Pentoxifylline in vivo and in vitro down-regulates the expression of the intercellular adhesion molecule-1 in monocytes

Since pentoxifylline (PTX) was recently recognized as a substance with antiinflammatory capacities, we studied the in vivo and in vitro effect of PTX on the expression of the intercellular adhesion molecule-1 (ICAM-1) on human monocytes. For this purpose four healthy Volunteers were treated with PTX (5 x 400 mg/day) for 2 days. Monocytes were isolated before and after PTX treatment and ICAM-1 expression was investigated. As shown by fluorescence-activated cell sorter (FAGS) analysis, cultured monocytes isolated after oral application of PTX expressed significantly decreased amounts of ICAM-1 when compared with monocytes collected prior to oral PTX application. Northern blot analysis revealed reduced amounts of ICAM-1 mRNA in monocytes derived from volunteers after oral PTX treatment in comparison with monocytes isolated before oral PTX administration. Similarly, in monocytes treated with PTX (200 mu g/ml) in vitro ICAM-1 was found decreased both at the protein and mRNA level in comparison with untreated cells. The inhibitory effect of PTX on ICAM-1 expression in monocytes could be reversed by the addition of exogenous tumour necrosis factor-alpha (TNF-alpha; 200 U/ml) suggesting that ICAM-1 down-regulation is mediated secondary to TNF-alpha suppression by PTX. The specific role of TNF-alpha in mediating ICAM-1 expression in cultured monocytes could be confirmed by the finding that a neutralizing anti-TNF-alpha antibody partially down-regulated ICAM-1 expression. The observed suppressive in vivo and in vitro effects of PTX on ICAM-1 expression in monocytes may contribute to the recently described antiinflammatory effects of PTX, e.g. in sepsis or allergic contact dermatitis.