Abbruscato T J, Thomas S A, Hruby V J, Davis T P
Department of Pharmacology, University of Arizona, College of Medicine, Tucson 85724, U.S.A.
J Neurochem. 1997 Sep;69(3):1236-45. doi: 10.1046/j.1471-4159.1997.69031236.x.
Biphalin [(Tyr-D-Ala-Gly-Phe-NH)2] is a bivalent, opioid peptide containing two pharmacophores linked by a hydrazine bridge. When administered intracerebroventricularly, it has been shown to be more potent than morphine and etorphine at eliciting antinociception. Biphalin has also been shown to cross both the blood-brain and blood-cerebrospinal fluid barriers. To understand the basis of biphalin's potency, regional brain and spinal cord distribution studies with [125I-Tyr1]biphalin were performed 5, 20, and 40 min after intravenous bolus injections. A statistically greater amount of [125I-Tyr1]biphalin was detected in the nucleus accumbens compared with other brain regions (p < 0.05). This correlates with the high density of delta- and mu-opioid receptor mRNA and binding sites shown to be expressed in the nucleus accumbens. Also, a statistically greater amount of [125I-Tyr1] biphalin was detected in two other circumventricular organs, the choroid plexus and pituitary, when compared with other brain regions. These studies provide evidence that biphalin can reach not only brain sites, but also spinal sites to elicit antinociception. The overall CNS distribution of [125I-Tyr1]biphalin was decreased with naloxone, D-Phe-Cys-Tyr-D-Trp-Arg-Thr-Pen-Thr-NH2, or naltrindole pretreatment, showing that biphalin detected in the brain and spinal cord is binding to delta- and mu-opioid receptors. Additional in situ brain perfusion experiments identified a saturable component contributing to CNS entry of [125I-Tyr1]biphalin, which could be described by Michaelis-Menten kinetics with a Km of 2.6 +/- 4.8 microM, Vmax of 14.6 +/- 2.89 pmol(-1) x min(-1) x g(-1), and Kd of 0.568 +/- 0.157 microl x min(-1) x g(-1). Brain entry of [125I-Tyr1]biphalin was sensitive to 2-aminobicyclo[2.2.1]heptane-2-carboxylic acid and L-phenylalanine, suggesting use of the large neutral amino acid carrier. This work provides evidence that biphalin is a promising, potent analgesic that has a unique mechanism for reaching both spinal and supraspinal opioid receptor sites.
双啡肽[（酪氨酰-D-丙氨酰-甘氨酰-苯丙氨酰胺）2]是一种二价阿片肽，含有两个通过肼桥连接的药效基团。当脑室内给药时，已证明它在引发抗伤害感受方面比吗啡和埃托啡更有效。双啡肽也已被证明能穿过血脑屏障和血脑脊液屏障。为了了解双啡肽效力的基础，在静脉推注后5、20和40分钟，用[125I-酪氨酰1]双啡肽进行了脑区和脊髓分布研究。与其他脑区相比，伏隔核中检测到的[125I-酪氨酰1]双啡肽量在统计学上显著更高（p < 0.05）。这与伏隔核中显示表达的δ和μ阿片受体mRNA及结合位点的高密度相关。此外，与其他脑区相比，在另外两个室周器官脉络丛和垂体中也检测到统计学上显著更多的[125I-酪氨酰1]双啡肽。这些研究提供了证据，表明双啡肽不仅能到达脑区，还能到达脊髓部位以引发抗伤害感受。用纳洛酮、D-苯丙氨酰-半胱氨酰-酪氨酰-D-色氨酰-精氨酰-苏氨酰-青霉胺-苏氨酰胺或纳曲吲哚预处理后，[125I-酪氨酰1]双啡肽在中枢神经系统的总体分布减少，表明在脑和脊髓中检测到的双啡肽与δ和μ阿片受体结合。额外的原位脑灌注实验确定了一个促成[125I-酪氨酰1]双啡肽进入中枢神经系统的可饱和成分，可用米氏动力学描述，其Km为2.6±4.8微摩尔，Vmax为14.6±2.89皮摩尔（-1）×分钟（-1）×克（-1），Kd为0.568±0.157微升×分钟（-1）×克（-1）。[125I-酪氨酰1]双啡肽进入脑对2-氨基双环[2.2.1]庚烷-2-羧酸和L-苯丙氨酸敏感，提示使用了大中性氨基酸载体。这项工作提供了证据，表明双啡肽是一种有前景的强效镇痛药，具有到达脊髓和脊髓上阿片受体部位的独特机制。
