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PubMed1999

Effect of troglitazone on plasma lipid metabolism and lipoprotein lipase.

AIMS: To clarify how troglitazone, an insulin-sensitizing agent, affects lipid metabolism and postheparin plasma lipoprotein lipase (LPL). METHODS: Fifteen patients (3 male, 12 female) (the average age 62+/-7 years; the mean body mass index (BMI) 25+/-3 kg/m2 ) were recruited for this study. The serum lipids and postheparin plasma lipoprotein lipase (LPL) mass before and 4 weeks after oral administration of troglitazone (200 mg day-1 ) were measured. A mouse preadipocyte cell line, 3T3-L1, was incubated with troglitazone and LPL enzyme protein mass in the culture media was measured by an enzyme linked immunosorbent assay. A reverse transcription polymerase chain reaction (RT-PCR) using primers specific for the carboxyl terminal 135 amino acid of mouse LPL cDNA was used to evaluate the effect of troglitazone on expression of LPL and Northern blot analysis carried out to determine expression of LPL. RESULTS: The average levels before treatment of fasting serum total cholesterol, triglycerides, high density lipoprotein cholesterol, plasma glucose and glycohaemoglobin A1c were 5.6+/-0.9, 1.8+/-1.0, 1.5+/-0.5, 8.1+/-1.7 mmol l-1 and 7.8+/-1.6% respectively. Four weeks after treatment, those levels were 5.4+/-0.9, 1.2+/-0.3 (P=0.004), 1.6+/-0.5 (P=0.02) mmol l-1, 7.7+/-2.3 mmol l-1 and 7. 3+/-0.6% (P=0.01), respectively. The postheparin plasma LPL mass increased from 226+/-39 to 257+/-68 ng ml-1 (P=0.03) during that period. The LPL mass in the media of 3T3 L1 cells cultured in the presence of 10, 20 or 30 microm of this compound increased in a dose dependent manner. RT-PCR revealed that the area of the bands of the RT-PCR products on 1.5% agarose gel analyzed with NIH image from the cell extracts cultured in the presence of 10 microm troglitazone was significantly larger (P=0.0069) than that in the absence of this compound. Northern blot analysis revealed that in the cultured 3T3-L1 cells, the expression of LPL was enhanced in the presence of 10 microm troglitazone. CONCLUSIONS: Troglitazone improves plasma triglyceride-rich lipoproteins metabolism by enhancing the expression of LPL in adipocytes.

3T3 Cells↗

PubMed2000

Potential interaction between troglitazone and atorvastatin.

BACKGROUND: Troglitazone is a CYP3A4 isoenzyme inducer known to decrease the plasma concentration of drugs metabolized by CYP3A4. Atorvastatin, a known substrate of the CYP3A4 pathway, is often used in combination with troglitazone for diabetic patients with dyslipidemia. AIMS: The purpose of this study was to investigate the clinical effects of troglitazone on the fasting lipid profiles of patients receiving atorvastatin. METHOD: We retrospectively reviewed the medical records of patients who received concomitant troglitazone and atorvastatin therapy during a 24-month period. Patients were included in the analysis if during the study period, complete laboratory data were available (fasting lipid profile and glycosylated haemoglobin), the dose of atorvastatin remained unchanged, there were no changes in the diabetic drug regimen, patients received at least 3 months of combination therapy and patients were adherent with their medication. RESULTS: Four out of 31 (13%) patients satisfied the inclusion criteria. All of these patients were male, with a mean age of 63. All patients were receiving insulin only for diabetes control when the troglitazone was added. There was an increase in LDL-cholesterol and triglycerides of 23.3% and 21.3%, respectively. CONCLUSION: The increase in LDL-cholesterol and triglycerides on atorvastatin and troglitazone combination therapy compared with atorvastatin mono-therapy is suggestive of a drug interaction. Further studies involving troglitazone and atorvastatin may be warranted to substantiate this interaction.

Aged↗

PubMed2003

Hydrogen peroxide overproduction in megamitochondria of troglitazone-treated human hepatocytes.

Troglitazone has been withdrawn from therapeutic options for diabetes mellitus because of its severe hepatocyte toxicity of unknown pathogenesis. The aim of the present study was to assess both morphologic and functional alterations in the mitochondria of troglitazone-treated hepatocytes. A polarized human hepatocyte cell line, OUMS-29, was used in this study. The mitochondrial volume and the mitochondrial transmembrane potential (DeltaPsi(m)) were examined using flow cytometry with nonylacridine orange (NAO) and rhodamine-123, respectively. An ultrastructural examination of the troglitazone-treated OUMS-29 cells was performed using transmission electron microscopy (TEM). Reactive oxygen species (ROS) production was assessed using flow cytometry with dihydroethidium and 2',7'-dichlorodihydrofluorescein diacetate. A significant increase in the mitochondrial volume of the troglitazone-treated cells was found by the NAO analysis, in comparison with pioglitazone-treated and ciglitazone-treated cells. The increase in volume was due to a marked enlargement in the mitochondria. The markedly enlarged mitochondria with intramitochondrial electron-dense deposits were confirmed on TEM, which showed myelin-like structures, indicating degraded membrane constituents. The troglitazone-treated cells showed a significant decline in the DeltaPsi(m) per unit mitochondrial volume but resulted in no clear cell death. ROS analysis revealed a significant production of hydrogen peroxide in the troglitazone-treated hepatocytes. This production was attenuated using an antioxidant, N-acetyl-L-cysteine. In conclusion, troglitazone caused overproduction of hydrogen peroxide, which deteriorated both mitochondrial membrane structures and mitochondrial function, leading to a possible priming for the severe hepatocyte toxicity.

Acetylcysteine↗

PubMed2002

The effect of troglitazone on plasma homocysteine, hepatic and red blood cell S-adenosyl methionine, and S-adenosyl homocysteine and enzymes in homocysteine metabolism in Zucker rats.

We studied the effect of troglitazone on the plasma concentrations of homocysteine (tHcy), the erythrocyte and hepatic concentrations of S-adenosylmethionine (SAM) and S-adenosylhomocysteine (SAH), and the hepatic activities of cystathionine-beta-synthase (C beta S) and methylenetetrahydrofolate reductase (MTHFR) in lean and fatty Zucker rats (a model of insulin resistance). Four groups of female Zucker rats were studied. Troglitazone (200 mg/kg) was administered by gavage daily for 3 weeks to lean and fatty Zucker rats. The other 2 groups served as controls. The blood parameters were determined at days 0, 10, and 21. The hepatic SAM and SAH concentrations and MTHFR and C beta S were measured in the 3-week liver samples. Plasma homocysteine fell significantly in all troglitazone-treated animals from a mean +/- SD of 7.6 +/- 1.5 micromol/L to 4.5 +/- 1.1 micromol/L (P <.02) but not in control animals (5.7 +/-1.8 micromol/L to 5.9 +/- 1.8 micromol/L). The decreases induced by troglitazone in homocysteine were seen in both the lean and the fatty Zucker rats. This was accompanied by significant rises in the hepatic concentrations of SAH and SAM + SAH. In addition, a significant decline in the hepatic SAM/SAH ratio was observed. The mean +/- SD hepatic C beta S (expressed as nmol of cystathionine formed at 37 degrees C) in the troglitazone-treated rats was 1,226 +/- 47 nmol/h/mg protein, which was significantly higher than that in the control group (964 +/- 64 nmol/h/mg protein; P =.03). We conclude that troglitazone lowers plasma homocysteine in insulin-resistant animals. The homocysteine-lowering effects of troglitazone may be mediated in part by a shift in the concentrations of tHcy and its related metabolites from the blood to the liver as well as by an upregulation of hepatic C beta S activity. These data support the hypothesis that insulin may regulate homocysteine metabolism through regulation of hepatic C beta S activity, although activity of other hepatic enzymes not studied here may also contribute to these observations.

Animals↗

PubMed2006

Effect of troglitazone on serum gamma-glutamyltransferase activity and plasma t-PA/PAI-1 complex in type 2 diabetic patients.

BACKGROUND: This study was conducted to determine whether troglitazone (CAS 97322-87-7, Noscal), a thiazolidinedione with alpha-tocopherol in the side chain, had an antioxidant effect in patients with Type 2 diabetes. METHODS: In 46 Type 2 diabetic outpatients aged 64 +/- 7 years (male/female: 33/13), with a body mass index of 23.4 +/-2.8 kg/m2, a 2-year prospective study was performed. Patients were given troglitazone tablet (200 mg) twice a day. After treatment for 4 months, troglitazone was withheld for one month (washout period). Then troglitazone was resumed for a further 19 months. RESULTS: The study was completed in 28 patients. In 18 patients, it was not completed because of side effects in 4 female patients and because of withdrawal of troglitazone from the Japanese market in 14 patients. Fasting plasma glucose was decreased by troglitazone treatment from 170.2 +/- 38.2 mg/dl to 151.6 +/- 34.5 mg/dl (ANOVA: F = 8.054, p < 0.001). Washout caused it to return to the pre-treatment level (170.9 +/- 38.0 mg/dl), but it decreased again to 145.4 +/- 33.4 mg/dl with the resumption of treatment (F = 3.845, p < 0.001). Glycated hemoglobin was decreased by treatment from 8.2 +/- 1.6 % to 7.9 +/- 1.6 % (F = 7.558, D < 0.001). Washout caused it to return to the pre-treatment level (8.0 +/- 1.6 %), but it decreased again to 7.6 +/- 1.2 % with the resumption of treatment (F = 1.985, p = 0.041). Fasting serum immunoreactive insulin was decreased by treatment from 5.5 +/- 3.4 pU/ml to 4.0 +/- 2.2 pU/ml (F = 9.098, p < 0.001). Washout caused it to return to near the pre-treatment level (4.6 +/- 2.4 pU/ml). After resumption of treatment, it remained unchanged. Serum n-glutamyltransferase (gamma-GT) activity was decreased by treatment from 37.5 +/- 25.7 U/I to 25.6 +/- 12.3 U/I (F = 19.406, p < 0.001). Washout caused it to return to the pre-treatment level (36.5 +/- 25.1 U/I), but it decreased again to 24.2 +/- 10.1 U/l with the resumption of treatment (F = 7.931, p < 0.001). Plasma tissue plasminogen activator(t-PA)/plasminogen activator inhibitor-1 (PAI-1) complex was decreased by treatment from 21.7 + 8.6 ng/ml to 19.0 +/- 6.6 ng/ml (F = 8.784, p < 0.001). Washout caused it to return to the pretreatment level (21.9 +/- 7.4 ng/ml), but it decreased again to 14.3 +/- 4.3 ng/ml after the resumption of treatment (F = 12.341, p < 0.001). CONCLUSION: Decreases in serum gamma-GT activity and plasma t-PA/PAI-1 complex were closely related with antioxidant action of troglitazone.

Aged↗

PubMed1994

Improvement in glucose tolerance and insulin resistance in obese subjects treated with troglitazone.

BACKGROUND: Troglitazone decreases insulin resistance and hyperglycemia in patients with non-insulin-dependent diabetes mellitus (NIDDM), but its effects on subjects without diabetes are not known. METHODS: We performed oral and intravenous glucose-tolerance tests, studies with the euglycemic-hyperinsulinemic clamp, meal-tolerance tests, and 24-hour blood-pressure measurements at base line and after the administration of troglitazone, 200 mg orally twice daily, or placebo for 12 weeks in 18 nondiabetic obese subjects, 9 of whom had impaired glucose tolerance. RESULTS: The mean (+/- SD) rates of glucose disposal increased from 4.7 +/- 1.7 to 6.0 +/- 1.7 mg per kilogram of body weight per minute (P = 0.004) and from 9.0 +/- 1.8 to 9.9 +/- 1.3 mg per kilogram per minute (P = 0.02) during insulin infusions of 40 and 300 mU per square meter of body-surface area per minute, respectively, in the troglitazone group. The insulin-sensitivity index, calculated from the results of intravenous glucose-tolerance tests, increased from 0.7 +/- 0.6 x 10(-4) to 1.6 +/- 0.9 x 10(-4) in subjects given troglitazone, and their glycemic response to oral glucose and to mixed meals decreased. The mean fasting plasma insulin concentration decreased by 48 percent (P = 0.002), and the plasma insulin response to oral glucose and mixed meals decreased by 40 and 41 percent, respectively. The changes were similar in the subjects with normal glucose tolerance and those with impaired glucose tolerance. Systolic and diastolic blood pressure decreased by 5 +/- 2 mm Hg (P = 0.05) and 4 +/- 2 mm Hg (P = 0.04), respectively, after treatment with troglitazone. There were virtually no changes in the placebo group. CONCLUSIONS: Troglitazone decreases insulin resistance and improves glucose tolerance in obese subjects with either impaired or normal glucose tolerance. The ability of troglitazone to reduce insulin resistance could be useful in preventing NIDDM:

Adult↗

PubMed2005

A peroxisome proliferator-activated receptor-gamma agonist, troglitazone, facilitates caspase-8 and -9 activities by increasing the enzymatic activity of protein-tyrosine phosphatase-1B on human glioma cells.

Despite dramatic advances in adjuvant therapies, patients with malignant glioma face a bleak prognosis. Because many adjuvant therapies seek to induce glioma apoptosis, strategies that lower thresholds for the induction of apoptosis may improve patient outcomes. Therefore, elucidation of the biological mechanisms that underlie resistance to current therapies is needed to develop new therapeutic strategies. Here we proposed a novel mechanism of proapoptotic effect induced by a pharmacological peroxisome proliferator-activated receptor-gamma (PPARgamma) agonist, troglitazone, that facilitates caspase signaling in human glioma cells. Troglitazone activates protein-tyrosine phosphatase (PTP)-1B, which subsequently reduces phosphotyrosine 705 STAT3 (pY705-STAT3) via a PPARgamma-independent pathway. Reduction of pY705-STAT3 in glioma cells caused down-regulation of FLIP (FADD-like IL-1beta-converting enzyme-inhibitory protein) and Bcl-2. Furthermore, troglitazone induced Ser-392 phosphorylation of p53 via a PPARgamma-dependent pathway and up-regulation of Bax in a p53 wild-type glioma. When given with tumor necrosis factor-related apoptosis-inducing ligand or caspase-dependent chemotherapeutic agents, such as etoposide and paclitaxel, troglitazone exhibited a synergistic effect by facilitating caspase-8/9 activities. A PPARgamma antagonist, GW9662, did not block this effect, although a PTP inhibitor abrogated it. Knockdown of STAT3 by STAT3-small interfering RNA negated the inhibitory effect of PTP inhibitor on troglitazone, indicating that troglitazone uses a STAT3 inactivation mechanism that makes caspase-8/9 activities susceptible to cytotoxic agents in glioma cells and that PTP1B plays a critical role in the down-regulation of activated STAT3, as well as FLIP and Bcl-2. When taken with caspase-dependent anti-neoplastic agents, troglitazone may be a promising drug for use against malignant gliomas because it facilitates the caspase cascade, thereby lowering thresholds for the apoptosis induction of glioma cells.

Antineoplastic Agents↗

PubMed2000

In vitro inhibitory effects of troglitazone and its metabolites on drug oxidation activities of human cytochrome P450 enzymes: comparison with pioglitazone and rosiglitazone.

1. Investigated were the effects of a new oral antidiabetic drug, troglitazone, and its three metabolites and antidiabetic drug candidates pioglitazone and rosiglitazone on xenobiotic oxidations catalyzed by nine recombinant human cytochrome P450 (P450 or CYP) enzymes and by human liver microsomes. 2. Troglitazone (5 microM) significantly inhibited CYP2C8-dependent paclitaxel 6alpha-hydroxylation and CYP2C9-dependent S-warfarin 7-hydroxylation. On the other hand, pioglitazone and rosiglitazone (50 microM) only slightly inhibited these xenobiotic oxidation activities catalyzed by CYP2C enzymes. 3. The inhibitory potential of troglitazone (50% inhibition concentration, IC50) was approximately 5 microM for drug oxidations catalyzed by CYP2C9 and CYP2C8 and approximately 20 microM for activities catalyzed by CYP2C19 and CYP3A4 respectively. For the three metabolites of troglitazone tested, a quinone-type metabolite (M3) was the most potent inhibitor for CYP2C enzymes, followed by a sulphate conjugate (M1); effects of a glucuronide (M2) were very weak. The inhibitory effects of the parent drug were more potent than those of metabolites. Troglitazone and M3 inhibited P450 activities mainly through a competitive manner with Ki = 0.2-1.7 microM and 1.4-8.8 microM respectively. 4. In three human liver microsomes, troglitazone and its metabolites also inhibited paclitaxel 6alpha-hydroxylation, S-warfarin 7-hydroxylation, S-mephenytoin 4'-hydroxylation, and testosterone 6beta-hydroxylation with similar IC50, as observed for the recombinant P450 enzyme systems. 5. These results suggest that xenobiotic oxidations by P450 enzymes are more substantially affected by troglitazone and its metabolites than pioglitazone or rosiglitazone, and that drug interactions may be of much importance to understand the basis for the pharmacological and toxicological actions of this new oral antidiabetic drug.

Chromans↗

PubMed2003

Solid-state variation of troglitazone drug substance by using a different recrystallization method.

Rapid and slow crystallization methods (A and B) were applied for troglitazone, an equal mixture of four stereoisomers. Differences in the powder x-ray diffractometry patterns and hygroscopic patterns were observed among the samples crystallized by these methods, suggesting that troglitazone has solid-state variation. In this article, troglitazone recrystallized by method A was evaluated to clarify its structural characteristics and physical property. The crystal structure of predried troglitazone recrystallized by method A was proved to be a dihydrate. By drying, it changed reversibly to an anhydrate, which is the same structure as the RS/SR form, keeping the same enantiomer ratio. The solubility of the troglitazone by method A higher than that by method B at all enantiomer levels. But making the troglitazone amorphous equalized the enantiomeric solubilities of the substances by both methods as well as increased the intrinsic solubilities. Troglitazone by both methods was proved to be stable and retained the ratio of the stereoisomers.

Adsorption↗

PubMed2000

Troglitazone protects human erythrocytes from oxidant damage.

The antidiabetic drug troglitazone contains the active chromanol ring of alpha-tocopherol, which should give it antioxidant properties within cells. In these studies, the antioxidant effects of troglitazone were tested in human erythrocytes and in their ghosts. Troglitazone bound to erythrocyte ghosts in a linear manner and was retained even after centrifugation washes. In response to an oxidant stress generated by a water-soluble free radical initiator, troglitazone that was bound to erythrocyte ghosts was oxidized, but induced a lag-phase in the disappearance of endogenous alpha-tocopherol and in the appearance of lipid hydroperoxides. Troglitazone also delayed loss of endogenous alpha-tocopherol and hemolysis in washed intact erythrocytes in response to free radical-induced extracellular oxidant stress. To mimic exposure of erythrocytes to lipid hydroperoxides in vivo, erythrocytes were incubated with phospholipid liposomes that contained small amounts of preformed lipid hydroperoxides. This induced an oxidant stress in both the liposomes and cells. Troglitazone in concentrations above 4 microM almost completely prevented further appearance of lipid hydroperoxides in the liposomes, and also completely preserved alpha-tocopherol in the erythrocytes. The present results suggest that troglitazone will help to prevent peroxidative damage to erythrocytes in areas of excessive oxidant stress in the vascular bed.

Antioxidants↗

PubMed2001

Effects of troglitazone and temocapril in spontaneously hypertensive rats with chronic renal failure.

OBJECTIVE: The insulin resistance state is common in humans and animals with chronic renal failure. We investigated the effects of troglitazone, an insulin sensitizer, on blood pressure and nephropathy in the remnant kidney model of spontaneously hypertensive rats (SHR). METHODS: Eight-week-old male SHR were subjected to five-sixth nephrectomy. At the age of 10 weeks, the rats were randomly allocated to groups that received troglitazone (70 mg/kg per day); the angiotensin converting enzyme inhibitor temocapril (10 mg/kg per day); troglitazone (70 mg/kg per day) plus temocapril (10 mg/kg per day), or a vehicle alone as an untreated control group. Systolic blood pressure (SBP) and urinary protein excretion were measured every 2 weeks. At the age of 22 weeks, biochemical measurements and histological examination were performed. RESULTS: Blood glucose, glycosylated hemoglobin and body weight were similar in the four groups. SBP, serum creatinine and glomerular sclerosis index were significantly reduced in all treated groups compared with those in the control group. Urinary protein excretion, glomerular volume and aortic media thickness were significantly decreased in temocapril-treated rats and troglitazone plus temocapril-treated rats compared with those in control rats. Although antihypertensive effects of troglitazone were minute compared with those of temocapril or troglitazone plus temocapril, there was no significant difference between the glomerular sclerosis indices in these three drug-treated groups. CONCLUSIONS: The results suggest that troglitazone has renoprotective effects in this rat model. These effects might be due to the inhibition of growth factors rather than to the minute hypotensive effect, although the mechanism remains to be elucidated.

Angiotensin-Converting Enzyme Inhibitors↗

PubMed2003

A retrospective review of thiazolidinediones with development of a troglitazone conversion protocol.

The objective of this paper was (1) to assess compliance with the National Veterans Affairs Guidelines for the use of troglitazone and rosiglitazone and (2) to develop and implement a conversion protocol that allows effective management of patients receiving troglitazone. A retrospective chart review was conducted to assess adherence to guidelines for all patients receiving troglitazone and rosiglitazone at the medical center. Appropriateness of therapy through indication evaluation, safety through alanine aminotransferase (ALT) monitoring compliance, and efficacy through hemoglobin A1c (HbA1c) changes were used to assess adherence. According to National Veterans Affairs (VA) Guidelines, 68% of troglitazone and 63% of rosiglitazone patients had an appropriate indication for the use of these agents. Baseline ALT levels were obtained in 40% of troglitazone and 71% of rosiglitazone patients. Full compliance with continual ALT monitoring was seen in 6 and 54% of patients, respectively. Goal HbA1c was achieved in 57 and 29% of patients, respectively. Of the 33 patients receiving troglitazone, 19 were converted to rosiglitazone therapy; 11 were maintained on current regimens without troglitazone, and 3 were lost to follow up. Adherence to guidelines needs to be reinforced, in particular, compliance with ALT monitoring. However, there were no reported cases of hepatotoxicity in the patients reviewed. Many patients did not achieve a HbA1c < 8% on either agent. Development of the protocol allowed for efficient conversion of the patients" diabetes regimen while safely identifying those that should remain on this class of medication.

Aged↗

PubMed2002

Phenol sulfotransferase, ST1A3, as the main enzyme catalyzing sulfation of troglitazone in human liver.

Since sulfation is the main metabolic pathway of troglitazone, accounting for about 70% of the metabolites detected in human plasma, we have aimed to identify human cytosolic sulfotransferases catalyzing the sulfation of troglitazone and to examine a possible role of the sulfation in the cytotoxicity observed in cell lines of human origin (HepG2 and Hep3B). Experiments using the recombinant sulfotransferases and human liver cytosols indicated that phenol sulfotransferase (ST1A3) and estrogen sulfotransferase (ST1E4) were the sulfotransferases most active toward troglitazone. Immunoblot analyses indicated that hepatic content of ST1A3 is about 13 times higher than that of ST1E4, suggesting that ST1A3 is mainly responsible for the sulfation of troglitazone in the liver. Lactate dehydrogenase (LDH) leakage was elicited by troglitazone in a concentration-dependent manner in the hepatoma cells. The troglitazone metabolites (the sulfate, glucuronide, and quinone forms) caused negligible LDH leakage. These findings suggest that accumulation of unmetabolized troglitazone causes the cytotoxicity in the hepatoma cells and may be responsible for toxicity in human liver.

Animals↗

PubMed2001

Troglitazone stimulates pancreatic growth in congenitally CCK-A receptor-deficient OLETF rats.

We examined the effect of troglitazone treatment on pancreatic growth in the CCK-A receptor-deficient Otsuka Long-Evans Tokushima fatty (OLETF) rat, an animal model for type 2 diabetes mellitus. A troglitazone-rich diet (0.2%) was given from 12 to 28 wk of age or from 12 or 28 wk of age to 72 wk of age. Fasting serum glucose concentrations in control OLETF rats increased progressively with age, which was almost completely prevented by troglitazone treatment. Insulin levels in serum and pancreatic content in the control rat markedly increased at 28 wk of age but significantly decreased at 72 wk of age compared with those at 12 wk of age, whereas those in troglitazone-treated rats were nearly the same at all ages and were similar to those in control rats at 12 wk of age. Pancreatic wet weight in control rats decreased with age irrespective of whether they were hyperinsulinemic (28 wk old) or hypoinsulinemic (72 wk old). Troglitazone treatment significantly increased pancreatic wet weight and protein, DNA, and enzyme contents compared with those in the control rats. Moreover, troglitazone treatment completely prevented or reversed histological alterations such as fibrosis, fatty replacement, and inflammatory cell infiltration. Our results indicate that troglitazone stimulates pancreatic growth in the congenitally CCK-A receptor-deficient OLETF rat not only by reducing insulin resistance and potentiating insulin action but also by suppressing inflammatory changes in the pancreas.

Aging↗

PubMed1999

Vasodilatory effects of troglitazone improve blood pressure at rest and during mental stress in type 2 diabetes mellitus.

The present study examined the hemodynamic mechanisms of blood pressure (BP) lowering by troglitazone in patients with type 2 diabetes mellitus (DM) at rest and during a mental arithmetic test (MAT). Twenty-two patients with DM with normal to high-normal BP and 12 controls matched for age, gender, glucose tolerance, and BP were studied. DM subjects showed significantly higher systolic BP response during MAT than controls (157 versus 139 mm Hg; P<0.01). All 22 DM patients and 5 of 12 controls had systolic BP >140 mm Hg during MAT. Heart rate and diastolic BP were not significantly different between the 2 groups. The DM group was then randomized to receive troglitazone (n=10; 400 mg/d) or glyburide (n=12; 20 mg/d). MAT was repeated after 6 months of treatment. Both treatments reduced glucose equally (-1.7 mmol/L for troglitazone and -1.5 mmol/L for glyburide), but only troglitazone reduced insulin (-15 microU/mL; P<0.001) and C-peptide (-0.9 ng/mL; P<0.02) levels. Troglitazone significantly reduced BP at baseline (P<0.05) and systolic BP response to MAT (P<0.01), whereas glyburide did not affect BP at baseline or during MAT. Stroke volume and cardiac output did not change with either drug, but troglitazone decreased peripheral vascular resistance (-112 dyne. s. cm(-5); P<0.05). Improved insulin resistance rather than an improved glycemic control is associated with lower resting and stress BP values in patients with DM. A reduction in vascular resistance may be a primary hemodynamic mechanism of the manner in which troglitazone lowers BP. Insulin sensitizers may offer potential therapeutic advantage in subjects with DM with elevated BP.

Adult↗

PubMed1997

Mechanisms of action of troglitazone in the prevention of high glucose-induced migration and proliferation of cultured coronary smooth muscle cells.

Recent findings suggest that high glucose levels may promote atherosclerosis in coronary vascular smooth muscle cells (VSMCs). To explore the intracellular mechanisms of action by which troglitazone affects this process, we examined the effect of troglitazone on the migration and growth characteristics of cultured rabbit coronary VSMCs. Treatment with chronic high glucose medium (22.2 mmol/L) for 5 days increased VSMC migration by 92%, [3H]thymidine incorporation by 135%, and cell number by 32% compared with VSMCs treated with normal glucose (5.5 mmol/L glucose + 16.6 mmol/L mannose) medium. Trolitazone at 100 nmol/L and 1 mumol/L significantly suppressed high glucose-induced VSMC migration by 34% and 42%, respectively, the proliferative effect (as measured by cell number) by 17% and 27%, and [3H]thymidine incorporation by 45% and 60% (n = 6, P < .05). The high glucose-induced impairment of insulin-mediated [3H]deoxyglucose uptake was blocked by a protein kinase C (PKC) inhibitor (calphostin C, 1 mumol/L) and was also improved by troglitazone without any change in insulin receptor number and affinity. The high glucose-induced insulin-mediated increase in cell number and in [3H]thymidine incorporation was suppressed by troglitazone. Troglitazone (1 mumol/L) also suppressed high glucose-induced phospholipase D activation, elevation of the cytosolic NADH/NAD+ ratio (as measured by the cytosolic ratio of lactate/pyruvate), and membrane-bound PKC activation. Flow cytometric DNA histogram analysis of cell cycle stage showed that high glucose-induced increase in the percentage of cells in the S phase was suppressed by 1 mumol/L troglitazone. These findings suggest that PKC may be a link between impairment of insulin-mediated glucose uptake and the increase in migration and proliferation induced by high glucose levels and that troglitazone may be clinically useful for the treatment of high glucose-induced coronary atherosclerosis.

Animals↗

PubMed1996

Troglitazone inhibits vascular smooth muscle cell growth and intimal hyperplasia.

Vascular smooth muscle cell (VSMC) proliferation and migration are responses to arterial injury that are highly important to the processes of restenosis and atherosclerosis. In the arterial balloon injury model in the rat, platelet-derived growth factor (PDGF) and basic fibroblast growth factor (bFGF) are induced in the vessel wall and regulate these VSMC activities. Novel insulin sensitizing agents, thiazolidinediones, have been demonstrated to inhibit insulin and epidermal growth factor-induced growth of VSMCs. We hypothesized that these agents might also inhibit the effect of PDGF and bFGF on cultured VSMCs and intimal hyperplasia in vivo. Troglitazone (1 microM), a member of the thiazolidinedione class, produced a near complete inhibition of both bFGF-induced DNA synthesis as measured by bromodeoxyuridine incorporation (6.5+/-3.9 vs. 17.6+/-4.3% cells labeled, P < 0.05) and c-fos induction. This effect was associated with an inhibition (by 73+/-4%, P < 0.01) by troglitazone of the transactivation of the serum response element, which regulates c-fos expression. Inhibition of c-fos induction by troglitazone appeared to occur via a blockade of the MAP kinase pathway at a point downstream of MAP kinase activation by MAP kinase kinase. At this dose, troglitazone also inhibited PDGF-BB-directed migration of VSMC (by 70+/-6%, P < 0.01). These in vitro effects were operative in vivo. Quantitative image analysis revealed that troglitazone-treated rats had 62% (P < 0.001) less neointima/media area ratio 14 d after balloon injury of the aorta compared with injured rats that received no troglitazone. These results suggest troglitazone is a potent inhibitor of VSMC proliferation and migration and, thus, may be a useful agent to prevent restenosis and possibly atherosclerosis.

Animals↗

PubMed1997

Troglitazone action is independent of adipose tissue.

We have investigated the antidiabetic action of troglitazone in aP2/DTA mice, whose white and brown fat was virtually eliminated by fat-specific expression of diphtheria toxin A chain. aP2/DTA mice had markedly suppressed serum leptin levels and were hyperphagic, but did not gain excess weight. aP2/DTA mice fed a control diet were hyperlipidemic, hyperglycemic, and had hyperinsulinemia indicative of insulin-resistant diabetes. Treatment with troglitazone alleviated the hyperglycemia, normalized the tolerance to intraperitoneally injected glucose, and significantly decreased elevated insulin levels. Troglitazone also markedly decreased the serum levels of cholesterol, triglycerides, and free fatty acids both in wild-type and aP2/DTA mice. The decrease in serum triglycerides in aP2/DTA mice was due to a marked reduction in VLDL- and LDL-associated triglyceride. In skeletal muscle, triglyceride levels were decreased in aP2/DTA mice compared with controls, but glycogen levels were increased. Troglitazone treatment decreased skeletal muscle, but not hepatic triglyceride and increased hepatic and muscle glycogen content in wild-type mice. Troglitazone decreased muscle glycogen content in aP2/DTA mice without affecting muscle triglyceride levels. The levels of peroxisomal proliferator-activated receptor gamma mRNA in liver increased slightly in aP2/DTA mice and were not changed by troglitazone treatment. The results demonstrate that insulin resistance and diabetes can occur in animals without significant adipose deposits. Furthermore, troglitazone can alter glucose and lipid metabolism independent of its effects on adipose tissue.

Adipose Tissue↗