Tandem mass spectrometric characterization of bile acids and steroid conjugates based on low-energy collision-induced dissociation

Abstract

We examined the characteristics of several bile acids and some steroid conjugates under low-energy-collision-induced dissociation conditions using a triple quadrupole tandem mass spectrometer. According to conjugation types, we observed characteristic product ions and/or neutral losses in the product ion spectra. Amino acid conjugates afforded specific product ions. For example, glycine-conjugated metabolites routinely produced a product ion at m/z 74, and taurine-conjugated metabolites produced product ions at m/z 124, 107, and 80. When a strong peak appeared at m/z 97, the molecule contained a sulfate group. In contrast to amino acid conjugates, carbohydrate conjugates required a combination of product ions and neutral losses for identification. We could discriminate a glucoside from an acyl galactoside according to the presence or absence of a product ion at m/z 161 and a neutral loss of 180 Da. Discrimination among esters, aliphatic ethers, and phenolic ether types of glucuronides was based upon differences in the intensities of a product ion at m/z 175 and a neutral loss of 176 Da. Furthermore, N-acetylglucosamine conjugates showed a characteristic product ion at m/z 202 and a neutral loss of 203 Da, and the appearance of a product ion at m/z 202 revealed the existence of N-acetylglucosamine conjugated to an aliphatic hydroxyl group without a double bond in the immediate vicinity. Together, the data presented here will help to enable the identification of unknown conjugated cholesterol metabolites by using low-energy collision-induced dissociation.

Keywords: 3β-sulfo-7β-N-acetylglucosaminyl-5-cholen-24-oic acid; Bile acid conjugate; CA; CDCA; CID; DCA; ESI; GlcNAc; LC; LCA; Low-energy collision-induced dissociation; MS; MS/MS; N-acetylglucosamine; NPC; Neutral loss; Niemann–Pick disease type C1; Product ion; SNAG-Δ(5)-CA; SNAG-Δ(5)-CG; SNAG-Δ(5)-CT; Steroid conjugate; UDCA; chenodeoxycholic acid; cholic acid; collision-induced dissociation; deoxycholic acid; electrospray ionization; glycine-conjugated 3β-sulfo-7β-N-acetylglucosaminyl-5-cholen-24-oic acid; liquid chromatography; lithocholic acid; mass spectrometry; tandem mass spectrometry; taurine-conjugated 3β-sulfo-7β-N-acetylglucosaminyl-5-cholen-24-oic acid; ursodeoxycholic acid.