The effect of the nonselective TNF inhibitor etanercept and of the selective TNF inhibitor XPro1595 on lesioned supraspinatus muscle

The cytokine tumor necrosis factor (TNF), a major regulator of inflammatory responses, exists in both a membrane-bound form and a soluble form. We used the nonselective TNF inhibitor etanercept and the selective inhibitor XPro1595 and compared supraspinatus muscle cytokine levels, histology, and proteomic signatures in mice after supraspinatus tendon tear. The aim was to investigate the effect of anti-TNF treatment on the early inflammatory response in the muscle after tendon tear. In addition, the effect on body composition and bone mineral content was compared in naive mice after 2 months of treatment with either etanercept or XPro1595 using dual-energy X-ray absorptiometry (DEXA) and micro-CT. Inhibition of TNF did not significantly affect DEXA indexes of body composition nor bone microarchitecture, apart from increased structure model index and decreased bone surface density at 14 days, and bone surface to volume ratio at 2 months. Supraspinatus tendon tear caused extensive inflammatory changes in the supraspinatus muscle and initiated a regenerative response. However, TNF inhibition did not significantly affect these processes recorded as density in the lesioned supraspinatus muscle of macrophages and myogenin-positive nuclei. Although both inhibitors had an effect on mitochondrial proteins, particularly etanercept tended to modulate mitochondrial function, and eternacept also influenced NF-κB signaling. Modulation of the mitochondrial proteome and the influence on NF-κB signaling seen after etanercept treatment could correspond with its known effect on apoptosis.