Attenuation of oxalate-induced nephrotoxicity by eicosapentaenoate-lipoate (EPA-LA) derivative in experimental rat model

Omega-3 fatty acids eicosapentaenoic acid and docosahexaenoic acid in the management of hypercalciuric stone formers

OBJECTIVE

To investigate the use of fish oil in the dietary management of hypercalciuric stone formers. Prostaglandins have been linked to urinary calcium excretion, suggesting a role for omega-3 fatty acids in the treatment of hypercalciuric urolithiasis.

METHODS

We retrospectively studied a cohort of patients treated at our stone clinics from July 2007 to February 2009. Patients' urinary risk factors for stone disease were evaluated with pre- and post-intervention 24-hour urine collections. All patients received empiric dietary recommendations for intake of fluids, sodium, protein, and citric juices. All subjects with hypercalciuria (urinary calcium>250 mg/d for males or >200 mg/d for females) on at least two 24-hour urine collections were counseled to supplement their diet with fish oil (1200 mg/d).

RESULTS

Twenty-nine patients were followed for 9.86±8.96 months. The mean age was 43.38±13.78 years. Urinary calcium levels decreased in 52% of patients, with 24% converting to normocalciuria. The average urinary calcium (mg/d) decreased significantly from baseline (329.27±96.23 to 247.47±84.53, P<.0001). Urinary oxalate excretion decreased in 34% of patients. The average urinary oxalate (mg/d) decreased significantly from baseline (45.40±9.90 to 32.9±8.21, P=.0004). Urinary citrate (mg/d) increased in 62% of subjects from baseline (731.67±279.09 to 940.22±437.54, P=.0005). Calcium oxalate supersaturation decreased in 38% of the subjects significantly from baseline (9.73±4.48 to 3.68±1.76, P=.001).

CONCLUSION

Omega-3 fatty acids combined with empiric dietary counseling results in a measurable decrease in urinary calcium and oxalate excretion and an increase in urinary citrate in hypercalciuric stone formers.

Cats and Calcium Oxalate

Practical relevance Calcium oxalate (CaOx) containing stones are among the most common of the urinary tract stones identified in cats.

Risk factors Risk factors for CaOx stone formation include such things as breed, gender and diet; stress and obesity have also been hypothesized to be risk factors for this disease.

Management approach A tailored, individual management strategy for preventing CaOx stone recurrence is important and should include addressing the diet, environment and any other comorbid conditions present. Increasing the cat's moisture intake is one of the key mechanisms for preventing recurrence.

Clinical challenges CaOx ureterolithiasis has emerged as a difficult and sometimes life-threatening problem for cats. In those cats where stones are found incidentally, periodic monitoring may be required to assess for disease progression. Interventional procedures such as ureteral stent placements are now increasingly being performed for recurrent cases or those with larger stone burdens. Periodic radiographs for more severe cases and frequent client communication can help ensure successful outcomes for cats with lower and upper CaOx stone disease.

Evidence base Limited evidence-based studies are published regarding management of feline upper and lower urinary tract CaOx stone disease, making this a difficult condition to manage in some cats. Studies designed to evaluate the relationship to dietary modifications, medical management, stress, obesity and surgical techniques are warranted in cats with upper and lower urinary tract CaOx stones.

Zinc disc implantation model of urinary bladder calculi and humane endpoints

The zinc disc implantation-induced urinary bladder calculi model in the rat is commonly used for preclinical evaluation of the antiurolithiatic activity of test compounds. Certain published reports state that relatively long durations for which zinc discs must be implanted in the bladders of rats. Hence, there is a need to refine this model. These investigations aimed to determine whether long-term studies using the zinc disc implantation model provide any additional data that affect the final outcomes of the study. In this study, we evaluated the effects of a well-known antiurolithiatic polyherbal drug, Cystone, for different treatment durations of 10, 20 and 48 days postimplantation. Our results indicate that even the shortest duration of 10 days is sufficient to reveal antiurolithiatic effects of a test drug. Hence, in the zinc disc implantation-induced urinary bladder calculi model, the study duration is proposed to be minimized so as to reduce the distress caused to the rats due to long-term exposure to the implant. Further, it is suggested that the growth of the bladder calculi can be monitored by taking X-ray radiographs of the bladder deposits to decide the time to terminate the study. Use of preformed calcium oxalate crystal instead of zinc discs, as suggested in earlier reports by others, may also be considered to avoid the sacrifice of rats at the end of the study.

Oxidative renal injury and lipoprotein oxidation in hypercholesterolemic atherogenesis: Role of eicosapentaenoate-lipoate (EPA-LA) derivative

Hypercholesterolemia, an independent risk factor for increased oxidative renal injury, is associated with the formation of oxidized low-density lipoprotein. Production of reactive oxygen species and nitrogen species have been implicated in diet-induced hypercholesterolemia, principally as means of oxidising low-density lipoproteins. This in turn initiates the accumulation of cholesterol in macrophages, which sets key event in the initiation of atherosclerosis. The aim of the present work is to evaluate the effects of eicosapentaenoic acid (EPA), DL alpha-lipoic acid (LA) and eicosapentaenoate-lipoate derivative (EPA-LA) in controlling the atherogenic disturbances. Four groups of male Wistar rats were fed with a high cholesterol diet (rat chow supplemented with 4% cholesterol and 1% cholic acid; HCD) for 30 days. Among them, 3 groups of rats were treated with either EPA (35 mg/kg body weight/day, oral gavage), LA (20 mg/kg body weight/day, oral gavage) or EPA-LA derivative (50 mg/kg body weight/day, oral gavage) from 16th day to 30th day of the experimental period. Abnormal increase in the levels of reactive oxygen species, 3-nitrotyrosine, malondialdehyde and protein carbonyl as well as an elevation in the activities of xanthine oxidase, lactate dehydrogenase, alkaline phosphatase and acid phosphatase was observed in renal tissue of HCD fed rats. HCD fed rats also showed an increased susceptibility of the apo B-containing lipoproteins to in vitro oxidation. These changes were restored partially in the EPA and LA administered groups. However, the combined derivative EPA-LA almost ameliorated the hypercholesterolemic-oxidative changes in the HCD fed rats.

Oxalate is toxic to renal tubular cells only at supraphysiologic concentrations

BACKGROUND

Oxalate-induced tissue damage may play an initiating role in the pathophysiology of calcium oxalate nephrolithiasis. The concentration of oxalate is higher in the renal collecting ducts ( approximately 0.1 to 0.5 mmol/L) than in the proximal tubule ( approximately 0.002 to 0.1 mmol/L). In the present investigation, we studied the damaging effect of oxalate to renal proximal and collecting tubule cells in culture.

METHODS

Studies were performed with the renal proximal tubular cell lines, LLC-PK1 and Madin Darby canine kidney II (MDCK-II), and the renal collecting duct cell lines, rat renal cortical collecting duct (RCCD1) and MDCK-I. Confluent monolayers cultured on permeable growth substrates in a two-compartment culture system were apically exposed for 24 hours to relatively low (0.2, 0.5, and 1.0 mmol/L) and high (5 and 10 mmol/L) oxalate concentrations, after which several cellular responses were studied, including monolayer morphology (confocal microscopy), transepithelial electrical resistances (TER), prostaglandin E(2) (PGE(2)) secretion, lactate dehydrogenase (LDH) release, DNA synthesis ([(3)H]-thymidine incorporation), total cell numbers, reactive oxygen species (H(2)O(2)) generation, apoptotic (annexin V and DNA fragmentation), and necrotic (propidium iodide influx) cell death.

RESULTS

Visible morphologic alterations were observed only at high oxalate concentrations. TER was concentration-dependently decreased by high, but not by low, oxalate. Elevated levels of PGE(2), LDH, and H(2)O(2) were measured in both cell types after exposure to high, but not to low oxalate. Exposure to high oxalate resulted in elevated levels of DNA synthesis with decreasing total cell numbers. High, but not low, oxalate induced necrotic cell death without signs of programmed cell death.

CONCLUSION

This study shows that oxalate is toxic to renal tubular cells, but only at supraphysiologic concentrations.

Mitigation of free radical toxicity in hyperoxaluric condition by a novel derivative eicosapentaenoate-lipoate

Lipoic acid (LA) and eicosapentaenoic acid (EPA) have been shown to ameliorate the changes associated with hyperoxaluria. This prompted us to study the effect of EPA-LA, a new derivative, in experimental urolithiatic condition. Foreign body implantation method followed by supplementation of ammonium oxalate was adopted to induce stone formation in the bladder. Significant depletion in the antioxidant status was observed in the kidney and bladder of stone-forming animals, associated with increased lipid peroxidation. The present observations provide supporting evidence to the hypothesis that free radicals might be involved in causing toxicity in hyperoxaluric condition. The three drugs, namely LA, EPA and EPA-LA had reversed the above changes, but the effect was more pronounced in EPA-LA-treated stone formers. These features highlight the beneficial effect of EPA-LA wherein the potency of two drugs has been combined. The practical outcome of these findings is that the cellular antioxidant defence can be increased by the supplementation of lipoate and its derivative EPA-LA.