Thesis (PhD)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Paraoxonase (PON) 1 is a high density lipoprotein (HDL) - bound antioxidant enzyme that
was originally discovered and better known for its role in protecting against organophosphate
(OP) - induced neurotoxicity. In the past two decades, the enzyme has gained prominence
as a protective agent against atherosclerosis on account of increasing evidence that it
accounts for many of the anti-atherogenic roles attributed to HDL. PON1 is a polymorphic
enzyme displaying a high variability in human populations which is associated with a
considerable degree of inter-individual differences in enzyme phenotype that translates to
differential risk for OP toxicity and cardiovascular disease (CVD). In a series of studies and
analyses, this thesis describes investigations regarding the possible involvement of PON 1 in
the risk for CVD in a mixed ancestry population from Bellville, Western Cape, South Africa.
This was done by evaluating the distribution of PON1 coding region polymorphisms (Q192R
and L55M) and their influence on PON1 phenotype as well as the latter‟s relation to CVD risk
factors (oxidative stress, inflammation and atherogenic dyslipidemia) and possible
involvement in early CVD assessed by measuring intima media thickness of the carotid
artery (CIMT).
Since PON1 is increasingly measured in samples that have been stored for varied periods of
time, the main study was preceded by a pilot study evaluating the influence of baseline
conditions on the stability of PON 1 activity and antioxidant status in human sera stored for
up to 12 months. It was shown that baseline glycemic status enhances the degradation of
antioxidants in stored samples with indications of also accelerating the decline of PON1
levels and activity. Thus baseline glycemic status should be a factor to be considered in
analyses involving stored samples.
The Q192R polymorphism was found to be the functional variant influencing both
concentration and activity of plasma PON1. Contrary to expectation, the L55M was nonfunctional,
possibly due to its unusual distribution in this population where the 55M (83%)
allele overwhelmingly predominated over the L55 allele. The R allele was the more frequent
(60.4%) of the 192 polymorphism. The R allele has previously been associated with less
efficient breakdown of lipid peroxides and a subsequent higher risk for atherosclerotic heart
disease while the 55M is recognized as a “low concentration/activity” variant. Thus the
predominant PON1 genotype distribution in this population constitutes a risk profile that may
relate to increased risk for CVD. The risk for CVD was confirmed to be very high in this population indicated by high
prevalence of the metabolic syndrome (48%) and its key components (and CVD risk factors)
diabetes (28%), obesity (53%) and high blood pressure (57%). Paraoxonase activity
associated inversely with indices of inflammation (high sensitive C- reactive protein [hs-CRP]
and leptin) and oxidative stress (oxidized low density lipoprotein [LDL]) and directly with
adiponectin and markers of systemic antioxidant status. These findings suggest that low
paraoxonase-I activity contributes to increased cardiovascular risk possibly via involvement
in early atherogenesis. However, only a modest inverse relation was observed between
PON1 phenotype and CIMT thus suggesting that PON1 may not play a major role in early
atherosclerosis.
Taken together, the findings presented in this thesis demonstrate the presence of a risk
PON1 genotypic profile and indication that the enzyme may play a role in the enhanced CVD
risk in this population possibly via interactions with inflammation and oxidative stress.
However, conclusive evidence for the involvement of PON1 in early CVD was not
demonstrated indicating a need to explore the participation of PON1 in later stages of CVD. / AFRIKAANSE OPSOMMING: Paraoksonase (PON) 1 is 'n antioksidant ensiem wat aan HDL gebind is. Oorspronklik is dit
ontdek en het bekend geword as 'n beskermer teen organofosfaat (OF)-gedrewe
neurotoksisiteit. In die afgelope twee dekades het die ensiem belangrik geraak as 'n
beskermer teen arterosklerose as gevolg van toenemende bewyse dat dit 'n belangrike rol
speel in die beskermende effekte van HDL teen arterosklerose. PON1 is 'n polimorfiese
ensiem wat groot variasie toon in verskillende populasies. Daar is ook inter-individuele
verskille in ensiem fenotipe wat uitloop op 'n differensiele risiko vir OF toksisiteit en
kardiovaskulêre hartsiekte (KVH). Hierdie tesis beskryf 'n reeks analises en ondersoeke
betreffende die moontlike betrokkenheid van PON1 in die risiko vir KVH in 'n gemengdeafkoms
populasie van Bellville, Wes-Kaap, Suid Afrika. Dit was gedoen deur die evaluering
van die verspreiding van die PON-1 koderende omgewing polimorfismes (Q192R en L55M),
hulle invloed op PON1 fenotipe en laasgenoemde se verhouding tot KVH risikofaktore
(oksidatiewe stress, inflammasie en arterogeniese dislipedimie) en moontlike voorkoms in
vroeë kardiovaskulêre siekte bepaal deur die meting van die intima media dikte van die
karotied slagaar.
Aangesien PON1 al hoe meer gemeet word in monsters wat vir verskeie tydperke gestoor
word, was die hoofstudie voorafgegaan deur 'n loodsstudie wat die invloed van basislyn
kondisies op die stabiliteit van PON1 aktiwiteit en antioksidant status in menslike sera wat vir
tot 12 maande gestoor was, bepaal het. Dis is duidelik aangetoon dat basislyn glisemiese
status die afbraak van antioksidante in gestoorde monsters verhoog het, asook aanduidings
van die afname van PON1 vlakke en aktiwitetit. Basislyn glisemiese status behoort dus ook
as 'n faktor ingereken te word in analises van gestoorde monsters.
Die Q192R polimorfisme is aangetoon om 'n funksionele variant te wees wat beide die
konsentrasie asook die aktiwiteit van PON1 beïnvloed het. Anders as wat verwag is, was die
L55M polimorfisme nie-funksioneel, moontlik as gevolg van sy ongewone distribusie in
hiedie populasie waar die voorkoms van die 55M (83%) alleel die L55 alleel oorheers het.
Die R alleel was die mees algemene (60.4%) van die 192 polimorfisme. Die R alleel is
voorheen reeds geassosieer met minder effektiewe afbraak van lipied peroksides en
gevolglike hoër voorkoms van arteriosklerotiese hartsiekte, terwyl die 55M erken word as 'n
“lae konsentrasie/aktiwiteit” variant. Die oorheersende PON1 genotipe distribusie in hierdie
populasie behels dus 'n risikoprofiel wat betrekkking mag hê op verhoogde KVH. Die risiko vir KVH was bevestig om baie hoog te wees in hierdie populasie, soos aangedui
deur 'n hoë voorkoms van die metaboliese sindroom (48%) en die sleutelkomponente
daarvan (insluitend KVH risikofaktore), diabetes (28%), obesiteit (53%) en hipertensie
(57%). Paraoksinase aktiwiteit was omgekeerd geassosieer met indekse van inflammasie
(hoë C-reaktiewe proteïen [hs-CRP] en leptien) en oksidatiewe stres (geoksideerde lae
digtheid lipoproteïen [LDL], en direk geassosieer met adiponektien en merkers van
sistemiese antioksidantstatus. Hierdie bevindings mag aandui dat lae paraoksonase-1
aktiwiteit bydra tot verhoogde kardiovaskulêre risiko, moontlik via betrokkenheid in vroeë
arterogenese. Slegs 'n klein omgekeerde verhouding is egter waargeneem tussen die PON1
fenotipe en karotied intima media dikte, wat mag aandui dat PON1 nie 'n beduidende rol
speel in vroeë arterosklerose nie.
In geheel, die bevindinge voorgedra in hierdie tesis demonstreer die voorkoms van 'n risiko
PON1 genotipiese profiel wat 'n aanduiding mag wees dat die ensiem 'n rol mag speel in die
verhoogde KVH risiko in hierdie populasie, moontlik deur interaksies met inflammasie en
oksidatiewe stress. Afdoende bewys van die betrokkenheid van PON1 in vroeë KVH was
egter nie gedemonstreer nie, wat die nodigheid aandui om die deelname van PON1 in latere
stadiums van KVH te ondersoek.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/86724 |
| Date | 04 1900 |
| Creators | Macharia, Muiruri |
| Contributors | Matsha, Tandi E., Erasmus, Rajiv T., Blackhurst, Diane M., Stellenbosch University. Faculty of Medicine and Health Sciences. Dept. of Biomedical Sciences. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Rights | Stellenbosch University |
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