Pharmacological characterization of desensitization in scratching behavior induced by intrathecal administration of hemokinin-1 in the rat

Hemokinin-1 and substance P stimulate production of inflammatory cytokines and chemokines in human colonic mucosa via both NK1 and NK2 tachykinin receptors

There is increasing focus on the involvement of tachykinins in immune and inflammatory responses. Hemokinin-1 (HK-1) is a recently identified tachykinin that originates primarily from immune cells, and has structural similarities to substance P (SP), found mainly in neurons. However, there are species differences in HK-1, and the role of HK-1 in humans, particularly the intestine, has received minimal attention. The aim of this study was to investigate the inflammatory role of human HK-1 in the human colon. The effects of HK-1 and SP were compared on the production of multiple inflammatory cytokines and chemokines from human colonic mucosal explants. Data generated by Procarta multiplex assay and QuantiGene assay demonstrated that 4 h incubation with HK-1 (0.1 μM) significantly stimulated transcript expression and release of MCP-1, MIP-1α and β, RANTES, TNF-α, IL-1β and IL-6 from the mucosa. SP (0.1 μM) had comparable actions, but had no effect on MCP-1 or RANTES. These effects were inhibited separately by tachykinin NK₁ and NK₂ receptor antagonists SR140333 and SR48968 (both 0.1 μM), suggesting that these responses were mediated by both NK1 and NK2 receptors. In conclusion, these data support a novel inflammatory role for HK-1 in human colon, signaling via NK1 and NK2 receptors (and possibly other tachykinin-preferring receptors) to regulate the release of a broad spectrum of proinflammatory mediators. The study suggests that along with SP, HK-1 is also a proinflammatory mediator, likely involved in colonic inflammation, including inflammatory bowel disease (IBD).

Hemokinin-1 competitively inhibits substance P-induced stimulation of osteoclast formation and function

Hemokinin-1 (HK-1) is a novel member of the tachykinin family that is encoded by preprotachykinin 4 (TAC4) and shares the neurokinin-1 receptor (NK1-R) with substance P (SP). Although HK-1 is thought to be an endogenous peripheral SP-like endocrine or paracrine molecule in locations where SP is not expressed, neither the distribution of HK-1 in the maxillofacial area nor the role HK-1 in bone tissue have been examined. In this study, we investigated the distribution of HK-1 in trigeminal ganglion (TG) and maxillary bone, and assessed the expression of HK-1 during osteoclast differentiation. In vivo, rat molars were loaded for 5 days using the Waldo method. In vitro, rat osteoclast-like cells were induced from bone marrow cells. HK-1 distribution and expression were examined by immunofluorescence staining and reverse transcription polymerase chain reaction (RT-PCR). In vivo, HK-1 was localized in rat TG neurons; however, the number of HK-1-positive neurons was less than that of SP-positive neurons. In the maxillary bone, nerve fibers, blood vessels, and osteocytes were immunopositive for HK-1. Furthermore, HK-1-positive immunoreactivity was found in osteoclasts on the pressure side. In vitro, PCR showed that TAC4 and NK1-R mRNA was expressed in osteoclasts as well as in bone marrow cells. Although SP (10⁻⁷ M) treatment led to an increased number of osteoclasts, HK-1 (10⁻⁷ M) treatment did not. The numbers of biotin-labeled HK-1 peptides bound osteoclasts significantly decreased upon incubation with unlabeled SP and biotin-labeled HK-1 compared with biotin-labeled HK-1 alone. These results suggest that HK-1 may not stimulate the differentiation and function of osteoclasts. SP-stimulated osteoclast formation is competitively regulated by peripheral HK-1 through NK1-Rs.

The amino-terminal region of hemokinin-1 regulates the induction of thermal hyperalgesia in rats

It is known that intrathecal administration of substance P (SP) induces thermal hyperalgesia, whereas hemokinin-1 (HK-1), a member of the same tachykinin family as SP, hardly induces thermal hyperalgesia; however, the underlying mechanism remains to be elucidated. Therefore, we aimed to clarify which amino acid of these peptides contributes to the induction of thermal hyperalgesia. When two chimera peptides between the N-terminal region of SP and the C-terminal region of HK-1, and vice versa, SP (1-5)/HK-1 and HK-1 (1-5)/SP, were intrathecally administered, SP (1-5)/HK-1 induced thermal hyperalgesia whereas HK-1 (1-5)/SP had hardly any effect; furthermore, thermal hyperalgesia was induced by only C-terminal fragments of HK-1 and SP. These findings indicate that the N-terminal region of HK-1 is involved in the non-induction of thermal hyperalgesia. Next, we synthesized and intrathecally administered these chimera peptides in which part of the N-terminal region of HK-1 was replaced with that of SP, and vice versa, and all synthesized peptides induced thermal hyperalgesia. Both SP (1-2)/HK-1 and HK-1 (1-4)/SP certainly induced thermal hyperalgesia, although HK-1 and HK-1 (1-5)/SP had hardly any effect; therefore, it is probable that Ser at the 2nd position and Arg at the 5th position of HK-1 may be involved in the non-induction of thermal hyperalgesia. Furthermore, peptides in which amino acid at the 3rd and/or 4th positions of HK-1 was replaced with that of SP were synthesized. Intrathecal administration of HK-1 (1-2,4-5)/SP, but not HK-1 (1-2,5)/SP and HK-1 (1-3,5)/SP, hardly induced thermal hyperalgesia. These findings indicate that three amino acids, Ser, Thr and Arg at the 2nd, 4th and 5th positions of HK-1, respectively, regulate the induction of thermal hyperalgesia by HK-1.

Differential effects of substance P or hemokinin-1 on transient receptor potential channels, TRPV1, TRPA1 and TRPM8, in the rat

Two tachykinin peptides, substance P (SP) and hemokinin-1 (HK-1), and three transient receptor potential (TRP) channels, TRPV1, TRPA1 and TRPM8, are similarly localized in the spinal dorsal horn and dorsal root ganglion, suggesting that TRP channels may be related or modulated by these tachykinin peptides. Thus, to clarify whether the responses of TRP channels are modulated by SP or HK-1, the effects of pretreatment with SP or HK-1 on the induction of scratching behavior by TRP channel agonists were examined. Pretreatment with SP or HK-1 enhanced the induction of scratching behavior by resiniferatoxin, a TRPV1 agonist, whereas scratching behavior induced by menthol, a TRPM8 agonist, was suppressed by pretreatment with these peptides. On the other hand, pretreatment with SP, but not HK-1, suppressed the induction of scratching behavior by cinnamaldehyde, a TRPA1 agonist. Taken together, the present results indicate that SP or HK-1 differentially modulated the response of TRPV1, TRPA1 or TRPM8 channel.

NMDA and AMPA receptors contribute to the maintenance of substance P-induced thermal hyperalgesia

It is well known that intrathecal administration of substance P (SP) induces thermal hyperalgesia, but the mechanisms underlying the maintenance of SP-induced thermal hyperalgesia remain to be clarified. Thus, to clarify the receptors involved in the maintenance of SP-induced thermal hyperalgesia, the effect of administering SP or glutamate receptor agonists, NMDA or AMPA, under SP-induced thermal hyperalgesia was investigated. Also, the effect of pretreatment with protein kinase inhibitors on scratching behavior by NMDA or AMPA under SP-induced thermal hyperalgesia was examined. Under SP-induced thermal hyperalgesia, the number of scratchings following SP administration was time-dependently suppressed, whereas the number of scratchings after NMDA or AMPA administration was markedly enhanced and SP-induced thermal hyperalgesia was attenuated by pretreatment with NMDA or AMPA receptor antagonist. Furthermore, pretreatment with kinase inhibitors significantly attenuated the enhancement of scratching behavior by NMDA or AMPA under SP-induced thermal hyperalgesia. These findings indicate that SP-induced thermal hyperalgesia may be maintained through the enhanced responsiveness of NMDA or AMPA receptors, but not the receptor of SP, mediated by kinases.

Regulatory mechanisms in the differential expression of Hemokinin-1

Hemokinin-1, encoded by the TAC4 gene, is the most recent addition to the tachykinin family. Although most closely related to the neuropeptide Substance P, Hemokinin-1 distinguishes itself from other tachykinins by its predominantly non-neuronal expression pattern. Its expression in T and B lymphocytes, macrophages, and dendritic cells points to an important role for Hemokinin-1 in the immune system. To seek reasons for its preferential expression in the immune system and ultimately to provide clues to its function, we investigated the molecular mechanisms driving the differential expression pattern of this unique tachykinin. Our study provides the first analysis of the promoter region of the TAC4 gene, which reveals regulatory mechanism different from the Substance P promoter. We demonstrate for the first time that Hemokinin-1 initiates transcription from multiple start sites through a TATA-less promoter. Conservation of the 5' non-coding region indicates the importance of the upstream regulatory region in directing expression of Hemokinin-1 in specific cell types, during cell differentiation and activation. Furthermore, NFkappaB, a transcription factor important in the activation of immune cells was shown to be involved in promoting increased TAC4 transcription during PMA induction of a T cell line. Our studies reveal that Hemokinin-1 is regulated by a unique transcription regulation system that likely governs its differential expression pattern and suggests a role for Hemokinin-1 distinct from Substance P.