Lawrence D. McGill

Influence of geometry, porosity, and surface characteristics of silica nanoparticles on acute toxicity: Their vasculature effect and tolerance threshold

Silica nanoparticles (SiO(2)) are widely used in biomedical applications such as drug delivery, cell tracking, and gene transfection. The capability to control the geometry, porosity, and surface characteristics of SiO(2) further provides new opportunities for their applications in nanomedicine. Concerns however remain about the potential toxic effects of SiO(2) upon exposure to biological systems. In the present study, the acute toxicity of SiO(2) of systematically varied geometry, porosity, and surface characteristics was evaluated in immune-competent mice when administered intravenously. Results suggest that in vivo toxicity of SiO(2) was mainly influenced by nanoparticle porosity and surface characteristics. The maximum tolerated dose (MTD) increased in the following order: mesoporous SiO(2) (aspect ratio 1, 2, 8) at 30-65 mg/kg < amine-modified mesoporous SiO(2) (aspect ratio 1, 2, 8) at 100-150 mg/kg < unmodified or amine-modified nonporous SiO(2) at 450 mg/kg. The adverse reactions above MTDs were primarily caused by the mechanical obstruction of SiO(2) in the vasculature that led to congestion in multiple vital organs and subsequent organ failure. It was revealed that hydrodynamic sizes of SiO(2) post-protein exposure had an important implication in relating SiO(2) physicochemical properties with their vasculature impact and resultant tolerance threshold, as the larger the hydrodynamic size in the presence of serum protein, the lower the MTD. This study sheds light on the rational design of SiO(2) to minimize in vivo toxicity and provides a critical guideline in selecting SiO(2) as the appropriate system for nanomedicine applications.

Composition of hyaluronan affects wound healing in the rabbit maxillary sinus.

Background Hyaluronan (HA) is a ubiquitous component of the extracellular matrix. HA and its derivatives have been used in the sinuses to reduce scarring and possibly promote wound healing. However, in recent animal studies, HA esters exhibited inflammatory effects. Mitomycin C (MMC) is another potential antiscarring treatment. This study prospectively evaluated the effects of three different HA constructs on wound healing in the rabbit maxillary sinus: (i) a novel cross-linked HA hydrogel, (ii) the cross-linked HA gel containing covalently bound MMC, and (iii) a commercially available woven HA ester (Merogel). Methods Ostia were created with a 4-mm otologic drill in the maxillary sinuses of 15 New Zealand white rabbits with one side randomly chosen for treatment. After 14 or 21 days the size of the maxillary ostia were recorded and the tissue was examined under light microscopy. Results Sinuses treated with the novel HA and HA-MMC hydrogels showed an increased ostial diameter compared with untreated controls. Woven HA ester–treated sinuses showed no improvement, with a trend toward a smaller ostium than controls. Histological examination showed that woven HA ester tended to cause increased fibrosis and granulomatous inflammation, and heterophilia was slightly increased in the HA hydrogel-treated sinuses. Blinded observation noted foamy macrophages surrounding the residual woven HA ester in each specimen while no similar reaction was noted near the residual HA or HA-MMC hydrogels. Conclusion This study suggests that the degree of ostial narrowing, inflammation, and fibrosis depends on the formulation of the HA used. Minimal, if any, additional benefit is seen with addition of MMC to the HA hydrogel in this pilot study.

Poly(amido amine) dendrimers as absorption enhancers for oral delivery of camptothecin.

Oral delivery of camptothecin has a treatment advantage but is limited by low bioavailability and gastrointestinal toxicity. Poly(amido amine) or PAMAM dendrimers have shown promise as intestinal penetration enhancers, drug solubilizers and drug carriers for oral delivery in vitro and in situ. There have been very limited studies in vivo to evaluate PAMAM dendrimers for oral drug delivery. In this study, camptothecin (5 mg/kg) was formulated and co-delivered with cationic, amine-terminated PAMAM dendrimer generation 4.0 (G4.0) (100 and 300 mg/kg) and anionic, carboxylate-terminated PAMAM generation 3.5 (G3.5) (300 and 1000 mg/kg) in CD-1 mice. Camptothecin associated to a higher extent with G4.0 than G3.5 in the formulation, attributed to an electrostatic interaction on the surface of G4.0. Both PAMAM G4.0 and G3.5 increased camptothecin solubilization in simulated gastric fluid and caused a 2-3 fold increase in oral absorption of camptothecin when delivered at 2 h. PAMAM G4.0 and G3.5 did not increase mannitol transport suggesting that the oral absorption of camptothecin was not due to tight junction modulation. Histologic observations of the epithelial layer of small intestinal segments of the gastrointestinal tract (GIT) at 4 h post dosing supported no evidence of toxicity at the evaluated doses of PAMAM dendrimers. This study demonstrates that both cationic (G.4) and anionic (G3.5) PAMAM dendrimers were effective in enhancing the oral absorption of camptothecin. Results suggest that drug inclusion in PAMAM interior controlled solubilization in simulated gastric and intestinal fluids, and increased oral bioavailability.

Crosslinked hydrogels for tympanic membrane repair

PROBLEM: To provide a less expensive and more convenient protocol for the treatment of tympanic membrane perforations (TMPs). METHODS: Several materials were prepared and compared for TMP repair including Carbylan-SX, Gelatin-DTPH-PEGDA (GX), Carbylan-S/Gelatin-DTPH (Carbylan-GSX) (injectable and sponge), Gelfoam, Epifilm, and crosslinked thiolated chondroitin sulfate (CS-DTPH-PEGDA [CS-SX]). Hartley pigmented guinea pigs (Elm Hill) underwent bilateral myringotomy with 1 ear left as a control and the other treated with one of the previously mentioned materials. RESULTS: Carbylan-GSX (injectable and sponge), Gelfoam with saline, and CS-SX had the shortest time for TMP closure. Epifilm, Carbylan, and gelatin preparations resulted in closure rates similar to controls. CS-SX showed a marked inflammatory reaction compared with controls and other materials based on neutrophil, lymphocyte, epitheloid counts, and degree of fibrosis. CONCLUSIONS: This study shows the validity of Carbylan-GSX compared with Gelfoam as a material to promote TMP closure in an acute TMP guinea pig model.

Percutaneous implants with porous titanium dermal barriers: An in vivo evaluation of infection risk

Osseointegrated percutaneous implants are a promising prosthetic alternative for a subset of amputees. However, as with all percutaneous implants, they have an increased risk of infection since they breach the skin barrier. Theoretically, host tissues could attach to the metal implant creating a barrier to infection. When compared with smooth surfaces, it is hypothesized that porous surfaces improve the attachment of the host tissues to the implant, and decrease the infection risk. In this study, four titanium implants, manufactured with a percutaneous post and a subcutaneous disk, were placed subcutaneously on the dorsum of eight New Zealand White rabbits. Beginning at four weeks post-op, the implants were inoculated weekly with 10(8) CFU Staphylococcus aureus until signs of clinical infection presented. While we were unable to detect a difference in the incidence of infection of the porous metal implants, smooth surface (no porous coating) percutaneous and subcutaneous components had a 7-fold increased risk of infection compared to the implants with a porous coating on one or both components. The porous coated implants displayed excellent tissue ingrowth into the porous structures; whereas, the smooth implants were surrounded with a thick, organized fibrotic capsule that was separated from the implant surface. This study suggests that porous coated metal percutaneous implants are at a significantly lower risk of infection when compared to smooth metal implants. The smooth surface percutaneous implants were inadequate in allowing a long-term seal to develop with the soft tissue, thus increasing vulnerability to the migration of infecting microorganisms.

Comparative vaccine-specific and other injectable-specific risks of injection-site sarcomas in cats.

OBJECTIVE To compare associations between vaccine types and other injectable drugs with development of injection-site sarcomas in cats. DESIGN Case-control study. ANIMALS 181 cats with soft tissue sarcomas (cases), 96 cats with tumors at non-vaccine regions (control group I), and 159 cats with basal cell tumors (control group II). PROCEDURES Subjects were prospectively obtained from a large pathology database. Demographic, sarcoma location, basal cell tumor, and vaccine and other injectable history data were documented by use of a questionnaire and used to define case, control, and exposure status. Three control groups were included: cats with sarcomas at non-vaccine sites, cats with basal cell tumors, and a combined group of cats with sarcomas at non-vaccine sites and cats with basal cell tumors. χ(2) tests, marginal homogeneity tests, and exact logistic regression were performed. RESULTS In the broad interscapular region, the frequency of administration of long-acting corticosteroid injections (dexamethasone, methylprednisolone, and triamcinolone) was significantly higher in cases than in controls. In the broad rear limb region, case cats were significantly less likely to have received recombinant vaccines than inactivated vaccines; ORs from logistic regression analyses equaled 0.1, with 95% confidence intervals ranging from 0 to 0.4 and 0 to 0.7, depending on control group and time period of exposure used. CONCLUSIONS AND CLINICAL RELEVANCE This case-control study measuring temporal and spatial exposures efficiently detected associations between administrations of various types of vaccines (recombinant vs inactivated rabies) and other injectable products (ie, long-acting corticosteroids) with sarcoma development without the need to directly measure incidence. These findings nevertheless also indicated that no vaccines were risk free. The study is informative in allowing practitioners to weigh the relative merits and risks of commonly used pharmaceutical products.

Cross-linked hydrogels for middle ear packing.

Objective: To develop an ideal supportive packing material for ossiculoplasty, tympanoplasty, or other otologic procedures. Materials and Methods: Several materials, namely, Carbylan-SX (P-C; Sentrx Surgical, Inc., Salt Lake City, UT), Gelfoam (P-GF; Pharmacia & Upjohn, Kalamazoo, MI), and Merogel (P-MG; Medtronics, Inc., Minneapolis, MN), were prepared and then placed into a Hartley guinea pigs (Elm Hill, Chelmsford, MA) middle ear cavities through a large myringotomy incision. The contralateral ear underwent a large myringotomy without packing material being placed. Preoperative and posteroperative auditory brainstem response studies were performed using Intelligent Hearing system software. The animals were examined weekly. Two weeks after packing placement, the animals were killed, and the temporal bones were harvested. Whole temporal bone sectioning was performed to analyze the presence of implant, surrounding inflammation, presence of osteoneogenesis and fibrosis, or adhesions. Results: All the materials, except the P-MG, were easy to place into the middle ear cavity. The P-MG contains woven strands that are difficult to trim into the small sizes needed for placement. The P-MG group had a smaller average amount of implant present compared with the other groups at 2 weeks. The degree of osteoneogenesis was similar among the P-GF, P-C, and P-MG groups. The P-MG and P-C groups contained the lowest amount of fibrosis between the implant and surrounding middle ear structures. Conclusion: This study demonstrates promising results with P-C as a potential supportive packing material for otologic procedures. P-C compares favorably with P-MG and P-GF in a guinea pig model with respect to ease of placement and amount of fibrosis.

Foreign body response to subcutaneous biomaterial implants in a mast cell-deficient Kitw-Sh murine model

Mast cells (MCs)_are recognized for their functional role in wound-healing and allergic and inflammatory responses - host responses that are frequently detrimental to implanted biomaterials if extended beyond acute reactivity. These tissue reactions impact especially on the performance of sensing implants such as continuous glucose monitoring (CGM) devices. Our hypothesis that effective blockade of MC activity around implants could alter the host foreign body response (FBR) and enhance the in vivo lifetime of these implantable devices motivated this study. Stem cell factor and its ligand c-KIT receptor are critically important for MC survival, differentiation and degranulation. Therefore, an MC-deficient sash mouse model was used to assess MC relationships to the in vivo performance of CGM implants. Additionally, local delivery of a tyrosine kinase inhibitor (TKI) that inhibits c-KIT activity was also used to evaluate the role of MCs in modulating the FBR. Model sensor implants comprising polyester fibers coated with a rapidly dissolving polymer coating containing drug-releasing degradable microspheres were implanted subcutaneously in sash mice for various time points, and the FBR was evaluated for chronic inflammation and fibrous capsule formation around the implants. No significant differences were observed in the foreign body capsule formation between control and drug-releasing implant groups in MC-deficient mice. However, fibrous encapsulation was significantly greater around the drug-releasing implants in sash mice compared to drug-releasing implants in wild-type (e.g. MC-competent) mice. These results provide insights into the role of MCs in the FBR, suggesting that MC deficiency provides alternative pathways for host inflammatory responses to implanted biomaterials.

Structural variations in a single hyaluronan derivative significantly alter wound-healing effects in the rabbit maxillary sinus.

Background: Biomaterials based on hyaluronan (HA) are currently used after sinus surgery but have not been found to decrease scarring or enhance wound healing. Chemical composition of these modified HA molecules may impact their biological and clinical effects.

Comparison of silk-elastinlike protein polymer hydrogel and poloxamer in matrix-mediated gene delivery.

The silk-elastinlike protein polymer, SELP 815K, and poloxomer 407, a commercially available synthetic copolymer, were evaluated to compare their relative performance in matrix-mediated viral gene delivery. Using a xenogenic mouse tumor model of human head and neck squamous cell carcinoma, the efficacy of viral gene-directed enzyme prodrug therapy with these polymers was characterized by viral gene expression in the tumor tissue, tumor size reduction, and survivability with treatment. Viral injection in SELP 815K produced a greater level and more prolonged extent of gene expression in the tumor, a statistically greater tumor size reduction, a longer time until tumor rebound, and a significantly increased survivability, as compared to injection of virus alone or in Poloxamer 407. Safety of treatment with these polymers was evaluated in a non-tumor bearing immunocompetent mouse model. Compared to virus injected alone or in Poloxamer 407, virus injected in SELP 815K had fewer and less severe indications of toxicity related to treatment as assessed by blood analysis, body weight, and histopathology of distant organs and the injection sites. Similar to virus alone or in Poloxamer 407, virus injected in SELP 815K elicited a mild injection site inflammatory response characterized primarily by a mononuclear leukocyte infiltrate and the formation of granulation tissue. Virus injected in SELP 815K resulted in fewer animals with elevated white blood cell counts and a less pronounced local toxicity reaction than was observed with virus in Poloxamer 407. In contrast to virus injected alone or in Poloxamer 407, which were not retained in the injection site tissues beyond week 1, SELP 815K was retained at the injection sites and by the end of the study (week 12), displayed limited absorption, and mild encapsulation. These results demonstrate the benefits of SELP 815K for matrix-mediated gene delivery over the injection of free virus and the injection of virus in Poloxamer 407. Virus in SELP 815K had greater efficacy of tumor suppression, promoted greater levels and greater duration of viral gene expression, and displayed reduced levels of injection site toxicity. Combining these performance and safety benefits with the degree of control with which they can be designed, synthesized and formulated, SELPs continue to show promise for their application in viral gene delivery.