Endogenous versus exogenous glucocorticoid responses to experimental bacterial sepsis

Pleiotropic Effects of Glucocorticoids on the Immune System in Circadian Rhythm and Stress

Glucocorticoids (GCs) are a class of steroid hormones secreted from the adrenal cortex. Their production is controlled by circadian rhythm and stress, the latter of which includes physical restraint, hunger, and inflammation. Importantly, GCs have various effects on immunity, metabolism, and cognition, including pleiotropic effects on the immune system. In general, GCs have strong anti-inflammatory and immunosuppressive effects. Indeed, they suppress inflammatory cytokine expression and cell-mediated immunity, leading to increased risks of some infections. However, recent studies have shown that endogenous GCs induced by the diurnal cycle and dietary restriction enhance immune responses against some infections by promoting the survival, redistribution, and response of T and B cells via cytokine and chemokine receptors. Furthermore, although GCs are reported to reduce expression of Th2 cytokines, GCs enhance type 2 immunity and IL-17-associated immunity in some stress conditions. Taken together, GCs have both immunoenhancing and immunosuppressive effects on the immune system.

Drug Repositioning to Alleviate Systemic Inflammatory Response Syndrome Caused by Gram-Negative Bacterial Outer Membrane Vesicles

Sepsis is characterized by systemic inflammatory response syndrome (SIRS) accompanied with infection. Gram-negative bacteria can evoke sepsis by activating the host immune system, such as the release of IL-6 and TNF-α, through their virulence factors. Outer membrane vesicles (OMVs), nanosized bilayered proteolipids derived from Gram-negative bacteria, harbor various virulence factors and are shown to induce SIRS. Here, drugs are repositioned to alleviate SIRS caused by Gram-negative bacterial OMVs. Using novel OMV-based drug screening systems, a total of 178 commercially available drugs are primarily screened, and a total of 18 repositioned drug candidates are found to effectively block IL-6 and TNF-α production from OMV-stimulated macrophages. After excluding the compounds which are previously known to intervene sepsis or which show cytotoxicity to macrophages, the compounds which show dose-dependency in inhibiting the release of IL-6 and TNF-α by the OMV-stimulated macrophages in vitro and which reduce OMV-induced SIRS in vivo are selected. Salbutamol, a β2 adrenergic receptor agonist, is selected as a novel candidate to alleviate OMV-induced SIRS. This study sheds light on using Gram-negative bacterial OMVs in exploring novel candidate compounds to alleviate inflammatory diseases including sepsis.

Review: D-Galactosamine lethality model: scope and limitations

D-Galactosamine (D-galN) is well established as sensitizing mice and other animals to the lethal effects of TNF, specifically, and by several orders of magnitude. Protection by anti-TNF neutralizing antibody is complete, as is (metabolically-based) protection by uridine. Sensitization occurs regardless of the origin of the released TNF, whether it is released from macrophages and/or T-cells. The same is true for the challenging agent which leads to the release of TNF, whether it is endotoxin, a superantigen, lipoprotein, bacterial DNA, or bacteria, either killed or proliferating. Most studies have utilized endotoxin as the challenging agent, and more than 70 agents have been reported to confer protection against LPS and/or TNF challenge in the model. The model has provided new insight regarding modes of protection, including from dexamethasone, which protects against challenge from LPS but not from challenge by TNF. The D-galN lethality model has also been used to test for synergistic behavior between different bacterial components, and to test for lethality when only small amounts of the challenging agent are available (lipid A chemistry).

Differential effects of low- and high-dose glucocorticoids on the innate immunity of corneal epithelium in vitro

PURPOSE

To evaluate the effect of glucocorticoids on the innate immunity of corneal epithelial cells.

METHODS

Human corneal epithelial cell lines (HCEC) were co-cultured with LPS and hydrocortisone to determine whether hydrocortisone modulates the expression and function of TLR2, 4. The release of IL-6, 8 from cultured HCEC was measured in the presence and absence of specific blocking antibodies to TLR2, 4. The proteins of TLR2, 4 were also compared by Western blot.

RESULTS

Incubation of HCEC with LPS upregulated the expression of TLR2, 4 and increased the release of IL-6, 8. This upregulation was enhanced by low-concentration hydrocortisone, but inhibited by high-concentration hydrocortisone. The concentration of IL-6, 8 was also enhanced by low-concentration hydrocortisone and inhibited by high-concentration hydrocortisone.

CONCLUSIONS

Low-concentration hydrocortisone enhances the expression and function of TLRs in HCEC and provides evidence for a novel function of glucocorticoids in innate immunity.

Enhanced resistance of restraint-stressed mice to sepsis

Sepsis remains a major health concern across the world. The effects of stress on host resistance to sepsis are still not very clear. To explore the effects of chronic stress on sepsis(') we examined the impact of restraint stress on the resistance of mice to sepsis. Interestingly, it was found that restraint stress enhanced the antisepsis resistance of mice and the concentrations of the proinflammatory cytokines IL-1, IL-6, IL-12, and TNF-alpha in the blood of stressed mice were dramatically reduced post Escherichia coli infection or LPS treatment as compared with that of controls (p < 0.05). In addition, the mRNA expressions of glucocorticoid-induced leucine zipper (GILZ) were up-regulated in the spleen and peritoneal macrophages of mice receiving restraint stress or dexamethasone treatment. These results demonstrate that restraint stress enhances the resistance of mice to sepsis, supporting corticotherapy for sepsis and proposing restraint-stressed mouse as an animal model to elucidate mechanisms of stress-associated, antisepsis resistance.

Cell-specific regulation of PTX3 by glucocorticoid hormones in hematopoietic and nonhematopoietic cells

PTX3 (prototypic long pentraxin 3) is a fluid phase pattern recognition receptor, which plays nonredundant roles in the resistance against diverse pathogens, in the assembly of a hyaluronic acid-rich extracellular matrix, and in female fertility. Inflammatory signals induce production of PTX3 in diverse cell types, including myeloid dendritic cells (DC), fibroblasts, and endothelial cells (EC). The present study was designed to explore the effect of glucocorticoid hormones (GC) on PTX3 production in different cellular contexts. In myeloid DC, GC inhibited the PTX3 production. In contrast, in fibroblasts and EC, GC alone induced and, under inflammatory conditions, enhanced and extended PTX3 production. In vivo administration of GC augmented the blood levels of PTX3 in mice and humans. Moreover, patients with Cushing syndrome had increased levels of circulating PTX3, whereas PTX3 levels were decreased in subjects affected by iatrogenic hypocortisolism. In nonhematopoietic cells, GC receptor (GR) functioned as a ligand-dependent transcription factor (dimerization-dependent) to induce PTX3 gene expression. In contrast, in hematopoietic cells, GR repressed PTX3 gene transcription by interfering (dimerization-independent) with the action of other signaling pathways, probably NFkappaB and AP-1. Thus, divergent effects of GC were found to be due to different GR mechanisms. The results presented here indicate that GC have divergent effects on PTX3 production in hematopoietic (DC and macrophages) and nonhematopoietic (fibroblasts and EC) cells. The divergent effects of GC on PTX3 production probably reflect the different functions of this multifunctional molecule in innate immunity and in the construction of the extracellular matrix.

Endocrine aspects of critical illness

Metabolic disorders and endocrine changes are common and relevant in critically ill patients. Thereby, endocrinopathies, electrolyte or metabolic derangements may either pre-exist or develop, and left unattended, may lead to significant morbidity and mortality. The homeostatic corrections which have emerged in the course of human evolution to cope with the catastrophic events during critical illness involve a complex multisystem endeavour, of which the endocrine contribution is an integral component. Although the repertoire of endocrine changes has been probed in some detail, discerning the vulnerabilities and failures of this system is far more challenging. The ensuing endocrine topics illustrate some of the current issues reflecting attempts to gain an improved insight and clinical outcome for critical illness. Disturbances in glucose and cortisol homeostasis during critical illness are two controversially debated topics in the current literature. The term "hormokine" encompasses the cytokine like behaviour of hormones during inflammation and infections. The concept is based on an ubiquitous expression of calcitonin peptides during sepsis. Adrenomedullin, another member of the calcitonin peptide superfamily, was shown to complement and improve the current prognostic assessment in lower respiratory tract infections. Procalcitonin is the protopye of "hormokine" mediators circulating procalcitonin levels increase several 10,000-fold during sepsis improve the clinical assessment especially of respiratory tract infections and sepsis safely and markedly reduces antibiotic usage in non-bacterial respiratory tract infections and meningitis. Adrenomedullin, another member of the calcitonin peptide superfamily, was shown to complement and improve the current prognostic assessment in lower respiratory tract infections. Hormokines are not only biomarkers of infection. Hormokines are also pivotal inflammatory mediators. Like all mediators, their role during systemic infections is basically beneficial, possibly to combat invading microbes. Yet, with increasing levels they can become harmful for their host. Multiple mechanisms of action were proposed. In several animal models the modulation and neutralization of hormokines during infection was shown to improve survival and thus might open new treatment options for severe infections, especially of the respiratory tract.

Influence of Stress and Nutrition on Cattle Immunity

Today, the scientific community readily embraces the fact that stress and nutrition impact every physiologic process in the body. At last, the specific mechanisms by which stress and nutrition affect the immune function are being elucidated. The debate among animal scientists concerning the definition and quantification of stress as it relates to animal productivity and well-being is ongoing. However, an increased appreciation and understanding of the effects of stress on livestock production has emerged throughout the scientific community and with livestock producers. The intent of this article is to provide an overview of the general concepts of stress and immunology, and to review the effects of stress and nutrition on the immune system of cattle.

The hypothalamic-pituitary-adrenal axis in critical illness

The hypothalamic-pituitary-adrenal response to stress is a dynamic process. The homeostatic corrections that have emerged in the course of human evolution to cope with the catastrophic events during critical illness involve a complex multisystem endeavor. Although the repertoire of endocrine changes has been probed in some detail, discerning the vulnerabilities and failures of this system is far more challenging. One of the most controversially debated topics in the current literature is the characterization and optimal treatment of allegedly inadequate adaptations of the hypothalamic-pituitary-adrenal axis during critical illness. This outline attempts to touch briefly some of the debated issues, stir the discussion, and thereby contribute to resolving the dispute.

Endogenous and exogenous glucocorticoids in experimental enterococcal infection

The potentially protective role of the host adrenal-glucocorticoid response to enterococcal infection was evaluated in an experimental model in which mice were infected intraperitoneally with two distinct Enterococcus faecalis strains (K9 and CP-1). We demonstrated that corticosterone levels in serum and peritoneal-lavage fluid were elevated within 1 hour of infection with either E. faecalis strain. We also demonstrated that adrenalectomized mice generated a more robust localized peritoneal tumor necrosis factor alpha (TNF-alpha) response to both E. faecalis strains than did sham-adrenalectomized mice but that neither E. faecalis strain induced a systemic TNF-alpha response. Further, peritoneal TNF-alpha production in adrenalectomized mice infected with either E. faecalis K9 or CP-1 was suppressed by prior treatment with an exogenous glucocorticoid (dexamethasone). The potential clinical significance of these results was suggested by our findings that adrenalectomy markedly increased susceptibility (a>100-fold decrease in the 50% lethal dose) to lethal infections with E. faecalis CP-1 and that prior dexamethasone treatment partially compensated for adrenalectomy. In marked contrast to these findings, however, adrenalectomy did not substantially increase susceptibility to lethal E. faecalis K9 infection. Further, preinfection with E. faecalis CP-1 1 hour before infection with E. faecalis K9 did not protect mice from lethal E. faecalis K9 infections. Collectively, these studies indicate that the host can generate a glucocorticoid response to E. faecalis infection that suppresses TNF-alpha production. Further, this glucocorticoid response can protect the host from potentially lethal E. faecalis infections, but different strains show heterogeneity with respect to the extent of protection afforded by the adrenal-glucocorticoid response.