Association of Plasma Level of TNF-Related Apoptosis-Inducing Ligand with Severity and Outcome of Sepsis

Bioinformatics Analysis of Gene Expression Profiles for Diagnosing Sepsis and Risk Prediction in Patients with Sepsis

: Although early recognition of sepsis is essential for timely treatment and can improve sepsis outcomes, no marker has demonstrated sufficient discriminatory power to diagnose sepsis. This study aimed to compare gene expression profiles between patients with sepsis and healthy volunteers to determine the accuracy of these profiles in diagnosing sepsis and to predict sepsis outcomes by combining bioinformatics data with molecular experiments and clinical information. We identified 422 differentially expressed genes (DEGs) between the sepsis and control groups, of which 93 immune-related DEGs were considered for further studies due to immune-related pathways being the most highly enriched. Key genes upregulated during sepsis, including S100A8, S100A9, and CR1, are responsible for cell cycle regulation and immune responses. Key downregulated genes, including CD79A, HLA-DQB2, PLD4, and CCR7, are responsible for immune responses. Furthermore, the key upregulated genes showed excellent to fair accuracy in diagnosing sepsis (area under the curve 0.747-0.931) and predicting in-hospital mortality (0.863-0.966) of patients with sepsis. In contrast, the key downregulated genes showed excellent accuracy in predicting mortality of patients with sepsis (0.918-0.961) but failed to effectively diagnosis sepsis.In conclusion, bioinformatics analysis identified key genes that may serve as biomarkers for diagnosing sepsis and predicting outcomes among patients with sepsis.

The Impact of TRAIL on the Immunological Milieu during the Early Stage of Abdominal Sepsis

Despite intensive scientific efforts, the therapy of peritonitis is presently limited to symptomatic measures, including infectious source control and broad-spectrum antibiotics. Promising therapeutic approaches to reduce morbidity and mortality are still missing. Within the early phase of abdominal sepsis, apoptosis of neutrophil granulocytes is inhibited, which is linked to tissue damage and septic shock. TNF-related apoptosis-inducing ligand (TRAIL) is a promising agent to stimulate neutrophil apoptosis. However, the underlying mechanisms have not been elucidated so far. The objective of the present study was to characterize the molecular mechanisms of TRAIL-stimulated apoptosis in early abdominal sepsis. Therefore, the murine sepsis model Colon ascendens stent peritonitis (CASP) was applied in wild type (WT) and TRAIL knock-out (TRAIL–/–) C57/BL6j mice. Neutrophil granulocytes were isolated from spleen, blood, bone marrow, and peritoneal lavage using magnetic-activated cell sorting. Neutrophil maturation was analyzed by light microscopy, and apoptotic neutrophils were quantified by fluorescence-activated cell sorting (FACS). Western blot and FACS were used to investigate expression changes in apoptotic proteins and TRAIL receptors. The impact of TRAIL-induced apoptosis was studied in vitro. In septic mice (CASP 6 h), the number of neutrophils in the BM was reduced but increased in the blood and peritoneal lavage. This was paralleled by an increased maturation of neutrophils from rod-shaped to segmented neutrophils (right shift). In vitro, extrinsic TRAIL stimulation did not alter the apoptosis level of naïve neutrophils but stimulated apoptosis in neutrophils derived from septic WT and TRAIL–/– mice. Neutrophils of the bone marrow and spleen showed enhanced protein expression of anti-apoptotic Flip, c-IAP1, and McL-1 and reduced expression levels of pro-apoptotic Bax in neutrophils, which might correlate with apoptosis inhibition in these cells. CASP increased the expression of intrinsic TRAIL in neutrophils derived from the bone marrow and spleen. This might be explained by an increased expression of the TRAIL receptors DR5, DcR1, and DcR2 on neutrophils in sepsis. No differences were observed between septic or naïve WT and TRAIL–/– mice. In conclusion, the present study shows that neutrophil granulocytes are sensitive to TRAIL-stimulated apoptosis in the early stage of abdominal sepsis, emphasizing the promising role of TRAIL as a therapeutic agent.

Plasma Mitochondrial DNA and Necroptosis as Prognostic Indicators in Critically Ill Patients with Sepsis

Mitochondrial DNA (mtDNA) has been identified as a biomarker for predicting sepsis mortality. Although preclinical studies suggested that necroptosis could explain the mechanistic link of mtDNA in sepsis, this is not yet evident in patients with sepsis. This study evaluated the association between mtDNA and essential necroptosis mediators in prospectively enrolled patients with sepsis. Plasma mtDNA copy number was measured using quantitative PCR assay and necroptosis mediators, including receptor-interacting protein kinase-3 (RIPK3), mixed lineage domain-like pseudokinase (MLKL), and high-mobility group box 1 (HMGB1), were measured by ELISA. Receiver operating characteristic (ROC) analysis was conducted to evaluate the predictive ability of mtDNA copy number as a predictor of hospital mortality. Among the 142 patients with sepsis, the mtDNA copy number was significantly higher in non-survivors than in survivors (median, 4040 copies/µL vs. 2585 copies/µL; p < 0.001), and the area under the ROC curve was 0.73 (95% CI, 0.64−0.82) for the relationship between mtDNA and hospital mortality. Furthermore, the correlation between mtDNA copy number and each necroptosis mediator was excellent (p < 0.001 for all): RIPK3 (r = 0.803), MLKL (r = 0.897), and HMGB1 (r = 0.603). The plasma mtDNA copy number was highly correlated with essential necroptosis mediators, suggesting that mtDNA propagates necroptosis and increases sepsis mortality.

The Diagnostic Value of Mitochondrial Mass of Peripheral T Lymphocytes in Early Sepsis

Background

Studies have shown that lymphocyte dysfunction can occur during the early stages of sepsis and that cell dysfunction is associated with mitochondrial dysfunction. Therefore, quantifying the mitochondrial function of lymphocytes in patients with sepsis could be valuable for the early diagnosis of sepsis.

Methods

Seventy-nine patients hospitalized from September 2020 to September 2021 with Sepsis-3 were retrospectively analyzed and subsequently compared with those without sepsis.

Results

Univariate analysis showed statistical differences between the data of the two groups regarding age, neutrophil/lymphocyte, procalcitonin (PCT), C-reactive protein, total bilirubin, serum creatinine, type B natriuretic peptide, albumin, prothrombin time, activated partial thromboplastin time, lactic acid, single-cell mitochondrial mass (SCMM)-CD3, SCMM-CD4, SCMM-CD8, and Acute Physiology and Chronic Health Evaluation II score (P < 0.05). Multivariate logistic regression analysis performed on the indicators mentioned above demonstrated a statistical difference in PCT, lactic acid, SCMM-CD4, and SCMM-CD8 levels between the two groups (P < 0.05). The receiver operating characteristic curves of five models were subsequently compared [area under the curve: 0.740 (PCT) vs. 0.933 (SCMM-CD4) vs. 0.881 (SCMM-CD8) vs. 0.961 (PCT + SCMM-CD4) vs. 0.915 (PCT+SCMM-CD8), P < 0.001].

Conclusion

SCMM-CD4 was shown to be a better diagnostic biomarker of early sepsis when compared with the traditional biomarker, PCT. Furthermore, the value of the combination of PCT and SCMM-CD4 in the diagnosis of early sepsis was better than that of SCMM-CD4 alone.

Perspectives on the Immune System in Sepsis

Beyond the modifications shown by the biochemistry labs, profound and ample modifications are seen in septic patients at a molecular level stemming from DNA translation and gene expression, manifested as unique profiles of mRNA (messenger), as well as non-coding, functional RNAs: miRNA (micro) and lncRNAs (long non-coding). Counteracting these modifications requires treatment with pleiotropic molecules and/or combination of molecules and opens the possibility of future treatments with arrays of siRNAs and/or specific panels of small molecules tailored for each patient subpopulation.

Fractalkine deficiency attenuates LPS-induced acute kidney injury and podocyte apoptosis by targeting the PI3K/Akt signal pathway

BACKGROUND

Podocyte injury is a major biomarker of primary glomerular disease, which leads to massive proteinuria and kidney failure. The increased production of the chemokine, fractalkine (FKN, CX3CL1), is a hallmark of multiple inflammatory diseases. However, the underlying mechanism of FKN in podocyte injury remains unknown.

METHODS

In this study, we performed an LPS infusion model in FKN knockout (FKN^-/-, FKN-KO) mice. In cultured podocytes, we used plasmids to knockdown FKN and treated the podocytes with PI3K/Akt inhibitor (LY294002). Haematoxylin and eosin (HE) staining, Western Bolt, Co-immunoprecipitation (Co-IP), Immunofluorescence staining and flow cytometric analysis were employed to establish the role of FKN in podocyte injury.

RESULTS

LPS stimulation resulted in kidney damage, increased the expression of the Bcl-2 family apoptosis protein, and decreased podocyte marker protein (nephrin, podocin and WT1) abundance compared with the WT mice. LPS-induced FKN-KO mice exhibited reduced lethality and inflammatory cell infiltration, podocyte apoptosis, and PI3K/Akt signal pathway inhibition compared to WT mice. In cultured podocytes, the interaction between FKN and the PI3K/Akt signalling pathway was well confirmed. FKN knockdown reduced podocyte apoptosis by regulating the Bcl-2 family; however, this protective effect was reversed by the co-administration of a PI3K/Akt inhibitor (LY294002).

CONCLUSION

Overall, these findings reveal a novel mechanistic property of FKN, PI3K/Akt signalling, and podocyte apoptosis.

Plasma levels of receptor-interacting protein kinase 3 is associated with postoperative acute kidney injury in acute DeBakey type I aortic dissection

Background

Postoperative acute kidney injury (AKI) in acute DeBakey type I aortic dissection (ADIAD) is common but has unclear pathogeneses and limited treatments. Receptor-interacting protein kinase 3 (RIP3), a mediator of necroptosis, is associated with human sepsis-induced and posttraumatic AKI, but its role in human postoperative AKI in ADIAD remains unclear. We assumed that RIP3 levels is associated with postoperative AKI in ADIAD.

Methods

Plasma samples and the clinical data of continuous patients with ADIAD were collected prospectively. The patients were divided into three groups according to AKI stage postoperatively. The plasma RIP3 levels were compared among the groups, and the relationship between RIP3 and serum creatinine (sCr), inflammatory cytokines as well as clinical results were analyzed.

Results

Eighty patients were enrolled. The postoperative and elevated RIP3 levels among the three groups were significantly different (P < 0.0001), both with a positive trend across the AKI stage (P for trend < 0.001), and they were also independent risk factors for postoperative AKI in ADIAD (OR = 1.018 and 1.026, P < 0.05). The postoperative RIP3 levels were positively correlated with the aortic crossclamp time (R = 0.253, P < 0.05); the peak values of sCr, procalcitonin, interleukin-6 and lactate postoperatively; the mechanical ventilation time; and the ICU stay time (R = 0.66, 0.369, 0.409, 0.397, 0.474 and 0.435, respectively; all P < 0.001). Plasma RIP3 level and sCr were comparable in diagnosing postoperative AKI in ADIAD (P = 0.898), and higher postoperative RIP3 level was associated with lower survival rate.

Conclusion

The plasma RIP3 levels are associated with postoperative AKI, inflammatory response and clinical outcomes in ADIAD.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13019-022-01783-0.

Exosomal CD63 in critically ill patients with sepsis

CD63 is one of the tetraspanin protein family members that is ubiquitously expressed on exosomes and is involved in the signal transduction of various types of immune cells. It may thus contribute to immunometabolic mechanisms of cellular and organ dysfunction in sepsis. Nonetheless, the association of exosomal CD63 with the severity and mortality of sepsis is not well known. Therefore, in the present study, the overall levels of exosomal CD63 were evaluated to ascertain whether they were associated with organ failure and mortality in patients with sepsis. Exosomal CD63 was measured from prospectively enrolled critically-ill patients with sepsis (n = 217) and healthy control (n = 20). To detect and quantify exosomes in plasma, a commercially available enzyme-linked immunosorbent assay kit was used according to the manufacturer's protocol. The total number of exosomal CD63 was determined by quantifying the immunoreactive CD63. The association between plasma levels of exosomal CD63 and sequential organ failure assessment (SOFA) score was assessed by a linear regression method. The best cut-off level of exosomal CD63 for 28-day mortality prediction was determined by Youden's index. Among 217 patients with sepsis, 143 (66%) patients were diagnosed with septic shock. Trends of increased exosomal CD63 levels were observed in control, sepsis, and septic-shock groups (6.6 µg/mL vs. 42 µg/mL vs. 90 µg/mL, p < 0.001). A positive correlation between exosomal CD63 and SOFA scores was observed in patients with sepsis (r value = 0.35). When patients were divided into two groups according to the best cut-off level, the group with higher exosomal CD63 levels (more than 126 µg/mL) was significantly associated with 28-day and in-hospital mortality. Moreover, the Kaplan-Meier survival method showed a significant difference in 90-day survival between patients with high- and low-exosomal CD63 levels (log-rank p = 0.005). Elevated levels of exosomal CD63 were associated with the severity of organ failure and predictive of mortality in critically ill patients with sepsis.

Association of plasma level of high-mobility group box-1 with necroptosis and sepsis outcomes

The role of high-mobility group box-1 (HMGB1) in outcome prediction in sepsis is controversial. Furthermore, its association with necroptosis, a programmed cell necrosis mechanism, is still unclear. The purpose of this study is to identify the association between the plasma levels of HMGB1 and the severity and clinical outcomes of sepsis, and to examine the correlation between HMGB1 and key executors of necroptosis including receptor-interacting kinase 3 (RIPK3) and mixed lineage kinase domain-like- (MLKL) proteins. Plasma HMGB1, RIPK3, and MLKL levels were measured with the enzyme-linked immunosorbent assay from the derivation cohort of 188 prospectively enrolled, critically-ill patients between April 2014 and December 2016, and from the validation cohort of 77 patients with sepsis between January 2017 and January 2019. In the derivation cohort, the plasma HMGB1 levels of the control (n = 46, 24.5%), sepsis (n = 58, 30.9%), and septic shock (n = 84, 44.7%) groups were significantly increased (P < 0.001). A difference in mortality between high (≥ 5.9 ng/mL) and low (< 5.9 ng/mL) HMGB1 levels was observed up to 90 days (Log-rank test, P = 0.009). There were positive linear correlations of plasma HMGB1 with RIPK3 (R² = 0.61, P < 0.001) and MLKL (R² = 0.7890, P < 0.001). The difference in mortality and correlation of HMGB1 levels with RIPK3 and MLKL were confirmed in the validation cohort. Plasma levels of HMGB1 were associated with the severity and mortality attributed to sepsis. They were correlated with RIPK3 and MLKL, thus suggesting an association of HMGB1 with necroptosis.