Exploring the Changes of Peroxisomal Polarity in the Liver of Mice with Nonalcoholic Fatty Liver Disease

Dual-reporter fluorescent probe for precise identification of liver cancer by sequentially responding to carboxylesterase and polarity

Early treatment significantly improves the survival rate of liver cancer patients, so the development of early diagnostic methods for liver cancer is urgent. Liver cancer can develop from viral hepatitis, alcoholic liver, and fatty liver, thus making the above diseases share common features such as elevated viscosity, reactive oxygen species, and reactive nitrogen species. Therefore, accurate differentiation between other liver diseases and liver cancer is both a paramount practical need and challenging. Numerous fluorescent probes have been reported for the diagnosis of liver cancer by detecting a single biomarker, but these probes lack specificity for liver cancer in complex biological systems. Obviously, using multiple liver cancer biomarkers as the basis for judgment can dramatically improve diagnostic accuracy. Herein, we report the first fluorescent probe, LD-TCE, that sequentially detects carboxylesterase (CE) and lipid droplet polarity in liver cancer cells with high sensitivity and selectivity, with linear detection of CE in the range of 0-6 U/mL and a 65-fold fluorescence enhancement in response to polarity. The probe first reacts with CE and releases weak fluorescence, which is then dramatically enhanced due to the decrease in lipid droplet polarity in liver cancer cells. This approach allows the probe to enable specific imaging of liver cancer with higher contrast and accuracy. The probe successfully achieved the screening of liver cancer cells and the precise identification of liver cancer in mice. More importantly, it is not disturbed by liver fibrosis, which is a common pathological feature of many liver diseases. We believe that the LD-TCE is expected to be a powerful tool for early diagnosis of liver cancer.

Quinone Methide Based Self-Immobilizing Molecular Fluorescent Probes for In Situ Imaging of Enzymes

Enzymes play important roles not only in normal physiological processes but in the development of many diseases. In situ imaging of enzymes with high-resolution in living systems would helpful for clinical diagnosis and treatment. However, many molecular fluorescent probes suffer from the drawback of diffusing away from the reaction site of enzymes even out of the cells, losing the in situ information and resulting in poor imaging resolution. Quinone methide (QM) based self-immobilizing probes allow the fluorescent signal to be immobilized near the target for an extended period without deactivating the target enzymes, ensuring that it will provide amplified signals and in situ information of the target with high resolution. In this review, we summarized the recent progress of QM-based self-immobilizing probes including their design strategies, working mechanisms, classifications and applications in in situ enzyme imaging. This review calls for the development of more activatable QM-based probe with the advantages of high stability in the absence of the target but very high labeling efficiency after activation.

Activatable fluorescent probes for early diagnosis and evaluation of liver injury

With the increase in people's living standards, the number of patients suffering from liver injury keeps on increasing. Traditional diagnostic methods can no longer meet the needs of early and accurate diagnosis due to their limitations in application. However, fluorescent probes based on different fluorophores and nanomaterials have been gradually lighting up medical research due to their unique properties, such as high specificity and non-invasiveness. In addition, accurate identification of the different types of liver injury biomarkers can significantly improve the level of early diagnosis. Therefore, this review reviews the fluorescent probes used in the detection of biomarkers of liver injury over recent years and briefly summarizes the corresponding biomarkers of different types of liver injury. Impressively, this review also lists the structures and the response mechanisms of the different probes, and concludes with an outlook, suggesting directions in which improvements can be made. Finally, we hope that this review will contribute to the further development of fluorescent probes for the early diagnosis and assessment of liver injury.

A Lipid Droplet-Specific NIR Fluorescent Probe with a Large Stokes Shift for In Vivo Visualization of Polarity in Contrast-Induced Acute Kidney Injury

The research on lipid droplets (LDs) has attracted great attention in the field of biomedical science in recent years. LD malfunction is found to be associated with the development of acute kidney injury (AKI). To monitor this biological process and explain related pathological behavior, the development of excellent LD fluorescent probes with a polarity-sensitive character would provide a desirable strategy. Herein, we designed a new polarity-susceptible fluorescent probe named LD-B with LD targetability, which exhibits very weak fluorescence in highly polar solvents based on the twisted intramolecular charge transfer effect but enhanced fluorescence in low polar environments, enabling us to visualize polarity alteration. The probe LD-B also possesses the merits of intense near-infrared (NIR) emission, good photostability, large Stokes shift, low toxicity, faster metabolic rate, and wash-free ability; thereby, it would contribute to efficient LD fluorescence visualization application. Using LD-B via confocal laser scanning fluorescence imaging and a small-animal imaging system in vivo, we first manifested a prominent rise of LD polarity in contrast-induced AKI (CI-AKI), not only at the cellular level but also in animals in vivo. Furthermore, the in vivo studies suggest that LD-B could accumulate in the kidney. In addition, the normal cell lines (including kidney cells) exhibiting a greater polarity of LDs than the cancer cells have been demonstrated systemically. Altogether, our work presents an effective approach for the medical diagnosis of LDs related to CI-AKI and identification of potential therapeutic markers.

Monitoring Cell Plasma Membrane Polarity by a NIR Fluorescence Probe with Unexpected Cell Plasma Membrane-Targeting Ability

The cell plasma membrane, the natural barrier of a cell, plays critical roles in a mass of cell physiological and pathological processes. Therefore, revealing and monitoring the local status of the cell plasma membrane are of great significance. Herein, using a near-infrared (NIR) fluorescence probe BTCy, microenvironmental polarity in the cell plasma membrane was in situ monitored. BTCy showed sensitive and selective fluorescence decrease response at 706 nm with the increase of polarity as its polarity-responsive D-π-A structure. Most importantly, BTCy showed unexpected cell plasma membrane-targeting ability, probably due to its amphiphilic structure. With BTCy, the distinguishing imaging of cancer and normal cells was done, in which cancer cells exhibited significantly stronger signals due to their lower cell plasma membrane polarity. In addition, with the imaging of BTCy, the ferroptosis process was revealed with no significant cell plasma membrane polarity variation for the first time. Furthermore, BTCy was employed for in vivo imaging of tumor tissue in the 4T1-tumor-bearing mice. The polarity-responsive and cell plasma membrane-targeting properties of BTCy make it a useful tool for monitoring cell plasma membrane polarity variation, providing an efficient and simple method for tumor diagnosis.

Rational Design of a Near-Infrared Ratiometric Probe with a Large Stokes Shift: Visualization of Polarity Abnormalities in Non-Alcoholic Fatty Liver Model Mice

Tracking liver polarity with noninvasive and dynamic imaging techniques is helpful to better understand the non-alcoholic fatty liver (NAFL). Herein, a novel near-infrared (NIR) fluorescent probe Cy-Mp is constructed using a "symmetry collapse" strategy. The structure modification leads to the conversion of locally excited state fluorescence to charge transfer state fluorescence. Cy-Mp emits at near-infrared (NIR) wavelengths with high photostability as well as a large Stokes shift. Cy-Mp exhibits a ratiometric response to polarity, providing more accurate analysis of intracellular polarity via the built-in internal reference correction. Most importantly, the in vivo studies indicate that Cy-Mp can accumulate in the liver and the decreased polarity in the liver of mice with NAFL is verified by the ratiometric imaging, implying the great potential of Cy-Mp in the diagnosis of NAFL.

Enhancing probe's sensitivity for peroxynitrite through alkoxy modification of dicyanovinylchromene

An intramolecular charge transfer (ICT)-based fluorescent probe P-ONOO^- was synthesized to detect ONOO^-. After responding to peroxynitrite, the dicyano-vinyl group of P-ONOO^- generates the aldehyde group, emitting strong green fluorescence accompanied by quenching of the yellow fluorescence. According to the calculated Fukui function, the modification of the alkoxy group can enhance the f⁺ of P-ONOO^-, which can enhance the probe's nucleophilic addition reactivity with ONOO^-. It has been experimentally verified that P-ONOO^- shows fast response (within 30 s), excellent sensitivity (the detection limit = 10.4 nM), and good selectivity towards ONOO^-. Additionally, the probe P-ONOO^- has high membrane permeability and good biocompatibility, which can image endogenous ONOO^- and exogenous ONOO^- in HeLa cells.

Polarity-Sensitive Probe: Dual-Channel Visualization of the "Chameleon" Migration with the Assistance of Reactive Oxygen Species

The real-time and differentiated visualization of the organelles is favorable for exploring the distribution and interaction. However, most visual probes emit monochromatic fluorescence and target a single organelle, which impedes the in-depth study of their interplay. To overcome this obstacle, we tactfully conceived a polarity-sensitive fluorescent DPDO-C that could accurately discriminate polarity changes in the cellular environment, exhibiting distinct fluorescence in lipid droplets (LDs) and mitochondria. Remarkably, the probe DPDO-C could migrate from mitochondria to LDs with the assistance of reactive oxygen species, which was conducive to further monitoring of the number and size of LDs as well as the interactions between LDs and other organelles. Moreover, the nuanced difference between normal and fatty liver tissues was also distinguished by two-color fluorescence imaging, which could act as a promising candidate for the early diagnosis of fatty liver.

Advances in Optical Imaging of Nonalcoholic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD), emerging as one of the most common chronic liver diseases including simple steatosis and non-alcoholic steatohepatitis (NASH), is likely to progress to liver fibrosis and hepatic carcinoma if not treated in time. Therefore, early diagnosis and treatment of NAFLD are necessary. Currently, liver biopsy, as the gold standard for clinical diagnosis of NAFLD, is not widely accepted by patients due to its invasiveness. However, other non-invasive methods that had been reported for NAFLD (such as magnetic resonance imaging, positron emission tomography, and ultrasound) still suffer from low resolution and sensitivity, which are available as a guide for liver biopsy sometimes. As a non-invasive modality with high spatiotemporal resolution and superior sensitivity, optical imaging methods have been widely favored in recent years, mainly including fluorescence imaging, photoacoustic imaging, and bioluminescence imaging. With these optical imaging approaches, a series of optical probes based on optical and molecular-specific design have been developed for the biomarker diagnosis and research of diseases. In this review, we summarize the existing non-invasive optical imaging probes for the detection of biomarkers in NAFLD, including microenvironment (viscosity, polarity), ROS, RSS, ions, proteins, and nucleic acids. Design strategies for optical imaging probes and their applications in NAFLD bioimaging are discussed and focused on. We also highlight the potential challenges and prospects of designing new generations of optical imaging probes in NAFLD studies, which will further enhance the diversity, practicality, and clinical feasibility of NAFLD research.

A Dual-Response Fluorescent Probe for Simultaneous Monitoring Polarity and ATP During Autophagy

Autophagy plays a vital role in maintaining intracellular homeostasis through a lysosome-dependent intracellular degradation pathway, which is closely related to the polarity and ATP. Herein, the first example of the...

Low Polarity-Triggered Basic Hydrolysis of Coumarin as an AND Logic Gate for Broad-Spectrum Cancer Diagnosis

The ability to accurately diagnose cancer is the cornerstone of early cancer treatment. The mitochondria in cancer cells maintain a higher pH and lower polarity relative to that in normal cells. A probe that reports signals only when both conditions are met may provide a reliable method for cancer detection with reduced false positives. Here, we construct an AND logic gate fluorescent probe using mitochondrial microenvironments as inputs. Utilizing the hydrolysis of a coumarin scaffold, the probe generates fluorescence signals ("ON") only when high pH (>7.0) and low polarity conditions exist simultaneously. Additionally, the higher mitochondrial membrane potential in cancer cells provides an additional level of selectivity because probe has increased affinity for cancer cell mitochondria. These capabilities endow the probe with a high contrast fluorescence diagnosis ability of cancer at cellular and tissue levels (as high as 51.9 fold), which is far exceeding the clinic threshold of 2.0 fold.