A single dose of anti-IL-1ß antibodies prevents Western diet-induced immune activation during early stage collagenase-induced osteoarthritis, but does not ameliorate end-stage pathology.

OBJECTIVE: Metabolic dysfunction can cause IL-1ß mediated activation of the innate immune system, which could have important implications for the therapeutic efficacy of IL-1ß neutralizing drugs as treatment for OA in the context of metabolic syndrome (MetS). In the present study, we investigated whether early treatment with a single dose of IL-1ß blocking antibodies could prevent Western diet (WD) induced changes to systemic monocyte populations and their cytokine secretion profile and herewith modulate collagenase induced osteoarthritis (CiOA) pathology. METHODS: CiOA was induced in female C57Bl/6 mice fed either a standard diet (SD) or WD and treated with a single dose of either polyclonal anti-IL-1ß antibodies or control. Monocyte subsets and granulocytes in bone marrow and blood were analyzed with flow cytometry, and cytokine expression by bone marrow cells was analyzed using qPCR. Synovial cellularity, cartilage damage and osteophyte formation were assessed on histology. RESULTS: WD feeding of C57Bl/6 mice led to increased serum levels of low-density lipoprotein (LDL) and innate immune activation in the form of an increased number of Ly6Chigh cells in bone marrow and blood and increased cytokine expression of IL-6 and TNF-α by bone marrow cells. The increase in monocyte number and activity was ameliorated by anti-IL-1ß treatment. However, anti-IL-1ß treatment did not significantly affect synovial lining thickness, cartilage damage and ectopic bone formation during WD feeding. CONCLUSIONS: Single-dose systemic anti-IL-1ß treatment prevented WD-induced innate immune activation during early stage CiOA in C57Bl/6 mice, but did not ameliorate joint pathology.

Osteoarthritis year in review 2020: biology.

This year in review about osteoarthritis biology highlights a selection of articles published between the 2019 and 2020 Osteoarthritis Research Society International (OARSI) World Congress meetings, within the field of osteoarthritis biology. Highlights were selected from PubMed searches covering osteoarthritis (OA) cartilage, subchondral bone, synovium and aging. Subsequently, a personal selection was based on new and emerging themes together with common research topics that were studied by multiple groups. Themes discussed include novel insights into the inflammatory changes during OA, with a number of noteworthy publications concerning the role of macrophages in healthy and osteoarthritic joints. Next, the application of mesenchymal stem cells as OA-dampening therapy is discussed, including possible ways to improve their efficacy by pre-treatment. Other significant themes including treatment of OA with metformin, enhancing autophagy to alleviate OA and the involvement of the gastro-intestinal microbiome in development of OA symptoms and structural damage are discussed. An effort was made to connect the seemingly distant topics from which the overarching conclusion can be drawn that over the last year promising breakthroughs have been achieved in further understanding the biology of OA development and that new therapeutic possibilities have been explored.

High LDL levels lessen bone destruction during antigen-induced arthritis by inhibiting osteoclast formation and function.

Rheumatoid arthritis (RA) is a chronic inflammatory disease, characterized by severe joint inflammation and bone destruction as the result of increased numbers and activity of osteoclasts. RA is often associated with metabolic syndrome, whereby elevated levels of LDL are oxidized into oxLDL, which might affect osteoclastogenesis. In this study, we induced antigen-induced arthritis (AIA) in Apoe-/- mice, which spontaneously develop high LDL levels, to investigate the effects of high LDL/oxLDL levels on osteoclast differentiation and bone destruction. Whereas basal levels of bone resorption were comparable between naive WT and Apoe-/- mice, induction of AIA resulted in a significant reduction of bone destruction in Apoe-/- mice as compared to WT controls. In line with that, the TRAP+ area on the cortical bone was significantly decreased. The absence of Apoe did affect neither the numbers of CD11b+Ly6Chigh and CD11b-/Ly6Chigh osteoclast precursors (OCPs) in the BM of naïve mice nor their in vitro osteoclastogenic potential as indicated by comparable mRNA expression of osteoclast markers. Addition of oxLDL, but not LDL, to pre-osteoclasts from day 3 and mature osteoclasts from day 6 of osteoclastogenesis strongly reduced the number of TRAP+ osteoclasts and their resorptive capacity. This coincided with a decreased expression of various osteoclast markers. Interestingly, oxLDL significantly lowered the expression of osteoclast-associated receptor (Oscar) and the DNAX adaptor protein-12 encoding gene Tyrobp, which regulate the immunoreceptor tyrosine-based activation motif (ITAM) co-stimulation pathway that is strongly involved in osteoclastogenesis. Collectively, our findings suggest that under inflammatory conditions in the joint, high LDL levels lessen bone destruction during AIA, probably by formation of oxLDL that inhibits osteoclast formation and activity through modulation of the ITAM-signaling.

The role of NOX2-derived reactive oxygen species in collagenase-induced osteoarthritis.

OBJECTIVE: Synovitis in collagenase-induced osteoarthritis (CiOA) is driven by locally released S100A8/A9 proteins and enhances joint destruction. S100A8/A9 can induce reactive oxygen species (ROS) release by phagocytes in OA synovium via neutrophil cytosolic factor-1 (Ncf1)-regulated NOX2 activation. In the present study we investigated whether NOX2-derived ROS affect joint pathology during CiOA. METHODS: CiOA was induced in knee joints of wild type (WT) and Ncf1-deficient (Ncf1**) mice. Synovial gene expression of NOX2-subunits was measured with quantitative real-time polymerase chain reaction (qRT-PCR). Joint pathology was assessed using histology and immunohistochemistry for aggrecan neo-epitope VDIPEN. Levels of inflammatory proteins were measured with Luminex or ELISA. Phagocytes in synovium, blood, bone marrow (BM) and spleen were analyzed with flow cytometry. ROS release by phagocytes was measured with a ROS detection kit. RESULTS: CiOA induction in knee joints of WT mice caused significantly increased synovial gene expression of NOX2 subunits. On day 7 of CiOA, cartilage damage and MMP activity, as measured by VDIPEN, were comparable between WT and Ncf1** mice. Synovial thickening, synovial S100A8/A9 levels and percentages of synovial macrophages, polymorphonuclear cells (PMNs), and monocytes were not different, as were levels of inflammatory mediators in serum and phagocyte percentages in blood, BM and spleen. On day 42 of CiOA, synovitis, cartilage damage, and osteophyte formation in Ncf1** mice were unaltered when compared to WT mice. ROS detection confirmed that Ncf1** PMNs lack functional NOX2, but in vitro macrophages showed ROS production, suggesting activation of compensatory mechanisms. CONCLUSIONS: Absence of Ncf1-mediated ROS production does not alter joint pathology in CiOA.

Alarmins S100A8/S100A9 aggravate osteophyte formation in experimental osteoarthritis and predict osteophyte progression in early human symptomatic osteoarthritis.

OBJECTIVE: Alarmins S100A8 and S100A9 are major products of activated macrophages regulating cartilage damage and synovial activation during murine and human osteoarthritis (OA). In the current study, we investigated whether S100A8 and S100A9 are involved in osteophyte formation during experimental OA and whether S100A8/A9 predicts osteophyte progression in early human OA. METHODS: OA was elicited in S100A9-/- mice in two experimental models that differ in degree of synovial activation. Osteophyte size, S100A8, S100A9 and VDIPEN neoepitope was measured histologically. Chondrogenesis was induced in murine mesenchymal stem cells in the presence of S100A8. Levels of S100A8/A9 were determined in plasma of early symptomatic OA participants of the Cohort Hip and Cohort Knee (CHECK) cohort study and osteophytes measured after 2 and 5 years. RESULTS: Osteophyte size was drastically reduced in S100A9-/- mice in ligaments and at medial femur and tibia on days 21 and 42 of collagenase-induced OA, in which synovial activation is high. In contrast, osteophyte size was not reduced in S100A9-/- mice during destabilised medial meniscus OA, in which synovial activation is scant. S100A8 increased expression and activation of matrix metalloproteinases during micromass chondrogenesis, thereby possibly increasing cartilage matrix remodelling allowing for larger osteophytes. Interestingly, early symptomatic OA participants of the CHECK study with osteophyte progression after 2 and 5 years had elevated S100A8/A9 plasma levels at baseline, while C-reactive protein, erythrocyte sedimentation rate and cartilage oligomeric matrix protein were not elevated at baseline. CONCLUSIONS: S100A8/A9 aggravate osteophyte formation in experimental OA with high synovial activation and may be used to predict osteophyte progression in early symptomatic human OA.

Prophylactic treatment with S100A9 inhibitor paquinimod reduces pathology in experimental collagenase-induced osteoarthritis.

OBJECTIVES: Alarmins S100A8/A9 regulate pathology in experimental osteoarthritis (OA). Paquinimod is an immunomodulatory compound preventing S100A9 binding to TLR-4. We investigated the effect of paquinimod on experimental OA and human OA synovium. MATERIALS AND METHODS: Two OA mouse models differing in level of synovial activation were treated prophylactic with paquinimod. Synovial thickening, osteophyte size and cartilage damage were measured histologically, using an arbitrary score, adapted Pritzker OARSI score or imaging software, respectively. Human OA synovia were stimulated with S100A9, with or without paquinimod. RESULTS: Paquinimod treatment of collagenase-induced OA (CIOA) resulted in significantly reduced synovial thickening (57%), osteophyte size at the medial femur (66%) and cruciate ligaments (67%) and cartilage damage at the medial tibia (47%) and femur (75%; n=7, untreated n=6). In contrast, paquinimod did not reduce osteophyte size and reduced cartilage damage at one location only in destabilised medial meniscus, an OA model with considerably lower synovial activation compared with CIOA. In human OA synovium, paquinimod blocked proinflammatory (interleukin (IL)-6, IL-8, tumour necrosis factor-α) and catabolic (matrix metalloproteinases 1 and 3) factors induced by S100A9 (n=5). CONCLUSIONS: Prophylactic treatment of paquinimod reduces synovial activation, osteophyte formation and cartilage damage in experimental OA with high synovial activation (CIOA) and ameliorates pathological effects of S100A9 in OA synovium ex vivo.