Rapid Quantification of Oxidized and Reduced Forms of Glutathione Using Ortho -phthalaldehyde in Cultured Mammalian Cells In Vitro.

Glutathione has long been considered a key biomarker for determining the antioxidant response of the cell. Hence, it is a primary marker for reactive oxygen species studies. The method utilizes Ortho-phthalaldehyde (OPA) to quantify the cellular concentration of glutathione(s). OPA conjugates with reduced glutathione (GSH) via sulfhydryl binding to subsequently form an isoindole, resulting in a highly fluorescent conjugate. To attain an accurate result of both oxidized glutathione (GSSG) and GSH, a combination of masking agents and reducing agents, which have been implemented in this protocol, are required. Treatments may also impact cellular viability. Hence, normalization via protein assay is presented in this multiparametric assay. The assay demonstrates a pseudo-linear detection range of 0.234 - 30µM (R2=0.9932±0.007 (N=12)) specific to GSH. The proposed assay also allows for the determination of oxidized glutathione with the addition of the masking agent N-ethylmaleimide to bind reduced glutathione, and the reducing agent tris(2-carboxyethyl) phosphine is introduced to cleave the disulfide bond in GSSG to produce two molecules of GSH. The assay is used in combination with a validated bicinchoninic acid assay for protein quantification and an adenylate kinase assay for cytotoxicity assessment.

Interference of reversible redox compounds in enzyme catalysed assays - Electrochemical limitations.

BACKGROUND: Several commercial assay kits exist with limited explanation of the kit components and reagent constituents, which greatly increases potential incompatibility issues resulting in the loss of samples, time, and data. Herein we explore such issues via the redox ion [Fe(CN)6]3/4- in two commercial l-lactate and pyruvate assay kits. RESULTS: We clearly demonstrate significant interference from redox compounds with the l-lactate and pyruvate assays; a significance in signal inhibition/mechanism restriction, and false/mechanism exhaustion, respectively. Potential mechanisms are explored to explain interference. CONCLUSION: The need for transparency is crucial for consistency of assay kit performance from lab to lab. There is a need for suppliers to list the components of kits and/or list the potential for interference from specific agents to ensure that results obtained from these kits are reliable and reproducible.

Ubiquinone modified printed carbon electrodes for cell culture pH monitoring.

The measurement of pH is important throughout many biological systems, but there are limited available technologies to enable its periodical monitoring in the complex, small volume, media often used in cell culture experiments across a range of disciplines. Herein, pad printed electrodes are developed and characterised through modification with: a commercially available fullerene multiwall carbon nanotube composite applied in Nafion, casting of hydrophobic ubiquinone as a pH probe to provide the electrochemical signal, and coated in Polyethylene glycol to reduce fouling and potentially enhance biocompatibility, which together are proven to enable the determination of pH in cell culture media containing serum. The ubiquinone oxidation peak position (Epa) provided an indirect marker of pH across the applicable range of pH 6-9 (R2 = 0.9985, n = 15) in complete DMEM. The electrochemical behaviour of these sensors was also proven to be robust; retaining their ability to measure pH in cell culture media supplemented with serum up to 20% (v/v) [encompassing the range commonly employed in cell culture], cycled > 100 times in 10% serum containing media and maintain > 60% functionality after 5 day incubation in a 10% serum containing medium. Overall, this proof of concept research highlights the potential applicability of this, or similar, electrochemical approaches to enable to detection or monitoring of pH in complex cell culture media.