Investigation of the transport of lipophilic drugs in structurally diverse lipid formulations through caco-2 cell monolayer using mathematical modeling

Introduction: To be absorbed from the gastrointestinal tract, a drug has to be sufficiently soluble, because, with some exceptions, passive diffusion of dissolved drug molecules from high to low drug concentration is the driving force of drug absorption. Different physicochemical and physiological properties determine the reasons for poor drug absorption, which are poor water solubility, low membrane permeability, carrier mediated drug efflux, drug metabolism, and pharmacological interactions. A successful strategy to improve the oral bioavailability of poorly water soluble drugs in vivo is the use of lipid containing dosage forms. Lipid formulation can reduce the inherent limitation of slow and incomplete dissolution of poorly water soluble drugs by facilitating the formation of solubilized phases containing the drug, from which absorption may occur. Only few commercially available products on this basis have been approved so far. Reasons for this small number of approved products may be the limited knowledge about formulation parameters that are responsible for good in vivo performance because of limited understanding of the underlying mechanisms. Compared to an aqueous suspension of lipophilic drug, it is generally agreed so far that improved drug absorption takes place because the drug is solubilized already in a lipid containing dosage form. There is little information in literature dealing with the effect of lipid containing dosage forms on the passive permeation. The objective of this thesis was to elucidate mechanisms by which a lipophilic drug that is contained in a lipid formulation is absorbed by the intestine. For this purpose, a theoretical model and experimental procedures were developed, using Caco-2 cell monolayer. Methods: Different formulations were tested as model formulations. Since it is known that several formulation components may work as permeation enhancers by tight junction modulation, trans-epithelial electrical resistance (TEER) was used as criteria to test monolayer integrity. As model formulations phosphatidylcholine liposomes, an emulsion with a lipid phase consisting of 67% (m/m) triglyceride (Captex 8000), 5% (m/m) mixture of mono- and diglycerides (Capmul MCM), 18% (m/m) surfactant (Cremophor EL), and 10% (m/m) ethanol, and a microemulsion with a lipid phase consisting of 35.05% (m/m) Captex 8000, 17.58% (m/m) Capmul MCM, 36.84% (m/m) Cremophor EL, and 10% (m/m) ethanol were chosen. To determine the influence of these model formulations on the permeation of lipophilic drugs, different drugs were evaluated as suitable model compounds. Propranolol, progesterone, saquinavir, and triclabendazole were finally selected. An equilibrium dialysis method to determine the free fraction of the drugs in the different formulations was developed. The influence of liposomes, microemulsion, and emulsion on transport processes of the model drugs through Caco-2 monolayer was determined with a bi-directional Caco-2 assay, using purely aqueous drug solutions as reference. At least three different lipid concentrations for each formulation in the range of 0.1-50 mg/ml were tested. Within each lipid concentration at least three different drug concentrations were tested per drug. Apparent passive permeability coefficient of the apical (Pa) and of the basal membrane (Pb), formulation-to-cell partition coefficient, and carrier mediated apical efflux rate were deduced by fitting a mathematical model to the experimental concentration data of the bi-directional assay using Easy Fit® fitting software. Further, a biophysical model was developed to delineate the contribution of drug transport in the diffusion boundary layer and drug permeation through cell membrane to the determined apparent permeability coefficient. Additionally, a differentiation was introduced between permeation of free drug through the cell membrane and permeation following direct drug transfer from the lipid particles to the membrane upon collision. Drug uptake and passive drug efflux for selected drugs and formulations were further studied in the Caco-2 cell monolayer. Results and Discussion: Both, the model for the determination of absorption parameters in Caco-2 cells and the biophysical model for delineating the components of apparent permeability coefficient explained the experimental data satisfactorily. Generally Pa, Pb, and free fraction decreased with increasing lipid concentration. Within the same lipid concentration, no influence of drug concentration on Pa, Pb, and free fraction was determined. Triclabendazole showed lower Pb than Pa whereas permeability coefficients of all other drugs were equal for both membranes. Carrier mediated apical drug efflux was found for saquinavir only and its rate, when expressed as zero order, decreased with increasing lipid concentration and increased with increasing drug concentration. Formulation-to-cell partition coefficient increased with increasing lipid concentration for all drugs and formulations. Deduced permeability coefficients of diffusion boundary layer, reflecting drug transport in the apical and basal solution, was smaller than overall permeability coefficient of cell membrane for all drugs except saquinavir for which values were comparable. This indicates that the compounds are good permeable for cell membrane. Permeability coefficient of the drug corresponding to direct mass transfer from lipid particle to cell membrane (Pm,L) was for progesterone greater than the permeability coefficient corresponding to permeation of free drug through cell membrane (Pm,d). For triclabendazole Pm,L was smaller than Pm,d. For saquinavir Pm,L was comparable or smaller than Pm,d. Finally for propranolol Pm,L was smaller than Pm,d for liposome formulation. For propranolol emulsion and microemulsion, no interaction of formulation and drug was observed, therefore no meaningful values were obtained for Pm,L. The rate limiting step of transport and the dominating mechanism of membrane permeation depend on the corresponding permeability coefficients and the free and lipid bound drug concentration. These observations apply to all three structurally different lipid formulations used in this study. Permeability coefficients of drug uptake of progesterone formulations and passive drug efflux of progesterone and triclabendazole formulations in the Caco-2 monolayer decreased with increasing lipid concentration, which was consistent with the permeation experiments. Drug fluxes increased with increasing drug concentration within the same lipid concentration and decreased with increasing lipid concentration within the same drug concentration. Fluxes of progesterone in experiments with equal free drug concentration increased with simultaneously increasing drug and lipid concentration. This was demonstrated with progesterone liposomes and can be related to the larger Pm,L compared to Pm,d found for this drug. Conclusions: Lipid formulations containing the drug in a molecular form provide the possibility to increase the concentration of poorly water soluble drugs in a macroscopically aqueous system. Apparent drug permeability coefficient for the cell membrane is decreased by these formulations. Apparent drug permeability coefficient depends on free fraction, whereas drug flux depends on absolute amount of free drug in water phase. Therefore simultaneous increase of drug and lipid concentration can provide an undiminished drug flux, which may improve bioavailability by prolonged intestinal absorption at a sustained rate. These findings are independent of the composition and the structure of the lipid formulation lending support to the universal nature of this conclusion. In addition flux can be further increased by direct drug transfer from lipid particle to cellular membrane. This was observed for only one drug in the present work. The necessary drug properties for this direct transfer to take place should be investigated in the future. The results of this work shed light into the mechanism of drug absorption from lipid formulations and demonstrate potential beneficial effects of these formulations on absorption of lipophilic drugs in vivo. They may be used for the development of efficient oral dosage forms to improve bioavailability for these drugs

Advanced oxidation processes for the removal of cyanobacterial toxins from drinking water

Drinking water production faces many different challenges with one of them being naturally produced cyanobacterial toxins. Since pollutants become more abundant and persistent today, conventional water treatment is often no longer sufficient to provide adequate removal. Among other emerging technologies, advanced oxidation processes (AOPs) have a great potential to appropriately tackle this issue. This review addresses the economic and health risks posed by cyanotoxins and discusses their removal from drinking water by AOPs. The current state of knowledge on AOPs and their application for cyanotoxin degradation is synthesized to provide an overview on available techniques and effects of water quality, toxin- and technique-specific parameters on their degradation efficacy. The different AOPs are compared based on their efficiency and applicability, considering economic, practical and environmental aspects and their potential to generate toxic disinfection byproducts. For future research, more relevant studies to include the degradation of less-explored cyanotoxins, toxin mixtures in actual surface water, assessment of residual toxicity and scale-up are recommended. Since actual surface water most likely contains more than just cyanotoxins, a multi-barrier approach consisting of a series of different physical, biological and chemical-especially oxidative-treatment steps is inevitable to ensure safe and high-quality drinking water

Im Fokus: Studiengebühren verändern Hochschullandschaft

Mit dem im August 2007 von Bund und Ländern unterzeichneten Hochschulpakt 2020 verpflichten sich die Länder, dem erwarteten Anstieg der Zahl an Studienberechtigten durch eine Ausweitung der Hochschulkapazitäten Rechnung zu tragen. Aufgrund unterschiedlicher demographischer Entwicklungstrends in den Ländern, doch auch durch die mit den Doppelabiturjahrgängen verbundenen Sondereffekte ergibt sich dabei ein Bedarf der räumlichen Umverteilung von Studienanfängern. In diesem Zusammenhang ist die Attraktivität einer Hochschule von entscheidender Bedeutung. Ein wichtiges Instrument zur Beeinflussung der Studienplatzwahl stellen Studiengebühren dar. Bislang haben alle Neuen Bundesländer darauf verzichtet, Studiengebühren einzuführen – nicht zuletzt zur Steigerung der Attraktivität der ostdeutschen Hochschulen. Mit Blick auf die Einführung von Studiengebühren bzw. den Verzicht darauf durch die einzelnen Bundesländer beschreibt der vorliegende Beitrag das Wanderungsverhalten von Studienanfängern.

Die Peano-Kurve für Dünngitterhierarchisierung mit raumfüllenden Kurven

Übliche Gitteransätze zur Diskretisierung von Räumen leiden an einem exponentiellen Anstieg der Anzahl Freiheitsgrade mit der Dimensionszahl und sind deshalb nicht für höherdimensionale Probleme geeignet. Einen Ausweg bieten dünne Gitter, die deutlich weniger Freiheitsgrade benötigen. Allerdings ist die Struktur der dünnen Gitter komplexer, was praktisch zu Problemen der Cache-Ausnutzung führt: bei der Dünngittertraversierung können viele Speicherzugriffe nicht aus Cache-Speichern bedient werden. In dieser Arbeit werden raumfüllende Kurven benutzt, um eine Operation auf dünnen Gittern, die Hierarchisierung, Cache-effizient durchzuführen. Dazu wird ein Stack & Stream Verfahren vorgestellt, das als alleinige Datenstruktur Stacks verwendet und so Cache-Effizienz garantiert, ohne das spezifische Annahmen über die Cache-Struktur gemacht werden müssen

Modelling Hourly Particulate Matter (PM10) Concentrations at High Spatial Resolution in Germany Using Land Use Regression and Open Data

Air pollution is a major health risk factor worldwide. Regular short- and long-time exposures to ambient particulate matter (PM) promote various diseases and can lead to premature death. Therefore, in Germany, air quality is assessed continuously at approximately 400 measurement sites. However, knowledge about this intermediate distribution is either unknown or lacks a high spatial–temporal resolution to accurately determine exposure since commonly used chemical transport models are resource intensive. In this study, we present a method that can provide information about the ambient PM concentration for all of Germany at high spatial (100 m × 100 m) and hourly resolutions based on freely available data. To do so we adopted and optimised a method that combined land use regression modelling with a geostatistical interpolation technique using ordinary kriging. The land use regression model was set up based on CORINE (Coordination of Information on the Environment) land cover data and the Germany National Emission Inventory. To test the model’s performance under different conditions, four distinct data sets were used. (1) From a total of 8760 (365 × 24) available h, 1500 were randomly selected. From those, the hourly mean concentrations at all stations (ca. 400) were used to run the model (n = 566,326). The leave-one-out cross-validation resulted in a mean absolute error (MAE) of 7.68 μg m−3 and a root mean square error (RMSE) of 11.20 μg m−3. (2) For a more detailed analysis of how the model performs when an above-average number of high values are modelled, we selected all hourly means from February 2011 (n = 256,606). In February, measured concentrations were much higher than in any other month, leading to a slightly higher MAE of 9.77 μg m−3 and RMSE of 14.36 μg m−3, respectively. (3) To enable better comparability with other studies, the annual mean concentration (n = 413) was modelled with a MAE of 4.82 μg m−3 and a RMSE of 6.08 μg m−3. (4) To verify the model’s capability of predicting the exceedance of the daily mean limit value, daily means were modelled for all days in February (n = 10,845). The exceedances of the daily mean limit value of 50 μg m−3 were predicted correctly in 88.67% of all cases. We show that modelling ambient PM concentrations can be performed at a high spatial–temporal resolution for large areas based on open data, land use regression modelling, and kriging, with overall convincing results. This approach offers new possibilities in the fields of exposure assessment, city planning, and governance since it allows more accurate views of ambient PM concentrations at the spatial–temporal resolution required for such assessments.Peer Reviewe

Causal Analysis of an Agent-Based Model of Human Behaviour

This article investigates causal relationships leading to emergence in an agent-based model of human behaviour. A new method based on nonlinear structural causality is formulated and practically demonstrated. The method is based on the concept of acausal partitionof a model variable which quantifies the contribution of various factors to its numerical value. Causal partitions make it possible to judge the relative importance of contributing factors over crucial early periods in which the emergent behaviour of a system begins to form. They can also serve as the predictors of emergence. The time-evolution of their predictive power and its distribution among their components hint at the deeper causes of emergence and the possibilities to control it

Simplified modeling of the evolution of skills in a spatially resolved environment

We present a model for the spread, transmission and competition of skills with an emphasis on the role of spatial mobility of individuals. From a methodological point of view, we seek mathematical and computational simplicity in the sense of a minimal model. This minimalism lets us use a infinite dimensional simplex space and not a Euclidean space as underlying structure. Such a simplex captures the essentials of spatial heterogeneity without the mathematical difficulties of neighborhood structures. In the presented model, individuals may have no skill or either skill A or B. Individuals are born unskilled and may acquire skills by learning from a skilled individual. Skill A results in a small reproductive advantage and is easy to transmit (teaching happens at high rate), whereas skill B is harder to teach but results in a high benefit. The model exhibits a rich behavior; after an initial transient, the system settles to a fix point (constant distribution of skills), whereby the distribution of skills depends on a mobility parameter m. We observe different regimes, and as the main result, we conclude that for some settings of the system parameters, the spread of the (harder to learn but more beneficial) skill B is only possible within a specific range of the mobility parameter. From a technical point of view, this paper presents the application of the PRESS–method (probability reduced evolution of spatially resolved species) that enables the study of spatial effects in a very efficient manner. We analyze the consequences of spatial organization and argue that we can study aspects of social dynamics in an infinite dimensional simplex space. In spite of this maybe daunting name, the dynamics on such a structure is comparably easy to implement. The model we present is far from reflecting all the details of human interaction. On the contrary, we deliberately tailored the model to be as simple as possible from a mathematical point of view (but still reflecting central properties of spatial organization). This approach is guided by physics, where seemingly simple models which obviously don’t reflect the true physical behavior of a system (such as the Ising model) are nevertheless suited to reveal fundamental aspects and limiting cases of the real world

Teoria do Reconhecimento. A proposta hegeliana para uma ética social

Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro de Filosofia e Ciências Humanas. Programa de Pós-Graduação em FilosofiaO estudo pautado pela teoria do reconhecimento sobre a Fenomenologia do Espírito e a Filosofia do Direito de Hegel abre caminho para se estabelecer o âmbito de uma ética social a fim de ver reconciliados os âmbitos da liberdade individual e do ideal ético de comunidade. A proposta de extrair a Eticidade de um Estado social a partir da filosofia política de Hegel, passa por uma análise de cunho sociológico sobre os conceitos de Espírito e Eticidade considerados enquanto ferramentas teóricas adequadas para se abordar a questão da relação entre indivíduo e comunidade. Neste sentido, a pesquisa aborda os momentos através dos quais se estabelece a relação entre indivíduo e comunidade na Modernidade com a finalidade de evidenciar, como Hegel entende, o fato da individualidade ser considerada como indissociável da intersubjetividade.The present study follows the theory of recognition as exposed in Hegel's Phenomenology of Spirit and Philosophy of Right in order to establish a social ethics which might reconcile the scopes of individual freedom and the ethical ideal of community. The proposal to extract a kind of ethics for a Social State from Hegel's Philosophy passes through a sociological analysis of the concepts of Spirit and Ethical life, as well of the issue of the social shaping of individuality in Hegel. In this sense, the research seeks to highlight the meaning of the moments through which Hegel establishes the modern relation between individual and community in order to show how Hegel's theory contributes to the understanding of the fact that individuality is to be regarded as inseparable from intersubjectivity

The impact of guidance counselling on gender segregation: Major choice and persistence in higher education; an experimental study

Gender segregation in higher education is considered one of the main drivers of persistent economic gender inequality. Yet, though there has been considerable research identifying and describing the underlying mechanisms that cause gendered educational choices in higher education, little is known about how gender segregation in higher education could be changed. Accordingly, this article aims to determine the potential of educational interventions during high school to foster gender desegregation in higher education. We focused on two different processes that contribute to gender segregation in majors among higher education graduates: first, the selection into specific majors and, second, the selection out of specific majors. We investigated whether an intensive counselling programme leads to more gender-atypical choices among high-school graduates and examined whether intensive counselling supports several indicators of students' persistence in gender-atypical majors. Based on data from an experimental study of a counselling programme for German high-school students ( N = 625), we estimated the programme's effect with linear probability models and intention-to-treat analysis. Our results show that high-school graduates are more likely to choose a gender-atypical major if they have received intensive counselling. This applies more to men than to women. In addition, the programme improved some persistence indicators for students in gender-atypical majors. Although we found a significant programme effect only for perceived person-major fit and student satisfaction, the coefficients of all aspects of students' persistence show a trend indicating that the programme was beneficial for students in gender-atypical majors. As experimental studies can also be affected by various types of bias, we performed several robustness checks. All analyses indicated stable results. In conclusion, we suggest that intensive counselling programmes have the potential to reduce gender segregation in higher education. More students were motivated to choose a gender-atypical major, and different aspects of student persistence were supported by the programme for students in gender-atypical majors