Anxiogenic-like effects induced by hemopressin in rats

Hemopressin (PVNFKFLSH; HP) is an orally active peptide derived from rat hemoglobin alpha-chain that could act as an inverse agonist at cannabinoid type 1 receptors (CB1). Here, we aim to investigate possible behavioral effects of HP in male Wistar rats tested in the elevated plus maze (EPM), following HP intraperitoneal (i.p., 0.05 mg/kg), oral (P.O., 0.05 and 0.5 mg/kg) or intracerebroventricular (I.C.V., 3 and 10 nmol) administration. HP induced a decrease in EPM open arm exploration, indicating an anxiogenic-like effect. However, i.p. administration of HP (1 mg/kg) followed by mass spectrometry analysis of brain-peptide extracts suggested that the intact HP does not cross the blood brain barrier. I.C.V. administrated HP produced anxiogenic-like effects that were prevented by Transient Receptor Potential Vanilloid Type 1 (TRPV1) antagonists, 6-iodonordihydrocapsaicin (1 nmol) or SB366791 (1 nmol), but not by the CB1 receptor antagonist AM2S1 (0.1 and 1 nmol). Altogether, these data suggest that I.C.V. administrated HP induces anxiogenic-like effects by activating TRPV1 receptors. The similar anxiogenic effects observed after i.p. or P.O. administration could be due to HP fragment(s) crossing the blood brain barrier. The present results advance our knowledge about HP pharmacology and suggest concerns in future clinical studies.

The C-terminus of murine S100A9 protein inhibits hyperalgesia induced by the agonist peptide of protease-activated receptor 2 (PAR2)

Background and purpose: S100A9 protein induces anti-nociception in rodents, in different experimental models of inflammatory pain. Herein, we investigated the effects of a fragment of the C-terminus of S100A9 (mS100A9p), on the hyperalgesia induced by serine proteases, through the activation of protease-activated receptor-2 (PAR2). Experimental approach: Mechanical and thermal hyperalgesia induced by PAR2 agonists (SLIGRL-NH2 and trypsin) was measured in rats submitted to the paw pressure or plantar tests, and Egr-1 expression was determined by immunohistochemistry in rat spinal cord dorsal horn. Calcium flux in human embryonic kidney cells (HEK), which naturally express PAR2, in Kirsten virus-transformed kidney cells, transfected (KNRK-PAR2) or not (KNRK) with PAR2, and in mouse dorsal root ganglia neurons (DRG) was measured by fluorimetric methods. Key results: mS100A9p inhibited mechanical hyperalgesia induced by trypsin, without modifying its enzymatic activity. Mechanical and thermal hyperalgesia induced by SLIGRL-NH2 were inhibited by mS100A9p. SLIGRL-NH2 enhanced Egr-1 expression, a marker of nociceptor activation, and this effect was inhibited by concomitant treatment with mS100A9p. mS100A9p inhibited calcium mobilization in DRG neurons in response to the PAR2 agonists trypsin and SLIGRL-NH2, but also in response to capsaicin and bradykinin, suggesting a direct effect of mS100A9 on sensory neurons. No effect on the calcium flux induced by trypsin or SLIGRL in HEK cells or KNRK-PAR2 cells was observed. Conclusions and implications: These data demonstrate that mS100A9p interferes with mechanisms involved in nociception and hyperalgesia and modulates, possibly directly on sensory neurons, the PAR2-induced nociceptive signal.