Global testing of shifts in metabolic phenotype

Abstract

Introduction: Current metabolomics approaches to unravel impact of diet- or lifestyle induced phenotype variation and shifts predominantly deploy univariate or multivariate approaches, with a posteriori interpretation at pathway level. This however often provides only a fragmented view on the involved metabolic pathways.

Objectives: To demonstrate the feasibility of using Goeman's global test (GGT) for assessment of variation and shifts in metabolic phenotype at the level of a priori defined pathways.

Methods: Two intervention studies with identified phenotype variations and shifts were examined. In a weight loss (WL) intervention study obese subjects received a mixed meal challenge before and after WL. In a polyphenol (PP) intervention study obese subjects received a high fat mixed meal challenge (61E% fat) before and after a PP intervention. Plasma samples were obtained at fasting and during the postprandial response. Besides WL- and PP-induced phenotype shifts, also correlation of plasma metabolome with phenotype descriptors was assessed at pathway level. The plasma metabolome covered organic acids, amino acids, biogenic amines, acylcarnitines and oxylipins.

Results: For the population of the WL study, GGT revealed that HOMA correlated with the fasting levels of the TCA cycle, BCAA catabolism, the lactate, arginine-proline and phenylalanine-tyrosine pathways. For the population of the PP study, HOMA correlated with fasting metabolite levels of TCA cycle, fatty acid oxidation and phenylalanine-tyrosine pathways. These correlations were more pronounced for metabolic pathways in the fasting state, than during the postprandial response. The effect of the WL and PP intervention on a priori defined metabolic pathways, and correlation of pathways with insulin sensitivity as described by HOMA was in line with previous studies.

Conclusion: GGT confirmed earlier biological findings in a hypothesis led approach. A main advantage of GGT is that it provides a direct view on involvement of a priori defined pathways in phenotype shifts.

Trial registration: ClinicalTrials.gov NCT01675401 NCT02381145.

Keywords: Goeman’s global test; Metabolic pathways; Phenotype shifts.

Conflict of interest statement

Conflict of interest

JvD is employed by a company that manufactures and markets food products. None of the materials or products used in this study originates from this company. The other authors declare they have no conflict of interest.

Ethical approval

The studies were approved by the Medical Ethics Committee of Maastricht University Medical Center and registered at clinicaltrials.gov as NCT01675401 and NCT02381145.

Informed consent

All participants gave written, informed consent before entering the study.

Figures

Fig. 1

Schematic overview of Goeman’s global testing of differences in pathways between different phenotype groups (lean, obese) and due to WL and PP interventions. In the WL and PP intervention studies respectively also control (CTRL) and placebo groups were included. For all groups plasma was sampled at fasting state (T0) and during the postprandial response to a meal challenge. The postprandial response was captured in the incremental area under the curve (iAUC). The effect of the WL, CRTL, PP and placebo interventions was summarized in ΔT0 and ΔiAUC. The vertical arrows indicate application of Goeman’s test (indicated in red) to comparison of lean versus obese (based on T0 and iAUC) and on comparison of WL versus CRTL and PP versus placebo groups (based on ΔT0 and ΔiAUC)

Fig. 2

P-value distribution of effect of WL on fasting state values in obese subjects (ΔWL T0 vs. Δ CTRL T0). a Effect of WL on challenge response values in obese subjects (iAUC WL vs. iAUC CTRL). b Effect of PP intervention on fasting state values in obese subjects (Δ PP T0 vs. Δ placebo T0). c Effect of PP intervention on challenge response values in obese subjects (iAUC PP vs. iAUC placebo). d Metabolites with P < 0.05 were coloured green and otherwise red