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

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.