Different susceptibility to neurokinin 1 receptor antagonists of substance P and septide-induced interleukin-6 release from U373 MG human astrocytoma cell line

Abstract

In a human astrocytoma cell line U373 MG, the activation of the neurokinin 1 (NK1) receptor by substance P (SP) increase, in a concentration-related manner (1 nM to 10 μM), the basal release of interleukin-6 (IL-6) as assayed by an ELISA method, in cell supernatants after 18 h of incubation. Septide, a selective NK1 receptor agonist, is equipotent to SP in inducing the IL-6 release showing similar E max (2644 ± 285 and 2830 ± 271 pg/ml) and EC 50 (15.6 ± 3.6 and 13.8 ± 3.2 nM). However, in binding assays on intact cells, septide was an about 50-fold weaker displacer of the binding of [ 3H][Sar 9,Met(O 2) 11]SP than SP ( K i's were 0.28 ± 0.1 nM and 14.2 ± 5.0 nM for SP and septide, respectively). NK2- and NK3-selective agonists (up to 1 μM) had no binding or functional effect. Highly selective non-peptide (CP96,345) or peptide (GR 82,334) NK1 receptor antagonists were more effective in antagonizing septide- (IC 50's 0.2 ± 0.06 nM and 70 ± 18 nM) than SP- (IC 50's 6.7 ± 1.3 nM and 1.95 ± 0.4 μM) induced IL-6 secretion. These data support the existence, also in human U373 MG cells, of a septide-sensitive NK1 receptor subtype(s) and/or epitope(s) blocked with high affinity by NK1 antagonist.