Citrulline Modulates Inflammation, Oxidative Stress, and Metabolic Reprogramming in LPS-Stimulated Macrophages

Although citrulline is a nonessential amino acid, its anti-inflammatory properties have recently garnered attention. However, the integrated regulatory mechanisms underlying their effects on the inflammatory responses in macrophages remain unclear. This study aimed to test the hypothesis that citrulline integrates the control of inflammatory mediator production, metabolic reprogramming, and oxidative stress responses through direct inhibition of the NF-κB pathway in LPS-stimulated RAW 264 macrophages. Citrulline treatment resulted in concentration-dependent suppression of LPS-induced mRNA expression of inflammatory mediators. TNF-α expression was suppressed in a dose-dependent manner, while IL-6 and IL-1β expression were similarly reduced. Citrulline significantly suppressed COX-2 and iNOS expression. Western blotting demonstrated that citrulline inhibited LPS-induced NF-κB phosphorylation. ROS production decreased, and SOD activity, which was reduced by LPS stimulation, was restored in a concentration-dependent manner. Furthermore, citrulline significantly suppressed the LPS-induced upregulation of GLUT1 mRNA expression and exerted inhibitory effects on lactate production. This study revealed that citrulline integrates control of inflammatory mediator production suppression, oxidative stress reduction, and normalization of inflammatory metabolic reprogramming through inhibition of the NF-κB pathway. These preliminary findings suggest the potential of citrulline as a comprehensive regulatory molecule for inflammatory responses and as a novel target for nutritional intervention in inflammation-related diseases.