Investigating the Modulating effects of Fermented Rooibos (Aspalathus linearis) and Fermented Honeybush (Cyclopia intermedia) on aortic endothelial function and antioxidant status in Streptozotocin (STZ) – induced diabetic Wistar rats

Mahlangu, Dawn Nomusa (2020-03)

Thesis (MScMedSc)--Stellenbosch University, 2020.

Thesis

ENGLISH ABSTRACT: Introduction: Diabetes mellitus is a metabolic disorder that causes chronic hyperglycaemia due to insulin resistance and deficiency. The implications that chronic hyperglycaemia has on vascular function have established diabetes mellitus as a risk factor for the development of endothelial dysfunction and the associated cardiovascular effects such as hypertension. Aspalathus linearis and the Cyclopia species are medicinal plants that have antioxidant, anti-inflammatory, anti-mutagenic and anti-diabetic properties. However, not enough research has been done to determine the modulating effects of fermented rooibos and fermented honeybush on vascular function, hypertension and antioxidant status in the context of diabetes mellitus. Aim: To investigate the modulating capacity of 2% fermented rooibos (RB) (Aspalathus linearis) and 4% fermented honeybush (HB) (Cyclopia intermedia) on vascular function, hypertension and antioxidant status in streptozotocin-induced diabetic rats. Methods: Adult male Wistar rats were divided into 7 groups and acclimatized to human handling and the blood pressure apparatus for 1 week. Subsequently, diabetic rats treated with 2% RB or 4% HB were acclimatized to the taste of the infusions for 1 week prior to receiving an intraperitoneal injection of 45mg/kg bw streptozotocin. Animals were then treated with 2% RB or 4% HB infusions for 6 weeks. Thereafter biometric measurements; body weight, fluid intake, food intake, blood glucose, relative kidney organ weight and intraperitoneal glucose tolerance test (IPGTT) were performed. Aortic tissue was used to assess the endothelial proteins eNOS and PKB/Akt involved in vascular function and to conduct vascular contraction/relaxation studies. Furthermore, antioxidant status was assessed in the kidney tissue by means of the superoxide dismutase (SOD) and catalase (CAT) antioxidant enzyme assays. Additionally, the TBARS assay was conducted in kidney tissue to assess lipid peroxidation, a biomarker of oxidative stress. Results: At the end of the 6-week treatment period, the diabetic animals developed hyperglycaemia, impaired glucose tolerance, weight loss, increased fluid and food intake and increased kidney weight that was not ameliorated by the 2% RB and 4% HB treatment. Furthermore, the streptozotocin injury model exerted a pro-contractile and an anti-relaxation effect on aortic vascular reactivity. Treatment with 2% RB or 4% HB significantly reduced the vasoconstriction caused by streptozotocin and restored the vasorelaxation response of the aorta, with the RB exhibiting a greater restorative effect than HB. Furthermore, in the aortic tissue, the STZ injury model significantly reduced total and phosphorylated eNOS and iii PKB/Akt expression which was not ameliorated by treatment with 2% RB and 4% HB. Additionally, no significant changes were observed in the blood pressure, antioxidant enzyme and TBARS measurements of all treatment groups. Conclusion: Streptozotocin-induced diabetic animals developed hyperglycaemia, polydipsia, polyphagia, weight loss and impaired glucose tolerance. Furthermore, the fermented RB and fermented HB infusions ameliorated the streptozotocin-induced vascular injury of the aorta, thus improving aortic vascular reactivity and endothelial function. Furthermore, treatment with RB and HB did not alleviate hyperglycaemia or affect blood pressure and the antioxidant status of the diabetic rats as measured in the kidney in the 6week treatment duration.

AFRIKAANSE OPSOMMING: Inleiding: Diabetes mellitus is 'n metaboliese afwyking wat chroniese hiperglikemie as gevolg van insulien-weerstandigheid en tekort veroorsaak. Die gevolge wat chroniese hiperglikemie op die vaskulêre funksie het, het daartoe gelei dat diabetes mellitus as 'n risikofaktor vir die ontwikkeling van endoteel disfunksie en gepaardgaande kardiovaskulêre effekte soos hipertensie beskou word. Aspalathus linearis en die Cyclopia-spesie is medisinale plante wat antioksidant, anti-inflammatoriese, antimutageniese en antidiabetiese eienskappe het. Daar is egter nog nie genoeg navorsing gedoen om die modulerende effekte van gefermenteerde rooibos en gefermenteerde heuningbos op vaskulêre funksie, hipertensie en antioksidantstatus in die konteks van diabetes mellitus te bepaal nie. Doel: Om die modulasievermoë van 2% gefermenteerde rooibos (RB) (Aspalathus linearis) en 4% gefermenteerde heuningbos (HB) (Cyclopia intermedia) op vaskulêre funksie, hipertensie en antioksidantstatus in streptosotosien (STZ)-geïnduseerde diabetiese rotte te ondersoek. Metodes: Volwasse mannetjies Wistar-rotte is in 7 groepe verdeel en vir 'n week aan menslike hantering en die bloeddrukapparaat blootgestel. Daarna is diabetiese rotte vir 'n week behandel met 2% RB of 4% HB om sodoende aan die smaak van die infusies gewoond te raak, voordat 'n intraperitoneale inspuiting van 45 mg / kg liggaamsgewig streptosotosien gegee is. Diere is daarna behandel met 2% RB of 4% HB-infusies vir 6 weke. Daarna is biometriese metings; liggaamsgewig, vloeistofinname, voedselinname, bloedglukose, relatiewe gewig van die nierorgaan en intraperitoneale glukosetoleransietoetsing (IPGTT) uitgevoer. Aortaweefsel is gebruik om die endoteelproteïene eNOS en PKB / Akt, wat by vaskulêre funksie betrokke is, te ondersoek en om vaskulêre kontraksie / ontspanningsstudies te doen. Verder is die antioksidantstatus in nierweefsel aan die hand van die superoksieddismutase (SOD) en katalase (CAT) antioksidant ensiem analises geassesseer. Daarbenewens is TBARS-toetsing in die nierweefsel uitgevoer om lipiedperoksidasie, 'n biomerker van oksidatiewe spanning, te bepaal. Resultate: Aan die einde van die behandelingsperiode van 6 weke het die diabetiese diere hiperglisemie ontwikkel, tesame met ingekorte glukosetoleransie, gewigsverlies, verhoogde vloeistof- en voedselinname sowel as verhoogde niergewigte, wat nie deur die 2% RB of 4% HB-behandeling verbeter is nie. Verder het die STZ-beseringsmodel 'n pro-kontraktiele en 'n anti-ontspanningseffek op die vaskulêre reaktiwiteit van die aorta uitgeoefen. Behandeling met 2% RB of 4% HB het die vasokonstriksie wat deur streptosotosien veroorsaak is, aansienlik verminder en die vaatverslappings-respons van die aorta herstel, met die gefermenteerde RB wat 'n groter herstellende effek as HB ontlok het. Verder, in die aortaweefsel, het die STZ-beseringsmodel die totale en gefosforileerde eNOS- en PKB / Akt-uitdrukking aansienlik verminder, wat nie verbeter het na behandeling met 2% RB of 4% HB nie. Boonop is geen noemenswaardige veranderinge in die bloeddruk-, antioksidantensiem- en TBARS-metings van alle behandelingsgroepe waargeneem nie. Gevolgtrekking: Streptosotosien-geïnduseerde diabetiese diere het hiperglisemie, polidipsie, polifagie, gewigsverlies en verswakte glukosetoleransie ontwikkel. Verder, het die gefermenteerde rooibos en gefermenteerde heuningbos infusies die streptosotosiengeïnduseerde vaskulêre letsels van die aorta verlig. Dus het dit ʼn verbetering in aortiese vaskulêre reaktiwiteit en endoteel funksie meegebring. Verder het die behandeling met RB en HB nie die hiperglukemie verlig nie en ook nie die bloeddruk of die antioksidantstatus van diabetiese rotte, soos gemeet in die nier, gedurende die 6 weke behandelingsperiode beïnvloed nie.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/108036
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