Improved fluorimetric determination of dissolved aluminium by micelle-enhanced lumogallion complex in natural waters

Self-plasticized, lumogallion-based fluorescent optical sensor for the determination of aluminium (III) with ultra-low detection limits

Aluminium-selective ion optical sensor based on covalently attached lumogallion methacrylate was synthesized and investigated in this study. Lumogallion based derivatives were copolymerized with various methacrylate monomers via a simple one step free radical polymerization to produce a "self-plasticized" copolymer. We demonstrate that covalently attached lumogallion moieties provide adequate functionality to the optical film thus achieving a very simple, one component sensing membrane. Fluorescence experiments demonstrated excellent sensitivity towards aluminium (III) ions with the detection limits found at 4.8 × 10^-12 M. Furthermore, proposed sensor displays high selectivity towards aluminium over a number of biologically relevant cations. Moreover, the synthesized copolymer was used for the fabrication of nanoparticles that exhibit strong fluorescence upon contact with aluminium (III) ions. It is anticipated that lumogallion-based copolymers may form the basis for the development of highly sensitive and robust aluminium selective sensors capable of in situ measurements.

Aluminum and Neurofibrillary Tangle Co-Localization in Familial Alzheimer's Disease and Related Neurological Disorders

BACKGROUND

Protein misfolding disorders are frequently implicated in neurodegenerative conditions. Familial Alzheimer's disease (fAD) is an early-onset and aggressive form of Alzheimer's disease (AD), driven through autosomal dominant mutations in genes encoding the amyloid precursor protein and presenilins 1 and 2. The incidence of epilepsy is higher in AD patients with shared neuropathological hallmarks in both disease states, including the formation of neurofibrillary tangles. Similarly, in Parkinson's disease, dementia onset is known to follow neurofibrillary tangle deposition.

OBJECTIVE

Human exposure to aluminum has been linked to the etiology of neurodegenerative conditions and recent studies have demonstrated a high level of co-localization between amyloid-β and aluminum in fAD. In contrast, in a donor exposed to high levels of aluminum later developing late-onset epilepsy, aluminum and neurofibrillary tangles were found to deposit independently. Herein, we sought to identify aluminum and neurofibrillary tangles in fAD, Parkinson's disease, and epilepsy donors.

METHODS

Aluminum-specific fluorescence microscopy was used to identify aluminum in neurofibrillary tangles in human brain tissue.

RESULTS

We observed aluminum and neurofibrillary-like tangles in identical cells in all respective disease states. Co-deposition varied across brain regions, with aluminum and neurofibrillary tangles depositing in different cellular locations of the same cell.

CONCLUSION

Neurofibrillary tangle deposition closely follows cognitive-decline, and in epilepsy, tau phosphorylation associates with increased mossy fiber sprouting and seizure onset. Therefore, the presence of aluminum in these cells may exacerbate the accumulation and misfolding of amyloidogenic proteins including hyperphosphorylated tau in fAD, epilepsy, and Parkinson's disease.

The interaction of aluminium-based adjuvants with THP-1 macrophages in vitro: Implications for cellular survival and systemic translocation

Within clinical vaccinations, recombinant antigens are routinely entrapped inside or adsorbed onto the surface of aluminium salts in order to increase their immunological potency in vivo. The efficacy of these immunisations is highly dependent upon the recognition and uptake of these complexes by professional phagocytes and their subsequent delivery to the draining lymph nodes for further immunological processing. While monocytes have been shown to internalise aluminium adjuvants and their adsorbates, the role of macrophages in this respect has not been fully established. Furthermore, this study explored the interaction of THP-1 macrophages with aluminium-based adjuvants (ABAs) and how this relationship influenced the survival of such cells in vitro. THP-1 macrophages were exposed to low concentrations of ABAs (1.7 μg/mL Al) for a maximum of seven days. ABA uptake was determined using lumogallion staining and cell viability by both DAPI (4',6-diamidino-2-phenylindole) staining and LDH (lactate dehydrogenase) assay. Evidence of ABA particle loading was identified within cells at early junctures following treatment and appeared to be quite prolific (>90% cells positive for Al signal after 24 h). Total sample viability (% LDH release) in treated samples was predominantly similar to untreated cells and low levels of cellular death were consistently observed in populations positive for Al uptake. It can thus be concluded that aluminium salts can persist for some time within the intracellular environment of these cells without adversely affecting their viability. These results imply that macrophages may play a role in the systemic translocation of ABAs once administered in the form of an inoculation.

Unequivocal imaging of aluminium in human cells and tissues by an improved method using morin

Aluminium is biologically reactive and its ability to potentiate the immune response has driven its inclusion in both veterinary and human vaccines. Consequently, the need for unequivocal visualisation of aluminium in vivo has created a focused research effort to establish fluorescent molecular probes for this purpose. The most commonly used direct fluorescent labels for the detection of aluminium are morin (2',3,4',5,7-pentahydroxyflavone) and lumogallion [4-chloro-3-(2,4-dihydroxyphenylazo)-2-hydroxybenzene-1-sulphonic acid]. While the former has gained popularity in the detection of aluminium in plants and predominantly within root tips, the latter boasts greater sensitivity and selectivity for the detection of aluminium in human cells and tissues. Herein, we have developed a simplified morin staining protocol using the autofluorescence quenching agent, Sudan Black B. This modified protocol improves tissue morphology and increases analytical sensitivity, which allows intracellular aluminium to be detected in monocytes and when co-localised with senile plaques in human brain tissue of donors diagnosed with familial Alzheimer's disease. Overall, our results demonstrate a simple approach to minimise false positives in the use of morin to unequivocally detect aluminium in vivo.

Unraveling the enigma: elucidating the relationship between the physicochemical properties of aluminium-based adjuvants and their immunological mechanisms of action

Aluminium salts are by far the most commonly used adjuvants in vaccines. There are only two aluminium salts which are used in clinically-approved vaccines, Alhydrogel® and AdjuPhos®, while the novel aluminium adjuvant used in Gardasil® is a sulphated version of the latter. We have investigated the physicochemical properties of these two aluminium adjuvants and specifically in milieus approximating to both vaccine vehicles and the composition of injection sites. Additionally we have used a monocytic cell line to establish the relationship between their physicochemical properties and their internalisation and cytotoxicity. We emphasise that aluminium adjuvants used in clinically approved vaccines are chemically and biologically dissimilar with concomitantly potentially distinct roles in vaccine-related adverse events.

A coumarin based Schiff base probe for selective fluorescence detection of Al3+ and its application in live cell imaging

A new coumarin based Schiff base compound, CSB-1 has been synthesized to detect metal ion based on the chelation enhanced fluorescence (CHEF). The cation binding properties of CSB-1 was thoroughly examined in UV-vis and fluorescence spectroscopy. In fluorescence spectroscopy the compound showed high selectivity toward Al³⁺ ion and the Al³⁺ can be quantified in mixed aqueous buffer solution (MeOH: 0.01M HEPES Buffer; 9:1; v/v) at pH7.4 as well as in BSA media. The fluorescence intensity of CSB-1 was enhanced by ~24 fold after addition of only five equivalents of Al³⁺. The fluorescence titration of CSB-1 with Al³⁺ in mixed aqueous buffer afforded a binding constant, K_a=(1.06±0.2)×10⁴M^-1. The colour change from light yellow to colourless and the appearance of blue fluorescence, which can be observed by the naked eye, provides a real-time method for Al³⁺ sensing. Further the live cell imaging study indicated that the detection of intracellular Al³⁺ ions are also readily possible in living cell.

Naphthol-based fluorescent sensors for aluminium ion and application to bioimaging

Three naphthol Schiff base-type fluorescent sensors, 1,3-Bis(2-hydroxy-1-naphthylideneamino)propane (L1), 1,3-Bis(1-naphthylideneamino)-2-hydroxypropane (L2) and 1,3-Bis(2-hydroxy-1-naphthylideneamino)-2-hydroxypropane (L3), have been synthesized. Their recognition abilities for Al(3+) are studied by fluorescence spectra. Coordination with Al(3+) inhibited the CN isomerization of Schiff base which intensely increase the fluorescence of L1-L3. Possessing a suitable space coordination structure, L3 is a best selective probe for Al(3+) over other metal ions in MeOH-HEPES buffer (3/7, V/V, pH=6.6, 25°C, λem=435nm). A turn-on ratio over 140-fold is triggered with the addition of 1.0 equiv. Al(3+) to L3. The binding constant Ka of L3-Al(3+) is found to be 1.01×10(6.5)M(-1) in a 1:1 complex mode. The detection limit for Al(3+) is 0.05μM. Theoretical calculations have also been included in support of the configuration of the L3-Al(3+) complex. Importantly, the probe L3 has been successfully used for fluorescence imaging in colon cancer SW480 cells.

A single probe to sense Al(III) colorimetrically and Cd(II) by turn-on fluorescence in physiological conditions and live cells, corroborated by X-ray crystallographic and theoretical studies

A pyridine-2-carbohydrazide functionalized conjugated fluorophoric Schiff base ligand (L₁) specifically senses Al(3+) and Cd(2+) ions through significant changes in its absorption and emission spectral behavior, respectively, in physiological conditions. The spectral changes are in the visible region of the spectrum and thus facilitate naked eye detection. Apart from the visible changes, an in-field device application was demonstrated by sensing these ions in paper strips coated with L₁. The crystal structure of the L₁-Cd complex provided additional insight of the metal coordination attributes of L₁. Interestingly, fluorescence microscopic studies demonstrated that the ligand L₁ could also be used as an effective probe in imaging experiments for the detection of intracellular Cd(2+) ions in HeLa cells, without any toxicity to these model human cells.

A polynuclear hetero atom containing molecular organic scaffold to detect Al3+ ion through a fluorescence turn-on response

A simple polynuclear hetero atom (N and O) containing molecular organic scaffold/probe, 3 has been designed and synthesized and explored as a potential chemosensor to detect Al³⁺ (22 nM; ∼0.6 ppb) ion in a HEPES buffer.

Pre-Column Derivatization HPLC Procedure for the Quantitation of Aluminium Chlorohydrate in Antiperspirant Creams Using Quercetin as Chromogenic Reagent

This article describes the development and validation of a selective high-performance liquid chromatography method that allows, after liquid–liquid extraction and pre-column derivatization reaction with quercetin, the quantification of aluminium chlorohydrate in antiperspirant creams. Chromatographic separation was achieved on an XTerra MS C18 analytical column (150 × 3.0 mm i.d., particle size 5 μm) using a mobile phase of acetonitrile:water (15:85, v/v) containing 0.08 % trifluoroacetic acid at a flow rate of 0.30 mL min⁻¹. Ultraviolet spectrophotometric detection at 415 nm was used. The assay was linear over a concentration range of 3.7–30.6 μg mL⁻¹ for aluminium with a limit of quantitation of 3.74 μg mL⁻¹. Quality control samples (4.4, 17.1 and 30.6 μg mL⁻¹) in five replicates from five different runs of analysis demonstrated intra-assay precision (% coefficient of variation <3.8 %), inter-assay precision (% coefficient of variation <5.4 %) and an overall accuracy (% recovery) between 96 and 101 %. The method was used to quantify aluminium in antiperspirant creams containing 11.0, 13.0 and 16.0 % (w/w) aluminium chlorohydrate, respectively.

Unequivocal identification of intracellular aluminium adjuvant in a monocytic THP-1 cell line

Aluminium-based adjuvants (ABA) are the predominant adjuvants used in human vaccinations. While a consensus is yet to be reached on the aetiology of the biological activities of ABA several studies have identified shape, crystallinity and size as critical factors affecting their adjuvanticity. In spite of recent advances, the fate of ABA following their administration remains unclear. Few if any studies have demonstrated the unequivocal presence of intracellular ABA. Herein we demonstrate for the first time the unequivocal identification of ABA within a monocytic T helper 1 (THP-1) cell line, using lumogallion as a fluorescent molecular probe for aluminium. Use of these new methods revealed that particulate ABA was only found in the cell cytoplasm. Transmission electron microscopy revealed that ABA were contained within vesicle-like structures of approximately 0.5-1 μm in diameter.

A novel pyrene-2-(pyridin-2-ylmethylsulfanyl)ethylamine based turn-on dual sensor for Al3+: experimental and computational studies

A pyrene based pyrene-2-(pyridin-2-ylmethylsulfanyl)-ethylamine (PP) is found to exhibit a turn-on chemo- and fluorogenic dual sensing of Al³⁺ through PET blocking and CHEF effect.

A quinazoline derivative as quick-response red-shifted reporter for nanomolar Al3+and applicable to living cell staining

A newly designed and structurally characterized non-cytotoxic quinazoline based ratiometric chemosensor (L) selectively detects Al³⁺ions upto 1.48 nM through ICT and CHEF processes in water–DMSO (9 : 1, v/v) and it is also applicable in living cell staining.

Dual channel selective fluorescence detection of Al(III) and PPi in aqueous media with an 'off-on-off' switch which mimics molecular logic gates (INHIBIT and EXOR gates)

In this study, we have synthesized a simple Schiff base type isophthaloyl salicylaldehyde hydrazone (ISH) moiety which selectively detects Al(III) and PPi with a fluorescence enhancement at two different wavelengths in aqueous solution. The sensing phenomenon is also reversible and thus the sensor beautifully mimics logic gates (INHIBIT and EXOR gates).

Salicylimine-based fluorescent chemosensor for aluminum ions and application to bioimaging

In this study, an assay to quantify the presence of aluminum ions using a salicylimine-based receptor was developed utilizing turn-on fluorescence enhancement. Upon treatment with aluminum ions, the fluorescence of the sensor was enhanced at 510 nm due to formation of a 1:1 complex between the chemosensor and the aluminum ions at room temperature. As the concentration of Al(3+) was increased, the fluorescence gradually increased. Other metal ions, such as Na(+), Ag(+), K(+), Ca(2+), Mg(2+), Hg(2+), Mn(2+), Co(2+), Ni(2+), Cu(2+), Zn(2+), Cd(2+), Pb(2+), Cr(3+), Fe(3+), and In(3+), had no such significant effect on the fluorescence. In addition, we show that the probe could be used to map intracellular Al(3+) distribution in live cells by confocal microscopy.

Pyrimidine based highly sensitive fluorescent receptor for Al3+ showing dual signalling mechanism

A new fluorescent probe (5-[(4-diethylamino-2-hydroxy-benzylidene)-amino]-1H-pyrimidine-2, 4-dione) (Receptor 1) has been synthesized by the Schiff base condensation of 5-aminouracil with 4-(diethylamino)salicylaldehyde. The receptor 1 exhibits high selectively for Al(3+) in DMSO as well as in aqueous solution even in the presence of biologically relevant cations such as Na(+), K(+), Ca(2+), Mg(2+), Pb(2+) and several transition metal ions. The lowest detection limit for the receptor 1 was found to be 1.62 × 10(-10) M with its linear response towards Al(3+) in the concentration range of 1.75 × 10(-9) to 3.3 × 10(-8) M in DMSO. Receptor 1 is the first ever example where a single molecular probe is able to show imine (C=N) isomerization inhibition along with twisted intramolecular charge transfer (TICT) in combinatorial fashion.