Albumin inhibits adipogenesis and stimulates cytokine release from human adipocytes

Magnetic hybrid materials interact with biological matrices

Magnetic hybrid materials are a promising group of substances. Their interaction with matrices is challenging with regard to the underlying physical and chemical mechanisms. But thinking matrices as biological membranes or even structured cell layers they become interesting with regard to potential biomedical applications. Therefore, we established in vitro blood-organ barrier models to study the interaction and processing of superparamagnetic iron oxide nanoparticles (SPIONs) with these cellular structures in the presence of a magnetic field gradient. A one-cell-type–based blood-brain barrier model was used to investigate the attachment and uptake mechanisms of differentially charged magnetic hybrid materials. Inhibition of clathrin-dependent endocytosis and F-actin depolymerization led to a dramatic reduction of cellular uptake. Furthermore, the subsequent transportation of SPIONs through the barrier and the ability to detect these particles was of interest. Negatively charged SPIONs could be detected behind the barrier as well as in a reporter cell line. These observations could be confirmed with a two-cell-type–based blood-placenta barrier model. While positively charged SPIONs heavily interact with the apical cell layer, neutrally charged SPIONs showed a retarded interaction behavior. Behind the blood-placenta barrier, negatively charged SPIONs could be clearly detected. Finally, the transfer of the in vitro blood-placenta model in a microfluidic biochip allows the integration of shear stress into the system. Even without particle accumulation in a magnetic field gradient, the negatively charged SPIONs were detectable behind the barrier. In conclusion, in vitro blood-organ barrier models allow the broad investigation of magnetic hybrid materials with regard to biocompatibility, cell interaction, and transfer through cell layers on their way to biomedical application.

Vitamin D attenuates human gingival fibroblast inflammatory cytokine production following advanced glycation end product interaction with receptors for AGE

BACKGROUND AND OBJECTIVES

Vitamin D [1,25(OH)₂ D₃ or 1,25D3] is critical in musculoskeletal health, inflammation, immune response, and glucose metabolism. Patients with vitamin D deficiency may be at higher risk of diabetes and periodontitis. Diabetic patients exhibit exacerbated inflammation and more periodontal destruction. Advanced glycation end products (AGEs), formed during diabetic hyperglycemia, activate inflammatory pathways in periodontitis. Human gingival fibroblasts (HGFs) express receptors for AGEs (RAGEs) and can contribute to inflammation.

OBJECTIVES

Determine whether glycated human serum albumin (G-HSA) augments HGF IL-6 and IL-8 production, and whether treatment with 1,25D3 attenuates cytokine production following stimulation with G-HSA + IL-1β and/or IL-17.

MATERIAL AND METHODS

HGFs were incubated ±G-HSA or normal human serum albumin (HSA), ±IL-1β and/or IL-17, ±1,25D3. Cytokines were measured by ELISA. Neutralizing anti-RAGE was used to assess AGE-RAGE interaction. Endotoxin was measured using the ToxinSensor™ System. Data were expressed as mean ± standard deviation and analyzed using a one-way analysis of variance (ANOVA) and Scheffe's F procedure for post hoc comparisons.

RESULTS

G-HSA or IL-1β, but not HSA, significantly stimulated IL-6 and IL-8 production. G-HSA or HSA when combined with IL-1β or IL-1β + IL-17 synergistically stimulated IL-6 and IL-8. Neutralizing anti-RAGE inhibited IL-6 and IL-8 produced by cells stimulated with IL-1β + G-HSA but not (+HSA). Synergism caused by HSA did not appear to be mediated by endotoxin since its levels in G-HSA and HSA were not sufficient to stimulate fibroblasts. Vitamin D inhibited IL-6 and IL-8 production stimulated by G-HSA or HSA + IL-1β or IL-1β + IL-17.

CONCLUSIONS

Results suggest that the "perioprotective" effects of vitamin D are related to its ability to regulate inflammatory cytokine production by HGFs following AGE-RAGE interaction.

Phenotypic Alteration of Hepatocytes in Non-Alcoholic Fatty Liver Disease

Non-Alcoholic Fatty Liver Disease (NAFLD) has been recognized as the most common liver disorder in developed countries. NAFLD progresses from fat accumulation in hepatocytes to steatohepatitis to further stages of fibrosis and cirrhosis. Simple steatosis, i.e. fat deposition in the liver, is considered benign and gives way to non-alcoholic steatohepatitis (NASH) with a higher probability of progressing to cirrhosis, and liver-related mortality. Evidence has been found that this progression has been associated with marked alterations in hepatocyte histology and a shift in marker expression of healthy hepatocytes including increased expression of peroxisome proliferator-activated receptor gamma (PPARγ), adipocyte protein (aP2), CD36, interleukin-6 (IL-6), interleukin-18 (IL-18) and adiponectin. This progression shares much in common with the obesity phenotype, which involves a transformation of adipocytes from small, healthy cells to large, dysfunctional ones that contribute to redox imbalance and the progression of metabolic syndrome. Further, activation of Src/ERK signaling via the sodium potassium adenosine triphosphatase (Na/K-ATPase) α-1 subunit in impaired hepatocytes may contribute to redox imbalance, exacerbating the progression of NAFLD. This review hypothesizes that an adipogenic transformation of hepatocytes propagates redox imbalance and that the processes occurring in adipogenesis become activated in fat-laden hepatocytes in liver, thereby driving progression to NAFLD. Further, this review discusses therapeutic interventions to reverse NAFLD including the thiazolidinediones (TZDs) and a variety of antioxidant species. The peptide, pNaKtide, which is an antagonist of Na/K-ATPase signaling, is also proposed as a potential pharmacologic option for reducing reactive oxygen species (ROS) and reversing NAFLD by inhibiting the Na/K-ATPase-modulated ROS amplification loop.

Cell culture models of fatty acid overload: Problems and solutions

High plasma levels of fatty acids occur in a variety of metabolic diseases. Cellular effects of fatty acid overload resulting in negative cellular responses (lipotoxicity) are often studied in vitro, in an attempt to understand mechanisms involved in these diseases. Fatty acids are poorly soluble, and thus usually studied when complexed to albumins such as bovine serum albumin (BSA). The conjugation of fatty acids to albumin requires care pertaining to preparation of the solutions, effective free fatty acid concentrations, use of different fatty acid species, types of BSA, appropriate controls and ensuring cellular fatty acid uptake. This review discusses lipotoxicity models, the potential problems encountered when using these cellular models, as well as practical solutions for difficulties encountered.

Long-acting insulin analog detemir displays reduced effects on adipocyte differentiation of human subcutaneous and visceral adipose stem cells

BACKGROUND AND AIMS

Since treatment with insulin detemir results in a lower weight gain compared to human insulin, we investigated whether detemir is associated with lower ability to promote adipogenesis and/or lipogenesis in human adipose stem cells (ASC).

METHODS AND RESULTS

Human ASC isolated from both the subcutaneous and visceral adipose tissues were differentiated for 30 days in the presence of human insulin or insulin detemir. Nile Red and Oil-Red-O staining were used to quantify the rate of ASC conversion to adipocytes and lipid accumulation, respectively. mRNA expression levels of early genes, including Fos and Cebpb, as well as of lipogenic and adipogenic genes, were measured at various phases of differentiation by qRT-PCR. Activation of insulin signaling was assessed by immunoblotting. ASC isolated from subcutaneous and visceral adipose tissue were less differentiated when exposed to insulin detemir compared to human insulin, showing lower rates of adipocyte conversion, reduced triglyceride accumulation, and impaired expression of late-phase adipocyte marker genes, such as Pparg2, Slc2a4, Adipoq, and Cidec. However, no differences in activation of insulin receptor, Akt and Erk and induction of the early genes Fos and Cebpb were observed between insulin detemir and human insulin.

CONCLUSION

Insulin detemir displays reduced induction of the Pparg2 adipocyte master gene and diminished effects on adipocyte differentiation and lipogenesis in human subcutaneous and visceral ASC, in spite of normal activation of proximal insulin signaling reactions. These characteristics of insulin detemir may be of potential relevance to its weight-sparing effects observed in the clinical setting.

Effects of selected bioactive food compounds on human white adipocyte function

Background

Previous studies suggest that intake of specific bioactive compounds may have beneficial clinical effects on adipose tissue partly due to their anti-inflammatory and insulin-sensitizing properties. With the overall aim to contribute to better understanding of the mechanisms of selected bioactive nutrients on fat metabolism, we investigated their role on human white adipocyte function.

Methods

The influence of the omega-3-fatty acid docosahexaenoic acid (DHA), the anthocyanin (AC) cyanidin-3-glucoside and its metabolite protocatechuic acid, and the beta-glucan metabolite propionic acid (PI) on adipokine secretion, fatty acid metabolism (lipolysis/lipogenesis) and adipocyte differentiation (lipid accumulation) was studied in human fat cells differentiated in vitro. To investigate possible synergistic, additive or antagonistic effects, DHA was also combined with AC or PI.

Results

Each compound, alone or together with DHA, suppressed basal adipocyte lipolysis compared to control treated cells. DHA alone attenuated the secretion of pro-inflammatory adipokines such as chemerin, interleukin-6 (IL-6) and monocyte chemoattractant protein-1 (MCP-1/CCL2), whereas AC suppressed only the latter two. Treatment with PI decreased IL-6, tumour necrosis factor alpha (TNFα) and adiponectin secretion. A combination of DHA and AC decreased TNFα secretion and increased insulin-stimulated lipogenesis. No effect was found on adipocyte differentiation. At the selected concentrations, none of the compounds was found to be cytotoxic.

Conclusion

The studied bioactive food compounds or their metabolites have beneficial effects in human primary fat cells measured as decreased basal lipolytic activity and secretion of inflammatory markers. A minor effect was also observed on insulin-stimulated glucose uptake albeit only with the combination of DHA and AC. Taken together, our results may link the reported health benefits of the selected bioactives on metabolic disorders such as insulin resistance, hypertension and dyslipidemia to effects on white adipocytes.

Electronic supplementary material

The online version of this article (doi:10.1186/s12986-016-0064-3) contains supplementary material, which is available to authorized users.

LC-MS/MS analysis of visceral and subcutaneous adipose tissue proteomes in young goats with focus on innate immunity and inflammation related proteins

The endocrine role of adipose tissue and its involvement in several physiological and pathological processes are well recognized. Studies on human, mouse and rat adipose tissues have made clear that subcutaneous and visceral deposits play different roles, which is also reflected by different protein and gene expression patterns. In ruminants, fat tissues play important biological roles not only for animal health, but also for quality and gain in meat and milk production. Yet very few studies have explored the ruminant adipose tissue proteomes. The aim of our study was to compare subcutaneous and visceral adipose tissues of goat, focusing on proteins involved in immune and inflammatory response. A 2-D LC-MS/MS approach followed by cluster analysis shows a clear distinction between subcutaneous and visceral fat tissue proteomes, and qualitative RT-PCR based analysis of 30 potential adipokines further confirmed the individual expression patterns of 26 of these, including 7 whose mRNA expression was observed for the first time in adipose tissues. This study provides a first description of adipose tissue proteomes in goat, and presents observations on novel proteins related to metabolic and inflammatory pathways. The mass spectrometry data have been deposited to the ProteomeXchange Consortium with the data set identifier PXD000564.

BIOLOGICAL SIGNIFICANCE

The proteomic analysis of different subcutaneous and visceral adipose tissue deposits showed tissue specific differences in protein expressions of well known as well as novel adipokines. This highlights the importance of sampling site when studying adipose tissue's metabolic roles. The protein expression characteristics of adipose tissues was evaluated by quantitative RT-PCR, and confirmed that adipose tissues play a central role in controlling inflammation, detoxification and coagulation pathways, as well as regulation of body fat mobilization in dairy animals. These findings are of particular interest in farm animals where health and production traits are important for animal welfare and for economic gains.

Adiponectin, chemerin, cytokines, and dipeptidyl peptidase 4 are released from human adipose tissue in a depot-dependent manner: an in vitro system including human serum albumin

BACKGROUND

Adipose tissue (AT) contributes to metabolic dysfunction through imbalanced production of adipokines, including cytokines. Visceral AT in particular is associated with metabolic disorders, indicating a specific secretory status. The relative significance of different human AT depots in adipokine release is not fully known. Further, previous in vitro systems usually included medium containing bovine serum albumin (BSA), which may induce cytokine release. Our aim was to compare release of a number of adipokines/cytokines - all implicated in insulin resistance - from human subcutaneous and visceral AT in a short-term incubation system minimizing cytokine induction and including repeated measurements during 24 h. A prerequisite was to evaluate a potential alternative to BSA in the incubation medium.

METHODS

Subcutaneous and/or visceral AT from 17 patients (age 20-68 years; BMI 22.6-56.7 kg/m2) undergoing elective surgery was incubated for 2, 4, 6, 8, and 24 h in medium with or without 1% BSA or human serum albumin (HSA). Medium concentrations of adiponectin, chemerin, nine cytokines, dipeptidyl peptidase 4 (DPP4), and omentin were analyzed by multiplex immunoassay or ELISA. Adipocyte size, AT macrophage density, and medium concentrations of endotoxin were determined.

RESULTS

Cytokine release was induced by BSA but not by HSA. In evaluation of the final incubation protocol including 1% HSA, and as expected, adiponectin release was higher from subcutaneous biopsies of nonobese than of obese subjects and inversely associated with adipocyte size; omentin was released almost exclusively from visceral AT. Exploratory incubations revealed more abundant release of chemerin, cytokines (except IL-6), and DPP4 from the visceral depot, while adiponectin release was higher from subcutaneous than visceral AT. Release was linear for a maximum of 2-6 h. Macrophage density was higher in visceral than subcutaneous AT. Levels of endotoxin in the medium were negligible.

CONCLUSIONS

Adiponectin, chemerin, many cytokines, and DPP4 are released from human AT in a depot-dependent manner. These results highlight functional differences between visceral and subcutaneous AT, and a mechanistic link between regional fat accumulation and metabolic disorders. Supplementation of human AT incubation medium with HSA rather than BSA is recommended to minimize induction of cytokine release.

Functional TRPV and TRPM channels in human preadipocytes

Preadipocytes are widely used as an in vitro model to investigate proliferation, adipogenic differentiation, and lipodystrophy; however, cellular physiology and biology are not fully understood in human preadipocytes. The present study was to investigate the expression of transient receptor potential (TRP) channels in human preadipocytes and their potential roles in regulating proliferation and adipogenic differentiation using approaches of confocal microscopy, whole-cell patch voltage-clamp, reverse transcription polymerase chain reaction, Western blot, etc. We found that TRPV2, TRPV4, and TRPM7 channels were abundantly expressed in human preadipocytes. The intracellular Ca(2+) transient activated by the TRPV2 activator probenecid was reversed or prevented by ruthenium red, a TRPV2 blocker. The TRPV4 channel activator, 4α-phorbol 12-13-dicaprinate, enhanced intracellular Ca(2+) oscillations, and the effect was inhibited by the TRPV4 blocker RN-1734. TRPM7 current was recorded with dialysis of Mg(2+)-free pipette solution, which was inhibited by the TRP channel blocker 2-aminoethoxydiphenyl borate and enhanced by acidic extracellular pH. Silencing TRPV2 or TRPM7, but not TRPV4, significantly reduced cell proliferation via inhibiting cyclin D1, cyclin E, and p-ERK1/2. Interestingly, individually silencing these three channels decreased adipogenic differentiation of human preadipocytes by reducing p-Akt kinase. Our results demonstrate for the first time that functional TRPV2, TRPV4, and TRPM7 channels are abundantly expressed in human preadipocytes. TRPV2 and TRPM7, but not TRPV4, regulate cell proliferation via activating cyclin D1, cyclin E, and p-ERK1/2, while they are all involved in adipogenesis in human preadipocytes via phosphorylating Akt kinase.

Methyl-β-cyclodextrin alters adipokine gene expression and glucose metabolism in swine adipose tissue

This study was designed to determine whether methyl-β-cyclodextrin (MCD) can substitute for albumin in incubation medium for neonatal swine adipose tissue explants, or whether MCD affects metabolism and cytokine expression. Subcutaneous adipose tissue explants (100 ± 10 mg) were prepared from 21-day-old pigs. Explants were incubated in medium 199 supplemented with 25 mM HEPES, 1.0 nM insulin at 37°C. The medium also contained bovine serum albumin (BSA) or MCD at 0%, 0.05%, 0.1%, 0.2% or 0.3%. Tissue explants were treated with these media for 1 h and then switched to the same basal incubation medium containing 0.05% BSA. Explants were removed from basal medium at 2 or 8 h of incubation, and real-time PCR was performed to assess expression of tumor necrosis α (TNF) and interleukin 6 (IL6), acetyl CoA carboxylase (ACAC) and fatty acid synthase (FASN). Alternatively, rates of 14C-glucose oxidation and lipogenesis were monitored ± insulin (100 nM), following MCD treatment. Incubation with BSA had minimal effects on gene expression or adipose tissue metabolism, only producing a doubling in TNF mRNA abundance (P < 0.01). Treatment with MCD increased TNF mRNA abundance by eightfold (P < 0.009), whereas IL6 gene expression increased a 100-fold (P < 0.001) with a suppression in ACAC and FASN expression (P < 0.01). This was paralleled by MCD inhibition of insulin-stimulated glucose oxidation and lipogenesis (P < 0.001). Addition of a TNF antibody to the incubation medium alleviated this inhibition of insulin-stimulated glucose metabolism by ~30% (P < 0.05).

Influence of secreted factors from human adipose tissue on glucose utilization and proinflammatory reaction

The objective of the present study was to characterize the nature of the autocrine/paracrine signal within human adipose tissue that may alter glucose metabolism and the inflammatory status in adipocytes. We prepared a conditioned medium from abdominal dermolipectomies in the absence (CM) or the presence (CMBSA) of bovine serum albumin (BSA), and we tested the influence of CM and CMBSA on glucose transport, maximal insulin response, and the expression of inflammation marker genes in differentiated human SGBS adipocytes. We found that CMBSA increased basal and reduced insulin-stimulated glucose incorporation along with a reduced mRNA level of the glucose transport GLUT4, and an increased expression of GLUT1. These effects were associated with a potent upregulation in the mRNA level of the proinflammatory cytokines IL-6 and MCP-1. These regulations were strongly attenuated in the absence of BSA during the preparation of CM, or after BSA depletion of CM, and were attributed to water-soluble molecules rather than lipids. Finally, fractionation of CMBSA by isoelectric focusing showed that part of its bioactivity could be reproduced with proteins with pHi ranging from 6.6 to 7.6. In conclusion, our results demonstrate that the production by human adipose tissue of autocrine/paracrine neutral proteins is able to increase the inflammatory status of the adipocytes and to deteriorate their glucose metabolism and maximal insulin response, and their release is greatly amplified by the presence of albumin.

The inflammatory response seen when human omental adipose tissue explants are incubated in primary culture is not dependent upon albumin and is primarily in the nonfat cells

Background

The present studies were designed to investigate the changes in gene expression during in vitro incubation of human visceral omental adipose tissue explants as well as fat cells and nonfat cells derived from omental fat.

Methods

Adipose tissue was obtained from extremely obese women undergoing bariatric surgery. Explants of the tissue as well as fat cells and the nonfat cells derived by digestion with collagenase were incubated for 20 minutes to 48 h. The expression of interleukin 1β [IL-1β], tumor necrosis factor α [TNFα], interleukin 8 [IL-8], NFκB₁p50 subunit, hypoxia-inducible factor 1α [HIF1α], omentin/intelectin, and 11β-hydroxysteroid dehydrogenase 1 [11β-HSD1] mRNA were measured by qPCR as well as the release of IL-8 and TNFα.

Results

There was an inflammatory response at 2 h in explants of omental adipose tissue that was reduced but not abolished in the absence of albumin from the incubation buffer for IL-8, IL-1β and TNFα. There was also an inflammatory response with regard to upregulation of HIF1α and NFκB1 gene expression that was unaffected whether albumin was present or absent from the medium. In the nonfat cells derived by a 2 h collagenase digestion of omental fat there was an inflammatory response comparable but not greater than that seen in tissue. The exception was HIF1α where the marked increase in gene expression was primarily seen in intact tissue. The inflammatory response was not seen with respect to omentin/intelectin. Over a subsequent 48 h incubation there was a marked increase in IL-8 mRNA expression and IL-8 release in adipose tissue explants that was also seen to the same extent in the nonfat cells incubated in the absence of fat cells.

Conclusion

The marked inflammatory response seen when human omental adipose tissue is incubated in vitro is reduced but not abolished in the presence of albumin with respect to IL-1β, TNFα, IL-8, and is primarily in the nonfat cells of adipose tissue.

Expression of liver-specific markers in naïve adipose-derived mesenchymal stem cells

BACKGROUND

Increasing evidence suggests that adipose tissue contains mesenchymal stem cells (MSC) that possess the ability to transdifferentiate into other cell types including hepatocytes, similar to bone marrow-derived stem cells. The existence of precommitted cells in the MSC population may explain transdifferentiation.

AIMS

Our aim was to identify a population of putative hepatocyte-like precursor cells in human adipose tissue.

METHODS

We analysed the 'basal' hepatic potential of undifferentiated, naïve human adipose-derived mesenchymal stem cells (hADMSC). hADMSC were isolated from human adipose tissue and characterized for cell surface markers and for liver-specific gene expression.

RESULTS

The isolated undifferentiated naïve hADMSCs expressed MSC surface markers. They also expressed alpha-fetoprotein, CK18, CK19 and HNF4, which are known as early liver expressing genes. Interestingly, the undifferentiated naïve hADMSC were also positive for albumin, G-6-P and alpha-1-antitrypsin (AAT), which are all known to be predominantly expressed in adult liver cells. These cells acquired a hepatocyte-specific phenotype and function upon treatment with a differentiation medium, resulting in the upregulation of albumin, G-6-P and AAT. Moreover, urea production, glycogen storage ability and cellular uptake of indocyanine green, which were absent in the basal state, were evident in the treated cells.

CONCLUSIONS

Our findings suggest the presence of cells with hepatocyte-like properties that are isolated from human adipose tissue and that can readily acquire hepatocyte-like functions. Adipose tissue could thus be an exciting alternative means for repopulating the liver after various injuries, and might serve as a source for the transplantation of liver cells.

Palmitate modulates intracellular signaling, induces endoplasmic reticulum stress, and causes apoptosis in mouse 3T3-L1 and rat primary preadipocytes

Although fatty acids enhance preadipocyte differentiation in the presence of adequate hormone cocktails, little is known regarding their effects in the absence of these hormones. We have now shown that palmitate, a common long-chain saturated fatty acid, induced apoptosis in both mouse 3T3-L1 and rat primary preadipocytes grown in a normal serum-containing medium. Treatment of preadipocytes with palmitate induced multiple endoplasmic reticulum (ER) stress responses, evidenced by increased protein content of CHOP and GRP78 and splicing of XBP-1 mRNA, as well as altered phosphorylation of eIF2alpha and increased phosphorylation of JNK and Erk1/2. Intriguingly, palmitate induced an early activation of Akt but diminished both Akt activation and its protein mass after prolonged incubation (>6 h). In association with these changes, palmitate reduced expression of beta-catenin and its downstream target, c-Myc and cyclin D1, two key prosurvival proteins. Overexpression of constitutively active Akt did not block the apoptotic effect of palmitate. Cotreatment with unsaturated fatty acids (oleate, linoleate) or with LiCl (a glycogen synthase kinase-3beta inhibitor) attenuated the palmitate-induced apoptosis. Subsequent analysis suggested that the unsaturated fatty acids probably counteracted palmitate by reducing, not eliminating, ER stress, whereas LiCl probably improved viability by activating the Wnt signaling pathway. Cotreatment of palmitate with a standard adipogenic hormone cocktail also abolished the apoptotic effect and promoted adipocyte differentiation. Collectively, our results suggest that palmitate causes multiple cellular stresses that may lead to apoptosis in preadipocytes in the absence of adipogenic stimuli, highlighting the importance of exogenous hormones in directing cell fate in response to increased fatty acid influx.

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.

Albumin functions as an inhibitor of T cell adhesion in vitro

Jurkat T cells were found to adhere to a tissue culture flask or cover glass when 10% fetal bovine serum (FBS) was withdrawn. However, the cells adhered to extracellular matrix, especially fibronectin, regardless of the presence of FBS. We hypothesized that a substance in FBS inhibits T cells' adherence. Through a purification and identification procedure performed on the substance, bovine serum albumin (BSA) was found to inhibit T cell adhesion. BSA, furthermore, inhibited the adhesion of human primary cultured T cells. These results suggest a novel function for albumin as a T cell adhesion inhibitor.