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Two starch to protein ratios (high starch [HS], 25% starch and 36% protein; high protein [HP], 15% starch and 53% protein on DM basis) and two moisture contents (5%, dry kibbles; 80%, wet food) were compared in a 2 x 2 factorial arrangement totaling 4 diets. Each diet was evaluated in 9 cats, with 8 d of total collection of urine and feces. Results were subjected to an analysis of variance of the effects of starch to protein ratio, moisture content and their interactions (P<0.05). Urine density was lower and volume was higher in cats fed wet foods (P<0.01). Calcium (Ca) urine concentration was higher for dry and HP diets (P<0.05). The oxalate urine concentration was 60% higher for cats fed both HS formulations (dry and wet; P<0.05). The relative supersaturation (RSS) of urine for calcium oxalate was higher for dry foods and HS formulations (P<0.01), and for struvite, it was lower for both wet foods, and among the dry diets, it was lower for the HS than for the HP formulation (P<0.01). Foods with a high protein-to-starch ratio reduced urine oxalate and RSS for calcium oxalate in wet and dry diets, and wet foods reduced RSS for calcium oxalate and struvite.

Magnesium (Mg) is the main intracellular divalent cation, and under basal conditions the small intestine absorbs 30–50% of its intake. Normal serum Mg ranges between 1.7–2.3 mg/dl (0.75–0.95 mmol/l), at any age. Even though eighty percent of serum Mg is filtered at the glomerulus, only 3% of it is finally excreted in the urine. Altered magnesium balance can be found in diabetes mellitus, chronic renal failure, nephrolithiasis, osteoporosis, aplastic osteopathy, and heart and vascular disease. Three physiopathologic mechanisms can induce Mg deficiency: reduced intestinal absorption, increased urinary losses, or intracellular shift of this cation. Intravenous or oral Mg repletion is the main treatment, and potassium-sparing diuretics may also induce renal Mg saving. Because the kidney has a very large capacity for Mg excretion, hypermagnesemia usually occurs in the setting of renal insufficiency and excessive Mg intake. Body excretion of Mg can be enhanced by use of saline diuresis, furosemide, or dialysis depending on the clinical situation.

Phosphorus (P) recovery was carried out through struvite precipitation from urines. Human urine, however, contains not only high nutrients for plants, such as P and nitrogen, but also pharmaceuticals and hormones. In this work, effects of magnesium (Mg) dose (in terms of Mg:P ratio) on P recovery efficiency and pharmaceutical amounts contained in struvite were investigated. Batch-scale experiments of synthetic and human urines revealed that struvite precipitation formed more X-shaped crystals with an increased molar ratio of Mg:P, while the amount of pharmaceuticals (tetracycline, demeclocycline, and oxytetracycline) in struvite decreased with an increased molar ratio of Mg:P. The lowest pharmaceutical amounts in struvite were found at the Mg:P ratio of 2:1 from both samples. Moreover, the maximum P recovery efficiency, quantity and purity of struvite were found in the range of 1.21 to 2:1. It indicated that the molar ratio of Mg:P has a significant impact on struvite precipitation in terms of pharmaceutical amounts in struvite; morphology, quantity and purity of struvite; and P recovery.

Summary points Calcium oxalate (alone or in combination) is the most common type of urinary stone Low urine volume is the most common abnormality and the single most important factor to correct so as to avoid recurrences Risk of a recurrent stone is about 50% within five to seven years Diets low in salt (<5 0 mmol/day) and animal proteins (< 52 g/day) are helpful in decreasing the frequency of recurrent calcium oxalate stones Low calcium diets are not recommended to prevent recurrent stones, as they increase urinary oxalate excretion and may result in negative calcium balance Most ureteral stones under 5 mm pass spontaneously

It has been reported that daily fluid intake influences urinary dilution, and consequently the risk of urolithiasis in human subjects and dogs. The aim of the present study was to investigate the role of dietary moisture on urinary parameters in healthy adult cats by comparing nutritionally standardised diets, varying only in moisture content. A total of six cats were fed a complete dry food (6·3 % moisture) hydrated to 25·4, 53·2 and 73·3 % moisture for 3 weeks in a randomised block cross-over design. Urinary specific gravity (SG), urine volume, water drunk and total fluid intake were measured daily; relative supersaturation (RSS) for calcium oxalate (CaOx) and struvite was calculated using the SUPERSAT computer program. Cats fed the 73·3 % moisture diet produced urine with a significantly lower SG (P < 0·001) compared with diets containing 53·2 % moisture or lower. Mean RSS for CaOx was approaching the undersaturated zone (1·14 (sem 0·21); P = 0·001) for cats fed the diet with 73·3 % moisture and significantly lower than the 6·3 % moisture diet (CaOx RSS 2·29 (sem 0·21)). The effect of diet on struvite RSS was less clear, with no significant difference between treatment groups. Total fluid intake was significantly increased (P < 0·001) in the 73·3 % moisture diet (144·7 (sem 5·2) ml, or 30 ml/kg body weight per d) compared with the 6·3 % (103·4 (sem 5·3) ml), 25·4 % (98·6 (sem 5·3) ml) and 53·3 % (104·7 (sem 5·3) ml) moisture diets, despite voluntary water intake decreasing as dietary moisture intake increased. Cats fed the 73·3 % moisture diet had a higher total daily fluid intake resulting in a more dilute urine with a lower risk of CaOx when compared with the lower-moisture diets.

Interest in phosphorus recovery from urine diverted from faeces has been growing recently. Phosphorus in urine can be precipitated out as struvite (MgNH4PO4•6H2O) with addition of magnesium salt under alkaline conditions. Struvite formation, however, should be more well understood for its practical application. We predicted the struvite formation with a development of a new equilibrium model. The model considered the formation of eight different kinds of precipitates, including struvite, with effects of ionic strength and temperature. In addition, experiments on struvite formation in urine were conducted for the model validation. The model prediction of struvite formation had good agreement with the experimental results. The optimum pH to form struvite was predicted to be 9.4–9.7. In order to precipitate 99% of phosphate in urine with 1.5 fold Mg concentration to PO4-P, the pH value was necessary to be more than 8.1 based on the model prediction.

We investigated contents and classes of urinary and stone matrix lipids, and evaluated their clinical relevance in nephrolithiasis patients. Lithogenic role of major lipid classes was explored. Urine (24 h) and stone samples were collected from 47 patients with nephrolithiasis. Control urines were obtained from 29 healthy subjects. Urinary 8-hydroxy-deoxyguanosine (8-OHdG), malondialdehyde (MDA), N-acetyl-β-glucosaminidase (NAG) activity and total proteins were measured. Total lipids were extracted from centrifuged urines (10,000 rpm, 30 min) and stones by chloroform/methanol method. Major classes of lipids were identified using multi-one-dimensional thin-layer chromatography (MOD-TLC). Influence of each lipid class purified from stone matrices on stone formation was evaluated using crystallization and crystal aggregation assays. Urinary NAG activity and 8-OHdG were significantly elevated in nephrolithiasis patients. Total lipids in centrifuged urines of the patients were not significantly different from that of controls. In nephrolithiasis, urinary excretion of total lipids was linearly correlated to urinary MDA, 8-OHdG, NAG activity and total proteins. Lipid contents in stone matrices varied among stone types. Uric acid stone contained lower amount of total lipids than calcium oxalate and magnesium ammonium phosphate stones. MOD-TLC lipid chromatograms of healthy urines, nephrolithiasis urines and stone matrices were obviously different. Triacylglyceride was abundant in urines, but scarcely found in stone matrices. Stone matrices were rich in glycolipids and high-polar lipids (phospholipids/gangliosides). Partially purified glycolipids significantly induced crystal aggregation while cholesterol was a significant inducer of both crystal formation and agglomeration. In conclusion, total lipids in centrifuged urines did not differ between nephrolithiasis and healthy subjects. Our finding suggests that the significant sources of lipids in patients' urine may be large lipids-containing particles, which are removed in centrifuged urines. However, urinary lipid excretion in nephrolithiasis patients was associated with the extent of oxidative stress and renal tubular injury. Triacylglyceride was abundant in urines, but rarely incorporated into stones. Glycolipids were principal lipid constituents in stone matrices and functioned as crystal aggregator. Cholesterol purified from stone matrices bared crystal nucleating and aggregating activities.

Purpose We propose a simple and inexpensive in vitro crystallization assay of measuring turbidity by spectrophotometry in synthetic urine. We validated our method by investigating the effect of potassium (K) citrate on the crystallization of calcium oxalate monohydrate (CaOx), calcium phosphate, and magnesium ammonium phosphate using synthetic urine. Methods The crystallization of CaOx was studied using turbidimetric measurements of solution produced by mixing calcium chloride and sodium oxalate at 37 °C, pH 5.7. The turbidity of the crystal suspension was measured immediately with double-beam spectrophotometer as the absorbance of light at 660 nm wavelength. The rates of crystal formation and aggregation were obtained by measuring optical density (OD) over 30 min. The obtained results were compared to CaOx crystal concentration with and without citrate assessed by optical microscopy. Results The sensitivity of spectrophotometry in measuring turbidity was confirmed by the linear correlation between the crystal concentration and OD readings at 660 nm seen on the standard curve. Under similar experimental conditions, the results were comparable to the ones obtained by optical microscopy. The OD readings over 30 min revealed an instant decrease in the number of crystals, with maximum aggregation noted at 18 min. Addition of K-citrate at 1.25 mg/ml led to initial less crystal formation (OD = 0.236 nm vs. OD = 0.527 nm), with a maximum aggregation reached at 18 min. Overall, citrate addition decreased nucleation with a small change in the aggregation (OD = 0.316 vs. OD = 0.359). Conclusion Spectrophotometric measurement of urinary turbidity is feasible and sensitive in assessing the potential clinical usefulness of different medications in inhibiting crystallization in urine.