Concentration-dependent effects of pentoxifylline on migration and myelin phagocytosis by macrophages

The effects of pentoxifylline (POX) on macrophage migration and myelin uptake were studied in an in vitro model of myelin phagocytosis. The POX is a phosphodiesterase inhibitor which inhibits TNF-alpha (tumor necrosis factor alpha) production and reduces ICAM-1 (intercellular adhesion molecule-1) expression by macrophages. Both of these molecules have earlier been shown to be involved in the process of myelin recognition and degradation. In the present series of experiments, cocultured peripheral nerves and macrophages were treated with different concentrations of POX. Untreated controls were massively invaded by macrophages which ingested the degenerating myelin sheaths. High concentrations of POX (100 microg ml(-1)) inhibited macrophage invasion of the nerves. Lower POX concentrations (50 microg ml(-1)), in contrast, lead to an increased myelin uptake by phagocytic cells without affecting macrophage migration. These data indicate that POX may regulate different effector functions of macrophages such as migration and myelin phagocytosis during Wallerian degeneration. This is important for inflammatory demyelinating conditions in the central or peripheral nervous system (PNS) in which macrophages are also important effector cells. Since POX is used as an immunomodulatory drug in demyelinating diseases, its effects on the described macrophage functions may be of high relevance. An increased myelin uptake during Wallerian degeneration may also support a more efficient axonal regeneration by removing axonal outgrowth inhibitors.