Advances in Optical Imaging of Nonalcoholic Fatty Liver Disease

Combination of two-photon fluorescent probes for carboxylesterase and ONOO- to visualize the transformation of nonalcoholic fatty liver to nonalcoholic steatohepatitis in liver orthotopic imaging

As the most common cause of liver diseases, nonalcoholic fatty liver disease (NAFLD) can be classified into nonalcoholic fatty liver (NAFL) and nonalcoholic steatohepatitis (NASH). While NAFL is generally benign, the transition from NAFL to NASH is a cardinal feature of the non-benign liver disease that leads to cirrhosis and cancer, which indicates that tracking the transformation of NAFL to NASH timely is significant for precision management of liver diseases. Therefore, two fluorescent probes (CNFCl and DRNO) have been developed to visualize this pathological event. α-Fluorochloroacetamide and α-ketoamide was employed as the recognition site for carboxylesterase (CE) in CNFCl and peroxynitrite (ONOO-) in DRNO, respectively. CNFCl (λem = 445 nm) and DRNO (λem = 560 nm) showed high specificity and sensitivity towards CE and ONOO- respectively. By incubating with CE/ONOO- for 0.5 h respectively, both the emission intensity of CNFCl (linear range: 0-0.2 U/mL) and DRNO (linear range: 0-17.5 μM) displayed significant enhancement. As a result, the detection limit of CNFCl and DRNO for CE and ONOO- was calculated as 4.2 mU/L and 0.05 μM respectively. More importantly, the emission spectra of CNFCl and DRNO in the presence of CE and ONOO- respectively were cross-talk free under the two-photon excitation of 720 nm. This greatly facilitated the simultaneous detection of CE and ONOO- at distinctive channel, thus ensuring the high fidelity of the detection. These two probes were combined to image the fluctuation of CE and ONOO- during the conversion of NAFL to NASH in vitro and in vivo. It was found that while CE displayed a tendency to rise and then reduce during the transition from NAFL to NASH, ONOO- increased continuously, confirming that the combined imaging by CNFCl and DRNO might visualize the transformation of NAFL to NASH. The results provide robust visual tool to decipher the relationship between the stage of NAFLD and the level of CE/ONOO-. We anticipate this study may open new avenues to distinguish NASH from NAFL, which may further promote the study of intracellular biological activities of CE and the development of NAFLD diagnostic methods.

Isophorone-based AIEgens fluorescent probe with red emission for targeting lipid droplets and identifying non-alcoholic fatty liver disease

Due to the disorder of lipid metabolism, the excessive accumulation of lipid droplets (LDs) in liver cells can result in the occurrence of non-alcoholic fatty liver disease (NAFLD). Therefore, it is great of significance to design and synthesized LDs-specific fluorescent probes for the early diagnosis of NAFLD. Herein, we developed a series of aggregation-induced emission (AIE) probes ISO-LD1, ISO-LD2 and ISO-LD3 based on isophorone group for LDs-specific imaging in living cells. The photophysical properties demonstrated that all the probes with red emission (λem > 600 nm) exhibited a strong fluorescence in high polarity solvents. In particular, probe ISO-LD3 has a highest fluorescence quantum yield (except for 1,4-dioxane) and a larger Stokes shift. Confocal laser scanning microscopy experiments indicated that probe ISO-LD3 could specifically stain LDs via a "washing-free" procedure within 10 s, and monitor the dynamic behaviors of LDs exhibiting a high signal/noise ratio. Importantly, given the satisfactory performance of probe ISO-LD3, it has been successfully used for the detection of the normal liver tissues and fatty liver tissues, respectively. This work illustrated that ISO-LD3 is a promising tool for the detection of LDs and LDs-related diseases.

Simultaneous detection of mitochondrial viscosity and peroxynitrite in livers from subjects with drug-induced fatty liver disease using a novel fluorescent probe

Drug-induced fatty liver disease (DIFLD) is a basic clinicopathological example of drug-induced liver injury (DILI). Some drugs can inhibit β-oxidation in hepatocyte mitochondria, leading to steatosis in the liver. Additionally, drug-induced inhibition of β-oxidation and the electron transport chain (ETC) can lead to increased production of reactive oxygen species (ROS) such as peroxynitrite (ONOO^-). Therefore, it is reasonable to suspect that compared to a healthy liver, viscosity and ONOO^- levels are elevated in livers during DIFLD. A novel, smart, dual-response fluorescent probe-Mito-VO-was designed and synthesized for the simultaneous detection of viscosity and ONOO^- content. This probe had a large emission shift of 293 nm and was capable of monitoring the viscosity of, and the ONOO^- content in, cell and animal models alike, either individually or simultaneously. For the first time, Mito-VO was successfully used to demonstrate the elevated viscosity and the amount of ONOO^- in livers from mice with DIFLD.

Recent Advances in Small Molecular Fluorescence Probes for Fatty Liver Diseases

Fatty liver diseases are a spectrum of liver disorders consisting of the benign fatty liver, which could eventually lead to cirrhosis or even hepatocellular cancer (HCC) without timely treatment. Therefore, early diagnosis is crucial for fatty liver diseases. Liver biopsy is regarded as the gold standard in the diagnosis of fatty liver diseases. However, it is not recommended for routine use due to its invasiveness and complicated operation. Thus, it is urgent to diagnose fatty liver diseases with non-invasive and precise methods. In this regard, fluorescence imaging technology has attracted intensive attention and become a robust non-invasive method for fatty liver visualization, and a series of fluorescent probes are being intensively designed to track the biomarkers in fatty liver. In this brief review, the small molecular fluorescent probes employed in fatty liver are summarized, mainly focusing on the last four years. Moreover, current opportunities and challenges in the development of fluorescent probes for fatty liver will be highlighted.

Dual-Channel Fluorescent Probe for Detecting Viscosity and ONOO- without Signal Crosstalk in Nonalcoholic Fatty Liver

Nonalcoholic fatty liver disease (NAFLD) is a global health issue. Peroxynitrite and liver viscosity have recently been found to be potential biomarkers of NAFLD. Therefore, it is of great significance to develop dual-response fluorescent probes for simultaneous detecting peroxynitrite and viscosity. We report herein a new probe (CQ) that can simultaneously detect peroxynitrite and viscosity at two independent fluorescent channels without signal crosstalk. CQ shows high selectivity, rapid response, good water solubility, low cytotoxicity, and mitochondrial localization properties. In particular, CQ responds sensitively to viscosity and peroxynitrite with off-on fluorescence changes at 710 and 505 nm, respectively. The wavelength gap between these two channels is more than 200 nm, ensuring that there is no signal crosstalk during detection. With this property, the probe was applied to simultaneously detect mitochondrial viscosity and peroxynitrite and image the changes of liver viscosity and peroxynitrite concentration during the pathogenesis of NAFLD. All results show that the CQ probe is a powerful tool for simultaneous detection of viscosity and peroxynitrite and provides a potential new diagnostic method for NAFLD.