Metabolic Reprogramming of Macrophages by Walnut Peptides: Interference with Arginine-to-Creatine Conversion

Walnut protein is a promising candidate for the development of functional health supplements. In this study, peptides were prepared via the limited trypsin hydrolysis of walnut protein, and their immunomodulatory effects on macrophages were evaluated through both in vivo and in vitro experiments. We found that peptide administration modulated systemic arginine metabolism. In macrophages, the peptides induced transcriptional reprogramming toward a pro-inflammatory phenotype, regardless of their immunosuppressive status. Specifically, peptide treatment upregulated Slc7a2 expression, concomitant with enhanced arginine uptake, while concurrently suppressing the arginine-to-guanidinoacetic acid/creatine pathway. These findings reveal a mechanistic role of walnut-derived peptides in regulating macrophage polarization through arginine metabolic reprogramming. Consequently, the stimulation of M2-polarized macrophages with these peptides reversed their tumor-promoting propensity and restored their cytotoxicity against tumor cells. Together, these findings provide a scientific basis for the value-added processing and high-end utilization of walnut proteins in nutraceutical applications.