The Pharmacogenetics of Body Odor: As Easy as ABCC?

What determines human body odour?

Human body odour and earwax type are genetically dependent on a single-nucleotide polymorphism (SNP) located in the ABCC11 gene. So far, it still remains to be clear how SNP in the ABCC11 gene is associated with human malodour. In a recent issue of Experimental Dermatology, Baumann et al. propose one of the underlying molecular pathways. Although one of the amino acid conjugated of the odorants, Cys-Gly-3-methyl-3-sulfanylhexanol (3M3SH), was not taken up by the transporter ABCC11, glutathione conjugate of 3MSH (SG-3MSH) was transported by ABCC11. Moreover, SG-3MSH was processed to 3M3SH by γ-glutamyl-transferase 1 (GGT1), which was abundantly expressed in apocrine sweat glands. These findings may pave a way for the pharmacogenetics of human body odour and the development of innovative deodorant products.

Tomatoes cause under-arm odour

Under arm odour [axillary odour AO, bromidrosis] is a deeply unpleasant problem that can affect a person's self confidence and esteem and reduce social interaction. It is generally managed by good hygiene along with antiperspirants and deodorants, but the axillary apocrine glands may need surgical removal in severe cases of odour. The odour comes from microbial conversion of the apocrine secretions into short chain fatty acids like isovaleric acid and volatile sulphur compounds like 3-sulphanylhexan-1-ol. These can be detected at a few parts per billion to parts per trillion by the human nose so an unhygienic state is soon apparent. Recently genetics have been found to play an important role too as people with the AA variant of the ATP-binding cassette (ABC) transporter gene, ABCC11, do not secrete preodour substrates for bacterial conversion, while those with GA or GG variants do. Hygiene and genetics, are an incomplete explanation though, because the longitudinal ALSPAC study found that there is a mismatch between patients' secretory status, as determined by genetics, and their use of deodorants. This suggests that other metabolic pathways or compounds contribute to the odour. In this paper I propose that under arm odour is commonly caused by terpenes excreted via the axillary apocrine glands. I also show that these come from terpene and carotenoid-rich dietary sources including lycopene, tomatoes, orange peel and the glandular trichomes of tomato plants. These observations suggest that the axillary apocrine glands are a prominent excretory route for terpenes. Considering the quantities eaten, tomatoes are likely to be the main source of dietary terpenes, and under arm odour in turn. This study also shows that lycopene is probably metabolised by β-carotene 9 10 monooxygenase which cleaves β-carotene eccentrically at the 9 10 or 9'10' position of the chain. Direct evidence of lycopene metabolism by β-carotene 9 10 monooxygenase has hitherto been lacking. The study of terpene and carotenoid metabolism can be greatly advanced by analysing the content of axillary gland excretions.