Ellagic Acid and Quercetin are High‐Affinity Ligands of Human Peroxisome Proliferator‐Activated Receptor Alpha in an In‐Vitro Competitive Binding Assay
Authors: Sasaki Geoff , Luo Ting , Shay Neil F 
Published: November 2023

Introduction

Non‐Alcoholic Fatty Liver Disease (NAFLD) is a condition characterized by fat accumulation in the liver, and can be a precursor to more severe liver diseases, such as Non‐Alcoholic Steatohepatitis, cirrhosis and liver cancer. Currently, there is no accepted therapy for NAFLD, except for diet and exercise, which is difficult to administer successfully to often obese individuals diagnosed with NAFLD.

Objective

The objective was to measure the potential for a set of select phytochemicals to serve as ligands for human peroxisome proliferator‐activated receptor‐alpha (hPPARα), a member of the nuclear hormone receptor (NHR) superfamily. PPARα is a key regulator factor controlling intracellular lipid oxidation in tissues including liver and muscle.

Methods

A time‐resolved fluorescence resonance energy transfer (TR‐FRET) competitive binding assay was used, with hPPARα as the ligand binding domain (ThermoFisher). The compounds tested consisted of two positive controls: GW 9662 and fenofibric acid and the phytochemicals tested were daidzein, ellagic acid, genistein, quercetin, and raspberry ketone. Compounds were tested across a range of concentrations. Binding affinity to the human PPARα receptor was measured by detecting the fluorescent emission at 520 nm and 495 nm; competition curves and an IC50 values were determined for each of the compounds.

Results

The tested compounds demonstrated a wide range of binding affinities. Positive controls had IC50 values consistent with their accepted values: GW9662 = 332 nM and Fenofibric acid =@ 48 μM. For the phytochemicals, ellagic acid and quercetin showed the greatest affinities with IC50 values of 269 nM and 1.3 μM, respectively. The other phytochemicals did not bind to the PPARα receptor as well: genistein = 241 μM, daidzein = 4.3 M, and raspberry ketone = 19 mM.

Conculsions

The identification of ellagic acid and quercetin as compounds with relatively high affinity for PPARα was unexpected, and to our knowledge, not previously reported. Their binding affinities were in close to that of the high‐affinity compound, GW9662, and in fact, ellagic acid had greater affinity for PPARα than GW9662. Both of these phytochemicals had higher affinity to PPARα than fenofibric acid, the pharmacologically active metabolite of fenofibrate. Despite a lower affinity, this compound produces significant metabolic effects in humans, administered as a drug with the trade name Tricor. Although ellagic acid may not be absorbed to a significant degree, its downstream metabolites, the urolithins, have similar structure to ellagic acid and quercetin, and the potential for urolithins to be agonists of PPARα remains to be tested. Quercetin, on the other hand, is absorbed into the blood stream in the small intestine and thus could interact subsequently with the liver and/or other tissues such as the muscle.

To our knowledge, this work is the first to demonstrate direct ligand binding of phytochemicals to the human PPARα NHR and suggests some natural compounds may have the potential to enhance fatty acid oxidation by transactivation of the PPARα pathway.

Support or Funding Information

Oregon State University Undergraduate Research, Innovation, Scholarship and Creativity Award Program