A combination of (+)-catechin and (−)-epicatechin underlies the in vitro adipogenic action of Labrador tea (Rhododendron groenlandicum), an antidiabetic medicinal plant of the Eastern James Bay Cree pharmacopeia

Journal of Ethnopharmacology

Volume 178, 3 February 2016, Pages 251–257

• Hoda M. Eid^{a, c, d, 1},
• Meriem Ouchfoun^{a, c, 1},
• Ammar Saleem^{b, c},
• Jose A. Guerrero-Analco^{b, c, e},
• Brendan Walshe-Roussel^{b, c},
• Lina Musallam^{a, c},
• Michel Rapinski^{c, f},
• Alain Cuerrier^{c, f},
• Louis C. Martineau^{a, c},
• John T. Arnason^{b, c},
• Pierre S. Haddad^{a, c, ,}

• 
  

doi:10.1016/j.jep.2015.12.021

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Abstract

Ethnopharmacological relevance

Rhododendron groenlandicum (Oeder) Kron & Judd (Labrador tea) was identified as an antidiabetic plant through an ethnobotanical study carried out with the close collaboration of Cree nations of northern Quebec in Canada.

Objectives

In a previous study the plant showed glitazone-like activity in a 3T3-L1 adipogenesis bioassay. The current study sought to identify the active compounds responsible for this potential antidiabetic activity using bioassay guided fractionation based upon an in vitro assay that measures the increase of triglycerides content in 3T3-L1 adipocyte.

Materials and methods

Isolation and identification of the crude extract’s active constituents was carried out. The 80% ethanol extract was fractionated using silica gel column chromatography. Preparative HPLC was then used to isolate the constituents. The identity of the isolated compounds was confirmed by UV and mass spectrometry.

Results

Nine chemically distinct fractions were obtained and the adipogenic activity was found in fraction 5 (RGE-5). Quercetins, (+)-catechin and (−)-epicatechin were detected and isolated from this fraction. While (+)-catechin and (−)-epicatechin stimulated adipogenesis (238±26% and 187±21% relative to vehicle control respectively) at concentrations equivalent to their concentrations in the active fraction RGE-5, none afforded biological activity similar to RGE-5 or the plant’s crude extract when used alone. When cells were incubated with a mixture of the two compounds, the adipogenic activity was close to that of the crude extract (280.7±27.8 vs 311± 30%).

Conclusion

Results demonstrate that the mixture of (+)-catechin and (−)-epicatechin is responsible for the adipogenic activity of Labrador tea. This brings further evidence for the antidiabetic potential of R. groenlandicum and provides new opportunities to profile active principles in biological fluids or in traditional preparations.

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Graphical abstract

Keywords

• Aboriginal traditional medicine;
• Adipogenesis;
• Bioassay-guided fractionation;
• Labrador tea;
• 3T3-L1 adipocytes

Corresponding author at: Department of Pharmacology, Université de Montréal, P.O. Box 6128, Downtown Station, Montréal, Québec, Canada H3C 3J7.

1

These authors contributed equally to this work.

Copyright © 2015 Published by Elsevier Ireland Ltd.