Effect of Low-Dose Progesterone on Glycemic Metabolism, Morphology and Function of Adipose Tissue and Pancreatic Islets in Diet-Induced Obese Female Mice.

BACKGROUND: Obesity is a worldwide concern due to its global rapid expansion and remarkable impact on individual's health by predisposing to several other diseases. About twice as many women as men suffer from severe obesity and, in fact, there are stages in a woman's life when weight gain and adiposity can result in greater damage to health. For example, obesity triples the chance of a woman developing gestational diabetes. Many hormones promote the metabolic adaptations of pregnancy, including progesterone, whose role in female obesity is still not well known despite being involved in many physiological and pathological processes. METHODS: Here we investigated whether progesterone treatment at low dose can worsen the glucose metabolism and the morpho functional aspects of adipose tissue and pancreas in obese females. Mice were assigned into four groups: normocaloric diet control (NO-CO), high-fat and -fructose diet control (HFF-CO), normocaloric diet plus progesterone (NO-PG) and high-fat and -fructose diet plus progesterone (HFF-PG) for 10 weeks. Infusion of progesterone (0.25 mg/kg/day) was done by osmotic minipump in the last 21 days of protocol. RESULTS: Animals fed a hypercaloric diet exhibited obesity with increased body weight (p < 0.0001), adipocyte hypertrophy (p < 0.0001), hyperglycemia (p = 0.03), and glucose intolerance (p = 0.001). HFF-CO and HFF-PG groups showed lower adiponectin concentration (p < 0.0001) and glucose-stimulated insulin secretion (p = 0.03), without differences in islet size. Progesterone attenuated glucose intolerance in the HFF-PG group (p = 0.03), however, did not change morphology or endocrine function of adipose tissue and pancreatic islets. CONCLUSIONS: Taken together, our results showed that low dose of progesterone does not worsen the effects of hypercaloric diet in glycemic metabolism, morphology and function of adipose tissue and pancreatic islets in female animals. These results may improve the understanding of the mechanisms underlying the pathogenesis of obesity in women and eventually open new avenues for therapeutic strategies and better comprehension of the interactions between progesterone effects and obesity.

Effects of a moderate iron overload and its interaction with yacon flour, and/or phytate, in the diet on liver antioxidant enzymes and hepatocyte apoptosis in rats.

The effect of moderate Fe overload in the diet and its interaction with phytate, and/or yacon flour (YF), recognized as an inhibitor, and facilitator, of Fe absorption, respectively, was evaluated in healthy rats. For this purpose the following parameters were analyzed: (1) apparent iron (Fe), copper (Cu) and zinc (Zn) absorption; (2) blood Fe; (3) blood lipids (cholesterol, tryacylglicerol); (4) blood AST and ALT; (5) liver histology (histopathology, hemosiderin depots, apoptosis index; (6) liver fatty acid incorporation; (7) liver antioxidant enzyme activity. Moderate Fe overload may cause change in some liver markers (hemosiderin depots, apoptosis index and GPx) and blood lipids (total cholesterol and VLDL) and the interaction with yacon flour, and phytate, in the Fe overloaded diets may exert a protective effect on these alterations.

Persistent activation of Akt or ERK prevents the toxicity induced by saturated and polyunsaturated fatty acids in RINm5F ß-cells.

The aim of this study was to investigate whether the toxicity of saturated and polyunsaturated fatty acids (PUFA) on RINm5F cells is related to the phosphorylation state of Akt, ERK and PKC delta. The regulation of these kinases was compared in three experimental designs: (a) 4h-exposure, (b) 4h-exposure and a subsequent withdrawn of the FA for a 20 h period and (c) 24h-exposure. Saturated and PUFA were toxic to RINm5F cells even at low concentrations. Also, evidence is provided for a late (i.e. the effect only appeared hours after the treatment) and a persistent regulation (i.e. maintenance of the effect for several hours) of Akt, ERK and PKC delta phosphorylation by the FA. Late activation of PKC delta seems important for palmitate cytotoxicity. Persistent activation of the survival proteins Akt and ERK by stearate, oleate and arachidonate might play an important role to prevent the toxic effect of posterior PKC delta activation. The results shown may explain why a short-period exposure to FA is not enough to induce cytotoxicity in pancreatic beta-cells, since survival pathways are activated. Besides, when this activation is persistent, it may overcome a posterior induction of death pathways.

Fatty acid-induced toxicity and neutral lipid accumulation in insulin-producing RINm5F cells.

Fatty acids have been shown to cause death of rat and human primary pancreatic beta cells and of insulin-producing cell lines. These studies focused mainly on saturated and monounsaturated FA such as palmitic, stearic and oleic acids. In this study, we have performed a comparison of the toxicity of a wider range of FA. The toxicity of different FA to insulin-producing RINm5F cells was assessed by flow cytometry measuring loss of plasma membrane integrity and increase in DNA fragmentation. Additionally, the FA induced neutral lipid accumulation and the FA composition were determined. Palmitic, linoleic, gamma-linolenic, oleic, stearic, and eicosapentaenoic acid caused DNA fragmentation of insulin-producing RINm5F cells. Loss of membrane integrity was mainly caused by linoleic and gamma-linolenic acid. There was no correlation between cytotoxicity and the abundance of the FA in the cells as determined by HPLC analysis. Taken as whole, the toxic effect of the FA on insulin-producing RINm5F cells varied irrespective of the chain length and the degree of unsaturation. In these cells PA and LA exhibited the highest toxicity, whereas AA was not toxic. In addition, the toxicity of most tested FA was inversely related to low NLA, except for AA and EPA. The results of this study contribute to the understanding of the role of FA in the impairment of pancreatic beta cell function that occurs in type 2 diabetes and obesity.

Improvement of the mitochondrial antioxidant defense status prevents cytokine-induced nuclear factor-kappaB activation in insulin-producing cells.

Proinflammatory cytokines (interleukin-1beta [IL-1beta], tumor necrosis factor-alpha [TNF-alpha], and gamma-interferon [IFN-gamma]) initiate a variety of signal cascades in pancreatic beta-cells that affect the expression level of genes involved in both the destruction and the protection of the beta-cell. The generation of nitric oxide (NO) via the inducible NO synthase (iNOS) and oxygen free radicals play a key role in cytokine-mediated beta-cell destruction. Within these signal cascades, the activation of the transcription factor nuclear factor-kappaB (NF-kappaB) is crucial, and many cytokine-sensitive genes contain binding sites for this transcription factor in their promoter regions. The aim of this study was to characterize the cytokine-mediated activation of NF-kappaB and the subsequent expression of iNOS protein in insulin-producing RINm5F cells with an improved antioxidant defense status by overexpression of the cytoprotective enzymes catalase (Cat), glutathione peroxidase (Gpx), and the cytoplasmic Cu/Zn superoxide dismutase (Cu/ZnSOD). RINm5F cells with diverse mitochondrial antioxidative defense status were generated by stable overexpression of MnSOD constructs in sense (MnSOD sense) and antisense orientation (MnSOD antisense). Cytokine-induced (IL-1beta or cytokine mix consisting of IL-1beta + TNF-alpha + IFN-gamma) activation of NF-kappaB in RINm5F cells was reduced by >80% through overexpression of MnSOD. The activity of the iNOS promoter remained at basal levels in cytokine-stimulated MnSOD sense cells. In contrast, the suppression of MnSOD gene expression in cytokine-stimulated MnSOD antisense cells resulted in a threefold higher activation of NF-kappaB and a twofold higher activation of the iNOS promoter as compared with control cells. The iNOS protein expression was significantly reduced after a 6- and 8-h cytokine incubation of MnSOD sense cells. The low activity level of MnSOD in RINm5F MnSOD antisense cells increased the iNOS protein expression in particular during the early phase of cytokine-mediated toxicity. Cat, Gpx, and the cytoplasmic Cu/ZnSOD did not affect the activation of NF-kappaB and the iNOS promoter. In conclusion, the overexpression of MnSOD, which inactivates specifically mitochondrially derived oxygen free radicals, significantly reduced the activation of NF-kappaB in insulin-producing cells. As a consequence of this protective effect in the early cytokine signaling pathways, the induction of iNOS, an important event in the beta-cell destruction process, was also significantly reduced. The results provide evidence that mitochondrially derived reactive oxygen species (ROS) play a critical role in the activation of the cytokine-sensitive transcription factor NF-kappaB. Overexpression of MnSOD may thus be beneficial for beta-cell survival through suppression of oxygen free radical formation, prevention of NF-kappaB activation, and iNOS expression.