A natural propenoic acid derivative activates peroxisome proliferator-activated receptor-β/δ (PPARβ/δ)

AimsPrevious studies showed that natural prenyloxyphenylpropanoid derivatives have potent biological properties in vivo. Given the structural similarities between these compounds and known peroxisome proliferator-activated receptor (PPAR) agonists, the present study examined the hypothesis that propenoic acid derivatives activate PPARs.Main methodsChimeric reporter assays were performed to identify propenoic acid derivates that could activate PPARs. Quantitative polymerase chain reaction (qPCR) analysis of wild-type and Pparβ/δ-null mouse primary keratinocytes was performed to determine if a test compound could specifically activate PPARβ/δ. A human epithelial carcinoma cell line and primary mouse keratinocytes were used to determine the effect of the compound on cell proliferation.Key findingsThree of the propenoic acid derivatives activated PPARs, with the greatest efficacy being observed with prenyloxycinnamic acid derivatives 4′-geranyloxyferulic acid (compound 1) for PPARβ/δ. Compound 1 increased expression of a known PPARβ/δ target gene through a mechanism that requires PPARβ/δ. Inhibition of cell proliferation by compound 1 was found in a human epithelial carcinoma cell line.SignificanceResults from these studies demonstrate that compound 1 can activate PPARβ/δ and inhibit cell proliferation of a human skin cancer cell line, suggesting that the biological effects of 4′-geranyloxyferulic acid may be mediated in part by activating this PPAR isoform.     

Activation of peroxisome proliferator-activated receptor-α (PPARα) suppresses postprandial lipidemia through fatty acid oxidation in enterocytes

Activation of peroxisome proliferator-activated receptor (PPAR)-α which regulates lipid metabolism in peripheral tissues such as the liver and skeletal muscle, decreases circulating lipid levels, thus improving hyperlipidemia under fasting conditions. Recently, postprandial serum lipid levels have been found to correlate more closely to cardiovascular diseases than fasting levels, although fasting hyperlipidemia is considered an important risk of cardiovascular diseases. However, the effect of PPARα activation on postprandial lipidemia has not been clarified. In this study, we examined the effects of PPARα activation in enterocytes on lipid secretion and postprandial lipidemia. In Caco-2 enterocytes, bezafibrate, a potent PPARα agonist, increased mRNA expression levels of fatty acid oxidation-related genes, such as acyl-CoA oxidase, carnitine palmitoyl transferase, and acyl-CoA synthase, and oxygen consumption rate (OCR) and suppressed secretion levels of both triglycerides and apolipoprotein B into the basolateral side. In vivo experiments revealed that feeding high-fat-diet containing bezafibrate increased mRNA expression levels of fatty acid oxidation-related genes and production of CO₂ and acid soluble metabolites in enterocytes. Moreover, bezafibrate treatment suppressed postprandial lipidemia after oral administration of olive oil to the mice. These findings indicate that PPARα activation suppresses postprandial lipidemia through enhancement of fatty acid oxidation in enterocytes, suggesting that intestinal lipid metabolism regulated by PPARα activity is a novel target of PPARα agonist for decreasing circulating levels of lipids under postprandial conditions.     

Bidirectional fluorescence properties of pyrene-based peroxisome proliferator-activated receptor (PPAR) α/δ dual agonist

Based on X-ray crystallographic analysis of a peroxisome proliferator-activated receptor (PPAR) α/δ dual agonist complexed with human PPARs ligand binding domain (LBD), we previously reported the design and synthesis of a pyrene-based fluorescent PPARα/δ co-agonist 2. Here, we found that the fluorescence intensity of 2 increased upon binding to hPPARα-LBD, in a manner dependent upon the concentration of the LBD. But, surprisingly, the fluorescence intensity of 2 decreased concentration-dependently upon binding to hPPRδ-LBD. Site-directed mutagenesis of the two hPPAR subtypes clearly indicated that Trp264 of hPPARδ-LBD, located between H2' helix and H3 helix (omega loop), is critical for the concentration-dependent decrease in fluorescence intensity, which is suggested to be due to fluorescence resonance energy transfer (FRET) from the pyrene moiety of bound 2 to the nearby side-chain indole moiety of Trp264 in the hPPARδ-LBD.     

Activation of peroxisome proliferator-activated receptor-α enhances fatty acid oxidation in human adipocytes

Peroxisome proliferator-activated receptor-α (PPARα) is a key regulator for maintaining whole-body energy balance. However, the physiological functions of PPARα in adipocytes have been unclarified. We examined the functions of PPARα using human multipotent adipose tissue-derived stem cells as a human adipocyte model. Activation of PPARα by GW7647, a potent PPARα agonist, increased the mRNA expression levels of adipocyte differentiation marker genes such as PPARγ, adipocyte-specific fatty acid-binding protein, and lipoprotein lipase and increased both GPDH activity and insulin-dependent glucose uptake level. The findings indicate that PPARα activation stimulates adipocyte differentiation. However, lipid accumulation was not changed, which is usually observed when PPARγ is activated. On the other hand, PPARα activation by GW7647 treatment induced the mRNA expression of fatty acid oxidation-related genes such as CPT-1B and AOX in a PPARα-dependent manner. Moreover, PPARα activation increased the production of CO₂ and acid soluble metabolites, which are products of fatty acid oxidation, and increased oxygen consumption rate in human adipocytes. The data indicate that activation of PPARα stimulates both adipocyte differentiation and fatty acid oxidation in human adipocytes, suggesting that PPARα agonists could improve insulin resistance without lipid accumulation in adipocytes. The expected effects of PPARα activation are very valuable for managing diabetic conditions accompanied by obesity, because PPARγ agonists, usually used as antidiabetic drugs, induce excessive lipid accumulation in adipocytes in addition to improvement of insulin resistance.     

Switching subtype-selectivity: Fragment replacement strategy affords novel class of peroxisome proliferator-activated receptor α/δ (PPARα/δ) dual agonists

Peroxisome proliferator-activated receptors (PPARs) are important drug targets for treatment of dyslipidemia, type 2 diabetes, cardiovascular disease, nonalcoholic fatty liver disease and nonalcoholic steatohepatitis, and great efforts have been made to develop novel PPAR ligands. However, most existing PPAR ligands contain a carboxylic acid (CA) or thiazolidinedione (TZD) structure (acidic head group) that is essential for activity. We recently discovered non-CA/TZD class PPARα/δ partial agonists, which contain an acetamide moiety and adjacent methyl group, linked to a 1,2,4-oxadiazole ring (“fragment a”). We hypothesized that the acetamide structure might interact with the CA/TZD-binding pocket. To test this idea, we firstly replaced fragment a in one of our compounds with the α-alkoxy-CA structure often found in PPAR agonists. Secondly, we replaced the α-alkoxy-CA head group of several reported PPAR agonists with our acetamide-based fragment a. The agonistic activities of the synthesized hybrid compounds toward PPARs (PPARα, PPARγ and PPARδ) were evaluated by means of cell-based reporter gene assays. All the hybrid molecules showed PPAR-agonistic activities, but replacement of the α-alkoxy-CA head group altered the maximum efficacy and the subtype-specificity. The acetamide-based hybrid molecules showed partial agonism toward PPARα and PPARδ, whereas the α-alkoxy-CA-based molecules were generally selective for PPARα and PPARγ, with relatively high activation efficacies. Thus, the fragment replacement strategy appears promising for the development of novel acetamide-based PPARα/δ dual agonists.     

Involvement of peroxisome proliferator-activated receptor β/δ (PPAR β/δ) in BDNF signaling during aging and in Alzheimer disease: Possible role of 4-hydroxynonenal (4-HNE)

Aging and many neurological disorders, such as AD, are linked to oxidative stress, which is considered the common effector of the cascade of degenerative events. In this phenomenon, reactive oxygen species play a fundamental role in the oxidative decomposition of polyunsaturated fatty acids, resulting in the formation of a complex mixture of aldehydic end products, such as malondialdehyde, 4-hydroxynonenal, and other alkenals. Interestingly, 4-HNE has been indicated as an intracellular agonist of peroxisome proliferator-activated receptor β/δ. In this study, we examined, at early and advanced AD stages (3, 9, and 18 months), the pattern of 4-HNE and its catabolic enzyme glutathione S-transferase P1 in relation to the expression of PPARβ/δ, BDNF signaling, as mRNA and protein, as well as on their pathological forms (i.e., precursors or truncated forms). The data obtained indicate a novel detrimental age-dependent role of PPAR β/δ in AD by increasing pro-BDNF and decreasing BDNF/TrkB survival pathways, thus pointing toward the possibility that a specific PPARβ/δ antagonist may be used to counteract the disease progression.     

Design and synthesis of benzoxazole containing indole analogs as peroxisome proliferator-activated receptor-γ/δ dual agonists

A series of benzoxazole or benzothiazole containing indole analogs, 6-alkoxyindole-2-carboxylic acids and 5-alkoxy-3-indolylacetic acids, were synthesized as novel candidates of PPARγ/δ dual agonists and their ligand activities for PPAR subtypes (α, γ, and δ) were investigated. In transient transactivation assay, several compounds activated PPARγ and δ with little activity of PPARα. Putative binding mode of the compounds 1a and 2a in the active site of PPARγ was similar with that of rosiglitazone and the molecular modeling provides molecular insight to the observed activity.     

Design and synthesis of alkoxyindolyl-3-acetic acid analogs as peroxisome proliferator-activated receptor-γ/δ agonists

A series of carbazole or phenoxazine containing alkoxyindole-3-acetic acid analogs were prepared as PPARγ/δ agonists and their transactivation activities for PPAR receptor subtypes (α, γ and δ) were investigated. Structure–activity relationship studies disclosed the effect of the lipophilic tail, attaching position of the alkoxy group and N-benzyl substitution at indole. Compound 1b was the most potent for PPARδ and 3b for PPARγ. Molecular modeling suggested two different binding modes of our alkoxyindole-3-acetic acid analogs providing the insight into their PPAR activity.     

Increased peroxisomal fatty acid β-oxidation and enhanced expression of peroxisome proliferator-activated receptor-α in diabetic rat liver

To determine whether the increased fatty acid -oxidation in the peroxisomes of diabetic rat liver is mediated by a common peroxisome proliferation mechanism, we measured the activation of long-chain (LC) and very long chain (VLC) fatty acids catalyzed by palmitoyl CoA ligase (PAL) and lignoceryl CoA ligase and oxidation of LC (palmitic acid) and VLC (lignoceric acid) fatty acids by isotopic methods. Immunoblot analysis of acyl-CoA oxidase (ACO), and Northern blot analysis of peroxisome proliferator-activated receptor (PPAR-), ACO, and PAL were also performed. The PAL activity increased in peroxisomes and mitochondria from the liver of diabetic rats by 2.6-fold and 2.1-fold, respectively. The lignoceroyl-CoA ligase activity increased by 2.6-fold in diabetic peroxisomes. Palmitic acid oxidation increased in the diabetic peroxisomes and mitochondria by 2.5-fold and 2.7-fold, respectively, while lignoceric acid oxidation increased by 2.0-fold in the peroxisomes. Immunoreactive ACO protein increased by 2-fold in the diabetic group. The mRNA levels for PPAR-, ACO and PAL increased 2.9-, 2.8- and 1.6-fold, respectively, in the diabetic group. These results suggest that the increased supply of fatty acids to liver in diabetic state stimulates the expression of PPAR- and its target genes responsible for the metabolism of fatty acids.     

Peroxisome proliferator-activated receptor β/δ agonism protects the kidney against ischemia/reperfusion injury in diabetic rats

Diabetes is an important risk factor for ischemic acute kidney injury, whose pharmacological treatment remains an unmet medical need. The peroxisome proliferator-activated receptor (PPAR) β/δ is highly expressed in the kidney, although its role has not yet been elucidated. Here, we used an in vivo model of renal ischemia/reperfusion (I/R) in streptozotocin-induced diabetic rats (i) to evaluate whether diabetes increases kidney susceptibility to I/R injury and (ii) to investigate the effects of PPARβ/δ activation. The degree of renal injury (1h ischemia/6h reperfusion) was significantly increased in diabetic rats compared with nondiabetic littermates. PPARβ/δ expression was increased after I/R, with the highest levels in diabetic rats. Administration of the selective PPARβ/δ agonist GW0742 attenuated the renal dysfunction, leukocyte infiltration, and formation of interleukin-6 and tumor necrosis factor-α. These effects were accompanied by an increased expression of the suppressor of cytokine signaling (SOCS)-3, which plays a critical role in the cytokine-activated signaling pathway. The beneficial effects of GW0742 were attenuated by the selective PPARβ/δ antagonist GSK0660. Thus, we report herein that PPARβ/δ activation protects the diabetic kidney against I/R injury by a mechanism that may involve changes in renal expression of SOCS-3 resulting in a reduced local inflammatory response.     

Case-control study on association of peroxisome proliferator-activated receptor-δ and SNP-SNP interactions with essential hypertension in Chinese Han population

The aim of this study was to investigate the association of peroxisome proliferator-activated receptor-δ (PPAR-δ) and additional SNP-SNP interaction with essential hypertension (EH) in Chinese Han population. A total of 1248 subjects (625 males, 623 females), including 620 EH patients and 628 normotension subjects, were included in the study. The mean age was 51.2?±?15.1 years old. Logistic regression model was used to examine the association between four SNP and EH; odds ratio (OR) and 95 % confident interval (95 %CI) were calculated. Generalized multifactor dimensionality reduction (GMDR) was employed to analyze SNP-SNP interaction. EH risk was significantly lower in carriers of C allele of the rs2016520 polymorphism than those with TT (TC?+?CC versus TT, adjusted OR (95 %CI)?=?0.61 (0.49–0.78)). In addition, we also found a significant association between rs9794 and EH; EH risk was also significantly lower in carriers of G allele of the rs9794 polymorphism than those with CC (CG?+?GG versus CC, adjusted OR (95 %CI)?=?0.65 (0.53–0.83)). We also found a potential SNP-SNP interaction between rs2016520 and rs9794; subjects with TC or CC of rs2016520 and CG or GG of rs9794 genotype have the lowest EH risk, compared to subjects with TT of rs2016520 and CC of rs9794 genotype; OR (95 %CI) was 0.32 (0.23–0.62) after covariate adjustment. Our results support an important association between rs2016520 and rs9794 minor allele of PPAR-δ and decreased risk of EH and additional interaction between rs2016520 and rs9794.     

Activation of peroxisome proliferator-activated receptor-γ by rosiglitazone improves lipid homeostasis at the adipose tissue-liver axis in ethanol-fed mice

The development of alcohol-induced fatty liver is associated with a reduction of white adipose tissue (WAT). Peroxisome proliferator-activated receptor (PPAR)-γ prominently distributes in the WAT and plays a crucial role in maintaining adiposity. The present study investigated the effects of PPAR-γ activation by rosiglitazone on lipid homeostasis at the adipose tissue-liver axis. Adult C57BL/6 male mice were pair fed liquid diet containing ethanol or isocaloric maltose dextrin for 8 wk with or without rosiglitazone supplementation to ethanol-fed mice for the last 3 wk. Ethanol exposure downregulated adipose PPAR-γ gene and reduced the WAT mass in association with induction of inflammation, which was attenuated by rosiglitazone. Ethanol exposure stimulated lipolysis but reduced fatty acid uptake capacity in association with dysregulation of lipid metabolism genes. Rosiglitazone normalized adipose gene expression and corrected ethanol-induced lipid dyshomeostasis. Ethanol exposure induced steatosis and upregulated inflammatory genes in the liver, which were attenuated by rosiglitazone. Hepatic peroxisomal fatty acid β-oxidation was suppressed by ethanol in associated with inhibition of acyl-coenzyme A oxidase 1. Rosiglitazone elevated plasma adiponectin level and normalized peroxisomal fatty acid β-oxidation rate. However, rosiglitazone did not affect ethanol-reduced very low-density lipoprotein secretion from the liver. These results demonstrated that activation of PPAR-γ by rosiglitazone reverses ethanol-induced adipose dysfunction and lipid dyshomeostasis at the WAT-liver axis, thereby abrogating alcoholic fatty liver.