Abstract: BACKGROUND: Mitochondrial reactive oxygen bursts have been shown to play a key role in skeletal muscle ischemia-reperfusion injury. 3-Nitro-N-methylsalicylamide (3-NNMS) can effectively reduce the electron transport rate and has a potential protective effect on limb ischemia-reperfusion injury, but there is no clear research and clinical application.
OBJECTIVE: To investigate the protective effect of 3-NNMS on the skeletal muscle after limb ischemia-reperfusion injury in rats and its mechanism. 
METHODS: Forty healthy 8-week-old Sprague-Dawley rats were randomly divided into control group, 0, 25 and 125 μg/mL 3-NNMS groups, with 10 rats in each group. Animal models of limb ischemia-reperfusion injury were prepared in the latter three groups. 3-NNMS was injected into the injury site 30 minutes before reperfusion. The animals were sacrificed 2 hours after reperfusion. Blood from the apical part of the heart, and the tissue of the rectus femoris muscle of the right lower limb were taken for testing. The pathological morphology of the rectus femoris muscle was detected by hematoxylin-eosin staining. Serum levels of creatine kinase found in the skeletal muscle (CK-MM), lactate dehydrogenase, and myeloperoxidase were detected using ELISA; the levels of nuclear factor κB, tumor necrosis factor α, interleukin 1β, cyclooxygenase 2, malondialdehyde, reactive oxygen species, superoxide dismutase, catalase and glutathione peroxidase in the rectus femoris muscle were measured; and adenosine triphosphate (ATP) level, ATPase activity, and mitochondrial respiratory control rate were tested.
RESULTS AND CONCLUSION: Compared with the control group, the model rats with ischemia-reperfusion injury had increased serum levels of CK-MM, lactate dehydrogenase, and myeloperoxidase, increased levels of nuclear factor κB, tumor necrosis factor α, interleukin 1β, cyclooxygenase 2, malondialdehyde and reactive oxygen species in the rectus femoris muscle, decreased levels of catalase and glutathione peroxidase in the rectus femoris muscle, and reduced ATPase activity and mitochondrial respiratory control rate. Moreover, cell morphology was irregular, inflammatory cell infiltration was obvious, and the cells were swollen in rats after ischemia-reperfusion injury. Compared with the 0 μg/mL group, the serum CK-MM and lactate dehydrogenase levels decreased, the levels of nuclear factor κB and cyclooxygenase 2 in the rectus femoris muscle decreased, reactive oxygen species level decreased, and superoxide dismutase activity increased in the 25 μg/mL group; cell morphology was more regular, inflammatory cell infiltration was lighter, and cell swelling was alleviated. Compared with the 0 μg/mL group, the 125 μg/mL group had a reduction in the serum levels of CK-MM, lactate dehydrogenase, and myeloperoxidase and the levels of nuclear factor κB, tumor necrosis factor α, cyclooxygenase 2, malondialdehyde and reactive oxygen species in the rectus femoris muscle, as well as an increase in the levels of superoxide dismutase and glutathione peroxidase in the rectus femoris muscle, and mitochondrial respiratory control rate. Moreover, the cells were arranged neatly, the outline was clear and complete, and the inflammatory cell infiltration was light. To conclude, 3-NNMS can alleviate the functional impairment of the skeletal muscle caused by limb ischemia-reperfusion, and its mechanism of action may be through improving mitochondrial function, reducing reactive oxygen species production, decreasing oxidative stress and inflammatory response, and thus reducing tissue damage and repairing skeletal muscle function.

Key words: 3-NNMS, limb ischemia-reperfusion, skeletal muscle, mitochondria, oxidative stress, inflammatory factor