The contribution of inflammatory mediators to delayed secondary muscle damage

[摘要] ENGLISH ABSTRACT: Background: Understanding the contribution of divergent individual response patterns remains a key objective in identifying mechanisms of inflammation and potential factors limiting the resolution of inflammation. The purpose of this research project was to investigate downstream effects of inflammation following exercise-induced muscle damage in human subjects.Methods: For three different studies, a total of 53 untrained healthy male participants were recruited and divided into a non-exercising control (n=13) and exercise-induced muscle damage groups (n=40). The study design for the three studies was the same (with few exceptions): Downhill running (DHR) (12 x 5min bouts, 10% decline, 15 km.h-1) with blood samples taken pre, post, after 2 and 4 hours post-exercise (2h, 4h) and on days 1, 2, 3, 4 and 7 (d1-d7). Serum was analysed for creatine kinase activity (CK), myoglobin (Mb), cortisol, cytokine (TNFα, IL-1ra, IL-1β, IL-4, IL-6, IL-8, IL-10, sIL-6R), chemokine (G-CSF, MIP-1β) and adhesion factor (sICAM-1, sP-selectin) concentrations. Tissue degradation was assessed by serum matrix metalloprotease (MMP-9) and myeloperoxidase (MPO) content. White blood cell differential count was determined and the surface expression of various cluster of differentiation factors (CD11b, CD163, CD68, CD88, CD34) as well as intracellular MPO were assessed in whole bood using flow cytometry. Nuclear localization of the inflammatory mediator NFĸB in isolated perhipheral blood mononuclear cells (PBMCs) was determined using immunofluorescence microscopy. Muscle biopsies (vastus lateralis) taken at baseline, 4h, d1 and d2 were analysed for fibre type, inflammatory and stress-induced pathways (STAT3, IĸBα, p38MAPK), myogenic factors (MyoD, myogenin), neutrophil activity (MPO) and satellite cell number (Pax7).Results: Participants in the DHR group were subdivided into those with a normal recovery (DHR1) and those who developed secondary damage (DHR2). CK peaked on d1 in both subgroups (DHR1: 1512 ± 413 u.L-1, DHR2: 1434 ± 202 u.L-1) and again on d4 only in the DHR2 group (1110 ± 184 u.L-1). A similar IL-6 and IL-10 response was evident immediately post DHR in all individuals. Additional IL-6 was released in the DHR2 subgroup peaking at 4h (10.3 ± 4.2 pg.mL-1) whereas IL-10 had returned to baseline. IL-1ra (23.6 ± 8.8 pg.mL-1), CD68+ (5%) and CD163+ (3%) monocytes were significantly higher in the DHR2 subgroup. Neutrophil count at 2h (DHR1: 8.6 ± 0.8 x109 cells.L-1, DHR2: 11.4 ± 1.8 x109 cells.L-1) was significantly (p<0.02) correlated to CK activity on d4. PBMC NFĸB p65 nuclear localization was slightly less at 2h in the DHR2 compared to the DHR1 and control groups. Intramuscular STAT3 signalling and MPO were significantly higher in the DHR2 compared to the DHR1 subgroup at 4h and d2 respectively. The progenitor cell response was similar for all DHR individuals with an increase in Pax7+ SC observed at 4h (0.06 ± 0.01 Pax+ SCs/fibre) and d1 (0.07 ± 0.02 Pax+ SCs/fibre).Conclusion: Healthy young men can be divided into those with a adequate and those with a less efficient capacity to control the post damage inflammatory response. The early cytokine response, especially IL-6, seems to be a key role player in the cascade of events leading to late secondary skeletal muscle damage.

[发布机构] Stellenbosch University