Interleukin-6 secretion from human astrocytoma cells induced by substance P

Abstract

Functional NK-1 (substance P) receptors have been demonstrated previously on astrocyted from primary newborn rat brain cultures and human astrocytoma cells lines by specific [ 125I]-Bolton Hunter substance P (SP) binding and by SP-induced phosphoinositol turnover. In addition, these cells have been shown to release cytokines upon stimulation with interleukin-1 (IL-1) and lipopolysaccharide (LPS). Since SP has also been shown to induce cytokine release from rat glial cells, this neuropeptide may contribute to the pathophysiology of neuronal inflammation in humans by stimulating cytokine production in the brain. We, therefore, explored whether SP could induce U-373 human astocytoma cells, via specific NK-1 receptor activation, to secrete interleukin-6 (IL-6), a cytokine implicated as a key mediator of immune and inflammatory responses. SP stimulated IL-6 production in a concentration-dependent manner with an MC 50 (concentration inducing 50% of the maximum response) of 45 nM. IL-6 was detected in the cell culture supernatant fluids 2 h post stimulattion and secretion pealed at 12 h. SP induced IL-6 secretion was not mediated by IL-1 since neutralizing anti-IL-1 (α and β) antibody treatment had no effect on the SP response. The selective NK-1 receptor agonist, [Sar 9, Met(O 2) 11]-SP, was comparably effective to SP in stimulatinf IL-6 secretion; however, selective NK-2 and NK-3 receptor agonists were 250–500-fold less effective. In addition, the non-peptide NK-1 receptor antagonist, (±)CP-96,345 inhibited SP ( K i = 4 nM), but not IL-1-induced IL-6 release. These selectivity and specificity studies confirmed the presence of functional NK-1 type rece[tors linked to IL-6 release. The results of this study support a role for SP as a modulator of immune and/or inflammatory processes in the human CNS.