Advances in radical-trapping antioxidant chemistry in the 21st century: a kinetics and mechanisms perspective

Ferroptosis in health and disease

Ferroptosis is a pervasive non-apoptotic form of cell death highly relevant in various degenerative diseases and malignancies. The hallmark of ferroptosis is uncontrolled and overwhelming peroxidation of polyunsaturated fatty acids contained in membrane phospholipids, which eventually leads to rupture of the plasma membrane. Ferroptosis is unique in that it is essentially a spontaneous, uncatalyzed chemical process based on perturbed iron and redox homeostasis contributing to the cell death process, but that it is nonetheless modulated by many metabolic nodes that impinge on the cells' susceptibility to ferroptosis. Among the various nodes affecting ferroptosis sensitivity, several have emerged as promising candidates for pharmacological intervention, rendering ferroptosis-related proteins attractive targets for the treatment of numerous currently incurable diseases. Herein, the current members of a Germany-wide research consortium focusing on ferroptosis research, as well as key external experts in ferroptosis who have made seminal contributions to this rapidly growing and exciting field of research, have gathered to provide a comprehensive, state-of-the-art review on ferroptosis. Specific topics include: basic mechanisms, in vivo relevance, specialized methodologies, chemical and pharmacological tools, and the potential contribution of ferroptosis to disease etiopathology and progression. We hope that this article will not only provide established scientists and newcomers to the field with an overview of the multiple facets of ferroptosis, but also encourage additional efforts to characterize further molecular pathways modulating ferroptosis, with the ultimate goal to develop novel pharmacotherapies to tackle the various diseases associated with - or caused by - ferroptosis.

Ferrostatin-1 mitigates cellular damage in a ferroptosis-like environment in Caenorhabditis elegans

Although iron (Fe) is the most biologically abundant transition metal, it is highly toxic when it accumulates as Fe2+, forming a labile Fe pool and favoring the Fenton reaction. This oxidative scenario leads to a type of caspase-independent programmed cell death, referred to as ferroptosis, where following processes take place: (i) Fe2+ overload, (ii) glutathione peroxidase 4 inactivation, (iii) lipid peroxidation, and (iv) glutathione depletion. The present study sought to evaluate the consequences of Fe2+ administration on ferroptosis induction in Caenorhabditis elegans. We demonstrated higher mortality, increased lipid peroxidation, reduced glutathione peroxidase activity, and morphological damage in dopaminergic neurons upon Fe2+ overload. Pharmacological intervention at the level of lipid peroxidation with ferrostatin-1 (250 μM) mitigated the damage and returned the biochemical parameters to basal levels, revealing the potential of this therapeutical approach. Finally, to assess the relationship between ferroptosis and dopamine in a Parkinsonian background, we evaluated the UA44 worm strain which overexpresses the alpha-synuclein protein in cherry-labeled dopaminergic neurons. We demonstrated that Fe2+ administration reduced lethality associated with similar alterations in biochemical and dopaminergic morphological parameters in wild-type animals. These experiments provide mechanistic-based evidence on the efficacy of a pharmacological approach to mitigate the physiological, biochemical, and morphological consequences of Fe2+ overload. At the same time, they encourage further research on the impact of the combined effects resulting from the genetic background and dopamine signaling in a Parkinsonian phenotype.

Computational assessment of the radical scavenging activity of cleomiscosin

Coumarinolignans such as cleomiscosin A (CMA), cleomiscosin B (CMB), and cleomiscosin C (CMC) are secondary metabolites that were isolated from diverse plant species. Cleomiscosins (CMs) have numerous interesting biological activities, including noteworthy cytotoxicity of cancer cell lines along with hepatoprotective and assumed antioxidant activities. In this present study, the antioxidant properties of three cleomiscosins were investigated with a focus on the structure-activity relationship using thermodynamic and kinetic calculations with the M06-2X/6-311++G(d,p) method. The results show that CMs, including CMA, CMB, and CMC, are weak antioxidants in apolar environments, with k overall of 7.52 × 102 to 6.28 × 104 M-1 s-1 for the HOO˙ radical scavenging reaction in the gas phase and 3.47 × 102 to 6.44 × 104 M-1 s-1 in pentyl ethanoate. Remarkably, the difference in the fusion of phenylpropanoid structure with coumarin via two ortho-hydroxyl groups (CMA and CMB) does not cause any noticeable effect on their antioxidant activity, while the presence of a methoxy substitute on the aromatic ring of phenylpropanoid units (CMC) increases the reaction rate to about 61 to 84 times faster than that of CMA. In contrast, the studied CMs exhibit a good antioxidant capacity in polar environments, with a k overall range from 4.03 × 107 to 8.66 × 107 M-1 s-1, 102-103 times faster than that of Trolox, equal to that of ascorbic acid and resveratrol. The angular fusion of the phenylpropanoid and coumarin structures, as well as the methoxy substitution on the aromatic ring of the phenylpropanoid unit of the studied CMs, do not have any considerable effect on their antioxidant activity under the studied conditions.

Kinetic study of the reaction of thiophene-tocopherols with peroxyl radicals enlightenings the role of O˙⋯S noncovalent interactions in H-atom transfer

Three new α-tocopherol thiophene derivatives were efficiently synthesized, characterized and used for the first time as chain-breaking antioxidants for the inhibition of the autoxidation of reference oxidizable substrates. The rate constant of the reaction with alkylperoxyl (ROO˙) radicals and the stoichiometry of radical trapping (n) for the thiophene-tocopherol compounds were determined by measuring the oxygen consumption during the autoxidation of styrene or isopropylbenzene, using a differential pressure transducer. The measurement of the reaction with ROO˙ radicals in an apolar solvent at 30 °C showed inhibition rate constants (kinh) in the order of 104 M-1 s-1. To rationalise the kinetic results, the effect of the thiophene ring on the H-atom donation by O-H groups of the functionalized tocopherols was investigated by theoretical calculations. The importance of noncovalent interactions (including an unusual O˙⋯S bond) for the stability of the conformers has been shown, and the O-H bond dissociation enthalpy (BDE(OH)) of these derivatives was determined. Finally, the photophysical properties of these new compounds were investigated to understand if the addition of thiophene groups changes the absorption or emission spectra of the tocopherol skeleton for their possible application as luminescent molecular probes.

Oxidative stress modulating nanomaterials and their biochemical roles in nanomedicine

Many pathological conditions are predominantly associated with oxidative stress, arising from reactive oxygen species (ROS); therefore, the modulation of redox activities has been a key strategy to restore normal tissue functions. Current approaches involve establishing a favorable cellular redox environment through the administration of therapeutic drugs and redox-active nanomaterials (RANs). In particular, RANs not only provide a stable and reliable means of therapeutic delivery but also possess the capacity to finely tune various interconnected components, including radicals, enzymes, proteins, transcription factors, and metabolites. Here, we discuss the roles that engineered RANs play in a spectrum of pathological conditions, such as cancer, neurodegenerative diseases, infections, and inflammation. We visualize the dual functions of RANs as both generator and scavenger of ROS, emphasizing their profound impact on diverse cellular functions. The focus of this review is solely on inorganic redox-active nanomaterials (inorganic RANs). Additionally, we deliberate on the challenges associated with current RANs-based approaches and propose potential research directions for their future clinical translation.

Low-Temperature Rapid Polymerization of Intrinsic Conducting PAD/OC Hydrogels with a Self-Adhesive and Sensitive Sensor for Outdoor Damage Repair and Detection

Intrinsic conducting hydrogels fabricated in situ at low temperatures with self-adhesive properties and excellent flexibility hold significant promise for energy applications and outdoor damage repair. However, challenges such as low polymerization rate and self adhesion, insufficient ionic conductivity, inflexibility, and poor stability under extreme cold conditions have hindered their utilization as high-performance sensors. In this study, we designed an intrinsic conducting hydrogel (PADOC) composed of acrylic acid, acryloyloxyethyltrimethylammonium chloride, N,N'-methylenebis(2-propenamide), self-fabricated oxidized curdlan (OC), and a water/glycerol binary solvent. The novel hydrogel exhibited rapid gelation (30 s) at 0 °C facilitated by the promotion of OC, without the need for external energy input. Our findings from FT-IR, NMR, XPS, XRD, EPR spectra, MS, and DSC analyses revealed that OC underwent selective oxidation via the evolved Fenton reaction at 30 °C, serving as bioaccelerators for PAD polymerization. Due to OC's reductive structure and increased solubility, the reaction activation energy of the PAD polymerization reaction significantly reduced from 103.2 to 54.4 kJ/mol. PADOC ionic hydrogels demonstrated an electrical conductivity of 1.00 S/m, 0.7% low hysteresis, 39.6 kPa self-adhesive strength, and 923% strain-at-break and kept even at -20 °C owing to dense hydrogen and ionic bonds between PAD and OC chains. Furthermore, PADOC ionic hydrogels exhibited antifatigue properties for 10 cycles (0-100%) due to electrostatic interactions and hydrogen bonding. Remarkably, using a self-designed device, the rapid polymerization of PADOC effectively repaired copper pipeline leakage under 86 kPa pressure and detected 1% strain variation as a strain sensor. This study opens a new avenue for the rapid gelation of self-adhesive and flexible intrinsic conducting hydrogels with robust sensor performance.

Photocatalytic systems: reactions, mechanism, and applications

The photocatalytic field revolves around the utilization of photon energy to initiate various chemical reactions using non-adsorbing substrates, through processes such as single electron transfer, energy transfer, or atom transfer. The efficiency of this field depends on the capacity of a light-absorbing metal complex, organic molecule, or substance (commonly referred to as photocatalysts or PCs) to execute these processes. Photoredox techniques utilize photocatalysts, which possess the essential characteristic of functioning as both an oxidizing and a reducing agent upon activation. In addition, it is commonly observed that photocatalysts exhibit optimal performance when irradiated with low-energy light sources, while still retaining their catalytic activity under ambient temperatures. The implementation of photoredox catalysis has resuscitated an array of synthesis realms, including but not limited to radical chemistry and photochemistry, ultimately affording prospects for the development of the reactions. Also, photoredox catalysis is utilized to resolve numerous challenges encountered in medicinal chemistry, as well as natural product synthesis. Moreover, its applications extend across diverse domains encompassing organic chemistry and catalysis. The significance of photoredox catalysts is rooted in their utilization across various fields, including biomedicine, environmental pollution management, and water purification. Of course, recently, research has evaluated photocatalysts in terms of cost, recyclability, and pollution of some photocatalysts and dyes from an environmental point of view. According to these new studies, there is a need for critical studies and reviews on photocatalysts and photocatalytic processes to provide a solution to reduce these limitations. As a future perspective for research on photocatalysts, it is necessary to put the goals of researchers on studies to overcome the limitations of the application and efficiency of photocatalysts to promote their use on a large scale for the development of industrial activities. Given the significant implications of the subject matter, this review seeks to delve into the fundamental tenets of the photocatalyst domain and its associated practical use cases. This review endeavors to demonstrate the prospective of a powerful tool known as photochemical catalysis and elucidate its underlying tenets. Additionally, another goal of this review is to expound upon the various applications of photocatalysts.

Selective Binding of Tannic Acid-Conjugated Lipid Nanovesicles to Proline-Rich Proteins Enhances Transdermal Lipophilic-Antioxidant Delivery

Tannic acid (TA) possesses a notable ability to adhere to proline-rich proteins that make up skin cells and the extracellular matrix (ECM) in the skin tissue. Drug carriers with this specific adhesion ability exhibit improved drug delivery efficiency on the skin. Taking advantage of this, this study presents skin-adhesive TA-conjugated lipid nanovesicles (TANVs) for enhanced transdermal antioxidant delivery. We found that TANVs exhibited selective intermolecular interactions with keratinocyte proline-rich proteins (KPRPs) and collagen that makes up skin cells by hydrogen bonding and van der Waals interactions, further enabling the strong bonding to macroscopic skin itself and ECM. We used vitamin E (α-tocopherol), which is known to effectively reduce oxidative stress but has limited skin penetration, as a drug to verify improved in vitro delivery and therapeutic efficacy. The evaluation revealed that the antioxidant-loaded TANVs exerted excellent scavenging effects against reactive oxygen species induced by ultraviolet light or peroxides in the skin, thereby enabling the development of an active drug delivery system for dermal therapy.

Proton-Coupled Electron Transfer and Hydrogen Tunneling in Olive Oil Phenol Reactions

Olive oil phenols are recognized as molecules with numerous positive health effects, many of which rely on their antioxidative activity, i.e., the ability to transfer hydrogen to radicals. Proton-coupled electron transfer reactions and hydrogen tunneling are ubiquitous in biological systems. Reactions of olive oil phenols, hydroxytyrosol, tyrosol, oleuropein, oleacein, oleocanthal, homovanillyl alcohol, vanillin, and a few phenolic acids with a DPPH• (2,2-diphenyl-1-picrylhydrazyl) radical in a 1,4-dioxane:water = 95:5 or 99:1 v/v solvent mixture were studied through an experimental kinetic analysis and computational chemistry calculations. The highest rate constants corresponding to the highest antioxidative activity are obtained for the ortho-diphenols hydroxytyrosol, oleuropein, and oleacein. The experimentally determined kinetic isotope effects (KIEs) for hydroxytyrosol, homovanillyl alcohol, and caffeic acid reactions are 16.0, 15.4, and 16.7, respectively. Based on these KIEs, thermodynamic activation parameters, and an intrinsic bond orbital (IBO) analysis along the IRC path calculations, we propose a proton-coupled electron transfer mechanism. The average local ionization energy and electron donor Fukui function obtained for the phenolic compounds show that the most reactive electron-donating sites are associated with π electrons above and below the aromatic ring, in support of the IBO analysis and proposed PCET reaction mechanism. Large KIEs and isotopic values of Arrhenius pre-exponential factor AH/AD determined for the hydroxytyrosol, homovanillyl alcohol, and caffeic acid reactions of 0.6, 1.3, and 0.3, respectively, reveal the involvement of hydrogen tunneling in the process.

E3 ligases and DUBs target ferroptosis: A potential therapeutic strategy for neurodegenerative diseases

Ferroptosis is a form of cell death mediated by iron and lipid peroxidation (LPO). Recent studies have provided compelling evidence to support the involvement of ferroptosis in the pathogenesis of various neurodegenerative diseases (NDDs), such as Alzheimer's disease (AD), Parkinson's disease (PD). Therefore, understanding the mechanisms that regulate ferroptosis in NDDs may improve disease management. Ferroptosis is regulated by multiple mechanisms, and different degradation pathways, including autophagy and the ubiquitinproteasome system (UPS), orchestrate the complex ferroptosis response by directly or indirectly regulating iron accumulation or lipid peroxidation. Ubiquitination plays a crucial role as a protein posttranslational modification in driving ferroptosis. Notably, E3 ubiquitin ligases (E3s) and deubiquitinating enzymes (DUBs) are key enzymes in the ubiquitin system, and their dysregulation is closely linked to the progression of NDDs. A growing body of evidence highlights the role of ubiquitin system enzymes in regulating ferroptosis sensitivity. However, reports on the interaction between ferroptosis and ubiquitin signaling in NDDs are scarce. In this review, we first provide a brief overview of the biological processes and roles of the UPS, summarize the core molecular mechanisms and potential biological functions of ferroptosis, and explore the pathophysiological relevance and therapeutic implications of ferroptosis in NDDs. In addition, reviewing the roles of E3s and DUBs in regulating ferroptosis in NDDs aims to provide new insights and strategies for the treatment of NDDs. These include E3- and DUB-targeted drugs and ferroptosis inhibitors, which can be used to prevent and ameliorate the progression of NDDs.

Analysis of the Efficiency of Antioxidants in Inhibiting Lipid Oxidation in Terms of Characteristic Kinetic Parameters

In this work, we aim to find physical evidence demonstrating the crucial role that the effective concentration of antioxidants (AOs) present at the interfacial region of emulsions has in controlling the inhibition of the lipid oxidation reaction. We prepared a series of antioxidants of different hydrophobicities derived from chlorogenic and protocatechuic acids. We first monitored, in intact emulsions, the (sigmoidal) production of conjugated dienes and determined the corresponding induction times, tind. Independently, we determined the effective concentrations of the antioxidants in the same intact emulsions. Results show that both the length of the induction periods and the antioxidant interfacial concentrations parallel each other, with a maximum at the octyl-dodecyl derivatives. The ratio between the interfacial antioxidant concentrations and the induction periods remains constant for all AOs in the same series, so that the rates of initiation of lipid oxidation are the same regardless of the hydrophobicity of the antioxidant employed. The constancy in the rate of initiation provides strong experimental evidence for a direct relationship between interfacial concentrations and antioxidant efficiencies. Results suggest new possibilities to investigate lipid peroxidation under non-forced conditions and are of interest to formulators interested in preparing emulsions with antimicrobial properties.

Classification and application of metal-based nanoantioxidants in medicine and healthcare

Antioxidants play an important role in the prevention of oxidative stress and have been widely used in medicine and healthcare. However, natural antioxidants have several limitations such as low stability, difficult long-term storage, and high cost of large-scale production. Along with significant advances in nanotechnology, nanomaterials have emerged as a promising solution to improve the limitations of natural antioxidants because of their high stability, easy storage, time effectiveness, and low cost. Among various types of nanomaterials exhibiting antioxidant activity, metal-based nanoantioxidants show excellent reactivity because of the presence of an unpaired electron in their atomic structure. In this review, we summarize some novel metal-based nanoantioxidants and classify them into two main categories, namely chain-breaking and preventive antioxidant nanomaterials. In addition, the applications of antioxidant nanomaterials in medicine and healthcare are also discussed. This review provides a deeper understanding of the mechanisms of metal-based nanoantioxidants and a guideline for using these nanomaterials in medicine and healthcare.

Ferroptosis mechanisms and its novel potential therapeutic targets for DLBCL

Diffuse large B-cell lymphoma (DLBCL), a heterogeneous lymphoid malignancy, poses a significant threat to human health. The standard therapeutic regimen for patients with DLBCL is rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisone (R-CHOP), with a typical cure rate of 50-70%. However, some patients either relapse after complete remission (CR) or exhibit resistance to R-CHOP treatment. Therefore, novel therapeutic approaches are imperative for managing high-risk or refractory DLBCL. Ferroptosis is driven by iron-dependent phospholipid peroxidation, a process that relies on the transition metal iron, reactive oxygen species (ROS), and phospholipids containing polyunsaturated fatty acids-containing phospholipids (PUFA-PLs). Research indicates that ferroptosis is implicated in various carcinogenic and anticancer pathways. Several hematological disorders exhibit heightened sensitivity to cell death induced by ferroptosis. DLBCL cells, in particular, demonstrate an increased demand for iron and an upregulation in the expression of fatty acid synthase. Additionally, there exists a correlation between ferroptosis-associated genes and the prognosis of DLBCL. Therefore, ferroptosis may be a promising novel target for DLBCL therapy. In this review, we elucidate ferroptosis mechanisms, its role in DLBCL, and the potential therapeutic targets in DLBCL. This review offers novel insights into the application of ferroptosis in treatment strategies for DLBCL.

Recent Advances in Nanomaterials for the Treatment of Acute Kidney Injury

Acute kidney injury (AKI) is a serious clinical syndrome with high morbidity, elevated mortality, and poor prognosis, commonly considered a "sword of Damocles" for hospitalized patients, especially those in intensive care units. Oxidative stress, inflammation, and apoptosis, caused by the excessive production of reactive oxygen species (ROS), play a key role in AKI progression. Hence, the investigation of effective and safe antioxidants and inflammatory regulators to scavenge overexpressed ROS and regulate excessive inflammation has become a promising therapeutic option. However, the unique physiological structure and complex pathological alterations in the kidneys render traditional therapies ineffective, impeding the residence and efficacy of most antioxidant and anti-inflammatory small molecule drugs within the renal milieu. Recently, nanotherapeutic interventions have emerged as a promising and prospective strategy for AKI, overcoming traditional treatment dilemmas through alterations in size, shape, charge, and surface modifications. This Review succinctly summarizes the latest advancements in nanotherapeutic approaches for AKI, encompassing nanozymes, ROS scavenger nanomaterials, MSC-EVs, and nanomaterials loaded with antioxidants and inflammatory regulator. Following this, strategies aimed at enhancing biocompatibility and kidney targeting are introduced. Furthermore, a brief discussion on the current challenges and future prospects in this research field is presented, providing a comprehensive overview of the evolving landscape of nanotherapeutic interventions for AKI.

Antioxidant Polymers with Phenolic Pendants for the Mitigation of Cellular Oxidative Stress

Overproduction of reactive oxygen species (ROS) in cells is a major health concern as it may lead to various diseases through oxidative damage of biomolecules. Commonly used traditional small molecular antioxidants (polyphenols, carotenoids, vitamins, etc.) have inadequate efficacy in lowering excessive levels of ROS due to their poor aqueous solubility and bioavailability. In response to the widespread occurrence of antioxidant polyphenols in various biorenewable resources, we aimed to develop water-soluble antioxidant polymers with side chain phenolic pendants. Four different types of copolymers (P1-P4) containing phenyl rings with different numbers of hydroxy (-OH) substituents (0: phenylalanine, 1: tyrosyl, 2: catechol, or 3: gallol) were synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization with a desired molar mass (8500-10000 g/mol) and a narrow dispersity (Đ ≤ 1.3). After successful characterizations of P1-P4, their in vitro antioxidant properties were analyzed by different methods, including 2,2-diphenyl-1-picrylhydrazyl (DPPH•), 2,2-azino-bis-3-ethylbenzothiazoline-6-sulfonic acid (ABTS•+), 4,4'-diamino-3,3',5,5'-tetramethylbiphenyl (TMB), and β-carotene (βC) assays. Our results revealed that the gallol pendant polymers can effectively scavenge ROS. Furthermore, electron paramagnetic resonance (EPR) spectroscopy with DPPH• also confirmed the radical quenching ability of the synthesized polymers. The gallol pendant polymers, at a well-tolerated concentration, could effectively penetrate the macrophage cells and restore the H2O2-induced ROS to the basal level. Overall, the present approach demonstrates the efficacy of water-soluble antioxidant polymers with gallol pendants toward the mitigation of cellular oxidative stress.

Effect of In Vitro Micropropagation on the Chemical, Antioxidant, and Biological Characteristics of Senecio nutans Sch. Bip., an Endemic Plant of the Atacama Desert Andean Region

The species Senecio nutans Sch. Bip., commonly called "chachacoma", is widely used as a medicinal plant by the Andean communities of Northern Chile. Ethanolic extracts of S. nutans and the main compound, 4-hydroxy-3-(3-methyl-2-butenyl) acetophenone, have shown interesting biological activity. However, due to the high-altitude areas where this species is found, access to S. nutans is very limited. Due to the latter, in this work, we carried out micropropagation in vitro and ex vitro adaptation techniques as an alternative for the massive multiplication, conservation, and in vitro production of high-value metabolites from this plant. The micropropagation and ex vitro adaptation techniques were successfully employed, and UHPLC-DAD analysis revealed no significant changes in the phenolic profile, with acetophenone 4 being the most abundant metabolite, whose antioxidant and antibacterial activity was studied. Independently of the applied culture condition, the ethanolic extracts of S. nutans presented high activity against both Gram-positive and Gram-negative bacteria, demonstrating their antimicrobial capacity. This successful initiation of in vitro and ex vitro cultures provides a biotechnological approach for the conservation of S. nutans and ensures a reliable and consistent source of acetophenone 4 as a potential raw material for pharmacological applications.

Lipid Peroxidation in Muscle Foods: Impact on Quality, Safety and Human Health

The issue of lipid changes in muscle foods under the action of atmospheric oxygen has captured the attention of researchers for over a century. Lipid oxidative processes initiate during the slaughtering of animals and persist throughout subsequent technological processing and storage of the finished product. The oxidation of lipids in muscle foods is a phenomenon extensively deliberated in the scientific community, acknowledged as one of the pivotal factors affecting their quality, safety, and human health. This review delves into the nature of lipid oxidation in muscle foods, highlighting mechanisms of free radical initiation and the propagation of oxidative processes. Special attention is given to the natural antioxidant protective system and dietary factors influencing the stability of muscle lipids. The review traces mechanisms inhibiting oxidative processes, exploring how changes in lipid oxidative substrates, prooxidant activity, and the antioxidant protective system play a role. A critical review of the oxidative stability and safety of meat products is provided. The impact of oxidative processes on the quality of muscle foods, including flavour, aroma, taste, colour, and texture, is scrutinised. Additionally, the review monitors the effect of oxidised muscle foods on human health, particularly in relation to the autooxidation of cholesterol. Associations with coronary cardiovascular disease, brain stroke, and carcinogenesis linked to oxidative stress, and various infections are discussed. Further studies are also needed to formulate appropriate technological solutions to reduce the risk of chemical hazards caused by the initiation and development of lipid peroxidation processes in muscle foods.

Neurotoxicant effects of bisphenol A, nonylphenol, and tert‑butyl phenol in the Nile tilapia (Oreochromis niloticus)

Worldwide production of alkyl phenols and ethoxylated alkyl phenols is high due to their broad industrial uses. It has been widely documented that they are endocrine disruptors, and it has been suggested that they could exert neurotoxic effects. However, a lack of information about the neurotoxic effects of APs and APEs prevails. In this study, the bisphenol A (BPA), 4-nonylphenol (NP), and 3‑tert-butylphenol (tertBP) effects on brain and spinal cord of Nile tilapia exposed to environmental concentrations were evaluated by assessing acetylcholinesterase (AChE), butyrylcholinesterase (BuChE), and carboxylesterases (CES) activities, and γ-aminobutyric acid (GABA) levels and their effects were evaluated by molecular docking. BPA and NP, tertBP behave as agonists and antagonists of AChE, BuChE, CES, and GABA, with notable differences among organs. However, none of these compounds or their metabolites interact with the enzymes' catalytic triad, suggesting an indirect alteration of enzymatic activities. While inhibiting these enzymes stand out hydrophobic interactions with the peripheral anion site, contacts with the inner face of the active site and blocking the mouth of the gorge of the active site, and steric hindrance in the enzyme pocket of glutamate decarboxylase (GAD). In contrast, inductions probably are by homotropic pseudo-cooperative phenomenon, where APEs behave as anchors favoring the active site to remain open and interactions that confer a conservative stabilization of the regulatory domain. Although the results of this study are complex, with notable differences between organs and toxicants, they are some of the first evidence of the neurotoxicity of alkylphenols and their ethoxylated derivatives.

Catalytic Antioxidant Activity of Two Diterpenoid Polyphenols of Rosemary, Carnosol, and Isorosmanol, against Lipid Oxidation in the Presence of Cysteine Thiol

Lamiaceae herbs such as rosemary have excellent antioxidant properties, and lipidic diterpenoid constituents, such as carnosol, are known as characteristic components to exhibit strong antioxidant activity. This study investigates the effect of thiol compounds on the antioxidant properties of diterpenoid polyphenols. The results concerning the antioxidant activity of polyphenols in the presence of thiol showed that two polyphenols, namely, carnosol and isorosmanol, enhanced antioxidant capacity against the radical-induced oxidation of lipids. Further examination of the mechanism revealed that both polyphenols exhibit excellent catalytic antioxidant activity by using the thiol group as a reduction source. Using density functional theory calculations, we attempted to explain why only these two polyphenols exhibit catalytic antioxidant properties. The calculation results and the assumed reaction mechanism suggested that the orthoquinones produced in the antioxidant reactions of carnosol and isorosmanol are more unstable than the others and that the regioselectivity of their reactions with thiols contributes to their catalytic antioxidant properties.

The radical scavenging activity of monocaffeoylquinic acids: the role of neighboring hydroxyl groups and pH levels

Caffeoylquinic acids (CQAs) are well-known antioxidants. However, a key aspect of their radical scavenging activity - the mechanism of action - has not been addressed in detail thus far. Here we report on a computational study of the mechanism of activity of CQAs in scavenging hydroperoxyl radicals. In water at physiological pH, the CQAs demonstrated ≈ 104 times higher HOO˙ antiradical activity than in lipid medium (k(lipid) ≈ 104 M-1 s-1). The activity in the aqueous solution was determined by the hydrogen transfer mechanism of the adjacent hydroxyl group (O6'-H) of the dianion states (Γ = 93.2-95.2%), while the single electron transfer reaction of these species contributed 4.8-6.8% to the total rate constants. The kinetics estimated by the calculations are consistent with experimental findings in water (pH = 7.5), yielding a kcalculated/kexperimental = 2.4, reinforcing the reliability and precision of the computational method and demonstrating its utility for evaluating radical reactions in silico. The results also revealed the pH dependence of the HOO˙ scavenging activity of the CQAs; activity was comparable for all compounds below pH 3, however at higher pH values 5CQA reacted with the HOO˙ with lower activity than 3CQA or 4CQA. It was also found that CQAs are less active than Trolox below pH 4.7, however over pH 5.0 they showed higher activity than the reference. The CQAs had the best HOO˙ antiradical activity at pH values between 5.0 and 8.6. Therefore, in the physiological environment, the hydroperoxyl antiradical capacity of CQAs exhibits similarity to renowned natural antioxidants including resveratrol, ascorbic acid, and Trolox.

Ferroptosis and its modulators: A raising target for cancer and Alzheimer's disease

The process of ferroptosis, a recently identified form of regulated cell death (RCD) is associated with the overloading of iron species and lipid-derived ROS accumulation. Ferroptosis is induced by various mechanisms such as inhibiting system Xc, glutathione depletion, targeting excess iron, and directly inhibiting GPX4 enzyme. Also, ferroptosis inhibition is achieved by blocking excessive lipid peroxidation by targeting different pathways. These mechanisms are often related to the pathophysiology and pathogenesis of diseases like cancer and Alzheimer's. Fundamentally distinct from other forms of cell death, such as necrosis and apoptosis, ferroptosis differs in terms of biochemistry, functions, and morphology. The mechanism by which ferroptosis acts as a regulatory factor in many diseases remains elusive. Studying the activation and inhibition of ferroptosis as a means to mitigate the progression of various diseases is a highly intriguing and actively researched topic. It has emerged as a focal point in etiological research and treatment strategies. This review systematically summarizes the different mechanisms involved in the inhibition and induction of ferroptosis. We have extensively explored different agents that can induce or inhibit ferroptosis. This review offers current perspectives on recent developments in ferroptosis research, highlighting the disease's etiology and presenting references to enhance its understanding. It also explores new targets for the treatment of cancer and Alzheimer's disease.

Interrupted Homolytic Substitution Enables Organoboron Compounds to Inhibit Radical Chain Reactions Rather than Initiate Them

The reactions of organoboranes with peroxyl radicals are key to their use as radical initiators for a vast array of radical chain reactions, particularly at low temperatures where high stereoselectivity or regioselectivity is desired. Whereas these reactions generally proceed via concerted homolytic substitution (SH2) mechanisms, organoboranes that bear groups that can stabilize tetracoordinate boron radical "ate" complexes (e.g., catecholboranes) undergo this reaction via a stepwise addition/fragmentation sequence and serve as useful stoichiometric alkyl radical precursors. Here we show that arylboronic esters and amides derived from catecholborane and diaminonaphthaleneborane, respectively, are potent radical-trapping antioxidants (RTAs). Mechanistic studies reveal that this is because the radical "ate" complexes derived from peroxyl radical addition to boron are sufficiently persistent to trap another radical in an interrupted SH2 reaction. Remarkably, the reactivity of these organoboranes as inhibitors of autoxidation was shown to translate from simple hydrocarbons to the phospholipids of biological membranes such that they can inhibit ferroptosis, the cell death modality driven by lipid autoxidation and relevant in neurodegeneration and other major pathologies. The unique mechanism of these organoboranes is one of only a handful of RTA mechanisms that are not based on H-atom transfer processes and provide a new dimension to boron chemistry and its applications.

Discovery of 4-hydroxyl pyrazole derivatives as potent ferroptosis inhibitors

Ferroptosis, an iron-dependent form of regulated cell death, has been well recognized as a pathogenic mechanism in driving many diseases, such as neurodegenerative disorders, ischemia-reperfusion (I/R) injury. Blocking ferroptosis has been emerging as a feasible therapeutic strategy for the prevention and treatment of these diseases. However, novel potent ferroptosis inhibitors remain to be developed for further clinical applications. In this study, we screened our in-house compound libraries by phenotypic assays and identified a 4-hydroxyl pyrazole derivative HW-3 with good ferroptosis inhibitory activity (EC50 = 120.1 ± 3.5 nM). Based on the structure of HW-3, a series of 4-hydroxyl pyrazole derivatives were further designed and synthesized. Among these compounds, compound 25 could significantly inhibit RSL3-induced ferroptosis with an EC50 value of 8.6 ± 2.2 nM in HT-1080 cells, which was 3-fold more potent than the classical ferroptosis inhibitor ferrostatin-1 (Fer-1) (EC50 = 23.4 ± 1.3 nM). The potent ferroptosis inhibitory activity of compound 25 was further validated in multiple additional cell lines. Our mechanistic study revealed that compound 25 inhibited ferroptosis via intrinsic radical-trapping antioxidative capacity. Taken together, the findings of our study demonstrate 4-hydroxyl pyrazole derivative 25 is a potent ferroptosis inhibitor, which holds a great therapeutic potential for further development.

The Theoretical and Experimental Insights into the Radical Scavenging Activity of Rubiadin

Rubiadin (RBD), an anthraquinone derivative, is obtained from Rubia cordifolia, a plant species classified under the Rubiaceae family. Rubiadin has proven beneficial properties, such as anticancer, neuroprotective, anti-inflammatory, and antidiabetic activity. The antioxidant activity of this molecule was suggested by some experimental results but has not been clearly established thus far. In this study, we employ DFT calculations to comprehensively assess the mechanism and kinetics of the HO•/HOO• radical scavenging activity of this compound in relation to solvents. RBD showed moderate HO• radical scavenging activity, with rate constants of 2.95 × 108 and 1.82 × 1010 M-1 s-1 in lipid and polar media, respectively. In the aqueous solution, the compound exhibited remarkable superoxide anion radical scavenging activity (k = 4.93 × 108 M-1 s-1) but modest HOO• antiradical activity. RBD also showed promising antiradical activity against a variety of radicals (CCl3O•, CCl3OO•, NO2, SO4•-, and N3•), while experimental and computational results confirmed that RBD has moderate activity in DPPH/ABTS•+ assays. Thus, RBD is predicted to be a good, albeit selective, radical scavenger.

Modulation of terpenoid indole alkaloid pathway via elicitation with phytosynthesized silver nanoparticles for the enhancement of ajmalicine, a pharmaceutically important alkaloid

MAIN CONCLUSION

The use of silver nanoparticles as elicitors in cell cultures of Rauwolfia serpentina resulted in increased levels of ajmalicine, upregulated structural and regulatory genes, elevated MDA content, and reduced activity of antioxidant enzymes. These findings hold potential for developing a cost-effective method for commercial ajmalicine production. Plants possess an intrinsic ability to detect various stress signals, prompting the activation of defense mechanisms through the reprogramming of metabolites to counter adverse conditions. The current study aims to propose an optimized bioprocess for enhancing the content of ajmalicine in Rauwolfia serpentina callus through elicitation with phytosynthesized silver nanoparticles. Initially, callus lines exhibiting elevated ajmalicine content were established. Following this, a protocol for the phytosynthesis of silver nanoparticles using seed extract from Rauwolfia serpentina was successfully standardized. The physicochemical attributes of the silver nanoparticles were identified, including their spherical shape, size ranging from 6.7 to 28.8 nm in diameter, and the presence of reducing-capping groups such as amino, carbonyl, and amide. Further, the findings indicated that the presence of 2.5 mg L-1 phytosynthesized silver nanoparticles in the culture medium increased the ajmalicine content. Concurrently, structural genes (TDC, SLS, STR, SGD, G10H) and regulatory gene (ORCA3) associated with the ajmalicine biosynthetic pathway were observed to be upregulated. A notable increase in MDA content and a decrease in the activities of antioxidant enzymes were observed. A notable increase in MDA content and a decrease in the activities of antioxidant enzymes were also observed. Our results strongly recommend the augmentation of ajmalicine content in the callus culture of R. serpentina through supplementation with silver nanoparticles, a potential avenue for developing a cost-effective process for the commercial production of ajmalicine.

A Comprehensive Study of the Radical Scavenging Activity of Rosmarinic Acid

Rosmarinic acid (RA) is reported in separate studies to be either an inducer or reliever of oxidative stress, and this contradiction has not been resolved. In this study, we present a comprehensive examination of the radical scavenging activity of RA using density functional theory calculations in comparison with experimental data. In model physiological media, RA exhibited strong HO• radical scavenging activity with overall rate constant values of 2.89 × 1010 and 3.86 × 109 M-1 s-1. RA is anticipated to exhibit excellent scavenging properties for HOO• in an aqueous environment (koverall = 3.18 × 108 M-1 s-1, ≈2446 times of Trolox) following the hydrogen transfer and single electron transfer pathways of the dianion state. The neutral form of the activity is equally noteworthy in a lipid environment (koverall = 3.16 × 104 M-1 s-1) by the formal hydrogen transfer mechanism of the O6(7,15,16)-H bonds. Chelation with RA may prevent Cu(II) from reduction by the ascorbic acid anion (AA-), hence blocking the OIL-1 pathway, suggesting that RA in an aqueous environment also serves as an OIL-1 antioxidant. The computational findings exhibit strong concurrence with the experimental observations, indicating that RA possesses a significant efficacy as a radical scavenger in physiological environments.

Some Aspects of α-(Acyloxy)alkyl Radicals in Organic Synthesis

The preparation and use of α-(acyloxy)alkyl xanthates to generate and capture α-(acyloxy)alkyl radicals is briefly reviewed. Their inter- and intramolecular additions to both activated and unactivated, electronically unbiased, alkenes, and to (hetero)aromatic rings, as well as their radical allylation and vinylation reactions are described. Application to the total synthesis of two 4-hydroxytetralone natural products is also presented.

Fermentation of Robinia pseudoacacia flower for improving the antioxidation: optimized conditions, active composition, mechanism, and biotransformation process

Robinia pseudoacacia flower is a natural product with many biological activities, including antioxidation. To further develop its antioxidation, the extract was fermented by Aspergillus niger FFCC 3112 in the medium with carbon to nitrogen ratio of 1.4:1 and initial pH of 4.2 for 3.5 days to form the best antioxidant activity of the fermentation product by strain screening, single factor optimization, and response surface methodology. Further analysis, isolation and activity determination showed that a main chemical component, kaempferol-3-O-α-L-rhamnopyranosyl-(1→6)-β-D-galactopyranosyl-7-O-α-L-rhamnopyranoside, in the extract was completely hydrolyzed to kaempferol-7-O-α-L-rhamnopyranoside and kaempferol with better antioxidant activity through biotransformation, which was the basis for improving the antioxidant activity of fermentation products. Moreover, the mechanism of antioxidant and the contribution of phenolic hydroxyl groups were investigated by density functional theory. The result indicated that the antioxidant capacity of kaempferol-7-O-α-L-rhamnopyranoside and kaempferol increased with the increase of solvent polarity. In high-polarity solvents, they mainly scavenge free radicals through single electron transfer followed by proton transfer.

Antiradical Activity of Lignans from Cleistanthus sumatranus: Theoretical Insights into the Mechanism, Kinetics, and Solvent Effects

Sumatranus lignans (SL) isolated from Cleistanthus sumatranus have demonstrated bioactivities, e.g., they were shown to exhibit immunosuppressive properties in previous research. Their structure suggests potential antioxidant activity that has not attracted any attention thus far. Consistently, a comprehensive analysis of the antioxidant activity of these compounds is highly desirable with the view of prospective medical applications. In this work, the mechanism and kinetics of the antiradical properties of SL against hydroperoxyl radicals were studied by using calculations based on density functional theory (DFT). In the lipid medium, it was discovered that SL reacted with HOO• through the formal hydrogen transfer mechanism with a rate constant of 101-105 M-1 s-1, whereas in aqueous media, the activity primarily occurred through the sequential proton loss electron transfer mechanism with rate constants of 102-108 M-1 s-1. In both lipidic and aqueous environments, the antiradical activity of compounds 6 and 7 exceeds that of resveratrol, ascorbic acid, and Trolox. These substances are therefore predicted to be good radical scavengers in physiological environments.

Lipid Peroxidation and Antioxidant Protection

Lipid peroxidation (LP) is the most important type of oxidative-radical damage in biological systems, owing to its interplay with ferroptosis and to its role in secondary damage to other biomolecules, such as proteins. The chemistry of LP and its biological consequences are reviewed with focus on the kinetics of the various processes, which helps understand the mechanisms and efficacy of antioxidant strategies. The main types of antioxidants are discussed in terms of structure-activity rationalization, with focus on mechanism and kinetics, as well as on their potential role in modulating ferroptosis. Phenols, pyri(mi)dinols, antioxidants based on heavy chalcogens (Se and Te), diarylamines, ascorbate and others are addressed, along with the latest unconventional antioxidant strategies based on the double-sided role of the superoxide/hydroperoxyl radical system.

Leveraging the Persistent Radical Effect in the Synthesis of trans-2,3-Diaryl Dihydrobenzofurans

A simple method for accessing trans-2,3-diaryl dihydrobenzofurans is reported. This approach leverages the equilibrium between quinone methide dimers and their persistent radicals. This equilibrium is disrupted by phenols that yield comparatively transient phenoxyl radicals, leading to cross-coupling between the persistent and transient radicals. The resultant quinone methides with pendant phenols rapidly cyclize to form dihydrobenzofurans (DHBs). This putative biomimetic access to dihydrobenzofurans provides superb functional group tolerance and a unified approach for the synthesis of resveratrol-based natural products.

The role of ferroptosis in intervertebral disc degeneration

Nucleus pulposus, annulus fibrosus, and cartilage endplate constitute an avascular intervertebral disc (IVD), which is crucial for spinal and intervertebral joint mobility. As one of the most widespread health issues worldwide, intervertebral disc degeneration (IVDD) is recognized as a key contributor to back and neck discomfort. A number of degenerative disorders have a strong correlation with ferroptosis, a recently identified novel regulated cell death (RCD) characterized by an iron-dependent mechanism and a buildup of lipid reactive oxygen species (ROS). There is growing interest in the part ferroptosis plays in IVDD pathophysiology. Inhibiting ferroptosis has been shown to control IVDD development. Several studies have demonstrated that in TBHP-induced oxidative stress models, changes in ferroptosis marker protein levels and increased lipid peroxidation lead to the degeneration of intervertebral disc cells, which subsequently aggravates IVDD. Similarly, IVDD is significantly relieved with the use of ferroptosis inhibitors. The purpose of this review was threefold: 1) to discuss the occurrence of ferroptosis in IVDD; 2) to understand the mechanism of ferroptosis and its role in IVDD pathophysiology; and 3) to investigate the feasibility and prospect of ferroptosis in IVDD treatment.

A DFT Study on the Kinetics of HOO•, CH3OO•, and O2•- Scavenging by Quercetin and Flavonoid Catecholic Metabolites

Reaction kinetics have been theoretically examined to ascertain the potency of quercetin (Q) and flavonoid catecholic metabolites 1-5 in the inactivation of HOO^•, CH₃OO^•, and O₂^•- under physiological conditions. In lipidic media, the koverallTST/Eck rate constants for the proton-coupled electron transfer (PCET) mechanism indicate the catecholic moiety of Q and 1-5 as the most important in HOO^• and CH₃OO^• scavenging. 5-(3,4-Dihydroxyphenyl)-γ-valerolactone (1) and alphitonin (5) are the most potent scavengers of HOO^• and CH₃OO^•, respectively. The koverallMf rate constants, representing actual behavior in aqueous media, reveal Q as more potent in the inactivation of HOO^• and CH₃OO^• via single electron transfer (SET). SET from 3-O^- phenoxide anion of Q, a structural motif absent in 1-5, represents the most contributing reaction path to overall activity. All studied polyphenolics have a potency of O₂^•- inactivation via a concerted two-proton-coupled electron transfer (2PCET) mechanism. The obtained results indicate that metabolites with notable radical scavenging potency, and more bioavailability than ingested flavonoids, may contribute to human health-promoting effects ascribed to parent molecules.

Recapitulating Antioxidant and Antibacterial Compounds into a Package for Tissue Regeneration: Dual Function Materials with Synergistic Effect

Oxidative damage and infection can prevent or delay tissue repair. Moreover, infection reinforces reactive oxygen species (ROS) formation, which makes the wound's condition even worse. Therefore, the need for antioxidant and antibacterial agents is felt for tissue regeneration. There are emerging up-and-coming biomaterials that recapitulate both properties into a package, offering an effective solution to turn the wound back into a healing state. In this article, the principles of antioxidant and antibacterial activity are summarized. The review starts with biological aspects, getting the readers to familiarize themselves with tissue barriers against infection. This is followed by the chemistry and mechanism of action of antioxidant and antibacterial materials (dual function). Eventually, the outlook and challenges are underlined to provide where the dual-function biomaterials are and where they are going in the future. It is expected that the present article inspires the designing of dual-function biomaterials to more advanced levels by providing the fundamentals and comparative points of view and paving the clinical way for these materials.

Combination Chemotherapy with Selected Polyphenols in Preclinical and Clinical Studies-An Update Overview

This review article describes studies published over the past five years on the combination of polyphenols, which are the most studied in the field of anticancer effects (curcumin, quercetin, resveratrol, epigallocatechin gallate, and apigenin) and chemotherapeutics such as cisplatin, 5-fluorouracil, oxaliplatin, paclitaxel, etc. According to WHO data, research has been limited to five cancers with the highest morbidity rate (lung, colorectal, liver, gastric, and breast cancer). A systematic review of articles published in the past five years (from January 2018 to January 2023) was carried out with the help of all Web of Science databases and the available base of clinical studies. Based on the preclinical studies presented in this review, polyphenols can enhance drug efficacy and reduce chemoresistance through different molecular mechanisms. Considering the large number of studies, curcumin could be a molecule in future chemotherapy cocktails. One of the main problems in clinical research is related to the limited bioavailability of most polyphenols. The design of a new co-delivery system for drugs and polyphenols is essential for future clinical research. Some polyphenols work in synergy with chemotherapeutic drugs, but some polyphenols can act antagonistically, so caution is always required.

Ferroptosis: A flexible constellation of related biochemical mechanisms

It is common to think about and depict biological processes as being governed by fixed pathways with specific components interconnected by concrete positive and negative interactions. However, these models may fail to effectively capture the regulation of cell biological processes that are driven by chemical mechanisms that do not rely absolutely on specific metabolites or proteins. Here, we discuss how ferroptosis, a non-apoptotic cell death mechanism with emerging links to disease, may be best understood as a highly flexible mechanism that can be executed and regulated by many functionally related metabolites and proteins. The inherent plasticity of ferroptosis has implications for how to define and study this mechanism in healthy and diseased cells and organisms.

Linkage and Stereochemistry Characters of Phenolic Antioxidant Product Formation

The present study developed a smart and novel strategy to elucidate the linkage and stereochemistry characters during phenolic antioxidant product formation. A series of phenolic isomers or analogues were treated with 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide radical, to create 16 antioxidant dimerization reactions in aqueous solution. The products were rapidly identified by ultraperformance liquid chromatography coupled with electrospray ionization quadrupole time-of-flight tandem mass-spectrometry. Through a systematic function-structure relationship analysis of these reactions and theoretical calculations, it is concluded that the phenolic antioxidant product is formed via linear linkage or furanocyclic linkage. The linear linkage is fulfilled via a radical coupling and controlled by the O-O linkage exclusion, meta-linkage exclusion, and catechol-activated principles. However, when an exocyclic π-bond conjugates with the phenolic core and is affixed at the -OH para-position, the furanocyclic linkage may occur via a subsequent intramolecular Michael addition. The intramolecular addition always lacks Re-attack to show "α,β diastereoselectivity." The α,β diastereoselectivity is the stereochemistry character of furanocyclic linkage during phenolic antioxidant product formation. All these novel findings can benefit not only the field food science but also other fields as well.

General Approach to Identify, Assess, and Characterize Inhibitors of Lipid Peroxidation and Associated Cell Death

Lipid peroxidation (LPO) is associated with a variety of pathologies and drives a form of regulated necrosis called ferroptosis. There is much interest in small-molecule inhibitors of LPO as potential leads for therapeutic development for neurodegeneration, stroke, and acute organ failure, but this has been hampered by the lack of a universal high-throughput assay that can identify and assess candidates. Herein, we describe the development and validation of such an approach. Phosphatidylcholine liposomes loaded with ∼10% phospholipid hydroperoxide and STY-BODIPY, a fluorescent signal carrier that co-autoxidizes with polyunsaturated phospholipids, are shown to autoxidize at convenient and constant rates when subjected to an optimized Fe²⁺-based initiation cocktail. The use of this initiation system enables the identification of each of the various classes of LPO inhibitors which have been shown to rescue from cell death in ferroptosis: radical-trapping antioxidants (RTAs), peroxidase mimics, and iron chelators. Furthermore, a limited dose-response profile of inhibitors enables the resolution of RTA and non-RTA inhibitors─thereby providing not only relative efficacy but mechanistic information in the same microplate-based experiment. Despite this versatility, the approach can still be used to estimate rate constants for the reaction of RTAs with chain-propagating peroxyl radicals, as demonstrated for a representative panel of RTAs. To illustrate the utility of this assay, we carried out a preliminary investigation of the 'off-target' activity of several ferroptosis suppressors that have been proposed to act independently of inhibition of LPO, including lipoxygenase inhibitors, cannabinoids, and necrostatins, the archetype inhibitors of necroptosis.

Polyunsaturated Fatty Acids Drive Lipid Peroxidation during Ferroptosis

Ferroptosis is a form of regulated cell death that is intricately linked to cellular metabolism. In the forefront of research on ferroptosis, the peroxidation of polyunsaturated fatty acids has emerged as a key driver of oxidative damage to cellular membranes leading to cell death. Here, we review the involvement of polyunsaturated fatty acids (PUFAs), monounsaturated fatty acids (MUFAs), lipid remodeling enzymes and lipid peroxidation in ferroptosis, highlighting studies revealing how using the multicellular model organism Caenorhabditis elegans contributes to the understanding of the roles of specific lipids and lipid mediators in ferroptosis.

Theoretical study on the free radical scavenging potency and mechanism of natural coumestans: Roles of substituent, noncovalent interaction and solvent

The free radical scavenging potency and mechanisms of seven representative natural coumestans were systematically evaluated using density functional theory (DFT) approach. Thermodynamic feasibility of different mechanisms was assessed by various physio-chemical descriptors involved in the double (2H⁺/2e^‒) radical-trapping processes. Energy diagram and related transition state structures of the reaction between wedelolactone (WEL) and hydroperoxyl radical were constructed to further uncover the radical-trapping details. Results showed that the studied coumestans prefer to scavenge radicals via formal hydrogen atom transfer (fHAT) mechanism in the gas phase and non-polar environment, whereas sequential proton loss electron transfer (SPLET) is favored in polar media. Moreover, the feasibility of second fHAT and SPLET processes was also revealed. Sequential double proton loss double electron transfer (SdPLdET) mechanism represents the preferred pathway in aqueous solution at physiological pH. Our findings highlight the essential role of ortho-dihydroxyl group, noncovalent interaction and solvents on radical-trapping potency. 4'-OH in D-ring was found to be the most favorable site to trap radical for most of the studied coumestans, whereas 3-OH in A-ring for lucernol (LUN).

Molecular Design of Interfaces of Model Food Nanoemulsions: A Combined Experimental and Theoretical Approach

The composition and structure of the interfacial region of emulsions frequently determine its functionality and practical applications. In this work, we have integrated theory and experiments to enable a detailed description of the location and orientation of antioxidants in the interfacial region of olive-oil-in-water nanoemulsions (O/W) loaded with the model gallic acid (GA) antioxidant. For the purpose, we determined the distribution of GA in the intact emulsions by employing the well-developed pseudophase kinetic model, as well as their oxidative stability. We also determined, by employing an in silico design, the radial distribution functions of GA to gain insights on its insertion depth and on its orientation in the interfacial region. Both theoretical and experimental methods provide comparable and complementary results, indicating that most GA is located in the interfacial region (~81.2%) with a small fraction in the aqueous (~18.82%). Thus, GA is an effective antioxidant to inhibit lipid oxidation in emulsions not only because of the energy required for its reaction with peroxyl radical is much lower than that between the peroxyl radical and the unsaturated lipid but also because its effective concentration in the interfacial region is much higher than the stoichiometric concentration. The results demonstrate that the hybrid approach of experiments and simulations constitutes a complementary and useful pathway to design new, tailored, functionalized emulsions to minimize lipid oxidation.

Modulation of the chain-breaking antioxidant activity of phenolic organochalcogens with various co-antioxidants at various pH values

Phenolic organochalcogen chain-breaking antioxidants, i.e. 6-bromo-8 (hexadecyltellanyl)-3,3-dimethyl-1,5-dihydro-[1,3]dioxepino[5,6-c]pyridin-9-ol and 2-methyl-2,3-dihydrobenzo[b]selenophene-5-ol, have been investigated in a two-phase (chlorobenzene/water) lipid peroxidation model system as potent inhibitors of lipid peroxyl radicals with various co-antioxidants at various pH values. The pH has a significant effect on the chain-breaking antioxidant activities of phenolic organochalcogens. The key chain-breaking mechanism profile was attributed to the first oxygen atom transfer from the lipid peroxyl radicals to the Se/Te atom, followed by hydrogen atom transfer in a solvent cage from the nearby phenolic group to the resulting alkoxyl radical. Finally, regeneration of organochalcogen antioxidants could take place in the presence of aqueous-soluble co-antioxidants. Also, in the presence of aqueous soluble N-acetylcysteine at pH 1-7, both antioxidants behaved as very good inhibitors of lipid peroxyl radicals. The role of aqueous soluble mild co-antioxidants in the regeneration studies of organochalcogen antioxidants has been investigated in a two-phase lipid peroxidation model system. The importance of the phase transfer catalyst has been explored in the inhibition studies of selenium containing antioxidants using an Fe(II) source. The overall pH-dependent antioxidant activities of organochalcogens depend on their hydrogen atom transfer ability, relative stability, and distribution in the aqueous/lipid phase.

Rational Design of a Low-Data Regime of Pyrrole Antioxidants for Radical Scavenging Activities Using Quantum Chemical Descriptors and QSAR with the GA-MLR and ANN Concepts

A series of pyrrole derivatives and their antioxidant scavenging activities toward the superoxide anion (O₂^•-), hydroxyl radical (^•OH), and 1,1-diphenyl-2-picryl-hydrazyl (DPPH^•) served as the training data sets of a quantitative structure-activity relationship (QSAR) study. The steric and electronic descriptors obtained from quantum chemical calculations were related to the three O₂^•-, ^•OH, and DPPH^• scavenging activities using the genetic algorithm combined with multiple linear regression (GA-MLR) and artificial neural networks (ANNs). The GA-MLR models resulted in good statistical values; the coefficient of determination (R²) of the training set was greater than 0.8, and the root mean square error (RMSE) of the test set was in the range of 0.3 to 0.6. The main molecular descriptors that play an important role in the three types of antioxidant activities are the bond length, HOMO energy, polarizability, and AlogP. In the QSAR-ANN models, a good R² value above 0.9 was obtained, and the RMSE of the test set falls in a similar range to that of the GA-MLR models. Therefore, both the QSAR GA-MLR and QSAR-ANN models were used to predict the newly designed pyrrole derivatives, which were developed based on their starting reagents in the synthetic process.

Reactions of nicotine and the hydroxyl radical in the environment: Theoretical insights into the mechanism, kinetics and products

Nicotine (NCT) is a prevalent and highly poisonous tobacco alkaloid found in wastewater discharge. Advanced oxidative processes (AOP) are radical interactions between harmful pollutants and ambient free radicals that, theoretically, result in less toxic compounds. For a better understanding of the chemical transformations and long-term environmental effects of toxic discharges, the study of these processes is crucial. Here, quantum chemical calculations are used to investigate the AOP of the NCT in aqueous and lipidic environments. It was found that NCT interacted with HO^• in polar and nonpolar media, with an overall rate constant k_overall = 10⁶ - 10¹⁰ M^-1 s^-1. The computed kinetic data are reasonably accurate as seen by the comparison with the experimental rate constant in water (pH = 7.0), which results in a k_calculated/k_experimetal ratio of 1.4. The hydrogen transfer (C7, C9, C12)-single electron transfer pathways are the main mechanisms for the HO^• + NCT reaction in pentyl ethanoate solvent to form the cations as the primary products of the two-step reaction. However, in aqueous environments, the degradation of NCT by HO^• radicals increases with increasing pH levels. It is predicted that oxidation products are less toxic than nicotine itself, especially in an aqueous environment with a pH < 7.0.

The xanthate route to tetralones, tetralins, and naphthalenes. A brief account

The present account summarises routes to tetralones, tetralines, and naphthalenes based on the chemistry of xanthates developed in the authors' laboratory. The degenerative reversible transfer of xanthates allows radical addition even to unactivated, electronically unbiased alkenes, and tolerates a broad range of functional groups, in particular common polar groups such as esters, ketones, nitriles, amides, carbamates, etc. Xanthates also allow radical ring closures onto aromatic rings. This feature, in combination with the intermolecular addition to alkenes, can be used to construct tetralones and tetralines. With the appropriate appendages, the former can be converted into napthalenes with a variety of substitution patterns. This translates into a convergent approach to a vast array of building blocks of interest to the pharmaceutical and agrochemical industries, and to material sciences.

The NLRP1 and CARD8 inflammasomes detect reductive stress

The danger signals that activate the related nucleotide-binding domain leucine-rich repeat pyrin domain-containing 1 (NLRP1) and caspase activation and recruitment domain-containing 8 (CARD8) inflammasomes have not been fully established. We recently reported that the oxidized form of TRX1 binds to NLRP1 and represses inflammasome activation. These findings suggested that intracellular reductive stress, which would reduce oxidized TRX1 and thereby abrogate the NLRP1-TRX1 interaction, is an NLRP1 inflammasome-activating danger signal. However, no agents that induce reductive stress were known to test this premise. Here, we identify and characterize several radical-trapping antioxidants, including JSH-23, that induce reductive stress. We show that these compounds accelerate the proteasome-mediated degradation of the repressive N-terminal fragments of both NLRP1 and CARD8, releasing the inflammasome-forming C-terminal fragments from autoinhibition. Overall, this work validates chemical probes that induce reductive stress and establishes reductive stress as a danger signal sensed by both the NLRP1 and CARD8 inflammasomes.