Thesis (PhD(FoodSc))--Stellenbosch University, 2012. / ENGLISH ABSTRACT: Potential beneficial and/or adverse modulatory effects of polyphenol-enriched extracts of
rooibos (Aspalathus linearis) and honeybush (Cyclopia spp.) on the antioxidant homeostasis in
the liver were investigated. Phase II metabolism of aspalathin and mangiferin, the major
polyphenols of rooibos and honeybush respectively, was assessed for potential glucuronidation
and sulphation. Glucuronidation resulted in a loss of antioxidant activity for aspalathin and
mangiferin in post-column HPLC-DAD-DPPH• and HPLC-DAD-ABTS•+ assays and also a
decreased activity of iron chelating properties of mangiferin in the FRAP assay. Two
independent studies for 28 and 90 days with polyphenol-enriched extracts (PEEs) of
unfermented rooibos [Aspalathus linearis (PER)] and honeybush [Cyclopia. subternata
(PECsub) and C. genistoides (PECgen)] in male Fischer rats were conducted to assess
possible beneficial and/or adverse biological effects. PECgen was only included in the 28 day
study. PEEs were characterised by in vitro antioxidant assays and HPLC analysis. The
importance of detailed chemical characterization of rooibos and honeybush when investigating
biological effects in vivo is clear as distinctive biological effects and major differences in
compositions were evident. Biological parameters included were serum chemical parameters,
activities of selected antioxidant enzymes, levels of glutathione and the modulation of
expression of oxidative stress and antioxidant defense related genes in the liver. Sub-chronic
(90 days) exposure of rats to PER and PECsub both adversely affected iron absorption
significantly (P<0.05) and significantly (P<0.05) and markedly lowered levels of reduced
glutathione (GSH) in the liver. The high levels of polyphenol intake were implicated and
interaction with glutathione was postulated to occur via catechol o-quinone conjugations with GSH. This was also implicated in the significantly (P<0.05) increased activity of glutathione
reductase (GR) following 28 days. These findings suggest that PEEs from rooibos and
honeybush have the potential to alter the glutathione homeostasis, which could contribute to
oxidative status in the liver. PECsub resulted in alterations in the liver biliary system which was
manifested as significantly (P<0.05) increased serum total bilirubin (Tbili) and alkaline
phosphatase (ALP), depending on the age of the rats, level of total polyphenols and duration of
exposure. The expression of a number of oxidative stress and antioxidant defense related
genes were differentially altered by the PEEs of rooibos and honeybush in rat liver and further
indicated potential oxidative stress. Modulatory effects of PEEs on expression of 84 of these
genes in rat liver were assessed with a quantitative real-time reverse transcription polymerase
chain reaction (RT-PCR) array and provided additional insights into the possible adverse and
protective effects of rooibos and honeybush. Further investigation on total polyphenol dose
levels and time of exposure in the application of PEEs of rooibos and honeybush as dietary supplements and functional foods is recommended and will also be of value in anticipated
regulatory requirements for future substantiation of safety and efficacy. / AFRIKAANSE OPSOMMING: Die moontlike voordelige en/of nadelige modulerende effekte van polifenol-verrykde ekstrakte
van rooibos (Aspalathus linearis) en heuningbos (Cyclopia spp.) op die antioksidant
homeostasis in die lewer is ondersoek. Die fase II metaboliete van aspalatien en mangiferin,
die hoof verbindings in rooibos en heuningbos onderskeidelik, is ondersoek t.o.v.
glukuronidering en sulfonering. Glukuronidasie het gelei tot n verlies in antioksidant aktiwiteit
van aspalatien en mangiferin soos bepaal in post-kolom HPLC-DAD-DPPH• en HPLC-DADABTS•+
toetse, asook verminderde interaksie met yster van mangiferin in die FRAP toets. Twee
onafhanklike studies van 28 en 90 dae is onderneem met polifenol-verrykde ekstrakte (PVEs)
van ongefermenteerde rooibos [Aspalathus linearis (PVR)] en heuningbos [Cyclopia. subternata
(PVCsub) and C. genistoides (PVCgen)] in manlike Fisher rotte om die moontlike voordelige
en/of nadelige biologiese effekte te ondersoek. PECgen was slegs in die 28 dae studie
ingesluit. PVEs is gekarrakteriseer deur in vitro antioksidant en HPLC analises. Die belang van
chemiese karaktirisering van rooibos en heuningbos tydens ondersoeke na biologiese aktiwiteit
is duidelik aangesien verskeie en variërende biologiese aktiwiteite en verskille in die komposisie
in die huidige studie gesien is. Die biologiese parameters wat ondersoek is om die effek van die
PVEs te bepaal het serum kliniese parameters, aktiwiteit van geselekteerde ensieme, glutatioon
en evaluering van die ekspressie van oksidatiewe en antioksidant verwante gene in die lewer,
ingesluit. Sub-kroniese (90 dae) blootstelling van rotte aan PVR en PVCgen het yster absorpsie
negatief beïnvloed. Die beduidende (P<0.05) verlaagde vlak van gereduseerde glutatioon in die
lewer was toegeskryf aan die hoë vlakke van polifenole ingeneem tydens die studie en word
moontlik veroorsaak deur n spesifieke katekol o-konjugasie van GSH. Hierdie interaksie was ook moontlik die oorsaak van n beduidende (P<0.05) toename in die aktiwiteit van glutatioon
reduktase. Dié bevindinge het moontlike implikasies t.o.v die glutatioon homeostase en is n
moontlike indikase dat PVEs van rooibos kan bydra tot oksidatiewe stres. PVCsub het
veranderinge in die lewer gal-sisteem tot gevolg gehad aangesien daar n beduidende (P<0.05)
verhoging in die serum totale bilirubin en alkalien fosfaat was. Hierdie veranderinge is
beïnvloed deur die ouderdom, vlakke van die totale polifenole en die periode van blootstelling.
Die uitdrukking van oksidatiewe en antioksidant verwante gene is op verskillende maniere
beïnvloed deur die PVEs van rooibos en heuningbos in rot lewer and dien as n verdere
indikasie van onderliggende oksidatiewe stres. Die modulerende effekte van PVEs op
geenuitdrukking het gelei tot additionele insig aangaande die moontlike skadelike of
beskermende eienskappe van PVEs vir gebruik as kruie produkte of dieet aanvullings. Die
indikasies van moontlike oksidatiewe stres was duidelik van biologiese parameters en
modulering van geenuitdrukking in die lewer, en vereis verdere ondersoek na die polifenool dosis en periode van toediening voordat PVEs van rooibos en heuningbos as funksionele
voedsel produkte gebruik word. Hierdie ondersoek sowel as toekomstige ondersoeke in hierdie
verband sal van waarde wees vir regulatoriese vereistes omtrent die veiligheid en effektiwiteit
van rooibos en heuningbos kruie produkte.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/71804 |
| Date | 12 1900 |
| Creators | Van der Merwe, J. Debora |
| Contributors | Gelderblom, W. C. A., Joubert, E., Manley, M., Stellenbosch University. Faculty of AgriSciences. Dept. of Food Science. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | xx, 233 p. : ill. |
| Rights | Stellenbosch University |
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