Biomedical subjects

Louis Scampavia

Publications and source records attributed to Louis Scampavia.

9 recordsLinked to original sources

PubMed2006

Automated method, based on micro-sequential injection, for the study of enzyme kinetics and inhibition.

A micro-reactor system with continual spectrophotometric detection has been operated in Sequential Injection lab-on-valve (SI-LOV) mode and applied to enzyme kinetics and inhibition studies, using acetylcholinesterase (AChE) and angiotensin-converting enzyme (ACE) as model systems. With the advantages of automation, real-time kinetic measurement, and thorough mixing, the SI-LOV micro-reactor system allows for the monitoring of initial reaction rates and determination of reactant concentrations in the reaction mixture, both of which are essential for the determination of kinetic constants for enzymes and inhibitors. Enzyme, substrate, and inhibitor are precisely metered by the syringe pump and delivered to a stirred micro-reactor, followed by a reference scan that establishes the baseline for the following reaction rate measurement. Michaelis constants (Km) for AChE and ACE were determined to be 0.16 mM and 0.30 mM, respectively, which are consistent with literature values. The type of inhibition (competitive, uncompetitive, or mixed), the dissociation constants for the inhibitors, and the inhibitor dose-response curves were also determined.

Acetylcholinesterase↗

PubMed2004

Automated affinity chromatography measurements of compound mixtures using a lab-on-valve apparatus coupled to electrospray ionization mass spectrometry.

We report a fully automated affinity chromatography system using a lab-on-valve (LOV) apparatus coupled to an electrospray ionization ion-trap mass spectrometer (ESI-MS). The system allows simultaneous measurements of multiple ligand affinities to proteins immobilized on beads. Bead regeneration, column repacking, and repetitive measurements are achieved on the time scale of several minutes. In this study, the system was used to screen the binding of a peptide mixture to human and Trypanosoma brucei (T. brucei) truncated Pex5 (tPex5) proteins. Equilibrium dissociation constants (K(d)) were measured for T. brucei tPex5 and compared to the values obtained by a fluorescence-based competition assay. The three peptides that showed affinity toward tPex5 had K(d) values that were comparable in magnitude (within a factor of 5) and showed the same ranking order as those from manual fluorescence measurements. With 12 min of sample infusion, the entire sample-to-sample cycle takes about 15 min and can be repeated without any preparation between runs. For T. brucei tPex5 affinity measurements, 1 mg of protein was sufficient for 35 repetitive analyses in the automated LOV-ESI-MS apparatus. The system allows rapid determination of K(d) in the range of 10(-5)-10(-7) M for sample mixtures and is suitable for screening a large number of compounds against multiple proteins.

Animals↗

PubMed2004

A novel approach for monitoring extracellular acidification rates: based on bead injection spectrophotometry and the lab-on-valve system.

Monitoring extracellular acidification rates (ECARs) is important for the study of cellular activities, since it allows for the evaluation of factors that alter metabolic function, such as stimulants, inhibitors, toxins as well as receptor and non-receptor mediated events. While the light addressable potentiometric sensor (Cytosensor Microphysiometer) has been the principal tool for ECARs measurement in the past, this work introduces a novel method that exploits an immobilized pH indicator on the surface of microcarrier beads (Sephadex) and is probed with a fiber optic coupled spectrophotometer. Likewise, live cells under investigation were also immobilized on microcarrier beads (Cytopore). These beads are metered, transported and monitored within a microfluidic system, termed as the Lab-on-Valve (LOV). Use of carrier beads in conjunction with Bead Injection Spectrophotometry and a Lab-on-Valve module (BIS-LOV), makes ECAR measurements reliable and automated. The feasibility of the BIS-LOV approach is demonstrated measuring ECARs of the mouse hepatocyte cell line, TABX.2S, grown on Cytopore beads packed within the central channel of the LOV system. These immobilized cells were perfused in a phosphate buffer carrier solution (capacity: 1 mmol L(-1), pH 7.4). Protons extruded from 10(5) to 10(6) cells were accumulated during a stopped flow period of 220 s followed by a pH measurement, detected by changes in absorbance of the pH indicator bonded to the microcarrier beads. Addition of metabolic inhibitors (sodium azide, oxamic acid) to the carrier buffer solution can induced an increase or decrease of the basal proton extrusion rate in a very reproducible manner. Comparison of the BIS-LOV technique to the Cytosensor microphysiometer and literature confirms the validity of this novel approach, highlighting its advantages and suggesting future improvements that will make the BIS-LOV a practical tool for routine ECARs measurement.

Animals↗

PubMed2003

Micro sequential injection: automated insulin derivatization and separation using a lab-on-valve capillary electrophoresis system.

Automated sampling and fluorogenic derivatization of islet proteins (insulin, proinsulin, c-peptide) are separated and analyzed by a novel lab-on-valve capillary electrophoresis (LOV-CE) system. This fully integrated device is based on a micro sequential injection instrument that uses a lab-on-valve manifold to integrate capillary electrophoresis. The lab-on-valve manifold is used to perform all microfluidic tasks such as sampling, fluorogenic labeling, and CE capillary rejuvenation providing a very reliable system for reproducible CE separations. Fluorescence detection was coupled to an epiluminescence fluorescence microscope using a customized capillary positioning plate. This customized plate incorporated two fused-silica fiber optic probes that allow for simultaneous absorbance and fluorescence detection, extending the utility of this device. Derivatization conditions with respect to the sequence of addition, timing, injection position, and volumes were optimized through iterative series of experiments that are executed automatically by software control. Reproducibility in fluorogenic labeling was tested with repetitive injections of 3.45 mM insulin, yielding 1.3% RSD for peak area, 0.5% RSD for electromigration time, and 2.8% RSD for peak height. Fluorescence detection demonstrated a linear dynamic range of 3.43 to 6.87 microM for insulin (r2 = 0.99999), 0.39 to 1.96 pM for proinsulin (r2 = 0.99195) and 260 to 781 nM for c-peptide (r2 = 0.99983). By including hydrodynamic flushing immediately after the detection of the last analyte, the sampling frequency for islet protein analysis was increased. Finally, an in vitro insulin assay using rat pancreatic islet excretions was tested using this lab-on-valve capillary electrophoresis system.

Autoanalysis↗

PubMed2003

Bead injection ELISA for the determination of antibodies implicated in type 1 diabetes mellitus.

This work introduces a novel analytical method for the detection and study of GAD65 autoantibodies, which have been implicated in the onset of type 1 diabetes. There is a clinical need for a rapid and automated assay for GAD65 autoantibodies. Therefore, this method was designed to exploit the advantages of bead injection (BI) analysis for enzyme-linked immunosorbent assays (ELISA). BI ELISA is a microscale technique that uses enzyme labeled secondary antibodies to detect the capture of target antibodies on immobilized antigen in the flow cell of the lab-on-valve (LOV) manifold. A detection limit of 20 ng mL(-1) of GAD65 monoclonal antibody 144 compares favorably with the sensitivity and precision of a standard ELISA currently employed to detect GAD65 autoantibodies. Compared to the standard ELISA protocol, BI ELISA offers a significantly reduced assay time and complete automation of solution handling and detection.

Autoanalysis↗

PubMed2002

Automated affinity capture-release of biotin-containing conjugates using a lab-on-valve apparatus coupled to UV/visible and electrospray ionization mass spectrometry.

We report a new method for automated affinity capture and release of biotin-containing conjugates on immobilized streptavidin using a lab-on-valve (LOV) bead injection apparatus. The apparatus is also coupled to UV/visible and electrospray ionization mass spectrometry (ESI-MS) for monitoring the captured and released biotin-containing conjugates. Dissociation rate constants for release from streptavidin of two chromophore-tagged biotin conjugates were measured by UV/visible spectrometry and the dissociation was simultaneously monitored by ESI-MS. The LOV-ESI-MS instrument was also used for repetitive assays of lysosomal beta-galactosidase in human cell homogenates. Fast analysis in 4.5 min/full cycle and robust operation in 60 repetitive analyses are demonstrated that are promising for transfer of the LOV-ESI-MS technology into clinical practice.

Affinity Labels↗

PubMed2002

Microsequential injection: anion separations using 'lab-on-valve' coupled with capillary electrophoresis.

Microsequential injection (microSI) has been successfully coupled with capillary electrophoresis (CE). Presented is the microSI-CE system, interfaced with an integrated Lab-on-Valve (LOV) manifold that provides an efficient sample delivery conduit and a versatile means of sample pretreatment along with total automation of the separation process. Programmable microSI protocols control all critical system peripherals to perform various types of CE sample injections automatically such as electrokinetic (EK) injection, hydrodynamic (HD) injection, and head column field amplification (HCFA) sample stacking injection. Novel features of the microSI-CE technique are demonstrated on assays of samples containing 10 anions that had been used previously as a model system. Calibration studies by EK sample injection yielded linear concentration ranges of 0.5-3.0 mM with linear regression responses of r2 = 0.9999 for both chloride and sulfate using conductivity corrected peak area (CCPA) as concentration responses. Calibration using an internal standard was studied at the same concentration range giving r2 = 0.9992 for both chloride and sulfate and r2 = 0.9997 for both when CCPA correction was deployed. With HCFA sample stacking injection, a linear concentration dynamic range of 0.034-3.419 mM for chloride and 0.014-1.408 mM for sulfate were produced with linear regression responses of r2 = 0.9999 for chloride and r2 = 0.9998 for sulfate.

Anions↗

PubMed2002

Label dilution method: a novel tool for bioligand interaction studies using bead injection in the lab-on-valve format.

This work introduces a novel method, label dilution, which is analogous to the well-established isotope dilution method. The principle is tested on a model system of commercially available antibodies and protein-coated Sepharose beads and implemented using micro-bead injection in the lab-on-valve format. This micro-scale method uses a labeled form of the target molecule as an internal standard. Label dilution employs ratiometric measurements using the absorbance signals from the label and the target molecules for quantitative determination of an analyte. The label dilution method is shown to discriminate between selective and non-selective binding and provides a means for monitoring bioligand interactions in real time. With a detection limit of 470 ng of IgG, this method provides a sensitive, automated technique for the determination of low-level analytes in complex samples. This technique has been developed with the aim of using it to facilitate diabetes research in which the interactions between autoantibodies and the molecules they target are a central focus.

Autoantibodies↗

PubMed2002

Real-time monitoring of lactate extrusion and glucose consumption of cultured cells using a lab-on-valve system.

Microsequential injection (microST) provides microfluidic operations that are ideally suited for cellular function studies and as a means of validating targets for drug discovery. MicroSI carried out within the lab-on-valve (LOV) manifold, is an ideal platform for spectroscopic studies on living cells that are grown on microcarrier beads and kept thermostated while their metabolism is probed in real-time. In this paper a microbioreactor is integrated into the LOV manifold allowing measurement of cellular lactate extrusion and glucose consumption rates of a cell culture that is automatically renewed prior to each measurement. Glucose consumption and lactate extrusion are monitored using NAD-linked enzymatic assays. The microSI-LOV setup has demonstrated a linear analysis range of 0.05-1.00 mM for lactate and 0.1-5.6 mM for glucose. These assays were conducted in a serial fashion requiring 3 microL of cellular perfusate and 10 s for glucose determination and 30 s for the lactate assay. Overall waste generated per lactate/glucose assay is < 200 microL. This work was performed using two different transfected hepatocyte cell lines, which adhere to Cytopore microcarrier beads. This novel approach to metabolic screening allows for the rapid evaluation of the effects of dosing cells with chemical agents.

Animals↗