SUNScholar - Browsing by Author "Myburgh, Kathryn H."

Browsing by Author "Myburgh, Kathryn H."

Now showing 1 - 10 of 10

Assessment of endocrine stress status in athletes – new twists to the tale
(Health and Medical Publishing Group, 2005) Smith, C.; Myburgh, Kathryn H.
Objective. Cortisol concentration at rest seems to be an insensitive marker for endocrine stress status in athletes. Therefore, the aim of this review was to identify potentially more sensitive parameters which could be used to monitor endocrine stress status during chronic exercise training. In order to gain more insight from studies not directly related to exercise science, this review also includes findings from studies investigating responses to psychological stress in healthy individuals and in patients suffering from chronic disease. Data sources. Medline. Study selection and data extraction. Key words (e.g. exercise stress, psychological stress, overtraining, chronic fatigue, dehydroepiandrosterone (DHEA), chronic inflammation). Only studies published in peer-reviewed journals included in the International Science Index were used. Care was specifically taken not to over-represent any particular research group’s articles. Data synthesis. A qualitative synthesis was done, based on all papers included in the review. Conclusions. Four main conclusions were drawn: (i) instead of considering changes in mean cortisol concentration over time for a group of athletes, high- and low-responders should be identified at baseline and their responses considered separately; (ii) it may be more useful to express cortisol concentration as a ratio to either testosterone or DHEA-sulphate (DHEAs) concentration than assessing either the catabolic or anti-catabolic variable on its own; (iii) in response to stress, cortisol binding globulin (CBG) and sex hormone binding globulin (SHBG) do not seem to play major roles in the regulation of circulating concentrations of bioactive cortisol and testosterone respectively; and (iv) it is crucial to allow sufficient recovery from the most recent exercise session to ensure that proper resting blood samples are obtained for assessment of chronic effects of training on endocrine status.
Body composition in women with HIV/AIDS : the relevance of exercise
(Health and Medical Publishing Group (HMPG), 2008-07) Myburgh, Kathryn H.; De Bruto, Petro C.
Untreated infection with the human immunodeficiency virus (HIV) leads to severe physical debilitation, culminating in the acquired immune deficiency syndrome (AIDS). Multiple infections, body mass loss, physical weakness and wasting are characteristic manifestations of each of the four stages of HIV/AIDS, respectively (Table I). The latter two impact especially on the affected person’s ability to function, as well as on social and economic levels. However, even though antiretroviral treatment (ART) is now available at many selected public clinics in South Africa, it only complicates the issues surrounding body composition and physical function.
C-reactive protein is elevated only in high creatine kinase responders to muscle damaging exercise
(Frontiers Media, 2017-02-11) Isaacs, Ashwin W.; Macaluso, Filippo; Smith, Carine; Myburgh, Kathryn H.; Seelaender, Marilia
The purpose of this study was to investigate if exertional rhabdomyolysis induced by an acute bout of plyometric exercise in untrained individuals was associated with histological characteristics of skeletal muscle, creatine kinase (CK) polymorphism or secondary damage. Twenty-six healthy male untrained individuals completed a bout of plyometric exercise (10 sets of 10 maximal squat jumps, with each standardized to achieve at least 95% of individual maximal jump height). Blood samples were taken, and perceived pain was scored immediately before the exercise intervention and 6 h, 1, 2, and 3 days post-intervention. Muscle biopsies were collected 9 or 4 days before (baseline) and 3 days after plyometric jumps. Subjects were divided into two groups, high (n = 10) and low responders (n = 16), based on a cut-off limit for exertional rhabdomyolysis of peak CK activity ≥ 1000 U/L in any post-exercise blood sample. Perceived pain was more severe assessed in squat than standing position. Low responders perceived more pain at 6 h and 1 day, while high responders perceived more pain than low responders on days three and four after exercise; structural (dystrophin staining) and ultra-structural (transmission electron microscopy) analysis of muscle fibers revealed no baseline pathology; damage was evident in all individuals in both groups, with no difference between high and low responders in either damage or fiber type proportion. High responders had significantly higher total white blood cell and neutrophil counts 6 h and significantly higher C-reactive protein (CRP) 6 h and days one and two after exercise compared to low responders. High responders had significantly greater muscle myeloperoxidase (MPO) levels in baseline and 3 day post-exercise biopsies compared to baseline of low responders. MLCK C49T single polymorphism was present in 26% of volunteers, whose CK responses were not higher than those with MLCK CC or CT genotype. In conclusion, perceived pain is more effectively assessed with potentially affected muscle under eccentric strain, even if static. High CK responders also have pronounced CRP responses to unaccustomed plyometric exercise intervention. Exertional rhabdomyolysis after unaccustomed eccentric exercise may be related to underlying inability to resolve intramuscular MPO.
In vitro induction of quiescence in isolated primary human myoblasts
(Springer Nature, 2020-01-28) Gudagudi, Kirankumar B.; d'Entrèves, Niccolò Passerin; Woudberg, Nicholas J.; Steyn, Paul J.; Myburgh, Kathryn H.
Adult skeletal muscle stem cells, satellite cells, remain in an inactive or quiescent state in vivo under physiological conditions. Progression through the cell cycle, including activation of quiescent cells, is a tightly regulated process. Studies employing in vitro culture of satellite cells, primary human myoblasts (PHMs), necessitate isolation myoblasts from muscle biopsies. Further studies utilizing these cells should endeavour to represent their native in vivo characteristics as closely as possible, also considering variability between individual donors. This study demonstrates the approach of utilizing KnockOut™ Serum Replacement (KOSR)-supplemented culture media as a quiescence-induction media for 10 days in PHMs isolated and expanded from three different donors. Cell cycle analysis demonstrated that treatment resulted in an increase in G1 phase and decreased S phase proportions in all donors (p < 0.005). The proportions of cells in G1 and G2 phases differed in proliferating myoblasts when comparing donors (p < 0.05 to p < 0.005), but following KOSR treatment, the proportion of cells in G1 (p = 0.558), S (p = 0.606) and G2 phases (p = 0.884) were equivalent between donors. When cultured in the quiescence-induction media, expression of CD34 and Myf5 remained constant above > 98% over time from day 0 to day 10. In contrast activation (CD56), proliferation (Ki67) and myogenic marker MyoD decreased, indicated de-differentiation. Induction of quiescence was accompanied in all three clones by fold change in p21 mRNA greater than 3.5 and up to tenfold. After induction of quiescence, differentiation into myotubes was not affected. In conclusion, we describe a method to induce quiescence in PHMs from different donors.
Interleukin-6 Induces myogenic differentiation via JAK2-STAT3 signaling in mouse C2C12 myoblast cell line and primary human myoblasts
(MDPI, 2019-10-24) Steyn, Paul J.; Dzobo, Kevin; Smith, Robert I.; Myburgh, Kathryn H.
Postnatal muscle growth and exercise- or injury-induced regeneration are facilitated by myoblasts. Myoblasts respond to a variety of proteins such as cytokines that activate various signaling cascades. Cytokines belonging to the interleukin 6 superfamily (IL-6) influence myoblasts’ proliferation but their effect on differentiation is still being researched. The Janus kinase (JAK)-signal transducer and activator of transcription (STAT) pathway is one of the key signaling pathways identified to be activated by IL-6. The aim of this study was to investigate myoblast fate as well as activation of JAK-STAT pathway at different physiologically relevant IL-6 concentrations (10 pg/mL; 100 pg/mL; 10 ng/mL) in the C2C12 mouse myoblast cell line and primary human myoblasts, isolated from eight young healthy male volunteers. Myoblasts’ cell cycle progression, proliferation and differentiation in vitro were assessed. Low IL-6 concentrations facilitated cell cycle transition from the quiescence/Gap1 (G0/G1) to the synthesis (S-) phases. Low and medium IL-6 concentrations decreased the expression of myoblast determination protein 1 (MyoD) and myogenin and increased proliferating cell nuclear antigen (PCNA) expression. In contrast, high IL-6 concentration shifted a larger proportion of cells to the pro-differentiation G0/G1 phase of the cell cycle, substantiated by significant increases of both MyoD and myogenin expression and decreased PCNA expression. Low IL-6 concentration was responsible for prolonged JAK1 activation and increased suppressor of cytokine signaling 1 (SOCS1) protein expression. JAK-STAT inhibition abrogated IL-6-mediated C2C12 cell proliferation. In contrast, high IL-6 initially increased JAK1 activation but resulted in prolonged JAK2 activation and elevated SOCS3 protein expression. High IL-6 concentration decreased interleukin-6 receptor (IL-6R) expression 24 h after treatment whilst low IL-6 concentration increased IL-6 receptor (IL-6R) expression at the same time point. In conclusion, this study demonstrated that IL-6 has concentration- and time-dependent effects on both C2C12 mouse myoblasts and primary human myoblasts. Low IL-6 concentration induces proliferation whilst high IL-6 concentration induces differentiation. These effects are mediated by specific components of the JAK/STAT/SOCS pathway.
Investigation of circulating extracellular vesicle microRNA following two consecutive bouts of muscle-damaging exercise
(Frontiers Media, 2018-08-20) Lovett, Jason A. C.; Durcan, Peter J.; Myburgh, Kathryn H.
Background: Extracellular vesicles (EVs) are nano-sized vesicles that are known to be powerful mediators of intercellular communication via their microRNA (miR) content. A paucity of information on EV-mediated communication arising from skeletal muscle (SkM) in response to exercise-induced muscle damage is present in the published literature. Lack of such information inhibits our understanding of muscle injury and repair processes. Aims: To assess circulating EV levels and selected miR content within them, in response to two consecutive bouts of muscle-damaging exercise. Methods: Serum creatine kinase activity (CK) and EVs were analyzed from the blood of 9 healthy, untrained males at baseline, and at 2 and 24 h post-exercise. The exercise regimen consisted of a combination of plyometric jumping and downhill running. Perceived muscle pain (PMP) was assessed on a scale from 1 to 10. Plasma EVs were isolated using size exclusion columns and visualized with transmission electron microscopy (TEM). EV size and number were quantified using nanoparticle tracking analysis (NTA). miR expression was quantified using qPCR, with normalization to an exogenous control (cel-miR-39). Results: PMP and CK were significantly elevated post-exercise compared to baseline levels, providing indirect evidence for muscle damage. EV visualization using TEM revealed an abundant and heterogeneously sized pool of intact particles within the exosome size range (30–150 nm). No significant change in mean EV size or number was seen over time. The SkM-specific miR-206 in EVs was found to be variable among participants and no significant change occurred in SkM-important miRs; 1, 133a, 133b, 486, and 499a. However, EV miR-31 decreased from baseline to 24 h post-exercise (p = 0.027). Conclusion: Mild to moderate exercise-induced muscle damage altered the miR-31 profile of circulating EVs within the first 24 h post-exercise, but not that of myomiRs in EVs. These data demonstrate that EVs carry selectively packaged cargo which can be affected by exercise. Future research into the total miR content of EVs in response to exercise-induced muscle damage may reveal other miRs responsive to this relatively mild perturbation. More time points post-muscle-damaging exercise would provide a better understanding of the temporal EV myomiR response.
Pre-exercise glutamine supplementation could prevent decreases in postexercise serum glutamine following a single bout of intensive exercise
(2001) Strauss, Johannes A. de W.; Myburgh, Kathryn H.; Kruger, Annalie; Smith, Carine; Robson, Paula J.
ENGLISH ABSTRACT: The objective is to determine if glutamine supplementation prior to exercise would cause an increase in serum glutamine concentration, as opposed to supplementation during exercise or in the post-exercise period. The subjects were fourteen female athletes of the local athletic club who volunteered to participate in the study. Design. This was a single-blind cross-over design. A single dose of 5 g L-glutamine, dissolved in 250 ml of a sugar-free orange drink, or a placebo, was given 45 min utes before the VO₂max test. Blood samples were col lected before supplementation, 45 minutes after supplementation, immediately after the VO₂max test, and 45 minutes into the recovery period. Blood samples were analysed for serum glutamine concentrations, using an enzymatic method with standard reagents (Glutamine / Glutamate Statpack, Sigma Bio Science™). Haematological variables were analysed by means of a Coulter Counter and a differential white blood cell (WBC) count was obtained from a stained (Leishman's stain) blood film. Results. The mean ± standard error of the mean (±SEM) age, mass, height and VO₂max of the subjects were 19.6 ± 0.4 years, 56.6 ± 1.6 kg, 168.6 ± 1.6 cm and 56.1 ± 1.4 ml/kg/min respectively. During the placebo trial the glutamine concentrations, when adjusted for haemoconcentration, decreased from the resting and pre-exercise concentrations of 675 ± 39 µmol/I and 652 ± 45 µmol/I respectively, to 499 ± 38 µmol/I immediately after exercise (P < 0.01). During the recovery period, glutamine concentrations (606 ± 44 µmol/I) returned to levels close to the resting and pre-exercise levels (P > 0.05). During the glutamine trial, pre-exercise concen trations of glutamine were raised from 725 ± 30 µmol/I to 1 252 ± 31 µmol/1 (P < 0.01). This increased level of glu tamine was maintained throughout the rest of the proto col. Following exercise, an expected increase in the absolute WBC count {almost doubled) was observed in both the placebo and glutamine trials (P < 0.01). No other differences in the absolute WBC and WBC-sub population counts were observed between trials. Conclusion. We conclude that glutamine supplementa tion before exercise could increase serum glutamine concentrations and may thus prevent the fall in glutamine observed during intensive exercise. This may influence WBC function, but has no effect on WBC concentrations.
Sarcopenic obesity in Africa: a call for diagnostic methods and appropriate interventions
(Frontiers Media S.A, 2021-04) Mendham, Amy E.; Lundin-Olsson, Lillemor; Goedecke, Julia H.; Micklesfield, Lisa K.; Christensen, Dirk L.; Gallagher, Iain J.; Myburgh, Kathryn H.; Odunitan-Wayas, Feyisayo A.; Lambert, Estelle V.; Kalula, Sebastiana; Hunter, Angus M.; Brooks, Naomi E.
This perspective aims to highlight the lack of current knowledge on sarcopenic obesity in Africa and to call for diagnostic methods and appropriate interventions. Sarcopenic obesity has been defined as obesity that occurs in combination with low muscle mass and function, which is typically evident in older adults. However, there has been no clear consensus on population-specific diagnostic criterion, which includes both gold-standard measures that can be used in a more advanced health care system, and surrogate measures that can be used in low-income settings with limited resources and funding. Importantly, low and middle-income countries (LMICs) across Africa are in an ongoing state of economic and social transition, which has contributed to an increase in the aging population, alongside the added burden of poverty, obesity, and associated co-morbidities. It is anticipated that alongside the increased prevalence of obesity, these countries will further experience an increase in age-related musculoskeletal diseases such as sarcopenia. The developmental origins of health and disease (DOHaD) approach will allow clinicians and researchers to consider developmental trajectories, and the influence of the environment, for targeting high-risk individuals and communities for treatment and/or prevention-based interventions that are implemented throughout all stages of the life course. Once a valid and reliable diagnostic criterion is developed, we can firstly assess the prevalence and burden of sarcopenic obesity in LMICs in Africa, and secondly, develop appropriate and sustainable interventions that target improved dietary and physical activity behaviors throughout the life course.
Simple silicone chamber system for in vitro three-dimensonal skeletal muscle tissue formation
(Frontiers, 2013-11-28) Snyman, Celia; Goetsch, Kyle P.; Myburgh, Kathryn H.; Niesler, Carola U.
Bioengineering skeletal muscle often requires customized equipment and intricate casting techniques. One of the major hurdles when initially trying to establish in vitro tissue engineered muscle constructs is the lack of consistency across published methodology. Although this diversity allows for specialization according to specific research goals, lack of standardization hampers comparative efforts. Differences in cell type, number and density, variability in matrix and scaffold usage as well as inconsistency in the distance between and type of adhesion posts complicates initial establishment of the technique with confidence. We describe an inexpensive, but readily adaptable silicone chamber system for the generation of skeletal muscle constructs that can readily be standardized and used to elucidate myoblast behavior in a three-dimensional space. Muscle generation, regeneration and adaptation can also be investigated in this model, which is more advanced than differentiated myotubes.
Treatment with Sutherlandia frutescens ssp. microphylla alters the corticosterone response to chronic intermittent immobilization stress in rats
(Academy of Science of South Africa, 2004) Smith Carine; Myburgh, Kathryn H.
Much anecdotal evidence suggests a stress-relieving effect of the Sutherlandia frutescens herb. We investigated this in a model of chronic intermittent immobilization stress in 40 adult male Wistar rats. A warm water extract of Sutherlandia leaves (4 mg/ml) was used as treatment and isotonic saline as placebo, both injected intraperitoneally. The four experimental groups were: a) control + treatment (CS); b) control + placebo (CP); c) immobilization + treatment (IS) and d) immobilization + placebo (IP). After 28 days, resting blood corticosterone, testosterone, interleukin (IL)-6 and tumor necrosis factor (TNF)-α concentrations were measured. Data were analysed with two-way ANOVA. Immobilization stress resulted in significantly increased corticosterone concentrations in IP vs CP (81 ± 11 vs 22 ±7 ng/ml, P < 0.001), whereas corticosterone concentrations were significantly decreased in IS (43 ± 14 ng/ml, P < 0.05) compared to IP. The two Sutherlandia-treated groups did not differ (CS 57 ± 11 ng/ml). Neither testosterone nor IL-6 and TNF-α concentrations were significantly different among groups. In summary, our data show that Sutherlandia frutescens treatment effectively decreased the corticosterone response to chronic stress, thereby scientifically confirming the indigenous wisdom.

Browsing by Author "Myburgh, Kathryn H."

Results Per Page

Sort Options