Abuhamdah S, Fürstner A, Lees G, Chazot P L
School of Biological and Biomedical Sciences, Science Park, South Road, Durham University, Durham DH1 3LE, UK.
Biochem Pharmacol. 2005 Nov 1;70(9):1382-8. doi: 10.1016/j.bcp.2005.07.026.
Caloporoside is a natural active fungal metabolite, which was isolated from Caloporous dichrous and was described to exhibit antibacterial, antifungal and phospholipase C inhibitory activity. We have previously reported evidence that related beta-linked compounds, lactose and octyl-beta-d-mannoside, bind and functionally modulate rodent GABA(A) receptors, respectively. We have characterized the binding pharmacology of synthetic caloporoside and two further congeners, 2-hydroxy-6-([(16R)-(beta-d-mannopyranosyloxy)heptadecyl]) benzoic acid and octyl-beta-d-glucoside on GABA(A) receptors using a [35S]-t-butylbicyclophosphoorothionate (TBPS) radioligand binding assay. Caloporoside and 2-hydroxy-6-([(16R)-(beta-d-mannopyranosyloxy)heptadecyl]) benzoic acid produced concentration-dependent complete inhibition of specific [35S] TBPS binding with overall apparent IC50 values of 14.7+/-0.1 and 14.2+/-0.1 microM, respectively. In contrast, octyl-beta-d-glucoside elicited a concentration-dependent stimulation of specific [35S] TBPS binding (E(max)=144+/-4%; EC50=39.2+/-22.7 nM). The level of stimulation was similar to that elicited by diazepam (E(max)=147+/-6%; EC50=0.8+/-0.1 nM), and was occluded by GABA (0.3 microM). However, the three test compounds failed to elicit any significant effect (positive or negative) upon [3H] flunitrazepam or [3H] muscimol binding, indicating that they did not bind directly, or allosterically couple, to the benzodiazepine or agonist binding site of the GABA(A) receptor, respectively. The constituent monosaccharide, glucose, and both the closely related congeners octyl-beta-d-glucoside or hexyl-beta-d-glucoside have no significant effect upon [35S] TBPS binding. These data, together, provide strong evidence that a beta-glycosidic linkage and chain length are crucial for the positive modulation of [35S] TBPS binding to the GABA(A) receptor by this novel chemical class.
卡波苷是一种天然活性真菌代谢产物，从双色多孔菌中分离得到，据报道具有抗菌、抗真菌和磷脂酶C抑制活性。我们之前曾报道过相关的β-连接化合物乳糖和辛基-β-D-甘露糖苷分别结合并功能性调节啮齿动物γ-氨基丁酸A（GABA(A)）受体的证据。我们使用[35S]-叔丁基双环磷硫代酸盐（TBPS）放射性配体结合试验，对合成的卡波苷以及另外两种同系物2-羟基-6-([(16R)-(β-D-甘露吡喃糖氧基)十七烷基])苯甲酸和辛基-β-D-葡萄糖苷在GABA(A)受体上的结合药理学进行了表征。卡波苷和2-羟基-6-([(16R)-(β-D-甘露吡喃糖氧基)十七烷基])苯甲酸对特异性[35S]TBPS结合产生浓度依赖性的完全抑制，总体表观IC50值分别为14.7±0.1和14.2±0.1微摩尔。相比之下，辛基-β-D-葡萄糖苷引起特异性[35S]TBPS结合的浓度依赖性刺激（E(max)=144±4%；EC50=39.2±22.7纳摩尔）。刺激水平与地西泮引起的相似（E(max)=147±6%；EC50=0.8±0.1纳摩尔），并被GABA（0.3微摩尔）阻断。然而，这三种受试化合物对[3H]氟硝西泮或[3H]蝇蕈醇结合均未产生任何显著影响（阳性或阴性），表明它们分别未直接结合或变构偶联至GABA(A)受体的苯二氮䓬或激动剂结合位点。其组成单糖葡萄糖以及密切相关的同系物辛基-β-D-葡萄糖苷或己基-β-D-葡萄糖苷对[35S]TBPS结合均无显著影响。这些数据共同提供了有力证据，表明β-糖苷键和链长对于这类新型化学物质对[35S]TBPS结合至GABA(A)受体的正向调节至关重要。
