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 μmol/g kidney (P < 0.01) and 20.11 ± 4.60 to 11.83 ± 3.54 μmol/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 LD₅₀ 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.