Shotgun steroidomics

Besides hormonal steroid conjugates (Figure 2.7), bile alcohol and bile acid conjugates can also be analyzed by shotgun steroidomics. These metabolites are often elevated in abundance in plasma as a consequence of an inborn error of bile acid biosynthesis or as a consequence... 

Figure 2.6 Shotgun steroidomic analysis of infant plasma. Steroids were isolated from infant plasma by SPE on a Qg cartridge. Direct negative-ion ESI-MS analysis was performed on an LTQ Orbitrap XL (Thermo Fisher). Peaks which correspond to steroid sulphates are indicated. Steroid structures (see Figure 2.7) are postulated but have not been confirmed. (A) Androstane. (p) Pregnane, location of double bonds indicated by a superscript.

Even when adopting a targeted approach, the coverage of lipids in a specific class can still be restricted by the dominance of a few very abundant lipids. This may be the case for steroid analysis where cholesterol is often the most abundant steroid by two orders of magnitude. This problem can be minimized by subdivision of the steroid class according to hydropho-bicity where cholesterol and more hydrophobic steroids represent one class, and oxysterols (oxidized forms of cholesterol and its precursors) and less hydrophobic metabolites represent a second class [45]. This is an approach we adopted for the analysis of steroid sulphates and bile acid/ alcohol conjugates by shotgun steroidomics, and in our LC-ESl-MS/MS work on oxysterols and cholestenoic acids in brain [46,47], plasma [48], and cerebrospinal fluid (CSF) [49]. 

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