Resolving the Role of Lipoxygenases in the Initiation and Execution of Ferroptosis

Threshold protective effect of deuterated polyunsaturated fatty acids on peroxidation of lipid bilayers

Autoxidation of polyunsaturated fatty acids (PUFAs) damages lipid membranes and generates numerous toxic by-products implicated in neurodegeneration, aging, and other pathologies. Abstraction of bis-allylic hydrogen atoms is the rate-limiting step of PUFA autoxidation, which is inhibited by replacing bis-allylic hydrogens with deuterium atoms (D-PUFAs). In cells, the presence of a relatively small fraction of D-PUFAs among natural PUFAs is sufficient to effectively inhibit lipid peroxidation (LPO). Here, we investigate the effect of various D-PUFAs on the stability of liposomes under oxidative stress conditions. The permeability of vesicle membranes to fluorescent dyes was measured as a proxy for bilayer integrity, and the formation of conjugated dienes was monitored as a proxy for LPO. Remarkably, both approaches reveal a similar threshold for the protective effect of D-PUFAs in liposomes. We show that protection rendered by D-PUFAs depends on the structure of the deuterated fatty acid. Our findings suggest that protection of PUFAs against autoxidation depends on the total level of deuterated bi-sallylic (CD₂ ) groups present in the lipid bilayer. However, the phospholipid containing 6,6,9,9,12,12,15,15,18,18-d₁₀ -docosahexaenoic acid exerts a stronger protective effect than should be expected from its deuteration level. These findings further support the application of D-PUFAs as preventive/therapeutic agents in numerous pathologies that involve LPO.

Ferroptosis is a type of autophagy-dependent cell death

Macroautophagy (hereafter referred to as autophagy) involves an intracellular degradation and recycling system that, in a context-dependent manner, can either promote cell survival or accelerate cellular demise. Ferroptosis was originally defined in 2012 as an iron-dependent form of cancer cell death different from apoptosis, necrosis, and autophagy. However, this latter assumption came into question because, in response to ferroptosis activators (e.g., erastin and RSL3), autophagosomes accumulate, and because components of the autophagy machinery (e.g., ATG3, ATG5, ATG4B, ATG7, ATG13, and BECN1) contribute to ferroptotic cell death. In particular, NCOA4-facilitated ferritinophagy, RAB7A-dependent lipophagy, BECN1-mediated system x_c^- inhibition, STAT3-induced lysosomal membrane permeabilization, and HSP90-associated chaperone-mediated autophagy can promote ferroptosis. In this review, we summarize current knowledge on the signaling pathways involved in ferroptosis, while focusing on the regulation of autophagy-dependent ferroptotic cell death. The molecular comprehension of these phenomena may lead to the development of novel anticancer therapies.

Role of GPX4 in ferroptosis and its pharmacological implication

Ferroptosis is a non-apoptotic form of cell death characterized by iron-dependent lipid peroxidation and metabolic constraints. Dependence on NADPH/H⁺, polyunsaturated fatty acid metabolism, and the mevalonate and glutaminolysis metabolic pathways have been implicated in this novel form of regulated necrotic cell death. Genetic studies performed in cells and mice established the selenoenzyme glutathione peroxidase (GPX4) as the key regulator of this form of cell death. Besides these genetic models, the identification of a series of small molecule ferroptosis-specific inhibitors and inducers have not only helped in the delineation of the molecular underpinnings of ferroptosis but they might also prove highly beneficial when tipping the balance between cell death inhibition and induction in the context of degenerative diseases and cancer, respectively. In the latter, the recent recognition that a subset of cancer cell lines including certain triple negative breast cancer cells and those of therapy-resistant high-mesenchymal cell state present a high dependence on this lipid make-up offers unprecedented opportunities to eradicate difficult to treat cancers. Due to the rapidly growing interest in this form of cell death, we provide an overview herein what we know about this field today and its future translational impact.

Striking while the iron is hot: Iron metabolism and ferroptosis in neurodegeneration

Perturbations in iron homeostasis and iron accumulation feature in several neurodegenerative disorders including Alzheimer's disease (AD), Parkinson's disease (PD) and Amyotrophic lateral sclerosis (ALS). Proteins such as α-synuclein, tau and amyloid precursor protein that are pathologically associated with neurodegeneration are involved in molecular crosstalk with iron homeostatic proteins. Quantitative susceptibility mapping, an MRI based non-invasive technique, offers proximal evaluations of iron load in regions of the brain and powerfully predicts cognitive decline. Further, small molecules that target elevated iron have shown promise against PD and AD in preclinical studies and clinical trials. Despite these strong links between altered iron homeostasis and neurodegeneration the molecular biology to describe the association between enhanced iron levels and neuron death, synaptic impairment and cognitive decline is ill defined. In this review we discuss the current understanding of brain iron homeostasis and how it may be perturbed under pathological conditions. Further, we explore the ramifications of a novel cell death pathway called ferroptosis that has provided a fresh impetus to the "metal hypothesis" of neurodegeneration. While lipid peroxidation plays a central role in the execution of this cell death modality the removal of iron through chelation or genetic modifications appears to extinguish the ferroptotic pathway. Conversely, tissues that harbour elevated iron may be predisposed to ferroptotic damage. These emerging findings are of relevance to neurodegeneration where ferroptotic signalling may offer new targets to mitigate cell death and dysfunction.

Ferroptosis and Brain Injury

Ferroptosis is a nonapoptotic form of cell death characterized by the iron-dependent accumulation of toxic lipid reactive oxygen species. Small-molecule screening and subsequent optimization have yielded potent and specific activators and inhibitors of this process. These compounds have been employed to dissect the lethal mechanism and implicate this process in pathological cell death events observed in many tissues, including the brain. Indeed, ferroptosis is emerging as an important mechanism of cell death during stroke, intracerebral hemorrhage, and other acute brain injuries, and may also play a role in certain degenerative brain disorders. Outstanding issues include the practical need to identify molecular markers of ferroptosis that can be used to detect and study this process in vivo, and the more basic problem of understanding the relationship between ferroptosis and other forms of cell death that can be triggered in the brain during injury.

Mechanisms of Ferroptosis and Relations With Regulated Cell Death: A Review

Ferroptosis is a newly identified form of nonapoptotic regulated cell death (RCD) characterized by iron-dependent accumulation of lipid peroxides. It is morphologically and biochemically different from known types of cell death. Ferroptosis plays a vital role in the treatment of tumors, renal failure, and ischemia reperfusion injury (IRI). Inhibition of glutathione peroxidase 4 (GPX4), starvation of cysteine, and peroxidation of arachidonoyl (AA) trigger ferroptosis in the cells. Iron chelators, lipophilic antioxidants, and specific inhibitor prevent ferroptosis. Although massive researches have demonstrated the importance of ferroptosis in human, its mechanism is not really clear. In this review, we distanced ourselves from this confusion by dividing the mechanisms of ferroptosis into two aspects: processes that facilitate the formation of lipid peroxides and processes that suppress the reduction of lipid peroxides. At the same time, we summarize the relations between ferroptosis and several types of cell death.

Ischemia-induced ACSL4 activation contributes to ferroptosis-mediated tissue injury in intestinal ischemia/reperfusion

Ferroptosis is a recently identified form of regulated cell death defined by the iron-dependent accumulation of lipid reactive oxygen species. Ferroptosis has been studied in various diseases such as cancer, Parkinson's disease, and stroke. However, the exact function and mechanism of ferroptosis in ischemia/reperfusion (I/R) injury, especially in the intestine, remains unknown. Considering the unique conditions required for ferroptosis, we hypothesize that ischemia promotes ferroptosis immediately after intestinal reperfusion. In contrast to conventional strategies employed in I/R studies, we focused on the ischemic phase. Here we verified ferroptosis by assessing proferroptotic changes after ischemia along with protein and lipid peroxidation levels during reperfusion. The inhibition of ferroptosis by liproxstatin-1 ameliorated I/R-induced intestinal injury. Acyl-CoA synthetase long-chain family member 4 (ACSL4), which is a key enzyme that regulates lipid composition, has been shown to contribute to the execution of ferroptosis, but its role in I/R needs clarification. In the present study, we used rosiglitazone (ROSI) and siRNA to inhibit ischemia/hypoxia-induced ACSL4 in vivo and in vitro. The results demonstrated that ACSL4 inhibition before reperfusion protected against ferroptosis and cell death. Further investigation revealed that special protein 1 (Sp1) was a crucial transcription factor that increased ACSL4 transcription by binding to the ACSL4 promoter region. Collectively, this study demonstrates that ferroptosis is closely associated with intestinal I/R injury, and that ACSL4 has a critical role in this lethal process. Sp1 is an important factor in promoting ACSL4 expression. These results suggest a unique and effective mechanistic approach for intestinal I/R injury prevention and treatment.

Ferroptosis: The Greasy Side of Cell Death

Ferroptosis is a form of cell death that requires phospholipid peroxidation and has attracted increased attention, both as a means to eradicate tumors resistant to standard chemotherapy and for its potential contribution to tissue damage such as in ischemia/reperfusion. The center stage taken by phospholipid peroxidation in ferroptosis is highlighted by recent discoveries that demonstrate an intricate regulation of both the metabolism of polyunsaturated fatty acids as well as mechanisms leading to their oxidation. These metabolic steps converge at the point of ferroptosis execution through mechanisms that are now only starting to be understood. In this short review, we provide an appraisal of some of the recent advances in the understanding of the ferroptosis process and also provide some perspectives of where this knowledge could take us.

Excitotoxicity, neuroinflammation and oxidant stress as molecular bases of epileptogenesis and epilepsy-derived neurodegeneration: The role of vitamin E

Glutamate-mediated excitotoxicity, neuroinflammation, and oxidative stress are common underlying events in neurodegeneration. This pathogenic "triad" characterizes the neurobiology of epilepsy, leading to seizure-induced cell death, increased susceptibility to neuronal synchronization and network alterations. Along with other maladaptive changes, these events pave the way to spontaneous recurrent seizures and progressive degeneration of the interested brain areas. In vivo models of epilepsy are available to explore such epileptogenic mechanisms, also assessing the efficacy of chemoprevention and therapy strategies at the pre-clinical level. The kainic acid model of pharmacological excitotoxicity and epileptogenesis is one of the most investigated mimicking the chronicization profile of temporal lobe epilepsy in humans. Its pathogenic cues include inflammatory and neuronal death pathway activation, mitochondrial disturbances and lipid peroxidation of several regions of the brain, the most vulnerable being the hippocampus. The importance of neuroinflammation and lipid peroxidation as underlying molecular events of brain damage was demonstrated in this model by the possibility to counteract the related maladaptive morphological and functional changes of this organ with vitamin E, the main fat-soluble cellular antioxidant and "conditional" co-factor of enzymatic pathways involved in polyunsaturated lipid metabolism and inflammatory signaling. The present review paper provides an overview of the literature supporting the potential for a timely intervention with vitamin E therapy in clinical management of seizures and epileptogenic processes associated with excitotoxicity, neuroinflammation and lipid peroxidation, i.e. the pathogenic "triad".

Ferroptosis and necroinflammation, a yet poorly explored link

Ferroptosis is a non-apoptotic form of cell death characterized by overwhelming iron-dependent lipid peroxidation, which contributes to a number of pathologies, most notably tissue ischemia/reperfusion injury, neurodegeneration and cancer. Cysteine availability, glutathione biosynthesis, polyunsaturated fatty acid metabolism and modulation of the phospholipidome are the key events of this necrotic cell death pathway. Non-enzymatic and enzymatic lipoxygenase (LOX)-mediated lipid peroxidation of lipid bilayers is efficiently counteracted by the glutathione (GSH)/glutathione peroxidase 4 (GPX4) axis. Preliminary studies suggest that bursting ferroptotic cells release pro-inflammatory damage-associated molecular patterns (DAMPs) that trigger the innate immune system as exemplified by diseased kidney and brain tissues where ferroptosis contributes to organ demise in a predominant manner. The GSH/GPX4 node is known to control the activities of LOX and prostaglandin-endoperoxide synthase (PTGS) via the so-called peroxide tone. Since LOX and PTGS products do have pro- and anti-inflammatory effects, one may speculate that these enzymes contribute to the ferroptotic process on several levels in cell-autonomous and non-autonomous ways. Hence, this review provides the reader with an outline on what is currently known about the link between ferroptosis and necroinflammation and discusses critical events that may alert the innate immune system in early phases when cells become sensitized towards ferroptosis.

Deuterated Arachidonic Acids Library for Regulation of Inflammation and Controlled Synthesis of Eicosanoids: An In Vitro Study

The synthesis of signal lipids, including eicosanoids, is not fully understood, although it is key to the modulation of various inflammatory states. Recently, isotopologues of essential polyunsaturated fatty acids (PUFAs) deuterated at bis-allylic positions (D-PUFAs) have been proposed as inhibitors of non-enzymatic lipid peroxidation (LPO) in various disease models. Arachidonic acid (AA, 20:4 n-6) is the main precursor to several classes of eicosanoids, which are produced by cyclooxygenases (COX) and lipoxygenases (LOX). In this study we analyzed the relative activity of human recombinant enzymes COX-2, 5-LOX, and 15-LOX-2 using a library of arachidonic acids variably deuterated at the bis-allylic (C7, C10, and C13) positions. Kinetic parameters (KM, V_max) and isotope effects calculated from kH/kD for seven deuterated arachidonic acid derivatives were obtained. Spectroscopic methods have shown that deuteration at the 13th position dramatically affects the kinetic parameters of COX-2 and 15-LOX-2. The activity of 5-LOX was evaluated by measuring hydroxyeicosatetraenoic acids (8-HETE and 5-HETE) using ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). Deuteration at the seventh and 10th positions affects the performance of the 5-LOX enzyme. A flowchart is proposed suggesting how to modulate the synthesis of selected eicosanoids using the library of deuterated isotopologues to potentially fine-tune various inflammation stages.

Spatio-temporal monitoring of lipid peroxyl radicals in live cell studies combining fluorogenic antioxidants and fluorescence microscopy methods

Lipid peroxidation of polyunsaturated fatty acids in cells may occur via their catalytic autoxidation through peroxyl radicals under oxidative stress conditions. Lipid peroxidation is related to a number of pathologies, and may be invoked in new forms of regulated cell death, yet it may also have beneficial roles in cell signaling cascades. Antioxidants are a natural line of defense against lipid peroxidation, and may accordingly impact the biological outcome associated with the redox chemistry of lipid peroxidation. Critical to unraveling the physiological and pathological role of lipid peroxidation is the development of novel probes with the partition, chemical sensitivity and more importantly, molecular specificity, enabling the spatial and temporal imaging of peroxyl radicals in the lipid membranes of live cells, reporting on the redox status of the cell membrane. This review describes our recent progress to visualize lipid peroxidation in model membrane systems and in live cell studies. Our work portrays the mechanistic insight leading to the development of a highly sensitive probe to monitor lipid peroxyl radicals (LOO^•). It also describes technical aspects including reagents and fluorescence microscopy methodologies to consider in order to achieve the much sought after monitoring of rates of lipid peroxyl radical production in live cell studies, be it under oxidative stress but also under cell homeostasis. This review seeks to bring attention to the study of lipid redox reactions and to lay the groundwork for the adoption of fluorogenic antioxidant probeshancement and maximum intensity recorded in turn provide a benchmark to estimate, when compared to the control BODIPY dye lacking the intramolecular PeT based switch, the overall exte and related fluorescence microscopy methods toward gaining rich spatiotemporal information on lipid peroxidation in live cells.

Ferroptosis and Its Role in Diverse Brain Diseases

Ferroptosis is a recently identified, iron-regulated, non-apoptotic form of cell death. It is characterized by cellular accumulation of lipid reactive oxygen species that ultimately leads to oxidative stress and cell death. Although first identified in cancer cells, ferroptosis has been shown to have significant implications in several neurologic diseases, such as ischemic and hemorrhagic stroke, Alzheimer's disease, and Parkinson's disease. This review summarizes current research on ferroptosis, its underlying mechanisms, and its role in the progression of different neurologic diseases. Understanding the role of ferroptosis could provide valuable information regarding treatment and prevention of these devastating diseases.

The clinical relevance of necroinflammation-highlighting the importance of acute kidney injury and the adrenal glands

Necroinflammation is defined as the inflammatory response to necrotic cell death. Different necrotic cell death pathways exhibit different immune reponses, despite a comparable level of intracellular content release (referred to as damage associated molecular patterns or DAMPs). In addition to DAMP release, which is inevitably associated with necrotic cell death, the active production of pro/anti-inflammatory cytokines characterizes certain necrotic pathways. Necroptosis, ferroptosis and pyroptosis, therefore, are immunogenic to a different extent. In this review, we discuss the clinical relevance of necroinflammation highlighting potential human serum markers. We focus on the role of the adrenal glands and the lungs as central organs affected by systemic and/or local DAMP release and underline their role in intensive care medicine. In addition, data from models of acute kidney injury (AKI) and kidney transplantation have significantly shaped the field of necroinflammation and may be helpful for the understanding of the potential role of dialysis and plasma exchange to treat ongoing necroinflammation upon intensive care unit (ICU) conditions. In conclusion, we are only beginning to understand the importance of necroinflammation in diseases and transplantation, including xenotransplantation. However, given the existing efforts to develop inhibitors of necrotic cell death (ferrostatins, necrostatins, etc), we consider it likely that interference with necroinflammation reaches clinical routine in the near future.

Vitamin E hydroquinone is an endogenous regulator of ferroptosis via redox control of 15-lipoxygenase

Ferroptosis is a form of programmed cell death associated with inflammation, neurodegeneration, and ischemia. Vitamin E (alpha-tocopherol) has been reported to prevent ferroptosis, but the mechanism by which this occurs is controversial. To elucidate the biochemical mechanism of vitamin E activity, we systematically investigated the effects of its major vitamers and metabolites on lipid oxidation and ferroptosis in a striatal cell model. We found that a specific endogenous metabolite of vitamin E, alpha-tocopherol hydroquinone, was a dramatically more potent inhibitor of ferroptosis than its parent compound, and inhibits 15-lipoxygenase via reduction of the enzyme's non-heme iron from its active Fe3+ state to an inactive Fe2+ state. Furthermore, a non-metabolizable isosteric analog of vitamin E which retains antioxidant activity neither inhibited 15-lipoxygenase nor prevented ferroptosis. These results call into question the prevailing model that vitamin E acts predominantly as a non-specific lipophilic antioxidant. We propose that, similar to the other lipophilic vitamins A, D and K, vitamin E is instead a pro-vitamin, with its quinone/hydroquinone metabolites responsible for its anti-ferroptotic cytoprotective activity.

Tryparedoxin peroxidase-deficiency commits trypanosomes to ferroptosis-type cell death

Tryparedoxin peroxidases, distant relatives of glutathione peroxidase 4 in higher eukaryotes, are responsible for the detoxification of lipid-derived hydroperoxides in African trypanosomes. The lethal phenotype of procyclic Trypanosoma brucei that lack the enzymes fulfils all criteria defining a form of regulated cell death termed ferroptosis. Viability of the parasites is preserved by α-tocopherol, ferrostatin-1, liproxstatin-1 and deferoxamine. Without protecting agent, the cells display, primarily mitochondrial, lipid peroxidation, loss of the mitochondrial membrane potential and ATP depletion. Sensors for mitochondrial oxidants and chelatable iron as well as overexpression of a mitochondrial iron-superoxide dismutase attenuate the cell death. Electron microscopy revealed mitochondrial matrix condensation and enlarged cristae. The peroxidase-deficient parasites are subject to lethal iron-induced lipid peroxidation that probably originates at the inner mitochondrial membrane. Taken together, ferroptosis is an ancient cell death program that can occur at individual subcellular membranes and is counterbalanced by evolutionary distant thiol peroxidases.

Plants, animals and fungi all belong to a group of organisms known as eukaryotes. Their cells host a variety of compartments, with each having a specific role. For example, mitochondria are tasked with providing the energy that powers most of the processes that keep the cell alive. Membranes delimit these compartments, as well as the cells themselves.

Iron is an element needed for chemical reactions that are essential for the cell to survive. Yet, the byproducts of these reactions can damage – ‘oxidize’ – the lipid molecules that form the cell’s membranes, including the one around mitochondria. Unless enzymes known as peroxidases come to repair the oxidized lipids, the cell dies in a process called ferroptosis. Scientists know that this death mechanism is programmed into the cells of humans and other complex eukaryotes.

However, Bogacz and Krauth-Siegel wanted to know if ferroptosis also exists in creatures that appeared early in the evolution of eukaryotes, such as the trypanosome Trypanosoma brucei. This single-cell parasite causes sleeping sickness in humans and a disease called nagana in horses and cattle. Before it infects a mammal, T. brucei goes through an ‘insect stage’ where it lives in the tsetse fly; there, it relies on its mitochondrion to produce energy.

Bogacz and Krauth-Siegel now show that if the parasites in the insect stage do not have a specific type of peroxidases, they die within a few hours. In particular, problems in the membranes of the mitochondrion stop the compartment from working properly. These peroxidases-free trypanosomes fare better if they are exposed to molecules that prevent iron from taking part in the reactions that can harm lipids. They also survive more if they are forced to create large amounts of an enzyme that relies on iron to protect the mitochondrion against oxidation. Finally, using drugs that prevent ferroptosis in human cells completely rescues these trypanosomes. Taken together, the results suggest that ferroptosis is an ancient cell death program which exists in T. brucei; and that, in the insect stage of the parasite's life cycle, this process first damages the mitochondrion.

This last finding could be particularly relevant because the role of mitochondria in ferroptosis in mammals is highly debated. Yet, most of the research is done in cells that do not rely on this cellular compartment to get their energy. During their life cycle, trypanosomes are either dependent on their mitochondria, or they can find their energy through other sources: this could make them a good organism in which to dissect the precise mechanisms of ferroptosis.

Regulation of lipid peroxidation and ferroptosis in diverse species

This review by Conrad et al. reviews the functions and regulation of lipid peroxidation, ferroptosis, and the antioxidant network in diverse species, including humans, other mammals and vertebrates, plants, invertebrates, yeast, bacteria, and archaea, and discusses the potential evolutionary roles of lipid peroxidation and ferroptosis.

Lipid peroxidation is the process by which oxygen combines with lipids to generate lipid hydroperoxides via intermediate formation of peroxyl radicals. Vitamin E and coenzyme Q₁₀ react with peroxyl radicals to yield peroxides, and then these oxidized lipid species can be detoxified by glutathione and glutathione peroxidase 4 (GPX4) and other components of the cellular antioxidant defense network. Ferroptosis is a form of regulated nonapoptotic cell death involving overwhelming iron-dependent lipid peroxidation. Here, we review the functions and regulation of lipid peroxidation, ferroptosis, and the antioxidant network in diverse species, including humans, other mammals and vertebrates, plants, invertebrates, yeast, bacteria, and archaea. We also discuss the potential evolutionary roles of lipid peroxidation and ferroptosis.

Targeting Nrf2 to Suppress Ferroptosis and Mitochondrial Dysfunction in Neurodegeneration

Ferroptosis is a newly described form of regulated cell death, distinct from apoptosis, necroptosis and other forms of cell death. Ferroptosis is induced by disruption of glutathione synthesis or inhibition of glutathione peroxidase 4, exacerbated by iron, and prevented by radical scavengers such as ferrostatin-1, liproxstatin-1, and endogenous vitamin E. Ferroptosis terminates with mitochondrial dysfunction and toxic lipid peroxidation. Although conclusive identification of ferroptosis in vivo is challenging, several salient and very well established features of neurodegenerative diseases are consistent with ferroptosis, including lipid peroxidation, mitochondrial disruption and iron dysregulation. Accordingly, interest in the role of ferroptosis in neurodegeneration is escalating and specific evidence is rapidly emerging. One aspect that has thus far received little attention is the antioxidant transcription factor nuclear factor erythroid 2-related factor 2 (Nrf2). This transcription factor regulates hundreds of genes, of which many are either directly or indirectly involved in modulating ferroptosis, including metabolism of glutathione, iron and lipids, and mitochondrial function. This potentially positions Nrf2 as a key deterministic component modulating the onset and outcomes of ferroptotic stress. The minimal direct evidence currently available is consistent with this and indicates that Nrf2 may be critical for protection against ferroptosis. In contrast, abundant evidence demonstrates that enhancing Nrf2 signaling is potently neuroprotective in models of neurodegeneration, although the exact mechanism by which this is achieved is unclear. Further studies are required to determine to extent to which the neuroprotective effects of Nrf2 activation involve the prevention of ferroptosis.

Unsolved mysteries: How does lipid peroxidation cause ferroptosis?

Ferroptosis is a cell death process driven by damage to cell membranes and linked to numerous human diseases. Ferroptosis is caused by loss of activity of the key enzyme that is tasked with repairing oxidative damage to cell membranes—glutathione peroxidase 4 (GPX4). GPX4 normally removes the dangerous products of iron-dependent lipid peroxidation, protecting cell membranes from this type of damage; when GPX4 fails, ferroptosis ensues. Ferroptosis is distinct from apoptosis, necroptosis, necrosis, and other modes of cell death. Several key mysteries regarding how cells die during ferroptosis remain unsolved. First, the drivers of lipid peroxidation are not yet clear. Second, the subcellular location of lethal lipid peroxides remains an outstanding question. Finally, how exactly lipid peroxidation leads to cell death is an unsolved mystery. Answers to these questions will provide insights into the mechanisms of ferroptotic cell death and associated human diseases, as well as new therapeutic strategies for such diseases.

Dialysis encephalopathy: precipitating factors and improvement in prognosis

Cancer stem cells (CSCs) contribute to the initiation, recurrence, and metastasis of cancer; however, there are still no drugs targeting CSCs in clinical application. There are several signaling pathways playing critical roles in CSC progression, such as the Wnt, Hedgehog, Notch, Hippo, and autophagy signaling pathways. Additionally, targeting the ferroptosis signaling pathway was recently shown to specifically kill CSCs. Therefore, targeting these pathways may suppress CSC progression. The structure of small-molecule drugs shows a good spatial dispersion, and its chemical properties determine its good druggability and pharmacokinetic properties. These characteristics make small-molecule drugs show a great advantage in drug development, which is increasingly popular in the market. Thus, in this review, we will summarize the current researches on the small-molecule compounds suppressing CSC progression, including inhibitors of Wnt, Notch, Hedgehog, and autophagy pathways, and activators of Hippo and ferroptosis pathways. These small-molecule compounds emphasize CSC importance in tumor progression and propose a new strategy to treat cancer in clinic via targeting CSCs.