Overproduction of collagen (I) by activated hepatic stellate cells is a critical step in the development of liver fibrosis. It has been established that these cells express interleukin (IL)-6 and respond to this cytokine with an increase in alpha(I) collagen. Pentoxifylline, a methylxanthine derivate, has been reported to have antifibrotic properties, but the mechanism responsible for this effect is unknown. The aim of this study was to determine the effect of pentoxifylline on acetaldehyde-induced collagen production in a rat hepatic stellate cell line (CFSC-2G cells). Cells were treated with 100 microM acetaldehyde and 200 microM pentoxifyline for 3 h. IL-6 and alpha(I) collagen messenger RNA (mRNA) were determined by reverse transcriptase polymerase chain reaction (RT-PCR) assay. NFkappaB activation was determined by electrophoretic mobility shift assay. To corroborate NFkappaB participation in pentoxifylline effect, cells were pretreated with 10 microM TPCK, a NFkappaB inhibitor. IkappaBalpha was determined by Western blot. IL-6 expression decreased significantly in acetaldehyde-pentoxifylline-treated cells. Acetaldehyde-treated cells pretreated with an anti-IL-6 monoclonal antibody did not show any increase in alpha (I) collagen expression. Acetaldehyde-treated cells increased 1.48 times NFkappaB activation, whereas acetaldehyde-pentoxifylline-treated cells decreased NFkappaB activation to control values. TPCK pretreated acetaldehyde cells did not present NFkappaB activation. To corroborate NFkappaB participation in pentoxifylline effect, IkappaBalpha was determined. IkappaBalpha protein level decreased 50% in acetaldehyde-treated cells, while acetaldehyde-pentoxifylline-treated cells showed IkappaBalpha control cells value. The data suggest that acetaldehyde induced alpha(I) collagen and IL-6 expression via NFkappaB activation. Pentoxifylline prevents acetaldehyde-induced alpha(I) collagen and IL-6 expression by a mechanism dependent on IkappaBalpha degradation, which in turn blocks NFkappaB activation.