A randomised trial examining inflammatory signaling in acutely induced hyperinsulinemia and hyperlipidemia in normal weight women-the reprometabolic syndrome

Abstract

Context: Obesity, is a state of chronic inflammation, characterized by elevated lipids, insulin resistance and relative hypogonadotropic hypogonadism. We have defined the accompanying decreased Luteinizing Hormone (LH), Follicle-Stimulating Hormone (FSH), ovarian steroids and reduced pituitary response to Gonadotropin-releasing Hormone (GnRH) as Reprometabolic syndrome, a phenotype that can be induced in healthy normal weight women (NWW) by acute infusion of free fatty acids and insulin.

Objective: To identify potential mediators of insulin and lipid-related reproductive endocrine dysfunction.

Design, setting, participants: Secondary analysis of crossover study of eumenorrheic reproductive aged women of normal Body Mass Index (BMI) (<25 kg/m2) at an academic medical center.

Intervention: Participants underwent 6-hour infusions of either saline/heparin or insulin plus fatty acids (Intralipid plus heparin), in the early follicular phase of sequential menstrual cycles, in random order. Euglycemia was maintained by glucose infusion. Frequent blood samples were obtained.

Main outcome measures: Pooled serum from each woman was analyzed for cytokines, interleukins, chemokines, adipokines, Fibroblast Growth Factor-21 (FGF-21) and markers of endoplasmic reticulum (ER) stress (CHOP and GRP78). Wilcoxon signed-rank tests were used to compare results across experimental conditions.

Results: Except for Macrophage Inflammatory Protein-1β (MIP-1β), no significant differences were observed in serum levels of any of the inflammatory signaling or ER stress markers tested.

Conclusion: Acute infusion of lipid and insulin, to mimic the metabolic syndrome of obesity, was not associated with an increase in inflammatory markers. These results imply that the endocrine disruption and adverse reproductive outcomes of obesity are not a consequence of the ambient inflammatory environment but may be mediated by direct lipotoxic effects on the hypothalamic-pituitary-ovarian (HPO) axis.

Fig 1. Depiction of each study arm and timeline.

Crossover study of 11 NWW. Bolus of GnRH administered at 240 min in both visits, done to measure pulsatility as part of related but separate study.

Fig 2. Flow diagram showing process for participants screening, enrollment and randomization for study visit infusions.

The total participants analyzed was 11.

Fig 3

The Effect of Insulin + Fatty Acid Infusion on A) Chemokines, B) Cytokines and C) Proinflammatory molecules. Serum levels were determined by V-Plex human cytokine 30-plex immunoassay or ELISA as described in Methods. Numbers indicate p values, *p<0.05 (N = 11).

Fig 4. The Effect of Insulin + Fatty Acid Infusion on ER Stress Markers and FGF-21.

Serum CHOP, GRP78 and FGF-21levels were determined by immunoassay as described in Methods. Numbers indicate p values (N = 11).