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M Raghoebar

Publications and source records attributed to M Raghoebar.

29 records · Page 2Linked to original sources
PubMed1989

The polymorphonuclear leukocyte: its pharmacological transport and target properties: an overview.

The need for experimental models to study cellular pharmacokinetics and mechanisms of cell association of drugs in relation to the (patho)physiology is obvious. These models, although never identical to the in vivo physiological environment, can provide fundamental insights with respect to cellular transport mechanisms of drugs in vivo. This knowledge contributes to the development of drug targeting. The human polymorphonuclear leukocyte (PMN) was chosen in our studies as model and target cell because of its involvement in the action of different groups of drugs. First, the physiology and transport characteristics of the PMN has been described. Secondly, the mechanisms of association of some drugs with the PMN are considered. The possible contribution of cellular pharmacokinetics to drug targeting to the PMN is discussed.

Humans↗
PubMed1988

On the mechanisms of association of the macrolide antibiotic erythromycin with isolated human polymorphonuclear leucocytes.

In contrast to other antibiotics, the macrolide antibiotic erythromycin (ERY) has been demonstrated in previous studies to accumulate strongly in PMNs. In this study the mechanisms of association of ERY with human polymorphonuclear leucocytes (PMNs) were investigated. A kinetic approach was followed to establish the processes involved. It is argued that only passive and no active energy-dependent mechanisms contribute to the association process, since it has been demonstrated that (a) no counter-transport could be observed, (b) no consistent competition of ERY with structural analogues could be realized, and (c) no energy was required from oxidative pathways. Furthermore several other arguments point to passive mechanisms of ERY-PMN interaction. The extracellular concentration of ERY was linearly related to the degree of ERY-PMN association. The degree of association of ERY with both intact and lysed cells was dependent on its ionization state. In addition, the association and dissociation process of ERY was slow at 37 degrees. From these results it is deduced that the 17-fold accumulation of ERY in PMNs found at the usual in vivo ERY blood levels is due to binding of ERY to intracellular sites. In fact this intracellular binding might prevent intracellular activity of ERY. In addition, association of ERY with intact PMNs is inhibited by human serum, human serum albumin and alpha 1-acid-glycoprotein. Activation of the PMNs by phorbol ester and chemotactic peptide did not influence ERY-PMN association. Our results suggest that the intact PMN membrane permits free diffusive penetration of ERY only at physiological temperatures.

Biological Transport↗
PubMed1988

Mechanisms of cell association of some non-steroidal anti-inflammatory drugs with isolated leucocytes.

In the present study the degree and the mode of association of the radiolabelled drugs acetylsalicylic acid, sodium salicylate, and sodium benzoate with leucocytes were studied in view of the hypothesis that leucocytes are target cells for the anti-inflammatory activity of drugs. The overall association rate of acetylsalicylic acid is larger than that of sodium salicylate and sodium benzoate at 37 degrees, but smaller at 4 degrees. The ratio of the intracellular to the extracellular concentration varied between 1 and 2 for sodium salicylate and sodium benzoate, and between 3 and 6 for acetylsalicylic acid. The intracellular concentrations of these drugs were comparable in red blood cells and polymorphonuclear leucocytes, but lower in mononuclear leucocytes. The association of acetylsalicylic acid and sodium salicylate is markedly increased when the extracellular pH decreases. Lysis of cells decreases the association of acetylsalicylic acid and enhances the association of sodium salicylate and benzoate at 37 degrees twofold. It is suggested that the association of these drugs with leucocytes comprises binding to the membrane and uptake of undissociated species. Phorbol myristate acetate extensively inhibits the intracellular concentration of acetylsalicylic acid, while this inflammatory stimulus tends to increase the intracellular concentration of sodium salicylate. The major metabolites of salicylate enhance cell association of acetylsalicylic acid and salicylic acid. In conclusion, these findings indicate that the tested benzoic acid-like drugs associate with leucocytes in vitro to some extent and that environmental differences, e.g. pH, lysed cells, inflammatory stimuli and metabolites, may determine in vivo the degree of accumulation.

Anti-Inflammatory Agents, Non-Steroidal↗
PubMed1988

Chloroquine interaction with inflammatory human polymorphonuclear leucocytes.

The molecular in vitro association of radiolabelled chloroquine (CQ) with both normal resting and inflammatory polymorphonuclear leucocytes (PMNs) was measured. For this purpose a suitable ligand-association assay was developed to measure the cell association and the intracellular concentration of CQ. Under the influence of inflammatory stimuli PMNs display altered interaction with CQ. The intracellular concentration of CQ is reduced with 30 to 40% under inflammatory (disease) states when compared with non-inflammatory conditions. The mechanisms of CQ-PMN interaction associated with these altered intracellular concentrations of CQ are considered, with particular attention to the effects of rheumatic disease. Association experiments of CQ with PMNs performed in the presence of different established transport inhibitors showed that both diffusive uptake and carrier-mediated transport are involved in the cell accumulation of CQ in inflammatory PMNs. From these results, emphasis is given to three explanations for the decrease of the intracellular CQ concentration in inflamed PMNs. a) the expansion of the PMN volume under inflammatory conditions; b) the cytoplasmic or lysosomal pH changes and activation of the PMN Na+/H+ antiport by inflammatory stimuli; and c) the exocytic release of the granules (degranulation). Our data suggest that all these mechanisms, based on the events involved in inflammatory responses, may be involved in the decrease of the intracellular CQ concentration in inflammatory PMNs.

Arthritis, Rheumatoid↗
PubMed1987

Characteristics of the transport of ascorbic acid into leucocytes.

The degree and the mode of association of [14C]-ascorbic acid with leucocytes are examined. The degree of association of ascorbic acid with polymorphonuclear leucocytes (1-3%) is dependent on cell type, extracellular concentration of ascorbic acid, incubation temperature, intactness of the cells and the extracellular pH. All experiments are performed according to strict protocols as these compounds are labile in aqueous solutions. Further it is noticed that in all experiments an outward gradient of leucocyte endogenic ascorbic acid exists. The results suggest that the association process comprises at least one saturable pathway. The activation of polymorphonuclear leucocytes by phorbol myristate acetate increases the accumulation of ascorbic acid threefold.

Adult↗
PubMed1987

The cellular association of sodium salicylate and indomethacin in peritoneal fluid of ascites bearing mice.

The degree of association of sodium salicylate and indomethacin with inflammatory cells was measured under in vivo conditions in ascites bearing mice. These animals had sufficient volume of inflammatory effusion in the peritoneal cavity which enabled measurement of drug concentrations extravascularly, both in the effusion and in the inflammatory cells. A single anti-inflammatory dose of 200 mg/kg sodium salicylate or 10 mg/kg indomethacin was administered orally or intraperitoneally. The peritoneal salicylate levels exceeded blood levels starting approximately 4 h following oral drug application. Indomethacin peritoneal levels were substantially lower within 6 h after oral drug intake and exceeded the blood levels at 24 h. Intraperitoneal dosing of salicylate resulted after approximately 4 h in similar vascular and extravascular drug concentrations. Indomethacin was slowly cleared from the peritoneal compartment after intraperitoneal administration. Salicylate and indomethacin accumulated under in vivo inflammatory conditions in peritoneal cells. The degree of accumulation (the intracellular concentration was at most 6 times the extracellular concentration) was dependent on compound, time of sampling, protein binding and administration route. These results were confirmed in in vitro cell association experiments. Protein appeared to affect the macro- and micropartition of these drugs. The differences in biodistribution at macro level (tissue distribution) and at micro level (cellular association) between sodium salicylate and indomethacin were sought in the apparent disparities in protein binding and affinity for protein in mouse serum and exudate.

Administration, Oral↗
PubMed1987

An in vitro approach to study cellular kinetics of drugs.

We adapted different existing techniques in order to optimize the methodology for studying kinetic interactions between drugs and cells in vitro. Using the polymorphonuclear leukocyte as a target cell, we measured the binding of various ligands and intracellular drug concentrations. We also studied pharmacological modulation of drug transport under normal and inflammatory conditions. Our approach allows reproducible measurements on ligands with low affinity for association sites on polymorphonuclear leukocytes. We present data for various nonsteroidal antiinflammatory drugs and other ligands to validate our methodological approach. On the basis of the results thus obtained, we proposed a tentative model to fit data and concepts of drug-cell interactions.

Adult↗
PubMed1987

Alteration of chloroquine accumulation in human polymorphonuclear leucocytes under inflammatory conditions.

The present study concerns the established antirheumatic drug chloroquine (CQ) in relation to a possible target for drug therapy, the polymorphonuclear leucocyte (PMN). Its primary aim was to find out whether inflammatory conditions would influence the cell association of CQ. After a suitable ligand-binding assay was developed to measure the cellular association of CQ, the normal characteristics of the cellular transport of CQ were determined. The effect of the inflammatory conditions on CQ cell association was investigated with peripheral PMNs from rheumatoid arthritis (RA) patients, and with normal PMNs, in the absence and presence of the soluble cell-stimulators phorbol ester and chemotactic peptide. Under inflammatory conditions the intracellular concentration of CQ is reduced. This decrease is explained by three possibilities which are involved in cell activation: the leucocyte volume expansion, the cytoplasmic or lysosomal pH changes, and the exocytic release of the granules (degranulation). Our results suggest that this decrease will adversely affect the therapeutic effects, if the mode of anti-inflammatory action of CQ is related to the intracellular drug concentrations.

Chloroquine↗
PubMed1986

Mechanisms of cell association of chloroquine to leucocytes.

One approach currently being used to get more insight into the molecular mechanisms of action of drugs and their (micro)pharmacokinetic events is to perform cellular association studies. We have examined the association of the antimalarial and antirheumatic drug chloroquine (CQ) to isolated human blood cells. This study dealt with the hypothesis that inflammatory cells such as the leucocytes are the mediators of the anti-inflammatory activity of drugs, both as target cells and as potential vehicles for the transport of drugs to inflamed tissues. A suitable ligand-binding assay was developed to measure the cellular association of CQ. The polymorphonuclear leucocytes (PMNs) accumulated CQ to a greater extent than mononuclear leucocytes and red blood cells; this can be explained by the presence of a lot of acidic cellular organelles as lysosomes in the PMS, which trap the weak base CQ. The accumulation in the PMNs was dependent on temperature, cellular intactness and the extracellular pH. The apparent temperature dependency indicates that one or more energy delivery steps are involved in the entire process of cellular association. Scatchard analysis of the association of CQ to human PMNs revealed two different sites, with KD values of 1.7 microM and 0.12 mM for the low and high affinity site, respectively. The cellular association of CQ is inhibited by supratherapeutic concentrations of some nonsteroidal anti-inflammatory drugs. This is possibly due to an interaction at the level of the cellular transport pathways and emphasizes the value of micropharmacokinetic studies.

Aspirin↗
PubMedDate not supplied

A pharmacokinetic approach to the establishment of biopharmaceutic characteristics of different acetylsalicylic acid formulations in man.

Eleven acetylsalicylic acid (ASA) formulations were administered to 26 healthy volunteers in a cross-over design. The properties of the preparations differed from conventional, effervescent, buffered to buccal. The objectives of this study were: Consideration of the general aspects of a biopharmaceutical study: which parameter for which biopharmaceutic characteristic? Measurement of the kinetic parameters of ASA: first-pass effect, mean residence time, mean appearance time, total body clearance, apparent volume of distribution, half-lives, etc. Comparison of the formulations. Most of the formulations yield mean residence times for ASA of 0.3-1.0 h, which do not differ significantly (p greater than 0.05). For most of the products the first-pass effect is about 40 per cent; the average values of the apparent volume of distribution and whole body clearance, corrected for the first-pass effect, are about 201 and 650 ml min-1, respectively. Peak levels are reached slowly for the buccal formulations, and rapidly for the buffered products. It is difficult, especially for ASA, to characterize the gastro-intestinal absorption with pharmacokinetic model parameters, because the first-pass effect is large and often elimination of ASA is faster than absorption. The model-independent approach has the special advantages of calculating reliable pharmacokinetic parameters, and creating theoretical possibilities to characterize the absorption patterns of the different formulations in a quantitative way. No significant differences in the values of the parameters are found between most of the formulations. The ASA first-pass effect is reasonably constant and buccal application has no advantage. Enteric coating of the outer layer of ASA formulations causes inconsistent absorption and may be categorized under 'artificial mistakes'.

Adolescent↗