Metabolic Profile Reveals the Immunosuppressive Mechanisms of Methionyl-Methionine in Lipopolysaccharide-Induced Inflammation in Bovine Mammary Epithelial Cell

SIMPLE SUMMARY: Bovine mastitis results in substantial problems in terms of animal health, food safety, and profitability of farmers. Methionyl-methionine dipeptide confers protection in the bovine mammary epithelial cells as evidenced by our previous transcriptomic study at the molecular level. However, whether the metabolic production of Met-Met confers protection remains unknown. In this study, Met-Met significantly suppressed LPS-induced TNF-α, IL-8, AP-1, and MCP-1 expression; reversed decreased tryptophan, phenylalanine, and histidine levels; and inhibited LPS-induced palmitic acid and stearic acid levels as well as purine metabolism disorder. Overlapping metabolites were mainly involved in the cysteine and methionine metabolism, fatty acids biosynthesis, and purines degradation. These metabolites and pathways might contribute to the protective action of methionyl-methionine. ABSTRACT: Our previous transcriptomic study found that methionyl-methionine (Met-Met) exerts an anti-inflammatory effect in the bovine mammary epithelial cell (MAC-T) at a molecular level. However, evidence of whether the metabolic production of Met-Met confers protection was scarce. To investigate the inflammatory response and metabolite changes of Met-Met in lipopolysaccharide (LPS)-induced inflammation of MAC-T, mass spectrometry-based metabolomics and qPCR were conducted. The increased levels of IL-8, TNF-α, AP-1, and MCP-1 were reduced by pretreating with 2 mM Met-Met after LPS exposure. Metabolomics profiling analysis demonstrated that LPS induced significant alteration of metabolites, including decreased tryptophan, phenylalanine, and histidine levels and increased palmitic acid and stearic acid levels as well as purine metabolism disorder, whereas Met-Met reversed these changes significantly. Pathways analysis revealed that overlapping metabolites were mainly enriched in the cysteine and methionine metabolism, fatty acids biosynthesis, and purines degradation. Correlation networks showed that the metabolic profile was significantly altered under the conditions of inflammation and Met-Met treatment. Collectively, Met-Met might relieve MAC-T cell inflammation via hydrolysate methionine, which further changes the processes of amino acid, purine, and fatty acid metabolism.