Model for evaluating the effect of growth factors on the larynx

A systematic review of simulated laryngotracheal reconstruction animal models

OBJECTIVES

Review of the literature to identify practical, high-fidelity, commercially available animal models for simulation training and surgical skills maintenance in laryngotracheal reconstruction (LTR).

METHODS

A systematic review of PubMed and Embase databases was conducted independently by two authors, according to Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Search terms included "laryngotracheal reconstruction," "laryngotracheoplasty," "pig and larynx," "sheep and larynx," and "rabbit and larynx." Articles were then assessed, identifying model cost and availability, model validation, feasibility as a training tool, and verisimilitude to pediatric LTR.

RESULTS

In total, 79 articles were considered suitable for inclusion in the study, incorporating both in vitro and in vivo models. Models utilized included rabbit (n = 69), pig (n = 7), sheep (n = 1), and goat (n = 2). The rabbit model was similar in size to the neonate, but differences in laryngeal anatomy and cartilage texture made graft insertion difficult. The anatomy of the pig, sheep, and goat larynges more closely resembled the pediatric patient, allowing improved grafting, but corresponded more in size to that of an older child. Commercial availability of the pig and sheep was considered greatest, and was reflected in cost. None of the animal models identified in the literature have been validated as a simulation tool.

CONCLUSIONS

The rabbit, sheep and pig models seemed to demonstrate the greatest potential for use as advanced pediatric airway surgery simulation models, with the rabbit model being most utilized in the literature. However, as yet there have been no models formally validated as a simulation training tool. Laryngoscope, 129:235-243, 2019.

Posterior cricoid-graft mismatch in laryngotracheal reconstruction

INTRODUCTION/OBJECTIVE

In laryngotracheal reconstruction (LTR) with sutureless posterior cricoid grafting (PCG), the inset graft's thickness may not precisely approximate the anterior-posterior depth of the divided posterior cricoid plate. This case series highlights this phenomenon and describes the clinical profiles and airway characteristics of children with similar subglottic stenosis grades undergoing LTR with PCG with varying degrees of graft-cricoid mismatch.

METHODS

This is a case series with retrospective chart review of children who underwent LTR with PCG by a single surgeon at a tertiary care urban children's hospital from 2008 to 2014.

RESULTS

Twenty-one patients with twenty-two operations were identified. Varying degrees of graft-cricoid mismatch were present. Of the 22 operations, 15 were classified as grade I (flush), 5 grade II (<3 mm), and 2 grade III (>3 mm). Median preoperative grade of stenosis was III in all groups. Mean one month granulation grade was 1.84, compared to 1.92 in grade I, 1.6 in grade II mismatch, 2 in grade III mismatch, and 1.7 in any mismatch (p = 0.65). Mean follow up was 24 months.

CONCLUSION

Graft-cricoid mismatch may occur at variable degrees during laryngotracheal reconstruction utilizing sutureless posterior cricoid grafting. Our preliminary data suggest several millimeters of graft-cricoid mismatch can be tolerated without significantly affecting postoperative granulation formation or adding to postoperative morbidity.

Potential Role of Growth Factors and Extracellular Matrix in Wound Healing after Laryngotracheal Reconstruction

Laryngotracheal reconstruction (LTR) has been used for more than 20 years to treat infants and children with subglottic stenosis. Results after pediatric LTR have been satisfactory; however, approximately 10% of children have recurrent airway narrowing after LTR. The purpose of our study was to determine whether a correlation existed between specific growth factors and extracellular matrix in patients with adequate wound healing capability as compared with patients with poor wound healing capability. Histologic sections from 27 patients who underwent LTR were cut, and immunohistochemical staining was performed for transforming growth factor-β, platelet-derived growth factor, fibronectin, tenascin, transforming growth factor-α, and vascular endothelial growth factor. Results showed that patients with adequate wound healing capability had a positive correlation with vasculature fibronectin, vasculature tenascin, and stromal fibronectin. Patients with poor wound healing capability had a positive correlation with stromal vascular endothelial growth factor.

Local treatment of cricoid cartilage defects with rhBMP-2 induces growth plate–like morphology of chondrogenesis

Objective

The ultrastructural characteristics of new bone and cartilage, induced at the site of cricoid cartilage defects treated with rhBMP-2 in rabbits, were investigated.

Study Design and Setting

A cricoid defect model was used. Fifteen rabbits were randomly and equally divided into 3 groups. Four rabbits from each group were treated with rhBMP-2, while one rabbit from each group was used as control. The rabbits were killed 1, 2, or 4 weeks after surgery. The healing pattern of the laryngeal wound was evaluated by light and transmission electron microscopy.

Results

Mineralized collagen type I matrix, osteoblasts, and osteoclast-like cells were present as early as 1 week after surgery. Well-structured bone trabeculas and growth plate-like structures were present 4 weeks after surgery.

Conclusion

Intramembranous and endochondral osteogenesis take place at the site of cricoid cartilage defects treated with rhBMP-2. Progenitor cells of cricoid perichondrium form a growth plate-like structure similar to the epiphyseal growth plate.

Significance

This study reveals the pattern of BMP-2-induced repair of airway cartilage defects.

Effect of Vascular Endothelial Growth Factor on Laryngeal Wound Healing in Rabbits

OBJECTIVE: Study the effects of vascular endothelial growth factor (VEGF) on laryngeal wound healing in a rabbit model. STUDY DESIGN: Prospective, randomized, blinded.

METHODS: The anterior cricoid cartilage of 10 rabbits was split and a VEGF-soaked collagen sponge was sewn between the cut edges. In 10 control animals, the collagen sponge was soaked with phosphate-buffered saline solution. The larynx was harvested on day 10. The degree of epithelial closure, the degree of soft tissue closure, and the presence of inflammatory cells was graded.

RESULTS: There was complete epithelial closure in the control group. There was a slightly higher, but not statistically significant, grade of soft tissue closure in the experimental group. The experimental group had a lower but not statistically significant acute inflammatory response score.

CONCLUSIONS: The topical application of VEGF through an implanted collagen sponge to an anterior, subglottic incision in a rabbit has no significant effect on tracheal luminal epithelial closure, acute inflammatory response, or soft tissue repair at postsurgical day 10.

Effect of recombinant human BMP-2 on the repair of cricoid cartilage defects in young and adult rabbits: a comparative study

OBJECTIVE

The study evaluated the possible differences in the repair of cricoid cartilage defects treated with recombinant human BMP-2 in young and adult rabbits.

METHODS

A cricoid defect rabbit model was used. Thirty rabbits were randomly divided into eight groups. Two groups of young rabbits and two groups of adult rabbits were treated with rhBMP-2 delivered on an absorbable collagen sponge, while the other two groups of young rabbits and two groups of adult rabbits were used as controls. The rabbits were killed at 1 week or 4 weeks after surgery. A histomorphometric analysis and an evaluation of the expression of collagen types I, II, and X, and proliferating cell nuclear antigen as well as a study of distribution of calcified matrix, were performed.

RESULTS

rhBMP-2 induced a marked chondrogenesis in both experimental age groups. However, in young rabbits the newly formed cartilage appeared more elongate, and the length of perichondrium involved was greater. The host cricoid cartilage of adult rabbits was calcified in large areas and displayed a strong matrix expression of collagen type X as well as collagen type I in the perichondrium, compared to the cricoid of young rabbits. In spite of these differences no immunohistochemical differences were found in the newly formed cartilage of both age groups treated with rhBMP-2. The cricoid cartilage defect was filled with new bone at 4 weeks in both age groups treated with rhBMP-2. New bone tissue had a well-defined trabecular structure.

CONCLUSIONS

rhBMP-2 triggers appositional cartilage growth from the cricoid perichondrium of young rabbits more easily than from that of adult rabbits. The new bone induced by rhBMP-2 showed a similar immunohistochemical and morphological pattern in both age groups of rabbits.

Recombinant human bone morphogenetic protein-2 enhances experimental laryngotracheal reconstruction in rabbits

OBJECTIVE

Bone morphogenetic protein-2 offers potential benefits for cartilage regeneration. We investigated the effect of recombinant human bone morphogenetic protein-2 (rhBMP-2) on the regeneration of laryngeal cartilage and respiratory epithelium in a rabbit model.

MATERIAL AND METHODS

We used a cricoid defect rabbit model. Twenty-four rabbits were randomly divided into four equal groups. Two groups were treated with 5 microg of rhBMP-2 delivered on an absorbable collagen sponge and the other two groups were used as controls. One group of treated rabbits and one group of control rabbits were euthanized 1 week after surgery, while the others were euthanized 4 weeks after surgery. The healing pattern of the laryngeal wound was evaluated by means of histomorphometry.

RESULTS

Regeneration of both the epithelial layer and cartilage was significantly better in rabbits treated with rhBMP-2. Four weeks after surgery, the cricoid cartilage defect was completely repaired by new cartilage and new bone in rabbits treated with rhBMP-2. Furthermore, the lining respiratory epithelium healed more rapidly in treated rabbits.

CONCLUSION

rhBMP-2, delivered via an absorbable collagen sponge, induces complete regeneration and repair of rabbit cricoid cartilage defects. It also induces faster relining and regeneration of airway epithelium than in control rabbits.

Structural characteristics of repair tissue of cricoid cartilage defects treated with recombinant human bone morphogenetic protein-2

We examined the structural characteristics of repair tissue induced by recombinant human bone morphogenetic protein-2 in a rabbit model of laryngotracheal reconstruction. Twenty-four New Zealand White rabbits were randomly divided into four groups of six rabbits. Two groups were treated with recombinant human bone morphogenetic protein-2 delivered on an absorbable collagen sponge, while two groups were used as controls. Rabbits were euthanized at 1 and 4 weeks after surgery. The larynx was removed, fixed, and sectioned. The sections were stained with hematoxylin-eosin, safranine O/fast green, and immunostained with an antibody for tissue inhibitor of metalloproteinases-1. In rabbits treated with bone morphogenetic protein-2, the defects were filled with new cartilage and bone at 4 weeks after surgery. There were no discontinuities or gaps at the margins of the cartilage defects. Proteoglycans were synthesized in new cartilage in rabbits treated with bone morphogenetic protein-2, and were present 4 weeks after surgery. The general aspects of the vascular pattern and the pattern of tissue inhibitor of metalloproteinases-1 expression were similar in control and treated rabbits, both 1 week and 4 weeks after surgery. The repair tissue induced by recombinant human bone morphogenetic protein-2 consisted of new cartilage and bone perfectly integrated with host tissue at the site of the cricoid cartilage defects. This new cartilage was able to mature and produce proteoglycans.

Improved airway healing using transforming growth factor beta-3 In a rabbit model

Laryngeal wound healing is essential following laryngotracheal surgery. Patients with poor wound healing develop poor epithelial closure and increased granulation tissue which cause a stenosis of the repaired airway. Transforming growth factor-beta3 has been shown to enhance wound healing in cutaneous wounds, but has never been used in the airway. This study utilized a rabbit laryngeal wound-healing model that has been shown to be reproducible with limited morbidity. Thirty-four rabbits underwent a cricoid-split operation with collagen sponge insertion. All animals were classified randomly into three groups: local administration of placebo (Group G1, n = 13), 0.18 microg transforming growth factor-beta3 (Group G2, n = 11) and of 1.0 microg transforming growth factor-beta3 (Group G3, n = 10). All animals survived the postoperative period without respiratory distress. The airway was harvested six days after surgery and assessed by light microscopy. Histologic evidence for healing was subjectively graded by two blinded, independent investigators, and the results were statistically analyzed for significance. A significant improvement in the epithelial closure (p < 0.01) and subepithelial connective tissue closure (p < 0.005) was found in the 1.0 microg transforming growth factor-beta3 group (G3) compared with the placebo group (G1). Analysis of the 0.18 microg transforming growth factor-beta3 group (G2) did not reveal any significant differences compared with the placebo group (G1). These results suggest an application for transforming growth factor-beta3 in accelerating wound healing in the larynx.

Potential role of growth factors and extracellular matrix in wound healing after laryngotracheal reconstruction

Laryngotracheal reconstruction (LTR) has been used for more than 20 years to treat infants and children with subglottic stenosis. Results after pediatric LTR have been satisfactory; however, approximately 10% of children have recurrent airway narrowing after LTR. The purpose of our study was to determine whether a correlation existed between specific growth factors and extracellular matrix in patients with adequate wound healing capability as compared with patients with poor wound healing capability. Histologic sections from 27 patients who underwent LTR were cut, and immunohistochemical staining was performed for transforming growth factor-beta, platelet-derived growth factor, fibronectin, tenascin, transforming growth factor-alpha, and vascular endothelial growth factor. Results showed that patients with adequate wound healing capability had a positive correlation with vasculature fibronectin, vasculature tenascin, and stromal fibronectin. Patients with poor wound healing capability had a positive correlation with stromal vascular endothelial growth factor.