Exhaled breath metabolites reveal postmenopausal gut-bone cross-talk and non-invasive markers for osteoporosis

Abstract

Menopause driven decline in estrogen exposes women to risk of osteoporosis. Detection of early onset and silent progression are keys to prevent fractures and associated burdens. In a discovery cohort of 120 postmenopausal women (aged: 49 – 90 years), we combined repeated quantitative pulse-echo ultrasonography of bone, assessment of grip strength and serum bone markers with mass-spectrometric analysis of exhaled metabolites to find breath volatile markers and quantitative cutoff levels for osteoporosis. Obtained markers and cutoffs were validated in an independent cohort of 49 age-matched women with 6 months apart seasonal follow-ups. Within the discovery cohort median concentrations (ppbV) of exhaled end-tidal dimethyl sulfide (DMS), allyl-methyl sulfide, butanethiol and butyric acid increased significantly (p≤0.005) by 45.24%, 42.83%, 38.29% and 33.66% in subjects (n=27) with bone density at high-risk of osteoporosis and fracture, when compared to subjects (n=62) with normal bone mineral density (BMD). Increased age and decreased grip strength were concomitant. All these changes were reproduced within the independent validation cohort including seasonal follow-ups. Exhaled metabolite expressions remained age independent in either cohort. Serum bone markers showed random expressions without any reproducibility. DMS exhalations even differed between patients with recent (<1 year), old and without fractures. Metabolite exhalations and BMDs were down-regulated during winter mirroring the regional climate change. ROC analysis in the discovery cohort yielded high classification accuracy (AUC=0.86) of DMS with a cutoff at 15.88 ppbV for osteoporosis, which predicted subjects at high-risk within the independent validation cohort with high (>91%) sensitivity and specificity during both follow-ups. Non-invasive analysis of exhaled DMS allowed more reliable classification of osteoporosis risk than conventional serum bone markers. We identified associations of exhaled organosulfur and short-chain fatty acid markers to bone metabolism in postmenopausal osteoporosis via a gut-bone axis.