Carpenedo R, Chiarugi A, Russi P, Lombardi G, Carlà V, Pellicciari R, Mattoli L, Moroni F
Department of Preclinical and Clinical Pharmacology, University of Florence, Italy.
Neuroscience. 1994 Jul;61(2):237-43. doi: 10.1016/0306-4522(94)90227-5.
Kynurenate is an endogenous antagonist of the ionotropic glutamate receptors. It is synthesized from kynurenine, a tryptophan metabolite, and a significant increase in its brain concentration could be useful in pathological situations. We attempted to increase its neosynthesis by modifying kynurenine catabolism. Several kynurenine analogues were synthesized and tested as inhibitors of kynurenine hydroxylase (E.C.1.14.13.9) and of kynureninase (E.C.3.7.1.3), the two enzymes which catalyse the conversion of kynurenine to excitotoxin quinolinate. Among these analogues we observed that nicotinylalanine, a compound whose pharmacological properties have previously been reported, had an IC50 of 900 +/- 180 microM as inhibitor of kynurenine hydroxylase and of 800 +/- 120 microM as inhibitor of kynureninase. In the search for more potent molecules we noticed that meta-nitrobenzoylalanine had an IC50 of 0.9 +/- 0.1 microM as inhibitor of kynurenine hydroxylase and of 100 +/- 12 microM as inhibitor of kynureninase. When administered to rats meta-nitrobenzoylalanine (400 mg/kg) significantly increased the concentration of kynurenine (up to 10 times) and kynurenate (up to five times) in the brain. Similar results were obtained in the blood and in the liver. Furthermore meta-nitrobenzoylalanine increased in a dose dependent, long lasting (up to 13 times and up to 4 h) manner the concentration of kynurenate in the hippocampal extracellular fluid, as evaluated with a microdialysis technique. This increase was associated with a decrease in the locomotor activity and with protection from maximal electroshock-induced seizures in rats or from audiogenic seizures in DBA/2 mice. The conclusions drawn from the present study are: (i) meta-nitrobenzoylalanine is a potent inhibitor of kynurenine hydroxylase also affecting kynureninase; (ii) the inhibition of these enzymes causes a significant increase in the brain extracellular concentration of kynurenate; (iii) this increase is associated with sedative and anticonvulsant actions, suggesting a functional antagonism of the excitatory amino acid receptors.
犬尿喹啉酸是离子型谷氨酸受体的内源性拮抗剂。它由色氨酸代谢产物犬尿氨酸合成，其脑内浓度的显著升高在病理情况下可能有用。我们试图通过改变犬尿氨酸分解代谢来增加其新合成。合成了几种犬尿氨酸类似物，并测试它们作为犬尿氨酸羟化酶（E.C.1.14.13.9）和犬尿氨酸酶（E.C.3.7.1.3）的抑制剂，这两种酶催化犬尿氨酸转化为兴奋性毒素喹啉酸。在这些类似物中，我们观察到烟酰丙氨酸（一种药理特性先前已有报道的化合物）作为犬尿氨酸羟化酶抑制剂的IC50为900±180微摩尔，作为犬尿氨酸酶抑制剂的IC50为800±120微摩尔。在寻找更有效的分子时，我们注意到间硝基苯甲酰丙氨酸作为犬尿氨酸羟化酶抑制剂的IC50为0.9±0.1微摩尔，作为犬尿氨酸酶抑制剂的IC50为100±12微摩尔。给大鼠注射间硝基苯甲酰丙氨酸（400毫克/千克）后，脑内犬尿氨酸浓度（高达10倍）和犬尿喹啉酸浓度（高达5倍）显著升高。在血液和肝脏中也得到了类似结果。此外，用微透析技术评估，间硝基苯甲酰丙氨酸以剂量依赖性、持久（高达13倍，长达4小时）的方式增加海马细胞外液中犬尿喹啉酸的浓度。这种增加与运动活动减少以及对大鼠最大电休克诱导的惊厥或DBA/2小鼠听源性惊厥的保护作用相关。本研究得出的结论是：（i）间硝基苯甲酰丙氨酸是犬尿氨酸羟化酶的有效抑制剂，也影响犬尿氨酸酶；（ii）这些酶的抑制导致脑内细胞外犬尿喹啉酸浓度显著升高；（iii）这种升高与镇静和抗惊厥作用相关，提示对兴奋性氨基酸受体有功能性拮抗作用。
