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Peroxisomal proliferator-activated receptor gamma (PPARγ) is a nuclear hormone receptor whose agonist, rosiglitazone has a neuroprotective effect to hippocampal neurons in pilocarpine-induced seizures. Hippocampal slice preparations treated in Mg2+ free medium can induce ictal and interictal-like epileptiform discharges, which is regarded as an in vitro model of N-methyl-D-aspartate (NMDA) receptor-mediated temporal lobe epilepsy (TLE). We applied rosiglitazone in hippocampal slices treated in Mg2+ free medium. The effects of rosiglitazone on hippocampal CA1-Schaffer collateral synaptic transmission were tested. We also examined the neuroprotective effect of rosiglitazone toward NMDA excitotoxicity on cultured hippocampal slices. Application of 10 μM rosiglitazone significantly suppressed amplitude and frequency of epileptiform discharges in CA1 neurons. Pretreatment with the PPARγ antagonist GW9662 did not block the effect of rosiglitazone on suppressing discharge frequency, but reverse the effect on suppressing discharge amplitude. Application of rosiglitazone suppressed synaptic transmission in the CA1-Schaffer collateral pathway. By miniature excitatory-potential synaptic current (mEPSC) analysis, rosiglitazone significantly suppressed presynaptic neurotransmitter release. This phenomenon can be reversed by pretreating PPARγ antagonist GW9662. Also, rosiglitazone protected cultured hippocampal slices from NMDA-induced excitotoxicity. The protective effect of 10 μM rosiglitazone was partially antagonized by concomitant high dose GW9662 treatment, indicating that this effect is partially mediated by PPARγ receptors. In conclusion, rosiglitazone suppressed NMDA receptor-mediated epileptiform discharges by inhibition of presynaptic neurotransmitter release. Rosiglitazone protected hippocampal slice from NMDA excitotoxicity partially by PPARγ activation. We suggest that rosiglitazone could be a potential agent to treat patients with TLE.

Type 2 diabetic men commonly experience erectile dysfunction for which phosphodiesterase-5 (PDE5) inhibitors like sildenafil (Viagra) are often recommended. By preventing degradation of cyclic guanosine monophosphate (cGMP) in vascular smooth muscle, these inhibitors also enhance arterial vasorelaxant effects of nitric oxide donors (which stimulate cGMP synthesis). In the present work, we confirmed this enhancing effect after co-administration of sildenafil with nitroprusside to freshly-isolated rat tail arterial tissues. However, in the same tissues we also observed that sildenafil does not enhance but rather attenuates vasorelaxant effects of three commonly-used antidiabetic drugs, i.e. the biguanide metformin and the thiazolidinediones pioglitazone and rosiglitazone. Indeed, sildenafil completely blocked vasorelaxant effects of low concentrations of these drugs. In addition, we found that this same novel anti-vasorelaxant interaction of sildenafil with these agents was abolished by either 1) omitting extracellular glucose or 2) inhibiting specific smooth muscle glycolytic pathways; pathways known to preferentially utilize extracellular glucose to fuel certain adenosine triphosphate (ATP)-dependent ion transporters: e.g. ATP-sensitive K channels, sarcoplasmic reticulum Ca-ATPase, plasma membrane Ca-ATPase and Na/K-ATPase. Accordingly, we suspect that altered activity of one or more of these ion transporters mediates the observed attenuating (anti-vasorelaxant) interaction of sildenafil with the antidiabetic drugs. The present results are relevant because hypertension is so common and difficult to control in Type 2 diabetes. The present data suggest that sildenafil might interfere with the known antihypertensive potential of metformin and the thiazolidinediones. However, they do not suggest that it will interact with them to cause life-threatening episodes of severe hypotension, as can occur when it is co-administered with nitrates.

Purpose: The present study has been undertaken to investigate the possible involvement of the glutamatergic pathway in the beneficial effects of pioglitazone on consolidation and retrieval phases of memory., Materials and Methods: The Y-maze task was used to assess short-term spatial recognition memory in animals. Scopolamine (1mg/kg, i.p.) or MK-801 (dizocilpine) (0.03, 0.1 and 0.3mg/kg, i.p.) were administered immediately after the training session to impair memory consolidation or 30min before the retention trial to impair memory retrieval. Pioglitazone (10, 20, 40 and 80mg/kg, p.o.) was administered 2h before the retention session in memory retrieval experiments or immediately after the training session in consolidation experiments. And finally NMDA (N-methyl-d-aspartate) (75mg/kg, i.p) was administered 15min before the administration of pioglitazone., Results: 1) MK-801 (0.3mg/kg) impaired the retrieval of spatial recognition memory. 2) Pioglitazone failed to improve MK-801 induced impairment of retrieval of spatial recognition memory. 3) The 20mg/kg dose of pioglitazone significantly improved memory in mice with scopolamine induced impairment of memory retrieval. 4) Sub-effective dose of MK-801 (0.1mg/kg) was capable of reversing the beneficial effect of pioglitazone on retrieval of memory in scopolamine-treated mice, 5) Administration of NMDA (75mg/kg) and a sub-effective dose of pioglitazone (10mg/kg) reversed the effect of scopolamine and promoted memory retrieval. 6) MK-801 did not affect the consolidation phase of spatial recognition memory. 7) Pioglitazone did not affect scopolamine-induced impairment of memory consolidation., Conclusions: Sub-effective dose of MK-801 is capable of reversing the protective action of pioglitazone on scopolamine-induced impairment of memory retrieval. Additionally, co-administration of 75mg/kg NMDA and a sub-effective dose of pioglitazone potentiated the effect of pioglitazone on memory retrieval impaired by scopolamine. These results support the idea that pioglitazone plays its memory retrieval enhancement role through the glutamatergic pathway., (Copyright © 2014 Elsevier Inc. All rights reserved.)

Peroxisome proliferator-activated receptor gamma (PPARγ) is emerging as a new pharmacotherapeutic target for chronic pain. When oral (3-30 mg/kg/day in chow for 7 wk) or twice-daily intraperitoneal (1-10 mg/kg/day for 2 wk) administration began before spared nerve injury (SNI), pioglitazone, a PPARγ agonist, dose-dependently prevented multiple behavioral signs of somatosensory hypersensitivity. The highest dose of intraperitoneal pioglitazone did not produce ataxia or reductions in transient mechanical and heat nociception, indicating that inhibitory effects on hypersensitivity were not secondary to adverse drug-induced behaviors or antinociception. Inhibitory effects on hypersensitivity persisted at least one week beyond cessation of pioglitazone administration, suggestive of long-lasting effects on gene expression. Blockade of PPARγ with GW9662, an irreversible and selective PPARγ antagonist, dose-dependently reduced the inhibitory effect of pioglitazone on hypersensitivity, indicating a PPARγ-dependent action. Remarkably, a single preemptive injection of pioglitazone 15 min before SNI attenuated hypersensitivity for at least 2 weeks; this was enhanced with a second injection delivered 12 h after SNI. Pioglitazone injections beginning after SNI also reduced hypersensitivity, albeit to a lesser degree than preemptive treatment. Intraperitoneal pioglitazone significantly reduced the nerve injury-induced up-regulation of cd11b, GFAP, and p-p38 in the dorsal horn, indicating a mechanism of action involving spinal microglia and/or astrocyte activation. Oral pioglitazone significantly reduced touch stimulus-evoked phospho-extracellular signal-related kinase (p-ERK) in lamina I-II, indicating a mechanism of action involving inhibition of central sensitization. We conclude that pioglitazone reduces spinal glial and stimulus-evoked p-ERK activation and that PPARγ activation blocks the development of and reduces established neuropathic pain., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

Unlabelled: Besides the receptor-mediated effects of pioglitazone, the involvement of nitric oxide (NO) has been previously demonstrated in some pioglitazone-induced central and peripheral effects. In the present study, the effects of acutely administered pioglitazone on pentylenetetrazole (PTZ)-induced seizures and involvement of NO were evaluated in mice. To determine the threshold for clonic seizures, PTZ was administered intravenously. A single dose of pioglitazone (10, 20, 40 and 80 mg/kg, p.o.) was administered either 2 or 4h prior to induction of seizures. For determination of possible role of peroxisome proliferator activated receptor gamma (PPAR-γ) and nitric oxide pathway in this effect, the effects of a PPAR-γ antagonist, GW9662 (2 mg/kg); a non-specific nitric oxide synthase (NOS) inhibitor, NG-nitro-L-arginine methyl ester (L-NAME; 0.3, 1, 3, and 10 mg/kg); a specific iNOS inhibitor, aminoguanidine (100mg/kg, i.p.) or a nitric oxide precursor, L-arginine (30, 60, 100 and 200mg/kg, i.p.); each administered 15 min prior to pioglitazone, were investigated on the anticonvulsant effect of this drug. Administration of pioglitazone (40 and 80 mg/kg) increased the threshold of PTZ-induced seizure in a dose-dependent, and time-dependent manner. GW9662 reversed the anticonvulsant effect of pioglitazone (40 mg/kg). Acute administration of L-NAME (1, 3 and 10mg/kg) inhibited the anticonvulsant effect of pioglitazone (40 mg/kg), the same result was detected with aminoguanidine (100mg/kg); whereas L-arginine, in the noneffective dose (100mg/kg), potentiated the seizure threshold when co-administered with a subeffective dose of pioglitazone (20mg/kg)., Conclusion: The present study demonstrates the anticonvulsant effect of acute pioglitazone on PTZ-induced seizures in mice. This effect was reversed by PPAR-γ antagonist, and both a specific- and a non-specific nitric oxide synthase inhibitors, and augmented by nitric oxide precursor, L-arginine. These results support that the anticonvulsant effect of pioglitazone is mediated through PPAR-γ receptor-mediated pathway and also, at least partly, through the nitric oxide pathway., (Copyright © 2012 Elsevier B.V. All rights reserved.)

The peroxisome proliferator-activated receptor γ (PPARγ) is a target for treatment of type II diabetes and other conditions. PPARγ full agonists, such as thiazolidinediones (TZDs), are effective insulin sensitizers and anti-inflammatory agents, but their use is limited by adverse side effects. Luteolin is a flavonoid with anti-inflammatory actions that binds PPARγ but, unlike TZDs, does not promote adipocyte differentiation. However, previous reports suggested variously that luteolin is a PPARγ agonist or an antagonist. We show that luteolin exhibits weak partial agonist/antagonist activity in transfections, inhibits several PPARγ target genes in 3T3-L1 cells (LPL, ORL1, and CEBPα) and PPARγ-dependent adipogenesis, but activates GLUT4 to a similar degree as rosiglitazone, implying gene-specific partial agonism. The crystal structure of the PPARγ ligand-binding domain (LBD) reveals that luteolin occupies a buried ligand-binding pocket (LBP) but binds an inactive PPARγ LBD conformer and occupies a space near the β-sheet region far from the activation helix (H12), consistent with partial agonist/antagonist actions. A single myristic acid molecule simultaneously binds the LBP, suggesting that luteolin may cooperate with other ligands to bind PPARγ, and molecular dynamics simulations show that luteolin and myristic acid cooperate to stabilize the Ω-loop among H2', H3, and the β-sheet region. It is noteworthy that luteolin strongly suppresses hypertonicity-induced release of the pro-inflammatory interleukin-8 from human corneal epithelial cells and reverses reductions in transepithelial electrical resistance. This effect is PPARγ-dependent. We propose that activities of luteolin are related to its singular binding mode, that anti-inflammatory activity does not require H12 stabilization, and that our structure can be useful in developing safe selective PPARγ modulators.

Thiazolidinediones (TZD), a class of anti-diabetic drugs, determine bone loss and increase fractures particularly in post-menopausal women, thus suggesting a protective role of sex steroids. We have previously demonstrated that the TZD rosiglitazone (RGZ) negatively affects bone mass by inhibiting osteoblastogenesis, yet inducing adipogenesis, in bone marrow-derived human mesenchymal stem cells (hMSC). The aim of this study was to determine whether estrogens and androgens are able to revert the effects of RGZ on bone. hMSC express estrogen receptor α and β and the androgen receptor. We found that 17β-estradiol (10 nM), the phytoestrogen genistein (10 nM), testosterone (10 nM) and the non-aromatizable androgens dihydrotestosterone (10 nM) and methyltrienolone (10 nM) effectively counteracted the adipogenic effect of RGZ (1 μM) in hMSC induced to differentiate into adipocytes, as determined by evaluating the expression of the adipogenic marker peroxisome proliferator-activated receptor γ and the percentage of fat cells. Furthermore, when hMSC were induced to differentiate into osteoblasts, all the above-mentioned molecules and also quercetin, another phytoestrogen, significantly reverted the inhibitory effect of RGZ on the expression of the osteogenic marker osteocalcin and decreased the number of fat cells observed after RGZ exposure. Our study represents, to our knowledge, the first demonstration in hMSC that androgens, independently of their aromatization, and estrogens are able to counteract the negative effects of RGZ on bone. Our data, yet preliminary, suggest the possibility to try to prevent the negative effects of TZD on bone, using steroid receptor modulators, such as plant-derived phytoestrogens, which lack evident adverse effects.

Unlabelled: In this study, the potential antidepressant-like effects of pioglitazone and the possible involvement of peroxisome proliferator-activated receptor gamma (PPARγ) and nitric oxide system in antidepressant effects of pioglitazone were determined using forced swimming test (FST) in mice., Method: After assessment of locomotor activity in open-field test, mice were forced to swim individually and the immobility time of the last 4 min was evaluated. Pioglitazone was administered orally with doses (5, 10, 20 and 30 mg/kg) 2 and 4h before FST. To assess the involvement of PPARγ in the possible antidepressant effect of pioglitazone, GW9662, a PPARγ antagonist (2mg/kg) was administered before pioglitazone (20mg/kg). For determination of possible role of nitric oxide pathway in this effect, a non-specific NOS inhibitor, Nω-nitro-L-arginine methyl ester (L-NAME, 10mg/kg, i.p.), a specific iNOS inhibitor, aminoguanidine (50mg/kg, i.p.), or a NO precursor, L-arginine (750 mg/kg, i.p.) was co-administered with pioglitazone, either 2 or 4h before FST., Results: The immobility time significantly decreased after pioglitazone administration (20 and 30 mg/kg). GW-9662 significantly reversed antidepressant effect of pioglitazone administered 2 and 4h prior to FST. Co-administration of non-effective doses of pioglitazone and l-NAME revealed antidepressant-like effect in FST; while, co-administration of non-effective doses of aminoguanidine and pioglitazone did not affect the immobility time. l-Arginine also reversed the antidepressant-like effect of pioglitazone., Conclusion: The antidepressant-like effect of pioglitazone on mice in the FST is mediated at least in part through PPARγ receptors and nitric oxide pathway., (Copyright © 2011 Elsevier B.V. All rights reserved.)

Pioglitazone improves insulin resistance in diabetics but often causes body weight gain. The lipoprotein lipase activator NO-1886 has been shown to exert both anti-obesity and anti-insulin-resistance effects. In this study, we investigated the effect of the combined administration of pioglitazone with NO-1886 (pioglitazone+NO-1886) in preventing body weight gain in insulin-resistant, high-fat fed rats. The rats were fed a standard or high-fat diet for 16 weeks. The high-fat fed rats were randomized at week 9 into 4 groups (i.e., control, pioglitazone (30 mg/kg/day), NO-1886 (100mg/kg/day), and pioglitazone+NO-1886 (30 and 100mg/kg/day, respectively)). The high-fat fed control rats developed obesity and insulin resistance. After 7 weeks of drug treatment, pioglitazone+NO-1886 was found to prevent the body weight gain caused by pioglitazone alone (pioglitazone+NO-1886: Δ76.0 ± 16.8 g vs. pioglitazone: Δ127.8 ± 39.5 g, P<0.05) and to increase glucose infusion rate during insulin clamp, compared with the results in the high-fat fed control group. No differences in plasma nonesterified fatty acid, leptin, adiponectin, glucose, or insulin levels were observed between the pioglitazone+NO-1886 and the pioglitazone-alone groups. However, plasma total cholesterol and HDL-cholesterol levels were significantly increased and plasma triglyceride levels were slightly decreased in the pioglitazone+NO-1886 group, compared with the values in the pioglitazone-alone group. In summary, the combined administration of pioglitazone and NO-1886 prevented the pioglitazone-induced body weight gains and ameliorated insulin resistance observed in high-fat fed rats. These results indicate that combined therapy with pioglitazone and NO-1886 may be beneficial for the treatment of type 2 diabetes., (Copyright © 2011 Elsevier B.V. All rights reserved.)

Long-term treatment with the insulin-sensitizer rosiglitazone reduces bone mass and increases fracture risk. We have recently shown that orally administered metformin stimulates bone reossification and increases the osteogenic potential of bone marrow progenitor cells (BMPC). In the present study we investigated the effect of a 2-week metformin and/or rosiglitazone treatment on bone repair, trabecular bone microarchitecture and BMPC osteogenic potential, in young male Sprague-Dawley rats. Compared to untreated controls, rosiglitazone monotherapy decreased bone regeneration, femoral metaphysis trabecular area, osteoblastic and osteocytic density, and TRAP activity associated with epiphyseal growth plates. It also decreased the ex vivo osteogenic commitment of BMPC, inducing an increase in PPARγ expression, and a decrease in Runx2/Cbfa1 expression, in AMP-kinase phosphorylation, and in osteoblastic differentiation and mineralization. After monotherapy with metformin, with the exception of PPARγ expression which was blunted, all of the above parameters were significantly increased (compared to untreated controls). Metformin/rosiglitazone co-treatment prevented all the in vivo and ex vivo anti-osteogenic effects of rosiglitazone monotherapy, with a reversion back to control levels of PPARγ, Runx2/Cbfa1 and AMP-kinase phosphorylation of BMPC. In vitro co-incubation of BMPC with metformin and compound C-an inhibitor of AMPK phosphorylation-abrogated the metformin-induced increase in type-1 collagen production, a marker of osteoblastic differentiation. In conclusion, in rodent models metformin not only induces direct osteogenic in vivo and ex vivo actions, but when it is administered orally in combination with rosiglitazone it can prevent several of the adverse effects that this thiazolidenedione shows on bone tissue., (Copyright © 2011 Elsevier B.V. All rights reserved.)

Emerging evidence indicates that PPARUpsilon activators attenuate neurodegeneration and related complications. Therefore, the present study focused on the neuroprotective potential of pioglitazone against quinolinic acid (QUIN) induced neurotoxicity. Intrastriatal (unilaterally) administration of QUIN significantly altered body weight and motor function (locomotor activity, rotarod and beam walk performance). Further, QUIN treatment significantly caused oxidative damage (increased lipid peroxidation, nitrite concentration and depleted endogenous antioxidant defense enzymes), altered mitochondrial enzyme complex (I, II and IV) activities and TNF-alpha level as compared to sham treated animals. Pioglitazone (10, 20 and 40mg/kg, p.o.) treatment significantly improved body weight and motor functions, oxidative defense. Further, pioglitazone treatment restored mitochondrial enzyme complex activity as well as TNF-alpha level as compared to QUIN treated group. While Bisphenol A diglycidyl ether (BADGE) (15mg/kg), PPARUpsilon antagonist significantly reversed the protective effect of the pioglitazone (40mg/kg) in the QUIN treated animals. Further, pioglitazone treatment significantly attenuated the striatal lesion volume in QUIN treated animals, suggesting a role for the PPARUpsilon pathway in QUIN induced neurotoxicity. Altogether, this evidence indicates that PPARUpsilon activation by pioglitazone attenuated QUIN induced neurotoxicity in animals and which could be an important therapeutic avenue to ameliorate Huntington like symptoms., (Copyright 2010 Elsevier Inc. All rights reserved.)

Peroxisome proliferator activated receptor (PPARgamma) has been suggested as a target for anti-inflammatory therapy in chronic lung disease, including infection with Pseudomonas aeruginosa. However, the P. aeruginosa signal molecule N-(3-oxo-dodecanoyl)-l-homoserine lactone (3-oxo-C12-HSL) has been reported to inhibit function of PPARs in mammalian cells. This suggests that binding of 3-oxo-C12-HSL to PPARs could increase inflammation during P. aeruginosa infection, particularly if it could compete for binding with other PPAR ligands. We investigated the ability of 3-oxo-C12-HSL to bind to a PPARgamma ligand binding domain (LBD) construct, and to compete for binding with the highly active synthetic PPARgamma agonist rosiglitazone. We demonstrate that 3-oxo-C12-HSL binds effectively to the PPARgamma ligand binding domain, and that concentrations of 3-oxo-C12-HSL as low as 1 nM can effectively interfere with the binding of rosiglitazone to the PPARgamma ligand binding domain. Because 3-oxo-C12 HSL has been demonstrated in lungs during P. aeruginosa infection, blockade of PPARgamma-dependent signaling by 3-oxo-C12-HSL produced by the infecting P. aeruginosa could exacerbate infection-associated inflammation, and potentially impair the action of PPAR-activating therapy. Thus the proposed use of PPARgamma agonists as anti-inflammatory therapy in lung P. aeruginosa infection may depend on their ability to counteract the effects of 3-oxo-C12-HSL., (Copyright 2010 Elsevier Masson SAS. All rights reserved.)

Luteolin (3',4',5,7-tetrahydroxyflavone), a flavonoid, has been known to possess antimutagenic, antitumorigenic, antioxidant, and anti-inflammatory properties. In this study, we investigated the role of luteolin in the regulation of adipogenic differentiation in 3T3-L1 preadipocytes. Luteolin inhibited intracellular triglyceride accumulation in a dose-dependent manner without cytotoxicity. Western blot and reverse transcription-polymerase chain reaction analyses showed that this inhibition was accompanied by attenuated expression of the adipogenic transcription factors: peroxisome proliferator-activated receptor gamma (PPARgamma) and CCAAT/enhancer-binding protein alpha. Luteolin inhibited the PPARgamma transactivation stimulated by rosiglitazone, a synthetic agonist, in COS-7 cells and inhibited rosiglitazone-induced adipogenic differentiation in 3T3-L1 cells. These data suggest that luteolin exerts antiadipogenic effects by suppressing adipogenic transcription factors and by inhibiting the transactivation of PPARgamma.

Objective: Thiazolidinediones (TZDs) are synthetic agonists for the peroxisome proliferator-activating receptor-gamma receptor and are currently in use as oral glucose-lowering drugs. TZDs have immune-modulating effects in vitro and in vivo. Because patients with type 2 diabetes have an increased risk for pneumonia, we evaluated the influence of ciglitazone, a TZD, on markers of inflammation and outcome during pneumonia caused by Streptococcus pneumoniae., Design: In vivo animal study and in vitro study., Setting: University research laboratory., Subjects: Female C57Bl/6 mice and murine alveolar macrophage-like MH-S cells., Interventions: C57Bl/6 mice were inoculated with 10 colony-forming units of S. pneumoniae intranasally. The following interventions were studied: 1) vehicle at t = 0; 2) ciglitazone 5 mg/kg intraperitoneally at t = 0; and 3) ciglitazone 5 mg/kg intraperitoneally at t = 0 and 24 hours. Mice were killed at either 24 or 48 hours after infection. Additionally, phagocytosis and killing of S. pneumoniae by MH-S cells were assessed in vitro., Measurements and Main Results: Single treatment with ciglitazone reduced bacterial loads at 24 hours but not at 48 hours, whereas repeated ciglitazone treatment did diminish bacterial loads at 48 hours. After 24 hours, cytokine levels in lung homogenate were lower in single-dose ciglitazone-treated mice; however, after 48 hours, there was no difference in lung cytokines between any of the experimental groups. Repeated ciglitazone treatment was associated with less pulmonary inflammation, as judged by histologic examination. On both time points, there was no difference in plasma cytokine levels or lung myeloperoxidase levels between experimental groups. In an additional experiment, ciglitazone treatment (given once daily) tended to reduce mortality. Ciglitazone did not influence phagocytosis or killing of S. pneumoniae by murine alveolar macrophages., Conclusions: Ciglitazone reduces bacterial outgrowth and local inflammation at least during the early stage of S. pneumoniae pneumonia in mice.

Background: Many patients with type 2 diabetes mellitus receive several oral hypoglycemic agents, including sulfonylurea drugs. Intravenous glyburide (Glyb), a sulfonylurea agent, blocks the protective effects of "ischemic" and pharmacologic preconditioning in various animal models without affecting myocardial infarct size when administered alone. However, there are conflicting results when other sulfonylurea drugs are used. Pioglitazone (PIO) reduces infarct size in the rat. We asked whether oral Glyb and glimepiride (Glim) affect the infarct size-limiting effects of PIO., Methods: Sprague-Dawley rats received 3-day oral treatment with: PIO (5 mg/kg/day); PIO + Glyb (10 mg/kg/day); PIO + Glim (4 mg/kg/day) or water alone (experiment 1) or PIO (5 mg/kg/day) with or without 5-hydroxydecanoate (5HD, 10 mg/kg), a specific mitochondrial ATP-sensitive K+ channels inhibitor, administered intravenously 30 min before coronary artery ligation. PIO, Glyb and Glim were administered by oral gavage. Sugar 5% was added to water to prevent hypoglycemia. Rats underwent 30 min coronary artery occlusion and 4 h reperfusion (n = 6 in each group). Ischemic area at risk was assessed by blue dye and infarct size by triphenyl-tetrazolium-chloride., Results: Body weight and the size of the area at risk were comparable among groups. Infarct size (% of the area at risk) was significantly smaller in the PIO (14.3 +/- 1.1%; p < 0.001) and PIO + Glim (13.2 +/- 0.8%; p < 0.001) groups than in the control group (37.7 +/- 1.2%). Glyb completely blocked the effect of PIO (43.0 +/- 1.7%; p < 0.001). Glim did not affect the protective effect of PIO (p = 0.993). 5HD blocked the protective effect of PIO (infarct size 48.5 +/- 0.8% versus 14.8 +/- 0.6%, respectively; p < 0.0001). In conclusion, the infarct size limiting effects of PIO are dependent on activation of mitochondrial ATP-sensitive K+ channels. Oral Glyb, but not Glim, blocks the infarct size limiting effects of PIO. It is plausible that Glyb affects other pleiotropic effects of PIO and thus may attenuate favorable effects on cardiovascular outcomes. In contrast, Glim does not attenuate the protective effect of PIO.

The Elovl3 gene, which putatively encodes for a protein involved in the elongation of saturated and monounsaturated fatty acids in the C20-C24 range, is expressed in murine liver, skin, and brown adipose tissue (BAT). In BAT, Elovl3 is dramatically upregulated during tissue activation in response to cold exposure, and functional data imply that ELOVL3 is a critical enzyme for lipid accumulation in brown adipocytes during the early phase of tissue recruitment. The activation of BAT is controlled by sympathetic nerve activity and norepinephrine release. By using primary cultures of brown adipocytes, we show here that the induced Elovl3 gene expression is synergistically regulated by norepinephrine and the peroxisome proliferator-activated receptor (PPAR) gamma ligand rosiglitazone. In addition, the potency of rosiglitazone to induce Elovl3 expression was several orders of magnitude higher than for the PPARalpha and PPARdelta ligands WY-14643 and L-165041, respectively. The maximal increase in mRNA level by norepinephrine and rosiglitazone is achieved by induced transcription as well as increased mRNA stability, and the whole process requires novel protein synthesis. We conclude that norepinehrine and PPARgamma, despite having different roles in brown adipocyte activation and differentiation, cooperate in expanding the intracellular lipid pool by synergistically stimulating Elovl3 expression.

Aim: JTP-426467 was identified as a result of screening in search of selective antagonist for peroxisome proliferator-activated receptor gamma (PPARgamma). We examined whether JTP-426467 functioned as a PPARgamma antagonist in vitro and in vivo and investigated physiological effects of JTP-426467., Methods: The effect of JTP-426467 as a PPARgamma antagonist was studied in a cell-based reporter assay and an adipocyte differentiation assay. Target mRNA expression levels were determined by branched DNA (bDNA) assay. To examine the effects as a PPARgamma antagonist in vivo, a competitive study between JTP-426467 and BRL49653 (rosiglitazone), a PPARgamma agonist, was performed using KK-Ay mice. The effects of JTP-426467 alone after administration to KK-Ay mice were also explored. JTP-426467 antagonized PPARgamma activity in a reporter assay system, but not PPARalpha., Results: JTP-426467 inhibited the expression of hormone-sensitive lipase (HSL) mRNA, an adipocyte-abundant gene, but not PPARgamma itself or cyclophilin mRNA (as constitutive mRNA), and also suppressed triglyceride accumulation in differentiated stromal vascular fraction cells (SVFs). JTP-426467 antagonized PPARgamma agonistic action by BRL49653 in KK-Ay mice on high-fat diet, in terms of plasma glucose, body weight gain and interscapular brown adipose tissue (IBAT) weight. JTP-426467 alone inhibited body weight gain and decreased plasma leptin level in KK-Ay mice., Conclusions: JTP-426467 acted as a pure and potent PPARgamma antagonist in vitro. Interestingly, JTP-426467 completely antagonized the effects of PPARgamma agonist BRL49653 in an obese diabetic model. JTP-426467 may be a useful tool for the study of PPARgamma in biological and physiological function.

The peroxisome proliferator-activated receptor gamma (PPARgamma) is an important therapeutic drug target for several conditions, including diabetes, inflammation, dyslipidemia, hypertension, and cancer. It is shown that an antagonist or partial agonist of PPARgamma has attractive potential applications in the discovery of novel antidiabetic agents that may retain efficacious insulin-sensitizing properties and minimize potential side effects. In this work, the dipeptide H-Trp-Glu-OH (G3335) was discovered to be a novel PPARgamma antagonist. Biacore 3000 results based on the surface plasmon resonance (SPR) technique showed that G3335 exhibits a highly specific binding affinity against PPARgamma (K(D) = 8.34 microM) and is able to block rosiglitazone, a potent PPARgamma agonist, in the stimulation of the interaction between the PPARgamma ligand-binding domain (LBD) and RXRalpha-LBD. Yeast two-hybrid assays demonstrated that G3335 exhibits strong antagonistic activity (IC50 = 8.67 microM) in perturbing rosiglitazone in the promotion of the PPARgamma-LBD-CBP interaction. Moreover, in transactivation assays, G3335 was further confirmed as an antagonist of PPARgamma in that G3335 could competitively bind to PPARgamma against 0.1 microM rosiglitazone to repress reporter-gene expression with an IC50 value of 31.9 muM. In addition, homology modeling and molecular-docking analyses were performed to investigate the binding mode of PPARgamma-LBD with G3335 at the atomic level. The results suggested that residues Cys285, Arg288, Ser289, and His449 in PPARgamma play vital roles in PPARgamma-LBD-G3335 binding. The significance of Cys285 for PPARgamma-LBD-G3335 interaction was further demonstrated by PPARgamma point mutation (PPARgamma-LBD-Cys285Ala). It is hoped our current work will provide a powerful approach for the discovery of PPARgamma antagonists, and that G3335 might be developed as a possible lead compound in diabetes research.

Aims/hypothesis: Fibrates and thiazolidinediones are commonly used for the treatment of dyslipidemia and type 2 diabetes, respectively. The aim of this study was to investigate the effects on body weight as well as on glucose and lipid homeostasis of ligands for PPARalpha and PPARgamma, Fenofibrate and Rosiglitazone, alone or in association., Methods: Ob/ob mice were divided into four groups: control, and mice daily injected (intraperitoneally), either with 10 mg/kg Rosiglitazone, 100 mg/kg Fenofibrate or both molecules. Body weight and food intake were monitored daily. After 13 days of treatment, mice were killed, and blood samples were collected for posterior metabolite quantification. The liver and adipose tissues were dissected and weighed., Results: Body weight was significantly reduced or increased by Fenofibrate and Rosiglitazone, respectively. The effect of Rosiglitazone was prevented by coadministration of Fenofibrate. This was accompanied by a normalization of the daily food efficiency. Compared to those treated with Rosiglitazone, animals treated with Fenofibrate alone or in combination presented a decreased white adipose tissue mass. Fenofibrate or Rosiglitazone alone significantly reduced the levels of plasma lipid parameters. Surprisingly, Fenofibrate also decreased blood glucose levels in ob/ob mice, despite having no effect on insulin levels. By contrast, both glucose and insulin levels were decreased by Rosiglitazone treatment. Coadministration of both drugs improved all parameters as with Rosiglitazone. Fenofibrate restored almost normal hepatocyte morphology and significantly reduced the triglyceride content of the liver. This was accompanied by an increase in fatty acid oxidation in the liver in all groups receiving Fenofibrate., Conclusion/interpretation: These biological effects suggest that combined therapy with a PPARalpha and a PPARgamma ligand is more effective in ameliorating, specifically, lipid homeostasis than in activating any of this receptor separately. Furthermore, Fenofibrate prevents one of the most undesirable effects of Rosiglitazone, namely increased adiposity and body weight gain.

Aims: Rosiglitazone, a thiazolidinedione antidiabetic medication used in the treatment of Type 2 diabetes mellitus, is predominantly metabolized by the cytochrome P450 (CYP) enzyme CYP2C8. The anti-infective drug trimethoprim has been shown in vitro to be a selective inhibitor of CYP2C8. The purpose of this study was to evaluate the effect of trimethoprim on the CYP2C8 mediated metabolism of rosiglitazone in vivo and in vitro., Methods: The effect of trimethoprim on the metabolism of rosiglitazone in vitro was assessed in pooled human liver microsomes. The effect in vivo was determined by evaluating rosiglitazone pharmacokinetics in the presence and absence of trimethoprim. Eight healthy subjects (four men and four women) completed a randomized, cross-over study. Subjects received single dose rosiglitazone (8 mg) in the presence and absence of trimethoprim 200 mg given twice daily for 5 days., Results: Trimethoprim inhibited rosiglitazone metabolism both in vitro and in vivo. Inhibition of rosiglitazone para-hydroxylation by trimethoprim in vitro was found to be competitive with apparent K(i) and IC(50) values of 29 microm and 54.5 microm, respectively. In the presence of trimethoprim, rosiglitazone plasma AUC was increased by 31% (P = 0.01) from 2774 +/- 645 microg l(-1) h to 3643 +/- 1051 microg l(-1) h (95% confidence interval (CI) for difference 189, 1549), and half-life was increased by 27% (P = 0.006) from 3.3 +/- 0.5 to 4.2 +/- 0.8 h (95% CI for difference 0.36, 1.5). Trimethoprim reduced the para-O-sulphate rosiglitazone/rosiglitazone and the N-desmethylrosiglitazone/rosiglitazone AUC(0-24) ratios by 22% and 38%, respectively., Conclusions: These results indicate that trimethoprim is a competitive inhibitor of CYP2C8-mediated rosiglitazone metabolism in vitro and that trimethoprim administration increases plasma rosiglitazone concentrations in healthy subjects.

Troglitazone and other thiazolidinediones (TZDs) are thought to relax arterial smooth muscle by directly inhibiting calcium channels in smooth muscle cell membranes. However, until recently such inhibition was only examined acutely, ie, within only seconds or minutes after administration of these agents to arterial smooth muscle preparations. Recently, a novel experiment was reported in which troglitazone caused a 2-phase relaxation of perfused resistance arteries, namely, an acute relaxation (within the first 20 minutes of treatment), which was blocked by a nonselective calcium channel blocker and a delayed relaxation (after 2 hours), which was not. We sought to determine if any of the 4 major potassium (K) channels in vascular smooth muscle play a role in the delayed relaxation. We incubated vascular contractile rings prepared from ventral tail arteries of rats with physiological buffer containing either 0 or 4 micromol/L troglitazone for 3 hours (4 micromol/L is typical of plasma levels from diabetic patients). Different K channel inhibitors (1 mmol/L 4-aminopyridine [4AP]; 1 mmol/L tetraethylammonium [TEA]; 5 micromol/L glyburide; 20 micromol/L barium) were coadministered with each level of troglitazone in additional preparations. Then these arterial rings were contracted with either norepinephrine (NE), arginine vasopressin (AVP), or high-K buffer. All contractions were significantly relaxed by troglitazone (P <.05). Only 4AP significantly attenuated troglitazone's relaxation of NE and AVP contractions (P <.05), though not high-K-induced contractions. TEA, glyburide, and barium had no such influence. Thus, for both adrenergic (NE) and nonadrenergic (AVP) contractions, the delayed arterial vasorelaxation by troglitazone may be mediated at least in part by activation of 4AP-sensitive K channels. Furthermore, the specific subtype of the channels involved is most likely those bound in the outer cell membrane where their effectiveness in terms of mediating relaxation would depend on an intact transmembrane K ion gradient.

Peroxisome proliferator-activated receptors (PPARs) are members of the nuclear hormone receptor superfamily of ligand-activated transcription factors that are related to retinoid, steroid and thyroid hormone receptors. The PPAR-gamma receptor subtype appears to play a pivotal role in the regulation of cellular proliferation and inflammation. The thiazolidinedione rosiglitazone (Avandia) is a peroxisome proliferator-activated receptor-gamma (PPAR-gamma) agonist, that was recently approved by the Food and Drug Administration for treatment of type II diabetes mellitus. In the present study, we have investigated the effects of rosiglitazone in animal models of acute inflammation (carrageenan-induced paw oedema and carrageenan-induced pleurisy). We report here for the first time that rosiglitazone (given at 1, 3 or 10 mg/kg i.p. concomitantly with carrageenan injection in the paw oedema model, or at 3, 10 or 30 mg/kg i.p. 15 min before carrageenan administration in the pleurisy model) exerts potent anti-inflammatory effects (e.g. inhibition of paw oedema, pleural exudate formation, mononuclear cell infiltration and histological injury) in vivo. Furthermore, rosiglitazone reduced: (1) the increase in the staining (immunohistochemistry) for nitrotyrosine and poly (ADP-ribose) polymerase (PARP), (2) the expression of inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (COX-2), intercellular adhesion molecules-1 (ICAM-1) and P-selectin in the lungs of carrageenan-treated rats. In order to elucidate whether the protective effect of rosiglitazone is related to activation of the PPAR-gamma receptor, we also investigated the effect of a PPAR-gamma antagonist, bisphenol A diglycidyl ether (BADGE), on the protective effects of rosiglitazone. BADGE (30 mg/kg i.p.) administered 30 min prior to treatment with rosiglitazone significantly antagonized the effect of the PPAR-gamma agonist and thus abolished the anti-inflammatory effects of rosiglitazone. We propose that rosiglitazone and other potent PPAR-gamma agonists may be useful in the therapy of inflammation.

The thiazolidinedione (TZD), rosiglitazone, has previously been found to tyrosine-phosphorylate Cbl and activate Cbl-dependent phosphatidylinositol (PI) 3-kinase and atypical protein kinase Cs (aPKCs) while stimulating glucose transport in 3T3/L1 adipocytes. Presently, the role of Cbl in rosiglitazone action was further assessed in both 3T3/L1 and human adipocytes by expressing Y371F and/or Y731F mutant forms of Cbl that nullified the functionality of canonical pYXXM motifs in Cbl. These mutants diminished the interaction of Cbl with the p85 subunit of PI 3-kinase and inhibited subsequent increases in Cbl-dependent PI 3-kinase activity, aPKC activity, and glucose transport. These mutants also inhibited the interaction of Cbl with Crk, which has been implicated in the activation of other PI 3-kinase-independent signaling factors that have been found to be required during activation of glucose transport by insulin and other agonists. We conclude that pYXXM motifs in Cbl serve to activate PI 3-kinase-dependent and possibly PI 3-kinase-independent pathways that are required for TZD-dependent glucose transport in adipocytes.