On the onset of incipient fluidization

The onset of incipient fluidization is investigated theoretically and simulated by a computational fluid dynamics (CFD) procedure. The onset of incipient instability in a particle bed is preceded by stable gas diffusion in the interstices and is caused by a critical momentum force that may overcome the inertia of the particles. The critical momentum force is provided by the critical superficial gas velocity Uc in the form of critical mass flux of diffusion. It is found that the first movement of particles may be predicted by a critical transient Rayleigh number determined by a critical superficial velocity equals to the minimum fluidization velocity, Umf. The onset of incipient fluidization was found to occur at a critical transient Rayleigh number of 3.1, which is close to the lowest theoretical value for buoyancy convection in a porous medium bounded by free surfaces. Consequently the onset times of incipient fluidization may be predicted accurately. The finding has been found to be supported by the present CFD study, past experiments and simulations in the literature

Plasminogen binding and activation at the breast cancer cell surface: the integral role of urokinase activity

INTRODUCTION: The regulation of extracellular proteolytic activity via the plasminogen activation system is complex, involving numerous activators, inhibitors, and receptors. Previous studies on monocytic and colon cell lines suggest that plasmin pre-treatment can increase plasminogen binding, allowing the active enzyme to generate binding sites for its precursor. Other studies have shown the importance of pre-formed receptors such as annexin II heterotetramer. However, few studies have used techniques that exclusively characterise cell-surface events and these mechanisms have not been investigated at the breast cancer cell surface. METHODS: We have studied plasminogen binding to MCF-7 in which urokinase plasminogen activator receptor (uPAR) levels were upregulated by PMA (12-O-tetradecanoylphorbol-13-acetate) stimulation, allowing flexible and transient modulation of cell-surface uPA. Similar experiments were also performed using MDA-MB-231 cells, which overexpress uPAR/uPA endogenously. Using techniques that preserve cell integrity, we characterise the role of uPA as both a plasminogen receptor and activator and quantify the relative contribution of pre-formed and cryptic plasminogen receptors to plasminogen binding. RESULTS: Cell-surface plasminogen binding was significantly enhanced in the presence of elevated levels of uPA in an activity-dependent manner and was greatly attenuated in the presence of the plasmin inhibitor aprotinin. Pre-formed receptors were also found to contribute to increased plasminogen binding after PMA stimulation and to co-localise with uPA/uPAR and plasminogen. Nevertheless, a relatively modest increase in plasminogen-binding capacity coupled with an increase in uPA led to a dramatic increase in the proteolytic capacity of these cells. CONCLUSION: We show that the majority of lysine-dependent plasminogen binding to breast cancer cells is ultimately regulated by plasmin activity and is dependent on the presence of significant levels of active uPA. The existence of a proteolytic positive feedback loop in plasminogen activation has profound implications for the ability of breast cancer cells expressing high amounts of uPA to accumulate a large proteolytic capacity at the cell surface, thereby conferring invasive potential

Novel Retinoic Acid Receptor Alpha Agonists for Treatment of Kidney Disease

Development of pharmacologic agents that protect podocytes from injury is a critical strategy for the treatment of kidney glomerular diseases. Retinoic acid reduces proteinuria and glomerulosclerosis in multiple animal models of kidney diseases. However, clinical studies are limited because of significant side effects of retinoic acid. Animal studies suggest that all trans retinoic acid (ATRA) attenuates proteinuria by protecting podocytes from injury. The physiological actions of ATRA are mediated by binding to all three isoforms of the nuclear retinoic acid receptors (RARs): RARα, RARβ, and RARγ. We have previously shown that ATRA exerts its renal protective effects mainly through the agonism of RARα. Here, we designed and synthesized a novel boron-containing derivative of the RARα-specific agonist Am580. This new derivative, BD4, binds to RARα receptor specifically and is predicted to have less toxicity based on its structure. We confirmed experimentally that BD4 binds to RARα with a higher affinity and exhibits less cellular toxicity than Am580 and ATRA. BD4 induces the expression of podocyte differentiation markers (synaptopodin, nephrin, and WT-1) in cultured podocytes. Finally, we confirmed that BD4 reduces proteinuria and improves kidney injury in HIV-1 transgenic mice, a model for HIV-associated nephropathy (HIVAN). Mice treated with BD4 did not develop any obvious toxicity or side effect. Our data suggest that BD4 is a novel RARα agonist, which could be used as a potential therapy for patients with kidney disease such as HIVAN

Medicaid prescription limits and their implications for naloxone accessibility.

BACKGROUND: Expanding access to and utilization of naloxone is a vitally important harm reduction strategy for preventing opioid overdose deaths, particularly in vulnerable populations like Medicaid beneficiaries. The objective of this study was to characterize the landscape of monthly prescription fill limit policies in Medicaid programs and their potential implications for expanding naloxone use for opioid overdose harm reduction. METHODS: A cross-sectional, multi-modal online and telephonic data collection strategy was used to identify and describe the presence and characteristics of monthly prescription fill limit policies across state Medicaid programs. Contextual characteristics were described regarding each state's Medicaid enrollment, opioid prescribing rates, and overdose death rates. Data collection and analysis occurred between February and May 2020. RESULTS: Medicaid-covered naloxone fills are currently subject to monthly prescription fill limit policies in 10 state Medicaid programs, which cover 20 % of the Medicaid population nationwide. Seven of these programs are located in states ranking in the top 10 highest per-capita opioid prescribing rates in the country. However, 8 of these programs are located in states with opioid overdose death rates below the national average. CONCLUSIONS: Medicaid beneficiaries at high risk of opioid overdose living in states with monthly prescription fill limits may experience significant barriers to obtaining naloxone. Exempting naloxone from Medicaid prescription limit restrictions may help spur broader adoption of naloxone for opioid overdose mortality prevention, especially in states with high opioid prescribing rates. Achieving unfettered naloxone coverage in Medicaid is critical as opioid overdoses and Medicaid enrollment increase amid the COVID-19 pandemic