Revealing the redox status in endoplasmic reticulum by a selenium fluorescence probe

Selective delivery of imaging probes and therapeutics to the endoplasmic reticulum or Golgi apparatus: Current strategies and beyond

To maximize therapeutic effects and minimize unwanted effects, the interest in drug targeting to the endoplasmic reticulum (ER) or Golgi apparatus (GA) has been recently growing because two organelles are distributing hubs of cellular building/signaling components (e.g., proteins, lipids, Ca2+) to other organelles and the plasma membrane. Their structural or functional damages induce organelle stress (i.e., ER or GA stress), and their aggravation is strongly related to diseases (e.g., cancers, liver diseases, brain diseases). Many efforts have been developed to image (patho)physiological functions (e.g., oxidative stress, protein/lipid-related processing) and characteristics (e.g., pH, temperature, biothiols, reactive oxygen species) in the target organelles and to deliver drugs for organelle disruption using organelle-targeting moieties. Therefore, this review will overview the structure, (patho)physiological functions/characteristics, and related diseases of the organelles of interest. Future direction on ER or GA targeting will be discussed by understanding current strategies and investigations on targeting, imaging/sensing, and therapeutic systems.

Synthesis, Photophysical Properties, Theoretical Studies, and Living Cancer Cell Imaging Applications of New 7-(Diethylamino)quinolone Chalcones

In this article, three unsymmetrical 7-(diethylamino)quinolone chalcones with D-π-A-D and D-π-A-π-D type push-pull molecular arrangements were synthesized via a Claisen-Schmidt reaction. Using 7-(diethylamino)quinolone and vanillin as electron donor (D) moieties, these were linked together through the α,β-unsaturated carbonyl system acting as a linker and an electron acceptor (A). The photophysical properties were studied, revealing significant Stokes shifts and strong solvatofluorochromism caused by the ICT and TICT behavior produced by the push-pull effect. Moreover, quenching caused by the population of the TICT state in THF-H2O mixtures was observed, and the emission in the solid state evidenced a red shift compared to the emission in solution. These findings were corroborated by density functional theory (DFT) calculations employing the wb97xd/6-311G(d,p) method. The cytotoxic activity of the synthesized compounds was assessed on BHK-21, PC3, and LNCaP cell lines, revealing moderate activity across all compounds. Notably, compound 5b exhibited the highest activity against LNCaP cells, with an LC50 value of 10.89 μM. Furthermore, the compounds were evaluated for their potential as imaging agents in living prostate cells. The results demonstrated their favorable cell permeability and strong emission at 488 nm, positioning them as promising candidates for cancer cell imaging applications.

A New and Fast-Response Fluorescent Probe for Monitoring Hypochlorous Acid Derived from Myeloperoxidase

Hypochlorous acid (HOCl) has been implicated in numerous pathologies associated with an inflammatory component, but its selective and sensitive detection in biological settings remains a challenge. In this report, imaging of HOCl was realized with a thiomorpholine-based probe as derivative of nitrobenzothiadiazole (NBD-S-TM). The fluorescence is based on photoinduced electron transfer by using nitrobenzothiadiazole core as a donor and thiomorpholine substituent as an acceptor. NBD-S-TM showed high sensitivity and a fast response to HOCl k = (2.6 ± 0.2) × 107 M-1s-1 with a 1:1 stoichiometry. The detection limit for HOCl was determined to be 60 nM. Furthermore, the desirable features of NBD-S-TM for the detection of HOCl in aqueous solutions, such as its reliability at physiological pH, rapid fluorescence response, and biocompatibility, enabled its application in the detection of HOCl in myeloperoxidase enzymatic system. Moreover, NBD-S-TM exhibited excellent selectivity and sensitivity for HOCl over other biologically relevant species, such as hydrogen peroxide and peroxynitrite. The fluorescent S-oxidized product (NBD-S-TSO) is only formed in the presence of HOCl. Probing with NBD-S-TM may be helpful to further the development of high throughput screening assays to monitor the activity of myeloperoxidase.

A thiomorpholine-based fluorescent probe for the far-red hypochlorous acid monitoring

A simple thiomorpholine-based fluorescent probe was designed and synthesized by combining thiomorpholine (TM) and nitrobenzenoselenadiazoles fluorophore (NBD-Se). The thiomorpholine group quenches the fluorescence of NBD-Se efficiently through the photoinduced electron transfer (PET) effect. Hypochlorous acid (HOCl) oxidizes the NBD-Se-TM probe to its fluorescent S-oxide (NBD-Se-TSO) with a 1:1 stoichiometry. The desirable features of NBD-Se-TM for detecting HOCl in aqueous solutions, such as its high sensitivity and selectivity, reliability at physiological pH, and rapid fluorescence response, enabled its application in the detection of HOCl produced by myeloperoxidase. The results proved that NBD-Se-TM is a promising fluorescent probe that can be used in screening assays for MPO inhibitors. Its high reaction rate constant with HOCl (²k = 2.0 × 10⁷M^-1s^-1) indicates the possibility of application in more complex biological systems.

Recent progress in small-molecule fluorescent probes for endoplasmic reticulum imaging in biological systems

Endoplasmic reticulum (ER) is an indispensable organelle in eukaryotic cells involved in protein synthesis and processing, as well as calcium storage and release. Therefore, maintaining the quality of ER is of great importance for cellular homeostasis. Aberrant fluctuations of bioactive species in the ER will result in homeostasis disequilibrium and further cause ER stress, which has evolved to contribute to the pathogenesis of various diseases. Therefore, the real-time monitoring of various bioactive species in the ER is of high priority to ascertain the mysterious roles of ER, which will contribute to unveiling the corresponding mechanism of organism disturbances. Recently, fluorescence imaging has emerged as a robust technique for the direct visualization of molecular events due to its outstanding sensitivity, high temporal-spatial resolution and noninvasive nature. In this review, we comprehensively summarize the recent progress in design strategies, bioimaging applications, potential directions and challenges of ER-targetable small-molecular fluorescent probes.

A dual-targeting fluorescent probe for simultaneous and discriminative visualization of lipid droplets and endoplasmic reticulum

A single fluorescent probe (SF-probe) that can simultaneously and discriminatively visualize two organelles is a powerful tool to investigate their interaction in cellular processes.

A redox reversible endoplasmic reticulum-targeted fluorescent probe for revealing the redox status of living cells

The endoplasmic reticulum (ER) is one of the most important organelles in cells and is involved in protein synthesis, folding and orderly transport. Redox balance is the key to its normal function. In this work, we designed and synthesized an endoplasmic reticulum-targeted fluorescent probe N-Se with selenomorpholine as the redox reversible detection moiety. N-Se could selectively respond to ClO^- within only 8 s with a LOD of 28.8 nM. Furthermore, such a response is reversible in the regulation of GSH. Confocal fluorescence imaging confirmed the excellent endoplasmic reticulum targeting ability of N-Se. Thus, it could real-time monitor the dynamic changes of the redox status in the endoplasmic reticulum through the variation of the fluorescence intensity.

A novel ER-targeted two-photon fluorescent probe for monitoring abnormal concentrations of HClO in diabetic mice

Diabetes is closely related to the presence of excess HClO induced by endoplasmic reticulum stress. Thus, a novel two-photon fluorescent probe was designed and synthesized for the detection of HClO in the endoplasmic reticulum. Significantly, it has been verified that high glucose can indeed induce oxidative stress of the endoplasmic reticulum and produce excessive HClO. Moreover, the probe has also been successfully used in tissue imaging of diabetic mice.

An endoplasmic reticulum-targeting fluorescent probe for discriminatory detection of Cys, Hcy and GSH in living cells

Endoplasmic reticulum, known to us as the ER, is the largest organelle in many kinds of eukaryotic cells and plays vital roles in maintaining the normal function of cells. Biothiols (Cys, Hcy, GSH) in secretory proteins will be modified as they enter the ER and are of great importance in balancing redox state of ER environments. In this article, we have developed the first endoplasmic reticulum-targeting fluorescent probe, ER-CP, for concurrent distinguishment of Cys, Hcy and GSH with favorable sensitivity and selectivity. ER-CP was successfully used in fluorescence imaging of Cys, Hcy and GSH in HeLa cells. In addition, ER-CP exhibited a good ER-targeting property (Pearson's correlation coefficient = 0.90).

Discussions of Fluorescence in Selenium Chemistry: Recently Reported Probes, Particles, and a Clearer Biological Knowledge

In this review from literature appearing over about the past 5 years, we focus on selected selenide reports and related chemistry; we aimed for a digestible, relevant, review intended to be usefully interconnected within the realm of fluorescence and selenium chemistry. Tellurium is mentioned where relevant. Topics include selenium in physics and surfaces, nanoscience, sensing and fluorescence, quantum dots and nanoparticles, Au and oxide nanoparticles quantum dot based, coatings and catalyst poisons, thin film, and aspects of solar energy conversion. Chemosensing is covered, whether small molecule or nanoparticle based, relating to metal ion analytes, H2S, as well as analyte sulfane (biothiols-including glutathione). We cover recent reports of probing and fluorescence when they deal with redox biology aspects. Selenium in therapeutics, medicinal chemistry and skeleton cores is covered. Selenium serves as a constituent for some small molecule sensors and probes. Typically, the selenium is part of the reactive, or active site of the probe; in other cases, it is featured as the analyte, either as a reduced or oxidized form of selenium. Free radicals and ROS are also mentioned; aggregation strategies are treated in some places. Also, the relationship between reduced selenium and oxidized selenium is developed.

A Fluorescent Probe for the Fast Detection of Hypochlorite and its Applications in Water, Test Strip and Living Cells

Hypochlorite (ClO^-) mediated by oxidative stress play an important role in the body's defense system due to their physiological and pathological significance. In this work, a new and simple probe was designed and synthesized to detect hypochlorite. This probe could rapidly respond to hypochlorite in a short time (20 s) in aqueous media, and showed excellent selectivity and sensitivity, and a wide pH range of 3 ̶ 12, as well as the low detection limit of 1.44 nM. In addition, it was successfully applied to the detection of ClO^- in water sample, test paper experiment, and cell imaging.

Viscosity sensitive endoplasmic reticulum fluorescent probes based on oxazolopyridinium

A series of viscosity sensitive fluorescent probes 1a-e were synthesized by linking coumarin and oxazolopyridinium via dimethylene in this paper. The viscosity test of probes 1a-e indicated that the fluorescence intensity of the probes enhanced significantly with the increase of viscosity of the system (0.89-865 cP), and exhibited a nearly OFF-ON response to viscosity at 648 nm, 650 nm and 650 nm, respectively. In addition, cells still had a high survival rate after co-culturing with probes 1a-e for 12 h (94-98%). Meanwhile, the laser confocal experiment showed that the variation of the carbon chain length in the oxazolopyridinium could affect the subcellular region of the localization of the probes in cells. When the length of the carbon chain in oxazolopyridinium was between n-C7H15 and n-C12H23, probes 1b-d had the ability to target the endoplasmic reticulum in the cells. Moreover, probes 1b-d showed no significant change in fluorescence intensity after 35 min of continuous laser confocal irradiation, indicating that they had excellent anti-photobleaching properties.

A simple pyridine-based highly specific fluorescent probe for tracing hypochlorous acid in lysosomes of living cells

A simple pyridine-based highly specific fluorescent probe was constructed to trace hypochlorous acid in lysosomes of living cells.

Photoexcited molecular probes for selective and revertible imaging of cellular reactive oxygen species

Redox homeostasis is key to maintaining the normal physiological status of living cells.

Reductive stress promotes protein aggregation and impairs neurogenesis

Redox homeostasis regulates key cellular signaling in both physiology and pathology. While perturbations result in shifting the redox homeostasis towards oxidative stress are well documented, the influence of reductive stress (RS) in neurodegenerative diseases and its mechanisms are unknown. Here, we postulate that a redox shift towards the reductive arm (through the activation of Nrf2 signaling) will damage neurons and impair neurogenesis. In proliferating and differentiating neuroblastoma (Neuro 2a/N2a) cells, sulforaphane-mediated Nrf2 activation resulted in increased transcription/translation of antioxidants and glutathione (GSH) production along with significantly declined ROS in a dose-dependent manner leading to a reductive-redox state (i.e. RS). Interestingly, this resulted in endoplasmic reticulum (ER) stress leading to subsequent protein aggregation/proteotoxicity in neuroblastoma cells. Under RS, we also observed elevated Tau/α-synuclein and their co-localization with other protein aggregates in these cells. Surprisingly, we noticed that acute RS impaired neurogenesis as evidenced from reduced neurite outgrowth/length. Furthermore, maintaining the cells in a sustained RS condition (for five consecutive generations) dramatically reduced their differentiation and prevented the formation of axons (p < 0.05). This impairment in RS mediated neurogenesis occurs through the alteration of Tau dynamics i.e. RS activates the pathogenic GSK3β/Tau cascade thereby promoting the phosphorylation of Tau leading to proteotoxicity. Of note, intermittent withdrawal of sulforaphane from these cells suppressed the proteotoxic insult and re-activated the differentiation process. Overall, this results suggest that either acute or chronic RS could hamper neurogenesis through GSK3β/TAU signaling and proteotoxicity. Therefore, investigations identifying novel redox mechanisms impacting proteostasis are crucial to preserve neuronal health.

Organoselenium chemistry-based polymer synthesis

Novel synthesis of selenium containing polymers with pre-determined structures and applications thereof.