Dietary modification of metabolic pathways via nuclear hormone receptors

Mulberrin extends lifespan in Caenorhabditis elegans through detoxification function

Mulberrin, a naturally occurring flavone found in mulberry and Romulus Mori, exhibits diverse biological functions. Here, we showed that mulberrin extended both the lifespan and healthspan in C. elegans. Moreover, mulberrin increased the worms' resistance to toxicants and activated the expression of detoxification genes. The longevity-promoting effect of mulberrin was attenuated in nuclear hormone receptor (NHR) homologous nhr-8 and daf-12 mutants, indicating that the lifespan extending effects of mulberrin in C. elegans may depend on nuclear hormone receptors NHR-8/DAF-12. Further analyses revealed the potential associations between the longevity effects of mulberrin and the insulin/insulin-like growth factor signaling (IIS) and adenosine 5'-monophosphate-activated protein kinase (AMPK) pathways. Together, our findings suggest that mulberrin may prolong lifespan and healthspan by activating detoxification functions mediated by nuclear receptors.

Mechanism by which Eucommia ulmoides leaves Regulate Nonalcoholic fatty liver disease based on system pharmacology

ETHNOPHARMACOLOGICAL RELEVANCE

Eucommia ulmoides (E. ulmoides) leaves are included in the Chinese Pharmacopoeia, and are traditionally used to treat hypertension, obesity, diabetes, and other diseases. Numerous pharmacological studies have shown that E. ulmoides has a good effect on lowering blood lipids and can improve obesity and nonalcoholic fatty liver.

AIM

To study the mechanism of E. ulmoides leaves in regulating nonalcoholic fatty liver disease by combining prediction and validation.

METHODS

Using network pharmacology, and molecular docking to predict E. ulmoides in regulating the action mechanism and potential active ingredients of nonalcoholic fatty liver, large hole adsorption resin enrichment active sites, in vitro experiments were performed to verify its fat-lowering effect and mechanism.

RESULTS

The major components of E. ulmoides leaves exhibited good combination with lipid metabolism-regulating core proteins, particularly flavonoids. EUL 50 significantly reduced lipid accumulation, and increased PPARγ. Compared with the control group, the autophagy level increased after the administration of EUL 50. PPARγ decreased significantly after the addition of chloroquine (CQ, autophagy inhibitor).

CONCLUSION

The active ingredients in E. ulmoides leaves regulating nonalcoholic fatty liver disease are mainly flavonoids and phenolics. EUL 50 may play a role in lowering lipids by regulating PPARγ expression through inducing autophagy.

Peroxisome Proliferator-Activated Receptor-Gamma (PPAR-ɣ): Molecular Effects and Its Importance as a Novel Therapeutic Target for Cerebral Ischemic Injury

Cerebral ischemic injury is a leading cause of death and long-term disability throughout the world. Peroxisome proliferator-activated receptor gamma (PPAR-ɣ) is a ligand-activated nuclear transcription factor that is a member of the PPAR family. PPAR-ɣ has been shown in several in vitro and in vivo models to prevent post-ischemic inflammation and neuronal damage by negatively controlling the expression of genes modulated by cerebral ischemic injury, indicating a neuroprotective effect during cerebral ischemic injury. A extensive literature review of PubMed, Medline, Bentham, Scopus, and EMBASE (Elsevier) databases was carried out to understand the nature of the extensive work done on the mechanistic role of Peroxisome proliferator activated receptor gamma and its modulation in Cerebral ischemic injury. PPAR-ɣ can interact with specific DNA response elements to control gene transcription and expression when triggered by its ligand. It regulates lipid metabolism, improves insulin sensitivity, modulates antitumor mechanisms, reduces oxidative stress, and inhibits inflammation. This review article provides insights on the current state of research into the neuroprotective effects of PPAR-ɣ in cerebral ischemic injury, as well as the cellular and molecular mechanisms by which these effects are modulated, such as inhibition of inflammation, reduction of oxidative stress, suppression of pro-apoptotic production, modulation of transcription factors, and restoration of injured tissue through neurogenesis and angiogenesis.

Cafestol preconditioning attenuates apoptosis and autophagy during hepatic ischemia-reperfusion injury by inhibiting ERK/PPARγ pathway

OBJECTIVE

The study was aimed to explore the hepatocellular protective functions of cafestol during hepatic ischemia-reperfusion injury and the possible mechanisms.

METHODS

Ninety male Balb/c mice were randomly divided into seven groups, including normal control group, L-cafestol(20mg/kg) group, H-cafestol(40mg/kg) group, sham group, IR group, L-cafestol(20mg/kg) + IR group, H-cafestol(40mg/kg) + IR group. Serum liver enzymes (ALT, AST), inflammation mediators, proteins associated with apoptosis and autophagy, indicators linked with ERK/PPARγ pathway, and liver histopathology were measured using ELISA, qRT-PCR, immunohistochemical staining, and western blotting at 2, 8, and 24 hours after reperfusion.

RESULTS

Our findings confirmed that cafestol preconditioning groups could reduce the levels of ALT and AST, alleviate liver pathological damage, suppress the release of inflammation mediators, inhibit the production of pro-apoptosis protein including caspase-3, caspase-9 and Bax, decrease the expression of autophagy-linked protein including Beclin-1 and LC3, increase anti-apoptosis protein Bcl-2, and restrain the activation of ERK and PPARγ.

CONCLUSION

Cafestol preconditioning could attenuate inflammatory response, apoptosis and autophagy on hepatic ischemia reperfusion injury by suppressing ERK/PPARγ pathway.

Saponins as modulators of nuclear receptors

As plant-derived natural products, saponins have been widely applied for the dietary modification of metabolic syndrome. However, the underlying mechanisms of their preventive and therapeutic effects are still largely unclear. Nuclear receptors have been identified as potential pharmaceutical targets for treating various types of metabolic disorders. With similar structure to endogenous hormones, several saponins may serve as selective ligands for nuclear receptors. Recently, a series of saponins are proved to exert their physiological activities through binding to nuclear receptors. This review summarizes the biological and pharmacological activities of typical saponins mediated by some of the most well described nuclear receptors, including the classical steroid hormone receptors (ER, GR, MR, and AR) and the adopted orphan receptors (PPAR, LXR, FXR, and PXR).

Conserved transcriptional activity and ligand responsiveness of avian PPARs: Potential role in regulating lipid metabolism in mirgratory birds

Migratory birds undergo metabolic remodeling in tissues, including increased lipid storage in white adipose and fatty acid uptake and oxidation in skeletal muscle, to optimize energy substrate availability and utilization in preparation for long-distance flight. Different tissues undergo gene expression changes in keeping with their specialized functions and driven by tissue specific transcriptional pathways. Peroxisome proliferator-activated receptors (PPARs) are lipid-activated nuclear receptors that regulate metabolic pathways involved in lipid and glucose utilization or storage in mammals. To examine whether PPARs might mediate fatty acid activation of metabolic gene programs that would be relevant during pre-migratory fattening, we used gray catbird as the focal species. PPAR isoforms cloned from catbird share high amino acid identity with mammalian homologs (% vs human): gcPPARα (88.1%), gcPPARδ (87.3%), gcPPARγ (91.2%). We tested whether gcPPARs activated fatty acid (FA) utilization genes using Lpl and Cpt1b gene promoter-luciferase reporters in mammalian cell lines. In C2C12 mouse myocytes gcPPARα was broadly activated by the saturated and unsaturated FAs tested; while gcPPARδ showed highest activation by the mono-unsaturated FA, 18:1 oleic acid (+80%). In CV-1 monkey kidney cells gcPPARγ responded to the poly-unsaturated fatty acid, 20:5 eicosapentaenoic acid (+60%). Moreover, in agreement with their structural conservation, gcPPARs were activated by isoform selective synthetic agonists similar to the respective mammalian isoform. Adenoviral mediated over-expression of PPARα in C2C12 myocytes induced expression of genes involved in fatty acid transport, including Cd36/Fat, as well as Cpt1b, which mediates a key rate limiting step of mitochondrial β-oxidation. These gene expression changes correlated with increased lipid droplet accumulation in C2C12 myoblasts and differentiated myotubes and enhanced β-oxidation in myotubes. Collectively, the data predict that the PPARs play a conserved role in gray catbirds to regulate lipid metabolism in target tissues that undergo metabolic remodeling throughout the annual migratory cycle.

An extract from date palm fruit (Phoenix dactylifera) acts as a co-agonist ligand for the nuclear receptor FXR and differentially modulates FXR target-gene expression in vitro

Date palm fruit (Phoenix dactylifera) consumption reduces serum triglyceride levels in human subjects. The objective of this study was to prepare an extract from dates and determine whether it acts as a ligand for the farnesoid x receptor (FXR), a nuclear receptor important for maintaining triglyceride and cholesterol homeostasis. Freeze-dried extracts were isolated from California-grown dates (Deglet Noor and Medjool) from the 2014 and 2015 harvests, by means of liquid extraction and solid phase separation. Each date palm extract (DPE) was characterized via HPLC and MALDI-TOF mass spectrometry, and the procyanidin content was qualitatively determined. Extracts were tested to determine their ability to modulate nuclear receptor-mediated transactivation using transient transfection. The effect of DPE on FXR-target genes regulating bile acid absorption and transport was then assessed in vitro, in Caco-2 cells. Characterization reveals that DPE is a rich source of polyphenols including hydroxycinnamic acids, proanthocyanidins, and lipohilic polyphenols, and comprises 13% proanthocyanidins. Transactivation results show that DPE acts as a co-agonist ligand for both mouse and human FXR, wherein it activates bile acid-bound FXR greater than that seen with bile acid alone. Additionally, DPE alone activated a peroxisome proliferator activated receptor alpha (PPARα) chimera in a dose-dependent manner. Consistent with DPE as a co-agonist ligand for FXR, studies in Caco-2 cells reveal that co-incubation with bile acid, dose-dependently enhances the expression of fibroblast growth factor 19 (FGF19), compared to treatment with bile acid alone. In contrast, DPE inhibited bile acid-induced expression of ileal bile acid binding protein (IBABP). Our results demonstrate that DPE acts as a potent co-agonist ligand for FXR, and that it differentially regulates FXR-target gene expression in vitro in human intestinal cells. This study provides novel insight into a potential mechanism by which dates may exert a hypotriglyceridemic effect via FXR and modulation of bile acid homeostasis.

Molecular factors involved in the hypolipidemic- and insulin-sensitizing effects of a ginger (Zingiber officinale Roscoe) extract in rats fed a high-fat diet

Hypolipidemic and hypoglycemic properties of ginger in animal models have been reported. However, information related to the mechanisms and factors involved in the metabolic effects of ginger at a hepatic level are limited. The aim of the present study was to investigate molecular factors involved in the hypoglycemic and hypolipidemic effects of a hydroethanolic ginger extract (GE) in the liver of rats fed a high-fat diet (HFD). The study was conducted in male Wistar rats divided into the following 3 groups: (i) Rats fed a standard diet (3.5% fat), the control group; (ii) rats fed an HFD (33.5% fat); and (iii) rats fed an HFD treated with GE (250 mg·kg-1·day-1) for 5 weeks (HFD+GE). Plasma levels of glucose, insulin, lipid profile, leptin, and adiponectin were measured. Liver expression of glycerol phosphate acyltransferase (GPAT), cholesterol 7 alpha-hydroxylase, peroxisome proliferator-activated receptors (PPAR), PPARα and PPARγ, glucose transporter 2 (GLUT-2), liver X receptor, sterol regulatory element-binding protein (SREBP1c), connective tissue growth factor (CTGF), and collagen I was measured. Data were analyzed using a 1-way ANOVA, followed by a Newman-Keuls test if differences were noted. The study showed that GE improved lipid profile and attenuated the increase of plasma levels of glucose, insulin, and leptin in HFD rats. This effect was associated with a higher liver expression of PPARα, PPARγ, and GLUT-2 and an enhancement of plasma adiponectin levels. Furthermore, GE reduced liver expression of GPAT, SREBP1c, CTGF, and collagen I. The results suggest that GE might be considered as an alternative therapeutic strategy in the management of overweight and hepatic and metabolic-related alterations.

Nuclear receptor-mediated alleviation of alcoholic fatty liver by polyphenols contained in alcoholic beverages

To elucidate the effect of the polyphenols contained in alcoholic beverages on the metabolic stress induced by ethanol consumption, four groups of mice were fed for five weeks on Lieber's diet with or without ethanol, with ethanol plus ellagic acid, and with ethanol plus trans-resveratrol. Alcoholic fatty liver was observed in the group fed the ethanol diet but not in those fed the ethanol plus polyphenol diets. Liver transcriptome analysis revealed that the addition of the polyphenols suppressed the expression of the genes related to cell stress that were up-regulated by ethanol alone. Conversely, the polyphenols up-regulated the genes involved in bile acid synthesis, unsaturated fatty acid elongation, and tetrahydrofolate synthesis that were down-regulated by ethanol alone. Because parts of these genes were known to be regulated by the constitutive androstane receptor (CAR), we performed the same experiment in the CAR-deficient mice. As a result, fatty liver was observed not only in the ethanol group but also with the ethanol plus polyphenol groups. In addition, there was no segregation of the gene expression profiles among these groups. These results provide a molecular basis for the prevention of alcohol-induced stress by the polyphenols in alcoholic beverages.

Role of PPAR, LXR, and PXR in epidermal homeostasis and inflammation

Epidermal lipid synthesis and metabolism are regulated by nuclear hormone receptors (NHR) and in turn epidermal lipid metabolites can serve as ligands to NHR. NHR form a large superfamily of receptors modulating gene transcription through DNA binding. A subgroup of these receptors is ligand-activated and heterodimerizes with the retinoid X receptor including peroxisome proliferator-activated receptor (PPAR), liver X receptor (LXR) and pregnane X receptor (PXR). Several isotypes of these receptors exist, all of which are expressed in skin. In keratinocytes, ligand activation of PPARs and LXRs stimulates differentiation, induces lipid accumulation, and accelerates epidermal barrier regeneration. In the cutaneous immune system, ligand activation of all three receptors, PPAR, LXR, and PXR, has inhibitory properties, partially mediated by downregulation of the NF-kappaB pathway. PXR also has antifibrotic effects in the skin correlating with TGF-beta inhibition. In summary, ligands of PPAR, LXR and PXR exert beneficial therapeutic effects in skin disease and represent promising targets for future therapeutic approaches in dermatology. This article is part of a Special Issue entitled The Important Role of Lipids in the Epidermis and their Role in the Formation and Maintenance of the Cutaneous Barrier. Guest Editors: Kenneth R. Feingold and Peter Elias.