Differentiating members of the thiazolidinedione class: a focus on safety

Thiazolidinediones decrease vascular endothelial growth factor (VEGF) production by human luteinized granulosa cells in vitro

OBJECTIVE

To determine the effect of thiazolidenedione derivatives (TZDs) on vascular endothelial growth factor (VEGF) production by human luteinized granulosa cells and the morphologic development of murine embryos.

DESIGN

Prospective, experimental, in vitro and in vivo study.

SETTING

Research laboratory.

PATIENT(S)

Follicular aspirates from 10 women undergoing oocyte retrieval.

INTERVENTION(S)

Isolated human granulosa cells were treated with a dimethyl sulfoxide (DMSO) control or ciglitazone, in the presence and absence of an hCG stimulus. Embryos extracted from superovulated B6C3F1 female mice were cultured in the presence of DMSO or pioglitazone.

MAIN OUTCOME MEASURE(S)

Vascular endothelial growth factor concentrations at 24 and 48 hours. Morphologic development of murine embryos at 96 hours.

RESULT(S)

Following an hCG stimulus, treatment with 20 microM or 40 microM ciglitazone decreased VEGF production in a statistically significant manner at both time intervals. Blastocyst development at 96 hours did not significantly differ between untreated zygotes and those treated with pioglitazone.

CONCLUSION(S)

Ciglitazone significantly decreased VEGF production by human granulosa cells in an in vitro model. Pioglitazone did not adversely impact the development of cultured murine embryos. Although mechanistic evidence is not provided, the pivotal role of VEGF in ovarian hyperstimulation syndrome prompts investigation of TZDs as a novel treatment for this condition.

The role of insulin-sensitizing agents in the treatment of polycystic ovary syndrome

Polycystic ovary syndrome (PCOS) represents a heterogeneous spectrum of disorders, mainly characterized by chronic oligoanovulation and hyperandrogenism. Although not included in the diagnostic criteria, insulin resistance is recognized as a fundamental pathogenetic factor of the syndrome. Thus, the use of insulin-sensitizing drugs, such as metformin and thiazolidinediones, has been proposed for PCOS treatment. These agents are unique because they exert both metabolic and endocrine/ovarian beneficial effects. In this review the results of up-to-date clinical studies and meta-analyses on the possible gynaecological actions of insulin sensitizers are discussed. It has been shown that, as well as favourable metabolic influences, such as improvement in glucose, lipid and proinflammatory profiles, these agents also exert beneficial endocrine and ovarian effects, including amelioration of reproductive abnormalities, restoration of ovulation and menstrual cycles, increase in pregnancy rates and reduction of androgen production. Therefore, current data support the use of insulin sensitizers, along with lifestyle measures and/or other agents, in women with PCOS, especially in the presence of insulin- or clomifene-resistance.

Pioglitazone enhances collateral blood flow in ischemic hindlimb of diabetic mice through an Akt-dependent VEGF-mediated mechanism, regardless of PPARgamma stimulation

Background

Type 2 diabetes mellitus (T2DM) is commonly associated with both microvascular and macrovascular complications and a strong correlation exists between glycaemic control and the incidence and progression of vascular complications. Pioglitazone, a Peroxisome proliferator-activated receptor-γ (PPARγ) ligand indicated for therapy of type T2DM, induces vascular effects that seem to occur independently of glucose lowering.

Methods

By using a hindlimb ischemia murine model, in this study we have found that pioglitazone restores the blood flow recovery and capillary density in ischemic muscle of diabetic mice and that this process is associated with increased expression of Vascular Endothelial Growth Factor (VEGF). Importantly, these beneficial effects are abrogated when endogenous Akt is inhibited; furthermore, the direct activation of PPARγ, with its selective agonist GW1929, does not restore blood flow recovery and capillary density. Finally, an important collateral vessel growth is obtained with combined treatment with pioglitazone and selective PPARγ inhibitor GW9662.

Conclusion

These data demonstrate that Akt-VEGF pathway is essential for ischemia-induced angiogenic effect of pioglitazone and that pioglitazone exerts this effect via a PPARγ independent manner.

A cardiologic approach to non-insulin antidiabetic pharmacotherapy in patients with heart disease

Classical non-insulin antihyperglycemic drugs currently approved for the treatment of type 2 diabetes mellitus (T2DM) comprise five groups: biguanides, sulfonylureas, meglitinides, glitazones and alpha-glucosidase inhibitors. Novel compounds are represented by the incretin mimetic drugs like glucagon like peptide-1 (GLP-1), the dipeptidyl peptidase 4 (DPP-4) inhibitors, dual peroxisome proliferator-activated receptors (PPAR) agonists (glitazars) and amylin mimetic drugs. We review the cardiovascular effects of these drugs in an attempt to improve knowledge regarding their potential risks when treating T2DM in cardiac patients. Metformin may lead to lethal lactic acidosis, especially in patients with clinical conditions that predispose to this complication, such as recent myocardial infarction, heart or renal failure. Sulfonylureas exert their effect by closing the ATP-dependent potassium channels. This prevents the opening of these channels during myocardial ischemia, impeding the necessary hyperpolarization that protects the cell. The combined sulfonylurea/metformin therapy reveals additive effects on mortality in patients with coronary artery disease (CAD). Meglitinides effects are similar to those of sulfonylureas, due to their almost analogous mechanism of action. Glitazones lower leptin levels, leading to weight gain and are unsafe in NYHA class III or IV. The long-term effects of alpha-glucosidase inhibitors on morbidity and mortality rates is yet unknown. The incretin GLP-1 is associated with reductions in body weight and appears to present positive inotropic effects. DPP-4 inhibitors influences on the cardiovascular system seem to be neutral and patients do not gain weight. The future of glitazars is presently uncertain following concerns about their safety. The amylin mimetic drug paramlintide, while a satisfactory adjuvant medication in insulin-dependent diabetes, is unlikely to play a major role in the management of T2DM. Summarizing the present information it can be stated that 1. Four out the five classical oral antidiabetic drug groups present proven or potential cardiac hazards; 2. These hazards are not mere 'side effects', but biochemical phenomena which are deeply rooted in the drugs' mechanism of action; 3. Current data indicate that the combined glibenclamide/metformin therapy seems to present special risk and should be avoided in the long-term management of T2DM with proven CAD; 4. Glitazones should be avoided in patients with overt heart failure; 5, The novel incretin mimetic drugs and DPP-4 inhibitors--while usually inadequate as monotherapy--appear to be satisfactory adjuvant drugs due to the lack of known undesirable cardiovascular effects; 6. Customized antihyperglycemic pharmacological approaches should be implemented for the achievement of optimal treatment of T2DM patients with heart disease. In this context, it should be carefully taken into consideration whether the leading clinical status is CAD or heart failure.

Rosiglitazone-induced immune thrombocytopenia

Rosiglitazone is one of the members in the thiazolidinedione (TZD) class of anti-diabetic agents that have proven efficacy in the treatment of patients with type 2 diabetes. We studied serum from a patient who developed acute, severe thrombocytopenia after exposure to rosiglitazone maleate (Avandia) and proposed the mechanisms for rosiglitazone-induced thrombocytopenia. Tested by flow cytometry, the patient's serum was positive for rosiglitazone-induced antibody with the binding ratio of 5.93 (mean fluorescence intensity, MFI) in the presence of the patient's serum and rosiglitazone in a final concentration of 0.53 mmol/l. The antibody was found to bind both glycoprotein (GP) IIb-IIIa complex and GP Ib/IX complex by MAIPA assay using five different monoclonal antibodies (mAbs) against GP complexes Ib/IX, GPIIb/IIIa or GPIa/IIa. Immunoprecipitation studies showed that both GPIIb/IIIa and GP Ib/IX complex were precipitated by antibody in the presence, but not in the absence of rosiglitazone. These findings provide evidence that immune thrombocytopenia can be caused by sensitivity to the antidiabetic agent rosiglitazone maleate. This report documents the first case of rosiglitazone-induced immune thrombocytopenia.

How safe is the use of thiazolidinediones in clinical practice?

BACKGROUND

Thiazolidinediones (TZDs) are widely used antidiabetic drugs with proven efficacy regarding mainly surrogate markers of diabetes management. However, efficacy on surrogate markers may not always translate into benefits in clinical outcomes. Thiazolidinediones are usually well tolerated; however, their use may be associated with several adverse effects. The first TZD, troglitazone, was withdrawn from the market owing to serious hepatotoxicity. However, this does not seem to be the case with newer TZDs.

OBJECTIVE

The aim of the present review is to discuss the safety profile of this drug class.

METHODS

We searched PubMed up to July 2008 using relevant keywords.

CONCLUSIONS

Common side effects associated with TZDs include edema, weight gain, macular edema and heart failure. Moreover, they may cause hypoglycemia when combined with other antidiabetic drugs as well as decrease hematocrit and hemoglobin levels. Increased bone fracture risk is another TZD-related side effect. Thiazolidinediones tend to increase serum low density lipoprotein cholesterol levels, with rosiglitazone having a more pronounced effect compared with pioglitazone. Moreover, rosiglitazone increases low density lipoprotein particle concentration in contrast to pioglitazone where a decrease is observed. Rosiglitazone has been associated with an increase in myocardial infarction incidence. On the other hand, pioglitazone may reduce cardiovascular events. Overall, TZDs are valuable drugs for diabetes management but physicians should keep in mind that they are associated with several adverse events, the most prominent of which is heart failure.

Differential modulation of farnesoid X receptor signaling pathway by the thiazolidinediones

Thiazolidinediones (TZD), including troglitazone, rosiglitazone, and pioglitazone, are agonists of peroxisome proliferator-activated receptor (PPAR)-gamma and belong to a class of insulin-sensitizing drugs for type 2 diabetes mellitus. However, member-specific, PPARgamma-independent activities and toxicity have been reported, especially for troglitazone. Currently, the underlying mechanisms are not fully understood. In this study, we demonstrated that troglitazone but not rosiglitazone or pioglitazone modulated expression of farnesoid X receptor (FXR) target genes bile salt export pump (BSEP) and small heterodimer partner (SHP) in Huh-7 cells. More specifically, troglitazone acted as a partial agonist of FXR to weakly increase BSEP and SHP expression but functioned as a potent antagonist to significantly suppress bile acid-induced expression. Consistent with the finding, troglitazone partially induced but markedly antagonized bile acid-mediated BSEP promoter transactivation. However, such modulating effects were not detected with rosiglitazone or pioglitazone. Using the crystal structure of ligand-bound FXR ligand binding domain (LBD), molecular docking predicted that troglitazone, but not rosiglitazone or pioglitazone, could form a stable complex with FXR LBD. The specific alpha-tocopherol side chain of troglitazone significantly contributed to the formation of such a stable complex through extensive interactions with FXR LBD. The docking model was further validated by functional analyses of a series of docking-guided FXR mutants. In summary, the data demonstrated that troglitazone, but not rosiglitazone or pioglitazone, was an FXR modulator and potently antagonized bile acid-induced expression of FXR target genes. Such differential modulation of FXR signaling pathway by TZDs may represent one of the mechanisms for member-specific, PPARgamma-independent activities and toxicity.

Structure-dependent activation of peroxisome proliferator-activated receptor (PPAR) gamma by organotin compounds

Organotin compounds such as tributyltin (TBT) and triphenyltin (TPT) are frequent environmental contaminants and are suspected of disrupting endocrine function in vertebrates and invertebrates. Previously, we reported that TBT and TPT function as powerful agonists for peroxisome proliferator-activated receptor (PPAR) gamma and stimulate adipocyte differentiation via the PPARgamma signaling pathway. Our current study investigates the structure-dependent binding of butyltin and phenyltin compounds to PPARgamma and their ability to activate the receptor. A Scatchard analysis with purified recombinant PPARgamma demonstrated that [(14)C]TPT binds to PPARgamma with an equilibrium dissociation constant (K(d)) of 66.6+/-5.2 nM, which approximated the 46.2+/-2.5 nM K(d) of a typical PPARgamma agonist, [(3)H]rosiglitazone (Rosi). TBT, TPT, diphenyltin (DPT), and tetrabutyltin (TeBT) blocked the binding of [(3)H]Rosi to PPARgamma in a competitive manner, and all tested organotin compounds except monobutyltin blocked the binding of [(14)C]TPT to PPARgamma in a competitive manner. Unexpectedly, Rosi did not compete at all with [(14)C]TPT for binding to PPARgamma, and contrary to the results of the competition assay, TBT and TeBT, but not dibutyltin, transcriptionally activated a GAL-PPARgamma chimeric receptor. All tested phenyltin compounds transcriptionally activated GAL-PPARgamma with an order of potency of TPT>DPT>monophenyltin. In addition, treatment of human choriocarcinoma cells with TBT, TeBT, and all tested phenyltin compounds stimulated production of human chorionic gonadotropin, which is upregulated by PPARgamma-mediated transcription. Our observations indicate that trialkylated and triphenylated tin compounds are the most potent PPARgamma agonists among the alkylated and phenylated tin compounds, and a phenyl substituent on a tin atom enhances the potency of organotin compounds as a PPARgamma agonist much more than a butyl substituent.

Combination Therapy of PPARgamma Ligands and Inhibitors of Arachidonic Acid in Lung Cancer

Lung cancer is the leading cause of cancer death in the United States and five-year survival remains low. Numerous studies have shown that chronic inflammation may lead to progression of carcinogenesis. As a result of inflammatory stimulation, arachidonic acid (AA) metabolism produces proliferation mediators through complex and dynamic interactions of the products of the LOX/COX enzymes. One important mediator in the activation of the AA pathways is the nuclear protein PPARgamma. Targeting LOX/COX enzymes and inducing activation of PPARgamma have resulted in significant reduction of cell growth in lung cancer cell lines. However, specific COX-inhibitors have been correlated with an increased cardiovascular risk. Clinical applications are still being explored with a novel generation of dual LOX/COX inhibitors. PPARgamma activation through synthetic ligands (TZDs) has revealed a great mechanistic complexity since effects are produced through PPARgamma-dependent and -independent mechanisms. Furthermore, PPARgamma could also be involved in regulation of COX-2. Overexpression of PPARgamma has reported to play a role in control of invasion and differentiation. Exploring the function of PPARgamma, in this new context, may provide a better mechanistic model of its role in cancer and give an opportunity to design a more efficient therapeutic approach in combination with LOX/COX inhibitors.

Fat poetry: a kingdom for PPAR gamma

Adipose tissue is not an inert cell mass contributing only to the storage of fat, but a sophisticated ensemble of cellular components with highly specialized and complex functions. In addition to managing the most important energy reserve of the body, it secretes a multitude of soluble proteins called adipokines, which have beneficial or, alternatively, deleterious effects on the homeostasis of the whole body. The expression of these adipokines is an integrated response to various signals received from many organs, which depends heavily on the integrity and physiological status of the adipose tissue. One of the main regulators of gene expression in fat is the transcription factor peroxisome proliferator-activated receptor gamma (PPARgamma), which is a fatty acid- and eicosanoid-dependent nuclear receptor that plays key roles in the development and maintenance of the adipose tissue. Furthermore, synthetic PPARgamma agonists are therapeutic agents used in the treatment of type 2 diabetes.This review discusses recent knowledge on the link between fat physiology and metabolic diseases, and the roles of PPARgamma in this interplay via the regulation of lipid and glucose metabolism. Finally, we assess the putative benefits of targeting this nuclear receptor with still-to-be-identified highly selective PPARgamma modulators.

Regulation of breast cancer-associated aromatase promoters

By converting androstenedione to estrone, or testosterone to estradiol, aromatase is a key enzyme in estrogen biosynthesis. Encoded by a single gene CYP19, aromatase is expressed in various tissues, including ovary, placenta, bone, brain, skin, and adipose tissue, via partially tissue-specific promoters, and is essential for normal estrogen-dependent physiological functions. In disease-free breast tissue, aromatase mRNA is primarily transcribed from the weak promoter I.4 and maintained at low levels in breast adipose stromal fibroblasts. In breast cancer a distinct set of aromatase promoters, i.e. I.3, II, and I.7, is activated, leading to a marked increase in aromatase expression in breast tumors and breast adipose tissue adjacent to a breast tumor, and a consequent local overproduction of estrogen that promotes growth and progression of breast cancer. In addition, the total amount of promoter I.4-specific aromatase transcript in breast adipose fibroblasts may also be increased due to both cytokine-induced desmoplastic reaction and cytokine-stimulated promoter I.4 activity in breast cancer. Targeting aromatase has proven beneficial in treating breast cancer, since aromatase inhibitors are the most effective endocrine treatment of breast cancer to date. However, aromatase inhibitors cause major side effects such as bone loss and abnormal lipid metabolism, due to indiscriminate reduction of aromatase activity in all expression sites of the body. Therefore, inhibition of aromatase expression via breast cancer-associated aromatase promoters is a useful strategy to selectively block local aromatase production, and hence estrogen synthesis, in breast cancer. This review will summarize the significant findings on regulation of the breast cancer-associated aromatase promoters, and highlight the discovery of chemical compounds and nuclear receptor ligands that specifically inhibit activation of these aromatase promoters. Clinical side effects of these agents require development of new drugs with better specificity and efficacy, and epigenetic therapies with breast cancer tissue-selective aromatase siRNA-conjugated nanoparticles.

Renal cytochrome P450 as a determinant of impaired natriuresis by PPAR-gamma ligands in ovariectomized obese rats

OBJECTIVE

Peroxisome proliferator-activated receptor (PPAR)-gamma ligand, pioglitazone (PIO), is reported to induce edema especially in postmenopausal women. The aim of this study was to elucidate the mechanism for PIO-induced sodium retention and to discover the therapeutic strategy for the PIO-induced changes in renal sodium handling.

METHODS AND PROCEDURES

Zucker obese rats were ovariectomized and were given PIO for 8 weeks. Renal sodium excretion and renal expressions of several enzymes that generate natriuretic substances were examined.

RESULTS

Sodium excretion was decreased in ovariectomized (OVX) rats that were given PIO when compared with OVX rats that were not. Urinary nitrites/nitrates excretion was decreased in OVX rats, but was restored by PIO. The expressions of nitric oxide synthases (NOSs) and cyclooxygenases-1/2 (COX-1/2) were unaltered. Similarly, the expression of epithelial sodium channels (ENaC), identified as a PPAR-gamma-regulated gene product, was unaffected. In contrast, the expression of cytochrome P450 4A (CYP4A) was increased in OVX rats, and was downregulated by PIO. Co-treatment of OVX rats with PIO and PPAR-alpha ligand, fenofibrate, a putative inducer of CYP4A, restored not only the impaired sodium excretion but also the downregulated CYP4A expression.

DISCUSSION

PIO-induced sodium retention is specific in female OVX rats. Ovariectomy decreases renal NO production, but upregulates renal CYP4A expression to compensate for renal sodium balance. In this setting, PIO downregulates CYP4A, leading to sodium retention. Furthermore, PPAR-alpha ligands can provide a novel strategy for preventing the PIO-induced sodium retention.

Late-Onset Rosiglitazone-Associated Acute Liver Failure in a Patient with Hodgkin's Lymphoma

Objective:

To report a case of rosiglilazone-associated hepatotoxicity in a patient with Hodgkin's lymphoma.

Case Summary:

A 52-year-old man presented with low-grade fever and fatigue that had been present for 4 months. He had been receiving insulin for 5 years and rosiglitazone 4 mg/day for 11 months for control of type 2 diabetes; he was receiving no other drug therapy. During hospitalization, hepatotoxicity was shown, with abnormal liver function test results including alanine aminotransferase 488 U/L, aspartate aminotransferase 344 U/L, alkaline phosphatase B32 U/L, total bilirubin 4.61 mg/dL, and direct bilirubin 3.63 mg/dL. Rosiglitazone was discontinued after further elevation of bilirubin (total 14.67 mg/dL, direct 12.10 mg/dL) occurred. Other causes for hepatotoxicity were ruled out, Hodgkin's lymphoma was diagnosed during the workup; however, liver imaging and biopsy also excluded this as the direct cause of acute liver failure. Despite discontinuation of rosiglitazone, the bilirubin level continued to increase to 49.29 mg/dL (direct >20 mg/dL). The patient died 3 months after admission.

Discussion:

Rosiglitazone maleate is a thiazolidinedione approved for treatment of type 2 diabetes mellitus. The first member of this drug class, troglitazone, was withdrawn from the market due to reports of acute liver failure. Rosiglitazone has been shown to be much safer than troglitazone, despite some reported cases of early-onset nonfatal hepatotoxicity. Use of the Naranjo probability scale indicated that rosiglitazone was the probable cause of acute liver failure in our patient.

Conclusions:

We conclude that rosiglitazone may be associated with late-onset acute liver failure. Clinicians should be aware of such a complication and monitor liver function in patients receiving the drug.

[Nuclear receptor PPAR and hepatology: pathophysiological and therapeutical aspects]

In last few years, the topic of nuclear receptor has been developed in the field of hepatology allowing envisaging therapeutic strategies for the most frequent chronic liver diseases. Peroxysome proliferator-activated receptors (PPAR) contribute to wide physiological processes within the liver such as lipid/glucid metabolisms, inflammatory response, cell differenciation and cell cycle. In vitro experiments and animal studies showed that PPARalpha discloses anti-inflammatory property and PPARgamma discloses anti-inflammatory, antifibrogenic and antiproliferative properties in the liver. Main available agonists are fibrates (PPARalpha) used for 20 years in cases of lipid metabolism abnormalities and glitazones (PPARgamma) used since 2000 for type 2 diabetes. In terms of therapy, animal studies and human trials have been conducted in steatopathies. However, clinicians have to be aware of potential specific side effects related to glitazones especially on cardiovascular system.

The influence of thiazolidinediones on adipogenesis in vitro and in vivo: Potential modifiers of intramuscular adipose tissue deposition in meat animals1,2

Thiazolidinediones (TZD) are insulin sensitizing agents currently used for the treatment of type 2 diabetes and are widely used as adipogenic agents because they are ligands of peroxisome proliferator-activated receptor gamma (PPARgamma), a key adipogenic transcription factor. In vivo and in vitro studies of TZD as potential modifiers of intramuscular or marbling adipogenesis are reviewed. Thiazolidinedione-induced adipogenesis has been reported in numerous cell culture systems, including rodent, human, bovine, and porcine adipose tissue stromal-vascular (S-V) cell cultures. Studies of porcine S-V cell cultures derived from semitendinosus muscle show that TZD can potentially modify intramuscular or marbling adipogenesis. Preadipocyte recruitment was TZD-dependent in muscle S-V cultures but TZD-independent in adipose S-V cultures. There appear to be differences between adipocytes in muscle and subcutaneous adipose tissue, reminiscent of differences observed in adipocytes from different adipose tissue depots. Troglitazone, a TZD, induces marbling adipogenesis without inhibiting myogenesis when cells are grown on laminin precoated culture dishes. Additionally, troglitazone treatment does not increase lipid content in porcine adipose tissue or muscle S-V cell cultures. Thiazolidinedione treatment increases lipid content of muscle in rodents and humans; however, rosiglitazone treatment for 49 d in pigs did not influence muscle lipid content and meat quality, but several significant changes in muscle fatty acid composition were observed. Although timing of treatment with TZD needs to be optimized, evidence suggests these compounds may enhance marbling deposition in swine.

Why insulin sensitizers but not secretagogues should be retained when initiating insulin in type 2 diabetes

The stringent targets set for HbA(1c) levels in type 2 diabetes are currently achieved by fewer than half the patients in the United States. Failure to manage hyperglycaemia in the early stages of disease results in progressive loss of beta-cell function, which ultimately necessitates the initiation of insulin therapy. At this point, choices have to be made on whether to continue oral anti-diabetic drug therapy and, if so, with which agent(s). Historically, sulfonylureas have been the mainstay of oral anti-diabetic drug therapy; however, their long-term efficacy in patients with depleted beta-cell capacity is doubtful, and other classes of oral anti-diabetic drugs, notably the insulin sensitizers, may prove more reliable. These agents (metformin and thiazolidinediones) appear to provide various benefits over and above sustained glycaemic control, which may variably include reduced loss of beta-cell function as well as improvements to cardiovascular risk factors, morbidity, and mortality. Metformin also limits weight gain associated with insulin therapy. This manuscript presents the case that when insulin therapy is initiated it should be tailored to individual needs through combination with one or more insulin sensitizers rather than a secretagogue.

The influence of hepatic impairment on the pharmacokinetics of the dipeptidyl peptidase IV (DPP-4) inhibitor vildagliptin

OBJECTIVE

Vildagliptin is a potent and selective dipeptidyl peptidase-IV (DPP-4) inhibitor that improves glycemic control in patients with type 2 diabetes mellitus by increasing alpha- and beta-cell responsiveness to glucose. This study investigated the pharmacokinetics of vildagliptin in patients with hepatic impairment compared with healthy subjects.

METHODS

This was an open-label, parallel-group study in patients with mild (n = 6), moderate (n = 6) or severe (n = 4) hepatic impairment and healthy subjects (n = 6). All subjects received a single 100-mg oral dose of vildagliptin, and plasma concentrations of vildagliptin and its main pharmacologically inactive metabolite LAY151 were measured up to 36 h post-dose.

RESULTS

Exposure to vildagliptin (AUC(0-infinity) and C(max)) decreased non-significantly by 20 and 30%, respectively, in patients with mild hepatic impairment [geometric mean ratio (90% CI): AUC(0-infinity), 0.80 (0.60, 1.06), p = 0.192; C(max), 0.70 (0.46, 1.05), p = 0.149]. Exposure to vildagliptin was also decreased non-significantly in patients with moderate hepatic impairment [-8% for AUC(0-infinity), geometric mean ratio (90% CI): 0.92 (0.69, 1.23), p = 0.630; -23% for C(max), geometric mean ratio (90% CI): 0.77 (0.51, 1.17), p = 0.293]. In patients with severe hepatic impairment, C(max) was 6% lower than that in healthy subjects [geometric mean ratio (90% CI): 0.94 (0.59, 1.49), p = 0.285], whereas AUC(0-infinity) was increased by 22% [geometric mean ratio (90% CI): 1.22 (0.89, 1.68), p = 0.816). Across the hepatic impairment groups, LAY151 AUC(0-infinity) and C(max) were increased by 29-84% and 24-63%, respectively, compared with healthy subjects. The single 100-mg oral dose of vildagliptin was well tolerated by patients with hepatic impairment.

CONCLUSIONS

There was no significant difference in exposure to vildagliptin in patients with mild, moderate or severe hepatic impairment; therefore, no dose adjustment of vildagliptin is necessary in patients with hepatic impairment.

Combination of dipeptidylpeptidase IV inhibitor and low dose thiazolidinedione: preclinical efficacy and safety in db/db mice

Thiazolidinediones (TZDs) are currently the most efficacious class of oral antidiabetics. However, they carry the burden of weight gain and haemodilution, which may lead to cardiovascular complications. The present study was designed to ascertain whether a combination of dipeptidyl peptidase IV (DPP IV) inhibitor with low dose of a thiazolidinedione absolves TZD associated weight gain and oedema without compromising its efficacy. In this study, we examined the efficacy and safety of lower dose (1 mg/kg/day) of rosiglitazone, a thiazolidinedione, in combination with 5 mg/kg/day dose of LAF-237 (vildagliptin), a known DPP IV inhibitor, in aged db/db mice after 14 days of treatment and compared the combination with therapeutic dose (10 mg/kg) of rosiglitazone. The combination therapy showed similar efficacy as that of 10 mg/kg/day rosiglitazone in lowering random blood glucose (53.8%, p<0.001 and 54.3%, p<0.001 respectively), AUC ((0-120) min) during oral glucose tolerance test (OGTT) (38.6 %, p<0.01; 38.3%, p<0.01 respectively) and triglyceride levels (63.9% and 61% respectively; p<0.01). Plasma active glucagon like peptide-1 (GLP-1) and insulin levels were found to be elevated significantly (p<0.01 and p<0.05 respectively) in both LAF-237 and combination treated groups following oral glucose load. LAF-237 alone had no effect on random glucose and glucose excursion during OGTT in severely diabetic db/db mice. Interestingly, the combination treatment showed no significant increase in body weight as compared to the robust weight gain by therapeutic dose of rosiglitazone. Rosiglitazone at 10 mg/kg/day showed significant reduction (p<0.05) in haematocrit, RBC count, haemoglobin pointing towards haemodilution associated with increased mRNA expression of Na(+), K(+)-ATPase-alpha and epithelial sodium channel gamma (ENaCgamma) in kidney. The combination therapy escaped these adverse effects. The results suggest that combination of DPP IV inhibitor with low dose of thiazolidinedione can interact synergistically to represent a therapeutic advantage for the clinical treatment of type 2 diabetes without the adverse effects of haemodilution and weight gain associated with thiazolidinediones.

Reduction in hematocrit and hemoglobin following pioglitazone treatment is not hemodilutional in Type II diabetes mellitus

Peripheral edema, mild weight gain, and anemia are often observed in type II diabetic patients treated with thiazolidinediones (TZDs). Small decreases in hemoglobin (Hb) and hematocrit (Hct) appear to be a class effect of TZDs and are generally attributed to fluid retention, although experimental data are lacking. We analyzed 50 patients with type II diabetes mellitus undergoing either placebo or pioglitazone (PIO, 45 mg/day) for 16 weeks. Before and after therapy, we measured Hb/Hct and used (3)H(2)O and bioimpedance to quantitate total body water (TBW), extracellular water, and fat-free mass. The majority (89%) of the increment in body weight was accounted for by increased body fat. Hb and Hct fell significantly in the PIO group (-0.9+/-0.2 g/dl, -2.4+/-0.5%, both P<0.0001), without change in TBW. A decline in white blood cell (-0.8+/-0.1 x 10(3)/mm(3), P<0.0001) and platelet (-15+/-6 x 10(3)/mm(3), P<0.02) counts was seen after PIO. In conclusion, the small decreases in Hb/Hct observed after 16 weeks of PIO treatment cannot be explained by an increase in TBW. Other causes, such a mild marrow suppressive effect, should be explored.

The PPARgamma agonist rosiglitazone impairs colonic inflammation in mice with experimental colitis

Various animal models showed that peroxisome proliferator-activated receptor (PPAR)γ agonists, when given as a gavage shortly preceding colitis induction, protect against inflammatory bowel disease (IBD). We have examined the effects of 16 days rosiglitazone treatment via the diet prior to dextran sodium sulphate (DSS)-induced colitis in mice. After 7 days DSS in the drinking water, rosiglitazone-fed mice had lost significantly more weight than control mice. Rosiglitazone-treated mice had more diarrhea, weight of colon and spleen were increased, and length of colon was decreased. Histology showed that rosiglitazone-treated mice had more severe colitis, mainly caused by more ulceration, crypt loss, and edema. Immunofluorescence showed a loss of tight junction structure Zonula Occludens protein 1 (ZO-1) in colons of rosiglitazone-treated mice as compared to control mice. Also, serum amyloid P component (SAP) concentrations in plasma were increased. However, concentrations of tumor necrosis factor (TNF)-α and interferon (IFN)-γ in colon homogenates, and TNF-α in spleen homogenates were significantly decreased, whereas interleukin (IL)-10 in spleen homogenates was increased. Other cytokines (IL-2, IL-4, IL-6, IL-12p70 and monocyte chemotactic protein (MCP)-1) and myeloperoxidase (MPO) concentrations showed no differences. In conclusion, 16 days pretreatment with rosiglitazone impaired DSS-induced colitis in mice.

Effect of thiazolidinediones on bile acid transport in rat liver

The thiazolidinedione derivatives, troglitazone, rosiglitazone, and pioglitazone, are novel insulin-sensitizing drugs that are useful in the treatment of type 2 diabetes. However, hepatotoxicity associated with troglitazone led to its withdrawal from the market in March 2000. In view of case reports of hepatotoxicity from rosiglitazone and pioglitazone, it is unclear whether thiazolidinediones as a class are associated with hepatotoxicity. Although the mechanism of troglitazone-associated hepatotoxicity has not been elucidated, troglitazone and its major metabolite, troglitazone sulfate, competitively inhibit adenosine triphosphate (ATP)-dependent taurocholate transport in isolated rat canalicular liver plasma membrane vesicles mediated by the canalicular bile salt export pump (Bsep). These results suggest that cholestasis may be a factor in troglitazone-associated hepatotoxicity. To determine whether this effect is 1) limited to canalicular bile acid transport and 2) is specific to troglitazone, the effect of troglitazone, rosiglitazone, and ciglitazone on bile acid transport was examined in rat basolateral (blLPM) and canalicular (cLPM) liver plasma membrane vesicles. In cLPM vesicles, troglitazone, rosiglitazone, and ciglitazone (100 microM) all significantly inhibited ATP-dependent taurocholate transport. In blLPM vesicles, these three thiazolidinediones also significantly inhibited Na(+)-dependent taurocholate transport. Inhibition of bile acid transport was concentration dependent and competitive in both cLPM and blLPM vesicles. In conclusion, these findings are consistent with a class effect by thiazolidinediones on hepatic bile acid transport. If hepatotoxicity is associated with this effect, then hepatotoxicity is not limited to troglitazone. Alternatively, if hepatotoxicity is limited to troglitazone, other mechanisms are responsible for its reported hepatotoxicity.

Oral antidiabetic agents as cardiovascular drugs

The increased risk of cardiovascular disease associated with type 2 diabetes is well documented. Lesser degrees of abnormal glucose metabolism including impaired fasting glycaemia and impaired glucose tolerance are also associated with increased cardiovascular risk. Studies showing improved cardiovascular outcomes with oral antidiabetic agents are limited, with the UKPDS demonstrating improved macrovascular outcomes only in a subgroup of obese patients with type 2 diabetes treated with metformin, and the heavily criticized STOP NIDDM trial showing a reduction in the number of cardiovascular events with the alpha glucosidase inhibitor acarbose. In recent years there has been an increase in the number of oral antidiabetic drugs available to treat the hyperglycaemia of diabetes. Some of these drugs have complex metabolic properties, additional to their antihyperglycaemic effect, improving endothelial function and markers of atherogenesis, with the potential to reduce cardiovascular morbidity and mortality, as supported by the recently published results of the PROACTIVE study. The results of further long-term cardiovascular outcome studies with these newer agents are awaited.

A one-year study comparing the efficacy and safety of rosiglitazone and glibenclamide in the treatment of type 2 diabetes

BACKGROUND AND AIM

This study was designed to compare the efficacy of rosiglitazone and glibenclamide in individuals with type 2 diabetes over a 12-month period.

METHODS AND RESULTS

A total of 598 patients were randomized to double-blind treatment for 52 weeks with rosiglitazone 4 mg/d (n=200), rosiglitazone 8 mg/d (n=191) or glibenclamide (n=207; dose adjusted up to 15 mg/d over the first 12 weeks according to clinical response). Changes in fasting plasma glucose (FPG), haemoglobin A1c (HbA1c), fasting insulin and its precursor peptides, and lipids were measured and safety was evaluated. Significant reductions in HbA1c levels at 52 weeks compared with baseline were seen in all treatment groups (rosiglitazone 4 mg/d=-0.3%, P=0.0003; rosiglitazone 8 mg/d=-0.5%, P<0.0001; glibenclamide=-0.7%, P<0.0001). Mean FPG levels were also significantly reduced in all treatment groups (rosiglitazone 4 mg/d=-1.4 mmol/l; rosiglitazone 8 mg/d=-2.3 mmol/l; glibenclamide=-1.7 mmol/l; P<0.0001 vs. baseline for all treatments). Rosiglitazone therapy reduced plasma insulin, proinsulin, split proinsulin and free fatty acid levels compared with glibenclamide. Rosiglitazone improved insulin resistance while a worsening was seen with glibenclamide. Total:high-density lipoprotein cholesterol ratios were reduced with glibenclamide and unchanged with rosiglitazone. All treatments were generally well tolerated.

CONCLUSIONS

The efficacy of rosiglitazone 8 mg/d in improving glycaemic control in patients with type 2 diabetes is comparable to that of glibenclamide. However, rosiglitazone reduced insulin resistance and proinsulin levels whereas glibenclamide use was associated with an increase in fasting insulin and proinsulin. This suggests that in the long term, rosiglitazone may protect the beta-cell whereas glibenclamide is likely to increase the burden.

Rosiglitazone inhibits mouse liver regeneration

The remarkable regenerative potential of the liver is well known. Recent investigations have shown that this regenerative response is impaired in mouse models of fatty liver disease. Other studies demonstrate that mice engineered for liver-specific overexpression of the peroxisome proliferator activated receptor gamma (PPARgamma) develop significant hepatic steatosis. These observations suggest that precise regulation of hepatic PPARgamma activity may be essential for normal liver regeneration. To test this hypothesis, we analyzed the effects of PPARgamma-activating thiazolidinediones on liver regeneration in the rodent partial hepatectomy model. Thiazolidinediones with different PPARgamma-activating potencies were administered to mice, and those mice were subjected to partial hepatectomy and analyzed for resulting effects on hepatocellular proliferation and signaling pathways important during normal liver regeneration. The results showed that thiazolidinediones suppress liver regeneration with efficacies that correlate with their relative PPARgamma-activating potencies. These studies provide the first evidence linking regulation of PPARgamma activity and the hepatic regenerative response.

Thiazolidinediones, insulin resistance and obesity: Finding a balance

The clinical efficacy of currently available thiazolidinediones (TZDs) in improving glycaemic control and ameliorating several risk factors for cardiovascular disease (linked to their insulin-sensitising actions as well as direct vascular effects) is well established. Treatment-associated weight gain, however, which has been identified as a class effect of the TZDs, is seen in a number of patients. The magnitude of weight gain correlates in part with improved metabolic control, i.e. better responders are more prone to increases in body weight. The cardiovascular risk associated with obesity appears to be depot specific; while peripheral obesity is associated with a low risk of cardiovascular complications, central obesity confers a greater degree of risk. Evidence is reviewed that increases in body weight associated with TZD treatment are associated with neutral effects (or even, decreases) in visceral fat, the adipose depot that is associated with central obesity.

Long-term Safety of Pioglitazone versus Glyburide in Patients with Recently Diagnosed Type 2 Diabetes Mellitus

STUDY OBJECTIVE

To evaluate the long-term safety and efficacy of glyburide versus pioglitazone in patients with a recent diagnosis of type 2 diabetes mellitus.

DESIGN

Prospective, randomized, multicenter, double-blind trial with a 16-week titration period and a 40-week maintenance period.

SETTING

Sixty-five investigative sites in the United States and Puerto Rico.

PATIENTS

Five hundred two subjects with a recent diagnosis of type 2 diabetes that was unsuccessfully treated with diet and exercise were randomly assigned to study treatment. Of the 251 patients in each treatment group, 128 (51.0%) glyburide-treated patients and 134 (53.4%) pioglitazone-treated patients completed the study.

INTERVENTIONS

Dosages of randomly assigned glyburide and pioglitazone were titrated every 4 weeks for 16 weeks in 5-mg/day and 15-mg/day increments, respectively, until a fasting plasma glucose level between 69 and 141 mg/dl was achieved. The optimized regimen was maintained during the subsequent 40-week double-blind phase.

MEASUREMENTS AND MAIN RESULTS

At week 56, glyburide and pioglitazone improved glucose control comparably (change in hemoglobin A(1c) -2.02% and -2.07%, respectively, p=0.669). Withdrawal due to lack of efficacy or adverse events occurred more frequently with glyburide (20.8%) than pioglitazone (12.8%, p<0.032). Significantly higher percentages of glyburide- than pioglitazone-treated patients had a hypoglycemic (24.3% vs 4.4%, p=0.0001) or cardiac (8.8% vs 4.4%, p=0.0478) event. Edema (4.8% vs 7.9%, p=0.1443) and weight gain (4.4% vs 4.0%, p=0.8238) did not differ significantly between the glyburide and pioglitazone groups. Only a few patients discontinued study drug because of weight gain (one glyburide, one pioglitazone), edema (one pioglitazone), or a cardiac event (two glyburide).

CONCLUSION

With long-term treatment, both glyburide and pioglitazone resulted in comparable glycemic control; however, pioglitazone was associated with less hypoglycemia and fewer withdrawals due to lack of efficacy or adverse events.

Troglitazone acutely inhibits protein synthesis in endothelial cells via a novel mechanism involving protein phosphatase 2A-dependent p70 S6 kinase inhibition

Thiazolidinediones (TZDs), synthetic peroxisome proliferator-activated receptor gamma (PPARgamma) ligands, have been implicated in the inhibition of protein synthesis in a variety of cells, but the underlying mechanisms remain obscure. We report that troglitazone, the first TZD drug, acutely inhibited protein synthesis by decreasing p70 S6 kinase (p70S6K) activity in bovine aortic endothelial cells (BAEC). This inhibition was not accompanied by decreased phosphorylation status or in vitro kinase activity of mammalian target of rapamycin (mTOR). Furthermore, cotreatment with rapamycin, a specific mTOR inhibitor, and troglitazone additively inhibited both p70S6K activity and protein synthesis, suggesting that the inhibitory effects of troglitazone are not mediated by mTOR. Overexpression of the wild-type p70S6K gene significantly reversed the troglitazone-induced inhibition of protein synthesis, indicating an important role of p70S6K. Okadaic acid, a protein phosphatase 2A (PP2A) inhibitor, partially reversed the troglitazone-induced inhibition of p70S6K activity and protein synthesis. Although troglitazone did not alter total cellular PP2A activity, it increased the physical association between p70S6K and PP2A, suggesting an underlying molecular mechanism. GW9662, a PPARgamma antagonist, did not alter any of the observed inhibitory effects. Finally, we also found that the mTOR-independent inhibitory mechanism of troglitazone holds for the TZDs ciglitazone, pioglitazone, and rosiglitazone, in BAEC and other types of endothelial cells tested. In conclusion, our data demonstrate for the first time that troglitazone (and perhaps other TZDs) acutely decreases p70S6K activity through a PP2A-dependent mechanism that is independent of mTOR and PPARgamma, leading to the inhibition of protein synthesis in endothelial cells.

KR-62980: a novel peroxisome proliferator-activated receptor gamma agonist with weak adipogenic effects

The nuclear receptor peroxisome proliferator-activated receptor gamma (PPARgamma) is the target for the anti-diabetic drugs including thiazolidinediones. We report here the identification and characterization of a novel PPARgamma agonist KR-62980. KR-62980 acted as a selective PPARgamma agonist in transactivation assay with an EC50 of 15 nM. In fully differentiated 3T3-L1 adipocytes, KR-62980 induced [3H]-deoxyglucose uptake in a concentration-dependent manner in the presence of insulin. KR-62980 was weakly adipogenic with little induction of aP2 mRNA, and was able to antagonize the adipogenic effects of rosiglitazone in C3H10T1/2 cells. In vivo pharmacokinetic profile of KR-62980 revealed that the compound exhibited good oral bioavailability of 65% with a terminal elimination half-life of 2.5 h in the rat. Treatment of high fat diet-induced C57BL/6J mice with KR-62980 for 14 days reduced plasma glucose levels with little side effects with regard to weight gain, cardiac hypertrophy and hepatotoxicity. These results suggest that KR-62980 acts as a selective PPARgamma modulator with anti-hyperglycemic activity, and that the mechanism of actions of KR-62980 appears to be different from that of rosiglitazone with improved side effect profiles.

Adipose-specific effect of rosiglitazone on vascular permeability and protein kinase C activation: novel mechanism for PPARgamma agonist's effects on edema and weight gain

PPARgamma agonists, thiazolidinediones, cause fluid retention and edema due to unknown mechanisms. We characterized the effect of rosiglitazone (RSG), a thiazolidinedione, to induce vascular permeability, vascular endothelial growth factor (VEGF) expression, and protein kinase C (PKC) activation with edema and wt gain. In lean, fatty and diabetic Zucker rats, and endothelial insulin receptor knockout mice, RSG increased wt and vascular permeability, selectively in fat and retina, but not in heart or skeletal muscle. H2O content and wt of epididymal fat were increased by RSG and correlated to increases in capillary permeability in fat and body wt. RSG induced VEGF mRNA expression and PKC activation in fat and retina up to 2.5-fold. Ruboxistaurin, a PKCbeta isoform inhibitor, in the latter 2 wk of a 4-wk study, normalized vascular permeability in fat and decreased total wt gain, H2O content, and wt of fat vs. RSG alone but did not decrease VEGF expression, basal permeability, or food intake. Finally, RSG did not increase wt or vascular permeability in PKCbeta knockout vs. control mice. Thus, thiazolidinedione's effects on edema and wt are partially due to an adipose tissue-selective activation of PKC and vascular permeability that may be prevented by PKCbeta inhibition.

The effect of the PPARgamma ligand rosiglitazone on energy balance regulation

BACKGROUND AND AIM

Fat mass generation requires an energy surplus and the activity of the peroxisome proliferator-activated receptor gamma (PPARgamma). We investigated if the PPARgamma ligand rosiglitazone influences substrate usage, energy expenditure (EE) and energy intake (EI) and, thereby, how PPARgamma activity contributes to susceptibility to obesity.

METHODS

Twenty healthy males (20-29 years) were randomly assigned to receive a placebo (n = 10) or rosiglitazone (8 mg/d) (n = 10) for seven consecutive days, while staying in a respiration chamber. Food intake was ad libitum. Body composition was determined by underwater weighing (day 1) and deuterium dilution (day 1 and 8).

RESULTS

Mean (+/-SE) EI was 15.9 +/- 0.9 MJ/d in the placebo group and 18.9 +/- 1.2 MJ/d in the rosiglitazone group. Mean EE was 11.3 +/- 0.3 MJ/d and 12.5 +/- 0.5 MJ/d for the placebo and rosiglitazone groups respectively. This resulted in a cumulative positive energy balance (EB) of 32.3 +/- 5.1 MJ for placebo and 44.7 +/- 6.9 MJ for rosiglitazone. There were no significant differences in EI, EE, and EB between treatments. Both groups did not adjust their fat oxidation to the increased fat intake, but fat oxidation decreased faster in the rosiglitazone group (significantly lower on days 6 and 7). During treatment with rosiglitazone, significantly more fat storage was seen in overweight subjects while this was not the case in the placebo group.

CONCLUSIONS

Our results suggest a shift in substrate usage during PPARgamma stimulation leading to a preference for fat storage, especially in subjects with a higher BMI.

Pioglitazone: a review of its use in type 2 diabetes mellitus

Pioglitazone is an antihyperglycaemic agent that, in the presence of insulin resistance, increases hepatic and peripheral insulin sensitivity, thereby inhibiting hepatic gluconeogenesis and increasing peripheral and splanchnic glucose uptake. Pioglitazone is generally well tolerated, weight gain and oedema are the most common emergent adverse events, and there are no known drug interactions between pioglitazone and other drugs. In clinical trials in patients with type 2 diabetes mellitus, pioglitazone as monotherapy, or in combination with metformin, repaglinide, insulin or a sulphonylurea, induced both long- and short-term improvements in glycaemic control and serum lipid profiles. Pioglitazone was also effective in reducing some measures of cardiovascular risk and arteriosclerosis. Pioglitazone thus offers an effective treatment option for the management of patients with type 2 diabetes.

Fluid retention and vascular effects of rosiglitazone in obese, insulin-resistant, nondiabetic subjects

OBJECTIVE

The use of thiazolidinedione (TZD) derivatives is associated with fluid retention, especially when combined with insulin. Because TZDs improve the metabolic effect of insulin, they may also reverse the blunted vascular response to insulin. We hypothesize that improvement of the action of insulin on vascular tone or permeability is the key mechanism of TZD-related fluid retention.

RESEARCH DESIGN AND METHODS

In a randomized, double-blind, placebo-controlled, cross-over study in 18 obese, nondiabetic subjects with features of the metabolic syndrome, we investigated the effects of a 12-week treatment with 4 mg rosiglitazone twice a day on glucose disposal, hemodynamics (including forearm vasoconstrictor response to nitric oxide [NO]), synthase inhibition by N-monomethyl-L-arginine-acetate (L-NMMA), vascular permeability (transcapillary escape rate of albumin), and plasma volume during a hyperinsulinemic-euglycemic clamp (120 min, 120 mU/m(2) per min).

RESULTS

As expected, rosiglitazone increased the glucose infusion rate during clamping. However, neither vascular permeability nor forearm blood flow response to hyperinsulinemia or L-NMMA was affected by rosiglitazone. Compared with placebo, rosiglitazone decreased diastolic blood pressure by 5 mmHg (95% CI 2.35-6.87, P = 0.0005) and increased plasma volume by 255 ml/1.73 m(2) (80-430, P = 0.007). Interestingly, the positive effect of rosiglitazone on glucose disposal correlated with change in foot volume (R(2) = 0.53, P = 0.001).

CONCLUSIONS

Rosiglitazone improved insulin sensitivity but had no effect on NO-dependent vasodilatation in the forearm or vascular permeability in obese, insulin-resistant, nondiabetic subjects. As such, TZD-related fluid retention was not caused by improvement of the vascular actions of insulin. Nonetheless, rosiglitazone-induced improvement in insulin sensitivity appears to be correlated to edema formation.

PPAR-gamma: a nuclear receptor with affinity for cannabinoids

An increasing number of cannabinoid actions are being reported that do not appear to be mediated by either CB1 or CB2, the known cannabinoid receptors. One such example is the synthetic analog ajulemic acid (AJA), which shows potent analgesic and anti-inflammatory effects in rodents and humans. AJA binds weakly to CB1 only at concentrations many fold higher than its therapeutic range, and is, therefore, completely free of psychotropic effects in both normal subjects and pain patients suggesting the involvement of a target site other than CB1. AJA as well as several other cannabinoids appear to have profound effects on cellular lipid metabolism as evidenced by their ability to transform fibroblasts into adipocytes where the accumulation of lipid droplets can be readily observed. Such transformations can be mediated by the activation of the nuclear receptor PPAR-gamma. A variety of small molecule ligands including AJA have been shown to induce the activation of PPAR-gamma and, in some cases this has led to the introduction of clinically useful agents. It is suggested that PPAR-gamma may serve a receptor function for certain actions of some cannabinoids.

Different residues mediate recognition of 1-O-oleyllysophosphatidic acid and rosiglitazone in the ligand binding domain of peroxisome proliferator-activated receptor gamma

Here we showed that a naturally occurring ether analog of lysophosphatidic acid, 1-O-octadecenyl-2-hydroxy-sn-glycero-3-phosphate (AGP), is a high affinity partial agonist of the peroxisome proliferator-activated receptor gamma (PPARgamma). Binding studies using the PPARgamma ligand binding domain showed that [32P]AGP and [3H]rosiglitazone (Rosi) both specifically bind to PPARgamma and compete with each other. [32P]AGP bound PPARgamma with an affinity (Kdapp 60 nm) similar to that of Rosi. However, AGP displaced approximately 40% of bound [3H]Rosi even when applied at a 2000-fold excess. Activation of PPARgamma reporter gene expression by AGP and Rosi showed similar potency, yet AGP-mediated activation was approximately 40% that of Rosi. A complex between AGP and PPARgamma was generated using molecular modeling based on a PPARgamma crystal structure. AGP-interacting residues were compared with Rosi-interacting residues identified within the Rosi-PPARgamma co-crystal complex. These comparisons showed that the two ligands occupy partially overlapping positions but make different hydrogen bonding and ion pairing interactions. Site-specific mutants of PPARgamma were prepared to examine individual ligand binding. H323A and H449A mutants showed reduced binding of Rosi but maintained binding of AGP. In contrast, the R288A showed reduced AGP binding but maintained Rosi binding. Finally, alanine replacement of Tyr-473 abolished binding and activation by Rosi and AGP. These observations indicate that the endogenous lipid mediator AGP is a high affinity ligand of PPARgamma but that it binds via interactions distinct from those involved in Rosi binding. These distinct interactions are likely responsible for the partial PPARgamma agonism of AGP.

Peroxisome proliferator-activated receptor gamma as a drug target in the pathogenesis of insulin resistance

Peroxisome proliferator-activated receptors (PPARs) are ligand-activated transcription factors that belong to the nuclear hormone receptor superfamily. The activation of PPAR-gamma, an isotype of PPARs, can either increase or decrease the transcription of target genes. The genes controlled by this form of PPAR have been shown to encode proteins or peptides that participate in the pathogenesis of insulin resistance. Insulin resistance is defined as a state of reduced responsiveness to normal circulating concentrations of insulin and it often co-exists with central obesity, hypertension, dyslipidemia, and atherosclerosis. There is substantial evidence that links obesity with insulin resistance and type-2 diabetes. The early phase of obesity-related insulin resistance has 2 components: (a) interruption of lipid homeostasis leading to the increased plasma concentration of fatty acids that is normally suppressed by the activation of PPAR-gamma, and (b) activation of factors such as cytokines depressed by PPAR-gamma that cause insulin resistance. Therefore, it is logical to suggest that activation of PPAR-gamma may partially reverse the state of insulin resistance. Evidently, activation of the nuclear receptor, PPAR-gamma, by thiazolidinediones has been reported to ameliorate insulin resistance. Although hepatotoxity and possibility to induce congestive heart failure (CHF) limit the widely use of thiazolodinediones, they are still powerful weapon to fight against insulin resistance and type-2 diabetes if use properly. This article reviews the physiology of PPAR-gamma and insulin-signaling transduction, the pathogenesis of insulin resistance in obesity-related type-2 diabetes, the pharmacological role of PPAR-gamma in insulin resistance, and additional effects of thiazolidinediones.

Safety and tolerability of pioglitazone, metformin, and gliclazide in the treatment of type 2 diabetes

This analysis compares the safety and tolerability of pioglitazone (a thiazolidinedione), metformin (a biguanide), and gliclazide (a sulfonylurea). Data collected from four 1-year, double-blind studies comparing treatment of over 3700 patients with type 2 diabetes with pioglitazone, metformin, or gliclazide have been combined to provide comparative tolerability and safety profiles. All treatments were well tolerated with approximately 6% of patients withdrawing from treatment because of side-effects. The side-effects profile varied between treatments, with pioglitazone being associated with edema, metformin with gastrointestinal side-effects, and gliclazide with hypoglycemia. Cardiovascular outcome was similar with all treatments, with no excess reports of cardiac failure with pioglitazone treatment. Both pioglitazone and gliclazide resulted in mean weight gain, whilst with metformin there was mean weight loss. Mean liver enzyme values decreased with pioglitazone and to a lesser extent with metformin. With gliclazide, mean liver enzyme values increased. The expected small decreases in mean hemoglobin and hematocrit seen with pioglitazone also occurred with metformin and to a lesser degree with gliclazide. The results show that all three drugs are safe, but that tolerability profiles vary. Each treatment provides an alternative therapy for type 2 diabetes, dependent on the particular needs of individual patients.

BP-1107 [{2-[4-(2,4-Dioxo-thiazolidin-5-ylmethyl)-phenoxy]-ethyl}-methyl-amide]: A Novel Synthetic Thiazolidinedione That Inhibits Epidermal Hyperplasia in Psoriatic Skin-Severe-Combined Immunodeficient Mouse Transplants after Topical Application

Recent studies have demonstrated that orally administered thiazolidinedione ligands of the peroxisome proliferator-activated receptor-gamma can ameliorate clinical features of psoriasis in humans. Thiazolidinediones also inhibit the proliferation of psoriatic keratinocytes in monolayer and organ culture, and at least one of these agents (troglitazone) inhibits epidermal hyperplasia of human psoriatic skin transplanted to severe-combined immunodeficient (SCID) mice. In the present study, we show that a novel, synthetic, thiazoladinedione derivative, BP-1107 ({2-[4-(2,4-dioxo-thiazolidin-5-ylmethyl)-phenoxy]-ethyl}-methyl-amide), is capable of inhibiting psoriatic hyperplasia in the SCID mouse transplant model after topical application. Like other thiazolidinediones, BP-1107 inhibits proliferation of rapidly growing keratinocytes in monolayer culture, but compared with these agents, the effective dose of BP-1107 needed to suppress keratinocyte proliferation is much lower. Concentrations of BP-1107 that effectively inhibit keratinocyte function have no detrimental effect on dermal fibroblasts. These data suggest that effective topical antipsoriatic therapy may be provided with this agent.

New technologies and screening strategies for hepatotoxicity: use of in vitro models

Hepatotoxicity remains a significant cause for drug failures during clinical trials. This is due, in part, to the idiosyncratic nature of toxicity in humans and inherent physiological differences between humans and preclinical species leading to limited correct prediction of adverse responses in humans. To address this issue, robust screening assays are being developed, which have heightened predictive capacity for human hepatotoxicity, and may be utilized throughout the discovery and development phases in conjunction with traditional in vivo methods, for decision making during drug selection and risk assessment. This manuscript describes an example application of in vitro-based strategies using human hepatocyte cultures in lead optimization screening in conjunction with ADME profiling, for evaluation of compound-associated CYP450 induction potential, and the identification of potentially useful biomarkers as predictors of hepatotoxicity for use in vitro, and in preclinical species and humans.

Spotlight on rosiglitazone 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 hemoglobin levels [HbA(1c); -0.6 to -0.7% (-0.8 to -1.1% in drug-naive patients) with 8 mg/day]. Significant decreases in hyperglycemic markers occurred when rosiglitazone was combined with metformin (HbA(1c) -0.8 to -1.0%), a sulfonylurea (-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 anemia 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 antihyperglycemic efficacy and is generally well tolerated, both as monotherapy and in combination with other antihyperglycemic 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.