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

Abstract

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.