Delayed resolution of acute inflammation during zymosan-induced arthritis in leptin-deficient mice

Elevated serum leptin may be associated with disease activity and secondary osteoporosis in Chinese patients with rheumatoid arthritis

INTRODUCTION

Rheumatoid arthritis (RA) is a systemic chronic autoimmune disease in adults that is associated with significant joint issues and systemic inflammation. One of the signs of bone damage in RA is osteoporosis (OP). Leptin is an inflammatory protein that has been reported to be related to RA. The potential relationships among leptin, disease activity, and OP in Chinese patients with RA are not well known.

METHODS

In total, 245 patients with RA and 120 healthy controls were included in this study. Detailed data on the clinical characteristics and laboratory features were collected. Information about physical activity and functional status was recorded using specific questionnaires. Bone mineral density (BMD) was measured by dual-energy X-ray absorptiometry (DXA). The MECALL castor-50-hf model X-ray scanner was used for the two-hand (including wrist) photographs.

RESULTS

Serum leptin levels differed significantly between the RA group and healthy control subjects (1.27/3.29 vs. 0.17/0.24, Z=13.29, P<0.001). The positive rate of leptin protein in RA patients was 86.35%, which was higher than that in controls (19.55%) (χ2=28.51, P<0.001). Pearson's correlation test showed that morning stiffness, disease duration, joint swelling, joint tenderness, swollen joint count (SJC), tender joint count (TJC), health assessment questionnaire (HAQ) score, and Sharp-van der Heijde method (Sharp) score were positively correlated with the level of serum leptin (r=0.212, r=0.312, r=0.322, r=0.501, r=0.291, r=0.334, P<0.05). There was a clear increasing trend in the level of serum leptin according to the different disease activity scores and in the 28 joint activity (DAS28) groups (F=13.936, P<0.001). Elevated leptin was a risk factor for increased disease activity and OP according to logistic regression analysis. The median leptin level differed significantly between the normal bone mass group, osteopenia group, and OP group (P<0.001). An increased serum leptin level was a risk factor for RA-induced osteoporosis according to logistic regression analysis (P<0.001).

CONCLUSION

These results suggest that the level of serum leptin is associated with disease activity and secondary OP among Chinese patients with RA. Key Points • Serum leptin levels in RA patients are higher than those in normal control group. • Leptin was associated with disease activity. • Leptin was associated with the occurrence of systemic osteoporosis and affects bone erosion in RA patients.

Leptin Signaling Suppression in Macrophages Improves Immunometabolic Outcomes in Obesity

Obesity is a major concern for global health care systems. Systemic low-grade inflammation in obesity is a major risk factor for insulin resistance. Leptin is an adipokine secreted by the adipose tissue that functions by controlling food intake, leading to satiety. Leptin levels are increased in obesity. Here, we show that leptin enhances the effects of LPS in macrophages, intensifying the production of cytokines, glycolytic rates, and morphological and functional changes in the mitochondria through an mTORC2-dependent, mTORC1-independent mechanism. Leptin also boosts the effects of IL-4 in macrophages, leading to increased oxygen consumption, expression of macrophage markers associated with a tissue repair phenotype, and wound healing. In vivo, hyperleptinemia caused by diet-induced obesity increases the inflammatory response by macrophages. Deletion of leptin receptor and subsequently of leptin signaling in myeloid cells (ObR-/-) is sufficient to improve insulin resistance in obese mice and decrease systemic inflammation. Our results indicate that leptin acts as a systemic nutritional checkpoint to regulate macrophage fitness and contributes to obesity-induced inflammation and insulin resistance. Thus, specific interventions aimed at downstream modulators of leptin signaling may represent new therapeutic targets to treat obesity-induced systemic inflammation.

miR-34a overexpression protects against hippocampal neuron damage caused by ketamine-induced anesthesia in immature rats through the Notch-1/NF-κB signaling pathway

OBJECTIVE

To investigate the protective effect of miR-34a overexpression on hippocampal neuron damage caused by ketamine-induced anesthesia in immature rats and the underlying mechanism.

METHODS

A total of 48 male SD rats were divided into control group (CG, n=12), ketamine group (KG, n=12), negative control group (NCG, n=12), and intervention group (IG, n=12) by using the random number table method. Neurological function, cognitive function, pathological changes of brain tissues, inflammatory cytokines, as well as mRNA expression levels of Notch-1, NICD, RBP-JK, and Hes-1 in brain tissues were detected in the four groups.

RESULTS

The scores of auricular, paw withdrawal, corneal reflex, and escape reflexes of IG were higher than those of KG and NCG (P<0.05). At day 3 after intervention, the escape latency, time of staying in the quadrants of original platform, and times of crossing the quadrants of original platform of IG were lower than those of KG and NCG (P<0.05). HE staining results revealed that the morphology and structure of a few neurons and glial cells in IG were changed, and the intercellular space was increased. The brain tissues of NCG demonstrated marked neuron damage with unclear structure; these changes were less significant for KG. The levels of TNF-α, IL-1β, and IL-6 of IG were lower than those of KG and CG (P<0.05).

CONCLUSIONS

miR-34a overexpression exhibited a potent protective effect on hippocampal neuron damage caused by ketamine-induced anesthesia in immature rats.

Leptin modulates gene expression in the heart, cardiomyocytes and the adipose tissue thus mitigating LPS-induced damage

Leptin is an adipokine of pleiotropic effects linked to energy metabolism, satiety, the immune response, and cardioprotection. We have recently shown that leptin causally conferred resistance to myocardial infarction-induced damage in transgenic αMUPA mice overexpressing leptin compared to their wild type (WT) ancestral mice FVB/N. Prompted by these findings, we have investigated here if leptin can counteract the inflammatory response triggered after LPS administration in tissues in vivo and in cardiomyocytes in culture. The results have shown that LPS upregulated in vivo and in vitro all genes examined here, both pro-inflammatory and antioxidant, as well as the leptin gene. Pretreating mice with leptin neutralizing antibodies further upregulated the expression of TNFα and IL-1β in the adipose tissue of both mouse types, and in the αMUPA heart. The antibodies also increased the levels of serum markers for cell toxicity in both mouse types. These results indicate that under LPS, leptin actually reduced the levels of these inflammatory-related parameters. In addition, pretreatment with leptin antibodies reduced the levels of HIF-1α and VEGF mRNAs in the heart, indicating that under LPS leptin increased the levels of these mRNAs. In cardiomyocytes, pretreatment with exogenous leptin prior to LPS reduced the expression of both pro-inflammatory genes, enhanced the expression of the antioxidant genes HO-1, SOD2 and HIF-1α, and lowered ROS staining. In addition, results obtained with leptin antibodies and the SMLA leptin antagonist indicated that endogenous and exogenous leptin can inhibit leptin gene expression. Together, these findings have indicated that under LPS, leptin concomitantly downregulated pro-inflammatory genes, upregulated antioxidant genes, and lowered ROS levels. These results suggest that leptin can counteract inflammation in the heart and adipose tissue by modulating gene expression.

Lipidomic analysis of local inflammation models shows a specific systemic acute phase response to lipopolysaccharides

Toll-like receptors (TLR) are crucial for recognizing bacterial, viral or fungal pathogens and to orchestrate the appropriate immune response. The widely expressed TLR2 and TLR4 differentially recognize various pathogens to initiate partly overlapping immune cascades. To better understand the physiological consequences of both immune responses, we performed comparative lipidomic analyses of local paw inflammation in mice induced by the TLR2 and TLR4 agonists, zymosan and lipopolysaccharide (LPS), respectively, which are commonly used in models for inflammation and inflammatory pain. Doses for both agonists were chosen to cause mechanical hypersensitivity with identical strength and duration. Lipidomic analysis showed 5 h after LPS or zymosan injection in both models an increase of ether-phosphatidylcholines (PC O) and their corresponding lyso species with additional lipids being increased only in response to LPS. However, zymosan induced stronger immune cell recruitment and edema formation as compared to LPS. Importantly, only in LPS-induced inflammation the lipid profile in the contralateral paw was altered. Fittingly, the plasma level of various cytokines and chemokines, including IL-1β and IL-6, were significantly increased only in LPS-treated mice. Accordingly LPS induced distinct changes in the lipid profiles of ipsilateral and contralateral paws. Here, oxydized fatty acids, phosphatidylcholines and phosphatidylethanolamines were uniquely upregulated on the contralateral side. Thus, both models cause increased levels of PC O and lyso-PC O lipids at the site of inflammation pointing at a common role in inflammation. Also, LPS initiates systemic changes, which can be detected by changes in the lipid profiles.

Therapeutic Effects of Tryptanthrin and Tryptanthrin-6-Oxime in Models of Rheumatoid Arthritis

Rheumatoid arthritis (RA) is a chronic autoimmune disease involving joint and bone damage that is mediated in part by proteases and cytokines produced by synovial macrophages and fibroblast-like synoviocytes (FLS). Although current biological therapeutic strategies for RA have been effective in many cases, new classes of therapeutics are needed. We investigated anti-inflammatory properties of the natural alkaloid tryptanthrin (TRYP) and its synthetic derivative tryptanthrin-6-oxime (TRYP-Ox). Both TRYP and TRYP-Ox inhibited matrix metalloproteinase (MMP)-3 gene expression in interleukin (IL)-1β-stimulated primary human FLS, as well as IL-1β–induced secretion of MMP-1/3 by FLS and synovial SW982 cells and IL-6 by FLS, SW982 cells, human umbilical vein endothelial cells (HUVECs), and monocytic THP-1 cells, although TRYP-Ox was generally more effective and had no cytotoxicity in vitro. Evaluation of the therapeutic potential of TRYP and TRYP-Ox in vivo in murine arthritis models showed that both compounds significantly attenuated the development of collagen-induced arthritis (CIA) and collagen-antibody–induced arthritis (CAIA), with comparable efficacy. Collagen II (CII)-specific antibody levels were similarly reduced in TRYP- and TRYP-Ox-treated CIA mice. TRYP and TRYP-Ox also suppressed proinflammatory cytokine production by lymph node cells from CIA mice, with TRYP-Ox being more effective in inhibiting IL-17A, granulocyte-macrophage colony-stimulating factor (GM-CSF), and receptor activator of nuclear factor-κB ligand (RANKL). Thus, even though TRYP-Ox generally had a better in vitro profile, possibly due to its ability to inhibit c-Jun N-terminal kinase (JNK), both TRYP and TRYP-Ox were equally effective in inhibiting the clinical symptoms and damage associated with RA. Overall, TRYP and/or TRYP-Ox may represent potential new directions for the pursuit of novel treatments for RA.

The Impact of Dietary Components on Regulatory T Cells and Disease

The rise in the prevalence of autoimmune diseases in developed societies has been associated with a change in lifestyle patterns. Among other factors, increased consumption of certain dietary components, such as table salt and fatty acids and excessive caloric intake has been associated with defective immunological tolerance. Dietary nutrients have shown to modulate the immune response by a direct effect on the function of immune cells or, indirectly, by acting on the microbiome of the gastrointestinal tract. FOXP3⁺ regulatory T cells (Tregs) suppress immune responses and are critical for maintaining peripheral tolerance and immune homeostasis, modulating chronic tissue inflammation and autoimmune disease. It is now well-recognized that Tregs show certain degree of plasticity and can gain effector functions to adapt their regulatory function to different physiological situations during an immune response. However, plasticity of Tregs might also result in conversion into effector T cells that may contribute to autoimmune pathogenesis. Yet, which environmental cues regulate Treg plasticity and function is currently poorly understood, but it is of significant importance for therapeutic purposes. Here we review the current understanding on the effect of certain dietary nutrients that characterize Western diets in Treg metabolism, stability, and function. Moreover, we will discuss the role of Tregs linking diet and autoimmunity and the potential of dietary-based interventions to modulate Treg function in disease.

Are obesity and rheumatoid arthritis interrelated?

OBJECTIVES

In recent years, both the prevalence of obesity and the incidence of RA have been rising. Our aim was to assess the association between overweight or obesity and rheumatoid arthritis (RA).

DESIGN

Patients who were diagnosed with RA were compared with population-based controls, matched for age and sex (by a ratio of 1:5). Body measurements and smoking status were collected from medical records. Body mass index was classified in WHO categories of underweight, normal, overweight and obese (<18.5, 18.5-<25, 25-<30, ≥30 kg/m² ). χ² and t-tests and logistic regression models were used to compare the study groups and to assess the association between obesity and RA.

SETTING

A cross-sectional analysis performed utilizing the database of Clalit Health Services, the largest healthcare provider organisation in Israel. Data were collected from the beginning of computerised database usage (around year 2000) until 2015.

PARTICIPANTS

CHS covers over 4.4 million enrollees, of which all RA patients and matched controls were selected.

MAIN OUTCOME MEASURES

Proportion of obesity (BMI≥30.0 kg/m² ) among RA patients and controls.

RESULTS

The study included 11 406 patients with RA and 54 701 controls. The proportion of obese subjects among RA patients was higher in comparison with controls, (33.4% vs 31.6%, respectively). In multivariate regression model, smoking and obesity were found to be associated with RA, whereas male gender was found as inversely related to RA.

CONCLUSIONS

Our findings demonstrate that obesity is significantly associated with RA. This finding underlines the role that obesity plays in inflammation and autoimmune conditions.

Smoking Functions as a Negative Regulator of IGF1 and Impairs Adipokine Network in Patients with Rheumatoid Arthritis

Objectives. Smoking is pathogenic for rheumatoid arthritis (RA) being tightly connected to the genetic and serological risk factors for this disease. This study aims to understand connections between cigarette smoking and serum levels of IGF1 and adipokines in RA. Methods. Serum levels of IGF1 and adipokines leptin, adiponectin, resistin, and visfatin were measured in two independent cohorts of RA patients from Gothenburg (n = 350) and Leiden (n = 193). An association of these parameters with smoking was tested in a direct comparison and proved by bivariate correlation analysis. The obtained associations were further tested in multivariate regression models where the confounders (age, gender, disease duration, and BMI) were controlled. Results. The smokers had significantly lower serum levels of IGF1, adiponectin, and leptin compared to never smokers. In regression analysis, smoking and low leptin, but not adiponectin, were associated and predicted low IGF1. Additionally, high disease activity and high BMI increased the probability of low leptin. Conclusions. The study indicates cigarette smoking as an important cause of a relative IGF1 and leptin deficiency in RA patients. This novel association between smoking and hypoleptinemia may be of importance for long-term prognosis of RA and for prediction of comorbidities.

Anti-Inflammatory Effects and Joint Protection in Collagen-Induced Arthritis after Treatment with IQ-1S, a Selective c-Jun N-Terminal Kinase Inhibitor

c-Jun N-terminal kinases (JNKs) participate in many physiologic and pathologic processes, including inflammatory diseases. We recently synthesized the sodium salt of IQ-1S (11H-indeno[1,2-b]quinoxalin-11-one oxime) and demonstrated that it is a high-affinity JNK inhibitor and inhibits murine delayed-type hypersensitivity. Here we show that IQ-1S is highly specific for JNK and that its neutral form is the most abundant species at physiologic pH. Molecular docking of the IQ-1S syn isomer into the JNK1 binding site gave the best pose, which corresponded to the position of cocrystallized JNK inhibitor SP600125 (1,9-pyrazoloanthrone). Evaluation of the therapeutic potential of IQ-1S showed that it inhibited matrix metalloproteinase 1 and 3 gene expression induced by interleukin-1β in human fibroblast-like synoviocytes and significantly attenuated development of murine collagen-induced arthritis (CIA). Treatment with IQ-1S either before or after induction of CIA resulted in decreased clinical scores, and joint sections from IQ-1S-treated CIA mice exhibited only mild signs of inflammation and minimal cartilage loss compared with those from control mice. Collagen II-specific antibody responses were also reduced by IQ-1S treatment. By contrast, the inactive ketone derivative 11H-indeno[1,2-b]quinoxalin-11-one had no effect on CIA clinical scores or collagen II-specific antibody titers. IQ-1S treatment also suppressed proinflammatory cytokine and chemokine levels in joints and lymph node cells. Finally, treatment with IQ-1S increased the number of Foxp3(+)CD4(+)CD25(+) regulatory T cells in lymph nodes. Thus, IQ-1S can reduce inflammation and cartilage loss associated with CIA and can serve as a small-molecule modulator for mechanistic studies of JNK function in rheumatoid arthritis.

Mannan induces ROS-regulated, IL-17A-dependent psoriasis arthritis-like disease in mice

Psoriasis (Ps) and psoriasis arthritis (PsA) are poorly understood common diseases, induced by unknown environmental factors, affecting skin and articular joints. A single i.p. exposure to mannan from Saccharomyces cerevisiae induced an acute inflammation in inbred mouse strains resembling human Ps and PsA-like disease, whereas multiple injections induced a relapsing disease. Exacerbation of disease severity was observed in mice deficient for generation of reactive oxygen species (ROS). Interestingly, restoration of ROS production, specifically in macrophages, ameliorated both skin and joint disease. Neutralization of IL-17A, mainly produced by γδ T cells, completely blocked disease symptoms. Furthermore, mice depleted of granulocytes were resistant to disease development. In contrast, certain acute inflammatory mediators (C5, Fcγ receptor III, mast cells, and histamine) and adaptive immune players (αβ T and B cells) were redundant in disease induction. Hence, we propose that mannan-induced activation of macrophages leads to TNF-α secretion and stimulation of local γδ T cells secreting IL-17A. The combined action of activated macrophages and IL-17A produced in situ drives neutrophil infiltration in the epidermis and dermis of the skin, leading to disease manifestations. Thus, our finding suggests a new mechanism triggered by exposure to exogenous microbial components, such as mannan, that can induce and exacerbate Ps and PsA.

Adipose tissue dendritic cells enhances inflammation by prompting the generation of Th17 cells

BACKGROUND

Obesity has become a global challenge for public health. It has been reported that obesity is associated with chronic inflammation. However, the mechanism for the chronic inflammation contributes to obesity remains elusive.

METHODOLOGY/PRINCIPAL FINDINGS

In our study, we found a novel CD11c+ dendritic cell subset existed in murine adipose tissues which was immature phenotype. Moreover, as compared to the lean controls, the number of CD11c+ DCs and CD4+IL-17+T cells were higher in adipose tissue of high fat diet (HFD) mice. Adipose tissues derived dendritic cells (ATDCs) displayed lower levels of CD40, CD80, CD86, MHCI and MHCII expression than splenic DCs (SPDCs). However, ATDCs showed higher levels of IL-6, TGF-β and IL-23 secretion. Moreover, our in vitro experiments demonstrated that ATDCs were capable of promoting Th17 cell generation.

CONCLUSIONS/SIGNIFICANCE

Our results indicate the existence of CD11c+ DCs in adipose tissues, which displays an immature phenotype but possessing pro-inflammatory function.

The role of growth factor Sadat-Habdan mesenchymal stimulating peptide in healing of burn wounds

BACKGROUND

Burns occur in everyday life and cause morbidity and mortality due to delayed healing. Many agents were tried to accelerate healing of burns. The aim of this study was to assess for the first time Sadat-Habdan mesenchymal stimulating peptide (SHMSP) known angiogenesis factor in healing of experimentally created burns in rats.

METHODS

Forty male rats weighing (200-250 g) were randomly divided into 2 groups of 20 each. Under general anesthesia, reproducible, deep, partial-thickness, thermal burn injury was created by 1-cm aluminum template on the dorsal aspect of the body of each animal by heating the template at 80 °C for 10 seconds. Alternate rats were assigned to 1 of the 2 groups to minimize the difference of timing of the burn. Sadat-Habdan mesenchymal stimulating peptide 10 mg was applied on daily burn area, covered with a nonabsorbent dressing. All animals were kept in similar standard laboratory conditions. Its application continued 14 days as described by the inventors, and burned areas were photographed. On day 15, blood was collected from the animals for serum albumin levels, and the animals were killed, then the entire burn areas were excised for biopsy for general morphology and histopathology.

RESULTS

There were no deaths among groups. The majority of the animals showed good to excellent healing compared with the control group. Clinical pictures revealed better healing in the SHMSP-treated group. Quantitative and qualitative analyses of images revealed significant contraction of burned areas. Image analysis showed that improved healing in the form of exaggerated fibroplasia in 19 of 20 in the study group and 11 of 20 in the control group. Regeneration of the panniculous muscle layer was observed in 19 of 20 of the study group and 5 of 20 of the control group. The mean vessel index in the study group was 53.18 ± 4.74 mm(2) and in the control group 23.7 ± 6.37 mm(2) (P < 0.001; confidence interval, 25.88-33.04), whereas the mean of vessel area density was 24.76 ± 7.35 versus 8.68 ± 4.04 mm(2) (P < 0.001; confidence interval, 12.28-19.88) in the control group. Histopathologic analysis by hematoxylin-eosin stain, CD31, and factor VIII stains showed significant angiogenesis in the quantity and quality of the new blood vessels in the study group compared with the control group.

CONCLUSIONS

Sadat-Habdan mesenchymal stimulating peptide has potential of early healing of experimentally produced burns in rats. Healing was effective and better in the study group compared with the control group, in qualitative and quantitative measures.

Cross-sectional and longitudinal associations between circulating leptin and knee cartilage thickness in older adults

Objective

To investigate cross-sectional and longitudinal associations between serum leptin levels and knee cartilage thickness in older adults.

Methods

A prospective cohort of 163 randomly selected subjects (mean 63 years, range 52–78, 46% women) was studied. Knee cartilage thickness at medial tibial, lateral tibial, femoral and patellar sites was determined using T1-weighted fat-suppressed MRI. Serum leptin levels were measured by radioimmunoassay. Radiographic osteoarthritis, body fat (%), trunk fat (%), weight and height were measured, and body mass index (BMI) was calculated.

Results

Cross-sectionally, serum levels of leptin were negatively associated with femoral (β: −0.013, 95% CI −0.022 to −0.003), medial tibial (β: −0.009, 95% CI −0.018 to −0.001), lateral tibial (β: −0.012, 95% CI −0.021 to −0.003) and patellar (β: −0.014, 95% CI −0.026 to −0.002) cartilage thickness after adjustment for covariates. Moreover, BMI, trunk fat and total body fat were negatively associated with cartilage thickness, and the significant associations disappeared after further adjustment for leptin. Longitudinally, both baseline leptin and change in leptin were associated with greater changes in medial tibial cartilage thickness (β: −0.004, 95% CI −0.007 to −0.001 and β: −0.009, 95% CI −0.018 to −0.001, respectively) in multivariable analyses.

Conclusions

Serum levels of leptin are independently and consistently associated with reduced cartilage thickness cross-sectionally and longitudinally. In addition, the associations between adiposity measures and cartilage thickness are mediated by leptin, suggesting leptin may play a key role in cartilage thinning.

IL-17 in obesity and adipogenesis

The pro-inflammatory cytokine interleukin (IL)-17 (also known as IL-17) has been associated with induction of tissue inflammation. Obese individuals exhibit many symptoms of chronic low-grade inflammation, suggesting that IL-17 may impact adipose tissue. However, the role of IL-17 in obesity is largely unexplored. Emerging studies indicate that obesity selectively promotes expansion of the Th17 T-cell lineage, exacerbating disease in murine models of autoimmunity such as EAE and colitis. Human studies support this concept, as new clinical studies suggest that IL-17 is expressed at elevated levels in obese individuals. Conversely, however, an anti-adipogenic role for IL-17 is becoming evident, and therefore the interconnections between IL-17 and fat metabolism may be quite complex. Here, we consolidate the potential implications of IL-17 in relation to obesity and describe the emerging data regarding the role of IL-17 in adipose tissue.

Leptin treatment confers clinical benefit at multiple stages of virally induced type 1 diabetes in BB rats

The adipokine, leptin, regulates blood glucose and the insulin secretory function of beta cells, while also modulating immune cell function. We hypothesized that the dual effects of leptin may prevent or suppress the autoreactive destruction of beta cells in a virally induced rodent model of type 1 diabetes. Nearly 100% of weanling BBDR rats treated with the combination of an innate immune system activator, polyinosinic:polycytidylic acid (pIC), and Kilham rat virus (KRV) become diabetic within a predictable time frame. We utilized this model to test the efficacy of leptin in preventing diabetes onset, remitting new onset disease, and preventing autoimmune recurrence in diabetic rats transplanted with syngeneic islet grafts. High doses of leptin delivered via an adenovirus vector (AdLeptin) or alzet pump prevented diabetes in>90% of rats treated with pIC+KRV. The serum hyperleptinemia generated by this treatment was associated with decreased body weight, decreased non-fasting serum insulin levels, and lack of islet insulitis in leptin-treated rats. In new onset diabetics, hyperleptinemia prevented rapid weight loss and diabetic ketoacidosis, and temporarily restored euglycemia. Leptin treatment also prolonged the survival of syngeneic islets transplanted into diabetic BBDR rats. In diverse therapeutic settings, we found leptin treatment to have significant beneficial effects in modulating virally induced diabetes. These findings merit further evaluation of leptin as a potential adjunct therapeutic agent for treatment of human type 1 diabetes.

Maternal plasma retinol binding protein 4 in acute pyelonephritis during pregnancy

OBJECTIVE

Adipokines have been implicated in metabolic regulation and the immune response thus providing a molecular mechanism for the interaction between these two systems. Retinol binding protein 4 (RBP4) is a novel adipokine that plays a role in the pathophysiology of obesity-induced insulin resistance, as well as in the modulation of inflammation. The aim of this study was to determine whether there are changes in maternal plasma concentrations of RBP4 in pregnant women with acute pyelonephritis.

STUDY DESIGN

This cross-sectional study included pregnant women in the following groups: 1) normal pregnancy (n=80); 2) pyelonephritis (n=39). Maternal plasma RBP4 concentrations were determined by enzyme-linked immunoassays. Non-parametric statistics were used for analyses.

RESULTS

1) The median maternal plasma RBP4 concentration was lower in patients with acute pyelonephritis than in those with a normal pregnancy (3709.6 ng/mL, interquartile range (IQR) 2917.7-5484.2 vs. 9167.6 ng/mL, IQR 7496.1- 10,384.1, P<0.001; 2) the median maternal plasma RBP4 concentration did not differ significantly between patients with acute pyelonephritis who had a positive blood culture and those with a negative culture (3285.3 ng/mL, IQR 2274.1-4741.1 vs. 3922.6 ng/mL, IQR 3126.8-5547.1, respectively, P=0.2); and 3) lower maternal plasma RBP4 concentrations were independently associated with pyelonephritis after adjustment for confounding factors.

CONCLUSIONS

In contrast to what has been reported in preeclampsia, acute pyelonephritis during pregnancy is associated with lower maternal plasma RBP4 concentrations than in normal pregnancy. This finding suggests that the acute maternal inflammatory process associated with pyelonephritis is fundamentally different from that of the chronic systemic inflammatory process suggested in preeclampsia, in which RBP4 concentrations were found to be elevated.

Retinol binding protein 4--a novel association with early-onset preeclampsia

OBJECTIVE

Dysregulation of maternal circulating adipokines has been implicated in several "great obstetrical syndromes" including preeclampsia (PE), small-for-gestational age (SGA) neonate and fetal death (FD). It has been suggested that adipokines provide a molecular link between metabolic derangements and inflammatory response in complicated pregnancies. Retinol binding protein 4 (RBP4), a novel adipokine, plays a role in obesity-related disorders, as well as in the regulation of the immune response. The aim of this study was to determine whether there are changes in maternal plasma concentrations of RBP4 in patients with PE and in those with an SGA neonate or FD.

STUDY DESIGN

This cross-sectional study included patients in the following groups: 1) normal pregnancy (n=134); 2) PE (n=104); 3) SGA neonate (n=28); and 4) FD (n=37). Maternal plasma RBP4 concentrations were determined by ELISA. Non-parametric statistics were used for analysis.

RESULTS

1) The median maternal plasma RBP4 concentration was higher among patients with PE than in those with a normal pregnancy (P=0.03); 2) The median maternal plasma RBP4 concentrations of patients with preterm PE (<37 weeks) was higher than that of those with term PE (P=0.017) and than that of those with a normal pregnancy (P=0.002); 3) The median maternal plasma RBP4 concentration did not differ significantly between patients with a normal pregnancy and those with an SGA neonate or with an FD; 4) Among normal pregnant women, the maternal plasma RBP4 concentrations did not correlate with pre-pregnancy body mass index, gestational age at blood sampling and neonatal birthweight.

CONCLUSIONS

1) Preeclampsia, but not pregnancy with an SGA neonate or an FD, is associated with a higher median maternal plasma concentration of RBP4 than normal pregnancy; 2) Preterm PE, and specifically early-onset PE, is associated with higher median RBP4 concentrations in maternal plasma compared to term PE. These findings suggest a role for RBP4 in the pathogenesis of preterm PE, but not in SGA and FD.

Retinol binding protein 4: an adipokine associated with intra-amniotic infection/inflammation

OBJECTIVE

Retinol binding protein 4 (RBP4), a specific carrier for retinol in the blood, is a novel adipokine that has been implicated in the pathophysiology of insulin resistance, and its gene expression has been associated with adipose tissue inflammation. Recently, proteomic profiling of amniotic fluid (AF) from women with preterm labor (PTL) revealed over-expression of RBP4 in those who delivered preterm. The aim of this study was to determine whether RBP4 is present in AF, and if its concentrations change with gestational age, in the presence of labor, and intra-amniotic infection/inflammation (IAI) in patients with spontaneous PTL.

STUDY DESIGN

This cross-sectional study included pregnant women in the following groups: (1) mid-trimester (n = 30); (2) term not in labor (n = 31); (3) term in labor (n = 30); (4) spontaneous PTL without IAI who delivered at term (n = 60); (5) PTL without IAI who delivered preterm (n = 64); and (6) PTL with IAI (n = 56). RBP4 concentrations in AF were determined by ELISA. Non-parametric statistics were used for analyses.

RESULTS

(1) RBP4 was detected in all AF samples; (2) among patients with PTL, women with IAI had a higher median AF RBP4 concentration than those without IAI who delivered preterm (1268.9 ng/ml, interquartile range (IQR) 900.3-1970.1 vs. 815.8 ng/ml, IQR 592.4-1098.1; p < 0.001) and at term (828.7 ng/ml, IQR 499.7-1119.6; p < 0.001); (3) the median AF RBP4 concentration was higher in women in the mid-trimester than in those at term not in labor (1861.1 ng/ml, IQR 1486.2-2034.3 vs. 766.1 ng/ml, IQR 608.5-1154.1; p < 0.0001; (4) the median AF RBP4 concentration did not differ significantly between patients with PTL without IAI who delivered preterm and those who delivered at term (p = 0.7); and (5) among women at term, the median AF RBP4 concentrations was not significantly different between those in labor and those not in labor (p = 0.4).

CONCLUSIONS

RBP4 is a physiologic constituent of the AF. Among patients with PTL, the median AF concentration of immunoreactive RBP4 is elevated in pregnancies complicated by IAI. These results suggest that RBP4 may participate in the host response against IAI.

The PPAR-gamma agonist, darglitazone, restores acute inflammatory responses to cerebral hypoxia-ischemia in the diabetic ob/ob mouse

Diabetes is an increased risk factor for stroke and results in increased brain damage in experimental animals and humans. The precise mechanisms are unclear, but our earlier studies in the db/db mice suggested that the cerebral inflammatory response initiating recovery was both delayed and diminished in the diabetic mice compared with the nondiabetic db/+ mice. In this study, we investigated the actions of the peroxisome proliferator-activated receptor (PPAR)-gamma agonist darglitazone in treating diabetes and promoting recovery after a hypoxic-ischemic (H/I) insult in the diabetic ob/ob mouse. Male ob/+ and ob/ob mice received darglitazone (1 mg/kg) for 7 days before induction of H/I. Darglitazone restored euglycemia and normalized elevated corticosterone, triglycerides, and very-low-density lipoprotein levels. Darglitazone dramatically reduced the infarct size in the ob/ob mice at 24 h of recovery compared with the untreated group (30+/-13% to 3.3+/-1.6%, n=6 to 8) but did not show any significant effect in the ob/+ mice. Microglial and astrocytic activation monitored by cytokine expression (interleukin-1beta and tumor necrosis factor-alpha) and in situ hybridization studies (bfl1 and glial fibrillary acidic protein) suggest a biphasic inflammatory response, with darglitazone restoring the compromised proinflammatory response(s) in the diabetic mouse at 4 h but suppressing subsequent inflammatory responses at 8 and 24 h in both control and diabetic mice.

Low circulating maternal adiponectin in patients with pyelonephritis: adiponectin at the crossroads of pregnancy and infection

OBJECTIVE

An emerging theme in modern biology is that adipose tissue can respond to metabolic stress, and to inflammatory stimuli, by regulating the secretion of a complex network of soluble mediators, termed adipokines. Adiponectin, the most prevalent circulating adipokine in human, has profound insulin-sensitizing and anti-inflammatory properties. Indeed, the notion that adiponectin plays an important role in the interactions between the metabolic and the immune systems has been strongly suggested. Thus, the aim of this study was to determine if pyelonephritis during pregnancy is associated with changes in maternal serum adiponectin concentrations.

STUDY DESIGN

This cross-sectional study included women in the following groups: 1) normal pregnant women (n=200); and 2) pregnant women with pyelonephritis (n=50). Maternal plasma adiponectin concentrations were determined by ELISA. Non-parametric statistics were used for analyses.

RESULTS

1) The median maternal plasma adiponectin concentration was lower in patients with pyelonephritis than in those with a normal pregnancy (P<0.001); 2) among pregnant women with a normal weight, patients with pyelonephritis had a lower median plasma adiponectin concentration than those with a normal pregnancy (P<0.001); 3) similarly, among overweight/obese patients, those with pyelonephritis had a lower median plasma adiponectin concentration than those with a normal pregnancy (P<0.001); and 4) the presence of pyelonephritis was independently associated with maternal plasma adiponectin concentrations after adjustment for maternal age, smoking, gestational age at sampling, and pregestational body mass index (BMI).

CONCLUSION

1) The findings that acute pyelonephritis in pregnancy is characterized by low maternal plasma concentrations of adiponectin in both lean and overweight/obese patients are novel and concur with the antiinflammatory properties of adiponectin; and 2) the results of this study support the notion that adiponectin may play a role in the intricate interface between inflammation and metabolism during pregnancy.

Extreme obesity due to impaired leptin signaling in mice does not cause knee osteoarthritis

OBJECTIVE

To test the hypothesis that obesity resulting from deletion of the leptin gene or the leptin receptor gene results in increased knee osteoarthritis (OA), systemic inflammation, and altered subchondral bone morphology.

METHODS

Leptin-deficient (ob/ob) and leptin receptor-deficient (db/db) female mice compared with wild-type mice were studied, to document knee OA via histopathology. The levels of serum proinflammatory and antiinflammatory cytokines were measured using a multiplex bead immunoassay. Cortical and trabecular subchondral bone changes were documented by microfocal computed tomography, and body composition was quantified by dual x-ray absorptiometry.

RESULTS

Adiposity was increased by approximately 10-fold in ob/ob and db/db mice compared with controls, but it was not associated with an increased incidence of knee OA. Serum cytokine levels were unchanged in ob/ob and db/db mice relative to controls, except for the level of cytokine-induced neutrophil chemoattractant (keratinocyte chemoattractant; murine analog of interleukin-8), which was elevated. Leptin impairment was associated with reduced subchondral bone thickness and increased relative trabecular bone volume in the tibial epiphysis.

CONCLUSION

Extreme obesity due to impaired leptin signaling induced alterations in subchondral bone morphology without increasing the incidence of knee OA. Systemic inflammatory cytokine levels remained largely unchanged in ob/ob and db/db mice. These findings suggest that body fat, in and of itself, may not be a risk factor for joint degeneration, because adiposity in the absence of leptin signaling is insufficient to induce systemic inflammation and knee OA in female C57BL/6J mice. These results imply a pleiotropic role of leptin in the development of OA by regulating both the skeletal and immune systems.

Dysregulation of maternal serum adiponectin in preterm labor

OBJECTIVE

Intra-amniotic and systemic infection/inflammation have been causally linked to preterm parturition and fetal injury. An emerging theme is that adipose tissue can orchestrate a metabolic response to insults, but also an inflammatory response via the production of adipocytokines, and that these two phenomenons are interrelated. Adiponectin, an insulin-sensitising, anti-inflammatory adipocytokine, circulates in multimeric complexes including low-molecular weight (LMW) trimers, medium-molecular weight (MMW) hexamers and high-molecular weight (HMW) isoforms. Each of these complexes can exert differential biological effects. The aim of this study was to determine whether spontaneous preterm labor (PTL) with intact membranes and intra-amniotic infection/inflammation (IAI) is associated with changes in maternal serum circulating adiponectin multimers.

STUDY DESIGN

This cross-sectional study included patients in the following groups: (1) normal pregnant women (n=158); (2) patients with an episode of preterm labor and intact membranes without IAI who delivered at term (n=41); (3) preterm labor without IAI who delivered preterm (n=27); and (4) preterm labor with IAI who delivered preterm (n=36). Serum adiponectin multimers (total, HMW, MMW and LMW) concentrations were determined by ELISA. Non-parametric statistics were used for analyses.

RESULTS

(1) Preterm labor leading to preterm delivery or an episode of preterm labor that does not lead to preterm delivery was associated with a lower median maternal serum concentration of total and HMW adiponectin, a lower median HMW/total adiponectin ratio and a higher median LMW/total adiponectin ratio than normal pregnancy; (2) among patients with preterm labor, those with IAI had the lowest median concentration of total and HMW adiponectin, as well as the lowest median HMW/total adiponectin ratio; (3) the changes in maternal adiponectin and adiponectin multimers remained significant after adjusting for confounding factors such as maternal age, BMI, gestational age at sampling and parity.

CONCLUSION

(1) Preterm labor is characterised by a change in the profile of adiponectin multimers concentrations and their relative isoforms. These changes were observed in patients with an episode of preterm labor not leading to preterm delivery, in patients with intra-amniotic inflammation, or in those without evidence of intra-amniotic inflammation. (2) The changes in adiponectin multimer concentrations reported in preterm labor are different from those previously reported in spontaneous labor at term, suggesting that there is a fundamental difference between preterm labor and labor at term. (3) The findings reported herein provide the first evidence for the participation of adiponectin multimer in preterm parturition. We propose that adiponectins and adipokines in general provide a mechanism to organise the metabolic demands generated by the process of preterm parturition regardless of the nature of the insult (intra-amniotic inflammation or not).

Adipocytokines are associated with radiographic joint damage in rheumatoid arthritis

OBJECTIVE

Obesity protects against radiographic joint damage in rheumatoid arthritis (RA) through poorly defined mechanisms. Adipocytokines are produced in adipose tissue and modulate inflammatory responses and radiographic joint damage in animal models. The purpose of this study was to examine the hypothesis that adipocytokines modulate inflammation and radiographic joint damage in patients with RA.

METHODS

We compared serum concentrations of leptin, resistin, adiponectin, and visfatin in 167 RA patients and 91 control subjects. The independent association between adipocytokines and body mass index (BMI), measures of inflammation (C-reactive protein [CRP], interleukin-6 [IL-6], and tumor necrosis factor alpha [TNFalpha]), and radiographic joint damage (Larsen score; n = 93 patients) was examined in RA patients by multivariable regression analysis first controlling for age, race, and sex, and then for obesity (BMI) and inflammation (TNFalpha, IL-6, and CRP).

RESULTS

Concentrations of all adipocytokines were significantly higher in RA patients than in controls; for visfatin and adiponectin, this association remained significant after adjusting for BMI, inflammation, or both. Visfatin concentrations were associated with higher Larsen scores, and this association remained significant after adjustment for age, race, sex, disease duration, BMI, and inflammation (odds ratio [OR] 2.38 [95% confidence interval (95% CI) 1.32-4.29], P = 0.004). Leptin concentrations showed a positive association with the BMI (rho = 0.58, P < 0.01) and showed a negative association with the Larsen score after adjustment for inflammation (OR 0.32 [95% CI 0.17-0.61], P < 0.001), but not after adjustment for BMI (OR 0.86 [95% CI 0.42-1.73], P = 0.67).

CONCLUSION

Concentrations of adipocytokines are increased in patients with RA and may modulate radiographic joint damage. Visfatin is associated with increased, and leptin with reduced, levels of radiographic joint damage.

Enhanced production of IL-17A during zymosan-induced peritonitis in obese mice

IL-17A is a proinflammatory cytokine critical for host defense and involved in the pathogenesis of autoimmune disorders. Obesity is associated with chronic low-grade inflammation but also with a heightened acute inflammatory response. We investigated the effect of obesity on IL-17A production using the model of ZY-induced peritonitis. Compared with lean controls, administration of ZY induced a significantly exacerbated inflammatory response in obese leptin-deficient ob/ob mice and in mice with diet-induced obesity (DIO). Levels of IL-17A in the peritoneal fluid in response to ZY were elevated significantly in ob/ob and DIO mice compared with lean animals. Reconstitution of ob/ob mice with exogenous leptin did not alter production of IL-17A significantly in response to ZY. Peritoneal cells and adipose tissue obtained from ZY-injected obese mice expressed significantly higher levels of IL-17A mRNA compared with lean mice. Approximately 2% of peritoneal Ly6G(+) neutrophils from ZY-injected obese mice expressed IL-17A protein, compared with 0.2% of cells obtained from lean mice. Neutralization of IL-17 in ob/ob mice inhibited neutrophil recruitment and production of neutrophil-attracting CXC chemokines and IL-6, without affecting macrophage infiltration or levels of IL-10 and the chemokine CCL2. In contrast, neutralization of IL-6 did not affect production of IL-17A or chemokines while reducing production of the acute-phase protein serum amyloid A significantly. These data demonstrate that neutrophil-derived IL-17A is increased in obese mice during acute inflammation and contributes to exacerbation of inflammatory responses.

Maternal plasma visfatin in preterm labor

OBJECTIVE

Visfatin, a novel adipokine with diabetogenic and immunoregulatory properties, has been implicated in the pathophysiology of insulin resistance, as well as in various acute and chronic inflammatory disorders. We have previously reported that amniotic fluid concentrations of visfatin are higher in patients with preterm labor (PTL) and intra-amniotic infection than in patients with PTL without infection. The aim of this study was to determine whether spontaneous PTL with intact membranes and intra-amniotic infection/inflammation (IAI) is associated with changes in maternal plasma circulating visfatin concentrations.

STUDY DESIGN

This cross-sectional study included patients in the following groups: (1) normal pregnant women (n = 123); (2) patients with an episode of PTL and intact membranes without IAI who delivered at term (n = 57); (3) PTL without IAI who delivered preterm (n = 47); and (4) PTL with IAI who delivered preterm (n = 57). Plasma visfatin concentrations were determined by ELISA. Non-parametric statistics were used for analysis.

RESULTS

(1) PTL with IAI leading to preterm delivery was associated with a higher median maternal plasma concentration of visfatin than normal pregnancy; (2) among patients with PTL, those with IAI had the highest median maternal concentration of visfatin; (3) the changes in maternal plasma visfatin remained significant after adjusting for maternal age, body mass index, gestational age at sampling, and birth weight.

CONCLUSION

(1) PTL with IAI is characterized by high maternal circulating visfatin concentrations; (2) these findings suggest that visfatin plays a role in the regulation of the metabolic adaptations to insults resulting in PTL in the context of IAI.

Vaccination without autoantigen protects against collagen II-induced arthritis via immune deviation and regulatory T cells

Anti-inflammation immunotherapy has been successfully applied for the treatment of autoimmune diseases. Mucosal vaccines against autoimmune disorders are beneficial by influencing the regulatory compartment of gut and systemic adaptive immune systems. A Salmonella vector expressing colonization factor Ag I (CFA/I), shown to behave as an anti-inflammatory vaccine, stimulates the production of CD4(+)CD25(+) T cells and regulatory cytokines. In this work, we queried whether Salmonella-CFA/I can protect DBA/1 mice from collagen-induced arthritis. The incidence of arthritis and cartilage loss in vaccinated DBA/1 mice was remarkably lower when compared with unprotected mice. Clinical findings were accompanied by the suppression of inflammatory cytokines TNF-alpha, IL-1beta, IL-6, and IL-27. Vaccination evoked a multi-tier response consisting of IL-4 producing Th2 cells, an increased production of TGF-beta by CD4(+) T cells, and suppression of collagen II-specific CD4(+) T cell proliferation. To assess the contribution of Salmonella-CFA/I-primed CD4(+) T cells, adoptive transfer studies with total CD4(+), CD4(+)CD25(-), or CD4(+)CD25(+) T cells were performed 15 days postchallenge. Mice receiving either subset showed reduced disease incidence and low clinical scores; however, mice receiving total CD4(+) T cells showed delayed disease onset by 10 days with reduced clinical scores, reduced IL-17 and IL-27, but enhanced IL-4, IL-10, IL-13, and TGF-beta. Inhibition of TGF-beta or IL-4 compromised protective immunity. These data show that Salmonella-CFA/I vaccination of DBA/1 mice protects against collagen-induced arthritis by stimulating TGF-beta- and IL-4-producing regulatory CD4(+) T cells.

Role and regulation of adipokines during zymosan-induced peritoneal inflammation in mice

Adipokines, cytokines mainly produced by adipocytes, are active participants in the regulation of inflammation. Administration of zymosan (ZY) was used to investigate the regulation and role of adipokines during peritonitis in mice. Injection of ZY led to a significant increase in leptin levels in both serum and peritoneal lavage fluid, whereas a differential trend in local vs. systemic levels was observed for both resistin and adiponectin. The role of leptin in ZY-induced peritonitis was investigated using leptin-deficient ob/ob mice, with and without reconstitution with exogenous leptin. Leptin deficiency was associated with delayed resolution of peritoneal inflammation induced by ZY, because ob/ob mice had a more pronounced cellular infiltrate in the peritoneum as well as higher and prolonged local and systemic levels of IL-6, TNFalpha, IL-10, and chemokine (C-X-C motif) ligand 2 compared with wild-type mice. Reconstitution with exogenous leptin exacerbated the inflammatory infiltrate and systemic IL-6 levels in ob/ob mice while inhibiting production of TNFalpha, IL-10, and chemokine (C-X-C motif) ligand 2. In contrast with the important role of leptin in regulating each aspect of ZY-induced peritonitis, adiponectin deficiency was associated only with a decreased inflammatory infiltrate, without affecting cytokine levels. These findings point to a complex role for adipokines in ZY-induced peritonitis and further emphasize the interplay between obesity and inflammation.

Burn wound angiogenesis is increased by exogenously administered recombinant leptin in rats

BACKGROUND: Leptin is a potent direct angiogenic factor that stimulates endothelial cell migration and activation in vitro and angiogenesis in vivo. In addition, leptin has been discussed to play an important role in angiogenesis, as it promotes the formation of new blood vessels. PURPOSE: The effect of exogenously administered leptin on the healing process of a full tissue burn wound model. METHODS: Sixty-three Sprague-Dawley male rats were used. Full tissue burn wound was created by electrocautery. The width of the pin was 0.3 cm; its length was 2 cm and was used at the "cut" modulation. Rats were divided into seven groups of nine animals each. Burn wounds were injected with murine recombinant leptin and the rats were sacrificed 3, 7 and 9 days after surgery. Every group had obtained three animals for the three different days of sacrifice. Three different leptin doses of 250 pg/ml, 500 pg/ml and 1000 pg/ml were used in different animal groups (A, B and C). For every one of the three leptin doses used, another animal group was evaluated by using the combined injection of leptin and antileptin (A1, B1, and C1), in order to study the inhibitory effect to the leptin factor. Nine rats were served as controls. These were injected with 0.3 ml water for injection solution and sacrificed at the same time intervals. After sacrifice of the animals, the skin was grossly determined by its appearance, colour and texture. Full thickness burn wounds were dissected for histological examination. A qualitative analysis of angiogenesis in the burn wound was conducted following a standard hematoxylin and eosin stain. The wound tissue samples from each experimental group underwent immunohistochemical evaluation of microvessel density by endothelial cell staining with mouse anti-rat CD 34 monoclonal antibody. RESULTS: The most impressive growth of new blood vessels appeared seven and nine days after treatment with the highest leptin doses. There were no significant differences in microvessel density between the seventh and the ninth postoperative day among different groups treated with leptin. All wounds from the control group, as well as those from animal groups treated with the combined injection of leptin and antileptin did not develop any new vessels. CONCLUSION: Exogenous administration of recombinant leptin increases early tissue angiogenesis in the burn wound level of an experimental animal model.

Leptin in autoimmunity: many questions, some answers

It has recently become apparent that several molecules involved in the control of metabolism also play an important function in the regulation of immune responses. Among those molecules, the adipocyte-derived cytokine leptin has been shown to significantly influence innate and adaptive immune responses both in normal and in pathological conditions. For example, levels of leptin are typically low in infection and high in autoimmunity, both systemically and at the site of inflammation. Moreover, in addition to its long-known effects on the promotion of T helper 1 immune responses and cell-mediated immunity, leptin has more recently been found capable to constrain proliferation of regulatory T cells. As such, leptin represents not only a link between metabolism and immune responses in general but also a pivotal modulator of the magnitude of selected mechanisms of peripheral immunity in relation to body fat mass. We review here the most recent advances on the role of leptin in the control of immune tolerance and critically discuss how strategies aimed at neutralizing the leptin axis could represent innovative tools for the therapy of autoimmune disorders.

Differential expression of leptin and leptin's receptor isoform (Ob-Rb) mRNA between advanced and minimally affected osteoarthritic cartilage; effect on cartilage metabolism

OBJECTIVE

To investigate leptin's effect on cartilage metabolism and the pathophysiology of osteoarthritis (OA).

METHODS

Messenger RNA (mRNA) expression and protein levels of leptin and leptin's receptor isoforms were measured by real-time reverse transcription-PCR and Western blot in osteoarthritic and normal cartilage. Osteoarthritic cartilage samples were obtained from two locations of the knee (n=11) and hip (n=6); from the main defective area (advanced OA) and from adjacent macroscopically and histological intact regions (minimal OA). Paired serum and synovial fluid (SF) leptin levels were measured. The effect of leptin was evaluated on chondrocyte proliferation, IL-1beta (interleukin-1beta), NO and metalloproteinases 9 and 13 (MMP-9, MMP-13) protein expression.

RESULTS

Leptin's and leptin's receptor (Ob-Rb) expression levels were significantly increased in advanced OA cartilage compared to minimal. Leptin was significantly increased in SF than serum samples. Also, leptin had a detrimental effect on chondrocyte proliferation and induced IL-1beta production and MMP-9 and MMP-13 protein expression. Furthermore, leptin's mRNA expression in advanced OA cartilage was significantly correlated with BMI of the patients.

CONCLUSION

The increased leptin levels in SF point toward a local effect of leptin in articular cartilage, while the observed intrajoint differences of leptin and Ob-Rb mRNA expression may be related to the grade of cartilage destruction. The observed production of IL-1beta, MMP-9 and MMP-13 by chondrocytes after leptin treatment indicates a pro-inflammatory and catabolic role of leptin on cartilage metabolism. Furthermore, the observed correlation of leptin's mRNA expression with BMI suggests that leptin may be a metabolic link between obesity and OA.

Leptin-dependent toll-like receptor expression and responsiveness in preadipocytes and adipocytes

Leptin, an adipokine mainly produced by adipocytes, has been well characterized with regard to its regulatory function on immune cells. Thus the question occurred of how adipocytes and preadipocytes interact with the immune system and whether or not this communication is regulated by leptin. With the present study we evaluated the Toll-like receptor (TLR) expression and TLR ligand-specific activation of murine preadipocytes and adipocytes in the presence [wild type (WT), 3T3L1] or absence of leptin (ob/ob) or leptin signaling (db/db). The ob/ob as well as db/db adipocytes and preadipocytes were characterized by a significant up-regulation of TLR1 to -9 expression when compared with WT cells. In WT preadipocytes the TLR responsiveness increased during maturation to adipocytes; however, stimulation of ob/ob and db/db cells resulted in a 10- to 20-fold higher interleukin-6 production. Signaling studies revealed, in addition to the increased TLR expression, alterations in the phosphoinositide 3 kinase signaling cascade in ob/ob and db/db cells as an explanation for this increased responsiveness. In conclusion, the present study indicates the expression and responsiveness of TLR1 to -9 in murine preadipocytes as well as adipocytes, both of which are strongly regulated by the adipokine leptin. In summary, these data further emphasize the role of fat tissue in the immune system.

Role of adipose tissue as an inflammatory organ in human diseases

Reviews on the inflammatory role of adipose tissue outside the field of metabolism are rare. There is increasing evidence provided by numerous basic research studies from nearly all internal medicine subspecializations that adipocytes and adipocytokines are involved in primary inflammatory processes and diseases. Therefore, it is the aim of the present review to discuss and to summarize the current knowledge on the inflammatory role of adipocytokines and special types of regional adipocytes such as retroorbital, synovial, visceral, subdermal, peritoneal, and bone marrow adipocytes in internal medicine diseases. Future clinical and therapeutic implications are discussed.

Differential distribution of adipokines between serum and synovial fluid in patients with osteoarthritis. Contribution of joint tissues to their articular production

OBJECTIVE

To analyze the distribution of leptin, adiponectin and resistin between paired serum and synovial fluid (SF) samples of patients with osteoarthritis (OA) and to determine the potential sources of these adipokines in the joint. The active free form of leptin was also examined by evaluating the level of the soluble leptin receptor (sOb-R).

METHODS

Levels of adipokines and sOb-R were measured by a sandwich enzyme-linked immunosorbent assay in serum and SF collected from OA patients. The levels of adipokines were also determined in conditioned media from cultured joint tissues (synovium, infrapatellar fat pad, meniscus, osteophyte, cartilage and bone).

RESULTS

The adipokines exhibited different patterns of distribution between the joint and the circulating compartment. Serum levels of resistin and adiponectin exceeded those in the paired SF. Conversely, leptin SF concentrations were similar or higher than those measured in serum counterparts. Leptin and adiponectin in SF may derive from each joint tissue examined, whereas resistin was not detected in conditioned media of cultured explants. Synovium and infrapatellar fat pad were the major sources of adipokines, but osteophytes released also large amounts of leptin. The sOb-R deficiency found in SF further increased the difference in the bioactive leptin levels between serum and SF. A gender-specific difference was observed with women exhibiting the highest level of free leptin in the joint.

CONCLUSION

These data demonstrated that adipokines serum levels are not predictive values for SF determination. The joint cavity is a special space where each adipokine undergoes specific regulatory pathways, strengthening the hypothesis that adipokines may have local effects in the joint and may account for the high prevalence of OA in women.

The role of leptin in innate and adaptive immune responses

Leptin is produced primarily by adipocytes and functions in a feedback loop regulating body weight. Leptin deficiency results in severe obesity and a variety of endocrine abnormalities in animals and humans. Several studies indicated that leptin plays an important role in immune responses. It exerts protective anti-inflammatory effects in models of acute inflammation and during activation of innate immune responses. In contrast, leptin stimulates T lymphocyte responses, thus having rather a proinflammatory role in experimental models of autoimmune diseases. Clinical studies have so far yielded inconsistent results, suggesting a rather complex role for leptin in immune-mediated inflammatory conditions in humans.

Adipose tissue: a regulator of inflammation

Adipose tissue is a highly active organ. In addition to storing calories as triglycerides, it also secretes a large variety of proteins, including cytokines, chemokines and hormone-like factors, such as leptin, adiponectin and resistin. Intriguingly, many, if not most, of these adipose-derived proteins have dual actions; cytokines have both immunomodulatory functions and act as systemic or auto-/paracrine regulators of metabolism, while proteins such as leptin and adiponectin are regulators of both metabolism and inflammation. The production of pro-atherogenic chemokines by adipose tissue is of particular interest since their local secretion, e.g. by perivascular adipose depots, may provide a novel mechanistic link between obesity and the associated vascular complications.

Leptin in immunology

Leptin is an adipokine which conveys information on energy availability. In humans, leptin influences energy homeostasis and regulates neuroendocrine function primarily in states of energy deficiency. As a cytokine, leptin also affects thymic homeostasis and, similar to other proinflammatory cytokines, leptin promotes Th1 cell differentiation and cytokine production. We review herein recent advances on the role of leptin in the pathophysiology of immune responses.

TLR2 modulates inflammation in zymosan-induced arthritis in mice

The interplay between the innate and acquired immune systems in chronic inflammation is not well documented. We have investigated the mechanisms of inflammation in murine zymosan-induced arthritis (ZIA) in the light of recent data on the roles of Toll-like receptor 2 (TLR2) and Dectin-1 in the activation of monocyte/macrophages by zymosan. The severity of inflammation, joint histology, lymphocyte proliferation and antibody production in response to zymosan were analyzed in mice deficient in TLR2 and complement C3, and the effects of Dectin-1 inhibition by laminarin were studied. In comparison with wild-type animals, TLR2-deficient mice showed a significant decrease in the early (day 1) and late phases (day 24) of joint inflammation. C3-deficient mice showed no differences in technetium uptake or histological scoring. TLR2-deficient mice also showed a significant decrease in lymph node cell proliferation in response to zymosan and a lower IgG antibody response to zymosan at day 25 in comparison with wild-type controls, indicating that TLR2 signalling has a role in the development of acquired immune responses to zymosan. Although laminarin, a soluble beta-glucan, was able to significantly inhibit zymosan uptake by macrophages in vitro, it had no effect on ZIA in vivo. These results show that ZIA is more prolonged than was originally described and involves both the innate and acquired immune pathways. C3 does not seem to have a major role in this model of joint inflammation.