Inhibition of Glycolate Oxidase With Dicer-substrate siRNA Reduces Calcium Oxalate Deposition in a Mouse Model of Primary Hyperoxaluria Type 1.

Primary hyperoxaluria type 1 (PH1) is an autosomal recessive, metabolic disorder caused by mutations of alanine-glyoxylate aminotransferase (AGT), a key hepatic enzyme in the detoxification of glyoxylate arising from multiple normal metabolic pathways to glycine. Accumulation of glyoxylate, a precursor of oxalate, leads to the overproduction of oxalate in the liver, which accumulates to high levels in kidneys and urine. Crystalization of calcium oxalate (CaOx) in the kidney ultimately results in renal failure. Currently, the only treatment effective in reduction of oxalate production in patients who do not respond to high-dose vitamin B6 therapy is a combined liver/kidney transplant. We explored an alternative approach to prevent glyoxylate production using Dicer-substrate small interfering RNAs (DsiRNAs) targeting hydroxyacid oxidase 1 (HAO1) mRNA which encodes glycolate oxidase (GO), to reduce the hepatic conversion of glycolate to glyoxylate. This approach efficiently reduces GO mRNA and protein in the livers of mice and nonhuman primates. Reduction of hepatic GO leads to normalization of urine oxalate levels and reduces CaOx deposition in a preclinical mouse model of PH1. Our results support the use of DsiRNA to reduce liver GO levels as a potential therapeutic approach to treat PH1.

Effect of sulphated polysaccharides on erythrocyte changes due to oxidative and nitrosative stress in experimental hyperoxaluria.

Kidney stones are known to haunt humanity for centuries and increase in oxalate is a predominant risk factor for stone formation. The present study was initiated with a notion to study the oxidative and nitrosative stress on erythrocytes under oxalate stress and the putative role of sulphated polysaccharides. Hyperoxaluria was induced in two groups by the administration of 0.75% ethylene glycol in drinking water for 28 days and one of them was treated with sulphated polysaccharides from Fucus vesiculosus from the 8th day to the end of the experimental period of 28 days at a dose of 5 mg/kg body weight subcutaneously. Control and drug control (sulphated polysaccharides alone) were also included in the study. Glycolic and glyoxylic acid levels of urine were analyzed as an index of hyperoxaluria. The plasma enzymic markers of cellular integrity, redox status of red blood cells, osmotic fragility, and (14)C-oxalate binding were investigated. Urine and plasma nitric oxide metabolites, expression of inducible nitric oxide synthase protein, and mRNA were assessed in kidney to evaluate the nitrosative stress. Increased levels of glycolic and glyoxylic acid in urine indicated the prevalence of hyperoxaluria in ethylene glycol-administered groups. Plasma aspartate and alanine transaminase were not altered, but alkaline phosphatase and lactate dehydrogenase of hyperoxaluric group were increased indicating tissue damage. Activities of antioxidant enzymes were decreased, whereas erythrocyte membrane lipid peroxidation was increased in hyperoxaluric rats. Moreover, an altered fragility with an increase in oxalate binding activity was observed in hyperoxaluric group. Increase in nitric oxide metabolites levels in urine and plasma along with an increase in expression of inducible nitric oxide synthase protein and mRNA in kidney were observed in hyperoxaluric rats. Administration of sulphated polysaccharides to hyperoxaluric rats averted the abnormal increase in urinary glycolic and glyoxylic acid levels and enzyme activities, decreased lipid peroxidation, and increased the activities of antioxidant enzymes. Furthermore, increased nitrosative stress accompanying hyperoxaluria was also normalized on sulphated polysaccharides treatment. To conclude, sulphated polysaccharide administration was able to maintain the integrity of erythrocyte membrane and decrease the damage to erythrocytes in hyperoxaluria.

Urinary oxalate, glycolate, glyoxylate, and citrate after acute intravenous administration of glyoxylate in rats.

BACKGROUND AND PURPOSE: Urinary oxalate plays an important role in the formation of calcium oxalate renal stones, and approximately 50% to 60% of urinary oxalate is derived from the endogenous metabolism of glyoxylate. Therefore, we measured urinary oxalate, glycolate, glyoxylate, and citrate concentrations after acute intravenous administration of various doses of glyoxylate in rats to study oxalate metabolism. MATERIALS AND METHODS: Male Wistar rats weighing approximately 200 g were divided into six groups of eight animals each. Anesthetized rats received glyoxylate (0, 1, 2, 5, 10, and 20 mg) intravenously. Urine specimens were collected before and every hour after each dose for 4 hours, and the concentrations of oxalate, glycolate, glyoxylate, and citrate were measured by capillary electrophoresis. RESULTS: Hourly oxalate excretion in the urine peaked at 1 hour after glyoxylate administration, and the peak concentration increased in a dose-dependent manner. Approximately 15% to 30% (mol/mol) of the dose was converted to oxalate within 4 hours and 2% to 4.6% was converted to glycolate. Urinary glyoxylate was not detectable before glyoxylate administration, but large doses resulted in a significant amount of glyoxylate (0.7%-2.3%) appearing in the urine, and the level peaked at 1 hour after administration. Urinary glycolate also peaked at 1 hour after administration of glyoxylate. The urinary citrate concentration generally decreased by 3% to 33% after each dose of glyoxylate, except that it increased slightly after the 20-mg dose. CONCLUSION: Administration of glyoxylate increased urinary oxalate and glycolate excretion in rats, supporting the importance of the glycolate-glyoxylate-oxalate pathway.

The influence of banana stem extract on urinary risk factors for stones in normal and hyperoxaluric rats.

OBJECTIVE: To study the effect of banana stem (Family Musaceae) extract on urinary risk factors in an animal model of hyperoxaluria. MATERIALS AND METHODS: Thirty male rats were divided into five groups of six rats each. The rats in Group I acted as the control, in Group II rats hyperoxaluria was induced using sodium glycollate, Group III were given aqueous banana stem extract alone, Group IV were given both sodium glycollate and aqueous banana stem extract and Group V were given sodium glycollate alone followed by aqueous banana stem extract. Urine analysis (24 h) was carried out to determine the levels of calcium, phosphorous, oxalate, glycollic acid and glyoxylic acid in each of the five groups. RESULTS: In the rats treated with aqueous banana stem extract, urinary oxalate excretion was significantly reduced when compared with the controls. The extract reduced urinary oxalate, glycollic and glyoxylic acid and phosphorus excretion in the hyperoxaluric rats. The extract appeared to have no effect on urinary calcium excretion. CONCLUSION: Banana stem extract from the Musaceae family may be a useful agent in the treatment of patients with hyperoxaluric urolithiasis.

Effect of dose on the metabolism of 1,1,2,2-tetrabromoethane in F344/N rats after gavage administration.

1,1,2,2-Tetrabromo[U-14C]ethane ([14C]TBE) was used to study the metabolism of TBE in rats. Three graded doses of TBE (1.17, 13.6, and 123 mg/kg; 1 microCi 14C/rat at each dose) were administered by gavage to three groups of four rats each. Excreta samples were collected at various time intervals up to 96 hr. Following euthanization, 14C activity was measured in the excreta, tissues, and carcass. The fraction of the dose exhaled as volatile metabolites of TBE, excluding 14CO2, was approximately 9-10% higher in rats given the high dose of TBE compared to that in rats given either the low or the medium dose. The fraction excreted in the urine decreased with increasing TBE dosage. 1,2-Dibromoethylene and tribromoethylene were identified as exhaled metabolites at the high dose. Three major urinary metabolites were identified: dibromoacetic acid, glyoxylic acid, and oxalic acid. The results of this study indicate that the metabolism of TBE was linear up to a dose of 13.6 mg/kg, but the contribution of various TBE metabolic pathways was different at a dose of 123 mg/kg.