Central administration of ibuprofen failed to block the anorexia induced by interleukin-1

Hypothalamic mechanisms in cachexia

The role of nutrition and balanced metabolism in normal growth, development, and health maintenance is well known. Patients affected with either acute or chronic diseases often show disorders of nutrient balance. In some cases, a devastating state of malnutrition known as cachexia arises, brought about by a synergistic combination of a dramatic decrease in appetite and an increase in metabolism of fat and lean body mass. Other common features that are not required for the diagnosis include decreases in voluntary movement, insulin resistance, and anhedonia. This combination is found in a number of disorders including cancer, cystic fibrosis, AIDS, rheumatoid arthritis, renal failure, and Alzheimer's disease. The severity of cachexia in these illnesses is often the primary determining factor in both quality of life, and in eventual mortality. Indeed, body mass retention in AIDS patients has a stronger association with survival than any other current measure of the disease. This has led to intense investigation of cachexia and the proposal of numerous hypotheses regarding its etiology. Most authors suggest that cytokines released during inflammation and malignancy act on the central nervous system to alter the release and function of a number of neurotransmitters, thereby altering both appetite and metabolic rate. This review will discuss the salient features of cachexia in human diseases, and review the mechanisms whereby inflammation alters the function of key brain regions to produce stereotypical illness behavior. The paper represents an invited review by a symposium, award winner or keynote speaker at the Society for the Study of Ingestive Behavior [SSIB] Annual Meeting in Portland, July 2009.

Homeostatic alterations after IL-1beta microinjection into the nucleus accumbens of the rat

The present study investigates the effects of direct administration of interleukin-1beta (IL-1beta) into the nucleus accumbens (NAcc) on homeostatic regulation. Short- and long-term food intakes (FI), water intakes (WI) and body temperature (BT) were measured before and after bilateral microinjection of IL-1beta (with or without paracetamol pretreatment) into the NAcc of Wistar rats, and the effects were compared with those found in vehicle treated control animals. In addition, blood glucose levels, along with a glucose tolerance test (GTT), and plasma concentrations of metabolic parameters, such as total cholesterol, triglycerides, HDL, LDL and uric acid were determined in cytokine treated and control rats. Short-term FI and WI were suppressed after intraaccumbens application of IL-1beta. A significant increase of BT was also observed after the cytokine microinjection. Pretreatment with paracetamol failed to influence the anorexigenic, adipsogenic, and pyrogenic effects of IL-1beta. A definite glucose intolerance of the cytokine treated animals and their pathologically elevated blood glucose levels became obvious in the acute GTT. Following IL-1beta microinjection, plasma levels of triglycerides, total cholesterol and LDL were found increased. Our present findings show that the NAcc is an important site of action of IL-1beta mediated processes in central homeostatic regulation.

Differential Effects of Selective Cyclooxygenase (COX)-1 and COX-2 Inhibitors on Anorexic Response and Prostaglandin Generation in Various Tissues Induced by Zymosan

We have shown that anorexic response is induced by intraperitoneal injection of zymosan in mice, although the role of prostaglandins in this response is relatively unknown as compared with lipopolysaccharide (LPS)-induced anorexic response. Indomethacin (0.5 and 2.0 mg/kg), a non-selective cyclooxygenase (COX) inhibitor, as well as meloxicam (0.5 mg/kg), a selective COX-2 inhibitor, but not FR122047 (2.0 mg/kg), a selective COX-1 inhibitor, attenuated zymosan-induced anorexia. Zymosan injection elevated COX-2 expression in brain and liver but not in small intestine and colon. Meloxicam (0.5 mg/kg) and FR122047 treatment (2.0 mg/kg) similarly suppressed the generation of brain prostaglandin E(2) (PGE(2)) and peritoneal prostacyclin (PGI(2)) upon zymosan injection. PGE(2) generation in liver upon zymosan injection was suppressed by meloxicam (0.5 mg/kg) but not by FR122047 treatment (2.0 mg/kg). Our observations suggest that COX-2 plays an important role in zymosan-induced anorexia, which is a similar feature in LPS-induced anorexic response. However, non-selective inhibition by selective COX-1 and COX-2 inhibitors of brain PGE(2) generation upon zymosan injection does not support the role of COX-2 expressed in brain in zymosan-induced anorexic response. PGE(2) generation in liver may account for peripheral role of COX-2 in zymosan-induced anorexic response.

Homeostatic alterations induced by interleukin-1β microinjection into the orbitofrontal cortex in the rat

The present experiments were designed to elucidate the effect of direct orbitofrontal cortical administration of interleukin-1beta (IL-1beta) on the homeostatic regulation. Short- and long-term food intakes (FI), water intakes and body temperature (BT) were measured before and after a bilateral microinjection of IL-1beta (with or without paracetamol /P/ pretreatment) into the orbitofrontal cortex (OBF) of Wistar rats, and the effects were compared with those found in vehicle-treated and i.p. injected IL-1beta, IL-1beta+P or control animals. In addition, blood glucose levels (BGLs), along a glucose tolerance test, and plasma concentrations of insulin, leptin, cholesterol, triglycerides and urate were determined in cytokine treated and control rats. Short-term FI was suppressed after orbitofrontal cortical or peripheral application of IL-1beta. In the long-term FI, however, there was no significant difference among the groups. Cytokine microinjection into the OBF, similar to the i.p. administration, was also followed by a significant increase in BT. Pretreatment with P failed to influence the anorexigenic and hyperthermic effects of the centrally administered IL-1beta. The sugar load led to a diabetes-like prolonged elevation of BGL in the IL-1beta treated animals. Following cytokine administration, plasma levels of insulin and that of triglycerides were found decreased, whereas that of uric acid increased. The present findings confirm that the OBF is one of the neural routes through which IL-1beta exerts modulatory effect on the central homeostatic regulation.

EP3 and EP4 receptor mRNA expression in peptidergic cell groups of the rat parabrachial nucleus

This study examines the distribution of prostaglandin E2 receptors of subtype EP3 and EP4 among brain stem parabrachial neurons that were characterized with respect to their neuropeptide expression. By using a dual-labeling in situ hybridization method, we show that preprodynorphin mRNA expressing neurons in the dorsal and central lateral subnuclei express EP3 receptor mRNA. Such receptors are also expressed in preproenkephalin, calcitonin gene related peptide and preprotachykinin mRNA positive neurons in the external lateral subnucleus, whereas preprodynorphin mRNA expressing neurons in this subnucleus are EP receptor negative. In addition, EP3 receptor expression is seen among some enkephalinergic neurons in the Kölliker-Fuse nucleus. Neurons in the central part of the cholecystokininergic population in the regions of the superior lateral subnucleus express EP4 receptor mRNA, whereas those located more peripherally express EP3 receptors. Taken together with previous findings showing that discrete peptidergic cell groups mediate nociceptive and/or visceral afferent information to distinct brain stem and forebrain regions, the present results suggest that the processing of this information in the parabrachial nucleus is influenced by prostaglandin E2. Recent work has shown that prostaglandin E2 is released into the brain following peripheral immune challenge; hence, the parabrachial nucleus may be a region where humoral signaling of peripheral inflammatory events may interact with neuronal signaling elicited by the same peripheral processes.

Involvement of the arcuate nucleus of the hypothalamus in interleukin-1-induced anorexia

Cytokine-mediated anorexia is a component of "sickness behavior" and presents a significant obstacle in the treatment of chronic illnesses. We hypothesized an involvement of the hypothalamic arcuate nucleus (ARH) in mediating the anorexic effects of a systemic interleukin-1 (IL-1) challenge based on its content of peptidergic neurons involved in feeding, its expression of IL-1 receptors and its sensitivity to systemic IL-1. IL-1 (6 microg/kg, i.v.) was found to induce Fos expression in both pro-opiomelanocortin- and neuropeptide Y-expressing neurons in and around the ARH. Contrary to expectations, rats that had sustained lesions of the arcuate nucleus, produced by neonatal monosodium glutamate treatment, displayed a more pronounced suppression (by 25%) of food intake than nonlesioned controls when treated with IL-1 after a 20 hr fast. To confirm and further characterize this unexpected result, a second ablation method was used in a similar paradigm. Animals bearing knife cuts designed to sever major ARH projections displayed an even more accentuated loss of appetite (by 60%, relative to controls) in response to systemic IL-1. This effect exhibited at least some degree of specificity, because the knife cuts did not alter either IL-1 effects on another centrally mediated acute phase response (fever) or the anorexia produced by an alternate agent, fenfluramine. These results fail to support the hypothesized ARH mediation of IL-1-induced anorexia and may suggest rather that the net output of this cell group may serve normally to restrain cytokine-induced reductions in food intake.

Cytokines and the anorexia of infection: potential mechanisms and treatments

Anorexia during infection is thought to be mediated by immunoregulatory cytokines such as interleukins 1 and 6 and tumor necrosis factor. This article reviews the potential mechanisms of action by which these cytokines are thought to suppress food intake during infection and examines the proposition that blocking of cytokine activity might be one approach to improving food intake of the infected host.

Leptin actions on food intake and body temperature are mediated by IL-1

Leptin regulates energy balance through its actions in the brain on appetite and energy expenditure and also shares properties with cytokines such as IL-1. We report here that leptin, injected into rats intracerebroventricularly or peripherally, induces significant dose-dependent increases in core body temperature as well as suppression of appetite. Leptin failed to affect food intake or body temperature in obese (fa/fa) Zucker rats, which posses a defective leptin receptor. Furthermore, injection of leptin increased levels of the proinflammatory cytokine IL-1beta in the hypothalamus of normal Sprague-Dawley rats. Central injection of IL-1 receptor antagonist (IL-1ra) inhibited the suppression of food intake caused by central or peripheral injection of leptin (60 and 84%, respectively) and abolished the leptin-induced increase in body temperature in both cases. Mice lacking (gene knockout) the main IL-1 receptor (80 kDa, R1) responsible for IL-1 actions showed no reduction in food intake in response to leptin. These data indicate that leptin actions in the brain depend on IL-1, and we show further that the effect of leptin on fever, but not food intake, is abolished by a cyclooxygenase inhibitor. Thus, we propose that in addition to its role in body weight regulation, leptin may mediate neuroimmune responses via actions in the brain dependent on release of IL-1 and prostaglandins.

Activation of vagal afferents after intravenous injection of interleukin-1beta: role of endogenous prostaglandins

Intravenous administration of interleukin-1 (IL-1) activates central autonomic neuronal circuitries originating in the nucleus of the solitary tract (NTS). The mechanism(s) by which blood-borne IL-1 regulates brain functions, whether by operating across the blood-brain barrier and/or by activating peripheral sensory afferents, remains to be characterized. It has been proposed that vagal afferents originating in the periphery may monitor circulating IL-1 levels, because neurons within the NTS are primary recipients of sensory information from the vagus nerve and also exhibit exquisite sensitivity to blood-borne IL-1. In this study, we present evidence that viscerosensory afferents of the vagus nerve respond to intravenously administered IL-1beta. Specific labeling for mRNAs encoding the type 1 IL-1 receptor and the EP3 subtype of the prostaglandin E2 receptor was detected in situ over neuronal cell bodies in the rat nodose ganglion. Moreover, intravenously applied IL-1 increased the number of sensory neurons in the nodose ganglion that express the cellular activation marker c-Fos, which was matched by an increase in discharge activity of vagal afferents arising from gastric compartments. This response to IL-1 administration was attenuated in animals pretreated with the cyclooxygenase inhibitor indomethacin, suggesting partial mediation by prostaglandins. In conclusion, these results demonstrate that somata and/or fibers of sensory neurons of the vagus nerve express receptors to IL-1 and prostaglandin E2 and that circulating IL-1 stimulates vagal sensory activity via both prostaglandin-dependent and -independent mechanisms.

Interleukin-1beta sensitizes the response of the gastric vagal afferent to cholecystokinin in rat

Interleukin-1beta (IL-1beta) and cholecystokinin (CCK) are important mediators in the development of anorexic response during disease. The role of IL-1beta and CCK in the peripheral mechanisms of anorexia was studied by recording the mass afferent activity of the gastric vagal nerve in anesthetized rats. The i.v. administration of CCK (1 nmol) increased the activity of the vagal nerve, and this response was raised by 55-72% 2 h after i.v. injection of IL-1beta. It is proposed that IL-1beta-induced anorexia is mediated via the sensitization of type A CCK receptors in the periphery.

Mechanisms of sickness-induced decreases in food-motivated behavior

Interleukin-1 beta (IL-1 beta) is a cytokine released by activated macrophages and monocytes, which mediates many of the local and systemic responses to inflammation. Interleukin-1 beta induces anorexia in rats when administered peripherally or centrally. An endogenous antagonist for the IL-1 type I receptor has been characterized and cloned (IL-1ra). We have used this protein to ascertain the site of action for the anorexic effects of IL-1 beta. Male rats were food restricted and trained on an operant schedule for food reinforcement. Administration of recombinant human IL-1 beta (4 micrograms i.p. or 40 ng i.c.v.) induced profound decreases in operant responding, with maximal effects 1-4 h post-injection. Interleukin-1ra pretreatment (2.4 mg i.p. or 24 micrograms i.c.v.) completely blocked these effects when administered by the same route. In contrast, i.c.v. Il-1ra only partially blocked the effects of i.p. IL-1 beta, and i.p. IL-1ra was unable to block the effects of i.c.v. IL-1 beta. Interleukin-1ra did not affect responding by itself. These results suggest that IL-1 beta acts as both peripheral and central IL-1 receptors to reduce food motivated behavior. To determine the central site of action of IL-1 beta, small quantities of IL-1 beta (5 and 30 ng) were infused into the ventromedial hypothalamus of male rats. Both doses produced profound decreases in responding; the magnitude and time course of these effects were nearly identical to those observed after i.c.v. administration. These results suggest that the VMH may serve as a central site of action for the depressive effects of IL-1 beta on food intake. There is much controversy over the pathways of communication from the immune system to the brain. To test the hypothesis that the peripheral immune stimulus is transmitted to the brain via a neutral communication pathway, mice were injected with lipopolysaccharide at a behaviorally active dose (10 micrograms i.p.). This treatment increased the concentrations of substance P, neurokinin A, and calcitonin gene-related peptide in mouse spinal cord in a prostaglandin-dependent manner. Maximal increases in neuropeptide content were observed 1 h post-injection. Finally, subdiaphragmatic vagotomy was found to attenuate the reduction in food-motivated behavior induced by both IL-1 beta and lipopolysaccharide in mice.

Reduction in food and water intake induced by microinjection of interleukin-1 beta in the ventromedial hypothalamus of the rat

Interleukin-1 (IL-1) is a cytokine which is released during immune activation and mediates some of the host's responses to infection and inflammation. Increasing evidence suggests that it also has a role as an intrinsic neuromodulator in the central nervous system. We report here that microinjections of 5 and 30 ng (286 fmol and 1.71 pmol) of recombinant human IL-1 beta in the ventromedial nucleus of the hypothalamus (VMH) of adult male rats time- and dose-dependently induce anorexia and weight loss in two experimental paradigms: rats allowed free-access to food and water and food-restricted rats trained to press a lever for food on a fixed ratio 10 schedule. IL-1 beta (5 ng) diminished food and water consumption by 45 and 30%, respectively, and decreased body weight for at least 24 h postinjection in rats fed ad lib. These effects were more severe and lasted at least 48 h after infusion of the larger dose of 30 ng. The IL-1 beta-induced anorexia and weight loss were neither as large nor as long-lasting in food-restricted rats. Operant responding for food was decreased 2-4 h postinfusion of 5 ng IL-1 beta and 2-8 h after 30 ng IL-1 beta, but in both cases returned to baseline within 24 h. Body weight was decreased compared to saline injections from 4 to 24 h postinfusion. Nevertheless, when allowed to eat ad lib for the 24 h immediately following the behavioral testing, body weight returned to control (5 ng) or near control levels (30 ng).(ABSTRACT TRUNCATED AT 250 WORDS)

The role of cholecystokinin in interleukin-1-induced anorexia

Anorexia is a common response to infection which is thought to be mediated, at least in part, by interleukin (IL-1), an immunoregulatory peptide secreted by activated monocytes. Cholecystokinin (CCK) is a neuropeptide that suppresses food intake and gastric emptying when injected into healthy animals. There is increasing evidence of bidirectional interactions between neuropeptides, immune cell function, and secretion of immunoregulatory cytokines. Therefore, the present study was undertaken to determine if administration of L364,718 (L364), a CCK receptor antagonist, might block the anorexigenic effects of recombinant human IL-1 alpha (IL-1 alpha) in rats. We report that injection of IL-1 alpha significantly increased plasma CCK 1 h after injection, and decreased food intake and emptying of gastric contents. Pretreatment with 1 mg/kg L364 partially blocked the decrease in food intake and gastric stasis induced by IL-1 alpha. We conclude CCK may mediate, at least in part, IL-1 alpha-induced anorexia.

Central and peripheral prostaglandins are involved in sickness behavior in birds

Many of the behavioral manifestations of mammals and birds following infection are now recognized as important mechanisms for maintaining homeostasis and promoting recovery. To investigate the role of prostaglandins (PGs) in the behavioral and physiological effects of lipopolysaccharide (LPS) in birds, chickens were injected with indomethacin (Ind) peripherally (IP, 5 mg) or centrally (ICV, 100 micrograms) and their behavior and body temperature following a challenge IP injection of LPS (2.5 mg) were assessed at 1 and 2 h, respectively. Pretreatment with Ind IP or ICV completely inhibited the hyperthermia caused by LPS. Ind injected IP but not ICV significantly attenuated the LPS-induced anorexia. The drowsiness caused by LPS was completely inhibited by Ind injected IP and partially inhibited by Ind administered ICV. These results are interpreted to indicate that LPS induces hyperthermia in the chicken by activating a PG system in the brain. Peripheral PGs appear to be involved in the anorectic response to LPS, whereas drowsiness caused by LPS may involve both peripheral and central PGs. These data are consistent with the hypothesis that multiple PG systems are activated during the acute-phase response, which may explain the dissociation between mechanisms controlling the behavioral and physiological responses to infection.

Food intake and body temperature responses of rats to recombinant human interleukin-1 beta and a tripeptide interleukin-1 beta antagonist

Food intake and body temperature are two of many factors affected by IL-1 beta, a cytokine which is produced in response to tissue injury and inflammatory processes. In the present experiment, a tripeptide IL-1 beta antagonist which blocked IL-1 beta-induced hyperalgesia was tested for the ability to block IL-1 beta-induced effects on food intake and body temperature. Food intake was decreased 4-22 h after intraperitoneal (IP) administration of 1.25, 1.88, or 2.50 micrograms IL-1 beta/rat, and 0-22 h food intake was decreased by 1.88 and 2.50 micrograms IL-1 beta/rat. The effect of 1.25 micrograms IL-1 beta/rat on food intake measured 4 and 22 h after (IP) injection was blocked by coadministration of 5 mg tripeptide IL-1 beta antagonist. However, 25 mg tripeptide IL-1 beta antagonist/rat plus 1.25 micrograms IL-1 beta/rat decreased 0-22 h food intake more than IL-1 beta alone. Administration (IP) of 1.25 micrograms IL-1 beta/rat increased body temperature 1 degrees C 4 h later, and 5 and 25 mg tripeptide IL-1 beta antagonist/rat blocked this increase. Although food intake remained decreased after IL-1 beta administration alone or with 25 mg tripeptide IL-1 beta antagonist/rat for 22 h, body temperature returned to normal under these conditions. Thus, a tripeptide IL-1 beta antagonist shown to block IL-1 beta-induced hyperalgesia also blocked food intake and body temperature responses to IL-1 beta, although the effective doses of IL-1 beta and the tripeptide IL-1 beta antagonist differ by 4,000-fold when both are administered peripherally.

Potent inhibition of gastric acid secretion and ulcer formation by centrally and peripherally administered interleukin-1

IL-1 beta is one of the most potent centrally acting inhibitors of gastric acid secretion in rats. Sites of action have been located in the anterior/preoptic area and paraventricular nucleus of the hypothalamus where other biological activities of IL-1 have also been described. IL-1 beta action is, so far, quite unique to this cytokine and its action is not reproduced by IL-2 or TNF alpha. The IL-1 effect involves prostaglandin pathways and is unrelated to CRF. Similarly, systemic injection of IL-1 induces a long lasting inhibition of acid secretion through prostaglandin-dependent mechanisms. Several findings support the possibility that the effect of systemic IL-1 can be CNS-mediated and/or exerted at the periphery through local release of PG in the stomach. Exogenous IL-1 given into either the circulation or the cerebrospinal fluid also inhibits gastric injury induced by a variety of experimental models (stress, aspirin, ethanol). Such a protective effect is mediated through the inhibition of acid secretion and prostaglandin release, although other mechanisms may also contribute. Whether endogenously released IL-1 beta exerts a protective role in the gastric mucosa is still to be investigated.