Department of Dermatology and Allergy, Hannover Medical School, Germany.
Br J Pharmacol. 2013 Sep;170(1):136-43. doi: 10.1111/bph.12237.
Since the identification of the histamine H₄ receptor, several ligands activating this receptor have been described and more compounds are in development. These ligands are well characterized in pharmacological assays, including radioligand competition binding studies, GTPγS and GTPase assays. In most cases, these experiments are performed in transfected cell lines, expressing unnaturally high levels of target receptors and G-protein signalling components. In this study we investigated the specific properties of H₄ receptor ligands in native cells.
Histamine and five different H₄ receptor agonists - 4-methylhistamine, UR-PI376, clobenpropit, VUF8430 and ST-1006 - were characterized in freshly isolated human monocytes. The ligands (10 nM-10 μM) were tested as inhibitors of IL-12p70 secretion from human monocytes and the effects of the H₂ receptor antagonist ranitidine and the H₄ receptor antagonist JNJ7777120 on their action was investigated.
Histamine and all the tested agonists reduced IL-12p70 secretion into monocyte supernatants by 40-70%. The potencies varied with pEC50 values ranging from 5.7 to 6.9, depending on the agonist used. All potencies were lower than those determined in the original investigations of the compounds. Pretreatment of monocytes with H₂ or H₄ receptor antagonists showed that some H₄ receptor ligands also had low activity at the H₂ receptor.
Our study demonstrates discrepancies between the potencies obtained from assays in transfected cell lines and assays in native human cells, indicating the importance of evaluating H₄ receptor ligands in native cells.
自组胺 H₄ 受体被发现以来，已经描述了几种激活该受体的配体，并且还有更多的化合物正在开发中。这些配体在药理学测定中得到了很好的表征，包括放射性配体竞争结合研究、GTPγS 和 GTPase 测定。在大多数情况下，这些实验是在转染的细胞系中进行的，这些细胞系表达异常高水平的靶受体和 G 蛋白信号成分。在这项研究中，我们研究了天然细胞中 H₄ 受体配体的特定特性。
组胺和五种不同的 H₄ 受体激动剂——4-甲基组胺、UR-PI376、氯苯丙胺、VUF8430 和 ST-1006——在新鲜分离的人单核细胞中进行了表征。这些配体（10 nM-10 μM）被测试为抑制人单核细胞中白细胞介素 12p70 的分泌，并且研究了 H₂ 受体拮抗剂雷尼替丁和 H₄ 受体拮抗剂 JNJ7777120 对其作用的影响。
组胺和所有测试的激动剂使单核细胞上清液中白细胞介素 12p70 的分泌减少了 40-70%。根据所使用的激动剂，效力随 pEC50 值从 5.7 到 6.9 变化。所有的效力都低于这些化合物最初研究中确定的效力。用 H₂ 或 H₄ 受体拮抗剂预处理单核细胞表明，一些 H₄ 受体配体在 H₂ 受体上也具有低活性。
我们的研究表明，在转染细胞系中进行的测定与在天然人细胞中进行的测定之间存在效力差异，这表明在天然细胞中评估 H₄ 受体配体的重要性。
