Monosodium glutamate-induced damage in liver and kidney:a morphological and biochemical approach 在肝和肾脏中的感应谷氨酸钠的损坏：一个形态学和

生物化学的方法

Abstract

It has been demonstrated that high concentrations of monosodium glutamate in the central nervous system induce neuronal necrosis and damage in retina and circumventricular organs. In this model, the monosodium glutamate is used to induce an epileptic state; one that requires highly concentrated doses. The purpose of this study was to evaluate the toxic effects of the monosodium glutamate in liver and kidney after an intra-peritoneal injection. For the experiment, we used 192 Wistar rats to carry out the following assessments: a) the quantification of the enzymes alanine aminotransferase and aspartate aminotransferase, b) the quantification of the lipid peroxidition products and c) the morphological evaluation of the liver and kidney. During the experiment, all of these assessments were carried out at 0, 15, 30 and 45 min after the intraperitoneal injection. In the rats that received monosodium glutamate, we observed increments in the concentration of alanine aminotransferase and aspartate aminotransferase at 30 and 45 min. Also, an increment of the lipid preoxidition products, in kidney, was exhibited at 15, 30 and 45 min while in liver it was observed at 30 and 45 min. Degenerative changes were observed (edema-degeneration-necrosis) at 15, 30 and 45 min.

摘要

它已经被证明，中枢神经系统在高浓度的谷氨酸钠环境下引起视网膜神经细胞坏死和心室周围的器官损害。在这种模式下，谷氨酸钠是被用来诱发一个需要高度集中的剂量的癫痫状态。这研究的目的将评估一个腹膜内注入谷氨酸钠后的

肝和肾脏中的毒性效应。在实验中，我们用192只大鼠进行以下评估：a）定量化的谷丙转氨酶和天冬氨酸转氨酶。b）对脂质过氧化产物的定量和c）肝脏和肾脏的形态学评价。

在实验过程中，所有这些评估在腹腔注射后的第0,15,30,45分钟时进行。在大鼠接受味精，我们观察到在30和45分钟的谷丙转氨酶和天冬氨酸转氨酶的浓度在曾加。此外，在肾脏中，脂质过氧化产物的增加在15，30和45分钟被发现，而在肝脏中只有30和45分钟才能观察出来。变性的变化（水肿－退化－坏死）在第 15, 30 和第 45 分钟被观察到了。

Introduction

L-glutamate is an excitatory neurotransmitter in the central nervous system (CNS) of mammals. Glutamate is present in high levels in the brain and select groups of neurons. The endogenous L-glutamate, as the derived L-glutamate of exogenous precursors, is liberated in a Ca2+-dependent way after a depolarizing stimulus in the CNS.

Early studies in the 70’s, demonstrated that the administration of high concentrations of glutamate and other excitatory amino acids to the nervous system, produced degeneration and neuronal death in certain cerebral regions and that these effects are related to the excitotoxicity or neuronal damage due to excessive neuronal excitation through a specific on-activation of their ionotropic receptors.

Two different groups of receptors, ionotropic and metabotropic, have been described for glutamate in the CNS. The ionotropic receptors are those that include; the N-methyl-D-aspartate (NMDA) type, the non-NMDA, the kainic receptor (KA) and the propionic alfa-amino-3-hydroxy-5-methyl-4-isoxasol(AMPA). The metabotropic receptors are present in the presynaptic membrane and do not form ion channels; they are associated with G proteins and respond to the stimulus of second intracellular messengers.

The neurotoxicity that is induced by an on-activation of these glutamatergic receptors has been associated with diverse neurodegenerative diseases, as well as the

excitotoxicity by nutritious ingestion of glutamate in the form of monosodic salts when consumed in high concentrations. It has also been demonstrated that the administration of monosodium glutamate(MSG) to immature animals induces destruction in certain regions of the brain that lack a blood–brain barrier, such as the arcuatus nucleus of the hypothalamus that is involved in the regulation of neuroendocrine functions. However, these demonstrations have ignored the effects of the systemic administration of MSG that can develop high concentrations in organs such as liver and kidney; even when the presence of glutamatergicreceptors has been demonstrated outside the CNS. These sub-types of receptors have been observed as the NMDA-R1, GluR 2/3 and mGluR 2/3 in liver, kidney,lungs, spleen and testicles.

前言

L－氨酸盐是在哺乳动物的中枢神经系统 （CNS）中的一个有刺激性的神经传递素。谷氨酸在脑中和选择神经元组中是高水平的存在。内源性L -谷氨酸，作为派生L-谷氨酸的外源前体是一种钙离子依赖性的方式解放之后，在中枢神经系统中去极化刺激。

在xx年代早期的研究中，我们证明了施用高浓度的谷氨酸和其他兴奋性氨基酸的神经系统会产生变性和在某些脑区的神经细胞死亡，而这些影响都与兴奋性中毒神经元由于过多神经元的激发在这些亲离子受体一个特有的命令执行期间的受损有关

两个不同群体的受体，离子型和代谢型，被描述为在中枢神经系统中谷氨酸。离子型受体的是那些N-甲基- D-天冬氨酸（NMDA）型，非NMDA受体，红藻受体（KA）和丙酸α-氨基- 3 -羟基- 5 -甲基- 4 - isoxasol（AMPA）.代谢型受体在突触前膜目前并没有形成离子通道，它们都与G蛋白和回应第二细胞内的信使的刺激有关。

一个被谷氨酸受体的激活引导的神经毒性与不同的神经退化性疾病有关，以及营养的摄取谷氨酸的兴奋毒性以monosodic盐形式在高浓度下被消耗。它也已

经被证明，对味精（MSG）的处理诱导未成熟动物的大脑某些区域的破坏，缺乏血脑屏障，像是如丘脑弓状核的是在参与调节神经内分泌功能。然而，这些示范已经忽略能在像是肝和肾脏等器官中高浓度的味精的被吸收的效应,甚至当谷氨酸受体的存在被表明是中枢神经系统外。这些受体亚型一直被视为对NMDA- R1的，GluR2 / 3的和代谢型谷氨酸受体2 / 3在肝，肾，肺，脾和睾丸中。 Discussion

MSG, a dose of 4 mg/g of body weight administered by intra-peritoneal injection to rats, is toxic for the liver and the kidney.

In this study,starting from 15 min post injection, we ob-served high levels of ALAT and ASAT (Fig. 1a, b), which indicate that the serum concentration of these enzymes fluctuates with the hepatic damage. The localization of ALAT and ASAT in the hepatocyte is cytoplasmatic; the MSG cytotoxic effect induced tissue damage and enzyme release increasing their serum levels.

The circulating MSG was dissociated in sodium (Na+) and L-glutamate. The L-glutamate crosses the mesothelial peritoneal cells and arrives at the bloodstream by means of a transport system using ATP. A part of the L-glutamate in the cell conjugates,in order to be eliminated, and another part is transformed into glutamine. When this occurs, the cells try to repair some of the damages by using enzymes that are present in the smooth endoplasmic reticulum but the cell is not able to completely remove the excess glutamine. Probably, for this reason, the liver (15 min) presented cloudy swelling (turbid swelling) at 30 min. It is possible to observe vesicular degeneration and necrosis at 45 min.

When the L-glutamate arrives in high concentrations through the renal artery,the kidney tries to excrete it. The renal corpuscle receives the L-glutamate through the afferent arteriole, it is absorbed, filtrated, and crosses the membrane damaging the cell. The convoluted proximal tubules were more susceptible to damage in comparison to the distal convoluted tubules.The kidney at 15, and 30 min exhibited edema; hydropic degeneration and necrosis were observed at 45 min.

Glutamate, a major excitatory amino acid neurotransmitter is also an endogenous

excitotoxin. The effects of the glutamate excitotoxicity in different brain regions, and lipid peroxidation are well documented.

In this study, the increase of lipid peroxidation products(MDA and 4-OH alkenals) was the response of the liver and kidney damage. At the same times, there were observed increases in malonaldehyde and 4-OH alkenals as well as ALAT and ASAT enzymes. The morphology of the damage shows a correlation between the progressive damage and the lipid peroxidation products, especially during the 30 and 45 min after glutamate administration. In liver the steatosis and necrosis were observed with high levels of malonaldehyde and 4-OH alkenals. In kidney, very similar responses were exhibited with hydropic degeneration and necrosis. All of these data could be explained by the excitotoxic role of the glutamate.