Electrodes for in vivo localised subcutaneous electropulsation and associated drug and nucleic acid delivery.

BACKGROUND: Drug and nucleic acids can be delivered in vivo by an injection of the product followed by the application of a train of electric pulses. OBJECTIVE: The success of the method is linked to the proper distribution of the electric field in the target tissue. This is under the control of the design of the electrodes. METHODS: The field distribution can be obtained by computer simulation mainly by using numerical methods and simplifying hypothesis. The conclusions are validated by comparing the computed current and its experimental values on phantoms. A good agreement is obtained. RESULTS/CONCLUSION: Targeting the delivery to the skin can be obtained by using an array of very short needle electrodes, by pinching the skin between two parallel plate electrodes, or by using contact wire electrodes.

Lateral distribution of cholesterol in membranes probed by means of a pyrene-labelled cholesterol: effects of acyl chain unsaturation.

The lateral distribution of cholesterol in membranes in the fluid state was investigated by studying the variation of the molar absorption coefficient of pyrene-labelled cholesterol (Py-chol) vs. its concentration in vesicles made of phosphatidylcholine, with variable acyl chain unsaturations. Absorption measurements indicated non-ideal mixing of Py-chol in unsaturated lipids, a process mainly controlled by the cholesterol moiety of the probe. Similar abilities of cholesterol and Py-chol in perturbing the phase properties of pure saturated phosphatidylcholine were observed by DSC experiments. Immiscibility of sterols was corroborated by fluorescence polarization measurements, which indicated a weaker ordering effect of cholesterol in unsaturated membranes. The sizes and the quantities of sterol oligomers formed were calculated. A model for the lateral distribution of cholesterol in membranes is proposed and is applied to known cholesterol/phosphatidylcholine phase diagrams. Finally, the results are discussed with regard to recent models of biological membrane organization, (i.e. rafts).

Probing the lateral organization of membranes: fluorescence repercussions of pyrene probe distribution.

Phospholipids pyrene labeled are widely used to investigate dynamics and organizations of membranes. We studied pyrene probe lateral distribution by analyzing the variations of the molar absorption coefficient (epsilon) versus probe concentrations, in small unilamellar vesicles (SUV) made of phospholipids and/or glycolipids, with pyrene labeled phosphatidylcholine (PyPC) or phosphatidylglycerol (PyPG). The results were interpreted according to an infinite associative model. They indicated that an effective self-association process corresponding to K ranging from 30 to 100 M(-1) occurred with those probes incorporated in dimannosyl diacylglycerol (DMDG). In contrast, after SUV labeling of egg yolk phosphatidylcholine (EggPC) or phosphatidylglycerol (EggPG), K values < 1 M(-1) were determined. The corresponding percentages of various stacked forms of pyrene probes were calculated. They indicated that, for a 3% PyPG labeling, the monomer represented 21% of n-mers in DMDG and 94% in EggPC. The analysis of fluorescence experiments carried out on the same samples indicated that: (i) the fluorescence process of pyrene probes was generated by the monomers: and (ii) the excimer forming resulted from a diffusional encounter between one excited and one non-excited monomer. A correction of fluorescence data allowing a more correct interpretation of fluorescence measurements was proposed.

7-nitrobenz-2-oxa-1,3-diazole-4-yl-labeled phospholipids in lipid membranes: differences in fluorescence behavior.

Steady-state and time-resolved fluorescence properties of the 7-nitrobenz-2-oxa-1, 3-diazole-4-yl (NBD) fluorophore attached either to the sn-2 acyl chain of various phospholipids (phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, and phosphatidic acid) or to the polar headgroup of phosphatidylethanolamine were studied after insertion of these NBD-labeled lipid probes into unilamellar vesicles of phosphatidylcholine, phosphatidylglycerol, phosphatidic acid, and phosphatidylserine. The fluorescence response of the NBD group was observed to strongly depend on the chemical structure and physical state of the host phospholipids and on the chemical structure of the lipid probe itself. Among the various fluorescence parameters studied, i.e., Stokes' shifts, lifetimes, and quantum yields, the quantum yields were by far the most affected by these structural and environmental factors, whereas the Stokes' shifts were practically unaffected. Thus, depending on the phospholipid probe and the host phospholipid, the fluorescence emission of the NBD group was found to vary by a factor of up to 5. Careful analysis of the data shows that for the various couples of probe and host lipid molecules studied, deexcitation of the fluorophore was dominated by nonradiative deactivation processes. This great sensitivity of the NBD group to environmental factors originates from its well-known solvatochromic properties, and comparison of these knr values with those obtained for n-propylamino-NBD in a set of organic solvents covering a large scale of polarity indicates that in phospholipids, the NBD fluorophore experiences a dielectric constant of around 27-41, corresponding to a medium of relatively high polarity. From these epsilon values and on the basis of models of the dielectric transition that characterizes any water-phospholipid interface, it can be inferred that for all of the phospholipid probes and host phospholipids tested, the NBD group is located in the region of the polar headgroups, near the phosphoglycerol moiety of the lipids.

Certain properties of isoniazid inhibition of mycolic acid synthesis in cell-free systems of M. aurum and M. avium.

In Mycobacterium tuberculosis isoniazid (INH)-susceptibility and the presence of a thermolabile catalase-peroxidase (T-catalase) are nearly always associated. It is shown in this study that an INH-susceptible strain of M. aurum had a T-catalase activity while its resistant mutants did not, but an in vitro susceptible strain of M. avium had a strong catalase activity without any detectable peroxidase properties. Synthesis of mycolic acids is a genus-specific target for INH and there is an excellent parallelism between INH-susceptibility of intact cells and that of a cell-free system synthesizing mycolic acids. We investigated whether the INH-inhibition of mycolic acid cell-free synthesis was dependent on a T-catalase activity in M. aurum and M. avium: no catalase activity was detectable in any of the cell-free systems tested, and addition of T-catalase from susceptible M. aurum strain to an INH-resistant system did not render it sensitive. So INH can inhibit mycolic acid synthesis independently of the presence of a T-catalase. An INH-susceptible cell-free system prepared from INH-treated (at the MIC) cells was progressively and irreversibly inhibited, while incubation of the same susceptible system in the presence of INH did not result in a significant irreversible inhibition. The possible participation of T-catalase in the irreversible effect of INH is discussed.