Lipoproteins and the progression/regression of atherosclerosis

Cholesterol diet and effect of long-term withdrawal on plaque development and composition in the thoracic aorta of New Zealand White rabbits

AIMS

Experimental study on plaque progression, regression and composition in atherosclerotic thoracic aorta of hypercholesterolemic rabbits after long-term withdrawal of cholesterol-enriched diet (CED).

METHODS

Rabbits were fed 2% cholesterol for 6 weeks followed by withdrawal periods for 15, 23, 34, 68, or 78 weeks. Cholesterol, triglyceride, and phospholipids levels in blood and cholesterol concentrations in aorta were quantified. Plaque size and cellularity, phenotype of macrophages and smooth muscle cells were (immuno)histomorphometrically analyzed in segments of the thoracic aorta.

RESULTS

After 6 weeks of CED, blood cholesterol levels were about 80-fold higher, whereas atherosclerosis and cholesterol content in the thoracic aorta were only minimally increased. However, the latter significantly increased within 15 weeks after cholesterol withdrawal, while serum cholesterol level was still 10-fold increased. Thereafter plaque area and cholesterol content remained almost unchanged until the end of the study despite a long-term normalization of serum cholesterol level after withdrawal of CED. Directly after 6 weeks of CED the densities of macrophages and apoptotic cells within plaques were highest, decreasing after cholesterol withdrawal, whereas, vice versa the density of smooth muscle cells (SMCs) significantly increased.

CONCLUSION

We suggest that atherosclerotic plaques respond to long-term withdrawal of CED by decrease in number and phenotype of macrophages and increase of SMCs without regression of the lesion size. The cellular changes are suggested to considerably contribute to higher plaque stability.

Response of the left anterior descending coronary artery to acetylcholine in patients with chest pain and angiographically normal coronary arteries

Because atherosclerotic plaque burden affects the likelihood of plaque rupture, it is important to determine the presence and extent of atherosclerotic plaque. We hypothesized that endothelial dysfunction becomes more prominent with development of atherosclerotic plaque; therefore, we examined the relation between coronary endothelial dysfunction and the presence of atherosclerotic plaque. In 36 patients with normal coronary arteries, acetylcholine (ACh; 3 and 30 microg/min) and nitroglycerin were infused into the left coronary ostium, and the diameter of the left anterior descending (LAD) coronary artery was quantitatively measured in response to each drug. The plaque burden was measured in the same segment using intravascular ultrasonography. The plaque burden was 31.2 +/- 2.1% and correlated inversely with changes in coronary diameter induced by 3 microg/min of ACh (r = -0.754, p <0.0001), 30 microg/min of ACh (r = -0.552, p = 0.0005), and nitroglycerin (r = -0.531, p = 0.0009). Multivariate regression analysis showed that the change in coronary diameter induced by 3 microg/min of ACh was associated with plaque burden, independent of the effects of nitroglycerin-induced dilation. Receiver-operating characteristics analysis demonstrated that a cut-off value for the change in coronary diameter induced by 3 microg/min of ACh for predicting a plaque burden of >30% was 0%, with a sensitivity of 0.82 and a specificity of 0.95. These findings suggest that coronary endothelial dysfunction is correlated with atherosclerotic plaque burden, indicating that atherosclerotic plaque may be detected based on coronary endothelial function as assessed by low-dose ACh infusion.

Significance of skeletal muscle properties on fitness, long-term physical training and serum lipids

The percentage of slow-twitch (ST) fibers in a person's skeletal muscle, e.g. muscle fiber composition (ST-%), may have a significant impact on physical activity, fitness level, serum high density lipoprotein cholesterol (HDL-C) concentration, and ultimately, on the risk of coronary heart disease (CHD). We studied the effect of a 12 month home-based exercise training program on skeletal muscle metabolic activity, serum lipids, and hormones in 12 healthy middle-aged men (sedentary men) with a low level of fitness and leisure-time physical activity (LTPA). Their parameters and changes in them were compared with 12 men of the same age with defined CHD and with two groups (15 each) of physically active men, who had either a high ST-% (high-ST-men) or a low ST-% (low-ST-men). In the sedentary men, CHD-patients and low-ST-men, the mean ST-% (42, 44, and 49%, respectively) was similar but was significantly higher in the high-ST-men (73%). The sedentary men whose LTPA mean was 34 and 19% of the mean of low-ST-men (mean of 2137 kcal/week) and high-ST-men (mean of 3845 kcal/week), respectively, increased their LTPA from a mean of 728-1526 kcal/week (P < 0.01). After training, we found an increase in serum HDL-C by 21%, (P < 0.01) and apo A-I by 36% (P < 0.01), and a decrease in serum LDL-C by 8%. The cholesterol/HDL-C ratio decreased by 17(% (P < 0.01) and the LDL-C/HDL-C ratio decreased by 22% (P < 0.01). Skeletal muscle lipoprotein lipase (LPL) activity increased by 65% (P < 0.001). Moreover, the increase in LPL as well as in HDL-C concentration tended to be more pronounced the higher the level was before training. The oxidative enzyme activity of alpha-ketoglutarate dehydrogenase (KGDH) in skeletal muscle and the activity of carnitine palmitoyltransferase (CPT) in lipid metabolism increased, whereas glycolytic phosphofructokinase (PFK) did not change but the PFK to CPT ratio decreased, which was reflected as a decrease of lactate accumulation during exercise. Increase in CPT activity correlated significantly (r(s) = 0.81, P < 0.01) with the increase in HDL-C concentration. In all men (n = 54), the CPT activity correlated negatively with serum triglyceride concentration (r(s) = -0.34, P < 0.05) but positively with serum HDL-C concentration and ST-% (r(s) = 0.34, P < 0.05 and r(s) = 0.47, P < 0.01, respectively). In all healthy men, (n = 42) LTPA correlated with both Vo2max, and ST-% (r(s) = 0.76, P < 0.001 and r(s) = 0.54, P < 0.001, respectively) and with serum HDL-C and apo A-I concentrations (r(s) = 0.35, P < 0.05 and r(s) = 0.54, P < 0.001, respectively). Serum sex hormones did not show significant associations with serum lipids, but in sedentary men, serum total and free testosterone as well as the ratio of free testosterone to free estradiol decreased significantly after training. These findings confirm the pronounced effects of a home-based exercise training program on CHD risk factors and they underline the importance of considering skeletal muscle properties when studying serum lipids and lipoproteins and their modifications in the field of health-related fitness and physical activity.

Treatment effects on serum lipoprotein lipids, apolipoproteins and low density lipoprotein particle size and relationships of lipoprotein variables to progression of coronary artery disease in the Bezafibrate Coronary Atherosclerosis Intervention Trial (BECAIT)

OBJECTIVES

To investigate the mechanisms by which bezafibrate retarded the progression of coronary lesions in the Bezafibrate Coronary Atherosclerosis Intervention Trial (BECAIT), we examined the relationships of on-trial lipoproteins and lipoprotein subfractions to the angiographic outcome measurements.

BACKGROUND

BECAIT, the first double-blind, placebo-controlled, randomized serial angiographic trial of a fibrate compound, showed that progression of focal coronary atherosclerosis in young survivors of myocardial infarction could be retarded by bezafibrate treatment.

METHODS

A total of 92 dyslipoproteinemic men who had survived a first myocardial infarction before the age of 45 years were randomly assigned to treatment for 5 years with bezafibrate (200 mg three times daily) or placebo; 81 patients underwent baseline and at least one post-treatment coronary angiography.

RESULTS

In addition to the decrease in very low density lipoprotein (VLDL) cholesterol (-53%) and triglyceride (-46%) and plasma apolipoprotein (apo) B (-9%) levels, bezafibrate treatment resulted in a significant increase in high density lipoprotein-3 (HDL3) cholesterol (+9%) level and a shift in the low density lipoprotein (LDL) subclass distribution toward larger particle species (peak particle diameter +032 nm). The on-trial HDL3 cholesterol and plasma apo B concentrations were found to be independent predictors of the changes in mean minimum lumen diameter (r=-0.23, p < 0.05), and percent (%) stenosis (r = 0.30, p < 0.01), respectively. Decreases in small dense LDL and/or VLDL lipid concentrations were unrelated to disease progression.

CONCLUSIONS

Our results suggest that the effect of bezafibrate on progression of focal coronary atherosclerosis could be at least partly attributed to a rise in HDL3 cholesterol and a decrease in the total number of apo B-containing lipoproteins.

Familial resemblance of plasma lipids, lipoproteins and postheparin lipoprotein and hepatic lipases in the HERITAGE Family Study

The familial aggregation of lipids and lipoproteins and plasma postheparin triglyceride lipases was investigated in 86 Caucasian families participating in the HERITAGE Family study, a study investigating the role of genetic factors in the adaptation to exercise training and its relationships with cardiovascular disease risk factors. Accordingly, sedentary subjects were recruited, tested for a battery of measurements, exercise trained for 20 weeks, and were re-measured. The present report includes plasma levels of total cholesterol, high-density lipoprotein (HDL) cholesterol, low-density lipoprotein (LDL) cholesterol and triglycerides, and postheparin plasma lipoprotein lipase (LPL) and hepatic lipase (HL) activities measured in 437 sedentary individuals (171 parents and 266 adult offspring) before training. Significant familial resemblance was observed for all the age-adjusted phenotypes. The pattern of familial correlations reveals no spouse correlations but significant parent-offspring and sibling correlations for total cholesterol, HDL-cholesterol and LDL-cholesterol with heritability (h2) estimates of 62%, 83%, and 50%, respectively. For plasma triglyceride concentrations (h2 = 55%) and HL activity (h2 = 40%), significant spouse correlations were found in addition to parent-offspring and sibling correlations, suggesting that common familial environment in addition to genetic factors contribute to the familial resemblance. For plasma LPL activity, there was no spouse correlation, but sex differences were found in the familial correlations with higher heritabilities in female pairs (h2 = 76%) compared to male pairs (h2 = 30%) and opposite-sex pairs (h2 = 44%). These results confirm the findings of previous family studies showing that genetic factors are major determinants of the familial resemblance in plasma lipids and lipoproteins and suggest the presence of sex differences in the heritability of postheparin LPL activity.