Real-Time Monitoring Mitochondrial Viscosity during Mitophagy Using a Mitochondria-Immobilized Near-Infrared Aggregation-Induced Emission Probe

A golgi targeting viscosity rotor for cancer diagnosis in living cells and tissues

Unveiling the intricate relationship between cancer and Golgi viscosity remains an arduous endeavor, primarily due to the lack of Golgi-specific fluorescent probes tailored for viscosity measurement. Considering this formidable obstacle, we have triumphed over the challenge by devising a bespoke Golgi-specific viscosity probe, aptly named GOL-V. This ingenious innovation comprises the viscosity rotor BODIPY intricately tethered to the Golgi-targeting moiety benzsulfamide. GOL-V exhibits remarkable sensitivity to fluctuations in viscosity, the fluorescence intensity of GOL-V increased 114-fold when the viscosity value was increased from 2.63 to 937.28 cP. Owing to its remarkable capacity to suppress the TICT state under conditions of heightened viscosity. Moreover, its efficacy in sensitively monitoring Golgi viscosity alterations within living cells is also very significant. Astonishingly, our endeavors have culminated in not only the visualization of Golgi viscosity at the cellular and tissue levels but also in the clinical tissue samples procured from cancer patients. Harnessing the prowess of GOL-V, we have successfully demonstrated that Golgi viscosity could serve as a discerning marker for detecting the presence of cancer. The convergence of these exceptional attributes firmly establishes GOL-V as an immensely potent instrument, holding immense potential in the realm of cancer diagnosis.

Novel 99mTc-Labeled Mannose Derivative as a Highly Promising Single Photon Emission Computed Tomography Probe for Tumor Imaging

18F-2-fluoro-2-deoxy-d-glucose ([18F]FDG) has been the most used positron emission tomography imaging agent for clinical applications. Single photon emission computed tomography (SPECT) imaging is cheaper and used more widely for diagnostic use, but there is no SPECT tumor imaging agent for clinical applications comparable to [18F]FDG. Mannose is a C2 epimer of glucose and can also be transported into tumor cells via glucose transporters (GLUTs). To develop a novel SPECT tumor imaging agent with satisfactory tumor uptake and tumor/nontarget ratios, here a mannose derivative (CN7DM) was synthesized and radiolabeled with technetium-99m to prepare [99mTc]Tc-CN7DM. The six-coordinated structure of [99mTc]Tc-CN7DM was confirmed by the corresponding rhenium compound (Re-CN7DM). [99mTc]Tc-CN7DM was transported into cancer cells via GLUTs and may be trapped in the cancer cells by electrostatic attraction. The probe exhibited high uptake in tumors and low uptake in nontarget tissues in mice bearing different tumors, indicating that [99mTc]Tc-CN7DM exhibited promising potential for SPECT tumor imaging and warranted further clinical investigation.

Near-Infrared Fluorescent Probe Reveals Elevated Mitochondrial Viscosity during Acute Alcoholic Liver Injury

Acute alcoholic liver injury (AALI) has become an important cause of liver disease worldwide, and there is an urgent need to develop noninvasive and sensitive methods to detect and evaluate AALI. We report herein three novel but readily available mitochondrial targeting fluorescence probes (ICR, ICJ, and ICQ) for AALI detection. These probes contain different electron-donating groups, among which ICQ exhibits NIR fluorescence (740 nm), a large Stokes shift (110 nm), and a sensitive response to viscosity (73-fold enhancement in fluorescence from water to glycerol), making it suitable for in vivo imaging. ICQ also exhibits an excellent ability to image mitochondrial viscosity changes in cells. More importantly, ICQ can target the liver selectively and image the viscosity changes in the liver noninvasively. Through establishing an AALI mouse model, ICQ was successfully applied to the in situ imaging changes in liver viscosity during the AALI process. The results showed a significant increase in liver viscosity in AALI mice, indicating that viscosity can serve as a marker for AALI, and ICQ is a promising noninvasive and sensitive tool for detecting and evaluating AALI.

Dynamic insights into mitochondrial function: Monitoring viscosity and SO2 levels in living cells

Mitochondria, central organelles pivotal for eukaryotic cell function, extend their influence beyond ATP production, encompassing roles in apoptosis, calcium signaling, and biosynthesis. Recent studies spotlight two emerging determinants of mitochondrial functionality: intramitochondrial viscosity and sulfur dioxide (SO2) levels. While optimal mitochondrial viscosity governs molecular diffusion and vital processes like oxidative phosphorylation, aberrations are linked with neurodegenerative conditions, diabetes, and cancer. Similarly, SO2, a gaseous signaling molecule, modulates energy pathways and oxidative stress responses; however, imbalances lead to cytotoxic sulfite and bisulfite accumulation, triggering disorders such as cancer and cardiovascular anomalies. Our research focused on development of a dual-channel fluorescent probe, applying electron-withdrawing acceptors within a coumarin dye matrix, facilitating monitoring of mitochondrial viscosity and SO2 in live cells. This probe distinguishes fluorescence peaks at 650 nm and 558 nm, allowing ratiometric quantification of SO2 without interference from other sulfur species. Moreover, it enables near-infrared viscosity determination, particularly within mitochondria. The investigation employed theoretical calculations utilizing Density Functional Theory (DFT) methods to ascertain molecular geometries and calculate rotational energies. Notably, the indolium segment of the probe exhibited the lowest rotational energy, quantified at 7.38 kcals/mol. The probe featured heightened mitochondrial viscosity dynamics when contained within HeLa cells subjected to agents like nystatin, monensin, and bacterial lipopolysaccharide (LPS). Overall, our innovative methodology elucidates intricate mitochondrial factors, presenting transformative insights into cellular energetics, redox homeostasis, and therapeutic avenues for mitochondrial-related disorders.

Unveiling Cellular Microenvironments with a Near-Infrared Fluorescent Sensor: A Dual-Edge Tool for Cancer Detection and Drug Screening

Mitochondria and lysosomes are pivotal intracellular organelles, and the injury or dysfunction of these organelles can trigger a range of pathological processes. Early diagnosis and treatment of cancer are of paramount importance due to cancer's status as a leading health threat. This study introduces a novel fluorescent probe, BDHV, for detecting mitochondrial and lysosomal viscosity and pH abnormalities in tumors, facilitating early cancer detection and screening of anticancer drugs. Under acidic conditions, the red fluorescence of the probe gradually increases with increasing viscosity. Conversely, in alkaline environments, an increase in viscosity leads to a decrease in green fluorescence and an increase in red fluorescence. The inclusion of a benzothiazole group endows BDHV with strong dual-targeting capability for mitochondria and lysosomes and without being affected by the mitochondrial membrane potential. Most notably, BDHV has potential applications for early cancer diagnosis and in effectively assessing the efficacy of various anticancer drugs.

A mitochondria-specific NIR fluorescence probe for dual-detection of sulfur dioxide and viscosity in living cells and mice

The level of sulfur dioxide (SO2) and viscosity in mitochondria play vital roles in various physiological and pathological processes. Abnormalities in mitochondrial SO2 and viscosity are closely associated with numerous biological diseases. It is of great significance to develop novel fluorescence probes for simultaneous detection of SO2 and viscosity within mitochondria. Herein, we have developed a water-soluble, mitochondrial-targeted and near-infrared fluorescent probe, CMBT, for the simultaneous detection of SO2 and viscosity. The probe CMBT incorporates benzothiazolium salt as a mitochondrial targeting moiety and 7-diethylaminocoumarin as a rotor for viscosity detection, respectively. Based on the prompt reaction between nucleophilic HSO3-/SO32- and the backbone of the benzothiazolium salt derivative, probe CMBT displayed high sensitivity and selectivity toward SO2 with a limit of detection as low as 0.17 μM. As viscosity increased, the twisted intramolecular charge transfer (TICT) process was restricted, resulting in fluorescence emission enhancement at 690 nm. Moreover, probe CMBT demonstrated exceptional mitochondrial targeting ability and was successfully employed to image variations of SO2 and viscosity in living cells and mice. The work highlights the great potential of the probe as a convenient tool for revealing the relationship between SO2 and viscosity in biological systems.

Signal-sustained imaging of mitophagy with an Enzyme-Activatable Metabolic Lipid-Labeling Probe

Imaging of mitophagy is of significance as aberrant mitophagy is engaged in multiple diseases. Mitophagy has been imaged with synthetic or biotic pH sensors by reporting pH acidification en route delivery into lysosomes. To circumvent uncertainty of acidity-dependent signals, we herein report an enzyme-activatable probe covalently attached on mitochondrial inner membrane (ECAM) for signal-persist mitophagy imaging. ECAM is operated via ΔΨm-driven accumulation of Mito-proGreen in mitochondria and covalent linking of the trapped probe with azidophospholipids metabolically incorporated into the mitochondrial inner membrane. Upon mitophagy, ECAM is delivered into lysosomes and hydrolyzed by LNPEP/leucyl aminopeptidase, yielding turn-on green fluorescence that is immune to lysosomal acidity changes and stably retained in fixed cells. With ECAM, phorbol-12-myristate-13-acetate (PMA) was identified as a highly potent inducer of mitophagy. Overcoming signal susceptibility of pH probes and liability of ΔΨm probes to dissipation from stressed mitochondria, ECAM offers an attractive tool to study mitophagy and mitophagy-inducing therapeutic agents.

A thiol-anchored solvatochromic and fluorogenic molecular rotor for covalent protein labeling in SDS-PAGE and mitochondria specific fluorescence imaging

Fluorescent labeling is a widely used method for protein detection and fluorescence imaging. A solvatochromic and fluorogenic molecular rotor DASPBCl was developed for covalent protein labeling in solution and SDS-PAGE, and also for stable mitochondria labeling and fluorescence imaging. The dye DASPBCl consisted of a 4-(N,N-dimethylamino)phenyl moiety as the electron donor and a positively charged N-benzylpyridinium moiety as the electron acceptor. A benzyl chloride group was introduced into the pyridine moiety for covalent labeling of thiol in proteins. When the fluorescent dye DASPBCl is covalently labeled to the thiol of proteins, significantly enhanced fluorescence was obtained, which is attributed to the polarity sensitivity caused solvatochromic effect from the hydrophobic protein structure and the viscosity sensitivity caused fluorogenic effect from the restriction of single bond rotation. DASPBCl exhibits high sensitivity and good linear response for protein detection in SDS-PAGE analysis with both the pre-staining method and post-staining method. DASPBCl was also successfully used for covalently protein-anchored fluorescence imaging of mitochondria in living cells.

Rational design of mitochondria-targeted fluorescent biosensors for in vivo elucidation of the interaction between breast cancer metastasis and mitochondrial autophagy

Breast cancer lung metastases (BCLM) are a major cause of high mortality in patients. The shortage of therapeutic targets and rapid drug screening tools for BCLM is a major challenge at present. Mitochondrial autophagy, which involves the degradation of proteins associated with cancer cell aggressiveness, represents a possible therapeutic approach for the treatment of BCLM. Herein, four fluorescent biosensors with different alkyl chains were designed and synthesized to monitor mitochondrial autophagy. Among them, PMV-12 demonstrated the highest sensitivity to viscosity variance, the least impact on polarity, and the longest imaging time. The introduction of the C12-chain made PMV-12 anchored in the mitochondrial membrane without being disturbed by changes of the mitochondrial membrane potential (MMP), thereby achieving the long-term monitor in situ for mitochondrial autophagy. Mitochondria stained with PMV-12 induced swelling and viscosity increase after treating with apigenin, which indicated that apigenin is a potential mitochondrial autophagy inducer. Apigenin was subsequently verified to inhibit cancer cell invasion by 92%. Furthermore, PMV-12 could monitor the process of BCLM in vivo and evaluate the therapeutic effects of apigenin. This work provides a fluorescent tool for elucidating the role of mitochondrial autophagy in the BCLM process and for anti-metastatic drug development.

A Red-Emission Fluorescent Probe with Large Stokes Shift for Detection of Viscosity in Living Cells and Tumor-Bearing Mice

Abnormal viscosity is closely related to the occurrence of many diseases, such as cancer. Therefore, real-time detection of changes in viscosity in living cells is of great importance. Fluorescent molecular rotors play a critical role in detecting changes in cellular viscosity. Developing red emission viscosity probes with large Stokes shifts and high sensitivity and specificity remains an urgent and important topic. Herein, a novel viscosity-sensitive fluorescent probe (TCF-VIS1) with a large stokes shift and red emission was prepared based on the 2-dicyanomethylene-3-cyano-4,5,5-trimethyl-2,5-dihydrofuran (TCF) skeleton. Due to intramolecular rotation, the probe itself does not fluorescence at low viscosity. With the increase in viscosity, the rotation of TCF-VIS1 is limited, and its fluorescence is obviously enhanced. The probe has the advantages of simple preparation, large Stokes shift, good sensitivity and selectivity, and low cytotoxicity, which make it successfully used for viscosity detection in living cells. Moreover, TCF-VIS1 showed its potential for cancer diagnosis at the cell level and in tumor-bearing mice by detecting viscosity. Therefore, the probe is expected to enrich strategies for the detection of viscosity in biological systems and offer a potential tool for cancer diagnosis.

Novel mitochondrial and DNA damaging fluorescent Calix[4]arenes bearing isatin groups as aromatase inhibitors: Design, synthesis and anticancer activity

Breast cancer causes a high rate of mortality all over the world. Therefore, the present study focuses on the anticancer activity of new lower rim-functionalized calix[4]arenes integrated with isatin and the p-position of calixarenes with 1,4-dimethylpyridinium iodine against various human cancer cells such as MCF-7 and MDA-MB-231 breast cancer cell lines, as well as the PNT1A healthy epithelial cell line. It was observed that compound 6c had the lowest values in MCF-7 (8.83 µM) and MDA-MB-231 (3.32 µM). Cell imaging and apoptotic activity studies were performed using confocal microscopy and flow cytometry, respectively. The confocal imaging studies with 6c showed that the compound easily entered the cell, and it was observed that 6c accumulated in the mitochondria. The Comet assay test was used to detect DNA damage of compounds in cells. It was found that treated cells had abnormal tail nuclei and damaged DNA structures compared with untreated cells. In vitro human aromatase enzyme inhibition profiles showed that compound 6c had a remarkable inhibitory effect on aromatase. Compound 6c displayed a significant inhibition capacity on aromatase enzyme with the IC50 value of 0.104 ± 0.004 µM. Thus, not only the anticancer activity of the new fluorescent derivatives, which are the subject of this study, but the aromatase inhibitory profiles have also been proven.

A near-infrared fluorescent probe for viscosity: Differentiating cancer cells from normal cells and dual-modal imaging in tumor mice

As a basic parameter of the intracellular microenvironment, viscosity is closely related to the development of cancer. Thus, it is necessary to utilize a sensitive tool to visualize the viscosity in tumor cells and mice, which is helpful for the diagnosis of cancer. Herein, a novel dual-modal probe (IX-V) that has a near-infrared fluorescence (NIRF) and photoacoustic (PA) response to viscosity is synthesized. In low viscosity media, the probe has no fluorescence. With the increase of viscosity, the fluorescence is produced in the near-infrared region due to the inhibition of the TICT process. At the same time, the probe shows different photoacoustic (PA) signals in different viscosity media. Most notably, the viscosity in tumor cells has been imaged successfully by the application of IX-V, and the probe can effectively distinguish cancer cells from normal cells co-cultured in one dish by the difference of fluorescence intensity. In addition, the probe has been used for dual-modal imaging (NIRF and PA) of viscosity in tumor mice, which provides a tool for exploring the relationship between viscosity and diseases. That is to say, IX-V can achieve complementary imaging effects and has great application prospects in the tumor diagnosis.

Unveiling the hypoxia-induced mitophagy process through two-channel real-time imaging of NTR and viscosity under the same excitation

Mitophagy is an essential physiological process that eliminates damaged mitochondria via lysosomes. It is reported that hypoxia, inflammatory stimuli or other stress conditions could lead to mitochondrial damage and mitochondrial dysfunction, which induces the process of mitophagy. Herein, we report a novel fluorescent probe PC-NTR for imaging hypoxia-induced mitophagy by monitoring the change of nitroreductase and viscosity simultaneously. To our delight, PC-NTR could respond simultaneously to nitroreductase and viscosity at different fluorescence channels with no mutual interference under the same excitation wavelength. The fluorescence emission around 535 nm was enhanced dramatically after addition of nitroreductase while the fluorescence emission around 635 nm heightened as the viscosity increased. The probe would be able to selectively targeting of mitochondria in cells because of the positively charged pyridine salt structure of PC-NTR. The probe was successfully applied to assess the different levels of hypoxia and real-time imaging of mitochondrial autophagy in live cells. More importantly, using dual channel imaging, PC-NTR could be used to distinguish cancer cells from normal cells and was successfully applied to imaging experiments in HeLa-derived tumor-bearing nude mice. Therefore, PC-NTR would be an important molecular tool for hypoxia imaging and detecting solid tumors in vivo.

Hemicyanine-based sensor for mitochondrial viscosity imaging in BV2 cells

Mitochondrial viscosity is a critical factor affecting numerous physiological processes, including phagocytosis. Abnormal viscosity in mitochondria is related to some pathological activities and diseases. Evaluating and detecting the changes in mitochondrial viscosity in vivo is crucial. Thus, a mitochondria-targeted red-emitting fluorescent probe (VP) was prepared, and can be used to detect viscosity with high selectivity and sensitivity. The synthesis of probe VP was as simple as two steps and the cost was low. In addition, the fluorescence intensity (log I615) exhibited an excellent relationship with viscosity (log η) in the range of 0.5 - 2.5 (R2 = 0.9985) in water/glycerol mixture. It is noteworthy that the probe VP displayed the highest signal-to-noise ratio (about 50-fold) for viscosity in water and glycerol system. The probe VP can visualize the mitochondrial viscosity change in living cells. More importantly, phagocytic test for BV2 cells further demonstrated that phagocytosis decreased with increased viscosity. Furthermore, VP was successfully used for monitoring the mitophagy process induced by starvation, and mitochondrial viscosity exhibited enhancement during mitophagy. The probe was a potential tool for studying viscosity and phagocytosis.

NIR Light-Activated Mitochondrial RNA Cross-Linking Strategy for H2S Monitoring and Prolonged Colorectal Tumor Imaging

Molecular diffusion and leakage impede the long-term retention of probes/drugs and may cause potential adverse effects in theranostic fields. Spatiotemporally manipulating the organelle-immobilization behavior of probes/drugs for prolonged tumor retention is indispensable to achieving effective cancer diagnosis and therapy. Herein, we propose a rational strategy that could realize near-infrared light-activated ribonucleic acids (RNAs) cross-linking for prolonged tumor retention and simultaneously endogenous hydrogen sulfide (H2S) monitoring in colorectal tumors. Profiting from efficient singlet oxygen (1O2) generation from Cy796 under 808 nm light irradiation, the 1O2-animated furan moiety in Cy796 could covalently cross-link with cytoplasmic RNAs via a cycloaddition reaction and realize organelle immobilization. Subsequently, specific thiolysis of Cy796 assisted with H2S resulted in homologous product Cy644 with reduced 1O2 generation yields and enhanced absolute fluorescence quantum yields (from 7.42 to 27.70%) with blue-shifted absorption and emission, which avoided the molecular oxidation fluorescence quenching effect mediated by 1O2 and validated fluorescence imaging. Furthermore, studies have demonstrated that our proposed strategy possessed adequate capacity for fluorescence imaging and endogenous H2S detection in HCT116 cells, particularly accumulated at the tumor sites, and retained long-term imaging with excellent biocompatibility. The turn-on fluorescence mode and turn-off 1O2 generation efficiency in our strategy successfully realized a diminished fluorescence cross-talk and oxidation quenching effect. It is adequately envisioned that our proposed strategy for monitoring biomarkers and prolonged tumor retention will contribute tremendous dedication in the clinical, diagnostic, and therapeutic fields.

An Aggregation-induced Emission Probe to Detect the Viscosity Change in Lipid Droplets during Ferroptosis

Ferroptosis is a recently identified form of cell death characterized by iron-dependent lipid peroxidation. Understanding the effects of lipid peroxidation on cellular processes during ferroptosis requires insights into lipid droplets (LDs) and their viscosity changes. To gain further insights into the intricacies of ferroptosis, it is crucial to have a fluorescent probe that targets LDs and responds to changes in viscosity. In this study, we introduce a novel LD-targeting viscosity fluorescent probe named TQE, based on the principles of aggregation-induced emission (AIE). The probe displayed AIE characteristics in tetrahydrofuran, possessing a partition coefficient (logP) of 5.87. With increased viscosity, intramolecular rotation was restricted, leading to a remarkable 3.3-fold enhancement in emission. Notably, TQE exhibited robust resistance to photo-bleaching during cellular imaging, maintaining approximately 75% of its emission intensity even after 30 min of laser irradiation. Importantly, the AIEgen could not generate hydroxyl radicals when exposed to light for up to 3 h, suggesting the low photo-toxicity of TQE to cells. Leveraging these properties, we successfully employed the probe for fluorescent imaging of the viscosity change in LDs during ferroptosis.

Visualization of Lysosomal Dynamics during Autophagy by Fluorescent Probe

Lysosomes are one of the important organelles within cells, and their dynamic movement processes are associated with many biological events. Therefore, real-time monitoring of lysosomal dynamics processes has far-reaching implications. A lysosome-targeted fluorescent probe N(CH2)3-BD-PZ is proposed for real-time monitoring of lysosomal kinetic motility. Using this probe, the dynamic process of lysosomes under starvation induction was successfully explored through fluorescence imaging. Importantly, we observed a new pattern of lysosomal dynamic movement, in which an irregular lysosome was slowly cleaved into two different-sized touching lysosomes and then fused to form a new round lysosome. This research provides a powerful fluorescence tool to understand the dynamic motility of intracellular lysosomes under fluorescence imaging.

Evaluation of intracellular lipid droplets viscosity by a probe with high fluorescence quantum yield

BACKGROUND

Lipid droplets (LDs) are an important organelle as the main energy storage site in cells. LDs viscosity controls the material and energy exchange between it and other organelles. Furthermore, the LDs metabolic abnormalities, cell dysfunction, some diseases may be attributed to the singular LDs viscosity. Currently, the fluorescent probes for sensing the variations of LDs viscosity are still scarce and expose some drawbacks of low fluorescence quantum yield, low sensitivity and LDs polarity interference. Thus, the development of high performance probes is significant to detect LDs viscosity.

RESULTS

We hereby provide a lipophilic fluorescent probe (TPE-BET) with high fluorescence quantum yield (Φf, 0.91 in glycerol) for imaging LDs viscosity in living cells. With the increase of viscosity from 0.54 cp to 934 cp, the fluorescence at λex/λem = 405/520 nm and the fluorescence quantum yield of TPE-BET linearly increased by 64.9 and 128.5 folds, respectively. Meanwhile, the outstanding LDs staining capability of TPE-BET may provide a high spatial resolution for LDs imaging. The cell imaging of TPE-BET not only successfully observed the viscosity variations of LDs in cell stress models, e.g., ferroptosis, inflammation and mitophagy, but also revealed the increased viscosity and extracellular delivery of LDs in heavy metal cell injury models (Hg/As) for the first time, which may supply concrete evidence for understanding the structure and function of LDs.

SIGNIFICANCE

This represents a new fluorescent probe TPE-BET with high fluorescence quantum yield for imaging LDs viscosity, which may decrease the dose of probe and excitation light intensity along with the improvement on signal noise ratio (S/N). The imaging results of TPE-BET clarified that LDs viscosity may be an appraisal index on cell differentiation, state evaluation and drug screening.

Rational Design of Orange-Red Emissive Carbon Dots for Tracing Lysosomal Viscosity Dynamics in Living Cells and Zebrafish

Lysosomal viscosity is an essential microenvironment parameter in lysosomes, which is closely associated to the occurrence and development of various diseases, including cancer. Thus, accurately quantifying lysosomal viscosity changes is highly desirable for a better understanding of the dynamics and biological functions of lysosomes. In this study, lysosome self-targetable orange-red emissive carbon dots (OR-CDs) were rationally designed and developed for monitoring lysosomal viscosity fluctuations. The enhanced fluorescence of OR-CDs could be obviously observed as the viscosity increased from 1.07 to 950 cP. Moreover, the as-prepared OR-CDs could quickly enter cells for lysosome-targeting imaging and visualize viscosity variations in living cells and zebrafish. More importantly, by utilizing OR-CDs, we successfully achieved tracing the variations in lysosomal viscosity during the autophagy process. Additionally, as cancer cells possess high viscosity than normal cells, the OR-CDs have been effectively utilized for cancer imaging from cell, tissue, and organ to in vivo levels. It is expected that the developed OR-CDs not only provide a meaningful tool for visualizing investigations of lysosome viscosity-related diseases but also shed light on the development based on the nanomaterial for the clinical diagnosis of cancer.

Ratiometric and discriminative visualization of autophagic processes with a novel dual-responded lysosome-specific fluorescent probe

BACKGROUND

Autophagy is a critical self-eating pathway involved in numerous physiological and pathological processes. Lysosomal degradation of dysfunctional organelles and invading microorganisms is central to the autophagy mechanism and essential for combating disease-related conditions. Therefore, monitoring fluctuations in the lysosomal microenvironment is vital for tracking the dynamic process of autophagy. Although much effort has been put into designing probes for measuring lysosomal viscosity or pH separately, there is a need to validate the concurrent imaging of the two elements to enhance the understanding of the dynamic progression of autophagy.

METHODS

Probe HFI was synthesized in three steps and was developed to visualize changes in viscosity and pH within lysosomes for real-time autophagy tracking. Then, the spectrometric determination was carried out. Next, the probe was applied to image autophagy in cells under nutrient-deprivation or external stress. Additionally, the performance of HFI to monitor autophagy was employed to evaluate acetaminophen-induced liver injury.

RESULTS

We constructed a ratiometric dual-responsive probe, HFI, with a large Stokes shift over 200 nm, dual-wavelength emission, and small background interference. The ratiometric fluorescent signal (R = I ₆₁₀/I ₄₆₀) of HFI had an excellent correlation with both viscosity and pH. More importantly, high viscosity and low pH had a synergistic promotion effect on the emission intensity of HFI, which enabled it to specially lit lysosomes without disturbing the inherent microenvironment. We then successfully used HFI to monitor intracellular autophagy induced by starvation or drugs in real-time. Interestingly, HFI also enabled us to visualize the occurrence of autophagy in the liver tissue of a DILI model, as well as the reversible effect of hepatoprotective drugs on this event.

CONCLUSIONS

In this study, we developed the first ratiometric dual-responsive fluorescent probe, HFI, for real-time revealing autophagic details. It could image lysosomes with minimal perturbation to their inherent pH, allowing us to track changes in lysosomal viscosity and pH in living cells. Ultimately, HFI has great potential to serve as a useful indicator for autophagic changes in viscosity and pH in complex biological samples and can also be used to assess drug safety.

Mitochondria-Targeting Multifunctional Fluorescent Probe toward Polarity, Viscosity, and ONOO- and Cell Imaging

Abnormal changes occurring in the mitochondrial microenvironment are important markers indicating mitochondrial and cell dysfunction. Herein, we designed and synthesized a multifunctional fluorescent probe DPB that responds to polarity, viscosity, and peroxynitrite (ONOO^-). DPB is composed of an electron donor (diethylamine group) and electron acceptor (coumarin, pyridine cations, and phenylboronic acid esters), in which the pyridine group with a positive charge is responsible for targeting to mitochondria. D-π-A structure with strong intramolecular charge transfer (ICT) and twisted intramolecular charge transfer (TICT) properties give rise to respond to polarity and viscosity. The introduction of cyanogroup and phenylboronic acid esters increases the electrophilicity of the probe, which is prone to oxidation triggered by ONOO^-. The integrated architecture satisfies the multiple response requirements. As the polarity increases, the fluorescence intensity of probe DPB at 470 nm is quenched by 97%. At 658 nm, the fluorescence intensity of DPB increases with viscosity and decreases with the concentration of ONOO^-. Furthermore, the probe is not only successfully used to monitor mitochondrial polarity, viscosity, and endogenous/exogenous ONOO^- level fluctuations but also to distinguish cancer cells from normal cells by multiple parameters. Therefore, as-prepared probe provides a reliable tool for better understanding of the mitochondrial microenvironment and also a potential approach for the diagnosis of disease.

Development of meso-Five-Membered Heterocycle BODIPY-Based AIE Fluorescent Probes for Dual-Organelle Viscosity Imaging

Fluorescent rotors with aggregation-induced emission (AIE) and organelle-targeting properties have attracted great attention for sensing subcellular viscosity changes, which could help understand the relationships of abnormal fluctuations with many associated diseases. Despite the numerous efforts spent, it remains rare and urgent to explore the dual-organelle targeting probes and their structural relationships with viscosity-responsive and AIE properties. Therefore, in this work, we reported four meso-five-membered heterocycle-substituted BODIPY-based fluorescent probes, explored their viscosity-responsive and AIE properties, and further investigated their subcellular localization and viscosity-sensing applications in living cells. Interestingly, the meso-thiazole probe 1 showed both good viscosity-responsive and AIE (in pure water) properties and could successfully target both mitochondria and lysosomes, further imaging cellular viscosity changes by treating lipopolysaccharide and nystatin, attributing to the free rotation and potential dual-organelle targeting ability of the meso-thiazole group. The meso-benzothiophene probe 3 with a saturated sulfur only showed good viscosity-responsive properties in living cells with the aggregation-caused quenching effect and no subcellular localization. The meso-imidazole probe 2 showed the AIE phenomenon without an obvious viscosity-responsive property with a C═N bond, while the meso-benzopyrrole probe 4 displayed fluorescence quenching in polar solvents. Therefore, for the first time, we investigated the structure-property relationships of four meso-five-membered heterocycle-substituted BODIPY-based fluorescent rotors with viscosity-responsive and AIE properties, and among these, 1 with a C═N bond and a saturated sulfur on the meso-thiazole, potentially contributing to their corresponding AIE and viscosity-responsive properties, served as a sensitive AIE fluorescent rotor for imaging dual-organelle viscosity in both mitochondria and lysosomes.

Multifunctional Mitochondria-Targeting Near-Infrared Fluorescent Probe for Viscosity, ONOO-, Mitophagy, and Bioimaging

Irregularities in mitochondrial viscosity and peroxynitrite (ONOO-) concentration can lead to mitochondrial dysfunction. It is still a great challenge to develop near-infrared (NIR) fluorescent probes to simultaneously detect viscosity, endogenous ONOO-, and mitophagy. Herein, a multifunctional mitochondria-targeting NIR fluorescent probe P-1 was first synthesized for simultaneously detecting viscosity, ONOO-, and mitophagy. P-1 used quinoline cations as a mitochondrial targeting moiety, arylboronate as an ONOO- responsive group, and detected the change of viscosity by the twisted internal charge transfer (TICT) mechanism. The probe has an excellent response to the viscosity during inflammation by lipopolysaccharides (LPSs) and mitophagy induced by starvation at 670 nm. The viscosity changes of the probe induced by nystatin in zebrafish showed that P-1 was able to detect microviscosity in vivo. P-1 also showed good sensitivity with a detection limit of 6.2 nM for ONOO- detection and was successfully applied to the endogenous ONOO- detection in zebrafish. Moreover, P-1 has the ability to distinguish between cancer cells and normal cells. All of these features make P-1 a promising candidate to detect mitophagy and ONOO- -associated physiological and pathological processes.

Bioimaging and detecting endogenous and exogenous cyanide in foods, living cells and mice based on a turn-on mitochondria-targeted fluorescent probe

A novel fluorescent probe, with advanced features including "turn-on" fluorescence response, high sensitivity, good compatibility, and mitochondria-targeting function, has been synthesized based on structural design for detecting and visualizing cyanide in foods and biological systems. An electron-donating triphenylamine group (TPA) was employed as the fluorescent and an electron-accepting 4-methyl-N-methyl-pyridinium iodide (Py) moiety was used as a mitochondria-targeted localization unit, which formed intramolecular charge transfer (ICT) system. The "turn-on" fluorescence response of the probe (TPA-BTD-Py, TBP) toward cyanide is attributed two reasons, one is the insertion of an electron-deficient benzothiadiazole (BTD) group into the conjugated system between TPA and Py, and the other is the inhibition of ICT induced by the nucleophilic addition of CN^-. Two active sites for reacting with CN^- were involved in TBP molecule and high response sensitivity were observed in tetrahydrofuran solvent containing 3 % H₂O. The response time could be reduced to 150 s, the linear range was 0.25-50 μM, and the limit of detection was 0.046 μM for CN^- analysis. The TBP probe was successfully applied to the detection of cyanide in food samples prepared in aqueous solution, including the sprouting potato, bitter almond, cassava, and apple seeds. Furthermore, TBP exhibited low cytotoxicity, clear mitochondria-localizing capability in HeLa cells and excellent fluorescence imaging of exogenous and endogenous CN^- in living PC12 cells. Moreover, exogenous CN^- with intraperitoneal injection in nude mice could be well monitored visually by the "turn-on" fluorescence. Therefore, the strategy based on structural design provided good prospects for optimizing fluorescent probes.

Rational design of water-soluble mitochondrial-targeting near-infrared fluorescent probes with large Stokes shift for distinguishing cancerous cells and bioimaging

In the paper, two new near-infrared fluorescent probes (TTHPs) with D-π-A structure were successfully synthesized. TTHPs exhibited polarity and viscosity sensitivity and mitochondrial targeting under physiological conditions. The emission spectra of TTHPs showed strong polarity/viscosity dependence with more than a large Stokes shift of 200 nm. Based on their unique merits, TTHPs were used to distinguish cancerous and normal cells, which could be new tools for cancer diagnosis. Moreover, TTHPs were the first to achieve biological imaging of Caenorhabditis elegans, which could be labeling probes to apply in multicellular organisms.

Rational Design of MMP-Independent Near-Infrared Fluorescent Probes for Accurately Monitoring Mitochondrial Viscosity

Mitochondrial viscosity affects metabolite diffusion and mitochondrial metabolism and is associated with many diseases. However, the accuracy of mitochondria-targeting fluorescent probes in measuring viscosity is unsatisfactory because these probes can diffuse from mitochondria during mitophagy with a decreased mitochondrial membrane potential (MMP). To avoid this problem, by incorporating different alkyl side chains into dihydroxanthene fluorophores (denoted as DHX), we developed six near-infrared (NIR) probes for the accurate detection of mitochondrial viscosity, and the sensitivity to viscosity and the mitochondrial targeting and anchoring capability of these probes increased by increasing the alkyl chain length. Among them, DHX-V-C₁₂ had a highly selective response to viscosity variations with minimum interference from polarity, pH, and other biologically relevant species. Furthermore, DHX-V-C₁₂ was used to monitor the mitochondrial viscosity changes of HeLa cells treated by ionophores (nystatin, monensin) or under starvation conditions. We hope that this mitochondrial targeting and anchoring strategy based on increasing the alkyl chain length will be a general strategy for the accurate detection of mitochondrial analytes, enabling the accurate study of mitochondrial functions.

Fluorescence microscopic platforms imaging mitochondrial abnormalities in neurodegenerative diseases

Neurodegenerative diseases (NDs) are progressive disorders that cause the degeneration of neurons. Mitochondrial dysfunction is a common symptom in NDs and plays a crucial role in neuronal loss. Mitochondrial abnormalities can be observed in the early stages of NDs and evolve throughout disease progression. Visualizing mitochondrial abnormalities can help understand ND progression and develop new therapeutic strategies. Fluorescence microscopy is a powerful tool for dynamically imaging mitochondria due to its high sensitivity and spatiotemporal resolution. This review discusses the relationship between mitochondrial dysfunction and ND progression, potential biomarkers for imaging dysfunctional mitochondria, advances in fluorescence microscopy for detecting organelles, the performance of fluorescence probes in visualizing ND-associated mitochondria, and the challenges and opportunities for developing new generations of fluorescence imaging platforms for monitoring mitochondria in NDs.

Multifunctional Fluorescent Probe for Simultaneous Detection of ONOO-, Viscosity, and Polarity and Its Application in Ferroptosis and Cancer Models

Intracellular peroxynitrite anions (ONOO^-) and microenvironments (such as viscosity and polarity) play an important role in maintaining redox homeostasis, regulating diffusion, transportation, and signal transduction in living cells. The abnormality of these factors is often closely related to various physiological/pathological processes. However, owing to the lack of suitable probes, the simultaneous visualization of ONOO^-, viscosity, and polarity in ferroptosis and cancer models has not been achieved. To meet urgent needs, we presented a multifunctional near-infrared (NIR) fluorescent probe, named MQA-P, for simultaneously detecting ONOO^-, viscosity, and polarity within mitochondria. The probe exhibited a remarkable turn-on response to ONOO^- with the far-red emission of about 645 nm and was highly sensitive to viscosity/polarity in the NIR channel with λ_em > 704 nm. Facilitated by MQA-P, for the first time, we revealed that erastin-induced ferroptosis was accompanied by a significant upregulation of ONOO^- and an increase of viscosity (or decrease of polarity) at the same time. Moreover, the concurrent use of ONOO^-, viscosity, and polarity for the diagnosis of cancer has been successfully achieved not only at cell/tissue levels but also in tumor mice models. Compared with detecting only one factor, this simultaneous detection of multimarkers provides a more sensitive and reliable method/tool for tracking ferroptosis-related pathological processes and cancer diagnosis, holding great potential in preclinical research, medical diagnosis, and imaging-guided surgery.

Mitochondrial Membrane Potential Independent Near-Infrared Mitochondrial Viscosity Probes for Real-Time Tracking Mitophagy

Mitophagy is a vital cellular process playing vital roles in regulating cellular metabolism and mitochondrial quality control. Mitochondrial viscosity is a key microenvironmental index, closely associated with mitochondrial status. To monitor mitophagy and mitochondrial viscosity, three molecular rotors (Mito-1, Mito-2, and Mito-3) were developed. All probes contain a cationic quinolinium unit and a C₁₂ chain so that they can tightly bind mitochondria and are not affected by the mitochondrial membrane potential. Optical studies showed that all probes are sensitive to viscosity changes with an off-on fluorescence response, and Mito-3 shows the best fluorescence enhancement. Bioimaging studies showed that all these probes can not only tightly locate and visualize mitochondria with near-infrared fluorescence but also effectively monitor the mitochondrial viscosity changes in cells. Moreover, Mito-3 was successfully applied to visualize the mitophagy process induced by starvation, and mitochondrial viscosity was found to show an increase during mitophagy. We expect Mito-3 to become a useful imaging tool for studying mitochondrial viscosity and mitophagy.

Dihydroxanthene-Based Near-infrared Fluorescent Probes for Monitoring Mitochondrial Viscosity in Living Cells and Mice

Aberrant mitochondrial viscosity is closely associated with many diseases and cellular malfunctions. Thus, the development of reliable methods for monitoring mitochondrial viscosity variations has attracted considerable attention. Herein, through stepwise structural modulation of the dihydroxanthene fluorophore (DHX), we developed three NIR fluorescent probes, named DHX-V-1-3, for detecting mitochondrial viscosity. Among them, DHX-V-3 displayed the highest signal-to-noise ratio (67-fold) for viscosity with outstanding selectivity and showed excellent mitochondria targeting and immobilization ability. At the cellular level, the DHX-V-3 probe was successfully applied to image the mitochondrial viscosity in live cells upon treatment with lipopolysaccharide (LPS) or nystatin. Moreover, benefiting from its NIR emission and the increased depth of tissue imaging, DHX-V-3 demonstrated the ability to visualize the increased viscosity in LPS-treated mice.

A 'double locked' ratiometric fluorescent probe for detection of cysteine in a viscous system and its application in cancer cells

Intracellular viscosity is a physicochemical property that regulates the consequences of several biological progressions. Cysteine (Cys) is an important signaling molecule that commands many cellular activities, such as antioxidant generation. Predicting that both may be interconnected with a diversity of pathological processes, their contemporaneous measurement would be valuable for studying the pathological ailment of cells. Herein, we have synthesized a 'double locked' probe, acrylic acid 6-[4-(2-benzothiazol-2-yl-2-cyano-vinyl)-phenyl]-naphthalen-2-yl ester (ABN) for the detection of Cys in a viscous medium and explored its application to living cells that were exposed to dexamethasone to regulate the intracellular viscosity level. ABN displayed a satisfactory ratiometric (blue to orange) fluorescence response in solution and in living cells when Cys and viscosity coexisted. A turn-on fluorescence signal was visualized when the probe was individually treated with Cys and glycerol (a standard viscosity source). Therefore, we propose that ABN is a fluorescent probe that permits the monitoring of variations in intracellular viscosity and Cys levels in a biological environment, and it can be utilized in innumerable cellular damage models.

Photo-Activated Ratiometric Fluorescent Indicator for Real-Time and Visual Detection of Plasma Membrane Homeostasis

Development of an activated ratiometric indicator that is specific to plasma membrane (PM) viscosity exhibits great application prospects in disease diagnosis and treatment but remains a great challenge. Herein, a photo-activated fluorescent probe (CQ-IC) was designed and prepared tactfully, which could analyze and real-time monitor the microenvironmental homeostasis of the PM based on a two-channel ratiometric imaging model. Interestingly, upon light irradiation, CQ-IC generates reactive oxygen species and thus increases the cellular viscosity, which increases two emission peaks at 480 and 610 nm. This work would propose a new strategy to sensor PM homeostasis and effectively guide the treatment of viscosity-related diseases among various physiological and pathological processes.

Multiple organelle-targeted near-infrared fluorescent probes toward pH and viscosity

Organelles, including mitochondria (mito), lysosomes (lyso), endoplasmic reticulum (ER), Golgi apparatus (Golgi), and ribosome et al., play a vital role in maintaining the regular work of the cell. Viscosity is an essential parameter in the cellular microenvironment. Herein, four viscosity-sensitive near-infrared fluorescent probes DMPC, DEPC, DHDM and DHDV that can simultaneously target multiple organelles were synthesized. As the viscosity increased, the fluorescence intensity of the probes gradually increased due to the hindrance of the rotation of the carbon-carbon single bond. The fluorescence intensity of DHDV increased by about 453 times, and the fluorescence quantum yield also increased from 0.051 to 0.681. Cell experiments indicated the probes could simultaneously target four kinds of organelles, and the four probes could also track mitochondria with no dependence on membrane potential. Further experiments showed that the probes could detect viscosity changes in lyso and mito. In addition, the probes also demonstrated the advantages of low cytotoxicity, good anti-interference and stability, providing a simple and effective tool for studying the activity of organelles with changing viscosity signals.

Visual monitoring of the mitochondrial pH changes during mitophagy with a NIR fluorescent probe and its application in tumor imaging

Mitophagy, a mitochondria-selective autophagy process, plays critical roles in maintaining intracellular homeostasis by removing the damaged mitochondria and recycling the nutrients in a lysosome-dependent manner. Mitophagy process could result in the changes of mitochondrial pH. So fluorescent probes for detecting mitochondrial pH during mitophagy are highly needed for exploring the functions of mitochondria. Herein, a series of near-infrared pH probes were designed based on the rhodamine framework. The probes showed high sensitivity for pH with the tunable pKa from 4.74 to 6.54. Particularly, for probe 5 (with the pKa of 6.54), a linear relationship between fluorescence intensity and pH in the range of 5.6-7.2 was observed, which was suitable for mitochondrial pH detection. The probe displayed excellent mitochondria-targeting ability. It was applied to monitor pH changes during mitophagy caused by starvation. Besides, in vivo non-invasive visualization of tumor pH variations was achieved via the fluorescence imaging in the near-infrared region. We anticipate that the probe may be a useful tool for revealing essential information about mitophagy-related research and clinical tumor diagnosis.

Mitophagy Induced by Metal Nanoparticles for Cancer Treatment

Research on nanoparticles, especially metal nanoparticles, in cancer therapy is gaining momentum. The versatility and biocompatibility of metal nanoparticles make them ideal for various applications in cancer therapy. They can bring about apoptotic cell death in cancer cells. In addition to apoptosis, nanoparticles mediate a special type of autophagy facilitated through mitochondria called mitophagy. Interestingly, nanoparticles with antioxidant properties are capable of inducing mitophagy by altering the levels of reactive oxygen species and by influencing signaling pathways like PINK/Parkin pathway and P13K/Akt/mTOR pathway. The current review presents various roles of metal nanoparticles in inducing mitophagy in cancer cells. We envision this review sheds some light on the blind spots in the research related to mitophagy induced by nanoparticles for cancer treatment.

Novel Meso-Benzothiazole-Substituted BODIPY-Based AIE Fluorescent Rotor for Imaging Lysosomal Viscosity and Monitoring Autophagy

Meso-substituted boron dipyrromethenes (BODIPYs) provide a potential and innovative strategy for the synergistic construction of aggregation-induced emission (AIE) probes and fluorescent rotors for monitoring cellular viscosity changes, which play critical roles in understanding the function of viscosity in its closely associated diseases. Therefore, for the first time, a BODIPY-based fluorescent probe (1) with a rotatable meso-benzothiazole group was rationally designed and synthesized, showing both good viscosity-responsive and AIE properties. Probe 1 through direct linkage with the thiazole group, showed nearly no emission in low viscous solvents; however, a strong emission at 534 nm appeared and increased gradually with the increase in viscosity, attributing to the efficient restriction of the rotatable meso-benzothiazole group. The intensity (log I₅₃₄) displayed a good linear relationship with viscosity (log η) in the viscous range of 0.59-945 cP in methanol/glycerol mixtures. Interestingly, 1 showed enhanced emission at 534 nm in 70% water compared to pure acetonitrile due to the aggregation-induced inhibited rotations. Cellular imaging suggested that 1 could successfully sense lysosomal viscosity changes induced by lipopolysaccharide, nystatin, low temperature, and dexamethasone in living cells, which could be further applied in autophagy monitoring by tracing viscosity changes. As a comparison, its analogue 2 directly linking with the phenyl group showed no viscosity-responsive or AIE properties. Therefore, for the first time, we reported a meso-benzothiazole-BODIPY-based fluorescent rotor with AIE and lysosomal viscosity-responsive properties in nervous cells, which was further applied in monitoring autophagy, and this work thus could provide an innovative strategy for the design of potential AIE and viscosity-responsive probes.

Recent Progress in Fluorescent Probes for Diabetes Visualization and Drug Therapy

Diabetes has become one of the most prevalent endocrine and metabolic diseases that threaten human health, and it is accompanied by serious complications. Therefore, it is vital and pressing to develop novel strategies or tools for prewarning and therapy of diabetes and its complications. Fluorescent probes have been widely applied in the detection of diabetes due to the fact of their attractive advantages. In this report, we comprehensively summarize the recent progress and development of fluorescent probes in detecting the changes in the various biomolecules in diabetes and its complications. We also discuss the design of fluorescent probes for monitoring diabetes in detail. We expect this review will provide new ideas for the development of fluorescent probes suitable for the prewarning and therapy of diabetes in future clinical transformation and application.

Precision Navigation of Hepatic Ischemia-Reperfusion Injury Guided by Lysosomal Viscosity-Activatable NIR-II Fluorescence

Hepatic ischemia-reperfusion injury (HIRI) is responsible for postoperative liver dysfunction and liver failure. Precise and rapid navigation of HIRI lesions is critical for early warning and timely development of pretreatment plans. Available methods for assaying liver injury fail to provide the exact location of lesions in real time intraoperatively. HIRI is intimately associated with oxidative stress which impairs lysosomal degradative function, leading to significant changes in lysosomal viscosity. Therefore, lysosomal viscosity is a potential biomarker for the precise targeting of HIRI. Hence, we developed a viscosity-activatable second near-infrared window fluorescent probe (NP-V) for the detection of lysosomal viscosity in hepatocytes and mice during HIRI. A reactive oxygen species-malondialdehyde-cathepsin B signaling pathway during HIRI was established. We further conducted high signal-to-background ratio NIR-II fluorescence imaging of HIRI mice. The contour and boundary of liver lesions were delineated, and as such the precise intraoperative resection of the lesion area was implemented. This research demonstrates the potential of NP-V as a dual-functional probe for the elucidation of HIRI pathogenesis and the direct navigation of HIRI lesions in clinical applications.

Coumarin-based fluorescent probes toward viscosity in mitochondrion/lysosome

Viscosity is an important microenvironmental indicator that plays an important role in the process of information transmission in various regions. Herein, two coumarin-based viscosity-sensitive fluorescent probes (CHB, CHN) were synthesized and the photophysical properties of the two probes were studied. The fluorescence quantum yields of CHB and CHN in glycerol can be as high as 25.2% and 18.3% respectively. The two probes can linearly detect viscosity in the viscosity logarithm range of 0.83-2.07, which is not interfered with pH, metal ions, anions and biomolecules. Fluorescent confocal cell experiments show CHB and CHN have good targeting ability to mitochondrion, lysosome, Endoplasmic reticulum and Golgi apparatus, and can be used to detect viscosity in mitochondrion/lysosome.

Near-Infrared Mitochondria-Targetable Single-Molecule probe for Dual-Response of viscosity and sulfur dioxide in vivo

Studies have demonstrated that the viscosity and SO₂ in mitochondria are involved in various physiological processes, which are both important for maintaining the normal function of mitochondria. In this research, we rationally designed and synthesized a novel mitochondria-targetable fluorescent probe Mito-MG with near-infrared absorption and emission for dual-response of viscosity and SO₂. Based on the TICT mechanism and Michael addition reaction, the probe Mito-MG responds to viscosity and SO₂ with different near-infrared fluorescence signals. Importantly, Mito-MG presented outstanding mitochondrial targeting ability (Pearson's colocalization coefficient is 0.8602) and has been successfully applied to imaging of the cells, zebrafish and mice. We believe that Mito-MG could be applied as a powerful tool for a deep understanding of the connection of viscosity and SO₂ in biological systems.

Liposome-Based Nanoencapsulation of a Mitochondria-Stapling Photosensitizer for Efficient Photodynamic Therapy

Mitochondria-targeting photodynamic therapy (PDT) can block mitochondrial function and trigger the inherent proapoptotic cascade signal of mitochondria, which has been considered to have the potential to amplify the efficiency of PDT. However, the dynamic change of mitochondrial membrane potential (MMP) makes most cationic photosensitizers easily fall off from the mitochondria, which greatly limits the efficiency of PDT. Here, we have developed a smart liposome encapsulation method based on a mitochondria-stapling photosensitizer for efficient theranostic photodynamic therapy. The stapling photosensitizer can be covalently bound inside mitochondria via two reaction sites without a falloff effect, regardless of the change of MMP. As a result, the liposome-based nanophotosensitizer showed a high efficiency of PDT (IC₅₀ = 0.98 μM) under 630 nm light. At the same time, the nanophotosensitizer had fluorescence imaging-guided ability to monitor abnormal mitochondrial morphology during PDT. Importantly, the results of mice experiments also showed that the liposome-based nanophotosensitizer possessed excellent antitumor PDT activity because the released photosensitizer can stay inside mitochondria during the whole process of PDT.

Mitochondrial-Targeting Near-Infrared Fluorescent Probe for Visualizing Viscosity in Drug-Induced Cells and a Fatty Liver Mouse Model

Mitochondria, as "cell energy stations", are involved in the regulation of various cell functions. Recent investigations revealed that mitochondrial dysfunction that can cause an intracellular viscosity mutation, a process that is associated with an increasing number of diseases that are not curable or manageable. However, conventional viscometers cannot be used to monitor the viscosity changes in living cells and in vivo. In order to cater to the complex biological environment, we present a chemical toolbox, MI-BP-CC, that employs N,N-diethyl and double bonds as sensitive sites for viscosity based on the TICT mechanism (twisted intramolecular charge transfer) to monitor the viscosity of living cells and fatter liver mice. MI-BP-CC features good mitochondrial targeting and a near-infrared emission. Surprisingly, in the presence of viscosity, the MI-BP-CC probe exhibited an ultrasensitive model for viscosity detection showing a red fluorescence signal from a silent "off" state to "on". More importantly, utilizing the satisfactory detection performance of MI-BP-CC, we have successfully visualized increased viscosity under the pathological models of Parkinson's (PD) and fatty liver mice. We anticipate that these findings will provide a convenient and efficient tool to understand physiological functions of viscosity in more biosystems.

Antipermeability Strategy to Achieve Extremely High Specificity and Ultralong Imaging of Diverse Cell Membranes Based on Restriction-Induced Emission of AIEgens

Long-term in situ cell membrane-targeted bioimaging is of great significance for studying specific biological processes and functions, but currently developed membrane probes are rarely simultaneously used to image the plasma membrane of animal and plant cells, and these probes lack sufficiently high long-term targeting ability. Herein, we proposed an antipermeability strategy to achieve highly specific and long-term imaging of plasma membranes of both human and plant cells using the steric hindrance effect and restriction-induced emission of AIE-active probes based on an updated membrane model. A certain degree of rigidity of plasma membrane containing a large ratio of rigid cholesterol molecules in the updated membrane model provides a promising opportunity to design antipermeable probes by introducing a rigid steric hindrance group in the probe. The designed antipermeable probes can anchor inside plasma membrane for a long term relying on the combination of the steric hindrance effect and the electrostatic and hydrophobic interactions between the probe and the membrane, as well as light up the membrane via the restriction-induced emission mechanism. The excellent performance in imaging completeness and specificity for both human cells and plant cells clearly shows that these designed probes possess outstanding antipermeability to achieve long-term specific imaging of membrane. These probes also show some advanced features such as ultrafast staining, wash-free merit, favorable biocompatibility, good photostability, and effective resistance to viscosity and pH alteration. This work also provides a valuable design principle for membrane probes of plant cells that the designed probes require a suitable molecular size favoring the penetration of small pores of cell walls.

A novel mitochondria-targeted fluorescent probe for detecting viscosity in living cells and zebrafishes†

Based on the twisted intramolecular charge transfer (TICT) mechanism, a new mitochondria-targeted fluorescent probe CSS-1 for detection of viscosity variations was developed. The probe featured in a strong response to...