Addictions and stress: clues for cocaine pharmacotherapies.

Addictions are chronic relapsing brain diseases, with behavioral manifestations. Three main factors contribute to the development of an addiction: environment, including stress, the reinforcing effects of the drug, and genetics. In this review we will discuss the involvement of the dysregulation of the stress responsive hypothalamic-pituitary-adrenal (HPA) axis in the acquisition of, and persistence to drug addiction (Section B). Addictions to specific drugs such as cocaine/psychostimulants, alcohol, and mu-opioid receptor agonists (e.g., heroin) have some common direct or downstream effects, including modulation of dopaminergic systems. Through its action on the dopaminergic signaling pathways, cocaine affects the HPA axis, and brain nuclei responsible for movements, and rewarding effects. Several neurobiological systems have been implicated with cocaine addiction, including dopamine, serotonin and glutamate systems, opioid receptor and opioid neuropeptide gene systems, stress-responsive systems including CRF, vasopressin and orexin. The use of animal models (Sections C and D) has been essential for studying the individual vulnerabilities to the effects of drugs of abuse and the neural pathways and neurotransmitters affected by these drugs. Basic clinical research has revealed important relationship between cocaine use, HPA axis responsiveness, and gender (Section E). Finally, we will discuss gene polymorphisms that are associated with drug use (Section F). Results from animal models and basic clinical research have shown important interactions between the dopaminergic and the opioid systems. Hence, compounds modulating the opioid system may be beneficial in treating cocaine addiction.

Nuclear delivery of a therapeutic peptide by long circulating pH-sensitive liposomes: benefits over classical vesicles.

The purpose of this study is to propose a suitable vector combining increased circulation lifetime and intracellular delivery capacities for a therapeutic peptide. Long circulating classical liposomes [SPC:CHOL:PEG-750-DSPE (47:47:6 molar% ratio)] or pH-sensitive stealth liposomes [DOPE:CHEMS:CHOL:PEG(750)-DSPE (43:21:30:6 molar% ratio)] were used to deliver a therapeutic peptide to its nuclear site of action. The benefit of using stealth pH-sensitive liposomes was investigated and formulations were compared to classical liposomes in terms of size, shape, charge, encapsulation efficiency, stability and, most importantly, in terms of cellular uptake. Confocal microscopy and flow cytometry were used to evaluate the intracellular fate of liposomes themselves and of their hydrophilic encapsulated material. Cellular uptake of peptide-loaded liposomes was also investigated in three cell lines: Hs578t human epithelial cells from breast carcinoma, MDA-MB-231 human breast carcinoma cells and WI-26 human diploid lung fibroblast cells. The difference between formulations in terms of peptide delivery from the endosome to the cytoplasm and even to the nucleus was investigated as a function of time. Characterization studies showed that both formulations possess acceptable size, shape and encapsulation efficiency but cellular uptake studies showed the important benefit of the pH-sensitive formulation over the classical one, in spite of liposome PEGylation. Indeed, stealth pH-sensitive liposomes were able to deliver hydrophilic materials strongly to the cytoplasm. Most importantly, when encapsulated in pH-sensitive stealth liposomes, the peptide was able to reach the nucleus of tumorigenic and non tumorigenic breast cancer cells.

Liposome surface charge influence on skin penetration behaviour.

Vesicular systems have shown their ability to increase dermal and transdermal drug delivery. Their mechanism of drug transport into and through the skin has been investigated but remains a much debated question. Several researchers have outlined that drug penetration can be influenced by modifying the surface charge of liposomes. In the present work we study the influence of particle surface charge on skin penetration. The final purpose is the development of a carrier system which is able to enhance the skin delivery of two model drugs, betamethasone and betamethasone dipropionate. Liposomes were characterised by their size, morphology, zeta potential, encapsulation efficiency and stability. Ex vivo diffusion studies using Franz diffusion cells were performed. Confocal microscopy was performed to visualise the penetration of fluorescently labelled liposomes into the skin. This study showed the potential of negatively charged liposomes to enhance the skin penetration of betamethasone and betamethasone dipropionate.

Skin penetration behaviour of liposomes as a function of their composition.

Deformable liposomes have been developed and evaluated as a novel topical and transdermal delivery system. Their mechanism of drug transport into and through the skin has been investigated but remains a much debated question. The present study concerns ex vivo diffusion experiments using pig ear skin in order to explain the penetration mechanism of classical and deformable liposomes. Classical and deformable vesicles containing betamethasone in the aqueous compartment through the use of cyclodextrin inclusion complexes were compared to vesicles encapsulating betamethasone in their lipid bilayer. Deformable liposomes contained sodium deoxycholate as the edge activator. Liposomes were characterised by their diameter, encapsulation efficiency, deformability, stability (in terms of change in diameter) and release of encapsulated drug. Ex vivo diffusion studies using Franz diffusion cells were performed. Confocal microscopy was performed to visualise the penetration of fluorescently labelled liposomes into the skin. This study showed that liposomes do not stay intact when they penetrate the deepest layers of the skin. Betamethasone is released from the vesicles after which free drug molecules can diffuse through the stratum corneum and partition into the viable skin tissue.