Dietary arachidonate in milk replacer triggers dual benefits of PGE2 signaling in LPS-challenged piglet alveolar macrophages

Kathleen R Walter; Xi Lin; Sheila K Jacobi; Tobias Käser; Debora Esposito; Jack Odle

doi:10.1186/s40104-019-0321-1

Dietary arachidonate in milk replacer triggers dual benefits of PGE₂ signaling in LPS-challenged piglet alveolar macrophages

J Anim Sci Biotechnol. 2019 Feb 15:10:13. doi: 10.1186/s40104-019-0321-1. eCollection 2019.

Authors

Kathleen R Walter^{1

2}, Xi Lin², Sheila K Jacobi³, Tobias Käser⁴, Debora Esposito^{1

2}, Jack Odle²

Affiliations

¹ 1Department of Animal Science, Plants for Human Health Institute, North Carolina State University, Kannapolis, North Carolina USA.
² 2Department of Animal Science, North Carolina State University, Raleigh, North Carolina USA.
³ 3Department of Animal Science, Ohio State University, Columbus, Ohio USA.
⁴ 4Department of Population Health and Pathobiology, College of Veterinary Medicine, North Carolina State University, Raleigh, North Carolina USA.

Abstract

Background: Respiratory infections challenge the swine industry, despite common medicinal practices. The dual signaling nature of PGE₂ (supporting both inflammation and resolution) makes it a potent regulator of immune cell function. Therefore, the use of dietary long chain n-6 PUFA to enhance PGE₂ effects merits investigation.

Methods: Day-old pigs (n = 60) were allotted to one of three dietary groups for 21 d (n = 20/diet), and received either a control diet (CON, arachidonate = 0.5% of total fatty acids), an arachidonate (ARA)-enriched diet (LC n-6, ARA = 2.2%), or an eicosapentaenoic (EPA)-enriched diet (LC n-3, EPA = 3.0%). Alveolar macrophages and lung parenchymal tissue were collected for fatty acid analysis. Isolated alveolar macrophages were stimulated with LPS in situ for 24 h, and mRNA was isolated to assess markers associated with inflammation and eicosanoid production. Culture media were collected to assess PGE₂ secretion. Oxidative burst in macrophages was measured by: 1) oxygen consumption and extracellular acidification (via Seahorse), 2) cytoplasmic oxidation and 3) nitric oxide production following 4, 18, and 24 h of LPS stimulation.

Results: Concentration of ARA (% of fatty acids, w/w) in macrophages from pigs fed LC n-6 was 86% higher than CON and 18% lower in pigs fed LC n-3 (P < 0.01). Following LPS stimulation, abundance of COX-2 and TNF-α mRNA (P < 0.0001), and PGE₂ secretion (P < 0. 01) were higher in LC n-6 PAM vs. CON. However, ALOX5 abundance was 1.6-fold lower than CON. Macrophages from CON and LC n-6 groups were 4-fold higher in ALOX12/15 abundance (P < 0.0001) compared to LC n-3. Oxygen consumption and extracellular acidification rates increased over 4 h following LPS stimulation (P < 0.05) regardless of treatment. Similarly, increases in cytoplasmic oxidation (P < 0.001) and nitric oxide production (P < 0.002) were observed after 18 h of LPS stimulation but were unaffected by diet.

Conclusions: We infer that enriching diets with arachidonic acid may be an effective means to enhance a stronger innate immunologic response to respiratory challenges in neonatal pigs. However, further work is needed to examine long-term safety, clinical efficacy and economic viability.

Keywords: Arachidonic acid; Cyclooxygenase; Eicosanoid; Eicosapentaenoic acid; Inflammation; LPS; Lipid mediator class switch; Lipoxin; Porcine alveolar macrophage.