A Date Palm Extract Modulates Nuclear Receptor‐Mediated Transactivation In vitro
Authors: Ricketts Marie‐Louise , Alfaro‐Viquez Emilia , Reed Jess , Krueger Christian , Rainey Charlene 
Published: November 2023

Date palm (Phoenix dactylifera) is one of the oldest cultivated trees and its fruit has been a dietary staple around the world for many centuries. Several beneficial health effects are associated with date consumption. For example, consuming 100g dates/day for 4 weeks reduced serum triglyceride (TG) levels in human subjects however, the underlying mechanism remains unknown. Nuclear receptors (NRs) play a pivotal role in metabolic regulation and are activated by bioactive dietary compounds. This study aimed to test the ability of a polyphenol‐rich extract made from whole dates to modulate NR‐mediated transactivation in vitro, in order to elucidate a potential mechanism by which dates may reduce TG levels.

A freeze‐dried whole date palm extract (DPE) was isolated from California dates from the 2014 and 2015 harvests, by means of liquid extraction and solid phase separation. Each DPE was characterized via High Performance Liquid Chromatography (HPLC) and Matrix‐Assisted Laser Desorption Ionization Time‐Of‐Flight Mass Spectrometry (MALDI‐TOF MS), and analyzed using Butanol‐HCl to qualitatively detect proanthocyanidins (PAC). The extracts were subsequently tested using transient transfection in CV‐1 cells to assess their ability to modulate NR‐mediated transactivation. In a Gal4‐based transactivation assay, the ligand‐binding domain (LBD) of different NRs is fused to the Gal4 DNA binding domain, and effects on expression directed by a Gal4‐dependent reporter plasmid are tested. Data were statistically analyzed via t‐test.

HPLC analysis shows that the 2014 and 2015 extracts have a similar composition. The predominant polyphenols have spectral characteristics indicative of hydroxycinnamic acids and PAC. MALDI‐TOF MS indicates the presence of a series of compounds that are oligomeric in nature with repeatable extension units. Butanol‐HCl analysis supports the HPLC data indicating the presence of PAC.

In the Gal4‐based transactivation assay, DPE acted as a co‐agonist ligand for the farnesoid × receptor (FXR) by activating the LBD of bile acid (BA)‐bound FXR 20‐fold greater than that seen with the BA alone (p<0.001). Additionally, DPE alone activated the LBD of mouse peroxisome proliferator‐activated receptor alpha (PPARα) in a dose‐dependent manner (p<0.001); and mouse pregnane × receptor (PXR) (20mg/L DPE p<0.01; 50 and 100mg/L p<0.0001), but not human PXR. Several chimeras were not activated by DPE including mouse and human constitutive androstane receptor (CAR), liver × receptor alpha (LXRα), RAR‐related orphan receptor beta (RORβ) and small heterodimer partner (SHP). To confirm co‐activation of FXR, the effect of DPE on full‐length human FXR was tested. Results confirmed a dose‐dependent co‐agonist ligand effect by DPE on BA‐bound FXR transactivation.

We present novel evidence showing that DPE acts as a potent co‐agonist ligand for FXR, an NR important in maintaining TG and cholesterol homeostasis. Furthermore, DPE acts as an agonist ligand for PPARα, which is essential for fatty acid β‐oxidation. Dates contain a high concentration of fructose, which is known to increase TG when consumed in large amounts. However, this work suggests that date polyphenols, via NRs, may counteract any negative effects of fructose on TG synthesis, thereby contributing to the TG‐lowering ability of dates observed in vivo.

Support or Funding Information

California Date Commission