Identification of rat brainstem neuronal structures activated during cancer-induced anorexia

Dynamics of cachexia-associated inflammatory changes in the brain accompanying intra-abdominal fibrosarcoma growth in Wistar rats

Accumulated data indicate that inflammation affecting brain structures participates in the development of cancer-related cachexia. However, the mechanisms responsible for the induction and progression of cancer-related neuroinflammation are still not fully understood. Therefore, we studied the time-course of neuroinflammation in selected brain structures and cachexia development in tumor-bearing rats. After tumor cells inoculation, specifically on the 7th, 14th, 21st, and 28th day of tumor growth, we assessed the presence of cancer-associated cachexia in rats. Changes in gene expression of inflammatory factors were studied in selected regions of the hypothalamus, brain stem, and circumventricular organs. We showed that the initial stages of cancer growth (7th and 14th day after tumor cells inoculation), are not associated with cachexia, or increased expression of inflammatory molecules in the brain. Even when we did not detect cachexia in tumor-bearing rats by the 21st day of the experiment, the inflammatory brain reaction had already started, as we found elevated levels of interleukin 1 beta, interleukin 6, tumor necrosis factor alpha, and glial fibrillary acidic protein mRNA levels in the nucleus of the solitary tract. Furthermore, we found increased interleukin 1 beta expression in the locus coeruleus and higher allograft inflammatory factor 1 expression in the vascular organ of lamina terminalis. Ultimately, the most pronounced manifestations of tumor growth were present on the 28th day post-inoculation of tumor cells. In these animals, we detected cancer-related cachexia and significant increases in interleukin 1 beta expression in all brain areas studied. We also observed significantly decreased expression of the glial cell activation markers allograft inflammatory factor 1 and glial fibrillary acidic protein in most brain areas of cachectic rats. In addition, we showed increased expression of cluster of differentiation 163 and cyclooxygenase 2 mRNA in the hypothalamic paraventricular nucleus, A1/C1 neurons, and area postrema of cachectic rats. Our data indicate that cancer-related cachexia is associated with complex neuroinflammatory changes in the brain. These changes can be found in both hypothalamic as well as extrahypothalamic structures, while their extent and character depend on the stage of tumor growth.

Brainstem prolactin-releasing peptide contributes to cancer anorexia-cachexia syndrome in rats

Up to 80% of cancer patients are affected by the cancer anorexia-cachexia syndrome (CACS), which leads to excessive body weight loss, reduced treatment success and increased lethality. The area postrema/nucleus of the solitary tract (AP/NTS) region emerged as a central nervous key structure in this multi-factorial process. Neurons in this area are targeted by cytokines and signal to downstream sites involved in energy homeostasis. NTS neurons expressing prolactin-releasing peptide (PrRP) are implicated in the control of energy intake and hypothalamus-pituitary-adrenal (HPA) axis activation, which contributes to muscle wasting. To explore if brainstem PrRP neurons contribute to CACS, we selectively knocked down PrRP expression in the NTS of hepatoma tumor-bearing rats by an AAV/shRNA gene silencing approach. PrRP knockdown reduced body weight loss and anorexia compared to tumor-bearing controls treated with a non-silencing AAV. Gastrocnemius and total hind limb muscle weight was higher in PrPR knockdown rats. Corticosterone levels were increased in the early phase after tumor induction at day 6 in both groups but returned to baseline levels at day 21 in the PrRP knockdown group. While we did not detect significant changes in gene expression of markers for muscle protein metabolism (MuRF-1, myostatin, mTOR and REDD1), mTOR and REDD1 tended to be lower after disruption PrRP signalling. In conclusion, we identified brainstem PrRP as a possible neuropeptide mediator of CACS in hepatoma tumor-bearing rats. The central and peripheral downstream mechanisms require further investigation and might involve HPA axis activation.

NF-κB signaling in tanycytes mediates inflammation-induced anorexia

Objectives

Infections, cancer, and systemic inflammation elicit anorexia. Despite the medical significance of this phenomenon, the question of how peripheral inflammatory mediators affect the central regulation of food intake is incompletely understood. Therefore, we have investigated the sickness behavior induced by the prototypical inflammatory mediator IL-1β.

Methods

IL-1β was injected intravenously. To interfere with IL-1β signaling, we deleted the essential modulator of NF-κB signaling (Nemo) in astrocytes and tanycytes.

Results

Systemic IL-1β increased the activity of the transcription factor NF-κB in tanycytes of the mediobasal hypothalamus (MBH). By activating NF-κB signaling, IL-1β induced the expression of cyclooxygenase-2 (Cox-2) and stimulated the release of the anorexigenic prostaglandin E₂ (PGE₂) from tanycytes. When we deleted Nemo in astrocytes and tanycytes, the IL-1β-induced anorexia was alleviated whereas the fever response and lethargy response were unchanged. Similar results were obtained after the selective deletion of Nemo exclusively in tanycytes.

Conclusions

Tanycytes form the brain barrier that mediates the anorexic effect of systemic inflammation in the hypothalamus.

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Systemic IL-1β activates NF-κB in tanycytes.

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IL-1β induces the expression of Ptgs2 (Cox-2) and the release of PGE₂ from tanycytes.

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NEMO-dependent NF-κB signaling in tanycytes is required for anorexia induced by IL-1β.

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Tanycytes are not involved in fever and lethargy induced by IL-1β.

Changes in gene expression in brain structures related to visceral sensation, autonomic functions, food intake, and cognition in melanoma-bearing mice

The brain exerts complex effects on the initiation and progression of cancer in the body. However, the influence of cancer localized in peripheral tissues on the brain has been only partially described. Therefore, we investigated gene expression in brain structures that participate in transmitting viscerosensory signals, regulating autonomic functions and food intake, as well as cognition in C57Bl/6J mice with B16-F10 melanoma. In addition, we investigated the relationship between peripheral inflammation and neuroinflammation. We found increased neuronal activity in the nucleus of the solitary tract of tumor-bearing mice, whereas neuronal activity in the A1/C1 catecholaminergic cell group, parabrachial nucleus, lateral hypothalamic area, ventromedial nucleus of the hypothalamus, paraventricular nucleus of the hypothalamus, and hippocampus was decreased. In the majority of investigated brain structures, we found increased gene expression of IL-1β, whereas gene expression of IL-6 and NF-κB was reduced or unchanged compared with controls. Melanoma-bearing mice also showed increased gene expression of tyrosine hydroxylase in the A1/C1 catecholaminergic cell group, nucleus of the solitary tract, and locus coeruleus, as well as reduced mRNA levels of hypocretin neuropeptide precursor protein in the lateral hypothalamic area, and proopiomelanocortin in the arcuate nucleus. In addition, we found reduced mRNA levels of Bcl-2, brain-derived neurotrophic factor, and doublecortin in the hippocampus. Our data indicate that skin melanoma induces complex changes in the brain, and these changes are most probably caused by cancer-related signals mediated by pro-inflammatory cytokines.

Involvement of interleukin-1 type 1 receptors in lipopolysaccharide-induced sickness responses

Sickness responses to lipopolysaccharide (LPS) were examined in mice with deletion of the interleukin (IL)-1 type 1 receptor (IL-1R1). IL-1R1 knockout (KO) mice displayed intact anorexia and HPA-axis activation to intraperitoneally injected LPS (anorexia: 10 or 120µg/kg; HPA-axis: 120µg/kg), but showed attenuated but not extinguished fever (120µg/kg). Brain PGE₂ synthesis was attenuated, but Cox-2 induction remained intact. Neither the tumor necrosis factor-α (TNFα) inhibitor etanercept nor the IL-6 receptor antibody tocilizumab abolished the LPS induced fever in IL-1R1 KO mice. Deletion of IL-1R1 specifically in brain endothelial cells attenuated the LPS induced fever, but only during the late, 3rd phase of fever, whereas deletion of IL-1R1 on neural cells or on peripheral nerves had little or no effect on the febrile response. We conclude that while IL-1 signaling is not critical for LPS induced anorexia or stress hormone release, IL-1R1, expressed on brain endothelial cells, contributes to the febrile response to LPS. However, also in the absence of IL-1R1, LPS evokes a febrile response, although this is attenuated. This remaining fever seems not to be mediated by IL-6 receptors or TNFα, but by some yet unidentified pyrogenic factor.

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.

Anorexia-cachexia syndrome in hepatoma tumour-bearing rats requires the area postrema but not vagal afferents and is paralleled by increased MIC-1/GDF15

BACKGROUND

The cancer-anorexia-cachexia syndrome (CACS) negatively affects survival and therapy success in cancer patients. Inflammatory mediators and tumour-derived factors are thought to play an important role in the aetiology of CACS. However, the central and peripheral mechanisms contributing to CACS are insufficiently understood. The area postrema (AP) and the nucleus tractus solitarii are two important brainstem centres for the control of eating during acute sickness conditions. Recently, the tumour-derived macrophage inhibitory cytokine-1 (MIC-1) emerged as a possible mediator of cancer anorexia because lesions of these brainstem areas attenuated the anorectic effect of exogenous MIC-1 in mice.

METHODS

Using a rat hepatoma tumour model, we examined the roles of the AP and of vagal afferents in the mediation of CACS. Specifically, we investigated whether a lesion of the AP (APX) or subdiaphragmatic vagal deafferentation (SDA) attenuate anorexia, body weight, muscle, and fat loss. Moreover, we analysed MIC-1 levels in this tumour model and their correlation with tumour size and the severity of the anorectic response.

RESULTS

In tumour-bearing sham-operated animals mean daily food intake significantly decreased. The anorectic response was paralleled by a significant loss of body weight and muscle mass. APX rats were protected against anorexia, body weight loss, and muscle atrophy after tumour induction. In contrast, subdiaphragmatic vagal deafferentation did not attenuate cancer-induced anorexia or body weight loss. Tumour-bearing rats had substantially increased MIC-1 levels, which positively correlated with tumour size and cancer progression and negatively correlated with food intake.

CONCLUSIONS

These findings demonstrate the importance of the AP in the mediation of cancer-dependent anorexia and body weight loss and support a pathological role of MIC-1 as a tumour-derived factor mediating CACS, possibly via an AP-dependent action.

Oral Treatment with the Ghrelin Receptor Agonist HM01 Attenuates Cachexia in Mice Bearing Colon-26 (C26) Tumors

The gastrointestinal hormone ghrelin reduces energy expenditure and stimulates food intake. Ghrelin analogs are a possible treatment against cancer anorexia-cachexia syndrome (CACS). This study aimed to investigate whether oral treatment with the non-peptidergic ghrelin receptor agonist HM01 counteracts CACS in colon-26 (C26) tumor-bearing mice. The C26 tumor model is characterized by pronounced body weight (BW) loss and muscle wasting in the absence of severe anorexia. We analyzed the time course of BW loss, body composition, muscle mass, bone mineral density, and the cytokines interleukin-6 (IL-6) and macrophage-inhibitory cytokine-1 (MIC-1). Moreover, we measured the expression of the muscle degradation markers muscle RING-finger-protein-1 (MuRF-1) and muscle atrophy F-box (MAFbx). After tumor inoculation, MIC-1 levels increased earlier than IL-6 and both cytokines were elevated before MuRF-1/MAFbx expression increased. Oral HM01 treatment increased BW, fat mass, and neuronal hypothalamic activity in healthy mice. In tumor-bearing mice, HM01 increased food intake, BW, fat mass, muscle mass, and bone mineral density while it decreased energy expenditure. These effects appeared to be independent of IL-6, MIC-1, MuRF-1 or MAFbx, which were not affected by HM01. Therefore, HM01 counteracts cachectic body weight loss under inflammatory conditions and is a promising compound for the treatment of cancer cachexia in the absence of severe anorexia.

High-fat diet-induced downregulation of anorexic leukemia inhibitory factor in the brain stem

OBJECTIVE

High-fat diet (HFD) is known to induce low-grade hypothalamic inflammation. Whether inflammation occurs in other brain areas remains unknown. This study tested the effect of short-term HFD on cytokine gene expression and identified leukemia inhibitory factor (LIF) as a responsive cytokine in the brain stem. Thus, functional and cellular effects of LIF in the brain stem were investigated.

METHODS

Male rats were fed chow or HFD for 3 days, and then gene expression was analyzed in different brain regions for IL-1β, IL-6, TNF-α, and LIF. The effect of intracerebroventricular injection of LIF on chow intake and body weight was also tested. Patch clamp recording was performed in the nucleus tractus solitarius (NTS).

RESULTS

HFD increased pontine TNF-α mRNA while downregulating LIF in all major parts of the brain stem, but not in the hypothalamus or hippocampus. LIF injection into the cerebral aqueduct suppressed food intake without conditioned taste aversion, suggesting that LIF can induce anorexia via lower brain regions without causing malaise. In the NTS, a key brain stem nucleus for food intake regulation, LIF induced acute changes in neuronal excitability.

CONCLUSIONS

HFD-induced downregulation of anorexic LIF in the brain stem may provide a permissive condition for HFD overconsumption. This may be at least partially mediated by the NTS.

The ghrelin receptor agonist HM01 mimics the neuronal effects of ghrelin in the arcuate nucleus and attenuates anorexia-cachexia syndrome in tumor-bearing rats

The gastric hormone ghrelin positively affects energy balance by increasing food intake and reducing energy expenditure. Ghrelin mimetics are a possible treatment against cancer anorexia-cachexia syndrome (CACS). This study aimed to characterize the action of the nonpeptidergic ghrelin receptor agonist HM01 on neuronal function, energy homeostasis and muscle mass in healthy rats and to evaluate its possible usefulness for the treatment of CACS in a rat tumor model. Using extracellular single-unit recordings, we tested whether HM01 mimics the effects of ghrelin on neuronal activity in the arcuate nucleus (Arc). Furthermore, we assessed the effect of chronic HM01 treatment on food intake (FI), body weight (BW), lean and fat volumes, and muscle mass in healthy rats. Using a hepatoma model, we investigated the possible beneficial effects of HM01 on tumor-induced anorexia, BW loss, muscle wasting, and metabolic rate. HM01 (10(-7)-10(-6) M) mimicked the effect of ghrelin (10(-8) M) by increasing the firing rate in 76% of Arc neurons. HM01 delivered chronically for 12 days via osmotic minipumps (50 μg/h) increased FI in healthy rats by 24%, paralleled by increased BW, higher fat and lean volumes, and higher muscle mass. Tumor-bearing rats treated with HM01 had 30% higher FI than tumor-bearing controls and were protected against BW loss. HM01 treatment resulted in higher muscle mass and fat mass. Moreover, tumor-bearing rats reduced their metabolic rate following HM01 treatment. Our studies substantiate the possible therapeutic usefulness of ghrelin receptor agonists like HM01 for the treatment of CACS and possibly other forms of disease-related anorexia and cachexia.

Interleukin-1β induced activation of the hypothalamus-pituitary-adrenal axis is dependent on interleukin-1 receptors on non-hematopoietic cells

The proinflammatory cytokine interleukin-1β (IL-1β) plays a major role in the signal transduction of immune stimuli from the periphery to the central nervous system, and has been shown to be an important mediator of the immune-induced stress hormone release. The signaling pathway by which IL-1β exerts this function involves the blood-brain-barrier and induced central prostaglandin synthesis, but the identity of the blood-brain-barrier cells responsible for this signal transduction has been unclear, with both endothelial cells and perivascular macrophages suggested as critical components. Here, using an irradiation and transplantation strategy, we generated mice expressing IL-1 type 1 receptors (IL-1R1) either in hematopoietic or non-hematopoietic cells and subjected these mice to peripheral immune challenge with IL-1β. Following both intraperitoneal and intravenous administration of IL-1β, mice lacking IL-1R1 in hematopoietic cells showed induced expression of the activity marker c-Fos in the paraventricular hypothalamic nucleus, and increased plasma levels of ACTH and corticosterone. In contrast, these responses were not observed in mice with IL-1R1 expression only in hematopoietic cells. Immunoreactivity for IL-1R1 was detected in brain vascular cells that displayed induced expression of the prostaglandin synthesizing enzyme cyclooxygenase-2 and that were immunoreactive for the endothelial cell marker CD31, but was not seen in cells positive for the brain macrophage marker CD206. These results imply that activation of the HPA-axis by IL-1β is dependent on IL-1R1s on non-hematopoietic cells, such as brain endothelial cells, and that IL-1R1 on perivascular macrophages are not involved.

Regulation of the chemosensory control of breathing by Kölliker-Fuse neurons

The Kölliker-Fuse region (KF) and the lateral parabrachial nucleus (LPBN) have been implicated in the maintenance of cardiorespiratory control. Here, we evaluated the involvement of the KF region and the LPBN in cardiorespiratory responses elicited by chemoreceptor activation in unanesthetized rats. Male Wistar rats (280-330 g; n = 5-9/group) with bilateral stainless-steel guide cannulas implanted in the KF region or the LPBN were used. Injection of muscimol (100 and 200 pmol/100 nl) in the KF region decreased resting ventilation (1,140 ± 68 and 978 ± 100 vs. saline: 1,436 ± 155 ml·kg(-1)·min(-1)), without changing mean arterial pressure (MAP) and heart rate (HR). Bilateral injection of the GABA-A antagonist bicuculline (1 nmol/100 nl) in the KF blocked the inhibitory effect on ventilation (1,418 ± 138 vs. muscimol: 978 ± 100 ml·kg(-1)·min(-1)) elicited by muscimol. Muscimol injection in the KF reduced the increase in ventilation produced by hypoxia (8% O2) (1,827 ± 61 vs. saline: 3,179 ± 325 ml·kg(-1)·min(-1)) or hypercapnia (7% CO2) (1,488 ± 277 vs. saline: 3,539 ± 374 ml·kg(-1)·min(-1)) in unanesthetized rats. Bilateral injection of bicuculline in the KF blocked the decrease in ventilation produced by muscimol in the KF during peripheral or central chemoreflex activation. Bilateral injection of muscimol in the LPBN did not change resting ventilation or the increase in ventilation elicited by hypoxia or hypercapnia. The results of the present study suggest that the KF region, but not the LPBN, has mechanisms to control ventilation in resting, hypoxic, or hypercapnic conditions in unanesthetized rats.

Proteomic profiling of the hypothalamus in a mouse model of cancer-induced anorexia-cachexia

BACKGROUND

Anorexia-cachexia is a common and severe cancer-related complication but the underlying mechanisms are largely unknown. Here, using a mouse model for tumour-induced anorexia-cachexia, we screened for proteins that are differentially expressed in the hypothalamus, the brain's metabolic control centre.

METHODS

The hypothalamus of tumour-bearing mice with implanted methylcholanthrene-induced sarcoma (MCG 101) displaying anorexia and their sham-implanted pair-fed or free-fed littermates was examined using two-dimensional electrophoresis (2-DE)-based comparative proteomics. Differentially expressed proteins were identified by liquid chromatography-tandem mass spectrometry.

RESULTS

The 2-DE data showed an increased expression of dynamin 1, hexokinase, pyruvate carboxylase, oxoglutarate dehydrogenase, and N-ethylmaleimide-sensitive factor in tumour-bearing mice, whereas heat-shock 70 kDa cognate protein, selenium-binding protein 1, and guanine nucleotide-binding protein Gα0 were downregulated. The expression of several of the identified proteins was similarly altered also in the caloric-restricted pair-fed mice, suggesting an involvement of these proteins in brain metabolic adaptation to restricted nutrient availability. However, the expression of dynamin 1, which is required for receptor internalisation, and of hexokinase, and pyruvate carboxylase were specifically changed in tumour-bearing mice with anorexia.

CONCLUSION

The identified differentially expressed proteins may be new candidate molecules involved in the pathophysiology of tumour-induced anorexia-cachexia.

The time-course of hindbrain neuronal activity varies according to location during either intraperitoneal or subcutaneous tumor growth in rats: single Fos and dual Fos/dopamine β-hydroxylase immunohistochemistry

Neuronal activity in the nucleus of the solitary tract, ventrolateral medulla, area postrema, and parabrachial nucleus was studied in rats with intraperitoneal or subcutaneous tumors on the 7th, 14th, 21st, and 28th day after injection of fibrosarcoma tumor cells. We found that the number of Fos and dopamine β-hydroxylase immunopositive neurons differs between animals with intraperitoneal and subcutaneous tumors and also between tumor-bearing rats at different times following injection. Our data indicate that responses of the brainstem structures to peripheral tumor growth depend on the localization as well as the stage of the tumor growth.

Cancer-induced anorexia in tumor-bearing mice is dependent on cyclooxygenase-1

It is well-established that prostaglandins (PGs) affect tumorigenesis, and evidence indicates that PGs also are important for the reduced food intake and body weight loss, the anorexia-cachexia syndrome, in malignant cancer. However, the identity of the PGs and the PG producing cyclooxygenase (COX) species responsible for cancer anorexia-cachexia is unknown. Here, we addressed this issue by transplanting mice with a tumor that elicits anorexia. Meal pattern analysis revealed that the anorexia in the tumor-bearing mice was due to decreased meal frequency. Treatment with a non-selective COX inhibitor attenuated the anorexia, and also tumor growth. When given at manifest anorexia, non-selective COX-inhibitors restored appetite and prevented body weight loss without affecting tumor size. Despite COX-2 induction in the cerebral blood vessels of tumor-bearing mice, a selective COX-2 inhibitor had no effect on the anorexia, whereas selective COX-1 inhibition delayed its onset. Tumor growth was associated with robust increase of PGE(2) levels in plasma - a response blocked both by non-selective COX-inhibition and by selective COX-1 inhibition, but not by COX-2 inhibition. However, there was no increase in PGE(2)-levels in the cerebrospinal fluid. Neutralization of plasma PGE(2) with specific antibodies did not ameliorate the anorexia, and genetic deletion of microsomal PGE synthase-1 (mPGES-1) affected neither anorexia nor tumor growth. Furthermore, tumor-bearing mice lacking EP(4) receptors selectively in the nervous system developed anorexia. These observations suggest that COX-enzymes, most likely COX-1, are involved in cancer-elicited anorexia and weight loss, but that these phenomena occur independently of host mPGES-1, PGE(2) and neuronal EP(4) signaling.

Fos-activation of FoxP2 and Lmx1b neurons in the parabrachial nucleus evoked by hypotension and hypertension in conscious rats

The parabrachial nucleus (PB) is a brainstem cell group that receives a strong input from the nucleus tractus solitarius regarding the physiological status of the internal organs and sends efferent projections throughout the forebrain. Since the neuroanatomical organization of the PB remains unclear, our first step was to use specific antibodies against two neural lineage transcription factors: Forkhead box protein2 (FoxP2) and LIM homeodomain transcription factor 1 beta (Lmx1b) to define the PB in adult rats. This allowed us to construct a cytoarchitectonic PB map based on the distribution of neurons that constitutively express these two transcription factors. Second, the in situ hybridization method combined with immunohistochemistry demonstrated that mRNA for glutamate vesicular transporter Vglut2 (Slc17a6) was present in most of the Lmx1b+ and FoxP2+ parabrachial neurons, indicating these neurons use glutamate as a transmitter. Third, conscious rats were maintained in a hypotensive or hypertensive state for 2h, and then, their brainstems were prepared by the standard c-Fos method which is a measure of neuronal activity. Both hypotension and hypertension resulted in c-Fos activation of Lmx1b+ neurons in the external lateral-outer subdivision of the PB (PBel-outer). Hypotension, but not hypertension, caused c-Fos activity in the FoxP2+ neurons of the central lateral PB (PBcl) subnucleus. The Kölliker-Fuse nucleus as well as the lateral crescent PB and rostral-most part of the PBcl contain neurons that co-express FoxP2+ and Lmx1b+, but none of these were activated after blood pressure changes. Salt-sensitive FoxP2 neurons in the pre-locus coeruleus and PBel-inner were not c-Fos activated following blood pressure changes. In summary, the present study shows that the PBel-outer and PBcl subnuclei originate from two different neural progenitors, contain glutamatergic neurons, and are affected by blood pressure changes, with the PBel-outer reacting to both hypo- and hypertension, and the PBcl signaling only hypotensive changes.

Muscle wasting in animal models of severe illness

Muscle wasting is a serious complication of various clinical conditions that significantly worsens the prognosis of the illnesses. Clinically relevant models of muscle wasting are essential for understanding its pathogenesis and for selective preclinical testing of potential therapeutic agents. The data presented here indicate that muscle wasting has been well characterized in rat models of sepsis (endotoxaemia, and caecal ligation and puncture), in rat models of chronic renal failure (partial nephrectomy), in animal models of intensive care unit patients (corticosteroid treatment combined with peripheral denervation or with administration of neuromuscular blocking drugs) and in murine and rat models of cancer (tumour cell transplantation). There is a need to explore genetically engineered mouse models of cancer. The degree of protein degradation in skeletal muscle is not well characterized in animal models of liver cirrhosis, chronic heart failure and chronic obstructive pulmonary disease. The major difficulties with all models are standardization and high variation in disease progression and a lack of reflection of clinical reality in some of the models. The translation of the information obtained by using these models to clinical practice may be problematic.

Molecular mechanisms of cachexia in chronic disease

Cachexia is a metabolic syndrome that manifests with excessive weight loss and disproportionate muscle wasting. It is related to many different chronic diseases, such as cancer, infections, liver disease, inflammatory bowel disease, cardiac disease, chronic obstructive pulmonary disease, chronic renal failure and rheumatoid arthritis. Cachexia is linked with poor outcome for the patients. In this article, we explore the role of the hypothalamus, liver, muscle tissue and adipose tissue in the pathogenesis of this syndrome, particularly concentrating on the role of cytokines, hormones and cell energy-controlling pathways (such as AMPK, PI3K/Akt and mTOR). We also look at possible future directions for therapeutic strategies.

Ghrelin agonists impact on Fos protein expression in brain areas related to food intake regulation in male C57BL/6 mice

Many peripheral substances, including ghrelin, induce neuronal activation in the brain. In the present study, we compared the effect of subcutaneously administered ghrelin and its three stable agonists: Dpr(3)ghr ([Dpr(N-octanoyl)(3)] ghrelin) (Dpr - diaminopropionic acid), YA GHRP-6 (H-Tyr-Ala-His-DTrp-Ala-Trp-DPhe-Lys-NH(2)), and JMV1843 (H-Aib-DTrp-D-gTrp-CHO) on the Fos expression in food intake-responsive brain areas such as the hypothalamic paraventricular (PVN) and arcuate (ARC) nuclei, the nucleus of the solitary tract (NTS), and area postrema (AP) in male C57BL/6 mice. Immunohistochemical analysis showed that acute subcutaneous dose of each substance (5mg/kg b.w.), which induced a significant food intake increase, elevated Fos protein expression in all brain areas studied. Likewise ghrelin, each agonist tested induced distinct Fos expression overall the PVN. In the ARC, ghrelin and its agonists specifically activated similarly distributed neurons. Fos occurrence extended from the anterior (aARC) to middle (mARC) ARC region. In the latter part of the ARC, the Fos profiles were localized bilaterally, especially in the ventromedial portions of the nucleus. In the NTS, all substances tested also significantly increased the number of Fos profiles in neurons, which also revealed specific location, i.e., in the NTS dorsomedial subnucleus (dmNTS) and the area subpostrema (AsP). In addition, cells located nearby the NTS, in the AP, also revealed a significant increase in number of Fos-activated cells. These results demonstrate for the first time that ghrelin agonists, regardless of their different chemical nature, have a significant and similar activating impact on specific groups of neurons that can be a part of the circuits involved in the food intake regulation. Therefore there is a real potency for ghrelin agonists to treat cachexia and food intake disorders. Thus, likewise JMV1843, the other ghrelin agonists represent substances that might be involved in trials for clinical purposes.

Fto immunoreactivity is widespread in the rodent brain and abundant in feeding-related sites, but the number of Fto-positive cells is not affected by changes in energy balance

A single nucleotide polymorphism in the FTO gene is associated with obesity in humans. Evidence gathered in animals mainly relates energy homeostasis to the central FTO mRNA levels, but our knowledge of the Fto protein distribution and regulation is limited. Fto, a demethylase and transcriptional coactivator, is thought to regulate expression of other genes. Herein, we examined Fto immunoreactivity (IR) in the mouse and rat brain with emphasis on sites governing energy balance. We also studied whether energy status affects central Fto IR. We report that Fto IR, limited to nuclear profiles, is widespread in the brain, in- and outside feeding circuits; it shows a very similar distribution in feeding-related sites in mice and rats. Several areas regulating energy homeostasis display enhanced intensity of Fto staining: the arcuate, paraventricular, supraoptic, dorsomedial, ventromedial nuclei, and dorsal vagal complex. Some regions mediating feeding reward, including the bed nucleus of the stria terminalis, have ample Fto IR. We found that differences in energy status between rats fed ad libitum, deprived or refed following deprivation, did not affect the number of Fto-positive nuclei in 10 sites governing consumption for energy or reward. We conclude that Fto IR, widespread in the rodent brain, is particularly abundant in feeding circuits, but the number of Fto-positive neurons is unaffected by changes in energy balance.

Deletion of the gene encoding MyD88 protects from anorexia in a mouse tumor model

The anorexia-cachexia syndrome, characterized by a rise in energy expenditure and loss of body weight that paradoxically are associated with loss of appetite and decreased food intake, contributes significantly to the morbidity and mortality in cancer. While the pathophysiology of cancer anorexia-cachexia is poorly understood, evidence indicates that pro-inflammatory cytokines are key mediators of this response. Although inflammation hence is recognized as an important component of cancer anorexia-cachexia, the molecular pathways involved are largely unknown. We addressed this issue in mice carrying a deletion of the gene encoding MyD88, the key intracellular adaptor molecule in Toll-like and interleukin-1 family receptor signaling. Wild-type and MyD88-deficient mice were transplanted subcutaneously with a syngenic methylcholanthrene-induced tumor (MCG 101) and daily food intake and body weight were recorded. Wild-type mice showed progressively reduced food intake from about 5days after tumor transplantation and displayed a slight body weight loss after 10days when the experiment was terminated. In contrast, MyD88-deficient mice did not develop anorexia, and displayed a positive body weight development during the observation period. While the MyD88-deficient mice on average developed somewhat smaller tumors than wild-type mice, this did not explain the absence of anorexia, because anorexia was seen in wild-type mice with similar tumor mass as non-anorexic knock-out mice. These data suggest that MyD88-dependent mechanisms are involved in the metabolic derangement during cancer anorexia-cachexia and that innate immune signaling is important for the development of this syndrome.

Neurobiology of inflammation-associated anorexia

Compelling data demonstrate that inflammation-associated anorexia directly results from the action of pro-inflammatory factors, primarily cytokines and prostaglandins E2, on the nervous system. For instance, the aforementioned pro-inflammatory factors can stimulate the activity of peripheral sensory neurons, and induce their own de novo synthesis and release into the brain parenchyma and cerebrospinal fluid. Ultimately, it results in the mobilization of a specific neural circuit that shuts down appetite. The present article describes the different cell groups and neurotransmitters involved in inflammation-associated anorexia and examines how they interact with neural systems regulating feeding such as the melanocortin system. A better understanding of the neurobiological mechanisms underlying inflammation-associated anorexia will help to develop appetite stimulants for cancer and AIDS patients.

Update on melanocortin interventions for cachexia: progress toward clinical application

Cachexia is a devastating syndrome of body wasting that is associated with multiple common chronic diseases including cancer, chronic kidney disease, and chronic heart failure. These underlying diseases are associated with increased levels of inflammatory cytokines and result in anorexia, increased resting energy expenditure, and loss of fat and lean body mass. Prior experiments have implicated the central melanocortin system in the hypothalamus with the propagation of these symptoms of cachexia. Pharmacologic blockade of this system using melanocortin antagonists causes attenuation of the signs of cachexia in laboratory models. Recent advances in our knowledge of this disease process have involved further elucidation of the pathophysiology of melanocortin activation and demonstration of the efficacy of melanocortin antagonists in new models of cachexia, including cardiac cachexia. In addition, small molecule antagonists of the melanocortin-4 receptor continue to be introduced, including ones with oral bioavailability. These developments generate optimism that melanocortin antagonism will be used to treat humans with disease-associated cachexia. However, to date, human application has remained elusive and it is unclear when we will know whether humans with cachexia would benefit from treatment with these compounds.

Inducible prostaglandin E2 synthesis interacts in a temporally supplementary sequence with constitutive prostaglandin-synthesizing enzymes in creating the hypothalamic-pituitary-adrenal axis response to immune challenge

Inflammation-induced activation of the hypothalamic-pituitary-adrenal (HPA) axis has been suggested to depend on prostaglandins, but the prostaglandin species and the prostaglandin-synthesizing enzymes that are responsible have not been fully identified. Here, we examined HPA axis activation in mice after genetic deletion or pharmacological inhibition of prostaglandin E(2)-synthesizing enzymes, including cyclooxygenase-1 (Cox-1), Cox-2, and microsomal prostaglandin E synthase-1 (mPGES-1). After immune challenge by intraperitoneal injection of lipopolysaccharide, the rapid stress hormone responses were intact after Cox-2 inhibition and unaffected by mPGES-1 deletion, whereas unselective Cox inhibition blunted these responses, implying the involvement of Cox-1. However, mPGES-1-deficient mice showed attenuated transcriptional activation of corticotropin-releasing hormone (CRH) that was followed by attenuated plasma concentrations of adrenocorticotropic hormone and corticosterone. Cox-2 inhibition similarly blunted the delayed corticosterone response and further attenuated corticosterone release in mPGES-1 knock-out mice. The expression of the c-fos gene, an index of synaptic activation, was maintained in the paraventricular hypothalamic nucleus and its brainstem afferents both after unselective and Cox-2 selective inhibition as well as in Cox-1, Cox-2, and mPGES-1 knock-out mice. These findings point to a mechanism by which (1) neuronal afferent signaling via brainstem autonomic relay nuclei and downstream Cox-1-dependent prostaglandin release and (2) humoral, CRH transcription-dependent signaling through induced Cox-2 and mPGES-1 elicited PGE(2) synthesis, shown to occur in brain vascular cells, play distinct, but temporally supplementary roles for the stress hormone response to inflammation.

Administration of IL-1beta to the 4th ventricle causes anorexia that is blocked by agouti-related peptide and that coincides with activation of tyrosine-hydroxylase neurons in the nucleus of the solitary tract

Inflammation-associated cachexia is associated with multiple chronic diseases and involves activation of appetite regulating centers in the arcuate nucleus of the hypothalamus (ARH). The nucleus of the solitary tract (NTS) in the brainstem has also been implicated as an important nucleus involved in appetite regulation. We set out to determine whether the NTS may be involved in inflammation-associated anorexia by injecting IL-1 beta into the 4th ventricle and assessing food intake and NTS neuronal activation. Injection of IL-1 beta produced a decrease in food intake at 3 and 12h after injection which was ameliorated at the 12h time point by a sub-threshold dose of agouti-related peptide (AgRP). Investigation into neuron types in the NTS revealed that IL-1 beta injection was associated with an increase in c-Fos activity in NTS neurons expressing tyrosine hydroxylase (TH). Additionally, injection of IL-1 beta into the 4th ventricle did not produce c-Fos activation of neurons expressing pro-opiomelanocortin (POMC) in the ARH, cells known to be involved in producing anorexia in response to systemic inflammation. Double-label in situ hybridization revealed that TH neurons did not express IL-1 receptor I (IL1-RI) transcript, demonstrating that c-Fos activation of TH neurons in this setting was not via direct stimulation of IL-1 beta on TH neurons themselves. We conclude that IL-1 beta injection into the 4th ventricle produces anorexia and is accompanied by an increase in activation in TH neurons in the NTS. This provides evidence that the brainstem may be an important mediator of anorexia in the setting of inflammation.

Neural control of the anorexia-cachexia syndrome

The anorexia-cachexia syndrome is a debilitating clinical condition characterizing the course of chronic diseases, which heavily impacts on patients' morbidity and quality of life, ultimately accelerating death. The pathogenesis is multifactorial and reflects the complexity and redundancy of the mechanisms controlling energy homeostasis under physiological conditions. Accumulating evidence indicates that, during disease, disturbances of the hypothalamic pathways controlling energy homeostasis occur, leading to profound metabolic changes in peripheral tissues. In particular, the hypothalamic melanocortin system does not respond appropriately to peripheral inputs, and its activity is diverted largely toward the promotion of catabolic stimuli (i.e., reduced energy intake, increased energy expenditure, possibly increased muscle proteolysis, and adipose tissue loss). Hypothalamic proinflammatory cytokines and serotonin, among other factors, are key in triggering hypothalamic resistance. These catabolic effects represent the central response to peripheral challenges (i.e., growing tumor, renal, cardiac failure, disrupted hepatic metabolism) that are likely sensed by the brain through the vagus nerve. Also, disease-induced changes in fatty acid oxidation within hypothalamic neurons may contribute to the dysfunction of the hypothalamic melanocortin system. Ultimately, sympathetic outflow mediates, at least in part, the metabolic changes in peripheral tissues. Other factors are likely involved in the pathogenesis of the anorexia-cachexia syndrome, and their role is currently being elucidated. However, available evidence shows that the constellation of symptoms characterizing this syndrome should be considered, at least in part, as different phenotypes of common neurochemical/metabolic alterations in the presence of a chronic inflammatory state.