Antibiotic-releasing microspheres prevent mesh infection in vivo.

BACKGROUND: Infection remains a dreaded complication after implantation of surgical prosthetics, particularly after hernia repair with synthetic mesh. We previously demonstrated the ability of a newly developed polymer to provide controlled release of an antibiotic in a linear fashion over 45 d. We subsequently showed that coating mesh with the drug-releasing polymer prevented a Staphylococcus aureus (SA) infection in vivo. To broaden the applicability of this technology, the polymer was synthesized as isolated "microspheres" and loaded with vancomycin (VM) before conducting a noninferiority analysis. MATERIALS AND METHODS: Seventy-three mice underwent creation of a dorsal subcutaneous pocket that was inoculated with 104 colony forming units (CFU) of green fluorescent protein (GFP)-labeled SA (105 CFU/mL). Multifilament polyester mesh (7 × 7 mm) was placed into the pocket, and the skin was closed. Mesh was either placed alone (n = 16), coated with VM-loaded polymer (n = 20), placed next to VM-loaded microspheres (n = 20) or unloaded microspheres (n = 10), or flushed with VM solution (n = 7). Quantitative tissue/mesh cultures were performed at 2 and 4 week. Mice with open wounds and explanted mesh were excluded. RESULTS: Twenty-two of 23 (96%) tissue-mesh samples from mesh alone or empty miscrospheres were positive for GFP-labeled SA at 2 and 4 wk. Six of seven (86%) samples from the VM flush group were positive for GFP SA at 4 wk. Thirty-eight of 38 (100%) VM-loaded crosslinked cyclodextrin polymers-coated mesh or VM-loaded microspheres were negative for GFP SA at 2 and 4 wk. CONCLUSIONS: Slow affinity-based drug-releasing polymers in the form of microspheres are able to adequately clear a bacterial burden of SA and prevent mesh infection.

Polymerized cyclodextrin microparticles for sustained antibiotic delivery in lung infections.

Pulmonary infections complicate chronic lung diseases requiring attention to both the pathophysiology and complexity associated with infection management. Patients with cystic fibrosis (CF) struggle with continuous bouts of pulmonary infections, contributing to lung destruction and eventual mortality. Additionally, CF patients struggle with airways that are highly viscous, with accumulated mucus creating optimal environments for bacteria colonization. The unique physiology and altered airway environment provide an ideal niche for bacteria to change their phenotype often becoming resistant to current treatments. Colonization with multiple pathogens at the same time further complicate treatment algorithms, requiring drug combinations that can challenge CF patient tolerance to treatment. The goal of this research initiative was to explore the utilization of a microparticle antibiotic delivery system, which could provide localized and sustained antibiotic dosing. The outcome of this work demonstrates the feasibility of providing efficient localized delivery of antibiotics to manage infection using both preclinical in vitro and in vivo CF infection models. The studies outlined in this manuscript demonstrate the proof-of-concept and unique capacity of polymerized cyclodextrin microparticles to provide site-directed management of pulmonary infections.

Elucidating the Structure-Function Relationship of Solvent and Cross-Linker on Affinity-Based Release from Cyclodextrin Hydrogels.

Minocycline (MNC) is a tetracycline antibiotic capable of associating with cyclodextrin (CD), and it is a frontline drug for many instances of implant infection. Due to its broad-spectrum activity and long half-life, MNC represents an ideal drug for localized delivery; however, classic polymer formulations, particularly hydrogels, result in biphasic release less suitable for sustained anti-microbial action. A polymer delivery system capable of sustained, steady drug delivery rates poses an attractive target to maximize the antimicrobial activity of MNC. Here, we formed insoluble hydrogels of polymerized CD (pCD) with a range of crosslinking densities, and then assessed loading, release, and antimicrobial activity of MNC. MNC loads between 5-12 wt % and releases from pCD hydrogels for >14 days. pCD loaded with MNC shows extended antimicrobial activity against S. aureus for >40 days and E. coli for >70 days. We evaluated a range of water/ethanol blends to test our hypothesis that solvent polarity will impact drug-CD association as a function of hydrogel swelling and crosslinking. Increased polymer crosslinking and decreased solvent polarity both reduced MNC loading, but solvent polarity showed a dramatic reduction independent of hydrogel swelling. Due to its high solubility and excellent delivery profile, MNC represents a unique drug to probe the structure-function relationship between drug, affinity group, and polymer crosslinking ratio.

Periadventitial Delivery of Simvastatin-Loaded Microparticles Attenuate Venous Neointimal Hyperplasia Associated With Arteriovenous Fistula.

Background Venous neointimal hyperplasia and venous stenosis (VS) formation can result in a decrease in arteriovenous fistula (AVF) patency in patients with end-stage renal disease. There are limited therapies that prevent VNH/VS. Systemic delivery of simvastatin has been shown to reduce VNH/VS but local delivery may help decrease the side effects associated with statin use. We determined if microparticles (MP) composed of cyclodextrins loaded with simvastatin (MP-SV) could reduce VS/VNH using a murine arteriovenous fistula model with chronic kidney disease. Methods and Results Male C57BL/6J mice underwent nephrectomy to induce chronic kidney disease. Four weeks later, an arteriovenous fistula was placed and animals were randomized to 3 groups: 20 µL of PBS or 20 µL of PBS with 16.6 mg/mL of either MP or MP-SV. Animals were euthanized 3 days later and the outflow veins were harvested for quantitative reverse transcriptase-polymerase chain reaction analysis and 28 days later for immunohistochemistical staining with morphometric analysis. Doppler ultrasound was performed weekly. Gene expression of vascular endothelial growth factor-A (Vegf-A), matrix metalloproteinase-9 (Mmp-9), transforming growth factor beta 1 (Tgf-ß1), and monocyte chemoattractant protein-1 (Mcp-1) were significantly decreased in MP-SV treated vessels compared with controls. There was a significant decrease in the neointimal area, cell proliferation, inflammation, and fibrosis, with an increase in apoptosis and peak velocity in MP-SV treated outflow veins. MP-SV treated fibroblasts when exposed to hypoxic injury had decreased gene expression of Vegf-A and Mmp-9. Conclusions In experimental arteriovenous fistulas, periadventitial delivery of MP-SV decreased gene expression of Vegf-A, Mmp-9, Tgf-ß1 and Mcp-1, VNH/VS, inflammation, and fibrosis.

Local delivery polymer provides sustained antifungal activity of amphotericin B with reduced cytotoxicity.

IMPACT STATEMENT: Amphotericin B (AmB) is an effective and commonly used antifungal agent. However, nephrotoxicity and poor solubility limits its usage. The proposed polymerized cyclodextrin (pCD) system therefore is an attractive method for AmB delivery, as it retains the antifungal activity of AmB while decreasing toxicity, and confining drug release to the local environment. This system could potentially be used for both prevention and treatment of established fungal infections, as AmB is toxic to fungus whether associated or released from pCD.

Affinity interactions drive post-implantation drug filling, even in the presence of bacterial biofilm.

Current post-operative standard of care for surgical procedures, including device implantations, dictates prophylactic antimicrobial therapy, but a percentage of patients still develop infections. Systemic antimicrobial therapy needed to treat such infections can lead to downstream tissue toxicities and generate drug-resistant bacteria. To overcome issues associated with systemic drug administration, a polymer incorporating specific drug affinity has been developed with the potential to be filled or refilled with antimicrobials, post-implantation, even in the presence of bacterial biofilm. This polymer can be used as an implant coating or stand-alone drug delivery device, and can be translated to a variety of applications, such as implanted or indwelling medical devices, and/or surgical site infections. The filling of empty affinity-based drug delivery polymer was analyzed in an in vitro filling/refilling model mimicking post-implantation tissue conditions. Filling in the absence of bacteria was compared to filling in the presence of bacterial biofilms of varying maturity to demonstrate proof-of-concept necessary prior to in vivo experiments. Antibiotic filling into biofilm-coated affinity polymers was comparable to drug filling seen in same affinity polymers without biofilm demonstrating that affinity polymers retain ability to fill with antibiotic even in the presence of biofilm. Additionally, post-implantation filled antibiotics showed sustained bactericidal activity in a zone of inhibition assay demonstrating post-implantation capacity to deliver filled antibiotics in a timeframe necessary to eradicate bacteria in biofilms. This work shows affinity polymers can fill high levels of antibiotics post-implantation independent of biofilm presence potentially enabling device rescue, rather than removal, in case of infection. STATEMENT OF SIGNIFICANCE: Post-operative prophylactic antimicrobial therapy greatly reduces risk of infection, such as on biomedical implants, but does not totally eliminate infections, and the healthcare cost of these remaining infections remains a major concern. Systemic antimicrobial therapy to treat these infections can lead to tissue toxicity and drug-resistant bacteria. In order to treat only those patients who have developed infections, a customizable antimicrobial delivery system made of cyclodextrin-based affinity polymer has been developed that is capable of filling post-implantation and delivering the filled antibiotic in a sustained manner even when the delivery device covered in bacterial biofilm. These observations have the potential to be translated to a wide variety of applications, such as implanted or indwelling medical devices, and/or surgical site infections.

Characterizing the structure/function parameter space of hydrocarbon-conjugated branched polyethylenimine for DNA delivery in vitro.

Polyethylenimine is a popular DNA transfection reagent, and many approaches have been explored to further enhance its transfection efficiency. Substitution of branched polyethylenimine's primary amine groups is an attractive approach because it is amenable to a variety of chemistries and is also implicated as a primary factor in its cytotoxicity. The purpose of this work was to serially substitute saturated hydrocarbons to branched polyethylenimine and determine what structure/function relationships exist between the hydrocarbon length and its degree of substitution, relative to transfection efficiency in multiple cell lines. Specifically, acetate, butanoate and hexanoate were conjugated to branched polyethylenimine (M(w) = 25,000) using an aqueous condensation protocol. Transfections were performed in culture using HeLa, NIH/3T3 and Clone 9 cell lines. Biophysical characteristics of the polyelectrolyte complexes were also measured (hydrodynamic diameter, relative binding affinity) and correlated to transfection efficiency. The results show that substitution of the primary amines generally increases transfection efficiency relative to unconjugated polyethylenimine, but increasing the degree of substitution beyond approximately 25 mol% generally decreases transfection efficiency from the optimum. Additionally, increasing hydrocarbon length generally decreased transfection efficiency. There was little correlation between particle size and binding efficiency to transfection efficiency.

One-step synthesis, biodegradation and biocompatibility of polyesters based on the metabolic synthon, dihydroxyacetone.

The one-step synthesis of a polyester family containing dihydroxyacetone is described along with a quantitative analysis of in vitro/in vivo degradation kinetics and initial biocompatibility. Polyesters were synthesized by combining dihydroxyacetone, which is a diol found in the eukaryotic glucose metabolic pathway, with even-carbon aliphatic diacids (adipic, suberic, sebacic) represented in the long-chain alpha carboxylic acid metabolic pathway, by SchÓ§tten-Baumann acylation. We show that by using a crystalline monomeric form of dihydroxyacetone, well-defined polyesters can be formed in one step without protection and deprotection strategies. Both diacid length and polyester molecular weight were varied to influence polymer physical and thermal properties. Polyesters were generated with number-averaged (Mn) molecular weights ranging from 2200-11,500. Polydispersities were consistent with step-growth polymerization and ranged from 2 to 2.6. The melting (Tm) and recrystallization (Tc) temperatures were impacted in an unpredictable manner. Thermal transitions for the polyesters were highest for the adipic acid followed by suberic acid and sebacic acid, respectively. It was shown that the thermal response of the DHA-based polyesters was influenced by both the diacid length and molecular weight. In vitro degradation studies revealed first-order weight loss kinetics, the molecular weight loss followed first order kinetics with 25%-40% of the original mass remaining after 8 weeks. In vivo testing over 16 weeks highlighted that mass loss ranged from ∼70% to ∼6% depending upon initial molecular weight and diacid length. Histological analysis revealed rapid resolution of both acute and chronic inflammatory responses, normal foreign body responses were observed and no inflammation was present after week 4. This one-step synthesis proved robust with unique copolymers warranting further study as potential biomaterials.