- 1-(5-oxohexyl)-3,7-Dimethylxanthine, a phosphodiesterase inhibitor, activates MAPK cascades and promotes osteoblast differentiation by a mechanism independent of PKA activation (pentoxifylline promotes osteoblast differentiation). Rawadi, G., Ferrer, C., Spinella-Jaegle, S., Roman-Roman, S., Bouali, Y., Baron, R. Endocrinology (2001)