Effects of α-conotoxin ImI on TNF-α, IL-8 and TGF-β expression by human macrophage-like cells derived from THP-1 pre-monocytic leukemic cells

alpha 7 nicotinic acetylcholine receptors (nAChRs) are ubiquitous in the nervous system and ensure important neurophysiological functionality for many processes. However, they are also found in cells of the immune system, where their role has been less studied. Here we report the pro-inflammatory effect of ImI, a well characterized conotoxin that inhibits alpha 7 nAChRs, on differentiated THP-1 premonocyte macrophages (MDM) obtained by phorbol 12-myristate 13 acetate (PMA) treatment. Enzyme-linked immunosorbent assay (ELISA) performed on supernatant fluids of LPS challenged MDM showed ImI-mediated upregulation of pro-inflammatory cytokine TNF-alpha in an ImI concentration-dependent manner from 0.5 to 5.0 mu mol/L and for IL-8 up to 1.0 mu mol/L. Levels of anti-inflammatory cytokine TGF-beta remained practically unaffected in ImI treated MDMs. Nicotine at 10 mu mol/L significantly downregulated the release of TNF-alpha, but showed a lesser effect on IL-8 secretion and no effect on TGF-beta. Fluorescent competitive assays involving ImI, alpha-bungarotoxin and nicotine using MDM and the murine macrophage RAW 264.7 suggest a common binding site in the alpha 7 receptor. This work extends the application of conotoxins as molecular probes to non-excitatory cells, such as macrophages and supports the involvement of the alpha 7 nAChR in regulating the inflammatory response via the cholinergic anti-inflammatory pathway (CAP).