Search PubMed⌕ Search

Biomedical subjects

F Grases

Publications and source records attributed to F Grases.

At least 37 records · Page 2Linked to original sources
PubMed2001

Phytate levels in diverse rat tissues: influence of dietary phytate.

Phytate (inositol hexaphosphate; InsP6) was determined in rat tissues fed on diets with different phytate contents, using a GC-mass detection methodology that permitted the evaluation of the total amount of this substance present in such tissues. The highest InsP6 concentrations were found in brain 5.89 x 10(-2)(SE 5.7 x 10(-3)) mg/g DM), whereas the concentrations detected in kidneys, liver and bone were similar to each other 1.96 x 10(-3) (SE 0.20 x 10(-3), 3.11 x 10(-3) (SE 0.24 x 10(-3), 1.77 x 10(-3) (SE 0.17 x 10(-3)) mg/g DM respectively) and 10-fold less than those detected in brain. When rats were fed on a purified diet in which InsP6 was undetectable, the InsP6 levels of the organs mentioned earlier decreased dramatically (9.0 x 10(-4), 3.8 x 10(-5), 1.4 x 10(-5) mg/g DM in brain, kidneys and liver respectively) and in some cases became undetectable (bone). The addition of InsP6 to this purified diet led to the increase of InsP6 levels in these tissues. This clearly demonstrated that the majority of the InsP6 found in organs and tissues has a dietary origin and is not a consequence of endogenous synthesis. Consequently, considering that InsP6 could be involved in some important biological roles, the value of any diet on supplying this substance is noteworthy.

Analysis of Variance↗
PubMed2001

Study on concretions developed around urinary catheters and mechanisms of renal calculi development.

AIMS: To study the structure and composition of encrustation and concretions developed on urinary catheters to better understand their formation mechanism to be able to prevent them. METHODS: The surface of catheters was studied by direct and scanning electron microscopy observation. In vitro formation of encrustations was performed in synthetic urine. RESULTS: The surface of catheters was covered by a continuous layer of organic matter, on which a thin scale consisting of crystals of calcium oxalate monohydrate (COM), uric acid anhydrous or calcium phosphate developed. Encrustations observed on catheters generally exhibited the same composition as the previously developed renal calculi. In catheters collected from patients without previous episodes of renal calculi or with previous episodes of infected renal calculi in which infection was afterwards eradicated, on the first organic layer, in that case plate-like COM crystals forming a columnar layer were observed. In vitro experiments demonstrated that COM columnar structures were only formed when normocalciuric urine containing organic matter was used, and the presence of crystallization inhibitors, as phytate, notably delayed their formation. CONCLUSION: Calcium oxalate was the main crystalline phase developed on catheters inserted in patients, specially in the absence of urinary infection or urinary pH values <5.5 and high urinary uric acid levels. Thus, prophylaxis of encrustations may consist of preventive measures usually applied in cases of recurrent idiopathic calcium oxalate urolithiasis.

Adult↗
PubMed2000

Phytate prevents tissue calcifications in female rats.

The AIN-76 A, a purified rodent diet, has a propensity to cause kidney calcifications in female rats which is not observed with non-purified rodent diets, suggesting a nutritional factor that avoids these calcifications. One candidate is phytate, which inhibits crystallisation of calcium salts and is practically absent in purified diets. Therefore, the effects on calcification of kidney tissue of phytate addition to the AIN-76 A diet using female Wistar rats were studied. The rats were assigned to three groups: AIN-76 A, AIN-76 A + 1% phytate and standard nonpurified chow. Urinary phytate of the AIN-76 A fed group was undetectable. Urinary phytate of AIN-76 A + 1% phytate and standard fed groups did not differ and was significantly higher than in the AIN-76 A group. The concentrations of calcium and phosphorus in kidneys were greater in the AIN-76 A group than in AIN-76 A + 1% phytate and standard groups. Only rats of the AIN-76 A group displayed mineral deposits at the corticomedullary junction. These findings demonstrated that the absence of phytate in the AIN-76 A diet is one of the causes of renal calcification in female rats.

Animal Feed↗
PubMed2000

Effects of phytate and pyrophosphate on brushite and hydroxyapatite crystallization. Comparison with the action of other polyphosphates.

This is a comparative study of the effects of phytate and pyrophosphate and other polyphosphates on the crystallization of hydroxyapatite and brushite, the most frequent calcium phosphates involved in calcium oxalate urolithiasis. Brushite and hydroxyapatite crystal formation was studied in synthetic urine, through kinetic-turbidimetric measurements that allowed evaluation of the inhibitory effects on crystallization of insoluble salts. The effectiveness in preventing brushite crystallization decreases in the sequence phytate > polyphosphate > EDTPO > etidronate > pyrophosphate > triphosphate > medronate; whereas the order of effectiveness in preventing hydroxyapatite crystallization was EDTPO > etidronate = pyrophosphate > triphosphate > medronate > polyphosphate > phytate. Phytate, a natural inhibitor in urine, most effectively blocked brushite precipitation (1.21x10(-5) M prevented crystallization during time periods of at least 1 h), and pyrophosphate was the natural inhibitor that most effectively blocked hydroxyapatite precipitation (2.87x10(-6) M prevented crystallization during time periods of at least 1 h). This demonstrates that low excretion of these substances would pose a risk of renal lithiasis.

Calcium Phosphates↗
PubMed2000

Uric acid calculi: types, etiology and mechanisms of formation.

The study of the composition and structure of 41 stones composed of uric acid was complemented by in vitro investigation of the crystallization of uric acid. Uric acid dihydrate (UAD) precipitates from synthetic urine under physiological conditions when the medium is supersaturated with respect to this compound, though uric acid anhydrous (UAA) represents the thermodynamically stable form. Solid UAD in contact with liquid transforms into UAA within 2 days. This transition is accompanied by development of hexagonal bulky crystals of UAA and appearance of cracks in the UAD crystals. Uric acid calculi can be classified into two groups, differing in outer appearance and inner structure. Type I includes stones with a little central core and a compact columnar UAA shell and stones with interior structured in alternating densely non-columnar layers developed around a central core; both of them are formed mainly by crystalline growth at low uric acid supersaturation. Type II includes porous stones without inner structure and stones formed by a well developed outermost layer with an inner central cavity; this type of stones is formed mainly by sedimentation of uric acid crystals generated at higher uric acid supersaturation.

Chemical Phenomena↗
PubMed2000

Kinetic versus thermodynamic factors in calcium renal lithiasis.

Calcium renal lithiasis formation depends on the balance between thermodynamic (supersaturation) and kinetic (inhibitors, nucleants) factors. In this paper, the importance of both groups was evaluated using (a) the complete urine analysis data obtained from 32 healthy volunteers and 141 active stone-formers, and (b) a comprehensive computer model to calculate the supersaturation values of calcium oxalate monohydrate, hydroxyapatite and brushite in each urine sample. The results of this evaluation were used to assess the possible effectiveness of a given pharmacological treatment.

Calcium↗
PubMed2000

Inositol hexakisphosphate in urine: the relationship between oral intake and urinary excretion.

OBJECTIVE: To study the relationship between the oral intake of inositol hexakisphosphate (InsP6, phytic acid, an inhibitor of urinary crystallization) and its urinary excretion, to establish their possible mutual influence. MATERIALS AND METHODS: Two groups of male Wistar rats (six animals each) received either; tap water and normal rat food pellets (controls); or a liquid diet in which InsP6 was absent and which then received gradually increasing amounts of InsP6. The urinary levels of InsP6 were then assessed regularly in both groups. RESULTS: When InsP6 was absent from the diet, urinary excretion declined to undetectable levels after 22 days. The addition of increasing amounts of InsP6 to the liquid diet caused an increase in its urinary excretion after about 10 days. Adding InsP6 in amounts > 425 mg/L caused no further increases in urinary excretion. Adding inositol (with no InsP6) to the liquid diet caused only a slight increase in the urinary excretion of InsP6. CONCLUSION: These results showed that InsP6 urinary levels were related to its oral intake; consequently, a low consumption of InsP6 would cause a urinary deficit of this crystallization inhibitor and thus an increase in the risk of developing urinary calcium stones. Although urinary excretion was dose-dependent, there was an ingested amount (20.9 mg/kg) above which there was no increase in the amount excreted. This intake is easily obtained by consuming a normal diet (rich in InsP6) indicating that to maintain appropriate urinary levels of InsP6, the consumption of InsP6 supplements is only necessary when the diet is particularly poor in InsP6.

Administration, Oral↗
PubMed2000

Urinary phytate in calcium oxalate stone formers and healthy people--dietary effects on phytate excretion.

The phytate urinary levels in a group of active calcium oxalate stone formers were studied and compared with those found in healthy people. Urinary phytate was significantly lower for stone formers. If deficit of the capacity to inhibit crystallization of calcium salts is considered an important factor related to calcium stone formation, the excretion of low phytate amounts could be an important risk factor in the development of this type of renal calculi. The influence of dietary phytate on urinary excretion was also studied. Clearly maintenance of a phytate-free diet significantly decreased the urinary excretion of phytate (about 50% after 36 h). This demonstrated the importance of dietary phytate in maintaining adequate urinary levels to permit effective crystallization inhibition of calcium salts and consequently preventing renal stone development.

Adult↗
PubMed1999

Ammonium and sodium urates precipitating from synthetic urine and fine structure of urate renal calculi.

A study of ammonium and sodium urate precipitation in vitro and the fine structure of several urate renal calculi was carried out to contribute to an understanding of the participation of ammonium and sodium urates in urolithiasis. Ammonium urate precipitated in vitro in two different morphologies: a typical spherulite morphology formed at high supersaturation and disorganized needle-like crystals formed at low supersaturation. In all cases sodium urate precipitated in vitro as bundles of curved fibrils, its crystallization being inhibited by calcium in concentrations between 20 and 60 mg/l depending on the sodium urate supersaturation. From a collection of 1300 renal calculi, only three had ammonium urate as their main component (0.2%), three were mixed calculi (0.2%) consisting of ammonium urate and calcium oxalate (two) or uric acid (one), and in one calculus ammonium urate was present as a minor component. Only in a mixed calculus of uric acid and calcium oxalate was sodium urate detected in a very low quantity. The study of the fine structure of the renal calculi constituted mainly by ammonium urate demonstrated similar patterns in which spherulites, needle-like individual crystals and an amorphous mass of ammonium urate with abundant organic matter in non-organized structures coexist. As minor components, struvite or calcium oxalate crystals were found. A general mechanism of the formation of such calculi is proposed.

Chemical Precipitation↗
PubMed1999

Indinavir crystallization and urolithiasis.

The crystallization of indinavir in synthetic urine at different pH values and indinavir concentrations was kinetically studied. It was found that precipitation time notably decreases at urinary pH values above 6.0. The effects of some products as potential crystallization inhibitors were studied. Some natural saponins such as escin and glycyrrhizic acid provoked a notable increase in the precipitation time of indinavir, this pointing out their possible use to prevent renal tubular solid deposition.

Chemical Precipitation↗
PubMed1999

Renal stone formation and development.

A concise account of formation mechanisms of attached (papillary) and unattached renal stones is presented. Urinary conditions prevailing at least during the stone forming period are indicated. Ten main categories of renal stones, covering over 95% of all conceivable calculi, are distinguished based on their composition and structure. Aetiologic factors leading to stone formation of every category are specified and general outlines of recommended treatment procedures indicated.

Humans↗
PubMed1999

Fluorimetric determination of phytic acid based on the activation of the oxidation of 2,2'-dipyridyl ketone hydrazone catalysed by Cu(II).

Phytic acid exerts an activation effect on the oxidation of 2,2'-dipyridyl ketone hydrazone catalysed by Cu(II) ion and the oxidation product is highly fluorescent. A fixed time method for the fluorimetric determination of phytic acid based on this effect is described. The calibration graph is linear over the range 0.05-0.6 mg l-1 phytic acid, resulting in a limit of detection of 0.03 mg l-1 phytic acid. The relative standard deviation is in the range 1.4-1.8%, depending on the sample analysed. The method was successfully applied to the determination of phytic acid in human urine (20 samples) and food samples (nine different products). The results obtained for urine samples ranged from 0.31 to 3.6 mg l-1 phytic acid and for food samples from 3.8 to 22 mg g-1 phytic acid. This is the first procedure to be reported for the determination of phytic acid based on fluorimetric measurements.

Fluorometry↗
PubMed1999

Uric acid urolithiasis and crystallization inhibitors.

An in vitro study of the inhibitory effects that some substances occasionally present in urine can provoke on the crystallization of uric acid has been performed. The most remarkable crystallization inhibitory effects were produced by mucine at concentrations of >0.5 mg/l. Pentosan polysulfate and chondroitin sulfate also clearly increased the uric acid crystallization times at concentrations of >100 mg/l. Saponins, such as escin and glycyrrhizic acid, also produced a notable delay in uric acid crystallization times at concentrations of >10 mg/l. Similar effects were observed in the presence of a surfactant substance, lauryl sulfate. N-Acetyl-L-cysteine caused crystallization perturbations only when it was present at concentrations of >50 mg/l. Citric acid and phytic acid caused no effects on uric acid crystallization even at the highest concentrations assayed (1,000 and 5 mg/l, respectively). From the results obtained it can be deduced that mainly glycoproteins, glycosaminoglycans and surfactant substances can exert protective effects against uric acid crystallization.

Acetylcysteine↗
PubMed1999

Urinary lithogen risk test: usefulness in the evaluation of renal lithiasis treatment using crystallization inhibitors (citrate and phytate).

OBJECTIVES: This paper presents the results of a test to globally determine the urinary risk factor of calcium stone formation in the evaluation of treatments using crystallization inhibitors, such as citrate and phytate. METHODS: Three groups of active calcium oxalate stone-formers have been selected. The lithogen urinary risk was determined using a specially designed disposable test before any medical treatment. After evaluation group I did not receive any treatment, group II was treated with potassium citrate and group III with a phytate-rich dietary complement. When 15 days had elapsed, the test to evaluate the risk of urinary calcium stone formation was applied again to the three groups. The main lithogenic biochemical parameters of each tested urine were also determined before and after treatment. RESULTS: An important number of calcium oxalate stone-formers with high urinary risk factor (positive test) became negative after medical treatment (52% of the citrate-treated patients and 50% of the phytate-treated patients), but only 7% of the untreated patients (1 patient) showed a decrease in their urinary risk factor for calcium stones (negative test) after 15 days had elapsed. When the treatment was not effective, in an important number of cases, the urine contained high levels of calcium or showed pH values greater than 6.5. CONCLUSION: From the obtained results it can be concluded that the test is useful to evaluate the efficacy of a given renal lithiasis medical treatment, and also the efficacy of the treatment of calcium oxalate renal lithiasis using crystallization inhibitors, such as citrate and phytate, in an important number of cases.

Citrates↗
PubMed1998

Vitamin A and urolithiasis.

The effects of vitamin A deficiency on urolithiasis were investigated in male rats. A vitamin A-deficient diet caused important changes in the composition of the urine of the treated rats when compared with controls. One of the main effects was a decrease in the concentration of urinary glycosaminoglycans and zinc in the rats receiving the vitamin A-deficient diet. Significant differences were also found in plasma vitamin E and in the relation of vit E/vit A between treated and control groups but, in general, with no important differences in vitamin A. Nevertheless, significant differences in kidney content of vitamin A were observed between both groups. On the other hand, lesions of the cuboidal epithelium that covers the papillae in rats treated with the vitamin A-deficient diet were severe when compared with controls. The vitamin A and E plasma levels in urolithiasic humans were also investigated and compared with those found in a control group. No significant differences were observed in plasma vitamin A levels; nevertheless a significant increase in vitamin E and in the vit E/vit A ratio was clearly observed. These results could be related to a possible deficit of vitamin A in kidneys of stone formers, this being one of the diverse factors that can contribute to urolith development. Moreover, the deficit of important urinary crystallization inhibitors normally found in stone-formers, such as pyrophosphate and phytate, can also be related to the presence of low levels of renal vitamin A which prevents the enzymatic degradation of such inhibitors.

Animals↗
PubMed1998

Evolution of lithogenic urinary parameters with a low dose potassium citrate treatment.

The changes in some nocturnal urine urolithogenic parameters in response to the extradietary ingestion of 2.16 g potassium citrate (20 meq) after dinner have been determined. The study included 15 patients (hypocitraturic calcium oxalate stone formers). On the basis of the different pH changes three groups have been differentiated. Different kinetics of citrate metabolism can justify the existence of these three groups. In general, a beneficial effect on urolithogenic parameters was confirmed, and a pH control of patients under treatment was recommended.

Adult↗
PubMed1998

Biopathological crystallization: a general view about the mechanisms of renal stone formation.

A general classification of most common renal calculi (calcium oxalate, phosphate and uric acid stones) based on their formation mechanism is presented. The main etiological factors that enable their development are discussed considering present knowledge of calcium oxalate, insoluble urinary phosphates and uric acid crystallization and the fine structure of respective renal stones. Considering the formation mechanisms of the discussed calculi, common aspects permit us to distinguish two general mechanisms of calculi formation: development of calculi attached to papillary epithelium and development of calculi in cavities without any attachment to urothelium.

Calcium Oxalate↗