Celestino González

Role of 17β-estradiol administration on insulin sensitivity in the rat: implications for the insulin receptor

The role of 17beta-estradiol in the early steps of insulin action is only partially known, although its effect on glucose homeostasis has been reported. In this paper, we attempt to prove the influence of 17beta-estradiol on the insulin receptor of ovariectomized rats treated with different hormonal doses. Our results show that high doses of estradiol impair insulin sensitivity while low doses improve it. We think that these results are the consequence of changes at a molecular level, because high doses of estradiol produced lower expression of the insulin receptor gene, lower content of this receptor in target tissues, and lower phosphorylation of insulin receptor in these tissues. However, low doses of estradiol seem to produce just the opposite. The possible existence of consensus response elements in the insulin receptor gene promoter to estradiol could be controlling the expression of this gene, this control being dose and timing dependent. Moreover, we cannot discard a possible effect of estradiol on the activity of protein tyrosine phosphatases, and therefore, on the activity of the insulin receptor. These new findings improve knowledge about the possible risk for insulin resistance in women taking oral contraceptives or receiving hormonal replacement therapy around the menopause, but could also open the door towards the possible utilization of 17beta-estradiol in some diabetes cases.

Safety and intestinal microbiota modulation by the exopolysaccharide-producing strains Bifidobacterium animalis IPLA R1 and Bifidobacterium longum IPLA E44 orally administered to Wistar rats

Bifidobacterium animalis subsp. lactis IPLA R1 and Bifidobacterium longum IPLA E44 strains were tested for their safety and ability to modulate the intestinal microbiota in vivo. Chemically simulated gastrointestinal digestion showed considerably lower survival of E44 than R1 strain, the first microorganism also being more sensitive to refrigerated storage in 10% skimmed milk at 4°C. Harmful glycosidic activities were absent, or at low levels, in the strains R1 and E44. Both strains were sensitive to most antibiotics and resistant to aminoglycosides, a common feature in bifidobacteria. Similar to several other bifidobacteria strains, B. animalis subsp. lactis IPLA R1 displayed a moderate resistance against tetracycline which correlated with the presence of tet(W) gene in its genome. The general parameters indicating well-being status, as well as translocation to different organs and histological examination of the gut tissues, revealed no changes induced by the administration of bifidobacteria to rats. Twelve-week-old male Wistar rats were distributed into three groups, eight rats in each. Two groups were administered daily over 10⁸cfu of the corresponding strain suspended in 10% skimmed milk for 24 days, whereas rats in the placebo group received skimmed milk without microorganisms added. The microbiota and short chain fatty acids (SCFA) were monitored in faeces at different time points during treatment and in caecum content at the end of the assay. Quantitative PCR (qPCR) showed that faecal and caecal Bifidobacterium levels were higher in bifidobacteria-fed rats than in the placebo rats at the end of the intervention, whereas total anaerobic plate counts did not show significant differences. Quantification of B. animalis and B. longum by qPCR showed that, independent of the microorganism administered, treatment with bifidobacteria resulted in higher levels of B. animalis in the caecum. PCR-DGGE analysis of microbial populations revealed a higher diversity of bands in caecum content of rats fed B. animalis IPLA R1 than in the placebo group and rats fed B. longum IPLA E44. Remarkably, although no variations in the proportion of acetate, propionate and butyrate were found, at the end of the assay the total SCFA concentration in the faeces of rats fed bifidobacteria was significantly higher and those in caecum content significantly lower, than that of the placebo group. This suggests a displacement of the SCFA production to parts of the colon beyond the caecum in rats receiving bifidobacteria. Therefore, the oral administration of B. animalis IPLA R1 and B. longum E44 can be considered safe, these microorganisms having the ability to modulate the intestinal microbiota of rats by influencing SCFA and the bifidobacterial population levels.

Effects of pregnancy on insulin receptor in liver, skeletal muscle and adipose tissue of rats

The mechanism responsible for insulin resistance during pregnancy remains unclear. Considerable evidence indicates that the insulin receptor plays an important role in insulin sensitivity. It seems possible that the hormonal milieu during gestation could have an effect on the insulin receptor. In the present study, measurements of tyrosine phosphorylation and protein content of the insulin receptor and expression of its gene in liver, skeletal muscle and adipose tissue indicate that during pregnancy significant changes occur in these parameters. We found that at the end of early gestation (day 10), muscle and adipose tissue are very sensitive to insulin action because the amount, phosphorylation and gene expression of insulin receptor is higher than in late gestation (days 15–20), while the tissue which is most sensitive to insulin action in late gestation is the liver. Our hypothesis is that these results are connected with changes in the concentrations of estradiol and progesterone observed during pregnancy. In conclusion, our previous and present findings seem to demonstrate that the different concentrations of gestational hormones play an important role in insulin sensitivity in this period and that each tissue responds in the most appropriate manner to guarantee the gestation in its entirety.

Soy isoflavones, diet and physical exercise modify serum cytokines in healthy obese postmenopausal women

OBJECTIVES Evaluate the effect of diet, physical exercise, and a daily oral intake of a soy isoflavones extract (Fisiogen(®)) contained 200 mg of Glycine max, which corresponded to 80 mg of isoflavone (60.8 mg of genistein, 16 mg of daidzein and 3.2 mg of glicitein) on leptin and other adipokines plasma levels in healthy obese postmenopausal women. METHODS A multicentric randomized longitudinal prospective cohort study was conducted in a sample of 87 healthy obese postmenopausal women. Patients were randomly assigned to a 1200 kcal diet and exercise group (control group) or a group of 1200 kcal diet, exercise, and daily oral intake of daily oral intake of a soy isoflavones extract (Fisiogen(®)) contained 200 mg of Glycine max, which corresponded to 80 mg of isoflavone (60.8 mg of genistein, 16 mg of daidzein and 3.2 mg of glicitein) (soy isoflavones group) along 6 months. Main outcome measures were: anthropometric measures, body composition, leptin, adiponectin, TNF-alpha, homocysteine, C-reactive protein, glucose, insulin, lipid profile and oestradiol serum levels, Kupperman index and Cervantes Scale. RESULTS Mean serum leptin and TNF-alpha levels declined after 6 months in both groups of the study, but only women in the soy isoflavones group showed a significant increase of mean serum levels of adiponectin. CONCLUSIONS Diet, physical exercise and daily oral intake of a soy isoflavones extract (Fisiogen(®)) contained 200 mg of Glycine max, which corresponded to 80 mg of isoflavone (60.8 mg of genistein, 16 mg of daidzein and 3.2 mg of glicitein) have a beneficial effect on serum leptin, adiponectin and TNF-α in healthy obese postmenopausal women after 6 months of treatment.

Chronic 17β-estradiol treatment improves skeletal muscle insulin signaling pathway components in insulin resistance associated with aging

Insulin resistance is a common feature of aging in both humans and rats. In the case of females, it seems to be related to loss of gonadal function, due mainly due to a decrease in plasma estrogen levels. Several causes have been postulated for this insulin resistance, among them changes in several steps of the insulin pathway. In view of these findings, the purpose of the present study was to examine the role of chronic 17β-estradiol treatment on insulin sensitivity during the aging process, and its effects on levels of the insulin-sensitive glucose transporter Glut4 (both total and plasma membrane localized), the interaction between p85α subunit of PI3-k and IRS-1, Tyr- and Ser-612 phosphorylation of IRS-1 levels, and Ser-473 phosphorylation of Akt. The present findings indicate that 17β-estradiol treatment is able to minimize the deleterious effect of aging on insulin sensitivity, at least at the level of plasma membrane localized Glut4. Nevertheless further research is needed to determine this conclusively.

Acute effects of 17β-estradiol and genistein on insulin sensitivity and spatial memory in aged ovariectomized female rats

Aging is characterized by decline in metabolic function and insulin resistance, and both seem to be in the basis of neurodegenerative diseases and cognitive dysfunction. Estrogens prevent age-related changes, and phytoestrogens influence learning and memory. Our hypothesis was that estradiol and genistein, using rapid-action mechanisms, are able to modify insulin sensitivity, process of learning, and spatial memory. Young and aged ovariectomized rats received acute treatment with estradiol or genistein. Aged animals were more insulin-resistant than young. In each age, estradiol and genistein-treated animals were less insulin-resistant than the others, except in the case of young animals treated with high doses of genistein. In aged rats, no differences between groups were found in spatial memory test, showing a poor performance in the water maze task. However, young females treated with estradiol or high doses of genistein performed well in spatial memory task like the control group. Only rats treated with high doses of genistein showed an optimal spatial memory similar to the control group. Conversely, acute treatment with high doses of phytoestrogens improved spatial memory consolidation only in young rats, supporting the critical period hypothesis for the beneficial effects of estrogens on memory. Therefore, genistein treatment seems to be suitable treatment in aged rats in order to prevent insulin resistance but not memory decline associated with aging. Acute genistein treatment is not effective to restore insulin resistance associated to the early loss of ovarian function, although it can be useful to improve memory deficits in this condition.

17β-Estradiol and/or progesterone protect from insulin resistance in STZ-induced diabetic rats

Recent clinical and experimental evidences suggest that sex steroids protect from insulin resistance associated with diabetes. Therefore, we have assessed the influence of E2 and/or P4 on insulin sensitivity by euglicaemic-hyperinsulinaemic clamp in ovariectomized streptozotocin-induced diabetic rats, focusing on key proteins of insulin signaling in skeletal muscle. Although low plasma levels of E2 (days 6 and 11) increased Glut-4 plasma membrane content and subsequent improved insulin sensitivity, they could not fully reverse hyperglycaemia negative effects on p85alpha-IRS-1 association and IRS-1 content during 11 days. However, high plasma levels of E2 (day 16) could reverse hyperglycaemia effects not only on Glut-4 plasma membrane content but also on p85alpha-IRS-1 association and IRS-1 protein content level. In contrast, P4 treatment only improved insulin sensitivity when its plasma concentration was low (days 6 and 11) and its effects were not associated with any proteins study in this paper. The combined therapy had a synergic effect on insulin sensitivity when their plasma levels were low (day 6) or high (day 16), that could be associated with Glut-4 plasma membrane content modulation, p85alpha-IRS-1 association and IRS-1 amount. These new findings improve our understanding of biochemical basis of insulin resistance due to hyperglycaemia and could open up new possibilities of treatment in uncontrolled type 1 DM.

Effects of gestational diabetes mellitus on proteins implicated in insulin signaling in human placenta

Objective. Placenta plays a central role in fetal nutrition. During gestational diabetes mellitus (GDM), it suffers structural and functional alterations which affect the health of both mother and fetus. In the present study we aimed to clarify if GDM modifies the amounts of leptin receptor (Ob-R) and of the main proteins implicated in insulin signal transmission (insulin receptor, insulin receptor substrate-1 and phosphatidylinositol-3-kinase subunit p85α) in human placenta; we also attempted to confirm the presence of estrogen receptor-α to determine the effect of GDM on its amount. Methods. Placentas were recovered from 30 women with uncomplicated pregnancies and 20 women who developed GDM. Western blotting and immunocytochemistry experiments were performed to investigate the above-mentioned proteins. Results. We observed that all proteins studied were increased in GDM. However, it is unknown if this is a consequence of GDM or the result of medical treatments used to mitigate the injurious effects of GDM. Conclusions. Probably, the changes we found are indicative of the protective role of the placenta prior to the injurious effects of GDM and/or an important indicator of placental aging. Some aspects related to the link between non-genomic estrogen action, the mitogenic action of insulin and the role of Ob-R in placenta from normal and GDM women need to be investigated in greater depth.

Regulation of insulin receptor substrate-1 in the liver ,skeletal muscle and adipose tissue of rats throughout pregnancy

The mechanism responsible for insulin resistance during pregnancy remains unclear. Considerable evidence indicates that insulin receptor substrate-1 could play an important role in insulin sensitivity. It seems possible that the gestational hormonal milieu could affect insulin receptor substrate-1. In the present study ,measurements of tyrosine phosphorylation and protein content of insulin receptor substrate-1 and gene expression in the liver ,skeletal muscle and adipose tissue in the rat indicated that ,during pregnancy ,significant changes occurred in these parameters. We found in early gestation that muscle and adipose tissue were highly sensitive to insulin action ,because the phosphorylation of insulin receptor substrate-1 is greater than in late gestation. However ,in late gestation the tissue most sensitive to insulin action ,reflecting insulin receptor substrate-1 phosphorylation ,was the liver. Our hypothesis was that these results are connected with the changes in concentrations of estradiol and progesterone observed during pregnancy. It was concluded that the present findings demonstrate that different concentrations of gestational hormones play an important role in insulin sensitivity in this period ,and that each tissue responds in the most appropriate manner to guarantee the gestation in its entirety ,controlling the phosphorylation of insulin receptor substrate-1 in response to insulin receptor activation.

Leptin and its receptor are controlled by 17β-estradiol in peripheral tissues of ovariectomized rats

It has been widely shown that there is a complex interaction between sex steroids and leptin effects on body weight. In this sense, the absence of female sex steroids is linked to a significant increase in body weight, which seems to be related to an impairment of the central actions of leptin. The present study was designed to elucidate the effects of two different treatments with 17β-estradiol on leptin receptor and serum leptin levels in ovariectomized rats, a model of postmenopausal condition. Our results have shown that plasma leptin levels in ovariectomized rats were lower than in estradiol-treated animals, thereby supporting a positive effect of this steroid. Recent information has extended leptin actions to peripheral tissues, mainly to insulin-dependent tissues, this effect being related to metabolic actions. To better understand the peripheral effects of leptin and their possible regulation by estradiol treatment, we have analyzed leptin receptor expression in the skeletal muscle and the adipose tissue. Our results showed a tissue-specific regulation of this protein: Ob-Rb expression in the adipose tissue decreased when the time of treatment or the dose of estradiol administered increased, suggesting less sensitivity to leptin in this tissue, whereas in the skeletal muscle the changes in this protein followed the same profile as the plasma leptin levels. We think that this specific regulation could ensure a different response of each tissue toward the same serum leptin level. Further studies to clarify this situation are ongoing.