The contribution of inflammatory mediators to delayed secondary muscle damage

Van de Vyver, Mari (2013-03)

Thesis (PhD)--Stellenbosch University, 2013.

Thesis

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.

AFRIKAANSE OPSOMMING: Agtergrond: Die begrip van uiteenlopende individuele reaksie patrone, is belangrik in die identifisering van faktore asook meganismes betrokke in die ontwikkeling en resolusie van inflammasie. Die doel van hierdie navorsingsprojek was om die gevolge van oefening-geïnduseerde spierskade en inflammasie te ondersoek in menslike proefpersone. Metodiek: ‘n Totaal van 53 gesonde mans is tydens drie verskillende studies, gegroepeer in ’n kontrole (geen oefening) (n=13) en oefening geinduseerde spier skade (DHR) groep (n=40). Die uitleg van de studies was eenders (met min uitsonderings): Afdraende hardloop (12 x 5min hardloop sessies, 10% afdraende, 15km.h-1) met bloed monsters geneem voor, na, 2 ure, 4 ure (pre, post, 2h, 4h) en op dag 1, 2, 3, 4 en 7 (d1-7). Serum is ontleed vir die volgende: kreatien kinase aktiwiteit (CK), kortisol, sitokiene (TNFα, IL-1ra, IL-1β, IL-4, IL-6, IL-8, IL-10, sIL-6R), chemokien (G-CSF, MIP-1β) en adhesie molekuul (sICAM-1, sP-selectin) konsentrasies. Weefsel degradasie is vasgestel deur die teenwoordigheid van matriks metalo-protease-9 (MMP-9) en miëloperoksidase (MPO) in serum te meet. Differensiële witbloed sel (WBC) telling asook die teenwoordigheid van sekere differensiasie faktore (CD11b, CD163, CD68, CD88, CD34) op die sel oppervlak asook intrasellulêre MPO vlakke is bepaal deur gebruik te maak van vloeisitometrie. Die lokalisering van NFĸB in die selkerne van geïsoleerde bloed mononukleêre selle (PBMC) is bepaal deur fluoriserende mikroskopie. Spierbiopsies (vastus lateralis) geneem tydens rus (basislyn), na 4h, en op d1 en d2 is ontleed vir veseltipe, inflammatoriese en stresverwante faktore (STAT3, IĸBα, p38 MAPK), miogeniese faktore (myoD, myogenin), neutrofiel aktiwiteit (MPO) en aantal satelliet selle (Pax7). Resultate: Deelnemers in die DHR-groep is onderverdeel in twee groepe. Persone wat normaalweg herstel het is saam gegroepeer (DHR1) en diegene wat sekondêre skade ontwikkel het is saam gegroepeer (DHR2). CK aktiwiteit in serum het hoogtepunte bereik op d1 in beide subgroepe (DHR1: 1512 ± 413 u.L-1, DHR2: 1434 ± 202 u.L-1) en weer op d4 in die DHR2 groep (1110 ± 184 u.L-1). 'n Soortgelyke IL-6 en IL-10 reaksie is onmiddellik na oefening (in al die proefpersone) waargeneem. Addisionele IL-6 is vrygestel in die DHR2 subgroep en het ’n hoogtepunt bereik na 4h (10.3 ± 4.2 pg.mL-1), terwyl IL-10 reeds teruggekeer het na rustende waardes. IL-1ra (23.6 ± 8.8 pg.mL-1), CD68+ (5%) en CD163+ (3%) monosiete was aansienlik hoër in die DHR2 subgroep. Neutrofieltelling na 2h (DHR1: 8.6 ± 0.8 x109cells.L-1, DHR2: 11.4 ± 1.8 x109cells.L-1) het verband (p <0,02) gehou met CK-aktiwiteit op d4. In vergelyking met die DHR1 en kontrole groep was die lokalisering van NFĸB p65 in PBMC selkerne na 2h effens minder in die DHR2 subgroep. STAT3- en MPO-vlakke in die spiere was aansienlik hoër in die DHR2 subgroep as in die DHR1 subgroep na 4h en op d2 onderskeidelik. Die spierherstel proses was eenders vir alle individue wat aan die oefening deelgeneem het; 'n toename in Pax7+ Satelietselle (SC) is waargeneem na 4h (0.06 ± 0.01 Pax+ SC/spiervesel) en op d1 (0.07 ± 0.02 Pax+ SC/spiervesel). Gevolgtrekking: Gesonde jong mans kan verdeel word in diegene met 'n bevoegde en diegene met 'n minder doeltreffende vermoë om oefenings-geïnduseerde spierskade en die inflammatoriese reaksie te beheer. Die sitokien-reaksie, veral IL-6, blyk om 'n belangrike rolspeler in die ontwikkeling van sekondêre skeletspierskade te wees.

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