In Vivo TGF-beta 3 expression during wound healing in irradiated tissue. An experimental study.

BACKGROUND

Wound-healing disorders frequently present a clinical problem in patients with squamous epithelial carcinomas of the head and neck region after surgical interventions such as grafts of free flaps in preirradiated graft bed tissues. Here, inflammatory changes and the expression of cytokines can lead to delayed healing and to the induction of fibrosis. The isoforms of the transforming growth factor beta (TGF-beta(1-3)) play a central role in this process. While it was possible to experimentally show a fibrosis-inducing activity for TGF-beta(1) and TGF-beta(2), a fibrosis-reducing and radioprotective effect has been described for TGF-beta(3) on epithelial cells and fibroblasts. The influence of irradiation and tissue grafting on the TGF-beta(3) expression, however, remains uncertain. The objective of the in vivo study was therefore to analyze the expression profile of TGF-beta(3) in the graft bed and in the transition area between the graft and the graft bed after irradiation and/or after surgery.

MATERIAL AND METHODS

A total of 48 Wistar rats (male, weight 300-500 g) were used in the study. A free myocutaneous gracilis flap was transplanted in 30 rats: group 1 (n = 18 rats) no transplantation, only irradiation (3 x 10 Gy); group 2 (n = 14 rats) transplantation without preoperative irradiation; group 3 (n = 16 rats) transplantation following preoperative irradiation (3 x 10 Gy). The interval between radiotherapy and grafting was 4 weeks. Tissue samples were taken perioperatively and postoperatively after 3, 4, 7, 11, 14, 28, and 30 days from the transition area between the graft and the graft bed and from the graft bed itself. The TGF-beta(3) expression was analyzed immunohistochemically (labeling index) both qualitatively and quantitatively and checked for statistical differences between the groups (p < 0.05).

RESULTS

The success rate for graft healing was 75% in the group irradiated with 30 Gy, and 86% in the nonirradiated group. The rats that were irradiated but not operated on showed significantly (p = 0.04) reduced TGF-beta(3) expression in the graft bed immediately after the end of the irradiation. Whereas only minor differences in TGF-beta(3) expression were observed postoperatively in the graft bed and in the transition area between the graft and the graft bed in the group where a graft was carried out without preirradiation, the group that was preirradiated with subsequent grafting showed a significantly reduced expression in the bed (p = 0.018).

CONCLUSION

After irradiation, it was possible to measure reduced TGF-beta(3) expression in the irradiated graft bed. The exogenous application of TGF-beta(3) could therefore present a new therapeutic approach for improving wound healing through radioprotection of nontransformed epithelial cells and fibroblasts after preoperative radiotherapy and surgery.