Inborn Errors of Metabolism, Molecular Pediatrics, Lausanne University Hospital, Lausanne, Switzerland.
PLoS One. 2013;8(1):e53735. doi: 10.1371/journal.pone.0053735. Epub 2013 Jan 10.
Glutaric aciduria type I (glutaryl-CoA dehydrogenase deficiency) is an inborn error of metabolism that usually manifests in infancy by an acute encephalopathic crisis and often results in permanent motor handicap. Biochemical hallmarks of this disease are elevated levels of glutarate and 3-hydroxyglutarate in blood and urine. The neuropathology of this disease is still poorly understood, as low lysine diet and carnitine supplementation do not always prevent brain damage, even in early-treated patients. We used a 3D in vitro model of rat organotypic brain cell cultures in aggregates to mimic glutaric aciduria type I by repeated administration of 1 mM glutarate or 3-hydroxyglutarate at two time points representing different developmental stages. Both metabolites were deleterious for the developing brain cells, with 3-hydroxyglutarate being the most toxic metabolite in our model. Astrocytes were the cells most strongly affected by metabolite exposure. In culture medium, we observed an up to 11-fold increase of ammonium in the culture medium with a concomitant decrease of glutamine. We further observed an increase in lactate and a concomitant decrease in glucose. Exposure to 3-hydroxyglutarate led to a significantly increased cell death rate. Thus, we propose a three step model for brain damage in glutaric aciduria type I: (i) 3-OHGA causes the death of astrocytes, (ii) deficiency of the astrocytic enzyme glutamine synthetase leads to intracerebral ammonium accumulation, and (iii) high ammonium triggers secondary death of other brain cells. These unexpected findings need to be further investigated and verified in vivo. They suggest that intracerebral ammonium accumulation might be an important target for the development of more effective treatment strategies to prevent brain damage in patients with glutaric aciduria type I.
I 型戊二酸血症(戊二酰辅酶 A 脱氢酶缺乏症)是一种先天性代谢缺陷病,通常在婴儿期表现为急性脑病危象,常导致永久性运动障碍。这种疾病的生化特征是血液和尿液中戊二酸和 3-羟基戊二酸水平升高。由于低赖氨酸饮食和肉碱补充并不能始终预防脑损伤,即使在早期治疗的患者中也是如此,因此这种疾病的神经病理学仍知之甚少。我们使用重复给予 1mM 戊二酸或 3-羟基戊二酸的大鼠器官型脑细胞培养物聚集的 3D 体外模型,在两个时间点模拟 I 型戊二酸血症,这两个时间点代表不同的发育阶段。两种代谢物对发育中的脑细胞都有损害,而 3-羟基戊二酸是我们模型中最具毒性的代谢物。星形胶质细胞是受代谢物暴露影响最大的细胞。在培养基中,我们观察到培养基中铵的含量增加了 11 倍,同时谷氨酰胺减少。我们还观察到乳酸增加和葡萄糖减少。暴露于 3-羟基戊二酸会导致细胞死亡率显著增加。因此,我们提出了 I 型戊二酸血症脑损伤的三步模型:(i)3-OHGA 导致星形胶质细胞死亡,(ii)星形胶质细胞酶谷氨酰胺合成酶的缺乏导致脑内铵积累,(iii)高铵触发其他脑细胞的继发性死亡。这些意外发现需要进一步在体内进行研究和验证。它们表明,脑内铵积累可能是开发更有效治疗策略以预防 I 型戊二酸血症患者脑损伤的重要目标。