Abstract
Dietary sphingomyelin (SM) is hydrolyzed by intestinal alkaline sphingomyelinase and neutral ceramidase to sphingosine, which is absorbed and converted to palmitic acid and acylated into chylomicron triglycerides (TGs). SM digestion is slow and is affected by luminal factors such as bile salt, cholesterol, and other lipids. In the gut, SM and its metabolites may influence TG hydrolysis, cholesterol absorption, lipoprotein formation, and mucosal growth. SM accounts for approximately 20% of the phospholipids in human plasma lipoproteins, of which two-thirds are in LDL and VLDL. It is secreted in chylomicrons and VLDL and transferred into HDL via the ABCA1 transporter. Plasma SM increases after periods of large lipid loads, during suckling, and in type II hypercholesterolemia, cholesterol-fed animals, and apolipoprotein E-deficient mice. SM is thus an important amphiphilic component when plasma lipoprotein pools expand in response to large lipid loads or metabolic abnormalities. It inhibits lipoprotein lipase and LCAT as well as the interaction of lipoproteins with receptors and counteracts LDL oxidation. The turnover of plasma SM is greater than can be accounted for by the turnover of LDL and HDL particles. Some SM must be degraded via receptor-mediated catabolism of chylomicron and VLDL remnants and by scavenger receptor class B type I receptor-mediated transfer into cells.
Highlights
Dietary sphingomyelin (SM) is hydrolyzed by intestinal alkaline sphingomyelinase and neutral ceramidase to sphingosine, which is absorbed and converted to palmitic acid and acylated into chylomicron triglycerides (TGs)
Supplementary key words chylomicron . very low density lipoprotein . low density lipoprotein . sphingomyelinase . ceramidase . phospholipid transfer protein increased in hypercholesterolemia and that SM-rich lipoproteins accumulate in arteriosclerotic lesions [3,4,5]
SM accounts for z2% of the phospholipids in human bile, which means that 100–200 mg is delivered to the gut Abbreviations: apoB, apolipoprotein B; BSSL, bile salt-stimulated lipase; CE, cholesteryl ester; CETP, cholesteryl ester transfer protein; ER, endoplasmic reticulum; IDL, intermediate density lipoprotein; LRP, low density lipoprotein receptor-related protein; PC, phosphatidylcholine; PE, phosphatidylethanolamine; PLTP, phospholipid transfer protein; SM, sphingomyelin; SMase, sphingomyelinase; SR-BI, scavenger receptor class B type I; TG, triglyceride
Summary
Dietary sphingomyelin (SM) is hydrolyzed by intestinal alkaline sphingomyelinase and neutral ceramidase to sphingosine, which is absorbed and converted to palmitic acid and acylated into chylomicron triglycerides (TGs). The proportion of apoA-I found in chylomicrons increases with lipid feeding, but the secretion in denser lipoproteins, including HDL, continues during fasting [93].
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