who had formed at least one urinary stone (UA or mixed) and 52 healthy controls. The total GAG concentration was measured by a dye-binding assay, and the values were normalized against creatinine to obtain values in micrograms of GAG per milligram creatinine. Statistical analysis was performed using t tests and logistic regression analysis.

RESULTS

No significant difference was found between the two groups with respect to calcium and oxalate concentrations. Nonetheless, stone formers had significantly lower levels of GAGs (29.5 +/- 2.2 versus 36.4 +/- 3.9 microg/mg creatinine, P = 0.003) and greater levels of UA (385.11 +/- 38.2 versus 298.43 +/- 31.4 mg/12 hr, P = 0.0010) than did the normal controls.

CONCLUSIONS

We report that the lower excretion of GAGs in stone formers could impair their inhibitory activity on UA stone formation, and, as a consequence, it may represent a risk factor for this form of urolithiasis.

Clinical association with urinary glycosaminoglycans and urolithiasis

OBJECTIVES

To determine the clinical association between urinary glycosaminoglycan (GAG) concentration and kidney stone disease.

METHODS

Thirty-five patients (14 women and 21 men) with a history of stone disease and 37 controls (13 women and 24 men) were evaluated for urinary GAG concentration. By using a new dye-binding assay, the total GAG concentration in the urine was measured and corrected to urinary creatinine levels (micrograms of GAG per milligram creatinine).

RESULTS

The mean urinary GAG concentration in those with stones was significantly lower (31.5 +/- 2.6 microg GAG/mg creatinine) than in the controls (43.8 +/- 3.8 microg GAG/mg creatinine, P = 0.01). Male patients with stones also had a significantly lower mean GAG concentration (26.1 +/- 1.8) than did the female patients (39.6 +/- 5.3, P = 0.009). The mean GAG concentration between ureteral (n = 13) versus renal (n = 22), single (n = 19) versus multiple (n = 16), family history (n = 11) versus no family history (n = 24), large (n = 13) versus small (n = 20), and the presence (n = 22) versus absence (n = 13) of residual stones did not show any significant differences. However, patients with recurrent stone formation (n = 21) had significantly lower mean GAG levels (26.4 +/- 1.6) compared with those with single stone formation (n = 14; 39.2 +/- 5.5, P = 0.01).

CONCLUSIONS

Lower urinary GAG levels are more common in patients with stone formation. This may play a more determinant role in male patients and those with recurrent stone formation.

Metabolic evaluation of stone disease patients: a practical approach

In the last three decades, minimally invasive techniques have progressed significantly, replacing traditional open surgery as the mainstay of stone disease surgical treatment. The challenge for the next millennium remains medical prevention of calcium urolithiasis, a field where less dramatic progress has been achieved during the same period of time. The purpose of this article is to provide the practicing urologist with current practical guidelines for the assessment and management of calcium urolithiasis patients. The recommendations are based on the latest available information regarding the pathogenesis, medical treatment options, and decision-making rationale when managing these challenging patients. Every urolithiasis patient should undergo a basic evaluation, which is considered the minimal essential diagnostic work-up, in order to rule out obvious, treatable systemic causes of urinary stone disease. All patients should be advised about conservative nonspecific preventive measures. High-risk stone patients should have a more extensive metabolic evaluation based on two 24-hour urine samples. Treatment protocols for each patient are tailored individually according to the metabolic evaluation findings.

Crystal±macromolecule interactions in urolithiasis: lessons from healthy biomineralization systems

Recent advances in understanding the molecular level mechanisms that control biomineralization and organic-inorganic interactions in urolithiasis are reviewed, and the validity of drawing parallels between them are considered. The multifunctional nature of many biomineralization molecules, particularly proteins, and the different roles they play in and out of solution suggest avenues for resolving the apparent paradox that urinary macromolecules have been observed both to inhibit and to promote stone formation.