Mechanisms of Fluoroquinolone Transport by Human Neutrophils

Neutrophils accumulate ciprofloxacin and other fluoroquinolones, a process that enhances the killing of intracellular pathogens and could facilitate the delivery of these agents to infection sites by migrating neutrophils. The mechanisms by which transport occurs have not been characterized. In the present study, quiescent neutrophils transported ciprofloxacin with an observed K(m) of 167 μg/ml (501 μM) and a maximum velocity of 25.2 ng/min/10(6) cells. When neutrophils were stimulated with phorbol myristate acetate (PMA), a second component of ciprofloxacin transport was induced. This pathway had an apparent K(m) of 9.76 μg/ml (29.3 μM) and a maximum velocity of 59.3 ng/min/10(6) cells. Transport by both pathways was Na(+) independent. Ciprofloxacin transport by quiescent cells was relatively insensitive to pH and N-ethylmaleimide but was competitively inhibited by adenine (K(i) = 1.55 mM). Papaverine, a benzylisoquinoline known to inhibit nucleobase transport, also inhibited ciprofloxacin transport by quiescent cells. In contrast, transport by PMA-stimulated cells was enhanced at pH 8.2, inhibited at pH 6.2, and blocked by N-ethylmaleimide. Cationic and neutral amino acids and cystine competitively inhibited ciprofloxacin transport by PMA-stimulated neutrophils (K(i) = 158 μM for ornithine) but had little effect on quiescent cells. PMA-activated transport was not inhibited when the Na(+) in the medium was replaced with K(+) or Li(+), and the pattern of inhibition by cationic and neutral amino acids was similar. In summary, neutrophils continuously transport ciprofloxacin via a transport pathway shared by adenine. Activation by PMA induces a separate, higher-affinity transport pathway shared by a broad scope of amino acids. Neutrophils utilize one or both of these mechanisms to transport other fluoroquinolones.