Effect of troglitazone in insulin-treated patients with type II diabetes mellitus. Troglitazone and Exogenous Insulin Study Group

Thiazolidinediones: a new class of antidiabetic drugs

Thiazolidinediones (TZDs) are a new class of oral antidiabetic agents. They selectively enhance or partially mimic certain actions of insulin, causing a slowly generated antihyperglycaemic effect in Type 2 (noninsulin dependent) diabetic patients. This is often accompanied by a reduction in circulating concentrations of insulin, triglycerides and nonesterified fatty acids. TZDs act additively with other types of oral antidiabetic agents (suphonylureas, metformin and acarbose) and reduce the insulin dosage required in insulin-treated patients. The glucose-lowering effect of TZDs is attributed to increased peripheral glucose disposal and decreased hepatic glucose output. This is achieved substantively by the activation of a specific nuclear receptor - the peroxisome proliferator-activated receptor-gamma (PPARgamma), which increases transcription of certain insulin-sensitive genes. To date one TZD, troglitazone, has been introduced into clinical use (in Japan, USA and UK in 1997). This was suspended after 2 months in the UK pending further investigation of adverse effects on liver function. TZDs have been shown to improve insulin sensitivity in a range of insulin-resistant states including obesity, impaired glucose tolerance (IGT) and polycystic ovary syndrome (PCOS). In Type 2 diabetes, the TZDs offer a new type of oral therapy to reduce insulin resistance and assist glycaemic control.

Troglitazone in combination with sulphonylurea improves glycaemic control in Type 2 diabetic patients inadequately controlled by sulphonylurea therapy alone. Troglitazone Study Group

AIM

The aim of this study was to investigate the effectiveness of troglitazone (a peroxisome proliferator-activated receptor-gamma agonist developed primarily for the treatment of Type 2 diabetes mellitus (DM)), 100 or 200mg/day, in terms of glycaemic control, lipid profile and tolerability, when given in addition to existing sulphonylurea therapy.

METHODS

A 16-week, randomized, parallel-group placebo-controlled trial in 259 Type 2 diabetic patients already on sulphonylurea therapy.

RESULTS

At week 16, adjusted geometric mean HbA1c with troglitazone 100mg (7.7%; P=0.023) and 200mg (7.4%; P<0.001) was lower with sulphonylurea alone (8.2%). At all weeks, adjusted geometric mean fasting serum glucose levels were lower in both troglitazone groups, compared with sulphonylurea alone (P=0.007 to P<0.001). At week 16, both troglitazone groups showed reductions in immune reactive insulin compared with sulphonylurea alone (200mg, 13%; P=0.032: 100mg, 5%; NS). Troglitazone reduced serum levels of nonesterified fatty acids at week 16 (100 g, 12%; P=0.042) and at all weeks (200mg, 17-24%; P=0.014 to P<0.001). The incidence of drug-related adverse events was similar in all groups (23-24% of patients). There was no apparent association between hypoglycaemia and the addition of troglitazone to sulphonylurea therapy.

CONCLUSIONS

Troglitazone 100 or 200 mg added to usual sulphonylurea therapy in patients with Type 2 DM is associated with a significant improvement in glycaemic control, without altering the adverse-event profile of the sulphonylurea.

Improving the adverse cardiovascular prognosis of type 2 diabetes

Approximately 80% of all patients with diabetes die of cardiovascular disease. The traditional management of type 2 diabetes has been ineffective in altering this dismal prognosis. Insulin resistance is the fundamental defect of type 2 diabetes. Insulin resistance often leads to hyperinsulinemia, which is associated with hypertension, atherogenic dyslipidemia, left ventricular hypertrophy, impaired fibrinolysis, visceral obesity, and sedentary lifestyle. Although all these conditions are associated with atherosclerosis and adverse cardiovascular events, the therapeutic efforts in patients with diabetes have focused predominantly on normalizing glucose levels. Improved insulin sensitivity through lifestyle modifications or pharmacologic therapy (troglitazone and metformin) will lower both insulin and glucose levels as well as diminish dyslipidemia and hypertension. In contrast, sulfonylurea agents lower glucose by increasing insulin levels and may increase the risk of cardiovascular events. Therapy including aspirin, lipid agents (for example, statins), angiotensin-converting enzyme inhibitors, beta-adrenergic blockers, postmenopausal estrogen replacement, and vitamin E should be considered for patients with type 2 diabetes. In most patients with diabetes who have multivessel coronary artery disease, coronary artery bypass grafting is superior to coronary angioplasty for improving long-term cardiovascular prognosis. This superiority is mediated in part by the use of a left internal mammary graft to the left anterior descending coronary artery. Urgent coronary angioplasty or thrombolytic therapy should be considered for all patients with diabetes who have acute myocardial infarction.

Acute troglitazone action in isolated perfused rat liver

1. The thiazolidinedione compound, troglitazone, enhances insulin action and reduces plasma glucose concentrations when administered chronically to type 2 diabetic patients. 2. To analyse to what extent thiazolidinediones interfere with liver function, we examined the acute actions of troglitazone (0.61 and 3.15 microM) on hepatic glucose and lactate fluxes, bile secretion, and portal pressure under basal, insulin- and/or glucagon-stimulated conditions in isolated perfused rat livers. 3. During BSA-free perfusion, high dose troglitazone increased basal (P < 0.01), but inhibited glucagon-stimulated incremental glucose production by approximately 75% (10.0 +/- 2.5 vs control: 40.0 +/- 7.2 micromol g liver(-1), P < 0.01). In parallel, incremental lactate release rose approximately 6 fold (13.1 +/- 5.9 vs control: 2.2 +/- 0.8 mmol g liver(-1), P < 0.05), while bile secretion declined by approximately 67% [0.23 +/- 0.02 vs control: 0.70 +/- 0.05 mg g liver(-1) min(-1)), P < 0.001]. Low dose troglitazone infusion did not enhance the inhibitory effect of insulin on glucagon-stimulated glucose production, but rapidly increased lactate release (P < 0.0005) and portal venous pressure (+0.17 +/- 0.07 vs +0.54 +/- 0.07 cm buffer height, P < 0.0001). 4. These results indicate that troglitazone exerts both insulin-like and non-insulin-like hepatic effects, which are blunted by addition of albumin, possibly due to troglitazone binding.

Peroxisome proliferator-activated receptor gamma activators inhibit gene expression and migration in human vascular smooth muscle cells

Migration of vascular smooth muscle cells (VSMCs) plays an important role in atherogenesis and restenosis after arterial interventions. The expression of matrix metalloproteinases (MMPs), particularly MMP-9, contributes to VSMC migration. This process requires degradation of basal laminae and other components of the arterial extracellular matrix. Peroxisome proliferator-activated receptors (PPARs), members of the nuclear receptor family, regulate gene expression after activation by various ligands. Recent studies have suggested opposing effects of PPAR gamma (PPARgamma) activation on atherogenesis. The present study tested the hypotheses that human VSMCs express PPAR alpha (PPARalpha) and PPARgamma and that PPAR agonists in VSMCs modulate MMP-9 expression and activity, as well as VSMC migration. Human VSMCs expressed PPARalpha and PPARgamma mRNA and protein. Treatment of VSMCs with the PPARgamma ligands troglitazone and the naturally occurring 15-deoxy-Delta12, 14-prostaglandin J2 (15d-PGJ2) decreased phorbol 12-myristate 13-acetate-induced MMP-9 mRNA and protein levels, as well as MMP-9 gelatinolytic activity in the supernatants in a concentration-dependent manner. Six different PPARalpha activators lacked such effects. Addition of prostaglandin F2alpha, known to limit PPARgamma activity, diminished the MMP-9 inhibition seen with either troglitazone or 15d-PGJ2, further implicating PPARgamma in these effects. Finally, troglitazone and 15d-PGJ2 inhibited the platelet-derived growth factor-BB-induced migration of VSMCs in vitro in a concentration-dependent manner. PPARgamma activation may regulate VSMC migration and expression and activity of MMP-9. Thus, PPARgamma activation in VSMCs, via the antidiabetic agent troglitazone or naturally occurring ligands, may act to counterbalance other potentially proatherosclerotic PPARgamma effects.

Obesity associated with a mutation in a genetic regulator of adipocyte differentiation

BACKGROUND

There is increasing evidence of genetic factors leading to obesity, but the exact genes involved have not been defined. Peroxisome-proliferator-activated receptor gamma2 (PPARgamma2) is a transcription factor that has a key role in adipocyte differentiation, and therefore mutations of the gene for this factor might predispose people to obesity.

METHODS

We studied 358 unrelated German subjects, including 121 obese subjects (defined as those with a body-mass index [the weight in kilograms divided by the square of the height in meters] of more than 29). We evaluated these subjects for mutations in the gene for PPARgamma2 at or near a site of serine phosphorylation at position 114 that negatively regulates the transcriptional activity of the protein, using a polymerase-chain-reaction-based assay coupled with specific endonuclease digestion. The activity of the mutation identified was analyzed by retroviral transfection and overexpression in murine fibroblasts.

RESULTS

Four of the 121 obese subjects had a missense mutation in the gene for PPARgamma2 that resulted in the conversion of proline to glutamine at position 115, as compared with none of the 237 subjects of normal weight (P=0.01). All the subjects with the mutant allele were markedly obese, with body-mass-index values ranging from 37.9 to 47.3, as compared with a mean of 33.6 in the other obese subjects. Overexpression of the mutant gene in murine fibroblasts led to the production of a protein in which the phosphorylation of serine at position 114 was defective, as well as to accelerated differentiation of the cells into adipocytes and greater cellular accumulation of triglyceride than with the wild-type PPARgamma2. These effects were similar to those of an in vitro mutation created directly at the Ser114 phosphorylation site.

CONCLUSIONS

A Pro115Gln mutation in PPARgamma2 accelerates the differentiation of adipocytes and may cause obesity.

Transcription-factor-modulating agents: precision and selectivity in drug design

Transcription factors play an important role in the long-term regulation of cell growth, differentiation and responses to environmental cues. There is growing evidence that these proteins are closely associated with control at the genetic level of the development and maintenance of the diseased state, and might therefore provide selective targets for novel pharmaceutical intervention. The vast array of information available on the three-dimensional structure of transcription factors and the intricate molecular machineries that fine-tune their activity offer opportunities for embarking on the rational design of drugs directed against specific transcription factors, thus producing potent new agents that modulate their function in a plethora of clinically important situations.

Macrophages in human atheroma contain PPARgamma: differentiation-dependent peroxisomal proliferator-activated receptor gamma(PPARgamma) expression and reduction of MMP-9 activity through PPARgamma activation in mononuclear phagocytes in vitro

Mononuclear phagocytes play an important role in atherosclerosis and its sequela plaque rupture in part by their secretion of matrix metalloproteinases (MMPs), including MMP-9. Peroxisomal proliferator-activated receptor gamma (PPARgamma), a transcription factor in the nuclear receptor superfamily, regulates gene expression in response to various activators, including 15-deoxy-delta12,14-prostaglandin J2 and the antidiabetic agent troglitazone. The role of PPARgamma in human atherosclerosis is unexplored. We report here that monocytes/macrophages in human atherosclerotic lesions (n = 12) express immunostainable PPARgamma. Normal artery specimens (n = 6) reveal minimal immunoreactive PPARgamma. Human monocytes and monocyte-derived macrophages cultured for 6 days in 5% human serum expressed PPARgamma mRNA and protein by reverse transcription-polymerase chain reaction and Western blotting, respectively. In addition, PPARgamma mRNA expression in U937 cells increased during phorbol 12-myristate 13 acetate-induced differentiation. Stimulation of PPARgamma with troglitazone or 15-deoxy-delta12,14-prostaglandin J2 in human monocyte-derived macrophages inhibited MMP-9 gelatinolytic activity in a concentration-dependent fashion as revealed by zymography. This inhibition correlates with decreased MMP-9 secretion as determined by Western blotting. Thus, PPARgamma is present in macrophages in human atherosclerotic lesions and may regulate expression and activity of MMP-9, an enzyme implicated in plaque rupture. PPARgamma is likely to be an important regulator of monocyte/macrophage function with relevance for human atherosclerotic disease.