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Increased brain radioactivity by intranasal 32P-labeled siRNA dendriplexes within in situ-forming mucoadhesive gels

Authors Perez AP, Mundinio C, Romero EL, Morilla MJ

Received 15 November 2011

Accepted for publication 5 January 2012

Published 12 March 2012 Volume 2012:7 Pages 1373—1385


Review by Single-blind

Peer reviewer comments 4

Ana Paula Perez1, Cecilia Mundiña-Weilenmann2, Eder Lilia Romero1, Maria Jose Morilla1

1Programa de Nanomedicinas, Departamento de Ciencia y Tecnología, Universidad Nacional de Quilmes, Buenos Aires, 2Centro de Investigaciones Cardiovasculares, CCT-La Plata, CONICET, Facultad de Ciencias Médicas, Universidad Nacional de La Plata, La Plata, Argentina

Background: Molecules taken up by olfactory and trigeminal nerve neurons directly access the brain by the nose-to-brain pathway. In situ-forming mucoadhesive gels would increase the residence time of intranasal material, favoring the nose-to-brain delivery. In this first approach, brain radioactivity after intranasal administration of 32P-small interference RNA (siRNA) complexed with poly(amidoamine) G7 dendrimers (siRNA dendriplexes) within in situ-forming mucoadhesive gels, was determined.
Materials: 32P-siRNA dendriplexes were incorporated into in situ-forming mucoadhesive gels prepared by blending thermosensitive poloxamer (23% w/w) with mucoadhesive chitosan (1% w/w, PxChi) or carbopol (0.25% w/w, PxBCP). Rheological properties, radiolabel release profile, and local toxicity in rat nasal mucosa were determined. The best-suited formulation was intranasally administered to rats, and blood absorption and brain distribution of radioactivity were measured.
Results: The gelation temperature of both formulations was 23°C. The PxChi liquid showed non-Newtonian pseudoplastic behavior of high consistency and difficult manipulation, and the gel retained 100% of radiolabel after 150 minutes. The PxCBP liquid showed a Newtonian behavior of low viscosity and easy manipulation, while in the gel phase showed apparent viscosity similar to that of the mucus but higher than that of aqueous solution. The gel released 35% of radiolabel and the released material showed silencing activity in vitro. Three intranasal doses of dendriplexes in PxCBP gel did not damage the rat nasal mucosa. A combination of 32P-siRNA complexation with dendrimers, incorporation of the dendriplexes into PxCBP gel, and administration of two intranasal doses was necessary to achieve higher brain radioactivity than that achieved by intravenous dendriplexes or intranasal naked siRNA.
Conclusion: The increased radioactivity within the olfactory bulb suggested that the combination above mentioned favored the mediation of a direct brain delivery.

Keywords: nucleic acids, gel, dendrimers, mucosa, olfactory bulb

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