Revealing the viscosity variations in the organs of an acute kidney injury model using a fluorescence lifetime probe under FLIM

Abstract

Acute kidney injury (AKI) represents a complex clinical syndrome, and the precise measurement of organ viscosity fluctuations within AKI models holds significant importance for its pathology and treatment. Fluorescence lifetime probes, which provide imaging results unaffected by external factors, are powerful tools for studying microenvironment viscosity changes in biological systems. Herein, we constructed an easily synthesized fluorescent probe, HQI, for exploring viscosity changes in organs in an AKI model under fluorescence lifetime imaging microscopy (FLIM). The probe was developed by linking a cationic salt and phenol via a rotatable double bond, thereby achieving mitochondrial targeting and a viscosity response. As expected, HQI exhibited an excellent response to viscosity, as detected by monitoring the variations in fluorescent intensity and lifetime, and it possessed a large Stokes shift (118 nm), which could efficiently avoid crosstalk between excitation and emission spectra and improve the imaging signal-to-noise ratio. Additionally, benefiting from the sensitivity of HQI to viscosity, the probe rarely fluoresced in low-viscosity cytoplasm, which significantly reduced background fluorescence, and thus, HQI could label the mitochondria in cells and skeletal muscle tissue with a high signal-to-noise ratio. Furthermore, HQI successfully detected the mitochondrial viscosity increase induced by different drugs under confocal laser scanning microscopy and FLIM. More importantly, HQI could successfully and accurately reveal the viscosity changes in the organs of an AKI model, as suggested by the variations in the fluorescence lifetime. In an AKI model mouse, the viscosity of the kidneys significantly increased, the viscosities of the heart and lungs slightly increased, and the viscosities of the liver and spleen remained almost unchanged compared with those of normal mice. We believe that HQI has potential as a powerful tool to monitor the viscosity of biological microenvironments and could promote further developments in pathology and medicine.