Comprehensive Investigation of the Antioxidant and Pro-oxidant Effects of Phenolic Compounds: A Double-Edged Sword in the Context of Oxidative Stress?

3-Methyl Thiophene-Modified Boron-Doped Diamond (BDD) Electrodes as Efficient Catalysts for Phenol Detection-A Case Study for the Detection of Gallic Acid in Three Specific Tea Types

Polymer modification has been established as a cost-effective, simple, in situ method for overcoming some of the inherent disadvantages of boron-doped diamond (BDD) electrodes, and its application has been extended to reliable, low-cost environmental monitoring solutions. The present review focuses on modifying BDD electrodes with semi-conductive polymers acting as redox mediators. This article reports on the development of a 3-methyl thiophene-modified boron-doped diamond (BDD/P3MT) sensor for the electrochemical determination of total phenolic compounds (TPCs) in tea samples, using gallic acid (GA) as a marker. GA is a significant polyphenol with various biological activities, making its quantification crucial. Thus, a simple, fast, and sensitive GA sensor was fabricated using the electroanalytical square wave voltammetry (SWV) technique. The sensor utilizes a semi-conductive polymer, 3-methyl thiophene, as a redox mediator to enhance BDD's sensitivity and selectivity. Electrochemical synthesis was used for polymer deposition, allowing for greater purity and avoiding solubility problems. The BDD/P3MT sensor exhibits good electrochemical properties, including rapid charge transfer and a large electrochemical area, enabling GA detection with a limit of detection of 11 mg/L. The sensor's response was correlated with TPCs measured by the Folin-Ciocalteu method. Square wave voltammetry (SWV) showed a good linear relationship between peak currents and GA concentrations in a wide linear range of 3-71 mg/L under optimal conditions. The BDD/P3MT sensor accurately measured TPCs in green tea, rooibos tea, and black tea samples, with green tea exhibiting the highest TPC levels. The results demonstrate the potential of the modified BDD electrode for the rapid and accurate detection of phenolic compounds in tea, with implications for quality control and antioxidant activity assessments. The prolific publications of the past decade have established BDD electrodes as robust BDD sensors for quantifying polyphenols. Fruits, vegetables, nuts, plant-derived beverages such as tea and wine, traditional Eastern remedies and various herbal nutritional supplements contain phenolic chemicals. The safety concerns of contaminated food intake are significant health concerns worldwide, as there exists a critical nexus between food safety, nutrition, and food security. It has been well established that green tea polyphenol consumption promotes positive health effects. Despite their potential benefits, consuming high amounts of these polyphenols has sparked debate due to concerns over potential negative consequences.

Anticancer Therapies Based on Oxidative Damage: Lycium barbarum Inhibits the Proliferation of MCF-7 Cells by Activating Pyroptosis through Endoplasmic Reticulum Stress

Lycium barbarum, commonly recognized as goji berry or wolfberry, is highly appreciated not only for its organoleptic and nutritional properties but also as an important source of bioactive compounds such as polysaccharides, carotenoids, phenolics, and various other non-nutritive compounds. These constituents give it a multitude of health benefits, including antioxidant, anti-inflammatory, and anticancer properties. However, the precise biochemical mechanisms responsible for its anticancer effects remain unclear, and the comprehensive composition of goji berry extracts is often insufficiently explored. This study aimed to investigate the biochemical pathways modulated in breast cancer cells by an ethanolic extract of Lycium barbarum fruit (LBE). Following metabolomic profiling using UHPLC-HRMS/MS, we assessed the antitumoral properties of LBE on different breast cancer cell lines. This investigation revealed that LBE exhibited cytotoxic effects, inducing a pro-oxidant effect that triggered pyroptosis activation through endoplasmic reticulum (ER) stress and subsequent activation of the P-IRE1α/XBP1/NLRP3 axis in MCF-7 cells. In addition, LBE did not display cytotoxicity toward healthy human cells but demonstrated antioxidant properties by neutralizing ROS generated by doxorubicin. These findings underscore the potential of LBE as a highly promising natural extract in cancer therapy.

The paradox of Picroside II: As a natural antioxidant, but may instead futher aggravate liver injury by exacerbating mitochondrial oxidative stress

Background

Picroside II (PII), an iridoid glycoside extracted from the rhizomes and stems of the genus Picroside, exhibits pronounced hepatoprotective properties. Pre-administration of PII protects against acute liver injury caused by D-galactosamine (D-Gal), carbon tetrachloride (CCl4), and acetaminophen (APAP). This study aimed to elucidate the ramifications of PII administration subsequent to the initiation of acute hepatic injury.

Methods

Exploring the role of PII treatment in APAP-treated cell and rat models and in D-Gal and CCl4-treated rat models.

Results

In rats, APAP treatment increased serum aspartate transaminase, alanine transaminase, and alkaline phosphatase levels and decreased glutathione activity and the fluidity of the liver mitochondrial membrane. In L-02 cells, APAP exposure resulted in a decrement in membrane potential, an augmentation in the liberation of reactive oxygen species, and an acceleration of apoptotic processes. Moreover, PII pre-administration protected against D-Gal-induced acute hepatic injury and CCl4-induced chronic hepatic injury in rodent models, whereas PII administration post-injury aggravated CCl4-induced chronic hepatic injury.

Conclusions

Our results suggest that the effects of PII depend on the hepatic physiological or pathological state at the time of intervention. While PII possesses the potential to avert drug-induced acute hepatic injury through the mitigation of oxidative stress, its administration post-injury may exacerbate the hepatic damage, underscoring the critical importance of timing in therapeutic interventions.

Exploring enzyme inhibition and comprehensive mechanisms of antioxidant/prooxidative activity of natural furanocoumarin derivatives: A comparative kinetic DFT study

This study aimed to explore the antioxidant and prooxidative activity of two natural furanocoumarin derivatives, Bergaptol (4-Hydroxy-7H-furo [3,2-g] [1]benzopyran-7-one, BER) and Xanthotoxol (9-Hydroxy-7H-furo [3,2-g] [1]benzopyran-7-one, XAN). The collected thermodynamic and kinetic data demonstrate that both compounds possess substantial antiradical activity against HO• and CCl3OO• radicals in physiological conditions. BER exhibited better antiradical activity in comparison to XAN, which can be attributed to the enhanced deprotonation caused by the positioning of the -OH group on the psoralen ring. In contrast to highly reactive radical species, newly formed radical species BER• and XAN• exhibited negligible reactivity towards the chosen constitutive elements of macromolecules (fatty acids, amino acids, nucleobases). Furthermore, in the presence of O2•─, the ability to regenerate newly formed radicals BER• and XAN• was observed. Conversely, in physiological conditions in the presence of Cu(II) ions, both compounds exhibit prooxidative activity. Nevertheless, the prooxidative activity of both compounds is less prominent than their antioxidant activity. Furthermore, it has been demonstrated that anionic species can engage in the creation of a chelate complex, which restricts the reduction of metal ions when reducing agents are present (O2•─ and Asc─). Moreover, studies have demonstrated that these chelating complexes can be coupled with other radical species, hence enhancing their ability to inactivate radicals. Both compounds exhibited substantial inhibitory effects against enzymes involved in the direct or indirect generation of ROS: Xanthine Oxidase (XOD), Lipoxygenase (LOX), Myeloperoxidase (MPO), NADPH oxidase (NOX).

Kaempferol as an Alternative Cryosupplement for Bovine Spermatozoa: Cytoprotective and Membrane-Stabilizing Effects

Kaempferol (KAE) is a natural flavonoid with powerful reactive oxygen species (ROS) scavenging properties and beneficial effects on ex vivo sperm functionality. In this paper, we studied the ability of KAE to prevent or ameliorate structural, functional or oxidative damage to frozen-thawed bovine spermatozoa. The analysis focused on conventional sperm quality characteristics prior to or following thermoresistance tests, namely the oxidative profile of semen alongside sperm capacitation patterns, and the levels of key proteins involved in capacitation signaling. Semen samples obtained from 30 stud bulls were frozen in the presence of 12.5, 25 or 50 μM KAE and compared to native ejaculates (negative control-CtrlN) as well as semen samples cryopreserved in the absence of KAE (positive control-CtrlC). A significant post-thermoresistance test maintenance of the sperm motility (p < 0.001), membrane (p < 0.001) and acrosome integrity (p < 0.001), mitochondrial activity (p < 0.001) and DNA integrity (p < 0.001) was observed following supplementation with all KAE doses in comparison to CtrlC. Experimental groups supplemented with all KAE doses presented a significantly lower proportion of prematurely capacitated spermatozoa (p < 0.001) when compared with CtrlC. A significant decrease in the levels of the superoxide radical was recorded following administration of 12.5 (p < 0.05) and 25 μM KAE (p < 0.01). At the same time, supplementation with 25 μM KAE in the cryopreservation medium led to a significant stabilization of the activity of Mg2+-ATPase (p < 0.05) and Na+/K+-ATPase (p < 0.0001) in comparison to CtrlC. Western blot analysis revealed that supplementation with 25 μM KAE in the cryopreservation medium prevented the loss of the protein kinase A (PKA) and protein kinase C (PKC), which are intricately involved in the process of sperm activation. In conclusion, we may speculate that KAE is particularly efficient in the protection of sperm metabolism during the cryopreservation process through its ability to promote energy synthesis while quenching excessive ROS and to protect enzymes involved in the process of sperm capacitation and hyperactivation. These properties may provide supplementary protection to spermatozoa undergoing the freeze-thaw process.

Concentration-dependent dual roles of proanthocyanidins on oxidative stress and docosahexaenoic acid production in Schizochytrium sp. ATCC 20888

Antioxidant addition is an effective strategy to achieve docosahexaenoic acid (DHA) overproduction in oleaginous microorganisms. Nevertheless, antioxidants like phenolic compounds sometimes exert pro-oxidant activity. In this work, effects of proanthocyanidins (PAs) on fermentation performance and oxidative stress in Schizochytrium sp. were investigated. Low PAs addition (5 mg/L) reduced reactive oxygen species and enhanced lipogenic enzymes activities and NADPH, resulting in significant increase in lipid (20.3 g/L) by 33.6 % and DHA yield (9.8 g/L) by 53.4 %. In contrast, high PAs addition (500 mg/L) exerted pro-oxidant effects, aggravated oxidative damage and lipid peroxidation, leading to sharp decrease in biomass (21.3 g/L) by 35.1 %, lipid (8.2 g/L) by 46.0 %, and DHA (2.9 g/L) by 54.8 %. Therefore, the antioxidant concentration is especially crucial in DHA production. This study is the first to report concentration-dependant dual roles of PAs in oxidative stress and DHA production in Schizochytrium sp., providing new insights into microbial DHA production.

Side-stream lignins: Potential antioxidant and antimicrobial agents in milk

In recent years, lignin has drawn increasing attention due to its intrinsic antibacterial and antioxidant activities, biodegradability, and biocompatibility. Yet, like several other biogenic structures, its compositional heterogeneity represents a challenge to overcome. In addition, there are few studies regarding food applications of lignin. Herein, we evaluate the antimicrobial and antioxidant effects of lignin from two different sources. These lignins were characterized by attenuated total reflectance Fourier-transform infrared (ATR-FTIR) and hydrogen nuclear magnetic resonance (1H NMR) spectroscopies. Their antibacterial and antioxidant capacities (DPPH and Folin-Ciocalteu methods) were also investigated. Susceptibility tests were performed with the minimal inhibitory (MIC) and bactericidal (MBC) concentrations using the micro-broth dilution technique. Kraft lignin presented higher radical-scavenging and antibacterial activities than alkali lignin, indicating the dependence of antioxidant and antibacterial activities on the precursor biomass. Scanning electron microscopy shows morphologic changes in the bacteria after exposure to lignin, while confocal microscopy suggests that kraft lignin has affinity towards bacterial surfaces and the ability to cause cell membrane destabilization. Lignin inhibited the growth of Staphylococcus aureus and Salmonella Enteritidis in skimmed milk, herein taken as food model. Our results suggest that lignins are promising candidates for green additives to improve quality and safety within the food chain.

The Association of Tryptophan and Its Metabolites With Incident Hip Fractures, Mortality, and Prevalent Frailty in Older Adults: The Cardiovascular Health Study

Amino acids are the building blocks of proteins, and sufficient protein intake is important for skeletal health. We utilized stored serum from the Cardiovascular Health Study in 1992-1993 to examine the relationship between levels of the essential amino acid tryptophan (trp) and its oxidized and nonoxidized metabolites to risk for incident hip fractures and mortality over 12 years of follow-up. We included 131 persons who sustained a hip fracture during this time period and 131 without a hip fracture over these same 12 years of follow-up; 58% female and 95% White. Weighted multivariable Cox hazards models were used to estimate the hazard ratios (HR) and 95% confidence intervals (CI) of incident hip fracture associated with a one standard deviation (SD) higher trp or its metabolites exposure. Relative risk regression was used to evaluate the cross-sectional association of trp and its metabolites with frailty. Higher serum levels of trp were significantly associated with lower risk of incident hip fractures (HR = 0.75 per SD of trp (95% CI 0.57-0.99) but were not significantly associated with mortality or frailty status by Freid's frailty index. There were no statistically significant associations between any of the oxidized or nonoxidized products of trp with incident hip fractures (p ≥ 0.64), mortality (p ≥ 0.20), or cross-sectional frailty status (p ≥ 0.13) after multiple testing adjustment. Randomized clinical trials examining whether increasing trp intake is beneficial for osteoporosis are needed. © 2023 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.

In vitro anti-inflammatory activity and ameliorative effects on gastric ulcers of Licania rigida benth seed extract

Licania rigida Benth., a Brazilian endemic plant, has been traditionally used for treating inflammation and stomach pain. This work investigates the anti-inflammatory and gastroprotective activities of the ethanolic extract from L. rigida seeds (EELr) by in vitro and in vivo methods. The phytochemical profile was determined and the in vitro antioxidant activity was investigated by radical scavenging and thiobarbituric acid reactive substances methods. The ovalbumin denaturation method was used with sodium diclofenac as standard for the in vitro anti-inflammatory activity assessment. Acetylsalicylic acid was used to induce gastric ulcers in male mice and then to evaluate the preventive and therapeutic gastroprotective effect of EELr, using omeprazole as the reference drug. The extract exhibited relevant amount of phenolic compounds and flavonoids, in particular, demonstrating in vitro antioxidant capacity. EELr was able to inhibit almost 60% of ovalbumin denaturation at a concentration considered low. It also prevented the decrease of biochemical markers for oxidative stress such as superoxide dismutase (SOD) and reduced glutathione (GSH) in the stomach and SOD and catalase (CAT) in the liver. EELr also significantly decreased the number of lesions as well as reduced the ulcerated area when used as therapy. The observed effect may be due to its phenolic compounds, such as chlorogenic acid, caffeic acid and tannins, as previously reported. EELr is a potential source of compounds with anti-inflammatory activity, protects the liver from oxidative damage and improves healing of aspirin-induced ulcers. This work contributes to the knowledge of L. rigida species.

Effects of Plant-Based Antioxidants in Animal Diets and Meat Products: A Review

The perceived level of risk associated with a food product can influence purchase and consumption decisions. Thus, current trends in food safety address an issue of general interest-the identification of healthy and economical alternatives to synthetic antioxidants that may have harmful effects on human health. Still, the processors' target is to increase the shelf life of food products using preserving substances. Natural antioxidants can be extracted and used in the food industry from different plants, such as blueberry, broccoli, chokeberry, cinnamon, ginger, olives, oregano, etc. The identification of the main natural antioxidant types that have been used in the food industry is very important in order to provide a comprehensive analysis of the researched topic. In this regard, the aim of this paper was to illustrate the positive aspects of using natural antioxidants with preservative roles in meat products, while, at the same time, highlighting the potential risks induced by these compounds. All of those aspects are correlated with the impact of sensorial attributes and the improvement of the nutritional value of meat products.

Degradation Mechanisms of 4,7-Dihydroxycoumarin Derivatives in Advanced Oxidation Processes: Experimental and Kinetic DFT Study

Coumarins represent a broad class of compounds with pronounced pharmacological properties and therapeutic potential. The pursuit of the commercialization of these compounds requires the establishment of controlled and highly efficient degradation processes, such as advanced oxidation processes (AOPs). Application of this methodology necessitates a comprehensive understanding of the degradation mechanisms of these compounds. For this reason, possible reaction routes between HO^• and recently synthesized aminophenol 4,7-dihydroxycoumarin derivatives, as model systems, were examined using electron paramagnetic resonance (EPR) spectroscopy and a quantum mechanical approach (a QM-ORSA methodology) based on density functional theory (DFT). The EPR results indicated that all compounds had significantly reduced amounts of HO^• radicals present in the reaction system under physiological conditions. The kinetic DFT study showed that all investigated compounds reacted with HO^• via HAT/PCET and SPLET mechanisms. The estimated overall rate constants (k_overall) correlated with the EPR results satisfactorily. Unlike HO^• radicals, the newly formed radicals did not show (or showed negligible) activity towards biomolecule models representing biological targets. Inactivation of the formed radical species through the synergistic action of O₂/NO_x or the subsequent reaction with HO^• was thermodynamically favored. The ecotoxicity assessment of the starting compounds and oxidation products, formed in multistage reactions with O₂/NO_x and HO^•, indicated that the formed products showed lower acute and chronic toxicity effects on aquatic organisms than the starting compounds, which is a prerequisite for the application of AOPs procedures in the degradation of compounds.

Effect of Polyphenols and Zinc Co-Supplementation on the Development of Neoplasms in Rats with Breast Cancer

The aim of the study was to evaluate the effect of selected polyphenolic compounds: epicatechin, apigenin, and naringenin, administered separately or in combination with zinc (Zn), on the growth and development of the neoplastic process induced by 7,12-dimethylbenz[a]anthracene (DMBA) in rats. The impact of supplementation with the above-mentioned compounds on the content of modified derivatives: 1-methyladenosine, N6-methyl-2'-deoxyadenosine, O-methylguanosine, 7-methylguanine, 3-methyladenine, 1-methylguanine, 2-amino-6,8-dihydroxypurine, and 8-hydroxy-2'-deoxyguanosine in the urine of rats with mammary cancer was also assessed. Female Sprague-Dawley rats divided into 7 groups were used in the study: animals without supplementation and animals supplemented with apigenin, epicatechin, and naringenin separately or in combination with zinc. To induce mammary cancer, rats were treated with DMBA. Modified derivatives were determined by a validated high-performance liquid chromatography coupled to mass spectrometry method. Based on the obtained results, it can be said that supplementation of the animals with naringenin inhibits the development and progression of the neoplastic process in rats treated with 7,12-dimethylbenzanthracene. Neoplastic tumors were found in only 2 of 8 rats (incidence: 25%) and were considered to be at most grade 1 malignancy. The first palpable tumors in the group of animals receiving naringenin appeared two-three weeks later when compared to other groups. The combination of zinc with flavonoids (apigenin, epicatechin, and naringenin) seems to stimulate the process of carcinogenesis. The level of N6-methyl-2'-deoxyadenosine and 3-methyladenine in the urine of rats was statistically significantly higher in the groups supplemented with apigenin, epicatechin, and naringenin administered in combination with Zn than in the groups receiving only polyphenolic compounds. In conclusion, supplementation of rats with selected flavonoids administered separately or in combination with Zn has an impact on the development of neoplasms and the level of modified nucleosides in the urine of rats with breast cancer. Our results raise the question of whether simultaneous diet supplementation with more than one anti-cancer agent may reduce/stimulate the risk of carcinogenesis.

Lignin-Based Nanoparticles as Both Structural and Active Elements in Self-Assembling and Self-Healing Multifunctional Hydrogels for Chronic Wound Management

Efficient wound healing is feasible when the dressing materials simultaneously target multiple factors causing wound chronicity, such as deleterious proteolytic and oxidative enzymes and bacterial infection. Herein, entirely bio-based multifunctional self-assembled hydrogels for wound healing were developed by simply mixing two biopolymers, thiolated hyaluronic acid (HA-SH) and silk fibroin (SF), with lignin-based nanoparticles (NPs) as both structural and functional elements. Sono-enzymatic lignin modification with natural phenolic compounds results in antibacterial and antioxidant phenolated lignin nanoparticles (PLN) capable of establishing multiple interactions with both polymers. These strong and dynamic polymer-NP interactions endow the hydrogels with self-healing and shear-thinning properties, and pH-responsive NP release is triggered at neutral to alkaline pH (7-9). Despite being a physically crosslinked hydrogel, the material was stable for at least 7 days, and its mechanical and functional properties can be tuned depending on the polymer and NP concentration. Furthermore, human skin cells in contact with the nanocomposite hydrogels for 7 days showed more than 93% viability, while the viability of clinically relevant Staphylococcus aureus and Pseudomonas aeruginosa was reduced by 99.7 and 99.0%, respectively. The hydrogels inhibited up to 52% of the activity of myeloperoxidase and matrix metalloproteinases, responsible for wound chronicity, and showed a strong antioxidant effect, which are crucial features promoting wound healing.

ROS-Induced DNA-Damage and Autophagy in Oral Squamous Cell Carcinoma by Usnea barbata Oil Extract-An In Vitro Study

Oxidative stress is associated with aging, cancers, and numerous metabolic and chronic disorders, and phenolic compounds are well known for their health-promoting role due to their free-radical scavenging activity. These phytochemicals could also exhibit pro-oxidant effects. Due to its bioactive phenolic secondary metabolites, Usnea barbata (L.) Weber ex. F.H. Wigg (U. barbata) displays anticancer and antioxidant activities and has been used as a phytomedicine for thousands of years. The present work aims to analyze the properties of U. barbata extract in canola oil (UBO). The UBO cytotoxicity on oral squamous cell carcinoma (OSCC) CLS-354 cell line and blood cell cultures was explored through complex flow cytometry analyses regarding apoptosis, reactive oxygen species (ROS) levels, the enzymatic activity of caspase 3/7, cell cycle, nuclear shrinkage (NS), autophagy (A), and synthesis of deoxyribonucleic acid (DNA). All these studies were concomitantly performed on canola oil (CNO) to evidence the interaction of lichen metabolites with the constituents of this green solvent used for extraction. The obtained data evidenced that UBO inhibited CLS-354 oral cancer cell proliferation through ROS generation (316.67 × 10⁴), determining higher levels of nuclear shrinkage (40.12%), cell cycle arrest in G0/G1 (92.51%; G0 is the differentiation phase, while during G1 phase occurs preparation for cell division), DNA fragmentation (2.97%), and autophagy (62.98%) than in blood cells. At a substantially higher ROS level in blood cells (5250.00 × 10⁴), the processes that lead to cell death-NS (30.05%), cell cycle arrest in G0/G1 (86.30%), DNA fragmentation (0.72%), and autophagy (39.37%)-are considerably lower than in CLS-354 oral cancer cells. Our work reveals the ROS-mediated anticancer potential of UBO through DNA damage and autophagy. Moreover, the present study suggests that UBO pharmacological potential could result from the synergism between lichen secondary metabolites and canola oil phytoconstituents.

Antibacterial lignin-based nanoparticles and their use in composite materials

Lignin, one of the most abundant biopolymers on earth, has been traditionally considered a low-value by-product of the pulp and paper industries. This renewable raw material, besides being a source of valuable molecules for the chemical industry, also has antioxidant, UV-absorbing, and antibacterial properties in its macromolecular form. Moreover, lignin in the form of nanoparticles (LigNPs) presents advantages over bulk lignin, such as higher reactivity due to its larger surface-to-volume ratio. In view of the rapid surge of antimicrobial resistance (AMR), caused by the overuse of antibiotics, continuous development of novel antibacterial agents is needed. The use of LigNPs as antibacterial agents is a suitable alternative to conventional antibiotics for topical application or chemical disinfectants for surfaces and packaging. Besides, their multiple and unspecific targets in the bacterial cell may prevent the emergence of AMR. This review summarizes the latest developments in antibacterial nano-formulated lignin, both in dispersion and embedded in materials. The following roles of lignin in the formulation of antibacterial NPs have been analyzed: (i) an antibacterial active in nanoformulations, (ii) a reducing and capping agent for antimicrobial metals, and (iii) a carrier of other antibacterial agents. Finally, the review covers the inclusion of LigNPs in films, fibers, hydrogels, and foams, for obtaining antibacterial lignin-based nanocomposites for a variety of applications, including food packaging, wound healing, and medical coatings.

Cardioprotective potential of the antioxidant-rich bioactive fraction of Garcinia pedunculata Roxb. ex Buch.-Ham. against isoproterenol-induced myocardial infarction in Wistar rats

This Study aimed to characterise the phenolic compounds in Garcinia pedunculata extract and assess their potential antioxidant activity as well as its cardioprotective potential in isoproterenol-induced cardiac hypertrophy in an experimental animal model. In vitro antioxidant properties were determined using DPPH, ABTS, FRAP, PMD assays. In vitro lipid peroxidation experiment was also performed with heart tissues. Cardioprotective and cardiotoxicity effects were determined using the cell line studies. The cardioprotective effect of GP was assessed in a rat model of isoproterenol-(ISO-) induced cardiac hypertrophy by subcutaneous administration. Heart weight/tail length ratio and cardiac hypertrophy indicators were reduced after oral administration of GP. Additionally, GP reduced oxidative stress and heart inflammation brought on by ISO. In H9c2 cells, the antihypertrophic and anti-inflammatory effects of the extract of GP were seen in the presence of ISO, which were further supported by the in vivo observations. This study makes a compelling case for the possibility that supplementing with dried GP fruit can prevent heart hypertrophy by reducing oxidative stress and inflammation.

Fe(III) and Cu(II) Complexes of Chlorogenic Acid: Spectroscopic, Thermal, Anti-/Pro-Oxidant, and Cytotoxic Studies

Complexes of chlorogenic acid (5-CQA) with copper(II) and iron(III) were synthesized in a solid state and examined by means of FT-IR, thermogravimetric, and elemental analyses. The molar stoichiometric ratios of metal:ligand for the solid forms of the complexes were established as Cu(II):L = 1:2 and Fe(III):L = 2:3 (L: 5-CQA), with the possible coordination through the carboxylate group and the hydroxyl group from the catechol moiety. In an aqueous solution at pH = 7.4, the composition of the complexes was Cu(II):L = 1:1, and Fe(III):L = 1:1 and 1:2. The Cu(II) and Fe(III) complexes with 5-CQA showed lower antioxidant properties, as estimated by the spectrophotometric methods with DPPH^•, ABTS^•+, and HO^• radicals, than the ligand alone, whereas in the lipid peroxidation inhibition assay, the metal complexes revealed a higher antioxidant activity than 5-CQA. Cu(II) 5-CQA showed the highest pro-oxidant activity in the Trolox oxidation assays compared to the other studied compounds. The lipophilic parameters of the compounds were estimated using the HPLC method. 5-CQA and its complexes with Fe(III) and Cu(II) were not toxic to HaCaT cells in a tested concentration range of 0.15-1000 nM after a 24 h incubation time.

Evaluation of Phenolic Content Diversity along with Antioxidant/Pro-Oxidant, Glutathione Transferase Inhibition, and Cytotoxic Potential of Selected Commonly Used Plants

The function of antioxidant polyphenols has been demonstrated for their ability to protect against a variety of diseases. However, some antioxidants have been shown to be pro-oxidant. Some of the important antioxidant enzymes are glutathione transferases (GST), which are involved in maintaining redox homeostasis. GST class Pi (GSTP1-1) hyper-activation is a feature that is found in cancer. This work aims to demonstrate the relationship between the phytochemicals of 18 plants and their ability to act as antioxidant/pro-oxidant agents, as well as their effects on the activity of GSTP1-1 and their cellular toxicity. Tamarindus indica, Cinnamomum verum, and Alpinia galanga extracts had high phytochemical contents, moderate heavy metal levels, and antioxidant/pro-oxidant activities. Among the main plant components identified using high-performance liquid chromatography, only chlorogenic acid, catechin, and quercetin can function as antioxidants and pro-oxidants. Hibiscus sabdariffa, C. verum, A. galanga, T. indica, Gossypium arboreum, and Punica granatum were among the plant extracts examined that inhibited the activity of the purified recombinant GSTP1-1, with the inhibition constant values ranging from 0.48 to 1.67 mg of gallic acid equivalent/g. The level of cytotoxicity was also studied to determine the effects of these extracts on human Caucasian breast cancer. The findings revealed that plants with high phenol content had an antioxidant/pro-oxidant capacity as well as inhibition of the activity of GST. However, the cytotoxic effect was not associated with all of the extracts, which indicates that polyphenols interact with other components that may influence their observed behavior.

Antibacterial Properties and Mechanisms of Action of Sonoenzymatically Synthesized Lignin-Based Nanoparticles

In recent years, lignin has drawn increasing attention for different applications due to its intrinsic antibacterial and antioxidant properties, coupled with biodegradability and biocompatibility. However, chemical modification or combination with metals is usually required to increase its antimicrobial functionality and produce biobased added-value materials for applications wherein bacterial growth should be avoided, such as biomedical and food industries. In this work, a sonoenzymatic approach for the simultaneous functionalization and nanotransformation of lignin to prepare metal-free antibacterial phenolated lignin nanoparticles (PheLigNPs) is developed. The grafting of tannic acid, a natural phenolic compound, onto lignin was achieved by an environmentally friendly approach using laccase oxidation upon the application of high-intensity ultrasound to rearrange lignin into NPs. PheLigNPs presented higher antibacterial activity than nonfunctionalized LigNPs and phenolated lignin in the bulk form, indicating the contribution of both the phenolic content and the nanosize to the antibacterial activity. Studies on the antibacterial mode of action showed that bacteria in contact with the functionalized NPs presented decreased metabolic activity and high levels of reactive oxygen species (ROS). Moreover, PheLigNPs demonstrated affinity to the bacterial surface and the ability to cause membrane destabilization. Antimicrobial resistance studies showed that the NPs did not induce resistance in pathogenic bacteria, unlike traditional antibiotics.

On The Radical Scavenging and DNA Repairing Activities by Natural Oxygenated Diterpenoids: Theoretical Insights

Diterpenoids are abundant and important compounds in Euphorbia species owing to their structural diversity; therefore, in this study, we investigate the modern-concept antioxidant activities, including free-radical scavenging and oxidative DNA damage repairing, of highly oxygenated diterpenoids originating from the aerial part of Euphorbia helioscopia. Four compounds with structural types of ent-abietane, containing a fused furan ring in their structures, including euphelionolide A (1), euphelionolide D (2), euphelionolide I (3), and euphelionolide L (4) are selected. First, the radical-scavenging activity of these compounds was evaluated with two typical radicals HOO^• and HO^• in water and pentyl ethanoate (PEA, to mimic lipid environment) via three main mechanisms, namely, hydrogen atom transfer (HAT), radical adduct formation (RAF), and single electron transfer. It is found that the studied compounds are able to scavenge free radicals at multiple reactive sites favorably via HAT and RAF mechanisms, in which the former dominates in the case with HOO^• while both mechanisms are competitive in the reaction with HO^•. Second, chemical repairing of DNA damage is modeled with the H-atom and single electron being transferred from the studied molecules to damaged 2'-deoxyguanosine (2dG) (i.e., 2dG^• radicals and 2dG^•+ radical cation). Among the four compounds, euphelionolide A is shown as the most effective radical scavenger and also the highest potential species for chemical repairing of radical-damaged DNA in both water and PEA.

Tannic Acid Coating Augments Glioblastoma Cellular Uptake of Magnetic Nanoparticles with Antioxidant Effects

Coating of nanoparticles with gallates renders them antioxidant and enhances cellular internalization. In this study, (amino)silica magnetic particles modified with tannic acid (TA) and optionally with chitosan (CS) were developed, and their physicochemical properties and antioxidant activity were evaluated. The results demonstrated that the TA-modified aminosilica-coated particles, as well as the silica-coated particles with a double TA layer, exhibited high antioxidant activity, whereas the silica-coated particles with no or only a single TA layer were well-internalized by LN-229 cells. In addition, a magnet placed under the culture plates greatly increased the cellular uptake of all TA-coated magnetic nanoparticles. The coating thus had a considerable impact on nanoparticle–cell interactions and particle internalization. The TA-coated magnetic nanoparticles have great potential as intracellular carriers with preserved antioxidant activity.

Advances in the control of lipid peroxidation in oil-in-water emulsions: kinetic approaches†

Large efforts have been, and still are, devoted to minimize the harmful effects of lipid peroxidation. Much of the early work focused in understanding both the lipid oxidation mechanisms and the action of antioxidants in bulk solution. However, food-grade oils are mostly present in the form of oil-in-water emulsions, bringing up an increasing complexity because of the three-dimensional interfacial region. This review presents an overview of the kinetic approaches employed in controlling the oxidative stability of edible oil-in-water emulsions and of the main outcomes, with particular emphasis on the role of antioxidants and on the kinetics of the inhibition reaction. Application of physical-organic chemistry methods, such as the pseudophase models to investigate antioxidant partitioning, constitute a remarkable example on how kinetic methodologies contribute to model chemical reactivity in multiphasic systems and to rationalize the role of interfaces, opening new opportunities for designing novel antioxidants with tailored properties and new prospects for modulating environmental conditions in attempting to optimize their efficiency. Here we will summarize the main kinetic features of the inhibition reaction and will discuss on the main factors affecting its rate, including the determination of antioxidant efficiencies from kinetic profiles, structure-reactivity relationships, partitioning of antioxidants and concentration effects.

Effect of Hempseed Cake (Cannabis sativa L.) Incorporation on the Physicochemical and Antioxidant Properties of Reconstructed Potato Chips

Hempseed (Cannabis sativa L.) cake is a by-product after cold-pressing of oil from the hempseed, which is rich in protein and fiber. This study investigated the effect of hempseed cake incorporation on the physicochemical and antioxidant properties of reconstructed potato chips. Varying levels of hempseed cake (0, 5%, 10%, 15%, and 20%) were added, and the results showed that the addition of hempseed cake at 20% level significantly increased the protein and total dietary fiber content from 2.74 ± 0.62 g/100 g to 9.66 ± 0.28 g/100 g and from 2.76 ± 0.31 g/100 g to 13.57 ± 0.42 g/100 g, respectively. In addition, a 20% reduction in lipid content was observed in the 20% hempseed cake addition group. Furthermore, lightness value (L*) was significantly reduced from 72.23 ± 1.22 to 46.40 ± 1.76, while the hardness was enhanced with a higher level of hempseed cake supplementation in the potato chips sample. Compared with the control (no hempseed cake), the supplement of 20% cake increased the total phenolic content from 0.19 ± 0.01 to 0.26 ± 0.01 mg GAE/g. The ABTS radical scavenging rate was also significantly enhanced with the increased levels of hemp cake. However, the peroxide value and TBARS results showed that the addition of hempseed cake accelerated the lipid oxidation in the sample, possibly due to the highly unsaturated fatty acid residues in the hempseed cake. The results suggested that more research is needed for the incorporation of hempseed cake in potato chips.

Biomedical applications of tannic acid

Tannic Acid (TA) is a naturally occurring antioxidant polyphenol that has gained popularity over the past decade in the field of biomedical research for its unique biochemical properties. Tannic acid, typically extracted from oak tree galls, has been used in many important historical applications. TA is a key component in vegetable tanning of leather, iron gall ink, red wines, and as a traditional medicine to treat a variety of maladies. The basis of TA utility is derived from its many hydroxyl groups and its affinity for forming hydrogen bonds with proteins and other biomolecules. Today, the study of TA has led to the development of many new pharmaceutical and biomedical applications. TA has been shown to reduce inflammation as an antioxidant, act as an antibiotic in common pathogenic bacterium, and induce apoptosis in several cancer types. TA has also displayed antiviral and antifungal activity. At certain concentrations, TA can be used to treat gastrointestinal disorders such as hemorrhoids and diarrhea, severe burns, and protect against neurodegenerative diseases. TA has also been utilized in biomaterials research as a natural crosslinking agent to improve mechanical properties of natural and synthetic hydrogels and polymers, while also imparting anti-inflammatory, antibacterial, and anticancer activity to the materials. TA has also been used to develop thin film coatings and nanoparticles for drug delivery. In all, TA is fascinating molecule with a wide variety of potential uses in pharmaceuticals, biomaterials applications, and drug delivery strategies.

New insights into the competition between antioxidant activities and pro-oxidant risks of rosmarinic acid

Direct and indirect antioxidant activities of rosmarinic acid (RA) based on HOO˙/CH3OO˙ radical scavenging and Fe(iii)/Fe(ii) ion chelation were theoretically studied using density functional theory at the M05-2X/6-311++G(2df,2p) level of theory. First, four antioxidant mechanisms including hydrogen atom transfer (HAT), radical adduct formation (RAF), proton loss (PL) and single electron transfer (SET) were investigated in water and pentyl ethanoate (PEA) phases. Regarding the free radical scavenging mechanism, HAT plays a decisive role with overall rate coefficients of 1.84 × 103 M-1 s-1 (HOO˙) and 4.49 × 103 M-1 s-1 (CH3OO˙) in water. In contrast to PL, RAF and especially SET processes, the HAT reaction in PEA is slightly more favorable than that in water. Second, the [Fe(iii)(H2O)6]3+ and [Fe(ii)(H2O)6]2+ ion chelating processes in an aqueous phase are both favorable and spontaneous especially at the O5, site-1, and site-2 positions with large negative Δr G 0 values and great formation constant K f. Finally, the pro-oxidant risk of RA- was also considered via the Fe(iii)-to-Fe(ii) complex reduction process, which may initiate Fenton-like reactions forming reactive HO˙ radicals. As a result, RA- does not enhance the reduction process when ascorbate anions are present as reducing agents, whereas the pro-oxidant risk becomes remarkable when superoxide anions are found. The results encourage further attempts to verify the speculation using more powerful research implementations of the antioxidant activities of rosmarinic acid in relationship with its possible pro-oxidant risks.

Antioxidants into Nopal (Opuntia ficus-indica), Important Inhibitors of Free Radicals' Formation

Nopal (Opuntia ficus indica) belonging to the Cactacea family has many nutritional benefits attributed to a wide variety of phenolic and flavonoid compounds. Coumaric acid (COA), ferulic acid (FLA), protocatechuic acid (PRA), and gallic acid (GAA) are the phenolic acids (PhAs) present in nopal. In this study, the role of these PhAs in copper-induced oxidative stress was investigated using the density functional theory (DFT). The PhAs form 5 thermodynamically favorable complexes with Cu(II), their conditional Gibbs free energies of reaction (ΔG’, at pH = 7.4, in kcal/mol) are from −23 kcal/mol to −18 kcal/mol. All of them are bi-dentate complexes. The complexes of PRA and GAA are capable of inhibiting the Cu(II) reduction by both O₂^•− and Asc⁻, their reactions with the chelated metal are endergonic having rate constants about ~10⁻⁵–10² M⁻¹ s⁻¹, PhAs can prevent the formation of hydroxyl free radicals by chelating the copper ions. Once the hydroxyl radicals are formed by Fenton reactions, the complexes of PhAs with Cu(II) can immediately react with them, thus inhibiting the damage that they can cause to molecules of biological interest. The reactions between PhAs-Cu(II) complexes and hydroxyl free radical were estimated to be diffusion-limited (~10⁸ M⁻¹s⁻¹). Thus, these chelates can reduce the harmful effects caused by the most reactive free radical existent immediately after it is formed by Fenton reactions.

Design and Antioxidant Properties of Bifunctional 2H-Imidazole-Derived Phenolic Compounds-A New Family of Effective Inhibitors for Oxidative Stress-Associated Destructive Processes

The synthesis of inhibitors for oxidative stress-associated destructive processes based on 2H-imidazole-derived phenolic compounds affording the bifunctional 2H-imidazole-derived phenolic compounds in good-to-excellent yields was reported. In particular, a series of bifunctional organic molecules of the 5-aryl-2H-imidazole family of various architectures bearing both electron-donating and electron-withdrawing substituents in the aryl fragment along with the different arrangements of the hydroxy groups in the polyphenol moiety, namely derivatives of phloroglucinol, pyrogallol, hydroxyquinol, including previously unknown water-soluble molecules, were studied. The structural and antioxidant properties of these bifunctional 5-aryl-2H-imidazoles were comprehensively studied. The redox transformations of the synthesized compounds were carried out. The integrated approach based on single and mixed mechanisms of antioxidant action, namely the AOC, ARC, Folin, and DPPH assays, were applied to estimate antioxidant activities. The relationship “structure-antioxidant properties” was established for each of the antioxidant action mechanisms. The conjugation effect was shown to result in a decrease in the mobility of the hydrogen atom, thus complicating the process of electron transfer in nearly all cases. On the contrary, the conjugation in imidazolyl substituted phloroglucinols was found to enhance their activity through the hydrogen transfer mechanism. Imidazole-derived polyphenolic compounds bearing the most electron-withdrawing functionality, namely the nitro group, were established to possess the higher values for both antioxidant and antiradical capacities. It was demonstrated that in the case of phloroglucinol derivatives, the conjugation effect resulted in a significant increase in the antiradical capacity (ARC) for a whole family of the considered 2H-imidazole-derived phenolic compounds in comparison with the corresponding unsubstituted phenols. Particularly, conjugation of the polyphenolic subunit with 2,2-dimethyl-5-(4-nitrophenyl)-2H-imidazol-4-yl fragment was shown to increase ARC from 2.26 to 5.16 (10⁴ mol-eq/L). This means that the considered family of compounds is capable of exhibiting an antioxidant activity via transferring a hydrogen atom, exceeding the activity of known natural polyphenolic compounds.

Metal-Free C-H/C-H Coupling of 2H-Imidazole 1-Oxides with Polyphenols toward Imidazole-Linked Polyphenolic Compounds

The methodology of nucleophilic substitution of hydrogen (S_N^H) was successfully applied as a convenient synthetic tool to afford azaheterocyclic derivatives of phenols of various architectures. A series of 26 novel imidazole-linked polyphenolic compounds were first prepared in 72-95% yields through the direct metal-free C-H/C-H coupling of polyphenols with 2H-imidazole 1-oxides. Comprehensive studies on the reaction condition optimization, scope, and limitations enabled the development of a straightforward method toward novel bifunctional derivatives bearing both phenolic and imidazole scaffolds of particular interest in the design of challenging molecules for versatile applications in medicinal chemistry and materials science.

Phenolic compounds as antidiabetic, anti-inflammatory, and anticancer agents and improvement of their bioavailability by liposomes

Phenolic compounds, widespread in plants, are a necessary part of the human regimen due to their antioxidant and pro-oxidative properties. Naturally, phenolics structurally range from a very simple phenolic molecule moiety to an intricate polymer. For decades, phenolic compounds have gained pronounced attention because of their protective effects against degenerative disorders such as inflammation, diabetes and cancer. Physico-chemical properties (eg, solubility) restricted their bioactivity and also limited their usage as nutraceutical ingredients. However, encapsulation technology like liposomal formulations has been developed for the delivery of phenolic compounds without affecting their original aesthetic and organoleptic property. Hence, this review outlines the antioxidant and pro-oxidative properties of phenolic compounds and focuses on biological activity reports of flavonoids and phenolic acids as antidiabetic, anti-inflammatory and anticancer agents. Also, the delivery applications of phenolic compounds as liposomes are discussed with few examples.

The Role of Selected Natural Biomolecules in Sperm Production and Functionality

Emerging evidence from in vivo as well as in vitro studies indicates that natural biomolecules may play important roles in the prevention or management of a wide array of chronic diseases. Furthermore, the use of natural compounds in the treatment of male sub- or infertility has been proposed as a potential alternative to conventional therapeutic options. As such, we aimed to evaluate the effects of selected natural biomolecules on the sperm production, structural integrity, and functional activity. At the same time, we reviewed their possible beneficial or adverse effects on male reproductive health. Using relevant keywords, a literature search was performed to collect currently available information regarding molecular mechanisms by which selected natural biomolecules exhibit their biological effects in the context of male reproductive dysfunction. Evidence gathered from clinical trials, in vitro experiments and in vivo studies suggest that the selected natural compounds affect key targets related to sperm mitochondrial metabolism and motion behavior, oxidative stress, inflammation, DNA integrity and cell death. The majority of reports emphasize on ameliorative, stimulating and protective effects of natural biomolecules on the sperm function. Nevertheless, possible adverse and toxic behavior of natural compounds has been indicated as well, pointing out to a possible dose-dependent impact of natural biomolecules on the sperm survival and functionality. As such, further research leading to a deeper understanding of the beneficial or adverse roles of natural compounds is necessary before these can be employed for the management of male reproductive dysfunction.

Critical overview of the use of plant antioxidants in the meat industry: Opportunities, innovative applications and future perspectives

The number of articles devoted to study the effect of "natural antioxidants" on meat systems has remarkably increased in the last 10 years. Yet, a critical review of literature reveals recurrent flaws in regards to the rationale of the application, the experimental design, the characterisation of the plant sources, the discussion of the molecular mechanisms and of the potential benefits. The selection of the appropriate source of these antioxidants and the identification of their bioactive constituents, are essential to understand their mode of action and set effective and safe doses. The methodological approach should also be planned with care as the recorded effects and main conclusions largely depend on the accuracy and specificity of the methods. This article aims to critically review the recent advances in the application of plant antioxidants in meat and meat products and briefly covers current trends of innovative application and future trends.

A comprehensive evaluation of the chemical profiles and biological properties of six geophytes from Turkey: Sources of bioactive compounds for novel nutraceuticals

Geophytes are gaining interest as sources of natural ingredients in nutraceutical and pharmaceutical area. In this sense, six bulbous plant species from Turkey are investigated, namely Hyacinthella campanulata K.Perss. & Wendelbo, Muscari neglectum Guss. ex Ten., Tulipa humilis herb., Iris stenophylla Hausskn. ex Baker, Galanthus elwesii Hook. f. and Crocus danfordiae Maw. with the aim to highlight their chemical compositions and biological properties. Polyphenolic profiles of the different plant parts (flower, bulb and leaf) of the six genotypes were evaluated using colorimetric methods as well LC-MS/MS. The antioxidant properties and enzymes inhibitory potential (α-amylase, α-glucosidase, tyrosinase and cholinesterases) of the extracts were determined. Overall, highest total phenolic content and total flavonoid content were observed in the leaf extracts of the studied species, except for M. neglectum (flower extract) and T. humilis (flower extract). LC-MS/MS analysis revealed the abundance of some phenolic compounds including quinic acid, hesperidin and chlorogenic acid in selective extracts. The extracts showed significant antioxidant potentials, with leaf extract of the I. stenophylla being more potent, which is linked to its high phenolic contents. All the extracts displayed notable anti-acetylcholinesterase (1.77 - 2.53 mg GALAE/g) and tyrosinase (54.9-67.20 mg KAE/g). Selective extracts have showed activity against butyrylcholinesterase, with bulb extract of M. neglectum (2.99 mg GALAE/g), I. stenophylla (2.53 mg GALAE/g) and G. elwesii (2.52 mg GALAE/g) showing highest activity. Modest activity was observed against α-amylase and α-glucosidase. The experimental data gathered herein is the first report on the phytochemical and biological attributes of these bulbous plant species which project them as potential sources of biologically active compounds for phytomedicines and nutraceuticals development.

Computationally designed p-coumaric acid analogs: searching for neuroprotective antioxidants

Newly designed p-coumaric acid derivatives are promising candidates as multifunctional antioxidants with neuroprotective effects.

Comparison of the scavenging capacities of phloroglucinol and 2,4,6-trihydroxypyridine towards HO˙ radical: a computational study

In this work the scavenging capacities of biologically active phloroglucinol (1,3,5-trihydroxybenzene, THB-OH) and structurally similar 2,4,6-trihydroxypyridine (THP-OH) towards HO˙ were examined. This task was realized by means of density functional theory, through investigation of all favorable antioxidative pathways in two solvents of different polarity: benzene and water. It was found that in benzene both compounds conform to the hydrogen atom transfer (HAT) and radical adduct formation (RAF) mechanisms. In water, the mechanisms of antioxidative action of the investigated compounds are far more complex, especially those of THB-OH. This compound and HO˙ undergo all four investigated mechanisms: HAT, RAF, sequential proton loss electron transfer (SPLET), and single electron transfer-proton transfer (SET-PT). HAT, RAF and SPLET are operative mechanisms in the case of THP-OH. Independently of solvent polarity, both investigated compounds are more reactive towards HO˙ in comparison to Trolox. Our final remark is as follows: the electron-withdrawing effect of the nitrogen is stronger than the electron-donating effect of the OH groups in the molecule of THP-OH. As a consequence, THB-OH is more powerful antioxidant than THP-OH, thus implying that the presence of nitrogen decreases the scavenging capacity of the respective compound.

Concentration Dependence of the Antioxidant and Prooxidant Activity of Trolox in HeLa Cells: Involvement in the Induction of Apoptotic Volume Decrease

Trolox (6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid), a hydrophilic analog of vitamin E, is known for its strong antioxidant activity, being a high radical scavenger of peroxyl and alkoxyl radicals. Under particular conditions, Trolox may also exhibit prooxidant properties. The present work aimed at studying the dual antioxidant/prooxidant behavior of Trolox over a wide range of concentrations (from 2.5 to 160 µM) in HeLa cells. In particular, the study addressed the dose-dependent effects of Trolox on the oxidative cell status and vitality of HeLa cells, focusing on the potential role of the vitamin E analog in the induction of one of the first steps of the apoptotic process, Apoptotic Volume Decrease (AVD). In HeLa cells, Trolox showed significant antioxidant activity, expressed as the ability to reduce the endogenous ROS production detected by the ROS-sensitive probe 5-(and-6)-chloromethyl-2′,7′-dichlorodihydrofluorescein diacetate (CM-H₂DCFDA), at low concentrations (range: 2.5–15 µM), but exerted a dose-dependent prooxidant effect at higher concentrations after 24 h exposure. The prooxidant effect was paralleled by the reduction in cell viability due to the induction of the apoptotic process. The dual behavior, antioxidant at lower concentrations and prooxidant at higher concentrations, was evident also earlier after 2 h incubation, and it was paralleled by the isotonic shrinkage of the cells, ascribed to AVD. The use of SITS, known Cl⁻ channel blocker, was able to completely inhibit the Trolox-induced isotonic cell shrinkage, demonstrating the involvement of the vitamin E analog in the alteration of cell volume homeostasis and, in turn, in the AVD induction. In conclusion, the study shed light on the concentration dependence of the Trolox antioxidant/prooxidant activity in HeLa cells and revealed its role in the induction of one of the first events of apoptosis, AVD, at high concentrations.

Theoretical Study of the Iron Complexes with Aminoguanidine: Investigating Secondary Antioxidant Activity

A thorough analysis of the thermodynamic stability of various complexes of aminoguanidine (AG) with Fe(III) at a physiological pH is presented. Moreover, the secondary antioxidant activity of AG is studied with respect to its kinetic role in the Fe(III) reduction to Fe(II) when reacting with the superoxide radical anion or ascorbate. Calculations are performed at the M05(SMD)/6-311+G(d,p) level of theory. Solvent effects (water) are taken into account in both geometry optimizations and frequency calculations employing the SMD solvation method. Even though the results of this study show that AG can form an extensive number of stable complexes with Fe(III), none of these can reduce the rate constant of the initial step of the Haber-Weiss cycle when the reducing agent is O2•-. However, when the reductant is the ascorbate anion, AG is capable of reducing the rate constant of this reaction significantly, to the point of inhibiting the production of •OH radicals. In fact, the most stable complex of Fe(III) with AG, having a ∆Gf° of -37.9 kcal/mol, can reduce the rate constant of this reaction by 7.9 × 105 times. Thus, AG possesses secondary antioxidant activity relative to the Fe(III)/Fe(II) reduction with ascorbate, but not with O2•-. Similar results have also been found for AG relative to the Cu(II)/Cu(I) reduction, in agreement with experimental results.

Theoretical Study of the Iron Complexes with Lipoic and Dihydrolipoic Acids: Exploring Secondary Antioxidant Activity

The thermodynamic stability of twenty-nine Fe(III) complexes with various deprotonated forms of lipoic (LA) and dihydrolipoic (DHLA) acids, with coordination numbers 4, 5 and 6, is studied at the M06(SMD)/6-31++G(d,p) level of theory in water under physiological pH conditions at 298.15 K. Even though the complexes with LA- are more stable than those with DHLA-, the most thermodynamically stable Fe(III) complexes involve DHLA2-. The twenty-four exergonic complexes are used to evaluate the secondary antioxidant activity of DHLA and LA relative to the Fe(III)/Fe(II) reduction by O2•- and ascorbate. Rate constants for the single-electron transfer (SET) reactions are calculated. The thermodynamic stability of the Fe(III) complexes does not fully correlate with the rate constant of their SET reactions, but more exergonic complexes usually exhibit smaller SET rate constants. Some Cu(II) complexes and their reduction to Cu(I) are also studied at the same level of theory for comparison. The Fe(III) complexes appear to be more stable than their Cu(II) counterparts. Relative to the Fe(III)/Fe(II) reduction with ascorbate, DHLA can fully inhibit the formation of •OH radicals, but not by reaction with O2•-. Relative to the Cu(II)/Cu(I) reduction with ascorbate, the effects of DHLA are moderate/high, and with O2•- they are minor. LA has minor to negligible inhibition effects in all the cases considered.

The Antioxidant Capability of Higenamine: Insights from Theory

Density functional theory was employed to highlight the antioxidant working mechanism of higenamine in aqueous and lipid-like environments. Different reaction mechanisms were considered for the reaction of higenamine with the •OOH radical. The pH values and the molar fraction at physiological pH were determined in aqueous solution. The results show that the preferred reaction mechanism was the hydrogen atom transfer from the catecholic ring. The computed kinetic constants revealed that, in order to obtain reliable results, it is important to consider all the species present in water solution derived from acid-base equilibria. From the present investigation, it emerges that at physiological pH (7.4), the scavenging activity of higenamine against the •OOH radical is higher than that of Trolox, chosen as a reference antioxidant. Furthermore, higenamine results to be more efficient for that purpose than melatonin and caffeine, whose protective action against oxidative stress is frequently associated with their reactive oxygen species (ROS) scavenging activity.