Pentoxifylline modulates p47phox activation and downregulates neutrophil oxidative burst through PKA-dependent and -independent mechanisms.

BACKGROUND AND AIM: Pentoxifylline (PTX) has been proven to be an inhibitor of fMLP-induced neutrophil (PMN) oxidative burst and is thought to function by increasing cAMP and Protein kinase A (PKA). We hypothesized that PTX diminishes production of the neutrophil respiratory burst by both PKA-dependent and independent mechanisms.
MATERIAL AND METHODS: Human neutrophils were isolated and stimulated with fMLP (1microM) alone or in combination with PTX (2mM). PMN activation was determined by the cytochrome C reduction method in the presence and absence of p38 MAPK (SB203580), ERK (PD98059), and PKA inhibitors (H89). Western blot analysis of Ras, Raf, p38 MAPK, ERK, and Akt was performed in PMNs exposed to fMLP and PTX. Cell membranes were fractionated to measure membrane-associated p47 phox. Treated cells were imaged using confocal microscopy to examine changes in localization of Akt and p47phox.
RESULTS: PTX produced a decrease in oxidative burst that was diminished but not abrogated by H89 exposure. The reduction in Ras, Raf, and Akt activation seen with PTX was not effected by the presence of H89. The ability of PTX to attenuate phosphorylation of p38 MAPK and ERK was significantly decreased in the presence of H89, suggesting a PKA-dependent mechanisms. Membrane fractions of neutrophils demonstrate that PTX decreased membrane-associated p47phox, thus diminishing the ability to generate oxidative burst. PTX also decreased membrane localization of Akt and p47phox by confocal microscopy.
CONCLUSIONS: PTX attenuates activation of signaling molecules involved in activation of p47phox and suppress the subsequent assembly of the NADPH machinery through both PKA-dependent and PKA-independent mechanisms.