Araújo P, Wassermann G F, Tallini K, Furlanetto V, Vargas C R, Wannmacher C M, Dutra-Filho C S, Wyse A T, Wajner M
Departamento de Bioquímica, Instituto de Ciências Básicas da Saúde, Universidade Federal do Rio Grande do Sul, Rua Ramiro Barcelos 2600, CEP 90.035-003, Porto Alegre, RS, Brazil.
Neurochem Int. 2001 May;38(6):529-37. doi: 10.1016/s0197-0186(00)00100-5.
Neurological dysfunction is common in patients with maple syrup urine disease (MSUD). However, the mechanisms underlying the neuropathology of this disorder are poorly known. In the present study we investigated the effect of acute hyperleucinemia on plasma and brain concentrations of amino acids. Fifteen-day-old rats were injected subcutaneously with 6 micromol L-leucine per gram body weight. Controls received saline in the same volumes. The animals were sacrificed 30--120 min after injection, blood was collected and their brain rapidly removed and homogenized. The amino acid concentrations were determined by HPLC using orthophtaldialdehyde for derivatization and fluorescence for detection. The results showed significant reductions of the large neutral amino acids (LNAA) L-phenylalanine, L-tyrosine, L-isoleucine, L-valine and L-methionine, as well as L-alanine, L-serine and L-histidine in plasma and of L-phenylalanine, L-isoleucine, L-valine and L-methionine in brain, as compared to controls. In vitro experiments using brain slices to study the influence of leucine on amino acid transport and protein synthesis were also carried out. L-Leucine strongly inhibited [14C]-L-phenylalanine transport into brain, as well as the incorporation of the [14C]-amino acid mixture, [14C]-L-phenylalanine and [14C]-L-lysine into the brain proteins. Although additional studies are necessary to evaluate the importance of these effects for MSUD, considering previous findings of reduced levels of LNAA in plasma and CSF of MSUD patients during crises, it may be speculated that a decrease of essential amino acids in brain may lead to reduction of protein and neurotransmiter synthesis in this disorder.
神经功能障碍在枫糖尿症（MSUD）患者中很常见。然而，这种疾病神经病理学的潜在机制却鲜为人知。在本研究中，我们调查了急性高亮氨酸血症对血浆和脑内氨基酸浓度的影响。给15日龄大鼠皮下注射每克体重6微摩尔的L-亮氨酸。对照组注射相同体积的生理盐水。注射后30 - 120分钟处死动物，采集血液并迅速取出大脑进行匀浆。使用邻苯二甲醛进行衍生化、荧光检测的高效液相色谱法测定氨基酸浓度。结果显示，与对照组相比，血浆中大分子中性氨基酸（LNAA）L-苯丙氨酸、L-酪氨酸、L-异亮氨酸、L-缬氨酸和L-蛋氨酸以及L-丙氨酸、L-丝氨酸和L-组氨酸显著降低，脑内L-苯丙氨酸、L-异亮氨酸、L-缬氨酸和L-蛋氨酸也显著降低。还进行了使用脑片的体外实验，以研究亮氨酸对氨基酸转运和蛋白质合成的影响。L-亮氨酸强烈抑制[14C]-L-苯丙氨酸转运入脑，以及[14C]-氨基酸混合物、[14C]-L-苯丙氨酸和[14C]-L-赖氨酸掺入脑蛋白。尽管需要进一步研究来评估这些影响对MSUD的重要性，但考虑到之前在MSUD患者危机期间血浆和脑脊液中LNAA水平降低的发现，可以推测脑内必需氨基酸的减少可能导致该疾病中蛋白质和神经递质合成的减少。
