Comparison of Histopathological and CT Findings in Experimental Rabbit Sinusitis

Sustained co-release of ciprofloxacin and dexamethasone in rabbit maxillary sinus using polyvinyl alcohol-based hydrogel microparticle

Topical delivery to paranasal sinuses through sustained-release stents is one of the new horizons in treating chronic rhinosinusitis (CRS). This study aims to introduce and evaluate sustained co-release of encapsulated ciprofloxacin (CIP) and dexamethasone (DEX) in polyvinyl alcohol-based carriers within the maxillary sinus of rabbit animals. DEX and CIP were loaded in a tyramine-substituted polyvinyl alcohol microparticle (PVATyr MP). The mechanical stability, degradability, and sustained-release patterns of both drugs as well as cellular cytocompatibility were assessed in vitro. The PVATyr MPs were then injected into the maxillary sinus of rabbits and they were monitored weekly for 21 days. Nasal endoscopy, MRI imaging, and tissue microscopy were used to follow the changes and compared them with the control condition. Also, the concentrations of drugs were evaluated in the maxillary sinus and blood samples over the study period. Produced PVA-based MPs possessed a relatively narrow particle size distribution (CV 7.7%) with proper physical stability until 30 days of incubation. The uniform-sized PVATyr MPs and their surrounding hydrogel showed sustained-release profiles for DEX and CIP for up to 32 days in vitro. The injected drugs-loaded hydrogel showed complete clearance from the maxillary sinus of rabbits within 28 days. The concentrations of DEX and CIP in mucosal remained within the therapeutic window when measured on days 7, 14, and 21, which were well above the plasma concentrations without any pathological changes in endoscopy, MRI imaging, and histological examinations. DEX/CIP loaded PVATyr MPs provided an effective, controlled, and safe sustained-drug delivery in both in vitro and in vivo analyses at therapeutic concentrations with minimal systemic absorption, suggesting a promising treatment approach for CRS.

Impact of Zinc Oxide on the Development of Aspergillus-Induced Maxillary Sinusitis Rabbit Model

Aspergillus fumigatus is commonly found in the airway and is associated with airway inflammatory diseases. Zinc oxide (ZO) is known to be an essential microelement that facilitates fungal survival, growth, and proliferation. This study aimed to investigate the impact of ZO on A. fumigatus-induced fungal sinusitis in rabbits. Twenty-eight New Zealand white rabbits were divided into four groups for this study. Group 1 (6 sides) was treated with intramaxillary phosphate buffer saline (PBS) served as the negative control, Group 2 (6 sides) received intramaxillary PBS and ZO, Group 3 (8 sides) was treated with intramaxillary A. fumigatus alone, and Group 4 (8 sides) treated with intramaxillary A. fumigatus with ZO. After 4 and 12 weeks, sinus mucosal cytokine and transcription factor expressions were determined. A histological analysis was performed to determine inflammatory cell infiltration, number of secretory cells, and mucosal thickness. Fungal biofilm formation was determined using confocal laser microscopy. The intramaxillary instillation of A. fumigatus conidia led to an increase in protein and mRNA expression of interleukin (IL)-1β and IL-8 in the maxillary sinus mucosa. They were associated with mitogen-activated protein kinase and activator protein-1. Furthermore, intramaxillary instillation of fungal conidia resulted in significant enhancement of inflammatory cell infiltration, epithelial thickening, and fungal biofilm formation. However, intramaxillary ZO did not have a significant impact on A. fumigatus-induced cytokine protein and mRNA expression, and inflammatory cell infiltration and epithelial thickness in sinonasal mucosa. While intramaxillary instillation of A. fumigatus increased mucosal inflammation, cytokine production, and biofilm formation, the intramaxillary application of ZO did not have a significant influence on inflammation in the maxillary sinus mucosa.

Evaluation of Two Configurations of Hydroxyapatite and Beta-Tricalcium Phosphate in Sinus Grafts with Simultaneous Implant Installation: An Experimental Study in Rabbits

BACKGROUND

This study aimed to evaluate peri-implant bone formation in rabbits after sinus grafting mediated by hydroxyapatite and beta-tricalcium phosphate (HA + β-TCP) in granule or paste configurations, concomitant with immediate implant installation.

MATERIAL & METHODS

Thirty-four rabbit maxillary sinuses were grafted with HA + β-TCP, half of which were applied in a granule and half in a paste composition. Implant placement was performed simultaneously. At 7 and 40 days postoperatively, the animals were euthanized, and samples were prepared for tomographic, microtomographic, histological, histometric (hematoxylin and eosin staining, HE), and immunohistochemical (labeling of transcription factor Runx-2 [RUNX2], vascular endothelial growth factor [VEGF], osteocalcin [OCN], and tartrate-resistant acid phosphatase [TRAP]) analysis. Implant removal torque was also measured.

RESULTS

On tomography, maintenance of sinus membrane integrity was observed in both the groups. Higher values of morphometric parameters evaluated by micro-CT were found in the "paste group" after seven days. At 40 days, there were no significant differences between the groups in most of the microtomographic parameters evaluated. In histological sections stained with HE, a higher percentage of newly formed bone was observed in the "granule group" after 40 days. Similar positive immunolabeling was observed for both RUNX2 and OCN in both the experimental groups. TRAP immunolabeling was similar in both groups as well. VEGF labeling increased in the "granule group", indicating a higher osteoconductive potential in this biomaterial. Similar removal torque values were observed in both groups. Thus, the two HA + β-TCP configurations showed similar healing patterns of simultaneously installed implants adjacent to sinus floor elevation. However, significantly higher bone values were observed for the "granule configuration".

CONCLUSIONS

The HA + β-TCP granules and paste presentations showed favorable long-term healing results, with bone formation in similar quantities and quality adjacent to the implants.

Unilateral Intervention in the Sinuses of Rabbits Induces Bilateral Inflammatory and Microbial Changes

Background

Chronic rhinosinusitis (CRS) is a globally prevalent inflammatory condition of the paranasal sinuses which severely impairs patients' quality of life. An animal model of unilateral sinusitis by transient sinus occlusion has been described previously in rabbits. The aim of this study was to characterise the sinusitis rabbit model by investigating temporal and bilateral changes in the bacterial community and mucosal inflammation.

Methods

Development of sinusitis was achieved by endoscopically placing Merocel ^® , a sterile nasal packing material, in the left middle meatus of six New Zealand white rabbits for four weeks. After a total period of 14 weeks, rabbits were assessed for sinusitis by endoscopic examination, magnetic resonance imaging (MRI) and histology. Swabs from the left and right middle meatus were obtained for bacterial community analysis at three time points (week 0, week 4, week 14) during the study.

Results

Endoscopic evaluation showed unilateral inflammation in all animals examined after the 4-week blocking period and at week 14. Notably, inflammatory changes were also seen in the contralateral sinus of all animals at week 4. MRI images demonstrated unilateral sinus opacification at week 4 in two rabbits, and partial unilateral sinus opacification at week 14 in one rabbit only. Histological analyses revealed substantial spatial heterogeneity of mucosal inflammation with inconsistent findings across all animals. No significant differences in mucosal inflammatory markers (such as goblet cell hyperplasia, epithelial denudation and oedema) could be identified between nostrils at week 14. The bacterial community in the rabbit sinuses was heavily dominated by Helicobacter at week 0 (baseline). At the end of the blocking period (week 4), bacterial alpha and beta diversity were significantly increased in both nostrils. The bacterial community composition at week 14 had primarily returned to baseline, reflecting the endoscopic and radiological results.

Conclusion

This study reaffirmed the ability for development of sinusitis without inoculation of any pathogens in a rabbit model. We were able to demonstrate bilateral sinonasal mucosal inflammation, by inducing unilateral sinus blockage, which resulted in significant changes to the sinonasal bacterial community. These findings may explain some of the clinical observations seen in CRS and warrant further research to reveal potential implications for its therapeutic management.

Biodegradable Electrospun Nanofibers: A New Approach For Rhinosinusitis Treatment

Biodegradable polymeric nanofibers containing mometasone furoate can be a new approach to drug delivery to treat chronic rhinosinusitis, providing controlled steroid delivery to the sinonasal mucosa. This study aimed to develop biodegradable polymeric nanofibers and explore the safety of these fibers in an in vivo rabbit model. The nanofibers' development has been optimized using the Response Surface Methodology (RSM) obtained with Design of Experiments (DoE) with the best conditions related to the polymer concentration and proportion of solvents used in the electrospinning process. The nanofibers were prepared, operating as a determinant factor, the nanofiber formation and its diameter evaluated by Scanning Electron Microscopy (SEM). The ideal system obtained was assessed by SEM, thermogravimetric analysis (TGA), X-ray diffraction (XRD), differential scanning calorimetry (DSC), assay, and drug delivery by UHLPC validated method. The results showed that the drug is dispersed in the polymeric matrix, is stable, and showed sustained release kinetics in a bio-relevant nasal environment (Higuchi model kinetics). In vivo tests, the level of inflammation at the animals' mucosa which received the nanofiber with the mometasone furoate was lower than those that received the nanofibers without the drug (α = 0.05). Histopathology analysis showed that the polymeric nanofibers containing mometasone are safe when topically applied on the sinonasal mucosa, opening a new horizon in chronic rhinosinusitis treatment.

A thermoresponsive hydrogel system for long-acting corticosteroid delivery into the paranasal sinuses

Delivering localized treatment to the paranasal sinuses for diseases such as chronic rhinosinusitis (CRS) is particularly challenging because of the small natural openings leading from the sinuses that can be further obstructed by presence of inflammation. As such, oral steroids, topical nasal sprays or irrigation, and surgery can be utilized to treat persistent sinonasal inflammation, but there exists a need for post-operative options for long-term steroid delivery to prevent disease recurrence. In the present study, a Thermogel, Extended-release Microsphere-based-delivery to the Paranasal Sinuses (TEMPS) is developed with the corticosteroid mometasone furoate. Specifically, the bioactive steroid is released for 4 weeks from poly(lactic-co-glycolic acid) (PLGA) microspheres embedded in a poly(N-isopropylacrylamide) (p-NIPAAm)-based hydrogel. The temperature-responsive system undergoes a reversible sol-gel transition at 34-35 °C such that it can be applied as a liquid at ambient temperature, conforming to the sinonasal epithelium as it gels. In a rabbit model of CRS, TEMPS was maintained in rabbit sinuses and effectively reduced sinonasal inflammation as characterized by micro-computed tomography and histopathology analysis. Ultimately, the combination of controlled release microspheres with a thermoresponsive hydrogel provides flexibility for encapsulating therapeutics in a reversible and conforming system for localized delivery to the sinuses.

Bilateral pararhinotomy with middle meatal antrostomy of the maxillary sinus in a rabbit (Oryctolagus cuniculus) with chronic rhinitis

CASE DESCRIPTION

A 4-year-old spayed female mixed-breed rabbit was evaluated because of a 3-year history of sneezing and nasal discharge that were refractory to medical management.

CLINICAL FINDINGS

Signs of chronic left-sided rhinitis and sinusitis were observed on physical examination and confirmed by CT evaluation. Lysis of the rostral aspect of the left maxillary bone and destruction of nasal turbinates were evident on CT images.

TREATMENT AND OUTCOME

Pararhinotomy of the left maxillary sinus through the facies cribrosa was performed. Purulent material was removed from the maxillary sinus recesses, a middle meatal antrostomy was completed to allow permanent drainage into the left middle nasal meatus, and the tissues were closed routinely. Microbial culture of a sample from the maxillary sinus recesses revealed Bordetella bronchiseptica, undetermined fastidious nonenteric bacteria, and Streptococcus viridans. Medical management was continued, and nasal discharge resolved but sneezing persisted. Increased sneezing and bilateral nasal discharge developed 1.5 years later; CT examination revealed right-sided rhinitis, and culture of a nasal swab sample revealed Bordetella spp, Staphylococcus spp, and Micrococcus spp. Right-sided pararhinotomy and middle meatal antrostomy were performed, and medical management continued. A subsequent recurrence was managed without additional surgery; 4 years after the initial surgery, the rabbit was still receiving medical treatment, with mild intermittent nasal discharge and sneezing reported.

CLINICAL RELEVANCE

This report describes a surgical approach for treatment of chronic rhinitis in companion rabbits with maxillary sinus involvement that included creation of a permanent drainage pathway from the maxillary sinus to the middle nasal meatus.

An Experimental Model of Eosinophilic Chronic Rhinosinusitis Induced by Bacterial Toxins in Rabbits

Background

The pathophysiology of chronic rhinosinusitis (CRS) is still not well known due to the multifactorial etiologies involved. Bacteria play a role in the pathogenesis of CRS by various means, including biofilm adhesion, intracellular persistence, or inducing inflammation secondary to toxins. Endotoxins and exotoxins, especially Staphylococcus aureus superantigens, can produce significant immune responses in the host and are implicated in patients with CRS. The majority of animal models described for CRS revalidates the pathophysiology of acute sinusitis, ostium occlusion, or foreign body associated infection.

Objectives

To evaluate an experimental model of eosinophilic CRS using prolonged exposure to bacterial toxins. The histological changes in rabbits exposed to S. aureus enterotoxin B (SEB), lipopolysaccharide (LPS), or lipoteichoic acid (LTA) were compared.

Methods

After induction with ovalbumin (OVA) sensitization with subcutaneous injection for 2 weeks, rabbits underwent surgery to insert an indwelling catheter into the maxillary sinus. The sinus was irrigated with OVA 3 times weekly for 2 weeks, followed by sinus irrigation with bacterial toxin (SEB: 1 µg/mL, LPS: 100 ng/mL, or LTA: 100 ng/mL) 3 times weekly for 4 weeks. The histological changes in the treated sinus were compared with control rabbits.

Results

Sinuses exposed to bacterial toxins (SEB, LPS, and LTA) produced significant mucosal thickening with infiltration of inflammatory cells, notably eosinophils. SEB was the only toxin that promoted a mixed pattern of inflammation, including eosinophilic and neutrophilic infiltration.

Conclusion

Our experimental model of eosinophilic CRS in rabbits produced significant mucosal thickening and inflammation in the sinuses exposed to bacterial toxins, with histological changes analogous to what is observed in patients with CRS with nasal polyps. This model may serve as a basis for future investigation of the pathogenesis of eosinophilic CRS in relation to bacterial toxins or as a model for testing new therapeutic modalities for this disease.

Preclinical therapeutic efficacy of the ciprofloxacin-eluting sinus stent for Pseudomonas aeruginosa sinusitis

BACKGROUND

The ciprofloxacin-coated sinus stent (CSS) has unique therapeutic potential to deliver antibiotics to the sinuses. The objective of this study is to evaluate the efficacy of the CSS stent in eliminating Pseudomonas aeruginosa infection in a rabbit model of sinusitis.

METHODS

A ciprofloxacin-eluting sinus stent was created by coating ciprofloxacin/Eudragit RS100 on biodegradable poly-D/L-lactic acid (2 mg). After analyzing in-vitro inhibition of P aeruginosa (PAO-1 strain) biofilm formation, a total of 8 stents (4 shams, 4 CSSs) were placed unilaterally in rabbit maxillary sinuses via dorsal sinusotomy after inducing infection for 1 week with PAO-1. Animals were assessed 2 weeks after stent insertion with nasal endoscopy, sinus culture, computed tomography (CT) scan, histopathology, and scanning electron microscopy (SEM).

RESULTS

PAO-1 biofilm formation was significantly reduced in vitro with exposure to the CSS (p < 0.0001). Insertion of the stent in PAO-1-infected rabbits for 2 weeks resulted in significant improvement in sinusitis according to endoscopy scoring (p < 0.0001) and CT scoring (p < 0.002). Histology and SEM revealed marked improvement in the structure of the mucosa and submucosa with no detection of biofilm structures in the CSS cohort.

CONCLUSION

Although this study had a small sample size, we identified robust therapeutic efficacy of the CSS by reducing bacterial load and biofilm formation of P aeruginosa in a preclinical model of sinusitis after placement for 2 weeks.

Sinus Microanatomy and Microbiota in a Rabbit Model of Rhinosinusitis

Background: Rabbits are useful for preclinical studies of sinusitis because of similar physiologic features to humans. The objective of this study is to develop a rabbit model of sinusitis that permits assessment of microanatomy and sampling for evaluating shifts in the sinus microbiota during the development of sinusitis and to test how the mucociliary clearance (MCC) defect might lead to dysbiosis and chronic rhinosinusitis (CRS).

Methods: Generation of CRS was accomplished with an insertion of a sterile sponge into the left middle meatus of New Zealand white rabbits (n = 9) for 2 weeks. After sponge removal, 4 rabbits were observed for another 10 weeks and evaluated for CRS using endoscopy, microCT, visualization of the functional micro-anatomy by micro-optical coherence tomography (μOCT), and histopathological analysis of the sinus mucosa. Samples were taken from the left middle meatus and submitted for microbiome analysis.

Results: CT demonstrated opacification of all left sinuses at 2 weeks in all rabbits (n = 9), which persisted in animals followed for another 12 weeks (n = 4). Histology at week 2 showed mostly neutrophils. On week 14, significant infiltration of plasma cells and lymphocytes was noted with increased submucosal glands compared to controls (p = 0.02). Functional microanatomy at 2 weeks showed diminished periciliary layer (PCL) depth (p < 0.0001) and mucus transport (p = 0.0044) compared to controls despite a thick mucus layer. By 12 weeks, the thickened mucus layer was resolved but PCL depletion persisted in addition to decreased ciliary beat frequency (CBF; p < 0.0001). The mucin fermenting microbes (Lactobacillales, Bacteroidales) dominated on week 2 and there was a significant shift to potential pathogens (e.g., Pseudomonas, Burkholderia) by week 14 compared to both controls and the acute phase (p < 0.05).

Conclusion: We anticipate this reproducible model will provide a means for identifying underlying mechanisms of airway-surface liquid (ASL) depletion and fundamental changes in sinus microbial communities that contribute to the development of CRS. The rabbit model of sinusitis exhibited diminished PCL depth with delayed mucus transport and significant alterations and shift in the sinus microbiome during the development of chronic inflammation.

Experimental maxillary sinus augmentation using a highly bioactive glass ceramic

Physicochemical characteristics of a biomaterial directly influence its biological behavior and fate. However, anatomical and physiological particularities of the recipient site also seem to contribute with this process. The present study aimed to evaluate bone healing of maxillary sinus augmentation using a novel bioactive glass ceramic in comparison with a bovine hydroxyapatite. Bilateral sinus augmentation was performed in adult male rabbits, divided into 4 groups according to the biomaterial used: BO-particulate bovine HA Bio-Oss(®) (BO), BO+G-particulate bovine HA + particulate autogenous bone graft (G), BS-particulate glass ceramic (180-212 μm) Biosilicate(®) (BS), and BS+G-particulate glass ceramic + G. After 45 and 90 days, animals were euthanized and the specimens prepared to be analyzed under light and polarized microscopy, immunohistochemistry, scanning electron microscopy (SEM), and micro-computed tomography (μCT). Results revealed different degradation pattern between both biomaterials, despite the association with bone graft. BS caused a more intense chronic inflammation with foreign body reaction, which led to a difficulty in bone formation. Besides this evidence, SEM and μCT confirmed direct contact between newly formed bone and biomaterial, along with osteopontin and osteocalcin immunolabeling. Bone matrix mineralization was late in BS group but became similar to BO at day 90. These results clearly indicate that further studies about Biosilicate(®) are necessary to identify the factors that resulted in an unfavorable healing response when used in maxillary sinus augmentation.

Evaluation of the ability of an experimental model to induce bacterial rhinosinusitis in rabbits

INTRODUCTION

For decades, animals have been used in sinonasal experimental models, and the practice has increased substantially in the last few years. This study aimed to assess the pathogenesis of infectious process and medication efficiency to treat rhinosinusitis.

OBJECTIVE

To evaluate the efficiency of the proposed experimental model to induce an acute bacterial sinonasal infectious process through histological analysis and sinus secretion cultures.

METHODS

This was an experimental study with 22 New Zealand rabbits, divided into: group A (six rabbits), group B (seven rabbits), group C (seven rabbits), and group D (control group with two rabbits). Rhinosinusitis was induced by the insertion of a synthetic sponge into the right nasal cavity of 20 animals (study groups), followed by the instillation of bacterial strains (50% Staphylococcus sp. and 50% Streptococcus sp.). The groups were euthanized within 10 days (group A), 17 days (group B), and 30 days (groups C and D).

RESULTS

All the rabbits of the study group developed acute bacterial rhinosinusitis, which was diagnosed through macroscopic evaluation, histological analysis, and sinus secretion culture.

CONCLUSION

The proposed model is technically simple to perform, it is similar to the rhinogenic model in human beings, and it is highly efficient to reproduce an acute bacterial sinus infection.

Assessing the maxillary sinus mucosa of rabbits in the presence of biodegradable implants

In an attempt to improve the quality of life of patients with vitreous humor disease, ophthalmologists began offering steroid-eluting biodegradable implants to their patients. These implants can be used as an alternative treatment for CRS and this is why this experimental study was carried out on rabbit maxillary sinuses.

Objective

This study aims to assess the histology of the mucosa of the maxillary sinuses of rabbits after the placement of a prednisolone-eluting biodegradable implant.

Method

Eighteen rabbits were randomly divided into two groups: group 1 - subjects had drug-eluting implants placed on their left maxillary sinuses; group 2 - subjects had non-drug-eluting implants placed on their left maxillary sinuses. The right maxillary sinuses served as the controls. After seven, 14, and 28 days three rabbits in each group were randomly picked to have their tissue inflammatory response assessed.

Results

Levels of mucosal inflammation were not significantly different between the groups with and without drug-eluting implants and the control group, or when the groups with drug-eluting implants and non-drug-eluting implants were compared.

Conclusion

Signs of toxicity or mucosal inflammation were not observed in the maxillary sinuses of rabbits given prednisolone-eluting implants or non-drug-eluting implants.