Highly sensitive analysis of polyphenols and their metabolites in human blood cells using dispersive SPE extraction and LC-MS/MS

Blood cells, particularly erythrocytes, present a significant compartment for distribution of drugs and endogenous compounds and have been suggested to be factored in pharmacokinetic and pharmacodynamic evaluations. We previously detected the binding of polyphenols to red blood cells and found indications for a facilitated uptake of the bioactive procyanidin metabolite δ-(3,4-dihydroxy-phenyl)-γ-valerolactone (M1) into human erythrocytes. The purpose of the present investigation was to develop an effective, sensitive and robust liquid chromatography tandem mass spectrometry (LC-MS/MS) method to quantify low concentrations of polyphenols in human blood cells. Various sample preparation methods including classic sample clean-up techniques and variations of the QuEChERS (quick, easy, cheap, effective, rugged and safe) approach were compared regarding compound recovery, matrix effects and overall process efficiency. The QuEChERS technique which involves a liquid-liquid extraction and clean-up by dispersive solid-phase extraction yielded best results. The method was fully validated for the six analytes: (+)-catechin, ferulic acid, M1, taxifolin, caffeic acid and δ-3-methoxy-4-hydroxy-phenyl- γ-valerolactone (M2) in human blood cells with an optimised QuEChERS sample preparation and prior enzymatic hydrolysis of analyte conjugates. The lower limits of quantification for the analytes ranged from 0.12 ng/mL for M1, M2 and taxifolin to 48.40 ng/mL for caffeic acid. The application of the method to a blood cell sample of a volunteer ingesting 100 mg/day of the standardised pine bark extract Pycnogenol®over the course of 3 weeks revealed measurable steady-state concentrations of catechin, M1, taxifolin, ferulic acid and M2. To our knowledge, this is the first report of using the QuEChERS approach for detection and quantification of plant-derived compounds in human blood cells. The method can be applied in pharmacokinetic studies to determine the distribution of polyphenols and their metabolites in human whole blood, blood cells or erythrocytes. This might contribute in gaining deeper insights into the in vivo distribution of polyphenols and their metabolites.