Rooibos and Melatonin: Putative modulation of nicotine-induced effects on vascular function

Date
2016-12
Journal Title
Journal ISSN
Volume Title
Publisher
Stellenbosch : Stellenbosch University
Abstract
ENGLISH ABSTRACT : Introduction and aims: Cigarette smoking is an important risk factor for cardiovascular disease, and nicotine, the addictive substance in tobacco, is implicated in the pathogenesis of atherosclerosis via oxidative stress. Oxidative stress can lead to loss of vascular homeostasis, via reduced nitric oxide (NO) bioavailability, which in turns leads to endothelial dysfunction. Endothelial dysfunction is an early, reversible precursor of atherosclerosis and cardiovascular disease. This dissertation aimed to investigate whether treatment with the indigenous South African plant rooibos (fermented and unfermented) and the hormone melatonin can ameliorate the harmful effects of nicotine on the vascular and endothelial systems. Methodology: This study made use of an in vivo model (male Wistar rats) and ex vivo model (rat aortic ring segments), complemented by an in vitro model of cultured rat aortic endothelial cells (AECs). Biometric data, fluid intakes, blood pressure measurements, vascular function, antioxidant/oxidative stress status, inflammatory markers and serum lipids were determined as measures of the effects of nicotine (5 mg/kg bw/day; subcutaneously administered) in the rat model. The effects of nicotine co-treated with rooibos (2% administered as drinking fluid) and nicotine co-treated with melatonin (4 mg/kg bw/day; administered as drinking fluid) were assessed according to the same endpoints to determine if the nicotine-induced effects observed could be ameliorated. The modulating effects of fermented rooibos (RF) were further investigated in an in vitro model of AECs. Nicotine injury (100 μM over a 24 hour treatment period) was assessed by means of NO production and cell viability assays. The effects of nicotine, pre-treated with RF (0.015 mg/ml) were assessed according to the same endpoints. Results: Nicotine-induced vascular injury: Nicotine treatment (six weeks) in rats exerted significant effects on biometric parameters, reduced fluid consumption, increased blood pressure, and elicited pro-contractile responses in aortic rings. Furthermore, nicotine administration led to a decrease in superoxide dismutase (SOD) activity (liver) and catalase (CAT) activity (heart and liver), and increased lipid peroxidation. The harmful vascular effects of nicotine were further underscored by reduced intracellular NO levels and reduced cell viability in AECs. Nicotine and rooibos co-treatment: RF exerted anti-contractile and prorelaxation responses in aortic rings and increased SOD and CAT activity (liver) in nicotinetreated animals. RF pre-treatment led to increased intracellular NO levels in nicotine-treated AECs. Unfermented rooibos (RUF) exerted anti-contractile responses in aortic rings and increased CAT activity (heart) in nicotine-treated animals. Nicotine and melatonin cotreatments: Melatonin reduced blood pressure, exerted anti-contractile and pro-relaxation responses in aortic rings, increased SOD activity (heart) and CAT activity (heart and liver), as well as decreased lipid peroxidation in nicotine-treated animals. Conclusion: Nicotine administration resulted in significant vascular and endothelial injury, associated with increased oxidative stress and reduced antioxidant activity. Overall, our data showed that rooibos, specifically RF, and melatonin exerted beneficial effects on the vascular and endothelial system of nicotine exposed rats. Mechanisms identified in this dissertation included their antioxidant properties, although other mechanisms cannot be ruled out. Restoration of vascular homeostasis, underscored by eNOS activation and subsequent release of NO, could underlie the modulating actions of both rooibos and melatonin.
AFRIKAANSE OPSOMMING : Inleiding en doelwitte: Sigaretrook is ‘n belangrike risikofaktor vir kardiovaskulêre siekte, en nikotien, die verslawende substans in tabak, word met die patogenese van aterosklerose via oksidatiewe stres, geassosieer. Oksidatiewe stres kan lei tot ‘n verlies aan vaskulêre homeostase via verlaagde stikstofoksied (NO) biobeskikbaarheid, wat tot endodeeldisfunksie aanleiding kan gee. Endoteeldisfunksie is ‘n vroeë, omkeerbare voorloper van aterosklerose en kardiovaskulêre siekte. Die doel van hierdie proefskrif was om te bepaal of behandeling met die inheemse Suid-Afrikaanse plant, rooibos (gefermenteer of ongefermenteer) en die hormoon, melatonien, die skadelike effekte van nikotien op die vaskulêre en endoteel stelsels kan teenwerk. Metodes: Daar is van ‘n in vivo model (manlike Wistar rotte) en ex vivo model (aorta ring segmente) gebruik gemaak, sowel as ‘n in vitro model van rot aorta endoteelselle (AECs). Biometriese data, vloeistof inname, bloeddruk, vaskulêre funksie, antioksidant/oksidatiewe stres status, inflammatoriese merkers en serum lipiede is gemeet as eindpunte van die effekte van nikotien (5 mg/kg liggaamsgewig/dag; subkutaan toegedien) in die rot model. Die gevolge van gesamentlike toediening van nikotien en rooibos (2% toegedien in drinkwater) en nikotien en melatonien (4 mg/kg liggaamsgewig/dag; toegedien in drinkwater) was vervolgens gemeet om te bepaal of die nikotien-geïnduseerde effekte teengewerk kon word. Die modulerende effekte van gefermenteerde rooibos (RF) is verder ondersoek in ‘n in vitro model van AECs. Nikotien besering (100 μM oor 24 uur) is deur middel van intrasellulêre NO-produksie en sellewensvatbaarheid metings bepaal. Die gevolge van nikotien, vooraf behandel met RF (0.015 mg/ml) is beoordeel volgens dieselfde eindpunte. Resultate: Nikotien-geïnduseerde vaskulêre besering: Nikotientoediening (ses weke) het ‘n beduidende uitwerking op biometriese eindpunte gehad, vloeistof inname verminder, bloeddruk verhoog en ‘n pro-kontraktiele respons in aorta ringe ontlok. Nikotientoediening het ook superoksied dismutase (SOD) en katalase (CAT) aktiwiteit (hart en lewer) verlaag, en lipiedperoksidasie verhoog. Die skadelike vaskulêre effekte van nikotien is bevestig deur die waarneming van verlaagde intrasellulêre NO-vlakke en sellewensvatbaarheid in nikotienbehandelde AECs. Gesamentlike nikotien en rooibos toediening: RF het anti-kontraktiele en pro-dilaterende effekte in aorta ringe, asook verhoogde SOD en CAT aktiwiteit (lewer) in nikotien-behandelde diere tot gevolg gehad. Vooraf behandeling met RF het gelei tot verhoogde intrasellulêre NO-vlakke in nikotien-behandelde AECs. Ongefermenteerde rooibos (RUF) het anti-kontraktiele effekte in aorta ringe en verhoogde CAT aktiwiteit (hart) in nikotienbehandelde diere tot gevolg gehad. Gesamentlike nikotien en melatonien toediening: Melatonien het bloeddruk verlaag, anti-kontraktiele en pro-dilaterende effekte in aorta ringe, verhoogde SOD aktiwiteit (hart) en CAT aktiwiteit (hart en lewer), asook verlaagde lipied peroksidasie in nikotien-behandelde diere tot gevolg gehad. Gevolgtrekkings: Nikotientoediening het beduidende vaskulêre en endoteel skade veroorsaak, wat met verhoogde oksidatiewe stres en verlaagde anti-oksidant aktiwiteit gepaard gegaan het. Oor die algemeen toon ons resultate dat rooibos, spesifiek RF, en melatonien voordelige effekte op die vaskulêre en endoteel sisteme van nikotien-behandelde rotte gehad het. Die proefskrif het anti-oksidant aktiwiteit as ‘n moontlike meganisme geïdentifiseer wat hierdie effekte kan verklaar, alhoewel ander meganismes nie uitgesluit kan word nie. Die herstel van vaskulêre homeostase, weens eNOS aktivering en daaropvolgende vrystelling van NO, kan verder onderliggend tot die beskermende aksies van beide rooibos en melatonien wees.
Description
Thesis (PhD)--Stellenbosch University, 2016
Keywords
Nicotine, Rooibos, Melatonin, Endothelial dysfunction, UCTD, Vascular function
Citation