Receptor-mediated pathways of endothelium activity in experimental atherosclerosis

Purinergic signaling and blood vessels in health and disease

Purinergic signaling plays important roles in control of vascular tone and remodeling. There is dual control of vascular tone by ATP released as a cotransmitter with noradrenaline from perivascular sympathetic nerves to cause vasoconstriction via P2X1 receptors, whereas ATP released from endothelial cells in response to changes in blood flow (producing shear stress) or hypoxia acts on P2X and P2Y receptors on endothelial cells to produce nitric oxide and endothelium-derived hyperpolarizing factor, which dilates vessels. ATP is also released from sensory-motor nerves during antidromic reflex activity to produce relaxation of some blood vessels. In this review, we stress the differences in neural and endothelial factors in purinergic control of different blood vessels. The long-term (trophic) actions of purine and pyrimidine nucleosides and nucleotides in promoting migration and proliferation of both vascular smooth muscle and endothelial cells via P1 and P2Y receptors during angiogenesis and vessel remodeling during restenosis after angioplasty are described. The pathophysiology of blood vessels and therapeutic potential of purinergic agents in diseases, including hypertension, atherosclerosis, ischemia, thrombosis and stroke, diabetes, and migraine, is discussed.

Purinergic signaling, dyslipidemia and inflammatory disease

Metabolic syndrome is a compound obesity disorder, wherein the abnormal metabolism of glucose and lipid is associated with the development of chronic inflammatory diseases. The prevalence of this disease is increasing in the developed world, but the causative linkage between these metabolic disorders has remained obscure. Metabolic disease may be associated with chronic nucleotide secretion, purinergic signaling and activation of inflammatory pathways. Purinergic signaling has been implicated in impaired glucose metabolism and inflammatory disease and may contribute to dyslipidemia. Our research shows that purinergic signaling disrupts hepatic lipoprotein metabolism by blocking insulin receptor signaling and by activating cellular autophagic pathways. Chronic stimulation of purinergic signaling may therefore be causative to glucose and lipid metabolic disorders and associated with the development of cardiovascular disease.

Extracellular-purine metabolism in blood vessels (part I). Extracellular-purine level in blood of patients with abdominal aortic aneurysm

Adenosine and adenosine derivatives are the main regulators of purinoceptors (P1 and P2) mediated hemostasis and blood pressure. Since impaired hemostasis and high blood pressure lead to atherosclerosis and to the development of aneurysm, in this study we tested and compared the concentration of extracellular purines (e-purines) in the blood in of patients having abdominal aortic aneurysm with that from healthy volunteers. Whereas adenine nucleosides and nucleotides level in human blood plasma was analysed using reverse phase high performance liquid chromatography (HPLC), cholesterol concentration was estimated by an enzymatic assay. We did not find any correlation between e-purines concentration and the age of healthy volunteers. Furthermore, the sum level of e-purines (ATP, ADP, AMP, adenosine, and inosine) in the control group did not exceed 70 microM, while it was nearly two-fold higher in the blood of patients having abdominal aortic aneurysm, (123 microM). In a special case of people with Leriche Syndrome, a disease characterized by deep atherosclerotic changes, the e-purines level had further increased. Additionally, we also report typical atherosclerotic changes in the aorta using histological assays as well as total cholesterol rise. The significant rise in cholesterol concentration in the blood of the patients with abdominal aortas aneurysm, compared with the control groups, was not unique since 23% of the healthy people also exceeded the normal level of cholesterol. Therefore, our results strongly indicate that the estimation of e-purines concentration in the blood may serve as another indicator of atherosclerosis and warrant further consideration as a futuristic diagnostic tool.

Extracellular purine metabolism in blood vessels (Part II): Activity of ecto-enzymes in blood vessels of patients with abdominal aortic aneurysm

Both platelet aggregation and high blood pressure are associated with development of atherosclerosis. Among other factors that modulate platelet aggregation and blood pressure, extracellular purines (e-purines) influence these processes via purinoceptors P1 and P2 for which they are natural ligands. We hypothesized that ecto-enzymes such as nucleoside triphosphate diphosphohydrolases (NTPDases), adenylate kinase, 5'-nucleotidase, and adenosine deaminase that regulate the level of e-purines may be involved in the development of atherosclerosis. The enzymatic assays were performed either on the fragments of human abdominal aortas obtained after death or on abdominal aneurysm samples collected during surgery. The substrates and products such as adenine nucleosides and nucleotides were analyzed using reverse phase high-performance liquid chromatography (HPLC) method. Here, we estimated and demonstrated the activities of these ecto-enzymes in the patients with atherosclerosis or atherosclerosis-like diseases such as abdominal aneurysm, myocardial infarction, or Leriche syndrome (LS) with worse thrombosis of extremities. In particular, we noticed reduction in activity of NTPDase1(app), NTPDase2(app), ecto-adenylate kinase( app), and ecto-adenosine deaminase(app); however, ecto-5'-nucleotidase(app) that hydrolyzed e-adenosine monophosphate (e-AMP) into e-adenosine did not show any significant changes. This led us to suggest that alteration of the activity of examined ecto-enzymes is responsible for the development of atherosclerosis or atherosclerosis-like diseases.

Free radical generators cause changes in endothelial and inducible nitric oxide synthases and endothelin-1 immunoreactivity in endothelial cells from hyperlipidemic rabbits

Reactive oxygen species (ROS) play an important role in the damage of vascular endothelium during atherogenesis and impaired endothelium-dependent vasorelaxation. We have studied the effect of two ROS generators (H2O2 and menadione) and one of the most potent antioxidants (morin) on the double immunofluorescent staining of endothelial cells (EC) from both Watanabe Heritable Hyperlipidemic (WHHL) and New Zealand White (NZW) rabbits in primary cultures using antibodies against endothelin-1 (ET-1), endothelial (eNOS), and inducible nitric oxide synthase (iNOS). In aortic EC from normal rabbits, ROS decreased the immunoreactivity of eNOS and ET-1 and this effect was significantly reversed by morin. In atherosclerotic rabbits, ROS had the same effect on the immunoreactivity of eNOS and ET-1 but also induced the expression of iNOS immunoreactivity. In general, the cells from WHHL rabbits were less sensitive to the protective effects of morin and more sensitive to the effects of ROS. It thus appears that the protective effect of morin may be due to neutralization of ROS and may be considered for the treatment of early stages of atherosclerosis, before macroscopic lesions have occurred.

Chronic treatment with cyclosporine A in New Zealand rabbit: aortic and erectile tissue alterations

Transplanted patients frequently present erectile impotence. In order to test any interference by cyclosporine A (CsA), which is commonly used in the post-transplantation management, we investigated the in vitro contractile and relaxant responses of corpus cavernosum and aorta from rabbits chronically treated with CsA. Male New Zealand White rabbits 6 months of age were treated with CsA (25 mg/kg per day s.c.) or solvent (corn oil) for 3 weeks. Descending thoracic aorta and erectile tissue were studied in vitro at the end of treatment. Isometric tension was recorded. In thoracic aorta, noradrenaline (0.1-30 mM) induced a concentration-dependent contraction with no difference between the two groups. Acetylcholine (30 nM-3 mM) produced relaxation (52 +/- 4% at 1 mM) that was significantly reduced in comparison to controls (67 +/- 4%, P < 0.05). ATP (3-10 mM) relaxation was not significantly different (maximal 78 +/- 10% and 62 +/- 12% in CsA-treated and controls). The relaxation produced by sodium nitrite was reduced in CsA-treated rabbits (at 10 mM and 0.1 mM concentrations). In erectile tissue, no significant variation in the response of isolated erectile tissue to the above drugs was observed between CsA-treated and control animals. These data indicate that chronic treatment with CsA in rabbits, despite alteration of the in vitro response of thoracic aorta, does not directly influence the function of penile tissue with relaxants.

Characterization of in vitro relaxant mechanisms in erectile tissue from rabbits of different ages

In the present study we investigated the in vitro relaxant response of erectile tissue obtained from rabbits of different ages (3, 7 and 24 months) in order to detect the progression with age of cavernosal activity in response to substances acting via endothelium-dependent or -independent mechanisms. Noradrenaline induced a concentration-dependent contraction (0.1 microM-3 mM), with an increase in the contractility in the 24-month-old group. Acetylcholine produced a concentration-dependent relaxant effect in the three age groups, with a reduction of the maximal relaxant effect in older animals. ATP (10 microM-1 mM) and adenosine (10 microM-1 mM) induced a concentration-dependent relaxant effect that was higher in the older group. The presence of the NO2-synthase inhibitor N omega-nitro-L-arginine methyl ester (L-NAME) (0.1 mM) or of the P2-purinoceptor antagonist suramin did not affect ATP relaxation. Relaxation induced by sodium nitrite and nifedipine was reduced in older animals. In conclusion, aging selectively alters the in vitro responsiveness of rabbit erectile tissue. Purinergic system remains more active despite a decrease in the maximal endothelial cholinergic activity and the direct smooth muscle relaxant component.

Mesenteric and hepatic vascular reactivity in Donryu rats with and without a cholesterol-supplemented diet

Vascular function of Donryu rats fed on a normal or cholesterol-supplemented diet was examined in the isolated perfused mesenteric arterial bed and portally perfused liver. In mesenteric preparations, frequency-dependent vasoconstriction to electrical field stimulation (4-32 Hz, 1 ms, 90 V, 30 s) and dose-dependent vasoconstriction to noradrenaline (0.15-1500 nmol) was similar in both groups. Dose-dependent vasoconstriction to alpha, beta-methylene ATP (0.05-500 nmol) via P2x purinoceptors was significantly impaired in Donryu rats fed on a cholesterol-supplemented diet. In preparations with raised tone (methoxamine 5-35 microM), there was no significant difference in endothelium-dependent relaxation to acetylcholine and ATP, or endothelium-independent relaxation to sodium nitroprusside. In liver preparations, there was no difference in frequency-dependent vasoconstriction to electrical field stimulation (2-32 Hz, 1 ms, 90 V, 30 s), or dose-dependent vasoconstriction to noradrenaline (0.05-500 nmol) and alpha, beta-methylene ATP (0.05-500 nmol) between the groups. In conclusion, in mesenteric arteries, but not in the hepatic portal vasculature of Donryu rats fed on cholesterol P2x purinoceptor function is impaired, but sympathetic neurotransmission is unaffected. Mesenteric endothelial and smooth muscle function is unimpaired.