Free iron has long been assumed to be a deteriorating factor in an oxidative insult and was recently found to be directly associated with ferroptosis, a specific type of cell death. The free iron-involved production of lipid peroxides activates the fetal pathway, resulting in nonapoptotic, programed cell death. Lipid peroxides appear to destroy membrane integrity, leading to cell rupture. Glutathione is a major redox molecule that functions to protect against ferroptosis by its ability to donate an electron to glutathione peroxidase 4 (GPX4), the sole enzyme that reduces phospholipid hydroperoxides. The availability of free cysteine determines the levels of glutathione synthesis, and, hence, its deprivation causes ferroptosis. Free iron is provided via ferritinophagy, the chaperone-mediated autophagic degradation of ferritin, but GPX4 also undergoes degradation via chaperone-mediated autophagy. Activated Nrf2 and ATF4 induce the expression of the cystine transporter xCT to cope with ferroptosis. To the contrary, the excessive activation of p53 induces ferroptosis by suppressing the expression of xCT in genetic and nongenetic manners. It therefore appears that xCT functions as the gatekeeper for determining cellular survival by regulating the availability of cysteine in the cell. The issue of the extent of involvement of ferroptosis in an in-vivo situation largely remains ambiguous. Establishing tools for specifying ferroptotic cells in situ would facilitate our understanding of its roles in pathogenesis.

Red blood cells (RBC) are specifically differentiated to transport oxygen and carbon dioxide in the blood and they lack most organelles, including mitochondria. The autoxidation of hemoglobin constitutes a major source of reactive oxygen species (ROS). Nitric oxide, which is produced by endothelial nitric oxide synthase (NOS3) or via the hemoglobin-mediated conversion of nitrite, interacts with ROS and results in the production of reactive nitrogen oxide species. Herein we present an overview of anemic diseases that are closely related to oxidative damage. Because the compensation of proteins by means of gene expression does not proceed in enucleated cells, antioxidative and redox systems play more important roles in maintaining the homeostasis of RBC against oxidative insult compared to ordinary cells. Defects in hemoglobin and enzymes that are involved in energy production and redox reactions largely trigger oxidative damage to RBC. The results of studies using genetically modified mice suggest that antioxidative enzymes, notably superoxide dismutase 1 and peroxiredoxin 2, play essential roles in coping with oxidative damage in erythroid cells, and their absence limits erythropoiesis, the life-span of RBC and consequently results in the development of anemia. The degeneration of the machinery involved in the proteolytic removal of damaged proteins appears to be associated with hemolytic events. The ubiquitin-proteasome system is the dominant machinery, not only for the proteolytic removal of damaged proteins in erythroid cells but also for the development of erythropoiesis. Hence, despite the fact that it is less abundant in RBC compared to ordinary cells, the aberrant ubiquitin-proteasome system may be associated with the development of anemic diseases via the accumulation of damaged proteins, as typified in sickle cell disease, and impaired erythropoiesis.

Ferroptosis is a type of iron-dependent, non-apoptotic cell death, which is typically induced by the suppression of phospholipid hydroperoxide-glutathione peroxidase (GPX4) activity and a corresponding elevation in lipid peroxidation products. While the inhibition of the xCT-mediated uptake of cystine commonly causes ferroptosis, the sensitivity of cells to the inhibition of the glutathione (GSH) synthesis by buthionine sulfoximine (BSO) varies considerably. The objective of this study was to clarify the underlying mechanism responsible for these differential responses to the targeted inhibition of either the cysteine (Cys) supply to or GSH synthesis in the cells. While intracellular GSH levels were depleted when mouse hepatoma Hepa 1-6 cells were treated with BSO, intracellular Cys levels rather increased and viability of the cells remained unchanged, suggesting that Cys has a role in this resistance to ferroptosis under conditions of GSH depletion. When the cells were treated with pioglitazone (PGZ), a potent inhibitor of CDGSH iron sulphur domain-containing proteins (CISDs), PGZ alone had no effect on either cell viability or GSH levels but induced ferroptosis under conditions of GSH depletion by the BSO treatment. In the case of the co-treatment with PGZ and BSO, ferrous iron and the levels of lipid peroxides were robustly increased in the cells, but neither endoplasmic reticulum stress nor apoptosis was evident. Collectively, CISDs appeared to exert an anti-ferroptotic function by suppressing free iron toxicity and the subsequent lipid peroxidation with assistance provided by Cys.

Ferroptosis, a type of iron-dependent necrotic cell death, is triggered by the accumulation of excessive lipid peroxides in cells. Glutathione (GSH), a tripeptide redox molecule that contains a cysteine (Cys) unit in the center, plays a pivotal role in protection against ferroptosis. When the transsulfuration pathway is activated, the sulfur atom of methionine (Met) is utilized to generate Cys, which can then suppress Cys-starvation-induced ferroptosis. In the current study, we cultured HeLa cells in Met- and/or cystine (an oxidized Cys dimer)- deprived medium and investigated the roles of Met in ferroptosis execution. The results indicate that, in the absence of cystine or Met, ferroptosis or cell cycle arrest, respectively, occurred. Contrary to our expectations, however, the simultaneous deprivation of both Met and cystine failed to induce ferroptosis, although the intracellular levels of Cys and GSH were maintained at low levels. Supplementation with S-adenosylmethionine (SAM), a methyl group donor that is produced during the metabolism of Met, caused the cell cycle progression to resume and lipid peroxidation and the subsequent induction of ferroptosis was also restored under conditions of Met/cystine double deprivation. DNA methylation appeared to be involved in the resumption in the SAM-mediated cell cycle because its downstream metabolite S-adenosylhomocysteine failed to cause either cell cycle progression or ferroptosis to be induced. Taken together, our results suggest that elevated lipid peroxidation products that are produced during cell cycle progression are involved in the execution of ferroptosis under conditions of Cys starvation.