Photodynamic Therapy for Airway Stenosis in Rabbit Models

Point-of-care ultrasound-guided submucosal paclitaxel injection in tracheal stenosis model

Background and Objectives

Transcutaneous point-of-care ultrasound (POCUS) is a good tool to monitor the trachea in many clinical practices. The aim of our study is to verify the feasibility of POCUS-guided submucosal injection as a potential drug delivery method for the treatment of tracheal stenosis.

Materials and methods

The inner wall of the trachea was monitored via a bronchoscope during the POCUS-guided submucosal injection of methylene blue in fresh ex vivo porcine trachea to evaluate the distribution of methylene blue. The feasibility and eficacy of POCUS-guided submucosal injection were evaluated in a tracheal stenosis rabbit model. Animals were divided into sham group, tracheal stenosis group, and treatment group. Ten days after the scraping of the tracheal mucosa or sham operation, POCUS-guided submucosal injection of paclitaxel or saline was performed. Seven days after the submucosal injection, the trachea was assessed by cervical computed tomography (CT) scan and ultrasound.

Results

The distribution of methylene blue in trachea proved the technical feasibility of POCUS-guided submucosal injection. CT evaluation revealed that the tracheal stenosis index and the degree of tracheal stenosis increased significantly in the stenosis group, while POCUS-guided submucosal injection of paclitaxel partially reversed the tracheal stenosis. POCUS-guided submucosal injection of paclitaxel also decreased the lamina propria thickness and collagen deposition in the stenosed trachea.

Conclusion

POCUS-guided submucosal paclitaxel injection alleviated tracheal stenosis induced by scraping of the tracheal mucosa. POCUS-guided submucosal injection might be a potential method for the treatment of tracheal stenosis.

Photomodulative effects of low-level laser therapy on tracheal fenestration developed in in vivo model

The effect of low-level laser therapy (LLLT) on variable mucosal lesions in the upper aerodigestive tract has been reported. However, the effect of LLLT on tracheostomy sites or tracheal fenestration is rarely reported. In this study, we evaluate the effect of LLLT performed using 635 nm laser light based on a cylindrical diffuser and an animal model with tracheal fenestration. An animal model of tracheal fenestration is developed by suturing the trachea to the skin after performing a vertical tracheostomy from the second to the fifth tracheal ring of Wistar rats (male, body weight 200-250 g). LLLT (spot size: 2 cm²) is conducted once daily for five days using a handheld cylindrical device. Twenty-four rats are randomly assigned to a no-therapy or LLLT group with an energy density of 20 J/cm². Histological analysis is performed at 7 and 14 days after tracheal fenestration. Irradiation at the tracheal fenestration site with an energy density of 20 J/cm² improves the wound healing, as shown at 2 weeks after tracheostomy. Histological analysis shows significantly decreased acute inflammation and granulation tissue, as well as better cartilage regeneration and less tracheal wall thickening. Therefore, LLLT demonstrates therapeutic potential for preventing tracheal stenosis and granuloma after tracheostomy.

Establishing a novel model of malignant airway stenosis in rabbit

Background

Malignant central airway stenosis is a life-threatening condition. However, treatment of malignant airway stenosis remains challenging. There is currently a severe lack of an excellent animal model of malignant airway stenosis to facilitate treatment approaches. This is the first study to establish a rabbit model of malignant airway stenosis for bronchoscopic interventional studies.

Materials and methods

New Zealand White rabbits were used in this study, randomly divided into group A (18 rabbits) and group B (6 rabbits). A VX2 fragment suspension was injected into the submucosal layer of rabbits’ airway by bronchoscopy. Bronchoscopic examinations were performed once a week after VX2 tumor implantation to observe tumor growth and the degree of airway stenosis. Randomly, three rabbits were generally dissected after a weekly bronchoscopic examination in group A. The rabbits that reached grade III airway stenosis underwent stent implantation in group B.

Results

A total of 24 rabbits were successfully implanted with the VX2 fragment suspension in the airway without significant adverse events, and the success rate of the tumor growth was 100%. The degree of airway stenosis reaching grade III took 2 to 3 weeks after implantation of the VX2 tumor. The median survival time of rabbit models without stent implantation and rabbits with stent implantation was 32.5 and 32.0 days, respectively.

Conclusions

The implanting method is safe and effective for the establishment of a rabbit model of malignant airway stenosis. When the tumor grows to 2 to 3 weeks, the rabbit model is available for stent implantation. We recommend the models for more preclinical animal studies on bronchoscopic interventional treatments.

Evaluation of Tracheal Stenosis in Rabbits Using Multispectral Optoacoustic Tomography

Objective: Photoacoustic tomography (PAT) and multispectral optoacoustic tomography (MSOT) are evolving technologies that are capable of delivering real-time, high-resolution images of tissues. The purpose of this study was to evaluate the feasibility of using PAT and MSOT for detecting histology in a rabbit tracheal stenosis model.
 Method: A total of 12 rabbits (9 stenosis and three control) were randomly divided into four groups (A, B, C and D). Each group consisted of three rabbits, which were staged at the first, fourth, and eighth weeks of stenosis progression, respectively. PAT/MSOT images and corresponding histology from these experimental animals were compared, for analyzing the morphologic features and quantitative tracheal measurements in different tracheal stenosis stage. Result: Both the PAT images and corresponding histology indicated the most severe degree of stenosis in group C. MSOT images indicated notable differences in tracheal contents of group B and D. Conclusion: This study suggests that PAT/MSOT are potentially valuable non-invasive modality which are capable of evaluating tracheal structure and function in vivo.

Photodynamic therapy using intra-articular Photofrin for murine MRSA arthritis: biphasic light dose response for neutrophil-mediated antibacterial effect

BACKGROUND AND OBJECTIVE

Bacterial arthritis does not respond well to antibiotics and moreover multidrug resistance is spreading. We previously tested photodynamic therapy (PDT) mediated by systemic Photofrin® in a mouse model of methicillin-resistant Staphylococcus aureus (MRSA) arthritis, but found that neutrophils were killed by PDT and therefore the infection was potentiated.

STUDY DESIGN/MATERIALS AND METHODS

The present study used an intra-articular injection of Photofrin® and optimized the light dosimetry in order to maximize bacterial killing and minimize killing of host neutrophils. MRSA (5 × 10(7)  CFU) was injected into the mouse knee followed 3 days later by 1 µg of Photofrin® and 635-nm diode laser illumination with a range of fluences within 5 minutes. Synovial fluid was sampled 6 hours or 1-3, 5, and 7 days after PDT to determine MRSA colony-forming units (CFU), neutrophil numbers, and levels of cytokines.

RESULTS

A biphasic light dose response was observed with the greatest reduction of MRSA CFU seen with a fluence of 20 J cm(-2), whereas lower antibacterial efficacy was observed with fluences that were either lower or higher. Consistent with these results, a significantly higher concentration of macrophage inflammatory protein-2, a CXC chemokine, and greater accumulation of neutrophils were seen in the infected knee joint after PDT with a fluence of 20 J cm(-2) compared to fluences of 5 or 70 J cm(-2).

CONCLUSION

PDT for murine MRSA arthritis requires appropriate light dosimetry to simultaneously maximize bacterial killing and neutrophil accumulation into the infected site, while too little light does not kill sufficient bacteria and too much light kills neutrophils and damages host tissue as well as bacteria and allows bacteria to grow unimpeded by host defense.

Influence of intra-articular neutrophils on the effects of photodynamic therapy for murine MRSA arthritis

Although there have been some reports about the cytotoxic effects of photodynamic therapy (PDT) on multidrug-resistant bacteria, there have been few reports in which favorable results of PDT on a local infection site are described. This study aimed to verify the hypothesis that the low efficacy of PDT on a local infection site is due to the cytotoxic effect of PDT on leukocytes. PDT using Photofrin exerted significant cytotoxicity for cultured methicillin-resistant Staphylococcus aureus (MRSA). Nevertheless, this therapeutic modality was not effective for a murine MRSA arthritis model. Approximately 30% of intra-articular leukocytes, mainly neutrophils, died immediately after PDT, and a further decrease in the number of intra-articular leukocytes and atrophy of the synovial tissue were seen 24 h after PDT. Isolated peripheral neutrophils showed significant affinity for Photofrin and showed significant morphological damage, resulting in cell death, when they were subject to PDT using Photofrin. These results indicate that intra-articular neutrophils have an influence on the effects of PDT for MRSA arthritis.

Amelioration of airway stenosis in rabbit models by photodynamic therapy with talaporfin sodium (NPe6)

It is difficult to treat patients with acquired airway stenosis, and the quality of life of such patients is therefore lowered. We have suggested the application of photodynamic therapy (PDT) as a new treatment for airway stenosis and have determined the efficacy of PDT in animal disease models using a second-generation photosensitizer with reduced photosensitivity. An airway stenosis rabbit model induced by scraping of the tracheal mucosa was administered NPe6 (5 mg kg(-1)), and the stenotic lesion was irradiated with 670 nm light emitted from a cylindrical diffuser tip at 60 J cm(-2) under bronchoscopic monitoring. PDT using NPe6 improved airway stenosis (P = 0.043) and respiratory stridor. A significant prolongation of survival time was seen in the PDT-treated animals compared to that in the untreated animals (P = 0.025) and 44% of the treated animals achieved long-term survival (>60 days). In conclusion, PDT using NPe6 is effective for improvement in airway stenosis.