Abstract
Cryopreservation has an immunomodulating effect on tracheal tissue as a result of class II antigen depletion due to epithelium exfoliation. However, not all epithelium is detached. We evaluated the role of apoptosis in the remaining epithelium of 30 cryopreserved tracheal grafts. Caspase-3 immunoreactivity of tracheal epithelium was studied in canine tracheal segments cryopreserved with F12K medium, with or without subsequent storage in liquid nitrogen at -196°C for 15 days. Loss of structural integrity of tracheal mixed glands was observed in all cryopreserved tracheal segments. Caspase-3 immunoreactivity in tracheal mucosa and in mixed glands was significantly decreased, in contrast to the control group and to cryopreserved tracheal segments in which it remained high, due to the effect of storage in liquid nitrogen (P < 0.05, ANOVA and Tukey test). We conclude that apoptosis can be triggered in epithelial cells during tracheal graft harvesting even prior to cryopreservation, and although the epithelial caspase-3 immunoreactivity is reduced in tracheal cryopreservation, this could be explained by increased cell death. Apoptosis cannot be stopped during tracheal cryopreservation.
Highlights
To date, there are no definitive clinical surgical strategies to repair tracheal defects longer than 7 cm, despite the fact that experimental tracheal transplants and synthetic or biological prostheses have been used to repair lesions [1,2,3,4,5].Different experimental reconstruction models have been prepared with cryopreserved tracheal grafts frozen in cellular culture media [6]
Based on freezing temperature and liquid nitrogen storage, cryopreserved tracheal graft protocols can be divided into two types: a) tracheal grafts frozen at -60° to -140°C and stored in liquid nitrogen until their use in surgical repair [7,8,9,10,11,12,13,14,15,16,17,18,19,20], and b) tracheal grafts cryopreserved within a more homogeneous range of temperature (-80°/-85°C), without liquid nitrogen storage [3,21,22,23,24]
Thirty 5-ring long tracheal segments were obtained from the tracheas of 4 unrelated mongrel dogs, for a total of 90 tracheal rings
Summary
Different experimental reconstruction models have been prepared with cryopreserved tracheal grafts frozen in cellular culture media [6]. The results obtained for experimental tracheal reconstruction with cryopreserved grafts are contradictory, and this material has not been considered for clinical application. Most investigators agree that cryopreservation has an immunomodulating effect on tracheal allografts since it decreases antigenicity (5-7,1214,25-28). This is attributed to the depletion of class II leukocyte antigen expression due to the exfoliation of tracheal epithelium produced during the freezing and defrosting process [3,5,6,11,28,29]
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