Monocyte- and Cytokine-Induced Downregulation of Angiotensin-Converting Enzyme in Cultured Human and Porcine Endothelial Cells

We investigated the effects of monocytes on endothelial cell (EC) ectoenzyme activity. Coculture of human aortic ECs with human monocytes (2 times 10 monocytes per 2-cm well) led to a decrease in EC angiotensin-converting enzyme (ACE) activity (64.5+/-3.5% of control) but not aminopeptidase N, aminopeptidase P, and 5 prime-nucleotidase activities. Similar results were obtained using human umbilical vein EC-human monocyte and porcine aortic EC-porcine monocyte cocultures. The decrease in ACE activity was monocyte concentration and coculture time dependent, reaching a maximum of 65% decrease in activity at 120 hours. Monocyte-mediated reduction in ACE activity did not require cell to cell contact, since exposure of ECs to conditioned medium from cocultures (CCCM) or from monocyte cultures (MCM) produced a decrease in ACE activity similar to that observed in EC-monocyte cocultures. Exogenously added tumor necrosis factor (TNF)-alpha and interleukin (IL)-1 alpha, two known secretory products of monocytes, simulated the effects of monocytes on ACE activity. Western blot analysis revealed a decrease in the amount of ACE protein in TNF-alpha-treated and CCCM-treated ECs compared with control ECs. Both TNF-alpha and IL-1 alpha were present in CCCM and MCM but not EC-conditioned medium. Incubation of the cocultures with a mixture of neutralizing antibodies against TNF-alpha and IL-1 totally abolished the monocyte-induced decrease in ACE activity. In conclusion, monocytes decrease ACE activity in cultured ECs through the release of cytokines such as TNF-alpha and IL-1.(Circ Res. 1996;79:512-523.)