Lipid mobilization and lipid mediators biosynthesis in periparturient dairy cows

The transition period of dairy cattle is characterized by changes in metabolism and host defense mechanisms that are associated with increased disease susceptibility. Intense lipid mobilization is a metabolic adaptation common to periparturient cows that results in significant release of non-esterified fatty acids (NEFA) into circulation. Whereas these fatty acids are important sources of energy during times of increased metabolic demands, elevated plasma NEFA may disrupt several immune and inflammatory functions. The main hypothesis of this dissertation is that shifts in plasma fatty acid composition induced during lipid mobilization can influence inflammatory responses and alter cyclooxygenase and lipoxygenase lipid mediator biosynthesis. The hypothesis was tested through the following objectives. The first objective determined the influence of lipid mobilization on plasma lipid fractions and leukocyte phospholipid fatty acid profiles. Around parturition and during early lactation, the proportion of palmitic acid significantly increased in plasma NEFA and phospholipid fractions with a concomitant increase in leukocyte phospholipids. In contrast, long chain polyunsaturated fatty acids content was reduced in leukocytes phospholipids, especially during the first two weeks following parturition. The second objective evaluated the effects of lipid mobilization on vascular cells inflammatory responses. Bovine aortic endothelial cells (BAEC) were cultured with different concentrations of a NEFA mixture that reflected plasma NEFA composition of periparturient cows during the first week of lactation. Gene expression and protein quantification of inflammatory markers were used to evaluate inflammatory response. Changes in cyclooxygenase (COX) and 15 lipoxygenase (15LOX) gene expression and metabolite biosynthesis in response to NEFA exposure were also assessed. Addition of NEFA altered BAEC phospholipid fatty acid content by increasing the concentration of stearic acid and decreasing arachidonic acid and other long chain polyunsaturated fatty acids. These changes induced a significant increase of mRNA expression of COX2, interleukin 6, interleukin 8, inter-cellular adhesion molecule 1 (ICAM1), and vascular adhesion molecule 1. Changes in gene expression were reflected in protein expression by a significant increment in the protein expression of COX2 and ICAM1. Significant increases in the biosynthesis of COX metabolite prostaglandin E2, and the 15LOX derivatives 9- and 13-hydroxyoctadecadienoic acids, resulted after treatment with NEFA complexes. The third objective of this study was to assess in vitro changes of inflammatory responses in BAEC induced by supplementation with a NEFA mixture that included eicosapentaenoic acid (EPA) and docosahexapentaenoic acid (DHA). Changes in inflammatory responses were assessed similar to objective 2. In vitro supplementation of EPA and DHA to BAEC successfully increased the concentration of both fatty acids in cellular phospholipids. Furthermore, EPA and DHA reduced endothelial inflammatory responses by diminishing the expression of pro-inflammatory cytokines and adhesion molecules. There were also shifts in the biosynthesis of COX and 15LOX derived eicosanoids. This research demonstrated for the first time that in dairy cows lipid mobilization induces endothelial inflammatory responses and alters eicosanoid biosynthesis and that EPA and DHA supplementation may reduce such responses. Further studies should examine in detail how altered eicosanoid biosynthesis may affect vascular inflammatory responses during lipid mobilization, possibly identifying pharmaceutical or nutraceutical targets that would improve health not only in dairy cows, but also in humans under the concept of one health one medicine.