Neuroendocrine regulation of in vivo cytokine production and effects: I. In vivo regulatory networks involving the neuroendocrine system, interleukin-1 and tumor necrosis factor-alpha

Succinate mediates inflammation-induced adrenocortical dysfunction

The hypothalamus-pituitary-adrenal (HPA) axis is activated in response to inflammation leading to increased production of anti-inflammatory glucocorticoids by the adrenal cortex, thereby representing an endogenous feedback loop. However, severe inflammation reduces the responsiveness of the adrenal gland to adrenocorticotropic hormone (ACTH), although the underlying mechanisms are poorly understood. Here, we show by transcriptomic, proteomic, and metabolomic analyses that LPS-induced systemic inflammation triggers profound metabolic changes in steroidogenic adrenocortical cells, including downregulation of the TCA cycle and oxidative phosphorylation, in mice. Inflammation disrupts the TCA cycle at the level of succinate dehydrogenase (SDH), leading to succinate accumulation and disturbed steroidogenesis. Mechanistically, IL-1β reduces SDHB expression through upregulation of DNA methyltransferase 1 (DNMT1) and methylation of the SDHB promoter. Consequently, increased succinate levels impair oxidative phosphorylation and ATP synthesis and enhance ROS production, leading to reduced steroidogenesis. Together, we demonstrate that the IL-1β-DNMT1-SDHB-succinate axis disrupts steroidogenesis. Our findings not only provide a mechanistic explanation for adrenal dysfunction in severe inflammation, but also offer a potential target for therapeutic intervention.

Sepsis: a failing starvation response

Sepsis is involved in ~ 20% of annual global deaths. Despite decades of research, the current management of sepsis remains supportive rather than curative. Clinical trials in sepsis have mainly been focused on targeting the inflammatory pathway, but without success. Recent data indicate that metabolic dysregulation takes place in sepsis, and targeting metabolic pathways might hold much promise for the management of sepsis. Sepsis yields a strong starvation response, including the release of high-energy metabolites such as lactate and free fatty acids. However, the activity of two major transcription factors, GR and PPARα, is downregulated in hepatocytes, leading to the accumulation and toxicity of metabolites that, moreover, fail to be transformed into useful molecules such as glucose and ketones. We review the literature and suggest mechanisms and potential therapeutic targets that might prevent or revert the fatal metabolic dysregulation in sepsis.

Glucocorticoids in Sepsis: To Be or Not to Be

Sepsis is a highly lethal syndrome resulting from dysregulated immune and metabolic responses to infection, thereby compromising host homeostasis. Activation of the hypothalamic–pituitary–adrenal (HPA) axis and subsequently adrenocortical glucocorticoid (GC) production during sepsis are important regulatory processes to maintain homeostasis. Multiple preclinical studies have proven the pivotal role of endogenous GCs in tolerance against sepsis by counteracting several of the sepsis characteristics, such as excessive inflammation, vascular defects, and hypoglycemia. Sepsis is however often complicated by dysfunction of the HPA axis, resulting from critical-illness-related corticosteroid insufficiency (CIRCI) and GC resistance. Therefore, GCs have been tested as an adjunctive therapy in sepsis and septic shock in different randomized clinical trials (RCTs). Nonetheless, these studies produced conflicting results. Interestingly, adding vitamin C and thiamin to GC therapy enhances the effects of GCs, probably by reducing GC resistance, and this results in an impressive reduction in sepsis mortality as was shown in two recent preliminary retrospective before–after studies. Multiple RCTs are currently underway to validate this new combination therapy in sepsis.

Critical Roles of Endogenous Glucocorticoids for Disease Tolerance in Malaria

During malaria, the hypothalamic-pituitary-adrenal (HPA) axis is activated and glucocorticoid (GC) levels are increased, but their essential roles have been largely overlooked. GCs are decisive for systemic regulation of vital processes such as immune responses, vascular function, and metabolism, which are crucial in malaria. Here, we introduce GCs in general, followed by their versatile roles for disease tolerance in malaria. A complementary comparison is provided with their role in sepsis. Finally, potential translational implications are considered. The failed clinical trials of dexamethasone against cerebral malaria in the past have diminished the interest in GCs in malaria. However, the issue of relative corticosteroid insufficiency has barely been explored in malaria patients, but may hold promise for a better understanding and treatment of specific malaria complications.

Regulatory and Mechanistic Actions of Glucocorticoids on T and Inflammatory Cells

Glucocorticoids (GCs) play an important role in regulating the inflammatory and immune response and have been used since decades to treat various inflammatory and autoimmune disorders. Fine-tuning the glucocorticoid receptor (GR) activity is instrumental in the search for novel therapeutic strategies aimed to reduce pathological signaling and restoring homeostasis. Despite the primary anti-inflammatory actions of GCs, there are studies suggesting that under certain conditions GCs may also exert pro-inflammatory responses. For these reasons the understanding of the GR basic mechanisms of action on different immune cells in the periphery (e.g., macrophages, dendritic cells, neutrophils, and T cells) and in the brain (microglia) contexts, that we review in this chapter, is a continuous matter of interest and may reveal novel therapeutic targets for the treatment of immune and inflammatory response.

The recent progress in animal models of depression

Major depression disorder (MDD) is a debilitating mental illness with significant morbidity and mortality. Despite the growing number of studies that have emerged, the precise underlying mechanisms of MDD remain unknown. When studying MDD, tissue samples like peripheral blood or post-mortem brain samples are used to elucidate underlying mechanisms. Unfortunately, there are many uncontrollable factors with such samples such as medication history, age, time after death before post-mortem tissue was collected, age, sex, race, and living conditions. Although these factors are critical, they introduce confounding variables that can influence the outcome profoundly. In this regard, animal models provide a crucial approach to examine neural circuitry and molecular and cellular pathways in a controlled environment. Further, manipulations with pharmacological agents and gene editing are accepted methods of studying depression in animal models, which is impossible to employ in human patient studies. Here, we have reviewed the most widely used animal models of depression and delineated the salient features of each model in terms of behavioral and neurobiological outcomes. We have also illustrated the current challenges in using these models and have suggested strategies to delineate the underlying mechanism associated with vulnerability or resilience to developing depression.

The HPA - Immune Axis and the Immunomodulatory Actions of Glucocorticoids in the Brain

In response to physiological and psychogenic stressors, the hypothalamic–pituitary–adrenal (HPA) axis orchestrates the systemic release of glucocorticoids (GCs). By virtue of nearly ubiquitous expression of the GC receptor and the multifaceted metabolic, cardiovascular, cognitive, and immunologic functions of GCs, this system plays an essential role in the response to stress and restoration of an homeostatic state. GCs act on almost all types of immune cells and were long recognized to perform salient immunosuppressive and anti-inflammatory functions through various genomic and non-genomic mechanisms. These renowned effects of the steroid hormone have been exploited in the clinic for the past 70 years and synthetic GC derivatives are commonly used for the therapy of various allergic, autoimmune, inflammatory, and hematological disorders. The role of the HPA axis and GCs in restraining immune responses across the organism is however still debated in light of accumulating evidence suggesting that GCs can also have both permissive and stimulatory effects on the immune system under specific conditions. Such paradoxical actions of GCs are particularly evident in the brain, where substantial data support either a beneficial or detrimental role of the steroid hormone. In this review, we examine the roles of GCs on the innate immune system with a particular focus on the CNS compartment. We also dissect the numerous molecular mechanisms through which GCs exert their effects and discuss the various parameters influencing the paradoxical immunomodulatory functions of GCs in the brain.

LCAT deficiency in mice is associated with a diminished adrenal glucocorticoid function

In vitro studies have suggested that HDL and apoB-containing lipoproteins can provide cholesterol for synthesis of glucocorticoids. Here we assessed adrenal glucocorticoid function in LCAT knockout (KO) mice to determine the specific contribution of HDL-cholesteryl esters to adrenal glucocorticoid output in vivo. LCAT KO mice exhibit an 8-fold higher plasma free cholesterol-to-cholesteryl ester ratio (P < 0.001) and complete HDL-cholesteryl ester deficiency. ApoB-containing lipoprotein and associated triglyceride levels are increased in LCAT KO mice as compared with C57BL/6 control mice (44%; P < 0.05). Glucocorticoid-producing adrenocortical cells within the zona fasciculata in LCAT KO mice are devoid of neutral lipids. However, adrenal weights and basal corticosterone levels are not significantly changed in LCAT KO mice. In contrast, adrenals of LCAT KO mice show compensatory up-regulation of genes involved in cholesterol synthesis (HMG-CoA reductase; 516%; P < 0.001) and acquisition (LDL receptor; 385%; P < 0.001) and a marked 40-50% lower glucocorticoid response to adrenocorticotropic hormone exposure, endotoxemia, or fasting (P < 0.001 for all). In conclusion, our studies show that HDL-cholesteryl ester deficiency in LCAT KO mice is associated with a 40-50% lower adrenal glucocorticoid output. These findings further highlight the important novel role for HDL as cholesterol donor for the synthesis of glucocorticoids by the adrenals.

Immunological responses in patients with tuberculosis and in vivo effects of acetyl-L-carnitine oral administration

Tuberculosis (TBC) is characterized by a complex immune response which parallels the clinical course of the disease. In this respect, acquired resistance, delayed hypersensitivity reaction and anergy are the main types of immune reactivity to mycobacterial antigens. In view of the presence of nonspecific and specific immune deficits in TBC patients, a clinical trial was carried out in a group of 20 individuals with active pulmonary TBC by oral administration of acetyl-L-carnitine (ALC). This drug, which has been shown to possess immunomodulating activities, was able to upregulate the T-dependent antibacterial activity in TBC patients after 30 days' treatment, while the same activity decreased in patients receiving placebo only. On the other hand, ALC did not modify serum levels of tumour necrosis factor-α, in the same individuals. This cytokine plays a detrimental rather than beneficial role in TBC pathogenesis. In the light of these data, ALC seems to be a powerful immunomodulator in the course of Mycobacterium tuberculosis infection and other mycobacteriosis.

Immunoregulatory biological response modifiers: effect of cytokines on septic shock

Whole bacteria or bacterial components or their extracts were employed to restore or augment the immune system. Beneficial effects were attained with these agents in treating various diseases. These agents were named biological response modifiers (BRMs) because they regulated certain cellular components of the immune system. The cellular regulation induced by these BRMs was found to be due to cytokines. The cytokines were shown to act directly on the various cellular components and to provide therapeutic benefit in various autoimmune and immune deficiency diseases. Overproduction of specific cytokines however leads to a deleterious effect on the host. Overproduction of tumour necrosis factor (endotoxin, lipopolysaccharide) leads to septic shock. Bacteraemia is the leading cause of overproduction of tumour necrosis factor (TNF). Septic shock in many cases leads to death. Several monoclonal antibodies to lipopolysaccharide (LPS) and anticytokines have demonstrated protection against septic shock.

TNF-α in CRPS and 'normal' trauma--significant differences between tissue and serum

Posttraumatic TNF-alpha signaling may be one of the factors responsible for pain and hyperalgesia in complex regional pain syndromes (CRPS). In order to further specify the role of TNF-alpha we investigated tissue (skin) and serum concentrations in three different patient groups: patients with osteoarthritis and planned surgery, with acute traumatic upper limb bone fracture waiting for surgery, and with CRPS I. Thirty patients (10 in each group) were recruited. Mean CRPS duration was 36.1 ± 8.1 weeks (range 8- 90 weeks). Skin punch biopsies were taken at the beginning of the surgery in osteoarthritis and fracture patients and from the affected side in CRPS patients. Blood samples were taken before the respective procedures. Skin and serum TNF-alpha levels were quantified by ELISA. Compared to patients with osteoarthritis, skin TNF-alpha was significantly elevated in CRPS (p<0.001) and fracture patients (p<0.04). Skin TNF-alpha in CRPS patients was higher than in patients with acute bone fracture (p<0.02). In contrast, serum TNF-alpha values were the same in osteoarthritis and CRPS, and lower in fracture patients (p<0.03). Our results indicate a local but not systemic increase of TNF-alpha in CRPS patients. This increase persists for months after limb trauma and may offer the opportunity for targeted treatment.

The glucocorticoid receptor: a revisited target for toxins

The hypothalamic-pituitary-adrenal (HPA) axis activation and glucocorticoid responses are critical for survival from a number of bacterial, viral and toxic insults, demonstrated by the fact that removal of the HPA axis or GR blockade enhances mortality rates. Replacement with synthetic glucocorticoids reverses these effects by providing protection against lethal effects. Glucocorticoid resistance/insensitivity is a common problem in the treatment of many diseases. Much research has focused on the molecular mechanism behind this resistance, but an area that has been neglected is the role of infectious agents and toxins. We have recently shown that the anthrax lethal toxin is able to repress glucocorticoid receptor function. Data suggesting that the glucocorticoid receptor may be a target for a variety of toxins is reviewed here. These studies have important implications for glucocorticoid therapy.

Psychoneuroimmune implications of type 2 diabetes: redux

A sizable body of knowledge has arisen demonstrating that type 2 diabetes (T2D) is associated with alterations in the innate immune system. The resulting proinflammatory-leaning imbalance is implicated in the development of secondary disease complications and comorbidities, such as delayed wound healing, accelerated progress of atherosclerosis, and retinopathy, in people who have T2D. New experimental data and the results of recently published health-related quality-of-life surveys indicate that individuals who have T2D experience diminished feelings of happiness, well being, and satisfaction with life. These emotional and psychological consequences of T2D point to altered neuroimmunity as a previously unappreciated complication of T2D. This article discusses recent data detailing the impact of T2D on a person's PNI response.

Differential glucocorticoid effects on proliferation and invasion of human trophoblast cell lines

Several clinical situations require continuous glucocorticoid (GC) treatment during pregnancy. A well-known deleterious side effect of such treatment is the higher incidence of growth-restricted fetuses, for which a too shallow trophoblast invasion is presently hypothesised as the underlying cause. This study investigated whether the synthetic GC triamcinolone acetonide (TA) influences proliferation, invasion and endocrine activity of human trophoblast. BeWo and JEG-3 choriocarcinoma cell lines both express GC receptors (western blotting) and were used as models for human trophoblast. JAR devoid cells of GC receptor were used as negative control. The cells were cultured for 48 h without (control) or with 0.5, 5 and 50 microM TA. In the presence and absence of serum, proliferation was determined by cell counting and measuring the cell cycle regulating protein cyclin B1 (Western blotting); invasion was determined by a conventional Matrigel invasion assay and by measuring the secretion (ELISA) of matrix-metalloproteinases (MMP-2, MMP-9) into the culture medium; endocrine activity was assessed by measuring the levels of human chorionic gonadotropin (ELISA) into the culture medium. TA altered the number of viable and dead cells as well as cyclin B1 levels and, to a lesser extent, invasion of BeWo and JEG-3, with a strong influence of serum. BeWo and JEG-3 cells reacted differently and in most instances reverse. In the cell lines used as models of human trophoblast, TA alter some functions relevant to proliferation and invasion, and suggest that caution should be exercised when treating women with GCs during pregnancy.

TUMOUR NECROSIS FACTOR: IMPLICATIONS FOR SURGICAL PATIENTS

Tumour necrosis factor alpha (TNF-alpha) is an inflammatory cytokine primarily produced by macrophages. It is a unique protein with contradictive properties; it has the ability to induce cellular death by apoptosis and oncosis, but can also induce cellular regeneration and growth. Genetic polymorphisms in TNFA have been associated with poor outcome in some surgical patients and this may provide a useful tool to screen for high-risk patients. Manipulating TNF-alpha levels in vivo may influence the progression of several pathological conditions. TNF-alpha has anti-cancer properties and has been used to treat cancer patients. Treatment with anti-TNF-alpha drugs and antibodies has been successful in rheumatoid arthritis and other autoimmune diseases, but disappointing in the management of patients with sepsis. This review article focuses on the biological activities, genetic polymorphism of TNFA and the role of TNF-alpha and anti-TNF-alpha treatments, based on animal experiments and clinical trials.

Psychoneuroimmune Implications of Type 2 Diabetes

The idea that type 2 diabetes is associated with augmented innate immune function characterized by increased circulating levels of acute phase reactants and altered macrophage biology is fairly well established, even though the mechanisms involved in this complex interaction still are not entirely clear. To date, the majority of studies investigating innate immune function in type 2 diabetes are limited to the context of wound healing, atherosclerosis, stroke, and other commonly identified comorbidities. Several important recurring themes come out of these data. First, type 2 diabetes is associated with a state of chronic, subclinical inflammation. Second, in macrophages, type 2 diabetic conditions enhance proinflammatory reactions and impair anti-inflammatory responses. Third, after acute activation of the innate immune system in type 2 diabetes, recovery or resolution of inflammation is impaired. The consequences of type 2 diabetes-associated inflammatory alterations on PNI processes have been recognized only recently. Given the impact of diminished emotional well-being on the quality of life in patients who have type 2 diabetes, diabetes-induced exacerbation of PNI responses should be considered a serious complication of type 2 diabetes that warrants further clinical attention.

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.

A new function of the leptin receptor: mediation of the recovery from lipopolysaccharide-induced hypothermia

Obese (f/f) Koletsky rats lack the leptin receptor (LR), whereas their lean (F/?) counterparts bear a fully functional LR. By using f/f and F/? rats, we studied whether the LR is involved in lipopolysaccharide (LPS)-induced fever and hypothermia. The body temperature responses to LPS (10 or 100 microg/kg iv) were measured in Koletsky rats exposed to a thermoneutral (28 degrees C) or cool (22 degrees C) environment. Rats of both genotypes responded to LPS with fever at 28 degrees C and with dose-dependent hypothermia at 22 degrees C. The fever responses of the f/f and F/? rats were identical. The hypothermic response of the f/f rats was markedly prolonged compared with that of the F/? rats. The prolonged hypothermic response to LPS in the f/f rats was accompanied by enhanced NF-kappaB signaling in the hypothalamus and an exaggerated rise in the plasma concentration of tumor necrosis factor (TNF)-alpha. The f/f rats did not respond to LPS with an increase in the plasma concentration of corticosterone or adrenocorticotropic hormone, whereas their F/? counterparts did. The hypothermic response to TNF-alpha (80 microg/kg iv) was markedly prolonged in the f/f rats. These data show that the LR is essential for the recovery from LPS hypothermia. LR-dependent mechanisms of the recovery from LPS hypothermia include activation of the anti-inflammatory hypothalamo-pituitary-adrenal axis, inhibition of both the production and hypothermic action of TNF-alpha, and suppression of inflammatory (via NF-kappaB) signaling in the hypothalamus.

Endogenous glucocorticoids attenuate Shiga toxin-2-induced toxicity in a mouse model of haemolytic uraemic syndrome

The concept that during an immune challenge the release of glucocorticoids (GC) provides feedback inhibition on evolving immune responses has been drawn primarily from studies of autoimmune and/or inflammatory processes in animal models. The epidemic form of haemolytic uraemic syndrome (HUS) occurs secondary to infection with Gram-negative bacteria that produce Shiga toxin (Stx). Although Stx binding to the specific receptors present on renal tissue is the primary pathogenic mechanism, inflammatory or immune interactions are necessary for the development of the complete form of HUS. The aim of this study was to investigate the influence of endogenous GC on Stx-toxicity in a mouse model. Stx2 was injected into GC-deprived mice and survival rate, renal damage and serum urea levels were evaluated. Plasma corticosterone and cytosolic GC receptor (GR) concentration were also determined at multiple intervals post-Stx2 treatment. Higher sensitivity to Stx2 was observed in mice lacking endogenous GC, evidenced by an increase in mortality rates, circulating urea levels and renal histological damage. Moreover, Stx2 injection was associated with a transient but significant rise in corticosterone secretion. Interestingly, 24 h after Stx inoculation significant increases in total GR were detected in circulating neutrophils. These results indicate that interactions between the neuroendocrine and immune systems can modulate the level of damage significantly during a bacterial infection.

The inflammatory reflex

Inflammation is a local, protective response to microbial invasion or injury. It must be fine-tuned and regulated precisely, because deficiencies or excesses of the inflammatory response cause morbidity and shorten lifespan. The discovery that cholinergic neurons inhibit acute inflammation has qualitatively expanded our understanding of how the nervous system modulates immune responses. The nervous system reflexively regulates the inflammatory response in real time, just as it controls heart rate and other vital functions. The opportunity now exists to apply this insight to the treatment of inflammation through selective and reversible 'hard-wired' neural systems.

Globin attenuates the innate immune response to endotoxin

Hemoglobin is an endotoxin (lipopolysaccharide; LPS)-binding protein that synergistically increases the release of proinflammatory cytokines from the innate immune system in response to LPS. It has been suggested that this activity of hemoglobin facilitates the recognition of Gram-negative bacteria in a wound, thereby maximizing immune efficiency. This synergy may be important to the pathogenesis of a broad spectrum of clinical conditions because elevated hemoglobin levels frequently are observed in patients after the transfusion of red cells, trauma, cardiopulmonary bypass surgery, hemolysis, in addition to other disorders. To determine the molecular basis of the specific hemoglobin-LPS synergy, in this article we tested the effects of globin itself on macrophage responses to LPS. Paradoxically, these studies revealed that globin suppressed tumor necrosis factor (TNF) synthesis in LPS-stimulated murine and human macrophage cultures. LPS comigrated with globin on non-denaturing electrophoretic gels, giving direct evidence for binding. Globin specifically inhibited LPS activity in the standard Limulus assay but did not inhibit interleukin-1beta-mediated TNF synthesis. Iron supplementation of macrophage cultures significantly increased interleukin-1beta-induced TNF release. Intraperitoneal administration of globin protected mice against both LPS-induced lethality and experimentally induced bacterial infection. Thus, the heme-iron moiety of hemoglobin, and not the binding of LPS to globin, enhanced macrophage responses to LPS.

Prior stressor exposure primes the HPA axis

Exposure to stressors often alters the subsequent responsiveness of many systems. The present study tested whether prior exposure to inescapable tailshock (IS) alters the corticosterone (CORT) or adrenocorticotropin hormone (ACTH) response to either an injection of bacterial endotoxin (lipopolysaccharide; LPS) or subsequent placement on a pedestal. Rats were exposed to IS or remained as home cage controls (HCC). 1, 4, 10, or 21 days later animals were injected i.p. with either 10 microg/kg LPS or equivolume sterile saline. Prior IS significantly increased plasma CORT 1 h, but not 2 or 5 h after LPS, compared to controls 1, 4, and 10 days, but not 21 days after IS. Exposure to IS 24 h earlier also significantly increased plasma ACTH 1 h after LPS. Additional animals were placed on a pedestal 24 h after IS, and plasma CORT was measured 15, 30, and 60 min later. IS significantly increased plasma CORT 15 min after pedestal exposure, but not after 30 or 60 min. These results suggest that exposure to IS sensitizes the CORT and ACTH response to subsequent HPA activation.

COX-2 inhibition attenuates anorexia during systemic inflammation without impairing cytokine production

Anorexia and weight loss are frequent complications of acute and chronic infections and result from induction of cytokines, prostaglandins, and other inflammatory mediators that are critical for pathogen elimination. Selective attenuation of the hypophagic response to infection and maintenance of the production of factors essential for infection control would be a useful addition to antimicrobial therapy in the treatment of human disease. Here, we evaluate the relative contribution of cyclooxygenase (COX)-1- and COX-2-derived prostaglandins to anorexia and weight loss precipitated by systemic immune activation by lipopolysaccharide (LPS). Using COX isoform-selective pharmacological inhibitors and gene knockout mice, we found that COX-2 inhibition during LPS-induced inflammation results in preserved food intake and maintenance of body weight, whereas COX-1 inhibition results in augmented and prolonged weight loss. Regulation of neuropeptide Y, corticotropin-releasing hormone, leptin, and interleukin-6 does not change as a function of COX-2 inhibition after LPS administration. Our data implicate COX-2 inhibition as a therapeutic target to maintain nutritional status while still allowing a normal cytokine response during infection.

Potentiation of interleukin-1beta adjuvant effects on the humoral immune response to antigen in adrenalectomized mice

OBJECTIVES

Activation of the hypothalamic-pituitary-adrenal (HPA) axis is a primary effect of interleukin-1 (IL-1), with elevated glucocorticoids considered a mechanism for negative feedback immunoregulation. However, there is little direct evidence of such a functional relationship between IL-1-mediated immunoregulation and neuroendocrine influences elicited by IL-1. Therefore, the goal of this study was to examine whether the known adjuvant effects of IL-1 are altered in the absence of neuroendocrine feedback due to adrenalectomy.

METHODS

Male BALB/c mice subjected to adrenalectomy (ADX) or sham surgery were administered with saline or recombinant human IL-1beta (rhIL-1beta) and at the same time immunized with 100 microg ovalbumin (OVA). In vivo and in vitro measures of antigen-specific IgG antibody production, IL-6 production and spleen cell proliferation were taken 6 and 12 days later.

RESULTS

It was demonstrated that administration of rhIL-1beta at a dose that activates the HPA axis resulted in a significant augmentation of serum anti- OVA IgG antibody levels. Interestingly, this augmentation was potentiated in ADX animals. In addition, the in vitro spleen cell memory IgG antibody response to OVA was significantly augmented in rhIL-1beta-treated animals, and again, further potentiated in ADX animals. Interestingly, while hrIL-1beta treatment augmented antigen-stimulated IL-6 production - suggesting an effect of IL-1 on antigen-specific T helper 2 cell memory formation - potentiation was not evident in ADX animals.

CONCLUSIONS

These results are consistent with the concept of HPA axis-mediated neuroendocrine feedback on excessive immune responsiveness due to IL-1. Such feedback may prevent disturbances to the self-limiting functions of the immune system, which are important to the prevention of autoimmune diseases, some of which involve elevated IL-1 production.

Interleukin-6 is an essential, corticotropin-releasing hormone-independent stimulator of the adrenal axis during immune system activation

Glucocorticoids play a critical role in control of the cytokine response after immune challenge. Conversely, cytokines modulate glucocorticoid production by the hypothalamic-pituitary-adrenal axis. To define the potency and mechanism of interleukin-6 (IL-6) for augmentation of adrenal function, we exploited mice deficient in corticotropin-releasing hormone (CRH), IL-6, or both. Mice deficient in CRH action demonstrate severely impaired glucocorticoid production in response to psychological and metabolic challenge, but near normal responses to stressors that activate the immune system. In this paper, we demonstrate that IL-6 is essential for activation of the hypothalamic-pituitary-adrenal axis during immunological challenge in the absence of hypothalamic input from CRH. IL-6 receptors are present on pituitary corticotrophs and adrenocortical cells, consistent with the ability of IL-6 to bypass CRH in augmentation of adrenal function. Plasma corticosterone levels after bacterial lipopolysaccharide injection in mice deficient in CRH or IL-6 were significantly lower than in wild-type mice but significantly greater than in mice deficient in both CRH and IL-6. A second model of immune system activation using 2C11, an antibody to the T cell receptor, demonstrated a normal corticosterone response in mice deficient in CRH or IL-6, but a markedly decreased response in mice deficient in both CRH and IL-6. Surprisingly, the relative contribution of IL-6 for modulation of the adrenal response to stress is greater in female than in male mice. This gender-specific difference in IL-6 action in mice suggests the utility of further analysis of IL-6 in determining the female predominance seen in many human inflammatory/autoimmune diseases.

Aged mice exhibit greater mortality concomitant to increased brain and plasma TNF-alpha levels following intracerebroventricular injection of lipopolysaccharide

BACKGROUND

Age-related defects in the development of peripheral inflammatory responses have been observed in rodents and humans.

OBJECTIVE

We examined the effects of age on a centrally injected endotoxin-induced cytokine production and cellular activation in mice.

METHODS

Male C57BL/6J (B6) mice, C3H/HeN mice, and C3H/HeJ mice received an intracerebroventricular injection of lipopolysaccharide (LPS) and were sacrificed at various times (2, 4, 8 h) thereafter. ELISA for IL-1beta, IL-6, IL-12, and TNF-alpha were conducted on forebrain tissue homogenates as well as plasma samples, and lectin staining to detect activated microglia was prepared for selected brain slices.

RESULTS

Intracerebroventricular injection of LPS in B6 mice produced an age-associated increase in mortality which was paralleled with a significant increase in brain and plasma levels of TNF-alpha. AntiTNF-alpha- and IL-6-immunoreactive cells possessed macrophagelike morphologies and were observed along the LPS injection tract and scattered throughout the hilus of the dorsal hippocampus and cerebral cortices. This LPS-mediated response was found to be specific in that the LPS-hyporesponsive mouse strain (C3H/HeJ) failed to demonstrate significant brain or plasma levels of TNF-alpha after LPS administration compared to C3H/HeN mice.

CONCLUSION

These results suggest that the age-related increases in TNF-alpha production and mortality following the intracerebroventricular administration of LPS may be due to an increased endotoxin hypersensitivity of brain microglia/macrophages within aged animals.

Effect of orchidectomy on the age-related modulation of IL-1beta and IL-1 receptors following lipopolysaccharide treatment in the mouse

OBJECTIVE

To compare the effect of orchidectomy (ODX) in 7- and 24-week-old C57BL/6 mice on the age-related responses of the cytokine interleukin (IL)-1beta and its receptor to intraperitoneal injection of the bacterial endotoxin, lipopolysaccharide (LPS).

METHODS

We measured IL-1beta concentrations in the plasma, hippocampus, hypothalamus and adrenal gland using ELISA and iodine-125-labeled recombinant human IL-1alpha ([(125)I]IL-1alpha) binding in the hippocampus following the intraperitoneal administration of saline or LPS.

RESULTS

There were no significant differences in the concentrations of IL-1beta and its receptors in the brain and peripheral tissues between sham-operated and ODX mice in both age groups injected with saline. LPS induced significantly higher IL-1beta production in the plasma and hippocampus in sham-operated 24-week-old mice than in 7-week-old mice. Coincident with the heightened IL-1beta response to LPS, hippocampal [(125)I]IL-1alpha binding was lower in 24-week-old mice than in 7-week-old mice after LPS injection in the sham-operated group. The age-related differences in the IL-1beta concentrations in the plasma and hippocampus and [(125)I]IL-1alpha binding in the hippocampus in response to LPS administration were abolished by ODX. Although LPS dramatically increased IL-1beta levels in the hypothalamus, no significant age-related differences in IL-1beta concentrations were seen, and ODX did not affect IL-1beta levels. In contrast, there were no significant differences between saline- and LPS-injected 7-week-old mice in relation to concentrations in the adrenal gland. Moreover, although the adrenal IL-1beta concentrations in 24-week-old mice were significantly higher than those in 7-week-old mice, ODX did not abolish these age-related differences in concentrations in the adrenal gland.

CONCLUSIONS

Our data suggest the involvement of testosterone (or gonadal product) in plasma and hippocampal IL-1beta regulation in relation to age, and demonstrate the importance of the gonadal development in mediating the effects of infectious challenge on the brain and immune function.

Plasma levels of tumor necrosis factor-alpha in patients with panic disorder: effect of alprazolam therapy

Plasma concentrations of tumor necrosis factor-alpha (TNF-alpha) were measured in 10 outpatients with panic disorder, twice (at a 48-h interval) before and twice on days 30-32 of treatment with alprazolam (2-2.5 mg/day), and twice in 10 age- and sex-matched healthy controls. TNF-alpha concentrations did not differ in patients and control subjects, either before therapy or at days 30-32 of therapy. In five patients before therapy, and in three of them after therapy, TNF-alpha values were higher than the maximal concentrations of the cytokine in controls.

Cytokines in de obsessief compulsieve stoornis en in anorexia nervosa: een overzicht

The alterations in the inflammatory response system (IRS) appear to be quite different between OCD and anorexia nervosa and are also different from the changes observed in major depression. In anorexia nervosa, there is some evidence for increased production of monocytic cytokines, i.e. tumor necrosis factor-α (TNFα) and interleukin-6 (IL-6), and decreased production of Th-1 like cytokines, i.e. IL-2 and IFNγ. In the same patients there are also signs of immunosuppression, e.g. lowered numbers of CD4 and CD8 T cells and increased production of transforming growth factor-beta (TGFβ). The increased production of monocytic cytokines may be the consequence of the hyponutritional status of those patients. The diminished production of the Th-1 like cytokines may be the consequence of at least four different factors: 1) the deficiency in nutritional factors; 2) neuroendocrine disorders, such as increased Cortisol production; 3) the increased TGFβ production; and 4) lower serum dipeptidyl peptidase activity. In OCD no consistent or specific alterations in the IRS are observed. There is no evidence that IRS activation may play a role in the pathophysiology of OCD and anorexia nervosa.

Animal models of CRH deficiency

Corticotropin-releasing hormone (CRH), the major regulator of hypothalamic-pituitary-adrenal (HPA) axis, was first isolated due to its ability to stimulate the release of adrenocorticotropic hormone from the anterior pituitary. Later, it was also found to have also a wide spectrum of actions within the central nervous system and the periphery. Studies with pharmacological administration of this peptide and/or antagonists and antibody neutralization techniques have yielded important information concerning the physiological relevance of CRH. The development of CRH knockout mice (CRH KO) has been an important tool for addressing the physiologic and pathologic roles of CRH. This review describes the phenotype of CRH-deficient mice, as well as the use of this model to study the roles of CRH on fetal development and postnatal life. The role of CRH in prenatal development and postnatal regulation of the HPA axis, in activation of the reproductive system during stress, and in modulation of the immune function will be discussed. The review concludes with a comparison of CRH KO mice with other models of CRH deficiency.

Nonstressed rat model of acute endotoxemia that unmasks the endotoxin-induced TNF-alpha response

Previous investigators have demonstrated that the tumor necrosis factor-alpha (TNF-alpha) response to endotoxin is inhibited by exogenous corticosterone or catecholamines both in vitro and in vivo, whereas others have reported that surgical and nonsurgical stress increase the endogenous concentrations of these stress-induced hormones. We hypothesized that elevated endogenous stress hormones resultant from experimental protocols attenuated the endotoxin-induced TNF-alpha response. We used a chronically catheterized rat model to demonstrate that the endotoxin-induced TNF-alpha response is 10- to 50-fold greater in nonstressed (NS) rats compared with either surgical-stressed (SS, laparotomy) or nonsurgical-stressed (NSS, tail vein injection) models. Compared with the NS group, the SS and NSS groups demonstrated significantly lower mean peak TNF-alpha responses at 2 mg/kg and 6 micrograms/kg endotoxin [NS 111.8 +/- 6.5 ng/ml and 64.3 +/- 5.9 ng/ml, respectively, vs. SS 3.9 +/- 1.1 ng/ml (P < 0.01) and 1.3 +/- 0.5 ng/ml (P < 0.01) or NSS 5.2 +/- 3.2 ng/ml (P < 0.01) at 6 micrograms/kg]. Similarly, baseline concentrations of corticosterone and catecholamines were significantly lower in the NSS group [84.5 +/- 16.5 ng/ml and 199.8 +/- 26.2 pg/ml, respectively, vs. SS group 257. 2 +/- 35.7 ng/ml (P < 0.01) and 467.5 +/- 52.2 pg/ml (P < 0.01) or NS group 168.6 +/- 14.4 ng/ml (P < 0.01) and 1,109.9 +/- 140.7 pg/ml (P < 0.01)]. These findings suggest that the surgical and nonsurgical stress inherent in experimental protocols increases baseline stress hormones, masking the endotoxin-induced TNF-alpha response. Subsequent studies of endotoxic shock should control for the effects of protocol-induced stress and should measure and report baseline concentrations of corticosterone and catecholamines.

Role of the Hypothalamic Pituitary Adrenal Axis and IL-6 in Stress-Induced Reactivation of Latent Herpes Simplex Virus Type 1

Hyperthermic stress induces reactivation of herpes simplex virus type 1 (HSV-1) in latently infected mice and also stimulates corticosterone release from the adrenals via activation of the hypothalamic pituitary adrenal axis. In the present study, we tested the hypothesis that stress-induced elevation of corticosterone potentiates HSV-1 reactivation in latently infected mice. Because of the putative role of IL-6 in facilitating HSV-1 reactivation in mice, the effect of hyperthermic stress and cyanoketone treatment on IL-6 expression in the trigeminal ganglion was also measured. Preadministration of cyanoketone, a glucocorticoid synthesis inhibitor, blocked the stress-induced elevation of corticosterone in a dose-dependent manner. Furthermore, inhibition of corticosterone synthesis was correlated with reduced levels of HSV-1 reactivation in latently infected mice. Hyperthermic stress elicited a transient rise in IL-6 mRNA levels in the trigeminal ganglion, but not other cytokine transcripts investigated. In addition, there was a significant reduction in MAC-3+, CD8+, and DX5+ (NK cell marker) cells in the trigeminal ganglion of latent HSV-1-infected mice 24 h after stress. Cyanoketone blocked the stress-induced rise in IL-6 mRNA and protein expression in the trigeminal ganglion latently infected with HSV-1. Collectively, the results indicate that the activation of the hypothalamic pituitary adrenal axis plays an important role in stimulating IL-6 expression and HSV-1 reactivation in the trigeminal ganglion following hyperthermic stress of mice.

An assessment of the effects of central interleukin-1beta, -2, -6, and tumor necrosis factor-alpha administration on some behavioural, neurochemical, endocrine and immune parameters in the rat

Despite a vast amount of research into the actions of cytokines within the central nervous system, the pharmacological role and/or physiological function of the various cytokines within the central nervous system is still not fully understood. The present study evaluated the effects of intracerebroventricular administration of interleukin-1beta, -2, -6 (20 ng) and tumour necrosis factor-alpha (40 ng) on elevated plus maze behaviour, monoamine levels in the hypothalamus, hippocampus and amygdala, plasma corticosterone and catecholamine concentrations and Concanavalin A-induced splenic lymphocyte proliferation in the rat. Both interleukin-1beta and tumour necrosis factor-alpha induced "anxiogenic-like" effects on the elevated plus maze, whereas interleukin-2 and interleukin-6 did not. However only interleukin-1beta led to endocrine variations often associated with stress and anxiety. Cytokine specific alterations in monoamine levels were evident in the hypothalamus and hippocampus, while neurotransmitter concentrations in the amygdala were not significantly altered by cytokine treatment. In addition, interleukin-1beta reduced Concanavalin A-induced lymphocyte proliferation, whereas the other cytokine treatments failed to significantly alter this response. These results demonstrate that in some, but not all, respects interleukin-1beta administration produced "stress like" effects on behaviour, monoamine neurotransmitters, hypothalamic pituitary adrenal axis activity and immune function, while the other cytokines produced less consistent effects on these parameters. It is noteworthy that although interleukin-1beta and tumour necrosis factor-alpha provoked an anxiogenic response in the elevated plus maze test of anxiety, neither cytokine significantly altered amygdaloid noradrenergic or serotonergic activity, as many previous studies have implicated increased amygdaloid noradrenergic and/or serotonergic activity in the pathophysiology of anxiety.

Glucocorticoid regulation of adrenomedullin in a rat model of endotoxic shock

Wistar rats were injected intravenously with bacterial lipopolysaccharide (LPS) and developed endotoxic shock with severe hypotension. This was accompanied by significantly elevated concentrations of adrenomedullin (AM) in the plasma and expression of high levels of AM mRNA in the lung. Pretreatment of the rats with dexamethasone (DEX) prevented hypotension caused by LPS administration, but plasma AM concentrations and AM mRNA levels in the lung remained elevated. Adrenalectomized (ADX) rats developed a more severe form of circulatory shock in response to a low-dose of LPS. This was accompanied by only a slight increase in circulating AM in the plasma. However, pretreatment of ADX rats with DEX caused substantial elevations of plasma AM concentrations and expression of AM mRNA in the lung. Our studies demonstrate that glucocorticoid upregulates the expression and secretion of AM in vivo, and endogenous glucocorticoid is required for increased AM secretion under certain conditions such as endotoxic shock.

Depression, stress and immunological activation: the role of cytokines in depressive disorders

Traditionally, both stress and depression have been associated with impaired immune function and increased susceptibility to infectious and neoplastic disease. However over the last number of years a large body of evidence suggests that major depression is associated with signs of immunological activation. Moreover it has been suggested that cytokine hypersecretion may be involved in the aetiology of depressive disorders. The present article reviews the evidence from both clinical and experimental studies which implicates immunological activation and particularly hypersecretion of cytokines in the onset and maintenance of depressive illness. Both clinical and experimental studies indicate that stress and depression are associated with increased circulating concentrations of cytokines such as IL-1beta, IL-6 and gamma-IFN and positive acute phase proteins, and hyperactivity of the HPA-axis. In addition, it has been reported that immunological activation induces "stress-like" behavioural and neurochemical changes in laboratory animals. Although for many years it has been suggested that stress acts a predisposing factor to depressive illness, the precise mechanisms by which stress-induced depressive symptoms occur are not fully understood. Nevertheless, behavioural changes due to stress have often been explained in terms of changes in neurotransmitter function in the brain. In the present article increased cytokine secretion is implicated as a mechanism whereby stress can induce depression.

Plasma interleukin-1 beta and tumor necrosis factor concentrations in obsessive-compulsive disorders

Plasma interleukin-1 beta (Il-1 beta) and tumor necrosis factor-alpha (TNF-alpha) concentrations were measured twice, at a 48-hour interval, in 27 drug-free obsessive-compulsive patients (12 women and 15 men) and in 27 sex-age-matched healthy controls. Il-1 beta and TNF-alpha concentrations were significantly lower in patients than in controls, whereas there were no differences in either group between men and women, between the samples of the two days, or, in the patients, between those who had and those who had not been previously treated with psychopharmacologic drugs.

Regulation of tumour necrosis factor production by adrenal hormones in vivo: insights into the antiinflammatory activity of rolipram

1. The role of adrenal hormones in the regulation of the systemic and local production of tumour necrosis factor (TNF alpha) was examined in male Balb/c mice. 2. Intraperitoneal injection of 0.3 mg E. coli lipopolysaccharide (LPS, 0111:B4) led to high levels of circulating TNF alpha without stimulating TNF alpha production in the peritoneal cavity. Systemic production of TNF alpha in response to LPS was increased in adrenalectomized animals and in normal animals treated with the beta-adrenoceptor antagonist, propranolol. The glucocorticoid antagonist, RU 486, did not modify systemic TNF alpha production. These results indicate that systemic TNF alpha production is regulated by adrenaline but not by corticosterone. 3. When mice were primed with thioglycollate, TNF alpha was produced in the peritoneal cavity in response to low dose LPS (1 micrograms). The levels of TNF alpha in the peritoneal cavity were not enhanced by adrenalectomy or by treatment with either propranolol or RU 486, indicating local production of TNF alpha in the peritoneal cavity is not regulated by adrenaline or corticosterone. 4. The phosphodiesterase type IV (PDE-IV) inhibitor, rolipram, inhibited both the systemic production of TNF alpha in response to high dose endotoxin (ED50 = 1.3 mg kg-1) and the local production of TNF alpha in the peritoneal cavity in response to low dose endotoxin (ED50 = 9.1 mg kg-1). In adrenalectomized mice there was a slight reduction in the ability of rolipram to inhibit the systemic production of TNF alpha (ED50 = 3.3 mg kg-1) while the ability of rolipram to inhibit the local production of TNF alpha in the peritoneal cavity was virtually abolished (24% inhibition at 30 mg kg-1). The glucocorticoid antagonist, RU 486, also reduced the ability of rolipram to inhibit local TNF alpha production while propranolol was without effect. 5. Systemic treatment with rolipram increased the plasma concentrations of corticosterone in normal mice but not in adrenalectomized mice indicating that rolipram can cause adrenal stimulation in vivo. 6. In summary, these data indicate that systemic production of TNF alpha in response to high dose endotoxin is controlled differently from the local production of TNF alpha in response to low dose endotoxin. The systemic production of TNF alpha is regulated by catecholamines, but not by corticosterone, while the local production of TNF alpha in the peritoneal cavity is not regulated by basal levels of either catecholamines or corticosterone. 7. These data also show that the ability of rolipram to inhibit the local production of TNF alpha is dependent on the release of corticosterone from the adrenal glands.

The protective role of the hypothalamic-pituitary-adrenal axis against lethality produced by immune, infectious, and inflammatory stress

We have shown that ADX and HYPOX rats exhibit a markedly increased sensitivity to the lethal effects of IL-1-beta and LPS compared to sham controls with an intact HPAA. These results indicated that the reports of lethal effects of cytokines and LPS which generates cytokines in mice with a compromised HPAA were not idiosyncratic or specific to mice but represented a general response that would have been expected in any organism with a compromised HPAA. We further demonstrated that protection against lethal effects due to IL-1-beta or LPS could be produced by treating ADX rats with glucocorticoid in a quantity estimated to be equivalent to corticosterone secretion provoked during stress. In contrast, we found that acutely stalk-sectioned rats with pituitaries disconnected from hypothalamic regulation did not show a markedly increased susceptibility to lethal effects of LPS as did ADX or HYPOX rats. Although a minority of stalk-sectioned rats were killed by LPS, the majority of rats were protected from lethal actions of LPS. This response suggested that an intact pituitary-adrenal axis without the normal hypothalamic control could still provide significant protection presumably due to generation of cytokines which stimulated the pituitary over several hours. The results from our lethality studies clearly underscore the importance of activating the stress axis and increasing glucocorticoid secretion to protect against potentially lethal effects of cytokines that can be induced by immune, infectious, or inflammatory stimuli. Cytokine-stimulated effects can initially result in beneficial actions to the host by promoting immune/inflammatory responses that are protective in nature and help defend against a variety of invading stimuli (infectious, immune, inflammatory, traumatic, neoplastic). Normally the HPAA responds to cytokine stimulation by ultimately increasing glucocorticoid secretion in order to counterregulate cytokine actions, modulate the host response, and protect the host from excessively catabolic effects of unregulated cytokine generation and actions. For many years, clinicians have recognized that patients with deficient glucocorticoid secretion (e.g., Addison's disease or pituitary ACTH deficiency) require increased glucocorticoid replacement during episodes of fever, infection, or inflammatory stress. However, the reasons why stress-equivalent glucocorticoid replacement were required were not entirely clear. Now, we understand that glucocorticoids are critically important for protecting the host against its own defense mechanisms so that the stimulation of cytokines can facilitate a protective response against an invading insult without also killing the host.

Interleukin-1 receptors in the brain-endocrine-immune axis. Modulation by stress and infection

In the present study, we examined the in vitro and in vivo modulation of IL-1 receptors by stress and endotoxin treatment. The treatment of AtT-20 mouse pituitary adenoma cells for 24 h with neuroendocrine mediators of stress such as CRF and catecholamines produced dose-dependent increases in cAMP production and [125I]IL-1 alpha binding. In contrast, somatostatin and dexamethasone significantly inhibited CRF-stimulated cAMP production and decreased both basal and CRF-mediated increases in [125I]IL-1 alpha binding. Furthermore, in keeping with the effects of stress mediators to up-regulate IL-1 receptors in AtT-20 cells, ether-laparotomy stress in mice resulted in a significant increase in [125I]IL-1 alpha binding in the pituitary with no significant alterations observed in the brain; in contrast, [125I]oCRF binding in the pituitary was significantly decreased after the ether-laparotomy stress. Next, we investigated the modulation of IL-1 beta levels and [125I]IL-1 alpha binding following endotoxin treatment. IL-1 beta levels were dramatically increased in the peripheral tissues (pituitary, testis, and spleen) at 2-6 h after a single LPS injection (30 micrograms LPS/mouse); however, no significant changes were observed in brain (hippocampus and hypothalamus). [125I]IL-1 alpha binding in the pituitary gland, liver, spleen, and testis was significantly decreased at 2 h following a single administration of both low (30 micrograms LPS/mouse) and high (300 micrograms LPS/mouse) doses of endotoxin. [125I]IL-1 alpha binding in the hippocampus was not significantly altered at 2 h by low dose of LPS and was significantly decreased by high-dose administration of LPS (300 micrograms/mouse). Following two LPS injections (at 0 and 12 h), dramatic increases in IL-1 beta concentrations in the hypothalamus, hippocampus, spleen, and testis were observed at 2 h after the second LPS injection; a small but statistically nonsignificant change was evident in the pituitary. Moreover, dramatic decreases in [125I]IL-1 alpha binding were seen after two injections of 30 micrograms LPS/mouse in both central and peripheral tissues. These data provide further support for a role for IL-1 in coordinating brain-endocrine-immune responses to stress and infection.

Type 1 interleukin-1 receptor in the rat brain: distribution, regulation, and relationship to sites of IL-1-induced cellular activation

Systemic interleukin-1 (IL-1) activates the hypothalamo-pituitary-adrenal (HPA) axis, an effect exerted through increased synthesis and secretion of corticotropin-releasing factor (CRF) by parvicellular neurosecretory neurons. The site(s) and mechanism(s) through which circulating IL-1 may access central systems governing HPA axis output remain obscure. To identify potential cellular targets for blood-borne IL-1, we analyzed the distribution of mRNA encoding the rat type 1 IL-1 receptor (IL-1R1) in rat brain. Regional ribonuclease protection assays detected a single protected fragment corresponding to the membrane-bound form of the IL-1R1 mRNA in all areas analyzed. In situ hybridization revealed labeling predominantly over barrier-related cells, including the leptomeninges, non-tanycytic portions of the ependyma, the choroid plexus, and vascular endothelium. Low to moderate levels of the IL-1R1 mRNA were detected in just a few neuronal cell groups, including the basolateral nucleus of the amygdala, the arcuate nucleus of the hypothalamus, the trigeminal and hypoglossal motor nuclei, and the area postrema. No specific labeling for IL-1R1 mRNA was detected over neurons that respond to intravenous IL-1 beta by induction of transcription factor Fos, including hypophysiotropic CRF cells and brainstem catecholamine neurons. Injection of IL-1 beta did, however, provoke induction of mRNA encoding the immediate-early gene, NGFI-B, but not c-fos, in two major loci of IL-1R1 expression, vascular endothelial cells, and the area postrema. Intravenous injection of IL-1 beta acutely down-regulated IL-1R1 mRNA in perivascular cells, but not in neuronal cell groups. These results suggest the parenchymal sites of IL-1R1 expression in rat to be distinct from those reported previously in mouse. The common expression in both species of an IL-1R in non-neuronal elements highlights the possibility that IL-1-mediated activation of CRF neurons may result from cytokine-receptor interaction at vascular, and/or other barrier-related, sites to trigger release of secondary signalling molecules in a position to interact with components of HPA control circuitry.

Modulation of interleukin-1 receptors in the neuro-endocrine-immune axis

Interleukin-1 (IL-1) receptors with kinetics, pharmacological and biochemical characteristics of type I IL-1 receptors have been identified in the mouse neuro-endocrine-immune axis. In the present study, we examined the in-vitro and in-vivo modulation of IL-1 receptors by stress and endotoxin treatment. The treatment of AtT-20 mouse pituitary adenoma cells for 24 hr with neuro-endocrine mediators of stress such as corticotropin releasing factor (CRF) and catecholamine (beta 2 adrenergic) receptor agonists produced a dose-dependent increase in cAMP and [125I]IL-1 alpha binding. In contrast, somatostatin and dexamethasone significantly inhibited CRF-stimulated cAMP production and decreased both basal and CRF-mediated increase of [125I]IL-1 alpha binding. Furthermore, in keeping with the effects of stress mediators to upregulate IL-1 receptors in AtT-20 cells, ether-laparotomy stress in mice resulted in a significant increase in [125I]IL-1 alpha binding in the pituitary with no significant alterations observed in the brain; in contrast, [125I]oCRF binding in the pituitary was significantly decreased after the ether-laparotomy stress. Next, we investigated the modulation of IL-1 beta levels and [125I]IL-1 alpha binding following endotoxin lipopolysaccharide (LPS) treatment. IL-1 beta levels were dramatically increased in the peripheral tissues (pituitary, testis and spleen) at 2-6 hr after a single LPS injection (30 micrograms LPS/mouse). However, no significant changes were observed in brain (hippocampus and hypothalamus). [125I]IL-1 alpha binding in the pituitary gland, liver, spleen and testis was significantly decreased at 2 hr following a single administration of both low (30 micrograms LPS/mouse) and high (300 micrograms LPS/mouse) doses of endotoxin. [125I]IL-1 alpha binding in the hippocampus was not significantly altered at 2 hr by a low dose of LPS and was significantly decreased by high dose administration of LPS (300 micrograms/mouse). Following two LPS injections (at 0 and 12 hr), dramatic increases in IL-1 beta concentrations in the hypothalamus, hippocampus, spleen and testis were observed at 2 hr after the second LPS injection; a small but statistically nonsignificant change was evident in the pituitary. Moreover, dramatic decreases in [125I]IL-1 alpha binding were seen after two injections of 30 micrograms LPS/mouse in both central and peripheral tissues. These data provide further support for a role for IL-1 in co-ordinating neuro-endocrine-immune responses to stress and infection.

Regulation of interleukin-1 receptors and hypothalamic-pituitary-adrenal axis by lipopolysaccharide treatment in the mouse

We measured iodine-125-labeled recombinant human interleukin-1 alpha (125I-IL-1 alpha) binding in the hippocampus, pituitary, liver, spleen and testis, and plasma adrenocorticotropic hormone (ACTH) and corticosterone levels after i.p. injection of various dose and treatment regimens of the bacterial endotoxin, lipopolysaccharide (LPS). Plasma ACTH and corticosterone levels were significantly increased at 2 h after acute administration of LPS (60 or 300 micrograms/mouse). 125I-IL-1 alpha binding in all peripheral tissues examined was significantly and comparably decreased at 2 h after a single injection of 30 micrograms or 300 micrograms LPS/mouse. On the other hand, 125I-IL-1 alpha binding in hippocampus was significantly decreased only after high dose administration of LPS (300 micrograms/mouse). In order to evaluate if activation of IL-1 in brain resulting in the observed decrease in 125I-IL-1 alpha binding may require more sustained exposure to endotoxin, we compared the effects of a single injection (60 micrograms/mouse) and two injections of LPS (30 micrograms/mouse each at 0 and 12 h). A single injection of LPS (60 micrograms/mouse) decreased 125I-IL-1 alpha binding in the testis but not in the hippocampus, while two LPS injections (30 micrograms/mouse each at 0 and 12 h) caused dramatic reductions in 125I-IL-1 alpha binding in both the hippocampus and testis.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential effect of glucocorticoids on tumour necrosis factor production in mice: up-regulation by early pretreatment with dexamethasone

Glucocorticoids (GC) are well known inhibitors of tumour necrosis factor (TNF) production. We investigated the role of endogenous GC in the regulation of TNF production in mice treated with lipopolysaccharide (LPS) using a pretreatment with dexamethasone (DEX) to down-regulate the hypothalamus-pituitary-adrenal axis (HPA). Short-term DEX pretreatment (up to 12 h before LPS) inhibited TNF production, but earlier (24-48 h) pretreatments potentiated it. This up-regulating effect was not observed in adrenalectomized mice or when GC synthesis was inhibited with cyanoketone (CK). This effect could not be explained only by the suppression of LPS-induced corticosterone (CS) levels induced by DEX, since a 48-h pretreatment potentiated TNF production without affecting LPS-induced CS levels. On the other hand, mice chronically pretreated with DEX were still responsive to its inhibitory effect on TNF production, thus ruling out the possibility of a decreased responsiveness to GC.

Activation of the hypothalamus-pituitary-adrenal axis by bacterial endotoxins: routes and intermediate signals

Peripheral administration of endotoxin induces brain-mediated responses, including activation of the hypothalamus-pituitary-adrenal (HPA) axis and changes in thermoregulation. This paper reviews the mechanisms by which endotoxin affects these responses. The effects on thermoregulation are complex and include macrophage-dependent hyperthermic and hypothermic responses. Low doses of endotoxin, given IP, activate peripheral macrophages to produce interleukin (IL)-1 beta, which enters the circulation and acts as a hormonal signal. IL-1 may pass fenestrated endothelium in the median eminence to stimulate corticotropin-releasing hormone (CRH) secretion from the CRH nerve-terminals. In addition, IL-1 may activate brain endothelial cells to produce IL-1, IL-6, prostaglandins, etc., and secrete these substances into the brain. By paracrine actions, these substances may affect neurons (e.g., CRH neurons) or act on microglial cells, which show IL-1-induced IL-1 production and therefore amplify and prolong the intracerebral IL-1 signal. In contrast, high doses of endotoxin given i.v. may directly stimulate endothelial cells to produce IL-1, IL-6, and prostaglandin-E2 (PGE2) and thereby activate the HPA axis in a macrophage-independent manner.

Glucocorticoid-mediated control of the activation and clonal deletion of peripheral T cells in vivo

Poly- and oligoclonal T cell stimuli like anti-CD3 epsilon monoclonal antibody or Staphylococcus aureus enterotoxin B (SEB), injected at doses that per se are not lethal, provoke acute death within less than 24 h, provided that endogenous glucocorticoids (GC) are depleted by adrenalectomy or by injection of saturating amounts of the GC receptor antagonist RU-38486 (mifepristone). Pharmacological doses of the GC agonist dexamethasone (DEX) alter the in vivo response of splenic V beta 8+ T cells to SEB, thus impeding the expansion of such cells and causing their rapid (3 d) clonal deletion. In contrast, coadministration of RU-38486 counteracts a SEB-induced early (12 h) reduction of V beta 8+CD4+ and V beta 8+CD8+ spleen cells. In vivo T cell stimulation by injection of bacterial superantigen induces a rapid (peak at 90-120 min) increase in corticosterone serum levels, suggesting that endogenous GC might control early T cell activation. Accordingly, kinetic studies revealed that RU-38486 has to be administered within 2 h after superantigen administration to exert its lethal effect. Similarly, exogenous GC must be injected during this critical phase (2 h) to rescue animals from acute death induced by coinjection of SEB and D-galactosamine (GalN). Adrenalectomy, injection of RU-38486 and priming with GalN per se provoke the programmed death of peripheral CD4+ and CD8+ T cells. Thus, three manipulations that sensitize mice for the lethal effect of T cell stimulation also exert a proapoptotic effect on peripheral T cells. In synthesis, endogenous and exogenous GC regulate T cell responses and determine the propensity of peripheral T cells to undergo apoptosis.