A comprehensive overview of the changes in IGF system peptides in the follicular fluid (FF) of women with Polycystic Ovarian Syndrome (PCOS) and their relationships with BMI and HMGB1

Background: PCOS is characterised by chronic low-grade inflammation, ovulatory dysfunction, hyperandrogenism, and insulin-resistance. The IGFsystem includes IGF-I, -II and seven IGFBPs, which regulate IGFbioavailability. Chronic inflammation modifies the IGF system that regulates ovarian function and glucose metabolism. HMGB1 is related with both inflammation and insulin sensitivity;we previously described increased HMGB1 FF in PCOS. This study aim ed to investigate the IGFsystem in PCOS. Methods: 70 women with PCOS [age: 34.1±4.7yr; BMI: 25.6±5.6 kg/m2] diagnosed following the Rotterdam criteria, and 70 healthy controls [age: 36.8±3.8yr; BMI: 24±5 kg/m2] were enrolled. Subjects were stratified based on BMI <25 (underweight/normal weight) or ≥25 (overweight/obese). Induction of follicular development for IVFwas conducted according to a long luteal GnRH agonist protocol. FF were collected during oocyte retrieval and centrifuged to remove red blood cells and debris. IGF-I, IGF-II, IGFBP-1-7, and HMGB1 were measured in FF using specific ELISAkits. The concentrations were converted to nM and bioactivity was calculated as ratios between IGFs and IGFBPs. Student’sT-test, ANOVA and Pearson’s correlation were used to analyze the data. Results: IGF-II (387.2±210.5 vs 495.7±157.9 ng/ml, P = 0.0007) and IGFBP-4 (16.5±7.7 vs 20.7±9.5 ng/ml; P = 0.005) were lower whereas IGFBP-6 (55570±27793 vs 46417±22110ng/ml; P = 0.03) and IGFBP-7 (405.9±211.6 vs 324.1 ± 145.8ng/ml; P = 0.009) were increased in PCOS compared with controls. IGF-I, IGFBP-1, -2, and -3 were similar in both groups. IGFBP-5 was undetectable. HMGB1 was increased in PCOS (41.5±22.1 vs 29.5±20.4ng/ml; P = 0.002). Interestingly, stratification based on BMI showed that IGF-II (380.7±201.8 vs 514.1±165.3ng/ml P = 0.005) and IGFBP-4 (15.2±6.9 vs 20.0 ± 9.7ng/ml, P = 0.04) were lower whereas IGFBP-7 (444.7±251.5 vs 300.6±103.6ng/ml P = 0.001) was increased in underweight/normalweight PCOS with respect to underweight/normal weight controls. IGFBP-2 was reduced in the overweight/obese subjects in both controls and PCOS, and was negatively correlated with BMI in both groups. IGFBP-3 was correlated with IGFBP-4 (r =+0.45, P <0.0001) in controls, and HMGB1 was correlated with IGFBP-2 (r =+0.34, P = 0.007) in PCOS. When considering the molar ratios, IGF-II bioavailability was confirmed to be significantly lower in PCOS whereas IGF-I bioavailability was unchanged. Conclusion: The reduction of IGF-II and IGFBP-4 in PCOS is compatible with reduced follicular development. The changes in IGF-II, IGFBP-4, and IGFBP-7in the underweight/normalweight PCOS suggests that these are specific to PCOS and unrelated to weight changes, although obesity determines changes in FF(IGFBP-2). The correlation between HMGB1 and IGFBP2 is compatible with the increased inflammatory status in PCOS. The increase of IGFBP-6 and -7opens the way for further understanding of the pathogenesis of PCOS. This work was funded by the Italian Ministry of Health (grant number GR-2018-12367635”).