Pentoxifylline (POF) is a new candidate for the treatment of nonalcoholic steatohepatitis (NASH). Its effects on the cytokine production in patients with NASH are not completely understood. This study was designed to investigate the effect of POF on TNF-alpha production by peripheral blood mononuclear cells (PBMC) in patients with NASH. After preliminary experiments in healthy control subjects to determine the range of POF concentration to be used in NASH patients, PBMCs from patients with NASH (n = 13) were cultured in the presence of lipopolysaccharide (LPS, 100 ng/ml) and various concentrations of POF for 24 hr. Concentrations of TNF-alpha in culture supernatants were measured by ELISA and the transcriptional activity was determined by RT-PCR. As dictated by the results of our pre-liminary study in PBMC from healthy control subjects, we treated LPS stimulated PBMCs from NASH patients with 10, 100, and 500 mu g/ml of POF. Stimulation of PBMCs from NASH patients wit LPS resulted in a strong up-regulation of TNF-alpha production from median 355.9 (interquartile range, 206.7-463.5) pg/ml to 1,670 pg/ml (interquartile range, 1,121-2,414) pg/ml. In this LPS-stimulated culture system, POF caused a dose-dependent suppression of TNF-alpha levels (P < 0.001, ANOVA on ranks for repeated measures). TNF alpha levels in culture supernatants decreased to 870.3 (range, 598.3-2,077) pg/ml with 10 mu g/ml of POF treatment, and to levels similar to those obtained in baseline unstimulated cultures (133.4 (range, 95.8-1518.5)pg/ml) at 100 mu g/ml. At 500 mu g/ml, POF suppressed TNF-alpha a production to levels significantly lower than that obtained in unstimulated ( baseline) culture supernatants (76.3 (range, 33-94.5) pg/ml; P = 0.001). The mRNA expression was consistent with the effects on protein concentration. Demographic characteristics of the patients, laboratory results, such as AST, ALT, alkaline phosphatase, GGT, and triglyceride levels, and the liver histology did not seem to influence the in vitro TNF-alpha response of the PBMCs from NASH patients. POF can significantly decrease the LPS-stimulated TNF-alpha production by PBMCs in NASH patients. Our results support the notion that POF might be a good candidate for the treatment of NASH.