Small molecule fluorescent probes of protein vicinal dithiols

Fluorescence lifetime imaging of human pancreatic lipase activity using a novel probe for early diagnosis of severe acute pancreatitis

Severe Acute Pancreatitis, a serious condition caused by factors such as gallstones and chronic excessive alcohol consumption, with a very high mortality rate. Human pancreatic lipase (hPL) is a key digestive enzyme and abnormal activity levels of this enzyme are important indicators for diagnosing and monitoring pancreatic diseases. A fluorescent probe, LPP, has been developed to monitor the activity of hPL, especially in cases of SAP. The probe is based on cyanine isoindole derivatives, in vitro experiments confirmed the high specificity and sensitivity of the probe, with a detection limit of 0.012 U/mL, reactions completed within 10 min, and effective monitoring of pancreatic lipase activity in various biological samples. The stability and low cytotoxicity of LPP make it suitable for clinical applications, providing new tools and perspectives for the research and treatment of pancreatic diseases and related metabolic abnormalities. In addition, the change in fluorescence lifetime after the reaction of the probe with lipase allows for fluorescence lifetime imaging (FLIM), effectively monitoring the dynamic changes of hPL and enabling early diagnosis and monitoring of pancreatitis. This research not only enhances the understanding of pancreatic lipase activity detection but also has the potential to improve the diagnostics and treatment of pancreatitis.

An activatable red emitting fluorescent probe for monitoring vicinal dithiol protein fluctuations in a stroke model

Vicinal dithiol proteins (VDPs) facilitate cellular redox homeostasis, modulate protein synthesis and participate in post-translational modifications through the dynamic equilibrium of dithiol and disulfide bonds. Herein, an activatable red emitting fluorescent probe, VDP-red, is developed for detecting VDPs. With the aid of this probe, we have discovered for the first time a reduction in the levels of reduced VDPs in a stroke mouse model. This work provides a fresh viewpoint for understanding stroke mechanisms.

Targeting thioredoxin reductase by eupalinilide B promotes apoptosis of colorectal cancer cells in vitro and in vivo

Aberrant activation of thioredoxin reductase (TrxR) is correlated with tumor occurrence and progression, suggesting that TrxR inhibitors can be used as antitumor agents. In this study, we evaluated the anticancer efficacy of eupalinilides B on colorectal cancer cells. Eupalinilides B primarily targeted the conserved selenocysteine 498 residues in TrxR. Besides, it inhibited the enzyme activity in an irreversible manner. After eupalinilides B was used to pharmacologically inhibit TrxR, reactive oxygen species accumulated, and the intracellular redox balance was broken, finally causing oxidative stress-induced tumor cell apoptosis. Significantly, eupalinilides B treatment inhibited in vivo tumor growth. Targeting TrxR by eupalinilides B reveals the new mechanism underlying eupalinilides B and provides insight in developing eupalinilides B as the candidate antitumor chemotherapeutic agent for the treatment of cancer.

Mobility capillary electrophoresis-native mass spectrometry reveals the dynamic conformational equilibrium of calmodulin and its complexes

Benefitting from the rapid evolution of artificial intelligence and structural biology, an expanding collection of high-resolution protein structures has greatly improved our understanding of protein functions. Yet, proteins are inherently flexible, and these static structures can only offer limited snapshots of their true dynamic nature. The conformational and functional changes of calmodulin (CaM) induced by Ca2+ binding have always been a focus of research. In this study, the conformational dynamics of CaM and its complexes were investigated using a mobility capillary electrophoresis (MCE) and native mass spectrometry (native MS) based method. By analyzing the ellipsoidal geometries of CaM in the solution phase at different Ca2+ concentrations, it is interesting to discover that CaM molecules, whether bound to Ca2+ or not, possess both closed and open conformations. Moreover, each individual CaM molecule actively "jumps" (equilibrium exchange) between these two distinct conformations on a timescale ranging from milli- to micro-seconds. The binding of Ca2+ ions did not affect the structural dynamics of CaM, while the binding of a peptide ligand would stabilize CaM, leading to the observation of a single, compact conformation of the resulting protein complex. A target recognition mechanism was also proposed based on these new findings, suggesting that CaM's interaction with targets may favor a conformational selection model. This enriches our understanding of the binding principles between CaM and its numerous targets.

Histidine tag modified magnetic beads for analysis of arsenic binding proteins

BACKGROUND

Many proteins with thiol groups can bind with trivalent arsenic which are termed as arsenic binding proteins, thus change their physiological functions. Therefore, it is vital to analyze the arsenic binding proteins in cells. The Pull-Down strategy based on biotinylated phenylarsenic acid (Bio-PAO(III)) probes is an effective way for analysis of arsenic binding proteins. In this strategy, streptavidin magnetic beads (SA-MBs) was applied to capture the arsenic binding proteins conjugating with Bio-PAO(III) probe. However, strong interaction between SA and biotin makes the elution of arsenic binding proteins not easy.

RESULTS

We developed a novel affinity separation strategy to address the challenge of eluting arsenic binding proteins, a key issue with the existing Bio-PAO(III) Pull-Down method. By employing magnetic beads modified with Nα-Bis(carboxymethyl)-l-lysine (NTA-Lys), polyhistidine-tag (His6-Tag), and SA (MB-NTA(Ni)-His6-SA), we established a more efficient purification process. This innovative approach enables selective capture of arsenic binding proteins in HepG2 cells labeled by Bio-PAO(III) probes, facilitating gentle digestion by trypsin for precise identification through capillary high performance liquid chromatography (Cap HPLC)-electrospray ionization (ESI)-tandem mass spectrometry (MS/MS). What is more, the magnetic beads can be regenerated by using imidazole as the eluent, and the obtained MB-NTA(Ni) can be reloaded with His6-SA for next use. Our method successfully identified 41 arsenic binding proteins, including those involved in cytoskeletal structure, heat shock response, transcriptional regulation, DNA damage repair, redox state regulation, mitochondrial dehydrogenase function, and protein synthesis and structure.

SIGNIFICANCE

This work contributes to a more comprehensive understanding of the toxic mechanisms of arsenic, potentially providing valuable insights for the prevention or treatment of arsenic-related diseases.

Plasma-Droplet Fusion-Mass Spectrometry Reveals Sub-Millisecond Protein Unfolding Dynamics Induced by Reactive Oxygen Species

Investigating the connection between reactive oxygen species (ROS) and oxidative protein unfolding is critical to reveal the mechanisms underlying disease involving elevated ROS and protein misfolding. This could inform the development of therapeutics targeting cells based on their redox status. In this study, we developed a plasma-droplet fusion-mass spectrometry platform to rapidly assess protein resilience to ROS. This home-built system fuses ROS generated from the microplasma source with protein microdroplets from a tunable nanospray source. At the droplet-plasma intersection, ROS interact with proteins before entering the mass spectrometer for mass identification and structural characterization. Benefiting from the small-sized microdroplet with adjustable traveling velocity, the platform enables the first sub-millisecond kinetic study of ROS-induced protein unfolding, with a rate constant of approximately 1.81 ms-1. Capturing ROS-induced protein unfolding intermediates and the resultant ligand release dynamics can be extended to many more protein systems. We foresee broad applications for establishing previously undetected protein unfolding events when biologically impactful ROS are enriched in time and space with functional proteins and complexes.

Chemoselective Fluorogenic Bioconjugation of Vicinal Dithiol-Containing Proteins for Live Cellular Imaging via Small Molecular Conjugate Acceptors

To develop small molecular fluorogenic tools for the chemoselective labeling of vicinal dithiol-containing proteins (VDPs) in live cells is important for studying intracellular redox homeostasis. With this research, we developed small molecule-based fluorescent probes, achieving selective labeling of VDPs through thiol-thiol substitutions on bisvinylogous thioester conjugated acceptors (IDAs). Initially, IDAs demonstrated its ability to bridge vicinal cysteine-sulfhydryls on a peptide as a mimic. Then, the peptide complex could be decoupled to recover the original peptide-SH in the presence of dithiothreitol. Furthermore, fluorometric signal amplification of the fluorescent probes occurred with high sensitivity, low limit of detection, and selectivity toward vicinal dithiols on reduced bovine serum albumin, as an example of real world VDPs. More importantly, the probes were utilized successfully for labeling of endogenous VDPs at different redox states in live cells. Thus, the bisvinylogous thioester-based receptor as a functional probe represents a new platform for uncovering the function of VDPs in live cells.

A "dual-key-and-lock" ratiometric fluorescent probe with biocompatibility and selectivity for imaging vicinal dithiol proteins

TMR-TPE, a ratiometric fluorescent probe, was reported for the imaging of vicinal dithiol proteins (VDPs) in living cells. Profiting from the "dual-key-and-lock" design, TMR-TPE solves the toxicity problem of VDP probes (98% cell viability at 50 μM) and avoids the interference of small thiols (up to 10 mM GSH). The change of VDPs during drug-induced liver injury was monitored for the first time using TMR-TPE.

Ultrabright Renal-Clearable Cyanine-Protein Nanoprobes for High-Quality NIR-II Angiography and Lymphography

The renal-clearable aspect of imaging agent with minimum toxicity issues and side effects is essential for clinical translation, yet clinical near-infrared-I/II (NIR-I/II) fluorophores with timely renal-clearance pathways are very limited. Herein, we rationally develop the cyanine-protein composite strategy through covalent bonding of β-lactoglobulin (β-LG) and chloride-cyanine dye to produce a brilliant and stable NIR-I/II fluorophore (e.g., β-LG@IR-780). The β-LG acts as a protecting shell with small molecular weight (18.4 kDa) and ultrasmall size (<5 nm), thus endowing the β-LG@IR-780 with excellent biocompatibility and renal excretion. Our β-LG@IR-780 probe enables noninvasive and precise NIR-II visualization of the physiological and pathological conditions of the vascular and lymphatic drainage system, facilitating intraoperative imaging-guided surgery and postoperative noninvasive monitoring. The minimum accumulation of our probes in the main organs improves the overall biosafety. This study provides a facile methodology for new-generation NIR-II fluorophores and largely improves the brightness and pharmacokinetics of small molecular dyes.

Recent Progress on NIR Fluorescent Probes for Enzymes

The majority of diseases’ biomarkers are enzymes, and the regulation of enzymes is fundamental but crucial. Biological system disorders and diseases can result from abnormal enzymatic activity. Given the biological significance of enzymes, researchers have devised a plethora of tools to map the activity of particular enzymes in order to gain insight regarding their function and distribution. Near-infrared (NIR) fluorescence imaging studies on enzymes may help to better understand their roles in living systems due to their natural imaging advantages. We review the NIR fluorescent probe design strategies that have been attempted by researchers to develop NIR fluorescent sensors of enzymes, and these works have provided deep and intuitive insights into the study of enzymes in biological systems. The recent enzyme-activated NIR fluorescent probes and their applications in imaging are summarized, and the prospects and challenges of developing enzyme-activated NIR fluorescent probes are discussed.

A NIR fluorescence probe for monitoring Cys upregulation induced by balsam pear polysaccharide and imaging in zebrafish

In this work, we introduced the acrylate recognition group into dicyanoisophorone derivative DCI-C-OH to construct the NIR fluorescent probe DCI-C-Cys with a large Stokes shift (240 nm). DCI-C-Cys could specifically respond to Cys, resulting in a 22-fold increase in fluorescence intensity at 702 nm. Meanwhile, the probe has the advantages of good water solubility, high sensitivity (93 nM), and excellent biocompatibility. Moreover, DCI-C-Cys successfully monitored endogenous and exogenous Cys in HepG2 cells and zebrafish. Most importantly, we found that balsam pear polysaccharide could lead to the increase of intracellular Cys levels, which might be conducive to the further study of the antioxidant mechanism of balsam pear polysaccharide.

1,3-Benzodioxole Derivatives Improve the Anti-Tumor Efficiency of Arsenicals

Arsenicals have been widely used in the treatment of cancers such as leukemia and other tumors. However, their side effects limit their clinical application. Stiripentol, a second-line adjunctive treatment for epilepsy with a good safety profile, inhibits microsomal cytochrome-P450-family enzymes to extend the retention time of co-administration. Inspired by the metabolism of stiripentol, the 1,3-benzodioxole responsible for the inhibition and its metabolic derivatives were conjugated with arsenical precursors. The fabricated arsenicals were eliminated much slower in mice and maintained an efficient concentration in the blood for a longer time than that of the arsenical precursors. They also performed better in anti-proliferation by inhibiting the thioredoxin system to induce oxidative stress, and concomitantly to initiate apoptosis in vitro and in vivo. The fabricated arsenicals reversed the hemogram of tumor-bearing mice to normal and eliminated the tumor without causing damage to any organs, exhibiting a good design strategy and pre-clinical application for leukemia and other tumors.

Phosphorogenic Iridium(III) bis-Tetrazine Complexes for Bioorthogonal Peptide Stapling, Bioimaging, Photocytotoxic Applications, and the Construction of Nanosized Hydrogels

The dual functionality of 1,2,4,5-tetrazine as a bioorthogonal reactive unit and a luminescence quencher has shaped tetrazine-based probes as attractive candidates for luminogenic labeling of biomolecules in living systems. In this work, three cyclometalated iridium(III) complexes featuring two tetrazine units were synthesized and characterized. Upon photoexcitation, the complexes were non-emissive but displayed up to 3900-fold emission enhancement upon the inverse electron-demand Diels-Alder (IEDDA) [4+2] cycloaddition with (1R,8S,9s)-bicyclo[6.1.0]non-4-yne (BCN) substrates. The rapid reaction kinetics (k₂ up to 1.47×10⁴  M^-1  s^-1 ) of the complexes toward BCN substrates allowed effective peptide labeling. The complexes were also applied as live cell bioimaging reagents and photocytotoxic agents. One of the complexes was utilized in the preparation of luminescent nanosized hydrogels that exhibited interesting cargo delivery properties.

Simultaneous Discrimination of Cys/Hcy and GSH With Simple Fluorescent Probe Under a Single-Wavelength Excitation and its Application in Living Cells, Tumor Tissues, and Zebrafish

Owing to the important physiological sits of biothiols (Cys, Hcy, and GSH), developing accurate detection methods capable of qualitative and quantitative analysis of biothiols in living systems is needed for understanding the biological profile of biothiols. In this work, we have designed and synthesized a 4'-hydroxy-[1,1'-biphenyl]-4-carbonitrile modified with NBD group-based fluorescent probe, BPN-NBD, for sensitive detection of Cys/Hcy and GSH by dual emission signals via a single-wavelength excitation. BPN-NBD exhibited an obvious blue fluorescence (λmaxem = 475 nm) upon the treatment with GSH and reacted with Cys/Hcy to give a mixed blue-green fluorescence (λmaxem = 475 and 545 nm). Meanwhile, BPN-NDB performed sufficient selectivity, rapid detection (150 s), high sensitivity (0.011 µM for Cys, 0.015 µM for Hcy, and 0.003 µM for GSH) and could work via a single-wavelength excitation to analytes and had the ability to image Cys/Hcy from GSH in living MCF-7 cells, tumor tissues, and zebrafish by exhibiting different fluorescence signals. Overall, this work provided a powerful tool for thiols visualization in biological and medical applications.

Rheumatoid arthritis drug sinomenine induces apoptosis of cervical tumor cells by targeting thioredoxin reductase in vitro and in vivo

Overexpression of thioredoxin reductase (TrxR) has been linked to tumorigenesis and phenotypic maintenance of malignant tumors. Thus, targeting TrxR with natural molecules is a promising strategy for developing anticancer drugs. Sinomenine is a naturally occurring alkaloid isolated from Sinomenium acutum. The drug, Zhengqing Fengtongning made from sinomenine, has been universally applied in rheumatoid arthritis treatment in China as well as other Asian countries for decades. Recently, increasing evidence indicates that sinomenine appears to be a promising therapeutic agent against various cancer cells. However, the exact mechanism underlying the anticancer activity of sinomenine remains unclear. In this study, we identified sinomenine as a kind of new inhibitor for TrxR. Pharmacological inhibition of TrxR by sinomenine results in the decrease of thiols content, increases the levels of reactive oxygen species, and finally facilitates oxidative stress-mediated cancer cell apoptosis. It is vital that knockdown in TrxR1 by shRNA can increase cell sensitivity to sinomenine. Treatment with sinomenine in vivo leads to a decrease in TrxR activity and tumor growth, and an increase in apoptosis. Our findings provide a novel action mechanism related to sinomenine and presents an insight on how to develop sinomenine as a chemotherapeutic agent for cancer therapy.

Inhibition of thioredoxin reductase by natural anticancer candidate β-lapachone accounts for triggering redox activation-mediated HL-60 cell apoptosis

β-Lapachone as a natural novel anticancer candidate is under clinical trials. Previous studies suggested that β-lapachone works by redox activation to ablate cancer cells. However, it is still unclear whether thioredoxin reductase (TrxR), one of the key redox catalytic enzymes in cells, plays a role in the pharmacological effects of β-lapachone. Herein, we present that β-lapachone kills human promyelocytic leukemia HL-60 cells with preference over other cancer cells and normal cells. The follow-up studies demonstrate that β-lapachone induces the HL-60 cell apoptosis through inhibition of TrxR and further elevation of oxidative stress. Overexpression of the TrxR alleviates the efficiency of β-lapachone while knockdown of the enzyme increases the β-lapachone cytotoxicity, scientifically underpinning the correlation of the observed biological behaviors of β-lapachone to TrxR inhibition. The disclosure of the novel action mechanism of β-lapachone sheds light on understanding its capacity in interfering with cellular redox signaling and supports β-lapachone as an anticancer drug candidate.

Assay of selenol species in biological samples by the fluorescent probe Sel-green

Selenium (Se) is an essential trace element for diverse cellular functions. The biological significance of Se is predominantly dependent on its incorporation into the selenocysteine (Sec) for synthesis of selenoproteins (SePs), such as thioredoxin reductase family enzymes and glutathione peroxidase family enzymes. In general, the hyperactivity of the selenol group in Sec confers the Sec residue critical for functions of SePs. The Sec is much less abundant than its sulfur analog cysteine (Cys), and it remains a high challenge to detect Sec, especially in complex biological samples. We recently reported a selective fluorescent probe Sel-green for selenols and summarized the principles for design of selenol (and thiophenol) probes. Sel-green discriminates selenols from other biological species, especially thiols, under physiological conditions, and has been applied to detect both endogenous and exogenous selenol species in live cells. In this chapter, we describe a protocol and guideline for the selective detection of Sec by applying the Sel-green. This protocol is also suitable for detection of other selenol species. This practical and convenient assay would assist scientists to better understand the pivotal roles of Sec as well as SePs.

α-Vinyl azide–cysteine click coupling reaction enabled bioorthogonal peptide/protein modification

α-Alkyl and α-aryl vinyl azides were found to be able to couple with cysteine-derived alkyl thiols chemoselectively under mild conditions, providing the corresponding β-ketosulfides with simultaneous extrusion of N2 and ammonia.

Natural diterpenoid eriocalyxin B covalently modifies glutathione and selectively inhibits thioredoxin reductase inducing potent oxidative stress-mediated apoptosis in colorectal carcinoma RKO cells

Increasing evidence suggests the significant contribution of high levels of thioredoxin reductase (TrxR) in various stages of tumorigenesis and resistance to tumor chemotherapy. Thus, inhibition of TrxR with small molecules is an attractive strategy for cancer therapy. Eriocalyxin B (EriB), a naturally occurring diterpenoid extracted from Isodon eriocalyx, has reflected potential anticancer activities through numerous pathways. Here, we describe that EriB covalently modifies GSH and selectively inhibits TrxR activity by targeting the Sec residue of the enzyme. Pharmacological inhibition of TrxR by EriB results in elevated ROS levels, reduced total GSH and thiols content, which ultimately induced potent RKO cell apoptosis mediated by oxidative stress. Importantly, EriB indicates potent synthetic lethality with GSH inhibitors, BSO, in RKO cells. In summary, our results highlight that targeting TrxR by EriB explores a novel mechanism for the biological action of EriB. This opened up a new therapeutic indication for using EriB to combat cancers.

Amphiphilic Asymmetric Diblock Copolymer with pH-Responsive Fluorescent Properties

Stimuli-responsive polymers with changeable fluorescent properties have numerous applications in sensing, bioimaging, and detection. Here we describe the facile synthesis of a pH-responsive amphiphilic asymmetric diblock copolymer of acrylic acid and butyl acrylate that incorporates a polarity-sensitive fluorophore. The asymmetric structure enhances the stimuli-responsive behavior: as the environmental pH decreases, the fluorescent intensity of the asymmetric diblock copolymer gradually increases, whereas its symmetric block counterpart shows limited and stepwise change. Besides, this remarkable difference was demonstrated to be concentration-independent, as similar emission behavior was found for both polymers at lower concentrations. These results indicate that the fluorescence properties of the copolymer can be adjusted by rationally designing the copolymer structure. This work provides a novel and general strategy for the design and synthesis of polymeric materials with encapsulated structures showing stimuli-responsive fluorescent properties to be applied as fluorescent probes with a smoothly varying response curve rather than the simple on-off switch that is typical of block copolymer systems.

Structural Modification of Aminophenylarsenoxides Generates Candidates for Leukemia Treatment via Thioredoxin Reductase Inhibition

Upregulation of the selenoprotein thioredoxin reductase (TrxR) is of pathological significance in maintaining tumor phenotypes. Thus, TrxR inhibitors are promising cancer therapeutic agents. We prepared different amino-substituted phenylarsine oxides and evaluated their cytotoxicity and inhibition of TrxR. Compared with our reported p-substituted molecule (8), the o-substituted molecule (10) shows improved efficacy (nearly a fourfold increase) to kill leukemia HL-60 cells. Although the compounds 8 and 10 display similar potency to inhibit the purified TrxR, the o-substitution 10 exhibits higher potency than the p-substitution 8 to inhibit the cellular TrxR activity. Molecular docking results demonstrate the favorable weak interactions of the o-amino group with the TrxR C-terminal active site. Efficient inhibition of TrxR consequently induces the oxidative stress-mediated apoptosis of cancer cells. Silence of the TrxR expression sensitizes the cells to the arsenic compound treatment, further supporting the critical involvement of TrxR in the cellular actions of compound 10.

Targeting thioredoxin reductase by deoxyelephantopin from Elephantopus scaber triggers cancer cell apoptosis

Elevated expression of thioredoxin reductase (TrxR) is associated with the tumorigenesis and resistance to cancer chemoradiotherapy, highlighting the potential of TrxR inhibitors as anticancer drugs. Deoxyelephantopin (DET) is the major active ingredient of Elephantopus scaber and reveals potent anticancer activity. However, the potential mechanism of action and the cellular target of DET are still unknown. Here, we found that DET primarily targets the Sec residue of TrxR and irreversibly prohibits enzyme activity. Suppression of TrxR by DET leads to accumulation of reactive oxygen species and dysregulation in intracellular redox balance, eventually inducing cancer cell apoptosis mediated by oxidative stress. Noticeably, down-regulation of TrxR1 by shRNA increases cell sensitivity to DET. Collectively, targeting of TrxR1 by DET uncovers a novel mechanism of action in DET and deepens the understanding of developing DET as a potential chemotherapeutic agent for treating cancers.

Recent Advances in Small Molecule-Based Intracellular pH Probes

Intracellular pH plays an important role in many biological and pathological processes. Small-molecule based pH probes are found to be the most effective for pH sensing because of ease of preparation, high sensitivity, and quick response. They have many advantages such as small perturbation to the functions of the target, functional adaptability, cellular component-specific localization, etc. The present review highlights the flurry of recent activity in the development of such probes. The probes are categorized based on the type of fluorophore used like quinoline, coumarin, BODIPY, rhodamine, indolium, naphthalimide, etc., and their analytical performance is discussed.

Inhibition of Thioredoxin Reductase by Santamarine Conferring Anticancer Effect in HeLa Cells

Natural products frequently have unique physiological activities and new action mechanisms due to their structural diversity and novelty, and are an important source for innovative drugs and lead compounds. We present herein that natural product santamarine targeted thioredoxin reductase (TrxR) to weaken its antioxidative function in cells, accompanied by accumulation of high levels of reactive oxygen species (ROS), and finally induced a new mechanism of tumor cell oxidative stress-mediated apoptosis. TrxR knockdown or overexpression cell lines were employed to further evaluate the cytotoxicity of santamarine regulated by TrxR, demonstrated that TrxR played a key role in the physiological effect of santamarine on cells. Santamarine targeting TrxR reveals its previously unrecognized mechanism of antitumor and provides a basis for the further development of santamarine as a potential cancer therapeutic agent.

2-IPMA Ameliorates PM2.5-Induced Inflammation by Promoting Primary Ciliogenesis in RPE Cells

Primary cilia mediate the interactions between cells and external stresses. Thus, dysregulation of primary cilia is implicated in various ciliopathies, e.g., degeneration of the retina caused by dysregulation of the photoreceptor primary cilium. Particulate matter (PM) can cause epithelium injury and endothelial dysfunction by increasing oxidative stress and inflammatory responses. Previously, we showed that PM disrupts the formation of primary cilia in retinal pigment epithelium (RPE) cells. In the present study, we identified 2-isopropylmalic acid (2-IPMA) as a novel inducer of primary ciliogenesis from a metabolite library screening. Both ciliated cells and primary cilium length were increased in 2-IPMA-treated RPE cells. Notably, 2-IPMA strongly promoted primary ciliogenesis and restored PM2.5-induced dysgenesis of primary cilia in RPE cells. Both excessive reactive oxygen species (ROS) generation and activation of a stress kinase, JNK, by PM2.5 were reduced by 2-IPMA. Moreover, 2-IPMA inhibited proinflammatory cytokine production, i.e., IL-6 and TNF-α, induced by PM2.5 in RPE cells. Taken together, our data suggest that 2-IPMA ameliorates PM2.5-induced inflammation by promoting primary ciliogenesis in RPE cells.

A cysteine-selective fluorescent probe for monitoring stress response cysteine fluctuations

Rare studies provided evidence for the real-time monitoring of stress response cysteine fluctuations. Here, we have successfully designed and synthesized a cysteine-selective fluorescent probe 1 to monitor stress response Cys fluctuations, providing visual evidence of Hg2+ regulated cysteine fluctuations for the first time, which may open a new way to help researchers to reveal the mechanism of heavy metal ion poisoning.

Natural Molecules Targeting Thioredoxin System and Their Therapeutic Potential

Significance: Thioredoxin (Trx) and thioredoxin reductase are two core members of the Trx system. The system bridges the gap between the universal reducing equivalent NADPH and various biological molecules and plays an essential role in maintaining cellular redox homeostasis and regulating multiple cellular redox signaling pathways. Recent Advance: In recent years, the Trx system has been well documented as an important regulator of many diseases, especially tumorigenesis. Thus, the development of potential therapeutic molecules targeting the system is of great significance for disease treatment. Critical Issues: We herein first discuss the physiological functions of the Trx system and the role that the Trx system plays in various diseases. Then, we focus on the introduction of natural small molecules with potential therapeutic applications, especially the anticancer activity, and review their mechanisms of pharmacological actions via interfering with the Trx system. Finally, we further discuss several natural molecules that harbor therapeutic potential and have entered different clinical trials. Future Directions: Further studies on the functions of the Trx system in multiple diseases will not only improve our understanding of the pathogenesis of many human disorders but also help develop novel therapeutic strategies against these diseases. Antioxid. Redox Signal. 34, 1083-1107.

Individual and successive detection of H2S and HClO in living cells and zebrafish by a dual-channel fluorescent probe with longer emission wavelength

Reactive oxygen species (ROS) and reactive sulfur species (RSS) participate in many physiological activities and help maintaining the redox homeostasis in biological system. The complicated intrinsic connection between specific ROS/RSS needs to be further explored. Herein, a novel fluorescent probe (MB-NAP-N₃) with longer emission wavelength has been rationally designed and synthesized based on the conjugation of the methylene blue moiety and the naphthalimide moiety for the detection of hypochlorous acid (HClO) and hydrogen sulfide (H₂S). The dual-signal probe exhibits rapid turn-on fluorescence responses for individual and successive detection of H₂S and HClO in green and red channels, respectively. Owning to its advantages such as fast response, good selectivity and high sensitivity, the probe was successfully applied to detect endogenous and exogenous HClO/H₂S in living cells. Furthermore, the outstanding luminescence performance makes it suitable for the visualization of the in vivo interaction between the two analytes in zebrafish.

Recent Progress in Fluorescent Sensors for Drug-Induced Liver Injury Assessment

Drug-induced liver injury (DILI) is a persistent concern in drug discovery and clinical medicine. The current clinical methods to assay DILI by analyzing the enzymes in serum are still not optimal. Recent studies showed that fluorescent sensors would be efficient tools for detecting the concentration and distribution of DILI indicators with high sensitivity and specificity, in real-time, in situ, and with low damage to biosamples, as well as diagnosing DILI. This review focuses on the assessment of DILI, introduces the current mechanisms of DILI, and summarizes the design strategies of fluorescent sensors for DILI indicators, including ions, small molecules, and related enzymes. Some challenges for developing DILI diagnostic fluorescent sensors are put forward. We believe that these design strategies and challenges to evaluate DILI will inspire chemists and give them opportunities to further develop other fluorescent sensors for accurate diagnoses and therapies for other diseases.

Fluorescent Probes for Imaging Protein Disulfides in Live Organisms

Cellular redox homeostasis is predominantly controlled by the ratio of thiols and disulfides, and reversible thiol-disulfide exchange reactions are fundamental of the biological redox regulation. However, due to the dynamic exchanges of thiols and disulfides, the detection, especially the in situ detection, of protein disulfides (PDS) is challenging. We employ the strategy, i.e., the increase of emission upon an environment-sensitive dye binding to proteins, to design PDS probes and discover a two-photon probe PDSTP590 (S6) that selectively recognizes PDS in live organisms. With the aid of the probe, we further disclose the elevation of PDS in brains of the mouse stroke model.

A Cell Membrane Fluorogenic Probe for Gram-Positive Bacteria Imaging and Real-Time Tracking of Bacterial Viability

Bacterial infections are a global healthcare problem, resulting in serious clinical morbidities and mortality. Real-time monitoring of live bacteria by fluorescent imaging technology has potential in diagnosis of bacterial infections, elucidating antimicrobial agents' mode of action, assessing drug toxicity, and examining bacterial antimicrobial resistance. In this work, a naphthalimide-derived fluorescent probe ZTRS-BP was developed for wash-free Gram-positive bacteria imaging. The probe aggregated in aqueous solutions and exhibited aggregation-caused fluorescence quenching (ACQ). The interaction with Gram-positive bacteria cell walls would selectively disaggregate the probe and the liberated probes were dispersed on the outside of the bacteria cell walls to achieve surface fluorescence imaging. There were no such interactions with Gram-negative bacteria, which indicates that selective binding and imaging of Gram-positive bacteria was achieved. The binding of zinc ions by ZTRS-BP can enhance the fluorescent signals on the bacterial surface by inhibiting the process of photoinduced electron transfer. ZTRS-BP-Zn(II) complex was an excellent dye to discriminate mixed Gram-positive and Gram-negative bacteria. Also, live and dead bacteria can be differentially imaged by ZTRS-BP-Zn(II). Furthermore, ZTRS-BP-Zn(II) was used for real-time monitoring bacteria viability such as B. cereus treated with antibiotic vancomycin.

Synthesis and biological evaluation of disulfides as anticancer agents with thioredoxin inhibition

Altered redox homeostasis as a hallmark of cancer cells is exploited by cancer cells for growth and survival. The thioredoxin (Trx), an important regulator in maintaining the intracellular redox homeostasis, is cumulatively recognized as a promising target for the development of anticancer drugs. Herein, we synthesized 72 disulfides and evaluated theirinhibition for Trx and antitumor activity. First, we established an efficient and fast method to screen Trx inhibitors by using the probe NBL-SS that was developed by our group to detect Trx function in living cells. After an initial screening of the Trx inhibitory activity of these compounds, 8 compounds showed significant inhibition activity against Trx. We then evaluated the cytotoxicity of these 8 disulfides, compounds 68 and 69 displayed high cytotoxicity to HeLa cells, but less sensitive to normal cell lines. Next, we performed kinetic studies of both two disulfides, 68 had faster inhibition of Trx than 69. Further studies revealed that 68 led to the accumulation of reactive oxygen species and eventually induced apoptosis of Hela cells via inhibiting Trx. The establishment of a method for screening Trx inhibitors and the discovery of 68 with remarkable Trx inhibition provide support for the development of anticancer candidates with Trx inhibition.

A semi-naphthorhodafluor-based red-emitting fluorescent probe for tracking of hydrogen polysulfide in living cells and zebrafish

Hydrogen polysulfides (H₂S_n, n ≥ 2) is recently regarded as a potential signaling molecule which shows a higher efficiency than hydrogen sulfides (H₂S) in regulating enzymes and ion channels. However, the development of specific fluorescent probes for H₂S_n with long-wavelength emission (>600 nm) are still rare. In this work, a semi-naphthorhodafluor-based red-emitting fluorescent probe SNARF-H₂S_n containing a phenyl 2-(benzoylthio) benzoate responsive unit was constructed. SNARF-H₂S_n was capable of selectively detecting H₂S_n over other reactive sulfur species. Treatment with H₂S_n would result in a > 1000-fold fluorescence enhancement within 10 min. SNARF-H₂S_n showed a low limit of detection down to 6.7 nM, and further enabled to visualize exogenous/endogenous H₂S_n in living A549 cells and zebrafish.

An ICT-based fluorescent probe guided by theoretical calculation for selectively mapping endogenous GSH in living cells

Glutathione (GSH) is one of the most essential bio-thiols to maintain the redox balance of organisms which is strongly associated with many physiological processes. Detecting the concentration and mapping the distribution of GSH in the living system is significant to study many related diseases. In this work, we have successfully constructed an ICT-based model to guide the design and synthesis of GSH specific fluorescent probe CF1. A serials spectroscopy test demonstrated that the response of CF1 towards GSH owned large stokes shift (~167 nm) and an excellent linear relationship (0-120 μM, R² = 0.9961). Furthermore, CF1 was successfully applied to image endogenous GSH in different cell lines with high sensitivity. This work is instructive for the oriented synthesis of ICT-based functional fluorescent probe and the further visualization of intracellular targets in the living system.

Design and synthesis of a novel "turn-on" long range measuring fluorescent probe for monitoring endogenous cysteine in living cells and Caenorhabditis elegans

Cysteine (Cys) is an indispensable small organic molecule containing sulfhydryl groups, which has essential regulatory effects on the physiological process of human body. In this work, a red emission fluorescent probe TCFQ-Cys was designed and exploited based on 2-(3-cyano-4,5,5-trimethylfuran-2(5H)-ylidene) malononitrile-derivatives. The probe could effectively monitor Cys through the typical acrylate cleavage. The detecting system showed a red emission at 633 nm and the fluorescence was stable within the pH range of 6-9. The detection could be completed in 30 min. TCFQ-Cys presented high sensitivity with a detection limit of 0.133 μM and high selectivity towards Cys from other biological mercaptans. The most important feature was that the system had a wide linear range of 0-300 μM, which covered the physiological requirements of Cys detection. Subsequently, we conducted the biological imaging of Cys in MCF-7 cells and Caenorhabditis elegans (C. elegans). Therefore, TCFQ-Cys had a practical application prospect for further investigating the physiological function of Cys.

Fluorescent probes for bioimaging of potential biomarkers in Parkinson's disease

This review comprehensively summarizes various types of fluorescent probes for PD and their applications for detection of various PD biomarkers.