Glycoprotein-glycoprotein Receptor Binding Detection Using Bioluminescence Resonance Energy Transfer

The glycoprotein receptors, members of the large G protein-coupled receptor family, are characterized by a large extracellular domains responsible for binding their glycoprotein hormones. Hormone-receptor interactions are traditionally analyzed by ligand-binding assays, most often using radiolabeling but also by thermal shift assays. Despite their high sensitivity, these assays require appropriate laboratory conditions and, often, purified plasma cell membranes, which do not provide information on receptor localization or activity because the assays typically focus on measuring binding only. Here, we apply bioluminescence resonance energy transfer in living cells to determine hormone-receptor interactions between a Gaussia luciferase (Gluc)-luteinizing hormone/chorionic gonadotropin receptor (LHCGR) fusion and its ligands (human chorionic gonadotropin or LH) fused to the enhanced green fluorescent protein. The Gluc-LHCGR, as well as other Gluc-G protein-coupled receptors such as the somatostatin and the C-X-C motif chemokine receptors, is expressed on the plasma membrane, where luminescence activity is equal to membrane receptor expression, and is fully functional. The chimeric enhanced green fluorescent protein-ligands are properly secreted from cells and able to bind and activate the wild-type LHCGR as well as the Gluc-LHCGR. Finally, bioluminescence resonance energy transfer was used to determine the interactions between clinically relevant mutations of the hormones and the LHCGR that show that this bioassay provides a fast and effective, safe, and cost-efficient tool to assist the molecular characterization of mutations in either the receptor or ligand and that it is compatible with downstream cellular assays to determine receptor activation/function.

Anti-cancer activity of green synthesized silver nanoparticles using Ardisia gigantifolia leaf extract against gastric cancer cells

Using extracts from herbs for silver nanoparticle synthesis is attracting attention for its anticancer activity. Ardisia gigantifolia is a herb used in traditional Chinese medicine for treating stomach ailments, and some compounds isolated from this plant exhibit the inhibitory activity against different cancer cells. However, the synthesis of silver nanoparticle using extract of Ardisia gigantiflia leaves and their anti-cancer activity was not reported. In this report, the green synthesized silver nanoparticles using Ardisia gigantiflia extract (Arg-AgNPs) has average diameter of 6 nm with functional groups including O-H, C-H, and CO founded on the surface of these nanoparticles. The viability assays results revealed Arg-AgNPs reduced gastric cancer cell proliferation in a dose-dependent manner, with IC₅₀ values of 1.37 and 0.65 μg/mL for AGS cells and 1.03 and 0.96 μg/mL for MKN45 cells. Arg-AgNPs caused cell cycle arrest at the G0/G1 phase and suppressed cell migration. Additionally, Arg-AgNPs significantly increased the percentage of senescent cells and promoted overproduction of reactive oxygen species (ROS) compared to the control. Thus, this study indicates that Arg-AgNPs can be considered as a promising candidate against human gastric cancer cells.

Identification of putative viroplasms within banana cells infected by banana streak MY virus

The badnavirus replication cycle is poorly understood and most knowledge is based on extrapolations from model viruses such as Cauliflower mosaic virus (CaMV). However, in contrast to CaMV, badnaviruses are thought not to produce viroplasms and therefore it has been a mystery as to where virion assembly occurs. In this study, ultrathin sections of a banana leaf infected with a badnavirus, banana streak MY virus (BSMYV), were examined by transmission electron microscopy. Electron-dense inclusion bodies (EDIBs) were sporadically distributed in parenchymatous tissues of the leaf, most commonly in the palisade and spongy mesophyll cells. These EDIBs had a characteristic structure, comprising an electron-dense core, a single, encircling lacuna and an outer ring of electron-dense material. However, much less frequently, EDIBs with two or three lacunae were observed. In the outer ring, densely packed virions were visible with a shape and size consistent with that expected for badnaviruses. Immunogold labelling was done with primary antibodies that detected the N-terminus of the capsid protein and strong labelling of the outer ring but not the central core or lacuna was observed. It is concluded that the EDIBs that were observed are equivalent in function to the viroplasms of CaMV, although obviously different in composition as there is not a paralogue of the transactivation/viroplasm protein in the badnavirus genome. It is postulated that production of a viroplasm could be a conserved characteristic of all members of the Caulimoviridae.

The microstructure, local indium composition and photoluminescence in green-emitting InGaN/GaN quantum wells

In this work, we analyse the microstructure and local chemical composition of green-emitting In_x Ga_1-x N/GaN quantum well (QW) heterostructures in correlation with their emission properties. Two samples of high structural quality grown by metalorganic vapour phase epitaxy (MOVPE) with a nominal composition of x = 0.15 and 0.18 indium are discussed. The local indium composition is quantitatively evaluated by comparing scanning transmission electron microscopy (STEM) images to simulations and the local indium concentration is extracted from intensity measurements. The calculations point out that the measured indium fluctuations may be correlated to the large width and intensity decrease of the PL emission peak.

Porphyrinoid rotaxanes: building a mechanical picket fence

Building on recent progress in the synthesis of functional porphyrins for a range of applications using the Cu-mediated azide-alkyne cycloaddition (CuAAC) reaction, we describe the active template CuAAC synthesis of interlocked triazole functionalised porphyrinoids in excellent yield. By synthesising interlocked analogues of previously studied porphyrin-corrole conjugates, we demonstrate that this approach gives access to rotaxanes in which the detailed electronic properties of the axle component are unchanged but whose steric properties are transformed by the mechanical "picket fence" provided by the threaded rings. Our results suggest that interlocked functionalised porphyrins, readily available using the AT-CuAAC approach, are sterically hindered scaffolds for the development of new catalysts and materials.

A simple bridging flocculation assay for rapid, sensitive and stringent detection of gene specific DNA methylation

The challenge of bringing DNA methylation biomarkers into clinic is the lack of simple methodologies as most current assays have been developed for research purposes. To address the limitations of current methods, we describe herein a novel methyl-protein domain (MBD) enrichment protocol for simple yet rapid and highly stringent selection of highly methylated DNA from limiting input samples. We then coupled this with a DNA-mediated flocculation assay for rapid and low cost naked-eye binary evaluation of highly methylated genes in cell line and blood DNA. The low resource requirements of our method may enable widespread adoption of DNA methylation-based diagnostics in clinic and may be useful for small-scale research.

Colorimetric detection of both total genomic and loci-specific DNA methylation from limited DNA inputs

BACKGROUND

Aberrant DNA methylation marks are potential disease biomarkers, and detecting both total genomic and gene-specific DNA methylation can aid in clinical decisions. While a plethora of methods exist in research, simpler, more convenient alternatives are needed to enhance both routine diagnostics and research.

RESULTS

Herein, we describe colorimetric assays using methyl-binding domain (MBD) proteins for rapid and convenient evaluation of total genomic and gene-specific methylation from 50 ng or less DNA input in under 2 h. As little as 5 % methylation differences can be detected and are enhanced by a novel MBD protocol for improved specificity. Our assays could differentiate naïve from de-methylating drug-treated cells and detect the presence of a methylated prostate cancer biomarker in the urine. Finally, the assay was evolved onto disposable screen-printed electrodes for convenient detection of gene-specific methylation in urine.

CONCLUSIONS

Rapid MBD-based colorimetric and electrochemical approaches to detect DNA methylation from limited samples were successfully demonstrated and applied to clinical samples. We envision that the ease, low sample requirements and speed of these assays could have both clinical and research-wide applications.

Prostate cancer: another aspect of the insulin-resistance syndrome?

Insulin resistance and compensatory hyperinsulinaemia are thought to be the underlying factors in the metabolic or insulin-resistance syndrome and can be controlled by diet and exercise. Hyperinsulinaemia has been shown to have a direct effect on the live, suppressing the production of sex hormone-binding globulin (SHBG) and insulin-like growth factor-binding proteins 1 and 2 (IGFBP-1, -2) while stimulating the production of insulin-like growth factor 1 (IGF-1). These factors have been proposed to be important modulators of hormone-related cancers, such as prostate cancer. Men adopting a low-fat diet and daily exercise reduced their levels of serum insulin and IGF-1, while increasing their levels of IGFBP-1 and sex hormone-binding globulin (SHBG). Cell-culture studies with LNCaP prostate cancer cells showed apoptosis of tumour cells and a reduction in serum-stimulated cell growth in the post diet and exercise serum. These results suggest that prostate cancer may be another aspect of the insulin-resistance syndrome and that adopting a low-fat diet combined with regular exercise may reduce the risk for prostate and other hormone-related cancers. This needs to be tested with prospective studies.

Identification of a target site in plasminogen activator inhibitor-1 that allows neutralization of its inhibitor properties concomitant with an allosteric up-regulation of its antiadhesive properties

The serpin plasminogen activator inhibitor-1 (PAI-1) has a dual function: 1) it plays an important role as a direct inhibitor of the plasminogen activation system, and 2) its interaction with the adhesive glycoprotein vitronectin suggests a role in tissue remodeling and metastasis, independent from its proteinase inhibitory properties. Unique to this serpin is the close association between its conformational and functional properties. Indeed, PAI-1 can occur in an active and a latent conformation, but both functions are exclusively present in the active conformation. We report here the epitope localization and functional effects of a monoclonal antibody (MA-124K1) that inhibits rat PAI-1 activity and simultaneously increases the binding of inactive PAI-1 to vitronectin (the affinity constant of PAI-1 for vitronectin is 2 x 10(7) m(-1) in the absence of MA-124K1 and 160 x 10(7) m(-1) in the presence of MA-124K1). To the best of our knowledge, this is the first monoclonal antibody dissociating the proteinase inhibitory properties from the vitronectin binding properties in PAI-1. Mutation of Glu(212) and/or Glu(220) in rat PAI-1 to Ala results in a strongly reduced affinity or absence of binding to MA-124K1. The three-dimensional structure of PAI-1 reveals that these residues constitute a conformational epitope close to the reactive-site loop and compatible with the effect of MA-124K1 on the inhibitory properties of PAI-1. However, the vitronectin binding site is localized at the opposite site of the molecule, indicating that the effect of MA-124K1 involves an allosteric modulation of the vitronectin binding site. Cell culture experiments revealed a significant reduction of cell attachment and migration in the presence of MA-124K1, providing evidence for the functional relevance of this antibody-mediated up-regulation of the vitronectin binding properties of PAI-1. In conclusion, a novel mechanism for interference with PAI-1 functions has been identified and is of importance in the modulation of cell migration and related events (e.g. tumor metastasis).

Elucidation of the binding regions of PAI-1 neutralizing antibodies using chimeric variants of human and rat PAI-1

Increased levels of plasminogen activator inhibitor-1 (PAI-1), the main physiological inhibitor of tissue-type plasminogen activator (t-PA) in plasma, are a known risk factor for thromboembolic and cardiovascular diseases. The elucidation of the binding site of inhibitory monoclonal antibodies may contribute to the rational design of PAI-1 modulating therapeutics. In this study, homolog-scanning mutagenesis was used to identify the binding region of a variety of human PAI-1 inhibitory antibodies, lacking cross-reactivity with rat PAI-1. Therefore. eight chimeric human/rat PAI-1 variants, containing rat PAI-1 substitutions at the N-terminal or C-terminal end with splicing sites at positions 26, 81, 187, 277 or 327, were generated and purified. Biochemical characterization revealed that all chimeras were folded properly. Subsequently, surface plasmon resonance was used to determine the affinity of various monoclonal antibodies for these chimera. Comparative analysis of the affinity and ELISA data allowed the identification of the major binding region of the inhibitory antibodies MA-8H9D4, MA-33B8F7, MA-44E4, MA-42A2F6 and MA-56A7C10. Thus, three segments in human PAI-1 containing each at least one site involved in the neutralization of PAI-1 activity could be identified, i.e. (1) the segment from residue 81 to residue 187 (comprising alpha-helices hD, hE and hF, beta-strands s4C, s3A, s2A and s1A and the loops connecting these elements). (2) the segment between residues 277 and 327 (hI, thIs5A, s5A and s6A) and (3) the region C-terminal from amino acid 327, including the reactive site loop. The current data. together with previous data, indicate that PAI-1 contains at least four different regions that could be considered as putative targets to modulate its activity.

Immunological quantitation of rabbit plasminogen activator inhibitor-1 in biological samples: evidence that rabbit platelets do not contain PAI-1

Two immunoassays for the specific quantitation of rabbit plasminogen activator inhibitor-1 (PAI-1) antigen and activity in biological samples were developed and applied for the evaluation of PAI-1 in rabbits. Levels of PAI-1 antigen in rabbit plasma were 9.8+/-4.6 ng/ml (mean +/- SD, n = 6), with a corresponding value of 20.5+/-13.5 ng/ml for PAI-1 activity. In rabbit serum PAI-1 antigen was 11.8+/-4.9 ng/ml (n = 6) and PAI-1 activity was 2.9+/-2.0 ng/ml (n = 6). Endotoxin injection (20 microg/kg, i.v.) induced a time-dependent increase of both PAI-1 antigen and PAI-1 activity levels in rabbit plasma, eventually resulting in a 40- to 90-fold increase (p<0.0001 vs. baseline). A linear correlation was found between PAI-1 antigen and activity levels in normal plasma (r = 0.90, n = 6, p<0.05) and in plasma from endotoxin-treated rabbits (r = 0.98, n = 20, p<0.001). Analysis of PAI-1 antigen and activity in lysates of washed rabbit platelets revealed the absence of PAI-1 (i.e. <0.03 ng/10(8) platelets). In conclusion, development of specific immunological assays allowed the quantitation of PAI-1 in rabbit samples. In striking contrast to other species (human, rat, mouse, pig) rabbit platelets lack detectable amounts of PAI-1 (i.e. >100-1000 fold lower vs other species studied). This observation may have important implications for the use of experimental rabbit models especially in studies on the role of platelets in various pathological conditions including thrombosis and atherosclerosis.

Monoclonal antibody-based immunoassays for the specific quantitation of rat PAI-1 antigen and activity in biological samples

Two enzyme-linked immunosorbent assays (ELISAs) for the quantitation of rat plasminogen activator inhibitor-1 (PAI-1) antigen and activity, respectively, in biological fluids were developed using monoclonal antibodies raised against recombinant rat PAI-1. These assays had a lower limit of sensitivity in plasma of 0.3 and 0.15 ng/ml, respectively. The intra-assay, inter-assay and inter-dilution coefficients of variation were 9, 14 and 9%, respectively, for the antigen assay and 8, 17 and 13%, respectively for the activity assay. Assay recoveries of recombinant rat PAI-1 (5 to 20 ng/ml) added to plasma were 73 to 88% and 89 to 93% for the antigen and the activity assay, respectively. The level of PAI-1 antigen in rat plasma was 1.8 +/- 0.9 ng/ml (mean +/- SD, n = 18), with a corresponding value of 1.0 +/- 0.5 ng/ml for PAI-1 activity. In lysed platelet-rich rat plasma PAI-1 antigen was 6.0 +/- 1.0 ng/ml (n = 8) and PAI-1 activity was 2.3 +/- 0.4 ng/ml (n = 8). Endotoxin injection (0.5 mg/kg) induced a time-dependent increase of both PAI-1 antigen and PAI-1 activity levels in rat plasma. eventually resulting in a 100- to 200-fold increase (p < 0.0001 vs. baseline). A linear correlation was found between PAI-1 antigen and activity levels in normal plasma (r = 0.63, n = 18, p < 0.01) and in plasma from endotoxin-treated rats (r = 0.90, n = 35, p < 0.001). Application of these assays for the analysis of gel filtration experiments of plasma from endotoxin-treated rats demonstrated that PAI-1 antigen eluted as two peaks (with corresponding Mr of approximately 430 kDa and 61 kDa) whereas PAI-1 activity eluted as a single peak corresponding with the high molecular weight antigen form. Thus, these unique assays allowing the specific determination of rat PAI-1 antigen and rat PAI-1 activity may constitute important tools for further investigations on the pathophysiological role of PAI-1 in a variety of experimental rat models.

Identification of functional synergism between monoclonal antibodies. Application to the enhancement of plasminogen activator inhibitor-1 neutralizing effects

The serpin plasminogen activator inhibitor-1 (PAI-1), an important risk factor for thrombotic disease can be neutralized by distinct mechanisms. We hypothesized that the combination of two compounds, with PAI-1 neutralizing properties based on different mechanisms, may result in a synergistic effect. Therefore, seven monoclonal antibodies with PAI-1 neutralizing properties were pairwise evaluated for the possible presence of synergistic or antagonistic effects. Out of 21 combinations, three particular combinations, i.e. MA-33H1/MA-33B8, MA-33B8/MA-7D4B7, and MA-7D4B7/MA-33H1 exhibited strong synergistic effects in comparison with their properties when evaluated individually. The observed synergism resulted in a maximum enhancement between 2- and 5-fold (P < 0.05, vs. theoretically expected effect calculated based on additive effects). Strikingly, synergism was only observed between monoclonal antibodies directed against different epitopes and with different molecular mechanisms of PAI-1 neutralization. This phenomenon of synergism opens new perspectives in the design of therapeutic or preventive strategies aimed at enhancing endogenous fibrinolysis through modulation of PAI-1 activity.

Bioavailability of different artemisinin tablet formulations in rabbit plasma--correlation with results obtained by an in vitro dissolution method

The demonstration of a good overall correlation with in vivo data is the ultimate proof of qualification for any dissolution-rate test. For artemisinin, a very hydrophobic compound at a high content in oral solid dosage forms, all official dissolution apparatus were estimated unsuitable. A modified two phase partition-dissolution method was applied to solve this problem. This study reports on the bioavalability of three different formulations of artemisinin tablets in rabbit plasma. Artemisinin concentrations in plasma were determined by liquid chromatography. A linear correlation between results obtained by the partition-dissolution method described and the obtained in vivo data confirmed the validity of the dissolution method.

Characterization of recombinant rat plasminogen activator inhibitor-1 and development of immunological tools for its quantitation

Plasminogen activator inhibitor-1 (PAI-1) is the primary physiological inhibitor of both tissue-type plasminogen activator (t-PA) and urokinase-type plasminogen activator (u-PA). Elevated plasma levels of PAI-1 have been associated with several important thrombotic diseases. A large number of studies have demonstrated that rats are suitable for in vivo investigations on thrombolysis and fibronolysis. In this study, we have expressed, in Escherichia coli, purified and characterized recombinant rat PAI-1 in comparison with human PAI-1. Subsequently this material was used to raise monoclonal antibodies using the hybridoma technology. Characterization of purified recombinant rat PAI-1 revealed that its functional and biochemical properties are similar to those of human PAI-1. Two fusions, with spleen cells from mice immunized with recombinant rat PAI-1, yielded 118 positive hybridomas. From these, 36 monoclonal antibodies were purified and evaluated for their applicability in the construction of sandwich-type ELISAs. Out of 860 combinations tested, 2 combinations were selected for the measurement of rat PAI-1 (antigen and activity) in biological samples (e.g., plasma, platelet lysates, cell-culture media, ...).