Stayer Kelsey, Pathan Saliha, Biswas Aalekhya, Li Huiqiao, Zhu Yi, Lam Fong Wilson, Marini Juan, Thevananther Sundararajah
Division of Critical Care Medicine, Department of Pediatrics, Baylor College of Medicine, Houston, TX, United States.
Division of Gastroenterology, Hepatology & Nutrition, Department of Pediatrics, Baylor College of Medicine, Houston, TX, United States.
Immunohorizons. 2025 Jul 14;9(8). doi: 10.1093/immhor/vlaf028.
Immune dysfunction and late mortality from multiorgan failure are hallmarks of severe sepsis. Arginine, a semi-essential amino acid important for protein synthesis, immune response, and circulatory regulation, is deficient in sepsis. However, arginine supplementation in sepsis remains controversial due to the potential to upregulate inducible nitric oxide synthase (iNOS)-mediated excessive nitric oxide (NO) generation in macrophages, leading to vasodilation and hemodynamic catastrophe. Citrulline supplementation has been considered an alternative to replenishing arginine via de novo synthesis, orchestrated by argininosuccinate synthase 1 (ASS1) and argininosuccinate lyase (ASL). However, the functional relevance of the ASS1-ASL pathway in macrophages after endotoxin stimulation is unclear but it is crucial to consider amino acid restoration as a tool for treating sepsis. We demonstrate that lipopolysaccharide (LPS)-mediated iNOS, ASS1, and ASL protein expression and nitric oxide generation were dependent on exogenous arginine in RAW 264.7 macrophages. Exogenous citrulline was not sufficient to restore nitric oxide generation in arginine-free conditions. Despite the induction of iNOS and ASS1 mRNA in arginine-free conditions, exogenous arginine was necessary and citrulline was not sufficient to overcome eIF2-α (elongation initiation factor 2-α)-mediated translational repression of iNOS and ASS1 protein expression. Moreover, exogenous arginine, but not citrulline, selectively modified the inflammatory cytokine and chemokine expression profile of the LPS-activated RAW 264.7 and bone marrow-derived macrophages. Our study highlights the complex, differential regulation of proinflammatory cytokine expression, and NO generation by exogenous arginine in macrophages.
免疫功能障碍和多器官功能衰竭导致的晚期死亡是严重脓毒症的特征。精氨酸是一种对蛋白质合成、免疫反应和循环调节很重要的半必需氨基酸，在脓毒症中会缺乏。然而，由于精氨酸补充可能会上调巨噬细胞中诱导型一氧化氮合酶（iNOS）介导的过量一氧化氮（NO）生成，导致血管舒张和血流动力学灾难，因此在脓毒症中补充精氨酸仍存在争议。瓜氨酸补充已被认为是通过精氨酸琥珀酸合成酶1（ASS1）和精氨酸琥珀酸裂解酶（ASL）精心安排的从头合成来补充精氨酸的一种替代方法。然而，内毒素刺激后巨噬细胞中ASS1-ASL途径的功能相关性尚不清楚，但将氨基酸恢复作为治疗脓毒症的一种工具至关重要。我们证明，脂多糖（LPS）介导的iNOS、ASS1和ASL蛋白表达以及一氧化氮生成在RAW 264.7巨噬细胞中依赖于外源性精氨酸。在无精氨酸条件下，外源性瓜氨酸不足以恢复一氧化氮生成。尽管在无精氨酸条件下诱导了iNOS和ASS1 mRNA，但外源性精氨酸是必需的，瓜氨酸不足以克服eIF2-α（延伸起始因子2-α）介导的iNOS和ASS1蛋白表达的翻译抑制。此外，外源性精氨酸而非瓜氨酸选择性地改变了LPS激活的RAW 264.7和骨髓来源巨噬细胞的炎性细胞因子和趋化因子表达谱。我们的研究强调了巨噬细胞中促炎细胞因子表达和外源性精氨酸产生NO的复杂、差异调节。
