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

Rosiglitazone-induced PPARγ activation promotes intramuscular adipocyte adipogenesis of pig

Intramuscular fat (IMF) positively influences various aspects of meat quality, while the subcutaneous fat (SF) has negative effect on carcass characteristics and fattening efficiency. Peroxisome proliferator-activated receptor gamma (PPARγ) is a key regulator of adipocyte differentiation, herein, through bioinformatic screen for the potential regulators of adipogenesis from two independent microarray datasets, we identified that PPARγ is a potentially regulator between porcine IMF and SF adipogenesis. Then we treated subcutaneous preadipocytes (SA) and intramuscular preadipocytes (IMA) of pig with RSG (1 µmol/L), and we found that RSG treatment promoted the differentiation of IMA via differentially activating PPARγ transcriptional activity. Besides, RSG treatment promoted apoptosis and lipolysis of SA. Meanwhile, by the treatment of conditioned medium, we excluded the possibility of indirect regulation of RSG from myocyte to adipocyte and proposed that AMPK may mediate the RSG-induced differential activation of PPARγ. Collectively, the RSG treatment promotes IMA adipogenesis, and advances SA lipolysis, this effect may be associated with AMPK-mediated PPARγ differential activation. Our data indicates that targeting PPARγ might be an effective strategy to promote intramuscular fat deposition while reduce subcutaneous fat mass of pig.

Peroxisome proliferator-activated receptors as targets to treat metabolic diseases: Focus on the adipose tissue, liver, and pancreas

The world is experiencing reflections of the intersection of two pandemics: Obesity and coronavirus disease 2019. The prevalence of obesity has tripled since 1975 worldwide, representing substantial public health costs due to its comorbidities. The adipose tissue is the initial site of obesity impairments. During excessive energy intake, it undergoes hyperplasia and hypertrophy until overt inflammation and insulin resistance turn adipocytes into dysfunctional cells that send lipotoxic signals to other organs. The pancreas is one of the organs most affected by obesity. Once lipotoxicity becomes chronic, there is an increase in insulin secretion by pancreatic beta cells, a surrogate for type 2 diabetes mellitus (T2DM). These alterations threaten the survival of the pancreatic islets, which tend to become dysfunctional, reaching exhaustion in the long term. As for the liver, lipotoxicity favors lipogenesis and impairs beta-oxidation, resulting in hepatic steatosis. This silent disease affects around 30% of the worldwide population and can evolve into end-stage liver disease. Although therapy for hepatic steatosis remains to be defined, peroxisome proliferator-activated receptors (PPARs) activation copes with T2DM management. Peroxisome PPARs are transcription factors found at the intersection of several metabolic pathways, leading to insulin resistance relief, improved thermogenesis, and expressive hepatic steatosis mitigation by increasing mitochondrial beta-oxidation. This review aimed to update the potential of PPAR agonists as targets to treat metabolic diseases, focusing on adipose tissue plasticity and hepatic and pancreatic remodeling.

Combination therapy with semaglutide and rosiglitazone as a synergistic treatment for diabetic retinopathy in rodent animals

OBJECTIVE

To investigate the protective efficacies and potent mechanisms of combination therapy with semaglutide and rosiglitazone (RSG) on the high-glucose incubated human ARPE-19 cells and diabetic retinopathy (DR) model rats.

MAIN METHODS

The CCK-8 methods were used to evaluate the protective effects of semaglutide and RSG alone or combination on the cell viability of high-glucose treated ARPE-19 cells. After the DR rat model was established, the effects of combined treatment on general indexes, retinal morphological changes, retinal Müller cells as well as PI3K/Akt/MTOR related factors of DR model rats were investigated.

RESULTS

The CCK-8 assay showed obviously enhanced protective efficacies of combination therapy with semaglutide and RSG on the ARPE-19 with oxidative stress induced by high-glucose with combination index all below 1.5 demonstrating obvious synergistic effects. Combined incubation could also effectively decrease the expression of inflammatory factors, including TNF-α, IL-1β, IL-6, and the increase of ROS content in ARPE cell culture supernatant induced by high-glucose. Combined use of the antioxidant, PI3K/Akt and mTOR inhibitors, we further demonstrated that combined incubation of semaglutide and RSG could effectively by reduce high glucose-induced inflammatory injury inhibiting ROS/PI3K/Akt/mTOR signaling. Furthermore, chronic combination treatment effectively improved the histopathological characteristics and down-regulated the GFAP expression in Müller cells as well as PI3K/Akt/MTOR signaling pathway-related factors in retina which was better than any monomer treatment group.

CONCLUSIONS

Combined semaglutide with RSG exhibited synergistically protective efficacies on retinal cells by decreasing the GFAP expression, inhibiting oxidative stress and PI3K/Akt/MTOR signaling-transduction in DR model rats.

Hepatocyte-specific PKCβ deficiency protects against high-fat diet-induced nonalcoholic hepatic steatosis

OBJECTIVE

Nonalcoholic hepatic steatosis, also known as fatty liver, is a uniform response of the liver to hyperlipidic-hypercaloric diet intake. However, the post-ingestive signals and mechanistic processes driving hepatic steatosis are not well understood. Emerging data demonstrate that protein kinase C beta (PKCβ), a lipid-sensitive kinase, plays a critical role in energy metabolism and adaptation to environmental and nutritional stimuli. Despite its powerful effect on glucose and lipid metabolism, knowledge of the physiological roles of hepatic PKCβ in energy homeostasis is limited.

METHODS

The floxed-PKCβ and hepatocyte-specific PKCβ-deficient mouse models were generated to study the in vivo role of hepatocyte PKCβ on diet-induced hepatic steatosis, lipid metabolism, and mitochondrial function.

RESULTS

We report that hepatocyte-specific PKCβ deficiency protects mice from development of hepatic steatosis induced by high-fat diet, without affecting body weight gain. This protection is associated with attenuation of SREBP-1c transactivation and improved hepatic mitochondrial respiratory chain. Lipidomic analysis identified significant increases in the critical mitochondrial inner membrane lipid, cardiolipin, in PKCβ-deficient livers compared to control. Moreover, hepatocyte PKCβ deficiency had no significant effect on either hepatic or whole-body insulin sensitivity supporting dissociation between hepatic steatosis and insulin resistance.

CONCLUSIONS

The above data indicate that hepatocyte PKCβ is a key focus of dietary lipid perception and is essential for efficient storage of dietary lipids in liver largely through coordinating energy utilization and lipogenesis during post-prandial period. These results highlight the importance of hepatic PKCβ as a drug target for obesity-associated nonalcoholic hepatic steatosis.

Soluble (pro)renin receptor treats metabolic syndrome in mice with diet-induced obesity via interaction with PPARγ

The therapies available for management of obesity and associated conditions are limited, because they are often directed toward an individual component of metabolic syndrome and are associated with adverse effects. Here, we report the multifaceted therapeutic potential of histidine-tagged recombinant soluble (pro)renin receptor (sPRR), termed sPRR-His, in a mouse model of diet-induced obesity (DIO). In the DIO model, 2-week administration of sPRR-His lowered body weight and remarkably improved multiple metabolic parameters in the absence of fluid retention. Conversely, inhibition of endogenous sPRR production by PF429242 induced diabetes and insulin resistance, both of which were reversed by the sPRR-His supplement. At the cellular level, sPRR-His enhanced insulin-induced increases in glucose uptake via upregulation of phosphorylated AKT and protein abundance of glucose transporter 4. Promoter and gene expression analysis revealed PRR as a direct target gene of PPARγ. Adipocyte-specific PPARγ deletion induced severe diabetes and insulin resistance associated with reduced adipose PRR expression and circulating sPRR. The sPRR-His supplement in the null mice nearly normalized blood glucose and insulin levels. Additionally, sPRR-His treatment suppressed DIO-induced renal sodium-glucose cotransporter-2 (SGLT2) expression. Overall, sPRR-His exhibits a therapeutic potential in management of metabolic syndrome via interaction with PPARγ.

Peroxisome proliferator-activated receptor gamma participates in the acquisition of brain ischemic tolerance induced by ischemic preconditioning via glial glutamate transporter 1 in vivo and in vitro

Glial glutamate transporter 1 (GLT-1) plays a vital role in the induction of brain ischemic tolerance (BIT) by ischemic preconditioning (IPC). However, the mechanism still needs to be further explained. The aim of this study was to investigate whether peroxisome proliferator-activated receptor gamma (PPARγ) participates in regulating GLT-1 during the acquisition of BIT induced by IPC. Initially, cerebral IPC induced BIT and enhanced PPARγ and GLT-1 expression in the CA1 hippocampus in rats. The ratio of nuclear/cytoplasmic PPARγ was also increased. At the same time, the up-regulation of PPARγ expression in astrocytes in the CA1 hippocampus was revealed by double immunofluorescence for PPARγ and glial fibrillary acidic protein. Then, the mechanism by which PPARγ regulates GLT-1 was studied in rat cortical astrocyte-neuron cocultures. We found that IPC [45 min of oxygen glucose deprivation (OGD)] protected neuronal survival after lethal OGD (4 h of OGD), which usually leads to neuronal death. The activation of PPARγ occurred earlier than the up-regulation of GLT-1 in astrocytes after IPC, as determined by western blot and immunofluorescence. Moreover, the preadministration of the PPARγ antagonist T0070907 or PPARγ siRNA significantly attenuated GLT-1 up-regulation and the neuroprotective effects induced by IPC in vitro. Finally, the effect of the PPARγ antagonist on GLT-1 expression and BIT was verified in vivo. We observed that the preadministration of T0070907 by intracerebroventricular injection dose-dependently attenuated the up-regulation of GLT-1 and BIT induced by cerebral IPC in rats. In conclusion, PPARγ participates in regulating GLT-1 during the acquisition of BIT induced by IPC. Cover Image for this issue: doi: 10.1111/jnc.14532. Open Science: This manuscript was awarded with the Open Materials Badge For more information see: https://cos.io/our-services/open-science-badges/.

Biotransformation of polyunsaturated fatty acids to bioactive hepoxilins and trioxilins by microbial enzymes

Hepoxilins (HXs) and trioxilins (TrXs) are involved in physiological processes such as inflammation, insulin secretion and pain perception in human. They are metabolites of polyunsaturated fatty acids (PUFAs), including arachidonic acid, eicosapentaenoic acid and docosahexaenoic acid, formed by 12-lipoxygenase (LOX) and epoxide hydrolase (EH) expressed by mammalian cells. Here, we identify ten types of HXs and TrXs, produced by the prokaryote Myxococcus xanthus, of which six types are new, namely, HXB₅, HXD₃, HXE₃, TrXB₅, TrXD₃ and TrXE₃. We succeed in the biotransformation of PUFAs into eight types of HXs (>35% conversion) and TrXs (>10% conversion) by expressing M. xanthus 12-LOX or 11-LOX with or without EH in Escherichia coli. We determine 11-hydroxy-eicosatetraenoic acid, HXB₃, HXB₄, HXD₃, TrXB₃ and TrXD₃ as potential peroxisome proliferator-activated receptor-γ partial agonists. These findings may facilitate physiological studies and drug development based on lipid mediators.

Hepoxilins (HXs) and trioxilins (TrXs) are lipid metabolites with roles in inflammation and insulin secretion. Here, the authors discover a prokaryotic source of HXs and TrXs, identify the biosynthetic enzymes and heterologously express HXs and TrXs in E. coli.

PPARγ and Its Role in Cardiovascular Diseases

Peroxisome proliferator-activated receptor Gamma (PPARγ), a ligand-activated transcription factor, has a role in various cellular functions as well as glucose homeostasis, lipid metabolism, and prevention of oxidative stress. The activators of PPARγ are already widely used in the treatment of diabetes mellitus. The cardioprotective effect of PPARγ activation has been studied extensively over the years making them potential therapeutic targets in diseases associated with cardiovascular disorders. However, they are also associated with adverse cardiovascular events such as congestive heart failure and myocardial infarction. This review aims to discuss the role of PPARγ in the various cardiovascular diseases and summarize the current knowledge on PPARγ agonists from multiple clinical trials. Finally, we also review the new PPARγ agonists under development as potential therapeutics with reduced or no adverse effects.

Mechanisms by which the thiazolidinedione troglitazone protects against sucrose-induced hepatic fat accumulation and hyperinsulinaemia

BACKGROUND AND PURPOSE

Thiazolidinediones (TZD) are known to ameliorate fatty liver in type 2 diabetes. To date, the underlying mechanisms of their hepatic actions remain unclear.

EXPERIMENTAL APPROACH

Hepatic triglyceride content and export rates were assessed in 2 week high-sucrose-fed Wistar rats treated with troglitazone and compared with untreated high-sucrose rodent controls. Fractional de novo lipogenesis (DNL) contributions to hepatic triglyceride were quantified by analysis of triglyceride enrichment from deuterated water. Hepatic insulin clearance and NO status during a meal tolerance test were also evaluated.

KEY RESULTS

TZD significantly reduced hepatic triglyceride (P < 0.01) by 48%, decreased DNL contribution to hepatic triglyceride (P < 0.01) and increased postprandial non-esterified fatty acids clearance rates (P < 0.01) in comparison with the high-sucrose rodent control group. During a meal tolerance test, plasma insulin AUC was significantly lower (P < 0.01), while blood glucose and plasma C-peptide levels were not different. Insulin clearance was increased (P < 0.001) by 24% and was associated with a 22% augmentation of hepatic insulin-degrading enzyme activity (P < 0.05). Finally, hepatic NO was decreased by 24% (P < 0.05).

CONCLUSIONS

Overall, TZD show direct actions on liver by reducing hepatic DNL and increasing hepatic insulin clearance. The alterations in hepatic insulin clearance were associated with changes in insulin-degrading enzyme activity, with possible modulation of NO levels.

Does Thiazolidinedione therapy exacerbate fluid retention in congestive heart failure?

The ever-growing global burden of congestive heart failure (CHF) and type 2 diabetes mellitus (T2DM) as well as their co-existence necessitate that anti-diabetic pharmacotherapy will modulate the cardiovascular risk inherent to T2DM while complying with the accompanying restrictions imposed by CHF. The thiazolidinedione (TZD) family of peroxisome proliferator-activated receptor γ (PPARγ) agonists initially provided a promising therapeutic option in T2DM owing to anti-diabetic efficacy combined with pleiotropic beneficial cardiovascular effects. However, the utility of TZDs in T2DM has declined in the past decade, largely due to concomitant adverse effects of fluid retention and edema formation attributed to salt-retaining effects of PPARγ activation on the nephron. Presumably, the latter effects are potentially deleterious in the context of pre-existing fluid retention in CHF. However, despite a considerable body of evidence on mechanisms responsible for TZD-induced fluid retention suggesting that this class of drugs is rightfully prohibited from use in CHF patients, there is a paucity of experimental and clinical studies that investigate the effects of TZDs on salt and water homeostasis in the CHF setting. In an attempt to elucidate whether TZDs actually exacerbate the pre-existing fluid retention in CHF, our review summarizes the pathophysiology of fluid retention in CHF. Moreover, we thoroughly review the available data on TZD-induced fluid retention and proposed mechanisms in animals and patients. Finally, we will present recent studies challenging the common notion that TZDs worsen renal salt and water retention in CHF.

Cardioprotective role of peroxisome proliferator-activated receptor-γ agonist, rosiglitazone in a unique murine model of diabetic cardiopathy

AIMS

Rosiglitazone (RSZ), a PPARγ agonist was potent efficacious insulin sensitizing blockbuster drug for treatment of Type 2 diabetes mellitus (T2DM) but the benefit of PPARγ activation in congestive heart failure (CHF) was controversial. The present work was planned to study the role of RSZ in diabetic cardiopathy.

MAIN METHODS

Zucker fa/fa rats, the genetic model of T2DM were subjected to constriction of suprarenal abdominal aorta so that they represent a combined model of diabetes and cardiopathy. The development cardiopathy was assessed biochemically (plasma BNP and aldosterone levels), using echocardiography and expression angiotensin II receptor type 1a gene in heart and Endothelin-1 gene in aorta. Rats were treated with RSZ and in combination with amiloride for four weeks and were assessed to evaluate the effect of RSZ or amiloride or its combination on antidiabetic activity, adverse or toxic effects and congestive heart failure status.

KEY FINDINGS

RSZ shows its anti-diabetic effect from 0.3mg/kg dose onwards and at 3mg/kg dose levels it caused beneficial effects (reduction of blood pressure) on cardiovascular system and at highest (30mg/kg) dose it starts showing adverse effects like body weight gain, edema, left ventricular hypertrophy. However, when highest dose of RSZ animals were treated with amiloride (ENaC inhibitor) at 2mg/kg the reversal of the adverse effects was evident, indicating the combination of RSZ and amiloride is beneficial in diabetic cardiopathy model.

SIGNIFICANCE

RSZ and amiloride combination appeared promising treatment in diabetic patients with cardiopathy without any side effect.

Amorphous nanosilica particles evoke vascular relaxation through PI3K/Akt/eNOS signaling

There have been several reported studies on the distribution and/or toxicity of nanosilica particles. However, the influence of these particles on blood vessels through which they are distributed is poorly understood. Hence, we investigated the effects of nano- and micromaterials on blood vessel shrinkage and relaxation. Nanosilica particles with diameters of 70 nm (nSP70) were used as the nanomaterial, and particles of 300 and 1000 nm (nSP300 and mSP1000, respectively) were used as micromaterials. A rat thoracic aorta was used as the test blood vessel. The nano- and micromaterials had no effect on vessel shrinkage. Of the nano- and micromaterials tested, only nSP70 strongly evoked vascular relaxation. Vascular relaxation evoked by nSP70 was almost completely inhibited by the phosphoinositide 3-kinase (PI3K) inhibitor wortmannin. In addition, the selective nitric oxide synthesis inhibitor NG-nitro-l-arginine methyl ester, which inhibits endothelial nitric oxide synthase (eNOS) downstream of PI3K signaling, inhibited vascular relaxation evoked by nSP70. In an analysis using bovine aortic endothelial cells (bAECs), nSP70 phosphorylated protein kinase B (AKT) and eNOS acted downstream of PI3K signaling. PI3K inhibition by wortmannin reduced AKT and eNOS phosphorylation. These results demonstrated that 70-nm amorphous nanosilica particles evoked vascular relaxation through PI3K/Akt/eNOS signaling. Moreover, it was suggested that nanomaterials, in general, control or disrupt vascular function by activating a known signal cascade.

VEGFB/VEGFR1-Induced Expansion of Adipose Vasculature Counteracts Obesity and Related Metabolic Complications

Impaired angiogenesis has been implicated in adipose tissue dysfunction and the development of obesity and associated metabolic disorders. Here, we report the unexpected finding that vascular endothelial growth factor B (VEGFB) gene transduction into mice inhibits obesity-associated inflammation and improves metabolic health without changes in body weight or ectopic lipid deposition. Mechanistically, the binding of VEGFB to VEGF receptor 1 (VEGFR1, also known as Flt1) activated the VEGF/VEGFR2 pathway and increased capillary density, tissue perfusion, and insulin supply, signaling, and function in adipose tissue. Furthermore, endothelial Flt1 gene deletion enhanced the effect of VEGFB, activating the thermogenic program in subcutaneous adipose tissue, which increased the basal metabolic rate, thus preventing diet-induced obesity and related metabolic complications. In obese and insulin-resistant mice, Vegfb gene transfer, together with endothelial Flt1 gene deletion, induced weight loss and mitigated the metabolic complications, demonstrating the therapeutic potential of the VEGFB/VEGFR1 pathway.

Systemic PPARγ deletion causes severe disturbance in fluid homeostasis in mice

The pharmacological action of peroxisome proliferator-activated receptor (PPAR)γ in promoting sodium and water retention is well documented as highlighted by the major side-effect of body weight gain and edema associated with thiazolidinedione use. However, a possible physiological role of PPARγ in regulation of fluid metabolism has not been reported by previous studies. Here we analyzed fluid metabolism in inducible whole-body PPARγ knockout mice. The null mice developed severe polydipsia and polyuria, reduced urine osmolality, and modest hyperphagia. The phenomenon persisted during 3 days of pair feeding and pair drinking, accompanied by progressive weight loss. After 24 h water deprivation, the null mice had a lower urine osmolality, a higher urine volume, a greater weight loss, and a greater rise in hematocrit than the floxed control. Urinary vasopressin (AVP) excretion was not different between the genotypes under basal condition or after WD. The response of urine osmolality to acute and chronic 1-desamino-8-D-arginine vasopressin treatment was attenuated in the null mice, but the total abundance or phosphorylation of aquaporin 2 (AQP2) in the kidney or AVP-induced cAMP production in inner medullary collecting duct suspensions was unaffected. Overall, PPARγ participates in physiological control of fluid homeostasis through an unknown mechanism involving cAMP/AQP2-independent enhancement of AVP response.

Thiazolidinediones and Edema: Recent Advances in the Pathogenesis of Thiazolidinediones-Induced Renal Sodium Retention

Thiazolidinediones (TZDs) are one of the major classes of antidiabetic drugs that are used widely. TZDs improve insulin resistance by activating peroxisome proliferator-activated receptor gamma (PPARγ) and ameliorate diabetic and other nephropathies, at least, in experimental animals. However, TZDs have side effects, such as edema, congestive heart failure, and bone fracture, and may increase bladder cancer risk. Edema and heart failure, which both probably originate from renal sodium retention, are of great importance because these side effects make it difficult to continue the use of TZDs. However, the pathogenesis of edema remains a matter of controversy. Initially, upregulation of the epithelial sodium channel (ENaC) in the collecting ducts by TZDs was thought to be the primary cause of edema. However, the results of other studies do not support this view. Recent data suggest the involvement of transporters in the proximal tubule, such as sodium-bicarbonate cotransporter and sodium-proton exchanger. Other studies have suggested that sodium-potassium-chloride cotransporter 2 in the thick ascending limb of Henle and aquaporins are also possible targets for TZDs. This paper will discuss the recent advances in the pathogenesis of TZD-induced sodium reabsorption in the renal tubules and edema.

PPARγ agonist-induced fluid retention depends on αENaC expression in connecting tubules

BACKGROUND/AIMS

Thiazolidinediones (TZDs, like rosiglitazone (RGZ)) are peroxisome proliferator-activated receptor γ (PPARγ) agonists used to treat type 2 diabetes. Clinical limitations include TZD-induced fluid retention and body weight (BW) increase, which are inhibited by amiloride, an epithelial-sodium channel (ENaC) blocker. RGZ-induced fluid retention is maintained in mice with αENaC knockdown in the collecting duct (CD). Since ENaC in the connecting tubule (CNT) rather than in CD appears to be critical for normal NaCl retention, we aimed to further explore the role of ENaC in CNT in RGZ-induced fluid retention.

METHODS

Mice with conditional inactivation of αENaC in both CNT and CD were used (αENaC lox/lox AQP2-Cre; 'αENaC-CNT/CD-KO') and compared with littermate controls (αENaC lox/lox mice; 'WT'). BW was monitored and total body water (TBW) and extracellular fluid volume (ECF) were determined by bioelectrical impedance spectroscopy (BIS) before and after RGZ (320 mg/kg diet for 10 days).

RESULTS

On regular NaCl diet, αENaC-CNT/CD-KO had normal BW, TBW, ECF, hematocrit, and plasma Na(+), K(+), and creatinine, associated with an increase in plasma aldosterone compared with WT. Challenging αENaC-CNT/CD-KO with a low NaCl diet unmasked impaired NaCl and K homeostasis, consistent with effective knockdown of αENaC. In WT, RGZ increased BW (+6.1%), TBW (+8.4%) and ECF (+10%), consistent with fluid retention. These changes were significantly attenuated in αENaC-CNT/CD-KO (+3.4, 1.3, and 4.3%).

CONCLUSION

Together with the previous studies, the current results are consistent with a role of αENaC in CNT in RGZ-induced fluid retention, which dovetails with the physiological relevance of ENaC in this segment.

Dipeptidyl peptidase IV inhibitor lowers PPARγ agonist-induced body weight gain by affecting food intake, fat mass, and beige/brown fat but not fluid retention

Peroxisome proliferator-activated receptor-γ (PPARγ) agonists like pioglitazone (PGZ) are effective antidiabetic drugs, but they induce fluid retention and body weight (BW) gain. Dipeptidyl peptidase IV (DPP IV) inhibitors are antidiabetic drugs that enhance renal Na(+) and fluid excretion. Therefore, we examined whether the DPP IV inhibitor alogliptin (ALG) ameliorates PGZ-induced BW gain. Male Sv129 mice were treated with vehicle (repelleted diet), PGZ (220 mg/kg diet), ALG (300 mg/kg diet), or a combination of PGZ and ALG (PGZ + ALG) for 14 days. PGZ + ALG prevented the increase in BW observed with PGZ but did not attenuate the increase in body fluid content determined by bioimpedance spectroscopy (BIS). BIS revealed that ALG alone had no effect on fat mass (FM) but enhanced the FM-lowering effect of PGZ; MRI analysis confirmed the latter and showed reductions in visceral and inguinal subcutaneous (sc) white adipose tissue (WAT). ALG but not PGZ decreased food intake and plasma free fatty acid concentrations. Conversely, PGZ but not ALG increased mRNA expression of thermogenesis mediator uncoupling protein 1 in epididymal WAT. Adding ALG to PGZ treatment increased the abundance of multilocular cell islets in sc WAT, and PGZ + ALG increased the expression of brown-fat-like "beige" cell marker TMEM26 in sc WAT and interscapular brown adipose tissue and increased rectal temperature vs. vehicle. In summary, DPP IV inhibition did not attenuate PPARγ agonist-induced fluid retention but prevented BW gain by reducing FM. This involved ALG inhibition of food intake and was associated with food intake-independent synergistic effects of PPARγ agonism and DPP-IV inhibition on beige/brown fat cells and thermogenesis.

New Insights into the PPAR γ Agonists for the Treatment of Diabetic Nephropathy

Diabetic nephropathy (DN) is a severe complication of diabetes and serves as the leading cause of chronic renal failure. In the past decades, angiotensin-converting enzyme inhibitors (ACEIs)/angiotensin II receptor blockers (ARBs) based first-line therapy can slow but cannot stop the progression of DN, which urgently requests the innovation of therapeutic strategies. Thiazolidinediones (TZDs), the synthetic exogenous ligands of nuclear receptor peroxisome proliferator-activated receptor- γ (PPAR γ ), had been thought to be a promising candidate for strengthening the therapy of DN. However, the severe adverse effects including fluid retention, cardiovascular complications, and bone loss greatly limited their use in clinic. Recently, numerous novel PPAR γ agonists involving the endogenous PPAR γ ligands and selective PPAR γ modulators (SPPARMs) are emerging as the promising candidates of the next generation of antidiabetic drugs instead of TZDs. Due to the higher selectivity of these novel PPAR γ agonists on the regulation of the antidiabetes-associated genes than that of the side effect-associated genes, they present fewer adverse effects than TZDs. The present review was undertaken to address the advancements and the therapeutic potential of these newly developed PPAR γ agonists in dealing with diabetic kidney disease. At the same time, the new insights into the therapeutic strategies of DN based on the PPAR γ agonists were fully addressed.

PPARγ agonists upregulate sphingosine 1-phosphate (S1P) receptor 1 expression, which in turn reduces S1P-induced [Ca(2+)]i increases in renal mesangial cells

We previously identified peroxisome proliferator-activated receptor gamma (PPARγ) agonists (thiazolidinediones, TZDs) as modulators of the sphingolipid metabolism in renal mesangial cells. TZDs upregulated sphingosine kinase 1 (SK-1) and increased the formation of intracellular sphingosine 1-phosphate (S1P), which in turn reduced the expression of pro-fibrotic connective tissue growth factor. Since S1P also acts as extracellular ligand at specific S1P receptors (S1PR, S1P1-5), we investigated here the effect of TZDs on S1PR expression in mesangial cells and evaluated the functional consequences by measuring S1P-induced increases in intracellular free Ca(2+) concentration ([Ca(2+)]i). Treatment with two different TZDs, troglitazone and rosiglitazone, enhanced S1P1 mRNA and protein expression in rat mesangial cells, whereas S1P2-5 expression levels were not altered. Upregulation of S1P1 mRNA upon TZD treatment was also detected in human mesangial cells and mouse glomeruli. PPARγ antagonism and promoter studies revealed that the TZD-dependent S1P1 mRNA induction involved a functional PPAR response element in the S1P1 promoter. Pharmacological approaches disclosed that S1P-induced [Ca(2+)]i increases in rat mesangial cells were predominantly mediated by S1P2 and S1P3. Interestingly, the transcriptional upregulation of S1P1 by TZDs resulted in a reduction of S1P-induced [Ca(2+)]i increases, which was reversed by the S1P1/3 antagonist VPC-23019, the protein kinase C (PKC) inhibitor PKC-412, and by S1P1 siRNA. These data suggest that PPARγ-dependent upregulation of S1P1 leads to an inhibition of S1P-induced Ca(2+) signaling in a PKC-dependent manner. Overall, these results reveal that TZDs not only modulate intracellular S1P levels but also regulate S1PR signaling by increasing S1P1 expression in mesangial cells.

Adipose tissue angiogenesis: impact on obesity and type-2 diabetes

The growth and function of tissues are critically dependent on their vascularization. Adipose tissue is capable of expanding many-fold during adulthood, therefore requiring the formation of new vasculature to supply growing and proliferating adipocytes. The expansion of the vasculature in adipose tissue occurs through angiogenesis, where new blood vessels develop from those pre-existing within the tissue. Inappropriate angiogenesis may underlie adipose tissue dysfunction in obesity, which in turn increases type-2 diabetes risk. In addition, genetic and developmental factors involved in vascular patterning may define the size and expandability of diverse adipose tissue depots, which are also associated with type-2 diabetes risk. Moreover, the adipose tissue vasculature appears to be the niche for pre-adipocyte precursors, and factors that affect angiogenesis may directly impact the generation of new adipocytes. Here we review recent advances on the basic mechanisms of angiogenesis, and on the role of angiogenesis in adipose tissue development and obesity. A substantial amount of data points to a deficit in adipose tissue angiogenesis as a contributing factor to insulin resistance and metabolic disease in obesity. These emerging findings support the concept of the adipose tissue vasculature as a source of new targets for metabolic disease therapies. This article is part of a Special Issue entitled: Modulation of Adipose Tissue in Health and Disease.

Oral green tea catechins transiently lower plasma glucose concentrations in female db/db mice

Polyphenols, including green tea catechins, are secondary plant compounds often discussed in the context of health-promoting potential. Evidence for such effects is mainly derived from epidemiological and cell culture studies. The aim of the present study was to investigate antidiabetic, antiadipogenic, and anti-inflammatory effects at nonpharmacological doses in an obese diabetic mouse model that exerts early relevant clinical signs of non-insulin-dependent diabetes mellitus. Female db/db mice received a flavonoid-poor diet either without additive, with rosiglitazone (RSG, 0.02 g/kg diet), or with green tea extract (low-dose green tea extract [LGTE] and high-dose green tea extract [HGTE], 0.1 and 1 g/kg diet). Food and water were freely available. The body weight was monitored weekly. Blood was sampled (12-h fasted) from the tail vein on day 28 and analyzed for glucose, cholesterol, triacylglycerol, nonesterified fatty acids, insulin, adiponectin, and soluble intercellular adhesion molecule-1 (sICAM-1). Blood glucose was also analyzed on day 14. Furthermore, sICAM-1 release was investigated in tumor necrosis factor alpha-stimulated EAhy926 cells. After 14 days, fasting glycemia was improved by RSG or HGTE supplementation compared to controls. However, at the end of the study (day 28), only RSG exhibited glucose-lowering effects and induced plasma adiponectin concentrations, paralleled by higher body weight gain and reduced periuterine fat pads compared to controls. However, only GTE treatment reduced sICAM-1 release in vitro and in vivo. Nonpharmacological HGTE supplementation in db/db mice caused (1) no adiponectin-inducing or antiadipogenic effects, (2) reduced sICAM-1 release, thereby potentially exerting anti-inflammatory effects in the progressive diabetic state, and (3) a transient improvement in glycemia.

Short-Term Therapy with Rosiglitazone, a PPAR-γ Agonist, Improves Metabolic Profile and Vascular Function in Nonobese Lean Wistar Rats

A number of preclinical and clinical studies have reported blood-pressure-lowering benefits of thiazolidinediones in diabetic subjects and animal models of diabetes. This study was designed to further elucidate vascular effects of rosiglitazone, on healthy nonobese, lean animals. Adult male Wistar rats were randomized and assigned to control and rosiglitazone-treated groups and were dosed daily with either vehicle or rosiglitazone (10 mg kg(-1) day(-1)) by oral gavage for 5 days. Compared with control group, rosiglitazone treatment significantly reduced plasma levels of triglycerides (>240%) and nonesterified free fatty acids (>268%) (both, P < 0.001). There were no changes in vascular contractility to KCl or noradrenaline between two groups. However, rosiglitazone therapy improved carbamylcholine-induced vasorelaxation (93 ± 3 % versus control 78 ± 2, P < 0.01) an effect which was abolished by L-NAME. There was no difference in sodium nitroprusside-induced vasorelaxation between the control and rosiglitazone-treated animals. These results indicate that short-term rosiglitazone therapy improves both metabolic profile and vascular function in lean rats. The vascular effect of rosiglitazone appears to be mediated by alteration in NO production possibly by activation of endothelial PPARγ. This increased NO production together with improved lipid profile may explain mechanism(s) of blood-pressure-lowering effects of thiazolidinediones on both human and experimental animals.

Acute rosiglitazone treatment during reperfusion after hyperglycemic stroke is neuroprotective not vascular protective

Reperfusion therapy for ischemic stroke can cause secondary brain injury, especially under hyperglycemic (HG) conditions. Here we investigated the effect of acute treatment with rosiglitazone, a peroxisome proliferator-activated receptor-gamma (PPAR-γ) agonist, prior to postischemic reperfusion, on stroke outcome during HG stroke. Male Wistar rats that were either normoglycemic (NG) or HG by STZ (50 mg/kg; for 5-6 days) underwent middle cerebral artery occlusion (MCAO) for 2 hours with 2 hours of reperfusion. Animals were treated i.v. with rosiglitazone (1mg/kg; n=16), rosiglitazone (1mg/kg) + the free radical scavenger Tempol (50mg/kg; n=10) or vehicle (n=16) ten minutes prior to reperfusion and infarct volume, edema formation and cerebral blood flow (CBF) were measured. Compared to NG, HG stroke significantly increased infarct volume from 5.2±3.0% vs. 14.7±3.6% (p<0.05). Rosiglitazone prevented the increased infarct volume induced by HG that was only 6.9±2.0% (p<0.05 vs. HG) but did not have any effect on edema formation that was increased by 3.0% in both HG vehicle and rosiglitazone-treated ipsilateral vs. contralateral hemispheres (p<0.05). Combined treatment of rosiglitazone + Tempol did not significantly change brain water content that remained 2.2% greater than contralateral (p<0.05), but reversed the neuroprotective properties of rosiglitazone in HG MCAO animals such that infarct volume was 14.3±4.4% (p>0.05 vs. vehicle). The lack of an effect of combined treatment of rosiglitazone + Temple may be due to a decrease in reperfusion CBF that was only 60% of baseline (p<0.01) compared to 82% and 89% for HG vehicle and rosiglitazone treated animals (p>0.05). In conclusion, acute rosiglitazone treatment prior reperfusion was neuroprotective but not vascular protective during HG stroke.

Cardiac mTOR protects the heart against ischemia-reperfusion injury

Cardiac mammalian target of rapamycin (mTOR) is necessary and sufficient to prevent cardiac dysfunction in pathological hypertrophy. However, the role of cardiac mTOR in heart failure after ischemic injury remains undefined. To address this question, we used transgenic (Tg) mice with cardiac-specific overexpression of mTOR (mTOR-Tg mice) to study ischemia-reperfusion (I/R) injury in two animal models: 1) in vivo I/R injury with transient coronary artery ligation and 2) ex vivo I/R injury in Langendorff-perfused hearts with transient global ischemia. At 28 days after I/R, mortality was lower in mTOR-Tg mice than littermate control mice [wild-type (WT) mice]. Echocardiography and MRI demonstrated that global cardiac function in mTOR-Tg mice was preserved, whereas WT mice exhibited significant cardiac dysfunction. Masson's trichrome staining showed that 28 days after I/R, the area of interstitial fibrosis was smaller in mTOR-Tg mice compared with WT mice, suggesting that adverse left ventricular remodeling is inhibited in mTOR-Tg mice. In the ex vivo I/R model, mTOR-Tg hearts demonstrated improved functional recovery compared with WT hearts. Perfusion with Evans blue after ex vivo I/R yielded less staining in mTOR-Tg hearts than WT hearts, indicating that mTOR overexpression inhibited necrosis during I/R injury. Expression of proinflammatory cytokines, including IL-6 and TNF-α, in mTOR-Tg hearts was lower than in WT hearts. Consistent with this, IL-6 in the effluent post-I/R injury was lower in mTOR-Tg hearts than in WT hearts. These findings suggest that cardiac mTOR overexpression in the heart is sufficient to provide substantial cardioprotection against I/R injury and suppress the inflammatory response.

Update on adipose tissue blood flow regulation

According to Fick's principle, any metabolic or hormonal exchange through a given tissue depends on the product of the blood flow to that tissue and the arteriovenous difference. The proper function of adipose tissue relies on adequate adipose tissue blood flow (ATBF), which determines the influx and efflux of metabolites as well as regulatory endocrine signals. Adequate functioning of adipose tissue in intermediary metabolism requires finely tuned perfusion. Because metabolic and vascular processes are so tightly interconnected, any disruption in one will necessarily impact the other. Although altered ATBF is one consequence of expanding fat tissue, it may also aggravate the negative impacts of obesity on the body's metabolic milieu. This review attempts to summarize the current state of knowledge on adipose tissue vascular bed behavior under physiological conditions and the various factors that contribute to its regulation as well as the possible participation of altered ATBF in the pathophysiology of metabolic syndrome.

The differential role of Hif1β/Arnt and the hypoxic response in adipose function, fibrosis, and inflammation

In obesity, adipocytes distant from vasculature become hypoxic and dysfunctional. This hypoxic response is mediated by hypoxia-inducible factors (Hif1α, Hif2α, and Hif3α) and their obligate partner, Hif1β (Arnt). We show that mice lacking Hif1β in fat (FH1βKO) are lean, exhibit reduced adipocyte size, and are protected from age- and diet-induced glucose intolerance. There is also reduced Vegf and vascular permeability in FH1βKO fat, but diet-induced inflammation and fibrosis is unchanged. Adipocytes from FH1βKO mice have reduced glucose uptake due to decreased Glut1 and Glut4, which is mirrored in 3T3-L1 adipocytes with Hif1β knockdown. Hif1β knockdown cells also fail to respond appropriately to hypoxia with reduced cellular respiration and reduced mitochondrial gene expression. Some, but not all, of these effects are reproduced by Hif1α knockdown. Thus, Hif1β/Arnt regulates glucose uptake, mitochondrial gene expression, and vascular permeability to control adipose mass and function, providing a target for obesity therapy.

Neuroprotection by rosiglitazone in transient focal cerebral ischemia might not be mediated by glutamate transporter-1

Glutamate transport represents a key mechanism for maintaining low level of glutamate in the extracellular milieu to restrict the excitotoxic action of glutamate released during ischemia/reperfusion (I/R) injury. Recently, it has been reported that glutamate transporter-1 (GLT-1) is a novel target for peroxisome proliferator-activated receptor-γ (PPARγ) agonist, which shows neuroprotection following oxygen glucose deprivation (OGD) in neuronal-astrocytic cocultures. Hence, the present study was undertaken to investigate the role of rosiglitazone in neuroprotection mediated by GLT-1 following focal cerebral I/R injury in rat. We found that rosiglitazone (2 mg/kg i.p) administered pre- or post-I/R injury significantly improved behavioral outcome and decreased cerebral infarct volume. However, no significant changes were observed in GLT-1 mRNA and protein expression in rosiglitazone-treated rats following 1 hr of ischemia/24 hr of reperfusion (1/24 hr I/R) injury. Interestingly, bioinformatics analysis also does not reveal any PPAR response element on the GLT-1/EAAT2 promoter region. Further rosiglitazone neither increased [(3) H]glutamate uptake in glia-enriched preparations nor caused any change in glutamine synthetase activity. On the other hand, there was a significant (P < 0.05) downregulation in tumor necrosis factor-α and interleukin-1β gene expression, which were more pronounced in the posttreatment group. The posttreatment with rosiglitazone also significantly reduced the increase in prostaglandin E2 level in the ischemic brain. Therefore, the present findings suggest that the neuroprotective effect of rosiglitazone does not seem to be mediated by modulation of GLT-1 protein expression/activity in a focal cerebral ischemia model. However, the results do provide increasing evidence that the neuroprotective effect may be mediated by its antiinflammatory action.

Renal and vascular mechanisms of thiazolidinedione-induced fluid retention

Thiazolidinediones (TZDs) are peroxisome proliferator-activated receptor subtype gamma (PPARgamma) activators that are clinically used as an insulin sensitizer for glycemic control in patients with type 2 diabetes. Additionally, TZDs exhibit novel anti-inflammatory, antioxidant, and antiproliferative properties, indicating therapeutic potential for a wide variety of diseases associated with diabetes and other conditions. The clinical applications of TZDs are limited by the common major side effect of fluid retention. A better understanding of the molecular mechanism of TZD-induced fluid retention is essential for the development of novel therapies with improved safety profiles. An important breakthrough in the field is the finding that the renal collecting duct is a major site for increased fluid reabsorption in response to rosiglitazone or pioglitazone. New evidence also indicates that increased vascular permeability in adipose tissues may contribute to edema formation and body weight gain. Future research should therefore be directed at achieving a better understanding of the detailed mechanisms of TZD-induced increases in renal sodium transport and in vascular permeability.

Omega-3 fatty acids and metabolic syndrome: effects and emerging mechanisms of action

Epidemiological, human, animal, and cell culture studies show that n-3 fatty acids, especially α-linolenic acid (ALA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA), reduce the risk factors of cardiovascular diseases. EPA and DHA, rather than ALA, have been the focus of research on the n-3 fatty acids, probably due to the relatively inefficient conversion of ALA to EPA and DHA in rodents and humans. This review will assess our current understanding of the effects and potential mechanisms of actions of individual n-3 fatty acids on multiple risk factors of metabolic syndrome. Evidence for pharmacological responses and the mechanism of action of each of the n-3 fatty acid trio will be discussed for the major risk factors of metabolic syndrome, especially adiposity, dyslipidemia, insulin resistance and diabetes, hypertension, oxidative stress, and inflammation. Metabolism of n-3 and n-6 fatty acids as well as the interactions of n-3 fatty acids with nutrients, gene expression, and disease states will be addressed to provide a rationale for the use of n-3 fatty acids to reduce the risk factors of metabolic syndrome.

Protective effects of PPARγ agonist in acute nephrotic syndrome

BACKGROUND

Peroxisome proliferator-activated receptor gamma (PPARγ) agonists have beneficial effects on renal structure and function in models of diabetes and chronic kidney diseases. However, the increased incidence of weight gain and edema potentially limits their usefulness. We studied an acute minimal-change disease-like nephrotic syndrome model to assess effects of PPARγ agonist on acute podocyte injury and effects on fluid homeostasis.

METHODS

Acute podocyte injury and nephrotic syndrome were induced by puromycin aminonucleoside (PAN) injection in rats.

RESULTS

PPARγ agonist, given at the time or after, but not before PAN, reduced proteinuria, restored synaptopodin, decreased desmin and trended to improve foot process effacement. There was no significant difference in glomerular filtration, effective circulating volume, blood pressure or fractional sodium excretion. PAN-injured podocytes had decreased PPARγ, less nephrin and α-actinin-4, more apoptosis and reduced phosphorylated Akt. In PAN-injured cultured podocytes, PPARγ agonist also reversed abnormalities only when given simultaneously or after injury.

CONCLUSIONS

These results show that PPARγ agonist has protective effects on podocytes in acute nephrotic syndrome without deleterious effects on fluid homeostasis. PPARγ agonist-induced decrease in proteinuria in acute nephrotic syndrome is dependent at least partially on regulation of peroxisome proliferator-response element-sensitive gene expression such as α-actinin-4 and nephrin and the restoration of podocyte structure.

Effects of Chronic Rosiglitazone Treatment on Renal Handling of Salt and Water in Rats With Volume-Overload Congestive Heart Failure

Background—

The side effects of fluid retention and edema of the thiazolidinedione (TZD) class of peroxisome proliferator-activated receptor-γ agonists limit their use in patients with congestive heart failure (CHF). The present study aims to explore whether chronic treatment with the TZD compound rosiglitazone (RGZ) is associated with worsening of salt and water retention in male Sprague-Dawley rats with aorto-caval fistula, an experimental model of volume-overload CHF.

Methods and Results—

The effects of oral RGZ (30 mg/kg per day for 4 weeks) in CHF rats on plasma volume, cumulative sodium excretion, renal expression of Na + channels and transporters, and selected biomarkers of CHF were compared with those in CHF rats and sham-operated control rats treated with vehicle only (n=7 to 10). Additionally, the response to acute saline loading (3.5% of body weight) was evaluated after 2 weeks of treatment by renal clearance methodology. Chronic RGZ treatment caused no further increase in plasma volume compared with vehicle-treated CHF rats. Moreover, no increase in renal expression of Na + transport-linked channels/transporters was observed in response to RGZ. Cumulative sodium excretion was enhanced in CHF rats after RGZ and by another TZD compound, pioglitazone. In response to saline loading, RGZ-treated animals displayed a higher natriuretic/diuretic response than did vehicle-treated rats. Chronic RGZ treatment was not associated with any deterioration in selected biomarkers of CHF, whereas indices of cardiac hypertrophy and blood pressure were improved.

Conclusions—

Chronic RGZ treatment was not associated with worsening of fluid retention or cardiac status in rats with experimental volume-overload CHF. Rather, RGZ appeared to improve renal handling of salt and water in rats with CHF.

Antidiabetic activity of some pentacyclic acid triterpenoids, role of PTP-1B: in vitro, in silico, and in vivo approaches

The aim of the current study was to investigate the oral antidiabetic activity of four structurally-related triterpenic acids: ursolic (RE-01), oleanolic (RE-02), moronic (RE-03) and morolic (RE-04) acids. STZ-nicotinamide diabetic rats were treated with these triterpenes (50 mg/kg) and the antidiabetic effects in acute experiment were determined. All compounds showed significant antidiabetic activity in comparison with control group (p<0.05). The in vitro inhibitory activity of compounds against protein tyrosine phosphatase 1B (PTP-1B) was also evaluated. At 50 μM, the enzymatic activity was almost completely inhibited. All compounds were docked with a crystal structure of PTP-1B. Docking results suggested the potential binding of the triterpenic acids in a binding pocket next to the catalytic site. An extensive hydrogen bond network with the carboxyl group and Van der Waals interactions stabilize the protein-ligand complexes.

Telmisartan inhibits vasoconstriction via PPARγ-dependent expression and activation of endothelial nitric oxide synthase

AIMS

Telmisartan activates peroxisome proliferator-activated receptor-γ (PPARγ) in addition to serving as an angiotensin II type 1 receptor (AT(1)R) blocker. The PPARγ activity of telmisartan on resistance arteries has remained largely unknown. The present study investigated the hypothesis that telmisartan inhibited vascular tension in mouse mesenteric resistance arteries, which was attributed to an increased nitric oxide (NO) production through the PPARγ-dependent augmentation of expression and activity of endothelial nitric oxide synthase (eNOS).

METHODS AND RESULTS

Second-order mesenteric arteries were isolated from male C57BL/6J, eNOS knockout and PPARγ knockout mice and changes in vascular tension were determined by isometric force measurement with a myograph. Expression and activation of relevant proteins were analysed by Western blotting. Real-time NO production was measured by confocal microscopy using the dye DAF. Telmisartan inhibited 9,11-dideoxy-11α,9α-epoxymethanoprostaglandin F(2α) (U46619)- or endothelin-1-induced contractions. An NOS inhibitor, N(G)-nitro-L-arginine methyl ester (l-NAME), or an inhibitor of soluble guanylate cyclase, 1H-[1,2,4]-oxadizolo[4,3-a]quinoxalin-1-one (ODQ), prevented telmisartan-induced inhibition of U46619 contractions. A PPARγ antagonist, GW9662, abolished telmisartan-induced inhibition. Likewise, the PPARγ antagonist rosiglitazone attenuated U46619-induced contractions. The effects of telmisartan and rosiglitazone were prevented by actinomycin-D, a transcription inhibitor. In contrast, losartan, olmesartan, and irbesartan did not inhibit contractions. The inhibition was absent in mesenteric arteries from eNOS knockout or PPARγ knockout mice. Telmisartan augmented eNOS expression, phosphorylation, and NO production, which were reversed by the co-treatment with GW9662.

CONCLUSIONS

The present results suggest that telmisartan-induced inhibition of vasoconstriction in resistance arteries is mediated through a PPARγ-dependent increase in eNOS expression and activity that is unrelated to AT₁R blockade.

A novel strategy for designing the selective PPAR agonist by the "sum of activity" model

Peroxisome proliferator-activated receptors alpha, delta and gamma are a collection of ligand-activated transcription factors crucial in lipid and glucose homeostasis. The involvement of these receptors in lipid metabolism makes them perfect therapeutic target for treating obesity and stroke. In this study, 'sum of activity' model was employed to design multi-target agonists. We used a new strategy to design agonists that fit both alpha and delta but not gamma, to avoid side effect. The CoMFA and CoMSIA models were used to explore the pharmacophore features by constructing three individual models: (a) alpha-model, (b) delta-model and (c) gamma-model, and two sum models: (d) alpha, delta- model, and (e) alpha, delta and gamma-model. The CoMFA model yielded a significant cross validation value, q(2), of 0.729 and non-cross validation value, r(2), of 0.933 in the alpha, delta-model. The CoMSIA studies yielded the best predictive models with q(2) of 0.622 in A+S and with r(2) of 0.911 in the alpha, delta-model. Finally, we proposed that distinct features shown in models (a), (b), (d) but not (c) and (e) should be accounted in designing weight-controlling drugs.

WY-14 643, a Selective PPARα Agonist, Induces Proinflammatory and Proangiogenic Responses in Human Ocular Cells

Peroxisome proliferator-activated receptor α (PPARα) agonism in ocular inflammation has not been thoroughly investigated. The objective of this investigation was to determine the effect of WY-14 643, a selective PPARα agonist, on inflammatory cytokine release in human ocular cells. Stimulation of primary human corneal epithelial cells, keratocytes, and retinal endothelial cells with 1 to 10 ng/mL interleukin 1β (IL-1β) resulted in a significant increase in numerous inflammatory cytokines, including IL-6, IL-8, and tumor necrosis factor α (TNF-α); and dexamethasone was able to significantly inhibit these effects. However, WY-14 643 did not effectively block IL-1β-induced cytokine release in ocular cells; rather, significant increases in IL-1β-induced inflammatory cytokines were observed in these cells but not in aortic smooth muscle cells. WY-14 643 also significantly upregulated vascular endothelial growth factor (VEGF) expression in corneal epithelial cells and keratocytes. These studies demonstrate for the first time that PPARα agonism may be proinflammatory and proangiogenic in a variety of ocular cells and suggest that therapeutic applications of such agents in ophthalmology may be limited.

Therapeutic Implications of PPARgamma in Cardiovascular Diseases

Peroxisome proliferator-activated receptor-γ (PPARγ) is the members of the nuclear receptor superfamily as a master transcriptional factor that promotes differentiation of preadipocytes by activating adipose-specific gene expression. Although PPARγ is expressed predominantly in adipose tissue and associated with adipocyte differentiation and glucose homeostasis, PPARγ is also present in a variety of cell types including vascular cells and cardiomyocytes. Activation of PPARγ suppresses production of inflammatory cytokines, and there is accumulating data that PPARγ ligands exert antihypertrophy of cardiomyocytes and anti-inflammatory, antioxidative, and antiproliferative effects on vascular wall cells and cardiomyocytes. In addition, activation of PPARγ is implicated in the regulation of endothelial function, proliferation and migration of vascular smooth muscle cells, and activation of macrophages. Many studies suggest that PPARγ ligands not only ameliorate insulin sensitivity, but also have pleiotropic effects on the pathophysiology of atherosclerosis, cardiac hypertrophy, ischemic heart, and myocarditis.

Microvascular responses to cardiovascular risk factors

Hypertension, hypercholesterolemia, diabetes, and obesity are among a growing list of conditions that have been designated as major risk factors for cardiovascular disease (CVD). While CVD risk factors are well known to enhance the development of atherosclerotic lesions in large arteries, there is also evidence that the structure and function of microscopic blood vessels can be profoundly altered by these conditions. The diverse responses of the microvasculature to CVD risk factors include oxidative stress, enhanced leukocyte- and platelet-endothelial cell adhesion, impaired endothelial barrier function, altered capillary proliferation, enhanced thrombosis, and vasomotor dysfunction. Emerging evidence indicates that a low-grade systemic inflammatory response that results from risk factor-induced cell activation and cell-cell interactions may underlie the phenotypic changes induced by risk factor exposure. A consequence of the altered microvascular phenotype and systemic inflammatory response is an enhanced vulnerability of tissues to the deleterious effects of secondary oxidative and inflammatory stresses, such as ischemia and reperfusion. Future efforts to develop therapies that prevent the harmful effects of risk factor-induced inflammation should focus on the microcirculation.

PPARgamma agonists upregulate the barrier function of tight junctions via a PKC pathway in human nasal epithelial cells

Peroxisome proliferator activated (PPAR)gamma plays a critical role in the control of not only adipocyte differentiation, lipid metabolism and immunity but also the barrier functions of epithelial and endothelial cells. In the present study, to investigate effects of PPAR gamma agonists on the tight junctional barrier of human nasal epithelial cells (HNECs), hTERT-transfected HNECs, which highly express both PPAR gamma and tight junction proteins, were treated with the PPAR gamma agonists rosiglitazone and troglitazone. Treatment with the PPAR gamma agonists enhanced the barrier function of hTERT-transfected HNECs together with the upregulation of tight junction molecules claudin-1 and -4, occludin, and tricellulin at the transcriptional level. A significant increase of tight junction strands was also observed after treatment with rosiglitazone. Treatment with PPAR gamma agonists induced the activity of phospho-PKC in hTERT-transfected HNECs. The upregulation of the tight junction molecules in hTERT-transfected HNECs by rosiglitazone was inhibited by not only PPAR gamma antagonists GW9662 and T0070907, but also the panPKC inhibitor GF109203X. These findings suggest that PPAR gamma agonists upregulate the barrier function of tight junctions of human nasal epithelial cells via a PKC signaling pathway and could be novel drugs for protection against inhaled substances and pathogens in the airway epithelium of human nasal mucosa.

Molecular pathology of oxidative stress in diabetic angiopathy: role of mitochondrial and cellular pathways

Diabetes mellitus is characterized by chronic hyperglycaemia and a significant risk of developing micro- and macrovascular complications. Growing evidence suggests that increased oxidative stress, induced by several hyperglycaemia-activated pathways, is a key factor in the pathogenesis of endothelial dysfunction and vascular disease. Reactive oxidant molecules, which are produced at a high rate in the diabetic milieu, can cause oxidative damage of many cellular components and activate several pathways linked with inflammation and apoptosis. Among the mechanisms involved in oxidative stress generation, mitochondria and uncoupling proteins are of particular interest and there is growing evidence suggesting their pivotal role in the pathogenesis of diabetic complications. Other important cellular sources of oxidants include nicotinamide adenine dinucleotide phosphate oxidases and uncoupling endothelial nitric oxide synthase. In addition, diabetes is associated with reduced antioxidant defences, which generally contrast the deleterious effect of oxidant species. This concept underlines a potential beneficial role of antioxidant therapy for the prevention and treatment of diabetic vascular disease. However, large scale trials with classical antioxidants have failed to show a significant effect on major cardiovascular events, thus underlying the need of further investigations in order to develop therapies to prevent and/or delay the development of micro- and macrovascular complications.

Effects of intensive insulin therapy alone and with added pioglitazone on renal salt/water balance and fluid compartment shifts in type 2 diabetes

OBJECTIVE

To evaluate the effects of intensive insulin therapy alone or with added pioglitazone on renal salt/water balance and body fluid compartment shifts in type 2 diabetes.

METHODS

A total of 25 insulin-treated, obese patients with type 2 diabetes were randomized to pioglitazone 45 mg (n = 12) or placebo (n = 13) and treated intensively for 12-16 weeks to achieve equivalent glycaemic control. We measured total body water (TBW) and extracellular/intracellular fluid by bioimpedance analysis; plasma/RBC volume with I(131)albumin; sodium handling by fractional excretion of sodium/lithium (FeNa/FeLi) and other renal/hormonal parameters.

RESULTS

Intensification of insulin therapy and the addition of pioglitazone significantly improved glycaemia (HbA1C 7.8-7.2% and 7.6-7.1%) and increased body weight (1.7 and 4.9 kg) respectively. TBW increased 1.7 l with insulin alone (65% intracellular) and 1.6 l with added pioglitazone (75% extracellular) (p = 0.06 and 0.09 respectively). Plasma volume increased 0.2 +/- 0.1 l with insulin alone (p = 0.05) and 0.4 +/- 0.1 l with added pioglitazone (p < 0.05). Extravascular, extracellular (interstitial) fluid increased significantly and more with added pioglitazone (0.8 +/- 0.2 l, p < 0.01) than with insulin alone (0.4 +/- 0.2 l, p = ns). At steady-state, FeLi (marker of proximal-tubular sodium delivery to the distal nephron) increased significantly with added pioglitazone (12.4 +/- 1.3 to 18.0 +/- 3.2%) vs. no significant change with insulin alone (15.4 +/- 1.2 to 14.5 +/- 2.3%). There were no significant changes in the other parameters.

CONCLUSION

In intensively insulin-treated obese type 2 diabetic patients, at equivalent glycaemic control, the addition of pioglitazone causes greater weight gain, but a similar increase in body water that is mainly extracellular and interstitial compared with intracellular increase with insulin therapy alone. Pioglitazone also increases the filtered load of sodium reabsorbed at the distal nephron with no net change in FeNa.

The role of hypoxia in 2-butoxyethanol-induced hemangiosarcoma

To understand the molecular mechanisms underlying compound-induced hemangiosarcomas in mice, and therefore, their human relevance, a systems biology approach was undertaken using transcriptomics and Causal Network Modeling from mice treated with 2-butoxyethanol (2-BE). 2-BE is a hemolytic agent that induces hemangiosarcomas in mice. We hypothesized that the hemolysis induced by 2-BE would result in local tissue hypoxia, a well-documented trigger for endothelial cell proliferation leading to hemangiosarcoma. Gene expression data from bone marrow (BM), liver, and spleen of mice exposed to a single dose (4 h) or seven daily doses of 2-BE were used to develop a mechanistic model of hemangiosarcoma. The resulting mechanistic model confirms previous work proposing that 2-BE induces macrophage activation and inflammation in the liver. In addition, the model supports local tissue hypoxia in the liver and spleen, coupled with increased erythropoeitin signaling and erythropoiesis in the spleen and BM, and suppression of mechanisms that contribute to genomic stability, events that could be contributing factors to hemangiosarcoma formation. Finally, an immunohistochemistry method (Hypoxyprobe) demonstrated that tissue hypoxia was present in the spleen and BM. Together, the results of this study identify molecular mechanisms that initiate hemangiosarcoma, a key step in understanding safety concerns that can impact drug decision processes, and identified hypoxia as a possible contributing factor for 2-BE-induced hemangiosarcoma in mice.

INT131: a selective modulator of PPAR gamma

The nuclear hormone receptor peroxisome proliferator-activated receptor gamma (PPAR gamma; NR1C3) plays a central role in adipogenesis and is the molecular target of the thiazolidinedione class of antidiabetic drugs. To overcome the well-known shortcomings of thiazolidinediones, we have identified INT131 (formerly T131 and AMG131) as a potent selective ligand for PPAR gamma that is structurally and pharmacologically distinct from glitazone agonists. In vitro biochemical and cell-based functional assays showed that INT131 mediates a distinct pattern of coregulator recruitment to PPAR gamma. In adipocytes, INT131 showed minimal stimulation of adipocyte differentiation and partially activated PPAR gamma target genes involved in adipogenesis and, at the same time, showed more agonistic activity on another set of target genes that may influence insulin sensitivity directly. These unique properties of INT131 may provide a mechanistic basis for its distinct pharmacological profile. In vivo, increases in glucose tolerance were observed in Zucker (fa/fa) rats following a 14-day oral treatment with INT131. Although the maximal efficacies of INT131 and rosiglitazone were similar with respect to improvements in glucose tolerance, INT131 had less effect on heart and lung weights, weight gain, hemodilution, and plasma volume. Thus, INT131 appears to selectively modulate PPAR gamma responses in an in vivo preclinical model, showing antidiabetic efficacy while exhibiting an improved hemodynamic and cardiovascular adverse effect profile compared to the full agonist rosiglitazone. X-ray crystallography revealed that INT131 interacts with PPAR gamma through a distinct binding mode, forming primarily hydrophobic contacts with the ligand-binding pocket without direct hydrogen-bonding interactions to key residues in helix 12 that are characteristic of full agonists. Mutagenesis studies on Tyr473 in helix 12 demonstrated this residue as essential for rosiglitazone-induced receptor activation, but nonessential for INT131 function in vitro, providing one possible molecular determinant for INT131's distinct pharmacology. INT131 is currently being evaluated in a clinical setting as a therapeutic agent for the treatment of type 2 diabetes.

Effects of chronic PPAR-agonist treatment on cardiac structure and function, blood pressure, and kidney in healthy sprague-dawley rats

PPAR-γ agonists have been associated with heart failure (HF) in diabetic patients. These incidences have been reported mostly in patient populations who were at high risk for HF or had pre-existing impaired cardiovascular function. However, whether there are similar effects of these agents in subjects with no or reduced cardiovascular pathophysiology is not clear. In this study, the effects of chronic treatment with PD168, a potent peroxisome proliferator activated receptor (PPAR) subtype-γ agonist with weak activity at PPAR-α, and rosiglitazone (RGZ), a less potent PPAR-γ agonist with no PPAR-α activity, were evaluated on the cardiovascular-renal system in healthy male Sprague-Dawley (SD) rats by serial echocardiography and radiotelemetry. Rats were treated with vehicle (VEH), PD168, @ 10 or 50 mg/kg.bw/day (PD-10 or PD-50, resp.) or RGZ @ 180 mg/kg.bw/day for 28 days (n = 10/group). Relative to VEH, RGZ, and both doses of PD168 resulted in a significant fall in blood pressure. Furthermore, RGZ and PD168 increased plasma volume (% increase from baseline) 18%, 22%, and 48% for RGZ, PD-10, and PD-50, respectively. PD168 and RGZ significantly increased urinary aldosterone excretion and heart-to-body weight ratio relative to VEH. In addition, PD168 significantly decreased (10-16%) cardiac ejection fraction (EF) and increased left ventricular area (LVA) in systole (s) and diastole (d) in PD-10 and -50 rats. RGZ significantly increased LVAd; however, it did not affect EF relative to VEH. In conclusion, chronic PPAR-γ therapy may predispose the cardiorenal system to a potential sequela of structural and/or functional changes that may be deleterious with regard to morbidity and mortality.

Reduced adipose tissue oxygenation in human obesity: evidence for rarefaction, macrophage chemotaxis, and inflammation without an angiogenic response

OBJECTIVE

Based on rodent studies, we examined the hypothesis that increased adipose tissue (AT) mass in obesity without an adequate support of vascularization might lead to hypoxia, macrophage infiltration, and inflammation.

RESEARCH DESIGN AND METHODS

Oxygen partial pressure (AT pO2) and AT temperature in abdominal AT (9 lean and 12 overweight/obese men and women) was measured by direct insertion of a polarographic Clark electrode. Body composition was measured by dual-energy X-ray absorptiometry, and insulin sensitivity was measured by hyperinsulinemic-euglycemic clamp. Abdominal subcutaneous tissue was used for staining, quantitative RT-PCR, and chemokine secretion assay.

RESULTS

AT pO2 was lower in overweight/obese subjects than lean subjects (47 +/- 10.6 vs. 55 +/- 9.1 mmHg); however, this level of pO2 did not activate the classic hypoxia targets (pyruvate dehydrogenase kinase and vascular endothelial growth factor [VEGF]). AT pO2 was negatively correlated with percent body fat (R = -0.50, P < 0.05). Compared with lean subjects, overweight/obese subjects had 44% lower capillary density and 58% lower VEGF, suggesting AT rarefaction (capillary drop out). This might be due to lower peroxisome proliferator-activated receptor gamma1 and higher collagen VI mRNA expression, which correlated with AT pO2 (P < 0.05). Of clinical importance, AT pO2 negatively correlated with CD68 mRNA and macrophage inflammatory protein 1alpha secretion (R = -0.58, R = -0.79, P < 0.05), suggesting that lower AT pO2 could drive AT inflammation in obesity.

CONCLUSIONS

Adipose tissue rarefaction might lie upstream of both low AT pO2 and inflammation in obesity. These results suggest novel approaches to treat the dysfunctional AT found in obesity.