Kaurane diterpenes protect against apoptosis and inhibition of phagocytosis in activated macrophages

Background and purpose: The kaurane diterpenes foliol and linearol are inhibitors of the activation of nuclear factor kappa B, a transcription factor involved in the inflammatory response. Effects of these diterpenes on apoptosis and phagocytosis have been analysed in cultured peritoneal macrophages and in the mouse macrophage cell line, RAW 264.7. Experimental approach: Macrophages were maintained in culture and activated with pro-inflammatory stimuli in the absence or presence of diterpenes. Apoptosis and the phagocytosis in these cells under these conditions were determined. Key results: Incubation of macrophages with a mixture of bacterial lipopolysaccharide ( LPS)/interferon-gamma ( IFN-gamma) induced apoptosis through a NO-dependent pathway, an effect significantly inhibited by foliol and linearol in the low mu M range, without cytotoxic effects. Apoptosis in macrophages induced by NO donors was also inhibited. The diterpenes prevented apoptosis through a mechanism compatible with the inhibition of caspase-3 activation, release of cytochrome c to the cytosol and p53 overexpression, as well as an alteration in the levels of proteins of the Bcl-2 family, in particular, the levels of Bax. Cleavage of poly( ADP-ribose) polymerase, a well-established caspase substrate, was reduced by these diterpenes. Treatment of cells with foliol and linearol decreased phagocytosis of zymosan bioparticles by RAW 264.7 cells and to a greater extent by peritoneal macrophages. Conclusions and implications: Both diterpenes protected macrophages from apoptosis and inhibited phagocytosis, resulting in a paradoxical control of macrophage function, as viability was prolonged but inflammatory and phagocytic functions were impaired.