Although the exact mechanisms remain to be delineated, oxidant stress , lipid abnormalities  as well as chronic inflammation  have been identified as the main trigger mechanisms of atherosclerosis. Atherosclerosis is fundamentally a metabolic disease subject to important dietary influences, and dietary lipids play a key role in the regulation of the development of atherosclerosis. High-fat diets, especially high-fat diet enriched with saturated fatty acid exert more deleterious effect on CVD and can lead to atherosclerosis , whereas the consumption of different kinds of fatty acids have various effects on atherosclerotic risk factors and even direct effects on atherogenesis [24–26]. Because of rich in ALA, FO has been proven to exert positive effect on atherosclerosis [25, 26]. ASX is a potent natural antioxidant and may play a beneficial role in cardiovascular disease prevention . In the study reported here, we evaluated the effect of FO and ASX combination on atherosclerosis risk factors in rats fed a high-fat diet.
Oxidative stress represents an imbalance between the free radical production and the antioxidant defense. The relative excessive production of free radicals, which can lead to oxidative damage to any biochemical component including lipids, proteins and DNA, plays a causative role in atherosclerosis . For example, as a result of oxidative stress, LDL can be modified to oxidized LDL (oxLDL) which is clearly a critical factor in the atherosclerotic process and the cellular accumulation of oxidized LDL is considered a hallmark of atherosclerosis . There is now consensus that oxidative stress is the pivotal pathogenetic factor and unifying mechanism for atherosclerosis and other cardiovascular diseases . Therefore, an efficient antioxidant defense system is required to counteract the deleterious effects of oxidative stress. The primary antioxidant enzymes in mammals include SOD which converts superoxide to hydrogen peroxide, GPx and CAT which are responsible for converting hydrogen peroxide to water . GSH is a very important non-enzymatic antioxidant which can react directly with free radicals or act as an electron donor in the reduction of peroxides catalyzed by GPx . High consumption of dietary fat is a known cause of increased plasma oxidative stress , whereas in this experiment, the combination of FO and ASX remarkably elevated the plasma SOD, CAT and GPx activities as well as GSH level, which led to the pronounced enhancement of total antioxidant capability. As a result, lipid peroxidation levels in plasma markedly declined with the supplement of FO and ASX. However, FO itself is hardly thought to have an authoritative antioxidative activity and further, it may cause lipid peroxidation because of its susceptibility to oxidation [12, 13]. Thus, ASX is anticipated to impart the entire antioxidative potency in this study. ASX has a unique chemical structure featured by the presence of polar moieties on both end of its polyene chain, and this structural property of ASX confers much greater free radical scavenging capability than β-carotene as well as α-tocopherol [33–35]. Besides, ASX is able to restore the activities of antioxidant enzymes SOD, CAT and GPx by inducing, at least in part, the Nrf2 pathway and other non-enzymatic antioxidants such as GSH, vitamins C and E in plasma and other various tissues in pathological conditions [36–38].
Hyperlipidemia is a well-known risk factor for arteriosclerosis as well as other cardiovascular disease and treatment of hyperlipidemia retards progression of arteriosclerosis . There is mounting evidence that high-fat diet rich in saturated fatty acid leads to hyperlipidemia. However, in the present experiment, the levels of TG, TC and LDL-C in plasma declined in response to the consumption of FO and ASX combination and both of FO and ASX undoubtedly contributed to these beneficial changes. ALA has been shown to suppress the expression and activities of numerous hepatic fatty acid syntheses such as fatty acid synthase (FAS), malic enzyme and glucose 6-phosphate dehydrogenase [40, 41], and hence decrease fatty acid synthesis in liver. On the other hand, ALA sharply enhances hepatic peroxisomal and mitochondrial fatty acid oxidation rate by increasing the expression and activities of a series of fatty acid oxidation enzymes [41, 42]. As a peroxisome proliferator-activated receptor α (PPARα) agonist, ASX also shows the similar action on inducing fatty acid oxidation [36, 43]. In addition, the hypocholesterolemic effects of FO and ASX are likely owing to elevated hepatic expression of LDL receptor [9, 36] as well as declined cholesterol biosynthesis [43, 44].
Contemporary advances in cardiovascular research have established a pivotal role for chronic inflammation in all stages of atherosclerosis [45–47]. Various proinflammatory risk factors such as oxLDL and infectious agents have a capability to trigger the production of proinflammatory cytokines which are deeply involved in the development and progression of atherosclerosis. As primary proinflammatory cytokines, IL-6 and CRP are sensitive measures of the burden of systemic atherosclerosis and extent of atherosclerotic activity [48–50]. In the present experiment, when the lard was replaced with the combination of FO and ASX, both the plasma levels of IL-6 and CRP collapsed, which implied that the FO and ASX combination is fully competent to improve inflammation status. Supporting our results, FO has been shown to suppress the expression of various inflammatory cytokines such as IL-6, IL-1, CRP and TNF-α via an activation of peroxisome proliferator-activated receptor γ (PPARγ) and/or a reduction in NF-κB induced gene expression [6, 10, 51]. Similarly, ASX also exerts antiinflammatory properties by suppressing NF-κB activation and thus decreased inflammatory markers levels in circulation [52, 53].
In conclusion, supplement of FO and ASX combination has satisfactory efficacy at ameliorating oxidative stress, lipid profile and inflammation, which suggested that the combination of FO and ASX might contribute to prevent atherogenesis and then reduce the incidence of CVD. In addition, the presence of astaxanthin in FO lowers the lipid oxidation rate of FO and, on the other hand, astaxanthin is stable in FO in room temperature . This makes the combination of FO and ASX very promising functional food in cardiovascular health promotion.