Chelator Ethylenediaminetetraacetate Research Articles

Vitamin K and Calcium Chelation in Vascular Health.

The observation that the extent of artery calcification correlates with the degree of atherosclerosis was the background for the alternative treatment of cardiovascular disease with chelator ethylenediamine tetraacetate (EDTA). Recent studies have indicated that such chelation treatment has only marginal impact on the course of vascular disease. In contrast, endogenous calcium chelation with removal of calcium from the cardiovascular system paralleled by improved bone mineralization exerted, i.e., by matrix Gla protein (MGP) and osteocalcin, appears to significantly delay the development of cardiovascular diseases. After post-translational vitamin-K-dependent carboxylation of glutamic acid residues, MGP and other vitamin-K-dependent proteins (VKDPs) can chelate calcium through vicinal carboxyl groups. Dietary vitamin K is mainly provided in the form of phylloquinone from green leafy vegetables and as menaquinones from fermented foods. Here, we provide a review of clinical studies, addressing the role of vitamin K in cardiovascular diseases, and an overview of vitamin K kinetics and biological actions, including vitamin-K-dependent carboxylation and calcium chelation, as compared with the action of the exogenous (therapeutic) chelator EDTA. Consumption of vitamin-K-rich foods and/or use of vitamin K supplements appear to be a better preventive strategy than EDTA chelation for maintaining vascular health.

The food additive EDTA aggravates colitis and colon carcinogenesis in mouse models

Inflammatory bowel disease is a group of conditions with rising incidence caused by genetic and environmental factors including diet. The chelator ethylenediaminetetraacetate (EDTA) is widely used by the food and pharmaceutical industry among numerous other applications, leading to a considerable environmental exposure. Numerous safety studies in healthy animals have revealed no relevant toxicity by EDTA. Here we show that, in the presence of intestinal inflammation, EDTA is surprisingly capable of massively exacerbating inflammation and even inducing colorectal carcinogenesis at doses that are presumed to be safe. This toxicity is evident in two biologically different mouse models of inflammatory bowel disease, the AOM/DSS and the IL10−/− model. The mechanism of this effect may be attributed to disruption of intercellular contacts as demonstrated by in vivo confocal endomicroscopy, electron microscopy and cell culture studies. Our findings add EDTA to the list of food additives that might be detrimental in the presence of intestinal inflammation, but the toxicity of which may have been missed by regulatory safety testing procedures that utilize only healthy models. We conclude that the current use of EDTA especially in food and pharmaceuticals should be reconsidered. Moreover, we suggest that intestinal inflammatory models should be implemented in the testing of food additives to account for the exposure of this primary organ to environmental and dietary stress.

Electrochemical sensor based on EDTA intercalated into layered double hydroxides of magnesium and aluminum for ultra trace level detection of lead (II)

The chelator ethylene diaminetetraacetate (EDTA) has been intercalated into layered double hydroxides by the anion exchange method. The resulting composites were characterized by powder X-ray diffraction, FTIR spectroscopy, thermogravimetry and X-ray photoelectron spectrometry. They were applied to modify a carbon paste electrode for the stripping voltammetric determination of lead (II) ions at ng L−1 levels. Stripping currents are linearly related to the logarithm of Pb (II) concentrations from 2 ng L−1 to 33 μg L−1. The detection limit (3σ) is as low as 0.95 ng L−1. The method was successfully applied to the determination of Pb (II) in spiked tap water without any pretreatment.

Effect of Fe(II) and Fe(III) Transformation Kinetics on Iron Acquisition by a Toxic Strain of Microcystis aeruginosa

We have investigated the mechanism of Fe uptake by a toxic strain of the freshwater cyanobacterium Microcystis aeruginosa (PCC7806) with particular attention given to the effect of Fe(II) and Fe(III) transformation kinetics on Fe uptake. Chemiluminescence analysis revealed that M. aeruginosa produces extracellular superoxide (a moderate Fe reducing agent) at rates of 0.4-1.2 amol cell(-1) h(-1) depending on initial Fe concentration in the culture medium. Short-term assimilation assays using (55)Fe showed that reduction of Fe(III) in both organic and inorganic forms by cell-generated superoxide or ascorbate facilitated Fe uptake via formation of unchelated Fe(II), when Fe availability was low because of the use of the strong Fe chelator ethylenediaminetetraacetate (EDTA) as a ligand. In contrast, Fe reduction was unimportant for Fe uptake in the presence of low concentrations (< or =100 microM) of the weak Fe-binding ligand citrate because of a high concentration of unchelated Fe(III), indicating that the contribution of reduction to Fe uptake depends on the nature of Fe binding and availability of unchelated Fe(III) in the external medium. A kinetic model incorporating uptake of both unchelated Fe(II) and Fe(III) and based on similar models developed for marine microalgae successfully described Fe uptake rates by M. aeruginosa PCC7806.

Determination of Fe2+ in Rice Leaves (Oryza sativa L.) by Using the Chelator BPDS Alone or Combined with the Chelator EDTA

Iron toxicity is a problem in many areas of wetland rice. Since Fe2+ is considered to be the toxic form of iron, the objective of this research was to determine the Fe2+ concentration in rice leaves using the chelator bathophenanthroline disulfonate (BPDS), disodium salt alone or combined with the chelator ethylenediaminetetraacetate (EDTA), disodium salt, where BPDS should solely chelate the Fe2+ and EDTA chelate only Fe3+. Thus, the combination of these chelators should stabilize the Fe oxidation states. It was also tested whether the chelators BPDS and EDTA could stabilize the oxidation states of Fe during the extraction of rice leaves. Extractions of rice leaves were carried out using an 1 mM BPDS or BPDS‐EDTA extractant solution. To test the stabilization of the Fe oxidation states by the combination of BPDS with EDTA, the extraction solution for one part of the samples contained 0.07 mM Fe3+. An extraction without plant material as control was also taken into consideration. The results indicated that the chelators were able to stabilize the oxidation states of Fe in the control (extraction without plant material). However, in the presence of plant material, Fe3+ was partly reduced to Fe2+, i.e., the chelators could not stabilize the oxidation states of Fe. Accordingly, we concluded that the BPDS‐EDTA method may function for the Fe2+ determination in water and soil, but it is apparently not suited for rice leaves.

Metal binding and oxidation of amyloid-beta within isolated senile plaque cores: Raman microscopic evidence.

Alzheimer's disease (AD) is characterized by the deposition of amyloid plaques in the parenchyma and vasculature of the brain. Although previous analytical studies have provided much information about the composition and structure of synthetic amyloid-beta fibrils, there is, surprisingly, a dearth of data on intact amyloid plaques from AD brain. Therefore, to elucidate the structure and detailed composition of isolated amyloid plaque cores, we utilized a high-resolution, nondestructive technique, Raman microscopy. The data are of very high quality and contain detailed information about protein composition and conformation, about post-translational modification, and about the chemistry of metal binding sites. Remarkably, spectra obtained for senile plaque (SP) cores isolated from AD brain are essentially identical both within and among brains. The Raman data show for the first time that the SP cores are composed largely of amyloid-beta and confirm inferences from X-ray studies that the structure is beta-sheet with the additional possibility that this may be present as a parallel beta-helix. Raman bands characteristic of methionine sulfoxide show that extensive methionine oxidation has occurred in the intact plaques. The Raman spectra also demonstrate that Zn(II) and Cu(II) are coordinated to histidine residues in the SP cores, at the side chains' N(tau) and N(pi) atoms, respectively. Treatment of the senile plaques with the chelator ethylenediaminetetraacetate reverses Cu binding to SP histidines and leads to a broadening of amide features, indicating a "loosening" of the beta-structure. Our results indicate that Abeta in vivo is a metalloprotein, and the loosening of the structure following chelation treatment suggests a possible means for the solubilization of amyloid deposits. The results also reveal a direct chemical basis for oxidative damage caused by amyloid-beta protein in AD.

Effects of supplemental dietary calcium on the intestinal association of calcium, phosphate, and bile acids

It has been suggested that supplemental dietary calcium decreases hyperproliferation of colonic epithelial cells because calcium precipitates and thus inactivates luminal bile acids. Therefore, 12 healthy men were studied before and after dietary calcium supplementation (35.5 mmol/day) to quantify intestinal associations of calcium, phosphate, and bile acids. The supplemental dietary calcium was almost completely (95%) recovered, mainly in feces. Calcium increased the fecal excretion of both phosphate (31%) and bile acids (53%) and decreased the ratio of dihydroxy to trihydroxy bile acids in duodenal bile almost twofold. In vitro studies showed that precipitation of glycodeoxycholic acid was caused by the formation of insoluble calcium phosphate. Watersoluble and calcium-associated amounts of phosphate and bile acids in feces were measured by resolubilization studies, using the calcium chelator ethylenediaminetetraacetate. In both the control and calcium periods, significant amounts of phosphate (80% and 90%) and bile acids (33% and 50%) were calcium-associated. Moreover, the calcium-induced increments in fecal phosphate and bile acids were completely calcium-associated. Calcium decreased the amount of water-soluble phosphate but not of bile acids. These results indicate that supplemental calcium stimulates formation of insoluble calcium phosphate in the intestinal lumen and thus increases binding of luminal bile acids.

Effect of antagonists of calcium and phospholipase A on the cytopathogenicity of Entamoeba histolytica.

The in vitro mechanisms by which Entamoeba histolytica trophozoites lyse target Chinese hamster ovary (CHO) cells were examined. Calcium chelators ethylenediaminetetraacetate and ethyleneglycol bis (beta-aminoethyl ether)-N,N'-tetraacetate (10 mM) inhibited amebic cytolysis of target CHO cells (P less than .01). A putative antagonist of intracellular calcium flux, 8-(N,N-diethylamino)octyl-3,4,5-trimethoxybenzoate (TMB-8; greater than or equal to 250 microM), inhibited amebic adherence and cytolysis (P less than .001). Quinacrine, Rosenthal's inhibitor (dimethyl-dl-2,3-distearoyloxypropyl-2'-hydroxyethyl ammonium acetate), phosphatidylcholine, and hydrocortisone (greater than or equal to 10(-4) M), all pharmacological antagonists of eukaryotic phospholipase A enzymes, inhibited amebic killing of target CHO cells (P less than .001). At 37 C quinacrine and hydrocortisone reduced amebic adherence to CHO cells, whereas Rosenthal's inhibitor and phosphatidylcholine did not. Phosphatidylcholine and TMB-8 demonstrated a synergistic inhibitory effect on amebic killing of target CHO cells (P less than .001). These studies indicate that extracellular calcium ions, amebic intracellular calcium flux, and amebic phospholipase A activity are required for cytolysis of target cells by E. histolytica.

Free nickel ion inhibits growth of two species of green algae

Two species of green algae, Scenedesmus quadricauda (UTEX 76) and Ankistrodesmus falcatus var. acicularis (UTEX 101), were grown in a chemically defined medium containing 10·2 μ m Ni. The concentration of free metal ion was manipulated by adding the chelators EDTA (ethylenediamine tetraacetate) or NTA (nitrilotriacetic acid). For both algal species, growth rates were inversely related to the calculated concentration of free divalent nickel and independent of the total nickel in solution. For A. falcatus var. acicularis, the 14-day cell number was inversely related to the free divalent nickel concentration, while the mean individual cell volume decreased as the free divalent nickel concentration lessened. Nickel inhibition of algal growth appears to be related to the presence of the free divalent ion and is thus similar to copper, zinc and cadmium.

Outer membrane protein H1 of Pseudomonas aeruginosa: involvement in adaptive and mutational resistance to ethylenediaminetetraacetate, polymyxin B, and gentamicin

It is well established that Pseudomonas aeruginosa cells grown in Mg2+-deficient medium acquire nonmutational resistance to the chelator ethylenediaminetetraacetate and to the cationic antibiotic polymyxin B; this type of resistance can be reversed by transferring the cells to Mg2+-sufficient medium for a few generations. Stable mutants resistant to polymyxin B were isolated and shown to have also gained ethylenediaminetetraacetate resistance. Both the mutants and strains grown on Mg2+-deficient medium had greatly enhanced levels of outer membrane protein H1 when compared with the wild-type strain or with revertants grown in Mg2+-sufficient medium. It was determined that in all strains and at all medium Mg2+ concentrations, the cell envelope Mg2+ concentration varied inversely with the amount of protein H1. In addition, the increase in protein H1 in the mutants was associated with an increase in resistance to another group of cationic antibiotics, the aminoglycosides, e.g., gentamicin. We propose that protein H1 acts by replacing Mg2+ at a site on the lipopolysaccharide which can otherwise be attacked by the cationic antibiotics or ethylenediaminetetraacetate.

A Separate Antibiotic Binding Site in Xanthosine 5'-Phosphate Aminase: DIFFERENTIAL ALTERATION OF CATALYTIC PROPERTIES AND SENSITIVITY TO INHIBITION

Abstract The sensitivity of xanthosine 5'-phosphate aminase to the inhibitory effect of the antibiotic psicofuranine can be reduced by exposure to several kinds of agents capable of modifying protein structure. These include urea and ethylene glycol, reducing agents such as 2-mercaptoethanol, the chelators ethylenediaminetetraacetate and o-phenanthroline, and photo-oxidation with methylene blue. Urea, in causing a 3-fold reduction in the capacity of the aminase to bind psicofuranine and a similar reduction in sensitivity to inhibition by the aminase, also affects other properties of the aminase; the affinity constants for Mg++, NH3, adenosine triphosphate, and xanthosine 5'-phosphate are increased while the activity of the aminase is greatly reduced. 2-Mercaptoethanol reduces the sensitivity of the aminase to inhibition by psicofuranine, but reduces neither its activity nor its ability to bind psicofuranine. In contrast photo-oxidation with methylene blue desensitizes by selectively reducing the ability of the aminase to bind psicofuranine; the substrate-binding capacities of the aminase are not affected by the photo-oxidation. Psicofuranine increases the availability of sulfhydryl groups of the aminase for reaction with sulfhydryl reagents. This indication of a change in the tertiary structure of the aminase together with the additional evidence that the aminase contains a separate binding site for psicofuranine suggests that although the antibiotic is probably bound at a nonessential part of the enzyme it nevertheless may act by distorting the active center.