Hydrogen sulfide (H(2)S), an endogenous gasotransmitter, modulates various biological events such as inflammation in the mammalian body. The present study investigated possible involvement of H(2)S in peripheral nociceptive processing. Intraplantar (i.pl.) administration of NaHS, a H(2)S donor, produced prompt hyperalgesia in rats, accompanied by expression of Fos in the spinal dorsal horn. The H(2)S-evoked hyperalgesia was blocked by 5,5'-dithio-bis-(2-nitrobenzoic acid) (DTNB), an oxidizing agent, or ethosuximide and mibefradil, T-type Ca(2+) channel inhibitors. L-Cysteine, an endogenous source for H(2)S, given i.pl., also elicited hyperalgesia, an effect being abolished by DL-propargylglycine (PPG) and beta-cyanoalanine (BCA), inhibitors of cystathionine-gamma-lyase, a H(2)S synthesizing enzyme. PPG and/or BCA partially inhibited the hyperalgesia induced by i.pl. lipopolysaccharide, an effect being reversed by i.pl. NaHS. In the patch-clamp study using undifferentiated NG108-15 cells that express T-type, but not other types, of Ca(2+) channels, NaHS enhanced the currents through the T-type channels, an effect being blocked by DTNB. Thus, H(2)S appears to function as a novel nociceptive messenger through sensitization of T-type Ca(2+) channels in the peripheral tissues, particularly during inflammation.

To develop potent and metabolically stable agonists for protease-activated receptor-2 (PAR-2), we prepared 2-furoylated (2f) derivatives of native PAR-2-activating peptides, 2f-LIGKV-OH, 2f-LIGRL-OH, 2f-LIGKV-NH 2 , and 2f-LIGRL-NH 2 , and systematically evaluated their activity in PAR-2-responsive cell lines and tissues. In both HCT-15 cells and NCTC2544 cells overexpressing PAR-2, all furoylated peptides increased cytosolic Ca 2ϩ levels with a greater potency than the corresponding native peptides, although a similar maximum response was recorded. The absolute potency of each peptide was greater in NCTC2544, possibly due to a higher level of receptor expression. Furthermore, the difference in potency between the 2-furoylated peptides and the native peptides was enhanced when evaluated in the rat superior mesenteric artery and further increased when measuring PAR-2-mediated salivation in ddY mice in vivo. The potency of 2f-LIGRL-NH 2 , the most powerful peptide, relative to SLIGKV-OH, was about 100 in the cultured cell Ca 2ϩ signaling assays, 517 in the vasorelaxation assay, and 1100 in the salivation assay. Amastatin, an aminopeptidase inhibitor, augmented salivation caused by native peptides, but not furoylated peptides. The PAR-2-activating peptides, including the furoylated derivatives, also produced salivation in the wild-type C57BL/6 mice, but not the PAR-2-deficient mice. Our data thus demonstrate that substitution of the N-terminal serine with a furoyl group in native PAR-2-activating peptides dramatically enhances the agonistic activity and decreases degradation by aminopeptidase, leading to development of 2f-LIGRL-NH 2 , the most potent peptide. Furthermore, the data from PAR-2-deficient mice provide ultimate evidence for involvement of PAR-2 in salivation and the selective nature of the 2-furoylated peptides.

1 Proteinase-activated receptor-2 (PAR2), a receptor activated by trypsin and tryptase, is abundantly expressed in the gastrointestinal tract including the C-fiber terminal, and might play a role in processing of visceral pain. In the present study, we examined and characterized the roles of PAR2 in pancreatitis-related abdominal hyperalgesia/allodynia in mice. 2 Caerulein, administered i.p. once, caused a small increase in abdominal sensitivity to stimulation with von Frey hairs, without causing pancreatitis, in PAR2-knockout (KO) mice, but not wild-type (WT) mice. 3 Caerulein, given hourly six times in total, caused more profound abdominal hyperalgesia/allodynia in PAR2-KO mice, as compared with WT mice, although no significant differences were detected in the severity of pancreatitis between the KO and WT animals. 4 The PAR2-activating peptide, 2-furoyl-LIGRL-NH 2 , coadministered repeatedly with caerulein six times in total, abolished the caerulein-evoked abdominal hyperalgesia/allodynia in WT, but not PAR2-KO, mice. Repeated doses of 2-furoyl-LIGRL-NH 2 moderately attenuated the severity of caerulein-induced pancreatitis in WT animals. 5 Our data from experiments using PAR2-KO mice provide evidence that PAR2 functions to attenuate pancreatitis-related abdominal hyperalgesia/allodynia without affecting pancreatitis itself, although the PAR2AP applied exogenously is not only antinociceptive but also anti-inflammatory.

We characterized the tracheal and bronchial relaxation caused by proteinase-activated receptor-2 (PAR-2) activation in ddY mice and/or in wild-type and PAR-2-knockout mice of C57BL/6 background. Ser-Leu-Ile-Gly-Arg-Leu-amide (SLIGRL-NH 2 ) and Thr-Phe-Leu-Leu-Arg-amide, PAR-2-and PAR-1-activating peptides, respectively, caused relaxation in the isolated ddY mouse trachea and main bronchus. The relaxation was abolished by specific inhibitors of cyclooxygenase (COX)-1, COX-2, mitogen-activated protein kinase kinase (MEK), and p38 MAP kinase. The MEK and p38 MAP kinase inhibitors did not affect prostaglandin E 2 -induced relaxation. Inhibitors of cytosolic Ca 2ϩ -dependent phospholipase A 2 (PLA 2 ), Ca 2ϩ -independent PLA 2 , diacylglycerol lipase, tyrosine kinase, and protein kinase C exhibited no or only minor inhibitory effects on the PAR-mediated relaxation. Trypsin, a PAR-2 activator, and 2-furoyl-Leu-Ile-Gly-Arg-Leu-amide, a potent PAR-2-activating peptide, in addition to SLIGRL-NH 2 , caused airway relaxation in wild-type C57BL/6 mice, as in ddY mice. In PAR-2-knockout mice, the peptide effects were absent and the potency of trypsin decreased. Desensitization of PAR-2 and/or PAR1greatly suppressed the relaxant effect of trypsin. The bronchial and tracheal tissues displayed distinct sensitivities toward trypsin and the PAR-2-activating peptides. Our data indicate an involvement of both COX-1 and COX-2, and the MEK-extracellular signal-regulated kinase and p38 MAP kinase signaling pathways in the PAR-2-and PAR-1-triggered relaxation of mouse airway tissue, and substantiate a role for PAR-2 in regulating both the trachea and bronchial responsiveness in the mouse lung.

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