Pathological Role and Diagnostic Value of Endogenous Host Defense Peptides in Adult and Neonatal Sepsis: A Systematic Review

Identification and Characterization of RK22, a Novel Antimicrobial Peptide from Hirudinaria manillensis against Methicillin Resistant Staphylococcus aureus

Staphylococcus aureus (S. aureus) infections are a leading cause of morbidity and mortality, which are compounded by drug resistance. By manipulating the coagulation system, S. aureus gains a significant advantage over host defense mechanisms, with hypercoagulation induced by S. aureus potentially aggravating infectious diseases. Recently, we and other researchers identified that a higher level of LL-37, one endogenous antimicrobial peptide with a significant killing effect on S. aureus infection, resulted in thrombosis formation through the induction of platelet activation and potentiation of the coagulation factor enzymatic activity. In the current study, we identified a novel antimicrobial peptide (RK22) from the salivary gland transcriptome of Hirudinaria manillensis (H. manillensis) through bioinformatic analysis, and then synthesized it, which exhibited good antimicrobial activity against S. aureus, including a clinically resistant strain with a minimal inhibitory concentration (MIC) of 6.25 μg/mL. The RK22 peptide rapidly killed S. aureus by inhibiting biofilm formation and promoting biofilm eradication, with good plasma stability, negligible cytotoxicity, minimal hemolytic activity, and no significant promotion of the coagulation system. Notably, administration of RK22 significantly inhibited S. aureus infection and the clinically resistant strain in vivo. Thus, these findings highlight the potential of RK22 as an ideal treatment candidate against S. aureus infection.

Endothelial dysfunction and immunothrombosis in sepsis

Sepsis is a life-threatening clinical syndrome characterized by multiorgan dysfunction caused by a dysregulated or over-reactive host response to infection. During sepsis, the coagulation cascade is triggered by activated cells of the innate immune system, such as neutrophils and monocytes, resulting in clot formation mainly in the microcirculation, a process known as immunothrombosis. Although this process aims to protect the host through inhibition of the pathogen’s dissemination and survival, endothelial dysfunction and microthrombotic complications can rapidly lead to multiple organ dysfunction. The development of treatments targeting endothelial innate immune responses and immunothrombosis could be of great significance for reducing morbidity and mortality in patients with sepsis. Medications modifying cell-specific immune responses or inhibiting platelet–endothelial interaction or platelet activation have been proposed. Herein, we discuss the underlying mechanisms of organ-specific endothelial dysfunction and immunothrombosis in sepsis and its complications, while highlighting the recent advances in the development of new therapeutic approaches aiming at improving the short- or long-term prognosis in sepsis.

Feasibility of phagocytes functional testing in neonatal sepsis diagnostics

Neonatal sepsis is a problem still relevant for healthcare in Russia and worldwide due to high mortality and resistance to treatment. Generalization of infection in newborns occurs because of innate immunity deficiency that particularly leads to neutrophil and monocyte malfunction. Nowadays clinical practice of neonatal sepsis diagnostics does not include phagocytes functional testing. Purpose. The study aims at evaluating the ability of sepsis biomarkers (CRP, PCT, lactate, CD64, CD16, HLA-DR) to differentiate the pathogenesis of organ dysfunction in newborns in the ICU setting.Material and methods. We assessed the surface expression of neutrophil CD64 and CD16, as well as monocytic HLA-DR in newborn ICU patients with different genesis of multiple organ failure — sepsis, asphyxia and combined; as well as different outcomes of hospitalization in the ICU — survivors and deaths.Results. We have shown a significant increase in the neutrophil CD64 expression and a decrease in the monocytic HLA-DR in infectious and combined genesis of multiple organ failure compared with severe asphyxia; deaths were associated with reduced expression of neutrophil CD16.Conclusion. Our data could substantiate combined use of the phagocytes functional testing indicators together with conventional sepsis biomarkers in order to increase their prognostic and predictive value.

A designed antimicrobial peptide with potential ability against methicillin resistant Staphylococcus aureus

Staphylococcus aureus (S. aureus) is a Gram-positive pathogenic bacterium, which persistently colonizes the anterior nares of approximately 20–30% of the healthy adult population, and up to 60% is intermittently colonized. With the misuse and overuse of antibiotics, large-scale drug-resistant bacteria, including methicillin-resistant S. aureus (MRSA), have been appeared. MRSA is among the most prevalent pathogens causing community-associated infections. Once out of control, the number of deaths caused by antimicrobial resistance may exceed 10 million annually by 2050. Antimicrobial peptides (AMPs) are regarded as the best solution, for they are not easy to develop drug resistance. Based on our previous research, here we designed a new antimicrobial peptide named GW18, which showed excellent antimicrobial activity against S. aureus, even MRSA, with the hemolysis less than 5%, no cytotoxicity, and no acute toxicity. Notably, administration of GW18 significantly decreased S. aureus infection in mouse model. These findings identify GW18 as the ideal candidate against S. aureus infection.

Human Neutrophil Defensins Disrupt Liver Interendothelial Junctions and Aggravate Sepsis

Human neutrophil peptides 1-3 (HNP1-3), also known as human α-defensins, are the most abundant neutrophil granule proteins. The genes that encode HNP1-3, DEFA1/DEFA3, exhibit extensive copy number variations, which correlate well with their protein levels. Human and mouse studies have shown that increased copy numbers of DEFA1/DEFA3 worsen sepsis outcomes. Additionally, high concentrations of HNP1-3 in body fluids have been reported in patients with sepsis. However, direct evidence for the pathogenic role of HNP1-3 proteins during sepsis progression is lacking. In current study, sepsis was induced by means of cecal puncture and ligation. Various doses of HNP-1 (low dose with 0.5 mg/kg body weight and high dose with 10 mg/kg body weight) or phosphate buffer saline were intraperitoneally administered to mice at six hours after sepsis onset. Survival rate was monitored, and vascular permeability, endothelial cell pyroptosis, and immunofluorescence of endothelial adherens junction protein vascular endothelial-cadherin were evaluated. The administration of a high dose of HNP-1 after sepsis onset led to increased mortality, more severe liver injury, and increased vascular permeability in the liver and mesentery. The injection of high dose of HNP-1 did not directly induce liver endothelial cell death but destroyed interendothelial junctions in the liver. Moreover, genetic deficiency of nucleotide-binding oligomerization domain-like receptor protein-3 or caspase-1 abrogated the high mortality and disrupted liver interendothelial junctions caused by high dose of HNP-1 during sepsis. This study directly demonstrates that neutrophil defensins play a key role in regulating endothelial stability during sepsis development.

Cord blood antimicrobial peptide LL37 levels in preterm neonates and association with preterm complications

BACKGROUND

Cathelicidin/LL-37 plays a significant role in the human immune defense reaction. Preterm human immature organs being exposed to inflammation-induced injury was the critical denominator leading to the common preterm associated complications. Previous study showed LL37 concentration in preterm neonates was lower in tracheal aspirates and breast milk as compared to term infants. An adults study showed decreased LL-37 levels was a risk factor for patients in developing severe chronic obstructive pulmonary disease (COPD). However, little is known about the regulation of human cord blood LL37 in preterm neonates and the association with preterm complications. This study was designed to investigate the concentration of LL37 in cord blood of preterm infants and correlation with preterm complications.

METHODS

Singleton infants born in June 2017 to August 2021 in the study hospital were enrolled. Maternal and neonatal clinical characteristics were collected. LL37 levels, pro-inflammatory factor interleukin-6 (IL-6) and tumor necrosis factor-a (TNF-a) in cord blood and LL37 levels in serum 48-72 hours after birth were measured by enzyme-linked immunosorbent assay. The serum level of LL37 in preterm and term neonates were compared, the perinatal factors possibly affecting the LL37 levels were investigated and the relationship between LL37 level and preterm outcomes were analyzed.

RESULTS

Cord blood LL37 levels in preterm infants were lower than that in term neonates. Cord blood LL37 level was positively correlated with gestational age in preterm. Prenatal steroid administration in preterm neonates decreased cord blood LL37 level. LL37 level was obviously lower in patients with bronchopulmonary dysplasia (BPD). Multiple line regression analysis showed higher LL37 level in cord blood was an independent protective factor for BPD. The concentration of pro-inflammatory factor IL-6 was negatively correlated with LL37.

CONCLUSION

Cord blood LL37 levels increased during gestation and decreased after perinatal steroid usage. Very preterm infants who displayed higher cord blood LL37 level had reduced risk of developing BPD. Regulation of pro-inflammatory cytokine IL-6 may be associated with the protective effect of LL37 on BPD.

Diagnosis of neonatal sepsis: the past, present and future

Sepsis remains a significant cause of neonatal mortality and morbidity, especially in low- and middle-income countries. Neonatal sepsis presents with nonspecific signs and symptoms that necessitate tests to confirm the diagnosis. Early and accurate diagnosis of infection will improve clinical outcomes and decrease the overuse of antibiotics. Current diagnostic methods rely on conventional culture methods, which is time-consuming, and may delay critical therapeutic decisions. Nonculture-based techniques including molecular methods and mass spectrometry may overcome some of the limitations seen with culture-based techniques. Biomarkers including hematological indices, cell adhesion molecules, interleukins, and acute-phase reactants have been used for the diagnosis of neonatal sepsis. In this review, we examine past and current microbiological techniques, hematological indices, and inflammatory biomarkers that may aid sepsis diagnosis. The search for an ideal biomarker that has adequate diagnostic accuracy early in sepsis is still ongoing. We discuss promising strategies for the future that are being developed and tested that may help us diagnose sepsis early and improve clinical outcomes. IMPACT: Reviews the clinical relevance of currently available diagnostic tests for sepsis. Summarizes the diagnostic accuracy of novel biomarkers for neonatal sepsis. Outlines future strategies including the use of omics technology, personalized medicine, and point of care tests.

Knowledge gaps in late-onset neonatal sepsis in preterm neonates: a roadmap for future research

Late-onset neonatal sepsis (LONS) remains an important threat to the health of preterm neonates in the neonatal intensive care unit. Strategies to optimize care for preterm neonates with LONS are likely to improve survival and long-term neurocognitive outcomes. However, many important questions on how to improve the prevention, early detection, and therapy for LONS in preterm neonates remain unanswered. This review identifies important knowledge gaps in the management of LONS and describe possible methods and technologies that can be used to resolve these knowledge gaps. The availability of computational medicine and hypothesis-free-omics approaches give way to building bedside feedback tools to guide clinicians in personalized management of LONS. Despite advances in technology, implementation in clinical practice is largely lacking although such tools would help clinicians to optimize many aspects of the management of LONS. We outline which steps are needed to get possible research findings implemented on the neonatal intensive care unit and provide a roadmap for future research initiatives. IMPACT: This review identifies knowledge gaps in prevention, early detection, antibiotic, and additional therapy of late-onset neonatal sepsis in preterm neonates and provides a roadmap for future research efforts. Research opportunities are addressed, which could provide the means to fill knowledge gaps and the steps that need to be made before possible clinical use. Methods to personalize medicine and technologies feasible for bedside clinical use are described.

Airway Epithelial Hepcidin Coordinates Lung Macrophages and Immunity Against Bacterial Pneumonia

BACKGROUND

Hepcidin is a liver-derived master regulator of iron metabolism through its molecular target ferroportin, the only known mammalian iron exporter. Accumulated evidence has shown the important roles of hepatic hepcidin in host defense and infections. Hepcidin is also expressed by airway epithelial cells. However, the function of epithelial hepcidin during bacterial pneumonia remains unknown.

METHODS

Pneumonia was induced in hepcidin-1-deficient and wild-type mice using the most common bacterial agents, and the effects of hepcidin on survival, bacterial burden, iron status, and macrophage phagocytosis after bacterial pneumonia were assessed.

RESULTS

Hepcidin levels decreased in airway epithelium during common pneumonia, while lung macrophage-derived ferroportin levels and pulmonary iron concentrations increased. Lack of hepcidin in the airway epithelium worsened the outcomes of pneumonia. Manipulation of hepcidin level in the airway epithelium in mice with macrophage-specific ferroportin deletion did not affect the progress of pneumonia. Increased pulmonary iron concentration not only facilitated bacterial growth but also led to the defective phagocytic function of lung macrophages via activation of RhoA GTPase through oxidation of RhoGDI. Furthermore, enhancing the hepcidin level in the airway epithelium rescued mice from lethal bacterial pneumonia.

CONCLUSIONS

These findings identify an uncharacterized important role of airway epithelial hepcidin in protection against bacterial pneumonia and provide the basis for novel alternative therapeutic strategies for combatting bacterial pneumonia in future translational research.

The Paneth Cell: The Curator and Defender of the Immature Small Intestine

Paneth cells were first described in the late 19th century by Gustav Schwalbe and Josef Paneth as columnar epithelial cells possessing prominent eosinophilic granules in their cytoplasm. Decades later there is continued interest in Paneth cells as they play an integral role in maintaining intestinal homeostasis and modulating the physiology of the small intestine and its associated microbial flora. Paneth cells are highly specialized secretory epithelial cells located in the small intestinal crypts of Lieberkühn. The dense granules produced by Paneth cells contain an abundance of antimicrobial peptides and immunomodulating proteins that function to regulate the composition of the intestinal flora. This in turn plays a significant role in secondary regulation of the host microvasculature, the normal injury and repair mechanisms of the intestinal epithelial layer, and the levels of intestinal inflammation. These critical functions may have even more importance in the immature intestine of premature infants. While Paneth cells begin to develop in the middle of human gestation, they do not become immune competent or reach their adult density until closer to term gestation. This leaves preterm infants deficient in normal Paneth cell biology during the greatest window of susceptibility to develop intestinal pathology such as necrotizing enterocolitis (NEC). As 10% of infants worldwide are currently born prematurely, there is a significant population of infants contending with an inadequate cohort of Paneth cells. Infants who have developed NEC have decreased Paneth cell numbers compared to age-matched controls, and ablation of murine Paneth cells results in a NEC-like phenotype suggesting again that Paneth cell function is critical to homeostasis to the immature intestine. This review will provide an up to date and comprehensive look at Paneth cell ontogeny, the impact Paneth cells have on the host-microbial axis in the immature intestine, and the repercussions of Paneth cell dysfunction or loss on injury and repair mechanisms in the immature gut.

Cathelicidin preserves intestinal barrier function in polymicrobial sepsis

Objectives

The intestinal epithelium compartmentalizes the sterile bloodstream and the commensal bacteria in the gut. Accumulating evidence suggests that this barrier is impaired in sepsis, aggravating systemic inflammation. Previous studies reported that cathelicidin is differentially expressed in various tissues in sepsis. However, its role in sepsis-induced intestinal barrier dysfunction has not been investigated.

Design

To examine the role of cathelicidin in polymicrobial sepsis, cathelicidin wild-(Cnlp^+/+) and knockout (Cnlp^−/−) mice underwent cecal-ligation and puncture (CLP) followed by the assessment of septic mortality and morbidity as well as histological, biochemical, immunological, and transcriptomic analyses in the ileal tissues. We also evaluated the prophylactic and therapeutic efficacies of vitamin D3 (an inducer of endogenous cathelicidin) in the CLP-induced murine polymicrobial sepsis model.

Results

The ileal expression of cathelicidin was increased by three-fold after CLP, peaking at 4 h. Knockout of Cnlp significantly increased 7-day mortality and was associated with a higher murine sepsis score. Alcian-blue staining revealed a reduced number of mucin-positive goblet cells, accompanied by reduced mucin expression. Increased number of apoptotic cells and cleavage of caspase-3 were observed. Cnlp deletion increased intestinal permeability to 4kD fluorescein-labeled dextran and reduced the expression of tight junction proteins claudin-1 and occludin. Notably, circulating bacterial DNA load increased more than two-fold. Transcriptome analysis revealed upregulation of cytokine/inflammatory pathway. Depletion of Cnlp induced more M1 macrophages and neutrophils compared with the wild-type mice after CLP. Mice pre-treated with cholecalciferol (an inactive form of vitamin D3) or treated with 1alpha, 25-dihydroxyvitamin D3 (an active form of VD3) had decreased 7-day mortality and significantly less severe symptoms. Intriguingly, the administration of cholecalciferol after CLP led to worsened 7-day mortality and the associated symptoms.

Conclusions

Endogenous cathelicidin promotes intestinal barrier integrity accompanied by modulating the infiltration of neutrophils and macrophages in polymicrobial sepsis. Our data suggested that 1alpha, 25-dihydroxyvitamin D3 but not cholecalciferol is a potential therapeutic agent for treating sepsis.

Preclinical evidence of sphingosine kinase 1 inhibition in alleviation of intestinal epithelial injury in polymicrobial sepsis

BACKGROUND

Intestinal epithelial injury in septic patients predicts subsequent development of multiple organ failure, but its regulation by host factors remains unclear. Sphingosine kinase 1 is an enzyme-regulating inflammatory response.

METHODS

Cecal ligation and puncture was used to induce sepsis in C57BL/6 mice with and without N,N-dimethylsphingosine, a SphK1 inhibitor. Symptom severity was monitored by murine sepsis severity score. The intestinal barrier function was determined using 4KDa fluorescein-dextran. Bacterial load in the bloodstream was determined by 16S rRNA gene amplification.

RESULTS AND CONCLUSIONS

Our preliminary experimental data showed that expression of sphingosine kinase 1 in ileum was increased by sixfold in septic mice. Pharmacological blockade of sphingosine kinase 1 alleviated septic symptoms. The intestinal permeability and bacterial load in the bloodstream were also reduced in these animals. We hypothesized that inhibition of sphingosine kinase 1 may reduce pro-inflammatory cytokine production, and alleviate intestinal epithelial injury during sepsis. Further mechanistic studies and clinical specimen analyses are warranted.

Human beta-defensin-1 is a highly predictive marker of mortality in patients with acute-on-chronic liver failure

BACKGROUND & AIM

Human beta-defensin-1 (hBD-1) is a natural antimicrobial peptide expressed in the epithelia of multiple tissues including the digestive tract. In the current study, hBD-1 levels were determined in different subsets of patients with decompensated cirrhosis including acute-on-chronic liver failure (ACLF). In addition, the association with mortality of hBD-1, C-reactive protein (CRP) and procalcitonin (PCT) was assessed.

METHODS

A total of 125 patients were divided into three groups: 39 with ACLF (derivation cohort), 46 with acute decompensation without ACLF (AD) and 40 with decompensated cirrhosis without an acute event (DC). The data from 24 different ACLF patients were used for validation and 15 healthy individuals as control group.

RESULTS

Serum hBD-1, CRP and PCT levels were higher in ACLF compared to both AD and DC groups (P < 0.001). Healthy controls demonstrated similar hBD-1 and PCT values compared to DC group. In ROC curve, the performance of hBD-1 to predict 60-day mortality in ACLF group was similar in derivation and validation cohorts (c-statistic 0.834 and 0.879, respectively). CRP was a poor predictor of mortality. In ACLF group, patients with high hBD-1 (>36.625 ng/mL) had a poor prognosis at 60 days compared to those with lower values (log-rank P = 0.001). In Cox multivariate regression analysis, only hBD-1 (HR 1.020, 95%CI 1.006-1.035, P = 0.006) emerged as an independent predictor of death in ACLF group. In AD group, neither hBD-1 nor PCT or CRP variables were associated with mortality.

CONCLUSIONS

High hBD-1 was detected at presentation in patients with ACLF who died during follow-up period. hBD-1 is an accurate predictor of short-term mortality in patients with ACLF.

Host-defense peptides and their potential use as biomarkers in human diseases

Since the early 19th century, host-defense peptides (HDPs) have been known to play a crucial role in innate host defense. Subsequent work has demonstrated their role in adaptive immunity as well as their involvement in cancer and also a number of inflammatory and/or autoimmune diseases. In addition to these multiple functional activities, several studies have shown that HDP accumulation might be correlated with various human diseases and, therefore, could be used as a biomarkers for such. Thus, research has aimed to validate the clinical use of HDPs for diagnosis, prognosis, and further treatment. In this review, we outline the most recent findings related to the use of HDPs as biomarkers, their clinical and epidemiological value, and the techniques used to determine the levels of HDPs.