LARGE NEUTRAL AMINO ACIDS--TRANSPORT AND EFFECTS ON OXIDATIVE BRAIN METABOLISM

我们假设支链氨基酸水平升高 它们的α-酮酸(BCKA)不仅扰乱了氨基酸的运输， 而且还会影响大脑的能量代谢，破坏大脑的平衡 细胞间运输，并通过参与的酶改变通量 氨基酸类神经递质合成。最终，这种扰动可能 对神经发育有深远的影响，导致智力低下。 我们实验室的四个最新发现支持这一假说：1) 通过以下途径引起的α-酮基异己酸(α-KIC)水平升高 微透析刺激体内谷氨酸和谷氨酰胺的氧化， 改变电池的能量状态并降低电池的可用性 谷氨酸对神经递质的作用；2)我们已经在 谷氨酸和谷氨酰胺的氧化代谢是完整的大脑 海马区的谷氨酰胺氧化率是 大约是谷氨酸氧化率的5倍；3)提高 通过微透析引入的亮氨酸和α-KIC水平 大鼠脑间质间隙，导致大鼠脑内 大分子中性氨基酸(LNAA)和 谷氨酰胺和培养的大鼠皮质神经元和星形胶质细胞 细胞内对外源BCAA和BCKA的反应不同。 拟议的研究将：1)结合两种既定的方法，即， 微透析和特定细胞消融，以确定其效果 BCAA和BCKA对不同细胞类型氧化代谢的影响 2)测定支链氨基酸和支链氨基酸对氨基酸的影响 特定消融术后酸交换到间质液体中 神经毒性化合物对脑细胞类型的影响；3)表征 LNAA和BCKA在神经细胞中的作用 谷氨酸/谷氨酰胺在正常大鼠脑内和培养中的代谢 已知细胞类型的脑细胞。包括人星形胶质细胞，正常和 21三体，应提供有价值的病因学信息 新陈代谢先天缺陷引起的智力低下 染色体异常，将为临床提供指导 应对这些情况的方法。

We hypothesize that elevated levels of branched chain amino acids (BCAA) and their alpha-keto acids (BCKA) perturb not only amino acid transport, but also affect brain energy metabolism, disrupt the equilibrium of intercellular trafficking, and alter flux through enzymes involved in amino acid neurotransmitter synthesis. Ultimately such perturbations may have profound effects on neurodevelopment leading to mental retardation. Four recent findings from our laboratory support this hypothesis: 1) elevated levels of alpha-ketoisocaproate (alpha-KIC) introduced via microdialysis stimulate the in vivo oxidation of glutamate and glutamine, altering the energy states of the cells and decreasing the availability of glutamate for neurotransmitter function; 2) we have demonstrated in the intact brain that the oxidative metabolism of glutamate and glutamine is compartmentalized with glutamine oxidation rates in the hippocampus being approximately 5-fold greater than glutamate oxidation rates; 3) elevated levels of leucine and alpha-KIC, introduced via microdialysis to the interstitial space of rat brain, result in a 2-4 fold increase in the interstitial concentrations of large neutral amino acids (LNAA) and glutamine and 4) cultured rat cortical neurons and astrocytes have a pronounced different intracellular response to exogenous BCAA and BCKA. The proposed studies will: 1) combine two established methodologies, i.e., microdialysis and specific cellular ablation, to determine the effect of BCAA and BCKA on the oxidative metabolism by specific cell types in different brain regions; 2) determine the effect of BCAA and BCKA on amino acid exchanges into the interstitial fluid following ablation of specific types of brain cells by neurotoxic compounds; 3) characterize transport of LNAA by neuronal cells; 4) characterize the effect of LNAA and BCKA on glutamate/glutamine metabolism in the intact rat brain and in culture brain cells of know cell type. Inclusion of human astrocytes, normal and trisomic 21, should provide valuable information about the etiology of mental retardation resulting from in born errors of metabolism and chromosomal abnormalities and will provide guidelines for clinical approaches to these conditions.