Simultaneous visualization of lipid droplets and tracking of the endogenous hypochlorous acid in psoriatic mice models with a novel fluorescent probe in a wash-free fashion

Abstract

Psoriasis is an autoimmune inflammation-related disease accompanied by a variety of complications. Reactive oxygen species (ROS) are modulators of inflammation, and their excessive production caused by oxidative/anti-oxidative imbalance has been observed in psoriatic patients. Hypochlorous acid (HOCl) is a ROS produced by myeloperoxidase (MPO) from chloride ions (Cl^-) and hydrogen peroxide (H₂O₂). Endogenous HOCl has recently been studied as a potential biomarker of psoriasis underlying the necessity for the development of efficient analytical tools for its detection and real time monitoring. Herein, we designed a novel highly sensitive and selective coumarin-based fluorescent probe for HOCl detection, named CN₂-CF₃-S. The probe itself featured negligible fluorescence because of the heavy atom effect of the thiocarbonyl group. However, upon responding to HOCl a conversion to sulfur-free derivative CN₂-CF₃-O occurs, resulting in a dramatical fluorescent enhancement setting the detection limit for HOCl of 3.2 nM. The HOCl-recognition mechanism could be ascribed to the HOCl-triggered oxidative desulfurization process that agrees with liquid chromatography-mass spectrometry (LC-MS) analysis and density functional theory (DFT) computations. The probe's design incorporated a synergistic combination of two structural features for efficient lipid droplets (LDs)-targeting imaging. An efficient push-pull system reinforced by the presence of two strongly electron-donating dimethylamino groups equipped CN₂-CF₃-O with pronounced solvatochromism realized through the enhanced blue-shifted emission in non-polar media. Meanwhile, the presence of trifluormethylphenyl moiety at the acceptor side led to an increased lipophilicity. The CN₂-CF₃-S probe has been successfully utilized to track the endogenous HOCl in cells and on skin of the psoriatic mice in a wash-free manner. As a result, we have demonstrated that the concentration of HOCl in skin might correlate positively with the degree of inflammation in psoriasis. Thus, CN₂-CF₃-S constitutes the first example of LDs-imaging fluorescent probe for detecting the psoriasis-linked HOCl, offering a convenient tool for further in-depth investigation of psoriasis pathophysiology.

Keywords: Fluorescent probe; Hypochlorous acid; Lipid droplets; Psoriasis; Washing-free.