Carmen Álvarez

Contrasted Impact of Maternal Rat Food Restriction on the Fetal Endocrine Pancreas

The effects of food restriction of the mother (65% restriction of ad libitum food intake) on fetal and maternal insulin secretion and islet function were studied at 21 days gestation in three different rat populations: 1) undernourished from 0–7 days gestation, 2) undernourished from 7–14 days gestation, and 3) undernourished from 14–21 days gestation. The body weights of mothers were decreased in groups 2 and 3 vs. those in control fed pregnant animals, and no changes in basal parameters were found in any group. A glucose tolerance test in mothers from group 3 showed a mild intolerance to glucose and a decreased islet insulin content, although islet stimulation in vitro with glucose alone or plus arginine showed a normal insulin secretory response. Body weight was decreased in fetuses from the three groups (P < 0.01), and pancreas weight was reduced only in group 3. Insulinemia was increased in groups 2 and 3, and pancreatic insulin content increased only in group 3. However, fetuses from mothers of grou...

Microbial phenolic metabolites improve glucose-stimulated insulin secretion and protect pancreatic beta cells against tert-butyl hydroperoxide-induced toxicity via ERKs and PKC pathways

Oxidative stress is accepted as one of the causes of beta cell failure in type 2 diabetes. Therefore, identification of natural antioxidant agents that preserve beta cell mass and function is considered an interesting strategy to prevent or treat diabetes. Recent evidences indicated that colonic metabolites derived from flavonoids could possess beneficial effects on various tissues. The aim of this work was to establish the potential anti-diabetic properties of the microbial-derived flavonoid metabolites 3,4-dihydroxyphenylacetic acid (DHPAA), 2,3-dihydroxybenzoic acid (DHBA) and 3-hydroxyphenylpropionic acid (HPPA). To this end, we tested their ability to influence beta cell function and to protect against tert-butyl hydroperoxide-induced beta cell toxicity. DHPAA and HPPA were able to potentiate glucose-stimulated insulin secretion (GSIS) in a beta cell line INS-1E and in rat pancreatic islets. Moreover, pre-treatment of cells with both compounds protected against beta cell dysfunction and death induced by the pro-oxidant. Finally, experiments with pharmacological inhibitors indicate that these effects were mediated by the activation of protein kinase C and the extracellular regulated kinases pathways. Altogether, these findings strongly suggest that the microbial-derived flavonoid metabolites DHPAA and HPPA may have anti-diabetic potential by promoting survival and function of pancreatic beta cells.

Changes in insulin action and insulin secretion in the rat after dietary restriction early in life: Influence of dood restriction versus low-protein food restriction

The effect of a limited period of undernutrition in young rats on insulin secretion and insulin action during adulthood has been studied. Four-week-old female rats were either food-restricted (35% restriction, 15% protein diet) or protein-calorie-restricted (35% restriction, 5% protein diet) for 4 weeks. Food-restricted rats gained weight at a lower rate than control rats. In the protein-calorie-restricted group, the alteration of weight gain was more severe. Basal plasma insulin was reduced only in protein-calorie-restricted rats. Glucose-stimulated insulin secretion (delta I) obtained in vivo after an intravenous glucose load was only moderately decreased in food-restricted group, whereas it was severely blunted in the protein-calorie-restricted group. In this last group, impairment of the insulin secretory response to glucose was related to an intrinsic impairment of beta-cell secretory capacity, since the insulin secretory response to glucose or arginine was decreased when tested in vitro (perfused pancreas). In food-restricted rats, basal plasma glucose level was kept normal, while a mild deterioration of glucose tolerance was detectable. This was related, of course, to the decrease of delta I as identified in vivo. However, data obtained under basal or euglycemic-hyperinsulinemic conditions provided direct evidence that insulin-mediated total glucose uptake (weight-related expression) was paradoxically enhanced. A similar conclusion was reached in protein-calorie-restricted rats; the increase of overall insulin-mediated glucose uptake was even more important. Such an adaptation, which was operating in both types of restriction, may help limit the deterioration of glucose tolerance in the face of impaired insulin release. In the basal postabsorptive state, the higher glucose utilization rate in both models originated from increased hepatic glucose production rates. During hyperinsulinemia, endogenous glucose production in food-restricted rats was normally blunted, but not in protein-calorie--restricted rats, thus indicating resistance of the hepatic glucose production pathway to insulin action in this group.

Regulation of IGF-I and -II by Insulin in Primary Cultures of Fetal Rat Hepatocytes

During perinatal development, insulin and nutrients, rather than GH, regulate the IGF system. A selective primary culture of fetal rat hepatocytes has been established in our laboratory to elucidate the molecular mechanism of action of the above regulatory factors on IGF-I and -II gene expression during the late fetal period of the rat. In this model we have previously reported a regulatory role for glucose on IGF-I and -II synthesis and secretion. In the same experimental model, we now report that doses of insulin (0.1–5 μm) within the physiological range in rat fetuses during the last stages of gestation evoke an increase of IGF-I and -II mRNA abundance. Insulin regulated in a parallel manner IGF peptide secretion, and an excellent correlation was observed between IGF-I and -II mRNA and IGF-I and -II peptide levels in the conditioned media in response to the hormone. Finally, the insulin-induced rise in IGF-I and -II mRNA was not mediated by stimulation of gene transcription but by increased transcript ...

Cocoa-rich diet attenuates beta cell mass loss and function in young Zucker diabetic fatty rats by preventing oxidative stress and beta cell apoptosis

We have recently shown that cocoa flavanols may have anti-diabetic potential by promoting survival and function of pancreatic beta-cells in vitro. In this work, we investigated if a cocoa-rich diet is able to preserve beta-cell mass and function in an animal model of type 2 diabetes and the mechanisms involved. Our results showed that cocoa feeding during the prediabetic state attenuates hyperglycaemia, reduces insulin resistant, and increases beta cell mass and function in obese Zucker diabetic rats. At the molecular level, cocoa-rich diet prevented beta-cell apoptosis by increasing the levels of Bcl-xL and decreasing Bax levels and caspase-3 activity. Cocoa diet enhanced the activity of endogenous antioxidant defenses, mainly glutathione peroxidase, preventing thus oxidative injury induced by the pre-diabetic condition and leading to apoptosis prevention. These findings provide the first in vivo evidence that a cocoa-rich diet may delay the loss of functional beta-cell mass and delay the progression of diabetes by preventing oxidative stress and beta-cell apoptosis.

Type 2 diabetes – a matter of failing β‐cell neogenesis? Clues from the GK rat model

Now that reduction in β‐cell mass has been clearly established in humans with type 2 diabetes mellitus (T2D), the debate focuses on the possible mechanisms responsible for decreased β‐cell number. Appropriate inbred rodent models are essential tools for this purpose. The information available from the Goto‐Kakizaki (GK) rat, one of the best characterized animal models of spontaneous T2D, is reviewed in such a perspective. We propose that the defective β‐cell mass in the GK model reflects mostly a persistently decreased β‐cell neogenesis. The data discussed in this review are consistent with the notion that poor proliferation and/or survival of the endocrine precursor cells during GK foetal life will result in a decreased pool of endocrine precursors in the pancreas, and hence an impaired capacity of β‐cell neogenesis (either primary in the foetus or compensatory in the newborn and the adult). As we also demonstrated that β‐cell neogenesis can be pharmacologically reactivated in the GK model, our work supports, on a more prospective basis, the concept that facilitation of T2D treatment may be obtained through β‐cell mass expansion after stimulation of β‐cell regeneration/neogenesis in diabetic patients.

Cocoa-rich diet ameliorates hepatic insulin resistance by modulating insulin signaling and glucose homeostasis in Zucker diabetic fatty rats

Insulin resistance is the primary characteristic of type 2 diabetes and results from insulin signaling defects. Cocoa has been shown to exert anti-diabetic effects by lowering glucose levels. However, the molecular mechanisms responsible for this preventive activity and whether cocoa exerts potential beneficial effects on the insulin signaling pathway in the liver remain largely unknown. Thus, in this study, the potential anti-diabetic properties of cocoa on glucose homeostasis and insulin signaling were evaluated in type 2 diabetic Zucker diabetic fatty (ZDF) rats. Male ZDF rats were fed a control or cocoa-rich diet (10%), and Zucker lean animals received the control diet. ZDF rats supplemented with cocoa (ZDF-Co) showed a significant decrease in body weight gain, glucose and insulin levels, as well as an improved glucose tolerance and insulin resistance. Cocoa-rich diet further ameliorated the hepatic insulin resistance by abolishing the increased serine-phosphorylated levels of the insulin receptor substrate 1 and preventing the inactivation of the glycogen synthase kinase 3/glycogen synthase pathway in the liver of cocoa-fed ZDF rats. The anti-hyperglycemic effect of cocoa appeared to be at least mediated through the decreased levels of hepatic phosphoenolpyruvate carboxykinase and increased values of glucokinase and glucose transporter 2 in the liver of ZDF-Co rats. Moreover, cocoa-rich diet suppressed c-Jun N-terminal kinase and p38 activation caused by insulin resistance. These findings suggest that cocoa has the potential to alleviate both hyperglycemia and hepatic insulin resistance in type 2 diabetic ZDF rats.

Resveratrol treatment restores peripheral insulin sensitivity in diabetic mice in a sirt1‐independent manner

SCOPE Mice with deletion of insulin receptor substrate (IRS) 2 develop hyperglycaemia, impaired hepatic insulin signaling and elevated gluconeogenesis. Protein tyrosine phosphatase 1B (PTP1B) inhibition by resveratrol improves peripheral insulin sensitivity of these mice. Although resveratrol activates Sirtuin1 (Sirt1), the mechanisms underlying its beneficial effects are not totally elucidated. In this study, we have investigated whether Sirt1 mediates the effects of resveratrol in controlling insulin resistance in diabetic mice. METHODS AND RESULTS We attempted to ameliorate peripheral insulin resistance in two diabetic models, Irs2-deficient (Irs2(-/-)) mice and streptozotocin (STZ)-injected mice by resveratrol treatment or Sirt1 overexpression. Resveratrol improved systemic insulin sensitivity of Irs2-deficient mice. Irs2-deficient mice are characterized by high levels of PTP1B expression in liver and muscle. Interestingly, resveratrol decreased PTP1B in both tissues, thereby restoring IRS1-mediated insulin signaling. Moreover, resveratrol also restored insulin sensitivity and hepatic insulin signaling in STZ-diabetic mice. In contrast, moderate overexpression of Sirt1 neither normalized PTP1B levels nor restored insulin signaling in Irs2-deficient mice or STZ-diabetic mice. CONCLUSION Resveratrol improves peripheral insulin signaling independently of Sirt1 in diabetic mice in association with the inhibition of PTP1B and, therefore, this polyphenol could be an effective adjuvant for the treatment of diabetes.

PTP1B deficiency enhances liver growth during suckling by increasing the expression of insulin-like growth factor-I

Protein tyrosine phosphatase 1B (PTP1B) is a negative regulator of insulin and tyrosine kinase growth factor signaling. We have recently demonstrated that PTP1B deficiency increases GLUT2/insulin receptor (IR) A complexes and glucose uptake in suckling, but not adult, primary hepatocytes. Herein we have investigated intrahepatic glucose utilization in 3–5 days old wild‐type and PTP1B−/− mice. PTP1B deficiency decreased glycogen, lactate, and pyruvate content in the livers from suckling mice. Conversely, the activity of glucose 6‐phosphate dehydrogenase (G6PD), the rate limiting enzyme of the pentose phosphate cycle (PPC) which provides substrates for DNA synthesis, was enhanced in the liver of PTP1B−/− animals. Liver weight, liver‐to‐body mass ratio, DNA content, and PCNA expression were increased in PTP1B−/− suckling mice compared to the wild‐type controls. At the molecular level, STAT 5B phosphorylation, IGF‐I mRNA, and protein levels as well as IGF‐IR tyrosine phosphorylation were increased in the livers of PTP1B‐deficient neonates. Unexpectedly, hepatic and serum triglycerides (TG) were increased by PTP1B deficiency, although the expression of lipogenic enzymes remained as in the wild‐type controls. However, the analysis of milk composition revealed higher TG content in lactating females lacking PTP1B. The effects of PTP1B deficiency on G6PD activity, STAT 5B/IGF‐I/IGF‐IR axis, PCNA expression and liver growth during suckling were maintained by transferring PTP1B−/− embryos (PTP1B−/−T) to a wild‐type female. Conversely, PTP1B−/−T mice did not show hepatic fat accumulation. In conclusion, the present study suggests that PTP1B plays a unique role in the control of the physiological liver development after birth. J. Cell. Physiol. 225: 214–222, 2010.

A novel glucagon‐like peptide 1/glucagon receptor dual agonist improves steatohepatitis and liver regeneration in mice

Because nonalcoholic steatohepatitis (NASH) is associated with impaired liver regeneration, we investigated the effects of G49, a dual glucagon‐like peptide‐1/glucagon receptor agonist, on NASH and hepatic regeneration. C57Bl/6 mice fed chow or a methionine and choline–deficient (MCD) diet for 1 week were divided into 4 groups: control (chow diet), MCD diet, chow diet plus G49, and M+G49 (MCD diet plus G49). Mice fed a high‐fat diet (HFD) for 10 weeks were divided into groups: HFD and H+G49 (HFD plus G49). Following 2 (MCD groups) or 3 (HFD groups) weeks of treatment with G49, partial hepatectomy (PH) was performed, and all mice were maintained on the same treatment schedule for 2 additional weeks. Analysis of liver function, hepatic regeneration, and comprehensive genomic and metabolic profiling were conducted. NASH was ameliorated in the M+G49 group, manifested by reduced inflammation, steatosis, oxidative stress, and apoptosis and increased mitochondrial biogenesis. G49 treatment was also associated with replenishment of intrahepatic glucose due to enhanced gluconeogenesis and reduced glucose use through the pentose phosphate cycle and oxidative metabolism. Following PH, G49 treatment increased survival, restored the cytokine‐mediated priming phase, and enhanced the proliferative capacity and hepatic regeneration ratio in mice on the MCD diet. NASH markers remained decreased in M+G49 mice after PH, and glucose use was shifted to the pentose phosphate cycle and oxidative metabolism. G49 administered immediately after PH was also effective at alleviating the pathological changes induced by the MCD diet. Benefits in terms of liver regeneration were also found in mice fed HFD and treated with G49. Conclusion: Dual‐acting glucagon‐like peptide‐1/glucagon receptor agonists such as G49 represent a novel therapeutic approach for patients with NASH and particularly those requiring PH. (Hepatology 2017;65:950‐968).