Studies have shown [8] that MPO is abundantly accumulated in the basement membrane under the vascular endothelium in hypercholesterolemia, and it is speculated that it may lead to endothelial dysfunction from the precipitation of NO. in vascular rings in vitro. The vascular MPO activity, NOcontent, and cGMP level were measured from the MPO activity assay kit, NO assay kit, and cGMP RIA kit. Results Compared with rats fed with normal diet, endothelium-dependent vasodilation, NOcontent, and cGMP level were decreased, and MPO activity was improved in thoracic aortas of rats fed with HC diet. There was a negative correlation between vascular endothelial function, NOcontent or cGMP level, and MPO activity. PIO obviously reduced the Hoechst 33258 trihydrochloride MPO activity, improved NOcontent and cGMP level, and improved endothelium-dependent vasodilation function in HC rats, which was essentially the same as that seen with DDS. And, there was a negative correlation between vascular endothelial function, NOcontent or cGMP level, and MPO activity in the HC group and the PIO treatment group. Summary MPO might provoke vascular endothelial dysfunction in hypercholesterolemic rats by reducing the NO biological activity and impairing the NO/cGMP/cGK signaling pathway. PIO might inhibit vascular MPO activity and increase NO bioavailability with the net result of reversing endothelial dysfunction. 1. Intro Coronary artery disease (CAD) becomes probably one of the most important diseases that impact longevity and survival quality of ageing [1]. Endothelial dysfunction is the 1st stage in the progression of atherogenesis [2], and hypercholesterolemia is one of the most important causes of endothelial dysfunction [3]. The mechanism of vascular endothelial dysfunction Hoechst 33258 trihydrochloride caused by hypercholesterolemia is complex, in which a decrease in the bioavailability of nitric oxide (NO) [4] and impaired NO/cGMP/cGK signaling are considered important contributory mechanisms [5]. Consequently, if the cause responsible for decreased NO bioavailability in hypercholesterolemia is determined and then clogged, it is thought that vascular endothelial function could be efficiently managed, therefore reducing the event of atherosclerosis. Myeloperoxidase (MPO) is an oxidase that is stored in azurophilic granules of neutrophils and monocytes, which is definitely released extracellularly during swelling [6]. MPO takes on an important part in the formation and development of many diseases, including atherosclerosis [7]. Studies have shown [8] that MPO is definitely abundantly accumulated in the basement membrane under the vascular endothelium in hypercholesterolemia, and it is speculated that it may lead to endothelial dysfunction from the precipitation of NO. However, the specific mechanism of action of MPO remains to be elucidated. Upon activation of peroxisome proliferator-activated receptor (PPARagonists can restore NO bioavailability by regulating MPO, therefore improving vascular endothelial function and delaying the progression of atherogenesis in hypercholesterolemia, have not been confirmed. Consequently, the aims of this investigation were as follows: 1st, to verify that vascular endothelial dysfunction is usually caused by a decrease in NO bioavailability in hypercholesterolemia, and on this basis, to observe and analyze whether MPO directs endothelial dysfunction in hypercholesterolemia by affecting the vascular NO/cGMP/cGK signaling pathway. We also aimed to further observe whether PPARagonists could reverse vascular endothelial dysfunction in hypercholesterolemia and, if possible, to determine whether or not this was related to the regulation of vascular MPO and subsequent restoration of NO bioavailability. 2. Materials and Methods 2.1. Animals All animal procedures utilized in the investigations conformed to the Guiding Principles in the Use and Care of Animals, published by the National Institutes of Health (NIH Publication No. 85-23, Revised 1996) and were approved by the Institutional Animal Care and Use Committee of Capital Medical University. Healthy male Wistar rats weighing 110.0??10.0?g (SPF grade) were purchased from Beijing Vital River Laboratory Animal Technology Co., Ltd, China. Animals were maintained in 12?h light-dark cycles, and food and water were available ad libitum. Before conducting the experiment, blood was drawn from the tail of each rat, and baseline plasma lipids were decided using Hoechst 33258 trihydrochloride assay kits (Nanjing Jiancheng Bioengineering Institute, China). Then, rats were randomly divided into two different dietary groups: the normal group Hoechst 33258 trihydrochloride ((+?NO2?+?NO3) concentration has been demonstrated to reflect total NO formation. The NOcontent in thoracic aortic tissue was decided using the NO assay kit (nitrate reductase method) (Nanjing Jiancheng Bioengineering Institute, China) and calculated as nmol/mg protein. 2.5. Determination of cGMP in Thoracic Aortic Tissue The cGMP levels in the thoracic aortic tissue were determined by [125I] cGMP radioimmunoassay with commercially available kits (Shanghai Chinese Medicine University, China) and assayed for cGMP in duplicates according to the manufacturer’s instructions. The results of duplicate assays were averaged. The cGMP level was calculated as pmol/mg protein. 2.6..And, there was a negative correlation between vascular endothelial function, NOcontent or cGMP level, and MPO activity in the HC group and the PIO intervention group. ACh, an endothelium-dependent vasodilator, and SNP, an endothelium-independent vasodilator in vascular rings in vitro. The vascular MPO activity, NOcontent, and cGMP level were measured by the MPO activity assay kit, NO assay kit, and cGMP RIA kit. Results Compared with rats fed with normal diet, endothelium-dependent vasodilation, NOcontent, and cGMP level were decreased, and MPO activity was increased in thoracic aortas of rats fed with HC diet. There was a negative correlation between vascular endothelial function, NOcontent or cGMP level, and MPO activity. PIO obviously reduced the MPO activity, increased NOcontent and cGMP level, and improved endothelium-dependent vasodilation function in HC rats, which was essentially the same as that seen with DDS. And, there was a negative correlation between vascular endothelial function, NOcontent or cGMP level, and MPO activity in the HC group and the PIO intervention group. Conclusion MPO might provoke vascular endothelial dysfunction in hypercholesterolemic rats by reducing the NO biological activity and impairing the NO/cGMP/cGK signaling pathway. PIO might inhibit vascular MPO activity and increase NO bioavailability with the net result of reversing endothelial dysfunction. 1. Introduction Coronary artery disease (CAD) becomes one of the most important diseases that affect longevity and survival quality of aging [1]. Endothelial dysfunction is the first stage in the progression of atherogenesis [2], and hypercholesterolemia is one of the most important causes of endothelial dysfunction [3]. The mechanism of vascular endothelial dysfunction caused by hypercholesterolemia is complex, in which a decrease in the bioavailability of nitric oxide (NO) [4] and impaired NO/cGMP/cGK signaling are considered important contributory mechanisms [5]. Therefore, if the cause responsible for decreased NO bioavailability in hypercholesterolemia is determined and then blocked, it is thought that vascular endothelial function could be effectively maintained, thereby reducing the occurrence of atherosclerosis. Myeloperoxidase (MPO) is an oxidase that is stored in azurophilic granules of neutrophils and monocytes, which is usually released extracellularly during inflammation [6]. MPO plays an important role in the formation and development of many diseases, including atherosclerosis [7]. Studies have shown [8] that MPO is usually abundantly accumulated in the basement Hoechst 33258 trihydrochloride membrane under the vascular endothelium in hypercholesterolemia, and it is speculated that it may lead to endothelial dysfunction by the precipitation of NO. However, the specific mechanism of action of MPO remains to be elucidated. Upon activation of peroxisome proliferator-activated receptor (PPARagonists can restore NO bioavailability by regulating MPO, thereby improving vascular endothelial function and delaying the progression of atherogenesis in hypercholesterolemia, have not been confirmed. Therefore, the aims of this investigation were as follows: first, to verify that vascular endothelial dysfunction is usually caused by a decrease in NO bioavailability in hypercholesterolemia, and on this basis, to observe and analyze whether MPO directs endothelial dysfunction in hypercholesterolemia by affecting the vascular NO/cGMP/cGK signaling pathway. We also aimed to further observe whether PPARagonists could reverse vascular endothelial dysfunction in hypercholesterolemia and, if possible, to determine whether or not this was related to the regulation of vascular MPO and subsequent restoration of NO bioavailability. 2. Materials and Methods 2.1. Animals All animal procedures utilized in the investigations conformed to the Guiding Principles in the Use and Care of Animals, published by the National Institutes of Health (NIH Publication No. 85-23, Revised 1996) and were approved by the Institutional Animal Care and Use Committee of Capital Medical University. Healthy male Wistar rats weighing 110.0??10.0?g (SPF grade) were purchased from Beijing Vital River Laboratory Animal Technology Co., Ltd, China. Animals were maintained in 12?h light-dark cycles, and food and water were available ad libitum. Before conducting the experiment, blood was drawn from the tail of each rat, and baseline plasma lipids were decided using assay kits (Nanjing Jiancheng Bioengineering Institute, China). Then, rats were randomly divided into two different dietary groups: the normal group ((+?NO2?+?NO3) concentration has been demonstrated to reflect total NO formation. The NOcontent RGS8 in thoracic aortic tissue was decided using the NO assay kit (nitrate reductase method) (Nanjing Jiancheng Bioengineering Institute, China) and calculated as nmol/mg protein. 2.5. Determination of cGMP in Thoracic Aortic Tissue The cGMP levels in the thoracic aortic tissue were determined by [125I] cGMP radioimmunoassay with commercially available kits (Shanghai Chinese Medicine University, China) and assayed for cGMP in duplicates according to the manufacturer’s instructions. The results of duplicate assays.