Improvement of the encapsulation efficiency of oligonucleotide-containing biodegradable microspheres.

The objective of this study was to encapsulate an oligonucleotide drug within poly(lactide) microparticles with high encapsulation efficiencies at high theoretical drug loadings by the solvent evaporation method. With the conventional W/O/W method, the encapsulation efficiency decreased with increasing internal water content, increasing stirring time prior to filtration of the microparticles and increasing drug loading. The encapsulation was improved by replacing methylene chloride with ethyl acetate, by using micronized drug powder instead of an internal aqueous phase or by adding electrolytes or nonelectrolytes to the external phase. With ethyl acetate, a pre-emulsification step into a smaller volume of external aqueous phase was necessary in order to avoid premature polymer precipitation and to obtain microparticles. The addition of salts (NaCl or MgCl(2)) or sorbitol to the external aqueous phase significantly improved the encapsulation efficiency, even at high theoretical drug loadings. The microparticles had a denser structure with a smooth, pore-free surface.

Effect of proteases and other treatments on the proliferative assembly of tight junction strands in the rat prostate tissue.

As already observed with the freeze-fracture technique by Kachar and Pinto da Silva (1981) incubation of excised rat ventral prostate tissue at 37 degrees C results in proliferation of tight junction strands over the lateral membranes of the epithelial cells, an effect not occurring after incubation at 4 degrees C. Our investigations have shown that a pretreatment with protease inhibitor Contrykal at 4 degrees C suppresses the proliferation of tight junction strands at 37 degrees C. On the other hand the added proteases trypsin and pronase induce the proliferation already at 4 degrees C. The effect was lowered by higher concentrations of pronase. Incubation with solutions of the non-ionic detergent Triton X-100 at 4 degrees C could also induce tight junction proliferation, whereas this effect was nearly absent after an incubation at 4 degrees C with a hyperosmotic solution of arabinose and with 50% acetone. No relation was found between proliferation of tight junction strands and cluster formation of intramembraneous particles. In conclusion of the results a small protein or a peptide resembling fusions proteins is assumed as trigger for formation of tight junction strands, acting by destabilization of the bilayer arrangement of membrane lipids.

Teratogenic effects of chronic ingestion of high levels of vitamin A in cats.

High concentrations of retinoids occur in some commercial cat food formulations as a result of the use of animal liver as an ingredient. Our objective was to study the teratogenic potential of dietary vitamin A in cats. We investigated the incidence of birth defects in kittens of queens given diets with retinyl acetate concentrations of 6000, 306000, or 606000 retinol equivalents (RE)/kg diet (control, 306K, or 606K groups, respectively) for approximately 3 years [1 RE=1 micro g retinol=3.3 International Units (IU)]. Each group comprised 12-15 age-matched, nulliparous domestic short-haired queens that were exposed to toms. There were a total of 396 kittens born in 97 litters. Pregnancy rate, number of kittens per gestation and gestations per year were not significantly different among treatment groups. A total of 2, 5 and 11 malformed kittens occurred in the control, 306K and 606K groups, respectively. Malformations included cleft palate, cranioschisis, foreshortened mandible, stenotic colon, enlarged heart and agenesis of the spinal cord and small intestine, which are typical foetal defects consistent with ingestion of excess retinoids in other species. This study demonstrated that a concentration of 306000 RE/kg diet has a potential for causing birth defects in the kittens.