The effect of exercise-induced hypoxemia on blood redox status in well-trained rowers

Exercise-induced arterial hypoxemia (EIAH), characterized by decline in arterial oxyhemoglobin saturation (SaO(2)), is a common phenomenon in endurance athletes. Acute intensive exercise is associated with the generation of reactive species that may result in redox status disturbances and oxidation of cell macromolecules. The purpose of the present study was to investigate whether EIAH augments oxidative stress as determined in blood plasma and erythrocytes in well-trained male rowers after a 2,000-m rowing ergometer race. Initially, athletes were assigned into either the normoxemic (n = 9, SaO(2) >92%, [Formula: see text]: 62.0 ± 1.9 ml kg(-1) min(-1)) or hypoxemic (n = 12, SaO(2) <92%, [Formula: see text]: 60.5 ± 2.2 ml kg(-1 )min(-1), mean ± SEM) group, following an incremental [Formula: see text] test on a wind resistance braked rowing ergometer. On a separate day the rowers performed a 2,000-m all-out effort on the same rowing ergometer. Following an overnight fast, blood samples were drawn from an antecubital vein before and immediately after the termination of the 2,000-m all-out effort and analyzed for selective oxidative stress markers. In both the normoxemic (SaO(2): 94.1 ± 0.9%) and hypoxemic (SaO(2): 88.6 ± 2.4%) rowers similar and significant exercise increase in serum thiobarbituric acid-reactive substances, protein carbonyls, catalase and total antioxidant capacity concentration were observed post-2,000 m all-out effort. Exercise significantly increased the oxidized glutathione concentration and decreased the ratio of reduced (GSH)-to-oxidized (GSSG) glutathione in the normoxemic group only, whereas the reduced form of glutathione remained unaffected in either groups. The increased oxidation of GSH to GSSG in erythrocytes of normoxemic individuals suggest that erythrocyte redox status may be affected by the oxygen saturation degree of hemoglobin. Our findings indicate that exercise-induced hypoxemia did not further affect the increased blood oxidative damage of lipids and proteins observed after a 2,000-m rowing ergometer race in highly-trained male rowers. The present data do not support any potential link between exercise-induced hypoxemia, oxidative stress increase and exercise performance.     

Student Award for Outstanding Research Winner in the Ph.D. Category for the 9th World Biomaterials Congress, Chengdu, China, June 1-5, 2012: The interplay of bone-like extracellular matrix and TNF-α signaling on in vitro osteogenic differentiation of mesenchymal stem cells

As an initial step in the development of a bone tissue engineering strategy to rationally control inflammation, we investigated the interplay of bone-like extracellular matrix (ECM) and varying doses of the inflammatory cytokine tumor necrosis factor alpha (TNF-α) on osteogenically differentiating mesenchymal stem cells (MSCs) cultured in vitro on 3D poly(ε-caprolactone) (PCL) microfiber scaffolds containing pregenerated bone-like ECM. To generate the ECM, PCL scaffolds were seeded with MSCs and cultured in medium containing the typically required osteogenic supplement dexamethasone. However, since dexamethasone antagonizes TNF-α, the interplay of ECM and TNF-α was investigated by culturing na?ve MSCs on the decellularized scaffolds in the absence of dexamethasone. MSCs cultured on ECM-coated scaffolds continued to deposit mineralized matrix, a late stage marker of osteogenic differentiation. Mineralized matrix deposition was not adversely affected by exposure to TNF-α for 4-8 days, but was significantly reduced after continuous exposure to TNF-α over 16 days, which simulates the in vivo response, where brief TNF-α signaling stimulates bone regeneration, while prolonged exposure has damaging effects. This underscores the exciting potential of PCL/ECM constructs as a more clinically realistic in vitro culture model to facilitate the design of new bone tissue engineering strategies that rationally control inflammation to promote regeneration.     

Introduction of enzymatically degradable poly(trimethylene carbonate) microspheres into an injectable calcium phosphate cement

Poly(trimethylene carbonate) (PTMC) is an enzymatically degradable polyester with rubber-like properties. Introduction of this polymer into an injectable calcium phosphate bone cement can therefore be used to introduce macroporosity into the cement for tissue engineering purposes as well as to improve mechanical properties. Aim of this study was to investigate calcium phosphate cements with incorporated PTMC microspheres (PTMC CPCs) on their physical/mechanical properties and in vitro degradation characteristics. Therefore, composites were tested on setting time and mechanical strength as well as subjected to phosphate buffered saline (PBS) and enzyme containing medium. PTMC CPCs (12.5 and 25 wt%) with molecular weights of 52.7 kg mol(-1) and 176.2 kg mol(-1) were prepared, which showed initial setting times similar to that of original CPC. Though compression strength decreased upon incorporation of PTMC microspheres, elastic properties were improved as strain-at-yield increased with increasing content of microspheres. Sustained degradation of the microspheres inside PTMC CPC occurred when incubated in the enzymatic environment, but not in PBS, which resulted in an interconnected macroporosity for the 25 wt% composites.     

Lack of TNF-α-induced MMP-9 production and abnormal E-cadherin redistribution associated with compromised fusion in MCP-1-null macrophages

Homotypic cell fusion occurs in several cell types including macrophages in the formation of foreign body giant cells. Previously, monocyte chemoattractant protein-1 (MCP-1) was demonstrated to be required for foreign body giant cell formation in the foreign body response. The present study investigated the fusion defect in MCP-1-null macrophages by implanting biomaterials intraperitoneally in wild-type and MCP-1-null mice and monitoring the macrophage response at 12 hours to 4 weeks. MCP-1-null mice exhibited reduced accumulation and fusion of macrophages on implants, which was associated with attenuation of the foreign body response. Consistent with previous in vitro findings, the level of matrix metalloproteinase-9 (MMP-9) was reduced in MCP-1-null macrophages adherent to implants. In contrast, CCR2 expression was unaffected. In vitro studies revealed reduced tumor necrosis factor-α (TNF-α) production and abnormal subcellular redistribution of E-cadherin and β-catenin during fusion in MCP-1-null macrophages. Exogenous TNF-α caused an increase in the production of MMP-9 and rescued the fusion defect. Addition of GM6001 (MMP inhibitor) or NSC23766 (Rac1 inhibitor) indicated two distinct induction pathways, one for E-cadherin/β-catenin and one for MCP-1, TNF-α, and MMP-9. Considered together, these observations demonstrate that induction of E-cadherin/β-catenin is not sufficient for fusion in the absence of MCP-1 or the downstream mediators TNF-α and MMP-9. Moreover, attenuation of the foreign body response in intraperitoneal implants in MCP-1-null mice demonstrates that the process depends on tissue-specific factors.     

Development of an injectable,in situ crosslinkable,degradable polymeric carrier for osteogenic cell populations. Part 2. Viability of encapsulated marrow stromal osteoblasts cultured on crosslinking poly(propylene fumarate)

The effect of temporary encapsulation of rat marrow stromal osteoblasts in crosslinked gelatin microparticles on cell viability and proliferation was investigated in this study for microparticles placed on a crosslinking poly(propylene fumarate) (PPF) composite over a 7 day time period. Encapsulated cells were seeded on crosslinking PPF composites at times up to 10 min following initiation of the crosslinking reaction, and also on fully crosslinked PPF composites and tissue culture polystyrene controls, with a cell seeding density of 5.3 x 10(4) cells/cm2. The crosslinked PPF composite exhibited an average gel point of 10.3 min and an average maximum crosslinking temperature of 47.5 degrees C. Cell viability and proliferation were assessed by DNA and 3H-thymidine assays and the results were compared with those for nonencapsulated cells. The results showed that the addition time of cells to a crosslinking PPF composite had a large effect on cell viability and proliferation for both encapsulated and nonencapsulated cells with more surviving cells added at later time points. Most importantly, the temporary encapsulation of cells significantly enhanced cell viability at earlier time points. The data indicate that the presence of gelatin microparticles does not affect the crosslinking of a PPF composite. They further suggest that the temporary encapsulation of cells in crosslinked gelatin microparticles may preserve the viability of cells contained in an actively crosslinking PPF composite used as an injectable polymeric scaffold serving also as a carrier for osteogenic cell populations.     

Reliability evaluation of inter-eminence line,Akagi and Dalury lines for intraoperative tibial rotation: An osteology-based study

Background

This large osteology study examined the reliability, reproducibility and correlation between previously described tibial tray rotation alignment lines (including Akagi and Dalury lines). In addition, it described a novel inter-eminence line utilising the tibial plateau inter-condylar eminences as a landmark.

Three months of moderate-intensity exercise reduced plasma 3-nitrotyrosine in rheumatoid arthritis patients

Purpose

Rheumatoid arthritis (RA) patients display high levels of oxidative stress. Transient exercise-induced increases in oxidative stress are thought to be adaptive in healthy populations. This study investigated the effect of exercise on markers of oxidative stress in RA, following acute exercise and a period of exercise training.

Methods

Acute exercise study: RA patients (N = 12, age: 56 ± 11) undertook a bout of exercise (30–40 min, 70 % VO_2MAX), and blood samples were taken before and after exercise to assess markers of oxidative stress. Training study: RA patients (N = 19, age: 56 ± 10) were randomised into either a control or exercise group, who undertook 3 exercise sessions per week (30–40 min @70 % VO_2MAX) for 3 months. Plasma markers of oxidative stress (protein carbonyls (PC), lipid hydroperoxides (LOOH), 3-nitrotyrosine (3-NT), total antioxidant capacity (TAC) and catalase (CAT) activity), inflammation (interleukin-8 (IL-8) and C-reactive protein (CRP)) and nitric oxide metabolites (NOx) were assessed before and after training.

Results

Acute exercise study: Protein carbonyls (PC) (+18 %) and NOx (+27 %) were significantly increased following exercise. Training study: 3-nitrotyrosine (3-NT) decreased (2.18 ± 1.78 to 1.10 ± 0.93 μM) in the exercise group only, alongside increases in aerobic fitness (24.45 ± 4.98 to 27.10 ± 4.51 ml/kg/min^?1) and reductions in disease activity score (DAS: 3.47 ± 1.17 to 2.88 ± 0.76). PC, LOOH, TAC, IL-8, CRP and NOx concentrations, and CAT activity were unchanged in both groups.

Conclusions

Aerobic exercise training did not increase markers of oxidative stress in RA patients. 3-Nitrotyrosine and disease activity were decreased following exercise training.     

In vitro generation of an osteochondral construct using injectable hydrogel composites encapsulating rabbit marrow mesenchymal stem cells

Injectable, biodegradable hydrogel composites of crosslinked oligo(poly(ethylene glycol) fumarate) (OPF) and gelatin microparticles (MPs) were utilized to fabricate a bilayered osteochondral construct consisting of a chondrogenic layer and an osteogenic layer, and to investigate the differentiation of rabbit marrow mesenchymal stem cells (MSCs) encapsulated in both layers in vitro. The results showed that MSCs in the chondrogenic layer were able to undergo chondrogenic differentiation, especially in the presence of TGF-β1-loaded MPs. In the osteogenic layer, cells maintained their osteoblastic phenotype. Although calcium deposition in the osteogenic layer was limited, cells in the osteogenic layer significantly enhanced chondrogenic differentiation of MSCs in the chondrogenic layer. The greatest effect was observed when MSCs were encapsulated with TGF-β1-loaded MPs and cultured with osteogenic cells in the bilayered constructs. Overall, this study demonstrates the fabrication of bilayered hydrogel composites that mimic the structure and function of osteochondral tissue, along with the application of these composites as cell and growth factor carriers.     

In vitro degradation of polymeric networks of poly(propylene fumarate) and the crosslinking macromer poly(propylene fumarate)-diacrylate

Polymeric networks of poly(propylene fumarate) (PPF) crosslinked with poly(propylene fumarate)-diacrylate (PPF-DA) are currently being investigated as an injectable, biodegradable bone cement. This study examined the effect of crosslinking density, medium pH, and the incorporation of a beta-tricalcium phosphate (beta-TCP) filler on the in vitro degradation of PPF/PPF-DA. Cylindrical specimens were submerged in buffered saline at 37 degrees C and the change in weight, geometry, and compressive mechanical properties were monitored over a 52-week period. All formulations showed an initial increase in modulus and yield strength over the first 12 weeks, achieving maxima of 1307+/-101 and 51+/-3MPa, respectively, for the beta-TCP composite. PPF/PPF-DA networks with the lower crosslinking density demonstrated the greatest degradation with a 17% mass loss. Samples in the lower buffer pH 5.0 compared to physiological pH 7.4 did not show any differences in mass loss, but exhibited a faster decrease in the compressive strength over time. The beta-TCP composites maintained their mechanical properties at the level following their initial increase. These results show that the degradation of PPF/PPF-DA networks can be controlled by the crosslinking density, accelerated at a lower pH, and prolonged with the incorporation of the beta-TCP filler.