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Sphingomyelin

About the structure and biological function of SM

Sphingomyelins are a type of phosphosphingolipids, a class of sphingolipids. Their structure consists of a ceramide base bound to a phosphorylcholine molecule. The ceramide base contains two hydrocarbon chains, the long-chain base and a fatty acid. Sphingomyelins are found in all animal cells, blood plasma, and some protozoa. On a subcellular level, they are enriched in the cell membrane and in the nucleus membrane.

Sphingomyelins play a key role in the cell membrane of animals. They are vital to the formation of lipid rafts and required for the activity of some membrane proteins such as some ion channels. In the nucleus, sphingomyelins are involved in assembly and dynamics of chromatin, the material chromosomes are made of. They also serve as precursors for sphingolipids in the ‘sphingomyelin cycle’. Further, sphingomyelin metabolism aberrations have been linked to Alzheimer’s and cardiovascular disease.

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Cholesteryl esters

About the structure and biological function of CE

Cholesteryl esters are a type of sterol lipids. Their structure consists of cholesterol where an ester bond is formed between the hydroxyl group of the steroid structure and a fatty acid. The fatty acid can be of variable length, hydroxylated, and contain double bonds. Cholesteryl esters are mainly found in animal blood plasma and cells. On a subcellular level, they are enriched in cellular lipid droplets.

Cholesteryl esters function as transport form of cholesterol in blood plasma and as storage to buffer an excess of cholesterol. They also serve as pool for cholesterol, for example for hormone synthesis in the adrenal glands, but also for free fatty acids. Cholesteryl esters accumulate in fatty lesions of atherosclerotic plaques. Further, cholersterol is inefficienlty converted to cholesteryl esters in the blood of cardiovascular disease patients.

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Cholesterol

About the structure and biological function of Chol

Cholesterol is a type of sterol lipid. Its structure consists of four linked hydrocarbon rings, the steroid structure. A hydrocarbon tail is linked to one end of the steroid, a hydroxyl group linked to the other end. It contains no fatty acids. Cholesterol is the major sterol lipid in animals and can be found in cells and body fluids like blood. On a subcellular level, it is enriched in the cell membrane and in lipid rafts.

Cholesterol has a vital function in animals. It is an essential component of cell membranes and lipid rafts, involved in lipid digestion, and a precursor of steroid hormones and other metabolites such as vitamin D or bile acids. Cholesterol also is important for cell signalling, transport processes, and regulation of gene readout, and an abundant constituent of the water permeability barrier in skin and of myelin in the brain. Further, excess cholesterol is linked to cardiovascular disease.

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Ether-linked phosphatidylethanolamine

About the structure and biological function of PE O-

Ether-linked phosphatidylethanolamine (PE O-) are a type of glycerophosphoethanolamines, a class of glycerophospholipids. Their structure consists of a glycerol backbone linked to two fatty acids and a phosphoethanolamine molecule. One of the fatty acids is bound to the glycerol backbone via an ether bond. PE O- lipids are found in animals and microbes. On a subcellular level, they are enriched in the cell membrane and lipid droplets.

Ether-linked phosphatidylethanolamines contain high amounts of arachidonic acid required for the biosynthesis of eicosanoids, bioactive lipids with a great role in inflammation. Levels of PE O- lipids are reduced in the blood of the chronic inflammatory condition multiple sclerosis. That said, elevated levels have been found in cancers, especially in aggressive forms. Further, PE O- lipids are important membrane constituents of neutrophils, the most abundant type of white blood cells in humans.

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Ether-linked phosphatidylcholine

About the structure and biological function of PC O-

Ether-linked phosphatidylcholines (PC O-) are a type of glycerophosphocholines, a class of glycerophospholipids. Their structure consists of a glycerol backbone linked to two fatty acids and a phosphocholine molecule. One of the fatty acids is bound to the glycerol backbone via an ether bond. PC O- lipids are found in animals and microbes. On a subcellular level, they are enriched in the cell membrane and lipid droplets.

Ether-linked phosphatidylcholines contain high amounts of arachidonic acid required for the biosynthesis of eicosanoids, bioactive lipids with a great role in inflammation. Levels of PC O- lipids are reduced in the blood of the chronic inflammatory condition multiple sclerosis. On the other hand, elevated levels have been found in cancers, especially in aggressive forms. Further, they are precursors to platelet activating factor.

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Lyso-phosphatidylethanolamine

About the structure and biological function of LPE

Lyso-phosphatidylethanolamines (LPE) are a type of glycerophosphoethanolamines, a class of glycerophospholipids. Their structure consists of a glycerol backbone linked to a fatty acid and a phosphoethanolamine molecule. The fatty acid can be of variable length, hydroxylated, and contain double bonds. LPE lipids are found in all organisms. On a subcellular level, they are enriched in animal blood plasma and in biological membranes of plants and bacteria.

Lyso-phosphatidylethanolamines are involved in cellular processes such as differentiation and migration of certain neuronal cells, but also of various cancer cells. In plants, LPEs function as inhibitors for a key enzyme in membrane lipid degradation, thus retarding senescence of leaves, flowers, and fruits. They are used commercially to stimulate ripening and extend shelf-life of fruit, and increase vase life of cut flowers. Further, LPE lipids serve as precursors for phosphatidylethanolamines.

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Lyso-phosphatidylcholine

About the structure and biological function of LPC

Lyso-phosphatidylcholines (LPC) are a type of glycerophosphocholines, a class of glycerophospholipids. Their structure consists of a glycerol backbone linked to a fatty acid and a phosphocholine molecule. The fatty acid can be of variable length, hydroxylated, and contain double bonds. LPC lipids are mainly found in animal blood plasma. On a subcellular level, they are enriched in lipoprotein particles.

Lyso-phosphatidylcholines are potent signaling molecules and they habe many functions related to inflammation and the immune system. They are suggested an important factor for neurodegeneration such as cognitive decline and dementia, and promote demyelination of neurons. Impaired levels of LPCs are also linked to cardiovascular disease and cancers. They have some functions in cell signaling. Further, LPC lipids have beneficial effects on the innate immune system as they can activate macrophages.

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Ceramide

About the structure and biological function of Cer

Ceramides are a type of sphingolipids. Their structure consists of a long-chain base, the sphingoid base, linked to a fatty acid via an amide bond. The fatty acid can be of variable length, hydroxylated, and contain double bonds. Ceramides are found in all organisms and each cell type but are elevated in skin tissue. On a subcellular level, they are enriched in cell membranes and in lipid rafts.

Ceramides are essential intermediates in the biosynthesis of all complex sphingolipids. Except for skin, ceramides are rapidly converted and present at trace amounts only, yet they serve important biological roles. They can form ceramide-rich lipid rafts within the cell membrane, and have a vital function in cellular signaling related to apoptosis, cell differentiation, and proliferation. Further, ceramides are linked to metabolic diseases, cancer, neurodegeneration, and cardiovascular disease.

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Phosphatidylinositol

About the structure and biological function of PI

Phosphatidylinositols are a type of glycerophosphoinositols, a class of glycerophospholipids. Their structure consists of a glycerol backbone linked to two fatty acids and a phosphoinositol molecule. The fatty acids can be of variable length, hydroxylated, and contain double bonds. Phosphatidylinositols are mainly found in eukaryotic cells but elevated in animal brain tissue. On a subcellular level, they are enriched in biological membranes.

Phosphatidylinositols are key membrane components and vital to many cellular processes. They are the major source for arachidonic acid for the synthesis of eicosanoids, bioactive lipids with signaling functions in allergy, inflammation, childbirth, pain perception, cell growth, blood pressure, and more. Further, phosphatidylinositols are the precursors to polyphosphoinositides with further signaling and other functional activities. Phosphatidylinositols are a focus for human health research.

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Phosphatidylethanolamine

About the structure and biological function of PE

Phosphatidylethanolamines are a type of glycerophosphoethanolamines, a class of glycerophospholipids. Their structure consists of a glycerol backbone linked to two fatty acids and a phosphoethanolamine molecule. The fatty acids can be of variable length, hydroxylated, and contain double bonds. Phosphatidylethanolamines are found in all organisms and each cell type. On a subcellular level, they are enriched in biological membranes.

Phosphatidylethanolamines serve as key building blocks for biological membranes. They are a functional component of membrane contact sites between endoplasmic reticulum and mitochondria, and vital for mitochondria functionality in general. Phosphatidylethanolamines interact with a wide range of proteins, thus influencing biological processes such as neuronal development or signaling pathways. Further, phosphatidylethanolamines are linked to plant embryo viability and plant pathogen resistance.

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