A diet containing a nonfat dry milk matrix significantly alters systemic oxylipins and the endocannabinoid 2-arachidonoylglycerol (2-AG) in diet-induced obese mice

Abstract

Background: Diets rich in dairy and/or calcium (Ca) have been associated with reductions in adiposity and inflammation, but the mechanisms underlying this remain to be fully elucidated. Oxylipins and endocannabinoids are bioactive lipids, which influence energy homeostasis, adipose function, insulin signaling, and inflammation. Our objective was to determine if these metabolites associate with metabolic and inflammatory phenotypes stemming from dietary Ca and dairy in diet induced obese mice.

Methods: In one study, C57BL6/J mice were fed high fat diets (45% energy) with varying dietary matrices for 12 weeks: soy protein and Ca adequate (0.5%; CONTROL), soy protein and high Ca (1.5%; HighCa), or nonfat-dry-milk based high Ca (NFDM). In a second study, mice were pre-fattened for 12 weeks on the CONTROL high fat diet, and then fed one of three high fat diets for an additional 8 weeks: CONTROL, HighCa, or NFDM. In both studies, adiposity and associated metabolic and inflammatory outcomes were measured and a targeted lipidomics analysis was performed on plasma collected during the post-absorptive condition.

Results: As reported previously, mice fed NFDM had less body fat and reduced mRNA markers of adipose inflammation (p < 0.05) than CONTROL mice despite greater cumulative energy intake. Moreover, NFDM fed mice lipid mediator profiles were distinct from CONTROL and HighCa mice. NFDM fed mice showed elevated plasma monoacylglycerols (6 - 46% increase from CONTROL), including 2-arachidonoylglycerol (2-AG), and reduced fatty acid diols (8-75% decrease from CONTROL).

Conclusions: Differences in specific plasma lipid mediator profiles reflect the metabolic and inflammatory phenotypes seen in NFDM feeding.

Figure 1

Discriminant analysis clearly segregates dietary treatment groups in a mouse model of developing obesity (Cohort 1). A PLS-DA model using physiological measurements, 61 plasma lipid metabolites, and mRNA relative abundance in retroperitoneal adipose tissue (A-), liver (L-), and nodose ganglia (N-) illustrates differential distribution between DIO mice fed 0.5% calcium (Control; pink), 1.5% calcium (HighCa; yellow), or 1.5% calcium + nonfat dry milk (NFDM; green). A plots the latent variable 1 (LV1; X axis) and 2 (LV2; Y axis) scores for each mouse, while B plots the variable weights in these axes. Variables were grouped and color coded based on a hierarchical cluster analysis. Selected variables in clusters and lipid classes driving group segregation are labeled (for a complete list of variables, see Additional file 3: Tables S1 and S2). Plasma fatty acid diols cluster with Adiposity Index and 18 carbon acylethanolamides (green cluster) and are reduced in NFDM-fed mice relative to Control and HighCa fed mice, along LV1. Conversely, monoacylglycerols cluster with expression of soluble epoxide hydrolase and adipose triglyceride lipase in the liver, and are elevated in NFDM-fed mice. Body weight, adiposity index, energy intake, and mRNA abundance of retroperitoneal adipose tissue inflammatory markers (purple cluster) drive the separation of HighCa fed mice from NFDM mice and controls in LV2.

Figure 2

Discriminant analysis clearly segregates dietary treatment groups in a mouse model of pre-existing obesity (Cohort 2). In a pre-existing obesity mouse model (control DIO diet for 12 weeks), a PLS-DA model using 61 plasma lipid metabolites, physiologic measurements, and mRNA abundance in retroperitoneal adipose tissue (A-), liver (L-), and nodose ganglia (N-) illustrates differential distribution between dietary treatment groups. A plots the latent variable 1 (LV1; X axis) and 2 (LV2; Y axis) scores for each mouse fed 0.5% calcium (Control; pink) and 1.5% calcium (HighCa; yellow) or 1.5% calcium + nonfat dry milk (NFDM; green), while B plots the variable weights in these axes. Variables were grouped and color coded based on a hierarchical cluster analysis. Selected variables from clusters and lipid classes driving group segregation are labeled (for a complete list of variables, see Additional file 3: Tables S3 and S4). Plasma fatty acid diols cluster together (green cluster) and are reduced in NFDM-fed mice relative to Control and HighCa-fed mice. Conversely, monoacylglycerols cluster with a variety of adipose, liver and nodose ganglia gene expression levels (purple cluster), and are elevated in the NFDM-fed mice.