M. J. A. Saad

Defects in insulin signal transduction in liver and muscle of pregnant rats.

Summary Pregnancy is known to induce insulin resistance, but the exact molecular mechanism involved is unknown. In the present study, we have examined the levels and phosphorylation state of the insulin receptor and of insulin receptor substrate 1(IRS-1), as well as the association between IRS-1 and phosphatidylinositol 3-kinase (PI 3-kinase) in the liver and muscle of pregnant rats (day 20 of gestation) by immunoprecipitation and immunoblotting with anti-insulin receptor, anti-IRS-1, anti-PI 3-kinase and anti-phosphotyrosine antibodies. There were no changes in the insulin receptor concentration in the liver and muscle of pregnant rats. However, insulin stimulation of receptor autophosphorylation, as determined by immunoblotting with antiphosphotyrosine antibody, was reduced by 30 ± 6 % (p < 0.02) in muscle and 36 ± 5 % (p < 0.01) in liver at day 20 of gestation. IRS-1 protein levels decreased by 45 ± 6 % (p < 0.002) in liver and by 56 ± 9 % (p < 0.002) in muscle of pregnant rats. In samples previously immunoprecipitated with anti-IRS-1 antibody and blotted with antiphosphotyrosine antibody, the insulin-stimulated IRS-1 phosphorylation levels in the muscle and liver of pregnant rats decreased by 70 ± 9 % (p < 0.01) and 75 ± 8 % (p < 0.01), respectively. The insulin-stimulated IRS-1 association with PI 3-kinase decreased by 81 ± 6 % in muscle (p < 0.01) and 79 ± 11 % (p < 0.01) in the liver during pregnancy. These data suggest that changes in the early steps of insulin signal transduction may have a role in the insulin resistance observed in pregnancy. [Diabetologia (1997) 40: 179–186]

Peroxisome proliferator-activated receptor γ coactivator-1-dependent uncoupling protein-2 expression in pancreatic islets of rats: a novel pathway for neural control of insulin secretion

Aims/hypothesisSympathetic inputs inhibit insulin secretion through α2-adrenergic receptors coupled with Gi protein. High adrenergic tonus generated by exposure of homeothermic animals to cold reduces insulin secretion. In this study we evaluate the participation of UCP-2 in cold-induced regulation of insulin secretion.MethodsStatic insulin secretion studies, western blotting and immunohistochemistry were used in this investigation.ResultsExposure of rats to cold during 8 days promoted 60% (n=15, p<0.05) reduction of basal serum insulin levels concentration accompanied by reduction of the area under insulin curve during i.p. GTT (50%, n=15, p<0.05). Isolated islets from cold-exposed rats secreted 57% (n=6, p<0.05) less insulin following a glucose challenge. Previous sympathectomy, partially prevented the effect of cold exposure upon insulin secretion. Islets isolated from cold-exposed rats expressed 51% (n=6, p<0.5) more UCP-2 than islets from control rats, while the inhibition of UCP-2 expression by antisense oligonucleotide treatment partially restored insulin secretion of islets obtained from cold-exposed rats. Cold exposure also induced an increase of 69% (n=6, p<0.05) in PGC-1 protein content in pancreatic islets. Inhibition of islet PGC-1 expression by antisense oligonucleotide abrogated cold-induced UCP-2 expression and partially restored insulin secretion in islets exposed to cold.Conclusion/interpreatationOur data indicate that sympathetic tonus generated by exposure of rats to cold induces the expression of PGC-1, which participates in the control of UCP-2 expression in pancreatic islets. Increased UCP-2 expression under these conditions could reduce the beta-cell ATP/ADP ratio and negatively regulate insulin secretion.

Linking Gut Microbiota and Inflammation to Obesity and Insulin Resistance

Obesity and insulin resistance are the major predisposing factors to comorbidities, such as Type 2 diabetes, nonalcoholic fatty liver disease, cardiovascular and neurodegenerative diseases, and several types of cancer. The prevalence of obesity is still increasing worldwide and now affects a large number of individuals. Here, we review the role of the gut microbiota in the pathophysiology of insulin resistance/obesity. The human intestine is colonized by ∼100 trillion bacteria, which constitute the gut microbiota. Studies have shown that lean and overweight rodents and humans may present differences in the composition of their intestinal flora. Over the past 10 years, data from different sources have established a causal link between the intestinal microbiota and obesity/insulin resistance. It is important to emphasize that diet-induced obesity promotes insulin resistance by mechanisms independent and dependent on gut microbiota. In this review, we present several mechanisms that contribute to explaining the link between intestinal flora and insulin resistance/obesity. The LPS from intestinal flora bacteria can induce a chronic subclinical inflammatory process and obesity, leading to insulin resistance through activation of TLR4. The reduction in circulating SCFA may also have an essential role in the installation of reduced insulin sensitivity and obesity. Other mechanisms include effects of bile acids, branched-chain amino acids (BCAA), and some other lesser-known factors. In the near future, this area should open new therapeutic avenues for obesity/insulin resistance and its comorbidities.

Short-term inhibition of peroxisome proliferator-activated receptor-γ coactivator-1α expression reverses diet-induced diabetes mellitus and hepatic steatosis in mice

Aims/hypothesisThe coactivator of nuclear receptors, peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) has been implicated in a series of events that contribute to the control of glucose metabolism. We have recently reported the use of a PGC-1α antisense oligonucleotide (PGC-1αAS) that inhibits up to 60% of PGC-1α expression in pancreatic islets, leading to increased insulin secretion. This oligonucleotide was used in this study to try to ameliorate diet-induced type 2 diabetes in a genetically predisposed mouse strain (Swiss mice).Materials and methodsGlucose and insulin tolerance tests, euglycaemic–hyperinsulinaemic clamp, immunoprecipitation assays, immunoblotting assays and immunohistochemistry were used in this investigation.ResultsSwiss mice became obese and overtly diabetic after 8 weeks of feeding with chow containing 24% saturated fat. One daily dose (1.0xa0nmol) of PGC-1αAS significantly reduced glucose and increased insulin blood levels without affecting food intake and body weight. These effects were accompanied by a reduced area under the glucose curve during an intraperitoneal glucose tolerance test, an increased constant of glucose decay (Kitt) during an insulin tolerance test, and an increased glucose consumption rate during a euglycaemic–hyperinsulinaemic clamp. Moreover, mice treated with PGC-1αAS presented an outstanding reduction of macroscopic and microscopic features of hepatic steatosis. These effects were accompanied by reduced expression or function of a series of proteins involved in lipogenesis.Conclusions/interpretationPGC-1α is an attractive target for pharmacological therapeutics in type 2 diabetes mellitus and diet-induced hepatic steatosis.

Expression of Concern: Circulating ghrelin concentrations are lowered by intracerebroventricular insulin

On the basis of the recommendation of the EASD’s Scientific Integrity Panel, the Editor-in-Chief is issuing this expression of concern to alert readers to questions about the reliability of some of the data in the article cited above. In particular, it appears that the bands for p-Akt in Fig. 1b may be the same as those in Fig. 2b after 180 degree rotation in both axes (see below). In line with guidelines issued by the Committee on Publication Ethics (COPE), the journal has informed the corresponding author, Mario Saad, of this concern. Dr Saad has confirmed that the original data are no longer available (these need only be retained for a 5 year period according to Brazilian law). It has therefore not been possible to use image forensics to conclusively confirm or refute this concern. Dr Saad offered to supply new western blot images; however the EASD’s Scientific Integrity Panel did not consider it appropriate to publish a corrigendum with the new data. The University of Campinas (São Paulo, Brazil) is undertaking an institutional investigation into the work carried out by members of this group. The results of this investigation are not yet available, thus this expression of concern is being issued in the interim to alert readers to exercise caution when interpreting the content and conclusions of this article. This expression of concern will remain in place until such a time as further evidence is available.

Liraglutide modulates gut microbiota and reduces NAFLD in obese mice

Metabolic disorders such as insulin resistance and diabetes are associated with obesity and nonalcoholic fatty liver disease (NAFLD). The aggressive form of a fatty liver disease may progress to cirrhosis and hepatocellular carcinoma. Furthermore, recent studies demonstrated that there is a dysbiosis in the gut microbiota associated with early stages of metabolic disease. Therefore, the identification and repurposing of drugs already used to treat insulin resistance may be an excellent option for other disorders. We evaluated the effect of liraglutide on obesity, NAFLD and gut microbiota modulation in two different animal models of obesity: the ob/ob mice and the high-fat diet (HFD)-fed mice. Liraglutide treatment induced significant weight loss in both obesity models, showed improvements in glycemic parameters and reduced inflammatory cell infiltration in the cecum and the liver. In ob/ob mice, the liraglutide treatment was able to reduce the accumulation of liver fat by 78% and reversed steatosis in the HFD mice. The gut microbiota analysis showed that liraglutide changed the overall composition as well as the relative abundance of weight-relevant phylotypes such as a reduction of Proteobacteria and an increase of Akkermansia muciniphila in the treated HFD group. We show that liraglutide can lead to weight loss and gut microbiota modulations, and is associated with an improvement of NAFLD. Furthermore, by generating a profile of the intestinal microbiota, we compiled a list of potential bacterial targets that may modulate metabolism and induce a metabolic profile that is considered normal or clinically controlled.

Retraction Note to: L-glutamine supplementation induces insulin resistance in adipose tissue and improves insulin signalling in liver and muscle of rats with diet-induced obesity (Diabetologia, (2017), 10.1007/s00125-007-0723-z)

In light of forensic evidence indicating duplication and/or manipulation of western blot images the Editor-in-Chief is retracting the article cited above.

Expression of Concern: Modulation of gut microbiota by antibiotics improves insulin signalling in high-fat fed mice

On the basis of the recommendation of the EASD’s Scientific Integrity Panel, the Editor-in-Chief is issuing this expression of concern to alert readers to questions about the reliability of some of the data in the article cited above. In particular it appears that the immunoblots for total IKKβ in Fig. 4g and k of this paper may have been duplicated. In line with guidelines issued by the Committee on Publication Ethics (COPE), the journal has informed the corresponding author, Mario Saad, of this concern. The author’s response was considered unsatisfactory and the low resolution of the images provided to us prevented further analysis to conclusively confirm or refute this possible duplication. The University of Campinas (São Paulo, Brazil) was asked, in March 2016, to undertake an institutional investigation. As no results from this investigation have been forthcoming this expression of concern is being issued to alert readers to exercise caution when interpreting the content and conclusions of this article. This expression of concern will remain in place until such a time as further evidence is available.