Browsing by Author "Van Vuuren, Mignon Albertha"
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- ItemAn 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.