Rosiglitazone prevents the impairment of human islet function induced by fatty acids: evidence for a role of PPARgamma2 in the modulation of insulin secretion

Pancreatic beta-cell mass and function and therapeutic implications of using antidiabetic medications in type 2 diabetes

Nowadays, the focus of diabetes treatment has switched from lowering the glucose level to preserving glycemic homeostasis and slowing the disease progression. The main pathophysiology of both type 1 diabetes and long-standing type 2 diabetes is pancreatic β-cell mass loss and dysfunction. According to recent research, human pancreatic β-cells possess the ability to proliferate in response to elevated insulin demands. It has been demonstrated that in insulin-resistant conditions in humans, such as obesity or pregnancy, the β-cell mass increases. This ability could be helpful in developing novel treatment approaches to restore a functional β-cell mass. Treatment strategies aimed at boosting β-cell function and mass may be a useful tool for managing diabetes mellitus and stopping its progression. This review outlines the processes of β-cell failure and detail the many β-cell abnormalities that manifest in people with diabetes mellitus. We also go over standard techniques for determining the mass and function of β-cells. Lastly, we provide the therapeutic implications of utilizing antidiabetic drugs in controlling the mass and function of pancreatic β-cells.

Adipose tissue macrophages secrete small extracellular vesicles that mediate rosiglitazone-induced insulin sensitization

The obesity epidemic continues to worsen worldwide, driving metabolic and chronic inflammatory diseases. Thiazolidinediones, such as rosiglitazone (Rosi), are PPARγ agonists that promote 'M2-like' adipose tissue macrophage (ATM) polarization and cause insulin sensitization. As ATM-derived small extracellular vesicles (ATM-sEVs) from lean mice are known to increase insulin sensitivity, we assessed the metabolic effects of ATM-sEVs from Rosi-treated obese male mice (Rosi-ATM-sEVs). Here we show that Rosi leads to improved glucose and insulin tolerance, transcriptional repolarization of ATMs and increased sEV secretion. Administration of Rosi-ATM-sEVs rescues obesity-induced glucose intolerance and insulin sensitivity in vivo without the known thiazolidinedione-induced adverse effects of weight gain or haemodilution. Rosi-ATM-sEVs directly increase insulin sensitivity in adipocytes, myotubes and primary mouse and human hepatocytes. Additionally, we demonstrate that the miRNAs within Rosi-ATM-sEVs, primarily miR-690, are responsible for these beneficial metabolic effects. Thus, using ATM-sEVs with specific miRNAs may provide a therapeutic path to induce insulin sensitization.

Beta-cell function in type 2 diabetes (T2DM): Can it be preserved or enhanced?

Type 2 diabetes (T2DM) is a complex metabolic disorder manifested by hyperglycemia, insulin resistance, and deteriorating beta-cell function. A way to prevent progression of the disease might be to enhance beta-cell function and insulin secretion. However, most previous studies examined beta-cell function while patients were using glycemia-lowering agents without an adequate period off medications (washout). In the present review we focus on studies with a washout period. We performed a literature search (2010 to June 2021) using beta-cell function and enhancement. The evidence shows that beta-cell function can be enhanced. Bariatric surgery and very low calorie diets show improvement in beta-cell function in many individuals. In addition, use of glucagon-like peptide-1 receptor agonists for prolonged periods (3 years or more) can also lead to improvement of beta-cell function. Further research is needed to understand the mechanisms leading to improved beta-cell function and identify agents that could enhance beta-cell function in patients with T2DM.

Association of increased risk of cardiovascular diseases with higher levels of perfluoroalkylated substances in the serum of adults

Evidence showing the association of perfluoroalkylated substance (PFAS) exposure with CVD risk is scarce. The objective of this study was to explore the relationships of CVD risk with mixed or individual serum PFAS levels among general adults. We analyzed combined data of 7904 adults who participated in the National Health and Nutrition Examination Survey 2003-2012 with a Bayesian kernel machine regression (BKMR) to examine the relationships of individual or mixed PFAS exposure with total CVD risk. A logistic regression model and restricted cubic spline (RCS) regression with multivariate adjustment were conducted to assess the relationships between individual serum PFAS levels and the risk of total CVD or its subtypes. A mediation model was applied to investigate how C-reactive protein (CRP) levels mediate the strength of the association. The BKMR results indicated a positive relationship between mixed PFAS exposure and total CVD risk; among the PFASs, perfluorooctane sulfonic acid (PFOS) had the highest posterior inclusion probability. As determined by logistic regression, a log-unit change in PFOS levels was positively related to a higher risk of heart attack and stroke in males (both P < 0.05). A nonlinear relationship was found between PFOS levels and stroke risk (P for nonlinearity = 0.04), as illustrated in the RCS plot. The mediation analysis showed that CRP levels mediated 8% and 1.2% of the relationship between serum PFOS and PFNA levels, respectively, and the prevalence of stroke. A significant relationship between higher serum PFAS concentrations and an increased risk of CVD was observed, mainly in males.

Physiologic Insulin Resensitization as a Treatment Modality for Insulin Resistance Pathophysiology

Prevalence of type 2 diabetes increased from 2.5% of the US population in 1990 to 10.5% in 2018. This creates a major public health problem, due to increases in long-term complications of diabetes, including neuropathy, retinopathy, nephropathy, skin ulcers, amputations, and atherosclerotic cardiovascular disease. In this review, we evaluated the scientific basis that supports the use of physiologic insulin resensitization. Insulin resistance is the primary cause of type 2 diabetes. Insulin resistance leads to increasing insulin secretion, leading to beta-cell exhaustion or burnout. This triggers a cascade leading to islet cell destruction and the long-term complications of type 2 diabetes. Concurrent with insulin resistance, the regular bursts of insulin from the pancreas become irregular. This has been treated by the precise administration of insulin more physiologically. There is consistent evidence that this treatment modality can reverse the diabetes-associated complications of neuropathy, diabetic ulcers, nephropathy, and retinopathy, and that it lowers HbA1c. In conclusion, physiologic insulin resensitization has a persuasive scientific basis, significant treatment potential, and likely cost benefits.

Metabolic implications of pancreatic fat accumulation

Fat accumulation outside subcutaneous adipose tissue often has unfavourable effects on systemic metabolism. In addition to non-alcoholic fatty liver disease, which has received considerable attention, pancreatic fat has become an important area of research throughout the past 10 years. While a number of diagnostic approaches are available to quantify pancreatic fat, multi-echo Dixon MRI is currently the most developed method. Initial studies have shown associations between pancreatic fat and the metabolic syndrome, impaired glucose metabolism and type 2 diabetes mellitus. Pancreatic fat is linked to reduced insulin secretion, at least under specific circumstances such as prediabetes, low BMI and increased genetic risk of type 2 diabetes mellitus. This Review summarizes the possible causes and metabolic consequences of pancreatic fat accumulation. In addition, potential therapeutic approaches for addressing pancreatic fat accumulation are discussed.

Vitamin D Combined with Pioglitazone Mitigates Type-2 Diabetes-induced Hepatic Injury Through Targeting Inflammation, Apoptosis, and Oxidative Stress

Inflammation is a major pathophysiological factor in development of type-2 diabetes mellitus (T2DM). Vitamin D (VITD) plays an imperative role in modulation of several inflammatory responses. The current study aimed to investigate the possible beneficial effects of coadministration of VITD with pioglitazone (PIO), a PPAR-γ agonist, in fructose/streptozotocin (F/STZ) T2DM model in male Wistar rats. T2DM was induced by maintaining rats on 10% (w/v) fructose in drinking water for 9 weeks with an intraperitoneal injection of sub-diabetogenic dose of STZ (35 mg/kg) by the end of the fourth week. One week after STZ injection, PIO (10 mg/kg/day) alone or with VITD (500 IU/kg/day) was administered orally to diabetic rats till the end of the experiment. Blood samples were collected, livers were homogenized to determine biochemical parameters, and samples of livers were fixed in 10% formalin in saline for histological examination. Administration of PIO alone improved diabetes-induced inflammatory and oxidative states besides controlling hyperglycemia and decreasing apoptosis. Coadministration of VIT D with PIO promoted additional improvement in glycemic and lipid profiles, provided further control on diabetic-induced hepatic inflammation evident by downregulating TLR2, TLR4, and IKK-β while upregulating IκB-α expression and reducing inflammatory cytokines namely; NF-κB, TNF-α, IL-6, and IL-1β, decreasing apoptosis and oxidative stress by hampering caspase-3 and MDA contents, respectively, and improved liver histology than PIO alone. These beneficial effects of VIT D may expand its use by diabetics combined with antidiabetic drugs due to its anti-inflammatory, antioxidant, and antiapoptotic properties.

Non-glucose modulators of insulin secretion in healthy humans: (dis)similarities between islet and in vivo studies

Optimal metabolic homeostasis requires precise temporal and quantitative control of insulin secretion. Both in vivo and in vitro studies have often focused on the regulation by glucose although many additional factors including other nutrients, neurotransmitters, hormones and drugs, modulate the secretory function of pancreatic β-cells. This review is based on the analysis of clinical investigations characterizing the effects of non-glucose modulators of insulin secretion in healthy subjects, and of experimental studies testing the same modulators in islets isolated from normal human donors. The aim was to determine whether the information gathered in vitro can reliably be translated to the in vivo situation. The comparison evidenced both convincing similarities and areas of discordance. The lack of coherence generally stems from the use of exceedingly high concentrations of test agents at too high or too low glucose concentrations in vitro, which casts doubts on the physiological relevance of a number of observations made in isolated islets. Future projects resorting to human islets should avoid extreme experimental conditions, such as oversized stimulations or inhibitions of β-cells, which are unlikely to throw light on normal insulin secretion and contribute to the elucidation of its defects.

Targeting β-cell dedifferentiation and transdifferentiation: opportunities and challenges

The most distinctive pathological characteristics of diabetes mellitus induced by various stressors or immune-mediated injuries are reductions of pancreatic islet β-cell populations and activity. Existing treatment strategies cannot slow disease progression; consequently, research to genetically engineer β-cell mimetics through bi-directional plasticity is ongoing. The current consensus implicates β-cell dedifferentiation as the primary etiology of reduced β-cell mass and activity. This review aims to summarize the etiology and proposed mechanisms of β-cell dedifferentiation and to explore the possibility that there might be a time interval from the onset of β-cell dysfunction caused by dedifferentiation to the development of diabetes, which may offer a therapeutic window to reduce β-cell injury and to stabilize functionality. In addition, to investigate β-cell plasticity, we review strategies for β-cell regeneration utilizing genetic programming, small molecules, cytokines, and bioengineering to transdifferentiate other cell types into β-cells; the development of biomimetic acellular constructs to generate fully functional β-cell-mimetics. However, the maturation of regenerated β-cells is currently limited. Further studies are needed to develop simple and efficient reprogramming methods for assembling perfectly functional β-cells. Future investigations are necessary to transform diabetes into a potentially curable disease.

Sclerostin-Neutralizing Antibody Treatment Rescues Negative Effects of Rosiglitazone on Mouse Bone Parameters

Obesity, a growing pandemic, is a risk factor for many cancers and causes increased bone marrow adipose tissue (BMAT). in vitro studies and obese animal models suggest that BMAT contributes to cancer progression, but there is a lack of preclinical models to directly test BMAT's role in cancer. Overactivation of peroxisome-proliferator-activated receptor-γ (PPARγ) can skew bone formation and resorption rates, resulting in increased BMAT and trabecular bone loss. Thiazolidinediones (eg, rosiglitazone) are anti-diabetic therapies that promote adipogenesis through PPARγ activation. We investigated if rosiglitazone increases BMAT in an immunocompromised model, commonly used in cancer research, and if these effects could be reversed by co-administering a bone anabolic agent (sclerostin-neutralizing antibody [Scl-Ab]), which has been shown to inhibit adipogenesis, using DXA, μCT, OsO4 μCT, and dynamic histomorphometry. Four weeks of rosiglitazone in female SCID Beige mice (cohort 1) significantly decreased trabecular bone volume (BV/TV) by about one-half, through increased osteoclast and suppressed osteoblast activity, and significantly increased BMAT. In cohort 2, mice were administered rosiglitazone ± Scl-Ab for 4 weeks, and then rosiglitazone was discontinued and Scl-Ab or vehicle were continued for 6 weeks. Scl-Ab significantly increased bone parameters (eg, BV/TV, N.Ob/B.Pm, and MS/BS) in both groups. Scl-Ab also overcame many negative effects of rosiglitazone (eg, effects on trabecular bone parameters, increased mineralization lag time [MLT], and decreased bone formation rate [BFR]). Interestingly, Scl-Ab significantly decreased rosiglitazone-induced BMAT in the femur, mostly due to a reduction in adipocyte size, but had a much weaker effect on tibial BMAT. These data suggest targeting sclerostin can prevent rosiglitazone-induced bone loss and reduce BM adiposity, in some, but not all BMAT locations. Collectively, our data demonstrate that rosiglitazone increases BMAT in SCID Beige mice, but concomitant changes in bone may confound its use to specifically determine BMAT's role in tumor models. © 2020 American Society for Bone and Mineral Research (ASBMR).

Association between exposure to per- and polyfluoroalkyl substances and blood glucose in pregnant women

Increasing evidence shows that exposure to per- and polyfluoroalkyl substances (PFASs), common and persistent anthropogenic pollutants, may affect glucose homeostasis. However, data is limited for pregnant women, and it is less clear how novel fluorinated pollutants affect glucose homeostasis during pregnancy. Our goal was to investigate the relationships of exposure to13 PFASs including some novel fluorinated pollutants with blood glucose in 874 Chinese pregnant women from the general population. We measured blood glucose following an oral glucose tolerance test (OGTT) in the second trimester and quantified PFAS concentrations in umbilical cord blood. The associations of PFAS exposure with fasting, 1-h OGTT and 2-h OGTT glucose were examined using the general linear regression model. For every doubling of perfluorobutane sulfonate (PFBS), a short-chain PFAS, the 1-h and 2-h OGTT blood glucose increased 0.09 mmol/L (β = 0.09, 95%CI: 0.02, 0.17) and 0.07 mmol/L (β = 0.07, 95%CI: 0.01, 0.13), respectively. In addition, perfluoroheptanoate (PFHpA), an alternative of perfluorooctanoate (PFOA), was positively associated with fasting glucose (β = 0.07, 95%CI: 0.02, 0.13; high vs low). Higher levels of PFAS exposure were related to increased blood glucose in pregnant women, indicating PFAS exposure may impair glucose homeostasis during pregnancy.

Concentrations of perfluoroalkyl and polyfluoroalkyl substances and blood glucose in pregnant women

BACKGROUND

Evidence on the association between exposure to perfluoroalkyl and polyfluoroalkyl substances (PFASs) and blood glucose concentrations in pregnant women is inconsistent. This study aimed to examine the association between PFAS exposure and the concentrations of fasting plasma glucose (FPG) and one-hour plasma glucose (1 h-PG) after a 50-g oral glucose tolerance test in pregnant women.

METHODS

The study was based on the Shanghai-Minhang Birth Cohort, in which 1292 pregnant women were recruited. Among them, 981 women provided blood samples (at 12-16 gestational weeks) for PFAS measurement. FPG data collected from 856 women at 12-20 GW and 1 h-PG data collected from 705 women at 20-28 GW were obtained through medical records from the routine prenatal care system. High FPG or 1 h-PG was defined as ≥90th percentile of FPG or 1 h-PG. The analysis of eight PFASs was conducted in this study: perfluorohexane sulfonate (PFHxS), perfluorooctane sulfonate (PFOS), perfluorooctanoic acid (PFOA), perfluorononanoic acid (PFNA), perfluorodecanoic acid (PFDA), perfluoroundecanoic acid (PFUdA), perfluorododecanoic acid (PFDoA), and perfluorotridecanoic acid (PFTrDA). The odds ratios (ORs) and associated 95% confidence intervals (CIs) were estimated to determine the associations of each PFAS compound with high FPG and 1 h-PG from a logistic regression model.

RESULTS

After adjustment for potential confounders, most PFASs were positively associated with high 1 h-PG concentrations. The OR for high 1 h-PG concentrations was 1.87 (95% CI: 1.15-3.05) with a one log unit increase of PFOS; similar associations were observed for PFNA (OR: 2.15, 95% CI: 1.24-3.74), PFDA (OR: 1.61, 95% CI: 1.10-2.44), PFUdA (OR: 1.71, 95% CI: 1.12-2.62), and PFDoA (OR: 1.34, 95% CI: 1.00-1.81). When the PFAS concentrations were categorized into three groups by tertiles, the highest tertiles of PFOS, PFOA, PFNA, PFDA, PFDoA, and PFTrDA had a statistically significant increase in the risk of high 1 h-PG concentrations compared with the lowest tertiles. No statistically significant association was observed between PFAS exposure and high FPG.

CONCLUSION

PFAS exposure was associated with an increased risk of high 1 h-PG among pregnant women, but no such association was observed for FPG.

S. Ferreira KC, Neto JCR. Pharmacological Strategies for Insulin Sensitivity in Obesity and Cancer: Thiazolidinediones and Metformin

Background:

Chronic diseases, such as obesity and cancer, have high prevalence rates. Both diseases have hyperinsulinemia, hyperglycemia, high levels of IGF-1 and inflammatory cytokines in common. Therefore, these can be considered triggers for cancer development and growth. In addition, low-grade inflammation that modulates the activation of immune cells, cellular metabolism, and production of cytokines and chemokines are common in obesity, cancer, and insulin resistance. Pharmacological strategies are necessary when a change in lifestyle does not improve glycemic homeostasis. In this regard, thiazolidinediones (TZD) possess multiple molecular targets and regulate PPARγ in obesity and cancer related to insulin resistance, while metformin acts through the AMPK pathway.

Objective:

The aim of this study was to review TZD and metformin as pharmacological treatments for insulin resistance associated with obesity and cancer.

Conclusions:

Thiazolidinediones restored adiponectin secretion and leptin sensitivity, reduced lipid droplets in hepatocytes and orexigen peptides in the hypothalamus. In cancer cells, TZD reduced proliferation, production of reactive oxygen species, and inflammation by acting through the mTOR and NFκB pathways. Metformin has similar effects, though these are AMPK-dependent. In addition, both drugs can be efficient against certain side effects caused by chemotherapy.

Insulin Resistance and Atherosclerosis: Implications for Insulin-Sensitizing Agents

Patients with type 2 diabetes mellitus (T2DM) are at high risk for macrovascular complications, which represent the major cause of mortality. Despite effective treatment of established cardiovascular (CV) risk factors (dyslipidemia, hypertension, procoagulant state), there remains a significant amount of unexplained CV risk. Insulin resistance is associated with a cluster of cardiometabolic risk factors known collectively as the insulin resistance (metabolic) syndrome (IRS). Considerable evidence, reviewed herein, suggests that insulin resistance and the IRS contribute to this unexplained CV risk in patients with T2DM. Accordingly, CV outcome trials with pioglitazone have demonstrated that this insulin-sensitizing thiazolidinedione reduces CV events in high-risk patients with T2DM. In this review the roles of insulin resistance and the IRS in the development of atherosclerotic CV disease and the impact of the insulin-sensitizing agents and of other antihyperglycemic medications on CV outcomes are discussed.

Recent Insights Into Mechanisms of β-Cell Lipo- and Glucolipotoxicity in Type 2 Diabetes

The deleterious effects of chronically elevated free fatty acid (FFA) levels on glucose homeostasis are referred to as lipotoxicity, and the concurrent exposure to high glucose may cause synergistic glucolipotoxicity. Lipo- and glucolipotoxicity have been studied for over 25 years. Here, we review the current evidence supporting the role of pancreatic β-cell lipo- and glucolipotoxicity in type 2 diabetes (T2D), including lipid-based interventions in humans, prospective epidemiological studies, and human genetic findings. In addition to total FFA quantity, the quality of FFAs (saturation and chain length) is a key determinant of lipotoxicity. We discuss in vitro and in vivo experimental models to investigate lipo- and glucolipotoxicity in β-cells and describe experimental pitfalls. Lipo- and glucolipotoxicity adversely affect many steps of the insulin production and secretion process. The molecular mechanisms underpinning lipo- and glucolipotoxic β-cell dysfunction and death comprise endoplasmic reticulum stress, oxidative stress and mitochondrial dysfunction, impaired autophagy, and inflammation. Crosstalk between these stress pathways exists at multiple levels and may aggravate β-cell lipo- and glucolipotoxicity. Lipo- and glucolipotoxicity are therapeutic targets as several drugs impact the underlying stress responses in β-cells, potentially contributing to their glucose-lowering effects in T2D.

Anemia is inversely associated with serum C-peptide concentrations in individuals with type 2 diabetes

The purpose of the study was to test the hypothesis that anemia is related with serum C-peptide concentrations in individuals with type 2 diabetes mellitus (DM).This cross-sectional study was carried out in 1300 individuals with type 2 DM. We measured fasting C-peptide, 2-hour postprandial C-peptide, and postprandial C-peptide minus fasting C-peptide (ΔC-peptide) concentrations. Anemia was defined as hemoglobin (Hb) concentrations <130 g/L in men and <120 g/L in women. Anemia was graded into 2 groups: grade I anemia of Hb concentrations ≥110 g/L and grade II anemia of Hb concentrations <110 g/L.Fasting C-peptide, postprandial C-peptide, and ΔC-peptide concentrations were lower in individuals with anemia. According to the grade of anemia, the average C-peptide concentrations differed significantly after adjusting for other covariates. In the multivariable model, the statistically significant relation between anemia and serum C-peptide concentrations remained after adjusting for confounders, including age, gender, family history of diabetes, body mass index, duration of diabetes, glycated Hb, free fatty acids, hypertension, and hyperlipidemia (fasting C-peptide concentration: β = -0.057, P = .032; postprandial C-peptide concentration: β = -0.098, P < .001; ΔC-peptide concentration: β = -0.095, P < .001).Anemia was inversely associated with serum C-peptide concentrations in individuals with type 2 DM.

Vildagliptin/pioglitazone combination improved the overall glycemic control in type I diabetic rats

Type I diabetes (TID) is generally assumed to be caused by an immune associated, if not directly immune-mediated, destruction of pancreatic β-cells. In patients with long-term diabetes, the pancreas lacks insulin-producing cells and the residual β-cells are unable to regenerate. Patients with TID are subjected to a lifelong insulin therapy which shows risks of hypoglycemia, suboptimal control and ketosis. In this study, we investigated the potential role of vildagliptin (Vilda) alone or in combination with pioglitazone (Pio), as treatment regimens for TID using streptozotocin (STZ)-induced TID model in rats. Daily oral administration of Vilda (5 mg/kg) alone or in combination with Pio (20 mg/kg) for 7 weeks significantly reduced blood glucose levels and HbA1c. It increased serum insulin levels and decreased serum glucagon. It also showed a strong antioxidant activity. Immunohistochemical analysis showed a marked improvement in β-cells in treated groups when compared with the diabetic group, which appeared in the normal cellular and architecture restoration of β-cells in the islets of Langerhans. Vilda alone or in combination with Pio has the ability to improve the overall glycemic control in type I diabetic rats and may be considered a hopeful and effective remedy for TID.

PFOA is associated with diabetes and metabolic alteration in US men: National Health and Nutrition Examination Survey 2003-2012

Exposure to perfluoroalkyl substances (PFAS) is associated with a range of adverse health effects. However, it remains unclear whether PFAS at environmentally relevant exposure levels are related to diabetes and metabolite concentrations in adults. Using cross-sectional data from 7904 adults (age≥20years) in the 2003-2012 National Health and Nutrition Examination Survey (NHANES), we examined the association of PFAS with the prevalence of diabetes and metabolite concentrations. A multivariate logistic regression was applied to investigate the associations of diabetes prevalence with serum perfluorooctanoate (PFOA), perfluorooctane sulfonate (PFOS), perfluorohexane sulfonate (PFHxS) and perfluorononanoate (PFNA) levels. A multivariate generalised linear regression was further performed to investigate the associations between PFAS exposure and some metabolites. We identified a strong positive association between serum PFOA and diabetes prevalence in men with an adjusted model (OR: 2.66, 95% CI: 1.63-4.35; P for trend=0.001). No significant association between serum PFOA and diabetes prevalence was observed in women (OR: 1.47, 95% CI: 0.88-2.46; P for trend=0.737). Furthermore, diabetes was not related to PFOS, PFHxS and PFNA, regardless of gender. In the gender-stratified generalised linear models, men and women with the highest PFOA levels demonstrated a 1.43% (95% CI: 0.62%-2.34%) and a 1.07% (95% CI: 0.27%-1.97%) greater increase in serum total cholesterol (P for trend=0.006 and 0.001) compared to those with the lowest PFOA levels. There were no significant associations between serum PFOA and other metabolites. These results provide epidemiological evidence that environment-related levels of serum PFOA may be positively associated with the prevalence of diabetes in men and with total cholesterol in adults. Further clinical and animal studies are urgently needed to elucidate putative causal relationships and shed light on the potential mode of action involved.

Practical strategies for improving outcomes in T2DM: The potential role of pioglitazone and DPP4 inhibitors

T2DM is a complex disease underlined by multiple pathogenic defects responsible for the development and progression of hyperglycaemia. Each of these factors can now be tackled in a more targeted manner thanks to glucose-lowering drugs that have been made available in the past 2 to 3 decades. Recognition of the multiplicity of the mechanisms underlying hyperglycaemia calls for treatments that address more than 1 of these mechanisms, with more emphasis placed on the earlier use of combination therapies. Although chronic hyperglycaemia contributes to and amplifies cardiovascular risk, several trials have failed to show a marked effect from intensive glycaemic control. During the past 10 years, the effect of specific glucose-lowering agents on cardiovascular risk has been explored with dedicated trials. Overall, the cardiovascular safety of the new glucose-lowering agents has been proven with some of the trials summarized in this review, showing significant reduction of cardiovascular risk. Against this background, pioglitazone, in addition to exerting a sustained glucose-lowering effect, also has ancillary metabolic actions of potential interest in addressing the cardiovascular risk of T2DM, such as preservation of beta-cell mass and function. As such, it seems a logical agent to combine with other oral anti-hyperglycaemic agents, including dipeptidyl peptidase-4 inhibitors (DPP4i). DPP4i, which may also have a potential to preserve beta-cell function, is available as a fixed-dose combination with pioglitazone, and could, potentially, attenuate some of the side effects of pioglitazone, particularly if a lower dose of the thiazolidinedione is used. This review critically discusses the potential for early combination of pioglitazone and DPP4i.

Improving glycaemic control in type 2 diabetes: Stimulate insulin secretion or provide beta-cell rest?

Type 2 diabetes (T2D) is characterized by a gradual decline in pancreatic beta cell function that determines the progressive course of the disease. While beta-cell failure is an important contributor to hyperglycaemia, chronic hyperglycaemia itself is also detrimental for beta-cell function, probably by inducing prolonged secretory stress on the beta cell as well as through direct glucotoxic mechanisms that have not been fully defined. For years, research has been carried out in search of therapies targeting hyperglycaemia that preserve long-term beta-cell function in T2D, a quest that is still ongoing. Current strategies aim to improve glycaemic control, either by promoting endogenous insulin secretion, such as sulfonylureas, or by mechanisms that may impact the beta cell indirectly, for example, providing beta-cell rest through insulin treatment. Although overall long-term success is limited with currently available interventions, in this review we argue that strategies that induce beta-cell rest have considerable potential to preserve long-term beta-cell function. This is based on laboratory-based studies involving human islets as well as clinical studies employing intensive insulin therapy, thiazolidinediones, bariatric surgery, short-acting glucagon-like peptide (GLP)-1 receptor agonists and a promising new class of diabetes drugs, sodium-glucose-linked transporter (SGLT)-2 inhibitors. Nevertheless, a lack of long-term clinical studies that focus on beta-cell function for the newer glucose-lowering agents, as well as commonly used combination therapies, preclude a straightforward conclusion; this gap in our knowledge should be a focus of future studies.

Early Combination Therapy with Oral Glucose-Lowering Agents in Type 2 Diabetes

Despite the considerable burden of disease associated with type 2 diabetes mellitus (T2DM), most patients are not at, or are unable to achieve, recommended glycemic targets. This is partly because of the relentless progressive nature of the disease, but it may also be attributable to the current diabetes treatment paradigm. The recommended stepwise approach may lead to frequent early treatment failure with prolonged periods of elevated glucose as a consequence of clinical inertia and delays in achieving optimal glycemic control. Thus, it is most appropriate to consider the current treatment paradigm for T2DM in the context of a more aggressive initial therapy with early combination therapy. Current guidelines advise that initial combination therapy should be used for patients presenting with elevated glycated hemoglobin (HbA_1c). However, several studies and recent meta-analyses suggest a potential benefit from initial combination therapy on glycemic outcomes in diabetes compared with metformin monotherapy across a wide range of baseline HbA_1c levels. Indeed, combination therapy can increase the number of patients achieving glycemic goals, and the newer glucose-lowering agents may reduce the risk of hypoglycemia and body weight gain. Moreover, our improving understanding of the complex pathophysiology of T2DM and the availability of treatments tackling specific mechanisms contributing to hyperglycemia should lead to more pathophysiologically sound combination therapy. We discuss the rationale behind and evidence for early combination therapy as well as what is needed in the future to better understand its potential.

Circulating levels of perfluoroalkyl substances (PFASs) and carotid artery atherosclerosis

BACKGROUND AND OBJECTIVE

During recent years, some persistent organic pollutants (POPs) have been linked to atherosclerosis. One group of POPs, the poly- and perfluoroalkyl substances (PFASs) have not been investigated with regard to atherosclerotic plaques.

METHODS

Carotid artery atherosclerosis was assessed by ultrasound in 1016 subjects aged 70 years in the Prospective Investigation of the Vasculature in Uppsala Seniors (PIVUS) study. Eight PFASs were detected in >75% of participants' plasma by ultra-performance liquid chromatography coupled to tandem mass spectrometry (UPLC-MS/MS).

RESULTS

No significant linear associations were observed between the PFASs and intima-media thickness (IMT), or the echogenicity in the intima-media complex (IM-GSM, a marker of lipid infiltration in the artery) when men and women were analyzed together. Neither was occurrence of carotid plaques related to PFASs levels. However, highly significant interactions were observed between some PFASs and sex regarding both IM-GSM and plaque prevalence. Perfluorononanoic acid (PFNA), perfluorodecanoic acid (PFDA), and perfluoroundecanoic acid (PFUnDA), were all related to IM-GSM in a positive fashion in women (p=0.002-0.003), while these relationships were negative in men. The levels of PFUnDA were significantly related to carotid plaque in women (OR 1.59, 95%CI 1.03-2.43, p=0.03), but not in men (OR 0.93, 95%CI 0.62-1.42, p=0.75).

CONCLUSIONS

In this cross-sectional study, a pronounced gender difference was observed regarding associations between some PFASs, especially the long-chain PFUnDA, and markers of atherosclerosis, with more pronounced relationships found in women. These findings suggest a sex-specific role for PFASs in atherosclerosis.

Glucose plus metformin compared with glucose alone on β-cell function in mouse pancreatic islets

Metformin is currently the first drug of choice for treatment of type II diabetes. The primary function of metformin is to decrease hepatic glucose production mainly by inhibiting gluconeogenesis. The aim of the present study was to investigate the effects of glucose alone (control groups) and glucose and metformin (treatment groups) on pancreatic islets functions. Pancreatic islets were isolated by collagenase digestion and incubated for 24 or 48 h in RPMI-1640 containing 5 mmol/l glucose (control groups 1 and 2, respectively) or 24 h with 25 mmol/l glucose (control group 3) and 15 µmol/l metformin (treatment groups 1, 2 and 3, corresponding to the control groups, respectively). Subsequently, the rate of insulin output from islets, pancreatic and duodenal homeobox 1 (Pdx-1) and insulin genes expression and islet viability were assayed. The rate of insulin secretion in a 5 mmol/l glucose concentration in the 48 h treatment group increased significantly compared with that of the 24 h treatment group (P<0.05). An increase of the glucose concentration (25 mmol/l) caused insulin secretion to increase compared with that of 5 mmol/l glucose. Pdx-1 gene expression in treatment group 2 significantly decreased compared with the control group 2 (P<0.05). The the Pdx-1 gene expression in treatment group 2 decreased compared with that of the treatment group 1. The expression of the insulin gene in treatment group 1 increased compared with control group 1, and in treatment group 2, there was a 2-fold increase in insulin gene expression compared with control group 2. The insulin gene expression in treatment group 2 increased compared with treatment group 1. The percentage of islet cell viability was increased in treatment group 3 by ~40% compared with the islet cells of treatment groups 1 and 2 (P<0/05). These data indicate that glucose and metformin have direct effects on β-cell function.

Therapeutic Approaches for Preserving or Restoring Pancreatic β-Cell Function and Mass

The goal for the treatment of patients with diabetes has today shifted from merely reducing glucose concentrations to preventing the natural decline in β-cell function and delay the progression of disease. Pancreatic β-cell dysfunction and decreased β-cell mass are crucial in the development of diabetes. The β-cell defects are the main pathogenesis in patients with type 1 diabetes and are associated with type 2 diabetes as the disease progresses. Recent studies suggest that human pancreatic β-cells have a capacity for increased proliferation according to increased demands for insulin. In humans, β-cell mass has been shown to increase in patients showing insulin-resistance states such as obesity or in pregnancy. This capacity might be useful for identifying new therapeutic strategies to reestablish a functional β-cell mass. In this context, therapeutic approaches designed to increase β-cell mass might prove a significant way to manage diabetes and prevent its progression. This review describes the various β-cell defects that appear in patients with diabetes and outline the mechanisms of β-cell failure. We also review common methods for assessing β-cell function and mass and methodological limitations in vivo. Finally, we discuss the current therapeutic approaches to improve β-cell function and increase β-cell mass.

Pharmacological treatment and therapeutic perspectives of metabolic syndrome

Metabolic syndrome is a disorder based on insulin resistance. Metabolic syndrome is diagnosed by a co-occurrence of three out of five of the following medical conditions: abdominal obesity, elevated blood pressures, elevated glucose, high triglycerides, and low high-density lipoprotein-cholesterol (HDL-C) levels. Clinical implication of metabolic syndrome is that it increases the risk of developing type 2 diabetes and cardiovascular diseases. Prevalence of the metabolic syndrome has increased globally, particularly in the last decade, to the point of being regarded as an epidemic. The prevalence of metabolic syndrome in the USA is estimated to be 34% of adult population. Moreover, increasing rate of metabolic syndrome in developing countries is dramatic. One can speculate that metabolic syndrome is going to induce huge impact on our lives. The metabolic syndrome cannot be treated with a single agent, since it is a multifaceted health problem. A healthy lifestyle including weight reduction is likely most effective in controlling metabolic syndrome. However, it is difficult to initiate and maintain healthy lifestyles, and in particular, with the recidivism of obesity in most patients who lose weight. Next, pharmacological agents that deal with obesity, diabetes, hypertension, and dyslipidemia can be used singly or in combination: anti-obesity drugs, thiazolidinediones, metformin, statins, fibrates, renin-angiotensin system blockers, glucagon like peptide-1 agonists, sodium glucose transporter-2 inhibitors, and some antiplatelet agents such as cilostazol. These drugs have not only their own pharmacologic targets on individual components of metabolic syndrome but some other properties may prove beneficial, i.e. anti-inflammatory and anti-oxidative. This review will describe pathophysiologic features of metabolic syndrome and pharmacologic agents for the treatment of metabolic syndrome, which are currently available.

Serum bilirubin concentrations are positively associated with serum C-peptide levels in patients with Type 2 diabetes

AIMS

To investigate the relationship between physiological serum total bilirubin concentrations and serum C-peptide levels in Korean patients with Type 2 diabetes.

METHODS

A total of 588 patients with Type 2 diabetes were investigated in this cross-sectional study. Fasting C-peptide level, 2-h postprandial C-peptide level and ΔC-peptide (postprandial C-peptide minus fasting C-peptide) level were measured in all patients.

RESULTS

Fasting C-peptide level, postprandial C-peptide level and ΔC-peptide level tended to be higher in patients with higher bilirubin concentrations. Partial correlation analysis showed that serum bilirubin levels were significantly correlated with fasting C-peptide level (r = 0.159, P < 0.001), postprandial C-peptide level (r = 0.209, P < 0.001) and ΔC-peptide level (r = 0.186, P < 0.001) after adjustment for other covariates. In the multivariate model, the association between serum bilirubin concentrations and serum C-peptide levels remained significant after adjustment for confounding factors including age, gender, familial diabetes, hypertension, hyperlipidaemia, BMI, HbA1c , duration of diabetes and associated liver function tests (fasting C-peptide level: β = 0.083, P = 0.041; postprandial C-peptide level: β = 0.106, P = 0.005; ΔC-peptide level: β = 0.096, P = 0.015, respectively).

CONCLUSIONS

Serum bilirubin concentrations within the physiological range were positively associated with serum C-peptide levels in patients with Type 2 diabetes.

β-Cell function in type 2 diabetes

Different in vivo tests explore different aspects of β-cell function. Because intercorrelation of insulin secretion indices is modest, no single in vivo test allows β-cell function to be assessed with accuracy and specificity comparable to insulin sensitivity. Physiologically-based mathematical modeling is necessary to interpret insulin secretory responses in terms of relevant parameters of β-cell function. Models can be used to analyze intravenous glucose tests, but secretory responses to intravenous glucose may be paradoxical in subjects with diabetes. Use of oral glucose (or mixed meal) data may be preferable not only for simplicity but also for physiological interpretation. While the disposition index focuses on the relationship between insulin secretion and insulin resistance, secretion parameters reflecting the dynamic response to changing glucose levels over a time frame of minutes or hours--such as β-cell glucose sensitivity--are key to explain changes in glucose tolerance and are largely independent of insulin sensitivity. Pathognomonic of the β-cell defect of type 2 diabetes is a reduced glucose sensitivity, which is accompanied by normal or raised absolute insulin secretion rates--compensatory to the attendant insulin resistance--and impaired incretin-induced potentiation. As β-cell mass is frequently within the range of nondiabetic individuals, these defects are predominantly functional and potentially reversible. Any intervention, on lifestyle or with drugs, that improves glucose tolerance does so primarily through increased β-cell glucose sensitivity. So far, however, no intervention has proven unequivocally capable of modifying the natural course of β-cell dysfunction.

Circulating levels of perfluoroalkyl substances and prevalent diabetes in the elderly

AIMS/HYPOTHESIS

Several environmental contaminants, such as polychlorinated biphenyls, dioxins, bisphenol A and phthalates, have been linked to diabetes. We therefore investigated whether other kinds of contaminants, perfluoroalkyl substances (PFAS), also called perfluorinated compounds (PFCs), are also associated with diabetes.

METHODS

The Prospective Investigation of the Vasculature in Uppsala Seniors (PIVUS) study investigated 1,016 men and women aged 70 years. Seven PFAS were detected in almost all participant sera by ultra-high performance liquid chromatograph/tandem mass spectrometry. Diabetes was defined as use of hypoglycaemic agents or fasting glucose >7.0 mmol/l.

RESULTS

114 people had diabetes. In the linear analysis, no significant relationships were seen between the seven PFAS and prevalent diabetes. However, inclusion of the quadratic terms of the PFAS revealed a significant non-linear relationship between perfluorononanoic acid (PFNA) and diabetes, even after adjusting for multiple confounders (OR 1.96, 95% CI 1.19, 3.22, p = 0.008 for the linear term and OR 1.25, 95% CI 1.08, 1.44, p = 0.002 for the quadratic term). Perfluorooctanoic acid (PFOA) also showed such a relationship (p = 0.01). PFOA was related to the proinsulin/insulin ratio (a marker of insulin secretion), but none of the PFAS was related to the HOMA-IR (a marker of insulin resistance) following adjustment for multiple confounders.

CONCLUSIONS/INTERPRETATION

PFNA was related to prevalent diabetes in a non-monotonic fashion in this cross-sectional study, supporting the view that this perfluoroalkyl substance might influence glucose metabolism in humans at the level of exposure seen in the general elderly population.

Do thiazolidinediones still have a role in treatment of type 2 diabetes mellitus?

Thiazolidinediones have been introduced in the treatment of type 2 diabetes mellitus (T2DM) since the late 1990s. Although troglitazone was withdrawn from the market a few years later due to liver toxicity, both rosiglitazone and pioglitazone gained widespread use for T2DM treatment. In 2010, however, due to increased risk of cardiovascular events associated with its use, the European Medicines Agency recommended suspension of rosiglitazone use and the Food and Drug Administration severely restricted its use. Thus pioglitazone is the only thiazolidinedione still significantly employed for treating T2DM and it is the only molecule of this class still listed in the American Diabetes Association-European Association for the Study of Diabetes 2012 Position Statement. However, as for the other thiazolidinediones, use of pioglitazone is itself limited by several side effects, some of them potentially dangerous. This, together with the development of novel therapeutic strategies approved in the last couple of years, has made it questionable whether or not thiazolidinediones (namely pioglitazone) should still be used in the treatment of T2DM. This article will attempt to formulate an answer to this question by critically reviewing the available data on the numerous advantages and the potentially worrying shortcomings of pioglitazone treatment in T2DM.

Pleiotropic effects of thiazolidinediones: implications for the treatment of patients with type 2 diabetes mellitus

Thiazolidinediones (TZDs) are insulin-sensitizing antidiabetes agents that act through the peroxisome proliferator-activated receptor-γ to cause a durable improvement in glycemic control in patients with type 2 diabetes mellitus. Although less well recognized, TZDs also exert a protective effect on β-cell function. In addition to their beneficial effects on glucose homeostasis, TZDs-especially pioglitazone-exert a number of other pleiotropic effects that make them ideal agents as monotherapy or in combination with other oral agents, glucagon-like peptide-1 analogs, or insulin. Pioglitazone improves endothelial dysfunction, reduces blood pressure, corrects diabetic dyslipidemia, and reduces circulating levels of inflammatory cytokines and prothrombotic factors. Pioglitazone also redistributes fat and toxic lipid metabolites in muscle, liver, β cells, and arteries, and deposits the fat in subcutaneous adipocytes where it cannot exert its lipotoxic effects. Consistent with these antiatherogenic effects, pioglitazone reduced major adverse cardiac event endpoints (ie, mortality, myocardial infarction, and stroke) in the Prospective Pioglitazone Clinical Trial in Macrovascular Events and in a meta-analysis of all other published pioglitazone trials. Pioglitazone also mobilizes fat out of the liver, improving liver function and histologic abnormalities in patients with nonalcoholic fatty liver disease and nonalcoholic steatohepatitis. Pioglitazone also reduces proteinuria, all-cause mortality, and cardiovascular events in patients with type 2 diabetes mellitus with a reduced glomerular filtration rate. These benefits must be weighed against the side effects of the drug, including weight gain, fluid retention, atypical fractures, and, possibly, bladder cancer. When low doses of pioglitazone are used (eg, 7.5-30 mg/d) with gradual titration, and physician recognition of the potential side effects are applied, the risk-to-benefit ratio is very favorable. Despite having similar effects on glycemic control, pioglitazone and rosiglitazone appear to have different effects on cardiovascular outcomes. Rosiglitazone has been associated with an increased risk of myocardial infarction, and its use in the United States is restricted because of cardiovascular safety concerns.

Interventions to preserve beta-cell function in the management and prevention of type 2 diabetes

The International Diabetes Federation estimates that there are currently 336 million people worldwide who have type 2 diabetes (T2DM), and the global prevalence of diabetes has more than doubled since 1980. The rapid rise in rates of T2DM echoes a similar rise in rates of obesity, which causes insulin resistance and places an increased insulin secretory demand on pancreatic β cells. While diabetes is diagnosed clinically by elevated plasma glucose levels, loss of β-cell function is progressive over time and β-cell dysfunction is far advanced by the time diabetes is diagnosed. Methods for preserving or restoring β-cell function are important for the prevention and treatment of T2DM. Interventions that reduce body fat or that change fat biology provide the best evidence for slowing or arresting the deterioration of β-cell function that causes T2DM. These interventions should form the basis of interventions to prevent and treat T2DM, particularly early in its course.

Apoptosis rate and transcriptional response of pancreatic islets exposed to the PPAR gamma agonist Pioglitazone

To explore the molecular pathways underlying thiazolidinediones effects on pancreatic islets in conditions mimicking normo- and hyperglycemia, apoptosis rate and transcriptional response to Pioglitazone at both physiological and supraphysiological glucose concentrations were evaluated. Adult rat islets were cultured at physiological (5.6 mM) and supraphysiological (23 mM) glucose concentrations in presence of 10 μM Pioglitazone or vehicle. RNA expression profiling was evaluated with the PancChip 13k cDNA microarray after 24-h, and expression results for some selected genes were validated by qRT-PCR. The effects of Pioglitazone were investigated regarding apoptosis rate after 24-, 48- and 72-h. At 5.6 mM glucose, 101 genes were modulated by Pioglitazone, while 1,235 genes were affected at 23 mM glucose. Gene networks related to lipid metabolism were identified as altered by Pioglitazone at both glucose concentrations. At 23 mM glucose, cell cycle and cell death pathways were significantly regulated as well. At 5.6 mM glucose, Pioglitazone elicited a transient reduction in islets apoptosis rate while at 23 mM, Bcl2 expression was reduced and apoptosis rate was increased by Pioglitazone. Our data demonstrate that the effect of Pioglitazone on gene expression profile and apoptosis rate depends on the glucose concentration. The modulation of genes related to cell death and the increased apoptosis rate observed at supraphysiological glucose concentration raise concerns about Pioglitazone's direct effects in conditions of hyperglycemia and reinforce the necessity of additional studies designed to evaluate TZDs effects on the preservation of β-cell function in situations where glucotoxicity might be more relevant than lipotoxicity.

The pancreatic beta cells in human type 2 diabetes

Bell-cell (beta-cell) impairment is central to the development and progression of human diabetes, as a result of the combined effects of genetic and acquired factors. Reduced islet number and/or reduced beta cells amount in the pancreas of individuals with Type 2 diabetes have been consistently reported. This is mainly due to increased beta cell death, not adequately compensated for by regeneration. In addition, several quantitative and/or qualitative defects of insulin secretion have been observed in Type 2 diabetes, both in vivo and ex vivo with isolated islets. All this is associated with modifications of islet cell gene and protein expression. With the identification of several susceptible Type 2 diabetes loci, the role of genotype in affecting beta-cell function and survival has been addressed in a few studies and the relationships between genotype and beta-cell phenotype investigated. Among acquired factors, the importance of metabolic insults (in particular glucotoxicity and lipotoxicity) in the natural history of beta-cell damage has been widely underlined. Continuous improvements in our knowledge of the beta cells in human Type 2 diabetes will lead to more targeted and effective strategies for the prevention and treatment of the disease.

Rosiglitazone treatment does not decrease amyloid deposition in transplanted islets from transgenic mice expressing human islet amyloid polypeptide

In human islet transplantation, insulin independence decreases over time. We previously showed that amyloid deposition following transplantation of islets from human islet amyloid polypeptide (hIAPP) transgenic mice resulted in ß-cell loss and that rosiglitazone treatment decreased islet amyloid deposition and preserved ß-cell area in the endogenous pancreas of hIAPP transgenic mice. Thus, we sought to determine if rosiglitazone treatment decreases islet amyloid deposition and the associated ß-cell loss after islet transplantation. Streptozocin-diabetic mice were transplanted with 100 islets from hIAPP transgenic (T) mice or nontransgenic (NT) littermates under the kidney capsule and received either rosiglitazone (R) in drinking water or plain drinking water (C). The resultant groups (NTC [n = 11], NTR [n = 9], TC [n = 14], and TR [n = 10]) were followed for 12 weeks after which the graft was removed and processed for histology. Amyloid was detected in nearly all T islet grafts (TC = 13/14, TR = 10/10) but not in NT grafts. Rosiglitazone did not alter amyloid deposition (% graft area occupied by amyloid; TC: 2.15 ± 0.7, TR: 1.72 ± 0.66; P = .86). % ß-cell/graft area was decreased in the TC grafts compared to NTC (56.2 ± 3.1 vs 73.8 ± 1.4; P < .0001) but was not different between TC and TR groups (56.2 ± 3.1 vs 61.0 ± 2.9; P = .34). Plasma glucose levels before and after transplantation did not differ between NTC and TC groups and rosiglitazone did not affect plasma glucose levels post-islet transplantation. Rosiglitazone did not decrease amyloid deposition in hIAPP transgenic islet grafts. Therefore, rosiglitazone treatment of recipients of amyloid forming islets may not improve transplantation outcomes.

Disordered insulin secretion in the development of insulin resistance and Type 2 diabetes

For many years, the development of insulin resistance has been seen as the core defect responsible for the development of Type 2 diabetes. However, despite extensive research, the initial factors responsible for insulin resistance development have not been elucidated. If insulin resistance can be overcome by enhanced insulin secretion, then hyperglycaemia will never develop. Therefore, a β-cell defect is clearly required for the development of diabetes. There is a wealth of evidence to suggest that disorders in insulin secretion can lead to the development of decreased insulin sensitivity. In this review, we describe the potential initiating defects in Type 2 diabetes, normal pulsatile insulin secretion and the effects that disordered secretion may have on both β-cell function and hepatic insulin sensitivity. We go on to examine evidence from physiological and epidemiological studies describing β-cell dysfunction in the development of insulin resistance. Finally, we describe how disordered insulin secretion may cause intracellular insulin resistance and the implications this concept has for diabetes therapy. In summary, disordered insulin secretion may contribute to development of insulin resistance and hence represent an initiating factor in the progression to Type 2 diabetes.

Circulating levels of phthalate metabolites are associated with prevalent diabetes in the elderly

OBJECTIVE

Phthalates are ubiquitous industrial high-volume chemicals known as ligands to peroxisome proliferator-activated receptors (PPARs). Because PPAR-γ agonists modulate insulin sensitivity and are used to treat type 2 diabetes, we investigated whether circulating levels of phthalate metabolites are related to prevalent type 2 diabetes.

RESEARCH DESIGN AND METHODS

A total of 1,016 subjects, aged 70 years, were investigated in the Prospective Investigation of the Vasculature in Uppsala Seniors Study. Four phthalate metabolites were detected in almost all participant sera by an API 4000 liquid chromatograph/tandem mass spectrometer. Type 2 diabetes was defined as the use of pharmacological hypoglycemic agents or a fasting plasma glucose >7.0 mmol/L.

RESULTS

A total of 114 subjects were shown to have diabetes. Following adjustment for sex, BMI, serum cholesterol and triglycerides, educational level, and smoking and exercise habits, high levels of the phthalate metabolites monomethyl phthalate (MMP) (P < 0.01), monoisobutyl phthalate (MiBP) (P < 0.05), and monoethyl phthalate (MEP) (P < 0.05), but not mono(2-ethylhexyl) phthalate, were associated with an increased prevalence of diabetes. Using the fasting proinsulin-to-insulin ratio as a marker of insulin secretion and the homeostasis model assessment-insulin resistance index as a marker of insulin resistance, MiBP was mainly related to poor insulin secretion, whereas MEP and MMP mainly were related to insulin resistance.

CONCLUSIONS

The findings in this cross-sectional study showed that several phthalate metabolites are related to diabetes prevalence, as well as to markers of insulin secretion and resistance. These findings support the view that these commonly used chemicals might influence major factors that are regulating glucose metabolism in humans at the level of exposure of phthalate metabolites seen in the general elderly population.

Procyanidins modify insulinemia by affecting insulin production and degradation

Previous studies from our research group have suggested that procyanidins modify glycemia and insulinemia. The aim of this work was to evaluate the effects of procyanidins on β-cell functionality in a nonpathological system. Four groups of healthy rats were studied. The animals were given daily acute doses of grape seed procyanidin extract (GSPE) for different time periods and at different daily amounts. A β-cell line (INS-1E) was treated with 25 mg GSPE/L for 24 h to identify possible mechanisms of action for the procyanidins. In vivo experiments showed that different doses of GSPE affected insulinemia in different ways by modifying β-cell functionality and/or insulin degradation. The islets isolated from rats that were treated with 25 mg GSPE/kg of body weight for 45 days exhibited a limited response to glucose stimulation. In addition, insulin gene expression, insulin synthesis and expression of genes related to insulin secretion were all down-regulated. In vitro studies revealed that GSPE decreased the ability of β-cells to secrete insulin in response to glucose. GSPE increased glucose uptake in β-cells under high-glucose conditions but impaired glucose-induced mitochondrial hyperpolarization, decreased adenosine triphosphate (ATP) synthesis and altered cellular membrane potentials. GSPE also modified Glut2, glucokinase and Ucp2 gene expression as well as altered the expression of hepatic insulin-degrading enzyme (Ide), thereby altering insulin degradation. At some doses, procyanidins changed β-cell functionality by modifying insulin synthesis, secretion and degradation under nonpathological conditions. Membrane potentials and Ide provide putative targets for procyanidins to induce these effects.

Metabolic effects of muraglitazar in type 2 diabetic subjects

AIM

To assess the effect of muraglitazar, a dual peroxisome proliferator-activated receptor (PPAR)γ-α agonist, versus placebo on metabolic parameters and body composition in subjects with type 2 diabetes mellitus (T2DM).

METHODS

Twenty-seven T2DM subjects received oral glucose tolerance test (OGTT), euglycaemic insulin clamp with deuterated glucose, measurement of total body fat (DEXA), quantitation of muscle/liver (MRS) and abdominal subcutaneous and visceral (MRI) fat, and then were randomized to receive, in addition to diet, muraglitazar (MURA), 5 mg/day, or placebo (PLAC) for 4 months.

RESULTS

HbA1c(c) decreased similarly (2.1%) during both MURA and PLAC treatments despite significant weight gain with MURA (+2.5 kg) and weight loss with PLAC (-0.7 kg). Plasma triglyceride, LDL cholesterol, free fatty acid (FFA), hsCRP levels all decreased with MURA while plasma adiponectin and HDL cholesterol increased (p < 0.05-0.001). Total body (muscle), hepatic and adipose tissue sensitivity to insulin and β cell function all improved with MURA (p < 0.05-0.01). Intramyocellular, hepatic and abdominal visceral fat content decreased, while total body and subcutaneous abdominal fat increased with MURA (p < 0.05-0.01).

CONCLUSIONS

Muraglitazar (i) improves glycaemic control by enhancing insulin sensitivity and β cell function in T2DM subjects, (ii) improves multiple cardiovascular risk factors, (iii) reduces muscle, visceral and hepatic fat content in T2DM subjects. Despite similar reduction in A1c with PLAC/diet, insulin sensitivity and β cell function did not improve significantly.

The protective effect of berberine on β-cell lipoapoptosis

AIMS

To evaluate the protective effect of berberine on β-cell lipoapoptosis induced by palmitate and to explore the possible underlying mechanisms.

MATERIALS AND METHODS

HIT-T15 pancreatic β-cells were divided into the following treatment groups: untreated controls; 100 μM berberine; 0.5 mM palmitate; 0.5 mM palmitate + 0.1 μM berberine; 0.5 mM palmitate + 1 μM berberine; 0.5 mM palmitate + 10 μM berberine; and 0.5 mM palmitate + 100 μM berberine. After 48 h, cell apoptosis was assessed by flow cytometry and the Hoechst 33258 fluorescent assay. Basal and glucose-stimulated insulin levels in culture medium were measured by radioimmunoassay. Peroxisome proliferator- activated receptor-γ (PPAR-γ) mRNA and protein levels were determined by real-time PCR and immunocytochemistry, respectively.

RESULTS

Apoptosis was significantly increased upon treatment with palmitate as compared to the untreated controls (p<0.0001). In addition, glucose-stimulated insulin secretion (GSIS), PPAR-γ mRNA and protein expression were significantly reduced in response to palmitate (p<0.0001); however, palmitate-induced apoptosis and reduction in PPAR-γ expression were reversed in response to berberine in a dose-dependent manner (p<0.05). Furthermore, there was a non-significant increase in GSIS with increasing berberine dose.

CONCLUSION

Palmitate exerted lipotoxic effects on HIT-T15 cells, inducing apoptosis and reducing GSIS. Berberine reduced palmitate-induced lipoapoptosis and tended to increase GSIS in HIT-T15 cells, possibly through increased PPAR-γ expression.

Rosiglitazone improves glucose metabolism in obese adolescents with impaired glucose tolerance: a pilot study

Impaired glucose tolerance (IGT) is a prediabetic state fueling the rising prevalence of type 2 diabetes mellitus (T2DM) in adolescents with marked obesity. Given the importance of insulin resistance, the poor β-cell compensation and the altered fat partitioning as underlying defects associated with this condition, it is crucial to determine the extent to which these underlying abnormalities can be reversed in obese adolescents. We tested, in a pilot study, whether rosiglitazone (ROSI) restores normal glucose tolerance (NGT) in obese adolescents with IGT by improving insulin sensitivity and β-cell function. In a small randomized, double-blind, placebo (PLA)-controlled study, lasting 4 months, 21 obese adolescents with IGT received either ROSI (8 mg daily) (n = 12, 5M/7F, BMI z-score 2.44 ± 0.11) or PLA (n = 9, 4M/5F, BMI z-score 2.41 ± 0.09). Before and after treatment, all subjects underwent oral glucose tolerance test (OGTT), hyperinsulinemic-euglycemic clamp, magnetic resonance imaging, and (1)H NMR assessment. After ROSI treatment, 58% of the subjects converted to NGT compared to 44% in the PLA group (P = 0.528). Restoration of NGT was associated with a significant increase in insulin sensitivity (P < 0.04) and a doubling in the disposition index (DI) (P < 0.04), whereas in the PLA group, these changes were not significant. The short-term use of ROSI appears to be safe in obese adolescents with IGT. ROSI restores NGT by increasing peripheral insulin sensitivity and β-cell function, two principal pathophysiological abnormalities of IGT.

Failure to metformin and insulin secretagogue monotherapy: an observational cohort study

The aim of the present cohort study is the assessment of treatment failure rates in patients on monotherapy with metformin or insulin secretagogues, observed in a routine clinical setting. A cohort of patients without any pharmacological treatment was also observed. A retrospective observational cohort study was performed on a consecutive series of 2,020 type 2 diabetic patients receiving monotherapy with an oral agent (metformin or insulin secretagogue, n = 1,126) or drug-naive (n = 894). HbA1c and prescribed hypoglycemic therapy were recorded yearly. Patients were followed until death, change of residence, failure to treatment, or up to 48 months. The mean duration of follow up was 34.8 ± 18.0 months. In a Cox regression analysis, metformin was associated with a significant reduction, and insulin secretagogues with a significant increase, in the risk of failure to therapy during follow up. When duration of diabetes and baseline BMI were added to the model, insulin secretagogues, but not metformin, were still associated with increased risk of failure. In conclusion, insulin secretagogues are associated with increased failure rate in comparison with metformin. This difference could be due to detrimental effect of secretagogues, rather than to a beneficial action of metformin.

The role of peroxisome proliferator-activated receptor γ in pancreatic β cell function and survival: therapeutic implications for the treatment of type 2 diabetes mellitus

The pathogenesis of type 2 diabetes mellitus involves both peripheral insulin resistance and dysfunctional insulin secretion from the pancreatic β cell. Currently, there is intense research focus on delineating the etiologies of pancreatic β cell dysfunction in type 2 diabetes. However, there remains an unmet clinical need to establish therapeutic guidelines and strategies that emphasize the preservation of pancreatic β cell function in at-risk and affected individuals. Thiazolidinediones are orally active agents approved for use in type 2 diabetes and act as agonists of the nuclear hormone receptor PPAR-γ. These drugs improve insulin sensitivity, but there is also a growing appreciation of PPAR-γ actions within the β cell. PPAR-γ has been shown to regulate directly key β cell genes involved in glucose sensing, insulin secretion and insulin gene transcription. Further, pharmacologic PPAR-γ activation has been shown to protect against glucose-, lipid-, cytokine- and islet amyloid polypeptide (IAPP)-induced activation of numerous stress pathways. This article will review the mechanisms by which PPAR-γ activation acts to maintain β cell function and survival in type 2 diabetes mellitus and highlight some of the current controversies in this field.

Reversibility of metabolic and morphological changes associated with chronic exposure of pancreatic islet beta-cells to fatty acids

Pancreatic beta-cells metabolise both lipid and glucose nutrients but chronic exposure (>24 h) to elevated fatty acid (FA) concentrations results in deleterious metabolic and morphological changes. The aims of this study were to assess the adaptive morphological, metabolic and secretory responses of islet beta-cells to exposure and removal of FA. Isolated mouse islets and INS-1 beta-cells were exposed to oleate or palmitate (0.5 mM) or a 1:1 mixture of both FA for 48 h prior to a 24 h period without FA. Subsequent changes in lipid storage and composition (triglycerides, TG and phospholipids, PL), gene expression, beta-cell morphology and glucose-stimulated insulin secretion (GSIS) were determined. Intracellular TG content increased during exposure to FA and was lower in cells subsequently incubated in FA-free media (P < 0.05); TG storage was visible as oil red O positive droplets (oleate) by light microscopy or 'splits' (palmitate) by electron microscopy. Significant desaturation of beta-cell FA occurred after exposure to oleate and palmitate. After incubation in FA-free media, there was differential handling of specific FA in TG, resulting in a profile that tended to revert to that of control cells. FA treatment resulted in elevated lipolysis of intracellular TG, increased FA oxidation and reduced GSIS. After incubation in FA-free media, oxidation remained elevated but inhibition of FA oxidation with etomoxir (10 microM) had no effect on the improvement in GSIS. The beta-cell demonstrates metabolic flexibility as an adaptive response to ambient concentrations of FA.

Pharmacogenetics of Anti-Diabetes Drugs

A variety of treatment modalities exist for individuals with type 2 diabetes mellitus (T2D). In addition to dietary and physical activity interventions, T2D is also treated pharmacologically with nine major classes of approved drugs. These medications include insulin and its analogues, sulfonylureas, biguanides, thiazolidinediones (TZDs), meglitinides, α-glucosidase inhibitors, amylin analogues, incretin hormone mimetics, and dipeptidyl peptidase 4 (DPP4) inhibitors. Pharmacological treatment strategies for T2D are typically based on efficacy, yet favorable responses to such therapeutics are oftentimes variable and difficult to predict. Characterization of drug response is expected to substantially enhance our ability to provide patients with the most effective treatment strategy given their individual backgrounds, yet pharmacogenetic study of diabetes medications is still in its infancy. To date, major pharmacogenetic studies have focused on response to sulfonylureas, biguanides, and TZDs. Here, we provide a comprehensive review of pharmacogenetics investigations of these specific anti-diabetes medications. We focus not only on the results of these studies, but also on how experimental design, study sample issues, and definition of 'response' can significantly impact our interpretation of findings. Understanding the pharmacogenetics of anti-diabetes medications will provide critical baseline information for the development and implementation of genetic screening into therapeutic decision making, and lay the foundation for "individualized medicine" for patients with T2D.

Insulin resistance, lipotoxicity, type 2 diabetes and atherosclerosis: the missing links. The Claude Bernard Lecture 2009

Insulin resistance is a hallmark of type 2 diabetes mellitus and is associated with a metabolic and cardiovascular cluster of disorders (dyslipidaemia, hypertension, obesity [especially visceral], glucose intolerance, endothelial dysfunction), each of which is an independent risk factor for cardiovascular disease (CVD). Multiple prospective studies have documented an association between insulin resistance and accelerated CVD in patients with type 2 diabetes, as well as in non-diabetic individuals. The molecular causes of insulin resistance, i.e. impaired insulin signalling through the phosphoinositol-3 kinase pathway with intact signalling through the mitogen-activated protein kinase pathway, are responsible for the impairment in insulin-stimulated glucose metabolism and contribute to the accelerated rate of CVD in type 2 diabetes patients. The current epidemic of diabetes is being driven by the obesity epidemic, which represents a state of tissue fat overload. Accumulation of toxic lipid metabolites (fatty acyl CoA, diacylglycerol, ceramide) in muscle, liver, adipocytes, beta cells and arterial tissues contributes to insulin resistance, beta cell dysfunction and accelerated atherosclerosis, respectively, in type 2 diabetes. Treatment with thiazolidinediones mobilises fat out of tissues, leading to enhanced insulin sensitivity, improved beta cell function and decreased atherogenesis. Insulin resistance and lipotoxicity represent the missing links (beyond the classical cardiovascular risk factors) that help explain the accelerated rate of CVD in type 2 diabetic patients.