Aluminum ion in biological systems

Airborne Aluminum as an Underestimated Source of Human Exposure: Quantification of Aluminum in 24 Human Tissue Types Reveals High Aluminum Concentrations in Lung and Hilar Lymph Node Tissues

Aluminum (Al) is the most abundant metal in the earth's crust, and humans are exposed to Al through sources like food, cosmetics, and medication. So far, no comprehensive data on the Al distribution between and within human tissues were reported. We measured Al concentrations in 24 different tissue types of 8 autopsied patients using ICP-MS/MS (inductively coupled plasma-tandem mass spectrometry) under cleanroom conditions and found surprisingly high concentrations in both the upper and inferior lobes of the lung and hilar lymph nodes. Al/Si ratios in lung and hilar lymph node samples of 12 additional patients were similar to the ratios reported in urban fine dust. Histological analyses using lumogallion staining showed Al in lung erythrocytes and macrophages, indicating the uptake of airborne Al in the bloodstream. Furthermore, Al was continuously found in PM2.5 and PM10 fine dust particles over 7 years in Upper Austria, Austria. According to our findings, air pollution needs to be reconsidered as a major Al source for humans and the environment.

Imipenem-metal complexes: Computational analysis and toxicity studies with wastewater model microorganisms

The occurrence of antibiotic residues in diverse water sources has long been acknowledged as a potential health concern due to the emergence and spread of antibiotic-resistant bacteria and genes. However, there have been limited studies into the presence of antibiotic-metal complexes (AMCs) in real-time wastewater matrices, and their impact on wastewater microbial communities. The present work, in this regard, investigated the stability of Imipenem-metal complexes (Me = Mg (II), Ca (II), Fe (II), Cu (II), and Al (III)) with computational studies, stoichiometry with potentiometric measurements, and their antibacterial activity towards wastewater model microorganisms- Bacillus subtilis (B. subtilis) and Escherichia coli (E. Coli) by Colony Forming Unit (CFU) method. The lower energy of Imipenem-metal complexes than the parent antibiotic- Imipenem, during energy optimization using density functional (DFT) methods, revealed that metal interactions of Imipenem stabilize the drug by minimizing its energy. Further, CFU studies indicated that these complexes display higher antimicrobial activity than parent antibiotics. The electron delocalization over the entire chelated system (AMCs) reduces polarity and increases the lipophilicity of the complexes, thereby facilitating stronger interaction between AMCs and the bacterial cell membrane. Results indicate increased antibacterial activity of Imipenem-metal complexes for both E. coli and B. subtilis. The antibacterial activity, was however, more pronounced in B. subtilis, with >97% growth inhibition for metal complexes of Imipenem (at a Minimum Inhibitory Concentration of 20 nM or 6 ppb (i.e., MIC90)), for both the stoichiometric ratios (metal to ligand) ratios (M: L 1: 1 and 2: 1). All around, with increased stability and toxicity, AMCs are emerging as contaminants of concern and demand immediate attention to devise methods for their removal.

Influence of metal binding on the conformational landscape of neurofilament peptides

In order to understand the preferred modes of chelation in metal-binding peptides, quantum mechanical calculations can be used to compute energies, resulting in a hierarchy of binding affinities. These calculations often produce increasing stabilization energies the higher the coordination of the complex. However, as the coordination of a metal increases, the conformational freedom of the polypeptide chain is inevitably reduced, resulting in an entropic penalty. Estimating the magnitude of this penalty from the many different degrees of freedom of biomolecular systems is very challenging, and as a result this contribution to the free energy is often ignored. Here we explore this problem focusing on a family of phosphorylated neuropeptides that bind to aluminum. We find that there is a general negative correlation between both stabilization energy and entropy. Our results suggest that a subtle interplay between enthalpic and entropic forces will determine the population of the most favourable species. Additionally, we discuss the requirements for a possible "Metal Ion Hypothesis" based on our findings.

How Theoretical Evaluations Can Generate Guidelines for Designing/Engineering Metalloproteins with Desired Metal Affinity and Selectivity

Almost half of all known proteins contain metal co-factors. Crucial for the flawless performance of a metalloprotein is the selection with high fidelity of the cognate metal cation from the surrounding biological fluids. Therefore, elucidating the factors controlling the metal binding and selectivity in metalloproteins is of particular significance. The knowledge thus acquired not only contributes to better understanding of the intimate mechanism of these events but, also, significantly enriches the researcher's toolbox that could be used in designing/engineering novel metalloprotein structures with pre-programmed properties. A powerful tool in aid of deciphering the physical principles behind the processes of metal recognition and selectivity is theoretical modeling of metal-containing biological structures. This review summarizes recent findings in the field with an emphasis on elucidating the major factors governing these processes. The results from theoretical evaluations are discussed. It is the hope that the physical principles evaluated can serve as guidelines in designing/engineering of novel metalloproteins of interest to both science and industry.

Characterization of GmMATE13 in its contribution of citrate efflux and aluminum resistance in soybeans

Citrate exudation mediated by a citrate transporter of the MATE protein family is critical for resisting aluminum (Al) toxicity in soybeans. However, the expression patterns of citrate transporter genes differ under Al stress. Thus, exploring the responsive pattern of GmMATEs in response to Al stress is of great importance to understand the Al resistance mechanism in soybeans. In the present study, the phylogenetic analysis, transcriptionally expressed pattern, and function of GmMATE13 were investigated. The results show that soybean GmMATE13 is highly homologous to known citrate transporter proteins from other plants. Under Al exposure, the transcript abundance of GmMATE13 was increased during a 24 h Al treatment period. The expression of GmMATE13 is specifically induced by Al exposure, but not by the status of Fe, Cu, Cd, or La. Moreover, it was also highly increased when soybean seedlings were grown on acidic soil with a high Al content. Subcellular localization showed that GmMATE13 was localized on the plasma membrane when it was transiently expressed in Arabidopsis protoplasts. Investigation of tissue localization of GmMATE13 expression by investigating GUS activity staining under control of the GmMATE13 promoter showed that it was mainly expressed in the central cylinder in the root tips of the soybean under Al-free conditions, yet extended to cortical and epidermis cells under Al stress. Finally, overexpressing GmMATE13 in soybean hairy roots enhanced Al resistance by increasing citrate efflux. Collectively, we conclude that GmMATE13 is a promising candidate to improve the resistance of soybean to Al toxicity in acidic soil.

Wild mushrooms from Ilgaz Mountain National Park (Western Black Sea, Turkey): element concentrations and their health risk assessment

The purpose of this study was to determine Fe, Cd, Cr, Se, P, Cu, Mn, Zn, Al, Ca, Mg, and K contents of some edible (Chlorophyllum rhacodes, Clavariadelphus truncatus, Clitocybe nebularis, Hydnum repandum, Hygrophorus pudorinus, Infundibulicybe gibba, Lactarius deliciosus, L. piperatus, L. salmonicolor, Macrolepiota mastoidea, Russula grata, Suillus granulatus, and Tricholoma imbricatum), inedible (Amanita pantherina, Geastrum triplex, Gloeophyllum sepiarium, Hypholoma fasciculare, Phellinus vorax, Pholiota limonella, Russula anthracina, and Tapinella atrotomentosa), and poisonous mushroom species (Amanita pantherina and Hypholoma fasciculare) collected from Ilgaz Mountain National Park (Western Black Sea, Turkey). The element contents of the mushrooms were determined to be 18.0-1239.1, 0.2-4.6, 0.1-3.4, 0.2-3.2, 1.0-8.9, 3.3-59.9, 3.7-220.4, 21.3-154.1, 6.4-754.3, 15.8-17,473.0, 413.0-5943.0, and 2803.0-24,490.0 mg·kg^-1, respectively. In addition to metal contents, the daily intakes of metal (DIM) and Health Risk Index (HRI) values of edible mushrooms were also calculated. Both DIM and HRI values of mushroom species except L. salmanicolor, M. mastoidea, and R. grata were within the legal limits. However, it was determined that the Fe content of L. salmanicolor and M. mastoidea and Cd content of R. grata were above the legal limits.

Phytoplankton Sensitivity to Heavy Metals in Baltic Coastal Lakes

This study aimed to compare concentrations of chlorophyll-a between individual phytoplankton groups for four shallow Baltic coastal lakes, varying in type of connection with the sea. For two years, the research focused on quantifying the effects of abiotic factors—concentrations of heavy metals (Ba, Bi, Cr, Cu, Mn, Fe, Ni, Pb, and Zn) and hydrological connectivity—on phytoplankton composition, biomass, and photosynthetic activity. Our results show that hydrological factors are the main predictors of phytoplankton structure. The lakes differed in salinity: freshwater vs. brackish vs. transitional lakes. Irrespective of lake type, the dominant group was that of Cyanobacteria (~80%), but their percentage contribution was lower in the brackish lake. Baltic seawater intrusion resulted in a decrease in heavy-metal concentrations in lake water for Fe, Zn, Pb, and Bi. Redundancy analysis (RDA) suggested positive effects of some heavy metals on the biomass of the Chlorophyta and Bacillariophyta. For the Cryptophyta only, a slight decrease in biomass was linked with increased metal concentrations in open water.

Evaluation of Cerebellar Function and Integrity of Adult Rats After Long-Term Exposure to Aluminum at Equivalent Urban Region Consumption Concentrations

High amounts of aluminum (Al) are found in soil and water. It is highly bioavailable, which makes it an important agent of environmental imbalance. Moreover, Al is considered a neurotoxic agent that is associated with several neurodegenerative diseases. Thus, this study investigated the effects of long-term Al chloride (AlCl₃) exposure on motor behavior, oxidative biochemistry, and cerebellar tissue parameters. For this, adult Wistar rats were divided into three groups: Al-D1 (8.3 mg kg^-1 day^-1), Al-D2 (5.2 mg kg^-1 day^-1), and control (distilled water); all groups were orally exposed for 60 days by intragastric gavage. After the exposure period, animals performed the open field, elevated plus maze, rotarod, and beam walking tests. Then, the blood and cerebellum were collected to evaluate Al levels and biochemical and morphological analyses, respectively. Our results demonstrate that animals exposed to Al doses presented a higher Al level in the blood. In the spontaneous locomotor activity, Al exposure groups had traveled a lower total distance when compared with the control group. There was no statistically significant difference (p > 0.05) between exposed and control groups when anxiogenic profile, forced locomotion, fine motor coordination/balance, pro-oxidative parameter, and density Purkinje cells were compared. Thus, aluminum exposure in equivalent doses to human consumption in urban regions did not promote significant changes in the cerebellum or motor parameters.

Transcriptome analysis reveals significant difference in gene expression and pathways between two peanut cultivars under Al stress

Aluminum (Al) toxicity is an important factor in limiting peanut growth on acidic soil. The molecular mechanisms underlying peanut responses to Al stress are largely unknown. In this study, we performed transcriptome analysis of the root tips (0-1 cm) of peanut cultivar ZH2 (Al-sensitive) and 99-1507 (Al-tolerant) respectively. Root tips of peanuts that treated with 100 μM Al for 8 h and 24 h were analyzed by RNA-Seq, and a total of 8,587 differentially expressed genes (DEGs) were identified. GO and KEGG pathway analysis excavated a group of important Al-responsive genes related to organic acid transport, metal cation transport, transcription regulation and programmed cell death (PCD). These homologs were promising targets to modulate Al tolerance in peanuts. It was found that the rapid transcriptomic response to Al stress in 99-1507 helped to activate effective Al tolerance mechanisms. Protein and protein interaction analysis indicated that MAPK signal transduction played important roles in the early response to Al stress in peanuts. Moreover, weighted correlation network analysis (WGCNA) identified a predicted EIL (EIN3-like) gene with greatly increased expression as an Al-associated gene, and revealed a link between ethylene signaling transduction and Al resistance related genes in peanut, which suggested the enhanced signal transduction mediated the rapid transcriptomic responses. Our results revealed key pathways and genes associated with Al stress, and improved the understanding of Al response in peanut.

Catechin Photolysis Suppression by Aluminum Chloride under Alkaline Conditions and Assessment with Liquid Chromatography-Mass Spectrometry

Tea is rich in catechins and aluminum. In this study, the process of catechin photolysis was applied as a model for examining the effects of aluminum chloride (AlCl₃) on the structural changes of catechin and the alteration of aluminum complexes under blue light irradiation (BLI) at pH 8 using liquid chromatography and mass spectrometry techniques. Additionally, the effects of anions on catechin upon the addition of AlCl₃ and treatment with BLI were also studied. In this study, when 1 mM catechin was treated with BLI, a superoxide anion radical (O2•-) was generated in an air-saturated aqueous solution, in addition to forming a dimeric catechin (proanthocyanidin) via a photon-induced redox reaction. The relative percentage of catechin was found to be 59.0 and 95.7 for catechin treated with BLI and catechin upon the addition of 1 mM AlCl₃ treated with BLI, respectively. It suggested that catechin treated with BLI could be suppressed by AlCl₃, while AlCl₃ did not form a complex with catechin in the photolytic system. However, under the same conditions, it was also found that the addition of AlCl₃ inhibited the photolytic formation of O2•-, and reduced the generation of proanthocyanidin, suggesting that the disconnection of proanthocyanidin was achieved by AlCl₃ acting as a catalyst under treatment with BLI. The influence of 1 mM fluoride (F-) and 1 mM oxalate (C2O42-) ions on the photolysis of 1 mM catechin upon the addition of 1 mM AlCl₃ and treatment with BLI was found to be insignificant, implying that, during the photolysis of catechin, the Al species were either neutral or negatively charged and the aluminum species did not form a complex with anions in the photolytic system. Therefore, aluminum, which is an amphoteric species, has an inherent potential to stabilize the photolysis of catechin in an alkaline conditions, while suppressing the O2•- and proanthocyanidin generation via aluminum ion catalysis in the catechin/Al system under treatment with BLI.

The GDP-Bound State of Mitochondrial Mfn1 Induces Membrane Adhesion of Apposing Lipid Vesicles through a Cooperative Binding Mechanism

Mitochondria are double-membrane organelles that continuously undergo fission and fusion. Outer mitochondrial membrane fusion is mediated by the membrane proteins mitofusin 1 (Mfn1) and mitofusin 2 (Mfn2), carrying a GTP hydrolyzing domain (GTPase) and two coiled-coil repeats. The detailed mechanism on how the GTP hydrolysis allows Mfns to approach adjacent membranes into proximity and promote their fusion is currently under debate. Using model membranes built up as giant unilamellar vesicles (GUVs), we show here that Mfn1 promotes membrane adhesion of apposing lipid vesicles. The adhesion forces were sustained by the GDP-bound state of Mfn1 after GTP hydrolysis. In contrast, the incubation with the GDP:AlF4−, which mimics the GTP transition state, did not induce membrane adhesion. Due to the flexible nature of lipid membranes, the adhesion strength depended on the surface concentration of Mfn1 through a cooperative binding mechanism. We discuss a possible scenario for the outer mitochondrial membrane fusion based on the modulated action of Mfn1.

Theoretical characterization of Al(III) binding to KSPVPKSPVEEKG: Insights into the propensity of aluminum to interact with key sequences for neurofilament formation

Classical molecular dynamic simulations and density functional theory are used to unveil the interaction of aluminum with various phosphorylated derivatives of the fragment KSPVPKSPVEEKG (NF13), a major multiphosphorylation domain of human neurofilament medium (NFM). Our calculations reveal the rich coordination chemistry of the resultant structures with a clear tendency of aluminum to form multidentate structures, acting as a bridging agent between different sidechains and altering the local secondary structure around the binding site. Our evaluation of binding energies allows us to determine that phosphorylation has an increase in the affinity of these peptides towards aluminum, although the interaction is not as strong as well-known chelators of aluminum in biological systems. Finally, the presence of hydroxides in the first solvation layer has a clear damping effect on the binding affinities. Our results help in elucidating the potential structures than can be formed between this exogenous neurotoxic metal and key sequences for the formation of neurofilament tangles, which are behind of some of the most important degenerative diseases.

Aluminum content and effect of in vitro digestion on bioaccessible fraction in cereal-based baby foods

The aim of this work was to determine the total concentration and the effect of in vitro digestion on the bioaccessible fraction of aluminum (Al) in 35 different cereal-based baby food samples and estimate the exposure to this element considering the consumption of this product. Total Al content was determined by inductively coupled plasma optical emission spectrometry after oxidative microwave digestion. An in vitro digestion method was applied and optimized to evaluate the bioaccessible fraction. The methods performance was efficient for both approached analysis and presented limits of detection and quantitation of 53 μg kg^-1 and 89 μg kg^-1, respectively. Total concentration and bioaccessibility varied according to the product composition (rice, oat, wheat, barley, corn, multicereal and fruit). Multicereals and fruit-based (plum) cereals presented the highest total Al concentrations (8.82 mg kg^-1 and 7.49 mg kg^-1, respectively), whilst lower values were observed for corn and rice flour cereals (0.92 mg kg^-1 and 1.09 mg kg^-1, respectively). The bioaccessible fraction varied from 1.5% to 10.4% in the evaluated samples. Exposure to Al was estimated and compared with the Provisional Tolerable Weekly Intake (PTWI) of 2 mg kg^-1 body weight. The results showed that the daily consumption of three portions of cereals contributes up to 10.48% of the PTWI, when considering the total Al concentration reported in this study.

Aluminum in liver cells - the element species matters

Aluminum (Al) can be ingested from food and released from packaging and can reach key organs involved in human metabolism, including the liver via systemic distribution. Recent studies discuss the occurrence of chemically distinct Al-species and their interconversion by contact with biological fluids. These Al species can vary with regard to their intestinal uptake, systemic transport, and therefore could have species-specific effects on different organs and tissues. This work aims to assess the in vitro hepatotoxic hazard potential of three different relevant Al species: soluble AlCl₃ and two nanoparticulate Al species were applied, representing for the first time an investigation of metallic nanoparticles besides to mineral bound γ-Al₂O₃ on hepatic cell lines. To investigate the uptake and toxicological properties of the Al species, we used two different human hepatic cell lines: HepG2 and differentiated HepaRG cells. Cellular uptake was determined by different methods including light microscopy, transmission electron microscopy, side-scatter analysis, and elemental analysis. Oxidative stress, mitochondrial dysfunction, cell death mechanisms, and DNA damage were monitored as cellular parameters. While cellular uptake into hepatic cell lines occurred predominantly in the particle form, only ionic AlCl₃ caused cellular effects. Since it is known, that Al species can convert one into another, and mechanisms including 'trojan-horse'-like uptake can lead to an Al accumulation in the cells. This could result in the slow release of Al ions, for which reason further hazard cannot be excluded. Therefore, individual investigation of the different Al species is necessary to assess the toxicological potential of Al particles.

Does phosphorylation increase the binding affinity of aluminum? A computational study on the aluminum interaction with serine and O-phosphoserine

Several toxic effects arise from aluminum's presence in living systems, one of these effects is to alter the natural role of enzymes and non-enzyme proteins. Aluminum promotes the hyperphosphorylation of normal proteins. In order to assess the aluminum-binding abilities of phosphorylated proteins and peptides, the interaction of aluminum at different pH with serine and phosphoserine is studied by a Density Functional Theory study, combined with polarizable continuum models to account for bulk solvent effects, and the electronic structure of selected complexes are analyzed by Quantum Theory of "Atoms in Molecules". Our results confirm the high ability of aluminum to bind polypeptides as the pH lowers. Moreover, the phosphorylation of the building blocks increases the affinity for aluminum, in particular at physiological pH. Finally, aluminum shows a tendency to be chelated forming different size rings.

A review of heavy metal cation binding to deoxyribonucleic acids for the creation of chemical sensors

Various human activities lead to the pollution of ground, drinking, and wastewater with toxic metals. It is well known that metal ions preferentially bind to DNA phosphate backbones or DNA nucleobases, or both. Foreman et al. (Environ Toxicol Chem 30(8):1810-1818, 2011) reported the use of a DNA-dye based assay suitable for use as a toxicity test for potable environmental water. They compared the results of this test with the responses of live-organism bioassays. The DNA-based demonstrated that the loss of SYBR Green I fluorescence dye bound to calf thymus DNA was proportional to the toxicity of the water sample. However, this report raised questions about the mechanism that formed the basis of this quasi-quantitatively test. In this review, we identify the unique and preferred DNA-binding sites of individual metals. We show how highly sensitive and selective DNA-based sensors can be designed that contain multiple binding sites for 21 heavy metal cations that bind to DNA and change its structure, consistent with the release of the DNA-bound dye.

Chlorogenic acid protects against aluminium-induced cytotoxicity through chelation and antioxidant actions in primary hippocampal neuronal cells

Chlorogenic acid (CGA), a major polyphenolic component of many plants, displays antioxidant and neuroprotective properties in neurodegenerative diseases. To investigate whether CGA may influence aluminium (Al) induced cytotoxicity, aluminium chloride (50 μM Al) was administered in primary hippocampal neuronal cells presupplemented with CGA (10, 50 and 100 μM). Our study shows that the exposure to Al caused cell death, Al³⁺ accumulation, reactive oxygen species generation and mitochondrial damage in cells. The administration of CGA (50 μM) increased cell viability by 37.5%, decreased the levels of Al³⁺ by 26.0%, together with significantly weakening the oxidative damage compared with Al treatment alone. CGA protected neurons against Al-induced oxidative stress by increasing the expression of nuclear factor-E2-related factor 2 and its target phase 2 enzymes. The administration of CGA remarkably promoted the activities of superoxide dismutase, catalase, glutathione peroxidase, glutathione S-transferase, creatine kinase and acetylcholinesterase and attenuated the rate of ATP hydrolysis. Our finding shows that CGA has neuroprotective effects against Al-induced cytotoxicity by chelation and antioxidant activation.

Transcriptome Analysis of Al-Induced Genes in Buckwheat (Fagopyrum esculentum Moench) Root Apex: New Insight into Al Toxicity and Resistance Mechanisms in an Al Accumulating Species

Relying on Al-activated root oxalate secretion, and internal detoxification and accumulation of Al, buckwheat is highly Al resistant. However, the molecular mechanisms responsible for these processes are still poorly understood. It is well-known that root apex is the critical region of Al toxicity that rapidly impairs a series of events, thus, resulting in inhibition of root elongation. Here, we carried out transcriptome analysis of the buckwheat root apex (0-1 cm) with regards to early response (first 6 h) to Al stress (20 μM), which is crucial for identification of both genes and processes involved in Al toxicity and tolerance mechanisms. We obtained 34,469 unigenes with 26,664 unigenes annotated in the NCBI database, and identified 589 up-regulated and 255 down-regulated differentially expressed genes (DEGs) under Al stress. Functional category analysis revealed that biological processes differ between up- and down-regulated genes, although 'metabolic processes' were the most affected category in both up- and down-regulated DEGs. Based on the data, it is proposed that Al stress affects a variety of biological processes that collectively contributes to the inhibition of root elongation. We identified 30 transporter genes and 27 transcription factor (TF) genes induced by Al. Gene homology analysis highlighted candidate genes encoding transporters associated with Al uptake, transport, detoxification, and accumulation. We also found that TFs play critical role in transcriptional regulation of Al resistance genes in buckwheat. In addition, gene duplication events are very common in the buckwheat genome, suggesting a possible role for gene duplication in the species' high Al resistance. Taken together, the transcriptomic analysis of buckwheat root apex shed light on the processes that contribute to the inhibition of root elongation. Furthermore, the comprehensive analysis of both transporter genes and TF genes not only deep our understanding on the responses of buckwheat roots to Al toxicity but provide a good start for functional characterization of genes critical for Al tolerance.

Lactobacillus plantarum CCFM639 Alleviate Trace Element Imbalance-Related Oxidative Stress in Liver and Kidney of Chronic Aluminum Exposure Mice

Aluminum (Al) has various adverse effects on health of humans and animals. The aim of present study was to demonstrate that Lactobacillus plantarum CCFM639 can alleviate the adverse effects on liver and kidney of mice caused by chronic Al exposure. Animals were assigned into control, CCFM639 only, Al only, Al plus CCFM639, and Al plus deferiprone groups. The strain was given by oral gavage for 14 weeks, and Al was introduced via drinking water for the first 8 weeks. Analyses of Al and trace elements levels in feces, blood, and tissues were performed. The biochemical markers (GSH, GPx, SOD, CAT, and MDA) of oxidative stress in livers and kidneys, as well as the levels of ALT, AST, BUN, and CRE in blood, were determined. Our results showed that L. plantarum CCFM639 can significantly reduce Al accumulation in tissues, regulate imbalance of trace elements, and thereby alleviate oxidative stress and pathological changes in hepatic and renal tissues. Therefore, L. plantarum CCFM639 could alleviate Al-induced hepatic and renal injuries, and the possible mechanisms may involve in regulating the imbalance of trace elements.

Antibacterial Activity of Aluminum in Clay from the Colombian Amazon

The problems of antibiotic overuse compel us to seek alternative antibacterial agents. Some clays have been shown to kill antibiotic-resistant human pathogens and may provide an alternative to known antibiotics. Here we show that Al toxicity plays a central role in the antibacterial action of a kaolin-rich clay from the Colombian Amazon (AMZ). Antibacterial susceptibility testing shows minimum inhibitory concentrations of 80 mg/mL against a model Escherichia coli (ATCC 25922). The clay buffered the media pH to ∼4.6 and Eh values to +360 mV. Chemical analysis of AMZ and bacteria showed that Al, P, and transition metals (Fe, Cu, Mn, and Zn) were exchanged during incubation at 37 °C. Only Al derived from the clay exceeded the minimum inhibitory concentrations for E. coli under acidic conditions. Ion imaging showed elevated Al levels in the bacterial membrane, and high intracellular Fe levels, relative to those of untreated controls. Phosphorus depletion in E. coli after reaction with AMZ, together with evidence of membrane permeabilization, suggests that Al reacts with membrane phospholipids, enhancing intracellular transport of metals. These results highlight the importance of dissolved Al for amplifying the toxicity of transition metals to human pathogens.

A computational study on interaction of aluminum withd-glucose 6-phosphate for various stoichiometries

The interaction of aluminum with glucose 6-phosphate is thought to disrupt key processes of the glucide metabolism in cells. Complex and rich aluminum chelation chemistry is found in Aluminum-glucose 6-phosphate speciation study.

Unraveling the antibacterial mode of action of a clay from the Colombian Amazon

Natural antibacterial clays can inhibit growth of human pathogens; therefore, understanding the antibacterial mode of action may lead to new applications for health. The antibacterial modes of action have shown differences based on mineralogical constraints. Here we investigate a natural clay from the Colombian Amazon (AMZ) known to the Uitoto natives as a healing clay. The physical and chemical properties of the AMZ clay were compared to standard reference materials: smectite (SWy-1) and kaolinite (API #5) that represent the major minerals in AMZ. We tested model Gram-negative (Escherichia coli ATCC #25922) and Gram-positive (Bacillus subtilis ATCC #6633) bacteria to assess the clay's antibacterial effectiveness against different bacterial types. The chemical and physical changes in the microbes were examined using bioimaging and mass spectrometry of clay digests and aqueous leachates. Results indicate that a single dose of AMZ clay (250 mg/mL) induced a 4-6 order of magnitude reduction in cell viability, unlike the reference clays that did not impact bacterial survival. AMZ clay possesses a relatively high specific surface area (51.23 m(2)/g) and much higher total surface area (278.82 m(2)/g) than the reference clays. In aqueous suspensions (50 mg clay/mL water), soluble metals are released and the minerals buffer fluid pH between 4.1 and 4.5. We propose that the clay facilitates chemical interactions detrimental to bacteria by absorbing nutrients (e.g., Mg, P) and potentially supplying metals (e.g., Al) toxic to bacteria. This study demonstrates that native traditional knowledge can direct scientific studies.

Gallium as a Therapeutic Agent: A Thermodynamic Evaluation of the Competition between Ga(3+) and Fe(3+) Ions in Metalloproteins

Gallium has been employed (in the form of soluble salts) to fight various forms of cancer, infectious, and inflammatory diseases. The rationale behind this lies in the ability of Ga(3+) cation to mimic closely in appearance the native ferric ion, Fe(3+), thus interfering with the biological processes requiring ferric cofactors. However, Ga(3+) ion cannot participate in redox reactions and, when substituting for the "native" Fe(3+) ion in the enzyme active site, renders it inactive. Although a significant body of information on the Ga(3+)-Fe(3+) competition in biological systems has been accumulated, the intimate mechanism of the process is still not well understood and several questions remain: What are the basic physical principles governing the competition between the two trivalent cations in proteins? What type of metal centers are the most likely targets for gallium therapy? To what extent are the Fe(3+)-binding sites in the key enzyme ribonucleotide reductase vulnerable to Ga(3+) substitution? Here, we address these questions by studying the competition between Ga(3+) and Fe(3+) ions in model metal binding sites of various compositions and charge states. The results obtained are in line with available experimental data and shed light on the intimate mechanism of the Ga(3+)/Fe(3+) selectivity in various model metal binding sites and biological systems such as serum transferrin and ribonucleotide reductase.

Phosphorylation promotes Al(iii) binding to proteins: GEGEGSGG as a case study

Aluminum, the third most abundant element in the Earth's crust and one of the key industrial components of our everyday life, has been associated with several neurodegenerative diseases due to its ability to promote neurofilament tangles and β-amyloid peptide aggregation.

An in vivo model to assess magnesium alloys and their biological effect on human bone marrow stromal cells

Magnesium (Mg) alloys have many unique qualities which make them ideal candidates for bone fixation devices, including biocompatibility and degradation in vivo. Despite a rise in Mg alloy production and research, there remains no standardized system to assess their degradation or biological effect on human stem cells in vivo. In this study, we developed a novel in vivo model to assess Mg alloys for craniofacial and orthopedic applications. Our model consists of a collagen sponge seeded with human bone marrow stromal cells (hBMSCs) around a central Mg alloy rod. These scaffolds were implanted subcutaneously in mice and analyzed after eight weeks. Alloy degradation and biological effect were determined by microcomputed tomography (microCT), histological staining, and immunohistochemistry (IHC). MicroCT showed greater volume loss for pure Mg compared to AZ31 after eight weeks in vivo. Histological analysis showed that hBMSCs were retained around the Mg implants after 8 weeks. Furthermore, immunohistochemistry showed the expression of dentin matrix protein 1 and osteopontin around both pure Mg and AZ31 with implanted hBMSCs. In addition, histological sections showed a thin mineral layer around all degrading alloys at the alloy-tissue interface. In conclusion, our data show that degrading pure Mg and AZ31 implants are cytocompatible and do not inhibit the osteogenic property of hBMSCs in vivo. These results demonstrate that this model can be used to efficiently assess the biological effect of corroding Mg alloys in vivo. Importantly, this model may be modified to accommodate additional cell types and clinical applications.

STATEMENT OF SIGNIFICANCE

Magnesium (Mg) alloys have been investigated as ideal candidates for bone fixation devices due to high biocompatibility and degradation in vivo, and there is a growing need of establishing an efficient in vivo material screening system. In this study, we assessed degradation rate and biological effect of Mg alloys by transplanting Mg alloy rod with human bone marrow stromal cells seeded on collagen sponge subcutaneously in mice. After 8 weeks, samples were analyzed by microcomputed tomography and histological staining. Our data show that degrading Mg alloys are cytocompatible and do not inhibit the osteogenic property of hBMSCs in vivo. These results demonstrate that this model can be used to efficiently assess the biological effect of corroding Mg alloys in vivo.

Metabolomics reveals differences of metal toxicity in cultures of Pseudomonas pseudoalcaligenes KF707 grown on different carbon sources

Co-contamination of metals and organic pollutants is a global problem as metals interfere with the metabolism of complex organics by bacteria. Based on a prior observation that metal tolerance was altered by the sole carbon source being used for growth, we sought to understand how metal toxicity specifically affects bacteria using an organic pollutant as their sole carbon source. To this end metabolomics was used to compare cultures of Pseudomonas pseudoalcaligenes KF707 grown on either biphenyl (Bp) or succinate (Sc) as the sole carbon source in the presence of either aluminum (Al) or copper (Cu). Using multivariate statistical analysis it was found that the metals caused perturbations to more cellular processes in the cultures grown on Bp than those grown on Sc. Al induced many changes that were indicative of increased oxidative stress as metabolites involved in DNA damage and protection, the Krebs cycle and anti-oxidant production were altered. Cu also caused metabolic changes that were indicative of similar stress, as well as appearing to disrupt other key enzymes such as fumarase. Additionally, both metals caused the accumulation of Bp degradation intermediates indicating that they interfered with Bp metabolism. Together these results provide a basic understanding of how metal toxicity specifically affects bacteria at a biochemical level during the degradation of an organic pollutant and implicate the catabolism of this carbon source as a major factor that exacerbates metal toxicity.

Tricholoma matsutake can absorb and accumulate trace elements directly from rock fragments in the shiro

Tricholoma matsutake, a highly valued delicacy in Japan and East Asia, is an ectomycorrhizal fungus typically found in a complex soil community of mycorrhizae, soil microbes, and host-tree roots referred to as the shiro in Japan. A curious characteristic of the shiro is an assortment of small rock fragments that have been implicated as a direct source of minerals and trace elements for the fungus. In this study, we measured the mineral content of 14 samples of shiro soil containing live matsutake mycelium and the extent to which the fungus can absorb minerals directly from the rock fragments. X-ray powder diffraction identified major phases of quartz, microcline, orthoclase, and albite in all shiro samples. PCR-denaturing gradient gel electrophoresis (DGGE) fingerprinting and direct sequencing confirmed the presence of T. matsutake on 32 of 33 rock fragments. Piloderma sp. co-occurred on 40% of fragments and was positively correlated with locations known to produce good mushroom crops. The ability of T. matsutake to absorb trace elements directly from rock fragments was examined in vitro on nutrient-agar plates supplemented with rock fragments from the shiro. In comparison to the mineral content of tissues grown on control media, the concentration of Al, Cu, Fe, Mn, P, and Zn increased from 1.1 to 106.4 times for both T. matsutake and Piloderma sp. Mineral content of dried sporocarps sampled from the study site partially reflected the results of the in vitro study. We discuss the implications of our results with respect to the natural development and artificial culture of this important fungus.

In vitro apatite formation on nano-crystalline titania layer aligned parallel to Ti6Al4V alloy substrates with sub-millimeter gap

Pure titanium substrates were chemically oxidized with H2O2 and subsequent thermally oxidized at 400 °C in air to form anatase-type titania layer on their surface. The chemically and thermally oxidized titanium substrate (CHT) was aligned parallel to the counter specimen such as commercially pure titanium (cpTi), titanium alloy (Ti6Al4V) popularly used as implant materials or Al substrate with 0.3-mm gap. Then, they were soaked in Kokubo's simulated body fluid (SBF, pH 7.4, 36.5 °C) for 7 days. XRD and SEM analysis showed that the in vitro apatite-forming ability of the contact surface of the CHT specimen decreased in the order: cpTi > Ti6Al4V > Al. EDX and XPS surface analysis showed that aluminum species were present on the contact surface of the CHT specimen aligned parallel to the counter specimen such as Ti6Al4V and Al. This result indicated that Ti6Al4V or Al specimens released the aluminum species into the SBF under the spatial gap. The released aluminum species might be positively or negatively charged in the SBF and thus can interact with calcium or phosphate species as well as titania layer, causing the suppression of the primary heterogeneous nucleation and growth of apatite on the contact surface of the CHT specimen under the spatial gap. The diffusion and adsorption of aluminum species derived from the half-sized counter specimen under the spatial gap resulted in two dimensionally area-selective deposition of apatite particles on the contact surfaces of the CHT specimen.

Aluminum interaction with 2,3-diphosphoglyceric acid. A computational study

Favorable formation of aluminum–2,3-DPG complexes in a variety of forms: 1 : 1, 1 : 2 and ternary complexes with citrate.

A remarkable effect of N,N-diethylamino functionality on the optoelectronic properties of a salicylimine-based probe for Al(3+)

A new live-cell permeable, fluorescent probe comprised of a simple salicylimine-based Schiff base (SA1) has been developed for Al3+ with nano-molar sensitivity in aqueous media. SA1 was synthesized through a simple structural modification of a recently reported receptor SA2 by the incorporation of the N,Ndiethylamino (DEA) group as a fine controllable unit. This modification affects the performance of SA1 remarkably in terms of its sensitivity, water compatibility and efficiency as well as its mechanistic aspect. The presence of the DEA group in SA1 led to its dual channel emission due to the TICT state and at the same time its hydrophobic nature was also responsible for controlling the strong hydration of Al3+ ions in aqueous media which ultimately led to the high sensitivity of SA1 for Al3+. The structure of SA1 was confirmed by single crystal X-ray diffraction and its binding with Al3+ was studied in detail using UVvisible, fluorescence and 1H NMR spectral studies along with mass determination. The effort of getting a single crystal of Al3+–SA1 led to single crystals of Cl−/NO3 − complexes of protonated SA1 which were fully characterized by their XRD studies.

Al³⁺-induced far-red fluorescence enhancement of conjugated polymer nanoparticles and its application in live cell imaging

Fluorescent nanoparticles (NPs) for Al(3+) sensing with high selectivity were developed from a type of carbazole-based conjugated polymer with a two-dimensional donor-π bridge-acceptor (D-π-A) structure. These NPs are characterized by their small particle diameter (∼18 nm), far-red fluorescence emission (centered ∼710 nm), and Al(3+)-induced fluorescence enhancement with high selectivity owing to an Al(3+)-triggered inhibition on the intramolecular charge transfer (ICT) processes between the conjugated backbone and the pendant acceptors. This type of nanoparticle is easily suspended in aqueous solutions, indicating their practical applicability in physiological media, and their ability for intracellular Al(3+) sensing was confirmed. As compared to other types of conjugated polymer based probes showing metal ion mediated fluorescence quenching, these as-prepared NPs possess analyte-enhanced fluorescence emission, which is analytically favored in terms of sensitivity and selectivity. Fluorescence emission with wavelengths in the biological window of maximum optical transparency (∼700 to 1000 nm) is expected to impart a salient advantage for biological detection applications to these as-prepared probes. The superior features of merit of this new type of fluorescent probe, together with the validation of practicability for intracellular Al(3+) ion sensing, are indicative of their potential for application in fluorescence-based imaging and sensing, such as investigations on Al(3+)-related physiological and pathological processes.

Characterization of AtSTOP1 orthologous genes in tobacco and other plant species

Aluminum (Al) and proton (H⁺) tolerances are essential traits for plants to adapt to acid soil environments. In Arabidopsis (Arabidopsis thaliana), these tolerances are mediated by a zinc-finger transcription factor, SENSITIVE TO PROTON RHIZOTOXICITY1 (AtSTOP1), which regulates the transcription of multiple genes critical for tolerance to both stressors. Here, the functions of orthologous proteins (STOP1-like proteins) in other plant species were characterized by reverse genetics analyses and in planta complementation assays. RNA interference of a gene for NtSTOP1 repressed Al and H⁺ tolerances of tobacco (Nicotiana tabacum) roots. Tobacco roots released citrate in response to Al, concomitant with the up-regulated transcription of an ortholog of an Al tolerance gene encoding a citrate-transporting multidrug and toxic compound extrusion protein. The RNA interference repression of NtSTOP1 blocked this process and also repressed the transcription of another orthologous gene for Al tolerance, ALUMINUM SENSITIVE3, which encodes a prokaryote-type transporter. These results demonstrated that NtSTOP1 regulates Al tolerance in tobacco through the transcriptional regulation of these genes. The in planta complementation assays revealed that other plant species, including woody plants, a legume, and a moss (Physcomitrella patens), possess functional STOP1-like proteins that can activate several H⁺ and Al-tolerance genes in Arabidopsis. Knocking out the gene encoding the STOP1-like protein decreased the Al tolerance of P. patens. Together, our results strongly suggest that transcriptional regulation by STOP1-like proteins is evolutionarily conserved among land plants and that it confers the ability to survive in acid soils through the transcriptional regulation of Al- and H⁺-tolerance genes.

Phosphatidylserine stimulation of Drs2p·Cdc50p lipid translocase dephosphorylation is controlled by phosphatidylinositol-4-phosphate

Here, Drs2p, a yeast lipid translocase that belongs to the family of P(4)-type ATPases, was overexpressed in the yeast Saccharomyces cerevisiae together with Cdc50p, its glycosylated partner, as a result of the design of a novel co-expression vector. The resulting high yield allowed us, using crude membranes or detergent-solubilized membranes, to measure the formation from [γ-(32)P]ATP of a (32)P-labeled transient phosphoenzyme at the catalytic site of Drs2p. Formation of this phosphoenzyme could be detected only if Cdc50p was co-expressed with Drs2p but was not dependent on full glycosylation of Cdc50p. It was inhibited by orthovanadate and fluoride compounds. In crude membranes, the phosphoenzyme formed at steady state at 4 °C displayed ADP-insensitive but temperature-sensitive decay. Solubilizing concentrations of dodecyl maltoside left this decay rate almost unaltered, whereas several other detergents accelerated it. Unexpectedly, the dephosphorylation rate for the solubilized Drs2p·Cdc50p complex was inhibited by the addition of phosphatidylserine. Phosphatidylserine exerted its anticipated accelerating effect on the dephosphorylation of Drs2p·Cdc50p complex only in the additional presence of phosphatidylinositol-4-phosphate. These results explain why phosphatidylinositol-4-phosphate tightly controls Drs2p-catalyzed lipid transport and establish the functional relevance of the Drs2p·Cdc50p complex overexpressed here.

Effect of root age on the allocation of metals, amino acids and sugars in different cell fractions of the perennial grass Paspalum notatum (bahiagrass)

This work aimed to compare the allocation of Al, Fe, Cu, Ni, amino acids and sugars in different fractions of root cells of Paspalum notatum with 21 and 120 days old grown in quartz sand. In general younger roots showed a higher content of Al, Fe, Cu Ni, amino acids and sugars, compared to older roots. This can be due to a higher metabolic activity of younger roots and/or to structural changes that can occur with cell ageing. Al and Fe were mainly allocated to fractions with pectin, hemicellulose and cellulose, both in younger and older roots. However, older roots also showed a significant fraction of Al allocated to the intracellular fraction. It seems that older roots were less able to prevent the entry of Al in the cytoplasm. The proportion of Cu was higher in intracellular components, both in younger and older roots, as expected from an essential nutrient. Ni content was very low in older roots and in younger roots it was mainly allocated to the intracellular fraction and to the cell wall polysaccharides fraction. The amino acids were mainly allocated to the cytoplasm and polysaccharide fraction. Although younger roots showed a higher total amount of amino acids compared to older roots, the amino acids profile and allocation, mainly in the cytoplasm polysaccharides, was quite similar. Arabinose, a major component of structural glycoproteins of the primary cell wall matrix, was only detected in younger roots. Thus, it seems that root cells of P. notatum suffered changes in the composition of the cell wall components with ageing. To further understand the structural changes of root cells with ageing and its effect on metal allocation, it is important to quantify several components of the cell wall matrix, namely pectins and glycoproteins.