The anti-diabetic AMPK activator AICAR reduces IL-6 and IL-8 in human adipose tissue and skeletal muscle cells

Increased production of inflammatory cytokines is suggested to be of importance for initiation and progression of insulin resistance. Chronic treatment with the AMP analogue 5-aminoimidazole-4-carboxamide-1-beta-d-ribonucleoside (AICAR) has been shown to improve insulin sensitivity and prevent the development of diabetes in rodents. We investigated the effects of AICAR on the expression and production of inflammatory cytokines from human adipose tissue and skeletal muscle cells as well as intact rat skeletal muscles in vitro. AICAR dose-dependently decreased interleukin-6 (IL-6) gene expression and secretion in human adipose tissue and in human skeletal muscle cells. In parallel, AICAR inhibited interleukin-8 (IL-8) secretion in human adipose tissue and skeletal muscle cells, as well as reduced IL-8 gene expression in skeletal muscle cells. In intact rat extensor digitorum longus (EDL) muscle fibres AICAR markedly decreased IL-6 and IL-8 gene expression. In conclusion, AICAR inhibits the production of IL-6 and IL-8 human adipose tissue and in skeletal muscle cells. We suggest that decreased cytokine production might play a role for the AICAR-induced increase in insulin sensitivity.     

Proinflammatory cytokines and chemokine production and expression by human osteoblasts isolated from patients with rheumatoid arthritis and osteoarthritis

OBJECTIVE: To evaluate whether subchondral osteoblasts (OB) are involved in the production of cytokines and chemokines in rheumatic diseases. METHODS: OB were isolated from subchondral bone of rheumatoid arthritis (RA), osteoarthritis (OA) and post-traumatic (PT) patients, cultured in vitro in the presence or absence of interleukin 1beta (IL-1beta) and tumor necrosis factor-alpha (TNF-alpha), and assessed for the production, immunolocalization, and mRNA expression of proinflammatory cytokines (IL-1alpha, IL-1beta, TNF-alpha) and alpha and beta chemokines [IL-8, growth related gene product (GRO-alpha), monocyte chemoattractant protein 1 (MCP-1), RANTES, and macrophage inflammatory proteins MIP-1alpha, MIP-1beta]. RESULTS: Cultured OB from different patients did not release IL-1alpha, IL-1beta, or TNF-alpha, and constitutively secreted IL-8, GRO-alpha, and MCP-1, while RANTES, MIP-1alpha, MIP-1beta were undetectable or near the lower level of sensitivity of the immunoenzymatic assay. GRO-alpha was significantly higher in RA than in OA and PT patients. IL-1beta and TNF-alpha alone or in combination strongly stimulated chemokine release by OB. Only RANTES production was not increased by the combination of the 2 cytokines. IL-1alpha, IL-1beta, and TNF-alpha were expressed as cytoplasmic proteins and were not secreted by OB even after stimulation. CONCLUSION: OB from subchondral bone release chemokines that could be involved in the mechanisms that directly or indirectly cause bone remodelling and cartilage destruction.     

Transforming growth factor beta1 release by human adipose tissue is enhanced in obesity

The present studies examined the effect of obesity in humans on the release of transforming growth factor beta1 (TGF-beta1) by human adipose tissue. The regulation of TGF-beta1 release by adipose tissue as well as the question of whether its release is due to the adipocytes or the nonfat cells in adipose tissue was also examined. There was a statistically significant (r=0.50) correlation between the body mass index of the fat donors and the subsequent release of TGF-beta1 release by subcutaneous adipose tissue. There was also a positive correlation between total TGF-beta1 release by adipose tissue explants and body fat content (r=0.69). The question of whether tumor necrosis factor alpha (TNF-alpha) and/or interleukin 1 beta (IL-1 beta) regulate the release of TGF-beta1 was investigated by incubation of adipose tissue explants with a soluble human TNF-alpha receptor (etanercept) and a neutralizing antihuman IL-1 beta antibody. The release of TGF-beta1 over 48 hours by adipose tissue explants was significantly enhanced in the presence of both the inhibitor of TNF-alpha and of IL-1 beta. It is of interest, in view of the elevated circulating insulin in blood of morbidly obese women, that the release of TGF-beta1 by adipose tissue was enhanced in the presence of insulin. The question of whether the release of TGF-beta1 by human adipose tissue explants was primarily due to adipocytes, as is the case for leptin, or the nonfat cells present in human adipose tissue, as is the case for IL-8 and prostaglandin E(2), was examined. The release of TGF-beta1 was primarily by the nonfat cells of human adipose tissue because release by adipocytes was less than 10% of that by the nonfat cells of adipose tissue.     

Effect of interleukin-1, tumor necrosis factor-alpha, and interferon-alpha on the blast cells of acute myeloblastic leukemia.

In this study, we further established the role of interleukin-1 alpha (IL-1 alpha), interleukin-1 beta, tumor necrosis factor-alpha (TNF-alpha), and interferon-alpha (IFN-alpha) as regulators of proliferation of acute myeloid leukemia (AML) cells. AML cells from 8 of 15 patients incorporated high levels of 3H-thymidine (3H-TdR) in the absence of exogenous growth factors. The spontaneous DNA synthesis could be abrogated with monospecific antibodies directed toward IL-1 alpha, IL-1 beta, or TNF-alpha, as well as with antigranulocyte-macrophage colony-stimulating factor (GM-CSF). Human recombinant GM-CSF reversed the inhibitory action of each of these antibodies and reinduced DNA synthesis in AML cells. Thus, in these cases, constitutively produced IL-1 or TNF-alpha had stimulated the synthesis of GM-CSF, which resulted in GM-CSF-dependent proliferation of AML blasts. Exogenous IL-1 up-regulated the endogenous production of GM-CSF, suggesting a positive regulation of autocrine growth factor production. We also present evidence that TNF-alpha may exert both stimulative as well as inhibitory effects on DNA synthesis in AML cells. The enhancing effect of TNF-alpha was mediated through the induction of GM-CSF production, as stimulation of DNA synthesis in AML blasts could be abrogated with anti-GM-CSF antibody. A concentration-dependent inhibitory effect of TNF-alpha on 3H-TdR incorporation into AML blasts was observed only when these cells were grown in the absence of GM-CSF. Finally, we show that human recombinant IFN-alpha is a potent inhibitor of AML cell proliferation in vitro.     

Cytokine release from adipose tissue of nonobese individuals

Explants of human adipose tissue from nonobese subjects were cultured for 24 h with or without the presence of 20 ng/ml TNFalpha. Gene expression and/or medium concentrations of interleukin (IL)-1beta, IL-1 receptor antagonist (IL-1 RA), TNFalpha, IL-6, IL-8, resistin, PAI-1 and leptin were analysed. TNFalpha increased the mRNA levels of TNFalpha itself as well as IL-6, IL-8, IL-1beta and PAI-1, but not leptin. The medium concentrations of IL-1 RA, IL-6 and IL-8 were markedly increased by TNFalpha while no measurable release of TNFalpha, resistin or IL-1beta to the medium was found. Thus, human adipose tissue from nonobese individuals releases substantial amounts of IL-6, IL-8 and IL-1 RA and the gene expression of these cytokines, like that of IL-1beta and PAI-1, is regulated by TNFalpha. However, since neither TNFalpha, resistin or IL-1beta was found in the culture medium, such a regulatory effect by TNFalpha on adipose tissue in vivo is likely to be mediated through a paracrine mechanism where invaded inflammatory cells may play a critical role.     

Increased adipose tissue secretion of interleukin-6, but not of leptin, plasminogen activator inhibitor-1 or tumour necrosis factor alpha, in Graves' hyperthyroidism

OBJECTIVE: This study was designed to investigate adipose tissue secretion of interleukin-6 (IL-6), leptin, tumour necrosis factor alpha (TNF-alpha) and plasminogen activator inhibitor-1 (PAI-1) in Graves' hyperthyroidism. DESIGN: We studied 10 patients before and during (after 8 weeks) anti-thyroid treatment for Graves' hyperthyroidism and 16 healthy, euthyroid control subjects. METHODS: Plasma levels of thyroid hormones and serum/plasma levels of IL-6, leptin, TNF-alpha and PAI-1 were analysed. Subcutaneous fat biopsies were taken for subsequent measurement of IL-6, leptin, TNF-alpha and PAI-1 protein secretion. RESULTS: In patients with Graves' disease, the anti-thyroid treatment resulted in significant reductions of plasma thyroxine and triiodothyronine levels. No differences in serum concentration or adipose tissue secretion of leptin or TNF-alpha were observed either before, as compared with during, anti-thyroid treatment, or in comparison with euthyroid controls. In contrast, plasma PAI-1 activity, but not adipose tissue secretion of PAI-1, was increased both in Graves' disease before as compared with during anti-thyroid treatment (P=0.01) and in thyrotoxic patients compared with euthyroid controls (P=0.0001). Finally, adipose secretion of IL-6 was increased both before (8-fold, P=0.001) and during (6-fold, P<0.0001) treatment as compared with control subjects. Accordingly, serum concentration of IL-6 was also increased by about 50% in thyrotoxic patients as compared with healthy controls (P=0.03). CONCLUSIONS: In Graves' hyperthyroidism regardless of thyroid status, adipose tissue secretion of IL-6, but not of leptin, TNF-alpha or PAI-1, is markedly increased in comparison with euthyroid controls. This suggests that autoimmune thyroidal disorder may regulate adipose tissue release of IL-6.     

ACTH and alpha-MSH inhibit leptin expression and secretion in 3T3-L1 adipocytes: model for a central-peripheral melanocortin-leptin pathway

Leptin is the 167 amino-acid protein product of the Lep (obese) gene that is released predominantly from adipose tissue and circulates at levels related to the amount of fat. Leptin expression is hormonally regulated: insulin and glucocorticoids are stimulators, while inhibitors include beta-adrenergic agonists and testosterone. Recently, adenylate cyclase-coupled melanocortin receptors have been identified in murine adipose tissue, the 3T3-L1 adipocyte cell line, and in human fat tissue. These studies prompted us to evaluate the effects of pro-opiomelanocortin (POMC)-derived peptides on leptin production and expression in 3T3-L1 adipocytes in culture. 3T3-L1 pre-adipocytes differentiated by the insulin/indomethacin (I/I) method produced leptin at levels that were two times higher than those obtained in cells differentiated by the more traditional insulin/dexamethasone/isobutylmethylxanthine (I/D/M) method. By RT-PCR studies, 3T3-L1 cells expressed both the melanocortin 2 receptors (MC2-R) and melanocortin 5 receptors (MC5-R) isoforms of the melanocortin receptor at an early stage of differentiation. When I/I differentiated 3T3-L1 adipocytes were incubated with different concentrations of dibutyryl cAMP (db-cAMP) or POMC-derived peptides (ACTH and alpha-MSH), ACTH and alpha-MSH stimulated cAMP production after 30 min (2-fold increase) associated with a dose-dependent inhibition of leptin secretion (ACTHz.Gt;alpha-MSH; IC(50)=3.2+/-0.4 SE and 36+/-5 nM, respectively), maximal after 3 h of incubation (30% inhibition). In addition, 100 nM ACTH and alpha-MSH induced a 60% reduction in leptin expression by RT-PCR. Incubation of cells with 0.5 mM db-cAMP led to a more prominent inhibition of leptin expression and secretion (up to 80% at 1 and 24 h, respectively). The ACTH and alpha-MSH inhibitory effects on leptin secretion were mediated by activation of the MC2-R and MC5-R and were reversed by the MC-R antagonists ACTH(11-24) and ACTH(7-38). In summary, we have shown that POMC-peptides are potent inhibitors of leptin expression and production in 3T3-L1 adipocytes. The finding of ACTH/alpha-MSH receptor-induced inhibition of leptin production and expression in adipocytes support the possibility that there is a control mechanism for modulation of adipose tissue function via a melanocortin-leptin axis.     

Increased subcutaneous and epicardial adipose tissue production of proinflammatory cytokines in cardiac surgery patients: possible role in postoperative insulin resistance

CONTEXT: Hyperglycemia and insulin resistance frequently occur in critically ill patients even without a history of diabetes. OBJECTIVE: Our objective was to study the role of adipose tissue hormonal production in the development of insulin resistance in cardiac surgery patients. PARTICIPANTS, INTERVENTIONS, AND SETTINGS: Fifteen patients with elective cardiac surgery underwent blood sampling before, at the end, and 6, 12, 24, 48, and 120 h after the end of their operation. Epicardial and sc adipose tissue sampling was done at the beginning and at the end of surgery in the Department of Cardiac Surgery. MAIN OUTCOME MEASURES: We measured serum concentrations and sc and epicardial adipose tissue mRNA expression of IL-6, monocyte chemoattractant protein-1 (MCP-1), TNF-alpha, leptin, resistin, and adiponectin and sc and epicardial adipose tissue mRNA expression of CD14, CD45, and CD68. RESULTS: The rate of insulin infusion required to maintain euglycemia increased up to 7-fold 12 h after the operation, suggesting the development of insulin resistance. Serum IL-6 levels increased 43-fold 12 h after surgery. MCP-1 peaked 6-fold at the end of surgery. Smaller peaks of TNF-alpha and leptin appeared 6 and 12 h after surgery, respectively. Resistin levels peaked 4-fold 24 h after surgery, but adiponectin levels were not significantly affected. TNF-alpha and CD45 mRNA expression increased markedly during the operation in sc adipose tissue. IL-6, resistin, and MCP-1 mRNA expression increased in both sc and epicardial adipose tissue. Leptin, adiponectin, CD14, and CD68 mRNA expression did not change significantly. CONCLUSIONS: Both sc and epicardial adipose tissue is a source of proinflammatory cytokines in cardiac surgery patients and may contribute to the development of postoperative insulin resistance.     

Adipokines: the missing link between insulin resistance and obesity

White adipose tissue was believed to be just an energy-storage organ, but it is now recognized to be an active participant in energy homoeostasis and physiological functions such as immunity and inflammation. Macrophages are components of adipose tissue and actively participate in its activities. Adipose tissue is known to express and secrete a variety of products known as 'adipokines', including leptin, adiponectin, resistin and visfatin, as well as cytokines and chemokines such as tumor necrosis factor-alpha, interleukin-6 and monocyte chemoattractant protein-1. The release of adipokines by either adipocytes or adipose tissue-infiltrated macrophages leads to a chronic subinflammatory state that could play a central role in the development of insulin resistance and type 2 diabetes, and the increased risk of cardiovascular disease associated with obesity.     

Expression of adipokines and estrogen receptors in adipose tissue and placenta of patients with gestational diabetes mellitus

The purpose of this study was to assess the expression profile of genes with potential role in the development of insulin resistance (adipokines, cytokines/chemokines, estrogen receptors) in subcutaneous adipose tissue (SAT), visceral adipose tissue (VAT) and placenta of pregnant women with gestational diabetes mellitus (GDM) and age-matched women with physiological pregnancy at the time of Caesarean section. qRT-PCR was used for expression analysis of the studied genes. Leptin gene expression in VAT of GDM group was significantly higher relative to control group. Gene expressions of interleukin-6 and interleukin-8 were significantly increased, whereas the expressions of genes for estrogen receptors α and β were significantly reduced in SAT of GDM group relative to controls, respectively. We found no significant differences in the expression of any genes of interest (LEP, RETN, ADIPOR1, ADIPOR2, TNF-α, CD68, IL-6, IL-8, ERα, ERβ) in placentas of women with GDM relative to controls. We conclude that increased expression of leptin in visceral adipose depot together with increased expressions of proinflammatory cytokines and reduced expressions of estrogen receptors in subcutaneous fat may play a role in the etiopathogenesis of GDM.     

Lipopolysaccharide-induced cytokine and chemokine expression in human carotid lesions

The release of cytokines and chemokines from activated immune-competent cells plays a crucial role in determining the pathology of the atherogenic progress. We investigated the effect of bacterial lipopolysaccharide (LPS) on cytokine/chemokine expression in carotid lesions and normal renal arteries. The lesions or renal arteries were incubated for 6 h at 37 degrees C in serum-free media treated with or without LPS. After LPS treatment, increased protein levels of IL-1beta, IL-6, IL-8, IL-10, TNF-alpha and MCP-1 were observed in the culture medium from the lesions measured with cytometric bead array. We were able to detect the induction of IL-1beta, IL-6, IL-8, IL-10, TNF-alpha and MCP-1 mRNA in the lesions after stimulation with LPS using real-time PCR. In renal arteries, LPS also induces mRNA expression of all chemokines and cytokines investigated with the exception of IL-6. However, LPS induces significantly higher levels of TNF-alpha, IL-1beta and IL-10 mRNA in lesions compared to renal arteries. The results suggest that infectious agents are capable of enhancing the production of cytokines/chemokines in an already ongoing inflammatory process such as in atherosclerosis, and that low levels of circulating LPS may affect the levels of pro-inflammatory cytokines much more in atherosclerotic vessels than in normal vessels and may contribute to the development of the atherosclerotic lesion.     

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-α, 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-α 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.     

Pro-inflammatory delipidizing cytokines reduce adiponectin secretion from human adipocytes without affecting adiponectin oligomerization

Adiponectin and, especially, its oligomeric complex composition have been suggested to be critical in determining insulin sensitivity. Pro-inflammatory cytokines play an important role in the development of insulin resistance in obesity and associated diseases. Therefore, we investigated the effect of long-term exposure of tumour necrosis factor (TNF)-alpha, interleukin (IL)-6, IL-1beta, and interferon (IFN)-gamma on total insulin-sensitizing adiponectin secretion and adiponectin complex formation from human adipocytes. In parallel, adipocyte delipidation and leptin production levels were monitored. The present study demonstrates that TNF-alpha, IL-1beta, and IFN-gamma dose and time dependently suppressed total adiponectin secretion within 7 days (60, 70, and 35% reduction respectively). IL-6 was also able to reduce (50%) adiponectin production, although only in combination with exogenous soluble IL-6 receptors (sIL-6R). However, the oligomeric distribution (high, middle, and low molecular weight (HMW) complexes) of secreted adiponectin was not altered by any of these cytokines. All studied pro-inflammatory cytokines resulted in delipidation and reduction of lipid-laden adipocyte numbers. Despite this reduction of lipid-laden adipocytes, TNF-alpha, IL-6/sIL-6R, and IL-1beta stimulated leptin release. Our data indicate that (i) long-term pro-inflammatory cytokine exposure downregulates total adiponectin secretion from delipidizing adipocytes and (ii) pro-inflammatory cytokines are not important regulators of adipocyte-derived adiponectin oligomerization. Hence, their individual contribution to low expression of HMW adiponectin found in insulin-resistant conditions seems unlikely. Furthermore, delipidizing adipocytes and preadipocytes are active leptin producers when stimulated by TNF-alpha, IL-6/sIL-6R, and IL-1beta.     

Cytokines, endothelial dysfunction, and insulin resistance

Endothelial dysfunction is associated with several vascular conditions as atherosclerosis, hypertension, hyperlipidemia and diabetes mellitus. In all these conditions insulin resistance (IR) is present. Cytokines are low molecular weight proteins with several endocrine and metabolic functions that participate of inflammation and immune response. Several of these cytokines are independent risk factors for cerebrovascular and coronary artery disease. The major sources of cytokines (adipokines) are the visceral and subcutaneous adipose tissues. Thus, increased adipose tissue mass is associated with alteration in adipokine production as over expression of tumor necrosis factor alpha, interleukin 6, plasminogen activator inhibitor 1, and under expression of adiponectin in adipocite tissue. The pro-inflammatory status associated with these changes provides a potential link between IR and endothelial dysfunction, the early stage in the atherosclerotic process, in obese individuals, and type 2 diabetic patients. Reduction of adipose tissue mass through weight reduction in association with exercise reduces TNF-alpha, IL-6, and PAI-1, increases adiponectin, and is associated with improved insulin sensitivity and endothelial function. This review will focus on the evidence for regulation of endothelial function by insulin and the adypokines such as adyponectin, leptin, resistin, IL-6 and TNF-alpha. Interaction between insulin signaling and adypokines will be discussed, as well as the concept that aberrant adypokine secretion in IR and/or obesity impairs endothelial function and contributes further to reduce insulin sensitivity.     

Relative overexpression of macrophage-derived cytokines in orbital adipose tissue from patients with graves' ophthalmopathy

Graves' ophthalmopathy (GO) is an autoimmune disorder involving the adipose and connective tissues of the orbit. The study of cytokines present in these tissues may reveal the nature of the cells and immune responses involved in GO pathogenesis. In the current study, we performed relative quantification of the expression of cytokine genes in orbital adipose tissue from patients with GO (n = 6) and normal individuals (n = 2). Real-time RT-PCR was performed using fluorescent probes and primers for cytokines including IL-1 beta, IL-2, IL-4, IL-5, IL-8, IL-10, IFN-gamma, and TNF-alpha. Results showed IL-1 beta to be the gene having the greatest fold expression increase over normal in four of six patients. TNF-alpha was increased in all six GO patients. In addition, IL-8, IL-10, and IFN-gamma were increased in five of six GO patients. We found no evidence of either IL-4 or IL-5 expression in any of the GO or normal samples. The increased expression of the macrophage-derived cytokines IL-1 beta, TNF-alpha, and IL-10 suggests the presence of macrophage activation and ongoing antigen presentation within the orbit in GO. In addition, the overexpression of IFN-gamma, without evidence of IL-4 or IL-5 expression, supports the concept that cell-mediated, rather than humoral, immunity plays the predominant role in pathogenesis of this disorder.     

The endocrine function of adipose tissue: an update

Adipose tissue secretes bioactive peptides, termed 'adipokines', which act locally and distally through autocrine, paracrine and endocrine effects. In obesity, increased production of most adipokines impacts on multiple functions such as appetite and energy balance, immunity, insulin sensitivity, angiogenesis, blood pressure, lipid metabolism and haemostasis, all of which are linked with cardiovascular disease. Enhanced activity of the tumour necrosis factor and interleukin 6 are involved in the development of obesity-related insulin resistance. Angiotensinogen has been implicated in hypertension and plasminogen activating inhibitor-1 (PAI-1) in impaired fibrinolysis. Other adipokines like adiponectin and leptin, at least in physiological concentrations, are insulin sparing as they stimulate beta oxidation of fatty acids in skeletal muscle. The role of resistin is less understood. It is implicated in insulin resistance in rats, but probably not in humans. Reducing adipose tissue mass, through weight loss in association with exercise, can lower TNF-alpha and IL-6 levels and increase adiponectin concentrations, whereas drugs such as thiazolinediones increase endogenous adiponectin production. In-depth understanding of the pathophysiology and molecular actions of adipokines may, in the coming years, lead to effective therapeutic strategies designed to protect against atherosclerosis in obese patients.     

Transforming growth factor beta expression in human marrow stromal cells

The effects of hematopoietic cytokines on the expression of transforming growth factors (TGF beta) mRNA and the effect of TGF beta on cytokine and on a major extracellular matrix protein, collagen I, mRNA expression was studied in human marrow stromal cells. As with other cultured mesenchymal cells, stromal cells constitutively express TGF beta 1 but not TGF alpha mRNA. In simian virus 40 (SV40)-transformed stromal cells downregulation of TGF beta 1 expression was observed 2 hours after incubation with recombinant human (rh) tumor-necrosis factor alpha (TNF alpha) and 144 h after addition of rh granulocyte macrophage colony-stimulating factor (GM-CSF). Neither interleukin-1 (IL-1)beta nor IL-6 had an observable effect on TGF beta 1 mRNA expression. TGF beta upregulated collagen I mRNA expression. These data suggest that cytokines may influence TGF beta mRNA expression.     

Nerve growth factor release by human synovial fibroblasts prior to and following exposure to tumor necrosis factor-alpha, interleukin-1 beta and cholecystokinin-8: the possible role of NGF in the inflammatory response

OBJECTIVE: Aim of this study was to investigate the synthesis, release and effects of nerve growth factor (NGF) in human synovial cells isolated from synovial tissue specimen from healthy and osteoarthritis (OA) patients. METHODS: Human synovial fibroblasts cultures were established starting from healthy and osteoarthritis patients. NGF protein levels in the culture medium, NGFmRNA and high-affinity NGF receptor (Tyrosine kinase A: TrkA) expression in the cells were evaluated in basal conditions and after stimulation with pro-inflammatory cytokines or with the neuropeptide cholecystokinin-8 (CCK-8). The effect of NGF supplement to culture medium on cell proliferation, TrkA expression, and tumour necrosis factor-alpha (TNF-alpha) and inducible-nitric oxide synthase (iNOS) production was investigated. RESULTS: Under basal conditions human synovial cells produce and release NGF. Both interleukin-1-beta (IL-1 beta) and TNF-alpha, but not CCK-8 promote NGF synthesis and release from OA cells. TrkA NGF receptors are also expressed in both normal and OA synovial cells. NGF, but not IL-1 beta, TNF-alpha and CCK-8, enhances the expression of TrkA in isolated synovial cells. NGF down-regulates IL-1 beta-induced TNF-alpha and iNOS production by OA synovial fibroblasts. CONCLUSIONS: NGF is produced and released and TrkA receptors are expressed in synovial inflammation. Overexpression of NGF in inflammed joints might be involved in the modulation rather than in the induction of the joint inflammatory response.