Clinical evidence of thiazolidinedione-induced improvement of pancreatic beta-cell function in patients with type 2 diabetes mellitus

Nutrient Regulation of Pancreatic Islet β-Cell Secretory Capacity and Insulin Production

Pancreatic islet β-cells exhibit tremendous plasticity for secretory adaptations that coordinate insulin production and release with nutritional demands. This essential feature of the β-cell can allow for compensatory changes that increase secretory output to overcome insulin resistance early in Type 2 diabetes (T2D). Nutrient-stimulated increases in proinsulin biosynthesis may initiate this β-cell adaptive compensation; however, the molecular regulators of secretory expansion that accommodate the increased biosynthetic burden of packaging and producing additional insulin granules, such as enhanced ER and Golgi functions, remain poorly defined. As these adaptive mechanisms fail and T2D progresses, the β-cell succumbs to metabolic defects resulting in alterations to glucose metabolism and a decline in nutrient-regulated secretory functions, including impaired proinsulin processing and a deficit in mature insulin-containing secretory granules. In this review, we will discuss how the adaptative plasticity of the pancreatic islet β-cell's secretory program allows insulin production to be carefully matched with nutrient availability and peripheral cues for insulin signaling. Furthermore, we will highlight potential defects in the secretory pathway that limit or delay insulin granule biosynthesis, which may contribute to the decline in β-cell function during the pathogenesis of T2D.

The case for combination therapy as first-line treatment for the type 2 diabetic patient

The glycosylated hemoglobin (HbA(1c)) goal in patients with type 2 diabetes mellitus should be to achieve as low a value as can be obtained without causing significant or frequent hypoglycemia. This is best achieved by utilizing agents that lower glucose levels without causing hypoglycemia (thiazolidinediones and metformin). To maintain these low HbA(1c) values and avoid the utilization of insulin secretagogues or insulin, which are associated with hypoglycemia and suboptimal dosing leading to higher HbA(1c) values, drugs that maintain or improve pancreatic beta-cell function (thiazolidinediones and possibly incretin-based therapies) should be utilized. Restoration of first-phase insulin release, as has been shown with thiazolidinediones, will not only improve postprandial hyperglycemia but will also improve postprandial hyperlipidemia, both of which will decrease cardiac risk. Utilizing small doses of two drugs will also result in a decreased incidence of adverse effects compared with a large dose of a single drug. The use of fixed-dose combination oral antihyperglycemics will not only improve compliance but will often decrease costs compared with individual component dual therapy.

Comparison of the effects on glycaemic control and β-cell function in newly diagnosed type 2 diabetes patients of treatment with exenatide, insulin or pioglitazone: a multicentre randomized parallel-group trial (the CONFIDENCE study)

OBJECTIVE

Progressive β-cell dysfunction hinders the maintenance of glycaemic control in type 2 diabetes, but comparative data on β-cell-protective therapies are lacking in the early stage of type 2 diabetes. Here we evaluated the comparative glycaemic efficacy and impact on β-cell function of three antihyperglycaemic agents that have a β-cell-protective effect, exenatide, insulin and pioglitazone, in newly diagnosed patients with type 2 diabetes.

DESIGN AND METHODS

In this 48-week, multicentre, parallel-group study, 416 patients newly diagnosed with type 2 diabetes were randomly assigned 1 : 1 : 1 to receive exenatide, insulin or pioglitazone. The primary end-point was the change in glycosylated haemoglobin (HbA1c) from baseline. Secondary end-points included effects on weight, blood pressure, lipid profiles and β-cell function assessed by homeostasis model assessment, fasting proinsulin:insulin (PI/I), disposition index (DI) and acute insulin response (AIR).

RESULTS

At week 48, mean [95% confidence interval (CI)] HbA1c changes from baseline were -1.8% (-1.55% to -2.05%) with exenatide, -1.7% (-1.52% to -1.96%) with insulin and -1.5% (-1.23% to -1.71%) with pioglitazone. Treatment differences were -0.20% (95% CI -0.46% to 0.06%) for exenatide versus insulin (P = 0.185), and -0.37% (95% CI -0.63% to -0.12%) for exenatide versus pioglitazone (P = 0.002). Significant improvements from baseline in AIR, PI/I and DI were observed with all treatments, with the greatest improvements in DI, as well as weight, blood pressure and lipid profile, observed with exenatide.

CONCLUSIONS

All three agents showed efficacy regarding glycaemic control and metabolic benefits; however, exenatide showed the greatest efficacy. β-cell function improved in all treatment groups; hence, early initiation of β-cell-protective therapy may halt the decline in β-cell function in type 2 diabetes.

Beta cell dysfunction and insulin resistance

Beta cell dysfunction and insulin resistance are inherently complex with their interrelation for triggering the pathogenesis of diabetes also somewhat undefined. Both pathogenic states induce hyperglycemia and therefore increase insulin demand. Beta cell dysfunction results from inadequate glucose sensing to stimulate insulin secretion therefore elevated glucose concentrations prevail. Persistently elevated glucose concentrations above the physiological range result in the manifestation of hyperglycemia. With systemic insulin resistance, insulin signaling within glucose recipient tissues is defective therefore hyperglycemia perseveres. Beta cell dysfunction supersedes insulin resistance in inducing diabetes. Both pathological states influence each other and presumably synergistically exacerbate diabetes. Preserving beta cell function and insulin signaling in beta cells and insulin signaling in the glucose recipient tissues will maintain glucose homeostasis.

Serum lipid peroxides and magnesium levels following three months of treatment with pioglitazone in patients with type-2 diabetes mellitus

BACKGROUND

Higher levels of lipid peroxidation and hypomagnesaemia are frequently associated with Type 2 Diabetes mellitus (T2DM). Addressing these issues would definitely help us in preventing or prolonging the onset of pathogenesis of micro and macrovascular complications. Pioglitazone is used as a trusted insulin sensitizer and an adjuvant to the conventional oral hypoglycemic agents. This study was planned to explore the effects of pioglitazone on oxidative stress, serum magnesium, blood pressure, hepato-biliary and renal systems in addition to its effects on glycemic control.

METHODS

Sixty-three T2DM cases, who were started on pioglitazone were included in this study. All the physiological and biochemical parameters were estimated prior to and following three months of therapy with pioglitazone.

RESULTS

There was significant improvement in the glycemic control, serum magnesium and MDA levels with p values of 0.000, 0.023 and 0.000 respectively. Pioglitazone did not have any significant effects on the serum lipids and blood pressure in T2DM cases following three months of treatment. We did not observe any pronounced changes in hepato-biliary enzymes, serum urea and creatinine levels reaffirming safety of pioglitazone in T2DM.

CONCLUSION

Three-month duration of treatment with Pioglitazone in T2DM cases helps in alleviating the levels of lipid peroxides, besides being associated with improved serum magnesium status and glycemic control.

Adiponectin increases insulin content and cell proliferation in MIN6 cells via PPARγ-dependent and PPARγ-independent mechanisms

AIMS

Adiponectin is an important adipokine whose levels are decreased in obesity despite increases in adipocyte mass. Studies in animal models implicate adiponectin as an insulin sensitizer in skeletal muscle and liver. Thiazolidinediones (TZDs) are insulin sensitizers and ligands for peroxisome proliferator-activated γ receptors (PPARγ) and these receptors are expressed in β cells where their activation promotes cell survival. We hypothesize that adiponectin promotes β cell survival by activating PPARγ.

METHODS

We used MIN6 cells to investigate the effect of adiponectin on PPARγ expression, β-cell proliferation, insulin synthesis and insulin secretion.

RESULTS

We demonstrate that MIN6 cells contain adiponectin receptors and that adiponectin activates PPARγ mRNA and protein expression. This increase in PPARγ expression is blocked by the PPARγ antagonist, GW9662, indicating a transcriptional feedback loop involving PPARγ activation of itself. Adiponectin causes a significant increase in insulin content and secretion and this occurs also via PPARγ activation due to the inhibitory effect of GW9662. Adiponectin also promotes MIN6 cell proliferation, however, this effect is independent of PPARγ activation.

CONCLUSIONS

Our results identify novel roles for the adipokine, adiponectin, in β-cells function. Adiponectin upregulates PPARγ expression, insulin content and insulin secretion through PPARγ-dependent mechanisms. Reductions in circulating adiponectin levels in obese individuals could therefore result in negative effects on β-cell function and this may have direct relevance to β-cell dysfunction in type 2 diabetes.

A VGF-derived peptide attenuates development of type 2 diabetes via enhancement of islet β-cell survival and function

Deterioration of functional islet β-cell mass is the final step in progression to Type 2 diabetes. We previously reported that overexpression of Nkx6.1 in rat islets has the dual effects of enhancing glucose-stimulated insulin secretion (GSIS) and increasing β-cell replication. Here we show that Nkx6.1 strongly upregulates the prohormone VGF in rat islets and that VGF is both necessary and sufficient for Nkx6.1-mediated enhancement of GSIS. Moreover, the VGF-derived peptide TLQP-21 potentiates GSIS in rat and human islets and improves glucose tolerance in vivo. Chronic injection of TLQP-21 in prediabetic ZDF rats preserves islet mass and slows diabetes onset. TLQP-21 prevents islet cell apoptosis by a pathway similar to that used by GLP-1, but independent of the GLP-1, GIP, or VIP receptors. Unlike GLP-1, TLQP-21 does not inhibit gastric emptying or increase heart rate. We conclude that TLQP-21 is a targeted agent for enhancing islet β-cell survival and function.

Preservation of beta-cell function in type 2 diabetes

OBJECTIVE

To review available data on preservation and potential improvement of beta-cell function in patients with type 2 diabetes mellitus (T2DM) with use of currently available strategies and agents.

METHODS

Using key words, we performed a MEDLINE search of the relevant literature published through 2009 regarding the effects of available agents on beta-cell function in humans with T2DM.

RESULTS

On the basis of current clinical data, no uniformly effective treatment for beta-cell preservation has been found. Lifestyle intervention and early intensive insulin therapy appear to have some preservative properties on beta-cell function. Glucagonlike peptide-1 agonists, dipeptidyl- peptidase-4 inhibitors, and thiazolidinediones result in maintenance and often improvement of beta-cell function during their active use; however, data on their ability to preserve beta-cell function when patients are not receiving active treatment are limited.

CONCLUSION

The continuous loss of beta-cell mass and beta-cell function is a critical mechanism underlying the progressive deterioration of glycemic control in T2DM. In light of the projected increase in individuals at risk for developing T2DM, strategies and agents aimed at delaying or preventing the progression and inducing a remission of the disease are needed. Future research on this topic should include comparative efficacy trials with washout periods incorporating currently available and novel medications and strategies for preservation of beta cells.

Serine-385 phosphorylation of inwardly rectifying K+ channel subunit (Kir6.2) by AMP-dependent protein kinase plays a key role in rosiglitazone-induced closure of the K(ATP) channel and insulin secretion in rats

AIMS/HYPOTHESIS

Rosiglitazone, an insulin sensitiser, not only improves insulin sensitivity but also enhances insulin secretory capacity by ameliorating gluco- and lipotoxicity in beta cells. Rosiglitazone can stimulate insulin secretion at basal and high glucose levels via a phosphatidylinositol 3-kinase (PI3K)-dependent pathway. We hypothesised that regulation of phosphorylation of the ATP-sensitive potassium (K(ATP)) channel might serve as a key step in the regulation of insulin secretion.

METHODS

Insulin secretory responses were studied in an isolated pancreas perfusion system, cultured rat islets and MIN6 and RINm5F beta cells. Signal transduction pathways downstream of PI3K were explored to link rosiglitazone to K(ATP) channel conductance with patch clamp techniques and insulin secretion measured by ELISA.

RESULTS

Rosiglitazone stimulated AMP-activated protein kinase (AMPK) activity and induced inhibition of the K(ATP) channel conductance in islet beta cells; both effects were blocked by the PI3K inhibitor LY294002. Following stimulation of AMPK by 5-aminoimidazole-4-carboxamide ribonucleoside (AICAR), a pharmacological activator, both AICAR-stimulated insulin secretion and inhibition of K(ATP) channel conductance were unaffected by LY294002, indicating that AMPK activation occurs at a site downstream of PI3K activity. The serine residue at amino acid position 385 of Kir6.2 was found to be the substrate phosphorylation site of AMPK when activated by rosiglitazone or AICAR.

CONCLUSIONS/INTERPRETATION

Our data indicate that PI3K-dependent activation of AMPK is required for rosiglitazone-stimulated insulin secretion in pancreatic beta cells. Phosphorylation of the Ser(385) residue of the Kir6.2 subunit of the K(ATP) channel by AMPK may play a role in insulin secretion.

Effect of chronic rosiglitazone, metformin and glyburide treatment on beta-cell mass, function and insulin sensitivity in mZDF rats

Here we investigate the effect of rosiglitazone (RSG), metformin (MET) and glyburide (GLIB) on plasma glucose levels, beta-cell mass, function and insulin sensitivity in 10-week-old diabetic male Zucker diabetic fatty (mZDF) rats using quantitative morphometry and a mathematical model beta-cell mass, insulin and glucose kinetics (betaIG). At treatment start, 10-week-old diabetic mZDF rats were severely hyperglycaemic and had very low beta-cell function (insulin secretory capacity). RSG treatment significantly lowered plasma glucose levels in 67% of the mZDF rats. MET was effective at lowering plasma glucose levels in 33% of the mZDF rats, while GLIB was completely ineffective at lowering blood glucose levels in 10-week-old mZDF rats. RSG treatment prevented the fall in beta-cell mass after 6-8 weeks of treatment accompanied by a significant decrease in beta-cell death while MET treatment had no effect on beta-cell mass. RSG treatment increased insulin sensitivity 10-fold, increased beta-cell function fivefold and modestly increased beta-cell mass 1.4-fold. MET treatment increased insulin sensitivity fourfold, with no significant effect on beta-cell function or mass. Although RSG treatment was highly successful in lowering plasma glucose levels, the 33% of mZDF rats that did not respond to the treatment had significantly lower beta-cell function prior to treatment start compared with the responder group. Thus, the low level of beta-cell function at treatment start may explain why none of these agents were completely effective at lowering blood glucose levels in 10-week-old diabetic mZDF rats. Nevertheless, these data suggest that the preservation of beta-cell mass and improvement in beta-cell function play a role in the overall beneficial effect of RSG in 10-week-old diabetic mZDF rats.

Potential benefits of early addition of rosiglitazone in combination with glimepiride in the treatment of type 2 diabetes

AIM

To assess the efficacy and tolerability of early combination therapy with rosiglitazone (RSG) and glimepiride (GLIM) vs. GLIM monotherapy in patients with type 2 diabetes mellitus (T2DM).

METHODS

Strategies for the addition of RSG in combination with GLIM were evaluated with data from two randomized, double-blind, placebo (PBO)-controlled studies. Study A - addition of RSG (4 or 8 mg) or PBO to continued GLIM 3 mg once daily; study B - addition of low-dose RSG (4 mg) prior to uptitration of GLIM (from 2 to 4 mg) vs. continued uptitration of GLIM (from 2 to 8 mg).

RESULTS

Study A reported significant reductions in fasting plasma glucose (FPG) from baseline to week 26 with the addition of both 4 and 8 mg RSG to GLIM 3 mg [-21 mg/dl (-1.2 mmol/l), p = 0.0019 and -43 mg/dl (-2.4 mmol/l), p < 0.0001, respectively] and in haemoglobin A(1c) (HbA(1c)) (-0.63%, p = 0.00015 and -1.17%, p < 0.0001, respectively) from a baseline of 8.2 and 8.1%, respectively. At the end of the study, target HbA(1c) <7.0% was achieved in 43 and 68% of patients in the RSG 4 mg + GLIM and RSG 8 mg + GLIM groups, respectively, compared with 32% in the PBO + GLIM (GLIM alone) group. In study B, addition of RSG to GLIM reduced mean FPG and HbA(1c) levels at week 24 from baseline [-28 mg/dl (-1.5 mmol/l), p < 0.0001, and -0.68%, p < 0.0001, respectively]. There were no significant changes with GLIM monotherapy in either study. Favourable effects of RSG + GLIM on insulin sensitivity, beta-cell function and cardiovascular disease biomarkers were also observed. All treatments were similarly well tolerated.

CONCLUSIONS

Early addition of RSG to GLIM is an effective and well-tolerated treatment option to improve glycaemic control in sulphonylurea-treated patients with T2DM.

Thiazolidinediones and the preservation of beta-cell function, cellular proliferation and apoptosis

The thiazolidinediones (TZDs) or glitazones are pharmaceutical agents that have profound effects on energy expenditure and conservation. They also exert significant anti-inflammatory effects and influence cell proliferation and cell death. The drugs are primarily used in clinical practice in the treatment of patients with type 2 diabetes mellitus, a disorder of insulin resistance that occurs when the pancreatic beta-cells are unable to produce adequate amounts of insulin to maintain euglycaemia. Loss of pancreatic beta-cell function in type 2 diabetes is progressive and often precedes overt diabetes by 10 years or more, as was shown by the United Kingdom Prospective Diabetes Study. Any therapeutic or preventive approach that would limit or reverse loss of beta-cell function in diabetes would have profound effects on the morbidity associated with this widespread disease. Evidence suggesting a potential role of TZDs in preserving beta-cell function in type 2 diabetes as well as the ability of these agents to exert anti-inflammatory and proapoptotic anticancer effects, and their ability to promote cellular proliferation in various organs is reviewed.

Reduced postprandial proinsulinaemia and 32-33 split proinsulinaemia after a mixed meal in type 2 diabetic patients following sensitization to insulin with pioglitazone

OBJECTIVE

Reduced insulin sensitivity associated with fasting hyperproinsulinaemia is common in type 2 diabetes. Proinsulinaemia is an established independent cardiovascular risk factor. The objective was to investigate fasting and postprandial release of insulin, proinsulin (PI) and 32-33 split proinsulin (SPI) before and after sensitization to insulin with pioglitazone compared to a group treated with glibenclamide.

DESIGN AND PATIENTS

A randomized double-blind placebo-controlled trial. Twenty-two type 2 diabetic patients were recruited along with 10 normal subjects. After 4 weeks washout, patients received a mixed meal and were assigned to receive pioglitazone or glibenclamide for 20 weeks, after which patients received another identical test meal. The treatment regimes were designed to maintain glycaemic control (HbA1c) at pretreatment levels so that beta-cells received an equivalent glycaemic stimulus for both test meals.

MEASUREMENTS

Plasma insulin, PI, SPI and glucose concentrations were measured over an 8-h postprandial period. The output of PI and SPI was measured as the integrated postprandial response (area under the curve, AUC).

RESULTS

Pioglitazone treatment resulted in a significant reduction in fasting levels of PI and SPI compared to those of the controls. Postprandially, pioglitazone treatment had no effect on the insulin AUC response to the meal but significantly reduced the PI and SPI AUCs. Glibenclamide increased fasting insulin and the postprandial insulin AUC but had no effect on the PI and SPI AUCs.

CONCLUSIONS

Sensitization to insulin with pioglitazone reduces the amount of insulin precursor species present in fasting and postprandially and may reduce cardiovascular risk.

Clinical presentation and treatment of type 2 diabetes in children

Type 2 diabetes mellitus (T2DM) has dramatically increased throughout the world in many ethnic groups and among people with diverse social and economic backgrounds. This increase has also affected the young such that over the past decade, the increase in the number of children and youth with T2DM has been labeled an 'epidemic'. Before the 1990s, it was rare for most pediatric centers to have significant numbers of patients with T2DM. However, by 1994, T2DM patients represented up to 16% of new cases of diabetes in children in urban areas and by 1999, depending on geographic location, the range of percentage of new cases because of T2DM was 8-45% and disproportionately represented among minority populations. Although the diagnosis was initially regarded with skepticism, T2DM is now a serious diagnostic consideration in all young people who present with signs and symptoms of diabetes in the USA.

beta-cell function and anti-diabetic pharmacotherapy

Type 2 diabetes is a chronic disease characterized by progressive worsening of glycaemic control as indicated by the United Kingdom Prospective Diabetes Study (UKPDS). The progressive nature of the disease is mainly due to continuous loss of beta-cell mass and function. Though much of this loss is due to intrinsic defects of the beta-cell several factors may accelerate such process. These include the metabolic environment where hyperglycaemia and increased circulating free-fatty acid exert a toxic effect on the beta-cell. Therefore, tight metabolic control may prevent not only the risk of long-term diabetic complication but also preserve beta-cell function. Several therapeutic agents are currently used for treatment of type 2 diabetic patients. However, their effect on maintenance of beta-cell function has not been yet systematically reviewed. By literature searching we have then analysed in detail the effect of sulfonylureas and non-sulfonylureic secretagogues, incretin-mimetics, insulin sensitizers, alpha-glucosidase inhibitors, and insulin on beta-cell function. Moreover, promising future approaches aiming at preserving beta-cell function and mass are discussed.

Comparison of the alteration of the concentration of C-peptide in 24-h urine according to the combination patterns of hypoglycemic agents in type 2 diabetes patients

AIMS

Urinary C-peptide (UCP) has been considered as a simple method for monitoring beta-cell function in diabetic patients clinically. The aim of the study is to compare the changes of 24-h urinary C-peptide levels according to subgroups divided by therapeutic agents for subjects with type 2 diabetes.

METHODS

In 206 participants, under treatment for type 2 diabetes, 24-h urinary C-peptide levels were assessed yearly for 3 years. All participants were subdivided into four groups according to the therapeutic agents. Changes for the measured values during the follow-up were compared between groups.

RESULTS

Mean HbA1C was 7.1% and mean 24-h UCP was 61.7 microg/24h and mean duration of diabetes was 8.7 years in all subjects at baseline. Mean 24-h UCP levels increased significantly from a baseline to at 36 months in the insulin sensitizers (IS) only group, in the IS plus sulfonylurea combination group and in IS plus insulin combination group (p<0.001), whereas in the sulfonylurea only group, we could not find statistically significant changes (p=0.152). Treatment with only IS significantly reduced fasting plasma glucose (FPG) and HbA1C level (p=0.045, p<0.001). Differences between baseline and last 24-h UCP were significantly different between-groups and this difference was more significant after adjustment in FPG, HbA1C, and the duration of diabetes (p=0.024). Especially, IS plus sulfonylurea combination group resulted in greatest increase of 24-h UCP (DeltaC-peptide=51.19 microg/24h).

CONCLUSIONS

This study suggested that IS, in mono- or in combination, significantly improved pancreatic beta-cell function, especially when combined with sulfonylurea as evidenced by the increase of 24-h UCP.

Differential effects of rosiglitazone and insulin glargine on inflammatory markers, glycemic control, and lipids in type 2 diabetes

Type 2 diabetes remains a difficult clinical challenge characterized by progressive insulin deficiency and frequent cardiovascular events requiring multiple therapeutic decisions. In this randomized clinical trial, we assessed the comparative effects of rosiglitazone (RSG) and insulin glargine (IG) on inflammatory biomarkers, glycemic control, and lipids. Forty subjects with type 2 diabetes and inadequate glycemic control on sulfonylurea and metformin therapy received 24 weeks of add-on therapy with either RSG 4mg daily or IG 10 units daily. Subjects on RSG with fasting glucose values >120mg/dl at 12 weeks were increased from 4 to 8mg. Subjects on IG increased insulin doses until fasting glucose was <120mg/dl. Markers of glycemic control and inflammation including HbA1c, hsCRP, PAI-1, plasma F2-isoprostanes, and lipids were measured at baseline, 12, 18, and 24 weeks. RSG and IG demonstrated similar efficacy in reducing HbA1c levels by 1.5 and 1.4%, respectively, with greater weight gain with RSG. Hypoglycemic events occurred with equal frequency. IG did not reduce hsCRP, but RSG reduced hsCRP levels 45% from baseline. Both IG and RSG reduced F2-isoprostanes similarly. IG did not affect PAI-1 levels, but did reduce total, LDL, and non-HDL cholesterol levels. Despite similar HbA1c reductions with RSG and IG, differential effects were found on inflammatory biomarkers and lipids that deserve consideration in the clinical decision process of selecting a therapeutic agent.

Ketosis-prone type 2 diabetes: effect of hyperglycemia on beta-cell function and skeletal muscle insulin signaling

OBJECTIVE

To determine the underlying mechanism for the severe and transient beta-cell dysfunction and impaired insulin action in obese African American patients with ketosis-prone diabetes.

METHODS

The effect of sustained hyperglycemia (glucotoxicity) and increased free fatty acids (lipotoxicity) on beta-cell function was assessed by changes in insulin secretion during a 20-hour glucose (200 mg/m2 per minute) and a 48-hour Intralipid (40 mL/h) infusion, respectively. Insulin-activated signaling pathways and pattern of Akt-1 and Akt-2 expression and insulin-stimulated phosphorylation were analyzed in skeletal muscle biopsy specimens. Studies were performed in an obese African American woman within 48 hours after resolution of diabetic ketoacidosis and 1 week after discontinuation of insulin treatment.

RESULTS

Dextrose infusion rapidly increased C-peptide levels from a baseline of 3.2 ng/mL to a mean of 7.1 +/- 0.5 ng/mL during the first 8 hours of infusion; thereafter, C-peptide levels progressively declined. Lipid infusion was not associated with any deleterious effect on insulin and C-peptide secretion. Initial in vitro stimulation of muscle tissue with insulin resulted in a substantial and selectively decreased Akt-2 expression and insulin-stimulated phosphorylation on the serine residue. Improved metabolic control resulted in 70% greater Akt expression at near-normoglycemic remission in comparison with the period of hyperglycemia.

CONCLUSION

Hyperglycemia, but not increased free fatty acid levels, led to progressive beta-cell dysfunction and impaired insulin secretion. Hyperglycemia was also associated with diminished skeletal muscle Akt expression and phosphorylation in an African American woman with ketosis-prone diabetes, and this defect improved notably with aggressive insulin therapy. These results indicate the importance of glucose toxicity in the pathogenesis of ketosis-prone diabetes in obese African American patients.

Metformin/rosiglitazone combination pill (Avandamet) for the treatment of patients with Type 2 diabetes

More than 150 million people worldwide have diabetes, the prevalence of which is increasing so rapidly that the number of adults with diabetes in the world will rise to 300 million by the year 2025. In the US, approximately 21 million people have diabetes and in some areas of the country, the prevalence is as high as 50%. The pathophysiologic hallmarks consist of insulin resistance and progressive pancreatic beta-cell dysfunction. An increased metabolic demand for insulin due to increased insulin resistance usually precedes the development of hyperglycemia. At early stages, pancreatic beta cells compensate for insulin resistance by hypersecretion of insulin. However, the period of beta-cell compensation is followed by beta-cell failure, in which the pancreas fails to secrete sufficient insulin and diabetes ensues. Biguanides and thiazolidinediones (TZDs) are two unique classes of oral antidiabetic agents that are the most commonly used medications to improve insulin sensitivity. They have no direct effect on beta-cell function, although some indirect mechanisms of actions may help to preserve beta-cell function or slow beta-cell apoptosis. Their glucose-lowering effect results from improving insulin sensitivity in a complementary fashion: metformin reduces hepatic glucose production and TZDs increase skeletal muscle glucose use. The combination of metformin and rosiglitazone in a single pill (Avandamet), was approved by the FDA in October 2002 for the treatment of diabetes. As insulin resistance is a pathophysiologic cornerstone of diabetes and cardiovascular disease, the use of Avandamet represents an optimal approach to the treatment of diabetes. This manuscript reviews the pharmacology, safety and benefits of the combination pill Avandamet.

beta-cell failure in diabetes and preservation by clinical treatment

There is a progressive deterioration in beta-cell function and mass in type 2 diabetics. It was found that islet function was about 50% of normal at the time of diagnosis, and a reduction in beta-cell mass of about 60% was shown at necropsy. The reduction of beta-cell mass is attributable to accelerated apoptosis. The major factors for progressive loss of beta-cell function and mass are glucotoxicity, lipotoxicity, proinflammatory cytokines, leptin, and islet cell amyloid. Impaired beta-cell function and possibly beta-cell mass appear to be reversible, particularly at early stages of the disease where the limiting threshold for reversibility of decreased beta-cell mass has probably not been passed. Among the interventions to preserve or "rejuvenate" beta-cells, short-term intensive insulin therapy of newly diagnosed type 2 diabetes will improve beta-cell function, usually leading to a temporary remission time. Another intervention is the induction of beta-cell "rest" by selective activation of ATP-sensitive K+ (K(ATP)) channels, using drugs such as diazoxide. A third type of intervention is the use of antiapoptotic drugs, such as the thiazolidinediones (TZDs), and incretin mimetics and enhancers, which have demonstrated significant clinical evidence of effects on human beta-cell function. The TZDs improve insulin secretory capacity, decrease beta-cell apoptosis, and reduce islet cell amyloid with maintenance of neogenesis. The TZDs have indirect effects on beta-cells by being insulin sensitizers. The direct effects are via peroxisome proliferator-activated receptor gamma activation in pancreatic islets, with TZDs consistently improving basal beta-cell function. These beneficial effects are sustained in some individuals with time. There are several trials on prevention of diabetes with TZDs. Incretin hormones, which are released from the gastrointestinal tract in response to nutrient ingestion to enhance glucose-dependent insulin secretion from the pancreas, aid the overall maintenance of glucose homeostasis through slowing of gastric emptying, inhibition of glucagon secretion, and control of body weight. From the two major incretins, glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP), only the first one or its mimetics or enhancers can be used for treatment because the diabetic beta-cell is resistant to GIP action. Because of the rapid inactivation of GLP-1 by dipeptidyl peptidase (DPP)-IV, several incretin analogs were developed: GLP-1 receptor agonists (incretin mimetics) exenatide (synthetic exendin-4) and liraglutide, by conjugation of GLP-1 to circulating albumin. The acute effect of GLP-1 and GLP-1 receptor agonists on beta-cells is stimulation of glucose-dependent insulin release, followed by enhancement of insulin biosynthesis and stimulation of insulin gene transcription. The chronic action is stimulating beta-cell proliferation, induction of islet neogenesis, and inhibition of beta-cell apoptosis, thus promoting expansion of beta-cell mass, as observed in rodent diabetes and in cultured beta-cells. Exenatide and liraglutide enhanced postprandial beta-cell function. The inhibition of the activity of the DPP-IV enzyme enhances endogenous GLP-1 action in vivo, mediated not only by GLP-1 but also by other mediators. In preclinical studies, oral active DPP-IV inhibitors (sitagliptin and vildagliptin) also promoted beta-cell proliferation, neogenesis, and inhibition of apoptosis in rodents. Meal tolerance tests showed improvement in postprandial beta-cell function. Obviously, it is difficult to estimate the protective effects of incretin mimetics and enhancers on beta-cells in humans, and there is no clinical evidence that these drugs really have protective effects on beta-cells.

Effects of rosiglitazone and metformin on inflammatory markers and adipokines: decrease in interleukin-18 is an independent factor for the improvement of homeostasis model assessment-beta in type 2 diabetes mellitus

OBJECTIVE

We examined the individual pharmacological effects of the addition of rosiglitazone and metformin to glimepiride on inflammatory markers and adipokines in patients with type 2 diabetes mellitus. We analysed the relationships between these variables, the measurements of insulin sensitivity and beta-cell function in patients treated with rosiglitazone plus glimepiride.

DESIGN AND PATIENTS

One hundred twenty (120) patients with type 2 diabetes mellitus were randomized and treated with glimepiride plus rosiglitazone or glimepiride plus metformin for 12 weeks. The plasma concentrations of the inflammatory markers and adipokines were measured at baseline and after 12 weeks.

MEASUREMENTS

Markers of insulin sensitivity and beta-cell function were determined by the quantitative insulin sensitivity check index (QUICKI) and the homeostasis model assessment of beta-cell function (HOMA-beta), respectively. Plasma concentrations of adiponectin were measured by radioimmunoassay. Plasma concentrations of resistin, tumour necrosis factor-alpha (TNF-alpha), interleukin-6 (IL-6) and interleukin-18 (IL-18) were measured using ELISA.

RESULTS

Improvements in fasting insulin level, QUICKI and HOMA-beta were noted in the rosiglitazone-treated group. Only the QUICKI value improved in the metformin-treated group. Adiponectin concentrations significantly increased in the rosiglitazone-treated group after 12 weeks. Significant decreases in resistin, C-reactive protein, TNF-alpha, IL-6 and IL-18 were seen in the rosiglitazone-treated patients but not in the metformin-treated patients. The independent risk factor for the HOMA-beta change according to stepwise multivariate regression analysis was a change in IL-18.

CONCLUSIONS

Rosiglitazone, but not metformin, improved the plasma concentrations of inflammatory markers and adipokines in patients with type 2 diabetes mellitus. A decrease in IL-18 is an independent factor for the improvement of HOMA-beta in type 2 diabetes mellitus.

Thiazolidinediones for the treatment of type 2 diabetes

Thiazolidinediones (TZD), or glitazones, represent a new generation of antidiabetic drugs that have recently been introduced in Europe. They improve insulin resistance, one of the key anomalies involved in the pathogenesis of type 2 diabetes mellitus, by activating the nuclear peroxoxisome proliferator activated receptor-gamma (PPAR-gamma), leading to crucial metabolic alterations in adipose tissue. Rosiglitazone and pioglitazone have been shown to be active as monotherapy, in combination therapy with metformin or sulfonylureas, and even in triple therapy. They are generally well tolerated but can induce fluid retention. Cardiac failure is a contraindication for the use of TZDs, as is the concomitant administration of insulin. Aside from their effect on glycemic control, TZDs act on several cardiovascular risk factors and may protect pancreatic beta cells from apoptosis. The cardiovascular protective effect of TZDs has recently been demonstrated with the results of the PROactive study, and long-term preservation of beta-cell function is currently under further investigation.

The metabolic syndrome: evolving evidence that thiazolidinediones provide rational therapy

The metabolic syndrome, also known as the dysmetabolic syndrome, syndrome X or the insulin resistance syndrome, refers to the clustering of cardiovascular disease risk factors that are present in many individuals who are at increased risk for both cardiovascular events and type 2 diabetes. Prediabetic subjects typically exhibit an atherogenic pattern of cardiovascular risks that is associated with hyperinsulinaemia. Thus, identification of components of the metabolic syndrome is important if patients are to be treated early enough to prevent cardiovascular events and other complications related to diabetes. Therapies targeted to specific components of the metabolic syndrome such as improving glycaemic control, managing dyslipidaemia and reducing the prothrombotic state should help to minimize cardiovascular risk, particularly if initiated early. Traditional pharmacologic agents used to manage the individual components of the metabolic syndrome do not typically impact the other components. The thiazolidinediones, a new class of agents that improve insulin resistance, have the ability, in addition to their glucose-lowering effects, to exert several powerful anti-atherogenic properties, including anti-inflammatory effects in the vascular endothelium, redistribution of visceral fat and reduction of insulin resistance, hyperinsulinaemia and hyperproinsulinaemia. This makes the thiazolidinediones ideal candidates for the early treatment of many components associated with the metabolic syndrome.

Closing the gap between clinical research and clinical practice: can outcome studies with thiazolidinediones improve our understanding of type 2 diabetes?

Recent clinical research has provided a wealth of information to support optimal management strategies in type 2 diabetes mellitus (T2DM). In particular, outcome studies appropriately have had an increasingly important impact on clinical decision-making. Additional, new data are required, however, to close the current gaps in clinical knowledge and improve patient outcomes in T2DM. These outcome studies are particularly important in assessing the long-term benefit of newer agents for which data are available for short-term glycaemic control, effects on lipids and some data on non-traditional cardiovascular risk markers, but outcome data for harder end points relevant to the natural history of T2DM, particularly beta-cell function, are lacking. Outcome studies such as ADOPT and DREAM are investigating the impact of thiazolidinediones (TZDs) on beta-cell function and disease progression in T2DM and impaired glucose tolerance, respectively, the results of which are eagerly anticipated. The primary focus of this article is on TZD outcome studies evaluating beta-cell function and disease progression.

Therapeutic approaches to preserve islet mass in type 2 diabetes

Type 2 diabetes is characterized by hyperglycemia resulting from insulin resistance in the setting of inadequate beta-cell compensation. Currently available therapeutic agents lower blood glucose through multiple mechanisms but do not directly reverse the decline in beta-cell mass. Glucagon-like peptide-1 (GLP-1) receptor agonists, exemplified by Exenatide (exendin-4), not only acutely lower blood glucose but also engage signaling pathways in the islet beta-cell that lead to stimulation of beta-cell replication and inhibition of beta-cell apoptosis. Similarly, glucose-dependent insulinotropic polypeptide (GIP) receptor activation stimulates insulin secretion, enhances beta-cell proliferation, and reduces apoptosis. Moreover, potentiation of the endogenous postprandial levels of GLP-1 and GIP via inhibition of dipeptidyl peptidase-IV (DPP-IV) also expands beta-cell mass via related mechanisms. The thiazolidinediones (TZDs) enhance insulin sensitivity, reduce blood glucose levels, and also preserve beta-cell mass, although it remains unclear whether TZDs affect beta-cell mass via direct mechanisms. Complementary approaches to regeneration of beta-cell mass involve combinations of factors, exemplified by epidermal growth factor and gastrin, which promote islet neogenesis and ameliorate diabetes in rodent studies. Considerable preclinical data support the concept that one or more of these therapeutic approaches, alone or in combination, may potentially reverse the decline in beta-cell mass that is characteristic of the natural history of type 2 diabetes.

Thiazolidinediones for the Therapeutic Management of Polycystic Ovary Syndrome

Polycystic ovary syndrome (PCOS) is a diagnosis made between late adolescence and the menopause in 5-10% of women. PCOS is a heterogeneous disorder of unknown etiology characterized by hyperandrogenic chronic anovulation. This syndrome consists of a diverse constellation of signs and symptoms, such as hirsutism, acne, acanthosis nigricans, obesity, menstrual irregularities, anovulation, and/or infertility. Features of the metabolic syndrome, including obesity, insulin resistance, and dyslipidemia, are common in this patient population. Recent insights into the pathophysiology of PCOS have shown insulin resistance and hyperinsulinemia to play a substantial role. Insulin resistance is increasingly recognized as a chronic, low-level, inflammatory state. Recent studies show that serum levels of inflammatory mediators, such as tumor necrosis factor-alpha and interleukin-6, are increased in the insulin-resistant conditions of obesity and PCOS. The optimal modality for long-term treatment should have positive effects on androgen synthesis, sex hormone-binding globulin production, the lipid profile, insulin sensitivity, inflammatory mediators, and clinical symptoms including acne, hirsutism, and irregular menstrual cycles. Treatment with insulin-sensitizing agents is a relatively new therapeutic strategy in women with PCOS. Current research has shown that the use of diabetes mellitus management practices aimed at reducing insulin resistance and hyperinsulinemia (such as weight reduction and the administration of oral antidiabetic drugs) can not only reverse testosterone and luteinizing hormone abnormalities and restore menstrual cycles, but can also improve glucose, insulin, proinflammatory cytokine, and lipid profiles.Clinical treatment with troglitazone, a member of the thiazolidinedione family, for the management of PCOS complications such as insulin resistance, hyperandrogenism, and anovulation was found to have beneficial effects; however, it was taken off the market over concerns of hepatotoxicity. Although troglitazone is no longer available in the US, numerous clinical trials have established the role of thiazolidinediones in the treatment of women with PCOS. Clinical data emerging regarding the utility of two of the newer, safer thiazolidinediones, pioglitazone and rosiglitazone, for this patient population, consistently demonstrate effective improvements of endocrine and ovulatory performance in women with PCOS. The benefit and importance of lifestyle modification and weight reduction, when it can be achieved, is still an important component in the long-term treatment of PCOS. Pharmacologic reduction in insulin levels using thiazolidinediones appears to offer another therapeutic modality for PCOS, which may ameliorate the progress of both hyperinsulinemia and hyperandrogenism. However, additional studies of patients so treated are necessary before these agents can be considered first-line treatment for PCOS. Convincing data from randomized controlled trials with sufficient power to detect both the benefits and risks of long-term treatment with thiazolidinediones in women with PCOS remain to be obtained.

Long-term glycaemic efficacy and weight changes associated with thiazolidinediones when added at an advanced stage of type 2 diabetes

OBJECTIVE

To describe the outcome of 35 patients with type 2 diabetes prospectively followed for 6 years after the addition of a thiazolidinedione (TZD) to a failing regimen of a sulphonylurea and metformin -- triple oral therapy.

METHODS

Study patients were assessed for the need for the addition of insulin to their regimen, and follow-up clinical and laboratory findings were analysed.

RESULTS

At a mean follow-up of 72 +/- 1.5 months (range 53-80), 18 (51%) of patients remained well controlled on triple oral therapy with a mean glycosylated haemoglobin (HbA1c) value of 6.9 +/- 0.2% (upper limit of normal 6.2%). In 17 other patients, triple oral therapy failed and the use of insulin was necessary after a mean duration of 38 (range 18-68) months. The mean HbA1c in these patients was 8.0 +/- 0.3%. The group that was maintained on triple oral therapy gained 15.2 +/- 1.9 lbs over the 6-year study which was significantly higher than the baseline weight. Alternatively, the group that failed and had insulin added to their therapy gained 20.2 +/- 4.5 lbs over the same period which was also significantly different from baseline but not from the triple oral therapy group. Although after 3 years a trend towards weight loss occurred in the triple oral therapy group, the insulin-added group continued to gain weight. Stimulated C-peptide levels increased significantly in the triple therapy group from 3.6 +/- 0.9 to 4.3 +/- 1.2 ng/ml and had not increased or decreased non-significantly from 3.7 +/- 0.8 to 3.2 +/- 0.6 ng/ml at the time of insulin initiation in the insulin-requiring group.

CONCLUSION

When used late in the course of type 2 diabetes, TZDs result in improved and prolonged glycaemic control which persisted for a median time of 6 years. Weight gain with TZDs peaks and then plateaus (and even trends downwards) at 3 years, although the addition of insulin to a failing oral therapy regimen results in a further and continuing weight gain in spite of inferior glycaemic control. Continuing glycaemic control with triple oral therapy is dependent on preservation or augmentation of endogenous insulin production.

Factors associated with insulin discontinuation in subjects with ketosis-prone diabetes but preserved beta-cell function

AIM

To evaluate factors predictive of insulin discontinuation in subjects with ketosis-prone Type 2 diabetes.

METHODS

One hundred and six subjects with ketosis-prone Type 2 diabetes were recruited during the index episode of diabetic ketoacidosis (DKA). All subjects were followed in a special clinic for at least 6 months. If the subject's glycaemic control reached specified glycaemic goals, exogenous insulin was gradually decreased until discontinuation. Baseline and follow-up characteristics were compared between the off-insulin and the on-insulin groups.

RESULTS

At the end of the follow-up period (915+/-375 days) insulin was discontinued in 47% subjects. Subjects in the off-insulin group were significantly older at the time of diagnosis of diabetes. In the off-insulin group the majority of subjects were newly diagnosed with diabetes. After 6 months of follow-up, subjects in the off-insulin group had significantly lower mean HbA(1c), higher mean C-peptide-to-glucose ratio and had more clinic visits per year. In the proportional hazard analysis, new-onset diabetes [hazard ratio (HR) 1.54; 95% confidence interval (CI) 1.02-2.45], and a higher C-peptide-to-glucose ratio at 6 months of follow-up (HR 1.77; 95% CI 1.22-2.63) were significant predictors of insulin discontinuation.

CONCLUSIONS

In subjects with ketosis-prone Type 2 diabetes, the best predictors of insulin discontinuation are having new-onset diabetes, and higher beta-cell functional reserve (as measured by the C-peptide-to-glucose ratio).

Presence of the metabolic syndrome distinguishes patients with ketosis-prone diabetes who have a Type 2 diabetic phenotype

OBJECTIVE

This study was designed to determine if patients with ketosis-prone diabetes could be distinguished clinically on the basis of features of the metabolic syndrome (MetS).

METHODS

Participants with ketosis-prone diabetes admitted to our institution during a 3-year period were studied. One hundred seventy-two patients from four ethnic backgrounds were divided into two groups: with or without MetS, as defined by the World Health Organization. Pearson's chi-square test or one-way ANOVA was used as appropriate to evaluate group differences.

RESULTS

Of the 172 patients, 74 (43%) had at least three characteristics of MetS (+MetS group), while 98 (57%) had less than three characteristics of MetS (-MetS group). The +MetS group had significantly higher beta-cell functional reserve as measured by the glucagon stimulation test [area under the curve (AUC) for C-peptide levels 19.50+/-2.26 compared with 8.66+/-1.66 ng/ml over 10 min; P=.0001]. A significantly higher proportion of patients in the +MetS group had preserved beta-cell functional reserve than in the -MetS group (70% compared with 30%; P<.00001). After 12 months of follow-up, +MetS patients had significantly lower HbA1c levels (8.3+/-0.4% compared with 9.8+/-0.4%; P=.01) and higher C-peptide/glucose ratios (2.01+/-0.28 compared with 1.14+/-0.21; P=.02) than the -MetS patients did.

CONCLUSIONS

Patients with ketosis-prone diabetes with the MetS are more likely to have features associated with Type 2 diabetes, despite having developed diabetic ketoacidosis (DKA), with better beta-cell functional reserve and glycemic control after the index DKA episode.

Beta-cell preservation: a potential role for thiazolidinediones to improve clinical care in Type 2 diabetes

Type 2 diabetes is caused by progressively increasing insulin resistance coupled with deteriorating beta-cell function, and there is a growing body of evidence to suggest that both of these defects precede hyperglycaemia by many years. Several studies have demonstrated the importance of maintaining beta-cell function in patients with Type 2 diabetes. This review explores parameters used to indicate beta-cell dysfunction, in Type 2 diabetes and in individuals with a predisposition to the disease. A genetic element undoubtedly underlies beta-cell dysfunction; however, a number of modifiable components are also associated with beta-cell deterioration, such as chronic hyperglycaemia and elevated free fatty acids. There is also evidence for a link between pro-inflammatory cytokines and impairment of insulin-signalling pathways in the beta-cell, and the potential role of islet amyloid deposition in beta-cell deterioration continues to be a subject for debate. The thiazolidinediones are a class of agents that have demonstrated clinical improvements in indices of beta-cell dysfunction and have the potential to improve beta-cell function. Data are accumulating to show that this therapeutic group offers a number of advantages over traditionally employed oral agents, and these data demonstrate the growing importance of thiazolidinediones in Type 2 diabetes management.

Long-term therapy with addition of pioglitazone to metformin compared with the addition of gliclazide to metformin in patients with type 2 diabetes: a randomized, comparative study

BACKGROUND

This 52-week, randomized, double-blind study compared the efficacy and safety of metformin plus pioglitazone with the established combination of metformin plus gliclazide in type 2 diabetes mellitus.

METHODS

Patients with poorly controlled type 2 diabetes (HbA1c > or = 7.5% to < or =11.0%) received either pioglitazone 15 mg o.d. (titrated up to 45 mg; n = 317) or gliclazide 80 mg o.d. (titrated up to 320 mg; n = 313) and metformin at the pre-study dose. HbA1c, fasting plasma glucose (FPG), insulin, lipids and the urinary albumin/creatinine ratio were measured.

RESULTS

There were no significant differences in HbA1c (1% decrease in both groups) and FPG between groups. There was a decrease in fasting insulin in the pioglitazone group compared to an increase in the gliclazide group (p < 0.001). There were significantly greater improvements in triglycerides and HDL-cholesterol in the metformin plus pioglitazone group compared to the metformin plus gliclazide group (p < 0.001). Mean LDL-cholesterol decreased with metformin plus gliclazide and increased with metformin plus pioglitazone (p < 0.001); however, this increase was considerably less marked than that in HDL-cholesterol. The mean urinary albumin/creatinine ratio was reduced by 10% in the metformin plus pioglitazone group compared to an increase of 6% in the metformin plus gliclazide group (p = 0.027). The incidence of adverse events was comparable between groups and both combinations were well tolerated.

CONCLUSIONS

Compared to the established combination of metformin plus gliclazide, this study indicates potential benefits of addition of pioglitazone to metformin in terms of improvements in microalbuminuria and specific abnormalities associated with diabetic dyslipidemia.

Thiazolidinediones and Insulin

The range of therapeutic modalities to treat type 2 diabetes mellitus has broadened in recent years. Biguanides and thiazolidinediones are the two currently available classes of anti-hyperglycemic agents with insulin-sensitizing properties. Thiazolidinediones, in particular, have received much attention, not only for the well documented hepatotoxicity of troglitazone that led to its removal from the market in 2000, but also for the emerging data that support the beneficial effects of the thiazolidinedione class of drugs on beta-cell rejuvenation and cardiovascular risk reduction. In the US, thiazolidinediones are indicated either as monotherapy or in combination with a sulfonylurea, metformin, or insulin in cases where diet, exercise, and a single drug fail. In contrast, the UK National Institute for Clinical Excellence included in its re-appraisal of 'glitazones' in August 2003 the continued exclusion from licensed use in the UK of combination therapy with thiazolidinediones and insulin. When added to insulin therapy, thiazolidinediones appear to effectively lower glucose levels and reduce insulin dosage in clinical trials involving individuals with poorly controlled type 2 diabetes. However, weight gain, hypoglycemia, and fluid retention pose problems in certain patients. The fluid retention may exacerbate or even precipitate congestive heart failure, which usually necessitates discontinuation of the drug. Risk stratification and careful management of patients at risk for heart failure, including those taking insulin concomitantly, allow healthcare providers to safely administer combination therapy with thiazolidinediones in patients with type 2 diabetes. Hepatic toxicity with currently available thiazolidinediones has been found to be minimal overall.

Thiazolidinediones: a review of their mechanisms of insulin sensitization, therapeutic potential, clinical efficacy, and tolerability

The thiazolidinediones (TZDs) rosiglitazone and pioglitazone are newer additions to the antidiabetic armamentarium and are indicated for the treatment of type 2 diabetes mellitus (T2DM) in the United States. The TZDs are peroxisome proliferator-activated receptor-gamma (PPAR-gamma) agonists that provide clinically effective glycemic control and unique pharmacologic effects on multiple risk factors for T2DM-related morbidity, including improvement of insulin sensitivity and endothelial dysfunction, reduction of blood pressure, and amelioration of dyslipidemia. Weight gain and fluid retention occur with TZD therapy, especially when they are administered in higher doses and in combination with insulin. Although fluid retention associated with the use of TZDs is generally mild and reversible, these agents should not be used in patients with New York Heart Association Class III or IV heart failure symptoms. The findings of ongoing, long-term, prospective studies will clarify the role of the TZDs in the treatment of T2DM, particularly in terms of the durability of improvements in glycemic control, insulin sensitivity, pancreatic beta- cell function, and cardiovascular health.

Effect of rosiglitazone versus insulin on the pancreatic beta-cell function of subjects with type 2 diabetes

OBJECTIVE

In a previous study, we found observational evidence of improvement in beta-cell function when rosiglitazone was added to a failing oral antihyperglycemic regimen consisting of sulfonylureas and metformin. To confirm our previous observations, we designed and performed a prospective, randomized, and controlled study.

RESEARCH DESIGN AND METHODS

A total of 17 subjects with type 2 diabetes, inadequately controlled on a maximized oral antihyperglycemic double regimen of glimepiride and metformin, were randomized to the addition of rosiglitazone or insulin to their treatment regimens for a period of 6 months. At baseline and at 6 months, the following were performed: measurement of fasting plasma glucose, fasting proinsulin, and insulin levels; frequently sampled intravenous glucose tolerance test; and glucagon stimulation test for C-peptide.

RESULTS

Nine subjects were randomized to the addition of 8 mg rosiglitazone, and eight subjects were randomized to the addition of one injection of insulin (premixed 70/30) before their evening meal. The treatment groups were well matched for age, duration of diabetes, and BMI. Most important, the HbA(1c) was well matched between groups before treatment (8.7 +/- 0.3 and 9.0 +/- 0.3%; NS) and at the end of the 6 months (7.8 +/- 0.5 and 7.8 +/- 0.3%; NS). After 6 months, at the end of the study, there was a significant improvement in acute insulin response to glucose in the rosiglitazone group (+15.3 microIU x ml(-1) x 10 min(-1); P < 0.001) that led to an increase in the disposition index from 0.18 at baseline to 4.18 at 6 months (P = 0.02). Furthermore, at the end of the study, the proinsulin-to-insulin ratio had decreased in the rosiglitazone group by 36% (P = 0.03) but did not change significantly in the insulin treatment group.

CONCLUSIONS

Rosiglitazone, but not insulin, induced a recovery of pancreatic beta-cell function, as evidenced by the restoration of the first-phase insulin response to glucose, improvement in the disposition index, and a decrease in the proinsulin-to-insulin ratio in subjects with type 2 diabetes in whom oral antihyperglycemic therapy failed. This improvement was independent of the correction of glucotoxicity.

Outcomes of initiation of therapy with once-daily combination of a thiazolidinedione and a biguanide at an early stage of type 2 diabetes

CONTEXT

Utilization of the biguanide metformin and a thiazolidinedione (TZD) with new onset diabetes has the benefit of lowering A1cs into the normal range without the problem of severe hypoglycaemia.

OBJECTIVE

To assess the effectiveness of once-daily combined metformin and TZD therapy compared with other therapeutic regimens typically utilized at later stages of type 2 diabetes.

METHODS

A random chart review of 300 type 2 diabetic patients and extraction of data for body mass index (BMI), duration of diabetes and C-peptide and A1c was performed. In the 210 type 2 diabetic subjects in whom this information was currently available, the data were analysed.

RESULTS

Eighty-six patients on once-daily metformin and rosiglitazone had an average A1c of 6.2% (group A), and 58 subjects on triple therapy (metformin, rosiglitazone and glimepiride) (group B) had an average haemoglobin A1c (HbA1c) of 6.9%. The 22 subjects on one injection of insulin per day in addition to triple therapy (group C) had an average HbA1c of 7.6%, and the 44 subjects on more than one insulin injection per day plus metformin and/or rosiglitazone (group D) had an average HbA1c of 8.3%. HbA1cs below 7.0% were found in 91.9% of group A, 21.7% of group B, 36.4% of group C and 56.8% of group D. HbA1cs below 6.5% were found in 78.2% in group A, 15.5% in group B, 22.7% in group C and 31.8% in group D. HbA1cs below 6.0% were found in 41.9% in group A, 6.9% in group B, 9.1% in group C and 13.6% in group D. On univariate analyses, the HbA1c was positively associated with the duration of diabetes and the BMI and negatively associated with random C-peptide levels. Alternatively, on multiple regression analysis, there was no statistical correlation between the duration of diabetes or BMI with the HbA1c. However, there was a strong statistical correlation between the random C-peptide level and the HbA1c (p = 0.002).

CONCLUSION

Early initiation of therapy for type 2 diabetes with a once-daily combination of metformin and rosiglitazone provides the greatest opportunity to achieve A1cs within the normal range. The level of achieved glycaemic control is not dependent on the number or potency of the therapies utilized but is dependent on the level of endogenous insulin production. The use of a TZD as part of initial therapy of type 2 diabetes with its documented ability to preserve or improve beta-cell function has the potential to achieve prolonged normoglycaemia in the type 2 diabetic patient.

What impact would pancreatic beta-cell preservation have on life expectancy, quality-adjusted life expectancy and costs of complications in patients with type 2 diabetes? A projection using the CORE Diabetes Model

OBJECTIVE

Type 2 diabetes is characterised by progressive failure of pancreatic beta-cell function against a background of insulin resistance. Multifactorial interventions, including intensive glycaemic and blood pressure control, reduce the risk of onset and progression of complications. However, current management of type 2 diabetes focuses on treatment of signs and symptoms of disease instead of targeting underlying causes. A number of newer pharmacological interventions, including thiazolidinediones and glucagon-like peptides, have shown early promise in preserving pancreatic beta-cell function. The aim of this study was to investigate the impact of stabilising beta-cell function on long-term outcomes in patients with type 2 diabetes.

METHODS

The CORE Diabetes Model was used to project life expectancy (LE), quality-adjusted LE (QALE) and total lifetime complication costs (TC) for a cohort of newly-diagnosed patients with type 2 diabetes, either with a typical increase of HbA1c over time as observed in the UKPDS, or assuming stabilisation of HbA1c after diagnosis with a hypothetical new treatment, representing beta-cell function stabilisation. Costs due to diabetes-related complications (from a US third-party payer perspective), were discounted at 3% annually. Both non-discounted and discounted (at 3% annually) LE and QALE were calculated. Sensitivity analyses were performed to test the robustness of results.

RESULTS

Over a time period of 50 years, in a cohort with no increase of HbA1c over time, LE and QALE were improved by mean (SD) 1.02 (0.36) and 0.96 (0.25) years, and total costs of complications were reduced by 6,377 dollars (2,568) per patient compared to the cohort with a typical increase in HbA1c over time. Results were robust under a wide range of plausible assumptions.

CONCLUSIONS

New interventions that stabilise pancreatic betacell function may have an important impact on length and quality of life, and lead to reduced costs of complications in patients with type 2 diabetes.

Expression and functional activity of PPARgamma in pancreatic beta cells

Rosiglitazone is an agonist of peroxisome proliferator activated receptor-gamma (PPARgamma) and ameliorates insulin resistance in type II diabetes. In addition, it may also promote increased pancreatic beta-cell viability, although it is not known whether this effect is mediated by a direct action on the beta cell. We have investigated this possibility. Semiquantitative real-time reverse transcription-polymerase chain reaction analysis (Taqman) revealed that freshly isolated rat islets and the clonal beta-cell line, BRIN-BD11, express PPARgamma, as well as PPARalpha and PPARdelta. The levels of expression of PPARgamma were estimated by reference to adipose tissue and were found to represent approximately 60% (islets) and 30% (BRIN-BD11) of that found in freshly isolated visceral adipose tissue. Western blotting confirmed the presence of immunoreactive PPARgamma in rat (and human) islets and in BRIN-BD11 cells. Transfection of BRIN-BD11 cells with a PPARgamma-sensitive luciferase reporter construct was used to evaluate the functional competence of the endogenous PPARgamma. Luciferase activity was modestly increased by the putative endogenous ligand, 15-deoxy-Delta12,14 prostaglandin J2 (15dPGJ2). Rosiglitazone also caused activation of the luciferase reporter construct but this effect required concentrations of the drug (50-100 microm) that are beyond the expected therapeutic range. This suggests that PPARgamma is relatively insensitive to activation by rosiglitazone in BRIN-BD11 cells. Exposure of BRIN-BD11 cells to the lipotoxic effector, palmitate, caused a marked loss of viability. This was attenuated by treatment of the cells with either actinomycin D or cycloheximide suggesting that a pathway of programmed cell death was involved. Rosiglitazone failed to protect BRIN-BD11 cells from the toxic actions of palmitate at concentrations up to 50 microm. Similar results were obtained with a range of other PPARgamma agonists. Taken together, the present data suggest that, at least under in vitro conditions, thiazolidinediones do not exert direct protective effects against fatty acid-mediated cytotoxicity in pancreatic beta cells.

The prospective pioglitazone clinical trial in macrovascular events (PROactive): can pioglitazone reduce cardiovascular events in diabetes? Study design and baseline characteristics of 5238 patients

OBJECTIVE

The PROspective pioglitAzone Clinical Trial In macroVascular Events (PROactive) assesses the effect of pioglitazone, a peroxisome proliferator-activated receptor agonist, with anti-inflammatory and vascular properties, on the secondary prevention of macrovascular events in type 2 diabetes.

RESEARCH DESIGN AND METHODS

PROactive is an on-going randomized, double-blind outcome study in patients with type 2 diabetes managed with diet and/or oral blood glucose-lowering drugs (combination of oral agents with insulin is permitted) who have a history of macrovascular disease. Patients are randomized to receive pioglitazone (forced titration from 15 to 30 to 45 mg, depending on tolerability) or placebo in addition to existing therapy. The primary end point is the time from randomization to occurrence of a new macrovascular event or death. Follow-up is estimated to span 4 years.

RESULTS

A total of 5238 patients have been randomized from 19 countries. At entry into the study, patients enrolled are a mean age of 61.8 years, with type 2 diabetes for a mean of 9.5 years; 60.9 and 61.5% are taking metformin or a sulfonylurea, respectively; and 33.6% are using insulin in addition to oral glucose-lowering drugs. The majority of patients are men (66.1%). Patients are required to meet one or more of entry criteria, as follows: >6 months' history of myocardial infarction (46.7%); coronary artery revascularization (30.8%), stroke (18.8%), or acute coronary syndrome for >3 months (13.7%); other evidence of coronary artery disease (48.1%); or peripheral arterial occlusive disease (19.9%). One-half (48.5%) of the patients have two or more of these risk factors. Three-quarters (75.4%) have hypertension, and 58.8% are current or previous smokers.

CONCLUSIONS

The cohort of patients enrolled in PROactive is a typical type 2 diabetic population at high risk of further macrovascular events. The characteristics of this population are ideal for assessing the ability of pioglitazone to reduce the cardiovascular risk of patients with type 2 diabetes.

Peroxisome Proliferator Activator Receptors (PPAR), Insulin Resistance, and Cardiomyopathy

Diabetes is a risk factor for coronary atherosclerosis, myocardial infarction, and ischemic cardiomyopathy. Insulin resistance is associated with left ventricular (LV) hypertrophy and hypertensive cardiomyopathy. Even in the absence of coronary artery disease or hypertension, "diabetic cardiomyopathy" can develop because of myocardial autonomic dysfunction or impaired coronary flow reserve. The relationship between insulin resistance and cardiomyopathy is bidirectional. Systemic and myocardial glucose uptake is compromised in heart failure independent of etiology. These abnormalities are associated with cellular deficits of insulin signaling. Insulin resistance in heart failure can be detrimental, because transcriptional shifts in metabolic gene expression favor glucose over fat as a substrate for high-energy phosphate production. Although preexisting diabetes accelerates this process of "metabolic death," insulin resistance can also develop secondary to cardiomyopathy-associated overabundance of neurohormones and cytokines. Insulin resistance and fatty acid excess are potential therapeutic targets in heart failure, striving for efficient myocardial substrate utilization. Peroxisome proliferator activator receptor gamma (PPARgamma) agonists are antidiabetic agents with antilipemic and insulin-sensitizing activity. Experimental studies suggest salutary effects in limiting infarct size, attenuating myocardial reperfusion injury, inhibiting hypertrophic signaling and vascular antiinflammatory actions through cytokine inhibition. However, clinical applicability in diabetic patients experiencing heart failure has been hampered because of increased edema and even fewer reports of exacerbation associated with these compounds. Evidence to date argues for peripheral mechanisms of edema unrelated to central hemodynamics. Nevertheless, they are currently contraindicated in New York Heart Association (NYHA) III-IV patients, particularly in combination with insulin. Investigations are underway to decipher mechanisms, risks, and benefits of PPARgamma agonists, as well as the role of the structurally related PPARalpha receptor on cardiovascular metabolism and function.

Type 2 diabetes mellitus: what is the optimal treatment regimen?

Treatment options for type 2 diabetes mellitus currently consist of insulin sensitizers, alpha-glucosidase inhibitors, secretagogues, and insulin. However, the emphasis on initial therapy has been shifting from secretagogues and alpha-glucosidase inhibitors to insulin sensitizers such as metformin and the thiazolidinediones (TZDs). This article outlines the benefits of treatment with sensitizers vis à vis alpha-glucosidase inhibitors and secretagogues as part of a comprehensive treatment algorithm for type 2 diabetes. Secretagogues and alpha-glucosidase inhibitors effectively lower plasma glucose levels only, whereas insulin sensitizers reduce several important cardiac risk factors in addition to reducing plasma glucose levels. TZDs, in particular, are also beneficial for their ability to preserve or even rejuvenate pancreatic beta-cell function. The treatment algorithm has a layered approach, beginning with a combination of insulin-sensitizer therapy and incrementally progressing to triple oral therapy with the addition of secretagogues and, if necessary, the addition of subcutaneous insulin to maintain glycemic control.

Progress with thiazolidinediones in the management of type 2 diabetes mellitus

BACKGROUND

Much progress has been made in the field of medicine within the past 20 years; however, cardiovascular outcomes in patients with diabetes mellitus have not improved to a corresponding degree. Although numerous treatments are available for the management of type 2 diabetes, current approaches appear to address the spectrum of the disease and its complications insufficiently.

OBJECTIVES

This article reviews evidence for the minimal effects of standard antidiabetic treatments on the macrovascular complications associated with type 2 diabetes, discusses the improvements in markers of cardiovascular risk seen with the thiazolidinediones (TZDs), and explores the rationale for their earlier use.

METHODS

Relevant articles and guidelines on the use of oral antidiabetic agents in the treatment of type 2 diabetes were identified through a search of MEDLINE for the past 15 years using the terms cardiovascular, insulin resistance, metabolic syndrome, metformin, sulfonylurea, type 2 diabetes, and thiazolidinediones. The reference lists of selected articles also were searched. Articles chosen for review were required to assess clinically important outcomes or surrogate markers that have been shown to have a direct link to clinically important outcomes.

RESULTS

The data reviewed suggest that the sulfonylureas and/or metformin are able to reduce microvascular complications associated with type 2 diabetes but do not substantially affect macrovascular complications. In contrast, the TZDs demonstrate insulin-sensitizing effects attributable to their novel mechanism of action on the peroxisome proliferator-activated receptor gamma. The resulting reduction in insulin resistance appears to improve many of the metabolic and cardiovascular pathways influenced by insulin activity. Blood pressure, vascular and coagulation defects, lipid abnormalities, and beta-cell function have been found to improve in patients receiving TZD treatment. For example, there are reports of significant reductions in levels of C-reactive protein (P < 0.01); small, dense low-density lipoprotein cholesterol particles (P < 0.05); and circulating free fatty acids (P < 0.003), in addition to improvements in the proinsulin-to-insulin ratio (P < 0.05).

CONCLUSIONS

In this review of the literature, use of TZDs as monotherapy or as part of combination therapy has been associated with effective glycemic control and reductions in markers of various macrovascular complications of type 2 diabetes. Although outcomes trials are ongoing, the preliminary effects of TZD therapy are promising and suggest that earlier use of TZDs in the pharmacologic management of type 2 diabetes has the potential to minimize severe disease sequelae.

Long-term glycaemic control with pioglitazone in patients with type 2 diabetes

Patients with type 2 diabetes have dual defects: insulin resistance and beta-cell dysfunction. Thiazolidinediones (TZDs), a new class of oral drugs used for the treatment of type 2 diabetes, reduce insulin resistance via an action on peroxisome proliferator-activated receptors. There is also growing evidence that TZDs may preserve beta-cell function. Pioglitazone is a TZD that provides appropriate monotherapy or combination treatment for patients with type 2 diabetes. Studies of up to 32-week duration have shown that pioglitazone significantly reduces HbA1c and fasting plasma glucose when used alone or in combination with another glucose-lowering agent. Four recently published 52-week clinical trials, involving over 3700 patients with type 2 diabetes, show that pioglitazone is an effective long-term treatment, both as monotherapy and in combination with metformin or sulphonylurea. As well as maintaining glycaemic control over the long term, pioglitazone also confers benefits in terms of improvements in fasting insulin, lipid parameters, C-peptide and 32,33-split proinsulin (independent predictors of cardiovascular risk) and hypoglycaemia compared with other monotherapies or combination therapies. It is well tolerated, with a low incidence of adverse events. These long-term data support the concept that pioglitazone should be used earlier in the treatment of type 2 diabetes, either as monotherapy or as add-on therapy.