Manipulations of Glutathione Metabolism Modulate IP3-Mediated Store-Operated Ca2+ Entry on Astroglioma Cell Line

The regulation of the redox status involves the activation of intracellular pathways as Nrf2 which provides hormetic adaptations against oxidative stress in response to environmental stimuli. In the brain, Nrf2 activation upregulates the formation of glutathione (GSH) which is the primary antioxidant system mainly produced by astrocytes. Astrocytes have also been shown to be themselves the target of oxidative stress. However, how changes in the redox status itself could impact the intracellular Ca2+ homeostasis in astrocytes is not known, although this could be of great help to understand the neuronal damage caused by oxidative stress. Indeed, intracellular Ca2+ changes in astrocytes are crucial for their regulatory actions on neuronal networks. We have manipulated GSH concentration in astroglioma cells with selective inhibitors and activators of the enzymes involved in the GSH cycle and analyzed how this could modify Ca2+ homeostasis. IP3-mediated store-operated calcium entry (SOCE), obtained after store depletion elicited by Gq-linked purinergic P2Y receptors activation, are either sensitized or desensitized, following GSH depletion or increase, respectively. The desensitization may involve decreased expression of the proteins STIM2, Orai1, and Orai3 which support SOCE mechanism. The sensitization process revealed by exposing cells to oxidative stress likely involves the increase in the activity of Calcium Release-Activated Channels (CRAC) and/or in their membrane expression. In addition, we observe that GSH depletion drastically impacts P2Y receptor-mediated changes in membrane currents, as evidenced by large increases in Ca2+-dependent K+ currents. We conclude that changes in the redox status of astrocytes could dramatically modify Ca2+ responses to Gq-linked GPCR activation in both directions, by impacting store-dependent Ca2+-channels, and thus modify cellular excitability under purinergic stimulation.

Comparative kinetic analysis of ascorbate (Vitamin-C) recycling dehydroascorbate reductases from plant and human.

Ascorbate, a primary antioxidant, gets readily oxidized to dehydroascorbate (DHA). Hence, recycling by dehydroascorbate reductase (DHAR) enzymes is vital for protection from cellular oxidative stress in eukaryotes. However, a detailed kinetic analysis of plant DHARs and their human orthologs; chloride intracellular channels (HsCLICs) is lacking. We demonstrate that DHAR from stress adapted pearl millet Pennisetum glaucum (PgDHAR) shows the highest turnover rate whereas HsCLIC1, 3, and 4 reduce DHA, albeit at lower rates. We further show that the catalytic cysteine is susceptible to varying levels of oxidation, supported by crystal structures and mass-spectrometry analysis. The differences in kinetic parameters among plant and human DHA reductases corroborate with the levels of reactive oxygen species H2O2 encountered in their respective intracellular environment. Our findings may have broader implications in crop improvement using pearl millet DHAR, and anti-cancer therapeutics targeting Vitamin-C recycling capability of human CLICs.

Fucoidan Extracted From Sporophyll of Undaria pinnatifida Grown in Weihai, China – Chemical Composition and Comparison of Antioxidant Activity of Different Molecular Weight Fractions

Fucoidan is a multifunctional marine carbohydrate polymer that differs in its chemical composition and bioactivity both between seaweed species and within species from different locations across the globe. In this study, fucoidan was extracted from the sporophyll of Undaria pinnatifida grown in Weihai, Shandong Province, China. Fucoidan fractions with molecular weight cutoffs (MWCO) of >300 kDa and <10 kDa were obtained via dialysis. The fucoidan standard from Sigma (Fstd, ≥95, CAS: 9072-19-9), fucoidan crude extract (WH), >300 kDa fraction (300k) and <10 kDa fraction (10k) were compared in terms of chemical composition and antioxidant capacity. Based on Fourier transform infrared spectroscopy (FT-IR) analysis, Fstd, WH, and 300k all showed strong bands around 830 cm−1, corresponding to the sulfate substituent in the molecule. The results showed that compared with WH and 300 k, the degree of sulfation at 10k was the lowest. From Nuclear magnetic resonance spectroscopy (NMR) result, the four fucoidan samples all contain α-L-fucose. The primary antioxidant ability of the 10k is significantly higher than that of the 300k, WH, and Fstd, but the secondary antioxidant capabilities of the 10k and 300k were similar, and both were higher than that of the butylated hydroxyanisole (BHA). The ferric reducing antioxidant ability was higher in the 300k and WH fractions. This demonstrates that fucoidan extracted from U. pinnatifida grown in Weihai, China should be a useful nutraceutical resource.

Antioxidant Potential of Novel Designed Phenolic Derivatives: Computational Insights

Density functional theory calculations were applied for designed phenolic antioxidant derivatives. The reaction enthalpies related to various mechanisms of primary antioxidant action were deliberated in detail. How antioxidant activity of designed phenolic compounds has been perturbed by electron donor and withdrawing substituents present at ortho, meta and para positions, allylic conjugation and the dimerization effect were computed.

ON THE THERMODYNAMICS OF ANTIOXIDANT ACTION OF NATURALLY OCCURRING HYDROXYDERIVATIVES OF CIS-CINNAMIC ACID

Antioxidant activity represents one of the important features of phenolic acids, such as hydroxyderivatives of cinnamic acid. However, in the case of cis-cinnamic acid derivatives, corresponding thermochemistry data can be still considered scarce. This work is focused on the two most relevant mechanisms of primary antioxidant action in gas-phase, non-polar benzene and in aqueous solution. Reaction enthalpies describing thermodynamics of Hydrogen Atom Transfer (HAT) and Sequential Proton-Loss – Electron Transfer (SPLET) mechanisms were theoretically investigated using (SMD) M06-2X/6-311++G(d,p) method for cis-ortho-coumaric, cis-meta-coumaric, cis-para-coumaric, cis-ferulic, cis-sinapic and cis-caffeic acid and their carboxylate anions. The effect of carboxyl COOH group deprotonation on the thermodynamics of studied mechanisms was assessed for the three environments.

Effects of Long-Term Supplementation with Aluminum or Selenium on the Activities of Antioxidant Enzymes in Mouse Brain and Liver

The aim of this study was to investigate the effects of aluminum (Al) or selenium (Se) on the “primary” antioxidant defense system enzymes (superoxide dismutase, catalase, and glutathione reductase) in cells of mouse brain and liver after long-term (8-week) exposure to drinking water supplemented with AlCl3 (50 mg or 100 mg Al/L in drinking water) or Na2SeO3 (0.2 mg or 0.4 mg Se/L in drinking water). Results have shown that a high dose of Se increased the activities of superoxide dismutase and catalase in mouse brain and liver. Exposure to a low dose of Se resulted in an increase in catalase activity in mouse brain, but did not show any statistically significant changes in superoxide dismutase activity in both organs. Meanwhile, the administration of both doses of Al caused no changes in activities of these enzymes in mouse brain and liver. The greatest sensitivity to the effect of Al or Se was exhibited by glutathione reductase. Exposure to both doses of Al or Se resulted in statistically significant increase in glutathione reductase activity in both brain and liver. It was concluded that 8-week exposure to Se caused a statistically significant increase in superoxide dismutase, catalase and glutathione reductase activities in mouse brain and/or liver, however, these changes were dependent on the used dose. The exposure to both Al doses caused a statistically significant increase only in glutathione reductase activity of both organs.

Chalcogen effects on the primary antioxidant activity of chrysin and quercetin

The effect of chalcogens on the scavenging power of chrysin and quercetin antioxidants against peroxyl radicals has been investigated in lipid and aqueous solutions, using the density functional theory.

In vitro assessment of time-dependent changes in red cell cytoplasmic antioxidants of donkey blood preserved in citrate phosphate dextrose adenine 1 anticoagulant

Background and Aim: Stored blood is continuously exposed to oxidative stress, which affects its antioxidant protective system. Erythrocytes are naturally armed with antioxidant protective capacity. Blood antioxidant system functions to protect the blood cells against oxidative damage by free radicals. However, during storage, blood is continuously exposed to oxidative stress, which affects its antioxidant system. The aim of this work was to investigate alteration in malondialdehyde (MDA) levels, reduced glutathione (glutathione reductase [GSH-Rd]), catalase (CAT), and superoxide dismutase (SOD) activities in stored donkey blood. Materials and Methods: Blood (250 ml) was drawn from four clinically healthy donkeys into citrate phosphate dextrose adenine 1 blood bags and preserved at 4°C. MDA, GSH-Rd, CAT, and SOD activities were assayed by colorimetric methods, over a period of 42 days. Results: The result showed that SOD enzyme activities significantly (p<0.05) increased by day 7 post-storage (PS) while MDA levels significantly (p<0.05) increased by day 21 PS. However, activities of GSH-Rd and CAT enzymes decreased (p<0.05) by day 21 PS. Pearson's product-moment correlation showed a negative correlation between the levels of MDA and enzymatic antioxidant markers (CAT and GSH-Rd). Conclusion: The findings revealed that GSH-Rd and CAT are the primary antioxidant defense markers in donkey red blood cells. The observed alterations in these principal antioxidants suggest a 14 days optimum keeping time of donkey blood for blood banking purposes.

Peroxiredoxin 6 regulates the phosphoinositide 3-kinase/AKT pathway to maintain human sperm viability

Peroxiredoxins (PRDXs) are antioxidant enzymes proven to control the levels of reactive oxygen species (ROS) and to avoid oxidative damage in the spermatozoon. Previously, we have shown that low amounts of PRDXs are associated with male infertility and that PRDX6 is the primary antioxidant defence in human spermatozoa, maintaining survival and DNA integrity (Gong et al., 2012, Fernandez and O’Flaherty, 2018). Oxidative stress can trigger different pathway cascades in the spermatozoa, including truncated apoptosis. It has been reported that the phosphorylation status of phosphoinositide 3-kinase (PI3K) and its target AKT (protein kinase B) prevent the spermatozoon from entering the truncated apoptotic cascade. Here, we aim to study the regulation of the PI3K/AKT pathway by PRDX6 and assess its role in maintaining sperm viability. Human semen samples were obtained over 1 year from 20 healthy non-smoking volunteers aged 22–30 years old. Sperm viability, lipid peroxidation and apoptosis-like changes were determined by flow cytometry while phosphorylation of PI3K and AKT substrates were assessed by immunoblotting using anti-phospho-PI3K and anti-phospho-AKT substrates antibodies. We found that the addition of arachidonic acid and lysophosphatidic acid, products of PRDX6 calcium independent phospholipase A2 (Ca2+-iPLA2), prevented loss of sperm viability and maintained the phosphorylation of PI3K. Antioxidant compounds such as D-penicillamine partially prevented the oxidative damage on spermatozoa that led to a reduction of their viability. Thus, other pathways can also participate in sperm survival and be regulated by PRDXs. In conclusion, PRDX6 contributes to the regulation of ROS production and the PI3K/AKT pathway for the maintenance of sperm survival.