The effect of verapamil and thiazide in the prevention of renal stone formation

Renal oxidative vulnerability due to changes in mitochondrial-glutathione and energy homeostasis in a rat model of calcium oxalate urolithiasis

Calcium oxalate monohydrate (COM) crystals are the commonest component of kidney stones. Oxalate and COM crystals in renal cells are thought to contribute to pathology via prooxidant events. Using an in vivo rat model of crystalluria induced by hyperoxaluria plus hypercalciuria [ethylene glycol (EG) plus 1,25-dihydroxycholecalciferol (DHC)], we measured glutathione and energy homeostasis of kidney mitochondria. Hyperoxaluria or hypercalciuria without crystalluria was also investigated. After 1–3 wk of treatment, kidney cryosections were analyzed by light microscopy. In kidney subcellular fractions, glutathione and antioxidant enzymes were measured. In mitochondria, oxygen consumption and superoxide formation as well as cytochrome c content were measured. EG plus DHC treatment increased formation of renal birefringent crystal. Histology revealed increased renal tubular pathology characterized by obstruction, distension, and interstitial inflammation. Crystalluria at all time points led to oxidative stress manifest as decreased cytosolic and mitochondrial glutathione and increased activity of the antioxidant enzymes glutathione reductase and -peroxidase (mitochondria) and glucose-6-phosphate dehydrogenase (cytosol). These changes were followed by a significant decrease in mitochondrial cytochrome c content at 2–3 wk, suggesting the involvement of apoptosis in the renal pathology. Mitochondrial oxygen consumption was severely impaired in the crystalluria group without increased mitochondrial superoxide formation. Some of these changes were also evident in hyperoxaluria at week 1 but were absent at later times and in all calciuric groups. Our data indicate that impaired electron flow did not cause superoxide formation; however, mitochondrial dysfunction contributes to pathological events when tubular crystal-cell interactions are uncontrolled, as in kidney stones disease.

Stone formation in genetic hypercalciuric rats

Our genetic hypercalciuric (GH) rats have been selected and inbred for 29 generations to maximize urine calcium (UCa) excretion compared to identical gender controls (Ctl). To determine the effect of the increased UCa on urinary supersaturation and stone formation, we pair fed 15 GH and 15 Ctl rats a standard 1.2% calcium diet for 18 weeks, measured urine supersaturation every two weeks, and examined the urinary tract of 1/3 of the rats for the presence of stones every six weeks. Any stones formed were studied by SEM, X-ray and electron diffraction and X-ray microanalysis. Over the entire study UCa was increased in the GH compared to Ctl, resulting in greater supersaturation with respect to calcium hydrogen phosphate (CaHPO4) at all times and calcium oxalate (CaOx) at most times. There was a progressive increase in the incidence of stone formation in GH rats with one of five rats having stones at six weeks, three of five with stones at 12 weeks and five of five with stones at 18 weeks. There were no stones formed in Ctl rats. SEM reveals discrete stones and not nephrocalcinosis. X-ray and electron diffraction and X-ray microanalysis reveal the stones to be poorly crystalline apatite which is a solid phase of calcium and phosphate. Compared to Ctl, in the GH rats the saturation ratio for CaHPO4 increased proportionally more than that for CaOx, perhaps explaining why the rats formed apatite and not oxalate stones. This is the first description of an animal model of spontaneous nephrolithiasis.

Uninephrectomy enhances urolithiasis in ethylene glycol treated rats

Uninephrectomy (uNX) usually induces compensatory hyperfunction of the remaining kidney in an attempt to preserve the homeostasis of body fluid composition. The present study used uninephrectomized Sprague-Dawley rats on a lithogenic diet (0.5% ethylene glycol, EG) to evaluate the influence on urinary stone formation and calcium oxalate crystal deposition of compensatory excretion of lithogenic substances in the remnant kidney. The results showed that there were no urinary stones or calcium oxalate crystal deposits in the intact or uNX rats fed a normal diet. In the EG feeding groups, the incidence of massive (grade 3) crystal deposits was significantly higher in the uNX rats (87.5%) than that in the intact rats (37.5%; P less than 0.05). The incidence of urinary stone formation was also higher in the uNX rats as compared to that of the intact rats, although the difference did not achieve statistical significance. The serum magnesium, phosphorus and creatinine increased significantly, whereas creatinine clearance (CCr), 24-hour urinary excretions of citrate, sodium, potassium and chloride decreased significantly in the uNX rats fed EG. These data indicate that uninephrectomy increases the vulnerability of the contralateral remnant kidney to urolithiasis and crystal deposition when the lithogenic risk factors are present. Furthermore, once the remnant kidney forms urolithiasis or massive calcium oxalate crystal deposits, the renal function is severely compromised.