From Live Cells to Caenorhabditis elegans: Selective Staining and Quantification of Lipid Structures Using a Fluorescent Hybrid Benzothiadiazole Derivative

Caenorhabditis elegans endorse bacterial nanocellulose fibers as functional dietary Fiber reducing lipid markers

Bacterial nanocellulose (BNC) is a promising dietary fiber with potential as a functional food additive. We evaluated BNC fibers (BNCf) in the Caenorhabditis elegans model to obtain insight into the BNCf's biointeraction with its gastrointestinal tract while reducing the variables of higher complex animals. BNCf were uptaken and excreted by worms without crossing the intestinal barrier, confirming its biosafety regarding survival rate, reproduction, and aging for concentrations up to 34 μg/ml BNCf. However, a slight decrease in the worms' length was detected. A possible nutrient shortage or stress produced by BNCf was discarded by measuring stress and chemotactic response pathways. Besides, we detected a lipid-lowering effect of BNCf in N2 C. elegans in normal and high-caloric diets. Oxidative damage was computed in N2 worms and Rac1/ced-10 mutants. The GTPase Rac1 is involved in neurological diseases, where its dysregulation enhances ROS production and neuronal damage. BNCf reduced the lipid oxidative markers produced by ROS species in this worm strain. Finally, we detected that BNCf activated the genetic expression of the immunological response and lipid catabolic process. These results strengthen the use of BNCf as a functional dietary fiber and encourage the potential treatment of neurological disease by modulating diet.

Synthesis of Pyridin-1(2H)-ylacrylates and the Effects of Different Functional Groups on Their Fluorescence

While fluorescent organic materials have many potential as well as proven applications and so have attracted significant attention, pyridine-olefin conjugates remain a less studied subset of such systems. Herein, therefore, we report on the development of the straightforward syntheses of pyridin-1(2H)-ylacrylates and the outcomes of a study of the effects of substituents on their fluorescent properties. Such compounds were prepared using a simple, metal-free and three-component coupling reaction involving 2-aminopyridines, sulfonyl azides and propiolates. The fluorescent properties of the ensuing products are significantly affected by the positions of substituents on the cyclic framework, with those located in central positions having the greatest impact. Electron-withdrawing groups tend to induce blue shifts while electron-donating ones cause red shifts. This work highlights the capacity that the micro-modification of fluorescent materials provides for fine-tuning their properties such that they may be usefully applied to, for example, the study of luminescent materials.

Visualizing and quantifying molecular and cellular processes in C. elegans using light microscopy

Light microscopes are the cell and developmental biologists' "best friend", providing a means to see structures and follow dynamics from the protein to the organism level. A huge advantage of C. elegans as a model organism is its transparency, which coupled with its small size means that nearly every biological process can be observed and measured with the appropriate probe and light microscope. Continuous improvement in microscope technologies along with novel genome editing techniques to create transgenic probes have facilitated the development and implementation of a dizzying array of methods for imaging worm embryos, larvae and adults. In this review we provide an overview of the molecular and cellular processes that can be visualized in living worms using light microscopy. A partial inventory of fluorescent probes and techniques successfully used in worms to image the dynamics of cells, organelles, DNA, and protein localization and activity is followed by a practical guide to choosing between various imaging modalities, including widefield, confocal, lightsheet, and structured illumination microscopy. Finally, we discuss the available tools and approaches, including machine learning, for quantitative image analysis tasks, such as colocalization, segmentation, object tracking, and lineage tracing. Hopefully, this review will inspire worm researchers who have not yet imaged their worms to begin, and push those who are imaging to go faster, finer, and longer.

Recent advances in fluorescent probes for lipid droplets

Lipid droplets (LDs) have been known as a non-negligible cellular organelle for lipid storage and metabolism. Fluorescent probes for imaging LDs would be paramount for depicting their functions in cells. Although commercially available Nile Red and BODIPY^tm 493/503 have been widely used for labelling LDs, they exhibit unsatisfactory specificity and spectroscopic properties. This feature article reviews the recent advances in organic fluorescent probes for imaging LDs. We first introduce the key points for probe design, including regulating hydrophobicity and enhancing fluorescence quantum yield in LDs. Then, we summarize the structural features and biological applications of some representative LD probes classified by their frameworks. In addition, the current challenges and future research trends for the fluorescent probes of LDs are discussed as well.

A water-soluble polymer fluorescent probe via RAFT polymerization for dynamic monitoring cellular lipid droplet levels and zebrafish imaging

The realization of dynamic detection of intracellular lipid droplet levels carries far-reaching implications for both the prevention of major diseases and the monitoring of therapeutic environments. Based on such purpose,...

Fluorescent Benzothiadiazole Derivatives as Fluorescence Imaging Dyes: A Decade of New Generation Probes

The current review describes advances in the use of fluorescent 2,1,3-benzothiadiazole (BTD) derivatives after nearly one decade since the first description of bioimaging experiments using this class of fluorogenic dyes. The review describes the use of BTD-containing fluorophores applied as, inter alia, bioprobes for imaging cell nuclei, mitochondria, lipid droplets, sensors, markers for proteins and related events, biological processes and activities, lysosomes, plasma membranes, multicellular models, and animals. A number of physicochemical and photophysical properties commonly observed for BTD fluorogenic structures are also described.

Tunable NIR AIE-active optical materials for lipid droplet imaging in typical model organisms and photodynamic therapy

Near infrared (NIR) luminescent materials with aggregation-induced emission (AIE) features have attracted enormous attention in the areas of medical imaging and diagnostic therapeutics because of their low background fluorescence and strong tissue penetration. This study reports a series of easily synthesized AIEgen molecules that feature NIR emission. These molecules have a donor-donor-π-acceptor (D1-D2-π-A) structure with intramolecular charge transfer (ICT) character. The nature of charge transfer transition can be modified by different structures of D2, i.e. phenyl, thiophene, and furan ring. These AIEgens have high selectivity towards lipid droplets (LDs) in vitro and in vivo, such as zebrafish, Caenorhabditis elegans, and oil crop tissue. In addition, the effect of photodynamic therapy (PDT) on SMMC-7721 cells was investigated, and the results indicate that these AIEgens have potential application for PDT on cancer cells with white light illumination. This study reveals that these triphenylamine (TPA)-based AIEgens have great potential for biological imaging and preclinical applications of PDT.

Deciphering the Dynamics of Organic Nanoaggregates with AIEE Effect and Excited States: Lipophilic Benzothiadiazole Derivatives as Selective Cell Imaging Probes

An aggregation-induced emission enhancement (AIEE) effect in fluorescent lipophilic 2,1,3-benzothiadiazole (BTD) derivatives and their organic nanoaggregates were studied. A set of techniques such as single-crystal X-ray, dynamic light scattering (DLS), electron paramagnetic resonance (EPR), UV-vis, fluorescence, and density functional theory (DFT) calculations have been used to decipher the formation/break (kinetics), properties, and dynamics of the organic nanoaggregates of three BTD small organic molecules. An in-depth study of the excited-state also revealed the preferential relaxation emissive pathways for the BTD derivatives and the dynamics associated with it. The results described herein, for the first time, explain the formation of fluorescent BTD nanoaggregate derivatives and allow for the understanding of their dynamics in solution as well as the ruling forces of both aggregation and break processes along with the involved equilibrium. One of the developed dyes could be used at a nanomolar concentration to selectively stain lipid droplets emitting an intense and bright fluorescence at the red channel. The other two BTDs could also stain lipid droplets at very low concentrations and were visualized preferentially at the blue channel.

Fluorescent Benzoselenadiazoles: Synthesis, Characterization, and Quantification of Intracellular Lipid Droplets and Multicellular Model Staining

In this work, we described the synthesis of 10 new fluorescent 2,1,3-benzoselenadiazole small-molecule derivatives and their chemical- and photocharacterizations. The new derivatives could, for the first time, be successfully applied as selective live cell imaging probes (at nanomolar concentrations) and stained lipid-based structures preferentially. Density functional theory (DFT) calculations were used to help in understanding the photophysical data and the intramolecular charge-transfer (ICT) processes of the synthesized dyes. Some derivatives showed impressive cellular responses, allowing them to be tested as probes in a complex multicellular model (i.e., Caenorhabditis elegans). When compared with the commercially available dye, the new fluorescent compounds showed far better results both at the cellular level and inside the live worm. Inside the multicellular complex model, the tested probes also showed selectivity, a feature not observed when the commercial dye was used to carry out the bioimaging experiments.

Visualization of Lipid Droplets in Living Cells and Fatty Livers of Mice Based on the Fluorescence of π-Extended Coumarin Using Fluorescence Lifetime Imaging Microscopy

Lipid droplets (LDs) are closely related to lipid metabolism in living cells and are highly associated with diverse diseases such as fatty liver, diabetes, and cancer. Herein we describe a π-extended fluorescent coumarin (PC6S) for visualizing LDs in living cells and in the tissues of living mice using confocal fluorescence lifetime imaging microscopy (FLIM). PC6S showed a large positive solvatochromic shift and high fluorescence quantum yield (>0.80) in both nonpolar and polar solvents. Additionally, the fluorescence lifetimes of PC6S were largely dependent on solvent polarity. The excellent spectral and photophysical properties of PC6S allowed its selective staining of LDs in living and fixed cells, and multicolor imaging. Fluorescence lifetime measurements of PC6S allowed estimation of the apparent polarity of LDs. The high photostability and long intracellular retention of PC6S supported in situ visualization of the formation processes of LDs resulting from the accumulation of fatty acid. Furthermore, intravenous administration of PC6S and use of the FLIM system allowed the imaging of LDs in hepatocytes in living normal mice and the growth of LDs resulting from the excess accumulation of lipids in high-fat-diet-fed mice (fatty liver model mice). Taking advantage of the high selectivity and sensitivity of PC6S for LDs in liver, we could visualize the adipocytes of lipid-rich tissues and LDs in kidney peritubular cells by PC6S fluorescence. These results demonstrated that PC6S combined with a FLIM system can be useful for monitoring and tracking the formation of LDs in both cultured cells and specific tissues and organs.

Highly selective staining and quantification of intracellular lipid droplets with a compact push–pull fluorophore based on benzothiadiazole

A robust lipophilic dye, based on the structures of the benzothiadiazole heterocycle, was shown to be a potent fluorescent stain for the selective imaging of lipid droplets (LDs) within both live and fixed human cells.

Plasma membrane imaging with a fluorescent benzothiadiazole derivative

This work describes a novel fluorescent 2,1,3-benzothiadiazole derivative designed to act as a water-soluble and selective bioprobe for plasma membrane imaging. The new compound was efficiently synthesized in a two-step procedure with good yields. The photophysical properties were evaluated and the dye proved to have an excellent photostability in several solvents. DFT calculations were found in agreement with the experimental data and helped to understand the stabilizing intramolecular charge-transfer process from the first excited state. The new fluorescent derivative could be applied as selective bioprobe in several cell lines and displayed plasma-membrane affinity during the imaging experiments for all tested models.

Expanding the Biological Application of Fluorescent Benzothiadiazole Derivatives: A Phenotypic Screening Strategy for Anthelmintic Drug Discovery Using Caenorhabditis elegans

The current methodologies used to identify promising new anthelmintic compounds rely on subjective microscopic examination of worm motility or involve genetic modified organisms. We describe a new methodology to detect worm viability that takes advantage of the differential incorporation of the fluorescent molecular marker propidium iodide and the 2,1,3-benzothiadiazole core, which has been widely applied in light technology. The new assay developed could be validated using the "Pathogen Box" library. By use of this bioassay, it was possible to identify three molecules with activity against Caenorhabditis elegans that were previously described as effective in in vitro assays against other pathogens, such as Schistosoma mansoni, Mycobacterium tuberculosis, and Plasmodium falciparum, accelerating the identification of molecules with anthelmintic potential. The current fluorescence-based bioassay may be used for assessing C. elegans viability. The described methodology replaces the subjectivity of previous assays and provides an enabling technology that is useful for rapid in vitro screens of both natural and synthetic compound libraries. It is expected that the results obtained from these robust in vitro screens would select the most effective compounds for follow-up in vivo experimentation with pathogenic helminths.

Recent Advances in Fluorescent Probes for Lipid Droplets

Lipid droplets (LDs) are organelles that serve as the storage of intracellular neutral lipids. LDs regulate many physiological processes. They recently attracted attention after extensive studies showed their involvement in metabolic disorders and diseases such as obesity, diabetes, and cancer. Therefore, it is of the highest importance to have reliable imaging tools. In this review, we focus on recent advances in the development of selective fluorescent probes for LDs. Their photophysical properties are described, and their advantages and drawbacks in fluorescence imaging are discussed. At last, we review the reported applications using these probes including two-photon excitation, in vivo and tissue imaging, as well as LDs tracking.

The fluorescent biomarkers for lipid droplets with quinolone-coumarin unit

Two dyes with high quantum yields were designed and synthesized for imaging lipid droplets in living and fixed cells.