Enantioselectivity of α-Benzyl-α-methyl-γ-butyrolactone-Mediated Modulation of Anticonvulsant Activity and GABA<sub>A</sub> Receptor Function
作者:Eric B. Gonzales、Cathy L. Bell-Horner、Maria Antonette M. de la Cruz、James A. Ferrendelli、Douglas F. Covey、Glenn H. Dillon
DOI:10.1124/jpet.103.063008
日期:2004.5
Alkyl-substituted butyrolactones have both inhibitory and stimulatory effects on GABAA receptors. Lactones with small alkyl substitutions at the α-position positively modulate the channel, whereas β-substituted lactones tend to inhibit the GABAA receptor. These compounds mediate inhibition through the picrotoxin site of the receptor. A distinct binding site that mediates the stimulatory actions of lactones is presumed to exist, although no definitive evidence to support this claim exists. In the present study, we used in vivo and in vitro assays to evaluate the effects of the enantiomers of a novel lactone, α-benzyl-α-methyl-γ-butyrolactone (α-BnMeGBL), on the GABAA receptor. R -(-)-α-BnMeGBL was 2-fold more potent than the S -(+)-α-BnMeGBL in blocking pentylenetetrazol-induced seizures in CF-1 mice. The (+)-enantiomer inhibited binding of t -butylbicyclophosporothionate with a higher affinity than the (-)-enantiomer (IC50 of 0.68 and 1.1 mM, respectively). Whole cell patch-clamp recordings from recombinant α1β2γ2 receptors stably expressed in HEK293 cells demonstrated that both compounds stimulated GABA-activated current. The maximal stimulation was approximately 2-fold greater with (+)-α-BnMeGBL than that seen with (-)-α-BnMeGBL. Both enantiomers of α-BnMeGBL directly gated the GABAA receptor at mM concentrations, in a nonstereoselective manner. Our data demonstrate the stimulatory actions of α-BnMeGBL on GABAA receptor function display enantioselectivity and provide strong evidence for the existence of a true “lactone site” on the receptor.
烷基取代的丁内酯对GABAA受体具有抑制性和刺激性两种作用。在α位点上小烷基取代的内酯具有正调节通道的作用,而β取代的内酯则倾向于抑制GABAA受体。这些化合物通过受体的皮克罗毒素位点介导抑制作用。虽然没有确凿证据支持这一说法,但推测存在一个独特的结合位点介导内酯的刺激作用。在本研究中,我们使用体内和体外实验评估了一种新型内酯,α-苄基-α-甲基-γ-丁内酯(α-BnMeGBL)各对映体对GABAA受体的影响。R -(-)-α-BnMeGBL在阻断CF-1小鼠由戊烯四氮唑诱导的癫痫发作方面的效果是S -(+)-α-BnMeGBL的2倍。(+)-对映体对t-丁基双环磷酸酯的结合亲和力高于(-)-对映体(IC50分别为0.68和1.1 mM)。来自稳定表达α1β2γ2受体的HEK293细胞的全细胞膜片钳记录显示这两种化合物均刺激GABA激活的电流。(+)-α-BnMeGBL的最大刺激作用约为(-)-α-BnMeGBL的2倍。两种α-BnMeGBL对映体在毫摩尔浓度下直接调节GABAA受体,且以非立体选择性方式作用。我们的数据表明,α-BnMeGBL对GABAA受体功能的刺激作用表现出对映体选择性,并提供强有力的证据证明受体上存在真正的“内酯位点”。