Autophagy functions as a survival mechanism during cellular stress and contributes to resistance against anticancer agents. The selective antitumor and antimetastatic chelator di-2-pyridylketone 4,4-dimethyl-3-thiosemicarbazone (Dp44mT) causes lysosomal membrane permeabilization and cell death. Considering the integral role of lysosomes in autophagy and cell death, it was important to assess the effect of Dp44mT on autophagy to further understand its mechanism of action. Notably, Dp44mT affected autophagy by two mechanisms. First, concurrent with its antiproliferative activity, Dp44mT increased the expression of the classical autophagic marker LC3-II as a result of induced autophagosome synthesis. Second, this effect was supplemented by a reduction in autophagosome degradation as shown by the accumulation of the autophagic substrate and receptor p62. Conversely, the classical iron chelator desferrioxamine induced autophagosome accumulation only by inhibiting autophagosome degradation. The formation of redox-active iron or copper Dp44mT complexes was critical for its dual effect on autophagy. The cytoprotective antioxidant N-acetylcysteine inhibited Dp44mT-induced autophagosome synthesis and p62 accumulation. Importantly, Dp44mT inhibited autophagosome degradation via lysosomal disruption. This effect prevented the fusion of lysosomes with autophagosomes to form autolysosomes, which is crucial for the completion of the autophagic process. The antiproliferative activity of Dp44mT was suppressed by Beclin1 and ATG5 silencing, indicating the role of persistent autophagosome synthesis in Dp44mT-induced cell death. These studies demonstrate that Dp44mT can overcome the prosurvival activity of autophagy in cancer cells by utilizing this process to potentiate cell death. 相似文献
To investigate the effect of subsequently absorbed metal chelators on recently absorbed 59Fe, duodenal segments from iron-deficient and iron-adequate rats were perfused ex vivo until the 59Fe tissue load had reached a steady state. Subsequently, the segments were perfused with 3 model chelators and their iron complexes: nitrilotriacetic acid (NTA), ethylenediaminetetraacetic acid (EDTA) and citrate. Of these, NTA and EDTA bind iron much tighter than citrate, and Fe–NTA complexes exchange iron within seconds while Fe-EDTA complexes need 48 h to reach equilibrium.
Duodenal mucosa-to-serosa transport rates were comparable for all 3 chelators and correlated linearly with luminal concentration. Subsequent perfusion with increasing NTA, Fe–NTA(1:2) and EDTA concentrations mobilised increasing amounts of 59Fe from the duodenum. Mobilised 59Fe moved preferentially back into the luminal perfusate in iron-adequate segments. In iron-deficient segments, 59Fe preferentially continued the absorption process across the basolateral membrane. Fe–EDTA(1:1) hardly mobilised any 59Fe back into the lumen, though basolateral transfer increased at high concentrations. Citrate and Fe–citrate(1:1) mobilised 59Fe only at very high concentrations.
This behaviour is in accordance with the rules of complex chemistry: strong, fast reacting ligands like NTA show most impact. Slowly reacting complexes like Fe–EDTA(1:1) have little mobilising impact in spite of strong affinity between EDTA and iron. The low affinity between iron and citrate can be compensated by large concentration. Moreover, iron-deficient segments show stronger re-uptake of mobilised 59Fe from the lumen and a stronger transfer of 59Fe from the tissue across the basolateral membrane. Both are compatible with the more marked expression of divalent metal transporter 1 (DMT-1) and IREG-1 at the brushborder and basolateral membrane of iron-deficient enterocytes. The data suggest that iron ions interact with food ligands during their passage from the apical to the basolateral side of duodenal enterocytes. 相似文献
In 1991, treatment with low dose intramuscular desferrioxamine (DFO), a trivalent chelator that can remove excessive iron and/or aluminum from the body, was reported to slow the progression of Alzheimer's disease (AD) by a factor of two. Twenty years later this promising trial has not been followed up and why this treatment worked still is not clear. In this critical interdisciplinary review, we provide an overview of the complexities of AD and involvement of metal ions, and revisit the neglected DFO trial. We discuss research done by us and others that is helping to explain involvement of metal ion catalyzed production of reactive oxygen species in the pathogenesis of AD, and emerging strategies for inhibition of metal-ion toxicity. Highlighted are insights to be considered in the quests to prevent potentially toxic effects of aluminum toxicity and prevention and intervention in AD. 相似文献
The effect of chelators on free radical damage to deoxyribose induced by iron, on IgG by UV irradiation, and on mouse muscle by homogenisation has been studied using the Thiobarbituric acid method and the increase in fluorescence in IgG mixtures.Although there were some variations on the effects of the chelators in the three models, it was shown that most of the chelators could inhibit the noxious effects of the free radicals and some which are orally effective in increasing iron excretion in animals could be potentially useful in preventing iron toxicity in related pathogenic diseases. 相似文献
Copper is essential for several important cellular processes, but an excess of copper can also lead to oxidative damage. In brain, astrocytes are considered to play a pivotal role in the copper homeostasis and antioxidative defence. To investigate whether antioxidants and copper chelators can modulate the uptake and the toxicity of copper ions in brain astrocytes, we used primary astrocytes as cell culture model. These cells accumulated substantial amounts of copper during exposure to copper chloride. Copper accumulation was accompanied by a time- and concentration-dependent loss in cell viability, as demonstrated by a lowering in cellular MTT reduction capacity and by an increase in membrane permeability for propidium iodide. During incubations in the presence of the antioxidants ascorbate, trolox or ebselen, the specific cellular copper content and the toxicity in copper chloride-treated astrocyte cultures were strongly increased. In contrast, the presence of the copper chelators bathocuproine disulfonate or tetrathiomolybdate lowered the cellular copper accumulation and the copper-induced as well as the ascorbate-accelerated copper toxicity was fully prevented. These data suggest that predominantly the cellular content of copper determines copper-induced toxicity in brain astrocytes. 相似文献
Popular chelators (desferrioxamine, SIH, EDTA, EGTA, DTPA, and NTA) were demonstrated to have antioxidant properties, being able to reduce ABTS radical cation and react with peroxyl radicals, peroxynitrite, and hypochlorite. Desferrioxamine and SIH were most potent antioxidants in all cases. These results point to the necessity of a careful interpretation of experiments in which the inhibition of free radical reactions by antioxidants is used as a proof of involvement of metal ions in a reaction. 相似文献
The inner shell coordination properties of zinc proteins have led to the identification of four types of zinc binding sites:
catalytic, cocatalytic, structural, and protein interface. Outer shell coordination can influence the stability of the zinc site and its function as exemplified herein by the zinc
sites in carbonic anhydrase, promatrix metalloproteases and alcohol dehydrogenase. Agents that disrupt these interactions,
can lead to increased off rate constants for zinc. d-penicillamine is the first drug to inhibit a zinc protease by catalyzing the removal of the metal. Since it can accept the
released zinc we have referred to it as a catalytic chelator. Agents that catalyze the release of the metal in the presence
of a scavenger chelator will also inhibit enzyme catalysis and are referred to as enhanced dechelation inhibitors. 相似文献
Anthrax lethal factor (LF) is a zinc-dependent metalloendopeptidase previously shown to require calcium and magnesium for the restoration of its catalytic function upon exposure of the apoprotein (apoLF) to Zn2+. Since concrete Ca2+/Mg2+ binding sites have not been identified in LF, the effects of alkaline earth metals on the enzymatic function of holoLF (ZnLF) and on the reconstitution of apoLF were reinvestigated. The current study reveals alkaline earth metals to be inhibitory at concentrations higher than 1 mM. A combination of activity/inhibition assays and Tb3+ luminescence spectroscopy was employed to unequivocally establish the presence of at least one inhibitory low-affinity Ca2+-site in LF. A comparative analysis of apoLF preparations obtained by dialysis and centrifugal filtration (following treatment of ZnLF with chelators) revealed the exposure of apoLF to low equimolar amounts of Zn2+ to be sufficient for the full restoration of the protein’s catalytic competence, a finding constistent with the picomolar dissociation constant of ZnLF determined in this study. The previously documented requirement of Ca2+ and Mg2+ in apoLF reconstitution may be explicable on the basis of contamination of dialyzed apoprotein preparations with residual chelator, a phenomenon not encountered with apoLF obtained by centrifugal filtration. 相似文献
The present study deals with technique for improving phytoremediation of trace metals from synthetic leachate in the presence of recycled waste material (crushed brick and steel slag) as substrates. It is an economic and environment-friendly approach as compared to chelators. Chelators induce adverse effects on plant growth, which might affect the phytoextraction capability. This study was conducted to compare the removal of copper and zinc by Phragmites australis and Typha latifolia with chelators (ethylenediaminetetraacetic acid ~2.5 mmol, citric acid ~2.5 mmol) and substrates (slag ~2 kg, crushed brick ~2 kg) for 21 days. Translocation of copper in T. latifolia and P. australis increased with increase in its applied concentration and this increase was higher in presence of slag as compared to crushed brick. In treatment systems with chelators, translocation decreased with increase in copper concentration. Principal component analysis revealed correlation between the removal of copper and zinc with adsorption by substrates, which statistically proved that slag and crushed brick played a significant role in treating leachate. Phragmites australis and T. latifolia with substrates was found to be equivalent to that of chelators. Phytoremediation with crushed brick and steel slag is an environment friendly, cost effective and practical approach for developing countries. 相似文献