Endothelium,thrombosis and atherosclerosis

The endothelium constitutes a specialized organ, with unique metabolic properties. Since the introduction of in vitro culture techniques, studies on the function of endothelial cells have rapidly increased and our knowledge has been greatly enhanced. It is now established that endothelial cells can either promote hemostasis or exert antithrombotic activities. These activities are in well controlled balance. Injuries to the intimal vascular monolayer may play a role in the pathogenesis of atherosclerosis and its complications. Two types of endothelial cell injury have been described: a denuding injury, secondary to endothelial cell necrosis and desquamation, which triggers platelet/subendothelial interactions, and a non-denuding injury, which induces new endothelial properties and the loss of intimal thromboresistance. Thrombosis may complicate atherosclerosis at different stages. A role for inflammatory mediators in the pathogenesis of thrombosis has been stressed recently and this may have implications for future directions in the study of atherothrombotic disease.     

Animal models of atherosclerosis

In this mini-review several commonly used animal models of atherosclerosis have been discussed. Among them, emphasis has been made on mice, rabbits, pigs and non-human primates. Although these animal models have played a significant role in our understanding of induction of atherosclerotic lesions, we still lack a reliable animal model for regression of the disease. Researchers have reported several genetically modified and transgenic animal models that replicate human atherosclerosis, however each of current animal models have some limitations. Among these animal models, the apolipoprotein (apo) E-knockout (KO) mice have been used extensively because they develop spontaneous atherosclerosis. Furthermore, atherosclerotic lesions developed in this model depending on experimental design may resemble humans’ stable and unstable atherosclerotic lesions. This mouse model of hypercholesterolemia and atherosclerosis has been also used to investigate the impact of oxidative stress and inflammation on atherogenesis. Low density lipoprotein (LDL)-r-KO mice are a model of human familial hypercholesterolemia. However, unlike apo E-KO mice, the LDL-r-KO mice do not develop spontaneous atherosclerosis. Both apo E-KO and LDL-r-KO mice have been employed to generate other relevant mouse models of cardiovascular disease through breeding strategies. In addition to mice, rabbits have been used extensively particularly to understand the mechanisms of cholesterol-induced atherosclerosis. The present review paper details the characteristics of animal models that are used in atherosclerosis research.     

Platelets,thrombosis, coagulation,and atherosclerosis

When I first got the invitation to join a medical delegation going to Moldova, I thought for a moment that our destination was the fictional country in the old Marx Brothers movie Duck Soup. On further checking, it turns out that entertaining place was called Freedonia. I now know that Moldova is indeed a real country, bordered on the west by Romania and on the other three sides by the Ukraine. It is a proud country, rich with traditions, and its people are warm, giving, eager to learn ways to improve their healthcare system, and deeply appreciative of our attempts to help them in the task.     

Lipoprotein(a) as a risk factor for atherosclerosis and thrombosis: mechanistic insights from animal models

Evidence continues to accumulate from epidemiological studies that elevated plasma concentrations of lipoprotein(a) [Lp(a)] are a risk factor for a variety of atherosclerotic and thrombotic disorders. Lp(a) is a unique lipoprotein particle consisting of a moiety identical to low-density lipoprotein to which the glycoprotein apolipoprotein(a) [apo(a)] that is homologous to plasminogen is covalently attached. These features have suggested that Lp(a) may contribute to both proatherogenic and prothrombotic/antifibrinolytic processes and in vitro studies have identified many such candidate mechanisms. Despite intensive research, however, definition of the molecular mechanisms underlying the epidemiological data has proven elusive. Moreover, an effective and well-tolerated regimen to lower Lp(a) levels has yet to be developed. The use of animal models holds great promise for resolving these questions. Establishment of animal models for Lp(a) has been hampered by the absence of this lipoprotein from common small laboratory animals. Transgenic mice and rabbits expressing human apo(a) have been developed and these have been used to: (i) examine regulation of apo(a) gene expression; (ii) study the mechanism and molecular determinants of Lp(a) assembly from LDL and apo(a); (iii) demonstrate that apo(a)/Lp(a) are indeed proatherogenic and antifibrinolytic; and (iv) identify structural domains in apo(a) that mediate its pathogenic effects. The recent construction of transgenic apo(a) rabbits is a particularly promising development in view of the excellent utility of the rabbit as a model of advanced atherosclerosis.     

Inflammation, thrombosis and atherosclerosis: results of the Glostrup study

Summary.  Inflammation and thrombosis are important mechanisms in cardiovascular disease, as illustrated by the consistent association between inflammatory and hemostatic variables and the risk of cardiovascular events in epidemiological studies. However, the relationship between plasma concentrations of inflammatory and hemostatic markers and the severity of atherosclerosis is not yet well studied. We have evaluated 325 men and 370 women of 60 years, participating in the Danish Glostrup study. We diagnosed atherosclerosis by ultrasonographic measurement of intima-media thickness (IMT) of the right carotid artery and the assessment of plaque occurrence. Plasma samples were analyzed for the concentration of C-reactive protein (CRP), fibrinogen, d -dimer, plasminogen activator inhibitor type-1 (PAI-1) antigen and activity, tissue-type plasminogen activator (t-PA) antigen and activity, factor VII (FVII) antigen, FVII coagulant activity (FVII:C) and activated FVII (FVIIa). DNA variations were determined for fibrinogen, PAI-1, t-PA, FVII, factor XIII and methylene tetrahydrofolate reductase (MTHFR). Subjects with high IMT (upper 10% of distribution, n  = 63) had higher CRP levels [2.2 mg L⁻¹ (SE 0.3)] than subjects with IMT in the lowest tertile ( n  = 217) [1.7 mg L⁻¹ (SE 0.1), P  = 0.04], whereas there was no association between the hemostatic variables and IMT. There was an association between fibrinogen and d -dimer concentrations and number of plaques ( P  < 0.01), whereas there were no associations between CRP and the other hemostatic variables and the number of plaques. Genetic variation in the t-PA and MTHFR gene was associated with IMT. In conclusion, in the Glostrup population study, thrombosis and inflammation are associated with the severity of atherosclerosis, as reflected by IMT and plaque occurrence.     

Experimental atherosclerosis: effects of oestrogen and atherosclerosis on thromboxane and prostacyclin formation

We evaluated the effect of oestrogen and experimental atherosclerosis on the in vivo formation of thromboxane and prostacyclin in rabbits. Twenty-four New Zealand White rabbits were divided into four groups. One group received control diet, one group received control diet and oestrogen, one group received control diet supplemented with 1% cholesterol and one group received cholesterol supplemented diet and oestrogen during 3 months. The in vivo formation of thromboxane and prostacyclin were measured as 2,3-dinor-TxB2 and 2,3-dinor-6-keto-PGF1 alpha in urine by gas chromatography/mass spectrometry. All rabbits on cholesterol diet became hypercholesterolaemic and developed atherosclerosis. As in previous experiments cholesterol and oestrogen-treated rabbits had only minor atherosclerosis compared to purely cholesterol-fed rabbits. The in vivo production of thromboxane in oestrogen-treated rabbits decreased from 1641 +/- 162 pg mg-1 creatinine pretreatment to 808 +/- 92 pg mg-1 creatine at 12 weeks (P = 0.0001). In contrast, the in vivo production of prostacyclin increased during oestrogen treatment (P = 0.0027). The in vivo production of prostacyclin decreased during pure cholesterol feeding without oestrogen 1384 +/- 219 pg mg-1 creatinine to 702 +/- 142 pg mg-1 creatinine (P = 0.0091). The ratio of in vivo prostacyclin to thromboxane formation increased 2-3-fold during oestrogen therapy (P = 0.0007).(ABSTRACT TRUNCATED AT 250 WORDS)     

冠心病患者血栓形成相关因素的变化

目的探讨冠状动脉病变中血清纤维蛋白原(Fg)、组织型纤溶酶原激活物(t-PA)、血浆D-二聚体(D-Di-mer)与血栓形成关系,并就其作用机制进行研究。方法急性心肌梗死(AMI)组28例、不稳定心绞痛(UAP)组24例、稳定心绞痛(SAP)组30例和正常对照组20例。分别检测血清Fg、血浆D-Dimer、t-PA及其抑制物(PAI)活性,并对照比较其含量与冠状动脉粥样硬化血栓形成的关系。结果血浆t-PA活性:AMI和UAP明显低于SAP与健康对照组(P<0.01);AMI组和UAP组之间,SAP组与健康对照组之间差异无显著性(P>0.05)。血浆PAI活性、D-Dimer和Fg含量:AMI和UAP组明显高于SAP和健康对照组(P<0.01);AMI组和UAP组之间,SAP组与健康对照组之间差异无显著性(P>0.05)。结论监测冠状动脉粥样硬化患者血清中血清Fg含量、t-PA、D-Dimer含量,可以及时判断凝血和纤溶功能失衡状况,预防和干扰血栓形成,提高患者良性预后。     

冠心病患者纤溶系统的异常变化

目的探讨冠状动脉病变中血清纤维蛋白原（Fg）、组织型纤溶酶原激活物（t-PA）、血浆D-二聚体（D-Dimer）与血栓形成关系，并就其作用机理进行研究，为临床治疗提供科学依据。方法急性心肌梗死（AMI）组28例、不稳定心绞痛（UAP）组24例、稳定心绞痛（SAP）组30例和正常对照组20例。分别检测血清Fg、血浆D-Dimer、t-PA及其抑制物（PAI）活性，并对照比较其含量与冠状动脉粥样硬化血栓形成的关系。结果血浆t-PA活性：AMI和UAP明显低于SAP与健康对照组（P〈0．01）；AMI组和UAP组之间，SAP组与健康对照组之间差异无统计学意义（P〉0．05）。血浆PAI活性、D-Dimer和Fg含量：AMI和UAP组明显高于SAP和健康对照组（P〈0．01）；AMI组和UAP组之间，SAP组与健康对照组之间差异无统计学意义（P〉0．05）。结论监测冠状动脉粥样硬化患者血清中血清Fg含量、t-PA、D-Dimer含量，可以及时判断凝血和纤溶功能失衡状况，预防和干扰血栓形成，提高患者良性预后。     

Experimental atherosclerosis and cardiac infarcts in rats

Marked obesity was induced in rats by feeding a high fat, egg yolk-rich diet. The obese rats were hyperlipemic and showed an increased incidence of lipomatous coronary lesions, but did not develop severe atheromatous lesions. Spontaneous vascular lesions of several kinds have been observed in aging rats. Among them, plaques containing a fibrin-like material seem to be conspicuous. However, these lesions differ from the experimentally induced changes, which were more fatty. Atherosclerosis, as it is defined in human pathology, has not been observed to develop spontaneously in rats. Experimental induction of marked hyperlipemia and hypercholesterolemia by feeding a high fat egg yolk-rich diet (supplemented with cholesterol, choleate, and thiouracil), and use of viosterol to cause vascular injury, led to severe atherosclerosis, coronary occlusion, and myocardial infarction. A consideration of all the findings reported here leads to renewed support of the concept that atherosclerosis has a combination of causes (Aschoff, Anitschkow, Page). Of all the etiological factors considered here, elevation of blood lipides and vascular injury are thought to be the most important ones.     

Homocyst(e)ine, atherosclerosis, and thrombosis.

Ample clinical and epidemiologic evidence exists to implicate homocyst(e)ine as a risk factor for atherosclerotic vascular disease and thrombosis. The precise mechanisms by which this occurs are uncertain but probably involve injury to endothelium, impairment of endothelial function, lipid peroxidation, oxidation of low-density lipoprotein, and creation of a prothrombotic environment in areas of endothelial injury. Plasma homocyst(e)ine concentration (PHC) can be effectively reduced with oral administration of folic acid. Whether vitamins B6 and B12 are also required in the absence of vitamin deficiency remains uncertain. Studies currently in progress may help to determine whether reduction of PHC will translate into a decrease in clinical vascular events.     

Subclinical atherosclerosis and the risk of future venous thrombosis in the Cardiovascular Health Study

BACKGROUND: Recent reports have suggested an association of atherosclerosis with risk of venous thrombosis. OBJECTIVE: To confirm whether subclinical atherosclerosis is a risk factor for venous thrombosis (VT) among men and women age 65 and older. METHODS: Participants of the Cardiovascular Health Study (n = 4,108) without baseline clinical cardiovascular disease, anticoagulant use or previous VT were followed for a median of 11.7 years after non-invasive assessment of subclinical atherosclerosis using carotid ultrasound (intima-media thickness and presence of plaques), ankle-brachial blood pressure index and electrocardiogram. Each event was classified as idiopathic or secondary. We used Cox proportional hazards regression to estimate the relative risk of overall and idiopathic VT for individuals with and without baseline subclinical atherosclerosis. RESULTS: There were 133 first time VT events. No subclinical atherosclerosis measures were associated with increased risk of overall or idiopathic VT. The adjusted relative risks of overall and idiopathic VT for presence of any type of subclinical disease were 0.60 (95% confidence interval 0.39-0.91) and 0.32 (0.18-0.59), respectively. Most of this association was explained by an inverse association of high-risk carotid plaques (prevalent in 54% of those at risk) with VT. CONCLUSION: Non-invasively measured subclinical atherosclerosis was not associated with increased risk of overall or idiopathic VT in this observational study. Carotid plaques and arterial events during follow up were inversely associated, a finding that requires further study.     

Experimental production of gross atherosclerosis in the rat

Gross atherosclerosis was produced in the rat by feeding purified diets containing cholesterol, sodium cholate, and thiouracil for periods up to 363 days. In a few weeks a marked increase of the serum cholesterol and beta lipoproteins as well as of the liver lipides was observed. Lesions visible in the gross were found on the intimal surfaces of the vessels of all 46 animals examined. These were most prominent in the heart valves and aortic arch. The earliest lesions, which were seen at 31 days, required Sudan staining for gross demonstration. Older lesions were visible without staining. Microscopic coronary artery lesions were present and in one instance were accompanied by massive myocardial infarction. Vascular lesions were characterized by medial and intimal lipide infiltration and cellular intimal plaque formation. In a part of this study the protein level of the diet was altered at the expense of sucrose. The hypercholesteremic response among the rats varied according to the dietary protein level. The lowest response was observed among those animals receiving the highest level of dietary protein. A difference, however, in the severity and extent of the arterial lesions among these relatively small groups of rats could not be established under these experimental conditions. In all these experiments a close correlation existed between the serum cholesterol levels and beta lipoproteins of the S_f20–100 range.