Effects Of Troglitazone Research Articles

Troglitazone, a peroxisome proliferator-activated receptor γ ligand, induces growth inhibition and apoptosis of HepG2 human liver cancer cells

To examine the effect of troglitazone, a peroxisome proliferator-activated receptor gamma (PPAR gamma) ligand, on the proliferation and apoptosis of human liver cancer cells. Liver cancer cell line HepG2 was cultured and treated with troglitazone. Cell proliferation was detected by 3-(4-,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay; apoptosis was detected by flow cytometry and terminal deoxynucleotidyl transferase-mediated nick end labeling of DNA fragmentation sites (TUNEL) assay; and apoptosis-related protein was detected by immunocytochemistry and Western blotting. Troglitazone inhibited growth and induced apoptosis of HepG2 cells in a dose-dependent manner, and induced activation of caspase-3 expression. Troglitazone not only drove apoptosis-inhibiting factor survivin to translocate incompletely from the nucleus to the cytoplasm, but also inhibited expression of survivin, while it did not affect expression of apoptosis-promoting factor Bax. PPAR gamma ligands inhibit growth and induce apoptosis of liver cancer cells, and may have applications for the prevention and treatment of liver cancer.

Effect of Troglitazone on expression of adhesion molecules and eNOS in human saphenous vein gaft

To investigate whether peroxisome proliferators-activated receptor-gamma (PPARgamma) ligand Troglitazone can reduce endothelial injury and activation during storage of harvested saphenous vein grafts. Segments of human saphenous vein graft were collected from 9 patients undergoing coronary bypass surgery and then divided into two equal parts of control and test specimens, were stored in either heparinized blood (control group) or heparinized blood containing 20 mumol/L troglitazone (test group) for 1 h at room temperature. Tissue distribution and protein expression of VCAM-1, ICAM-1, and endothelial nitric oxide synthase (eNOS) were compared using immunohistochemistry and Western blot analysis. Myeloperoxidase (MPO) activity, a marker of neutrophil sequestration in human saphenous vein grafts, was also measured in each group. The expression of ICAM-1 (753+/-132 versus 7201+/-934; P<0.01), VCAM-1 (3731+/-294 versus 8292+/-793; P<0.01), and MPO activity (1.52+/-0.42 U/g, 5.04+/-1.26 U/g P<0.01) were significantly lower in test group. In contract, eNOS expression (7983+/-834 versus 3989+/-1008; P<0.01) was significantly higher in test group. PPARgamma ligand troglitazone might reduce endothelial injury during the storage period of human saphenous vein grafts.

Activation of AMP‐activated protein kinase, inhibition of pyruvate dehydrogenase activity, and redistribution of substrate partitioning mediate the acute insulin‐sensitizing effects of troglitazone in skeletal muscle cells

The aim of this study was to investigate the acute effects of troglitazone on several pathways of glucose and fatty acid (FA) partitioning and the molecular mechanisms involved in these processes in skeletal muscle. Exposure of L6 myotubes to troglitazone for 1 h significantly increased phosphorylation of AMPK and ACC, which was followed by approximately 30% and approximately 60% increases in palmitate oxidation and carnitine palmitoyl transferase-1 (CPT-1) activity, respectively. Troglitazone inhibited basal ( approximately 25%) and insulin-stimulated ( approximately 35%) palmitate uptake but significantly increased basal and insulin-stimulated glucose uptake by approximately 2.2- and 2.7-fold, respectively. Pharmacological inhibition of AMPK completely prevented the effects of troglitazone on palmitate oxidation and glucose uptake. Interestingly, even though troglitazone exerted an insulin sensitizing effect, it reduced basal and insulin-stimulated rates of glycogen synthesis, incorporation of glucose into lipids, and glucose oxidation to values corresponding to approximately 30%, approximately 60%, and 30% of the controls, respectively. These effects were accompanied by an increase in basal and insulin-stimulated phosphorylation of Akt(Thr308), Akt(Ser473), and GSK3alpha/beta. Troglitazone also powerfully suppressed pyruvate decarboxylation, which was followed by a significant increase in basal ( approximately 3.5-fold) and insulin-stimulated ( approximately 5.5-fold) rates of lactate production by muscle cells. In summary, we provide novel evidence that troglitazone exerts acute insulin sensitizing effects by increasing FA oxidation, reducing FA uptake, suppressing pyruvate dehydrogenase activity, and shifting glucose metabolism toward lactate production in muscle cells. These effects seem to be at least partially dependent on AMPK activation and may account for potential acute PPAR-gamma-independent anti-diabetic effects of thiazolidinediones in skeletal muscle.

Protective Effects of Peroxisome Proliferator-Activated Receptor γ Ligand on Apoptosis and Hepatocyte Growth Factor Induction in Renal Ischemia-Reperfusion Injury

Renal ischemia-reperfusion injury affects the long-term outcome of renal graft survival. Thiazolidinediones (TZDs), synthetic peroxisome proliferator-activated receptor (PPAR)-gamma ligands, have been shown to exert therapeutic effects upon renal ischemia-reperfusion injury far beyond their use as insulin sensitizers. It has also been reported that hepatocyte growth factor (HGF) has a beneficial effect on renal ischemia-reperfusion injury and that TZDs induce increased HGF mRNA expression and protein secretion. We investigated the effect of troglitazone, one of the TZDs, in a rat model of renal ischemia-reperfusion injury. A 45-minute period of warm renal ischemia was induced by bilateral clamping at 37 degrees C with rats being sacrificed before the onset of ischemia and at 2, 4, 6, and 12 hr after reperfusion. The expression of PPAR-gamma was measured by reverse-transcriptase polymerase chain reaction (RT-PCR) and western blotting while the production of HGF was investigated by RT-PCR and immunohistochemistry. The effect of troglitazone treatment on the level of apoptosis was determined by staining for cleaved caspase-3 and single-stranded DNA (ssDNA). The numbers of cleaved caspase-3 and ssDNA positive cells were decreased in rats treated with troglitazone. The production of HGF mRNA and protein was most intense at 4 hr. The expression of PPAR-gamma and HGF was increased in the group treated with troglitazone compared with the control group. CONCLUSIONS.: Pretreatment of rats with the PPAR-gamma ligand troglitazone decreased apoptotic cell death in renal ischemia-reperfusion injury as a result of the induction of HGF.

Troglitazone acutely activates AMP-activated protein kinase and inhibits insulin secretion from beta cells

Changes in AMP-activated protein kinase (AMPK) activity contribute to the regulation of insulin secretion. Troglitazone has been shown to lower serum insulin levels and protect beta cell function. The aim of the present study was to examine the effects of troglitazone on AMPK activity and insulin secretion in beta cells. Isolated rat islets and MIN6 cells were treated for a short (1 h) or a long time (20 h) with troglitazone. One-hour troglitazone treatment activated AMPK and inhibited both glucose-stimulated insulin secretion (GSIS) and the response of insulin secretion to combined stimuli of glucose and palmitate. Long (20 h) treatment with troglitazone caused a sustained phosphorylation of AMPK and acetyl-CoA carboxylase, and increased GSIS after withdrawal of the drug. This study provided evidence that troglitazone activated AMPK in beta cells. In addition to the insulin-sensitizing effects in peripheral tissues, troglitazone also directly inhibits insulin hypersecretion by the elevated glucose and fatty acids, and thus protects beta cells from glucolipotoxicity.

Troglitazone induces differentiation in Trypanosoma brucei

Trypanosoma brucei, a protozoan parasite causing sleeping sickness, is transmitted by the tsetse fly and undergoes a complex lifecycle including several defined stages within the insect vector and its mammalian host. In the latter, differentiation from the long slender to the short stumpy form is induced by a yet unknown factor of trypanosomal origin. Here we describe that some thiazolidinediones are also able to induce differentiation. In higher eukaryotes, thiazolidinediones are involved in metabolism and differentiation processes mainly by binding to the intracellular receptor peroxisome proliferator activated receptor γ. Our studies focus on the effects of troglitazone on bloodstream form trypanosomes. Differentiation was monitored using mitochondrial markers (membrane potential, succinate dehydrogenase activity, inhibition of oxygen uptake by KCN, amount of cytochrome transcripts), morphological changes (Transmission EM and light microscopy), and transformation experiments (loss of the Variant Surface Glycoprotein coat and increase of dihydroliponamide dehydrogenase activity). To further investigate the mechanisms responsible for these changes, microarray analyses were performed, showing an upregulation of expression site associated gene 8 (ESAG8), a potential differentiation regulator.

Role of mitogen-activated protein kinase (MAPK) in troglitazone-induced osteoblastic cell death

Troglitazone, a PPARγ agonist, has been reported to induce cell death on different cell types. However, its mechanism of action remains unclear. The present study was undertaken to investigate the effect of troglitazone on cell death and to determine its underlying mechanism in MC3T3-E1 cells, an established osteoblast cell line. Troglitazone induced loss of cell viability in a dose- and time-dependent manner, which was accompanied by apoptosis. Troglitazone increased reactive oxygen species (ROS), but troglitazone-induced cell death was not affected by the antioxidant N-acetylcysteine, suggesting that the ROS generation is not involved in the cytotoxicity of troglitazone. Troglitazone-induced cell death was prevented by the PPARγ antagonist GW9662. Troglitazone treatment inhibited activation of extracellular signal-regulated protein kinase (ERK) and stimulated p38 activation. Troglitazone-induced cell death was increased by the ERK inhibitor U0126 and prevented by transfection with constitutively active MEK1 and the p38 inhibitor SB203580. Troglitazone induced depolarization of mitochondrial membrane potential and its effect was blocked by SB203580 and GW9662. Caspase-3 was activated by troglitazone treatment and pharmacological inhibition of caspase blocked troglitazone-induced cell death. Taken together, these data suggest that troglitazone induces apoptosis via a caspase-dependent mechanism associated with down-regulation of ERK and up-regulation of p38.

Differential effects of PPARγ agonists on the metabolic properties of gliomas and astrocytes

Recent studies show that thiazolinediones (TZDs), agonists of the peroxisome proliferator-activated receptor gamma (PPARγ), induce apoptosis in glioma and glioblastoma cells. Here we compared the effects of troglitazone (Trog), a TZD with low affinity for binding to PPARγ but with potent metabolic effects, on survival and metabolism in GL261 glioma cells versus primary astrocytes. Trog dose-dependently induced cell death in GL261 cells (with over 90% death at 30 μM) but did not cause any toxicity in astrocytes at the same doses. Measurements of glucose and lactate levels after incubation with Trog (30 μM) indicated an overall increase of glucose consumption and lactate production in both cell types. In astrocytes the ratio of lactate produced to glucose utilized was not significantly altered by Trog, while in glioma cells this ratio was decreased by about 40%. Trog dose-dependently reduced mitochondrial membrane potential (Δ Ψ m) in both cell types; and the loss of Δ Ψ m was greater in the tumor cells (90% loss at 20 μM) than in astrocytes (70% loss at 20 μM). These results suggest that differences in metabolic responses could contribute to the selective resistance of astrocytes to cytotoxic effects of Trog. TZDs such as Trog should therefore be considered for testing in treatment of gliomas.

Effect of Thiazolidinedione on the Proliferation of Bovine Retinal Endothelial Cells Stimulated by Vascular Endothelial Cell Growth Factor

To investigate the effect of troglitazone, an antidiabetic drug, on the cytosolic Ca(2+) concentrations ([Ca(2+)]i) and the cell cycles of bovine retinal endothelial cells (RECs) stimulated with vascular endothelial growth factor (VEGF). The changes in [Ca(2+)]i were monitored using microfluorometry with Fura-2. The phase of the cell cycle was examined by an immunocytochemical analysis using monoclonal antibodies against cell cycle-specific nuclear antigens. In the presence of extracellular Ca(2+), VEGF-induced transient [Ca(2+)]i elevation followed by continuous steady-state elevation resulted in cell cycle progression in RECs. The removal of extracellular Ca(2+) inhibited the continuous component, but transient [Ca(2+)]i elevation was still observed. These results are compatible with the hypothesis that a continuous steady-state elevation of [Ca(2+)]i may be mediated mainly through the influx of extracellular Ca(2+). Pretreatment with 10 microM troglitazone prevented the transient and continuous steady-state elevation of [Ca(2+)]i, resulting in an inhibition of the cell cycle in RECs stimulated with VEGF. These data suggest that troglitazone inhibits VEGF-induced cell cycle progression through the inhibition of [Ca(2+)]i in RECs.

Connective tissue growth factor and fibronectin secretion in renal tubular epithelial cells induced by TGF‐β1: Suppressive effects of troglitazone

Although some studies have suggested that troglitazone could retard the progression of glomerulosclerosis, its effects on renal tubulointerstitial fibrosis have not been completely clarified. The aim of this study was to investigate the effects of troglitazone on the secretion of connective tissue growth factor (CTGF) and fibronectin (FN) in human renal proximal tubular epithelial (HK-2) cells induced by transforming growth factor-beta1 (TGF-beta1). The mRNA of CTGF and FN were measured by semi-quantitative RT-PCR. CTGF and FN protein were detected by Western blot and ELISA, respectively. Our results revealed that troglitazone could inhibit CTGF and FN expression in a dose-dependent manner in human renal proximal tubular epithelial cells induced by TGF-beta1, which may be one of the mechanisms of troglitazone contributing to retard the progression of renal tubulointerstitial fibrosis.

Effects of Troglitazone on the Expression of VEGF and TGF-β in Cultured Rat Mesangial Cells

Background: Clinical study reported that troglitazone ameliorated microalbuminuria in diabetic nephropathy. However, the mechanism of action is not fully understood. Vascular endothelial growth factor (VEGF) is known as vascular permeability factor and it is considered the most likely cause of glomerular hyperfiltration and proteinuria in diabetic nephropathy. Transforming growth factor-beta (TGF-β) is a potent inducer of extracellular matrix production and fibrosis in renal cells and one of the important cytokine in the pathogenesis of diabetic nephropathy. To determine whether troglitazone affects VEGF and TGF-β production in diabetic nephropathy, we examined the effects of troglitazone on the VEGF and TGF-β expression in cultured rat mesangial cells exposed to high glucose concentration.Methods: Rat mesangial cells were cultured in media with D-glucose 5.5 mM (NG) or D-glucose 30 mM (HG), or D-glucose 30 mM/troglitazone 20 μM (HTz) and for 6, 24, or 72 hours, respectively. VEGF and TGF-β expression were assessed by semiquantitative RT-PCR and western blot analysis.Results: Troglitazone decreased the VEGF164 and VEGF120 mRNA expressions in cultured rat mesangial cells exposed to high glucose concentration with incubation for 24 and 72 hours, respectively. VEGF protein was also decreased in experimental group treated with troglitazone (HTz) than in those with HG for 24 and 72 hours. However troglitazone had no effect on the expression of TGF-β mRNA in mesangial cells. Conclusion: This study suggested that troglitazone may modulate the development and progression of diabetic nephropathy by reducing the expression of VEGF in mesangial cells (J Kor Diabetes Assoc 31:220~229, 2007)

Troglitazone-Induced Hepatic Necrosis in an Animal Model of Silent Genetic Mitochondrial Abnormalities

Troglitazone, a first-generation thiazolidinedione antidiabetic drug, was withdrawn from the market due to an unacceptable risk of idiosyncratic hepatotoxicity. Troglitazone does not cause hepatotoxicity in normal healthy rodents, but it produces mitochondrial injury in vitro at high concentrations. The aim of this study was to explore whether genetic mitochondrial abnormalities might sensitize mice to hepatic adverse effects of troglitazone. We used heterozygous superoxide dismutase 2 (Sod2(+/-)) mice as a model of clinically silent mitochondrial stress. Troglitazone was daily administered for 4 weeks (0, 10 or 30 mg/kg/day, ip). We found that troglitazone caused overt liver injury in the high-dose group, manifested by increased serum alanine aminotransferase activity (> twofold) and midzonal areas of hepatic necrosis, in Sod2(+/-) but not in wild-type mice. No signs of hepatotoxicity were apparent at 2 weeks of treatment. Hepatic mitochondria isolated from troglitazone-treated mice exhibited decreased activities of aconitase (by 45%) and complex I (by 46%) and increased (by 58%) protein carbonyls, indicative of enhanced mitochondrial oxidant stress. This was paralleled by compensatory increases in mitochondrial glutathione levels. Finally, in hepatocytes isolated from untreated Sod2(+/-), but not wild-type mice, troglitazone caused a concentration-dependent increase in superoxide anion levels as demonstrated with a selective mitochondria-targeting fluorescent probe. In conclusion, prolonged administration of troglitazone can superimpose oxidant stress, potentiate mitochondrial damage, and induce delayed hepatic necrosis in mice with genetically compromised mitochondrial function. These data are consistent with our hypothesis that inherited or acquired mitochondrial abnormalities may be one of the contributing determinants of susceptibility to troglitazone-induced idiosyncratic liver injury.

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 μM) 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.

Rosiglitazone treatment alleviates inflammation and improves liver function in overweight women with polycystic ovary syndrome: a randomized placebo-controlled study

In a randomized, placebo-controlled study, we studied the effects of 4 months' treatment with rosiglitazone on low-grade inflammation, liver function, lipid levels, and blood pressure in 30 overweight women with polycystic ovary syndrome. Rosiglitazone significantly decreased serum C-reactive protein levels, white blood cell count, and alanine aminotransferase enzyme activity but did not affect lipid or blood pressure levels. Placebo had no effect on any parameters.

Phorbol ester potentiates the growth inhibitory effects of troglitazone via up-regulation of PPARγ in A549 cells

The activation of peroxisome proliferator-activated receptor gamma (PPARγ) has been shown to induce growth arrest and differentiation of various cancer cells. In the current study, we investigated the effect of 12-O-tetradecanoylphorbol-13-acetate (TPA) on the expression of PPARγ and proliferation of A549 cells. TPA elicited a dose- and time-dependent increase in PPARγ mRNA and protein levels. PPARγ expression in response to TPA was attenuated by pretreatment with bisindolylmaleimide I, N-acetyl-L-cysteine (NAC) and PD98059. TPA-induced protein kinase C (PKC) activation was linked to the generation of reactive oxygen species (ROS), both of which were indispensable for PPARγ expression in A549 cells. Pretreatment with bisindolylmaleimide I or NAC blocked TPA-induced phosphorylation of extracellular signal-regulated kinase (ERK), suggesting that ERK-mediated signaling is also involved in the induction of PPARγ. Furthermore, the growth inhibitory effect of troglitazone was significantly potentiated by prolonged incubation with TPA and was attenuated in the presence of GW9662, a specific inhibitor of PPARγ. These effects were associated with an induction of cell cycle arrest at G0/G1 phase, which was accompanied by the induction of p21Waf1/Cip1 expression and decreased cyclin D1 expression. Taken together, these observations indicate that TPA synergizes with PPARγ ligand to inhibit cell growth through up-regulation of PPARγ expression.

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.

Troglitazone and 9cis,11trans,13trans-Conjugated Linolenic Acid: Comparison of Their Antiproliferative and Apoptosis-Inducing Effects on Different Colon Cancer Cell Lines

Background: We have previously reported that troglitazone, a synthetic ligand for peroxisome proliferator-activated receptor γ (PPARγ), and bitter gourd seed oil rich in 9cis,11trans,13trans-conjugated linolenic acid (9c,11t,13t-CLN) prevent colon carcinogenesis. To evaluate the chemotherapeutic effect and potency of these compounds on colon cancer cells, we investigated their antiproliferative and apoptosis-inducing effects using different human colon cancer cell lines. Methods: The antiproliferative and apoptosis-inducing effects of troglitazone and 9c,11t,13t-CLN were evaluated and compared using HT-29, DLD-1 and Caco-2 cells at different stages of enterocytic differentiation. Results: Troglitazone and 9c,11t,13t-CLN decreased cell viability and induced apoptosis in three colon cancer cell lines. The susceptibility of HT-29, which expresses PPARγ at high levels, to troglitazone and 9c,11t,13t-CLN was higher than that of Caco-2 cells with low levels of PPARγ. Conclusion: Troglitazone and 9c,11t,13t-CLN exhibited more effective chemotherapeutic effects on HT-29 cells than on Caco-2 cells.

Troglitazone sensitizes tumor cells to TRAIL-induced apoptosis via down-regulation of FLIP and Survivin

Induction of apoptosis by the death ligand TRAIL might be a promising therapeutic approach in cancer therapy. However, since not all tumor cells are sensitive to TRAIL, there is a need for the development of strategies to overcome TRAIL-resistance. The results of the present study show that the anti-diabetic drug troglitazone sensitizes human glioma and neuroblastoma cells to TRAIL-induced apoptosis. This process is accompanied by a substantial increase of active caspase 8 and active caspase 3, but it is independent of troglitazone's effects on the nuclear receptor PPAR-gamma. Troglitazone induces a pronounced reduction in protein expression levels of the anti-apoptotic FLICE-inhibitory protein (FLIP) without affecting FLIP mRNA levels. Further, protein and mRNA expression levels of the anti-apoptotic protein Survivin significantly decrease upon treatment with troglitazone. Moreover, sensitization to TRAIL is partly accompanied by an up-regulation of the TRAIL receptor, TRAIL-R2. A combined treatment with troglitazone and TRAIL might be a promising experimental therapy because troglitazone sensitizes tumor cells to TRAIL-induced apoptosis via various mechanisms, thereby minimizing the risk of acquired tumor cell resistance.

Low-Dose Rosiglitazone Exerts an Antiinflammatory Effect with an Increase in Adiponectin Independently of Free Fatty Acid Fall and Insulin Sensitization in Obese Type 2 Diabetics

We have previously demonstrated an early and potent antiinflammatory effect of troglitazone and rosiglitazone. Because inflammatory mediators interfere with insulin signal transduction, we have now hypothesized that rosiglitazone exerts an initial antiinflammatory effect independently of its metabolic actions including the suppression of the plasma concentration of free fatty acids (FFAs), insulin, and glucose after which insulin sensitization occurs. Fourteen patients with type 2 diabetes were included in the study. Eight patients were given 2 mg daily of rosiglitazone for 6 wk, whereas the other six patients were given a placebo for the same period. After a 2-mg dose of rosiglitazone, plasma FFAs, insulin, and glucose concentrations and homeostasis model assessment of insulin resistance did not change. Plasma C-reactive protein, serum amyloid A, and matrix metalloproteinase concentrations fell significantly at wk 1 and continued to be significantly lower than the baseline levels by 25, 29, and 24%, respectively, at wk 6. Leukocyte count was significantly lower at wk 6 after rosiglitazone, whereas there was no change in the control group. Plasma adiponectin concentrations increased significantly at wk 2 and continued to increase during the treatment period with rosiglitazone. Resistin concentrations fell significantly by 10% at wk 6 only. There were no changes in any of these indices in the placebo group. A low dose of rosiglitazone exerts an early and potent antiinflammatory effect with an increase in adiponectin and a fall in resistin concentrations without causing any metabolic changes (fall in plasma glucose, FFAs, and insulin concentrations) over a 6-wk period. The increase in adiponectin and the decrease in resistin after rosiglitazone are thus related primarily to its antiinflammatory effects rather than its metabolic actions. These observations have implications in relation to the mode of action of this drug as an insulin-sensitizing agent and also its use as a potential antiinflammatory and antiatherogenic drug in the future.

PPARr agonist, troglitazone induce growth arrest and apoptosis in MDA-MB-231 human breast cancer cell

13155 Background: Estrogen receptor (ER)-negative breast carcinomas do not respond to hormone therapy, making their effective treatment very difficult. It is recently reported that peroxisome proliferator-activated receptor-gamma (PPAR-γ) has become a potential target for the prevention and treatment of human cancer. Therefore, PPAR-γ agonist, troglitazone has been extensively studied as a chemopreventive or therapeutic agent in several types of cancer. The purpose of this study was to assess whether troglitazone (TRO) would induce cell growth arrest and apoptosis in MDA-MB-231 (ER-negative) human breast cancer cells. Methods: Cytostatic/cytotoxic effects of troglitazone were measured with MTT assay. The cell cycle distribution was evaluated with flow cytometer. The expression of cyclin-dependent kinase inhibitors, p21, p27, and cell cycle dependent kinases was measured with Western blotting. Apoptotic cells were determined by Hoechst staining and TUNEL assay. Results: Troglitazone inhibited cell proliferation by inducing 65% G0/G1 arrest after 48 h. Accumulation of cells in G0/G1 was accompanied by a decrease of Rb protein phosphorylation associated with reduced activities of cell cycle dependent kinases (CDKs) such as cdk2 and cyclin D. Troglitazone increased the expression cyclin kinase inhibitors, p21 and p27 as MDA-MB-231 cell underwent G0/G1 arrest. Apoptotic effect by troglitazone demonstrated that apoptotic cells elevated from 2.5-fold of the control level at 10 uM, to 3.6-fold at 50 uM and to 4.7-fold at 75 uM. Conclusion: These results indicate that activation of PPAR-gamma with troglitazone induces apoptosis through cell cycle inhibition in estrogen receptor-negative breast cancer cell MDA-MB-231. PPAR-gamma therefore represents a putative molecular target for chemopreventive therapy or inhibition of breast cancer growth. No significant financial relationships to disclose.