Gbahou Florence, Vincent Ludwig, Humbert-Claude Marie, Tardivel-Lacombe Joel, Chabret Claude, Arrang Jean-Michel
INSERM, Unité de Neurobiologie et Pharmacologie Moléculaire (U573), Centre Paul Broca, 2 ter rue d'Alésia, 75014 Paris, France.
Br J Pharmacol. 2006 Apr;147(7):744-54. doi: 10.1038/sj.bjp.0706666.
Various histamine derivatives were investigated at the human H3 receptor (H3R) and H4 receptor (H4R) stably expressed in human embryonic kidney (HEK)-293 cells using [125I]iodoproxyfan and [3H]histamine binding, respectively. In Tris buffer, [3H]histamine binding to membranes of HEK(hH4R) cells was monophasic (K(D) of 3.8+/-0.8 nM). In phosphate buffer, the Hill coefficient was decreased (n(H) = 0.5+/-0.1) and a large fraction of the binding was converted into a low-affinity component (K(D) = 67+/-27 nM). The inhibition of [3H]histamine binding by two agonists, a protean agonist and five antagonists/inverse agonists confirms that the potency of many H3R ligands is retained or only slightly reduced at the H4R. Histamine derivatives substituted with methyl groups in alpha, beta or N(alpha) position of the side chain retained a nanomolar potency at the H3R, but their affinity was dramatically decreased at the H4R. With relative potencies to histamine of 282 and 0.13% at the H3R and H4R, respectively, (+/-)-alpha,beta-dimethylhistamine is a potent and selective H3R agonist. Chiral alpha-branched analogues exhibited a marked stereoselectivity at the H3R and H4R, the enantiomers with a configuration equivalent to L-histidine being preferred at both receptors. The methylsubstitution of the imidazole ring was also studied. The relative potency to histamine of 4-methylhistamine (4-MeHA) at the H4R (67%) was similar to that reported at H2 receptors but, owing to its high affinity at the H4R (Ki = 7.0+/-1.2 nM) and very low potency at H1- and H3-receptors, it can be considered as a potent and selective H4R agonist. On inhibition of forskolin-induced cAMP formation, all the compounds tested, including 4-MeHA, behaved as full agonists at both receptors. However, the maximal inhibition achieved at the H4R (approximately -30%) was much lower than at the H3R (approximately -80%). Thioperamide behaved as an inverse agonist at both receptors and increased cAMP formation with the same maximal effect (approximately +25%). In conclusion, although the pharmacological profiles of the human H3R and H4R overlap, the structure-activity relationships of histamine derivatives at both receptors strongly differ and lead to the identification of selective compounds.
分别使用[125I]碘普罗庚和[3H]组胺结合法，在稳定表达于人类胚胎肾（HEK）-293细胞中的人类H3受体（H3R）和H4受体（H4R）上研究了各种组胺衍生物。在Tris缓冲液中，[3H]组胺与HEK（hH4R）细胞膜的结合是单相的（解离常数K(D)为3.8±0.8 nM）。在磷酸盐缓冲液中，希尔系数降低（n(H)=0.5±0.1），并且大部分结合转化为低亲和力成分（K(D)=67±27 nM）。两种激动剂、一种可变激动剂以及五种拮抗剂/反向激动剂对[3H]组胺结合的抑制作用证实，许多H3R配体在H4R上仍保留其效力或仅略有降低。在侧链的α、β或N(α)位被甲基取代的组胺衍生物在H3R上保留了纳摩尔级别的效力，但其在H4R上的亲和力显著降低。(±)-α,β-二甲基组胺在H3R和H4R上相对于组胺的相对效力分别为282和0.13%，是一种强效且选择性的H3R激动剂。手性α-支链类似物在H3R和H4R上表现出明显的立体选择性，在两个受体上，构型与L-组氨酸相当的对映体更受青睐。还研究了咪唑环的甲基取代情况。4-甲基组胺（4-MeHA）在H4R上相对于组胺的相对效力（67%）与在H2受体上报道的相似，但由于其在H4R上具有高亲和力（Ki=7.0±1.2 nM）且在H1和H3受体上效力极低，它可被视为一种强效且选择性的H4R激动剂。在抑制福司可林诱导的cAMP形成方面，所有测试的化合物，包括4-MeHA，在两个受体上均表现为完全激动剂。然而，在H4R上达到的最大抑制率（约-30%）远低于在H3R上的（约-80%）。硫代哌酰胺在两个受体上均表现为反向激动剂，并以相同的最大效应（约+25%）增加cAMP的形成。总之，尽管人类H3R和H4R的药理学特征有重叠，但组胺衍生物在两个受体上的构效关系差异很大，并导致了选择性化合物的鉴定。
