Bioreducible Liposomes for Gene Delivery: From the Formulation to the Mechanism of Action

BACKGROUND: A promising strategy to create stimuli-responsive gene delivery systems is to exploit the redox gradient between the oxidizing extracellular milieu and the reducing cytoplasm in order to disassemble DNA/cationic lipid complexes (lipoplexes). On these premises, we previously described the synthesis of SS14 redox-sensitive gemini surfactant for gene delivery. Although others have attributed the beneficial effects of intracellular reducing environment to reduced glutathione (GSH), these observations cannot rule out the possible implication of the redox milieu in its whole on transfection efficiency of bioreducible transfectants leaving the determinants of DNA release largely undefined. METHODOLOGY/PRINCIPAL FINDINGS: With the aim of addressing this issue, SS14 was here formulated into binary and ternary 100 nm-extruded liposomes and the effects of the helper lipid composition and of the SS14/helper lipids molar ratio on chemical-physical and structural parameters defining transfection effectiveness were investigated. Among all formulations tested, DOPC/DOPE/SS14 at 25:50:25 molar ratio was the most effective in transfection studies owing to the presence of dioleoyl chains and phosphatidylethanolamine head groups in co-lipids. The increase in SS14 content up to 50% along DOPC/DOPE/SS14 liposome series yielded enhanced transfection, up to 2.7-fold higher than that of the benchmark Lipofectamine 2000, without altering cytotoxicity of the corresponding lipoplexes at charge ratio 5. Secondly, we specifically investigated the redox-dependent mechanisms of gene delivery into cells through tailored protocols of transfection in GSH-depleted and repleted vs. increased oxidative stress conditions. Importantly, GSH specifically induced DNA release in batch and in vitro. CONCLUSIONS/SIGNIFICANCE: The presence of helper lipids carrying unsaturated dioleoyl chains and phosphatidylethanolamine head groups significantly improved transfection efficiencies of DOPC/DOPE/SS14 lipoplexes. Most importantly, this study shows that intracellular GSH levels linearly correlated with transfection efficiency while oxidative stress levels did not, highlighting for the first time the pivotal role of GSH rather than oxidative stress in its whole in transfection of bioreducible vectors

Fast Control Systems: Nonlinear Approach

International audienceThis chapter treats the problem of fast control design for nonlinear systems. First, we discusses the question: which nonlinear system can be called fast? Next, we develop some tools for analysis and design of such control systems. The method generalized homogeneity is mainly utilized for these purposes. Finally, we survey possible research directions of the fast control systems

Social Jealousy and Stigma - Negative Externalities of Social Assistance Payments in Germany

This paper examines the role of social assistance payments (SAP or Sozialhilfe) in determining levels of life satisfaction in Germany using the SOEP 1995-2004. We find strong evidence that individuals in Germany are negatively influenced by increased SAP payments controlling for income, whether or not they actually receive such payments (stigma and social jealousy). While there are obvious benefits to making SAP to those needy, there are substantial negative externalities experienced by those who neither receive SAP nor qualify (counterfactual SAP). Furthermore, these negative effects are even stronger for those who do receive benefits (stigma) suggesting that social jealousy and stigma are a force to be reckoned with when evaluating social policy. We show that the added benefits of increasing SAP are reduced by 50 to 100% because of social jealousy and stigma costs, whereas child benefits (Kindergeld) are seen to enhance life satisfaction over and above a simple income effect. Further, own-earned income, over and above the SAP subsistence level is valued much higher than transfer payments at the SAP subsistence level, suggesting a policy focus on increasing employment integration efforts for SAP recipients as opposed merely to providing SAP transfers