Effects of supplemental leucine and lysine on metabolic and inflammatory responses of neutrophils and peripheral blood mononuclear cells in growing cattle

This study evaluated effects of postruminal leucine and lysine supplementation on hematological variables and ex vivo neutrophil and peripheral mononuclear cell (PBMC) responses in steers. Rumen-cannulated steers (n = 7; BW = 173 kg, 5 mo) were assigned to a 6 × 6 Latin square, with one treatment sequence replicated in the seventh steer. Treatments were a factorial arrangement of leucine (0, 15, or 30 g/d) and lysine (0 or 6 g/d) administered via continuous abomasal infusion. Blood was collected on d 7 of infusion for hematological analysis and isolation of neutrophils and PBMC. Neutrophil function was assessed by phagocytosis and oxidative burst, and metabolic responses by glucose concentrations in spent media with or without lipopolysaccharide (LPS). Peripheral mononuclear cells were cultured under concanavalin A (ConA) with or without LPS to evaluate cytokine production, glucose, and mRNA expression. Data were analyzed using the MIXED procedure of SAS with period, lysine, and leucine as fixed effects and steer as a random effect, and orthogonal contrasts were used to evaluate linear and quadratic effects of leucine and their interactions with lysine and LPS. Most hematological variables were not affected by treatment. Lysine increased platelet counts and decreased lymphocyte counts (P = 0.04), whereas hemoglobin tended to increase linearly with increasing leucine (P = 0.10). Neutrophil glucose utilization was not affected by main effects; however, a linear leucine × LPS was detected (P = 0.04), with glucose decreasing as leucine increased in the absence of LPS, but not under LPS. Neutrophil phagocytosis and oxidative burst were not affected by treatment. For PBMC, glucose concentrations were lower under ConA than ConA + LPS (P < 0.001), and a lysine × quadratic leucine was detected (P = 0.01). For PBMC, leucine linearly decreased TNFA (P = 0.05), GLUT1 (P = 0.07), and GLUT3 (P = 0.05) mRNA abundance, whereas lysine tended to increase NFKB1 (P = 0.09). Production of TNF-α was greater under ConA than ConA + LPS (P < 0.001) and was not affected by treatment. In contrast, IFN-γ increased under ConA + LPS (P < 0.001), increased linearly with leucine (P = 0.02), and tended to increase with lysine (P = 0.10). These results show that leucine modulated metabolic responses in neutrophils and both metabolic and inflammatory responses in PBMC, whereas lysine primarily influenced selected hematological variables, with limited effects on PBMC inflammatory signaling.