Anodic stripping voltammetry of arsenic determination with edible mushroom-nafion-modified glassy carbon electrode.

An edible Mushroom-Nafion modified glassy carbon electrode (M2N5-GCE) was prepared using a homogeneous mixture varying the concentrations of these, in addition to the origin of the mushroom (Shiitake, Lentinula edodes, M1 and Abrantes, Agariscus bisporus, M2) and applied to the As(III) determination by anodic stripping voltammetry. After choosing the optimal conditions in the preparation of the electrode, the second stage was to study the effects of various parameters such as supporting electrolyte, pH, accumulation potential, and time (Eacc, tacc). The optimum experimental conditions chosen were Britton Robinson buffer 0.01 mol L-1 pH:4.6; Eacc: -1.0 and tacc: 60 s obtaining a signal of oxidation of As(0) to As(III) about 0.08 V. Peak current was proportional to arsenic concentration over the 19.6-117.6 µg L-1 range, with a 3σ detection limit of 13.4 µg L-1. The method was validated using As(III) spiked tap water from the laboratory with satisfactory results (RE:3.0 %). Finally, the method was applied to the determination of As(III) in water samples from the Loa River (Northern Chile) in the presence of As(V) in a concentration >20 times higher (RE: 2.3 %).

The effect of aged microglia on synaptic impairment and its relevance in neurodegenerative diseases.

Microglia serve key functions in the central nervous system (CNS), participating in the establishment and regulation of synapses and the neuronal network, and regulating activity-dependent plastic changes. As the neuroimmune system, they respond to endogenous and exogenous signals to protect the CNS. In aging, one of the main changes is the establishment of inflamm-aging, a mild chronic inflammation that reduces microglial response to stressors. Neuroinflammation depends mainly on the increased activation of microglia. Microglia over-activation may result in a reduced capacity for performing normal functions related to migration, clearance, and the adoption of an anti-inflammatory state, contributing to an increased susceptibility for neurodegeneration. Oxidative stress contributes both to aging and to the progression of neurodegenerative diseases. Increased production of reactive oxygen species (ROS) and neuroinflammation associated with age- and disease-dependent mechanisms affect synaptic activity and neurotransmission, leading to cognitive dysfunction. Astrocytes prevent microglial cell cytotoxicity by mechanisms mediated by transforming growth factor ß1 (TGFß1). However, TGFß1-Smad3 pathway is impaired in aging, and the age-related impairment of TGFß signaling can reduce protective activation while facilitating cytotoxic activation of microglia. A critical analysis on the effect of aging microglia on neuronal function is relevant for the understanding of age-related changes on neuronal function. Here, we present evidence in the context of the "microglial dysregulation hypothesis", which leads to the reduction of the protective functions and increased cytotoxicity of microglia, to discuss the mechanisms involved in neurodegenerative changes and Alzheimer's disease.

A electrochemical biosensor for As(III) detection based on the catalytic activity of Alcaligenes faecalis immobilized on a gold nanoparticle-modified screen-printed carbon electrode.

A electrochemical biosensor for As(III) determination has been developed by immobilization of the Alcaligenis faecalis bacteria on gold nanoparticle-modified screen-printed carbon electrode (AuNPs-SPCE). The detection of As(III) is due to the catalytic activity of arsenite oxidase enzyme which oxidizes As(III) to As(V) producing an analytical signal. To enhance the performance of the biosensor, was optimized the amount of bacteria, amount of glutaraldehyde and incubation time applied in the preparation of the electrode, in addition to the effect of pH and applied potential. The analytical application was carried out applying 300 mV (pH = 7) obtaining a LOD of 6.61 µmol L-1 (R = 0.9975) and 700 mV (pH = 12) obtaining a LOD of 1.84 µmol L-1 (R = 0.9983). AF/AuNPs-SPCE was applied to the determination of total arsenic in Loa river water samples after reduction, with satisfactory results.

TGFß1-Smad3 signaling mediates the formation of a stable serine racemase dimer in microglia.

d-serine is synthesized by serine racemase (SR), a fold type II class of pyridoxal-5'-phosphate (PLP)-dependent enzyme. Whereas X-ray crystallography reveals that SR can be monomeric, reversible dimers having the highest racemase activity, or stable SR dimers resistant to both denaturation and reductive treatment, showing reduced racemase activity have been detected in microglia and astrocytes; the latter especially in oxidative or inflammatory environments. The microglial inflammatory environment depends largely on the TGFß1-mediated regulation of inflammatory cytokines such as TNFα and IL1ß. Here we evaluated the participation of TGFß1 in the regulation of SR, and whether that regulation is associated with the induction of stable SR dimers in the microglia from adult mice. In contrast to the effect of lipopolysaccharide (LPS), TGFß1 increased the formation of stable SR dimers and reduced the detection of monomers in microglia in culture. LPS or TGFß1 did not change the amount of total SR. The increase of stable SR dimer was abolished when TGFß1 treatment was done in the presence of the Smad inhibitor SIS3, showing that Smad3 has a role in the induction of stable dimers. Treatment with TGFß1 + SIS3 also reduced total SR, indicating that the canonical TGFß1 pathway participates in the regulation of the synthesis or degradation of SR. In addition, the decrease of IL1ß, but not the decrease of TNFα induced by TGFß1, was mediated by Smad3. Our results reveal a mechanism for the regulation of d-serine through the induction of stable SR dimers mediated by TGFß1-Smad3 signaling in microglia.

A new strategy for the modification of a carbon paste electrode with carrageenan hydrogel for a sensitive and selective determination of arsenic in natural waters.

An adsorptive stripping voltammetric method for the determination of As(III) and Astotal in water samples using a carrageenan modified carbon paste electrode is presented for the first time (CAR-CPE). The modified electrode was prepared in different ways: by adding CAR in solid form or as a hydrogel together with graphite and paraffin, as well as adsorbing CAR by applying a potential on an unmodified carbon paste electrode. The best results were obtained when CAR was incorporated as hydrogel (HCAR-CPE). The selection of the ratio amounts for electrode preparation was carried out applying a multivariate experimental design. Variables like amount of graphite (U1), HCAR (U2) and paraffin (U3) were optimized using a (2K+2K+C) model. The results showed that the amount of HCAR was the most significant factor, and the adequate U1:U2:U3 ratio to prepare the electrode was: 493 mg of graphite, 214 µL of paraffin and 134 µL of carrageenan as gel. The optimum parameters for the determination of As(III) were pH = 3.25 (0.01 mol L-1 H3PO4/H2PO4- solution); Eacc = -0.50 V and tacc = 30 s. The electrode presents good linear behavior concentration range from 0.50 to 6.70 µg L-1, with a limit of detection of 0.22 µg L-1. The relative standard deviation was 5.0% at the 1.5 µg L-1 As(III) level (n = 16). The method was validated by quantifying As(III) in spiked tap water from laboratory (RE: 3.0%), and it was applied for the determination of Astotal in water samples from the Loa River (North of Chile) prior reduction of As(V) with Na2S2O3 solution, obtaining 814.00 ±â€¯0.03 µg L-1. The results of the proposed method were compared with those obtained by adsorptive stripping voltammetry with HMDE and by Inductively Coupled Plasma Mass Spectrometry (ICP-MS) techniques.