Naassila M, Hammoumi S, Legrand E, Durbin P, Daoust M
INSERM U 295, UFR de Médecine-Pharmacie de Rouen, Saint Etienne Rouvray, France.
Alcohol Clin Exp Res. 1998 Jun;22(4):802-9.
It has been suggested that the anticraving drug, acamprosate, acts via the glutamatergic system, but the exact mechanism of action is still unknown. The aim of this study was to characterize [3H]acamprosate binding and establish whether this showed any relation to sites on the NMDA receptor complex. We found saturable specific binding of [3H]acamprosate to rat brain membranes with a KD of 120 microM and a Bmax of 450 pmol/mg of protein. This acamprosate binding site was sensitive to inhibition by spermidine (IC50: 13.32 +/- 1.1 microM; Hill coefficient = 1.04), and arcaine and glutamate both potentiated the inhibitory effect of spermidine. Acamprosate binding to the acamprosate binding site was also sensitive to inhibition by divalent cations (Ca2+, Mg2+, and Sr2+). Conversely, acamprosate displaced [14C]spermidine binding from rat brain membranes with an IC50 of 645 microM and a Hill coefficient = 1.74. This inhibitory effect of acamprosate was not affected by arcaine, and was associated with a significant reduction in Bmax and binding affinity for spermidine, suggesting an allosteric interaction between acamprosate and a spermidine binding site. These data are consistent with an effect of acamprosate on the NMDA receptor protein complex, and acamprosate was also found to alter binding of [3H]dizocilpine to rat brain membranes. When no agonists were present in vitro (minimal NMDA receptor activation), acamprosate markedly potentiated [3H]dizocilpine binding at concentrations in the 5 to 200 microM range. However, under conditions of maximal receptor activation (100 microM glutamate, 30 microM glycine), acamprosate only inhibited [3H]dizocilpine binding (at concentrations concentrations >100 microM). When these binding studies were performed in the presence of 1 microM spermidine, the enhancing effects of acamprosate on [3H]dizocilpine binding were inhibited. The results show that acamprosate binds to a specific spermidine-sensitive site that modulates the NMDA receptor in a complex way. Together, with data from al Quatari et al. (see next paper), this work suggests that acamprosate acts as "partial co-agonist" at the NMDA receptor, so that low concentrations enhance activation when receptor activity is low, whereas higher concentrations are inhibitory to high levels of receptor activation. This may be relevant to the clinical effects of acamprosate in alcohol-dependent patients during abstinence.
有人提出，抗渴求药物阿坎酸通过谷氨酸能系统发挥作用，但其确切作用机制仍不清楚。本研究的目的是表征[3H]阿坎酸的结合情况，并确定其是否与NMDA受体复合物上的位点存在任何关系。我们发现[3H]阿坎酸与大鼠脑膜存在可饱和的特异性结合，解离常数（KD）为120微摩尔，最大结合容量（Bmax）为450皮摩尔/毫克蛋白质。该阿坎酸结合位点对亚精胺的抑制敏感（半数抑制浓度[IC50]：13.32±1.1微摩尔；希尔系数=1.04），精胍和谷氨酸均增强了亚精胺的抑制作用。阿坎酸与阿坎酸结合位点的结合也对二价阳离子（Ca2+、Mg2+和Sr2+）的抑制敏感。相反，阿坎酸从大鼠脑膜上取代[14C]亚精胺的结合，IC50为645微摩尔，希尔系数=1.74。阿坎酸的这种抑制作用不受精胍影响，且与亚精胺的Bmax和结合亲和力显著降低有关，表明阿坎酸与亚精胺结合位点之间存在变构相互作用。这些数据与阿坎酸对NMDA受体蛋白复合物的作用一致，并且还发现阿坎酸会改变[3H]地佐环平与大鼠脑膜的结合。当体外不存在激动剂（最小NMDA受体激活）时，阿坎酸在5至200微摩尔范围内的浓度下显著增强[3H]地佐环平的结合。然而，在最大受体激活条件下（100微摩尔谷氨酸、30微摩尔甘氨酸），阿坎酸仅抑制[3H]地佐环平的结合（浓度>100微摩尔）。当在1微摩尔亚精胺存在下进行这些结合研究时，阿坎酸对[3H]地佐环平结合的增强作用受到抑制。结果表明，阿坎酸与一个特定的、对亚精胺敏感的位点结合，该位点以复杂的方式调节NMDA受体。结合al Quatari等人的数据（见下一篇论文），这项工作表明阿坎酸在NMDA受体上充当“部分协同激动剂”，因此当受体活性较低时，低浓度会增强激活，而较高浓度则抑制高水平的受体激活。这可能与阿坎酸在戒酒期间对酒精依赖患者的临床效果相关。
