Doctoral Degrees (Medical Physiology)

Permanent URI for this collection

https://scholar.sun.ac.za/handle/10019.1/3554

Browse

Browsing Doctoral Degrees (Medical Physiology) by browse.metadata.advisor "Dietrich, Daneel"

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    An investigation into the anti-hypertensive effects of Green Rooibos Tea Extract (GRT).
    (Stellenbosch : Stellenbosch University, 2019-03) Van Vuuren, Mignon Albertha; Huisamen, Barbara; Dietrich, Daneel; Windvogel, Shantal; Stellenbosch University. Faculty of Medicine and Health Sciences. Dept. of Biomedical Sciences: Medical Physiology.
    Introduction and Aims: Obesity is defined as a primary cause of insulin resistance,hypertension and cardiovascular diseases. Rooibos (Aspalathus linearis), an indigenous South African herbal plant, presents with two unique polyphenolic compounds i.e. aspalathin and aspalalinin, which are associated with anti-obesity, anti-diabetic, anti-hypertensive and a lower risk for developing cardiovascular diseases. Green “unfermented” rooibos is dried directly after harvesting thereby preserving its polyphenolic compounds. Afriplex GRT™ is an aspalathin-rich spray-dried powder prepared from green rooibos under Good Manufacturing Practice (GMP) standards, thus ensuring high quality products. To date, the potential anti-hypertensive abilities of Afriplex GRT™ have not yet been investigated. We aimed to (i) monitor blood pressure changes in animals on a high fat diet (HFD) and determine whether the Afriplex GRT™ extract modulates diet-induced blood pressure changes within 6 weeks and (ii) elucidate mechanisms responsible for any changes induced by Afriplex GRT™. Methods: In vivo model: Adult male Wistar rats were randomly divided into a control (n=40) and HFD group (n=48) which respectively received rat chow and HFD food for 16 weeks. The HFD was specifically developed to induce obesity, insulin resistance and hypertension. After 10 weeks, 20 rats of each group received aspalathin-rich Afriplex GRT™ (60 mg/kg/day) and 8 HFD animals received Captopril (positive control for blood pressure lowering effects of Afriplex GRT™) (50 mg/kg/day) for the last 6 weeks of the 16-week diet regimen. Food and water intake, body weight, intraperitoneal fat (IP-fat), liver weight, insulin sensitivity, blood pressure and urine parameters were determined. Ex vivo model: Vascular reactivity (contraction and relaxation of aorta with perivascular adipose tissue (PVAT)) were determined using phenylephrine, acetylcholine and sodium nitroprusside respectively. Expression and activation of enzymes in the nitric oxide (NO)- synthesis pathway such as AMPK, eNOS and PKB was determined by Western blotting using aortas with PVAT. Serum was collected at sacrifice for determination leptin, adiponectin and endothelin-1 (ET-1). In vitro model: Aortic endothelial cells (AECs) were cultured to determine the effect of Afriplex GRT™ on cellular apoptosis, cellular metabolic activity and NO production. Angiotensin converting enzyme (ACE)-inhibitor activity was determined using a Fluorescence resonance energy transfer (FRET) assay in AECs in response to treatment with Afriplex GRT™ extract or with non-fasting serum (collected previously from the experimental animals). Results: HFD (vs control) animals presented with increased: food intake (p<0.0001), bodyweight (p<0.0001), IP-fat accumulation (p<0.0001); liver weight (p<0.0001), leptin levels (p<0.01), adiponectin levels (p<0.01) and decreased glucose clearance (p<0.0001). Treatment with Afriplex GRT™ attenuated food intake (p<0.01), body weight (p<0.0001) liver weight (p<0.05) and increased glucose clearance (p<0.001). Furthermore, the HFD (vs control) reduced water intake (p<0.0001), urine excretion (p<0.05), vascular contraction (p<0.05), vascular relaxation (p<0.0001), and increased systolic (p<0.001) and diastolic (p<0.001) blood pressure; whereas treatment with Afriplex GRT™ reduced water intake (p<0.05), improved vascular relaxation (p<0.001), decreased systolic (p=0.0348) and diastolic (p=0.0434) blood pressure and interestingly, increased glucose excretion via the urine. In addition the HFD downregulated AMPK expression (p<0.0001), increased AMPK activation according to the AMPK phosphorylated(P):total(T) ratio (p<0.001), increased eNOS expression (p<0.01), decreased eNOS activation according to the P:T ratio (p<0.01), and lastly decreased PKB activation (p<0.05). Treatment with Afriplex GRT™ increased AMPK phosphorylation (p<0.05) as well as PKB expression (p<0.05) and phosphorylation (p<0.05). Afriplex GRT™ treatment did not result in cellular apoptosis, NO production or ACE inhibition according to in vitro studies, however cellular metabolic activity was increased at a high Afriplex GRT™ concentration (p<0.001). Conclusion: Treatment with Afriplex GRT™ in this animal model was closely associated with anti-obesogenic, anti-diabetic and anti-hypertensive effects and improved vascular function. Increased glucose excretion via the urine is indicative of sodium-glucose co-transporter (SGLT2) inhibition and we therefore conclude that the associated health benefits of Afriplex GRT™ can amongst other, be ascribed to SGLT2 inhibition.
  • Thumbnail Image
    Item
    The regenerative and anti-inflammatory capability of Prosopis Glandulosa
    (Stellenbosch : Stellenbosch University, 2014-12) George, Cindy; Huisamen, Barbara; Smith, Carine; Dietrich, Daneel; Stellenbosch University. Faculty of Medicine and Health Sciences. Dept. of Biomedical Sciences: Medical Physiology.
    ENGLISH ABSTRACT: Introduction and aims: The use of herbal preparations for the treatment of various ailments has gained enormous prominence. The aim of this study was to evaluate the effects of a plant-derived product, consisting solely of dry-milled pods of the Prosopis glandulosa tree, on various altered metabolic demands placed on skeletal muscle. This study included the evaluation of (i) altered glucose uptake as a result of insulin resistance, (ii) exercise-induced fatigue and (iii) the inflammatory and regenerative process of skeletal muscle after a contusion injury, with particular attention paid to the infiltration of immune cells and the adaptation of regenerative markers. Methodology: P. glandulosa (100 mg/kg/day) mixed into jelly, was orally administered daily to rats for a period of 8-10 weeks. Aim 1: Rats were rendered insulin resistant after being on a high caloric diet for 16 weeks, where after half the animals underwent a 120 min intra-peritoneal glucose tolerance test. The rest were fasted, body weight and intra-peritoneal fat weight determined, sacrificed, blood collected for blood glucose- and insulin level determination and soleus muscles removed for insulin sensitivity determination. Aim 2: Soleus muscles were excised, weighed, measured and mounted for isometric force determination. Muscles were vertically placed in Krebs Henseleit buffer solution in a water-jacketed organ bath (25˚C). Twitch- and tetanic force production, contraction time, half-relaxation time, force-frequency relationship and fatigue were measured. Aim 3: The gastrocnemius muscle was injured by a contusion injury (mass-drop model) and left for 1-, 3 hours, 1- or 7 days before further experimentation commenced. Following the different time periods, the gastrocnemius muscles were removed, divided and stored either in liquid nitrogen or 4% formaldehyde. Immune cell infiltration was analyzed with immunohistochemistry (neutrophils - His48-positive; macrophages - F4/80-positive). ADAM12 (Western blotting) and desmin (immunohistochemistry) were used as markers to evaluate muscle regeneration. Results: Aim 1: P. glandulosa treatment had no effect on body- or fat mass. Treatment significantly decreased the elevated blood glucose levels observed in the obese rats. Aim 2: P. glandulosa treatment had: (i) no effect on muscle mass or optimal muscle length; (ii) no significant effect on muscle fatigue tolerance, as both treated and untreated groups fatigued at the same rate and (iii) P. glandulosa-treated rats generated significantly increased force when the muscle was stimulated to generate a single twitch and tetanus. This augmented effect disappeared after the fatigue protocol. Aim 3: Chronic P. glandulosa treatment as well as post-injury treatment led to a significant reduction in neutrophil infiltration into the injured area. Additionally, chronic P. glandulosa treatment significantly increased the expression of both ADAM12 (day 1) and desmin (day 7) after injury, indicating faster muscle regeneration. Conclusion: The data obtained from this study is novel, since there is no known literature on the effect of P. glandulosa on insulin resistance, force generation, fatigue tolerance or muscle recovery after injury. Given the current evidence, we conclude that P. glandulosa treatment might prove beneficial as supplement, aiding physical ability and assisting in the sooner recovery.