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Biomedical subjects

P Verboven

Publications and source records attributed to P Verboven.

14 recordsLinked to original sources
PubMed2005

Spray drift as affected by meteorological conditions.

Spray drift can be defined as the quantity of plant protection product that is carried out of the sprayed (treated) area by the action of air currents during the application process. This continues to be a major problem in applying agricultural pesticides. The purpose of this research is to measure and compare the amount of drift for different climatological conditions under field conditions. Spray drift was determined by sampling in a defined downwind area at different positions in a flat meadow using horizontal drift collectors (sedimenting spray drift) and pipe cleaners (airborne spray drift) for a reference spraying. Meteorological conditions were monitored during each experiment. A drift prediction equation for the reference spraying was set up to predict the expected magnitude of sedimenting drift at various drift distances and atmospheric conditions (wind speed and temperature). This equation can be used to compare measurements using other spraying techniques under different weather conditions to the reference spraying. In 2005, more measurements will be performed to validate the statements and the model reflected in this paper.

Agriculture↗
PubMed2005

A pdpa laser-based measuring set-up for the characterisation of spray nozzles.

The characteristics of agricultural sprays belong to the most critical factors affecting spray drift, deposition on plants, spray coverage and biological efficacy. Hence, within the framework of a research project about agricultural spray drift, a measuring set-up for the characterisation of spray nozzles using a Phase Doppler Particle Analyser (PDPA) was developed. This set-up is able to measure droplet sizes and velocities based on light-scattering principles. It is composed of different parts i.e.: a climate room, a spray unit, a three-dimensional automated positioning system and an Aerometrics PDPA 1D system. This paper presents a detailed description of this measuring set-up along with some first measuring results. These measurements will be used as an input for a Computational Fluid Dynamics drift-prediction model and to classify nozzles based on their driftability.

Agriculture↗
PubMed2004

Fast monolithic micellar liquid chromatography: an alternative drug permeability assessing method for high-throughput screening.

Several methods estimating the partitioning over biological membranes and thus the biological activity of potential oral drug molecules have been developed and are described in the literature. A previous study suggested that fast micellar liquid chromatography on a monolithic column could be one of them. For a set of diverse pharmaceuticals, retention by this fast chromatographic method was determined, besides other parameters also thought or established to describe oral permeability or absorption, e.g., from the Caco-2 permeability method. In view of a high-throughput determination of membrane permeability, a study was made of which information fast micellar liquid chromatography is providing and to what degree this system can replace other methods, i.e., deliver similar information. The retention with this fast method, which is mainly based on hydrophobic interactions, proved useful to sort substances into classes of Caco-2 and percent intestinal absorption.

Caco-2 Cells↗
PubMed2004

Wind tunnel evaluation of several tracer and collection techniques for the measurement of spray drift.

In the history of pesticide drift measuring techniques, different tracers and a lot of different collection techniques have been used. At the start of a new Flemish project 'Protecting the Flemish environment against drift - The importance of drift-reducing techniques', wind tunnel tests have been executed to select the most efficient tracer and collection technique. As tracer types a fluorescent tracer Renaissance W15, 2 different chelates, a NaCl-solution and a fungicide Tolylfluanide were used. 2 different collection techniques were tested: drains incorporated in the wind tunnel floor filled with filter paper and filled with cloths. The recovery of the different tracers combined with the 2 collection materials was calculated. The advantages and disadvantages of the tracers and collection materials are enumerated in this article.

Air Pollutants↗
PubMed2001

Strategies for absorption screening in drug discovery and development.

This review gives an overview of the current approaches to evaluate drug absorption potential in the different phases of drug discovery and development. Methods discussed include in silico models, artificial membranes as absorption models, in vitro models such as the Ussing chamber and Caco-2 monolayers, in situ rat intestinal perfusion and in vivo absorption studies. In silico models such as iDEA can help optimizing chemical synthesis since the fraction absorbed (Fa) can be predicted based on structural characteristics only. A more accurate prediction of Fa can be obtained by feeding the iDEA model with Caco-2 permeability data and solubility data at various pH's. Permeability experiments with artificial membranes such as the filter-IAM technology are high-throughput and offer the possibility to group compounds according to a low and a high permeability. Highly permeable compounds, however, need to be further evaluated in Caco-2 cells, since artificial membranes lack active transport systems and efflux mechanisms such as P-glycoprotein (PgP). Caco-2 and other "intestinal-like" cell lines (MDCK, TC-7, HT29-MTX, 2/4/A1) permit to perform mechanistic studies and identify drug-drug interactions at the level of PgP. The everted sac and Ussing chamber techniques are more advanced models in the sense that they can provide additional information with respect to intestinal metabolism. In situ rat intestinal perfusion is a reliable technique to investigate drug absorption potential in combination with intestinal metabolism, however, it is time consuming, and therefore not suited for screening purposes. Finally, in vivo absorption in animals can be estimated from bioavailability studies (ratio of the plasma AUC after oral and i.v. administration). The role of the liver in affecting bioavailability can be evaluated by portal vein sampling experiments in dogs.

Animals↗
PubMed2000

Identification of the cytochrome P450 enzymes involved in the metabolism of cisapride: in vitro studies of potential co-medication interactions.

Cisapride is a prokinetic drug that is widely used to facilitate gastrointestinal tract motility. Structurally, cisapride is a substituted piperidinyl benzamide that interacts with 5-hydroxytryptamine-4 receptors and which is largely without central depressant or antidopaminergic side-effects. The aims of this study were to investigate the metabolism of cisapride in human liver microsomes and to determine which cytochrome P-450 (CYP) isoenzyme(s) are involved in cisapride biotransformation. Additionally, the effects of various drugs on the metabolism of cisapride were investigated. The major in vitro metabolite of cisapride was formed by oxidative N-dealkylation at the piperidine nitrogen, leading to the production of norcisapride. By using competitive inhibition data, correlation studies and heterologous expression systems, it was demonstrated that CYP3A4 was the major CYP involved. CYP2A6 also contributed to the metabolism of cisapride, albeit to a much lesser extent. The mean apparent K(m) against cisapride was 8.6+/-3.5 microM (n = 3). The peak plasma levels of cisapride under normal clinical practice are approximately 0.17 microM; therefore it is unlikely that cisapride would inhibit the metabolism of co-administered drugs. In this in vitro study the inhibitory effects of 44 drugs were tested for any effect on cisapride biotransformation. In conclusion, 34 of the drugs are unlikely to have a clinically relevant interaction; however, the antidepressant nefazodone, the macrolide antibiotic troleandomycin, the HIV-1 protease inhibitors ritonavir and indinavir and the calcium channel blocker mibefradil inhibited the metabolism of cisapride and these interactions are likely to be of clinical relevance. Furthermore, the antimycotics ketoconazole, miconazole, hydroxy-itraconazole, itraconazole and fluconazole, when administered orally or intravenously, would inhibit cisapride metabolism.

Anti-Ulcer Agents↗