Use of animal model of sepsis to evaluate novel herbal therapies

Survival and Pulmonary Injury After Neonatal Sepsis: PD1/PDL1's Contributions to Mouse and Human Immunopathology

Morbidity and mortality associated with neonatal sepsis remains a healthcare crisis. PD1-/- neonatal mice endured experimental sepsis, in the form of cecal slurry (CS), and showed improved rates of survival compared to wildtype (WT) counterparts. End-organ injury, particularly of the lung, contributes to the devastation set forth by neonatal sepsis. PDL1-/- neonatal mice, in contrast to PD1-/- neonatal mice did not have a significant improvement in survival after CS. Because of this, we focused subsequent studies on the impact of PD1 gene deficiency on lung injury. Here, we observed that at 24 h post-CS (but not at 4 or 12 h) there was a marked increase in pulmonary edema (PE), neutrophil influx, myeloperoxidase (MPO) levels, and cytokine expression sham (Sh) WT mice. Regarding pulmonary endothelial cell (EC) adhesion molecule expression, we observed that Zona occludens-1 (ZO-1) within the cell shifted from a membranous location to a peri-nuclear location after CS in WT murine cultured ECs at 24hrs, but remained membranous among PD1-/- lungs. To expand the scope of this inquiry, we investigated human neonatal lung tissue. We observed that the lungs of human newborns exposed to intrauterine infection had significantly higher numbers of PD1+ cells compared to specimens who died from non-infectious causes. Together, these data suggest that PD1/PDL1, a pathway typically thought to govern adaptive immune processes in adult animals, can modulate the largely innate neonatal pulmonary immune response to experimental septic insult. The potential future significance of this area of study includes that PD1/PDL1 checkpoint proteins may be viable therapeutic targets in the septic neonate.

Narciclasine improves outcome in sepsis among neonatal rats via inhibition of calprotectin and alleviating inflammatory responses

Sepsis is associated with exacerbated inflammatory response which subsequently results in multiple organ dysfunction. Sepsis accounts for high mortality and morbidity among newborns worldwide. Narciclasine is a plant alkaloid which has shown to possess anti-inflammatory properties. In this study we investigated the effect and mechanism of action of narciclasine in neonatal sepsis rat models. The excessive release of S100A8/A9 or calprotectin in neonatal sepsis could be detrimental as it could exacerbate the inflammatory responses. We found that narciclasine significantly reduced the plasma levels of S100A8/A9 and also suppressed its expression in the liver and lung. The systemic and local bacterial load was also reduced in the narciclasine treated rats. The systemic and local production of pro-inflammatory cytokines in plasma and organs (liver and lungs) was significantly reduced in the narciclasine treated rats. The histopathological studies showed that narciclasine prevents the organ damage associated with sepsis and improved the survival of neonatal rats. Sepsis increased the phosphorylated NF-κβ p65 protein expression in the liver. Narciclasine suppressed the phosphorylation of NF-κβ p65 and the degradation of NF-κβ inhibitory protein alpha. It could also suppress the expression of adaptor proteins of the toll like receptor signaling pathway viz., myeloid differentiation factor 88 (MyD88), Interleukin-1 receptor-associated kinase 1 (IRAK1) and TNF receptor associated factor 6 (TRAF6). These results suggest that narciclasine protects against sepsis in neonatal rats through the inhibition of calprotectin, pro-inflammatory cytokines and suppression of NF-κβ signaling pathway.

Xenobiotic receptors in mediating the effect of sepsis on drug metabolism

Sepsis is an infection-induced systemic inflammatory syndrome. The immune response in sepsis is characterized by the activation of both proinflammatory and anti-inflammatory pathways. When sepsis occurs, the expression and activity of many inflammatory cytokines are markedly affected. Xenobiotic receptors are chemical-sensing transcription factors that play essential roles in the transcriptional regulation of drug-metabolizing enzymes (DMEs). Xenobiotic receptors mediate the functional crosstalk between sepsis and drug metabolism because the inflammatory cytokines released during sepsis can affect the expression and activity of xenobiotic receptors and thus impact the expression and activity of DMEs. Xenobiotic receptors in turn may affect the clinical outcomes of sepsis. This review focuses on the sepsis-induced inflammatory response and xenobiotic receptors such as pregnane X receptor (PXR), aryl hydrocarbon receptor (AHR), glucocorticoid receptor (GR), and constitutive androstane receptor (CAR), DMEs such as CYP1A, CYP2B6, CYP2C9, and CYP3A4, and drug transporters such as p-glycoprotein (P-gp), and multidrug resistance-associated protein (MRPs) that are affected by sepsis. Understanding the xenobiotic receptor-mediated effect of sepsis on drug metabolism will help to improve the safe use of drugs in sepsis patients and the development of new xenobiotic receptor-based therapeutic strategies for sepsis.

Pre-B cell leukemia transcription factor 3 induces inflammatory responses in human umbilical vein endothelial cells and murine sepsis via acting a competing endogenous RNA for high mobility group box 1 protein

The present study investigated the roles of pre-B cell leukemia transcription factor 3 (PBX3) in sepsis. Reverse transcription-quantitative polymerase chain reaction and western blot analysis indicated that overexpression of the PBX 3′-untranslated region (UTR) promoted high mobility group box 1 (HMGB1) protein expression in human umbilical vein endothelial cells (HUVECs) (P<0.01). Furthermore, post-treatment of PBX3 small interfering (si)RNA suppressed lipopolysaccharide (LPS)-mediated HMGB1 release and attenuated HMGB1-mediated hyperpermeability and leukocyte migration in HUVECs and septic mice (P<0.01). Additionally, post-injection of PBX3 siRNA also induced the downregulation of cecal ligation and puncture-induced HMGB1 release, production of IL-6 and mortality (P<0.01). Mechanistically, the 3′UTRs of PBX3 and HMGB1 were identified to harbor six common micro (mi)RNA binding sites, and PBX 3′UTR increased HMGB1 expression in a 3′UTR- and miRNA-dependent manner. Notably, the coding sequence of PBX3 did not increase HMGB1 expression in HUVECs. Collectively, the present study indicates that PBX 3′UTR may induce inflammatory responses and sepsis via acting as a competing endogenous RNA for HMGB1.

EGCG induces G-CSF expression and neutrophilia in experimental sepsis

A major green tea component, epigallocatechin-3-gallate (EGCG), has been proven protective against lethal sepsis in experimental setting, but its protective mechanisms remain incompletely understood. Here, we provide evidence to support EGCG's capacities in stimulating G-CSF production and neutrophilia in vivo. In an animal model of sepsis, EGCG significantly elevated peritoneal levels of G-CSF and several chemokines (e.g., MCP-1/CCL2 and MIP-1γ/CCL9), and consequently increased peritoneal neutrophil numbers (neutrophilia) at a late stage. In vitro, EGCG divergently affected HMGB1-mediated production of several chemokines: reducing CXCL15 and RANTES/CCL5, but elevating G-CSF and MIP-1α/CCL3 production by peritoneal macrophages. Similarly, it significantly induced the expression and secretion of G-CSF and MIP-1α/CCL3 in human peripheral blood mononuclear cells. Based on our preliminary data, it may be important to search for anti-inflammatory and G-CSF-stimulating agents for the clinical management of inflammatory diseases.

Serum Amyloid A Stimulates PKR Expression and HMGB1 Release Possibly through TLR4/RAGE Receptors

Serum amyloid A (SAA) proteins are known to be surrogate markers of sepsis, but their pathogenic roles remain poorly elucidated. Here we provide evidence to support a possible role of SAA as a pathogenic mediator of lethal sepsis. In a subset of septic patients for which serum high mobility group box 1 (HMGB1) levels paralleled the clinical scores, some anti-HMGB1 antibodies detected a 12-kDa protein belonging to the SAA family. In contrast to the most abundant SAA1, human SAA induced double-stranded RNA-activated protein kinase R (PKR) expression and HMGB1 release in the wild-type, but not toll-like receptor 4/receptor for advanced glycation end products (TLR4/RAGE)-deficient, macrophages. Pharmacological inhibition of PKR phosphorylation blocked SAA-induced HMGB1 release, suggesting an important role of PKR in SAA-induced HMGB1 release. In animal models of lethal endotoxemia and sepsis, recombinant SAA exacerbated endotoxemic lethality, whereas SAA-neutralizing immunoglobulins G (IgGs) significantly improved animal survival. Collectively, these findings have suggested SAA as an important mediator of inflammatory diseases. Highlights of this study include: human SAA is possibly only expressed in a subset of septic patients; SAA induces HMGB1 release via TLR4 and RAGE receptors; SAA supplementation worsens the outcome of lethal endotoxemia; whereas SAA-neutralizing antibodies confer protection against lethal endotoxemia and sepsis.

Green tea catechins quench the fluorescence of bacteria-conjugated Alexa fluor dyes

Accumulating evidence suggests that Green tea polyphenolic catechins, especially the (-)-epigallocatechin gallate (EGCG), can be cross-linked to many proteins, and confer a wide range of anti-bacterial activities possibly by damaging microbial cytoplasmic lipids and proteins. At the doses that conferred protection against lethal polymicrobial infection (induced by cecal ligation and puncture), EGCG significantly reduced bacterial loads particularly in the liver and lung. To elucidate its bactericidal mechanisms, we determined whether EGCG affected the fluorescence intensities of bacteria-conjugated Alexa Fluor 488 or 594 dyes. When mixed with unconjugated Alexa Fluor 488 or 594 dyes, EGCG or analogs did not affect the fluorescence intensity of these dyes. In a sharp contrast, EGCG and some analogs (e.g., Catechin Gallate, CG), markedly reduced the fluorescence intensity of Gram-positive Staphylococcus aureus-conjugated Alexa 594 and Gram-negative Escherichia coli-conjugated Alexa 488. Interestingly, co-treatment with ethanol impaired the EGCG-mediated fluorescence quenching of the G(+) S. aureus, but not of the G(-) E. coli-conjugated Alexa Flour dyes. In light of the notion that Alexa Fluor dyes can be quenched by aromatic amino acids, it is plausible that EGCG exerts antimicrobial activities possibly by altering microbial protein conformations and functions. This possibility can now be explored by screening other fluorescence-quenching agents for possible antimicrobial activities.

Targeting HMGB1 in the treatment of sepsis

INTRODUCTION

Sepsis refers to the host's deleterious and non-resolving systemic inflammatory response to microbial infections and represents the leading cause of death in the intensive care unit. The pathogenesis of sepsis is complex, but partly mediated by a newly identified alarmin molecule, the high mobility group box 1 (HMGB1).

AREAS COVERED

Here we review the evidence that support extracellular HMGB1 as a late mediator of experimental sepsis with a wider therapeutic window and discuss the therapeutic potential of HMGB1-neutralizing antibodies and small molecule inhibitors (herbal components) in experimental sepsis.

EXPERT OPINION

It will be important to evaluate the efficacy of HMGB1-targeting strategies for the clinical management of human sepsis in the future.

Carbenoxolone blocks endotoxin-induced protein kinase R (PKR) activation and high mobility group box 1 (HMGB1) release

The pathogen- and damage-associated molecular patterns (for example, bacterial endotoxin and adenosine 5'-triphosphate [ATP]) activate the double-stranded RNA-activated protein kinase R (PKR) to trigger the inflammasome-dependent high mobility group box 1 (HMGB1) release. Extracellular ATP contributes to the inflammasome activation through binding to the plasma membrane purinergic P2X7 receptor (P2X7R), triggering the opening of P2X7R channels and the pannexin-1 (panx-1) hemichannels permeable for larger molecules up to 900 daltons. It was previously unknown whether panx-1 channel blockers can abrogate lipopolysaccharide (LPS)-induced PKR activation and HMGB1 release in innate immune cells. Here we demonstrated that a major gancao (licorice) component (glycyrrhizin, or glycyrrhizic acid) derivative, carbenoxolone (CBX), dose dependently abrogated LPS-induced HMGB1 release in macrophage cultures with an estimated IC50 ≈ 5 μmol/L. In an animal model of polymicrobial sepsis (induced by cecal ligation and puncture [CLP]), repetitive CBX administration beginning 24 h after CLP led to a significant reduction of circulating and peritoneal HMGB1 levels, and promoted a significant increase in animal survival rates. As did P2X7R antagonists (for example, oxidized ATP, oATP), CBX also effectively attenuated LPS-induced P2X7R/panx-1 channel activation (as judged by Lucifer Yellow dye uptake) and PKR phosphorylation in primary peritoneal macrophages. Collectively, these results suggested that CBX blocks LPS-induced HMGB1 release possibly through impairing PKR activation, supporting the involvement of PKR in the regulation of HMGB1 release.

It Is Not Just Folklore: The Aqueous Extract of Mung Bean Coat Is Protective against Sepsis

Mung bean (Vigna Radiata) has been traditionally used in China both as nutritional food and herbal medicine against a number of inflammatory conditions since the 1050s. A nucleosomal protein, HMGB1, has recently been established as a late mediator of lethal systemic inflammation with a relatively wider therapeutic window for pharmacological interventions. Here we explored the HMGB1-inhibiting capacity and therapeutic potential of mung bean coat (MBC) extract in vitro and in vivo. We found that MBC extract dose-dependently attenuated LPS-induced release of HMGB1 and several chemokines in macrophage cultures. Oral administration of MBC extract significantly increased animal survival rates from 29.4% (in saline group, N = 17 mice) to 70% (in experimental MBC extract group, N = 17 mice, P < 0.05). In vitro, MBC extract stimulated HMGB1 protein aggregation and facilitated both the formation of microtubule-associatedprotein-1-light-chain-3-(LC3-)containing cytoplasmic vesicles, and the production of LC3-II in macrophage cultures. Consequently, MBC extract treatment led to reduction of cellular HMGB1 levels in macrophage cultures, which was impaired by coaddition of two autophagy inhibitors (bafilomycin A1 and 3-methyladenine). Conclusion. MBC extract is protective against lethal sepsis possibly by stimulating autophagic HMGB1 degradation.