Impact of prior exposures on biomarkers of blast during military tactical training

Abstract

Introduction: Blast injuries and subclinical effects are of significant concern among those Service Members (SMs) participating in military operations and tactical trainings. Studies of SMs repeatedly exposed during training find concussion-like symptomology with transient decrements in neurocognitive performance, and alterations in blood biomarkers. How prior mild TBI (mTBI) history interacts with low-level blast (LLB) exposure, however, remains unexplored, which we investigate in the present study, to identify interindividual biomarker changes from LLB exposures influenced by prior history of mTBI.

Methods: Gene transcript and amyloid-beta (Aβ40 and Aβ42) protein levels were assayed using timeseries blood specimens collected at pre-blast, post-blast (within ~1 h), and follow-up-blast (~16 h) after LLB exposure for 30 SMs (age 30.3 ± 7.5) via RNA-seq and Single Molecule Array (SIMOA). Statistical models with timepoint and mTBI status interaction adjusted for age were used, and p-values adjusted for multiple testing.

Results: We found enrichment of genes involved in blood brain barrier, inflammatory, and immune responses associated with blast exposure, with significant elevated expression of target genes among SMs with mTBI history. Levels of Aβ40 and Aβ42 did not differ pre-blast vs. post/follow-up-blast LLB exposure when comparing SMs by prior mTBI history. Aβ40 and Aβ42 levels were significantly decreased in response to blast at the follow-up (~16 h) LLB exposure timepoint, concomitant with elevated expression of genes involved in amyloid-beta regulation and clearance in SMs with mTBI.

Conclusion: Findings show inter-individual differences in biomarker levels following exposures to blast that may be attributed to prior mTBI history.

Keywords: amyloid beta; biomarker; blast overpressure; breacher; gene expression; mTBI.

Figure 1

Upset plots of selected GO:BP pathways enriched with genes identified from the pre-blast vs. post-blast and pre-blast vs. follow-up-blast timepoint comparisons by mTBI status interaction model. Results are depicted with different colors by 4 functional groups: (A) Pre vs. post analysis identified 32 pathways involved in immune response (orange) and 17 vascular processes (green). (B) Pre-blast vs. follow-up-blast analysis identified 12 pathways involved in immune response (orange), 5 in vascular processes (green), 4 in Aβ regulation (pink), and 4 in apoptosis (blue). Bar plots on top show the number of gene(s) unique to or shared across pathways. Dot and line plots indicate pathways with shared gene(s), shown with the bar plots above.

Figure 2

Heatmaps depicting differential gene expression among non-TBI and TBI participants for comparison of the timepoints: pre-blast vs. post-blast with enrichment of genes involved in (A) immune and (B) vascular processes, and pre-blast vs follow-up-blast with enrichment of genes involved in (C) immune, (D) vascular, (E) apoptosis, and (F) Amyloid Beta processes. Data are shown as log2 Fold change in gene expression across all comparisons.

Figure 3

Boxplots with overlaying jitter plots show the Aβ proteins’ levels across the three timepoints. (A) Aβ40 levels and (B) Aβ42 levels across the three timepoints with overlaying jitter colored by subject’s mTBI history (green: no mTBI, orange: mTBI). p-values reported came from the linear mixed effect model which assessed the changes of proteins’ level between follow-up-blast and pre-blast exposure.