Septic Stability? Gut Microbiota in Young Adult Mice Maintains Overall Stability After Sepsis Compared to Old Adult Mice

Inflammatory Response and Anti-Inflammatory Treatment in Persistent Inflammation-Immunosuppression-Catabolism Syndrome (PICS)

Many patients now survive their initial critical events but subsequently develop chronic critical illness (CCI). CCI is characterized by prolonged hospital stays, poor outcomes, and significant long-term mortality. The incidence of chronic critical illness (CCI) is estimated to be 34.4 cases per 100,000 population. The incidence varies significantly with age, peaking at 82.1 cases per 100,000 in individuals aged 75-79. The one-year mortality rate among CCI patients approaches 50%. A subset of these patients enters a state of persistent inflammation, immune suppression, and ongoing catabolism, a condition termed persistent inflammation, immunosuppression, and catabolism syndrome (PICS) in 2012. In recent years, some progress has been made in treating PICS. For instance, recent advancements such as the persistent expansion of MDSCs (myeloid-derived suppressor cells) and the mechanisms underlying intestinal barrier dysfunction have provided new directions for therapeutic strategies, as discussed below. Persistent inflammation, a key feature of PICS, has received comparatively little research attention. In this review, we examine the potential pathophysiological changes and molecular mechanisms underlying persistent inflammation and its role in PICS. We also discuss current therapies about inflammation and offer recommendations for managing patients with PICS.

The Gut Microbiome in Aging and Ovarian Cancer

The gut microbiome changes with age and affects regions beyond the gut, including the ovarian cancer tumor microenvironment. In this review summarizing the literature on the gut microbiome in ovarian cancer and in aging, we note trends in the microbiota composition common to both phenomena and trends that are distinctly opposite. Both ovarian cancer and aging are characterized by an increase in proinflammatory bacterial species, particularly those belonging to phylum Proteobacteria and genus Escherichia, and a decrease in short chain fatty acid producers, particularly those in Clostridium cluster XIVa (family Lachnospiraceae) and the Actinobacteria genus Bifidobacterium. However, while beneficial bacteria from family Porphyromonadaceae and genus Akkermansia tend to increase with normal, healthy aging, these bacteria tend to decrease in ovarian cancer, similar to what is observed in obesity or unhealthy aging. We also note a lack in the current literature of research demonstrating causal relationships between the gut microbiome and ovarian cancer outcomes and research on the gut microbiome in ovarian cancer in the context of aging, both of which could lead to improvements to ovarian cancer diagnosis and treatment.

Aging exacerbates cardiac dysfunction and mortality in sepsis through enhancing TLR2 activity

Introduction

Sepsis is prevalent in the elderly population with increased incidence and mortality. Currently, the mechanism by which aging increases the susceptibility to sepsis and worsens outcome is unclear. We tested the hypothesis that aging exacerbates cardiac dysfunction in sepsis through a Toll-like receptor 2 (TLR2)-dependent mechanism.

Methods

Male young adult (4-6 months) and old (18-20 months) wild type (WT) and TLR2 knockout (KO) mice were subject to moderate sepsis by cecal ligation and puncture. Additional groups of young adult and old WT mice were treated with TLR2 agonist Pam3CSK4. Left ventricle (LV) performance was evaluated with a pressure-volume microcatheter. Tumor necrosis factor-α (TNF-α), interleukin (IL)-1β, IL-6 and monocyte chemoattractant protein-1 (MCP-1) in the myocardium and plasma were assessed using enzyme-linked immunosorbent assay.

Results

Sepsis reduced LV ejection fraction and cardiac output in both young adult and old WT mice. However, identical CLP caused more severe cardiac dysfunction and high mortality in old WT mice that were accompanied by greater levels of TNF-α, IL-1β, IL-6 and MCP-1 in the myocardium and plasma. TLR2 KO diminished aging-related difference in myocardial and systemic inflammatory response, resulting in improved cardiac function and decreased mortality in old septic mice. In addition, higher myocardial TLR2 levels in old WT mice resulted in greater myocardial inflammatory response and worse cardiac dysfunction following administration of TLR2 agonist.

Conclusion

Moderate sepsis results in greater cardiac dysfunction and significant mortality in old mice. Aging elevates TLR2 level/activity to exacerbate the inflammatory response to sepsis, leading to worse cardiac dysfunction and mortality.

Gut-muscle axis and sepsis-induced myopathy: The potential role of gut microbiota

Sepsis is described as an immune response disorder of the host to infection in which microorganisms play a non-negligible role. Most survivors of sepsis experience ICU-acquired weakness, also known as septic myopathy, characterized by skeletal muscle atrophy, weakness, and irreparable damage/regenerated or dysfunctional. The mechanism of sepsis-induced myopathy is currently unclear. It has been believed that this state is triggered by circulating pathogens and their related harmful factors, leading to impaired muscle metabolism. Sepsis and its resulting alterations in the intestinal microbiota are associated with sepsis-related organ dysfunction, including skeletal muscle wasting. There are also some studies on interventions targeting the flora, including fecal microbiota transplants, the addition of dietary fiber and probiotics in enteral feeding products, etc., aiming to improve sepsis-related myopathy. In this review, we critically assess the potential mechanisms and therapeutic prospects of intestinal flora in the development of septic myopathy.

From Gut to Blood: Spatial and Temporal Pathobiome Dynamics during Acute Abdominal Murine Sepsis

Abdominal sepsis triggers the transition of microorganisms from the gut to the peritoneum and bloodstream. Unfortunately, there is a limitation of methods and biomarkers to reliably study the emergence of pathobiomes and to monitor their respective dynamics. Three-month-old CD-1 female mice underwent cecal ligation and puncture (CLP) to induce abdominal sepsis. Serial and terminal endpoint specimens were collected for fecal, peritoneal lavage, and blood samples within 72 h. Microbial species compositions were determined by NGS of (cell-free) DNA and confirmed by microbiological cultivation. As a result, CLP induced rapid and early changes of gut microbial communities, with a transition of pathogenic species into the peritoneum and blood detected at 24 h post-CLP. NGS was able to identify pathogenic species in a time course-dependent manner in individual mice using cfDNA from as few as 30 microliters of blood. Absolute levels of cfDNA from pathogens changed rapidly during acute sepsis, demonstrating its short half-life. Pathogenic species and genera in CLP mice significantly overlapped with pathobiomes from septic patients. The study demonstrated that pathobiomes serve as reservoirs following CLP for the transition of pathogens into the bloodstream. Due to its short half-life, cfDNA can serve as a precise biomarker for pathogen identification in blood.

Gut microbiota involved in myocardial dysfunction induced by sepsis

Myocardial dysfunction is an important complication of sepsis and an important cause of death in sepsis patients. Sepsis will significantly change the composition of gut microbiota, and the destruction of gut microbiota also creates conditions for the occurrence and progression of sepsis. Gut microbiota is an important player in myocardial injury in sepsis. This review elaborates on the possible mechanisms of gut microbiota affecting myocardial injury in sepsis, including short-chain fatty acids, trimethylamine and trimethylamine oxides, various cytokines, and mitochondrial dysfunction. A better understanding of the mechanism could help improve the treatment of sepsis and get a better prognosis for sepsis patients.

Akkermansia muciniphila Alleviates Persistent Inflammation, Immunosuppression, and Catabolism Syndrome in Mice

Many patients in intensive care units, especially the elderly, suffer from chronic critical illness and exhibit a new pathophysiological phenotype: persistent inflammation, immunosuppression, and catabolism syndrome (PICS). Most patients with PICS have a constellation of digestive-system symptoms and gut failure. Akkermansia muciniphila (Akk) is a commensal gut bacterium that reduces inflammation, balances immune responses, modulates energy metabolism, and supports gut health. This study investigated the protective effects and underlying mechanisms of live and pasteurized Akk in treating PICS in a mouse model. PICS was induced on day 14 after performing cecal ligation and puncture (CLP) on day 1 and administrating lipopolysaccharide on day 11. Pasteurized or live Akk, or phosphate-buffered saline was administered twice daily by oral gavage for 7 days. Both live and pasteurized Akk attenuated PICS, as evidenced by reduced weight loss, and a reduction in symptoms and serum cytokine/chemokine levels. Liver and intestinal injuries were mitigated, and intestinal barrier integrity improved with Akk administration. Analysis of 16S rRNA amplicon sequences showed that Akk induced significant intestinal microbiota alterations, including increased abundance of Akk, Muribaculaceae, Parabacterbides goldsteinii, and decreased abundance of Escherichia_Shigella and Enterobacteriaceae. Collectively, Akk alleviates PICS by enhancing gut barrier function and reshaped the microbial community.

Sex differences associate with late microbiome alterations after murine surgical sepsis

BACKGROUND

Sepsis-induced gut microbiome alterations contribute to sepsis-related morbidity and mortality. Given evidence for improved postsepsis outcomes in females compared with males, we hypothesized that female mice maintain microbiota resilience versus males.

METHODS

Mixed-sex C57BL/6 mice underwent cecal ligation and puncture (CLP) with antibiotics, saline resuscitation, and daily chronic stress and were compared with naive (nonsepsis/no antibiotics) controls. For this work, the results of young (3-5 months) and old (18-22 months) adult mice were analyzed by sex, independent and dependent of age. Mice were sacrificed at days 7 and 14, and 16S rRNA gene sequencing was performed on fecal bacterial DNA. α and β diversity were determined by Shannon index and Bray-Curtis with principal coordinate analysis, respectively. False discovery rate (FDR) correction was implemented to account for potential housing effect.

RESULTS

In control mice, there was no difference in α or β diversity between male and female mice (FDR, 0.76 and 0.99, respectively). However, male mice that underwent CLP with daily chronic stress had a decrease in microbiota α diversity at 7 days post-CLP (Shannon FDR, 0.005), which was sustained at 14 days post-CLP (Shannon FDR, 0.001), compared with baseline. In addition, male mice maintained differences in β diversity even at day 14 compared with controls (FDR, <0.0001). In contrast, female mice had a decreased microbiota α diversity (Shannon FDR, 0.03) and β diversity (FDR, 0.02) 7 days post-CLP but recovered their α and β diversity by post-CLP day 14 (Shannon FDR, 0.5, and FDR, 0.02, respectively). Further analysis of females revealed that only young female mice were not different (β diversity) post-CLP day 14 to controls.

CONCLUSION

Although sepsis-induced perturbations of the intestinal microbiota occur initially in both male and female C57BL/6 mice, females demonstrate different microbiota by day 14. This may be seen primarily in younger females. This difference in recovery may play a role in outcome differences between sexes after sepsis.

Age and Injury Size Influence the Magnitude of Fecal Dysbiosis in Adult Burn Patients

Clinical studies have demonstrated that age 50 years or older is an independent risk factor associated with poor prognosis after burn injury, the second leading cause of traumatic injuries in the aged population. While mechanisms driving age-dependent postburn mortality are perplexing, changes in the intestinal microbiome, may contribute to the heightened, dysregulated systemic response seen in aging burn patients. The fecal microbiome from 22 patients admitted to a verified burn center from July 2018 to February 2019 was stratified based on the age of 50 years and total burn surface area (TBSA) size of ≥10%. Significant differences (P = .014) in overall microbiota community composition (ie, beta diversity) were measured across the four patient groups: young <10% TBSA, young ≥10% TBSA, older <10% TBSA, and older ≥10% TBSA. Differences in beta diversity were driven by %TBSA (P = .013) and trended with age (P = .087). Alpha diversity components, richness, evenness, and Shannon diversity were measured. We observed significant differences in bacterial species evenness (P = .0023) and Shannon diversity (P = .0033) between the groups. There were significant correlations between individual bacterial species and levels of short-chain fatty acids. Specifically, levels of fecal butyrate correlated with the presence of Enterobacteriaceae, an opportunistic gut pathogen, when elevated in burn patients lead to worsen outcomes. Overall, our findings reveal that age-specific changes in the fecal microbiome following burn injuries may contribute to immune system dysregulation in patients with varying TBSA burns and potentially lead to worsened clinical outcomes with heightened morbidity and mortality.

Sepsis-Induced Myopathy and Gut Microbiome Dysbiosis: Mechanistic Links and Therapeutic Targets

ABSTRACT

Sepsis is currently defined as a life-threatening organ dysfunction caused by a dysregulated host response to infection. The skeletal muscle system is among the host organ systems compromised by sepsis. The resulting neuromuscular dysfunction and impaired regenerative capacity defines sepsis-induced myopathy and manifests as atrophy, loss of strength, and hindered regeneration after injury. These outcomes delay recovery from critical illness and confer increased vulnerability to morbidity and mortality. The mechanisms underlying sepsis-induced myopathy, including the potential contribution of peripheral organs, remain largely unexplored. The gut microbiome is an immunological and homeostatic entity that interacts with and controls end-organ function, including the skeletal muscle system. Sepsis induces alterations in the gut microbiota composition, which is globally termed a state of "dysbiosis" for the host compared to baseline microbiota composition. In this review, we critically evaluate existing evidence and potential mechanisms linking sepsis-induced myopathy with gut microbiota dysbiosis.

Identification of unique microRNA expression patterns in bone marrow hematopoietic stem and progenitor cells after hemorrhagic shock and multiple injuries in young and old adult mice

BACKGROUND

After severe trauma, the older host experiences more dysfunctional hematopoiesis of bone marrow (BM) hematopoietic stem and progenitor cells (HSPCs), and dysfunctional differentiation of circulating myeloid cells into effective innate immune cells. Our main objective was to compare BM HSPC microRNA (miR) responses of old and young mice in a clinically relevant model of severe trauma and shock.

METHODS

C57BL/6 adult male mice aged 8 to 12 weeks (young) and 18 to 24 months (old) underwent multiple injuries and hemorrhagic shock (polytrauma [PT]) that engenders the equivalent of major trauma (Injury Severity Score, >15). Pseudomonas pneumonia (PNA) was induced in some young and old adult mice 24 hours after PT. MicroRNA expression patterns were determined from lineage-negative enriched BM HSPCs isolated from PT and PT-PNA mice at 24 and 48 hours postinjury, respectively. Genome-wide expression and pathway analyses were also performed on bronchoalveolar lavage (BAL) leukocytes from both mouse cohorts.

RESULTS

MicroRNA expression significantly differed among all experimental conditions (p < 0.05), except for old-naive versus old-injured (PT or PT-PNA) mice, suggesting an inability of old mice to mount a robust early miR response to severe shock and injury. In addition, young adult mice had significantly more leukocytes obtained from their BAL, and there were greater numbers of polymorphonuclear cells compared with old mice (59.8% vs. 2.2%, p = 0.0069). Despite increased gene expression changes, BAL leukocytes from old mice demonstrated a more dysfunctional transcriptomic response to PT-PNA than young adult murine BAL leukocytes, as reflected in predicted upstream functional pathway analysis.

CONCLUSION

The miR expression pattern in BM HSPCs after PT (+/-PNA) is dissimilar in old versus young adult mice. In the acute postinjury phase, old adult mice are unable to mount a robust miR HSPC response. Hematopoietic stem and progenitor cell miR expression in old PT mice reflects a diminished functional status and a blunted capacity for terminal differentiation of myeloid cells.

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.