Urine citrate and calcium in calcium nephrolithiasis

Urinary analysis of nephrolithiasis markers

Renal stone disease is an ancient and common affliction, common in industrialised nations. The causes and incidence of nephrolithiasis are presented. Afterwards, the promoters and inhibitors of renal stone formation analysis in urine are described including enzymatic methods, chromatography, capillary electrophoresis and other techniques. Aspects such as sample collection and storage are also included. The review article includes referenced tables that provide summaries of methodology for the analysis of nephrolithiasis related compounds.

Adhesion of uric acid crystals to the surface of renal epithelial cells

Adhesion of microcrystals that nucleate in tubular fluid to the apical surface of renal tubular cells could be a critical step in the formation of kidney stones, 12% of which contain uric acid (UA) either alone or admixed with calcium oxalates or calcium phosphates. UA crystals bind rapidly to monolayer cultures of monkey kidney epithelial cells (BSC-1 line), used to model the surface of the nephron, in a concentration-dependent manner. The urinary glycoproteins osteopontin, nephrocalcin, and Tamm-Horsfall glycoprotein had no effect on binding of UA crystals to the cell surface, whereas other polyanions including specific glycosaminoglycans blocked UA crystal adhesion. Specific polycations also inhibited adhesion of UA crystals and appeared to exert their inhibitory effect by coating cells. However, removal of anionic cell surface molecules with neuraminidase, heparitinase I, or chondroitinase ABC each increased UA crystal binding, and sialic acid-binding lectins had no effect. These observations suggest that hydrogen bonding and hydrophobic interactions play a major role in adhesion of electrostatically neutral UA crystals to renal cells, unlike the interaction of calcium-containing crystals with negatively charged molecules on the apical cell surface via ionic forces. After adhesion to the plasma membrane, subsequent cellular events could contribute to UA crystal retention in the kidney and the development of UA or mixed calcium and UA calculi.

Mechanisms involved in calcium oxalate endocytosis by Madin-Darby canine kidney cells

Calcium oxalate (CaOx) crystals adhere to and are internalized by tubular renal cells and it seems that this interaction is related (positively or negatively) to the appearance of urinary calculi. The present study analyzes a series of mechanisms possibly involved in CaOx uptake by Madin-Darby canine kidney (MDCK) cells. CaOx crystals were added to MDCK cell cultures and endocytosis was evaluated by polarized light microscopy. This process was inhibited by an increase in intracellular calcium by means of ionomycin (100 nM; N = 6; 43.9% inhibition; P<0.001) or thapsigargin (1 microM; N = 6; 33. 3% inhibition; P<0.005) administration, and via blockade of cytoskeleton assembly by the addition of colchicine (10 microM; N = 8; 46.1% inhibition; P<0.001) or cytochalasin B (10 microM; N = 8; 34.2% inhibition; P<0.001). Furthermore, CaOx uptake was reduced when the activity of protein kinase C was inhibited by staurosporine (10 nM; N = 6; 44% inhibition; P<0.01), or that of cyclo-oxygenase by indomethacin (3 microM; N = 12; 17.2% inhibition; P<0.05); however, the uptake was unaffected by modulation of potassium channel activity with glibenclamide (3 microM; N = 6), tetraethylammonium (1 mM; N = 6) or cromakalim (1 microM; N = 6). Taken together, these data indicate that the process of CaOx internalization by renal tubular cells is similar to the endocytosis reported for other systems. These findings may be relevant to cellular phenomena involved in early stages of the formation of renal stones.

Epidemiology of canine calcium oxalate uroliths. Identifying risk factors

Calcium oxalate uroliths are most commonly encountered in Miniature Schnauzers, Lhaso Apsos, Yorkshire Terriers, Bichons Frises, Shih Tzus, and Miniature Poodles. They are more common in males than females, and more common in older than young dogs. Dogs that form abnormal nephrocalcin are also predisposed to calcium oxalate uroliths. Dietary risk factors for calcium oxalate uroliths include excessive calcium supplementation or excessive calcium restriction, excessive oxalic acid, high protein, high sodium, restricted phosphorus, restricted potassium, and restricted moisture (dry formulations). Dogs with hyperadrenocorticism or hypercalcemia are predisposed to calcium oxalate urolith formation.

Simultaneous determination of oxalic and citric acids in urine by high-performance liquid chromatography

A simple method for the simultaneous determination of oxalic and citric acids had been developed using reversed-phase HPLC. An aqueous solution containing potassium dihydrogen phosphate (0.25%) and tetrabutylammonium hydrogen sulphate (2.5 mmol) at pH 2.0 was used as mobile phase. Under these conditions both the components were well resolved and detected at 210 nm. The recovery for oxalic and citric acids was 97% and 102%, respectively. The method presented here was applied to urine specimens of a large number of urolithic patients and control subjects. Because of the simplicity of the method its application provides better means of monitoring the concentration of oxalic and citric acids in the formation of renal calculi.