Conformational restraint as a strategy for navigating towards lysosomes

Monitoring Glutathione Content of the Endoplasmic Reticulum under Scrap Leather-Induced Endoplasmic Reticulum Stress via an Endoplasmic Reticulum-Targeted Two-Photon Fluorescent Probe

Maintaining tissue homeostasis necessitates the coordinated efforts of various cell types to regulate inflammation. Endoplasmic reticulum (ER) stress, a hallmark of inflammation, exacerbates tissue pathology in various human diseases. Glutathione (GSH), a pivotal regulator of cellular redox balance, controls disulfide bond formation in the ER, thereby shielding cells from oxidative stress. In this study, we developed a two-photon fluorescent probe, ER-GSH, with specific ER targeting and demonstrated its high sensitivity and rapid response to GSH. Experiments conducted on BV2 cells and a mice model of neuroinflammation induced by scrap leather revealed that inflammatory reactions led to ER stress and a substantial reduction in GSH levels. Notably, the anti-inflammatory drug NS-398 effectively inhibited cell inflammation and ER stress by maintaining GSH levels. These findings underscore the potential therapeutic significance of modulating GSH levels to alleviate the impact of neuroinflammation.

Progress in the Study of Optical Probes for the Detection of Formaldehyde

Formaldehyde, one of the simplest reactive carbonyl substances, is involved in many physiological and pathological processes in living organisms. There is a large amount of data showing that abnormal elevation of formaldehyde is associated with a variety of diseases in the body, such as neurodegenerative diseases, Alzheimer's disease, cardiovascular diseases and cancer, and is also a representative carcinogen, so monitoring formaldehyde is of great importance for disease diagnosis and treatment. In this review, In this paper, we summarize and classify the last ten years of probes for the detection of formaldehyde according to different reaction mechanisms and discuss the structures and applications of the probes. Finally, we briefly describe the challenges and possible solutions in this field. We believe that more new probes provide powerful tools to study the function of formaldehyde in living systems.

Modular development of organelle-targeting fluorescent probes for imaging formaldehyde in live cells

Formaldehyde (FA) is endogenously generated via fundamental biological processes in living systems. Aberrant FA homeostasis in subcellular microenvironments is implicated in numerous pathological conditions. Fluorescent probes for detecting FA in specific organelles are thus of great research interest. Herein, we present a modular strategy to construct diverse organelle-targeting FA probes by incorporating selective organelle-targeting moieties into the scaffold of a 1,8-naphthalimide-derived FA fluorescent probe. These probes react with FA through the 2-aza-Cope arrangement and exhibit highly selective fluorescence increases for detecting FA in aqueous solutions. Moreover, these organelle-targeting probes, i.e., FFP551-Nuc, FFP551-ER, FFP551-Mito, and FFP551-Lyso, allow selective localization and imaging of FA in the nucleus, endoplasmic reticulum, mitochondria, and lysosomes of live mammalian cells, respectively. Furthermore, FFP551-Nuc has been successfully employed to monitor changes of endogenous FA levels in the nucleus of live mammalian cells. Overall, these probes should represent new imaging tools for studying the biology and pathology associated with FA in different intracellular compartments.

A mitochondria-targeted ratiometric fluorescent sensor based on naphthalimide derivative-functionalized silica-based nanodots for imaging formaldehyde in living cells and zebrafish

A mitochondria-targeted ratiometric fluorescent sensor (Mito-Si-NA) for formaldehyde (FA) has been constructed by functionalizing silica-based nanodots (silica-based ND). As the fluorescence reference and carrier, the silica-based ND conjugate with small molecule probe for FA via covalent. Further modifying with mitochondria targeting moiety enables the sensor to specifically target mitochondria. In the presence of FA, the emission of silica-based ND remain constant to act as an internal reference (445 nm) while the response signal of small molecule probe was gradually enhanced (545 nm). This sensor exhibits excellent selectivity towards FA with great changes of fluorescence intensity ratio values (I545/I445). The FA ratiometric fluorescence imaging in mitochondria was achieved successfully. In addition, the sensor was also successfully used for imaging FA in zebrafish. The good performance of Mito-Si-NA for FA bioimaging confirms that Mito-Si-NA is an appealing imaging tool to monitor FA in mitochondria and shows great potential to study the functions of FA on mitochondria.

Discrimination of Cell Death Types with an Activatable Fluorescent Probe through Visualizing the Lysosome Morphology

Cell death plays a vital role in body development, maintenance of tissue function, and homeostasis. Accurate evaluation of cell death types is of great importance for pharmacological and pathological research. However, there is a lack of efficient fluorescent probes to discriminate various cell states. Here, we design and synthesize a novel activatable fluorescent probe PNE-Lyso to detect intracellular pH and hexosaminidases with two kinds of fluorescence signals. PNE-Lyso could distinguish dead cells from healthy cells based on a dual-color mode by targeting the lysosome and evaluating lysosomal hexosaminidase activity. Significantly, PNE-Lyso could also discriminate apoptotic and necrotic cells through visualizing lysosome morphology that is adjusted by the integrity of the lysosome membrane. Moreover, probe PNE-Lyso was successfully applied to investigate the drug-induced cell death process. To the best of our knowledge, this work is the first time cell death types have been distinguished based on a single fluorescent probe.

A Tandemly Activated Fluorescence Probe for Detecting Senescent Cells with Improved Selectivity by Targeting a Biomarker Combination

The heterogeneous and complex phenotypes of cellular senescence necessitate a biomarker combination for the accurate detection of senescent cells from others. However, this raises the challenge of detecting multiple senescent biomarkers in the same live cell simultaneously. Herein we reported the strategy of biomarker combination triggered tandem activation for designing senescence-specific fluorogenic probes, which resulted in the development of the probe P_Gal-FA. The fluorescence of P_Gal-FA can only be activated by the sequential stimulation by the senescent biomarker combination of β-galactosidase (βGal) and formaldehyde (FA), with βGal activating the sensing ability of the probe toward FA. Facilitated by probe P_Gal-FA, the simultaneous detection of a biomarker combination in the same live cell was realized. We have demonstrated the improved selectivity of probe P_Gal-FA toward senescent cells compared to the traditional single-biomarker-based probe. Probe P_Gal-FA was also successfully used to detect senescent cells in bleomycin-induced pulmonary fibrosis tissues. We expect probe P_Gal-FA to be a reliable tool for the study on cellular senescence and envision that this probe design strategy may be expanded to other biological events to improve accuracy.

Chemiluminescence Detection in the Study of Free-Radical Reactions. Part 2. Luminescent Additives That Increase the Chemiluminescence Quantum Yield

The present review examines the use of chemiluminescence detection to evaluate the course of free radical reactions in biological model systems. The application of the method is analyzed by using luminescent additives that enhance the luminescence thanks to a triplet-singlet transfer of the electron excitation energy from radical reaction products and its emission in the form of light with a high quantum yield; these additives are called chemiluminescence enhancers or activators. Examples of these substances are provided; differences between the so-called chemical and physical enhancers are described; coumarin derivatives, as the most promising chemiluminescence enhancers for studying lipid peroxidation, are considered in detail. The main problems related to the use of coumarin derivatives are defined, and possible ways of solving these problems are presented. Intrinsic chemiluminescence and the mechanism of luminescence accompanying biomolecule peroxidation are discussed in the first part of the review.

Systematic investigation of the aza-Cope reaction for fluorescence imaging of formaldehyde in vitro and in vivo

Increasing evidence has highlighted the endogenous production of formaldehyde (FA) in a variety of fundamental biological processes and its involvement in many disease conditions ranging from cancer to neurodegeneration. To examine the physiological and pathological relevance and functions of FA, fluorescent probes for FA imaging in live biological samples are of great significance. Herein we report a systematic investigation of 2-aza-Cope reactions between homoallylamines and FA for identification of a highly efficient 2-aza-Cope reaction moiety and development of fluorescent probes for imaging FA in living systems. By screening a set of N-substituted homoallylamines and comparing them to previously reported homoallylamine structures for reaction with FA, we found that N-p-methoxybenzyl homoallylamine exhibited an optimal 2-aza-Cope reactivity to FA. Theoretical calculations were then performed to demonstrate that the N-substituent on homoallylamine greatly affects the condensation with FA, which is more likely the rate-determining step. Moreover, the newly identified optimal N-p-methoxybenzyl homoallylamine moiety with a self-immolative β-elimination linker was generally utilized to construct a series of fluorescent probes with varying excitation/emission wavelengths for sensitive and selective detection of FA in aqueous solutions and live cells. Among these probes, the near-infrared probe FFP706 has been well demonstrated to enable direct fluorescence visualization of steady-state endogenous FA in live mouse brain tissues and elevated FA levels in a mouse model of breast cancer. This study provides the optimal aza-Cope reaction moiety for FA probe development and new chemical tools for fluorescence imaging and biological investigation of FA in living systems.

Chemiluminescence Detection in the Study of Free-Radical Reactions. Part 1

The present review, consisting of two parts, considers the application of the chemiluminescence detection method in evaluating free radical reactions in biological model systems. The first part presents a classification of experimental biological model systems. Evidence favoring the use of chemiluminescence detection in the study of free radical reactions, along with similar methods of registering electromagnetic radiation as electron paramagnetic resonance, spectrophotometry, detection of infrared radiation (IR spectrometry), and chemical methods for assessing the end products of free radical reactions, is shown. Chemiluminescence accompanying free radical reactions involving lipids has been the extensively studied reaction. These reactions are one of the key causes of cell death by either apoptosis (activation of the cytochrome c complex with cardiolipin) or ferroptosis (induced by free ferrous ions). The concept of chemiluminescence quantum yield is also discussed in this article. The second part, which is to be published in the next issue, analyzes the application of chemiluminescence detection using luminescent additives that are called activators, a.k.a. chemiluminescence enhancers, and enhance the emission through the triplet-singlet transfer of electron excitation energy from radical reaction products, followed by light emission with a high quantum yield.

Tailored Engineering of Novel Xanthonium Polymethine Dyes for Synergetic PDT and PTT Triggered by 1064 nm Laser toward Deep-Seated Tumors

Small molecular dye that simultaneously exerts dual PDT/PTT effects as well as florescence imaging triggered by a single NIR-II light has never been reported to date. Apart from the huge challenge in pushing absorption profile into NIR-II region, fine-tuning dyes' excited state via rational structure design to meet all three functions, especially oxygen photosensitization, remains the most prominent throttle. Herein, five novel NIR-II dyes (BHs) are productively developed by strategically conjugating dyad innovative xanthonium with sequentially extended polymethine bridges, enabling intense absorption from 890 to 1206 nm, significantly 400 nm longer than conventional cyanine dyes with same polymethines. More importantly, owning to high resonance and favorable excited state energy population induced by greater rigidity via ring-fused amino, BH 1024 exhibits best singlet oxygen generation capability, moderate photothermal heating, and considerable fluorescence under 1064 nm laser irradiation. Furthermore, BH 1024 is encapsulated into folate-functionalized polymer, which demonstrated a synergetic PDT/PTT effect in vitro and in vivo, eventually achieving solid tumors elimination under NIR-II fluorescence guide. As far as it is known, this is the first time small molecular dyes for NIR-II PDT or NIR-II PDT/PTT are explored and designed.

Heterocyclic N-Oxides as Small-Molecule Fluorogenic Scaffolds: Rational Design and Applications of Their "On-Off" Fluorescence

Small-molecule fluorescent probes are powerful tools in chemical analysis and biological imaging. However, as the foundation of probe design, the meager existing set of core fluorophores have largely limited the diversity of current probes. Consequently, there is a high demand to discover fluorophores with new scaffolds and optimize the existing fluorophores. Here, we put forward a facile strategy of heterocyclic N-oxidation to address these challenges. The introduced N-O bond reconstructs the electron "push-pull" system of heterocyclic scaffolds and dramatically improves their photophysical properties by red-shifting the spectra and increasing the Stokes shift. Meanwhile, the heterocyclic N-O bond also enables a function of the fluorescence switch. It can turn on the fluorescence of pyridine and increase the fluorescence of quinoline and, conversely, decrease the fluorescence of acridines and resorufin. As a further practical application, we successfully utilized the quinoline N-oxide scaffold to design fluorogenic probes for H₂S (8) and formaldehyde (FA, 9). Given their ultraviolet-visible spectra, both probes with high selectivity and sensitivity could be conveniently used in the naked eye detection of target analytes under illumination with a portable UV lamp. More interestingly, the probes could be effectively used in the imaging of nuclear and cytoplasmic H₂S or nuclear and perinuclear FA. This potentially overcomes the weaknesses of existing H₂S or FA probes that can only work in the cytoplasm. These interesting findings demonstrate the ability to rapidly expand and optimize the existing fluorophore library through heterocyclic N-oxidation.

State-of-the-art: functional fluorescent probes for bioimaging and pharmacological research

Cardiovascular diseases, neuropsychiatric disorders, and cancers seriously endanger human health. Mechanistic and pharmacological mechanisms of candidate drugs are central to the translational paradigm. Since many signal transduction and molecular events are implicated in these diseases, a novel method to interrogate the key pharmacological mechanisms is required to accelerate innovative drug discovery. Much attention now focuses on the real-time visualization of molecular disease events to yield new insights to the pathogenesis of the diseases. This review focuses on recent advances in the development of chemical probes for imaging pathological events to facilitate the study of the underlying pharmacodynamics and toxicity involved. As reviewed here, optical imaging is now frequently viewed as an indispensable technique in the field of biological research. Promoting interdisciplinary collaboration among chemistry, biology and medicine, is necessary to further refine functional fluorescent probes for diagnostic and therapeutic applications.