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

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.

LC/ESI-MS/MS analysis of urinary 3β-sulfooxy-7β-N-acetylglucosaminyl-5-cholen-24-oic acid and its amides: new biomarkers for the detection of Niemann-Pick type C disease

We developed a sensitive, reliable, and accurate LC/ESI-MS/MS method for measurement of 3β-sulfooxy-7β-N-acetylglucosaminyl-5-cholen-24-oic acid and its glycine and taurine amides in urine. This atypical C24 bile acid has been reported previously to be present in the urine of patients with Niemann-Pick Type C (NPC) disease. In the method, targeted analytes are concentrated at the front edge of a trapping column, Shim-pack MAYI-C8, which permits elimination of contaminating molecules in the urinary matrix. The trapped analytes are then eluted, separated on a YMC-Pack Pro C18, and quantified with MS/MS using selected reaction monitoring. The method could detect (as amount injected) 2pg of nonamidated 3β-sulfooxy-7β-N-acetylglucosaminyl-5-cholen-24-oic acid, 2pg of its glycine-amide, and 0.6pg of its taurine-amide, and is linear up to 300pg. The method was then used to measure the three analytes in the urine of NPC patients (N=2), 3β-hydroxysteroid dehydrogenase deficiency patients (N=2), and healthy volunteers (N=8). Measurable concentrations of all three analytes were present in all subjects. The urinary concentration of the sum of all three analytes was four hundred times greater in the 3month NPC patient and 40times greater in the adult patient than that of healthy volunteers. The markedly elevated urinary concentration of 3β-sulfooxy-7β-N-acetylglucosaminyl-5-cholen-24-oic acid and its amides in NPC patients suggests that these compounds may be valuable biomarkers for detection of NPC disease.