Phosphinate-benzoindocyanin fluorescent probe for endogenous mitochondrial peroxynitrite detection in living cells and gallbladder access in inflammatory zebrafish animal models

A Novel Methacryloyl-Masked NIR Fluorescent Probe for Detection of Cysteine and Its Application in Bioimaging

Cysteine (Cys) detection is recognized as an essential element in this investigation due to the critical function of Cys in several physiological processes in living organisms. A new NIR fluorescent probe SNC-Cys has been synthesized by incorporating a five-membered malononitrile derivatized ring as an electron withdrawing group, and a methacryloyl group detection moiety for cysteine. After adding Cys, SNC-Cys shows an emission of 654 nm and further works as a "Turn-on" probe via ICT photomechanism. SNC-Cys has high sensitivity and selectivity for Cys (LOD=0.46 μM) and can discriminate it from other closely related amino acids, molecules with structural similarity, and in some cases very close functional group likeness. Thus, these results allow the effective imaging of Cys in living A549 cells which indicates good cell permeability and high applicability in live cell imaging. This study anticipates that SNC-Cys could be an aid in the detection of Cys-relevant diseases.

Recent progress in organelle-targeting fluorescent probes for the detection of peroxynitrite

Peroxynitrite (ONOO-), as an important reactive nitrogen species, plays a pivotal role in the regulation of intracellular redox homeostasis, signal transduction, cell growth and metabolism, and other physiological processes. Organelles are important for regulating ONOO-, and the dysregulation of ONOO- in organelles is closely related to various diseases. Therefore, it is essential to monitor ONOO- in cellular organelles, including mitochondria, lysosome, endoplasmic reticulum (ER), Golgi apparatus, and lipid droplets. However, the latest advances in organelle-targeting ONOO- fluorescent probes have not been reviewed systematically. In this review, we focus on the design, sensing mechanism, and organelle-targeting imaging applications of ONOO- fluorescent probes that were reported since 2018. This review will help to facilitate the comprehension of organelle-targeting fluorescent probes for the detection of ONOO-.

Role of Peroxynitrite in the Pathogenesis of Parkinson's Disease and Its Fluorescence Imaging-Based Detection

Parkinson's disease (PD) is the second most common neurodegenerative disorder, affecting the lives of millions of people worldwide. Although the mechanism underlying PD pathogenesis is largely undefined, increasing evidence indicates that oxidative and nitrosative stresses play a crucial role in PD occurrence and development. Among them, the role of oxidative stress has been widely acknowledged, but there is relatively less attention given to nitrosative stress, which is mainly derived from peroxynitrite. In the present review, after briefly introducing the background of PD, we discuss the physiopathological function of peroxynitrite and especially highlight how overloaded peroxynitrite is involved in PD pathogenesis. Then, we summarize the currently reported fluorescence imaging-based peroxynitrite detection probes. Moreover, we specifically emphasize the probes that have been applied in PD research. Finally, we propose perspectives on how to develop a more applicable peroxynitrite probe and leverage it for PD theranostics. Conclusively, the present review broadens the knowledge on the pathological role of peroxynitrite in the context of PD and sheds light on how to develop and utilize fluorescence imaging-based strategies for peroxynitrite detection.

Ex Tenebris Lux: Illuminating Reactive Oxygen and Nitrogen Species with Small Molecule Probes

Reactive oxygen and nitrogen species are small reactive molecules derived from elements in the air─oxygen and nitrogen. They are produced in biological systems to mediate fundamental aspects of cellular signaling but must be very tightly balanced to prevent indiscriminate damage to biological molecules. Small molecule probes can transmute the specific nature of each reactive oxygen and nitrogen species into an observable luminescent signal (or even an acoustic wave) to offer sensitive and selective imaging in living cells and whole animals. This review focuses specifically on small molecule probes for superoxide, hydrogen peroxide, hypochlorite, nitric oxide, and peroxynitrite that provide a luminescent or photoacoustic signal. Important background information on general photophysical phenomena, common probe designs, mechanisms, and imaging modalities will be provided, and then, probes for each analyte will be thoroughly evaluated. A discussion of the successes of the field will be presented, followed by recommendations for improvement and a future outlook of emerging trends. Our objectives are to provide an informative, useful, and thorough field guide to small molecule probes for reactive oxygen and nitrogen species as well as important context to compare the ecosystem of chemistries and molecular scaffolds that has manifested within the field.

An indole-based near-infrared fluorescent "Turn-On" probe for H2O2: Selective detection and ultrasensitive imaging of zebrafish gallbladder

Fluorescent probes play essential roles in medical imaging, where the researchers can select one of many molecules to use to help monitor the status of living systems under investigation. To date, a few scaffolds that allow the in vivo detection of H2O2 are available only. Herein, we provide a highly sensitive and selective near-infrared fluorescent probe that detects H2O2 based on the ICT sensing mechanism. We report the first indole-incorporated fluorescent probe Indo-H2O2 that allows H2O2 detection with a LOD of 25.2 nM featuring a boronate group conjugated to an indole scaffold; the boronate cleaves upon reaction with H2O2. A 5-membered malononitrile derivative was incorporated; Indo-H2O2 has near-infrared (NIR) properties and the reaction time is low (∼25 min) compared to other related probes. Indo-H2O2 was successfully employed in both endogenous and exogenous imaging trials of H2O2 in living cells. Indo-H2O2 also allows the real-time monitoring of H2O2in vivo. It preferentially accesses the gallbladder of zebrafish. Our findings support Indo-H2O2 as a highly sensitive fluorescent NIR probe for detecting H2O2, and an idea to incorporate a central indole unit in future fluorescent probe designs.

Highly sensitive and rapid detection of hypochlorous acid in aqueous media and its bioimaging in live cells and zebrafish using an ESIPT-driven mycophenolic acid-based fluorescent probe

Excessive production of potent biological oxidants such as HOCl has been implicated in numerous diseases. Thus, it is crucial to develop highly specific and precise methods to detect HOCl in living systems, preferably with molecules that can show a distinct therapeutic effect. Our study introduces the synthesis and application of a highly sensitive fluorescence "turn-on" probe, Myco-OCl, based on the mycophenolic acid scaffold with exceptional water solubility. The ESIPT-driven mechanism enables Myco-OCl to specifically and rapidly detect (<5 s) HOCl with an impressive Stokes shift of 105 nm (λex = 417 nm, λem = 522 nm) and a sub-nanomolar (97.3 nM) detection limit with the detection range of 0 to 50 μM. The potential of Myco-OCl as an excellent biosensor is evident from its successful application for live cell imaging of exogenous and endogenous HOCl. In addition, Myco-OCl enabled us to detect HOCl in a zebrafish inflammatory animal model. These underscore the great potential of Myco-OCl for detecting HOCl in diverse physiological systems. Our findings thus offer a highly promising tool for detecting HOCl in living organisms.

A mitochondria-targeted dual-response sensor for monitoring viscosity and peroxynitrite in living cells with distinct fluorescence signals

Viscosity and peroxynitrite (ONOO-) are two significant indicators to affect and evaluate the mitochondrial functional status, which are nearly relational with pathophysiological process in many diseases. Developing suitable analytical methods for monitoring mitochondrial viscosity changes and ONOO- is thus of great importance. In this research, a new mitochondria-targeted sensor DCVP-NO2 for the dual determination of viscosity and ONOO- was exploited based on the coumarin skeleton. DCVP-NO2 displayed a red fluorescence "turn-on" response toward viscosity along with about 30-fold intensity increase. Meanwhile, it could be used as ratiometric probe for detection of ONOO- with excellent sensitivity and extraordinary selectivity for ONOO- over other chemical and biological species. Moreover, thanks to its good photostability, low cytotoxicity and ideal mitochondrion-targeting capability, DCVP-NO2 was successfully utilized for fluorescence imaging of viscosity variations and ONOO- in mitochondria of living cells through different channels. In addition, the results of cell imaging revealed that ONOO- would lead to the increase of viscosity. Taken together, this work provides a potential molecular tool for researching biological functions and interactions of viscosity and ONOO- in mitochondria.

"Lighting up" fluoride: cellular imaging and zebrafish model interrogations using a simple ESIPT-based mycophenolic acid precursor-based probe

The discovery and implementation of media that derive from bioinspired designs and bear optical readouts featuring large Stokes shifts are of continued interest to a wide variety of researchers and clinicians. Myco-F, a novel mycophenolic acid precursor-based probe features a cleavable tert-butyldimethylsiloxy group to allow for fluoride detection. Myco-F exhibits high selectivity and specificity towards F^- (Stokes shift = 120 nm). All measurements were performed in complete aqueous media (LOD=0.38 μM). Myco-F enables detection of fluoride ions in living HEK293 cells and localizes in the eye region (among other regions) of the zebrafish. DFT calculations support the proposed ESIPT working photomechanism.

A xanthene-based fluorescent probe for detection of peroxynitrite in living cells and zebrafish

Peroxynitrite (ONOO^-) is one of quite critical reactive oxygen species that acts critical roles in a number of diverse biological functions and pathological events. Notably, excessive ONOO^- will lead to sorts of diseases. Thus, monitoring of endogenous ONOO^- levels will be conducive to exploring the physiological activities and functions of ONOO^-. Here, a simple turn-on fluorescent probe named DMX is reported using CN bond as the ONOO^- recognition site and xanthene as the fluorophore. DMX possessed a good linear dependence with ONOO^- concentration (0-9 μM), highly sensitive detection (DL = 37 nM), and excellent selectivity towards ONOO^-. What is more, the biological experiments reveal that DMX is able to be utilized to track exogenous/endogenous ONOO^- employing confocal laser scanning microscopy. Visualization of ONOO^- in zebrafish was also successfully conducted, suggesting that DMX might be used to study ONOO^- roles in vivo. We believe that DMX will have potential for exploring the pivotal role of ONOO^- during all sorts of physiological and pathological activities.

A ratiometric fluorescent nanoprobe for ultrafast imaging of peroxynitrite in living cells

For ratiometrically imaging peroxynitrite (ONOO^-) in living cells, we devised and fabricated a novel fluorescent nanoprobe, NC-NP_530/460, in this study. To achieve ratiometric fluorescence response towards ONOO^-, NC-NP_530/460 used 3-(2-benzothiazolyl) coumarin (Cou-Bz) as the internal reference and 1,8-naphthimide derivative (Naph-PN) as a fluorescent ONOO^- probe. These compounds were incorporated into an amphiphilic block polymer called Pluronic F-127. In addition to an ultrafast response to ONOO^-, NC-NP_530/460 also showed great selectivity and sensitive detection (detection limit was 4.51 μM). It was important to note that NC-NP_530/460 demonstrated solid performance for ONOO^- fluorescence ratio imaging in living cells, highlighting its potential for ONOO^--related chemical biology research.

Photocontrollable Fluorescence Imaging of Mitochondrial Peroxynitrite during Ferroptosis with High Fidelity

Ferroptosis, a new regulatory cell death modality, underlies the pathogenesis of a broad range of disorders. Although much efforts have been made to uncover the molecular mechanisms, some mechanistic details of ferroptosis still remain poorly understood. Particularly, the functional relevance of mitochondrial reactive oxygen species (ROS) in ferroptosis is still highly controversial, which is partially due to the fact that it still remains puzzled how the mitochondrial ROS level varies during ferroptosis. The conventional mitochondria-targeted probes may react with cytosolic ROS and show fluorescence variation before entering mitochondria, thus probably giving a false result on the mitochondrial ROS level and leading to the misjudgment on its biofunction. To circumvent this issue, we rationally designed a photocontrollable and mitochondria-targeted fluorescent probe to in situ visualize the mitochondrial peroxynitrite (ONOO^-), which is the ROS member and mediator of ferroptosis. The photoactivated probe was endowed with a highly specific and sensitive fluorescence response to ONOO^-. Notably, the response activity could be artificially regulated with light irradiation, which ensured that all the probe molecules passed through the cytosol in the locked status and were then photoactivated after reaching mitochondria. This photocontrolled fluorescence imaging strategy eliminated the interference of ONOO^- outside the mitochondria, thus potentially afforded improved fidelity for mitochondrial ONOO^- bioimaging in live cells and animal models. With this probe, for the first time, we revealed the mitochondrial ONOO^- flux and its probable biological source during erastin-induced ferroptosis. These results suggest a tight correlation between mitochondrial ONOO^-/ROS and ferroptotic progression, which will further facilitate the comprehensive exploration and manipulation of ferroptosis.

Endoplasmic Reticulum-Targeting Near-Infrared Fluorescent Probe for CYP2J2 Activity and Its Imaging Application in Endoplasmic Reticulum Stress and Tumor

CYP2J2 as an endoplasmic reticulum (ER)-expressed vital cytochrome P450 isoform participates in the metabolism of endogenous polyunsaturated fatty acids. Its abnormal expression and function are closely related to the progress of cancer and cardiovascular diseases. Herein, an ER-targeting near-infrared (NIR) fluorescent probe ER-BnXPI was developed for monitoring CYP2J2 activity, which possessed a high selectivity and sensitivity toward CYP2J2 among various CYP450 isoforms and exhibited excellent subcellular localization for ER. Then, the CYP2J2 variation behavior under the ER stress model was imaged by ER-BnXPI in living cells and successfully used for the in vivo imaging in different tumors that well distinguished tumor tissues from para-cancerous tissues. All these findings fully demonstrated that ER-BnXPI could be used as a promising tool for exploring the physiological function of CYP2J2 and provided some novel approach for the diagnosis and therapy of CYP2J2-related vascular inflammation and cancer.