Future studies to investigate LPS-induced CGRP synthesis in monocytes/macrophages of RAMP1 over-expressing

transgenic mice20 and knockout mice37 should verify this hypothesis. In the present study, we have used exogenous CGRP, peptide CGRP receptor antagonist CGRP8-37 and non-peptide CGRP receptor antagonist BIBN4096BS, HSP inhibitor clinical trial to establish the possible role of CGRP receptor signalling in basal and LPS-induced pro-inflammatory and anti-inflammatory chemokines and cytokines in the RAW 264.7 macrophage cell line. The affinities of αCGRP, CGRP8-37 and BIBN4096BS to bind human CGRP receptors have been well established, with the affinities BIBN4096BS (Ki = 14·4 ± 6·3 pm) > αCGRP (Ki = 31·7 ± 1·6 pm) > CGRP8-37 (Ki = 3·6 ± 0·7 nm), respectively.25 Hence, the physiological concentrations for MG132 both CGRP and BIBN4096BS are within nm range25 whereas for CGRP8-37, it is within the μm range.38 We used the physiological range of concentrations of the antagonists in the current study. The mechanisms underlying the blocking activities of both antagonists on CGRP receptors are rather different. Since CGRP8-37 peptide includes all but the first seven amino acids at the C-terminal

of CGRP, it works as a competitive antagonist to block the binding of full-length CGRP to its receptor. In contrast, the specific affinities of BIBN4096BS depend on its interaction with the RAMP1 subunit of CGRP receptor.39 From the literature, the role of CGRP in the induction of pro-inflammatory and anti-inflammatory chemokines and cytokines is controversial.21–23 In these studies, depending on the cell type and concentration, CGRP exhibits either stimulating or suppressing effect on the production of MCP-1, IL-1β, TNFα, IL-6 and IL-10. Consistently, CGRP receptor signalling in the current study also demonstrates positive or negative effects on basal and LPS-induced release of these inflammatory mediators depending on the concentration of CGRP and CGRP receptor antagonists. Generally speaking, a lower concentration of CGRP seems to facilitate the basal Bcl-w release of MCP-1, TNFα and IL-6 but had no effect on the basal release of IL-1β and IL-10. The facilitating effects were

blocked by a lower concentration of CGRP8-37 (10 nm), suggesting that CGRP receptor mediates the effect. In contrast, a higher concentration of CGRP suppressed basal TNFα release but had no effect on others. Contrary to the effect of CGRP, a higher concentration of the peptide antagonist CGRP8-37 significantly increased the basal release of all chemokines and cytokines examined, but the lower concentration had no effect at all. Non-peptide antagonist BIBN4096BS also manifested the same tendency. However, at higher concentration, it only significantly increased the basal release of MCP-1, IL-6 and IL-10 but had no effect on IL-1β and TNFα. Similar to CGRP8-37, a lower concentration of BIBN4096BS had no effect on the basal release of chemokines and cytokines.