Intravascular ultrasound observations of atherosclerotic lesion formation and restenosis in patients with diabetes mellitus

Coronary artery disease is more aggressive in diabetic patients than in nondiabetics; they have more diffuse disease, higher mortality rates and worse clinical outcomes after coronary interventions. Intravascular ultrasound (IVUS) produces transmural tomographic images of the coronary arteries in vivo. Recent IVUS studies have provided new insights into the mechanisms of stenosis formation and restenosis in both nondiabetic and diabetic patients. Arterial remodeling is defined as a change in arterial area. During atherogenesis, an increase in arterial area usually accompanies plaque accumulation to delay lumen compromise. Stenosis formation is related to: (a) the rate of plaque accumulation versus the rate of positive remodeling; and (b) the limits and ultimate failure of positive remodeling. However, there is a marked variability in remodeling. IVUS studies have suggested that remodeling may be impaired in some diabetic patients during atherogenesis. Following non-stent catheter-based interventions, serial (post-intervention and follow-up) IVUS studies have shown that the change in lumen area correlates better with the change in arterial area (remodeling) than with the change in plaque area (neointimal hyperplasia). In some patients, a positive remodeling response mitigates against the increase in plaque area to limit late lumen loss and restenosis. Neointimal hyperplasia is exaggerated in diabetic patients. Despite this, there is a reduced frequency of positive remodeling, potentially similar to the impaired positive remodeling in some diabetic patients during atherogenesis. Failed or inadequate arterial remodeling may contribute to the pathogenesis and natural history of atherosclerotic coronary artery disease in diabetic patients.     

The onset of atherosclerotic lesion formation in hypercholesterolemic rabbits is delayed by iron depletion.

The theory that iron may play a significant role in atherogenesis by promoting the formation of free radicals is controversial. Previous results using the new technique of nuclear microscopy showed a seven-fold increase in iron concentrations within newly formed atherosclerotic lesions in hypercholesterolemic rabbits compared to healthy artery tissue. In a follow-up time sequence study described here, we show that iron accumulation occurs at the onset of lesion formation. In addition, weekly bleeding decreases the iron uptake into the artery wall and delays the onset of atherogenesis. These results provide direct evidence for a key role of iron in initiating atherogenesis.     

How HIV protease inhibitors promote atherosclerotic lesion formation

PURPOSE OF REVIEW: One of the aims of this review is to summarize recent clinical approaches used to determine the role of HIV protease inhibitors in the development of cardiovascular disease. Another aim is to discuss possible molecular mechanisms whereby HIV protease inhibitors may promote atherogenesis. RECENT FINDINGS: Several clinical studies have recently used ultrasonography to demonstrate increased intimal medial thickness and alterations in the structural characteristics of epi-aortic lesions in patients receiving HIV protease inhibitors. Molecular studies have indicated that several mechanisms are likely involved in mediating the effects of protease inhibitors. Possible mechanisms include inhibition of the proteasome, increased CD36 expression in macrophage, inhibition of lipoprotein lipase-mediated lipolysis, decreased adiponectin levels, and dysregulation of the NF-kappaB pathway. SUMMARY: The currently available data strongly suggest that HIV protease inhibitors negatively impact the cardiovascular system. As is often the case with complex diseases like atherosclerosis it appears that HIV protease inhibitors affect the cardiovascular system through several distinct mechanisms by affecting various components of the arterial wall directly or indirectly by influencing lipoprotein and glucose metabolism of the body.     

Exposure to ambient particles accelerates monocyte release from bone marrow in atherosclerotic rabbits

Exposure to air pollution [particulate matter, particles <10 microm (PM(10))] causes a systemic inflammatory response that includes stimulation of the bone marrow (BM) and progression of atherosclerosis. Monocytes are known to play a key role in atherogenesis by migration into subendothelial lesions where they appear as foam cells. The present study was designed to quantify the BM monocyte response in Watanabe heritable hyperlipidemic (WHHL) rabbits after PM(10) exposure. WHHL rabbits were given twice weekly intrapharyngeal instillations of 5 mg of PM(10) for 4 wk to a total of 40 mg and compared with control WHHL or New Zealand White (NZW) rabbits. The thymidine analog 5'-bromo-2'-deoxyuridine was used to label dividing cells in the BM and a monoclonal antibody to identify monocytes in peripheral blood. The transit time of monocytes through the BM was faster in WHHL than in NZW rabbits (30.4 +/- 1.9 h vs. 35.2 +/- 0.9 h, WHHL vs. NZW; P < 0.05). PM(10) instillation exposure increased circulating band cell counts, caused rapid release of monocytes from the BM, and further shortened their transit time through the BM to 23.2 +/- 1.6 h (P < 0.05). The percentage of alveolar macrophages containing particles in the lung correlated with the BM transit time of monocytes (r(2) = 0.45, P <0.05). We conclude that atherosclerosis increases the release of monocytes from the BM, and PM(10) exposure accelerates this process in relation to the amount of particles phagocytosed by alveolar macrophages.     

High purity tocotrienols attenuate atherosclerotic lesion formation in apoE-KO mice

Previous studies have demonstrated that tocotrienol (T3) has antiatherogenic effects. However, the T3 preparations used in those studies contained considerable amounts of tocopherol (Toc), which might affect the biological activity of T3. There is little information on the effect of highly purified T3 on atherosclerosis formation. This study investigated the effect of high-purity T3 on atherosclerotic lesion formation and the underlying mechanisms. Male apolipoprotein E knockout (apoE-KO) mice were fed a cholesterol-containing diet either alone or supplemented with T3 concentrate (Toc-free T3) or with α-Toc for 12 weeks. ApoE-KO mice fed the 0.2% T3-supplemented diet showed reduced atherosclerotic lesion formation in the aortic root. The 0.2% T3 diet induced Slc27a1 and Ldlr gene expression levels in the liver, whereas the α-Toc-supplemented diet did not affect those expression levels. T3 was predominantly deposited in fat tissue in the T3 diet-fed mice, whereas α-Toc was preferentially accumulated in liver in the α-Toc diet-fed mice. Considered together, these data demonstrate that dietary T3 exerts anti-atherosclerotic effect in apoE-KO mice. The characteristic tissue distribution and biological effects of T3, that are substantially different from those of Toc, may contribute to the antiatherogenic properties of T3.     

Relationship of vascular 15-lipoxygenase induction to atherosclerotic plaque formation in rabbits

Aortas from atherosclerotic rabbits have increased levels of 15-lipoxygenase, but the relationship between induction of this enzyme and the atherosclerotic process has not been defined. We found that dietary administration of cortisone acetate significantly suppressed atherosclerotic plaque formation in both Watanabe Heritable Hyperlipidemic (WHHL) and cholesterol-fed WHHL/NZW heterozygous rabbits. There was, however, no corresponding decrease in the elevated 15-lipoxygenase activity. In addition, the elevated 15-lipoxygenase activity in atherosclerotic rabbit aortas was uniformly distributed throughout the aorta, and was not preferentially localized in the lesions. These results indicate that induction of the 15-lipoxygenase is not necessarily causally related to plaque development, and that plaques are not the major source of the increased enzyme activity. However, the results confirm that hypercholesterolemia is a necessary condition for both atherosclerosis and 15-lipoxygenase induction, suggesting that perhaps the 15-lipoxygenase may represent a protective response to the hyperlipidemic stress. This possibility is supported by the finding that the induced 15-lipoxygenase converts linoleic acid, which is the predominant essential fatty acid in aorta, to 13-hydroxyoctadecadienoic acid (13-HODE). This compound is a chemorepellant factor for platelets, inhibits platelet thromboxane synthesis, and stimulates prostacyclin synthesis by endothelial cells.     

组织蛋白酶S与ApoE-/-小鼠动脉粥样硬化的实验研究

目的:观察组织蛋白酶S(Cathepsin S)在不同周龄我脂蛋白E基因缺陷(ApoE-/-)小鼠主动脉的表达,初步探讨Cathepsin S对ApoE-/-小鼠动脉粥样硬化(As)病变的影响.方法:将16只8周龄ApoE-/-小鼠随机分为两组:16周龄组(n=8),24周龄组(n=8),均饲以高脂饮食,分别在16周龄和24周龄处死动物.采用普通光镜、病理图象分析法测定主动脉As斑块面积及管腔面积;免疫组织化学染色方法观察组织蛋白酶S(Cathepsin S)在不同周龄ApoE-/-小鼠主动脉的表达.结果:16周龄组ApoE-/-小鼠主动脉根部出现As病变;与16周龄组ApoE-/-小鼠相比,24周龄组ApoE-/-小鼠主动脉根部As病变显著增强(P＜0.01),免疫组化显示Cathepsin S表达明显增加(P＜0.01).结论:Cathepsin S在ApoE-/-小鼠主动脉的表达随As病变程度增强而显著增加.     

A direct role for the macrophage low density lipoprotein receptor in atherosclerotic lesion formation.

To evaluate the contribution of the macrophage low density lipoprotein receptor (LDLR) to atherosclerotic lesion formation, we performed bone marrow transplantation studies in different mouse strains. First, LDLR(-/-) mice were transplanted with either LDLR(+/+) marrow or LDLR(-/-) marrow and were challenged with an atherogenic Western type diet. The diet caused severe hypercholesterolemia of a similar degree in the two groups, and no differences in the aortic lesion area were detected. Thus, macrophage LDLR expression does not influence foam cell lesion formation in the setting of extreme LDL accumulation. To determine whether macrophage LDLR expression affects foam cell formation under conditions of moderate, non-LDL hyperlipidemia, we transplanted C57BL/6 mice with either LDLR(-/-) marrow (experimental group) or LDLR(+/+) marrow (controls). Cholesterol levels were not significantly different between the two groups at baseline or after 6 weeks on a butterfat diet, but were 40% higher in the experimental mice after 13 weeks, mostly due to accumulation of beta-very low density lipoprotein (beta-VLDL). Despite the increase in cholesterol levels, mice receiving LDLR(-/-) marrow developed 63% smaller lesions than controls, demonstrating that macrophage LDLR affects the rate of foam cell formation when the atherogenic stimulus is beta-VLDL. We conclude that the macrophage LDLR is responsible for a significant portion of lipid accumulation in foam cells under conditions of dietary stress.     

Pneumococcal vaccination decreases atherosclerotic lesion formation: molecular mimicry between Streptococcus pneumoniae and oxidized LDL

During the progression of atherosclerosis, autoantibodies are induced to epitopes of oxidized low-density lipoprotein (oxLDL) and active immunization of hypercholesterolemic mice with oxLDL ameliorates atherogenesis. We unexpectedly found that many autoantibodies to oxLDL derived from 'naive' atherosclerotic mice share complete genetic and structural identity with antibodies from the classic anti-phosphorylcholine B-cell clone, T15, which protect against common infectious pathogens, including pneumococci. To investigate whether in vivo exposure to pneumococci can affect atherogenesis, we immunized Ldlr(-/-) mice with Streptococcus pneumoniae. This induced high circulating levels of oxLDL-specific IgM and a persistent expansion of oxLDL-specific T15 IgM-secreting B cells primarily in the spleen, which were cross-reactive with pneumococcal determinants. Pneumococcal immunization decreased the extent of atherosclerosis, and plasma from these mice had an enhanced capacity to block the binding of oxLDL to macrophages. These studies show molecular mimicry between epitopes of oxLDL and S. pneumoniae and indicate that these immune responses can have beneficial effects.     

Hemodynamics simulation and identification of susceptible sites of atherosclerotic lesion formation in a model abdominal aorta

Employing the rabbit's abdominal aorta as a suitable atherosclerotic model, transient three-dimensional blood flow simulations and monocyte deposition patterns were used to evaluate the following hypotheses: (i) simulation of monocyte transport through a model of the rabbit abdominal aorta yields cell deposition patterns similar to those seen in vivo, and (ii) those deposition patterns are correlated with hemodynamic wall parameters related to atherosclerosis. The deposition pattern traces a helical shape down the aorta with local elevation in monocyte adhesion around vessel branches. The cell deposition pattern was altered by an exercise waveform with fewer cells attaching in the upper abdominal aorta but more attaching around the renal orifices. Monocyte deposition was correlated with the wall shear stress gradient and the wall shear stress angle gradient. The wall stress gradient, the wall shear stress angle gradient and the normalized monocyte deposition fraction were correlated with the distribution of monocytes along the abdominal aorta and monocyte deposition is correlated with the measured distribution of monocytes around the major abdominal branches in the cholesterol-fed rabbit. These results suggest that the transport and deposition pattern of monocytes to arterial endothelium plays a significant role in the localization of lesions.     

Endothelial autophagic flux hampers atherosclerotic lesion development

Blood flowing in arteries generates shear forces at the surface of the vascular endothelium that control its anti-atherogenic properties. However, due to the architecture of the vascular tree, these shear forces are heterogeneous and atherosclerotic plaques develop preferentially in areas where shear is low or disturbed. Here we review our recent study showing that elevated shear forces stimulate endothelial autophagic flux and that inactivating the endothelial macroautophagy/autophagy pathway promotes a proinflammatory, prosenescent and proapoptotic cell phenotype despite the presence of atheroprotective shear forces. Specific deficiency in endothelial autophagy in a murine model of atherosclerosis stimulates the development of atherosclerotic lesions exclusively in areas of the vasculature that are normally resistant to atherosclerosis. Our findings demonstrate that adequate endothelial autophagic flux limits atherosclerotic plaque formation by preventing endothelial apoptosis, senescence and inflammation.     

A nerve-conditioning lesion accelerates limb regeneration in the newt

A nerve-conditioning lesion induced sustained acceleration of limb regeneration. Newt limb nerves were subjected to a conditioning lesion by unilateral axotomy at the elbow 2 weeks prior to amputating both limbs above the elbows. Limbs on the side that had received a conditioning lesion began the regeneration process 3-4 days earlier than contralateral controls and this difference was observed up to recognizable digit formation. Limb buds on the conditioned sides had a twofold greater axonal density than contralateral counterparts at 2 weeks after amputation. Since limb bud formation is dependent on a sufficient quantity of axonal regrowth, accelerated limb regeneration is apparently due to accelerated reinnervation.     

Development of atherosclerotic lesions in cholesterol-loaded rabbits.

To examine both of the target vessels and the optimal time of their endothelial denudation to study vascular restenosis after balloon injury in cholesterol-loaded rabbits, we made 36 atherosclerotic rabbits by feeding a hypercholesterol diet, and histologically examined the onset time and the development of atherosclerosis. Atheromatous changes were observed first after the 5th week in the thoracic aorta from the start of the diet, and then extended to the abdominal aorta, coronary artery with time. The atherosclerotic lesions in the thoracic aorta and the proximal portion of the coronary artery showed high-grade concentric intimal thickening with luminal stenosis. The abdominal aortic lesion mildly progressed. In the renal, carotid and femoral arteries, in contrast, slight atheroscleromatous changes developed during the diet period. These results suggest that the thoracic and abdominal aortas and the coronary artery would be suitable as target vessels to study vascular restenosis after balloon injury, and the endothelial denudation of these vessels should be performed between the 8th and 15th week in this diet protocol for an accurate analysis.     

Gene expression in atherosclerotic lesion of ApoE deficient mice

BACKGROUND: Atherosclerosis, the major cause of mortality and invalidity in industrialized countries, is a multifactorial disease associated with high plasma cholesterol levels and inflammation in the vessel wall. Many different genes have previously been demonstrated in atherosclerosis, although limited numbers of genes are dealt with in each study. In general, data on dynamic gene expression during disease progress is limited and large-scale evaluation of gene expression patterns during atherogenesis could lead to a better understanding of the key events in the pathogenesis of atherosclerosis. We have therefore applied a mouse gene filter array to analyze gene expression in atherosclerotic ApoE-deficient mice. MATERIALS AND METHODS: ApoE-deficient mice were fed atherogenic western diet for 10 or 20 weeks and aortas isolated. C57BL/6 mice on normal chow were used as controls. The mRNAs of 15 animals were pooled and hybridized onto commercially available Clontech mouse gene array filters. RESULTS: The overall gene expression in the ApoE-deficient and control mice correlated well at both time points. Gene expression profiling showed varying patterns including genes up-regulated at 10 or 20 weeks only. At 20 weeks of diet, an increasing number of up-regulated genes were found in ApoE-deficient mice. CONCLUSIONS: The gene expression in atherogenesis is not a linear process with a maximal expression at advanced lesion stage. Instead, several genes demonstrate a dynamic expression pattern with peaks at the intermediate lesions stage. Thus, detailed evaluation of gene expression at several time points should help understanding the development of atherosclerosis and establishment of preventive intervention.     

Iron-ion radiation accelerates atherosclerosis in apolipoprotein E-deficient mice

Radiation exposure from a number of terrestrial sources is associated with an increased risk for atherosclerosis. Recently, concern over whether exposure to cosmic radiation might pose a similar risk for astronauts has increased. To address this question, we examined the effect of 2 to 5 Gy iron ions ((56)Fe), a particularly damaging component of cosmic radiation, targeted to specific arterial sites in male apolipoprotein E-deficient (apoE(-/-)) mice. Radiation accelerated the development of atherosclerosis in irradiated portions of the aorta independent of any systemic effects on plasma lipid profiles or circulating leukocytes. Further, radiation exposure resulted in a more rapid progression of advanced aortic root lesions, characterized by larger necrotic cores associated with greater numbers of apoptotic macrophages and reduced lesional collagen compared to sham-treated mice. Intima media thickening of the carotid arteries was also exacerbated. Exposure to (56)Fe ions can therefore accelerate the development of atherosclerotic lesions and promote their progression to an advanced stage characterized by compositional changes indicative of increased thrombogenicity and instability. We conclude that the potential consequences of radiation exposure for astronauts on prolonged deep-space missions are a major concern. Knowledge gained from further studies with animal models should lead to a better understanding of the pathophysiological effects of accelerated ion radiation to better estimate atherogenic risk and develop appropriate countermeasures to mitigate its damaging effects.     

Sustained hypothermia accelerates microvascular thrombus formation in mice

Cold is supposed to be associated with alterations in blood coagulation and a pronounced risk for thrombosis. We studied the effect of clinically encountered systemic hypothermia on microvascular thrombosis in vivo and in vitro. Ferric chloride-induced microvascular thrombus formation was analyzed in cremaster muscle preparations from hypothermic mice. Additionally, flow cytometry and Western blot analysis was used to evaluate the effect of hypothermia on platelet activation. To test whether preceding hypothermia predisposes for enhanced thrombosis, experiments were repeated after hypothermia and rewarming to 37 degrees C. Control animals revealed complete occlusion of arterioles and venules after 742 +/- 150 and 824 +/- 172 s, respectively. Systemic hypothermia of 34 degrees C accelerated thrombus formation in arterioles and venules (279 +/- 120 and 376 +/- 121 s; P < 0.05 vs. 37 degrees C). This was further pronounced after cooling to 31 degrees C (163 +/- 57 and 281 +/- 71 s; P < 0.05 vs. 37 degrees C). Magnitude of thrombin receptor activating peptide (TRAP)-induced platelet activation increased with decreasing temperatures, as shown by 1.8- and 3.0-fold increases in mean fluorescence after PAC-1 binding to glycoprotein (GP)IIb-IIIa and 1.6- and 2.9-fold increases of fibrinogen binding on incubation at 34 degrees C and 31 degrees C. Additionally, tyrosine-specific protein phosphorylation in platelets was increased at hypothermic temperatures. In rewarmed animals, kinetics of thrombus formation were comparable to those in normothermic controls. Concomitantly, spontaneous and TRAP-enhanced GPIIb-IIIa activation did not differ between rewarmed platelets and those maintained continuously at 37 degrees C. Moderate systemic hypothermia accelerates microvascular thrombosis, which might be mediated by increased GPIIb-IIIa activation on platelets but does not cause predisposition with increased risk for microvascular thrombus formation after rewarming.