BackgroundPeroxisome proliferator-activated receptor gamma (PPARγ) agonists are clinically used to counteract hyperglycemia. However, so far experienced unwanted side effects, such as weight gain, promote the search for new PPARγ activators.MethodsWe used a combination of in silico, in vitro, cell-based and in vivo models to identify and validate natural products as promising leads for partial novel PPARγ agonists.ResultsThe natural product honokiol from the traditional Chinese herbal drug Magnolia bark was in silico predicted to bind into the PPARγ ligand binding pocket as dimer. Honokiol indeed directly bound to purified PPARγ ligand-binding domain (LBD) and acted as partial agonist in a PPARγ-mediated luciferase reporter assay. Honokiol was then directly compared to the clinically used full agonist pioglitazone with regard to stimulation of glucose uptake in adipocytes as well as adipogenic differentiation in 3T3-L1 pre-adipocytes and mouse embryonic fibroblasts. While honokiol stimulated basal glucose uptake to a similar extent as pioglitazone, it did not induce adipogenesis in contrast to pioglitazone. In diabetic KKAy mice oral application of honokiol prevented hyperglycemia and suppressed weight gain.ConclusionWe identified honokiol as a partial non-adipogenic PPARγ agonist in vitro which prevented hyperglycemia and weight gain in vivo.General significanceThis observed activity profile suggests honokiol as promising new pharmaceutical lead or dietary supplement to combat metabolic disease, and provides a molecular explanation for the use of Magnolia in traditional medicine.

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Peroxisome proliferator-activated receptor gamma (PPAR␥) agonists are used for the treatment of type 2 diabetes and metabolic syndrome. However, the currently used PPAR␥ agonists display serious side effects, which has led to a great interest in the discovery of novel ligands with favorable properties. The aim of our study was to identify new PPAR␥ agonists by a PPAR␥ pharmacophore-based virtual screening of 3D natural product libraries. This in silico approach led to the identification of several neolignans predicted to bind the receptor ligand binding domain (LBD). To confirm this prediction, the neolignans dieugenol, tetrahydrodieugenol, and magnolol were isolated from the respective natural source or synthesized and subsequently tested for PPAR␥ receptor binding. The neolignans bound to the PPAR␥ LBD with EC 50 values in the nanomolar range, exhibiting a binding pattern highly similar to the clinically used agonist pioglitazone. In intact cells, dieugenol and tetrahydrodieugenol selectively activated human PPAR␥-mediated, but not human PPAR␣-or -␤/␦-mediated luciferase reporter expression, with a pattern suggesting partial PPAR␥ agonism. The coactivator recruitment study also demonstrated partial agonism of the tested neolignans. Dieugenol, tetrahydrodieugenol, and magnolol but not the structurally related eugenol induced 3T3-L1 preadipocyte differentiation, confirming effectiveness in a cell model with endogenous PPAR␥ expression. In conclusion, we identified neolignans as novel ligands for PPAR␥, which exhibited interesting activation profiles, recommending them as potential pharmaceutical leads or dietary supplements.Western lifestyle with a high intake of simple sugars, saturated fat, and physical inactivity promotes pathologic conditions such as type 2 diabetes, obesity, and metabolic syndrome, which are currently taking a devastating epidemical spread worldwide. Compounds that are activating PPAR␥ may help to fight these pathological conditions (Cho and Momose, 2008).PPARs are ligand-activated transcription factors belonging to the nuclear receptor superfamily, and their main function relates to the regulation of genes involved in glucose and lipid metabolism (Tenenbaum et al., 2003;Desvergne et al., 2006). Three isoforms of this nuclear receptor have been identified so far: PPAR␣, PPAR␤/␦, and PPAR␥. PPAR␣ is highly expressed in skeletal muscle, liver, kidney, heart, and the vascular wall, and it was shown to be mainly involved in the regulation of lipid catabolism (Fruchart, 2009). PPAR␥ is

Long-term exposure to ascorbate is known to enhance endothelial nitric oxide synthase (eNOS) activity by stabilizing the eNOS cofactor tetrahydrobiopterin (BH4). We investigated acute effects of ascorbate on eNOS function in primary (HUVEC) and immortalized human endothelial cells (EA.hy926), aiming to provide a molecular explanation for the rapid vasodilatation seen in vivo upon administration of ascorbate. Enzymatic activity of eNOS and intracellular BH4 levels were assessed by means of an arginine–citrulline conversion assay and HPLC analysis, respectively. Over a period of 4 h, ascorbate steadily increased eNOS activity, although endothelial BH4 levels remained unchanged compared to untreated control cells. Immunoblot analyses revealed that as early as 5 min after treatment ascorbate dose-dependently increased phosphorylation at eNOS-Ser1177 and concomitantly decreased phosphorylation at eNOS-Thr495, a phosphorylation pattern indicative of increased eNOS activity. By employing pharmacological inhibitors, siRNA-mediated knockdown approaches, and overexpression of the catalytic subunit of protein phosphatase 2A (PP2A), we show that this effect was at least partly owing to reduction of PP2A activity and subsequent activation of AMP-activated kinase. In this report, we unravel a novel mechanism for how ascorbate rapidly activates eNOS independent of its effects on BH4 stabilization.

The roots of Krameria lappacea are used traditionally against oropharyngeal inflammation. So far, the astringent and antimicrobial properties of its proanthocyanidin constituents are considered to account for the anti-inflammatory effect. The aim of the present study was to characterize pharmacologically a lipophilic extract of K. lappacea roots and several isolated lignan derivatives (1–11) in terms of their putative anti-inflammatory activity. The dichloromethane extract (ID50 77 μg/cm2) as well compounds 1–11 (ID50 0.31–0.60 μmol/cm2) exhibited topical antiedematous properties comparable to those of indomethacin (ID50 0.29 μmol/cm2) in a mouse ear in vivo model. Two of the most potent compounds, 2-(2-hydroxy-4-methoxyphenyl)-5-(3-hydroxypropyl)benzofuran (5) and (+)-conocarpan (7), were studied regarding their time-dependent edema development and leukocyte infiltration up to 48 h after croton oil-induced dermatitis induction, and they showed activity profiles similar to that of hydrocortisone. In vitro studies of the isolated lignan derivatives demonstrated the inhibition of NF-κB, cyclooxygenase-1 and -2, 5-lipoxygenase, and microsomal prostaglandin E2 synthase-1 as well as antioxidant properties, as mechanisms possibly contributing to the observed in vivo effects. The present findings not only support the ethnopharmacological use of K. lappacea roots but also reveal that the isolated lignan derivatives contribute strongly to the anti-inflammatory activity of this herbal drug.