Disposition and functions of clarithromycin in human THP-1 monocytes during stimulated and unstimulated conditions

The macrolide antibiotics are bacteriostatic agents interfering with protein synthesis but they are taken up by phagocytic cells, e.g. macrophages, neutrophils and fibroblasts which take up infectious organisms into phagosome-lysosomal vaculoes. Recent studies have suggested that these macrolide antibiotics block the spread of infections by mechanisms associated with the inflammation process. Herein is a study with clarithromycin using human THP-1 monocytes, a phagocytic cell which has not been studied to date. Clarithromycin was rapidly taken up by the monocytes (approximately 1%) utilizing both saturable carrier and passive processes at pH 7.4 but was exclusively passive at pH 6.8 and 5.0. The carrier process was energy and temperature dependent and appeared to be linked to certain ion channels. Efflux of the drug was rapid and complete in 1 hr. Intracellular disposition showed 74% in the cell sap and 11% in the nucleus. Upon stimulation with zymogen A or bacteria significant increases of uptake occurred in the isolated lysosome-phagosomes. Examination showed that initially clarithromycin treatment triggered the release of NO, H2O2, IL-1 and TNFalpha from the monocytes, known mediators of inflammation, but also mediators which cause bacterial cell death or apoptosis. The activity of the monocyte marker hydrolytic enzyme NAG was elevated at this time as well as protein kinase C activity. Treatment from 2-4 hr with clarithromycin appeared to reverse this process in that the chemical mediator release was reduced along with the activities of hydrolytic enzymes, e.g. NAG and cathepsin D with no evidence of lipid peroxidation and protective SOD enzyme activity elevation. The latter effects of the antibiotic would be useful in blocking the spread of infection or inflammation from the original site. The normal bacterial static killing effects of clarithromycin was evident at 24 but not 2 hr in both extracellular free bacteria and those bacteria phagocytosed by the THP-1 monocytes.