Dopamine D2 receptor agonist, bromocriptine, remodels adipose tissue dopaminergic signalling and upregulates catabolic pathways, improving metabolic profile in type 2 diabetes.

BACKGROUND AND OBJECTIVES: The therapeutic effects of the dopamine D2 receptor (D2R) agonist, bromocriptine, in type 2 diabetes (T2D) have been attributed to central nervous system actions. However, peripheral dopamine directly modulates glucose uptake in insulin-sensitive tissues and lipid metabolism in adipose tissue (AT). We hypothesized that the dopaminergic system may be impaired in the adipose tissue of patients with T2D and that the therapeutic actions of bromocriptine could involve the modulation of metabolism in this tissue. METHODS: The expression of dopamine receptors was evaluated in visceral AT samples from patients with obesity and stratified in several groups: insulin sensitive (IS); insulin resistance (IR) normoglycaemic; insulin resistant prediabetic; insulin resistant diabetic, according to Ox-HOMA2IR, fasting glycaemia and HbA1c levels. T2D Goto-Kakizaki rats (GK) were fed a high-caloric diet (HCD) for five months and treated with bromocriptine (10 mg/kg/day, i.p.) in the last month. The levels of dopaminergic system mediators and markers of insulin sensitivity and glucose and lipid metabolism were assessed in the peri-epididymal adipose tissue (pEWAT) and brown (BAT) adipose tissues, liver, and skeletal muscle. RESULTS: Patients with IR presented a decreasing trend of DRD1 expression in the visceral adipose tissue, being correlated with the expression of UCP1, PPARA, and insulin receptor (INSR) independently of insulin resistance and body mass index. Although no differences were observed in DRD2, DRD4 expression was significantly decreased in patients with prediabetes and T2D. In HCD-fed diabetic rats, bromocriptine increased D1R and tyrosine hydroxylase (TH) levels in pEWAT and the liver. Besides reducing adiposity, bromocriptine restored GLUT4 and PPARγ levels in pEWAT, as well as postprandial InsR activation and postabsorptive activation of lipid oxidation pathways. A reduction of liver fat, GLUT2 levels and postprandial InsR and AMPK activation in the liver was observed. Increased insulin sensitivity and GLUT4 levels in BAT and an improvement of the overall metabolic status were observed. CONCLUSIONS: Bromocriptine treatment remodels adipose tissue and the liver dopaminergic system, with increased D1R and TH levels, resulting in higher insulin sensitivity and catabolic function. Such effects may be involved in bromocriptine therapeutic effects, given the impaired expression of dopamine receptors in the visceral adipose tissue of IR patients, as well as the correlation of D1R expression with InsR and metabolic mediators.

Dietary Glycotoxins Impair Hepatic Lipidemic Profile in Diet-Induced Obese Rats Causing Hepatic Oxidative Stress and Insulin Resistance.

Nonalcoholic fatty liver disease (NAFLD) is caused by excessive liver lipid accumulation, but insulin resistance is specifically associated with impaired lipid saturation, oxidation, and storage (esterification), besides increased de novo lipogenesis. We hypothesized that dietary glycotoxins could impair hepatic lipid metabolism in obesity contributing to lipotoxicity-driven insulin resistance and thus to the onset of nonalcoholic steatohepatitis (NASH). In diet-induced obese rats with methylglyoxal-induced glycation, magnetic resonance spectroscopy, mass spectrometry, and gas chromatography were used to assess liver composition in fatty acyl chains and phospholipids. High-fat diet-induced obesity increased liver lipid fraction and suppressed de novo lipogenesis but did not change fatty acid esterification and saturation or insulin sensitivity. Despite a similar increase in total lipid fraction when supplementing the high-fat diet with dietary glycotoxins, impairment in the suppression of de novo lipogenesis and decreased fatty acid unsaturation and esterification were observed. Moreover, glycotoxins also decreased polyunsaturated cardiolipins and caused oxidative stress, portal inflammation, and insulin resistance in high-fat diet-induced obese rats. Dietary glycated products do not change total lipid levels in the liver of obese rats but dramatically modify the lipidemic profile, leading to oxidative stress, hepatic lipotoxicity, and insulin resistance in obesity and thus contribute to the onset of NASH.

Insulin resistance is associated with tissue-specific regulation of HIF-1α and HIF-2α during mild chronic intermittent hypoxia.

Chronic intermittent hypoxia (CIH) is a feature of obstructive sleep apnea (OSA). Whereas clinical studies have demonstrated the association between OSA and insulin resistance, the molecular mechanisms behind it are still unknown. Herein we investigated the effect of mild CIH on insulin sensitivity and we evaluated the changes in insulin and HIF signaling pathways that occur in CIH-induced insulin resistance. We showed that mild CIH obtained by 5/6 hypoxic (5%O2) cycles/h, 10.5h/day during 28 and 35 days increased arterial blood pressure. Insulin resistance and insulinemia increased with CIH duration, being significantly different after 35 days of CIH. Thirty-five days of CIH decreased insulin receptor expression and phosphorylation in skeletal muscle and adipose tissue, but not in the liver. Conversely, Glut2 expression increased in the liver of CIH-animals. Thirty-five days of CIH up-regulated HIF-1α in the liver and down-regulated HIF-1α and HIF-2α in skeletal muscle. We concluded that the effect of CIH on insulin sensitivity and signaling is time-dependent and is associated with changes in HIF signaling in insulin-sensitive tissues.

Long-term globular adiponectin administration improves adipose tissue dysmetabolism in high-fat diet-fed Wistar rats.

Adiponectin administration to obese or type 2 diabetic patients is still far off, due to its expensive costs and absence of studies demonstrating the effectiveness of its chronic administration. We performed long-term globular adiponectin administration, testing its usefulness in improving adipose tissue metabolism. Adiponectin (98 υg/day) was administered through a subcutaneous minipump with continued release (28 days) to Wistar rats fed a high-fat diet. Adiponectin decreased body weight and adipocyte size, while decreasing circulating leptin levels. More, adiponectin was able to increase IkappaBalpha and PPARgamma levels and to prevent high-fat diet-induced impairment of insulin signalling, especially in epididymal adipose tissue. This resulted in improved glucose profile. High-fat diet caused an impairment of lipolysis in epididymal adipose tissue, which was partially restored by adiponectin treatment. Long-term globular adiponectin administration was able to improve pathways of insulin signalling and lipid storage in adipose tissue of high-fat diet-fed rats, contributing to a better metabolic profile.

Effects of atorvastatin and insulin in vascular dysfunction associated with type 2 diabetes.

Atorvastatin and insulin have distinct mechanisms of action to improve endothelial function. Therefore, we hypothesized that atorvastatin and insulin therapies alone or in combination could have beneficial effects on endothelium-dependent vascular reactivity, oxidative stress, inflammation and metabolic parameters in Goto-Kakizaki (GK) rats, a model of type 2 diabetes fed with atherogenic diet (GKAD). In parallel with the development of diabetes and lipid profile, the generation of oxidative stress was determined by measurement of lipid peroxides and oxidized proteins and the presence of inflammation was evaluated by assessing C-reactive protein (CRP). Additionally, endothelial dependent and independent vascular sensitivity to acetylcholine and sodium nitroprusside were evaluated. GKAD showed increased carbonyl stress, inflammation, fasting glycemia, dyslipidemia and endothelial dysfunction when compared to control GK rats. Noteworthy, supplementation with insulin deteriorated endothelial dysfunction while atorvastatin induced an improvement. Atorvastatin and insulin therapies in combination improved metabolic parameters, CRP levels and insulin resistance indexes and ameliorated endothelial dysfunction in GKAD rats while they were unable to reduce urinary 8-isoprostranes and plasma carbonyl compounds. The therapeutic association of atorvastatin and insulin provided a better metabolic control with a reduction in endothelial dysfunction in GKAD rats by a mechanism that involves an improvement in systemic inflammation.

Methylglyoxal chronic administration promotes diabetes-like cardiac ischaemia disease in Wistar normal rats.

BACKGROUND AND AIMS: The influence of lifestyle is well documented, especially the diet regime, in the development of type 2 diabetes (T2D) and associated cardiovascular diseases. Diabetic patients have increased risk of suffering cardiac ischemia and impaired response to such accidents. Methylglyoxal (MG) circulates at high concentration in diabetics' blood and is linked to the development of diabetes chronic complications. We propose that besides promoting the cardiovascular disease, MG may also negatively regulate the endogenous cardioprotection pathways after ischemia. METHODS AND RESULTS: We performed a comparative study between three animal groups: normal Wistar (W), type 2 diabetic non-obese Goto-Kakizaki (GK) and normal rats submitted to MG chronic administration (3 months) with gradually enhanced concentration, up to 75 mg/Kg (WMG). Hearts were submitted to different experimental conditions: control, ischemia and ischemia-reperfusion. Levels of oxidative stress markers, advanced glycation end-products (AGEs) and their receptors (RAGEs) were evaluated. The serine/threonine protein kinase Akt (Akt), crucial for cardiomyocytes recovery after ischemia, and apoptosis markers were also assessed. Levels of MG, systemic and cardiac oxidative stress markers, AGEs and RAGEs were similar in GK and WMG groups. Akt protein was negatively regulated by MG, leading to impaired apoptotic markers. CONCLUSION: Chronic MG administration to normal rodents mimicked most diabetic alterations, being associated with the development of cardiovascular disease and the impairment of survival pathways. Our results demonstrate the negative effect of MG rich diet in healthy animals and suggest the potential of methylglyoxal as a therapeutic target in diabetes.

Common mechanisms of dysfunctional adipose tissue and obesity-related cancers.

The relation between cancer and metabolic disorders was recognized several decades ago, but the underlying mechanisms involved in cancer development and progression remain obscure. In the last years, many groups have been studying systemic adipose tissue markers in cancer patients. However, few consistent results were obtained. On the other hand, several studies revealed many aspects of adipose tissue physiology in obesity. Nowadays, it is recognized that excessive lipid uptake in adipocytes leads to hypertrophy and consequently to metabolic dysregulation, hypoxia, inflammation, impaired adipocytokine expression and angiogenesis, insulin resistance and macrophage recruitment. In obese patients, tumours commonly colocalize with excessive adipose tissue accumulation, and most of the features of hypertrophic adipose tissue are observed in cancer patients, namely breast and colon. This review aimed to summarize pathological adipose tissue alterations that may contribute to cancer aetiology and development.

Methylglyoxal causes structural and functional alterations in adipose tissue independently of obesity.

CONTEXT: Adipose tissue is one of the first organs to develop insulin resistance even with moderate BMI. However, the contribution of developing hyperglycaemia and concomitant methylglyoxal increment to tissue dysfunction during type 2 diabetes progression was not addressed before. METHODS: Young and aged Wistar and Goto-Kakizaki rats (non-obese model of type 2 diabetes) and a group of MG-treated W rats were used to investigate the chronic effects of hyperglycaemia and ageing and specifically MG-induced mechanisms. RESULTS: Diabetic and aged rats showed decreased adipose tissue irrigation and interstitial hypoxia. Hyperglycaemia of diabetic rats leaded to fibrosis and accumulation of PAS-positive components, exacerbated in aged animals, which also showed decreased hipoadiponectinemia, increased MCP-1 expression and macrophage infiltration to glycated fibrotic regions. MG leaded to increased free fatty acids, hipoadiponectinemia, decreased irrigation, hypoxia and macrophage recruitment for glycated fibrotic regions. CONCLUSIONS: MG contributes to dysfunction of adipose tissue during type 2 diabetes progression.

Metformin and atorvastatin combination further protect the liver in type 2 diabetes with hyperlipidaemia.

BACKGROUND: non-alcoholic fatty liver disease (NAFLD) and type 2 diabetes are associated with dyslipidaemia, inflammation and oxidative stress. However, the pathophysiology of NAFLD in type 2 diabetes with hyperlipidaemia is not fully known, as well as the utility of the commonly prescribed anti-diabetic and lipid-lowering drugs in ameliorating liver injury markers. METHODS: hepatic complications of type 2 diabetes with hyperlipidaemia and the effects of atorvastatin and metformin, isolated and in association, in systemic and hepatic inflammatory and oxidative stress markers were tested using genetic type 2 diabetic Goto-Kakizaki rats fed with a high-fat diet. RESULTS: the high-fat diet aggravated the overall metabolic state and the hepatic markers of injury. All treatments decreased fasting glycaemia, insulin resistance and free fatty acid levels. Combined treatment further decreased C-reactive protein (CRP), adiponectin, liver tumour necrosis factor-α (TNF-α) and interleukin-6 (IL-6), systemic and hepatic oxidative stress and portal inflammation. CONCLUSIONS: our data provides evidence of a greater benefit with a combination of atorvastatin and metformin in improving liver injury in type 2 diabetes with hyperlipidaemia.

Methylglyoxal-induced imbalance in the ratio of vascular endothelial growth factor to angiopoietin 2 secreted by retinal pigment epithelial cells leads to endothelial dysfunction.

Progressive microvascular complications are a main feature of diabetes and are associated with impairment of the angiogenic response. Methylglyoxal (MGO) has been implicated in the molecular events that lead to endothelial dysfunction in diabetes. In this study, we hypothesize that increased levels of MGO disrupt the ratio of vascular endothelial growth factor (VEGF) to angiopoietin 2 (Ang 2) secreted by retinal pigment epithelial (RPE) cells, which provides a key destabilizing signal that leads to apoptosis and decreased proliferation of retinal endothelial cells. Indeed, we show that MGO increases the levels of Ang 2 and dramatically decreases the levels of VEGF secreted by RPE cells in response to hypoxia. Downregulation of VEGF is likely to be related to decreased hypoxia-inducible factor-1alpha (HIF-1alpha) protein levels and HIF-1 transcriptional activity. Data further show that MGO-induced imbalance in the VEGF/Ang II ratio significantly changes the levels of BAX and Bcl-2 in endothelial cells. Moreover, this imbalance is accompanied by an increase in the activity of caspase-3 and decreased proliferation of endothelial cells. Data obtained in cell culture systems are consistent with observations in retinas of diabetic animals, where increased availability of MGO is associated with changes in distribution and levels of HIF-1alpha, VEGF and Ang 2 and increased microvascular permeability. In conclusion, the MGO-induced imbalance in the VEGF/Ang 2 ratio secreted by retinal epithelial cells activates apoptosis and decreases proliferation of retinal endothelial cells, which are likely to contribute to endothelial dysfunction in diabetic retinopathy.

Food deprivation promotes oxidative imbalance in rat brain.

The present study was aimed to evaluate the effect of food deprivation in brain oxidative status of Wistar and Goto-Kakizaki (GK) rats. For this purpose, we evaluated several oxidative stress parameters: lipid peroxidation (thiobarbituric acid reactive substances [TBARS]) and protein oxidation markers, hydrogen peroxide (H(2)O(2)) levels, nonenzymatic (reduced [GSH] and oxidized glutathione [GSSG] and vitamin E) and enzymatic (glutathione peroxidase [GPx], glutathione reductase [GRed], and manganese superoxide dismutase [MnSOD]) antioxidant defenses. Four-mo-old Wistar and GK rats were divided into 2 groups. One group of each rat strain was maintained under normal diet and the other groups were maintained under 50% food deprivation during 2 mo. GK rats under normal diet presented lower levels of vitamin E and higher GRed activity and GSH/GSSG ratio when compared with Wistar control rats. In Wistar rats, food deprivation induced a significant decrease in vitamin E levels and a significant increase in GPx activity, H(2)O(2) production, and TBARS formation in the presence of the prooxidant pair ADP/Fe(2+). However, GK rats under food deprivation presented a significant decrease in vitamin E levels and GRed activity and a significant increase in H(2)O(2) production when compared with GK under normal diet. In summary, our results indicate that food deprivation affects brain oxidative status, which could predispose brain cells to degeneration and death.

A role for atorvastatin and insulin combination in protecting from liver injury in a model of type 2 diabetes with hyperlipidemia.

Non-alcoholic fatty liver disease (NAFLD) is a major complication linked with the metabolic syndrome associated with dyslipidemia, inflammation, and oxidative stress. Impact of type 2 diabetes with hyperlipidemia in NAFLD has to be established, as well as the utility of commonly prescribed anti-diabetic and lipid-lowering agents in improving liver injury markers. Genetic type 2 diabetic Goto-Kakizaki rats were fed with a high-fat diet to test hepatic effects of type 2 diabetes with hyperlipidemia and the effect of atorvastatin and insulin, individually and in combination, in systemic and hepatic inflammatory and oxidative stress markers. High-fat diet aggravated fasting glycemia, systemic and liver lipids, and inflammatory and oxidative stress markers. Individual treatments improved glycemic and lipid profiles, but failed to improve inflammatory markers, whereas insulin was able to reduce liver oxidative stress parameters. Combination of insulin and atorvastatin further improved glycemic and lipid profiles and decreased circulating C-reactive protein levels and liver inflammatory and oxidative stress markers. Insulin and atorvastatin combination leads to better glycaemic and lipid profiles and to better protection against liver inflammation and oxidative stress, giving a superior level of liver protection in type 2 diabetic with hyperlipidemia.

Antioxidant and vascular effects of gliclazide in type 2 diabetic rats fed high-fat diet.

Diabetes mellitus is characterized by oxidative stress, which in turn determines endothelial dysfunction. Gliclazide is a sulphonylurea antidiabetic drug with antioxidant effects due to its azabicyclo-octyl ring. It has been reported to potentially protect the vasculature through improvements in plasma lipid levels and platelet function. We hypothesized that gliclazide has a beneficial effect on endothelial function in Goto-Kakizaki rats (GK), an animal model of type 2 diabetes fed an atherogenic diet for 4 months. We evaluated the influence of gliclazide on both metabolic and oxidative status and NO-mediated vasodilation. GKAD rats showed increased oxidative stress and impaired endothelium-dependent vasodilation. GKAD rats treated with gliclazide showed increased sensitivity to NO-mediated vasodilation, a significant decrease in fasting glycemia and insulinemia, and a significant decrease in systemic oxidative stress. In conclusion, our results suggest that gliclazide treatment improves NO-mediated vasodilation in diabetic GK rats with dyslipidemia probably due to its antioxidant effects, although we cannot rule out substantial benefits due to a reduction in fasting blood glucose. The availability of a compound that simultaneously decreases hyperglycemia, hyperinsulinemia, and inhibits oxidative stress is a promising therapeutic candidate for the prevention of vascular complications of diabetes.

Therapeutic association of atorvastatin and insulin in cardiac ischemia: study in a model of type 2 diabetes with hyperlipidemia.

UNLABELLED: Combination therapy recently emerged as a potential therapeutic option in order to improve cardiovascular risk in diabetics, since therapies commonly used in monotherapy failed in significantly optimizing this risk. METHODS: A type 2 diabetes animal model was used to test the effects of a high-fat diet, atorvastatin and insulin (isolated or in association), in glycemic, lipid and inflammatory profiles, oxidative stress markers and cardiac mitochondrial function in ischemia-reperfusion conditions. RESULTS: High-fat diets significantly worsened fasting glycemia and lipid profile; it also increased C-reactive protein (CRP) and oxidative stress and compromised mitochondrial response to ischemia. Insulin decreased fasting glucose and free fatty acid levels and insulin resistance, while increasing HDL-cholesterol, but had no effect in inflammatory markers. Atorvastatin decreased circulating adiponectin levels and did not improve inflammatory markers, although it improved fasting glycemia, glucose tolerance, free fatty acids and HDL-cholesterol. The combined use of atorvastatin and insulin improved several parameters, as did each of the treatments separately. However, treatment association went beyond these results, by decreasing atherogenicity index and circulating CRP levels. Insulin and its association with atorvastatin significantly prevented mitochondrial dysfunction observed in the high-fat diet group, while atorvastatin showed some beneficial effects but in much less extent. CONCLUSIONS: Altogether, these results show that administration of an high-fat diet in a model of type 2 diabetes increases cardiovascular risk and combined use of atorvastatin and insulin provides a superior control of cardiovascular risk markers in diabetic and hyperlipidemic subjects.

Soybean oil treatment impairs glucose-stimulated insulin secretion and changes fatty acid composition of normal and diabetic islets.

We investigated the effect of sub-chronic soybean oil (SO) treatment on the insulin secretion and fatty acid composition of islets of Langerhans obtained from Goto-Kakizaki (GK), a model of type 2 diabetes, and normal Wistar rats. We observed that soybean-treated Wistar rats present insulin resistance and defective islet insulin secretion when compared with untreated Wistar rats. The decrease in insulin secretion occurred at all concentrations of glucose and arginine tested. Furthermore we observed that soybean-treated normal islets present a significant decrease in two saturated fatty acids, myristic and heneicosanoic acids, and one monounsaturated eicosenoic acid, and the appearance of the monounsaturated erucic acid. Concerning diabetic animals, we observed that soybean-treated diabetic rats, when compared with untreated GK rats, present an increase in plasma non-fasting free fatty acids, an exacerbation of islet insulin secretion impairment in all conditions tested and a significant decrease in the monounsaturated palmitoleic acid. Altogether our results show that SO treatment results in a decrease of insulin secretion and alterations on fatty acid composition in normal and diabetic islets. Furthermore, the impairment of insulin secretion, islet erucic acid and fasting plasma insulin levels are similar in treated normal and untreated diabetic rats, suggesting that SO could have a deleterious effect on beta-cell function and insulin sensitivity.