Molecular and pathobiological involvement of fetuin-A in the pathogenesis of NAFLD

The liver acts as a manufacturing unit for the production of fetuin-A, which is essential for various physiological characteristics. Scientific research has shown that a moderate upward push in fetuin-A serum levels is associated with a confirmed non-alcoholic fatty liver disease (NAFLD) diagnosis. Fetuin-A modulation is associated with a number of pathophysiological variables that cause liver problems, including insulin receptor signaling deficiencies, adipocyte dysfunction, hepatic inflammation, fibrosis, triacylglycerol production, macrophage invasion, and TLR4 activation. The focus of the present review is on the various molecular pathways, and genetic relevance of mRNA expression of fetuin-A which is correlated with progression of NAFLD. The other major area of exploration in the present review is based on the new targets for the modulation of fetuin-A, like calorie restriction and novel pharmacological agents, such as rosuvastatin, metformin, and pioglitazone which are successfully implicated in the management of various liver-related complications.

Adiponectin: The Potential Regulator and Therapeutic Target of Obesity and Alzheimer's Disease

Animal and human mechanistic studies have consistently shown an association between obesity and Alzheimer’s disease (AD). AD, a degenerative brain disease, is the most common cause of dementia and is characterized by the presence of extracellular amyloid beta (Aβ) plaques and intracellular neurofibrillary tangles disposition. Some studies have recently demonstrated that Aβ and tau cannot fully explain the pathophysiological development of AD and that metabolic disease factors, such as insulin, adiponectin, and antioxidants, are important for the sporadic onset of nongenetic AD. Obesity prevention and treatment can be an efficacious and safe approach to AD prevention. Adiponectin is a benign adipokine that sensitizes the insulin receptor signaling pathway and suppresses inflammation. It has been shown to be inversely correlated with adipose tissue dysfunction and may enhance the risk of AD because a range of neuroprotection adiponectin mechanisms is related to AD pathology alleviation. In this study, we summarize the recent progress that addresses the beneficial effects and potential mechanisms of adiponectin in AD. Furthermore, we review recent studies on the diverse medications of adiponectin that could possibly be related to AD treatment, with a focus on their association with adiponectin. A better understanding of the neuroprotection roles of adiponectin will help clarify the precise underlying mechanism of AD development and progression.

Multiple myeloma increases nerve growth factor and other pain-related markers through interactions with the bone microenvironment

Interactions between multiple myeloma (MM) and bone marrow (BM) are well documented to support tumour growth, yet the cellular mechanisms underlying pain in MM are poorly understood. We have used in vivo murine models of MM to show significant induction of nerve growth factor (NGF) by the tumour-bearing bone microenvironment, alongside other known pain-related characteristics such as spinal glial cell activation and reduced locomotion. NGF was not expressed by MM cells, yet bone stromal cells such as osteoblasts expressed and upregulated NGF when cultured with MM cells, or MM-related factors such as TNF-α. Adiponectin is a known MM-suppressive BM-derived factor, and we show that TNF-α-mediated NGF induction is suppressed by adiponectin-directed therapeutics such as AdipoRON and L-4F, as well as NF-κB signalling inhibitor BMS-345541. Our study reveals a further mechanism by which cellular interactions within the tumour-bone microenvironment contribute to disease, by promoting pain-related properties, and suggests a novel direction for analgesic development.

Anti-obesity effects of Laminaria japonica fermentation on 3T3-L1 adipocytes are mediated by the inhibition of C/EBP-α/β and PPAR-γ

Obesity is global problem that contributes to disease, and is partly caused by fast-food, high-fat diets. Much attention has been focused on developing anti-obesity foods and chemical materials from natural sources. Seaweed has bioactive properties that influence immune activity and have anti-cancer and anti-obesity effects. Laminaria japonica is a widely consumed seaweed, and has been promoted as a health food in Korea. The bioactive properties of L. japonica include anti-cancer, anti-diabetic, and anti-inflammation effects. Most Laminaria japonica are distributed in a simple processing form such as drying, and their availability is very low. Therefore, various types of functional products can be developed if they can be applied to foods through functionalization using fermentation techniques. It is a structural problem that is the most problematic in seaweed processing. In this study, we used fermented Laminaria japonica. To increase physiological activity, fermentation treatment was performed to loosen the structure, thereby increasing the activity of the glycoprotein. First, we screened the anti-obesity potential of an L. japonica fermentation extract (LJF) using 3T3-L1 adipocyte cells. We determined cytotoxicity using an MTS assay and measured LJF for its ability to affect adipogenesis through glucose uptake, triglyceride levels, and Oil Red O staining. We confirmed that LJF inhibited adipocyte differentiation. CCAAT/enhancer-binding proteins α/β (C/EBP-α/β) and peroxisome proliferator-activated receptor-γ (PPAR-γ) are involved in the early and late stages of adipocyte differentiation. LJF significantly reduced the expression levels of C/EBP-α/β and PPAR-γ and decreased the concentration of adiponectin. Thus, our results suggest that LJF inhibits adipogenesis in 3T3-L1 cells, and may be valuable for its anti-obesity effects.

Cardioprotection of ischemic preconditioning in rats involves upregulating adiponectin

It has been reported that ischemic preconditioning (IPC) and adiponectin (APN) are cardioprotective in many cardiovascular disorders. However, whether APN mediates the effect of IPC on myocardial injury has not been elucidated. This study was conducted to investigate whether IPC affects myocardial ischemic injury by increasing APN expression. Male adult rats with cardiac knockdowns of APN and its receptors via intramyocardial small-interfering RNA injection were subjected to IPC and then myocardial infarction (MI) at 24 h after IPC. Globular APN (gAd) was injected at 10 min before MI. APN mRNA and protein levels in myocardium as well as the plasma APN concentration were markedly high at 6 and 12 h after IPC. IPC ameliorated myocardial injury as evidenced by improved cardiac functions and a reduced infarct size. Compared with the control MI group, rats in the IPC + MI group had elevated levels of left ventricular ejection fraction and fractional shortening and a smaller MI size (P < 0.05). However, the aforementioned protective effects were ameliorated in the absence of APN and APN receptors, followed by the inhibition of AMP-activated protein kinase (AMPK) phosphorylation, but reversed by gAd treatment in wild-type rats, and AMPK phosphorylation increased (P < 0.05). Overall, our results suggest that the cardioprotective effects of IPC are partially due to upregulation of APN and provide a further insight into IPC-mediated signaling effects.

Prolactin regulatory element-binding protein is involved in suppression of the adiponectin gene in vivo

PURPOSE

Prolactin regulatory element-binding protein (PREB), a member of the WD-repeat protein family, has been recognized as a transcriptional factor that regulates prolactin promoter activity in the anterior pituitary of rats. PREB is expressed not only in the pituitary but also in various other tissues, including the adipose tissue. Previous studies have shown that PREB acts as a transcriptional regulator and suppresses the expression of the adiponectin gene in cultured 3T3L1 preadipocytes. The aim of this study was to further examine the potential role of PREB in adipose tissue in vivo.

METHODS

Transgenic mice that overexpressing PREB (PREB transgenic mice) were generated. Insulin resistance was evaluated in PREB transgenic mice using glucose and insulin tolerance tests. Adiponectin expression in the adipose tissue was examined by western blot analysis and quantitative polymerase chain reaction (qPCR). The expression levels of stearoyl-CoA desaturase (Scd) and adiponectin receptor 2(ADIPOR2) were quantified by qPCR.

RESULTS

Glucose and insulin tolerance tests revealed insulin resistance in PREB transgenic mice. Serum adiponectin and leptin concentrations were decreased. Adiponectin gene expression was decreased in the adipose tissue, which was confirmed by the downregulation of the adiponectin-dependent hepatic Scd gene and upregulation of the ADIPOR2 gene in the liver of PREB transgenic mice. We also found that pioglitazone, an agonist for the peroxisome proliferator-activated receptor-r, improved the insulin resistance in the PREB transgenic mice after a 10-day feeding period.

CONCLUSIONS

These results demonstrated that PREB might contribute to the regulation of adiponectin gene expression in vivo.

Central adiponectin administration reveals new regulatory mechanisms of bone metabolism in mice

Adiponectin (APN), the most abundant adipocyte-secreted adipokine, regulates energy homeostasis and exerts well-characterized insulin-sensitizing properties. The peripheral or central effects of APN regulating bone metabolism are beginning to be explored but are still not clearly understood. In the present study, we found that APN-knockout (APN-KO) mice fed a normal diet exhibited decreased trabecular structure and mineralization and increased bone marrow adiposity compared with wild-type (WT) mice. APN intracerebroventricular infusions decreased uncoupling protein 1 (UCP1) expression in brown adipose tissue, epinephrine and norepinephrine serum levels, and osteoclast numbers, whereas osteoblast osteogenic marker expression and trabecular bone mass increased in APN-KO and WT mice. In addition, centrally administered APN increased hypothalamic tryptophan hydroxylase 2 (TPH2), cocaine- and amphetamine-regulated transcript (CART), and 5-hydroxytryptamine (serotonin) receptor 2C (Htr2C) expressions but decreased hypothalamic cannabinoid receptor-1 expression. Treatment of immortalized mouse neurons with APN demonstrated that APN-mediated effects on TPH2, CART, and Htr2C expression levels were abolished by downregulating adaptor protein containing pleckstrin homology domain, phosphotyrosine domain, and leucine zipper motif (APPL)-1 expression. Pharmacological increase in sympathetic activity stimulated adipogenic differentiation of bone marrow stromal cells (BMSC) and reversed APN-induced expression of the lysine-specific demethylases involved in regulating their commitment to the osteoblastic lineage. In conclusion, we found that APN regulates bone metabolism via central and peripheral mechanisms to decrease sympathetic tone, inhibit osteoclastic differentiation, and promote osteoblastic commitment of BMSC.

Central adiponectin acutely improves glucose tolerance in male mice

Adiponectin, an adipocyte-derived hormone, regulates glucose and lipid metabolism. It is also antiinflammatory. During obesity, adiponectin levels and sensitivity are reduced. Whereas the action of adiponectin in the periphery is well established the neuroendocrine role of adiponectin is largely unknown. To address this we analyzed the expression of adiponectin and the 2 adiponectin receptors (AdipoR1 and AdipoR2) in response to fasting and to diet-induced and genetic obesity. We also investigated the acute impact of adiponectin on central regulation of glucose homeostasis. Adiponectin (1 μg) was injected intracerebroventricularly (ICV), and glucose tolerance tests were performed in dietary and genetic obese mice. Finally, the influence of ICV adiponectin administration on central signaling cascades regulating glucose homeostasis and on markers of hypothalamic inflammation was assessed. Gene expression of adiponectin was down-regulated whereas AdipoR1 was up-regulated in the arcuate nucleus of fasted mice. High-fat (HF) feeding increased AdipoR1 and AdipoR2 gene expression in this region. In mice on a HF diet and in leptin-deficient mice acute ICV adiponectin improved glucose tolerance 60 minutes after injection, whereas normoglycemia in control mice was unaffected. ICV adiponectin increased pAKT, decreased phospho-AMP-activated protein kinase, and did not change phospho-signal transducer and activator of transcription 3 immunoreactivity. In HF-fed mice, ICV adiponectin reversed parameters of hypothalamic inflammation and insulin resistance as determined by the number of phospho-glycogen synthase kinase 3 β(Ser9) and phospho-c-Jun N-terminal kinase (Thr183/Tyr185) immunoreactive cells in the arcuate nucleus and ventromedial hypothalamus. This study demonstrates that the insulin-sensitizing properties of adiponectin are at least partially based on a neuroendocrine mechanism that involves centrally synthesized adiponectin.

Leptin and adiponectin: emerging therapeutic targets in breast cancer

Obesity is a recognized risk factor for breast cancer development and poorer response to therapy. Two major fat tissue-derived adipokines, leptin and adiponectin have been implicated in mammary carcinogenesis. Leptin appears to promote breast cancer progression through activation of mitogenic, antiapoptotic, and metastatic pathways, while adiponectin may restrict tumorigenic processes primarily by inhibiting cell metabolism. Furthermore, adiponectin is known to counteract detrimental leptin effects in breast cancer models. Thus, therapeutic inhibition of pro-neoplastic leptin pathways and reactivation of anti-neoplastic adiponectin signaling may benefit breast cancer patients, especially the obese subpopulation. This review focuses on current experimental strategies aiming at leptin and adiponectin pathways in breast cancer models. Novel leptin receptor antagonists and adiponectin receptor agonists as well as other compounds for therapeutic modulation of adipokine pathways are discussed in detail, including potential pharmacological advantages and limitations of these approaches.

Measurement and validation of the nature of salivary adiponectin

Adiponectin (Ad) is an adipocyte-derived hormone that plays an essential role in regulating insulin sensitivity, inflammation, and atherogenesis. Levels of some hormones in saliva change in a fashion similar to that in plasma in response to a disease or physiological condition. Since saliva is an easy to obtain biological fluid, measurements of salivary hormonal changes are preferred in diagnoses and treatments. Therefore, it was of interest to examine the nature of salivary Ad. While there have been two publications in the literature reporting presence of Ad in human saliva, the nature of salivary Ad has not been characterized. To this end, we investigated the effect of sample dilution on the measurement of Ad in saliva. To our surprise, we observed an increase in measurable level of Ad in saliva on sample dilution. One explanation for this paradoxical observation may be the presence of inhibitor(s) of Ad/anti-Ad binding in saliva that following dilution relieves the inhibitory effect. Working with this hypothesis, we were able to demonstrate the presence of an inhibitor in saliva that co-eluted with the dimeric form of Ad and was capable of inhibiting Ad assay. The presence of such inhibitor(s) may lead to underestimation of Ad in saliva.

Adiponectin prevents islet ischemia-reperfusion injury through the COX2-TNFα-NF-κB-dependent signal transduction pathway in mice

Islets are exceptionally susceptible to ischemia-reperfusion injury, an increased incidence of primary graft nonfunctionality, and β-cell death during a transplant procedure. Therefore, islets require protection during the early stages of the transplant procedure. Based on the beneficial vascular and anti-inflammatory activity of adiponectin, we hypothesize that adiponectin protects islet cells against ischemia-reperfusion injury and graft dysfunction after transplantation. To examine the effects of adiponectin on the resistance of islet ischemia-reperfusion injury, we used the islet hypoxia-reoxygenation injury model and performed kidney subcapsular syngeneic islet transplants to assess the islets' vitality and function. Furthermore, we utilized lipopolysaccharide (LPS)-induced or tumor necrosis factor α (TNFα)-induced damage to islet cells to model the inflammation of post-transplant ischemia-reperfusion injury and transplanted islets in adiponectin knockout mice to explore whether the protective action of adiponectin is involved in TNFα production and nuclear transcription factor-κB (NF-κB) activation. Adiponectin suppressed TNFα production and IκB-α phosphorylation; decreased hypoxia-reoxygenation and LPS-induced and TNFα-induced islet apoptosis; and improved islet function in vivo and in vitro. Our results demonstrate that adiponectin protects the islet from injury. We show that islet protection occurs in response to ischemia-reperfusion and is dependent on the suppression of islet production by TNFα through cyclooxygenase 2 and the inhibition of the TNFα-induced NF-κB activation pathways.

Perivascular adipose tissue control of insulin-induced vasoreactivity in muscle is impaired in db/db mice

Microvascular recruitment in muscle is a determinant of insulin sensitivity. Whether perivascular adipose tissue (PVAT) is involved in disturbed insulin-induced vasoreactivity is unknown, as are the underlying mechanisms. This study investigates whether PVAT regulates insulin-induced vasodilation in muscle, the underlying mechanisms, and how obesity disturbs this vasodilation. Insulin-induced vasoreactivity of resistance arteries was studied with PVAT from C57BL/6 or db/db mice. PVAT weight in muscle was higher in db/db mice compared with C57BL/6 mice. PVAT from C57BL/6 mice uncovered insulin-induced vasodilation; this vasodilation was abrogated with PVAT from db/db mice. Blocking adiponectin abolished the vasodilator effect of insulin in the presence of C57BL/6 PVAT, and adiponectin secretion was lower in db/db PVAT. To investigate this interaction further, resistance arteries of AMPKα2(+/+) and AMPKα2(-/-) were studied. In AMPKα2(-/-) resistance arteries, insulin caused vasoconstriction in the presence of PVAT, and AMPKα2(+/+) resistance arteries showed a neutral response. On the other hand, inhibition of the inflammatory kinase Jun NH(2)-terminal kinase (JNK) in db/db PVAT restored insulin-induced vasodilation in an adiponectin-dependent manner. In conclusion, PVAT controls insulin-induced vasoreactivity in the muscle microcirculation through secretion of adiponectin and subsequent AMPKα2 signaling. PVAT from obese mice inhibits insulin-induced vasodilation, which can be restored by inhibition of JNK.

Inhibition of CTRP9, a novel and cardiac-abundantly expressed cell survival molecule, by TNFα-initiated oxidative signaling contributes to exacerbated cardiac injury in diabetic mice

Recently identified as adiponectin (APN) paralogs, C1q/TNF-related proteins (CTRPs) share similar metabolic regulatory functions as APN. The current study determined cardiac expression of CTRPs, their potential cardioprotective function, and investigated whether and how diabetes may regulate cardiac CTRP expression. Several CTRPs are expressed in the heart at levels significantly greater than APN. Most notably, cardiac expression of CTRP9, the closest paralog of APN, exceeds APN by >100-fold. Cardiac CTRP9 expression was significantly reduced in high-fat diet-induced diabetic mice. In H9c2 cells, tumor necrosis factor-alpha (TNF-α) strongly inhibited CTRP9 expression (>60%), and significantly reduced peroxisome proliferator activated receptor-gamma (PPARγ), a known transcription factor promoting adiponectin expression. The inhibitory effect of TNF-α on PPARγ and CTRP9 was reversed by Tiron or rosiglitazone. CTRP9 knockdown significantly enhanced, whereas CTRP9 overexpression significantly attenuated simulated ischemia/reperfusion injury in H9c2 cells. In vivo CTRP9 administration to diabetic mice significantly attenuated NADPH oxidase expression and superoxide generation, reduced infarct size, and improved cardiac function. To the best of our knowledge, this is the first study providing evidence that downregulation of CTRP9, an abundantly expressed and novel cell survival molecule in the heart, by TNF-α-initiated oxidative PPARγ suppression contributes to exacerbated diabetic cardiac injury. Preservation of CTRP9 expression or augmentation of CTRP9-initiated signaling mechanisms may be the potential avenues for ameliorating ischemic diabetic cardiac injury.

Fat-specific DsbA-L overexpression promotes adiponectin multimerization and protects mice from diet-induced obesity and insulin resistance

The antidiabetic and antiatherosclerotic effects of adiponectin make it a desirable drug target for the treatment of metabolic and cardiovascular diseases. However, the adiponectin-based drug development approach turns out to be difficult due to extremely high serum levels of this adipokine. On the other hand, a significant correlation between adiponectin multimerization and its insulin-sensitizing effects has been demonstrated, suggesting a promising alternative therapeutic strategy. Here we show that transgenic mice overexpressing disulfide bond A oxidoreductase-like protein in fat (fDsbA-L) exhibited increased levels of total and the high-molecular-weight form of adiponectin compared with wild-type (WT) littermates. The fDsbA-L mice also displayed resistance to diet-induced obesity, insulin resistance, and hepatic steatosis compared with WT control mice. The protective effects of DsbA-L overexpression on diet-induced insulin resistance, but not increased body weight and fat cell size, were significantly decreased in adiponectin-deficient fDsbA-L mice (fDsbA-L/Ad(-/-)). In addition, the fDsbA-L/Ad(-/-) mice displayed greater activity and energy expenditure compared with adiponectin knockout mice under a high-fat diet. Taken together, our results demonstrate that DsbA-L protects mice from diet-induced obesity and insulin resistance through adiponectin-dependent and independent mechanisms. In addition, upregulation of DsbA-L could be an effective therapeutic approach for the treatment of obesity and its associated metabolic disorders.

Suppression of adiponectin by aberrantly glycosylated IgA1 in glomerular mesangial cells in vitro and in vivo

The pathogenesis of IgA nephropathy (IgAN) may be associated with the mesangial deposition of aberrantly glycosylated IgA1. To identify mediators affected by aberrantly glycosylated IgA1 in cultured human mesangial cells (HMCs), we generated enzymatically modified desialylated and degalactosylated (deSial/deGal) IgA1. The state of deglycosylated IgA1 was confirmed by lectin binding to Helix aspersa (HAA) and Sambucus nigra (SNA). In the cytokine array analysis, 52 proteins were upregulated and 34 were downregulated in HMCs after stimulation with deSial/deGal IgA1. Among them, the secretion of adiponectin was suppressed in HMCs after stimulation with deSial/deGal IgA1. HMCs expressed mRNAs for adiponectin and its type 1 receptor, but not the type 2 receptor. Moreover, we revealed a downregulation of adiponectin expression in the glomeruli of renal biopsy specimens from patients with IgAN compared to those with lupus nephritis. We also demonstrated that aberrantly glycosylated IgA1 was deposited in the mesangium of patients with IgAN by dual staining of HAA and IgA. Moreover, the urinary HAA/SNA ratio of lectin binding was significantly higher in IgAN compared to other kidney diseases. Since adiponectin has anti-inflammatory effects, including the inhibition of adhesion molecules and cytokines, these data suggest that the local suppression of this adipokine by aberrantly glycosylated IgA1 could be involved in the regulation of glomerular inflammation and sclerosis in IgAN.

Testosterone therapy decreases subcutaneous fat and adiponectin in aging men

OBJECTIVE

Testosterone therapy increases lean body mass and decreases total fat mass in aging men with low normal testosterone levels. The major challenge is, however, to determine whether the metabolic consequences of testosterone therapy are overall positive. We have previously reported that 6-month testosterone therapy did not improve insulin sensitivity. We investigated the effect of testosterone therapy on regional body fat distribution and on the levels of the insulin-sensitizing adipokine, adiponectin, in aging men with low normal bioavailable testosterone levels.

DESIGN

A randomized, double-blinded, placebo-controlled study on 6-month testosterone treatment (gel) in 38 men, aged 60-78 years, with bioavailable testosterone <7.3 nmol/l, and a waist circumference >94 cm.

METHODS

Central fat mass (CFM) and lower extremity fat mass (LEFM) were measured by dual X-ray absorptiometry. Subcutaneous abdominal adipose tissue (SAT), visceral adipose tissue (VAT), and thigh subcutaneous fat area (TFA) were measured by magnetic resonance imaging. Adiponectin levels were measured using an in-house immunofluorometric assay. Coefficients (b) represent the placebo-controlled mean effect of intervention.

RESULTS

LEFM was decreased (b = -0.47 kg, P = 0.07) while CFM did not change significantly (b = -0.66 kg, P = 0.10) during testosterone therapy. SAT (b = -3.0%, P = 0.018) and TFA (b = -3.0%, P < 0.001) decreased, while VAT (b = 1.0%, P = 0.54) remained unchanged. Adiponectin levels decreased during testosterone therapy (b = -1.3 mg/l, P = 0.001).

CONCLUSION

Testosterone therapy decreased subcutaneous fat on the abdomen and lower extremities, but visceral fat was unchanged. Moreover, adiponectin levels were significantly decreased during testosterone therapy.

Adiponectin upregulates hepatocyte CMKLR1 which is reduced in human fatty liver

Chemokine-like receptor 1 (CMKLR1) ligands chemerin and resolvin E1 are suggested to have a role in non-alcoholic fatty liver disease (NAFLD). Here, expression of CMKLR1 in liver cells and NAFLD was studied. CMKLR1 was detected in primary human hepatocytes (PHH), Kupffer cells, bile-duct cells and hepatic stellate cells. In human and rodent fatty liver and in fibrotic liver of mice fed a methionine-choline deficient diet CMKLR1 was reduced. Hepatocytes are the major cells in the liver and effects of adipokines, cytokines and lipids on CMKLR1 in PHH were analyzed. Increased cellular triglyceride or cholesterol content, lipopolysaccharide, IL-6, TNF and leptin did not influence CMKLR1 levels in PHH whereas profibrotic TGFβ tended to reduce CMKLR1. Adiponectin strongly upregulated CMKLR1 mRNA and protein in PHH and hepatic CMKLR1 when injected into wild type mice. Further, CMKLR1 was suppressed in the liver of adiponectin deficient mice. These data indicate that low CMKLR1 in NAFLD may partly result from reduced adiponectin activity.

Adiponectin, a downstream target gene of peroxisome proliferator-activated receptor γ, controls hepatitis B virus replication

In this study, HepG2-hepatitis B virus (HBV)-stable cells that did not overexpress HBx and HBx-deficient mutant-transfected cells were analyzed for their expression of HBV-induced, upregulated adipogenic and lipogenic genes. The mRNAs of CCAAT enhancer binding protein α (C/EBPα), peroxisome proliferator-activated receptor γ (PPARγ), adiponectin, liver X receptor α (LXRα), sterol regulatory element binding protein 1c (SREBP1c), and fatty acid synthase (FAS) were expressed at higher levels in HepG2-HBV and lamivudine-treated stable cells and HBx-deficient mutant-transfected cells than in the HepG2 cells. Lamivudine treatment reduced the mRNA levels of PPARγ and C/EBPα. Conversely, HBV replication was upregulated by adiponectin and PPARγ agonist rosiglitazone treatments and was downregulated by adiponectin siRNAs. Collectively, our results demonstrate that HBV replication and/or protein expression, even in the absence of HBx, upregulated adipogenic or lipogenic genes, and that the control of adiponectin might prove useful as a therapeutic modality for the treatment of chronic hepatitis B.

Adiponectin promotes syncytialisation of BeWo cell line and primary trophoblast cells

BACKGROUND

In human pregnancy, a correct placentation depends on trophoblast proliferation, differentiation, migration and invasion. These processes are highly regulated by placental hormones, growth factors and cytokines. Recently, we have shown that adiponectin, an adipokine, has anti-proliferative effects on trophoblastic cells. Here, we complete this study by demonstrating that adiponectin modulates BeWo and human villous cytotrophoblast cell differentiation.

RESULTS

We showed that hCG secretion was up-regulated by adiponectin treatment in both BeWo cells and human cytotrophoblasts from very early placentas (5-6 weeks). The expression of two trophoblast differentiation markers, leptin and syncytin 2, was also up-regulated by adiponectin in BeWo cells. Moreover, adiponectin treatment induced a loss of E-cadherin staining in these cells. In parallel, we demonstrated that AdipoR1 and AdipoR2 are up-regulated during forskolin induced BeWo cell differentiation, reinforcing the role of adiponectin in trophoblast syncytialization. SiRNA mediated down-regulation of AdipoR1 and AdipoR2 was used to demonstrate that adiponectin effects on differentiation were essentially mediated by these receptors. Finally, using a specific inhibitor, we demonstrated that the PKA signalling pathway could be one pathway involved in adiponectin effects on trophoblast differentiation.

CONCLUSION

Adiponectin enhances the differentiation process of trophoblast cells and could thus be involved in functional syncytiotrophoblast formation.

Distribution of adiponectin multimeric forms in Chinese women with polycystic ovary syndrome and their relation to insulin resistance

OBJECTIVE

Adiponectin, an abundant adipokine with insulin-sensitizing properties, exists in different multimeric forms, including low-molecular weight, medium-molecular weight, and high-molecular weight (HMW) species. Alterations in the distribution of adiponectin multimers and the relationship between adiponectin multimers and insulin resistance (IR) in women with polycystic ovary syndrome (PCOS) remain unclear. The objective of this study was to compare adiponectin multimerization status and estimate insulin sensitivity in Chinese women with PCOS compared with age- and body mass index (BMI)-matched controls.

METHODS

Cross-sectional study involving 64 Chinese women with PCOS and 59 normal women. Circulating total adiponectin and its multimeric forms were determined by ELISA, and IR was estimated using the homeostasis model assessment IR index (HOMA-IR).

RESULTS

After controlling for BMI status, levels of both total and HMW adiponectin were significantly lower in women with PCOS compared with normal women (P<0.05). Furthermore, HMW adiponectin provided a stronger contribution to models predicting IR than total adiponectin. Lastly, decreased HMW adiponectin was associated with increased HOMA-IR in both normal and PCOS women, and this association was independent of both overall adiposity and visceral adiposity.

CONCLUSION

Levels of both total and HMW adiponectin were decreased in Chinese women with PCOS compared with normal control women, and the differences in HMW adiponectin persisted after controlling for BMI. Furthermore, HMW adiponectin is a stronger predictor of IR than total adiponectin in both women with PCOS and normal women.

Bisphenol A at environmentally relevant doses inhibits adiponectin release from human adipose tissue explants and adipocytes

BACKGROUND

The incidence of obesity has risen dramatically over the last few decades. This epidemic may be affected by exposure to xenobiotic chemicals. Bisphenol A (BPA), an endocrine disruptor, is detectable at nanomolar levels in human serum worldwide. Adiponectin is an adipocyte-specific hormone that increases insulin sensitivity and reduces tissue inflammation. Thus, any factor that suppresses adiponectin release could lead to insulin resistance and increased susceptibility to obesity-associated diseases.

OBJECTIVES

In this study we aimed to compare a) the effects of low doses of BPA and estradiol (E(2)) on adiponectin secretion from human breast, subcutaneous, and visceral adipose explants and mature adipocytes, and b) expression of putative estrogen and estrogen-related receptors (ERRs) in these tissues.

METHODS

We determined adiponectin levels in conditioned media from adipose explants or adipocytes by enzyme-linked immunosorbant assay. We determined expression of estrogen receptors (ERs) alpha and beta, G-protein-coupled receptor 30 (GPR30), and ERRs alpha, beta, and gamma by quantitative real-time polymerase chain reaction.

RESULTS

BPA at 0.1 and 1 nM doses suppressed adiponectin release from all adipose depots examined. Despite substantial variability among patients, BPA was as effective, and often more effective, than equimolar concentrations of E(2). Adipose tissue expresses similar mRNA levels of ERalpha, ERbeta, and ERRgamma, and 20- to 30-fold lower levels of GPR30, ERRalpha, and ERRbeta.

CONCLUSIONS

BPA at environmentally relevant doses inhibits the release of a key adipokine that protects humans from metabolic syndrome. The mechanism by which BPA suppresses adiponectin and the receptors involved remains to be determined.

Lower plasma adiponectin is correlated to higher alanine aminotransferase independent of metabolic factors and hepatitis B virus carrier status

BACKGROUND

Adiponectin has been linked to the metabolic syndrome and coronary artery disease in recent years. The animal and human data also suggest that adiponectin may be beneficial for liver functions. The aim of this study was to investigate the correlation between plasma adiponectin level and liver function tests in adults with or without chronic hepatitis B virus (HBV) infection.

METHODS

We analysed the blood levels of liver enzymes and adiponectin in 140 apparently healthy adults, including 21 HBV carriers.

RESULTS

We found that the plasma adiponectin levels were inversely correlated to aspartate aminotransferase (r = -0.314, P = 0.000) and alanine aminotransferase (ALT) (r = -0.430, P = 0.000). Among the HBV carriers, the ALT correlated with the plasma adiponectin levels (r = -0.521, P = 0.015). In linear regression models adjusting for age, sex and the other metabolic variables, the ALT was independently related to the plasma adiponectin levels (beta = -0.371 +/- 0.134, P = 0.007), even in HBV carriers (beta = -1.143 +/- 0.482, P = 0.034). The ALT was also independently correlated to the plasma adiponectin levels (beta = 0.552 +/- 0.132, P < 0.001) with adjustment for age, sex and insulin-resistance index by homeostasis model assessment, even in HBV carriers (beta = -1.202 +/- 0.562, P = 0.048). The subjects with normal ALT had a significantly higher least square mean of plasma adiponectin than those with abnormal ALT (4.01 +/- 0.19 vs 3.30 +/- 0.30, P = 0.014) with adjustment for age, sex, homeostasis model assessment insulin resistance and HBV status.

CONCLUSION

ALT was inversely related to adiponectin levels, independent of the metabolic factors and HBV status. Whether there is any potential prognostic and therapeutic value of adiponectin in human liver diseases remains to be investigated.

Atrial natriuretic peptide inhibits the production of adipokines and cytokines linked to inflammation and insulin resistance in human subcutaneous adipose tissue

AIMS/HYPOTHESIS

Increased adipose tissue secretion of adipokines and cytokines has been implicated in the chronic low-grade inflammation state and insulin resistance associated with obesity. We tested here whether the cardiovascular and metabolic hormone atrial natriuretic peptide (ANP) was able to modulate adipose tissue secretion of several adipokines (derived from adipocytes) and cytokines (derived from adipose tissue macrophages).

SUBJECTS AND METHODS

We used protein array to measure the secretion of adipokines and cytokines after a 24-h culture of human subcutaneous adipose tissue pieces treated or not with a physiological concentration of ANP. The effect of ANP on protein secretion was also directly studied on isolated adipocytes and macrophages. Gene expression was measured by real-time RT-quantitative PCR.

RESULTS

ANP decreased the secretion of the pro-inflammatory cytokines IL-6 and TNF-alpha, of several chemokines, and of the adipokines leptin and retinol-binding protein-4 (RBP-4). The secretion of the anti-inflammatory molecules IL-10 and adiponectin remained unaffected. The cytokines were mainly expressed in macrophages that expressed all components of the ANP-dependent signalling pathway. The adipokines, leptin, adiponectin and RBP-4 were specifically expressed in mature adipocytes. ANP directly inhibited the secretion of IL-6 and monocyte chemoattractant protein-1 by macrophages. The inhibitory effects of ANP on leptin and growth-related oncogene-alpha secretions were not seen under selective hormone-sensitive lipase inhibition.

CONCLUSIONS/INTERPRETATION

We suggest that ANP, either by direct action on adipocytes and macrophages or through activation of adipocyte hormone-sensitive lipase, inhibits the secretion of factors involved in inflammation and insulin resistance.

Targeted disruption of AdipoR1 and AdipoR2 causes abrogation of adiponectin binding and metabolic actions

Adiponectin plays a central role as an antidiabetic and antiatherogenic adipokine. AdipoR1 and AdipoR2 serve as receptors for adiponectin in vitro, and their reduction in obesity seems to be correlated with reduced adiponectin sensitivity. Here we show that adenovirus-mediated expression of AdipoR1 and R2 in the liver of Lepr(-/-) mice increased AMP-activated protein kinase (AMPK) activation and peroxisome proliferator-activated receptor (PPAR)-alpha signaling pathways, respectively. Activation of AMPK reduced gluconeogenesis, whereas expression of the receptors in both cases increased fatty acid oxidation and lead to an amelioration of diabetes. Alternatively, targeted disruption of AdipoR1 resulted in the abrogation of adiponectin-induced AMPK activation, whereas that of AdipoR2 resulted in decreased activity of PPAR-alpha signaling pathways. Simultaneous disruption of both AdipoR1 and R2 abolished adiponectin binding and actions, resulting in increased tissue triglyceride content, inflammation and oxidative stress, and thus leading to insulin resistance and marked glucose intolerance. Therefore, AdipoR1 and R2 serve as the predominant receptors for adiponectin in vivo and play important roles in the regulation of glucose and lipid metabolism, inflammation and oxidative stress in vivo.

Insulin-like growth factor binding protein-3 induces insulin resistance in adipocytes in vitro and in rats in vivo

Insulin-like growth factor binding protein (IGFBP)-3 binds to IGF and modulates their actions and also possesses intrinsic activities. We investigated its effects on insulin action and found that when IGFBP-3 was added to fully differentiated 3T3-L1 adipocytes in culture, insulin-stimulated glucose transport was significantly inhibited to 60% of control in a time- and dose-dependent manner. Tumor necrosis factor (TNF)-alpha treatment also inhibited glucose transport to the same degree as IGFBP-3 and, in addition, increased IGFBP-3 levels 3-fold. Co-treatment with TNF-alpha and IGFBP-3 antisense partially prevented the inhibitory effect of TNF-alpha on glucose transport, indicating a role for IGFBP-3 in cytokine-induced insulin resistance. Insulin-stimulated phosphorylation of the insulin receptor was markedly decreased by IGFBP-3 treatment. IGFBP-3 treatment suppressed adiponectin expression in 3T3-L1 adipocytes. Infusion of IGFBP-3 to Sprague-Dawley rats for 3 h decreased peripheral glucose uptake by 15% compared with controls as well as inhibiting glycogen synthesis. Systemic administration of IGFBP-3 to rats for 7 d resulted in a dramatic 40% decrease in peripheral glucose utilization and glycogen synthesis. These in vitro and in vivo findings demonstrate that IGFBP-3 has potent insulin-antagonizing capability and suggest a role for IGFBP-3 in cytokine-induced insulin resistance and other mechanisms involved in the development of type-2 diabetes.

Hypoadiponectinemia in lean lactating women: Prolactin inhibits adiponectin secretion from human adipocytes

Adiponectin is an adipocyte-derived hormone involved in glucose, lipid and energy metabolism. A low plasma adiponectin concentration is associated with insulin resistance, obesity and atherosclerosis. In women, energy homeostasis is remarkably changed during gestation and lactation in order to supply sufficient nutrition for a fetus or newborn. In this study we aimed to elucidate the physiological impact of gestation and lactation on the plasma adiponectin levels and the influence of reproduction-related hormones on adiponectin secretion. We studied the longitudinal changes in plasma adiponectin concentration during pregnancy (1st, 2nd and 3rd trimester) and lactation (3 days and 1 month after the delivery) in lean healthy women (n = 22). The plasma adiponectin level declined slightly as the pregnancy advanced and reached its lowest level during lactation (12.25 +/- 0.182 microg/ml at early pregnancy vs. 6.88 +/- 0.375 microg/ml at 3 days postpartum, p < 0.001). In order to investigate the role of the lactogenic hormone prolactin in the decrease of plasma adiponectin levels during lactation, we further performed in vitro experiments using human primary cultured adipocytes. Western blotting of the adipocyte lysate and ELISA of the culture medium revealed that exogenous prolactin inhibited both production and secretion of adiponectin in a dose-dependent manner. Our results thus suggests that prolactin affects the regulation of maternal metabolism through suppression of adiponectin.

Identification of amino-terminal region of adiponectin as a physiologically functional domain

Adiponectin is an abundant adipose-specific protein, which acts as an anti-diabetic, anti-atherogenic, and anti-inflammatory adipokine. Although recent advances in the field of adiponectin have been made by the identification of adiponectin receptors and by the understanding about relationship between its multimerization and functions, detailed molecular background remains unclear. Our established anti-human adiponectin antibodies, ANOC 9103 and ANOC 9104, blocked some adiponectin functions such as the growth inhibition of B-lymphocytes on stromal cells and the inhibition of acetylated LDL uptake in macrophages, suggesting that they may recognize important functional regions of adiponectin. As a result of epitope mapping based on the ability to bind to the deleted adiponectin mutants, we identified that these antibodies recognize amino-terminal region of adiponectin before the beginning of the collagen-like domain. Notably, a peptide fragment (DQETTTQGPGVLLPLPKGACTGWMA) corresponding to amino acid residues 17-41 of human adiponectin could bind to restricted types of cells and block adiponectin-induced cyclooxygenase-2 gene expression and prostaglandin E2 production in MS-5 stromal cells. Moreover, the deletion of its amino-terminal region reduced the abilities to inhibit not only collagen-induced platelet aggregation but also diet-induced hepatic steatosis. These data indicate that amino-terminal region of adiponectin is a physiologically functional domain and that a novel receptor, which recognizes amino-terminal region of adiponectin, may exist on some types of cells. Further investigations will contribute to the understanding of molecular mechanisms about adiponectin functions as well as to the designing of novel strategies for the treatment of patients with insulin-resistance, vascular dysfunction, and chronic inflammation.

Concentration of Adiponectin in Peritoneal Fluid is Decreased in Women with Endometriosis

PROBLEM

Adiponectin is a novel adipocytokine of extreme importance for the metabolism. Recent studies have indicated that adiponectin suppresses inflammation, angiogenesis, and fibrosis, which are central pathogenic factors for endometriosis. We addressed the possibility that adiponectin is implicated in endometriosis.

METHOD OF STUDY

We measured concentrations of adiponectin in peritoneal fluid (PF) of women with (n = 54) or without (n = 26) endometriosis using specific enzyme-linked immunosorbent assay.

RESULTS

Adiponectin concentrations in PF of women with endometriosis were significantly lower than those of women without endometriosis. With respect to the stages of the disease, the concentrations of adiponectin in women with stage III/IV endometriosis were significantly lower compared to those in women without endometriosis and with stage I/II endometriosis. Body mass index were comparable among the groups.

CONCLUSIONS

These findings imply that adiponectin may be an anti-endometriotic factor, possibly due to its anti-inflammatory, anti-angiogenic, and anti-fibrotic properties.