A prospective study in severely injured patients reveals an altered gut microbiome is associated with transfusion volume

Lung Protection After Severe Thermal Burns With Adenosine, Lidocaine, and Magnesium (ALM) Resuscitation and Importance of Shams in a Rat Model

The management of severe burns remains a complex challenge. Adenosine, lidocaine, and magnesium (ALM) resuscitation therapy has been shown to protect against hemorrhagic shock and traumatic injury. The aim of the present study was to investigate the early protective effects of small-volume ALM fluid resuscitation in a rat model of 30% total body surface area (TBSA) thermal injury. Male Sprague-Dawley rats (320-340 g; n = 25) were randomly assigned to: 1) Sham (surgical instrumentation and saline infusion, without burn, n = 5), 2) Saline resuscitation group (n = 10), or 3) ALM resuscitation group (n = 10). Treatments were initiated 15-min after burn trauma, including 0.7 mL/kg 3% NaCl ± ALM bolus and 0.25-0.5 mL/kg/h 0.9% NaCl ± ALM drip, with animals monitored to 8.25-hr post-burn. Hemodynamics, cardiac function, blood chemistry, hematology, endothelial injury markers and histopathology were assessed. Survival was 100% for Shams and 90% for both ALM and Saline groups. Shams underwent significant physiological, immune and hematological changes over time as a result of surgical traums. ALM significantly reduced malondialdehyde levels in the lungs compared to Saline (P = .023), and showed minimal alveolar destruction and inflammatory cell infiltration (P < .001). ALM also improved cardiac function and oxygen delivery (21%, P = .418 vs Saline), reduced gut injury (P < .001 vs Saline), and increased plasma adiponectin (P < .001 vs baseline). Circulating levels of the acute phase protein alpha 1-acid glycoprotein (AGP) increased 1.6-times (P < .001), which may have impacted ALM's therapeutic efficacy. We conclude that small-volume ALM therapy significantly reduced lung oxidative stress and preserved alveolar integrity following severe burn trauma. Further studies are required to assess higher ALM doses with longer monitoring periods.

Radiation-induced multi-organ injury

PURPOSE

Natural history studies have been informative in dissecting radiation injury, isolating its effects, and compartmentalizing injury based on the extent of exposure and the elapsed time post-irradiation. Although radiation injury models are useful for investigating the mechanism of action in isolated subsyndromes and development of medical countermeasures (MCMs), it is clear that ionizing radiation exposure leads to multi-organ injury (MOI).

METHODS

The Radiation and Nuclear Countermeasures Program within the National Institute of Allergy and Infectious Diseases partnered with the Biomedical Advanced Research and Development Authority to convene a virtual two-day meeting titled 'Radiation-Induced Multi-Organ Injury' on June 7-8, 2022. Invited subject matter experts presented their research findings in MOI, including study of mechanisms and possible MCMs to address complex radiation-induced injuries.

RESULTS

This workshop report summarizes key information from each presentation and discussion by the speakers and audience participants.

CONCLUSIONS

Understanding the mechanisms that lead to radiation-induced MOI is critical to advancing candidate MCMs that could mitigate the injury and reduce associated morbidity and mortality. The observation that some of these mechanisms associated with MOI include systemic injuries, such as inflammation and vascular damage, suggests that MCMs that address systemic pathways could be effective against multiple organ systems.

Sex-specific intestinal dysbiosis persists after multicompartmental injury

BACKGROUND

Preclinical studies of the gut microbiome after severe traumatic injury have demonstrated severe dysbiosis in males, with sex-specific microbial differences up to 2 days after injury. However, the impact of host sex on injury-driven dysbiosis over time remains unknown. We hypothesized that sex-specific differences in intestinal microbiome diversity and composition after traumatic injury with and without stress would persist after 7 days.

METHODS

Male and proestrus female Sprague-Dawley rats (n = 8/group) were subjected to either polytrauma (lung contusion, hemorrhagic shock, cecectomy, bifemoral pseudofractures), polytrauma plus chronic restraint stress, or naïve controls. The fecal microbiome was measured on days 0, 3, and 7 using 16S rRNA sequencing and Quantitative Insights into Microbial Ecology bioinformatics analyses. Microbial alpha-diversity (Chao1 and Shannon indices) and beta-diversity were assessed. Analyses were performed in GraphPad and "R," with significance defined as P < .05.

RESULTS

Polytrauma and polytrauma plus chronic restraint stress reduced alpha-diversity (Chao1, Shannon) within 3 days postinjury, which persisted up to day 7 in both sexes; polytrauma and polytrauma plus chronic restraint stress females had significantly decreased Chao1 compared to male counterparts at day 7 (P = .02). At day 7, the microbiome composition in polytrauma females had higher proportion of Mucispirillum, whereas polytrauma plus chronic restraint stress males demonstrated elevated abundance of Ruminococcus and Akkermansia.

CONCLUSION

Multicompartmental trauma induces intestinal dysbiosis that is sex-specific with persistence of decreased diversity and unique "pathobiome" signatures in females after 1 week. These findings underline sex as an important biological variable that may influence variable host-specific responses and outcomes after severe trauma and critical illness. This underscores the need to consider precision medicine strategies to ameliorate these outcomes.

Meta-Analysis of Publicly Available Clinical and Preclinical Microbiome Data From Studies of Burn Injury

Following burn injury, alterations in host commensal microbiota across body spaces may leave patients susceptible to opportunistic pathogens and serious sequelae such as sepsis. Generally, studies examining the microbiome postburn have had a limited sample size and lack of longitudinal data, which coupled with experimental and analytic variation, impacts overall interpretation. We performed a meta-analysis of publicly available sequencing data from preclinical and clinical burn studies to determine if there were consistent alterations in the microbiome across various anatomical sites and hosts. Ten human and animal 16S rRNA sequencing studies spanning respiratory, urinary, cutaneous, and gastrointestinal microbiomes were included. Taxonomic classification and alpha and beta diversity metrics were analyzed using QIIME2 v2021.8. Alpha diversity was consistently higher in control samples compared to burn-injured samples which were also different based on host and anatomical location; however, phylogenetic evaluation (ie, Faith PD) elucidated more significant differences compared to taxonomic metrics (ie, Shannon entropy). Beta diversity analysis based on weighted UniFrac showed that rodent specimens clustered less closely to humans than pig samples for both rectal and skin sources. Host species and performing institute were found to have a significant impact on community structure. In rectal samples, bacterial composition in pig and human burn samples included Bacteroidetes, Firmicutes, and Proteobacteria, while rodent samples were dominated by Firmicutes. Proteobacteria and Firmicutes increased on burned skin in each host species. Our results suggest that host species and the performing institute strongly influence microbiome structure. Burn-induced alterations in microbiome diversity and taxa exist across hosts, with phylogenetic metrics more valuable than others. Coordinated, multicenter studies, both clinical and preclinical, within the burn community are needed to more completely realize the diagnostic and therapeutic potential of the microbiome for improving outcomes postburn.

The Intestinal Microbiome after Traumatic Injury

The intestinal microbiome plays a critical role in host immune function and homeostasis. Patients suffering from-as well as models representing-multiple traumatic injuries, isolated organ system trauma, and various severities of traumatic injury have been studied as an area of interest in the dysregulation of immune function and systemic inflammation which occur after trauma. These studies also demonstrate changes in gut microbiome diversity and even microbial composition, with a transition to a pathobiome state. In addition, sex has been identified as a biological variable influencing alterations in the microbiome after trauma. Therapeutics such as fecal transplantation have been utilized to ameliorate not only these microbiome changes but may also play a role in recovery postinjury. This review summarizes the alterations in the gut microbiome that occur postinjury, either in isolated injury or multiple injuries, along with proposed mechanisms for these changes and future directions for the field.

Dysbiome and Its Role in Surgically Relevant Medical Disease

Several surgically relevant conditions are directly or indirectly influenced by the human microbiome. Different microbiomes may be found within, or along, specific organs and intra-organ variation is common. Such variations include those found along the course of the gastrointestinal tract as well as those on different regions of the skin. A variety of physiologic stressors and care interventions may derange the native microbiome. A deranged microbiome is termed a dysbiome and is characterized by decreased diversity and an increase in the proportion of potentially pathogenic organisms; the elaboration of virulence factors coupled with clinical consequences defines a pathobiome. Specific conditions such as Clostridium difficile colitis, inflammatory bowel disease, obesity, and diabetes mellitus are tightly linked to a dysbiome or pathobiome. Additionally, massive transfusion after injury appears to derange the gastrointestinal microbiome as well. This review explores what is known about these surgically relevant clinical conditions to chart how non-surgical interventions may support surgical undertakings or potentially reduce the need for operation.

Multicompartmental traumatic injury and the microbiome: Shift to a pathobiome

BACKGROUND

Previous animal models have demonstrated altered gut microbiome after mild traumatic injury; however, the impact of injury severity and critical illness is unknown. We hypothesized that a rodent model of severe multicompartmental injuries and chronic stress would demonstrate microbiome alterations toward a "pathobiome" characterized by an overabundance of pathogenic organisms, which would persist 1 week after injury.

METHODS

Male Sprague-Dawley rats (n = 8 per group) were subjected to either multiple injuries (PT) (lung contusion, hemorrhagic shock, cecectomy, and bifemoral pseudofractures), PT plus daily chronic restraint stress for 2 hours (PT/CS), or naive controls. Fecal microbiome was measured on days 0, 3, and 7 using high-throughput 16S rRNA sequencing and Quantitative Insights Into Microbial Ecology 2 bioinformatics analysis. Microbial α diversity was assessed using Chao1 and Shannon indices, and β diversity with principle coordinate analysis. Intestinal permeability was evaluated by plasma occludin; ileum and descending colon tissues were reviewed for injury. Analyses were performed in GraphPad (GraphPad Software, La Jolla, CA) and R (R Foundation for Statistical Computing, Vienna, Austria), with significance defined as p < 0.05.

RESULTS

There were significant alterations in β diversity at day 3 and between all groups. By day 3, both PT and PT/CS demonstrated significantly depleted bacterial diversity (Chao1) ( p = 0.01 and p = 0.001, respectively) versus naive, which persisted up to day 7 in PT/CS only ( p = 0.001). Anaerostipes and Rothia dominated PT and Lactobacillus bloomed in PT/CS cohorts by day 7. Plasma occludin was significantly elevated in PT/CS compared with naive ( p = 0.04), and descending colon of both PT and PT/CS showed significantly higher injury compared with naive ( p = 0.005, p = 0.006).

CONCLUSIONS

Multiple injuries with and without chronic stress induces significant alterations in microbiome diversity and composition within 3 days; these changes are more prominent and persist for 1 week postinjury with stress. This rapid and persistent transition to a "pathobiome" phenotype represents a critical phenomenon that may influence outcomes after severe trauma and critical illness.

Fecal microbiota of horses with colitis and its association with laminitis and survival during hospitalization

BACKGROUND

The association of microbiota with clinical outcomes and the taxa associated with colitis in horses remains generally unknown.

OBJECTIVES

Describe the fecal microbiota of horses with colitis and investigate the association of the fecal microbiota with the development of laminitis and survival.

ANIMALS

Thirty-six healthy and 55 colitis horses subdivided into laminitis (n = 15) and non-laminitis (n = 39, 1 horse with chronic laminitis was removed from this comparison) and survivors (n = 27) and nonsurvivors (n = 28).

METHODS

Unmatched case-control study. The Illumina MiSeq platform targeting the V4 region of the 16S ribosomal RNA gene was used to assess the microbiota.

RESULTS

The community membership (Jaccard index) and structure (Yue and Clayton index) were different (analysis of molecular variance [AMOVA]; P < .001) between healthy and colitis horses. The linear discriminant analysis effect size (LEfSe; linear discriminant analysis [LDA] >3; P < .05) and random forest analyses found Enterobacteriaceae, Lactobacillus, Streptococcus, and Enterococcus enriched in colitis horses, whereas Treponema, Faecalibacterium, Ruminococcaceae, and Lachnospiraceae were enriched in healthy horses. The community membership and structure of colitis horses with or without laminitis was (AMOVA; P > .05). Enterobacteriaceae, Streptococcus, and Lactobacillus were enriched in horses with laminitis (LDA > 3; P < .05). The community membership (AMOVA; P = .008) of surviving and nonsurviving horses was different. Nonsurviving horses had an enrichment of Enterobacteriaceae, Pseudomonas, Streptococcus, and Enterococcus (LDA >3; P < .05).

CONCLUSION AND CLINICAL IMPORTANCE

Differences in the microbiota of horses with colitis that survive or do not survive are minor and, similarly, the microbiota differences in horses with colitis that do or do not develop laminitis are minor.

CFNAs of RBCs affect the release of inflammatory factors through the expression of CaMKIV in macrophages

BACKGROUND

Blood transfusions reportedly modulate the recipient's immune system. Transfusion-related immunomodulation has been suggested as a mechanism of some adverse clinical outcomes. Extracellular nucleic acids circulate in plasma and activate relevant immune responses, but little is known about their mechanism of action in transfusion-related immunomodulation (TRIM). The aim of this study was to investigate the effects of cell-free nucleic acids (CFNAs) produced by red blood cells (RBCs) on innate immunity, especially peripheral blood mononuclear cells (PBMCs) and macrophages, and to investigate the mechanism of action.

METHODS

Differentially expressed genes (DEGs) between PBMCs exposed to RBC-produced CFNA and normal PBMCs were analyzed by gene expression data combined with bioinformatics. KEGG and GO enrichment analyses were performed for the DEGs, and in vitro experiments were performed for the effects of key genes on the release of inflammatory factors from macrophages.

RESULTS

Analysis of microarray data showed that exposure of monocytes to RBC-produced CFNAs increased the expression of genes involved in the innate immune response, including chemokines, chemokine receptors, and innate response receptors, and that calcium channel activity was highly regulated, with a key gene being CaMKIV. CaMKIV played a critical role in LPS-induced inflammatory factor release from macrophages, which was exacerbated by overexpression of the CaMKIV gene.

CONCLUSION

RBCs regulate the release of inflammatory factors during blood transfusion by releasing CFNAs and affecting expression of the CaMKIV gene in PBMCs or macrophages, which is a potential regulatory mechanism of blood transfusion-related immune regulation and related adverse reactions.

Small animal models of thermal injury

Burns are a severe form of trauma that account for 1.1 million cases necessitating medical attention and 4500 mortalities annually in the United States alone. Importantly, the initial trauma is succeeded by extensive, prolonged physiological alterations that detrimentally impact multiple organ systems. Given the complexity of post-burn pathophysiology, in vitro experiments are insufficient to model thermal injuries. Therefore, compatible animal burn models are essential for studying burn-related phenomena. In this chapter, we discuss commonly employed small animal burn models and their comparability and applicability to human studies. In particular, we compare post-burn wound healing between the species as well as relevant hypermetabolic and inflammatory characteristics, providing a better understanding of the pros and cons of utilizing a small animal surrogate for human burns. We further provide an overview of the rodent scald burn model methodology as well as a comparison between elderly, aged and young animals, providing a guide for tailoring animal model choice based on the relevant research question.

Whole blood resuscitation restores intestinal perfusion and influences gut microbiome diversity

OBJECTIVE

Gut dysbiosis, an imbalance in the gut microbiome, occurs after trauma, which may be ameliorated with transfusion. We hypothesized that gut hypoperfusion following trauma causes dysbiosis and that whole blood (WB) resuscitation mitigates these effects.

METHODS

Anesthetized rats underwent sham (S; laparotomy only, n = 6); multiple injuries (T; laparotomy, liver and skeletal muscle crush injuries, and femur fracture, n = 5); multiple injuries and 40% hemorrhage (H; n = 7); and multiple injuries, hemorrhage, and WB resuscitation (R; n = 7), which was given as 20% estimated blood volume from donor rats 1 hour posttrauma. Baseline cecal mesenteric tissue oxygen (O2) concentration was measured following laparotomy and at 1 hour and 2 hours posttrauma. Fecal samples were collected preinjury and at euthanasia (2 hours). 16S rRNA sequencing was performed on purified DNA, and diversity and phylogeny were analyzed with QIIME (Knight Lab, La Jolla, CA; Caporaso Lab, Flagstaff, AZ) using the Greengenes 16S rRNA database (operational taxonomic units; 97% similarity). α and β diversities were estimated using observed species metrics. Permutational analysis of variance was performed for overall significance.

RESULTS

In H rats, an average decline of 36% ± 3.6% was seen in the mesenteric O2 concentration at 1 hour without improvement by 2 hours postinjury, which was reversed following resuscitation at 2 hours postinjury (4.1% ± 3.1% difference from baseline). There was no change in tissue O2 concentration in the S or T rats. β Diversity differed among groups for all measured indices except Bray-Curtis, with the spatial median of the S and R rats more similar compared with S and H rats (p < 0.05). While there was no difference in α diversity found among the groups, indices were significantly correlated with mesenteric O2 concentration. Members of the family Enterobacteriaceae were significantly enriched in only 2 hours.

CONCLUSION

Mesenteric perfusion after trauma and hemorrhage is restored with WB resuscitation, which influences β diversity of the gut microbiome. Whole blood resuscitation may also mitigate the effects of hemorrhage on intestinal dysbiosis, thereby influencing outcomes.

Specific Pathogen-Free Animals for Civilian and Military Trauma: a Cautionary Note in the Translation of New Drug Therapies

Specific-pathogen free (SPF) animals were introduced into biomedical research in the early 1960s to reduce the incidence of disease into experimental design. The goal was to provide animals with selected microbiota compatible with sustained health. Sixty years later, SPF status has become a variable itself in biomedical research. Alterations in the gut microbiome-host relationship can profoundly influence basic physiology, immune/inflammatory function, susceptibility to infection and disease, and behavior. In addition, it can influence the translational success of a drug or technology from animal models to humans. We discuss this aspect of SPF status in animal models used for military or civilian trauma and shock research. Currently, there is a broad spectrum of SPF exclusion and inclusion criteria which vary from one supplier or animal husbandry facility. If translation to humans is the end-game of trauma research, we recommend replicating a gut microbiome similar to the wild-type for optimal success. We further suggest that at the end of each publication a URL access be provided on Animal Microbial/Pathogen Exclusion Status that a study was based upon. This may help address the differences in results within a single laboratory or between laboratories around the world and improve translation success.

The Effect of Burn Resuscitation Volumes on the Gut Microbiome in a Swine Model

INTRODUCTION

While recent reports underscore the significance of the gut microbiome (GM) in health and disease, its importance in burn outcomes remains unclear. Moreover, aggressive intravenous (IV) fluid resuscitation of patients may alter intestinal flora. Herein, we describe GM changes following a large burn in swine randomized to different volumes of IV Lactated Ringers' (LR).

METHODS

Anesthetized Yorkshire swine sustained 40% total body surface area full-thickness burns and were randomized to different volumes of IV LR: none (n = 5), 15 mL/kg/d (low; n = 6), or 80 mL/kg/d (high; n = 6). At baseline and days 1 and 2, fecal swabs were collected for 16s rDNA sequencing. Proximal jejunum was collected immediately after euthanasia (day 2) for western blot, histopathology, and cytokine analyses.

RESULTS

Burns produced significant shifts in β-diversity and non-significant reductions in α-diversity that did not recover regardless of treatment group. Burn-induced increases in Proteobacteria and decreases in Firmicutes were attenuated by IV fluids in a dose-dependent manner, and also correlated with α-diversity. IV fluids caused a dose-dependent increase in Bacteroides and prevented a transient increase in the opportunistic pathogen Haemophilus parainfluenzae. While high volumes of IV fluids increased intestinal Hsp70 levels (P = 0.0464), they reduced SGLT1 (P = 0.0213) and caspase3 (P = 0.0139) levels. IV fluids elicited a non-specific cytokine response; however, Bacteroidetes levels correlated with intestinal IL18 levels (P = 0.0166, R = 0.4201).

CONCLUSIONS

We present the first report on the gut microbiome in a porcine burn model, and present data to suggest that IV fluids may influence GM and gut functional proteins following a burn. Overall, burn-induced GM diversity shifts may expose diagnostic and/or therapeutic targets to improve outcomes.

Stress-related changes in the gut microbiome after trauma

BACKGROUND

The gut microbiome protects the host from infection by promoting epithelial integrity and providing basal immunologic stimulation. Disruption of this delicate ecosystem is linked to morbidity and mortality among critically ill patients, but the impact of traumatic injury on the gut microbiome is poorly understood. This study sought to identify alterations in gut microbiota following trauma and persistent stress in rodents without confounding antibiotics.

METHODS

Male Sprague-Dawley rats aged 9 weeks to 11 weeks were randomized to naive, lung contusion with hemorrhagic shock (LCHS), and LCHS plus either 7 (LCHS/CS 7/7) or 14 days (LCHS/CS 14) of restraint cylinder stress for 2 hours daily. Stool was collected on Days 0, 3, 7, and 14 for bacterial whole genome DNA isolation. Alpha diversity, or the number and relative abundance of unique bacterial species within each cohort, was assessed using Chao1 indices. Beta diversity, or the measure of differences in biodiversity across cohorts, was assessed by principle coordinate analysis. False discovery rate correction was applied to all statistical analyses and corrected for cohousing effects.

RESULTS

Rodent groups subject to restraint stress demonstrated a progressive increase in alpha diversity over time. These microbiota changes resolved after cessation of stress (LCHS/CS 7/7) but continued to increase among rats subjected to ongoing stress (LCHS/CS 14). The LCHS/CS 7/7 also demonstrated reductions in class Actinobacteria and increased abundance of the genus Bacteroides by Day 7, which resolved by Day 14. Increased abundance of Bacteroides was also noted in the LCHS/CS 14 cohort, suggesting the role of chronic stress in its destabilization.

CONCLUSION

This study points to persistent stress as a potential source of the destabilization of microbial diversity seen after trauma. This lack of microbiota stability could be associated with worse long-term outcomes in critically ill trauma patients. Further studies are warranted to elucidate mechanistic pathways and potential therapeutic modalities.

Burn resuscitation strategy influences the gut microbiota-liver axis in swine

Fluid resuscitation improves clinical outcomes of burn patients; however, its execution in resource-poor environments may have to be amended with limited-volume strategies. Liver dysfunction is common in burn patients and gut dysbiosis is an understudied aspect of burn sequelae. Here, the swine gut microbiota and liver transcripts were investigated to determine the impact of standard-of-care modified Brooke (MB), limited-volume colloid (LV-Co), and limited-volume crystalloid (LV-Cr) resuscitation on the gut microbiota, and to evaluate its' potential relationship with liver dysfunction. Independent of resuscitation strategy, bacterial diversity was reduced 24 h post-injury, and remained perturbed at 48 h. Changes in community structure were most pronounced with LV-Co, and correlated with biomarkers of hepatocellular damage. Hierarchical clustering revealed a group of samples that was suggestive of dysbiosis, and LV-Co increased the risk of association with this group. Compared with MB, LV-Co and LV-Cr significantly altered cellular stress and ATP pathways, and gene expression of these perturbed pathways was correlated with major dysbiosis-associated bacteria. Taken together, LV-Co resuscitation exacerbated the loss of bacterial diversity and increased the risk of dysbiosis. Moreover, we present evidence of a linkage between liver (dys)function and the gut microbiota in the acute setting of burn injury.

Traumatic brain injury causing intestinal dysfunction: A review

Traumatic brain injuries (TBI) and its sequelae are becoming one of the most pressing public health concerns worldwide. It is one of the leading causes of increased morbidity and mortality. The primary insult to the brain can cause ischemic brain injury, paralysis, concussions, death, and other serious complications. Brain injury also involves other systems through a secondary pathway resulting in multiple complications during and after hospitalization. The focus of our article is to assess the literature available on traumatic brain injury and intestinal dysfunctional to highlight the aspects of epidemiology, pathophysiology, and different diagnostic approaches for early diagnosis of gut dysfunction. We review studies done in both humans and animals, to better understand this underrated topic, as it costs billions of dollars to the healthcare industry because of delayed diagnosis.

The gut microbiome distinguishes mortality in trauma patients upon admission to the emergency department

BACKGROUND

Traumatic injury can lead to a compromised intestinal epithelial barrier, decreased gut perfusion, and inflammation. While recent studies indicate that the gut microbiome (GM) is altered early following traumatic injury, the impact of GM changes on clinical outcomes remains unknown. Our objective of this follow-up study was to determine if the GM is associated with clinical outcomes in critically injured patients.

METHODS

We conducted a prospective, observational study in adult patients (N = 67) sustaining severe injury admitted to a level I trauma center. Fecal specimens were collected on admission to the emergency department, and microbial DNA from all samples was analyzed using the Quantitative Insights Into Microbial Ecology pipeline and compared against the Greengenes database. α-Diversity and β-diversity were estimated using the observed species metrics and analyzed with t tests and permutational analysis of variance for overall significance, with post hoc pairwise analyses.

RESULTS

Our patient population consisted of 63% males with a mean age of 44 years. Seventy-eight percent of the patients suffered blunt trauma with 22% undergoing penetrating injuries. The mean body mass index was 26.9 kg/m. Significant differences in admission β-diversity were noted by hospital length of stay, intensive care unit hospital length of stay, number of days on the ventilator, infections, and acute respiratory distress syndrome (p < 0.05). β-Diversity on admission differed in patients who died compared with patients who lived (mean time to death, 8 days). There were also significantly less operational taxonomic units in samples from patients who died versus those who survived. A number of species were enriched in the GM of injured patients who died, which included some traditionally probiotic species such as Akkermansia muciniphilia, Oxalobacter formigenes, and Eubacterium biforme (p < 0.05).

CONCLUSION

Gut microbiome diversity on admission in severely injured patients is predictive of a variety of clinically important outcomes. While our study does not address causality, the GM of trauma patients may provide valuable diagnostic and therapeutic targets for the care of injured patients.

LEVEL OF EVIDENCE

Prognostic and epidemiological, level III.

Gut microbiota in surgical and critically ill patients

Microbiota-defined as a collection of microbial organisms colonising different parts of the human body-is now recognised as a pivotal element of human health, and explains a large part of the variance in the phenotypic expression of many diseases. A reduction in microbiota diversity, and replacement of normal microbes with non-commensal, pathogenic or more virulent microbes in the gastrointestinal tract-also known as gut dysbiosis-is now considered to play a causal role in the pathogenesis of many acute and chronic diseases. Results from animal and human studies suggest that dysbiosis is linked to cardiovascular and metabolic disease through changes to microbiota-derived metabolites, including trimethylamine-N-oxide and short-chain fatty acids. Dysbiosis can occur within hours of surgery or the onset of critical illness, even without the administration of antibiotics. These pathological changes in microbiota may contribute to important clinical outcomes, including surgical infection, bowel anastomotic leaks, acute kidney injury, respiratory failure and brain injury. As a strategy to reduce dysbiosis, the use of probiotics (live bacterial cultures that confer health benefits) or synbiotics (probiotic in combination with food that encourages the growth of gut commensal bacteria) in surgical and critically ill patients has been increasingly reported to confer important clinical benefits, including a reduction in ventilator-associated pneumonia, bacteraemia and length of hospital stay, in small randomised controlled trials. However, the best strategy to modulate dysbiosis or counteract its potential harms remains uncertain and requires investigation by a well-designed, adequately powered, randomised controlled trial.

MicroRNA Profiling of Exosomes Derived from Red Blood Cell Units: Implications in Transfusion-Related Immunomodulation

Purpose

To elucidate the microRNAs existent in exosomes derived from stored red blood cell (RBC) unit and their potential function.

Materials and Methods

Exosomes were isolated from the supernatant derived from stored RBC units by sequential centrifugation. Isolated exosomes were characterized by TEM (transmission electron microscopy), western blotting, and DLS (dynamic light scattering). MicroRNA (miRNA) microarray was performed to detect the expression of miRNAs in 3 exosome samples. Results revealed miRNAs that were simultaneously expressed in the 3 exosome samples and were previously reported to exist in mature RBCs. Functions and potential pathways of some detected miRNAs were illustrated by bioinformatic analysis. Validation of the top 3 abundant miRNAs was carried out by qRT-PCR (quantitative reverse transcription‐polymerase chain reaction).

Results

TEM and DLS revealed the mean size of the exosomes (RBC-derived) as 64.08 nm. These exosomes exhibited higher abundance of short RNA than the long RNA. 78 miRNAs were simultaneously detected in 3 exosome samples and mature RBCs. Several biological processes might be impacted by these miRNAs, through their target gene(s) enriched in a particular signalling pathway. The top 3 (abundant) miRNAs detected were as follows: miR-125b-5p, miR-4454, and miR-451a. qRT-PCR revealed higher abundance of miR-451a than others. Only miR-4454 and miR-451a abundance tended to increase with increasing storage time.

Conclusion

Exosomes derived from stored RBC units possessed multiple miRNAs and, hence, could serve various functions. The function of exosomes (RBC-derived) might be implemented partly by the predominantly enriched miR-451a.