Amino acid metabolic reprogramming in the tumor microenvironment and its implication for cancer therapy.

Amino acids are essential building blocks for proteins, crucial energy sources for cell survival, and key signaling molecules supporting the resistant growth of tumor cells. In tumor cells, amino acid metabolic reprogramming is characterized by the enhanced uptake of amino acids as well as their aberrant synthesis, breakdown, and transport, leading to immune evasion and malignant progression of tumor cells. This article reviews the altered amino acid metabolism in tumor cells and its impact on tumor microenvironment, and also provides an overview of the current clinical applications of amino acid metabolism. Innovative drugs targeting amino acid metabolism hold great promise for precision and personalized cancer therapy.

Photoelectrochemical aptasensing of oxytetracycline based on a BiVO4-carboxylated graphene-WO3 Z-scheme heterojunction.

A new BiVO4-carboxylated graphene (cG)-WO3 Z-scheme heterojunction was constructed on a fluorine-doped tin oxide (FTO) substrate electrode by ultrasonic mixing and cast-coating for determination of oxytetracycline (OTC). Since cG can absorb visible light and well match with the energy levels of WO3 and BiVO4 to promote the charge separation and transfer, the photocurrent on the BiVO4-cG-WO3/FTO photoelectrode is 4.4 times that on the control BiVO4-WO3/FTO photoelectrode. An amino-functionalized OTC aptamer was fixed on the BiVO4-cG-WO3/FTO photoelectrode by the 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide/N-hydroxysuccinimide mediated amide reaction, and then hexaammonium ruthenium(III) (Ru(NH3)63+) was attached to the OTC aptamer to increase the photocurrent response to the OTC binding. Under the optimized conditions, the photocurrent on the BiVO4-cG-WO3/FTO photoelectrode at 0 V vs SCE was linear with the common logarithm of OTC concentration from 0.01 nM to 500 nM, with a limit of detection of 3.1 pM (S/N = 3). Satisfactory recovery results were obtained in the analysis of real water samples.

Biocompatibility and Biological Effects of Surface-Modified Conjugated Polymer Nanoparticles.

Semiconductiong polymer nanoparticles (Pdots) have a wide range of applications in biomedical fields including biomolecular probes, tumor imaging, and therapy. However, there are few systematic studies on the biological effects and biocompatibility of Pdots in vitro and in vivo. The physicochemical properties of Pdots, such as surface modification, are very important in biomedical applications. Focusing on the central issue of the biological effects of Pdots, we systematically investigated the biological effects and biocompatibility of Pdots with different surface modifications and revealed the interactions between Pdots and organisms at the cellular and animal levels. The surfaces of Pdots were modified with different functional groups, including thiol, carboxyl, and amino groups, named Pdots@SH, Pdots@COOH, and Pdots@NH2, respectively. Extracellular studies showed that the modification of sulfhydryl, carboxyl, and amino groups had no significant effect on the physicochemical properties of Pdots, except that the amino modification affected the stability of Pdots to a certain extent. At the cellular level, Pdots@NH2 reduced cellular uptake capacity and increased cytotoxicity due to their instability in solution. At the in vivo level, the body circulation and metabolic clearance of Pdots@SH and Pdots@COOH were superior to those of Pdots@NH2. The four kinds of Pdots had no obvious effect on the blood indexes of mice and histopathological lesions in the main tissues and organs. This study provides important data for the biological effects and safety assessment of Pdots with different surface modifications, which pave the way for their potential biomedical applications.

Development and Performance Evaluation of a Low-Cost Portable PM2.5 Monitor for Mobile Deployment.

The concentration of fine particulate matter (PM2.5) is known to vary spatially across a city landscape. Current networks of regulatory air quality monitoring are too sparse to capture these intra-city variations. In this study, we developed a low-cost (60 USD) portable PM2.5 monitor called Smart-P, for use on bicycles, with the goal of mapping street-level variations in PM2.5 concentration. The Smart-P is compact in size (85 × 85 × 42 mm) and light in weight (147 g). Data communication and geolocation are achieved with the cyclist's smartphone with the help of a user-friendly app. Good agreement was observed between the Smart-P monitors and a regulatory-grade monitor (mean bias error: −3.0 to 1.5 µg m−3 for the four monitors tested) in ambient conditions with relative humidity ranging from 38 to 100%. Monitor performance decreased in humidity > 70% condition. The measurement precision, represented as coefficient of variation, was 6 to 9% in stationary mode and 6% in biking mode across the four tested monitors. Street tests in a city with low background PM2.5 concentrations (8 to 9 µg m−3) and in two cities with high background concentrations (41 to 74 µg m−3) showed that the Smart-P was capable of observing local emission hotspots and that its measurement was not sensitive to bicycle speed. The low-cost and user-friendly nature are two features that make the Smart-P a good choice for empowering citizen scientists to participate in local air quality monitoring.

Design and Engineering of Hypoxia and Acidic pH Dual-Stimuli-Responsive Intelligent Fluorescent Nanoprobe for Precise Tumor Imaging.

Stimulus-responsive fluorescence imaging modality shows great promise for detection of tumor due to the advantages of high sensitivity, simplicity and noninvasiveness. However, some non-cancer regions including nodules and inflammation may also exhibit a stimulus-related characteristic, which cause the problem of nonspecific responsiveness and then cause "false positive" results for tumor recognition. Herein, hypoxia and acidic pH, two typical features strongly associated with tumor invasion, progression and metastasis in tumor microenvironment (TME), are chosen as dual stimuli to fabricate "dual lock-and-key" fluorescent nanoprobe for highly specific and precise imaging of tumor cells. Mesoporous silica coated gold nanorods (AuNR@mSiO2 ) are employed as nanocarrier and nanoquencher to load the pH-sensitive fluorescent reporter (Rho-TP). Azobenzene (azo) which can be reduced to amines by the highly expressed azoreductase under hypoxic conditions, is elected as the effective gatekeeper for AuNR@mSiO2 by forming complex with ß-cyclodextrin polymer via host-guest interaction (azo/ß-CDP). By elaborately combining the hypoxia-responsive gatekeeper and pH-responsive fluorescent signal reporter into one nanoprobe, sensitive and specific imaging of tumor cells can be realized. The fabricated dual lock-and-key fluorescent nanoprobe successfully further apply in tumor-bearing mice model, which indicate potential of early diagnosis and assessment of cancer treatment.

Ligation-dependent rolling circle amplification method for ATP determination with high selectivity and sensitivity.

It is highly demanded to develop methods for the reliable detection of ATP, which plays an extremely important role in clinical diagnosis, biomedical engineering, and food chemistry. However, the methods currently available for ATP sensing strongly rely on the utilization of expensive and sophisticated instruments or the use of ATP aptamers with mediocre sensitivity and selectivity. To circumvent these drawbacks, we herein propose an efficient method for ATP detection by integrating highly specific ATP-dependent ligation reaction with dual-stage signal amplification techniques executed by rolling circle amplification (RCA) and the subsequently fabricated DNAzymes ready for the catalytic cleavage and fluorescence signal generation from molecular beacons (MBs). The detection limit is down to 35 pM with a linear range from 0.05 nM to 200 nM. More importantly, the sensing strategy can effectively discriminate ATP from its analogues and the results from the spiked human serum albumin (HSA) samples further confirm the reliability for practical applications. Considering the high sensitivity and selectivity, wash-free and isothermal convenience, and the simplicity in probe design, the strategy reported herein paves a new avenue for the effective determination of ATP and other biomolecules in fundamental and applied research.

Recent advances of fluorescent biosensors based on cyclic signal amplification technology in biomedical detection.

The cyclic signal amplification technology has been widely applied for the ultrasensitive detection of many important biomolecules, such as nucleic acids, proteins, enzymes, adenosine triphosphate (ATP), metal ions, exosome, etc. Due to their low content in the complex biological samples, traditional detection methods are insufficient to satisfy the requirements for monitoring those biomolecules. Therefore, effective and sensitive biosensors based on cyclic signal amplification technology are of great significance for the quick and simple diagnosis and treatment of diseases. Fluorescent biosensor based on cyclic signal amplification technology has become a research hotspot due to its simple operation, low cost, short time, high sensitivity and high specificity. This paper introduces several cyclic amplification methods, such as rolling circle amplification (RCA), strand displacement reactions (SDR) and enzyme-assisted amplification (EAA), and summarizes the research progress of using this technology in the detection of different biomolecules in recent years, in order to provide help for the research of more efficient and sensitive detection methods.

Improved tendon healing by a combination of Tanshinone IIA and miR-29b inhibitor treatment through preventing tendon adhesion and enhancing tendon strength.

Background: Despite significant advances in the materials and methods development used in surgical repair and postoperative rehabilitation, the adhesion formation remains the most common clinical problem in tendon injuries. Therefore, the development of novel therapies is necessary for targeting at preventing tendon adhesion formation and improving tendon strength. Methods: We used rat fibroblasts for in vitro experiments to determine the optimal concentration of TSA in rats, and then set up negative control group, TSA intervention group, mir-29b interference adenovirus intervention group and TSA and mir-29b interference adenovirus co-intervention group. By comparing cell proliferation and protein expression in different group, we verified the effect and mechanism of drugs on fibroblast function. At the same time, the Sprague-Dawley rat Achilles tendon model in vivo was established in this study, which was divided into sham operation group and operation group. Afterwards in the operation group, mir-29b inhibitor and placebo were injected every 3 days respectively. Then the injection inhibitor group was divided into 5 groups which mean TSA was injected into the marked area at 0, 6, 24 and 72 hours after operation for 1 week, finally all of the rats were died at 3 weeks after operation. Through the observation of general properties, histological observation of Achilles tendon injury, biomechanical test and cell and protein expression in rats' tendon cell, the effect of drugs on tendon adhesion formation was analyzed. Results: We demonstrated that the combination of miR-29b inhibitor and tanshinone IIA(TSA) could prevent tendon adhesion and also enhance tendon strength. Mechanically, the miR-29b inhibitor could activate the TGF-ß/Smad3 pathway to trigger endogenous pathways and induce a high proliferation of fibroblast. Subsequently, we also found adding TSA after 6 hours of miR-29b treatment gave less cell cytotoxicity in our rat model with better outcome of less tendon adhesion and enhanced strength. Conclusion: We conclude that the use of miR-29b inhibitor at the end of the tendon break could initiate endogenous repair mechanism and subsequently use of TSA should be able to inhibit the exogenous repair mechanism. Therefore, the combination of both treatments could prevent tendon adhesion and ensure tendon strength. Our findings suggested that this approach would be a feasible approach for tendon repair.

Exonuclease III-assisted signal amplification strategy for sensitive fluorescence detection of polynucleotide kinase based on poly(thymine)-templated copper nanoparticles.

A sensitive and label-free fluorometric method has been developed for the determination of polynucleotide kinase (PNK) activity, by employing exonuclease III (Exo III)-assisted cyclic signal amplification and poly(thymine)-templated copper nanoparticles (polyT-CuNPs). In the presence of PNK, cDNA with 5'-hydroxyl termini was phosphorylated and then hybridized with tDNA to form the cDNA/tDNA duplex, which subsequently triggered the λ exonuclease cleavage reaction, eventually resulting in the release of tDNA. The released tDNA could unfold the hairpin structure of HP DNA to generate partially complementary duplex (tDNA/HP DNA), wherein the HP DNA possessed T-rich sequences (T30) and tDNA recognition sequence. With the help of Exo III digestion, the tDNA was able to initiate the cycle for the generation of T-rich sequences, the template for the formation of fluorescent CuNPs. Conversely, the cDNA could not be cleaved by λ exonuclease without PNK and individual HP DNA could not be hydrolyzed by Exo III. The T-rich sequence was caged in HP DNA, resulting in a weak fluorescence signal. Under optimized conditions, the fluorescence intensity was linearly correlated to a concentration range of 0.001 to 1 U mL-1 with a low detection limit of 2 × 10-4 U mL-1. Considering the intriguing analytical performance, this approach could be explored to screen T4 PNK inhibitors and hold promising applications in drug discovery and disease therapy.

A novel fluorometric method for inorganic pyrophosphatase detection based on G-quadruplex-thioflavin T.

In this paper, we propose a fluorometric approach for the highly sensitive detection of inorganic pyrophosphatase (PPase) based on G-quadruplex-thioflavin T (ThT). In the absence of PPase, Cu2+ can coordinate with pyrophosphate (PPi) to generate a Cu2+/PPi complex. Then the G-rich sequence folds into the G-quadruplex structure, which can combine with ThT to generate a remarkable fluorescent signal. In the presence of PPase, the coordinated compound can be destroyed by the PPase catalyzed hydrolysis of PPi into inorganic phosphate (Pi). The subsequent release of Cu2+ can compete with ThT to induce a tighter G-quadruplex structure, causing the release of ThT and a sharp fluorescence decrease. Based on this mechanism, a facile and quantitative strategy for PPase detection was developed. The fluorescence intensity of the system shows a linear relationship with the PPase activities in the range of 0.5-30 U/L with a detection limit as low as 0.48 U/L. The proposed strategy for fluorescence spectrometric PPase detection is convenient, cost effective, and sensitive. This can be utilized to evaluate the inhibition effect of NaF on PPase as well as diagnose PPase-related diseases.

A label-free fluorescence method based on terminal deoxynucleotidyl transferase and thioflavin T for detecting prostate-specific antigen.

Prostate-specific antigen (PSA) is the only biomarker for the diagnosis of prostate cancer. So the PSA screening test is very important due to the high occurrence of prostate cancer in men. In this work, a label-free fluorescent method was developed based on terminal deoxynucleotidyl transferase (TdT) and G-quadruplex-thioflavin T complex for detecting PSA. In the absence of PSA, the PSA aptamer can be used as the primer for TdT extension reactions, resulting in the formation of G-quadruplexes and generation of strong fluorescent signals. After the addition of PSA, the PSA-aptamer complex prevented the TdT extension reaction due to steric hindrance, thus resulting in a poor fluorescent signal. The assay showed a wide linear range (0.1 to 80 pg/mL) and a detection limit of 0.086 pg/mL (S/N = 3). It also has good specificity for PSA determination and gives satisfactory results when applied to biological samples. Conceivably, its merits such as good selectivity and high sensitivity indicate that the proposed method has a promising application potential in the clinical diagnosis and treatment of prostate cancer. Graphical abstract.

Exonuclease III-assisted fluorometric aptasensor for the carcinoembryonic antigen using graphene oxide and 2-aminopurine.

A reliable fluorometric assay is described for the determination carcinoembryonic antigen (CEA) using exonuclease III (Exo III) and a 2-aminopurine binding aptamer. In the absence of CEA, dsDNA is degraded by Exo III, and free 2-AP (which has a blue fluorescence with excitation/emission maxima of 310/365 nm) is released. Strong fluorescence is generated after addition of graphene oxide (GO) to the solution. However, the 2-AP modified DNA (T2) cannot be degraded in the presence of CEA by Exo III due to the interaction between CEA and aptamer T1. Hence, only weak fluorescence can be detected after addition of GO. In this system, CEA can be quantified in the 0.05 - 2 ng·mL-1 concentration range with a detection limit of 30 pg·mL-1 (at S/N = 3). The method was successfully applied to analyze serum samples for CEA. Graphical Abstract An exonuclease III-assisted fluorometric aptasensor has been developed for the detection of carcinoembryonic antigen using graphene oxide and 2-aminopurine.

Fluorometric determination of the activity of uracil-DNA glycosylase by using graphene oxide and exonuclease I assisted signal amplification.

The base-excision repair enzyme uracil-DNA glycosylase (UDG) plays a crucial role in the maintenance of genome integrity. The authors describe a fluorometric method for the detection of the activity of UDG. It is making use of (a) a 3'-FAM-labeled hairpin DNA probe with two uracil deoxyribonucleotides in the self-complementary duplex region of its hairpin structure, (b) exonuclease I (Exo I) that catalyzes the release of FAM from the UDG-induced stretched ssDNA probe, and (c) graphene oxide that quenches the green FAM fluorescence of the intact hairpin DNA probe in the absence of UDG. If Exo I causes the release of FAM from the hairpin DNA probe, the fluorescence peaking at 517 nm is turned off in the absence of UDG but turned on in its presence. The resulting assay has a wide linear range (0.008 to 1 U·mL-1) and a detection limit as low as 0.005 U·mL-1. It has good specificity for UDG over potentially interfering enzymes and gave satisfactory results when applied to biological samples. Conceivably, the method may be used in a wide range of applications such as in diagnosis, drug screening, and in studying the repair of DNA lesions. Graphical abstract Schematic presentation of a fluorometric strategy for detection of the activity of uracil-DNA glycosylase by using on graphene oxide and exonuclease I assisted signal amplification.

Fluorescent Method for the Detection of Biothiols Using an Ag⁺-Mediated Conformational Switch.

In this work, a novel, simple, and time-saving fluorescence approach for the detection of biothiols (glutathione and cysteine) was developed by employing a DNA probe labeled with 2-aminopurine. As an adenine analogue, 2-aminopurine exhibits high fluorescence intensity that can be rapidly quenched in the presence of DNA. In the presence of Ag⁺, the fluorescence increased significantly, which was a result of the formation of cytosine⁻Ag⁺⁻cytosine base pairs and the release of 2-aminopurine. Upon addition of either glutathione or cysteine, the structure of cytosine⁻Ag⁺⁻cytosine was disrupted, a product of the stronger affinity between biothiols and Ag⁺. As a result, the 2-aminopurine-labeled DNA probe returned to its former structure, and the fluorescence signal was quenched accordingly. The detection limit for glutathione and cysteine was 3 nM and 5 nM, respectively. Furthermore, the determination of biothiols in human blood serum provided a potential application for the probe as a diagnostic tool in clinical practice.

Label-free detection of exonuclease III activity and its inhibition based on DNA hairpin probe.

In this paper, we have developed a label-free and rapid fluorescence assay for the detection of exonuclease III (exo III) activity via thioflavin T (ThT) as the G-quadruplex inducer. In this assay, a hairpin probe (HP) with a 5'-guanine-rich (G-rich) sequence is employed as the substrate for exo III. In the presence of exo III, HP can be digested at 3'-OH termini releasing 5'-G-rich sequence. Then, the 5'-G-rich sequence folds into a G-quadruplex, which can be recognized quickly by the ThT dye resulting in an increase in fluorescence emission. This strategy can detect exo III activity as low as 0.5 U/mL. This assay is simple and of low cost without the requirement of labeling with a fluorophore-quencher pair.

Is it appropriate to measure age-related lumbar disc degeneration on the mid-sagittal MR image? A quantitative image study.

PURPOSE: Even though phenotypes of disc degeneration vary on different sagittal magnetic resonance images (MRI), measurements typically are acquired on the mid-sagittal MRI. This study investigated the appropriateness of using the mid-sagittal MRI to measure various phenotypes of age-related disc degeneration. METHODS: Lumbar spine MRIs of 66 subjects (mean age 50.3 years, standard deviation 16.5 years, range 22-84 years) were studied. An image analysis program Spine Explorer was used to obtain quantitative measurements for disc height, bulging, and signal on para- and mid-sagittal T2-weighted MRIs. Measurements on para- and mid-sagittal MRIs and their associations with age were compared. RESULTS: Measurements of disc height, signal, and posterior disc bulging acquired on the mid-sagittal MRI were greater than those on the para-sagittal MRIs. Disc height measurements were not linearly associated with age. Greater age was correlated with greater anterior (r = 0.45, P < 0.001) and posterior (r = 0.33, P < 0.01) bulging on para-sagittal MRIs, but not posterior disc bulging on the mid-sagittal MRI (r = - 0.10, P > 0.05). Disc signal intensity measurements on the mid-sagittal MRI had stronger correlations with age than those on para-sagittal MRIs. Mean and standard deviation of disc signal intensity acquired on the mid-sagittal MRI had the strongest correlations with age among all measures of disc degeneration studied (r = - 0.50, - 0.67, respectively, P < 0.001 for both). CONCLUSIONS: Disc signal measurements acquired on the mid-sagittal MRI were reliable and had strong correlations with age and thus can be used as an appropriate measure of disc degeneration. Disc bulging had better be measured on para-sagittal MRIs. Although severe disc narrowing clearly is a sign of severe disc degeneration, disc height was not linearly associated with age.

Colorimetric determination of the activity of alkaline phosphatase based on the use of Cu(II)-modulated G-quadruplex-based DNAzymes.

A colorimetric detection scheme is introduced for the determination of alkaline phosphatase (ALP) activity based on Cu(II)-modulated G-quadruplex-based DNAzymes. It is exploiting the strong affinity of Cu(II) for pyrophosphate (PPi) upon which the cofactor PPi is trapped by Cu(II). Hence, the activity of the DNAzyme is inhibited. ALP catalyzes the hydrolysis of PPi, causing the release of Cu(II). DNAzyme, in turn, is activated and catalyzes the cleavage of the DNA probe substrate. The released G-rich sequence folds into the G-quadruplex, which can bind hemin and catalyze the oxidation of 2,2'-azinobis (3-ethylbenzothiozoline)-6-sulfonate (ABTS), and this leads to an increase in absorbance at 420 nm. Absorbance increases linearly with increasing ALP activity in 0.07 to 300 U.L-1 range, with a 70 mU.L-1 detection limit. The method was applied in ALP inhibition tests and to the determination of ALP activity in spiked serum samples where it gave satisfactory results. Graphical abstract A colorimetric method has been developed for the detection of alkaline phosphatase based on the use of Cu(II)-modulated G-quadruplex-based DNAzymes.

A Label-Free Fluorescent Assay for the Rapid and Sensitive Detection of Adenosine Deaminase Activity and Inhibition.

Adenosine deaminase (ADA), able to catalyze the irreversible deamination of adenosine into inosine, can be found in almost all tissues and plays an important role in several diseases. In this work, we developed a label-free fluorescence method for the detection of adenosine deaminase activity and inhibition. In the presence of ADA, ATP has been shown to be hydrolyzed. The ATP aptamer was shown to form a G-quadruplex/thioflavin T (ThT) complex with ThT and exhibited an obvious fluorescence signal. However, the ATP aptamer could bind with ATP and exhibited a low fluorescence signal because of the absence of ADA. This assay showed high sensitivity to ADA with a detection limit of 1 U/L based on an SNR of 3 and got a good linear relationship within the range of 1⁻100 U/L with R² = 0.9909. The LOD is lower than ADA cutoff value (4 U/L) in the clinical requirement and more sensitive than most of the reported methods. This technique exhibited high selectivity for ADA against hoGG I, UDG, RNase H and λexo. Moreover, this strategy was successfully applied for assaying the inhibition of ADA using erythro-9-(2-hydroxy-3-nonyl) adenine (EHNA) and, as such, demonstrated great potential for the future use in the diagnosis of ADA-relevant diseases, particularly in advanced drug development.

An Exonuclease I-Based Quencher-Free Fluorescent Method Using DNA Hairpin Probes for Rapid Detection of MicroRNA.

MicroRNAs (miRNAs) act as biomarkers for the diagnosis of a variety of cancers. Since the currently used methods for miRNA detection have limitations, simple, sensitive, and cost-effective methods for the detection of miRNA are required. This work demonstrates a facile, quencher-free, fluorescence-based analytical method for cost-effective and sensitive detection of miRNA using a super 2-aminopurine (2-AP)-labeled hairpin probe (HP) and exonuclease I activity. Specifically, the fluorescence of 2-AP is strongly quenched when it is incorporated within DNA. In the presence of a target miRNA, HP attains an open conformation by hybridizing with the target miRNA to form a double-stranded structure with a protruding 3'-terminus. Next, the digestion of the protruding 3'-terminus is triggered by exonuclease I, during which 2-AP is released free in solution from the DNA, thereby increasing fluorescence. This method is highly sensitive, with a detection limit of 0.5 nM-10 times lower than a previously reported quencher-free fluorescence method. Furthermore, this method has potential applications in clinical diagnosis and biomedical research.

A Novel Detection Method of Human Serum Albumin Based on the Poly(Thymine)-Templated Copper Nanoparticles.

In this work, we developed a facile fluorescence method for quantitative detection of human serum albumin (HSA) based on the inhibition of poly(thymine) (poly T)-templated copper nanoparticles (CuNPs) in the presence of HSA. Under normal circumstances, poly T-templated CuNPs can display strong fluorescence with excitation/emission peaks at 340/610 nm. However, in the presence of HSA, it will absorb cupric ion, which will prevent the formation of CuNPs. As a result, the fluorescence intensity will become obviously lower in the presence of HSA. The analyte HSA concentration had a proportional linear relationship with the fluorescence intensity of CuNPs. The detection limit for HSA was 8.2 × 10-8 mol·L-1. Furthermore, it was also successfully employed to determine HSA in biological samples. Thus, this method has potential applications in point-of-care medical diagnosis and biomedical research.