A central role for neuronal adenosine 5'-monophosphate-activated protein kinase in cancer-induced anorexia

The role of the hypothalamus in the development of cancer cachexia

Cachexia is a complex multiorgan syndrome associated with various chronic diseases, characterized by anorexia and increased tissue wasting in the context of chronic inflammation. A specific form of this syndrome, known as cancer cachexia (CC), occurs alongside different types of tumors. The pathogenesis of CC is multifactorial. Inflammatory mediators and hormones released by both tumor and host cells have a relevant role in driving the peripheral catabolic process through several direct mechanisms. Accumulating evidence indicates that the central nervous system (CNS) plays an integral role in the pathogenesis of CC. The hypothalamus has emerged as a critical brain region that senses and amplifies peripheral stimuli, generating inappropriate neuronal signaling and leading to the dysregulation of energy homeostasis under cachexia conditions. Circulating cytokines may act in concert with hormones and neurotransmitters and perturb critical hypothalamic neurocircuits shifting their activity towards the anorexigenic pathway and increase of energy expenditure. This review discusses the mechanisms mediating the hypothalamic homeostatic imbalance in the context of anorexia and cachexia associated with cancer.

Understanding Cachexia in Head and Neck Cancer

One of the major comorbidities of cancer and cancer therapy is posing a global health problem in cancer cachexia. Cancer cachexia is now considered a multifactorial syndrome that presents with drastic loss of body weight, anorexia, asthenia, and anemia. Head and neck cancer (HNC) patients are at a greater risk for development and severity of cachexia syndrome as there is direct involvement of structures associated with nutritional intake. Yet, the scientific evidence, approach, and management of cachexia in HNCs are yet to be largely explored. The article aims to succinctly review the concepts of cancer cachexia with relevance to HNCs and summarizes the current findings from recent research.

The AMPK-mTOR signaling pathway is involved in regulation of food intake in the hypothalamus of stressed chickens

Glucocorticoids (GCs) can stimulate the appetite and AMPK in broilers. The activation of hypothalamic mTOR has been proposed as an important anorexigenic signal. However, inhibitory effect of AMPK activity on appetite and AMPK downstream signaling pathway under stress has not been reported. In this study, we performed an intracerebroventricular (icv) injection of compound C, an AMPK inhibitor, in GC-treated birds to explore the regulatory mechanism on appetite and AMPK downstream signaling pathway. A total of 48 7-day-old broilers, which had received an icv cannula, were randomly subjected to one of two treatments: subcutaneous injection of dexamethasone (DEX) or saline. After 3 days of continuous DEX injection, chicks of each group received an icv injection with either compound C (6 μg/2 μL) or vehicle (dimethyl sulfoxide, 2 μL). The results showed that body weight gain was reduced by the DEX treatment. Compared with the control, icv injection of compound C reduced feed intake at 0.5-1.5 h. In the DEX-treated group, the inhibitory effect of compound C on appetite remained apparent at 0.5-1 h. The DEX treatment increased the gene expression of liver kinase B1 (LKB1), neuropeptide Y (NPY), and decreased p-mTOR protein level. In stressed broilers, inhibition of AMPK relieved the decreased mTOR activity. A significant interaction was noted in DEX and compound C on protein expression of phospho-AMPK. Taken together, in stressed broilers, the central injection of compound C could inhibit central AMPK activity and reduce appetite, in which the AMPK/mTOR signaling pathway might be involved.

Combined Effects of Exercise and Phytoanabolic Extracts in Castrated Male and Female Mice

Dry extracts from the Eurasian plants, Ajuga turkestanica, Eurycoma longifolia, and Urtica dioica have been used as anabolic supplements, despite the limited scientific data on these effects. To assess their actions on early sarcopenia signs, male and female castrated mice were supplemented with lyophilized extracts of the three plants, isolated or in association (named TLU), and submitted to resistance exercise. Ovariectomy (OVX) led to body weight increase and non-high-density cholesterol (HDL) cholesterol elevation, which had been restored by exercise plus U. dioica extract, or by exercise and TLU, respectively. Orchiectomy (ORX) caused skeletal muscle weight loss, accompanied by increased adiposity, being the latter parameter reduced by exercise plus E. longifolia or U. dioica extracts. General physical activity was improved by exercise plus herbal extracts in either OVX or ORX animals. Exercise combined with TLU improved resistance to fatigue in OVX animals, though A. turkestanica enhanced the grip strength in ORX mice. E. longifolia or TLU also reduced the ladder climbing time in ORX mice. Resistance exercise plus herbal extracts partly altered gastrocnemius fiber size frequencies in OVX or ORX mice. We provide novel data that tested ergogenic extracts, when combined with resistance exercise, improved early sarcopenia alterations in castrated male and female mice.

Appetite Regulation of TLR4-Induced Inflammatory Signaling

Appetite is the basis for obtaining food and maintaining normal metabolism. Toll-like receptor 4 (TLR4) is an important receptor expressed in the brain that induces inflammatory signaling after activation. Inflammation is considered to affect the homeostatic and non-homeostatic systems of appetite, which are dominated by hypothalamic and mesolimbic dopamine signaling. Although the pathological features of many types of inflammation are known, their physiological functions in appetite are largely unknown. This review mainly addresses several key issues, including the structures of the homeostatic and non-homeostatic systems. In addition, the mechanism by which TLR4-induced inflammatory signaling contributes to these two systems to regulate appetite is also discussed. This review will provide potential opportunities to develop new therapeutic interventions that control appetite under inflammatory conditions.

Understanding cachexia in the context of metastatic progression

Tumours reprogram host physiology, metabolism and immune responses during cancer progression. The release of soluble factors, exosomes and metabolites from tumours leads to systemic changes in distant organs, where cancer cells metastasize and grow. These tumour-derived circulating factors also profoundly impact tissues that are rarely inhabited by metastatic cancer cells such as skeletal muscle and adipose tissue. In fact, the majority of patients with metastatic cancer develop a debilitating muscle-wasting syndrome, known as cachexia, that is associated with decreased tolerance to antineoplastic therapy, poor prognosis and accelerated death, with no approved treatments. In this Perspective, we discuss the development of cachexia in the context of metastatic progression. We briefly discuss how circulating factors either directly or indirectly promote cachexia development and examine how signals from the metastatic process can trigger and amplify this process. Finally, we highlight promising therapeutic opportunities for targeting cachexia in the context of metastatic cancers.

Cancer-Associated Cachexia: A Systemic Consequence of Cancer Progression

Cancer is a life-threatening disease that has plagued humans for centuries. The vast majority of cancer-related mortality results from metastasis. Indeed, the invasive growth of metastatic cancer cells in vital organs causes fatal organ dysfunction, but metastasis-related deaths also result from cachexia, a debilitating wasting syndrome characterized by an involuntary loss of skeletal muscle mass and function. In fact, about 80% of metastatic cancer patients suffer from cachexia, which often renders them too weak to tolerate standard doses of anticancer therapies and makes them susceptible to death from cardiac and respiratory failure. The goals of this review are to highlight important findings that help explain how cancer-induced systemic changes drive the development of cachexia and to discuss unmet challenges and potential therapeutic strategies targeting cachexia to improve the quality of life and survival of cancer patients.

Altered brain levels of arachidonic acid-derived inflammatory eicosanoids in a rodent model of anorexia nervosa

Increasing evidence underline the role of inflammation in the behavioral, emotional and cognitive dysregulations displayed in anorexia nervosa (AN). Among the inflammatory mediators acting at both peripheral and central levels, growing attention receives a class of lipids derived from arachidonic acid (AA), called eicosanoids (eiCs), which exert a complex, multifaceted role in a wide range of neuroinflammatory processes, peripheral inflammation, and generally in immune system function. To date, little is known about their possible involvement in the neurobiological underpinnings of AN. The present study evaluated whether the activity-based model of AN (ABA) may alter AA-metabolic pathways by changing the levels of AA-derived eiCs in specific brain areas implicated in the development of the typical anorexic-like phenotype, i.e. in prefrontal cortex, cerebral cortex, nucleus accumbens, caudate putamen, amygdala, hippocampus, hypothalamus and cerebellum. Our results point to brain region-specific alterations of the cyclooxygenase (COX), lipoxygenase (LOX) and cytochrome P450 epoxygenase (CYP) metabolic pathways rendering altered levels of AA-derived eiCs (i.e. prostaglandins, thromboxanes and hydroxyeicosatetraenoic acids) in response to induction of and recovery from the ABA condition. These changes, supported by altered messenger RNA (mRNA) levels of genes coding for enzymes involved in eiCs-related methabolic pathways (i.e., PLA₂, COX-2, 5-LOX and 15-LOX), underlie a widespread brain dysregulation of pro- and anti-inflammatory eiC-mediated processes in the ABA model of AN. These data suggest the importance of eiCs signaling within corticolimbic areas in regulating key neurobehavioral functions and highlight eiCs as biomarker candidates for monitoring the onset and development of AN, and/or as possible targets for pharmacological management.

Effects of metformin on insulin resistance and metabolic disorders in tumor-bearing rats with advanced cachexia

Metformin (MET) is widely used in the correction of insulin (INS) resistance and metabolic abnormalities in type 2 diabetes. However, its effect on INS resistance and metabolic disorders associated with cancer cachexia is not established. We investigated the MET effects, isolated or associated with INS, on INS resistance and metabolic changes induced by Walker-256 tumor in rats with advanced cachexia. MET (500 mg·kg-1, oral) and MET + INS (1.0 IU·kg-1, s.c.) were administered for 12 days, starting on the day of tumor cell inoculation. Tumor-bearing rats showed adipose and muscle mass wasting, body mass loss, anorexia, decreased Akt phosphorylation in retroperitoneal and mesenteric adipose tissue, peripheral INS resistance, hypoinsulinemia, reduced INS content and secretion from pancreatic islets, and also inhibition of glycolysis, gluconeogenesis, and glycogenolysis in liver. MET and MET + INS treatments did not prevent these changes. It can be concluded that treatments with MET and MET + INS did not prevent the adipose and muscle mass wasting and body mass loss of tumor-bearing rats possibly by not improving INS resistance. Therefore, MET, used for the treatment of INS resistance in type 2 diabetes, is not effective in improving INS resistance in the advanced stage of cancer cachexia, evidencing that the drug does not have the same beneficial effect in these 2 diseases.

Neuroimmune mechanisms of behavioral alterations in a syngeneic murine model of human papilloma virus-related head and neck cancer

Patients with cancer often experience a high symptom burden prior to the start of treatment. As disease- and treatment-related neurotoxicities appear to be additive, targeting disease-related symptoms may attenuate overall symptom burden for cancer patients and improve the tolerability of treatment. It has been hypothesized that disease-related symptoms are a consequence of tumor-induced inflammation. We tested this hypothesis using a syngeneic heterotopic murine model of human papilloma virus (HPV)-related head and neck cancer. This model has the advantage of being mildly aggressive and not causing cachexia or weight loss. We previously showed that this tumor leads to increased IL-6, IL-1β, and TNF-α expression in the liver and increased IL-1β expression in the brain. The current study confirmed these features and demonstrated that the tumor itself exhibits high inflammatory cytokine expression (e.g., IL-6, IL-1β, and TNF-α) compared to healthy tissue. While there is a clear relationship between cytokine levels and behavioral deficits in this model, the behavioral changes are surprisingly mild. Therefore, we sought to confirm the relationship between behavior and inflammation by amplifying the effect using a low dose of lipopolysaccharide (LPS, 0.1mg/kg). In tumor-bearing mice LPS induced deficits in nest building, tail suspension, and locomotor activity approximately 24h after LPS. However, these mice did not display an exacerbation of LPS-induced weight loss, anorexia, or anhedonia. Further, while heightened serum IL-6 was observed there was minimal priming of liver or brain cytokine expression. Next we sought to inhibit tumor-induced burrowing deficits by reducing inflammation using minocycline. Minocycline (∼50mg/kg/day in drinking water) was able to attenuate tumor-induced inflammation and burrowing deficits. These data provide evidence in favor of an inflammatory-like mechanism for the behavioral alterations associated with tumor growth in a syngeneic murine model of HPV-related head and neck cancer. However, the inflammatory state and behavioral changes induced by this tumor clearly differ from other forms of inflammation-induced sickness behavior.

New insight for metformin against bladder cancer

International Agency for Research on Cancer (IARC) estimated that bladder cancer is the ninth most common cancer in the world, with 430,000 new cases and 165,000 deaths in 2012. Bladder cancer represents the fourth most common cancer in men and ninth most common cancer in women. It is the second most prevalent cancer in men 60 years of age or older in United States. Looking further down, continuing advancements in cancer research could potentially offer more choices for clinician and patient with longer survival and better quality of life. Although, bladder cancer represents an ideal tumor model to test and apply cancer prevention strategies; there are limited studies about application of metformin in the management of bladder cancer. Here, I will shed light on the proposed mechanisms of anti-carcinogenic effects of metformin and cohort of these mechanisms with the novel application of metformin as therapy of bladder cancer.

[Hypothalamic inflammation and energy balance deregulations: focus on chemokines.]

The hypothalamus is a key brain region in the regulation of energy balance. It especially controls food intake and both energy storage and expenditure through integration of humoral, neural and nutrient-related signals and cues. Hypothalamic neurons and glial cells act jointly to orchestrate, both spatially and temporally, regulated metabolic functions of the hypothalamus. Thus, the existence of a causal link between hypothalamic inflammation and deregulations of feeding behavior, such as involuntary weight-loss or obesity, has been suggested. Among the inflammatory mediators that could induce deregulations of hypothalamic control of the energy balance, chemokines represent interesting candidates. Indeed, chemokines, primarily known for their chemoattractant role of immune cells to the inflamed site, have also been suggested capable of neuromodulation. Thus, chemokines could disrupt cellular activity together with synthesis and/or secretion of multiple neurotransmitters/mediators that are involved in the maintenance of energy balance. Here, we relate, on one hand, recent results showing the primary role of the central chemokinergic signaling CCL2/CCR2 for metabolic and behavioral adaptation to high-grade inflammation, especially loss of appetite and weight, through its activity on hypothalamic neurons producing the orexigenic peptide Melanin-Concentrating Hormone (MCH) and, on the other hand, results that suggest that chemokines could also deregulate hypothalamic neuropeptidergic circuits to induce an opposite phenotype and eventually participate in the onset/development of obesity. In more details, we will emphasize a study recently showing, in a model of high-grade acute inflammation of LPS injection in mice, that central CCL2/CCR2 signaling is of primary importance for several aspects explaining weight loss associated with inflammation: after LPS injection, animals lose weight, reduce their food intake, increase their fat oxidation (thus energy consumption from fat storage)...These inflammation-induced metabolic and behavioral changes are reduced when central CCR2 signaling is disrupted either pharmacologically (by a specific inhibitor of CCR2) or genetically (in mice deficient for CCR2). This underlines the importance of this signaling in inflammation-related weight loss. We further determined that the LPS-induced and CCR2-mediated weight loss depends on the direct effect of CCR2 activation on MCH neurons activity. Indeed, the MCH neurons express CCR2, and the application of CCL2 on brain slices revealed that activation of CCR2 actually depolarizes MCH neurons and induces delays and/or failures of action potential emission. Furthermore, CCL2 is able to reduce KCl-evoked MCH secretion from hypothalamic explants. Taken together, these results demonstrate the role of the central CCL2/CCR2 signaling in metabolic and behavioral adaptation to inflammation. On the other hand, this first description of how the chemokinergic system can actually modulate the activity of the hypothalamic regulation of energy balance, but also some less advanced studies and some unpublished data, suggest that some other chemokines, such as CCL5, could participate in the development of the opposite phenotype, that is to say obesity.

Hypothalamic Inflammation and Energy Balance Disruptions: Spotlight on Chemokines

The hypothalamus is a key brain region in the regulation of energy balance as it controls food intake and both energy storage and expenditure through integration of humoral, neural, and nutrient-related signals and cues. Many years of research have focused on the regulation of energy balance by hypothalamic neurons, but the most recent findings suggest that neurons and glial cells, such as microglia and astrocytes, in the hypothalamus actually orchestrate together several metabolic functions. Because glial cells have been described as mediators of inflammatory processes in the brain, the existence of a causal link between hypothalamic inflammation and the deregulations of feeding behavior, leading to involuntary weight loss or obesity for example, has been suggested. Several inflammatory pathways that could impair the hypothalamic control of energy balance have been studied over the years such as, among others, toll-like receptors and canonical cytokines. Yet, less studied so far, chemokines also represent interesting candidates that could link the aforementioned pathways and the activity of hypothalamic neurons. Indeed, chemokines, in addition to their role in attracting immune cells to the inflamed site, have been suggested to be capable of neuromodulation. Thus, they could disrupt cellular activity together with synthesis and/or secretion of multiple neurotransmitters/mediators involved in the maintenance of energy balance. This review discusses the different inflammatory pathways that have been identified so far in the hypothalamus in the context of feeding behavior and body weight control impairments, with a particular focus on chemokines signaling that opens a new avenue in the understanding of the major role played by inflammation in obesity.

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.

Molecular and neuroendocrine mechanisms of cancer cachexia

Cancer and its morbidities, such as cancer cachexia, constitute a major public health problem. Although cancer cachexia has afflicted humanity for centuries, its underlying multifactorial and complex physiopathology has hindered the understanding of its mechanism. During the last few decades we have witnessed a dramatic increase in the understanding of cancer cachexia pathophysiology. Anorexia and muscle and adipose tissue wasting are the main features of cancer cachexia. These apparently independent symptoms have humoral factors secreted by the tumor as a common cause. Importantly, the hypothalamus has emerged as an organ that senses the peripheral signals emanating from the tumoral environment, and not only elicits anorexia but also contributes to the development of muscle and adipose tissue loss. Herein, we review the roles of factors secreted by the tumor and its effects on the hypothalamus, muscle and adipose tissue, as well as highlighting the key targets that are being exploited for cancer cachexia treatment.

Glucose regulates amyloid β production via AMPK

Alzheimer's disease (AD) is the most common form of dementia in the elderly. Accumulation of Aβ peptides in the brain has been suggested as the cause of AD (amyloid cascade hypothesis); however, the mechanism for the abnormal accumulation of Aβ in the brains of AD patients remains unclear. A plethora of evidence has emerged to support a link between metabolic disorders and AD. This study was designed to examine the relationship between energy status and Aβ production. Neuro 2a neuroblastoma cells overexpressing human amyloid precursor protein 695 (APP cells) were cultured in media containing different concentrations of glucose and agonist or antagonist of AMP-activated-protein-kinase (AMPK), a metabolic master sensor. The results showed that concentrations of glucose in the culture media were negatively associated with the activation statuses of AMPK in APP cells, but positively correlated with the levels of secreted Aβ. Modulating AMPK activities affected the production of Aβ. If APP cells were cultured in high glucose medium (i.e., AMPK was inactive), stimulation of AMPK activity decreased the production levels of Aβ. On the contrary, if APP cells were incubated in medium containing no glucose (i.e., AMPK was activated), inhibition of AMPK activity largely increased Aβ production. As AMPK activation is a common defect in metabolic abnormalities, our study supports the premise that metabolic disorders may aggravate AD pathogenesis.

In vitro and in vivo targeting of bladder carcinoma with metformin in combination with cisplatin

Bladder cancer is the ninth most common carcinoma worldwide, and improving the sensitivity of this cancer to chemotherapy is a current clinical challenge. Metformin is a potentially useful therapeutic agent for the treatment of certain types of cancer. In the present study, metformin and cisplatin (a first-line chemotherapeutic agent for the treatment of bladder cancer) were administered to T24 and BIU-87 bladder cancer cells lines alone or in combination, prior to undergoing MTT assay and fluorescence-activated cell sorting analysis to determine cell viability and cell cycle distribution, respectively. Western blotting was used to examine the expression of proteins associated with the AMP-activated protein kinase (AMPK) and mammalian target of rapamycin (mTOR) signaling pathways. In addition, a xenograft model was constructed to evaluate the antitumor efficacy of metformin and cisplatin treatment, alone or in combination. Immunohistochemistry was performed to detect the expression levels of proteins associated with xenograft growth and angiogenesis. Furthermore, western blotting was performed to observe the expression of proteins associated with the AKT/mTOR signaling pathway in the xenograft model. The results demonstrated that the treatment of T24 and BIU-87 cells with metformin or cisplatin resulted in decreased tumor cell proliferation. However, the joint application of metformin and cisplatin was significantly more effective than that of each compound alone (P<0.05). Similarly, cells more markedly accumulated in the sub-G1 phase following joint treatment with metformin and cisplatin, compared with metformin or cisplatin treatment alone. In addition, human cell cycle signaling pathway western blotting arrays were performed, which identified the marked downregulation of phosphorylated (p)-mTOR and unchanged expression of p-AMPK, AMPK and mTOR following combined treatment with cisplatin and metformin. Concurrently, combined use of metformin and cisplatin markedly inhibited the growth and angiogenesis of xenografts generated from BIU-87 cells. Immunohistochemical analysis revealed that downregulation of the expression of specific proteins associated with AMPK promoted xenograft growth and angiogenesis, while western blotting revealed inhibition of the AKT/mTOR signaling pathway in xenografts treated with metformin in combination with cisplatin. Overall, the results of the present study demonstrated that the concurrent administration of metformin and cisplatin may result in enhanced antitumor efficacy compared with that of one agent alone, thus, providing a potential novel therapeutic strategy for the treatment of bladder cell carcinoma.

Metformin reduces the Walker-256 tumor development in obese-MSG rats via AMPK and FOXO3a

AIMS

Studies have associated obesity with a wide variety of cancers. Metformin, an anti-diabetic drug, has recently received attention as a potentially useful therapeutic agent for treating cancer. Therefore, the objective of this study was to analyze the mechanisms involved in the increase in tumor development and the reduction of it by metformin in obesity using an experimental breast tumor model.

MATERIAL AND METHODS

Newborn male Wistar rats were subcutaneously injected with 400mg/kg monosodium glutamate (MSG) (obese) or saline (control) at 2, 3, 4, 5 and 6 days of age. After 16 weeks, 1 × 10(7) Walker-256 tumor cells were subcutaneously injected in the right flank of the rats and concomitantly the treatment with metformin 300 mg/kg/15 days, via gavage, started. The rats were divided into 4 groups: control tumor (CT), control tumor metformin (CTM), obese-MSG tumor (OT) and obese-MSG tumor metformin (OTM). On the 18th week the tumor development and metformin effect were analyzed.

KEY FINDINGS

Tumor development was higher in OT rats compared with CT rats. Activation of insulin-IR-ERK1/2 pathway and an anti-apoptotic effect might be the mechanisms involved in the higher development of tumor in obesity. The effect of metformin reducing the tumor development in obese rats might involve increased mRNA expression of pRb and p27, increased activity of AMPK and FOXO3a and decreased expression of p-ERK1/2 (Thr202/Tyr204) in Walker-256 tumor.

SIGNIFICANCE

Our data allow us to suggest that metformin, reducing the stimulatory effect of obesity on tumor development, has a potential role in the management of cancers.

Hypothalamic inflammation and the central nervous system control of energy homeostasis

The control of energy homeostasis relies on robust neuronal circuits that regulate food intake and energy expenditure. Although the physiology of these circuits is well understood, the molecular and cellular response of this program to chronic diseases is still largely unclear. Hypothalamic inflammation has emerged as a major driver of energy homeostasis dysfunction in both obesity and anorexia. Importantly, this inflammation disrupts the action of metabolic signals promoting anabolism or supporting catabolism. In this review, we address the evidence that favors hypothalamic inflammation as a factor that resets energy homeostasis in pathological states.

Metformin induces apoptosis and cell cycle arrest mediated by oxidative stress, AMPK and FOXO3a in MCF-7 breast cancer cells

Recent studies have demonstrated that the anti-diabetic drug, metformin, can exhibit direct antitumoral effects, or can indirectly decrease tumor proliferation by improving insulin sensitivity. Despite these recent advances, the underlying molecular mechanisms involved in decreasing tumor formation are not well understood. In this study, we examined the antiproliferative role and mechanism of action of metformin in MCF-7 cancer cells treated with 10 mM of metformin for 24, 48, and 72 hours. Using BrdU and the MTT assay, it was found that metformin demonstrated an antiproliferative effect in MCF-7 cells that occurred in a time- and concentration- dependent manner. Flow cytometry was used to analyze markers of cell cycle, apoptosis, necrosis and oxidative stress. Exposure to metformin induced cell cycle arrest in G₀-G₁ phase and increased cell apoptosis and necrosis, which were associated with increased oxidative stress. Gene and protein expression were determined in MCF-7 cells by real time RT-PCR and western blotting, respectively. In MCF-7 cells metformin decreased the activation of IRβ, Akt and ERK1/2, increased p-AMPK, FOXO3a, p27, Bax and cleaved caspase-3, and decreased phosphorylation of p70S6K and Bcl-2 protein expression. Co-treatment with metformin and H₂O₂ increased oxidative stress which was associated with reduced cell number. In the presence of metformin, treating with SOD and catalase improved cell viability. Treatment with metformin resulted in an increase in p-p38 MAPK, catalase, MnSOD and Cu/Zn SOD protein expression. These results show that metformin has an antiproliferative effect associated with cell cycle arrest and apoptosis, which is mediated by oxidative stress, as well as AMPK and FOXO3a activation. Our study further reinforces the potential benefit of metformin in cancer treatment and provides novel mechanistic insight into its antiproliferative role.

The role of neuronal AMPK as a mediator of nutritional regulation of food intake and energy homeostasis

Hypothalamic 5'-adenosine monophosphate-activated protein kinase (AMPK) senses intracellular metabolic stress, i.e., an increase in the cellular AMP:ATP ratio, and integrates diverse hormonal and nutritional signals to restore energy balance. Recent evidence suggests that different nutrients can modulate AMPK activity in the hypothalamus, thereby controlling weight gain through a leptin-independent mechanism. Understanding the mechanisms by which nutrients control hypothalamic AMPK activity is crucial to the development of effective nutritional interventions for the treatment of food intake-related disorders, such as anorexia and obesity. This article highlights the current evidence for the intricate relationship between nutrients and hypothalamic AMPK activity.

Intracerebroventricular injection of metformin induces anorexia in rats

BACKGROUND

Metformin, an oral biguanide insulin-sensitizing agent, is well known to decrease appetite. Although there is evidence that metformin could affect the brain directly, the exact mechanism is not yet known.

METHODS

To evaluate whether metformin induces anorexia via the hypothalamus, various concentrations of metformin were injected into the lateral ventricle of rats through a chronically implanted catheter and food intake was measured for 24 hours. The hypothalamic neuropeptides associated with regulation of food intake were also analyzed following 1 hour of intracerebroventricular (ICV) injections of metformin.

RESULTS

An ICV injection of metformin decreased food intake in a dose-dependent manner in unrestrained conscious rats. Hypothalamic phosphorylated AMP-activated protein kinase (pAMPK) increased by 3 µg with metformin treatment, but there was no further increase in pAMPK with increases in metformin dosage. The hypothalamic phosphorylated signal transducer and activator of transcription 3 (pSTAT3) increased by 3 µg with metformin treatment, but, there was no further increase in pSTAT3 level following increases of metformin dosage. Hypothalamic proopiomelanocortin was elevated with metformin treatment, while neuropeptide Y was not significantly changed.

CONCLUSION

Our results suggest that metformin induces anorexia via direct action in the hypothalamus and the increase in pSTAT3, at least in part, is involved in the process. However, hypothalamic pAMPK appears not to contribute to metformin-induced appetite reduction in normal rats. Further studies exploring new pathways connecting metformin and feeding regulation are needed.

The effect of metformin on food intake and its potential role in hypothalamic regulation in obese diabetic rats

Metformin appears to be involved in altering energy expenditure and thermogenesis, and could affect hypothalamic feeding circuits. However, it is not clear whether metformin is able to cross the blood-brain barrier (BBB) to reach the hypothalamus and exert a direct effect on the central nervous system. Here we show the presence of metformin in cerebrospinal fluid (CSF) of diabetic rats administered orally with metformin which was confirmed by detecting the concentration of metformin with liquid chromatography-tandem mass spectrometry. Food intake of diabetic rats treated with metformin was reduced, and glucose homeostasis was gained. Expression of orexigenic peptides neuropeptide Y (NPY) and agouti-related protein (AgRP) decreased in the hypothalamus of metformin-treated diabetic rats, though anorexigenic peptides pro-opiomelanocortin (POMC) did not change significantly. The phosphorylation of signal transducer and activator of transcription 3 (STAT3) was increased but phosphorylated AMP-activated kinase (AMPK) was similar in the hypothalamus of metformin-treated diabetic rats. Our findings suggest that metformin may cross BBB and play a central mechanism on regulation of food intake in the hypothalamus. The anorexic effect of metformin may be mediated by inhibition of NPY and AgRP gene expression through the STAT3 signaling pathway.

Central nervous system inflammation induces muscle atrophy via activation of the hypothalamic-pituitary-adrenal axis

Systemic and CNS-delimited inflammation triggers skeletal muscle catabolism in a manner dependent on glucocorticoid signaling.

Skeletal muscle catabolism is a co-morbidity of many chronic diseases and is the result of systemic inflammation. Although direct inflammatory cytokine action on muscle promotes atrophy, nonmuscle sites of action for inflammatory mediators are less well described. We demonstrate that central nervous system (CNS)–delimited interleukin 1β (IL-1β) signaling alone can evoke a catabolic program in muscle, rapidly inducing atrophy. This effect is dependent on hypothalamic–pituitary–adrenal (HPA) axis activation, as CNS IL-1β–induced atrophy is abrogated by adrenalectomy. Furthermore, we identified a glucocorticoid-responsive gene expression pattern conserved in models of acute and chronic inflammatory muscle atrophy. In contrast with studies suggesting that the direct action of inflammatory cytokines on muscle is sufficient to induce catabolism, adrenalectomy also blocks the atrophy program in response to systemic inflammation, demonstrating that glucocorticoids are requisite for this process. Additionally, circulating levels of glucocorticoids equivalent to those produced under inflammatory conditions are sufficient to cause profound muscle wasting. Together, these data suggest that a significant component of inflammation-induced muscle catabolism occurs indirectly via a relay in the CNS.

Low-grade hypothalamic inflammation leads to defective thermogenesis, insulin resistance, and impaired insulin secretion

Hypothalamic inflammation is present in animal models of obesity, and the intracerebroventricular injection of TNFα can reproduce a number of features of the hypothalamus of obese animals. Because obesity is a risk factor for type 2 diabetes (DM2) we hypothesized that, by inducing hypothalamic inflammation, we could reproduce some clinical features of DM2. Lean Wistar rats and TNF receptor 1-knockout mice were employed to determine the effects of hypothalamic actions of TNFα on thermogenesis and metabolic parameters. Signal transduction and protein expression were evaluated by immunoblot and real-time PCR. Thermogenesis was evaluated in living rats, and respirometry was determined in isolated muscle fiber. In Wistar rats, hypothalamic TNFα blunts the anorexigenic effect of leptin, which is accompanied by reduced leptin signaling and increased expression of suppressor of cytokine signaling 3. In addition, hypothalamic TNFα reduces O(2) consumption and the expression of thermogenic proteins in brown adipose tissue and skeletal muscle. Furthermore, hypothalamic inflammation increases base-line plasma insulin and insulin secretion by isolated pancreatic islets, which is accompanied by an impaired insulin signal transduction in liver and skeletal muscle. Hypothalamic inflammation induced by stearic acid also reduces O(2) consumption and blunts peripheral insulin signal transduction. The use of intracerebroventricular infliximab restores O(2) consumption in obese rats, whereas TNF receptor 1-knockout mice are protected from diet-induced reduced thermogenesis and defective insulin signal transduction. Thus, low-grade inflammation of the hypothalamus is sufficient to induce changes in a number of parameters commonly impaired in obesity and DM2, and TNFα is an important mediator of this process.

Metformin reduces the stimulatory effect of obesity on in vivo Walker-256 tumor development and increases the area of tumor necrosis

AIMS

The objective of this study was to analyze the influence of obesity and insulin resistance on tumor development and, in turn, the effect of insulin sensitizing agents.

MAIN METHODS

Male offspring of Wistar rats received monosodium glutamate (400mg/kg) (obese) or saline (control) from the second to sixth day after birth. Sixteen-week-old control and obese rats received 5×10(5) Walker-256 tumor cells, subcutaneously injected into the right flank. Some of the obese and control rats received concomitant treatment with metformin (300mg/kg) by gavage. At the 18th week, obesity was characterized. The percentage of rats that developed tumors, the tumor relative weight and the percentage of cachexia incidence were analyzed. The tumor tissue was evaluated histologically by means of hematoxylin and eosin staining.

KEY FINDINGS

Metformin did not correct the insulin resistance in obese rats. The tumor development was significantly higher in the obese group, whereas metformin treatment reduced it. After pathological analysis, we observed that the tumor tissues were similar in all groups except for adipocytes, which were found in greater quantity in the obese and metformin-treated obese groups. The area of tumor necrosis was higher in the group treated with metformin when compared with the untreated one.

SIGNIFICANCE

Metformin reduced Walker-256 tumor development but not cachexia in obese rats. The reduction occurred independently of the correction of insulin resistance. Metformin increased the area of necrosis in tumor tissues, which may have contributed to the reduced tumor development.

Prenatal androgenization of female mice programs an increase in firing activity of gonadotropin-releasing hormone (GnRH) neurons that is reversed by metformin treatment in adulthood

Prenatal androgenization (PNA) of female mice with dihydrotestosterone programs reproductive dysfunction in adulthood, characterized by elevated luteinizing hormone levels, irregular estrous cycles, and central abnormalities. Here, we evaluated activity of GnRH neurons from PNA mice and the effects of in vivo treatment with metformin, an activator of AMP-activated protein kinase (AMPK) that is commonly used to treat the fertility disorder polycystic ovary syndrome. Estrous cycles were monitored in PNA and control mice before and after metformin administration. Before metformin, cycles were longer in PNA mice and percent time in estrus lower; metformin normalized cycles in PNA mice. Extracellular recordings were used to monitor GnRH neuron firing activity in brain slices from diestrous mice. Firing rate was higher and quiescence lower in GnRH neurons from PNA mice, demonstrating increased GnRH neuron activity. Metformin treatment of PNA mice restored firing activity and LH to control levels. To assess whether AMPK activation contributed to the metformin-induced reduction in GnRH neuron activity, the AMPK antagonist compound C was acutely applied to cells. Compound C stimulated cells from metformin-treated, but not untreated, mice, suggesting that AMPK was activated in GnRH neurons, or afferent neurons, in the former group. GnRH neurons from metformin-treated mice also showed a reduced inhibitory response to low glucose. These studies indicate that PNA causes enhanced firing activity of GnRH neurons and elevated LH that are reversible by metformin, raising the possibility that central AMPK activation by metformin may play a role in its restoration of reproductive cycles in polycystic ovary syndrome.

Pathophysiology and treatment of inflammatory anorexia in chronic disease

Decreased appetite and involuntary weight loss are common occurrences in chronic disease and have a negative impact on both quality of life and eventual mortality. Weight loss in chronic disease comes from both fat and lean mass, and is known as cachexia. Both alterations in appetite and body weight loss occur in a wide variety of diseases, including cancer, heart failure, renal failure, chronic obstructive pulmonary disease and HIV. An increase in circulating inflammatory cytokines has been implicated as a uniting pathogenic mechanism of cachexia and associated anorexia. One of the targets of inflammatory mediators is the central nervous system, and in particular feeding centers in the hypothalamus located in the ventral diencephalon. Current research has begun to elucidate the mechanisms by which inflammation reaches the hypothalamus, and the neural substrates underlying inflammatory anorexia. Research into these neural mechanisms has suggested new therapeutic possibilities, which have produced promising results in preclinical and clinical trials. This review will discuss inflammatory signaling in the hypothalamus that mediates anorexia, and the opportunities for therapeutic intervention that these mechanisms present.

Hypothalamic actions of tumor necrosis factor alpha provide the thermogenic core for the wastage syndrome in cachexia

TNFalpha is an important mediator of catabolism in cachexia. Most of its effects have been characterized in peripheral tissues, such as skeletal muscle and fat. However, by acting directly in the hypothalamus, TNFalpha can activate thermogenesis and modulate food intake. Here we show that high concentration TNFalpha in the hypothalamus leads to increased O(2) consumption/CO(2) production, increased body temperature, and reduced caloric intake, resulting in loss of body mass. Most of the thermogenic response is produced by beta 3-adrenergic signaling to the brown adipose tissue (BAT), leading to increased BAT relative mass, reduction in BAT lipid quantity, and increased BAT mitochondria density. The expression of proteins involved in BAT thermogenesis, such as beta 3-adrenergic receptor, peroxisomal proliferator-activated receptor-gamma coactivator-1 alpha, and uncoupling protein-1, are increased. In the hypothalamus, TNFalpha produces reductions in neuropeptide Y, agouti gene-related peptide, proopiomelanocortin, and melanin-concentrating hormone, and increases CRH and TRH. The activity of the AMP-activated protein kinase signaling pathway is also decreased in the hypothalamus of TNFalpha-treated rats. Upon intracerebroventricular infliximab treatment, tumor-bearing and septic rats present a significantly increased survival. In addition, the systemic inhibition of beta 3-adrenergic signaling results in a reduced body mass loss and increased survival in septic rats. These data suggest hypothalamic TNFalpha action to be important mediator of the wastage syndrome in cachexia.

Metformin increases phagocytosis and acidifies lysosomal/endosomal compartments in AMPK-dependent manner in rat primary microglia

Recent evidence suggests that metformin shows beneficial effects in experimental models of neuroinflammatory diseases. The aim of the present study was to determine the effect of metformin on phagocytosis and acidification of lysosomal/endosomal compartments in rat primary microglia in the presence of lipopolysaccharide (LPS) and/or beta-peptides (25-35), (1-40), and (1-42). Metformin increased the phagocytosis of fluorescent microspheres in the presence or absence of all the beta-peptides. However, the drug had no effect on the phagocytosis in LPS-stimulated microglia regardless of the presence of all the beta-peptides. Metformin acidified the lysosomal/endosomal compartments in the presence or absence of the beta-peptide 1-40 in both resting and activated microglia. To elucidate the mechanism of metformin action, we used 5-aminoimidazole-4-carboxamide-1-beta-D-ribofuranoside as an activator of adenosine monophosphate-activated protein kinase (AMPK) and compound C as a confirmed pharmacological inhibitor of AMPK. We have shown that metformin increased AMPK activity in microglial cells and that all observed effects are AMPK-dependent because the pretreatment of microglia with compound C reversed the effects of the drug. Since degradation of proteins in lysosomal/endosomal compartments depends largely on their phagocytosis and acidification, metformin may be beneficial in proteinopathies affecting the brain.

Exercício físico reduz a hiperglicemia de jejum em camundongos diabéticos através da ativação da AMPK

INTRODUÇÃO: A deficiência na captação de glicose em tecidos periféricos e o aumento da gliconeogênese hepática são fenômenos fisiopatológicos observados em pacientes diabéticos do tipo 2. O exercício físico é considerado um importante aliado para a melhora do perfil glicêmico em pacientes diabéticos; entretanto, os mecanismos envolvidos nesse processo não estão completamente elucidados. OBJETIVO: Avaliar o papel da proteína AMPK no controle glicêmico em camundongos diabéticos após o exercício físico. MÉTODOS: Durante o jejum, o teste de tolerância à insulina (ITT) e a técnica de Western blot foram combinados para avaliar a homeostase da glicose em camundongos diabéticos (ob/ob e db/db) submetidos a uma única sessão de natação. RESULTADOS: A hiperglicemia de jejum, a severa resistência à insulina e a deficiência na sinalização da via AMPK/ACC no músculo e no fígado observadas nos camundongos diabéticos foram revertidas após a sessão de exercício. A restauração da via AMPK/ACC reduziu a expressão da enzima gliconeogênica PEPCK no fígado e aumentou a translocação do GLUT4 no músculo esquelético. Esses dados apontam que a ativação da via AMPK/ACC induzida pelo exercício físico é importante para a redução da glicemia de jejum em modelos experimentais de diabetes tipo 2. Esses dados abrem novas frentes para o entendimento de como a atividade física controla da homeostase da glicose em pacientes diabéticos.

Inhibition of hypothalamic Foxo1 expression reduced food intake in diet-induced obesity rats

Insulin signalling in the hypothalamus plays a role in maintaining body weight. The forkhead transcription factor Foxo1 is an important mediator of insulin signalling in the hypothalamus. Foxo1 stimulates the transcription of the orexigenic neuropeptide Y and Agouti-related protein through the phosphatidylinositol-3-kinase/Akt signalling pathway, but the role of hypothalamic Foxo1 in insulin resistance and obesity remains unclear. Here, we identify that a high-fat diet impaired insulin-induced hypothalamic Foxo1 phosphorylation and degradation, increasing the nuclear Foxo1 activity and hyperphagic response in rats. Thus, we investigated the effects of the intracerebroventricular (i.c.v.) microinfusion of Foxo1-antisense oligonucleotide (Foxo1-ASO) and evaluated the food consumption and weight gain in normal and diet-induced obese (DIO) rats. Three days of Foxo1-ASO microinfusion reduced the hypothalamic Foxo1 expression by about 85%. i.c.v. infusion of Foxo1-ASO reduced the cumulative food intake (21%), body weight change (28%), epididymal fat pad weight (22%) and fasting serum insulin levels (19%) and increased the insulin sensitivity (34%) in DIO but not in control animals. Collectively, these data showed that the Foxo1-ASO treatment blocked the orexigenic effects of Foxo1 and prevented the hyperphagic response in obese rats. Thus, pharmacological manipulation of Foxo1 may be used to prevent or treat obesity.

Brain lipogenesis and regulation of energy metabolism

PURPOSE OF REVIEW

To revise current available information related to the role of brain lipogenic pathways in the regulation of energy homeostasis.

RECENT FINDINGS

The 'classical' hypothalamic neuropeptide view of feeding regulation has been extensively reviewed and revised during the past few years. Accumulating evidence indicates that the modulation of lipogenesis de novo in the hypothalamus, through selective pharmacologic and genetic manipulation of acetyl-CoA carboxylase, AMP-activated protein kinase, carnitine palmitoyltransferase 1, fatty acid synthase and malonyl-CoA decarboxylase enzymes, has a severe impact on food intake and body weight homeostasis. Furthermore, as these manipulations alter the hypothalamic pool of lipids, such as malonyl-CoA or long chain fatty acyl-CoA or both, the concept of lipids as signals of nutrient abundance able to modulate feeding in the hypothalamus has recently re-emerged.

SUMMARY

In this review, we summarize what is known about brain lipogenesis and energy balance and propose further avenues of research. Defining these novel mechanisms could offer new targets for the treatment of obesity and metabolic syndrome.

A central role for neuronal AMP-activated protein kinase (AMPK) and mammalian target of rapamycin (mTOR) in high-protein diet-induced weight loss

OBJECTIVE

A high-protein diet (HPD) is known to promote the reduction of body fat, but the mechanisms underlying this change are unclear. AMP-activated protein kinase (AMPK) and mammalian target of rapamycin (mTOR) function as majors regulators of cellular metabolism that respond to changes in energy status, and recent data demonstrated that they also play a critical role in systemic energy balance. Here, we sought to determine whether the response of the AMPK and mTOR pathways could contribute to the molecular effects of an HPD.

RESEARCH DESIGN AND METHODS

Western blotting, confocal microscopy, chromatography, light microscopy, and RT-PCR assays were combined to explore the anorexigenic effects of an HPD.

RESULTS

An HPD reduced food intake and induced weight loss in both normal rats and ob/ob mice. The intracerebroventricular administration of leucine reduced food intake, and the magnitude of weight loss and reduction of food intake in a leucine-supplemented diet are similar to that achieved by HPD in normal rats and in ob/ob mice, suggesting that leucine is a major component of the effects of an HPD. Leucine and HPD decrease AMPK and increase mTOR activity in the hypothalamus, leading to inhibition of neuropeptide Y and stimulation of pro-opiomelanocortin expression. Consistent with a cross-regulation between AMPK and mTOR to control food intake, our data show that the activation of these enzymes occurs in the same specific neuronal subtypes.

CONCLUSIONS

These findings provide support for the hypothesis that AMPK and mTOR interact in the hypothalamus to regulate feeding during HPD in a leucine-dependent manner.