Downregulation of angiotensin converting enzyme by TNF-α in differentiating human macrophages

Objective: To investigate regulation of angiotensin converting enzyme (ACE) by tumour necrosis factor alpha (TNF-alpha) in differentiating human peripheral blood monocytes (PBM). Methods: Human PBM were allowed to differentiate to macrophages for 0-7 days and ACE amount was measured during differentiation. Experiments with TNF-alpha were performed after 2 days of differentiation. Cell cultures were incubated with TNF-alpha (0.5-10 ng/ml) without or with SB 202190 (5 muM), or PD 98059 (40 muM). ACE amounts were measured by an inhibitor binding assay (IBA) and ACE mRNA levels by RNase protection assay (RPA). Activated p44/42 and p38 MAP kinases were measured by Western Blot analysis using phospho-p44/42 and p38 MAPK antibodies. Results: ACE amount increased by 40-fold along with macrophage differentiation. TNF-a caused dose dependent suppression of the amount of ACE and decreased levels of ACE mRNA. TNF-a activated p44/42 and p38 MAP kinases, which was inhibited by the specific inhibitors of these kinases, PD98059 or SB202190, respectively. Pretreatment of the cells with SB 202190, or PD 98059 both partly reversed TNF-alpha induced ACE suppression. Conclusions: TNF-alpha downregulated ACE, which effect was probably mediated by both p44/42 and p38 MAPK pathways. Local downregulation of ACE by TNF-alpha may be a counterbalancing mechanism in inflammatory processes. (C) 2002 Published by Elsevier Science Ltd.