Effects of æ-Lipoic acid on injury, production of nitric oxide and expression of caveolin-3 in the isolated rat heart subjected to ischaemia and reperfusion
(Uncorrected OCR) ABSTRACT Abstract of the thesis titled EFFECTS OF a-LIPOIC ACID ON INJURY, PRODUCTION OF NITRIC OXIDE AND EXPRESSION OF CAVEOLIN-3 IN THE ISOLATED RAT HEART SUBJECTED TO ISCHAEMIA AND REPERFUSION Submitted by LEE Fung Kwan for the degree of Master of Philosophy at the University of Hong Kong in December 2004 Ischaemic heart disease is one of the major health problems of advanced as well as developing countries of the world. Extensive research through the last decade has shown beyond doubt that free radicals, particularly, reactive oxygen species (ROS) play a cardinal role in the pathogenesis of oxidative myocardial damage with consequential cardiac malfunction. The role of the free radical nitric oxide (NO), however, has remained controversial. While some researchers suggest this molecule to be protective, a number of studies have shown contradictive results. Caveolin-3 (Cav-3) is a muscle specific isoform of the caveolins. It is the major component of the membrane invaginations known as the caveolae. Besides being associated with the muscle components, it also interacts with a number of cellular signaling molecules, one of which is the enzyme responsible for producing NO, endothelial nitric oxide synthase (eNOS). It was demonstrated that the peptide of Cav-3 inhibited the activity of eNOS in vitro. Cav-3 may therefore modulate eNOS activity and thus NO physiology in vivo. a-lipoic acid (A-LA) is a well-known antioxidant and it has been shown to be cardioprotective. In ischaemia/reperfusion (I/R) settings it scavenges reactive oxygen species and recycles cellular antioxidants. However, little is known about its effect on nitric oxide physiology or the cellular signalling cascade(s) involved. To have a better understanding of the role of nitric oxide and the possible mechanism(s) underlying the protective effect of A-LA, the level of nitric oxide and the localization of Cav-3 in myocardial I/R were studied. The Langendorff isolated rat heart was used a myocardial I/R model. Lactate dehydrogenase (LDH) leakage and thiobarbituric acid reaction substances (TBARS) of the rat heart were measured as an index of tissue injury. Electron paramagnetic resonance (EPR) spectrometer was used to measure the level of NO. The expression and localisation of Cav-3 was quantified by Western blot analysis. From 0.5 ?10? A-LA decreased LDH leakage and TBARS in a dosage dependent manner (P<0.05). These changes were accompanied by the dissociation of Cav-3 from the membrane to the cytosol. Nitric oxide level, however, remained higher than the control at all concentrations of A-LA (P<0.05). This suggests that the cardioprotective effect of A-LA in myocardial I/R is independent of NO level and that Cav-3 may be one of the signalling molecules in myocardial I/R.
School:The University of Hong Kong
School Location:China - Hong Kong SAR
Source Type:Master's Thesis
Keywords:active oxygen physiological effect membrane proteins ischemia reperfusion injury rats as laboratory animals
Date of Publication:01/01/2005