Glitazones in type 2 diabetes: an update

The glitazones and their combination products are licensed for type 2 diabetes mellitus and now account for over 50% of NHS expenditure on oral hypoglycaemic drugs. In 2001, for pioglitazone and rosiglitazone (the two glitazones licensed in the UK), we concluded that evidence (from short-term studies) supported their use in combination with metformin or a sulphonylurea in patients unsuited to one or other of these drugs, but not more practical glitazone use, such as monotherapy or as part of triple therapy. We also said that their long-term effects were not yet clear. Since then, both drugs have also been licensed for monotherapy, as part of triple therapy that includes metformin and a sulphonylurea and, for pioglitazone, use with insulin. Here we reassess glitazones in light of published efficacy data and safety concerns raised in recent years.     

Anti-proliferative effect of peroxisome proliferator-activated receptor gamma agonists on human malignant melanoma cells in vitro

Malignant melanoma has a poor reputation for early spread and no curative treatment is yet available. As peroxisome proliferator-activated receptor gamma (PPARgamma) agonists (glitazones) have recently been shown to have growth-inhibiting effects on different cancer lineages, the aim of this study was to analyze the effects of four glitazones (rosiglitazone, ciglitazone, pioglitazone and troglitazone) on the growth of six human malignant melanoma cells in vitro. Proliferation of six human melanoma cell lines under glitazone treatment over a broad concentration range (0.15-300 micromol/l) was assessed by means of the XTT cell proliferation assay, and expression of PPARgamma in these cell lines was analyzed using both immunohistochemical and molecular biological techniques. All four glitazones showed a significant dose-dependent anti-proliferative effect on all six cell lines starting at a concentration of 0.3 micromol/l, with ciglitazone being the most potent inhibitor of cell growth, followed by troglitazone, rosiglitazone and pioglitazone. PPARgamma was predominantly localized in the cytoplasm; however, there were quantitative differences in PPARgamma expression between the different cell lines as demonstrated by quantification of Western blots. As an already approved class of drugs, glitazones have been found to significantly inhibit growth of human malignant melanoma cells in vitro and might be a promising tool for further therapeutic studies.     

Glitazones induce astroglioma cell death by releasing reactive oxygen species from mitochondria: modulation of cytotoxicity by nitric oxide

The glitazones (or thiazolidinediones) are synthetic compounds used in type-2 diabetes, but they also have broad antiproliferative and anti-inflammatory properties still not well understood. We described previously the apoptotic effects of glitazones on astroglioma cells ( J Biol Chem 279: 8976-8985, 2004 ). At certain concentrations, we found a selective lethality on glioma cells versus astrocytes that was dependent on a rapid production of reactive oxygen species (ROS) and seemed unrelated to the receptor peroxisome proliferator activated receptor-gamma. The present study was aimed at characterizing the oxygen derivatives induced by ciglitazone, rosiglitazone, and pioglitazone in C6 glioma cells and to investigate their intracellular source. We examined the interaction of ROS with nitric oxide (NO) and its consequences for glioma cell survival. Fluorescence microscopy and flow cytometry showed that glitazones induced superoxide anion, peroxynitrite, and hydrogen peroxide, with ciglitazone being the most active. ROS production was completely prevented by uncoupling of the electron transport chain and by removal of glucose as an energy substrate, whereas it was unaffected by inhibition of NADPH-oxidase and xanthine-oxidase. Moreover, glitazones inhibited state 3 respiration in permeabilized cells, and experiments with mitochondrial inhibitors suggested that complex I was the likely target of glitazones. Therefore, these results point to the mitochondrial electron transport chain as the source of glitazone-induced ROS in C6 cells. Glitazones also depolarized mitochondria and reduced mitochondrial pH. NO synthase inhibitors revealed that superoxide anion combines with NO to yield peroxynitrite and that the latter contributes to the cytotoxicity of glitazones in astroglioma cells. Future antitumoral strategies may take advantage of these findings.     

Pharmacokinetic interactions with thiazolidinediones

Type 2 diabetes mellitus is a complex disease combining defects in insulin secretion and insulin action. New compounds called thiazolidinediones or glitazones have been developed for reducing insulin resistance. After the withdrawal of troglitazone because of liver toxicity, two compounds are currently used in clinical practice, rosiglitazone and pioglitazone. These compounds are generally used in combination with other pharmacological agents. Because they are metabolised via cytochrome P450 (CYP), glitazones are exposed to numerous pharmacokinetic interactions. CYP2C8 and CYP3A4 are the main isoenzymes catalysing biotransformation of pioglitazone (as with troglitazone), whereas rosiglitazone is metabolised by CYP2C9 and CYP2C8. For both rosiglitazone and pioglitazone, the most relevant interactions have been described in healthy volunteers with rifampicin (rifampin), which results in a significant decrease of area under the plasma concentration-time curve [AUC] (54-65% for rosiglitazone, p<0.001; 54% for pioglitazone, p<0.001), and with gemfibrozil, which results in a significant increase of AUC (130% for rosiglitazone, p<0.001; 220-240% for pioglitazone, p<0.001). The relevance of such drug-drug interactions in patients with type 2 diabetes remains to be evaluated. However, in the absence of clinical data, it is prudent to reduce the dosage of each glitazone by half in patients treated with gemfibrozil. Conversely, rosiglitazone and pioglitazone do not seem to significantly affect the pharmacokinetics of other compounds. Although some food components have also been shown to potentially interfere with drugs metabolised with the CYP system, no published study deals specifically with these possible CYP-mediated food-drug interactions with glitazones.     

Hypertension and the absence of EDHF-mediated responses favour endothelium-dependent contractions in renal arteries of the rat

Background and purpose:Experiments were designed to determine the modulation by nitric oxide (NO) and endothelium-dependent hyperpolarizations (EDHF-mediated responses) of endothelium-dependent contractions in renal arteries of normotensive and hypertensive rats.Experimental approach:Rings, with or without endothelium, of renal arteries of 8-month-old Wistar Kyoto rats (WKY) and spontaneously hypertensive rats (SHR) were suspended in myographs for isometric force recording.Key results:ACh evoked relaxations in preparations contracted with phenylephrine. L-NAME (inhibitor of NOS) attenuated (WKY) or abolished (SHR) these relaxations. TRAM-34 plus UCL 1684 (inhibitors of EDHF-mediated responses) did not decrease the relaxation, except in rings of WKY when L-NAME was also present. High concentrations of ACh caused a secondary increase in tension, augmented in rings of WKY by L-NAME or TRAM-34 plus UCL 1684. The increase in tension was prevented by indomethacin. Under baseline tension, ACh induced endothelium-dependent contractions, prevented by indomethacin (COX inhibitor) or terutroban (TP receptor antagonist). The calculated endothelium-dependent contractions were larger in rings of SHR compared with those of WKY. In preparations of SHR, the contractions were augmented by L-NAME in the presence of SC19220 (EP-1 receptor antagonist). In arteries of WKY, the endothelium-dependent contractions were augmented by TRAM-34 plus UCL 1684. The responses were reduced by SC19220.Conclusions and implications:In the renal artery of the rat, EDCF-mediated contractions are augmented by hypertension. The endothelium-dependent contractions are facilitated by NOS inhibition (in the presence of an EP-1 receptor antagonist) and by the withdrawal of EDHF-mediated responses.British Journal of Pharmacology (2008) 155, 217-226; doi:10.1038/bjp.2008.256; published online 23 June 2008.     

Effects of ascorbic acid on impaired vascular reactivity in aortas isolated from age-matched hypertensive and diabetic rats

Impaired vascular reactivity is a hallmark of several cardiovascular diseases that include hypertension and diabetes. This study compared the changes in vascular reactivity in age-matched experimental hypertension and diabetes, and, subsequently, tested whether these changes could be affected directly by ascorbic acid (10 microM). Endothelium-derived nitric oxide (NO) modulation of ascorbic acid effects was also investigated. All the experiments were performed in the presence of a cyclooxygenase inhibitor, indomethacin (10 microM). Results showed that the endothelium-dependent and -independent relaxations induced by acetylcholine (ACh) and sodium nitroprusside (SNP), respectively, were blunted to a similar extent in isolated aortic rings from age-matched spontaneously hypertensive (SHR) (R(max): ACh = 72.83+/-1.86%, SNP = 96.6+/-1.90%) and diabetic (Rmax: ACh = 64.09+/-5.14%, SNP = 95.84+/-1.41%) rats compared with aortic rings of normal rats (Rmax: ACh = 89%, SNP = 104.0+/-1.0%). The alpha1-receptor-mediated contractions induced by phenylephrine (PE) were augmented in diabetic (Cmax = 148.8+/-9.0%) rat aortic rings compared to both normal (Cmax = 127+/-6.9%) and SHR (Cmax = 118+/-4.5%) aortic rings. Ascorbic acid pretreatment was without any significant effects on the vascular responses to ACh, SNP and PE in aortic rings from normal rats. Ascorbic acid significantly improved ACh-induced relaxations in SHR (Rmax = 89.09+/-2.82%) aortic rings to a level similar to that observed in normal aortic rings, but this enhancement in ACh-induced relaxations was only partial in diabetic aortic rings. Ascorbic acid lacked any effects on SNP-induced relaxations in both SHR and diabetic aortic rings. Ascorbic acid markedly attenuated contractions induced by PE in aortic rings from both SHR (Cmax = 92.9+/-6.68%) and diabetic (Cmax = 116.9+/-9.4%) rats. Additionally, following inhibition of nitric oxide synthesis with l-NAME, ascorbic acid attenuated PE-induced contractions in all aortic ring types studied. These results suggest that (1) vascular hyper-responsiveness to alpha(1)-receptor agonists in diabetic arteries is independent of endothelial nitric oxide dysfunction; (2) ascorbic acid directly modulates contractile responses of hypertensive and diabetic rat aortas, likely through mechanisms in part independent of preservation of endothelium-derived nitric oxide.     

Hepatotoxicity with thiazolidinediones: is it a class effect?

Decreased insulin sensitivity plays a major role in various human diseases. particularly type 2 diabetes mellitus, and is associated with a higher risk of atherosclerosis and cardiovascular complications. Thiazolidinediones, more commonly termed glitazones, are the first drugs to specifically target muscular insulin resistance. They have proven efficacy for reducing plasma glucose levels in patients with type 2 diabetes mellitus treated with diet alone, sulphonylureas, metformin or insulin. In addition, they are associated with some improvement of the cardiovascular risk profile. However, troglitazone, the first compound approved by the Food and Drug Administration in the US, proved to be hepatotoxic and was withdrawn from the market after the report of several dozen deaths or cases of severe hepatic failure requiring liver transplantation. It remains unclear whether or not hepatotoxicity is a class effect or is related to unique properties of troglitazone. Rosiglitazone and pioglitazone, two other glitazones, appear to have similar efficacy with regard to blood glucose control in patients with type 2 diabetes mellitus as compared with troglitazone. In controlled clinical trials, the incidence of significant (> or =3 x upper limit of normal) increases in liver enzyme levels (ALT in particular) was similar with rosiglitazone or pioglitazone as compared with placebo, whereas troglitazone was associated with a 3-fold greater incidence. In contrast to the numerous case reports of acute liver failure in patients receiving troglitzone, only a few case reports of hepatotoxicity have been reported in patients treated with rosiglitazone until now, with a causal relationship remaining uncertain. Furthermore, no single case of severe hepatotoxicity has been reported yet with pioglitazone. It should be mentioned that troglitazone, unlike pioglitazone and rosiglitazone, induces the cytochrome P450 isoform 3A4, which is partly responsible for its metabolism, and may be prone to drug interactions. Importantly enough, obesity, insulin resistance and type 2 diabetes mellitus are associated with liver abnormalities, especially non-alcoholic steatohepatitis, independent of any pharmacological treatment. This association obviously complicates the selection of patients who are good candidates for a treatment with glitazones as well as the monitoring of liver tests after initiation of therapy with any thiazolidinedione compound. While regular monitoring of liver enzymes is still recommended and more long term data are desirable, current evidence from clinical trials and postmarketing experience in the US supports the conclusion that rosiglitazone and pioglitazone do not share the hepatotoxic profile of troglitazone.     

Des-aspartate angiotensin I (DAA-I) reduces endothelial dysfunction in the aorta of the spontaneously hypertensive rat through inhibition of angiotensin II-induced oxidative stress

Des-aspartate angiotensin I (DAA-I), an endogenous nonapeptide, counteracts several effects of angiotensin II on vascular tone. The aim of this study was to investigate the acute protective effect of DAA-I on endothelial function in the spontaneously hypertensive rat (SHR) as well as its effect on angiotensin II-induced contractions and oxidative stress. Aortic rings were incubated with DAA-I (0.1 μM) for 30 min prior to the assessment of angiotensin II-induced contractions (0.1 nM–10 μM) in WKY and SHR aortas. Total nitrate and nitrite levels were assessed using a colorimetric method and reactive oxygen species (ROS) were measured by dihydroethidium (DHE) fluorescence and lucigenin-enhanced chemiluminescence. The effect of DAA-I was also assessed against endothelium-dependent and -independent relaxations to acetylcholine and sodium nitroprusside, respectively. Angiotensin II-induced contractions were significantly reduced by DAA-I, losartan and tempol. Incubation with ODQ (soluble guanylyl cyclase inhibitor) and removal of the endothelium prevented the reduction of angiotensin II-induced contractions by DAA-I. Total nitrate and nitrite levels were increased in DAA-I, losartan and tempol treated-SHR tissues while ROS level was reduced by DAA-I and the latter inhibitors. In addition, DAA-I significantly improved the impaired acetylcholine-induced relaxation in SHR aortas whilst sodium nitroprusside-induced endothelium-independent relaxation remained unaffected. The present findings indicate that improvement of endothelial function by DAA-I in the SHR aorta is mediated through endothelium-dependent release of nitric oxide and inhibition of angiotensin II-induced oxidative stress.     

Direct effects of quercetin on impaired reactivity of spontaneously hypertensive rat aortae: comparative study with ascorbic acid

1. There is a growing interest in the anti-oxidant characteristics and use of flavonoids in the management of cardiovascular diseases. The cardiovascular mechanism of action of these plant derivatives remains controversial. This study compared the effects of the flavonoid quercetin with those of the anti-oxidant vitamin ascorbic acid (vitamin C) on the reactivity of aortic rings from spontaneously hypertensive rats (SHR). 2. The phenylephrine (PE)-induced contractile and the endothelium-dependent and independent relaxant responses of aortic rings from 21 to 22 week old SHR and age-matched normotensive Wistar (WKY) rats were observed in the presence of quercetin or ascorbic acid. All the experiments were performed in the presence of the cyclooxygenase inhibitor, indomethacin (10 micromol/L). 3. The endothelium-dependent and independent relaxations to acetylcholine (ACh) and sodium nitroprusside (SNP), respectively, were significantly lesser in the SHR compared to the WKY tissues whereas the contractile responses to PE were similar in both tissues. Pretreatment of WKY rings with quercetin or ascorbic acid had no effect on the responses to ACh or PE. In the SHR tissues, however, quercetin or ascorbic acid significantly improved the relaxation responses to ACh and reduced the contractions to PE with greater potency for quercetin. Both compounds lacked any effects on the responses to SNP in either aortic ring types. N(omega)-nitro-L-arginine methyl ester (l-NAME, 10 micromol/L) significantly attenuated the vasodepressor effects of quercetin and ascorbic acid, raising the responses to PE to a level similar to that observed in the control SHR tissues. In l-NAME pretreated aortic rings, quercetin and ascorbic acid inhibited the contractile responses to PE with the same magnitude in WKY and SHR tissues. 4. The present results suggest that acute exposure to quercetin improves endothelium-dependent relaxation and reduces the contractile responses of hypertensive aortae with a greater potency than ascorbic acid. This suggests a better vascular protection with this flavonoid than ascorbic acid in the SHR model of hypertension and possibly in human cardiovascular diseases.     

Rosiglitazone and pioglitazone: new preparations. Two new oral antidiabetics both poorly assessed

(1) Treatment of type 2 (non insulin-dependent) diabetes is based on lifestyle measures and management of cardiovascular risk. (2) The reference first-line drug therapy for type 2 diabetes, when drug therapy is needed, is single-agent treatment with metformin (a biguanide) for overweight patients, or with glibenclamide (a glucose-lowering sulphonylurea) for other patients. (3) If monotherapy fails to control blood glucose levels adequately, most clinical guidelines then recommend a combination of metformin with a glucose-lowering sulphonylurea, although the few available comparative clinical data raise the possibility of excess mortality with this treatment. (4) Rosiglitazone and pioglitazone (glitazones that reduce insulin resistance) have been authorized in the European Union for combination with a glucose-lowering sulphonylurea (for patients in whom metformin is ineffective or poorly tolerated) or with metformin (for obese patients). (5) None of the available trials of rosiglitazone and pioglitazone include data on mortality or morbidity. (6) There are fewer data on pioglitazone than on rosiglitazone. (7) According to short-term comparative trials, rosiglitazone and pioglitazone are more effective than placebo on blood glucose levels. Combinations of rosiglitazone or pioglitazone with metformin or with glucose-lowering sulphonylureas have not been compared with the metformin + glucose-lowering sulphonylurea combination or with insulin. (8) Rosiglitazone and pioglitazone frequently cause weight gain. (9) Pioglitazone has a slightly favourable effect on lipid profiles, unlike rosiglitazone, which increases LDL-cholesterol levels. (10) The main side effect of rosiglitazone and pioglitazone is sodium and water retention, which can provoke oedema, anaemia (by haemodilution), and even heart failure. Rosiglitazone and pioglitazone are also hepatotoxic. (11) Combining rosiglitazone with insulin is contraindicated, owing to the increased risk of heart failure. The same applies to pioglitazone. (12) In practice, neither rosiglitazone nor pioglitazone has a place in the management of type 2 diabetes, except in the context of strictly controlled long-term comparative clinical trials.     

Epigallocatechin gallate elicits contractions of the isolated aorta of the aged spontaneously hypertensive rat

The present study examined the effect of the green tea catechin epigallocatechin gallate (EGCG) on endothelium-dependent responses in the aorta of 36-week-old spontaneously hypertensive rats (SHR). Isometric tension was measured in isolated aortic rings. The release of prostanoid end products was determined using enzyme immunoassay kits and the intracellular reactive oxygen species (ROS) concentration using confocal microscopy. EGCG did not improve endothelium-dependent relaxations evoked by acetylcholine, except in the presence of indomethacin. EGCG did not inhibit endothelium-dependent contractions induced by acetylcholine or ATP. At 10(-6) M and higher concentrations, EGCG caused increases in tension in the SHR aorta. The EGCG-induced contractions were accompanied by an increased production of ROS. The amount of prostanoid end products was increased significantly by EGCG, indicating that their production followed the activation of cyclooxygenase (COX). These prostanoids in turn stimulated thromboxane-prostanoid (TP) receptors and caused contractions. EGCG induced significantly smaller contractions in aortae of normotensive Wistar-Kyoto rats (WKY), accompanied with a lower production of ROS and a lesser release of prostanoids. These observations suggest that EGCG-induced contractions occur more readily in blood vessels of hypertensive than normotensive animals. The present findings indicate that the increased oxidative stress in the ageing hypertensive animals contributes to the loss of the beneficial effects and the enhancement of the adverse effects of EGCG.     

Alteration of vascular reactivity in diabetic human mammary artery and the effects of thiazolidinediones

Vascular reactivity was investigated in endothelium-denuded human internal mammary artery (IMA) rings from type 2 diabetic patients. It was also investigated whether insulin sensitizer thiazolidinedione drugs, pioglitazone and rosiglitazone, can directly affect the reactivity of IMA. Using organ bath techniques, cumulative concentration-response curves to phenylephrine (PE), KCl, cromakalim (CRO) and sodium nitroprusside (SNP) were constructed in diabetic and non-diabetic IMA rings. Means of maximal responses (% Emax) and pEC50 values (sensitivity) were compared. Emax values and the sensitivity to PE and KCl were increased while K(ATP)-channel-mediated relaxations were reduced significantly in diabetic rings compared with non-diabetic rings (n = 5-12, P < 0.05). No changes were observed for SNP responses (n = 5, P > 0.05). Incubations with pioglitazone (1 and 10 microM) and rosiglitazone (1 and 20 microM), for 30 min, did not affect K(ATP)-channel-mediated relaxations (n = 5 each, P > 0.05). Pioglitazone partly inhibited pre-contractions of PE and KCl at 10 microM, rosiglita-zone did not. Vascular dysfunction observed in diabetic IMA may be of specific importance since they are widely used as coronary bypass material. Thiazolidinedione drugs may not worsen arterial dilatation through K(ATP) channels in ischaemic or hypoxic insults in diabetic patients who are prone to such conditions. Pioglitazone has vasorelaxant property in the grafts.     

Effect of high extracellular Ca(2+) levels in spontaneously hypertensive rat aorta.

The release of endothelial relaxing factors has been suggested to be important in modulating the inhibition of the contractile activity caused by the increase in extracellular Ca(2+) concentration in arterial tissue. Since the hypertensive process in spontaneously hypertensive rats (SHR) could be associated with the release of endothelial vasoconstrictor factors (mainly cyclooxygenase-dependent endoperoxides and endothelin-1), we studied the contractile responses to KCl, methoxamine and phenylephrine in different aorta ring preparations (intact, de-endothelized, 10(-5) M indomethacin-treated, 10(-6) M CGS-27830 [meso-1,4-dihydro-5-methoxycarbonyl-2, 6-dimethyl-4-(3-nitrophenyl)-3-pyridine carboxylic acid anhydride]-treated, and treated simultaneously with 10(-5) M indomethacin and 10(-6) M CGS-27830) from SHR and normotensive Wistar Kyoto rats (WKY), at various Ca(2+) concentrations (1.25, 2.5, 5 and 10 mM) in the organ bath. In endothelium-intact preparations from WKY rats we observed a decrease in KCl, methoxamine and phenylephrine contractions with high Ca(2+) concentrations (5 and 10 mM), but in the endothelium-intact preparations from SHR, the increase in extracellular Ca(2+) concentration potentiated methoxamine contractions and caused no change in KCl and phenylephrine contractions. When the endothelium was disrupted in preparations from both WKY rats and SHR, we observed a decrease in KCl and methoxamine contractions with high Ca(2+) concentrations. The decrease in phenylephrine contractions caused by high Ca(2+) concentrations was clear in de-endothelized preparations from WKY rats but slight in de-endothelized preparations from SHR. In all indomethacin- and CGS-27830-treated preparations, and also in the preparations from WKY rats and SHR treated with both drugs, we observed a decrease in all the contractile responses with increased Ca(2+) concentration. Besides, there was a clear reduction in the responses of the alpha(1)-adrenoceptor agonists in the WKY and SHR preparations treated with both drugs. The results indicate that, in the hypertensive arteries, endothelium-derived contractile factors can counteract the relaxing effect of high extracellular Ca(2+) concentrations.     

Ligands for the peroxisome proliferator-activated receptor-gamma have inhibitory effects on growth of human neuroblastoma cells in vitro

The thiazolidinedione (TZD) or glitazone class of peroxisome proliferator-activated-gamma (PPAR-gamma) ligands not only induce adipocyte differentiation and increase insulin sensitivity, but also exert growth inhibitory effects on several carcinoma cell lines in vitro as well as in vivo. In the current study the in vitro effect of four PPAR-gamma agonists (ciglitazone, pioglitazone, troglitazone, rosiglitazone) on the cell growth of seven human neuroblastoma cell lines (Kelly, LAN-1, LAN-5, LS, IMR-32, SK-N-SH, SH-SY5Y) was investigated. Growth rates were assessed by a colorimetric XTT-based assay kit. Expression of PPAR-gamma protein was examined by immunohistochemistry and Western blot analysis. All glitazones inhibited in vitro growth and viability of the human neuroblastoma cell lines in a dose-dependent manner showing considerable effects only at high concentrations (10 microM and 100 microM). Effectiveness of the glitazones on neuroblastoma cell growth differed depending on the cell line and the agent. The presence of PPAR-gamma protein was demonstrated in all cell lines. Our findings indicate that ligands for PPAR-gamma may be useful therapeutic agents for the treatment of neuroblastoma. Thus the effect of glitazones on the growth of neuroblastoma should now be investigated in an in vivo animal model.     

Effects of glitazones on blood pressure and vascular structure in mesenteric resistance arteries and basilar artery from genetically hypertensive rats

1. The effects of two of the glitazone (thiazolidinedione) class of drugs, namely rosiglitazone and pioglitazone, on blood pressure and vascular remodelling in the New Zealand genetically hypertensive (GH) rat model were investigated. 2. In the first study, a GH group given rosiglitazone (5 mg/kg per day) from the age of 7 to 12 weeks was compared with a GH control group. In the second study, GH rats were given either pioglitazone, simvastatin, valsartan or combinations of pioglitazone with simvastatin or valsartan (all drugs at a dose of 10 mg/kg per day). 3. Tail-cuff systolic blood pressure was measured weekly. At the end of the experiment, blood vessels were fixed by perfusion and samples of mesenteric resistance arteries (MRA), second-order branches and basilar artery were embedded in Technovit and serial sections were cut and stained with Giemsa for stereological analysis. Media width, medial cross-sectional area and lumen diameter were determined and the ratio of media width/lumen diameter was calculated. 4. Rosiglitazone significantly reduced blood pressure in GH rats. 5. In MRA, rosiglitazone had a hypotrophic effect on media, reduced lumen diameter and reduced media/lumen ratio (P<0.001). 6. In basilar artery, there was also a hypotrophic effect of rosiglitazone on media and reduced media/lumen ratio (P<0.001). 7. Pioglitazone slowed down the rate of blood pressure increase with age in GH rats and had a greater effect on blood pressure when given in combination with simvastatin. 8. Pioglitazone had a hypotrophic effect on the media of MRA and basilar artery. The hypotrophic effect was enhanced when pioglitazone was given in combination with simvastatin. The media/lumen ratio was reduced by pioglitazone; in MRA, combination treatment with simvastatin reduced the ratio further to normal and, with valsartan, to below normal. In basilar artery, the media/lumen ratio was reduced further by both combination treatments, but was lowest in the pioglitazone-valsartan combination group. 9. The significant effects on MRA and basilar artery structure (and, thus, haemodynamics) seen after rosiglitazone monotherapy and after pioglitazone, given alone and in combination with simvastatin or valsartan, may well indicate a glitazone class effect on vascular structure and, hence, cardiovascular function.     

Troglitazone: the discovery and development of a novel therapy for the treatment of Type 2 diabetes mellitus

Prior to the introduction of troglitazone, it had been more than 30 years since the last significant improvement in antidiabetic therapy. In view of the pressing need for more effective oral agents for the treatment of Type 2 diabetes mellitus, troglitazone was granted priority review by the FDA and was launched in the USA in 1997. The first of the thiazolidinedione insulin sensitizing agents, troglitazone was quickly followed by rosiglitazone and pioglitazone. The glitazones proved to be effective not only in lowering blood glucose, but also to have beneficial effects on cardiovascular risk. Troglitazone was subsequently withdrawn because of concerns about hepatotoxicity, which appears to be less of a problem with rosiglitazone and pioglitazone. Recent insights into the molecular mechanism of action of the glitazones, which are ligands for the peroxisome proliferator-activated receptors, open the prospect of designing more effective, selective and safer antidiabetic agents. This document will review the history of troglitazone from discovery through clinical development.     

Modulation of vascular reactivity in normal, hypertensive and diabetic rat aortae by a non-antioxidant flavonoid.

In this study, we report the effects of a non-antioxidant flavonoid flavone on vascular reactivity in Wistar-Kyoto (WKY) rat isolated aortae. Whether flavone directly modulates vascular reactivity in spontaneously hypertensive rat (SHR) and streptozotocin-induced diabetic-WKY rat isolated aortae was also determined. Thoracic aortic rings were mounted in organ chambers and exposed to various drug treatments in the presence of flavone (10 microM) or its vehicle (DMSO), which served as control. Pretreatment with flavone enhanced relaxant effects to endothelium-dependent vasodilator acetylcholine (ACh) and attenuated contractile effects to alpha(1)-receptor agonist phenylephrine (PE) in WKY aortae compared to those observed in control aortic rings. Flavone had no effect on relaxations to ACh in WKY aortae incubated with either L-NAME or methylene blue, but enhanced relaxations to ACh in WKY aortae incubated with indomethacin or partially depolarized with KCl. Relaxations to ACh are totally abolished in both control or flavone pretreated endothelium-denuded WKY aortae. Flavone attenuated the inhibition by beta-NADH of ACh-induced relaxation in WKY aortae, but it had no significant effect on the transient contractions induced by beta-NADH nor the pyrogallol-induced abolishment of ACh-induced relaxation in WKY aortae. Flavone enhanced endothelium-independent relaxation to sodium nitroprusside (SNP) in both endothelium-intact and -denuded WKY aortae. Flavone enhanced relaxation to ACh and SNP as well as attenuated contractile effects to PE in SHR and diabetic aortae, a finding similar to that observed in normal WKY aortae. From these results, we conclude that flavone modulates vascular reactivity in normal as well as hypertensive and diabetic aortae. These effects of flavone results probably through enhanced bioactivity of nitric oxide released from the endothelium.     

Oxygen-derived free radicals mediate endothelium-dependent contractions to acetylcholine in aortas from spontaneously hypertensive rats

Experiments were designed to investigate whether or not oxygen-derived free radicals mediate endothelium-dependent contractions to acetylcholine in the aorta of spontaneously hypertensive rat (SHR). Isometric tension was measured in aortic rings taken from adult male SHR and Wistar-Kyoto rat (WKY) in the presence of NG-nitro-L-arginine. Endothelium-dependent contractions to acetylcholine were significantly greater in rings from SHR compared to WKY. Oxygen-derived free radicals, generated from xanthine plus xanthine oxidase, induced contractions that were larger in aortas from SHR than from WKY. Contractions to acetylcholine and free radicals were abolished by a selective TP-receptor antagonist, S 18886, and a preferential inhibitor of cyclo-oxygenase-1, valeryl salicylate, but not by a preferential inhibitor of cyclo-oxygenase-2, NS-398. Allopurinol, deferoxamine and the combination of superoxide dismutase plus catalase inhibited the contractions to oxygen-derived free radicals but did not significantly affect those to acetylcholine. In contrast, diethyldithiocarbamic acid, an inhibitor of superoxide dismutase, or Tiron, a scavenger of superoxide anion, reduced endothelium-dependent contractions to acetylcholine in aortas from SHR. The effect of these two drugs was additive. In SHR chronically treated with dimethylthiourea endothelium-dependent contractions to acetylcholine were decreased, and reduced further by acute in vitro exposure to deferoxamine or the combination of superoxide dismutase plus catalase. These results suggest that in the SHR aorta acetylcholine-induced endothelium-dependent contractions involve endothelial superoxide anion production and the subsequent dismutation into hydroxyl radicals and/or hydrogen peroxide. The free radicals activate cyclo-oxygenase-1, most likely to produce endoperoxides. Activation of TP-receptors is required to observe endothelium-dependent contractions to acetylcholine or endothelium-independent contractions in response to free radical generation.