Metabolism of bolasterone by LC-MS/MS and GC-MS/MS

Abstract

Bolasterone (7α,17α-dimethyltestosterone) is an anabolic steroid, is often illegally used in different kinds of sports disciplines. This study aims to investigate phase I and II metabolites of bolasterone (MW 316) through both in-vitro (rat liver microsome) and in-vivo (urine after oral administration to rats) experiments. The metabolites were identified by UHPLC-Q-Exactive Orbitrap MS and GC-MS/MS. Several metabolites (mono- and di-hydroxylated, reduced, and glucuronic conjugated form) have been identified and characterized based on their retention times in chromatograms and characteristic ionization from full MS and MS/MS spectra. For the LC-MS/MS analysis, full scan and dd-MS/MS modes were used to elucidate more detailed structural information for the metabolites. A total of 16 metabolites were identified. In-vitro were found 6 mono-hydroxylated (M8-M13 as m/z 333 of [M+H]+), 5 di-hydroxylated (M1, M5-M7, M14 as m/z 493 of [M+H]+), along with 1 from reduction (M15, as m/z 285 of [M+H-2H2O]+), and 1 glucuronide-conjugated metabolite (M16, as m/z 493 of [M+H]+). In-vivo, a total of 8 di-hydroxylated metabolites (M1-M7, M14 as m/z 349 of [M+H]+) were found. The plausible structures are tentatively identified as follows: mono-hydroxylation was observed in the A ring (M12), B ring (M8), and D ring (M9, M10, and M11). Reduced metabolite at 3-keto and Δ4 position (M15) was confirmed with authentic standard, and conjugated metabolite with glucuronic acid at D ring (M16) was observed. For the GC-MS/MS analysis, a full scan mode followed by product ion scan mode was used. By this method, a total of 4 in-vitro and 11 in-vivo metabolites were found by using GC-MS/MS. These are 3 mono-hydroxylated (m1-m3 as M+ 548), 7 di-hydroxylated (m4-m10 as M+ 636), and 2 di-hydroxylated and 1 dehydrogenation metabolites (m11, m12). Further investigation under the GC-MS/MS is still ongoing. These results showed that hydroxylation was the major biotransformation of bolasterone. The hydroxylation was not specified due to the mass spectra only and the lack of specific reference standards. These metabolites could be useful as potential new biomarkers for the detection of bolasterone abuse in athlets.