Fluorescence Imaging of Intracellular Glutathione Levels in the Endoplasmic Reticulum to Reveal the Inhibition Effect of Rutin on Ferroptosis

Ferroptosis is an emerging form of nonapoptotic cell
death, and
the search for novel ferroptosis inhibitors is of great importance
to explore unique cytoprotective strategies against ferroptosis-relevant
diseases. In this work, we present an endoplasmic reticulum-targeting
fluorescent probe (ER-G) for the imaging of intracellular
glutathione (GSH) levels and revealed the inhibition effect of rutin
on ferroptosis. Structurally, ER-G utilized a cyclohexyl
sulfonylurea as the endoplasmic reticulum-targeting unit, and single-crystal
X-ray diffraction analysis confirmed that ER-G possessed
a N-oxide pyridine sulfinyl group instead of sulfone. After the response
of ER-G to GSH, the fluorescence intensity at 523 nm
displayed a significant increase by 3900-fold. ER-G showed
extreme sensitivity and selectivity to GSH. The fluorescence imaging
results demonstrated that ER-G exhibited excellent endoplasmic
reticulum-targeting properties and could be applied to monitor GSH
levels in the endoplasmic reticulum during the erastin-induced ferroptosis
process. By the fluorescence imaging of GSH levels in the endoplasmic
reticulum, it was demonstrated that rutin could efficiently block
the depletion of GSH during erastin-induced ferroptosis and potentially
act as a novel ferroptosis inhibitor. Moreover, unlike traditional
ferroptosis inhibitors, it was speculated that the inhibition mechanism
of rutin to ferroptosis was the integration of the chelate effect
on Fe­(II) ions and antioxidant effect. We expect that fluorescence
imaging of GSH levels in the endoplasmic reticulum could provide a
convenient and feasible method to evaluate the inhibition effect of
small molecules on ferroptosis.