Paul Saltman

Chelation of iron by sugars

Abstract Reducing sugars and polyols are shown to form soluble stable complexes with a series of metal ions at alkaline pH. Several properties of an iron-fructose complex have been studied. The specific conditions of pH and concentrations of iron and fructose necessary for complex formation are described. Evidence for the existence of the complex is (a) its solubility at alkaline pH, (b) its characteristic spectral properties, (c) titration and redox measurements, and (d) the direct isolation of the water-soluble complex. Ferric-fructose can be isolated and purified by precipitation from an aqueous solution with ethanol or other organic solvents. Elemental analysis indicates the complex at pH 9.0 is formed with 2 Fe: 2 fructose: 1 Na. Ferric-fructose is a low-molecular-weight compound which rapidly dialyses through a Visking sac. It is isoionic at pH 4.5–4.7. Metal-sugar complexes may play an important biological role in the transport of the mineral elements across cell membranes.

Chelation of calcium by lactose: its role in transport mechanisms.

Lactose, like other sugars and polyols, prevents or delays the precipitation of calcium ion in the presence of bicarbonate buffer. That an uncharged calcium-lactose complex is formed was demonstrated by the use of paper electrophoresis and of calcium-45 as a label for the complex. Enhancement of the intestinal absorption of calcium ion by sugars could result from a complex of low molecular weight.

Hemoglobin: A mechanism for the generation of hydroxyl radicals

Oxyhemoglobin (HbO2) reduces Fe(III)NTA aerobically to become methemoglobin (metHb) and Fe(II)NTA. These conditions are favorable for the generation via Fenton chemistry of the hydroxyl radical that was measured by HPLC using salicylate as a probe. The levels of hydroxyl radicals generated are a function of both the percent metHb formed and the chemical nature of the buffer. The rates of formation of both metHb and hydroxyl radicals were dependent upon the concentration of Fe(III)NTA. Of the buffers tested, HEPES was the most effective scavenger of hydroxyl radicals while the other buffers scavenged in the order: HEPES > Tris > MPOS > > NaCL approximately unbuffered. The addition of catalase to remove H2O2 or bathophenanthroline to chelate Fe(II) inhibited virtually all hydroxyl radical formation. Carbonyl formation from free radical oxidation of amino acids was found to be 0.1 mol/mol of hemoglobin. These experiments demonstrate the ability of hemoglobin to participate directly in the generation of hydroxyl radicals mediated by redox metals, and provide insight into potential oxidative damage from metals released into the blood during some pathologic disorders including iron overload.

Different cellular targets for Cu- and Fe-catalyzed oxidation observed using a Cu-compatible thiobarbituric acid assay

The widely used thiobarbituric acid (TBA) assay for oxidative damage to biomolecules fails in Cu2(+)-containing solutions due to the formation of a cloudy precipitate. The chelation of Cu2+ ions with EDTA or Chelex was investigated. Both prevented precipitate formation, but only Chelex allowed proper color development in the TBA assay. The Chelex modified assay could be adapted to a variety of systems, and was applied to the detection of Cu2+/ascorbate dependent deoxyribose breakdown and oxidative damage in erythrocyte ghosts, lysates and whole cells. Using this method, it was shown that Cu2+/ascorbate caused membrane damage in ghosts but not in whole red blood cells (RBC). Fe3+/ascorbate, on the other hand, caused formation of TBA-reactive products even in whole RBC. When Cu2+ and Fe3+ were presented to isolated hemoglobin as their 1:1 nitrilotriacetate complexes, the protein bound 10-12 cupric ions per molecule, but no ferric ions. It is suggested that oxidative damage catalyzed by copper or iron ions has different cellular targets, determined by the different binding properties of the two metals to various cellular components.

The effect of deficiencies of manganese and copper on osteoinduction and on resorption of bone particles in rats

SummarySubcutaneous implantation of devitalized demineralized bone powders (DBP) and mineral-containing bone particles (BP) into rats raised on either a control (C), low manganese and low copper (L), or manganese-deplete (D) diet, allowed the separate evaluation of bone formation and of bone resorption, respectively. DBP failed to induce chondrogenesis or osteogenesis in D rats. Cartilage formation was delayed in the L rats compared to C rats. There was significantly less resorption of BP by L and D rats than C rats. These results show multiple cellular effects of long-term manganese (Mn) and copper (Cu) deficiencies on bone metabolism including decreased osteogenesis and a decrease in osteoclast activity.

The transport of iron by rat intestine.

Abstract To define more clearly the mechanisms operate in the transport of iron by intestinal mucosa, the short-circuit technique has been applied to isolated sections of small intestine of rat. Parallel experiments have been carried out in vivo using ligated sections of the small intestine in the intact rat. Low-molecular-weight chelates are necessary to maintain iron in a soluble and permeable from. Although the rate of mucosal to serosal transport appears to be directly dependent upon the concentration of iron chelate presented to the cell, a membrane-bound facilitating carrier also participates in the process. Evidence is presented for an active serosal to mucosal component for iron transport. Metabolic inhibitors, low temperatures and anaerobiosis abolish the net serosal to mucosal flux. The chemical nature of the chelate directly affects the rate of transmembrane transport as well as the tissue distribution of the iron molecule. Iron deficiency anemia causes both a decrease in the serosal to mucosal iron flux and an increase in the mucosal to serosal component. These factors appear to be responsible for the enhanced uptake of iron observed in anemic animals.

The mechanism of calcium transport by rat intestine

Abstract Short-circuit techniques for the study of ion transport by isolated membrane systems have been applied to defining the mechanism for calcium ion transport in the small intestine of the rat. In the absence of phosphate, the movement of calcium is passive. There is no evidence for a membrane-bound carrier to facilitate its transport. The calcium flux is a linear function of its concentration. However, phosphate ion is actively transported from the mucosal to the serosal surface. In the presence of phosphate, calcium appears to be actively transported, possibly as a counter-ion to the phosphate. The role of chelation in the transport of calcium has also been clarified.

Synthesis and structure of a trinuclear chromium(III)-nicotinic acid complex

Abstract The reaction of nicotinic acid (nic), chromic perchlorate hexahydrate, and sodium perchlorate in aqueous solution affords a Cr(III)-vitamin complex whose composition has been established to be Na[Cr 3 O(nicH) 6 (H 2 O) 3 ][ClO 4 ] 8 ·nicH·6H 2 O, based on analytical data and a single-crystal X-ray analysis. In the [Cr 3 O(nicH) 6 (H 2 O) 3 ] +7 ion a central oxygen atom is bonded to three chromium atoms. The nicotinic and zwitterions bridge these chromium centers through the carboxylate oxygen atoms. On each chromium atom a water oxygen, trans to the central oxygen atom, complexes the octahedral coordination. The ion has crystallographically imposed symmetry 6 . The binding of nicotinic acid in this Cr(III)-nicotinic acid complex is significantly different from that currently proposed for the glucose tolerance factor.

Oxidative damage to human red cells induced by copper and iron complexes in the presence of ascorbate.

The role of trace metals in the generation of free radical mediated oxidative stress in normal human red cells was studied. Ascorbate and either soluble complexes of Cu(II) or Fe(III) provoked changes in red cell morphology, alteration in the polypeptide pattern of membrane proteins, and significant increases in methemoglobin. Neither ascorbate nor the metal complexes alone caused significant changes to the cells. The rate of methemoglobin formation was a function of ascorbate and metal concentrations, and the chemical nature of the chelate. Cu(II) was about 10-times more effective than Fe(III) in the formation of methemoglobin. Several metals were tested for their ability to compete with Cu(II) and Fe(III). Only zinc caused a significant inhibition of methemoglobin formation by Fe(III)-fructose. These observations suggest that site-specific as well as general free radical damage is induced by redox metals when the metals are either bound to membrane proteins or to macromolecules in the cytoplasm. The Cu(II) and Fe(III) function in two catalytic capacities: (1) oxidation of ascorbate by O2 to yield H2O2, and (2) generation of hydroxyl radicals from H2O2 in a Fenton reaction. These mechanisms are different from the known damage to red cells caused by the binding of Fe(III) or Cu(II) to the thiol groups of glucose-6-phosphate dehydrogenase. Our system may be a useful model for understanding the mechanisms for oxidative damage associated with thalassemia and other congenital hemolytic anemias.

Trace Elements and Blood Pressure

Essential trace elements such as zinc, iron, and copper participate in various enzyme reactions directly related to the regulation of blood pressure and indirectly related to generation of oxidative metabolic energy, alterations in blood lipid levels, and alterations in taste acuity. The toxicological action of several heavy metal ions including cadmium, lead, mercury, and thallium can cause hypertension by affecting hormone metabolism, vasoconstriction, and renal tubular function. We conclude, however, that neither deficiencies of essential elements nor the presence of toxic heavy metals are primary causes of hypertension in our population.