BF2 group chelated AIE fluorescent probe for polarity mapping of lipid droplets in cells and in vivo

A novel near-infrared AIE probe for sensitive imaging of lipid droplet and dual-parameter cancer diagnosis

BACKGROUND

Lipid droplets (LDs) are vital intracellular organelles for lipid storage, closely associated with various metabolic disorders and cancers. Fluorescence imaging offers a powerful, non-invasive approach to study LDs in real time, but many existing probes suffer from non-specific staining and aggregation-caused quenching (ACQ), compromising their imaging specificity and contrast.

RESULT

In this study, we synthesized a novel LD fluorescent probe TPC-AN that takes advantage of near-infrared emission, large Stokes shift, high lipophilicity, polarity response and aggregation-induced emission (AIE) characteristics. TPC-AN effectively addresses issues of non-specific staining and ACQ commonly observed with traditional probes, enabling highly specific and high-contrast imaging of LDs. Utilizing TPC-AN, imaging of LDs in several kinds of cells was performed, and discrimination of cancerous and normal cells was achieved using dual-parameter through differences in LD fluorescence area and intensity.

SIGNIFICANCE

This work provides a promising tool for studying LDs in diseases and offers a reliable method for cancer diagnosis, with excellent LD-specificity, low cytotoxicity, and dual-parameter imaging capabilities.

Aggregation-induced emission-based fluorescent probes for cellular microenvironment detection

The cellular microenvironment exerts a pivotal regulatory influence on cell survival, function, and behavior. Dynamic analysis and detection of the cellular microenvironment can promptly elucidate changes in cellular microenvironmental information, uncover the pathogenesis of diseases associated with aberrant microenvironments, and aid in predicting disease risk and monitoring disease progression. Aggregation-induced emission (AIE) fluorescent molecules possess unique AIE characteristics and offer significant advantages in imaging and sensing cellular microenvironments. In this review, we present a profile of the remarkable progress achieved in utilizing AIE fluorescent molecules for detecting cellular microenvironments in recent years. We particularly focus on AIE fluorescent probes applied in imaging key parameters of the cellular microenvironment, including pH, viscosity, polarity, and temperature, as well as in analyzing critical biological components of the microenvironment, such as gas signal molecules, metal ions, redox state, and proteins. We underscore the design principles, detection mechanisms, sensing performance, and biological applications of these fluorescent probes. Furthermore, we address the current challenges confronting this field and provide prospects for the future development of AIE probes used for microenvironment detection. We trust that this review will inspire researchers to develop more precise and sensitive AIE fluorescent probes for the detection of cellular microenvironments.

Rational design of an AIEgen for imaging lipid droplets polarity change during ferroptosis

Ferroptosis can regulate cell death by accumulating lipid peroxides, affecting the structure and polarity of lipid droplets (LDs), but clear evidence is still lacking. Fluorescence imaging is the most powerful technique for studying LDs' function. However, developing AIE fluorescent probes with high selectivity and sensitivity for targeting LDs remains challenging. In this study, we rationally designed an AIEgen, as a novel fluorescent probe TPE-BD, by constructing a push-pull electron structure. The probe has benzo[b]thiophene-3(2H)-one 1,1-dioxide as the electron acceptor, tetraphenylethylene (AIE skeleton) as the electron donor, and thiophene as the bridging group. The optical performance of probe TPE-BD indicated that the UV-visible absorption spectrum of the probe was minimally affected by solvent polarity (except for glycerol and PBS solvents), but the fluorescence of probe is very sensitive to changes in polarity, achieving the goal of polarity detection in LDs. CCK-8 assay and cell imaging experiments demonstrated that probe TPE-BD exhibited good cell compatibility and effectively targeted LDs, enabling the monitoring of LDs' polarity and quantity during ferroptosis.

A fluorescence probe for imaging lipid droplet and visualization of diabetes-related polarity variations

Diabetes mellitus is a disorder that affects lipid metabolism. Abnormalities in the lipid droplets (LDs) can lead to disturbances in lipid metabolism, which is a significant feature of diabetic patients. Nevertheless, the correlation between diabetes and the polarity of LDs has received little attention in the scientific literature. In order to detect LDs polarity changes in diabetes illness models, we created a new fluorescence probe LD-DCM. This probe has a stable structure, high selectivity, and minimal cytotoxicity. The probe formed a typical D-π-A molecular configuration with triphenylamine (TPA) and dicyanomethylene-4H-pyran (DCM) as electron donor and acceptor parts. The LD-DCM molecule has an immense solvatochromic effect (λem = 544-624 nm), fluorescence enhancement of around 150 times, and a high sensitivity to polarity changes within the linear range of Δf = 0.28 to 0.32, all due to its distinctive intramolecular charge transfer effect (ICT). In addition, LD-DCM was able to monitor the accumulation of LDs and the reduction of LDs polarity in living cells when stimulated by oleic acid, lipopolysaccharide, and high glucose. More importantly, LD-DCM has also been used effectively to detect polarity differences in organs from diabetic, drug-treated, and normal mice. The results showed that the liver polarity of diabetic mice was lower than that of normal mice, while the liver polarity of drug-treated mice was higher than that of diabetic mice. We believe that LD-DCM has the potential to serve as an efficient instrument for the diagnosis of disorders that are associated with the polarity of LDs.

Dynamic Imaging of Lipid Droplets in Cells and Tissues by Using Dioxaborine Barbiturate-Based Fluorogenic Probes

Lipids are essential for various cellular functions, including energy storage, membrane flexibility, and signaling molecule production. Maintaining proper lipid levels is important to prevent health problems such as cancer, neurodegenerative disorders, cardiovascular diseases, obesity, and diabetes. Monitoring cellular lipid droplets (LDs) in real-time with high resolution can provide insights into LD-related pathways and diseases owing to the dynamic nature of LDs. Fluorescence-based imaging is widely used for tracking LDs in live cells and animal models. However, the current fluorophores have limitations such as poor photostability and high background staining. Herein, we developed a novel fluorogenic probe based on a push-pull interaction combined with aggregation-induced emission enhancement (AIEE) for dynamic imaging of LDs. Probe 1 exhibits favorable membrane permeability and spectroscopic characteristics, allowing specific imaging of cellular LDs and time-lapse imaging of LD accumulation. This probe can also be used to examine LDs in fruit fly tissues in various metabolic states, serving as a highly versatile and specific tool for dynamic LD imaging in cellular and tissue environments.

Constructing lipid droplet-targeting photosensitizers based on coumarins with NIR emission

The development of photosensitizers (PSs) with subcellular targeting capability has raised interest for photodynamic therapy (PDT) research. In this work, two coumarin-based photosensitizers (C-S-2 and C-S-3) were designed and synthesized via expanding their π-conjugation, introducing strong electron-donor and acceptor groups, and adopting sulfur substitution strategy. These sulfured-coumarins exhibited near-infrared emission (greater than 650 nm), lipid droplet-targeting ability and obvious photocytotoxicity under laser irradiation. In particular, C-S-3 exhibited better photostability, superior lipid droplet-targeting capability, and stronger photodynamic effect on cancer cells than C-S-2.

A fluorescent probe for lipid droplet polarity imaging with low viscosity crosstalk

Monitoring the variations of lipid droplet (LD) polarity is of great significance for the investigation of LD-related cellular metabolism and function. We hereby report a lipophilic fluorescent probe (BTHO) with the feature of intramolecular charge transfer (ICT) for imaging the LD polarity in living cells. BTHO exhibits an obvious attenuation of fluorescence emission in response to the increase of environmental polarity. The linear response range of BTHO to polarity (ε, the dielectric constant of solvents) is derived to be 2.21-24.40, and the fluorescence of BTHO in glyceryl trioleate falls in this range. Furthermore, BTHO has high molecular brightness, which may effectively improve the signal to noise ratio, along with the decrease of phototoxicity. BTHO exhibits excellent photostability and targeting capability to LDs with low cytotoxicity, which is satisfactory in long-term imaging in live cells. The probe was successfully applied for imaging LD polarity variation in live cells caused by oleic acid (OA), methyl-β-cyclodextrin (MβCD), H₂O₂, starvation, lipopolysaccharide (LPS), nystatin, and erastin. The low crosstalk caused by viscosity to BTHO measuring the LD polarity was confirmed from a calculation result.

Analytical Techniques for Single-Cell Biochemical Assays of Lipids

Lipids are essential cellular components forming membranes, serving as energy reserves, and acting as chemical messengers. Dysfunction in lipid metabolism and signaling is associated with a wide range of diseases including cancer and autoimmunity. Heterogeneity in cell behavior including lipid signaling is increasingly recognized as a driver of disease and drug resistance. This diversity in cellular responses as well as the roles of lipids in health and disease drive the need to quantify lipids within single cells. Single-cell lipid assays are challenging due to the small size of cells (∼1 pL) and the large numbers of lipid species present at concentrations spanning orders of magnitude. A growing number of methodologies enable assay of large numbers of lipid analytes, perform high-resolution spatial measurements, or permit highly sensitive lipid assays in single cells. Covered in this review are mass spectrometry, Raman imaging, and fluorescence-based assays including microscopy and microseparations.

Synthesis of a Red-Emitting Polarity-Sensitive Fluorescent Probe Based on ICT and Visualization for Lipid Droplet Dynamic Processes

Abnormal lipid droplets (LDs) have been recognized as critical factors in many diseases because they are metabolically active and dynamic organelles. Visualization for LD dynamic processes is fundamental for elucidating the relationship of LDs and related diseases. Herein, a red-emitting polarity-sensitive fluorescent probe (TPA-CYP) based on intramolecular charge transfer (ICT) was proposed, which was constructed by employing triphenylamine (TPA) and 2-(5,5-dimethyl-2-cyclohex-1-ylidene)propanedinitrile (CYP) as electron donor and acceptor moiety, respectively. The spectra results underlined the excellent characteristics of TPA-CYP, such as high polarity sensitivity (Δf = 0.209 to 0.312), strong solvatochromic effect (λ_em 595-699 nm), and the large Stokes shifts (174 nm). Moreover, TPA-CYP exhibited a specific ability to target LDs and effectively differentiated cancer cells and normal cells. Surprisingly, TPA-CYP had been successfully applied to dynamic tracking of LDs, not only in inflammation induced by lipopolysaccharide (LPS), the process of oxidative stress, but also in live zebrafish. We believe that TPA-CYP could serve as a powerful tool to gain insight into the dynamics of LDs and to understand and diagnose LD-associated diseases.

Exploring Coumarin-Based Boron Emissive Complexes as Temperature Thermometers in Polymer-Supported Materials

Three coumarin-based boron complexes (L1, L2 and L3) were designed and successfully incorporated into polymeric matrixes for evaluation as temperature probes. The photophysical properties of the complexes were carried out in different solvents and in the solid state. In solution, compound L1 exhibited the highest fluorescence quantum yield, 33%, with a positive solvatochromism also being observed on the absorption and emission when the polarity of the solvent increased. Additionally in the presence of anions, L1 showed a colour change from yellow to pink, followed by a quenching in the emission intensity, which is due to deprotonation with the formation of a quinone base. Absorption and fluorescence spectra of L1 were calculated at different temperatures by the DFT/B3LYP method. The decrease in fluorescence of compound L1 with an increase in temperature seems to be due to the presence of pronounced torsional vibrations of the donor and acceptor fragments relative to the single bond with C(carbonyl)-C (styrene fragment). L1, L2 and L3, through their incorporation into the polymeric matrixes, became highly emissive by aggregation. These dye@doped polymers were evaluated as temperature sensors, showing an excellent fluorescent response and reversibility after 15 cycles of heating and cooling.