In part A of the study, women with PCOS and obesity, identified from the previously established DAISy-PCOS cohort, and age- and BMI-matched healthy volunteers identified by advertisements, will be invited for a screening visit (Visit 1) at the National Institute of Health Research-Wellcome Trust Clinical Research Facility at the Queen Elizabeth Hospital Birmingham. Once eligibility (described in detail in Section 7.1) has been confirmed, a written informed consent will be obtained, and the volunteers will be invited to three further metabolic assessment visits after an overnight fast.

While Visits 2 and 3 (Study days 1 and 2, respectively) will be for the assessment of responses to an androgen-precursor challenge, Visit 4 (Study day 3) will run in the same format as the previous two Study days except no androgen will be administered. During each visit, study participants will undergo abdominal adipose tissue vein cannulation, whereby a catheter will be inserted (under ultrasound guidance and with local anaesthetic) into one of the veins of the abdominal fat tissue. Ultrasound Doppler and ethanol dilution by microdialysis will be employed to assess adipose tissue blood flow. A further catheter will be inserted into a vein on the back of the hand which will be placed a hot air box in order to obtain arterialised blood. Finally, a catheter will be inserted into an antecubital vein for the purposes of stable isotope infusion. Blood samples from the hand vein and from the abdominal adipose tissue vein will be taken in tandem every 30 minutes for measurement of various metabolites, androgens, and non-targeted metabolome studies. Salivary samples will be collected every 30 minutes in the first hour and hourly thereafter until the end of the study. Urine will be collected throughout the Study Visit. At time point 240 min, a standardised high-fat meal containing palmitate labelled with a stable isotope will be given to the participant, and measurements will continue, to assess how their metabolism responds to the meal. Furthermore, fat tissue biopsies will be taken from the subcutaneous abdominal adipose tissue at the end of each study day. These fat biopsies will undergo RNA extraction for transcriptional profiling by RNA-sequencing and will be used for tissue incubation to determine their androgen-generating and metabolic capacity.

On Visits 2 and 3, participants will be administered either the classic androgen pathway precursor dehydroepiandrosterone or the 11-oxygenated androgen pathway precursor 11-ketoandrostenedione at time point 0 min. No androgen precursors will be administered during Visit 4. Otherwise, Visits 2-4 will be identical in their flow.

In part B of the study, paired subcutaneous and omental adipose tissue samples (up to 5 g), as well as a blood sample, are collected from female volunteers undergoing elective abdominal surgery. These tissue samples alongside the subcutaneous tissue obtained from the in vivo study (part A) will be used for ex vivo incubations with androgen precursors to study androgen activation and its metabolic impact. Additionally, the effect of Aldo-Keto Reductase Family 1 Member C3 inhibition on androgen activation will be assessed in ex vivo incubations. After the incubation, the culture medium and/or the tissue will be used for metabolome analysis (non-targeted global metabolome and steroid metabolome profiling) and transcriptome analysis. The blood sample will be used for serum multi-steroid profiling.