A bioluminescent probe for imaging endogenous hydrogen polysulfides in live cells and a murine model of bacterial infection

Activity-Based Fluorescent Probes for Hydrogen Sulfide and Related Reactive Sulfur Species

Hydrogen sulfide (H2S) is not only a well-established toxic gas but also an important small molecule bioregulator in all kingdoms of life. In contemporary biology, H2S is often classified as a "gasotransmitter," meaning that it is an endogenously produced membrane permeable gas that carries out essential cellular processes. Fluorescent probes for H2S and related reactive sulfur species (RSS) detection provide an important cornerstone for investigating the multifaceted roles of these important small molecules in complex biological systems. A now common approach to develop such tools is to develop "activity-based probes" that couple a specific H2S-mediated chemical reaction to a fluorescent output. This Review covers the different types of such probes and also highlights the chemical mechanisms by which each probe type is activated by specific RSS. Common examples include reduction of oxidized nitrogen motifs, disulfide exchange, electrophilic reactions, metal precipitation, and metal coordination. In addition, we also outline complementary activity-based probes for imaging reductant-labile and sulfane sulfur species, including persulfides and polysulfides. For probes highlighted in this Review, we focus on small molecule systems with demonstrated compatibility in cellular systems or related applications. Building from breadth of reported activity-based strategies and application, we also highlight key unmet challenges and future opportunities for advancing activity-based probes for H2S and related RSS.

In Vivo Monitoring of Hydrogen Polysulfide via a NIR-Excitable Reversible Fluorescent Probe Based on Upconversion Luminescence Resonance Energy Transfer

Hydrogen polysulfide (H₂S_n), derived from hydrogen sulfide (H₂S), has attracted increasing attention, which is suggested to be the actual signal molecule instead of H₂S in physiological and pathological processes. Reversible detection of H₂S_n through a NIR-excitable fluorescence probe is an effective means to understand its functions but is quite challenging. Herein, we reported a NIR-excitable ratiometric nanoprobe for the reversible detection of H₂S_n based on luminescence resonance energy transfer principle with upconversion nanoparticles as the energy donor and an organic molecule, SiR1, as the energy acceptor and reversible recognition unit of H₂S_n. The as-prepared nanoprobe exhibited high selectivity and fast response for the reversible detection of H₂S_n, which can monitor the formation and consumption of endogenous H₂S_n in living cells. Because of the reduced autofluorescence by NIR excitation, it was successfully applied for tracking the fluctuation of H₂S_n concentration of mice in physiological and pathological processes including inflammation and liver injury.

Constructing firefly luciferin bioluminescence probes for in vivo imaging

Bioluminescence imaging (BLI) is a widely applied visual approach for real-time detecting many physiological and pathological processes in a variety of biological systems. Based on the caging strategy, lots of bioluminescent probes have been well developed. While the targets react with recognizable groups, caged luciferins liberate luciferase substrates, which react with luciferase generating a bioluminescent response. Among the various bioluminescent systems, the most widely utilized bioluminescent system is the firefly luciferin system. The H and carboxylic acid of luciferin are critically caged sites. The introduced self-immolative linker extends the applications of probes. Firefly luciferin system probes have been successfully applied for analyzing physiological processes, monitoring the environment, diagnosing diseases, screening candidate drugs, and evaluating the therapeutic effect. Here, we systematically review the general design strategies of firefly luciferin bioluminescence probes and their applications. Bioluminescence probes provide a new approach for facilitating investigation in a diverse range of fields. It inspires us to explore more robust light emission luciferin and novel design strategies to develop bioluminescent probes.

Chemiluminescence Measurement of Reactive Sulfur and Nitrogen Species

Significance: Reactive sulfur and nitrogen species such as hydrogen sulfide (H₂S) and nitric oxide (NO^•) are ubiquitous cellular signaling molecules that play central roles in physiology and pathophysiology. A deeper understanding of these signaling pathways will offer new opportunities for therapeutic treatments and disease management. Recent Advances: Chemiluminescence methods have been fundamental in detecting and measuring biological reactive sulfur and nitrogen species, and new approaches are emerging for imaging these analytes in living intact specimens. Ozone-based and luminol-based chemiluminescence methods have been optimized for quantitative analysis of hydrogen sulfide and nitric oxide in biological samples and tissue homogenates, and caged luciferin and 1,2-dioxetanes are emerging as a versatile approach for monitoring and imaging reactive sulfur and nitrogen species in living cells and animal models. Critical Issues: This review article will cover the major chemiluminescence approaches for detecting, measuring, and imaging reactive sulfur and nitrogen species in biological systems, including a brief history of the development of the most established approaches and highlights of the opportunities provided by emerging approaches. Future Directions: Emerging chemiluminescence approaches offer new opportunities for monitoring and imaging reactive sulfur and nitrogen species in living cells, animals, and human clinical samples. Widespread adoption and translation of these approaches, however, requires an emphasis on rigorous quantitative methods, reproducibility, and effective technology transfer. Antioxid. Redox Signal. 36, 337-353.

Molecular Design of d-Luciferin-Based Bioluminescence and 1,2-Dioxetane-Based Chemiluminescence Substrates for Altered Output Wavelength and Detecting Various Molecules

Optical imaging including fluorescence and luminescence is the most popular method for the in vivo imaging in mice. Luminescence imaging is considered to be superior to fluorescence imaging due to the lack of both autofluorescence and the scattering of excitation light. To date, various luciferin analogs and bioluminescence probes have been developed for deep tissue and molecular imaging. Recently, chemiluminescence probes have been developed based on a 1,2-dioxetane scaffold. In this review, the accumulated findings of numerous studies and the design strategies of bioluminescence and chemiluminescence imaging reagents are summarized.

A near-infrared fluorescent probe that can image endogenous hydrogen polysulfides in vivo in tumour-bearing mice

Hydrogen polysulfides (H₂S_n, n > 1), which are important reactive sulfur species, play crucial roles in H₂S-related bioactivities, including antioxidation, cytoprotection, activation of ion channels, transcription factor functions and tumour suppression. Monitoring H₂S_nin vivo is of significant interest for exploring the physiological roles of H₂S_n and the exact mechanisms of H₂S_n-related diseases. Herein, we conceive a novel near-infrared fluorescent probe, NIR-CPS, that is used to detect H₂S_n in living cells and in vivo. With the advantages of high sensitivity, good selectivity and a remarkably large Stokes shift (100 nm), NIR-CPS was successfully applied in visualizing H₂S_n in living cells and mice. More importantly, NIR-CPS monitored H₂S_n stimulated by lipopolysaccharide in tumour-bearing mice. These results demonstrate that the NIR-CPS probe is a potentially powerful tool for the detection of H₂S_nin vivo, thus providing a valuable approach in H₂S_n-related medical research.

Hydrogen sulfide sensing using an aurone-based fluorescent probe

Hydrogen sulfide detection and sensing is an area of interest from both an environmental and a biological perspective. While many methods are currently available, the most sensitive and biologically applicable ones are fluorescence based. In general, these fluorescent probes are based upon large, high-molecular weight, well-characterized fluorescent scaffolds that are synthetically demanding to prepare and difficult to tune and modify. In this study, we have reported a new reduction-based, rationally designed and synthesized turn-on fluorescent probe (Z)-2-(4′-azidobenzylidene)-5-fluorobenzofuran-3(2H)-one (6g) utilizing a low molecular weight aurone fluorophore. During these studies, the modular nature of the synthesis was used to quickly overcome problems with solubility, overlap of excitation of the probe and reduced product, and rate of reaction, resulting in a final compound that is efficient and sensitive for the detection of hydrogen sulfide. The limitation of slow reaction and the reduced fluorescence in a biologically relevent medium was solved by employing cationic surfactant cetyltrimethyl ammonium bromide (CTAB). The probe features a high fluorescence enhancement, fast response (10–30 min), and good sensitivity (1 μm) and selectivity for hydrogen sulfide.

Hydrogen sulfide detection and sensing is an area of interest from both an environmental and a biological perspective.

A new lysosome-targetable fluorescent probe for detection of endogenous hydrogen polysulfides in living cells and inflamed mouse model

Hydrogen polysulfides (H₂S_n, n > 1) belong to sulfane sulfur in the reactive sulfur species (RSS) family and play significant roles in maintaining biological homeostasis in organisms. The detection of H₂S_n in living systems is essential, but further understanding of its "intact" function in living cells has been limited, owing to the lack of appropriate analytical tools. In this work, a new fluorescent probe PP-PS was designed for the detection of endogenous H₂S_n. The probe has a large Stokes shift (178 nm), low detection limit (1 nM), and short response time (1 minute). Besides, PP-PS was successfully applied in the imaging of endogenous H₂S_n in lysosomes of living cancer cells, xenograft mouse tumor tissues, and LPS-induced mouse inflammation tissues. These results revealed that the probe PP-PS could act as a new fluorescence imaging tool to study the function of intracellular hydropolysulfides.