Abstract

The histamine H₄ receptor (H₄R) is the latest identified histamine receptor to emerge as a potential drug target for inflammatory diseases. Animal models are employed to validate this potential drug target. Concomitantly, various H₄R orthologs have been cloned, including the human, mouse, rat, guinea pig, monkey, pig, and dog H₄Rs. In this article, we expressed all these H₄R orthologs in human embryonic kidney 293T cells and compared their interactions with currently used standard H₄R ligands, including the H₄R agonists histamine, 4-methylhistamine, guanidinylethyl isothiourea (VUF 8430), the H₄R antagonists 1-[(5-chloro-1H-indol-2-yl)carbonyl]-4-methylpiperazine (JNJ 7777120) and [(5-chloro-1H-benzimidazol-2-yl)carbonyl]-4-methylpiperazine (VUF 6002), and the inverse H₄R agonist thioperamide. Most of the evaluated ligands display significantly different affinities at the different H₄R orthologs. These “natural mutants” of H₄R were used to study ligand-receptor interactions by using chimeric human-pig-human and pig-human-pig H₄R proteins and site-directed mutagenesis. Our results are a useful reference for ligand selection for studies in animal models of diseases and offer new insights in the understanding of H₄R-ligand receptor interactions.