On the mechanism of soft tissue calcification induced by complexed iron

The interaction of ferric lactate with Ehrlich carcinoma ascites cells induces a modification of Ca(2+)-uptake which is in direct relationship with the iron mass bound to the cells. Competitive binding of iron by deferoxamine indicates that only a part of the bound iron penetrates the cell, and that to trigger a Ca(2+)-influx this intracellular iron must be over a threshold concentration. The experimental finding that ferric lactate transfers its iron to albumin and to ATP suggests that in the Ca(2+)-uptake modification it works through its iron transfer which provokes the inhibition of the cell calcium homeostasis regulatory systems (Ca(2+)-channels, intracellular Ca(2+)-binding sites and Ca(2+)-pump ATPase). The involvement of ATP in the action of ferric lactate seems related to a higher stability of the complex, and to a larger availability of active iron able to perform the inhibitory process.

Role of lipid peroxidation in ferric lactate-enhanced calcium uptake by Ehrlich carcinoma cells

Comparison of Ca2+ uptake by Ehrlich carcinoma cells in presence of ferric lactate or aluminum lactate, and formation of thiobarbituric acid-reactive substances, suggests that lipid peroxidation is associated with but not the cause of calcium overload that can lead to cell injury and death.

Soft tissue calcification induced by iron complexes

Complexed iron (III) induces a local calcification of soft tissues in mice that is strongly dependent upon the nature of the complexing molecule. Ferric lactate is much more effective in inducing calcification than iron dextran.

Ehrlich tumour cells: Ca(2+)-uptake modification by aluminium lactate

Aluminium lactate provokes the same modification of 45Ca(2+)-uptake by Ehrlich ascites tumour cells as does ferric lactate. The increase of uptake is metal-complex concentration-dependent, and in contrast to ferric lactate, is only partially inhibited by albumin. Under the same experimental conditions, chromic lactate provoked no modification of that uptake. A plasma membrane rigidity increase provoked by coordination binding of aluminium to phospholipids is likely to be the main cause of Ca(2+)-uptake modification by aluminium lactate.

Changes in calcium uptake by liver induced by ferric lactate

In vitro and in vivo Ca(2+)-uptake by the liver is increased by ferric lactate. In vitro albumin and deferoxamine inhibit ferric lactate effects. Electrophoresis demonstrates the binding of ferric lactate to albumin. In vivo, ferric lactate induces a significant increase of Ca(2+)-uptake by liver, with a maximum of 2.9 nmol/g against 0.66 nmol/g for control livers (P less than 0.005) between 5 and 24 h after administration. This uptake modification is reversible, while the amount of iron (measured as 59Fe taken up) remains constant throughout the experiment. The affinity of ferric lactate for protein and the iron mass-dependence of Ca(2+)-uptake increase support for the hypothesis of a ferric lactate-cell membrane interaction rather than an iron-catalyzed cell injury by lipid peroxidation as the major event leading to an increased Ca(2+)-uptake.

The role of the interaction between Fe(III) and cell surface in the accumulation of 67Ga by tumor cells

The study of the interaction between complexed iron and tumor cells in the presence of 67Ga-citrate indicates that a phenomenon of iron-binding related to the thermodynamic constant of stability of the iron complex, and a hydrolysis (or anion penetration) of the interaction product determine the uptake of 67Ga. The effects of various parameters such as ionic composition of the medium, nature of the iron complex, time of incubation and number of cells are discussed.

In vivo behaviour of low molecular weight iron complexes

The in vivo distribution in mice of ferric citrate, ferric beta-glycerophosphate and ferric lactate complexes has been studied. There is a relationship between the 59Fe uptake by various tissues and the physicochemical characteristics of the complexes. Ferric lactate seems a useful preparation for iron deficiency therapy.

Effects of Fe(3+)-tumor cell interaction on Ca(2+)-uptake by Ehrlich ascites tumor cells

Fe3+ ions complexed by various ligands induce an increased Ca2+ uptake by Ehrlich carcinoma ascites cells that is proportional to the thermodynamic stability constant of the complex, and the greatest increase is observed with ferric lactate. The absence of ATPase inhibition showed by this ferric complex, suggests that an increased passive diffusion of Ca2+ due to structural modifications of the cell membrane is the most probable cause of this phenomenon.

Cell labelling with 67Ga-citrate

A method of cell labelling with carrier-free 67Ga-citrate, based on a co-binding with iron from ferric lactate has been developed. 67Ga-binding has a direct relationship with the iron incorporation by the cell. Using this method Ehrlich ascites tumor cells increase their uptake from 5% (no ferric lactate) to 89% (5 mumol of ferric lactate). Erythrocytes have shown the same pattern of 67Ga-binding. In vivo cytotoxic assays (ascites formation and animal survival) have demonstrated the lack of cytotoxicity of ferric lactate under these experimental conditions. Electrophoretic analyses of 67Ga-labelled tumor cells and erythrocytes have shown the absence of free 67Ga-citrate.

Improvement of Radioactive Colloid Binding by Tumor Cells

Treatment of P388 leukemia cells with poly-DL-lysine (Poly-lys) considerably increases the binding of colloidal chromic phosphate (32P). This augmentation of the number of particles that are bound is in direct relationship with Poly-lys concentration, and very significantly with its degree of polymerization. Treatment with Poly-lys molecular weight 77,000 shows a 100% increase of binding with 200 μg and of 50% with 100 μg. Poly-lys M.W. 8,000 presents no significant increase, and for the other molecular weights the binding is intermediate.

Effects of iron-binding proteins on in vitro uptake of 67Ga-citrate by tumor cells

A comparative study of carrier-free 67Ga-citrate uptake by Ehrlich ascites tumor cells in the presence of lactoferrin, transferrin and ferritin has demonstrated that lactoferrin considerably increases the uptake of 67Ga, and that this increase seems to be determined by its iron-load. The other iron-binding proteins assayed have a null or negative effect. Their behavior in the presence of sodium citrate supports the concept of lactoferrin-binding by the cells as responsible for the uptake. The different behavior of 67Ga-citrate iron-binding protein complexes appears to support this hypothesis.

Enhancement of colloid uptake by tumor cell surface electrical charge modification

Colloidal [51Cr]chromic phosphate uptake is considerably increased by preincubation of P388 ascites leukemia cells with poly(DL-lysine). The uptake increase is in direct relationship with the concentration and the degree of polymerization of poly(DL-lysine). The probable implication of cell surface electrical charge modification in these phenomena is discussed.

Iron-binding proteins and 67Ga accumulation by tumor cells

Tumor cells incubated with 67Ga-citrate plus lactoferrin showed a lactoferrin concentration-dependent increase of 67Ga uptake while for transferrin the effect was an inhibition. A correlation was observed between the binding of 131I-labelled lactoferrin or 131I-labelled transferrin and the uptake of 67Ga by the cells. Saturation with iron did not change significantly the effects of the iron-binding proteins. Preincubation with lactoferrin, transferrin or ferric citrate increased 67Ga uptake. The formation of a ternary complex in which 67Ga mimics iron is discussed.

Iron-Binding Proteins and 67Ga Accumulation by Tumor Cells

Tumor cells incubated with 67Ga-citrate plus lactoferrin showed a lactoferrin concentration-dependent increase of 67Ga uptake while for transferrin the effect was an inhibition. A correlation was observed between the binding of 131l-labelled lactoferrin or 131l-labelled transferrin and the uptake of 67Ga by the cells. Saturation with iron did not change significantly the effects of the ironbinding proteins. Preincubation with lactoferrin, transferrin or ferric citrate increased 67Ga uptake. The formation of a ternary complex in which 67Ga mimics iron is discussed.

In vivo changes of ionic composition of tumors treated by hyperthermia

Experimental tumors submitted in vivo to hyperthermia, in the presence, or not, of lanthanum (La3+), have shown modifications in the concentration of extra- and intracellular cations. Sacrificed immediately after hyperthermia, only the group treated with La3+ presented ionic changes (lower magnesium and potassium). After 48 hours, in both cases calcium and sodium were increased while magnesium and potassium were decreased.

On the role of transferrin in 67Ga uptake by tumor cells

In vitro uptake of 67Ga-citrate and 59Fe-citrate by DS sarcoma cells in the presence of tumor-bearing animal blood plasma showed a dramatic inhibition of both 67Ga and 59Fe uptakes: about 1/10 of 67Ga and 1/50 of the 59Fe are taken up by the cells. Subcellular fractionation appears to indicate no specific binding to cell structures, and the difference of binding seems to be related to the transferrin chelation and transmembrane transport differences.

Mechanisms of gallium-67 accumulation by tumors: role of cell membrane permeability

The effects of citrate ion on in vitro and in vivo uptake of [67Ga]citrate by tumor cells have been studied. Carrier-free [67Ga]citrate seems to follow the physical diffusion of citrate ions into the cell, and the presence of carrier gallium inhibits that diffusion, reducing considerably its uptake. These results appear to support the hypothesis that increased permeability of tumor cells is the principal cause of [67Ga]citrate accumulation by tumors.

On the Role of Transferrin in 67Ga Uptake by Tumor Cells

In vitro uptake of 67Ga-citrate and 59Fe-citrate by DS sarcoma cells in the presence of tumor-bearing animal blood plasma showed a dramatic inhibition of both 67Ga and 59Fe uptakes: about ii/io of 67Ga and 1/5o of the 59Fe are taken up by the cells. Subcellular fractionation appears to indicate no specific binding to cell structures, and the difference of binding seems to be related to the transferrin chelation and transmembrane transport differences

Antitumor activity of gallium and lanthanum: role of cation-cell membrane interaction

Using the vital dye inclusion method and the radioisotopic study of Ca2+-transport, we have investigated the involvement of the gallium and lanthanum plasma-membrane interaction in the cytotoxic and antitumor characteristics of both cations. The experimental results support the hypothesis that such an interaction is the principal cause of antitumor activity, either through structural changes of the cell membrane or through inhibition of the ATPase pumps.

Effects of hyperthermia and lanthanum on tumor cell leakage

The effects of hyperthermia temperature and the presence of lanthanum on the release of Ehrlich's ascites cell molecules labelled with radiophosphorus have been studied. The leakage of intracellular molecules is in relationship with the temperature and the time of incubation. The phenomenon presents the characteristics of an increased passive diffusion induced by a thermotropic modification of the protein-lipid environment of the plasma membrane. The possible implication of this phenomenon on hyperthermic energy depletion and enhanced cytotoxicity of chemotherapeutics with poor cell penetration is discussed.

Effects of concanavalin A on 67Ga binding by tumor cells

The in vitro uptakes of 67Ga-citrate and 45Ca-chloride in the presence of concanavalin A have shown that at low concentrations (10-50 micrograms/ml) 67Ga presents a significant increase not observed for 45Ca. At higher concentrations there is a sharp augmentation of both 67Ga and 45Ca incorporations. The augmentation of Trypan blue inclusion is a concomitant phenomenon at any concanavalin A concentration that indicates tumor cell plasma membrane changes in direct relationship with 67Ga uptake increase.

Effects of gallium chloride oral administration on transplanted C3HBA mammary adenocarcinoma: Ga, Mg, Ca and Fe concentration and anatomopathological characteristics

To determine the influence of the length of the treatment on the anatomopathological and biochemical intratumor changes induced by gallium, we treated C3H BA mammary adenocarcinoma-bearing C3H/HeJ mice with gallium chloride daily, for a period of either 21 or 42 days. In both cases the same dose of 200 mg/kg/24h was administered. An increase of collagen fibrosis in treated tumors as opposed to controls was only noted after 42 days, as well as a significant decrease of the intratumor magnesium and calcium concentrations that could be responsible for a reduction in the metabolic activities of the malignant cells. Remarkable intratumor gallium concentrations (38.4 +/- 30.3 nmol/g after 21 days of treatment; 13.4 +/- 7.3 nmol/g after 42 days where the necrosis is much more important) are obtained after this oral administration. There is no renal toxicity and a higher tumor/kidney concentration ratio is obtained than after acute parenteral administration. The effect of gallium may be different according to the mode of administration: it may be more cytotoxic after parenteral administration, while after oral administration it may act as a better metabolic regulator with a more selective tumor uptake and fewer side effects.

Experimental evidence for the probable involvement of calcium ion transport in 67Ga uptake by tumour cells

The study of 67Ga-citrate uptake and calcium transport in Ehrlich ascites tumour cells seems to indicate that their peculiar characteristic of increased permeability to extracellular calcium ion might be responsible for their 67Ga accumulation. Experiments performed under different conditions of extracellular calcium, temperature, and presence of ionophore and other plasma membrane modifying agents such as lanthanum appear to corroborate this hypothesis.

Calcium and ATPase activity during hepatic intoxication with thioacetamide

The effects of acute thioacetamide (TAA) intoxication on the calcium, magnesium, sodium and potassium content of liver and on its ATPase activities were studied in rats. Samples of liver were analyzed by atomic absorption spectrometry for their cationic content 6, 24 and 48 h after administration of TAA through a stomach tube. After sonification other samples were assayed for (Na+ + K+)-dependent, (Ca2+ + Mg2+)- and Ca2+-dependent ATPases. No apparent correlation has been found between the increased hepatic calcium after TAA treatment and the variations of ATPase activity. Both calcium movement and ATPase activity appear sex-determined. These results bring support to the hypothesis that an interaction between TAA or its metabolites with the cell membrane provokes an increased influx of extracellular calcium. The relationship between this calcium increase and the changes in ATPase activity with the events triggering the neoplastic transformation is discussed.