Dissertation (PhD)--University of Stellenbosch, 2005. / ENGLISH ABSTRACT: Activation of the NO-cGMP pathway is associated with myocardial protection
against ischaemia/reperfusion injury. However, high-cholesterol diets alter
function of this pathway and these alterations have been implicated in both
ischaemic/reperfusion injury and the development of ischaemic heart disease.
Little is known about the effects of supplements such as Red Palm Oil (RPO)
on the myocardial NO-cGMP-signalling pathway. RPO consists of saturated,
mono-unsaturated and poly-unsaturated fatty acids and is rich in antioxidants
such as β-carotene and Vitamin E (tocopherols and tocotrienols). The aims of
this study were: 1) to determine whether dietary RPO-supplemention protects
against ischaemia/reperfusion injury in rats fed a standard rat chow (control)
and cholesterol-enriched diets and 2) if so, to investigate possible mechanisms
for this protection.
Male Long-Evans rats were fed a standard rat chow or a standard rat chow
plus cholesterol and/or RPO-supplementation for 6 weeks. Myocardial
functional recovery was measured and hearts were freeze-clamped for
determination of myocardial phospholipid, cAMP/cGMP concentrations, total
myocardial nitric oxide concentrations, lipid hydroperoxide production and
superoxide dismutase- and nitric oxide synthase activity in isolated rat hearts
subjected to 25 minutes of normothermic total global ischaemia. In addition,
the degree of phosphorylation of extracellular signal-regulated kinase (ERK),
p38, c-Jun N-terminal protein kinase (JNK) and protein kinase B (PKB/Akt)
was investigated. Furthermore, the effect of RPO-supplementation on
caspase-3 activation and poly (ADP-ribose) polymerase (PARP)-cleavage in
hearts subjected to ischaemia and reperfusion was also investigated. Our data show that dietary RPO-supplementation protects the hearts of rats on
a standard rat chow (control) and hypercholesterolaemic diet against
ischaemia/reperfusion injury as reflected by improved aortic output recovery.
Increased intracellular cardiomyocyte NO concentrations as observed in
control hearts supplemented with RPO after 120 minutes hypoxia may
contribute to the elevated cGMP concentration and may confer some of the
cardioprotection to the ischaemic/reperfused heart. Although improved
functional recovery with RPO-supplementation of a high-cholesterol diet was
also associated with an increase in intracellular cardiomyocyte NO production
after hypoxia compared to the non-hypoxic conditions, it could not be linked to
increased NO-cGMP signalling. These data are in agreement with other
studies, which showed that high-cholesterol diet impairs NO-cGMP signalling
and confirms our hypothesis that elevated cGMP concentrations may not be
the only mechanism of protection. We have also shown that RPOsupplementation
caused increased phosphorylation of p38 and PKB, reduced
phosphorylation of JNK and attenuation of PARP cleavage, which may
contribute to the protection of the cell against apoptosis.
Based on our results we propose that the myocardial protection offered by
RPO-supplementation of rats on a normal and hypercholesterolaemic diet may
be associated with either its antioxidant characteristics and/or changes in the
fatty acid composition of the myocardium during ischaemia/reperfusion.
Furthermore, we demonstrated for the first time that RPO-supplementation
protects the isolated perfused working rat heart during reperfusion from
ischaemia/reperfusion-induced injury through a MAPK-dependent pathway. / AFRIKAANSE OPSOMMING: Aktivering van die NO-cGMP sein transduksie pad word geassosieer met
miokardiale beskerming teen isgemie/herperfusie skade. Hoë cholesterol diëte
verander egter die funksie van die pad en hierdie veranderings speel ‘n rol in
beide isgemie/herperfusie besering en die ontwikkeling van isgemiese
hartsiekte.
Daar is egter min inligting beskikbaar oor die uitwerking van aanvullings soos
rooi palm olie (RPO) op die miokardiale NO-cGMP sein transduksie pad. RPO
bevat versadigde, mono-onversadigde en poli-onversadigde vetsure en is ryk
aan anti-oksidante nl. β-karotene en vitamien E (tokoferole en tokotriënole).
Die doelwitte van hierdie studie was: 1) om vas te stel of ‘n RPO-aanvulling
beskerming bied teen isgemie/herperfusie besering in rotte wat gevoed is met
‘n standaard rotmengsel (kontrole) en cholesterol-verrykte dieet en 2) indien
wel, om moontlike meganismes van beskerming te ondersoek.
Long-Evans manlike rotte is vir 6 weke gevoer met ‘n standaard rotmengsel of
‘n standaard rotmengsel plus cholesterol en/of RPO-aanvulling. Miokardiale
funksionele herstel is gemeet en harte is gevriesklamp vir die bepaling van
miokardiale fosfolipied, cAMP/cGMP, totale stikstofoksied, lipied
hidroperoksied, superoksied dismutase en stikstofoksied sintase in
geïsoleerde rotharte wat vir 25 minute onderwerp was aan normotermiese
totale globale isgemie. Hiermee saam is die graad van fosforilering van
ekstrasellulêre sein gereguleerde kinase (ERK), p38 mitogeen-geaktiveerde
proteïen kinase (p38 MAPK), c-Jun-N-terminale proteïenkinase (JNK) en proteïen kinase B (PKB/Akt) ondersoek, asook kaspase-3 aktivering en poli
(ADP-ribose) polimerase (PARP) kliewing in harte blootgestel aan isgemie en
herperfusie.
Ons resultate toon dat RPO-aanvulling van rotte op ‘n normale en
hipercholesterolemiese dieet die hart beskerm soos getoon deur verbeterde
herstel van aortiese uitset. Verhoogde intrasellulêre miokardiale NO vlakke in
kontrole harte met ‘n RPO-aanvulling wat blootgestel was aan 120 minute
hipoksie, mag bygedra het tot die verhoogde cGMP vlakke en beskerming van
die hart tydens isgemie en herperfusie. Alhoewel verbeterde funksionele
herstel met RPO-aanvulling van ‘n hoë cholesterol dieet ook geassosieer is
met ‘n toename in intrasellulêre miokardiale NO produksie ná hipoksiese
toestande, kon dit nie verbind word met verhoogde aktivering van die NOcGMP
sein transduksie pad nie. Hierdie resultate stem ooreen met ander
studies wat aangetoon het dat hoë-cholesterol diëte die NO-cGMP seinpad
onderdruk. Hierdie bevinding bevestig ons hipotese dat verhoogde cGMP
vlakke moontlik nie die enigste beskermingsmeganisme is nie. Ons resultate
het ook gewys dat RPO-aanvulling fosforilering van p38 en PKB/Akt verhoog,
fosforilering van JNK verminder en PARP kliewing onderdruk. Dit dui op
beskerming van die sel teen apoptose.
Ons resultate dui aan dat die miokardiale beskerming wat RPO-dieet
aanvulling bied moontlik geassosieer kan word met sy anti-oksidant eienskap
en/of veranderinge in die vetsuur samestelling van die miokardium tydens
isgemie/herperfusie. Ons het ook vir die eerste keer bewys dat RPO-aanvulling die geïsoleerde geperfuseerde werkende rothart gedurende herperfusie
beskerm teen isgemie/herperfusie besering deur die aktivering en/of
deaktivering van die MAPK afhanklike pad.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/16514 |
| Date | 12 1900 |
| Creators | Esterhuyse, Adriaan Johannes |
| Contributors | Van Rooyen, Jacques, Du Toit, Eugene F., University of Stellenbosch. Faculty of Science. Dept. of Physiological Sciences. |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | xxv, 186 leaves : ill. |
| Rights | University of Stellenbosch |
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