Betulinic acid is a PPAR\u03b3 antagonist that improves glucose uptake, promotes osteogenesis and inhibits adipogenesis

Gloria Brusotti,Giulia Cattaneo,Antonio Laghezza,Alessandro Paiardini,Bernadette Bonardo,Giorgio Pochetti,Franck Peiretti,Paolo Tortorella,Enrica Calleri,Fulvio Loiodice,Roberta Montanari,Davide Capelli

doi:10.1038/s41598-017-05666-6

Abstract

PPAR antagonists are ligands that bind their receptor with high affinity without transactivation activity. Recently, they have been demonstrated to maintain insulin-sensitizing and antidiabetic properties, and they serve as an alternative treatment for metabolic diseases. In this work, an affinity-based bioassay was found to be effective for selecting PPAR ligands from the dried extract of an African plant (Diospyros bipindensis). Among the ligands, we identified betulinic acid (BA), a compound already known for its anti-inflammatory, anti-tumour and antidiabetic properties, as a PPARγ and PPARα antagonist. Cell differentiation assays showed that BA inhibits adipogenesis and promotes osteogenesis; either down-regulates or does not affect the expression of a series of adipogenic markers; and up-regulates the expression of osteogenic markers. Moreover, BA increases basal glucose uptake in 3T3-L1 adipocytes. The crystal structure of the complex of BA with PPARγ sheds light, at the molecular level, on the mechanism by which BA antagonizes PPARγ, and indicates a unique binding mode of this antagonist type. The results of this study show that the natural compound BA could be an interesting and safe candidate for the treatment of type 2 diabetes and bone diseases.

Highlights

Peroxisome proliferator-activated receptors (PPARs) are a group of transcription factors belonging to the nuclear receptor superfamily
To demonstrate that immobilized PPARγ recognizes ligands according to their affinity, three known ligands endowed with different potency were selected[43,44,45]
In the search for alternative PPAR modulators for the treatment of metabolic syndrome and type 2 diabetes, natural products have been shown to provide a promising pool of structures for drug discovery, especially those originating from traditionally used medicinal plants

Summary

Introduction

Peroxisome proliferator-activated receptors (PPARs) are a group of transcription factors belonging to the nuclear receptor superfamily. The thiazolidinedione (TZD) anti-diabetic agents (e.g., rosiglitazone and pioglitazone) are PPARγ agonists whose insulin-sensitizing actions are largely mediated by pleiotropic effects in adipose tissue[5,6,7,8], whereas the fibrate anti-atherosclerotic, hypolipidaemic agents (e.g., fenofibrate and gemfibrozil), are PPARα agonists[5, 6, 9, 10] Despite their widespread prescription, PPAR-activating drugs have unwanted effects that cannot be underestimated[11, 12]. African medicinal plants has not been studied as fully as Indian and Chinese treatments In this context, an ethnobotanical survey was conducted by our research group among the pygmies Baka, a community living in the south of Cameroon and possessing a consolidated vernacular knowledge in the field of traditional medicine through the use of medicinal plants. An assay based on PPARγ affinity of potential ligands from a dried plant extract of Diospyros bipindensis was developed to perform preliminary screening and ranking

Methods

Results

Conclusion