Characterization of bone and bone marrow lesions in the osteoarthritic hip

Bone marrow lesions (BMLs) are common in osteoarthritis (OA) of the hip and knee and present as cysts in computed tomography scans. BMLs in knee OA are associated with pain, cartilage loss, and attrition of subchondral bone, suggesting that they play a key role in progression of OA. However, the etiology of BMLs remains unclear. The goal of this study was to better understand the changes that occur in bone in OA, through the characterization of BMLs, bone microarchitecture, and bone stiffness. Femoral heads obtained from patients undergoing total hip arthroplasty because of end-stage OA were imaged using micro-computed tomography (µCT) to identify the cysts. The bone volume fraction (BV/TV), bone mineral density (BMD), and tissue mineral density (TMD) were evaluated for two volumes of interest: an area immediately surrounding the cysts and a cylindrical core from the primary load-bearing region of the femoral head. Further, the cylindrical core was modeled using finite element analysis in order to evaluate the stiffness of this mechanically critical region. After imaging, the heads were sectioned and stained for histological analysis. Overall, the specimens exhibited wide variation in the number of cysts and cyst volume normalized by total volume of the femoral head (CV/TV). The cysts were found primarily in the subchondral bone underlying regions of damaged cartilage. The µCT images and histological sections revealed the presence of sclerotic bone around the cysts. vi The lesions themselves contained fibrous, fatty, osseous, and cartilaginous tissues. Lesions were absent from the cylindrical cores, and no correlations were found between core stiffness and any cyst properties. The cores were also found to have a higher bone volume fraction compared to values from published studies on cadaveric samples obtained from a pool of donors not specifically limited to those with end-stage OA. The cores also exhibited a modestly different dependence of apparent modulus on volume fraction, as compared to those published data. A pilot study was next carried out on the femoral necks from four of the patients. This study consisted of using nanoindentation to measure the modulus of cortical, trabecular, and periosteal bone. These preliminary results suggested that the moduli varied substantially among patients, and that the modulus of cortical tissue was in some locations for some patients, lower than that of trabecular tissue, despite published reports to the contrary in non-OA bone. The results of this project demonstrate that cysts associated with severe OA involve extensive perturbations in local bone morphology and cellular activity, and yet comparatively minimal disruption to the primary load-bearing region of the femoral head. These findings suggest that despite the association of cysts with symptoms of OA in the knee, cysts in hip OA are not strongly associated with a global loss of function of the primary bony structure of the joint. Further study of these cysts is necessary to identify their mechanistic relationship with the progression of hip OA

KLOTHO methylation is linked to uremic toxins and chronic kidney disease

Epigenetic regulation plays a major role in uremic toxin-induced chronic kidney disease (CKD) progression. The KLOTHO protein is a key modulator of homeostasis in renal function. Uremic toxin accumulation can induce DNA methyltransferase (DNMT) protein expression, which is involved in the silencing of KLOTHO through hypermethylation. Treatment with DNMT inhibitors can induce a hypermethylated status of KLOTHO and suppress mRNA and protein expression. Epigenetic targeting of specific genes may become an effective strategy to prevent progression of uremia-related CKD

Understanding a Role for Synovium in Intra-Articular Drug Clearance: A Computational and Experimental Approach

The synovium is a membranous tissue that governs molecular transport between the intra-articular (IA) joint space and the systemic circulatory system. Drug delivery to the IA space is an attractive option to treat localized joint diseases such as osteoarthritis. However, short residence times due to rapid clearance from the joint diminishes efficacy of IA injected drugs. While many studies exist on the clearance of drugs from the IA space, these studies lack the ability to isolate and characterize trans-synovial transport.The first aim of this dissertation establishes a computational finite element (FE) model of trans-synovial transport using multiphasic mixture theory. The model simulates a bolus injection of drug into a bath representing the joint space, with unsteady drug concentrations over time as the drug clears from the bath through the tissue. Using parametric studies of the different tissue material properties, we identified key determinants of transport in the model. Effective diffusivity (Deff) of the model solute was determined to be the predominant property in governing transport, and is a property intrinsic to the solute and tissue. Hydraulic permeability and modulus of the tissue were also identified as relevant to solute transport under conditions with sufficient fluid movement through the tissue. Given the lack of knowledge of material properties of the synovium, the parametric studies were used to inform selection of material properties to be used in the model. In the second aim of this dissertation, an experimental model using devitalized porcine and human synovial explant tissue was combined with the model developed in the first aim to study the effect of molecular weight on Deff. Different molecular weight molecules, ranging from 60 Da – 70 kDa, were sampled from the upstream bath in an unsteady model of transport. The bath concentration profile was described with the using the computational model and with a single exponent curve-fit. This yielded parameters of Deff from the computational model and a time-constant from the exponential curve-fit. The two parameters correlated well with one another when sample thickness was controlled for, indicating the importance of geometry when evaluating intra-articular transport. This aim represents the first reports of solute diffusivity as dependent on molecular weight through the synovium, a key measurement towards understanding trans-synovial transport. In the final aim of this dissertation, the synovium underwent mechanical testing to determine previously unmeasured properties of the tissue relevant to transport. Synovial tissue underwent a confined compression stress-relaxation experiment to measure the modulus and hydraulic permeability of synovial tissue. Synovium modulus was found to be much softer than moduli of other joint tissues. Values of hydraulic permeability were estimated to be much lower than in any other connective tissue. The evaluation of modulus and permeability allows for refinement of the model used to estimate solute diffusivity in the previous aims. The work presented in this dissertation improves our understanding of the role molecular weight and synovium tissue properties have in governing trans-synovial transport. This work forms the basis for more complex models of transport incorporating charge, active transport, and intra-articular pressure, towards the goal of predicting factors that regulate solute clearance in healthy and pathological synovium

Ejection of Double knots from the radio core of PKS 1510--089 during the strong gamma-ray flares in 2015

PKS 1510--089 is a bright and active $\gamma$-ray source that showed strong and complex $\gamma$-ray flares in mid-2015 during which the Major Atmospheric Gamma Imaging Cherenkov telescopes detected variable very high energy (VHE; photon energies $>$100 GeV) emission. We present long-term multi-frequency radio, optical, and $\gamma$-ray light curves of PKS 1510--089 from 2013 to 2018, and results of an analysis of the jet kinematics and linear polarization using 43 GHz Very Long Baseline Array data observed between late 2015 and mid-2017. We find that a strong radio flare trails the $\gamma$-ray flares in 2015, showing an optically thick spectrum at the beginning and becoming optically thin over time. Two laterally separated knots of emission are observed to emerge from the radio core nearly simultaneously during the $\gamma$-ray flares. We detect an edge-brightened linear polarization near the core in the active jet state in 2016, similar to the quiescent jet state in 2008--2013. These observations indicate that the $\gamma$-ray flares may originate from compression of the knots by a standing shock in the core and the jet might consist of multiple complex layers showing time-dependent behavior, rather than of a simple structure of a fast jet spine and a slow jet sheath.Comment: 11 pages, 7 figures, To appear in Ap

Preparation of polylactide-co-glycolide nanoparticles incorporating celecoxib and their antitumor activity against brain tumor cells

Tae-Ho Kim1*, Young-Il Jeong2*, Shu-Guang Jin2, Jian Pei2, Tae-Young Jung1, Kyung-Sub Moon1, In-Young Kim1, Sam-Suk Kang1, Shin Jung1,21Department of Neurosurgery, 2Brain Tumor Research Laboratory, Chonnam National University Research Institute of Medical Science, Chonnam National University Hwasun Hospital and Medical School, Gwangju, Republic of Korea *These authors contributed equally to this work. Background: Celecoxib, a cyclo-oxygenase (COX)-2 inhibitor, has been reported to mediate growth inhibitory effects and to induce apoptosis in various cancer cell lines. In this study, we examined the potential effects of celecoxib on glioma cell proliferation, migration, and inhibition of COX-2 expression in vitro. Methods: Celecoxib was incorporated into poly DL-lactide-co-glycolide (PLGA) nanoparticles for antitumor drug delivery. Results: PLGA nanoparticles incorporating celecoxib had spherical shapes and their particle sizes were in the range of 50–200 nm. Drug-loading efficiency was not significantly changed according to the solvent used, except for acetone. Celecoxib was released from the PLGA nanoparticles for more than 2 days, and the higher the drug content, the longer the duration of drug release. PLGA nanoparticles incorporating celecoxib showed cytotoxicity against U87MG tumor cells similar to that of celecoxib administered alone. Furthermore, celecoxib did not affect the degree of migration of U87MG cells. PLGA nanoparticles incorporating celecoxib showed dose-dependent cytotoxicity similar to that of celecoxib alone in C6 rat glioma cells. Western blot assay of the C6 cells showed that neither celecoxib alone nor PLGA nanoparticles incorporating celecoxib affected COX-2 expression. Conclusion: PLGA nanoparticles incorporating celecoxib had antitumor activity similar to that of celecoxib alone, even though these particles did not affect the degree of migration or COX-2 expression in the tumor cells. Keywords: celecoxib, cyclo-oxygenase-2, PLGA nanoparticles, glioma, antitumor activit