Metabolic features of Gulf War illness

Abstract

Background: More than 230,000 veterans-about 1/3 of US personnel deployed in the 1990-1991 Persian Gulf War-developed chronic, multi-symptom health problems now called "Gulf War illness" (GWI), for which mechanisms and objective diagnostic signatures continue to be sought.

Methods: Targeted, broad-spectrum serum metabolomics was used to gain insights into the biology of GWI. 40 male participants, included 20 veterans who met both Kansas and CDC diagnostic criteria for GWI and 20 nonveteran controls without similar symptoms that were 1:1 matched to GWI cases by age, sex, and ethnicity. Serum samples were collected and archived at -80° C prior to testing. 358 metabolites from 46 biochemical pathways were measured by hydrophilic interaction liquid chromatography and tandem mass spectrometry.

Results: Veterans with GWI, compared to healthy controls, had abnormalities in 8 of 46 biochemical pathways interrogated. Lipid abnormalities accounted for 78% of the metabolic impact. Fifteen ceramides and sphingomyelins, and four phosphatidylcholine lipids were increased. Five of the 8 pathways were shared with the previously reported metabolic phenotype of males with Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS). However, 4 of the 5 shared pathways were regulated in opposite directions; key pathways that were up-regulated in GWI were down-regulated in ME/CFS. The single pathway regulated in the same direction was purines, which were decreased.

Conclusions: Our data show that despite heterogeneous exposure histories, a metabolic phenotype of GWI was clearly distinguished from controls. Metabolomic differences between GWI and ME/CFS show that common clinical symptoms like fatigue can have different chemical mechanisms and different diagnostic implications. Larger studies will be needed to validate these findings.

Fig 1. Metabolite and biochemical pathway abnormalities in Gulf War illness.

A. Multivariate metabolomic discrimination of GWI from controls. (n = 20 males with GWI; 20 male controls). PLSDA: partial least squares discriminant analysis. B. Pathway bubble plot indicating the fractional metabolic impact. C. Rank order of the top 25 discriminating metabolites by multivariate variable importance in projection (VIP) scores. D. Individual vs Diagnostic Metabolite Abnormalities. Diagnostic metabolites (blue) were defined as having VIP scores of ≥ 1.5 and a Z-score of ≥ 2.0 or ≤ -2.0 in the same direction, above or below the control mean, as found by multivariate PLSDA. Individualized abnormalities (yellow) met the Z-score criterion but were not significant by VIP score and were not diagnostic for GWI.

Fig 2. Top 25 metabolites most correlated with Gulf War illness vs healthy civilian controls.

A. Ranked by parametric Pearson r correlation. B. Ranked by non-parametric Spearman rank correlation. Pink bars represent metabolites that were increased in GWI. Blue bars represent metabolites that were decreased in GWI. Pairwise correlations were based on z-scores.

Fig 3. Intermetabolome correlations of the 6 metabolites selected as a classifier for the discrimination of Gulf War illness from healthy civilian controls.

A. 12-HETE, B. Taurine, C. Ceramide(d18:1/20:0), D. Sphingomyelin SM(d18:1/26:1 OH), E. Xanthosine, F. Plasmalogen (20:4/p18:1). Black arrows indicate that the metabolite was increased in GWI. Red arrows indicate that the metabolite was decreased in GWI.

Fig 4. Metabolic similarities and differences between Gulf War illness and chronic fatigue syndrome.

Four of five pathways shared by males with GWI and CFS were regulated in opposite directions (red font). Only purines were regulated in the same direction—decreased in both GWI and CFS. *One GWI pathway (endocannabinoids) was similarly decreased in females with CFS, but not in males with CFS [31].