Zádor Ferenc, Kocsis Dóra, Borsodi Anna, Benyhe Sándor
Institute of Biochemistry, Biological Research Centre, Hungarian Academy of Sciences, Temesvári krt. 62, H-6726 Szeged, Hungary.
Institute of Biochemistry, Biological Research Centre, Hungarian Academy of Sciences, Temesvári krt. 62, H-6726 Szeged, Hungary.
Neurochem Int. 2014 Feb;67:14-22. doi: 10.1016/j.neuint.2013.12.005. Epub 2014 Feb 4.
There is a growing number of evidence showing, that the cannabinoid receptor 1 (CB1) antagonist rimonabant has many non-cannabimimetic actions, such as affecting the opioid system. The direct effect of rimonabant on opioid receptors has been studied so far mainly on μ-opioid receptors. However recently the δ-opioid receptor (DOR) receives much more attention as before, due to its potential therapeutic applications, such as nociception or treatment for psychiatric disorders.
To investigate the direct effect of rimonabant on DOR specific ligand binding and on the DOR mediated G-protein activation.
Micromolar concentrations of rimonabant directly inhibited the DOR specific agonist binding in radioligand competition binding experiments using Chinese hamster ovary cells stably transfected with mouse DOR (CHO-mDOR). However the inhibition occurred also in the subnanomolar range during DOR specific antagonist binding in similar experimental conditions. In functional [(35)S]GTPγS binding assays rimonabant significantly decreased the basal receptor activity in CHO-mDOR but also in parental CHO cell membranes. During DOR agonist stimulation, micromolar concentration of rimonabant attenuated the DOR G-protein activation and the potency of the activator ligand in [(35)S]GTPγS binding assays performed in CHO-mDOR, in wild type and also in CB1/CB2 double knock-out mouse forebrain membranes. Yet again this inhibitory action was DOR specific, since it did not occur during other specific GPCR agonist mediated G-protein activation.
Rimonabant directly inhibited DOR function in the micromolar concentrations. The inhibitory actions indicate an antagonistic behavior towards DOR which was established by the followings: (i) rimonabant inhibited DOR antagonist binding more effectively than agonist binding, (ii) the inverse agonistic, agonistic effect of the compound can be excluded, and (iii) additionally according to previous findings the allosteric mechanism can also be foreclosed.
越来越多的证据表明，大麻素受体1（CB1）拮抗剂利莫那班具有许多非大麻素模拟作用，例如影响阿片系统。迄今为止，利莫那班对阿片受体的直接作用主要是针对μ-阿片受体进行研究的。然而，由于δ-阿片受体（DOR）在疼痛感受或精神疾病治疗等潜在治疗应用方面，近来比以往受到更多关注。
研究利莫那班对DOR特异性配体结合以及对DOR介导的G蛋白激活的直接作用。
在使用稳定转染小鼠DOR的中国仓鼠卵巢细胞（CHO-mDOR）进行的放射性配体竞争结合实验中，微摩尔浓度的利莫那班直接抑制了DOR特异性激动剂结合。然而，在类似实验条件下进行DOR特异性拮抗剂结合时，抑制作用也出现在亚纳摩尔范围内。在功能性[(35)S]GTPγS结合试验中，利莫那班显著降低了CHO-mDOR以及亲本CHO细胞膜中的基础受体活性。在DOR激动剂刺激期间，微摩尔浓度的利莫那班在CHO-mDOR、野生型以及CB1/CB2双敲除小鼠前脑细胞膜中进行的[(35)S]GTPγS结合试验中，减弱了DOR G蛋白激活以及激活配体的效力。而且这种抑制作用是DOR特异性的，因为在其他特异性GPCR激动剂介导的G蛋白激活过程中并未出现。
利莫那班在微摩尔浓度下直接抑制DOR功能。这些抑制作用表明其对DOR具有拮抗行为，这是通过以下几点确定的：（i）利莫那班抑制DOR拮抗剂结合比激动剂结合更有效；（ii）可以排除该化合物的反向激动、激动作用；（iii）此外，根据先前的研究结果，变构机制也可被排除。
