Long-term induction and regression of diet-induced atherosclerotic lesions in rhesus monkeys. I. Morphological and chemical evidence for regression of lesions in the aorta and carotid and peripheral arteries

Treatment of asymptomatic adults with elevated coronary calcium scores with atorvastatin, vitamin C, and vitamin E: the St. Francis Heart Study randomized clinical trial

OBJECTIVES

We sought to determine whether lipid-lowering therapy and antioxidants retard the progression of coronary calcification and prevent atherosclerotic cardiovascular disease (ASCVD) events.

BACKGROUND

The electron beam computed tomography-derived coronary calcium score predicts coronary disease events. Small, uncontrolled studies suggest that vigorous lipid-lowering therapy slows progression of coronary calcification and prevents coronary artery disease events, but controlled, scientific demonstration of these effects is lacking.

METHODS

We conducted a double-blind, placebo-controlled randomized clinical trial of atorvastatin 20 mg daily, vitamin C 1 g daily, and vitamin E (alpha-tocopherol) 1,000 U daily, versus matching placebos in 1,005 asymptomatic, apparently healthy men and women age 50 to 70 years with coronary calcium scores at or above the 80th percentile for age and gender. All study participants also received aspirin 81 mg daily. Mean duration of treatment was 4.3 years.

RESULTS

Treatment reduced total cholesterol by 26.5% to 30.4% (p < 0.0001), low-density lipoprotein cholesterol by 39.1% to 43.4% (p < 0.0001), and triglycerides by 11.2% to 17.0% (p < or = 0.02) but had no effect (p = 0.80) on progression of coronary calcium score (Agatston method). Treatment also failed to significantly reduce the primary end point, a composite of all ASCVD events (6.9% vs. 9.9%, p = 0.08). Event rates were related to baseline calcium score (pre-specified analysis) and may have been reduced in a subgroup of participants with baseline calcium score >400 (8.7% vs. 15.0%, p = 0.046 [not a pre-specified analysis]).

CONCLUSIONS

Treatment with alpha-tocopherol, vitamin C, and low doses of atorvastatin (20 mg once daily) did not affect the progression of coronary calcification. Treatment may have reduced ASCVD events, especially in subjects with calcium scores >400, but these effects did not achieve conventional levels of statistical significance.

Physical activity and atherosclerosis: which animal model?

Atherosclerosis is a progressive disease that is the most important single contributor to human cardiovascular morbidity and mortality. Epidemiologic studies show that physical activity, or routine exercise, reduces the risk of developing cardiovascular disease. The mechanisms through which exercise may function in primary or secondary prevention of atherosclerosis remain largely to be established. Most studies in humans are performed after the onset of clinical signs when disease is well advanced and the prescription of exercise is based on empirical evidence of benefit in secondary prevention. Animal models per-mit the study of the initiation and progression of preclinical stages of atherosclerosis. In order to provide information relevant to treatment and prevention, these models should mimic human disease and interactions of physical activity with disease processes as closely as possible. The purpose of this review is to compare animal models of atherosclerosis and to summarize the available data in those models in regard to the effects of exercise.

Relation of coronary calcium progression and control of lipids according to National Cholesterol Education Program guidelines

Tracking of coronary artery calcium (CAC) has been suggested for monitoring the effects of lipid control, but it is not known whether lipid control decreases progression of CAC. Seven hundred sixty-one subjects (mean age 64.5 +/- 7.3 years; 91% men; 69% positive for CAC) in an ongoing cohort study underwent baseline and follow-up (after 7.0 +/- 0.5 years) computed tomography for CAC. Subjects were stratified into low-risk (<2 risk factors), intermediate-risk (> or =2 risk factors but <20% risk of coronary heart disease over 10 years), or high-risk (> or =2 risk factors and >20% risk of coronary heart disease in 10 years or diabetes) groups. Lipid control was defined according to criteria of the National Cholesterol Education Program. Two-way analysis of covariance was used to examine the relation of low-density lipoprotein (LDL) cholesterol and risk group to change in CAC volume score. Control of levels of high-density lipoprotein (HDL) cholesterol and triglycerides was also examined in relation to progression of CAC. After adjustment for other risk factors and baseline CAC volume, CAC progression was similar between those with adequate and those with inadequate control of LDL cholesterol (p = 0.68) and across categories of optimal, intermediate, and higher risk LDL cholesterol (p = 0.40). However, higher levels of HDL cholesterol (> or =1.5 mmol/L [60 mg/dl]) were associated with less progression of CAC volume (151 vs 203 mm(3) in those with HDL cholesterol <1.0 mmol/L [40 mg/dl], p = 0.03). There was no relation between triglycerides and CAC progression (p = 0.54). Our findings do not support the use of CAC assessment for monitoring the control of LDL cholesterol, but greater progression of CAC may occur in those in whom HDL cholesterol is not controlled.

Removal of cholesteryl esters from diet-induced atherosclerotic lesions in two long-term studies in rhesus monkeys

In two long-term studies of dietary-cholesterol-induced atherosclerosis lesions in rhesus monkeys, we determined the fatty acid composition of cholesteryl esters in the arterial intima-media preparations. In the first study (2-year study) monkeys were fed an atherogenic diet for 2 years; in the second study, (5-year study), monkeys were fed the atherogenic diet for about 5.4 years. Dietary cholesterol was removed from regressed animals and the regression periods in the 2-year study were 30 and 52 weeks and in the 5-year study were 20, 30, 52, 101, and 191 weeks. In both studies in thoracic and abdominal aortic segments, the percent removal of 18:2 cholesteryl ester (CE) was small, whereas percent removal of 18:1 CE and other CEs was much higher. We postulate that 18:2 CE is not hydrolyzed to the extent comparable to 18:1 and other CEs in lesions. Perhaps 18:2 CE is not a preferred substrate for arterial neutral cholesterol ester hydrolase.

Advances in experimental dyslipidemia and atherosclerosis

Among the models of dyslipidemia and atherosclerosis, a number of wild-type, naturally defective, and genetically modified animals (rabbits, mice, pigeons, dogs, pigs, and monkeys) have been characterized. In particular, their similarities to and differences from humans in respect to relevant biochemical, physiologic, and pathologic conditions have been evaluated. Features of atherosclerotic lesions and their specific relationship to plasma lipoprotein particles have been critically reviewed and summarized. All animal models studied have limitations: the most significant advantages and disadvantages of using a specific animal species are outlined here. New insights in lipid metabolism and genetic background with regard to variations in pathogenesis of dyslipidemia-associated atherogenesis have also been reviewed. Evidence suggests that among wild-type species, strains of White Carneau pigeons and Watanabe Heritable Hyperlipidemic and St. Thomas's Hospital rabbits are preferable to the cholesterol-fed wild-type animal species in dyslipidemia and atherosclerosis research. Evidence for the usefulness of both wild-type and transgenic animals in studying the involvement of inflammatory pathways and Chlamydia pneumoniae infection in pathogenesis of atherosclerosis has also been summarized. Transgenic mice and rabbits are excellent tools for studying specific gene-related disorders. However, despite these significant achievements in animal experimentation, there are no suitable animal models for several rare types of fatal dyslipidemia-associated disorders such as phytosterolemia and cerebrotendinous xanthomatosis. An excellent model of diabetic atherosclerosis is unavailable. The question of reversibility of atherosclerosis still remains unanswered. Further work is needed to overcome these deficiencies.

HMG-CoA reductase inhibitor stabilizes rabbit atheroma by increasing basal NO and decreasing superoxide

Male rabbits fed a 0.5% cholesterol diet for 8 wk were divided into three groups. Group 1 was hypercholesterolemic; group 2 was fed a regular diet for an additional 12 wk; and group 3 was fed a regular diet with simvastatin (5 mg x kg(-1) x day(-1)). Simvastatin treatment reduced the atherosclerotic area and total and esterified cholesterol concentrations in the thoracic aorta. Tone-related basal nitric oxide (NO) release was highest in group 3. Acetylcholine-induced, NO-dependent relaxation was improved in group 3 compared with group 2. Amount of endothelial nitric oxide synthase (eNOS) mRNA in vessels increased in group 1, compared with normal aorta, and decreased in group 2; however, it did not decrease in group 3. The amount of O released from vessels increased in group 1 and group 2 compared with normal rabbits; however, it decreased in group 3, especially in the endothelial cells. Peroxynitrite determined by nitrotyrosine staining decreased in group 3. Additionally, the arteries of rabbits fed a regular diet with or without simvastatin were investigated. The aorta from simvastatin-treated group showed increase of tone-related basal NO release and eNOS mRNA and decrease of O release. Taken together, upregulation of eNOS and decrease of O treatment were observed in vivo in the process of the sufficient stabilization of atheroma following simvastatin.

The role of osteoprogenitors in vascular calcification

Calcification is a component of vascular disease that usually occurs in concert with atheroma formation but through distinct pathophysiological processes. Vessel wall osteoprogenitor cells known as calcifying vascular cells can form bone matrix proteins and calcified nodules, analogous to osteoblastic differentiation in bone. These cells have been isolated from the tunica media of bovine and human arteries, and both in-vitro tissue culture models and mouse models of vascular calcification have been established. Studies of the effects of diabetes mellitus, hyperlipidemia, estrogens and glucocorticoids on calcifying vascular cell function provide insight into the relationship between common human disease states and vascular calcification.

Endothelium-dependent relaxation of rabbit atherosclerotic aorta was not restored by control of hyperlipidemia: the possible role of peroxynitrite (ONOO(-))

We determined the role of ONOO(-) in nitric oxide (NO) mediated vascular response in atherosclerosis and regression following removal of dietary cholesterol. The effect of ONOO(-) on NO-mediated vascular responses was examined in vitro. Basal and stimulated NO release was estimated by an NO-selective electrode as well as vascular response and the plasma NO metabolites. An immunohistochemical study was also carried out. Responses were compared in normal controls, atherosclerotic rabbits fed 1% cholesterol diet for 6 or 9 weeks (atherosclerotic group) and animals fed a normal diet for 6-36 weeks after the high cholesterol diet for 6 or 9 weeks (regression group). ONOO(-) impaired the basal and acetylcholine-stimulated NO release, but did not affect endothelium-independent relaxation. After 15 weeks on a normal diet, the acetylcholine-stimulated and basal NO-mediated relaxation, which was diminished in the aorta induced by 6 weeks high cholesterol diet, became restored. However, the vascular response in the 9 weeks high cholesterol diet group did not return to normal after 36 weeks on a normal diet. iNOS was observed in atherosclerotic plaques in atherosclerotic and regression groups along with ONOO(-) in the 9 weeks high cholesterol diet group, but not in the 6 weeks group. Conclusively, ONOO(-) can play a role in impairment of NO-mediated vascular response during the regression of dietary cholesterol-induced atherosclerosis, not in the initiation of atherosclerosis.

Modulation of the regression of atherosclerosis in the hamster by dietary lipids: comparison of coconut oil and olive oil

The Golden Syrian hamster (Mesocricetus auratus) has been shown to be a useful model of both human lipoprotein metabolism and the development of atherosclerosis. We report the effects of dietary lipids on the progression and regression of atherosclerosis in this model. In the first study, hamsters fed on coconut oil (150 g/kg diet) and cholesterol (30 g/kg diet) developed lipid-rich lesions in the ascending aorta (0.28 (SD 0.14) mm2) and aortic arch (0.01 (SD 0.01) mm2) after 4 weeks that continued to progress over the next 8 weeks (0.75 (SD 0.41) mm2 and 0.12 (SD 0.11) mm2 for the ascending aorta and aortic arch respectively). Removal of cholesterol from the diet halted this progression. Furthermore, in animals fed on olive oil in the absence of added cholesterol, plasma LDL-cholesterol concentrations were lower (P < 0.05) and the extent of atherosclerotic lesions was reduced (P < 0.001 for both regions of the aorta) compared with animals fed on coconut oil (with no added cholesterol). In a second study, animals were fed on the atherogenic diet for 10 weeks, transferred to diets containing either coconut oil (150 g/kg diet) or olive oil (150 g/kg diet) without added cholesterol and monitored for up to 16 weeks. In the ascending aorta, lesion size doubled in animals fed on coconut oil but stabilized in those fed on olive oil. In the aortic arch, lesion size decreased linearly (P < 0.05, P < 0.001 for coconut oil and olive oil respectively) with the greatest reduction being seen in the olive-oil-fed animals (P < 0.05). Again, progression and regression of atherosclerosis appeared to reflect the relative concentrations of LDL-cholesterol and HDL-cholesterol in the plasma. We conclude that the male Golden Syrian hamster represents a useful model of dietary induced regression as well as progression of atherosclerosis.

Coronary calcium: the good, the bad, and the uncertain

BACKGROUND

Coronary calcium deposits have been widely regarded to result from a passive process of encrustation or adsorption of mineral onto advanced, complex atherosclerotic lesions. Increasing interest has focused on noninvasive radiologic detection of these calcium deposits as a diagnostic and prognostic adjunct to clinical evaluation of coronary artery disease, particularly with the use of newer, high-resolution imaging techniques such as electron beam computed tomography.

METHODS AND RESULTS

We reviewed the literature on coronary calcium and its relation to pathologic atherosclerosis, angiographic stenoses,and clinical events. Clinical calcium detection studies have demonstrated an association between coronary calcium and both extent of coronary artery disease and risk of adverse events. These studies have in the past tended to reinforce the perception that calcific deposits result from a passive mineralization process, signify advanced coronary artery disease, and foreshadow future coronary events.

CONCLUSIONS

Recent pathologic, genetic, clinical, and biochemical evidence reviewed in this article suggests that coronary calcium deposits are a manifestation of a complex, organized, and regulated process similar in many respects to new bone formation and may not be a reliable indicator of either the extent of coronary disease or the risk of a future event. These studies also suggest that atherosclerosis and calcific deposits may be distinct pathologic entities that frequently occur together and are related to each other in ways that are poorly understood.

Lack of regression of atherosclerotic lesions in phytosterol-treated apo E-deficient mice

We evaluated the effects of a phytosterol mixture (FCP-3PI) on the regression of atherosclerotic lesions in male apo E-deficient mice. Atherosclerosis was induced in fifteen mice by a "Western-type" diet containing 9% (w/w) fat and 0.15% (w/w) cholesterol over a period of 18 weeks (Induction phase). Then, two mice were used to evaluate the development of atherosclerosis, and the rest was divided into the control (n=6) and treated (n=7) groups. The control group was fed mouse chow (4.5% w/w fat) and the treated group fed the same chow supplemented with 2% (w/w) FCP-3PI for an additional 25 weeks (Regression phase). The mice developed severe hypercholesterolemia and advanced atherosclerotic lesions over the induction phase. During the first 6 weeks of regression phase, plasma cholesterol concentrations decreased at a similar rate (35%) in both groups of control and phytosterol-treated mice. Although evidence of lesion regression was not observed in either group of mice, the treated group had slightly smaller lesion size than the controls. During the induction phase, each mouse developed atherosclerotic lesions averaging 0.025 mm2 per week. However, during the regression phase, this was decreased to approximately one fifth and one third in the treated and control groups, respectively. Thus, compared to the end of the induction phase, the control group had a 40% increase in the lesion size, while this increase was only 28% in the treated animals. In conclusion, our previous findings along with a small decrease in the atherosclerotic lesion size observed in the treated group in the present study suggest that FCP-3PI treatment may slow the development of atherosclerotic lesions in apo E-deficient mice; however, a longer regression period may yield a greater benefit.