Ferroptosis is a newly discovered regulated cell death process. Unlike apoptosis, ferroptosis results from the iron-dependent accumulation of lipid peroxides, which is closely associated with reactive oxygen species (ROS). Hydroxyl radical (·OH), the most active ROS, is found to be capable of initiating lipid peroxidation. The generation of ·OH in biosystems is involved in the participation of iron.

On the other hand, cytoplasmic viscosity is a basic factor of living cells, and the increase of cytoplasmic viscosity is one of the most important morphological features of apoptosis. As ferroptosis is morphologically distinct from apoptosis, it is significant to disclose whether ferroptosis is accompanied by cytoplasmic viscosity alteration.

Recently, a research team led by Prof. MA Huimin from Institute of Chemistry of the Chinese Academy of Sciences characterized for the first time the changing behavior of ·OH and cytoplasmic viscosity during ferroptosis using a dual-functional fluorescence probe (H-V). The study was published in J. Am. Chem. Soc.

The researchers designed probe H-V via the molecular rotor strategy and the unique aromatic hydroxylation of ·OH. They found that with the increase in microenvironmental viscosity, the intramolecular rotation of H-V is restricted, leading to fluorescence enhancement at 520 nm.

Besides, they found that for ·OH detection, the specific hydroxylation by ·OH and subsequent structure rearrangement led to the π-conjugation extension of H-V, thereby showing a large spectral red shift and a sharp NIR fluorescent off-on response at 652 nm. This allows the independent detection of ·OH and viscosity in two different channels.

Furthermore, with H-V, the researchers found that ferroptosis is accompanied by noticeable ·OH generation, cytoplasmic viscosity increase and accelerated lipid droplet formation. Most notably, the raised ·OH comprises the majority of the total ROS in ferroptosis, and is probably the main cause of lipid peroxidation, which thus leads to the increase of cytoplasmic viscosity and the accelerated formation of lipid droplet.

The structure of probe H-V and its fluorescence imaging of ·OH and cytoplasmic viscosity during ferroptosis. (Image by Prof. MA Huimin)