Comparison of Lipid and Fatty Acid Composition of the Liver, Subcutaneous and Intra‐abdominal Adipose Tissue, and Serum

TLDR

Ceramides may mediate saturated fat–induced insulin resistance, but no data compare ceramide concentrations across human tissues. The study aimed to compare ceramide concentrations among human liver, subcutaneous and intra‑abdominal adipose tissue, and serum. The authors performed lipidomic analysis of these tissues and serum in eight subjects. The liver harbors markedly higher ceramide, sphingomyelin, phosphatidylethanolamine, and lysophosphatidylcholine levels, a greater proportion of saturated and long polyunsaturated fatty acids, and ceramide precursors and desaturase/elongase activities that correlate strongly with hepatic but not adipose tissue, indicating that the liver contains higher concentrations of ceramides and saturated free fatty acids than subcutaneous or intra‑abdominal adipose tissue.

Abstract

Ceramides may mediate saturated fat–induced insulin resistance, but there are no data comparing ceramide concentrations between human tissues. We therefore performed lipidomic analysis of human subcutaneous (SCfat) and intra‐abdominal (IAfat) adipose tissue, the liver, and serum in eight subjects. The liver contained (nmol/mg tissue) significantly more ceramides (1.5–3‐fold), sphingomyelins (7–8‐fold), phosphatidylethanolamines (10–11‐fold), lysophosphatidylcholines (7–12‐fold), less ether‐linked phosphatidylcholines (2–2.5‐fold) but similar amounts of diacylglycerols as compared to SCfat and IAfat. The amounts of ceramides and their synthetic precursors, such as palmitic (16:0) free fatty acids and sphingomyelins, differed considerably between the tissues. The liver contained proportionally more palmitic, stearic (18:0), and long polyunsaturated fatty acids than adipose tissues. Stearoyl‐CoA desaturase 1 (SCD1) activity reflected by serum, estimated from the 16:1/16:0‐ratio, was closely related to that in the liver ( r = 0.86, P = 0.024) but not adipose tissues. This was also true for estimated elongase (18:1/16:1, r = 0.89, P = 0.01), and Δ5 (20:4/20:3, r = 0.89, P = 0.012) and Δ6 (18:3[ n ‐6]/18:2, r = 1.0, P < 0.001) desaturase activities. We conclude that the human liver contains higher concentrations of ceramides and saturated free fatty acids than either SCfat or IAfat.