Ferroptosis Markers and Detection

Ferroptosis is a unique type of cell death first observed in 2003, marking it as a relatively recent discovery. However, the name "ferroptosis" was not introduced until 2012, when researchers identified that this process, driven by the buildup of lipid peroxides, notably relies on iron. Unlike more familiar types of regulated cell death (such as apoptosis, pyroptosis, and necroptosis), ferroptosis has key distinct features. These include the iron-dependent toxic accumulation of lipid peroxides in cell membranes, as well as abnormalities in mitochondrial morphology. Ferroptosis remains a relatively recent discovery, with many of its underlying mechanisms yet to be fully uncovered. This article highlights key molecular markers of ferroptosis to support and guide its investigation. 

Why ferroptosis?

Ferroptosis plays a critical role in both normal and disease-related biological processes. Under healthy conditions, it contributes to tumor suppression, immune defense against infections, development, and aging. In pathological settings, ferroptosis is implicated in iron-overload disorders, tissue damage, neurodegenerative diseases, immune system dysfunctions, infections, and cancer development.

Notably, several cancers have been found to exhibit mechanisms that suppress ferroptosis. Mesenchymal and dedifferentiated cancer cells, which are typically resistant to apoptosis and conventional treatments, show a heightened sensitivity to ferroptosis. Activating or modifying ferroptotic pathways could offer new avenues for cancer therapy. The pathway is already being explored as a promising target for treatment strategies, with existing drugs like sorafenib exploiting ferroptotic mechanisms to support their anti-cancer effects.

Hallmarks and markers of ferroptosis

Cell viability assays, such as the MTT assay, Cell Counting Kit-8 (CCK-8), and nuclear dye staining with Hoechst, SYTOX Green, or propidium iodide, are commonly used to assess cell death or damage resulting from ferroptosis. However, these assays are not fully specific to ferroptosis and may also reflect other forms of cell death. To distinguish ferroptosis, it is important to evaluate biochemical, morphological, and even genetic hallmarks that are unique to the pathway. Some common markers and detection methods are highlighted below.

Figure 1. This diagram highlights hallmarks of cells undergoing ferroptosis and key proteins involved in the pathway.

Lipid peroxidation

Polyunsaturated fatty acids (PUFAs) within membrane phospholipids are central drivers and substrates of ferroptosis. Upon incorporation into phospholipids by enzymes such as acyl-CoA synthetase ACSL4 and lysophosphatidylcholine acyltransferase LPCAT3, PUFAs become highly susceptible to oxidation by reactive oxygen species (ROS), particularly lipid-derived ROS. Oxidative stress triggers the accumulation of lipid hydroperoxides (PUFA-OOH), which represent a defining biochemical hallmark of ferroptosis. Enzymatic lipid peroxidation is catalyzed by non-heme iron-containing arachidonate lipoxygenases (ALOXs), including ALOX5, ALOX12, ALOX15, ALOX15B, and ALOXE3, which have all been implicated as key effectors in promoting ferroptotic cell death.

Lipid peroxidation can be detected using a range of methods with varying levels of sensitivity and specificity. In cell culture, lipid ROS can be detected using lipophilic fluorescent probes and quantified by fluorescence microscopy, flow cytometry, or plate-based assays. For more detailed lipidomic profiling, LC-MS/MS mass spectrometry enables the identification and quantification of oxidized phospholipids, specific lipid peroxide species, and oxidative post-translational protein modifications associated with ferroptosis. Additionally, biochemical lipid peroxidation assays that measure stable end products, such as malondialdehyde (MDA) and 4-hydroxynonenal (4-HNE), can serve as indirect but accessible indicators of oxidative lipid damage.

The glutathione (GSH) antioxidant system is the principal defense mechanism against lipid peroxidation during ferroptosis. This axis includes the cystine/glutamate antiporter system X_c^- (mediated by SLC7A11), intracellular GSH, and glutathione peroxidase 4 (GPX4). GPX4 enzymatically reduces lipid hydroperoxides to non-toxic byproducts. Direct inhibition of GPX4 (e.g., by RSL3 or FIN56), degradation of GPX4 protein, or depletion of GSH (e.g., via cystine starvation or erastin treatment) results in unchecked lipid peroxidation and ferroptotic cell death.

Intracellular iron

Ferrous iron (Fe²⁺) plays a central role in ferroptosis by catalyzing the formation of reactive oxygen species (ROS) through Fenton chemistry, in which Fe²⁺ reacts with hydrogen peroxide to generate hydroxyl radicals. These highly reactive species drive the peroxidation of polyunsaturated fatty acids (PUFAs) in membrane phospholipids, leading to ferroptotic cell death.

Intracellular iron homeostasis is tightly regulated by iron uptake, storage, utilization, and export mechanisms. Cellular iron uptake primarily occurs via transferrin (TF)-mediated endocytosis with transferrin receptor 1 (TFRC) on the plasma membrane. Within the endosome, ferric iron (Fe³⁺) is reduced to Fe²⁺ by the STEAP3 metalloreductase. Fe²⁺ is then transported into the cytosol by the divalent metal transporter DMT1 (SLC11A2), contributing to the labile iron pool. Iron-dependent enzymes, including lipoxygenases (ALOX family) and cytochrome P450 oxidoreductase (POR) utilize Fe²⁺ from the pool to initiate and propagate lipid peroxidation. Elevated iron levels thus enhance the likelihood of lipid ROS accumulation.

To prevent iron-mediated toxicity, cells sequester excess iron in ferritin, a cytosolic protein complex (composed of FTH1 and FTL), which stores iron in the Fe³⁺ state. Iron can also be removed by ferroportin (SLC40A1), the only known iron exporter. Overexpression of SLC40A1 reduces intracellular iron levels and suppresses ferroptosis, while its downregulation increases susceptibility. Ferritin turnover is regulated through ferritinophagy, in which ferritin is targeted for lysosomal degradation by the protein NCOA4.

Several methods can be used to assess cellular iron levels. Biochemical iron assays (e.g., colorimetric ferrozine-based assays) allow quantification of total or ferrous iron. Histochemical detection can be performed using Prussian blue staining to visualize ferric iron deposits, typically in tissue sections. Fluorescent iron-specific probes (e.g., Phen Green SK, RhoNox-1, or FerroOrange) can be used to measure intracellular Fe²⁺ by microscopy or flow cytometry.

Organelle-specific effects

Oxidative damage to subcellular membranes during ferroptosis manifests in distinct, organelle-specific alterations. In mitochondria, ferroptosis is commonly associated with elevated reactive oxygen species (ROS), morphological disruption, and a decline in mitochondrial membrane potential. These changes can be visualized using mitochondrial-targeted fluorescent probes (e.g., MitoSOX Red, MitoTracker, JC-1 or TMRE) and mitochondrial staining kits.

Endoplasmic reticulum (ER) stress during ferroptosis is linked to increased ER membrane viscosity, which can be detected using ER-localized fluorescent probes. In lysosomes, ferroptosis-associated iron accumulation can be monitored using fluorescent probes (e.g., LysoTracker Green), along with lysosomal staining kits. Notably, upregulation of cathepsin B has also been implicated as a lysosome-specific effector in ferroptotic cell death. Another protein, the cis-Golgi matrix protein GM130 has been used as a marker to monitor ferroptosis-associated Golgi stress and its diminished dispersal. 

Expert advice on ferroptosis

For more practical insight, we asked Jiajia Ji, Ph.D., Assay R&D Scientist II at Cayman Chemical and an expert in ferroptosis, for some experimental tips.

BC: What experimental approaches require particular caution when studying ferroptosis to avoid misinterpretation or incomplete conclusions?

Dr. Ji: The answer will vary depending on specific parameters to detect and the detection methods used.

When inducing ferroptosis in cells, it is often ignored that the inducers could have off-target effects that may affect the downstream readouts. For example, RSL3 non-selectively inhibits selenoproteins, not just GPX4. To minimize the risks of misinterpretation, we recommend using multiple inducers, ideally with different mechanisms of inducing ferroptosis.

As mentioned in the article, cell viability assays and nuclear dye staining detect general cytotoxicity rather than ferroptosis specifically. In addition to evaluating other hallmarks recommended in the article, it is necessary to include ferroptosis inhibitors, such as 5-lipoxygenase inhibitor zileuton, GPX4 activator PKUMDL-LC-101-D04, and iron chelator deferoxamine (DFO) as controls in the cell viability/staining assays. Apoptosis/necrosis inhibitors should also be considered in the assays.

When it comes to iron detection, although dyes like FerroOrange or Phen Green SK have been shown to distinguish labile Fe²⁺ from bound iron or other metals, it is advisable to confirm the data using a second method, such as the unified-ferene (u-ferene) assay, which enables the quantification of both labile and total iron in samples.

BC: Do you have other general advice?

Dr. Ji: I would recommend the following. Ferroptosis should be demonstrated with multiple parameters, such as decreased cell viability, increased lipid ROS, increased labile iron levels, and decreased GSH levels. For each parameter assessed, confirmation with an alternative method is advisable. Proper controls—including inhibitors of ferroptosis and alternative cell death types (e.g., apoptosis, necroptosis)—should also be incorporated into experiments.

When conducting ferroptosis research in the context of cancer, physiologically relevant models are highly desirable. For instance, 3D cultures and patient-derived cells may better reflect in vivo conditions than traditional 2D cultures. In addition, the tumor microenvironment (e.g., hypoxia, nutrient stress) could also affect the physiological relevance of the experiments.

The field is advancing rapidly, so stay updated. Researchers should stay informed about novel or refined methodologies, newly identified biomarkers, and physiological modifiers to minimize misinterpretations and progress their studies with greater confidence.

Dr. Ji is an Assay R&D scientist with 14+ years of lab experience, specializing in lipid biology and cell metabolism. At Cayman, she devotes herself to developing and optimizing highly reliable biochemical and cell-based assays for biomedical research.

Explore Cayman Chemical’s Guide to Ferroptosis: Mechanisms & Research Tools to learn more about the mechanisms underlying ferroptosis and find recommendations for assay kits, fluorescent probes, ferroptosis inducers and suppressors, and more.

Table of ferroptosis markers

Several key proteins and molecular products central to the ferroptosis pathway are consistently highlighted in the literature as informative biomarkers. These markers can be used to assess the activation state of ferroptosis or its modulation under various experimental or pathological conditions. The table below summarizes established ferroptosis markers, including regulatory proteins and small-molecule byproducts. Where applicable, links to validated antibodies and assay kits are provided to support related projects and experimentation.

References

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