Douglas A. Eggen

Localization and Sequence of Development of Atherosclerotic Lesions in the Carotid and Vertebral Arteries

The distribution of fatty streaks, fibrous plaques, complicated lesions, and calcified lesions were determined for each of five segments in the common carotid arteries, each of five segments of internal carotid arteries, and for each of seven segments of vertebral arteries in specimens from 961 autopsied cases in Oslo, Norway, and Guatemala. The pattern of distribution of the lesions along the length of the arteries is characteristic for the different arteries. This pattern seems to be independent of sex, age group, type of lesions, and geographic location.Fatty streaks and fibrous plaques have the same pattern of distribution within each artery at all ages. This close topographic association is consistent with the hypothesis that fibrous plaques are derived from fatty streaks. The early atherosclerotic lesions are located at the same sites where stenotic and occlusive lesions have been reported. Thus, it is likely that the early atherosclerotic lesions and the stenotic or occlusive lesions are pathogenetically closely associated with each other.

Depletion of aortic free and ester cholesterol by dietary means in rhesus monkeys with fatty streaks

This report presents findings concerning free and esterified cholesterol and specific fatty acids esterified to cholesterol in aortas of rhesus monkeys fed an atherogenic diet for 12 weeks followed by regression regimen for 32 and 64 weeks. Mean aortic total cholesterol of monkeys fed an atherogenic diet was more than twice that of the animals on a control diet. Esterified cholesterol showed a fourfold elevation while increase in free cholesterol was less than twofold. Free cholesterol and esterified cholesterol in the aorta of animals decreased by about 30 per cent and 70 per cent respectively after 32 weeks on the regression diet. Very little additional changes occurred in the animals on the regression regimen for 64 weeks. In fatty acids esterified to cholesterol, the largest proportional increase was in stearic (18:0) and oleic (18:1) acids and the least proportional increase was in linoleic (18:2) and arachidonic (20:4) acids after 12 weeks on the atherogenic diet. As a result of feeding the regression diet for a period of 32 weeks an overall depletion of about 85 per cent was observed from the levels in animals fed only an atherogenic diet. Cholesteryl sterate and oleate returned to near baseline levels with a reduction of about 90 per cent from levels observed after feeding the atherogenic diet.

NATURALLY OCCURRING AND EXPERIMENTAL ATHEROSCLEROSIS IN PRIMATES

In the last two decades, investigators have increasingly turned toward nonhuman primates as experimental models for the study of atherosclerosis. Kawamural and Hueper2 were not able to produce arterial lesions in rhesus monkeys, but Mann and coworkers in 1953 reported the experimental production of hypercholesterolemia and sudanophilic aortic lesions in Cebus monkeys fed high-cholesterol diets containing protein that was deficient in sulphur amino acids.3 Since their report, lipid-containing arterial lesions have been reported in rhesus, Cehus, woolly, and squirrel monkeys and in baboons and chimpanzees that have been fed experimental diets high in fat and cholesterol but varying in other constituents. Taylor and associates were first to produce a complete model of human atherosclerotic disease in prim a t e ~ . ~ One of their rhesus monkeys developed atherosclerotic coronary artery lesions leading to stenosis, thrombosis, and myocardial infarction. Taylor reviewed experimental atherosclerosis in primates in 1%5.6 Since his review, Wissler and his coworker^,^.^ Portinan and Andrus,B-lO and workers from Albany Medical College,f1-*3 Bowman Gray School of Medicine,l4-lU University of Cambridge,17 and Louisiana State U n i v e r ~ i t y ~ ~ ~ ~ ~ have reported experiments in which they have produced arterial lesions of varying severity in primates with different dietary regimens. Dr. Wisslers experimental models are described in this symposium.20

Lipoprotein profiles in rhesus monkeys with divergent responses to dietary cholesterol.

From a group of 53 rhesus monkeys, we selected 12 animals, the six wlth the highest and the six with the lowest response to a hlgh cholesterol diet, and we made detailed analyses of their cholesterol and apollpoproteln profile. The high responders differed from the low responders in several ways. During the hlgh cholesterol diet period, the high responders had much higher plasma apolipoprotein B and E concentratlons and much lower plasma apoilpoprotein A4 concentratlons than did the low responders. Nearly ail the increase in plasma cholesterol and apollpoproteins B and E concentrations in the hlgh responders occurred in the lower density fractions (d = 1.006–1.030 g/ml), while the decrease in plasma apoilpoprotein A-I concentratlons In the high responderswas confined to the lower denslty fraction of the hlgh denstty llpoprotelns (HDL), I.e., HDL2 (d = 1.063–1.125 mi) in the low responders, on the other hand, the slight increase in cholesterol concentrations was evenly dlstrlbuted between the lower denslty fractions and HDL, and the increase in apollpoprotein A-l concentm tlons was confined to the HDL2 fractlon. We suggest that the increase in the concentration of the lower denstty fractions is relatedto the decrease in the concentration in the HDL2 in the high responders.

RELATIONSHIP OF CALCIFIED LESIONS TO CLINICALLY SIGNIFICANT ATHEROSCLEROTIC LESIONS

I t has recently become possible to detect relatively small calcified plaques in the coronary arteries of living individuals by fluoroscopy with image intensifiers.1,2 I t is also possible to detect calcification in aortas and other peripheral arteries 11y radiographic methods, Since the calcified plaque itself probably plays little significant role in the development of morbidity or mortality due to atherosclerosis, the significance of the detection of such calcified plaques in the living depends on the strength of association with other more clinically significant lesions of atherosclerosis. Little is known about the role of calcification in etiology of the atherosclerotic lesion. I t has been shown that even in “normal” arterial tissue there is an increase in calcium content with The recent work of Y u and Blunientha16--8 has shown that this calcification process involves a nucleation of calcium apatite crystals in degenerating elastin fibers. These investigators have also shown that elastic fibers are a major component of the matrix associated with the formation of macroscopically detectable calcified plaques in atheroma. Whether the “normal” calcification of elastin fibers is involved in the pathogenesis of the atherosclerotic lesion and whether there is any association between this “normal“ calcification and the calcification occurring in the advanced stages of atheroma formation is not known. In view of this lack of knowledge of the role of calcification in the etiology of atheroscterotic lesions, the association between calcified plaques and the more clinically significant lesions must be obtained empirically. Epstein and associates”12 have used radiographic assessment of aortic calcification as an indicator of atherosclerosis in epidemiologic investigations. Other investigators have applied radiologic assessment of aortic or coronary calcification in diagnostic studies of a t h e r o s c l e r ~ s i s . ~ ~ ~ ~ Some of these have obtained autopsies on limited numbers of cases, and all have concluded that there is an association between arterial calcification observed in the living and coronary heart disease, especially in the younger individuals. There is, however, a need for a quantitative assessment of the strength of the association between arterial calcification and coronary heart disease or the clinically more significant atherosclerotic lesions. In view of the need for large samples and for detailed examination of the arteries and the heart, autopsy series, in spite of the inherent hias present, appear to be the only source of material for such studies. Blankenhorn20 has reviewed a number of early studies on limited numbers of cases that gave evidence for an association between calcified lesions detected in the living or in necropsy material and other advanced atherosclerotic lesions. More recently Baetlenkopf and coworkers21 have

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.

Atherosclerotic lesions were induced in rhesus monkeys by feeding a high-saturated fatty acid and high-cholesterol diet. After 5.4 years the extent of fatty streaks and raised lesions was evaluated in one group of animals (group P) by visual estimation in 10 arterial segments and chemically in four arterial segments. The remaining animals were switched to a basal regression diet low in cholesterol but high in saturated fatty acids for up to 3.7 years. Regression of lesions was evaluated in one group for 1.9 years (group R4) and in another for 3.7 years (group R5) after deleting cholesterol from the diet. The atherogenic diet increased serum cholesterol levels in all animals from a mean of 150 mg/dL to a mean of about 430 mg/dL. The atherogenic diet produced lesions in group P in all arterial segments (involving up to 50% of the arterial intimal surface) and increased cholesterol content in four arterial segments (varying between 443 and 506 micrograms/cm2). Switching to the basal regression diet decreased serum cholesterol levels to normal after 12 to 18 weeks. The switch to the basal diet significantly decreased the extent of fatty streaks in most arterial segments in both groups. Although differences in the mean extent of raised lesions among groups were not statistically significant, 7 of 10 arterial segments in group R4 and 9 of 10 segments in group R5 showed a lesser extent of raised lesions than in group P. Cholesterol content was lower (P < .05) in all four arterial segments in group R5 than in group P.(ABSTRACT TRUNCATED AT 250 WORDS)

Regression of experimental atherosclerotic lesions in rhesus monkeys consuming a high saturated fat diet.

Atherosclerotic lesions were induced in rhesus monkeys by feeding them a highfat, high-cholesterol diet for 2 years. Arteries were examined after autopsy of a subgroup of animals (group P) and cholesterol was removed from the diet of the remaining animals. Lesions were examined in other subgroups after 30 weeks (group R1) and after 52 weeks (group R2). A control group (group C) was fed the diet without cholesterol throughout the study. The mean total serum cholesterol concentration before, during, and after lesion induction was 151,390, and 157 mg/dl, respectively. The mean percent of surface area with fatty streak or fibrous plaque and the free and esterified cholesterol content of the artery increased in all six arterial segments examined in group P. The means for percent of surface with fatty streak and for arterial cholesterol content or concentration (but not for extent of surface with fibrous plaque) were consistently less in groups R1 and R2 than in group P, although they remained greater in groups R1 and R2 than in group C. The mean intimal thickness for coronary arteries was 10-fold greater in group P than in group C and 60 percent less in groups R1 and R2 than in group P; there was, however, much variability among animals and these differences among groups were not statistically significant. By using several measures in several arterial systems, we have shown that there was regression of dietinduced atherosclerotic lesions in rhesus monkeys while they were fed a diet high in saturated fat but without cholesterol for 30 or 52 weeks.

Relationships between dietary cholesterol, cholesterol absorption, cholesterol synthesis, and plasma cholesterol in rhesus monkeys

The relationships between the cholesterol content of the diet, plasma cholesterol concentration, cholesterol absorption, and cholesterol synthesis (measured indirectly by desmosterol suppression technique) are explored in groups of high- and low-responding rhesus monkeys fed diets containing 0.02, 0.15 and 0.75 mg cholesterol/kcal. The cholesterol content of the diet (expressed as mg/kcal) is positively correlated with plasma cholesterol concentration and is negatively correlated with percent cholesterol absorption in both groups. Also the cholesterol content of the diet is negatively correlated (r = -0.66) with cholesterol synthesis only in low-responders but not in high-responders. Similarly, the correlation between percent cholesterol absorption and cholesterol synthesis is significant in the low-responders (r = 0.82, P less than 0.01) but not in the high-responders (r = 0.12, P greater than 0.1). Further, a negative correlation (r = -0.61) is observed between cholesterol synthesis and plasma cholesterol concentration in the low-responders but in the high-responders, there is no relationship between the parameters. From these correlations we conclude that the higher cholesterol absorption in the high-responders than in the low-responders is one important mechanism responsible for the development of severe hypercholesterolemia in the high-responding monkeys fed cholesterol. The results also suggest that there might be a lower sensitivity in the feedback inhibition mechanism of cholesterol biosynthesis in the high-responding than in the low-responding rhesus monkeys.

Obesity, smoking and atherosclerosis. A study of interassociations.

The data gathered from male autopsied cases (25-64 years of age) in Orleans Parish have been analysed for association between measurements of athetosclerosis and measurements of obesity. The confounding effects of diseases such as hypertension and diabetes have been controlled by excluding from analysis cases known to have such diseases. The confounding effect of age and a measurement of smoking habit on the association between atherosclerosis and obesity has been controlled by the technique of multivariate regression analysis. An inverse association between smoking habit and obesity and the direct associations between smoking habit and atherosclerosis as measured by MCWT (mean coronary wall thickness), CALC (coronary calcification), RLAA (raised lesion in abdominal aorta), and RLCA (raised lesion in coronary arteries) have been confirmed. Positive though weak associations for mesasures of atherosclerosis (MCWT and RLCA) with adipose thickness have been found among whites but not among blacks. Among black cases a weak association between fatty streaks in coronary arteries and adipose thickness was found. It is suggested that obesity itself is not an atherogenic agent but that it is related to one or more atherogenic agents that affect aortas and coronary arteries differentially and that are more intensive among whites than among blacks.

Effects of feeding cholesterol and mixed plant sterols on the fecal excretion of acidic steroids in rhesus monkeys

The effects of feeding diets with high or low amounts of cholesterol and with low or high levels of mixed plant sterols (sitosterol: campesterol: stigmasterol, 60:35:5) on the daily fecal excretion of acidic steroids were studied in rhesus monkeys. During periods of low dietary plant sterol, total fecal acidic steroid excretion was 43% lower (P less than 0.01) during low dietary cholesterol than during high dietary cholesterol. During periods of high dietary plant sterols the fecal acidic steroid excretion was 113% higher (P less than 0.01) with low dietary cholesterol than with high dietary cholesterol. Addition of mixed plant sterols to the low-cholesterol diet produced nearly a 2-fold increase (P less than 0.005) whereas, such an addition to the high cholesterol diet produced a significant decrease by about 53% (P less than 0.025) in the total fecal acidic steroid excretion. The results suggest that the effect of cholesterol feeding on fecal acidic steroid excretion depends on the level of plant sterols in the diet. This interaction of the effects of cholesterol and plant sterols on the fecal acidic steroid excretion is probably related to the inhibitory effect of plant sterols on cholesterol absorption.