Stability of PEI-DNA and DOTAP-DNA complexes: effect of alkaline pH, heparin and serum.

DNA complexes formed with nonviral vectors such as polyethylenimine (PEI) or 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP) are widely used in gene therapy. These complexes prevent the interaction of DNA with the fluorescent probes usually employed to quantify DNA. We thus studied the procedures for DNA quantification from DNA complexes as well as their stability in the presence of DNase or mouse, rat and human sera. Release of the DNA from its complexes was accomplished by increasing the pH of the medium (from 7.3 to 13.4) or by adding heparin. The stability against degradation was tested in vitro, by incubating the complexes at 37 degrees C in the presence of DNase I and sera from the three species. Both high pH and heparin were able to release DNA from its complexes. Naked DNA formed aggregates with serum proteins that delayed electrophoresis migration, and this effect was reversed in the presence of heparin. However, these aggregates did not protect DNA from digestion by serum DNase, and the DNA digesting ability of serum was: mouse>rat>human. The DNA from the complexes was resistant to degradation by DNase I, although a low proportion of DNA from the complexes was partially digested, as determined by electrophoresis. In contrast, PEI-DNA and DOTAP-DNA complexes were stable in the presence of all sera. Heparin and high pH release DNA from its complexes. The order of DNA degradation is: mouse>rat>human, but DOTAP and PEI avoid degradation of DNA by serum compounds.

[Differences in the release of omeprazole in 4 commercial preparations: influence of pH and ionic concentration]. / Diferencias en la liberación de omeprazol en cuatro preparados comerciales: influencia del pH y la concentración iónica.

The influence of exposition to different ionic concentrations and pH values on the subsequent in vitro dissolution of omeprazole at pH 6.8 was studied in four enteric-coated commercial formulations. Assays were done using an experimental protocol similar to that recommended in Delayed-Release (Enteric Coated) Articles-General Drug Release Standards (USP 23) slightly modified to achieve similar pH values to commonly observed in patients under omeprazole treatment. Omeprazole capsules were exposed during 1 or 2 hours to four different pH values: 4.8, 5.0, 5.2, and 5.4 and two NaCl concentrations: 75 and 225 mM. After that, dissolution tests at pH 6.8 were performed. Three formulations (Emeprotón, Pepticum and Ulceral) released different percents of the encapsulated dose at the above acidic mediums and, consequently, the omeprazole dissolved underwent a remarkable degradation. The drug contained in the enteric-coated granules of Losec was not released and therefore the amount of omeprazole dissolved at pH 6.8 from Losec capsules was higher than the obtained with the other three preparations tested.