An endoplasmic reticulum-targeting malondialdehyde fluorescence probe for cell imaging and natural scavenger screening

Malondialdehyde (MDA), one of the final products of intracellular lipid peroxidation, serves as a pivotal biomarker for assessing oxidative stress damage. The large lipid membrane structure of the endoplasmic reticulum (ER) accounts for about half of the total cellular lipid membrane, making it the main site of lipid peroxidation damage within a cell. Therefore, in situ detection of MDA levels in ER is of great significance for studying intracellular oxidative damage and related pathological processes; but such analytical tools are still lacking. This work developed the first ER-targeting fluorescence probe (ER-MDA) that is specifically responsive to MDA. ER-MDA was designed with a benzoxadiazole as fluorophore, a p -methy benzenesulfonamide group for ER-targeting, and an electron-enriched hydrazine group as recognition unit, which could suppress the fluorescence of ER-MDA through a photo-induced electron transfer (PET) effect. However, in response to MDA, the formation of the electron-deficient pyrazole group lead to PET inhibition and sensitive fluorescence increase response (detection limit: 273.3 nM). ER-MDA exhibited high selectivity for MDA without interference from other biological aldehydes. Moreover, ER-MDA enabled real-time monitoring of MDA accumulation dynamics during dexamethasone-induced ER stress. Notably, through high-throughput screening of natural MDA scavengers using ER-MDA imaging, it was discovered for the first time that the flavonoid derivative baicalein can efficiently scavenge intracellular MDA, demonstrating an efficient non-enzymatic antioxidant mechanism. This study not only provided a usable tool for detecting MDA at the subcellular ER level, but also offered new insights into antioxidant mechanism of potential therapeutic drugs for related diseases.