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

Cellular localization of tumor necrosis factor mRNA in neurological tissue from HIV-infected patients by combined reverse transcriptase/polymerase chain reaction in situ hybridization and immunohistochemistry

HIV-induced neurological disease is postulated to be caused by indirect mechanisms. Tumor necrosis factor (TNF)alpha is increased in the brains in human immunodeficiency virus (HIV)-associated dementia and in the spinal cord in vacuolar myelopathy and may play a pathogenetic role in these diseases. Microglia, astrocytes and infiltrating macrophages can be induced to produce TNF alpha and each has been identified as a source of TNF alpha in neurological disease. Reverse transcriptase synthesis of cDNA and polymerase chain reaction amplification of the cDNA was combined with immunocytochemistry to identify the cellular source of TNF alpha in HIV-induced neurological disease. Cells positive for TNF alpha mRNA were more abundant in white matter than gray matter of the brain from demented individuals. TNF alpha mRNA-positive cells in brains and spinal cords were almost exclusively macrophage-lineage cells. Only rare TNF alpha mRNA-positive cells were astrocytes. We conclude that macrophage-lineage cells are the primary source of elevated central nervous system TNF alpha mRNA in providing further evidence that macrophage activation is an important element in the pathogenesis of HIV-associated neurological disease.

Hormones, lymphohemopoietic cytokines and the neuroimmune axis

The classical distinction between hormones and cytokines has become increasingly obscure with the realization that homeostatic responses to infection involve coordinated changes in both the neuroendocrine and immune systems. The hypothesis that these systems communicate with one another is supported by the ever-accruing demonstrations of a shared molecular network of ligands and receptors. For instance, leukocytes express receptors for hormones and these receptors modulate diverse biological activities such as the growth, differentiation and effector functions. Leukocyte lineages also synthesize and secrete hormones, such as insulin-like growth factor-I (IGF-I), in response to both growth hormone (GH) and also to cytokines such as tumor necrosis factor-alpha (TNF-alpha). Since hormones share intracellular signaling substrates and biological activities with classical lymphohemopoietic cytokines, neuroendocrine and immune tissues share a common molecular language. The physiological significance of this shared molecular framework is that these homeostatic systems can intercommunicate. One important example of this interaction is the mechanism by which bacterial lipopolysaccharide, by eliciting a pro-inflammatory cytokine cascade from activated leukocytes, modulate pituitary GH secretion as well as other CNS-controlled behavioral and metabolic events. This article reviews the cellular and molecular basis for this communication system and proposes novel mechanisms by which neuroendocrine-immune interactions converge to modulate disease resistance, metabolism and growth.

Is TNF really involved in cachexia?

A review on the possible involvement of tumor necrosis factor-alpha (TNF) in cachexia is presented. While this cytokine is definitely linked to sepsis and tumor-associated weight loss in some experimental models, other cytokines, such as interleukin-6 (IL-6) or interferon-gamma (IFN-gamma), alone or in combination with TNF, may also play an important role in the development of cachexia.

[Malnutrition and HIV infection]

The wasting syndrome is well known in HIV infected patients. Predominant free fatty mass deletion is achieved. The weight loss results from decrease of food intake, from gut disorders due to HIV or opportunistic infections. Metabolic disorders are reported too. Breakdown of carbohydrates and proteins presents energy source. Raised free fatty acid turn over and hypertriglyceridemia are reported. Polyunsatured fatty acid level is raised inducing free radicals increase. Free radicals delete immune functions (apoptosis). Vitamin and trace element decrease worsen negative effects of free radicals.

Cracking the riddle of cancer anorexia

During tumor growth, anorexia and reduced food intake are among the major causes leading to malnutrition and eventually cachexia, which negatively affect patients' outcome. Consistent evidence from our laboratories in rats and humans indicates a key role for ventromedial hypothalamic (VMH) serotonergic system in the development of cancer anorexia. Thus, we postulated that during cancer, increased plasma tryptophan levels (the precursor of serotonin) lead to increased cerebrospinal fluid tryptophan concentrations and increased VMH serotonin synthesis, which then mediates the occurrence of anorexia. However, recent data strongly suggest that factors other than tryptophan supplied to the central nervous system might be involved in the pathogenesis of reduced food intake during tumor growth. Particularly, a significant role appears to be played by interleukin-1 (IL-1). We recently showed that IL-1 infusion in normal rats causes changes in food intake and its determinants, meal number and meal size, similar to those characterizing cancer anorexia, thus supporting the involvement of this cytokine in the development of anorexia. Interestingly, IL-1 and the VMH serotonergic system appear to be closely linked: peripherally infused IL-1 increases brain tryptophan and serotonin concentrations, while intracerebrally infused IL-1 increases neuronal firing rate and serotonin release. We therefore hypothesize that during tumor growth, increased production/secretion of IL-1 occurs, which facilitates the tryptophan supply to the brain. IL-1 can then also act on the VHM itself, where IL-1 receptors exist, to increase its neuronal activity and serotonin release. In other words, we believe that centrally acting IL-1 increases hypothalamic neuronal firing rate and serotonin release, while peripherally acting IL-1 is critical in supplying the hypothalamus with the precursor, tryptophan, in order to maintain the high rate of serotonin synthesis. Also, additional factors recently proposed as mediators of anorexia (including neuropeptide Y and nitric oxide) appear to be part of the hypothesized pathogenic mechanism.

Vesnarinone: a potential cytokine inhibitor

Cytokines are soluble peptides that mediate cell-to-cell interactions via specific cell surface receptors. There is a growing body of evidence that cytokines may play an important role in the pathogenesis of heart failure, and the intriguing possibility has been postulated that anticytokine therapy may favorably alter the clinical outcome of heart failure. As cytokines are essentially pleiotropic and redundant in nature, elimination of a single cytokine from the biologic system often fails to have major consequences. Therefore, the prospect has been raised for developing immunomodulating therapy for heart failure, enabling the simultaneous modification of the actions of multiple cytokines. The recently observed clinical benefit of vesnarinone on mortality and morbidity in patients with heart failure has been attributed to this immunomodulation. In the murine model of myocarditis and heart failure, vesnarinone enhanced the cumulative survival rate without affecting virus replication on virus-induced cytopathic effects. Vesnarinone inhibited excessive cytotoxicity of natural killer cells presumably by suppressing activation mediated by K channel inhibition. Vesnarinone also inhibited the production of cytokines. Cytokine inhibitory effects were different from those of other phosphodiesterase inhibitors or direct elevation of intracellular cyclic adenosine monophosphate, suggesting that the effects did not appear to be derived solely from a cyclic adenosine monophosphate-elevating action. Such cytokine regulation also appeared to be different in normal patients and in patients with heart failure. In conclusion, vesnarinone exerts an immunomodulating effect by suppressing natural killer cell activity and inhibiting cytokine production. These findings may hold open the hope that immunomodulation could be a new therapeutic modality. However, further studies on the long-term safety and efficacy of vesnarinone are warranted to establish the eventual status of this agent in the treatment of heart failure.

Regulation of peptide-chain initiation in muscle during sepsis by interleukin-1 receptor antagonist

The mechanism by which interleukin-1 (IL-1) regulates protein synthesis in skeletal muscle during hypermetabolic sepsis in rats was investigated. Treatment of septic rats with a specific interleukin-1 receptor antagonist (IL-1ra) prevented the sepsis-induced inhibition of protein synthesis and translational efficiency in gastrocnemius. Analysis of ribosomal subunits revealed that the increase in free 40S and 60S ribosomal subunits observed in septic rats was prevented by infusion of IL-1ra, indicating peptide-chain initiation was maintained at control values. The failure of sepsis to inhibit peptide-chain initiation after infusion of IL-1ra correlated with a maintenance of the epsilon-subunit of eukaryotic initiation factor (eIF) 2B (eIF-2B epsilon) protein at control values. The alterations in the eIF-2B epsilon protein content in gastrocnemius of septic rats treated with or without IL-1ra were associated with corresponding changes in the abundance of eIF 2B epsilon mRNA. The results provide evidence that infusion of IL-1ra attenuates the sepsis-induced inhibition of protein synthesis by preventing the inhibition of peptide-chain initiation and downregulation of eIF-2B expression during sepsis.

Muscle wasting and dedifferentiation induced by oxidative stress in a murine model of cachexia is prevented by inhibitors of nitric oxide synthesis and antioxidants

Muscle wasting is a critical feature of patients afflicted by AIDS or cancer. In a murine model of muscle wasting, tumor necrosis factor alpha (TNF alpha) induces oxidative stress and nitric oxide synthase (NOS) in skeletal muscle, leading to decreased myosin creatinine phosphokinase (MCK) expression and binding activities. The impaired MCK-E box binding activities resulted from abnormal myogenin-Jun-D complexes, and were normalized by the addition of Jun-D, dithiothreitol or Ref-1, a nuclear redox protein. Treatment of skeletal muscle cells with a phorbol ester, a superoxide-generating system, an NO donor or a Jun-D antisense oligonucleotide decreased Jun-D activity and transcription from the MCK-E box, which were prevented by antioxidants, a scavenger of reducing equivalents, a NOS inhibitor and/or overexpression of Jun-D. The decreased body weight, muscle wasting and skeletal muscle molecular abnormalities of cachexia were prevented by treatment of TNF alpha mice with the antioxidants D-alpha-tocopherol of BW755c, or the NOS inhibitor nitro-L-arginine.

Effects of tumor necrosis factor alpha on skeletal muscle amino acid metabolism studied in-vivo

OBJECTIVE

The present study was performed to determine the chronology of the effects of a single 50 ug subcutaneous dose of TNF on food intake, weight gain, and skeletal muscle protein metabolism in normal rats. Earlier work demonstrated that a single subcutaneous dose of 50 ug of tumor necrosis factor alpha (TNF) significantly increased skeletal muscle protein synthesis and breakdown in the tumor bearing rat [1]. Some of the earlier work demonstrated that TNF can reduce food intake, weight gain and enhance muscle catabolism.

DESIGN

Twenty-five male Sprague Dawley rats were randomized assigned to treatment or saline arms of the study. Rates of in vivo incorporation of L-1-14C-leucine into skeletal muscle were measured by the flooding dose technique. Rats were studied 6 and 60 hours after TNF or saline.

RESULTS

Six hours after administration of the TNF, the total skeletal muscle amino acid concentration was significantly reduced by 20%. The greatest reductions were seen in lysine, arginine, and isoleucine (39-53%) followed by serine, tyrosine, ornithine, threonine and alanine (18-32%). Despite this drop in skeletal muscle amino acid concentrations, the rate of skeletal muscle protein synthesis was similar to the controls (12.2 +/- 4.1 vs 13.8 +/- 3.7 %/day, mean +/- sd, saline vs TNF treated, respectively). Dietary intake (8.2 +/- 0.5 vs 7.3 +/- 1.1 g/day) and weight gain (7.1 +/- 1.1 vs 9.1 +/- 3.8 g/day) were not affected by TNF administration. However, there was a significant increase in skeletal muscle protein synthesis rate in the TNF treated group after 60 hours (17.8 +/- 4.0 vs 12.2 +/- 4.1 %/day) but not after 6 hours (13.8 +/- 3.7 vs 13.7 +/- 3.3 %/day) compared to saline treated rats, respectively. TNF administration after 60 hours was not associated with an elevated skeletal muscle 3-methyl-histidine concentration or a reduced nitrogen balance.

CONCLUSION

These data suggest that at a 50 ug subcutaneous dose of TNF, an early (6 hours) effect is to reduce skeletal muscle of amino acids without effecting either synthesis or breakdown. A later effect (60 hours) is to normalize skeletal muscle amino acid concentration and to increase skeletal muscle protein synthesis. This suggests that TNF may acutely alter amino acid transport as one of its modes of action.

From laboratory to bedside: new strategies in the treatment of malnutrition in cancer patients

The objective of this review is to present and discuss the current and the possible future perspectives of artificial nutrition in preventing and treating cancer cachexia. English-language studies published in the last 25 years were retrieved using MEDLINE, bibliographies and consultation with experts. MEDLINE search terms included "cancer," "malnutrition," and "nutritional support." In vivo and in vitro controlled studies were selected, and data from each study were independently abstracted by the authors. Data obtained indicate that cancer cachexia is a common manifestation of advanced malignant disease, characterized by marasmus due to impaired nutrient metabolism, weight loss, and anemia. In patients, the presence of cachexia increases morbidity and mortality, delays or impedes the delivery of the adequate treatment, reduces the efficacy of anti-neoplastic therapy, and impairs patient's quality of life. Indirect evidence indicates that cancer cachexia is mediated by circulating cytokines, produced by the host in response to the presence of the malignancy. In the past two decades, nutritional support was used to counteract the detrimental effect of cancer cachexia on the host, but with limited success. More recently, the better understanding of the mechanisms of cancer cachexia and the identification of pharmacologic effects provided by specific nutrients, has formed the rationale for a "new" mode of nutrition therapy/nutritional support, adding pharmacotherapy to adjunctive initial care.

Cytokines and food intake: the relevance of the immune system to the student of ingestive behavior

The aims of this paper are to provide a selective review of the literature relating immune system mediators, especially cytokines, to the control of eating and to indicate why this literature is particularly relevant to the student of ingestive behavior. Four reasons are given. Firstly, many immune system mediators influence eating, providing excellent examples of neuroimmunological controls of behaviour. Secondly, the immune system appears to be involved in the profound eating pathology associated with several clinical conditions. Thirdly, cytokines affect both energy intake and energy expenditure. Fourthly, the anorexia typically associated with activation of the immune system provides an informative model for the analysis of gut-brain communication in the control of eating.

A serpin from human tumor cells with direct lymphoid immunomodulatory activity: mitogenic stimulation of human tumor-infiltrating lymphocytes

A serum-free supernatant from an epidermal carcinoma cell line has previously been shown to contain mitogenic activity for human tumor infiltrating lymphocytes in culture [1]. From this conditioned medium we have now purified to homogeneity, as determined by SDS-PAGE analysis, a ca. 45 kDa protein which stimulates [3H]thymidine incorporation into the DNA of these human T-lymphocytes. Amino acid composition data and immunoreactivity of the purified protein as well as sequence analyses of 7 tryptic fragments obtained therefrom suggest a strong similarity with human monocyte/neutrophil elastase inhibitor, which is a member of the serine protease inhibitor (serpin) superfamily. We have previously identified and purified from the same conditioned medium a 36 kDa protein with myeloid immunomodulatory activity [2]. Taken together, these two reports support the role of tumor-derived soluble factors in tumor immunosurveillance.

Soluble tumour necrosis factor receptors p55 and p75 in the urine monitor disease activity and the efficacy of treatment of inflammatory bowel disease

The aim of the study was to discover if soluble tumour necrosis factor receptors (sTNF-R p55 and p75) in the urine of patients with inflammatory bowel disease (IBD) could be used to monitor the different stages of the activity of the diseases. Twenty five patients with either Crohn's disease or ulcerative colitis were followed up during a longterm study. The 16 patients who become acutely ill with either Crohn's disease or ulcerative colitis had significantly higher concentrations of sTNF-R p55 and p75 in their urine compared with those who were in remission, or those who were normal controls. There was a significant correlation between increased concentrations (> 20 ng/ml) of both sTNF-R p55 and p75 in the urine and a high Crohn's disease activity index (CDAI) and colitis activity index (CAI). Therefore, determination of sTNF-R is a good non-invasive parameter that can be used to assess the activity of disease and the efficacy of treatment.

Neurotoxicity of advanced glycation endproducts during focal stroke and neuroprotective effects of aminoguanidine

Cerebral infarction (stroke) is a potentially disastrous complication of diabetes mellitus, principally because the extent of cortical loss is greater in diabetic patients than in nondiabetic patients. The etiology of this enhanced neurotoxicity is poorly understood. We hypothesized that advanced glycation endproducts (AGEs), which have previously been implicated in the development of other diabetic complications, might contribute to neurotoxicity and brain damage during ischemic stroke. Using a rat model of focal cerebral ischemia, we show that systemically administered AGE-modified bovine serum albumin (AGE-BSA) significantly increased cerebral infarct size. The neurotoxic effects of AGE-BSA administration were dose- and time-related and associated with a paradoxical increase in cerebral blood flow. Aminoguanidine, an inhibitor of AGE cross-linking, attenuated infarct volume in AGE-treated animals. We conclude that AGEs may contribute to the increased severity of stroke associated with diabetes and other conditions characterized by AGE accumulation.

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.

CNTF or (-)-deprenyl in immature rats: survival of axotomized facial motoneurons and weight loss

The application of ciliary neurotrophic factor (CNTF) to the cut ends of transected facial nerves in newborn rats has been reported to reduce the death of facial motoneurons (FMns) axotomized by the transection. Systemically delivered CNTF has been found to cause cachexia in adult mice. We compared the influence of dosage of CNTF and (-)-deprenyl on FMn death, weight loss, and animal survival in rat pups that underwent facial nerve transection at the 14th postnatal day (P14). CNTF was administered by osmotic mini-pumps connected to tubing ending either intrathecally or extrathecally near the craniocervical junction. CNTF caused weight loss and animal death that was similar to the cachexia reported in mice if administered in amounts of 1.1 microgram/day or greater. At the same doses, intrathecal CNTF was more effective than extrathecal CNTF in inducing the cachexia. (-)-Deprenyl did not alter animal survival or weight gain, even at high doses (10 mg/kg every 2 days). Intrathecal CNTF and intraperitoneal (-)-deprenyl, but not extrathecal CNTF, significantly increased the survival of the axotomized FMns. (-)-Deprenyl administered twice daily at 0.01 mg/kg was considerably more effective than CNTF in increasing FMn survival due to the limitation on CNTF dosage caused by the animal death.

Cytokine-mediated alterations in host metabolism prevent nutritional repletion in cachectic cancer patients

The clinical syndrome of cachexia is characterized by anorexia, continued losses of lean body mass, and altered carbohydrate and lipid metabolism. As early as the 1930s, this "chronic wasting" syndrome had been identified as the most frequent immediate cause of death in patients with cancer [Warren: Am J Med Sci 184:610-619, 1932]. At present, controversy remains as to the benefit of supplemental parenteral or enteral feedings in the nutritional repletion of cachectic cancer patients, since only selected patient groups have demonstrated clear benefit from their administration [Copeland et al.: Cancer 43:2108-2116, 1979; Copeland et al.: Cancer Res 37:2451-2456, 1977; Terepka and Waterhouse: Am J Med 20:225-238, 1956]. Despite having these advanced nutritional modalities firmly in our therapeutic armamentarium, the progression of cachexia in the nutritionally depleted cancer patient often continues unabated, and our ability to intervene successfully remains limited. This review proposes that host: tumor interactions lead to a nonspecific inflammatory response mediated in part by the chronic production and release of proinflammatory cytokines, including interleukin-1, tumor necrosis factor alpha, interleukin-6 and interferon-gamma, which antagonize the anabolic signals associated with enteral and parenteral nutrition support. Cytokine-mediated alterations can explain the inability of adequate dietary nitrogen and calories to result in lean tissue repletion. Based on this proposal, interrupting proinflammatory cytokine production or target organ action may be an appropriate therapeutic objective to improve nutrient utilization in patients with tumors.

Regional induction of tumor necrosis factor alpha expression in the mouse brain after systemic lipopolysaccharide administration

Tumor necrosis factor alpha (TNF-alpha) is a cytokine that is responsible, in part, for several aspects of the acute-phase response to inflammation, including the generation of fever. TNF-alpha has direct effects on central nervous system neurons deep within the hypothalamus that are involved in producing the febrile response, but the blood-brain barrier prevents circulating TNF-alpha from having access to these sites. We therefore have hypothesized that TNF-alpha may be produced in the brain and used as a mediator in the cerebral components of the acute-phase response. We used in situ hybridization to determine the distribution of production of TNF-alpha mRNA in the mouse brain after systemic administration of lipopolysaccharide. During the initial phase of fever, hybridization was observed in perivascular cells and neurons in circumventricular organs, including the vascular organ of the lamina terminalis, median eminence, and area postrema, as well as along the ventral surface of the medulla; hybridization was also prominent over many cell in the meninges. During the late phase of the response, hybridization was observed over neurons in the pericircumventricular nuclei such as the anteroventral periventricular and arcuate nuclei of the hypothalamus and the nucleus of the solitary tract. TNF-alpha produced by a cascade of neurons within the brain may participate in the complex autonomic, neuroendocrine, metabolic, and behavioral responses to infection and inflammation.

Tumor necrosis factor and cachexia: a current perspective

Anorexia, net proteolysis of skeletal muscle and consumption of body fat are hallmarks of the cachexia syndrome associated with chronic disease states. While inanition contributes to cachexia, this wasting diathesis has little in common with simple starvation. The cachexia syndrome is characterized by progressive weight loss and depletion of lean body mass in excess to that resulting from comparable caloric restriction. Accelerated mobilization and consumption of host protein stores from peripheral tissues occurs to support gluconeogenesis and acute phase protein synthesis [1, 2]. In contrast, simple starvation is associated with a relative sparing of lean tissue with the preferential consumption of fat. While the clinical manifestations of cachexia are readily apparent, identification of the specific mechanisms responsible for the development of cachexia remains an enigma. In recent years, interest has focused on the role that the immune system plays in the development of cachexia. Investigators initially hypothesized that the chronic production of two inflammatory cytokines, tumour necrosis factor alpha (TNF alpha) and/or interleukin-1 (IL-1), could explain the host non-specific responses resulting in cachexia [3-5]. Other pro-inflammatory cytokines, including interleukin-6 (IL-6) [6, 7] and interferon-gamma [8, 9], have been more recently proposed to be involved in this complex process. Although no consensus exists for the exclusive role of any one cytokine in the pathogenesis of cachexia, there is growing acceptance that the progression of cachexia results in part from the inappropriate release of one or more pro-inflammatory cytokines [10, 11]. In the present review, the current role of TNF alpha as a mediator of cachexia is examined.

Cytokines and metabolic dysfunction after severe head injury

Patients with head injury must overcome central as well as peripheral metabolic insults. In addition to specific tissue damage to the brain, a cellular biochemical cascade occurs that can negatively affect organ function, cause a systemic response to injury, and may cause secondary tissue injury. The metabolites involved in this cascade are numerous and complex. Cytokines are important cell-to-cell communication mediators during injury. It is speculated that cytokines, such as interleukin 1 (IL-1), interleukin 6 (IL-6), tumor necrosis factor (TNF), and interleukin 8 (IL-8), which are found in elevated amounts in both human and basic trials after head injury, play a role in the cellular cascade of injury. Some of the metabolic events produced by small doses of cytokine infusion in animals, as well as humans, include fever, neutrophilia, muscle breakdown, altered amino acid metabolism, depression of serum zinc levels, production of hepatic acute phase reactants, increased endothelial permeability, and expression of endothelial adhesion molecules. These are all known sequelae of severe head injury. Cytokines have also been implicated in organ failure. Infusion of cytokines in basic science trials revealed that organ functions of the gut, liver, and lung are negatively altered by high-dose cytokine infusion. Infusion of certain cytokines has been shown to cause death of brain cells, increase blood-brain barrier permeability, and cause cerebral edema. This suggests that cytokines may also play a role in the sequelae of organ demise. These effects of cytokines have been attenuated in basic trials by blocking the initial signaling system of cytokines or by decreasing serum cytokine activity. We hypothesize that cytokines that are elevated after head injury play a role in the pathology of injury, including altered metabolism and organ demise.

Control of established experimental allergic encephalomyelitis by inhibition of tumor necrosis factor (TNF) activity within the central nervous system using monoclonal antibodies and TNF receptor-immunoglobulin fusion proteins

Tumor necrosis factor (TNF) activity was inhibited during the development of actively-induced, chronic relapsing experimental allergic encephalomyelitis (CREAE) in Biozzi AB/H mice, using a mouse TNF-specific (TN3.19.12) antibody and bivalent human p55 and p75 TNF receptor-immunoglobulin (TNFR-Ig) fusion proteins. The development of disease could be inhibited when repeated doses of antibody were administered prior to the anticipated onset. It has now also been shown that a therapeutic effect is evident even when antibody is administered after the onset of clinical signs, further indicating an important role for TNF in pathogenic effector mechanisms in CREAE. Although biologically-active TNF was not detected in the circulation, TNF-alpha was detected in lesions within the central nervous system (CNS). This suggested that the CNS may be the main site for TNF-specific immunomodulation and was supported by the observation that intracranial injection was significantly more potent than that administered systemically, for both antibody and TNFR-Ig fusion proteins. The fusion proteins were as effective as antibody at doses 10-100-fold lower than that used for antibody, reflecting their higher neutralizing capacity in vitro. Although treatment was not curative and relapse inevitably occurred in this model if treatment was not sustained, the data indicate that anti-TNF immunotherapy, especially within the CNS, can inhibit CREAE and may, therefore, be useful in the control of human neuroimmunological diseases.

Nitrite/nitrate and cytokine levels in bronchoalveolar lavage fluid of lung cancer patients

BACKGROUND

Cytokines are produced by tumor cells in vitro, but evidence for in vivo increased production of cytokines in cancer patients is controversial. Conversely, nitric oxide (NO) is implicated increasingly in the mediation of cytokine effects. Lung cancer patients may show an increased local production of cytokines and NO, and chronic paracrine exposure of epithelial lung cells to these medicators may influence the production of surfactant phosphatidylcholine.

METHODS

The presence of the cytokine tumor necrosis factor (TNF alpha), interleukin-1 (IL-1), and interleukin-6 (IL-6), as well as NO, cyclic guanosine 3'5' monophosphate (cGMP) and phosphatidylcholine levels in bronchoalveolar lavage fluid (BLF) of lung cancer patients were investigated. Bronchoalveolar lavage fluid was obtained from 30 male smokers: 22 patients with squamous cell lung cancer and 8 subjects without cancer.

RESULTS

When compared with the control subjects, the cancer patients had elevated BLF levels of TNF alpha (1.58 +/- 0.47 vs. 0.04 +/- 0.02 pg/microgram protein, P < 0.001), IL-6 (1.39 +/- 0.29 vs. 0.04 +/- 0.02 pg/microgram protein, P < 0.001), and NO2-/NO3- (23.3 +/- 5.6 vs 1.1 +/- 0.6 nmol/mg protein, P < 0.001). However, phosphatidylcholine levels were lower in those with cancer than in the control subjects (3.0 +/- 1.2 vs. 24.8 +/- 6.4 micrograms protein, P < 0.001).

CONCLUSIONS

The results showed in vivo production of inflammatory cytokines in human lung cancer and increased tumor-associated NO production, as suggested by increased levels of nitrite/nitrate in the BLF. A decreased phosphatidylcholine content in the BLF also was found in patients with lung cancer.

The acute phase response: general aspects

The acute phase response in a given individual represents the integrated sum of multiple, separately regulated changes. Although many of these changes commonly occur together in affected individuals, clinical experience indicates that not all of them occur in all individuals, indicating that they must be individually regulated. For example, febrile patients may have normal blood levels of CRP and vice versa, leukocytosis does not always accompany other acute phase phenomena, and many instances of discordance between levels of the various acute phase proteins are seen. Cytokines function as part of a complex regulatory network, a signalling language in which information is conveyed to cells by combinations, and perhaps sequence, of intercellular messenger molecules. The effects of combinations of cytokines are complex. To use a somewhat crude simile, individual cytokines can be thought of as words which bear informational content and which may, on occasion, communicate a complete message. More commonly, however, the actual messages received by cells probably resemble sentences, in which combinations and sequences of words convey information. Currently available data suggest that hepatocytes receive a complex mixture of humoral or paracrine signals during the acute phase response. These are integrated by multiple interacting signal transducing mechanisms to cause finely regulated changes in plasma protein synthesis. Regulation largely occurs by transcriptional control, but post-transcriptional mechanisms, including translational regulation, may also participate. Both the extracellular and intracellular mechanisms that mediate the response of the hepatocyte to inflammatory stimuli appear to be highly complex and involve multiple overlapping, concurrent and parallel pathways. Enough is known at present to conclude that IL-6 is a major participant in these plasma protein changes. Regulation of non-hepatocyte acute phase phenomena has not been delineated as thoroughly, but clearly involves a number of inflammation-associated cytokines.

Tumor necrosis factor-alpha-induced inhibition of phosphatidylcholine synthesis by human type II pneumocytes is partially mediated by prostaglandins

TNF alpha seems to play an important role in the pathogenesis of adult respiratory distress syndrome. We studied the effect of TNF alpha on phospholipid synthesis by isolated type II pneumocytes and attempted to characterize the role of arachidonate metabolites and the influence of pentoxifylline on such an effect. Lung tissue obtained from both multiple organ donors (n = 14) and lung cancer patients (n = 11) was used for cell isolation. Surfactant synthesis was measured by the incorporation of D-[U-14C]glucose into phosphatidylcholine (PC). The basal PC synthesis was higher in the donor group than in the malignant group (3.44 +/- 0.19 vs 2.15 +/- 0.15 pmol/microgram protein x 120 min, P < 0.01), and, in the presence of 100 ng/ml of TNF alpha, the incorporation of labeled glucose into PC was reduced significantly in both donor (1.13 +/- 0.11 vs 3.44 +/- 0.19 pmol/microgram protein x 120 min, P < 0.01) and cancer (0.99 +/- 0.11 vs 2.15 +/- 0.15 pmol/microgram protein x 120 min, P < 0.01) groups. Indomethacin was able to completely block the cytokine-induced decrease in PC synthesis by pneumocytes from the malignant group and to attenuate the inhibitory effect of TNF alpha in those from donors, nordihydroguaiaretic acid having a similar effect. The TNF alpha effect can be blocked by pentoxifylline (100 micrograms/ml), a substance which can even succeed in reverting the basal secretory inhibition of cancer patients' pneumocytes to levels similar to those of the donor group. TNF alpha may contribute to the pathophysiology of adult respiratory distress syndrome by inhibiting the synthesis of surfactant. TNF alpha might be produced in lung tumors, resulting in chronic paracrine or systemic exposure of pneumocytes to low concentrations of the cytokine. The TNF alpha effect was not prevented completely by the blockage of the arachidonic acid metabolism, hence other mediators should also be implicated.

Early weight loss and high serum tumor necrosis factor-alpha levels in polyneuropathy, organomegaly, endocrinopathy, M protein, skin changes syndrome

We studied tumor necrosis factor-alpha (TNF-alpha) levels in serial serum samples from 3 consecutive patients who had a complete form of POEMS (polyneuropathy, organomegaly, endocrinopathy, M protein, skin changes) syndrome and early weight loss. Serum TNF-alpha levels were compared with those of 10 patients with multiple myeloma (5) or Waldenström's macroglobulinemia (5). Elevated serum levels of TNF-alpha were found in the patients with POEMS syndrome (two- to eightfold increase in 10 of 11 samples) and not in those with other malignant plasma cell dyscrasias. These results are in keeping with the hypothesis of a role for nonimmunoglobulinic mediators in the pathogenesis of the POEMS syndrome, and are consistent with previous reports of TNF-alpha overproduction in inflammatory demyelinating neuropathies and cachectic states.

Tumor necrosis factor: a pleiotropic cytokine and therapeutic target

Advances in the molecular biology of human diseases indicate that the most striking manifestations of illness may be caused not by exogenous pathogenic or tumor products, but rather by toxic peptides produced by the host itself. Tumor necrosis factor (TNF), a polypeptide cytokine produced during infection, injury, or invasion, has proved pivotal in triggering the lethal effects of septic shock syndrome, cachexia, and other systemic manifestations of disease. Because removing TNF from the diseased host may prevent development of the illness, this factor has recently been the focus of intensive research. This review discusses the biology of this cytokine, with particular emphasis on its potential therapeutic role in septic shock and cachexia.

The presence of tumour necrosis factor in CSF and plasma after severe head injury

In a cohort of victims of traumatic brain injury, 18 out of 50 patients had a plasma tumour necrosis factor (TNF) concentration above 2 pg/ml within 24 h of injury (mean 12.19, SD 45.96 pg/ml). Twenty-six had CSF samples available of which 17 demonstrated TNF concentrations above 1 pg/ml (mean 3.98, SD 3.61 pg/ml). We conclude that traumatized brain parenchyma is a significant source of TNF activity and implicate the cytokine in cellular metabolic derangements following head injury.

Synergy between tumor necrosis factor alpha and interleukin-1 in the induction of sickness behavior in mice

Like interleukin-1, recombinant human tumor necrosis factor alpha (TNF alpha) has been found to decrease social exploration and induce weight loss in mice in a dose and time-dependent manner. The present study was carried out to study the interaction between these two cytokines. Mice were injected IP with subthreshold doses of TNF alpha (2.5 micrograms/mouse) and IL-1 beta (50 ng/mouse). Social exploration was decreased 2 and 4 h after injection of TNF and IL-1, but body weight was not affected. Subthreshold doses of TNF alpha (90 ng/mouse) and IL-1 beta (100 pg/mouse) were also injected intracerebroventricularly (ICV). Social exploration was decreased 1.5 and 3 h after injections of the two cytokines and body weight was decreased for 6 h. To test the possibility of central induction of IL-1 by TNF alpha, mice pretreated with IL-1 receptor antagonist (IL-1ra, 1.8 micrograms/mouse, ICV) were injected with 90 ng TNF alpha. Pretreatment with IL-1ra antagonized the depressive effect of TNF alpha on behavior, but had no effect on weight loss induced by this cytokine. These results suggest that TNF alpha-induced behavioral alterations are mediated by endogenously released IL-1, whereas metabolic changes are dependent on the release of other cytokines.

Differential elevation of circulating interleukin-1 beta, tumor necrosis factor alpha, and interleukin-6 in AIDS-associated cachectic states

Elevation of serum interleukin-1 beta (IL-1 beta) levels, and to a lesser degree tumor necrosis factor alpha levels, was found in cachectic human immunodeficiency virus (HIV)-infected African patients without concurrent opportunistic infection or neoplasia (HIV wasting syndrome). A heterogeneous pattern of elevations of cytokine levels, including mild elevations of IL-1 beta and pronounced elevations of IL-6 levels, was found in other cachectic states.

The role of cytokines in the pathophysiology of chronic liver diseases

Many of the biological activities of cytokines are similar to clinical manifestations and abnormalities of laboratory parameters observed in chronic liver diseases (CLD). Evidence of impaired cytokine synthesis in CLD comes from studies of serum or plasma levels, supernatants of peripheral blood mononuclear cells stimulated with various agents and from studying cytokine expression locally in the liver. Circulating levels of several cytokine-regulated molecules such as neopterin, soluble IL-2 receptor, adhesion molecules, and metabolites of the nitric oxide pathway are elevated in patients with CLD. Thus inhibition of cytokine synthesis or modulation of their activity could provide not only important information about their pathophysiologic relevance but also have a profound impact on disease progression in CLD. These studies will also show whether prolonged anti-cytokine treatment with interleukin-1- or tumor necrosis factor-inhibitors interferes with host defense mechanism.

Distribution and characterization of tumor necrosis factor-alpha-like immunoreactivity in the murine central nervous system

Tumor necrosis factor-alpha (TNF alpha) is a protein released from macrophages during infection and inflammation. Recent studies suggest that it has several effects within the central nervous system, including generation of fever, enhancement of slow wave sleep, and stimulation of pituitary hormone secretion. We have proposed that TNF alpha may be synthesized by neurons in the CNS and used as a neuromodulator in the pathways involved in the central control of these activities. To test this hypothesis, we have used an antiserum raised against recombinant murine (rm) TNF alpha with an indirect immunoperoxidase technique to stain the murine CNS immunohistochemically. Western blot analysis of mouse brain homogenates revealed one band with electrophoretic mobility identical to that of rmTNF alpha. We identified TNF alpha-like immunoreactive (ir) neurons in the hypothalamus, in the bed nucleus of the stria terminalis, in the caudal raphe nuclei, and along the ventral pontine and medullary surface. TNF alpha ir innervation was widespread within the CNS, particularly in areas involved in autonomic and endocrine regulation, including the hypothalamus, amygdala, bed nucleus of the stria terminalis, parabrachial nucleus, dorsal vagal complex, nucleus ambiguus, and thoracic sympathetic preganglionic cell column. Our data suggest that TNF alpha may serve as a neuromodulator in central pathways involved in the regulation of the autonomic, endocrine and behavioral components of the acute-phase response to inflammation and infection.

Murine tumor necrosis factor alpha is transported from blood to brain in the mouse

The cytokines are important components of the brain-immune axis. Recent work has shown that [125I]IL-1 alpha and [125I]IL-1 beta are transported from the blood into the brain by a saturable system. Here we show that murine tumor necrosis factor alpha (mTNF alpha) labeled with 125I (I-mTNF alpha) crosses the blood-brain barrier (BBB) after i.v. injection by a transport system different from that for the interleukins. Self inhibition with mTNF alpha showed that this transport system was saturable, and lack of inhibition by IL-1 alpha, IL-1 beta, IL-6, or MIP-1 alpha showed selectivity of the system. High performance liquid chromatography (HPLC) of the radioactivity recovered from brain and from cerebrospinal fluid after the i.v. injection of I-mTNF alpha showed that the cytokine crossed the BBB largely in intact form. Capillary depletion showed that the accumulation of I-mTNF alpha in the cerebral cortex was due to passage across the BBB rather than to sequestration by capillaries. Transport rate was not changed by acute treatment with the neurotoxin aluminium or by acute and chronic treatment with the cationic chelator deferoxamine, but it was more than three times faster in neonatal rats. Efflux of I-mTNF alpha from the brain was slower than would have been predicted based on reabsorption of cerebrospinal fluid, suggesting that TNF alpha is sequestered by the brain. The BBB was not disrupted by up to 50 micrograms kg-1 of mTNF alpha i.v. in either adult mice or neonatal rats as assessed by the BBB's impermeability to radioactively labeled albumin.(ABSTRACT TRUNCATED AT 250 WORDS)

Interleukin-4 down-regulates adult human astrocyte DNA synthesis and proliferation

The T lymphocyte-derived cytokine, interleukin-4 (IL-4), was found to inhibit dose dependently basal DNA synthesis of cultured non-neoplastic human astrocytes isolated from epilepsy white matter tissue. The mitogenic effect of tumor necrosis factor on astrocytes was also inhibited by IL-4, and the inhibitory effect was abrogated by anti-IL-4 antibody but not by irrelevant IgG. Immunofluorescent analysis indicated significantly reduced numbers of glial fibrillary acidic protein-positive astrocytes incorporating nuclear bromodeoxyuridine in IL-4-treated cultures compared to control. These findings indicate that human adult astrocyte proliferation, in contrast to that reported for endothelial cells or fibroblasts, is sensitive to down-regulation by IL-4.

Expression of tumor necrosis factor by different tumor cell lines results either in tumor suppression or augmented metastasis

Tumor necrosis factor (TNF) produced by tumor cells after gene transfer can effectively suppress the growth of locally growing tumors. We wanted to test the effects of "local" TNF on the growth of a highly metastatic cell line. Therefore, a recombinant retrovirus allowing expression of the TNF gene by the beta-actin promotor has been constructed and used to infect the two tumor cell lines EB and ESB, which grow as solid tumor or metastasize, respectively. Expression of TNF by EB cells resulted in their rapid and dose-dependent rejection. In sharp contrast, mice injected with ESB cells producing similar amounts of TNF showed no signs of tumor suppression, but rather had reduced survival rates that correlated with enhanced hepatic metastases. The accelerated formation of liver metastases by ESB TNF cells could be reversed by an anti-TNF mAb. These results demonstrate the opposite effects TNF may have on tumor growth: suppression of a locally growing tumor and promotion of metastasis formation.

T cell responses to myelin basic protein in experimental autoimmune encephalomyelitis-resistant BALB/c mice

In strains of mice that are susceptible to experimental autoimmune encephalomyelitis (EAE), cloned CD4+ T cells reactive with autologous myelin basic protein (MBP) have been shown to cause disease when transferred to naive syngeneic recipients. Recent reports indicate that under particular experimental conditions, 'resistant' strains of mice can also develop EAE, although cloned cells have not been isolated and characterized. An analysis of the characteristics of a panel of MBP-specific T cells and the antigen presenting capability of CNS-derived cells obtained from the resistant strain BALB/c is presented here. The data demonstrate that immunization of EAE-resistant BALB/c mice results in the activation of a heterogeneous group of T cells reactive with autologous MBP. Both peripheral antigen presenting cells, as well as microglia isolated from brains of BALB/c mice, are capable of stimulating these cloned MBP-specific T cells to proliferate. When optimally activated in vitro and then injected in vivo into syngeneic BALB/c recipients, three clones studied induced severe cachexia, resulting in loss of up to 35% of body weight before death. Two of the clones also induced clinical and histological EAE, while the third induced only occasional histological evidence of disease. Differences in epitope recognition, T cell receptor usage, cytokine profiles or regulatory mechanisms of self tolerance, may play important roles in preventing potentially destructive autoimmune reactions by these T cells capable of recognizing autologous myelin in the central nervous system.

Intracerebral cytokine messenger RNA expression in acquired immunodeficiency syndrome dementia

The pathogenesis of the dementia associated with human immunodeficiency virus (HIV) infection is unclear, but has been postulated to be due to indirect effects of HIV infection including the local production of cytokines. To determine which cytokines are produced in the nervous system and to identify any correlations with dementia, cytokine and HIV messenger RNA expression was analyzed by reverse transcriptase-polymerase chain reaction in the brains from 24 HIV-infected patients with and without dementia and 9 HIV-uninfected control subjects. Levels of tumor necrosis factor-alpha messenger RNA were significantly higher and levels of interleukin (IL)-4 messenger RNA were significantly lower in demented compared to nondemented HIV-infected patients. Demented patients also had lower IL-1 beta levels than did nondemented patients. No significant differences were detected in the amounts of leukemia inhibitory factor, IL-6, transforming growth factor-beta 1 and -beta 2, monokine induced by gamma interferon-2 (MIG-2), or interferon-gamma messenger RNAs. IL-10 and IL-2 messenger RNAs were undetectable in all brains examined. Cytokine messenger RNA levels in nondemented HIV-positive patients were similar to those in HIV-negative control subjects. HIV transcripts were more abundant in subcortical white matter than in the basal ganglia, cortex, or deep white matter. Our findings suggest a possible role for tumor necrosis factor-alpha in the development of neurological dysfunction. Increased levels of tumor necrosis factor-alpha messenger RNA were not associated with increased levels of IL-1 beta messenger RNA, suggesting differential regulation of these monokines in acquired immunodeficiency syndrome dementia.(ABSTRACT TRUNCATED AT 250 WORDS)

Evidence for a direct central anorectic effect of tumor-necrosis-factor-alpha in the rat

This study was designed to investigate the effect of tumor necrosis factor-alpha (TNF) on the control of food intake in rat. The specific aims were: a) to evaluate the effects of central (ICV) or peripheral (IP) microdoses of TNF on food intake; b) to show that the TNF-induced anorexia results from a direct action of the mediator on the central nervous system; c) to demonstrate that the anorexic activity of TNF is not due to nonspecific malaise. In the first experiment, ICV administration (0.5-4.0 micrograms) of recombinant-murine tumor necrosis factor-alpha (rmTNF) significantly reduced food intake in a dose-dependent manner. The maximal effect (-66%) was observed 5 h after a 4.0 micrograms dose. In contrast, rm TNF did not affect feeding behavior when injected IP, indicating that the anorexic activity was centrally mediated. The estimated DE50 was 2.0 micrograms/rat by the ICV route. In the second experiment, the place conditioning paradigm was used to show that TNF administered ICV at 2.0 micrograms/rat did not induce aversive or deleterious effects as compared to naltrexone given IP at the equi-anorectic dose 5.0 mg/kg. It was concluded that TNF reduces food intake in rats by a direct action on the central nervous system.

Adipose expression of tumor necrosis factor-alpha: direct role in obesity-linked insulin resistance

Tumor necrosis factor-alpha (TNF-alpha) has been shown to have certain catabolic effects on fat cells and whole animals. An induction of TNF-alpha messenger RNA expression was observed in adipose tissue from four different rodent models of obesity and diabetes. TNF-alpha protein was also elevated locally and systemically. Neutralization of TNF-alpha in obese fa/fa rats caused a significant increase in the peripheral uptake of glucose in response to insulin. These results indicate a role for TNF-alpha in obesity and particularly in the insulin resistance and diabetes that often accompany obesity.

Nutritional, hepatic, and metabolic effects of cachectin/tumor necrosis factor in rats receiving total parenteral nutrition

BACKGROUND

In orally fed animals, infusion of cachectin/tumor necrosis factor (TNF) caused weight loss and muscular wasting, accompanied by anorexia. Despite muscle wasting, there were gains in weight and protein and DNA contents of the viscera, but no significant metabolic abnormalities.

METHODS

To observe the effect of cachectin/TNF on the nutritional-metabolic status, and without the confounding effect of anorexia, cachectin/TNF was infused into rats receiving total parenteral nutrition in sufficient amounts to induce weight gain in controls at the same rate as in orally fed rats.

RESULTS

TPN prevented loss of body weight, but cachectin-treated animals had reduced nitrogen retention and carcass weight. By contrast, there were gains in visceral protein levels, which in the liver was due to a marked proliferation of biliary epithelium. In addition, cachectin-treated animals receiving TPN developed hyperglycemia, hyperosmolality, diuresis, and dehydration. They also had azotemia and cholestasis.

CONCLUSIONS

In the absence of the effects of anorexia, cachectin reduced nitrogen retention and caused metabolic and multisystem dysfunction, comparable with the effects of clinical sepsis.

Tumor necrosis factor activities and cancer therapy--a perspective

Tumor necrosis factor (TNF) is a multifunctional cytokine which has excited and fascinated numerous investigators and commercial entities due to its promise as a therapeutic agent against cancer and as a target for drugs treating septic shock. TNF is a protein having cytotoxic, cytostatic, immunomodulatory as well as several other activities and is also involved in septic shock. This review covers the structure of TNF and its receptors, various in vitro activities and in vivo activities based on studies in animal model systems. The role of TNF as an anticancer therapeutic agent, based on various phase I and phase II clinical studies, has also been considered. The review concludes with several considerations for increasing the therapeutic utility of TNF in terms of targeting, toxicity and half-life.

Chronic intraperitoneal infusion of low doses of tumor necrosis factor alpha in rats induces a reduction in plasma triglyceride levels

Single and repeated bolus injections of tumor necrosis factor alpha (TNF) in laboratory animals have been reported to result in hypertriglyceridaemia, suggesting that TNF is a mediator of hypertriglyceridaemia occurring during infection. However, as during infection production of TNF is probably chronically elevated, we determined the effects of continuous infusion of low doses of TNF on plasma levels of triglycerides and cholesterol. Male rats, bearing a venous catheter to allow repeated blood sampling, were intraperitoneally equipped with osmotic minipumps which continuously delivered TNF or saline for 7 days. Infusion of rats with doses of TNF as low as 4.0 and 8.0 micrograms/24 h resulted in significant decreases in plasma levels of triglycerides as compared with those after saline infusion. Although plasma triglyceride concentrations were persistently lower in TNF than in saline animals throughout the study period, the differences were most prominent during the first days and reached statistical significance at day 1, 3, 4 and 5 and of the 4.0 micrograms experiment and on day 1, 2 and 3 of the 8.0 micrograms experiment. This suppression of plasma triglyceride concentrations was not accompanied by changes in plasma cholesterol levels. No effects of chronic TNF treatment on food intake, body weight change and rectal temperature of the animals were observed. These findings indicate that chronic infusion of low doses of TNF induces hypotriglyceridaemia in rats. The role of TNF as a factor in mediating hypertriglyceridaemia during infectious diseases needs to be reconsidered.

The role of cytokines in cancer cachexia

There is, at present, considerable interest in the possible role for the proinflammatory cytokines, tumor necrosis factor-alpha, interleukin-1, interleukin-6, and interferon-gamma in the pathogenesis of cancer cachexia. Indirect evidence for such a role is based on the observation that chronic administration of many of these cytokines, either alone or in combination, can reproduce the myriad of host responses seen in experimental and human cancer cachexia. Elevated plasma levels of tumor necrosis factor-alpha, interleukin-2, and interferon-gamma have rarely been detected in patients or experimental animals with cancer, although interleukin-6 levels appear to correlate with tumor progression in animal models. The strongest evidence for a causal role for cytokines has come from rodent studies in which tumor-bearing animals have been passively immunized with antibodies directed against individual cytokines. Several groups have shown modest but significant improvements in food intake and lean tissue retention with antibodies directed against tumor necrosis factor-alpha, interleukin-1, interleukin-6, and interferon-gamma. However, there has been no consistent finding that one cytokine is universally involved in cancer cachexia in histologically distinct tumor models. One ominous finding in several tumor models has been that the endogenous production of cytokines appears to support tumor growth. Such findings raise the intriguing possibility that these cytokines, although contributors to tissue wasting and anorexia, may also serve the tumor as either direct or indirect cell growth factors.(ABSTRACT TRUNCATED AT 250 WORDS)

The early cancer anorexia paradigm: changes in plasma free tryptophan and feeding indexes

Tumor growth is accompanied by an anorexia mediated by humoral factors that appear to influence appetitive mechanisms in the brain. Because tumor resection is followed by resumption of normal food intake, the circulating anorexigenic substance(s) are produced either by the neoplastic tissue or by the host in response to the tumor. Increased levels of plasma free tryptophan and plasma ammonia have been proposed to mediate cancer anorexia. With animal models, it is often difficult to ascertain whether changes in food intake depend upon metabolic changes or the progressively increasing tumor mass per se. The feeding patterns and biochemical changes that occur during tumor growth were evaluated in 96 male Fischer rats that were inoculated with 10(6) methylcholanthrene sarcoma cells or saline (controls). Rats were placed into metabolic cages equipped with an Automated Computerized Rat Eater Meter to continuously determine meal size and meal number. Plasma free tryptophan and ammonia were evaluated 6, 10, 16, 18, 22, and 26 days after tumor inoculation. Anorexia developed by day 17-18, when food intake started to decrease via a decrease in meal size but not meal number and reached 60% of control by day 26. However, long before anorexia developed, free tryptophan was significantly higher 6 days after tumor inoculation, and the greatest increase occurred after 18 days. Ammonia did not differ from control at any time. Data confirm tumor-associated increases in plasma free tryptophan that occurred before the manifestation of anorexia and support a possible role of brain serotonin in cancer anorexia.