Molecular-Dimension-Dependent ESIPT Break for Specific Reversible Response to GSH and Its Real-Time Bioimaging

Visualization of Acrolein Upregulation during Ferroptosis by a Ratiometric Fluorescent Probe

Ferroptosis is a pattern of cell death caused by iron-dependent accumulation of lipid peroxides and is closely associated with the occurrence and development of multiple diseases. Acrolein (ACR), one of the final metabolites of lipid peroxidation, is a reactive carbonyl species with strong biotoxicity. Effective detection of ACR is important for understanding its role in the progression of ferroptosis and studying the specific mechanisms of ferroptosis-mediated diseases. However, visualization detection of ACR during ferroptosis has not yet been reported. In this work, the first ratiometric fluorescent probe (HBT-SH) based on 2-(2'-hydroxyphenyl) benzothiazole (HBT) was designed for tracing endogenous ACR with an unprecedented regiospecific ACR-induced intramolecular cyclization strategy, which employs 2-aminoethanethiol as an ACR-selective recognition receptor. The experimental results showed that HBT-SH has excellent selectivity, high sensitivity (LOD = 0.26 μM) and good biocompatibility. More importantly, the upregulation of ACR levels was observed during ferroptosis in HeLa cells and zebrafish, indicating that ACR may be a specific active molecule that plays an essential biological role during ferroptosis or may serve as a potential marker of ferroptosis, which has great significance for studying the pathological process and treatment options of ferroptosis-related diseases.

A single mitochondria-targetable fluorescent probe for visualizing cysteine and glutathione in ferroptosis of myocardial ischemia/reperfusion injury

Ferroptosis plays an important role in the early stage of myocardial ischemia/reperfusion (MI/R) injury, which is closely associated with the antioxidant damage of mitochondrial cysteine (Cys)/glutathione (GSH)/glutathione peroxidase 4 (GPX4) axis. Visualization of Cys and GSH in mitochondria is meaningful to value ferroptosis and further contributes to understanding and preventing MI/R injury. Herein a mitochondria-targetable thiols fluorescent probe (MTTP) was designed and synthesized based on sulfonyl benzoxadiazole (SBD) chromophore with a triphenylphosphine unit as the mitochondria-targeted functional group. Cys and GSH can be differentiated by MTTP with two distinguishable emission bands (583 nm and 520 nm) through the controllable aromatic substitution-rearrangement reaction. Importantly, MTTP is capable of monitoring ferroptosis and its inhibition by measuring mitochondrial Cys and GSH. MTTP was also employed to non-invasively detect ferroptosis during oxygen and glucose deprivation/reoxygenation (OGD/R)-induced MI/R injury in H9C2 cells. In a word, MTTP provides a visual tool that can simultaneously detect Cys and GSH to monitor ferroptosis processes during MI/R injury, which helps for more deeper understanding of the role of ferroptosis in MI/R injury-related diseases.

Investigating Oxidative Stress Associated with Myocardial Fibrosis by High-Fidelity Visualization and Accurate Evaluation of Mitochondrial GSH Levels

Myocardial fibrosis is frequently accompanied by elevated levels of oxidative stress. Mitochondrial glutathione (mGSH), an essential biomolecule for maintaining redox homeostasis in mitochondria, could serve as an effective indicator for investigating the oxidative stress associated with myocardial fibrosis. In this study, a ratiometric fluorescent probe named Mito-NS6, capable of being anchored in mitochondria and reversibly responding to GSH with an appropriate dissociation equilibrium constant, was rationally designed and utilized to visualize and evaluate the changes of mGSH levels caused by oxidative stress in myocardial fibrosis. Benefiting from the good performance of Mito-NS6, we successfully achieved the quantification of mGSH in cardiac fibroblasts using a confocal laser-scanning microscope, revealing that salvianolic acid B (SalB) can act as an effective drug to alleviate myocardial fibrosis through depressing oxidative stress. Moreover, we employed ratio fluorescence imaging to track the fluctuation in GSH levels within a mice model of myocardial fibrosis induced by isoproterenol and found that myocardial fibrosis caused a higher oxidative stress level in myocardial tissue as well as heart organs. These results provide a novel point of view for the diagnosis and treatment of myocardial fibrosis.

Sequential activation strategy of triazinyl resorufin for high selectivity fluorescence GSH detection

The abnormally elevated expression level of glutathione (GSH) has been observed in various human cancer cells and tissue. Thus, effective methods for glutathione detection are of great importance in early diagnosis of cancer. However, many fluorescent probes for GSH detection suffer from the interference of the abundantly existent nucleophilic biomolecules in biological environment. In this work, we propose a sequential activation strategy to overcome this problem by designing and synthesizing a series of 1,3,5-triazinyl resorufin turn-on fluorescent probe (Probes 1-3). As two electrophilic sites are presented in probes, GSH sequentially reacts with the resorufin and the triazine moiety, resulting in significant fluorescence augmentation (up to 165.0-fold). Designed probes possess low limit of detection as low as 1.8 μM). Cellular fluorescent imaging has been successfully applied to selectively detect GSH in several living cells.

Meso-aryltellurium-BODIPY-based fluorescence turn-on probe for selective, sensitive and fast glutathione sensing in HepG2 cells

Glutathione (GSH) as one most abundant thiol, acts as important roles in regulating cellular redox activities, and various diseases are closely related with its abnormal levels. Thus, monitoring intracellular GSH levels is essential for understanding cellular metabolism of many related diseases. In this work, we firstly reported a new fluorescence turn-on sensor, which was capable of selectively, sensitively and rapid sensing GSH over other thiols, especially cysteine and homocysteine in solutions and living cells. A meso-aryltellurium boron dipyrromethene (BODIPY) was firstly designed and synthesized, which showed silenced emission due to an efficient photoinduced electron transfer (PET) process from electron-rich Te to BODIPY, and then upon exposure to GSH, the meso-Te-C bond could be rapidly cleaved by the thiol group of GSH, thus resulting in an obvious fluorescence "turn-on" phenomenon through inhibition of the PET effect. This probe exhibited excellent selectivity and sensitivity towards GSH with a short response time of 2 min, showing a remarkable fluorescence enhancement observed at 541 nm with a large fluorescence quantum yield increase from nearly 0 to 0.73 upon excitation at 500 nm in PBS/CH3CN (9/1, v/v). The detection limit towards GSH was further calculated to be 1.7 nM by the linear fluorescence change at 541 nm in the GSH-concentration ranging from 0 to 4 μM. Furthermore, its sensing mechanism was validated by using mass spectrometry, confirming the rapid cleavage of the Te-C bond by GSH. Finally, cell imaging experiments demonstrated that this probe could successfully detect GSH in living cells, highlighting its potential for rapid and sensitive detection of intracellular GSH level changes. Therefore, a new meso-aryltellurium-BODIPY fluorescence turn-on sensor was firstly developed, which could selectively, sensitively and fast detect cellular GSH over other thiols based on the rapid cleavage of the meso Te-C bond.

De Novo Design of Near-Infrared Fluorescent Agents Activated by Peroxynitrite and Glutathione-Responsive Imaging for Diabetic Liver Disease

Diabetes and its complications, such as diabetes liver disease, is a major problem puzzling people's health. The detection of redox states in its pathological process can effectively help us gain a deeper understanding of the disease. The pair of oxidation-reduction substances peroxynitrite (ONOO- ) and glutathione (GSH) is considered to be closely related to their occurrence and development. Thus, direct visualization of ONOO- and GSH in diabetes liver disease is critical to evaluate the disease at the molecular level. Herein, two activatable agents NTCF-ONOO- and NTCF-GSH are prepared for selectively detecting ONOO- and GSH through protection and deprotection strategies based on hydroxyl and amino groups of near-infrared fluorophore. Fluorescence imaging of exogenous and endogenous ONOO- and GSH changes in living cells and in vivo is observed. The ONOO- and GSH level in the diabetes liver disease cellular model are visualized and the possible redox imbalance mechanism related to the oxidized (NAD+ ) and reduced (NADH) nicotinamide adenine dinucleotides is explored in this process. Moreover, these probes can sensitively recognize ONOO- and GSH in the process of oxidative stress resulting from streptozotocin and streptozotocin/acetaminophen-induced complex diabetic liver disease in vivo. In addition, they can be applied for monitoring the clinical serum sample related with diabetic patients.

Modular Design of Biodegradable Ionizable Lipids for Improved mRNA Delivery and Precise Cancer Metastasis Delineation In Vivo

Lipid nanoparticles (LNPs) represent the most clinically advanced nonviral mRNA delivery vehicles; however, the full potential of the LNP platform is greatly hampered by inadequate endosomal escape capability. Herein, we rationally introduce a disulfide bond-bridged ester linker to modularly synthesize a library of 96 linker-degradable ionizable lipids (LDILs) for improved mRNA delivery in vivo. The top-performing LDILs are composed of one 4A3 amino headgroup, four disulfide bond-bridged linkers, and four 10-carbon tail chains, whose unique GSH-responsive cone-shaped architectures endow optimized 4A3-SCC-10 and 4A3-SCC-PH lipids with superior endosomal escape and rapid mRNA release abilities, outperforming their parent lipids 4A3-SC-10/PH without a disulfide bond and control lipids 4A3-SSC-10/PH with a disulfide bond in the tail. Notably, compared to DLin-MC3-DMA via systematic administration, 4A3-SCC-10- and 4A3-SCC-PH-formulated LNPs significantly improved mRNA delivery in livers by 87-fold and 176-fold, respectively. Moreover, 4A3-SCC-PH LNPs enabled the highly efficient gene editing of 99% hepatocytes at a low Cre mRNA dose in tdTomato mice following intravenous administration. Meanwhile, 4A3-SCC-PH LNPs were able to selectively deliver firefly luciferase mRNA and facilitate luciferase expression in tumor cells after intraperitoneal injection, further improving cancer metastasis delineation and surgery via bioluminescence imaging. We envision that the chemistry adopted here can be further extended to develop new biodegradable ionizable lipids for broad applications such as gene editing and cancer immunotherapy.

Recent Progress in the Rational Design of Biothiol-Responsive Fluorescent Probes

Biothiols such as cysteine, homocysteine, and glutathione play significant roles in important biological activities, and their abnormal concentrations have been found to be closely associated with certain diseases, making their detection a critical task. To this end, fluorescent probes have become increasingly popular due to their numerous advantages, including easy handling, desirable spatiotemporal resolution, high sensitivity, fast response, and favorable biocompatibility. As a result, intensive research has been conducted to create fluorescent probes for the detection and imaging of biothiols. This brief review summarizes recent advances in the field of biothiol-responsive fluorescent probes, with an emphasis on rational probe design, including the reaction mechanism, discriminating detection, reversible detection, and specific detection. Furthermore, the challenges and prospects of fluorescence probes for biothiols are also outlined.

Excited-state intramolecular proton transfer (ESIPT)-based fluorescent probes for biomarker detection: design, mechanism, and application

Biomarkers are essential in biology, physiology, and pharmacology; thus, their detection is of extensive importance. Fluorescent probes provide effective tools for detecting biomarkers exactly. Excited state intramolecular proton transfer (ESIPT), one of the significant photophysical processes that possesses specific photoisomerization between Keto and Enol forms, can effectively avoid annoying interference from the background with a large Stokes shift. Hence, ESIPT is an excellent choice for biomarker monitoring. Based on the ESIPT process, abundant probes were designed and synthesized using three major design methods. In this review, we conclude probes for 14 kinds of biomarkers based on ESIPT explored in the past five years, summarize these general design methods, and highlight their application for biomarker detection in vitro or in vivo.

Theoretical study on an intriguing excited-state proton transfer process induced by weakened intramolecular hydrogen bonds

In the present work, we have systematically investigated the dual hydrogen-bonded system 2Z,2'Z-3,3'-(4,4'-methylenebis(4,1-phenylene)bis(azanediyl)bis(1,3-diphenylprop-2-en-1-one)) (abbreviated as L) utilizing quantum chemistry methods, in which the excited-state intramolecular proton transfer (ESIPT) does not conform to the usual stereotype but proceeds along the weakened intramolecular hydrogen bonds (IHBs). Two primary configurations were confirmed to coexist in the ground state (i.e., anti-L and syn-L) by calculating the Boltzmann distribution in three different solvents. Based on the cardinal geometrical parameters involved in IHBs and the interaction region indicator (IRI) isosurface, it can be revealed that the dual IHBs of L were both weakened upon photoexcitation, not least the N₁-H₂⋯O₃ IHB was utterly destroyed in the excited state. The proton-transfer process of anti and syn in three solvents with different polarities has been analyzed by constructing S₀- and S₁-state potential energy surfaces (PESs). It can be concluded that only the single proton transfer behavior along N₁-H₂⋯O₃ occurs in the S₁ state, and the corresponding energy barrier is gradually enlarged with increasing solvent polarity. To further expound the weakened IHB-induced ESIPT mechanism, the scanned PESs connecting the transition state (TS) structures and the initial forms indicate that the ESIPT process is infeasible without the appropriate structural torsion. Our work not only unveils the extraordinary ESIPT process of L, but also complements the results obtained from previous experiments.

Recent Research Progress of Red-Emitting/Near-Infrared Fluorescent Probes for Biothiols

Small-molecule biological thiols, including cysteine (Cys), homocysteine (Hcy) and glutathione (GSH), occupy a vital position in physiological and pathological activities. Abnormal fluctuations of their concentrations are often closely connected with...

An activatable near-infrared hemicyanine-based probe for selective detection and imaging of Hg2+ in living cells and animals

A near-infrared hemicyanine-based probe (CyP) was designed for selective detection and imaging of Hg2+ in living cells and animals.