Selective Detection and Visualization of Exogenous/endogenous Hypochlorous Acid in Living Cells using a BODIPY-based Red-emitting Fluorescent Probe

Mechanism of two styryl BODIPYs as fluorescent probes and protective agents in lipid bilayers against aqueous ClO. RSC Adv 2024;14:28957-28964. [PMID: 39263435 PMCID: PMC11389514 DOI: 10.1039/d4ra03433c] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

Two styryl BODIPY derivatives, BOH and BOE, with different hydrophilic properties, were investigated for their reaction mechanisms in lipid bilayers against aqueous ClO-, by both experimental and theoretical methods. Density functional theory (DFT) calculations confirmed their identical conformations in solution. Fluorescence spectra and high-resolution mass spectra corroborated the central vinyl group as a common antioxidation moiety against ClO- oxidation. In giant unilamellar vesicles (GUVs), distinct reaction kinetics with ClO- suggested that BOE provided superior protective effects compared to BOH on lipids. Molecular dynamics simulations indicated that the lipophilic octyloxy group in BOE led to its deeper localization within the lipid phase, bringing it closer to the corresponding lipid target group. This study establishes the two styryl BODIPYs as promising fluorescent probes for detecting aqueous ClO- in lipid-water polyphasic systems.

Ex Tenebris Lux: Illuminating Reactive Oxygen and Nitrogen Species with Small Molecule Probes

Reactive oxygen and nitrogen species are small reactive molecules derived from elements in the air─oxygen and nitrogen. They are produced in biological systems to mediate fundamental aspects of cellular signaling but must be very tightly balanced to prevent indiscriminate damage to biological molecules. Small molecule probes can transmute the specific nature of each reactive oxygen and nitrogen species into an observable luminescent signal (or even an acoustic wave) to offer sensitive and selective imaging in living cells and whole animals. This review focuses specifically on small molecule probes for superoxide, hydrogen peroxide, hypochlorite, nitric oxide, and peroxynitrite that provide a luminescent or photoacoustic signal. Important background information on general photophysical phenomena, common probe designs, mechanisms, and imaging modalities will be provided, and then, probes for each analyte will be thoroughly evaluated. A discussion of the successes of the field will be presented, followed by recommendations for improvement and a future outlook of emerging trends. Our objectives are to provide an informative, useful, and thorough field guide to small molecule probes for reactive oxygen and nitrogen species as well as important context to compare the ecosystem of chemistries and molecular scaffolds that has manifested within the field.

A Hydroxytricyanopyrrole-Based Fluorescent Probe for Sensitive and Selective Detection of Hypochlorous Acid

Hypochlorous acid (HOCl) is a reactive substance that reacts with most biomolecules and is essential in physiological and pathological processes. Abnormally elevated HOCl levels may cause inflammation and other disease responses. To further understand its key role in inflammation, HOCl must be detected in situ. Here, we designed a hydroxytricyanopyrrole-based small-molecule fluorescent probe (HTCP-NTC) to monitor and identify trace amounts of HOCl in biological systems. In the presence of HOCl, HTCP-NTC released hydroxyl groups that emit strong fluorescence covering a wide wavelength range from the visible to near-infrared region owing to the resumption of the intramolecular charge transfer process. Additionally, HTCP-NTC demonstrated a 202-fold fluorescence enhancement accompanied by a large Stokes shift and a low detection limit (21.7 nM). Furthermore, HTCP-NTC provided a rapid response to HOCl within 18 s, allowing real-time monitoring of intracellular HOCl. HTCP-NTC exhibited rapid kinetics and biocompatibility, allowing effective monitoring of the exogenous and endogenous HOCl fluctuations in living cells. Finally, based on fluorescence imaging, HTCP-NTC is a potential method for understanding the relationship between inflammation and HOCl.

An AIE based fluorescent chemosensor for ratiometric detection of hypochlorous acid and its application

Detecting and imaging intracellular hypochlorous acid (HClO) is of great importance owning to its prominent role in numerous pathological and physiological processes. In this contribution, a novel AIE-based fluorescent chemosensor has been developed by employing a benzothiazole derivative. The synthesized probe displayed remarkable ratiometric fluorescent response to HClO with a large emission shift (139 nm), resulting in naked-eye fluorescence changes from red to blue. Under the optimal conditions, this probe was capable of quantitatively detecting HClO within 10 s, and possessed good sensitivity and high selectivity toward HClO over other biologically relevant species. Moreover, it has been successfully utilized to image the exogenous and endogenous HClO in living cells through dual channels, and conveniently detect hypochlorous acid solution on test strips with better accuracy, demonstrating its potential for monitoring HClO in biological and environment fields.

A BODIPY-Based Far-Red-Absorbing Fluorescent Probe for Hypochlorous Acid Imaging

Hypochlorous acid (HClO) is produced by white blood cells to defend against injury and bacteria. However, as one of the reactive oxygen species, high intracellular HClO concentration could lead to chronic diseases that affect the cardiovascular and nervous systems. To monitor HClO concentrations in bio-samples, the fluorescent probe is preferred to have: a) absorbability in the far-red window with reduced light-toxicity and improved tissue penetration depth, b) ratiometric feature for accurate analysis. In this study, we reported a far-red ratiometric HClO fluorescence probe based on BODIPY chromophore and aldoxime sensing group. Not only the color change of the probe solution can be detected by naked eyes, but also the emission ratios (I₆₄₅/I₆₇₀) showed a significant increase upon the introduction of HClO. More importantly, the feasibility of HClO monitoring in bio-samples was demonstrated in vitro using a confocal microscope.

Selective Imaging of HClO in the Liver Tissue In Vivo Using a Near-infrared Hepatocyte-specific Fluorescent Probe

Liver injury is typified by an inflammatory response. Hypochlorous acid (HClO), an important endogenous reactive oxygen species, is regarded as a biomarker associated with liver injury. Near-infrared (NIR) fluorescent probes with the advantage of deep tissue penetrating and low auto-fluorescence interference are more suitable for bioimaging in vivo. Thus, in this work, we designed and synthesized a novel NIR hepatocyte-specific fluorescent probe named NHF. The probe NHF showed fast response (<3 s), large spectral variation, and good selectivity to trace HClO in buffer solution. By employing N-acetylgalactosamine (GalNAc) as the targeting ligand, probe NHF can be actively delivered to the liver tissue of zebrafish and mice. It is important that probe NHF is the first NIR hepatocyte-specific fluorescent probe, which successfully visualized the up-regulation of endogenous HClO in the oxygen-glucose deprivation/reperfusion (OGD/R) model HepG2 cells and dynamically monitored APAP-induced endogenous HClO in the liver tissue of zebrafish and mice.

A resorufin-based red-emitting fluorescent probe with high selectivity for tracking endogenous peroxynitrite in living cells and inflammatory mice

Peroxynitrite (ONOO^-) plays essential roles on various physiological and pathological processes of living systems as a short-lived and highly reactive nitrogen (RNS) specie. The construction of novel long-wavelength fluorescent probes with high specificity towards ONOO^- for imaging in vivo is still demand urgently. About this work, a novel resorufin-based red-emitting fluorescent probe for tracking ONOO^- has been constructed. The probe RFP exhibited high selectivity towards ONOO^- anion over other analytes. Utilizing the probe, ONOO^- could be directly observed by the naked eye. Furthermore, RFP was successfully applied for imaging endogenous ONOO^- in RAW264.7 cells and inflammatory mice. This work offers a convenient method for monitoring the intercellur ONOO^- that be expected to be applied for explaining the bio-functional roles of ONOO^- in living system.

Preparation of Yellow Fluorescent N,O-CDs and its Application in Detection of ClO. J Fluoresc 2021;31:659-666. [PMID: 33534115 DOI: 10.1007/s10895-021-02686-4]

Accurate and efficient detection of ClO^- was extremely important due to the harm of ROS in the environment and organism. In this paper, yellow fluorescent N,O-CDs were successfully prepared by the solvothermal method. The microscopic size of the N,O-CDs was approximately spherical with an average particle size of 4.8 ± 0.8 nm. The fluorescence quantum yield in ethanol solution was calculated as 10.5 % using fluorescein as the standard reference. The as-fabricated N,O-CDs had high sensitivity and low detection limit (7.5 µM) for quantitatively detecting ClO^- with a linear range from 0.07 mM to 0.16 mM. The probe not only shows good selectivity and anti-interference to metal ions, anions and amino acids but also has excellent light stability and thermal stability. Also, a wide selection range for pH was demonstrated.