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PubMed1994

Effects of magnesium citrate and phytin on reducing urinary calcium excretion in rats.

The aim of this study was to determine and compare the effects of both magnesium citrate and phytin on reducing urinary calcium excretion under high-calcium-diet conditions during single and combined treatments. An animal experiment was carried out over a period of 4 weeks in 35 male rats. Urinary calcium excretion was reduced significantly by magnesium citrate and/or phytin in rats fed on high-calcium diets. The hypocalciuric effect of magnesium citrate was more evident than that of phytin. Urinary magnesium excretion was high in all experimental groups. However, the urinary magnesium/calcium ratios showed a consistent increase only in the groups treated with magnesium citrate. Urinary citrate excretion showed a relative increase with the introduction of magnesium citrate plus phytin; however, in both the high-calcium-diet group and the magnesium-citrate group this was found to be reduced. Urinary phosphate excretion was slightly higher in the groups treated with phytin. There was no definite difference in urinary oxalate concentration between the groups. No significant change was noted in the serum concentration of calcium, magnesium, or phosphate.

Animals↗
PubMed1988

Comparison of delayed hepatobiliary imaging using 99mTc-Sn-N-pyridoxyl-5-methyltryptophan and 67Ga-citrate imaging for diagnosis of hepatocellular carcinoma.

Images were obtained both with a biliary agent, 99mTc-Sn-N-pyridoxyl-5-methyltryptophan (99mTc-PMT), and with 67Ga-citrate in 40 cases of hepatocellular carcinoma and in 43 cases of other hepatic diseases and results were compared. Positive results were obtained by delayed 99mTc-PMT imaging in 25 (63%) of 40 cases of hepatoma: the hepatic tumor showed increased uptake in 18 cases (45%) and equilibrated uptake in 7 cases (18%). Positive 67Ga-citrate imaging was found in 28 (70%) of the 40 cases of hepatoma: increased uptake was seen in 24 cases (60%) and equilibrated uptake in 4 cases (10%). Of 15 cases of hepatoma giving negative results in the 99mTc-PMT study, 7 cases (47%) took up 67Ga-citrate, and 6 of these showed increased 67Ga-citrate uptake by the hepatic tumors. A certain relation existed between the degree of histological differentiation of hepatomas and the intensity of 99mTc-PMT uptake by those tumors, while such a histological correlation was denied for 67Ga-citrate uptake by the tumors. Delayed 99mTc-PMT imaging is preferable to 67Ga-citrate imaging for increasing the specificity of diagnosis of hepatoma. 67Ga-citrate should be used in those cases that do not give positive results with 99mTc-PMT.

Carcinoma, Hepatocellular↗
PubMed1992

Sodium citrate ingestion and its effects on maximal anaerobic exercise of different durations.

The effects of an alkalising agent were studied in ten subjects who participated in anaerobic testing on a cycle ergometer to determine the effectiveness of sodium citrate (0.5 g.kg-1 body mass) as an ergogenic aid during exercise of 10-s, 30-s, 120-s and 240-s duration. Blood was collected prior to, after ingestion of sodium citrate (NaHCO3), and postexercise, from a heated (43-46 degrees C) fingertip and analysed immediately postcollection for pH, partial pressure of oxygen and carbon dioxide, base excess and blood bicarbonate. Total work undertaken (kJ) and peak power (W) achieved during the tests was also obtained via a work monitor unit. The results indicated that a dose of 0.5 g.kg-1 body mass sodium citrate had no ergogenic benefit for exercise of either 10-s or 30-s duration. Blood bicarbonate concentrations, however, were significantly increased (P less than 0.05) following ingestion of the citrate during these trials. Exercise periods of 120 s and 240 s were significantly increased (P less than 0.05) above the control and placebo conditions following sodium citrate ingestion. Blood bicarbonate concentrations were again increased above control and placebo conditions and blood lactate concentrations were also increased following the citrate trials. The pH decreased significantly (P less than 0.05) in all trials below the control and placebo conditions. On the basis of the exercise undertaken in this study we would suggest that a dose of 0.5 g.kg-1 body mass of sodium citrate could improve anaerobic exercise performance of 120-s and 240-s duration.

Administration, Oral↗
PubMed1988

The influence of citrate on the duodenal absorption of calcium in the rat.

Using in situ perfusion in the rat, we studied the duodenal bidirectional fluxes (LP, lumen-to-plasma; PL, plasma-to-lumen) and the net absorption of calcium (Ca) at progressive molar citrate:Ca ratios (1:1, 2.1:1, 8.5:1) and three pH levels (pH 5.0, 6.25, 7.0) of the Ca-containing (4 mmol/liter) perfusion solution. Rats perfused with pH-adjusted, citrate-free solutions served as controls. LP-flux and net calcium absorption (net CaA) fell dose-dependently with increasing citrate concentrations. Also, at a given citrate:Ca ratio, LP-flux and net CaA fell with increasing pH of the perfusion solution. PL-fluxes did not change from control values, irrespective of the composition of the perfusion solution. The concomitant serum Ca and parathyroid hormone levels as well as blood pH and bicarbonate, were largely unchanged under any of the citrate-containing perfusion solutions. In conclusion, citrate inhibits duodenal CaA of the rat pH- and dose-dependently, without changing intestinal Ca secretion. This effect is not related to changes in the acid-base status or to suppressed parathyroid gland function of the animals and may be best explained by dose- and pH-dependent intraluminal complex formation between Ca and citrate.

Animals↗
PubMed1999

Uptake of positron emission tomography tracers in experimental bacterial infections: a comparative biodistribution study of radiolabeled FDG, thymidine, L-methionine, 67Ga-citrate, and 125I-HSA.

The purpose of this study was to evaluate the localization of positron emission tomography (PET) tracers [2-deoxy-2-fluoro-D-glucose (FDG), thymidine, and L-methionine] in sites of bacterial infection, and to contrast this with that of other tracers. The left calf muscles of rats were infected with a suspension of Escherichia coli and the biodistribution of 18F- or 3H-FDG, 3H-thymidine, L-11C- or 3H-methionine, gallium-67 citrate (67Ga-citrate) and iodine-125 human serum albumin (125I-HSA) was determined in these animals. 3H-FDG uptake in the infectious foci was evaluated by autoradiography of histological sections. Although 18F-FDG, 67Ga-citrate, and 125I-HSA showed comparatively high uptake in the infected muscle [the percentage activity of injected dose (ID) per gram of tissue normalized for rat weight in kilogram (%ID/g)xkg at 2 h postinjection was as follows: 18F-FDG, 0.184+/-0.026 to 0.218+/-0.046; 67Ga-citrate, 0.221+/-0.016; 125I-HSA, 0. 198+/-0.019], the infected muscle to blood ratio was much higher for 18F-FDG than for 67Ga-citrate or 125I-HSA (18F-FDG, 10.31+/-0.76 to 14.89+/-2.26; 67Ga-citrate, 1.24+/-0.67; 125I-HSA, 0.20+/-0.02). The draining reactive lymph nodes also showed higher accumulation of 18F-FDG than of 67Ga-citrate or 125I-HSA. The uptake of 3H-thymidine and L-11C- or 3H-methionine in the infected muscle was lower than that of 18F- or 3H-FDG (at 2 h postinjection, 3H-thymidine = 0. 039+/-0.005 and L-3H-methionine = 0.063+/-0.007 (%ID/g)xkg. Autoradiographs showed that the highest 3H-FDG uptake was seen in the area of inflammatory cell infiltration surrounding the necrotic region. In conclusion, 18F-FDG, which rapidly accumulates in sites of bacterial infection and in reactive lymph nodes with a high target to background ratio, appears to be a promising infection detection agent.

Animals↗
PubMed2003

Citrate anticoagulation in pediatric continuous venovenous hemofiltration.

Regional citrate anticoagulation has become a common alternative to systemic heparinization in adult continuous venovenous hemofiltration (CVVH) practice. We report our experience with the technique in critically ill children. We carried out a retrospective chart review of a 22-bed pediatric intensive care unit. CVVH with pre-filter citrate and systemic calcium replacement infusions was performed according to a strict protocol in nine consecutive critically ill children. All charts were reviewed for patient characteristics and CVVH circuit parameters, including filter survival. All complications were noted. Nurse specialists were interviewed about the practical management of citrate anticoagulation. All patient measurements of blood urea nitrogen, creatinine, sodium, ionized calcium (iCa), potassium, and bicarbonate were collected over the CVVH period. In seven patients, 12 simultaneous citrate measurements were taken from patient blood, pre-filter blood, and hemofiltrate fluid. Nine patients (mean age 8.8+/-6.8 years) were treated with CVVH and regional citrate anticoagulation for 1-14 days (mean 5.2+/-4.0 days). Of 19 filters used, 15 were replaced non-electively (mean filter survival 55.6+/-22.0 h). Control of azotemia and hyperkalemia was good. Sodium and iCa levels were well maintained. Bicarbonate levels were elevated in four patients without adverse effects. The mean systemic citrate level at equilibrium was 1.6+/-0.23 mmol/l. No systemic bleeding complications were observed. In children, regional citrate anticoagulation provides equivalent filter survival to heparin without bleeding complications. With good staff preparation, it is simple to perform and safe with respect to metabolic side effects.

Adolescent↗
PubMed2002

Rhodothermus marinus: a thermophilic bacterium producing dimeric and hexameric citrate synthase isoenzymes.

Two separate citrate synthases from the extremely thermophilic bacterium Rhodothermus marinus have been identified and purified. One of the enzymes is a hexameric protein and is the first thermostable, hexameric citrate synthase to be isolated. The other is a dimeric enzyme, which is also thermostable but possesses both citrate synthase and 2-methyl citrate synthase activities. 2-Methyl citrate synthase uses propionyl-coenzyme A as one of its substrates and in Escherichia coli, for example, it has been implicated in the metabolism of propionate. However, no growth of R. marinus was observed using minimal medium with propionate as the sole carbon source, and both hexameric and dimeric enzymes were produced irrespective of whether propionate was included in the growth medium. The data are discussed with respect to the evolutionary relationships between the known hexameric and dimeric citrate synthases and 2-methyl citrate synthase.

Amino Acid Sequence↗
PubMed1983

Complexes between mitochondrial enzymes and either citrate synthase or glutamate dehydrogenase.

Experiments performed in polyethylene glycol and with a divalent crosslinker indicate that both mitochondrial malate dehydrogenase and aspartate aminotransferase can form hetero enzyme--enzyme complexes with either glutamate dehydrogenase or citrate synthase. In general, these as previous results indicate that complexes with the aminotransferase are favored over those with malate dehydrogenase and complexes with glutamate dehydrogenase are favored over those with citrate synthase. When the levels of enzymes are low, the only detectable complex is between the aminotransferase and glutamate dehydrogenase. Under these conditions, palmitoyl-CoA is required for complexes between the other three enzyme pairs, however, palmitoyl-CoA also enhances interactions between glutamate dehydrogenase and the aminotransferase. DPNH disrupts complexes with malate dehydrogenase and has little effect on those with the aminotransferase, while oxalacetate disrupts complexes with citrate synthase but has little effect on those with glutamate dehydrogenase. The citrate synthase-aminotransferase complex was favored in the presence of DPNH plus malate, which disrupt the other three enzyme-enzyme complexes. Glutamate dehydrogenase has a higher affinity and capacity than citrate synthase for palmitoyl-CoA. Consequently, lower levels of palmitoyl-CoA are required to enhance interactions with glutamate dehydrogenase. Furthermore, glutamate dehydrogenase can compete with citrate synthase for palmitoyl-CoA and thus can prevent palmitoyl-CoA from enhancing interactions between citrate synthase and either malate dehydrogenase or the aminotransferase.

Acyl Coenzyme A↗
PubMed1991

Interaction of ligands with pig heart citrate synthase: conformational changes and catalysis.

The fluorescence polarization of 8-hydroxypyrene (1,3,6)trisulfonate (HPT) increases upon interaction with pig heart citrate synthase. Titration of HPT with increasing concentrations of citrate synthase exhibits a hyperbolic saturation behavior, from which the dissociation constant of the enzyme-HPT complex (3.64 +/- 0.3 microM) was determined. The enzyme-HPT interaction is competitively inhibited by oxaloacetate (but not affected by acetyl CoA) with a Ki of 4.3 +/- 1.8 microM. This value is similar to the dissociation constant (Kd = 4.5 +/- 1.6 microM) for the enzyme-oxalocetate complex (determined in the absence of any effector ligand), as well as to the Km for oxaloacetate (3.9 +/- 0.7 microM) in a steady-state citrate synthase catalyzed reaction at a saturating concentration of acetyl CoA. However, the dissociation constant for the citrate synthase-oxaloacetate complex determined by the urea denaturation method is at least 25-fold lower than those determined by the other methods. This suggests an effector role of urea in strengthening the enzyme-oxaloacetate interaction. At low nondenaturing concentrations, urea inhibits the citrate synthase catalyzed reaction in an uncompetitive manner with respect to oxaloacetate, i.e., the Km for oxaloacetate decreases with an increase in urea concentration. This further suggests that urea stabilizes the interaction between citrate synthase and oxaloacetate. The effect of urea is specific for the substrate oxaloacetate, and not for the substrate analogue, HPT, although both these ligands bind citrate synthase with equal affinities, and protect the enzyme against thermal denaturation with equal magnitudes. The results presented herein are discussed in the light of known conformational states of the enzyme.

Acetyl Coenzyme A↗
PubMed1982

Compartmentation of citrate in relation to the regulation of glycolysis and the mitochondrial transmembrane proton electrochemical potential gradient in isolated perfused rat heart.

Subcellular fractionation of tissue in nonaqueous media was employed to study metabolite compartmentation in isolated perfused rat hearts. The mitochondrial and cytosolic concentrations of citrate and 2-oxoglutarate, total concentrations of the glycolytic intermediates and rate of glycolysis were measured in connection with changes in the rate of cellular respiration upon modulation of the ATP consumption by changes of the mechanical work load of the heart. The concentrations of citrate and 2-oxoglutarate in the mitochondria were 16- and 14-fold, respectively, greater than those in the cytosol of beating hearts. The cytosolic citrate concentration was low compared with concentrations which have been employed in demonstrations of the citrate inhibition of glycolysis. In spite of the low activities reported for the tricarboxylate carrier in heart mitochondria, the cytosolic citrate concentration reacted to perturbations of the mitochondrial citrate concentration, and inhibition of glycolysis at the phosphofructokinase step could be observed concomitantly with an increase in the cytosolic citrate concentration. The delta pH across the inner mitochondrial membrane calculated from the 2-oxoglutarate concentration gradient and the mitochondrial membrane potential calculated from the adenylate distribution gave an electrochemical potential difference of protons compatible with chemiosmotic coupling in the intact myocardium.

Animals↗
PubMed1989

Lipid bilayer permeation by neutral aluminum citrate and by three alpha-hydroxy carboxylic acids.

Several groups have proposed that aluminum (Al) may permeate biological membranes as a neutral complex with citrate. We tested this hypothesis by measuring aluminum citrate flux across unilamellar phospholipid vesicles (liposomes). Results from two independent procedures show that lipid bilayer permeation by the neutral aluminum-citrate complex is slow (P approximately equal to 1 x 10(-11) cm.s-1). We then compared aluminum-citrate permeation with permeation by a series of alpha-hydroxy carboxylic acids and by trimethylcitrate. This comparison showed that the aluminum-citrate flux is limited by diffusion across the water/lipid interface. This is due to hydrogen bonding between water and the citrate carboxyl groups, and by hydration of the bound metal in the aqueous phase. By analogy with citric acid, steric hindrance of diffusion within the bilayer does not affect the permeation rate of aluminum citrate. Elevated tissue levels of Al in subjects fed a diet supplemented with citric acid and Al(OH)3 cannot be explained by lipid bilayer permeation of the neutral complex.

Aluminum↗
PubMed1983

Citrate accumulation by a Golgi apparatus-rich fraction from lactating bovine mammary gland.

1. Golgi apparatus-rich fractions from lactating bovine mammary gland rapidly accumulated citrate from incubation medium. Characteristics of this process suggested that a citrate transport system may be present in Golgi apparatus membranes. 2. Endoplasmic reticulum fractions accumulated citrate at nearly the same rate as Golgi apparatus; secretory vesicle fractions displayed lower ability to accumulate citrate. Intact epithelial cells (acini) from lactating mammary gland did not accumulate citrate. 3. Citrate accumulation by Golgi apparatus was pH and temperature sensitive but was not altered by metabolic inhibitors. 4. These observations suggest a role for Golgi apparatus in packaging intracellular citrate for secretion into milk.

Animals↗
PubMed1992

Citrate is an endogenous inhibitor of snake venom enzymes by metal-ion chelation.

Citrate levels in selected snake venoms were determined by an enzymatic assay coupled to NADP+ reduction. Citrate concentrations in different viper venoms (n = 5) varied from 95 to 150 mM, in crotalids (n = 3) from 63 to 142 mM, and in elapids (n = 4) from 17 to 163 mM. In Bothrops asper venom Ca(2+)-ion concentrations varied from 2.5 to 3.6 mM, suggesting that the high relative citrate levels may serve to chelate endogenous divalent metal cations, thereby inactivating divalent cation requiring enzymes. Control experiments with B. asper phospholipase A2 MIII in the presence of 2.5 mM Ca2+, showed that the enzyme is completely inhibited by 20 mM citrate. Crotalus adamanteus 5'-nucleotidase and phosphodiesterase are also inhibited 100 and 75%, respectively, by 100 mM citrate. By forming complexes with divalent metal ions, citrate markedly reduces the activities of selected enzymes in snake venoms. Secretion of high concentrations of citrate may represent an important mechanism by which snakes protect themselves against the toxic effects of their own venoms.

5'-Nucleotidase↗
PubMed1995

Direct effect of cadmium on citrate uptake by isolated rat renal brush border membrane vesicles.

High incidence of multiple kidney stone formation has been observed among workers exposed to cadmium (Cd). Citrate is known to be a protective factor against renal stone formation. To study the direct effect of cadmium on citrate uptake by the renal brush border membrane, we exposed isolated rat renal brush border membrane vesicles (BBMV) to cadmium and determined their citrate uptake characteristics. BBMV were prepared by the divalent cation precipitation method. Citrate uptake was measured by the Millipore rapid membrane filtration technique. Preincubation of BBMV with 2 and 10 mM CdCl2 for 1 min significantly inhibited citrate uptake compared with that of BBMV without Cd. Analysis of the time course of citrate uptake during 30-min preincubation of BBMV with 0.5 mM Cd also revealed significant reduction of the uptake compared with that of the control BBMV without preincubation. These findings indicate that preincubation of BBMV with cadmium results in time-dependent and concentration-dependent inhibition of citrate uptake.

Animals↗
PubMed2005

Synthesis and evaluation of poly(diol citrate) biodegradable elastomers.

Herein, we report the synthesis and evaluation of a novel family of biodegradable and elastomeric polyesters, poly(diol citrates). Poly(diol citrates) were synthesized by reacting citric acid with various diols to form a covalent cross-linked network via a polycondensation reaction without using exogenous catalysts. The tensile strength of poly(diol citrates) were as high as 11.15+/-2.62 MPa and Young's modulus ranged from 1.60+/-0.05 to 13.98+/-3.05 MPa under the synthesis conditions that were investigated. Elongation was as high as 502+/-16%. No permanent deformation was found during mechanical tests. The equilibrium water-in-air contact angles of measured poly(diol citrates) films ranged from 15 degrees to 53 degrees . The mechanical properties, degradation and surface characteristics of poly(diol citrates) could be controlled by choosing different diols as well as by controlling the cross-link density of the polyester network. Various types of poly(diol citrate) scaffolds were fabricated to demonstrate their processing potential. These scaffolds were soft and could recover from deformation. In vitro and in vivo evaluation using cell culture and subcutaneous implantation, respectively, confirmed cell and tissue compatibility. The introduction of poly(diol citrates) will expand the repertoire of currently available biodegradable polymeric elastomers and should help meet the requirements of tissue engineering applications.

Animals↗
PubMed2004

Recycling of Ni(II)-citrate complexes using precipitation in alkaline solutions.

When the excess of Ni(II) ions as compared to citrate concentration is used both Ni(II) ions and citrate can be precipitated in alkaline solutions. The ratio between Ni(II) and citrate in the precipitate and completeness of citrate precipitation depends on the ratio between the Ni(II) and citrate concentrations in the initial solution and its pH. The data of chemical analysis, potentiometric titration, FT-IR as well as visible spectrophotometric investigations suggest that Ni(II) in the insoluble compound is bound with three -COO- groups and -OH group of the citrate. The insoluble compound also contains SO4(2-) and hydroxides. The treatment of this precipitate with H2SO4 enables to recover a soluble Ni(II)-citrate complex, which can be reused in practice, and to remove the excess of Ni(II) in the form of insoluble Ni(OH)2.

Alkalies↗
PubMed1997

Potassium-magnesium citrate is an effective prophylaxis against recurrent calcium oxalate nephrolithiasis.

PURPOSE: We examined the efficacy of potassium-magnesium citrate in preventing recurrent calcium oxalate kidney calculi. MATERIALS AND METHODS: We conducted a prospective double-blind study of 64 patients who were randomly assigned to receive placebo or potassium-magnesium citrate (42 mEq. potassium, 21 mEq. magnesium, and 63 mEq. citrate) daily for up to 3 years. RESULTS. New calculi formed in 63.6% of subjects receiving placebo and in 12.9% of subjects receiving potassium-magnesium citrate. When compared with placebo, the relative risk of treatment failure for potassium-magnesium citrate was 0.16 (95% confidence interval 0.05 to 0.46). Potassium-magnesium citrate had a statistically significant effect (relative risk 0.10, 95% confidence interval 0.03 to 0.36) even after adjustment for possible confounders, including age, pretreatment calculous event rate and urinary biochemical abnormalities. CONCLUSIONS: Potassium-magnesium citrate effectively prevents recurrent calcium oxalate stones, and this treatment given for up to 3 years reduces risk of recurrence by 85%.

Adult↗
PubMed2002

Oral potassium citrate treatment for idiopathic hypocitruria in children with calcium urolithiasis.

PURPOSE: We evaluated the clinical and laboratory outcome of oral potassium citrate treatment in children with idiopathic hypocitruria and calcium stones. MATERIALS AND METHODS: The charts of 64 children 1 to 15 years old with hypocitruria and calcium stones (median age 7.2) treated with oral potassium citrate were reviewed. Evaluation parameters were tolerability, adverse reactions, metabolic profile and stone recurrence. RESULTS: No serious adverse reaction due to potassium citrate administration was recorded. Normal citrate excretion was restored in all patients. After treatment median urinary citrate daily plus or minus SD increased from 197 +/- 72 to 632 +/- 218 mg./1.73 m.2 (p <0.001) and mean urinary pH increased from 5.3 +/- 0.3 to 6.2 +/- 0.7 (p <0.01). Mean calcium excretion decreased from 3.5 +/- 2.7 to 2.5 +/- 2.7 mg./kg. (p <0.05). At an average followup of 22 months (range 3 to 67) the recurrence rate in the group overall was 0.07 per patient-year. The previous recurrence rate of 0.32 per patient-year in the 20 children with a history of recurrent stone disease decreased to 0.17 per patient-year after treatment. None of the 44 initial stone formers had recurrent stones. CONCLUSIONS: Our results show the safety and efficacy of oral potassium citrate treatment for restoring normal urinary citrate and suggest a preventive effect for recurrent calcium stone disease in children with hypocitruria and calcium stones.

Administration, Oral↗