Insulin-sensitizing effect of rosiglitazone (BRL-49653) by regulation of glucose transporters in muscle and fat of Zucker rats

Effect of the Association of Fixed Oils from Abelmoschus esculentus (L.) Moench, Euterpe oleracea Martius, Bixa orellana Linné and Chronic SM® on Atherogenic Dyslipidemia in Wistar Rats

Dyslipidemia presents high levels of serum cholesterol and is characterized as a risk factor for cardiovascular diseases, especially for the development of atherosclerosis. E. oleracea oil (OFEO), A. esculentus oil (OFAE), B. orellana oil (OFBO), and Chronic SM® granules (CHR) are rich in bioactive compounds with the potential to treat changes in lipid metabolism. This study investigated the effects of treatments with oils from A. esculentus, E. oleracea, B. orellana, and Chronic SM® on Cocos nucifera L. saturated-fat-induced dyslipidemia. The chromatographic profile showed the majority presence of unsaturated fatty acids in the tested oils. The quantification of tocotrienols and geranylgeraniol in OFBO and CHR was obtained. Treatments with OFEO, OFAE, OFBO, and CHR were able to significantly reduce glycemia, as well as hypertriglyceridemia, total cholesterol, and LDL-cholesterol, besides increasing HDL-cholesterol. The treatments inhibited the formation of atheromatous plaques in the vascular endothelium of the treated rats. The obtained results suggest that the OFEO, OFAE, OFBO, and CHR exhibit antidyslipidemic effects and antiatherogenic activity.

A System-Level Mechanism of Anmyungambi Decoction for Obesity: A Network Pharmacological Approach

Obesity is a low-grade systemic inflammatory disease involving adipocytokines. As though Anmyungambi decoction (AMGB) showed significant improvement on obesity in a clinical trial, the molecular mechanism of AMGB in obesity remains unknown. Therefore, we explored the potential mechanisms of action of AMGB on obesity through network pharmacological approaches. We revealed that targets of AMGB are significantly associated with obesity-related and adipocyte-elevated genes. Evodiamine, berberine, genipin, palmitic acid, genistein, and quercetin were shown to regulate adipocytokine signaling pathway proteins which mainly involved tumor necrosis factor receptor 1, leptin receptor. In terms of the regulatory pathway of lipolysis in adipocytes, norephedrine, pseudoephedrine, quercetin, and limonin were shown to affect adrenergic receptor-beta, protein kinase A, etc. We also found that AMGB has the potentials to enhance the insulin signaling pathway thereby preventing type II diabetes mellitus. Additionally, AMGB was discovered to be able to control not only insulin-related proteins but also inflammatory mediators and apoptotic regulators and caspases, hence reducing hepatocyte injury in nonalcoholic fatty liver disease. Our findings help develop a better understanding of how AMGB controls obesity.

Peroxisome Proliferator-Activated Receptors as Molecular Links between Caloric Restriction and Circadian Rhythm

The circadian rhythm plays a chief role in the adaptation of all bodily processes to internal and environmental changes on the daily basis. Next to light/dark phases, feeding patterns constitute the most essential element entraining daily oscillations, and therefore, timely and appropriate restrictive diets have a great capacity to restore the circadian rhythm. One of the restrictive nutritional approaches, caloric restriction (CR) achieves stunning results in extending health span and life span via coordinated changes in multiple biological functions from the molecular, cellular, to the whole-body levels. The main molecular pathways affected by CR include mTOR, insulin signaling, AMPK, and sirtuins. Members of the family of nuclear receptors, the three peroxisome proliferator-activated receptors (PPARs), PPARα, PPARβ/δ, and PPARγ take part in the modulation of these pathways. In this non-systematic review, we describe the molecular interconnection between circadian rhythm, CR-associated pathways, and PPARs. Further, we identify a link between circadian rhythm and the outcomes of CR on the whole-body level including oxidative stress, inflammation, and aging. Since PPARs contribute to many changes triggered by CR, we discuss the potential involvement of PPARs in bridging CR and circadian rhythm.

Therapeutic application of nutraceuticals in diabetic nephropathy: Current evidence and future implications

Diabetes mellitus (DM) is a common metabolic disease which may cause several complications, such as diabetic nephropathy (DN). The routine medical treatments used for DM are not effective enough and have many undesirable side effects. Moreover, the global increased prevalence of DM makes researchers try to explore potential complementary or alternative treatments. Nutraceuticals, as natural products with pharmaceutical agents, have a wide range of therapeutic properties in various pathologic conditions such as DN. However, the exact underlying mechanisms have not been fully understood. The purpose of this review is to summarize recent findings on the effect of nutraceuticals on DN.

Diabetic Cardiomyopathy: From Mechanism to Management in a Nutshell

Diabetic cardiomyopathy (DCM) is a significant complication of diabetes mellitus characterized by gradually failing heart with detrimental cardiac remodelings, such as fibrosis and diastolic and systolic dysfunction, which is not directly attributable to coronary artery disease. Insulin resistance and resulting hyperglycemia is the main trigger involved in the initiation of diabetic cardiomyopathy. There is a constellation of many pathophysiological events, such as lipotoxicity, oxidative stress, inflammation, inappropriate activation of the renin-angiotensin-aldosterone system, dysfunctional immune modulation promoting increased rate of cardiac cell injury, apoptosis, and necrosis, which ultimately culminates into interstitial fibrosis, cardiac stiffness, diastolic dysfunction, initially, and later systolic dysfunction too. These events finally lead to clinical heart failure of DCM. Herein, The pathophysiology of DCM is briefly discussed. Furthermore, potential therapeutic strategies currently used for DCM are also briefly mentioned.

Peroxisome Proliferator-Activated Receptors and Caloric Restriction-Common Pathways Affecting Metabolism, Health, and Longevity

Caloric restriction (CR) is a traditional but scientifically verified approach to promoting health and increasing lifespan. CR exerts its effects through multiple molecular pathways that trigger major metabolic adaptations. It influences key nutrient and energy-sensing pathways including mammalian target of rapamycin, Sirtuin 1, AMP-activated protein kinase, and insulin signaling, ultimately resulting in reductions in basic metabolic rate, inflammation, and oxidative stress, as well as increased autophagy and mitochondrial efficiency. CR shares multiple overlapping pathways with peroxisome proliferator-activated receptors (PPARs), particularly in energy metabolism and inflammation. Consequently, several lines of evidence suggest that PPARs might be indispensable for beneficial outcomes related to CR. In this review, we present the available evidence for the interconnection between CR and PPARs, highlighting their shared pathways and analyzing their interaction. We also discuss the possible contributions of PPARs to the effects of CR on whole organism outcomes.

The Journey of Thiazolidinediones as Modulators of PPARs for the Management of Diabetes: A Current Perspective

Peroxisome Proliferator-Activated Receptors (PPARs) also known as glitazone receptors are a family of receptors that regulate the expression of genes and have an essential role in carbohydrate, lipid and protein metabolism apart from other functions. PPARs come in 3 sub-types: PPAR-α, PPAR-β/δ and PPAR-γ - with PPAR-γ having 2 isoforms - γ1 and γ2. Upon activation, the PPARs regulate the transcription of various genes involved in lipid and glucose metabolism, adipocyte differentiation, increasing insulin sensitivity, prevention of oxidative stress and to a certain extent, modulation of immune responses via macrophages that have been implicated in the pathogenesis of insulin resistance. Hence, PPARs are an attractive molecular target for designing new anti-diabetic drugs. This has led to a boost in the research efforts directed towards designing of PPAR ligands - particularly ones that can selectively and specifically activate one or more of the PPAR subtypes. Though, PPAR- γ full agonists such as Thiazolidinediones (TZDs) are well established agents for dyslipidemia and type 2 diabetes mellitus (T2D), the side effect profile associated with TZDs has potentiated an imminent need to come up with newer agents that act through this pathway. Several newer derivatives having TZD scaffold have been designed using structure based drug designing technique and computational tools and tested for their PPAR binding affinity and efficacy in combating T2D and some have shown promising activities. This review would focus on the role of PPARs in the management of T2D; recently reported TZD derivatives which acted as agonists of PPAR- γ and its subtypes and are potentially useful in the new drug discovery for the disease.

Impact of curcumin treatment on diabetic albino rats

The current study was aimed to study the effect of curcumin on the expression levels of brain glucose transporter 1 protein (GLUT1) and femoral muscle glucose transporter 4 protein (GLUT4), in addition to study its possible therapeutic role in ameliorating insulin resistance and the metabolic disturbance in the obese and type 2 diabetic male albino Wistar rat model. Diabetes was induced by a high-fat (HF) diet with low dose streptozotocin (STZ). Curcumin was administered intragastrically for 8 weeks (80 mg/kg BW/day). The HF-diet group developed obesity, hyperglycemia, hyperinsulinemia, reduced liver glycogen content with significant dyslipidemia. In the diabetic control group, hyperglycemia and insulin resistance high calculated homeostasis model assessment (HOMA-IR-index score) were pronounced, with reductions in liver and muscle glycogen contents, concomitant with dyslipidemia and significantly elevated malondialdehyde levels in liver and pancreas. GLUT1 and GLUT4 were down-regulated in the obese and the diabetic control groups, respectively. Curcumin, showed glucose-lowering effect and decreased insulin resistance, dyslipidemia and malondialdehyde levels in both tissues, it increased liver & muscle glycogen contents, compared to the diabetic control. Curcumin significantly up-regulated GLUT4 gene expression, compared to the diabetic control group. In conclusions, these results indicate a therapeutic role of curcumin in improving the diabetic status, obesity and enhancing the expression of GLUT4 gene.

The Therapeutic Role of Xenobiotic Nuclear Receptors Against Metabolic Syndrome

BACKGROUND

Diabetes, with an increased prevalence and various progressive complications, has become a significant global health challenge. The concrete mechanisms responsible for the development of diabetes still remain incompletely unknown, although substantial researches have been conducted to search for the effective therapeutic targets. This review aims to reveal the novel roles of Xenobiotic Nuclear Receptors (XNRs), including the Peroxisome Proliferator-Activated Receptor (PPAR), the Farnesoid X Receptor (FXR), the Liver X Receptor (LXR), the Pregnane X Receptor (PXR) and the Constitutive Androstane Receptor (CAR), in the development of diabetes and provide potential strategies for research and treatment of metabolic diseases.

METHODS

We retrieved a large number of original data about these five XNRs and organized to focus on their recently discovered functions in diabetes and its complications.

RESULTS

Increasing evidences have suggested that PPAR, FXR, LXR ,PXR and CAR are involved in the development of diabetes and its complications through different mechanisms, including the regulation of glucose and lipid metabolism, insulin and inflammation response and related others.

CONCLUSION

PPAR, FXR, LXR, PXR, and CAR, as the receptors for numerous natural or synthetic compounds, may be the most effective therapeutic targets in the treatment of metabolic diseases.

Inhibition of Sodium Glucose Cotransporter 2 Attenuates the Dysregulation of Kelch-Like 3 and NaCl Cotransporter in Obese Diabetic Mice

BACKGROUND

Mechanisms underlying the frequent association between salt-sensitive hypertension and type 2 diabetes remain obscure. We previously found that protein kinase C (PKC) activation phosphorylates Kelch-like 3 (KLHL3), an E3 ubiquitin ligase component, at serine 433. We investigated whether impaired KLHL3 activity results in increased renal salt reabsorption via NaCl cotransporter (NCC).

METHODS

We used the db/db diabetes mouse model to explore KLHL3's role in renal salt handling in type 2 diabetes and evaluated mechanisms of KLHL3 dysregulation in cultured cells.

RESULTS

We observed PKC activity in the db/db mouse kidney and phosphorylation of serine 433 in KLHL3 (KLHL3^S433-P). This modification prevents binding of with-no-lysine (WNK) kinases; however, total KLHL3 levels were decreased, indicating severely impaired KLHL3 activity. This resulted in WNK accumulation, activating NCC in distal convoluted tubules. Ipragliflozin, a sodium glucose cotransporter 2 (SGLT2) inhibitor, lowered PKC activity in distal convoluted tubule cells and reduced KLHL3^S433-P and NCC levels, whereas the thiazolidinedione pioglitazone did not, although the two agents similarly reduced in blood glucose levels. We found that, in human embryonic kidney cells expressing KLHL3 and distal convoluted tubule cells, cellular glucose accumulation increased KLHL3^S433-P levels through PKC. Finally, the effect of PKC inhibition in the kidney of db/db mice confirmed PKC's causal role in KLHL3^S433-P and NCC induction.

CONCLUSIONS

Dysregulation of KLHL3 is involved in the pathophysiology of type 2 diabetes. These data offer a rationale for use of thiazide in individuals with diabetes and provide insights into the mechanism for cardiorenal protective effects of SGLT2 inhibitors.

Progress in the discovery of naturally occurring anti-diabetic drugs and in the identification of their molecular targets

Diabetes mellitus (DM), a chronic metabolic disease, severely affects patients' life and intensively increases risks of developing other diseases. It is estimated that 0.4 billion individuals worldwide are subjected to diabetes, especially type 2 diabetes mellitus. At present, although various synthetic drugs for diabetes such as Alogliptin and Rosiglitazone, etc. have been used to manage diabetes, some of them showed severe side effects. Given that the pathogenesis of type 2 diabetes mellitus, natural occurring drugs are beneficial alternatives for diabetes therapy with low adverse effects or toxicity. Recently, more and more plant-derived extracts or compounds were evaluated to have anti-diabetic activities. Their anti-diabetic mechanisms involve certain key targets like α-glucosidase, α-amylase, DPP-4, PPAR γ, PTP1B, and GLUT4, etc. Here, we summarize the newly found anti-diabetic (type 2 diabetes mellitus) natural compounds and extracts from 2011-2017, and give the identification of their molecular targets. This review could provide references for the research of natural agents curing type 2 diabetes mellitus (T2DM).

Gelidium elegans Extract Ameliorates Type 2 Diabetes via Regulation of MAPK and PI3K/Akt Signaling

Gelidium elegans, a red alga native to the Asia Pacific region, contains biologically active polyphenols. We conducted a molecular biological study of the anti-diabetic effect of Gelidium elegans extract (GEE) in C57BL/KsJ-db/db mice. Mice that had been administered GEE had significantly lower body mass, water consumption, and fasting blood glucose than db/db controls. Moreover, hemoglobin A1c (HbA1c), an indicator of the glycemic status of people with diabetes, was significantly lower in mice that had been administered GEE. We also found that 200 mg/kg/day GEE upregulates the insulin signaling pathway by activating insulin receptor substrate-1 (IRS-1) and phosphoinositide 3-kinase (PI3K), and increasing the expression of glucose transporter type 4 (GLUT4). In parallel, mitogen-activated protein kinase (MAPK) activity was lower in GEE-treated groups. In summary, these findings indicate that GEE regulates glucose metabolism by activating the insulin signaling pathway and downregulating the MAPK signaling pathway.

Antidiabetic plant-derived nutraceuticals: a critical review

Diabetes mellitus (DM) is one of the major health problems in the world, especially amongst the urban population. Chemically synthesized drugs used to decrease the ill effects of DM and its secondary complications cause adverse side effects, viz., weight gain, gastrointestinal disturbances, and heart failure. Currently, various other approaches, viz., diet control, physical exercise and use of antidiabetic plant-derived molecules/foods are advocated to manage DM, as they are economical with fewer or no side effects. This review mainly focuses on antidiabetic plants, chemically characterized plant molecules and plant-based foods in the treatment of DM. Very little science-based evidence is available on the mechanism of action of plant-derived food molecules on the DM targets. Critical DM targets include α-amylase, α-glucosidase, DPP-IV, aldose reductase, PPAR-γ, AMP kinase and GLUT4. In-depth studies carried out on a few of those targets with specific mechanisms of action are addressed in this review. This review may help future researchers in identifying a right plant molecule to treat DM or to develop food formulations for DM management.

Flavonoids

Diabetes Mellitus is one of the major healthcare problems faced by the society today and has become alarmingly epidemic in many parts of the world. Despite enormous knowledge and technology advancement, available diabetes therapeutics only provide symptomatic relief by reducing blood glucose level, thereby, just slows down development and progression of diabetes and its associated complications. Thus, the need of the day is to develop alternate strategies that can not only prevent the progression but also reverse already “set-in” diabetic complications. Many flavonoids are reported, traditionally as well as experimentally, to be beneficial in averting diabetes and lowering risk of its accompanying complications. In the present chapter we have convened different flavonoids beneficial in diabetes and comorbid complications and discussed their mechanisms of action. Further, we conclude that coupling current therapeutics with flavonoids might provide exceptional advantage in the management of diabetes and its complications.

PPARs in obesity-induced T2DM, dyslipidaemia and NAFLD

Obesity is a worldwide epidemic that predisposes individuals to cardiometabolic complications, such as type 2 diabetes mellitus (T2DM) and nonalcoholic fatty liver disease (NAFLD), which are all related to inappropriate ectopic lipid deposition. Identification of the pathogenic molecular mechanisms and effective therapeutic approaches are highly needed. The peroxisome proliferator-activated receptors (PPARs) modulate several biological processes that are perturbed in obesity, including inflammation, lipid and glucose metabolism and overall energy homeostasis. Here, we review how PPARs regulate the functions of adipose tissues, such as adipogenesis, lipid storage and adaptive thermogenesis, under healthy and pathological conditions. We also discuss the clinical use and mechanism of PPAR agonists in the treatment of obesity comorbidities such as dyslipidaemia, T2DM and NAFLD. First generation PPAR agonists, primarily those acting on PPARγ, are associated with adverse effects that outweigh their clinical benefits, which led to the discontinuation of their development. An improved understanding of the physiological roles of PPARs might, therefore, enable the development of safe, new PPAR agonists with improved therapeutic potential.

The effect of exercise training combined with PPARγ agonist on skeletal muscle glucose uptake and insulin sensitivity in induced diabetic obese Zucker rats

[Purpose]

Exercise training with PPARγ agonist is expected to increase glucose uptake and improve insulin sensitivity in skeletal muscle of patients with diabetes. However, its mechanisms to effect glucose uptake and insulin sensitivity in skeletal muscle are unclear.

[Methods]

The mechanism of action was determined by co-treatment with PPARγ agonist- rosiglitazone and exercise training in streptozotocin induced-diabetic obese Zucker rats. Exercise training was carried out for 6 weeks (swimming, 1 h/day, 5 times/week, 5% weight/g, 32±1℃) with rosiglitazone treatment (3mg/kg/day, 6weeks).

[Results]

Glucose uptake and insulin sensitivity was decreased in diabetic than normal animals. Exercise training and rosiglitazone treatment respectively increased the expression of PPAR(peroxisome proliferators-activated receptor)-α, -β/δ, -γ, PGC-1α(PPAR-γ coactivator-1α), adiponectin, GLUT-4(glucose transportor-4) and p-AMPK-α₂(phospho-AMP activated protein kinase-α₂) in EDL and SOL of diabetic, as compared to normal animals. Interestingly, training combined with rosiglitazone significantly increased glucose uptake and insulin sensitivity, which resulted in high expression of all molecules in diabetic than all other groups.

[Conclusion]

These results indicated that exercise training combined with rosiglitazone might mediate regulation of glucose uptake and insulin sensitivity in skeletal muscle. Therefore, exercise training combined with rosiglitazone may be recommended as complementary therapies for diabetes.

Developmental Programming: Prenatal Testosterone Excess and Insulin Signaling Disruptions in Female Sheep

Women with polycystic ovary syndrome often manifest insulin resistance. Using a sheep model of polycystic ovary syndrome-like phenotype, we explored the contribution of androgen and insulin in programming and maintaining disruptions in insulin signaling in metabolic tissues. Phosphorylation of AKT, ERK, GSK3beta, mTOR, and p70S6K was examined in the liver, muscle, and adipose tissue of control and prenatal testosterone (T)-, prenatal T plus androgen antagonist (flutamide)-, and prenatal T plus insulin sensitizer (rosiglitazone)-treated fetuses as well as 2-yr-old females. Insulin-stimulated phospho (p)-AKT was evaluated in control and prenatal T-, prenatal T plus postnatal flutamide-, and prenatal T plus postnatal rosiglitazone-treated females at 3 yr of age. GLUT4 expression was evaluated in the muscle at all time points. Prenatal T treatment increased mTOR, p-p70S6K, and p-GSK3beta levels in the fetal liver with both androgen antagonist and insulin sensitizer preventing the mTOR increase. Both interventions had partial effect in preventing the increase in p-GSK3beta. In the fetal muscle, prenatal T excess decreased p-GSK3beta and GLUT4. The decrease in muscle p-GSK3beta was partially prevented by insulin sensitizer cotreatment. Both interventions partially prevented the decrease in GLUT4. Prenatal T treatment had no effect on basal expression of any of the markers in 2-yr-old females. At 3 yr of age, prenatal T treatment prevented the insulin-stimulated increase in p-AKT in liver and muscle, but not in adipose tissue, and neither postnatal intervention restored p-AKT response to insulin stimulation. Our findings provide evidence that prenatal T excess changes insulin sensitivity in a tissue- and development-specific manner and that both androgens and insulin may be involved in the programming of these metabolic disruptions.

Salacia - The new multi-targeted approach in diabetics

Salacia species plant has been used traditionally as an Ayurvedic medicine for diabetes mellitus. Studies over the past decades have shown its multi-targeted role in diabetics. In the present review article, various mechanisms of action of Salacia on diabetics are discussed in detail. Apart from the well-known action of decreasing postprandial glucose sugar by inhibiting α-glucosidase and α-pancreatic amylase, it also inhibits aldose reductase which otherwise results in microvascular complications. Importantly, its peroxisome proliferator-activated receptor (PPAR)-γ agonist (such as thiazolidinediones, the insulin sensitizers) action increases the uptake of free fatty acid (FFA) and facilitates their storage in subcutaneous fat rather than the visceral fat. This reduces plasma FFA and insulin resistance. Furthermore, it increases the expression of and translocation to the cell surface of glucose transporter 1 and 4 receptors which result in glucose uptake by the liver and skeletal muscle and decreases plasma glucose levels. It also decreases inflammatory cytokines and increases adiponectin expression. Salacia as PPAR-α agonist (such as fibrates) has a role in the management of dyslipidemia. The activation of PPAR-α leads to the increased expression of lipoprotein lipase and apolipoprotein (Apo) A-V and decrease in hepatic Apo-C-III. These actions lower plasma triglycerides in chylomicrons and very low-density lipoprotein particles, thus liberating fatty acids, which are taken up and stored as fat in adipocytes. Salacia has been shown to suppress the overexpression of cardiac PPAR-α (similar to angiotensin-converting enzyme inhibitors/angiotensin receptor blockers) and thereby preventing diabetic cardiomyopathy. It also suppresses the cardiac angiotensin II Type 1 receptors resulting in antihypertrophic and antifibrogenic effect.

Deficiency of FcϵR1 Increases Body Weight Gain but Improves Glucose Tolerance in Diet-Induced Obese Mice

Prior studies demonstrated increased plasma IgE in diabetic patients, but the direct participation of IgE in diabetes or obesity remains unknown. This study found that plasma IgE levels correlated inversely with body weight, body mass index, and body fat mass among a population of randomly selected obese women. IgE receptor FcϵR1-deficient (Fcer1a(-/-)) mice and diet-induced obesity (DIO) mice demonstrated that FcϵR1 deficiency in DIO mice increased food intake, reduced energy expenditure, and increased body weight gain but improved glucose tolerance and glucose-induced insulin secretion. White adipose tissue from Fcer1a(-/-) mice showed an increased expression of phospho-AKT, CCAAT/enhancer binding protein-α, peroxisome proliferator-activated receptor-γ, glucose transporter-4 (Glut4), and B-cell lymphoma 2 (Bcl2) but reduced uncoupling protein 1 (UCP1) and phosphorylated c-Jun N-terminal kinase (JNK) expression, tissue macrophage accumulation, and apoptosis, suggesting that IgE reduces adipogenesis and glucose uptake but induces energy expenditure, adipocyte apoptosis, and white adipose tissue inflammation. In 3T3-L1 cells, IgE inhibited the expression of CCAAT/enhancer binding protein-α and peroxisome proliferator-activated receptor-γ, and preadipocyte adipogenesis and induced adipocyte apoptosis. IgE reduced the 3T3-L1 cell expression of Glut4, phospho-AKT, and glucose uptake, which concurred with improved glucose tolerance in Fcer1a(-/-) mice. This study established two novel pathways of IgE in reducing body weight gain in DIO mice by suppressing adipogenesis and inducing adipocyte apoptosis while worsening glucose tolerance by reducing Glut4 expression, glucose uptake, and insulin secretion.

Cardiovascular pharmacotherapy: Innovation stuck in translation

Systematic reviews of animal studies have revealed serious limitations in internal and external validity strongly affecting the reliability of this research. In addition inter-species differences are likely to further limit the predictive value of animal research for the efficacy and tolerability of new drugs in humans. Important changes in the research process are needed to allow efficient translation of preclinical discoveries to the clinic, including improvements in the laboratory and publication practices involving animal research and early incorporation of human proof-of-concept studies to optimize the interpretation of animal data for its predictive value for humans and the design of clinical trials.

Modulation of glucose transporter protein by dietary flavonoids in type 2 diabetes mellitus

Diabetes mellitus (DM) is a metabolic diseases characterized by hyperglycemia due to insufficient or inefficient insulin secretory response. This chronic disease is a global problem and there is a need for greater emphasis on therapeutic strategies in the health system. Phytochemicals such as flavonoids have recently attracted attention as source materials for the development of new antidiabetic drugs or alternative therapy for the management of diabetes and its related complications. The antidiabetic potential of flavonoids are mainly through their modulatory effects on glucose transporter by enhancing GLUT-2 expression in pancreatic β cells and increasing expression and promoting translocation of GLUT-4 via PI3K/AKT, CAP/Cb1/TC10 and AMPK pathways. This review highlights the recent findings on beneficial effects of flavonoids in the management of diabetes with particular emphasis on the investigations that explore the role of these compounds in modulating glucose transporter proteins at cellular and molecular level.

Rosiglitazone enhances apolipoprotein M (Apom) expression in rat's liver

Apolipoprotein M (APOM) has been suggested as a vasculoprotective constituent of high density lipoprotein (HDL), which plays a crucial role behind the mechanism of HDL-mediated anti-atherosclerosis. Previous studies demonstrated that insulin resistance could associate with decreased APOM expressions. In agreement with our previous reports, here, we further confirmed that the insulin sensitivity was also reduced in rats treated with high concentrations of glucose; such effect could be reversed by administration of rosiglitazone, a peroxisome proliferator-activated receptor-γ (PPARγ). The present study shows that Apom expression is significantly affected by either rosiglitazone or hyperglycemia alone without cross interaction with each other, which indicates that the pathway of Apom expression regulating by hyperglycemia might be differed from that by rosiglitazone. Further study indicated that hyperglycemia could significantly inhibit mRNA levels of Lxrb (P=0.0002), small heterodimer partner 1 (Shp1) (P<0.0001), liver receptor homologue-1 (Lrh1) (P=0.0012), ATP-binding cassette transporter 1 (Abca1) (P=0.0012) and Pparb/d (P=0.0043). Two-way ANOVA analysis demonstrated that the interactions between rosiglitazone and infusion of 25% glucose solution on Shp1 (P=0.0054) and Abca1 (4E, P=0.0004) mRNA expression was statistically significant. It is concluded that rosiglitazone could increase Apom expression, of which the detailed mechanism needs to be further investigated. The downregulation of Apom by hyperglycemia might be mainly through decreasing expression of Pparg and followed by inhibiting Lxrb in rats.

Targeting the Peroxisome Proliferator-Activated Receptor-γ to Counter the Inflammatory Milieu in Obesity

Adipose tissue, which was once viewed as a simple organ for storage of triglycerides, is now considered an important endocrine organ. Abnormal adipose tissue mass is associated with defects in endocrine and metabolic functions which are the underlying causes of the metabolic syndrome. Many adipokines, hormones secreted by adipose tissue, regulate cells from the immune system. Interestingly, most of these adipokines are proinflammatory mediators, which increase dramatically in the obese state and are believed to be involved in the pathogenesis of insulin resistance. Drugs that target peroxisome proliferator-activated receptor-γ have been shown to possess anti-inflammatory effects in animal models of diabetes. These findings, and the link between inflammation and the metabolic syndrome, will be reviewed here.

In vivo multi-tissue efficacy of peroxisome proliferator-activated receptor-γ therapy on glucose and fatty acid metabolism in obese type 2 diabetic rats

OBJECTIVE

To identify the disturbances in glucose and lipid metabolism observed in type 2 diabetes mellitus, we examined the interaction and contribution of multiple tissues (liver, heart, muscle, and brown adipose tissue) and monitored the effects of the Peroxisome Proliferator-Activated Receptor-γ (PPARγ) agonist rosiglitazone (RGZ) on metabolism in these tissues.

DESIGN AND METHODS

Rates of [(18) F]fluorodeoxyglucose ([(18) F]FDG) and [(11) C]Palmitate uptake and utilization in the Zucker diabetic fatty (ZDF) rat were quantified using noninvasive positron emission tomography imaging and quantitative modeling in comparison to lean Zucker rats. Furthermore, we studied two separate groups of RGZ-treated and untreated ZDF rats.

RESULTS

Glucose uptake is impaired in ZDF brown fat, muscle, and heart tissues compared to leans, while RGZ treatment increased glucose uptake compared to untreated ZDF rats. Fatty acid (FA) uptake decreased, but FA flux increased in brown fat and skeletal muscle of ZDF rats. RGZ treatment increased uptake of FA in brown fat but decreased uptake and utilization in liver, muscle, and heart.

CONCLUSION

Our data indicate tissue-specific mechanisms for glucose and FA disposal as well as differential action of insulin-sensitizing drugs to normalize substrate handling and highlight the role that preclinical imaging may play in screening drugs for obesity and diabetes.

Identification of PPARγ ligands with One-dimensional Drug Profile Matching

Introduction

Computational molecular database screening helps to decrease the time and resources needed for drug development. Reintroduction of generic drugs by second medical use patents also contributes to cheaper and faster drug development processes. We screened, in silico, the Food and Drug Administration-approved generic drug database by means of the One-dimensional Drug Profile Matching (oDPM) method in order to find potential peroxisome proliferator-activated receptor gamma (PPARγ) agonists. The PPARγ action of the selected generics was also investigated by in vitro and in vivo experiments.

Materials and methods

The in silico oDPM method was used to determine the binding potency of 1,255 generics to 149 proteins collected. In vitro PPARγ activation was determined by measuring fatty acid-binding protein 4/adipocyte protein gene expression in a Mono Mac 6 cell line. The in vivo insulin sensitizing effect of the selected compound (nitazoxanide; 50–200 mg/kg/day over 8 days; n = 8) was established in type 2 diabetic rats by hyperinsulinemic euglycemic glucose clamping.

Results

After examining the closest neighbors of each of the reference set’s members and counting their most abundant neighbors, ten generic drugs were selected with oDPM. Among them, four enhanced fatty acid-binding protein/adipocyte protein gene expression in the Mono Mac 6 cell line, but only bromfenac and nitazoxanide showed dose-dependent actions. Induction by nitazoxanide was higher than by bromfenac. Nitazoxanide lowered fasting blood glucose levels and improved insulin sensitivity in type 2 diabetic rats.

Conclusion

We demonstrated that the oDPM method can predict previously unknown therapeutic effects of generic drugs. Nitazoxanide can be the prototype chemical structure of the new generation of insulin sensitizers.

Transcriptomic analysis of insulin-sensitive tissues from anti-diabetic drug treated ZDF rats, a T2DM animal model

Gene expression changes have been associated with type 2 diabetes mellitus (T2DM); however, the alterations are not fully understood. We investigated the effects of anti-diabetic drugs on gene expression in Zucker diabetic fatty (ZDF) rats using oligonucleotide microarray technology to identify gene expression changes occurring in T2DM. Global gene expression in the pancreas, adipose tissue, skeletal muscle, and liver was profiled from Zucker lean control (ZLC) and anti-diabetic drug treated ZDF rats compared with those in ZDF rats. We showed that anti-diabetic drugs regulate the expression of a large number of genes. We provided a more integrated view of the diabetic changes by examining the gene expression networks. The resulting sub-networks allowed us to identify several biological processes that were significantly enriched by the anti-diabetic drug treatment, including oxidative phosphorylation (OXPHOS), systemic lupus erythematous, and the chemokine signaling pathway. Among them, we found that white adipose tissue from ZDF rats showed decreased expression of a set of OXPHOS genes that were normalized by rosiglitazone treatment accompanied by rescued blood glucose levels. In conclusion, we suggest that alterations in OXPHOS gene expression in white adipose tissue may play a role in the pathogenesis and drug mediated recovery of T2DM through a comprehensive gene expression network study after multi-drug treatment of ZDF rats.

Rosiglitazone attenuates hyperglycemia-enhanced hemorrhagic transformation after transient focal ischemia in rats

Hemorrhagic transformation (HT) has been claimed to represent the most feared complication of treatment with intravenous tissue plasminogen activator (t-PA) therapy. In this study, we tested the effect of rosiglitazone on HT in a rat focal cerebral ischemia model. Male Sprague-Dawley rats received an injection of 50% dextrose (6ml/kg intraperitoneally) and were subjected to middle cerebral artery occlusion (MCAO) 10 min later, with the regional cerebral blood flow monitored in vivo by laser-Doppler-flowmetry. Two groups were included: rosiglitazone treatment and vehicle group. In the treatment group, after 1.5h of ischemia, rosiglitazone (2mg/kg) was administered at the onset of reperfusion. Neurobehavioral scores, infarct volume, hemoglobin leakage, hemorrhage rate, the expression of collagen IV and glucose transporter 1 (GLUT1) were measured at 24h after ischemia. Rosiglitazone improved neurobehavioral deficits, reduced infarct volume and hemorrhage rate, and inhibited hemoglobin leakage, when compared with the vehicle group. In addition, it increased the expression of collagen IV and GLUT1 compared to the vehicle group. Our results suggest that rosiglitazone attenuated the hyperglycemia-induced HT after MCAO, possibly by preservation of GLUT1 expression.

Peroxisome proliferator-activated receptor targets for the treatment of metabolic diseases

Metabolic syndrome is estimated to affect more than one in five adults, and its prevalence is growing in the adult and pediatric populations. The most widely recognized metabolic risk factors are atherogenic dyslipidemia, elevated blood pressure, and elevated plasma glucose. Individuals with these characteristics commonly manifest a prothrombotic state and a proinflammatory state as well. Peroxisome proliferator-activated receptors (PPARs) may serve as potential therapeutic targets for treating the metabolic syndrome and its related risk factors. The PPARs are transcriptional factors belonging to the ligand-activated nuclear receptor superfamily. So far, three isoforms of PPARs have been identified, namely, PPAR- α, PPAR-β/δ, and PPAR-γ. Various endogenous and exogenous ligands of PPARs have been identified. PPAR- α and PPAR- γ are mainly involved in regulating lipid metabolism, insulin sensitivity, and glucose homeostasis, and their agonists are used in the treatment of hyperlipidemia and T2DM. Whereas PPAR- β / δ function is to regulate lipid metabolism, glucose homeostasis, anti-inflammation, and fatty acid oxidation and its agonists are used in the treatment of metabolic syndrome and cardiovascular diseases. This review mainly focuses on the biological role of PPARs in gene regulation and metabolic diseases, with particular focus on the therapeutic potential of PPAR modulators in the treatment of thrombosis.

Proteomic analysis of rosiglitazone and guggulsterone treated 3T3-L1 preadipocytes

Adipogenesis is the differentiation of preadipocytes to adipocytes which is marked by the accumulation of lipid droplets. Adipogenic differentiation of 3T3-L1 cells is achieved by exposing the cells to Insulin, Dexamethasone and IBMX for 5-7 days. Thiazolidinedione drugs, like rosiglitazone are potent insulin sensitizing agents and have been shown to enhance lipid droplet formation in 3T3-L1 cells, a model cell line for preadipocyte differentiation. Guggulsterone is a natural drug extracted from the gum resin of tree Commiphora mukul. Guggulsterone has been shown to inhibit adipogenesis and induce apoptosis in 3T3-L1 cells. In this study we treated the 3T3-L1 preadipocytes with rosiglitazone and guggulsterone and assessed the protein expression profile using 2D gel electrophoresis-based proteomics to find out differential target proteins of these drugs. The proteins that were identified upon rosiglitazone treatment generally regulate cell proliferation and/or exhibit anti-inflammatory effect which strengthens its differentiation-inducing property. Guggulsterone treatment resulted in the identification of the apoptosis-inducing proteins to be up regulated which rightly is in agreement with the apoptosis-inducing property of guggulsterone in 3T3-L1 cells. Some of the proteins identified in our proteomic screen such as Galectin1, AnnexinA2 & TCTP were further confirmed by Real Time qPCR. Thus, the present study provides a better outlook of proteins being differentially regulated/expressed upon treatment with rosiglitazone and guggulsterone. The detailed study of the differentially expressed proteins identified in this proteomic screen may further provide the better molecular insight into the mode of action of these anti-diabetic drugs rosiglitazone and guggulsterone.

Antidiabetic effects of rice hull smoke extract on glucose-regulating mechanism in type 2 diabetic mice

The aim of this study is to determine the protective effect of a liquid rice hull smoke extract (RHSE) against type 2 diabetes (T2D) in mice induced by a high-fat diet. As compared to the control group of mice on a high-fat diet (HFD), feeding the HFD supplemented with 0.5% or 1% RHSE for 7 weeks resulted in significantly reduced blood glucose and triglyceride and cholesterol concentrations, higher serum insulin levels, and improved glucose tolerance, as assessed by an oral glucose tolerance assay. The hypoglycemic effect of RHSE was accompanied by changes in enzyme activities and cognate gene expression assessed using RT-PCR. Among the glucose metabolism regulating genes evaluated, hepatic glucokinase (GCK), the glucose transporters GLUT2 and GLUT4, and peroxisome proliferator-activated receptor-γ (PPAR-γ) were up-regulated, whereas glucose-6-phosphatase (G6 Pase) and phosphoenolpyruvate carboxykinase (PEPCK) were down-regulated in the liver of mice with RHSE-supplementation. These changes resulted in restoration of glucose-regulating activities to normal control levels. Histopathology showed that a high-fat diet intake also induced liver necrosis and damage of the islet of Langerhans in the pancreas, whereas RHSE supplementation restored necrotic damage to normal levels. Immunohistochemistry showed that RHSE supplementation can restore the reduced insulin-producing β-cell population in islet of Langerhans associated with a high-fat diet intake to nondiabetic normal control levels in a dose-dependent manner. RHSE-supplemented food could protect insulin-producing islet cells against damage triggered by oxidative stress and local inflammation associated with diabetes.

Polyphenols in madhumega chooranam, a Siddha medicine, ameliorates carbohydrate metabolism and oxidative stress in type II diabetic rats

ETHNOPHARMACOLOGICAL RELEVANCE

Present study was undertaken to demonstrate the mode of anti-diabetic action of a polyherbal Siddha Medicine, Madhumega chooranam (MMC).

MATERIALS AND METHODS

MMC was fractionated into phenolic (PMMC) and non-phenolic (NPMMC) portions in order to identify bioactive fraction. Study was performed in type II diabetic rats. Role of PMMC and NPMMC on liver glucose-6-phosphatase, fructose-1,6-bisphosphatase, glucokinase and glycogen content were determined. Their role on superoxide dismutase, reduced glutathione and lipid peroxidation were investigated. In addition, their effects on GLUT4 and PPARγ gene expression were studied. Pancreas and liver histopathology was studied using hematoxylin and eosin stain.

RESULTS

PMMC improved carbohydrate metabolism by decreasing glucose-6-phosphatase and fructose-1,6-bisphosphatase and increasing glucokinase and glycogen contents in diabetic rats liver. It alleviated oxidative stress by increasing superoxide dismutase, glutathione and decreasing lipid peroxidation content. PMMC up-regulated liver GLUT4 and PPARγ mRNA expression in comparison to the vehicle or NPMMC rats.

CONCLUSION

Madhumega chooranam mediates its anti-diabetic action through the inhibition of gluconeogenesis and activation of glycolytic pathways in type II diabetic rats. Increased GLUT4 and PPARγ expressions provide additional information on its glucose uptake/sensitising and hypolipidemic potential. Phenolic components of MMC were found to be the bioactive principles.

Twelve weeks of pioglitazone therapy significantly attenuates dysmetabolism and reduces inflammation in continuous ambulatory peritoneal dialysis patients--a randomized crossover trial

BACKGROUND

The aim of the present study was to investigate the effect of oral pioglitazone (PIO) on lipid metabolism, insulin resistance, inflammation, and adipokine metabolism in continuous ambulatory peritoneal dialysis (CAPD) patients.

METHODS

In this randomized crossover trial, 36 CAPD patients with serum triglyceride levels above 1.8 mmol/L were randomly assigned to receive either oral PIO 15 mg once daily or no PIO for 12 weeks. Then, after a 4-week washout, the patients were switched to the alternative regimen. The primary endpoint was change in serum triglycerides during the PIO regimen compared with no PIO. Secondary endpoints included changes in other lipid levels, homeostatic model assessment of insulin resistance (HOMA-IR), adipocytokines, and C-reactive protein (CRP).

RESULTS

All 36 CAPD patients (age: 64 ± 11 years; 33% men; 27.8% with diabetes mellitus) completed the study. Comparing patients after PIO and no PIO therapy, we found no significant differences in mean serum triglycerides (3.83 ± 1.49 mmol/L vs 3.51 ± 1.98 mmol/L, p = 0.2). However, mean high-density lipoprotein (0.94 ± 0.22 mmol/L vs 1.00 ± 0.21 mmol/L, p = 0.004) and median total adiponectin [10.34 μg/mL (range: 2.59 - 34.48 μg/mL) vs 30.44 μg/mL (3.47 - 93.41 μg/mL), p < 0.001] increased significantly. Median HOMA-IR [7.51 (1.39 - 45.23) vs 5.38 (0.97 - 14.95), p = 0.006], mean fasting blood glucose (7.31 ± 2.57 mmol/L vs 6.60 ± 2.45 mmol/L, p = 0.01), median CRP [8.78 mg/L (0.18 - 53 mg/L) vs 3.50 mg/L (0.17 - 26.30 mg/L), p = 0.005], and mean resistin (32.70 ± 17.17 ng/mL vs 28.79 ± 11.83 ng/mL, p = 0.02) all declined. The PIO was well tolerated, with only one adverse event: lower-extremity edema in a patient with low residual renal function.

CONCLUSIONS

Blood triglycerides were not altered after 12 weeks of PIO 15 mg once daily in CAPD patients, but parameters of dysmetabolism were markedly improved, including insulin resistance, inflammation, and adipokine balance, suggesting that PIO could be of value for this high-risk patient group. Larger, more definitive studies are needed to confirm these findings.

Effects of the insulin sensitizing drug, pioglitazone, and lipopolysaccharide administration on markers of systemic inflammation and clinical parameters in horses

Equine metabolic syndrome (EMS) is a condition of obese horses characterized by insulin resistance, systemic inflammation, and an increased risk of laminitis. The pathogenesis of EMS is thought, in part, to be due to inflammatory proteins produced by adipose tissue. Reducing inflammation may decrease the incidence of laminitis in horses with EMS. Pioglitazone hydrochloride, a thiazolidinedione, has efficacy to reduce obesity associated inflammation in humans. Eight normal, adult, horses were administered 1mg/kg pioglitazone for 14 days, and eight horses served as controls. Physical examination and hematologic variables, transcript abundance of pro-inflammatory cytokines in skeletal muscle and adipose tissue, and circulating concentrations of the acute phase protein, serum amyloid A and pro-inflammatory cytokine, TNF-α were assessed prior to, and following, an LPS infusion (35 ng/kg). The objective was to determine if pre-treatment with pioglitazone would mitigate the development of inflammation and associated clinical markers of inflammation following LPS administration. Lipopolysaccharide administration induced systemic inflammation, as assessed by clinical and hematological aberrations, increased TNF-α, SAA and adipose tissue IL-6 mRNA abundance, however no mitigating effects of pioglitazone were detected. A longer treatment period or higher dose might be indicated for future experiments.

Pharmacological treatment of hyperinsulineamia in rats depends on coping style

Passive and proactive coping styles are associated with marked differences in behavioral and neuroendocrine responses. Previous studies revealed that the passive individuals are more prone to hyperinsulinemia. Likewise, we hypothesize that different coping styles may require different drugs to treat this. We tested this by treating passive and proactive rats (Roman Low Avoidance and Roman High Avoidance rats respectively) with either Rosiglitazone or with RU486. After eight days of treatment we performed and intravenous glucose tolerance test (IVGTT) and we compared the insulin and glucose levels with those measured during the IVGTT at baseline. Rosiglitazone improved insulin levels during an IVGTT in both passive and proactive coping styles. RU486, however, lowered insulin levels only in rats with a passive coping style. This study suggests that insight in the neuroendocrine differences between passive and proactive coping styles may provide an extra impulse to improve treatment of insulin resistance, since it allows the application of drugs targeted at the individual.

Lipocalin 2 is a selective modulator of peroxisome proliferator-activated receptor-gamma activation and function in lipid homeostasis and energy expenditure

We have previously identified lipocalin 2 (Lcn2) as a cytokine playing a critical role in the regulation of body fat mass, lipid metabolism, and insulin resistance. Lcn2 deficiency reduces PPARγ gene expression in adipocytes. In this study, we investigated the role of Lcn2 in PPARγ activation and function via assessing the insulin sensitization and fatty acid (FA) homeostasis of PPARγ agonist in high-fat diet (HFD)-induced obesity in Lcn2(-/-) mice. We found that rosiglitazone (Rosi) significantly improved insulin sensitivity in Lcn2(-/-) mice as effectively as in wild-type (WT) mice; unfed-state levels of blood glucose, free FAs, and triglycerides (TGs) were significantly reduced after a 25-d treatment of Rosi in Lcn2(-/-) mice. However, Rosi action on fat deposition and FA homeostasis was altered; Rosi-induced body weight and subcutaneous fat gain and liver lipid accumulation were markedly lessened in Lcn2(-/-) mice. The results of in vivo metabolic labeling showed that Rosi markedly reduced de novo lipogenesis in adipose tissue of Lcn2(-/-) mice. In brown adipose tissue (BAT), the expression of the genes functioning in TG hydrolysis and mitochondrial oxidation was up-regulated more in Lcn2(-/-) than in WT mice. Most strikingly, Rosi stimulated significantly higher levels of uncoupling protein-1 expression in BAT, and completely rescued cold intolerance in Lcn2(-/-) mice. We demonstrate that Lcn2 is a critical selective modulator of PPARγ activation and function in lipid homeostasis and energy expenditure.

PPAR-gamma agonists and their role in type 2 diabetes mellitus management

Type 2 diabetes mellitus and obesity are the most frequent endocrine-metabolic diseases in the world and their pathogenic basis are characterized by insulin resistance and insulin secretion defects that can be demonstrated through several alterations in carbohydrates, lipids, and protein metabolism. The peroxisome proliferator-activated receptors have been identified as key regulators of glucose and lipid metabolism, because they act as transcription factors that stimulate protein synthesis in a wide variety of processes (energetic metabolism, proliferation, and cellular differentiation), of which have been identified 3 types (alpha, beta/delta, gamma). The thiazolidenediones are compounds that act as agonists of the peroxisome proliferator-activated receptor-gamma increasing the tissues sensibility (muscle, adiposity tissue, and liver) to the insulin action; that is why they are used nowadays in treatment of type 2 diabetes mellitus. These drugs produce several of adverse effects, such as weight increased, edema, anemia, pulmonary edema, and congestive cardiac failure. Even their use have been related for some studies to an increased in the myocardium infarct risk; this correlation has not been a strong determinant to remove them from the market.

Anti-diabetic effects of lemon balm (Melissa officinalis) essential oil on glucose- and lipid-regulating enzymes in type 2 diabetic mice

The antioxidant activity of lemon balm (Melissa officinalis) essential oil (LBEO) on 2,2-diphenyl-1-picrylhydrazyl (DPPH) radicals and its hypoglycaemic effect in db/db mice were investigated. LBEO scavenged 97 % of DPPH radicals at a 270-fold dilution. Mice administered LBEO (0·015 mg/d) for 6 weeks showed significantly reduced blood glucose (65 %; P < 0·05) and TAG concentrations, improved glucose tolerance, as assessed by an oral glucose tolerance test, and significantly higher serum insulin levels, compared with the control group. The hypoglycaemic mechanism of LBEO was further explored via gene and protein expression analyses using RT-PCR and Western blotting, respectively. Among all glucose metabolism-related genes studied, hepatic glucokinase and GLUT4, as well as adipocyte GLUT4, PPAR-γ, PPAR-α and SREBP-1c expression, were significantly up-regulated, whereas glucose-6-phosphatase and phosphoenolpyruvate carboxykinase expression was down-regulated in the livers of the LBEO group. The results further suggest that LBEO administered at low concentrations is an efficient hypoglycaemic agent, probably due to enhanced glucose uptake and metabolism in the liver and adipose tissue and the inhibition of gluconeogenesis in the liver.

18F9 (4-(3,6-bis (ethoxycarbonyl)-4,5,6,7-tetrahydrothieno (2,3-c) pyridin-2-ylamino)-4-oxobutanoic acid) enhances insulin-mediated glucose uptake in vitro and exhibits antidiabetic activity in vivo in db/db mice

Insulin resistance is central to the pathogenesis of type 2 diabetes mellitus. Previous studies have demonstrated that compounds that cause adipogenesis and improve glucose uptake in 3T3-L1 cells are potential insulin sensitizers. Therefore, we evaluated one such compound, 18F9, for (1) adipogenesis in human subcutaneous preadipocyte (SQ) cells, (2) glucose uptake in human skeletal muscle myotubes and SQ cells, and (3) antidiabetic activity in db/db mice. We also investigated its effect on ex vivo glucose uptake in soleus muscle isolated from continuously treated db/db mice. Gene expression profiling in soleus muscle and epididymal fat of db/db mice was performed to understand its effect on glucose metabolism, lipid metabolism, and thermogenesis. 18F9 enhanced adipogenesis in SQ cells and increased glucose uptake in SQ and human skeletal muscle myotubes cells. In db/db mice, 18F9 exhibited dose-dependent reduction in plasma glucose and insulin level. Interestingly, 18F9 was as efficacious as rosiglitazone but did not cause body weight gain and hepatic adverse effects. In addition, 18F9 demonstrated no change in plasma volume in Wistar rats. Furthermore, it enhanced ex vivo glucose uptake in soleus muscles in these mice, which substantiates our in vitro findings. Human peroxisome proliferator activated receptor-gamma transactivation assay revealed a weak peroxisome proliferator activated receptor-gamma transactivation potential (44% of rosiglitazone at 10 mumol/L) of 18F9. Gene expression profiling indicated that 18F9 increased insulin sensitivity mainly through a phosphoinositide 3-kinase-dependent mechanism. 18F9 also up-regulated genes involved in lipid transport and synthesis at par with rosiglitazone. Unlike rosiglitazone, 18F9 elevated the expression of Pdk4. In addition, 18F9 elevated the expression of glycogen synthase and adiponectin significantly higher than rosiglitazone. Taken together, these observations suggest that 18F9 is a safer and potent insulin sensitizer that demonstrates promising antidiabetic activity and is worth further development.

Are all n-3 polyunsaturated fatty acids created equal?

N-3 Polyunsaturated fatty acids have been shown to have potential beneficial effects for chronic diseases including cancer, insulin resistance and cardiovascular disease. Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) in particular have been studied extensively, whereas substantive evidence for a biological role for the precursor, alpha-linolenic acid (ALA), is lacking. It is not enough to assume that ALA exerts effects through conversion to EPA and DHA, as the process is highly inefficient in humans. Thus, clarification of ALA's involvement in health and disease is essential, as it is the principle n-3 polyunsaturated fatty acid consumed in the North American diet and intakes of EPA and DHA are typically very low. There is evidence suggesting that ALA, EPA and DHA have specific and potentially independent effects on chronic disease. Therefore, this review will assess our current understanding of the differential effects of ALA, EPA and DHA on cancer, insulin resistance, and cardiovascular disease. Potential mechanisms of action will also be reviewed. Overall, a better understanding of the individual role for ALA, EPA and DHA is needed in order to make appropriate dietary recommendations regarding n-3 polyunsaturated fatty acid consumption.

A double-blind, placebo-controlled trial of rosiglitazone for clozapine-induced glucose metabolism impairment in patients with schizophrenia

OBJECTIVE

The primary purpose of this 8-week double-blind, placebo-controlled trial of rosiglitazone 4 mg/day was to examine its effect on insulin sensitivity index (SI) and glucose utilization (SG) in clozapine-treated subjects with schizophrenia with insulin resistance.

METHOD

Eighteen subjects were randomized and accessed with a Frequently Sampled Intravenous Glucose Tolerance Test (FSIVGTT) at baseline and at week 8 to estimate SG and SI.

RESULTS

Controlling for the baseline, comparing the rosiglitazone group with placebo group, there was a non-significant improvement in SG (0.016 +/- 0.006-0.018 +/- 0.008, effect size = 0.23, P = 0.05) with a trend of improvement in SI in the rosiglitazone group (4.6 +/- 2.8-7.8 +/- 6.7, effect size = 0.18, P = 0.08). There was a significant reduction in small low-density lipoprotein cholesterol (LDL-C) particle number (987 +/- 443-694 +/- 415, effect size = 0.30, P = 0.04).

CONCLUSION

Rosiglitazone may have a role in addressing insulin resistance and lipid abnormalities associated with clozapine.

Pan-PPAR agonist beneficial effects in overweight mice fed a high-fat high-sucrose diet

OBJECTIVE

We analyzed the effect of peroxisome proliferator-activated receptor (PPAR) agonists on adipose tissue morphology, adiponectin expression, and its relation to glucose and insulin levels in C57BL/6 mice fed a high-fat high-sucrose (HFHS) diet.

METHODS

Male C57BL/6 mice received one of five diets: standard chow, HFHS chow, or HFHS plus rosiglitazone (PPAR-gamma agonist), fenofibrate (PPAR-alpha agonist), or bezafibrate (pan-PPAR agonist). Diets were administered for 11 wk and medications from week 6 to week 11. Glucose intolerance (GI) and insulin resistance were evaluated by oral glucose tolerance testing and homeostasis model assessment for insulin resistance, respectively. Adipocyte diameter was analyzed in epididymal, inguinal, and retroperitoneal fat pads and by adiponectin immunostain.

RESULTS

Mice fed the HFHS chow had hyperglycemia, GI, insulin resistance, increased fat pad weight, adipocyte hypertrophy, and decreased adiponectin immunostaining. Rosiglitazone improved GI, insulin sensitiveness, and adiponectin immunostaining, but it resulted in body weight gain, hyperphagia, and adipocyte and heart hypertrophy. Fenofibrate improved all parameters except for fasting glucose and GI. Bezafibrate was the most efficient in decreasing body weight and glucose intolerance.

CONCLUSION

Activation of PPAR-alpha, -delta, and -gamma together is better than the activation of PPAR-alpha or -gamma alone, because bezafibrate showed a wider range of action on metabolic, morphologic, and biometric alterations due to an HFHS diet in mice.