Capillary gas chromatography with chemical ionization negative ion mass spectrometry in the identification of odorous steroids formed in metabolic studies of the sulphates of androsterone, DHA and 5α-androst-16-en-3β-ol with human axillary bacterial isolates

Abstract

The products of metabolism of the sulphates (0.5 μmol/l) of androsterone, dehydroepiandrosterone (DHA) and 5α-androst-16-en-3β-ol have been investigated after incubation with 72 h cultures of human axillary bacterial isolates for 3 days at 37°C. The medium used, tryptone soya broth (TSB), contained yeast extract and Tween 80. The isolates used were Coryneform F1 (known previously to metabolize testosterone and to be involved in under-arm odour (UAO) production, i.e. UAO +ve), Coryneform F46 (inactive in both the testosterone metabolism and UAO tests, i.e. UAO −ve) and Staphylococcus hominis/epidermidis (IIR3). Control incubations of TSB alone, TSB plus each of the steroid sulphates and TSB plus each of the bacterial isolates were also set up. After termination of reactions and addition of internal standards, 5α-androstan-3β-ol and 5α-androstan-3-one (50 ng each), extracted and purified metabolites were subjected to combined gas chromatography-mass spectrometry with specific ion monitoring. Steroidal ketones were derivatized as their O-pentafluor-obenzyl oximes; steroidal alcohols (only androst-16-enols in this study) were derivatized as their tert-butyldimethylsilyl ethers. Analysis was achieved by negative ion chemical ionization mass spectrometry for the pentafluorobenzyl oximes at [M-20] − and electron impact positive ion mass spectrometry for the tert-butyldimethylsilyl ethers at [M-57] +. The incubation broth contained two compounds which had gas chromatographic and mass spectrometric properties identical to those of DHA and 4-androstenedione. It was not possible, therefore, to show unequivocally that DHA sulphate (DHAS) was converted microbially into DHA, although this is implied by the finding of small quantities of testosterone and 5α-dihydrotestosterone in incubations with F1. With androsterone S, no free androsterone was recorded and only very small (5 pg or less) amounts of testosterone. Two odorous steroids, androsta-4,16-dien-3-one and 5α-androst-2-en-17-one (Steroid I) were formed (mean quantities 40 and 45 pg, respectively). The sulphate of 5α-androst-16-en-3β-ol was metabolized with F1 into large quantities of the odorous steroids, 5α-androst-16-en-3-one and Steroid I. In addition, much smaller quantities of androsta-4,16-dien-3-one were formed. In contrast, incubations of DHAS with F46 resulted in no metabolites except, possibly, DHA, but the sulphate moiety of androsterone S was also cleaved to yield the free steroid together with large amounts of Steroid I. In incubations of DHAS and androsterone S with F1, no 16-unsaturated steroids were formed, although 5α-androst-16-en-3β-yl S was de-sulphated and the free steroid further metabolized. No evidence was obtained for androst-16-ene metabolism in incubations with F46. In incubations with S. hominis/epidermidis (IIR3), androsterone S was converted into androsterone and, in high yield, to Steroid I plus some 5α-androst-16-en-3-one. Both DHAS and androsterone S were converted into androst-16-enols. Sulphatase activity was also manifested when 5α-androst-16-en-3β-yl S was utilized as substrate with IIR3, large quantities of Steroid I and 5α-androst-16-en-3-one being formed, together with further metabolism of androst-16-enes. In view of the fact that both DHAS and androsterone S occur in apocrine sweat, the metabolism of these endogenous substrates by human axillary bacteria to several odorous steroids may have important implications in the context of human odour formation.