Palmitic acid feeding increases hepatic ceramide accumulation and modulates expression of genes responsible for ceramide synthesis in mid-lactation dairy cows

Abstract Text:

Circulating sphingolipid ceramides are associated with elevated NEFA availability and reduced insulin sensitivity in dairy cows transitioning from gestation to lactation. In monogastrics, palmitic acid (C16:0) can increase hepatic synthesis and lipoprotein secretion of ceramides, lipid mediators that inhibit insulin action in skeletal muscle. Increasing ceramide synthesis by feeding C16:0 may be a means to restore insulin resistance and enhance milk yield during mid-lactation. Therefore, our objective was to determine whether dietary C16:0 can augment liver and skeletal muscle ceramide concentrations in mid-lactation dairy cows. Twenty multiparous Holstein cows were enrolled in a study consisting of a 5 d covariate and 49 d treatment period. Cows were randomly assigned to a sorghum silage-based diet containing no supplemental fat (control; n =10; 138 ± 45DIM) or C16:0 at 4% of ration DM (PALM; 98% C16:0; n =10; 136 ±44 DIM). Blood was collected routinely, and liver and skeletal muscle tissue were biopsied at d 47 of treatment. Intravenous glucose tolerance tests (GTT) were performed at d -1, 21, and 49 relative to start of treatment. Tissue concentrations of sphingolipids were determined using liquid chromatography tandem mass spectrometry. Expression of ceramide synthesis genes was evaluated using real-time PCR. Data were analyzed under the generalized linear model. Pearson correlations were analyzed. The most abundant liver and muscle sphingolipids detected were C24:0-ceramide, C24:0-monohexosylceramide (GlcCer), and C16:0-lactosylceramide (LacCer). Relative to control, PALM increased C24:0-ceramide and total hepatic ceramide levels by 29 and 20% at wk 7, respectively (P <0.05), a response not observed in muscle. Similarly, PALM increased hepatic C22:0-, C22:1-, C24:1-, and C26:0-ceramide at wk 7. PALM increased C16:1- and C24:1-GlcCer in liver (P <0.05). Plasma total ceramide and C24:0-ceramide were positively associated with hepatic total ceramide and C24:0-ceramide (r =0.63 and 0.58, respectively; P <0.05). Hepatic total ceramide and C24:0-ceramide were positively associated with plasma NEFA (r =0.63 and 0.57, respectively; P <0.001) and negatively associated with NEFA disappearance during GTT (r =-0.57 and -0.65, respectively; P <0.001). Ceramide synthase-6 (CerS6) was the predominant hepatic CerS isoform followed by CerS2 and CerS5. Surprisingly, PALM decreased CerS2 and CerS5 mRNA, and sphingomyelinase mRNA by 35, 36, and 62%, respectively (P <0.05). We conclude that feeding mid-lactation dairy cows C16:0 can increase hepatic ceramide accumulation, and generate hepatic ceramide profiles that are similar to circulating ceramide. Our work also demonstrates a possible relationship between hepatic ceramide supply and adipose tissue insulin sensitivity. 

Keywords: ceramide, insulin resistance, lactation