I.R. Klein-Wieringa

The infrapatellar fat pad of patients with osteoarthritis has an inflammatory phenotype

Objectives Obesity is a risk factor for the development of osteoarthritis (OA) in hands and knees. Adipose tissue can secrete different adipokines with powerful immunomodulatory effects. The infrapatellar fat pad (IFP) is an intra-articular organ in the vicinity of the synovium and cartilage. It is hypothesised that IFP-derived soluble factors could contribute to pathological processes in the knee joint. A study was therefore undertaken to compare the release of inflammatory mediators in the IFP and subcutaneous adipose tissue (ScAT) and to characterise the adipocytes and immune cell infiltrate in these tissues. Methods Paired IFP and ScAT samples were obtained from 27 patients with primary OA. The stromal vascular cell fraction (SVF) was isolated and characterised by fluorescence activated cell sorting. Cytokine and adipokine release in fat- and adipocyte-conditioned media was measured by luminex. Results IFP secreted higher levels of inflammatory mediators such as interleukin 6 (IL-6), adipsin, adiponectin and visfatin than ScAT. This could be due to differences in the phenotype of adipocytes and/or in the composition and phenotype of the SVF cells. IFP adipocyte-conditioned media showed a trend towards more IL-6 and adipsin than ScAT. Moreover, the SVF fraction of IFP contained more cells/g tissue, a lower percentage of T cells and a higher percentage of mast cells than ScAT. In addition, T cells had a predominantly pro-inflammatory phenotype while macrophages had a mixed pro- and anti-inflammatory phenotype in the IFP. Conclusion There are profound differences in secreted inflammatory factors and immune cell composition between the IFP and ScAT. These data indicate that IFP-derived soluble mediators could contribute to pathophysiological processes in the OA knee joint.

Inflammatory Cells in Patients with Endstage Knee Osteoarthritis: A Comparison between the Synovium and the Infrapatellar Fat Pad

Objective. To get a better understanding of inflammatory pathways active in the osteoarthritic (OA) joint, we characterized and compared inflammatory cells in the synovium and the infrapatellar fat pad (IFP) of patients with knee OA. Methods. Infiltrating immune cells were characterized by flow cytometry in 76 patients with knee OA (mean age 63.3, 52% women, median body mass index 28.9) from whom synovial tissue (n = 40) and IFP (n = 68) samples were obtained. Pain was assessed by the visual analog scale (VAS; 0–100 mm). Spearman rank correlations and linear regression analyses adjusted for sex and age were performed. Results. Macrophages and T cells, followed by mast cells, were the most predominant immune cells in the synovium and IFP, and were equally abundant in these tissues. Macrophages and T cells secreted mostly proinflammatory cytokines even without additional stimulation, indicating their activated state. Accordingly, most CD4+ T cells had a memory phenotype and contained a significant population of cells expressing activation markers (CD25+, CD69+). Interestingly, the percent of CD69+ T cells was higher in synovial than IFP CD4+ T cells. Preliminary analyses indicated that the number of synovial CD4+ T cells were associated with VAS pain (β 0.51, 95% CI 0.09–1.02, p = 0.02). Conclusion. Our data suggest that the immune cell composition of the synovium and the IFP is similar, and includes activated cells that could contribute to inflammation through secretion of proinflammatory cytokines. Moreover, preliminary analyses indicate that synovial CD4+ T cells might associate with pain in patients with endstage OA of the knee.

02.40 Lack of obesity-related features in adipocytes and inflammatory cells in the infrapatellar fat pad (ifp) of oa patients

Background Obesity is associated with the development and progression of osteoarthritis (OA). The infrapatellar fat pad (IFP) could contribute to this association due to its localization in the knee joint and secretion of inflammatory mediators. However, little is known about the effects of obesity on the IFP. Therefore, the aim of this study was to investigate the presence of obesity-related features in adipocytes and infiltrating immune cells in the IFP of OA patients. Materials and methods IFP volume was determined by MRI in 79 knee OA patients. IFP and subcutaneous adipose tissue (SCAT) were obtained from 106 knee OA patients (total n=155: 68% women, mean age 65 years, mean (SD) body mass index (BMI) 29.9 kg/m2 (5.7)) undergoing joint replacement surgery. Crown-like structures (CLS) were determined using immunohistochemistry. Adipocyte size was determined by light microscopy and histology. Stromal vascular fraction (SVF) cells were characterised by flow cytometry. Results IFP volume (mean(SD) 23.6 (5.4) mm3) associated with gender and height, but not with BMI. Likewise, volume and size of IFP adipocytes (mean 271 pl, mean 1933 μm) was not correlated with BMI. Few CLS were observed in IFP and the number did not correlate with BMI. Moreover, high BMI was not associated with higher SVF immune cell numbers in IFP, nor with changes in their phenotype. No molecular differences were observed with BMI, besides an increase in TNFα expression. Extensive characterisation of IFP macrophages revealed that CD206 and CD163, usually associated with an anti-inflammatory phenotype were the most abundantly expressed surface markers on macrophages (81% and 41% respectively), while macrophages produced predominantly IL-6 and TNFα, but little IL-10. Interestingly, surface marker and cytokine expression revealed that CD163+ macrophages had an activated and pro-inflammatory phenotype. Conclusions Obesity-related differences usually observed in SCAT and visceral adipose tissue could not be detected in IFP of OA patients, a fat depot implicated in OA pathogenesis.

SAT0001 Lack of obesity-related features in adipocytes and inflammatory cells in the infrapatellar fat pad (IFP)

Background Obesity is associated with the development and progression of osteoarthritis (OA), both for weight-bearing and non-weight bearing joints. Several lines of research indicate that obesity-related systemic factors, such as adipose tissue-derived factors, could be involved in this association. The infrapatellar fat pad (IFP) is an adipose tissue depot localized in the knee joint. and could mediate obesity-associated effects. However, it is currently unknown whether and how obesity affects IFP. Objectives To investigate the presence of obesity-related features in adipocytes and infiltrating immune cells in the IFP of OA patients. Methods Knee OA patients (N=155: 68% women, mean age 65 years, mean (SD) BMI 29.9 kg/m2 (5.7)) were recruited: IFP volume was determined by MRI in 79 knee OA patients, while IFP and subcutaneous adipose tissue (SCAT) were obtained from 106 patients undergoing arthroplasty. Crown-like structures (CLS) were determined using immunohistochemistry. Adipocyte size was determined by light microscopy and histology. Stromal vascular fraction (SVF) cells were characterized by flow cytometry. Results IFP volume (mean (SD) 23.6 (5.4) mm3) was associated with height, but not with BMI or other obesity-related features such as waist circumference, fat percentage and waist to hip ratio. The volume of IFP adipocytes did not correlate with BMI, in contrast to SCAT adipocytes. Few CLS were observed in IFP and their number did not differ between individuals with high and low BMI. Moreover, high BMI was not associated with higher infiltrating immune cell numbers in IFP, nor with changes in immune cell populations. Likewise, no molecular differences were observed in FCM-secreted factors between high and low BMI, except for an increased TNFa secretion in obesity. Since obesity is usually associated with a shift towards pro-inflammatory macrophages in conventional adipose tissue, we have extensively characterized IFP macrophages. Surprisingly, CD206 and CD163, usually associated with an anti-inflammatory phenotype were the most abundantly expressed surface markers on macrophages (81% and 41% respectively). In contrast, cytokine profiles revealed a pro-inflammatory phenotype of the total macrophage population, with cells producing predominantly IL-6 and TNFα, but little IL-10. Interestingly, the CD163+ macrophages were bigger and had a more activated and pro-inflammatory phenotype than their CD163- counterparts. However, no association with BMI could be observed for different macrophage populations or their cytokines. Conclusions BMI-related features usually observed in SCAT and visceral adipose tissue could not be detected in IFP of OA patients, a fat depot implicated in OA pathogenesis. Disclosure of Interest None declared

The infrapatellar fat pad of osteoarthritic patients has an inflammatory phenotype

Background and objectives Obesity is a risk factor for the development of osteoarthritis (OA) in hands and knees. It has become apparent during the last years that adipose tissue can secrete different adipokines with powerful immunomodulatory effects. Because the infrapatellar fat pad (IFP) is an intra-articular organ in the vicinity of synovium and cartilage, the authors hypothesised that IFP-derived soluble factors could contribute to pathological processes in the knee joint. Therefore the authors have extensively compared the release of inflammatory mediators and characterised the adipocytes and immune cell infiltrate in IFP and Sc adipose tissue (ScAT). Materials and methods Paired IFP and ScAT samples were obtained from 27 primary OA patients. The stromal vascular cell fraction (SVF) was isolated and characterised by FACS. Cytokine and adipokine release in fat- and adipocyte-conditioned media was measured by luminex. Results IFP secreted higher levels of inflammatory mediators, like IL-6, adipsin, adiponectin and visfatin than ScAT. This could be due to differences in the phenotype of adipocytes or/and in composition and phenotype of the SVF cells. Indeed, a similar trend was seen for IL-6 and adipsin when adipocyte-conditioned media from IFP and ScAT were compared. Moreover, the SVF fraction of IFP contained more cells per gram tissue, a lower percentage of T cells and a higher percentage of mast cells than ScAT. In addition, IFP-derived T cells displayed a predominantly proinflammatory phenotype, while macrophages in IFP presented a mixed pro- and anti-inflammatory phenotype. Finally, tumour necrosis factor-α release by IFP was correlated with BMI, indicating BMI-related inflammatory changes in IFP. Conclusions The authors show profound differences in secreted inflammatory factors and immune cell composition between IFP and ScAT. These data indicate that IFP is qualitatively different from ScAT and IFP-derived soluble mediators could contribute to pathophysiological processes in the OA knee joint.

Adiponectin is a predictor for radiographic progression in early RA patients, independently of anti-CCP antibodies

Background and objectives Adipose tissue can secrete soluble mediators (adipokines) with potent immune regulatory functions. Some adipokines have been previously associated with radiographic damage in rheumatoid arthritis (RA) in cross-sectional studies. In the present study we investigated the capacity of adipokines to predict radiographic progression over a period of 4 years and studied their contribution relative to other known risk factors, such as anticyclic citrullinated peptide (anti-CCP) antibodies. Materials and methods Serum concentrations of leptin, visfatin, resistin, adiponectin, adipsin, tumour necrosis factor (TNF) α and interleukin (IL) -6 were determined in baseline sera of 253 RA patients from the Early Arthritis Cohort. The association between levels of these adipokines, and radiographic progression was determined using multivariable regression analysis correcting for age, gender, body mass index (BMI) and the presence of antiCCP antibodies. Results IL-6, TNFα, visfatin and adiponectin levels associated positively with radiographic progression over four years. This association was independent of BMI. However, only adiponectin and IL-6 levels remained independent predictors for progression when corrected for anti-CCP antibodies. The association of both TNFα and visfatin with radiographic damage seemed dependent on anti-CCP antibodies, which is in line with the fact that the levels of both cytokines correlated significantly with anti-CCP levels in these patients. Stratification for the presence of anti-CCP antibodies revealed that adiponectin associated with progression only in anti-CCP+ disease, whereas a trend for a positive association was apparent for IL-6 in both anti-CCP+ and anti-CCP− disease. Conclusions Our results indicate that adipokines are predictors for radiographic progression in RA, possibly through distinct underlying biological mechanisms. Within the adipokines studied, adiponectin was found to predict radiographic progression independently of anti-CCP antibodies and only in anti-CCP+ disease, which indicates it as a potential therapeutic target in RA.