Differential effects of glucocorticoids in the establishment and maintenance of endotoxin tolerance

Peptidome profiling for the immunological stratification in sepsis: a proof of concept study

Sepsis has been called the graveyard of pharmaceutical companies due to the numerous failed clinical trials. The lack of tools to monitor the immunological status in sepsis constrains the development of therapies. Here, we evaluated a test based on whole plasma peptidome acquired by MALDI-TOF-mass spectrometer and machine-learning algorithms to discriminate two lipopolysaccharide-(LPS) induced murine models emulating the pro- and anti-inflammatory/immunosuppression environments that can be found during sepsis. The LPS group was inoculated with a single high dose of LPS and the IS group was subjected to increasing doses of LPS, to induce proinflammatory and anti-inflammatory/immunosuppression profiles respectively. The LPS group showed leukopenia and higher levels of cytokines and tissue damage markers, and the IS group showed neutrophilia, lymphopenia and decreased humoral response. Principal component analysis of the plasma peptidomes formed discrete clusters that mostly coincided with the experimental groups. In addition, machine-learning algorithms discriminated the different experimental groups with a sensitivity of 95.7% and specificity of 90.9%. Data reveal the potential of plasma fingerprints analysis by MALDI-TOF-mass spectrometry as a simple, speedy and readily transferrable method for sepsis patient stratification that would contribute to therapeutic decision-making based on their immunological status.

Glucocorticoid-induced leucine zipper (GILZ) in immuno suppression: master regulator or bystander?

Induction of glucocorticoid-induced leucine zipper (GILZ) by glucocorticoids has been reported to be essential for their anti-inflammatory actions. At the same time, GILZ is actively downregulated under inflammatory conditions, resulting in an enhanced pro-inflammatory response. Two papers published in the recent past showed elevated GILZ expression in the late stage of an inflammation. Still, the manuscripts suggest seemingly contradictory roles of endogenous GILZ: one of them suggested compensatory actions by elevated corticosterone levels in GILZ knockout mice, while our own manuscript showed a distinct phenotype upon GILZ knockout in vivo. Herein, we discuss the role of GILZ in inflammation with a special focus on the influence of endogenous GILZ on macrophage responses and suggest a cell-type specific action of GILZ as an explanation for the conflicting results as presented in recent reports.

Glucocorticoid-Induced Leucine Zipper: A Critical Factor in Macrophage Endotoxin Tolerance

Induction of glucocorticoid-induced leucine zipper (GILZ) by glucocorticoids plays a key role in their anti-inflammatory action. In activated macrophages, GILZ levels are downregulated via tristetraprolin-mediated GILZ mRNA destabilization. To assess the functional significance of GILZ downregulation, we generated myeloid-specific GILZ knockout (KO) mice. GILZ-deficient macrophages displayed a higher responsiveness toward LPS, as indicated by increased TNF-α and IL-1β expression. This effect was due to an activation of ERK, which was significantly amplified in GILZ KO cells. The LPS-induced activation of macrophages is attenuated upon pretreatment of macrophages with low-dose LPS, an effect termed endotoxin tolerance. In LPS-tolerant macrophages, GILZ mRNA was stabilized, whereas ERK activation was strongly decreased. In contrast, GILZ KO macrophages exhibited a strongly reduced desensitization. To explore the contribution of GILZ expression in macrophages to endotoxin tolerance in vivo, we treated GILZ KO mice with repeated i.p. injections of low-dose LPS followed by treatment with high-dose LPS. LPS pretreatment resulted in reduced proinflammatory mediator expression upon high-dose LPS treatment in serum and tissues. In contrast, cytokine induction was preserved in tolerized GILZ KO animals. In summary, our data suggest that GILZ is a key regulator of macrophage functions.

Resistance of LPS-activated bone marrow derived macrophages to apoptosis mediated by dexamethasone

Glucocorticoids (GC) display pleiotropic effects on the immune system. Macrophages are a major target for GC action. Here we show that dexamethasone (DEX), a synthetic GC, decreased viability of naïve bone marrow-derived macrophages (BMDM), involving an apoptotic mechanism. Administration of DEX together with lipopolysaccharide (LPS) protected BMDM against DEX-mediated cell death, suggesting that activated BMDM respond to DEX differently than naïve BMDM. An insight to the molecular basis of LPS actions was provided by a 7 fold increase in mRNA levels of glucocorticoid receptor beta (GRβ), a GR dominant-negative splice variant which inhibits GRα's transcriptional activity. LPS did not inhibit all DEX-mediated effects on BMDM; DEX significantly reduced the percentage of BMDM expressing high levels of the cell surface markers F4/80 and CD11b and led to a decrease in macrophage inflammatory protein 1 alpha (MIP1-α) mRNA and protein levels. These two DEX-mediated effects were not prevented by LPS. Our finding that LPS did not reduce the DEX-induced elevation of glucocorticoid-induced leucine zipper (GILZ), a mediator of GCs anti-inflammatory actions, may provide an underlying mechanism. These findings enable a better understanding of clinical states, such as sepsis, in which macrophages are activated by endotoxins and treatment by GCs is considered.

Effects of promethazine or dexamethasone pretreatment on mivacurium-induced histamine release in children

OBJECTIVE

To determine the effects of pretreatment with either promethazine or dexamethasone on mivacurium-induced histamine release in children.

METHODS

Eighty ASA I-II children (4-10 years of age) scheduled for tonsillectomy and/or adenoidectomy were randomly divided into 4 groups (n = 20 per group) designated as either the rocuronium, mivacurium, dexamethasone (DXM), or promethazine group. Children in the DXM and promethazine groups were treated separately with intramuscular DXM 0.2 mg·kg(-1) or promethazine 0.5 mg·kg(-1) injections 60 min before operation. Radial artery blood samples were collected to quantify plasma histamine concentrations 1 min before and 1, 3, and 5 min after administration of the relaxant. Mean arterial pressure (MAP), heart rate (HR), and skin flushing were recorded at the same time.

RESULTS

No significant decreases in plasma histamine concentrations were observed between groups; however, more stable MAP and HR and less skin flushing were observed in DXM group participants compared with individuals in the mivacurium group (P < 0.05). By contrast, children in the promethazine group had significantly decreased plasma histamine concentrations and stable MAP and HR (without a significant increase in HR) compared with patients in mivacurium group. In addition, skin flushing was significantly decreased compared with that observed in the rocuronium group (P < 0.05).

CONCLUSIONS

Pretreatment with promethazine significantly decreased mivacurium-induced histamine release in children and provided stable hemodynamics during administration of anesthesia.

Dehydroepiandrosterone and metyrapone partially restore the adaptive humoral and cellular immune response in endotoxin immunosuppressed mice

Prior exposure to endotoxins renders the host temporarily refractory to subsequent endotoxin challenge (endotoxin tolerance). Clinically, this state has also been pointed out as the initial cause of the non-specific humoral and cellular immunosuppression described in these patients. We recently demonstrated the restoration of immune response with mifepristone (RU486), a receptor antagonist of glucocorticoids. Here we report the treatment with other modulators of glucocorticoids, i.e. dehydroepiandrosterone (DHEA), a hormone with anti-glucocorticoid properties, or metyrapone (MET) an inhibitor of corticosterone synthesis. These drugs were able to partially, but significantly, restore the humoral immune response in immunosuppressed mice. A significant recovery of proliferative responsiveness was also observed when splenocytes were obtained from DHEA- or MET-treated immunosuppressed mice. In addition, these treatments restored the hypersensitivity response in immunosuppressed mice. Finally, although neither DHEA nor MET improved the reduced CD4 lymphocyte count in spleen from immunosuppressed mice, both treatments promoted spleen architecture reorganization, partially restoring the distinct cellular components and their localization in the spleen. The results from this study indicate that DHEA and MET could play an important role in the restoration of both adaptive humoral and cellular immune response in LPS-immunosuppressed mice, reinforcing the concept of a central involvement of endogenous glucocorticoids on this phenomenon.

Retention of anergy and inhibition of antibody responses during acute γ herpesvirus 68 infection

The majority of the human population becomes infected early in life by the gammaherpesvirus EBV. Some findings suggest that there is an association between EBV infection and the appearance of pathogenic Abs found in lupus. Gammaherpesvirus 68 infection of adult mice (an EBV model) was shown to induce polyclonal B cell activation and hypergammaglobulinemia, as well as increased production of autoantibodies. In this study, we explored the possibility that this breach of tolerance reflects loss of B cell anergy. Our findings show that, although anergic B cells transiently acquire an activated phenotype early during infection, they do not become responsive to autoantigen, as measured by the ability to mobilize Ca2+ following AgR cross-linking or mount Ab responses following immunization. Indeed, naive B cells also acquire an activated phenotype during acute infection but are unable to mount Ab responses to either T cell-dependent or T cell-independent Ags. In acutely infected animals, Ag stimulation leads to upregulation of costimulatory molecules and relocalization of Ag-specific B cells to the B-T cell border; however, these cells do not proliferate or differentiate into Ab-secreting cells. Adoptive-transfer experiments show that the suppressed state is reversible and is dictated by the environment in the infected host. Finally, B cells in infected mice deficient of CD4+ T cells are not suppressed, suggesting a role for CD4+ T cells in enforcing unresponsiveness. Thus, rather than promoting loss of tolerance, gammaherpesvirus 68 infection induces an immunosuppressed state, reminiscent of compensatory anti-inflammatory response syndrome.

Deficiency of corticotropin-releasing hormone type-2 receptor alters sleep responses to bacterial lipopolysaccharide in mice

In response to infectious stimuli, enhanced non-rapid eye movement sleep (NREMS) occurs, which is driven by pro-inflammatory cytokines. Those cytokines further elicit the release of corticotropin-releasing hormone (CRH), resulting in the activation of the hypothalamic-pituitary-adrenocortical axis. Signals of CRH are mediated by two receptor types, namely CRH-R1 and -R2. The role of CRH-R1 in wake-promoting effects of CRH has been rather clarified, whereas the involvement of CRH-R2 in sleep-wake regulation is poorly understood. To investigate whether CRH-R2 interferes with sleep responses to immune challenge, this study examined effects of bacterial lipopolysaccharide (LPS) on sleep in CRH-R2 deficient (KO) mice. CRH-R2 KO mice and control littermates (CL) were implanted with electrodes for recording electroencephalogram (EEG) and electromyogram. After recovery, LPS was applied by intraperitoneal injection at doses of 0.1, 1.0, or 10 μg at dark onset. In response to LPS injection NREMS of both genotypes was enhanced in a dose-dependent manner. However, CRH-R2 KO mice showed a larger increase, in particular after 10 μg of LPS compared to CL mice. During postinjection, reduced delta power for NREMS was detected in both genotypes after each dose, but the highest dose evoked a marked elevation of EEG activity in a limited frequency band (4 Hz). However, the EEG power of lower frequencies (1-2 Hz) increased more in CRH-R2 KO than in CL mice. The results indicated that CRH-R2 KO mice show greater NREMS responses to LPS, providing evidence that CRH-R2 participates in sleep-wake regulation via an interaction with the activated immune system.

The development of endotoxin tolerance, and the role of hypothalamo-pituitary-adrenal function and glucocorticoids in Pekin ducks

Endotoxin tolerance represents a state of abated immunological responsiveness to pyrogens, which, in mammals, leads to the decline or abolition of the fever response. The development of endotoxin tolerance in birds is not well understood; consequently, the impact of repeated pathogenic exposure on the avian febrile response, and thus on the ability of birds to fight recurrent infection, is not known. We determined the effect of repeated injections of lipopolysaccharide (LPS) on the febrile response of Pekin ducks. We gave ducks five injections of LPS, spaced 1, 4 or 10 days apart, and recorded their core body temperature with abdominally implanted temperature data loggers. Once we established that Pekin ducks developed endotoxin tolerance, we investigated the effect of repeated injections of LPS on the central and peripheral segments of the hypothalamo-pituitary-adrenal (HPA) axis in an attempt to elucidate the role of glucocorticoids in the modulation of the febrile response during the tolerant period. When our ducks became tolerant to LPS, they had significantly higher basal levels of plasma corticosterone (CORT, the principal glucocorticoid in birds), and their HPA response to treatment with LPS was blunted. We propose that the augmented levels of basal plasma CORT resulted from sensitized HPA function, and this, in turn, contributed to the development of endotoxin tolerance. Regulation of the circulating level of CORT might be a possible target for the re-establishment of appropriate immune responses in birds.

Mifepristone (RU486) restores humoral and T cell-mediated immune response in endotoxin immunosuppressed mice

Sepsis and septic shock can be caused by Gram-positive and -negative bacteria and other microorganisms. In the case of Gram-negative bacteria, endotoxin, a normal constituent of the bacterial wall, also known as lipopolysaccharide (LPS), has been considered as one of the principal agents causing the undesirable effects in this critical illness. The response to LPS involves a rapid secretion of proinflammatory cytokines such as tumour necrosis factor (TNF)-α, interleukin (IL)-1, IL-6, interferon (IFN)-γ and the concomitant induction of anti-inflammatory mediators such as IL-10, transforming growth factor (TGF)-β or glucocorticoids, which render the host temporarily refractory to subsequent lethal doses of LPS challenge in a process known as LPS or endotoxin tolerance. Although protective from the development of sepsis or systemic inflammation, endotoxin tolerance has also been pointed out as the main cause of the non-specific humoral and cellular immunosuppression described in these patients. In this report we demonstrate, using a mouse model, that mifepristone (RU486), a known glucocorticoid receptor antagonist, could play an important role in the restoration of both adaptive humoral and cellular immune response in LPS immunosuppressed mice, suggesting the involvement of endogenous glucocorticoids in this phenomenon. On the other hand, using cyclophosphamide and gemcitabine, we demonstrated that regulatory/suppressor CD4(+) CD25(+) forkhead boxP3(+) and GR-1(+) CD11b(+) cells do not play a major role in the establishment or the maintenance of endotoxin tolerance, a central mechanism for inducing an immunosuppression state.