K-685, a TRPV1 antagonist, blocks PKC-sensitized TRPV1 activation and improves the inflammatory pain in a rat complete Freund's adjuvant model.

Transient receptor potential vanilloid 1 (TRPV1) is a Ca(2+)-permeable non-selective cation channel that transmits pain signals. TRPV1 is activated by multiple stimuli such as capsaicin, acid, and heat. During inflammation, TRPV1 is reported to be sensitized by protein kinase C (PKC) in dorsal root ganglia (DRG) neurons, which leads to reduction in the threshold of the temperature for TRPV1 activation to body temperature. This sensitization is considered to contribute to chronic inflammatory pain. In a previous study, we discovered orally active 5,5-diarylpentadienamide TRPV1 antagonists. To examine the effects of our TRPV1 antagonists on PKC-sensitized TRPV1, we developed an in vitro assay system to monitor the TRPV1 sensitization by PKC. In this assay system, our TRPV1 antagonists, such as (2E,4Z)-N-[(3R)-3-hydroxy-2-oxo-1,2,3,4-tetrahydro-5-quinolyl]-5-(4-isopropoxyphenyl)-5-(4-trifluoromethylphenyl)-2,4-pentadienamide (K-685), inhibited the activation of TRPV1 sensitized by PKC. The potentiation of heat-induced inward currents by PKC was seen in rat DRG neurons, and K-685 attenuated these currents. Furthermore, K-685 reversed the thermal hyperalgesia and mechanical allodynia in a rat complete Freund's adjuvant-induced inflammatory pain model. These results therefore suggest that K-685 has a strong potential as a new analgesic drug for the treatment of inflammatory pain.

Phenotypic characterization of a new Grin1 mutant mouse generated by ENU mutagenesis.

In the RIKEN large-scale N-ethyl-N-nitrosourea (ENU) mutagenesis project we screened mice with a dominant mutation that exhibited abnormal behavior in the open-field test, passive avoidance test and home-cage activity test. We tested 2045 progeny of C57BL/6J males treated with ENU and untreated DBA/2J females in the open-field test and isolated behavioral mutant M100174, which exhibited a significant increase in spontaneous locomotor activity. We identified a missense mutation in the Grin1 gene, which encodes NMDA receptor subunit 1, and designated the mutant gene Grin1(Rgsc174). This mutation results in an arginine to cysteine substitution in the C0 domain of the protein. Detailed analyses revealed that Grin1(Rgsc174) heterozygote exhibited increased novelty-seeking behavior and slight social isolation in comparison with the wild type. In contrast to other Grin1 mutant mice, this mutant exhibited no evidence of heightened anxiety. These results indicate that this is a unique behavioral Grin1 gene mutant mouse that differs from the known Grin1 mutant mice. The results of immunohistochemical and biochemical analyses suggested that impaired interaction between the glutamatergic pathway and dopaminergic pathway may underlie the behavioral phenotypes of the Grin1(Rgsc174) mutant.

Diamine derivatives containing imidazolidinylidene propanedinitrile as a new class of histamine H3 receptor antagonists. Part I.

Novel diamine derivatives containing imidazolidinylidene propanedinitrile were synthesized and evaluated for histamine H(3) receptor-binding affinities. High-affinity ligands 3d, 3k, and 3n showed potent H(3) receptor antagonism and excellent selectivity over human H(1), H(2) and H(4) receptors.

Diamine derivatives containing imidazolidinylidene propanedinitrile as a new class of histamine H(3) receptor antagonists: conformationally restricted derivatives.

Novel conformationally restricted diamine derivatives containing imidazolidinylidene propanedinitrile were synthesized and evaluated for human and rat histamine H(3) receptor (H(3)R) binding affinities. Among them, compounds 2b, 2c, 2j, 2k and 2m were found to be potent ligands for both H(3)Rs with K(i) values in the sub-nanomolar range, and showed potent H(3) receptor antagonism.