Guest-host doped strategy for constructing ultralong-lifetime near-infrared organic phosphorescence materials for bioimaging.

Organic near-infrared room temperature phosphorescence materials have unparalleled advantages in bioimaging due to their excellent penetrability. However, limited by the energy gap law, the near-infrared phosphorescence materials (>650 nm) are very rare, moreover, the phosphorescence lifetimes of these materials are very short. In this work, we have obtained organic room temperature phosphorescence materials with long wavelengths (600/657-681/732 nm) and long lifetimes (102-324 ms) for the first time through the guest-host doped strategy. The guest molecule has sufficient conjugation to reduce the lowest triplet energy level and the host assists the guest in exciton transfer and inhibits the non-radiative transition of guest excitons. These materials exhibit good tissue penetration in bioimaging. Thanks to the characteristic of long lifetime and long wavelength emissive phosphorescence materials, the tumor imaging in living mice with a signal to background ratio value as high as 43 is successfully realized. This work provides a practical solution for the construction of organic phosphorescence materials with both long wavelengths and long lifetimes.

EpoR-tdTomato-Cre mice enable identification of EpoR expression in subsets of tissue macrophages and hematopoietic cells.

The erythropoietin receptor (EpoR) has traditionally been thought of as an erythroid-specific gene. Notably, accumulating evidence suggests that EpoR is expressed well beyond erythroid cells. However, the expression of EpoR in non-erythroid cells has been controversial. In this study, we generated EpoR-tdTomato-Cre mice and used them to examine the expression of EpoR in tissue macrophages and hematopoietic cells. We show that in marked contrast to the previously available EpoR-eGFPcre mice, in which a very weak eGFP signal was detected in erythroid cells, tdTomato was readily detectable in both fetal liver (FL) and bone marrow (BM) erythroid cells at all developmental stages and exhibited dynamic changes during erythropoiesis. Consistent with our recent finding that erythroblastic island (EBI) macrophages are characterized by the expression of EpoR, tdTomato was readily detected in both FL and BM EBI macrophages. Moreover, tdTomato was also detected in subsets of hematopoietic stem cells, progenitors, megakaryocytes, and B cells in BM as well as in spleen red pulp macrophages and liver Kupffer cells. The expression of EpoR was further shown by the EpoR-tdTomato-Cre-mediated excision of the floxed STOP sequence. Importantly, EPO injection selectively promoted proliferation of the EpoR-expressing cells and induced erythroid lineage bias during hematopoiesis. Our findings imply broad roles for EPO/EpoR in hematopoiesis that warrant further investigation. The EpoR-tdTomato-Cre mouse line provides a powerful tool to facilitate future studies on EpoR expression and regulation in various non-hematopoietic cells and to conditionally manipulate gene expression in EpoR-expressing cells for functional studies.

Small-molecule inhibitors of histone deacetylase improve CRISPR-based adenine base editing.

CRISPR-based base editors (BEs) are widely used to induce nucleotide substitutions in living cells and organisms without causing the damaging DNA double-strand breaks and DNA donor templates. Cytosine BEs that induce C:G to T:A conversion and adenine BEs that induce A:T to G:C conversion have been developed. Various attempts have been made to increase the efficiency of both BEs; however, their activities need to be improved for further applications. Here, we describe a fluorescent reporter-based drug screening platform to identify novel chemicals with the goal of improving adenine base editing efficiency. The reporter system revealed that histone deacetylase inhibitors, particularly romidepsin, enhanced base editing efficiencies by up to 4.9-fold by increasing the expression levels of proteins and target accessibility. The results support the use of romidepsin as a viable option to improve base editing efficiency in biomedical research and therapeutic genome engineering.

Engineering luminescent pectin-based hydrogel for highly efficient multiple sensing.

Luminescent hydrogels with sensing capabilities have attracted much interest in recent years, especially those responsive to stimuli, making such materials potential for various applications. Pectin is a high-molecular-weight carbohydrate polymer that has the ability to form hydrogel upon heating or mixing with divalent cations. However, intrinsic pectin gels are weak and lack of functionalities. In this study, lanthanide ions and silk fibroin derived carbon dots were incorporated into Pectin/PVA hydrogel (PPH) to form luminescent tough hydrogels. The luminescence of the hydrogel can be tuned by adjusting the ratio of blue emission carbon dots to Eu3+ ions (red emission) and Tb3+ ions (green emission). Such incorporation of emitters only slightly changed the mechanical properties of the tough hydrogel. Notably, the luminescent Pectin/PVA hydrogel (LPPH) showed chromic response to external stimuli, like pH and metal ions. By measuring the ratio of luminescent intensity at 473 nm and 617 nm (I473/I617), the pH response can be quantified in high sensitivity. In addition, the specific detection of Cu2+ and Fe3+ ions using the fabricated hydrogel were demonstrated, the mechanism was also proposed. The different chromic responses to Fe2+ and Fe3+ endow the luminescent tough Pectin/PVA hydrogel potential for multiple sensing applications.

Super-Resolution Live Cell Microscopy of Membrane-Proximal Fluorophores.

Here, we present a simple and robust experimental setup for the super-resolution live cell microscopy of membrane-proximal fluorophores, which is comparably easy to perform and to implement. The method is based on Structured Illumination Microscopy (SIM) with a switchable spatial light modulator (SLM) and exchangeable objective lenses for epi-illumination and total internal reflection fluorescence (TIRF) microscopy. While, in the case of SIM (upon epi-illumination), cell layers of about 1-2 µm in close proximity to the plasma membrane can be selected by software, layers in the 100 nm range are assessed experimentally by TIRF-SIM. To show the applicability of this approach, both methods are used to measure the translocation of the glucose transporter 4 (GLUT4) from intracellular vesicles to the plasma membrane upon stimulation by insulin or insulin-mimetic compounds, with a lateral resolution of around 100 nm and an axial resolution of around 200 nm. While SIM is an appropriate method to visualize the intracellular localization of GLUT4 fused with a green fluorescent protein, TIRF-SIM permits the quantitative evaluation of its fluorescence in the plasma membrane. These imaging methods are discussed in the context of fluorescence lifetime kinetics, providing additional data for the molecular microenvironment.

A Dual-Emissive Phosphorescent Polymeric Probe for Exploring Drug-Induced Liver Injury via Imaging of Peroxynitrite Elevation In Vivo.

Drug-induced liver injury (DILI) is a widespread clinical problem. The pathophysiological mechanisms of DILI are complicated, and the traditional diagnostic methods for DILI have their limitations. Owing to its convenient operation, high sensitivity, and high specificity, luminescent sensing and imaging as an indispensable tool in biological research and clinical trials may provide an important means for DILI study. Herein, we report the rational design and preparation of a near-infrared dual-phosphorescent polymeric probe (P-ONOO) for exploring the DILI via specific imaging of peroxynitrite (ONOO-) elevation in vivo, which was one of early markers of DILI and very difficult to be detected due to its short half-life and high reactive activity. With the utilization of P-ONOO, the raised ONOO- was visualized successfully in the drug-treated hepatocytes with a high signal-to-noise ratio via ratiometric and time-resolved photoluminescence imaging. Importantly, the ONOO- boost in the acetaminophen-induced liver injury in real time was verified, and the direct observation of the elevated ONOO- production in ketoconazole-induced liver injury was achieved for the first time. Our findings may contribute to understanding the exact mechanism of ketoconazole-induced hepatotoxicity that is still ambiguous. Notably, this luminescent approach for revealing the liver injury works fast and conveniently.

Engineering of galectin-3 for glycan-binding optical imaging.

Galectin-3 (Gal-3) is a multifunctional glycan-binding protein that participates in many pathophysiological events and has been described as a biomarker and potential therapeutic target for severe disorders, such as cancer. Several probes for Gal-3 or its ligands have been developed, however both the pathophysiological mechanisms and potential biomedical applications of Gal-3 remain not fully assessed. Molecular imaging using bioluminescent probes provides great sensitivity for in vivo and in vitro analysis for both cellular and whole multicellular organism tracking and target detection. Here, we engineered a chimeric molecule consisting of Renilla luciferase fused with mouse Gal-3 (RLuc-mGal-3). RLuc-mGal-3 preparation was highly homogenous, soluble, active, and has molecular mass of 65,870.95 Da. This molecule was able to bind to MKN45 cell surface, property which was inhibited by the reduction of Gal-3 ligands on the cell surface by the overexpression of ST6GalNAc-I. In order to obtain an efficient and stable delivery system, RLuc-mGal-3 was adsorbed to poly-lactic acid nanoparticles, which increased binding to MKN45 cells in vitro. Furthermore, bioluminescence imaging showed that RLuc-mGal-3 was able to indicate the presence of implanted tumor in mice, event drastically inhibited by the presence of lactose. This novel bioluminescent chimeric molecule offers a safe and highly sensitive alternative to fluorescent and radiolabeled probes with potential application in biomedical research for a better understanding of the distribution and fate of Gal-3 and its ligands in vitro and in vivo.

Targeted Luminescent Europium Peptide Conjugates: Comparative Analysis Using Maleimide and para-Nitropyridyl Linkages for Organelle Staining.

The syntheses and photophysical behavior of nine strongly luminescent nonadentate Eu(III) complexes are reported. Each complex is based on N-functionalized 1,4,7-triazacyclononane, and linkage to other groups or targeting vectors can occur either via amide bond formation to a coordinated pyridine p-aminopropyl group or via a nucleophilic substitution reaction involving thiol attack on a metal coordinated p-nitropyridyl moiety. Evidence is presented in favor of the latter conjugation strategy, as parallel work with maleimide conjugates was complicated or compromised by the propensity to undergo post-conjugation thiol exchange or succinimide ring hydrolysis reactions. Confocal microscopy and spectral imaging studies revealed that the peptide conjugate of AcCFFKDEL was found to localize selectively in the endoplasmic reticulum of mouse fibroblast cells, whereas the related maleimide conjugate was only observed in cellular lysosomes.

Beyond the Green Fluorescent Protein: Biomolecular Reporters for Anaerobic and Deep-Tissue Imaging.

Fluorescence imaging represents cornerstone technology for studying biological function at the cellular and molecular levels. The technology's centerpiece is a prolific collection of genetic reporters based on the green fluorescent protein (GFP) and related analogs. More than two decades of protein engineering have endowed the GFP repertoire with an incredible assortment of fluorescent proteins, allowing scientists immense latitude in choosing reporters tailored to various cellular and environmental contexts. Nevertheless, GFP and derivative reporters have specific limitations that hinder their unrestricted use for molecular imaging. These challenges have inspired the development of new reporter proteins and imaging mechanisms. Here, we review how these developments are expanding the frontiers of reporter gene techniques to enable nondestructive studies of cell function in anaerobic environments and deep inside intact animals-two important biological contexts that are fundamentally incompatible with the use of GFP-based reporters.

Low Dose of X-Ray-Excited Long-Lasting Luminescent Concave Nanocubes in Highly Passive Targeting Deep-Seated Hepatic Tumors.

Chromium-doped zinc gallate, ZnGa2 O4 :Cr3+ (ZGC), is viewed as a long-lasting luminescence (LLL) phosphor that can avoid tissue autofluorescence interference for in vivo imaging detection. ZGC is a cubic spinel structure, a typical agglomerative or clustered morphology lacking a defined cubic shape, but a sphere-like feature is commonly obtained for the nanometric ZGC. The substantial challenge remains achieving a well-defined cubic feature in nanoscale. The process by which dispersed and well-defined concave cubic ZGC is obtained is described, exhibiting much stronger LLL in UV and X-ray excitation for the dispersed cubic ZGC compared with the agglomerative form that cannot be excited using X-rays with a low dose of 0.5 Gy. The cubic ZGC reveals a specific accumulation in liver and 0.5 Gy used at the end of X-ray excitation is sufficient for imaging of deep-seated hepatic tumors. The ZGC nanocubes show highly passive targeting of orthotopic hepatic tumors.

Outer-Frame-Degradable Nanovehicles Featuring Near-Infrared Dual Luminescence for in Vivo Tracking of Protein Delivery in Cancer Therapy.

In vivo monitoring of cargo protein delivery is critical for understanding the pharmacological efficacies and mechanisms during cancer therapy, but it still remains a formidable challenge because of the difficulty in observing nonfluorescent proteins at high resolution and sensitivity. Here we report an outer-frame-degradable nanovehicle featuring near-infrared (NIR) dual luminescence for real-time tracking of protein delivery in vivo. Upconversion nanoparticles (UCNPs) and fluorophore-doped degradable macroporous silica (DS) with spectral overlap were coupled to form a core-shell nanostructure as a therapeutic protein nanocarrier, which was eventually enveloped with a hyaluronic acid (HA) shell to prevent protein leakage and for recognizing tumor sites. The DS layer served as both a container to accommodate the therapeutic proteins and a filter to attenuate upconversion luminescence (UCL) of the inner UCNPs. After the nanovehicles selectively accumulated at tumor sites and entered cancer cells, intracellular hyaluronidase (HAase) digested the outermost HA protective shell and initiated the outer frame degradation-induced protein release and UCL restoration of UCNPs in the intracellular environment. Significantly, the biodistribution of the nanovehicles can be traced at the 710 nm NIR fluorescence channel of DS, whereas the protein release can be monitored at the 660 nm NIR fluorescence channel of UCNPs. Real-time tracking of protein delivery and release was achieved in vitro and in vivo by NIR fluorescence imaging. Moreover, in vitro and in vivo studies manifest that the protein cytochrome c-loaded nanovehicles exhibited excellent cancer therapeutic efficacy. This nanoplatform assembled by the outer-frame-degradable nanovehicles featuring NIR dual luminescence not only advances our understanding of where, when, and how therapeutic proteins take effect in vivo but also provides a universal route for visualizing the translocation of other bioactive macromolecules in cancer treatment and intervention.

Luminescent anticancer ruthenium(ii)-p-cymene complexes of extended imidazophenanthroline ligands: synthesis, structure, reactivity, biomolecular interactions and live cell imaging.

Of late, cancer has become a terrible disease affecting people throughout the world. Keeping this in mind, we tried to design drugs that are more lipophilic, target-specific, water-soluble, cytoselective and fluorescent. In this regard, we reported novel ruthenium(ii)-p-cymene imidazophenanthroline scaffolds as effective DNA targeting agents. The planarity of imidazophenanthroline ligands caused the Ru(ii) complex to be a good intercalator. An extended π-electronic conjugation was introduced in the imidazophenanthroline moieties through the Suzuki and Sonogashira coupling reactions. Here, we synthesized nine Ru(ii) complexes (16a-b, 17a-d, and 19a-c). Among these, [(η6-p-cymene)RuCl(K2-N,N-2-(4'-methyl-[1,1'-BIphenyl]-4-yl)-1H-imidazo[4,5-f][1,10]phenanthroline)]·PF6 (16b) exhibited the best potency and selectivity with excellent cellular uptake; [(η6-p-cymene)RuCl(K2-N,N-2-(4-(phenylethynyl)phenyl)-1H-imidazo[4,5-f][1,10]phenanthroline)]·PF6 (17a) acted as a cytoselective probe for live cell imaging.

Transmigration of Trypanosoma cruzi Trypomastigotes through 3D Spheroids Mimicking Host Tissues.

While cellular invasion by T. cruzi trypomastigotes and intracellular amastigote replication are well-characterized events that have been described by using 2D monolayer cultures, other relevant parasite-host interactions, like the dynamics of tissue invasiveness, cannot be captured using monolayer cultures. Spheroids constitute a valuable three-dimensional (3D) culture system because they mimic the microarchitecture of tissues and provide an environment similar to the encountered in natural infections, which includes the presence of extracellular matrix as well as 3D cell-cell interactions. In this work, we describe a protocol for studying transmigration of T. cruzi trypomastigotes into 3D spheroids. In the experimental setup, cells and parasites are labelled with two fluorescent dyes, allowing their visualization by confocal microscopy. We also describe the general procedure and setting of the confocal microscope and downstream applications for acquisition and reconstruction of 3D images. This model was employed to analyze the transmigration of trypomastigotes from the highly virulent and pantropic RA T. cruzi strain. Of course, other aspects encountered by T. cruzi in the mammalian host environment can be studied with this methodology.

Exploiting Genetically Modified Dual-Reporter Strains to Monitor Experimental Trypanosoma cruzi Infections and Host-Parasite Interactions.

Trypanosoma cruzi is the causative agent of Chagas disease, the most important parasitic infection in Latin America. Despite a global research effort, there have been no significant treatment advances for at least 40 years. Gaps in our knowledge of T. cruzi biology and pathogenesis have been major factors in limiting progress. In addition, the extremely low parasite burden during chronic infections has complicated the monitoring of both disease progression and drug efficacy, even in predictive animal models. To address these problems, we genetically modified T. cruzi to express a red-shifted luciferase. Mice infected with these highly bioluminescent parasites can be monitored by in vivo imaging, with exquisite sensitivity. However, a major drawback of bioluminescence imaging is that it does not allow visualization of host-parasite interactions at a cellular level. To facilitate this, we generated T. cruzi strains that express a chimeric protein that is both bioluminescent and fluorescent. Bioluminescence allows the tissue location of infection foci to be identified, and fluorescence can then be exploited to detect parasites in histological sections derived from excised tissue. In this article, we describe in detail the in vivo imaging and confocal microscopy protocols that we have developed for visualizing T. cruzi parasites expressing these dual-reporter fusion proteins. The approaches make it feasible to locate individual parasites within chronically infected murine tissues, to assess their replicative status, to resolve the nature of host cells, and to characterize their immunological context.

In Situ Detection of Dormant Trypanosoma cruzi Amastigotes Using Bioluminescent-Fluorescent Reporters.

Chagas disease agent, Trypanosoma cruzi, is capable to persist after prolonged drug treatment using effective drugs. The reason of treatment failure is not known, but recent development of highly sensible bioluminescence imaging coupled to tissue clarification techniques has made possible the detection of individual amastigotes within chronically infected murine tissues and the study of their replicative status. In this chapter, we provide a step-by-step explanation for these protocols that allowed the visualization of nonproliferating amastigotes in tissues of chronically infected mice for the first time.

Comparison of phosphorescent agents for noninvasive sensing of tumor oxygenation via Cherenkov-excited luminescence imaging.

Cherenkov emission generated in tissue during radiotherapy can be harnessed for the imaging biochemistry of tissue microenvironments. Cherenkov-excited luminescence scanned imaging (CELSI) provides a way to optically and noninvasively map oxygen-related signals, which is known to correlate to outcomes in radiotherapy. Four candidate phosphorescent reagents PtG4, MM2, Ir(btb)2 ( acac ) , and MitoID were studied for oxygen sensing, testing in a progressive series of (a) in solution, (b) in vitro, and (c) in subcutaneous tumors. In each test, the signal strength and response to oxygen were assessed by phosphorescence intensity and decay lifetime measurement. MM2 showed the most robust response to oxygen changes in solution, followed by PtG4, Ir(btb)2 ( acac ) , and MitoID. However, in PANC-1 cells, their oxygen responses differed with Ir(btb)2 ( acac ) exhibiting the largest phosphorescent intensity change in response to changes in oxygenation, followed by PtG4, MM2, and MitoID. In vivo, it was only possible to utilize Ir(btb)2 ( acac ) and PtG4, with each being used at nanomole levels, to determine signal strength, lifetime, and pO2. Oxygen sensing with CELSI during radiotherapy is feasible and can estimate values from 1 mm regions of tissue when used in the configuration of this study. PtG4 was the most amenable to in vivo sensing on the timescale of external beam LINAC x-rays.

Development and Applications of Bioluminescent and Chemiluminescent Reporters and Biosensors.

Although fluorescent reporters and biosensors have become indispensable tools in biological and biomedical fields, fluorescence measurements require external excitation light, thereby limiting their use in thick tissues and live animals. Bioluminescent reporters and biosensors may potentially overcome this hurdle because they use enzyme-catalyzed exothermic biochemical reactions to generate excited-state emitters. This review first introduces the development of bioluminescent reporters, and next, their applications in sensing biological changes in vitro and in vivo as biosensors. Lastly, we discuss chemiluminescent sensors that produce photons in the absence of luciferases. This review aims to explore fundamentals and experimental insights and to emphasize the yet-to-be-reached potential of next-generation luminescent reporters and biosensors.

Imaging Intracellular Ca2+ in Cardiomyocytes with Genetically Encoded Fluorescent Probes.

Calcium (Ca2+) is a key player in cardiomyocyte homeostasis, and its roles span from excitation-contraction coupling to metabolic and structural signaling. Alterations in the function or expression of Ca2+-handling proteins are common findings in failing cardiomyocytes, which have been linked to impaired contractility and detrimental remodeling of the cellular structure. For these reasons, the study of intracellular Ca2+ handling in cardiomyocytes represents a central method in experimental molecular cardiology.

Construction of DNA-NanoLuc luciferase conjugates for DNA aptamer-based sandwich assay using Rep protein.

OBJECTIVE: We developed a DNA-NanoLuc luciferase (NnaoLuc) conjugates for DNA aptamer-based sandwich assay using the catalytic domain of the replication initiator protein derived from porcine circovirus type 2 (pRep). RESULTS: For construction of DNA aptamer and NanoLuc conjugate using the catalytic domain of Rep from PCV2. pRep fused to NanoLuc was genetically constructed and expressed in E. coli. After purification, the activities of fused pRep and NanoLuc were evaluated, and DNA-NanoLuc conjugates were constructed via the fused pRep. Finally, constructed DNA-NanoLuc conjugates were applied for use in a DNA aptamer-based sandwich assay. Here, pRep was used not only for conjugation of the NanoLuc to the detection aptamer, but also for immobilization of the capture aptamer on the plate surface. CONCLUSION: We have demonstrated that DNA-NanoLuc conjugates via the catalytic domain of PCV2 Rep could be applied for DNA aptamer-based sandwich assay system.

Generation and Characterization of a Dual-Reporter Transgenic Leishmania braziliensis Line Expressing eGFP and Luciferase.

In this study, we generated a transgenic strain of Leishmania braziliensis, an etiological agent associated with a diversity of clinical manifestations of leishmaniasis ranging from localized cutaneous to mucocutaneous to disseminated disease. Transgenic parasites expressing reporter proteins are valuable tools for studies of parasite biology, host-pathogen interactions, and anti-parasitic drug development. To this end, we constructed an L. braziliensis line stably expressing the reporters eGFP and luciferase (eGFP-LUC L. braziliensis). The integration cassette co-expressing the two reporters was targeted to the ribosomal locus (SSU) of the parasite genome. Transgenic parasites were characterized for their infectivity and stability both in vitro and in vivo. Parasite maintenance in axenic long-term culture in the absence of selective drugs did not alter expression of the two reporters or infection of BALB/c mice, indicating stability of the integrated cassette. Infectivity of eGFP-LUC, L. braziliensis, both in vivo and in vitro was similar to that obtained with the parental wild type strain. The possibility of L. braziliensis tracking and quantification using fluorescence and luminescence broadens the scope of research involving this neglected species, despite its importance in terms of public health concerning the leishmaniasis burden.