Simplified method for the measurement of plasma alkylresorcinols: Biomarkers of whole‐grain intake

Abstract

Rationale: Consumption of whole grains is negatively associated with cardiovascular disease (CVD) risk but quantification of whole‐grain intake is challenging. Alkylresorcinols (ARs) are biomarkers of whole‐grain intake. Current methods for AR quantification involve a time‐consuming multi‐step separation process that hampers applicability in large‐scale studies.Methods: We developed a streamlined method to quantify ARs in human plasma based on protein precipitation and direct injection into an ultra‐high‐performance liquid chromatograph coupled to a quadrupole time‐of‐flight mass spectrometer operating in atmospheric pressure chemical ionization negative ion mode.Results: Separation of five major ARs was achieved, with linearity in the 5 to 550 nmol/L range and a lower limit of detection (LOD) of 0.5 nmol/L and quantification (LOQ) of 5 nmol/L. The within‐run and between‐run precision and accuracy were below 15%, and recoveries above 90%. Once validated, the method was applied to measure concentrations of plasma ARs in subjects who participated in a randomized, crossover trial evaluating the effect of carbohydrate type on CVD risk factors. The unrefined carbohydrate diet with the highest fiber content resulted in the highest plasma AR concentration (93 ± 78 nmol/L), and was significantly different (p <0.01) from lower fiber diets (18 ± 26 nmol/L and 19 ± 26 nmol/L, simple and unrefined carbohydrate, respectively).Conclusions: This method offers a simplified approach to measure concentrations of plasma ARs as an objective biomarker of whole‐grain intake that can be applied to large‐scale cohort studies.