Karl Landsteiner Research Institute for Neurochemistry, Neuropharmacology, Neurorehabilitation and Pain Treatment Mauer, Mauer-Amstetten, Austria.
Faculty for Biology, University of Würzburg, Germany.
Cell Physiol Biochem. 2023 Aug 18;57(4):279-297. doi: 10.33594/000000643.
BACKGROUND/AIMS: Kynurenic acid (KYNA), a tryptophan metabolite along the kynurenine pathway, is an endogenous antagonist of glutamate ionotropic excitatory amino acid (EAA) receptors and the α7 nicotinic acetylcholine receptor (nAChR). The involvement of KYNA in various pathological conditions and during the aging process is significant. KYNA synthesis from L-kynurenine (L-KYN), through the action of several kynurenine aminotransferases (KATs), is present in the central nervous system (CNS) and periphery of mammals. We were interested in investigating the ability of the brain and peripheral organs of Helix pomatia snails to synthesize KYNA, in an in vitro study. In comparative studies between rat and snail, we looked for the synthesis of KYNA in the liver. We then looked for an effect of age on KYNA synthesis.
Ten shell parameters of the Helix pomatia snail were used to establish an Age Rating Scale (ARS), i.e. body weight, shell weight, shell length, width and height, shell opening length and width, lip width, number of shell turns and external shell growth rings. An age of the snails was determined according to the ARS and the snails were divided into three groups, i.e. young, middle and old age. Homogenates of dissected regions, i.e. cerebral ganglia (CG), subpharyngeal ganglia (SG) consisting of pedal, visceral and pleural ganglia, heart and liver, were examined. KYNA was measured by high performance liquid chromatography (HPLC) and KAT activities were measured by an enzymatic method.
With respect to ARS, an evaluation of the age of the snails between young (1-2 years), middle (5-7 years) and old (9-13 years) showed significant differences (p<0.001). Analysis of KYNA levels in different snail tissues, i.e. CG, SG, heart and liver, showed an occurrence in the low femtomolar range. Marked and significant increases of KYNA were found in the liver of middle and old age groups. In the SG, KYNA decreased significantly with age. There were no differences in KYNA levels between groups in CG and heart. The lowest KAT activity was found in CG and SG (5 pmol/mg/h), while in heart and liver the values were visibly higher (between 8 and 80 pmol/mg/h). Only in the liver, and exceptionally only for KAT I, the activity increased significantly with age, i.e. up to 14 years. No age-related changes in KAT I, II and III activities were found in CG and SG. Snail liver shows a different pattern of KAT activities compared to the rat liver.
Regions of the CNS and periphery of the snail Helix pomatia are able to synthesize KYNA due to KAT activities. In the snail liver, KAT I activity increased with age. Notably, there was no age-related increase in KAT activities in the heart and especially in the CNS of Helix pomatia, indicating significant differences from mammals. A moderate KYNA metabolism in the Helix pomatia snail in the periods studied, up to 14 years, could be a physiological phenomenon that protects organs from possible functional insufficiency due to high KYNA levels, as has been suggested. It is reasonable to search for the factor(s) that could regulate the concentration of KYNA in the body of the snail.
背景/目的：犬尿酸（KYNA）是色氨酸代谢途径中的一种代谢产物，是谷氨酸离子型兴奋性氨基酸（EAA）受体和α7 烟碱型乙酰胆碱受体（nAChR）的内源性拮抗剂。KYNA 在各种病理状况和衰老过程中的参与意义重大。哺乳动物中枢神经系统（CNS）和外周组织中存在从 L-犬尿氨酸（L-KYN）通过几种犬尿氨酸氨基转移酶（KAT）作用生成 KYNA 的途径。我们有兴趣在体外研究中研究蜗牛 Helix pomatia 的大脑和外周器官合成 KYNA 的能力。在大鼠和蜗牛之间的比较研究中，我们在肝脏中寻找 KYNA 的合成。然后，我们研究了年龄对 KYNA 合成的影响。
使用 Helix pomatia 蜗牛的 10 个壳参数来建立年龄评分量表（ARS），即体重、壳重、壳长、壳宽和壳高、壳开口长和宽、唇宽、壳层数和外部壳生长环。根据 ARS 确定蜗牛的年龄，将蜗牛分为三组，即年轻、中年和老年。检查解剖区域的匀浆，即脑神经节（CG）、由足神经节、内脏神经节和胸膜神经节组成的咽下神经节（SG）、心脏和肝脏。通过高效液相色谱法（HPLC）测量 KYNA，通过酶法测量 KAT 活性。
关于 ARS，对年轻（1-2 岁）、中年（5-7 岁）和老年（9-13 岁）蜗牛年龄的评估显示出显著差异（p<0.001）。对 CG、SG、心脏和肝脏等不同蜗牛组织中的 KYNA 水平进行分析，发现其处于低飞摩尔范围内。在中年和老年组的肝脏中发现 KYNA 显著增加。在 SG 中，KYNA 随年龄显著下降。在 CG 和心脏中，各组之间的 KYNA 水平没有差异。CG 和 SG 中的 KAT 活性最低（5 pmol/mg/h），而心脏和肝脏中的活性明显更高（8-80 pmol/mg/h）。只有在肝脏中，并且异常情况下仅对 KAT I 而言，活性随年龄增加而显著增加，即增加到 14 岁。在 CG 和 SG 中未发现 KAT I、II 和 III 活性的年龄相关变化。与大鼠肝脏相比，蜗牛肝脏显示出不同的 KAT 活性模式。
蜗牛 Helix pomatia 的 CNS 和外周组织区域由于 KAT 活性能够合成 KYNA。在蜗牛肝脏中，KAT I 活性随年龄增加而增加。值得注意的是，在蜗牛的心脏，特别是 CNS 中，没有与年龄相关的 KAT 活性增加，表明与哺乳动物有显著差异。在研究期间，蜗牛 Helix pomatia 中适度的 KYNA 代谢（最多 14 岁）可能是一种生理现象，可防止由于 KYNA 水平升高而导致器官功能不足，正如所建议的那样。寻找可能调节蜗牛体内 KYNA 浓度的因素是合理的。
