Preferential Partitioning of Rumen-Protected n-3 and n-6 Fatty Acids into Functionally Different Adipose Tissues

Long-term effects of abomasal infusion of linoleic and linolenic acids on the enrichment of n-6 and n-3 fatty acids into plasma lipid fractions of lactating cows

Our objective was to compare abomasal infusions of linoleic (18:2n-6) and α-linolenic (18:3n-3) acids on the enrichment of n-6 and n-3 fatty acids (FA) into the plasma lipid fractions of lactating dairy cows and evaluate their potential carryover effects in plasma lipid fractions post-infusion. Six rumen-cannulated multiparous Holstein cows (252 ± 33 d in milk) were fed the same diet and assigned to 1 of 2 treatments in a completely randomized design with repeated measures. Treatments were abomasal infusions (67 g/d total FA) of 1) n-6 FA blend (N6) to provide approximately 43 g/d 18:2n-6 and 8 g/d of 18:3n-3; or 2) n-3 FA blend (N3) providing 43 g/d 18:3n-3 and 8 g/d 18:2n-6. Treatments were dissolved in ethanol, and the daily dose for each treatment was divided into 4 equal infusions, occurring every 6 h. The treatment period lasted from d 1 to 20, and the carryover period lasted from d 21 to 40. Results are presented as FA contents within each of the 4 main plasma lipid fractions: cholesterol esters (CE), phospholipids (PL); triglycerides (TG), and plasma nonesterified fatty acids. Concentrations of individual lipid fractions in plasma were not quantified. Plasma CE and PL had the highest content of polyunsaturated FA (PUFA) during both the treatment and carryover periods. In plasma PL, N3 increased the contents of total n-3 FA (134%), 18:3n-3 (267%), and eicosapentaenoic acid (96.3%, 20:5n-3), and decreased total n-6 FA (8.14%) and 18:2n-6 (8.16%) from d 4 to 20 compared with N6. In plasma CE, N3 increased the contents of total n-3 FA (191%) from d 4 to 20, 18:3n-3 from d 2 to 20 (178%), and 20:5n-3 from d 6 to 20 (59.9%), while N3 decreased total n-6 FA from d 4 to 20 (11.2%) and 18:2n-6 from d 2 to 20 (10.5%) compared with N6. In addition, compared with N6, N3 decreased arachidonic acid (20:4n-6) at d 2 (45%) and from d 10 to 20 (14.7%) in PL and tended to decrease 20:4n-6 without interacting with time for CE. Phospholipids were the only lipid fraction with detectable levels of docosahexaenoic acid (22:3n-6) in all samples, but we did not observe differences between treatments. In plasma TG, N3 increased the contents of total n-3 FA (135%) and 18:3n-3 (146%) from d 4 to 20, increased 20:5n-3 from d 12 to 20 (89%), decreased or tended to decrease total n-6 FA content from d 6 and 8 (26.9%), and tended to decrease 18:2n-6 at d 8 compared with N6. A similar pattern was observed for plasma nonesterified fatty acids. We observed positive carryover effects for both N3 and N6 at different degrees in all lipid fractions, with N3 promoting more consistent outcomes and increasing total n-3 FA throughout the carryover period (from d 22 to 40) in both PL (52.8%) and CE (68.6%) compared with N6. It is important to emphasize that the higher magnitude responses observed for n-3 FA are also influenced by the content of n-3 FA being much lower than those of n-6 FA in all lipid fractions. While these data provide important and robust information, future research quantifying changes in concentrations of individual lipid fractions in plasma and the entry and exit rates of specific FA will further enhance our understanding. In conclusion, abomasally infusing N3 and N6 increased the contents of n-3 and n-6 FA, respectively, in all plasma lipid fractions. These responses were more evident in PL and CE. We also observed positive carryover effects in all lipid fractions, where N3 had more consistent outcomes than N6. Our results indicate that dairy cows have a robust mechanism to conserve essential FA, with a pronounced preference for n-3 FA.

The benefits of adipocyte metabolism in bone health and regeneration

Patients suffering from musculoskeletal diseases must cope with a diminished quality of life and an increased burden on medical expenses. The interaction of immune cells and mesenchymal stromal cells during bone regeneration is one of the key requirements for the restoration of skeletal integrity. While stromal cells of the osteo-chondral lineage support bone regeneration, an excessive accumulation of cells of the adipogenic lineage is thought to promote low-grade inflammation and impair bone regeneration. Increasing evidence indicates that pro-inflammatory signaling from adipocytes is responsible for various chronic musculoskeletal diseases. This review aims to summarize the features of bone marrow adipocytes by phenotype, function, secretory features, metabolic properties and their impact on bone formation. In detail, the master regulator of adipogenesis and prominent diabetes drug target, peroxisome proliferator-activated receptor γ (PPARG), will be debated as a potential therapeutic approach to enhance bone regeneration. We will explore the possibilities of using clinically established PPARG agonists, the thiazolidinediones (TZDs), as a treatment strategy to guide the induction of a pro-regenerative, metabolically active bone marrow adipose tissue. The impact of this PPARG induced bone marrow adipose tissue type on providing the necessary metabolites to sustain osteogenic-as well as beneficial immune cells during bone fracture healing will be highlighted.