Melatonin Prevents Immune Stimulation of Pituitary ACTH production in Rats Fed Sucrose Rich Diets

CALANNI, JUAN SALVADOR; MERCAU, MARÍA ELISA; ARANDA, MARCOS LUIS; SANCHEZ PUCH, SILVIA; REPETTO, ESTEBAN MARTÍN; CYMERYNG, CORA BEATRIZ

Buenos Aires

Congreso; IV INTERNATIONAL CONGRESS IN TRANSLATIONAL MEDICINE; 2018

IMBS/FFyB-UBA

Excessive consumption of simple carbohydrates has been associated with an increased incidence of insulin resistance and obesity. Several reports have shown a concomitant dysfunction of the hypothalamus pituitary adrenal (HPA) axis in these patients. We have previously reported that rats fed a sucrose rich diet (SRD, 30% sucrose in the drinking water) for 7 weeks show a significant decrease in insulin sensitivity. Analysis of HPA axis activity 3 weeks after the initiation of the dietary modification, when changes in insulin sensitivity were still not evident, showed augmented levels of circulating ACTH and a higher pituitary expression of POMC that was accompanied by increases in oxidative stress (OxS) and inflammatory parameters. A chronic low-grade inflammatory state has been associated with the development of insulin resistance and type 2 diabetes. As several inflammatory cytokines have been shown to activate the HPA axis, we hypothesized thatpituitary OxS and inflammation could result in the observed hyperactivation of the HPA axis by inducing ACTH production from corticotroph cells. To test this hypothesis we analyzed the effect of melatonin, a molecule with potent anti-oxidant and anti-inflammatory properties, on POMC/ACTH production both in vivo and in vitro. In-vivo experiments: Wistar rats were fed SRD and melatonin implants were surgically implanted. Animals were sacrificed after 3 weeks and pituitary glands were dissected and processed to obtain total proteins and RNA. Plasma ACTH levels were assessed by a chemiluminiscent assay and serum corticosterone concentration was determined by RIA. Expression of specific proteins and mRNAs were evaluated by western blot and RT-qPCR respectively. Compared to the corresponding controls our results showed an increase in the mRNA levels of TNFα, IL-1 beta and inflammasomecomponentsand also in the expression levels Iba-1, F4-80 and Caspase 1as determined by immunofluorescence and immunoblot. Melatonin treatment prevented all these changes in markers of inflammation. In addition, melatonin administration also prevented the increase in pituitary POMC expression levelsand in circulating levels of ACTH and cortIcosterone observed in the SRD group.In vitro experiments: AtT20 (murine corticotrophs) and J774 (murine macrophages) cells were used. Incubation of the corticotroph AtT20 cell line with conditioned media obtained from control (CMC) or activated J774 cells (with LPS and glucose, CMLG) showed an increase in the reporter activity of POMC-LUC by CMLG that was not observed when conditioned media was obtained in the presence of 50 nM melatonin. In summary, our results suggest thatthe early increase in the the synthesis and secretion ofACTH detected in SRD-treated rats, prior to the development of insulin resistance, could involve inflammation-related pathways activated in addition to or as a consequence of the generation of OxSin pituitary tissues from SRD-treated rats, as we previously demonstrated.