Increase in weight induced by muraglitazar, a dual PPARalpha/gamma agonist, in db/db mice: adipogenesis/or oedema?

A novel fatty acid mimetic with pan-PPAR partial agonist activity inhibits diet-induced obesity and metabolic dysfunction-associated steatotic liver disease

OBJECTIVE

The prevalence of metabolic diseases is increasing globally at an alarming rate; thus, it is essential that effective, accessible, low-cost therapeutics are developed. Peroxisome proliferator-activated receptors (PPARs) are transcription factors that tightly regulate glucose homeostasis and lipid metabolism and are important drug targets for the treatment of type 2 diabetes and dyslipidemia. We previously identified LDT409, a fatty acid-like compound derived from cashew nut shell liquid, as a novel pan-active PPARα/γ/δ compound. Herein, we aimed to assess the efficacy of LDT409 in vivo and investigate the molecular mechanisms governing the actions of the fatty acid mimetic LDT409 in diet-induced obese mice.

METHODS

C57Bl/6 mice (6-11-month-old) were fed a chow or high fat diet (HFD) for 4 weeks; mice thereafter received once daily intraperitoneal injections of vehicle, 10 mg/kg Rosiglitazone, 40 mg/kg WY14643, or 40 mg/kg LDT409 for 18 days while continuing the HFD. During treatments, body weight, food intake, glucose and insulin tolerance, energy expenditure, and intestinal lipid absorption were measured. On day 18 of treatment, tissues and plasma were collected for histological, molecular, and biochemical analysis.

RESULTS

We found that treatment with LDT409 was effective at reversing HFD-induced obesity and associated metabolic abnormalities in mice. LDT409 lowered food intake and hyperlipidemia, while improving insulin tolerance. Despite being a substrate of both PPARα and PPARγ, LDT409 was crucial for promoting hepatic fatty acid oxidation and reducing hepatic steatosis in HFD-fed mice. We also highlighted a role for LDT409 in white and brown adipocytes in vitro and in vivo where it decreased fat accumulation, increased lipolysis, induced browning of WAT, and upregulated thermogenic gene Ucp1. Remarkably, LDT409 reversed HFD-induced weight gain back to chow-fed control levels. We determined that the LDT409-induced weight-loss was associated with a combination of increased energy expenditure (detectable before weight loss was apparent), decreased food intake, increased systemic fat utilization, and increased fecal lipid excretion in HFD-fed mice.

CONCLUSIONS

Collectively, LDT409 represents a fatty acid mimetic that generates a uniquely favorable metabolic response for the treatment of multiple abnormalities including obesity, dyslipidemia, metabolic dysfunction-associated steatotic liver disease, and diabetes. LDT409 is derived from a highly abundant natural product-based starting material and its development could be pursued as a therapeutic solution to the global metabolic health crisis.

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.

MD001, a Novel Peroxisome Proliferator-activated Receptor α/γ Agonist, Improves Glucose and Lipid Metabolism

Peroxisome proliferator-activated receptor (PPAR)-α/γ dual agonists have been developed to treat metabolic diseases; however, most of them exhibit side effects such as body weight gain and oedema. Therefore, we developed a novel PPARα/γ dual agonist that modulates glucose and lipid metabolism without adverse effects. We synthesised novel compounds composed of coumarine and chalcone, determined their crystal structures, and then examined their binding affinity toward PPARα/γ. We investigated the expression of PPARα and PPARγ target genes by chemicals in HepG2, differentiated 3T3-L1, and C2C12 cells. We examined the effect of chemicals on glucose and lipid metabolism in db/db mice. Only MD001 functions as a PPARα/γ dual agonist in vitro. MD001 increased the transcriptional activity of PPARα and PPARγ, resulting in enhanced expression of genes related to β-oxidation and fatty acid and glucose uptake. MD001 significantly improved blood metabolic parameters, including triglycerides, free fatty acids, and glucose, in db/db mice. In addition, MD001 ameliorated hepatic steatosis by stimulating β-oxidation in vitro and in vivo. Our results demonstrated the beneficial effects of the novel compound MD001 on glucose and lipid metabolism as a PPARα/γ dual agonist. Consequently, MD001 may show potential as a novel drug candidate for the treatment of metabolic disorders.

Amodiaquine improves insulin resistance and lipid metabolism in diabetic model mice

AIMS

Although peroxisome proliferator-activated receptors (PPARs)α/γ dual agonists can be beneficial for treatment of dyslipidemia in patients with type 2 diabetes, their use is limited owing to various side effects, including body weight gain, edema, and heart failure. We aimed to demonstrate that amodiaquine, an antimalarial agent, has potential as a PPARα/γ dual agonist with low risk of adverse effects.

METHODS

We screened a Prestwick library (Prestwick Chemical; Illkirch, France) to identify novel PPARα/γ dual agonists and selected amodiaquine (4-[(7-chloroquinolin-4-yl)amino]-2-[(diethylamino)methyl]phenol), which activated both PPAR-α & -γ, for further investigation. We performed both in vitro, including glucose uptake assay and fatty acid oxidation assay, and in vivo studies to elucidate the anti-diabetic and anti-obesity effects of amodiaquine.

RESULTS

Amodiaquine selectively activated the transcriptional activities of PPARα/γ and enhanced both fatty acid oxidation and glucose uptake without altering insulin secretion in vitro. In high-fat diet-induced obese and genetically modified obese/diabetic mice, amodiaquine not only remarkably ameliorated insulin resistance, hyperlipidemia, and fatty liver but also decreased body weight gain.

CONCLUSION

Our findings suggest that amodiaquine exerts beneficial effects on glucose and lipid metabolism by concurrent activation of PPARα/γ. Furthermore, amodiaquine acts as an alternative insulin-sensitizing agent with a positive influence on lipid metabolism and has potential to prevent and treat type 2 diabetes while reducing the risk of lipid abnormalities.

Effect of pioglitazone on metabolic features in endotoxemia model in obese diabetic db/db mice

BACKGROUND

Infectious diseases are more frequent in diabetic patients, leading to increased morbidity and mortality. Endotoxemia affects glucose metabolism and lipolytic capacity. The aims of the present study were to determine whether endotoxemia exacerbates metabolic features (adipose inflammation, adipogenesis, and insulin resistance [IR]) in an animal model of diabetes (i.e. db/db mice) after acute infection and the effects of pioglitazone.

METHODS

Female db/db mice treated with pioglitazone (3 and 30 mg/kg, p.o.) for 14 days were challenged with lipopolysaccharide (LPS; 200 μg/kg), followed by an oral glucose tolerance test (OGTT). Quantitative real-time polymerase chain reaction (PCR) was used to evaluate the expression of genes in white adipose tissue (WAT) involved in: (i) adipogenesis (lipoprotein lipase [Lpl], fatty acid binding protein-4 [Ap2] and adiponectin [Adipoq]); (ii) insulin signaling (peroxisome proliferator-activated receptor gamma [Pparg], suppressor of cytokine signaling 3 [Socs3], solute carrier family 2 [facilitated glucose transporter], member 4 [Slc2a4]); and (iii) inflammation (tumor necrosis factor [Tnf], interleukin-6 [Il6], monocyte chemoattractant protein-1 [Ccl2], cyclo-oxygenase-2 [prostaglandin-endoperoxide synthase 2; Ptgs2]).

RESULTS

Experimental endotoxemia downregulated mRNA expression of Pparg, Slc2a4, Adipoq, Lpl, and Ap2, which coincided with upregulation of Il6, Tnf, Ccl2, Ptgs2, and Socs3 expression. Pioglitazone dose-dependently decreased Tnf, Il6, Ccl2, Ptgs2, and Socs3 expression in WAT, in association with upregulation of Lpl, Ap2, Slc2a4, and Adipoq expression, indicating improvement in endotoxin-induced IR.

CONCLUSIONS

The findings suggest that LPS challenge exacerbates IR in db/db mice by altering the expression of genes in WAT involved in adipogenesis and inflammation, which is effectively controlled by pioglitazone treatment.

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.

Multitargeted bioactive ligands for PPARs discovered in the last decade

Type 2 diabetes took insulin resistance as the main clinical manifestation. PPARs have been reported to be the therapeutic targets of metabolic disorders, such as obesity, hypertension, diabetes, and cardiovascular disease. Previously, PPARγ agonist rosiglitazone was restricted in clinic due to cardiomyocytes infarction, weight gain, and other serious side-effects, which were mainly due to the single and selective PPARγ agonism. In recent years, multitarget-directed PPAR agonists with synergistic reaction as well as fewer side-effect have been the hot topic in designing promising agents. In this review, we updated and generalized the development of PPARγ partial agonists, PPARγ antagonists, PPARα/γ dual agonists, PPARδ partial agonists, PPARδ antagonists, PPARα/δ dual agonists, PPARγ/δ dual agonists, and PPARα/γ/δ pan-agonists published in recent decade. Most of these molecules were modified from known structures or came from high-throughput screening. Among these molecules, some were expected to be promising drugs against metabolic disorders, while others seemed to provide new insight for designing novel PPAR agents.

Amorphastilbol exerts beneficial effects on glucose and lipid metabolism in mice consuming a high-fat-diet

In the present study, the anti-diabetic effects of amorphastilbol (APH) from Amorpha fruticosa (AF) were evaluated in high-fat-diet (HFD) mice. HFD-induced blood glucose and insulin levels are significantly reduced in AF extract or APH treatment groups. HFD-induced weight gain was reduced by AF treatment, which is accompanied by reduction of fat mass and adipocyte size and number in white adipose tissues. Furthermore, total cholesterol and low-density lipoprotein-cholesterol levels are decreased in AF- or APH-treated mice. In addition, AF and APH are able to improve insulin sensitivity through inhibition of protein tyrosine phosphatase 1B, a negative regulator of the insulin-signaling pathway. Taken together, the data suggest that AF has beneficial effects on glucose and lipid metabolism and its pharmacological effects are driven, in part, by its active component, APH. Therefore, AF and APH can be used as potential therapeutic agents against type 2 diabetes and associated metabolic disorders, including obesity, by enhancing glucose and lipid metabolism.

The peroxisome proliferator-activated receptors in cardiovascular diseases: experimental benefits and clinical challenges

The peroxisome proliferator-activated receptors, PPARα, PPARβ/δ and PPARγ, are ligand-activated transcriptional factors belonging to the nuclear receptors superfamily and they are known to play important roles in glucose and lipid metabolism. Experimental studies in animal models of metabolic diseases have also revealed that activation of PPARs protects against the vascular complications of diabetes, hypertension, atherosclerosis, myocardial infarction and stroke, through exerting their anti-inflammatory, anti-atherogenic and antioxidant effects. In clinical trials and post-market surveillance, agonists of PPARs have been shown to effectively prevent cardiovascular events. However, adverse effects, particularly for PPARγ agonists, are also observed with the use of investigational PPAR agonists and even some approved drugs. Further exploration of underlying mechanisms is needed to develop novel ways of PPAR activation without causing serious side effects. This article reviews the cardiovascular effects of PPARs, with emphasis on the therapeutic potential of PPAR agonists in combating metabolic vascular diseases.

Renoprotective effect of pioglitazone by the prevention of glomerular hyperfiltration through the possible restoration of altered macula densa signaling in rats with type 2 diabetic nephropathy

BACKGROUND/AIMS

Pioglitazone (PGZ), one of the thiazolidinediones, has been known to show renoprotective effects. In this study, we focused on the effect of PGZ on glomerular hyperfiltration (GHF), resultant glomerular injury and altered macula densa signaling as a cause of sustained GHF through modified tubuloglomerular feedback in rats with diabetic nephropathy.

METHODS

Kidneys from 24-week-old male OLETF rats and LET rats, nondiabetic controls, were used for the experiment. PGZ was administered (10 mg/kg/day, p.o.) for 2 weeks from 22 to 24 weeks of age in some of the OLETF rats (OLETF+PGZ).

RESULTS

Parameters relating GHF, kidney weight, creatinine clearance, urine albumin/creatinine ratio and glomerular surface were all increased in OLETF rats and partially restored in OLETF+PGZ rats. Expressions of desmin and TGF-β were also increased in OLETF rats and restored in OLETF+PGZ rats. The changes in TGF-β expression were confirmed to be independent of podocyte number. Finally, the immunoreactivity of neuronal nitric oxide synthase (nNOS) and cyclooxygenase 2 (COX-2) in the macula densa was assessed for the evaluation of macula densa signaling. Altered intensities of nNOS and COX-2 in OLETF rats were restored in OLETF+PGZ rats, which agreed with the gene expression analysis (nNOS: 100.2 ± 2.9% in LET, 64.2 ± 2.7% in OLETF, 87.4 ± 12.1% in OLETF+PGZ; COX-2: 100.8 ± 7.4% in LET, 249.2 ± 19.4% in OLETF, 179.9 ± 13.5% in OLETF+PGZ; n = 5) and the semiquantitative analysis of nNOS/COX-2-positive cells.

CONCLUSION

PGZ effectively attenuated the GHF and hyperfiltration-associated glomerular injury in diabetic nephropathy. The restoration of altered macula densa signaling might be involved in the renoprotective effect of PGZ.

Combination of peroxisome proliferator-activated receptor α/γ agonists may benefit type 2 diabetes patients with coronary artery disease through inhibition of inflammatory cytokine secretion

Patients with type 2 diabetes mellitus (T2DM) have a higher risk of cardiovascular disease (CVD). Peroxisome proliferator-activated receptors (PPARs) play an important role in the regulation of energy homeostasis. Therefore, we aimed to observe the effects of combined PPARα/γ agonists on T2DM patients with coronary artery disease (CAD). Patients were randomly divided into a rosiglitazone (RSG) group (n=20), a bezafibrate (BEZ) group (n=20), a combination of RSG and BEZ group (n=20) and a control group (n=20). Plasma C-reactive protein (CRP) and monocyte chemoattractant protein-1 (MCP-1) were measured by enzyme-linked immunosorbent assay before and 12 weeks after treatment. Fasting blood glucose (FBG), fasting insulin, insulin resistance index (IRI), hemoglobin A1c (HbA1c), lipid levels and body mass index were also investigated. At the end of the treatment, FBG, insulin, IRI, HbA1c and triglyceride levels decreased and the level of high-density lipoprotein cholesterol increased in the RSG, BEZ and combination groups. A decrease in low-density lipoprotein cholesterol was only observed in the combination group. Although the total cholesterol levels in all groups decreased, no significant difference was noted. The levels of CRP and MCP-1 were reduced in patients in the RSG, BEZ and combination groups. In addition, RSG, BEZ and the combination of RSG and BEZ also inhibited MCP-1 secretion. The combination of RSG and BEZ was more efficient than RSG or BEZ alone in downregulating cytokines. In conclusion, our results suggest that a combination of RSG and BEZ may be more efficient than RSG or BEZ alone in the treatment of T2DM patients with CAD.

Anti-diabetic and hypolipidemic effects of Sargassum yezoense in db/db mice

Peroxisome proliferator-activated receptors (PPARs) have been considered to be desirable targets for metabolic syndrome, even though their specific agonists have several side effects including body weight gain, edema and tissue failure. Previously, we have reported in vitro effects of Sargassum yezoense (SY) and its ingredients, sargaquinoic acid (SQA) and sargahydroquinoic acid (SHQA), on PPARα/γ dual transcriptional activation. In this study, we describe in vivo pharmacological property of SY on metabolic disorders. SY treatment significantly improved glucose and lipid impairment in db/db mice model. More importantly, there are no significant side effects such as body weight gain and hepatomegaly in SY-treated animals, indicating little side effects of SY in liver and lipid metabolism. In addition, SY led to a decrease in the expression of G6Pase for gluconeogenesis in liver responsible for lowering blood glucose level and an increase in the expression of UCP3 in adipose tissue for the reduction of total and LDL-cholesterol level. Altogether, our data suggest that SY would be a potential therapeutic agent against type 2 diabetes and related metabolic disorders by ameliorating the glucose and lipid metabolism.

A pirinixic acid derivative (LP105) inhibits murine 5-lipoxygenase activity and attenuates vascular remodelling in a murine model of aortic aneurysm

BACKGROUND AND PURPOSE Arachidonic acid derivatives play a central role in inflammation processes. Arachidonic acid is metabolized by several enzymes, particularly cyclooxygenases (COX), 5-lipoxygenase (5-LOX) and microsomal prostaglandin E-synthase-1 (mPGES-1) to pro-inflammatory mediators. EXPERIMENTAL APPROACH We determined the effect of LP105, a pirinixic acid derivative which acts as inhibitor of 5-LOX, COX and mPGES-1, on aortic aneurysm development in mice and on 5-LOX activity in murine monocytes. KEY RESULTS In a monocyte cell line (RAW264.7), LP105 inhibited 5-LOX in whole cells (IC(50) : 1-3 µM) and in supernatants (IC(50) : ∼10 µM). Oral administration of LP105 to mice resulted in therapeutic tissue and plasma levels. Aortic aneurysms were induced in ApoE(-/-) mice by angiotensin II (AngII) and LP105 (5 mg·day(-1) per animal) was co-administered to a subgroup. Compared with animals receiving AngII alone, the LP105+AngII group showed a lower heart rate, a trend towards reduced heart to body weight ratio but similar hypertensive responses. AngII alone significantly increased aortic weight and diameter but co-treatment with LP105+AngII prevented these changes. LC/MS-MS studies revealed increased 15-hydroxytetraenoic acid (15-HETE) and 14,15-epoxyeicosatrienoic acid (14,15-EET) plasma levels in LP105-treated animals. In the murine kidney, mRNAs of EET-generating or metabolizing enzymes and of 5-LOX and 15-LOX were unaffected by LP105. LP105 also did not inhibit the EET-metabolizing soluble epoxide hydrolase. CONCLUSIONS AND IMPLICATIONS LP105 was a potent inhibitor of monocyte 5-LOX and reduced AngII-induced vascular remodelling in mice. A shift of arachidonic acid metabolism to the protective EET pathway may contribute to the beneficial effects of LP105.

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.

Synergistic improvement in insulin resistance with a combination of fenofibrate and rosiglitazone in obese type 2 diabetic mice

Peroxisome proliferator-activated receptor (PPAR) α, which is abundant in the liver, increases lipoprotein lipase activity, resulting in a decrease of triglyceride (TG) levels. PPARγ, which is abundant in adipose tissue, stimulates adipocyte differentiation and adipogenesis, and results in an increase in insulin sensitivity. Fenofibrate, a PPARα agonist, is commonly used to treat dyslipidemia, and rosiglitazone, a PPARγ agonist, is effective in improving glycemic control. To examine the synergistic effects of rosiglitazone in combination with fenofibrate, an obese type 2 diabetes mellitus (DM) mouse model was established by the combined administration of streptozotocin and nicotinamide and fed on a high-fat diet (35% of energy as fat) for 3 weeks. The mice had significantly higher plasma glucose concentrations and insulin resistance, as examined by an oral glucose tolerance test and insulin challenge test compared with normal mice. After establishing a dose-response curve for each drug, the drugs were orally administered for 3 weeks either alone or in combination. After individual administration of fenofibrate, HDL cholesterol levels significantly increased, and plasma glucose and TG levels decreased in obese type 2 DM mice. The individual administration of rosiglitazone showed increased insulin resistance (QUICKI). However, HDL cholesterol and TG levels were not significantly changed. In a combination of fenofibrate at 25 mg/kg and rosiglitazone at 1.25 mg/kg there was a decrease in plasma glucose and TG levels, and a combination of fenofibrate at 50 mg/kg and rosiglitazone at 2.5 mg/kg showed an increase in plasma HDL cholesterol levels. Moreover, parameters related to insulin resistance (HOMA-IR) and insulin sensitivity (QUICKI) were improved significantly. Thus, our results show that combination therapy with lower doses of fenofibrate and rosiglitazone ameliorates the type 2 DM condition to a greater extent than high doses of either individual monotherapy.

A newly identified CG301269 improves lipid and glucose metabolism without body weight gain through activation of peroxisome proliferator-activated receptor alpha and gamma

OBJECTIVE

Peroxisome proliferator-activated receptor (PPAR)-α/γ dual agonists have been developed to alleviate metabolic disorders. However, several PPARα/γ dual agonists are accompanied with unwanted side effects, including body weight gain, edema, and tissue failure. This study investigated the effects of a novel PPARα/γ dual agonist, CG301269, on metabolic disorders both in vitro and in vivo.

RESEARCH DESIGN AND METHODS

Function of CG301269 as a PPARα/γ dual agonist was assessed in vitro by luciferase reporter assay, mammalian one-hybrid assay, and analyses of PPAR target genes. In vitro profiles on fatty acid oxidation and inflammatory responses were acquired by fatty acid oxidation assay and quantitative (q)RT-PCR of proinflammatory genes. In vivo effect of CG301269 was examined in db/db mice. Total body weight and various tissue weights were measured, and hepatic lipid profiles were analyzed. Systemic glucose and insulin tolerance were measured, and the in vivo effect of CG301269 on metabolic genes and proinflammatory genes was examined by qRT-PCR.

RESULTS

CG301269 selectively stimulated the transcriptional activities of PPARα and PPARγ. CG301269 enhanced fatty acid oxidation in vitro and ameliorated insulin resistance and hyperlipidemia in vivo. In db/db mice, CG301269 reduced inflammatory responses and fatty liver, without body weight gain.

CONCLUSIONS

We demonstrate that CG301269 exhibits beneficial effects on glucose and lipid metabolism by simultaneous activation of both PPARα and PPARγ. Our data suggest that CG301269 would be a potential lead compound against obesity and related metabolic disorders.

Dual acting and pan-PPAR activators as potential anti-diabetic therapies

The thiazolidinedione PPAR-γ activator drugs rosiglitazone and pioglitazone suppress insulin resistance in type 2 diabetic patients. They lock lipids into adipose tissue triglyceride stores, thereby preventing lipid metabolites from causing insulin resistance in liver and skeletal muscle and β-cell failure. They also reduce the secretion of inflammatory cytokines such as TNFα and increase the plasma level of adiponectin, which increases insulin sensitivity in liver and skeletal muscle. However, they have only a modest effect on dyslipidaemia, and they increase fat mass and plasma volume. Fibrate PPAR-α activator drugs decrease plasma triglycerides and increase HDL-cholesterol levels. PPAR-δ activators increase the capacity for fat oxidation in skeletal muscle.Clinical experience with bezafibrate, which activates PPAR-δ and -α, and studies on the PPAR-α/δ activator tetradecylthioacetic acid, the PPAR-δ activator GW501516, and combinations of the PPAR-α activator fenofibrate with rosiglitazone or pioglitazone have encouraged attempts to develop single molecules that activate two or all three PPARs. Most effort has focussed on dual PPAR-α/γ activators. These reduce both hyperglycaemia and dyslipidaemia, but their development has been terminated by issues such as increased weight gain, oedema, plasma creatinine and myocardial infarction or stroke. In addition, the FDA has stated that many PPAR ligands submitted to it have caused increased numbers of tumours in carcinogenicity studies.Rather than aiming for full potent agonists, it may be best to identify subtype-selective partial agonists or compounds that selectively activate PPAR signalling pathways and use these in combination. Nutrients or modified lipids that are low-affinity agonists may also have potential.

A nonthiazolidinedione peroxisome proliferator-activated receptor α/γ dual agonist CG301360 alleviates insulin resistance and lipid dysregulation in db/db mice

Activation of peroxisome proliferator-activated receptors (PPARs) have been implicated in the treatment of metabolic disorders with different mechanisms; PPARα agonists promote fatty acid oxidation and reduce hyperlipidemia, whereas PPARγ agonists regulate lipid redistribution from visceral fat to subcutaneous fat and enhance insulin sensitivity. To achieve combined benefits from activated PPARs on lipid metabolism and insulin sensitivity, a number of PPARα/γ dual agonists have been developed. However, several adverse effects such as weight gain and organ failure of PPARα/γ dual agonists have been reported. By use of virtual ligand screening, we identified and characterized a novel PPARα/γ dual agonist, (R)-1-(4-(2-(5-methyl-2-p-tolyloxazol-4-yl)ethoxy)benzyl)piperidine-2-carboxylic acid (CG301360), exhibiting the improvement in insulin sensitivity and lipid metabolism. CG301360 selectively stimulated transcriptional activities of PPARα and PPARγ and induced expression of their target genes in a PPARα- and PPARγ-dependent manner. In cultured cells, CG301360 enhanced fatty acid oxidation and glucose uptake and it reduced pro-inflammatory gene expression. In db/db mice, CG301360 also restored insulin sensitivity and lipid homeostasis. Collectively, these data suggest that CG301360 would be a novel PPARα/γ agonist, which might be a potential lead compound to develop against insulin resistance and hyperlipidemia.

Peroxisome proliferator-activated receptors and angiogenesis

The peroxisome proliferator-activated receptors (PPARs) are a group of three nuclear receptor isoforms, PPARalpha, PPARgamma and PPARdelta, encoded by different genes, and they form a subfamily of the nuclear receptor superfamily. The clinical interest in PPARs originates with fibrates and thiazolidinediones, which, respectively, act on PPARalpha and PPARgamma and are used to ameliorate hyperlipidaemia and hyperglycaemia in subjects with type 2 diabetes mellitus (T2DM). PPARs play a central role in these patients due to their ability to regulate the expression of numerous genes involved in glycaemic control, lipid metabolism, vascular tone and inflammation. Abnormal angiogenesis is implicated in several of the long-term complications of diabetes mellitus, characterized by vasculopathy associated with aberrant growth of new blood vessels. This pathological process plays a crucial role in diabetic retinopathy, nephropathy and neuropathy, impaired wound healing and impaired coronary collateral vessel development. In recent years, there has been increasing appreciation of the fact that PPARs might be involved in the molecular mechanisms that regulate angiogenesis through the action of growth factors and cytokines that stimulate migration, proliferation and survival of endothelial cells. During the last few years direct comparative analyses have been performed, using selective PPARs agonists, to clarify the angiogenic properties of the different members of the PPAR family. Lately, the findings provide new information to order to understand the biological, clinical and therapeutic effects of PPARs, and the role of these nuclear receptors in angiogenesis, with potentially important implications for the management of subjects affected by T2DM.

PAR-1622 is a selective peroxisome proliferator-activated receptor gamma partial activator with preserved antidiabetic efficacy and broader safety profile for fluid retention

Peroxisome proliferator-activated receptor (PPAR) gamma is known to be a key regulator of insulin resistance. PAR-1622 is a novel small molecule compound synthesized in Dong-A research center. In this study, we characterized the pharmacological profiles of PAR-1622, a selective partial activator of PPARgamma. In transient transactivation assays, PAR-1622 [(S)-2-ethoxy-3(4-(5-(4-(5-(methoxymethyl)isoxazol-3-yl)phenyl)-3-methylthiophen-2-yl)methoxy)phenyl)propanoic acid] showed a partial activator against human PPARgamma with an EC(50) of 41 nM and a maximal response of 37% relative to the full agonist rosiglitazone without activating human PPARdelta. PAR-1622 was 56 folds more selective for human PPARgamma than for human PPARalpha (EC(50), 2304 nM), which means that it is a selective partial activator of PPARgamma. PAR-1622 also showed a partial activator against mouse PPARgamma with an EC(50) of 427 nM and a maximal response was 57% of that of rosiglitazone. INT-131, a selective PPARgamma partial agonist in clinical stage, also was a partial activator against human PPARgamma with an EC(50) of 83 nM and a maximal response achieved by INT-131 was 49% of that observed with full agonist rosiglitazone. In functional assays using human mesenchymal stem cells, PAR-1622 induced adipocyte differentiation, which was 3-fold more potent with a comparable maximum response compared to INT-131. Furthermore, PAR-1622 significantly improved hyperglycemia in db/db when orally administered at a dose of 1 mg/kg/day for 5 days. In hemodilution assays with Evans Blue, rosiglitazone significantly increased the plasma volume in ICR mice that were orally administered 30 mg/kg/day for 9 days; however, PAR-1622 showed no significant effects on plasma volume, similar to INT-131. These results suggest that PAR-1622 is a selective partial activator of PPARgamma and has excellent antihyperglycemic activities and a broad safety profile for fluid retention.

Selective activation of peroxisome proliferator-activated receptor (PPAR)alpha and PPAR gamma induces neoangiogenesis through a vascular endothelial growth factor-dependent mechanism

OBJECTIVE

Peroxisome proliferator-activated receptors (PPARs) are therapeutic targets for fibrates and thiazolidinediones, which are commonly used to ameliorate hyperlipidemia and hyperglycemia in type 2 diabetes. In this study, we evaluated whether activation of PPAR alpha and PPAR gamma stimulates neoangiogenesis.

RESEARCH DESIGN AND METHODS

We used selective synthetic PPAR alpha and PPAR gamma agonists and investigated their angiogenic potentials in vitro and in vivo.

RESULTS

Activation of PPAR alpha and PPAR gamma leads to endothelial tube formation in an endothelial/interstitial cell co-culture assay. This effect is associated with increased production of the angiogenic cytokine vascular endothelial growth factor (VEGF). Neovascularization also occurs in vivo, when PPAR alpha and PPAR gamma agonists are used in the murine corneal angiogenic model. No vascular growth is detectable when PPAR alpha and PPAR gamma agonists are respectively used in PPAR alpha knockout mice and mice treated with a specific PPAR gamma inhibitor, demonstrating that this angiogenic response is PPAR mediated. PPAR alpha- and PPAR gamma-induced angiogenesis is associated with local VEGF production and does not differ in extent and morphology from that induced by VEGF. In addition, PPAR alpha- and PPAR gamma-induced in vitro and in vivo angiogenesis may be significantly decreased by inhibiting VEGF activity. Finally, in corneas treated with PPAR alpha and PPAR gamma agonists, there is increased phosphorylation of endothelial nitric oxide synthase and Akt.

CONCLUSIONS

These findings demonstrate that PPAR alpha and PPAR gamma activation stimulates neoangiogenesis through a VEGF-dependent mechanism. Neoangiogenesis is a crucial pathological event in type 2 diabetes. The ability of PPAR alpha and PPAR gamma agonists to induce neoangiogenesis might have important implications for the clinical and therapeutic management of type 2 diabetes.

Isodihydrocapsiate stimulates plasma glucose uptake by activation of AMP-activated protein kinase

AMP-activated protein kinase (AMPK) is an energy-sensing enzyme that is implicated as a key factor in controlling whole body homeostasis, including fatty acid oxidation and glucose uptake. We report that a synthetic structural isomer of dihydrocapsiate, isodihydrocapsiate (8-methylnonanoic acid 3-hydroxy-4-methoxy benzyl ester) improves type 2 diabetes by activating AMPK through the LKB1 pathway. In L6 myotube cells, phosphorylation of AMPK and acetyl-CoA carboxylase (ACC) and glucose uptake were significantly increased, whereas these effects were attenuated by an AMPK inhibitor, compound C. In addition, increased phosphorylation of AMPK and ACC by isodihydrocapsiate was significantly reduced by radicicol, an LKB1 destabilizer, suggesting that increased glucose uptake in L6 cells with isodihydrocapsiate treatment is predominantly accomplished by a LKB1-mediated AMPK activation pathway. Oral administration of isodihydrocapsiate to diabetic (db/db) mice reduced blood glucose levels by 40% after a 4-week treatment period. Our results support the development of isodihydrocapsiate as a potential therapeutic agent to target AMPK in type 2 diabetes.

PPAR Agonists and Cardiovascular Disease in Diabetes

Peroxisome proliferators activated receptors (PPARs) are ligand-activated nuclear transcription factors that play important roles in lipid and glucose homeostasis. To the extent that PPAR agonists improve diabetic dyslipidaemia and insulin resistance, these agents have been considered to reduce cardiovascular risk. However, data from murine models suggests that PPAR agonists also have independent anti-atherosclerotic actions, including the suppression of vascular inflammation, oxidative stress, and activation of the renin angiotensin system. Many of these potentially anti-atherosclerotic effects are thought to be mediated by transrepression of nuclear factor-kB, STAT, and activator protein-1 dependent pathways. In recent clinical trials, PPARalpha agonists have been shown to be effective in the primary prevention of cardiovascular events, while their cardiovascular benefit in patients with established cardiovascular disease remains equivocal. However, the use of PPARgamma agonists, and more recently dual PPARalpha/gamma coagonists, has been associated with an excess in cardiovascular events, possibly reflecting unrecognised fluid retention with potent agonists of the PPARgamma receptor. Newer pan agonists, which retain their anti-atherosclerotic activity without weight gain, may provide one solution to this problem. However, the complex biologic effects of the PPARs may mean that only vascular targeted agents or pure transrepressors will realise the goal of preventing atherosclerotic vascular disease.

Combination of dipeptidylpeptidase IV inhibitor and low dose thiazolidinedione: preclinical efficacy and safety in db/db mice

Thiazolidinediones (TZDs) are currently the most efficacious class of oral antidiabetics. However, they carry the burden of weight gain and haemodilution, which may lead to cardiovascular complications. The present study was designed to ascertain whether a combination of dipeptidyl peptidase IV (DPP IV) inhibitor with low dose of a thiazolidinedione absolves TZD associated weight gain and oedema without compromising its efficacy. In this study, we examined the efficacy and safety of lower dose (1 mg/kg/day) of rosiglitazone, a thiazolidinedione, in combination with 5 mg/kg/day dose of LAF-237 (vildagliptin), a known DPP IV inhibitor, in aged db/db mice after 14 days of treatment and compared the combination with therapeutic dose (10 mg/kg) of rosiglitazone. The combination therapy showed similar efficacy as that of 10 mg/kg/day rosiglitazone in lowering random blood glucose (53.8%, p<0.001 and 54.3%, p<0.001 respectively), AUC ((0-120) min) during oral glucose tolerance test (OGTT) (38.6 %, p<0.01; 38.3%, p<0.01 respectively) and triglyceride levels (63.9% and 61% respectively; p<0.01). Plasma active glucagon like peptide-1 (GLP-1) and insulin levels were found to be elevated significantly (p<0.01 and p<0.05 respectively) in both LAF-237 and combination treated groups following oral glucose load. LAF-237 alone had no effect on random glucose and glucose excursion during OGTT in severely diabetic db/db mice. Interestingly, the combination treatment showed no significant increase in body weight as compared to the robust weight gain by therapeutic dose of rosiglitazone. Rosiglitazone at 10 mg/kg/day showed significant reduction (p<0.05) in haematocrit, RBC count, haemoglobin pointing towards haemodilution associated with increased mRNA expression of Na(+), K(+)-ATPase-alpha and epithelial sodium channel gamma (ENaCgamma) in kidney. The combination therapy escaped these adverse effects. The results suggest that combination of DPP IV inhibitor with low dose of thiazolidinedione can interact synergistically to represent a therapeutic advantage for the clinical treatment of type 2 diabetes without the adverse effects of haemodilution and weight gain associated with thiazolidinediones.