Rational design of a reversible fluorescent probe for sensing GSH in mitochondria

Research Progress of Fluorescent Probes for Detection of Glutathione (GSH): Fluorophore, Photophysical Properties, Biological Applications

Intracellular biothiols, including cysteine (Cys), glutathione (GSH), and homocysteine (Hcy), play a critical role in many physiological and pathological processes. Among them, GSH is the most abundant non-protein mercaptan (1-10 mM) in cells, and the change in GSH concentration level is closely related to the occurrence of many diseases, such as Parkinson's disease, Alzheimer's disease, and neurological diseases. Fluorescent probes have attracted much attention due to their advantages of high specificity, high sensitivity, high selectivity, low cost, and high quantum yield. Methods that use optical probes for selective detection of GSH in vitro and in vivo are in high demand. In this paper, we reviewed the most recent five years of research on fluorescence probes for the detection of GSH, including the specific detection of GSH, dual-channel identification of GSH and other substances, and the detection of GSH and other biothiols. According to the type of fluorophore, we classified GSH fluorescent probes into eight classes, including BODIPY, 1,8-Naphthalimide, coumarin, xanthene, rhodamine, cyanine, benzothiazoles, and others. In addition, we roundly discuss the synthesis, detection mechanism, photophysical properties, and biological applications of fluorescent probes. We hope that this review will inspire the exploration of new fluorescent probes for GSH and other related analyses.

Dissecting lysosomal viscosity fluctuations in live cells and liver tissues with an ingenious NIR fluorescent probe

Viscosity is a pivotal component in the cell microenvironment, while lysosomal viscosity fluctuation is associated with various human diseases, such as tumors and liver diseases. Herein, a near-infrared fluorescent probe (BIMM) based on merocyanine dyes was designed and synthesized for detecting lysosomal viscosity in live cells and liver tissue. The increase in viscosity restricts the free rotation of single bonds, leading to enhanced fluorescence intensity. BIMM exhibits high sensitivity and good selectivity, and is applicable to a wide pH range. BIMM has near-infrared emission, and the fluorescent intensity shows an excellent linear relationship with viscosity. Furthermore, BIMM possessing excellent lysosomes-targeting ability, and can monitor viscosity changes in live cells stimulated by dexamethasone, lipopolysaccharide (LPS), and nigericin, and differentiate between cancer cells and normal cells. Noticeably, BIMM can accurately analyze viscosity changes in various liver disease models with HepG2 cells, and is successfully utilized to visualize variations in viscosity on APAP-induced liver injury. All the results demonstrated that BIMM is a powerful wash-free tool to monitor the viscosity fluctuations in living systems.

A Zn-modified PCN-224 fluorescent nanoprobe for selective and sensitive turn-on detection of glutathione

Monitoring endogenous glutathione (GSH) levels in living cells is essential for cancer diagnose and treatment. In this work, GSH responsive fluorescent nanoprobe with turn-on property was constructed using Zn-modified porphyrinic metal-organic frameworks (PCN-224-Zn). The introduced Zn2+ could quench the fluorescence of PCN-224 by the metallization of organic ligand (TCPP) and serves as sensing site for GSH. When exposed to GSH, the strong binding affinity of GSH generates the formation of Zn-GSH complex, eliminating the fluorescence quenching effect of Zn2+. Based on the constructed PCN-224-Zn nanoprobe, selective determination of GSH was achieved in the range of 0.01-6 μM with a detection limit of 1.5 nM. Furthermore, the constructed nanoprobe can realize the fluorescence imaging of endogenous GSH in MCF-7 and HeLa cells. Meanwhile, PCN-224-Zn could also monitor GSH in cell lysate with recovery rates from 93.8 % to 102.3 %. The performance of PCN-224-Zn demonstrates its capacities in the application of fluorescence sensing and bio-imaging fields.

Advances in fluorescent probe development for bioimaging of potential Parkinson's biomarkers

Parkinson's disease (PD) is a common neurodegenerative disease. The clinical symptoms of PD are usually related to motor symptoms, including postural instability, rigidity, bradykinesia, and resting tremors. At present, the pathology of PD is not yet clear. Therefore, revealing the underlying pathological mechanism of PD is of great significance. A variety of bioactive molecules are produced during the onset of Parkinson's, and these bioactive molecules may be a key factor in the development of Parkinson's. The emerging fluorescence imaging technology has good sensitivity and high signal-to-noise ratio, making it possible to deeply understand the pathogenesis of PD through these bioactive molecules. Currently, fluorescent probes targeting PD biomarkers are widely developed and applied. This article categorizes and summarizes fluorescent probes based on different PD biomarkers, systematically introduces their applications in the pathological process of PD, and finally briefly elaborates on the challenges and prospects of these probes. We hope that this review will provide in-depth reference insights for designing fluorescent probes, and contribute to study of the pathogenesis and clinical treatment of PD.

The Role of Oxidative Stress in Tumorigenesis and Progression

Oxidative stress refers to the imbalance between the production of reactive oxygen species (ROS) and the endogenous antioxidant defense system. Its involvement in cell senescence, apoptosis, and series diseases has been demonstrated. Advances in carcinogenic research have revealed oxidative stress as a pivotal pathophysiological pathway in tumorigenesis and to be involved in lung cancer, glioma, hepatocellular carcinoma, leukemia, and so on. This review combs the effects of oxidative stress on tumorigenesis on each phase and cell fate determination, and three features are discussed. Oxidative stress takes part in the processes ranging from tumorigenesis to tumor death via series pathways and processes like mitochondrial stress, endoplasmic reticulum stress, and ferroptosis. It can affect cell fate by engaging in the complex relationships between senescence, death, and cancer. The influence of oxidative stress on tumorigenesis and progression is a multi-stage interlaced process that includes two aspects of promotion and inhibition, with mitochondria as the core of regulation. A deeper and more comprehensive understanding of the effects of oxidative stress on tumorigenesis is conducive to exploring more tumor therapies.

A turn-on fluorescent probe for detecting and bioimaging of HOCl in inflammatory and liver disease models

Hypochlorous acid (HOCl) is a common reactive oxygen species (ROS) associated with the development of liver, tumor, inflammatory, and other diseases. In this work, the turn-on fluorescent probe named (WZ-HOCl) with a naphthalimide structure was designed and synthesized to detect endogenous HOCl in disease models. WZ-HOCl can achieve a fast response to HOCl with good linearity in the range of 0-45 μM (LOD = 147 nM). The application of WZ-HOCl in bioimaging was investigated by constructing a series of cellular disease models, and the results showed that WZ-HOCl could sensitively detect endogenous HOCl in inflammatory and liver disease models. It can also be used to differentiate between hepatocytes and hepatoma cells. WZ-HOCl will provide new methods and ideas for fluorescent probes in detecting drug-induced liver injury, alcoholic and non-alcoholic steatohepatitis, and some inflammation-related diseases.

Cheap and portable paper chip with terrific oxidase-like activity and SERS enhancement performance for SERS-colorimetric bimodal detection of intracellular glutathione

Glutathione (GSH) acts a crucial role in the normal operation of manifold life activities and is closely bound up with many human diseases. Here, a SERS-colorimetric bimodal paper-based biosensor based on Mn-doped CDs/silver nanoparticles (Mn-CDs/AgNPs) has been fabricated for high-efficiency quantification of intracellular GSH. The Mn-CDs/AgNPs with fine oxidase-like characteristic and SERS enhancement ability has been assembled onto the Whatman filter paper (WFP) to cleverly fabricate paper chip (Mn-CDs/AgNPs@WFP) which can trigger the oxidation of colorless 3,3',5,5'-tetramethylbenzidine (TMB) into blue TMBox and simultaneously enhance the SERS signal of TMBox. However, the introduction of GSH inhibits the oxidation of TMB, leading to color fading of paper chip and diminishment of SERS signal. Considering this, the bimodal paper-based sensing platform can be exploited for SERS-colorimetric detection of GSH, manifesting excellent selectivity, reliable stability, and satisfactory precision. The detection limits of SERS and colorimetric detection modes are as low as 0.41 μM and 0.53 μM, respectively. Furthermore, this proposed bimodal biosensor has been successfully utilized for the determination of intracellular GSH and validated by commercial GSH assay kit, which provides a mighty and convenient tool for intracellular GSH detection and can boost future effort about exploitation of other multimode paper-based biosensors as well as promote their appliances in disease diagnosis.

Engineering an activatable fluorescent probe for studying ONOO- in pyroptotic process

Pyroptosis, a recently discovered form of programmed cell death, plays a pivotal role in oncological treatment. Howbeit, the mechanisms underlying pyroptosis in tumor treatment remain unclear. Previous research has demonstrated that the occurrence of pyroptosis generally accompanies a surge of reactive oxygen species (ROS) generation, with ONOO- being one of these ROS and closely linked to numerous diseases. Therefore, it is imperative to investigate the potential association between ONOO- and pyroptosis. Herein, a highly sensitive and rapidly responsive near-infrared (NIR) probe, Rd700-PN, is fabricated for exploring unrevealed relationships between ONOO- and pyroptosis. We successfully harness Rd700-PN to detect ONOO- fluctuation during cellular pyroptosis for the first time. Furthermore, the results demonstrate that Rd700-PN can scout the chemotherapeutic drug's induction ability of tumor pyroptosis in vivo. Notably, this study provides an excellent means to shed light on the correlation between ONOO- and pyroptosis and to screen antitumor drugs activating pyroptosis.

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.

Screening and optimization of a water-soluble near-infrared fluorescent probe for drug-induced liver injury monitoring

Peroxynitrite (ONOO-) is a potential biomarker of drug-induced liver injury (DILI) and is involved in the process of DILI. Therefore, developing a reliable detection method for ONOO- will greatly contribute to ensuring drug safety and improving treatment efficiency. Here, based on the previous work, two kinds of NIR fluorescence probes PN and SPN were developed with phenyl-hydrazine as the ONOO- recognition group, which based on two fluorophores RN and SRN that are stable to ONOO-. A sensitive NIR probe SPN with good water solubility, low detection limit and good biocompatibility was selected through in vitro spectral property screening. Further experimental results show that there is a good linear relationship between the response intensity of probe SPN to ONOO- and the concentration of ONOO-, and the detection limit can reach 19.7 nM. At the cellular level, probe SPN can achieve a good and specific response to endogenous and exogenous ONOO-. Also, the probe SPN can be used for imaging and detection of DILI in zebrafish level and small animal level, indicating that probe SPN can be used as a powerful tool for diagnosis of DILI and efficacy evaluation of therapeutic drugs.

A robust activatable two-photon fluorescent probe for endogenous formaldehyde biomarker visualization diagnosis and evaluation of diabetes mellitus

Diabetes mellitus and its complications are one of the largest healthcare burdens in the world and are increasing every year. However, the lack of effective biomarkers and non-invasive real-time monitoring tools remains a great challenge for the early diagnosis of diabetes mellitus. Endogenous formaldehyde (FA) represents a key reactive carbonyl species in biological systems, and altered metabolism and functions of FA have been closely related to the pathogenesis and maintenance of diabetes. Among various noninvasive biomedical imaging techniques, the identification-responsive fluorescence (FL) imaging could greatly benefit the comprehensive multi-scale assessment of some diseases such as diabetes. Herein, we have designed a robust activatable two-photon probe DM-FA for the first highly selective monitoring of fluctuations in FA levels during diabetes mellitus. Through the density functional theory (DFT) theoretical calculations, we elucidated the rationality of the activatable fluorescent probe DM-FA turning on the FL before and after the reaction with FA. In addition, DM-FA has excellent high selectivity, high growth factor and good photostability in the process of recognizing FA. Due to the brilliant two-photon and one-photon FL imaging capabilities of DM-FA, it has been successfully used to visualize of exogenous and endogenous FA in cells and mice. Remarkably, as a powerful FL imaging visualization tool, DM-FA was introduced for the first time to visually diagnose and explore diabetes through the fluctuation of FA content. The successful application of DM-FA in two-photon and one-photon FL imaging experiments found elevated FA levels in high glucose-stimulated diabetic cell models. We successfully visualized upregulation of FA levels in diabetic mice and decreased of FA levels in diabetic mice scavenged by NaHSO₃ from multiple perspectives using multiple imaging modalities. This work may provide a novel strategy for the initial diagnosis of diabetes mellitus and the evaluation of the efficacy of drug therapy for treating diabetes mellitus, which will likely have a positive impact on clinical medicine.

Photoelectrochemical sensing of glutathione using bismuth vanadate (BiVO4) decorated with polyaniline (PANI) and cadmium sulfide (CdS)

A ternary nanocomposite photoelectrode composed of cadmium sulfide (CdS), polyaniline (PANI), and bismuth vanadate (BiVO₄) was successfully designed by combining cyclic voltammetry (CV) with electrochemical deposition and high-temperature calcination. The first synthesized CdS/PANI/BiVO₄ composite was used as a photoelectrochemical (PEC) monitoring platform for glutathione (GSH). The ternary CdS/PANI/BiVO₄ nanocomposites exhibited higher PEC activity, which was attributed to the accelerated electron transfer by the loading of CdS and PANI, which enables the material surface to better adsorb the electrons separated by GSH, thereby oxidizing it into GSSH. The photoanodes were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), UV-vis diffuse reflectance spectroscopy, and photoelectrochemical experiments. Under the optimal experimental conditions, the BiVO₄ electrode modified with CdS and PANI exhibited a linear response in the concentration range of 0.1-20 μM with a sensitivity of 0.669 μA mM^-1 cm^-2 and a detection limit of 40 nM. Moreover, the PEC sensor exhibits good reproducibility and long-term stability. In summary, the designed materials have excellent electrochemical properties, which make them ideal candidates for PEC detection of GSH.

Monitoring cell viability in N-nitrosodiethylamine induced acute hepatitis and detection of hydrazine in solution and gas phase with Dual-function fluorescent probes

The highly toxic N-nitrosodiethylamine (NDEA) and hydrazine (N₂H₄) caused severe environmental contamination and serious health risks. Herein, we designed the two-photon ratiometric fluorescent probe (Nap-2), emission maximum shifted from 466 nm to 571 nm, to monitor cell viability of NDEA induced acute hepatitis via esterase activity detection. Furthermore, the probe Nap-2 evaluate the hydrazine (N₂H₄) content in the solution and gas phase. It is worth mentioning that we used NDEA induced acute hepatitis in the mice and evaluated the negative correlation of esterase activity in the tissue cells and serum with Nap-2. The probe Nap-2 exhibited that acute hepatitis induced by NDEA decreased cell viability. Furthermore, we made convenient test papers using Nap-2 to detect N₂H₄ in solution and gas phase. After adding N₂H₄, the fluorescence color changed from blue to yellow and was visible to the naked eye. This work provides a convenient tool and method for evaluating the toxicity of NDEA induced acute hepatitis and detecting N₂H₄ in the environment.

Discriminating normal and inflammatory mice models by viscosity changes with a two-photon fluorescent probe

Studies have found that the intracellular viscosity changes have close relationship with many diseases, therefore design and synthesis of fluorescent probe for testing intracellular viscosity is of great significance to the development of clinical. Herein, we developed a new two-photon near infrared probe (HCT) for viscosity imaging to discriminate normal and inflammatory models. Experimental results displayed that HCT has great sensitivity for the detection of viscosity, and based on the excellent performance of its photostability and lower cytotoxicity, HCT was successfully utilized for single-photon/ two-photon fluorescence imaging of the viscosity in living cells. More importantly, we employ HCT to further showcase in living tissues. Additionally, HCT could be used to discriminate between normal and inflamed mice, heralding its practical application in biomedical aspects.

Fluorescent Sensing of Glutathione and Related Bio-Applications

Glutathione (GSH), as the most abundant low-molecular-weight biological thiol, plays significant roles in vivo. Abnormal GSH levels have been demonstrated to be related to the dysfunction of specific physiological activities and certain kinds of diseases. Therefore, the sensing of GSH is emerging as a critical issue. Cancer, with typical high morbidity and mortality, remains one of the most serious diseases to threaten public health. As it is clear that much more concentrated GSH is present at tumor sites than at normal sites, the in vivo sensing of GSH offers an option for the early diagnosis of cancer. Moreover, by monitoring the amounts of GSH in specific microenvironments, effective diagnosis of ROS levels, neurological diseases, or even stroke has been developed as well. In this review, we focus on the fluorescent methodologies for GSH detection, since they can be conveniently applied in living systems. First, the fluorescent sensing methods are introduced. Then, the principles for fluorescent sensing of GSH are discussed. In addition, the GSH-sensing-related biological applications are reviewed. Finally, the future opportunities in in the areas of fluorescent GSH sensing-in particular, fluorescent GSH-sensing-prompted disease diagnosis-are addressed.

A water-soluble fluorescent probe for monitoring mitochondrial GSH fluctuations during oxidative stress

In this research, we constructed a styrylpyridine derivative-based fluorescent probe MITO-PQDNs to monitor mitochondrial glutathione (GSH). The probe MITO-PQDNs could react rapidly (20 min) with GSH in PBS buffer and exhibited a strong fluorescence signal (586 nm) as well as a significant Stokes shift (200 nm). Moreover, MITO-PQDNs could quantitatively detect GSH with high sensitivity (LOD = 253 nM). Meanwhile, MITO-PQDNs possessed favorable biocompatibility and could detect both endogenous and exogenous GSH in MCF-7 cells. Above all, MITO-PQDNs enabled the detection of fluctuations in mitochondrial GSH concentrations during oxidative stress.