Whole-body lipolysis and triglyceride-fatty acid cycling in cachectic patients with esophageal cancer

Futile lipid cycling: from biochemistry to physiology

In the healthy state, the fat stored in our body isn't just inert. Rather, it is dynamically mobilized to maintain an adequate concentration of fatty acids (FAs) in our bloodstream. Our body tends to produce excess FAs to ensure that the FA availability is not limiting. The surplus FAs are actively re-esterified into glycerides, initiating a cycle of breakdown and resynthesis of glycerides. This cycle consumes energy without generating a new product and is commonly referred to as the 'futile lipid cycle' or the glyceride/FA cycle. Contrary to the notion that it's a wasteful process, it turns out this cycle is crucial for systemic metabolic homeostasis. It acts as a control point in intra-adipocyte and inter-organ cross-talk, a metabolic rheostat, an energy sensor and a lipid diversifying mechanism. In this Review, we discuss the metabolic regulation and physiological implications of the glyceride/FA cycle and its mechanistic underpinnings.

Energy Expenditure in Upper Gastrointestinal Cancers: a Scoping Review

Malnutrition is prevalent in people with upper gastrointestinal (GI) cancers and is associated with shorter survival and poor quality of life. In order to effectively prevent or treat malnutrition, nutrition interventions must ensure appropriate energy provision to meet daily metabolic demands. In practice, the energy needs of people with cancer are frequently estimated from predictive equations which are not cancer-specific and are demonstrated to be inaccurate in this population. The purpose of this scoping review was to synthesize the existing evidence regarding energy expenditure in people with upper GI cancer. Three databases (Ovid MEDLINE, Embase via Ovid, CINAHL plus) were systematically searched to identify studies reporting on resting energy expenditure using indirect calorimetry and total energy expenditure using doubly labeled water (DLW) in adults with any stage of upper GI cancer at any point from diagnosis. A total of 57 original research studies involving 2,125 individuals with cancer of the esophagus, stomach, pancreas, biliary tract, or liver were eligible for inclusion. All studies used indirect calorimetry, and one study used DLW to measure energy expenditure, which was reported unadjusted in 42 studies, adjusted for body weight in 32 studies, and adjusted for fat-free mass in 13 studies. Energy expenditure in upper GI cancer was compared with noncancer controls in 19 studies and measured compared with predicted energy expenditure reported in 31 studies. There was heterogeneity in study design and in reporting of important clinical characteristics between studies. There was also substantial variation in energy expenditure between studies and within and between cancer types. Given this heterogeneity and known inaccuracies of predictive equations in patients with cancer, energy expenditure should be measured in practice wherever feasible. Additional research in cohorts defined by cancer type, stage, and treatment is needed to further characterize energy expenditure in upper GI cancer.

Targeting Strategies for Aberrant Lipid Metabolism Reprogramming and the Immune Microenvironment in Esophageal Cancer: A Review

Esophageal cancer is of high importance to occurrence, development, and treatment resistance. As evidenced by recent studies, pathways (e.g., Wnt/β-catenin, AMPK, and Hippo) are critical to the proliferation, differentiation, and self-renewal of esophageal cancer. In addition, the above pathways play a certain role in regulating esophageal cancer and act as potential therapeutic targets. Over the past few years, the function of lipid metabolism in controlling tumor cells and immune cells has aroused extensive attention. It has been reported that there are intricate interactions between lipid metabolism reprogramming between immune and esophageal cancer cells, whereas molecular mechanisms should be studied in depth. Immune cells have been commonly recognized as a vital player in the esophageal cancer microenvironment, having complex crosstalk with cancer cells. It is increasingly evidenced that the function of immune cells in the tumor microenvironment (TME) is significantly correlated with abnormal lipid metabolism. In this review, the latest findings in lipid metabolism reprogramming in TME are summarized, and the above findings are linked to esophageal cancer progression. Aberrant lipid metabolism and associated signaling pathways are likely to serve as a novel strategy to treat esophageal cancer through lipid metabolism reprogramming.

Beyond appetite regulation: Targeting energy expenditure, fat oxidation, and lean mass preservation for sustainable weight loss

New appetite-regulating antiobesity treatments such as semaglutide and agents under investigation such as tirzepatide show promise in achieving weight loss of 15% or more. Energy expenditure, fat oxidation, and lean mass preservation are important determinants of weight loss and weight-loss maintenance beyond appetite regulation. This review discusses prior failures in clinical development of weight-loss drugs targeting energy expenditure and explores novel strategies for targeting energy expenditure: mitochondrial proton leak, uncoupling, dynamics, and biogenesis; futile calcium and substrate cycling; leptin for weight maintenance; increased sympathetic nervous system activity; and browning of white fat. Relevant targets for preserving lean mass are also reviewed: growth hormone, activin type II receptor inhibition, and urocortin 2 and 3. We endorse moderate modulation of energy expenditure and preservation of lean mass in combination with efficient appetite reduction as a means of obtaining a significant, safe, and long-lasting weight loss. Furthermore, we suggest that the regulatory guidelines should be revisited to focus more on the quality of weight loss and its maintenance rather than the absolute weight loss. Commitment to this research focus both from a scientific and from a regulatory point of view could signal the beginning of the next era in obesity therapies.

Challenges in parenteral nutrition in adult ultrashort gut: A case of cachexia

Patients with ultrashort gut have inadequate nutrient absorption. Parenteral nutrition (PN) is required to meet nutrition requirements caused by chronic intestinal failure (IF). We present a case of cachexia and IF caused by ultrashort gut following an extensive small-bowel resection caused by volvulus that was complicated by small-bowel ischemia. Targeting energy prescriptions to optimize PN using indirect calorimetry in this population with ultrashort gut has not been reported in adults. This case serves to outline the challenges in optimizing PN, including factors such as anabolic status, to meet nutrition requirements in patients with ultrashort gut and cachexia.

Mitochondrial TNAP controls thermogenesis by hydrolysis of phosphocreatine

Adaptive thermogenesis has attracted much attention because of its ability to increase systemic energy expenditure and to counter obesity and diabetes^1-3. Recent data have indicated that thermogenic fat cells use creatine to stimulate futile substrate cycling, dissipating chemical energy as heat^4,5. This model was based on the super-stoichiometric relationship between the amount of creatine added to mitochondria and the quantity of oxygen consumed. Here we provide direct evidence for the molecular basis of this futile creatine cycling activity in mice. Thermogenic fat cells have robust phosphocreatine phosphatase activity, which is attributed to tissue-nonspecific alkaline phosphatase (TNAP). TNAP hydrolyses phosphocreatine to initiate a futile cycle of creatine dephosphorylation and phosphorylation. Unlike in other cells, TNAP in thermogenic fat cells is localized to the mitochondria, where futile creatine cycling occurs. TNAP expression is powerfully induced when mice are exposed to cold conditions, and its inhibition in isolated mitochondria leads to a loss of futile creatine cycling. In addition, genetic ablation of TNAP in adipocytes reduces whole-body energy expenditure and leads to rapid-onset obesity in mice, with no change in movement or feeding behaviour. These data illustrate the critical role of TNAP as a phosphocreatine phosphatase in the futile creatine cycle.

Diverging metabolic programmes and behaviours during states of starvation, protein malnutrition, and cachexia

BACKGROUND

Our evolutionary history is defined, in part, by our ability to survive times of nutrient scarcity. The outcomes of the metabolic and behavioural adaptations during starvation are highly efficient macronutrient allocation, minimization of energy expenditure, and maximized odds of finding food. However, in different contexts, caloric deprivation is met with vastly different physiologic and behavioural responses, which challenge the primacy of energy homeostasis.

METHODS

We conducted a literature review of scientific studies in humans, laboratory animals, and non-laboratory animals that evaluated the physiologic, metabolic, and behavioural responses to fasting, starvation, protein-deficient or essential amino acid-deficient diets, and cachexia. Studies that investigated the changes in ingestive behaviour, locomotor activity, resting metabolic rate, and tissue catabolism were selected as the focus of discussion.

RESULTS

Whereas starvation responses prioritize energy balance, both protein malnutrition and cachexia present existential threats that induce unique adaptive programmes, which can exacerbate the caloric insufficiency of undernutrition. We compare and contrast the behavioural and metabolic responses and elucidate the mechanistic pathways that drive state-dependent alterations in energy seeking and partitioning.

CONCLUSIONS

The evolution of energetically inefficient metabolic and behavioural responses to protein malnutrition and cachexia reveal a hierarchy of metabolic priorities governed by discrete regulatory networks.

Sepsis Increases Muscle Proteolysis in Severely Burned Adults, but Does not Impact Whole-Body Lipid or Carbohydrate Kinetics

Sepsis is a common and often fatal consequence of severe burn injury, but its exact effects on whole body and muscle metabolism in the burn patient is unclear. To address this, 13 septic and 11 nonseptic patients (age: 36.9 ± 13.0 years) with burns encompassing >30% of their total body surface area underwent muscle protein kinetic studies under postabsorptive conditions using bolus injections of ring-C6 and N phenylalanine isotopes. In parallel, whole-body lipid and carbohydrate kinetics were assessed using constant infusions of [U-C6]palmitate, [6,6-H2]glucose, and [H5]glycerol, and during a 2-h hyperinsulinemic euglycemic clamp. Muscle mRNA levels of genes implicated in the development of muscle cachexia were assessed by qPCR. Fractional breakdown rates of mixed-muscle proteins were found to be 2.4-fold greater in septic versus nonseptic patients (P < 0.05). No discernable differences in fractional synthetic rate of mixed-muscle proteins or rate of appearance of plasma free fatty acids, glycerol, or glucose could be observed between patient groups, although the latter was significantly associated with burn size (P < 0.05). Hyperinsulinemia stimulated whole-body glucose uptake and suppressed endogenous glucose production and whole-body lipolytic rate to equivalent degrees in both groups. Muscle mRNA levels of genes spanning autophagy, lysosomal, and ubiquitin proteasome-mediated proteolysis were not enhanced in septic versus nonseptic patients. Our results demonstrate that accelerated muscle proteolysis appears to be the principal metabolic consequence of sepsis in severe burn patients and could be a contributing factor to the accelerated loss of muscle mass in these individuals. The exact mechanistic basis for these changes remains unclear.

Cisplatin-Induced Skeletal Muscle Dysfunction: Mechanisms and Counteracting Therapeutic Strategies

Among the severe side effects induced by cisplatin chemotherapy, muscle wasting is the most relevant one. This effect is a major cause for a clinical decline of cancer patients, since it is a negative predictor of treatment outcome and associated to increased mortality. However, despite its toxicity even at low doses, cisplatin remains the first-line therapy for several types of solid tumors. Thus, effective pharmacological treatments counteracting or minimizing cisplatin-induced muscle wasting are urgently needed. The dissection of the molecular pathways responsible for cisplatin-induced muscle dysfunction gives the possibility to identify novel promising therapeutic targets. In this context, the use of animal model of cisplatin-induced cachexia is very useful. Here, we report an update of the most relevant researches on the mechanisms underlying cisplatin-induced muscle wasting and on the most promising potential therapeutic options to preserve muscle mass and function.

Opportunities and challenges in the therapeutic activation of human energy expenditure and thermogenesis to manage obesity

The current obesity pandemic results from a physiological imbalance in which energy intake chronically exceeds energy expenditure (EE), and prevention and treatment strategies remain generally ineffective. Approaches designed to increase EE have been informed by decades of experiments in rodent models designed to stimulate adaptive thermogenesis, a long-term increase in metabolism, primarily induced by chronic cold exposure. At the cellular level, thermogenesis is achieved through increased rates of futile cycling, which are observed in several systems, most notably the regulated uncoupling of oxidative phosphorylation from ATP generation by uncoupling protein 1, a tissue-specific protein present in mitochondria of brown adipose tissue (BAT). Physiological activation of BAT and other organ thermogenesis occurs through β-adrenergic receptors (AR), and considerable effort over the past 5 decades has been directed toward developing AR agonists capable of safely achieving a net negative energy balance while avoiding unwanted cardiovascular side effects. Recent discoveries of other BAT futile cycles based on creatine and succinate have provided additional targets. Complicating the current and developing pharmacological-, cold-, and exercise-based methods to increase EE is the emerging evidence for strong physiological drives toward restoring lost weight over the long term. Future studies will need to address technical challenges such as how to accurately measure individual tissue thermogenesis in humans; how to safely activate BAT and other organ thermogenesis; and how to sustain a negative energy balance over many years of treatment.

Plasma Metabolomics Identifies Lipid and Amino Acid Markers of Weight Loss in Patients with Upper Gastrointestinal Cancer

Cachexia is a multifactorial wasting syndrome associated with high morbidity and mortality in patients with cancer. Diagnosis can be difficult and, in the clinical situation, usually relies upon reported weight loss. The ‘omics’ technologies allow us the opportunity to study the end points of many biological processes. Among these, blood-based metabolomics is a promising method to investigate the pathophysiology of human cancer cachexia and identify candidate biomarkers. In this study, we performed liquid chromatography mass spectrometry (LC/MS)-based metabolomics to investigate the metabolic profile of cancer-associated weight loss. Non-selected patients undergoing surgery with curative intent for upper gastrointestinal cancer were recruited. Fasting plasma samples were taken at induction of anaesthesia. LC/MS analysis showed that 6 metabolites were highly discriminative of weight loss. Specifically, a combination profile of LysoPC 18.2, L-Proline, Hexadecanoic acid, Octadecanoic acid, Phenylalanine and LysoPC 16:1 showed close correlation for eight weight-losing samples (≥5% weight loss) and nine weight-stable samples (<5%weight loss) between predicted and actual weight change (r = 0.976, p = 0.0014). Overall, 40 metabolites were associated with ≥5% weight loss. This study provides biological validation of the consensus definition of cancer cachexia (Fearon et al.) and provides feasible candidate markers for further investigation in early diagnosis and the assessment of therapeutic intervention.

Translational Pharmacology and Physiology of Brown Adipose Tissue in Human Disease and Treatment

Human brown adipose tissue (BAT) is experimentally modeled to better understand the biology of this important metabolic tissue, and also to enable the potential discovery and development of novel therapeutics for obesity and sequelae resulting from the persistent positive energy balance. This chapter focuses on translation into humans of findings and hypotheses generated in nonhuman models of BAT pharmacology. Given the demonstrated challenges of sustainably reducing caloric intake in modern humans, potential solutions to obesity likely lie in increasing energy expenditure. The energy-transforming activities of a single cell in any given tissue can be conceptualized as a flow of chemical energy from energy-rich substrate molecules into energy-expending, endergonic biological work processes through oxidative degradation of organic molecules ingested as nutrients. Despite the relatively tight coupling between metabolic reactions and products, some expended energy is incidentally lost as heat, and in this manner a significant fraction of the energy originally captured from the environment nonproductively transforms into heat rather than into biological work. In human and other mammalian cells, some processes are even completely uncoupled, and therefore purely energy consuming. These molecular and cellular actions sum up at the physiological level to adaptive thermogenesis, the endogenous physiology in which energy is nonproductively released as heat through uncoupling of mitochondria in brown fat and potentially skeletal muscle. Adaptive thermogenesis in mammals occurs in three forms, mostly in skeletal muscle and brown fat: shivering thermogenesis in skeletal muscle, non-shivering thermogenesis in brown fat, and diet-induced thermogenesis in brown fat. At the cellular level, the greatest energy transformations in humans and other eukaryotes occur in the mitochondria, where creating energetic inefficiency by uncoupling the conversion of energy-rich substrate molecules into ATP usable by all three major forms of biological work occurs by two primary means. Basal uncoupling occurs as a passive, general, nonspecific leak down the proton concentration gradient across the membrane in all mitochondria in the human body, a gradient driving a key step in ATP synthesis. Inducible uncoupling, which is the active conduction of protons across gradients through processes catalyzed by proteins, occurs only in select cell types including BAT. Experiments in rodents revealed UCP1 as the primary mammalian molecule accounting for the regulated, inducible uncoupling of BAT, and responsive to both cold and pharmacological stimulation. Cold stimulation of BAT has convincingly translated into humans, and older clinical observations with nonselective 2,4-DNP validate that human BAT's participation in pharmacologically mediated, though nonselective, mitochondrial membrane decoupling can provide increased energy expenditure and corresponding body weight loss. In recent times, however, neither beta-adrenergic antagonism nor unselective sympathomimetic agonism by ephedrine and sibutramine provide convincing evidence that more BAT-selective mechanisms can impact energy balance and subsequently body weight. Although BAT activity correlates with leanness, hypothesis-driven selective β3-adrenergic agonism to activate BAT in humans has only provided robust proof of pharmacologic activation of β-adrenergic receptor signaling, limited proof of the mechanism of increased adaptive thermogenesis, and no convincing evidence that body weight loss through negative energy balance upon BAT activation can be accomplished outside of rodents. None of the five demonstrably β3 selective molecules with sufficient clinical experience to merit review provided significant weight loss in clinical trials (BRL 26830A, TAK 677, L-796568, CL 316,243, and BRL 35135). Broader conclusions regarding the human BAT therapeutic hypothesis are limited by the absence of data from most studies demonstrating specific activation of BAT thermogenesis in most studies. Additionally, more limited data sets with older or less selective β3 agonists also did not provide strong evidence of body weight effects. Encouragingly, β3-adrenergic agonists, catechins, capsinoids, and nutritional extracts, even without robust negative energy balance outcomes, all demonstrated increased total energy expenditure that in some cases could be associated with concomitant activation of BAT, though the absence of body weight loss indicates that in no cases did the magnitude of negative energy balance reach sufficient levels. Glucocorticoid receptor agonists, PPARg agonists, and thyroid hormone receptor agonists all possess defined molecular and cellular pharmacology that preclinical models predicted to be efficacious for negative energy balance and body weight loss, yet their effects on human BAT thermogenesis upon translation were inconsistent with predictions and disappointing. A few new mechanisms are nearing the stage of clinical trials and may yet provide a more quantitatively robust translation from preclinical to human experience with BAT. In conclusion, translation into humans has been demonstrated with BAT molecular pharmacology and cell biology, as well as with physiological response to cold. However, despite pharmacologically mediated, statistically significant elevation in total energy expenditure, translation into biologically meaningful negative energy balance was not achieved, as indicated by the absence of measurable loss of body weight over the duration of a clinical study.

Differential Metabolic Responses to Adipose Atrophy Associated with Cancer Cachexia and Caloric Restriction in Rats and the Effect of Rikkunshito in Cancer Cachexia

Despite the similar phenotypes, including weight loss, reduction of food intake, and lower adiposity, associated with caloric restriction (CR) and cancer cachexia (CC), CC is a progressive wasting syndrome, while mild CR improves whole body metabolism. In the present study, we compared adipose metabolic changes in a novel rat model of CC, mild CR (70% of the food intake of control rats, which is similar to the food consumption of CC rats), and severe CR (30% of the food intake of controls). We show that CC and severe CR are associated with much smaller adipocytes with significantly lower mitochondrial DNA content; but, that mild CR is not. CC and both mild and severe CR similarly upregulated proteins involved in lipolysis. CC also downregulated proteins involved in fatty acid biosynthesis, but mild CR upregulated these. These findings suggest that CC might impair de novo fatty acid biosynthesis and reduce mitochondrial biogenesis, similar to severe CR. We also found that rikkunshito, a traditional Japanese herbal medicine, does not ameliorate the enhanced lipolysis and mitochondrial impairment, but rather, rescues de novo fatty acid biosynthesis, suggesting that rikkunshito administration might have partially similar effects to mild CR.

Perilipin 1 (Plin1) deficiency promotes inflammatory responses in lean adipose tissue through lipid dysregulation

Lipid droplets are specialized cellular organelles that contain neutral lipid metabolites and play dynamic roles in energy homeostasis. Perilipin 1 (Plin1), one of the major lipid droplet-binding proteins, is highly expressed in adipocytes. In mice, Plin1 deficiency impairs peripheral insulin sensitivity, accompanied with reduced fat mass. However, the mechanisms underlying insulin resistance in lean Plin1 knockout (Plin1^-/-) mice are largely unknown. The current study demonstrates that Plin1 deficiency promotes inflammatory responses and lipolysis in adipose tissue, resulting in insulin resistance. M1-type adipose tissue macrophages (ATMs) were higher in Plin1^-/- than in Plin1^+/+ mice on normal chow diet. Moreover, using lipidomics analysis, we discovered that Plin1^-/- adipocytes promoted secretion of pro-inflammatory lipid metabolites such as prostaglandins, which potentiated monocyte migration. In lean Plin1^-/- mice, insulin resistance was relieved by macrophage depletion with clodronate, implying that elevated pro-inflammatory ATMs might be attributable for insulin resistance under Plin1 deficiency. Together, these data suggest that Plin1 is required to restrain fat loss and pro-inflammatory responses in adipose tissue by reducing futile lipolysis to maintain metabolic homeostasis.

Chemotherapy diminishes lipid storage capacity of adipose tissue in a preclinical model of colon cancer

Background

Accelerated loss of adipose tissue in cancer is associated with shorter survival, and reduced quality of life. Evidence is emerging suggesting tumour association with alterations in adipose tissue, but much less is known about drug-related mechanisms contributing to adipose atrophy. Identification of mechanisms by which tumour and cancer treatments, such as chemotherapy, affect adipose tissue are required to develop appropriate therapeutic interventions to prevent fat depletion in cancer. This pre-clinical study aimed to assess alterations in adipose tissue during the clinical course of cancer.

Methods

Fischer 344 rats bearing the Ward colorectal tumour were euthanized before chemotherapy, after 1- cycle, or 2-cycles of a combination chemotherapy consisting of Irinotecan (CPT-11) combined with 5-fluorouracil (5-FU), which recapitulates first line treatment for human colorectal cancer. Periuterine adipose tissue was isolated. Healthy rats served as a reference group. Histological analysis (hematoxylin and eosin), Real-time PCR (TaqMan) and proteomic analysis (LC-MS/MS) were performed.

Results

Larger adipocytes (3993.7 ± 52.6 μm²) in tumour-bearing animals compared to the reference group (3227.7 ± 36.7 μm²; p < 0.001) was associated with reduced expression of proteins involved in mitochondrial fatty acid oxidation. The presence of a tumour has a significant effect on phospholipid but not triglyceride fatty acid composition. There were greater proportions of saturated fatty acids concurrent with lower monounsaturated fatty acids within the PL fraction of adipocytes in tumour-bearing animals. Chemotherapy treatment decreased the size of adipocytes (2243.9 ± 30.4 μm²; p < 0.001) and led to depletion of n-3 polyunsaturated fatty acids in adipose tissue triglyceride. Evaluation of the proteome profile revealed decreased expression of proteins involved in ATP generation, β-oxidation, and lipogenesis. Overall, adipose tissue may not be able to efficiently oxidize fatty acids to provide energy to maintain energy demanding pathways like lipogenesis inside the tissue.

Conclusions

In conclusion, metabolic adaptations to mitochondrial impairment may contribute to diminished lipid storage capacity of adipose tissue following chemotherapy delivery.

Electronic supplementary material

The online version of this article (10.1186/s12944-017-0638-8) contains supplementary material, which is available to authorized users.

The biochemical alterations underlying post-burn hypermetabolism

A severe burn can trigger a hypermetabolic state which lasts for years following the injury, to the detriment of the patient. The drastic increase in metabolic demands during this phase renders it difficult to meet the body's nutritional requirements, thus increasing muscle, bone and adipose catabolism and predisposing the patient to a host of disorders such as multi-organ dysfunction and sepsis, or even death. Despite advances in burn care over the last 50 years, due to the multifactorial nature of the hypermetabolic phenomenon it is difficult if not impossible to precisely identify and pharmacologically modulate the biological mediators contributing to this substantial metabolic derangement. Here, we discuss biomarkers and molecules which play a role in the induction and mediation of the hypercatabolic condition post-thermal injury. Furthermore, this thorough review covers the development of the factors released after burns, how they induce cellular and metabolic dysfunction, and how these factors can be targeted for therapeutic interventions to restore a more physiological metabolic phenotype after severe thermal injuries. This article is part of a Special Issue entitled: Immune and Metabolic Alterations in Trauma and Sepsis edited by Dr. Raghavan Raju.

Lipases and lipid droplet-associated protein expression in subcutaneous white adipose tissue of cachectic patients with cancer

Background

Cancer cachexia is a multifactorial metabolic syndrome characterized by marked loss of adipose tissue and skeletal muscle. Fat loss from adipose tissue in cancer cachexia is partly the result of increased lipolysis. Despite the growing amount of studies focused on elucidating the mechanisms through which lipolysis-related proteins regulate the lipolytic process, there are scarce data concerning that profile in the adipose tissue of cancer cachectic patients. Considering its fundamental importance, it was our main purpose to characterize the expression of the lipolysis-related proteins in the white adipose tissue of cachectic cancer patients.

Methods

Patients from the University Hospital were divided into three groups: control, cancer cachexia (CC), and weight-stable cancer patients (WSC). To gain greater insight into adipose tissue wasting during cancer cachexia progression, we have also analyzed an experimental model of cachexia (Walker 256 carcinosarcoma). Animals were divided into: control, intermediate cachexia (IC) and terminal cachexia (TC). Subcutaneous white adipose tissue of patients and epidydimal white adipose tissue of animals were investigated regarding molecular aspects by determining the protein content and gene expression of hormone-sensitive lipase (HSL), adipose triglyceride lipase (ATGL), comparative gene identification-58 (CGI-58), perilipin 1, leptin, adiponectin, visfatin, and tumour necrosis factor alpha (TNF-alpha).

Results

We found augmented lipolysis in CC associated with increased HSL expression, as well as upregulation of ATGL expression and reduction in perilipin 1 content. In IC, there was an imbalance in the secretion of pro- and anti-inflammatory factors. The alterations at the end-stage of cachexia were even more profound, and there was a reduction in the expression of almost all proteins analyzed in the animals.

Conclusions

Our findings show that cachexia induces important morphological, molecular, and humoral alterations in the white adipose tissue, which are specific to the stage of the syndrome.

An AMP-activated protein kinase-stabilizing peptide ameliorates adipose tissue wasting in cancer cachexia in mice

Cachexia represents a fatal energy-wasting syndrome in a large number of patients with cancer that mostly results in a pathological loss of skeletal muscle and adipose tissue. Here we show that tumor cell exposure and tumor growth in mice triggered a futile energy-wasting cycle in cultured white adipocytes and white adipose tissue (WAT), respectively. Although uncoupling protein 1 (Ucp1)-dependent thermogenesis was dispensable for tumor-induced body wasting, WAT from cachectic mice and tumor-cell-supernatant-treated adipocytes were consistently characterized by the simultaneous induction of both lipolytic and lipogenic pathways. Paradoxically, this was accompanied by an inactivated AMP-activated protein kinase (Ampk), which is normally activated in peripheral tissues during states of low cellular energy. Ampk inactivation correlated with its degradation and with upregulation of the Ampk-interacting protein Cidea. Therefore, we developed an Ampk-stabilizing peptide, ACIP, which was able to ameliorate WAT wasting in vitro and in vivo by shielding the Cidea-targeted interaction surface on Ampk. Thus, our data establish the Ucp1-independent remodeling of adipocyte lipid homeostasis as a key event in tumor-induced WAT wasting, and we propose the ACIP-dependent preservation of Ampk integrity in the WAT as a concept in future therapies for cachexia.

Potential Biomarkers of Fat Loss as a Feature of Cancer Cachexia

Fat loss is associated with shorter survival and reduced quality of life in cancer patients. Effective intervention for fat loss in cachexia requires identification of the condition using prognostic biomarkers for early detection and prevention of further depletion. No biomarkers of fat mass alterations have been defined for application to the neoplastic state. Several inflammatory cytokines have been implicated in mediating fat loss associated with cachexia; however, plasma levels may not relate to adipose atrophy. Zinc-α2-glycoprotein may be a local catabolic mediator within adipose tissue rather than serving as a plasma biomarker of fat loss. Plasma glycerol and leptin associate with adipose tissue atrophy and mass, respectively; however, no study has evaluated their potential as a prognostic biomarker of cachexia-associated fat loss. This review confirms the need for further studies to identify valid prognostic biomarkers to identify loss of fat based on changes in plasma levels of biomarkers.

Adipose tissue lipolysis and energy metabolism in early cancer cachexia in mice

Cancer cachexia is a progressive metabolic disorder that results in depletion of adipose tissue and skeletal muscle. A growing body of literature suggests that maintaining adipose tissue mass in cachexia may improve quality-of-life and survival outcomes. Studies of lipid metabolism in cachexia, however, have generally focused on later stages of the disorder when severe loss of adipose tissue has already occurred. Here, we investigated lipid metabolism in adipose, liver and muscle tissues during early stage cachexia - before severe fat loss - in the colon-26 murine model of cachexia. White adipose tissue mass in cachectic mice was moderately reduced (34-42%) and weight loss was less than 10% of initial body weight in this study of early cachexia. In white adipose depots of cachectic mice, we found evidence of enhanced protein kinase A - activated lipolysis which coincided with elevated total energy expenditure and increased expression of markers of brown (but not white) adipose tissue thermogenesis and the acute phase response. Total lipids in liver and muscle were unchanged in early cachexia while markers of fatty oxidation were increased. Many of these initial metabolic responses contrast with reports of lipid metabolism in later stages of cachexia. Our observations suggest intervention studies to preserve fat mass in cachexia should be tailored to the stage of cachexia. Our observations also highlight a need for studies that delineate the contribution of cachexia stage and animal model to altered lipid metabolism in cancer cachexia and identify those that most closely mimic the human condition.

Evidence and mechanisms of fat depletion in cancer

The majority of cancer patients experience wasting characterized by muscle loss with or without fat loss. In human and animal models of cancer, body composition assessment and morphological analysis reveals adipose atrophy and presence of smaller adipocytes. Fat loss is associated with reduced quality of life in cancer patients and shorter survival independent of body mass index. Fat loss occurs in both visceral and subcutaneous depots; however, the pattern of loss has been incompletely characterized. Increased lipolysis and fat oxidation, decreased lipogenesis, impaired lipid depositionand adipogenesis, as well as browning of white adipose tissue may underlie adipose atrophy in cancer. Inflammatory cytokines such as interleukin-6 (IL-6), tumor necrosis factor alpha (TNF-α), and interleukin-1 beta (IL-1β) produced by the tumor or adipose tissue may also contribute to adipose depletion. Identifying the mechanisms and time course of fat mass changes in cancer may help identify individuals at risk of adipose depletion and define interventions to circumvent wasting. This review outlines current knowledge of fat mass in cancer and illustrates the need for further studies to assess alterations in visceral and subcutaneous adipose depots and possible mechanisms for loss of fat during cancer progression.

A switch from white to brown fat increases energy expenditure in cancer-associated cachexia

Cancer-associated cachexia (CAC) is a wasting syndrome characterized by systemic inflammation, body weight loss, atrophy of white adipose tissue (WAT) and skeletal muscle. Limited therapeutic options are available and the underlying mechanisms are poorly defined. Here we show that a phenotypic switch from WAT to brown fat, a phenomenon termed WAT browning, takes place in the initial stages of CAC, before skeletal muscle atrophy. WAT browning is associated with increased expression of uncoupling protein 1 (UCP1), which uncouples mitochondrial respiration toward thermogenesis instead of ATP synthesis, leading to increased lipid mobilization and energy expenditure in cachectic mice. Chronic inflammation and the cytokine interleukin-6 increase UCP1 expression in WAT, and treatments that reduce inflammation or β-adrenergic blockade reduce WAT browning and ameliorate the severity of cachexia. Importantly, UCP1 staining is observed in WAT from CAC patients. Thus, inhibition of WAT browning represents a promising approach to ameliorate cachexia in cancer patients.

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.

Cancer cachexia prevention via physical exercise: molecular mechanisms

Cancer cachexia is a debilitating consequence of disease progression, characterised by the significant weight loss through the catabolism of both skeletal muscle and adipose tissue, leading to a reduced mobility and muscle function, fatigue, impaired quality of life and ultimately death occurring with 25-30 % total body weight loss. Degradation of proteins and decreased protein synthesis contributes to catabolism of skeletal muscle, while the loss of adipose tissue results mainly from enhanced lipolysis. These mechanisms appear to be at least, in part, mediated by systemic inflammation. Exercise, by virtue of its anti-inflammatory effect, is shown to be effective at counteracting the muscle catabolism by increasing protein synthesis and reducing protein degradation, thus successfully improving muscle strength, physical function and quality of life in patients with non-cancer-related cachexia. Therefore, by implementing appropriate exercise interventions upon diagnosis and at various stages of treatment, it may be possible to reverse protein degradation, while increasing protein synthesis and lean body mass, thus counteracting the wasting seen in cachexia.

Adipose triglyceride lipase contributes to cancer-associated cachexia

Cachexia is a multifactorial wasting syndrome most common in patients with cancer that is characterized by the uncontrolled loss of adipose and muscle mass. We show that the inhibition of lipolysis through genetic ablation of adipose triglyceride lipase (Atgl) or hormone-sensitive lipase (Hsl) ameliorates certain features of cancer-associated cachexia (CAC). In wild-type C57BL/6 mice, the injection of Lewis lung carcinoma or B16 melanoma cells causes tumor growth, loss of white adipose tissue (WAT), and a marked reduction of gastrocnemius muscle. In contrast, Atgl-deficient mice with tumors resisted increased WAT lipolysis, myocyte apoptosis, and proteasomal muscle degradation and maintained normal adipose and gastrocnemius muscle mass. Hsl-deficient mice with tumors were also protected although to a lesser degree. Thus, functional lipolysis is essential in the pathogenesis of CAC. Pharmacological inhibition of metabolic lipases may help prevent cachexia.

Nonoxidative free fatty acid disposal is greater in young women than men

CONTEXT

Large increases in systemic free fatty acid (FFA) availability in the absence of a corresponding increase in fatty acid oxidation can create a host of metabolic abnormalities. These adverse responses are thought to be the result of fatty acids being shunted into hepatic very low-density lipoprotein-triglyceride production and/or intracellular lipid storage and signaling pathways because tissues are forced to increase nonoxidative FFA disposal.

OBJECTIVE

The objective of the study was to examine whether variations in postabsorptive nonoxidative FFA disposal within the usual range predict insulin resistance and hypertriglyceridemia.

DESIGN

We measured: systemic FFA turnover using a continuous iv infusion of [9-10, (3)H]palmitate; substrate oxidation with indirect calorimetry combined with urinary nitrogen excretion; whole-body and peripheral insulin sensitivity with the labeled iv glucose tolerance test minimal model.

SETTING

the study was conducted at the Mayo Clinic General Clinical Research Center.

PARTICIPANTS

Participants included healthy, postabsorptive, nonobese adults (21 women and 21 men).

INTERVENTIONS

There were no interventions.

MAIN OUTCOME MEASURES

Nonoxidative FFA disposal (micromoles per minute), defined as the FFA disappearance rate minus fatty acid oxidation.

RESULTS

Women had 64% greater nonoxidative FFA disposal rate than men but a better lipid profile and similar insulin sensitivity. There was no significant correlation between nonoxidative FFA disposal and whole-body sensitivity, peripheral insulin sensitivity, or fasting serum triglyceride concentrations in men or women.

CONCLUSIONS

Healthy nonobese women have greater rates of nonoxidative FFA disposal than men, but this does not appear to relate to adverse health consequences. Understanding the sex-specific interaction between adipose tissue lipolysis and peripheral FFA removal will help to discover new approaches to treat FFA-induced abnormalities.

Cancer cachexia: a systematic literature review of items and domains associated with involuntary weight loss in cancer

BACKGROUND

The concept of cancer-related anorexia/cachexia is evolving as its mechanisms are better understood. To support consensus processes towards an updated definition and classification system, we systematically reviewed the literature for items and domains associated with involuntary weight loss in cancer.

METHODS

Two search strings (cachexia, cancer) explored five databases from 1976 to 2007. Citations, abstracts and papers were included if they were original work, in English/German language, and explored an item to distinguish advanced cancer patients with variable degrees of involuntary weight loss. The items were grouped into the 5 domains proposed by formal expert meetings.

RESULTS

Of 14,344 citations, 1275 abstracts and 585 papers reviewed, 71 papers were included (6325 patients; 40-50% gastrointestinal, 10-20% lung cancer). No single domain or item could consistently distinguish cancer patients with or without weight loss or having various degrees of weight loss. Anorexia and decreased nutritional intake were unexpectedly weakly related with weight loss. Explanations for this could be the imprecise measurement methods for nutritional intake, symptom interactions, and the importance of systemic inflammation as a catabolic drive. Data on muscle mass and strength is scarce and the impact of cachexia on physical and psychosocial function has not been widely assessed.

CONCLUSIONS

Current data support a modular concept of cancer cachexia with a variable combination of reduced nutritional intake and catabolic/hyper-metabolic changes. The heterogeneity in the literature revealed by this review underlines the importance of an agreed definition and classification of cancer cachexia.

Role of beta1-adrenoceptor in increased lipolysis in cancer cachexia

Increased production of hormone-sensitive lipase (HSL) protein has been demonstrated to be the major cause behind enhanced lipolysis in cancer cachexia. The mechanism governing this alteration is unknown and was presently investigated. This study was conducted to detect the expression of relevant receptors in the adipocytes of cancer cachexia patients, and to elucidate their implication in the increased lipolysis. Gene expressions of beta1-adrenoceptor (ADRB1), beta2-adrenoceptor (ADRB2), beta3-adrenoceptor (ADRB3), alpha2C-adrenoceptor (ADRA2C), natriuretic peptide receptor A (NPRA), insulin receptor (INSR), and HSL were determined in adipose tissues of 34 patients by real-time PCR. Protein levels of ADRB1 and HSL were determined by western blot analysis. beta1-Adrenoceptor (ADRB1) was also detected by immunofluorescence staining. mRNA expressions of both ADRB1 and HSL were approximately 50% elevated selectively in the cachexia group, whereas mRNA levels of the other receptors were unchanged. beta1-Adrenoceptor (ADRB1) protein expression was 1.5-fold increased in cachexia as compared with the cancer controls, and 3-fold increased as compared with nonmalignant controls, and was confirmed as a membrane protein in adipocytes by immunofluorescence. Hormone-sensitive lipase (HSL) protein expression was 2-2.5-fold increased selectively in cachectic patients. There was a positive correlation between the protein expressions of ADRB1 and HSL. As much as approximately 50% of the variations in HSL protein expression could be explained by variations in ADRB1 protein expression. There was a link between ADRB1 protein level and lipolytic rate. Increased ADRB1 expression may account for some of the functional changes of HSL in patients with cancer cachexia.

Cellular bioenergetics as a target for obesity therapy

Obesity develops when energy intake exceeds energy expenditure. Although most current obesity therapies are focused on reducing calorific intake, recent data suggest that increasing cellular energy expenditure (bioenergetics) may be an attractive alternative approach. This is especially true for adaptive thermogenesis - the physiological process whereby energy is dissipated in mitochondria of brown fat and skeletal muscle in the form of heat in response to external stimuli. There have been significant recent advances in identifying the factors that control the development and function of these tissues, and in techniques to measure brown fat in human adults. In this article, we integrate these developments in relation to the classical understandings of cellular bioenergetics to explore the potential for developing novel anti-obesity therapies that target cellular energy expenditure.

Computational modeling of cancer cachexia

PURPOSE OF REVIEW

Measurements of whole-body energy expenditure, body composition, and in-vivo metabolic fluxes are required to quantitatively understand involuntary weight loss in cancer cachexia. Such studies are rare because cancer cachexia occurs near the end of life when invasive metabolic tests may be precluded. Thus, models of cancer-associated weight loss are an important tool for helping to understand this debilitating condition.

RECENT FINDINGS

A computational model of human macronutrient metabolism was recently developed that simulates the normal metabolic adaptations to semi-starvation and re-feeding. Here, this model was used to integrate data on the metabolic changes in patients with cancer cachexia. The resulting computer simulations show how the known metabolic disturbances synergize with reduced energy intake to result in a progressive loss of body weight, fat mass, and fat-free mass. The model was also used to simulate the effects of nutritional support and investigate inhibition of lipolysis versus proteolysis as potential therapeutic approaches for cancer cachexia.

SUMMARY

Computational modeling is a new tool that can integrate clinical data on the metabolic changes in cancer cachexia and provide a conceptual framework to help understand involuntary weight loss and predict the effects of potential therapies.

A computational model of adipose tissue metabolism: evidence for intracellular compartmentation and differential activation of lipases

Regulation of lipolysis in adipose tissue is critical to whole body fuel homeostasis and to the development of insulin resistance. Due to the challenging nature of laboratory investigations of regulatory mechanisms in adipose tissue, mathematical models could provide a valuable adjunct to such experimental work. We have developed a computational model to analyze key components of adipose tissue metabolism in vivo in human in the fasting state. The various key components included triglyceride-fatty acid cycling, regulation of lipolytic reactions, and glyceroneogenesis. The model, consisting of spatially lumped blood and cellular compartments, included essential transport processes and biochemical reactions. Concentration dynamics for major substrates were described by mass balance equations. Model equations were solved numerically to simulate dynamic responses to intravenous epinephrine infusion. Model simulations were compared with the corresponding experimental measurements of the arteriovenous difference across the abdominal subcutaneous fat bed in humans. The model can simulate physiological responses arising from the different expression levels of lipases. Key findings of this study are as follows: (1) Distinguishing the active metabolic subdomain ( approximately 3% of total tissue volume) is critical for simulating data. (2) During epinephrine infusion, lipases are differentially activated such that diglyceride breakdown is approximately four times faster than triglyceride breakdown. (3) Glyceroneogenesis contributes more to glycerol-3-phosphate synthesis during epinephrine infusion when pyruvate oxidation is inhibited by a high acetyl-CoA/free-CoA ratio.

Mechanism of increased lipolysis in cancer cachexia

Loss of fat mass is a key feature of cancer cachexia and has been attributed to increased adipocyte lipolysis. The mechanism behind this alteration is unknown and was presently investigated. We studied mature s.c. fat cells and differentiated preadipocytes from 26 cancer patients with and without cachexia. Hormone-induced lipolysis and expression of lipolysis-regulating genes were determined together with body composition and in vivo lipolytic activity (fasting plasma glycerol or fatty acids related to body fat). Body fat was reduced by 40% and in vivo lipolytic activity was 2-fold increased in cachexia (P = 0.001). In mature adipocytes, the lipolytic effects of catecholamines and natriuretic peptide were 2- to 3-fold increased in cachexia (P < 0.001). This was completely counteracted by inhibiting the rate-limiting lipolysis enzyme hormone-sensitive lipase (HSL). In cachexia, the expression levels of HSL mRNA and protein were increased by 50% and 100%, respectively (P = 0.005-0.03), which strongly correlated with in vitro lipolytic stimulation (r = 0.7-0.9). The antilipolytic effect of insulin in mature fat cells and the stimulated lipolytic effect in differentiated preadipocytes were unaltered in cachexia. Patients who lost weight due to other factors than cancer cachexia had no change in adipocyte lipolysis. In conclusion, adipocyte lipolysis is increased in cancer cachexia not due to nonepigenic factors or to weight loss per se, but most probably because of enhanced expression and function of adipocyte HSL. The selective inhibition of this enzyme may prevent fat loss in cancer patients.

Pre-operative nutritional status does not alter the metabolic response to major gastrointestinal surgery in patients with oesophageal cancer

Malnutrition is associated with an increased incidence of perioperative morbidity and mortality. To evaluate the effect of malnutrition on the metabolic and inflammatory response to surgery in patients with oesophageal cancer, we studied the effects of oesophagectomy in six patients with major (13·9 (se 1·3) %) weight loss and five patients with minor (0·7 (se 0·6) %) weight loss in the 6 months before to surgery. Rates of appearance (Ra) of glucose, glycerol, leucine and urea were determined by stable isotopically labelled tracer infusion before and after surgery. C-reactive protein was measured as an inflammation marker. BMI was lower in the patients with major weight loss than those with minor weight loss (20·3 (se 0·7) and 24·9 (se 1·5) kg/m2, P = 0·02). With the exception of greater glucose Ra in the major weight loss than minor weight loss subjects (11·1 (se 0·3) v. 9·5 (se 0·3) μmol/kg per min, P = 0·01), there were no differences in substrate kinetics before surgery between groups. Surgery increased glucose Ra, leucine Ra and urea Ra by 41, 24 and 58 %, respectively, in the total group. Changes in substrate kinetics in response to surgery were not different between patients with major and minor weight loss. Surgery increased C-reactive protein concentrations to a comparable extent in both groups. In conclusion, major upper gastrointestinal tract surgery in patients with oesophageal cancer elicits a catabolic response, characterized by increased inflammation, glucose production and protein breakdown. However, this catabolic response does not seem to be influenced by pre-operative nutritional status.

Fat loss in cachexia—is there a role for adipocyte lipolysis?

A number of chronic diseases are associated with pronounced loss of fat and muscle mass (cachexia). The negative correlation between cachexia and survival probability, implies that prevention and treatment of this condition is essential. The mechanisms promoting cachexia are yet to be determined although several theories have been proposed. Most studies on cachexia have concentrated on muscle wasting and its possible impact on complications and survival. In this review, we present a synopsis of previous and recent studies focusing on the loss of adipose tissue. It appears that increased adipocyte lipolysis is an important factor in the cachexic process.

Multi-scale computational model of fuel homeostasis during exercise: effect of hormonal control

A mathematical model of the whole-body metabolism is developed to predict fuel homeostasis during exercise by using hormonal control over cellular metabolic processes. The whole body model is composed of seven tissue compartments: brain, heart, liver, GI (gastrointestinal) tract, skeletal muscle, adipose tissue, and "other tissues". Each tissue compartment is described by dynamic mass balances and major cellular metabolic reactions. The glucagon-insulin controller is incorporated into the whole body model to predict hormonal changes during exercise. Moderate [150 W power output at 60% of peak oxygen consumption (VO(2max))] exercise for 60 min was implemented by increasing ATP utilization rates in heart and skeletal muscle. Arterial epinephrine level was given as an input function, which directly affects heart and skeletal muscle metabolism and indirectly other tissues via glucagon-insulin controller. Model simulations were validated with experimental data from human exercise studies. The exercise induced changes in hormonal signals modulated metabolic flux rates of different tissues in a coordinated way to achieve glucose homeostasis, demonstrating the efficacy of hormonal control over cellular metabolic processes. From experimental measurements of whole body glucose balance and arterial substrate concentrations, this model could predict the dynamic changes of hepatic glycogenolysis and gluconeogenesis, which are not easy to measure experimentally, suggesting the higher contribution of glycogenolysis ( approximately 75%). In addition, it could provide dynamic information on the relative contribution of carbohydrates and lipids for fuel oxidation in skeletal muscle. Model simulations indicate that external fuel supplies from other tissue/organ systems to skeletal muscle become important for prolonged exercise emphasizing the significance of interaction among tissues. In conclusion, this model can be used as a valuable complement to experimental studies due to its ability to predict what is difficult to measure directly, and usefulness to provide information about dynamic behaviors.

Common symptoms in advanced cancer

The key points of this article are anorexia and cachexia are: A major cause of cancer deaths. Several drugs are available to treat anorexia and cachexia. Dyspnea in cancer usually is caused by several factors. Treatment consists of reversing underlying causes, empiric bronchodilators, cortico-steroids--and in the terminally ill patients-opioids, benzodiazepines,and chlorpromazine. Delirium is associated with advanced cancer. Empiric treatment with neuroleptics while evaluating for reversible causes is a reasonable approach to management. Nausea and vomiting are caused by extra-abdominal factors (drugs,electrolyte abnormalities, central nervous system metastases) or intra-abdominal factors (gastroparesis, ileus, gastric outlet obstruction, bowel obstruction). The pattern of nausea and vomiting differs depending upon whether the cause is extra- or intra-abdominal. Reversible causes should be sought and empiric metoclopramide or haloperidol should be initiated. Fatigue may be caused by anemia, depression, endocrine abnormalities,or electrolyte disturbances that should be treated before using empiric methylphenidate. Constipation should be treated with laxatives and stool softeners. Both should start with the first opioid dose.

Alterations in lipid kinetics in men with HIV-dyslipidemia

Hypertriglyceridemia is common in individuals with human immunodeficiency (HIV) infection, but the mechanisms responsible for increased plasma triglyceride (TG) concentrations are not clear. We evaluated fatty acid and VLDL-TG kinetics during basal conditions and during a glucose infusion that resulted in typical postprandial plasma glucose and insulin concentrations in six men with HIV-dyslipidemia [body mass index (BMI): 28 +/- 2 kg/m2] and six healthy men (BMI: 26 +/- 2 kg/m2). VLDL-TG secretion and palmitate rate of appearance (Ra) in plasma were measured by using stable-isotope-labeled tracer techniques. Basal palmitate Ra and VLDL-TG secretion rates were greater (P < 0.01 for both) in men with HIV-dyslipidemia (1.04 +/- 0.07 micromol palmitate x kg-1 x min-1 and 5.7 +/- 0.6 micromol VLDL-TG x l plasma-1 x min-1) than in healthy men (0.67 +/- 0.08 micromol palmitate. kg-1 x min-1 and 3.0 +/- 0.5 micromol VLDL-TG x l plasma-1 x min-1). Basal VLDL-TG plasma clearance was lower in men with HIV-dyslipidemia (13 +/- 1 ml/min) than in healthy men (19 +/- 2 ml/min; P < 0.05). Glucose infusion decreased palmitate Ra (by approximately 50%) and the VLDL-TG secretion rate (by approximately 30%) in both groups, but the VLDL-TG secretion rate remained higher (P < 0.05) in subjects with HIV-dyslipidemia. These findings demonstrate that increased secretion of VLDL-TG and decreased plasma VLDL-TG clearance, during both fasting and fed conditions, contribute to hypertriglyceridemia in men with HIV-dyslipidemia. Although it is likely that increased free fatty acid release from adipose tissue contributes to the increase in basal VLDL-TG concentration, other factors must be involved, because insulin-induced suppression of lipolysis and systemic fatty acid availability did not normalize the VLDL-TG secretion rate.

Integrated analysis of glucose, lipid, and urea metabolism in patients with bladder cancer. Impact of tumor stage

OBJECTIVE

The aim of the study was to characterize the metabolic changes in non-weight-losing patients with cancer of the bladder and to investigate the effect of tumor stage. The kinetics of glucose, glycerol, and urea metabolism were assessed in 22 weight-stable patients with non-metastatic bladder cancer (tumor stage p </= T2, n = 8; tumor stage p > T2, n = 14) and 10 patients with benign uterine myoma (controls).

METHODS

The kinetics of glucose, glycerol, and urea metabolism were assessed by [6,6-(2)H(2)]glucose, [1,1,2,3,3-(2)H(5)]glycerol, and [(15)N(2)]urea. Plasma concentrations of glucose, glycerol, urea, lactate, free fatty acids, insulin, glucagon, cortisol, epinephrine, and norepinephrine also were determined.

RESULTS

Plasma concentrations of glucose, urea, and insulin were higher in cancer patients than in controls (P < 0.05). Whereas glucose production was similar in both groups, glucose clearance was lower in patients with bladder cancer (P < 0.05). Glycerol turnover rate was comparable between groups. Whole-body urea synthesis rate was higher in the cancer group than in the control group (P < 0.05), but there was no difference in urea synthesis when calculated per kilogram of fat-free body mass. Plasma concentrations of glycerol, lactate, free fatty acids, glucagon, cortisol, epinephrine, and norepinephrine were similar in both groups. There was no difference in any parameter between patients with an early tumor stage (p < T2) and patients with a later tumor stage (p > T2).

CONCLUSION

Patients with bladder cancer had a lower rate of glucose clearance than did control subjects. Lipid metabolism was not affected, whereas urea synthesis rate was elevated in cancer patients. However, when expressed per kilogram of fat-free body mass, no difference in protein breakdown could be observed. The tumor stage had no effect on glucose, lipid, or protein metabolism.

Energy expenditure, sex, and endogenous fuel availability in humans

Adipose tissue lipolysis supplies circulating FFAs, which largely meet lipid fuel needs; however, excess FFAs, can contribute to the adverse health consequences of obesity. Because "normal" FFA release has not been well defined, average (mean of 4 days) basal FFA release and its potential regulation factors were measured in 50 lean and obese adults (25 women). Resting energy expenditure (REE), but not body composition, predicted most of the interindividual variation in FFA release. There was a significant, positive linear relationship between palmitate release and REE; however, women released approximately 40% more FFA than men relative to REE. Neither plasma palmitate concentrations nor respiratory quotient by indirect calorimetry differed between men and women. Glucose release rates were not different in men and women whether related to REE or fat free mass. These findings indicate that nonoxidative FFA clearance is greater in women than in men. This could be an advantage at times of increased fuel needs. We conclude that "normal" adipose tissue lipolysis is different in men and women and that the fuel export role of adipose tissue in obesity will need to be reassessed.

Sources of blood glycerol during fasting

To determine the source(s) of blood and very low density lipoprotein (VLDL)-triglyceride glycerol during fasting, four men ingested (2)H(2)O from 14 to 20 h into a 60-h fast to achieve ~0.5% body water enrichment. At 60 h of fasting, glycerol flux was measured using [2-(14)C]glycerol. Blood was taken for measurement of (2)H enrichment at carbon 6 of glucose and at carbon 3 of free glycerol and VLDL-triglyceride glycerol. (2)H enrichment of the 2 hydrogens bound to carbon 3 of VLDL-triglyceride glycerol was 105 +/- 2% of the (2)H enrichment of the 2 hydrogens bound to carbon 6 of glucose, indicating isotopic equilibrium between hepatic glyceraldehyde 3-P and glycerol 3-P. The (2)H enrichment of the 2 hydrogens bound to carbon 3 of free glycerol was 17 +/- 3% of VLDL-triglyceride glycerol, indicating that a significant percentage of free glycerol in blood originated from the hydrolysis of circulating VLDL-triglyceride or a pool of glycerol with similar (2)H enrichment. Glycerol flux was 6.3 +/- 1.1 micromol. kg(-1). min(-1). Glycerol appearing from nonadipose tissue sources was then approximately 1.1 micromol. kg(-1). min(-1). Seven other subjects were fasted for 12, 42, and 60 h. A small percentage of glycerol in the circulation after 12 h of fasting was enriched with (2)H. The enrichment of the 2 hydrogens bound to carbon 3 of free glycerol in the longer periods of fasting was approximately 16% of the enrichment of the 2 hydrogens bound to carbon 6 of glucose. Therefore, as much as 15-20% of systemic glycerol turnover during fasting is not from lipolysis of adipose tissue triglyceride.

Lipid metabolism during fasting

These studies were conducted to understand the relationship between measures of systemic free fatty acid (FFA) reesterification and regional FFA, glycerol, and triglyceride metabolism during fasting. Indirect calorimetry was used to measure fatty acid oxidation in six men after a 60-h fast. Systemic and regional (splanchnic, renal, and leg) FFA ([(3)H]palmitate) and glycerol ([(3)H]glycerol) kinetics, as well as splanchnic triglyceride release, were measured. The rate of systemic FFA reesterification was 366 +/- 93 micromol/min, which was greater (P < 0.05) than splanchnic triglyceride fatty acid output (64 +/- 6 micromol/min), a measure of VLDL triglyceride fatty acid export. The majority of glycerol uptake occurred in the splanchnic and renal beds, although some leg glycerol uptake was detected. Systemic FFA release was approximately double that usually present in overnight postabsorptive men, yet the regional FFA release rates were of the same proportions previously observed in overnight postabsorptive men. In conclusion, FFA reesterification at rest during fasting far exceeds splanchnic triglyceride fatty acid output. This indicates that nonhepatic sites of FFA reesterification are important, and that peripheral reesterification of FFA exceeds the rate of simultaneous intracellular triglyceride fatty acid oxidation.

Modulation of adipocyte G-protein expression in cancer cachexia by a lipid-mobilizing factor (LMF)

Adipocytes isolated from cachectic mice bearing the MAC 16 tumour showed over a 3-fold increase in lipolytic response to both low concentrations of isoprenaline and a tumour-derived lipid mobilizing factor (LMF). This was reflected by an enhanced stimulation of adenylate cyclase in plasma membrane fractions of adipocytes in the presence of both factors. There was no up-regulation of adenylate cyclase in response to forskolin, suggesting that the effect arose from a change in receptor number or G-protein expression. Immunoblotting of adipocyte membranes from mice bearing the MAC16 tumour showed an increased expression of Galphas up to 10% weight loss and a reciprocal decrease in Galpha. There was also an increased expression of Galphas and a decrease in Galpha in adipose tissue from a patient with cancer-associated weight loss compared with a non-cachectic cancer patient. The changes in G-protein expression were also seen in adipose tissue of normal mice administered pure LMF as well as in 3T3L1 adipocytes in vitro. The changes in G-protein expression induced by LMF were attenuated by the polyunsaturated fatty acid, eicosapentaenoic acid (EPA). This suggests that this tumour-derived lipolytic factor acts to sensitize adipose tissue to lipolytic stimuli, and that this effect is attenuated by EPA, which is known to preserve adipose tissue in cancer cachexia.

Eicosapentaenoic acid ethyl ester supplementation in cachectic cancer patients and healthy subjects: effects on lipolysis and lipid oxidation

BACKGROUND & AIMS

Recent reports suggest that weight loss in cachectic cancer patients may be inhibited by supplementation of the n-3 fatty acid eicosapentaenoic acid (20:5n-3; EPA), presumably due to inhibition of lipolysis. The aim of the present double-blind, randomized trial was to assess whether short-term oral EPA ethyl ester (EE) supplementation inhibits lipolysis and lipid oxidation in weight-losing cancer patients and in healthy subjects.

METHODS

Seventeen weight-losing, cancer patients of different tumor types, and 16 healthy subjects were randomized to receive EPA-EE (6 g/d) or placebo (oleic acid (OA)-EE; 6 g/d) for seven days. At baseline (day 0) and during supplementation (days 2 and 7) whole-body lipolysis and palmitic acid release were measured in the overnight fasting state using [1, 1, 2, 3, 3-(2)H(5)]glycerol and [1-(13)C]palmitic acid. Palmitate oxidation was determined by measuring(13)CO(2)enrichment in expired breath.

RESULTS

No significant effects of EPA-EE on whole-body lipolysis, palmitic acid release, or palmitate oxidation were detected in cancer patients nor in healthy subjects in comparison with OA-EE. EPA-EE supplementation reduced plasma-free fatty acid and triacylglycerol concentrations significantly in healthy subjects but not in cancer patients.

CONCLUSION

We conclude that supplementation of EPA-EE does not significantly inhibit lipolysis or lipid oxidation in weight-losing cancer patients or in healthy subjects during short-term supplementation when using OA-EE as a placebo supplement.