Ferroptosis, a form of programmed necrotic cell death mediated by lipid peroxidation, has been extensively researched for its critical role in various disease disorders resulting from accumulated reactive oxygen species (ROS) and their unbalanced cellular homeostasis [
1-
3]. Specifically in the context of liver pathology, the status of ferroptosis is increasingly recognized not only as an indicator of cell death but also as a significant biomarker reflecting the severity of associated conditions such as inflammation, fibrosis, and even tumorigenesis in progressive liver diseases [
4,
5].
The precise monitoring of lipid peroxidation, the key driving force behind ferroptosis, is essential for elucidating the mechanisms of disease progression and developing novel therapeutic agents. Currently, several probes are available for ex vivo applications. These include established tools for detecting lipid peroxidation, such as BODIPY 581/591 C11 [
6] and Liperfluo [
7], and probes for detecting ferrous iron (Fe2+), such as Ferrorange [
8] and Mito-FerroGreen [
9].
However, the majority of these existing probes operate in the visible light spectrum, presenting inherent limitations in complex biological systems. These limitations include poor tissue penetration, high background autofluorescence, and, crucially, a lack of specificity for changes occurring within specific cellular organelles [
10,
11]. Consequently, there remains a significant unmet need for robust tools capable of real-time, high-resolution observation of ferroptosis dynamics in the challenging
in vivo environment.
To address these challenges, the recent work by Pham et al. [
12] introduces TTM-4, a groundbreaking near-infrared (NIR) fluorescent probe designed to monitor ferroptosis through viscosity changes. As illustrated in the TTM-4 mechanism (
Fig. 1, left), the probe utilizes a donor-π-acceptor framework that facilitates intramolecular charge transfer. This molecular design allows the probe to remain in an “OFF” state under low-viscosity conditions, while exhibiting a sharp “ON” signal at 812 nm (excited at 576 nm) in response to the increased microviscosity that accompanies lipid peroxidation during ferroptosis. This red-shift into the NIR window significantly enhances tissue penetration and minimizes background interference, overcoming the hurdles of traditional visible-light probes.
The most striking innovation of this study lies in its revelation of the spatiotemporality of ferroptosis (
Fig. 1, middle). Unlike conventional markers that provide a static snapshot of cell death, TTM-4 enables real-time tracking of lipid peroxidation across different cellular compartments. The authors observed a dynamic progression where the ferroptotic signal originates in the cytoplasmic lipid droplets and the endoplasmic reticulum (ER) and subsequently migrates to the nucleoplasmic lipid droplets (nLDs).
Notably, the formation and oxidation of nLDs emerge as a critical temporal marker, appearing predominantly in the late stage of ferroptosis. This shift from the cytosol to the nucleus suggests that nLDs may play a specialized role as an adaptive response to ER stress or as a terminal stage of lipid ROS accumulation. By distinguishing these stages, TTM-4 provides a high-resolution, time-resolved map of how ferroptosis unfolds within a single hepatocyte.
Furthermore, the study demonstrates the potential clinical significance (
Fig. 1, right) of this technology. The probe successfully differentiated ferroptotic hepatocytes in metabolic dysfunction-associated steatotic liver disease (MASLD) and metabolic dysfunction-associated steatohepatitis (MASH) liver models, showing a dramatic increase in fluorescence intensity compared to control tissues. This robust performance in complex tissue environments highlights TTM-4 not only as a powerful research tool but also as a promising diagnostic platform for the early detection and monitoring of metabolic liver diseases.
Beyond its diagnostic utility, the intense TTM-4 signal observed within the nucleus during the late stage of ferroptosis invites us to reconsider the traditional definition of cellular identity in the context of liver disease. It raises a critical question: how does this localized nuclear stress impact the overall lipid-rich microenvironment of the MASLD/MASH hepatocyte? The increased viscosity and oxidation within nLDs may not be a contained event; rather, they could trigger a systemic shift in lipid metabolism and organelle interaction [
13], effectively ‘reprogramming’ the cellular environment into a pro-ferroptotic state [
14]. Understanding whether this nuclear physical stress serves as a critical threshold for the transition to advanced MASH will be a vital area for future investigation.
In conclusion, the work by Pham et al. [
12] extends far beyond the development of a high-performance imaging tool; it provides a new conceptual framework for understanding the biophysical landscape of ferroptosis. By integrating chemical oxidation with spatiotemporal dynamics and microviscosity changes, this study allows us to witness the progression of MASLD/MASH with unprecedented clarity. The high-resolution mapping enabled by TTM-4 not only holds promise for the early diagnosis of metabolic liver diseases but also serves as a vital foundation for the development of organelle-specific therapeutic strategies [
15,
16]. Ultimately, this research marks a significant step toward bridging the gap between basic cell biology and clinical hepatology, positioning the nucleus as a key frontier in our fight against liver disease.
FOOTNOTES
-
Authors’ contribution
J.W.J drafted the manuscript and S.F reviewed and edited the manuscript.
-
Acknowledgements
This work was supported by Korea Health Technology R&D Project through the Korea Health Industry Development Institute, funded by the Ministry of Health & Welfare, Korea (RS-2024-00437692).
-
Conflicts of Interest
The authors have no conflicts to disclose.
Figure 1.Left: Mechanism of TTM-4. In low-viscosity environments, the probe remains in an “OFF” state. Upon increased microviscosity accompanying lipid peroxidation during ferroptosis, TTM-4 exhibits a sharp “ON” signal in the NIR region at 812 nm (excited at 576 nm), allowing for deep tissue penetration and minimal background interference. Middle: Spatiotemporality of ferroptosis within a hepatocyte. The schematic illustrates the dynamic progression of lipid peroxidation. In the early stage, the ferroptotic signal originates in the cLDs and the ER. As ferroptosis progresses to the late stage, the oxidation signal migrates to the nLDs. The formation and oxidation of nLDs serve as a critical temporal marker for late-stage ferroptosis. Note that TTM-4 shows high specificity for cLDs/ER/nLDs while remaining nonresponsive in mitochondria. Right: Diagnostic application in MASLD and MASH. TTM-4 demonstrates robust performance in differentiating ferroptotic hepatocytes in MASLD and MASH. The fluorescence intensity is significantly elevated in diseased liver tissues compared to healthy controls, highlighting the probe’s potential as a diagnostic platform for monitoring metabolic liver disease progression. NIR, near-infrared; cLDs, cytosolic lipid droplets; nLDs, nuclear lipid droplets; MASLD, metabolic dysfunction-associated steatotic liver disease; MASH, metabolic dysfunction-associated steatohepatitis; ER, endoplasmic reticulum.
Abbreviations
metabolic dysfunction-associated steatohepatitis
metabolic dysfunction-associated steatotic liver disease
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- Correspondence to editorial on “Novel near-infrared probe for monitoring lipid peroxidation-mediated viscosity change in ferroptotic hepatocytes”
Taeeung Kim, Le Bich Hang Pham, Jeeyeon Lee, Keon Wook Kang
Clinical and Molecular Hepatology.2026; 32(3): e375. CrossRef
