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PubMed1997

Crystal growth and molecular modeling studies of inhibition of struvite by phosphocitrate.

The inhibition by phosphocitrate of struvite crystal formation and growth has been examined in the present study. Crystal growth in a gel matrix was controlled by phosphocitrate in a dose-dependent manner. The effects of inhibition were followed using scanning electron microscopy, optical microscopy, and single crystal X-ray analysis. The presence of phosphocitrate induced very strong, crystal face specific inhibition of struvite, leading to total cessation of crystal growth when sufficient concentration of the inhibitor was made available. Crystal growth studies and results from molecular modeling indicated strong affinity of phosphocitrate to (101) faces of struvite. This in turn led to an alteration in the expression of these faces and the development of a characteristic arrowhead struvite morphology. Similar changes were not observed in the presence of identical concentrations of citrate, acetohydroxamic acid, and N-sulfo-2 amino tricarballylate (an analog of phosphocitrate), emphasizing the unique interaction of phosphocitrate with the struvite crystal lattice.

Citrates↗
PubMed2004

Formation and transformation of struvite and newberyite in aqueous solutions under conditions similar to physiological.

The precipitation of magnesium phosphates in the system MgCl(2)-NH(4)H(2)PO(4)-NaOH-H(2)O was studied at a wide range of reactant concentrations at 37 degrees C and an initial pH(i) of 7.4. Precipitates were aged for 24 h and characterized by means of optical and scanning electron microscopy, x-ray diffractometry, FT-IR spectroscopy and thermogravimetry. Struvite was found to precipitate in nearly the whole concentration region investigated. Pure newberyite and a mixture of struvite and newberyite were obtained in a narrow range only with a pH(24 h)<6.4. The transformation of struvite into newberyite was studied by following changes in the liquid and solid phases. Thus, the changes of pH and the content of struvite in the precipitate as a function of time were recorded. The influence of the initial pH(i) and temperature on the transformation process is discussed. Analysis of the experimental data suggests a solution mediated transformation process as a possible mechanism of struvite transformation.

Chemical Precipitation↗
PubMed2005

Factors modulating the pH at which calcium and magnesium phosphates precipitate from human urine.

The factors controlling the rate at which crystalline bacterial biofilms develop on indwelling bladder catheters are poorly understood. It is known that normally the pH of voided urine (pHv) is lower than the pH at which calcium and magnesium phosphates come out of urine solution (pHn). In patients who develop infections with urease producing bacteria, however, the pHv rises above the pHn and precipitation of the phosphates occurs in the urine and the biofilm. The aim of this study was to examine ways of manipulating the pHn of urine so that more of its calcium and magnesium remain in solution under alkaline conditions. The experimental data show that pHn can be elevated by decreasing the calcium, magnesium and phosphate concentrations. Increasing the fluid intake of a human subject so that the urinary calcium fell from 120 mg/l to 25 mg/l, for example, resulted in the pHn increasing from 6.48 to 8.22. The addition of citrate to urine also produced a rise in the pHn. The daily consumption of 500 ml of fresh orange juice increased urinary citrate concentrations from 0.35 to around 1.21 mg/ml and the pHn rose from 7.24 to 8.2. The pHn of urine is thus a highly variable parameter. It can be manipulated by controlling the urinary concentrations of magnesium, calcium, phosphate and citrate ions. We suggest that increasing fluid intake with citrate containing drinks would reduce the extent of encrustation on catheters in patients infected with urease producing bacteria.

Adult↗
PubMed2001

Unusual facet cyst containing struvite and hydroxyapatite.

This case report describes a patient with severe back pain and radiculopathy. She was found to have a facet cyst within the lumbar spine that appeared to contain calcium on MRI and CT. Upon aspiration the cyst was found to contain calcium ammonium phosphate (struvite) and calcium phosphate (hydroxyapatite). Ammonia production in the presence of urease-producing bacteria is responsible for the production of struvite in the human body. We postulate that there was a prior infection of the facet with urease-producing bacteria, thus accounting for the production of the struvite within the facet cyst.

Durapatite↗
PubMed2004

Helical CT evaluation of the chemical composition of urinary tract calculi with a discriminant analysis of CT-attenuation values and density.

The aim of this study was to evaluate the efficacy of helical CT using a combination of CT-attenuation values and visual assessment of stone density as well as discriminant linear analysis to predict the chemical composition of urinary calculi. One hundred human urinary calculi were obtained from a stone-analysis laboratory and placed in 20 excised pig kidneys. They were scanned at 80, 120 and 140 kV with 3-mm collimation. Average, highest and lowest CT-attenuation values and CT variability were recorded. The internal calculus structure was assessed using a wide window setting, and visual assessment of stone density was recorded. A stepwise discriminant linear analysis was performed. The following three variables were discriminant: highest CT-attenuation value, visual density, and highest CT-attenuation value/area ratio, all at 80 kV. The probability of correctly classifying stone composition with these three variables was 0.64, ranging from 0.54 for mixed calculi to 0.69 for pure calculi. The probabilities of correctly classifying calculus composition were: 0.91 for calcium oxalate monohydrate and brushite, 0.89 for cystine, 0.85 for uric acid, 0.11 for calcium oxalate dihydrate, 0.10 for hydroxyapatite, and 0.07 for struvite calculi. When the first two ranks of highest probability for the accurate classification of each calculus type were taken into account, 81% of the calculi were correctly classified. Assessment at 80 kV of the highest CT-attenuation value, visual density and the highest CT-attenuation value/area ratio accurately predicts the chemical composition of 64-81% of urinary calculi. When the first two ranks of highest probability for the accurate classification of each calculus type were taken into account, all cystine, calcium oxalate monohydrate and brushite calculi were correctly classified.

Animals↗
PubMed1999

Causes of phosphate stone formation and the importance of metaphylaxis by urinary acidification: a review.

The most important phosphates involved in urinary stone disease are carbonate apatite, brushite, and struvite. Overall, phosphate stones account for 12-20% of all stones, with a downward trend for struvite and an increase in carbonate apatite being observed in the last decade. The physicochemical basis for the formation of phosphate calculi is supersaturation. Once the solubility product has been exceeded, a metastable process of supersaturation begins, with slow crystalline growth. If a critical limit of supersaturation is exceeded, large-scale spontaneous precipitation of crystals occurs in a second stage. No urinary tract infection is involved in brushite stone formation. Although infection is not a prerequisite for the formation of carbonate apatite stones, infective conditions favor carbonate apatite formation. Struvite is the characteristic infection calculus, formed as a result of urinary tract infection with urease-producing bacteria. During the first episode of urinary stone disease a definitive diagnosis of the type of stone involved is very difficult without analysis of the latter by infrared spectroscopy or X-ray diffraction. In recurrent disease, appropriate treatment can be initiated on the basis of the previous stone analysis in the majority of cases. The best means of preventing recurrent disease involving any type of phosphate stone is definitive calculus removal by shock-wave lithotripsy, percutaneous stone removal, or open surgery (especially in children). Chemolysis via acidification of the urine with Suby G solution or hemicidrin supported by oral acidification, achieved by the metabolism of L-methionine, and antibiotic therapy (especially for infectious stones) are important adjuvant modalities of therapy. After therapy of phosphate stones, metaphylaxis involving controlled urinary acidification with L-methionine supports the treatment of infection and, at a pH value of less than 6.2 and urine dilution to 2.5 l/24 h, prevents the crystallization of struvite, brushite, and carbonate apatite.

Acids↗
PubMed2005

Nephrolithiasis in children.

A metabolic etiology is the most common cause for pediatric kidney stones. Appropriate evaluation of affected children should include assessment of stone type, if available, and assessment of predisposing factors in all cases. This review discusses the metabolic disorders that lead to nephrolithiasis with respect to the development of calcium, uric acid, struvite, and cystine stones. Environmental and hereditary factors are summarized to provide a guide in the evaluation of pediatric stone formers.

Calcium↗
PubMed2004

Evidence for ditopic coordination of phosphate diesters to [Mg(15-crown-5)]2+. Implications for magnesium biocoordination chemistry.

The interaction of a series of phosphate diesters and triesters (1=diphenyl phosphate,2=dimethyl phosphate,3=bis(2-ethylhexyl) phosphate,4=trimethyl phosphate,5=methyldiphenyl phosphate,6=triphenyl phosphate) with [Mg(15-crown-5)](2+) (15-crown-5=1,4,7,10,13-pentaoxocyclopentadecane) was studied as a simplified model for the interaction of aqueous Mg(2+) ion with phosphate-containing biomolecules such as RNA. Using electrospray mass spectrometry, we confirm the formation of 1:1 adducts in the gas phase. Proton and (31)P NMR titration data were used to construct binding isotherms, and a 1:1 binding equilibrium was fit to the isotherms at room temperature to estimate the binding affinities. The binding affinity data are consistent with ditopic coordination of neutral dialkyl phosphate ligands to the [Mg(15-crown-5)](2+) unit. This involves inner-sphere coordination to the Mg(2+) via an oxygen atom, which is complemented by a weak hydrogen-bonding interaction with the crown ether ligand. Ditopic interaction is consistent with low-temperature NMR spectra showing four different configurations for1 coordinated to [Mg(15-crown-5)](2+), which are interpreted in terms of hindered rotation around the Mg-O(phos) bond. Thermochemical analysis of the binding affinity data suggests that the second-shell interaction contributes only about 1 kcal/mol to the binding free energy, so additional factors, such as steric constraints, must be operative to give a preferred phosphate orientation in this system. However, the experimental data do suggest that second-shell interactions contribute as much as 40% of the total binding energy, consistent with the pronounced ability of aqueous Mg(2+) to form salt-bridges linking secondary and tertiary elements of RNA structure.

Crown Ethers↗
PubMed2005

Mineralogy of atmospheric suspended dust in three indoor and one outdoor location in Oman.

The aim of this work is to characterize the mineral phases present in the atmosphere at three locations in northern Oman. Samples of atmospheric particles were collected using a high volume sampler. Three indoor and one outdoor location were chosen in this investigation. Sampling locations included a residential house located nearby the cement plant, a residential house located nearby a refinery plant, and a residential house located at Al-Suwayq residential area. Indoor air was sampled from these three houses. Moreover, for the Al-Suwayq residential house, sampling was also taken outside the house for comparison. The dust samples were analysed for their microanalysis characterization and their mineral contents as well. The microanalysis enabled us to identify the metals present in the particles. Furthermore, the mineralogical analysis of the sample filters showed the presence of quartz as the principal phase inside the house of Al-Suwayq, whereas quartz, dolomite, and gypsum were common phases outside the house. In the residential house nearby the cement plant, it was found that calcite, quartz, dolomite and goethite were the principal phases whereas the particles collected from the house nearby the refinery composed primarily of dolomite and calcite. The airborne dust collected at the refinery and Al-Suwayq were probably sourced in the natural environment and mobilised by natural processes. However, at the cement factory the crushing and grinding of limestone during the industrial process has contributed significantly to the airborne dust load. Generally, the information obtained in this study will be invaluable as no data for the mineral content of atmospheric dust existed in the Oman.

Air Pollutants↗
PubMed1990

A randomized, open-label comparison of nonprescription loperamide and attapulgite in the symptomatic treatment of acute diarrhea.

The efficacy of nonprescription doses of loperamide hydrochloride (Imodium A-D) was compared with nonfibrous activated attapulgite (Diasorb) in a randomized, parallel, open-label study of adult patients with acute diarrhea. The results of the study showed loperamide to be more effective than attapulgite in the control of diarrhea. Loperamide significantly reduced stool frequency compared with attapulgite, particularly within the first 12-hour period following the start of therapy, and significantly shortened the mean time to last unformed stool (loperamide, 14.2 hours, versus attapulgite, 19.5 hours). Subjective evaluations of severity of enteric symptoms, overall relief following treatment, and overall relief after 48 hours of treatment were equivalent for both drugs. Both treatments were well tolerated, and there was no difference between treatments with respect to the proportion of patients reporting adverse experiences.

Acute Disease↗
PubMed1986

Chemical modification of rabbit skeletal muscle phosphorylase kinase with phenylglyoxal.

Nonactivated phosphorylase kinase from rabbit skeletal muscle is inactivated by treatment with phenylglyoxal. Under mild reaction conditions, a derivative that retains 10-15% of the pH 8.2 catalytic activity is obtained. The kinetics of inactivation profile, differential effects of modification on pH 6.8 and 8.2 catalytic activities, and the insensitiveness of the modified enzyme to activation by ADP reveal that the 10-15% of catalytic activity remaining is very likely due to intrinsic catalytic activity of the derivative rather than to the presence of unmodified enzyme molecules. The kinetic results also suggest that the inactivation is correlatable with the reaction of one molecule of the reagent with the enzyme without any prior binding of phenylglyoxal. The phenylglyoxal modification reduces the autophosphorylation rate of the kinase. Autophosphorylated phosphorylase kinase is inactivated by phenylglyoxal at a much slower rate than the inactivation of nonactivated kinase. Thus, phenylglyoxal modification influences the phosphorylation and vice versa. The modified enzyme can be reactivated by treatment with trypsin or by dissociation using chatropic salts. The activity of the phenylglyoxal-modified enzyme after trypsin digestion or dissociation with LiBr reaches the same level as that of the native enzyme digested with trypsin or treated with LiBr under identical conditions. The results suggest that the effect of modification is overcome by dissociation of the subunits of phosphorylase kinase and that the catalytic site is not modified under conditions when 85% of the pH 8.2 catalytic activity is lost. Among various nucleotides and metal ions tested, only ADP, with or without Mg2+, afforded effective protection against inactivation with phenylglyoxal. At pH 6.8, 1 mM ADP afforded complete protection against inactivation. Experiments with 14C-labeled phenylglyoxal revealed that ADP seemingly protects one residue from modification. This result is in agreement with the kinetic result that the inactivation seemingly is due to reaction of one molecule of the reagent with the enzyme. The results confirm the existence of a high-affinity ADP binding site on nonactivated phosphorylase kinase and suggest the involvement of a functional arginyl residue at or near the ADP binding site in the regulation of of pH 8.2 catalytic activity of the enzyme.

Adenosine Diphosphate↗
PubMed1977

Effects of anions, pH and magnesium on calcium accumulation and release by sarcoplasmic reticulum vesicles.

In the absence of oxalate, Ca2+ accumulation by isolated sarcoplasmic reticulum vesicles may show a transient behavior in which the vesicles accumulate during the first 2 min of incubation as much as twice the amount of Ca2+ which is retained after 5-7 min, when Ca2+ accumulation approaches a steady state. Before Ca2+ release begins, the Ca2+ accumulation can reach 200-250 nmol/mg protein. The spontaneous release of the "extra" Ca2+ initially accumulated appears to be triggered by the attainment of a sufficiently high concentration of free Ca2+ inside the vesicles. The amplitude of the transient phase of Ca2+ accumulation reaches a high value near pH 6.0 and is increased by free Mg2+. At optimal concentrations of H+ and Mg2+, the amount of Ca2+ accumulated during the transient is augmented by various anions, in the order maleate > or = propionate > or = succinate > chloride > sulfate > acetylglycine. The divalent anions have their maximum effects at 20-40 mM and the monovalent anions, at 40-200 mM. At 200 mM, all of the carboxylic anions tested significantly reduce the amount of Ca2+ retained in the steady state.

Adenosine Triphosphate↗
PubMed1991

Pyrophosphate inhibition of Proteus mirabilis-induced struvite crystallization in vitro.

Struvite (MgNH4PO4.6H2O) crystals, the major mineral component of infectious urinary calculi, were produced in vitro by growth of a clinical isolate of Proteus mirabilis in artificial urine. P. mirabilis growth and urease-induced struvite production were monitored by phase contrast light microscopy and measurements of urease activity, pH, ammonia concentrations, turbidity, and culture viability. In the absence of pyrophosphate, struvite crystals appeared within 3-5 h due to the urease-induced elevation of pH and initially assumed a planar or 'X-shaped' crystal habit (morphology) characteristic of rapid growth. When pyrophosphate was present, initial precipitation and crystal appearance were significantly impaired and precipitates were largely amorphous. When crystals did appear (usually after 7 or 8 h) they were misshapen or octahedral in shape indicative of very slow growth. X-ray diffraction and Fourier transform infrared spectroscopy (FTIR) identified all crystals as struvite. Trace contaminates of carbonate-apatite (Ca10(PO4)6CO3) or newberyite (MgHPO4.H2O) were produced only in the absence of pyrophosphate. P. mirabilis viability and culture pH elevation were unaffected by the addition of pyrophosphate, whereas urease activity and ammonia concentrations were marginally reduced. Struvite could also be produced chemically by titration of the artificial urine with NH4OH. If pyrophosphate was present during titration, the same inhibitory effect on crystal growth occurred, so it is unlikely that urease inhibition is important. Lowering of pyrophosphate concentration from 13-0.45 mumol/l did not reduce its inhibitory activity so it is unlikely to act by chelating free Mg2+. We propose that pyrophosphate inhibits struvite growth principally through direct interference with the chemical mechanisms involved in crystal nucleation and growth, because of its effectiveness at very low concentrations.

Ammonia↗
PubMed1991

Effectiveness of palladium matrix modification for the determination of thallium by graphite furnace atomic absorption spectrometry.

The effect of palladium matrix modification on the determination of thallium has been investigated. The effect of palladium combined either with ammonium nitrate or with magnesium nitrate on the sodium chloride interference was systematically studied and was compared with that of the classical sulfuric acid modifier. A combination of 6 micrograms palladium with 100 micrograms ammonium nitrate allows the direct determination of thallium in ten-fold diluted blood against matrix-free standards. The detection limit (3 sigma) in the undiluted blood was calculated to be 25 micrograms.1(-1). For the urine analysis the standard addition technique is recommended because a complete thallium recovery for all different urine samples studied was not always obtained.

Hot Temperature↗
PubMed1996

Phosphates precipitating from artificial urine and fine structure of phosphate renal calculi.

Phosphates precipitating from artificial urine in the pH range 6-8 were identified using X-ray diffraction, chemical analysis and scanning electron microscopy. The influence of magnesium and citrate on phases precipitating from urine was established. From urine containing a normal quantity of magnesium (around 70 ppm), brushite accompanied by hydroxyapatite (HAP) precipitated at pH < or = 7.0 and struvite with HAP at pH > 7.0. HAP was formed exclusively from magnesium deficient urine at pH 7.0. Newberyite, octacalcium phosphate and whitlockite were not identified. The chemical and phase composition and inner fine structure of 14 phosphate calculi were studied. Three types of stones were distinguished based on their magnesium content: (i) stones rich in magnesium composed of struvite, hydroxyapatite and abundant organic matter, (ii) stones with low magnesium content constituted by calcium deficient hydroxyapatite, up to 5% of struvite, considerable amount of organic matter and occasionally brushite, and (iii) calculi without magnesium consisting of brushite, hydroxyapatite and little organic matter. Conditions prevaling during stone-formation assessed for each type of stone were confirmed by corresponding urinary biochemical data and corroborate the in vitro studies of phosphates precipitation.

Calcium Phosphates↗