Effects of oxalate on the re-initiation of DNA synthesis in LLC-PK1 cells do not involve p42/44 MAP kinase activation.
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BACKGROUND: Oxalate interaction with renal epithelial cells results in a program of events that include alterations in gene expression, re-initiation of DNA synthesis, cell growth and apoptosis. Our studies focused on understanding the mechanisms involved in the oxalate-induced re-initiation of the DNA synthesis. The effects of oxalate alone or in combination with epidermal growth factor (EGF), platelet-derived growth factor (PDGF) and insulin were investigated to determine whether oxalate utilized the p42/44 mitogen activated protein (MAP) kinase pathway, which is a common pathway used by a majority of the mitogens. METHODS: LLC-PK1 cells (a renal epithelial cell line of porcine origin) were exposed to oxalate in the presence or absence of three established growth factors, EGF, insulin and PDGF, and of the transcription/translation inhibitors, actinomycin-D and cycloheximide. DNA synthesis was assessed by [3H]-thymidine incorporation. p42/44 MAP kinase activity was assessed by super-shift analysis as well as by immunocomplex kinase assay. RESULTS: Exposure of growth-arrested LLC-PK1 cells to oxalate resulted in the re-initiation of the DNA synthesis was abolished by [corrected] pretreatment with transcription/translation inhibitors. Oxalate (1 mmol/L), EGF (50 ng/mL) and insulin (100 ng/mL) stimulated DNA synthesis in growth-arrested LLC-PK1 cells, while PDGF (50 ng/mL) had no effect. Effects of EGF and oxalate on DNA synthesis were additive. In contrast, oxalate and insulin had antagonistic effects on DNA synthesis. Additionally, oxalate did not activate the p42/44 MAP kinase pathway while EGF stimulated this pathway. CONCLUSIONS: These findings demonstrate that oxalate does not activate the p42/44 MAP kinase pathway, and the effects of oxalate are mediated by pathways that are distinct from those of EGF, PDGF and insulin. (+info)
Calcium oxalate stone formation in genetic hypercalciuric stone-forming rats.
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BACKGROUND: Over 54 generations, we have successfully bred a strain of rats that maximizes urinary calcium excretion. The rats now consistently excrete 8 to 10 times as much calcium as controls, uniformly form poorly crystalline calcium phosphate kidney stones, and are termed genetic hypercalciuric stone-forming (GHS) rats. These rats were used to test the hypothesis that increasing urinary oxalate excretion would not only increase the supersaturation with respect to the calcium oxalate solid phase, but also would increase the ratio of calcium oxalate-to-calcium phosphate supersaturation and result in calcium oxalate stone formation. METHODS: To increase urine oxalate excretion an oxalate precursor, hydroxyproline, was added to the diet of male GHS rats. The GHS rats were fed a standard 1.2% calcium diet alone or with 1%, 3% or 5% trans-4-hydroxy-l-proline (hydroxyproline). RESULTS: The addition of 1% hydroxyproline to the diet of GHS rats led to an increase in urinary oxalate excretion, which did not increase further with the provision of additional hydroxyproline. The addition of 1% and 3% hydroxyproline did not alter calcium excretion while the provision of 5% hydroxyproline led to a decrease in urine calcium excretion. The addition of 1% hydroxyproline led to an increase in urinary calcium oxalate supersaturation, which did not further increase with additional hydroxyproline. The addition of 1% and 3% hydroxyproline did not alter urinary supersaturation with respect to calcium hydrogen phosphate while the addition of 5% hydroxyproline tended to lower this supersaturation. Compared to rats fed the control and the 3% hydroxyproline diet the addition of 5% hydroxyproline increased the ratio of calcium oxalate supersaturation to calcium phosphate supersaturation. Virtually all rats formed stones. In the control and 1% hydroxyproline group, all of the stones were composed of calcium and phosphate (apatite), in the 3% hydroxyproline group the stones were a mixture of apatite and calcium oxalate, while in the 5% hydroxyproline group all of the stones were calcium oxalate. CONCLUSIONS: The provision of additional dietary hydroxyproline to GHS rats increases urinary oxalate excretion, calcium oxalate supersaturation and the ratio of calcium oxalate-to-calcium phosphate supersaturation, resulting in the formation of calcium oxalate kidney stones. Thus, with the addition of a common amino acid, the GHS rats now not only model the most common metabolic abnormality found in patients with nephrolithiasis, hypercalciuria, but form the most common type of kidney stone, calcium oxalate. (+info)
Studies on the pathophysiology of the low urine pH in patients with uric acid stones.
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BACKGROUND: A very low urine pH is the major risk factor for uric acid stone formation. METHODS: A subgroup of patients with a history of uric acid stones and a persistently low urine pH (<5.5 for at least 12 h/day) were selected for detailed study. Based on their relative ammonium (NH(+)(4)) and sulfate (SO(2-)(4)) excretions, patients were divided into two groups. RESULTS: The first group (N = 2) excreted 173 and 139% more NH(+)(4) than SO(2-)(4). Their daily urinary unmeasured anion excretion was higher than their calculated net diet alkali input (38 and 61 vs. 24 and 49 mEq, respectively). In the second group (N = 12), NH(+)(4) excretion was 69 +/- 5% that of SO(2-)(4). In 2 of 12, decreased renal ammoniagenesis was suspected due to a plasma potassium of 5.3 mmol/L and/or a lower GFR (65 and 59 L/day); these patients had an extremely low citrate excretion (3 and 1 mEq/day). In contrast, citrate excretion was not low in the remaining 10 patients (10.4 +/- 1.3 mEq/day). CONCLUSIONS: Patients in group 1 needed a higher NH(+)(4) excretion possibly because of a H+ load from excessive renal excretion of organic anions. We speculate that an alkaline proximal tubular cell pH could be the basis for the low NH(+)(4) and high citrate excretions in 10 of 12 patients in group 2. Dietary factors and/or a molecular lesion may contribute to their pathophysiology. (+info)
FKBP-12 exhibits an inhibitory activity on calcium oxalate crystal growth in vitro.
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Urolithiasis and calcium oxalate crystal deposition diseases are still significant medical problems. In the course of nephrocalcin cDNA cloning, we have identified FKBP-12 as an inhibitory molecule of calcium oxalate crystal growth. lambdagt 11 cDNA libraries were constructed from renal carcinoma tissues and screened for nephrocalcin cDNA clones using anti-nephrocalcin antibody as a probe. Clones expressing recombinant proteins, which appeared to be antigenically cross-reactive to nephrocalcin, were isolated and their DNA sequences and inhibitory activities on the calcium oxalate crystal growth were determined. One of the clone lambda gt 11 #31-1 had a partial fragment (80 bp) of FKBP-12 cDNA as an insert. Therefore, a full-length FKBP-12 cDNA was PCR-cloned from the lambda gt 11 renal carcinoma cDNA library and was subcloned into an expression vector. The resultant recombinant FKBP-12 exhibited an inhibitory activity on the calcium oxalate crystal growth (Kd=10(-7) M). Physiological effect of the extracellular FKBP-12 was investigated in terms of macrophage activation and proinflammatory cytokine gene induction. Extracellular FKBP-12 failed to activate macrophages even at high concentrations. FKBP-12 seems an anti-stone molecule for the oxalate crystal deposition disease and recurrent stone diseases. (+info)
A new operative fiberpyeloscope.
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Operative pyeloscopes developed up to now have been of limited effectivness because of an inadequate visual field and difficulties in handling procedure. The author has made up a flexible fiber pyeloscope with which it is possible to extract renal pelvic and caliceal stones easily. This pyeloscope has the following specifications: effective length, 630 mm; diameter, 8.5 mm; field of vision, 60 degrees. In addition, the tip of the scope can be deflected 90 degrees up or down from the basic position with a hand manipulated angle deflector knob on the scope grip. This allows the inside of the renal pelvis to be observed clearly from every direction. Through the channel of the scope, specially designed stone grasping forceps can be inserted into the renal pelvis, and it is possible to grasp renal pelvic stones under direct observation. The fiberpyeloscope has been used in 2 cases of renal pelvic stones, in which the pelvis was exposed by subcostal flank incision. The stones were successfully extracted with the scope which was introduced through a small incision on the renal pelvis. (+info)
Acute hyperuricemic nephropathy in rats. An electron microscopic study.
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Hyperuricemia and uricosuria were induced in rats fed uric acid and oxonic acid. Kidneys then were studied by light and electron microscopy. After 1 day of hyperuricemia, animals had deposits of uric acid and urate crystals within collecting tubules of the renal papillae, and tubular cells were altered. By 10 days, there was an exudative response with further injury to epithelium. Clear spaces within lumens, epithelium, and neutrophils suggested the presence of crystals; however, there was no direct ultrastructural evidence that neutrophils or epithelial cells ingested crystals and suffered injury. Presumably, crystals readily seen in frozen, unfixed tissue were lost during preparation for electron microscopy. Nonetheless, the ultrastructural findings indicated that hyperuricemic nephropathy was initiated in a fashion analogous to urate arthropathy. Urate crystals formed within collecting tubules, epithelial cells were altered, and most likely there was chemotaxis of neutrophils which underwent degranulation and vacuolation followed by lysis freeing any ingested urate. Release of ingested crystals plus precipitation of new crystals both might serve to sustain the nephritis. (+info)
Effect of calcium intake on urinary oxalate excretion in calcium stone-forming patients.
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Dietary calcium lowers the risk of nephrolithiasis due to a decreased absorption of dietary oxalate that is bound by intestinal calcium. The aim of the present study was to evaluate oxaluria in normocalciuric and hypercalciuric lithiasic patients under different calcium intake. Fifty patients (26 females and 24 males, 41 +/- 10 years old), whose 4-day dietary records revealed a regular low calcium intake (+info)
Primary hyperoxaluria: a rare but important cause of nephrolithiasis.
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We report on a middle-aged man with end-stage renal failure apparently secondary to recurrent renal stones. He developed systemic oxalosis soon after commencing dialysis. The diagnosis of primary hyperoxaluria type 1 was supported by the finding of high dialysate glycolate excretion. The patient subsequently received an isolated cadaveric renal transplant, but the outcome was a rapid recurrence of oxalosis and early graft failure. Although isolated liver or renal transplantation in addition to various adjuvant measures may be considered in the early stage, combined liver-kidney transplantation remains the only definitive therapy for a patient with end-stage renal failure and systemic oxalosis due to hyperoxaluria type 1. This case illustrates the possible late presentation of primary hyperoxaluria type 1 and the poor outcome with isolated renal transplantation after the development of systemic oxalosis. One should thus have a high index of suspicion in patients with recurrent renal stones of this rare, but nevertheless important, entity. (+info)