Oxidative stress, free radicals and protein peroxides

Microwave characterization of low-molecular-weight antioxidant specific biomarkers

Antioxidants play a crucial role in the life sciences, as the regulators of biochemical reactions. We studied the dielectric properties of the low-molecular weight antioxidant specific biomarkers sodium ascorbate and glutathione in solutions of different concentrations. The biomarkers are multifunctional metabolites relevant to the reactive oxygen species (ROS) scavenging system of cells. The newly developed high-Q microwave whispering-gallery-mode (WGM) dielectric resonator based technique was applied. The technique allows investigation of liquids of nanoliter volumes filled in microfluidic channel within several milliseconds. The revealed peculiarities in the dependence of permittivity on concentrations of the sodium ascorbate and glutathione solutions are explained by differences in relaxation times and loses introduced by molecules of different shapes. We suggest that this novel approach offers the potential for the detection and characterization of ROS-relevant biomarkers with millisecond-time resolution.

Activity-guided isolation of phase II enzyme inducers from buckwheat flour methanolic extracts

BACKGROUND

Buckwheat is an important alternative crop and a raw material for functional food formulation. Phase II detoxification proteins/enzymes provide cytoprotective roles against oxidative stress and inflammation originating from various stressors. We aimed to identify and characterize potential phase II enzyme inducers from methanolic extracts of buckwheat flour, using an activity-guided fractionation based on the induction of quinone reductase (QR) (EC 1.6.5.2) in Hepa 1c1c7 cells.

RESULTS

We isolated the QR inducers N-trans-feruloyltyramine (I), syringic acid (II), quercetin (III) and myricetin (IV). The relative QR-inducing ability, as well as the concentration required to double QR specific activity (CD values, in parentheses), decreased in the order: quercetin (3.0 µmol L^-1 ) > N-trans-feruloyltyramine (24 µmol L^-1 ) > myricetin (58 µmol L^-1 ) > syringic acid (5.4 mmol L^-1 ). Quercetin and N-trans-feruloyltyramine exhibited the greatest extent of QR induction of an approximately four-fold maximum induction and these compounds also exhibited the greatest values for the ratio of IC₅₀ (i.e. level to reduce viability by 50%): CD values of 11 and > 8.3, respectively, among the four QR inducers isolated. Isobologram analyses for binary combinations of compounds I-IV revealed primarily antagonistic interactions for QR induction.

CONCLUSION

These findings add to our understanding of the nutraceutical potential of buckwheat as a chemoprophylactic dietary component. © 2018 Society of Chemical Industry.

Photobiomodulation with red light-emitting diodes accelerates hepatocyte proliferation through reactive oxygen species/extracellular signal-regulated kinase pathway

AIM

Cell-based transplantation is an alternate method of liver transplantation to delay the onset of end-stage liver diseases. For successful treatment, cells need to be expended in vitro expeditiously. However, autogenetic hepatocytes as the ideal cell source for therapy remain in quiescence so proliferation is rare. Photobiomodulation therapy has been used to stimulate some kinds of cell proliferation, but is unknown whether red light-emitting diode (LED) irradiation can promote primary hepatocyte proliferation. The aim of this study was to evaluate the effect of red LED irradiation on hepatocytes in vitro.

METHODS

Mouse primary hepatocytes were isolated and received red LED treatment. The cell viability, reactive oxygen species (ROS) levels, phosphorylated extracellular signal-regulated kinase1/2 (pERK1/2) and some cell cycle-related proteins were observed. Additionally, ROS inhibition and pERK1/2 inhibition were carried out to determine the effect of ROS and ERK1/2 in red LED irradiation.

RESULTS

The red LED irradiation increased hepatocyte proliferation, elevated intracellular ROS levels, and stimulated ERK1/2 activation and cell cycle-related gene expression. The mitosis promoting effect of red LED irradiation could be disturbed by ROS or pERK inhibition. The red LED irradiation promoted hepatocyte proliferation through the ROS/pERK1/2 pathway.

CONCLUSIONS

Red LED irradiation could accelerate hepatocyte proliferation through the ROS/pERK1/2 pathway. Red LED irradiation might be a potential method to increase hepatocyte cell numbers in vitro and support cell-based transplantation in clinical work.

Oxidant-specific biomarkers of oxidative stress. Association with atherosclerosis and implication for antioxidant effects

The unregulated oxidative modification of lipids, proteins, and nucleic acids induced by multiple oxidants has been implicated in the pathogenesis of many diseases. Antioxidants with diverse functions exert their roles either directly or indirectly in the physiological defense network to inhibit such deleterious oxidative modification of biological molecules and resulting damage. The efficacy of antioxidants depends on the nature of oxidants. Therefore, it is important to identify the oxidants which are responsible for modification of biological molecules. Some oxidation products produced selectively by specific oxidant enable to identify the responsible oxidants, while other products are produced by several oxidants similarly. In this review article, several oxidant-specific products produced selectively by peroxyl radicals, peroxynitrite, hypochlorous acid, lipoxygenase, and singlet oxygen were summarized and their potential role as biomarker is discussed. It is shown that the levels of specific oxidation products including hydroxylinoleate isomers, nitrated and chlorinated products, and oxysterols produced by the above-mentioned oxidants are elevated in the human atherosclerotic lesions, suggesting that all these oxidants may contribute to the development of atherosclerosis. Further, it was shown that the reactivities of physiological antioxidants toward the above-mentioned oxidants vary extensively, suggesting that multiple antioxidants effective against these different oxidants are required, since no single antioxidant alone can cope with these multiple oxidants.

The Development of a Nano-based Approach to Alleviate Cisplatin-Induced Ototoxicity

Cisplatin-induced hearing loss is experienced by a high percentage of patients with squamous cell carcinoma undergoing cisplatin chemotherapy. A novel nano-construct capable of sequestering extracellular cisplatin was developed to combat this problem. The nano-construct consisted of superparamagnetic iron oxide nanoparticles (SPIONs) entrapped within polymeric micelles, which were formed from a glutathione diethyl ester-conjugated amphiphilic diblock copolymer. The glutathione-micelles were analyzed at the cellular level and in an organotypic study for safety evaluation. All utilized methods indicated that the micelles do not cause cellular toxicity or organ damage. The micelles' ability to reduce cisplatin-induced cytotoxicity was then probed in an in vitro model. Cisplatin was pre-treated with the novel nano-construct before being added to growing cells. When compared to cells that were exposed to untreated cisplatin, cells in the pre-treated cisplatin group showed a significant increase in cell viability. This clearly demonstrates that the construct is able to protect the cells from cisplatin cytotoxicity and makes it highly likely that the novel nano-construct will be able to play a role in the protection of the inner ear from cisplatin-induced ototoxicity.

Reaction rates of glutathione and ascorbate with alkyl radicals are too slow for protection against protein peroxidation in vivo

Reaction kinetics of amino acid and peptide alkyl radicals with GSH and ascorbate, the two most abundant endogenous antioxidants, were investigated by pulse radiolysis. Rate constants in the order of 10⁶ M^-1s^-1 were found. Alkyl radicals react at almost diffusion controlled rates and irreversibly with oxygen to form peroxyl radicals, and competition with this reaction is the benchmark for efficient repair in vivo. We consider repair of protein radicals and assume comparable rate constants for the reactions of GSH/ascorbate with peptide alkyl radicals and with alkyl radicals on a protein surface. Given physiological concentrations of oxygen, GSH and ascorbate, protein peroxyl radicals will always be a major product of protein alkyl radicals in vivo. Therefore, if they are formed by oxidative stress, protein alkyl radicals are a probable cause for biological damage.

Physiological Concentrations of Ascorbate Cannot Prevent the Potentially Damaging Reactions of Protein Radicals in Humans

The principal initial biological targets of free radicals formed under conditions of oxidative stress are the proteins. The most common products of the interaction are carbon-centered alkyl radicals which react rapidly with oxygen to form peroxyl radicals and hydroperoxides. All these species are reactive, capable of propagating the free radical damage to enzymes, nucleic acids, lipids, and endogenous antioxidants, leading finally to the pathologies associated with oxidative stress. The best chance of preventing this chain of damage is in early repair of the protein radicals by antioxidants. Estimate of the effectiveness of the physiologically significant antioxidants requires knowledge of the antioxidant tissue concentrations and rate constants of their reaction with protein radicals. Previous studies by pulse radiolysis have shown that only ascorbate can repair the Trp and Tyr protein radicals before they form peroxyl radicals under physiological concentrations of oxygen. We have now extended this work to other protein C-centered radicals generated by hydroxyl radicals because these and many other free radicals formed under oxidative stress can produce secondary radicals on virtually any amino acid residue. Pulse radiolysis identified two classes of rate constants for reactions of protein radicals with ascorbate, a faster one in the range (9-60) × 10⁷ M^-1 s^-1 and a slow one with a range of (0.5-2) × 10⁷ M^-1 s^-1. These results show that ascorbate can prevent further reactions of protein radicals only in the few human tissues where its concentration exceeds about 2.5 mM.

Neuroprotective potential of astroglia

Astroglia are the homoeostatic cells of the central nervous system, which participate in all essential functions of the brain. Astrocytes support neuronal networks by handling water and ion fluxes, transmitter clearance, provision of antioxidants, and metabolic precursors and growth factors. The critical dependence of neurons on constant support from the astrocytes confers astrocytes with intrinsic neuroprotective properties. On the other hand, loss of astrocytic support or their pathological transformation compromises neuronal functionality and viability. Manipulating neuroprotective functions of astrocytes is thus an important strategy to enhance neuronal survival and improve outcomes in disease states. © 2017 The Authors Journal of Neuroscience Research Published by Wiley Periodicals, Inc.

Cytoprotective Mechanisms Mediated by Polyphenols from Chilean Native Berries against Free Radical-Induced Damage on AGS Cells

The prevalence of cytoprotective mechanisms induced by polyphenols such as activation of intracellular antioxidant responses (ICM) and direct free radical scavenging was investigated in native Chilean species of strawberries, raspberries, and currants. Human gastric epithelial cells were co- and preincubated with polyphenolic-enriched extracts (PEEs) from Chilean raspberries (Rubus geoides), strawberries (Fragaria chiloensis ssp. chiloensis f. chiloensis), and currants (Ribes magellanicum) and challenged with peroxyl and hydroxyl radicals. Cellular protection was determined in terms of cell viability, glyoxalase I and glutathione s-transferases activities, and carboxymethyl lysine (CML) and malondialdehyde levels. Our results indicate that cytoprotection induced by ICM was the prevalent mechanism for Rubus geoides and F. chiloensis. This agreed with increased levels of glyoxalase I and glutathione S-transferase activities in cells preincubated with PEEs. ORAC index indicated that F. chiloensis was the most efficient peroxyl radical scavenger. Moreover, ICM mediated by F. chiloensis was effective in protecting cells from CML accumulation in contrast to the protective effects induced by free radical scavenging. Our results indicate that although both polyphenol-mediated mechanisms can exert protective effects, ICM was the most prevalent in AGS cells. These results suggest a potential use of these native berries as functional food.

Evaluation of globins expression in brain, heart, and lung in rats exposed to side stream cigarette smoke

The side stream cigarette smoke (SSCS) is a contributing factor in the pathogenesis of cigarette smoking-induced toxicity. Hemoglobin (Hb), myoglobin (Mb), neuroglobin (Ngb), and cytoglobin (Cygb) are globins with different distributions and functions in the tissues and have similar actions by providing O₂ (oxygen) for respiratory chain, detoxification of ROS and nitric oxide (NO), and protect tissues against irreversible lesions. We aimed to investigate the effects of SSCS exposure on gene and protein expression of Ngb, Cygb, and Mb in different tissue. The Ngb and Cygb gene and protein expression in the cerebral cortex increased after 1 week of rat exposure to SSCS. In hippocampus, the Ngb gene and protein expression increased after 1 week or more of exposure and no change was observed in Cygb gene and protein expression. In myocardium, Mb and Cygb gene expression increased at 1 and 4 weeks of exposure, while protein expression of both increased at 1, 2, 3, and 4 weeks. In lung, observed an increase in Cygb gene and protein expression after 2, 3, and 4 weeks of exposure. The findings suggest that SSCS modulates Ngb, Cygb, and Mb in central and peripheral tissue © 2016 Wiley Periodicals, Inc. Environ Toxicol 32: 1252-1261, 2017.

Effects of exercise on alterations in redox homeostasis in elite male and female endurance athletes using a clinical point-of-care test

Exercise causes alterations in redox homeostasis (ARH). Measuring ARH in elite athletes may aid in the identification of training tolerance, fatigued states, and underperformance. To the best of our knowledge, no studies have examined ARH in elite male and female distance runners at sea level. The monitoring of ARH in athletes is hindered by a lack of reliable and repeatable in-the-field testing tools and by the rapid turnaround of results. We examined the effects of various exercise intensities on ARH in healthy (non-over-reached) elite male and female endurance athletes using clinical point-of-care (POC) redox tests, referred to as the free oxygen radical test (FORT) (pro-oxidant) and the free oxygen radical defence (FORD) (antioxidant). Elite male and female endurance athletes (n = 22) completed a discontinuous incremental treadmill protocol at submaximal running speeds and a test to exhaustion. Redox measures were analyzed via blood sampling at rest, warm-up, submaximal exercise, exhaustion, and recovery. FORD was elevated above rest after submaximal and maximal exercise, and recovery (p < 0.05, d = 0.87–1.55), with only maximal exercise and recovery increasing FORT (p < 0.05, d = 0.23–0.32). Overall, a decrease in oxidative stress in response to submaximal and maximal exercise was evident (p < 0.05, d = 0.46). There were no gender differences for ARH (p > 0.05). The velocity at lactate threshold (vLT) correlated with the FORD response at rest, maximal exercise, and recovery (p < 0.05). Using the clinical POC redox test, an absence of oxidative stress after exhaustive exercise is evident in the nonfatigued elite endurance athlete. The blood antioxidant response (FORD) to exercise appears to be related to a key marker of aerobic fitness: vLT.

Electrons initiate efficient formation of hydroperoxides from cysteine

Amino acid and protein hydroperoxides can constitute a significant hazard if formed in vivo. It has been suggested that cysteine can form hydroperoxides after intramolecular hydrogen transfer to the commonly produced cysteine sulfur-centered radical. The resultant cysteine-derived carbon-centered radicals can react with oxygen at almost diffusion-controlled rate, forming peroxyl radicals which can oxidize other molecules and be reduced to hydroperoxides in the process. No cysteine hydroperoxides have been found so far. In this study, dilute air-saturated cysteine solutions were exposed to radicals generated by ionizing radiation and the hydroperoxides measured by an iodide assay. Of the three primary radicals present, the hydroxyl, hydrogen atoms and hydrated electrons, the first two were ineffective. However, electrons did initiate the generation of hydroperoxides by removing the -SH group and forming cysteine-derived carbon radicals. Under optimal conditions, 100% of the electrons reacting with cysteine produced the hydroperoxides with a 1:1 stoichiometry. Maximum hydroperoxide yields were at pH 5.5, with fairly rapid decline under more acid or alkaline conditions. The hydroperoxides were stable between pH 3 and 7.5, and decomposed in alkaline solutions. The results suggest that formation of cysteine hydroperoxides initiated by electrons is an unlikely event under physiological conditions.