1,2,4,5-Tetrazine-tethered probes for fluorogenically imaging superoxide in live cells with ultrahigh specificity

Bioorthogonally activated probes for precise fluorescence imaging

Over the past two decades, bioorthogonal chemistry has undergone a remarkable development, challenging traditional assumptions in biology and medicine. Recent advancements in the design of probes tailored for bioorthogonal applications have met the increasing demand for precise imaging, facilitating the exploration of complex biological systems. These state-of-the-art probes enable highly sensitive, low background, in situ imaging of biological species and events within live organisms, achieving resolutions comparable to the size of the biomolecule under investigation. This review provides a comprehensive examination of various categories of bioorthogonally activated in situ fluorescent labels. It highlights the intricate design and benefits of bioorthogonal chemistry for precise in situ imaging, while also discussing future prospects in this rapidly evolving field.

Ex Tenebris Lux: Illuminating Reactive Oxygen and Nitrogen Species with Small Molecule Probes

Reactive oxygen and nitrogen species are small reactive molecules derived from elements in the air─oxygen and nitrogen. They are produced in biological systems to mediate fundamental aspects of cellular signaling but must be very tightly balanced to prevent indiscriminate damage to biological molecules. Small molecule probes can transmute the specific nature of each reactive oxygen and nitrogen species into an observable luminescent signal (or even an acoustic wave) to offer sensitive and selective imaging in living cells and whole animals. This review focuses specifically on small molecule probes for superoxide, hydrogen peroxide, hypochlorite, nitric oxide, and peroxynitrite that provide a luminescent or photoacoustic signal. Important background information on general photophysical phenomena, common probe designs, mechanisms, and imaging modalities will be provided, and then, probes for each analyte will be thoroughly evaluated. A discussion of the successes of the field will be presented, followed by recommendations for improvement and a future outlook of emerging trends. Our objectives are to provide an informative, useful, and thorough field guide to small molecule probes for reactive oxygen and nitrogen species as well as important context to compare the ecosystem of chemistries and molecular scaffolds that has manifested within the field.

Photoinduced Charge Centralization Quenches the Fluorescence of Conjugation-Fused Tetrazine Labels with Red-to-Near-Infrared Emissions

Tetrazine-derived fluorogenic labels are extensively studied for their potential in biological and medical imaging. Nonetheless, the fluorescence quenching mechanism in numerous precursors continues to be debated, particularly as the wavelengths extend into the red and near-infrared (NIR) regions. This challenge poses obstacles to systematically optimizing their fluorogenicity, i.e., achieving red-shifted wavelengths and improved fluorescence turn-on signals through click reactions. This paper highlights the significance of photoinduced charge centralization (PCC), a quenching mechanism observed in tetrazine-fused fluorogenic labels with integrated π-conjugations. PCC is primarily responsible for the quenching effects observed in such labels emitting in the red-to-NIR spectrum. Drawing from structure-property relationships, this study proposes two molecular design strategies that incorporate the PCC mechanism and constitutional isomerization to develop high-performance tetrazine-based labels. These strategies facilitate multiplex fluorescence imaging following click reactions, promising significant advancements in bio-orthogonal imaging techniques.

Fluorescent Probes for Disease Diagnosis

The identification and detection of disease-related biomarkers is essential for early clinical diagnosis, evaluating disease progression, and for the development of therapeutics. Possessing the advantages of high sensitivity and selectivity, fluorescent probes have become effective tools for monitoring disease-related active molecules at the cellular level and in vivo. In this review, we describe current fluorescent probes designed for the detection and quantification of key bioactive molecules associated with common diseases, such as organ damage, inflammation, cancers, cardiovascular diseases, and brain disorders. We emphasize the strategies behind the design of fluorescent probes capable of disease biomarker detection and diagnosis and cover some aspects of combined diagnostic/therapeutic strategies based on regulating disease-related molecules. This review concludes with a discussion of the challenges and outlook for fluorescent probes, highlighting future avenues of research that should enable these probes to achieve accurate detection and identification of disease-related biomarkers for biomedical research and clinical applications.

A Sequentially Activated Probe for Imaging of Superoxide Anion and Peroxynitrite in PC12 Cells under Oxidative Stress

Superoxide anion (O2·-) and peroxynitrite (ONOO-), two important oxidants under oxidative stress, coexist in complex cell and organism systems, playing crucial roles in various physiological and pathological processes, particularly in neurodegenerative diseases. Despite the absence of robust molecular tools capable of simultaneously visualizing O2·- and ONOO- in biosystems, the relationship between these two species remains understudied. Herein, we present sequentially activated fluorescent probe, DHX-SP, which exhibits exceptional selectivity and sensitivity toward O2·- and ONOO-. This probe enables precise imaging of these species in living PC12 cells under oxidative stress conditions using distinct fluorescence signal combinations. Furthermore, the probe DHX-SP has the ability to visualize changes in O2·- and ONOO- levels during ferroptosis of PC12 cells and in the Parkinson's disease model. These findings establish a connection between the crosstalk of the phosphorus group of O2·- and ONOO- in PC12 cells under oxidative stress.

Deconvoluting nitric oxide-protein interactions with spatially resolved multiplex imaging

Simultaneous imaging of nitric oxide (NO) and its proximal proteins should facilitate the deconvolution of NO-protein interactions. While immunostaining is a primary assay to localize proteins in non-genetically manipulated samples, NO imaging probes with immunostaining-compatible signals remain unexplored. Herein, probe NOP-1 was developed with an NO-triggered proximal protein labeling capacity and fluorogenic signals. The trick is to fuse the native chemical ligation of acyl benzotriazole with the protein-conjugation-induced fluorogenic response of Si-rhodamine fluorophore. NOP-1 predominantly existed in the non-fluorescent spirocyclic form. Yet, its acyl o-phenylenediamine moiety was readily activated by NO into acyl benzotriazole to conjugate proximal proteins, providing a fluorogenic response and translating the transient cellular NO signal into a permanent stain compatible with immunostaining. NOP-1 was utilized to investigate NO signaling in hypoglycemia-induced neurological injury, providing direct evidence of NO-induced apoptosis during hypoglycemia. Mechanistically, multiplex imaging revealed the overlap of cellular NOP-1 fluorescence with immunofluorescence for α-tubulin and NO2-Tyr. Importantly, α-tubulin was resolved from NOP-1 labeled proteins. These results suggest that NO played a role in hypoglycemia-induced apoptosis, at least in part, through nitrating α-tubulin. This study fills a crucial gap in current imaging probes, providing a valuable tool for unraveling the complexities of NO signaling in biological processes.

Tri-mode Responses to Reactive Oxygen Species In Vivo by Chiral Vanadium-Based Nanoparticles

Reactive oxygen species (ROS) are closely associated with the redox balance of the physiological environment, and monitoring ROS can aid in the early diagnosis of many diseases, including cancer. In this study, chiral vanadium trioxide/vanadium nitride (V2O3/VN) nanoparticles (NPs) modified with an organic dye (cyanine 3 [Cy3]) were prepared for ROS sensing. Chiral V2O3/VN NPs were prepared with the "ligand-induced chirality" strategy and showed a g-factor of up to 0.12 at a wavelength of 512 nm. To the best of our knowledge, this g-factor is the highest value of all chiral ceramic nanomaterials. The very high g-factor of the nanoprobe confers very high sensitivity, because the higher g-factor, the higher sensitivity. In the presence of ROS, V3+ in the chiral V2O3/VN nanoprobe undergoes a redox reaction to form V2O5, reducing the circular dichroism and absorbance signals, whereas the fluorescence signal of Cy3 is restored. With this nanoprobe, the limits of detection for the circular dichroic and fluorescence signals in living cells are 0.0045 nmol/106 and 0.018 nmol/106 cells, respectively. This chiral nanoprobe can also monitor ROS levels in vivo by fluorescence. This strategy provides an innovative approach to the detection of ROS and is expected to promote the wider application of chiral nanomaterials for biosensing.

Microenvironment-differential Imaging of Demethylated Metabolites of Methionine for Identifying Ferroptosis Regional Preferences with Path-independent Equifinal Fluorescence Probes

We realized the microenvironment-differential Imaging of demethylated metabolites of methionine and the regional regulation of ferroptosis.

A Rationally Designed Prodrug for the Fluorogenic Labeling of Albumin and Theranostic Effects on Drug-Induced Liver Injury

The development of small-molecular fluorogenic tools for the chemo-selective labeling of proteins in live cells is important for the evaluation of intracellular redox homeostasis. Dynamic imaging of human serum albumin (HSA), an antioxidant protein under oxidative stress with concomitant release of antioxidant drugs to maintain redox homeostasis, affords potential opportunities for disease diagnosis and treatment. In this work, we developed a nonfluorogenic prodrug named TPA-NAC, by introducing N-acetyl-l-cysteine (NAC) into a conjugated acceptor skeleton. Through combined thiol and amino addition, coupling with HSA results in fluorescence turn-on and drug release. It was reasoned that the restricted intramolecular motion of the probe under an HSA microenvironment after covalent bonding inhibited the nonradiative transitions. Furthermore, the biocompatibility and photochemical properties of TPA-NAC enabled it to image exogenous and endogenous HSA in living cells in a wash-free manner. Additionally, the released drug evoked upregulation of superoxide dismutase (SOD), which synergistically eliminated reactive oxygen species in a drug-induced liver injury model. This study provides insights into the design of new theranostic fluorescent prodrugs for chemo-selective protein labeling and disease treatments.

Health position paper and redox perspectives - Disease burden by transportation noise

Transportation noise is a ubiquitous urban exposure. In 2018, the World Health Organization concluded that chronic exposure to road traffic noise is a risk factor for ischemic heart disease. In contrast, they concluded that the quality of evidence for a link to other diseases was very low to moderate. Since then, several studies on the impact of noise on various diseases have been published. Also, studies investigating the mechanistic pathways underlying noise-induced health effects are emerging. We review the current evidence regarding effects of noise on health and the related disease-mechanisms. Several high-quality cohort studies consistently found road traffic noise to be associated with a higher risk of ischemic heart disease, heart failure, diabetes, and all-cause mortality. Furthermore, recent studies have indicated that road traffic and railway noise may increase the risk of diseases not commonly investigated in an environmental noise context, including breast cancer, dementia, and tinnitus. The harmful effects of noise are related to activation of a physiological stress response and nighttime sleep disturbance. Oxidative stress and inflammation downstream of stress hormone signaling and dysregulated circadian rhythms are identified as major disease-relevant pathomechanistic drivers. We discuss the role of reactive oxygen species and present results from antioxidant interventions. Lastly, we provide an overview of oxidative stress markers and adverse redox processes reported for noise-exposed animals and humans. This position paper summarizes all available epidemiological, clinical, and preclinical evidence of transportation noise as an important environmental risk factor for public health and discusses its implications on the population level.