engleski

Macrolide uptake and release by HL-60 and human polymorphonuclear (PMN) cells

Macrolides concentrate within phagocytic and other cells, with a mean intracellular to extracellular (I/E) concentration ratio higher than 10 whatever the type of phagocyte. Among macrolide antibiotics there are considerable differences in uptake and release kinetics. HL-60 cells (human promyelocytic leukemia cell line) can be induced to differentiate to granulocytes by retinoic acid. The aim of this work was to compare uptake and release of different macrolides in PMNs and HL-60 cells. Uptake: PMNs were isolated from human blood. Differentiated HL-60 cells were obtained by 4-day incubation with all-trans-retinoic acid (ATRA) or 13-cis-retinoic acid (RA). Cells were incubated with azithromycin, erythromycin or HMR 3647 for up to 3h. PMNs were removed from the drug-containing medium by centrifugation through silicone oil. HL-60 cells were instead washed twice in ice-cold PBS. In both cases, cell pellet was lysed and antibiotic content was detected using microbiological bioassay. Release: Cells were loaded with macrolides as previously described. Afterwards, they were washed and incubated for up to 3h in drug free medium, washed twice in PBS, lysed and analysed as described in procedure for uptake. Compared to undifferentiated HL-60 cells and cells differentiated with RA, cells differentiated with ATRA showed significantly higher accumulation of azithromycin. Azithromycin and erythromycin each displayed similar uptake and release in PMNs and ATRA differentiated HL-60 cells. On the other hand, HMR 3647 displays saturable uptake kinetics in differentiated HL-60 cells but not in PMNs. Additionally, while in PMNs significant amount of accumulated HMR 3647 stays trapped in the cells during the whole incubation period, it egresses rapidly from the differentiated HL-60 cells during the first hour of incubation. Unlike azithromycin and erythromycin, uptake and release kinetics of HMR 3647 differs significantly between these two cell types.The observed discrepancies could indicate the existance of an additional release mechanism present in differentiated HL-60 cells but not in PMNs.

macrolide; HL-60; polymorphonuclear cells; uptake; release; azithromycin; erythromycin; HMR 3647

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