High-efficiency peroxidase mimics for fluorescence detection of H2O2 and L-cysteine.

Enzyme-based sensing platforms have undergone rapid development in the field of diagnosis and bioanalysis. Here we present a novel fluorescent artificial enzyme-based detection strategy for L-cysteine (Cys) and H2O2 by fabricating a series of Au-Ag bimetallic nanoparticles with peroxidase-like activity. Taking advantage of the enhanced performance of catalysts by optimizing the surface structure, the sensitive detection of Cys with an ultralow detection limit of 0.035 µM and accurate quantification in the range of 0.075-2 µM were achieved. It was revealed that the mechanism of the catalytic process on the Au-Ag surface follows the electron transfer mechanism rather than active species, that is the peroxidase-like catalysts work as electron transfer intermediates and the electron transfer efficiency will increase with the larger electron cloud density of active sites derived from the electronic synergistic effect between Au and Ag, contributing to the enhanced catalytic activity of peroxidase mimics. This finding could provide guidance for the structural design of high-activity peroxidase mimics.

Single-Molecule Nanocatalysis Reveals the Kinetics of the Synergistic Effect Based on Single-AuAg Bimetal Nanocatalysts.

Decades of extensive research efforts by scientists in the field of catalysis and nanomaterials have led to a large number of excellent bimetallic nanocatalysts. However, in many cases, the mechanism of the synergistic effect in bimetal catalyst-catalyzed reactions has been systematically neglected due to technical limitations. Herein, we use single-molecule fluorescence microscopy (SMFM) to reveal the mechanism of the synergy of the Au and Ag bimetal catalyst. Compared with that of the Ag nanocatalyst, the incorporation of Au changes the reaction pathway of Amplex Red and H2O2 from a noncompetitive to a competitive reaction mechanism, showing much higher catalytic efficiency. Additionally, the incorporation also inhibits the spontaneous surface reconstruction and facilitates the reaction-induced surface restructuring of the nanocatalyst, resulting in the enhancement of stability and reactivity. These findings provide useful insights into tailoring the reactivity of metal catalysts. This work also confirms the power of SMFM in revealing the origin of the catalytic activity of composite catalysts.

Graphene oxide-assisted synthesis of N, S Co-doped carbon quantum dots for fluorescence detection of multiple heavy metal ions.

Detection of heavy metal ions (HMIs) in water is an important topic in the field of analytical chemistry and environmental science. Fluorescence spectroscopy is one of the most promising strategies due to its simple instrument, low investment, rapid and convenient operation. However, current fluorescence probes for detecting HMIs are typically selective for certain ions. Herein we reported the development of a novel strategy that determined the total content of HMIs in water by fluorescence spectroscopy. A novel fluorescent nitrogen, sulfur co-doped carbon quantum dots (N, S-CQDs) was prepared via graphene oxide-assisted synthesis method. The results showed that, with the fluorescence quenching strategy, N, S-CQDs exhibited a wide linear response to a series of water-soluble metal ions. The fluorescence of N, S-CQDs is stable in a wide range of pH 4-11. The detection mechanism was proved that the integration, caused by coordination interaction between S element in N, S-CQDs and the d-orbital of associated metal ions, was the main reason for fluorescence quenching. In practice, the N, S-CQDs were applied to determine total content of HMIs in water successfully. Interestingly, further experiment proved that the N, S-CQDs could effectively remove HMIs in water after centrifuging and filtering thoroughly. It was shown that the fluorescence of N, S-CQDs was obviously quenched by the multiple-ions-involved water and scavenging effect of N, S-CQDs on HMIs with centrifugal in which the concentration of individuals meets the Chinese National Standard. This indicates that the N, S-CQDs are of a wide application prospect in water quality analysis.

Riligustilide alleviates hepatic insulin resistance and gluconeogenesis in T2DM mice through multitarget actions.

Riligustilide (RG), one of the dimeric phthalides of Angelica sinensis and Ligusticum chuanxiong, was confirmed effective against many diseases. However, its effects on type 2 diabetes mellitus (T2DM) and the underlying molecular mechanisms have not been clearly elucidated yet. The current study was designed to investigate the hypoglycemic potential by which RG affects the pathogenesis of T2DM. Comprehensive insights into the effects and underlying molecular mechanisms of RG on attenuating aberrant metabolism of glucose were determined in high-fat diet-induced T2DM mice and insulin-resistant (IR) HepG2 cells. In high-fat diet-induced C57BL/6J mice, RG administration significantly reduced hyperglycemia, decreased hyperinsulinemia, and ameliorated glucose intolerance. Mechanistically, RG activated PPARγ and insulin signaling pathway to improve insulin sensitivity, and increase glucose uptake as well as glycogenesis. In addition, RG also upregulated AMPK-TORC2-FoxO1 axis to attenuate gluconeogenesis in vivo and in vitro. According to the findings, RG may be a promising candidate for the treatment of T2DM.

Graphite-like Carbon Nitride Nanotube for Electrochemiluminescence Featuring High Efficiency, High Stability, and Ultrasensitive Ion Detection Capability.

Herein, for the first time, we introduced a novel electrochemiluminescence (ECL) luminophore based on a one-dimensional g-C3N4 nanotube using K2S2O8 as the coreactant. The g-C3N4 nanotube/K2S2O8 couple displayed very satisfactory ECL performance, i.e., an ECL efficiency (ΦECL) of 437% (vs 100% for the Ru(bpy)32+/K2S2O8 reference) and excellent ECL stability (the relative standard deviation (RSD) = 0.78%). By contrast, ΦECL and RSD of the control g-C3N4 nanosheet/K2S2O8 couple were merely 196% and 45.34%, respectively. The mechanism study revealed that the g-C3N4 nanotube features a large surface area and much lower interfacial impedance in the porous microstructure, which are beneficial for accelerating the charge transfer rate and stabilizing charge/excitons for ECL. Moreover, using the g-C3N4 nanotube/K2S2O8 system as a sensing platform, excellent Cu2+ detection capability was also achieved. Our work thus triggers a promising g-C3N4 nanomaterial system toward ECL application.

Adsorption and desorption mechanisms on graphene oxide nanosheets: Kinetics and tuning.

A knowledge of the adsorption and desorption behavior of sorbates on surface adsorptive site (SAS) is the key to optimizing the chemical reactivity of catalysts. However, direct identification of the chemical reactivity of SASs is still a challenge due to the limitations of characterization techniques. Here, we present a new pathway to determine the kinetics of adsorption/desorption on SASs of graphene oxide (GO) based on total internal reflectance fluorescence microscopy. The switching on and off of the fluorescent signal of SAS lit by carbon dots (CDs) was used to trace the adsorption process and desorption process. We find that sodium pyrophosphate (PPi) could increase the adsorption equilibrium of CDs thermodynamically and promote the substrate-assisted desorption pathway kinetically. At the single turnover level, it was disclosed that the species that can promote desorption may also be an adsorption promoter. Such discovery provides significant guidance for improving the chemical reactivity of the heterogeneous catalyst.

Oxazolomycins produced by Streptomyces glaucus and their cytotoxic activity.

Six oxazolomycins (1-6) were isolated from the fermentation broth of a soil-borne bacterial strain, Streptomyces glaucus. The structures of the new compounds, oxazolomycins D-F (1-3) and glaucumycins A, B (6a/6b), were elucidated by detailed spectroscopic data analysis. Oxazolomycins 1, 2, 4, and 5 demonstrated weak or modest cytotoxic activities against four human cancer cell lines, with IC50 values ranging from 10.6 ± 1.7 to 89.5 ± 6.6 µM (or >100 µM). Further study showed that 4 caused S phase cell cycle arrest in SMMC7721 cells through down-regulating the protein expression of cyclin A2, CDK2. Meanwhile, 4 induced apoptosis in SMMC7721 cells through down-regulating the protein levels of Bcl-2, up-regulating the levels of Bax, and activating the cleavage of caspase-3.

Levistolide A Attenuates Alzheimer's Pathology Through Activation of the PPARγ Pathway.

Alzheimer's disease (AD) is a neurodegenerative disease characterized by ß-amyloid (Aß) protein deposition, neurofibrillary tangle (NFT) formation, and neuronal loss in the brain. The current study was designed to investigate the potential mechanisms by which levistolide A affects the pathogenesis of AD in an amyloid precursor protein/presenilin 1 (APP/PS1) transgenic (Tg) mouse model of AD and N2a/APP695swe cells. Specifically, behavioral changes in levistolide A-treated APP/PS1 Tg mice were assessed by the nest-building and Morris water maze (MWM) tests. Levistolide A treatment clearly ameliorated memory deficits and cognitive decline in APP/PS1 Tg mice. Aß generation and the inflammatory response in APP/PS1 Tg mouse brains were clearly reduced after long-term levistolide A application. Mechanistically, levistolide A concurrently stimulated the expression of α-secretase and decreased the generation of ß- and γ-secretases. In addition, levistolide A inhibited the phosphorylation of tau in the brains of the Tg mice. Furthermore, in vitro and in vivo experiments suggested that peroxisome proliferator-activated receptor γ (PPARγ) is the key transcription factor that mediates the regulatory effects of levistolide A on the expression of α-, ß-, and γ-secretases and phosphorylation of tau. Collectively, these findings show that levistolide A may be a candidate for the treatment of AD.

A semisynthetic borrelidin analogue BN-3b exerts potent antifungal activity against Candida albicans through ROS-mediated oxidative damage.

In the process of investigating the antifungal structure-activity relationships (SAR) of borrelidin and discovering antifungal leads, a semisynthetic borrelidin analogue, BN-3b with antifungal activity against Candida albicans, was achieved. In this study, we found that oxidative damage induced by endogenous reactive oxygen species (ROS) plays an important role in the antifungal activity of BN-3b. Further investigation indicated that BN-3b stimulated ROS accumulation, increased malondialdehyde (MDA) levels, and decreased reduced/oxidized glutathione (GSH/GSSG) ratio. Moreover, BN-3b decreased mitochondrial membrane potential (MMP) and ATP generation. Ultrastructure analysis revealed that BN-3b severely damaged the cell membrane of C. albicans. Quantitative PCR (RT-qPCR) analysis revealed that virulence factors of C. albicans SAPs, PLB1, PLB2, HWP1, ALSs, and LIPs were all down-regulated after BN-3b exposure. We also found that BN-3b markedly inhibited the hyphal formation of C. albicans. In addition, in vivo studies revealed that BN-3b significantly prolonged survival and decreased fungal burden in mouse model of disseminated candidiasis.

The anti-inflammatory effects of jiangrines from Jiangella alba through inhibition of p38 and NF-κB signaling pathways.

Three pyrrol-2-aldehyde derivatives, including one new compound, jiangrine G (JG), two known compounds, jiangrine A (JA), and pyrrolezanthine (PZ), were isolated from the fermentation broth of Jiangella alba associated with a traditional Chinese medicinal plant Maytenus austroyunnanensis. The structure of jiangrine G was elucidated by a detailed spectroscopic data analysis including data from CD spectra. The anti-inflammatory activities assay demonstrated that JG and JA suppressed the production of pro-inflammatory cytokines including NO, IL-1ß, and IL-6 as well as inhibited the expression of iNOS in LPS-induced RAW 264.7 cells in a dose-dependent manner. While high concentration of PZ dramatically suppressed the protein expression of TNF-α, but stimulated the release of IL-1ß and IL-6. Western blot results revealed that JG, JA, and PZ modulated the expression of pro-inflammatory cytokines via MAPK p38 and NF-κB signaling pathways. For the unique structure of PZ, difference from JG and JA, the signaling pathway involved in mediating its effects on regulating the synthesis of IL-1ß and IL-6 are probably more complicated than that of JG and JA.

Anti-Inflammatory Activities and Liver Protection of Alisol F and 25-Anhydroalisol F through the Inhibition of MAPK, STAT3, and NF-κB Activation In Vitro and In Vivo.

Alisol F and 25-anhydroalisol F isolated from Alisma orientale, were proved to exhibit anti-inflammatory potential in our previous work. In the current study, the anti-inflammatory effects and action mechanisms of alisol F and 25-anhydroalisol F were investigated in vitro. Moreover, the pharmacological effects of alisol F in lipopolysaccharide (LPS)/d-galactosamine (d-gal)-induced acute liver-injured mice were evaluated. The results demonstrated that alisol F and 25-anhydroalisol F could suppress LPS-induced production of nitric oxide (NO), interleukin-6 (IL-6), tumor necrosis factor alpha (TNF-α), and interleukin-1ß (IL-1ß), as well as inhibit the mRNA and protein levels of inducible nitric oxide (iNOS) and cyclooxygenase-2 (COX-2). In addition, we investigated the role of alisol F and 25-anhydroalisol F in mediating mitogen-activated protein kinases (MAPKs), signal transducers, and activators of transcription 3 (STAT3) and nuclear factor κB (NF-κB) pathways involved in the inflammation process of LPS-stimulated RAW 264.7 cells. The phosphorylation of ERK, JNK, p38, and STAT3, and the NF-κB signaling pathway, were obviously suppressed in alisol F and 25-anhydroalisol F treated cells. Results obtained from in vitro experiments suggested alisol F obviously improved liver pathological injury by inhibiting the production of TNF-α, IL-1ß, and IL-6, and significantly decreasing the serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels in LPS/d-gal-induced mice. Furthermore, the reduction of phosphorylation of ERK and JNK, as well as suppression of the NF-κB signaling pathway, were also observed in liver tissues of the alisol F-treated mice model. Alisol F and 25-anhydroalisol F may serve as potential leads for development of anti-inflammatory agents for acute liver failure treatment.

Anti-Inflammatory Effects, SAR, and Action Mechanism of Monoterpenoids from Radix Paeoniae Alba on LPS-Stimulated RAW 264.7 Cells.

Nine monoterpenoids from Radix Paeoniae Alba, including paeoniflorin derivatives, paeoniflorin (PF), 4-O-methylpaeoniflorin (MPF), 4-O-methylbenzoylpaeoniflorin (MBPF); paeonidanin derivatives, paeonidanin (PD), paeonidanin A (PDA), albiflorin derivatives, albiflorin (AF), benzoylalbiflorin (BAF), galloylalbiflorin (GAF), and debenzoylalbiflorin (DAF), were obtained in our previous phytochemistry investigations. Their anti-inflammatory effects were determined in the present study. The expression and production of pro-inflammatory cytokines in lipopolysaccharides (LPS)-stimulated RAW 264.7 cells were measured using an Elisa assay and nitric oxide (NO) release was determined using the Griess method. The results demonstrated that the most of the monoterpenoids suppressed the LPS-induced production of NO, interleukin-6 (IL-6), and tumor necrosis factor alpha (TNF-α). The anti-inflammatory activities of these monoterpenoids were closely related to their structural characteristics. Paeoniflorins and paeonidanins presented stronger anti-inflammatory activities than those of albiflorin derivatives. Furthermore, the action mechanisms of MBPF, having a strong anti-inflammatory effect, were investigated using quantitative reverse transcription polymerase chain reaction (RT-PCR) and Western blot methods. The results indicated that MBPF could down-regulate the mRNA and protein expression level of inducible nitric oxide synthase (iNOS) in LPS-stimulated RAW 264.7 cells. The mitogen-activated protein kinase (MAPK), phosphatidylinositol 3-kinase (PI3K)/AKT and nuclear factor κB (NF-κB) signaling pathways are involved in mediating the role of MBPF in suppressing the expression and production of pro-inflammatory cytokines in RAW 264.7 cells.

Cytotoxic Fusicoccane-Type Diterpenoids from Streptomyces violascens Isolated from Ailuropoda melanoleuca Feces.

Six new fusicoccane-type diterpenoids (2-7) were isolated from the fermentation broth of Streptomyces violascens, which was isolated from Ailuropoda melanoleuca (giant panda) feces. The structures of these new compounds were elucidated by a detailed spectroscopic data and X-ray crystallographic analysis. Compounds 5-7 demonstrated cytotoxicity against five human cancer cell lines, with IC50 values ranging from 3.5 ± 0.7 to 14.1 ± 0.8 µM. Cell adhesion, migration, and invasion assays showed that 6 inhibited the migration and invasion of human hepatocellular carcinoma SMMC7721 cells in a dose-dependent manner. Through further investigation, it was revealed that 6 inhibited the enzymatic activity of matrix metalloproteinase-2 (MMP-2) and matrix metalloproteinase-9 (MMP-9), in addition to down-regulating the expressions of MMP-2 and MMP-9 at both the protein and mRNA levels to influence the migration and invasion of cancer cells.

Design, Synthesis and Evaluation of Novel Tacrine-Ferulic Acid Hybrids as Multifunctional Drug Candidates against Alzheimer's Disease.

Five novel tacrine-ferulic acid hybrid compounds (8a-e) were synthesized and their structures were identified on the basis of a detailed spectroscopic analysis. The activities of inhibiting acetyl cholinesterase (AChE) and butyryl cholinesterase (BuChE), reducing self-induced ß-amyloid (Aß) aggregation and chelating Cu2+ were evaluated in vitro. Among them, 8c and 8d displayed the higher selectivity in inhibiting AChE over BuChE. Moreover, 8d also showed dramatic inhibition of self-Aß aggregation, activity of chelating Cu2+ and activity against Aß-induced neurotoxicity in Neuro-2A cells.

Defect passivation induced strong photoluminescence enhancement of rhombic monolayer MoS2.

Growing high quality monolayer MoS2 with strong photoluminescence (PL) is essential to produce light-emitting devices on the atomic scale. In this study we show that rhombic monolayer MoS2 with PL intensity 8 times stronger than those of chemical vapour deposition (CVD)-grown triangular and mechanically exfoliated (ME) monolayer MoS2 can be prepared by using CVD. Both Raman and PL measurements indicate low density of defects in rhombic monolayer MoS2 with enhanced PL intensity. Density functional theory (DFT) calculations show that passivation of defects in MoS2 removes trapping gap states, which may finally result in PL enhancement.

Bafilomycins and Odoriferous Sesquiterpenoids from Streptomyces albolongus Isolated from Elephas maximus Feces.

From a fermentation broth of Streptomyces albolongus obtained from Elephas maximus feces, nine bafilomycins (1-9) and seven odoriferous sesquiterpenoids (10-16) were isolated. The structures of the new compounds, including three bafilomycins, 19-methoxybafilomycin C1 amide (1), 21-deoxybafilomycin A1 (2), and 21-deoxybafilomycin A2 (3), and two sesquiterpenoid degradation products, (1ß,4ß,4aß,8aα)-4,8a-dimethyloctahydronaphthalene-1,4a(2H)-diol (10) and (1ß,4ß,4aß,7α,8aα)-4,8a-dimethyloctahydronaphthalene-1,4a,7(2H)-triol (11), were elucidated by comprehensive spectroscopic data analysis. The cytotoxicity activity against four human cancer cell lines and antimicrobial activities against a panel of bacteria and fungi of all compounds isolated were evaluated. Compounds 1, 7, and 8 were cytotoxic, with IC50 values ranging from 0.54 to 5.02 µM. Compounds 2, 7, 8, and 10 showed strong antifungal activity against Candida parapsilosis, with MIC values of 3.13, 1.56, 1.56, and 3.13 µg/mL respectively.

Transplantation of placenta-derived mesenchymal stem cells in type 2 diabetes: a pilot study.

Mesenchymal stem cells (MSC) have been used in clinical trials for severe diabetes, a chronic disease with high morbidity and mortality. Bone marrow is the traditional source of human MSC, but human term placenta appears to be an alternative and more readily available source. Here, the therapeutic effect of human placenta-derived MSC (PD-MSC) was studied in type 2 diabetes patients with longer duration, islet cell dysfunction, high insulin doses as well as poor glycemic control in order to evaluate the safety, efficacy and feasibility of PDMSC treatment in type 2 diabetes (T2D). Ten patients with T2D received three intravenous infusions of PDSC, with one month interval of infusion. The total number of PDSC for each patient was (1.22-1.51) × 10(6)/kg, with an average of 1.35 × 10(6)/kg. All of the patients were followed up after therapy for at least 3 months. A daily mean dose of insulin used in 10 patients was decreased from 63.7±18.7 to 34.7±13.4 IU (P<0.01), and the C-peptide level was increased from 4.1 ±3.7 ng/mL to 5.6 ±3.8 ng/mL (P<0.05) respectively after therapy. In 4 of 10 responders their insulin doses reduced more than 50% after infusion. The mean levels of insulin and C-peptide at each time point in a total of 10 patients was higher after treatment (P<0.05). No fever, chills, liver damage and other side effects were reported. The renal function and cardiac function were improved after infusion. The results obtained from this pilot clinical trial indicate that transplantation of PD-MSC represents a simple, safe and effective therapeutic approach for T2D patients with islet cell dysfunction. Further large-scale, randomized and well-controlled clinical studies will be required to substantiate these observations.

Influence of body mass index and gender on growth hormone (GH) responses to GH-releasing hormone plus arginine and insulin tolerance tests.

The aim of this study is to assess whether gender and body mass index (BMI) should be considered in developing thresholds to define GH deficiency, using GH responses to GHRH + arginine (ARG) stimulation and insulin tolerance test (ITT). Thirty-nine healthy subjects (19 males, 20 females; ages 21-50 yr) underwent GHRH + ARG, and another 27 subjects (19 males, 8 females; ages 20-49 yr) underwent ITT. Peak GH response was significantly higher (P = 0.005) after GHRH + ARG than with ITT, and this difference could not be explained by age, gender, or BMI. Peak GH response was negatively correlated with BMI in both tests (GHRH + ARG, r = -0.76; and ITT, r = -0.65). Peak GH response to GHRH + ARG was higher in females than males (P = 0.004; ratio = 2.4), but it was attenuated after eliminating the influence of BMI (P = 0.13; ratio = 1.6). No significant gender differences were found in peak GH responses to ITT, which could be due to the smaller number of female subjects studied. GH response to GHRH + ARG and ITT stimulation is sensitive to BMI differences and less so to gender differences. A higher BMI is associated with a depressed GH response to both stimulation tests. BMI should therefore be considered as a factor when defining the diagnostic cut-off points in the assessment of GH deficiency, whereas whether gender should be likewise used is inconclusive from this study.