Deficient expression of bactericidal/permeability-increasing protein in immunocompromised hosts: translational potential of replacement therapy

A Polymorphism of Bactericidal/Permeability-Increasing Protein Affects Its Neutralization Efficiency towards Lipopolysaccharide

Gram-negative sepsis driven by lipopolysaccharide (LPS) has detrimental outcomes, especially in neonates. The neutrophil-derived bactericidal/permeability-increasing protein (BPI) potently neutralizes LPS. Interestingly, polymorphism of the BPI gene at position 645 (rs4358188) corresponds to a favorable survival rate of these patients in the presence of at least one allele 645 A as opposed to 645 G. When we exploited the existing X-ray crystal structure, the corresponding amino acid at position 216 was revealed as surface exposed and proximal to the lipid-binding pocket in the N-terminal domain of BPI. Our further analysis predicted a shift in surface electrostatics by a positively charged lysine (BPI_216K) exchanging a negatively charged glutamic acid (BPI_216E). To investigate differences in interaction with LPS, we expressed both BPI variants recombinantly. The amino acid exchange neither affected affinity towards LPS nor altered bactericidal activity. However, when stimulating human peripheral blood mononuclear cells, BPI_216K exhibited a superior LPS-neutralizing capacity (IC₅₀ 12.0 ± 2.5 pM) as compared to BPI_216E (IC₅₀ 152.9 ± 113.4 pM, p = 0.0081) in respect to IL-6 secretion. In conclusion, we provide a functional correlate to a favorable outcome of sepsis in the presence of BPI_216K.

Transcriptome Differences Suggest Novel Mechanisms for Intrauterine Growth Restriction Mediated Dysfunction in Small Intestine of Neonatal Piglets

Impaired intestinal function is frequently detected in newborns with intrauterine growth restriction (IUGR), whereas the mechanism between transcriptome profiles and small intestinal dysfunction is still unclear. Therefore, this study was conducted by using IUGR neonatal piglets to uncover the mechanism underlying intestinal dysfunction. Neonatal piglets with IUGR and normal birth weight (NBW) were sacrificed at birth. Transcriptomic sequencing was performed on jejunum samples and generated 18,997 and 17,531 genes in NBW and IUGR groups, respectively. A total of 10 differentially expressed genes (DEGs) were identified; of note, only seven were mapped to the genome reference database, with two up-regulated (HSF4 and NR1H4; heat shock transcription factor 4 and nuclear receptor subfamily 1 group H member 4, respectively) and five down-regulated (SLC35C1, BTNL3, BPI, NLRP6, and SLC5A8; Solute carrier family 35 member C1, butyrophilin like 3, bactericidal permeability increasing protein, NLR family pyrin domain containing 6, and solute carrier family 5 member 8, respectively). Combining an enrichment analysis and reverse transcriptase–quantitative polymerase chain reaction validation of DEGs, our results proved the lipid metabolism disorder, intestinal dysfunction, and inflammatory response in IUGR piglets. Here, IUGR piglets presented lower concentration of glucose and triglyceride and higher concentration of total cholesterol and low-density lipoprotein cholesterol in plasma, compared with NBW piglets. Histological analysis revealed decreased mucins and increased apoptosis in both jejunum and ileum for IUGR piglets. Collectively, we found that IUGR induced intestinal dysfunction by altering lipid metabolism, intestinal barrier, and inflammatory response in neonatal piglets at birth, which provides new insights into the prevention and treatment of IUGR that protects against metabolic disorders and inflammatory-related diseases.

Contribution of the Microbiota to Intestinal Homeostasis and its Role in the Pathogenesis of HIV-1 Infection

During HIV infection, massive destruction of CD4+ T cells ensues, preferentially depleting the Th17 subset at the gut-associated lymphoid tissue (GALT), leading to a loss of mucosal integrity and an increase in cell permeability. This process favors microbial translocation between the intestinal lumen and the circulatory system, contributing to persistent immune activation and chronic inflammation characteristic of HIV infection. Thus, the gut microbiota plays an integral role in maintaining the structure and function of the mucosal barrier, a critical factor for immune homeostasis. However, in the context of HIV infection, changes in the gut microbiota have been reported and have been linked to disease progression. Here, we review evidence for the role of the gut microbiota in intestinal homeostasis, its contribution to HIV pathogenesis, as well as its use in the development of therapeutic strategies.

Pilot experience with opebacan/rBPI 21 in myeloablative hematopoietic cell transplantation

Bacterial infection and inflammation contribute significantly to the morbidity and mortality of myeloablative allogeneic hematopoietic cell transplantation (HCT). Endotoxin, a component of the outer membrane of Gram-negative bacteria, is a potent inflammatory stimulus in humans. Bactericidal/permeability increasing protein (BPI), a constituent of human neutrophil granules, binds endotoxin thereby precluding endotoxin-induced inflammation and also has direct anti-infective properties against bacteria. As a consequence of myeloablative therapy used in preparation for hematopoietic cell infusion, patients experience gastrointestinal leak of bacteria and bacterial toxins into the systemic circulation and a period of inflammatory cytokine elevation associated with subsequent regimen-related toxicities.  Patients frequently become endotoxemic and febrile as well as BPI-deficient due to sustained neutropenia. To examine whether enhancing endotoxin-neutralizing and anti-infective activity by exogenous administration of a recombinant N-terminal fragment of BPI (rBPI ₂₁, generic name opebacan) might ameliorate regimen-related toxicities including infection, we recruited patients scheduled to undergo myeloablative HCT to participate in a proof-of-concept prospective phase I/II trial. After the HCT preparative regimen was completed, opebacan was initiated 18-36 hours prior to administration of allogeneic hematopoietic stem cells (defined as Day 0) and continued for 72 hours. The trial was to have included escalation of rBPI ₂₁ dose and duration but was stopped prematurely due to lack of further drug availability.  Therefore, to better understand the clinical course of opebacan-treated patients (n=6), we compared their outcomes with a comparable cohort meeting the same eligibility criteria and enrolled in a non-interventional myeloablative HCT observational study (n = 35).  Opebacan-treated participants had earlier platelet engraftment (p=0.005), mirroring beneficial effects of rBPI ₂₁ previously observed in irradiated mice, fewer documented infections (p=0.03) and appeared less likely to experience significant regimen-related toxicities (p=0.05). This small pilot experience supports the potential utility of rBPI ₂₁ in ameliorating HCT-related morbidity and merits further exploration.

Early gradual feeding with bovine colostrum improves gut function and NEC resistance relative to infant formula in preterm pigs

It is unclear when and how to start enteral feeding for preterm infants when mother's milk is not available. We hypothesized that early and slow advancement with either formula or bovine colostrum stimulates gut maturation and prevents necrotizing enterocolitis (NEC) in preterm pigs, used as models for preterm infants. Pigs were given either total parenteral nutrition (TPN, n = 14) or slowly advancing volumes (16-64 ml·kg(-1)·day(-1)) of preterm infant formula (IF, n = 15) or bovine colostrum (BC, n = 13), both given as adjunct to parenteral nutrition. On day 5, both enteral diets increased intestinal mass (27 ± 1 vs. 22 ± 1 g/kg) and glucagon-like peptide 2 release, relative to TPN (P < 0.05). The incidence of mild NEC lesions was higher in IF than BC and TPN pigs (60 vs. 0 and 15%, respectively, P < 0.05). Only the IF pigs showed reduced gastric emptying and gastric inhibitory polypeptide release, and increased tissue proinflammatory cytokine levels (IL-1β and IL-8, P < 0.05) and expression of immune-related genes (AOAH, LBP, CXCL10, TLR2), relative to TPN. The IF pigs also showed reduced intestinal villus-to-crypt ratio, lactose digestion, and some plasma amino acids (Arg, Cit, Gln, Tyr, Val), and higher intestinal permeability, compared with BC pigs (all P < 0.05). Colonic microbiota analyses showed limited differences among groups. Early feeding with formula induces intestinal dysfunction whereas bovine colostrum supports gut maturation when mother's milk is absent during the first week after preterm birth. A diet-dependent feeding guideline may be required for newborn preterm infants.

Intestinal barrier dysfunction in HIV infection: pathophysiology, clinical implications and potential therapies

INTRODUCTION

Current pathogenetic aspects on HIV infection highlight the importance of a chronic immune activation ultimately leading to T lymphocyte homeostasis disruption and immune deregulation associated with disease manifestations and progression. It is widely accepted that this continuous immune activation in HIV infection is principally driven by the phenomenon of pathological microbial translocation (MT).

METHODS

Review of the literature on the role of intestinal barrier dysfunction in HIV infection, with emphasis on the implicated pathophysiological mechanisms, clinical implications and potentially effective therapeutic interventions.

FINDINGS

MT in HIV infection is promoted by a multifactorial disruption of all major levels comprising the intestinal barrier defense. Specifically, HIV infection disrupts the integrity of the intestinal biological (quantitative and qualitative alterations of gut microecology, overgrowth of pathogenic bacteria), immune (depletion of CD4(+) T cells, especially Th17 cells, increased CD4+ FoxP3+ Tregs, decreased mucosal macrophages phagocytic capacity, development of intestinal proinflammatory milieu) and mechanical barrier (enterocytes' apoptosis, disruption of tight junctions). Intestinal barrier dysfunction allows the passage of microbes and immunostimulatory bioproducts from the gut lumen first in the lamina propria and thereafter in the systemic circulation, thus continuously promoting a local and systemic inflammatory response. This chronic immune activation is associated with HIV disease progression, suboptimal response to HAART and development of non-AIDS comorbidities.

CONCLUSIONS

We have reached a point where the effective control of HIV viremia by HAART should be combined with emerging pharmacological approaches aiming at the restoration of the intestinal barrier, targeting its diverse levels of structure and function. Elimination of the MT phenomenon would mitigate its effect on immune homeostasis, which might improve the prognosis of the HIV-infected patient in terms of morbidity and mortality.

Identification of single nucleotide polymorphisms in hematopoietic cell transplant patients affecting early recognition of, and response to, endotoxin

Hematopoietic cell transplant (HCT) is a life-saving therapy for many malignant and non-malignant bone marrow diseases. Associated morbidities are often due to transplant-related toxicities and infections, exacerbated by regimen-induced immune suppression and systemic incursion of bacterial products. Patients undergoing myeloablative conditioning for HCT become endotoxemic and display blood/plasma changes consistent with lipopolysaccharide (LPS)-induced systemic innate immune activation. Herein, we addressed whether patients scheduled for HCT display differences in recognition/response to LPS ex vivo traceable to specific single nucleotide polymorphisms (SNPs). Two SNPs of LPS binding protein (LBP) were associated with changes in plasma LBP levels, with one LBP SNP also associating with differences in efficiency of extraction and transfer of endotoxin to myeloid differentiation factor-2 (MD-2), a step needed for activation of TLR4. None of the examined SNPs of CD14, bactericidal/permeability-increasing protein (BPI), TLR4 or MD-2 were associated with corresponding protein plasma levels or endotoxin delivery to MD-2, but CD14 and BPI SNPs significantly associated with differences in LPS-induced TNF-α release ex vivo and infection frequency, respectively. These findings suggest that specific LBP, CD14 and BPI SNPs might be contributory assessments in studies where clinical outcome may be affected by host response to endotoxin and bacterial infection.

Bactericidal/permeability-increasing protein in the reproductive system of male mice may be involved in the sperm-oocyte fusion

Bactericidal/permeability-increasing protein (BPI) is a 455-residue (∼55 kDa) protein found mainly in the primary (azurophilic) granules of human neutrophils. BPI is an endogenous antibiotic protein that belongs to the family of mammalian lipopolysaccharide (LPS)-binding and lipid transport proteins. Its major function is to kill Gram-negative bacteria, thereby protecting the host from infection. In addition, BPI can inhibit angiogenesis, suppress LPS-mediated platelet activation, increase DNA synthesis, and activate ERK/Akt signaling. In this study, we found that Bpi was expressed in the testis and epididymis but not in the seminal vesicles, prostate, and solidification glands. BPI expression in the epididymis increased upon upregulation of testosterone, caused by injection of GNRH. In orchidectomized mice, BPI expression was significantly reduced, but its expression was restored to 30% of control levels in orchidectomized mice that received supplementary testosterone. The number of sperm fused per egg significantly decreased after incubation with anti-BPI antiserum. These results suggest that BPI may take part in the process of sperm-oocyte fusion and play a unique and significant role in reproduction.

Decreased pattern recognition receptor signaling, interferon-signature, and bactericidal/permeability-increasing protein gene expression in cord blood of term low birth weight human newborns

Background

Morbidity and mortality rates of low birth weight (LBW) newborns at term are higher than rates in normal birth weight (NBW) newborns. LBW newborns are at greater risk to acquire recurrent bacterial and viral infections during their first few weeks of life possibly as an outcome of compromised innate immune functions. As adaptive immunity is in a naive state, increased risk of infection of LBW as compared to NBW newborns may reflect impairments in innate immunity.

Methodology

To characterize the increased susceptibility to infections in LBW newborns we used microarray technology to identify differences in gene expression in LBW newborns (n = 8) compared to NBW newborns (n = 4) using cord blood. The results obtained from the microarray study were validated on a larger number of samples using real time RT-PCR (LBW = 22, NBW = 18) and western blotting (LBW = 12, NBW = 12). The Interferome database was used to identify interferon (IFN) signature genes and ingenuity pathway analysis identified canonical pathways and biological functions associated with the differentially expressed genes in LBW newborns. ELISAs for IFNs and bactericidal/permeability-increasing protein were performed in both LBW and NBW newborns and in adults (LBW = 18, NBW = 18, Adults  = 8).

Principal Findings

Upon microarray analysis, we identified 1,391 differentially expressed genes, of which, 1,065 genes were down-regulated and 326 genes were up-regulated in the LBW compared to NBW newborns. Of note, 70 IFN-signature genes were found to be significantly down-regulated in LBW compared to NBW newborns. Ingenuity pathway analysis revealed pattern recognition receptors signaling including Toll-Like Receptors (TLRs) -1, -5, and -8 genes and IFN signaling as the most significantly impacted pathways. Respiratory infectious diseases were the most significantly affected bio-functions in LBW newborns.

Conclusion and Significance

Diminished PRRs, IFN-signature, and BPI gene expression raises the possibility that impairments in these pathways contribute to the susceptibility of LBW term infants to infection.

Lipoxin A₄ and 15-epi-lipoxin A₄ protect against experimental cerebral malaria by inhibiting IL-12/IFN-γ in the brain

Cerebral malaria is caused by infection with Plasmodium falciparum and can lead to severe neurological manifestations and predominantly affects sub-Saharan African children. The pathogenesis of this disease involves unbalanced over-production of pro-inflammatory cytokines. It is clear that signaling though IL-12 receptor is a critical step for development of cerebral malaria, IL-12 genetic deficiency failed to show the same effect, suggesting that there is redundancy among the soluble mediators which leads to immunopathology and death. Consequently, counter-regulatory mediators might protect the host during cerebral malaria. We have previously showed that endogenously produced lipoxins, which are anti-inflammatory mediators generated by 5-lipoxygenase (5-LO)-dependent metabolism of arachidonic acid, limit host damage in a model of mouse toxoplasmosis. We postulated here that lipoxins might also play a counter-regulatory role during cerebral malaria. To test this hypothesis, we infected 5-LO-deficient hosts with P. berghei ANKA strain, which induces a mouse model of cerebral malaria (ECM). Our results show accelerated mortality concomitant with exuberant IL-12 and IFN-γ production in the absence of 5-lipoxygenase. Moreover, in vivo administration of lipoxin to 5-LO-deficient hosts prevented early mortality and reduced the accumulation of CD8⁺IFN-γ⁺ cells in the brain. Surprisingly, WT animals treated with lipoxin either at the time of infection or 3 days post-inoculum also showed prolonged survival and diminished brain inflammation, indicating that although protective, endogenous lipoxin production is not sufficient to optimally protect the host from brain damage in cerebral malaria. These observations establish 5-LO/LXA₄ as a host protective pathway and suggest a new therapeutic approach against human cerebral malaria (HCM). (255 words).

Plasma-mediated immune suppression: a neonatal perspective

Plasma is a rich mixture of immune regulatory factors that shape immune cell function. This immunomodulatory role of plasma is especially important in neonates. To maintain in utero feto-maternal tolerance and to allow for microbial colonization after birth, the neonatal immune system is biased against pro-inflammatory responses while favoring immune suppression. Therefore, the neonatal period provides a unique opportunity to study the physiologic mechanisms regulating the immune system. Several recent studies in neonates have identified plasma factors that play a key role in immune regulation. Insight into immune regulation by neonatal and adult plasma may have clinical implications, because plasma is easily accessible, affordable, and widely available. Herein, we review plasma-mediated immune regulation, with specific focus on neonatal plasma. We discuss how immune suppression is a key function of plasma and provide a systematic overview of the published literature regarding plasma-derived immune suppressive proteins, lipids, purines, and sugars. Finally, we outline how immune regulation by these factors, which are particularly abundant in neonatal plasma, may eventually be used to treat immune-mediated diseases, such as autoimmune, allergic, and inflammatory diseases.

Role of innate immunity in neonatal infection

Newborns are at increased risk of infection due to genetic, epigenetic, and environmental factors. Herein we examine the roles of the neonatal innate immune system in host defense against bacterial and viral infections. Full-term newborns express a distinct innate immune system biased toward T(H)2-/T(H)17-polarizing and anti-inflammatory cytokine production with relative impairment in T(H)1-polarizing cytokine production that leaves them particularly vulnerable to infection with intracellular pathogens. In addition to these distinct features, preterm newborns also have fragile skin, impaired T(H)17-polarizing cytokine production, and deficient expression of complement and of antimicrobial proteins and peptides (APPs) that likely contribute to susceptibility to pyogenic bacteria. Ongoing research is identifying APPs, including bacterial/permeability-increasing protein and lactoferrin, as well as pattern recognition receptor agonists that may serve to enhance protective newborn and infant immune responses as stand-alone immune response modifiers or vaccine adjuvants.

Innate immune activation in neonatal tracheal aspirates suggests endotoxin-driven inflammation

BACKGROUND

Tracheal aspirates (TAs) from critically ill neonates accumulate bacterial endotoxin and demonstrate mobilization of endotoxin-binding proteins, but the potential bioactivity of endotoxin in TAs is unknown. We characterized innate immune activation in TAs of mechanically ventilated neonates.

METHODS

Innate immune activation in TAs of mechanically ventilated neonates was characterized using a targeted 84-gene quantitative real-time (qRT) PCR array. Protein expression of cytokines was confirmed by multiplex assay. Expression and localization of the endotoxin-inducible antimicrobial protein Calgranulin C (S100A12) was assessed by flow cytometry. Endotoxin levels were measured in TA supernatants using the Limulus amoebocyte lysate assay.

RESULTS

Analyses by qRT-PCR demonstrated expression of pattern recognition receptors, Toll-like receptor-nuclear factor κB and inflammasome pathways, cytokines/chemokines and their receptors, and anti-infective proteins in TA cells. Endotoxin positivity increased with postnatal age. As compared with endotoxin-negative TAs, endotoxin-positive TAs demonstrated significantly greater tumor necrosis factor (TNF), interleukin (IL)-6, IL-10, and serpin peptidase inhibitor, clade E, member 1 (SERPINE1) mRNA, and IL-10, TNF, and IL-1β protein. Expression of S100A12 protein was localized to TA neutrophils.

CONCLUSION

Correlation of endotoxin with TA inflammatory responses suggests endotoxin bioactivity and the possibility that endotoxin antagonists could mitigate pulmonary inflammation and its sequelae in this vulnerable population.

17(R)-Resolvin D1 differentially regulates TLR4-mediated responses of primary human macrophages to purified LPS and live E. coli

Detection and clearance of bacterial infection require balanced effector and resolution signals to avoid chronic inflammation. Detection of GNB LPS by TLR4 on m induces inflammatory responses, contributing to chronic inflammation and tissue injury. LXs and Rvs are endogenous lipid mediators that enhance resolution of inflammation, and their actions on primary human m responses toward GNB are largely uncharacterized. Here, we report that LXA(4), LXB(4), and RvD1, tested at 0.1-1 μM, inhibited LPS-induced TNF production from primary human m, with ATL and 17(R)-RvD1, demonstrating potent inhibition at 0.1 μM. In addition, 17(R)-RvD1 inhibited LPS-induced primary human m production of IL-7, IL-12p70, GM-CSF, IL-8, CCL2, and MIP-1α without reducing that of IL-6 or IL-10. Remarkably, when stimulated with live Escherichia coli, m treated with 17(R)-RvD1 demonstrated increased TNF production and enhanced internalization and killing of the bacteria. 17(R)-RvD1-enhanced TNF, internalization, and killing were not evident for an lpxM mutant of E. coli expressing hypoacylated LPS with reduced inflammatory activity. Furthermore, 17(R)-RvD1-enhanced, E. coli-induced TNF production was evident in WT but not TLR4-deficient murine m. Thus, Rvs differentially modulate primary human m responses to E. coli in an LPS- and TLR4-dependent manner, such that this Rv could promote resolution of GNB/LPS-driven inflammation by reducing m proinflammatory responses to isolated LPS and increasing m responses important for clearance of infection.