Effect of intravenous lipid infusion on biomarkers of insulin resistance and immune functions of dry and nonpregnant dairy cows.

During the transition period, dairy cows often experience negative energy balance, which can induce metabolic and immunological disturbances. Previous work has shown that there is a relationship between the dysfunction of immune cells and the increase in blood nonesterified fatty acid (NEFA) concentration. Nevertheless, it is difficult to determine the exact effect of NEFA on the immune system, as other metabolic and hormonal perturbations occur simultaneously during the transition period. In the present study, we have determined the effect of NEFA on immune functions using an experimental model designed to assess the effects independently of energy balance, as well as hormonal and metabolic changes due to parturition. Six dry and nonpregnant cows were infused with either sterile water (control treatment) or a lipid emulsion (Intralipid 20%, Frenesius Kabi, lipid treatment) at a rate of 1 mL/kg per hour for 6 h according to a crossover design. Blood concentrations of NEFA, ß-hydroxybutyrate (BHB), and glucose were measured every hour throughout the infusion period, and 1 and 18 h after the end of infusion. Proliferation and interferon-γ secretion of lymphocytes, phagocytosis, and oxidative burst of neutrophils and blood insulin concentration were evaluated before, during, and at the end of the infusion. For NEFA, BHB, and glucose, treatment × time interactions were present. When compared with the control condition, NEFA and BHB levels were greater in the plasma of cows infused with lipids from 1 h after the start of infusion until 1 h after the end of infusion. Glucose level also increased in response to lipid infusion from 2 h of infusion until 1 h after the end of treatment. For sterile water and lipid infusions, respectively, maximal concentrations were 0.06 ± 0.10 mM and 1.39 ± 0.10 mM for NEFA, 0.70 ± 0.05 mM and 1.06 ± 0.05 mM for BHB, and 4.56 ± 0.27 mM and 6.90 ± 0.27 mM for glucose. For all blood metabolites, there were no differences between treatments 18 h postinfusion. Lipid infusion significantly increased blood insulin concentration at 3 and 6 h of infusion. However, it returned to its basal concentration 18 h after the end of the infusion. Lymphoproliferation declined as early as 3 h after the start of the lipid infusion. At 3 and 6 h of infusion, lipid treatment significantly reduced INF-γ concentration in the culture cell supernatant. The lipid infusion did not affect neutrophil phagocytosis. Nevertheless, the efficacy of the response was affected by a reduction of neutrophils' oxidative burst. These results confirm that NEFA inhibits immune functions independently of energy balance and other changes that occur during the transition period. They also indicate that high blood lipid concentration causes insulin resistance.

Effect of different fatty acids on the proliferation and cytokine production of dairy cow peripheral blood mononuclear cells.

During the transition period, dairy cows often experience negative energy balance, which induces metabolic and immunological disturbances. Our previous work has shown a relationship between the inhibition of immune functions and increased blood nonesterified fatty acid (NEFA) levels. In this study, we evaluated the effect of 11 fatty acids (palmitoleic, myristic, palmitic, stearic, oleic, linoleic, docosahexaenoic, conjugated linoleic, lauric, eicosapentaenoic, and linolenic acids) as well as a mix that represented the NEFA profile observed during the transition period at different concentrations (0, 50, 100, and 250 µM) on proliferation and cytokines secretion of lymphocytes. To assess lymphoproliferation, peripheral blood mononuclear cell (PBMC) from 5 healthy cows (166-189 d in milk) were isolated, stimulated with the mitogenic lectin concanavalin A (ConA), incubated for 72 h with or without fatty acids, and subjected to flow cytometry analysis. Our results showed that all fatty acids, except lauric acid, significantly reduced proliferation of PBMC in a dose-dependent manner. The most detrimental effect was observed with conjugated linoleic and stearic acids, where proliferation of PBMC was already inhibited at the lowest dose (50 µM). For cytokine secretion, we found that levels of IL-4 in culture supernatant of ConA-stimulated PBMC were reduced after a 24-h exposure to the lowest dose (50 µM) of oleic and palmitoleic acids. A dose of 100 µM of eicosapentaenoic acid, NEFA mixture, and myristic acid was necessary to observe a reduction in IL-4 levels. The PBMC also showed a decrease in the secretion of IFN-γ in response to lauric, linolenic, palmitoleic, and stearic acids at 50 µM and myristic acid at 100 µM. Overall, polyunsaturated fatty acids were more potent inhibitors of cytokine secretions than saturated fatty acids. In addition, we detected an inverse relationship between the melting points of fatty acids and their ability to inhibit IL-4 and IFN-γ secretions, as evidenced by greater inhibition with low-melting point fatty acids. Overall, our study confirmed that NEFA have a negative effect on some lymphocyte functions, and that their inhibitory effect on cytokine secretions increases with the degree of unsaturation.