A review of lipidomic technologies applicable to sphingolipidomics and their relevant applications

Abstract

Sphingolipidomics, a branch of lipidomics, focuses on the large-scale study of the cellular sphingolipidomes. In the current review, two main approaches for the analysis of cellular sphingolipidomes (i.e. LC-MS- or LC-MS/MS-based approach and shotgun lipidomics-based approach) are briefly discussed. Their advantages, some considerations of these methods, and recent applications of these approaches are summarized. It is the authors' sincere hope that this review article will add to the readers understanding of the advantages and limitations of each developed method for the analysis of a cellular sphingolipidome.

Figure 1

General structure of sphingoid-based lipids. The building block B1 represents a different polar moiety (linked to the oxygen at the C1 position of the sphingoid base). The building block B2 represents fatty acyl chains (acylated to the primary amine at the C2 position of the sphingoid base) with or without the presence of a hydroxyl group which is usually located at the α- or ω-position. The building block B3 represents the aliphatic chains in all of the possible sphingoid bases, which are carbon-carbon linked to the C3 position of sphingoid bases and vary with the aliphatic chain length, degree of unsaturation, the presence of branches, and the presence of an additional hydroxyl group. This illustration has been modified from ref. [11] with permission.

Figure 2

A simplified network of the common sphingolipid classes and other related lipids in the mammalian sphingolipidome. The sphingolipid classes with frames are those that can be quantitatively analyzed by shotgun (sphingo)lipidomics at its current stage.

Figure 3

A schematic illustration of sample preparation for shotgun sphingolipidomics (adapted from ref. [26] with permission).

Figure 4

Shotgun lipidomics analyses of sphingolipid molecular species before and after treatment of a mouse cortex lipid extract with lithium methoxide in the positive-ion mode in the presence of a small amount of LiOH. The mass spectra (A) and (B) were acquired directly from a lipid extract of mouse cortex before and after treatment with lithium methoxide, respectively, as illustrated in Fig. 3. IS denotes internal standard. Both spectra are displayed after being normalized to the base peak in each spectrum.

Figure 5

Shotgun lipidomics analyses of sphingolipid molecular species before and after treatment of a mouse cortex lipid extract with lithium methoxide in the NL mode in the presence of a small amount of LiOH. The mass spectra in (A) and (B) were acquired by using the NL scanning of 183.1 u (i.e. phosphocholine) from the lipid extract of mouse cortex before and after treatment with lithium methoxide, respectively, as illustrated in Fig. 3. IS denotes internal standard. The ion peaks in (B) represent lithiated CerPCho molecular species. Both spectra are displayed after being normalized to the base peak in each spectrum.

Figure 6

Shotgun lipidomics analyses of sulfatide molecular species before and after treatment of a mouse cortex lipid extract with lithium methoxide in the negative-ion mode. The mass spectra in (A) and (B) were acquired directly from a lipid extract of mouse cortex before and after treatment with lithium methoxide, respectively, as illustrated in Fig. 3, by using a nanomate device. IS denotes internal standard. Both mass spectra are displayed after being normalized to the base peak in each spectrum.

Figure 7

Two-dimensional mass spectrometric analyses of ceramide molecular species from a lipid extract of human brain temporal cerebellar white matter in a shotgun sphingolipidomics approach. The lipid sample from human temporal white matter for shotgun sphingolipidomics was prepared as illustrated in Fig. 3 in the presence of 1 nmol C17:1 ceramide/mg protein. A conventional ESI mass spectrum in the negative-ion mode was acquired prior to analysis of the building blocks of ceramide molecular species by NL scanning. These building blocks of ceramide molecular species include sphingoid bases of sphingosine (NL 256.2 and NL 327.3), sphinganine (NL 258.2 and NL 329.3), and C20-sphingoid base (NL 284.3 and NL 355.3) with or without the presence of a hydroxyl group in the fatty amide chains as previously described [74]. IS denotes internal standard. All mass spectra are displayed after normalization to the base peak in each individual spectrum.