Inflammatory bowel disease and intestinal cancer: a paradigm of the Yin-Yang interplay between inflammation and cancer.

Colon cancer represents a paradigm for the connection between inflammation and cancer in terms of epidemiology and mechanistic studies in preclinical models. Key components of cancer promoting inflammation include master transcription factors (for example, nuclear factor kappaB, STAT3), proinflammatory cytokines (for example, tumor necrosis factor, interleukin-6 (IL-6)), cyclooxygenase-2 and selected chemokines (for example, CCL2). Of no less importance are mediators that keep inflammation in check, including IL-10, transforming growth factorbeta, toll-like receptor and the IL-1 receptor inhibitor TIR8/SIGIRR, and the chemokine decoy and scavenger receptor D6. Dissection of molecular pathways involved in colitis-associated cancer may offer opportunities for innovative therapeutic strategies.

Activation of interleukin-1beta receptor suppresses the voltage-gated potassium currents in the small-diameter trigeminal ganglion neurons following peripheral inflammation.

The glial cytokine, interleukin-1beta (IL-1beta), potentiates the excitability of nociceptive trigeminal ganglion (TRG) neurons via membrane depolarization following peripheral inflammation. Perforated patch-clamp technique was used this study to show that the mechanism underlying the excitability of small-diameter TRG neurons following inflammation is due to IL-1beta. Inflammation was induced by injection of complete Freund's adjuvant (CFA) into the whisker pad. The TRG neurons innervating the site of inflammation were identified by fluorogold (FG) labeling. The threshold for escape from mechanical stimulation applied to the orofacial area in inflamed rats was significantly lower than observed for control rats. IL-1beta at 1nM suppressed total voltage-gated K(+) currents in most TRG neurons (70%) under voltage-clamp conditions in control and inflamed rats. IL-1beta significantly decreased the total, transient (I(A)) and sustained (I(K)) currents in FG-labeled small-diameter TRG neurons in both groups. The IL-1beta-induced suppression of TRG neuron excitability was abolished by co-administration of ILra, an IL-1beta receptor blocker. The magnitude of inhibition of I(A) and I(K) currents by IL-1beta was significantly greater in inflamed rats than in controls. IL-1beta inhibited I(A) to a significantly greater extent than I(K). These results suggest that the inhibitory effect of I(A) and I(K) currents by IL-1beta in small-diameter TRG neurons potentiates neuronal excitability thereby contributing to trigeminal inflammatory hyperalgesia. These findings provide evidence for the development of voltage-gated K(+) channel openers and IL-1beta antagonists as therapeutic agents for the treatment of trigeminal inflammatory hyperalgesia.

Topical interleukin-1 receptor antagonist inhibits inflammatory cell infiltration into the cornea.

Interleukin (IL)-1alpha and beta are important modulators of many functions of corneal epithelial and stromal cells that occur following injury to the cornea, including the influx of bone marrow-derived inflammatory cells into the stroma attracted by chemokines released from the stroma and epithelium. In this study, we examined the effect of topical soluble IL-1 receptor antagonist on bone marrow-derived cell influx following corneal epithelial scrape injury in a mouse model. C57BL/6 mice underwent corneal epithelial scrape followed by application of IL-1 receptor antagonist (Amgen, Thousand Oaks, CA) at a concentration of 20 mg/ml or vehicle for 24 h prior to immunocytochemical detection of marker CD11b-positive cells into the stroma. In two experiments, topical IL-1 receptor antagonist had a marked effect in blocking cell influx. For example, in experiment 1, topical IL-1 receptor antagonist markedly reduced detectible CD11b-positive cells into the corneal stroma at 24h after epithelial injury compared with the vehicle control (3.5+/-0.5 (standard error of the mean) cells/400x field and 13.9+/-1.2 cells/400x field, respectively, p<0.01). A second experiment with a different observer performing cell counting had the same result. Thus, the data demonstrate conclusively that topical IL-1 receptor antagonist markedly down-regulates CD-11b-positive monocytic cell appearance in the corneal stroma. Topical IL-1 receptor antagonist could be an effective adjuvant for clinical treatment of corneal conditions in which unwanted inflammation has a role in the pathophysiology of the disorder.

MyD88 is a key mediator of anorexia, but not weight loss, induced by lipopolysaccharide and interleukin-1 beta.

Systemic inflammatory signals can disrupt the physiological regulation of energy balance, causing anorexia and weight loss. In the current studies, we investigated whether MyD88, the primary, but not exclusive, intracellular signal transduction pathway for Toll-like receptor 4 and IL-1 receptor I, is necessary for anorexia and weight loss to occur in response to stimuli that activate these key innate immune receptors. Our findings demonstrate that the absence of MyD88 signaling confers complete protection against anorexia induced by either lipopolysaccharide (LPS) (20 h food intake in MyD88-/- mice 5.4 +/- 0.3 vs. 3.3 +/- 0.4 g in MyD88+/+ control mice, P < 0.001) or IL-1 beta (20 h food intake in MyD88-/- mice 4.9 +/- 0.5 vs. 4.0 +/- 0.3 g in MyD88+/+ control mice, P < 0.001). However, absent MyD88 signaling does not prevent these inflammatory mediators from causing weight loss (LPS, -0.4 +/- 0.1 g; IL1 beta, -0.1 +/- 0.1 g, both P < 0.01 vs. vehicle-injected MyD88-/- mice, +0.4 +/- 0.2 g). Furthermore, LPS-induced weight loss occurs in the absence of adipsia, fever, or hypothalamus-pituitary-adrenal axis activation in MyD88-deficient mice. In addition, the peripheral inflammatory response to LPS is surprisingly intact in mice lacking MyD88. Together, these observations indicate that LPS reduces food intake via a mechanism that is dissociated from its effect on peripheral cytokine production, and whereas the presence of circulating proinflammatory cytokines per se is insufficient to cause anorexia in the absence of MyD88 signaling, it may contribute to LPS-induced weight loss.

Dual effects of the lichen glucan PB-2, extracted from Flavoparmelia baltimorensis, on the induction of long-term potentiation in the dentate gyrus of the anesthetized rat: possible mediation via adrenaline beta- and interleukin-1 receptors.

We have previously found that oral or intravenous (i.v.) administration of the polysaccharide fraction PB-2, extracted from the lichen Flavoparmelia baltimorensis, facilitated the induction of long-term potentiation (LTP) in the dentate gyrus (DG) in vivo. In this study, the mechanism underlying the effect of PB-2 on the induction of LTP was investigated in the DG of anesthetized rat focusing on the contribution of the interleukin-1 (IL-1) receptor and the adrenaline beta-receptor. An i.v. injection of IL-1ra (10(-9) g/kg), an antagonist of the IL-1 receptor, had no effect on the basal response in the DG; however, this treatment augmented the enhancement of LTP induced by a single i.v. injection of PB-2 (10(-3) g/kg). This potentiating effect was also observed following intracerebroventricular (i.c.v.) injection of IL-1ra (10(-15)-10(-11) g). An i.v. injection of IL-1beta (3.5 x 10(-15)-3.5 x 10(-9) g/kg) inhibited the induction of LTP, which was diminished by the previous application of IL-1ra. These results suggest that the activation of the IL-1 receptor induces the suppression of LTP in PB-2-treated rats, and that endogenous IL-1beta contributes to the IL-1 receptor activation. An i.c.v. infusion of metoprolol (7.5 x 10(-6) g), an antagonist of the adrenaline beta(1)-receptor, attenuated the enhancement of LTP induced by an i.v. injection of PB-2. These results suggest that PB-2 has two different effects on the LTP, an enhancing effect and an inhibiting one, and that it exhibited the significant enhancing effect on the LTP as a total balance of these effects.

Causal links between brain cytokines and experimental febrile convulsions in the rat.

PURPOSE: Despite the prevalence of febrile convulsions (FCs), their pathophysiology has remained elusive. We tested the hypothesis that components of the immune response, particularly the proinflammatory cytokine interleukin-1beta (IL-1beta) and its naturally occurring antagonist interleukin-1 receptor antagonist (IL-1ra) may play a role in the genesis of FC. METHODS: Postnatal day 14 rats were treated with lipopolysaccharide (LPS; 200 microg/kg, i.p.) followed by a subconvulsant dose of kainic acid (1.75 mg/kg, i.p.). Brains were harvested at and 2 h after onset of FCs to measure brain levels of IL-1beta and IL-1ra. Separate groups of animals were given intracerebroventricular (ICV) injections of IL-1beta, or IL-1ra in an attempt to establish a causal relation between the IL-1beta/IL-1ra system and FCs. RESULTS: Animals with FCs showed increased IL-1beta in the hypothalamus and hippocampus but not in the cortex compared with noFC animals that also received LPS and kainic acid. This increase was first detected in the hippocampus at onset of FCs. No detectable difference in IL-1ra was found in brain regions examined in either group. When animals were treated with IL-1beta ICV, a dose-dependant increase was noted in the proportion of animals that experienced FCs, whereas increasing doses of IL-1ra, given to separate groups of animals, were anticonvulsant. CONCLUSIONS: Our results suggest that excessive amounts of IL-1beta may influence the genesis of FCs. This may occur by overproduction of IL-1beta, or by alteration in the IL-1beta/IL-1ra ratio in the brain after an immune challenge.

Innate immunity at the forefront of psychoneuroimmunology.

The last 15 years of research in psychoneuroimmunology have been marked by a renewed interest in the mechanisms of inflammation and participation of the brain in these mechanisms. Peripheral proinflammatory cytokines produced by activated accessory immune cells act in the brain to trigger sickness, in the form of fever, pituitary-adrenal axis activation, and sickness behavior. Communication between the periphery and brain takes place via both neural and humoral pathways. Recognition of the role of local production of cytokines and their downstream messengers in the central nervous system opens important new vistas for understanding and treating non-specific neurovegetative and psychiatric symptoms of diseases. In this presidential address, I present the main methodological and conceptual developments that have allowed such progress.

Cytokines in temporomandibular joint arthritis.

As the article in the current issue by Shinoda and colleagues shows, during the last two decades, there has been a dramatic increase in the understanding of basic biology behind chronic temporomandibular joint (TMJ) pain, inflammation and destruction. The involvement and contribution of cytokines to TMJ pain and inflammation must now be considered as established, evident and fundamental. Based on the present knowledge, it is now possible to design and investigate novel therapeutic strategies. These new and very encouraging approaches include manipulation of cytokine function, immune reactivity and the behaviour of inflammatory cells while maintaining the integrity of the affected tissue.

Inhibition of eosinophilic inflammation in allergen-challenged, IL-1 receptor type 1-deficient mice is associated with reduced eosinophil rolling and adhesion on vascular endothelium.

To determine the relative in vivo importance of IL-1 release after allergen challenge to the subsequent endothelial adhesion and recruitment of eosinophils, the authors used ovalbumin sensitization and inhalation challenge to induce airway eosinophilia in IL-1 receptor type 1-deficient and control wild-type mice. Bronchoalveolar lavage (BAL) eosinophil recruitment in IL-1 receptor type 1-deficient mice challenged with ovalbumin (24.3% +/- 6.3% BAL eosinophils) was significantly reduced compared with wild-type mice (63.7% +/- 2.5% BAL eosinophils). To determine whether the inhibition of eosinophil adhesion to vascular endothelium contributed to the inhibition of eosinophil recruitment in IL-1 receptor type 1-deficient mice, the authors used intravital microscopy to visualize the rolling and firm adhesion of fluorescence-labeled mouse eosinophils in the microvasculature of the allergen-challenged mouse mesentery. Eosinophil rolling, eosinophil firm adhesion to endothelium, and transmigration across endothelium (peritoneal eosinophils) were significantly inhibited in allergen-challenged IL-1 receptor type 1-deficient mice compared with wild-type mice. Overall, these studies demonstrate that cytokines such as IL-1, released after allergen challenge, are important in the induction of endothelial cell adhesiveness, a prerequisite for the recruitment of circulating eosinophils. (Blood. 2000;95:263-269)

The interleukin-1 type I receptor is expressed in human hypothalamus.

Several lines of evidence suggest that interleukin-1 (IL-1) acts directly on the central nervous system, probably within the hypothalamus, causing effects such as fever, activation of the immune response and sickness behaviour. IL-1 has also been shown to be involved in the aetiology of several neuronal diseases, including neurodegeneration, stroke and Alzheimer's disease. However, the question as to whether the full-length type I IL-1 receptor (IL-1RI) is expressed in the human hypothalamus has yet to be addressed. Using the polymerase chain reaction, we cloned a full-length cDNA encoding the human hypothalamic IL-1RI from human hypothalamic cDNA. The DNA sequence of the human hypothalamic receptor was identical to that of the human fibroblast IL-1RI. The IL-1RI receptor protein was detected in astrocytes of normal human hypothalamic brain sections using immunocytochemical techniques. To ascertain that the cloned receptor was functional, Chinese hamster ovary (CHO) cells were transfected with a plasmid vector containing the IL-1RI coding region. IL-1RI-mediated-signal transduction was assessed by microphysiometry and activation of p38 MAP (mitogen-activated protein) kinase. We report the first demonstration that both the type I IL-1 transcript and the protein are expressed in the human hypothalamus. The receptor was expressed in a stable CHO cell line, providing a tool with which to embark on a thorough analysis of the signalling mechanisms mediated by IL-1 via this receptor.

IL-1beta mediates diethyldithiocarbamate-induced granulocyte colony-stimulating factor production and hematopoiesis.

Diethyldithiocarbamate (DDTC) exhibits chemoprotective effects via reduced myelosuppression in mice treated with various chemotherapeutic agents. The mechanism of DDTC-mediated chemoprotection is believed to involve the induction and release of several cytokines, including interleukin-1 beta (IL-1beta), tumor necrosis factor-alpha (TNF-alpha), and granulocyte colony-stimulating factor (G-CSF). In the present study the roles of IL-1beta and TNF-alpha in DDTC-mediated G-CSF induction were examined using human long-term bone marrow cultures (hLTBMCs). Administration of IL-1 receptor antagonist (IL-1ra) to DDTC-treated hLTBMCs obviated the G-CSF induction profile and blocked the resultant colony proliferation, indicating that IL-1beta mediates DDTC-induced G-CSF release and hematopoiesis. IL-1beta mRNA levels were increased threefold over control following DDTC treatment of hLTBMCs, implying that DDTC induces IL-1beta at the level of transcription. Conversely, studies involving inhibition of DDTC-induced TNF-alpha synthesis, with the inhibitor MNX 160, had no effect on DDTC-induced G-CSF release or colony proliferation. These findings taken together strongly suggest that IL-1beta mediates the chemoprotective effects of DDTC.

Transgenic animals demonstrate a role for the IL-1 receptor in regulating IL-1beta gene expression at steady-state and during the systemic stress induced by acute pancreatitis.

Interleukin-1 (IL-1) gene expression is selectively induced in tissues involved in multisystem organ failure during acute pancreatitis, suggesting a role in the pathogenesis of distant organ dysfunction. This study was undertaken to investigate the mechanism of pancreatitis-induced end organ cytokine production and to better understand the processes by which IL-1 production is regulated. Seventy adult male transgenic mice in which the type 1 IL-1 receptor had been deleted by gene targeting in embryonic stem cells were utilized (homozygous -/- IL-1R knockout). Acute pancreatitis was induced by one of two methods: (A) IP injections of caerulein (50 microgram/kg/hr x 4) with animals sacrificed at 0, .5, 1, 2, 4, 6, and 8 hr; (B) 48-hr exposure to a choline deficient ethionine supplemented (CDE) diet with animals sacrificed at 0 and 72 hr. Knockout animals were compared to strain-specific control mice expressing the normal wild-type IL-1 receptor gene in which pancreatitis was similarly induced. The severity of pancreatitis was stratified by serum amylase, lipase, and blind histologic grading. IL-1 mRNA production was determined within the pancreas, lungs, liver, and spleen by quantitative differential RT-PCR. Deletion of the IL-1R1 attenuated the severity of pancreatitis, reaching statistical significance in the less severe edematous model. There was little or no constitutive expression of IL-1 mRNA within any of the tissues examined from wild-type animals; however, knockout animals showed elevated steady-state levels in each tissue. IL-1 mRNA became detectable in all tissues of wild-type animals shortly after either form of pancreatitis became apparent and increased significantly with worsening pancreatitis. Despite the attenuated pancreatitis, knockout animals produced significantly greater levels of IL-1 mRNA in each tissue, typically demonstrating a 30-50% increase over time matched IL-1 mRNA production in wild-type animals which was not pancreatitis model dependent. We conclude that genetic deletion of IL-1 receptors results in the overproduction of IL-1 mRNA in organs known to produce cytokines during pancreatitis even when the severity of pancreatitis is lessened. This suggests that a negative feedback loop exists between the IL-1 receptor and IL-1 gene expression.

Evidence that the interleukin-1 beta-induced prostaglandin E2 release from rat hypothalamus is mediated by type I and type II interleukin-1 receptors.

Interleukin-1 beta (IL-1 beta) has been shown to specifically increase the release of prostaglandin (PG) E2 from rat hypothalamic explants in short-term experiments. In this study we attempted to characterize the receptor subtype(s) involved in this response. Rat hypothalamic explants were incubated with mouse monoclonal antibodies (mAbs) raised against human IL-1 type I or type II receptors, IL-1 receptor antagonist (IL-1ra) and alpha-melanocyte-stimulating hormone (alpha-MSH) (which appears to antagonize certain IL-1 induced inflammatory effects in vivo), alone and in the presence of IL-1 beta. PGE2 released into the incubation medium was measured by radioimmunoassay. The anti-type I mAb reduced both basal and IL-1 beta-stimulated PGE2 release at 10 micrograms/ml, but not at lower concentrations. The anti-type II mAb also produced a significant decrease in stimulated release but had no effect on basal release. IL-1ra mimicked the effects of the anti-type I mAb, while alpha-MSH failed to alter either basal or stimulated PGE2 release. These findings suggest that IL-1 beta controls production and release of PGE2 by the rat hypothalamus via both type I and type II receptors, although the latter appear to be involved only in the response to high levels of IL-1.

Involvement of interleukin-1 in immobilization stress-induced increase in plasma adrenocorticotropic hormone and in release of hypothalamic monoamines in the rat.

We investigated whether interleukin-1 (IL-1) activity in the rat hypothalamus was increased by immobilization stress (IS), and whether pretreatment with an interleukin-1 receptor antagonist (IL-1Ra) is capable of inhibiting IS-induced elevations of hypothalamic norepinephrine (NE), dopamine (DA), and serotonin (5-HT) and the levels of their metabolites as well as of plasma adrenocorticotropic hormone (ACTH). IL-1 activity was estimated with a bioassay using mouse thymocyte proliferation in the presence of concanavalin A. IL-1Ra was administered directly into the anterior hypothalamus, and monoamines were determined using a microdialysis technique and an HPLC system. First, we found that levels of IL-1 activity in the rat hypothalamus reached a maximum at 60 min after starting IS. Second, IL-1Ra (2 micrograms) significantly inhibited IS-induced increases in hypothalamic NE, DA, and 5-HT levels as well as the levels of their metabolites. In addition, IL-1Ra (2 micrograms) also inhibited the IS-induced elevation of plasma ACTH levels. Third, timing effects of IL-1Ra administration on the IS-induced monoamines or ACTH responses were examined. IL-1Ra (2 micrograms) administered at 5 or 60 min before the start of IS, but not at 5 or 60 min after IS had been started, exerted inhibitory effects on these responses, indicating that the effects of IL-1 occurred within 5 min after the initiation of IS. In summary, these results suggest that IS enhances biologically active IL-1 in the hypothalamus, and that hypothalamic IL-1 plays a role in the regulation of IS-induced responses including elevated monoamine release in the hypothalamus and activation of the hypothalamo-pituitary-adrenal axis. Moreover, since 5 min is too short a time for IS to induce production of IL-1, IS may augment the effects of preexisting IL-1 in the hypothalamus.

Role of interleukin-1 in stress responses. A putative neurotransmitter.

Recently, the central roles of interleukin-1 (IL-1) in physical stress responses have been attracting attention. Stress responses have been characterized as central neurohormonal changes, as well as behavioral and physiological changes. Administration of IL-1 has been shown to induce effects comparable to stress-induced changes. IL-1 acts on the brain, especially the hypothalamus, to enhance release of monoamines, such as norepinephrine, dopamine, and serotonin, as well as secretion of corticotropin-releasing hormone (CRH). IL-1-induced activation of the hypothalamo-pituitary-adrenal (HPA) axis in vivo depends on secretion of CRH, an intact pituitary, and the ventral noradrenergic bundle that innervates the CRH-containing neurons in the paraventricular nucleus of the hypothalamus. Recent studies have shown that IL-1 is present within neurons in the brain, suggesting that IL-1 functions in neuronal transmission. We showed that IL-1 in the brain is involved in the stress response, and that stress-induced activation of monoamine release and the HPA axis were inhibited by IL-1 receptor antagonist (IL-1Ra) administration directly into the rat hypothalamus. IL-1Ra has been known to exert a blocking effect on IL-1 by competitively inhibiting the binding of IL-1 to IL-1 receptors. In the latter part of this review, we will attempt to describe the relationship between central nervous system diseases, including psychological disorders, and the functions of IL-1 as a putative neurotransmitter.