Effect of antioxidants on coronary risk markers in hypercholesterolaemia / Azlina A. Razak

Introduction: Antioxidant vitamins have been suggested to play a role in preventing atherosclerosis. Several vitamins with anti-oxidant properties, such as vitamin E and C, are thought to act cooperatively and possibly synergistically in vivo. However, the efficacy of tocotrienol, a potent vitamin E molecule as compared to -tocopherol, in reducing risk of heart disease has not been fully explored. The optimal dose of tocotrienol in atherogenesis and the synergism of tocotrienol with vitamin C remain unclear.
Objectives: (i) To study the effects of tocotrienol-rich fraction (TRF) supplement on fasting lipid profiles (FSL), oxidative stress, inflammation and atherosclerotic lesions in hypercholesterolaemic (HC) rabbits, (ii) To determine the dose response relationship of TRF treated HC rabbits, (iii) To examine the effects of antioxidants (TRF plus vitamin C) on the inflammatory markers and endothelial dysfunction (ED) in statin treated HC patients with high coronary risk.
Materials and Methods:
(i) Animal model experiment: Twenty-eight male New Zealand white rabbits were given 1% cholesterol diet for 5 months and randomised from the second month onwards into 5 groups: Placebo (n=7), TRF 15 mg/kg (n=5), TRF 30 mg/kg (n=6), TRF 60 mg/kg (n=5) and TRF 90 mg/kg (n=5) daily. Serum FSL, C-reactive protein (CRP), malondialdehyde (MDA) and 8-Isoprostane levels were measured at baseline (BL), 1 and 2 months post-HCD, 1, 2 and 3 months post-intervention. Aortic vessels were obtained to assess the atherosclerotic lesions and immunohistochemical studies for Intercellular Adhesion Molecule-1 (ICAM-1) and Nuclear Factor Kappa-B (NF B) were performed.
(ii) Clinical trial: Twenty-nine HC patients were identified in high risk category according to the National Cholesterol Education Programme Adult Panel Treatment III and treated with atorvastatin to achieve low density lipoprotein (LDL-c) target (LDL-c < 2.6 mmol/L) before being randomised into a double-blinded placebo- control clinical trial with 2 groups: Placebo and combined tocotrienols-vitamin C supplement (TRF-160mg plus C-500mg daily) for 3 months. FSL, high sensitivity CRP (hsCRP), interleukin-6 (IL-6), tumor necrosis factor alpha (TNF-) levels and ED by brachial artery flow mediated Dilatation (FMD) were measured at entry, BL, 2 weeks and 3 months post-intervention.
Results: (i) Animal model experiment: There were no differences in percentage changes of FSL, MDA, 8-Isoprostane, CRP levels and extent of atherosclerosis between the placebo and TRF groups. Reduced tissue expressions of ICAM-1 (57% vs. 20%, 29%, 50%, 25%: placebo vs. TRF 15, 30, 60, 90 mg/kg) and NFB (67% vs. 40%, 50%, 25%: placebo vs. TRF 15, 30, 90 mg/kg) were found with significant decrease in area of ICAM-1 expression (Mean  SEM; 3.8  2.0 % vs. 25.1  19.5 %, p<0.05) between the placebo and TRF 15 mg/kg groups.
(ii) Clinical trial: There were no differences in percent changes of FSL, hsCRP, IL- 6, sICAM-1, sVCAM-1, E-selectin levels and percentage of FMD between the placebo and combined supplement groups. Significantly higher endothelial- dependent FMD were found between the antioxidant and placebo group at 3 months (Mean  SEM; 8.8  1.6 % vs. 4.7  1.0 %, p<0.05).
Conclusion: TRF decreases ICAM-1 and NFB tissue expressions in established atherosclerosis despite neutral effects on lipids, oxidative stress, inflammation and atherosclerotic lesions. TRF at lower concentration has greater effects on tissue ICAM-1 and NFB expressions than at higher concentrations. These suggest that TRF has potential benefits in reducing vascular endothelial activation and tissue inflammation. Addition of vitamin C in TRF supplementation showed neutral effects on lipid profiles and inflammatory markers in human subjects. However, due to the limited number of patients and short treatment duration in investigating the effects of TRF alone, further study with larger sample size and longer treatment duration is required.