The function of nitric oxide in wound repair: Inhibition of inducible nitric oxide-synthase severely impairs wound reepithelialization

Recently, we demonstrated a large induction of inducible nitric oxide synth ase (iNOS) during cutaneous wound repair. In this study, we established an in vivo model in mice to investigate the role of NO during the wound healin g process. During excisional rep air, mice were treated with L-N-6-(1-imino ethyl)lysine (L-NIL), a selective inhibitor of iNOS enzymatic activity. Com pared with control mice, L-NIL-treated animals were characterized by a seve rely impaired reepithelialization process, as the hyperproliferative epithe lia at the wound edges appeared to be delayed and characterized by an atrop hied morphology, Immunohistochemical labeling for detection of proliferatin g cells (BrdU-, Ki67-staining) revealed a strong reduction in proliferating keratinocyte cell numbers during the process of reepithelialization after inhibition of iNOS activity during repair. Western blot analysis of total w ound lysates from PBS- and L-NIL-treated mice clearly demonstrated a reduct ion in proliferating cell nuclear antigen, representing a marker for cell p roliferation, in lysates isolated from L-NIL-treated mice. The dependency b etween keratinocyte proliferation and NO availability observed during wound repair in vivo is further supported by the observation that proliferation of the keratinocyte cell line (HaCaT) is stimulated by low concentrations o f NO-donors also in vitro. In summary, our data demonstrate that the presen ce of a functionally active iNOS is a crucial prerequisite for normal wound reepithelialization.