Purdy R H, Morrow A L, Blinn J R, Paul S M
Department of Organic Chemistry, Southwest Foundation for Biomedical Research, San Antonio, Texas 78228.
J Med Chem. 1990 Jun;33(6):1572-81. doi: 10.1021/jm00168a008.
Certain 3 alpha-hydroxy steroids have recently been shown to bind to the gamma-aminobutyric acid (GABA) receptor gated chloride ion channel with high affinity and to potentiate the inhibitory effects of GABA when measured both in vitro and in vivo. In the present study, a series of natural and synthetic 3 alpha-hydroxy steroids were tested for their ability to potentiate GABA-receptor-mediated chloride ion (Cl-) uptake into cerebral cortical synaptoneurosomes. The naturally occurring metabolites 3 alpha-hydroxy-5 alpha-pregnan-20-one (allopregnanolone) and 3 alpha,21-dihydroxy-5 alpha-pregnan-20-one (allotetrahydroDOC) were found to be the most active in augmenting GABAA-receptor-mediated Cl- uptake. Pharmacological activity was reduced in the corresponding isomers with the 5 beta-pregnane configuration and by some, but not all, modifications of the side chain. The ability of these steroids to potentiate muscimol-stimulated Cl- uptake is lost by acetylation at C3, introduction of unsaturation at C9(11), inversion to the 3 beta-hydroxy isomer, or inversion of configuration at C17. A facile procedure is reported for the synthesis of unlabeled and tritium-labeled allopregnanolone and allotetrahydroDOC. The 9 alpha,11 alpha,12 alpha-3H-labeled derivatives of allopregnanolone and allotetrahydroDOC were used to identify the distribution and metabolic products of these active steroids. Uptake of the more hydrophobic [3H]allopregnanolone into brain was significantly greater than that of [3H]allotetrahydroDOC. The principal 3H-labeled metabolites recovered from brain were the 3-ketone derivatives of allopregnanolone and allotetrahydroDOC, which are both inactive on GABA-receptor-mediated Cl- flux. Molecular modeling of the active steroids based on quantitative structure-activity relationships provides evidence to support the stereospecificity of the binding interactions and suggests that there may be more than one type of steroid binding site associated with the GABAA-receptor-mediated chloride ionophore.
最近研究表明，某些3α-羟基甾体能够与γ-氨基丁酸（GABA）受体门控氯离子通道高亲和力结合，并在体外和体内实验中均增强GABA的抑制作用。在本研究中，对一系列天然和合成的3α-羟基甾体进行了测试，以考察它们增强GABA受体介导的氯离子（Cl-）摄入大脑皮质突触神经小体的能力。发现天然存在的代谢产物3α-羟基-5α-孕烷-20-酮（别孕烯醇酮）和3α,21-二羟基-5α-孕烷-20-酮（别四氢脱氧皮质酮）在增强GABAA受体介导的Cl-摄入方面活性最高。相应的具有5β-孕烷构型的异构体以及侧链的某些（但不是全部）修饰会降低药理活性。这些甾体增强蝇蕈醇刺激的Cl-摄入的能力会因C3位乙酰化、C9(11)位引入不饱和键、转化为3β-羟基异构体或C17位构型翻转而丧失。本文报道了一种简便的方法来合成未标记和氚标记的别孕烯醇酮和别四氢脱氧皮质酮。别孕烯醇酮和别四氢脱氧皮质酮的9α,11α,12α-3H标记衍生物用于鉴定这些活性甾体的分布和代谢产物。疏水性更强的[3H]别孕烯醇酮进入大脑的量显著大于[3H]别四氢脱氧皮质酮。从大脑中回收的主要3H标记代谢产物是别孕烯醇酮和别四氢脱氧皮质酮的3-酮衍生物，它们对GABA受体介导的Cl-通量均无活性。基于定量构效关系对活性甾体进行分子模拟，为支持结合相互作用的立体特异性提供了证据，并表明可能存在不止一种与GABAA受体介导的氯离子载体相关的甾体结合位点。
