Development of a new biosensor for superoxide radicals

Novel Spectroscopic and Electrochemical Sensors and Nanoprobes for the Characterization of Food and Biological Antioxidants

Since an unbalanced excess of reactive oxygen/nitrogen species (ROS/RNS) causes various diseases, determination of antioxidants that can counter oxidative stress is important in food and biological analyses. Optical/electrochemical nanosensors have attracted attention in antioxidant activity (AOA) assessment because of their increased sensitivity and selectivity. Optical sensors offer advantages such as low cost, flexibility, remote control, speed, miniaturization and on-site/in situ analysis. Electrochemical sensors using noble metal nanoparticles on modified electrodes better catalyze bioelectrochemical reactions. We summarize the design principles of colorimetric sensors and nanoprobes for food antioxidants (including electron-transfer based and ROS/RNS scavenging assays) and important milestones contributed by our laboratory. We present novel sensors and nanoprobes together with their mechanisms and analytical performances. Our colorimetric sensors for AOA measurement made use of cupric-neocuproine and ferric-phenanthroline complexes immobilized on a Nafion membrane. We recently designed an optical oxidant/antioxidant sensor using N,N-dimethyl-p-phenylene diamine (DMPD) as probe, from which ROS produced colored DMPD-quinone cationic radicals electrostatically retained on a Nafion membrane. The attenuation of initial color by antioxidants enabled indirect AOA estimation. The surface plasmon resonance absorption of silver nanoparticles as a result of enlargement of citrate-reduced seed particles by antioxidant addition enabled a linear response of AOA. We determined biothiols with Ellman reagent-derivatized gold nanoparticles.

Carboxymethylcellulose-gelatin-superoxidase dismutase electrode for amperometric superoxide radical sensing

A novel, highly sensitive superoxide dismutase biosensor for the direct and simultaneous determination of superoxide radicals was developed by immobilization of superoxide dismutase within carboxymethylcellulose-gelatin on a Pt electrode surface. The parameters affecting the performance of the biosensor were investigated. The response of the CMC-G-SOD biosensor was proportional to O (2) (·-) concentration and the detection limit was 1.25 × 10(-3) mM with a correlation coefficient of 0.9994. The developed biosensor exhibited high analytical performance with wider linear range, high sensitivity and low response time. The biosensor retained 89.8% of its sensitivity after use for 80 days. The support system enhanced the immobilization of superoxide dismutase and promoted the electron transfer of superoxide dismutase minimizing its fouling effect. The biosensor was quite effective not only in detecting O (2) (·-) , but also in determining the antioxidant properties of acetylsalicylic acid-based drugs and the anti-radical activity of healthy and cancerous human brain tissues.

Determination of the antioxidants' ability to scavenge free radicals using biosensors

Free radicals are highly reactive molecules generated during cellular metabolism. However, their overproduction results in oxidative stress, a deleterious process that can damage cell structures, including lipids and membranes, proteins and DNA. Antioxidants respond to this problem, scavenging free radicals. This chapter critically reviews the electrochemical biosensors developed for the evaluation of the antioxidant capacity of specific compounds. Due to the ability of these devices to perform simple, fast and reliable analysis, they are promising biotools for the assessment ofantioxidant properties.

Rapid and sensitive gradient liquid chromatography method for the quantitation of ion from neutrophils

We developed an improved reversed-phase high-performance liquid chromatography (RPLC) assay for the rapid separation and determination of the 2-hydroxyethidium ion. The 2-hydroxyethidium ion is the specific product of the redox reaction between hydroethidine with superoxide radical. High resolution between the chromatographic bands corresponding to ethidium and 2-hydroxyethidium ions was achieved within a practicable analysis time. The RPLC-fluorescence method can reliably detect 2-hydroxyethidium ion concentrations down to 0.12 µM (or 1.2 pmol) and the signal is linear with concentration beyond 50 µM. An application of the method to neutrophil samples demonstrated that intracellular quantification of 2-hydroxyethidium was reproducible, as evidenced by low values of the relative standard deviations: 0.016 for non-stimulated cells, and 0.056 and 0.0125 for neutrophils incubated with agonists phorbol myristate acetate (PMA) and N-formyl-methionyl-leucyl-phenylalanine (fMLP), respectively. The resulting analytical method combines a rapid separation of the relevant peaks with the degree of sensitivity required for use in routine biological analyses.

Cloning, expression, and characterization of thermotolerant manganese superoxide dismutase from Bacillus sp. MHS47

A superoxide dismutase gene from thermotolerant Bacillus sp. MHS47 (MnSOD47) was cloned, sequenced, and expressed. The gene has an open reading frame of 612 bp, corresponding to 203 deduced amino acids, with high homology to the amino acid sequences of B. thuringiensis (accession no. EEN01322), B. anthracis (accession no. NP_846724), B. cereus (accession no. ZP_04187911), B. weihenstephanensis (accession no. YP_001646918), and B. pseudomycoides. The conserved manganese-binding sites (H28, H83, D165, and H169) show that MnSOD47 has the specific characteristics of the manganese superoxide dismutase (MnSOD) enzymes. MnSOD47 expressed an enzyme with a molecular weight of approximately 22.65 kDa and a specific activity of 3537.75 U/mg. The enzyme is active in the pH range 7–8.5, with an optimum pH of 7.5, and at temperatures in the range 30–45 °C, with an optimum temperature of 37 °C. Tests of inhibitors and metal ions indicated that the enzyme activity is inhibited by sodium azide, but not by hydrogen peroxide or potassium cyanide. These data should benefit future studies of MnSODs in other microorganisms and the biotechnological production of MnSOD47, and could also be used to develop a biosensor for the detection of antioxidants and free radical activity. In the future, this basic knowledge could be applicable to the detection of cancer risks in humans and therapeutic treatments.

Electrochemical biosensors in pharmaceutical analysis

Given the increasing demand for practical and low-cost analytical techniques, biosensors have attracted attention for use in the quality analysis of drugs, medicines, and other analytes of interest in the pharmaceutical area. Biosensors allow quantification not only of the active component in pharmaceutical formulations, but also the analysis of degradation products and metabolites in biological fluids. Thus, this article presents a brief review of biosensor use in pharmaceutical analysis, focusing on enzymatic electrochemical sensors.

Effects of the pig renal epithelial cell line LLC-PK1 and its conditioned medium on the phenotype of porcine microglia in vitro

Microglia are dispersed throughout the central nervous system. Under physiological circumstances they display a 'ramified' resting phenotype. In different neuropathologies microglia reversibly transform into the activated form, an amoeboid phagocyte with a broad spectrum of immune effector functions. In this study, a coculture of porcine microglia and the pig renal epithelial cell line LLC-PK1 was used to investigate microglial cell biology. The morphology of the cocultures was elucidated as well as the functionality of the microglia cells by proliferation, superoxide and phagocytosis assays. Our results demonstrate that direct intercellular contact between the two cell types was necessary for microglia to acquire a ramified morphology. Moreover, the conditioned medium of the renal cells promoted proliferation of microglia, inhibited giant cell formation and stimulated microglia to retain their capability to generate superoxide and to perform phagocytosis. In conclusion, we have constructed a cell culture system showing differentiation of microglia in vitro and keeping them in optimal conditions.