Endocrine and metabolic determinants of cardiometabolic risk in mild autonomous cortisol secretion

Background: Benign adrenal tumours, found in 1–7% of adults, can be non-functioning (NFAT) or show mild autonomous cortisol secretion (MACS), i.e., biochemical cortisol excess without manifestations of Cushing's syndrome (CS). MACS occurs in 20–50% of cases and is linked to increased cardiometabolic burden. Methods: In a cross-sectional study, we analysed the 24-h urinary steroid metabolome of 1305 prospectively recruited patients (649 NFAT, 591 MACS, 65 adrenal CS) by tandem mass spectrometry. A sub-group (104 NFAT, 140 MACS, 47 adrenal CS) underwent untargeted serum metabolome analysis by mass spectrometry. Data were analysed using linear regression and supervised machine learning. Findings: Alongside the expected increase in glucocorticoid excretion from NFAT over MACS to adrenal CS, steroid analysis revealed decreased classic androgen metabolite excretion. By contrast, adrenal-derived 11-oxygenated androgen metabolites remained unchanged. Both glucocorticoid metabolites and the major 11-oxygenated androgen metabolite 11β-hydroxyandrosterone correlated with a higher risk of hypertension and type 2 diabetes. Untargeted metabolome analysis revealed gradual changes towards a lipotoxic phenotype from NFAT over MACS to adrenal CS, with perturbations in glycerophospholipids, lysoglycerophospholipids, triacylglycerides, ceramides, sphingolipids, and acylcarnitines. Interpretation: MACS represents a metabolic continuum between NFAT and adrenal CS. Increased activity of the adrenal enzyme 11β-hydroxylase (CYP11B1), which catalyses key steps in cortisol and 11-oxygenated androgen biosynthesis, may contribute to steroid excess and cardiometabolic morbidity in MACS. These findings suggest that CYP11B1 may be a potential therapeutic target to ameliorate metabolic dysfunction in MACS. Funding: NIHR Birmingham Biomedical Research Centre; Diabetes UK; Wellcome Trust; European Commission; Medical Research Council.