Divalent Metal Chelates Research Articles

Complexation and Antimicrobial Studies of Some Divalent Metal Chelates

Metal chelates of Ni(II) and Cu(II) with the ligand 5‐acetamido‐1,3,4‐thiadiazole‐2‐sulphonamide have been synthesized. The isolated compounds have been characterized by elemental analysis, molar conductivity, magnetic moment, electronic and IR spectral studies. The analytical data reflects the metal to ligand stoichiometry to be 1: 2. The conductivity data of the complexes also suggests their non‐electrolytic nature. The stability constants and free energy change for the complexes have been calculated.. Ligand and their complexes have been screened for their biological activity and the data show good activity of these complexes and ligands.

Comparative study of quercetin and its two glycoside derivatives quercitrin and rutin against methylmercury (MeHg)-induced ROS production in rat brain slices

The hypothesis that methylmercury (MeHg) potently induces formation of reactive oxygen species (ROS) in the brain is supported by observations on the neuroprotective effects of various classes of antioxidants. Flavonoids have been reported to possess divalent metal chelating properties, antioxidant activities and to readily permeate the blood-brain barrier. They can also provide neuroprotection in a wide array of cellular and animal models of neurological diseases. Paradoxically, in vivo administration of quercetin displays unexpected synergistic neurotoxic effect with MeHg. Considering this controversy and the limited data on the interaction of MeHg with other flavonoids, the potential protective effect of quercetin and two of its glycoside analogs (i.e., rutin and quercitrin) against MeHg toxicity were evaluated in rat cortical brain slices. MeHg (100 microM) caused lipid peroxidation and ROS generation. Quercitrin (10 microg/mL) and quercetin (10 microg/mL) protected mitochondria from MeHg (5 microM)-induced changes. In contrast, rutin did not afford a significant protective effect against MeHg (100 microM)-induced lipid peroxidation and ROS production in cortical brain slices. MeHg-generated ROS in cortical slices was dependent upon an increase in intracellular Ca(2+) levels, because the over-production of MeHg-induced H(2)O(2) in mitochondria occurred with a concomitant increase in Ca(2+) transient. Here, we have extended the characterization of mechanisms associated with the neuroprotective effects of quercetin against MeHg-induced toxicity in isolated mitochondria, by performing an array of parallel studies in brain slices. We provide novel data establishing that (1) Ca(2+) plays a central role in MeHg toxicity and (2) in brain slices MeHg induces mitochondrial oxidative stress both via direct interaction with mitochondria (as previously reported in in vitro studies) as well as via mitochondria-independent (or indirect) mechanisms.

Astacin-like metalloproteases are a gene family of toxins present in the venom of different species of the brown spider (genus Loxosceles)

Brown spiders have a worldwide distribution, and their venom has a complex composition containing many different molecules. Herein, we report the existence of a family of astacin-like metalloprotease toxins in Loxosceles intermedia venom, as well as in the venom of different species of Loxosceles. Using a cDNA library from the L. intermedia venom gland, we cloned two novel cDNAs encoding astacin-like metalloprotease toxins, LALP2 and LALP3. Using an anti-serum against the previously described astacin-like toxin in L. intermedia venom (LALP1), we detected the presence of immunologically-related toxins in the venoms of L. intermedia, Loxosceles laeta, and Loxosceles gaucho. Zymographic experiments showed gelatinolytic activity of crude venoms of L. intermedia, L. laeta, and L. gaucho (which could be inhibited by the divalent metal chelator 1,10-phenanthroline) at electrophoretic mobilities identical to those reported for immunological cross-reactivity. Moreover, mRNAs extracted from L. laeta and L. gaucho venom glands were screened for astacin-like metalloproteases, and cDNAs obtained using LALP1-specific primers were sequenced, and their deduced amino acid sequences confirmed they were members of the astacin family with the family signatures (HEXXHXXGXXHE and MXY), LALP4 and LALP5, respectively. Sequence comparison of deduced amino acid sequences revealed that LALP2, LALP3, LALP4, and LALP5 are related to the astacin family. This study identified the existence of gene family of astacin-like toxins in the venoms of brown spiders and raises the possibility that these molecules are involved in the deleterious effects triggered by the venom.

Crystallographic snapshots of iterative substrate translocations during nicotianamine synthesis in archaea

Nicotianamine (NA), a small molecule ubiquitous in plants, is an important divalent metal chelator and the main precursor of phytosiderophores. Nicotianamine synthase (NAS) is the enzyme catalyzing NA synthesis by the condensation of three aminopropyl moieties of S-adenosylmethionine (SAM) and the cyclization of one of them to form an azetidine ring. Here we report five crystal structures of an archaeal NAS from Methanothermobacter thermautotrophicus, either free or in complex with its product(s) and substrate(s). These structures reveal a two-domains fold arrangement of MtNAS, a small molecule related to NA (named here thermoNicotianamine or tNA), and an original mechanism of synthesis in a buried reaction chamber. This reaction chamber is open to the solvent through a small inlet, and a single active site allows the selective entrance of only one substrate at a time that is then processed and translocated stepwise.

The lipophilic zinc chelator DP-b99 prevents zinc induced neuronal death

Zinc plays a key pathophysiological role in major neurological disorders as well as diabetes, while being essential for the activity of numerous zinc binding proteins. A major challenge in chelation based therapy must take into consideration these apparently conflicting effects of zinc. One approach is to limit the activity of the chelator to regions and levels of zinc pathology, making normal zinc-dependent processes invisible to the chelator. Combining fluorescent zinc imaging with cytotoxicity assays we studied the zinc chelation efficacy and neuroprotective effect of the lipophilic divalent transition metal chelator DP-b99 (1,2-Bis(2-amino-phenoxy)ethane-N,N,N′,N′-tetraacetic acid-N-N′-di[2-(octyloxy)ethyl ester],-N,N′-disodium salt). The affinity of DP-b99 to Zn 2+ and Ca 2+ ions is moderate in water and enhanced significantly in the lipid milieu. Application of DP-b99 to MIN6 β-cells that were preloaded with zinc was followed by a decrease in fluorescence of the intracellular Zn 2+ sensitive dye, ZnAF-2DA, to resting levels. Preloading of MIN6 cells with DP-b99 was also effective in attenuating subsequent cellular zinc rise. Concentration-dependence analysis of zinc accumulation indicated that DP-b99 acts as a zinc chelator with moderate affinity. DP-b99 preapplication attenuated both Zn 2+ and Ca 2+ rise in neuronal cultures and also Zn 2+ rise in brain slices. Finally, DP-b99 attenuated Zn 2+-induced neuronal death. Our results indicate that DP-b99 is effective in attenuating Zn 2+ and Ca 2+ surges and protecting neurons against a toxic Zn 2+-rise. This may underlie the efficacy of DP-b99 in stroke treatment.

High through-Put Screening of Chemicals That Stimulate Iron Uptake: A Novel Approach to Discovery of Anti-Cancer Drugs

Iron (Fe) is an essential nutrient required for growth of all cells. Actively growing cells appear to have a greater need for iron at least as measured by increased expression of the transferrin receptor (TfR), the major route by which iron enters cells. Various attempts have been made to use iron chelators to deplete cells of iron as a means for decreasing the growth of cancer cells. We hypothesized that a contrary approach of enhancing iron entry would allow for generation of increased reactive oxygen species which could then potentiate radiation and radiomimetic drugs. To identify small molecules that would accelerate iron uptake we used a high through-put screening system in conjunction with a reporter system of K562 cells loaded with the divalent metal chelator calcein whose fluorescence is quenched with chelation of Fe2+. Small molecules that stimulate Fe uptake were defined as causing an increase of calcein fluorescence quenching compared to Fe alone. K562 cells were exposed to 0.1 μM calcein for 10 minutes, thoroughly washed, and 1 × 105 cells plated into each well of multiple 96-well plates. After equilibration of the plates at 37° C, aliquots of the individual components of an in-house chemical library of ~10,000 compounds dissolved in DMSO were screened in duplicate or triplicate and fluorescence measurements made at 0 and 30 min after addition of 10 μM FeNH4SO4 in a Synergy IV plate reader. 30 chemicals were identified that stimulated iron-induced quenching of calcein fluorescence. The stimulation was verified by dose response curves and the lack of toxicity noted by having no significant cell death after exposure for up to 5 days. One of the compounds, LS-0108076, at 3 or 10 μM stimulated iron uptake from FeNH4SO4 by 50% in K562 cells. LS-0108076 also facilitated uptake from transferrinbound iron in a prostate cancer line as evidenced by a 2-fold increase in ferritin levels when PC-3 cells were cultured with 10% serum. LS-0108076 (3μM) also significantly increased generation of ROS from 100±0% to 150±18% as measured with DCFDA but only in the serum-free Hepes buffer with 2 μM FeNH4citrate. LS-0108076 was further examined in prostate cancer and normal prostate cells for the ability to enhance cell killing by bleomycin, a radiation mimetic anti-cancer drug that chelates Fe and causes cell death by interchelating with DNA and producing DNA strand breaks. In both the PC3 and DU145 prostate cancer cell lines, LS-0108076 enhanced bleomycin cell killing in serum-free medium with further potentiation by the addition of 2 μM Fe3+ to LS-0108076. Similarly, LS-0108076 potentiated radiation induced cell death with the effects also enhanced by the presence of Fe3+and with marked increase of DNA strand breaks as detected by a comet assay. In normal prostate cells LS-0108076 had no affect on bleomycin cell toxicity. In summary, we have developed a high through-put screening technique that identified small molecules that stimulate iron uptake and demonstrated that compounds which facilitate iron uptake increase cell sensitivity to radiation therapy and chemotherapy and can be used to potentiate anti-cancer agents.

Chelatable Fe (II) is generated in the rat kidneys exposed to ischemia and reperfusion, and a divalent metal chelator, 2, 2'-dipyridyl, attenuates the acute ischemia/reperfusion-injury of the kidneys: a histochemical study by the perfusion-Perls and -Turnbull methods

The perfusion-Perls and -Turnbull methods supplemented by diaminobenzidine intensification demonstrated the generation and localization of chelatable Fe (II) which can catalyze the generation of cytotoxic hydroxyl radicals (OH.) during the Fenton reaction in rat kidneys exposed to 40 min ischemia or 40 min-ischemia followed by 60 min-reperfusion. The kidneys exposed to 40 min-ischemia showed Fe (II)-deposits largely localized in the deeper half of the cortex, where the deposits densely filled the tubular cell nuclei, with a small amount of them in the cytoplasm of the proximal convoluted tubules (PCT). Intraluminally protruded or exfoliated tubular cell nuclei were also filled with the deposits. The kidneys subjected to 40 min-ischemia/ 60 min-reperfusion showed a more extensive distribution of Fe (II)-deposits, including most depths of the cortex. Furthermore, there were numerous exfoliated, Fe (II)-positive nuclei surrounded by a small amount of cytoplasm in the lumen of the PCT. These cells appeared to undergo apoptotic cell death since the lumen of strongly dilated, down-stream, proximal straight tubules were obstructed with numerous apoptotic cells in the kidneys exposed to 40 min-ischemia and 24 h-reperfusion. Pretreatment with a divalent metal chelator, 2, 2'-dipyridyl, effectively inhibited Fe (II)-staining, decreased the number of exfoliated cells in the kidneys with 40 min-ischemia/ 60 m-reperfusion, and decreased the number of apoptotic cells in the kidneys with 40 min-ischemia/24 h-reperfusion. The generation of highly reactive OH. during the Fe2+-catalyzed Fenton reaction was suggested to play a crucial role in ischemia/reperfusion-induced kidney injury.

Single-strand-specific nuclease from Basidiobolus haptosporus (Nuclease Bh1)

Nuclease Bh1 is a multifunctional enzyme and catalyses the hydrolysis of ssDNA, 3’AMP and RNA in a ratio of approximately 1:1:0.05. It is a single polypeptide chain of 30 kDa and contains 15% carbohydrate. All three activities of the enzyme showed the same pI, indicating that they are associated with the same protein. The ssDNase, 3’AMPase and RNase activities of nuclease Bh1 showed the same pH and temperature optima and stability. Nuclease Bh1 neither showed an obligate requirement metal ion for its activity nor the activity was stimulated in presence of metal ions but it is a zinc metallo-protein. Moreover, they exhibited similar sensitivity towards divalent cations, metal chelators, thiol reagents, protein denaturants and guanosine 5’ nucleotides. It hydrolyzed DNA endonucleolytically with a preference for guanylic acid linkages whereas; it showed an endo-exo mode of action on RNA, with a preference for adenylic acid linkages. Cytidylic acid linkages were resistant to cleavage. The phosphor-monoesterase activity of the enzyme is 3’ ribonucleotide specific. Active site nature suggested the involvement of lysine in substrate binding and carboxylate in catalysis. Key words: Basidiobolus haptosporus, single-strand-specific nuclease, nuclease Bh1, multifunctional enzyme, characteristics.

Nonheme-iron histochemistry for light and electron microscopy: a historical, theoretical and technical review

We reviewed the methods of nonheme-iron histochemistry with special focus on the underlying chemical principles. The term nonheme-iron includes heterogeneous species of iron complexes where iron is more loosely bound to low-molecular weight organic bases and proteins than that of heme (iron-protoporphyrin complex). Nonheme-iron is liberated in dilute acid solutions and available for conventional histochemistry by the Perls and Turnbull and other methods using iron chelators, which depend on the production of insoluble iron compounds. Treatment with strong oxidative agents is required for the liberation of heme-iron, which therefore is not stained by conventional histochemistry. The Perls method most commonly used in laboratory investigations largely stains ferric iron, but stains some ferrous iron as well, while the Turnbull method is specific for the latter. Although the Turnbull method performed on sections fails in staining ferrous iron or stains only such parts of the tissue where iron is heavily accumulated, an in vivo perfusion-Turnbull method demonstrated the ubiquitous distribution of ferrous iron, particularly in lysosomes. The Perls or Turnbull reaction is enhanced by DAB/silver/gold methods for electron microscopy. The iron sulfide method and the staining of redox-active iron with H(2)O(2) and DAB are also applicable for electron microscopy. Although the above histochemical methods have advantages for visualizing iron by conventional light and electron microscopy, the quantitative estimation of iron is not easy. Recent methods depending on the quenching of fluorescent divalent metal indicators by Fe(2+) and dequenching by divalent metal chelators have enabled the quantitative estimation of chelatable Fe(2+) in isolated viable cells.

Role and Regulation of the Shigella flexneri Sit and MntH Systems

Shigella flexneri possesses at least two putative high-affinity manganese acquisition systems, SitABCD and MntH. Mutations in the genes encoding the components of both of these systems were constructed in S. flexneri. The sitA mntH mutant showed reduced growth, relative to the wild type, in Luria broth (L broth) containing the divalent metal chelator ethylene diamino-o-dihydroxyphenyl acetic acid, and the addition of either iron or manganese restored growth to the level of the wild-type strain. Although the sitA mntH mutant was not defective in surviving exposure to superoxide generators, it was defective in surviving exposure to hydrogen peroxide. The sitA mntH mutant formed wild-type plaques on Henle cell monolayers but had a reduced ability to survive in activated macrophage lines. Expression of the S. flexneri sit and mntH promoters was higher when Shigella was in Henle cells than when it was in L broth. Expression of both the sit and mntH promoters was repressed by either iron or manganese, and this repression was partially dependent upon Fur and MntR, respectively. The mntH promoter, but not the sit promoter, exhibited OxyR-dependent induction in the presence of hydrogen peroxide.

Synthesis and biological evaluation of purine derivatives incorporating metal chelating ligands as HIV integrase inhibitors

Because of its essential role in HIV replication and lack of human counterpart, HIV integrase is an attractive target for the development of novel anti-AIDS agents. Among the recently developed integrase inhibitors, only the α,γ-diketo acid (DKA) compounds were biologically validated as potent and selective integrase inhibitors. The general structure of DKAs contains a diketo acid moiety as the Mg 2+ chelating pharmacophore, and an adjacent aryl group to provide selectivity. Numerous structure–activity relationship (SAR) studies on DKAs have been conducted, which generally involved substituting the carboxylate group or the aryl group. Our objective was to investigate the SARs of the DKA molecule by incorporating a purine ring in the aryl moiety and replacing the labile diketo acid moiety with other divalent metal (Me 2+) chelating ligands. A series of amide substituted purine derivatives were synthesized via palladium-catalyzed amidation reactions, and their biological activities against HIV integrase were evaluated. These purine derivatives showed anti-integrase activity at low micromolar range. The biological results indicated that the type of Me 2+ ligands, two-point ligand picolinamide or three-point ligand 8-hydroxy-quinoline-7-carboxamide, affected inhibitory potency depending on the substitution position of the para-fluorobenzyl group. The C 6-,C 8-dipicolinamide substituted purine ( 32) exhibited the best potency among this series.

Selective degradation of reverse gyrase and DNA fragmentation induced by alkylating agent in the archaeon Sulfolobus solfataricus

Reverse gyrase is a peculiar DNA topoisomerase, specific of hyperthermophilic Archaea and Bacteria, which has the unique ability of introducing positive supercoiling into DNA molecules. Although the function of the enzyme has not been established directly, it has been suggested to be involved in DNA protection and repair. We show here that the enzyme is degraded after treatment of Sulfolobus solfataricus cells with the alkylating agent MMS. MMS-induced reverse gyrase degradation is highly specific, since (i) neither hydroxyurea (HU) nor puromycin have a similar effect, and (ii) topoisomerase VI and two chromatin components are not degraded. Reverse gyrase degradation does not depend on protein synthesis. Experiments in vitro show that direct exposure of cell extracts to MMS does not induce reverse gyrase degradation; instead, extracts from MMS-treated cells contain some factor(s) able to degrade the enzyme in extracts from control cells. In vitro, degradation is blocked by incubation with divalent metal chelators, suggesting that reverse gyrase is selectively degraded by a metal-dependent protease in MMS-treated cells. In addition, we find a striking concurrence of extensive genomic DNA degradation and reverse gyrase loss in MMS-treated cells. These results support the hypothesis that reverse gyrase plays an essential role in DNA thermoprotection and repair in hyperthermophilic organisms.

Green tea catechins as brain‐permeable, natural iron chelators‐antioxidants for the treatment of neurodegenerative disorders

Neurodegeneration in Parkinson's, Alzheimer's, or other neurodegenerative diseases appears to be multifactorial, where a complex set of toxic reactions, including oxidative stress (OS), inflammation, reduced expression of trophic factors, and accumulation of protein aggregates, lead to the demise of neurons. One of the prominent pathological features is the abnormal accumulation of iron on top of the dying neurons and in the surrounding microglia. The capacity of free iron to enhance and promote the generation of toxic reactive oxygen radicals has been discussed numerous times. The observations that iron induces aggregation of inert alpha-synuclein and beta-amyloid peptides to toxic aggregates have reinforced the critical role of iron in OS-induced pathogenesis of neurodegeneration, supporting the notion that a combination of iron chelation and antioxidant therapy may be one significant approach for neuroprotection. Tea flavonoids (catechins) have been reported to possess divalent metal chelating, antioxidant, and anti-inflammatory activities, to penetrate the brain barrier and to protect neuronal death in a wide array of cellular and animal models of neurological diseases. This review aims to shed light on the multipharmacological neuroprotective activities of green tea catechins with special emphasis on their brain-permeable, nontoxic, transitional metal (iron and copper)-chelatable/radical scavenger properties.

Self‐Condensation of Activated Malonic Acid Half Esters: A Model for the Decarboxylative Claisen Condensation in Polyketide Biosynthesis.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Self-condensation of activated malonic acid half esters: a model for the decarboxylative Claisen condensation in polyketide biosynthesis

The reaction of a malonic acid half oxyester with a N-hydroxysuccinimidyl ester-forming reagent resulted in self-condensation to provide the corresponding 1,3-acetonedicarboxylic acid diester. This new method does not require a divalent metal chelator or a coordinating solvent for successful condensation.

Acquisition of Mn(II) in addition to Fe(II) is required for full virulence of Salmonella enterica serovar Typhimurium.

The roles of the genes feoB (ABC ferrous iron transporter), mntH (proton-dependent manganese transporter), and sitABCD (putative ABC iron and/or manganese transporter) in Salmonella pathogenicity were investigated by using mutant strains deficient in one, two, or three transporters. Our results indicated that sitABCD encodes an important transporter of Mn(II) and Fe(II) which is required for full virulence in susceptible animals (Nramp1(-/-)) and for replication inside Nramp1(-/-) macrophages in vitro. The mntH sitABCD double mutant (mutant MS) showed minimal Mn(II) uptake and increased sensitivity to H(2)O(2) and to the divalent metal chelator 2,2'-dipyridyl (DP) and was defective for replication in macrophages. In vivo MS appeared to be as virulent as the sitABCD mutant in Nramp1(-/-) animals. The ferrous iron transporter Feo was required for full virulence in 129/Sv Nramp1(-/-) mice, and infection with multiple mutants lacking FeoB was not fatal. The sitABCD feoB mutant (mutant SF) and the mntH sitABCD feoB mutant (mutant MSF) showed minimal Fe(II) uptake and were slightly impaired for replication in susceptible macrophages. MSF showed reduced growth in minimal medium deficient in divalent cations. The role of the mntH gene, which is homologous to mammalian Nramp genes, was also investigated after overexpression in the double mutant MS. MntH preferred Mn(II) over Fe(II) and could suppress MS sensitivity to H(2)O(2) and to DP, and it also improved the intracellular survival in Nramp1(-/-) macrophages. This study indicates that acquisition of Mn(II), in addition to Fe(II), is required for intracellular survival and replication of Salmonella enterica serovar Typhimurium in macrophages in vitro and for virulence in vivo.

Study on the catalytic behavior of metal acetylacetonates for epoxy curing reactions

AbstractMetal acetylacetonates are effective latent catalysts for epoxy/anhydride systems. A screen test on the catalytic behavior of metal acetylacetonate shows that this system offers a wide range of curing latency and material properties. It can be inferred that the curing behavior is closely related to the bonding strength of the metal ion to the ligand. Isothermal kinetic study on the catalytic behavior of metal chelates with first‐row transition metal ions is conducted and analyzed by using an autocatalytic model. It is found that the activation energy of the system containing the divalent metal chelates follows the Irving and Williams rule. The activation energies of the reaction obtained in the kinetic study are compared with the dissociation energies of the metal/ligand bond and the results are discussed. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1572–1579, 2002

The Arabidopsis TAG1 transposase has an N-terminal zinc finger DNA binding domain that recognizes distinct subterminal motifs.

The in vitro DNA binding activity of the Arabidopsis Tag1 transposase (TAG1) was characterized to determine the mechanism of DNA recognition. In addition to terminal inverted repeats, the Tag1 element contains four different subterminal repeats that flank a transcribed region encoding a 729-amino acid protein. A single site-specific DNA binding domain is located near the N terminus of TAG1, between residues 21 and 133. This domain binds specifically to the AAACCC and TGACCC subterminal repeats, found near the 5' and 3' ends of the element, respectively. The ACCC sequence within these repeats is critical for recognition because mutations at positions 3, 5, and 6 abolished binding, yet the first two bases also are important because substitutions at these positions decreased binding by up to 90%. Weak interaction also occurs with the terminal inverted repeats, but no binding was observed to the other two 3' subterminal repeat regions. Sequence analysis of the TAG1 DNA binding domain revealed a C(2)HC zinc finger motif. Tests for metal dependence showed that DNA binding activity was inhibited by divalent metal chelators and greatly enhanced by zinc. Furthermore, mutation of each cysteine residue predicted to be a metal ligand in the C(2)HC motif abolished DNA binding. Together, these data show that the DNA binding domain of TAG1 specifically binds to distinct subterminal repeats and contains a zinc finger.

S100β Interaction with Tau Is Promoted by Zinc and Inhibited by Hyperphosphorylation in Alzheimer's Disease

The zinc-binding protein S100beta has been identified as an interacting partner with the microtubule-associated protein tau. Both proteins are individually affected in Alzheimer's disease (AD). S100beta, is overexpressed in the disease, whereas hyperphosphorylated tau constitutes the primary component of neurofibrillary tangles. In this study, we examine factors that modulate their binding and the potential role the complex may play in AD pathogenesis. Zinc was identified as a critical component in the binding process and a primary modulator of S100beta-associated cellular responses. Abnormally phosphorylated tau extracted from AD tissue displayed a dramatically reduced capacity to bind S100beta, which was restored by pretreatment with alkaline phosphatase. In differentiated SH-SY5Y cells, exogenous S100beta was internalized and colocalized with tau consistent with an intracellular association. This was enhanced by the addition of zinc and eliminated by divalent metal chelators. S100beta uptake was also accompanied by extensive neurite outgrowth that may be mediated by its interaction with tau. S100beta-tau binding may represent a key pathway for neurite development, possibly through S100beta modulation of tau phosphorylation and/or functional stabilization of microtubules and process formation. S100beta-tau interaction may be disrupted by hyperphosphorylation and/or imbalances in zinc metabolism, and this may contribute to the neurite dystrophy associated with AD.

Inhibition of human gelatinases by metals released from dental amalgam

The interaction between metal ions and the oral environment is a major subject matter in dental research. Matrix metalloproteinases (MMPs) have been implicated in pathologic oral processes such as periodontal tissue destruction, root caries, tumor invasion and temporomandibular joint disorders. The aim of this study was to test the effect of metal ions released from dental amalgam on the major gingival gelatinolytic MMPs. Gingival human explants were cultured overnight in DMEM and the activity of secreted enzymes was analyzed by gelatin zymography in buffers conditioned with dispersed phase or concentional phase dental amalgams. The major enzymes present in conditioned media were characterized as MMP-2 and MMP-9 by immunoprecipitation. The proteolytic activities of MMP-2 and MMP-9 were strongly inhibited by dispersed phase amalgams conditioned buffers. Inhibition of MMP-2 and MMP-9 activities was partly prevented by the addition of 1,10 phenanthroline, a divalent metal chelator, to the amalgam conditioned buffers. Dental amalgam conditioned buffer also inhibited the degradation of denatured type I collagen by purified MMP-2 on liquid phase assays. These findings suggest that the activity of oral tissue MMPs may be modulated by metal ions released from dental amalgam.