Cholesterol crystals cause mechanical damage to biological membranes: a proposed mechanism of plaque rupture and erosion leading to arterial thrombosis

BACKGROUND: Plaque rupture and/or erosion is the leading cause of cardiovascular events; however, the process is not well understood. Although certain morphologic characteristics have been associated with ruptured plaques, these observations are of static histological images and not of the dynamics of plaque rupture. To elucidate the process of plaque rupture, we investigated the transformation of cholesterol from liquid to solid crystal to determine whether growing crystals are capable of injuring the plaque cap. HYPOTHESIS: We hypothesized that during cholesterol crystallization the spatial configuration rapidly changes, causing forceful expansion of sharp-edged crystals that can damage the plaque cap. METHODS: Two experiments were performed in vitro: first, cholesterol powder was melted in graduated cylinders and allowed to crystallize at room temperature. Volume changes from liquid to solid state were measured and timed. Second, thin biological membranes (20-40 microm) were put in the path of growing crystals to determine damage during crystallization. RESULTS: As cholesterol crystallized, the peak volume increased rapidly by up to 45% over 3 min and sharp-tipped crystals cut through and tore membranes. The amount of cholesterol and peak level of crystal growth correlated directly (r = 0.98; p < 0.01), as did the amount of cholesterol and rate of crystal growth (r = 0.99; p < 0.01). CONCLUSIONS: These observations suggest that crystallization of supersaturated cholesterol in atherosclerotic plaques can induce cap rupture and/or erosion. This novel insight may help in the development of therapeutic strategies that can alter cholesterol crystallization and prevent acute cardiovascular events.     

Killing the Culprit: Pharmacological Solutions to Get Rid of Cholesterol Crystals

Cholesterol crystals (CCs) play a key role in the pathophysiology of cardiovascular diseases (CVD) via triggering inflammation, plaque formation and subsequently plaque rupture. Although statins can stabilize plaques via calcification and alteration of the lipid composition within plaques, there is still a high residual risk of CVD events among statins users. Several studies have tried to blunt the detrimental effects of cholesterol crystals by pharmacological interventions. Cyclodexterins (CDs) and other nanoformulations, including polymers of CDs and liposomes, have the ability to dissolve CCs in vitro and in vivo. CDs were the first in their class that entered clinical trials and showed promising results, though their ototoxicity outweighed their benefits. Moreover, small molecules with structural similarity to cholesterol may also perturb cholesterol-cholesterol interactions and prevent from expansion of 2D crystalline domains to large 3D CCs. The results from ethyl eicosapentaenoic acid and ursodeoxycholic acid were encouraging and worth further consideration. In this review, the significance of CCs in pathogenesis of CVD is discussed and pharmacological agents with the ability to dissolve CCs or prevent from CCs formation are introduced.     

The dissolution of cholesterol monohydrate crystals in atherosclerotic plaque lipids

Uncomplicated human atherosclerotic plaques often contain large amounts of cholesterol esters and solid cholesterol monohydrate crystals. If such plaques are to regress the crystalline cholesterol would have to dissolve and be transported out of the arterial wall. Since cholesterol is quite insoluble in water, dissolution of plaque crystals might occur through lipids in the plaque, specifically, the cholesterol esters. As part of a study on feasibility of plaque reversal we have studied a specific step involving the dissolution of cholesterol monohydrate into cholesterol ester oil. With specific considerations of the composition and physical state of the cholesterol ester solvent, the size and form of cholesterol monohydrate crystals, the agitation rate, the temperature and the presence of water, we have found that cholesterol esters are an efficient solvent for cholesterol monohydrate crystals. The rate of dissolution was fast reaching 90% of saturation in 1 h. We conclude dissolution of cholesterol monohydrate into cholesterol ester oil is not a rate-limiting step in reversal of the atherosclerotic plaque. We suggest that transport of dissolved cholesterol from cholesterol ester oil may limit the removal. If transport of dissolved cholesterol could be enhanced, cholesterol monohydrate crystals could be rapidly dissolved and facilitate reversal of atherosclerotic lesions.     

Statins improve human coronary atherosclerotic plaque morphology

Statin treatment markedly reduces the incidence of acute coronary events in patients with coronary atherosclerosis. Although imaging studies have indirectly shown the beneficial effects of statins on plaque morphology, there has to our knowledge been no reported histologic comparison of the morphology of coronary plaque in statin-treated versus untreated patients who had substantial coronary artery atherosclerosis. We retrospectively studied arterial sections from the native hearts of patients who had experienced end-stage ischemic heart disease and subsequent cardiac transplantation. Of 44 qualified patients, 33 study patients had received pre-transplantation statin therapy, and 11 control patients had not. Pathologic examination of each explanted heart confirmed coronary artery disease and previous myocardial infarction in all patients. Diabetes mellitus was more prevalent in the study group. The groups were similar in levels of total and low-density lipoprotein cholesterol, and in the available number of arterial cross-sections per patient. All patients had plaques. High-grade lesions were found in 66.3% of cross-sections in the control group, and in 34.6% in the study group (P=0.011). Conversely, the degree of inflammation was markedly lower in the study group: low-grade fibrous plaques occurred in 45.7% of cross-sections in the study group, versus 11.3% in the control group (P=0.006). The study group had significantly fewer high-grade plaques and more fibrous plaques than did the control group at the time of transplantation. Our findings show that statin therapy substantially enhances plaque stabilization. We further suggest that reduction of plaque inflammation is an important aspect of this stabilization.     

Association of statin therapy with reduced coronary plaque rupture: an optical coherence tomography study

OBJECTIVE: Statin therapy induces plaque regression and may stabilize atheromatous plaques. Optical coherence tomography (OCT) is a high-resolution in-vivo imaging modality that allows characterization of atherosclerotic plaques. We aimed to demonstrate the potential utility of OCT in evaluating coronary plaques in patients with or without statin therapy. METHODS: Patients undergoing cardiac catheterization were enrolled. We identified culprit lesions and performed intracoronary OCT imaging. Plaque lipid pool, fibrous cap thickness, and frequency of thin-cap fibroatheroma were evaluated using previously validated criteria. Macrophage density was determined from optical signals within fibrous caps. Presence of calcification, thrombosis, and rupture was assessed. RESULTS: Forty-eight patients were included (26 on statins, 22 without statins). Baseline characteristics were similar apart from lipid profile. Patients on statin therapy had lower total and low-density lipoprotein cholesterol concentrations (4.45+/-1.35 vs. 5.26+/-0.83 mmol/l, P=0.02; 2.23+/-0.78 vs. 3.26+/-0.62 mmol/l, P<0.001, respectively). Frequencies of lipid-rich plaque (69 vs. 82%), thin-cap fibroatheroma (31 vs. 50%), plaque calcification (15 vs. 5%) and thrombosis (15 vs. 32%), and fibrous cap macrophage density were comparable between statin and nonstatin groups (5.9 vs. 6.3%; all P=NS). Ruptured plaques were, however, significantly less frequent in patients on established statin therapy (8 vs. 36%; P=0.03) with a trend toward increased minimum fibrous cap thickness (78 vs. 49 microm; P=0.07). CONCLUSION: We demonstrated the use of OCT in plaque characterization and found that patients on prior statin therapy have reduced incidence of ruptured plaques and a trend toward thicker fibrous caps. This suggests that statins may stabilize coronary plaques.     

Intracoronary Thermography: Does It Help Us in Clinical Decision Making?

The concept of the "vulnerable" plaque has recently emerged to explain how quiescent atherosclerotic lesions evolve to cause clinical events. The morphologic and immunologic determinants specific for the vulnerable plaque have been reported: a large lipid core (>or=40% plaque volume) composed of free cholesterol crystals, cholesterol esters, and oxidized lipids impregnated with tissue factor; a thin fibrous cap depleted of smooth muscle cells and collagen; an outward (positive) remodeling; inflammatory cell infiltration of fibrous cap and adventitia (mostly monocyte-macrophages, some activated T cells, and mast cells); and increased neovascularity. Despite the large amount of information regarding the morphological characteristics of remote lesions, we lack studies with functional assessment of non-culprit lesions. Coronary thermography is a technique for functional assessment of coronary atherosclerotic plaques. Several catheter designs have been proposed. There are catheters with thermistor(s) and wires with thermal sensors at the distal tip. All designs have several advantages and disadvantages. Despite the current limitations of coronary thermography, we gained important pathophysiological and clinical information regarding the vulnerability of atheromatic plaques. It has been documented both experimentally and clinically that increased heat generation is associated with increased macrophage concentration within the plaque. The correlation between local inflammatory involvement and local heat generation has also been observed with the peripheral inflammatory markers such as C-reactive protein. Whether systemic treatment, with agents such as statins or interventional techniques, such as drug-eluting stents, will have an impact on stabilizing vulnerable plaques need to be determined in future studies. In conclusion, although there are several techniques for evaluating morphologically atheromatic plaques, thermography is a promising method for the functional assessment of vulnerable plaque and has been introduced into clinical practice, with a good predictive value for clinical events in patients with increased temperature in the atherosclerotic plaque.     

Stabilization of carotid atheroma assessed by quantitative ultrasound analysis in nonhypercholesterolemic patients with coronary artery disease.

OBJECTIVES: This study examined whether intensive cholesterol-lowering therapy with statins in nonhypercholesterolemic patients is effective in improving echolucency of vulnerable plaques assessed by ultrasound with integrated backscatter (IBS) analysis. BACKGROUND: Atherosclerotic plaque stabilization is a promising clinical strategy to prevent cardiovascular events in patients with coronary artery disease (CAD). There is a correlation between coronary and carotid plaque instability, and echolucent plaques are recognized as vulnerable plaques. METHODS: Consecutive nonhypercholesterolemic patients with CAD were randomly assigned Adult Treatment Panel-III diet therapy (diet group; n = 30) or pravastatin (statin group; n = 30). Echolucent carotid plaques were monitored by measuring intima-media thickness (IMT) and echogenicity by IBS for six months. RESULTS: Total cholesterol, low-density lipoprotein cholesterol (LDL-C), and high-sensitivity C-reactive protein were significantly decreased in the statin group (from 197 +/- 15 mg/dl to 170 +/- 18 mg/dl [p < 0.001]; from 131 +/- 14 mg/dl to 99 +/- 14 mg/dl [p < 0.001]; and from 0.11 [0.04 to 0.22] mg/dl to 0.06 [0.04 to 0.11] mg/dl [p < 0.05]; respectively), whereas only total cholesterol was moderately reduced (from 193 +/- 24 mg/dl to 185 +/- 22 mg/dl [p < 0.05]) and LDL-C and triglycerides insignificantly reduced in the diet group. Significant increases of echogenicity of carotid plaques were noted in the statin group but not in the diet group (from -18.5 +/- 4.1 dB to -15.9 +/- 3.7 dB [p < 0.001] and from -18.2 +/- 4.0 dB to -18.9 +/- 3.5 dB [p = 0.13]; respectively) without significant regression of plaque-IMT values in both groups. CONCLUSIONS: Statin therapy is rapidly effective in increasing echogenicity of vulnerable plaques without regression of plaque size in nonhypercholesterolemic patients with CAD. Quantitative assessment of carotid plaque quality by ultrasound with IBS is clinically useful for monitoring atherosclerotic lesions by evaluating vulnerability of atheroma.     

Dietary cholesterol withdrawal reduces vascular inflammation and induces coronary plaque stabilization in miniature pigs

OBJECTIVE: To study the effect of dietary cholesterol withdrawal on size and composition of LDL-hypercholesterolemia-induced coronary plaques in miniature pigs. METHODS: Pigs were on normal chow (control group), on a cholesterol-rich diet for 37 weeks (hypercholesterolemic group) or on a cholesterol-rich diet followed by normal chow for 26 weeks (cholesterol withdrawal group). Endothelial function was assessed with quantitative angiography after intracoronary infusion of acetylcholine, plaque load with intra-coronary ultrasound and plaque composition with image analysis of cross-sections. The effect of porcine serum on coronary smooth muscle cell (SMC) function was studied in vitro. RESULTS: Cholesterol-rich diet caused LDL-hypercholesterolemia, increased plasma levels of oxidized LDL (ox-LDL) and C-reactive protein (CRP), and induced endothelial dysfunction and coronary atherosclerosis. Dietary cholesterol withdrawal lowered LDL, ox-LDL and CRP. It restored endothelial function, did not affect plaque size but decreased lipid, ox-LDL and macrophage content. Smooth muscle cells and collagen accumulated within the plaque. Increased smoothelin-to-alpha-smooth muscle actin ratio indicated a more differentiated SMC phenotype. Cholesterol lowering reduced proliferation and apoptosis. In vitro, hypercholesterolemic serum increased SMC apoptosis and decreased SMC migration compared to non-hypercholesterolemic serum. CONCLUSIONS: Cholesterol lowering induced coronary plaque stabilization as evidenced by a decrease in lipids, ox-LDL, macrophages, apoptosis and cell proliferation, and an increase in differentiated SMC and collagen. Increased migration and decreased apoptosis of SMC may contribute to the disappearance of the a-cellular core after lipid lowering.     

Mechanismen der Plaquestabilisierung

Numerous angiographic control regression studies have demonstrated that aggressive reduction of plasma cholesterol significantly reduces the incidence of clinical overt cardiovascular complications, but has almost no effect on the angiographically determined luminal diameter of the coronary arteries. These, as well as other morphological and molecular studies have led to a new paradigm of coronary heart disease, i.e. clinical prognosis is not mainly determined by the extent of a single stenosis but by the number and biological nature of atherosclerotic plaque. Accordingly, stable plaques can be differentiated from instable or vulnerable plaques. The vulnerable or instable plaque is characterized by a large lipid-rich core with surrounding inflammation and a thin friable overlying fibrous cap susceptible to rupture or fissuring and thereby a high risk of thrombus formation. Rupture and thrombus formation can cause an acute coronary syndrome, such as unstable angina or myocardial infarction. There is increasing clinical and experimental evidence that statins do not only lower plasma cholesterol, but might also have direct effects on the vessel wall, possibly explaining early benefits in cardiovascular complications. Reduction of plasma cholesterol by lipid lowering therapy has been shown to significantly improve paradoxic vasoconstriction of cardiac vessels, a phenomenon indicating endothelial dysfunction. In addition, lipid lowering therapy can result in a diminution of the lipid-rich core, a reduction of inflammatory cells within the plaques, decreased macrophage activation as well as foam cell formation and events related to thickening of the fibrous cap. A clinical prospective should be to better clinically morphologically characterize the vulnerability of plaques in order to therapeutically and preventively reduced specific events leading to acute coronary syndromes, such as unstable angina or myocardial infarction.     

Supersaturated bile from obese patients without gallstones supports cholesterol crystal growth but not nucleation

Cholesterol crystal formation was studied in gallbladder bile samples collected from 18 patients with cholesterol gallstones, 6 patients with black pigment stones, and 14 obese patients without gallstones. In the absence of seed crystals, bile from patients with cholesterol stones showed a much greater tendency to form cholesterol crystals in vitro than bile of similar cholesterol saturation from patients without cholesterol stones. The ability to form crystals was not related to the biliary hexosamine concentration, an indicator of mucin content. When small seed crystals of cholesterol monohydrate were added to each bile, the seed crystals dissolved in all biles (n = 8) with a cholesterol saturation index less than 0.76. In contrast, 29 of 30 biles with a cholesterol saturation index greater than 0.76 supported crystal growth, even when collected from patients without gallstones. These results indicate that the difference between supersaturated biles in the ability to form cholesterol crystals resides at the nucleation, rather than the growth, stage of crystal formation.     

Plant sterols in serum and in atherosclerotic plaques of patients undergoing carotid endarterectomy

OBJECTIVES: The purpose of this research was to determine whether serum plant sterol levels are associated with those in atheromatous plaque. BACKGROUND: Cholesterol of low-density lipoprotein (LDL) particles contributes to atheromatous plaque formation; LDL also contains most serum non-cholesterol sterols, including plant sterols. The role of plant sterols in atheromatous plaque formation is open. METHODS: Free, ester, and total cholesterol and the respective non-cholesterol sterols were measured by gas-liquid chromatography in serum and arterial tissue of 25 consecutive patients undergoing carotid endarterectomy. The population was ranked to triads according to tissue cholesterol concentration. RESULTS: Cholesterol concentration increased markedly in tissues but not in serum with triads. The ester percentage was lower in the third than in the first triad (47% vs. 56%; p < 0.01) and lower than in serum triads (70%; p < 0.001). Ratios to cholesterol of non-cholesterol sterols decreased in increasing tissue triads, but were unchanged in serum. A major new observation was that the higher the ratio to cholesterol of the surrogate absorption sterols (cholestanol, campesterol, sitosterol, and avenasterol) in serum, the higher was their ratio also in the carotid artery wall (e.g., r = 0.683 for campesterol). Despite undetectable differences in serum and tissue cholesterol concentrations off and on statins, an additional important novel finding was that statin treatment was associated with increased ratios of the absorption sterols in serum and also in the arterial plaque. CONCLUSIONS: The higher the absorption of cholesterol, the higher are the plant sterol contents in serum resulting also in their higher contents in atherosclerotic plaque. However, the role of dietary plant sterols in the development of atherosclerotic plaque is not known.     

Simvastatin attenuates plaque inflammation: evaluation by fluorodeoxyglucose positron emission tomography.

OBJECTIVES: We investigated whether simvastatin attenuates plaque inflammation by using 18F-fluorodeoxyglucose positron emission tomography (18FDG-PET) co-registered with computerized tomography. BACKGROUND: Inflammation plays a key role in progression and destabilization of atherosclerotic plaque. 18F-fluorodeoxyglucose PET is a promising tool for visualizing inflammation of atherosclerotic plaque. Antiinflammatory action is one of the pleiotropic effects of statins. METHODS: Forty-three consecutive subjects, who underwent 18FDG-PET for cancer screening and had 18FDG uptakes in the thoracic aorta and/or the carotid arteries, were randomized to either statin group receiving simvastatin (n = 21) or diet group receiving dietary management only (n = 22). The maximum standardized uptake values (SUVs) were measured in individual plaques, and were averaged for analysis of the subjectwise results. The responses were assessed after 3-month treatments. RESULTS: Positron emission tomography revealed 117 and 123 18FDG-positive plaques in the statin and diet groups, respectively. Simvastatin, but not diet alone, attenuated plaque (18)FDG uptakes and decreased the SUVs (p < 0.01). Simvastatin reduced low-density lipoprotein cholesterol (LDL-C) by 30% (p < 0.01) and increased high-density lipoprotein cholesterol (HDL-C) by 15% (p < 0.01), whereas LDL-C and HDL-C levels were not changed in the diet group. In the statin group, the decrease in the SUV was well correlated with the HDL-C elevation (p < 0.01) but not with the LDL-C reduction. CONCLUSIONS: 18F-fluorodeoxyglucose PET visualized plaque inflammation and simvastatin attenuated it. The LDL-C-independent effects of simvastatin may participate in the beneficial effect. 18F-fluorodeoxyglucose PET has a potential for visually monitoring plaque inflammation and the therapeutic effectiveness of statins.     

Atherosclerotic plaques composed of a large core of foam cells covered with thin fibrous caps in twice-injured carotid arterial specimens obtained from high cholesterol diet-fed rabbits.

We attempted to find atherosclerotic plaques including a large lipid core and thin fibrous cap in twice-injured arterial specimens obtained from high cholesterol diet (HCD) fed rabbits. Rabbits fed a HCD were subjected to carotid artery injury using a balloon catheter. After 2 or 4 weeks of cholesterol feeding, a second mild injury was induced in the same region as the first injury. The rabbits were given a standard diet for 2 weeks after the second injury. Typical atherosclerotic plaques with a fibrous cap formed by smooth muscle cells and extracellular matrix overlying a core formed by macrophage foam cells were observed in the lesion. Gelatin proteolytic activities were found in homogenates containing either media or intima from the injured artery, and activated matrix metalloproteinase-2 (MMP2) was detected. With prolongation of the HCD feeding period (interval between injuries) from 2 weeks to 4 weeks, typical plaque was observed more frequently. Furthermore, the neointimal area and the macrophage foam cells area increased, as did gelatin-proteolytic activity. Since the typical atherosclerotic plaques observed in the present study have some histopathological and pathogenic characteristics in common with unstable atherosclerotic plaque, we expect that the typical atherosclerotic plaque found in the present study will be useful for basic studies of plaque stabilization and prevention of acute coronary syndromes.     

Usefulness of follow-up low-density lipoprotein cholesterol level as an independent predictor of changes of coronary atherosclerotic plaque size as determined by intravascular ultrasound analysis after statin (atorvastatin or simvastatin) therapy

Using serial intravascular ultrasound (IVUS), we identified independent predictors of changes in coronary plaque size in relation to serum lipid levels. One hundred three patients with nonstenotic coronary plaques underwent baseline and 12-month follow-up IVUS studies; 54 patients (52%) were treated with statins. Standard IVUS analyses were performed. Baseline IVUS study showed no statistical differences in mean external elastic membrane, lumen, and plaque/media (P&M) area between statin-treated and nonstatin-treated patients. Although there was an increase in mean P&M cross-sectional area in nonstatin-treated patients, mean P&M cross-sectional area decreased in statin-treated patients (0.11 +/- 0.24 vs -0.20 +/- 0.30 mm(2), p <0.001). There was a positive relation between changes in mean P&M area and follow-up low-density lipoprotein (LDL) cholesterol level (r = 0.430, p <0.001), follow-up total cholesterol level (r = 0.365, p <0.001), changes in LDL cholesterol level (r = 0.312, p = 0.002), and changes in total cholesterol level (r = 0.252, p = 0.012). In multivariate linear regression analysis, the only independent predictor of changes in mean P&M area was follow-up LDL cholesterol level (r = 0.469, p <0.001, 95% confidence interval 0.003 to 0.006). The cut-off value of follow-up LDL cholesterol for no change or a decrease in mean P&M area was <100 mg/dl at regression analysis. In conclusion, the present 12-month follow-up IVUS study showed that follow-up LDL cholesterol level was the only independent predictor of changes in coronary plaque size. When patients achieved a follow-up LDL cholesterol level <100 mg/dl, regression or no progression of coronary plaque was expected. Aggressive lipid-lowering treatments with statins to decrease the follow-up LDL cholesterol level to <100 mg/dl are recommended.     

Cholesterol crystal binding of biliary immunoglobulin A: visualization by fluorescence light microscopy

AIM: To assess potential contributions of biliary IgA for crystal agglomeration into gallstones, we visualized cholesterol crystal binding of biliary IgA. METHODS: Crystal binding biliary proteins were extracted from human gallbladder bile using lectin affinity chromatography.Biliary IgA was isolated from the bound protein fraction by immunoaffinity chromatography. Pure cholesterol monohydrate crystals were incubated with biliary IgA and fluoresceine isothiocyanate (FITC)conjugated anti IgA at 37 degree. Samples were examined under polarizing and fluorescence light microscopy with digital image processing. RESULTS: Binding of biliary IgA to cholesterol monohydrate crystals could be visualized with FITC conjugated anti IgA antibodies.Peak fluorescence occurred at crystal edges and dislocations. Controls without biliary IgA or with biliary IgG showed no significant fluorescence. CONCLUSION: Fluorescence light microscopy provided evidence for cholesterol crystal binding of biliary IgA. Cholesterol crystal binding proteins like IgA might be important mediators of crystal agglomeration and growth of cholesterol gallstones by modifying the evolving crystal structures in vivo.     

Aortic Atherosclerosis and Embolic Events

Aortic plaques are a manifestation of the general process of atherosclerosis in which there is a progressive accumulation of cholesterol and other lipids in the intimal-medial layer of the aorta with secondary inflammation, repetitive fibrous tissue deposition, and eventually luminal surface erosions and appearance of often mobile thrombi protruding into the lumen of the aorta. Aortic plaques may give rise to two types of emboli: thromboemboli and atheroemboli (cholesterol crystal emboli). Thromboemboli are relatively large, tend to occlude medium to large arteries, and cause strokes, transient ischemic attacks, and renal infarcts and other forms of peripheral thromboembolism. Cholesterol crystal emboli are relatively minute, tend to occlude small arteries and arterioles, and may cause the blue toe syndrome, new or worsening renal insufficiency, gut ischemia, etc. Transesophageal echocardiography remains the gold standard for visualization of aortic plaques in the thoracic aorta. There are no proven therapies for aortic embolism per se; general atherosclerosis management strategies are recommended.     

他汀降脂治疗冠状动脉粥样硬化斑块的影像学研究进展

脂质代谢紊乱是导致动脉粥样硬化的主要危险因素,低密度脂蛋白的作用尤为显著。他汀能使低密度脂蛋白降低,许多临床试验已证实他汀能显著减少心血管事件的发生。通过血管内超声评价他汀降脂治疗能够延缓冠状动脉斑块的进展甚至使其退缩的研究也越来越多,但应用冠状动脉计算机体层成像进行评价的研究尚少。在我国冠状动脉计算机体层成像的使用较血管内超声更广泛。目前就能使冠状动脉斑块明显退缩的低密度脂蛋白降低的水平或降低的程度仍无定论,还需要更多的研究来证实。     

普伐他汀对兔腹主动脉易损斑块内细胞凋亡影响的研究

目的 探讨普伐他汀对兔动脉粥样硬化易损斑块内细胞凋亡的影响.方法 新西兰大白兔30只,随机分为三组,均通过动脉内膜损伤术加高脂饮食形成动脉粥样硬化斑块.术后一组给予高脂饮食（对照组）,另一组给予高脂饮食加普伐他汀（普伐他汀1组,P1组）,第三组术后2个月内给予高脂饮食,第3个月起加普伐他汀（普伐他汀2组,P2组）,三组均通过超声检测斑块形成情况,测量内中膜厚度（IMT）.饲养4个月后处死兔子,取易损斑块,通过TUNEL法检测斑块细胞凋亡情况.结果 兔腹主动脉IMT逐渐增厚,术后1个月后普伐他汀组明显小于高脂饮食组（P＜0.01）;细胞凋亡在高脂饮食组中的表达,集中在脂核区和纤维帽区,明显高于其他两区（P＜0.01,P＜0.01）;普伐他汀组凋亡细胞主要在脂核区,明显大于其他三区（P＜0.01）;两组比较细胞凋亡在纤维帽区,普伐他汀2组明显小于高脂饮食组（P＜0.01）.结论 IMT与动脉粥样硬化程度高度相关,普伐他汀能通过减少纤维帽区的细胞凋亡而稳定斑块.     

Crystallization of free cholesterol in model macrophage foam cells.

-The present study examined free cholesterol (FC) crystallization in macrophage foam cells. Model foam cells (J774 or mouse peritoneal macrophages [MPMs]) were incubated with acetylated low density lipoprotein and FC/phospholipid dispersions for 48 hours, resulting in the deposition of large stores of cytoplasmic cholesteryl esters (CEs). The model foam cells were then incubated for up to 5 days with an acyl-coenzyme A:cholesterol acyltransferase (ACAT) inhibitor (CP-113,818) in the absence of an extracellular FC acceptor to allow intracellular accumulation of FC. FC crystals of various shapes and sizes formed in the MPMs but not in the J774 macrophages. Examination of the MPM monolayers by microscopy indicated that the crystals were externalized rapidly after formation and thereafter continued to increase in size. Incubating J774 macrophages with 8-(4-chlorophenylthio)adenosine 3':5'-cyclic monophosphate (CPT-cAMP) in addition to CP-113,818 caused FC crystal formation as a consequence of CPT-cAMP stimulation of CE hydrolysis and inhibition of cell growth. In addition, 2 separate cholesterol phases (liquid-crystalline and cholesterol monohydrate) in the plane of the membrane bilayer were detected after 31 hours of ACAT inhibition by the use of small-angle x-ray diffraction of J774 macrophage foam cells treated with CPT-cAMP. Other compounds reported to inhibit ACAT, namely progesterone (20 microgram/mL) and N-acetyl-D-sphingosine (c(2)-ceramide, 10 microgram/mL), induced cellular toxicity in J774 macrophage foam cells and FC crystallization when coincubated with CPT-cAMP. Addition of the extracellular FC acceptors apolipoproteins (apo) E and A-I (50 microgram/mL) reduced FC crystal formation. In MPMs, lower cell density and frequent changes of medium were conducive to crystal formation. This may be due to "dilution" of apoE secreted by the MPMs and is consistent with our observation that the addition of exogenous apoE or apoA-I inhibits FC crystal formation in J774 macrophage foam cells cotreated with CP-113,818 plus CPT-cAMP. These data demonstrate that FC crystals can form from the hydrolysis of cytoplasmic stores of CEs in model foam cells. FC crystal formation can be modulated by the addition of extracellular FC acceptors or by affecting the cellular rate of CE hydrolysis. This process may contribute to the formation of FC crystals in atherosclerotic plaques.