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At least 19 recordsLinked to original sources

PubMed1977

[Various factors influencing toxicity and metabolism of metals--metal-metal interactions and host factors (author's transl)].

This paper is a brief overview on metal-metal interactions and various other factors involved in the toxicity and metabolism of metals, including host factors, nutrition, habits, etc. Humans and other organisms are exposed to various metals in many ways, and even in an occupation in which workers are exposed to a metal such as lead, they are at the same time also exposed to other metals, although concentrations of these latter metals are usually not very high. This can result in effects different from those produced by a single metal by itself. Furthermore, individual differences which are caused by genetic, nutritional, hormonal, habitual, and many other factors may alter the toxic or metabolic effects of a single metal. Information on this subject is rather limited. This paper is a brief introduction to the importance of future studies on the topic, and the author hopes that it will stimulate more studies by those who are interested in the field of metal toxicology.

Animals↗

PubMed1979

[Changes in the metallic phase at the metal-ceramic margin of baked alloys of nonprecious metals].

Five base metal alloys were investigated to determine if phase changes in the alloy microstructure occurred as a result of the porcelain baking procedure. It was found that during the oxidation treatments concentration changes in the alloy surface led to a depletion of certain elements in four of the alloys investigated. It was also found that phase changes could occur in a region 20 micrometers wide next to the alloy surface. Phase changes and alloying element depletion occurs as a result of the oxidation treatments prior to the fusion of porcelain and not as a result of or during porcelain fusion.

Acid Etching, Dental↗

PubMed1978

[Influence of the thickness of metal and porcelain upon metal-ceramics (author's transl)].

This paper deals with the strength of metal-ceramics and the influence of the thickness of metal and porcelain layer. The metal-ceramic specimens, 30 mm long and 10 mm wide of various each thickness, supported at each ends, were tested by bending to obtain the transverse strength. The thickness of metal layer was changed from 0.2 mm to 1.0 mm, while that of porcelain layer was changed from 0.5 mm to 1.3 mm respectively. Interaction of the thickness of metal or porcelain layer to the fixed total thickness was also investigated comparing with the results of the experiment in which the thickness of one side was constant. From the load-deflection diagram, the maximum work before breaking was surveyed and compared. Main results were as follows. 1) In case of the same total thickness of metal-ceramics, the thicker the metal layer, the greater the transverse strength, maximum work before breaking and maximum deflection. 2) When the metal thickness exceeded one half of the porcelain layer, the transverse strength increased in comparing with value of porcelain itself. 3) The maximum deflection of metal-ceramics by bending before breaking was approximately three or four times as great as that of simple porcelain. 4) The work of the metal-ceramics by bending before breaking was approximately two or three times as that of the simple porcelain. 5) It was imagined that the total strength of the metal-ceramics would be affected by the hardness of the constituent metal and boundary bonding strength.

Dental Alloys↗

PubMed1975

Role of metal ions in Escherichia coli alkaline phosphatase. A study of the metal-water interaction by nuclear relaxation rate measurements on water protons.

The binding of metal to alkaline phosphatase from Escherichia coli and the binding of water and orthophosphate to the Me-2+-enzyme binary complex have been examined by water proton relaxation rate (PRR) measurements. Titration of the three paramagnetic metals, Mn2+, Cu2+, and Co2+, into apoalkaline phosphatase and the titrations of apoenzyme into metal have been carried out. Analysis of the spin-lattice relaxation rates for these titrations and of Scatchard binding curves derived from these results, as well as EPR data, show four tight manganese sites, between two and three tight copper sites, or four cobalt sites per enzyme dimer of molecular weight 80,000. The multiple sites for each metal are indistinguishable by these magnetic resonance techniques. Both the spin-lattice- and spin-spin-relaxation rates exhibit a negative temperature coefficient, showing that these processes are not exchange-limited. From a frequency dependence study of T-1 and from the T-1:T-2 ratio measured at 220 MHz, correlation times from the water-enzyme complexes have been estimated. For H20-Mn-2+-alkaline phosphatase, gamma c equals 1.55 times 10-9 s; for H20-Cu-2+ -alkaline phosphatase, gamma c equals 1.82 times 10-s; and for the cobalt complex, gamma c equals 1.0 times 10-12 s at 4 degrees. Assuming 1 water molecule bound per metal site, these correlation times correspond to the following water-metal distances: gamma (A) is 4.0 A for Mn-2+-H20, 3.4 A for Cu-2+-H20, and 2.8 A for Co-2+-H20. Thus, water is shown to bind directly to the metal atoms of alkaline phosphatase. The correlation between the length of the water-metal bond and the relative activity of the various metalloenzymes support the importance of this binding in the monophosphoesterase reaction catalyzed by alkaline phosphatase. Addition of excess orthophosphate to any of the water-metalloenzyme complexes does not displace an exchangeable water molecule from the metal site. The Mn-PO-4 distance which we have reported earlier (Zukin, R.S., Hollis, D.P., and Gray, G.A. (1973) Biochem. Biophys. Res. Commun. 53, 238) to be 7.3 A is consistent with this finding and suggests a model in which Pi binds to Mn-2+-alkaline phosphatase through a water bridge.

Alkaline Phosphatase↗

PubMed1977

Regulation of heme pathway enzymes and cellular glutathione content by metals that do not chelate with tetrapyrroles: blockade of metal effects by thiols.

The trace metals nickel and platinum, which are not substrates for ferrochelatase and thus do not form heme in biological systems, were found to act similaryl to cobalt, and heme itself, in regulating heme metabolism in liver and kidney. These metals induced heme oxygenase activity in both organs with the peak of induced enzyme activity reached approximately 16 hr after single injections in rats. Both metals caused transient depression of cellular glutathione content followed by increases above normal after 12 hr in liver. Nickel and platinum were more potent inducers of heme oxygenase in kidney than in liver (10-13 times normal versus 5-6 times normal). At high concentrations, they inhibited heme oxygenase [heme, hydrogen-donor:oxygen oxidoreductase (alpha-methene-oxidizing, hydroxylating), EC 1.14.99.3] in vitro. Both were active in regulating heme metabolism only when administered in the ionic form. Complexing of the metals with sulfhydryl agents completely blocked their actions on heme metabolism. Administration of cysteine orally prior to or shortly after administration of the metals had a similar blocking effect. Nickel and platinum produced depression of delta-aminolevulinate synthase [succinyl-CoA:glycine c-succinyltransferase (decarboxylating), EC 2.3.1.37] activity in liver, but neigther inhibited this rate-limiting ennzyme for heme synthesis in vitro. Furthermore, despite the substantial decreases in cellular heme and hemoprotein contents mediated by the metal, production of delta-amimolevulinate synthase did not undergo the compensatory increase that would be expected if there were a direct reciprocal feedback relationship between cellular heme level and synthesis of this enzyme. These findings indicate that it is not necessary for metal ions to be chelated in the porphyrin ring in order to regulate the enzymes of heme synthesis and heme oxidation. Accordingly, it is suggested that the iron atom of heme is the proximately active regulator of delta-aminolevulinate synthase and heme oxygenase--actions generally ascribed to the iron-tetrapyrrole complex itself--and that the tetrapyrrole moiety of the complex functions primarily as a means of transport of the metal to regulatory sites in cells.

5-Aminolevulinate Synthetase↗

PubMed1978

[Flow of molten metal in denture base in horizontal centrifugal casting procedure. (Part 2) Flow, inflow volume and casting time of molten metal passing through several sprues into model denture plate mold (author's transl)].

Two types of spruing methods were used in the casting of the denture type model pattern (thickness, 0.43 mm). Flow of molten metal in the mold was filmed by the improved system of Part 1. When three sprues were attached to the pattern vertically, molten metal passed through each sprue gate flowed being affected by the direction of gravity and revolution of casting machine, and gathered at the lower part of the mold. Next molten metal filled the mold from the lower part to the upper part. In this spruing type, molten metal turned its direction of flow several times. At the middle stage of casting, the inflow volume per unit time (inflow rate), v (mm3/10-2)s)was evaluated as v = 12.36 + 5.16A-0.16 A2 (A: total cross-sectional areas of sprues). The inflow rate increased with increase of the area of the sprues, but it saturated. When the main sprue and the subsprues were attached at the posterior border, the molten metal filled the mold from the lower part to the upper part quietly. In this spruing type, the casting mold was set facing its sprue gates downwards. The inflow rate at the middle stage of casting was evaluated as v = 21.05 + 1.79 C (C: the cross-sectional area of the main sprue). The inflow rate increased linearly with increase of the area of the main sprue.

Dental Casting Technique↗

PubMed1976

[Flow of molten metal in denture base in horizontal centrifugal casting procedure. (Part 1) Flow, inflow volume and casting time of molten metal passing through single aprue into disk type mold (author's transl)].

A pyrex glass plate was fitted at the bottom of casting ring, and disk type wax pattern (thickness. 0.43 mm) was put on the plate. Five types of sprueing were applied. Pure tin was casted using holizontal centrifugal casting machine. Flow of molten metal was filmed by the motor drive camera with the method of stroboscope. The results were summarized as follows. 1) When the sprue was attached at the center of the disk type mold vertically, moten metal flowed like a concentric circle at the early stage of casting. It was affected gradually by the direction of gravity and revolution, and it filled the mold from the lower part to the upper part. 2) When the sprue gate was attached to the side edge of the mold, and the sprue gate was placed to the forward and backward direction against the revolution direction, molten metal filled from lower part to the upper part. 3) When the sprue gate was placed against upper edge, molten metal flow was affected by the direction of gravity and revolution. When the sprue gate was placed against lower edge, molten metal filled quietry from the lower part to the upper part. 4) Inflow volume per unit time (inflow rate) was small at the early stage of casting. Inflow rate increased and became constant at the next stage. At the latter stage it became small again. 5) Inflow rate increased with the increase of area of sprue. 6) The time which was necessary to fill the volume of 1 cm (about 80% of the mold volume) became short with the increase of area of sprue. It was also influenced by the type of sprueing.

Dental Casting Technique↗

PubMed2026

Metal-Organic Framework-Based and Metal-Organic Framework-Derived Nanomaterials for Cancer Theranostics and Antibacterial Applications: Advances, Challenges, and Perspectives.

Metal-organic frameworks (MOFs), constructed through coordination-driven self-assembly of metal ions/clusters and organic linkers, have emerged as a uniquely versatile class of porous nanomaterials with broad biomedical potential. Despite substantial clinical progress, both oncological treatment and antimicrobial intervention remain constrained by inadequate tumor-targeting selectivity, multidrug resistance, immunosuppressive tumor microenvironments, and the global proliferation of antibiotic-resistant pathogens, limitations that conventional nanocarrier platforms have addressed only in part. MOF-based and MOF-derived nanomaterials, distinguished by tunable pore architecture, structurally and compositionally adaptable metal nodes, high surface areas, and stimulus-responsive degradability, offer a rational framework for overcoming these barriers. This review systematically examines the synthetic strategies underlying MOF-based and MOF-derived nanomaterials, including pyrolysis, chemical etching, composite modification, and functional group introduction, and their structural determinants of performance. In cancer theranostics, we critically evaluate their roles as multimodal imaging contrast agents, stimulus-responsive drug delivery carriers, and platforms for combination therapies encompassing photodynamic, photothermal, chemodynamic, and immunomodulatory modalities. In antibacterial applications, we analyze the mechanistic basis of MOF-based and MOF-derived activity, including physical membrane disruption, reactive oxygen species-mediated oxidative stress, and sustained metal ion release, alongside strategies targeting biofilm formation and antibiotic resistance. Multifunctional platforms that concurrently integrate cancer theranostic and antibacterial capabilities are further discussed. This review also addresses the principal barriers to clinical translation, encompassing large-scale manufacturing, long-term biosafety, and regulatory approval, and proposes future directions incorporating artificial intelligence-assisted design and materials genomics, underscoring the transformative potential of MOF-based and MOF-derived nanomaterials as next-generation precision nanomedicines. This review establishes a unified mechanistic framework grounded in the intrinsic physicochemical properties of MOF-derived nanomaterials, systematically integrating their applications in cancer theranostics and antibacterial therapy. Critically, it bridges fundamental advances with translational reality by incorporating a rigorous assessment of regulatory pathways, scalable manufacturing constraints, and clinical implementation barriers, and offers a comprehensive, practice-oriented reference for the rational design and responsible translation of MOF-based and MOF-derived nanomaterials.

Theranostic Nanomedicine↗

PubMed1977

Lung tumor response in mice to metals and metal salts.

Two studies tested the ability of metals and their salts to produce lung tumors in strain A mice. Of 13 compounds examined, lead subacetate, manganous sulfate, molybdenum trioxide, and nickelous acetate elicited a weakly carcinogenic response following intraperitoneal injection. Nine metallic compounds were negative. There was no evidence of cocarcinogenic effect between metals and the chemical carcinogen, 3-methylcholanthrene. On the basis of these and other data, recommendation is made for further investigations in metal carcinogenesis.

Animals↗

PubMed1976

Photoelectrochemical effects in the electrolyte-pigment-metal system. I. Metal-free phthalocyanine film description of short-circuit photocurrents for thin films of pigment.

Using a semitransparent metallic electrode covered with a thin film of metal-free phthalocyanine, photoelectrochemical effects have been studied in the electrolyte-pigment-metal system. Measurement of the short-circuit photocurrent, produced by continuous illumination, allows description of a photodependent kinetic phase corresponding to the establishment of a stationary state in the charge separation region of the system after the creation of the current carriers.

Biological Transport↗

PubMed1976

Photoelectrochemical effects in the electrolyte-pigment-metal system. II. Metal-free phthalocyanine film action spectra of short-circuit photocurrents with increase of the film thickness.

The electrolyte-pigment-metal system can be described as analogous to a photosensitive junction region. When the thickness of the pigment film is increased, the action spectra of the maximum short-circuit photo-current under continuous illumination differ from the absorption spectra both in direct illumination (pigment-electrolyte) and in back illumination (metal-pigment). One is led to believe that there exist two photoactive regions in the system for the production of the short-circuit photocurrent; these two active regions are associated respectively with each interface. When the metallic semitransparent electrode is made of aluminum the two interfaces have opposite sign contributions to the photocurrent; this allows the determination of conditions in which one can observe specifically the contribution of the pigment-electrolyte interface, that is the interactions between excited pigment molecules and the redox system in the electrolyte.

Action Potentials↗

PubMed2026

Systematic mining and characterization of metal transporter families regulating zinc homeostasis provide insights into metal homeostasis in Camellia sinensis.

BACKGROUND AND AIMS: Zinc is essential for tea plant growth and quality formation, yet its homeostatic mechanisms remain poorly understood. This study identified metal transporter families regulating zinc homeostasis, analyzed their evolution, structure, and expression, and clarified zinc uptake, transport, detoxification networks, and their links to metabolism. METHODS: This study identified zinc homeostasis-related metal transporter families in the tea plant genome, characterized their structural features and expression profiles across tissues and developmental stages through integrative bioinformatics and transcriptomic analyses, and delineated the molecular mechanisms underlying zinc uptake, translocation, and detoxification by systematically integrating published evidence. RESULTS: This study identified 74 metal transporter genes from six families: 13 CsZIPs, 12 CsNRAMPs, 10 CsHMAs, 10 CsYSLs, 14 CsMTPs, and 15 CsCAXs in the 'Shuchazao2' genome, revealing closer affinity to woody species than to Arabidopsis. These proteins exhibit conserved domains, diverse subcellular localizations (cell membrane, vacuole, chloroplast, and Golgi apparatus), and tissue-specific expression with abundant stress/hormone-responsive cis-elements. At the plant-soil interface, tea plants mobilize rhizospheric zinc via proton and organic acid secretion; CsYSLs, CsNRAMPs, and CsZIPs mediate zinc uptake, aided by arbuscular mycorrhizal fungi (AMF) and plant growth-promoting rhizobacteria (PGPR) that expand root absorption zones. Xylem CsHMAs and phloem CsYSLs coordinate root-to-shoot zinc translocation, and vacuolar transporters (CsMTPs, CsCAXs), cell wall immobilization, and antioxidant systems alleviate high-zinc stress injury. CONCLUSIONS: These findings collectively delineate an integrated zinc "acquisition-distribution-buffering" network in tea plants, offering a repertoire of candidate genes with potential utility in zinc biofortification breeding and improving acid soil adaptation. Further experimental validation, including tea transgenesis, zinc-stress qRT-PCR, and heterologous functional complementation, is essential to substantiate their biological roles.

Camellia sinensis↗

PubMed2026

Comparative efficacy and safety of bi-flanged metal stents versus lumen-apposing metal stents for endoscopic drainage of pancreatic fluid collections: a systematic review and meta-analysis.

INTRODUCTION: Pancreatic fluid collections (PFCs), particularly walled-off necrosis, are common complications of acute pancreatitis that often require endoscopic drainage. Bi-flanged metal stents (BFMS; NAGI; Taewoong Medical, Gyenoggi-do, Korea) and electrocautery-enhanced lumen-apposing metal stents (LAMS; AXIOS, Boston Scientific Corporation, Marlborough, Massachusetts, USA) are frequently used, but comparative data remain limited. This study aims to compare the efficacy and safety of BFMS and LAMS in the endoscopic drainage of PFCs. METHODS: This meta-analysis followed the Cochrane Handbook for Systematic Reviews of Interventions and Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Comprehensive database searches were conducted through November 2024 to identify studies comparing BFMS and LAMS for endoscopic ultrasound-guided drainage of PFCs. Outcomes were pooled using a random-effects model with RevMan Web, and statistical significance was defined as a P value less than 0.05. RESULTS: Three studies ( n  = 627; 329 BFMS and 298 LAMS) met inclusion criteria. No significant differences were observed between BFMS and LAMS for technical success [odds ratio (OR): 1.16; 95% confidence interval (CI): 0.55-2.43] or clinical success (OR: 0.97; 95% CI: 0.51-1.87). Similarly, there were no differences in walled-off necrosis recurrence (OR: 2.01; 95% CI: 0.17-24.02), number of direct endoscopic necrosectomy sessions (OR: 0.52; 95% CI: 0.05-5.12), or mean number of endoscopic procedures (mean difference: 0.18, 95% CI: 2.08-2.45). Adverse events were also comparable between groups, including bleeding (OR: 0.64), infection (OR: 1.18), stent migration (OR: 1.83), and stent occlusion/dysfunction (OR: 1.71). CONCLUSION: BFMS and LAMS provide equivalent efficacy and safety in the endoscopic ultrasound-guided drainage of PFCs. Either stent type represents a viable therapeutic option. Further large-scale prospective studies are warranted to refine stent selection strategies.

Humans↗

PubMed1979

Fluoride inhibition of inorganic pyrophosphatase. IV. Evidence for metal participation in the active center and a four-site model of metal effect on catalysis.

Atomic spectroscopy of native yeast inorganic pyrophosphatase (pyrophosphate phosphohydrolase, EC 3.6.1.1) after gel filtration showed that it only binds activating Mg2% in an easily dissociable manner. Formation of a covalent intermediate between the enzyme and an entire substrate molecular in the presence of fluoride, however, dramatically strengthened the binding of two Mg2+ per subunit and eliminated at neutral pH the effect of added metals on protein fluorescence but not on the absorption spectrum, suggesting that different mental binding sites influence the two spectra. This conclusion was confirmed by spectra studied on native enzyme. A third, low-affinity site for Mg2+ was found on the enzyme pH greater than 8. A model of enzyme-substrate-metal interactions was proposed, according to which the fluorescence-controlling site belongs to the active center and substrate can only be bound to it as a 1 : 1 complex with metals.

Binding Sites↗

PubMed1979

Toxic trace metals in food. I. A new voltammetric procedure for toxic trace metal control of wines.

A new highly sensitive and particularly reliable analytical procedure for the precise determination of the most relevant toxic trace metals cadmium, lead and copper in wine is presented. It consists of a simple and convenient sample pretreatment by UV irradiation (1,5 h, 500-W-Hg-lamp) to release the toxic trace metals bound by organic substances and subsequent voltammetry (DPASV) of cadmium and lead simultaneously at a mercury film electrode (MFE) formed in situ on a vitreous carbon carrier and of copper on a gold electrode. Particular emphasis has been placed on the efficient exclusion of interference due to contamination. Only special wines, with more than 10% of sugar, require substitution of UV irradiation by a wet digestion also described. The procedure may be easily expanded to include the determination of mercury and zinc.

Electrodes↗

PubMed1979

Toxic trace metals in food. II. A comparative study of the levels of toxic trace metals in wine by differential pulse anodic stripping voltammetry and electrothermal atomic absorption spectrometry.

A new high-performance analytical procedure for the determination of the toxic trace metals cadmium, lead and copper in wines by differential pulse anodic-stripping voltammetry (DPASV) subsequent to UV irradiation of the sample is compared with the hitherto more common application of electrothermal atomic absorption spectrometry (AAS). In this manner also mutually the accuracy attainable with both alternatives has been established. The particularly favourable potentialities of the new voltammetric approach for toxic metal control of wines are demonstrated by the investigation of a typical selection of 36 wines from recent vintages and common vine types of the German and some European wine cultivating regions.

Cadmium↗

PubMed1977

Metal-free and metal-substituted cytochromes c. Use in characterization of the cytochrome c binding site.

The luminescent properties of metal-free, tin(IV) and zinc(II) cytochromes c have been used to characterize the interaction of cytochrome c with mitochondria and cytochrome oxidase. Diminution in the fluorescence yields of tin and zinc cytochrome c occur when these derivates bind to cytochrome oxidase or mitochondria. Based upon spectral overlap and quantum yield, the distance between the porphyrin rings of cytochrome a and cytochrome c is estimated according to Forster theory to be in the neighborhood of 3.5 nm. Measurements of the polarized emission of metal-free 'porphyrin' cytochrome c when bound to oriented layers of cytochrome c oxidase indicate that the porphyrin is bound obliquely to the plane of the oxidase layers with an angle of about 70 degrees C from heme plane to membrane plane. It is proposed that these data have significance for elucidation of electron transfer mechanisms.

Animals↗

PubMed1976

Directed metal determination in pre- and post-natal stages of development of the islets of Langerhans by combined histochemical metal demonstration with electron probe X-ray microanalysis.

On the examples shown above it was possible to demonstrate that electron-X-ray microanalysis does not only present an important additional method for studying histochemical heavy metal reactions but can also be expected to provide, in combination with these, essential findings for the illustration of basic biological processes.

Animals↗