Effects of Blood Cholesterol Levels and Dietary Fatty Acids on Sphingolipid Profiles in Plasma, Liver and Adipose Tissue
Authors: Chang Chuchun Liz , Kim Benjamin , Deckelbaum Richard J. , Worgall Tilla S. 
Published: November 2023

Objectives

Sphingolipids are bioactive lipid compounds that are involved in many cellular pathways. Ceramides, in particular ceramide C16, have been implicated as mediators of metabolic syndrome including weight gain, glucose intolerance and susceptibility to diet‐induced metabolic dysfunction. Increased ceramide C24 has been associated with protection against high‐fat diet induced obesity and glucose intolerance. Elevated blood cholesterol is a risk factor for atherosclerosis. We have showed that replacement of saturated fats (SAT) by n‐3 fatty acids (n‐3 FAs) in high‐fat, high‐cholesterol diets reduced elevated plasma lipid levels and atherosclerosis in LDL receptor knock‐out (LDLR−/−) mice. Elevated plasma free FAs or high‐fat diets have been shown to increase ceramides associated with diabetes and cardiovascular disease. We questioned whether increased blood cholesterol affects sphingolipid profiles in blood and tissues and then evaluated the effects of SAT and n‐3 FA on modulating sphingolipid composition in both wild type (WT) and LDLR−/− mice.

Methods

C57BL/6 WT and LDLR−/− mice were fed a regular rodent chow diet or a custom‐made eucaloric high‐fat (40% of fat) diet enriched in either SAT or n‐3 FA for 12 weeks. Mouse plasma, hepatic and white adipose tissue (WAT) sphingolipid profiles were determined by liquid chromatography coupled to electrospray ionization triple quad tandem mass spectrometry (ESI LC‐MS/MS). Assayed molecular species and their relative location in the sphingolipid metabolic pathway are summarized in Figure.

Results

Compared to WT, LDLR deletion increased plasma dihydroceramides (DHs), C24 ceramides (p<0.0003) and sphingomyelins (SMs) (p<0.001), WAT DHs (p<0.0001) and WAT total ceramides (p<0.0002). LDLR deletion did not affect ceramide C16 levels in plasma, WAT or liver sphingolipid profiles. Comparison of high‐fat diets show that compared to SAT, n‐3 diet markedly decreased plasma total DHs (p<0.005), ceramides (C16, C20, C24, C24:1) (p<0.0002) in WT and LDLR−/−. n‐3 diet decreased total plasma SMs in WT (p<0.006) but increased total plasma SMs in LDLR−/−(p<0.018). In contrast to an overall decrease in plasma sphingolipids mediated by n‐3 FA in LDLR−/− mice, major ceramides (C16, C18, C20 and C22) were decreased in WAT in n‐3 fed LDLR−/− mice. n‐3 FA also reduced hepatic DHs and SMs in both WT (~ 2 fold, p<0.023) and LDLR−/−(~50%, p=0.056). Ratios of DH/ceramide C16 to C24/C24:1 were markedly improved by n‐3 FA feeding in liver and WAT in both WT and LDLR−/− mice. Our previously published data show that n‐3 FA did not affect plasma cholesterol in WT, but led to > 2/3 decrease in hypercholesterolemic LDLR−/− mice (p<0.05).

Conclusion

Our results demonstrate that LDLR deletion and diet content of n‐3 FA modulate plasma sphingolipid levels in blood and major tissue components. We suggest one mechanism whereby n‐3 FA ameliorating metabolic dysfunction is through changes in ratios of C16/C24 in tissues, such as liver or adipose tissue, that are important in pathways related to metabolic and cardiovascular diseases.