Toxicity of accumulating substrates is a significant problem in several disorders of valine and isoleucine degradation notably short-chain enoyl-CoA hydratase (ECHS1 or crotonase) deficiency, 3-hydroxyisobutyryl-CoA hydrolase (HIBCH) deficiency, propionic acidemia (PA) and methylmalonic aciduria (MMA). Isobutyryl-CoA dehydrogenase (ACAD8) and short/branched-chain acyl-CoA dehydrogenase (SBCAD, ACADSB) function in the valine and isoleucine degradation pathways, respectively. Deficiencies of these acyl-CoA dehydrogenase (ACAD) enzymes are considered biochemical abnormalities with limited or no clinical consequences. We investigated whether substrate reduction therapy through inhibition of ACAD8 and SBCAD can limit the accumulation of toxic metabolic intermediates in disorders of valine and isoleucine metabolism. Using analysis of acylcarnitine isomers, we show that 2-methylenecyclopropaneacetic acid (MCPA) inhibited SBCAD, isovaleryl-CoA dehydrogenase, short-chain acyl-CoA dehydrogenase and medium-chain acyl-CoA dehydrogenase, but not ACAD8. MCPA treatment of wild-type and PA HEK-293 cells caused a pronounced decrease in C3-carnitine. Furthermore, deletion of ACADSB in HEK-293 cells led to an equally strong decrease in C3-carnitine when compared to wild-type cells. Deletion of ECHS1 in HEK-293 cells caused a defect in lipoylation of the E2 component of the pyruvate dehydrogenase complex, which was not rescued by ACAD8 deletion. MCPA was able to rescue lipoylation in ECHS1 KO cells, but only in cells with prior ACAD8 deletion. SBCAD was not the sole ACAD responsible for this compensation, which indicates substantial promiscuity of ACADs in HEK-293 cells for the isobutyryl-CoA substrate. Substrate promiscuity appeared less prominent for 2-methylbutyryl-CoA at least in HEK-293 cells. We suggest that pharmacological inhibition of SBCAD to treat PA should be investigated further.

中文翻译：

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酰基辅酶 A 脱氢酶底物混杂限制了底物还原疗法在缬氨酸和异亮氨酸代谢紊乱中的发展潜力

累积底物的毒性是缬氨酸和异亮氨酸降解的几种疾病中的一个重要问题，特别是短链烯酰辅酶 A 水合酶（ECHS1 或巴豆酶）缺乏症、3-羟基异丁酰辅酶 A 水解酶 (HIBCH) 缺乏症、丙酸血症 (PA) 和甲基丙二酸尿症（综合格斗）。异丁酰辅酶 A 脱氢酶 (ACAD8) 和短链/支链酰基辅酶 A 脱氢酶 (SBCAD, ACADSB) 分别在缬氨酸和异亮氨酸降解途径中起作用。这些酰基辅酶 A 脱氢酶 (ACAD) 酶的缺陷被认为是生化异常，临床后果有限或没有临床后果。我们调查了通过抑制 ACAD8 和 SBCAD 进行的底物减少疗法是否可以限制缬氨酸和异亮氨酸代谢紊乱中有毒代谢中间体的积累。通过对酰基肉碱异构体的分析，我们发现 2-亚甲基环丙烷乙酸 (MCPA) 抑制 SBCAD、异戊酰辅酶 A 脱氢酶、短链酰基辅酶 A 脱氢酶和中链酰基辅酶 A 脱氢酶，但不抑制 ACAD8。MCPA 处理野生型和 PA HEK-293 细胞导致 C3-肉碱显着减少。此外，删除ACADSB与野生型细胞相比，HEK-293 细胞中的 C3-肉碱同样强烈减少。HEK-293 细胞中ECHS1的缺失导致丙酮酸脱氢酶复合物的 E2 组分脂化缺陷，而ACAD8缺失并未挽救这种缺陷。MCPA 能够挽救ECHS1 KO 细胞中的脂肪化，但仅限于先前ACAD8缺失的细胞。SBCAD 并不是负责这种补偿的唯一 ACAD，这表明 HEK-293 细胞中异丁酰辅酶 A 底物的 ACAD 大量混杂。至少在 HEK-293 细胞中，2-甲基丁酰辅酶 A 的底物混杂似乎不太明显。我们建议进一步研究 SBCAD 治疗 PA 的药理学抑制作用。