Refractory hypothalamic alpha-mSH satiety and AGRP feeding systems in rats bearing MCA sarcomas

Cancer-induced anorexia and malaise are mediated by CGRP neurons in the parabrachial nucleus

Anorexia is a common manifestation of chronic diseases, including cancer. Here we investigate the contribution to cancer anorexia made by calcitonin gene-related peptide (CGRP) neurons in the parabrachial nucleus (PBN) that transmit anorexic signals. We show that CGRP^PBN neurons are activated in mice implanted with Lewis lung carcinoma cells. Inactivation of CGRP^PBN neurons before tumor implantation prevents anorexia and loss of lean mass, and their inhibition after symptom onset reverses anorexia. CGRP^PBN neurons are also activated in Apc^min/+ mice, which develop intestinal cancer and lose weight despite the absence of reduced food intake. Inactivation of CGRP^PBN neurons in Apc^min/+ mice permits hyperphagia that counteracts weight loss, revealing a role for these neurons in a 'nonanorexic' cancer model. We also demonstrate that inactivation of CGRP^PBN neurons prevents lethargy, anxiety and malaise associated with cancer. These findings establish CGRP^PBN neurons as key mediators of cancer-induced appetite suppression and associated behavioral changes.

The Melanocortin Receptor System: A Target for Multiple Degenerative Diseases

The melanocortin receptor system consists of five closely related G-protein coupled receptors (MC1R, MC2R, MC3R, MC4R and MC5R). These receptors are involved in many of the key biological functions for multicellular animals, including human beings. The natural agonist ligands for these receptors are derived by processing of a primordial animal gene product, proopiomelanocortin (POMC). The ligand for the MC2R is ACTH (Adrenal Corticotropic Hormone), a larger processed peptide from POMC. The natural ligands for the other 4 melanocortin receptors are smaller peptides including α-melanocyte stimulating hormone (α-MSH) and related peptides from POMC (β-MSH and γ-MSH). They all contain the sequence His-Phe-Arg-Trp that is conserved throughout evolution. Thus, there has been considerable difficulty in developing highly selective ligands for the MC1R, MC3R, MC4R and MC5R. In this brief review, we discuss the various approaches that have been taken to design agonist and antagonist analogues and derivatives of the POMC peptides that are selective for the MC1R, MC3R, MC4R and MC5R receptors, via peptide, nonpeptide and peptidomimetic derivatives and analogues and their differential interactions with receptors that may help account for these selectivities.

Pathophysiology of anorexia in the cancer cachexia syndrome

Anorexia is commonly present in persons with cancer and a major component of cancer cachexia. There are multiple causes of anorexia in cancer. Peripherally, these can be due to (i) substances released from or by the tumour, e.g. pro-inflammatory cytokines, lactate, and parathormone-related peptide; (ii) tumours causing dysphagia or altering gut function; (iii) tumours altering nutrients, e.g. zinc deficiency; (iv) tumours causing hypoxia; (v) increased peripheral tryptophan leading to increased central serotonin; or (vi) alterations of release of peripheral hormones that alter feeding, e.g. peptide tyrosine tyrosine and ghrelin. Central effects include depression and pain, decreasing the desire to eat. Within the central nervous system, tumours create multiple alterations in neurotransmitters, neuropeptides, and prostaglandins that modulate feeding. Many of these neurotransmitters appear to produce their anorectic effects through the adenosine monophosphate kinase/methylmalonyl coenzyme A/fatty acid system in the hypothalamus. Dynamin is a guanosine triphosphatase that is responsible for internalization of melanocortin 4 receptors and prostaglandin receptors. Dynamin is up-regulated in a mouse model of cancer anorexia. A number of drugs, e.g. megestrol acetate, cannabinoids, and ghrelin agonists, have been shown to have some ability to be orexigenic in cancer patients.

Pre-treatment effects of peripheral tumors on brain and behavior: neuroinflammatory mechanisms in humans and rodents

Cancer patients suffer high levels of affective and cognitive disturbances, which have been attributed to diagnosis-related distress, impairment of quality of life, and side effects of primary treatment. An inflammatory microenvironment is also a feature of the vast majority of solid tumors. However, the ability of tumor-associated biological processes to affect the central nervous system (CNS) has only recently been explored in the context of symptoms of depression and cognitive disturbances. In this review, we summarize the burgeoning evidence from rodent cancer models that solid tumors alter neurobiological pathways and subsequent behavioral processes with relevance to affective and cognitive disturbances reported in human cancer populations. We consider, in parallel, the evidence from human clinical cancer research demonstrating that affective and cognitive disturbances are common in some malignancies prior to diagnosis and treatment. We further consider the underlying neurobiological pathways, including altered neuroinflammation, tryptophan metabolism, prostaglandin synthesis and associated neuroanatomical changes, that are most strongly implicated in the rodent literature and supported by analogous evidence from human cancer populations. We focus on the implications of these findings for behavioral researchers and clinicians, with particular emphasis on methodological issues and areas of future research.

Hormonal, hypothalamic and striatal responses to reduced body weight gain are attenuated in anorectic rats bearing small tumors

Lack of compensatory or even reduced food intake is frequently observed in weight-losing cancer patients and contributes to increased morbidity and mortality. Our previous work has shown increased transcription factor expression in the hypothalamus and ventral striatum of anorectic rats bearing small tumors. mRNA expression of molecules known to be involved in pathways regulating appetite in these structures was therefore assessed in this study. Given that pain, pro-inflammatory cytokines and metabolic hormones can modify food intake, spinal cord cellular activation patterns and plasma concentrations of cytokines and hormones were also studied. Morris hepatoma 7777 cells injected subcutaneously in Buffalo rats provoked a 10% lower body weight and 15% reduction in food intake compared to free-feeding tumor-free animals 4 weeks later when the tumor represented 1-2% of body mass. No differences in spinal cord activation patterns or plasma concentration of pro-inflammatory cytokines were observed between groups. However, the changes in plasma ghrelin and leptin concentrations found in food-restricted weight-matched rats in comparison to ad libitum-fed animals did not occur in anorectic tumor-bearing animals. Real-time PCR showed that tumor-bearing rats did not display the increase in hypothalamic agouti-related peptide mRNA observed in food-restricted weight-matched animals. In addition, microarray analysis and real-time PCR revealed increased ventral striatal prostaglandin D synthase expression in food-restricted animals compared to anorectic tumor-bearing rats. These findings indicate that blunted hypothalamic AgRP mRNA expression, probably as a consequence of relatively high leptin and low ghrelin concentrations, and reduced ventral striatal prostaglandin D synthesis play a role in maintaining cancer-associated anorexia.

Effect of feeding status on adjuvant arthritis severity, cachexia, and insulin sensitivity in male Lewis rats

We studied the effect of food restriction, overfeeding, and normofeeding on cachexia, inflammatory and metabolic parameters, and insulin sensitivity in chronic adjuvant arthritis (AA) in rats. Food restriction during AA increased circulating ghrelin, corticosterone, decreased leptin, and ameliorated arthrogram score and systemic inflammation compared to normofeeding. Overfeeding worsened arthrogram score and systemic inflammation, and led to lipid accumulation in the liver, but not to alterations of adipokine and ghrelin plasma levels relative to normofeeding. Independently of feeding status, AA induced cachexia, in which modulation of mRNA expressions for appetite-regulating neuropeptides (NPY, AgRP, POMC, CART) in the arcuate nucleus (ARC) does not play a primary role. The overexpression of IL-1β mRNA in the ARC suggests its role in the mechanisms of impaired energy balance during AA under all feeding conditions. Normal HOMA index in all arthritic groups does not indicate the development of insulin resistance by feeding interventions in these rats.

Alteration of NPY and Y1 receptor in dorsomedial and ventromedial areas of hypothalamus in anorectic tumor-bearing rats

Although previous studies have implicated NPY in the etiology of experimental cancer anorexia, the results have been difficult to interpret. Studies have suggested that although NPY level and message were decreased in the dorsomedial hypothalamic area (DMA), they were elevated in the ventromedial hypothalamic area (VMA). To better assess specific intra-area alterations of NPY, Y(1) receptor (Y(1) R), and agouti-related peptide (AgRP) in TB rats, we used radioimmunoassay, quantitative real-time RT-PCR, and immunohistochemistry. We found that NPY and AgRP mRNA were elevated significantly in whole hypothalamus of anorectic TB rats, while Y(1) R mRNA was decreased. Based on two replicates of four pooled samples each, both NPY and AgRP mRNA appeared to be elevated in the VMA of anorectic TB rats, while only AgRP exhibited a similar increase in the DMA. Levels of NPY were elevated in the VMA of both TB and pair-fed (PF) rats, but in the DMA only PF rats exhibited a significant NPY increase. NPY and Y(1) R immunohistochemistry revealed reduced NPY staining in PVN and ARC nucleus of TB and PF rats. Y(1) R immunostaining was also reduced in the ARC and PVN of TB rats, while PF rats exhibited elevated immunostaining in the PVN. These results continue to implicate dysfunction of NPY feeding systems in experimental cancer anorexia and suggest down-regulation of Y(1) R receptors as well as possible problems in NPY translation.

Antimyopathic effects of carnitine and nicotine

PURPOSE OF REVIEW

The clinical course of most chronic diseases is associated with declined energy intake and nutrient-resistant progressive myopathy, characterized by accelerated proteolysis and impaired function. This anorexia/cachexia syndrome leads to deterioration of quality of life, and increased morbidity and mortality. The clinical efficacy of currently available therapeutic strategies is limited and more effective treatments are needed.

RECENT FINDINGS

Chronic systemic inflammation, triggered and sustained by cytokines, and increased oxidative stress contribute to the pathogenesis of the anorexia/cachexia syndrome. Carnitine and nicotine have recently been tested as immunomodulating and antioxidant agents. In particular, carnitine supplementation has been shown to reduce chronic inflammation and oxidative stress in hemodialysis patients and, in cancer patients, yielding to reduced fatigue and improved outcome. Nicotine is able to induce the anti-inflammatory activity of the vagus nerve. In animal models of sepsis and cancer, the nicotine-induced supplementation resulted in better protection of nutritional status and improved survival.

SUMMARY

In the continuous effort to develop more efficacious strategies against the anorexia/cachexia syndrome, carnitine and nicotine may represent a further therapeutic tool. More clinical studies are needed, however, before their use can be routinely suggested.

Adipokines that link obesity and diabetes to the hypothalamus

Adipose tissue plays a crucial role in energy homeostasis not only in storing triglyceride, but also responding to nutrient, neural, and hormonal signals, and producing factors which control feeding, thermogenesis, immune and neuroendocrine function, and glucose and lipid metabolism. Adipose tissue secretes leptin, steroid hormones, adiponectin, inflammatory cytokines, resistin, complement factors, and vasoactive peptides. The endocrine function of adipose tissue is typified by leptin. An increase in leptin signals satiety to neuronal targets in the hypothalamus. Leptin activates Janus-activating kinase2 (Jak2) and STAT 3, resulting in stimulation of anorexigenic peptides, e.g., alpha-MSH and CART, and inhibition of orexigenic peptides, e.g., NPY and AGRP. The reduction in leptin levels during fasting stimulates appetite, decreases thermogenesis, thyroid and reproductive hormones, and increases glucocorticoids. Leptin also stimulates fatty acid oxidation, insulin release, and peripheral insulin action. These effects involve regulation of PI-3 kinase, PTP-1B, suppressor of cytokine signaling-3 (SOCS-3), and AMP-activated protein kinase in the brain and peripheral organs. There is emerging evidence that leptin, adiponectin, and resistin act through overlapping pathways. Understanding the signal transduction of adipocyte hormones will provide novel insights on the pathogenesis and treatment of obesity, diabetes, and various metabolic disorders.

Hypothalamic integration of immune function and metabolism

The immune and neuroendocrine systems are closely involved in the regulation of metabolism at peripheral and central hypothalamic levels. In both physiological (meals) and pathological (infections, traumas and tumors) conditions immune cells are activated responding with the release of cytokines and other immune mediators (afferent signals). In the hypothalamus (central integration), cytokines influence metabolism by acting on nucleus involved in feeding and homeostasis regulation leading to the acute phase response (efferent signals) aimed to maintain the body integrity. Peripheral administration of cytokines, inoculation of tumor and induction of infection alter, by means of cytokine action, the normal pattern of food intake affecting meal size and meal number suggesting that cytokines acted differentially on specific hypothalamic neurons. The effect of cytokines-related cancer anorexia is also exerted peripherally. Increase plasma concentrations of insulin and free tryptophan and decrease gastric emptying and d-xylose absorption. In addition, in obesity an increase in interleukin (IL)-1 and IL-6 occurs in mesenteric fat tissue, which together with an increase in corticosterone, is associated with hyperglycemia, dyslipidemias and insulin resistance of obesity-related metabolic syndrome. These changes in circulating nutrients and hormones are sensed by hypothalamic neurons that influence food intake and metabolism. In anorectic tumor-bearing rats, we detected upregulation of IL-1beta and IL-1 receptor mRNA levels in the hypothalamus, a negative correlation between IL-1 concentration in cerebro-spinal fluid and food intake and high levels of hypothalamic serotonin, and these differences disappeared after tumor removal. Moreover, there is an interaction between serotonin and IL-1 in the development of cancer anorexia as well as an increase in hypothalamic dopamine and serotonin production. Immunohistochemical studies have shown a decrease in neuropeptide Y (NPY) and dopamine (DA) and an increase in serotonin concentration in tumor-bearing rats, in first- and second-order hypothalamic nuclei, while tumor resection reverted these changes and normalized food intake, suggesting negative regulation of NPY and DA systems by cytokines during anorexia, probably mediated by serotonin that appears to play a pivotal role in the regulation of food intake in cancer. Among the different forms of therapy, nutritional manipulation of diet in tumor-bearing state has been investigated. Supplementation of tumor bearing rats with omega-3 fatty acid vs. control diet delayed the appearance of tumor, reduced tumor-growth rate and volume, negated onset of anorexia, increased body weight, decreased cytokines production and increased expression of NPY and decreased alpha-melanocyte-stimulating hormone (alpha-MSH) in hypothalamic nuclei. These data suggest that omega-3 fatty acid suppressed pro-inflammatory cytokines production and improved food intake by normalizing hypothalamic food intake-related peptides and point to the possibility of a therapeutic use of these fatty acids. The sum of these data support the concept that immune cell-derived cytokines are closely related with the regulation of metabolism and have both central and peripheral actions, inducing anorexia via hypothalamic anorectic factors, including serotonin and dopamine, and inhibiting NPY leading to a reduction in food intake and body weight, emphasizing the interconnection of the immune and neuroendocrine systems in regulating metabolism during infectious process, cachexia and obesity.

Effects of peptides, with emphasis on feeding, pain, and behavior A 5-year (1999-2003) review of publications in Peptides

Novel effects of naturally occurring peptides are continuing to be discovered, and their mechanisms of actions as well as interactions with other substances, organs, and systems have been elucidated. Synthetic analogs may have actions similar or antagonistic to the endogenous peptides, and both the native peptides and analogs have potential as drugs or drug targets. The journal Peptides publishes many leading articles on the structure-activity relationship of peptides as well as outstanding reviews on some families of peptides. Complementary to the reviews, here we extract information from the original papers published during the past five years in Peptides (1999-2003) to summarize the effects of different classes of peptides, their modulation by other chemicals and various pathophysiological states, and the mechanisms by which the effects are exerted. Special attention is given to peptides related to feeding, pain, and other behaviors. By presenting in condensed form the effects of peptides which are essential for systems biology, we hope that this summary of existing knowledge will encourage additional novel research to be presented in Peptides.