Ischaemia-reperfusion modulates inflammation and fibrosis of skeletal muscle after contusion injury.

Regeneration of skeletal muscle following injury is dependent on numerous factors including age, the inflammatory response, revascularization, gene expression of myogenic and growth factors and the activation and proliferation of endogenous progenitor cells. It is our hypothesis that oxidative stress preceding a contusion injury to muscle modulates the inflammatory response to inhibit muscle regeneration and enhance fibrotic scar formation. Male F344/BN rats were assigned to one of four groups. Group 1: uinjured control; Group 2: ischaemic occlusion of femoral vessels for 2 h followed by reperfusion (I-R); Group 3: contusion injury of the tibialis anterior (TA); Group 4: I-R, then contusion injury. The acute inflammatory response (8 h, 3 days) was determined by expression of the chemokine CINC-1, TGF-beta1, IFN-gamma and markers of neutrophil (myeloperoxidase) and macrophage (CD68) activity and recruitment. Acute oxidative stress caused by I-R and/or contusion, was determined by measuring GP91(phox) and lipid peroxidation. Muscle recovery (21 days) was assessed by examining the fibrosis after I-R and contusion injuries to the TA with Sirius Red staining and quantification of collagen I expression. Consistent with our hypothesis, I-R preceding contusion increased all markers of the acute inflammatory response and oxidative stress after injury and elevated the expression of collagen. We conclude that ischaemia-induced oxidative stress exacerbated the inflammatory response and enhanced fibrotic scar tissue formation after injury. This response may be attributable to increased levels of TGF-beta1 and diminished expression of IFN-gamma in the ischaemic contused muscle.