Effects of atorvastatin therapy on hypercholesterolemic rabbits with respect to oxidative stress, nitric oxide pathway and homocysteine
Introduction
Hypercholesterolemia is a well-established risk factor for the development of cardiovascular disease (Zulli et al., 2004). It is known to reduce endothelial function either by decreasing the synthesis and release of endothelium-derived relaxing factors or by inactivating nitric oxide (NO) after its release from endothelial cells by its reaction with superoxide radicals (Ito et al., 1999, Böger, 2003b).
Decreased biological activity and bioavailability of NO may be due in part to the action of circulating endogenous NO synthase inhibitor asymmetric dimethyl arginine (ADMA) and may be involved in homocysteine associated endothelial dysfunction (Wang et al., 2006). ADMA represents a circulating marker for subclinical atherosclerosis and may be a novel risk factor for endothelial dysfunction and coronary artery disease. Thus, derangement of NO synthase pathway plays a crucial role in atherogenesis (Mügge et al., 2003, Böger, 2004).
Hyperhomocysteinemia is an independent putative risk factor for cardiovascular disease (Stühlinger et al., 2003). The redox activity of homocysteine may contribute to enhanced oxidative inactivation of NO which is characterized as an endogenous anti-atherosclerotic molecule (Böger, 2003a, Böger, 2003b). Homocysteine, through the formation of disulfides and the generation of H2O2 and O−2, increases oxidative degradation of NO (Stühlinger et al., 2001). Total homocysteine has been shown to increase endothelial generation of ADMA by inhibiting the activity of dimethylarginine dimethylaminohydrolase (DDAH) that is responsible for the metabolism of ADMA (Shai et al., 2004, Yoo and Lee, 2001).
Homocysteine thiolactone (HTL), which is both toxic and cytotoxic, is a metabolic product of homocysteine. It is detoxified by homocysteine thiolactonase activity of paraoxonase 1 (PON1) (Jakubowski, 2003). PON1, a protein component of HDL, degrades oxidized lipids and prevents protein homocysteinylation, the process involved in atherogenesis. Homocysteine thiolactonase activity of PON1 could be responsible for its anti-atherosclerotic and anti-oxidant action (Ferretti et al., 2003, Jakubowski, 2003).
Multiple interventional trials demonstrated that HMG-CoA reductase inhibitors (statins) effectively reduce serum cholesterol levels and cardiovascular events (morbidity and mortality) (Fuhrman et al., 2002.). Among the pleiotropic effects of statins; upregulation of eNOS expression/activity, increased serum PON1 activity, their anti-oxidant capacity either directly or indirectly by removing ‘aged LDL’ and reduced ROS formation are highlightened (Tomas et al., 2000, Lu et al., 2004, Van Nieuw Amerongen et al., 2000, Herdeg et al., 2003, Zhao et al., 2006).
Therefore, in this experimental study we were prompted to search for a possible interaction among homocysteine, ADMA, NO and PON1. In rabbits, we investigated the effects of hypercholesterolemia and atorvastatin administration on oxidative stress as reflected by thiobarbituric acid reactive substance (TBARS) and lipid hydroperoxide levels, NO synthase pathways markers ADMA, NO (NO−2 + NO−3) and PON1 activity and homocysteine levels.
Section snippets
Animals
Twenty male New Zealand White rabbits at 6 months of age (Experimental Animal-Research and Breeding Laboratory, Cerrahpasa Medical Faculty, Istanbul University, Istanbul, Turkey) were used in this study. The rabbits, weighing 2700–3500 g at the beginning of the study were housed individually with 12 h light periods, at temperature of 20 ± 2 °C. Food and fresh tap water were supplied ad libidum throughout the experiment. The study protocol was reviewed and approved by the ethical committee on
Results
Hypercholesterolemic diet for 4 weeks caused significant increases both in total cholesterol (p < 0.001), LDL-C (p < 0.001) and HDL-C levels (p < 0.001) and in oxidative stress markers — lipid peroxide (p < 0.001) and TBARS (p < 0.001). A significant increase in ADMA (p < 0.001) but a decrease in NO level was observed (p < 0.05). PON1 activity significantly decreased (p < 0.001) whereas homocysteine level significantly increased (p < 0.05) (Table 1).
Atorvastatin therapy to hypercholesterolemic
Discussion
Oxidative stress is known to contribute to atherogenesis and during atherogenesis lipid peroxidation takes place in lipoproteins as well as in arterial macrophages (Rosenblat et al., 2004). In this study AAPH-induced lipid peroxidation was measured by TBARS and lipid peroxide methods. In cholesterol-fed rabbits, significantly increased (p < 0.001) susceptibility to free radical-induced lipid peroxidation was observed when measured as lipid peroxide (60.03%) and TBARS (317.54%).
As to lipid profile
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