Tandem reaction-powered near-infrared fluorescent molecular reporter for real-time imaging of lung diseases

Diabetes and its complications have drawn growing research attention due to their detrimental effects on human health. Although optical probes have been used to help understand many aspects of diabetes, the lung diseases caused by diabetes remain unclear and have rarely been explored. Herein, a tandem-reaction (TR) strategy is proposed based on the adjacent diol esterification-crosslinking reaction and the nicotinamide reduction reaction of nicotinamide adenine dinucleotide (NADH) to design a lung-targeting near-infrared (NIR) small molecule probe (NBON) for accurate imaging of diabetic lung diseases. NBON was designed by coupling a phenylboronic acid analog that can form borate ester bonds by reversibly binding with NADH via an esterification-crosslinking reaction. Streptozotocin (STZ)-induced diabetic mice and metformin (MET)/epalrestat (EPS)-repaired model studies demonstrated that NBON allowed the sensitive imaging of NADH for lung disease diagnosis and therapeutic monitoring. The proposed antioxidant mechanism by which EPS alleviates diabetic lung disease was studied for the first time in living cells and in vivo. Furthermore, NBON was successfully applied in the detection of NADH in tumors and lung metastases. Overall, this work provides a general platform for a NIR NADH probe design, and advances the development of NADH probes for mechanistic studies in lung diseases.

Harnessing the power of iridium AIEgens for NAD(P)H detection in aqueous medium and living cells

A rationally designed luminescent probe based on cyclometalated iridium(III) AIEgens was developed for the rapid, sensitive, and specific detection of NAD(P)H in aqueous media. This probe was successfully utilized for bioimaging of NADH within the mitochondria of living cancer cells, highlighting its potential as a valuable tool for investigating NADH-associated cellular processes.

Molecular probe to visualize the effect of a glycolytic inhibitor on reducing NADH levels in a cellular system

The reduced form of nicotinamide adenine dinucleotide, commonly known as NADH, is an essential coenzyme existing in living organisms. Due to its involvement in various biological process, fluorescence imaging of intracellular NADH levels in different pathological conditions has emerged as an interesting area of research. We report here the exploration of a fluorescent probe, MQ-CN-BTZ, as a dual-channel NADH imaging agent (green and red channels) for cellular systems. Interestingly, depending on the ratio between the probe and NADH concentration in the solution phase, the probe showed emission at ∼529 nm and ∼656 nm when excited at 475 nm. It should be noted that the probe showed a very large Stokes shift of ∼180 nm with respect to the longer-wavelength emission with a good fluorescence response towards NADH. In general, such a large Stokes shift is highly beneficial for imaging applications, largely due to the better separation between the emission and excitation spectra and reduced spectral overlap. Finally, the probe was utilized to image a glycolysis pathway event by employing 3-bromopyruvic acid (3-BrPA) as a glycolytic inhibitor that significantly inhibits the activity of the enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH), which is involved in a crucial step of glycolysis. As the depletion of the NADH levels corresponds to the inactivity of GADPH upon treatment with the inhibitor, we attempted to image the modulation of the NADH concentration in the cellular system in the presence of the inhibitor 3-BrPA, indicating the importance of the glycolysis step in elevating NADH levels. Overall, the present study attempts to demonstrate the importance of a molecular probe for fluorescence imaging of intracellular NADH in the presence of a glycolytic inhibitor.

A Rhodamine-Based Ratiometric Fluorescent Sensor for Dual-Channel Visible and Near-Infrared Emission Detection of NAD(P)H in Living Cells and Fruit Fly Larvae

The detection and dynamic monitoring of intracellular NAD(P)H concentrations are crucial for comprehending cellular metabolism, redox biology, and their roles in various physiological and pathological processes. To address this need, we introduce sensor A, a near-infrared ratiometric fluorescent sensor for real-time, quantitative imaging of NAD(P)H fluctuations in live cells. Sensor A combines a 3-quinolinium electron-deficient acceptor with a near-infrared rhodamine dye, offering high sensitivity and specificity for NAD(P)H with superior photophysical properties. In its unbound state, sensor A emits strongly at 650 nm and weakly at 465 nm upon 400 nm excitation. Upon binding to NAD(P)H, it shows a fluorescence increase at 465 nm and a decrease at 650 nm, enabling accurate ratiometric measurements. Sensor A also exhibits ratiometric upconversion fluorescence when excited at 800 or 810 nm, offering additional flexibility for different experimental setups. The sensor's response relies on the reduction of the 3-quinolinium acceptor by NAD(P)H, forming a 1,4-dihydroquinoline donor that enhances fluorescence at 465 nm and quenches the near-infrared emission at 650 nm through photoinduced electron transfer. This mechanism ensures high sensitivity and reliable quantification of NAD(P)H levels while minimizing interference from sensor concentration, excitation intensity, or environmental factors. Sensor A was validated in HeLa and MD-MB453 cells under various metabolic and pharmacological conditions, including glucose and maltose stimulation and treatments with chemotherapeutic agents. Co-localization with mitochondrial-specific dyes confirmed its mitochondrial targeting, enabling precise tracking of NAD(P)H fluctuations. In vivo imaging of Drosophila larvae under nutrient starvation or chemotherapeutic exposure revealed dose-dependent fluorescence responses, highlighting its potential for tracking NAD(P)H changes in live organisms. Sensor A represents a significant advancement in NAD(P)H imaging, providing a powerful tool for exploring cellular metabolism and redox biology in biomedical research.

Near-Infrared Visualization of NAD(P)H Dynamics in Live Cells and Drosophila melanogaster Larvae Using a Coumarin-Based Pyridinium Fluorescent Probe

A near-infrared fluorescent probe, A, was designed by substituting the carbonyl group of the coumarin dye's lactone with a 4-cyano-1-methylpyridinium methylene group and then attaching an electron-withdrawing NADH-sensing methylquinolinium acceptor via a vinyl bond linkage to the coumarin dye at the 4-position. The probe exhibits primary absorption maxima at 603, 428, and 361 nm, and fluoresces weakly at 703 nm. The addition of NAD(P)H results in a significant blue shift in the fluorescence peak from 703 to 670 nm, accompanied by a substantial increase in fluorescence intensity. This spectral shift is attributed to the transformation from an A-π-A-π-D configuration to a D-π-A-π-D pyridinium platform in probe AH, owing to the addition of a hydride from NADH to the electron-accepting quinolinium acceptor producing the electron-contributing 1-methyl-1,4-dihydroquinoline donor in probe AH. This conclusion is supported by theoretical calculations. The probe was utilized to investigate NAD(P)H dynamics under various conditions. In HeLa cells, treatment with glucose or maltose resulted in a substantial elevation in near-infrared emission intensity, suggesting increased NAD(P)H levels. Chemotherapeutic agents including cisplatin and fludarabine at concentrations of 5, 10, and 20 μM brought about a dose-dependent increase in emission intensity, reflecting heightened NAD(P)H levels due to drug-induced stress and cellular damage. In vivo experiments with hatched, starved Drosophila melanogaster larvae were also conducted. The results showed a clear relationship between emission intensity and the levels of NADH, glucose, and oxaliplatin, confirming that the probe can detect variations in NAD(P)H levels in a living organism. Our investigation also demonstrates that NAD(P)H levels are significantly elevated in the cystic kidneys of ADPKD mouse models and human patients, indicating substantial metabolic alterations associated with the disease. This near-infrared emissive probe offers a highly sensitive and specific method for monitoring NAD(P)H levels across cellular, tissue and whole-organism systems. The ability to detect NAD(P)H variations in reaction to varying stimuli, including nutrient availability and chemotherapeutic stress, underscores its potential as a valuable resource for biomedical research and therapeutic monitoring.

Deep-Red and Near-Infrared Compact Cyanine Dyes for Sensitive NAD(P)H Sensing in Live Cells and Kidney Disease Tissues

Cyanine dyes constructed for NAD(P)H near-infrared sensing utilize extended π-conjugation but often exhibit delayed fluorescence responses to NAD(P)H due to reduced positive charge density in 3-quinolinium acceptors. This study introduces deep-red and near-infrared compact cyanine dyes represented by probes A and B for mitochondrial NAD(P)H detection in live cells. Probes A and B feature a unique structural design with a double bond connection linking 3-quinolinium to strategically positioned 1-methylquinolinium acceptor units at 2- and 4-positions, correspondingly. Probe A absorbs at 359 and 531 nm, while probe B absorbs at 324 and 370 nm, emitting subtle fluorescence at 587 and 628 nm, respectively, with no NADH present. Upon NADH exposure, probes A and B exhibit significant emission enhancements at 612 and 656 nm, correspondingly, attributed to the efficient reduction of 3-quinolinium units to electron-donative 1-methyl-1,4-dihydroquinoline units. Probe B, chosen for its near-infrared emission and fast response to NAD(P)H, effectively monitored dynamic intracellular NAD(P)H levels throughout diverse experimental conditions. In HeLa cells, minimal basal fluorescence increased upon NADH stimulation. It also identified increased NAD(P)H levels following chemical treatments with acesulfame potassium, cisplatin, carboplatin, and temozolomide, CoCl2-induced hypoxia, and TLR4 activation in macrophages and in disease models of kidney pathology, where diseased tissues exhibited higher fluorescence than normal tissues. In fruit fly larvae under starvation conditions, probe B tracked NAD(P)H increases triggered by exogenous NADH, demonstrating its in vivo applicability for metabolic studies. These findings highlight probe B's utility in elucidating dynamic NAD(P)H fluctuations in diverse biological contexts, offering insights into mitochondrial function and cellular metabolism.

An activated near-infrared mitochondrion-targetable fluorescent probe for rapid detection of NADH

A novel NIR fluorescent probe based on quinoline-conjugated benzo[cd]indol dual-salt for NADH was developed. This probe swiftly detects and responds sensitively to both endogenous and exogenous NADH alterations, enabling imaging of NADH fluctuations in type II diabetic and AD model cells.

Ratiometric fluorescence sensing NADH using AIE-dots transducers at the point of care

Reduced nicotinamide adenine dinucleotide (NADH) has a strong impact on physiological metabolism, and its concentration is related to metabolic and neurodegenerative diseases. A more reliable and accurate detection method for NADH quantitation is needed for early disease diagnosis and point-of-care testing. Aggregation-induced emission (AIE) materials are widely used to improve the sensitivity in analytes assays due to their anti-aggregation-caused quenching property. Here we developed TPA-BQD-Py AIE-dots transducers and evaluated its performance in NADH detection. The NADH concentration-dependent ratiometric sensing was based on electron transfer from TPA-BQD-Py AIE-dots to NADH with variable fluorescence intensity at 584 nm and 470 nm, resulting in high sensitivity (limit of detection at 110 nM), photostability, selectivity, and a rapid and reversible response. We further developed the application of TPA-BQD-Py AIE-dots transducers in in vivo NADH imaging using a smartphone and digital camera, respectively, demonstrating the potential for NADH point-of-care testing.

NAD(P)H Activated Fluorescent Probe for Rapid Intraoperative Pathological Diagnosis and Tumor Histological Grading

Rapid and accurate intraoperative pathological diagnosis (IOPD) is essential for intraoperative decision-making to improve patients' outcomes and avoid reoperations. In this study, using a NAD(P)H-activated fluorescent probe, a multifunctional fluorescent indicator has been developed to selectively identify tumor cells from normal tissue and to achieve cancer grading identification. This rapid response probe, CyQ-1, features unprecedented sensitivity and rapid response toward NADH at low nanomolar levels under physiological conditions. Moreover, this indicator allows both colorimetric and fluorescent NADH detection in HeLa, A549, MDA-MB-231, 4T1, MCF-7, HePG2, HUVEC, and HL-7702 cells. Expanding the use of this indicator to advanced tissue models, its ability to visualize NADH in 120 paraffin-embedded colorectal sections and 20 cases of intraoperative frozen sections of lung cancer was further verified. CyQ-1-based cancer grading identification shows an overall 92.5 and 100% agreement with the "gold standard test" of histologic grading toward paraffin and frozen sections, respectively. The sensitivity and specificity for discriminating poorly, moderately, and well-differentiated tumor sections were all above 90%. In a word, the rapid and accurate NADH detection ability for clinical sections makes this proposed indicator a potential candidate for clinical IOPD quantification and tumor differentiation grade recognition.

A dual-responsive ratiometric indicator designed for in vivo monitoring of oxidative stress and antioxidant capacity

The imbalance between oxidative stress and antioxidant capacity is strongly associated with the development of numerous degenerative diseases, including cardiovascular diseases, diabetes, neurodegenerative diseases, and cancer. Therefore, monitoring oxidative stress and antioxidant capacity in vivo is crucial for maintaining cellular homeostasis and the stability of the organism's internal environment. Here, we present the findings of our study on DQ1, a dual-responsive indicator designed specifically for imaging H2O2 and NAD(P)H, which are critical indicators of oxidative stress and antioxidant capacity. DQ1 facilitated the colorimetric and fluorescence detection of H2O2 and NAD(P)H in two well-separated channels, exhibiting a detection limit of 1.0 μM for H2O2 and 0.21 nM for NAD(P)H, respectively. Experiments conducted on living cells and zebrafish demonstrated that DQ1 could effectively detect changes in H2O2 and NAD(P)H levels when exposed to exogenous hypoxic conditions and chemical stimuli. Furthermore, the effectiveness of the as-fabricated indicator was investigated in two distinct mouse models: evaluating H2O2 and NAD(P)H levels in myocardial cell dysfunction during acute myocardial infarction and liver tissue damage under trichloroethylene stress conditions. In vivo experiments demonstrated that the levels of the two cardiac biomarkers increase progressively with the development of myocardial infarction, eventually reaching a steady state after 7 days when the damaged cells in the infarcted region become depleted. Moreover, during 14 continuous days of exposure to trichloroethylene, the two biomarkers in liver tissue exhibited a sustained increase, indicating a significant enhancement in intracellular oxidative stress and antioxidant capacity attributed to the mouse liver's robust metabolic capacity. The aforementioned studies underscore the efficacy of DQ1 as a valuable tool for scrutinizing redox states at both the single-cell and biological tissue levels. It presents significant potential for investigating the dynamic alternations in oxidative stress and antioxidant capacity within disease models as the disease progresses, thereby facilitating a more profound comprehension of these processes across various disease models.

Highly Sensitive Cyanine Dyes for Rapid Sensing of NAD(P)H in Mitochondria and First-Instar Larvae of Drosophila melanogaster

We have developed two highly sensitive cyanine dyes, which we refer to as probes A and B. These dyes are capable of quick and sensitive sensing of NAD(P)H. The dyes were fabricated by connecting benzothiazolium and 2,3-dimethylnaphtho[1,2-d]thiazol-3-ium units to 3-quinolinium through a vinyl bond. In the absence of NAD(P)H, both probes have low fluorescence and absorption peaks at 370 and 400 nm, correspondingly. This is because of their two electron-withdrawing acceptor systems with high charge densities. However, when NAD(P)H reduces the probes' electron-withdrawing 3-quinolinium units to electron-donating 1,4-dihydroquinoline units, the probes absorb at 533 and 535 nm and fluoresce at 572 and 586 nm for A and B correspondingly. This creates well-defined donor-π-acceptor cyanine dyes. We successfully used probe A to monitor NAD(P)H levels in live cells during glycolysis, under hypoxic conditions induced by CoCl2 treatment and after treatment with cancer drugs, including cisplatin, camptothecin, and gemcitabine. Probe A was also employed to visualize NAD(P)H in Drosophila melanogaster first-instar larvae. We observed an increase in NAD(P)H levels in A549 cancer cells both under hypoxic conditions and after treatment with cancer drugs, including cisplatin, camptothecin, and gemcitabine.

Fluorescent dyes based on rhodamine derivatives for bioimaging and therapeutics: recent progress, challenges, and prospects

Since their inception, rhodamine dyes have been extensively applied in biotechnology as fluorescent markers or for the detection of biomolecules owing to their good optical physical properties. Accordingly, they have emerged as a powerful tool for the visualization of living systems. In addition to fluorescence bioimaging, the molecular design of rhodamine derivatives with disease therapeutic functions (e.g., cancer and bacterial infection) has recently attracted increased research attention, which is significantly important for the construction of molecular libraries for diagnostic and therapeutic integration. However, reviews focusing on integrated design strategies for rhodamine dye-based diagnosis and treatment and their wide application in disease treatment are extremely rare. In this review, first, a brief history of the development of rhodamine fluorescent dyes, the transformation of rhodamine fluorescent dyes from bioimaging to disease therapy, and the concept of optics-based diagnosis and treatment integration and its significance to human development are presented. Next, a systematic review of several excellent rhodamine-based derivatives for bioimaging, as well as for disease diagnosis and treatment, is presented. Finally, the challenges in practical integration of rhodamine-based diagnostic and treatment dyes and the future outlook of clinical translation are also discussed.

Thiophene-based organic dye with large Stokes shift and deep red emission for live cell NAD(P)H detection under varying chemical stimuli

We report a novel method for synthesizing red and deep red cyanine dyes with large Stokes shifts, probes A and B, for live cell NAD(P)H detection. The probes were prepared using thiophene-based organic dyes featuring a π-conjugated bridge of thiophene and 3,4-ethylenedioxythiophene units linking the 1-methylquinolinium acceptor and formyl acceptor, respectively. These probes display weak absorption peaks at 315 nm (A) and 334 nm (B) and negligible fluorescence in the absence of NADH. However, upon the presence of NADH, new absorption and fluorescence peaks appear at 477 nm and 619 nm for probe A and at 486 nm and 576 nm for probe B, respectively. This is due to the NADH-facilitated reduction of the 1-methylquinolinium unit into 1-methyl-1,4-dihydroquinoline, which then acts as the electron donor for the probes, leading to the formation of well-defined electron donor-acceptor dye systems. Probe A has a large Stokes shift of 144 nm, which allows for better separation between the excitation and emission spectra, reducing spectral overlap and improving the accuracy of fluorescence measurements. The probes are highly selective for NAD(P)H, water-soluble, biocompatible, and easily permeable to cells. They are also photostable and were successfully used to monitor changes in NADH concentration in live cells during glycolysis in the presence of glucose, lactate, and pyruvate, treatment of FCCP and cancer drug cisplatin, and under hypoxia triggered by CoCl2. Furthermore, the probes were able to image NAD(P)H in Drosophila melanogaster larvae. Notably, cisplatin treatment increased the NAD(P)H concentration in A459 cells over time. Overall, this work presents a significant advancement in the field of live cell imaging by providing a simple and cost-effective method for detecting changes in NAD(P)H concentration under varying chemical stimuli.

A dual-salt fluorescent probe for specific recognition of mitochondrial NADH and potential cancer diagnosis

Reduced nicotinamide adenine dinucleotide (NADH) is a kind of coenzyme and widely works as a biomarker in cancer cells. It plays a crucial role in many cellular metabolic processes, especially NADH in mitochondria is indispensable for the mitochondrial respiration chain that produces ATP. Herein, we designed a fluorescent probe Mito-FCC based on an ethylene-bridging dual-salt structure, in which benzo[e]indolium fluorophore was used as the mitochondria-targeting group and 1-methylquinolinium moiety as the NADH recognition unit. Mito-FCC exhibited high sensitivity and selectivity for NADH with a rapid "turn-on" fluorescence signal. The dual-salt structure endowed the probe with a reliable mitochondria-targeted ability even after the recognition unit was reduced by NADH. With the help of the probe, the fluctuations of endogenous NADH induced by glucose or pyruvate were imaged. Besides, Mito-FCC had a capability to make a distinction between cancer cells and normal cells due that the content of NADH in cancer cells was distinctly higher than that in normal ones. Notably, the visualization of tumor in vivo through monitoring NADH using Mito-FCC was realized successfully. These experimental results showed that Mito-FCC hold a great perspective in study of mitochondrial function and potential diagnosis of cancer diseases.

A Mitochondria-Targeted Fluorescent Probe for Monitoring NADPH Overproduction during Influenza Virus Infection

Reduced nicotinamide adenine dinucleotide phosphate (NADPH) is an important cofactor in the progress of antioxidant synthesis and biosynthesis, and an abnormal NADPH level has been observed in many viral infection processes. However, efficient tools to monitor NADPH in living cells after viral infection have not been reported. In this work, we present a fluorescent probe, NAFP4, that could detect NADPH ex vivo with a low detection limit of 3.66 nM and image mitochondrial NADPH level changes in living cells. The probe exhibits excellent cell permeability, rapid reactivity, and high selectivity with minimal cytotoxicity. Using NAFP4, we reveal that the NADPH is overproduced in the host cells infected by influenza virus, which was caused by an elevated level of G6PDH during the virus infection. Moreover, there was positive association between the G6PDH level and virus replication. With the proposed probe NAFP4, our study highlights that the virus infection would influence the host metabolism in NADPH production and also suggests that G6PDH is expected to be a promising target for antiviral therapy.

An NIR fluorescent/photoacoustic dual-mode probe of NADPH for tumor imaging

A novel probe was synthesized with a turn-on NIR fluorescent (NIRF)/photoacoustic (PA) response to NADPH, which was successfully applied in both monitoring intracellular NADPH and dual-modal imaging of tumor-bearing mice. It exhibits good potential in studying and understanding the tumor energy metabolism and treatment process related to NADPH.

Cellular and Intravital Imaging of NAD(P)H by a Red-Emitting Quinolinium-Based Fluorescent Probe that Features a Shift of Its Product from Mitochondria to the Nucleus

NAD(P)H is a vital hydrogen donor and electron carrier involved in numerous biological processes. The development of small-molecule tools for intravital imaging of NAD(P)H is significant for further exploring their pathophysiological roles. Herein, we rationally designed a fluorescent probe NADH-R by a simple graft of pyridiniumylbutenenitrile on a 1-methylquinolinium moiety in the 3-position. Benefited from the reduction of quinolinium by NAD(P)H, this probe releases the free push-pull fluorophore NADH-RH, allowing a turn-on red-emitting fluorescence response together with an ultralow detection limit of 12 nM. Under the assistance of the probe, we first monitored exogenous and endogenous generation of NAD(P)H in living cells, subsequently observed dynamic changes of NAD(P)H levels in living cells under different metabolic perturbations, and finally visualized the declined NAD(P)H levels in live mouse brain in a stroke model. Unexpectedly, the time-dependent colocalization experiment revealed that the probe reacts with mitochondrial NAD(P)H, followed by a shift of its reduced product NADH-RH from mitochondria to the nucleus, highlighting that NADH-RH is a novel nucleus-directed dye scaffold, which would facilitate the development of nucleus-targeting fluorescent probes and drugs.

An NADH-selective and sensitive fluorescence probe to evaluate living cell hypoxic stress

Cellular disease and senescence are often accompanied by an imbalance in the local oxygen supply. Under hypoxia, mitochondrial NADH and FADH₂ cannot be oxidized by the mitochondrial electron transport chain, which leads to the accumulation of reducing equivalents and subsequent reduction stress. Detecting changes in intracellular NADH levels is expected to allow an assessment of stress. We synthesized a red fluorescent probe, DPMQL1, with high selectivity and sensitivity for detecting NADH in living cells. The probe DPMQL1 has strong anti-interference abilities toward various potential biological interferences, such as metal ions, anions, redox species, and other biomolecules. In addition, its detection limit can reach the nanomolar level, meaning it can display small changes in NADH levels in living cells, so as to realize the evaluation of cell-based hypoxic stress.

Biomimetic Molecular Clamp Nanopores for Simultaneous Quantifications of NAD+ and NADH

NADH/NAD⁺ is pivotal to fundamental biochemistry research and molecular diagnosis, but recognition and detection for them are a big challenge at the single-molecule level. Inspired by the biological system, here, we designed and synthesized a biomimetic NAD⁺/NADH molecular clamp (MC), octakis-(6-amino-6-deoxy)-γ-cyclomaltooctaose, and harbored in the engineered α-HL(M113R)₇ nanopore, forming a novel single-molecule biosensor. The single-molecule measurement possesses high selectivity and a high signal-to-noise ratio, allowing to simultaneously recognize and detect for sensing NADH/NAD⁺ and their transformations.

A novel ratiometric fluorescent probe from a hemicyanine derivative for detecting NAD(P)H in a cell microenvironment

In this paper, a fluorescent compound derived from coumarin and hemicyanine was synthesized and characterized. Herein, we present the fluorescence properties of the probe. Fluorescence selectivity experiments revealed that it exhibited higher ratiometric fluorescence response activity toward NAD(P)H than other commonly coexisting compounds in the cell microenvironment, in accord with the fluorescence shift from red to blue. In addition, the fluorescence identification mechanism was deduced to be a redox reaction between the sensor and NAD(P)H according to the fluorescence behavior. The ratiometric fluorescent probe provided an important theoretical basis for sensing NAD(P)H in vitro and in vivo. We also used this phenomenon to build a sensitive detection platform of NAD(P)H-dependent enzyme activity based on the fluorescence method.

NAD(P)H-triggered probe for dual-modal imaging during energy metabolism and novel strategy of enhanced photothermal therapy in tumor

The reduced coenzymes (NADH and NADPH) are an important product in energy metabolism and closely related to the occurrence and development of cancer. So it is necessary to use a powerful detection tool to visualize NAD(P)H in energy metabolism of tumor cells and find a new strategy to improve cancer treatment based on NAD(P)H. Herein, a novel multifunctional probe (Cy-N) is synthesized with good near-infrared fluorescence (NIRF) response to NAD(P)H and the photoacoustic (PA) and photothermal properties are successfully activated by NAD(P)H. The probe is successfully applied in visualizing NAD(P)H in energy metabolism of tumor cells and imaging NAD(P)H in bacteria. Moreover, the probe can be used to image NAD(P)H in energy metabolism of tumor-bearing mice by dual-modal imaging (NIRF and PA). More importantly, in terms of the role of NAD(P)H in energy metabolism, the photothermal therapy (PTT) is activated by NAD(P)H and a novel strategy of enhanced PTT is proposed by injecting glucose. As far as we know, this is the first probe to detect NAD(P)H in energy metabolism through dual-modal imaging, and also the first probe to activate PTT based on NAD(P)H, which will provide important information of the diagnosis and treatment of cancer.

The recent development of fluorescent probes for the detection of NADH and NADPH in living cells and in vivo

Reduced nicotinamide adenine dinucleotide (NADH) and its phosphate ester (NADPH) participate in numerous metabolic processes in living cells as electron carriers. The levels of NADH and NADPH in a cell are closely related to its metabolic and pathological state. It is important to monitor the levels of NADH and NADPH in living cells and in vivo in real-time. This review mainly focuses on fluorescent probes developed for monitoring NADH and NADPH in living cells and in vivo, and classifies them according to the recognition units. These fluorescence probes can rapidly respond to changes in NADH and NADPH levels without interference from other biomolecules, both in cell culture and in vivo. These probes have been employed to monitor NADH and NADPH levels in living cells, tumor spheroids, and in vivo; moreover, some of them can be used to discriminate normal cells from cancer cells, and detect cancer cell death due to reductive stress induced by natural antioxidants. This review is expected to inspire the generation of novel fluorescent probes for the detection of NADH and NADPH, and stimulate more attention in the development of fluorescent probes based on carbon dots and nanoparticles, as well as metal complex-based, time-gated luminescent probes for monitoring NADH and NADPH in both living cells and in vivo.

NADH-Activated Dual-Channel Fluorescent Probes for Multicolor Labeling of Live Cells and Tumor Mimic Spheroids

The 1,4-dihydronicotinamide adenine dinucleotide (NADH) is one of the key coenzymes that participates in various metabolic processes including maintaining the redox balance. Early information on the imbalance of NADH is crucial in the context of diagnosing the pathogenic conditions. Thus, a dual-channel fluorescent probe (MQN) is developed for tracking of NADH/NAD(P)H in live cells. In the presence of NADH, only it showed emission signals at 460 and 550 nm upon excitation at 390 and 450 nm, respectively. The probe could provide accurate information on NADH levels in cancer cells (HeLa) and normal cells (WI-38). We observed that the NADH level in cancer cells (HeLa) is relatively higher than that in normal WI-38 cells. We received similar information on NADH upon calibrating with a commercial NADH kit. Moreover, we evaluated substrate-specific NADH expression in the glycolysis pathway and oxidative phosphorylation process. Also, the dual-channel probe MQN has visualized NADH manipulation in the course of depletion of GSH to maintain cellular redox balance. This dual-channel molecular probe MQN comes out as a new detection tool for NADH levels in live cells and tumor mimic spheroids.

A dual-signal output ratiometric electrochemiluminescent sensor for NADH detection

Ratiometric electrochemiluminescence (ECL) has attracted great attention in the field of electrochemical analysis. In this study, a dual-signal-output ratiometric ECL sensor was developed for the detection of nicotinamide adenine dinucleotide (NADH). Nitrogen-doped graphene quantum dots (NGQDs) exhibit double ECL signal output capability, without the requirement of additional coreactants. NADH can amplify the anodic ECL response of NGQDs, while it can diminish the cathodic ECL response of NGQDs. Based on the principle between relative enhancing ECL intensity ratio and NADH concentrations, the constructed ratiometric ECL sensor was applied to NADH assays, with a wide concentration range of 10-400 μM and a low limit of detection (LOD) of 2.5 μM (S/N = 3). Furthermore, the proposed method was applied for the determination of spiked NADH, which was proved to be feasible in the biological sample matrix. The proposed strategy of modulating multiple-ECL signals of the single NGQD emitter not only provides a new ECL system for the accurate detection of NADH but also broadens the design pathway for ratiometric sensing fabrication.

Development of dansyl based copper(ii) complex to detect hydrogen sulfide in hypoxia

Hydrogen sulfide (H2S) has been reported as a gaseous signaling molecule in cells. H2S modulation is dependent on the partial pressure of oxygen in cells, which means hypoxia can induce H2S production under various pathophysiological conditions. Hypoxia is a common condition in solid tumors and can lead to malignant tumors that may become aggressive and result in worse prognosis. We designed and synthesized probe Cu-CD for H2S detection under hypoxia conditions. It is selective and sensitive toward various biological thiols, reactive nitrogen species (RNS), and reactive oxygen species (ROS). The fluorescence intensity of Cu-CD in the cytoplasms of HeLa and EMT6 cells was enhanced in proportion to the concentration of exogenous/endogenous H2S. Moreover, Cu-CD can be able to detect endogenous H2S production accompanied by expression of HIF-1α. Therefore, Cu-CD can be a key tool to explore how H2S contributes to neovascularization and growth of solid tumor tissues in pathophysiological or hypoxic conditions.