Experimental Induction of Calcium Oxalate Nephrolithiasis in Mice

Abstract

The availability of various transgenic and knockout mice provides an excellent opportunity to better understand the pathophysiology of calcium oxalate stone disease. However, attempts to produce calcium oxalate nephrolithiasis in mice have not been successful. We hypothesized that calcium oxalate nephrolithiasis in mice requires increasing urine calcium and oxalate excretion, and experimentally induced hyperoxaluria alone is not sufficient. To provide evidence we induced hyperoxaluria by administering hyperoxaluria inducing agents in normocalciuric and hypercalciuric mice, and investigating various aspects of nephrolithiasis. We administered ethylene glycol, glyoxylate or hydroxyl proline via diet in male and female normocalciuric B6 mice, and in hypercalciuric sodium phosphate co-transporter type 2 a -/- mice for 4 weeks. We collected 24-hour urine samples on days 0, 3, 7, 14, 21 and 28, and analyzed them for pH, creatinine, lactate dehydrogenase calcium and oxalate. Kidneys were examined using light microscopy. Urine was examined for crystals using light and scanning electron microscopy. Hypercalciuric mice on hydroxyl proline did not tolerate treatment and were sacrificed before 28 days. All mice on ethylene glycol, glyoxylate or hydroxyl proline became hyperoxaluric and showed calcium oxalate crystalluria. No female, normocalciuric or hypercalciuric mice showed renal calcium oxalate crystal deposits. Calcium oxalate nephrolithiasis developed in all mice on glyoxylate and in some on ethylene glycol. In all mice the kidneys showed epithelial injury. Male mice particularly on glyoxylate had more renal injury and inflammatory cell migration into the interstitium around the crystal deposits. Results confirm that hyperoxaluria induction alone is not sufficient to create calcium oxalate nephrolithiasis in mice. Hypercalciuria is also required. Kidneys in male mice are more prone to injury than those in female mice and are susceptible to calcium oxalate crystal deposition. Perhaps epithelial injury promotes crystal retention. Thus, calcium oxalate nephrolithiasis in mice is gender dependent, and requires hypercalciuria and hyperoxaluria.