Intestinal absorption of sphingosine: new insights on generated ceramide species using stable isotope tracing in vitro

Dietary sphingomyelin (SM) has been reported to favorably modulate postprandial lipemia. Mechanisms underlying these beneficial effects on cardiovascular risk markers are not fully elucidated. Rodent studies showed that tritiated SM was hydrolyzed in the intestinal lumen into ceramides (Cer) and further to sphingosine (SPH) and fatty acids (FA) that were absorbed by the intestine. Our objective was to investigate the uptake and metabolism of SPH and/or tricosanoic acid (C23:0), the main FA of milk SM, as well as lipid secretion in Caco-2/TC7 cells cultured on semipermeable inserts. Mixed micelles (MM) consisting of different digested lipids and taurocholate were prepared without or with SPH, SPH and C23:0 (SPH+C23:0), or C23:0. Triglycerides (TG) were quantified in the basolateral medium, and sphingolipids were analyzed by tandem mass spectrometry. TG secretion increased 11-fold in all MM-incubated cells compared with lipid-free medium. Apical supply of SPH-enriched MM led to increased concentrations of total Cer in cells, and coaddition of C23:0 in SPH-enriched MM led to a preferential increase of C23:0 Cer and C23:0 SM. Complementary experiments using deuterated SPH demonstrated that SPH-d9 was partly converted to sphingosine-1-phosphate-d9, Cer-d9, and SM-d9 within cells incubated with SPH-enriched MM. A few Cer-d9 (2% of added SPH-d9) was recovered in the basolateral medium of (MM+SPH)-incubated cells, especially C23:0 Cer-d9 in (MM+SPH+C23:0)-enriched cells. In conclusion, present results indicate that MM enriched with (SPH+C23:0), such as found in postprandial micelles formed after milk SM ingestion, directly impacts sphingolipid endogenous metabolism in enterocytes, resulting in the secretion of TG-rich particles enriched with C23:0 Cer.