Effect of thiazolidinediones on high-density lipoprotein subfractions

Lipoprotein subfractions in metabolic syndrome and obesity: clinical significance and therapeutic approaches

Small, dense low density lipoprotein (sdLDL) represents an emerging cardiovascular risk factor, since these particles can be associated with cardiovascular disease (CVD) independently of established risk factors, including plasma lipids. Obese subjects frequently have atherogenic dyslipidaemia, including elevated sdLDL levels, in addition to elevated triglycerides (TG), very low density lipoprotein (VLDL) and apolipoprotein-B, as well as decreased high density lipoprotein cholesterol (HDL-C) levels. Obesity-related co-morbidities, such as metabolic syndrome (MetS) are also characterized by dyslipidaemia. Therefore, agents that favourably modulate LDL subclasses may be of clinical value in these subjects. Statins are the lipid-lowering drug of choice. Also, anti-obesity and lipid lowering drugs other than statins could be useful in these patients. However, the effects of anti-obesity drugs on CVD risk factors remain unclear. We review the clinical significance of sdLDL in being overweight and obesity, as well as the efficacy of anti-obesity drugs on LDL subfractions in these individuals; a short comment on HDL subclasses is also included. Our literature search was based on PubMed and Scopus listings. Further research is required to fully explore both the significance of sdLDL and the efficacy of anti-obesity drugs on LDL subfractions in being overweight, obesity and MetS. Improving the lipoprotein profile in these patients may represent an efficient approach for reducing cardiovascular risk.

Lipoprotein subfractions in metabolic syndrome and obesity: clinical significance and therapeutic approaches

Small, dense low density lipoprotein (sdLDL) represents an emerging cardiovascular risk factor, since these particles can be associated with cardiovascular disease (CVD) independently of established risk factors, including plasma lipids. Obese subjects frequently have atherogenic dyslipidaemia, including elevated sdLDL levels, in addition to elevated triglycerides (TG), very low density lipoprotein (VLDL) and apolipoprotein-B, as well as decreased high density lipoprotein cholesterol (HDL-C) levels. Obesity-related co-morbidities, such as metabolic syndrome (MetS) are also characterized by dyslipidaemia. Therefore, agents that favourably modulate LDL subclasses may be of clinical value in these subjects. Statins are the lipid-lowering drug of choice. Also, anti-obesity and lipid lowering drugs other than statins could be useful in these patients. However, the effects of anti-obesity drugs on CVD risk factors remain unclear. We review the clinical significance of sdLDL in being overweight and obesity, as well as the efficacy of anti-obesity drugs on LDL subfractions in these individuals; a short comment on HDL subclasses is also included. Our literature search was based on PubMed and Scopus listings. Further research is required to fully explore both the significance of sdLDL and the efficacy of anti-obesity drugs on LDL subfractions in being overweight, obesity and MetS. Improving the lipoprotein profile in these patients may represent an efficient approach for reducing cardiovascular risk.

Effect of pioglitazone and its combination with statins in coronary artery disease patients with hyperinsulinemia

The objective of the study was to demonstrate the effect of pioglitazone and pioglitazone in combination with statin on East Indian patients with hyperinsulinemia and hyperlipidemia. It was a randomized, placebo-controlled, double-blind study with a parallel-group design comprising 83 patients. Patients of either sex with cardiac complications, including hyperlipidemia and (or) diabetes mellitus with or without hyperinsulinemia, were enrolled. Patients over 70 years of age, with renal or hepatic failure, or with severe diabetes mellitus (total glucose >400 mg/dL) were excluded from the study. Enrolled patients were randomly assigned to 4 groups that received placebo, pioglitazone, atorvastatin, or both. Blood samples were collected before and after treatment for analysis of serum glucose, insulin, lipid profile, apolipoprotein (apo) A1, apo B, and fibrinogen. Data were compared with that of patients with normal insulin or hyperinsulinemia. The patients with hyperinsulinemia receiving only pioglitazone showed a significant decrease in insulin levels compared with those with normal insulin levels. These patients also showed a significant increase in HDL levels. However, no significant change was observed in patients treated with both atorvastatin and pioglitazone. Pioglitazone was also found to increase significantly the apo A1 levels in patients with hyperinsulinemia, but there was no significant increase in patients given both atorvastatin and pioglitazone. Our data suggests that pioglitazone should be given preferably to the patients with hyperinsulinemia and statin should not be coadministered.

Impact of thiazolidenediones on serum lipoprotein levels

The thiazolidinediones, acting through peroxisome proliferator-activated receptor chi (PPARchi), affect multiple areas of metabolism. Of increasing importance is the recognition that these agents affect lipoprotein metabolism and cause changes in serum lipid and lipoprotein levels. All three thiazolidinediones, including troglitazone (which was withdrawn in the year 2000), rosiglitazone, and pioglitazone, tend to increase high-density lipoprotein (HDL) cholesterol, increase the size/decrease the density of low-density lipoprotein (LDL) particles, and raise the level of lipoprotein(a). In addition, troglitazone and pioglitazone, but not rosiglitazone, lower triglyceride levels modestly, thereby further contributing to increases in LDL and HDL size. The mechanism for these effects is still being clarified, but may involve enhancement of triglyceride clearance (in the case of pioglitazone), alteration of apolipoprotein C-III levels, reduction of hepatic lipase, and increase in ATP binding cassette A1 (ABCA1) activity. The clinical implications of these effects need further exploration.

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.

Rosiglitazone Evaluated for Cardiac Outcomes and Regulation of Glycaemia in Diabetes (RECORD): study design and protocol

AIMS/HYPOTHESIS

Studies suggest that in addition to blood glucose concentrations, thiazolidinediones such as rosiglitazone improve some cardiovascular (CV) risk factors and surrogate markers, that are abnormal in type 2 diabetes. However, fluid retention might lead to cardiac failure in a minority of people. The aim of the Rosiglitazone Evaluated for Cardiac Outcomes and Regulation of Glycaemia in Diabetes (RECORD) study is to evaluate the long-term impact of these effects on CV outcomes, as well as on long-term glycaemic control, in people with type 2 diabetes.

MATERIALS AND METHODS

RECORD is a 6-year, randomised, open-label study in type 2 diabetic patients with inadequate blood glucose control (HbA1c 7.1-9.0%) on metformin or sulphonylurea alone. The study is being performed in 327 centres in Europe and Australasia. After a 4-week run-in, participants were randomised by current treatment stratum to add-on rosiglitazone, metformin or sulphonylurea, with dose titration to a target HbA1c of < or = 7.0%. If confirmed HbA1c rises to > or = 8.5%, either a third glucose-lowering drug is added (rosiglitazone-treated group) or insulin is started (non-rosiglitazone group). The same criterion for failure of triple oral drug therapy in the rosiglitazone-treated group is used for starting insulin in this group. The primary endpoint is the time to first CV hospitalisation or death, blindly adjudicated by a central endpoints committee. The study aim is to evaluate non-inferiority of the rosiglitazone group vs the non-rosiglitazone group with respect to CV outcomes. Safety, tolerability and study conduct are monitored by an independent board. All CV endpoint and safety data are held and analysed by a clinical trials organisation, and are not available to the study investigators while data collection is open.

RESULTS

Over a 2-year period a total of 7,428 people were screened in 25 countries. Of these, 4,458 were randomised; 2,228 on background metformin, 2,230 on background sulphonylurea. Approximately half of the participants are male (52%) and almost all are Caucasian (99%).

CONCLUSIONS/INTERPRETATION

The RECORD study should provide robust data on the extent to which rosiglitazone, in combination with metformin or sulphonylurea therapy, affects CV outcomes and progression of diabetes in the long term.

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.

Mechanisms mediating insulin resistance in transgenic mice overexpressing mouse apolipoprotein A-II

We previously demonstrated that transgenic mice overexpressing mouse apolipoprotein A-II (apoA-II) exhibit several traits associated with the insulin resistance (IR) syndrome, including increased atherosclerosis, hypertriglyceridemia, obesity, and IR. The skeletal muscle appeared to be the insulin-resistant tissue in the apoA-II transgenic mice. We now demonstrate a decrease in FA oxidation in skeletal muscle of apoA-II transgenic mice, consistent with reports that decreased skeletal muscle FA oxidation is associated with increased skeletal muscle triglyceride accumulation, skeletal muscle IR, and obesity. The decrease in FA oxidation is not due to decreased carnitine palmitoyltransferase 1 activity, because oxidation of palmitate and octanoate were similarly decreased. Quantitative RT-PCR analysis of gene expression demonstrated that the decrease in FA oxidation may be explained by a decrease in medium chain acyl-CoA dehydrogenase. We previously demonstrated that HDLs from apoA-II transgenic mice exhibit reduced binding to CD36, a scavenger receptor involved in FA metabolism. However, studies of combined apoA-II transgenic and CD36 knockout mice suggest that the major effects of apoA-II are independent of CD36. Rosiglitazone treatment significantly ameliorated IR in the apoA-II transgenic mice, suggesting that the underlying mechanisms of IR in this animal model may share common features with certain types of human IR.

The effects of oral anti-hyperglycaemic medications on serum lipid profiles in patients with type 2 diabetes

AIM

Patients with type 2 diabetes often have dyslipidaemia, putting them at risk of cardiovascular disease, and are frequently treated with oral anti-hyperglycaemic medications (OAMs). This review compares the effects of OAMs on serum lipids [total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), triglycerides (TGs) and free fatty acids (FFAs)] in patients with type 2 diabetes.

METHODS

medline was searched for entries indexed from January 1966 to November 2002; search terms included the names of OAMs and serum lipids, limited to English language and human subjects. We selected clinical studies in type 2 diabetes of OAM monotherapy that included serum lipid data, treated all patients in a treatment group with the same drug, used therapeutic OAM doses not higher than the maximum recommended in the USA, compared therapy with baseline or placebo and specified statistical tests used. One unblinded investigator selected studies for inclusion. Data reported include number of patients, study length, OAM dose, serum lipid data at baseline and endpoint, p-values and statistical tests.

RESULTS

Data on the serum lipid effects of sulphonylureas, repaglinide, nateglinide and miglitol were inconclusive. Acarbose increased HDL-C and decreased LDL-C and voglibose reduced TC. Metformin at higher doses reduced TC; data on its effects on other lipids were inconclusive. Rosiglitazone increased LDL-C, HDL-C and TC and reduced FFAs but had no effect on TGs. Pioglitazone increased HDL-C and reduced TGs and FFAs but did not affect LDL-C or TC.

CONCLUSIONS

Lipid changes as a result of improved glycaemic control are not uniform findings associated with anti-diabetic therapy. Only metformin, acarbose, voglibose, rosiglitazone and pioglitazone had significant effects on the lipid profile. These effects should be considered when selecting OAMs for patients with type 2 diabetes.

Peroxisome Proliferator-Activated Receptor-γ Agonist Increases Both Low-Density Lipoprotein Cholesterol Particle Size and Small High-Density Lipoprotein Cholesterol in Patients with Type 2 Diabetes Independent of Diabetic Control

OBJECTIVE

To ascertain whether troglitazone, independent of control of diabetes, increases low-density lipoprotein (LDL) particle size.

METHODS

We administered 600 mg of troglitazone (a peroxisome proliferator-activated receptor-gamma agonist) daily for 8 weeks to 10 patients with type 2 diabetes (8 of whom completed the study). Then troglitazone therapy was discontinued, and alternative medication for diabetic control was used for another 4 weeks. The LDL, very-low-density lipoprotein (VLDL), and high-density lipoprotein (HDL) concentrations and subpopulations, as well as blood glucose and hemoglobin A1c (HbA1c), were determined at weeks 0, 4, 8, and 12 and analyzed statistically.

RESULTS

Small, dense LDL cholesterol is commonly seen in patients with diabetes and is thought to be associated with an increased risk for coronary artery disease. After both 4 and 8 weeks of troglitazone therapy, control of diabetes was significantly improved (mean HbA1c values at baseline, week 4, and week 8 were 8.0 +/- 0.7%, 7.4 +/- 0.5%, and 7.0 +/- 0.7%, respectively; P<0.05). HbA1c (6.5 +/- 0.6% at 12 weeks) and blood glucose levels (126 +/- 19 mg/dL at 8 weeks versus 145 +/- 9 mg/dL at 12 weeks) were not significantly different 4 weeks after troglitazone therapy was discontinued. Troglitazone treatment increased the large LDL particle at 4 and 8 weeks, a change that significantly (P<0.05) enlarged the LDL particle size (20.5 +/- 0.3 nm, 21.2 +/- 0.3 nm, and 21.3 +/- 0.2 nm at baseline, week 4, and week 8, respectively). After 8 weeks of troglitazone therapy, VLDL triglycerides were reduced (195 +/- 37 mg/dL versus 136 +/- 28 mg/dL; P<0.05) and HDL was increased (31.6 +/- 2.4 mg/dL versus 35.5 +/- 2.9 mg/dL; P<0.05). This greater HDL value was due to an increase in the small HDL particles. A decrease in the larger VLDL particles (V5 and V6) resulted in a reduction in the mean VLDL particle size (59 +/- 3 nm versus 46 +/- 2 nm; P<0.05). Despite the fact that control of diabetes remained significantly improved after troglitazone therapy was discontinued, the LDL particle size decreased to the baseline value. This change was due to a reduction in the large LDL cholesterol particle (L3).

CONCLUSION

This study shows that troglitazone therapy increases LDL particle size, reduces VLDL particle size, and increases small HDL particles. These changes may lower the risk for coronary artery disease.