Preparation of a Carrier to Achieve In Vivo Delivery of siRNA: The Example of Chitosan-Coated Poly(isobutylcyanoacrylate) Nanoparticles.

This chapter describes the preparation of chitosan-coated poly(isobutylcyanoacrylate) nanoparticles as a suitable carrier to deliver siRNAs to two types of xenograft tumor models of mice. The nanoparticles are prepared by a method of emulsion polymerization that includes steps of polymerization and purification. The polymerization method is carried out in a single pot in an aqueous medium. siRNAs are coupled with the nanoparticles at the end of the preparation by adsorption. The protocol also explains how to determine optimum yield/the titer of association of siRNA with the nanoparticles. It is described for a preparation scale at 4 mL of nanoparticle dispersion at a concentration of 42-46 mg nanoparticles/mL. Optimal loading capacity of the nanoparticles with the siRNA can be achieved by performing an association yield above 90% using a mass ratio of 1 mg siRNA/50 mg of nanoparticles (20 µg siRNA/mg nanoparticles, 1 nmol siRNA (Mw 14 kDa)/mg nanoparticles).

The counterbalanced effect of size and surface properties of chitosan-coated poly(isobutylcyanoacrylate) nanoparticles on mucoadhesion due to pluronic F68 addition.

PURPOSE: To evaluate of the effect of size and surface characteristics of poly(isobutylcyanoacrylate) nanoparticles coated with pluronic F68 and thiolated chitosan on mucoadhesion. METHODS: Nanoparticles were obtained by radical emulsion polymerization in presence of different amounts of F68 (0-4%w/v). Mucoadhesion was ex vivo evaluated by applying nanoparticle suspension on rat intestinal mucosa and quantifying the amount of attached nanoparticles after incubation. RESULTS: F68 unimers added in the polymerization medium allowed decreasing nanoparticle size from 251 to 83 nm, but resulted in nanoparticle surface modification. The amount of thiolated chitosan onto nanoparticle surface was decreased resulting in lower thiol groups and zeta potential. Consequently, the decrease of nanoparticle hydrodynamic diameter resulted in eight-fold-increase of the number of nanoparticles attached to the mucosa but a significant decrease of the weight of attached nanoparticles was observed. This unexpected result was due to a decrease of the amount of chitosan and thiolated chitosan available to interact with mucus upon addition of F68 in the polymerization medium. CONCLUSIONS: Addition of F68 should not be recommended to improve the amount of mucoadherent nanoparticles. Further studies could allow understanding if the low amount of small size nanoparticles could be able to improve oral bioavailability.

Determinants of staged endovascular and surgical treatment outcome of brain arteriovenous malformations.

BACKGROUND AND PURPOSE: Therapy of brain arteriovenous malformations (AVMs) often requires the combination of different treatment modalities. Independently assessed data on neurologic outcome after multidisciplinary AVM therapy are scarce. METHODS: The 119 consecutive patients (49% women, mean age 34+/-13 years) with brain AVMs receiving endovascular embolization followed by surgical treatment were analyzed. Neurologic impairment was assessed prospectively by a neurologist using the modified Rankin Scale (mRS) before, during, and after completed AVM therapy. The association of demographic, clinical, and morphologic characteristics with new treatment-related neurologic deficits was calculated. RESULTS: The 119 patients were treated with 240 superselective embolizations (median, 2; range, 1 to 8) using n-butyl cyanoacrylate. Mean follow-up time after surgery was 9.6+/-13.2 months. On the Spetzler-Martin scale, 8% of the AVMs were grade 1, 27% grade 2, 40% grade 3, 22% grade 4, and 3% grade 5. Disabling treatment-related complications (mRS> or =3) occurred in 5% (95% confidence interval [CI], 1% to 9%) of the patients. Nondisabling new deficits were observed in another 42% (95% CI, 33% to 51%). No patient died. Nonhemorrhagic AVM presentation (odds ratio [OR], 5.00; 95% CI, 1.75 to 14.29), deep venous drainage (OR, 3.09; 95% CI, 1.43 to 6.64), AVM location in an eloquent brain region (OR, 2.42; 95% CI, 1.10 to 5.33), and large AVM size (OR, 1.05; 95% CI, 1.01 to 1.09) were independently associated with new treatment-related deficits. CONCLUSIONS: Our results suggest an increased treatment risk for patients with previously unbled AVMs from combined endovascular and surgical AVM therapy. Additional risk factors for treatment-related neurologic deficits may be large AVM size, deep venous drainage, and AVM location in eloquent brain regions.

Scanning electron microscopic evaluation of the effects of intracameral injection of cyanoacrylate in the rabbit.

We examined, using scanning electron microscopy, the effects of the injection of an isobutyl cyanoacrylate into the rabbit anterior chamber. Injection of the adhesive produced a rapidly polymerized mass that remained in the anterior chamber throughout the course of the study. Additionally, an active inflammatory response was noted in the anterior chamber, characterized by a progressively enlarging "cocoon" of fibrin and inflammatory cells surrounding the polymerized adhesive, as well as inflammatory cells in the trabecular meshwork. Following cyanoacrylate injection, the corneal endothelial cells were noted to be swollen for the first 14 days of the study.

Prothrombotic cytotoxicity of cyanoacrylate tissue adhesive.

Alkyl-2-cyanoacrylates exhibit properties suggestive of their use as surgical adhesives; however, their cytotoxic and proinflammatory properties have prevented their widespread application. The question of whether cyanoacrylate cytotoxicity may be due to eicosanoid production was investigated. Endothelial cells from rats were exposed to increased concentrations of isobutyl-2-cyanoacrylate. The products from this exposure promoted enhanced, concentration-dependent thromboxane biosynthesis as detected by platelet aggregation. When platelets were pretreated with 1-carboxyheptylimidazole (2.0 mM), an inhibitor of thromboxane biosynthesis, up to 80% less aggregation was observed. Such aggregation was inhibited using 1-carboxyheptylimidazole in a dose-dependent manner. Treatment of endothelial cells with isobutyl-2-cyanoacrylate and 1-carboxyheptylimidazole did not significantly alter the amount of platelet aggregation. A soluble metabolite of isobutyl-2-cyanoacrylate appeared to activate platelet aggregation. The cytotoxicity associated with the surgical use of alkyl-2-cyanoacrylates may be mediated by enhanced local thromboxane production.

Histologic analysis of tissue response to bucrylate-pantopaque mixture.

A toxicologic-pathologic study of isobutyl-2-cyanoacrylate (Bucrylate) was carried out first in dogs and then in humans whose arteriovenous malformations were infused with this embolic agent. The canine specimens obtained at 7, 18, 28, and 147 days after embolization showed the development of a mild histiocytic giant cell reaction, which evolved to end-state sclerotic arteritis. The response was confined to the vessels and did not involve contiguous parenchymal tissues. Ten human specimens, obtained from 1 hr to 7 years after treatment, showed a similar bland reaction with no evidence of suppuration or premalignant changes.

[Intracranial saccular aneurysms: experimental evaluation of intravascular therapeutic procedures]. / Aneurismas saculares intracranianos: avaliação experimental de procedimento terapêutico por via intravascular.

Studies were performed on adult mongrel dogs to evaluate the possibility of occluding saccular aneurysms with an intravascular injection of the tissue adhesive Bucrylat (isobutyl-2-cyanoacrylate). Fourteen surgically constructed carotid aneurysms were occluded by the injection of Bucrylat through a fluoroscopically positioned intra-arterial catheter. Angiography performed immediately before and after injection and up to 1 month following treatment revealed progressive and persistent occlusion of the aneurysms. The specimens examined histologically 1 month after the injection showed an endothelialized fibrous tissue bridge crossing the neck of the aneurysm what appear to indicate a permanent occlusion of the structures treated. A similar approach to treat intracranial aneurysms will depend on advances in the field of selective intracranial catheterization that will permit safe and accurate catheterization of the aneurysm sac.

Cyanoacrylate tissue adhesive in osseous repair.

Isobutyl 2-cyanoacrylate monomer placed in an osseous defect excited an intense acute inflammatory response in the early stages of repair. Fibrous encapsulation of the adhesive followed, and chronic inflammation supervened for as long as the cyanoacrylate remaine. Damage to established bone, presumable due to toxic breakdown products, occurred even at a distance from the adhesive. Osteoblastic activity was retarded where cyanoacrylate was in close proximity, recovering as fibrous encapsulation and macrophage activity provided protection. Extensive marrow damage was seen, recovery similarly following fibrous protection. Repair progressed as cyanoacrylate was removed. The findings of this investigation, together with other reports of unfavourable bone reaction to isobutyl 2-cyanoacrylate (Kerr & Smyth, 1971; Corn et al., 1972) suggest that it should not be used in bone surgery. An ideal adhesive for use in bone repair should promote rather than retard osteoblastic activity, and should resorb apace with bone regeneration. Thus isobutyl 2-cyanoacrylate does not fulfil the criteria for the ideal adhesive. Hopefully, future development of the cyanoacrylates will circumvent their current disadvantages, resulting in an adhesive acceptable for clinical use in osseous repair.

Studies concerning the hsitotoxicity of isobutyl-2-cyanoacrylate tissue adhesive when employed as an oral hemostat.

An experimental study was implemented to determine the effectiveness of isobutyl-2-cyanoacrylate (bucrylate) as an oral hemostat, its influence on sequential wound healing, and its potential as a carcinogen. Segregated groups of equal numbers of male and female Long-Evans Hooded Rats underwent deep (socket) and superficial (surface) aerosol placement of bucrylate to maxillary molar extraction sites. Bucrylate proved to be an effective oral hemostat, rapidly retarding postextraction hemorrhage. Deep placement of the adhesive resulted in retarding of healing and lingering macrohistiocytic aggregates in wounds. Superficial placement of the material resulted in very little long-term macrohistiocytic response, and would healing showed little retardation. A neoplastic potential was not demonstrated for bucrylate.

In vitro determination of the antimicrobial properties of two cyanoacrylate preparations.

Isobutyl and trifluoro cyanoacrylates showed varying degrees of inhibition for Lactobacillus casei and Staphylococcus aureus when tested by the spread plate technique. Candida albicans and Pseudomonas aeruginosa were resistant. The results tend to support the view that inhibition of growth was due to the vapor effect and not the diffusibility of the cyanoacrylates.

Long-range effects of Ivalon sponge containing isobutyl cyanoacrylates on rat tissue. A quantitative planimetric study.

This study on seventy rats was undertaken to determine the long-range effects of Ivalon sponge containing isobutyl cyanoacrylates (IBC). Histologic examination revealed that IBC sponge was well tolerated by the connective tissue. IBC sponge was most effective during the first 2 weeks of healing. At observation periods of 1 and 2 weeks, the percentage values for connective tissue formed in IBC-treated animals were 2.02 and 1.58 times higher than those in the untreated animals.