Exposure to polyphenol-enriched rooibos (Aspalathus linearis) and honeybush (Cyclopia spp.) extracts : implications of metabolism for the oxidative status in rat liver

Van der Merwe, J. Debora (2012-12)

Thesis (PhD(FoodSc))--Stellenbosch University, 2012.

Thesis

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.

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