A novel pyridinium-based fluorescent probe for ratiometric detection of peroxynitrite in mitochondria

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.

Recent Progress of Spectroscopic Probes for Peroxynitrite and Their Potential Medical Diagnostic Applications

Peroxynitrite (ONOO-) is a crucial reactive oxygen species that plays a vital role in cellular signal transduction and homeostatic regulation. Determining and visualizing peroxynitrite accurately in biological systems is important for understanding its roles in physiological and pathological activity. Among the various detection methods, fluorescent probe-based spectroscopic detection offers real-time and minimally invasive detection, high sensitivity and selectivity, and easy structural and property modification. This review categorizes fluorescent probes by their fluorophore structures, highlighting their chemical structures, recognition mechanisms, and response behaviors in detail. We hope that this review could help trigger novel ideas for potential medical diagnostic applications of peroxynitrite-related molecular diseases.

Hypochlorous acid-activated near-infrared fluorescent probe for in vivo/exogenous detection and dairy toxicity evaluation

Oxidative stress has been reported to be closely associated with many diseases, and an excessive overdose of hypochlorite (ClO^-) can also induce stress-related diseases. In this study, we designed and synthesized a NIR probe, named W-1a based on computational analysis of DCM (4-(Dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran) derivatives for specific detection of ClO^-. The probe exhibited dual fluorescence and colorimetric sensing with a response time of <1 min and a detection limit of 0.15 μM. Additionally, the probe was successfully applied for fluorescence imaging of ClO^- at the cellular level and ebrafish endogenous/exogenous ClO^- assay and dairy toxicity assessment. Thus, we present a potential method for developing an efficient and reliable detection of ClO^- in early stage using near-infrared dyes.

Evaluation of peroxynitrite fluxes in inflammatory mice with a ratiometric fluorescence probe

Inflammation is a critical physiological process in the human body, which is closely related to numerous disorders and cancers. ONOO^- is generated and functionalized in the inflamed process, but the roles of ONOO^- are still blurred. To illuminate the roles of ONOO^-, we fabricated an intramolecular charge transfer (ICT)-based fluorescence probe, HDM-Cl-PN, for the ratiometric determination of ONOO^- in the inflamed mouse model. The probe displayed a gradual fluorescence increase at 676 nm and a fluorescence drop at 590 nm toward 0-10.5 μM ONOO^-, and the ratio of 676 nm fluorescence and 590 nm fluorescence varied from 0.7 to 24.7. The significantly changed ratio and favorable selectivity ensure the sensitive detection of subtle changes in cellular ONOO^-. Thanks to the excellent sensing performance, HDM-Cl-PNin vivo ratiometrically visualized ONOO^- fluctuations in the LPS-triggered inflammatory process. Overall, this work not only expatiated the rational design for a ratiometric ONOO^- probe but also built a bridge to investigate the connections between ONOO^- and inflammation in living mice.

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

Potent oxidants such as peroxynitrite (ONOO^-) play important roles in the regulation of different physiopathological processes; their overproduction is thought to potentially cause several diseases in living organisms. Hence, the precise and selective monitoring of ONOO^- is imperative for elucidating its interplay and roles in pathological and physiological processes. Herein, we present a novel diphenyl phosphinate-masked benzoindocyanin "turn-on" fluorogenic probe to help detect mitochondrial ONOO^- in living cells and zebrafish models. A pale yellow color solution of BICBzDP turns rose-red upon the addition of ONOO^-_, selectively, contrary to that of other competitive bioactive molecules. BICBzDP displays an ultra-sensitivity detection limit (47.8 nM) with outstanding selectivity and sensitivity towards mitochondrial ONOO^- and possesses a notable 68-fold fluorescence enhancement involving a large redshift of 91 nm. Importantly, further biological experimental investigations with BICBzDP indicate specific sensitivity and reliability of the probe to track the ONOO^- level, not only in live cells, but also demonstrates dynamic fluctuations in the inflammatory zebrafish animal models. Thus, BICBzDP could be employed as a future potential biological tool for exploiting the role of ONOO^- in a variety of different physiological systems.

Visualization of peroxynitrite in cyclophosphamide-induced oxidative stress by an activatable probe

Oxidative stress is considered to be one of the main contributors of cyclophosphamide (CP)-induced toxicity, and the generation of free radicals will cause the interruption of multiple signal transduction pathways. Peroxynitrite (ONOO^-) has strong oxidation and nitrification ability and is considered as an indirect indicator of oxidative stress. Therefore, it is necessary to design a fluorescent probe that can detect ONOO^- and monitor CP-induced oxidative stress during chemotherapy. Herein, we synthesized a lipid droplet targeting fluorescent probe SX-1 based on triphenylamine-benzoindocyanine. When ONOO^- is added to the probe SX-1, the CC bond in the probe is broken, thereby releasing fluorescence. The good spectral response characteristics enable SX-1 to successfully track the fluctuations of ONOO^- in living cells. Most importantly, we provided the first visual evidence that the level of ONOO^- in HeLa cells was up-regulated under CP induction. All results indicated that SX-1 has great potential in detecting drug-induced ONOO^-, and provided a new detection tool for a deeper understanding of drug-induced organism injury.

A morpholino hydrazone-based lysosome-targeting fluorescent probe with fast response and high sensitivity for imaging peroxynitrite in living cells

Peroxynitrite (ONOO^-) plays important roles in many pathophysiological processes and its subcellular detection draws increasing attention. In this study, we designed and prepared a novel lysosome-targetable fluorescent probe (E)-2-(benzo[d]thiazol-2- yl)-4-methyl-6-((morpholinoimino)methyl)phenol (BMP) for selective detection of ONOO^- in living systems by incorporating a reactive morpholino hydrazone as new ONOO^- response site into a benzothiazole derivative as fluorophore. After reaction with ONOO^-, an obvious fluorescence increase (83-fold) was observed accompanied with distinct dual colorimetric and fluorescence changes. Probe BMP displayed the merits of fast response (<3 s), ultrasensitivity (LOD = 6 nM) and high selectivity towards ONOO^- over other physiological species including ROS/RNS. Most importantly, the probe was capable of imaging ONOO^- in lysosomes of living cells with good cell permeation and negligible cytotoxicity. Therefore, this research provides an effective tool to study the functions of ONOO^- in lysosomes.

A novel fast-response and highly selective AIEgen fluorescent probe for visualizing peroxynitrite in living cells, C. elegans and inflammatory mice

Most of the ONOO^- fluorescent probes have restricted applications because of their aggregation-caused quenching (ACQ) effect, long response time and low fluorescence enhancement. Herein, we developed a novel AIEgen fluorescent probe (PE-XY) based on a benzothiazole and quinolin scaffold with high sensitivity and selectivity for imaging of ONOO^-. The results indicated that probe PE-XY exhibited fast response towards ONOO^- with 2000-fold enhancement of fluorescence intensity ratio in vitro. Moreover, PE-XY exhibited a relatively high sensitivity (limit of detection: 8.58 nM), rapid response (<50 s), high fluorescence quantum yield (δ = 0.81) and excellent selectivity over other analytes towards ONOO^-in vitro. Furthermore, PE-XY was successfully applied to detect endogenous ONOO^- levels in living HeLa cells, C. elegans and inflammatory mice with low cytotoxicity. Overall, this work provided a novel fast-response and highly selective AIEgen fluorescent probe for real-time monitoring ONOO^- fluctuations in living systems.

A resorufin-based red-emitting fluorescent probe with high selectivity for tracking endogenous peroxynitrite in living cells and inflammatory mice

Peroxynitrite (ONOO^-) plays essential roles on various physiological and pathological processes of living systems as a short-lived and highly reactive nitrogen (RNS) specie. The construction of novel long-wavelength fluorescent probes with high specificity towards ONOO^- for imaging in vivo is still demand urgently. About this work, a novel resorufin-based red-emitting fluorescent probe for tracking ONOO^- has been constructed. The probe RFP exhibited high selectivity towards ONOO^- anion over other analytes. Utilizing the probe, ONOO^- could be directly observed by the naked eye. Furthermore, RFP was successfully applied for imaging endogenous ONOO^- in RAW264.7 cells and inflammatory mice. This work offers a convenient method for monitoring the intercellur ONOO^- that be expected to be applied for explaining the bio-functional roles of ONOO^- in living system.

A novel borate fluorescent probe for rapid selective intracellular peroxynitrite imaging

Peroxynitrite (ONOO^-) is one of the species of reactive nitrogen (RNS), which plays an important role in antibacterial activity and signal transduction and other physiological and pathological processes. In this paper, based on the benzyl borate group, a new fluorescent probe capable of detecting ONOO^- with high selectivity and sensitivity is designed, and the possible mechanism of the interaction between probe and ONOO^- is proposed. The probe shows high fluorescence response to ONOO^- in a wide pH range (7.0-11.5). Moreover, the probe exhibit good permeability, and the content of ONOO^- in cancer cells and normal cells was successfully monitored.

Red/NIR neutral BODIPY-based fluorescent probes for lighting up mitochondria

Two mitochondrial-targeted fluorescent probes, 2 and 3, based on a BODIPY scaffold and one or two piperidinyl groups were easily synthesized by Knoevenagel condensation. The biological imaging applications of the two probes 2 and 3 in live HepG2 cells reveal that these two probes display excellent mitochondrial imaging ability. Thus, these probes appear as promising tools for visualization of mitochondrial within live cells.

Investigations of drug-induced liver injury by a peroxynitrite activatable two-photon fluorescence probe

Drug-induced liver injury (DILI) is a prevalent liver disease and the leading cause for acute liver failure (ALF) worldwide. Screening of DILI in patients is central to ensure drug safety and improve therapy efficiency. Mounting evidences revealed that peroxynitrite (ONOO^-) is involved in the DILI process and can be a potential biomarker for DILI. Thus far, there are few two-photon fluorescence probes for ONOO^- that can accomplish this challenging task in DILI liver tissues. Hereby, a peroxynitrite activatable two-photon fluorescence probe BN-PN for the imaging of ONOO^- in mice liver was elaborately constructed. The probe specifically reacted with peroxynitrite to furnish 140-fold fluorescence increase in vitro, which elucidated a high sensitivity for ONOO^-. Thus, subtle changes of ONOO^- levels in live cells can be sensitively imaged with this probe by two-photon microscopy. The probe also denoted the overproduction of ONOO^- in APAP-induced liver injury, and proved that administration with NAC can effectively alleviate DILI and reduce ONOO^- production in mouse liver. Further, the probe demonstrated the rapid rise of ONOO^- level in the liver of DILI mice administrated with alcohol. This work disclosed the rational construction of a two-photon fluorescence probe-based DILI screening method, which would help the estimation of drug safety and new drug development.

Selective detection of peroxynitrite in living cells by a near-infrared diphenyl phosphinate-based dicyanoisophorone probe

A new NIR fluorescent probe for detection of ONOO^- has been developed, which possesses a large Stokes shift, good selectivity and low cytotoxicity. This NR-ONOO probe exhibits a strong turn-on near-infrared fluorescence response toward ONOO^- ion under excitation at 560 nm and has been successfully applied in detecting ONOO^- in living HeLa cells.