Department of Animal Sciences, University of Illinois at Urbana-Champaign, Urbana 61801.
Joint International Research Laboratory of Agriculture and Agri-product Safety of Ministry of Education of China, Yangzhou University, Yangzhou, People's Republic of China 225009.
J Dairy Sci. 2019 Sep;102(9):8343-8351. doi: 10.3168/jds.2018-15737. Epub 2019 Jul 10.
Methionine (Met) is one of the 2 most limiting amino acids for milk production in dairy cow diets. The accepted "ideal" ratio of lysine (Lys) to Met (L:M) when formulating diets is 3:1. However, blood from cows fed corn silage-based diets without supplemental rumen-protected Met averages approximately 3.6:1 L:M. Recent in vivo research on cattle immunonutrition has revealed that the immune system could benefit from greater Met supply. To study more closely the effects of different L:M ratios, blood polymorphonuclear cells (PMN) were isolated from 5 Holstein cows in mid-lactation (238 ± 20 d postpartum, 33.8 ± 3.8 kg of milk/d; mean ± SD). The PMN were incubated at 3 different levels of L:M (3.6:1, 2.9:1, or 2.4:1) and stimulated with lipopolysaccharide (LPS) at either 0 or 50 μg/mL for 2 h at 37°C. Target genes were associated with cytokines, pathogen recognition, nuclear receptors, killing mechanisms, and Met and glutathione metabolism. Data were subjected to ANOVA using PROC MIXED in SAS, with L:M, LPS, and their interaction as fixed effects. Stimulation with LPS upregulated genes related to cytokines (IL1B, TNF, IL10 and IL6) and nuclear receptors, including nuclear factor kappa B (NFKB1) and glucocorticoid receptor (NR3C1), and downregulated the mRNA abundance of chemokine receptor 1 (CXCR1), lysozyme (LYZ) and glutathione reductase (GSR). A linear decrease was observed in the mRNA abundance of TNF when L:M was decreased. A similar response was observed for interleukin-1 receptor-associated kinase 1 (IRAK1) and NFKB1 abundance in cells stimulated with LPS (linear effect). A linear increase of LYZ mRNA expression as L:M decreased was detected in unstimulated cells. Furthermore, a decrease in L:M led to a linear decrease of superoxide dismutase 1 (SOD1) mRNA abundance in cells challenged with LPS. Overall, LPS challenge triggered the activation of isolated PMN from mid-lactation cows. However, data suggest the use of a shorter incubation time to capture the peak response and not the resolution of the inflammatory response as in the present study. Our results indicate a possible involvement of Met in modulating PMN inflammatory and oxidative stress status and in helping the resolution of inflammation after initial stimulation.
蛋氨酸（Met）是奶牛日粮中生产牛奶的 2 种最受限制的氨基酸之一。在配制日粮时，赖氨酸（Lys）与蛋氨酸（Met）的公认“理想”比例为 3：1。然而，饲喂玉米青贮日粮而不补充瘤胃保护性 Met 的奶牛的血液中，L：M 的平均比例约为 3.6：1。最近关于奶牛免疫营养的体内研究表明，免疫系统可能受益于更多的 Met 供应。为了更仔细地研究不同 L：M 比例的影响，从处于泌乳中期的 5 头荷斯坦奶牛（产后 238±20 天，33.8±3.8kg/d；平均值±SD）中分离出中性粒细胞（PMN）。PMN 在 3 种不同的 L：M（3.6：1、2.9：1 或 2.4：1）水平下孵育，并在 37°C 下用脂多糖（LPS）刺激，刺激物浓度为 0 或 50μg/mL，持续 2 小时。目标基因与细胞因子、病原体识别、核受体、杀伤机制以及 Met 和谷胱甘肽代谢有关。使用 SAS 中的 PROC MIXED 对数据进行方差分析，以 L：M、LPS 及其相互作用作为固定效应。LPS 的刺激上调了与细胞因子（IL1B、TNF、IL10 和 IL6）和核受体相关的基因，包括核因子 kappa B（NFKB1）和糖皮质激素受体（NR3C1），并下调了趋化因子受体 1（CXCR1）、溶菌酶（LYZ）和谷胱甘肽还原酶（GSR）的 mRNA 丰度。当 L：M 降低时，TNF 的 mRNA 丰度呈线性下降。在 LPS 刺激的细胞中，也观察到白细胞介素 1 受体相关激酶 1（IRAK1）和 NFKB1 丰度的类似反应（线性效应）。在未受刺激的细胞中，LYZ mRNA 表达随着 L：M 的降低呈线性增加。此外，在 LPS 挑战的细胞中，L：M 的降低导致超氧化物歧化酶 1（SOD1）mRNA 丰度的线性降低。总的来说，LPS 挑战激活了处于泌乳中期奶牛的分离中性粒细胞。然而，数据表明，需要使用更短的孵育时间来捕捉峰值反应，而不是像本研究中那样捕捉炎症反应的解决。我们的结果表明，Met 可能参与调节 PMN 的炎症和氧化应激状态，并有助于在初始刺激后炎症的解决。
