Effects of metformin and rosiglitazone monotherapy on insulin-mediated hepatic glucose uptake and their relation to visceral fat in type 2 diabetes

Advances and challenges in measuring hepatic glucose uptake with FDG PET: implications for diabetes research

The liver plays a crucial role in the control of glucose homeostasis and is therefore of great interest in the investigation of the development of type 2 diabetes. Hepatic glucose uptake (HGU) can be measured through positron emission tomography (PET) imaging with the tracer [18F]-2-fluoro-2-deoxy-D-glucose (FDG). HGU is dependent on many variables (e.g. plasma glucose, insulin and glucagon concentrations), and the metabolic state for HGU assessment should be chosen with care and coherence with the study question. In addition, as HGU is influenced by many factors, protocols and measurement conditions need to be standardised for reproducible results. This review provides insights into the protocols that are available for the measurement of HGU by FDG PET and discusses the current state of knowledge of HGU and its impairment in type 2 diabetes. Overall, a scanning modality that allows for the measurement of detailed kinetic information and influx rates (dynamic imaging) may be preferable to static imaging. The combination of FDG PET and insulin stimulation is crucial to measure tissue-specific insulin sensitivity. While the hyperinsulinaemic-euglycaemic clamp allows for standardised measurements under controlled blood glucose levels, some research questions might require a more physiological approach, such as oral glucose loading, with both advantages and complexities relating to fluctuations in blood glucose and insulin levels. The available approaches to address HGU hold great potential but await more systematic exploitation to improve our understanding of the mechanisms underlying metabolic diseases. Current findings from the investigation of HGU by FDG PET highlight the complex interplay between insulin resistance, hepatic glucose metabolism, NEFA levels and intrahepatic lipid accumulation in type 2 diabetes and obesity. Further research is needed to fully understand the underlying mechanisms and potential therapeutic targets for improving HGU in these conditions.

The effect of thiazolidinediones on body fat redistribution in adults: A systematic review and meta-analysis of randomized controlled trials

Visceral adiposity is a strong predictor of cardiometabolic risk. Thiazolidinediones (TZDs) are associated with a shift in fat redistribution from visceral adipose tissue (VAT) to subcutaneous adipose tissue (SAT). We aimed to compare the effects of TZD and other interventions on fat remodeling in adults in randomized controlled trials. Among the 1331 retrieved studies, 39 trials with 1765 participants were included in the meta-analysis. The standardized mean difference in VAT change was not significantly different between TZD and comparators across the overall studies. Intriguingly, TZD treatment resulted in significant decreases in VAT compared with placebo and sulfonylureas (p < 0.05), although recombinant human growth hormone was superior to TZD regarding VAT reduction (p < 0.05). Data from 216 participants showed TZD leading to a greater reduction in liver fat percentage than comparators (p < 0.05). Compared with the controls, TZD significantly increased SAT, total body fat, weight, waist circumference, and body mass index (p < 0.05). However, TZD pronouncedly improved glucose control, insulin resistance, adiponectin, and lipid profile (p < 0.05). TZD provides a favorable effect on fat redistribution and benefits insulin sensitivity, suggesting a potentially valuable approach in cardiometabolic risk management.

Youth-onset type 2 diabetes mellitus: an urgent challenge

The incidence and prevalence of youth-onset type 2 diabetes mellitus (T2DM) and its complications are increasing worldwide. Youth-onset T2DM has been reported in all racial and ethnic groups, but Indigenous peoples and people of colour are disproportionately affected. People with youth-onset T2DM often have a more aggressive clinical course than those with adult-onset T2DM or those with type 1 diabetes mellitus. Moreover, the available treatment options for children and adolescents with T2DM are more limited than for adult patients. Intermediate complications of youth-onset T2DM, such as increased albuminuria, often develop in late childhood or early adulthood, and end-stage complications, including kidney failure, develop in mid-life. The increasing frequency, earlier onset and greater severity of childhood obesity in the past 50 years together with increasingly sedentary lifestyles and an increasing frequency of intrauterine exposure to diabetes are important drivers of the epidemic of youth-onset T2DM. The particularly high risk of the disease in historically disadvantaged populations suggests an important contribution of social and environmental factors, including limited access to high-quality health care, healthy food choices and opportunities for physical activity as well as exposure to stressors including systemic racism and environmental pollutants. Understanding the mechanisms that underlie the development and aggressive clinical course of youth-onset T2DM is key to identifying successful prevention and management strategies.

Metformin maintains intrahepatic triglyceride content through increased hepatic de novo lipogenesis

OBJECTIVE

Metformin is a first-line pharmacotherapy in the treatment of type 2 diabetes, a condition closely associated with non-alcoholic fatty liver disease (NAFLD). Although metformin promotes weight loss and improves insulin sensitivity, its effect on intrahepatic triglyceride (IHTG) remains unclear. We investigated the effect of metformin on IHTG, hepatic de novo lipogenesis (DNL), and fatty acid (FA) oxidation in vivo in humans.

DESIGN AND METHODS

Metabolic investigations, using stable-isotope tracers, were performed in ten insulin-resistant, overweight/obese human participants with NAFLD who were treatment naïve before and after 12 weeks of metformin treatment. The effect of metformin on markers of s.c. adipose tissue FA metabolism and function, along with the plasma metabolome, was investigated.

RESULTS

Twelve weeks of treatment with metformin resulted in a significant reduction in body weight and improved insulin sensitivity, but IHTG content and FA oxidation remained unchanged. Metformin treatment was associated with a significant decrease in VLDL-triglyceride (TG) concentrations and a significant increase in the relative contribution of DNL-derived FAs to VLDL-TG. There were subtle and relatively few changes in s.c. adipose tissue FA metabolism and the plasma metabolome with metformin treatment.

CONCLUSIONS

We demonstrate the mechanisms of action of metformin whereby it improves insulin sensitivity and promotes weight loss, without improvement in IHTG; these observations are partly explained through increased hepatic DNL and a lack of change in FA oxidation.

Maturation of the Visceral (Gut-Adipose-Liver) Network in Response to the Weaning Reaction versus Adult Age and Impact of Maternal High-Fat Diet

Metabolic-associated fatty liver disease is a major cause of chronic pathologies, of which maternal obesity is a frequent risk factor. Gut wall and microbiota, visceral fat, and liver form a pre-systemic network for substrates and pro-inflammatory factors entering the body, undergoing accelerated maturation in early-life when the weaning reaction, i.e., a transitory inflammatory condition, affects lifelong health. We aimed to characterize organ metabolism in the above network, in relation to weaning reaction and maternal obesity. Weaning or 6-months-old offspring of high-fat-diet and normal-diet fed dams underwent in vivo imaging of pre-/post-systemic glucose uptake and tissue radiodensity in the liver, visceral fat, and intestine, a liver histology, and microbiota and metabolic pathway analyses. Weaning mice showed the dominance of gut Clostridia and Bacteroidia members, overexpressing pathways of tissue replication and inflammation; adulthood increased proneness to steatohepatitis, and Desulfovibrio and RF39 bacteria, and lipopolysaccharide, bile acid, glycosaminoglycan, and sphingolipid metabolic pathways. In vivo imaging could track organ maturation, liver inflammation, and protective responses. A maternal high-fat diet amplified the weaning reaction, elevating liver glucose uptake, triglyceride levels, and steatohepatitis susceptibility along the lifespan. The visceral network establishes a balance between metabolism and inflammation, with clear imaging biomarkers, and crucial modulation in the weaning time window.

Polyphenol-rich extract of Zhenjiang aromatic vinegar ameliorates high glucose-induced insulin resistance by regulating JNK-IRS-1 and PI3K/Akt signaling pathways

Zhenjiang aromatic vinegar is a famous traditional fermented cooking ingredient in China, with multiple nutritional and medicinal applications. Zhenjiang aromatic vinegar extract (100-400 μg/mL) is rich in polyphenols increased the glucose uptake and glucose consumption in high glucose-induced insulin resistant HepG2 (IR-HepG2) cells. Zhenjiang aromatic vinegar extract enhanced glycogen synthesis and attenuated gluconeogenesis by regulating key enzymes in IR-HepG2 cells. In addition, Zhenjiang aromatic vinegar extract ameliorated high glucose-induced IR by inhibiting phosphorylated insulin receptor substrate-1 (IRS-1) expression and activating phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt) pathway in IR-HepG2 cells. Moreover, Zhenjiang aromatic vinegar extract reduced reactive oxygen species generation and phosphorylated c-Jun NH2 terminal kinase (JNK) expression in IR-HepG2 cells. The attenuation of the high glucose is owned to the PI3K/Akt pathway activation, glycogen synthesis induction and gluconeogenesis suppression in IR-HepG2 cells.

Metformin to reduce metabolic complications and inflammation in patients on systemic glucocorticoid therapy: a randomised, double-blind, placebo-controlled, proof-of-concept, phase 2 trial

BACKGROUND

An urgent need to reduce the metabolic side-effects of glucocorticoid overexposure has been recognised, as glucocorticoid excess can lead to Cushing's syndrome, which is associated with high morbidity. We aimed to evaluate the potential of metformin to reverse such effects while sparing the anti-inflammatory benefits of glucocorticoids.

METHODS

We did a randomised, double-blind, placebo-controlled, proof-of-concept, phase 2 trial involving four hospitals in the UK. Patients without diabetes were eligible if they were between the ages of 18 and 75 years with an inflammatory disease treated with continuous prednisolone (≥20 mg/day for ≥4 weeks and remaining on ≥10 mg/day for the subsequent 12 weeks, or its cumulative dose-equivalent). Eligible patients were randomly allocated (1:1) to either the metformin or placebo groups, using a computer-generated randomisation table stratified according to age and BMI. Metformin and placebo were administered orally for 12 weeks in escalating doses: 850 mg/day for the first 5 days, 850 mg twice a day for the next 5 days, and 850 mg three times a day subsequently. The primary outcome was the between-group difference in visceral-to-subcutaneous fat area ratio over 12 weeks, assessed by CT. Secondary outcomes included changes in metabolic, bone, cardiovascular, and inflammatory parameters over 12 weeks. Our analysis followed a modified intention-to-treat principle for the primary outcome. This study is registered with ClinicalTrials.gov, NCT01319994.

FINDINGS

Between July 17, 2012, and Jan 14, 2014, 849 patients were assessed for study eligibility, of which 53 were randomly assigned to receive either metformin (n=26) or placebo (n=27) for 12 weeks. 19 patients in the metformin group and 21 in the placebo group were eligible for the primary outcome analysis. Both groups received an equivalent cumulative dose of glucocorticoids (1860 mg prednisolone-equivalent [IQR 1060-2810] in the metformin group vs 1770 mg [1020-2356] in the placebo group); p=0·76). No change in the visceral-to-subcutaneous fat area ratio between the treatment groups was observed (0·11, 95% CI -0·02 to 0·24; p=0·09), but patients in the metformin group lost truncal subcutaneous fat compared with the placebo group (-3835 mm², 95% CI -6781 to -888; p=0·01). Improvements in markers of carbohydrate, lipid, liver, and bone metabolism were observed in the metformin group compared with the placebo group. Additionally, those in the metformin group had improved fibrinolysis, carotid intima-media thickness, inflammatory parameters, and clinical markers of disease activity. The frequency of pneumonia (one event in the metformin group vs seven in the placebo group; p=0·01), overall rate of moderate-to-severe infections (two vs 11; p=0·001), and all-cause hospital admissions due to adverse events (one vs nine; p=0·001) were lower in the metformin group than in the placebo group. Patients in the metformin group had more events of diarrhoea than the placebo group (18 events vs eight; p=0·01).

INTERPRETATION

No significant changes in the visceral-to-subcutaneous fat area ratio between the treatment groups were observed; however, metformin administration did improve some of the metabolic profile and clinical outcomes for glucocorticoid-treated patients with inflammatory disease, which warrants further investigation.

FUNDING

Barts Charity and Merck Serono.

Changes in Visceral and Subcutaneous Fat in Youth With Type 2 Diabetes in the TODAY Study

OBJECTIVE

In the Treatment Options for Type 2 Diabetes in Adolescents and Youth (TODAY) study, metformin plus rosiglitazone (M + R) maintained glycemic control better than metformin alone (M) or metformin plus lifestyle (M + L) in youth with type 2 diabetes (T2D). We hypothesized that changes in visceral adipose tissue (VAT) and subcutaneous adipose tissue (SAT) would explain the differential treatment effects on glycemia.

RESEARCH DESIGN AND METHODS

In 626 youth ages 11-17 years with T2D duration <2 years, VAT and SAT were estimated by DXA at baseline and at 6 and 24 months. Changes from baseline were analyzed in linear mixed models.

RESULTS

Baseline mean age was 13.9 years, 66.4% were female, 72.2% were Hispanic/non-Hispanic black, and 20.3% were non-Hispanic white (NHW). Mean BMI was 33.7 kg/m². VAT increased more in M + R (13.1%) than M + L (3.9%, P = 0.0006) or M (6.5%, P = 0.0146). SAT also increased more in M + R (13.3%) than in M + L (5.4%, P < 0.0001) or M (6.4%, P = 0.0005), indicating no significant fat redistribution in M + R. In NHWs, VAT increased more in M + R than M (P = 0.0192) and M + L (P = 0.0482) but did not explain the race-ethnicity differences in treatment effects on glycemic control among treatment groups. VAT and SAT increases correlated with higher HbA_1c, lower insulin sensitivity, and lower oral disposition index (all P < 0.05), but associations did not differ by treatment group.

CONCLUSIONS

In contrast to the existing reports in adults with T2D, in TODAY, M + R resulted in the most VAT accumulation compared with M + L or M. Differential effects on depot-specific indirect measures of adiposity are unrelated to treatment effects in sustaining glycemic control. Additional studies are needed to understand the clinical markers of metabolic risk profile in youth with T2D on rosiglitazone.

Pilot Study to Diagnose Nonalcoholic Steatohepatitis With Dynamic 18F-FDG PET

OBJECTIVE

Nonalcoholic fatty liver disease (NAFLD) and nonalcoholic steatohepatitis (NASH) are major causes of chronic liver disease characterized by steatosis, inflammation, and fibrosis. Diagnosis of inflammation is limited by the need for liver biopsy. Dynamic PET with the widely used radiotracer ¹⁸F-FDG provides a novel method for evaluating spatial and temporal changes in liver inflammation.

MATERIALS AND METHODS

Patients with NAFLD or NASH underwent dynamic FDG PET and MRI within 6 months of undergoing liver biopsy. Liver time-activity curves were extracted to estimate kinetic parameters representing various rate constants of FDG transport using tracer kinetic modeling. Liver biopsy specimens were scored on the basis of NASH Clinical Research Network criteria.

RESULTS

This pilot study included 22 patients, 14 of whom were women. Patient age ranged from 18 to 70 years, and the mean body mass index (weight in kilograms divided by the square of height in meters) was 33.2 (range, 24-43.1). The K₁ value, which represents the rate of FDG transport from blood to hepatic tissue, was significantly correlated with inflammation (r = -0.7284; p = 0.0001) and the overall NAFLD activity score (NAS; r = -0.6750; p = 0.0006). K₁ values were inversely related to the hepatic inflammation score and NAS. Although heterogeneity in K₁ values across eight liver segments was noted, distinct segregation existed among segmental K₁ values dependent on the histologic inflammation score (p = 0.022) or NAS (p = 0.0091). K₁ had a strong association with both inflammation (ROC AUC value, 0.88) and the NAS (ROC AUC value, 0.89), with K₁ = 1.02 (mL/min/mL) corresponding to a sensitivity and specificity of 93% and 88%, respectively, for the NAS.

CONCLUSION

Dynamic FDG PET with tracer kinetic modeling has the potential to determine liver inflammation in patients with NAFLD and NASH and can fill an essential gap in diagnosis.

Metformin treatment significantly enhances intestinal glucose uptake in patients with type 2 diabetes: Results from a randomized clinical trial

AIMS

Metformin therapy is associated with diffuse intestinal ¹⁸F-fluoro-deoxyglucose (FDG) accumulation in clinical diagnostics using routine FDG-PET imaging. We aimed to study whether metformin induced glucose uptake in intestine is associated with the improved glycaemic control in patients with type 2 diabetes. Therefore, we compared the effects of metformin and rosiglitazone on intestinal glucose metabolism in patients with type 2 diabetes in a randomized placebo controlled clinical trial, and further, to understand the underlying mechanism, evaluated the effect of metformin in rats.

METHODS

Forty-one patients with newly diagnosed type 2 diabetes were randomized to metformin (1g, b.i.d), rosiglitazone (4mg, b.i.d), or placebo in a 26-week double-blind trial. Tissue specific intestinal glucose uptake was measured before and after the treatment period using FDG-PET during euglycemic hyperinsulinemia. In addition, rats were treated with metformin or vehicle for 12weeks, and intestinal FDG uptake was measured in vivo and with autoradiography.

RESULTS

Glucose uptake increased 2-fold in the small intestine and 3-fold in the colon for the metformin group and associated with improved glycemic control. Rosiglitazone increased only slightly intestinal glucose uptake. In rodents, metformin treatment enhanced intestinal FDG retention (P=0.002), which was localized in the mucosal enterocytes of the small intestine.

CONCLUSIONS

Metformin treatment significantly enhances intestinal glucose uptake from the circulation of patients with type 2 diabetes. This intestine-specific effect is associated with improved glycemic control and localized to mucosal layer. These human findings demonstrate directs effect of metformin on intestinal metabolism and elucidate the actions of metformin. Clinical trial number NCT02526615.

Metabolic imaging in obesity: underlying mechanisms and consequences in the whole body

Obesity is a phenotype resulting from a series of causative factors with a variable risk of complications. Etiologic diversity requires personalized prevention and treatment. Imaging procedures offer the potential to investigate the interplay between organs and pathways underlying energy intake and consumption in an integrated manner, and may open the perspective to classify and treat obesity according to causative mechanisms. This review illustrates the contribution provided by imaging studies to the understanding of human obesity, starting with the regulation of food intake and intestinal metabolism, followed by the role of adipose tissue in storing, releasing, and utilizing substrates, including the interconversion of white and brown fat, and concluding with the examination of imaging risk indicators related to complications, including type 2 diabetes, liver pathologies, cardiac and kidney diseases, and sleep disorders. The imaging modalities include (1) positron emission tomography to quantify organ-specific perfusion and substrate metabolism; (2) computed tomography to assess tissue density as an indicator of fat content and browning/ whitening; (3) ultrasounds to examine liver steatosis, stiffness, and inflammation; and (4) magnetic resonance techniques to assess blood oxygenation levels in the brain, liver stiffness, and metabolite contents (triglycerides, fatty acids, glucose, phosphocreatine, ATP, and acetylcarnitine) in a variety of organs.

A new compartmental method for the analysis of liver FDG kinetics in small animal models

Background

Compartmental analysis is a standard method to quantify metabolic processes using fluorodeoxyglucose-positron emission tomography (FDG-PET). For liver studies, this analysis is complex due to the hepatocyte capability to dephosphorylate and release glucose and FDG into the blood. Moreover, a tracer is supplied to the liver by both the hepatic artery and the portal vein, which is not visible in PET images. This study developed an innovative computational approach accounting for the reversible nature of FDG in the liver and directly computing the portal vein tracer concentration by means of gut radioactivity measurements.

Methods

Twenty-one mice were subdivided into three groups: the control group ‘CTR’ (n = 7) received no treatment, the short-term starvation group ‘STS’ (n = 7) was submitted to food deprivation with free access to water within 48 h before imaging, and the metformin group ‘MTF’ (n = 7) was treated with metformin (750 mg/Kg per day) for 1 month. All mice underwent a dynamic micro-PET study for 50 min after an ¹⁸F-FDG injection. The compartmental analysis considered two FDG pools (phosphorylated and free) in both the gut and liver. A tracer was carried into the liver by the hepatic artery and the portal vein, and tracer delivery from the gut was considered as the sole input for portal vein tracer concentration. Accordingly, both the liver and gut were characterized by two compartments and two exchange coefficients. Each one of the two two-compartment models was mathematically described by a system of differential equations, and data optimization was performed by applying a Newton algorithm to the inverse problems associated to these differential systems.

Results

All rate constants were stable in each group. The tracer coefficient from the free to the metabolized compartment in the liver was increased by STS, while it was unaltered by MTF. By contrast, the tracer coefficient from the metabolized to the free compartment was reduced by MTF and increased by STS.

Conclusions

Data demonstrated that our method was able to analyze FDG kinetics under pharmacological or pathophysiological stimulation, quantifying the fraction of the tracer trapped in the liver or dephosphorylated and released into the bloodstream.

Metformin, cancer and glucose metabolism

Metformin is the first-line treatment for type 2 diabetes. Results from several clinical studies have indicated that type 2 diabetic patients treated with metformin might have a lower cancer risk. One of the primary metabolic changes observed in malignant cell transformation is an increased catabolic glucose metabolism. In this context, once it has entered the cell through organic cation transporters, metformin decreases mitochondrial respiration chain activity and ATP production that, in turn, activates AMP-activated protein kinase, which regulates energy homeostasis. In addition, metformin reduces cellular energy availability and glucose entrapment by inhibiting hexokinase-II, which catalyses the glucose phosphorylation reaction. In this review, we discuss recent findings on molecular mechanisms that sustain the anticancer effect of metformin through regulation of glucose metabolism. In particular, we have focused on the emerging action of metformin on glycolysis in normal and cancer cells, with a drug discovery perspective.

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.

Metformin temporal and localized effects on gut glucose metabolism assessed using 18F-FDG PET in mice

In the course of metformin treatment, staging abdominal cancer lesions with (18)F-FDG PET images is often hindered by the presence of a high bowel radioactivity. The present study aimed to verify the mechanism underlying this phenomenon.

METHODS

Fifty-three mice were submitted to dynamic acquisitions of (18)F-FDG kinetics under fasting conditions. Three small-animal PET scans were obtained over a 4-mo study period. The animals were subdivided into 4 groups according to the following metformin administration protocol: group 1, untreated mice (n = 15); group 2, mice exposed to metformin treatment (750 mg/kg/d) for the 48 h before each PET study (pulsed, n = 10); group 3, mice treated for the whole study period (prolonged, n = 10); and group 4, mice in which prolonged treatment was interrupted 48 h before PET (interrupted, n = 8). The rate constant of (18)F-FDG uptake was estimated by Patlak analysis. At the end of the study, the ileum and colon were harvested, washed, and counted ex vivo. Two further groups, of 5 animals each, were included to evaluate the effect of prolonged metformin treatment on phosphorylated adenosine monophosphate (AMP)-activated protein kinase (pAMPK) form and gene expression for thioredoxin-interacting protein (TXNIP).

RESULTS

Pulsed treatment did not modify gut tracer retention with respect to the untreated group. Conversely, prolonged treatment induced a progressive increase in (18)F-FDG uptake that selectively involved the colonic wall, without any significant contamination of bowel content. This effect persisted after a complete drug washout in the interrupted group. These responses were paralleled by increased pAMPK availability and by reduced expression of TXNIP messenger RNA in colonic enterocytes exposed to prolonged metformin treatment.

CONCLUSION

Metformin causes a selective increase in colonic (18)F-FDG uptake. This effect appears after a relatively long period of treatment and persists soon after drug washout. Accordingly, the increased bowel glucose metabolism reflects a biologic response to chronic metformin treatment characterized by increased levels of pAMPK and reduced levels of TXNIP.

Metformin modifies the exercise training effects on risk factors for cardiovascular disease in impaired glucose tolerant adults

Impaired glucose tolerant (IGT) adults are at elevated risk for cardiovascular disease (CVD). Exercise or metformin reduce CVD risk, but the efficacy of combining treatments is unclear.

OBJECTIVE

To determine the effects of exercise training plus metformin (EM), compared with each treatment alone, on CVD risk factors in IGT adults.

DESIGN AND METHODS

Subjects were assigned to placebo (P), metformin (M), exercise training plus placebo (EP), or EM (8/group). In a double-blind design, P or 2,000 mg/d of M were administered for 12 weeks and half performed aerobic and resistance training 3 days/week for ≈ 60 min/day at 70% pretraining heart rate peak. Outcomes included adiposity, blood pressure (BP), lipids, and high sensitivity C-reactive protein (hs-CRP). Z-scores were calculated to determine metabolic syndrome severity.

RESULTS

M and EM, but not EP, decreased body weight compared with P (P < 0.05). M and EP lowered systolic blood pressure by 6% (P < 0.05), diastolic blood pressure by 6% (P < 0.05), and hs-CRP by 20% (M: trend P = 0.06; EP: P < 0.05) compared with P. Treatments raised high-density lipoprotein cholesterol (P < 0.05; EM: trend P = 0.06) compared with P and lowered triacyglycerol (P < 0.05) and metabolic syndrome Z-score compared with baseline (EP; trend P = 0.07 and EM or M; P < 0.05).

CONCLUSIONS

Although exercise and/or metformin improve some CVD risk factors, only training or metformin alone lowered hs-CRP and BP. Thus, metformin may attenuate the effects of training on some CVD risk factors and metabolic syndrome severity in IGT adults.

Evaluation of a mathematical model of diabetes progression against observations in the Diabetes Prevention Program

The seminal publication of the Diabetes Prevention Program (DPP) results in 2002 has provided insight into the impact of major therapies on the development of diabetes over a time span of a few years. In the present work, the publicly available DPP data set is used to calibrate and evaluate a recently developed mechanistic mathematical model for the long-term development of diabetes to assess the model's ability to predict the natural history of disease progression and the effectiveness of preventive interventions. A general population is generated from which virtual subject samples corresponding to the DPP enrollment criteria are selected. The model is able to reproduce with good fidelity the observed time courses of both diabetes incidence and average glycemia, under realistic hypotheses on evolution of disease and efficacy of the studied therapies, for all treatment arms. Model-based simulations of the long-term evolution of the disease are consistent with the transient benefits observed with conventional therapies and with promising effects of radical improvement of insulin sensitivity (as by metabolic surgery) or of β-cell protection. The mechanistic diabetes progression model provides a credible tool by which long-term implications of antidiabetic interventions can be evaluated.

Effects of rosiglitazone with insulin combination therapy on oxidative stress and lipid profile in left ventricular muscles of diabetic rats

PURPOSE

In this study, we tested the hypothesis that rosiglitazone (RSG) with insulin is able to quench oxidative stress initiated by high glucose through prevention of NAD(P)H oxidase activation.

METHODS AND MATERIALS

Male albino Wistar rats were randomly divided into an untreated control group (C), a diabetic group (D) that was treated with a single intraperitoneal injection of streptozotocin (45 mg kg(-1)), and rosiglitazone group that was treated with RSG twice daily by gavage and insulin once daily by subcutaneous injection (group B). HbA1c and blood glucose levels in the circulation and malondialdehyde and 3-nitrotyrosine levels in left ventricular muscle were measured.

RESULT

Treatment of D rats with group B resulted in a time-dependent decrease in blood glucose. We found that the lipid profile and HbA1c levels in group B reached the control group D rat values at the end of the treatment period. There was an increase in 3-nitrotyrosine levels in group D compared to group C. Malondialdehyde and 3-nitrotyrosine levels were found to be decreased in group B compared to group D (P < 0.05).

CONCLUSION

Our data suggests that the treatment of diabetic rats with group B for 8 weeks may decrease the oxidative/nitrosative stress in left ventricular tissue of rats. Thus, in diabetes-related vascular diseases, group B treatment may be cardioprotective.

Mitochondrial diabetes is associated with insulin resistance in subcutaneous adipose tissue but not with increased liver fat content

We recently showed that patients with mitochondrial diabetes are insulin resistant in skeletal muscle before the decline in insulin secretion is observed. In this study, we further evaluate whether insulin resistance is associated with increased ectopic fat accumulation and altered adipose and hepatic tissue insulin sensitivity. We studied 15 nonobese patients with the m.3243A > G mutation. Five were without diabetes (group 1), three had newly diagnosed diabetes (group 2), and seven had previously diagnosed diabetes (group 3). Thirteen healthy volunteers of similar age and body mass index (BMI) served as controls. Insulin-stimulated glucose uptake was measured with positron emission tomography using 2- [(18)F]-fluoro-2-deoxyglucose during euglycemic hyperinsulinemia. Fat masses and liver fat content were measured with magnetic resonance imaging and spectroscopy. Compared with controls, insulin-stimulated glucose uptake in adipose tissue was decreased by ∼50% in all groups with the m.3243A > G mutation. In addition, fat masses were not different, but insulin-mediated suppression of lipolysis and adiponectin metabolism were blunted in patients with the m.3243A > G mutation. Hepatic fat content was normal (<5.6%) in 80% of patients and significantly elevated in one case only. Hepatic glucose metabolism in patients with m.3243A > G did not differ from that of controls. In conclusion, m.3243A > G mutation affects subcutaneous adipose tissue metabolism. This seems to occur before aberrant liver metabolism, if any, can be observed or before beta-cell failure results in mitochondrial diabetes.

Metformin: taking away the candy for cancer?

Metformin is widely used in the treatment of diabetes mellitus type 2 where it reduces insulin resistance and diabetes-related morbidity and mortality. Population-based studies show that metformin treatment is associated with a dose-dependent reduction in cancer risk. The metformin treatment also increases complete pathological tumour response rates following neoadjuvant chemotherapy for breast cancer, suggesting a potential role as an anti-cancer drug. Diabetes mellitus type 2 is associated with insulin resistance, elevated insulin levels and an increased risk of cancer and cancer-related mortality. This increased risk may be explained by activation of the insulin- and insulin-like growth factor (IGF) signalling pathways and increased signalling through the oestrogen receptor. Reversal of these processes through reduction of insulin resistance by the oral anti-diabetic drug metformin is an attractive anti-cancer strategy. Metformin is an activator of AMP-activated protein kinase (AMPK) which inhibits protein synthesis and gluconeogenesis during cellular stress. The main downstream effect of AMPK activation is the inhibition of mammalian target of rapamycin (mTOR), a downstream effector of growth factor signalling. mTOR is frequently activated in malignant cells and is associated with resistance to anticancer drugs. Furthermore, metformin can induce cell cycle arrest and apoptosis and can reduce growth factor signalling. This review discusses the role of diabetes mellitus type 2 and insulin resistance in carcinogenesis, the preclinical rationale and potential mechanisms of metformin's anti-cancer effect and the current and future clinical developments of metformin as a novel anti-cancer drug.

Glucose supply and insulin demand dynamics of antidiabetic agents

BACKGROUND

For microvascular outcomes, there is compelling historical and contemporary evidence for intensive blood glucose reduction in patients with either type 1 diabetes mellitus (T1DM) or type 2 diabetes mellitus (T2DM). There is also strong evidence to support macrovascular benefit with intensive blood glucose reduction in T1DM. Similar evidence remains elusive for T2DM. Because cardiovascular outcome trials utilizing conventional algorithms to attain intensive blood glucose reduction have not demonstrated superiority to less aggressive blood glucose reduction (Action to Control Cardiovascular Risk in Diabetes; Action in Diabetes and Vascular Disease: Preterax and Diamicron Modified Release Controlled Evaluation; and Veterans Affairs Diabetes Trial), it should be considered that the means by which the blood glucose is reduced may be as important as the actual blood glucose.

METHODS

By identifying quantitative differences between antidiabetic agents on carbohydrate exposure (CE), hepatic glucose uptake (HGU), hepatic gluconeogenesis (GNG), insulin resistance (IR), peripheral glucose uptake (PGU), and peripheral insulin exposure (PIE), we created a pharmacokinetic/pharmacodynamic model to characterize the effect of the agents on the glucose supply and insulin demand dynamic. Glucose supply was defined as the cumulative percentage decrease in CE, increase in HGU, decrease in GNG, and decrease in IR, while insulin demand was defined as the cumulative percentage increase in PIE and PGU. With the glucose supply and insulin demand effects of each antidiabetic agent summated, the glucose supply (numerator) was divided by the insulin demand (denominator) to create a value representative of the glucose supply and insulin demand dynamic (SD ratio).

RESULTS

Alpha-glucosidase inhibitors (1.25), metformin (2.20), and thiazolidinediones (TZDs; 1.25-1.32) demonstrate a greater effect on glucose supply (SD ratio >1), while secretagogues (0.69-0.81), basal insulins (0.77-0.79), and bolus insulins (0.62-0.67) demonstrate a greater effect on insulin demand (SD ratio <1).

CONCLUSION

Alpha-glucosidase inhibitors, metformin, and TZDs demonstrate a greater effect on glucose supply, while secretagogues, basal insulin, and bolus insulin demonstrate a greater effect on insulin demand. Because T2DM cardiovascular outcome trials have not demonstrated macrovascular benefit with more aggressive blood glucose reduction when using conventional algorithms that predominantly focus on insulin demand, it would appear logical to consider a model that incorporates both the extent of blood glucose lowering (hemoglobin A1c) and the means by which the blood glucose was reduced (SD ratio) when considering macrovascular outcomes.

Adipose tissue, metabolic syndrome and polycystic ovary syndrome: from pathophysiology to treatment

In the last few years, polycystic ovary syndrome (PCOS) has deserved major attention because it is linked to the same cluster of events that promote the metabolic syndrome. This review will point out the relationships between fat excess, insulin resistance and the metabolic syndrome. Adipocytes are actually considered as endocrine cells that synthesize and release molecules (adipokines) that play an endocrine/paracrine role, such as adiponectin, atrial natriuretic peptide, leptin, resistin, tumour necrosis factor alpha (TNFalpha). Metabolic syndrome is a chronic low-grade inflammatory condition in which adipokines play a major role. Isolated adipocytes from women with PCOS express higher mRNA concentrations of some adipokines involved in cardiovascular risk and insulin resistance. However, environmental factors and lifestyle play a major role in determining the appearance of the phenotypes of PCOS. In morbid obese women with PCOS, bariatric surgery decreases bodyweight and fat excess and reverses hyperandrogenism and sterility. In lean or overweight women with PCOS, changes in lifestyle in combination with drugs reducing visceral fat and insulin resistance reverse the symptoms and signs of PCOS. Promising treatments for PCOS seem to be insulin sensitizers such as metformin and glitazones.

Targeting insulin sensitivity in the treatment of polycystic ovary syndrome

Targeting insulin resistance may result in a list of benefits for women with PCOS, including hormonal, metabolic and ovulatory (and fertility) improvements. The therapeutic strategy to treat PCOS should however depend on the clinical situation, the phenotype, the degree of androgen excess, age, the presence of infertility and the woman's desire to conceive, the presence of obesity and, finally, the spectrum of metabolic abnormalities and the need to treat or prevent long-term associated comorbidities. According to the needs, therapeutic options include, alone or in combination, lifestyle management, particularly in the presence of obesity, the use of insulin sensitizers, metformin and thiazolidinediones, antiandrogens or estro-progestins.

In vivo metabolic phenotyping of myocardial substrate metabolism in rodents: differential efficacy of metformin and rosiglitazone monotherapy

BACKGROUND

Cardiovascular disease is the leading cause of death among diabetic patients, with alteration in myocardial substrate metabolism being a likely contributor. We aimed to assess noninvasively the efficacy of metformin and rosiglitazone monotherapy in normalizing myocardial substrate metabolism in an animal model of type 2 diabetes mellitus.

METHODS AND RESULTS

The study used 18 male ZDF rats (fa/fa) with 6 rats in each group: an untreated group; a group treated with metformin (16.6 mg/kg/d), and a group treated with rosiglitazone (4 mg/kg). Each rat was scanned at age 14 weeks (baseline) and subsequently at 19 weeks with small-animal positron emission tomography to estimate myocardial glucose utilization (MGU) and myocardial utilization (MFAU), oxidation (MFAO), and esterification (MFAE). Treatment lasted for 5 weeks after baseline imaging. At week 19, rats were euthanized and hearts were extracted for expression analysis of select genes encoding for GLUT transporters and fatty acid transport and oxidation genes. In addition, echocardiography measurements were obtained at weeks 13 and 18 to characterize cardiac function. Metformin had no significant effect on either MGU or MFAU and MFAO. In contrast, rosiglitazone tended to enhance MGU and significantly reduced MFAU and MFAO. Rosiglitazone-induced increase in glucose uptake correlated significantly with increased expression of GLUT4, whereas diminished MFAO correlated significantly with decreased expression of FATP-1 and MCAD. Finally, changes in fractional shortening as a measure of cardiac function were unchanged throughout the study.

CONCLUSIONS

Treatment with rosiglitazone enhanced glucose utilization and diminished MFAO, thus reversing the metabolic phenotype of the diabetic heart.

Inverse association between liver fat content and hepatic glucose uptake in patients with type 2 diabetes mellitus

The objective of this research was to study (1) the mutual relationship between liver fat content (LFC) and hepatic glucose uptake (HGU) in patients with type 2 diabetes mellitus and (2) the relationship between changes in LFC and HGU uptake induced by rosiglitazone in these patients. Liver fat was measured with proton magnetic resonance spectroscopy and insulin-stimulated HGU with [(18)F]-labeled 2-fluoro-2-deoxyglucose positron emission tomography in 54 patients with type 2 diabetes mellitus and 8 healthy subjects. Measurements were repeated in diabetic patients after a 16-week intervention period with rosiglitazone (n = 27) or placebo (n = 27). Patients with diabetes had lower HGU (24.5 +/- 14.2 vs 35.6 +/- 9.7 micromol/[kg min], P < .01) and higher LFC (10.9% +/- 9.2% vs 2.5% +/- 1.4%, P < .001) compared with healthy subjects. Liver fat was inversely associated with HGU (r = -0.31, P < .05), but more strongly with whole-body insulin sensitivity and adiponectin levels. Rosiglitazone treatment reduced liver fat by 24.8% (P = .01 vs placebo) and increased HGU by 29.2% (P = .013 vs placebo). This decrease in LFC was best explained by the increment in suppression of nonesterified fatty acid levels during hyperinsulinemia (P < .001) and improved glycemic control (P = .034), but not by changes in HGU. A significant inverse relationship between LFC and HGU was observed, but changes were not related. This suggests that the beneficial effects of rosiglitazone on liver metabolism are indirect and can be partly explained by increased suppression of nonesterified fatty acid levels, leading to reduced liver fat.

The increase in abdominal subcutaneous fat depot is an independent factor to determine the glycemic control after rosiglitazone treatment

OBJECTIVE

The goal was to investigate the interrelationships between the hypoglycemic effects of rosiglitazone and the changes in the regional adiposity of type 2 diabetic patients.

DESIGN AND METHODS

We added rosiglitazone (4 mg/day) to 173 diabetic patients (111 males and 62 females) already taking a stable dose of conventional antidiabetic medications except for thiazolidinediones. The abdominal fat distribution was assessed by ultrasonography at baseline and 12 weeks later. Using ultrasonographic images, the s.c. and visceral fat thickness (SFT and VFT respectively) were measured.

RESULTS

Rosiglitazone treatment for 3 months improved the glycemic control. However, the response to rosiglitazone was no more than 36.4%; the deterioration of the glycemic control was found in 16.8% of subjects. In addition, rosiglitazone treatment significantly increased the body fat mass, especially the s.c. fat. However that did not alter the visceral fat content. The percentage changes in fasting plasma glucose (FPG) and glycated hemoglobin (HbA1c) concentrations after treatment were inversely correlated with the increase in SFT (r=-0.327 and -0.353, P<0.001 respectively) and/or body weight (r=-0.316 and -0.327, P<0.001 respectively). Multiple regression analysis revealed that the improvement in the FPG after rosiglitazone treatment was correlated with the baseline FPG (P<0.001) and the change in the SFT (P=0.019), and the reduction in the HbA1c was related with the baseline FPG (P=0.003) and HbA1c (P<0.001) and the changes in the SFT (P=0.010) or VFT (P=0.013).

CONCLUSIONS

The increase in the s.c. fat depot after rosiglitazone treatment may be an independent factor that determines the hypoglycemic efficacy.

Rosiglitazone for type 2 diabetes mellitus

BACKGROUND

Diabetes has long been recognised as a strong, independent risk factor for cardiovascular disease, a problem which accounts for approximately 70% of all mortality in people with diabetes. Prospective studies show that compared to their non-diabetic counterparts, the relative risk of cardiovascular mortality for men with diabetes is two to three and for women with diabetes is three to four. The two biggest trials in type 2 diabetes, the United Kingdom Prospective Diabetes Study (UKPDS) and the University Group Diabetes Program (UGDP) study did not reveal a reduction of cardiovascular endpoints through improved metabolic control. Theoretical benefits of the peroxisome proliferator activated receptor gamma (PPAR-gamma) activator rosiglitazone on endothelial function and cardiovascular risk factors might result in fewer macrovascular disease events in people with type 2 diabetes mellitus.

OBJECTIVES

To assess the effects of rosiglitazone in the treatment of type 2 diabetes.

SEARCH STRATEGY

Studies were obtained from computerised searches of MEDLINE, EMBASE and The Cochrane Library.

SELECTION CRITERIA

Studies were included if they were randomised controlled trials in adult people with type 2 diabetes mellitus and had a trial duration of at least 24 weeks.

DATA COLLECTION AND ANALYSIS

Two authors independently assessed trial quality and extracted data. Pooling of studies by means of fixed-effects meta-analysis could be performed for adverse events only.

MAIN RESULTS

Eighteen trials which randomised 3888 people to rosiglitazone treatment were identified. Longest duration of therapy was four years with a median of 26 weeks. Published studies of at least 24 weeks rosiglitazone treatment in people with type 2 diabetes mellitus did not provide evidence that patient-oriented outcomes like mortality, morbidity, adverse effects, costs and health-related quality of life are positively influenced by this compound. Metabolic control measured by glycosylated haemoglobin A1c (HbA1c) as a surrogate endpoint did not demonstrate clinically relevant differences to other oral antidiabetic drugs. Occurrence of oedema was significantly raised (OR 2.27, 95% confidence interval (CI) 1.83 to 2.81). The single large RCT (ADOPT - A Diabetes Outcomes Progression Trial) indicated increased cardiovascular risk. New data on raised fracture rates in women reveal extensive action of rosiglitazone in various body tissues.

AUTHORS' CONCLUSIONS

New studies should focus on patient-oriented outcomes to clarify the benefit-risk ratio of rosiglitazone therapy. Safety data and adverse events of all investigations (published and unpublished) should be made available to the public.

Short-term effects of metformin in type 2 diabetes

BACKGROUND

Although metformin is widely used in the management of type 2 diabetes, its mechanism(s) of action is not fully known, and there have been remarkably few reports on short-term effects of the drug. Here, we examined the early effects on glucose and lipid metabolism and on certain adipose tissue and inflammatory markers during treatment for 28 days.

METHODS

Twenty-one patients were randomized to metformin (n = 16) or placebo (n = 5) and studied at baseline, 1, 2 and 4 weeks with blood sampling and oral glucose tolerance tests (OGTT). The active group received 500 mg metformin daily in the first week, 500 mg twice daily during week 2 and 1000 mg twice daily during weeks 3 and 4.

RESULTS

After 7 days of treatment, a reduced area under curve (AUC) for glucose at OGTT with no change in AUC for insulin levels was observed compared to baseline. Insulin sensitivity, as derived from the OGTT by Gutt's index, was increased. Reductions in fasting plasma glucose, total cholesterol and low-density lipoprotein cholesterol appeared after 14 days, and reductions in triglycerides, plasminogen activator inhibitor-1 (PAI-1) and leptin after 28 days of treatment. There were no changes in body weight, adiponectin or C-reactive protein. Compared with placebo, the changes between day 0 and day 28 differed significantly with regard to AUC for glucose at OGTT and Gutt's index, and showed strong trends for PAI-1 and leptin.

CONCLUSIONS

The data demonstrate that in type 2 diabetes, metformin rapidly affects glucose handling without changing the concentrations of insulin. Reductions in PAI-1 and leptin levels indicate that the early effects of metformin involve also the adipose tissue.

Short-term effects of metformin in type 2 diabetes

BACKGROUND

Although metformin is widely used in the management of type 2 diabetes, its mechanism(s) of action is not fully known, and there have been remarkably few reports on short-term effects of the drug. Here, we examined early effects on glucose and lipid metabolism, and on certain adipose tissue and inflammatory markers during treatment for 28 days.

METHODS

Twenty-one patients were randomized to metformin (n = 16) or placebo (n = 5) and studied at baseline, 1, 2 and 4 weeks with blood sampling and oral glucose tolerance tests (OGTT). The active group received 500 mg metformin daily in week 1, 500 mg twice daily in week 2 and 1000 mg twice daily in week 3 and 4.

RESULTS

After 7 days of treatment, a reduced area under curve (AUC) for glucose at OGTT with no change in AUC for insulin levels was observed compared with baseline. Insulin sensitivity, as derived from the OGTT by Gutt's index, was increased. Reductions in fasting plasma glucose, total and LDL-cholesterol appeared after 14 days, and reductions in triglycerides, plasminogen activator inhibitor-1 (PAI-1) and leptin after 28 days of treatment. There were no changes in body weight, adiponectin or C-reactive protein. Compared with placebo, the changes between day 0 and day 28 differed significantly with regard to AUC for glucose at OGTT and Gutt's index, and showed strong trends for PAI-1 and leptin.

CONCLUSIONS

The data demonstrate that in type 2 diabetes metformin rapidly affects glucose handling without changing the concentrations of insulin. Reductions in PAI-1 and leptin levels indicate that the early effects of metformin involve also the adipose tissue.

The effect of pioglitazone on the liver: role of adiponectin

OBJECTIVE

Diabetic hyperglycemia results from insulin resistance of peripheral tissues and glucose overproduction due to increased gluconeogenesis (GNG). Thiazolidinediones (TZDs) improve peripheral insulin sensitivity, but the effect on the liver is less clear. The goal of this study was to examine the effect of TZDs on GNG.

RESEARCH DESIGN AND METHODS

Twenty sulfonylurea-treated type 2 diabetic subjects were randomly assigned (double-blind study) to receive pioglitazone (PIO group; 45 mg/day) or placebo (Plc group) for 4 months to assess endogenous glucose production (EGP) (3-(3)H-glucose infusion), GNG (D2O technique), and insulin sensitivity by two-step hyperinsulinemic-euglycemic clamp (240 and 960 pmol/min per m2).

RESULTS

Fasting plasma glucose (FPG) (10.0 +/- 0.8 to 7.7 +/- 0.7 mmol/l) and HbA1c (9.0 +/- 0.4 to 7.3 +/- 0.6%) decreased in the PIO and increased in Plc group (P < 0.05 PIO vs. Plc). Insulin sensitivity increased approximately 40% during high insulin clamp after pioglitazone (P < 0.01) and remained unchanged in the Plc group (P < 0.05 PIO vs. Plc). EGP did not change, while GNG decreased in the PIO group (9.6 +/- 0.7 to 8.7 +/- 0.6 micromol x min(-1) x kg(ffm)(-1)) and increased in the Plc group (8.0 +/- 0.5 to 9.6 +/- 0.8) (P < 0.05 PIO vs. Plc). Change in FPG correlated with change in GNG flux (r = 0.63, P < 0.003) and in insulin sensitivity (r = 0.59, P < 0.01). Plasma adiponectin increased after pioglitazone (P < 0.001) and correlated with delta FPG (r = -0.54, P < 0.03), delta GNG flux (r = -0.47, P < 0.05), and delta insulin sensitivity (r = 0.65, P < 0.005). Plasma free fatty acids decreased after pioglitazone and correlated with delta GNG flux (r = 0.54, P < 0.02). From stepwise regression analysis, the strongest determinant of change in FPG was change in GNG flux.

CONCLUSIONS

Pioglitazone improves FPG, primarily by reducing GNG flux in type 2 diabetic subjects.

Improvement of Solubility and Oral Bioavailability of 2-(N-Cyanoimino)-5-{(E)-4-styrylbenzylidene}-4-oxothiazolidine (FPFS-410) with Antidiabetic and Lipid-Lowering Activities in Dogs by 2-Hydroxypropyl-.BETA.-cyclodextrin

2-(N-Cyanoimino)-5-[(E)-4-styrylbenzylidene]-4-oxothiazolidine (FPFS-410) is a newly synthesized thiazolidine derivative having not only antidiabetic but also lipid-lowering activities. However, this compound has an extremely low aqueous solubility (2.8 (+/-0.33) x 10(-8) M (0.0094+/-0.0011 microg/ml) in 1.0 M phosphate buffer (pH 7.0) at 25 degrees C). In this study, we investigated the effect of various hydrophilic cyclodextrins (CyDs) on the solubility of FPFS-410 to select a CyD suitable for formulations of the compound. Among various CyDs, 2-hydroxypropyl-beta-CyD (HP-beta-CyD) had the highest solubilizing ability to FPFS-410, e.g., the solubility of the compound was increased 200000-fold by the addition of 40 mM HP-beta-CyD, which was attributable to the formation of the 1 : 2 (guest : host) inclusion complexes. The interaction of HP-beta-CyD with FPFS-410 was studied using 1H-nuclear magnetic resonance (NMR) spectroscopies including ROESY spectroscopy and a molecular modeling calculation. These results suggested that HP-beta-CyD forms a 1:2 (guest : host) inclusion complex with FPFS-410 by including both the stilbene and thiazolidine moieties. FPFS-410/HP-beta-CyD solid complexes with various stoichiometries were prepared by the spray drying and cogrinding methods, and confirmed by powder X-ray diffractometry that these complexes are in an amorphous state. The dissolution of FPFS-410 in water was significantly accelerated by the complexation with HP-beta-CyD. In vivo studies revealed that HP-beta-CyD markedly increases the bioavailability of FPFS-410 after oral administration in dogs. The present results suggest that HP-beta-CyD is useful for improvement of the extremely low bioavailability of FPFS-410.

Metformin revisited: re-evaluation of its properties and role in the pharmacopoeia of modern antidiabetic agents

BACKGROUND

The usefulness of metformin as an oral antidiabetic agent is widely accepted. However, several other classes of oral antidiabetic agents have been recently introduced, raising the need to evaluate the role of metformin as initial therapy and in combination with these newer drugs for treatment of type 2 diabetes mellitus (DM).

METHODS

Synthesis of information was preceded by a comprehensive review of the English language literature using Medline. We also reviewed bibliographies of relevant articles. The studies most pertinent to the mechanism of action, efficacy, toxicity and administration of metformin were selected for citation in this review.

RESULTS

Metformin acts by increasing tissue sensitivity to insulin, principally in the liver. Beneficial properties of metformin include weight reduction, favourable effects on the lipid profile and the fibrinolytic pathway, and improvement of ovarian function in some insulin-resistant women. It does not cause hyperinsulinaemia or hypoglycaemia. Metformin is effective as monotherapy and, in combination with both insulin secretagogues and thiazolidinediones (TZDs), may obviate the need for insulin treatment. Several fixed-dose combination pills containing metformin and other agents are available. A protocol for the initiation of therapy with contemporary oral agents for type 2 DM is presented, with emphasis on the continuing central role of metformin.

CONCLUSIONS

Metformin remains a safe and effective agent for the therapy of patients with type 2 DM. It is useful as monotherapy or in combination regimens with the newer insulin secretagogues, TZDs or insulin. It is still in most circumstances the agent of choice for initial therapy of the typical obese patient with type 2 DM and mild to moderate hyperglycaemia.

Rosiglitazone improves myocardial glucose uptake in patients with type 2 diabetes and coronary artery disease: a 16-week randomized, double-blind, placebo-controlled study

Rosiglitazone therapy improves insulin sensitivity and glucose uptake in patients with uncomplicated type 2 diabetes. In coronary artery disease (CAD), glucose is an important source of energy and preserved myocardial glucose uptake is essential for the viability of jeopardized myocardium. The aim was to test whether rosiglitazone changes myocardial metabolism in type 2 diabetic patients with CAD. We studied 54 patients (38 men and 16 women) with type 2 diabetes (HbA(1c) 7.2 + 0.9%) and CAD. Myocardial glucose uptake was measured with [(18)F]fluoro-2-deoxy-d-glucose positron emission tomography in ischemic (evaluated by single-photon emission tomography and coronary angiography) and nonischemic regions during euglycemic-hyperinsulinemic clamp before and after a 16-week intervention period with rosiglitazone (n = 27) or placebo (n = 27). Rosiglitazone significantly improved glycemic control (P < 0.0001) and whole-body insulin sensitivity (P < 0.0001). Rosiglitazone increased myocardial glucose uptake from 20.6 +/- 11.8 to 25.5 +/- 12.4 micromol . 100 g(-1) . min(-1) (P = 0.038 vs. baseline, P = 0.023 vs. placebo) in ischemic regions and from 21.7 +/- 12.1 to 28.0 +/- 12.7 micromol . 100 g(-1) . min(-1) (P = 0.014 vs. baseline, P = 0.003 vs. placebo) in nonischemic regions. The increase in myocardial glucose uptake was partly explained by the suppression of free fatty acid levels during clamp. Rosiglitazone therapy significantly increased insulin sensitivity and improved myocardial glucose uptake in type 2 diabetic patients with CAD. These results suggest that rosiglitazone therapy may facilitate myocardial glucose storage and utilization in these patients.

Variation in the gene for muscle-specific AMP deaminase is associated with insulin clearance, a highly heritable trait

The rising prevalence of the insulin resistance syndrome in our society necessitates a better understanding of the genetic determinants of all aspects of insulin action and metabolism. We evaluated the heritability of insulin sensitivity and the metabolic clearance rate of insulin (MCRI) as quantified by the euglycemic-hyperinsulinemic clamp in 403 Mexican Americans. We tested the candidate gene AMP deaminase 1 (AMPD1) for association with insulin-related traits because it codes for an enzyme that has the potential to influence multiple aspects of insulin pharmacodynamics. By converting AMP to inosine monophosphate, AMPD1 plays a major role in regulating cellular AMP levels; AMP activates AMP kinase, an enzyme that modulates cellular energy and insulin action. We determined that nine AMPD1 single nucleotide polymorphisms (SNPs) defined two haplotype blocks. Insulin clearance was found to have a higher heritability (h(2) = 0.58) than fasting insulin (h(2) = 0.38) or insulin sensitivity (h(2) = 0.44). The MCRI was associated with AMPD1 SNPs and haplotypes. Insulin clearance is a highly heritable trait, and specific haplotypes within the AMPD1 gene, which encodes a skeletal muscle-specific protein, are associated with variation in insulin clearance. We postulated that the processes of insulin action and insulin clearance in skeletal muscle are highly regulated and that AMPD1 function may play an important role in these phenomena.

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Clinical interest of PPARs ligands

Cardiovascular disease is significantly increased in patients with metabolic syndrome and type 2 diabetes. Several factors such as chronic hyperglycemia, lipId abnormalities, endothelium dysfunction, inflammation, oxIdative stress, increased thrombosis and decreased fibrinolysis are likely to promote cardiovascular events in these patients. Because of positive effects on glucose homeostasis, lipId metabolism, proteins involved in all stages of atherogenesis, endothelium function, inflammation, thrombosis and fibrinolysis, PPARS alpha (fibrates) and PPARs gamma (glitazones) agonists are good candIdates to reduce cardiovascular disease, more precisely in subjects with metabolic syndrome or type 2 diabetes. PPARS alpha agonists (fibrates) are potent hypolipIdemic agents increasing plasma HDL-cholesterol and reducing free fatty acIds, triglycerIdes, LDL-cholesterol and the number of small dense LDL pArticles. Moreover, they reduce vascular inflammation and thrombosis, promote fibrinolysis and inhibit the production of the vasoconstrictor factor, endothelin-1, by the endothelium. They have been shown, in clinical trials, to reduce cardiovascular disease, more particularly in patients displaying lipId abnormalities typical of metabolic syndrome and type 2 diabetes (high triglycerIdes, low HDL-cholesterol). PPARS gamma agonists (glitazones) have not only beneficial effects on glucose homeostasis, by increasing insulin sensitivity and reducing blood glucose level but also on lipId metabolism by elevating plasma HDL-cholesterol, decreasing free fatty acIds and the number of small dense LDL pArticles, and for pioglitazone by reducing plasma triglycerIdes. Furthermore, they diminish vascular inflammation and vasoconstriction, inhibit monocyte chemotaxis, proliferation and migration of smooth muscle cells, in the vascular wall and decrease the production of adhesion molecules and metalloproteinases. PPARs gamma agonists (glitazones) have been shown to reduce the development of atherosclerotic lesions in rats. The potential clinical benefit of PPARs gamma agonists on the reduction of cardiovascular disease, in type 2 diabetic patients, will be specified by the ongoing intervention studies.

Non-esterified fatty acids impair insulin-mediated glucose uptake and disposition in the liver

AIMS/HYPOTHESIS

We investigated the effect of elevated circulating NEFA on insulin-mediated hepatic glucose uptake (HGU) and whole-body glucose disposal (M) in eight healthy male subjects.

METHODS

Studies were performed using positron emission tomography (PET) and [(18)F]-2-fluoro-2-deoxyglucose ([(18)F]FDG) during euglycaemic hyperinsulinaemia (0-120 min) and an Intralipid/heparin infusion (IL/Hep; -90-120 min). On a different day, similar measurements were taken during euglycaemic hyperinsulinaemia and saline infusion (SAL). Graphical and compartmental analyses were used to model liver data.

RESULTS

Circulating NEFA increased approximately three-fold during IL/Hep, and declined by 81+/-7% in the SAL study ( p</=0.01). Both M (-28+/-7%) and HGU (-25+/-9%) were significantly lowered by NEFA elevation ( p=0.004 and p=0.035 respectively). In the whole data set, the decreases in M and HGU were positively correlated ( r=0.78, p=0.038). No evidence of [(18)F]FDG outflow was detected during the scanning time. HGU was correlated with the phosphorylation rate parameter ( r=0.71, p=0.003) as derived by compartmental modelling.

CONCLUSIONS/INTERPRETATION

In healthy men, NEFA impair insulin-mediated HGU and whole-body glucose uptake to a similar extent. Our data suggest that multiple intracellular NEFA targets may concur to down-regulate glucose uptake by the liver.

A comparison of the effects of thiazolidinediones and metformin on metabolic control in patients with type 2 diabetes mellitus

BACKGROUND

Type 2 diabetes mellitus is a condition characterized by impaired insulin secretion and resistance to insulin-mediated glucose uptake and utilization. A number of oral antidiabetic medication are available for its treatment, including metformin and the thiazolidinediones (TZDs). The TZDs have been shown to improve insulin resistance, and it has been suggested that metformin has similar effects. Although both types of agents improve glycemic control, their mechanisms of action and effects on metabolic processes differ.

OBJECTIVE

The goal of this review was to compare the effects of TZDs and metformin on metabolic control in patients with type 2 diabetes.

METHODS

A search of MEDLINE to March 2004 using the terms metformin and biguanides, and thiazolidinediones and glitazones was conducted to identify preclinical and clinical studies focusing on the mechanisms of action and comparative effects of TZDs and metformin. Also searched were published abstracts from recent major diabetes and endocrinology conferences.

RESULTS

In the studies reviewed, both TZDs and metformin demonstrated the ability to improve glycemic control, although long-term monotherapy with TZDs appeared to be more effective than metformin. There continues to be debate about whether metformin is more effective than TZDs in terms of inhibition of hepatic glucose production. However, various studies have found TZDs to be more effective in promoting an increase in whole-body insulin sensitivity. With respect to lipid metabolism, patients who received TZDs had a greater reduction in concentrations of both plasma triglycerides and free fatty acids. Metformin was more effective in promoting weight loss in patients with type 2 diabetes, although TZDs may decrease visceral fat levels. Treatment with either metformin or TZDs was associated with a reduction in the risk of cardiovascular disease, although the mechanisms by which they accomplished this seem to differ.

CONCLUSIONS

The evidence suggests that the predominant effect of metformin is inhibition of hepatic glucose production, whereas the primary effects of TZDs is reduction of insulin resistance and promotion of peripheral glucose uptake. TZDs appear to have more positive effects on other metabolic processes and to be associated with greater improvements in cardiovascular risk factors compared with metformin.