In Situ Fluorescence Imaging Reveals Contribution of Cerebral Hydroxyl Radicals in Hyperhomocysteinemia-Induced Alzheimer-like Dementia.

Elevated plasma level of homocysteine, also termed as hyperhomocysteinemia, is acknowledged as a significant and independent risk factor of Alzheimer's disease. However, the mechanistic insight has not been thoroughly elucidated yet. In this work, 3,5-dihydroxybenzyloxy was explored as the unique reaction trigger and integrated into the naphthalimide fluorophore via a carbamate linker to afford a new probe for • OH imaging. • OH treatment induced aromatic hydroxylation and subsequent elimination reaction to release the caged fluorophore, accompanied with a highly specific and sensitive turn-on fluorescence response. Cell imaging results revealed that excess homocysteine triggered overwhelming • OH production, which was mediated by N -methyl-d-aspartate receptor and NADPH oxidase, and the resultant • OH stress further initiated neuronal ferroptosis, also confirmed by western blot analyses. Additionally, hyperhomocysteinemic mouse models were established, and Alzheimer-like dementia of the mice was observed from behavioral tests. Most importantly, with this probe, cerebral • OH fluctuation was in situ visualized in live mice, which positively correlated with the severity of Alzheimer-like dementia induced by hyperhomocysteinemia. These results reveal that cerebral • OH stress may be the critical nexus linking hyperhomocysteinemia and Alzheimer's disease. This work provides a robust fluorescence probe for in situ visualizing the cerebral • OH fluctuations and illuminating critical insights into • OH contributions in brain disorders.