Up-regulation of histamine H4 receptors contributes to splenic apoptosis in septic mice: counteraction of the antiapoptotic action of nuclear factor-kappaB

Immunosuppression in Sepsis: Biomarkers and Specialized Pro-Resolving Mediators

Severe infection can lead to sepsis. In sepsis, the host mounts an inappropriately large inflammatory response in an attempt to clear the invading pathogen. This sustained high level of inflammation may cause tissue injury and organ failure. Later in sepsis, a paradoxical immunosuppression occurs, where the host is unable to clear the preexisting infection and is susceptible to secondary infections. A major issue with sepsis treatment is that it is difficult for physicians to ascertain which stage of sepsis the patient is in. Sepsis treatment will depend on the patient's immune status across the spectrum of the disease, and these immune statuses are nearly polar opposites in the early and late stages of sepsis. Furthermore, there is no approved treatment that can resolve inflammation without contributing to immunosuppression within the host. Here, we review the major mechanisms of sepsis-induced immunosuppression and the biomarkers of the immunosuppressive phase of sepsis. We focused on reviewing three main mechanisms of immunosuppression in sepsis. These are lymphocyte apoptosis, monocyte/macrophage exhaustion, and increased migration of myeloid-derived suppressor cells (MDSCs). The biomarkers of septic immunosuppression that we discuss include increased MDSC production/migration and IL-10 levels, decreased lymphocyte counts and HLA-DR expression, and increased GPR18 expression. We also review the literature on the use of specialized pro-resolving mediators (SPMs) in different models of infection and/or sepsis, as these compounds have been reported to resolve inflammation without being immunosuppressive. To obtain the necessary information, we searched the PubMed database using the keywords sepsis, lymphocyte apoptosis, macrophage exhaustion, MDSCs, biomarkers, and SPMs.

[Vascular hyperpermeable molecules potentially contributing to the development of pulmonary edema in sepsis-associated ARDS]

The acute respiratory distress syndrome (ARDS) is an important cause of respiratory failure in critically ill patients and may become a life-threatening condition where inflammation of the lungs may begin in one lung but eventually affects both, leading to damage to the alveoli and surrounding small blood vessels. ARDS is particularly characterized by noncardiogenic pulmonary edema caused by an increase in pulmonary capillary permeability. Several clinical disorders can precipitate in ARDS, including pneumonia, sepsis, aspiration of gastric contents, and major trauma. The most common cause of ARDS is sepsis, which is a serious and widespread infection of the bloodstream and is now defined as life-threatening organ dysfunction due to a dysregulated reponse of the host to infection. In sepsis, a number of vascular hyperpermeable factors, such as histamine, nitric oxide, thromboxane A₂, and vascular endothelial growth factor, can be overproducted and contribute to the development of pulmonary edema. Given that sepsis can be regarded as a gene-related disorder, the nucleic-acid based gene therapeutic strategy to regulate some transcription factors involved in expression of vascular hyperpermeable genes may be considered to be a promising novel approach for treatment of ARDS in sepsis.

The Critical Roles and Mechanisms of Immune Cell Death in Sepsis

Sepsis was first described by the ancient Greek physicians over 2000 years ago. The pathophysiology of the disease, however, is still not fully understood and hence the mortality rate is still unacceptably high due to lack of specific therapies. In the last decade, great progress has been made by shifting the focus of research from systemic inflammatory response syndrome (SIRS) to multiple organ dysfunction syndrome (MODS). Sepsis has been re-defined as infection-induced MODS in 2016. How infection leads to MODS is not clear, but what mediates MODS becomes the major topic in understanding the molecular mechanisms and developing specific therapies. Recently, the mechanism of infection-induced extensive immune cell death which releases a large quantity of damage-associated molecular patterns (DAMPs) and their roles in the development of MODS as well as immunosuppression during sepsis have attracted much attention. Growing evidence supports the hypothesis that DAMPs, including high-mobility group box 1 protein (HMGB1), cell-free DNA (cfDNA) and histones as well as neutrophil extracellular traps (NETs), may directly or indirectly contribute significantly to the development of MODS. Here, we provide an overview of the mechanisms and consequences of infection-induced extensive immune cell death during the development of sepsis. We also propose a pivotal pathway from a local infection to eventual sepsis and a potential combined therapeutic strategy for targeting sepsis.

Nucleic-acid based gene therapy approaches for sepsis

Despite advances in overall medical care, sepsis and its sequelae continue to be an embarrassing clinical entity with an unacceptably high mortality rate. The central reason for high morbidity and high mortality of sepsis and its sequelae is the lack of an effective treatment. Previous clinical trials have largely failed to identify an effective therapeutic target to improve clinical outcomes in sepsis. Thus, the key goal favoring the outcome of septic patients is to devise innovative and evolutionary therapeutic strategies. Gene therapy can be considered as one of the most promising novel therapeutic approaches for nasty disorders. Since a number of transcription factors, such as nuclear factor-κB (NF-κB) and activator protein-1 (AP-1), play a pivotal role in the pathophysiology of sepsis that can be characterized by the induction of multiple genes and their products, sepsis may be regarded as a gene-related disorder and gene therapy may be considered a promising novel therapeutic approach for treatment of sepsis. In this review article, we provide an up-to-date summary of the gene-targeting approaches, which have been developed in animal models of sepsis. Our review sheds light on the molecular basis of sepsis pathology for the development of novel gene therapy approaches and leads to the conclusion that future research efforts may fully take into account gene therapy for the treatment of sepsis.

[Role of histamine in sepsis-induced organ dysfunction: study using knockout mice of histamine-related genes]

Sepsis is the leading cause of death in critically ill patients, and its incidence continues to rise. Sepsis is now defined as life-threatening organ dysfunction due to a dysregulated host response to infection. Histamine assumes a critical role as a major mediator of many pathologic disorders with inflammation and immune reactions. However, direct evidence has not been provided showing the involvement of histamine in the development of multiple organ dysfunction or failure in sepsis. We have found that sepsis-induced major end-organ (lung, liver, and kidney) injury is attenuated in histidine decarboxylase (HDC) gene knockout mice. H1/H2-receptor gene-double knockout mice apparently behave similar to HDC knockout mice in reducing sepsis-related pathologic changes. Here we provide an overview on the role of endogenous histamine as an aggregating mediator that could contribute to the development of major end-organ injury in sepsis.

Modulation of Dendritic Cell Apoptosis and CD8+ Cytotoxicity by Histamine: Role of Protein Kinase C

Dendritic cells (DC) are able to present extracellular antigens associated with the molecules of the major histocompatibility complex class I. In a previous work, we demonstrated that the histamine (HIS), acting through H1/H4 receptors, increases the cross-presentation of soluble ovalbumin by murine DC and can enhance the recruitment of specific CD8⁺ T lymphocytes during the development of chronic inflammatory responses. Here, we studied in more depth the mechanisms underlying this enhancement. We showed that the cytotoxicity of specific CD8⁺ lymphocytes is increased in HIS-treated DC and it is lost by inhibition of vacuolar-ATPase that prevents endosome acidification. It is known that HIS acts through G protein-coupled receptors. The H1/H4 receptors are associated with a G_q subunit, which involves PKC signaling, a pathway related to the apoptotic process. Interestingly, we demonstrated for the first time that HIS prevents DC apoptosis induced by heat shock through the inhibition of caspase-3, a mechanism dependent on PKC activation, since it is reversed by its inhibition. By contrast, cytolytic activity of T lymphocytes induced by HIS-stimulated DC was independent of PKC pathway.

Higher serum caspase-cleaved cytokeratin-18 levels during the first week of sepsis diagnosis in non-survivor patients

Background:

Caspase-cleaved cytokeratin (CCCK)-18 is a protein released into the blood during apoptosis. Higher circulating CCCK-18 concentrations have been found in non-survivor than in survivor septic patients at moment of sepsis diagnosis. The following questions arise now: (1) How are serum CCCK-18 levels during the first week of sepsis? (2) Is there an association between sepsis severity and mortality and serum CCCK-18 levels during the first week? The aims of this study were to answer these questions.

Methods:

Multicenter study with 321 severe septic patients from eight Spanish intensive care units. We determined serum concentration of CCCK-18, tumor necrosis factor (TNF)-α, and interleukin (IL)-10 during the first week. Our end-point study was 30-day mortality.

Results:

Non-survivor (n=108) compared to survivor patients (n=213) showed higher serum CCCK-18 levels at days 1, 4 and 8 (p<0.001). ROC curve analyses showed that serum CCCK-18 levels at days 1 (AUC=0.77; 95% CI=0.72–0.82), 4 (AUC=0.81; 95% CI=0.76–0.85) and 8 (AUC=0.83; 95% CI=0.78–0.88) could predict mortality at 30 days (p<0.001). Logistic regression analyses showed that serum CCCK-18 levels at days 1 (OR=4.367; 95% CI=2.491–7.659), 4 (OR=10.137; 95% CI=4.741–21.678) and 8 (OR=8.781; 95% CI=3.626–21.268) were associated with 30-day mortality (p<0.001). We found a positive correlation between CCCK-18, SOFA, and lactic acid at days 1, 4 and 8.

Conclusions:

Non-survivor septic patients showed persistently during the first week higher serum CCCK-18 levels than survivor patients, and there is an association between sepsis severity and mortality and serum CCCK-18 levels during the first week.

Critical role of endogenous histamine in promoting end-organ tissue injury in sepsis

BACKGROUND

Histamine assumes an important role as a major mediator in various pathologic disorders associated with inflammation and immune reactions. However, the involvement of histamine in the pathological conditions and symptoms of sepsis remains entirely unknown. In this study, we establish that histamine is identified as a contributory mediator to promoting the development of organ injury in sepsis.

METHODS

Histidine decarboxylase (HDC) gene knockout (HDC^-/-) mice, histamine H₁-/H₂-receptor gene-double knockout (H₁R^-/-/H₂R^-/-) mice, and their littermate wild-type (WT) C57BL/6J mice underwent cecal ligation and puncture (CLP) or sham operation. Some WT mice were injected intraperitoneally with d-chlorpheniramine and famotidine 60 min before CLP to block H₁- and H₂-receptors, respectively.

RESULTS

In mice rendered septic by CLP, tissue histamine levels were elevated in association with increased HDC expression. Sepsis-induced abnormal cytokine production and multiple organ injury (lung, liver, and kidney) were significantly less pronounced in HDC^-/- mice as compared with WT controls, and HDC deficiency had improved survival in sepsis. This benefit corresponded with a significant reduction in activation levels of the nuclear factor (NF)-κB signaling pathway. H₁R^-/-/H₂R^-/- mice apparently behaved similar to HDC knockout mice in reducing sepsis-related pathological changes. Pharmacological interventions with H₁- and H₂-receptor antagonists indicated that both H₁- and H₂-receptors were involved in septic lung and liver injury, whereas only H₂-receptors contributed to septic kidney injury.

CONCLUSIONS

In the setting of sepsis, histamine, through activation of H₁- and H₂-receptors, serves as an aggravating mediator to contribute to the development of sepsis-driven major end-organ failure.

Cellular analysis of the histamine H4 receptor in human myeloid cells

The human histamine H4 receptor (H4R) is a Gαi/o-coupled receptor which is mainly expressed on hematopoietic cells. Accordingly, the receptor is implicated in the pathology of various diseases such as autoimmune disorders, bronchial asthma and pruritus. Due to complicated receptor pharmacology, the lack of a reliable antibody and limited availability of primary cells expressing the receptor the physiology of this receptor is still poorly understood. Therefore, we aimed to assess absolute receptor mRNA expression and functionality (intracellular Ca(2+) release) in various human myeloid cell types such as granulocytes, monocytes, macrophages and dendritic cells (DCs). This was put into context with the expression of the H1R and H2R. In addition, the influence of various inflammatory stimuli on H4R expression was investigated in macrophages and monocyte-derived DCs. We found that classically activated macrophages treated with pro-inflammatory stimuli down-regulated histamine receptor mRNA expression as did LPS and zymosan A matured monocyte-derived DCs. In contrast, alternatively activated macrophages (IL-4 or IL-13) upregulated H2R and H4R expression compared to controls. Consistent with existing literature, we found eosinophils to be the major source of the H4R. Since availability of primary eosinophils is limited, we developed a cell model based on the differentiated eosinophilic cell line EOL-1, in which H4R pharmacology and physiology may be studied.

International Union of Basic and Clinical Pharmacology. XCVIII. Histamine Receptors

Histamine is a developmentally highly conserved autacoid found in most vertebrate tissues. Its physiological functions are mediated by four 7-transmembrane G protein-coupled receptors (H1R, H2R, H3R, H4R) that are all targets of pharmacological intervention. The receptors display molecular heterogeneity and constitutive activity. H1R antagonists are long known antiallergic and sedating drugs, whereas the H2R was identified in the 1970s and led to the development of H2R-antagonists that revolutionized stomach ulcer treatment. The crystal structure of ligand-bound H1R has rendered it possible to design new ligands with novel properties. The H3R is an autoreceptor and heteroreceptor providing negative feedback on histaminergic and inhibition on other neurons. A block of these actions promotes waking. The H4R occurs on immuncompetent cells and the development of anti-inflammatory drugs is anticipated.

Insights into the apoptotic death of immune cells in sepsis

Sepsis with subsequent multiple-organ dysfunction is a distinct systemic inflammatory response to concealed or obvious infection, and it is a leading cause of death in intensive care units. Thus, one of the key goals in critical care medicine is to develop novel therapeutic strategies that will affect favorably on outcome of septic patients. In addition to systemic response to infection, apoptosis is implicated to be an important mechanism of the death of immune cells, including neutrophils, macrophages, T lymphocytes, and dendritic cells, and it is usually followed by the development of multiple-organ failure in sepsis. The implication of apoptosis of immune cells is now highlighted by multiple studies that demonstrate that prevention of cell apoptosis can improve survival in relevant animal models of severe sepsis. In this review, we focus on major apoptotic death pathways and molecular mechanisms that regulate apoptosis of different immune cells, and advances in these areas that may be translated into more promising therapies for the prevention and treatment of severe sepsis.

The significance and regulatory mechanisms of innate immune cells in the development of sepsis

Sepsis with subsequent multiple organ dysfunction is a pronounced systemic inflammatory response to concealed or known infection and is a leading cause of death in intensive care units. The survival rate of severe sepsis and septic shock has not markedly improved in recent decades despite a great number of receptors and molecules involved in its pathogenesis have been found and taken as therapeutic targets. It is essential to thoroughly understand the host cell-mediated immunity involved in the development of sepsis and sepsis-related organ injury. Recent studies indicate that innate immune cells (such as neutrophils, macrophages, dendritic cells, T lymphocytes, regulatory T cells, and natural killer T cells) play pivotal roles in the maintenance of peripheral homeostasis and regulation of immune responses during sepsis. Therefore, an understanding of the biological significance and pathophysiological roles of different cell populations might gain novel insights into the immunoregulatory mechanisms of sepsis. In this review, we focus on major immune cells that may play potential roles in the contribution of new therapeutic approaches for sepsis.

Olprinone and colforsin daropate alleviate septic lung inflammation and apoptosis through CREB-independent activation of the Akt pathway

Olprinone, a specific phosphodiesterase III inhibitor, and corforsin daropate, a direct adenylate cyclase activator, are now being used in critical conditions. We investigated whether their therapeutic use provides protection against septic acute lung injury (ALI) and mortality. Polymicrobial sepsis was induced by cecal ligation and puncture (CLP) in BALB/c mice. Olprinone or colforsin daropate was continuously given through an osmotic pump that was implanted into the peritoneal cavity immediately following CLP. These treatments prevented the ALI development in CLP mice, as indicated by the findings that severe hypoxemia, increased pulmonary vascular permeability, and histological lung damage were strikingly remedied. Furthermore, continued administration of olprinone or colforsin daropate suppressed apoptosis induction in septic lungs and improved the survival of CLP mice. Olprinone and corforsin daropate enhanced Akt phosphorylation in septic lungs. Wortmannin, which inhibits the Akt upstream regulator phosphatidylinositol 3-kinase, abrogated the protective effects of olprinone and corforsin daropate on sepsis-associated lung inflammation and apoptosis. In vivo transfection of cyclic AMP response element binding protein (CREB) decoy oligodeoxynucleotide failed to negate the abilities of these agents to increase Akt phosphorylation and to inhibit IκBα degradation in septic lungs. These results demonstrate for the first time that CREB-independent Akt-mediated signaling is a critical mechanism contributing to the therapeutic effects of olprinone and corforsin daropate on septic ALI. Moreover, our data also suggest that these cyclic AMP-related agents, by blocking both nuclear factor-κB activation and apoptosis induction, may represent an effective therapeutic approach to the treatment of the septic syndrome.

Histamine H4 receptor ligands and their potential therapeutic applications: an update

INTRODUCTION

Several studies underlined the critical role of histamine H4 receptor (H4R) in inflammation, thus H4 modulators have been suggested as promising drug candidates in inflammatory diseases. First H4 ligands typically have indole or amino-pyrimidine scaffolds. During the last few years, however, serious efforts have been made to identify novel H4 chemotypes with improved pharmacodynamic and pharmacokinetic properties.

AREAS COVERED

Areas covered in this review include an overview on H4 ligands published in scientific papers, as well as in patent applications between 2009 and 2011. Recently discovered scaffolds possessing significant H4 activity were analyzed and their therapeutic potential was reviewed.

EXPERT OPINION

Recent results from the scientific literature and novel patent applications reinforce the major role of H4R in inflammatory diseases such as pruritus, asthma, inflammatory pain and allergic rhinitis. Novel studies suggest further indications of H4 modulators in cancer, neuropathic pain, vestibular disorders and type 2 diabetes. The number of active H4 chemotypes was increased significantly. The first H4 antagonist entered to clinics and the results from a proof-of-concept Phase II clinical study is expected to be disclosed soon.

Attenuated expression of HRH4 in colorectal carcinomas: a potential influence on tumor growth and progression

BACKGROUND

Earlier studies have reported the production of histamine in colorectal cancers (CRCs). The effect of histamine is largely determined locally by the histamine receptor expression pattern. Recent evidence suggests that the expression level of histamine receptor H4 (HRH4) is abnormal in colorectal cancer tissues. However, the role of HRH4 in CRC progression and its clinical relevance is not well understood. The aim of this study is to evaluate the clinical and molecular phenotypes of colorectal tumors with abnormal HRH4 expression.

METHODS

Immunoblotting, real-time PCR, immunofluorescence and immunohistochemistry assays were adopted to examine HRH4 expression in case-matched CRC samples (n = 107) and adjacent normal tissues (ANTs). To assess the functions of HRH4 in CRC cells, we established stable HRH4-transfected colorectal cells and examined cell proliferation, colony formation, cell cycle and apoptosis in these cells.

RESULTS

The protein levels of HRH4 were reduced in most of the human CRC samples regardless of grade or Dukes classification. mRNA levels of HRH4 were also reduced in both early-stage and advanced CRC samples. In vitro studies showed that HRH4 over-expression caused growth arrest and induced expression of cell cycle proteins in CRC cells upon exposure to histamine through a cAMP -dependent pathway. Furthermore, HRH4 stimulation promoted the 5-Fu-induced cell apoptosis in HRH4-positive colorectal cells.

CONCLUSION

The results from the current study supported previous findings of HRH4 abnormalities in CRCs. Expression levels of HRH4 could influence the histamine-mediated growth regulation in CRC cells. These findings suggested a potential role of abnormal HRH4 expression in the progression of CRCs and provided some new clues for the application of HRH4-specific agonist or antagonist in the molecular therapy of CRCs.

Insights into sepsis therapeutic design based on the apoptotic death pathway

Sepsis remains the leading cause of death in critically ill patients. A major problem contributing to sepsis-related high mortality is the lack of effective medical treatment. Thus, the key goal in critical care medicine is to develop novel therapeutic strategies that will impact favorably on septic patient outcome. While it is generally accepted that sepsis is an inflammatory state resulting from the systemic response to infection, apoptosis is implicated to be an important mechanism of the death of lymphocytes, gastrointestinal and lung epithelial cells, and vascular endothelial cells associated with the development of multiple organ failure in sepsis. The pivotal role of cell apoptosis is now highlighted by multiple studies demonstrating that prevention of cell apoptosis can improve survival in clinically relevant animal models of sepsis. In this review article, we address the scientific rationale for remedying apoptotic cell death in sepsis and propose that therapeutic efforts aimed at blocking cell signaling pathways leading to apoptosis may represent an attractive target for sepsis therapy.