Interleukin-10 Regulated Gene Expression in Cells of Hypothalamic-Pituitary-Adrenal Axis Origin

1. Aim: The hypothalamic-pituitary-adrenal (HPA) axis is a mediator for interactions between the immune and neuroendocrine systems. Pro-inflammatory cytokines such as interleukin-1 (IL-1), interleukin-6 (IL-6), and tumor necrosis factor-alpha (TNF-α) have been shown to activate the HPA axis. Recently, interleukin-10, an important anti-inflammatory cytokine in the immune system, has been shown to be expressed in the central nervous system and neuroendocrine system. Little is known, however, about IL-10’s functions in the HPA axis. 2. Methods: The Affymetrix DNA microarray (mouse genome U74Av2 Probe Array) was conducted to determine the gene expression profile regulated by IL-10 in cells of HPA axis origin. 3. Results: In this study, we analyzed gene expression regulated by IL-10 in cells derived from the HPA axis. The results showed that quorums of genes are modulated by IL-10 in these neuroendocrine cells. 4. Conclusions: These findings will provide a valuable repository to aid in understanding IL-10’s functions in the HPA axis at the molecular level.     

Glutamate augments retrovirus-induced immunodeficiency through chronic stimulation of the hypothalamic-pituitary- adrenal axis

The mechanisms for activating the hypothalamic-pituitary-adrenal (HPA) axis and the roles glucocorticoids play in the pathogenesis of chronic infectious disease are largely undefined. Using the LP-BM5 model of retrovirus-induced immunodeficiency, we found alterations in HPA axis function, manifested as an increase in circulating levels of adrenocorticotropic hormone and corticosterone, beginning after only 3 mo of infection. These changes occurred contemporaneously with a shift in the profile of circulating cytokines from a Th1-dominant (IFN-gamma) to Th2-dominant (IL-4, IL-10) phenotype. No significant changes in either circulating IL-1beta, IL-6, or TNF-alpha levels were observed in infected mice. Administering the N-methyl-D-aspartate receptor antagonist MK-801 to infected mice normalized plasma adrenocorticotropic hormone and corticosterone levels, indicating that glutamate was a major activator of the HPA axis. Moreover, MK-801 treatment of late-stage mice also reversed the type 1 to type 2 cytokine shift to a degree comparable or superior to treatment with the glucocorticoid receptor antagonist RU-486. These findings indicate that HPA axis activation during LP-BM5 retrovirus infection is mediated by the chronic hyperactivation of glutamatergic pathways in the hypothalamus. Through this mechanism, the degree of peripheral immunodeficiency observed in the late-stage disease is profoundly augmented.     

Reduced adrenal response and increased mortality after systemic Klebsiella pneumoniae infection in interleukin-6-deficient mice.

During bacterial infections, both the immune system and the hypothalamus-pituitary-adrenal (HPA) axis are activated. The role of IL-6 in the activation of the HPA axis during bacterial sepsis is not fully understood. The aim of the present study was to investigate the role of endogenous IL-6 in a potentially lethal infection with Klebsiella pneumoniae and the concomitant activation of the HPA axis. We examined the mortality of IL-6-/- and IL-6+/+ mice after intravenous (i.v.) infection with K. pneumoniae as well as the bacterial outgrowth in several organs. Subsequently, the influence of endogenous IL-6 on the effect of i.v. administration of K. pneumoniae on the plasma levels of corticosterone and the pro-inflammatory cytokines TNF-alpha and IL-1alpha was investigated in these mice. The present study demonstrates that IL-6-/- mice are more susceptible than IL-6+/+ mice to a systemic Gram-negative infection with K. pneumoniae, leading to increased outgrowth of microorganisms in the organs of the mice. Moreover, this infection is associated with a reduced adrenal response in IL-6-/- mice. We conclude that IL-6-/- mice are more susceptible to Gram-negative bacterial infections, which is mainly due to an impaired recruitment of granulocytes to the site of infection in the absence of IL-6. Furthermore, the reduced adrenal response may be an explanation for the strong inflammatory response with higher TNF-alpha plasma levels in IL-6-/- mice.     

The hierarchical relationships between the organs of the hypothalamo-hypophyseal-adrenal system (HHAS) in inflammation

The HPA axis is the major system of adaptation to the action of different stressors, including inflammatory agents. The glucocorticoids, the end product of HPA axis prevent the extension of inflammation. In this article we discuss the classic direct and feedback loops in the HPA axis during acute bacterial inflammation. On the basis of literary and own findings we put forward a speculation that different systemic cytokines released one by one during inflammation induce the appearance of new functional relations between the organs of HPA axis. Because of cytokines are involved in the modulation of hormonal sensitivity in the HPA axis the serious modification of direct as well as feedback relations is postulated. On the other hand cytokines and immune cells induce autocrine and paracrine production of cytokines in the HPA axis, that result in autonomization of pituitary and adrenals functions. So, the acute inflammation factors could be seen as "short-time" functional dominants of HPA axis functioning.     

Inhibition of brain proinflammatory cytokine synthesis reduces hypothalamic excitation in rats with ischemia-induced heart failure

The expression of proinflammatory cytokines increases in the hypothalamus of rats with heart failure (HF). The pathophysiological significance of this observation is unknown. We hypothesized that hypothalamic proinflammatory cytokines upregulate the activity of central neural systems that contribute to increased sympathetic nerve activity in HF, specifically, the brain renin-angiotensin system (RAS) and the hypothalamic-pituitary-adrenal (HPA) axis. Rats with HF induced by coronary ligation and sham-operated controls (SHAM) were treated for 4 wk with a continuous intracerebroventricular infusion of the cytokine synthesis inhibitor pentoxifylline (PTX, 10 microg/h) or artificial cerebrospinal fluid (VEH). In VEH-treated HF rats, compared with VEH-treated SHAM rats, the hypothalamic expression of proinflammatory cytokines was increased, along with key components of the brain RAS (renin, angiotensin-converting enzyme, angiotensin type 1 receptor) and corticotropin-releasing hormone, the central indicator of HPA axis activation, in the paraventricular nucleus (PVN) of the hypothalamus. The expression of other inflammatory/excitatory mediators (superoxide, prostaglandin E(2)) was also increased, along with evidence of chronic neuronal excitation in PVN. VEH-treated HF rats had higher plasma levels of norepinephrine, ANG II, interleukin (IL)-1beta, and adrenocorticotropic hormone, increased left ventricular end-diastolic pressure, and increased wet lung-to-body weight ratio. With the exception of plasma IL-1beta, an indicator of peripheral proinflammatory cytokine activity, all measures of neurohumoral excitation were significantly lower in HF rats treated with intracerebroventricular PTX. These findings suggest that the increase in brain proinflammatory cytokines observed in rats with ischemia-induced HF is functionally significant, contributing to neurohumoral excitation by activating brain RAS and the HPA axis.     

CHRONIC STIMULATION OF THE HYPOTHALAMUS–PITUITARY–ADRENAL AXIS IN RATS BY INTERLEUKIN 1β: CENTRAL AND PERIPHERAL MECHANISMS

The authors have studied mechanisms which could be involved in the sustained activation of the hypothalamus–pituitary–adrenal (HPA) axis during continuous infusion of rats with recombinant human interleukin-1β (IL-1β). First, the effects of 3 days of intracerebroventricular (i.c.v.) infusion of rats with IL-1 on plasma adrenocorticotropin (ACTH) and corticosterone (B) levels were investigated. Thereafter, changes in plasma ACTH and B levels were followed in rats intraperitoneally (i.p.) infused with IL-1β after immunoneutralization of corticotropin-releasing hormone (CRH), hypophysectomy (HPX), macrophage depletion using dichloromethylene diphosphonate (Cl₂MDP)-containing liposomes, adrenalectomy (ADX) and dexamethasone (DEX) administration, respectively. Infusion of IL-1β i.c.v., even in doses as low as 0.1 μg/day, induced significant increases in plasma ACTH and B levels. HPX and ADX rats died within 18 h after starting the IL-1β infusion (0.5 μg/day). Immunoneutralization of CRH significantly decreased and macrophage depletion significantly increased the stimulation of the HPA axis by IL-1 (4.0 μg/day). Administration of high doses of DEX completely abolished the stimulation of the HPA axis by IL-1β (2.0 μg/day). The present study demonstrates that lower doses of IL-1β were able to activate the HPA axis when infused i.c.v. compared with i.p. Regarding stimulation of the HPA axis by chronic i.p. infusion of IL-1β the present study: (1) provides evidence that the CRH system is involved; (2) provides no evidence for a direct stimulatory effect of IL-1β on the release of B by the adrenal gland which is of sufficient magnitude to resist the stress of chronic i.p. IL-1β infusion; (3) shows that endogenous macrophage-derived mediators, induced by i.p. IL-1β infusion, express an overall inhibitory rather than a stimulatory effect on the activity of the HPA axis; (4) demonstrates that exogenous administration of DEX blocks the effect of IL-1β, which fits well in the concept of an immunoregulatory feedback between IL-1β and glucocorticoids.     

Interleukins 1α and 1β as regulators of steroidogenesis in human NCI-H295R adrenocortical cells

Inflammatory cytokines interleukin-1 (IL-1) and tumor necrosis factor-α (TNF-α) regulate the activity of the hypothalamo-pituitary-adrenal (HPA) axis at several levels. Although hypothalamic CRH secretion may be the primary mechanism by which these cytokines activate the HPA axis, IL-1 expression is increased within the adrenal glands in models for systemic inflammation, and IL-1 may augment adrenal glucocorticoid production. Our aim was to investigate the direct effects of IL-1α and IL-1β on adrenal steroidogenesis and expression of three key steroidogenic genes in human adrenocortical cells using the NCI-H295R cell line as a model. mRNAs encoding receptors for IL-1, TNF-α, and leukemia inhibitory factor (LIF) were detectable in the cell line (Affymetrix microarray analysis). Both IL-1α and IL-1β increased cortisol, androstenedione, dehydroepiandrosterone and dehydroepiandrosterone sulfate production, and the accumulation of mRNAs for steroidogenic acute regulatory protein (STAR), 17α-hydroxylase/17,20-lyase (CYP17A1) and 3β-hydroxysteroid dehydrogenase 2 (HSD3B2) in these cells (P<0.05 for all). Both ILs augmented TNF-α- and LIF-induced STAR and CYP17A1 mRNA accumulation, and TNF-α-induced cortisol production (P<0.05 for all). Both ILs also increased the apoptotic index of the cells (P<0.05), which was efficiently neutralized by their specific antibodies. The IL-induced changes in the STAR, HSD3B2, and CYP17A1 protein levels were not as evident as those in the respective mRNA levels. In conclusion, the combined effect of inflammatory cytokines at the adrenal level in acute or chronic inflammatory states could significantly stimulate glucocorticoid production, and thus explain the observed discrepancy between the cortisol and ACTH concentrations sometimes seen in sepsis and chronic inflammatory states.     

Cytokines and glucocorticoid receptors are associated with the antidepressant-like effect of alarin

Little is known about the physiological or pharmacological properties of alarin, a new neuropeptide belonging to the galanin family. We previously showed that alarin has an antidepressant-like effect and is associated with a decrease in the hyperactivity of hypothalamic–pituitary–adrenal (HPA) axis that is observed in patients with depression using unpredictable chronic mild stress (UCMS) mouse model of depression. However, the mechanisms underlying these effects have not been uncovered. Inflammatory cytokines are reportedly associated with depression. Animal studies and cytokine immune therapy in humans suggest that pro-inflammatory cytokines induce depressive symptomatology and potently activate the HPA axis, whereas anti-inflammatory cytokines may decrease activation. Thus, we first determined the levels of inflammatory cytokines in the blood and brain to evaluate whether the antidepressant-like effect of alarin in UCMS-treated mice is related to its regulation of these inflammatory cytokines. Pro-inflammatory cytokines disrupt the function and/or expression of glucocorticoid receptors (GRs), which mediate the negative feedback of glucocorticoids on the HPA axis to keep it from being overactivated. We next explored the expression level of GRs in the brains of mice subjected to UCMS and to the administration of alarin. We found that intracerebroventricular administration of alarin significantly ameliorated depression-like behaviors in the UCMS-treated mice. Alarin restored the UCMS-induced an increase in the levels of the pro-inflammatory cytokines interleukin (IL)-6 and tumor necrosis factor α and a decrease in the anti-inflammatory cytokine IL-10 level in the blood, prefrontal cortex, hippocampus and hypothalamus. Alarin also reversed the UCMS-induced down-regulation of GR expression in these brain regions. Thus, the antidepressant-like effects of alarin may be mediated by restoring altered pro-inflammatory and anti-inflammatory cytokine levels and GR expression to decrease HPA axis hyperactivity. Our findings provide additional knowledge to interpret the pathophysiology of depression.     

alpha-MSH and gamma-MSH inhibit IL-1beta induced activation of the hypothalamic-pituitary-adrenal axis through central melanocortin receptors

Alpha-melanocyte-stimulating hormone (alpha-MSH) is a neuroimmunomodulatory peptide that is involved in the control of host responses trough modulation of production and action of proinflammatory cytokines in inflammatory cells in the periphery and within the central nervous system (CNS). However, little is known about the receptors that mediate the modulatory effects of alpha-MSH in the CNS. The objective of the present study was to establish the specific melanocortin receptors involved in the inhibition by MSH peptides of IL-1beta-induced activation of the HPA. i.c.v. injection of 12.5 ng of IL-1beta caused significant changes in plasma corticosterone, as compared to basal levels. The treatment with gamma-MSH (1 microg), an MC3 receptor agonist, resulted in significant reduction of the IL-1beta-induced plasma corticosterone levels. Administration of the MC3/MC4 receptor antagonist SHU9119 blocked this effect. Besides, treatment with a high dose of alpha-MSH (1 microg) increased plasma corticosterone. When alpha-MSH was given at a lower dose (0.1 microg), it did not modify corticosterone levels but caused an inhibitory effect on the corticosterone release induced by IL-1beta. The administration of SHU9119 or a more selective MC4 receptor antagonist like HS014 blocked the effects of alpha-MSH. In conclusion, our results suggest that both alpha-MSH and gamma-MSH are capable of inhibiting the effect of the IL-1beta on the activation of HPA axis acting at the CNS, and that this effect is mediated by specific central melanocortin receptors.     

Effects of repeated injections of interleukin 1beta or lipopolysaccharide on the HPA axis in the newborn rat

The hypothalamic-pituitary-adrenal (HPA) axis is stimulated during immune and inflammatory processes. Interleukin 1beta (IL-1beta) and lipopolysaccharide (LPS) are known to be potent stimulators of this axis. During postnatal development, the rat seems to be hyporesponsive to many stimuli. The effects of repeated systemic injections of IL-1beta and LPS on the HPA axis were investigated in neonatal rats. IL-1beta (0.02 microg/pup, administered twice daily from postnatal day 1 to 4) induced marked elevation in plasma corticosterone (CORT) level as compared to controls and LPS groups (0.4 microg or 1.2 microg LPS/pup, injected once daily from postnatal day 1 to 4). Adrenal wet weight was significantly higher, thymus weight was significantly lower. In contrast to the organ weights, there were no differences in CORT concentrations between LPS-exposed groups and controls. However, the weights of the adrenals in rats treated with LPS were significantly increased in a dose-dependent manner as compared to controls. The high LPS dose was associated with significantly lower thymus weights as compared to controls and 0.4 microg LPS rats. Thymus weights were significantly lower following IL-1beta- than LPS-administration. It is supposed that a developing endotoxin tolerance could account for the observed absence of CORT rise after the last LPS injection.     

Virus and host factors that mediate the clinical and behavioral signs of experimental herpetic encephalitis. A short auto-review

Experimental models that mimic the clinical syndrome of human viral encephalitis and represent HSV-1 neurotropism were utilized to investigate neuro-pharmacologic changes mediating clinical and behavioral manifestations of encephalitic infection of the central nervous system with HSV-1-induced rapid activation of the hypothalamic--pituitary--adrenocortical (HPA) axis and production of brain derived interleukin-1 (IL-1) and prostaglandin E2 (PG-E2), independently of viral replication. HSV-1 infection induced clinical signs of fever, motor hyperactivity and aggressive behavior. These manifestations were dependent on a permissive action of circulating glucocorticoids and not related to the degree of viral replication in the brain. Hyperthermia and HPA axis activation were also specifically dependent on HSV-1-induced brain IL-1 and PG-E2. The chronic neurological sequel or fatal outcome of HSV-1 encephalitis may be due to viral replication and brain tissue destruction, which are dependent on virus encoded virulence genes. In contrast, the clinical and behavioral signs in the acute phase are a result of activation of neurochemical systems, including cytokines, prostaglandinds and catecholamines. Circulating glucocorticoids play an essential role in mediating the physiologic actions of HSV-1-induced brain products and the clinical syndrome of encephalitis.     

The role of cyclo-oxygenase and lipoxygenase in the interleukin-1-induced activation of the HPA axis: dependence on the route of injection.

Interleukin-1 (IL-1) has been shown to activate the hypothalamic-pituitary-adrenal (HPA) axis, and to elevate cerebral concentrations of tryptophan and the norepinephrine catabolite, 3-methoxy,4-hydroxyphenylethyleneglycol (MHPG). Eicosanoids have been shown to be involved in a number of the effects of IL-1, but their role in the activation of the HPA axis is controversial. We studied the effects of various cyclo- and lipoxygenase inhibitors on the neurochemical and HPA responses to IL-1. Pretreatment of mice with the cyclo-oxygenase inhibitors, indomethacin (10-25 mg/kg) or ibuprofen (10 mg/kg) failed to prevent the elevations of plasma corticosterone, or hypothalamic MHPG or tryptophan that followed intraperitoneally (IP) administered IL-1. Similar results were obtained with the nonspecific oxygenase inhibitor, BW 755C, and the lipoxygenase inhibitor, BW A4C. However, the cyclo-oxygenase inhibitor, diclofenac, did attenuate the IL-1-induced elevation of plasma corticosterone and the neurochemical changes. To resolve the conflicting data on the effect of indomethacin on the IL-1-induced elevation of plasma concentration, we studied the effects of indomethacin on the response to IL-1 injected intravenously (IV). By contrast with the response to IP IL-1, that to IV IL-1 was attenuated by indomethacin. Time course of the HPA response to IL-1 is more rapid following IP injections than IV, therefore we assessed the effects of IV IL-1, earlier than that to IP IL-1. Forty min following IP IL-1, the corticosterone response to IL-1 was markedly attenuated. This suggests that more than one mechanism is involved in the HPA response to IL-1. The more rapid one, predominant in the case of IV injections, is sensitive to cyclo-oxygenase inhibitors, whereas the slower one is not.     

Validation of urinary cortisol as an indicator of hypothalamic-pituitary-adrenal function in the bearded emperor tamarin (Saguinus imperator subgrisescens)

The use of cortisol levels as a measure of stress is often complicated by the use of invasive techniques that may increase hypothalamic-pituitary-adrenal (HPA) axis activity during sample collection. The goal of this study was to collect samples noninvasively and validate an enzyme-immunoassay (EIA) for the measurement of cortisol in urine to quantify HPA axis activity in the bearded emperor tamarin (Saguinus imperator subgrisescens). Urine samples were collected from trained subjects between 0700 and 0730 hr during a 1-month period, and were pooled for immunological validation. We validated the assay immunologically by demonstrating specificity, accuracy, precision, and sensitivity. For biological validation of the assay, we showed that levels of urinary cortisol (in samples collected between 0700 and 1700 hr) varied significantly across the day. Cortisol concentration was lowest at 0700 hr, increased to a mid-morning peak (0900 hr), and declined across the remainder of the day in a typical mammalian circadian pattern. We thus demonstrate that urinary cortisol can be used to quantify HPA activity in S.i. subgrisescens.     

Electrical stimulation of afferent vagus nerve induces IL-1beta expression in the brain and activates HPA axis

Possible roles of the afferent vagus nerve in regulation of interleukin (IL)-1beta expression in the brain and hypothalamic-pituitary-adrenal (HPA) axis were examined in anesthetized rats. Levels of IL-1beta mRNA and protein in the brain were measured by comparative RT-PCR and ELISA. Direct electrical stimulation of the central end of the vagus nerve was performed continuously for 2 h. The afferent stimulation of the vagus nerve induced increases in the expression of mRNA and protein levels of IL-1beta in the hypothalamus and the hippocampus. Furthermore, expression of corticotropin-releasing factor mRNA was increased in the hypothalamus 2 h after vagal stimulation. Plasma levels of ACTH and corticosterone were also increased by this stimulation. The present results indicate that activation of the afferent vagus nerves itself can induce production of IL-1beta in the brain and activate the HPA axis. Therefore, the afferent vagus nerve may play an important role in transmitting peripheral signals to the brain in the infection and inflammation.     

Neuropeptide Y regulates catecholamine release evoked by interleukin-1beta in mouse chromaffin cells

Activation of the hypothalamic-pituitary-adrenal gland (HPA) axis can modulate the immune system. Cytokines and neuropeptide Y (NPY) are potent regulators of the HPA axis and are both produced by the adrenal medulla. The cytokine interleukin-1beta (IL-1beta) belongs to the interleukin-1 family along with interleukin-1alpha and the interleukin receptor antagonist (IL-1ra). The aim of the present study was to determine the interaction between NPY and IL-1beta in catecholamine (norepinephrine, NE and epinephrine, EP) release from mouse chromaffin cells in culture. We found that IL-1beta increased the constitutive release of NPY, NE and EP from mouse chromaffin cells. This IL-1beta stimulatory effect was blocked by IL-1ra. The immunoneutralization of NPY and the use of the NPY Y(1) receptor antagonist (BIBP 3226) inhibited the stimulatory effect of IL-1beta on catecholamine release from these cells. The present work shows that IL-1beta induces catecholamine release, and in turn this peptide will induce an additional increase in catecholamine release acting through the Y(1) receptor. This work suggests that NPY is involved in the regulatory loop between the immune and the adrenal system in some pathophysiological conditions where plasmatic IL-1beta increases, like in sepsis, rheumatoid arthritis, stress or hypertension.     

Suppression of the HPA axis during extrahepatic biliary obstruction induces cholangiocyte proliferation in the rat

Cholestatic patients often present with clinical features suggestive of adrenal insufficiency. In the bile duct-ligated (BDL) model of cholestasis, the hypothalamic-pituitary-adrenal (HPA) axis is suppressed. The consequences of this suppression on cholangiocyte proliferation are unknown. We evaluated 1) HPA axis activity in various rat models of cholestasis and 2) effects of HPA axis modulation on cholangiocyte proliferation. Expression of regulatory molecules of the HPA axis was determined after BDL, partial BDL, and α-naphthylisothiocyanate (ANIT) intoxication. The HPA axis was suppressed by inhibition of hypothalamic corticotropin-releasing hormone (CRH) expression by central administration of CRH-specific Vivo-morpholinos or by adrenalectomy. After BDL, the HPA axis was reactivated by 1) central administration of CRH, 2) systemic ACTH treatment, or 3) treatment with cortisol or corticosterone for 7 days postsurgery. There was decreased expression of 1) hypothalamic CRH, 2) pituitary ACTH, and 3) key glucocorticoid synthesis enzymes in the adrenal glands. Serum corticosterone and cortisol remained low after BDL (but not partial BDL) compared with sham surgery and after 2 wk of ANIT feeding. Experimental suppression of the HPA axis increased cholangiocyte proliferation, shown by increased cytokeratin-19- and proliferating cell nuclear antigen-positive cholangiocytes. Conversely, restoration of HPA axis activity inhibited BDL-induced cholangiocyte proliferation. Suppression of the HPA axis is an early event following BDL and induces cholangiocyte proliferation. Knowledge of the role of the HPA axis during cholestasis may lead to development of innovative treatment paradigms for chronic liver disease.     

Time-dependent mediators of HPA axis activation following live Escherichia coli

The hypothalamus-pituitary-adrenal (HPA) axis is activated during an immune challenge to liberate energy and modulate immune responses via feedback and regulatory mechanisms. Inflammatory cytokines and prostaglandins are known contributors to HPA activation; however, most previous studies only looked at specific time points following LPS administration. Since whole bacteria have different immune stimulatory properties compared with LPS, the aim of the present studies was to determine whether different immune products contribute to HPA activation at different times following live Escherichia coli challenge. Sprague-Dawley rats were injected intraperitoneally with E. coli (2.5 × 10(7) CFU) and a time course of circulating corticosterone, ACTH, inflammatory cytokines, and PGE(2) was developed. Plasma corticosterone peaked 0.5 h after E. coli and steadily returned to baseline by 4 h. Plasma PGE(2) correlated with the early rise in plasma corticosterone, whereas inflammatory cytokines were not detected until 2 h. Pretreatment with indomethacin, a nonselective cyclooxygenase inhibitor, completely blocked the early rise in plasma corticosterone, but not at 2 h, whereas pretreatment with IL-6 antibodies had no effect on the early rise in corticosterone but attenuated corticosterone at 2 h. Interestingly, indomethacin pretreatment did not completely block the early rise in corticosterone following a higher concentration of E. coli (2.5 × 10(8) CFU). Further studies revealed that only animals receiving indomethacin prior to E. coli displayed elevated plasma and liver cytokines at early time points (0.5 and 1 h), suggesting prostaglandins suppress early inflammatory cytokine production. Overall, these data indicate prostaglandins largely mediate the early rise in plasma corticosterone, while inflammatory cytokines contribute to maintaining levels of corticosterone at later time points.     

General Anesthetics Inhibit LPS-Induced IL-1β Expression in Glial Cells

Background

Glial cells, including microglia and astrocytes, are considered the primary source of proinflammatory cytokines in the brain. Immune insults stimulate glial cells to secrete proinflammatory cytokines that modulate the acute systemic response, which includes fever, behavioral changes, and hypothalamic-pituitary-adrenal (HPA) axis activation. We investigated the effect of general anesthetics on proinflammatory cytokine expression in the primary cultured glial cells, the microglial cell line BV-2, the astrocytic cell line A-1 and mouse brain.

Methodology/Principal Findings

Primary cultured glial cells were exposed to lipopolysaccharide (LPS) in combination with general anesthetics including isoflurane, pentobarbital, midazolam, ketamine, and propofol. Following this treatment, we examined glial cell expression of the proinflammatory cytokines interleukin (IL)-1β, IL-6, and tumor necrosis factor-alpha (TNF-α). LPS-induced expression of IL-1β mRNA and protein were significantly reduced by all the anesthetics tested, whereas IL-6 and TNF-α mRNA expression was unaffected. The anesthetics suppressed LPS-induced extracellular signal-regulated kinase 1/2 (ERK 1/2) phosphorylation, but did not affect nuclear factor-kappaB and activator protein-1 activation. The same effect was observed with BV-2, but not with A-1 cells. In the mouse experiments, LPS was injected intraperitoneally, and isoflurane suppressed IL-1β in the brain and adrenocorticotropic hormone in plasma, but not IL-1β in plasma.

Conclusions/Significance

Taken together, our results indicate that general anesthetics inhibit LPS-induced IL-1β upregulation in glial cells, particularly microglia, and affects HPA axis participation in the stress response.