2.4. Morphological changes of rabbit aorta
Representative aortic sections stained with hematoxylin-eosin and obtained from each group are shown in Figure 1
. As shown in group (A) in the figure, the aortic walls in the control rabbits were smooth and intact. By feeding high cholesterol diet was developed a thick layer of lipid deposition within intima of aorta which is typical for atherosclerosis. The formations of atherosclerotic lesions were notably decreased by the supplementation with either dandelion leaf or root.
Treatment with the dandelion leaf and root resulted in positive changes of plasma enzyme activities and lipid levels, except CK and phospholipids. Not only the atherogenic index, which is recognized as a better arteriosclerosis marker than each of the lipid parameters alone, but they also prevented oxidative damage, an important etiologic factor in atherosclerosis. The relationship between ALT, as a possible marker of liver disorders including steatosis, and CHD risk factors, including the elements of the metabolic syndrome, has been shown in previous studies [7
]. AST activity was significantly decreased in the dandelion leaf group compared to the control group (p
> 0.05), ALT activity was significantly decreased in the dandelion root group.
We have recently reported [11
] the total phenol contents of the dandelion leaf and root were 7.9 ± 0.4% and 9.4 ± 0.3%, respectively. We also reported in this study that the cathechol, caffeic acid, ferulic acid, m-coumaric acid, p
-coumaric acid, vanillic acid and syringic acid were found to be phenolic compounds in the dandelion leaf and root, which is consistent with other reports [7
In the human body, high levels of triglycerides in the bloodstream have been linked to atherosclerosis, and, by extension, the risk of heart disease and stroke. TG level was significantly decreased in the experimental groups (dandelion leaf and root) compared to the control group (P
> 0.05). High cholesterol levels are strong indicators of those individuals that are prone to coronary heart disease. Elevated total cholesterol is a risk factor for coronary heart disease. The build-up of plaque in the artery may lead to narrowing (high blood pressure) or complete blockage (heart attack) of the vessel [12
]. It is widely accepted that reduction in plasma HDL is a risk factor for developing atherosclerosis. HDL facilitates the translocation of cholesterol from the peripheral tissue, such as arterial walls to liver for catabolism. The increase in HDL-C may slow down the atherosclerotic process [13
]. Atherosclerotic index (AI), defined as the ratio of LDL-C and HDL-C, is believed to be an important risk factor of atherosclerosis [14
]. Our results showed that the dandelion leaf supplemented-diet increased the concentrations of serum HDL-C when is compared with the cholesterol-rich diet, and the concentrations of serum LDL-C were decreased.
Oxidative stress is one of the causative factors that link hypercholesterolemia with atherogenesis [15
]. A cholesterol-rich diet brings about remarkable modifications in antioxidant defense mechanisms. In addition to, recently report shown that hypercholesterolemia diminishes the antioxidant defense system and decreases the activities of SOD and CAT, elevating the lipid peroxide content [16
]. The present results are in agreement with this theory. The oxidative parameters of only the cholesterol-fed rabbit (control group) were good results compared with these of the cholesterol-non fed rabbits (normal group). GST is the important detoxification enzyme involved in catalyzing the conjugation of a wide variety of electrophilic substrates to reduced glutathione and thus protects the cell from chemically induced damages in hepatic and extra hepatic tissues [17
]. GST contents increases when one is sick. GST of dandelion root group decreases activities compared with control group. GPx is more important than catalase for detoxification of hydrogen peroxide in brain, because the brain contains small amounts of catalase and GPx can also interact directly with lipid peroxides [18
].The result of GPx and CAT analysis significantly increased in the experimental groups (dandelion leaf and root) compared to the control group (P
> 0.05). Especially, the dandelion root group was significantly high antioxidant enzyme activity better than the dandelion leaf (P
MDA, the product of lipid peroxidation, is an index of the level of oxygen free radicals. A decrease in lipid peroxidation leads to a reduction of atherosclerosis caused by hypercholesterolemia [20
]. The content of MDA in rabbits fed a cholesterol-rich diet and a dandelion leaf diet were increased compared to rabbits fed standard laboratory diet, suggesting that hypercholesterolemia could enhance the process of lipid peroxidation. The dandelion leaf prevented a cholesterol-rich diet which induced elevation of MDA and resulted in a significantly decreased content of MDA in liver. The obtained data suggested that dandelion root might be capable of lowering or slowing down oxidative-related lipid peroxidation.
The thickening of the vascular wall and infiltration of macrophages and lymphocytes are hallmarks of atherosclerosis [21
]. In the result of histopathological examination, the formation of atheromatous plaque aortic media notably were decreased in the experimental groups (dandelion leaf and root) compared to the control group. In the case of serum enzyme activities and lipid levels the effect of the dandelion leaf is better, while in the case of the hepatic antioxidant activities the effect of the dandelion root is better. Hypercholesterolemia with high cholesterol diet was associated with development of atherosclerosis. These findings are consistent with the previous [22
]. Dandelion reduced the development of atherosclerosis. Hypercholesterolemic atherosclerosis was associated with increases of ROS suggesting increased levels of oxygen radicals. Increased levels of oxygen radicals are known to produce endothelial cell injury, which represents a critical initiating event in the development of atherosclerosis [24
]. Dandelion may have prevented the oxygen radical-induced endothelial cell injury through its antioxidant activity. The reduction in the extent of atherosclerosis could also be related to its lipid lowering activity.