Section Review: Oncologic, Endocrine & Metabolic: Thiazolidinediones

PPAR gamma gene--a review

Peroxisome proliferator-activated receptor gamma (PPARγ) has been the focus of intense research because ligands for this receptor have emerged as potent insulin sensitizers used in the treatment of type 2 diabetes. There have been described three PPAR isotypes α, δ and γ which have an integrated role in controlling the expression of genes playing key roles in the storage and mobilization of lipids, in glucose metabolism, in morphogenesis and inflammatory response. Recent advances include the discovery of novel genes that are regulated by PPARγ, which helps to explain how activation of this adipocyte predominant transcription factor regulates glucose and lipid homeostasis. Increased levels of circulating free fatty acids and lipid accumulation in non-adipose tissue have been implicated in the development of insulin resistance. This situation is improved by PPARγ ligands, which promotes fatty acid storage in fat deposits and regulates the expression of adipocyte-secreted hormones that impacts on glucose homeostasis. So the net result of the pleiotropic effects of PPARγ ligands is improvement of insulin sensitivity. This review highlights the roles that PPAR gamma play in the regulation of gene expression of multiple diseases including obesity, diabetes and cancer and highlights the gene isolation transformation role. Further studies are needed for the transformation of PPAR gamma gene in plants and evaluate in animals for the treatment of type 2 diabetes.

Circulatory adipocytokines and lipid profile variations in type-2 diabetic subjects: desirable side-effects of antidiabetic drugs

AIM

Inspite of availability of a variety of drugs to treat type 2 diabetes, little is known about their effects on other systems. Normalization of glucose metabolism by these drugs may consequently affect the secretory function in adipocytes. Secretory adipocytokines like adiponectin and leptin are emerging as novel therapeutic targets for type 2 diabetes mellitus (T2DM). The present study was undertaken to analyze the effects of commonly used Oral Hypoglycemic Agents (OHAs) alone, or in combination with other drugs and/or insulin on circulatory adiponectin and leptin levels, lipid profile, and blood pressure in diabetic subjects.

METHODS

The study was undertaken at IRSHA and Bharati Vidyapeeth Medical College and Hospital, MS, India. Clinically diagnosed T2DM subjects and age, gender matched healthy controls were recruited. Fasting blood was collected from each subject and the blood samples were analyzed for circulatory adipocytokines and lipid parameters using commercial kits.

RESULTS

Serum adiponectin levels were significantly increased while leptin significantly decreased in diabetic men (p<0.05) and women (p<0.001) on OHA, as compared to healthy controls. Triglyceride levels significantly decreased (p<0.05) in diabetic men, however, they remained unchanged in women despite same drug treatment. Serum HDL and LDL levels (p<0.001) were significantly lower in diabetic women as compared to healthy women. Systolic (p<0.05) and diastolic (p<0.001) blood pressure was significantly high in diabetic men but remained unchanged in women.

CONCLUSIONS

Frequently used OHAs significantly improve circulatory levels of adipocytokines. Selecting best treatment option for each patient is a key, and 2012 European Association for the Study of Diabetes (EASD) and ADA guidelines recommend diabetes treatment to be individualized depending on various socioeconomic and lifestyle factors. We recommend regular analysis of circulatory adipocytokines in T2DM patients to help clinicians select the best treatment option to normalize levels of these important therapeutic targets.

Microalbuminuria as a marker of cardiovascular risk in patients with type 2 diabetes

Diabetes is a major risk factor for coronary artery disease and most patients with diabetes die of cardiovascular complications. Reduction of cardiovascular risk is therefore a high priority in the management of patients with diabetes. Microalbuminuria is an important predictor of cardiovascular events and forms one of the components of the insulin resistance/metabolic syndrome, which confers a particularly high risk of cardiovascular death. The currently available glucose-lowering agents vary considerably in their ability to reduce microalbuminuria. The sulfonylureas and metformin appear to have little effect on microalbuminuria expressed as urinary albumin/creatinine ratio, while the thiazolidinediones have unique effects on this risk factor, in parallel with their effects on insulin resistance. In two 1-year European multicenter, randomized, double-blind monotherapy trials (n=2444), pioglitazone produced similar reductions in urinary albumin/creatinine ratio to gliclazide and greater reductions than metformin (P<0.001). Similarly, two further 1-year European multicenter, randomized, double-blind trials assessed the effects of add-on therapy (n=1269) on urinary albumin/creatinine ratio. In the first study, urinary albumin/creatinine ratio was reduced by pioglitazone add-on to sulfonylurea (-15%), but was largely unaffected by metformin add-on to sulfonylurea (2%; P<0.05). In the second, urinary albumin/creatinine ratio was also reduced by pioglitazone add-on to metformin (-10%), but increased by gliclazide add-on to metformin (6%, P<0.05). The results of these studies indicated that compared with metformin or gliclazide, pioglitazone may provide therapeutic benefits, over and above those due to improved glycemic control. These include significant reductions in urinary albumin/creatinine ratio, a known cardiovascular risk marker.

Mechanisms and clinical effects of thiazolidinediones

Studies of pioglitazone, troglitazone, BRL 49653 and other thiazolidinediones in preclinical animal models of non-insulin dependent diabetes mellitus (NIDDM) and obesity led to the observation that these compounds were effective in reducing hyperglycaemia and hyperlipidaemia. In these models, animals treated with thiazolidinediones had notable improvements in blood glucose levels, hepatic glucose output, peripheral insulin resistance, and serum lipid levels. Mechanistic studies indicate that thiazolidinediones act at many intracellular sites and can influence several processes to increase cell sensitivity to insulin. These include influence on insulin receptor kinase activity, control of insulin receptor phosphorylation, change in number of insulin receptors, quantity and activity of GLUT-4, modulation of tumour necrosis factor (TNF) activity, activation of peroxisome proliferator-activated receptor-gamma (PPAR-gamma) and alteration of hepatic glucose metabolism. Available data on pioglitazone and troglitazone from clinical studies support the efficacy and safety of this class of compounds in reducing hyperglycaemia, hypertriglyceridaemia and insulin resistance associated with NIDDM. Currently, only troglitazone is approved for use in the United States and only in combination with insulin. This new pharmacological class of drugs has great promise for the treatment of NIDDM and also as a valuable research tool to further the understanding of the mechanisms that underlie NIDDM and insulin resistance syndrome.

Addition of rosiglitazone to glimepirid and metformin combination therapy in type 2 diabetes

The study was planned to determine the efficacy and safety of adding rosiglitazone to a combination of glimepiride and metformin therapy with insufficiently controlled type 2 diabetes. This was an open-label study with a follow-up period of 26 weeks. Thirty patients were taking 3 mg glimepiride two times and 850 mg metformin two times per day. Patients were told to take one rosiglitazone 4 mg tablet before breakfast additionally. The primary efficacy measure was the mean change in HbA1c from baseline to the end of the study. Secondary efficacy parameters included the mean changes from baseline to the end of the study in fasting plasma glucose (FPG) and insulin levels, as well as total cholesterol, HDL-C, LDL-C, triglycerides, alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels. Mean HbA1c levels decreased significantly from 7.54 +/- 0.9% to 6.57 +/- 0.7% (p < 0.001) at 26th week. FPG levels fell from 169.39 +/- 37.8 mg/dl to 135.69 +/- 28.0 mg/dl (p < 0.001), respectively. Insulin levels decreased from 19.60 +/- 9.8 U/L to 14.66 +/- 11.6 U/L (p = 0.026) at 26th week. No one experienced elevations of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels greater than 2.5 times the upper limit of the reference range. This study confirms that the addition of rosiglitazone (4 mg/day) to sulphonylurea and metformin treatment for patients with type 2 diabetes improves glycemic control, is safe, and generally well tolerated.

Addition of rosiglitazone to metformin is most effective in obese, insulin-resistant patients with type 2 diabetes

AIM

These analyses were undertaken to evaluate the efficacy of the insulin sensitizer rosiglitazone (RSG) when added to the therapy of obese type 2 diabetes mellitus patients (T2DM) taking near-maximal doses (2.5 g/day) of metformin (MET). In obese, insulin-resistant patients with T2DM who are inadequately controlled on MET, the addition of an agent that reduces insulin resistance may be a more rational and innovative approach than the addition of an insulin secretagogue.

METHODS

Data were pooled from two double-blind studies of RSG added to 2.5 g/day MET, involving a total of 550 T2DM patients. Patients were categorized as non-overweight, overweight and obese according to their baseline BMI using WHO criteria (<25 kgm(-2), 25-30 kgm(-2), >30 kgm(-2) respectively).

RESULTS

RSG improved glycaemia (HbA1c) and fasting plasma glucose (FPG) to a clinically significant extent in all three subgroups but the effect was most pronounced in the obese patients. Improvements in HOMA estimates of insulin resistance and beta-cell function were also greatest in the obese patients (4 mg: -16% and +19%; 8 mg: -37% and + 33% respectively), as were reductions in fasting insulin. The profile of adverse events was not demonstrably different in obese patients from the non-obese.

CONCLUSIONS

In obese type 2 diabetic patients inadequately controlled on MET alone, addition of rosiglitazone improves glycaemic control, insulin sensitivity and beta-cell function to a clinically important extent.

Addition of rosiglitazone to existing sulfonylurea treatment in chinese patients with type 2 diabetes and exposure to hepatitis B or C

The effects of adding rosiglitazone to existing sulfonylurea (SU) treatment have not previously been studied in Chinese patients with type 2 diabetes and no known pre-existing hepatic impairment. Patients were randomized to receive rosiglitazone 2 mg twice daily (R4 + SU) or 4 mg twice daily (R8 + SU) or placebo (SU + P) for 24 weeks in addition to existing SU treatment. Most patients were taking concomitant glibenclamide (34%) or gliclazide (25%). Changes in glycosylated hemoglobin (HbA(1c)), fasting plasma glucose (FPG), and plasma insulin concentrations were measured. Of the 530 patients enrolled (45% male, mean age 59 years), 105 were in the SU + P group, 215 in the R4 + SU group, and 210 in the R8 + SU group. The mean baseline HbA(1c) was 9.8%, and FPG was 183.8 mg/dL. Compared with placebo, addition of rosiglitazone (2 or 4 mg twice daily) produced significant decreases in mean HbA(1c) (1.04% and 1.44%, respectively; p < 0.0001) and FPG (21.6 and 36.0 mg/dL, respectively; p < 0.0001). There were statistically significant (p < 0.0001) reductions from baseline in insulin concentration of 23.3 and 30.4 pmol/L in the R4 + SU and R8 + SU groups, respectively. Despite the high prevalence of seropositivity for hepatitis B and/or C at baseline (56%), there was no evidence of hepatotoxicity. No clinically significant changes in routine hematology, biochemistry, or electrocardiogram were observed. The addition of rosiglitazone to SU produced clinically significant improvements in glycemic control in Chinese patients with type 2 diabetes. Rosiglitazone plus SU was well tolerated irrespective of hepatitis B and C serological status.

Rosiglitazone reduces urinary albumin excretion in type II diabetes

This study examines the effect of rosiglitazone on urinary albumin excretion (UAE) in patients with type II diabetes. Urinary albumin: creatinine ratio (ACR) was measured in a 52-week, open-label, cardiac safety study comparing rosiglitazone and glyburide. Patients were randomised to treatment with rosiglitazone 4 mg b.i.d. or glyburide. ACR was measured at baseline and after 28 and 52 weeks of treatment. Statistically significant reductions from baseline in ACR were observed in both treatment groups at week 28. By week 52, only the rosiglitazone group showed a significant reduction from baseline. Similar results were observed for the overall study population and for the subset of patients with baseline microalbuminuria. For patients with microalbuminuria at baseline, reductions in ACR did not correlate strongly with reductions in glycosylated haemoglobin, or fasting plasma glucose, but showed strong correlation with changes in mean 24-h systolic and diastolic blood pressure for rosiglitazone-treated patients (deltaACR vs deltamean 24-h systolic blood pressure, r=0.875; deltaACR vs deltamean 24-h diastolic blood pressure, r=0.755; P < 0.05 for both). No such correlation was observed for glyburide-treated patients. In conclusion, rosiglitazone treatment was associated with a decrease in urinary albumin excretion. These findings suggest a potential beneficial effect of rosiglitazone in the treatment or prevention of renal and vascular complications of type II diabetes.

Troglitazone: the discovery and development of a novel therapy for the treatment of Type 2 diabetes mellitus

Prior to the introduction of troglitazone, it had been more than 30 years since the last significant improvement in antidiabetic therapy. In view of the pressing need for more effective oral agents for the treatment of Type 2 diabetes mellitus, troglitazone was granted priority review by the FDA and was launched in the USA in 1997. The first of the thiazolidinedione insulin sensitizing agents, troglitazone was quickly followed by rosiglitazone and pioglitazone. The glitazones proved to be effective not only in lowering blood glucose, but also to have beneficial effects on cardiovascular risk. Troglitazone was subsequently withdrawn because of concerns about hepatotoxicity, which appears to be less of a problem with rosiglitazone and pioglitazone. Recent insights into the molecular mechanism of action of the glitazones, which are ligands for the peroxisome proliferator-activated receptors, open the prospect of designing more effective, selective and safer antidiabetic agents. This document will review the history of troglitazone from discovery through clinical development.

Rosiglitazone: a review of its use in the management of type 2 diabetes mellitus

Rosiglitazone, a thiazolidinedione with a different side chain from those of troglitazone and pioglitazone, reduces plasma glucose levels and glucose production and increases glucose clearance in patients with type 2 diabetes mellitus. Insulin sensitivity, pancreatic beta-cell function and surrogate markers of cardiovascular risk factors are significantly improved by rosiglitazone. Double-blind trials of 8 to 26 weeks of rosiglitazone 4 or 8 mg/day monotherapy indicate significant decreases in fasting plasma glucose (-2 to -3 mmol/L with 8 mg/day) and glycosylated haemoglobin levels [HbA(1c); -0.6 to -0.7% (-0.8 to -1.1% in drug-naive patients) with 8 mg/day]. Significant decreases in hyperglycaemic markers occurred when rosiglitazone was combined with metformin (HbA(1c) -0.8 to -1.0%), a sulphonylurea (-1.4%) or insulin (-1.2%) for 26 weeks versus little change with active comparator monotherapy. Efficacy was maintained in trials of < or = 2 years, and was also apparent in various ethnic subgroups, elderly patients, and both obese and nonobese patients. Rosiglitazone is currently not indicated in combination with injected insulin. It should be administered in conjunction with diet and exercise regimens. Rosiglitazone is generally well tolerated. Despite rare individual reports of liver function abnormalities in rosiglitazone recipients, the incidence of these in clinical trials (< or = 2 years' duration) was similar to that in placebo and active comparator groups. Fluid retention associated with rosiglitazone may be the cause of the increased incidence of anaemia in clinical trials, and also means that patients should be monitored for signs of heart failure during therapy. Although bodyweight is increased overall with rosiglitazone therapy, increases are in subcutaneous, not visceral, fat; hepatic fat is decreased. The pharmacokinetic profile of rosiglitazone is not substantially altered by age or renal impairment, nor are there important drug interactions. Rosiglitazone is not indicated in patients with active liver disease or increased liver enzymes.

CONCLUSIONS

Oral rosiglitazone 4 or 8 mg/day provides significant antihyperglycaemic efficacy and is generally well tolerated, both as monotherapy and in combination with other antihyperglycaemic agents, in patients with type 2 diabetes mellitus who do not have active liver disease. Long-term data are required before conclusions can be drawn about the clinical significance of positive changes to surrogate markers of cardiovascular disease risk and improvements to pancreatic beta-cell function. Rosiglitazone significantly improves insulin sensitivity and, as such, is a welcome addition to the treatment options for patients with type 2 diabetes mellitus.

Synthetic peroxisome proliferator-activated receptor-gamma agonist, rosiglitazone, increases plasma levels of adiponectin in type 2 diabetic patients

OBJECTIVE

Adiponectin, a plasma protein exclusively synthesized and secreted by adipose tissue, has recently been shown to have anti-inflammatory, antiatherogenic properties in vitro and beneficial metabolic effects in animals. Lower plasma levels of adiponectin have been documented in human subjects with metabolic syndrome and coronary artery disease. We investigated whether the level of this putative protective adipocytokine could be increased by treatment with a peroxisome proliferator-activated receptor-gamma (PPAR-gamma) agonist in diabetic patients.

RESEARCH DESIGN AND METHODS

Type 2 diabetic patients (30 in the treatment group and 34 in the placebo group) were recruited for a randomized double-blind placebo-controlled trial for 6 months with the PPAR-gamma agonist rosiglitazone. Blood samples were collected and metabolic variables and adiponectin levels were determined in all patients before initiation of the study.

RESULTS

In the rosiglitazone group, mean plasma adiponectin level was increased by more than twofold (P < 0.0005), whereas no change was observed in the placebo group. Multivariate linear regression analysis showed that whether rosiglitazone was used was the single variable significantly related to the changes of plasma adiponectin. The amount of variance in changes of plasma adiponectin level explained by the treatment was approximately 24% (r(2) = 0.24) after adjusting for age, sex, and changes in fasting plasma glucose, HbA(1c), insulin resistance index, and BMI.

CONCLUSIONS

Rosiglitazone increases plasma adiponectin levels in type 2 diabetic subjects. Whether this may contribute to the antihyperglycemic and putative antiatherogenic benefits of PPAR-gamma agonists in type 2 diabetic patients warrants further investigation.

An international study of the effects of rosiglitazone plus sulphonylurea in patients with type 2 diabetes

This was an open-label, randomised 26-week study to determine the effects of adding 4 mg rosiglitazone (Avandia) daily to existing sulphonylurea (SU) therapy in patients with type 2 diabetes from India, Brazil, The Philippines, Thailand, Argentina and Tunisia. Of the 348 patients, 175 received 2 mg rosiglitazone twice daily plus SU (RSG+SU) and 173 received SU alone (at their normal dose). The RSG+SU group showed a significant reduction in HbA1c (mean HbA1c 9.05% at baseline, 7.92% at 26 weeks, mean change -1.13 (95% Cl -1.37, -0.89)). Mean HbA1c essentially remained unchanged in the control group (8.9 to 9.0%). The RSG+SU group showed a significant decrease in fasting plasma glucose concentration (FPG) (mean FPG 198.7 mg/dl at baseline, 160.3 mg/dl at 26 weeks, mean change -38.4 (95% Cl -47.1, -29.7)) while the controls showed a non-significant increase from 194 to 200 mg/dl. Significantly more patients in the RSG+SU group achieved FPG < 140 mg/dl, > or = 0.7% decrease in HbA1c, and > or = 30 mg/dl decrease in FPG between baseline and week 26 than the controls (p = 0.0001 in each case). Adverse events were similar in both groups; more patients in the RSG+SU group reported hypoglycaemia, but most cases were mild. This study shows that adding rosiglitazone to existing SU treatment improves glycaemic control and is well-tolerated in patients with type 2 diabetes from a wide range of non-Western countries.

Rosiglitazone (BRL 49653) enhances insulin secretory response via phosphatidylinositol 3-kinase pathway

To elucidate the direct effect of rosiglitazone (RSG), a new thiazolidinedione antihyperglycemic agent, on pancreatic insulin secretion, an in situ investigation by rat pancreatic perfusion was performed. At a basal glucose concentration of 6 mmol/l, RSG (0.045-4.5 micromol/l) stimulated insulin release in a dose-dependent manner. In addition, 4.5 micromol/l RSG potentiated the glucose (10 mmol/l)-induced insulin secretion. Both the first and second phases of glucose-induced insulin secretion were significantly enhanced by RSG, by 80.7 and 52.4%, respectively. The effects of RSG on insulin secretion were inhibited by a phosphatidylinositol 3-kinase (PI3K) inhibitor, LY294002. In contrast, the glucose-stimulated insulin secretion was not affected by LY294002. The potentiation effect of RSG on glucose-stimulated insulin secretion, in both the first and second phases, was significantly blocked by LY294002. These results suggest that RSG has a direct potentiation effect on insulin secretion in the presence of 10 mmol/l glucose, mediated through PI3K activity. The inability of LY294002 to inhibit glucose-induced insulin secretion suggests that different pathways are responsible for glucose and RSG signaling.

Postoperative management of the diabetic patient

Diabetic patients are at increased risk for adverse outcomes of surgery. These adverse outcomes are related to pre-existing complications of diabetes, especially atherosclerotic disease, nephropathy (and perhaps increased susceptibility to other renal toxins), and peripheral and autonomic neuropathy. Hyperglycemia is associated with likely risks for poorer wound healing, increased susceptibility to infection, and probable loss of administered nutrients through glycosuria. Insulin use has the flexibility of timing and dose in the postoperative management of most diabetic patients. The combinations of intermediate-acting and long-acting insulins and short-acting insulins usually are related to the experience and preferences of the treating physicians and allied health professionals. Intravenous insulin (always R) may be limited to administration in the ICU because of the need for frequent blood glucose monitoring and rapidity of glucose response to intravenous insulin. The use of short-acting insulin analogues has been shown to work well as premeal insulin or for rapidly treating marked hyperglycemia in the outpatient setting. Meal delivery in the hospitalized patient may not be timed as precisely as in the home situation. Nurses may be responsible for many patients. The rapid-acting analogues may be associated with increased risk for hypoglycemia in the hospitalized patient if insulin cannot be given immediately before a meal. These rapid-acting insulin analogues usually are limited to circumstances in which the patient can determine the dose and self-administer just before ingestion of the meal. The long-acting insulin analogues may not afford enough flexibility in many situations in which daily dosages changes are occurring in intermediate-acting and long-acting insulins. Oral glucose-lowering agent use in the postoperative state usually is limited to selected patients, including patients who have been on such agents before surgery, who have only mild elevations of blood glucose, who are able to ingest oral medications, and who do not have significant comorbid conditions (or significant risk for such conditions) that may be contraindications to use of such agents (see Table 3). Sulfonylureas and other insulin secretagogues (e.g., meglitinide, nateglinide) lower glucoses acutely. The risk for hypoglycemia is slightly less with the nonsulfonylurea agents. Efficacy and side effects limit the use of carbohydrase inhibitors for hospitalized patients. The glucose-lowering effects of biguanides and thiazolidinediones usually are not rapid enough for hospitalized patients who have never taken these medications. For patients who have been on a biguanide or thiazolidinedione before admission, these agents often are restarted in the postoperative period when oral intake of medications is possible and hepatic and renal function are stable. The hospital period affords an opportunity to review long-term management issues related to diabetes and its complications. Instruction on the importance of medical nutrition therapy, glycemic control, management of hypertension, dyslipidemia, and aspirin use as well as basic guidelines for foot care should be carried out during the hospitalization and at the time of discharge. Similarly, appropriate arrangements for medical nutrition therapy, general diabetes education (especially for newly diagnosed diabetic patients), and regular medical follow-up are important to ensure long-term, excellent surgical and medical outcomes.

Addition of low-dose rosiglitazone to sulphonylurea therapy improves glycaemic control in Type 2 diabetic patients

AIMS

This study was designed to test the efficacy and safety of low-dose rosiglitazone, a potent, insulin-sensitizing thiazolidinedione, in combination with sulphonylurea in Type 2 diabetic patients.

METHODS

For the intention-to-treat analysis, 574 patients (59% male, mean age 61 years) were available, randomized to receive 26 weeks of twice-daily placebo (n = 192), rosiglitazone 1 mg (n = 199) or rosiglitazone 2 mg (n = 183) in addition to existing sulphonylurea treatment with gliclazide (47.6% of patients), glibenclamide (41.8%) or glipizide (9.4%) (two patients were taking carbutamide or glimepiride). Change in haemoglobin A1c (HbA1c), fasting plasma glucose (FPG), fructosamine, insulin, C-peptide, albumin, and lipids were measured, and safety was evaluated.

RESULTS

Mean baseline HbA1c was 9.2% and FPG was 11.4 mmol/l. Rosiglitazone at doses of 1 and 2 mg b.d. plus sulphonylurea produced significant decreases, compared with sulphonylurea plus placebo, in HbA1c (-0.59% and -1.03%, respectively; both P<0.0001) and FPG (1.35 mmol/l and 2.44 mmol/l, respectively; both P<0.0001). Both HDL-cholesterol and LDL-cholesterol increased and potentially beneficial decreases in non-esterified fatty acids and gamma glutamyl transpeptidase levels were seen in both rosiglitazone groups. The overall incidence of adverse experiences was similar in all three treatment groups, with no significant cardiac events, hypoglycaemia or hepatotoxicity.

CONCLUSIONS

Overall, the combination of rosiglitazone and a sulphonylurea was safe, well tolerated and effective in patients with Type 2 diabetes.

Troglitazone and pioglitazone attenuate agonist-dependent Ca2+ mobilization and cell proliferation in vascular smooth muscle cells

1. The effects of troglitazone and pioglitazone on agonist-induced Ca2+ mobilization and cell proliferation were studied using fluorescent Ca2+ indicator fura-2 AM and incorporation of [3H]-thymidine in rat aortic smooth muscle cells. The patch clamp techniques were also employed. 2. Vasopressin and platelet-derived growth factor-BB (PDGF) caused a transient elevation in [Ca2+]i by Ca2+ mobilization from intracellular stores, followed by a sustained rise due to Ca2+ entry. Nicardipine partly inhibited the sustained phase, but La3+ completely abolished it. 3. Troglitazone and pioglitazone did not significantly affect the transient rise elicited by these agonists, but preferentially inhibited the sustained phase of [Ca2+]i. 4. Under voltage clamp conditions, troglitazone and pioglitazone inhibited voltage-dependent L-type Ca2+ current (ICa.L). They also inhibited nonselective cation channels (Icat) elicited by vasopressin in a concentration-dependent manner. The half maximal inhibitory concentrations of troglitazone on ICa.L and Icat were 4.6 and 5.7 microM, respectively. On the other hand, nifedipine and nicardipine did not inhibit Icat. 5. Vasopressin and PDGF increased incorporation of [3H]-thymidine, and nifedipine and nicardipine partly suppressed it. However, the inhibitory effects of La3+ and exclusion of extracellular Ca2+ were more potent than the Ca2+ blocking agents. Troglitazone and pioglitazone also inhibited it concentration-dependently. 6. These results suggest that troglitazone and pioglitazone preferentially inhibited agonist (vasopressin and PDGF)-induced Ca2+ entry and proliferation in rat vascular smooth muscle cells, where the inhibitory effects of thiazolidinediones on ICa.L and Icat might be partly involved. Thus, thiazolidinediones may exert hypotensive and antiatherosclerotic effects.

Drug selection and the management of corticosteroid-related diabetes mellitus

Glucocorticoid use is associated with the risk of hyperglycemia in patients without known diabetes mellitus and worsened glycemic control in diabetic patients. The effects are greater in the fed than fasting state. Management includes use of diet and exercise (as appropriate for the individual) in all patients. Mild hyperglycemia can often be managed with oral agents, especially those with rapid onset of action. Marked hyperglycemia, especially in diabetic patients or patients with liver or renal disease, requires insulin. Adjustments in insulin can be done both in anticipation of the glucocorticoid effect and based on home glucose monitoring. The effects of glucocorticoids on hyperglycemia usually remit within 48 hours of discontinuation of oral administration.

New strategies for the treatment of type 2 diabetes

This review of current developments in the treatment of type 2 diabetes focuses on the achievement of normoglycemia through appropriately defined goals of diet, exercise, and drug therapy. Clinical nutritionists are central partners in the management of type 2 diabetes, and nutrition therapy is still considered the first-line therapy of choice. A nutritionist's role in the treatment at type 2 diabetes is to ensure an individualized, nutritionally adequate diet for patients, uncomplicated by episodes of hypoglycemia. In this role, clinical nutritionists must be aware of potential drug interactions with diet therapy and may be able to provide essential feedback about possible drug interactions to other members of the health care team, including nurses, pharmacists, and physicians. The role of insulin in treating type 2 diabetes is reexamined in the light of newly available oral antidiabetic agents and increasing awareness of the importance of insulin resistance and hyperinsulinemia in the development of diabetes complications. Because many patients use insulin to reduce blood glucose and glycated hemoglobin (HbA1c) to acceptable levels, management should combine diet therapy with insulin and/or 1 or 2 oral antidiabetic agents to help minimize the dose of exogenous insulin needed for glucose control.

BM 17.0744: a structurally new antidiabetic compound with insulin-sensitizing and lipid-lowering activity

BM 17.0744 (2,2-dichloro-12-(p-chlorophenyl)-dodecanoic acid) is a substance from a group of omega-substituted alkyl carboxylic acids with the general formula, ring-spacer-carboxylic acid. With BM 17.0744-a compound structurally unrelated to thiazolidinediones--antihyperglycemic and antihyperinsulinemic potency has been demonstrated in various animal models of type II diabetes. The antidiabetic effect is independent of the genetic background of the disease, gender, and animal species. The 24-hour blood glucose profile was dose- and time-dependently improved in ob/ob mice after a single and fourth oral administration of 0.3, 1, and 3 mg/kg/d. A dose-dependent reduction of hyperglycemia (10%, 15%, 28%, and 66%) was found in db/db mice after the fifth oral administration of 3, 10, 30, and 100 mg/kg/d. Hyperinsulinemia was reduced dose-dependently in yellow KK mice by 1%, 24%, 34%, and 66% after the fifth oral administration of 0.3, 1, 3, and 10 mg/kg/d. Overall glucose metabolism was predominantly higher in euglycemic-hyperinsulinemic clamp studies in obese fa/fa rats pretreated for 14 days with 10 mg/kg/d BM 17.0744. The data in diabetic and insulin-resistant animals suggest an improvement of insulin action that is supported by enhancement of insulin effects in vitro. There is no evidence of a risk for hypoglycemia in diabetic and metabolically healthy animals. Triglyceride (TG) and cholesterol were reduced in the serum of metabolically healthy rats, as well as serum lipids in db/db mice, which suggests this effect is independent of amelioration of the diabetic status. Lipid-lowering effects in diabetic and healthy animals show an additional property of BM 17.0744. Because of its antidiabetic and lipid-lowering potency, the substance is of great interest in treating the metabolic syndrome. Lipid decreases in rats are associated with a dose-dependent increase in carnitine acetyltransferase activity in the liver to about 100-fold (12.5 mg/kg/d). This together with hepatomegaly in small rodents may indicate peroxisomal proliferation, a phenomenon considered species-specific. Its relevance for humans is well documented for other classes of compounds including fibrates. Specific side effects of insulin sensitizers of the thiazolidinedione type, such as an increase in body weight and heart weight, could not be observed after 4-week oral application of BM 17.0744 in rats. In general, BM 17.0744 was well tolerated in the pharmacological dose range in all species tested.

Pharmacological management of diabetes: recent progress and future perspective in daily drug treatment

Glycaemic control in Type 1 diabetes has been proven efficient in preventing microvascular and neurological complications. The assumption that good control of hyperglycaemia may also have significant impact on alleviation of complications in Type 2 diabetes has gained growing support in recent years. Measures such as body weight reduction and exercise improve the metabolic defects, but pharmacological therapy is most frequently used. The sulphonylureas stimulate insulin secretion. Metformin and troglitazone increase glucose disposal and decrease hepatic glucose output without causing hypoglycaemia. Acarbose helps to spread the dietary carbohydrate challenge to endogenous insulin over time. These pharmacological treatments can improve blood glucose regulation in Type 2 diabetes patients. However, the key to strict glycaemic control with use of exogenous insulin lies in the creation of delivery methods that emulate physiologic insulin secretion. Insulin lispro, a recombinant insulin analogue, is identical to human insulin except for the transposition of proline and lysine at positions 28 and 29 in the C-terminus of the B chain. Evidence suggests that patients perceive their quality of life to be improved with insulin lispro when compared with regular human insulin, and that satisfaction with treatment is greater with the insulin analogue. Numerous new pharmacological approaches are under active investigation, with the aim of promoting insulin secretion, improving the action of insulin, or slowing carbohydrate absorption. With respect to continuous subcutaneous insulin infusion therapy and implantable pumps, despite that this approach is not widely utilised, it appears to bring us as close to achieving glycaemic control as is feasible with current treatment approaches. However, general application of such technology requires significant improvements in several areas, such as improvement of patency of catheter, pump failures due to early battery depletion incidents, and pump miniaturisation. Future perspective resides on insulin analogues with longer half-lives that would provide better basal insulin coverage in association with fast-acting analogues.

Complementary measures for promoting insulin sensitivity in skeletal muscle

Insulin resistance of skeletal muscle is fundamental to both syndrome X and its frequent sequel, type II diabetes. In these disorders, excessive exposure of muscle to free fatty acids (FFAs) and their metabolic derivatives appears to play a prominent role in the induction of insulin resistance. Recent evidence suggests that activation of novel isoforms of protein kinase C (PKC) by diacylglycerol may mediate at least part of the adverse impact of FFAs on muscle insulin sensitivity. Vitamin E and fish oil omega-3s, by promoting the activity of diacylglycerol kinase and inhibiting that of phosphatidate phosphohydrolase, should reduce diacylglycerol levels, thus accounting for their documented favorable impact on insulin sensitivity. Thiazolidinediones such as troglitazone, on the other hand, appear to intervene in the signaling pathway whereby PKC down-regulates insulin function. The insulin-sensitizing activity of chromium picolinate may be attributable, at least in part, to increased expression of insulin receptors. In combination with lifestyle modifications which reduce FFA exposure--weight loss, very-low-fat eating, excessive training--these measures can be expected to work in a complementary way to promote increased numbers of insulin receptors that are more functionally competent. As these measures appear to be safe and well-tolerated, they may have utility for the prevention of diabetes as well as its therapy. When they do not prove sufficient to achieve optimal glycemic control, excessive hepatic glucose output and impaired cell response to glucose can be addressed with metformin and sulfonylureas, respectively. The prospects for a rational medical management of type II diabetes, obviating the need for injectible insulin, have never been brighter.

The new antidiabetic drug MCC-555 acutely sensitizes insulin signaling in isolated cardiomyocytes

Freshly isolated adult rat ventricular cardiomyocytes have been used to characterize the action profile of the new thiazolidinedione antidiabetic drug MCC-555. Preincubation of cells with the compound (100 microM for 30 min or 10 microM for 2 h) did not modify basal 3-O-methylglucose transport, but produced a marked sensitizing effect (2- to 3-fold increase in insulin action at 3 x 10(-11) M insulin) and a further enhancement of maximum insulin action (1.8-fold). MCC-555 did not modulate autophosphorylation of the insulin receptor and tyrosine phosphorylation of insulin receptor substrate-1 (IRS-1). However, insulin action (10(-10) and 10(-7) M) on IRS-1-associated phosphatidylinositol (PI) 3-kinase activity was enhanced 2-fold in the presence of MCC-555. Association of the p85 adapter subunit of PI 3-kinase to IRS-1 was not modified by the drug. Immunoblotting experiments demonstrated expression of the peroxisomal proliferator-activated receptor-gamma in cardiomyocytes reaching about 30% of the abundance observed in adipocytes. The insulin-sensitizing effect of MCC-555 was lost after inhibition of protein synthesis by preincubation of the cells with cycloheximide (1 mM; 30 min). Cardiomyocytes from obese Zucker rats exhibited a completely blunted response of glucose transport at 3 x 10(-11) M insulin. MCC-555 ameliorates this insulin resistance, producing a 2-fold stimulation of glucose transport, with maximum insulin action being 1.6-fold higher than that in control cells. This drug effect was paralleled by a significant dephosphorylation of IRS-1 on Ser/Thr. In conclusion, MCC-555 rapidly sensitizes insulin-stimulated cardiac glucose uptake by enhancing insulin signaling resulting from increased intrinsic activity of PI 3-kinase. Acute activation of protein expression leading to a modulation of the Ser/Thr phosphorylation state of signaling proteins such as IRS-1 may be underlying this process. It is suggested that MCC-555 may provide a causal therapy of insulin resistance by targeted action on the defective site in the insulin signaling cascade.

The development of overt diabetes in young Zucker Diabetic Fatty (ZDF) rats and the effects of chronic MCC-555 treatment

1. Young (6-week-old) pre-diabetic Zucker Diabetic Fatty (ZDF) rats displaying impaired glucose tolerance (IGT), moderate hyperglycaemia and hyperinsulinaemia were treated with the novel thiazolidinedione, MCC-555, for 28 days, during which time beta-cell failure and progression to overt diabetes occurs. 2. Treated ZDF rats exhibited consistently lower blood glucose levels than vehicle-treated diabetic controls, with a delayed rise and lower plateau levels. MCC-555 maintained plasma insulin levels throughout the treatment period, whereas these fell by 40% in untreated ZDF rats. 3. The rise in body weight was maintained in MCC-555-treated rats, whereas vehicle-treated rats exhibited blunted body weight gain after 8 weeks of age. Daily food intake was higher in diabetic, as compared to non-diabetic rats, but treatment did not modify food intake in diabetic rats. Water intake was lower in treated ZDF rats, concomitant with lowering of blood glucose. 4. The hyperinsulinaemic-euglycaemic clamp technique was applied to all rats after treatment to examine the effects of MCC-555 on insulin sensitivity. The glucose infusion rate to maintain normoglycaemia was lower in diabetic than in non-diabetic rats, demonstrating reduced glucose entry into insulin-sensitive tissues in diabetic rats. Increased glucose infusion rates were required to maintain euglycaemia in treated diabetic rats, demonstrating increased insulin sensitivity in these animals. 5. In conclusion, chronic MCC-555 treatment of young ZDF rats displaying IGT attenuates the development of overt diabetes through improved insulin sensitivity and maintenance of beta-cell function. MCC-555 may thus be beneficial in humans with IGT, to prevent or delay the progression of diabetes.

Effects of troglitazone and pioglitazone on the action potentials and membrane currents of rabbit ventricular myocytes

The effects of the antidiabetic thiazolidinediones troglitazone and pioglitazone on action potentials and membrane currents were studied in rabbit ventricular myocytes. Troglitazone (10 microM) reversibly reduced excitability of the myocytes and modified their action potential configuration. It significantly increased the stimulation threshold required to elicit action potentials and decreased action potential amplitude and the maximum upstroke velocity of the action potentials. The Inhibition of the maximum upstroke velocity by troglitazone was also significant at 1 microM. Voltage-clamp experiments revealed that troglitazone (10 microM) reversibly inhibited both the slow inward Ca2+ current and the steady-state K+ current. In contrast to troglitazone, pioglitazone (1-10 microM) had no significant effect on the excitability, action potential configuration, or membrane currents of myocytes. These results suggest that troglitazone, but not pioglitazone, modulates Na+, Ca2+ and K+ currents, leading to the changes in excitability and action potential configuration of ventricular myocytes.

Troglitazone: Current Therapeutic Role in Type 2 Diabetes Mellitus

OBJECTIVE

To describe the role of troglitazone in the treatment of non-insulin-dependent diabetes mellitus.

METHODS

The potential mechanisms of action of the thiazolidinediones are outlined, and studies that have been conducted in animals and in humans are reviewed.

RESULTS

Although the precise mode of action of troglitazone, a thiazolidinedione, is unknown, this agent is an insulin sensitizer that has been shown to decrease fasting insulin, fasting plasma glucose, and blood pressure levels in humans. The effect of troglitazone is progressively greater over time; in several studies, the maximal action occurred as long as 12 weeks after initiation of treatment. The usual daily dose is 200 to 600 mg, and no dosage adjustment is necessary in patients with renal insufficiency. Adverse events, including fluid retention and hepatic dysfunction, may limit the utility of troglitazone in some clinical situations.

CONCLUSION

Both in monotherapy and in combination with sulfonylureas, insulin, or metformin, troglitazone has proved to be an effective agent for the treatment of type 2 diabetes mellitus.

Troglitazone: review and assessment of its role in the treatment of patients with impaired glucose tolerance and diabetes mellitus

OBJECTIVE

To introduce troglitazone (CS-045, Rezulin), a new oral antidiabetic agent and discuss its pharmacology, therapeutics, pharmacokinetics, dosing guidelines, adverse effects, drug interactions, and clinical efficacy.

DATA SOURCES

A MEDLINE database search was completed to identify relevant articles including reviews, recent studies and abstracts, and data from Parke-Davis.

STUDY SELECTION

Due to the small number of published human studies available, some data are derived from animal studies and abstracts of human studies. Studies and abstracts chosen summarize the clinical action of troglitazone in healthy volunteers, in subjects with impaired glucose tolerance, and in patients with diabetes mellitus. Three of the six published human studies used subjects in a placebo-controlled, multicenter, randomized environment (type 2 diabetic patients or obese subjects with insulin resistance).

DATA EXTRACTION

All clinical trials available, including unpublished reports, were reviewed.

DATA SYNTHESIS

Troglitazone is the first member of a new class of medications, the thiazolidinediones, to be approved for clinical use. Troglitazone increases insulin sensitivity in skeletal muscle and in hepatic and adipose tissue. It has been shown to decrease hepatic glucose output while having no effect on stimulating insulin secretion from the pancreatic beta-cells. Its metabolic effects decrease fasting and postprandial hyperglycemia, insulin concentrations, and triglyceride concentrations, while increasing high-density lipoprotein concentrations. There is some evidence, based on short-term trials, that troglitazone causes only minimal decreases in glycosylated hemoglobin A1C (HbA1C) concentrations. Data suggest that troglitazone decreases impaired glucose tolerance in nondiabetic obese subjects and leads to a reduction in both systolic and diastolic blood pressure in hypertensive type 2 diabetes mellitus patients. Troglitazone has a mild adverse effect profile, with rare instances of abnormal liver function tests.

CONCLUSIONS

Troglitazone appears to be a safe, effective, and useful new agent in the treatment of insulin-requiring type 2 diabetes mellitus patients, although its HbA1C-lowering effects have been minimal in short-term trials, and its insulin dosage-reduction activity remains unclear. The Food and Drug Administration has also approved its use as monotherapy and in combination with sulfonylureas for patients with type 2 diabetes. It may have use in the treatment of patients with impaired glucose tolerance, but more clinical experience is needed before definitive conclusions can be made. The role of troglitazone therapy in diabetes mellitus and impaired glucose intolerance will continue to evolve as the results of studies and our clinical experience with this agent become available.

Insulin resistance: current concepts

Insulin sensitivity varies greatly within the general population; factors contributing to this variability include genetic pre-disposition, obesity, unfavorable body fat distribution, and lack of physical activity. Impaired insulin sensitivity may lead to impaired glucose tolerance and, even in individuals with modest insulin deficiency, to the development of type 2 diabetes mellitus. Of equal concern in patients with impaired insulin sensitivity is the development of the insulin resistance syndrome, in which hypertension, dyslipidemia, and impaired glucose tolerance form a cluster of risk factors for cardiovascular disease. Treatment of insulin resistance includes metformin and the thiazolidinedione troglitazone. Both drugs have been shown to be effective in the treatment of insulin resistance, one of the central abnormalities in type 2 diabetes mellitus. The purpose of this study was to review the current understanding of insulin resistance and its implications for the treatment of type 2 diabetes mellitus. To do this, a MEDLINE search of the clinical literature was conducted and the content analyzed.

Determinants of coronary vascular disease in patients with type II diabetes mellitus and their therapeutic implications

Cardiovascular morbidity and mortality are increased 4- to 6-fold in patients with type II diabetes. The high prevalence is multifactorial and reflects in part the adverse influence of covariate, cardiac risk factors such as hypertension and hyperlipidemia. Type II diabetes is characterized by insulin resistance, hyperinsulinemia, and altered carbohydrate and lipid metabolism resulting in hyperglycemia, increased concentrations in blood of very low-density and low-density lipoproteins, and decreased blood high-density lipoproteins. Abnormalities seen predispose to vasculopathy through lipid deposition into vessel walls associated with monocyte infiltration, vascular smooth muscle cell proliferation, arterial mural fibrosis, and thrombosis. Conventional therapy for cardiovascular disease such as angioplasty and bypass surgery are of only limited efficacy. Thus, retardation of progression of atherosclerosis is essential. In addition to focusing on co-existent cardiac risk factors such as hypertension, therapy for patients with type II diabetes should reduce or reverse insulin resistance, improve metabolic control, and, ideally, do so without exacerbating hyperinsulinemia. Diet and exercise are central, and novel orally active hyperglycemic agents such as the biguanides and the thiazolidinediones that sensitize diverse tissues to insulin offer particular promise.

Inhibition of KATP channel activity by troglitazone in CRI-G1 insulin-secreting cells

Patch-clamp recording techniques were used to examine the effect of troglitazone on KATP channel activity in Cambridge rat insulinoma-G1 (CRI-G1) insulin-secreting cells. In both inside-out and outside-out patch recordings, bath application of troglitazone reduced KATP channel activity. This inhibition was independent of the membrane voltage and was poorly reversible. In whole-cell studies, troglitazone inhibited KATP channel currents with an IC50 of 697 +/- 92 nM and an associated Hill coefficient of 1.2 +/- 0.2. In current clamp recordings 10 microM troglitazone depolarised the CRI-G1 cell membrane by 36.8 +/- 3.9 mV with a concomitant decrease in membrane conductance. However, in contrast to the rapid depolarisation produced by tolbutamide, the effects of troglitazone developed more slowly, usually taking 15-20 min to develop.