Differential expression of inflammatory mediators in radiation-impaired wound healing.
BACKGROUND
Radiation impairs healing, although the underlying mechanisms are not clearly defined. Normal healing requires a fine balance of promoting and inhibiting factors. We hypothesize that there may be a down-regulation of promoting factors (nitric oxide) and, in turn, an up-regulation of healing inhibiting factors (TNF-alpha and IFN-gamma) in the wound after radiation.


METHODS
Groups of 10 rats were irradiated using single dose 12 or 24 Gy electron radiation at the dorsal skin. Control rats were sham-irradiated. On Day 5 a skin incision in the irradiated area was performed and polyvinyl alcohol sponges were inserted subcutaneously. Rats were sacrificed 10 days later to determine the wound-breaking strength and reparative collagen deposition. Nitrite and nitrate (index of NO synthesis), TNF-alpha, and IFN-gamma were measured within the wound fluid. Expression of the inducible NO-synthase (iNOS) was investigated by immunohistochemistry. Wound-derived fibroblasts were tested in vitro for NO and collagen synthesis.


RESULTS
Irradiation significantly reduced wound collagen deposition and wound-breaking strength (P < 0.05). Impaired healing was reflected in diminished wound NO synthesis and iNOS expression (P < 0.01). TNF-alpha and IFN-gamma were increased in irradiated wounds (P < 0.05). Ex vivo, NO synthesis and collagen deposition by fibroblasts from irradiated rats were decreased (P < 0.01). In vitro irradiation of fibroblasts from nonirradiated rats decreased both NO and collagen production (P < 0.01).


CONCLUSIONS
Radiation-impaired healing is reflected in an imbalance of promoting and inhibiting factors, leading to increased levels of TNF-alpha and IFN-gamma and decreased NO expression in the wound.
Schäffer
Michael
M
Department of Surgery, University of Tübingen, Germany. michael.schaeffer@med.uni-tuebingen.de
Weimer
Wiebke
W
Wider
Susanne
S
Stülten
Christina
C
Bongartz
Martina
M
Budach
Wilfried
W
Becker
Horst-Dieter
HD
D000818:Animals; D003094:Collagen / Q000378:metabolism; D005347:Fibroblasts / Q000378:metabolism / Q000528:radiation effects; D018836:Inflammation Mediators / Q000378:metabolism*; D007371:Interferon-gamma / Q000378:metabolism; D008297:Male; D009569:Nitric Oxide / Q000096:biosynthesis; D019001:Nitric Oxide Synthase / Q000378:metabolism; D052247:Nitric Oxide Synthase Type II; D051381:Rats; D017207:Rats, Sprague-Dawley; D012867:Skin / Q000293:injuries; D013718:Tensile Strength; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism; D014945:Wound Healing / Q000502:physiology* / Q000528:radiation effects*; D014950:Wounds, Penetrating / Q000378:metabolism / Q000503:physiopathology
D018836:Inflammation Mediators; D014409:Tumor Necrosis Factor-alpha; D009569:Nitric Oxide; D007371:Interferon-gamma; D003094:Collagen; D019001:Nitric Oxide Synthase; D052247:Nitric Oxide Synthase Type II; C496318:Nos2 protein, rat