Ceramide structure of sphingomyelin from human milk fat globule membrane

Total Fatty Acid and Polar Lipid Species Composition of Human Milk

Human milk lipids are essential for infant health. However, little is known about the relationship between total milk fatty acid (FA) composition and polar lipid species composition. Therefore, we aimed to characterize the relationship between the FA and polar lipid species composition in human milk, with a focus on differences between milk with higher or lower milk fat content. From the Norwegian Human Milk Study (HUMIS, 2002–2009), a subset of 664 milk samples were analyzed for FA and polar lipid composition. Milk samples did not differ in major FA, phosphatidylcholine, or sphingomyelin species percentages between the highest and lowest quartiles of total FA concentration. However, milk in the highest FA quartile had a lower phospholipid-to-total-FA ratio and a lower sphingomyelin-to-phosphatidylcholine ratio than the lowest quartile. The only FAs associated with total phosphatidylcholine or sphingomyelin were behenic and tridecanoic acids, respectively. Milk FA and phosphatidylcholine and sphingomyelin species containing these FAs showed modest correlations. Associations of arachidonic and docosahexaenoic acids with percentages of phosphatidylcholine species carrying these FAs support the conclusion that the availability of these FAs limits the synthesis of phospholipid species containing them.

Invited review: Sphingolipid biology in the dairy cow: The emerging role of ceramide

The physiological control of lactation through coordinated adaptations is of fundamental importance for mammalian neonatal life. The putative actions of reduced insulin sensitivity and responsiveness and enhanced adipose tissue lipolysis spare glucose for the mammary synthesis of milk. However, severe insulin antagonism and body fat mobilization may jeopardize hepatic health and lactation in dairy cattle. Interestingly, lipolysis- and dietary-derived fatty acids may impair insulin sensitivity in cows. The mechanisms are undefined yet have major implications for the development of postpartum fatty liver disease. In nonruminants, the sphingolipid ceramide is a potent mediator of saturated fat-induced insulin resistance that defines in part the mechanisms of type 2 diabetes mellitus and nonalcoholic fatty liver disease. In ruminants including the lactating dairy cow, the functions of ceramide had remained virtually undescribed. Through a series of hypothesis-centered studies, ceramide has emerged as a potential antagonist of insulin-stimulated glucose utilization by adipose and skeletal muscle tissues in dairy cattle. Importantly, bovine data suggest that the ability of ceramide to inhibit insulin action likely depends on the lipolysis-dependent hepatic synthesis and secretion of ceramide during early lactation. Although these mechanisms appear to fade as lactation advances beyond peak milk production, early evidence suggests that palmitic acid feeding is a means to augment ceramide supply. Herein, we review a body of work that focuses on sphingolipid biology and the role of ceramide in the dairy cow within the framework of hepatic and fatty acid metabolism, insulin function, and lactation. The potential involvement of ceramide within the endocrine control of lactation is also considered.

Biochemical studies on sphingolipid of Artemia franciscana (I) isolation and characterization of sphingomyelin

Sphingomyelin was isolated from cysts of the brine shrimp Artemia franciscana using QAE-Sephadex A25, Florisil and Iatrobeads column chromatographies. The chemical structure was identified using thin-layer chromatography, gas-liquid chromatography, infrared spectroscopy and matrix-assisted laser desorption ionization time-of-flight mass spectrometry. The ceramide moiety of sphingomyelin consisted of stearic, arachidic, and behenic acids as fatty acids, and hexadeca-4- and heptadeca-4-sphingenines as sphingoids. By comparative analysis, the ceramide component of Artemia sphingomyelin appears unique in invertebrates and vertebrates. Biological functions of sphingomyelin have largely been investigated using mammalian-derived sphingomyelin. In mammals, a wide variety of molecular species of sphingomyelins have been reported, especially derived from nerve tissue, while the lower animal Artemia contains this unusual sphingomyelin perhaps because of having a much simpler nervous system. The purified unusual sphingomyelin derived from Artemia franciscana might be a very useful tool in elucidating the functions and mechanisms of action of this mediator.

Chemical and enzymatic transacylation of amide-linked FA of buttermilk gangliosides

The goal of this work was to alter the composition of amide-linked FA of bovine buttermilk gangliosides, particularly the disialoganglioside GD3, to adjust lipid sources to special food specifications and pharmacological or cosmetic applications. The chemical transacylation of amide-linked FA of buttermilk gangliosides with free arachidic acid (20:0) by a combination of basic hydrolysis and diethylphosphorylcyanide/triethylamine-catalyzed reacylation was compared to an enzymatic sphingolipid ceramide N-deacylase (EC 3.5.1.23)-catalyzed FA exchange by GC analysis and nano electrospray ionization-MS. The buttermilk predominantly contained the disialoganglioside GD3 and the monosialoganglioside GM3. The heterogeneity of FA that are incorporated into gangliosides, mainly palmitic acid (29.4 wt%), stearic acid (16.9 wt%), oleic acid (17.8 wt%), and myristic acid (8.5 wt%), was effectively altered by both transesterification techniques. Arachidic acid, which was not integrated into the initial buttermilk gangliosides, was transacylated to total gangliosides with 23.2 wt% (GD3, 6.7 wt%) by the chemical process and with 8.7 wt% (GD3, 13.8 wt%) when catalyzed enzymatically. Mainly behenic acid and lignoceric acid of GD3 were exchanged chemically, and stearic acid was exchanged by the enzymatic process. This observation might depend on hydrolytic sensitivities of amide-linked very long chain saturated FA or specific enzyme subtrate affinities, respectively. Results of chemical hydrolysis indicated there was a risk of sialic acid decomposition and unspecific degradations. Regarding specificity and avoidance of critical agents, the enzymatic transesterification is recommended for industrial-scale production of consumer goods.

Lipids in human milk

I have reviewed recent (March 1995-December 1997) papers on human milk lipids including many on fatty acid (FA) composition. The effects of maternal diets on the profiles are apparent. However, more data on the composition of milk lipids are needed. It is noteworthy that so few papers on milk FA composition have reported analyses using high-resolution gas-liquid chromatography columns. Two of these were on milk from women in North America. The diets in North America are varied and the number of analyses few. We do not have a reliable data base showing the ranges of biologically important acids. Except for the gangliosides, few new data on the other lipids appeared during this period.

The lipids in human milk

The summary will be limited to the areas that should be intensively investigated. The first is: determination of fatty acid profiles using modern methods on a world wide basis. We have no more than five or six papers in which my criterion was applied, one from Canada and the remainder from Europe with some data from Africa. Obviously, milk cannot be used as the gold standard on this meager data base. The second area is analysis of TG structure. These analyses are difficult, but structure is one of the factors controlling digestion. Data on the effects of maternal diet on structure would be useful. The third area is the role of primary or derived milk lipids as microbicidal agents. The fourth area is examination of globule parameters, i.e. number, size, volume, surface, and how they are affected by diet. There are many others which may interest the reader.

A method for separation and quantification of phospholipid classes in human milk

A simple, isocratic method for separating the major phospholipid classes of human milk by HPLC is described. Resolution of phosphatidylinositol, phosphatidylserine, phosphatidylethanolamine, lysophosphatidylethanolamine, phosphatidylcholine, and spingomyelin from human milk phospholipids was achieved in 30 min on a silica column. Total phospholipids were injected in 50 microliter of chloroform:diethyl ether (1:2, vol/vol) and eluted with a solvent mixture of acetonitrile:methanol:sulfuric acid (100:3:.05, vol/vol/vol) at a flow rate of 2.5 ml/min. Fractions were collected and each phospholipid class quantified by analysis of inorganic phosphorus after sulfuric acid digestion. A repeatability study with 19 samples had a coefficient of variation of 5.3%. The analytical recoveries of phospholipid standards averaged 98%. Recoveries varied with phospholipid class; variation was greatest with spingomyelin.

Fatty acid composition of polar lipids in goats' milk

Silicic acid column chromatography was used to separate the polar lipids of goats' milk into glycolipid, phosphatidylethanolamine, phosphatidylserine plus phosphatidylinositol, phosphatidylcholine, and sphingomyelin fractions. Each fraction was purified by column chromatography and its fatty acid profile determined by gas liquid chromatography and mass spectrometry. The glycerophospholipids each contained 18:1 as the predominant fatty acid (approximately 45%). The sphingolipids contained a high percentage of long-chain saturated fatty acids (C22 to C24 greater than 45%); the glycolipid fraction also contained ca. 2% 2-hydroxy fatty acids. The data represent a comprehensive cross-sectional study of the major polar lipids found in goats' milks.