(1134-A) Identification of halophyte plant extracts as agonists of G Protein-Coupled Receptor 35 (GPR35)

Abstract: GPR35 is a poorly characterized class A, rhodopsin-like G protein-coupled receptor, that has attracted interest as a therapeutic target for inflammatory bowel diseases, fatty liver diseases and stomach and lower-gut tumours. The identification of novel compounds with activity on GPR35 to further evaluate its pharmacology or potential as a therapeutic target is of considerable relevance. Natural products are frequently a source of novel ligands acting at various therapeutic targets.
The coastal and inland salt marshes of the Iberian Peninsula are areas of ecological and botanical interest, since they contain a wide range of plant species that develop their entire life cycle in this environment (halophytes). The metabolic adaptations of these plants include the synthesis of molecules that allow them to maintain internal osmotic balance and to protect themselves against oxidative stress. These may be of pharmacological interest. As part of a search for ligands for the G protein-coupled receptor GPR35, we have evaluated the ability of 80 extracts and 54 extract fractions from 28 species naturally growing in inland and coastal salt marshes of the Iberian Peninsula (Alicante, Ciudad Real, Huelva, Madrid, Toledo) to activate this receptor. Aerial parts, rhizomes and roots were used for the extractions. The crude materials were obtained by extraction in a soxhlet apparatus, by using solvents of increasing polarity at reflux temperature, and some of them were further fractionated by HPLC or flash chromatography to obtain purified fractions.
The crude extracts and purified fractions were dissolved in DMSO at concentrations close to 30 mg/ mL and tested in a BRET assay based on the use of a sensor containing human GPR35 and the C-terminal 27 aa of a Gα13 that permit the ability of hGPR35 to interact with Gα13 protein to be evaluated. An induced-ligand engagement of the G protein with GPR35 would result in an enhanced BRET signal.
Sixteen of the samples showed substantial increases in BRET signal (close or superior to the widely used GPR35 agonist zaprinast) with potency in the range of 2 to 2.5 µg/ mL. These samples include methanolic extracts of succulent halophytes (Suaeda braun-blanquetti, S. vera) and salt-exclusive halophytes (Limoniun carpetanicum and Tamarix canariensis). Crude extracts of Juncus maritimus and J. subulatus, as well as purified fractions of these extracts also showed activity, demonstrating robust activating effects of these extracts in the GPR35 assay.

We gratefully acknowledge grant support from Xunta de Galicia (ED431C 2022/20) and European Regional Development Fund (ERDF). This work is part of the project "Evaluation of the biological activities of extremophilic plant extracts" research project of the Call for Research Projects 2022 funded by the Francisco de Vitoria University.