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 -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.