Collins D, Smith D A, Messer W S
Department of Medicinal & Biological Chemistry, College of Pharmacy, University of Toledo, OH 43606.
Neurochem Int. 1993 Mar;22(3):237-47. doi: 10.1016/0197-0186(93)90051-6.
The binding of the muscarinic antagonist 4-diphenylacetoxy-N-methylpiperidine methobromide (4-DAMP), which has been suggested as an M3-selective antagonist in peripheral tissues, was examined through quantitative autoradiographic techniques in brain. The ability of 4-DAMP to displace 3H-quinuclindinyl benzilate (QNB) binding to rat brain sections was compared with the known distribution of M1 and M2 muscarinic receptor subtypes as measured previously with pirenzepine and AF-DX 116 (Messer et al., 1989a). 4-DAMP displayed a high affinity for 3H-QNB binding sites in rat brain sections. Analysis of 4-DAMP binding to various brain regions revealed heterogeneous binding profiles, suggesting an interaction with multiple receptor sites. Quantification of the autoradiograms indicated that 4-DAMP bound with the highest affinity to muscarinic receptors in the midline thalamus (IC50 values < 30 nM), and had a slightly lower affinity for hippocampal receptors (IC50 values between 30 and 46 nM). 4-DAMP also displayed a lower affinity for cortical receptors with IC50 values between 30 and 50 nM. The binding profile of the putative M3 muscarinic antagonist did not exhibit a marked selectivity for any single region of brain. The data suggest that whereas 4-DAMP may be selective for M3 receptors in peripheral tissues, it has limited selectivity in the CNS. Minimum energy conformations for 4-DAMP were calculated using molecular mechanics calculations. 4-DAMP displayed two global minimum energy conformations, differing in the relative position of the piperidine ring with respect to the aromatic rings. The minimum energy conformations of 4-DAMP were compared with conformations generated for pirenzepine (Messer et al., 1989a). The lowest energy conformation of 4-DAMP was superimposable on the lowest energy conformation of pirenzepine (RMS = 0.297 A). It is suggested that the conformations available to 4-DAMP permit binding to several muscarinic receptors in the CNS.
毒蕈碱拮抗剂4-二苯乙酰氧基-N-甲基哌啶甲基溴化物（4-DAMP）在周围组织中被认为是一种M3选择性拮抗剂，本研究通过定量放射自显影技术检测了其在脑中的结合情况。将4-DAMP取代3H-喹宁环基苯甲酸酯（QNB）与大鼠脑切片结合的能力，与先前用哌仑西平和AF-DX 116测定的已知M1和M2毒蕈碱受体亚型分布进行了比较（Messer等人，1989a）。4-DAMP对大鼠脑切片中3H-QNB结合位点表现出高亲和力。对4-DAMP与不同脑区结合的分析揭示了异质结合谱，表明其与多个受体位点相互作用。放射自显影片的定量分析表明，4-DAMP与中线丘脑的毒蕈碱受体结合亲和力最高（IC50值<30 nM），对海马体受体的亲和力略低（IC50值在30至46 nM之间）。4-DAMP对皮质受体的亲和力也较低，IC50值在30至50 nM之间。推测的M3毒蕈碱拮抗剂的结合谱在脑的任何单个区域均未表现出明显的选择性。数据表明，虽然4-DAMP在外周组织中可能对M3受体具有选择性，但它在中枢神经系统中的选择性有限。使用分子力学计算方法计算了4-DAMP的最低能量构象。4-DAMP显示出两种全局最低能量构象，哌啶环相对于芳香环的相对位置不同。将4-DAMP的最低能量构象与为哌仑西平生成的构象进行了比较（Messer等人，1989a）。4-DAMP的最低能量构象与哌仑西平的最低能量构象可叠加（均方根偏差=0.297 Å）。提示4-DAMP可利用的构象使其能够与中枢神经系统中的几种毒蕈碱受体结合。
