The purpose of this work was to investigate the ability of poly(isobutylcyanoacrylate) nanocapsules to protect insulin from degradation by proteolytic enzymes providing biologically active insulin by the oral route. Insulin was labeled with Texas Red® for release studies and microscopy observations. The fluorescent marker was mostly retained by the nanocapsules incubated in the reconstituted gastric medium but the release was 75% within 30 min when the nanocapsules were incubated in the reconstituted intestinal medium. Turbidimetric measurements and electron microscopy observations confirmed that the nanocapsules were degraded in the reconstituted intestinal medium, whereas nanocapsule integrity was preserved in the reconstituted gastric medium. In vivo studies of the gastrointestinal distribution of insulin‐loaded nanocapsules after oral feeding showed that nanocapsules were retained by the stomach for 30 min. One hour after oral administration, nanocapsules reached the lower part of the intestine (ileum). Fluorescence microscopy and confocal microscopy carried out on portions of the small intestine revealed the presence of concentrated fluorescent spots into the mucosa and even in the lamina propia, suggesting that insulin‐loaded nanocapsules could cross the intestinal epithelium. These data suggest that PIBCA nanocapsules can efficiently protect insulin when given orally. In addition, they seemed to be significantly involved in the absorption mechanism. Drug Dev. Res. 49:109–117, 2000. © 2000 Wiley‐Liss, Inc.
In previous studies, insulin-loaded poly(alkylcyanoacrylate) nanocapsules were found to reduce the blood glucose level after oral administration to diabetic rats and dogs. The reduction of the glycemia induced by the nanocapsules was the same regardless of the insulin doses administered, but the effect appeared only after a delay of a few days. The purpose of this study was to investigate the mechanism of insulin encapsulation and the type of interactions that may exist between the polymer forming the nanocapsule wall and the insulin. The results of this study showed, based on the interfacial polymerization of isobutylcyanoacrylate, that the insulin molecule is not chemically modified during the nanoencapsulation process. In addition, no interaction between the poly(isobutylcyanoacrylate) and the insulin could be observed. The observed high encapsulation efficiency of intact insulin may be explained by the fact that the ethanol used in the preparation of the nanocapsules is responsible for the initiation of the interfacial polymerization of isobutylcyanoacrylate instead of the insulin. The zeta potential measurements suggest that insulin is located within the core of the nanocapsules. Thus the biological activity of the nanoencapsulated peptide and the high efficiency of insulin encapsulation achieved with this nanoencapsulation process cannot be explained by a specific interaction of the insulin with the polymer forming the nanocapsule's wall. It may be due, however, to the fact that the encapsulated insulin molecule is chemically intact and located within the oily core of the nanocapsules.
The EWS/FLI-1 fusion gene, resulting from a t(11;22) translocation, plays a key role in the pathogenesis of Ewing sarcoma. Previously, we have shown that antisense oligonucleotides designed against EWS-Fli-1 inhibited tumor growth in nude mice provided they were delivered intratumorally by nanocapsules or by CTAB-coated nanospheres. In this study, we have used two types of nanospheres (designated as type 1 and type 2 nanospheres) stabilized with chitosan for both intratumoral and systemic administration of oligonucleotides. Inhibition of the tumor growth in vivo was found to be dependent on the carrier type as well as on antisense oligonucleotide modification. Indeed, whereas both types of nanospheres were efficient in reducing tumor growth after intratumoral injection, we have obtained only with type 2 nanospheres an antitumoral effect after intravenous injection in a preliminary experiment. Additionally, the anticancer efficacy of a localized modification of the EWS-Fli-1 phosphodiester/phosphorothioate chimeric antisense oligonucleotide was demonstrated. In cell culture the oligonucleotides inhibit cell growth by their antisense activity. Further investigations are needed in vivo to learn the mechanism of action of the complexes.
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