Redox lipidomics and adductomics - Advanced analytical strategies to study oxidized lipids and lipid-protein adducts

Lipid metabolism in ferroptosis: mechanistic insights and therapeutic potential

Ferroptosis, an iron-dependent form of regulated cell death driven by lipid peroxidation, plays a pivotal role in various physiological and pathological processes. In this review, we summarize the core mechanisms of ferroptosis, emphasizing its intricate connections to lipid metabolism, including fatty acid synthesis, phospholipid remodeling, and oxidation dynamics. We further highlight advancements in detection technologies, such as fluorescence imaging, lipidomics, and in vivo PET imaging, which have deepened our understanding of ferroptotic regulation. Additionally, we discuss the role of ferroptosis in human diseases, where it acts as a double-edged sword, contributing to cancer cell death while also driving ischemia-reperfusion injury and neurodegeneration. Finally, we explore therapeutic strategies aimed at either inducing or inhibiting ferroptosis, including iron chelation, antioxidant modulation, and lipid-targeted interventions. By integrating mechanistic insights, disease relevance, and therapeutic potential, this review provides a comprehensive perspective on ferroptosis as a crucial interface between lipid metabolism and oxidative stress.

Advances in clinical application of lipidomics in healthy ageing and healthy longevity medicine

It is imperative to optimise health and healthspan across the lifespan. The accumulation of reactive oxygen species (ROS) has been implicated in the hallmarks of ageing and inhibiting ROS production can potentially delay ageing whilst increasing healthy longevity. Lipids and lipid mediators (derivatives of lipids) are becoming increasingly recognized as central molecule in tissue and cellular function and are susceptible to peroxidation; hence linked with ageing. Lipid classes implicated in the ageing process include sterols, glycerophospholipids, sphingolipids and the oxidation products of polyunsaturated fatty acids but these are not yet translated into the clinic. Further mechanistic studies are required for the understanding of lipid classes in the ageing process. Lipidomics, the system level characterisation of lipid species with respect to metabolism and function, might provide a significant and useful biological age profiling tool through longitudinal studies. Lipid profiles in different ages among healthy individuals could be harnessed as lipid biomarkers of healthy ageing with potential integration for the development of lipid-based ageing clock (lipid clock). The potential of a lipid clock includes the prediction of future morbidity or mortality, which will promote precision and healthy longevity medicine.

Oxylipin profiling for clinical research: Current status and future perspectives

Oxylipins are potent lipid mediators with increasing interest in clinical research. They are usually measured in systemic circulation and can provide a wealth of information regarding key biological processes such as inflammation, vascular tone, or blood coagulation. Although procedures still require harmonization to generate comparable oxylipin datasets, performing comprehensive profiling of circulating oxylipins in large studies is feasible and no longer restricted by technical barriers. However, it is essential to improve and facilitate the biological interpretation of complex oxylipin profiles to truly leverage their potential in clinical research. This requires regular updating of our knowledge about the metabolism and the mode of action of oxylipins, and consideration of all factors that may influence circulating oxylipin profiles independently of the studied disease or condition. This review aims to provide the readers with updated and necessary information regarding oxylipin metabolism, their different forms in systemic circulation, the current limitations in deducing oxylipin cellular effects from in vitro bioactivity studies, the biological and technical confounding factors needed to consider for a proper interpretation of oxylipin profiles.

Defining roles of specific reactive oxygen species (ROS) in cell biology and physiology

'Reactive oxygen species' (ROS) is a generic term that defines a wide variety of oxidant molecules with vastly different properties and biological functions that range from signalling to causing cell damage. Consequently, the description of oxidants needs to be chemically precise to translate research on their biological effects into therapeutic benefit in redox medicine. This Expert Recommendation article pinpoints key issues associated with identifying the physiological roles of oxidants, focusing on H₂O₂ and O₂^.-. The generic term ROS should not be used to describe specific molecular agents. We also advocate for greater precision in measurement of H₂O₂, O₂^.- and other oxidants, along with more specific identification of their signalling targets. Future work should also consider inter-organellar communication and the interactions of redox-sensitive signalling targets within organs and whole organisms, including the contribution of environmental exposures. To achieve these goals, development of tools that enable site-specific and real-time detection and quantification of individual oxidants in cells and model organisms are needed. We also stress that physiological O₂ levels should be maintained in cell culture to better mimic in vivo redox reactions associated with specific cell types. Use of precise definitions and analytical tools will help harmonize research among the many scientific disciplines working on the common goal of understanding redox biology.

Reaction dynamics and residue identification of haemoglobin modification by acrolein, a lipid-peroxidation by-product

BACKGROUND

Lipid hydroperoxides decompose to reactive aldehydes, such as acrolein. Measurement of oxidative stress markers in the clinic could improve risk stratification for patients.

METHODS

To aid the development of diagnostic oxidative stress markers, we defined the acrolein modifications of haemoglobin using mass spectrometry.

RESULTS

Acrolein modifications have little effect on the secondary structure of haemoglobin. They do not disrupt the quaternary structure, but instead promote crosslinked octamers. For acrolein modified haemoglobin the response to O2 binding is altered such that cooperativity is lost. Mass spectrometry experiments at a 1:1 acrolein:haemoglobin molar ratio demonstrate that the α-chain quickly forms an aza-Michael adduct (+56 Da), which then forms a more stable adduct, Nε-(3-methylpyridinium)lysine (MP-lysine, +76 Da) over 7 days. The β-chain remains relatively unchanged over the duration of the 7 days and the aza-Michael adduct is dominant. At 2:1 and 5:1 molar ratios the α-chain was consistently modified at K7, H20, H50, and the β-chain at C93 and H97 with the aza-Michael adduct. Beyond 5 h, an MP-adduct (+76 Da) was located predominantly at K7 of the α-chain, while an FDP-adduct (+94 Da) was observed at K95 of the β-chain.

CONCLUSIONS

We have generated qualitative evidence identifying the acrolein target sites on haemoglobin, a potential oxidative stress marker that is easily measured in circulation.

GENERAL SIGNIFICANCE

We provide data for the community to develop targeted mass spectrometric or immunometric assays for acrolein modified haemoglobin to further validate the potential of haemoglobin as an oxidative stress marker in patients .

Lipid oxidation that is, and is not, inhibited by vitamin E: Consideration about physiological functions of vitamin E

Lipids are oxidized in vivo by multiple oxidizing species with different properties, some by regulated manner to produce physiological mediators, while others by random mechanisms to give detrimental products. Vitamin E plays an important role as a physiologically essential antioxidant to inhibit unregulated lipid peroxidation by scavenging lipid peroxyl radicals to break chain propagation independent of the type of free radicals which induce chain initiation. Kinetic data suggest that vitamin E does not act as an efficient scavenger of nitrogen dioxide radical, carbonate anion radical, and hypochlorite. The analysis of regio- and stereo-isomer distribution of the lipid oxidation products shows that, apart from lipid oxidation by CYP enzymes, the free radical-mediated lipid peroxidation is the major pathway of lipid oxidation taking place in humans. Compared with healthy subjects, the levels of racemic and trans,trans-hydro (pero)xyoctadecadienoates, specific biomarker of free radical lipid oxidation, are elevated in the plasma of patients including atherosclerosis and non-alcoholic fatty liver diseases. α-Tocopherol acts as a major antioxidant, while γ-tocopherol scavenges nitrogen dioxide radical, which induces lipid peroxidation, nitration of aromatic compounds and unsaturated fatty acids, and isomerization of cis-fatty acids to trans-fatty acids. It is essential to appreciate that the antioxidant effects of vitamin E depend on the nature of both oxidants and substrates being oxidized. Vitamin E, together with other antioxidants such as vitamin C, contributes to the inhibition of detrimental oxidation of biological molecules and thereby to the maintenance of human health and prevention of diseases.

Pre-analytical monitoring and protection of oxidizable lipids in human plasma (vitamin E and ω-3 and ω-6 fatty acids): An update for redox-lipidomics methods

Sample manipulation for storage and storage itself, interfere with the stability of labile lipids in human plasma, including vitamin E (α-tocopherol), polyunsaturated fatty acids (PUFAs), and their enzymatic and free radical-derived oxidation metabolites. This remains a main limit of lipidomics studies that often lack of sufficient standardization and validation at the pre-analytical level. In order to characterize the stability of these lipids in human plasma and to develop a standardized pre-analytical protocol for lipidomics methods, the oxidation metabolites of α-tocopherol, the free form of ω3 and ω6 PUFAs, and some arachidonic acid (AA)-derived eicosanoids were investigated in human plasma during storage at different freezing temperatures. The effect of a protection/defense cocktail of antioxidants and lipoxygenase inhibitors (PD solution) on these lipid parameters was also evaluated. The temperature of storage markedly affected the formation of α-tocopheryl quinone (α-TQ), the main lipoperoxyl radical-derived oxidation metabolite of vitamin E, with the lowest production rate observed in samples stored at -80 °C or in liquid nitrogen. A similar effect of the storage temperature was observed for the free form of the ω-3 species eicosapentaenoic and docosahexaenoic acid, and for the ω-6 AA. Freezing samples at -20 °C resulted in a time-dependent formation of the pro-inflammatory eicosanoid LTB4. The PD solution prevents non-specific alterations of these lipid parameters in samples that are processed for direct analysis and protects from the temperature-dependent modifications of free PUFAs. Combining PD solution and preservation at -80 °C or in liquid nitrogen, resulted in levels of α-TQ and PUFAs that remained stable over 1 month and up to 8 months of storage, respectively. This method paper provides indications for the optimal processing and storage of human plasma utilized in lipidomics studies.

New insights into human prefrontal cortex aging with a lipidomics approach

INTRODUCTION

Human prefrontal cortex (hPFC) is a recent evolutionarily developed brain region involved in cognitive functions. Human cognitive functions decline during aging. Yet the molecular mechanisms underlying the functional deterioration of the neural cells of this brain region still remain to be fully described.

AREAS COVERED

In this review, we explore the role of lipids in hPFC aging. Firstly, we briefly consider the approaches used to identify lipid species in brain tissue with special attention paid to a lipidomics analysis. Then, as the evolution process has conferred a specific lipid profile on the hPFC, we consider the lipidome of hPFC. In addition, the role of lipids in hPFC aging, and in particular, the cognitive decline associated with aging, is discussed. Finally, nutritional and pharmacological interventions designed to modulate this process are examined. It is suggested that the dysfunction of key cellular processes secondarily to the damage of lipid membrane underlies the cognitive decline of hPFC during aging.

EXPERT OPINION

Lipidomics methods are and will continue to be key tools in the effort to gain additional insights into the aging of the human brain.

Investigating metabolism by mass spectrometry: From steady state to dynamic view

Metabolism is the set of life-sustaining reactions in organisms. These biochemical reactions are organized in metabolic pathways, in which one metabolite is converted through a series of steps catalyzed by enzymes in another chemical compound. Metabolic reactions are categorized as catabolic, the breaking down of metabolites to produce energy, and/or anabolic, the synthesis of compounds that consume energy. The balance between catabolism of the preferential fuel substrate and anabolism defines the overall metabolism of a cell or tissue. Metabolomics is a powerful tool to gain new insights contributing to the identification of complex molecular mechanisms in the field of biomedical research, both basic and translational. The enormous potential of this kind of analyses consists of two key aspects: (i) the possibility of performing so-called targeted and untargeted experiments through which it is feasible to verify or formulate a hypothesis, respectively, and (ii) the opportunity to run either steady-state analyses to have snapshots of the metabolome at a given time under different experimental conditions or dynamic analyses through the use of labeled tracers. In this review, we will highlight the most important practical (e.g., different sample extraction approaches) and conceptual steps to consider for metabolomic analysis, describing also the main application contexts in which it is used. In addition, we will provide some insights into the most innovative approaches and progress in the field of data analysis and processing, highlighting how this part is essential for the proper extrapolation and interpretation of data.

Metabolic indices of polyunsaturated fatty acids: current evidence, research controversies, and clinical utility

The n-3 and n-6 polyunsaturated fatty acids (PUFA) are among the most studied nutrients in human metabolism. In the past few decades, prospective studies and controlled trials have supported the view that the effects of these essential fatty acids are clinically relevant. PUFA profiles in different blood compartments are reflections of both diet and metabolism, and their levels may be related to disease risk. Despite widespread interest, there is no consensus regarding which biomarkers best reflect PUFA status in the body. The measurement of PUFA levels is not straight-forward, and a wide variety of indices have been used in clinical studies, producing conflicting results. A major source of heterogeneity among studies is associated with research design, sampling, and laboratory analyses. To date, the n-3 index, n-6/n-3 ratio, and arachidonic acid (AA)/eicosapentaenoic acid (EPA) ratio are the most promising biomarkers associated with PUFA metabolism. Although hotly debated, these indices may be considered at least markers, if not risk factors, for several diseases, especially cardiovascular events and brain disorders. Here, we summarize the most updated evidence of n-3 and n-6 PUFA effects on human health, reviewing current controversies on the aforementioned indices and whether they can be considered valuable predictors of clinical outcomes.

Redox Epiphospholipidome in Programmed Cell Death Signaling: Catalytic Mechanisms and Regulation

A huge diversification of phospholipids, forming the aqueous interfaces of all biomembranes, cannot be accommodated within a simple concept of their role as membrane building blocks. Indeed, a number of signaling functions of (phospho)lipid molecules has been discovered. Among these signaling lipids, a particular group of oxygenated polyunsaturated fatty acids (PUFA), so called lipid mediators, has been thoroughly investigated over several decades. This group includes oxygenated octadecanoids, eicosanoids, and docosanoids and includes several hundreds of individual species. Oxygenation of PUFA can occur when they are esterified into major classes of phospholipids. Initially, these events have been associated with non-specific oxidative injury of biomembranes. An alternative concept is that these post-synthetically oxidatively modified phospholipids and their adducts with proteins are a part of a redox epiphospholipidome that represents a rich and versatile language for intra- and inter-cellular communications. The redox epiphospholipidome may include hundreds of thousands of individual molecular species acting as meaningful biological signals. This review describes the signaling role of oxygenated phospholipids in programs of regulated cell death. Although phospholipid peroxidation has been associated with almost all known cell death programs, we chose to discuss enzymatic pathways activated during apoptosis and ferroptosis and leading to peroxidation of two phospholipid classes, cardiolipins (CLs) and phosphatidylethanolamines (PEs). This is based on the available LC-MS identification and quantitative information on the respective peroxidation products of CLs and PEs. We focused on molecular mechanisms through which two proteins, a mitochondrial hemoprotein cytochrome c (cyt c), and non-heme Fe lipoxygenase (LOX), change their catalytic properties to fulfill new functions of generating oxygenated CL and PE species. Given the high selectivity and specificity of CL and PE peroxidation we argue that enzymatic reactions catalyzed by cyt c/CL complexes and 15-lipoxygenase/phosphatidylethanolamine binding protein 1 (15LOX/PEBP1) complexes dominate, at least during the initiation stage of peroxidation, in apoptosis and ferroptosis. We contrast cell-autonomous nature of CLox signaling in apoptosis correlating with its anti-inflammatory functions vs. non-cell-autonomous ferroptotic signaling facilitating pro-inflammatory (necro-inflammatory) responses. Finally, we propose that small molecule mechanism-based regulators of enzymatic phospholipid peroxidation may lead to highly specific anti-apoptotic and anti-ferroptotic therapeutic modalities.