Effect of zinc-alpha2-glycoprotein (ZAG) on expression of uncoupling proteins in skeletal muscle and adipose tissue

Adipose tissue rearrangement in cancer cachexia: The involvement of β3-adrenergic receptor associated pathways

Cancer-associated cachexia (CAC) is a complex multiple organ syndrome that significantly contributes to reduced quality of life and increased mortality among many cancer patients. Its multifactorial nature makes its early diagnosis and effective therapeutic interventions challenging. Adipose tissue is particularly impacted by cachexia, typically through increased lipolysis, browning and thermogenesis, mainly at the onset of the disease. These processes lead to depletion of fat mass and contribute to the dysfunction of other organs. The β-adrenergic signalling pathways are classical players in the regulation of adipose tissue metabolism. They are activated upon sympathetic stimulation inducing lipolysis, browning and thermogenesis, therefore contributing to energy expenditure. Despite accumulating evidence suggesting that β3-adrenergic receptor stimulation may be crucial to the adipose tissue remodelling during cachexia, the literature remains controversial. Moreover, there is limited knowledge regarding sexual dimorphism of adipose tissue in the context of cachexia. This review paper aims to present the current knowledge regarding adipose tissue wasting during CAC, with a specific focus on the role of the β3-adrenergic receptor, placing it as a potential therapeutic target against cachexia.

The Mitochondria-Targeting Agent MitoQ Improves Muscle Atrophy, Weakness and Oxidative Metabolism in C26 Tumor-Bearing Mice

Cancer cachexia is a debilitating syndrome characterized by skeletal muscle wasting, weakness and fatigue. Several pathogenetic mechanisms can contribute to these muscle derangements. Mitochondrial alterations, altered metabolism and increased oxidative stress are known to promote muscle weakness and muscle catabolism. To the extent of improving cachexia, several drugs have been tested to stimulate mitochondrial function and normalize the redox balance. The aim of this study was to test the potential beneficial anti-cachectic effects of Mitoquinone Q (MitoQ), one of the most widely-used mitochondria-targeting antioxidant. Here we show that MitoQ administration (25 mg/kg in drinking water, daily) in vivo was able to improve body weight loss in Colon-26 (C26) bearers, without affecting tumor size. Consistently, the C26 hosts displayed ameliorated skeletal muscle and strength upon treatment with MitoQ. In line with improved skeletal muscle mass, the treatment with MitoQ was able to partially correct the expression of the E3 ubiquitin ligases Atrogin-1 and Murf1. Contrarily, the anabolic signaling was not improved by the treatment, as showed by unchanged AKT, mTOR and 4EBP1 phosphorylation. Assessment of gene expression showed altered levels of markers of mitochondrial biogenesis and homeostasis in the tumor hosts, although only Mitofusin-2 levels were significantly affected by the treatment. Interestingly, the levels of Pdk4 and CytB, genes involved in the regulation of mitochondrial function and metabolism, were also partially increased by MitoQ, in line with the modulation of hexokinase (HK), pyruvate dehydrogenase (PDH) and succinate dehydrogenase (SDH) enzymatic activities. The improvement of the oxidative metabolism was associated with reduced myosteatosis (i.e., intramuscular fat infiltration) in the C26 bearers receiving MitoQ, despite unchanged muscle LDL receptor expression, therefore suggesting that MitoQ could boost β-oxidation in the muscle tissue and promote a glycolytic-to-oxidative shift in muscle metabolism and fiber composition. Overall, our data identify MitoQ as an effective treatment to improve skeletal muscle mass and function in tumor hosts and further support studies aimed at testing the anti-cachectic properties of mitochondria-targeting antioxidants also in combination with routinely administered chemotherapy agents.

Zinc and the Innovative Zinc-α2-Glycoprotein Adipokine Play an Important Role in Lipid Metabolism: A Critical Review

Numerous studies indicate that zinc and the new zinc-related adipokine, zinc-α2-glycoprotein (ZAG), are involved in lipid metabolism. Excess body fat lowers blood concentrations of Zn and ZAG, leading not only to the development of obesity but also to other components of the metabolic syndrome. Zinc homeostasis disorders in the body negatively affect the lipid profile and cytokine secretion. Zinc appears to be a very important ZAG homeostasis regulator. The physiological effects of ZAG are related to lipid metabolism, but studies show that ZAG also affects glucose metabolism and is linked to insulin resistance. ZAG has a zinc binding site in its structure, which may indicate that ZAG mediates the effect of zinc on lipid metabolism. The review aimed to verify the available studies on the effects of zinc and ZAG on lipid metabolism. A literature review within the scope of this research area was conducted using articles available in PubMed (including MEDLINE), Web of Science and Cochrane Library databases. An analysis of available studies has shown that zinc improves hepatic lipid metabolism and has an impact on the lipid profile. Numerous studies have found that zinc supplementation in overweight individuals significantly reduced blood levels of total cholesterol, LDL (Low-density lipoprotein)cholesterol and triglycerides, potentially reducing cardiovascular morbidity and mortality. Some results also indicate that it increases HDL-C (High-density lipoprotein) cholesterol levels. ZAG has been shown to play a significant role in reducing obesity and improving insulin sensitivity, both in experimental animal model studies and in human studies. Furthermore, ZAG at physiologically relevant concentrations increases the release of adiponectin from human adipocytes. In addition, ZAG has been shown to inhibit in vitro leptin production. Further studies are needed to provide more data on the role of zinc and zinc-α2-glycoprotein.

Cancer cachexia has many symptoms but only one cause: anoxia

During nearly 100 years of research on cancer cachexia (CC), science has been reciting the same mantra: it is a multifactorial syndrome. The aim of this paper is to show that the symptoms are many, but they have a single cause: anoxia. CC is a complex and devastating condition that affects a high proportion of advanced cancer patients. Unfortunately, it cannot be reversed by traditional nutritional support and it generally reduces survival time. It is characterized by significant weight loss, mainly from fat deposits and skeletal muscles. The occurrence of cachexia in cancer patients is usually a late phenomenon. The conundrum is why do similar patients with similar tumors, develop cachexia and others do not? Even if cachexia is mainly a metabolic dysfunction, there are other issues involved such as the activation of inflammatory responses and crosstalk between different cell types.  The exact mechanism leading to a wasting syndrome is not known, however there are some factors that are surely involved, such as anorexia with lower calorie intake, increased glycolytic flux, gluconeogenesis, increased lipolysis and severe tumor hypoxia. Based on this incomplete knowledge we put together a scheme explaining the molecular mechanisms behind cancer cachexia, and surprisingly, there is one cause that explains all of its characteristics: anoxia.  With this different view of CC we propose a treatment based on the physiopathology that leads from anoxia to the symptoms of CC.  The fundamentals of this hypothesis are based on the idea that CC is the result of anoxia causing intracellular lactic acidosis. This is a dangerous situation for cell survival which can be solved by activating energy consuming gluconeogenesis. The process is conducted by the hypoxia inducible factor-1α. This hypothesis was built by putting together pieces of evidence produced by authors working on related topics.

Zinc-α2-glycoprotein as an inhibitor of amine oxidase copper-containing 3

Zinc-α2-glycoprotein (ZAG) is a major plasma protein whose levels increase in chronic energy-demanding diseases and thus serves as an important clinical biomarker in the diagnosis and prognosis of the development of cachexia. Current knowledge suggests that ZAG mediates progressive weight loss through β-adrenergic signalling in adipocytes, resulting in the activation of lipolysis and fat mobilization. Here, through cross-linking experiments, amine oxidase copper-containing 3 (AOC3) is identified as a novel ZAG binding partner. AOC3-also known as vascular adhesion protein 1 (VAP-1) and semicarbazide sensitive amine oxidase (SSAO)-deaminates primary amines, thereby generating the corresponding aldehyde, H2O2 and NH3. It is an ectoenzyme largely expressed by adipocytes and induced in endothelial cells during inflammation. Extravasation of immune cells depends on amine oxidase activity and AOC3-derived H2O2 has an insulinogenic effect. The observations described here suggest that ZAG acts as an allosteric inhibitor of AOC3 and interferes with the associated pro-inflammatory and anti-lipolytic functions. Thus, inhibition of the deamination of lipolytic hormone octopamine by AOC3 represents a novel mechanism by which ZAG might stimulate lipolysis. Furthermore, experiments involving overexpression of recombinant ZAG reveal that its glycosylation is co-regulated by oxygen availability and that the pattern of glycosylation affects its inhibitory potential. The newly identified protein interaction between AOC3 and ZAG highlights a previously unknown functional relationship, which may be relevant to inflammation, energy metabolism and the development of cachexia.

ER Stress and Unfolded Protein Response in Cancer Cachexia

Cancer cachexia is a devastating syndrome characterized by unintentional weight loss attributed to extensive skeletal muscle wasting. The pathogenesis of cachexia is multifactorial because of complex interactions of tumor and host factors. The irreversible wasting syndrome has been ascribed to systemic inflammation, insulin resistance, dysfunctional mitochondria, oxidative stress, and heightened activation of ubiquitin-proteasome system and macroautophagy. Accumulating evidence suggests that deviant regulation of an array of signaling pathways engenders cancer cachexia where the human body is sustained in an incessant self-consuming catabolic state. Recent studies have further suggested that several components of endoplasmic reticulum (ER) stress-induced unfolded protein response (UPR) are activated in skeletal muscle of animal models and muscle biopsies of cachectic cancer patients. However, the exact role of ER stress and the individual arms of the UPR in the regulation of skeletal muscle mass in various catabolic states including cancer has just begun to be elucidated. This review provides a succinct overview of emerging roles of ER stress and the UPR in cancer-induced skeletal muscle wasting.

Serum levels of the adipokine zinc-alpha2-glycoprotein (ZAG) predict mortality in hemodialysis patients

Wasting has been associated with increased cardiovascular and all-cause mortality in chronic kidney disease (CKD). We investigated whether serum zinc-alpha2-glycoprotein (ZAG), a potent cachectic and lipid-mobilizing factor that is increased in patients with CKD, predicts clinical outcomes in patients on chronic hemodialysis. We quantified serum ZAG at baseline in a prospective cohort of 252 patients undergoing maintenance hemodialysis. Serum ZAG concentrations were inversely associated with serum albumin, creatinine, and triglycerides and, conversely, positively associated with age. Although ZAG is strongly linked to protein energy wasting (PEW) in patients with cancer, higher ZAG concentrations were not associated with PEW in our cohort. During a mean study follow-up of 954 days, 49 patients died and 62 patients experienced a cardiovascular event. Kaplan-Meier analysis revealed a significant correlation between serum ZAG concentrations and all-cause mortality and cardiovascular events. In separate multivariable Cox regression models, serum ZAG concentrations remained significantly associated with all-cause mortality and cardiovascular events after adjustment for demographic factors (age, sex, and dialysis vintage), metabolic parameters (serum albumin, prealbumin, triglycerides, cholesterol, normalized protein catabolic rate, and body mass index), and cardiovascular risk factors (diabetes, dyslipidemia, history of cardiovascular disease, smoking, and diuretic use as a proxy of residual renal function). Thus, serum ZAG appears to be a strong and independent predictor of mortality and cardiovascular events in patients with end-stage renal disease. Further studies are necessary to confirm this association and to elucidate the underlying mechanisms.

Adipokine zinc-α2-glycoprotein alleviates lipopolysaccharide-induced inflammatory responses through the β3-AR/PKA/CREB pathway

Humans and animals frequently experience dysmetabolism induced by inflammation. Zinc-α2-glycoprotein (ZAG), a newly identified adipokine, is potentially involved in lipid metabolism. Our previous study revealed that the ZAG content increased after lipopolysaccharide (LPS) treatment. To clarify ZAG's possible effects on inflammatory responses and lipid metabolism, we used gene overexpression and knockout mice as models to investigate the function of ZAG during inflammation. The results showed that LPS increased plasma triglyceride, non-esterified fatty acid and hepatic triglyceride, while ZAG overexpression decreased these effects. Furthermore, ZAG overexpression weakened inflammatory responses, suppressed lipogenesis, and improved mitochondrial function during inflammation. ZAG overexpression also increased β3-adrenoreceptor, protein kinase A, and phosphorylated cyclic adenosine monophosphate-response element binding protein (CREB), promoted the combination of CREB and CREB-binding protein (CBP), and competitively inhibited the combination of nuclear factor-κB and CBP. After ZAG knockout, LPS-induced the hyperlipidemia worsened. ZAG knockout aggravated inflammatory responses, promoted lipogenesis, and weakened mitochondrial function during inflammation. ZAG knockout also decreased β3-adrenoreceptor and protein kinase A. The present study demonstrated that ZAG alleviated lipid metabolism disorders by weakening inflammatory responses. The β3-adrenoreceptor/protein kinase A/CREB pathway mediated the effects of ZAG on inflammation. These results will provide new insight for research on anti-inflammation.

Expression and Function of Zinc-α2-Glycoprotein

Zinc-α2-glycoprotein (ZAG), encoded by the AZGP1 gene, is a major histocompatibility complex I molecule and a lipid-mobilizing factor. ZAG has been demonstrated to promote lipid metabolism and glucose utilization, and to regulate insulin sensitivity. Apart from adipose tissue, skeletal muscle, liver, and kidney, ZAG also occurs in brain tissue, but its distribution in brain is debatable. Only a few studies have investigated ZAG in the brain. It has been found in the brains of patients with Krabbe disease and epilepsy, and in the cerebrospinal fluid of patients with Alzheimer disease, frontotemporal lobe dementia, and amyotrophic lateral sclerosis. Both ZAG protein and AZGP1 mRNA are decreased in epilepsy patients and animal models, while overexpression of ZAG suppresses seizure and epileptic discharges in animal models of epilepsy, but knowledge of the specific mechanism of ZAG in epilepsy is limited. In this review, we summarize the known roles and molecular mechanisms of ZAG in lipid metabolism and glucose metabolism, and in the regulation of insulin sensitivity, and discuss the possible mechanisms by which it suppresses epilepsy.

ZAG alleviates HFD-induced insulin resistance accompanied with decreased lipid depot in skeletal muscle in mice

Over the past two decades, intramuscular lipids have been viewed as a cause of insulin resistance due to their ability to suppress insulin-stimulated glucose uptake in skeletal muscle. Zinc-α2-glycoprotein (ZAG) is an adipokine involved in lipolysis of white adipose tissue (WAT). To investigate the action of ZAG on insulin resistance induced by a high-fat diet (HFD), which affects the intramuscular fat, mice were divided into three groups, normal diet, HFD, and ZAG treatment under HFD (HFZ). The results showed that the insulin sensitivity of ZAG-treated mice was significantly improved. The body weight, WAT weight, and intramuscular fat were significantly decreased in the HFZ group compared with the HFD group. The lipolytic enzymes, including phosphorylation of hormone-sensitive lipase and adipose triglyceride lipase, were significantly upregulated in the skeletal muscle of mice that received the ZAG treatment compared with the HFD group. Insulin signaling proteins, such as phosphorylation of insulin receptor substrate 1 and cell membrane glucose transporter type 4, were also significantly increased in the skeletal muscle of the ZAG-treated group. Furthermore, a metabolic rate study showed that ZAG overexpression increases the respiratory exchange ratio and heat production. In vitro, ZAG treatment promotes glucose uptake and decreases intracellular lipids in C2C12 myotubes. Taken together, these data showed that overexpression of ZAG alleviates HFD-induced insulin resistance in mice, along with decreasing the lipid content of skeletal muscle.

Zinc alpha2 glycoprotein protects against obesity-induced hepatic steatosis

BACKGROUND/AIM

Nonalcoholic fatty liver disease (NAFLD) is characterized by hepatic steatosis, impaired insulin sensitivity, and chronic low-grade inflammation. Our previous studies indicated that zinc alpha2 glycoprotein (ZAG) alleviates palmitate (PA)-induced intracellular lipid accumulation in hepatocytes. This study is to further characterize the roles of ZAG on the development of hepatic steatosis, insulin resistance (IR), and inflammation.

METHODS

ZAG protein levels in the livers of NAFLD patients, high-fat diet (HFD)-induced or genetically (ob/ob) induced obese mice, and in PA-treated hepatocytes were determined by western blotting. C57BL/6J mice injected with an adenovirus expressing ZAG were fed HFD for indicated time to induce hepatic steatosis, IR, and inflammation, and then biomedical, histological, and metabolic analyses were conducted to identify pathologic alterations in these mice. The molecular mechanisms underlying ZAG-regulated hepatic steatosis were further explored and verified in mice and hepatocytes.

RESULTS

ZAG expression was decreased in NAFLD patient liver biopsy samples, obese mice livers, and PA-treated hepatocytes. Simultaneously, ZAG overexpression alleviated intracellular lipid accumulation via upregulating adiponectin and lipolytic genes (FXR, PPARα, etc.) while downregulating lipogenic genes (SREBP-1c, LXR, etc.) in obese mice as well as in cultured hepatocytes. ZAG improved insulin sensitivity and glucose tolerance via activation of IRS/AKT signaling. Moreover, ZAG significantly inhibited NF-ĸB/JNK signaling and thus resulting in suppression of obesity-associated inflammatory response in hepatocytes.

CONCLUSIONS

Our results revealed that ZAG could protect against NAFLD by ameliorating hepatic steatosis, IR, and inflammation.

The tumor secretory factor ZAG promotes white adipose tissue browning and energy wasting

Cachexia is a complex tissue-wasting syndrome characterized by inflammation, hypermetabolism, increased energy expenditure, and anorexia. Browning of white adipose tissue (WAT) is one of the significant factors that contribute to energy wasting in cachexia. By utilizing a cell implantation model, we demonstrate here that the lipid mobilizing factor zinc-α₂-glycoprotein (ZAG) induces WAT browning in mice. Increased circulating levels of ZAG not only induced lipolysis in adipose tissues but also caused robust browning in WAT. Stimulating WAT progenitors with ZAG recombinant protein or expression of ZAG in mouse embryonic fibroblasts (MEFs) strongly enhanced brown-like differentiation. At the molecular level, ZAG stimulated peroxisome proliferator-activated receptor γ (PPARγ) and early B cell factor 2 expression and promoted their recruitment to the PR/SET domain 16 (Prdm16) promoter, leading to enhanced expression of Prdm16, which determines brown cell fate. In brown adipose tissue, ZAG stimulated the expression of PPARγ and PPARγ coactivator 1α and promoted recruitment of PPARγ to the uncoupling protein 1 (Ucp1) promoter, leading to increased expression of Ucp1. Overall, our results reveal a novel function of ZAG in WAT browning and highlight the targeting of ZAG as a potential therapeutic application in humans with cachexia.-Elattar, S., Dimri, M., Satyanarayana, A. The tumor secretory factor ZAG promotes white adipose tissue browning and energy wasting.

Overexpression of zinc-α2-glycoprotein suppressed seizures and seizure-related neuroflammation in pentylenetetrazol-kindled rats

BACKGROUND

Zinc-α2-glycoprotein (ZAG) is a 42-kDa protein reported as an anti-inflammatory adipocytokine. Evidences from clinical and experimental studies revealed that brain inflammation plays important roles in epileptogenesis and seizure. Interestingly, closely relationship between ZAG and many important inflammatory mediators has been proven. Our previous study identified ZAG in neurons and found that ZAG is decreased in epilepsy and interacts with TGFβ and ERK. This study aimed to investigate the role of ZAG in seizure and explore its effect on seizure-related neuroinflammation.

METHODS

We overexpressed AZGP1 in the hippocampus of rats via adeno-associated virus vector injection and observed their seizure behavior and EEG after pentylenetetrazol (PTZ) kindling. The level of typical inflammation mediators including TNFα, IL-6, TGFβ, ERK, and ERK phosphorylation were determined.

RESULTS

The overexpression of AZGP1 reduced the seizure severity, prolonged the latency of kindling, and alleviated epileptiform discharges in EEG changes induced by PTZ. Overexpression of AZGP1 also suppressed the expression of TNFα, IL-6, TGFβ, and ERK phosphorylaton in PTZ-kindled rats.

CONCLUSIONS

ZAG may inhibit TGFβ-mediated ERK phosphorylation and inhibit neuroinflammation mediated by TNFα and IL-6, suggesting ZAG may suppress seizure via inhibiting neuroinflammation. ZAG may be a potential and novel therapeutic target for epilepsy.

Cord blood concentrations of leptin, zinc-α2-glycoprotein, and adiponectin, and adiposity gain during the first 3 mo of life

OBJECTIVES

Adipose tissue development starts in intrauterine life and cytokines are involved in this process. Therefore, understanding the role of cytokines in the fat mass gain of infants is crucial to prevent obesity later in life. Furthermore, recent evidence indicates a sex-specific link between cytokines and adipose tissue development. The objective of this study was to assess sex-specific relationships of cord blood concentrations of the cytokines leptin, zinc-α2-glycoprotein (ZAG), and adiponectin with infant adiposity during the first 3 mo of life.

METHODS

This was a prospective cohort study of 104 mother-infant pairs that were selected from a maternity hospital in Sao Paulo, Brazil. Cord blood leptin, ZAG, and adiponectin were determined by enzyme-linked immunosorbent assays. The body composition of the infants was assessed monthly by air displacement plethysmography. A multiple linear regression analysis was conducted with the average fat mass gain from birth to the third month of life as the outcome and cord blood leptin, ZAG, and adiponectin as the variables of interest.

RESULTS

Leptin was inversely associated with fat mass gain in the first 3 mo of life (P = 0.003; adjusted R² = 0.09). There were inverse associations of leptin (P = 0.021), ZAG (P = 0.042), and maternal body mass index (P = 0.04) with fat mass gain in girls (adjusted R² = 0.29) but fat mass gain in boys was positively associated with gestational age (P = 0.01; adjusted R² = 0.15).

CONCLUSIONS

The results of this study suggest that adiposity programming is sex-specific, which highlights the need to investigate the different metabolic mechanisms that are involved in adipogenesis.

Zinc-α2-Glycoprotein Is Associated with Obesity in Chinese People and HFD-Induced Obese Mice

Zinc-α2-glycoprotein (ZAG) plays an important role in the regulation of body weight, body fat, and glucose metabolism. In this study, we first measured ZAG levels in serum and ZAG mRNA levels in subcutaneous white adipose tissue (sWAT) among overweight/obese patients and lean control subjects. Second, we investigated the effects of ZAG administration on the body weight, body fat and glucose metabolism of high-fat diet (HFD)-induced obese ICR mice and the possible mechanisms involved. The results showed that serum ZAG and mRNA levels in sWAT were significantly decreased in overweight/obese patients and that both showed a negative association with body mass index (BMI) and body weight after adjustment for age and sex. Further partial correlation analysis found that ZAG mRNA expression was positively related with several WAT browning-related genes, including uncoupling protein 1 (UCP1) (r = 0.67) and peroxisome proliferator-activated receptor gamma coactivator 1 alpha (PGC1a) (r = 0.60), in the sWAT of all subjects. Additionally, intraperitoneal injection of a ZAG expression plasmid (5 μg/injection, four times a week) in HFD-induced obese mice for 8 weeks demonstrated that ZAG overexpression significantly decreased body weight and WAT mass, and greatly increased the glucose tolerance of obese mice, as shown by the intraperitoneal glucose tolerance test (IPGTT) and intraperitoneal insulin tolerance test (IPITT). The staining of UCP1-positive adipocytes was significantly stronger in the sWAT of ZAG-treated obese mice than in that of obese control mice. The mRNA and protein levels of PGC1α in sWAT were significantly increased to 2.2- and 5.3-fold, respectively, compared with HFD obese mice, and there was a strong positive correlation between the expression levels of Zag and Pgc1α in mouse sWAT (r = 0.74). A similar phenomenon was also observed in visceral white adipose tissue (vWAT): the mRNA and protein levels of PGC1α were increased to 1.9- and 3.6-fold, respectively, when obese mice were treated with ZAG. In conclusion, ZAG levels in both sWAT and serum are inversely related with BMI and body weight in Chinese subjects. The action of ZAG on body weight, fat mass and glucose metabolism may be realized through activating PGC1α expression in sWAT and vWAT, then promoting WAT browning in obese mice.

The relationship of serum adipokines with malnutrition inflammation score in haemodialysis

BACKGROUND

Protein-energy wasting is a prevalent disorder in haemodialysis. Zinc-α2-glycoprotein (ZAG) and adipose triglyceride lipase (ATGL) are novel adipokines with recognized lipolytic effects and proposed role in metabolic homoeostasis. This study was conducted to investigate the association of ZAG and ATGL concentrations with malnutrition-inflammation score (MIS) and metabolic profile of patients with haemodialysis.

MATERIALS AND METHODS

Eighty-eight patients under regular haemodialysis were divided based on MIS to normal to mild wasting (NMW; n = 35) or moderate wasting (MW; n = 53) group. Anthropometric measurements along with fasting serum concentrations of ZAG, ATGL, free fatty acids (FFAs), albumin, transferrin, total iron-binding capacity (TIBC), hs-CRP, lipid profile and glucose metabolism were assessed.

RESULTS

Adipose triglyceride lipase concentration was significantly higher in MW than NMW group (10·89 ± 5·7 vs. 8·02 ± 3·37 mIU/mL; P = 0·008). The ZAG and FFAs were not significantly different between two groups. ATGL was directly correlated with FFAs in all of the patients (r = 0·284, P = 0·007) and MW (r = 0·32, P = 0·021), and marginally in NMW (r = 0·31, P = 0·057) groups. ATGL and odds of having mild or moderate wasting were significantly correlated (OR = 1·21, P = 0·033). A positive association was observed between ATGL with TG (r = 0·31, P = 0·049) and also with transferrin and TIBC (r = 0·44, P = 0·001) only in MW group. An inverse relationship was observed between ATGL and HDL in all of the participants (r=-0·222, P = 0·04). No significant correlation was observed between ZAG and other parameters.

CONCLUSIONS

The serum concentrations of ATGL, but not ZAG, were significantly higher in MW compared to NMW group. Each unit increase in ATGL concentrations was correlated with 21% increase in the odds of wasting severity. ATGL might play a role in wasting pathogenesis and metabolic profile in haemodialysis.

Changes in zinc-α2-glycoprotein (ZAG) plasma concentrations pre and post Roux-En-Y gastric bypass surgery (RYGB) or a very low calorie (VLCD) diet in clinically severe obese patients: Preliminary Study

The purpose of this preliminary study was to investigate changes in plasma concentrations of zinc-α2-glycoprotein (ZAG), a lipid mobilizing hormone, in obese subjects following Roux-En-Y Gastric Bypass (RYGB) surgery or a very low calorie diet (VLCD). Fasting blood concentrations and anthropometric measurements were measured pre and 12 weeks post intervention. 14 healthy, obese individuals underwent either RYGB (N=6) surgery or a VLCD (N=8). Body composition and fasting plasma ZAG concentrations were measured at baseline (pre) and 12 weeks post intervention (post). At pre-intervention baseline, there was no difference in plasma ZAG between the two intervention groups. Post-intervention, there was a significant overall reduction (F(1,11) = 32.8, p<0.001) in plasma ZAG, which was significant only within the RYGB group from pre to post intervention (33.2 ± 5.7 μg/ml to 26.7 ± 4.8 μg/ml (p<0.015)) and significantly greater than the change within the VLCD group. The change in ZAG was inversely correlated across groups with BMI reduction (r= −0.60, p<0.05), % body fat reduction (r= −0.68, p<0.015), reduction in weight (r= −0.58, p<0.05), and % weight loss (r= −0.70, p<0.05). Overall, subjects who underwent RYGB or VLCD had a significant reduction in plasma ZAG. This reduction was significant within the RYGB group alone, who lost a larger amount of weight than the VLCD group, which suggests that ZAG may have a protective effect during marked weight loss.

Zinc-α2-Glycoprotein Modulates AKT-Dependent Insulin Signaling in Human Adipocytes by Activation of the PP2A Phosphatase

Objective

Evidence from mouse models suggests that zinc-α2-glycoprotein (ZAG) is a novel anti-obesity adipokine. In humans, however, data are controversial and its physiological role in adipose tissue (AT) remains unknown. Here we explored the molecular mechanisms by which ZAG regulates carbohydrate metabolism in human adipocytes.

Methods

ZAG action on glucose uptake and insulin action was analyzed. β1 and β2-adrenoreceptor (AR) antagonists and siRNA targeting PP2A phosphatase were used to examine the mechanisms by which ZAG modulates insulin sensitivity. Plasma levels of ZAG were measured in a lean patient cohort stratified for HOMA-IR.

Results

ZAG treatment increased basal glucose uptake, correlating with an increase in GLUT expression, but induced insulin resistance in adipocytes. Pretreatment of adipocytes with propranolol and a specific β1-AR antagonist demonstrated that ZAG effects on basal glucose uptake and GLUT4 expression are mediated via β1-AR, whereas inhibition of insulin action is dependent on β2-AR activation. ZAG treatment correlated with an increase in PP2A activity. Silencing of the PP2A catalytic subunit abrogated the negative effect of ZAG on insulin-stimulated AKT phosphorylation and glucose uptake but not on GLUT4 expression and basal glucose uptake. ZAG circulating levels were unchanged in a lean patient cohort stratified for HOMA-IR. Neither glucose nor insulin was associated with plasma ZAG.

Conclusions

ZAG inhibits insulin-induced glucose uptake in human adipocytes by impairing insulin signaling at the level of AKT in a β2-AR- and PP2A-dependent manner.

Cancer cachexia: understanding the molecular basis

Cancer cachexia is a devastating, multifactorial and often irreversible syndrome that affects around 50-80% of cancer patients, depending on the tumour type, and that leads to substantial weight loss, primarily from loss of skeletal muscle and body fat. Since cachexia may account for up to 20% of cancer deaths, understanding the underlying molecular mechanisms is essential. The occurrence of cachexia in cancer patients is dependent on the patient response to tumour progression, including the activation of the inflammatory response and energetic inefficiency involving the mitochondria. Interestingly, crosstalk between different cell types ultimately seems to result in muscle wasting. Some of the recent progress in understanding the molecular mechanisms of cachexia may lead to new therapeutic approaches.

Subcutaneous adipose tissue zinc-α2-glycoprotein is associated with adipose tissue and whole-body insulin sensitivity

OBJECTIVE

To examine the regulatory aspects of zinc-α2-glycoprotein (ZAG) association with obesity-related insulin resistance.

METHODS

ZAG mRNA and protein were analyzed in subcutaneous adipose tissue (AT) and circulation of lean, obese, prediabetic, and type 2 diabetic men; both subcutaneous and visceral AT were explored in lean and extremely obese. Clinical and ex vivo findings were corroborated by results of in vitro ZAG silencing experiment.

RESULTS

Subcutaneous AT ZAG was reduced in obesity, with a trend to further decrease with prediabetes and type 2 diabetes. ZAG was 3.3-fold higher in subcutaneous than in visceral AT of lean individuals. All differences were lost in extreme obesity. Obesity-associated changes in AT were not paralleled by alterations of circulating ZAG. Subcutaneous AT ZAG correlated with adiposity, adipocyte hypertrophy, whole-body and AT insulin sensitivity, mitochondrial content, expression of GLUT4, PGC1α, and adiponectin. Subcutaneous AT ZAG and adipocyte size were the only predictors of insulin sensitivity, independent on age and BMI. Silencing ZAG resulted in reduced adiponectin, IRS1, GLUT4, and PGC1α gene expression in primary human adipocytes.

CONCLUSIONS

ZAG in subcutaneous, but not in visceral AT, was markedly reduced in obesity. Clinical, cellular, and molecular evidence indicate that ZAG plays an important role in modulating whole-body and AT insulin sensitivity.

The relationship between renal function and plasma concentration of the cachectic factor zinc-alpha2-glycoprotein (ZAG) in adult patients with chronic kidney disease

Zinc-α2-glycoprotein (ZAG), a potent cachectic factor, is increased in patients undergoing maintenance dialysis. However, there is no data for patients before initiation of renal replacement therapy. The purpose of the present study was to assess the relationship between plasma ZAG concentration and renal function in patients with a large range of glomerular filtration rate (GFR). Plasma ZAG concentration and its relationship to GFR were investigated in 71 patients with a chronic kidney disease (CKD) stage 1 to 5, 17 chronic hemodialysis (HD), 8 peritoneal dialysis (PD) and 18 non-CKD patients. Plasma ZAG concentration was 2.3-fold higher in CKD stage 5 patients and 3-fold higher in HD and PD patients compared to non-CKD controls (P<0.01). The hemodialysis session further increased plasma ZAG concentration (+39%, P<0.01). An inverse relationship was found between ZAG levels and plasma protein (r_s = −0.284; P<0.01), albumin (r_s = −0.282, P<0.05), hemoglobin (r_s = −0.267, P<0.05) and HDL-cholesterol (r_s = −0.264, P<0.05) and a positive correlation were seen with plasma urea (r_s = 0.283; P<0.01). In multiple regression analyses, plasma urea and HDL-cholesterol were the only variables associated with plasma ZAG (r² = 0.406, P<0.001). In CKD-5 patients, plasma accumulation of ZAG was not correlated with protein energy wasting. Further prospective studies are however needed to better elucidate the potential role of ZAG in end-stage renal disease.

White adipose tissue overproduces the lipid-mobilizing factor zinc α2-glycoprotein in chronic kidney disease

Chronic kidney disease (CKD) is frequently associated with protein-energy wasting, a recognized strong predictive factor of mortality. Zinc α2-glycoprotein (ZAG) is a new adipokine involved in body weight control through its lipid-mobilizing activity. Here we tested whether the uremic environment in CKD could alter ZAG production by white adipose tissue and contribute to CKD-associated metabolic disturbances. Compared with normal plasma, uremic plasma induced a significant increase in ZAG synthesis (124%), was associated with a significant increase in basal lipolysis (31%), and significantly blunted lipogenesis (-53%) in 3T3-L1 adipocytes in vitro. In 5/6 nephrectomized rats and mice in vivo, there was a significant decrease in white adipose tissue accretion (-44% and -43%, respectively) and a significantly higher white adipose tissue content of ZAG protein than in sham-operated, pair-fed control animals (498% and 106%, respectively). Subcutaneous white adipose tissue biopsies from patients with end-stage renal disease exhibited a higher content of ZAG (573%) than age-matched controls. Thus, the ZAG content is increased in white adipose tissue from patients or animal models with CKD. Overproduction of ZAG in CKD could be a major contributor to metabolic disturbances associated with CKD.

Contrasts between the effects of zinc-α2-glycoprotein, a putative β3/2-adrenoceptor agonist and the β3/2-adrenoceptor agonist BRL35135 in C57Bl/6 (ob/ob) mice

Previous studies by Tisdale et al. have reported that zinc-α(2)-glycoprotein (ZAG (AZGP1)) reduces body fat content and improves glucose homeostasis and the plasma lipid profile in Aston (ob/ob) mice. It has been suggested that this might be mediated via agonism of β(3)- and possibly β(2)-adrenoceptors. We compared the effects of dosing recombinant human ZAG (100 μg, i.v.) and BRL35135 (0.5 mg/kg, i.p.), which is in rodents a 20-fold selective β(3)- relative to β(2)-adrenoceptor agonist, given once daily for 10 days to male C57Bl/6 Lep(ob)/Lep(ob) mice. ZAG, but not BRL35135, reduced food intake. BRL35135, but not ZAG, increased energy expenditure acutely and after sub-chronic administration. Only BRL35135 increased plasma concentrations of glycerol and non-esterified fatty acid. Sub-chronic treatment with both ZAG and BRL35135 reduced fasting blood glucose and improved glucose tolerance, but the plasma insulin concentration 30 min after administration of glucose was lowered only by BRL35135. Both ZAG and BRL35135 reduced β(1)-adrenoceptor mRNA levels in white adipose tissue, but only BRL35135 reduced β(2)-adrenoceptor mRNA. Both ZAG and BRL35135 reduced β(1)-adrenoceptor mRNA levels in brown adipose tissue, but neither influenced β(2)-adrenoceptor mRNA, and only BRL35135 increased β(3)-adrenoceptor and uncoupling protein-1 (UCP1) mRNA levels in brown adipose tissue. Thus, ZAG and BRL35135 had similar effects on glycaemic control and shared some effects on β-adrenoceptor gene expression in adipose tissue, but ZAG did not display the thermogenic effects of the β-adrenoceptor agonist, nor did it increase β(3)-adrenoceptor or UCP1 gene expression in brown adipose tissue. ZAG does not behave as a typical β(3/2)-adrenoceptor agonist.

Zinc-α2-glycoprotein: is there association between this new adipokine and body composition in hemodialysis patients?

Peptides involved in the regulation of body composition are of interest in hemodialysis (HD) patients because protein wasting associated with high fat mass (FM) is present in these patients. Zinc-α2-glycoprotein (ZAG), a new adipokine, is involved in the regulation of lipid metabolism, adiposity, and energy balance. The purpose of this study was to evaluate ZAG levels and its relationship with body composition and dietary intake in HD patients. Forty-nine HD patients (28 men, 53.1 ± 12.5 years, and BMI 24.0 ± 4.3 kg/m2) were studied and compared with 20 healthy subjects (9 men, 49.5 ± 15.2 years, and BMI 25.6 ± 4.1 kg/m(2)). Plasma ZAG levels were measured using the ELISA methods and body composition was evaluated through anthropometric data. Dietary intake was assessed 3 days by 24-hour food recall. Although most of the HD patients (59.2%) were eutrophic according to BMI, 92.3% presented high percentage of body fat (BF), and 43.5%, reduced fat-free mass according to midarm muscle circumference values. ZAG levels were ∼2.5-fold higher in HD patients (135.9 ± 40.9 mg/L) compared with healthy individuals (54.6 ± 23.0 mg/L) (p < 0.0001). Circulating ZAG was not associated with dietary intake; however, this peptide was negatively correlated with %BF and, for each 1% reduction in BF, ZAG levels increased by 2.4 mg/L (p = 0.02). In summary, circulating ZAG is increased and inversely correlated with adiposity in HD patients; however, in spite of its higher plasma levels, the majority of HD patients did not show low BF.

The Newest Hypothesis about Vitiligo: Most of the Suggested Pathogeneses of Vitiligo Can Be Attributed to Lack of One Factor, Zinc-α2-Glycoprotein

Zinc-α2-glycoprotein (ZAG) is a recently identified adipokine, assigned to the chromosome 7q22.1. It is a multidisciplinary protein, which is secreted in various body fluids. The ZAG plays roles in lipolysis, regulation of metabolism, cell proliferation and differentiation, regulation of melanin synthesis, cell adhesion, immunoregulation, and so forth. Vitiligo is the most common depigmenting skin disorder, characterized by acquired, progressive, and circumscribed amelanosis of the skin and hair. It commonly begins in childhood or young adulthood. The pathogenesis of this disorder is uncertain, but it appears to be dependent on the interaction of genetic, immunological, and neurological factors. For the first time, we pointed the probable association between ZAG and vitiligo. Herein, I have described this association in different views. By confirming this association, a surprising progression will occur in the treatment of this prevalent debilitating disease.

Molecular mechanisms of cachexia in chronic disease

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

Role of β-adrenergic receptors in the anti-obesity and anti-diabetic effects of zinc-α2-glycoprotien (ZAG)

OBJECTIVES

The goal of the current study is to determine whether the β-adrenoreceptor (β-AR) plays a role in the anti-obesity and anti-diabetic effects of zinc-α2-glycoprotein (ZAG).

MATERIAL AND METHODS

This has been investigated in CHO-K1 cells transfected with the human β1-, β2-, β3-AR and in ob/ob mice. Cyclic AMP assays were carried out along with binding studies. Ob/ob mice were treated with ZAG and glucose transportation and insulin were examined in the presence or absence of propranolol.

RESULTS

ZAG bound to the β3-AR with higher affinity (Kd 46±1nM) than the β2-AR (Kd 71±3nM) while there was no binding to the β1-AR, and this correlated with the increases in cyclic AMP in CHO-K1 cells transfected with the various β-AR and treated with ZAG. Treatment of ob/ob mice with ZAG increased protein expression of β3-AR in gastrocnemius muscle, and in white and brown adipose tissues, but had no effect on expression of β1- and β2-AR. A reduction of body weight was seen and urinary glucose excretion, increase in body temperature, reduction in maximal plasma glucose and insulin levels in the oral glucose tolerance test, and stimulation of glucose transport into skeletal muscle and adipose tissue, were completely attenuated by the non-specific β-AR antagonist propranolol.

CONCLUSION

The results suggest that the effects of ZAG on body weight and insulin sensitivity in ob/ob mice are manifested through a β-3AR, or possibly a β2-AR.

Is zinc-α2-glycoprotein a cardiovascular protective factor for patients undergoing hemodialysis?

BACKGROUND

Zinc-α2-glycoprotein (ZAG) is a lipid mobilizing factor. Its anti-inflammatory action and expression pattern suggest that ZAG could act by protecting against the obesity-associated disorders. In hemodialysis (HD) patients, ZAG levels were described to be elevated but its effects on markers of inflammation and LDL oxidation are still unclear. We investigated the relationship between ZAG and markers of systemic inflammation and LDL atherogenic modification profile in HD patients.

METHODS

Forty-three patients regularly on HD were studied and compared to 20 healthy subjects. Plasma ZAG, adiponectin, electronegative LDL [LDL(-)], an atherosclerotic negatively charged LDL subfraction, and anti-LDL(-) autoantibodies levels were measured by ELISA. Markers of inflammation and atherogenic cell recruitment (TNF-α, interleukin-6, VCAM-1, ICAM-1, MCP-1 and PAI-1) were also determined.

RESULTS

Inflammatory markers and atherogenic cell recruitment were higher in HD patients when compared to healthy subjects. ZAG levels were also higher in HD patients (151.5 ± 50.1 mg/l vs 54.6 ± 23.0 mg/l; p<0.0001) and its levels were negatively correlated with TNF-α (r=-0.39; p=0.001) and VCAM-1 (r=-0.52; p<0.0001) and, positively correlated with anti-LDL(-) autoantibodies (r=0.38; p=0.016). On multivariate analyses, plasma ZAG levels were independently associated with VCAM-1 (p=0.01).

CONCLUSION

ZAG is inversely associated with markers of pro-atherogenic factors linked to systemic inflammation and oxidative stress. Thus, this adipokine may constitute a novel marker of a favorable metabolic profile regarding cardiovascular risk factors in HD population.

Con A-binding protein Zn-α2-glycoprotein on human sperm membrane is related to acrosome reaction and sperm fertility

Fertilization, the recognition and fusion between spermatozoa and oocyte, involves various molecules on the spermatozoa and oocyte membranes. Concanavalin A (ConA)-binding proteins may be one of the molecules involved in mammal spermatozoa fertilization; however, their structure and function remain largely unknown. Here, we initially identified a ConA-binding protein, Zn-α2-glycoprotein (ZAG), involved in regulating the acrosome reaction (AR) of human spermatozoa. ZAG is localized on the pre-equatorial region covering the acrosome, neck and tail (some parts of middle piece and principal piece respectively) regions of the acrosome intact human spermatozoa, and disappears in the acrosomal region of the acrosome-reacted spermatozoa. Polyclonal antibodies against human recombinant ZAG significantly reduced the AR and sperm capability binding to human zona pellucida or penetration into zona-free hamster oocytes. Furthermore, assessment of the signaling pathways regulated by ZAG revealed that ZAG affects sperm AR through both the cAMP/PKA and PKC pathways. These results indicate that ZAG, which is present on the human sperm membrane, plays a critical role in the AR and subsequently, may be involved in sperm fertility.

The adipokine zinc-α2-glycoprotein activates AMP kinase in human primary skeletal muscle cells

CONTEXT

Zinc-α2-glycoprotein (ZAG) induces lipid mobilization in adipose tissue (AT) and stimulates energy utilization in AT and skeletal muscle by up-regulation of UCP isoforms and GLUT4.

OBJECTIVE

Our study aimed to investigate whether ZAG activates AMPKα, an important regulator of energy metabolism, in human skeletal muscle cells (SkMc).

MATERIALS AND METHODS

SkMc were treated with recombinant ZAG, and activation of AMPKα and ACC, protein abundance of GLUT4, and UCP2 and UCP3 gene expression were analysed.

RESULTS

Treatment of SkMc with ZAG induced short-time phosphorylation of AMPKα and ACC. Furthermore, AMPKα phosphorylation was elevated after 24 h, while for ACC no activation was observed. GLUT4 level was increased by 1.3-fold. However, UCP2 and UCP3 expression remained unaltered.

DISCUSSION AND CONCLUSION

These results show that ZAG leads to phosphorylation of AMPKα and ACC, thereby activating a pathway central to the regulation of energy metabolism. This mechanism may be involved in mediating the effects of ZAG in relation to increased energy utilization.

Targeting thermogenesis and related pathways in anti-obesity drug discovery

The health consequences of the obesity epidemic are a huge burden on patients and society. Yet it remains an unmet therapeutic need. Lifestyle or behaviour modification, although desirable, seems to benefit only a few and bariatric surgery is not an option for all and not without risks. Nevertheless, bariatric surgery is currently the gold standard in terms of weight loss therapy and any weight loss agent will be in combination with management of lifestyle modification. Sadly, there is a poor history for the pharmacological treatment of obesity and repeated safety concerns have attracted intense regulatory scrutiny. Indeed, recent market withdrawals leave us with just one agent approved for the long term treatment of obesity and that is only mildly efficacious in terms of weight loss, although it is beneficial in terms of metabolic health. There are two broad pharmacological approaches that can be applied in obesity drug discovery: reduce intake (or absorption) or increase expenditure (thermogenesis) of calories. In this review we will look at the latter approach. We will cover regulatory requirements and the rationale for this approach. We believe that post-obese subjects display abnormal metabolic responses to weight loss that almost inevitably leads to weight regain. We will then explore a number of approaches that potentially increase thermogenesis in humans. The challenge we have is in accumulating enough human data to validate this approach using drugs.

Structural diversity of class I MHC-like molecules and its implications in binding specificities

The binding groove of class I major histocompatibility complex (MHC) class is essentially important for antigen binding and presentation on T cells. There are several molecules that have analogous conformations to class I MHC. However, they bind specifically to varying types of ligands and cell-surface receptors in order to elicit an immune response. To elucidate how such recognition is achieved in classical MHC-I like molecules, we have extensively analyzed the structure of human leukocyte antigen (HLA-1), neonatal Fc receptor (FcRn), hereditary hemochromatosis protein (HFE), cluster of differentiation 1 (CD1), gamma delta T cell receptor ligand (Τ22), zinc-α2-glycoprotein (ZAG), and MHC class I chain-related (MIC-A) proteins. All these molecules have analogous structural anatomy, divided into three distinct domains, where α1-α2 superdomains form a groove-like structure that potentially bind to certain ligand, while the α3 domain adopts a fold resembling immunoglobulin constant domains, and holds this α1-α2 platform and the light chain. We have observed many remarkable features of α1-α2 platform, which provide specificities to these proteins toward a particular class of ligands. The relative orientation of α1, α2, and α3 domains is primarily responsible for the specificity to the light chain. Interestingly, light chain of all these proteins is β₂-microglobulin (β₂M), except ZAG which has prolactin-induced protein (PIP). However, MIC-A is devoid of any light chain. Residues on β₂M recognize a sequence motif on the α3 domain that is essentially restricted to specific heavy chain of MHC class I molecules. Our analysis suggests that the structural features of class I molecules determine the recognition of different ligands and light chains, which are responsible for their corresponding functions through an inherent mechanism.

Thermogenesis and related metabolic targets in anti-diabetic therapy

Exercise, together with a low-energy diet, is the first-line treatment for type 2 diabetes type 2 diabetes . Exercise improves insulin sensitivity insulin sensitivity by increasing the number or function of muscle mitochondria mitochondria and the capacity for aerobic metabolism, all of which are low in many insulin-resistant subjects. Cannabinoid 1-receptor antagonists and β-adrenoceptor agonists improve insulin sensitivity in humans and promote fat oxidation in rodents independently of reduced food intake. Current drugs for the treatment of diabetes are not, however, noted for their ability to increase fat oxidation, although the thiazolidinediones increase the capacity for fat oxidation in skeletal muscle, whilst paradoxically increasing weight gain.There are a number of targets for anti-diabetic drugs that may improve insulin sensitivity insulin sensitivity by increasing the capacity for fat oxidation. Their mechanisms of action are linked, notably through AMP-activated protein kinase, adiponectin, and the sympathetic nervous system. If ligands for these targets have obvious acute thermogenic activity, it is often because they increase sympathetic activity. This promotes fuel mobilisation, as well as fuel oxidation. When thermogenesis thermogenesis is not obvious, researchers often argue that it has occurred by using the inappropriate device of treating animals for days or weeks until there is weight (mainly fat) loss and then expressing energy expenditure energy expenditure relative to body weight. In reality, thermogenesis may have occurred, but it is too small to detect, and this device distracts us from really appreciating why insulin sensitivity has improved. This is that by increasing fatty acid oxidation fatty acid oxidation more than fatty acid supply, drugs lower the concentrations of fatty acid metabolites that cause insulin resistance. Insulin sensitivity improves long before any anti-obesity effect can be detected.

Identification of serum proteins involved in pancreatic cancer cachexia

AIMS

Treatment of cachexia requires pharmacological intervention which, in turn, requires knowledge of the mediators and processes. Cachexia markers that are specifically expressed in pancreatic cancer and secreted into the blood circulation have yet to be identified. The aim of our study was to investigate the serum protein profiles and protein alterations associated with cachexia and to identify potential disease protein biomarkers indicative for this syndrome.

MAIN METHODS

Serum samples from cachectic and non-cachectic patients undergoing pancreatic cancer (PaCa) surgery and controls were investigated by Surface Enhanced Laser Desorption/Ionization Time-of-Flight Mass Spectrometry (SELDI-TOF-MS). The identity of detected discriminatory markers was determined by a combination of protein fractionation, chromatographic purification steps, gel electrophoresis, and mass spectrometry.

KEY FINDINGS

Using Cu-IMAC array and CM-10 array based SELDI-TOF-MS. we identified eleven up- and four down-regulated proteins associated with cachexia. CiphergenExpress analysis revealed four disease-associated protein features (38559Da, 9138Da, 8925Da and 3358Da) that were elevated by a factor of 2.3, 1.7, 1.4 and 1.4, respectively. Zinc-α2-glycoprotein (ZAG), apolipoproteins apo C-II and apo C-III and glucagon-like peptide-1 (GLP-1) were identified as markers for PaCa-associated cachexia syndrome. ZAG levels were additionally evaluated in serum and tissue samples by ELISA and immunohistochemistry and the obtained data confirmed the SELDI-TOF-MS results.

SIGNIFICANCE

The identified proteins could be routinely and reliably measured in the serum of patients and provide an elegant non-invasive approach for early diagnosis of cachectic pancreatic cancer patients. Controlling ZAG and GLP-1 activity could be beneficial in the management of cancers and cachexia-induced conditions.

Studies on the anti-obesity activity of zinc-α2-glycoprotein in the rat

OBJECTIVE

To investigate the anti-obesity effect of the adipokine zinc-α(2)-glycoprotein (ZAG) in rats and the mechanism of this effect.

SUBJECTS

Mature male Wistar rats (540 ± 83 g) were administered human recombinant ZAG (50 μg per 100 g body weight given intravenously daily) for 10 days, while control animals received an equal volume of phosphate-buffered saline (PBS).

RESULTS

Animals treated with ZAG showed a progressive decrease in body weight, without a decrease in food and water intake, but with a 0.4 °C rise in body temperature. Body composition analysis showed loss of adipose tissue, but an increase in lean body mass. The loss of fat was due to an increase in lipolysis as shown by a 50% elevation of plasma glycerol, accompanied by increased utilization of non-esterified fatty acids, as evidenced by the 55% decrease in plasma levels. Plasma levels of glucose and triglycerides were also reduced by 36-37% and there was increased expression of the glucose transporter 4 in both skeletal muscle and adipose tissue. Expression of the lipolytic enzymes adipose triglyceride lipase and hormone-sensitive lipase in the white adipose tissue (WAT) were increased twofold after ZAG administration. There was almost a twofold increased expression of uncoupling proteins 1 and 3 in brown adipose tissue and WAT, which would contribute to increased substrate utilization. Administration of ZAG increased ZAG expression twofold in the gastrocnemius muscle, BAT and WAT, which was probably necessary for its biological effect.

CONCLUSION

These results show that ZAG produces increased lipid mobilization and utilization in the rat.

Are tumoral factors responsible for host tissue wasting in cancer cachexia?

Both cytokines and tumor factors have been implicated in tissue loss in cancer cachexia. Loss of adipose tissue is most likely due to the tumor (and host) factor zinc-alpha2-glycoprotein because of its direct lipolytic effect, ability to sensitize adipocytes to lipolytic stimuli and increased expression in cachexia. TNF-alpha and the tumor factor proteolysis-inducing factor are the major contenders for skeletal muscle atrophy; both increase protein degradation through the ubiquitin-proteasome pathway and depress protein synthesis through phosphorylation of eukaryotic initiation factor 2 alpha. However, while most studies report proteolysis-inducing factor levels to correlate with the appearance of cachexia, there is some disagreement regarding a correlation between serum levels of TNF-alpha and weight loss. Furthermore, only antagonists to proteolysis inducing factor prevent muscle loss in cancer patients, suggesting that tumor factors are the most important.

Studies on the antiobesity effect of zinc-α2-glycoprotein in the ob/ob mouse

OBJECTIVE

To investigate the mechanism of the lipid depletion by zinc-α(2)-glycoprotein (ZAG).

DESIGN

Studies were conducted in the ob/ob mouse, or on isolated adipocytes from these animals or their lean counterparts.

RESULTS

Treatment of these animals for 15 days with ZAG (100  μg, intravenously, daily) resulted in a reduction of body weight of 6.55  g compared with phosphate-buffered saline-treated controls, without a change in food or water intake, but with a 0.4 °C rise in rectal temperature. ZAG-treated mice had a 30% reduction in carcass fat mass and a twofold increase in weight of brown adipose tissue. Epididymal adipocytes from ZAG-treated mice showed an increased expression of ZAG and hormone-sensitive lipase (HSL), and this was maintained for a further 3 days in the absence of ZAG. There was an increased lipolytic response to isoproterenol, which was retained for 3 days in vitro in the absence of ZAG. Expression of HSL was also increased in subcutaneous and visceral adipose tissue, as was also adipose triglyceride lipase (ATGL). There was a rapid loss of labelled lipid from epididymal adipose tissue of ZAG-treated mice, but not from the other depots, reflecting the difference in sensitivity to lipolytic stimuli. The increased expression of HSL and ATGL may involve the extracellular signal-regulated kinase (ERK) pathway, as the active (phospho) form was upregulated in all adipose depots after ZAG administration, whereas in vitro studies showed induction of HSL and ATGL by ZAG to be attenuated by PD98059, an inhibitor of the ERK pathway.

CONCLUSION

These results suggest that ZAG not only induces direct lipolysis, but also sensitizes adipose tissue to other lipolytic stimuli.

Zinc-α2-glycoprotein: an adipokine modulator of body fat mass?

The importance of white adipose tissue in the control of energy balance is now firmly recognized. In addition to fuel storage, adipocytes secrete an array of proteins factors (adipokines), which regulate multiple physiological and metabolic processes as well as influence body fat accumulation. Zinc-α2-glycoprotein (ZAG), a lipid mobilizing factor initially characterized as a tumor product associated with cachexia, has recently been identified as a novel adipokine. Although the exact role of ZAG in adipose tissue remains to be clarified, there is evidence that ZAG expression appears to be inversely related to adiposity, being upregulated in cachexia whereas reduced in obesity. Investigations on the regulation of ZAG give insights into its potential function in adipose tissue with a link to lipid mobilization and an anti-inflammatory action. Recent work shows that ZAG stimulates adiponectin secretion by human adipocytes. Data from genetic studies suggest that ZAG may be a candidate gene for body weight regulation; this is supported by the demonstration that ZAG-knockout mice are susceptible to weight gain, whereas transgenic mice overexpressing ZAG exhibit weight loss. The present review summarizes these new perspectives of ZAG and the potential mechanisms by which it might modulate adipose tissue mass and function.

Role of uncoupling proteins in cancer

Uncoupling proteins (UCPs) are a family of inner mitochondrial membrane proteins whose function is to allow the re-entry of protons to the mitochondrial matrix, by dissipating the proton gradient and, subsequently, decreasing membrane potential and production of reactive oxygen species (ROS). Due to their pivotal role in the intersection between energy efficiency and oxidative stress, UCPs are being investigated for a potential role in cancer. In this review we compile the latest evidence showing a link between uncoupling and the carcinogenic process, paying special attention to their involvement in cancer initiation, progression and drug chemoresistance.

Antidiabetic properties of zinc-alpha2-glycoprotein in ob/ob mice

Zinc-alpha(2)-glycoprotein (ZAG) is an adipokine associated with fat loss in cancer cachexia. The purpose of this study was to evaluate the ability of recombinant human ZAG to attenuate type 2 diabetes in the ob/ob mouse model. ZAG (50 microg daily, iv) induced a progressive loss of body weight (3.5 g in 5 d), without an effect on food or water intake but with a 0.4 C rise in body temperature, suggesting an increased energy expenditure. Despite an increased plasma glycerol, indicative of increased lipolysis, levels of glucose, triglycerides, and nonesterified fatty acids were decreased by 17, 25, and 62%, respectively, due to an increased use of both glucose and lipids by muscle and brown adipose tissue. The weight of the latter increased 2-fold, and there was increased expression of uncoupling proteins-1 and -3. Plasma insulin levels were reduced by 36%, whereas pancreatic insulin was increased 4-fold, and there was a 53% decrease in the total area under the glucose curve in the glucose tolerance test and reduced insulin requirement. There was an increase in skeletal muscle mass due to an increase in protein synthesis and a decrease in protein degradation. These results suggest that ZAG may potentially be effective in the treatment of type 2 diabetes.

Zinc-alpha2-glycoprotein in cachexia and obesity

PURPOSE OF REVIEW

Control of adipose mass is important in the treatment of both cachexia and obesity. This review focuses on a novel adipokine, zinc-alpha2-glycoprotein (ZAG), which plays an important role in the mobilization and utilization of stored lipids.

RECENT FINDINGS

An increased lipolysis is responsible for the loss of adipose tissue in cachexia, through an increased lipolytic response to catecholamines, arising from an increased expression of hormone-sensitive lipase. In obesity, there is a decreased response of adipocytes to catecholamines and reduced expression of hormone-sensitive lipase. ZAG was identified as a lipolytic factor produced by certain cachexia-inducing tumours, and subsequently adipose tissue (both white and brown), the expression of which was found to increase in cachexia. In contrast, ZAG expression is low in obesity. ZAG not only increases lipolysis in white adipose tissue through the classical cyclic AMP pathway, but also stimulates an increase in expression of uncoupling protein-1 in brown adipose tissue, which would stimulate utilization of the release lipid to generate heat. Homozygous ZAG null mice show an increase in body weight, especially when fed a high-fat diet, whereas adipocytes from such animals show a resistance to lipolysis by catecholamines and agents that increase cyclic AMP levels.

SUMMARY

These results suggest that ZAG may play an important role in the regulation of adipose mass in obesity and cachexia.

Mechanisms of cancer cachexia

Up to 50% of cancer patients suffer from a progressive atrophy of adipose tissue and skeletal muscle, called cachexia, resulting in weight loss, a reduced quality of life, and a shortened survival time. Anorexia often accompanies cachexia, but appears not to be responsible for the tissue loss, particularly lean body mass. An increased resting energy expenditure is seen, possibly arising from an increased thermogenesis in skeletal muscle due to an increased expression of uncoupling protein, and increased operation of the Cori cycle. Loss of adipose tissue is due to an increased lipolysis by tumor or host products. Loss of skeletal muscle in cachexia results from a depression in protein synthesis combined with an increase in protein degradation. The increase in protein degradation may include both increased activity of the ubiquitin-proteasome pathway and lysosomes. The decrease in protein synthesis is due to a reduced level of the initiation factor 4F, decreased elongation, and decreased binding of methionyl-tRNA to the 40S ribosomal subunit through increased phosphorylation of eIF2 on the alpha-subunit by activation of the dsRNA-dependent protein kinase, which also increases expression of the ubiquitin-proteasome pathway through activation of NFkappaB. Tumor factors such as proteolysis-inducing factor and host factors such as tumor necrosis factor-alpha, angiotensin II, and glucocorticoids can all induce muscle atrophy. Knowledge of the mechanisms of tissue destruction in cachexia should improve methods of treatment.

Cigarette smoking induces overexpression of a fat-depleting gene AZGP1 in the human

BACKGROUND

Smokers weigh less and have less body fat than nonsmokers. Increased body fat and weight gain are observed following smoking cessation. To assess a possible molecular mechanism underlying the inverse association between smoking and body weight, we hypothesized that smoking may induce the expression of a fat-depleting gene in the airway epithelium, the cell population that takes the brunt of the stress of cigarette smoke.

METHODS

To assess whether smoking up-regulates expression in the airway epithelium of genes associated with weight loss, microarray analysis was used to evaluate genes associated with fat depletion in large airway epithelial samples obtained by fiberoptic bronchoscopy from healthy smokers and healthy nonsmokers. As a candidate gene we further evaluated the expression of alpha(2)-zinc-glycoprotein 1 (AZGP1), a soluble protein that stimulates lipolysis, induces a reduction in body fat in mice, is associated with the cachexia related to cancer, and is known to be expressed in secretory cells of lung epithelium. AZGP1 protein expression was assessed by Western analysis and localization in the large airway epithelium by immunohistochemistry.

RESULTS

Both microarray and TaqMan analysis demonstrated that AZGP1 messenger RNA levels were higher in the large airway epithelium of healthy smokers compared to healthy nonsmokers (p < 0.05, all comparisons). Western analysis of airway biopsy specimens from smokers compared with those from nonsmokers demonstrated up-regulation of AZGP1 at the protein level, and immunohistochemical analysis demonstrated up-regulation of AZGP1 in secretory as well as neuroendocrine cells of smokers.

CONCLUSIONS

In the context that AZGP1 is involved in lipolysis and fat loss, its overexpression in the airway epithelium of chronic smokers may represent one mechanism for the weight difference in smokers vs nonsmokers.

Zinc alpha 2-glycoprotein: a multidisciplinary protein

Zinc alpha 2-glycoprotein (ZAG) is a protein of interest because of its ability to play many important functions in the human body, including fertilization and lipid mobilization. After the discovery of this molecule, during the last 5 decades, various studies have been documented on its structure and functions, but still, it is considered as a protein with an unknown function. Its expression is regulated by glucocorticoids. Due to its high sequence homology with lipid-mobilizing factor and high expression in cancer cachexia, it is considered as a novel adipokine. On the other hand, structural organization and fold is similar to MHC class I antigen-presenting molecule; hence, ZAG may have a role in the expression of the immune response. The function of ZAG under physiologic and cancerous conditions remains mysterious but is considered as a tumor biomarker for various carcinomas. There are several unrelated functions that are attributed to ZAG, such as RNase activity, regulation of melanin production, hindering tumor proliferation, and transport of nephritic by-products. This article deals with the discussion of the major aspects of ZAG from its gene structure to function and metabolism.

The role of Zn-alpha2 glycoprotein in sperm motility is mediated by changes in cyclic AMP

Sperm motility is essential for male reproduction or natural fertilization. The cyclic AMP (cAMP)/cAMP-dependent protein kinase A (PKA) signaling pathway is generally recognized as one of the significant signaling pathways in the regulation of mammalian spermatozoan motility. Since Zn-alpha2-glycoprotein (ZAG) activity in mammalian adipose tissue is mediated via the beta(3)-adrenoreceptor, with upregulation of the cAMP pathway, we hypothesize that ZAG may play the same role in sperm motility regulation, a new factor of regulation of sperm motility. Therefore, the gene encoding human ZAG was cloned and polyclonal antibodies were generated, and then laser scanning confocal microscopy and flow cytometry were employed to identify this protein in human spermatozoa. The results showed that ZAG protein was mostly localized on the pre-equatorial region covering the acrosome, neck, and middle piece of the flagellum of spermatozoa. Furthermore, using computer-assisted sperm analysis, we found that anti-human ZAG antibodies could significantly reduce the motility of human swim-up spermatozoa after 90- or 120-min incubation (P<0.05 and P<0.01 respectively), together with the decreasing of intracellular cAMP and PKA levels. In conclusion, these data suggest that ZAG is present in human spermatozoa and may be involved in the regulation of sperm motility via the cAMP/PKA signaling pathway.

Thermogenic and metabolic antiobesity drugs: rationale and opportunities

Antiobesity drugs that target peripheral metabolism may avoid some of the problems that have been encountered with centrally acting anorectic drugs. Moreover, if they cause weight loss by increasing fat oxidation, they not only address a cause of obesity but also should promote loss of fat rather than lean tissue and improve insulin sensitivity. Weight loss may be slow but more sustained than with anorectic drugs, and thermogenesis may be insufficient to cause any discomfort. Some thermogenic approaches are the activation of adrenergic, thyroid hormone or growth hormone receptors and the inhibition of glucocorticoid receptors; the modulation of transcription factors [e.g. peroxisome proliferator-activated receptor delta (PPARdelta) activators] or enzymes [e.g. glutamine fructose-6-phosphate amidotransferase (GFAT) inhibitors] that promote mitochondrial biogenesis, and the modulation of transcription factors (PPAR alpha activators) or enzymes (AMP-activated protein kinase) that promote fatty acid oxidation. More surprisingly, studies on genetically modified animals and with enzyme inhibitors suggest that inhibitors of fatty acid synthesis [e.g. ATP citrate lyase, fatty acid synthase, acetyl-CoA carboxylase (ACC)], fatty acid interconversion [stearoyl-CoA desaturase (SCD)] and triglyceride synthesis (e.g. acyl-CoA : diacylglycerol acyltransferase) may all be thermogenic. Some targets have been validated only by deleting genes in the whole animal. In these cases, it is possible that deletion of the protein in the brain is responsible for the effect on adiposity, and therefore a centrally penetrant drug would be required. Moreover, whilst a genetically modified mouse may display resistance to obesity in response to a high fat diet, it requires a tool compound to demonstrate that a drug might actually cause weight loss. Even then, it is possible that differences between rodents and humans, such as the greater thermogenic capacity of rodents, may give a misleading impression of the potential of a drug.