Rosane Aparecida Ribeiro

Taurine supplementation improves liver glucose control in normal protein and malnourished mice fed a high-fat diet

SCOPE Poor nutrition during the perinatal period is associated with an increased risk for metabolic syndrome in adulthood. Taurine (TAU) regulates β-cell function and glucose homeo-stasis. Here, we assessed the effects of TAU supplementation upon adiposity and glucose control in malnourished mice fed a high-fat diet (HFD). METHODS AND RESULTS Weaned male C57BL/6J mice were fed a control (14% protein - C) or a protein-restricted (6% protein - R) diet for 6 weeks. Afterwards, mice received or not an HFD for 8 weeks (CH and RH). Half of the HFDmice were supplemented with 5% TAU after weaning (CHT and RHT). Protein restriction led to typical malnutrition features. HFD increased body weight, adiposity, and led to hyperleptinemia, hyperphagia, glucose intolerance, and higher liver glucose output in RH and CH groups. Fasted R mice showed higher plasma adiponectin levels and increased phosphorylation of the AMP-activated protein kinase (p-AMPK) in the liver. These parameters were reduced in RH mice and increased p-AMPK persisted in RHT. TAU prevented obesity and improved glucose tolerance only in CHT, but liver glucose control was ameliorated in both supplemented groups. Better CHT liver glucose control was linked to increased Akt (thymoma viral proto-oncogene/protein kinase B) phosphorylation. CONCLUSION Malnourished mice fed an HFD developed obesity, glucose intolerance, and increased liver glucose output. TAU preserved only normal liver glucose control in RHT mice, an effect associated with increased liver p-AMPK content.

Improvement in the expression of hepatic genes involved in fatty acid metabolism in obese rats supplemented with taurine

AIMS Fat deposition in the liver, which leads to nonalcoholic fatty liver disease is associated with obesity. Taurine (Tau) regulates lipid metabolism, representing a possible nutraceutical agent against obesity and its comorbidities. Here, we investigated whether Tau supplementation prevents hepatic lipid accumulation by regulation of the main hepatic genes involved in de novo lipogenesis and β-oxidation. MAIN METHODS Male rats received subcutaneous injections of monosodium glutamate (MSG; 4 mg/kg body weight/day) or saline (control group, CTL) during the first 5 days of life. From 21 to 120 days of age, half of each of the MSG and CTL groups received 2.5% Tau in drinking water (CTau and MTau). KEY FINDINGS MSG-treated rats were normoglycemic, hypertriglyceridemic and insulin resistant (IR). MSG rats also exhibited massive obesity and higher hepatic triglyceride (TG) content. This effect was associated with enhanced gene expression of fatty acid synthase (FASN), but reduced carbohydrate response element-binding protein (ChREBP), microsomal TG transfer protein (MTP) and carnitine palmitoyltransferase (CPT)-1a mRNAs in MSG livers. Tau supplementation decreased whole body fat accumulation and serum TG levels, without altering IR. Tau also normalized hepatic TG content by enhancing ChREBP, MTP, peroxisome proliferator-activated receptor (PPAR)-α, ACO (acyl-CoA oxidase) and CPT-1a gene expressions. SIGNIFICANCE Therefore, increased hepatic TG deposition in MSG-obese rats is associated with an enhanced FASN, and reduced MTP and CPT-1a genes. Tau supplementation prevented obesity and hepatic TG deposition by upregulating MTP mRNA, ameliorating hepatic lipid efflux, and consequently enhancing PPAR-α which increases lipid oxidation through ACO and CPT-1a gene expressions.

The bile acid TUDCA increases glucose-induced insulin secretion via the cAMP/PKA pathway in pancreatic beta cells.

OBJECTIVE While bile acids are important for the digestion process, they also act as signaling molecules in many tissues, including the endocrine pancreas, which expresses specific bile acid receptors that regulate several cell functions. In this study, we investigated the effects of the conjugated bile acid TUDCA on glucose-stimulated insulin secretion (GSIS) from pancreatic β-cells. METHODS Pancreatic islets were isolated from 90-day-old male mice. Insulin secretion was measured by radioimmunoassay, protein phosphorylation by western blot, Ca(2+) signals by fluorescence microscopy and ATP-dependent K(+) (KATP) channels by electrophysiology. RESULTS TUDCA dose-dependently increased GSIS in fresh islets at stimulatory glucose concentrations but remained without effect at low glucose levels. This effect was not associated with changes in glucose metabolism, Ca(2+) signals or KATP channel activity; however, it was lost in the presence of a cAMP competitor or a PKA inhibitor. Additionally, PKA and CREB phosphorylation were observed after 1-hour incubation with TUDCA. The potentiation of GSIS was blunted by the Gα stimulatory, G protein subunit-specific inhibitor NF449 and mimicked by the specific TGR5 agonist INT-777, pointing to the involvement of the bile acid G protein-coupled receptor TGR5. CONCLUSION Our data indicate that TUDCA potentiates GSIS through the cAMP/PKA pathway.

Taurine supplementation restores insulin secretion and reduces ER stress markers in protein-malnourished mice.

Endoplasmic reticulum (ER) stress is a cellular response to increased intra-reticular protein accumulation or poor ER function. Chronic activation of this pathway may lead to beta cell death and metabolic syndrome (MS). Poor nutrition during perinatal period, especially protein malnutrition, is associated with increased risk for MS in later life. Here, we analyzed the effects of taurine (TAU) supplementation upon insulin secretion and ER stress marker expression in pancreatic islets and in the liver from mice fed a low-protein diet. Malnourished mice had lower body weight and plasma insulin. Their islets secreted less insulin in response to stimulatory concentrations of glucose. TAU supplementation increased insulin secretion in both normal protein and malnourished mice. Western blot analysis revealed lower expression of the ER stress markers CHOP and ATF4 and increased phosphorylation of the survival protein Akt in pancreatic islets of TAU-supplemented mice. The phosphorylation of the mitogenic protein extracellular signal-regulated kinase (ERK1/2) was increased after acute incubation with TAU. Finally, the ER stress markers p-PERK and BIP were increased in the liver of malnourished mice and TAU supplementation normalized these parameters.In conclusion, malnutrition leads to impaired islet function which is restored with TAU supplementation possibly by increasing survival signals and lowering ER stress proteins. Lower ER stress markers in the liver may also contribute to the improvement of insulin action on peripheral organs.

Effects of taurine supplementation upon food intake and central insulin signaling in malnourished mice fed on a high-fat diet.

Feeding behavior is a major determinant of body composition, adiposity, and glucose homeostasis. Both obesity and malnutrition are risk factors for the metabolic syndrome and are associated with altered food intake. Here we assessed the effects of taurine (TAU) supplementation upon adiposity, food intake, and central insulin signaling in malnourished mice fed on a high-fat diet (HFD). Weaned male C57BL/6 mice were fed a control (14% protein-C) or a protein-restricted (6% protein-R) diet. After 6 weeks, both groups received or not HFD for 8 weeks (CH and RH). Half of the HFD groups were supplemented with 5% TAU (CHT and RHT). Both HFD groups were overweight and showed increased perigonadal and retroperitoneal fat pads. TAU supplementation attenuated obesity in CHT but not in RHT mice. HFD induced hypercholesterolemia and glucose intolerance, although only CH group presented fasting hyperglycemia. TAU supplementation also improved glucose homeostasis only in CHT mice. Western blot analysis showed a reduction of 55% in CH hypothalamic content of phosphorylated IRS-1 (pIRS-1) at basal condition compared with C. TAU treatment increased 35% Akt phosphorylation levels in CHT without modification in RHT hypothalamus. However, TAU supplementation did not alter hypothalamic pIRS-1 amount. CH and RH mice presented increased calorie intake that was normalized in CHT but not in RHT. In conclusion, mice fed on an HFD developed obesity, hypercholesterolemia, glucose intolerance, and increased calorie intake. TAU promoted increased hypothalamic insulin action only in CH mice which was linked to prevention of overfeeding, obesity, and glucose intolerance. Protein-restriction promoted metabolic damages that were not prevented by TAU supplementation.

Vagotomy ameliorates islet morphofunction and body metabolic homeostasis in MSG-obese rats

The parasympathetic nervous system is important for β-cell secretion and mass regulation. Here, we characterized involvement of the vagus nerve in pancreatic β-cell morphofunctional regulation and body nutrient homeostasis in 90-day-old monosodium glutamate (MSG)-obese rats. Male newborn Wistar rats received MSG (4 g/kg body weight) or saline [control (CTL) group] during the first 5 days of life. At 30 days of age, both groups of rats were submitted to sham-surgery (CTL and MSG groups) or subdiaphragmatic vagotomy (Cvag and Mvag groups). The 90-day-old MSG rats presented obesity, hyperinsulinemia, insulin resistance, and hypertriglyceridemia. Their pancreatic islets hypersecreted insulin in response to glucose but did not increase insulin release upon carbachol (Cch) stimulus, despite a higher intracellular Ca2+ mobilization. Furthermore, while the pancreas weight was 34% lower in MSG rats, no alteration in islet and β-cell mass was observed. However, in the MSG pancreas, increases of 51% and 55% were observed in the total islet and β-cell area/pancreas section, respectively. Also, the β-cell number per β-cell area was 19% higher in MSG rat pancreas than in CTL pancreas. Vagotomy prevented obesity, reducing 25% of body fat stores and ameliorated glucose homeostasis in Mvag rats. Mvag islets demonstrated partially reduced insulin secretion in response to 11.1 mM glucose and presented normalization of Cch-induced Ca2+ mobilization and insulin release. All morphometric parameters were similar among Mvag and CTL rat pancreases. Therefore, the higher insulin release in MSG rats was associated with greater β-cell/islet numbers and not due to hypertrophy. Vagotomy improved whole body nutrient homeostasis and endocrine pancreatic morphofunction in Mvag rats.

Decreased TNF-α gene expression in periodontal ligature in MSG-obese rats: A possible protective effect of hypothalamic obesity against periodontal disease?

The prevalence of obesity is increasing globally. There is evidence that the uncontrolled energetic metabolism in obese patients can accelerate periodontal disease. Therefore, the aim of this study was evaluate the possible relationship between hypothalamic obesity induced by neonatal treatment with MSG and experimental periodontal disease. Newborn male Wistar rats received subcutaneous injections in the cervical region, of 4g/Kg/day of body weight (BW) of MSG (MSG group) or hypertonic saline solution, 1.25/kg/day BW (control group, CTL). At 70 days of life periodontal disease was induced in these animals. After they were sacrificed, radiographic analyses of alveolar bone resorption and Tumor Necrosis Factor α (TNFα) gene expression in gingival tissue were performed. The neonatal treatment with MSG did not affect the concentration of plasma glucose and cholesterol (CHOL). However, plasma insulin, non-esterified fatty acids (NEFA) and triglycerides (TG) leves were higher in MSG compared with CTL group. The alveolar bone resorption was 44% lower in MSG-obese rats compared with CTL rats. In the presence of periodontal ligature, there was an increase in this parameter in all groups. The TNFα gene expression, an inflammatory marker, in periodontal tissue was similar in obese and CTL rats. The presence of ligature increased TNFα gene expression in both groups, but in a lower extension in MSG-obese rats. In conclusion these results suggested that hypothalamic obesity may produce a protective effect against periodontal disease, however further research is needed to understand the mechanisms involved in this process.

Long-Term Taurine Supplementation Leads to Enhanced Hepatic Steatosis, Renal Dysfunction and Hyperglycemia in Mice Fed on a High-Fat Diet

There is growing interest in the nutraceutical applications of taurine (TAU) for the prevention and treatment of obesity, diabetes and cardiovascular diseases. The lack of long-term clinical and animal studies available makes it difficult to address the safety of supraphysiological TAU exposure over prolonged periods. Here, we assessed growth parameters, renal function and glucose homeostasis in mice fed on a high-fat diet (HFD) and supplemented with 5 % TAU for 12 months. Body weight and fat depots were increased by the HFD and unaltered by TAU supplementation. TAU enhanced diet-induced hepatomegaly and liver steatosis. TAU-supplemented mice developed renal dysfunction as judged by increased urinary proteins and albumin, kidney weight and accumulation of lipid vacuoles in renal tubule. Long-term TAU enhanced the deleterious effects of the HFD upon glucose control, as indicated by fasting hyperglycemia, insulin hypersecretion, lower hepatic Akt activation and peripheral insulin resistance. In conclusion, long-term TAU supplementation enhanced the HFD-induced ectopic lipid accumulation in the liver and kidney and disrupted body glucose control and renal function. TAU-based interventions for obese and diabetic subjects should be carefully planned to avoid extended treatments over prolonged periods.

Decreased β‐cell insulin secretory function in aged rats due to impaired Ca2+ handling

Ageing is associated with an increased impairment in glucose homeostasis and an increased incidence of type 2 diabetes. In this study, we evaluated β‐cell function and its implications for glucose homeostasis in 24‐month‐old female Wistar rats. Aged rats showed lower plasma glucose levels in the fed and fasting states compared with control rats. In addition, insulinaemia in the fed state was reduced in the older rats. Insulin receptor β (IRβ) expression was lower in the livers of the aged animals, whereas IRβ and Akt1/2/3 protein expressions were higher in the muscles. These effects may contribute to the normal glucose tolerance observed in older rodents. Isolated islets from aged rats secreted less insulin in response to 8.3 and 16.7 mm glucose. Accordingly, this group presented a lower [Ca2+]i in the presence of glucose and a depolarizing stimulus (30 mm K+). In addition, islets from aged rats showed reduced insulin secretion in response to 100 μm carbachol (CCh), 10 nm phorbol 12‐myristate 13‐acetate and 10 μm forskolin. The expressions of protein kinase C, protein kinase A and exocytotic proteins, such as syntaxin 1 and synaptosomal‐associated protein 25 kDa (SNAP‐25), were similar in islets from aged and control rats. In conclusion, our evidence suggests that the increased incidence of type 2 diabetes with age may be due to a progressive decline in β‐cell secretory capacity due to disruption of Ca2+ handling. Furthermore, the expression of proteins of the insulin transduction cascade showed an adaptive profile, with a compensatory increase in IRβ and Akt1/2/3 in gastrocnemius muscles, which may maintain normal glucose homeostasis in 24‐month‐old rats.

Taurine Supplementation Enhances Insulin Secretion Without Altering Islet Morphology in Non-obese Diabetic Mice

Taurine (TAU) is a sulfated amino acid that improves pancreatic islet function and regulates β-cell mass in pre- and diabetic states. We herein analyzed glucose homeostasis and islet morphofunction in non-obese diabetic (NOD) mice supplemented with 2 % TAU in their drinking water from birth until 90-days of age. TAU-supplemented female NOD mice (TAU group) showed a better glucose tolerance without modification in insulinemia, when compared to non-supplemented NOD mice (CTL). Glucose-induced insulin secretion was higher in islets isolated from female and male TAU groups. In addition, a better insulin release was observed at 30 mM K+ in islets from female TAU mice. These effects were accompanied by a higher total intracellular Ca2+ concentration in islets from female and male TAU mice. TAU-treated mice did not show any alteration in β-cell and islet areas, compared with CTL mice. Islets from TAU female mice presented a higher ratio of phosphorylated Akt and ERK (extracellular signal-regulated kinase) related to Akt and ERK protein content, respectively, in comparison with CTL islets. Additional experiments using isolated islets from Swiss mice showed that 3 mM TAU prevented the reduction in insulin secretion induced by 12 h incubation with IL1-β or IL1-β + IFN-γ. In conclusion, TAU supplementation improved NOD islet function without altering endocrine pancreatic morphometry, an effect that may be associated with a protective TAU effect upon cytokine-induced islet dysfunction, together with an improved protein expression of Akt and ERK.