Electrochemical substrate for active profiling of cellular surface leucine aminopeptidase activity and drug resistance in cancer cells

A novel ratiometric electrochemical assay for detection of formaldehyde in real food samples

This study developed a novel ratiometric electrochemical sensor for detecting formaldehyde content in food. For the first time, we innovatively utilized 4-amino-3-hydrazino-5-mercapto-1,2,4-triazole (AHMT), a traditional colorimetric probe that specifically reacts with formaldehyde, as an electrochemical probe to construct the electrochemical assay. The reaction product of AHMT with formaldehyde exhibits different redox potentials from AHMT, thereby enabling ratiometric detection of formaldehyde. We systematically investigated the electrochemical behavior of AHMT and its reaction product with formaldehyde. Under optimized conditions, this novel ratiometric electrochemical assay demonstrated high sensitivity and selectivity for formaldehyde, with a response linear range of 0.1-20 μM and a detection limit of 21 nM. Additionally, the sensor was successfully applied to detect formaldehyde in various mushrooms and fish, with measured concentrations of 1.34 μg g-1 in shimeji mushrooms, 0.80 μg g-1 in oyster mushrooms, 1.41 μg g-1 in enoki mushrooms, and 1.12 μg g-1 in king oyster mushrooms. For seafood, concentrations of 2.45 μg g-1 in cuttlefish and 0.83 μg∙g-1 in cutlassfish fish were detected. These results were validated against the standard method, underscoring the sensor's potential and reliability for practical applications. This study is anticipated to offer valuable insights for the development of innovative electrochemical sensors for food analysis.

Serum Leucine Aminopeptidase Activity Patterns Across Various Disease States: Potential Implications for Bleeding and Thrombosis Risk

BACKGROUND

 Disruptions in the pathways for activating and deactivating proteases in the bloodstream can lead to thrombosis and bleeding issues. Leucine aminopeptidases (LAPs), which are exopeptidases essential for regulating protein and peptide activities, are recognized as clinical biomarkers for liver diseases. However, the relationship between serum LAP activity and the risks of bleeding or thrombosis, as well as the identification of the specific tissues or organs that control LAP levels, is not well understood.

METHODS

 We performed a retrospective study to evaluate serum LAP activities in 149,360 patients with 47 different diseases and 9,449 healthy individuals. The analysis was conducted using SPSS V2.6, RStudio V.1.3.1073, and libraries in Python 3.8.

RESULTS

 Our research revealed that 21 of the 47 diseases studied showed increased median serum LAP activities, while 26 diseases were associated with significantly lower activities, especially those related to thrombosis. Furthermore, most diseases were found to have an increased risk of bleeding and thrombosis, indicated by higher Q25 and lower Q75 LAP activities compared to the control group. Receiver operating characteristic curve analysis confirmed the effectiveness of LAP activities as biomarkers for specific conditions like hepatic encephalopathy, liver cancer, pancreatitis, and pancreatic cancer. Diseases were categorized into clusters with similar bleeding or thrombotic tendencies through principal component analysis.

CONCLUSION

 This study highlighted regulatory influence of the liver and pancreas on LAP levels. The established link between serum LAP concentrations and the risk of bleeding or thrombosis paved the way for the development of diagnostic and preventative approaches for various medical conditions.

Self-Immolative Electrochemical Redox Substrates: Emerging Artificial Receptors in Sensing and Biosensing

The development of artificial receptors has great significance in measurement science and technology. The need for a robust version of natural receptors is getting increased attention because the cost of natural receptors is still high along with storage difficulties. Aptamers, imprinted polymers, and nanozymes are some of the matured artificial receptors in analytical chemistry. Recently, a new direction has been discovered by organic chemists, who can synthesize robust, activity-based, self-immolative organic molecules that have artificial receptor properties for the targeted analytes. Specifically designed trigger moieties implant selectivity and sensitivity. These latent electrochemical redox substrates are highly stable, mass-producible, inexpensive, and eco-friendly. Combining redox substrates with the merits of electrochemical techniques is a good opportunity to establish a new direction in artificial receptors. This Review provides an overview of electrochemical redox substrate design, anatomy, benefits, and biosensing potential. A proper understanding of molecular design can lead to the development of a library of novel self-immolative redox molecules that would have huge implications for measurement science and technology.

Lysosome-targeted fluorescent probes: Design mechanism and biological applications

As an integral organelle in the eukaryote, the lysosome is the degradation center and metabolic signal center in living cells, and partakes in significant physiological processes such as autophagy, cell death and cellular senescence. Fluorescent probe has become a favorite tool for studying organelles and their chemical microenvironments because of its high specificity and non-destructive merits. Over recent years, it has been reported that increasingly new lysosome-targeted probes play a major role in the diagnosis and monitor of diseases, in particular cancer and neurodegenerative diseases. In order to deepen the relevant research on lysosome, it is challenging and inevitability to design novel lysosomal targeting probes. This review first introduces the concepts of lysosome and its closely related biological activities, and then introduces the fluorescent probes for lysosome in detail according to different detection targets, including targeting mechanism, biological imaging, and application in diseases. Finally, we summarize the specific challenges and discuss the future development direction facing the current lysosome-targeted fluorescent probes. We hope that this review can help biologists grasp the application of fluorescent probes and broaden the research ideas of researchers targeting fluorescent probes so as to design more accurate and functional probes for application in diseases.

Therapeutic effect on Alveolar echinococcosis by targeting EM-Leucine aminopeptidase

Alveolar echinococcosis (AE) is a parasitic disease caused by E. multilocularis metacestodes and it is highly prevalent in the northern hemisphere. We have previously found that vaccination with E. multilocularis Leucine aminopeptidase (EM-LAP) induced specific immune response and had an inhibiting effect on the parasites. In this study, the therapeutic effect of recombinant EM-LAP (rEM-LAP) on AE was evaluated and verified using Ubenimex, a broad-spectrum inhibitor of LAP. The results reveal that rEM-LAP could inhibit cyst growth and invasion and induce specific immunity response in BALB/c mice infected with E. multilocularis protoscoleces. The ultrasonic, MRI, and morphological results show that treatment with rEM-LAP inhibits E. multilocularis infection and reduces cyst weight, number, fibrosis and invasion. The same effect is observed for the treatment with Ubenimex by inhibiting LAP activity. The indirect ELISA shows that rEM-LAP could induce specific immunity response and produce high levels of IgG, IgG1, IgG2a, IgM, and IgA, and the serum levels of IFN-γ and IL-4 are significantly increased compared to the control groups, indicating that treatment with rEM-LAP leads to a Th1 and Th2 mixed-type immune response. This study suggests that EM-LAP could be a potential therapeutic target of E. multilocularis infection.

A ratiometric fluorescence probe for selective and sensitive detection of leucine aminopeptidase in lysosome

We designed a novel ratiometric fluorescent probe P1-Leu with a donor-acceptor-donor fluorophore for the detection of leucine aminopeptidase in lysosomes. P1-Leu exhibits a lower detection limit than the ratiometric donor-π-acceptor probe, due to the low ratiometric background. Besides, P1-Leu has good lysosome-targeting ability and realizes the distinction of LAP levels in different cells.

A label-free and modification-free ratiometric electrochemical strategy for enhanced natural enzyme detection using a bare electrode and nanozymes system

Ratiometric electrochemical assays have been demonstrated to be more sensitive and selective in various sensing events, mainly due to their affordable built-in correction and good self-reference capability. But it is known that complicated modification and labeling operations usually are necessary for the construction of ratiometric electrochemical assays, therefore is a hot and important issue needing consideration carefully. We herein report a new yet simple bare electrode-based ratiometric electrochemical bioassay to achieve sensitive and selective analysis of alkaline phosphatase (ALP), using a liquid phase system that contains CoOOH nanozymes and commercially available indicator substrate. This proposed bioassay works based on the ratiometric change of dual electrochemical signals, arising from an exclusive target ALP-triggered hydrolysis of electrochemical substrate p-nitrophenyl phosphate (PNPP). In this design, the two hydrolyzed products of electrochemically active p-nitrophenol (PNP) and electrochemically inactive phosphate anion (PO₄^3-) are responsible together for the ratiometric electrochemical analysis of ALP. PNP exhibits a straightforward current response toward ALP content; however, PO₄^3- cannot show a direct electrochemical signal thus is rationally designed to offer an alternative response by linking it with the specific CoOOH nanozyme-catalyzed reaction of 3,3',5,5'-tetramethylbenzidine (TMB) and H₂O₂, in which the nanozyme-catalyzed product oxTMB shows a direct reduction current at the GCE, and significantly decreases with increasing PO₄^3- species due to the good inhibition of PO₄^3- toward CoOOH nanozyme activity. As a result, a ratiometric electrochemical strategy for ALP analysis with a low limit of detection of 0.366 U/L (S/N = 3) was successfully achieved by integrating the above direct and indirect dual electrochemical responses. This developed bioassay can allow the quantitative diagnosis of ALP activity especially with a label-free and modification-free merit, therefore paving the way for simple, convenient, and portable electroanalytical tools in biosensing design and application.

Convenient and ultrasensitive detection of live Salmonella using ratiometric electrochemical molecular substrates

Salmonella contamination is a major concern in food and public health safety, and carrying out episodic monitoring of Salmonella contamination in food and water bodies is essential for safeguarding public health and the economy. Therefore, there is an urgent need to develop an easy-to-operate Salmonella-targeting point-of-care detection platform. To this end, we designed two activity-based latent ratiometric electrochemical molecular substrates, denoted as Sal-CAF and Sal-NBAF, specifically for achieving easy, rapid, and selective profiling of Salmonella esterase (a Salmonella biomarker) under physiological conditions. The octyl esters of the substrates were cleaved by the esterase and triggered the trimethyl lock to eject the electron-rich aminoferrocene derivatives (CAF and NBAF), and the corresponding electrochemical signals were tracked at the negative region (-0.08 V vs Ag/AgCl) of the voltammetric spectrum. The Sal-CAF substrate was used to determine the concentration of Salmonella in a wide dynamic range (1.03 × 10⁵-1.1 × 10¹⁰ CFU mL^-1) with a low detection limit of 39.27 × 10³ CFU mL^-1. The developed probes were tested against various bacteria but were only activated by live Salmonella. Furthermore, the Sal-CAF probe was used directly in quantifying spiked live Salmonella spiked in milk samples and also used to effectively monitor and quantify Salmonella production in real-time. These achievements indicated the Sal-CAF probe to be a promising platform for point-of-care Salmonella analysis.

A preliminary study for the development of cleavable linkers using activatable fluorescent probes targeting leucine aminopeptidase

The Kinetic and ex vivo stability studies of LAP-responsive fluorescent probes demonstrated that the stability and intrinsic drug releasing activity of the cleavalbe linker can be evaluated by a peptidase-responsive activatable fluorescent probe.

Rational design of a fluorescent probe for the detection of LAP and its application in drug-induced liver injury

Drug-induced liver injury (DILI) has become a common adverse effect in routine clinical practice, which would further cause the disorder of enzymatic system that respond to multiple pathological progresses. Leucine aminopeptidase (LAP) is regarded as a biomarker in the early course of various liver diseases, in this work, a fluorescent probe NCPL was designed and synthesized for the detecting of LAP. NCPL possessed excellent properties including high selectivity, sensitivity and affinity toward LAP, it could real-time image the LAP activity in living cells and tissues. Additionally, the upregulation of LAP under the APAP-induced liver injury model was also illustrated by NCPL. In conclusion, NCPL as a novel tool could be used for the detection of LAP and monitoring liver function in clinic.

A ratiometric fluorescent probe based on quinoline for monitoring and imaging of Leucine aminopeptidase in liver tumor cells

Leucine aminopeptidase (LAP) is known as an important potential biomarker for liver malignancy and it is urgent to develop an intuitive and effective method to monitor the activity of LAP in liver cancer. Although, numerous LAP fluorescent probes had been developed, it is still a challenge to detect LAP activity in liver cancer. Herein, combained with the DFT, we reported a novel galactose-appended hepatoma-specific ratiometric fluorescent probe (Gal-QL-Leu) based on quinoline group for imaging and tracing LAP in liver tumor cells. Probe Gal-QL-Leu demonstrated a obvious ratiometric characteristics, better selectivity, good biocompatibility and high sensitivity. Moreover, the selective imaging of LAP in HepG2, HCT116, A549 and HeLa cells had been achieved with probe Gal-QL-Leu, demonstrating good application prospect in the detection of LAP activity in liver tumor cells.