Chemigenetic indicators based on synthetic chelators and green fluorescent protein

Cerium-based nanoplatform for severe acute pancreatitis: Achieving enhanced anti-inflammatory effects through calcium homeostasis restoration and oxidative stress mitigation

Severe acute pancreatitis (SAP), a life-threatening inflammatory disease of the pancreas, has a high mortality rate (∼40 %). Current therapeutic approaches, including antibiotics, trypsin inhibitors, fasting, rehydration, and even continuous renal replacement therapy, yield limited clinical management efficacy. Abnormally elevated calcium levels and reactive oxygen species (ROS) overproduction by damaged mitochondria are key factors in the inflammatory cascade in SAP. The combination of calcium chelators and cerium-based nanozymes loaded with catalase (MOF808@BA@CAT) was developed to bind intracellular calcium, eliminate excessive ROS, and ameliorate the resulting mitochondrial dysfunction, thereby achieving multiple anti-inflammatory effects on SAP. A single low dose of the nanoplatform (1.5 mg kg-1) significantly reduced pancreatic necrosis in SAP rats, effectively ameliorated oxidative stress in the pancreas, improved mitochondrial dysfunction, reduced the proportion of apoptotic cells, and blocked the systemic inflammatory amplification cascade, resulting in the alleviation of systemic inflammation. Moreover, the nanoplatform restored impaired autophagy and inhibited endoplasmic reticulum stress in pancreatic tissue, preserving injured acinar cells. Mechanistically, the administration of the nanoplatform reversed metabolic abnormalities in pancreatic tissue and inhibited the signaling pathways that promote inflammation progression in SAP. This nanoplatform provides a new strategy for SAP treatment, with clinical translation prospects, through ion homeostasis regulation and pancreatic oxidative stress inhibition.

A High-Throughput Biosensing Approach for Rapid Screening of Compounds Targeting the hNav1.1 Channel: Marine Toxins as a Case Study

Voltage-gated sodium (Nav) channels play a crucial role in initiating and propagating action potentials throughout the heart, muscles and nervous systems, making them targets for a number of drugs and toxins. While patch-clamp electrophysiology is considered the gold standard for measuring ion channel activity, its labor-intensive and time-consuming nature highlights the need for fast screening strategies to facilitate a preliminary selection of potential drugs or hazards. In this study, a high-throughput and cost-effective biosensing method was developed to rapidly identify specific agonists and inhibitors targeting the human Nav1.1 (hNav1.1) channel. It combines a red fluorescent dye sensitive to transmembrane potentials with CHO cells stably expressing the hNav1.1 α-subunit (hNav1.1-CHO). In the initial screening mode, the tested compounds were mixed with pre-equilibrated hNav1.1-CHO cells and dye to detect potential agonist effects via fluorescence enhancement. In cases where no fluorescence enhancement was observed, the addition of a known agonist veratridine allowed the indication of inhibitor candidates by fluorescence reduction, relative to the veratridine control without test compounds. Potential agonists or inhibitors identified in the initial screening were further evaluated by measuring concentration-response curves to determine EC50/IC50 values, providing semi-quantitative estimates of their binding strength to hNav1.1. This robust, high-throughput biosensing assay was validated through comparisons with the patch-clamp results and tested with 12 marine toxins, yielding consistent results. It holds promise as a low-cost, rapid, and long-term stable approach for drug discovery and non-target screening of neurotoxins.

A chemigenetic indicator based on a synthetic chelator and a green fluorescent protein for imaging of intracellular sodium ions

A chemigenetic indicator with an affinity suitable for imaging of intracellular sodium ions (Na+) in mammalian cells was developed. The indicator, based on a chimera of green fluorescent protein (GFP) and HaloTag labeled with a synthetic crown ether chelator, was produced by a combination of rational design and directed evolution. In mammalian cells the indicator exhibited an approximately 100% increase in excitation ratio when the cells were treated with 20 mM Na+ and an ionophore.

The best of both worlds: Chemigenetic fluorescent sensors for biological imaging

Synthetic-based fluorescent chemosensors and protein-based fluorescent biosensors are two well-established classes of tools for visualizing and monitoring biological processes in living tissues. Chemigenetic sensors, created using a combination of both synthetic parts and protein parts, are an emerging class of tools that aims to combine the strengths, and overcome the drawbacks, of traditional chemosensors and biosensors. This review will survey the landscape of strategies used for fluorescent chemigenetic sensor design. These strategies include: attachment of synthetic elements to proteins using in vitro protein conjugation; attachment of synthetic elements to proteins using autonomous protein labeling; and translational incorporation of unnatural amino acids.

Hybrid Small-Molecule/Protein Fluorescent Probes

Hybrid small-molecule/protein fluorescent probes are powerful tools for visualizing protein localization and function in living cells. These hybrid probes are constructed by diverse site-specific chemical protein labeling approaches through chemical reactions to exogenous peptide/small protein tags, enzymatic post-translational modifications, bioorthogonal reactions for genetically incorporated unnatural amino acids, and ligand-directed chemical reactions. The hybrid small-molecule/protein fluorescent probes are employed for imaging protein trafficking, conformational changes, and bioanalytes surrounding proteins. In addition, fluorescent hybrid probes facilitate visualization of protein dynamics at the single-molecule level and the defined structure with super-resolution imaging. In this review, we discuss development and the bioimaging applications of fluorescent probes based on small-molecule/protein hybrids.

Bioluminescence Imaging of Potassium Ion Using a Sensory Luciferin and an Engineered Luciferase

Bioluminescent indicators are power tools for studying dynamic biological processes. In this study, we present the generation of novel bioluminescent indicators by modifying the luciferin molecule with an analyte-binding moiety. Specifically, we have successfully developed the first bioluminescent indicator for potassium ions (K+), which are critical electrolytes in biological systems. Our approach involved the design and synthesis of a K+-binding luciferin named potassiorin. Additionally, we engineered a luciferase enzyme called BRIPO (bioluminescent red indicator for potassium) to work synergistically with potassiorin, resulting in optimized K+-dependent bioluminescence responses. Through extensive validation in cell lines, primary neurons, and live mice, we demonstrated the efficacy of this new tool for detecting K+. Our research demonstrates an innovative concept of incorporating sensory moieties into luciferins to modulate luciferase activity. This approach has great potential for developing a wide range of bioluminescent indicators, advancing bioluminescence imaging (BLI), and enabling the study of various analytes in biological systems.

Inflammation and Acinar Cell Dual-Targeting Nanomedicines for Synergistic Treatment of Acute Pancreatitis via Ca2+ Homeostasis Regulation and Pancreas Autodigestion Inhibition

Severe acute pancreatitis (AP) is a life-threatening pancreatic inflammatory disease with a high mortality rate (∼40%). Existing pharmaceutical therapies in development or in clinical trials showed insufficient treatment efficacy due to their single molecular therapeutic target, poor water solubility, short half-life, limited pancreas-targeting specificity, etc. Herein, acid-responsive hollow mesoporous Prussian blue nanoparticles wrapped with neutrophil membranes and surface modified with the N,N-dimethyl-1,3-propanediamine moiety were developed for codelivering membrane-permeable calcium chelator BAPTA-AM (BA) and trypsin activity inhibitor gabexate mesylate (Ga). In the AP mouse model, the formulation exhibited efficient recruitment at the inflammatory endothelium, trans-endothelial migration, and precise acinar cell targeting, resulting in rapid pancreatic localization and higher accumulation. A single low dose of the formulation (BA: 200 μg kg-1, Ga: 0.75 mg kg-1) significantly reduced pancreas function indicators to close to normal levels at 24 h, effectively restored the cell redox status, reduced apoptotic cell proportion, and blocked the systemic inflammatory amplified cascade, resulting in a dramatic increase in the survival rate from 58.3 to even 100%. Mechanistically, the formulation inhibited endoplasmic reticulum stress (IRE1/XBP1 and ATF4/CHOP axis) and restored impaired autophagy (Beclin-1/p62/LC3 axis), thereby preserving dying acinar cells and restoring the cellular "health status". This formulation provides an upstream therapeutic strategy with clinical translation prospects for AP management through synergistic ion homeostasis regulation and pancreatic autodigestion inhibition.

Fluorescent Protein-Based Sensors for Detecting Essential Metal Ions across the Tree of Life

Genetically encoded fluorescent metal ion sensors are powerful tools for elucidating metal dynamics in living systems. Over the last 25 years since the first examples of genetically encoded fluorescent protein-based calcium indicators, this toolbox of probes has expanded to include other essential and non-essential metal ions. Collectively, these tools have illuminated fundamental aspects of metal homeostasis and trafficking that are crucial to fields ranging from neurobiology to human nutrition. Despite these advances, much of the application of metal ion sensors remains limited to mammalian cells and tissues and a limited number of essential metals. Applications beyond mammalian systems and in vivo applications in living organisms have primarily used genetically encoded calcium ion sensors. The aim of this Perspective is to provide, with the support of historical and recent literature, an updated and critical view of the design and use of fluorescent protein-based sensors for detecting essential metal ions in various organisms. We highlight the historical progress and achievements with calcium sensors and discuss more recent advances and opportunities for the detection of other essential metal ions. We also discuss outstanding challenges in the field and directions for future studies, including detecting a wider variety of metal ions, developing and implementing a broader spectral range of sensors for multiplexing experiments, and applying sensors to a wider range of single- and multi-species biological systems.

Bioluminescence Imaging of Potassium Ion Using a Sensory Luciferin and an Engineered Luciferase

Bioluminescent indicators are power tools for studying dynamic biological processes. In this study, we present the generation of novel bioluminescent indicators by modifying the luciferin molecule with an analyte-binding moiety. Specifically, we have successfully developed the first bioluminescent indicator for potassium ions (K+), which are critical electrolytes in biological systems. Our approach involved the design and synthesis of a K+-binding luciferin named potassiorin. Additionally, we engineered a luciferase enzyme called BRIPO (bioluminescent red indicator for potassium) to work synergistically with potassiorin, resulting in optimized K+-dependent bioluminescence responses. Through extensive validation in cell lines, primary neurons, and live mice, we demonstrated the efficacy of this new tool for detecting K+. Our research demonstrates an innovative concept of incorporating sensory moieties into luciferins to modulate luciferase activity. This approach has great potential for developing a wide range of bioluminescent indicators, advancing bioluminescence imaging (BLI), and enabling the study of various analytes in biological systems.

Maximizing the performance of protein-based fluorescent biosensors

Fluorescent protein (FP)-based biosensors are genetically encoded tools that enable the imaging of biological processes in the context of cells, tissues, or live animals. Though widely used in biological research, practically all existing biosensors are far from ideal in terms of their performance, properties, and applicability for multiplexed imaging. These limitations have inspired researchers to explore an increasing number of innovative and creative ways to improve and maximize biosensor performance. Such strategies include new molecular biology methods to develop promising biosensor prototypes, high throughput microfluidics-based directed evolution screening strategies, and improved ways to perform multiplexed imaging. Yet another approach is to effectively replace components of biosensors with self-labeling proteins, such as HaloTag, that enable the biocompatible incorporation of synthetic fluorophores or other ligands in cells or tissues. This mini-review will summarize and highlight recent innovations and strategies for enhancing the performance of FP-based biosensors for multiplexed imaging to advance the frontiers of research.

FNCaMP, ratiometric green calcium indicator based on mNeonGreen protein

Neurobiologists widely use green genetically encoded calcium indicators (GECIs) for visualization of neuronal activity. Among them, ratiometric GECIs allow imaging of both active and non-active neuronal populations. However, they are not popular, since their properties are inferior to intensiometric GCaMP series of GECIs. The most characterized and developed ratiometric green GECI is FGCaMP7. However, the dynamic range and sensitivity of its large Stock's shift green (LSS-Green) form is significantly lower than its Green form and its molecular design is not optimal. To address these drawbacks, we engineered a ratiometric green calcium indicator, called FNCaMP, which is based on bright mNeonGreen protein and calmodulin from A. niger and has optimal NTnC-like design. We compared the properties of the FNCaMP and FGCaMP7 indicators in vitro, in mammalian cells, and in neuronal cultures. Finally, we obtained and analyzed X-ray structure of the FNCaMP indicator.

Fluorescent Sensors for Detecting and Imaging Metal Ions in Biological Systems: Recent Advances and Future Perspectives

Metal ions play a crucial role in many biochemical processes, and when in a state of scarcity or surplus, they can lead to various diseases. Therefore, the development of a selective, sensitive, cost-effective, and fast-responding sensor to detect metal ions is critical for in vitro medical diagnostics. In recent years, fluorescent sensors have been extensively investigated as potent kits for the effective assessment of metal ions in living systems due to their high sensitivity, selectivity, ability to perform real-time, non-invasive monitoring, and versatility. This review is an overview of recent advances in fluorescent sensors for the detection and imaging of metal ions in biosystems from 2018 to date. Specifically, we discuss their application in detecting essential metal ions and non-essential metal ions for in vitro diagnostics, living cell imaging, and in vivo imaging. Finally, we summarize remaining challenges and offer a future outlook on the above topics.