Partial synthesis of ganglioside and lysoganglioside lipoforms as internal standards for MS quantification.

Within recent years, ganglioside patterns have been increasingly analyzed by MS. However, internal standards for calibration are only available for gangliosides GM1, GM2, and GM3. For this reason, we prepared homologous internal standards bearing nonnatural fatty acids of the major mammalian brain gangliosides GM1, GD1a, GD1b, GT1b, and GQ1b, and of the tumor-associated gangliosides GM2 and GD2.

Ganglioside biochemistry.

Gangliosides are sialic acid-containing glycosphingolipids. They occur especially on the cellular surfaces of neuronal cells, where they form a complex pattern, but are also found in many other cell types. The paper provides a general overview on their structures, occurrence, and metabolism.

Lipidomics of glycosphingolipids.

Glycosphingolipids (GSLs) contain one or more sugars that are attached to a sphingolipid moiety, usually to a ceramide, but in rare cases also to a sphingoid base. A large structural heterogeneity results from differences in number, identity, linkage, and anomeric configuration of the carbohydrate residues, and also from structural differences within the hydrophobic part. GSLs form complex cell-type specific patterns, which change with the species, the cellular differentiation state, viral transformation, ontogenesis, and oncogenesis.

Mass spectrometric analysis of neutral sphingolipids: methods, applications, and limitations.

Sphingolipids represent an important class among lipids, especially when considering their vital roles in lipid metabolism. Thus, a variety of methods have been created to accomplish their analysis and the term "sphingolipidomics" has recently been coined to underline the motivation to enable a comprehensive analysis of all sphingolipid species including the acidic and the neutral ones. In this review, we summarize selected mainly biomedical based mass spectrometric approaches for the analysis of neutral sphingolipids regarding their advantages, applications and limitations.

A view on sphingolipids and disease.

Sphingolipid and glycosphingolipid levels and expression of sphingolipid metabolizing enzymes are altered in a variety of diseases or in response to drug treatment. Inherited defects of enzymes and other proteins required for the lysosomal degradation of these lipids lead to human sphingolipidoses. Also genetic defects that affect sphingolipid biosynthesis are known.

Dihydroceramide desaturase inhibition by a cyclopropanated dihydroceramide analog in cultured keratinocytes.

Most mammalian sphingolipids contain a 4,5-(E)-double bond. We report on the chemical synthesis of a dihydroceramide derivative that prevents the introduction of the double bond into sphingolipids. Minimal alteration of the parent structure by formally replacing the hydrogen atoms in the 5- and in the 6-position of the sphinganine backbone by a methylene group leads to an inhibitor of dihydroceramide desaturase in cultured cells.

Lysosomal degradation of membrane lipids.

The constitutive degradation of membrane components takes place in the acidic compartments of a cell, the endosomes and lysosomes. Sites of lipid degradation are intralysosomal membranes that are formed in endosomes, where the lipid composition is adjusted for degradation. Cholesterol is sorted out of the inner membranes, their content in bis(monoacylglycero)phosphate increases, and, most likely, sphingomyelin is degraded to ceramide.

Normal phase liquid chromatography coupled to quadrupole time of flight atmospheric pressure chemical ionization mass spectrometry for separation, detection and mass spectrometric profiling of neutral sphingolipids and cholesterol.

Many lipidomic approaches focus on investigating aspects of sphingolipid metabolism. Special emphasis is put on neutral sphingolipids and cholesterol and their interaction. Such an interest is attributed to the fact that those lipids are altered in a series of serious disorders including various sphingolipidoses.

Principles of lysosomal membrane degradation: Cellular topology and biochemistry of lysosomal lipid degradation.

Cellular membranes enter the lysosomal compartment by endocytosis, phagocytosis, or autophagy. Within the lysosomal compartment, membrane components of complex structure are degraded into their building blocks. These are able to leave the lysosome and can then be utilized for the resynthesis of complex molecules or can be further degraded.

Mycobacterial phenolic glycolipid inhibits phagosome maturation and subverts the pro-inflammatory cytokine response.

Inhibition of phagosome maturation is an important hallmark of mycobacterial pathogenesis. A variety of genomic, transcriptomic and proteomic approaches have been used to pin down the molecule responsible for this pathogenic principle. We in this study characterize a glycolipid of Mycobacterium marinum identified through a screen of mutants disabled in inhibiting phagosome maturation to be phenolphthiocerol diester (phenolic glycolipid, PGL).

Effect of ceramide N-acyl chain and polar headgroup structure on the properties of ordered lipid domains (lipid rafts).

Ceramides are sphingolipids that greatly stabilize ordered membrane domains (lipid rafts), and displace cholesterol from them. Ceramide-rich rafts have been implicated in diverse biological processes. Because ceramide analogues have been useful for probing the biological function of ceramide, and may have biomedical applications, it is important to characterize how ceramide structure affects membrane properties, including lipid raft stability and composition.

Separation and mass spectrometric characterization of covalently bound skin ceramides using LC/APCI-MS and Nano-ESI-MS/MS.

Ceramides covalently bound to keratinocytes are essential for the barrier function of the skin, which can be disturbed in diseases, such as psoriasis and atopic dermatitis. These ceramides of the classes omega-hydroxyacyl-sphingosine and omega-hydroxyacyl-6-hydroxysphingosine contain an omega-hydroxy fatty acid. For their separation and identification, a new analytical approach based on normal phase liquid chromatography coupled to atmospheric pressure chemical ionization mass spectrometry and tandem nano-electrospray mass spectrometry, respectively, is presented here.

Sphingolipid metabolism diseases.

Human diseases caused by alterations in the metabolism of sphingolipids or glycosphingolipids are mainly disorders of the degradation of these compounds. The sphingolipidoses are a group of monogenic inherited diseases caused by defects in the system of lysosomal sphingolipid degradation, with subsequent accumulation of non-degradable storage material in one or more organs. Most sphingolipidoses are associated with high mortality.

Dopaminergic modulation of semantic priming in healthy volunteers.

Background: Semantic priming is a function related to prefrontal cortical (PFC) networks and is lateralized. There is evidence that semantic priming underlies dopaminergic modulation. It is known that the D1-receptor is more abundant in prefrontal networks; however, until now there have been no studies investigating the selective modulation of semantic priming with dopamine agonists.

The enzyme-binding region of human GM2-activator protein.

The GM2-activator protein (GM2AP) is an essential cofactor for the lysosomal degradation of ganglioside GM2 by beta-hexosaminidase A (HexA). It mediates the interaction between the water-soluble exohydrolase and its membrane-embedded glycolipid substrate at the lipid-water interface. Functional deficiencies in this protein result in a fatal neurological storage disorder, the AB variant of GM2 gangliosidosis.

Principles of lysosomal membrane digestion: stimulation of sphingolipid degradation by sphingolipid activator proteins and anionic lysosomal lipids.

Sphingolipids and glycosphingolipids are membrane components of eukaryotic cell surfaces. Their constitutive degradation takes place on the surface of intra-endosomal and intra-lysosomal membrane structures. During endocytosis, these intra-lysosomal membranes are formed and prepared for digestion by a lipid-sorting process during which their cholesterol content decreases and the concentration of the negatively charged bis(monoacylglycero)phosphate (BMP)--erroneously also called lysobisphosphatidic acid (LBPA)--increases.

Differential dopaminergic modulation of executive control in healthy subjects.

Rationale: Executive control (EC) has different subcomponents, e.g., response inhibition (measured, for example, by the Stroop task) and working memory (WM-measured, for example, by delayed response tasks, DRT).

Site-specific cleavage--a model system for the identification of lipid-modified glutamate residues in proteins.

Numerous proteins are modified post-translationally after their biosynthesis at the ribosomes of the cell. One such modification, only poorly characterized to date, is the formation of lipid esters of glutamate side chains in the skin proteins of land-living mammals; here a subset of very long chain fatty acids, ceramides and/or glucosylceramides, are bound through their omega-hydroxy groups to structural proteins of the so-called "cornified envelope" in the outermost layer of the skin, the stratum corneum. We report an approach for the identification of proteins containing ester-modified glutamic acid residues and the determination of their positions within the peptide sequence, designed for mass spectrometric investigation of human skin proteins.

Photoaffinity labelling of the human GM2-activator protein. Mechanistic insight into ganglioside GM2 degradation.

The GM2-activator protein (GM2AP) is an essential cofactor for the degradation of ganglioside GM2 by lysosomal beta-hexosaminidase A. It mediates the interaction between the water-soluble exohydrolase and its membrane-bound substrate at the lipid-water interphase. Inherited defects in the gene encoding this glycoprotein result in a fatal neurological storage disorder, the AB variant of GM2-gangliosidosis.