We have noticed that CGRP8-37 has a much stronger effect than BIBN4096BS on the basal release of these chemokines and cytokines. CGRP8-37 has been shown to bind both CGRP receptors (CLR/RAMP1) and AM2 receptors (CLR/RAMP3), whereas BIBN4096BS is more selective to CGRP receptor binding sites.40,41 Although it is unknown if AM receptors are present in RAW macrophages, CLR, RAMP1, RAMP2 and RAMP3 have been shown to exist in murine bone marrow macrophages.42 Adrenomedullin High Content Screening was also shown to exhibit both stimulating and inhibiting effects on the production of chemokines and cytokines in a macrophage cell line.43 It is therefore highly possible

that some effects of CGRP8-37 on the basal release in the current study may be mediated through its action on AM2 receptors. BIBN4096BS has been shown to exhibit species affinity because it binds primate CGRP receptors with higher affinity (100 times) over binding rodent CGRP receptors.25,39 Alternatively, the discrepancy of the effects of CGRP8-37 and BIBN4096BS on the basal release here may also be interpreted as the lower affinity of Autophagy activator BIBN4096BS

in binding murine CGRP receptors in RAW macrophages. Depending on its concentrations, exogenous CGRP was shown to either stimulate or inhibit LPS-induced cytokine production in macrophages in previous reports.23,44–46 In line with these studies, in a concentration-dependent manner, RG7420 in vitro exogenous CGRP increased LPS-induced release of IL-1β, TNFα and IL-6, suppressed LPS-induced TNFα release or had no effect on LPS-induced IL-10 release. The effects of CGRP8-37 on CGRP or LPS-induced pro-inflammatory cytokines in primary macrophages and other cell types have been reported previously.10,45–47 Depending on concentrations, CGRP8-37 either potentiated or inhibited CGRP or LPS-induced cytokine production in these studies.

Similarly, the effect of CGRP8-37 on LPS-induced chemokine and cytokine release in the current study is also concentration-dependent. It enhanced LPS-induced TNFα and IL-10 release, suppressed LPS-induced TNFα release or had no effect on LPS-induced release of MCP-1 and IL-6. Information regarding the effects of BIBN4096BS on CGRP or LPS-induced chemokines and cytokines is relatively scarce. We previously showed that 0·1 and 1 μm BIBN4096BS suppressed increased IL-6 levels in injured nerves as well as CGRP-induced IL-6 in injured nerve explants.10 Using the same concentrations here, BIBN4096BS potentiated LPS-induced IL-1β and TNFα release, inhibited LPS-induced TNFα release or had no effect on LPS-induced release of MCP-1 and IL-6. The discrepancy in the effects of CGRP8-37 and BIBN4096BS on LPS-induced release might also suggest that the two antagonists do not act only on the same CGRP receptors. Tha adrnomedullin receptors AM1 (CLR/RAMP2) and AM2 (CLR/RAMP3) may also be involved in CGRP8-37-exerted effects on LPS-induced release.