Association of sodium salicylate to isolated leucocytes

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.

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.

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.

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.

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.

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.