Insulin Sensitivity In Rats Research Articles

KIC (ketoisocaproic acid) and leucine have divergent effects on tissue insulin signaling but not on whole-body insulin sensitivity in rats.

Plasma levels of branched-chain amino acids and their metabolites, the branched-chain ketoacids are increased in insulin resistance. Our previous studies showed that leucine and its metabolite KIC suppress insulin-stimulated glucose uptake in L6 myotubes along with the activation of the S6K1-IRS-1 pathway. Because other tissue and fiber types can be differentially regulated by KIC, we analyzed the effect of KIC gavage on whole-body insulin sensitivity and insulin signaling in vivo. We hypothesized that KIC gavage would reduce whole-body insulin sensitivity and increase S6K1-IRS-1 phosphorylation in various tissues and muscle fibers. Five-week-old male Sprague-Dawley rats were starved for 24 hours and then gavaged with 0.75ml/100g of water, leucine (22.3g/L) or KIC (30g/L) twice, ten minutes apart. They were then euthanized at different time points post-gavage (0.5-3h), and muscle, liver, and heart tissues were dissected. Other sets of gavaged animals underwent an insulin tolerance test. Phosphorylation (ph) of S6K1 (Thr389), S6 (Ser235/6) and IRS-1 (Ser612) was increased at 30 minutes post leucine gavage in skeletal muscles irrespective of fiber type. Ph-S6 (Ser235/6) was also increased in liver and heart 30 minutes after leucine gavage. KIC gavage increased ph-S6 (Ser235/6) in the liver. Neither Leucine nor KIC influenced whole-body insulin tolerance, nor ph-Akt (Ser473) in skeletal muscle and heart. BCKD-E1 α abundance was highest in the heart and liver, while ph-BCKD-E1 α (Ser293) was higher in the gastrocnemius and EDL compared to the soleus. Our data suggests that only leucine activates the S6K1-IRS-1 signaling axis in skeletal muscle, liver and heart, while KIC only does so in the liver. The effect of leucine and KIC on the S6K1-IRS-1 signaling pathway is uncoupled from whole-body insulin sensitivity. These results suggest that KIC and leucine may not induce insulin resistance, and the contributions of other tissues may regulate whole-body insulin sensitivity in response to leucine/KIC gavage.

Adipocyte endothelin B receptor activation inhibits adiponectin production and causes insulin resistance in obese mice.

Endothelin-1 (ET-1) is elevated in patients with obesity and adipose tissue of obese mice fed high-fat diet (HFD); however, its contribution to the pathophysiology of obesity is not fully understood. Genetic loss of endothelin type B receptors (ETB) improves insulin sensitivity in rats and leads to increased circulating adiponectin, suggesting that ETB activation on adipocytes may contribute to obesity pathophysiology. We hypothesized that elevated ET-1 in obesity promotes insulin resistance by reducing the secretion of insulin sensitizing adipokines, via ETB receptor. Male adipocyte-specific ETB receptor knockout (adETBKO), overexpression (adETBOX), or control littermates were fed either normal diet (NMD) or high-fat diet (HFD) for 8 weeks. RNA-sequencing of epididymal adipose (eWAT) indicated differential expression of over 5500 genes (p < 0.05) in HFD compared to NMD controls, and changes in 1077 of these genes were attenuated in HFD adETBKO mice. KEGG analysis indicated significant increase in metabolic signaling pathway. HFD adETBKO mice had significantly improved glucose and insulin tolerance compared to HFD control. In addition, adETBKO attenuated changes in plasma adiponectin, insulin, and leptin that is observed in HFD versus NMD control mice. Treatment of primary adipocytes with ET-1 caused a reduction in adiponectin production that was attenuated in cells pretreated with an ETB antagonist. These data indicate elevated ET-1 in adipose tissue of mice fed HFD inhibits adiponectin production and causes insulin resistance through activation of the ETB receptor on adipocytes.

313. Gestational Food Restriction and Insulin Sensitivity in Rats: A Transcriptomic Analysis in the Nucleus Accumbens Across Developmental Stages

313. Gestational Food Restriction and Insulin Sensitivity in Rats: A Transcriptomic Analysis in the Nucleus Accumbens Across Developmental Stages

DEHP and DBP, common phthalates, induce glucose metabolism disorders in rats via oxidative damage of PI3K/Akt/GLUT4 signaling

Phthalic acid esters (PAEs) are environmental endocrine disruptors thought to interfere with glucose metabolism in humans. Most of the related research has focused on population epidemiological studies, with the underlying mechanisms remaining unresolved. Using an in vivo animal model, we examined the effects of oral administration of two commonly used PAEs [di(2-ethylhexyl) phthalate (DEHP) and dibutyl phthalate (DBP)] on glucose homeostasis and insulin secretion. DEHP (750 mg/kg, 1/40 LD50), DBP (500 mg/kg, 1/40 LD50), and DEHP (750 mg/kg) + DBP (500 mg/kg) exert an influence on glucose metabolism and elicit a reduction in insulin sensitivity in rats. Furthermore, these substances induce detrimental effects on the structure and functionality of pancreatic β-cells. DEHP and/or DBP triggered an increase in plasma malondialdehyde (MDA) and reduction in superoxide dismutase (SOD) activity; a reduction in the phosphorylation of phosphatidyl inositol 3 kinase (PI3K) and phospho-protein kinase B (p-Akt473) proteins; an increase in the relative expression of Bax, Caspase-8, cleaved-Caspase-9, and cleaved-Caspase-3; and a reduction in the relative expression of Bcl-2-related Bax in pancreatic tissue and of gastrocnemius glucose transporter 4 (GLUT4) in the gastrocnemius muscle. Based on these findings, these PAEs can disrupt glucose metabolism, possibly via oxidative damage of the PI3K/Akt/GLUT4 pathway; this damage induces pancreatic β-cell apoptosis, affects pancreatic β-cell function, and affects glucose metabolism and insulin resistance in rats. To the best of our knowledge, this study was the first to show that the combined effect of the two PAEs affects glucose metabolism and insulin resistance in rats that is significantly higher than the effects of each PAE. Thus, safety standards and studies do not consider this effect as a significant oversight when blending PAEs. We assert that this must be addressed and corrected for establishing more impactful and safer standards.

Dietary Supplementation with Yerba Mate (Ilex paraguariensis) Infusion Increases IRS-1 and PI3K mRNA Levels and Enhances Insulin Sensitivity and Secretion in Rat Pancreatic Islets.

"Yerba mate" (YM), an aqueous extract of Ilex paraguariensis, has antioxidant, diuretic, cardio-protective and hypoglycaemic properties. Since its effect on the pancreatic islets remains unclear, we evaluated insulin sensitivity and glucose-stimulated insulin secretion (GSIS) in rats consuming YM or tap water (C) for 21 days. Glucose tolerance, glycemia, triglyceridemia, insulinemia, TBARS and FRAP serum levels were evaluated. GSIS and mRNA levels of insulin signaling pathway and inflammatory markers were measured in isolated pancreatic islets from both groups. In C rats, islets were incubated with YM extract or its phenolic components to measure GSIS. YM improved glucose tolerance, enhanced GSIS, increased FRAP plasma levels and islet mRNA levels of IRS-1 and PI3K (p110), and decreased TBARS plasma levels and islet gene expression of TNF-α and PAI-1. Islets from C rats incubated with 100 µg/mL dry YM extract, 1 µM chlorogenic acid, 0.1 and 1 µM rutin, 1 µM caffeic acid or 1 µM quercetin showed an increase in GSIS. Our results suggest that YM enhances glucose tolerance because of its positive effects on GSIS, oxidative stress rate and insulin sensitivity in rat islets, suggesting that long-term dietary supplementation with YM may improve glucose homeostasis in pre-diabetes or type 2 diabetes.

Adipose tissue macrophage-derived exosomal miR-210-5p in modulating insulin sensitivity in rats born small for gestational age with catch-up growth.

Insulin resistance has been implicated in the pathogenesis of children born small for gestational age (SGA) with catch-up growth (CUG). Adipose tissue macrophages (ATMs) regulate insulin resistance by secreting exosomes containing microRNA (miRNA) cargo; however, their pathogenic roles and molecular mechanism are not fully understood. This study aimed to investigate the role of miR-210-5p in rats born SGA with CUG and insulin resistance. The dietary needs of pregnant rats were restricted to ensure the birth of SGA rats. Transmission electron microscopy (TEM) and Western blot analysis were used to identify the exosomes from ATMs of CUG-SGA and adequate-for-gestational-age (AGA) rats. PKH-67 staining was performed to confirm the uptake of exosomes. miR-210-5p expression was measured by quantitative reverse transcription polymerase chain reaction (qRT-PCR). Glucose uptake and output were detected with glucose uptake and output assays, respectively. Insulin resistance was detected with glucose and insulin tolerance tests in vivo. The interaction between miR-210-5p and SID1 transmembrane family member 2 (SIDT2) was validated with dual-luciferase reporter assay. miR-210-5p was observed to be highly expressed in the exosomes derived from the ATMs of CUG-SGA rats. ATM-derived exosomes can serve as vehicles to deliver miR-210-5p into adipocytes, myocytes, and hepatocytes, where it can enhance cellular insulin resistance. SIDT2 was identified as a direct target gene of miR-210-5p. The miR-210-5p-induced insulin resistance was reversed by the restored SIDT2 expression. However, overexpression of SIDT2 abolished the inhibitory effect of CUG-SGA-ATM-exosomal miR-210-5p on insulin sensitivity in vivo. ATM-derived exosomal miR-210-5p promoted insulin resistance in CUG-SGA rats by targeting SIDT2, which may act as a new potential therapeutic target for children born SGA with CUG.

Melatonin decreases plasma TNF-α and improves nonenzymatic antioxidant defence and insulin sensitivity in rats with apical periodontitis fed a high-fat diet.

To analyse the effects of melatonin (ME) treatment on oxidative stress and insulin resistance (IR) in rats with apical periodontitis (AP) fed a high-fat diet (HFD). Eighty 60-day-old rats were divided into eight groups: control (CN), AP, HFD with AP (HFDAP), control with ME (CNME), AP with ME (APME), HFD with ME (HFDME) and HFD with AP+ME (HFDAPME). The animals from the HFD groups were fed a HFD throughout the experimental period. On day 7, the animals from the AP groups were subjected to experimental AP, and after 70 days, the ME groups were treated for 30 days. Glycaemia, insulinaemia, homeostatic model assessment for IR index, tumour necrosis factor-α (TNF-α), and interleukin-6 were analysed in plasma using biochemical tests and enzyme-linked immunosorbent assay. Thiobarbituric acid-reactive substances (TBARS), carbonyl protein (CP), superoxide dismutase (SOD), catalase, glutathione peroxidase, glutathione (GSH) and total antioxidant capacity (ferric reducing antioxidant power [FRAP]) were analysed in the gastrocnemius muscle. (1) Association of AP and HDF exacerbated IR, and ME treatment improved this alteration; (2) AP and HFD and their association showed increased TNF-α, and ME reversed it; (3) TBARS increased in the AP and HFDAP groups, and ME reversed only in the group with the association of disease and diet; (4) CP increased in all HFD groups and improved in the ME groups; (5) GSH activity decreased in all experimental groups, and ME increased this parameter only in the CN and AP groups; (6) FRAP did not change between the groups, but ME treatment increased its activity in the AP and HFD groups; (7) ME increased SOD in the CN and AP groups. Apical periodontitis and HFD promoted IR, and the association of AP with diet promoted IR exacerbation; this resistance might have been caused by an increase in TNF-α. AP promoted more intense changes in lipid oxidative damage than in protein oxidative damage. In non-enzymatic antioxidant defence, it was observed that both AP and HFD and their association promoted a decrease in GSH levels. Overall, ME treatment reversed changes such as oxidative stress and IR.

Mitochondrial Dysfunction Dictates Energy Metabolism Reprogramming in Pulmonary Arterial Hypertension

IntroductionPulmonary arterial hypertension (PAH) is a progressive fatal disease with a complex pathogenic mechanism. Recent studies report that nearly 60% of patients with PAH have metabolic syndrome (MS). Unrecognized glucose intolerance and insulin resistance were also shown to be common in PAH, raising the possibility that metabolic disease predisposes to PAH. Nevertheless, the mechanistic link between the PAH and metabolic disorders remains unexplored. Mitochondrial dysfunction (MD) is one of the primary pathogenic events tightly associated with PAH and MS/ type 2 diabetes pathobiology and could play a causative role in severe metabolic perturbations.HypothesisWe hypothesized that dysfunctional mitochondria are sufficient to initiate metabolic rearrangements associated with PAH and classical metabolic disorders.MethodsIn this study, we used the recently established rat model reproducing a human mutation in the NFU1 protein, which is responsible for mitochondrial homeostasis. NFU1G206Crats develop a severe MD and spontaneously develop PAH characterized by increased right ventricle (RV) systolic pressure, RV hypertrophy, and obliterative disease of the small pulmonary arteries. An intraperitoneal glucose tolerance test (IPGTT) was used to assess the ability of NFU1G206Crats to metabolize glucose. Plasma insulin levels were measured to control insulin sensitivity. Pulmonary arterial smooth muscle cells (PASMCs) isolated from WT and NFU1G206C rats were used for measuring fatty acid oxidation (FAO) by Seahorse palmitate‐BSA oxidation assay, mitochondria isolations, and western blot analysis.ResultsAfter 5 hours of fasting, WT and NFU1G206C rats had the same baseline glucose levels (glucose (mg/dL) is 89.5±2.0 vs. 92.0±6.2; p=0.47 in WT (N=5) vs. NFU1G206C(N=6)). However, 15 min after glucose administration (2 g/kg), NFU1G206Cshowed significantly higher levels of blood glucose, which reached the peak by 30 min (193.4±32.3 vs. 340.8±50.1; p&lt;0.05 in WT vs. NFU1G206C) and remained high even after 120 min, when the glucose level of WT rats reached the baseline (96.1±11.1 vs. 155.9±15.9; p&lt;0.02 in WT vs. NFU1G206C). MD was also sufficient to induce a significantly delayed insulin response in NFU1G206Ccompared to WT, suggesting the reduced insulin sensitivity in rats with MD. We also discovered an upregulated expression of free fatty acid (FFA) transporters, CD36 and CPT1, in NFU1G206C PASMC, which corresponded to the increased levels of basal FAO in the mutant cells. This discovery was confirmed by mitochondrial proteome analysis, revealing a significantly upregulated FA metabolism and dysregulated FA synthesis in NFU1G206C PASMC. NFU1G206C PASMC also had an increased membrane translocation of PKCα, one of the diacylglycerol‐dependent PKCs activated by FFAs and involved in reduced insulin sensitivity.ConclusionWe conclude that the MD secondary to the NFU1 insufficiency induces significant metabolic derangements, such as increased flux of fatty acids, glucose intolerance, and insulin insensitivity associated with classic metabolic disorders and recently implemented in the pathogenesis of PAH. The severe metabolic reprogramming revealed in PASMC correlates with progressive pulmonary vascular disease in NFU1G206Crats.

Exercise ameliorates high-fat diet-induced insulin resistance accompanied by changes in protein levels of hepatic ATF3-related signaling in rats

PurposeExercise is an effective way to alleviate insulin resistance (IR). However, the underlying mechanisms remain to be elucidated. Previous studies demonstrated that cardiolipin synthase 1 (CRLS1)/interferon-regulatory factor-2 binding protein 2 (IRF2bp2)-activating transcription factor 3 (ATF3)-adiponectin receptor 2 (AdipoR2)-adaptor protein containing pH domain, PTB domain and leucine zipper motif 1 (APPL1)-protein kinase B (AKT/PKB)-related signaling was closely associated with obesity-induced IR-related diseases, but the correlation between exercise training alleviating obesity-induced IR and the protein levels of hepatic CRLS1/IRF2bp2-ATF3-AdipoR2-APPL1-AKT-related signaling in rats is unknown. Therefore, We want to investigate the effect of exercise training on IR and the protein levels of hepatic CRLS1/IRF2bp2-ATF3-AdipoR2-APPL1-AKT-related signaling in rat. MethodsThe male healthy Sprague-Dawley rats were divided into four groups: normal control group (NCG, n = 10), diet-induced obesity-sedentary group (DIO-SG, n = 10), diet-induced obesity-chronic exercise group (DIOCEG, n = 10) received chronic swim exercise training and diet-induced obesity-acute exercise group (DIO-AEG, n = 10) received acute swim exercise training. We measured the levels of IR-related indicators and the protein levels of hepatic CRLS1/IRF2bp2-ATF3-AdipoR2-APPL1-AKT-related signaling in NCG, DIO-SG, DIOCEG and DIO-AEG. ResultsWe found that high-fat diet (HFD)-induced obesity decreased insulin sensitivity in rats accompanied by decreased protein levels of hepatic CRLS1, IRF2bp2, AdipoR2, APPL1, p-AKT and increased protein level of hepatic ATF3. The acute exercise and the chronic exercise both increased insulin sensitivity in rats. The chronic exercise decreased hepatic ATF3 protein level and increased CRLS1, IRF2bp2, AdipoR2, APPL1, p-AKT protein levels in HFD-fed rats. The acute exercise decreased hepatic ATF3 protein level and increased hepatic IRF2bp2, APPL1 and p-AKT protein levels in HFD-fed rats. The acute exercise had no significant effect on hepatic CRLS1 and AdipoR2 protein levels in HFD-fed rats. ConclusionOur current findings indicated that exercise alleviated obesity-induced IR accompanied by changes in protein levels of hepatic ATF3-related signaling in rats. Our results are meaningful for exploring the molecular mechanism of exercise alleviating IR symptoms.

Study on effect of gypenosides on insulin sensitivity of rats with diabetes mellitus via regulating NF-κB signaling pathway

This study focused on the ameliorative effects of gypenosides(GPS) on insulin sensitivity and inflammatory factors in rats with type 2 diabetes mellitus(T2 DM) and explored their possible molecular mechanisms. After the successful establishment of T2 DM model, diabetic rats were randomly divided into four groups, including model group, GPS groups(200, 100 mg·kg~(-1)) and metformin group(100 mg·kg~(-1)), with healthy rats serving as the control. After 6-week intragastric administration, fasting blood glucose(FBG) and oral glucose tolerance were examined. The levels of insulin, C-peptide, tumor necrosis factor-α(TNF-α), interleukin-1β(IL-1β), interleukin-6(IL-6) and C-reactive protein(CRP) in serum were examined. Then the homeostasis model assessment of insulin resistance(HOMA-IR) and insulin sensitivity index(ISI) were calculated. The protein expression levels of phosphorylated insulin receptor substrate-1(p-IRS-1) and phosphorylated protein kinase B(p-Akt) in skeletal muscle were measured by Western blot, as well as those of phosphorylated inhibitor of nuclear factor-κB(NF-κB) kinase β(p-IKKβ), phosphorylated alpha inhibitor of NF-κB(p-IκBα) and phosphorylated p65 subunit of NF-κB(p-p65) in adipose tissue. The relative expression levels of glucose transporter 4(GLUT4) mRNA in skeletal muscle and NF-κB mRNA in adipose tissue were measured by qRT-PCR, and the morphological changes of pancreatic tissue were observed. Compared with the model group, the GPS groups witnessed significant decrease in FBG, marked amelioration of impaired oral glucose tolerance and significant increase in ISI. Further, the high-dose GPS group saw significantly reduced HOMA-IR, TNF-α, IL-1β and CRP, significantly increased expression levels of p-IRS-1(Tyr), p-Akt and GLUT4, and markedly inhibited p-IRS-1(Ser), p-IKKβ, p-IκBα, p-p65 and NF-κB. The concentration of CRP and the expression levels of p-IRS-1(Ser), p-IKKβ, p-IκBα and NF-κB were remarkably reduced in the low-dose GPS group. However, GPS was found less effective in the regulation of serum insulin, C-peptide and IL-6 levels and the alleviation of pancreatic islet injury. The results indicated that GPS can reduce FBG and improve insulin sensitivity in diabetic rats possibly by regulating the NF-κB signaling pathway, inhibiting inflammation, and thereby regulating the expression of key proteins in the insulin signaling pathway.

Potassium Loss Promotes Impairments in Insulin Sensitivity in Rats

Clinical observations have associated potassium (K+) wasting with metabolic syndrome and insulin resistance. Chronic alkali ingestion can lead to K+ wasting. The alkali sodium bicarbonate (NaHCO3) is now used commonly in chronic kidney disease (CKD) patients to slow renal functional decline, even in patients without metabolic acidosis. Whether chronic ingestion of alkali like NaHCO3 promotes K+ wasting and loss of insulin sensitivity in CKD remains unknown. We hypothesized that chronic NaHCO3 treatment leads to K+ wasting and impairs insulin sensitivity in a rat model of CKD. To test our hypothesis, 12 male, 12 week old Sprague Dawley (SD) rats underwent a 2/3 nephrectomy and were given 4 weeks to recover prior to being placed on either 0.1M NaHCO3 (n=6) or maintained on tap water (n=6) for 4 weeks. After 4 weeks, rats were given hydrochlorothiazide (HCTZ, 10 mg/kg/day) in the drinking water to promote additional K+ wasting in combination with NaHCO3 or tap water for another 4 weeks. Animals underwent insulin tolerance tests (ITT; 0.75 U/kg insulin i.v.) at 4 and 8 week time points. At the conclusion of the protocol, rats were sacrificed, a terminal blood gas measurement taken, and the remaining remnant kidney harvested. Following 4 weeks of NaHCO3 or tap water there was no difference in the blood glucose response to insulin or in the magnitude of the fall in blood glucose (inverse area under the curve (AUC)) in response to insulin. However, following HCTZ treatment, NaHCO3 treated rats were less sensitive to insulin compared to tap water treated rats (Two-way ANOVA, PRxGroup=0.0005, PTime<0.0001, PInteraction=0.17) and had a smaller AUC (NaHCO3 + HCTZ 1688 ± 815 vs tap water + HCTZ 4002 ± 774; unpaired t-test, p=0.06). To determine if K+ depletion could account for the loss of insulin sensitivity, we placed animals on a low K+ diet for 1 week to deplete total body K+ and then determined insulin sensitivity. 6 naïve male, 10 week old SD rats underwent a baseline ITT and an ITT after 1 week of low K+ diet (0K). There was a significant decrease in plasma K+ (baseline 3.55 ± 0.21 vs 0K 2.71 ± 0.29; paired t-test, p=0.01) and a significant effect of diet and time on the blood glucose response to insulin following dietary K+ restriction (RM Two-way ANOVA, PDiet=0.0004, PTime<0.0001, PInteraction=0.70, PSubjects=0.04). At baseline, fasted blood glucose was 144 ± 9.27 mg/dL and fell to its lowest point of 100 ± 7.05 mg/dL at 60 minutes (min), gradually recovering to 132 ± 4.95 mg/dL by end of study (120 min). In contrast, after 1 week of dietary K+ restriction, fasted blood glucose was 151 ± 5.13 mg/dL and fell to its lowest point of 112 ± 6.15 mg/dL by 40 min and recovered to 142 ± 5.30 mg/dL at 80 min, a level that was sustained until the end of the study. In conjunction with a thiazide, chronic NaHCO3 treatment results in reduced insulin sensitivity in rats. K+ depletion with dietary K+ restriction also results in loss of insulin sensitivity in rats. These data strongly implicate K+ wasting as the cause of reduced insulin sensitivity. These findings suggest that K+ wasting may be a cause of insulin resistance and underscore the importance of access to dietary K+, even for patients with CKD. CKD patients treated with NaHCO3 may be at increased risk due to the K+ wasting effects of alkali, particularly those without prior metabolic acidosis.

Effect of oxymatrine on liver gluconeogenesis is associated with the regulation of PEPCK and G6Pase expression and AKT phosphorylation.

An increase in liver gluconeogenesis is an important pathological phenomenon in type 2 diabetes mellitus (T2DM) and oxymatrine is an effective natural drug used for T2DM treatment. The present study aimed to explore the effect of oxymatrine on gluconeogenesis and elucidate the underlying mechanism. Male Sprague-Dawley rats were treated with a high-fat diet and streptozotocin for 4 weeks to induce T2DM, and HepG2 cells were treated with 55 mM glucose to simulate T2DM in vitro. T2DM rats were treated with oxymatrine (10 or 20 mg/kg weight) or metformin for 4 weeks, and HepG2 cells were treated with oxymatrine (0.1 or 1 µM), metformin (0.1 µM), or oxymatrine combined with MK-2206 (AKT inhibitor) for 24 h. Fasting blood glucose and insulin sensitivity of rats were measured to evaluate insulin resistance. Glucose production and uptake ability were measured to evaluate gluconeogenesis in HepG2 cells, and the expression of related genes was detected to explore the molecular mechanism. Additionally, the body weight, liver weight and liver index were measured and hematoxylin and eosin staining was performed to evaluate the effects of the disease. The fasting glucose levels of T2DM rats was 16.5 mmol/l, whereas in the control rats, it was 6.1 mmol/l. Decreased insulin sensitivity (K-value, 0.2), body weight loss (weight, 300 g), liver weight gain, liver index increase (value, 48) and morphological changes were observed in T2DM rats, accompanied by reduced AKT phosphorylation, and upregulated expression of phosphoenolpyruvate carboxykinase (PEPCK) and glucose-6-phosphatase (G6Pase). High-glucose treatment significantly increased glucose production and decreased glucose uptake in HepG2 cells, concomitant with a decrease in AKT phosphorylation and increase of PEPCK and G6Pase expression. In vivo, oxymatrine dose-dependently increased the sensitivity of T2DM rats to insulin, increased AKT phosphorylation and decreased PEPCK and G6Pase expression in the liver, and reversed the liver morphological changes. In vitro, oxymatrine dose-dependently increased AKT phosphorylation and glucose uptake of HepG2 cells subjected to high-glucose treatment, which was accompanied by inhibition of the expression of the gluconeogenesis-related genes, PEPCK and G6Pase. MK-2206 significantly inhibited the protective effects of oxymatrine in high-glucose-treated cells. These data indicated that oxymatrine can effectively prevent insulin resistance and gluconeogenesis, and its mechanism may be at least partly associated with the regulation of PEPCK and G6Pase expression and AKT phosphorylation in the liver.

Chronic Exposure to SCO-267, an Allosteric GPR40 Full Agonist, Is Effective in Improving Glycemic Control in Rats

Full agonist-mediated activation of free fatty acid receptor 1 (FFAR1/GPR40) alleviates diabetes in rodents. Considering that diabetes is a chronic disease, assessment of treatment durability of chronic exposure to a GPR40 full agonist is pivotal for treating patients with diabetes. However, the physiologic significance of chronic in vitro and in vivo exposure to GPR40 full agonists is largely unclear. Here, we evaluated the in vitro and in vivo effects of chronic treatment with SCO-267, a GPR40 full agonist, on signal transduction and glucose control. In vitro experiments showed that SCO-267 is an allosteric full agonist for GPR40, which activates the Gα q, Gα s, and Gα 12/13 pathways and β-arrestin recruitment. The calcium signal response was largely sustained in GPR40-overexpressing CHO cells even after prolonged incubation with SCO-267. To evaluate the in vivo relevance of chronic exposure to GPR40 full agonists, SCO-267 (1 and 10 mg/kg) was administered once daily to neonatally streptozotocin-induced diabetic rats for 15-33 days, and glucose control was evaluated. After 15 days of dosing followed by the drug washout period, SCO-267 improved glucose tolerance, most likely by increasing insulin sensitivity in rats. After 33 days, repeated exposure to SCO-267 was highly effective in improving glucose tolerance in rats. Furthermore, chronic exposure to SCO-267 increased pancreatic insulin content. These results demonstrated that even after chronic exposure, SCO-267 effectively activates GPR40 in cells and rats, suggesting the clinical application of SCO-267 in treating chronic diseases including diabetes. SIGNIFICANCE STATEMENT: GPR40 is a validated therapeutic target for diabetes. This study showed that even after chronic exposure, SCO-267, an allosteric GPR40 full agonist, effectively activates GPR40 in cells and rats; these results suggest a durable efficacy of SCO-267 in patients.

Long-term effects of moderate physical exercise during early childhood on insulin sensitivity in rats during adulthood

É de grande importância a investigação dos efeitos do exercício para a saúde metabólica quando realizado no início da vida, e quais seriam as respostas durante a fase adulta. O objetivo desse estudo é analisar os efeitos do exercício físico de intensidade moderada durante a infância na adiposidade e sensibilidade à insulina de ratos durante a fase adulta. Vinte ratos Wistar desmamados de 28 dias de vida foram divididos em grupos Controle e Treinado. O grupo Controle permaneceu sedentário, enquanto o grupo Treinado realizou exercício de natação a 80% do limiar anaeróbio (determinado pelo teste de lactato mínimo) por 1hora/dia, 5dias/semana do 28º até o 90º dia de vida. No fim do experimento, a massa corporal, adiposidade, sensibilidade à insulina, glicemia, insulinemia, insulina pancreática, atividade lipogênica do tecido adiposo mesentérico, atividade lipogênica e estoques de glicogênio no músculo gastrocnêmio e captação de glicose pelo músculo sóleo foram analizadas. O grupo Treinado apresentou menor ganho de massa corporal, acúmulo de gordura, síntese de lipídios, glicemia, insulinemia e insulina pancreática. Kitt, HOMA-IR, estoques de glicogênio no gastrocnêmio e captação de glicose pelo sóleo foram maiores nesse grupo. Portanto, concluímos que o exercício físico moderado realizado durante a infância pode contribuir para a redução da adiposidade corporal e resistência à insulina durante a fase adulta em ratos Wistar.

Long-term effects of moderate physical exercise during early childhood on insulin sensitivity in rats during adulthood

É de grande importância a investigação dos efeitos do exercício para a saúde metabólica quando realizado no início da vida, e quais seriam as respostas durante a fase adulta. O objetivo desse estudo é analisar os efeitos do exercício físico de intensidade moderada durante a infância na adiposidade e sensibilidade à insulina de ratos durante a fase adulta. Vinte ratos Wistar desmamados de 28 dias de vida foram divididos em grupos Controle e Treinado. O grupo Controle permaneceu sedentário, enquanto o grupo Treinado realizou exercício de natação a 80% do limiar anaeróbio (determinado pelo teste de lactato mínimo) por 1hora/dia, 5dias/semana do 28º até o 90º dia de vida. No fim do experimento, a massa corporal, adiposidade, sensibilidade à insulina, glicemia, insulinemia, insulina pancreática, atividade lipogênica do tecido adiposo mesentérico, atividade lipogênica e estoques de glicogênio no músculo gastrocnêmio e captação de glicose pelo músculo sóleo foram analizadas. O grupo Treinado apresentou menor ganho de massa corporal, acúmulo de gordura, síntese de lipídios, glicemia, insulinemia e insulina pancreática. Kitt, HOMA-IR, estoques de glicogênio no gastrocnêmio e captação de glicose pelo sóleo foram maiores nesse grupo. Portanto, concluímos que o exercício físico moderado realizado durante a infância pode contribuir para a redução da adiposidade corporal e resistência à insulina durante a fase adulta em ratos Wistar.

Loss of endothelin type B receptor function improves insulin sensitivity in rats.

High salt intake (HS) is associated with obesity and insulin resistance. ET-1, a peptide released in response to HS, inhibits the actions of insulin on cultured adipocytes through ET-1 type B (ETB) receptors; however, the in vivo implications of ETB receptor activation on lipid metabolism and insulin resistance is unknown. We hypothesized that activation of ETB receptors in response to HS intake promotes dyslipidemia and insulin resistance. In normal salt (NS) fed rats, no significant difference in body mass or epididymal fat mass was observed between control and ETB deficient rats. After 2 weeks of HS, ETB-deficient rats had significantly lower body mass and epididymal fat mass compared to controls. Nonfasting plasma glucose was not different between genotypes; however, plasma insulin concentration was significantly lower in ETB-deficient rats compared to controls, suggesting improved insulin sensitivity. In addition, ETB-deficient rats had higher circulating free fatty acids in both NS and HS groups, with no difference in plasma triglycerides between genotypes. In a separate experiment, ETB-deficient rats had significantly lower fasting blood glucose and improved glucose and insulin tolerance compared to controls. These data suggest that ET-1 promotes adipose deposition and insulin resistance via the ETB receptor.

Salvia hispanica L. (chia) seed improves skeletal muscle lipotoxicity and insulin sensitivity in rats fed a sucrose-rich diet by modulating intramuscular lipid metabolism

• Chia seed modulates muscle lipid metabolism in insulin resistant SRD-fed rats. • Chia seed increases key factors of muscle oxidative capacity in SRD-fed rats. • Chia seed attenuates the increased muscle lipogenic pathway in SRD-fed rats. • Chia seed increases n -3/ n -6 PUFA ratio in the skeletal muscle of SRD-fed rats. This study investigates the possible mechanisms involved in the beneficial effect of chia seed on skeletal muscle lipotoxicity and insulin resistance in rats fed a sucrose-rich diet (SRD). Results showed that chia seed reduced the increased lipid content in the skeletal muscle of SRD-fed rats. This was accompanied by an increase of muscle-type carnitine palmitoyltransferase 1 enzyme activity, peroxisome proliferator-activated receptors (PPARα, PPARγ) and phosphorylated AMP activated protein kinase protein levels. Moreover, the precursor and mature forms of sterol regulatory element-binding protein-1 and lipogenic enzyme activities were decreased. Fatty acid translocase FAT/CD 36 and n -3/ n -6 fatty acids ratio of membrane phospholipids were increased. This work shows that an increase in the key factors levels associated with muscle oxidative capacity and a reduction in the lipogenic pathway would be some mechanisms involved in the beneficial effects of chia seed on skeletal muscle lipotoxicity in insulin resistant SRD-fed rats.

Vitamin D supplementation enhanced oral glucose tolerance in normoglycemic rats and insulin sensitivity in rats fed high fat emulsion

Several reports have suggested possible role of vitamin D deficiency in the pathogenesis of both type 1 and 2 diabetes. However, there is no agreement on the level of vitamin D requirement for optimum glycemic control. This work evaluated the effect of vitamin D supplementation on oral glucose tolerance (OGT) and insulin sensitivity, with the aim of determining the possible supplementation rate of vitamin D required for optimum glycemic control. Oral glucose tolerance was evaluated in normoglycemic rats, with vitamin D supplementation (VDS) at the rate of 0.07, 0.14, and 0.35 μg/kg orally for 28 days. Oral glucose tolerance (OGT) was evaluated by administration of 2000 mg/kg glucose/rat orally and blood glucose determined at 30, 60, and 120 min post glucose administration. Insulin sensitivity was evaluated in normoglycemic rats fed high fat emulsion (HFE) at the rate of 5 ml/kg/rat for 10 days and VDS was at the rate of 0.04, 0.05, 0.07, and 0.35 μg/kg for 38 days. Insulin (0.05 u/kg) was injected intraperitoneally to each rat, and blood glucose level determined at 5, 30, 60, and 120 min post insulin administration. Blood glucose of VDS rats was significantly (p < 0.05) lower than the vitamin D restricted group at 120 min. Significantly, (p < 0.05) higher OGT was recorded in the VDS groups. Insulin sensitivity (K) values showed inverse dose dependency with higher K values at lower vitamin D doses. Vitamin D supplementation enhanced glucose tolerance and insulin sensitivity at lower doses.

Zinc supplementation reduces diet-induced obesity and improves insulin sensitivity in rats.

Rates of obesity have been growing at alarming rates, compromising the health of the world population. Thus, the search for interventions that address the metabolic repercussions of obesity are necessary. Here we evaluated the metabolic and antioxidant effects of zinc and branched-chain amino acids (BCAA) supplementation on obese rats. Male Wistar rats were fed either a high-fat/high-fructose diet (HFD) or a standard diet (SD) for 19 weeks. From the fifteenth week until the end of the experiment, HFD- and SD-fed rats received zinc (6 mg/kg) or BCAA (750 mg/kg) supplementation. Body weight, abdominal fat, lipid profile, blood glucose, insulin, leptin, and hepatic transaminases were evaluated. In the liver, superoxide dismutase and catalase activities and lipid peroxidation were also analyzed. HFD-fed animals showed increased weight gain, abdominal fat pad, plasma insulin, leptin, and triglycerides levels in comparison with SD-fed rats. Zinc supplementation reduced all these parameters, suggesting a beneficial role for the treatment of obesity. BCAA, on the other hand, did not show any beneficial effect. Liver antioxidant enzymes and hepatic transaminases plasma levels did not change among groups. Lipid peroxidation was higher in HFD-fed rats and was not reverted by zinc or BCAA supplementation. In conclusion, zinc supplementation may be a useful strategy for the treatment of the metabolic dysfunction associated with obesity.

Bilateral renal cryodenervation decreases arterial pressure and improves insulin sensitivity in fructose-fed Sprague-Dawley rats.

Consumption of food high in fructose is prevalent in modern diets. One week of moderately high fructose intake combined with high salt diet has been shown to increase blood pressure and failed to suppress plasma renin activity (PRA). We tested the hypothesis that the hypertension and high PRA are consequences of elevated renal sympathetic nerve activity (RSNA). In protocol 1, we assessed RSNA by telemetry in conscious Sprague-Dawley rats given 20% fructose or 20% glucose in drinking water on a 0.4% NaCl diet (NS) for 1 wk and then transitioned to a 4% NaCl diet (HS). After an additional week, mean arterial pressure (MAP) and RSNA increased significantly in fructose-fed but not glucose-fed HS rats. In protocol 2, fructose (Fruc)- or glucose (Glu)-fed rats on NS or HS diet for 3 wk underwent sham denervation (shamDNX) or bilateral renal denervation using cryoablation (cryoDNX). MAP was higher in Fruc-HS rats compared with Glu-NS, Glu-HS, or Fruc-NS rats and decreased after cryoDNX ( P < 0.01). MAP did not change in Fruc-HS shamDNX rats. Renal norepinephrine content decreased by 85% in cryoDNX ( P < 0.01 vs. shamDNX). PRA significantly decreased after cryoDNX in both Fruc-NS and Fruc-HS rats. Nonfasting blood glucose levels were similar among the four groups. Glucose-to-insulin ratio significantly increased in Fruc-HS cryoDNX rats, consistent with greater insulin sensitivity. Taken together, these studies show that renal sympathoexcitation is, at least in part, responsible for salt-dependent increases in MAP, increased PRA, and decreased insulin sensitivity in rats fed a moderately high fructose diet for as little as 3 wk.