Human Intervention Study: Alkylresorcinol Metabolites as Potential Biomarkers for Grain Intake and the Occurrence of Alkylresorcinols in Commonly Consumed Foods in the German Retail Sector

Abstract

Grains are one of the primary nutrients and are associated with many health benefits. To reflect the intake of grain-based products, two promising potential biomarkers are alkylresorcinol (AR) metabolites 3,5-dihydroxybenzoic acid (3,5-DHBA) and 3-(3,5-dihydroxyphenyl)-propanoic acid (3,5-DHPPA). The aim of this study was to validate the occurrence of AR in food samples and investigate the suitability of their metabolites as potential biomarkers in human intervention studies. In the first step, the AR content in different grain products from the German retail sector was analyzed by GC-MS. ARs were found in higher concentrations in whole grain products and in moderate contents in refined grains and quinoa. Based on these results, human intervention studies were performed in the next step, and the AR metabolites 3,5-DHBA and 3,5-DHPPA were analyzed by LC-MS/MS in urine samples. The intake of only whole grain products leads to an increasing level of both potential biomarkers, while a refined grain diet shows decreasing levels of the AR metabolites. The excretion of 3,5-DHBA after a whole grain-rich diet differs significantly (p = 0.043) from no grain intake.

Figure 1

Structure of AR metabolites 3,5-DHBA and 3,5-DHPPA (above) and the general structure of ARs (below).

Figure 2

Overview of the design of the three human intervention studies.

Figure 3

mean of the total AR concentration (mg/kg fresh mass) (sum of C15:0, C17:0, C19:0, C21:0, C23:0, and C25:0 alkylresorcinols) in various whole grain and refined flours.

Figure 4

Mean of the total AR concentration (mg/kg dry mass) (sum of C15:0, C17:0, C19:0, C21:0, C23:0, C25:0 alkylresorcinols) in various grain products and other food samples.

Figure 5

Kinetic profiles of 3,5-DHBA (black line) and 3,5-DHPPA (red line) in urine samples of all volunteers in study 1 after a whole grain rich breakfast. The urine samples were analyzed by HPLC-MS/MS and normalized to creatinine (*: under LOD, unfilled symbol: > LOD, but < LOQ; negative values for points in time on the x-axis indicate the blank sample before the whole grain breakfast (t = 0)).

Figure 6

Concentration of 3,5-DHBA (dark color) and 3,5-DHPPA (light color) in urine samples of volunteers in group 2.1 (above) after whole grain product intake and group 2.2 (below) after refined grain product intake. The urine samples were analyzed by LC-MS/MS and normalized to creatinine (*: > LOD, but < LOQ).