Ferroptosis: process and function

Structural and elemental changes in glioblastoma cells in situ: complementary imaging with high resolution visible light- and X-ray microscopy

The glioblastoma (GBM) is characterized by a short median survival and an almost 100% tumor related mortality. GBM cells exhibit highly invasive behavior whose mechanisms are not yet fully understood. The present study explores application of X-ray and visible light microscopy to display the elemental and structural images of cells from 3 patient derived GMB samples and an established GMB cell line. Slight differences in elemental concentrations, in actin cytoskeleton organization and cell morphology were noted between all cells types by X-ray fluorescence and full field soft X-ray microscopy, as well as the Structured Illumination Super-resolution Microscope (SIM). Different sample preparation approaches were used to match each imaging technique. While preparation for SIM included cell fixation and staining, intact frozen hydrated cells were used for the trace element imaging by hard X-ray fluorescence and exploration of the structural features by soft X-ray absorption tomography. Each technique documented differences between samples with regard to morphology and elemental composition and underscored the importance of use of multiple patient derived samples for detailed GBM study.

ESRD-associated immune phenotype depends on dialysis modality and iron status: clinical implications

BACKGROUND

End-stage renal disease (ESRD) causes premature ageing of the immune system. However, it is not known whether hemodialysis (HD) and peritoneal dialysis (PD) similarly affect the T cell system.

METHODS

The aim of our study was to analyse whether dialysis modality may mitigate ESRD-induced immune senescence. We explored a large population of patients (675 ESRD patients) and both confirmed and refined the results in a second cohort (84 patients).

RESULTS

HD patients exhibited higher inflammatory monocytes counts (44/mm3 (1-520) vs 36/mm3 (1-161); p = 0.005). Patients on HD also had higher frequency of CD8 T cells (24% (7-61) vs 22% (8-42); p = 0.003) and reduced CD4/CD8 ratio. Such results were confirmed in the second cohort. Moreover, both CD4 + CD57 + CD28- (3.25% (0-38.2) vs 1.05% (0-28.5); p = 0.068) and CD8 + CD57 + CD28- (38.5% (3.6-76.8) vs 26.1 (2.1-46.9); p = 0.039) T cells frequencies were increased in HD patients. Telomere length did not differ according to dialysis modality, but was inversely related to ferritin levels (r = - 0.33; p = 0.003). There was a trend towards higher telomerase activity in PD patients (11 ± 13 vs 6 ± 11; p = 0.053). Thymic function was not different in PD and HD patients. Patients on PD before transplantation had a higher risk of acute rejection after kidney transplantation (HR, 1.61; 95%CI, 1.02 to 2.56; p = 0.041).

CONCLUSIONS

More pronounced inflammation with hemodialysis may induce premature aging of the immune system. This observation correlates with a lower risk of acute kidney rejection in patients previously on HD. Clinical consequences in patients maintained on dialysis should be determined.

TRIAL REGISTRATION

Trial registration: NCT02843867, registered July 8, 2016.

Metformin: oxidative and proliferative parameters in-vitro and in-vivo models of murine melanoma

Cutaneous melanoma is one of the most lethal cancers because of its increased rate of metastasis and resistance to available therapeutic options. Early studies indicate that metformin has beneficial effects on some types of cancer, including melanoma. To clarify knowledge of the mechanism of action of metformin on this disease, two treatment-based approaches are presented using metformin on melanoma progression: an in-vitro and an in-vivo model. The in-vitro assay was performed for two experimental treatment periods (24 and 48 h) at different metformin concentrations. The results showed that metformin decreased cell viability, reduced proliferation, and apoptosis was a major event 48 h after treating B16F10 cells. Oxidative stress was characterized by the decrease in total thiol antioxidants immediately following 24 h of metformin treatment and showed an increase in lipid peroxidation. The in-vivo model was performed by injecting B16F10 cells into the subcutaneous of C57/BL6 mice. Treatment with metformin began on day 3 and on day 14, the mice were killed. Treatment of mice with metformin reduced tumor growth by 54% of its original volume compared with nontreatment. The decrease in systemic vascular endothelial growth factor, restoration of antioxidants glutathione and catalase, and normal levels of lipid peroxidation indicate an improved outcome for melanoma following metformin treatment, meeting a need for new strategies in the treatment of melanoma.

Mitochondrial dysfunction in the neuro-degenerative and cardio-degenerative disease, Friedreich's ataxia

Mitochondrial homeostasis is essential for maintaining healthy cellular function and survival. The detrimental involvement of mitochondrial dysfunction in neuro-degenerative diseases has recently been highlighted in human conditions, such as Parkinson's, Alzheimer's and Huntington's disease. Friedreich's ataxia (FA) is another neuro-degenerative, but also cardio-degenerative condition, where mitochondrial dysfunction plays a crucial role in disease progression. Deficient expression of the mitochondrial protein, frataxin, is the primary cause of FA, which leads to adverse alterations in whole cell and mitochondrial iron metabolism. Dys-regulation of iron metabolism in these compartments, results in the accumulation of inorganic iron deposits in the mitochondrial matrix that is thought to potentiate oxidative damage observed in FA. Therefore, the maintenance of mitochondrial homeostasis is crucial in the progression of neuro-degenerative conditions, particularly in FA. In this review, vital mitochondrial homeostatic processes and their roles in FA pathogenesis will be discussed. These include mitochondrial iron processing, mitochondrial dynamics (fusion and fission processes), mitophagy, mitochondrial biogenesis, mitochondrial energy production and calcium metabolism.

Cell Death Pathways: a Novel Therapeutic Approach for Neuroscientists

In the first part, the following mechanisms involved in different forms of cell death are considered, with a view to identifying potential therapeutic targets: tumour necrosis factor receptors (TNFRs) and their engagement by tumour necrosis factor-alpha (TNF-α); poly [ADP-ribose] polymerase (PARP)-1 cleavage; the apoptosis signalling kinase (ASK)-c-Jun N-terminal kinase (JNK) axis; lysosomal permeability; activation of programmed necrotic cell death; oxidative stress, caspase-3 inhibition and parthanatos; activation of inflammasomes by reactive oxygen species and the development of pyroptosis; oxidative stress, calcium dyshomeostasis and iron in the development of lysosomal-mediated necrosis and lysosomal membrane permeability; and oxidative stress, lipid peroxidation, iron dyshomeostasis and ferroptosis. In the second part, there is a consideration of the role of lethal and sub-lethal activation of these pathways in the pathogenesis and pathophysiology of neurodegenerative and neuroprogressive disorders, with particular reference to the TNF-α-TNFR signalling axis; dysregulation of ASK-1-JNK signalling; prolonged or chronic PARP-1 activation; the role of pyroptosis and chronic inflammasome activation; and the roles of lysosomal permeabilisation, necroptosis and ferroptosis. Finally, it is suggested that, in addition to targeting oxidative stress and inflammatory processes generally, neuropsychiatric disorders may respond to therapeutic targeting of TNF-α, PARP-1, the Nod-like receptor NLRP3 inflammasome and the necrosomal molecular switch receptor-interacting protein kinase-3, since their widespread activation can drive and/or exacerbate peripheral inflammation and neuroinflammation even in the absence of cell death. To this end, the use is proposed of a combination of the tetracycline derivative minocycline and N-acetylcysteine as adjunctive treatment for a range of neuropsychiatric disorders.

Magnesium isoglycyrrhizinate ameliorates liver fibrosis and hepatic stellate cell activation by regulating ferroptosis signaling pathway

Ferroptosis is recently reported as a new mode of regulated cell death. It is triggered by disturbed redox homeostasis, overloaded iron and increased lipid peroxidation. Howerver, the role of ferroptosis in hepatic fibrosis remains obscure. In the current study, we attempted to investigate the effect of Magnesium isoglycyrrhizinate (MgIG) on ferroptosis in liver fibrosis, and to further clarify the possible mechanisms. Our data showed that MgIG treatment markedly attenuated liver injury and reduced fibrotic scar formation in the rat model of liver fibrosis. Moreover, experiments in vitro also confirmed that MgIG treatment significantly decreased expression of hepatic stellate cell (HSC) activation markers. Interestingly, HSCs treated by MgIG presented morphological features of ferroptosis. Furthermore, MgIG treatment remarkably induced HSC ferroptosis by promoting the accumulation of iron and lipid peroxides, whereas inhibition of ferroptosis by specific inhibitor ferrostatin-1 (Fer-1) completely abolished MgIG-induced anti-fibrosis effect. More importantly, our results determined that heme oxygenase-1 (HO-1) was in the upstream position of MgIG-induced HSC ferroptosis. Conversely, HO-1 knockdown by siRNA evidently blocked MgIG-induced HSC ferroptosis and in turn exacerbated liver fibrosis. Overall, our research revealed that HO-1 mediated HSC ferroptosis was necessary for MgIG to ameliorate CCl₄-induced hepatic fibrosis.

Single-walled carbon-nanohorns improve biocompatibility over nanotubes by triggering less protein-initiated pyroptosis and apoptosis in macrophages

Single-walled carbon-nanohorns (SNH) exhibit huge application prospects. Notably, spherical SNH possess different morphology from conventional carbon nanotubes (CNT). However, there is a tremendous lack of studies on the nanotoxicity and mechanism of SNH, and their comparison with nanotubes. Here, the dissimilarity between SNH and CNT is found in many aspects including necrosis, pyroptosis, apoptosis, protein expression, hydrolases leakage, lysosome stress, membrane disturbance and the interaction with membrane proteins. The improved biocompatibility of SNH over four types of established CNT is clearly demonstrated in macrophages. Importantly, a key transmembrane protein, glycoprotein nonmetastatic melanoma protein B (GPNMB) is discovered to initiate the nanotoxicity. Compared to CNT, the weaker nano-GPNMB interaction in SNH group induces lower degree of cascade actions from nano/membrane interplay to final cell hypotoxicity. In conclusion, the geometry of single-construct unit, but not that of dispersive forms or intracellular levels of nanocarbons make the most difference.

CISD2 inhibition overcomes resistance to sulfasalazine-induced ferroptotic cell death in head and neck cancer

Sulfasalazine has been repurposed to induce ferroptotic cancer cell death via inhibition of x_c^--cystine/glutamate antiporter (xCT). However, cancer cells are capable of developing mechanisms to evade cell death. Therefore, we sought to determine the molecular mechanisms underlying resistance to sulfasalazine-induced ferroptosis in head and neck cancer (HNC). The effects of sulfasalazine and pioglitazone were tested in various HNC cell lines. The effects of these drugs and inhibition and overexpression of CISD2 gene were determined by evaluating viability, cell death, lipid ROS production, mitochondrial iron, and mouse tumor xenograft models. SAS induced ferroptotic cell death in HNC at different levels. CISD2 expression showed an association between its expression and ferroptosis resistance. CISD2 overexpression conferred resistance to ferroptosis by sulfasalazine. Silencing CISD2 gene rendered resistant HNC cells susceptible to sulfasalazine-induced ferroptosis, with increased levels of lipid ROS and mitochondrial ferrous iron. Pioglitazone induced over-accumulation of mitochondrial iron and ROS and sensitized resistant HNC cells to sulfasalazine treatment in vitro and in a mouse tumor-xenograft model. CISD2 inhibition overcomes HNC resistance to ferroptotic cell death induced by sulfasalazine via increased accumulation of mitochondrial ferrous iron and lipid ROS.

Human Cytomegalovirus Protein pUL38 Prevents Premature Cell Death by Binding to Ubiquitin-Specific Protease 24 and Regulating Iron Metabolism

Human cytomegalovirus (HCMV) protein pUL38 has been shown to prevent premature cell death by antagonizing cellular stress responses; however, the underlying mechanism remains unknown. In this study, we identified the host protein ubiquitin-specific protease 24 (USP24) as an interaction partner of pUL38. Mutagenesis analysis of pUL38 revealed that amino acids TFV at positions 227 to 230 were critical for its interaction with USP24. Mutant pUL38 TFV/AAA protein did not bind to USP24 and failed to prevent cell death induced by pUL38-deficient HCMV infection. Knockdown of USP24 suppressed the cell death during pUL38-deficient HCMV infection, suggesting that pUL38 achieved its function by antagonizing the function of USP24. We investigated the cellular pathways regulated by USP24 that might be involved in the cell death phenotype by testing several small-molecule compounds known to have a protective effect during stress-induced cell death. The iron chelators ciclopirox olamine and Tiron specifically protected cells from pUL38-deficient HCMV infection-induced cell death, thus identifying deregulated iron homeostasis as a potential mechanism. Protein levels of nuclear receptor coactivator 4 (NCOA4) and lysosomal ferritin degradation, a process called ferritinophagy, were also regulated by pUL38 and USP24 during HCMV infection. Knockdown of USP24 decreased NCOA4 protein stability and ferritin heavy chain degradation in lysosomes. Blockage of ferritinophagy by genetic inhibition of NCOA4 or Atg5/Atg7 prevented pUL38-deficient HCMV infection-induced cell death. Overall, these results support the hypothesis that pUL38 binds to USP24 to reduce ferritinophagy, which may then protect cells from lysosome dysfunction-induced cell death.IMPORTANCE Premature cell death is considered a first line of defense against various pathogens. Human cytomegalovirus (HCMV) is a slow-replicating virus that encodes several cell death inhibitors, such as pUL36 and pUL37x1, which allow it to overcome both extrinsic and intrinsic mitochondrion-mediated apoptosis. We previously identified HCMV protein pUL38 as another virus-encoded cell death inhibitor. In this study, we demonstrated that pUL38 achieved its activity by interacting with and antagonizing the function of the host protein ubiquitin-specific protease 24 (USP24). pUL38 blocked USP24-mediated ferritin degradation in lysosomes, which could otherwise be detrimental to the lysosome and initiate cell death. These novel findings suggest that iron metabolism is finely tuned during HCMV infection to avoid cellular toxicity. The results also provide a solid basis for further investigations of the role of USP24 in regulating iron metabolism during infection and other diseases.

Macrophage phenotype and bioenergetics are controlled by oxidized phospholipids identified in lean and obese adipose tissue

Adipose tissue macrophages (ATMs) maintain adipose tissue homeostasis. However, during obesity ATMs become inflammatory, resulting in impaired adipose tissue function. Oxidative stress increases during obesity, which is thought to contribute to adipose tissue inflammation. To date, the connection between oxidative stress and adipose tissue inflammation remain unclear. In this study, we identify two classes of phospholipid oxidation products in lean and obese adipose tissue, which polarize macrophages to an antioxidant or proinflammatory state, respectively. Furthermore, we show that these phospholipids differently affect macrophage cellular metabolism, reflecting the metabolisms of ATMs found in lean and obese adipose tissue. Identification of pathways controlling ATM metabolism will lead to novel therapies for insulin resistance.

Adipose tissue macrophages (ATMs) adapt their metabolic phenotype either to maintain lean tissue homeostasis or drive inflammation and insulin resistance in obesity. However, the factors in the adipose tissue microenvironment that control ATM phenotypic polarization and bioenergetics remain unknown. We have recently shown that oxidized phospholipids (OxPL) uniquely regulate gene expression and cellular metabolism in Mox macrophages, but the presence of the Mox phenotype in adipose tissue has not been reported. Here we show, using extracellular flux analysis, that ATMs isolated from lean mice are metabolically inhibited. We identify a unique population of CX3CR1^neg/F4/80^low ATMs that resemble the Mox (Txnrd1⁺HO1⁺) phenotype to be the predominant ATM phenotype in lean adipose tissue. In contrast, ATMs isolated from obese mice had characteristics typical of the M1/M2 (CD11c⁺CD206⁺) phenotype with highly activated bioenergetics. Quantifying individual OxPL species in the stromal vascular fraction of murine adipose tissue, using targeted liquid chromatography-mass spectrometry, revealed that high fat diet-induced adipose tissue expansion led to a disproportional increase in full-length over truncated OxPL species. In vitro studies showed that macrophages respond to truncated OxPL species by suppressing bioenergetics and up-regulating antioxidant programs, mimicking the Mox phenotype of ATMs isolated from lean mice. Conversely, full-length OxPL species induce proinflammatory gene expression and an activated bioenergetic profile that mimics ATMs isolated from obese mice. Together, these data identify a redox-regulatory Mox macrophage phenotype to be predominant in lean adipose tissue and demonstrate that individual OxPL species that accumulate in adipose tissue instruct ATMs to adapt their phenotype and bioenergetic profile to either maintain redox homeostasis or to promote inflammation.

The Roles of p53 in Mitochondrial Dynamics and Cancer Metabolism: The Pendulum between Survival and Death in Breast Cancer?

Cancer research has been heavily geared towards genomic events in the development and progression of cancer. In contrast, metabolic regulation, such as aberrant metabolism in cancer, is poorly understood. Alteration in cellular metabolism was once regarded simply as a consequence of cancer rather than as playing a primary role in cancer promotion and maintenance. Resurgence of cancer metabolism research has identified critical metabolic reprogramming events within biosynthetic and bioenergetic pathways needed to fulfill the requirements of cancer cell growth and maintenance. The tumor suppressor protein p53 is emerging as a key regulator of metabolic processes and metabolic reprogramming in cancer cells—balancing the pendulum between cell death and survival. This review provides an overview of the classical and emerging non-classical tumor suppressor roles of p53 in regulating mitochondrial dynamics: mitochondrial engagement in cell death processes in the prevention of cancer. On the other hand, we discuss p53 as a key metabolic switch in cellular function and survival. The focus is then on the conceivable roles of p53 in breast cancer metabolism. Understanding the metabolic functions of p53 within breast cancer metabolism will, in due course, reveal critical metabolic hotspots that cancers advantageously re-engineer for sustenance. Illustration of these events will pave the way for finding novel therapeutics that target cancer metabolism and serve to overcome the breast cancer burden.

The glutathione redox system is essential to prevent ferroptosis caused by impaired lipid metabolism in clear cell renal cell carcinoma

Metabolic reprogramming is a prominent feature of clear cell renal cell carcinoma (ccRCC). Here we investigated metabolic dependencies in a panel of ccRCC cell lines using nutrient depletion, functional RNAi screening and inhibitor treatment. We found that ccRCC cells are highly sensitive to the depletion of glutamine or cystine, two amino acids required for glutathione (GSH) synthesis. Moreover, silencing of enzymes of the GSH biosynthesis pathway or glutathione peroxidases, which depend on GSH for the removal of cellular hydroperoxides, selectively reduced viability of ccRCC cells but did not affect the growth of non-malignant renal epithelial cells. Inhibition of GSH synthesis triggered ferroptosis, an iron-dependent form of cell death associated with enhanced lipid peroxidation. VHL is a major tumour suppressor in ccRCC and loss of VHL leads to stabilisation of hypoxia inducible factors HIF-1α and HIF-2α. Restoration of functional VHL via exogenous expression of pVHL reverted ccRCC cells to an oxidative metabolism and rendered them insensitive to the induction of ferroptosis. VHL reconstituted cells also exhibited reduced lipid storage and higher expression of genes associated with oxidiative phosphorylation and fatty acid metabolism. Importantly, inhibition of β-oxidation or mitochondrial ATP-synthesis restored ferroptosis sensitivity in VHL reconstituted cells. We also found that inhibition of GSH synthesis blocked tumour growth in a MYC-dependent mouse model of renal cancer. Together, our data suggest that reduced fatty acid metabolism due to inhibition of β-oxidation renders renal cancer cells highly dependent on the GSH/GPX pathway to prevent lipid peroxidation and ferroptotic cell death.

RASSF6-mediated inhibition of Mcl-1 through JNK activation improves the anti-tumor effects of sorafenib in renal cell carcinoma

Ras association domain family member 6 (RASSF6) has been shown to act as a tumor suppressor and predictor of poor prognosis in renal cell carcinoma (RCC). However, little is known about the effects of RASSF6 on sorafenib resistance or the underlying mechanism. Here, we show that RASSF6 expression positively correlates with sorafenib sensitivity in RCC cells and human samples. Stable ectopic overexpression of RASSF6 in RCC cell lines reduces resistance to sorafenib in vitro and in vivo. At a molecular level, RASSF6 activates the JNK signaling pathway, which further contributes to Mcl-1 inhibition. Suppression of the JNK pathway can partially restore Mcl-1 expression and sorafenib resistance. Together, these findings suggest that RASSF6 inhibits sorafenib resistance by repressing Mcl-1 through the JNK-dependent pathway. RASSF6 may serve as a novel regulator for sorafenib therapy in RCC.

Haemin-induced cell death in human monocytic cells is consistent with ferroptosis

BACKGROUND

Iron overload is a major issue for transfusion-dependent patients. Repeated transfusions result in the loading of large amounts of haem-derived iron on macrophages, and the haemin in turn induces cell death and the generation of reactive oxygen species (ROS) in both murine macrophages and human monocytic THP-1 cells. This haemin-induced cell death process has been shown to be iron-dependent. Thus, we hypothesized that haemin-induced THP-1 cell death is a result of ferroptosis, an iron-dependent mechanism of cell death regulation.

MATERIAL AND METHODS

Human monocytic THP-1 cells were treated with haemin, and haemin-induced cell death and ROS generation were assessed using flow cytometry.

RESULTS

Haemin-induced THP-1 cell death showed a necrosis pattern, and treatment with iron chelators suppressed both haemin-induced cell death and ROS generation. Treatment with ferrostatin-1, a ferroptosis inhibitor, suppressed haemin-induced cell death without affecting ROS generation, whereas erastin, a ferroptosis inducer, enhanced both haemin-induced cell death and ROS generation.

DISCUSSION

Our findings support haemin-induced cell death as an example of ferroptosis. Therefore, ferroptosis inhibitors may be useful for the treatment or prevention of transfusion iron overload.

Till Death Do Us Part: The Marriage of Autophagy and Apoptosis

Autophagy is a widely conserved catabolic process that is necessary for maintaining cellular homeostasis under normal physiological conditions and driving the cell to switch back to this status quo under times of starvation, hypoxia, and oxidative stress. The potential similarities and differences between basal autophagy and stimulus-induced autophagy are still largely unknown. Both act by clearing aberrant or unnecessary cytoplasmic material, such as misfolded proteins, supernumerary and defective organelles. The relationship between reactive oxygen species (ROS) and autophagy is complex. Cellular ROS is predominantly derived from mitochondria. Autophagy is triggered by this event, and by clearing the defective organelles effectively, it lowers cellular ROS thereby restoring cellular homeostasis. However, if cellular homeostasis cannot be reached, the cells can switch back and choose a regulated cell death response. Intriguingly, the autophagic and cell death machines both respond to the same stresses and share key regulatory proteins, suggesting that the pathways are intricately connected. Here, the intersection between autophagy and apoptosis is discussed with a particular focus on the role ROS plays.

Lipopolysaccharide-Induced Necroptosis of Brain Microvascular Endothelial Cells Can Be Prevented by Inhibition of Endothelin Receptors

Over activation of the endothelin-1 (ET-1) system in disease states contributes to endothelial dysfunction. On the other hand, ET-1 promotes proliferation and survival of endothelial cells. Regulation of programmed cell death (PCD) pathways is critical for cell survival. Recently discovered necroptosis (regulated necrosis) is a pathological PCD mechanism mediated by the activation of toll like receptor 4 (TLR4), which also happens to stimulate ET-1 production in dendritic cells. To establish the effect of ET-1 on PCD and survival of human brain microvascular endothelial cells (BMVECs) under control and inflammatory conditions, BMVECs were treated with ET-1 (10 nM, 100 nM and 1 µM) or lipopolysaccharide (LPS, 100 ng/ml). ET receptors were blocked with bosentan (10 µM). Under normal growth conditions, exogenous ET-1 reduced BMVEC viability and migration at a relatively high concentration (1 µM). This was accompanied with activation of necroptosis and apoptosis marker genes. LPS decreased endogenous ET-1 secretion, increased ETB receptor expression and activated necroptosis. Even though ET-1 levels were low (less than 10 nM levels used under normal growth conditions), blocking of ET receptors with bosentan inhibited the necroptosis pathway and improved the cell migration ability of BMVECs, suggesting that under inflammatory conditions, ET-1 activates PCD pathways in BMVECs even at physiological levels.

Corosolic Acid Induces Non-Apoptotic Cell Death through Generation of Lipid Reactive Oxygen Species Production in Human Renal Carcinoma Caki Cells

Corosolic acid is one of the pentacyclic triterpenoids isolated from Lagerstroemia speciose and has been reported to exhibit anti-cancer and anti-proliferative activities in various cancer cells. In the present study, we investigated the molecular mechanisms of corosolic acid in cancer cell death. Corosolic acid induces a decrease of cell viability and an increase of cell cytotoxicity in human renal carcinoma Caki cells. Corosolic acid-induced cell death is not inhibited by apoptosis inhibitor (z-VAD-fmk, a pan-caspase inhibitor), necroptosis inhibitor (necrostatin-1), or ferroptosis inhibitors (ferrostatin-1 and deferoxamine (DFO)). Furthermore, corosolic acid significantly induces reactive oxygen species (ROS) levels, but antioxidants (N-acetyl-l-cysteine (NAC) and trolox) do not inhibit corosolic acid-induced cell death. Interestingly, corosolic acid induces lipid oxidation, and α-tocopherol markedly prevents corosolic acid-induced lipid peroxidation and cell death. Anti-chemotherapeutic effects of α-tocopherol are dependent on inhibition of lipid oxidation rather than inhibition of ROS production. In addition, corosolic acid induces non-apoptotic cell death in other renal cancer (ACHN and A498), breast cancer (MDA-MB231), and hepatocellular carcinoma (SK-Hep1 and Huh7) cells, and α-tocopherol markedly inhibits corosolic acid-induced cell death. Therefore, our results suggest that corosolic acid induces non-apoptotic cell death in cancer cells through the increase of lipid peroxidation.

The Tumor Suppressor p53 Limits Ferroptosis by Blocking DPP4 Activity

Ferroptosis is a form of regulated cell death that may facilitate the selective elimination of tumor cells. The tumor suppressor p53 (TP53) has been demonstrated to promote ferroptosis via a transcription-dependent mechanism. Here, we show that TP53 limits erastin-induced ferroptosis by blocking dipeptidyl-peptidase-4 (DPP4) activity in a transcription-independent manner. Loss of TP53 prevents nuclear accumulation of DPP4 and thus facilitates plasma-membrane-associated DPP4-dependent lipid peroxidation, which finally results in ferroptosis. These findings reveal a direct molecular link between TP53 and DPP4 in the control of lipid metabolism and may provide a precision medicine strategy for the treatment of colorectal cancer by induction of ferroptosis.

Ferroptosis is newly characterized form of neuronal cell death in response to arsenite exposure

Ferroptosis is a novel iron-dependent form of cell death implicated in brain pathology. However, whether arsenite is an inducer of ferroptosis in the neuron remains completely unknown. In this study, the seven-week-old healthy C57BL/6 J male mice were treated with environmental related doses (0.5, 5 and 50 mg/L) of arsenite for 6 months via drinking water, and the ferroptosis-related indicators were further determined. Our results demonstrated for the first time that, arsenite exposure significantly reduced the number of neuron and caused the pathological changes of mitochondria in the cerebral cortex of mice. We further revealed that arsenite induced ferroptotic cell death in neuron by accumulation of reactive oxygen species and lipid peroxidation products, disruption of Fe²⁺ homeostasis, depletion of glutathione and adenosine triphosphate, inhibition of cysteine/glutamate antiporter, activation of mitogen-activated protein kinases and mitochondrial voltage-dependent anion channels pathways, up-regulation of endoplasmic reticulum stress, all of which were involved in the process of ferroptosis. These findings were also verified in the cultured PC-12 cells by using ferropotosis inhibitor, desferoxamine. Taken together, our results not only reveal a novel mechanism that chronic arsenite exposure may trigger the new form of cell death, ferroptosis, but also shed a new light on a potential clue for the intervention and prevention against arsenite-related neurodegenerative diseases.

Increased erythrophagocytosis induces ferroptosis in red pulp macrophages in a mouse model of transfusion

Macrophages play important roles in recycling iron derived from the clearance of red blood cells (RBCs). They are also a critically important component of host defense, protecting against invading pathogens. However, the effects on macrophage biology of acutely ingesting large numbers of RBCs are not completely understood. To investigate this issue, we used a mouse model of RBC transfusion and clearance, which mimics the clinical setting. In this model, transfusions of refrigerator storage-damaged (ie, "old") RBCs led to increased erythrophagocytosis by splenic red pulp macrophages (RPMs). This robust erythrophagocytosis induced ferroptosis, an iron-dependent form of cell death, in RPMs. This was accompanied by increases in reactive oxygen species and lipid peroxidation in vivo, which were reduced by treatment in vitro with ferrostatin-1, a ferroptosis inhibitor. Old RBC transfusions also induced RPM-dependent chemokine expression by splenic Ly6C^hi monocytes, which signaled Ly6C^hi monocyte migration from bone marrow to spleen, where these cells subsequently differentiated into RPMs. The combination of cell division among remaining splenic RPMs, along with the influx of bone marrow-derived Ly6C^hi monocytes, suggests that, following RPM depletion induced by robust erythrophagocytosis, there is a coordinated effort to restore homeostasis of the RPM population by local self-maintenance and contributions from circulating monocytes. In conclusion, these findings may be clinically relevant to pathological conditions that can arise as a result of increased erythrophagocytosis, such as transfusion-related immunomodulation and impaired host immunity.

Low tumor glutathione level as a sensitivity marker for glutamate-cysteine ligase inhibitors

Previous metabolomic analyses of cancer have revealed elevated glutathione levels in tumors. An inhibitor of cystine uptake was identified to suppress glutathione biosynthesis, leading to ferroptosis, a novel iron-dependent form of cell death that differs from apoptosis and necrosis. Glutamate-cysteine ligase (GCL) is the rate-limiting enzyme in the glutathione biosynthesis pathway. Buthionine sulfoximine (BSO), a GCL inhibitor, has previously demonstrated limited clinical benefits. Therefore, selecting patients who respond well to the inhibitor is a key approach for successful future drug development. Ferroptosis induction by BSO has not been fully examined in prior studies. Therefore, the present study investigated the pharmacological effects of BSO and the association between basal intracellular glutathione levels and sensitivity to BSO in cultured cell lines derived from various types of cancer, including those of the kidney [769P, 786-O, A-498, A704, ACHN, Caki-1, Caki-2, G401, G402, RCC4 VHL(-/-), RCC4 VHL(+/+), SK-NEP-1 and SW156] and ovaries (A2780 and A2780/CDDP). BSO was demonstrated to suppress glutathione levels and induce lipid peroxidation, thereby inhibiting cell viability. The viability-reducing effects of BSO were attenuated by ferroptosis inhibition and enhanced by iron, indicating that BSO induced ferroptosis in cancer cells. The cell lines sensitive to BSO, including G402, tended to exhibit non-significantly lower levels of glutathione compared with the BSO-insensitive cell lines, including Caki-2 (P=0.08). Patient sample data indicated the existence of a population of colorectal tumors with lower glutathione levels compared with those of matched normal tissues that might be suitable for the clinical testing of sensitivity to GCLC inhibitors. Collectively, these data suggest that GCL inhibition leads to ferroptosis in cancer cells, and that low glutathione tumor levels may be a patient selection marker for the use of GCL inhibitors in the treatment of tumors.

Ferroptosis-Induced Endoplasmic Reticulum Stress: Cross-talk between Ferroptosis and Apoptosis

Since its discovery in 2012, ferroptosis has been well characterized by the accumulation of lipid peroxides due to the failure of glutathione-dependent antioxidant defenses. It is known as an iron-dependent form of programmed cell death, which is distinct from other forms of cell death such as apoptosis and necrosis. Nonetheless, little is known about the ferroptotic agent-induced endoplasmic reticulum (ER) stress response and its role in cell death. Recent studies reveal that the ferroptotic agent-induced ER stress response plays an important role in the cross-talk between ferroptosis and other types of cell death. Ferroptotic agents induce the unfolded protein response and subsequently ER stress-mediated activation of the PERK-eIF2α-ATF4-CHOP pathway. CHOP (C/EBP homologous protein) signaling pathway-mediated p53-independent PUMA (p53 upregulated modulator of apoptosis) expression is involved in the synergistic interaction between ferroptosis and apoptosis. This review highlights the recent literature on ferroptotic and apoptotic agent interactions through the ER stress-mediated PERK-eIF2α-ATF4-CHOP-PUMA pathway and implicates combined treatment to effectively enhance tumoricidal efficacy as a novel therapeutic strategy for cancer. Mol Cancer Res; 16(7); 1073-6. ©2018 AACR.

Quantitative Profiling of Protein Carbonylations in Ferroptosis by an Aniline-Derived Probe

Ferroptosis is a regulated form of necrotic cell death implicated in carcinogenesis and neurodegeneration that is driven by phospholipid peroxidation. Lipid-derived electrophiles (LDEs) generated during this process can covalently modify proteins ("carbonylation") and affect their functions. Here we report the development of a quantitative chemoproteomic method to profile carbonylations in ferroptosis by an aniline-derived probe. Using the method, we established a global portrait of protein carbonylations in ferroptosis with >400 endogenously modified proteins and for the first time, identified >20 residue sites with endogenous LDE modifications in ferroptotic cells. Specifically, we discovered and validated a novel cysteine site of modification on voltage-dependent anion-selective channel protein 2 (VDAC2) that might play an important role in sensitizing LDE signals and mediating ferroptosis. Our results will contribute to the understanding of ferroptotic signaling and pathogenesis and provide potential biomarkers for ferroptosis detection.

Overexpression of SLC7A11: a novel oncogene and an indicator of unfavorable prognosis for liver carcinoma

AIM

SLC7A11 is a gene that encodes a cystine-glutamate antiporter, which has been detected to be overexpressed in various cancers. Thus, we aimed to validate its expression and clinical significance in liver cancer.

METHODS

Bioinformatic analysis was conducted and a tissue microarray was utilized for detecting SLC7A11 expression in liver cancer tissues by immunohistochemistry assay.

RESULTS

High expressions of SLC7A11 have no association with clinical parameters such as age, sex and clinical stages, except for advanced pathological stages. Cox regression analysis revealed that SLC7A11 might be an independent prognostic factor for liver cancer patients.

CONCLUSION

SLC7A11 overexpression might be a novel biomarker and a potential unfavorable prognostic factor as well as a potential therapeutic target for liver carcinoma.

Molecular mechanisms of cell death: recommendations of the Nomenclature Committee on Cell Death 2018

Over the past decade, the Nomenclature Committee on Cell Death (NCCD) has formulated guidelines for the definition and interpretation of cell death from morphological, biochemical, and functional perspectives. Since the field continues to expand and novel mechanisms that orchestrate multiple cell death pathways are unveiled, we propose an updated classification of cell death subroutines focusing on mechanistic and essential (as opposed to correlative and dispensable) aspects of the process. As we provide molecularly oriented definitions of terms including intrinsic apoptosis, extrinsic apoptosis, mitochondrial permeability transition (MPT)-driven necrosis, necroptosis, ferroptosis, pyroptosis, parthanatos, entotic cell death, NETotic cell death, lysosome-dependent cell death, autophagy-dependent cell death, immunogenic cell death, cellular senescence, and mitotic catastrophe, we discuss the utility of neologisms that refer to highly specialized instances of these processes. The mission of the NCCD is to provide a widely accepted nomenclature on cell death in support of the continued development of the field.

Piperlongumine rapidly induces the death of human pancreatic cancer cells mainly through the induction of ferroptosis

Pancreatic cancer is one of the most lethal types of cancer with a mortality rate of almost 95%. Treatment with current chemotherapeutic drugs has limited success due to poor responses. Therefore, the development of novel drugs or effective combination therapies is urgently required. Piperlongumine (PL) is a natural product with cytotoxic properties restricted to cancer cells by significantly increasing intracellular reactive oxygen species (ROS) levels. In the present study, we demonstrated that PL induced cancer cell death through, at least in part, the induction of ferroptosis, as the cancer cell-killing activity was inhibited by the antioxidant, N‑acetylcysteine, ferroptosis inhibitors (ferrostatin‑1 and liproxstatin‑1) and the iron chelator, deferoxamine (DFO), but not by the apoptosis inhibitor, Z-VAD-FMK, or the necrosis inhibitor, necrostatin‑1. Cotylenin A (CN‑A; a plant growth regulator) exhibits potent antitumor activities in several cancer cell lines, including pancreatic cancer cell lines. We found that CN‑A and PL synergistically induced the death of pancreatic cancer MIAPaCa‑2 and PANC‑1 cells for 16 h. CN‑A enhanced the induction of ROS by PL for 4 h. The synergistic induction of cell death was also abrogated by the ferroptosis inhibitors and DFO. The present results revealed that clinically approved sulfasalazine (SSZ), a ferroptosis inducer, enhanced the death of pancreatic cancer cells induced by PL and the combined effects were abrogated by the ferroptosis inhibitors and DFO. SSZ further enhanced the cancer cell-killing activities induced by combined treatment with PL plus CN‑A. On the other hand, the synergistic induction of cell death by PL and CN‑A was not observed in mouse embryonic fibroblasts (MEFs), and SSZ did not enhance the death of MEFs induced by PL plus CN‑A. These results suggest that the triple combined treatment with PL, CN‑A and SSZ is highly effective against pancreatic cancer.

Emerging Strategies of Cancer Therapy Based on Ferroptosis

Ferroptosis, a new form of regulated cell death that is iron- and reactive oxygen species dependent, has attracted much attention in the research communities of biochemistry, oncology, and especially material sciences. Since the first demonstration in 2012, a series of strategies have been developed to induce ferroptosis of cancer cells, including the use of nanomaterials, clinical drugs, experimental compounds, and genes. A plethora of research work has outlined the blueprint of ferroptosis as a new option for cancer therapy. However, the published ferroptosis-related reviews have mainly focused on the mechanisms and pathways of ferroptosis, which motivated this contribution to bridge the gap between biological significance and material design. Therefore, it is timely to summarize the previous efforts on the emerging strategies for inducing ferroptosis and shed light on future directions for using such a tool to fight against cancer. Here, the current strategies of cancer therapy based on ferroptosis will be elaborated, the design considerations and the advantages and limitations are highlighted, and finally a future perspective on this emerging field is given.

Metabolic networks in ferroptosis

Ferroptosis is an iron-dependent and peroxidation-driven form of cell death associated with multiple metabolic disorders and disrupted homeostasis. A number of metabolic processes and homeostasis are affected by ferroptosis. The molecules that regulate ferroptosis are involved in metabolic pathways that regulate cysteine exploitation, glutathione state, nicotinamide adenine dinucleotide phosphate function, lipid peroxidation and iron homeostasis. The present review summarizes the metabolic networks involved in ferroptosis based on previous studies, and discusses the function of ferroptosis in pathological processes, including cancer. Finally, the clinical significance of ferroptosis is highlighted, to provide evidence for further studies.

Ferroptosis is associated with oxygen-glucose deprivation/reoxygenation-induced Sertoli cell death

Sertoli cell death contributes to spermatogenesis impairment, which is associated with male infertility. Testicular ischemia‑reperfusion (I/R) injury induces the cell death of germ cells and Sertoli cells, whereas inhibition of cell death ameliorates acute testicular I/R damage. The aim of the present study was to investigate the mechanism of I/R stress-induced cell death in TM4 cells. Oxygen‑glucose deprivation and reoxygenation (OGD/R) was demonstrated to induce I/R injury and cell death in TM4 cells. Cell death was blocked by the reactive oxygen species (ROS) inhibitor N‑acetylcysteine, as well as lipid peroxidation inhibitors Liproxstatin‑1 and iron chelator deferoxamine; however, inhibitors of apoptosis, necrosis or autophagy had no effect. It was also demonstrated that iron and lipid ROS levels were elevated in I/R injury and that mitochondria decreased in size and increased in membrane density, which is indicative of ferroptosis. Furthermore, the generation of lipid ROS suggests iron accumulation and glutathione (GSH) depletion. The expression of ferroportin (Fpn) protein and mRNA was decreased in TM4 cells. Notably, overexpression of Fpn inhibited ferroptosis, lipid ROS generation and iron accumulation. In addition, GSH‑dependent peroxidase 4 (GPX4) was inactivated via GSH depletion following I/R injury, whereas GPX4 activation blocked I/R‑induced ferroptosis by reducing lipid ROS levels. The mitogen‑activated protein kinase (MAPK) pathway was also investigated in the present study; it was observed that I/R‑induced ferroptosis was blocked by inhibiting p38 MAPK activation. The results of the present study demonstrate that ferroptosis is a pervasive and dynamic type of cell death induced by OGD/R injury in Sertoli cells. This may provide a novel insight into the application of cytoprotection in testicular I/R damage‑induced cell loss.

Cell death mechanisms of the anti-cancer drug etoposide on human cardiomyocytes isolated from pluripotent stem cells

Etoposide (ETP) and anthracyclines are applied for wide anti-cancer treatments. However, the ETP-induced cardiotoxicity remains to be a major safety issue and the underlying cardiotoxic mechanisms are not well understood. This study is aiming to unravel the cardiotoxicity profile of ETP in comparison to anthracyclines using physiologically relevant human pluripotent stem cell-derived cardiomyocytes (hPSC-CMs). Using xCELLigence real-time cell analyser (RTCA), we found that single high dose of ETP induces irreversible increase in hPSC-CMs beating rate and decrease in beating amplitude. We also identified 58 deregulated genes consisting of 33 upregulated and 25 downregulated genes in hPSC-CMs after ETP treatment. Gene ontology (GO) and pathway analysis showed that most upregulated genes are enriched in GO categories like positive regulation of apoptotic process, regulation of cell death, and mitochondria organization, whereas most downregulated genes were enriched in GO categories like cytoskeletal organization, muscle contraction, and Ca²⁺ ion homeostasis. Moreover, we also found upregulation in 5 miRNAs (has-miR-486-3p, has-miR-34c-5p, has-miR-4423-3p, has-miR-182-5p, and has-miR-139-5p) which play role in muscle contraction, arginine and proline metabolism, and hypertrophic cardiomyopathy (HCM). Immunostaining and transmission electron microscopy also confirmed the cytoskeletal and mitochondrial damage in hPSC-CMs treated with ETP, as well as noticeable alterations in intracellular calcium handling and mitochondrial membrane potential were also observed. The apoptosis inhibitor, Pifithrin-α, found to protect hPSC-CMs from ETP-induced cardiotoxicity, whereas hPSC-CMs treated with ferroptosis inhibitor, Liproxstatin-1, showed significant recovery in hPSC-CMs functional properties like beating rate and amplitude after ETP treatment. We suggest that the damage to mitochondria is a major contributing factor involved in ETP-induced cardiotoxicity and the activation of the p53-mediated ferroptosis pathway by ETP is likely the critical pathway in ETP-induced cardiotoxicity. We also conclude that the genomic biomarkers identified in this study will significantly contribute to develop and predict potential cardiotoxic effects of novel anti-cancer drugs in vitro.

Non-apoptotic cell death in malignant tumor cells and natural compounds

Traditional cancer therapy is mainly targeting on enhancing cell apoptosis, however, it is well established that many cancer cells are chemo-resistant and defective in apoptosis induction. Therefore, it may have important therapeutic implications to exploit some novel natural compounds based on non-apoptotic programmed cell death. Currently, accumulating evidence shows that the compounds from nature source can induce non-apoptotic programmed cell death in cancer cells, and therefore these natural compounds have gained a great promise for the future anticancer therapeutics. In this review, we will concentrate our efforts on the latest developments regarding major forms of non-apoptotic programmed cell death--autophagic cell death, necroptosis, ferroptosis, pyroptosis, glutamoptosis and exosome-associated cell death. Our increased understanding of the role of natural compounds in regulating non-apoptotic programmed cell death will hopefully provide prospective strategies for cancer therapy.

Cell death-based approaches in treatment of the urinary tract-associated diseases: a fight for survival in the killing fields

Urinary tract-associated diseases comprise a complex set of disorders with a variety of etiologic agents and therapeutic approaches and a huge global burden of disease, estimated at around 1 million deaths per year. These diseases include cancer (mainly prostate, renal, and bladder), urinary tract infections, and urolithiasis. Cell death plays a key role in the pathogenesis and therapy of these conditions. During urinary tract infections, invading bacteria may either promote or prevent host cell death by interfering with cell death pathways. This has been studied in detail for uropathogenic E. coli (UPEC). Inhibition of host cell death may allow intracellular persistence of live bacteria, while promoting host cell death causes tissue damage and releases the microbes. Both crystals and urinary tract obstruction lead to tubular cell death and kidney injury. Among the pathomechanisms, apoptosis, necroptosis, and autophagy represent key processes. With respect to malignant disorders, traditional therapeutic efforts have focused on directly promoting cancer cell death. This may exploit tumor-specific characteristics, such as targeting Vascular Endothelial Growth Factor (VEGF) signaling and mammalian Target of Rapamycin (mTOR) activity in renal cancer and inducing survival factor deprivation by targeting androgen signaling in prostate cancer. An area of intense research is the use of immune checkpoint inhibitors, aiming at unleashing the full potential of immune cells to kill cancer cells. In the future, this may be combined with additional approaches exploiting intrinsic sensitivities to specific modes of cell death such as necroptosis and ferroptosis. Here, we review the contribution of diverse cell death mechanisms to the pathogenesis of urinary tract-associated diseases as well as the potential for novel therapeutic approaches based on an improved molecular understanding of these mechanisms.

The Role of Ferroptosis in Cancer Development and Treatment Response

Ferroptosis is a process driven by accumulated iron-dependent lipid ROS that leads to cell death, which is a distinct regulated cell death comparing to other cell death. The lethal metabolic imbalance resulted from GSH depletion or inactivation of glutathione peroxidase 4 is the executor of ferroptosis within the cancer cell. Small molecules-induced ferroptosis has a strong inhibition of tumor growth and enhances the sensitivity of chemotherapeutic drugs, especially in the condition of drug resistance. These evidences have highlighted the importance of ferroptosis in cancer therapeutics, but the roles of ferroptosis in tumorigenesis and development remain unclear. This article provides an overview of the mechanisms of ferroptosis, highlights the role of ferroptosis in cancer and discusses strategies for therapeutic modulation.

Induction of ferroptosis and mitochondrial dysfunction by oxidative stress in PC12 cells

Neurodegenerative diseases (NDD) are typically associated with neuron loss in nervous system areas. Interventions with related death mechanisms may ameliorate NDD progression. Oxidative stress plays an important role in NDD cell death routines. However, tert-butylhydroperoxide (t-BHP), a widely used oxidative stress stimulus, induces neural cell death through a mechanism that remains elusive. In our study, the ferroptosis marker events occurred after co-treatment with 100 μM t-BHP for 1 h, all of which were reversed in the presence of the ferroptosis inhibitor ferrostatin-1 (Fer-1) and the iron chelator deferoxamine, implying the occurrence of ferroptosis. Moreover, mitochondrial dysfunction accompanied by a decreased in membrane potential and ATP production, increased mitochondrial ROS generation. Furthermore, this mitochondrial dysfunction could be reversed by Fer-1. In addition, JNK1/2 and ERK1/2 were activated upstream of the ferroptosis and mitochondrial dysfunction. In summary, these data suggest that ferroptosis, coupled with mitochondrial dysfunction, was involved in t-BHP-induced PC12 death. JNK1/2 and ERK1/2 played important roles in t-BHP-induced cell death. Overall, this study might provide clues to the oxidative stress-based strategies for cell protection in NDD.

The Role of BCL-2 Family Members in Acute Kidney Injury

B-cell lymphoma 2 (BCL-2) family proteins gather at the biologic cross-roads of renal cell survival: the outer mitochondrial membrane. Despite shared sequence and structural features, members of this conserved protein family constantly antagonize each other in a life-and-death battle. BCL-2 members innocently reside within renal cells until activated or de-activated by physiologic stresses caused by common nephrotoxins, transient ischemia, or acute glomerulonephritis. Recent experimental data not only illuminate the intricate mechanisms of apoptosis, the most familiar form of BCL-2-mediated cell death, but emphasizes their newfound roles in necrosis, necroptosis, membrane pore transition regulated necrosis, and other forms of acute cell demise. A major paradigm shift in non-cell death roles of the BCL-2 family has occurred. BCL-2 proteins also regulate critical daily renal cell housekeeping functions including cell metabolism, autophagy (an effective means for recycling cell components), mitochondrial morphology (organelle fission and fusion), as well as mitochondrial biogenesis. This article considers new concepts in the biochemical and structural regulation of BCL-2 proteins that contribute to membrane pore permeabilization, a universal feature of cell death. Despite these advances, persistent BCL-2 family mysteries continue to challenge cell biologists. Given their interface with many intracellular functions, it is likely that BCL-2 proteins determine cell viability under many pathologic circumstances relevant to the nephrologist and, as a consequence, represent an ideal therapeutic target.

Cell Death Mechanisms in Stroke and Novel Molecular and Cellular Treatment Options

As a result of ischemia or hemorrhage, blood supply to neurons is disrupted which subsequently promotes a cascade of pathophysiological responses resulting in cell loss. Many mechanisms are involved solely or in combination in this disorder including excitotoxicity, mitochondrial death pathways, and the release of free radicals, protein misfolding, apoptosis, necrosis, autophagy and inflammation. Besides neuronal cell loss, damage to and loss of astrocytes as well as injury to white matter contributes also to cerebral injury. The core problem in stroke is the loss of neuronal cells which makes recovery difficult or even not possible in the late states. Acute treatment options that can be applied for stroke are mainly targeting re-establishment of blood flow and hence, their use is limited due to the effective time window of thrombolytic agents. However, if the acute time window is exceeded, neuronal loss starts due to the activation of cell death pathways. This review will explore the most updated cellular death mechanisms leading to neuronal loss in stroke. Ischemic and hemorrhagic stroke as well as subarachnoid hemorrhage will be debated in the light of cell death mechanisms and possible novel molecular and cellular treatment options will be discussed.

Regulated Cell Death

In this chapter, the various subroutines of regulated cell death are neatly described by highlighting apoptosis and subforms of regulated necrosis such as necroptosis, ferroptosis, pyroptosis, and NETosis. Typically, all forms of regulated necrosis are defined by finite rupture of the plasma cell membrane. Apoptosis is characterized by an enzymatic machinery that consists of caspases which cause the morphologic features of this type of cell death. Mechanistically, apoptosis can be instigated by two major cellular signalling pathways: an intrinsic pathway that is initiated inside cells by mitochondrial release of pro-apoptotic factors or an extrinsic pathway that is initiated at the cell surface by various death receptors. In necroptosis, the biochemical processes are distinct from those found in apoptosis; in particular, there is no caspase activation. As such, necroptosis is a kinase-mediated cell death that relies on “receptor-interacting protein kinase 3” which mediates phosphorylation of the pseudokinase “mixed lineage kinase domain-like protein.” While ferroptosis is an iron-dependent, oxidative form of regulated necrosis that is biochemically characterized by accumulation of ROS from iron metabolism, oxidase activity, and lipid peroxidation products, pyroptosis is defined as a form of cell death (predominantly of phagocytes) that develops during inflammasome activation and is executed by caspase-mediated cleavage of the pore-forming protein gasdermin D. Finally, NETosis refers to a regulated death of neutrophils that is characterized by the release of chromatin-derived weblike structures released into the extracellular space. The chapter ends up with a discussion on the characteristic feature of regulated necrosis: the passive release of large amounts of constitutive DAMPs as a consequence of final plasma membrane rupture as well as the active secretion of inducible DAMPs earlier during the dying process. Notably, per cell death subroutine, the active secretion of inducible DAMPs varies, thereby determining different immunogenicity of dying cells.

Iron reduction response and demographic differences between diabetics and non-diabetics with cardiovascular disease entered into a controlled clinical trial

Filings of elemental iron separated magnetically from a homogenate of breakfast cereal implicated in the risk of cardiovascular disease and diabetes.

Why should neuroscientists worry about iron? The emerging role of ferroptosis in the pathophysiology of neuroprogressive diseases

Ferroptosis is a unique form of programmed death, characterised by cytosolic accumulation of iron, lipid hydroperoxides and their metabolites, and effected by the fatal peroxidation of polyunsaturated fatty acids in the plasma membrane. It is a major driver of cell death in neurodegenerative neurological diseases. Moreover, cascades underpinning ferroptosis could be active drivers of neuropathology in major psychiatric disorders. Oxidative and nitrosative stress can adversely affect mechanisms and proteins governing cellular iron homeostasis, such as the iron regulatory protein/iron response element system, and can ultimately be a source of abnormally high levels of iron and a source of lethal levels of lipid membrane peroxidation. Furthermore, neuroinflammation leads to the upregulation of divalent metal transporter1 on the surface of astrocytes, microglia and neurones, making them highly sensitive to iron overload in the presence of high levels of non-transferrin-bound iron, thereby affording such levels a dominant role in respect of the induction of iron-mediated neuropathology. Mechanisms governing systemic and cellular iron homeostasis, and the related roles of ferritin and mitochondria are detailed, as are mechanisms explaining the negative regulation of ferroptosis by glutathione, glutathione peroxidase 4, the cysteine/glutamate antiporter system, heat shock protein 27 and nuclear factor erythroid 2-related factor 2. The potential role of DJ-1 inactivation in the precipitation of ferroptosis and the assessment of lipid peroxidation are described. Finally, a rational approach to therapy is considered, with a discussion on the roles of coenzyme Q₁₀, iron chelation therapy, in the form of deferiprone, deferoxamine (desferrioxamine) and deferasirox, and N-acetylcysteine.

Acid sphingomyelinase promotes mitochondrial dysfunction due to glutamate-induced regulated necrosis

Inhibiting the glutamate/cystine antiporter system x_c^-, a key antioxidant defense machinery in the CNS, could trigger a novel form of regulated necrotic cell death, ferroptosis. The underlying mechanisms of system x_c^--dependent cell demise were elucidated using primary oligodendrocytes (OLs) treated with glutamate to block system x_c^- function. Pharmacological analysis revealed ferroptosis as a major contributing factor to glutamate-initiated OL death. A sphingolipid profile showed elevations of ceramide species and sphingosine that were preventable by inhibiting of an acid sphingomyelinase (ASM) activity. OL survival was enhanced by both downregulating ASM expression and blocking ASM activity. Glutamate-induced ASM activation seems to involve posttranscriptional mechanisms and was associated with a decreased GSH level. Further investigation of the mechanisms of OL response to glutamate revealed enhanced reactive oxygen species production, augmented lipid peroxidation, and opening of the mitochondrial permeability transition pore that were attenuated by hindering ASM. Of note, knocking down sirtuin 3, a deacetylase governing the mitochondrial antioxidant system, reduced OL survival. The data highlight the importance of the mitochondrial compartment in regulated necrotic cell death and accentuate the novel role of ASM in disturbing mitochondrial functions during OL response to glutamate toxicity, which is essential for pathobiology in stroke and traumatic brain injury.

Molecular crosstalk between ferroptosis and apoptosis: emerging role of ER stress-induced p53-independent PUMA expression

Ferroptosis is a type of programmed cell death that depends on iron and is characterized by the accumulation of lipid peroxides. In the present study, we investigated the nature of the interplay between ferroptosis and other forms of cell death such as apoptosis. Human pancreatic cancer PANC-1 and BxPC-3 and human colorectal cancer HCT116 cells were treated with ferroptotic agents such as erastin and artesunate (ART) in combination with the apoptotic agent tumor necrosis factor-related apoptosis-inducing ligand (TRAIL). We observed synergistic interaction of erastin or ART with TRAIL as determined by cell death assay, caspase activation, poly [ADP-ribose] polymerase 1 (PARP-1) cleavage, flow cytometry analysis, and lipid peroxidation assay. Moreover, erastin and ART induced endoplasmic reticulum (ER) stress and promoted p53 upregulated modulator of apoptosis (PUMA) expression via C/EBP-homologous protein (CHOP). Synergy of erastin/ART and TRAIL was abolished in PUMA-deficient HCT116 cells and CHOP-deficient mouse embryonic fibroblasts, but not in p53-deficient HCT116 cells. The results suggest the involvement of the p53-independent CHOP/PUMA axis in response to ferroptosis inducers, which may play a key role in ferroptotic agent-mediated sensitization to TRAIL-induced apoptosis.

Multifaceted Roles of Glutathione and Glutathione-Based Systems in Carcinogenesis and Anticancer Drug Resistance

SIGNIFICANCE

Glutathione is the most abundant antioxidant molecule in living organisms and has multiple functions. Intracellular glutathione homeostasis, through its synthesis, consumption, and degradation, is an intricately balanced process. Glutathione levels are often high in tumor cells before treatment, and there is a strong correlation between elevated levels of intracellular glutathione/sustained glutathione-mediated redox activity and resistance to pro-oxidant anticancer therapy. Recent Advances: Ample evidence demonstrates that glutathione and glutathione-based systems are particularly relevant in cancer initiation, progression, and the development of anticancer drug resistance.

CRITICAL ISSUES

This review highlights the multifaceted roles of glutathione and glutathione-based systems in carcinogenesis, anticancer drug resistance, and clinical applications.

FUTURE DIRECTIONS

The evidence summarized here underscores the important role played by glutathione and the glutathione-based systems in carcinogenesis and anticancer drug resistance. Future studies should address mechanistic questions regarding the distinct roles of glutathione in different stages of cancer development and cancer cell death. It will be important to study how metabolic alterations in cancer cells can influence glutathione homeostasis. Sensitive approaches to monitor glutathione dynamics in subcellular compartments will be an indispensible step. Therapeutic perspectives should focus on mechanism-based rational drug combinations that are directed against multiple redox targets using effective, specific, and clinically safe inhibitors. This new strategy is expected to produce a synergistic effect, prevent drug resistance, and diminish doses of single drugs. Antioxid. Redox Signal. 27, 1217-1234.

Diterpenoid natural compound C4 (Crassin) exerts cytostatic effects on triple-negative breast cancer cells via a pathway involving reactive oxygen species

PURPOSE

Triple-negative breast cancers (TNBC) lack expression of three common cell surface receptors, i.e., estrogen receptor (ER), progesterone receptor (PR) and human epidermal growth factor receptor-2 (HER2). Accordingly, TNBCs are associated with fewer treatment options and a relatively poor prognosis. Having screened a National Cancer Institute natural compound library, the purpose of this study was to investigate the bioactivity of compound C4 (Crassin) in TNBC cells.

METHODS

Cell viability assays were performed in two TNBC cell lines, MDA-MB-231 and 4T1, following C4 treatment in the presence or absence of the antioxidant N-acetyl-L-cysteine (NAC). Phosphorylation of Akt and ERK was assessed by Western blotting. Apoptosis, necrosis, autophagy, necroptosis, ferroptosis and cytostasis assays were performed to explain viability deficits resulting from C4 exposure.

RESULTS

We found that the viability of the TNBC cells tested decreased in a concentration- and time-dependent fashion following C4 treatment. This decrease coincided with an unexpected increase in the expression of the cell survival effectors pAkt and pERK. In addition, we found that both the decreased cell viability and the increased pAkt/pERK levels could be rescued by the antioxidant NAC, suggesting a central role for reactive oxygen species (ROS) in the mechanism of action of C4. Necrosis, apoptosis, necroptosis and ferroptosis could be ruled out as cell death mechanisms. Instead, we found that C4 induced cytostasis downstream of ROS activation. Finally, we observed a synergistic effect between C4 and the chemotherapeutic drug doxorubicin in TNBC cells.

CONCLUSIONS

From our in vitro data we conclude that C4 exerts cytostatic effects on triple-negative breast cancer cells via a pathway involving reactive oxygen species. Its potential value in combination with cytotoxic therapies merits deeper investigation in pre-clinical models.