14 research outputs found
Kinetic analysis of the role of plasma protein binding on brain drug uptake: effect of site specific binding and flow
No full textDrug delivery to brain is complicated by multiple factors including low blood-brain barrier (BBB) passive permeability, active BBB efflux transport, and plasma protein binding. The mechanism and quantitative contribution of plasma protein binding to brain drug uptake have been debated for >25 years. In most studies, measured brain drug uptake has exceeded that predicted by the in vitro serum free fraction (fu), leading to the hypothesis that an alteration occurs in the plasma protein as it passes through the capillary circulation producing enhanced disassociation and a marked increased in fu. Drugs bind to specific sites on plasma proteins with the primary contributors being Sudlow site I and II of albumin and the central binding site of á1-acid glycoprotein (AAG). We tested the enhanced dissociation hypothesis using drugs that bind selectively to albumin Sudlow I, albumin Sudlow II, AAG and drugs that bind to more than one site. Brain uptake (Kin) was measured in the absence and presence of plasma protein using the in situ rat brain perfusion technique. Drug fu in the arterial perfusate was measured by ultrafiltration and/or equilibrium dialysis. From the measured brain uptake, a BBB permeability-surface area (PSu) was calculated. Brain uptake Kin for each tested drug agreed with that predicted using the Kety-Crone-Renkin equation [Kin = F(1-e-fu x PSu/F)] from separate measurements of BBB PSu, fu and brain perfusion fluid flow (F). No statistically significant evidence was found for enhanced dissociation. In some experiments, drug uptake Kin was determined in the presence and absence of plasma protein at different F. For drugs with a BBB PSu/F 1.0, plasma protein binding was nonrestrictive on brain uptake so that the single-pass brain extraction exceeded fu. By decreasing F, a compound could be transitioned from restrictive to nonrestrictive. In summary, the results emphasize the importance of plasma protein binding in brain drug uptake and suggest that accurate predictions can be obtained using the modified Kety-Crone Renkin equation
Hydrous parental magmas of Early to Middle Permian gabbroic intrusions in western Inner Mongolia, North China: New constraints on deep-Earth fluid cycling in the Central Asian Orogenic Belt
No full textThe role of fluids in the formation of the Permian-aged Xigedan and Mandula gabbroic intrusions in western Inner Mongolia was significant to the evolution of the Xing'an Mongolia Orogenic Belt (XMOB), and the active northern margin of the North China Craton (NCC). Secondary Ion Mass Spectroscopy (SIMS) U-Pb zircon geochronology establishes that the Xigedan gabbroic intrusion in the northern NCC was emplaced at 266 Ma, and is therefore slightly younger than the ca 280 Ma Mandula gabbroic intrusion in the XMOB. Along with their felsic counterparts, the mafic igneous intrusions record extensive bimodal magmatism along the northern NCC and in the XMOB during the Early to Middle Permian. The Mandula gabbroic rocks have low initial Sr-87/Sr-86 ratios (0.7040-0.7043) and positive epsilon Nd(t) (+6.2 to +7.3) and epsilon Hf (t) values (+13.4 to +14.5), resembling to those of contemporaneous Mandula basalts. These features, together with the presence of amphibole and the enrichment of large ion lithophile elements (LILE, e.g., Rb, Ba, U and Sr) and depletion of Nb-Ta suggest that the parental magmas of the Mandula mafic igneous rocks were derived from a depleted mantle source metasomatized by water-rich fluids. In contrast, the Xigedan gabbroic rocks are characterised by high Sr-87/Sr-88 ratios (0.7078-0.7080) and zircon delta O-18 values (5.84-6.61 parts per thousand), but low epsilon Nd(t) (-9.3 to -10.2) and epsilon Hf(t) values (-8.76 to -8.54), indicative of a long-term enriched subcontinental lithosphere mantle source that was metasomatized by recycled, high delta O-18 crustal materials prior to partial melting. The high water contents (4.6-6.9 wt%) and arc-like geochemical signature (enrichment of fluid-mobile elements and depletion of Nb-Ta) of the parental magmas of the Xigedan gabbroic rocks further establish the existence of a mantle hydration event caused by fluid/melts released from hydrated recycled oceanic crust. Incompatible element modelling shows that 5-10% partial melting of an enriched mantle source by adding respectively 0.5% and 2% sediment melts and fluids, could have produced the parental magmas of the Xigedan gabbroic rocks. A range of geological evidence establishes an intracontinental origin for Late Paleozoic mafic igneous rocks along the northern NCC and in the XMOB, rather than a subduction-related setting. We therefore propose a deep-Earth water cycling process to account for mantle hydration and subsequent Late Paleozoic magmatism, supporting a geodynamic link between deep-Earth water cycling, and intracontinental magmatism and lithospheric extension. (C) 2017 Elsevier Ltd. All rights reserved.Natural Key Basic Research Program of China [2013CB429806]; Australian Research Council [FT140100826]; Fundamental Research Funds for the Central Universities [310827163412]; Natural Science Foundation of Guangxi Province, China [2015GXNSFCA139016]SCI(E)ARTICLE,SI184-20414
Nanometric depth resolution from multi-focal images in microscopy
No full textWe describe a method for tracking the position of small features in three dimensions from images recorded on a standard microscope with an inexpensive attachment between the microscope and the camera. The depth-measurement accuracy of this method is tested experimentally on a wide-field, inverted microscope and is shown to give approximately 8 nm depth resolution, over a specimen depth of approximately 6 mm, when using a 12-bit charge-coupled device (CCD) camera and very bright but unresolved particles. To assess low-flux limitations a theoretical model is used to derive an analytical expression for the minimum variance bound. The approximations used in the analytical treatment are tested using numerical simulations. It is concluded that approximately 14 nm depth resolution is achievable with flux levels available when tracking fluorescent sources in three dimensions in live-cell biology and that the method is suitable for three-dimensional photo-activated localization microscopy resolution. Sub-nanometre resolution could be achieved with photon-counting techniques at high flux levels
Role of site-specific binding to plasma albumin in drug availability to
No full textABSTRACT Many studies have reported greater drug uptake into brain than that predicted based upon existing models using the free fraction (f u ) of drug in arterial serum. To explain this difference, circulating plasma proteins have been suggested to interact with capillary membrane in vivo to produce a conformational change that favors net drug dissociation and elevation of f u . Albumin, the principal binding protein in plasma, has two main drug binding sites, Sudlow I and II. We tested this hypothesis using drugs that bind selectively to either site I (warfarin) or site II (ibuprofen), as well as mixed ligands that have affinity for both sites (tolbutamide and valproate). Brain uptake was determined in the presence and absence of albumin using the in situ rat brain perfusion technique. Unidirectional brain uptake transfer constants (K in ) were measured and compared with those predicted using the modified Kety-Crone-Renkin model: Ϫfu ϫ PSu/F ), where F is perfusion flow and PS u is the permeability-surface area product to free drug of brain capillaries. The results demonstrated good agreement between measured and predicted K in over a 100-fold range in perfusion fluid albumin concentration using albumin from three different species (i.e., human, bovine, and rat), as well as whole-rat serum. K in decreased in the presence of albumin in direct proportion to perfusion fluid f u with constant PS u . The results show that brain uptake of selected Sudlow site I and II ligands matches that predicted by the modified Kety-Crone-Renkin model with no evidence for enhanced dissociation
Long-term exhumation history of the Inner Mongolian Plateau constrained by apatite fission track analysis
No full textInternational audienceThe Inner Mongolian Plateau, along the southeastern flank of the wider Mongolian Plateau, is a vast undulating surface ranging in elevation between 900 and 1500 m above sea level. The peculiar topography of this area is assumed to be closely related to its complex tectono-thermal evolution since Late Paleozoic. The lithospheric structure of the Plateau includes three continental blocks: the Mandula and the Bart Obo blocks form the southern margin of the Central Asian Orogenic Belt in that area, and to the south, the Plateau includes the northern margin of the North China Craton. Apatite fission track (AFT) ages and track length distributions from 13 basement outcrops situated in the main tectonic blocks forming the Inner Mongolian Plateau were determined in order to reconstruct its denudation history. The thermal histories inferred from these data imply multi-phased, differential exhumation/burying processes from the Late Paleozoic to the Early Cretaceous. This complex thermal history is largely related to the Early/Middle Triassic closure of the Paleo-Asian Ocean, the Jurassic closure of the Mongol–Okhotsk Ocean, and the Early Cretaceous orogenic collapse of the Mongol–Okhotsk belt. Finally, since Late Cretaceous, no further major tectonic movement occurred and the Inner Mongolian Plateau has been largely peneplained
Applications of Clinically Relevant Dissolution Testing : Workshop Summary Report
No full textThis publication summarizes the proceedings of day 3 of a 3-day workshop on "Dissolution and Translational Modeling Strategies Enabling Patient-Centric Product Development." Specifically, this publication discusses the current approaches in building clinical relevance into drug product development for solid oral dosage forms, along with challenges that both industry and regulatory agencies are facing in setting clinically relevant drug product specifications (CRDPS) as presented at the workshop. The concept of clinical relevance is a multidisciplinary effort which implies an understanding of the relationship between the critical quality attributes (CQAs) and their impact on predetermined clinical outcomes. Developing this level of understanding, in many cases, requires introducing deliberate but meaningful variations into the critical material attributes (CMAs) and critical process parameters (CPPs) to establish a relationship between the resulting in vitro dissolution/release profiles and in vivo PK performance, a surrogate for clinical outcomes. Alternatively, with the intention of improving the efficiency of the drug product development process by limiting the burden of conducting in vivo studies, this understanding can be either built, or at least enhanced, through in silico efforts, such as IVIVC and physiologically based pharmacokinetic (PBPK) absorption modeling and simulation (M&S). These approaches enable dissolution testing to establish safe boundaries and reject drug product batches falling outside of the established safe range (e.g., due to inadequate in vivo performance) enabling the method to become clinically relevant. Ultimately, these efforts contribute towards patient-centric drug product development and allow regulatory flexibility throughout the lifecycle of the drug product.</p
Brain endothelial permeability, transport, and flow assessed over 10 orders of magnitude using the in situ brain perfusion technique
No full textBackground Cerebral blood flow normally places a limit on the magnitude of brain vascular permeability (P) that can be measured in vivo. At normal cerebral blood flow, this limit falls at the lower end of lipophilicity for most FDAapproved CNS drugs. In this study, we report on two methods that can be used to overcome this limitation and measure brain vascular permeability values that are up to ~1000 times higher using the in situ brain perfusion technique.
Methods Rat brain was perfused with physiological saline at increased flow rate and in the presence of various concentrations of plasma protein, serum albumin or alpha-acid glycoprotein. Plasma protein was added to the saline perfusion fluid to lower extraction into the measurable range using the Crone Renkin “diffusion-flow” equation to calculate brain PoS.
Results Cerebrovascular Po was determined for 125 solutes, of which 78 showed little or no evidence of active efflux transport. Fifty of the solutes were in the lipophilicity zone (Log Poct 1–5) of most FDA-approved CNS drugs. Care was taken to ensure the integrity of the brain vasculature during perfusion and to measure flow accurately using markers that had been verified for the flow rates. The results showed a linear relationship between Log Po and Log Poct over ~10 orders of magnitude with values for diazepam, estradiol, testosterone, and other agents that exceed prior published values by fivefold to 200-fold.
Conclusions The results show that brain vascular permeability can be measured directly in vivo for highly lipophilic solutes and the PS values obtained match reasonably with that predicted by the Crone-Renkin flow diffusion equation with care taken to validate the accuracy for the component measurements and with no need to invoke “enhanced” or “induced” dissociation
Impact of the US FDA “Biopharmaceutics Classification System” (BCS) Guidance on Global Drug Development
No full textBrain endothelial permeability, transport, and flow assessed over 10 orders of magnitude using the in situ brain perfusion technique
No full textBackground Cerebral blood flow normally places a limit on the magnitude of brain vascular permeability (P) that can be measured in vivo. At normal cerebral blood flow, this limit falls at the lower end of lipophilicity for most FDA-approved CNS drugs. In this study, we report on two methods that can be used to overcome this limitation and measure brain vascular permeability values that are up to similar to 1000 times higher using the in situ brain perfusion technique. Methods Rat brain was perfused with physiological saline at increased flow rate and in the presence of various concentrations of plasma protein, serum albumin or alpha-acid glycoprotein. Plasma protein was added to the saline perfusion fluid to lower extraction into the measurable range using the Crone Renkin "diffusion-flow" equation to calculate brain PoS. Results Cerebrovascular P-o was determined for 125 solutes, of which 78 showed little or no evidence of active efflux transport. Fifty of the solutes were in the lipophilicity zone (Log P-oct 1-5) of most FDA-approved CNS drugs. Care was taken to ensure the integrity of the brain vasculature during perfusion and to measure flow accurately using markers that had been verified for the flow rates. The results showed a linear relationship between Log P-o and Log P-oct over similar to 10 orders of magnitude with values for diazepam, estradiol, testosterone, and other agents that exceed prior published values by fivefold to 200-fold. Conclusions The results show that brain vascular permeability can be measured directly in vivo for highly lipophilic solutes and the PS values obtained match reasonably with that predicted by the Crone-Renkin flow diffusion equation with care taken to validate the accuracy for the component measurements and with no need to invoke "enhanced" or "induced" dissociation.Funding Agencies|National Institutes of Health</p
