Visualization of polarity changes in endoplasmic reticulum (ER) autophagy and rheumatoid arthritis mice with near-infrared ER-targeted fluorescent probe

The crucial cellular activities for maintaining normal cell functions heavily rely on the polarity of the endoplasmic reticulum (ER). Understanding how the polarity shifts, particularly in the context of ER autophagy (ER-phagy), holds significant promise for advancing knowledge of disorders associated with ER stress. Herein, a polarity-sensitive fluorescent probe CDI was easily synthesized from the condensation reaction of coumarin and dicyanoisophorone. CDI was composed of coumarin as the electron-donating moiety (D), ethylene and phenyl ring as the π-conjugation bridge, and malononitrile as the electron-accepting moiety (A), forming a typical D-π-A molecular configuration that recognition in the near-infrared (NIR) region. The findings suggested that as the polarity increased, the fluorescence intensity of CDI decreased, and it was accompanied by a redshift of emission wavelength at the excitation wavelength of 524 nm, shifting from 641 nm to 721 nm. Significantly, CDI exhibited a notable ability to effectively target ER and enabled real-time monitoring of ER-phagy induced by starvation or drugs. Most importantly, alterations in polarity can be discerned through in vivo imaging in mice model of rheumatoid arthritis (RA). CDI has been proven effective in evaluating the therapeutic efficacy of drugs for RA. ER fluorescent probe CDI can be optically activated in lysosomes, providing a sensitive tool for studying ER-phagy in biology and diseases.

Sulfur-based fluorescent probes for biological analysis: A review

The widespread adoption of small-molecule fluorescence detection methodologies in scientific research and industrial contexts can be ascribed to their inherent merits, including elevated sensitivity, exceptional selectivity, real-time detection capabilities, and non-destructive characteristics. In recent years, there has been a growing focus on small-molecule fluorescent probes engineered with sulfur elements, aiming to detect a diverse array of biologically active species. This review presents a comprehensive survey of sulfur-based fluorescent probes published from 2017 to 2023. The diverse repertoire of recognition sites, including but not limited to N, N-dimethylthiocarbamyl, disulfides, thioether, sulfonyls and sulfoxides, thiourea, thioester, thioacetal and thioketal, sulfhydryl, phenothiazine, thioamide, and others, inherent in these sulfur-based probes markedly amplifies their capacity for detecting a broad spectrum of analytes, such as metal ions, reactive oxygen species, reactive sulfur species, reactive nitrogen species, proteins, and beyond. Owing to the individual disparities in the molecular structures of the probes, analogous recognition units may be employed to discern diverse substrates. Subsequent to this classification, the review provides a concise summary and introduction to the design and biological applications of these probe molecules. Lastly, drawing upon a synthesis of published works, the review engages in a discussion regarding the merits and drawbacks of these fluorescent probes, offering guidance for future endeavors.

Superoxide dismutase and neurological disorders

Superoxide dismutase (SOD) is a common antioxidant enzyme found majorly in living cells. The main physiological role of SOD is detoxification and maintain the redox balance, acts as a first line of defence against Reactive nitrogen species (RNS), Reactive oxygen species (ROS), and other such potentially hazardous molecules. SOD catalyses the conversion of superoxide anion free radicals (O 2 -.) into molecular oxygen (O 2) and hydrogen peroxide (H 2O 2) in the cells. Superoxide dismutases (SODs) are expressed in neurons and glial cells throughout the CNS both intracellularly and extracellularly. Endogenous oxidative stress (OS) linked with enlarged production of reactive oxygen metabolites (ROMs), inflammation, deregulation of redox balance, mitochondrial dysfunction and bioenergetic crisis are found to be prerequisite for neuronal loss in neurological diseases. Clinical and genetic studies indicate a direct correlation between mutations in SOD gene and neurodegenerative diseases, like Amyotrophic Lateral Sclerosis (ALS), Huntington's disease (HD), Parkinson's Disease (PD) and Alzheimer's Disease (AD). Therefore, inhibitors of OS are considered as an optimistic approach to prevent neuronal loss. SOD mimetics like Metalloporphyrin Mn (II)-cyclic polyamines, Nitroxides and Mn (III)- Salen complexes are designed and used as therapeutic extensively in the treatment of neurological disorders. SODs and SOD mimetics are promising future therapeutics in the field of various diseases with OS-mediated pathology.

Development of an Endoplasmic Reticulum-targeting Fluorescent Probe for the Imaging of Superoxide Anion in Living Cells

Superoxide anion (O₂^•-) is an important reactive oxygen species (ROS), and plays critical roles in biological systems. ER stress has close relation with many metabolic diseases, and could lead to the abnormal production of ROS including O₂^•-. Herein, we present an ER-targeting probe (ER-Tf) for the detection of O₂^•- in living cells. The probe ER-Tf used triflate as the response site for O₂^•-, and employed p-methylbenzenesulfonamide as ER-targeting moiety. In response to O₂^•-, the triflate of the probe ER-Tf converted to hydroxyl group, providing strong blue emission under the excitation of ultraviolet light. The probe ER-Tf exhibited high sensitivity and selectivity to O₂^•-. Bioimaging experiments showed that the probe ER-Tf can be applied to detect O₂^•- at ER, and also demonstrated that rotenone could increase the generation of O₂^•- in living cells, while the O₂^•- level at ER showed no remarkable change during ferroptosis.

Liver-Targeted Near-Infrared Fluorescence/Photoacoustic Dual-Modal Probe for Real-Time Imaging of In Situ Hepatic Inflammation

Early diagnosis of hepatic inflammation is the key to timely treatment and avoid the worsening of liver inflammation. Near-infrared fluorescence (NIRF) probes have high sensitivity but low spatial resolution in lesion imaging, while photoacoustic (PA) imaging has good spatial location information. Therefore, the development of a NIRF/PA dual-modal probe integrated with high sensitivity and spatial location feedback can achieve an accurate early diagnosis of hepatic inflammation. Here, we report an activatable NIRF/PA dual-modal probe (hCy-Tf-CA) for the detection of the superoxide anion (O₂^·-) in early hepatic inflammation. hCy-Tf-CA showed high selectivity and sensitivity for detecting O₂^·- fluctuation in vitro. More importantly, by introducing hepatocyte-targeting cholic acid (CA), the probe successfully achieved accurate in situ imaging of acute inflammatory liver injury (AILI) and autoimmune hepatitis (AIH) in vivo. The introduced CA not only promotes the hepatic targeting accumulation of probes but also improves the performance of low background dual-modal imaging in vivo. Therefore, hCy-Tf-CA provides an effective strategy for significantly improving in situ imaging performance and holds great potential for early, sensitive, and accurate diagnosis of hepatic inflammation.

Theoretical study on a series of naphthalimide-contained two-photon fluorescent hypochlorite probe targeting endoplasmic reticulum: response mechanism and receptor effect

The development of detecting hypochlorous acid (HClO) in living endoplasmic reticulum has attracted much attention in the fields of biology, medicine, and pharmacy. In the present work, the one-photon absorption (OPA), one-photon emission (OPE), and two-photon absorption (TPA) properties of a series newly synthesized chemosensors with naphthalimide as the fluorophore were systematically investigated using time-dependent density functional theory in combination with response theory. Special emphasis is placed on evolution of the probes' optical properties in the presence of HClO. These compounds show drastic changes in their photoabsorption and photoemission properties when they react with HClO, indicating them to be excellent candidates as fluorescent chemosensors. To further understand the mechanisms of the two probes, we have employed the hole and electron analysis to investigate the charge transfer process for the photoemission of the molecules. The receptor effect is found to play a dominant role in the sensing performance of these probes. Specifically, two-photon absorption properties of the molecules are calculated. We have found that all probes show significant two-photon responses in the near-infrared light region. And the maximum two-photon absorption cross section of probe 2 is greatly enhanced with the presence of HClO, indicating that probe 2 can act as a potential two-photon excited fluorescent HClO probe. The theoretical investigations would be helpful to build the structure-property relationships for the naphthalimide-contained probes, providing information on the design of efficient two-photon fluorescent sensors that can be used for biological imaging of HClO in endoplasmic reticulum.

Recent progress in small-molecule fluorescent probes for endoplasmic reticulum imaging in biological systems

Endoplasmic reticulum (ER) is an indispensable organelle in eukaryotic cells involved in protein synthesis and processing, as well as calcium storage and release. Therefore, maintaining the quality of ER is of great importance for cellular homeostasis. Aberrant fluctuations of bioactive species in the ER will result in homeostasis disequilibrium and further cause ER stress, which has evolved to contribute to the pathogenesis of various diseases. Therefore, the real-time monitoring of various bioactive species in the ER is of high priority to ascertain the mysterious roles of ER, which will contribute to unveiling the corresponding mechanism of organism disturbances. Recently, fluorescence imaging has emerged as a robust technique for the direct visualization of molecular events due to its outstanding sensitivity, high temporal-spatial resolution and noninvasive nature. In this review, we comprehensively summarize the recent progress in design strategies, bioimaging applications, potential directions and challenges of ER-targetable small-molecular fluorescent probes.

Fluorescent probes for targeting endoplasmic reticulum: design strategies and their applications

Advances in developing organic fluorescent probes and fluorescence imaging techniques have enhanced our understanding of cell biology. The endoplasmic reticulum (ER) is a dynamic structure that plays a crucial role in protein synthesis, post-translational modifications, and lipid metabolism. The malfunction of ER contributes to several physiological and pathological conditions. Therefore, the investigations on the imaging and role of ER have attracted a lot of attention. Due to their simplicity, synthetic tunability, photostability, high quantum yields, easier cellular uptake, and lower cytotoxicity, organic fluorophores offer invaluable tools for the precision targeting of various cellular organelles and probe ER dynamics. The precision staining is made possible by incorporating specific functional groups having preferential and local organelle biomolecular interactions. For instance, functional moieties such as methyl sulfonamide, sulfonylurea, and pentafluorophenyl assist in ER targeting and thus have become essential tools to probe a deeper understanding of their dynamics. Furthermore, dual-function fluorescent probes that simultaneously image ER and detect specific physiological parameters or biological analytes were achieved by introducing special recognition or chemically reactive sites. This article attempts to comprehensively capture various design strategies currently employed by researchers utilizing small organic molecules to target the ER and detect specific analytes.

Recent Progress in Fluorescent Sensors for Drug-Induced Liver Injury Assessment

Drug-induced liver injury (DILI) is a persistent concern in drug discovery and clinical medicine. The current clinical methods to assay DILI by analyzing the enzymes in serum are still not optimal. Recent studies showed that fluorescent sensors would be efficient tools for detecting the concentration and distribution of DILI indicators with high sensitivity and specificity, in real-time, in situ, and with low damage to biosamples, as well as diagnosing DILI. This review focuses on the assessment of DILI, introduces the current mechanisms of DILI, and summarizes the design strategies of fluorescent sensors for DILI indicators, including ions, small molecules, and related enzymes. Some challenges for developing DILI diagnostic fluorescent sensors are put forward. We believe that these design strategies and challenges to evaluate DILI will inspire chemists and give them opportunities to further develop other fluorescent sensors for accurate diagnoses and therapies for other diseases.

Detection Technologies for Reactive Oxygen Species: Fluorescence and Electrochemical Methods and Their Applications

Reactive oxygen species (ROS) have been found in plants, mammals, and natural environmental processes. The presence of ROS in mammals has been linked to the development of severe diseases, such as diabetes, cancer, tumors, and several neurodegenerative conditions. The most common ROS involved in human health are superoxide (O2•-), hydrogen peroxide (H2O2), and hydroxyl radicals (•OH). Organic and inorganic molecules have been integrated with various methods to detect and monitor ROS for understanding the effect of their presence and concentration on diseases caused by oxidative stress. Among several techniques, fluorescence and electrochemical methods have been recently developed and employed for the detection of ROS. This literature review intends to critically discuss the development of these techniques to date, as well as their application for in vitro and in vivo ROS detection regarding free-radical-related diseases. Moreover, important insights into and further steps for using fluorescence and electrochemical methods in the detection of ROS are presented.

Anion-Responsive Molecules That Exhibit Switching of Two-Photon Optical Properties

Two-photon-excited fluorescent probes are important for two-photon microscopy for biomedical studies. In contrast to the many examples of probes for cationic species, such as metal ions, there have been fewer reports on the control of two-photon optical properties by anions because in such systems it is difficult to control the associated π-electronic states. This Minireview summarizes anion-responsive molecules that exhibit changes in two-photon optical properties and describes their molecular design and anion-response mechanisms, which are driven by changes in covalent bonds and noncovalent interactions. Results from a recent study of two-photon systems, where geometries and optical properties are modulated by anion binding, are also discussed.