Effects of a 12-week whole-grain or refined wheat intervention on plasma acylcarnitines, bile acids and signaling lipids, and association with liver fat: A post-hoc metabolomics study of a randomized controlled trial

Abstract

Background: We previously showed that whole-grain wheat (WGW) consumption had beneficial effects on liver fat accumulation, as compared to refined wheat (RW). The mechanisms underlying these effects remain unclear.

Objective: In this study, we investigated the effects of WGW vs. RW consumption on plasma metabolite levels to explore potential underlying mechanisms of the preventive effect of WGW consumption on liver fat accumulation.

Methods: Targeted metabolomics of plasma obtained from a concluded 12-week double-blind, randomized controlled trial was performed. Fifty overweight or obese men and women aged 45-70 years with mildly elevated levels of plasma cholesterol were randomized to either 98 g/d of WGW or RW products. Before and after the intervention, a total of 89 fasting plasma metabolite concentrations including acylcarnitines, trimethylamine-N-oxide (TMAO), choline, betaine, bile acids, and signaling lipids were quantified by UPLC-MS/MS. Intrahepatic triglycerides (IHTG) were quantified by 1H-MRS, and multiple liver markers, including circulating levels of β-hydroxybutyrate, alanine transaminase (ALT), aspartate transaminase (AST), γ-glutamyltransferase (γ-GT), serum amyloid A (SAA), and C-reactive protein, were assessed.

Results: The WGW intervention increased plasma concentrations of four out of 52 signaling lipids-lysophosphatidic acid C18:2, lysophosphatidylethanolamine C18:1 and C18:2, and platelet-activating factor C18:2-and decreased concentrations of the signaling lipid lysophosphatidylglycerol C20:3 as compared to RW intervention, although these results were no longer statistically significant after false discovery rate (FDR) correction. Plasma concentrations of the other metabolites that we quantified were not affected by WGW or RW intervention. Changes in the above-mentioned metabolites were not correlated to change in IHTG upon the intervention.

Conclusion: Plasma acylcarnitines, bile acids, and signaling lipids were not robustly affected by the WGW or RW interventions, which makes them less likely candidates to be directly involved in the mechanisms that underlie the protective effect of WGW consumption or detrimental effect of RW consumption on liver fat accumulation.

Clinical trial registration: [www.ClinicalTrials.gov], identifier [NCT02385149].

Keywords: acylcarnitines; bile acids; dietary intervention; glycerophospholipids; liver fat; metabolomics; wheat; whole-grain.

Conflict of interest statement

This study received funding from Topsector Agri and Food, TNO roadmap Nutrition and Health, Cereal Partners Worldwide, the Dutch Bakery Center, GoodMills Innovation GmbH, and ZonMW. The funders had the following involvement with the study: sponsorship. The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Copyright © 2022 Gijbels, Schutte, Esser, Wopereis, Gonzales and Afman.

Figures

FIGURE 1

Study design. After a 4-week run-in period with uncolored refined wheat (RW) products, participants were randomized to 12 weeks of 98 g/d whole-grain wheat (WGW) products or RW products. In week 0 (T0) and 12 (T12), the plasma metabolome was measured using targeted ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) and liver fat content was quantified using proton magnetic resonance spectroscopy (1H-MRS).

FIGURE 2

Effects of 12-week whole-grain wheat (WGW) vs. refined wheat (RW) intervention on plasma concentrations of 89 acylcarnitines, bile acids, and signaling lipids. (A) Volcano plot in which the differences in changes in individual metabolites between the WGW vs. RW group are plotted against –log 10(p-value), as tested by ANCOVA. The horizontal dotted line indicates p = 0.05. (B–F) Box plots of the change in plasma concentrations of lysophosphatidic acid C18:2 [LPA(18:2)] (B), lysophosphatidylethanolamine C18:1 [LPE(18:1)] (C), lysophosphatidylethanolamine C18:2 [LPE(18:2)] (D), lysophosphatidylglycerol C20:3 [LPG(20:3)] (E), and platelet-activating factor C18:2 [PAF(18:2)] (F) upon the WGW (blue) or RW (orange) intervention. The box plots represent the minimum, first quartile, median, third quartile, and maximum. Crude p-values are reported for the mean difference between the groups, as tested by ANCOVA.

FIGURE 3

Correlation heatmap of Pearson correlations between plasma levels of LPA(18:2), LPE(18:1), LPE(18:2), LPG(20:3), and PAF(18:2), and liver markers including liver fat (IHTG). (A) Correlations at baseline. (B) Correlations between changes in LPA(18:2), LPE(18:1), LPE(18:2), LPG(20:3), and PAF(18:2) (expressed as log2 ratios) with changes in liver markers upon the 12-week whole-grain wheat (WGW) (left) or refined wheat (RW) (right) intervention. Asterisks indicate crude p-value < 0.05, < 0.01, or < 0.001. LPA(18:2), lysophosphatidic acid C18:2; LPE(18:1), lysophosphatidylethanolamine C18:1; LPE(18:2), lysophosphatidylethanolamine C18:2; LPG(20:3), lysophosphatidylglycerol C20:3; PAF(18:2), platelet-activating factor C18:2; IHTG, intrahepatic triglycerides; β-HB, β-hydroxybutyrate; ALT, alanine transaminase; AST, aspartate transaminase; γ-GT, γ-glutamyltransferase; SAA, serum amyloid A; CRP, C-reactive protein.

FIGURE 4

Plasma betaine and choline and effects of RW vs. WGW on IHTG. Pearson correlations between plasma betaine and IHTG at baseline (A), change in plasma betaine and IHTG upon 12-week RW or WGW intervention (B), baseline plasma betaine and change in IHTG (C), plasma choline and IHTG at baseline (D), change in plasma choline and IHTG upon 12-week RW or WGW intervention (E), baseline plasma choline and change in IHTG (F). Adjustment for age, gender, and BMI attenuated the correlation between baseline choline and change in IHTG (r = 0.42, p = 0.12).