Tacrolimus impairs wound healing : A possible role of decreased nitric oxide synthesis

Background. The effect of the immunosuppressant tacrolimus on wound healing is not known. Tacrolimus has been shown to decrease nitric oxide synthesis. The systemic inhibition of wound nitric oxide synthesis leads to impaired healing. Methods. We studied the effect of systemic tacrolimus treatment on wound-breaking strength and collagen deposition 10 days after wounding in rats and to correlate the outcome of healing with wound nitric oxide synthesis. Beginning at the day of wounding, rats were treated once daily by intraperitoneal injections with 0.5, 1.0, or 2.0 mg tacrolimus/kg body weight. Nitrite and nitrate were measured in wound fluid as an index of wound nitric oxide synthesis. Expression of inducible nitric oxide synthase in the wound was investigated by immunohistochemistry. Splenic lymphocytes were tested for proliferative activity. Tacrolimus levels in blood and wound fluid were measured by enzyme-linked immunosorbent assay. Results. Systemic tacrolimus treatment was well tolerated by all rats. Tacrolimus accumulated in wound fluid. Tacrolimus levels in wound fluid were found to be approximately 10-fold higher than blood levels (P<0.001). Tacrolimus (2.0 mg/kg/day) reduced woundbreaking strength (P<0.01) and collagen deposition (P<0.05). This was paralleled by decreased wound nitrite 1 nitrate levels (P<0.001) and wound-inducible nitric oxide synthase expression. Splenic lymphocyte proliferative activity was significantly decreased by 1.0 and 2.0 mg tacrolimus/kg body weight/day (P<0.05), indicating that the tacrolimus doses used were immunosuppressive. Conclusion. Our data show for the first time that tacrolimus impairs wound healing, and this is reflected by diminished wound nitric oxide synthesis. The integrity of wound immune function is critical to normal wound healing. Cellular and acellular factors interact in a complex spatial and temporal composition to facilitate repair. Inflammatory cells and soluble mediators, such as cytokines or nitric oxide (NO*), are known to mediate repair mechanisms. Nitric oxide, a short-lived radical and biological mediator, has been shown to be synthesized in wounds (1, 2). Both wound-derived inflammatory cells and fibroblasts have been demonstrated to express the inducible form of nitric oxide synthase (iNOS) (3). The in vivo inhibition of wound NO synthesis has been shown to decrease wound mechanical strength and new collagen deposition (2, 4). It seems that nitric oxide is an autocrine and paracrine regulator of wound fibroblast synthetic activity (3). The immunosuppressant tacrolimus (TA), used in solid organ transplantation, decreases NO synthesis (5, 6). Immunosuppressive drugs, such as steroids and cyclosporine, impair wound healing (7, 8). The effect of tacrolimus on healing, however, is not known. Therefore, we studied the effect of systemic treatment with tacrolimus on standard parameters of dermal wound healing in rats and to correlate the outcome of healing with wound NO synthesis.