NARROWING THE GAP: PRECLINICAL TRAUMA WITH POSTINJURY SEPSIS MODEL WITH INCREASED CLINICAL RELEVANCE

POSTINJURY PNEUMONIA INDUCES A UNIQUE BLOOD MICROBIOME SIGNATURE

ABSTRACT

Background : Previous preclinical studies have demonstrated a pathobiome after traumatic injury; however, the impact of postinjury sepsis on gut epithelial permeability and bacterial translocation remains unknown. We hypothesized that polytrauma with postinjury pneumonia would result in impaired gut permeability leading to specific blood microbiome arrays. Methods : Male and proestrus female Sprague-Dawley rats were subjected to either polytrauma (PT), PT plus 2-hours daily chronic restraint stress (PT/CS), PT with postinjury day 1 inoculation with pseudomonas pneumonia (PT + PNA), PT/CS + PNA, or naive controls. Whole blood microbiome was measured serially using high-throughput 16S rRNA sequencing and QIIME2 bioinformatics analyses. Microbial diversity was assessed using Chao1/Shannon indices and principle coordinate analysis. Intestinal permeability was evaluated by plasma occludin and lipopolysaccharide-binding protein assays. Results : PT/CS + PNA had increased intestinal permeability compared to uninfected counterparts (PT/CS) with significantly elevated occludin ( P < 0.01). Bacteria was not detected in the blood of naïve controls, PT or PT/CS, but was present in both PT + PNA and PT/CS + PNA on days 2 and 7. The PT/CS + PNA blood biome showed dominance of Streptococcus compared to PT + PNA at day 2 ( P < 0.05). Females PT/CS + PNA had a significant abundance of Staphylococcus at day 2 and Streptococcus at day 7 in the blood biome compared to male counterparts ( P < 0.05). Conclusion : Multicompartmental trauma with postinjury pneumonia results in increased intestinal permeability and bacteremia with a unique blood biome, with sexual dimorphisms evident in the blood biome composition. These findings suggest that postinjury sepsis has clinical significance and could influence outcomes after severe trauma and critical illness.

Acute emergence of the intestinal pathobiome after postinjury pneumonia

BACKGROUND

Previous preclinical studies have demonstrated sex-specific alterations in the gut microbiome following traumatic injury or sepsis alone; however, the impact of host sex on dysbiosis in the setting of postinjury sepsis acutely is unknown. We hypothesized that multicompartmental injury with subsequent pneumonia would result in host sex-specific dysbiosis.

METHODS

Male and proestrus female Sprague-Dawley rats (n = 8/group) were subjected to either multicompartmental trauma (PT) (lung contusion, hemorrhagic shock, cecectomy, bifemoral pseudofracture), PT plus 2-hour daily restraint stress (PT/RS), PT with postinjury day 1 Pseudomonas aeruginosa pneumonia (PT-PNA), PT/RS with pneumonia (PT/RS-PNA), or naive controls. Fecal microbiome was measured on days 0 and 2 using high-throughput 16S rRNA sequencing and Quantitative Insights Into Microbial Ecology 2 bioinformatics analyses. Microbial α-diversity was assessed using Chao1 (number of different unique species) and Shannon (species richness and evenness) indices. β-diversity was assessed using principal coordinate analysis. Significance was defined as p < 0.05.

RESULTS

All groups had drastic declines in the Chao1 (α-diversity) index compared with naive controls ( p < 0.05). Groups PT-PNA and PT/RS-PNA resulted in different β-diversity arrays compared with uninfected counterparts (PT, PT/RS) ( p = 0.001). Postinjury sepsis cohorts showed a loss of commensal bacteria along with emergence of pathogenic bacteria, with blooms of Proteus in PT-PNA and Escherichia-Shigella group in PT/RS-PNA compared with other cohorts. At day 2, PT-PNA resulted in β-diversity, which was unique between males and females ( p = 0.004). Microbiome composition in PT-PNA males was dominated by Anaerostipes and Parasuterella , whereas females had increased Barnesiella and Oscillibacter . The PT/RS males had an abundance of Gastranaerophilales and Muribaculaceae .

CONCLUSION

Multicompartmental trauma complicated by sepsis significantly diminishes diversity and alters microbial composition toward a severely dysbiotic state early after injury, which varies between males and females. These findings highlight the role of sex in postinjury sepsis and the pathobiome, which may influence outcomes after severe trauma and sepsis.

Posttraumatic pneumonia exacerbates bone marrow erythropoietic dysfunction

INTRODUCTION

Pneumonia is a common complication after severe trauma that is associated with worse outcomes with increased mortality. Critically ill trauma patients also have persistent inflammation and bone marrow dysfunction that manifests as persistent anemia. Terminal erythropoiesis, which occurs in bone marrow structures called erythroblastic islands (EBIs), has been shown to be impacted by trauma. Using a preclinical model of polytrauma (PT) and pneumonia, we sought to determine the effect of infection on bone marrow dysfunction and terminal erythropoiesis.

METHODS

Male and female Sprague-Dawley rats aged 9 to 11 weeks were subjected to either PT (lung contusion, hemorrhagic shock, cecectomy, and bifemoral pseudofracture) or PT with postinjury day 1 Pseudomonas pneumonia (PT-PNA) and compared with a naive cohort. Erythroblastic islands were isolated from bone marrow samples and imaged via confocal microscopy. Hemoglobin, early bone marrow erythroid progenitors, erythroid cells/EBI, and % reticulocytes/EBI were measured on day 7. Significance was defined as p < 0.05.

RESULTS

Day 7 hemoglobin was significantly lower in both PT and PT-PNA groups compared with naive (10.8 ± 0.6 and 10.9 ± 0.7 vs. 12.1 ± 0.7 g/dL [ p < 0.05]). Growth of bone marrow early erythroid progenitors (colony-forming units-granulocyte, erythrocyte, monocyte, megakaryocyte; erythroid burst-forming unit; and erythroid colony-forming unit) on day 7 was significantly reduced in PT-PNA compared with both PT and naive. Despite a peripheral reticulocytosis following PT and PT-PNA, the percentage of reticulocytes/EBI was not different between naive, PT, and PT-PNA. However, the number of erythroblasts/EBI was significantly lower in PT-PNA compared with naive (2.9 ± 1.5 [ p < 0.05] vs. 8.9 ± 1.1 cells/EBI macrophage). In addition to changes in EBI composition, EBIs were also found to have significant structural changes following PT and PT-PNA.

CONCLUSION

Multicompartmental PT altered late-stage erythropoiesis, and these changes were augmented with the addition of pneumonia. To improve outcomes following trauma and pneumonia, we need to better understand how alterations in EBI structure and function impact persistent bone marrow dysfunction and anemia.

Shear Stress and Endothelial Mechanotransduction in Trauma Patients with Hemorrhagic Shock: Hidden Coagulopathy Pathways and Novel Therapeutic Strategies

Massive trauma remains a leading cause of death and a global public health burden. Post-traumatic coagulopathy may be present even before the onset of resuscitation, and correlates with severity of trauma. Several mechanisms have been proposed to explain the development of abnormal coagulation processes, but the heterogeneity in injuries and patient profiles makes it difficult to define a dominant mechanism. Regardless of the pattern of death, a significant role in the pathophysiology and pathogenesis of coagulopathy may be attributed to the exposure of endothelial cells to abnormal physical forces and mechanical stimuli in their local environment. In these conditions, the cellular responses are translated into biochemical signals that induce/aggravate oxidative stress, inflammation, and coagulopathy. Microvascular shear stress-induced alterations could be treated or prevented by the development and use of innovative pharmacologic strategies that effectively target shear-mediated endothelial dysfunction, including shear-responsive drug delivery systems and novel antioxidants, and by targeting the venous side of the circulation to exploit the beneficial antithrombogenic profile of venous endothelial cells.