Neutral endopeptidase (EC 3.4.24.11) does not hydrolyze recombinant human interleukin-1 beta

We have previously shown that neutral endopeptidase (NEP; EC 3.4.24.11) regulates neuropeptide-induced responses. Recently, Pierart et al. reported that NEP degraded purified interleukin-1 (IL-1) using thymocyte proliferation assay. Since IL-1 is an important cytokine in the immune response and inflammation, we have assessed whether NEP hydrolyzes recombinant human IL-1 beta using three assay systems (bioassay, immunoassay, and HPLC analysis). NEP on the NALM-6 cells (both intact cells and the solubilized plasma membrane fraction) efficiently hydrolyzed Met5-enkephalin and substance P. However, NEP did not significantly decrease the amount of rhIL-1 beta assessed by the growth inhibitory activity of a human melanoma, by the immunoassay, or by the direct analysis on HPLC. Therefore, we conclude that NEP does not significantly hydrolyze rhIL-1 beta. Our results suggest that, in contrast to the regulatory role of NEP in neuropeptide-induced responses, NEP is not a regulatory enzyme for IL-1-induced responses.