A physical approach to reduce nonspecific adhesion in molecular recognition atomic force microscopy

Atomic force microscopy is one of the few techniques that allow analysis of biological recognition processes at the single-molecule level. A major limitation of this approach is the nonspecific interaction between the force sensor and substrate. We have modeled the nonspecific interaction by looking at the interaction potential between a conical Si3N4 tip with a spherical end face and a mica surface in solution, using DLVO (Derjaguin, Landau, Verwey, Overbeek) theory and numerical calculations. Insertion of the tip-sample potential in a simulation of an approach-retract cycle of the cantilever gives the well-known force-distance curve. Simulating a force-distance curve at low salt concentration predicts a discrete hopping of the tip, caused by thermal fluctuations. This hopping behavior was observed experimentally and gave rise to a novel approach to making measurements in adhesion mode that essentially works in the repulsive regime. The distance between tip and sample will still be small enough to allow spacer-involved specific interactions, and the percentage of nonspecific interactions of the bare tip with the mica is minimized. We have validated this physical model by imaging intercellular adhesion molecule 1 (ICAM-1) antigen with a tip functionalized with anti-ICAM-1 antibody. The measurement demonstrated that a significant decrease in the number of nonspecific interactions was realized, and the topographical image quality and the specific bonding capability of the tip were not affected.     

Characterization of binding properties to human P-glycoprotein: development of a [3H]verapamil radioligand-binding assay

Interaction with the exsorptive transporter P-glycoprotein (P-gp) is a possible source of peculiarities in drug pharmacokinetics, including dose-dependent absorption, drug-drug interactions, intestinal secretion, and limited permeability of the blood-brain barrier. Among the established in vitro methods of the analysis of drug interactions with P-gp, none directly quantifies the affinity of ligands with P-gp. Instead, they measure the result of a membrane permeation and a receptor-binding process; this may lead to difficulties in the interpretation of results. An assay for quantification of drug affinity to the transporter is presented on the basis of the radioligand-binding assay principle. This has the advantage of directly quantifying the interaction between drugs and P-gp. Because of the reversible and competitive interaction of numerous substrates with P-gp, a radioligand-binding assay was developed by taking [3H]verapamil and [3H]vinblastine as radioligands and the human intestinal Caco-2 cells, overexpressed with P-gp by culturing in the presence of vinblastine or transfecting with multidrug resistance gene MDR-1 as receptor preparation. The assay was performed in 96-well plates and has the potential to be used as a high-throughput method. A clear induction of the expression of P-gp was demonstrated in the Caco-2 cells grown in the presence of vinblastine, as well as in the transfected cells, although to a lesser extent. Both radioligands were shown to bind to P-gp. Verapamil was the radioligand of choice for further investigations due to its lower nonspecific binding to the transporter preparation. Kinetics as well as specificity of the binding of verapamil to the P-gp preparation were demonstrated. A two-affinity model was found to adequately describe the data derived from saturation as well as from competition experiments, in accordance with previous findings on two exsorption sites for P-gp. The binding properties of [3H]verapamil and [3H]vinblastine to a P-gp preparation derived from induced Caco-2 cells are described. The concentration-dependent displacement of the radioligand by nonlabeled substrates for P-gp should be a suitable principle for the determination of drug affinity to the respective binding sites at the human intestinal multidrug transporter P-gp.     

Caries and fluorosis prevalence in communities with different concentrations of fluoride in the water

The need to defluoridate and fluoridate the water supplies in areas with drinking water naturally containing above-optimal (>/=2.5 mg/l) and suboptimal (相似文献   

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Preferential adsorption, internalization and resistance to degradation of the major isoform of the Alzheimer's amyloid peptide, A beta 1-42, in differentiated PC12 cells

A central question in Alzheimer's disease (AD) is the role of amyloid in pathogenesis. Recent discoveries implicating the longer A beta 1-42 form of amyloid in pathogenesis led us to characterize the interaction of A beta with cells to elucidate differences that might account for these observations. We characterized the adsorption, internalization and degradation of radiolabeled A beta in NGF-differentiated PC12 cells under conditions that are not acutely toxic. All A beta peptides examined absorb to the surface of PC12 cells and are internalized; however the adsorption and internalization of A beta 1-42 is significantly greater than that of A beta 1-40 and A beta 1-28. The adsorption of A beta 1-42 is decreased by treatment of the cells with neuraminidase, but not heparitinase. The fate of the internalized A beta 1-42 is also very different than shorter A beta peptides; a fraction of the internalized A beta 1-42 accumulates intracellularly and is resistant to degradation for at least 3 days while A beta 1-40 and shorter peptides are eliminated with a half life of about 1 h. A beta 1-42 does not appear to inhibit lysosomal hydrolases, since A beta 1-28 is degraded at the same rate in the presence or absence of A beta 1-42. The intracellular A beta 1-42 is located in a dense organellar compartment and colocalizes with the lysosomal markers Lucifer Yellow and horseradish peroxidase. These data indicate that there are significant differences in the cell surface adsorption, internalization and catabolism of A beta 1-42 compared to A beta 1-40 and A beta 1-28. These differences may be important for the preferential accumulation of the longer A beta 1-42 isoform and its association with AD pathogenesis.