Unraveling the Mechanisms of Hypertrophy-Induced Matrix Mineralization and Modifications in Articular Chondrocytes.

Chondrocyte hypertrophic differentiation is a main event leading to articular cartilage degradation in osteoarthritis. It is associated with matrix remodeling and mineralization, the dynamics of which is not well characterized during chondrocyte hypertrophic differentiation in articular cartilage. Based on an in vitro model of progressive differentiation of immature murine articular chondrocytes (iMACs) into prehypertrophic (Prehyp) and hypertrophic (Hyp) chondrocytes, we performed kinetics of chondrocyte differentiation from Prehyp to Hyp to follow matrix mineralization and remodeling by immunofluorescence, biochemical, molecular, and physicochemical approaches, including atomic force microscopy, scanning electron microscopy associated with energy-dispersive X-ray spectroscopy (SEM-EDS), attenuated total reflection infrared analyses, and X-ray diffraction. Chondrocyte apoptosis was determined by TUNEL assay. The results show the formation of a mineral phase 7 days after Hyp induction, which spreads within the matrices to form poorly crystalline carbonate-substituted hydroxyapatite after 14 days, then the proportions of crystalline relative to amorphous content increases over time. Hyp differentiation also induced a matrix turnover that occurs over the first 7 days, characterized by a decrease in type II collagen and aggrecan and the concomitant appearance of type X collagen. This is accompanied by an increase in the enzymatic activity of MMP-13, the main collagenase in cartilage. The number of apoptotic chondrocytes slightly increased with Hyp differentiation and SEM-EDS analyses detected phosphorus-rich structures that could correspond to apoptotic bodies. Our findings highlight the mechanisms of matrix remodeling events leading to the mineralization of articular cartilage that may occur in osteoarthritis.

Impact of Collagen Crosslinking on Dislocated Human Shoulder Capsules-Effect on Structural and Mechanical Properties.

Classical treatments of shoulder instability are associated with recurrence. To determine whether the modification of the capsule properties may be an alternative procedure, the effect of crosslinking treatment on the structure and mechanical properties of diseased human shoulder capsules was investigated. Joint capsules harvested from patients during shoulder surgery (n = 5) were treated or not with UV and/or riboflavin (0.1%, 1.0% and 2.5%). The structure and the mechanical properties of the capsules were determined by atomic force microscopy. The effect of treatments on cell death was investigated. Collagen fibrils were well-aligned and adjacent to each other with a D-periodicity of 66.9 ± 3.2 nm and a diameter of 71.8 ± 15.4 nm in control untreated capsules. No effect of treatments was observed on the organization of the collagen fibrils nor on their intrinsic characteristics, including D-periodicity or their mean diameter. The treatments also did not induce cell death. In contrast, UV + 2.5% riboflavin induced capsule stiffness, as revealed by the increased Young's modulus values (p < 0.0001 for each patient). Our results showed that the crosslinking procedure changed the biomechanics of diseased capsules, while keeping their structural organisation unchanged at the single fibril level. The UV/riboflavin crosslinking procedure may be a promising way to preserve the functions of collagen-based tissues and tune their elasticity for clinically relevant treatments.

Gremlin-1 and BMP-4 Overexpressed in Osteoarthritis Drive an Osteochondral-Remodeling Program in Osteoblasts and Hypertrophic Chondrocytes.

Osteoarthritis (OA) is a whole joint disease characterized by an important remodeling of the osteochondral junction. It includes cartilage mineralization due to chondrocyte hypertrophic differentiation and bone sclerosis. Here, we investigated whether gremlin-1 (Grem-1) and its BMP partners could be involved in the remodeling events of the osteochondral junction in OA. We found that Grem-1, BMP-2, and BMP-4 immunostaining was detected in chondrocytes from the deep layer of cartilage and in subchondral bone of knee OA patients, and was positively correlated with cartilage damage. ELISA assays showed that bone released more Grem-1 and BMP-4 than cartilage, which released more BMP-2. In vitro experiments evidenced that compression stimulated the expression and the release of Grem-1 and BMP-4 by osteoblasts. Grem-1 was also overexpressed during the prehypertrophic to hypertrophic differentiation of murine articular chondrocytes. Recombinant Grem-1 stimulated Mmp-3 and Mmp-13 expression in murine chondrocytes and osteoblasts, whereas recombinant BMP-4 stimulated the expression of genes associated with angiogenesis (Angptl4 and osteoclastogenesis (Rankl and Ccl2). In conclusion, Grem-1 and BMP-4, whose expression at the osteochondral junction increased with OA progression, may favor the pathological remodeling of the osteochondral junction by inducing a catabolic and tissue remodeling program in hypertrophic chondrocytes and osteoblasts.

Role of adipose tissues in osteoarthritis.

PURPOSE OF REVIEW: Epidemiologic studies reveal that the link between obesity and osteoarthritis cannot be uniquely explained by overweight-associated mechanical overload. For this reason, much attention focuses on the endocrine activity of adipose tissues. In addition to the systemic role of visceral and subcutaneous adipose tissues, many arguments highlight the involvement of local adipose tissues in osteoarthritis. RECENT FINDINGS: Alteration in MRI signal intensity of the infrapatellar fat pad may predict both accelerated knee osteoarthritis and joint replacement. In this context, recent studies show that mesenchymal stromal cells could play a pivotal role in the pathological remodelling of intra-articular adipose tissues (IAATs) in osteoarthritis. In parallel, recent findings underline bone marrow adipose tissue as a major player in the control of the bone microenvironment, suggesting its possible role in osteoarthritis. SUMMARY: The recent description of adipose tissues of various phenotypes within an osteoarthritic joint allows us to evoke their direct involvement in the initiation and progression of the osteoarthritic process. We can expect in the near future the discovery of novel molecules targeting these tissues.

The nuclear factor-erythroid 2-related factor/heme oxygenase-1 axis is critical for the inflammatory features of type 2 diabetes-associated osteoarthritis.

Epidemiological findings support the hypothesis that type 2 diabetes mellitus (T2DM) is a risk factor for osteoarthritis (OA). Moreover, OA cartilage from patients with T2DM exhibits a greater response to inflammatory stress, but the molecular mechanism is unclear. To investigate whether the antioxidant defense system participates in this response, we examined here the expression of nuclear factor-erythroid 2-related factor (Nrf-2), a master antioxidant transcription factor, and of heme oxygenase-1 (HO-1), one of its main target genes, in OA cartilage from T2DM and non-T2DM patients as well as in murine chondrocytes exposed to high glucose (HG). Ex vivo experiments indicated that Nrf-2 and HO-1 expression is reduced in T2DM versus non-T2DM OA cartilage (0.57-fold Nrf-2 and 0.34-fold HO-1), and prostaglandin E2 (PGE2) release was increased in samples with low HO-1 expression. HG-exposed, IL-1ß-stimulated chondrocytes had lower Nrf-2 levels in vitro, particularly in the nuclear fraction, than chondrocytes exposed to normal glucose (NG). Accordingly, HO-1 levels were also decreased (0.49-fold) in these cells. The HO-1 inducer cobalt protoporphyrin IX more efficiently attenuated PGE2 and IL-6 release in HG+IL-1ß-treated cells than in NG+IL-1ß-treated cells. Greater reductions in HO-1 expression and increase in PGE2/IL-6 production were observed in HG+IL-1ß-stimulated chondrocytes from Nrf-2-/- mice than in chondrocytes from wild-type mice. We conclude that the Nrf-2/HO-1 axis is a critical pathway in the hyperglucidic-mediated dysregulation of chondrocytes. Impairments in this antioxidant system may explain the greater inflammatory responsiveness of OA cartilage from T2DM patients and may inform treatments of such patients.

Knee and hip intra-articular adipose tissues (IAATs) compared with autologous subcutaneous adipose tissue: a specific phenotype for a central player in osteoarthritis.

OBJECTIVES: Compared with subcutaneous adipose tissue (SCAT), infrapatellar fat pad (IFP), the main knee intra-articular adipose tissue (IAAT), has an inflammatory phenotype in patients with osteoarthritis (OA). We phenotyped suprapatellar fat pad (SPFP) and hip acetabular fat pad (AFP), two other IAATs, to determinate the unique signature of IAATs compared with SCAT. METHODS: IFP, SPFP, AFP and autologous SCAT were obtained from patients with OA during total knee (n=38) or hip replacement (n=5). Fibrosis and adipocyte area were analysed by histology and vascularisation, leucocyte and mast cell infiltration were analysed by immunohistochemistry for von Willebrand factor, leucocytes and tryptase, respectively. Secretion of interleukin (IL)-6, IL-8 and prostaglandin E2 (PGE2) was assessed by ELISA. The mRNA expression of adipocyte-associated genes (ATGL, LPL, PPAR-γ, FABP4 and CD36) and developmental genes (SFRP2, HoxC9 and EN1) was determined. The inflammatory response of isolated fibroblast-like synoviocytes (FLS) to autologous IFP and SPFP conditioned media was examined. RESULTS: Fibrosis, vascularisation and leucocyte and mast cell infiltration were greater in IAATs than SCAT, and levels of IL-6, IL-8 and PGE2 were greater in all IAATs than SCAT. IFP and SPFP induced a similar inflammatory response to FLS. Adipocyte area was smaller in IAATs than SCAT. Adipocyte-associated and developmental genes showed a similar gene expression pattern in all IAATs, different from SCAT. CONCLUSIONS: IFP but also SPFP and AFP (gathered under the term 'IAAT') may play a deleterious role in OA by affecting joint homeostasis because of their inflammatory phenotype and their close interaction with synovium in the same functional unit.

Identification of soluble 14-3-3∊ as a novel subchondral bone mediator involved in cartilage degradation in osteoarthritis.

OBJECTIVE: Mechanical stress plays an important role in cartilage degradation and subchondral bone remodeling in osteoarthritis (OA). The remodeling of the subchondral bone could initiate cartilage loss in OA through the interplay of bone and cartilage. The aim of this study was to identify soluble mediators released by loaded osteoblasts/osteocytes that could induce the release of catabolic factors by chondrocytes. METHODS: Murine osteoblasts/osteocytes were subjected to cyclic compression, and then conditioned medium from either compressed (CCM) or uncompressed (UCM) cells was used to stimulate mouse chondrocytes. Chondrocyte expression of matrix metalloproteinase 3 (MMP-3), MMP-13, type II collagen, and aggrecan was assessed by reverse transcription-polymerase chain reaction, Western blotting, and enzyme-linked immunosorbent assay. Soluble mediators released by compressed osteoblasts/osteocytes were identified using iTRAQ (isobaric tags for relative and absolute quantification), a differential secretome analysis. Subchondral bone and cartilage samples were isolated from OA patients, and culture medium conditioned with OA subchondral bone or cartilage was used to stimulate human chondrocytes. RESULTS: Stimulation of mouse chondrocytes with CCM strongly induced the messenger RNA (mRNA) expression and protein release of MMP-3 and MMP-13 and inhibited the mRNA expression of type II collagen and aggrecan. Differential secretome analysis revealed that 10 proteins were up-regulated in compressed osteoblasts/osteocytes. Among them, soluble 14-3-3∊ (s14-3-3∊) dose-dependently induced the release of catabolic factors by chondrocytes, mimicking the effects of cell compression. Addition of a 14-3-3∊ blocking antibody greatly attenuated the CCM-mediated induction of MMP-3 and MMP-13 expression. Furthermore, in human OA subchondral bone, s14-3-3∊ was strongly released, and in cultures of human OA chondrocytes, s14-3-3∊ stimulated MMP-3 expression. CONCLUSION: The results of this study identify s14-3-3∊ as a novel soluble mediator critical in the communication between subchondral bone and cartilage in OA. Thus, s14-3-3∊ may be a potential target for future therapeutic or prognostic applications in OA.

Role of joint adipose tissues in osteoarthritis.

Osteoarthritis (OA) is the most common musculoskeletal disease, without any curative treatment. Obesity being the main modifiable risk factor for OA, much attention focused on the role of adipose tissues (AT). In addition to the involvement of visceral and subcutaneous AT via systemic ways, many arguments also highlight the involvement of local AT, present in joint tissues. Local AT include intra-articular AT (IAAT), which border the synovium, and bone marrow AT (BMAT) localized within marrow cavities in the bones. This review describes the known features and involvement of IAAT and BMAT in joint homeostasis and OA. Recent findings evidence that alteration in magnetic resonance imaging signal intensity of infrapatellar fat pad can be predictive of the development and progression of knee OA. IAAT and synovium are partners of the same functional unit; IAAT playing an early and pivotal role in synovial inflammation and fibrosis and OA pain. BMAT, whose functions have only recently begun to be studied, is in close functional interaction with its microenvironment. The volume and molecular profile of BMAT change according to the pathophysiological context, enabling fine regulation of haematopoiesis and bone metabolism. Although its role in OA has not yet been studied, the localization of BMAT, its functions and the importance of the bone remodelling processes that occur in OA argue in favour of a role for BMAT in OA.

Osteoarthritis, inflammation and obesity.

PURPOSE OF REVIEW: Obesity is one of the main risk factors of the incidence and prevalence of knee osteoarthritis. Recent epidemiological data showing an increased risk of hand osteoarthritis in obese patients opened the door to a role of systemic inflammatory mediators, adipokines, released by adipose tissue. RECENT FINDINGS: Recent experimental studies confirm the critical roles of adipokines in the pathophysiologic features of osteoarthritis, with an emphasis on a new member, chemerin. Animal models of diet-induced obesity show that overload cannot completely explain the aggravation of spontaneous or posttraumatic knee osteoarthritis. We now have data suggesting that some adipokines may be surrogate biomarkers for severity of osteoarthritis. SUMMARY: Preclinical studies targeting adipokines are now expected to provide new hope for patients with osteoarthritis, especially those with metabolic syndrome.

Homeostatic mechanisms in articular cartilage and role of inflammation in osteoarthritis.

Osteoarthritis (OA) is a whole joint disease, in which thinning and disappearance of cartilage is a critical determinant in OA progression. The rupture of cartilage homeostasis whatever its cause (aging, genetic predisposition, trauma or metabolic disorder) induces profound phenotypic modifications of chondrocytes, which then promote the synthesis of a subset of factors that induce cartilage damage and target other joint tissues. Interestingly, among these factors are numerous components of the inflammatory pathways. Chondrocytes produce cytokines, chemokines, alarmins, prostanoids, and adipokines and express numerous cell surface receptors for cytokines and chemokines, as well as Toll-like receptors. These receptors activate intracellular signaling pathways involved in inflammatory and stress responses of chondrocytes in OA joints. This review focuses on mechanisms responsible for the maintenance of cartilage homeostasis and highlights the role of inflammatory processes in OA progression.

Stress-induced cartilage degradation does not depend on the NLRP3 inflammasome in human osteoarthritis and mouse models.

OBJECTIVE: The main feature of osteoarthritis (OA) is degradation and loss of articular cartilage. Interleukin-1ß (IL-1ß) is thought to have a prominent role in shifting the metabolic balance toward degradation. IL-1ß is first synthesized as an inactive precursor that is cleaved to the secreted active form mainly in the "inflammasome," a complex of initiators (including NLRP3), adaptor molecule ASC, and caspase 1. The aim of this study was to clarify the roles of IL-1ß and the inflammasome in cartilage breakdown. METHODS: We assessed IL-1ß release by cartilage explants from 18 patients with OA. We also evaluated the lipopolysaccharide (LPS)-, IL-1α-, and tumor necrosis factor α (TNFα)-induced activity of matrix metalloproteinase 3 (MMP-3), MMP-9, and MMP-13 in NLRP3-knockout mice and wild-type mice and the inhibition of caspase 1 with Z-YVAD-FMK and the blockade of IL-1ß with IL-1 receptor antagonist (IL-1Ra). Cartilage explants from NLRP3-knockout mice and IL-1R type I (IL-1RI)-knockout mice were subjected to excessive dynamic compression (0.5 Hz, 1 MPa) to trigger degradation, followed by assessment of load-induced glycosaminoglycan (GAG) release and MMP enzymatic activity. RESULTS: Despite the expression of NLRP3, ASC, and caspase 1, OA cartilage was not able to produce active IL-1ß. LPS, IL-1α, and TNFα dose-dependently increased MMP-3, MMP-9, and MMP-13 activity in cultured chondrocytes and in NLRP3(-/-) chondrocytes, and this effect was not changed by inhibiting caspase 1 or IL-1ß. The load-induced increase in GAG release and MMP activity was not affected by knockout of NLRP3 or IL-1RI in cartilage explants. CONCLUSION: OA cartilage may be degraded independently of any inflammasome activity, which may explain, at least in part, the lack of effect of IL-1ß inhibitors observed in previous trials.

Deciphering pathological remodelling of the human cartilage extracellular matrix in osteoarthritis at the supramolecular level.

The extracellular matrix (ECM) of articular cartilage is a three-dimensional network mainly constituted of entangled collagen fibrils and interfibrillar aggrecan aggregates. During the development of osteoarthritis (OA), the most common musculoskeletal disorder, the ECM is subjected to a combination of chemical and structural changes that play a pivotal role in the initiation and the progress of the disease. While the molecular mechanisms involved in the pathological remodelling of the ECM are considered as decisive, they remain, however, not completely elucidated. Herein, we report a relevant way for unravelling the role and nature of OA progress on human cartilage tissues, in terms of chemical composition and morphological and mechanical properties at the level of supramolecular assemblies constituting the cartilage ECM. For this purpose, we used X-ray photoelectron spectroscopy (XPS), and developed an innovative methodological approach that provides the molecular composition of the ECM. Moreover, we used atomic force microscopy (AFM) to probe the tissues at the level of individual collagen fibrils, both imaging and force spectroscopy modes being explored to this end. Taken together, these nanoscale characterization studies reveal the existence of two stages in the OA progress. At the early stage, a marked increase in the aggrecan and collagen content is observed, reflecting the homeostatic chondrocyte activity that tends to repair the cartilage ECM. At the late stage, we observe a failed attempt to stabilize and/or restore the tissue, yielding significant degradation of the supramolecular assemblies. This suggests an imbalance in the chondrocyte activity that turns in favor of catabolic events. Chemical changes are also accompanied by ECM structural changes and stiffening. Interestingly, we showed the possibility to mimic the imbalanced activities of chondrocytes by applying enzymatic digestions of healthy cartilage, through the combined action of hyaluronidase and collagenase. This yields damage strictly analogous to that observed at high OA severity. These findings bring mechanistic insights leading to a better understanding of the mechanism by which OA is initiated and progresses in the cartilage ECM. They offer guidelines for the development of curative treatments, such as targeting the homeostatic balance of chondrocyte metabolism through the control of enzymatic reactions involved in catabolic processes.

Hypertension meets osteoarthritis - revisiting the vascular aetiology hypothesis.

Osteoarthritis (OA) is a whole-joint disease characterized by subchondral bone perfusion abnormalities and neovascular invasion into the synovium and articular cartilage. In addition to local vascular disturbance, mounting evidence suggests a pivotal role for systemic vascular pathology in the aetiology of OA. This Review outlines the current understanding of the close relationship between high blood pressure (hypertension) and OA at the crossroads of epidemiology and molecular biology. As one of the most common comorbidities in patients with OA, hypertension can disrupt joint homeostasis both biophysically and biochemically. High blood pressure can increase intraosseous pressure and cause hypoxia, which in turn triggers subchondral bone and osteochondral junction remodelling. Furthermore, systemic activation of the renin-angiotensin and endothelin systems can affect the Wnt-ß-catenin signalling pathway locally to govern joint disease. The intimate relationship between hypertension and OA indicates that endothelium-targeted strategies, including re-purposed FDA-approved antihypertensive drugs, could be useful in the treatment of OA.

MR imaging of iron phagocytosis in intraluminal thrombi of abdominal aortic aneurysms in humans.

PURPOSE: To prospectively determine if superparamagnetic iron oxide (SPIO)-enhanced magnetic resonance (MR) imaging could help visualize leukocyte phagocytic activities in human abdominal aortic aneurysms (AAAs). MATERIALS AND METHODS: This study was approved by the institutional ethics committee; all patients gave informed consent. Preoperative MR imaging data, including unenhanced and SPIO-enhanced T1-, T2*-, and T2-weighted transverse images of the entire AAA, obtained 1 hour after contrast enhancement from 15 patients (mean age, 72.7 years +/- 8.2; range, 60-83 years), 10 men (mean age, 73.5 years +/- 7.9; range, 60-83 years) and five women (mean age, 71.2 years +/- 9.4; range 60-82), were retrospectively evaluated. Morphologic appearance and semiquantitative and contrast-to-noise ratio (CNR) analyses of the thrombi were performed. Thrombi were analyzed semiquantitatively at microscopy after staining with hematoxylin-eosin, CD68, and CD66b. Levels of promatrix metalloproteinase (pro-MMP)-2 and pro-MMP-9, MMP-2 and MMP-9, and their mRNA located in the thrombus were assessed by using zymography and quantitative reverse transcriptase polymerase chain reaction analysis. Nonparametric statistics of the Spearman rank correlation were calculated to evaluate correlations between the aneurysm thrombus signal level decrease after SPIO and the levels of CD68(+), CD66b(+) cells, pro-MMP-2 and pro-MMP-9, MMP-2 and MMP-9, and MMP-9 mRNA. RESULTS: The pre-SPIO CNRs in the luminal sublayer of the thrombus and the deeper thrombus were -10.20 +/- 12.69 and -5.68 +/-10.38, respectively. After SPIO, the CNRs decreased to -21.34 +/-13.07 (P < .001) and -12.44 +/- 14.56, respectively (P < .012). There was a significant linear correlation between the thrombus signal level decrease and the levels of CD68(+) and CD66b(+) cells, pro-MMP-9, and MMP-9 mRNA (P < .05). CONCLUSION: MR imaging allows in vivo demonstration of SPIO uptake at the luminal interface of the thrombus. This uptake is correlated to the abundance of leukocytes. SUPPLEMENTAL MATERIAL: http://radiology.rsna.org/lookup/suppl/doi:10.1148/radiol.09090657/-/DC1.

Thrombus versus wall biological activities in experimental aortic aneurysms.

BACKGROUND/AIM: The intraluminal thrombus (ILT) is considered to participate in abdominal aortic aneurysm (AAA) evolution. To assess whether this role proceeds via ILT influence on biological activity of the AAA wall, we studied the relationships between the levels of some relevant proteases and microparticles (MP) released by ILT versus wall in rat experimental AAAs. METHODS AND RESULTS: Two weeks after elastase perfusion, ILT and AAA wall were incubated in cell culture medium and studies were performed on conditioned media. As shown by gelatin zymography, ILT released higher amounts of MMP9 than the wall, whereas the level of MMP2 activation (active/pro) was similar. Levels of elastase and urokinase plasminogen activator, plasmin and MPs, determined, respectively, by casein zymography, substrate hydrolysis and flow cytometry, were higher in ILT than in wall. Aneurysm diameter positively correlated with wall MMP9 levels, MMP2 activation, plasmin activity and MP release. Moreover, wall and ILT levels of pro- and active forms of MMP2, elastase and plasmin were positively correlated. Wall levels of MMP2 activation and plasmin activity also correlated with ILT weight. CONCLUSION: The present data suggest that, in this experimental model, ILT may contribute to AAA evolution via its influence on the level of aneurysmal wall protease activity.

Differential inflammatory activity across human abdominal aortic aneurysms reveals neutrophil-derived leukotriene B4 as a major chemotactic factor released from the intraluminal thrombus.

Development and progression of acquired abdominal aortic aneurysms (AAAs) have been associated with different inflammatory mediators. The aim of the present study was to elucidate the topology and the potential mechanisms linking the leukotriene pathway to human AAAs. Human aneurysmal lesions were obtained from 24 patients undergoing surgery, and the intraluminal thrombus was separated from the vascular wall. Histological examination revealed major expression of the leukotriene-producing enzymes 5-lipoxygenase and LTA(4) hydrolase, as well as the two receptors for leukotriene B(4) (BLT1R and BLT2R), corresponding to neutrophils in the luminal part of the thrombus. In contrast, in the vascular wall, the leukotriene pathway mainly localized in macrophage-rich adventitial areas. Furthermore, conditioned media of the intraluminal thrombus contained significantly higher concentrations of leukotriene B(4) than that derived from the vascular wall, which were significantly correlated to other neutrophil-derived mediators, such as elastase/alpha(1)-antitrypsin complexes, myeloperoxidase, and MMP9/NGAL complexes. Finally, the neutrophil-chemotactic activity of the conditioned media from the intraluminal thrombus exhibited major inhibition by antagonists of the leukotriene B(4) receptors. Taken together, these results indicate neutrophil-derived leukotriene B(4) as a major neutrophil chemotactic factor released from the intraluminal thrombus of human AAAs and suggest that targeting BLT receptors may represent a potential medical therapeutic strategy in the prevention of AAA progression in humans.

HDL antielastase activity prevents smooth muscle cell anoikis, a potential new antiatherogenic property.

Various studies using proteomic approaches have shown that HDL can carry many proteins other than its constitutive apolipoprotein A-I (apoA-I). Using mass spectrometry and Western blotting, we showed the presence of alpha(1)-antitrypsin (AAT) (SERPINA1, serpin peptidase inhibitor, clade A, an elastase inhibitor) in HDL, isolated either by ultracentrifugation or by selected-affinity immunosorption using an anti-apoA-I column. Furthermore, we report that HDL possesses potent antielastase activity. We further showed that only HDL but not LDL is able to bind AAT. HDL-associated AAT was able to inhibit extracellular matrix degradation, cell detachment, and apoptosis induced by elastase in human vascular smooth muscle cells (VSMCs) and in mammary artery cultured ex vivo. Degradation of fibronectin by elastase used as a marker of pericellular proteolysis was prevented by addition of HDL. Elastase present in aortic abdominal aneurysm (AAA) thrombus samples was also able to induce apoptosis of VSMCs in culture. This phenomenon was prevented by addition of HDL but not of LDL. Finally, we report that the proportion of AAT in HDL isolated from patients with an AAA is decreased relative to that from matched control subjects, suggesting a reduced capacity of HDL to inhibit elastase in these patients. In conclusion, our data provide evidence of a new potential antiatherogenic property of HDL attributable to AAT and its antielastase activity.

Effect of blocking platelet activation with AZD6140 on development of abdominal aortic aneurysm in a rat aneurysmal model.

BACKGROUND: Platelet activation and thrombus renewal are keys to intraluminal thrombus formation and progression of abdominal aortic aneurysms (AAA). This study explored the ability of AZD6140, a P2Y(12) receptor antagonist, to inhibit platelet activation and prevent aneurysm development in a rat experimental model of AAA. METHOD: Aortic aneurysms were induced by implanting a segment of sodium dodecyl sulfate-decellularized guinea pig aorta in rat aortas. One day later, rats were randomized to AZD6140 (10 mg/kg twice daily by mouth) or diluent (n = 23 per group) for either 10 (n = 18) or 42 days (n = 28). Adenosine diphosphate (ADP)-mediated platelet aggregation, aneurysm expansion, intraluminal thrombus formation, inflammatory infiltration, matrix metalloproteinase-9 (MMP-9) expression, and smooth muscle cell colonization were measured. RESULTS: AZD6140 inhibited ADP-induced platelet aggregation in vivo for 12 hours, justifying twice-daily administration in rats. The spontaneous increase in aortic diameter shown in the aneurysmal model (2.22 +/- 0.56 mm at day 10 vs 5.21 +/- 1.22 mm at day 42) was reduced with AZD6140 (3.61 +/- 1.46 mm at day 42, P < .01). This beneficial effect was associated with a significant reduction of thrombus development, platelet CD41 expression (P < .05), and leukocyte infiltration of the mural thrombus at days 10 and 42 (P < .01). MMP-9 expression correlated with mural thrombus area and was significantly reduced by AZD6140 (P < .05). AZD6140 limited elastic fiber degradation (P < .05) and enhanced progressive colonization of the thrombus by smooth muscle cells at day 42 (P < .01). CONCLUSIONS: These data suggest that inhibition of platelet activation limits intraluminal thrombus biologic activities, thereby impairing aneurysm development.

High-cholesterol + vitamin D2 regimen: a questionable in-vivo experimental model of aortic valve stenosis.

BACKGROUND AND AIM OF THE STUDY: Recent data have shown that aortic valve stenosis (AS) is an active and highly regulated process which shares similarities with atherosclerosis. However, AS cannot be considered as a purely atherosclerotic phenomenon, and a hypercholesterolemic rabbit model might not be fully representative of human AS pathophysiology. METHODS: Twenty-eight New Zealand White rabbits were assigned to three groups: group 1 (no dietary supplement for three months); group 2 (0.3% cholesterol-enriched-diet + 50,000 IU/day vitamin D2 for six months); and group 3 (1% cholesterol-enriched-diet + vitamin D2 for three months). The peak aortic gradient and permeability index (outflow tract/aortic velocity-time-integral) were assessed, as well as calcium staining within the aortic valve and ascending aorta. RESULTS: AS hemodynamic severity was not different among the groups. The peak gradient was 4 +/- 2 mmHg at baseline, 4 +/- 2 mmHg at three months in controls, 4 +/- 1 mmHg at three months and 6 +/-3 mmHg at six months in group 2, and 4 +/- 1 mmHg at three months in group 3 (p = NS). The permeability index was 64 +/- 7 at baseline, 60 +/- 12 at three months in controls, 63 +/- 14 at three months and 58 +/- 12 at six months in group 2, and 60 +/- 5 at three months in group 3 (p = NS). The aortic valve of cholesterol-enriched-diet rabbits was thickened but not calcified, whereas the ascending aorta was both thickened and calcified. CONCLUSION: When using a hypercholesterolemic rabbit model plus vitamin D2, no adverse hemodynamic effect or aortic valve calcification was observed, despite a high-level and prolonged cholesterol-regimen supplementation. These results raise questions with regard to the extrapolation of this animal model to humans.

Contribution of adipocyte precursors in the phenotypic specificity of intra-articular adipose tissues in knee osteoarthritis patients.

BACKGROUND: Intra-articular adipose tissues (IAATs) are involved in osteoarthritis (OA) pathophysiology. We hypothesize that mesenchymal cells residing in IAATs may account for the specific inflammatory and metabolic patterns in OA patients. METHODS: Adipocyte precursors (preadipocytes and dedifferentiated fat cells (DFATc)) from IAATs (infrapatellar and suprapatellar fat pads) and autologous subcutaneous adipose tissues (SCATs) were isolated from knee OA patients. The ability of these precursors to differentiate into adipocytes was assessed by oil red O staining after 14 days of culture in adipogenic medium. The gene expression of adipocyte-related transcription factors (C/EBP-α and PPAR-γ) and development-related factors (EN1 and SFRP2) were analyzed. The inflammatory pattern was assessed by RT-qPCR and ELISA (interleukin 6 (IL-6), IL-8, Cox2, and prostaglandin E2 (PGE2)) after a 24-h stimulation by IL-1ß (1 ng/mL) and by conditioned medium from OA synovium. RESULTS: IAAT preadipocytes displayed a significantly higher ability to differentiate into adipocytes and expressed significantly more C/EBP-α mRNA than SCAT preadipocytes. IAAT preadipocytes expressed significantly less EN-1 and SFRP2 mRNA than SCAT preadipocytes. Unstimulated IAAT preadipocytes displayed a less inflammatory pattern (IL-6, IL-8, and Cox2/PGE2) than SCAT preadipocytes. In contrast, the response of IAAT preadipocytes to an inflammatory stimulus (IL-1ß and conditioned media of OA synovium) was exacerbated compared to that of SCAT preadipocytes. Similar results were obtained with DFATc. CONCLUSION: IAAT adipocyte precursors from OA patients have a specific phenotype, which may account for the unique phenotype of OA IAATs. The exacerbated response of IAAT preadipocytes to inflammatory stimulation may contribute to OA pathophysiology.