A molecular mechanism of aluminium-induced Alzheimer's disease?

Study binding of Al-curcumin complex to ds-DNA, monitoring by multispectroscopic and voltammetric techniques

In this work a complex of Al3+ with curcumin ([Al(curcumin) (EtOH)2](NO3)2) was synthesized and characterized by UV-vis, FT-IR, elemental analysis and spectrophotometric titration techniques. The mole ratio plot revealed a 1:1 complex between Al3+ and curcumin in solution. For binding studies of this complex to calf thymus-DNA various methods such as: UV-vis, fluorescence, circular dichroism (CD), FT-IR spectroscopy and cyclic voltammetry were used. The intrinsic binding constant of ACC with DNA at 25°C was calculated by UV-vis and cyclic voltammetry as 2.1×10(4) and 2.6×10(4), respectively. The thermodynamic studies showed that the reaction is enthalpy and entropy favored. The CD results showed that only the Δ-ACC interacts with DNA and the Δ-ACC form has not any tendency to interact with DNA, also the pure curcumin has not any stereoselective interaction with CT-DNA. Fluorimetric studies showed that fluorescence enhancement was initiated by a static process in the ground state. The cyclic voltammetry showed that ACC interact with DNA with a binding site size of 2. From the FT-IR we concluded that the Δ-ACC interacts with DNA via partial electrostatic and minor groove binding. In comparison with previous works it was concluded that curcumin significantly reduced the affinity of Al3+ to the DNA.

Anti-washout carboxymethyl chitosan modified tricalcium silicate bone cement: preparation, mechanical properties and in vitro bioactivity

Anti-washout CaF(2) stabilized C(3)S (F-C(3)S) bone cement was prepared by adding water-soluble carboxymethyl chitosan (CMCS) to the hydration liquid. The setting time, compressive strength and in vitro bioactivity of the CMCS modified F-C(3)S (CMCS-C(3)S) pastes were evaluated. The results indicate that CMCS-C(3)S pastes could be stable in the shaking simulated body fluid (SBF) after immediately mixed. The addition of CMCS significantly enhances the cohesion of particles, at the same time restrains the penetration of liquid, and thus endows the anti-washout ability. The setting times of the pastes increase with the increase of CMCS concentrations in the hydration liquid. Besides, the compressive strengths of CMCS-C(3)S pastes after setting for 1-28 days are lower than that of the pure F-C(3)S paste, but the sufficient strengths would be suitable for the clinical applications. The crystalline apatite deposited on the paste surface is retarded from 1 to 2 days for the addition of CMCS, but the quantities of deposited apatite are same after soaking in SBF for 3 days. As the result that pure C(3)S paste has shorter setting times than pure F-C(3)S paste, CMCS modified pure C(3)S pastes would have better anti-washout ability. Our study provides a convenient way to use C(3)S bone cement with excellent anti-washout ability when the pastes are exposed to biological fluids. The novel anti-washout CMCS-C(3)S bone cement with suitable setting times, sufficient strengths and in vitro bioactivity would have good prospects for medical application.

Memory performance, brain excitatory amino acid and acetylcholinesterase activity of chronically aluminum exposed mice in response to soy isoflavones treatment

Memory performance, brain excitatory amino acid and acetylcholinesterase activity of chronically aluminum (Al) exposed mice in response to soy isoflavones (SI) treatment was investigated in the study. Forty eight mice were allotted randomly into a control group, an Al exposed group (100 mg/kg Al) and an Al exposed group treated with SI (100 mg/kg Al + 60 mg/kg SI) for 60 days. Chronic Al exposure significantly impaired long memory performance in mice as assessed using a passive avoidance task test (χ(2) analysis, p < 0.05). Interestingly, SI treatment markedly improved the memory performance score in the Al exposed mice. This improvement was associated with a total reversal of Al-induced increases in acetylcholinesterase activity in the cerebral cortex and hippocampus of mice. The Al exposure also led to significant decreases in brain levels of aspartic and glutamic acids, two excitatory amino acid neurotransmitters; whereas SI treatment partially reversed the decreased aspartic and glutamic acid contents in the hippocampus. The results suggest that SI can improve long memory performance in the Al exposed mice, possibly by modulating the metabolism of brain acetylcholine and amino acid neurotransmitters.

Aluminum does not enhance beta-amyloid toxicity in rat hippocampal cultures

A number of environmental factors have been implicated in neurodegenerative disorders, including metallotoxins such as aluminum (Al). In the present study, the toxicity of Al-quinate (AlQ), a well-characterized Al complex, was investigated in primary rat hippocampal cultures in comparison to inorganic Al (Al-S). AlQ was significantly less toxic than Al-S during both short- (3h) and long-term (24h) incubations. The neuroprotective properties of quinic acid (which constitutes the quinate moiety of AlQ) against short-term incubations with Al-S were subsequently assessed, and the organic compound was found to provide full protection, comparable to synthetic metal chelating agents desferrioxamine and clioquinol. Finally, potential synergistic actions between Al (AlQ and Al-S) and beta-amyloid (Abeta) were investigated. Neither Al form appeared to enhance Abeta toxicity, in fact, AlQ significantly reduced Abeta toxicity. Collectively, this study highlights further the impact of structural features and physiological ligands of metal complexes on toxicity profiles, and reveals promising properties of quinic acid as a metal chelator. Despite previous reports suggesting synergistic toxicity between Al and Abeta, we could not identify such a mechanism in our investigation.

The effect of acidic agents on surface ion leaching and surface characteristics of dental porcelains

STATEMENT OF PROBLEM

Acidic food and sour fruits and drinks have been investigated for their destructive effects on enamel. However, their effect on porcelain restorations has not been widely examined.

PURPOSE

The purpose of this study was to evaluate the ion leaching of porcelains immersed in acidic agents.

MATERIAL AND METHODS

Fifty-five discs (12.0 mm in diameter and 2.0 mm in thickness) were made from each of 4 types of porcelain (VITA VMK 95, Vitadur Alpha, IPS Empress Esthetic, and IPS e.max Ceram). Baseline data of elemental compositions of all storage agents were recorded. Four groups of discs (n=10) were then immersed in acidic agents (citrate buffer solution, pineapple juice, and green mango juice) and deionized water (control) at 37 degrees C for 168 hours. One group was immersed in 4% acetic acid at 80 degrees C for 168 hours. After immersion, fluids from all specimens for each acidic agent were measured for ion leaching with an inductively coupled plasma optical emission spectroscopy. Surface characteristics of specimens were examined using scanning electron microscopy (SEM). Data were analyzed using 3-way repeated ANOVA and Tukey HSD multiple comparisons (alpha=.05).

RESULTS

This study revealed that each type of porcelain had significantly leached the various ions to varying degrees after being immersed in acidic agents (P<.001 for all comparisons). SEM photomicrographs showed surface destruction of all porcelains.

CONCLUSIONS

Acidic agents used in this study affected elemental dissolution of the 4 types of porcelains evaluated.

Fabrication of spherical CaO-SrO-ZnO-SiO₂ particles by sol-gel processing

This study was concerned with the fabrication of ceramic CaO-SrO-ZnO-SiO(2) spherical particles, which are novel candidates for the glass phase in glass polyalkenoate cements (GPCs). GPCs made from these glasses have potential as bone cements because, unlike conventional GPCs, they do not contain aluminum ions, which inhibit the calcification of hydroxyapatite in the body. The glass phase of GPCs require a controllable glass morphology and particle size distribution. Sol-gel processing can potentially be used to fabricate homogenous ceramic particles with controlled morphology. However, a thorough study on preparation conditions of spherical CaO-SrO-ZnO-SiO(2) particles by sol-gel processing has, to date, not been reported. In this study, gels were prepared by hydrolysis and polycondensation of tetraethoxysilane (TEOS) in an aqueous solution containing polyethylene glycol and nitrates of calcium, strontium and zinc. It was possible to control the morphology and size of the gels by varying the H(2)O/TEOS molar ratio and the metal ion content in the starting compositions. An aliquot of 3-5 mum homogenous spherical particles were obtained at a H(2)O/TEOS molar ratio of 42.6 when the starting composition molar ratios were Sr(NO(3)):Ca(NO(3))(2):Zn(NO(3))(2):Si(OC(2)H(5))(4) = x:0.12:(0.40 - x):0.48 (0 </= x </= 0.8). Starting composition limitations are caused by the low solubility of strontium ions in the minimal amount of water used and the acceleration of hydrolysis as well as polycondensation at higher water content.

Preparation of Amorphous Calcium Phosphate/Triclcium Silicate Composite Powders

The amorphous calcium phosphate (ACP)/tricalcium silicate (Ca3SiO5, C3S) composite powders were synthesized in this paper. The exothermal behavior of C3S determined by isothermal conduction calorimetry indicated that the ACP could be synthesis by chemical precipitation method during the induction period (stage II) of C3S. The composite powders were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). The results indicated that nanosized ACP particles deposited on the surface of C3S particles to form core-shell structure at pH=10.5, and the nCa/nP of ACP could be controlled between 1.0 and 1.5. The core-shell structure is stable after sintered at 500 oC for 3 h to remove the β-cyclodextrin (β-CD). As compared with the irregular C3S particles (1~5 μm), the composite powders particles are spherical with a diameter of 40~150 μm. Therefore, to obtain the smaller size of composite powders, it is expected to avoid the aggregate of C3S particles in the aqueous solution by addition of dispersant. As compared with C3S, the composite powders may contribute better injectability, strength and biocompatibility.

The apatite formation ability of CaF2 doping tricalcium silicates in simulated body fluid

The purpose of this study was to investigate the effects of CaF(2) on the apatite formation ability of tricalcium silicates (Ca(3)SiO(5), C(3)S) and the mechanism of apatite formation on C(3)S pastes. Different amounts of CaF(2) (0, 1, 2 and 3 wt%) were mixed in the raw materials during the synthesis process of C(3)S. The apatite formation ability of the CaF(2) doping C(3)S was examined by soaking the one-day setting pastes in simulated body fluid (SBF). The fluoride concentrations, pH values, structural and morphological variations of the pastes were examined during soaking in SBF. With the addition of CaF(2), the initial crystalline apatite formation time of the pastes was decreased from three days to one day. After soaking for seven days, the thicknesses of apatite layers depositing on the surface of C(3)S doped with 0, 1, 2 and 3 wt% CaF(2) were about 88, 102, 168 and 136 microm, respectively. C(3)S doped with 2 wt% CaF(2) showed the better ability to induce the formation of apatite. Furthermore, the mechanism of the apatite formation of the CaF(2) doping C(3)S pastes may be attributed to the formation and stability of F-substituted apatite determined by x-ray photoelectron spectroscopy (XPS) at the early age. The results indicated that CaF(2) doping C(3)S has better in vitro bioactivity, and may be used to prepare novel bone cement.

Antibacterial coatings for medical devices based on glass polyalkenoate cement chemistry

A biofilm is an accumulation of micro-organisms and their extracellular products forming a structured community on a surface. Biofilm formation on medical devices has severe health consequences as bacteria growing in this lifestyle are tolerant to both host defense mechanisms and antibiotic therapies. However, silver and zinc ions inhibit the attachment and proliferation of immature biofilms. The objective of this study is to evaluate whether it is possible to produce silver and zinc-containing glass polyalkenoate cement (GPC) coatings for medical devices that have antibacterial activity and which may therefore inhibit biofilm formation on a material surface. Two silver and zinc-containing GPC coatings (A and B) were synthesised and coated onto Ti6Al4V discs. Their handling properties were characterised and atomic absorption spectrometery was employed to determine zinc and silver ion release with coating maturation up to 30 days. The antibacterial properties of the coatings were also evaluated against Staphylococcus aureus and a clinical isolate of Pseudomonas aeruginosa using an agar diffusion assay method. The majority of the zinc and silver ions were released within the first 24 h; both coatings exhibited antibacterial effect against the two bacterial strains, but the effect was more intense for B which contained more silver and less zinc than A. Both coatings produced clear zones of inhibition with each of the two organisms tested. In this assay, Ps. aeruginosa was more sensitive than S. aureus. The diameters of these zones were reduced after the coating had been immersed in water for varying periods due to the resultant effect on ion release.

Zinc-based glass polyalkenoate cements with improved setting times and mechanical properties

The suitability of glass polyalkenoate cements (GPCs) for skeletal applications is limited by the presence, in the glass phase, of the aluminium ion (Al3+), a neurotoxin. The zinc ion (Zn2+), a bacteriocide, has been incorporated into aluminium-free GPCs based on zinc silicate glasses. However, these GPCs have considerably shorter working times and poorer mechanical properties than their Al3+-containing counterparts. Based on results for calcium phosphate cements, there is an indication that mixing a GPC with an organic compound, tricalcium citrate (TSC), may lead to cements with improved rheological and mechanical properties. We developed a range of Zn-based GPCs and determined their working times (Tw), setting times (Ts), compressive strength (CS) and biaxial flexural strengths (BFS). A GPC composed of 1g of a calcium-zinc silicate glass (BT100) mixed with a 50wt.% aqueous solution on polyacrylic acid (coded E9, Mw 80,800) at a powder liquid ratio of 2:1.5 exhibited the best combination of Tw, Ts, CS and BFS. We also found that the addition of TSC (over the range 5-15wt.%) to a GPC led to significant increases in both Tw (from 40+/-3 to 100+/-4s) and Ts (from 70+/-2 to 3000+/-4s) accompanied by changes in both CS and BFS that were affected by the duration of the aging time of the specimens in distilled water (for example, after aging for 7 days CS dropped from 62+/-2 to 17+/-1MPa, while after aging for 30 days, BFS increased 27+/-6 to 31+/-7MPa and then dropped to 17+/-1MPa). Future modification and characterization of the examined GPCs are needed before they may be considered as candidates for orthopaedic applications.

The role of Sr2+ on the structure and reactivity of SrO-CaO-ZnO-SiO2 ionomer glasses

The suitability of Glass Polyalkenoate Cements (GPCs) for use in orthopaedics is retarded by the presence in the glass phase of aluminium, a neurotoxin. Unfortunately, the aluminium ion plays an integral role in the setting process of GPCs and its absence is likely to hinder cement formation. However, the authors have previously shown that aluminium free GPCs may be formulated based on calcium zinc silicate glasses and these novel materials exhibit significant potential as hard tissue biomaterials. To further improve their potential, and given that Strontium (Sr) based drugs have had success in the treatment of osteoporosis, the authors have substituted Calcium (Ca) with Sr in the glass phase of a series of aluminium free GPCs. However to date little data exists on the effect SrO has on the structure and reactivity of SrO-CaO-ZnO-SiO(2) glasses. The objective of this work was to characterise the effect of the Ca/Sr substitution on the structure of such glasses, and evaluate the subsequent reactivity of these glasses with an aqueous solution of Polyacrylic acid (PAA). To this end (29)Si MAS-NMR, differential scanning calorimetry (DSC), X-ray diffraction, and network connectivity calculations, were used to characterize the structure of four strontium calcium zinc silicate glasses. Following glass characterization, GPCs were produced from each glass using a 40 wt% solution of PAA (powder:liquid = 2:1.5). The working times and setting times of the GPCs were recorded as per International standard ISO9917. The results acquired as part of this research indicate that the substitution of Ca for Sr in the glasses examined did not appear to significantly affect the structure of the glasses investigated. However it was noted that increasing the amount of Ca substituted for Sr did result in a concomitant increase in setting times, a feature that may be attributable to the higher basicity of SrO over CaO.

Direct electrochemistry of lactate dehydrogenase immobilized on silica sol–gel modified gold electrode and its application

The direct electrochemistry of lactate dehydrogenase (LDH) immobilized in silica sol-gel film on gold electrode was investigated, and an obvious cathodic peak at about -200 mV (versus SCE) was found for the first time. The LDH-modified electrode showed a surface controlled irreversible electrode process involving a one electron transfer reaction with the charge-transfer coefficient (alpha) of 0.79 and the apparent heterogeneous electron transfer rate constant (K(s)) of 3.2 s(-1). The activated voltammetric response and decreased charge-transfer resistance of Ru(NH(3))(6)(2+/3+) on the LDH-modified electrode provided further evidence. The surface morphologies of silica sol-gel and the LDH embedded in silica sol-gel film were characterized by SEM. A potential application of the LDH-modified electrode as a biosensor for determination of lactic acid was also investigated. The calibration range of lactic acid was from 2.0 x 10(-6) to 3.0 x 10(-5) mol L(-1) and the detection limit was 8.0 x 10(-7) mol L(-1) at a signal-to-noise ratio of 3. Finally, the effect of environmental pollutant resorcinol on the direct electrochemical behavior of LDH was studied. The experimental results of voltammetry indicated that the conformation of LDH molecule was altered by the interaction between LDH and resorcinol. The modified electrode can be applied as a biomarker to study the pollution effect in the environment.

Does neurotransmission impairment accompany aluminium neurotoxicity?

Neurobehavioral disorders, except their most overt form, tend to lie beyond the reach of clinicians. Presently, the use of molecular data in the decision-making processes is limited. However, as details of the mechanisms of neurotoxic action of aluminium become clearer, a more complete picture of possible molecular targets of aluminium can be anticipated, which promises better prediction of the neurotoxicological potential of aluminium exposure. In practical terms, a critical analysis of current data on the effects of aluminium on neurotransmission can be of great benefit due to the rapidly expanding knowledge of the neurotoxicological potential of aluminium. This review concludes that impairment of neurotransmission is a strong predictor of outcome in neurobehavioral disorders. Key questions and challenges for future research into aluminium neurotoxicity are also identified.

Role of beer as a possible protective factor in preventing Alzheimer's disease

Aluminium (Al), a neurotoxin, has lately been implicated as one of the possible causal factors contributing to Alzheimer's disease. Because silicon (Si) intake can affect the bioavailability of aluminium, the object of the present study was to assess whether moderate beer consumption might, as a source of dietary Si, affect the toxicokinetics of Al and thereby limit that element's neurotoxicity. The results obtained confirmed that at moderately high levels of beer intake the Si present in the beer was able to reduce Al uptake in the digestive tract and thus was able to slow the accumulation of this metal in the body, brain tissue included. In consequence, moderate beer consumption, due to its content in bioavailability silicon, possibly affording a protective factor for preventing Alzheimer's disease, could perhaps be taken into account as a component of the dietary habits of the population.

Differential toxicity of novel aluminium compounds in hippocampal culture

The dependence of aluminium (Al) toxicity on its chemical form has been implicated in previous studies, but the complex chemistry of Al in solutions of biological preparations has hampered a reliable assessment. Here, we assessed the toxicity of select and pure Al(III) citrate compounds, well-characterized at physiological pH, and compared it with Al from standard solution (in HCl). Cell death rates of neurones and glia were established in hippocampal cultures following 3h incubations in a HEPES-buffered solution and 24h incubations in full culture medium. Overall, Al toxicity was found to vary considerably between compounds, with duration of exposure, medium type, and cell type as factors. While Al (from atomic absorption standard solution) induced the highest levels of cell death, AlCit1, ((NH(4))(5)[Al(C(6)H(4)O(7))(2)].2H(2)O) was the most toxic citrate compound, and affected viability of neurones more than glia (viability at 500 microM/3h-neurones: 40%; glia: 60%). AlCit2 (K(4)[Al(C(6)H(4)O(7))(C(6)H(5)O(7))].4H(2)O) did not show any toxicity after 3h, but severe toxicity after 24h in both cell types (viability at 500 microM/24h-neurones: 50%, glia: 30%). AlCit3 ((NH(4))(5)[Al(3)(C(6)H(4)O(7))(3)(OH)(H(2)O)].(NO(3)).6H(2)O), exhibited a cell type specific toxicity profile, and only affected neuronal viability at both time points (neuronal viability at 500 microM/3h: 20%). The medium type and presence of serum (FBS) was also found to contribute to the toxicity pattern, with serum providing partial protection. Since the Al(III) compounds introduced here are assumed to form in vivo, our data raise further awareness for the toxicity of Al(III) in general, and for the importance of Al speciation and cell type specific actions in its toxicity.

Brazilian female crack users show elevated serum aluminum levels

OBJECTIVE: There is no information in the literature on the impact of crack smoking using crushed aluminum cans as makeshift pipes, a common form of crack use in Brazil. Since aluminum intake is associated with neurological damage, we measured serum aluminum levels in crack smokers. The objective of this study was to ascertain the levels of aluminum in crack users who smoke on makeshift aluminum pipes. METHOD: 71 female crack smokers, their mean age being 28.0 (± 7.7), provided information about their drug use, and had blood samples tested for serum aluminum level. RESULTS: 56 (79%) subjects smoked crack from crushed can pipes, while 15 (21%) smoked from other containers. Fifty-two (73.2%) out of the 71 subjects presented a serum aluminum level of 2 µg/l and 13 (18.3%) had a serum aluminum level of 6 µg/l cut-off point, which is above the reference value. When compared to non-drug users matched by their mean age and gender, they had similar median values and interquartile ranges for serum aluminum level [3 (2-4.6) for crack smokers; 2.9 (1.6-4.1) for controls], but with different means and standard deviations (4.7 ± 4.9 and 2.9 ± 1.7, respectively). DISCUSSION: Crack smokers have high serum aluminum level, but we are unsure of its complete association with aluminum cans. Further studies are needed. If such association is proven true in future research, further issues will be raised in dealing with this important disorder, including proper planning and evaluation of public health policies in this area.

Phosphorylation-dependent metal binding by alpha-synuclein peptide fragments

Alpha-synuclein (alpha-syn) is the major protein component of the insoluble fibrils that make up Lewy bodies, the hallmark lesions of Parkinson's disease. Its C-terminal region contains motifs of charged amino acids that potentially bind metal ions, as well as several identified phosphorylation sites. We have investigated the metal-binding properties of synthetic model peptides and phosphopeptides that correspond to residues 119-132 of the C-terminal, polyacidic stretch of human alpha-syn, with the sequence Ac-Asp-Pro-Asp-Asn-Glu-Ala-Tyr-Glu-Met-Pro-Ser-Glu-Glu-Gly (alpha-syn119-132). The peptide pY125 replaces tyrosine with phosphotyrosine, whereas pS129 replaces serine with phosphoserine. By using Tb(3+) as a luminescent probe of metal binding, we find a marked selectivity of pY125 for Tb(3+) compared with pS129 and alpha-syn119-132, a result confirmed by isothermal titration calorimetry. Truncated or alanine-substituted peptides show that the phosphoester group on tyrosine provides a metal-binding anchor that is supplemented by carboxylic acid groups at positions 119, 121, and 126 to establish a multidentate ligand, while two glutamic acid residues at positions 130 and 131 contribute to binding additional Tb(3+) ions. The interaction of other metal ions was investigated by electrospray ionization mass spectrometry, which confirmed that pY125 is selective for trivalent metal ions over divalent metal ions, and revealed that Fe(3+) and Al(3+) induce peptide dimerization through metal ion cross-links. Circular dichroism showed that Fe(3+) can induce a partially folded structure for pY125, whereas no change was observed for pS129 or the unphosphorylated analog. The results of this study show that the type and location of a phosphorylated amino acid influence a peptide's metal-binding specificity and affinity as well as its overall conformation.

Study on the interaction of copper-zinc superoxide dismutase with aluminum ions by electrochemical and fluorescent method

The interaction of superoxide dismutase (SOD) with aluminum (Al) ions was investigated by cyclic voltammetry, fluorescence spectroscopy and synchronous fluorescence spectroscopy. The electrochemical activity of the SOD enzyme electrode was inhibited irreversibly by the addition of Al. Meanwhile, the static fluorescence quenching mechanism further revealed the existing of molecular complex of SOD with Al(3+). The association constant was obtained from Lineweaver-Burk plot. The experimental results of voltammetry and fluorescence spectroscopy indicated that the conformation of SOD molecule was altered by the formation of Al-SOD complex. It may influence the activity of SOD enzyme since the optimum action of SOD depends upon a particular configuration of electrostatic charges in the enzyme molecule.

The antibacterial effects of zinc ion migration from zinc-based glass polyalkenoate cements

Zinc-based glass polyalkenoate cements have been synthesised and their potential use in orthopaedic applications investigated. Zinc ions were released from the materials in a rapid burst over the first 24 h after synthesis, with the release rate falling below detectable levels after 7 days. Cement-implanted bone samples were prepared and the released zinc was shown, using energy dispersive X-ray analysis, to penetrate from the cement into the adjacent bone by up to 40 microm. Finally, the cements exhibited antibacterial activity against Streptococcus mutans and Actinomyces viscosus that reflected the pattern of zinc release, with the inhibition of growth greatest shortly after cement synthesis and little or no inhibition measureable after 30 days.

An investigation into the structure and reactivity of calcium-zinc-silicate ionomer glasses using MAS-NMR spectroscopy

The suitability of Glass Polyalkenoate Cements (GPCs) for orthopaedic applications is retarded by the presence in the glass phase of aluminium, a neurotoxin. Unfortunately, the aluminium ion plays an integral role in the setting process of GPCs and its absence is likely to hinder cement formation. However, the authors have previously shown that aluminium-free GPCs may be formulated based on calcium zinc silicate glasses and these novel materials exhibit significant potential as hard tissue biomaterials. However there is no data available on the structure of these glasses. (29)Si MAS-NMR, differential thermal analysis (DTA), X-ray diffraction (XRD), and network crosslink density (CLD) calculations were used to characterize the structure of five calcium zinc silicate glasses and relate glass structure to reactivity. The results indicate that glasses capable of forming Zn-GPCs are predominantly Q(2)/Q(3) in structure with corresponding network crosslink densities greater than 2. The correlation of CLD and MAS-NMR results indicate the primary role of zinc in these simple glass networks is as a network modifier and not an intermediate oxide; this fact will allow for more refined glass compositions, with less reactive structures, to be formulated in the future.

Microdermabrasion

BACKGROUND

Microdermabrasion has become one of the most popular forms of superficial resurfacing. The benefits and efficacy of microdermabrasion remain an intensely debated topic among dermatologic surgeons.

OBJECTIVE

This article reviews the efficacy, safety, epidermal barrier function, histopathologic effects, complications, advantages, and disadvantages of microdermabrasion.

CONCLUSION

In general, microdermabrasion studies have been conducted in small groups of patients. Protocols, units, and settings have differed. There remains a major disparity between the popularity of microdermabrasion in the public sector and cohesive and comprehensive scientific data documenting the efficacy of the procedure.

Exposure to aluminium changes the NADPH-diaphorase/ NPY pattern in the rat cerebral cortex

Aluminium (Al) impairs the glutamate-nitric oxide-cGMP pathway and reduces the number of nitroxidergic neurons in the rat somatosensory cortex. To understand better the effect of the time of exposure, we monitored the effect of aluminium administration on nitroxidergic neurons, identified by NADPH-diaphorase (NADPH-d) or by nitric oxide synthase (NOS) staining, after 0.5, 1, 2, 3, 6 and 12 months of aluminium administration. Since neuropeptide Y (NPY) is known to be colocalised with nitric oxide synthase in cortical neurons, the aim of this work was to study the effects of Al administration on the cortical expression of NADPH-d, nNOS, and NPY. NADPH-d or NOS positive neurons were found scattered in the cortex where they constituted about 1% of all neurons. Double staining using NADPH-d and NPY showed that almost all nitroxidergic neurons were co-localised with NPY neurons (NADPH-d/NPY double stained neurons) whereas some neurons were stained only with NPY (NPY single stained neurons) ; these were more numerous than NADPH-d/NPY double stained neurons. Al significantly reduced NADPH-d and nNOS positive neurons in the cerebral cortex time dependently, with the greatest effect appearing after 3 months. Also measured was the integrated optical density (IOD) of nNOS positive neurons showing a significant decrease of NOS immunostaining even in the remaining NOS positive neurons. The double staining experiment exhibited a decrease in NADPH-d/NPY double stained neurons with an apparent increase in NPY single stained neurons; these then decreased after 6-12 months. On the whole, the results confirm that Al impairs nitroxidergic pathways time dependently; moreover, the transient increase in NPY single stained neurons from 1 to 3 months suggests that there is an intraneuronal down-regulation of NOS, without affecting neuronal viability. In addition, the decrease in the NPY system found at 6 and 12 months may indicate that Al affected nitroxidergic and NPY systems at different times.

The processing, mechanical properties and bioactivity of zinc based glass ionomer cements

The suitability of Glass Ionomer Cements (GICs) for use in orthopaedics is retarded by the presence in the glass phase of aluminium, a neurotoxin. Unfortunately, the aluminium ion plays an integral role in the setting process of a GIC and its absence is likely to hinder cement formation. However, zinc oxide, a bacteriocide, can act both as a network modifying oxide and an intermediate oxide in a similar fashion to alumina and so ternary systems based on zinc silicates often have extensive regions of glass formation. The purpose of this research was to produce novel GICs based on calcium zinc silicate glasses and to evaluate their rheological, mechanical and biocompatible properties with the ultimate objective of developing a new range of cements for skeletal applications. The work reported shows that GICs based on two different glasses, A and B (0.05CaO.0.53ZnO.0.42SiO2 and 0.14CaO.0.29ZnO.0.57SiO2, respectively), exhibited handling properties and flexural strengths comparable to conventional GICs. Upon immersion in simulated body fluid of a GIC based on glass B, an amorphous calcium phosphate layer nucleated on the surface of the cement indicating that these cements are bioactive in nature.

Chelating effect of novel pyrimidines in a model of aluminum intoxication

Long time ago aluminum (Al) was considered as a non-toxic element and its use had no restrictions. However, over the last two decades, scientific publications have indicated that Al is a toxic element. In line with this, aluminum accumulation in the organism is associated with a variety of human pathologies. Efficient therapeutics approach to treat Al intoxication are still not available, but there is a consensus that chelation therapy is the procedure to be used. However, the development of new chelating agents are highly desirable to improve the efficacy of the treatment of Al intoxication. The present study evaluates the chelating effect of two novel pyrimidines: 4-tricloromethyl-1-H-pyrimidin-2-one (THP) and (4-methyl-6-trifluoromethyl-6-pyrimidin-2-il)-hydrazine (MTPH) in a mice model of aluminum intoxication and compares their efficacy with those of desferrioxamine (DFO), a classical agent used for treat Al accumulation. The animals were exposed to aluminum by gavage (0.1 mmol aluminum/kg/day) 5 days/week for 4 weeks. At the end of this period, DFO was injected i.p. and the novel pyrimidines were given by gavage at 0.2 mmol/kg/day for five consecutive days. Aluminum concentration in tissues (brain, liver, kidney and blood) was determined by graphite furnace atomic absorption spectroscopy (GFAAS). The results showed that when administered by gavage, aluminum accumulated in the brain, kidney and liver of mice. MTPH was able to decrease aluminum levels in aluminum plus citrate animal groups, whereas THP was inefficient for this purpose. However, the novel pyrimidines used in this study were unable to surpass the aluminum chelating property of DFO. Thus, new studies must be performed utilizing other chelating agents which can decrease aluminum toxicity.

Aluminium speciation in the Vienne river on its upstream catchment (Limousin region, France)

The aim of this study was to investigate the speciation of aluminium in the river Vienne on its upstream catchment (Limousin region, France) over a period of seven years (May 1998-September 2004) in order to assess harmful effects on aquatic life. Two sampling points were selected: the first at 4 km from the spring (Peyrelevade), and the second one at 89 km from the spring (Royères). The aluminium speciation was computed with Mineql+ 4.5 speciation software. Organic matter and phosphorous play a major role in aluminium speciation. If we consider the free aluminium ion (Al3+) as being the only toxic form of aluminium, the concentrations of toxic forms recorded at Peyrelevade and Royères were always below the toxic values for fish. However, if the sum of the concentrations of Al3+, Al(OH)2+, Al(OH)2+ and Al(OH)4- is taken into consideration, the concentration of aluminium recorded may have adverse effects on aquatic life in the upstream catchment of the river Vienne. Al(OH)4- is the major contributor to the concentration in toxic aluminium recorded. In general, Al(OH)4- forms appears in water during the summer with water alkalinisation due to an increase in photosynthetic activities.

Transport mechanism for aluminum citrate at the blood–brain barrier: kinetic evidence implies involvement of system Xc− in immortalized rat brain endothelial cells

Although accumulation of aluminum (Al) in the brain is known to cause neurodegenerative disorders and to be regulated mainly by the blood-brain barrier (BBB), the mechanism responsible for Al transport at the BBB has not been clarified yet. In this study, we investigated what kind of transporter is involved in the transport of Al citrate, which is the major species of Al in the brain, at the BBB using a rat immortalized brain endothelial cell line (RBEC1), focusing on the glutamate transporter family. The uptake of Al citrate showed temperature- and concentration-dependency, and did not require an inwardly directed Na+-gradient as a driving force, ruling out the involvement of Na+-dependent glutamate transporters in its transport. By RT-PCR, in RBEC1, there were mRNAs for the components of a Na+-independent glutamate transporter, system Xc-. L-Glutamate and L-cystine, representative ligands for system Xc-, significantly inhibited the uptake of Al citrate, and loading of them into the cells resulted in stimulation of its uptake in RBEC1. These results demonstrated that Al citrate is taken up into RBEC1 via system Xc-, and that this system might play an important role in Al citrate transport at the BBB.

Oxidative damage following chronic aluminium exposure in adult and pup rat brains

Aluminium is known to cause neurotoxic effects. In the past few years there has been an upsurge of interest in aluminium exposure through diet and environment, which might impair the development of mammals. The present in vivo study was designed to investigate the potential of aluminium to participate in either antioxidant or pro-oxidant processes in both developed and developing rat brain. Markers of oxidative stress were determined in rat brains exposed to AlCl3 (100 mg/kg body weight) for 8 weeks. The aluminium dose was given to adult rats for 8 weeks and in another group, exposure of aluminium for 60 days was done postnatally, 21 days to the feeding mother (lactation period) and 39 days to the rat pups. The results showed a statistically significant (p<or=0.01) increase in lipid peroxidation (LPx) as measured by production of malondialdehyde in both cerebrum and cerebellum of pup brains. A significant increase (p<or=0.001) in LPx was also observed in the adult group. Furthermore, aluminium exposure resulted in a significant decrease in superoxide dismutase and catalase activity in both regions of the brain of developing and developed rat brain. Thus the results of the present study suggest that in rats, aluminium (100 mg/kg body weight) has a pro-oxidant effect and thus acts as a neurotoxin.

Speciation of aluminum in drink samples by 8-hydroxyquinoline loaded silylanization silica gel microcolumn separation with off-line ICP-MS detection

A technique using a flow injection microcolumn separation coupled with ICP-MS detection has been developed for the speciation of Al in drink samples. The retention behaviors of different Al species were studied with 8-hydroxyquinoline (8-HQ) loaded silylanization silica gel as the packing material and inorganic acid (HNO3) as the elution. The results indicated that in a pH range of 5.0 to 8.0, all labile monomeric Al species were retained on the microcolumn while nonlabile monomeric Al species were directly passed through the column. Various Al species after separation were detected by ICP-MS. The detection limit of 0.2 ng mL(-1) and a relative standard deviation (RSD) of 4.2% at 10 ng mL(-1) (n = 11) were achieved, and the recoveries for the spiked samples were 95-108%. The proposed method has been applied to the analysis of Al species in tea infusions, coffee, and tap waters with satisfactory results. The results obtained by this method were compared with that obtained by the cation exchange microcolumn separation and ICP-MS detection system, and some valuable conclusions were drawn.

Molecular shuttle chelation: the use of ascorbate, desferrioxamine and Feralex-G in combination to remove nuclear bound aluminum

1. Abundant data suggest that aluminum (Al(III)) exposure may be an environmental risk factor contributing to the development, progression and/or neuropathology of several human neurodegenerative disorders, including Alzheimer's disease (AD). 2. Nuclei appear to be one directed target for Al(III) binding, accumulation, and Al(III)-mediated dysfunction due in part to their high content of polyphosphorylated nucleic acids, nucleotides, and nucleoproteins. 3. The design of chelation therapies dealing with the removal of Al(III) from these genetic compartments therefore represents an attractive strategy to alleviate the development and/or progression of central nervous system dysfunction that may arise from excessive Al(III) exposure. 4. In this study we have investigated the potential application of 10 natural and synthetic Al(III) chelators, including ascorbate (AS), desferrioxamine (DF), and Feralex-G (FG), used either alone or in combination, to remove Al(III) preincubated with intact human brain cell nuclei. 5. Although nuclear bound Al(III) was found to be highly refractory to removal, the combination of AS+FG was found to be particularly effective in removing Al(III) from the nuclear matrix. 6. Our data suggest that chelators carrying cis-hydroxy ketone groups, such as FG, are particularly suited to the removal of Al(III) from complex biological systems. 7. We further suggest a mechanism whereby small chelating molecules may penetrate the nucleus, bind Al(III), diffuse to regions accessible by the larger DF or FG molecules and transfer their Al(III) to DF or FG. 8. The proposed mechanism, called molecular shuttle chelation may provide a useful pharmacotherapy in the potential treatment of Al(III) overload disease.

Effect of long-term aluminum feeding on lipid/phospholipid profiles of rat brain myelin

Effect of long-term (90–100 days) exposure of rats to soluble salt of aluminum (AlCl₃) on myelin lipid profile was examined. The long-term exposure to AlCl₃ resulted in a 60 % decrease in the total phospholipid (TPL) content while the cholesterol (CHL) content increased by 55 %. Consequently the TPL / CHL molar ratio decreased significantly by 62 %. The phospholipid composition of the myelin membrane changed drastically; the proportion of practically all the phospholipid classes decreased by 32 to 60 % except for phosphatidylcholine (PC) and phosphatidylethanolamine (PE). Of the latter two, proportion of PC was unchanged while PE increased in proportion by 47 %. Quantitatively, all phospholipid classes decreased by from 42 to 76% with no change in the PE content. However the membrane fluidity was not altered in Al-treated rats. Many of the changes we observe here show striking similarities with the reported phospholipid profiles of Alzheimer brains.

The pro-oxidant activity of aluminum

Aluminum, a non-redox-active metal is, nevertheless, a pro-oxidant both in in vitro preparations and in vivo. It facilitates both superoxide- and iron-driven biological oxidation by mechanisms that remain to be resolved. More than 10 years ago Fridovich and colleagues suggested that the facilitation of superoxide-driven biological oxidation by aluminum was due to an interaction between the metal and the superoxide radical anion (Free Radic. Biol. Med. 13: 79-81; 1992). This thesis has been examined herein and it is concluded that much, if not all, of the pro-oxidant activity of aluminum might be explained by the formation of an aluminum superoxide semireduced radical ion.

The role of metals in neurodegenerative processes: aluminum, manganese, and zinc

Until the last decade, little attention was given by the neuroscience community to the neurometabolism of metals. However, the neurobiology of heavy metals is now receiving growing interest, since it has been linked to major neurodegenerative diseases. In the present review some metals that could possibly be involved in neurodegeneration are discussed. Two of them, manganese and zinc, are essential metals while aluminum is non-essential. Aluminum has long been known as a neurotoxic agent. It is an etiopathogenic factor in diseases related to long-term dialysis treatment, and it has been controversially invoked as an aggravating factor or cofactor in Alzheimer's disease as well as in other neurodegenerative diseases. Manganese exposure can play an important role in causing Parkinsonian disturbances, possibly enhancing physiological aging of the brain in conjunction with genetic predisposition. An increased environmental burden of manganese may have deleterious effects on more sensitive subgroups of the population, with sub-threshold neurodegeneration in the basal ganglia, generating a pre-Parkinsonian condition. In the case of zinc, there has as yet been no evidence that it is involved in the etiology of neurodegenerative diseases in humans. Zinc is redox-inactive and, as a result of efficient homeostatic control, does not accumulate in excess. However, adverse symptoms in humans are observed on inhalation of zinc fumes, or accidental ingestion of unusually large amounts of zinc. Also, high concentrations of zinc have been found to kill bacteria, viruses, and cultured cells. Some of the possible mechanisms for cell death are reviewed.

Study of aluminium concentration and speciation of surface water in four catchments in the Limousin region (France)

This study highlights the contamination of the upstream catchment of several rivers (Vienne, Gartempe, Vézère) in the Limousin (France) by aluminium in the absence of atmospheric pollution. The presence of acid soils on a granitic platform is a natural factor which contributes to the presence of protons and aluminium in water. In the Limousin, it seems that the presence of aluminium in surface water is due to a combination of natural factors: poor acid soils, numerous wet moors and peat bogs. It is currently difficult to evaluate the real impact of intensive cultivation of coniferous trees on the aluminium concentrations found in water in this area. In water, the concentration in total aluminium increases with a decrease in pH and an increase in organic matter. Despite, high concentrations of total aluminium at low pH (close to or lower than 6), the monomeric toxic forms of aluminium, computed with a speciation software, are always inferior to the toxic values for fish. Under such conditions, the concentration in aluminium recorded in some upstream catchments of the Limousin rivers may not cause damage to aquatic life.

Aluminum accumulation and membrane fluidity alteration in synaptosomes isolated from rat brain cortex following aluminum ingestion: effect of cholesterol

In the present work, we studied the effect of cholesterol/phospholipid (CH/PL) molar ratio on aluminum accumulation and aluminum-induced alteration of membrane fluidity in rat brain cortex synaptosomes. We observed that sub-acute (daily supply of 1.00 g of AlCl(3) during 10 days) and chronic (daily supply of 0.03 g of AlCl(3) during 4 months) exposure to dietary aluminum leads to a synaptosomal aluminum enrichment of 45 and 59%, respectively. During chronic exposure to AlCl(3), the enhancement of aluminum content was prevented by administration of colestipol (0.31 g/day), which decreased the synaptosomal membrane CH/PL molar ratio (nmol/nmol) from 1.2 to 0.4. Fluorescence anisotropy analysis, using 1,6-diphenyl-1,3,5-hexatriene (DPH) and 1-(4-(trimethylamino)phenyl)-6-phenylhexa-1,3,5-triene (TMA-DPH), showed that after treatment with colestipol a decrease in membrane order occurs at the level of hydrophilic lipid-water surface and deeper hydrophobic region of the synaptosomal membrane. When the rats were exposed to aluminum, it was observed a significant enhancement of membrane fluidity, which was more pronounced at the level of the membrane hydrophilic regions. Meanwhile, when chronic exposure to dietary AlCl(3) was accompanied by treatment with colestipol, the aluminum-induced decrease in membrane order was negligible when compared to TMA-DPH and DPH anisotropy values measured upon colestipol treatment. In contrast, in vitro incubation of synaptosomes (isolated from control rats) with AlCl(3) induced a concentration-dependent rigidification of this more hydrophilic membrane region. The opposite action of aluminum on synaptosomal membrane fluidity, during in vivo and in vitro experiments, appears to be explained by alteration of synaptosomal CH/PL molar ratio, since a significant reduction (approximately 80%) of this parameter occurs during in vivo exposure to aluminum. In conclusion, during in vivo exposure to aluminum, fluidification of hydrophilic regions and reduction of CH/PL molar ratio of presynaptic membranes accompany the accumulation of this cation, which appear to restrict aluminum retention in brain cortex nerve terminals.