Interleukin-1-induced anorexia in the rat. Influence of prostaglandins

Immunoregulators in the nervous system

The nervous system, through the production of neuroregulators (neurotransmitters, neuromodulators and neuropeptides) can regulate specific immune system functions, while the immune system, through the production of immunoregulators (immunomodulators and immunopeptides) can regulate specific nervous system functions. This indicates a reciprocal communication between the nervous and immune systems. The presence of immunoregulators in the brain and cerebrospinal fluid is the result of local synthesis--by intrinsic and blood-derived macrophages, activated T-lymphocytes that cross the blood-brain barrier, endothelial cells of the cerebrovasculature, microglia, astrocytes, and neuronal components--and/or uptake from the peripheral blood through the blood-brain barrier (in specific cases) and circumventricular organs. Acute and chronic pathological processes (infection, inflammation, immunological reactions, malignancy, necrosis) stimulate the synthesis and release of immunoregulators in various cell systems. These immunoregulators have pivotal roles in the coordination of the host defense mechanisms and repair, and induce a series of immunological, endocrinological, metabolical and neurological responses. This review summarizes studies concerning immunoregulators--such as interleukins, tumor necrosis factor, interferons, transforming growth factors, thymic peptides, tuftsin, platelet activating factor, neuro-immunoregulators--in the nervous system. It also describes the monitoring of immunoregulators by the central nervous system (CNS) as part of the regulatory factors that induce neurological manifestations (e.g., fever, somnolence, appetite suppression, neuroendocrine alterations) frequently accompanying acute and chronic pathological processes.

Fraction of hepatic cytosolic acetyl-CoA derived from glucose in vivo: relation to PDH phosphorylation state

We measured the contribution of glucose to hepatic cytosolic acetyl-CoA in vivo in rats and compared it with the phosphorylation state of a potentially regulatory enzyme complex [pyruvate dehydrogenase (PDH)]. Xenobiotic probes were used to sample hepatic cytosolic acetyl-CoA [acetylated sulfamethoxazole (SMX)] and UDP-glucose (glucuronidated acetaminophen) in vivo during [U-14C]glucose infusions. Percent active (dephosphorylated) form of PDH (PDHa) was determined on freeze-clamped liver. First, we confirmed using liver cell elutriation that acetylation of SMX occurs in parenchymal hepatocytes. Next, the fraction of cytosolic acetyl-CoA derived from [14C]glucose in vivo was shown to depend on dietary state. Specific activity of acetyl-CoA relative to plasma glucose or hepatic UDP-glucose was lower after 48 h fasting than after overnight fasting, and glucose refeeding (25 mg.kg-1.min-1 iv) maximally increased [14C]-glucose fractional contribution to acetyl-CoA within 2 h in the overnight-fasted but not in the prolonged fasted group. Hepatic PDHa demonstrated a similar but not identical pattern. The isotopic and enzymatic parameters showed significant correlations (r2 = 0.61 in 48-h fasted-refed group, r2 = 0.28 in overnight-fasted refed group), although [14C]glucose contribution to acetyl-CoA increased disproportionately compared with PDHa as refeeding progressed. The indirect pathway of UDP-glucose synthesis correlated inversely with the fractional contribution of glucose to acetyl-CoA. In summary, the fraction of hepatic acetyl-CoA derived from glucose in vivo is influenced by acute and chronic dietary factors and is only partially explained by PDHa. Regulation of the carbon source of hepatic acetyl-CoA in vivo and interactions suggested by these results (e.g., glucose-fatty acid cycle; branch-point regulation of glucose recycling) can be addressed in a quantitative fashion using this experimental framework.

Bioactivity of skeletal muscle proteolysis-inducing factors in the plasma proteins from cancer patients with weight loss

We determined the circulating level of bioactivity for skeletal muscle proteolysis-inducing factors (PIF) in the blood samples from cancer patients whose body weight loss was greater than 10%. The level of bioactivity was estimated by measurement of tyrosine release from isolated 1at diaphragm muscles incubated with an ultrafiltered fraction of plasma or serum proteins containing molecules from 0 to 25 kDa in molecular weight. Significant levels of bioactivity were detected in 25 of the 50 cancer samples. No activity was found in 18 of the samples from healthy human blood donors. The ability of 13 of the cancer samples to induce muscle proteolysis was significantly inhibited by incubation of muscles in presence of indomethacin (10 microM). The neutralisation of 12 of the cancer samples with the antibodies to recombinant human interleukin-1 (IL-1), alpha and beta forms, partially abrogated the activity in five samples. These results suggest that the accelerated breakdown of proteins induced by the cancer plasma factors is at least in part mediated by IL-1 in cooperation with other active factors not yet defined. Additionally, we have shown that the increased breakdown of proteins induced by PIF in the crude supernatant derived from activated mouse peritoneal macrophages is prevented by the treatment of muscles with either indomethacin or quin-2 (1 microM). These observations provide indirect evidence for a possible causal relationship between the production of PIF and the body-weight loss of cancer patients.

Pretranslational regulation of albumin synthesis in tumor-bearing mice. The role of anorexia and undernutrition

Hepatic albumin synthesis, serum albumin turnover, and hepatic albumin messenger RNA (mRNA) content were evaluated in mice bearing a transplantable low differentiated tumor (MCG 101). Results obtained on tumor-bearing mice were compared with results obtained from non-tumor-bearing animals that were either freely fed, food restricted so that their body composition was similar to tumor-bearing animals (pair-weighed), fed a protein-free diet for 5 days, or fasted for 48 hours. Tumor-bearing animals became hypoalbuminemic (33 +/- 5 vs. 44 +/- 3 g/L in freely fed mice), which could be explained by both depressed albumin synthesis (1.95% +/- 0.20% vs. 2.67% +/- 0.27%/h in freely fed mice) and increased albumin degradation. Pair-weighed and protein-calorie malnourished controls had reductions in albumin synthesis (1.81% +/- 0.18% and 1.67% +/- 0.17%/h, respectively) similar to tumor-bearing animals, and the starved controls had the lowest synthetic rates (1.07% +/- 0.10%/h). Albumin degradation was increased only in tumor-bearing animals. Hepatic albumin mRNA in undernourished animals was less (tumor bearing, 32% +/- 5%; pair weighed, 47% +/- 4%; 48 hours fasted, 18% +/- 2%; and protein-calorie malnourished, 26% +/- 3%) than 50% of the mRNA content in the livers of freely fed control mice. Messenger RNA-directed synthesis of albumin in vitro was also depressed to a variable degree in tumor-bearing and malnourished non-tumor-bearing controls. The hypoalbuminemia in tumor-bearing animals could not be prevented by daily injections of a prostaglandin synthesis inhibitor (indomethacin, 1 microgram/g body wt), but the hepatic acute phase protein serum amyloid P decreased from 157 +/- 12 to 103 +/- 9 micrograms/mL in indomethacin-treated tumor-bearing mice (P less than 0.01). It is concluded that increased albumin degradation seen in tumor-bearing animals cannot be explained by associated malnutrition, whereas tumor-associated malnutrition can explain to a large extent the depressed albumin synthesis. Decreased albumin synthesis in tumor-bearing animals correlated in part with a decreased quantity of liver albumin mRNA. The results of the current study are consistent with either a reduced transcription of the albumin gene or a change in albumin mRNA processing and stability communicated by anorexia and malnutrition.

Reduction of exploratory behavior by intraperitoneal injection of interleukin-1 involves brain corticotropin-releasing factor

The behavior of mice was scored in a multicompartment chamber one hour following intraperitoneal injection of recombinant human interleukin-1 (IL-1). Both IL-1 alpha and IL-1 beta dose-dependently reduced the mean duration for which mice were in contact with novel stimuli without altering measures of locomotor activity, such as movements between the compartments or rears. These behavioral changes resemble those previously observed with prior restraint or intracerebroventricular (ICV) injection of corticotropin-releasing factor (CRF). Effective doses were in the range 0.1-10 ng for IL-1 alpha, and 1-10 ng for IL-1 beta. The reduction in stimulus-contact times induced by 1 ng of IL-1 beta was reversed by prior ICV injection of the CRF antagonist, alpha-helical CRF9-41, suggesting that IL-1 causes secretion of brain CRF which in turn elicits the behavioral changes. These results indicate that peripheral administration of IL-1 alpha or IL-1 beta in low doses can alter behavior. They provide additional evidence that IL-1 administration stimulates brain CRF secretion, and that brain CRF can modulate exploratory behavior, and thus reinforces the concept that IL-1 administration can induce stress.

A recombinant human receptor antagonist to interleukin 1 improves survival after lethal endotoxemia in mice

Interleukin 1 (IL-1) is an endogenously produced cytokine that mediates a variety of physiological effects that may be beneficial or deleterious to the host. C57Bl/6 mice treated intravenously with a recently characterized human recombinant receptor antagonist protein to IL-1 (IL-1ra) had improved survival when treated after a lethal Escherichia coli endotoxin (lipopolysaccharide [LPS]) challenge. IL-1ra was effective when treatment was initiated after LPS, and intravenous administration every 4 h for 24 h was required. Serum levels of tumor necrosis factor (TNF) activity after LPS and in vitro TNF cytotoxicity were not altered by treatment with IL-1ra. These experiments provide direct evidence that the lethal effects of LPS may be mediated through the action of IL-1 and that the IL-1ra can provide a new treatment strategy for disease processes mediated via this cytokine.

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

Interleukins are synthesized by inflammatory cells and are thought to be involved in the anorexia associated with severe infection. In the present study, the possible involvement of prostaglandins in the anorexia caused by interleukin-1 was investigated. Recombinant human interleukin-1 beta (IL-1 beta). 17 ng/rat, injected into the third cerebroventricles significantly suppressed food intake and reduced the body weight gain in rats deprived of food for 18 h. Central administration of ibuprofen (IBP, 5-500 microgram/rat), a selective cyclooxygenase blocker, failed to attenuate the feeding suppression and body weight loss induced by IL-1 beta injection, although central administration of 50 microgram IBP blocked the increase of body temperature caused by central IL-1 beta. The data obtained suggest that a peripheral prostaglandin synthesizing system may play an important role in the anorexia caused by IL-1 beta.

Chlorpromazine protection against interleukin-1 and tumor necrosis factor-mediated activities in vivo

Interleukin (IL-1) and tumor necrosis factor (TNF) are thought to play a key role in septic shock and inflammation. We had previously shown that chlorpromazine (CPZ) has a protective effect in various models of endotoxic shock and IL-1 toxicity. We have tested the effect of CPZ on several activities of IL-1 in vivo. CPZ (4 mg/kg) inhibited increases in serum corticosterone, triglycerides and serum amyloid A (SAA). Chlorpromazine also antagonized these same effects when they were induced by endotoxin or TNF, suggesting that this activity could be implicated in the protective effect of CPZ in various models of endotoxic shock and IL-1 lethality.

Feed intake and rumen motility in dwarf goats. Effects of some alpha 2-adrenergic agonists, prostaglandins and posterior pituitary hormones

The purpose of the present investigation was to test the hypothesis that drug-induced changes in rumen contractions influence feed intake in dwarf goats. Intravenous (i.v.) administration of clonidine (1 microgram kg-1 min-1 for 10 min), xylazine (1 microgram kg-1 min-1 for 10 min), and PGF-2 alpha (10 micrograms kg-1 min-1 for 15 min) caused bradycardia and inhibition of rumen contractions. However, no appetite-stimulating effect of these drugs was observed. Other clinical changes induced by the alpha-adrenergic agonists included slight sedation and a decrease in body temperature; all clinical effects of clonidine and xylazine were partly antagonized by tolazoline pretreatment (10 micrograms kg-1 min-1 for 30 min). These results suggest that the CNS control of feeding differs in ruminants and monogastric species. In dwarf goats fasted for 2 h, i.v. administration of oxytocin (0.01 IU kg-1 min-1 for 15 min), vasopressin (0.01 IU kg-1 min-1 for 15 min), octapressin (0.003 IU kg-1 min-1 for 15 min) or PGE1 (0.8 microgram kg-1 min-1 for 15 min) did not change feeding behaviour during the two observation periods (0-30 min and 180-210 min after drug infusion, respectively). In previous studies, similar doses of these drugs induced changes in heart rate and inhibition of rumen contraction in goats. These findings demonstrate that drug-induced changes in forestomach contractions do not simply cause changes in feeding behaviour. The i.v. infusion of the PGF 2 alpha analogues etiproston (10 micrograms kg-1 min-1 for 15 min), luprostiol (30 micrograms kg-1 min-1 for 15 min), cloprostenol (1 microgram kg-1 min-1 for 15 min) and tiaprost (1 microgram kg-1 min-1 for 15 min) induced hypophagic effects and stimulated intestinal propulsion.

Metabolic effects of cachectin/tumor necrosis factor are modified by site of production. Cachectin/tumor necrosis factor-secreting tumor in skeletal muscle induces chronic cachexia, while implantation in brain induces predominantly acute anorexia

We have developed a murine model of wasting by injecting intracerebrally cells which continuously secrete h-cachectin/TNF (CHO-TNF) to: (a) determine the effects of cachectin/TNF produced continuously in the central nervous system (CNS), and (b) compare the metabolic effects of cachectin/TNF-secreting tumor in the brain to the cachexia caused by CHO-TNF tumor in peripheral tissue (IM). Intracerebral CHO-TNF tumors produced increased serum h-cachectin/TNF levels with lethal hypophagia and weight loss (mean survival time of 11 d); these changes were not observed in association with nonsecretory control brain tumors. The metabolic consequences of intracerebral cachectin/TNF production were indistinguishable from acute, lethal starvation: whole-body lipid content was decreased significantly but protein was conserved. Although intramuscular cachectin/TNF-secreting tumors caused similar increases of serum h-cachectin/TNF levels, profound anorexia did not develop; wasting developed after a longer period of tumor burden (50 d) with classical signs of cachexia (i.e., anemia and depletion of both protein and lipid). These studies provide a reproducible animal model of site-specific cytokine production and suggest that, regardless of serum levels, cachectin/TNF produced locally in brain influences both the rate of development of wasting and its net metabolic effects.

Intracerebroventricular administration of interleukin-1 to mice alters investigation of stimuli in a novel environment

The behavior of mice administered recombinant interleukin-1 (IL-1) was observed in a novel multicompartment chamber. Doses of human IL-1 alpha (4 pg to 40 ng) injected intracerebroventricularly (ICV) 20 min before testing significantly reduced the mean time mice spent in contact with novel stimuli. No other behavior scored (locomotor activity, grooming, scratching) was significantly affected. Similar results were obtained with murine IL-1 alpha (770 pg or 77 ng) and hIL-1 beta (1 pg to 10 ng). This behavioral change resembled that induced following restraint or ICV injection of corticotropin-releasing factor (CRF). The behavioral effect of ICV IL-1 was lost after it was heated for 10 min at 100 degrees C. Neither the CRF antagonist, alpha-helical CRF9-41 (10 or 20 micrograms ICV) nor the prostaglandin synthesis inhibitor indomethacin (50 mg/kg IP) significantly altered the hIL-1 alpha-induced behavioral changes, but naloxone (0.7 mg/kg SC) or sulpiride (5 mg/kg IP) completely prevented them. Our results suggest that intracerebral administration of IL-1 reduces the exploratory behavior of mice. This effect does not apparently involve CRF or prostaglandins, but may involve opioid and dopaminergic systems. This behavioral response to IL-1 administration is consistent with the behavioral effects of IL-1 reported previously, and strengthens the hypothesis that IL-1 secretion may be responsible for behavioral changes associated with immune activation.

Dietary modulation of cytokine production and biologic functions

Cytokines play a key role as communication signals during both normal immunologic responses and pathologic conditions leading to infectious, inflammatory, and neoplastic diseases. Production and biologic function of cytokines are affected by changes in macro- and micronutrients. On the other hand, metabolic and catabolic consequences of the action of cytokines change nutrient status and the distribution of nutrients in tissues. The effect of some nutrients on cytokine production as well as some of the biologic effects of cytokines are mediated through metabolites of arachidonic acid (prostaglandins, leukotrienes, etc.). Other mechanisms involved in nutrient-induced changes of cytokines needs to be determined. Understanding the role of nutrients in cytokine production and biologic function during normal homeostasis, as well as under pathologic conditions, can help in designing proper dietary modification for the prevention and therapy of diseases.

Cytokine modulation of pituitary hormone secretion

A rapidly expanding body of evidence indicates that cytokines do indeed regulate pituitary hormone secretion. Recent studies with cytokines in vivo and in vitro support the idea that cytokines are the principal mediators of the neuroendocrine responses previously observed in infectious and inflammatory states. The dominant route of this modulation appears to be via the brain and hypothalamus, although a role for direct effects on the pituitary has not been excluded. These effects may be mediated by circulating cytokines, endogenously produced cytokines, or both. A number of receptor systems and second messengers may be involved, and a role for arachidonate metabolite pathways appears particularly likely. A final question: Of what use to the organism is the ability of immune activation to control pituitary hormone secretion? For some pituitary secretions there is a reasonable basis for speculation. Glucocorticoids serve to limit the severity of immune responses and recent studies argue that defects in this pathway permit the expression of autoimmune disease. Inhibition of thyroid function may limit the catabolic side effects of infectious illness. Stimulation of growth hormone could have the same effect, and growth hormone and prolactin may serve to enhance some immune responses.

Interleukin-1, anorexia, and dietary fatty acids

IL-1 and other cytokines mediate several components of both acute and chronic pathological processes observed in patients with cancer and chronic infection. Cachexia ranks as one of the more prominent aspects of several diseases and the present studies demonstrate that recombinant forms of either IL-1 beta or IL-1 alpha reduce food intake in experimental animals. In meal-fed rats, a single injection of IL-1 induces a 40% reduction [table: see text] in food intake, whereas daily injections slow normal weight gain. The anorexic response to IL-1 is prevented by cyclooxygenase inhibitors, although this is unlikely due to a central nervous system effect. Reduced production of cyclooxygenase products such as PGE2 also occurs in rats fed supplemental N-3 fatty acids, and this was associated with a decreased anorexic response to IL-1. Therefore, one mechanism by which IL-1 induces anorexia appears to require cyclooxygenase metabolites, such as PGE2. N-3 fatty acid supplements also reduce the severity of host responses to inflammation and infection. Part of this is due to decreased cyclooxygenase products; however, part also may be due to reduced synthesis of IL-1. Blood leukocytes from human subjects taking oral N-3 supplements produce 60% less IL-1. The ability of N-3 fatty acids to reduce IL-1 synthesis appears to be via the lipoxygenase pathway. Therefore, N-3 fatty acids may be beneficial to patients with anorexia, since such supplements would decrease both the anorexic response to IL-1 via reduced cyclooxygenase metabolites and the production of IL-1, via altered lipoxygenase metabolites.

Comparison of the effects of bacterial lipopolysaccharide and muramyl dipeptide on food intake

For further characterization of the mechanism involved in the anorexia during bacterial infection, we investigated whether muramyl dipeptide (MDP), the minimal immunologically active structure of gram-positive bacterial cell walls, affects rats' food intake in the same way as lipopolysaccharide (LPS) from E. coli. MDP (1.6 mg/kg body weight = b.wt.) injected intraperitoneally (IP) reduced food intake by decreasing meal frequency without affecting meal size. Indomethacin (2.5 mg/kg b.wt., IP) but not verapamil (5 mg/kg b.wt., IP) attenuated the hypophagic effect of MDP. In further experiments, MDP and LPS (100 micrograms/kg b.wt., IP) both inhibited gastric emptying and indomethacin failed to block this effect of LPS. Hepatic vagotomy did not attenuate the hypophagic effects of MDP or LPS. LPS reduced water intake only when food was available, but reduced food intake also during water deprivation. MDP did not affect water intake. MDP and LPS both had an aversive effect, but LiCl, which was also aversive, failed to reduce feeding under the conditions tested. This questions the role of a conditioned taste aversion in the hypophagia induced by MDP or LPS. The results suggest that a stimulation of eicosanoid synthesis contributes to MDP-induced hypophagia and may therefore also contribute to the anorexia during infection. In contrast, an inhibition of gastric emptying, an activation of hepatic satiety signals or a reduction of water intake, does not seem to be crucial for the hypophagic effects of MDP or LPS.

Effects of peripheral administration of recombinant human interleukin-1 beta on feeding behavior of the rat

This study was undertaken to investigate the changes in feeding behavior, including ambulatory activity, induced by a single injection of Interleukin-1 beta (IL-1) (2 micrograms/rat) at 18:00, just before the dark phase. For this purpose, we used the Gunma University-type automatic apparatus for continuous and direct measurement of ambulation and drinking. A significant decrease in food intake was observed for 12 hours after treatment with IL-1. Peripheral administration of IL-1 also produced a marked decrease in ambulatory activity within 3 hours which continued for 6 hours. In addition, IL-1 produced a marked decrease in drinking behavior during the first 6 hours. We reported here the changes in consummatory and ambulatory behavior of rats after acute administration of IL-1. The sickness which IL-1 produced may, at least in part, contribute to these phenomena, although precise mechanisms are still unknown.

The therapeutic potential of interleukin-1 beta in the treatment of chemotherapy- or radiation-induced myelosuppression and in tumor therapy

In vivo administration of rHuIL-1 beta selectively enhanced the recovery from granulocytopenia and thrombocytopenia caused by sublethal irradiation or 5-FU treatment. Granulopoiesis and thrombopoiesis were stimulated by rHuIL-1 beta in a dose-dependent manner at doses ranging from 0.1 to 100 micrograms/kg. In this study, we have observed IL-1 to induce at least two distinct types of hematopoietic growth factors in vivo, namely GM-CSF and a thrombopoietin-like factor. Various kinds of CSFs alone did not stimulate colony formation of primitive hematopoietic progenitor cells obtained from 5-FU treated mice. However, the pretreatment of primitive hematopoietic progenitor cells with IL-1 in vitro or in vivo for 5 days accelerated the recovery of a cell population which respond to several types of CSFs. These data suggest that IL-1 may be useful clinically to enhance the recovery of granulocytes and platelets in myelosuppressed patients. In addition, we observed that rHuIL-1 beta is directly cytostatic for certain tumor cells in vitro. Intratumoral or subcutaneous injection of rHuIL-1 beta caused regression of a subcutaneous murine sarcoma by augmenting host antitumor responses. Together with the profound effects on hematopoiesis, these results point to potentially important uses of IL-1 beta in treatment of disease.

Interleukin-1 alpha: its possible roles in cancer therapy

Our studies on recombinant human IL-1 alpha polypeptide were summarized with respect to molecular cloning, production, quantitative assay systems, antitumor activity, myelorestorative activity and augmentation of host resistance to infections. Recombinant human IL-1 alpha (18 kDa) was produced through the expression of the cloned human IL-1 alpha cDNA in Escherichia coli and purified to an endotoxin-free homogeneous polypeptide. The human IL-1 alpha inhibited dose-dependently the growth of syngeneic murine tumors transplanted in mice and completely regressed the tumors in some cases, and its antitumor activity was significantly enhanced in combination with indomethacin. The human IL-1 alpha accelerated the recovery of the numbers of peripheral leukocytes and neutrophils in a dose-dependent manner at a dose as low as 10 ng/mouse/day in myelosuppressed mouse model produced by administering anticancer chemotherapeutic drugs. The myelorestorative effect of IL-1 alpha was observed not only on leukocytes/neutrophils, but also on platelets in myelosuppressed mice. In addition, the human IL-1 alpha markedly augmented dose-dependently resistance of normal and leukopenic mice to various microbial infections. These results suggested that recombinant human IL-1 alpha might be useful for cancer therapy from the viewpoints of improving adverse effects such as myelosuppression caused by chemotherapy and/or radiation therapy and preventing infections. In addition, use of IL-1 alpha may permit more intensive chemo- and radiation therapies using higher doses. Finally, the antitumor activity of the IL-1 alpha itself may play an important role.