ETUDE DES INTERACTIONS ENTRE LES CYCLODEXTRINES ET LES MEMBRANES LIPOSOMALES OU BIOLOGIQUES

Résumé : A ce jour, l’utilité des cyclodextrines comme adjuvant pharmaceutique n’est plus à démontrer. En biologie cellulaire, la méthyl-b-cyclodextrine est un outil couramment utilisé par les expérimentateurs. La déstructuration qu’elle induit au niveau des microdomaines membranaires que sont les radeaux lipidiques ou les cavéoles est mise à profit pour l’étude des fonctions cellulaires qui y sont associées.Le but de notre recherche est d’étudier les interactions de différentes cyclodextrines couramment utilisées dans le domaine pharmaceutique avec les constituants des membranes liposomales ou biologiques afin de mieux comprendre les conséquences de ces interactions au niveau cellulaire.L’hypothèse d’une interaction des cyclodextrines avec les constituants lipophiles des membranes cellulaires a souvent été énoncée pour expliquer la cytotoxicité de certains dérivés.Nous avons pu montrer à l’aide de liposomes unilamellaires utilisés comme modèles membranaires, que l’interaction des cyclodextrines avec leurs constituants, en particulier le cholestérol, est en relation avec une perte de l’intégrité de la membrane. Ces premières études nous ont permis de prédire quels seraient les dérivés qui induiraient la cytotoxicité la plus importante.La cytotoxicité importante de certains dérivés méthylés (D.S. proche de 2) a été corrélée avec une capacité d’extraction du cholestérol cellulaire relativement élevée. A l’inverse, nous avons montré que les dérivés faiblement substitués extraient peu le cholestérol, ce qui permet d’expliquer la meilleure tolérance observée au niveau biologique avec la Crysmeb et l’HP-b-CD.Nous nous sommes ensuite intéressés à l’effet de la b-CD et de ses dérivés méthylés sur la déstructuration des microdomaines membranaires. Nous avons étudié la relation entre leur capacité de déstructuration des cavéoles et d’extraction du cholestérol cellulaire. Une extraction relativement élevée du lipide induit un effet important au niveau des microdomaines voire très important dans le cas de la Dimeb, le dérivé ayant l’effet le plus délétère sur l’intégrité des membranes artificielles et biologiques. Un effet moins marqué a également pu être corrélé avec une extraction plus faible du cholestérol par certains dérivés (Crysmeb, Trimeb).Les taux d’extraction du cholestérol cellulaire mesurés sont en bonne corrélation, mis à part pour la Trimeb et la b-CD, avec les résultats des diagrammes de solubilité. La capacité de solubilisation du cholestérol par les cyclodextrines est en accord avec les interactions plus ou moins importantes observées en RMN. Les résultats de mesure de l’intégrité des membranes artificielles correspondent à ceux obtenus avec les membranes biologiques excepté pour la b-CD, cette dernière n’ayant pu être testée dans les mêmes conditions que les autres cyclodextrines sur les liposomes.Il est maintenant admis que les cyclodextrines pourraient avoir un intérêt thérapeutique potentiel. En effet, la modulation des taux de cholestérol par l’utilisation de cyclodextrines pourrait être mise à profit pour traiter des maladies ou infections impliquant ces microdomaines membranaires. Summary :Nowadays, the usefulness of cyclodextrins as pharmaceutical adjuvants is obvious. In cell biology, methyl-b-CD is a tool commonly used by scientists. The disruption of membrane microdomains (such as lipid rafts and caveolae) caused by cyclodextrins is used to study cellular functions.The aim of this research is to study the interactions of various cyclodextrins currently used in pharmaceutical development with the components of liposomal and biological membranes for a better understanding of the consequences of these interactions at the cell level.The hypothesis of an interaction between cyclodextrins and lipophilic components of cell membranes has often been suggested to explain the cytotoxicity of some cyclodextrin derivatives.Using unilamellar liposomes as model membranes, this research has shown that the interaction between cyclodextrins and their components, especially cholesterol, is linked with a loss of membrane integrity. This preliminary study has allowed predicting which derivatives will be the most cytotoxic.The high cytotoxicity of some methylated derivatives (D.S. close to 2) has been correlated with a relatively strong extraction capacity of cell cholesterol. On the other hand, it has been shown that low substituted derivatives do not extract much cholesterol, which is in agreement with the better biological compatibility observed with Crysmeb and HP-b-CD.The research has then focused on the effect of b-CD and its methylated derivatives on membrane microdomains disruption. The relation between caveolae disruption and cell cholesterol extraction capacities has been studied. A relatively strong extraction of the lipid highly disturbs the microdomains and this effect is even more important for Dimeb, the derivative showing the highest loss of integrity of artificial and biological membranes. A less marked effect has also been correlated with the lowest cholesterol extraction capacities of some derivatives (Crysmeb, Trimeb).The measured cell cholesterol extraction rates are in good correlation, except for Trimeb and b-CD, with the results of the solubility diagrams. The cholesterol solubilisation capacity of cyclodextrins is in accordance with the intensity of the interactions observed by NMR. The effects on the integrity of artificial membranes correspond to those obtained with biological membranes except for b-CD, which was not tested on liposomes in the same conditions as those used for the other cyclodextrins. It is now agreed that cyclodextrins could have a therapeutical potential. Indeed, the modulation of cholesterol levels could be applied for treating raft-related infections and diseases

Multi-objective constrained optimization of engine maps

International audienceNowadays, automotive manufacturers are submitted to strong constraints in engine calibration: lowest fuel consumption, emission-control legislation and driver requests for driving comfort and performances. These constraints lead to an increasingly complexity of the engines and thus an increasingly number of parameters to be tuned, making the empirical engine calibration by a scan of parameter values impossible at engine test-bench. New methodologies in automated engine calibration based on statistics and optimization have emerged in order to limit the number of experimental tests to be run. The optimization problem of engine calibration consists in the determination of engine tuning parameter maps that minimize the cumulated fuel consumption and pollutant emissions, under combustion noise constraints, on a driving cycle. The usual way to get this result is to select specific operating points representing this cycle in the engine working range and to define upper bounds applied on the different engine responses (allocations) for each of them, in order to obtain a weighted sum of these local responses respecting the global targets. The underlying problem is a multi-objective optimization problem: different compromises between fuel consumption, noise and pollutant emissions on each operating point are possible. We propose an adapted optimization method based on the MO-CMA-ES method (Multi-objective Covariance Adaptation Evolution Strategy) which takes into account the non trivial limits of the engine parameter variation domains and some robustness constraints. An other point addressed in this paper is the map optimization which consists in a global optimization of engine responses cumulated on the driving cycle. This method avoids the cumbersome choice of allocations for each considered operating point and includes directly the map regularity constraints in map parameterizations. Finally, application on real dataset obtained at automated test-bench for a diesel engine are presented

Engine calibration : towards an integrated approach.

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Effect of β-cyclodextrin and its derivatives on caveolae disruption, relationships with their cholesterol extraction capacities

peer reviewedEndothelial cells (HUVEC) were treated with b-cyclodextrin (b-CD) and hydroxypropylated or methylated derivatives solutions to confirm their lack of affinity with phospholipids and their specificity towards cholesterol. Further studies were performed on bovine aortic endothelial cells to assess the effect of b-CDs (mainly methylated derivatives) on membrane microdomains (lipid rafts or caveolae), by detecting the caveolae marker caveolin-1 in fractions of sucrose gradients. A displacement from the lighter to the heavier fractions, characteristic of caveolae disruption, was observed using CDs. The strongest effect was obtained with dimethyl-b-CD, for which an accumulation of caveolin-1 was observed in the bottom of the gradient. Crysmeb and trimethyl-b-CD seemed to have the weaker effects as a significative amount of caveolin-1 was still detected in the light fraction corresponding to caveolae. b-CD and CDs having a degree of methylation a bit lower than 2 showed intermediate effects. The results of the present study on microdomains seem in good correlation with the cell cholesterol extraction capacities of CDs previously determined

Preparation and evaluation of liposomes encapsulating synthetic MMP inhibitor (Ro 28-2653) - cyclodextrin complexes

peer reviewedIn this study, preparation and evaluation of liposomes, intended for intravenous administration, encapsulating synthetic MMP inhibitor (Ro 28-2653) - cyclodextrin complexes were realized. An increase in Ro solubility, via formation of binary (Ro/HP beta CD) or ternary (Ro/HP beta CD/L-lysine) complexes, permitted a similar increase in encapsulation efficiency of liposomes (Table 1). Moreover, Ro release kinetics depend on the encapsulation efficiency

Pharmacokinetic study of a new synthetic MMP inhibitor (Ro 28-2653) after IV and oral administration of cyclodextrin solutions

Ro 28-2653 (5-biphenyl-4-yl-5-[4-(4-nitro-phenyl)-piperazin-1-yl]-pyrimidine-2,4,6-trione) is a new synthetic inhibitor of matrix metalloproteinases (MMPs) with a high selectivity towards MMP2, MMP9 and membrane type 1-MMP. It has been shown that cyclodextrins (CDs) are able to form inclusion complexes with Ro 28-2653 and to increase its aqueous solubility. The aim of this study is to demonstrate that an increase in Ro 28-2653 solubility, via ternary complex formation, can lead to an increase in the oral bioavailability of this drug. This study shows that a synergistic effect exists between hydroxypropyl-beta-cyclodextrin (HP-beta-CD) and L-lysine. The use of this multicomponent system enabled the preparation of oral and intravenous solutions of Ro 28-2653. In vivo evaluation of the oral solution of the inclusion complex of Ro 28-2653 in comparison with a suspension of the same uncomplexed drug showed a significant (p < 0.05) increase in absolute bioavailability. The area under curve (AUC) and the peak serum concentration (C-max) were approximately 10 times higher than those obtained with the suspension, while the time (T-max) to reach C-max was reduced. Moreover, in vivo administration of Ro 28-2653 solutions highlighted some information about the pharmacokinetic behavior of Ro 28-2653: a long biologic half-life (about 15.5 h) and a small overall volume of distribution (81). (c) 2006 Elsevier B.V. All rights reserved