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

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

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

Differential effects of interleukin (IL)-1beta, IL-2 and IL-6 on responding for rewarding lateral hypothalamic stimulation

Bacterial endotoxin and interleukin-1 (IL-1) challenge induce a constellation of symptoms associated with illness. While such treatment may result in anhedonia, it is often difficult to dissociate this effect from the anorexia induced by these agents, particularly in paradigms that involve appetitive motivation. The present investigation assessed the effects of several systemically administered cytokines (IL-1beta, IL-2 and IL-6) on reward processes by evaluating responding for rewarding intracranial self-stimulation (ICSS) from the lateral hypothalamus. Systemic administration of interleukin-2 (IL-2) disrupted responding from the medial forebrain bundle, and this disturbance persisted as long as 1 week following initial cytokine treatment. In contrast to reinforced responding, following IL-2 treatment, non-reinforced behavior was unaffected, indicating that the cytokine did not provoke reward-unrelated performance deficits. It was suggested that the effects of IL-2 on ICSS likely do not involve motoric, soporific, attentional or cognitive changes, but instead involve specific actions on motivational arousal. Although IL-6 was previously found to produce mesolimbic dopamine (DA) changes as marked as those induced by IL-2, systemic IL-6 treatment did not influence responding for rewarding brain stimulation. Likewise, although IL-1 at the dosage used reliably induces sickness behavior, responding for rewarding brain stimulation was unaffected. Thus it seems that anhedonia is not necessarily a component of the sickness response associated with IL-1 treatment.

Immunonutrition

The immune system is designed to protect the individual from foreign substances or organisms. It is expressed as cellular and humoral immunity. The former is dependent upon T lymphocytes and the latter on B lymphocytes, which become plasma cells and secrete antibodies. The immune system can be influenced by protein-energy malnutrition (PEM) and by catabolic illnesses such as sepsis and trauma, which in turn cause PEM. Specific trace element and vitamin deficiencies can also alter the immune state. However, overnutrition and obesity can also influence immune mechanisms. Obesity can promote the development of diabetes, which can alter the immune state. Finally, immunity becomes less effective with ageing and this process is enhanced by associated malnutrition.

Macronutrient intake and malabsorption in HIV infection: a comparison with other malabsorptive states

BACKGROUND

Wasting is a major complication of HIV infection. The role of malabsorption in wasting is controversial.

AIMS

To assess oral intake and malabsorption in a cohort of weight losing HIV infected patients, with or without chronic diarrhoea.

METHODS

A prospective study using a predefined protocol for HIV infected patients was performed in a gastroenterology and nutrition unit in a university hospital. A retrospective comparison was made with HIV negative patients with malabsorption due either to small bowel disease or resection. Body weight and height, serum albumin, oral intake of macronutrients, faecal weight, and faecal fat were measured.

RESULTS

Seventy nine weight losing HIV infected patients were studied. Among the 66 patients with more than 5% lipid malabsorption, wasting was significantly greater in patients with cryptosporidiosis (n = 22) than in patients with microsporidiosis (n = 18) who exhibited significantly more wasting than patients with no identified enteropathogen (n = 26) (body mass index 16.8 (14.0-20.7), 18.9 (16.5-21.3), 19.7 (15.9-23), respectively). When controlling for the level of lipid malabsorption, HIV infected patients had a significantly lower energy intake than HIV negative patients with chronic malabsorption. In HIV infected patients, but not in other categories of malabsorbers, body mass index correlated significantly with energy intake (r = 0.33, 95% confidence intervals 0.12 to 0.51).

CONCLUSION

In weight losing HIV infected patients, reduced energy intake is superimposed on malabsorption and significantly contributes to wasting.

Infection-induced anorexia: active host defence strategy

In association with fever production, decreased food consumption is the most common sign of infection. This effect is often regarded as an undesirable manifestation of sickness. However, evidence suggests that just as many behaviours have now been shown to modify immunocompetence, infection-induced anorexia is a behaviour systematically organised for pathogen elimination. That is, anorexia is an active defence mechanism that is beneficial for host defence. This review details the mechanism of infection-induced anorexia, placing it within the framework of the intricately organised acute phase response--the host response to infection. Furthermore, the evolutionary, behavioural, metabolic and immunological consequences of infection-induced anorexia are outlined, each providing evidence for the beneficial nature of this response. The evidence suggests that food restriction is one of the important behavioural strategies that organisms have evolved for the fight against pathogenic invasion. Nevertheless, such benefits require fine homeostatic control, as chronic undernutrition has deleterious consequences for host defence.

Differential effects of immunologic challenge on self-stimulation from the nucleus accumbens and the substantia nigra

Paralleling the effects of uncontrollable stressors, systemic administration of sheep red blood cells (SRBC) provokes brain neurotransmitter alterations, including DA variations within mesocorticolimbic regions, coinciding with or slightly preceding the peak immune response. Inasmuch as stressors disrupt responding for brain stimulation from the nucleus accumbens, possibly reflecting the anhedonic consequences of stressors, the present investigation assessed whether antigenic challenge would also influence responding for brain stimulation. Sheep red blood cell administration was found to reduce responding for brain stimulation from the nucleus accumbens, without affecting performance from the substantia nigra. The alterations of self-stimulation from the nucleus accumbens occurred at times that approximated the peak immune response. These data suggest that antigenic challenge may induce anhedonic-like effects that may be secondary to central neurochemical alterations engendered by the treatment. The possibility is also entertained that antigenic challenge may be interpreted as a stressor and contribute to alterations of affect.

N-3 polyunsaturated fatty acids and immune cell function

The amount and type of eicosanoids made can be affected by the type of fat consumed in the diet. It is now apparent that both eicosanoids and n-3 PUFAs are potent modulators of lymphocyte and M phi functions in vitro. Inclusion in the diet of high levels of certain lipids containing n-3 PUFAs markedly affects the functions of cells of the immune system subsequently tested in vitro. Cellular components of both natural and acquired immunity are affected. In vivo tests are perhaps the most appropriate approach for determining the effect of different dietary n-3 PUFAs upon immune function. Several studies indicate that diets rich in n-3 PUFAs are anti-inflammatory and immunosuppressive in vivo, although there have been relatively few studies in man. Although some of the effects of n-3 PUFAs may be brought about by modulation of the amount and types of eicosanoids made, it is clear that these fatty acids can also elicit their effects by eicosanoid-independent mechanisms (Fig. 12). Such n-3 PUFA-induced effects may be of use as a therapy for acute and chronic inflammation, for disorders which involve an inappropriately-activated immune response and for the enhancement of graft survival.

Cytokines and cachexia

Prolonged production of cytokines associated with cancer and chronic infections, and other long-term immune reactions is increasingly recognized as a main causal factor of the often severe signs and symptoms that accompany these diseases: weight loss, anorexia, and metabolic breakdown termed cachexia. The cytokine that initially was held responsible for causing these changes was tumor necrosis factor (TNF). However, from various studies it has become clear that the action of TNF can only be understood in the context of simultaneous presence of other cytokines, some of which have activities that are at the least equally important as TNF in bringing about cachexia. This review summarizes the experimental evidence for the involvement of cytokines in the pathogenesis of cachexia. Indirect evidence comes from the observation that cachexia can be induced in animals by repeated injections of cytokines or by inoculation of cytokine-producing cells. Thus, cachexia has been described in mice inoculated with tumor cells carrying and expressing genes for either TNF, interleukin-6 (IL-6), leukemia inhibitory factor (LIF), ciliary neurotrophic factor (CNTF) and interferon-gamma (IFN-gamma). More direct evidence is provided by the observations that cachexia in experimental animal models can be mitigated by administration of specific antagonists of cytokines. These latter type of studies revealed that cachexia can rarely, if ever, be attributed to one single cytokine but rather to a set of cytokines that work in concert in cachexia. A pool of anticytokine antibodies or other cytokine inhibitors might, therefore, be considered as a potential intervention for the treatment of cachectic patients, but this approach may induce immunosuppression, and, therefore, danger exists that such treatment may benefit the infectious agent or tumor.

Effect of conjugated linoleic acid on body composition in mice

The effects of conjugated linoleic acid (CLA) on body composition were investigated. ICR mice were fed a control diet containing 5.5% corn oil or a CLA-supplemented diet (5.0% corn oil plus 0.5% CLA). Mice fed CLA-supplemented diet exhibited 57% and 60% lower body fat and 5% and 14% increased lean body mass relative to controls (P < 0.05). Total carnitine palmitoyltransferase activity was increased by dietary CLA supplementation in both fat pad and skeletal muscle; the differences were significant for fat pad of fed mice and skeletal muscle of fasted mice. In cultured 3T3-L1 adipocytes CLA treatment (1 x 10(-4)M) significantly reduced heparin-releasable lipoprotein lipase activity (-66%) and the intracellular concentrations of triacylglyceride (-8%) and glycerol (-15%), but significantly increased free glycerol in the culture medium (+22%) compared to control (P < 0.05). The effects of CLA on body composition appear to be due in part to reduced fat deposition and increased lipolysis in adipocytes, possibly coupled with enhanced fatty acid oxidation in both muscle cells and adipocytes.

Wasting illness as a disorder of body weight regulation

Recent major breakthroughs in our understanding of the negative feedback control of body weight have modified our understanding of disorders characterized by both too much and too little body fat. On the one hand, defective negative feedback signalling in the form of leptin contributes to certain forms of obesity, at least in rodent models. On the other, excessive leptin-like signalling, potentially resulting from the elaboration of inflammatory cytokines, may contribute to the pathogenesis of wasting illness. With the rapid pace of progress that has occurred in this field in recent years, it seems likely that breakthroughs in the treatment of these catastrophic illnesses may follow in the wake of new insights into the physiology and pathophysiology of body weight regulation.

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.

Influenza virus infection of mice induces anorexia: comparison with endotoxin and interleukin-1 and the effects of indomethacin

The effects of infection of mice with influenza virus on ingestive behavior were assessed by both 22-h intake of food pellets, and intake of sweetened milk in a 30-minute access period. Infection with a lethal dose of virus resulted in losses in body weight as well as a reduction in food pellet intake. By contrast, infection with a sublethal dose of virus decreased body weight and food pellet intake to a lesser extent, but did not alter milk intake. Acute intraperitoneal injection of endotoxin (LPS, 0.3-5 micrograms), interleukin-1 alpha (IL-1 alpha, 50-100 ng) or IL-1 beta (100 ng) reduced milk intake, suggesting that the reduction of ingestive behavior may be associated with immune activation in general, and IL-1 in particular Pretreatment of the mice with the cyclooxygenase inhibitor, indomethacin (10 mg/kg SC) substantially attenuated, but did not completely reverse, the reduction in milk intake by LPS and IL-1. However, chronic treatment with indomethacin failed to alter the body weight or the intake of sweetened milk in influenza-infected mice, although there was some attenuation of the reduction in food intake. These results suggest that although IL-1 may play a role in the anorexia caused by influenza virus infection, it is not the only factor involved.

Metabolic responses to interleukin-1: centrally and peripherally mediated

OBJECTIVE

The purpose of this study was to differentiate between the catabolic effects of interleukin-1 (IL-1) when infused into the central nervous system or into the periphery.

SUMMARY BACKGROUND DATA

After injury and infection, IL-1 has been found in the central nervous system. Chronic intracerebrovascular infusion of IL-1 produces protein catabolism, anorexia, and fever. However, IL-1 may act directly on liver and bone marrow to elicit metabolic responses. Although IL-1 is thought to be involved in a number of metabolic responses associated with injury-inflammation, the sites of action are unclear.

METHODS

Rats were implanted with chronic infusion pumps and received diluent or three doses of IL-1 infused subcutaneously for 6 days, and a variety of response variables were measured. In a second study, doses were adjusted so that similar systemic catabolic responses were obtained from peripheral and intracerebroventricular infusion of IL-1. The acute-phase responses then were compared in the two groups of animals receiving IL-1 by different routes.

RESULT

Subcutaneously infused IL-1 elicited catabolic responses in a dose-response manner. Similar catabolic responses were achieved by infusing one tenth of the dose of IL-1 given subcutaneously into the central nervous system. Although similar systemic responses (protein catabolism, anorexia, fever, and weight loss) were observed with both routes of infusion, the subcutaneous infusion produced a much greater lymphocytosis, elevation in acute-phase reactants, and fall in serum iron and albumin.

CONCLUSIONS

The IL-1 appears to have different effects depending on the site of production and site of action. Regionalization of signal proteins such as IL-1 should be taken into consideration when devising specific anticytokine treatment strategies.

Adjuvant arthritis as a model of inflammatory cachexia

OBJECTIVE

To determine whether adjuvant arthritis (AA) leads to changes in body composition and cytokine production similar to those seen in patients with rheumatoid arthritis.

METHODS

AA was induced in Lewis rats using Freund's complete adjuvant. Body cell mass was measured by determining the concentration of total exchangeable potassium using 42K gavage. Splenocyte production of interleukin-1 (IL-1) and tumor necrosis factor alpha (TNF alpha) was measured by bioassay. Weight and food intake were also measured.

RESULTS

Animals that developed AA lost 6% of their body weight by the onset of clinically evident arthritis (day 14; P < 0.01) and lost 20% by the end of the inflammatory phase of AA (day 28; P < 0.0001). Body cell mass fell 24.7 +/- 8.6% (mean +/- SEM) in animals with AA, but did not change significantly in controls (increase of 6.3 +/- 7.9%) (P < 0.03). Pair-fed animals lost one-fourth of the weight lost by the animals with AA (P < 0.01), indicating that anorexia alone does not explain inflammatory cachexia. Weight loss was correlated with TNF alpha production by spleen mononuclear cells (r = 0.68, P < 0.007), and a weaker correlation was seen with IL-1 production (r = 0.45, P < 0.04).

CONCLUSION

AA in rats is a useful model of inflammatory cachexia that mimics the human pathophysiology in important ways, and is consistent with cytokine-driven cachexia in chronic inflammatory arthritis.

Intracerebral administration of Mycoplasma fermentans produces sickness behavior: role of prostaglandins

Mycoplasmas are small microorganisms, which cause various diseases in animals and in humans, activate the immune system, and induce the release of various cytokines. Some of the effects of mycoplasmas are mediated by the CNS. Moreover, Mycoplasma fermentans (MF) has recently been found in the brain, as well as other tissues of some AIDS patients, who usually display severe neurobehavioral disturbances. The present study was designed to examine the behavioral effects of central administration of MF, and the role of prostaglandins in mediating these effects. In one set of experiments, rats were injected intracerebroventricularly (i.c.v.) with either saline or a dose of MF (5.1-36 microg per rat), and several behavioral parameters were measured. In addition, body temperature and locomotor activity were continuously monitored by a biotelemetric system. MF induced a significant elevation in body temperature and suppression of motor activity levels. MF also significantly reduced the time spent in social exploration, decreased locomotor and exploratory activity in the open field test, suppressed the consumption of food and saccharine solution, and reduced body weight. In a second set of experiments, i.c.v. administration of MF (7.2 microg) was found to produce a significant increase in the production of prostaglandin E2 (PGE2) in hypothalamic, hippocampal, and cortical tissues. This effect was blocked by indomethacin, a prostaglandin synthesis inhibitor. Indomethacin also attenuated the effects of MF on body temperature, motor activity and body weight, suggesting the involvement of prostaglandins in mediating some of the effects of MF. Together, these findings suggest that the presence of MF in the brain may be responsible for some of the neurobehavioral abnormalities in HIV-infected patients.

Induction of muscle protein degradation by a tumour factor

An antigen of apparent molecular weight of 24,000, reactive with a murine monoclonal antibody, has been isolated from a cachexia-inducing tumour (MAC 16) and has been shown to initiate muscle protein degradation in vitro using isolated soleus muscle. Administration of this material to female NMRI mice (20 g) produced a pronounced depression in body weight (2.72 +/- 0.14 g; P<0.005 from control) over a 24 h period. This weight loss was attenuated in mice pretreated with the monoclonal antibody (0.06 +/- 0.26 g over 24 h) and occurred without a reduction in food and water intake. There was no change in body water composition, and the major contribution to the decrease in body weight was a decrease in the non-fat carcass dry weight (mainly lean body mass). The plasma levels of glucose and most amino acids were also significantly depressed. The decrease in lean body mass was accounted for by an increase (by 50%) in protein degradation and a decrease (by 50%) in protein synthesis in gastrocnemius muscle. Protein degradation was significantly decreased and protein synthesis increased to control values in mice pretreated with the monoclonal antibody. Protein degradation initiated in vitro with the proteolysis-inducing factor was abolished in mice pretreated with eicosapentaenoic acid (EPA), which had been shown to prevent muscle wastage in mice bearing the MAC16 tumour. Protein degradation was associated with a significant elevation of prostaglandin E2 production by isolated soleus muscle, which was inhibited by both the monoclonal antibody and EPA. These results suggest that this material may be the humoral factor mediating changes in skeletal muscle protein homeostasis during the process of cancer cachexia in animals bearing the MAC16 tumour, and could potentially be involved in other cases of cachexia.

Tolerance to appetite suppression induced by peptidoglycan

Physiologically realistic peptidoglycan (PG) fragments, derived from Neisseria gonorrhoeae, were shown previously to dose-dependently suppress food consumption and body weight gain in rats following single intraperitoneal injections. The present study, examining the effects of repeated daily injection of PG, provides additional support to our underlying hypothesis, i.e., that soluble PG fragments contribute to the loss of appetite commonly associated with bacterial infections. An initial intraperitoneal injection of purified, soluble, macromolecular, extensively O-acetylated PG fragments (S-O-PG) (240 micrograms/kg of body weight) decreased overnight food consumption in male Lewis rats (150 g) by approximately 35% relative to animals receiving diluent alone (P < 0.05). However, subsequent daily injections of S-O-PG resulted in progressively smaller effects on food consumption until, by the fourth day, rats were completely nonresponsive (tolerant) to S-O-PG-induced hypophagia. Rats that developed tolerance to the effects of S-O-PG on appetite were also tolerant to three other known hypophagic agents, lipopolysaccharide (LPS), muramyl dipeptide, and interleukin-1, when challenged one day after establishment of S-O-PG tolerance. Similarly, rats developed tolerance to repeated injections of muramyl dipeptide or LPS and were cross-tolerant to S-O-PG when challenged 1 day later. However, 30 days after establishment of S-O-PG tolerance, rats remained nonresponsive to S-O-PG but regained full responsiveness to LPS-mediated hypophagia. Thus, at least two mechanisms of tolerance to S-O-PG hypophagia exist: an early tolerance which is nonspecific and a late tolerance which is specific for S-O-PG. Late, but not early, tolerance to S-O-PG-mediated suppression of appetite was associated with an increase in specific anti-PG antibody activity as measured in an enzyme-linked immunosorbent assay.

Neuroendocrine changes in systemic lupus erythematosus and Sjögren's syndrome

It has become clear that the neuroendocrine and immune systems are closely linked and interdependent. The exact mechanisms of this interaction are only beginning to be unravelled. The complexity of these connections may partly explain why the aetiopathogenesis of autoimmune diseases remains obscure and why genetic, hormonal, microbial, environmental, as well as a host of other factors, have all been put forward as explanations. What has become clear is that a number of neuroendocrine and hormonal factors have important immunomodulatory roles in health and disease.

Bacterial products and the control of ingestive behavior: clinical implications

Bacterial products such as lipopolysaccharides (LPS) and muramyl peptides are delivered in the course of infections. They trigger the host's acute phase responses to bacterial infections and are probably involved in the accompanying hypophagia because LPS and muramyl dipeptide (MDP, the minimal immunologically active muramyl peptide) reduce food intake after parenteral administration in animals. LPS and MDP inhibit feeding synergistically through separate but interacting mechanisms. The hypophagic effects of LPS and MDP are presumably mediated by the combined actions of interleukin-1, tumor necrosis factor, and other cytokines. More work is required to understand the interactions between these cytokines, and between bacterial products and cytokines, before cytokine antagonists can be used for treatment of the hypophagia during bacterial infections. As the hypophagia seems to be an early mechanism of host defense, a treatment should be carefully considered. If an intervention is indicated because of a patient's poor condition, inhibitors of eicosanoid synthesis and glucocorticoids may hold more promise for therapy because such substances block LPS and MDP hypophagia. Although LPS can reduce food intake by direct action on the brain, presently available evidence indicates that systemic LPS acts primarily in the periphery to generate a neural signal that is transmitted to the brain and inhibits feeding through the vagus. The exact site where LPS acts on peripheral nerves remains to be identified. LPS hypophagia is conditionable, but conditioning cannot solely account for LPS hypophagia under most test conditions. Whether MDP hypophagia is also conditionable and mediated by vagal afferents is not yet known. All in all, the putative mediators and mechanisms of LPS and MDP hypophagia suggest some options for a treatment of the hypophagia during bacterial infection, but present knowledge about the mechanisms and interactions of the involved substances is still fragmentary and requires further investigation.

Negative regulators of the interleukin-1 system: receptor antagonists and a decoy receptor

The IL-1 system includes 2 agonists, alpha and beta, processing and transport molecules, receptor antagonists, signalling receptor, a decoy receptor and an accessory molecule. Negative pathways of regulation include the antagonists, of which 3 isoforms have been cloned and the type II "decoy" receptor. Molecules that regulate inflammation and immunity coordinatively affect different components of the system. The complexity of the system and the existence of unique pathways of negative regulation, the antagonists and the decoy receptor, emphasize the need for a tight control of the production and action of IL-1.

Effects of dietary n-3 fatty acid supplementation in men with weight loss associated with the acquired immune deficiency syndrome: Relation to indices of cytokine production

Cytokines may be involved in weight loss and disturbances of metabolism associated with human immunodeficiency virus (HIV) infection. Dietary n-3 fatty acids reduce the production of interleukin-1 (IL-1) and tumor necrosis factor (TNF) by peripheral blood mononuclear cells (PBMC) in normal humans and prevent IL-1 and TNF anorexia in animals. Accordingly, we studied the nutritional and metabolic effects of a 10-week trial of dietary fish oil (MaxEPA 18 g/day) in men with weight loss due to acquired immune deficiency syndrome (AIDS). Twenty men were enrolled, and 16 completed the 10-week supplementation period. Prior weight loss was 13.7 +/- 1.8 kg(17.4 +/- 1.6% body weight, means +/- SE). Food intake, body composition, blood chemistries, serum cytokine concentrations, in vitro production of IL-1 and TNF by PBMC, and clinical course were followed. A subset of subjects (n=12) underwent stable isotope infusions to measure de novo hepatic lipogenesis (DNL), an in vivo metabolic index that is influenced by cytokine presence and has previously been found to be elevated in AIDS. An unsupplemented group of men with AIDS wasting (10.4 +/- 2.4 kg weight loss, 13.1 +/- 2.2% body weight) was monitored for 10 weeks as controls. Baseline food intake (2,395 +/- 177 kcal/day and 95.1 +/- 7.2 g protein/day), body weight, percent fat, and fat-free mass were unchanged over the 10-week supplementation period. Serum triglycerides were reduced in hypertriglyceridemic subjects, confirming compliance with fish oil supplementation and suggesting that their hypertriglyceridemia was at least in part due to overproduction. Serum TNF and IL-1 were undetectable before or after fish oil supplementation. Serum interferon alpha (IFN) was measurable but did not change. In vitro production of IL-1 and TNF by PBMC was markedly reduced both at baseline and after fish oil supplementation in this population, even in the presence of new AIDS complications, compared with normal controls. The metabolic measurement DNL fell and weight was gained (2.1 +/- 1.3 kg) in subjects who did not develop new AIDS-related complications, but further increases in DNL and further weight loss were observed in subjects who developed a new AIDS complication (p<0.05 for interaction between new complication and change in DNL). No changes in body weight, food intake, serum triglycerides, serum cytokines, or DNL were observed in the unsupplemented group. We conclude that fish oil is a weak anticytokine agent that is unable to overcome the metabolic and nutritional consequences of acute AIDS-related complications but may exert a clinical anticytokine effect in stable AIDS patients. Cytokine production by PBMC is not a useful or reliable marker of in vivo cytokine activity in AIDS patients with weight loss. In contrast, an integrative functional index that is sensitive to cytokine presence in tissues (hepatic DNL) correlated with clinical response. These findings are relevant to the design of future studies of more potent anticytokine agents, such as thalidomide.

Anorexia during acute and chronic disease

Anorexia is associated with disorders of all systems. Anorexia represents a consistent clinical manifestation during acute and chronic pathophysiological processes (infection, inflammation, injury, toxins, immunological reactions, malignancy and necrosis). Anorexia during disease can be beneficial or deleterious depending on the timing and duration. Temporary anorexia during acute disease may be beneficial to an organism since a restriction in the intake of micro- and macro-nutrients will inhibit bacterial growth. Long-term anorexia during chronic disease, however, is deleterious to an organism and may be associated with cachexia, which can ultimately result in death. Various mechanisms participate in the anorexia observed during disease, including cytokine action. Anorexia induced by cytokines is proposed to involve modulation of hypothalamic-feeding associated sites, prostaglandin-dependent mechanisms, modifications of neurotransmitter systems, gastrointestinal, metabolic, and endocrine factors. In addition, the anorexia-cachexia syndrome is multifactorial and may involve chronic pain, depression or anxiety, hypogeusia and hyposmia, chronic nausea, early satiety, malfunction of the gastrointestinal system, metabolic alterations, cytokine action, production of other anorexigenic substances and/or iatrogenic causes (chemotherapy, radiotherapy). Cachexia may result not only from anorexia and a decreased caloric intake, but also from malabsorption and losses from the body (ulcers, hemorrhage, effusions), or a change in body metabolism. Research has focused on potential interventions to modify anorexia during disease and the anorexia-cachexia syndrome. Nutritional modifications and the use of specific steroids (such as megestrol acetate) are being tested in the clinical setting. Understanding the specific mechanisms responsible for anorexia during disease as well as their interactions is essential to develop interventions for the control of anorexia (during a critical time in a specific disease), and to devise less toxic immunotherapeutic regimens using cytokines.

Studies on the regulation of food intake using rat total parenteral nutrition as a model

Total parenteral nutrition (TPN) is essential for maintaining the nutritional status of patients who are unable to eat sufficiently to meet their metabolic needs. However, TPN suppresses appetite and ultimately diminishes food intake. Theories concerning the role(s) of peripheral metabolites as signals, acting via the liver and the hypothalamus, for the metabolic control of food intake, have been put forward to explain the anorectic effect of TPN. In addition, it is postulated that changes in peripheral metabolites during TPN may be translated into changes in the levels of brain neurotransmitters known to decrease food intake. This review summarizes studies concerning the effect of TPN on food intake. These studies have involved: (1) characterizing the changes in feeding activity due to TPN; (2) investigating the involvement of the central nervous system; and (3) investigating the role of the periphery and its metabolites in the regulation of food intake during TPN. Some insight into the mechanism of action of TPN on food intake is provided.

Mechanisms mediating cancer cachexia

BACKGROUND

Cancer cachexia encompasses a wide range of metabolic, hormonal, and cytokine-related abnormalities that result in a wasting syndrome possibly accounting for up to 30% of cancer-related deaths.

METHODS

A literature search was performed to review those pathways of metabolic interference involved in cancer cachexia.

RESULTS

An elevated basal metabolic rate and increased energy expenditure combined with systemic catabolism of muscle and adipose tissue are the predominant manifestations of the metabolic and physiologic perturbations noted in this pathologic state.

CONCLUSIONS

To date, although some of the cachexia-related metabolic abnormalities have been elucidated, there has been little success in relation to therapeutic manipulation of these pathways. This review evaluates current knowledge relating to cancer cachexia and cautions against generalizations concerning treatment regimens.

Hypothalamic neuronal histamine modulates adaptive behavior and thermogenesis in response to endogenous pyrogen

Homeostatic involvement of hypothalamic neuronal histamine in adaptive behavior and thermogenesis was investigated when interleukin-1 beta (IL-1 beta), one of the endogenous pyrogens, was infused peripherally in rats. IL-1 beta decreased food and water intake and elevated body temperature. Depletion of neuronal histamine in the hypothalamus induced by alpha-fluoromethylhistidine, a suicide inhibitor of the histamine synthesizing enzyme histidine decarboxylase (HDC), attenuated the suppressive effect of IL-1 beta on food intake, facilitated the inhibitory effect on water intake, and enhanced its thermogenic effect. Simultaneously IL-1 beta increased activity of HDC and histamine-N-methyltransferase (HMT), a neuronal histamine catabolizing enzyme. Pretreatment with indomethacin completely blocked those increases in turnover of neuronal histamine induced by IL-1 beta. Hypothalamic prostaglandin E2 (PGE2) activated by peripheral IL-1 beta, but not peripheral PGE2, increased both activities of HDC and HMT. Ginsenoside Rg1, a major component of panax ginseng, modulated the suppressive effects of IL-1 beta on ingestive behavior, resulting in a lowering of body temperature. The findings suggest that the effects of IL-1 beta on ingestive behavior and thermogenesis may be modulated by dynamics of hypothalamic neuronal histamine through activation of hypothalamic PGE2 which is elevated by peripheral IL-1 beta.

Interleukin-1 beta-induced anorexia and pyrexia in rat: relationship to hypothalamic neuropeptide Y

We investigated the effect of recombinant human interleukin-1 beta (rhIL-1 beta)-induced anorexia and pyrexia on the hypothalamic neuropeptide Y (NPY)-ergic system, which stimulates feeding and reduces thermogenesis. In meal-fed rats, food intake decreased by 83%, 90 min after IL-1 beta treatment (1.3 micrograms/100 g ip; n - 8) vs. controls. NPY concentrations were significantly higher in the medial preoptic area (MPO), paraventricular (PVN), ventromedial (VMN), and dorsomedial (DMN) nuclei but unchanged in the arcuate nucleus (ARC) in both IL-1 beta-treated and pair-fed groups. Indomethacin (0.25 mg/100 g ip) reduced IL-1 beta-induced anorexia and tended to normalize NPY concentrations. In study 2, IL-1 beta increased core temperature by 1.1 degrees C above preinjection values (P < 0.001) and significantly raised NPY concentrations in the MPO, PVN, VMN, and DMN compared with controls, 60 min postinjection. Indomethacin prevented the pyrexia and normalized hypothalamic NPY levels. As NPY concentrations were not increased in the ARC (the hypothalamic site of synthesis), we suggest that the increased NPY levels may result from blocked release, which would be in accord with the known experimental effects of NPY.

Hypothalamic and thalamic sites of action of interleukin-1 beta on food intake, body temperature and pain sensitivity in the rat

Interleukin-1beta (IL-1beta ) has anorectic, hyperthermic, and analgesic or hyperalgesic (depending on the studies) effects in the rat. These effects appear to be mediated by the central nervous system; however, the exact localization of action of IL-1beta in the brain has never been delineated with precision. The purpose of this study was to determine precisely where IL- IO acts in the hypothalamus and in the thalamus to modulate food intake, body temperature, and pain sensitivity. Animals were tested after local intracerebral microinjections of 5 ng of IL-1beta dissolved in 0.3 microl of saline, or of 0.3 microl saline alone. The results show that IL-1beta has anorectic effects in 3 diencephalic sites (the perifornical area, an area above the optic chiasma, and an area internal to the mamillo-thalamic tract), and not in 9 other sites tested. IL-1beta has hyperthermic effects in 7 sites (the media] and lateral preoptic area, the hypothalamic periventricular substance, the dorso-medial and arcuate nuclei of the hypothalamus, and the centro-medial and gelatinosus nuclei of the thalamus), and not in 6 other sites. IL-1beta has analgesic effects in the centro-medial and gelatinosus nuclei of the thalamus, and not in 7 other sites. IL-1beta also increases food intake and decreases pain sensation thresholds in the paraventricular nucleus of the hypothalamus. Therefore IL-1beta has very selective anatomical sites of action in the brain, and the paraventricular nucleus of the hypothalamus appears to have special properties regarding the effects of IL-1beta on food intake and pain sensation regulation.

Behaviorally conditioned anorexia: role of gastric emptying and prostaglandins

The reduction of food intake in response to bacteria is posited to be a favourable host reaction. This report attempted to examine whether gastric emptying is involved in the known conditionability of this response. Additionally, this study investigated the role of prostaglandins in the conditioned anorexic response. To investigate this phenomenon, lipopolysaccharide (LPS) (100 micrograms/kg) was used as the unconditioned stimulus, and paired with a novel 1% saccharin solution (conditioned stimulus). Upon conditioned stimulus (CS) representation, experimental animals displayed a marked reduction in food consumption (experiment 1) and emptying of gastric contents (experiment 2). Additionally, treatment with indomethacin upon CS reexposition blocked both the conditioned anorexia and suppression of gastric emptying. These results indicate that conditioned anorexia is possibly the result of a conditioned inhibition of gastric emptying, and this process is mediated by conditioned alterations in PG levels.

Manifestations of cancer cachexia induced by colon 26 adenocarcinoma are not fully ascribable to interleukin-6

In order to further clarify the role of interleukin 6 (IL-6) in the pathogenesis of cachexia, recombinant human IL-6 (hIL-6) was administered s.c. by osmotic pump for 9 days at a dose of 1 or 10 micrograms/day into CDF1 mice inoculated with a non-cachexia-inducing subclone of colon 26 adenocarcinoma (clone 5), or with a cachexia-inducing subclone (clone 20) of this malignancy. The serum level of IL-6 in non-cachectic mice with clone-5 tumors was 35% lower than in cachectic mice bearing clone 20 of colon 26 adenocarcinoma on the 19th day after tumor inoculation. IL-6 administration induced anemia, thrombocytosis and visceral organ hypertrophy not only in mice with clone-5 tumors but also in control mice with no tumor burden. Lipolysis and proteolysis became conspicuous when a large dose (10 micrograms/day) of IL-6 was infused into mice with clone-5 tumors. However, IL-6 supplementation did not induce loss of body weight, a decline in food intake or lymphocytopenia, which were characteristically observed in cachectic mice with clone-20 tumors. In conclusion, IL-6 appears to be a permissive factor for the development of cachexia but, while it can induce some of the symptoms typical of cachexia, it cannot in itself induce the full cachectic syndrome.

Systemic lupus erythematosus: immunopathogenesis of neurologic dysfunction

Neurologic complications of systemic lupus erythematosus (neuro-SLE) are common. The most frequent manifestations of neuro-SLE are seizures, encephalopathy, and behavioral changes, but a wide variety of other neurologic abnormalities affecting the central and peripheral nervous system and muscle also occur. Although the prevalence of neuro-SLE is high, the diversity of clinical presentations, the multiple potential etiologies, and the absence of sensitive and specific diagnostic tests render diagnosis difficult. Recent advances in understanding mechanisms of neuronal dysfunction combined with advances in imaging techniques, including functional imaging, should help in diagnosis and management. The mechanisms of neurologic injury can be divided into three broad categories. First, neuronal dysfunction may result from direct effects of the immune system on brain cells such as autoantibody binding to cell surface, immune complex deposition with secondary inflammation, and effects of cytokines. Second, immune- mediated injury to supportive structures such as the vasculature may also affect the nervous system by producing ischemia. Finally, the neuraxis may be affected by any one of several immune and non- immune effects of infection, toxins, and metabolic disturbances.

Gluconeogenesis and intrahepatic triose phosphate flux in response to fasting or substrate loads. Application of the mass isotopomer distribution analysis technique with testing of assumptions and potential problems

We measured gluconeogenesis (GNG) in rats by mass isotopomer distribution analysis, which allows enrichment of the true biosynthetic precursor pool (hepatic cytosolic triose phosphates) to be determined. Fractional GNG from infused [3-13C]lactate, [1-13C]lactate, and [2-13C]glycerol was 88 +/- 2, 89 +/- 3, and 87 +/- 2%, respectively, after 48 h of fasting. [2-13C]Glycerol was the most efficient label and allowed measurement of rate of appearance of intrahepatic triose phosphate (Ra triose-P), by dilution. IV fructose (10-15 mg/kg/min) increased absolute GNG by 81-147%. Ra triose-P increased proportionately, but endogenous Ra triose-P was almost completely suppressed, suggesting feedback control. Interestingly, 15-17% of fructose was directly converted to glucose without entering hepatic triose-P. IV glucose reduced GNG and Ra triose-P. 24-h fasting reduced hepatic glucose production by half, but absolute GNG was unchanged due to increased fractional GNG (51-87%). Reduced hepatic glucose production was entirely due to decreased glycogen input, from 7.3 +/- 1.8 to 1.1 +/- 0.2 mg/kg/min. Ra triose-P fell during fasting, but efficiency of triose-P disposal into GNG increased, maintaining GNG constant. Secreted glucuronyl conjugates and plasma glucose results correlated closely. In summary, GNG and intrahepatic triose-P flux can be measured by mass isotopomer distribution analysis with [2-13C]glycerol.

Limited importance of a learned aversion in the hypophagic effect of interleukin-1 beta

This study addressed the possible role of a learned aversion in the hypophagic effect of interleukin-1 beta (IL-1 beta) in the rat. Two repetitive intraperitoneal injections of IL-1 beta (2 micrograms/kg body weight = b.wt.) progressively reduced intake of a novel-tasting saccharin diet (SD) presented immediately after injection. When SD and the familiar diet were offered some days after an injection, SD selection was in some but not all trials reduced by IL-1 beta pretreatment. When SD was offered alone several days after an injection, SD intake was not affected by the initial pairing of SD presentation with IL-1 beta injection. In further experiments, the novelty of a flavor added to the diet fed immediately after injection proved to be crucial for the aversive effect of IL-1 beta, and enhanced its hypophagic effect. Finally, lesion of the area postrema and the adjacent nucleus of the solitary tract failed to affect the hypophagia induced by IL-1 beta (1 microgram/kg b.wt.). The results indicate that, under certain conditions, IL-1 beta can induce an aversion to the taste and flavor of the food consumed after injection. This aversive effect of IL-1 beta appears to be rather weak and is presumably not involved in the hypophagic effect of IL-1 beta under normal feeding conditions. It may however enhance IL-1 beta's hypophagic effect under certain conditions, for instance after repeated injections.

Effects of early immune stress and changes in dietary metabolizable energy on the development of newly hatched turkeys. 1. Growth and nutrient utilization

Two experiments were conducted to document the effects of an early immunologic stress and changes in dietary ME(n) on growth and nutrient utilization of newly hatched turkeys. Treatments in both experiments consisted of a complete factorial arrangement of two types of injection and four isonitrogenous diets. Turkeys were injected i.p. with saline (SAL) or a solution of lipopolysaccharide (LPS) (100 micrograms LPS/mL SAL) at 1, 3, and 5 d of age. In Experiment 1, two diets were formulated to contain 2,800 kcal ME(n)/kg. One was a corn-soybean meal-based diet (CSBM) and the other contained 8% Solkafloc (SKF). A third diet (3,100 kcal ME(n)/kg) was formulated by substituting 8% sucrose (SUC) for the 8% SKF. The fourth diet included in Experiment 1 was formulated to contain 3,700 kcal ME(n)/kg. The CSBM and SUC diets were also included in Experiment 2. Two additional diets tested in Experiment 2 were the CSBM diet containing 74.5 mg ibuprofen/kg (IBU) and a corn-soybean meal-based diet with a ME(n) value of 3,100 kcal/kg (CS31). Injection with LPS reduced (P < .05) BW of turkeys throughout Experiment 1 and until 9 d of age in Experiment 2, as compared with injection with SAL, irrespective of dietary treatment. The reduction in BW was mainly due to a decrease in feed intake (FI) (P < .05). Turkeys fed diets with 3,100 kcal ME(n)/kg were heavier (P < .05) than those fed diets with 2,800 kcal ME(n)/kg, irrespective of injection. Inclusion of ibuprofen to the CSBM diet from 1 to 14 d improved (P < .05) BW and feed efficiency (P < .01) of turkeys at 14 d of age, compared with turkeys fed the CSBM diet. Determined ME(n) was not affected by LPS injection. Adverse effects of LPS injection on growth of turkey poults were mainly the consequence of a reduced FI and not of altered nutrient utilization. These effects were not fully alleviated by feeding a diet with 3,100 kcal ME(n)/kg.

Differential effects of IL-1ra on sickness behavior and weight loss induced by IL-1 in rats

Peripheral and central injections of recombinant human interleukin-1 beta (IL-1 beta) have been shown to decrease social exploration and to induce body weight loss in rats. To characterize the receptor mechanisms of these effects, we used as a tool a specific antagonist of the receptors of IL-1, IL-1ra. Intraperitoneal (i.p.) administration of IL-1ra (8 mg/kg) blocked the effect of i.p. injection of IL-1 beta (4 micrograms/rat) on social behaviour but not on body weight. Central administration of IL-1ra (60 micrograms/rat, i.c.v.) abrogated the effects of centrally administered IL-1 beta (30 ng/rat, i.c.v.) on both social behaviour and body weight. Central injection of IL-1ra (4 micrograms/rat, i.c.v.) also attenuated the effects of i.p. administered IL-1 beta (4 micrograms/rat) on social behaviour but not on body weight. These results suggest that the effects of IL-1 beta on social behavior are mediated centrally and that its effect on the loss of body weight involves different receptor mechanisms.

Synergism between IL-1 beta and TNF-alpha on the activity of the pituitary-adrenal axis and on food intake of rats

We investigated the effects of separate and combined intraperitoneal administration for 3 days of recombinant human interleukin-1 beta (IL-1) and recombinant human tumor necrosis factor-alpha (TNF) on plasma adrenocorticotropic hormone (ACTH) and corticosterone (B) levels, adrenal weight, food intake, and rectal temperature. Rats were equipped with a jugular cannula for daily blood sampling and with an intraperitoneally implanted Alzet osmotic minipump loaded with either saline, IL-1 (2.0 micrograms/day), TNF (0.2, 2.0, or 10.0 micrograms/day), or IL-1 in combination with TNF. Plasma ACTH and B levels and adrenal weight were significantly increased, in a dose-dependent way, by simultaneous infusion of IL-1 and TNF but not by administration of either cytokine alone. Chronic administration of IL-1 alone induced a significant decrease in food intake and a significant elevation of rectal temperature, whereas infusion of only the highest dose of TNF significantly elevated rectal temperature. Coinfusion of IL-1 and TNF induced both effects in a dose-dependent and synergistic way. Our data show that simultaneous infusion of IL-1 and TNF in rats has a synergistic effect on the activity of the pituitary-adrenal axis as well as on food intake and rectal temperature. The existence of two pathways, which act synergistically, may increase the sensitivity of the host to respond to subtle inflammatory stimuli.

A step towards developing the expertise to control hunger and satiety: regulatory role of satiomem--a membrane proteoglycan

Regulation of hunger and satiety is a complex process thought to be controlled by a complex interplay of neurotransmitters in the hypothalamic region of the brain. Reduced food intake or anorexia has also been observed under various disease or disorder conditions including AIDS and cancer. On the other hand, increased appetite because of some impairment of central mechanisms regulating the food intake could also cause/obesity. A large number of substances including neuropeptides, hormones, drugs, and synthetic peptides have been implicated in the regulation of appetite and food intake behavior in normal as well as disease or disorder conditions. Most of these substances are not directly involved in the regulation of normal hunger and satiety but exert their effect indirectly via other media. Some of them are involved under certain pathologic conditions and during the course they become involved directly or indirectly in the triggering of hunger and satiety regulatory mechanism. Recently, we have been able to isolate and purify an endogenous proteoglycan from membranes of animal and plant sources. This membrane anchored proteoglycan termed as 'Satiomem' reduces food intake without any rebound effects and has no apparent toxicity. It also fulfils all the criteria of a true satiety or anorexigenic substance. The release of satiomem from the cell surface could be mediated by a specific phospholipase-C. Satiomem seems to be involved in transducing activating signals and may also act as a source of second messenger for the regulatory mechanism of appetite. This article summarizes the regulatory aspects of hunger and satiety mechanisms controlled by endogenous substances with the emphasis on our present knowledge about satiomem.

Behavioral conditioning of lipopolysaccharide-induced anorexia

One manifestation of the acute phase response, sickness behavior, is now considered an important response in the organism's overall attempt to reinstate homeostasis. This report aimed to determine whether the sickness behavior of anorexia was conditionable using the conditioned taste aversion paradigm. To investigate this phenomenon, lipopolysaccharide (LPS) (100 micrograms/kg) was used as the unconditioned stimulus, and was paired with a novel 1% saccharin solution (conditioned stimulus). Upon conditioned stimulus representation, the anorectic effects of LPS were observed. These data are consistent with recent literature showing acute phase events to be conditionable.

Continuous systemic interleukin-1 alpha infusion suppresses food intake without increasing lateral hypothalamic dopamine activity

In addition to its immunomodulatory action, interleukin-1 (IL-1 alpha) induces anorexia centrally. Whether IL-1-induced anorexia is mediated by dopaminergic activity in the lateral hypothalamic area (LHA) was investigated by using microdialysis in freely moving rats. After recovery from jugular vein catheterization and LHA cannulation, rats had a microdialysis probe inserted into the LHA. Microdialysis samples were continuously collected in control rats not infused, and in IL-1-treated rats during and after a 24 h continuous systemic infusion of 6 micrograms IL-1 alpha. IL-1 alpha significantly suppressed food intake from 13.6 +/- 0.1 g to 4.3 +/- 0.8 g (p < 0.001), but there was no significant difference in dopamine concentration in the LHA dialysates before, during and after IL-1 alpha infusion relative to controls. Although IL-1 alpha has been shown to act centrally, our results suggest that the anorexic effect of IL-1 alpha is not mediated through dopaminergic activity in the LHA.