Shirley A. Tepper

Influence of Conjugated Linoleic Acid (CLA) on Establishment and Progression of Atherosclerosis in Rabbits

Objective: To determine effects of conjugated linoleic acid (CLA) on establishment and progression of experimentally-induced atherosclerosis in rabbits. Methods: For establishment of atherosclerosis, New Zealand White rabbits were fed a semipurified diet containing 0.1% to 0.2% cholesterol for 90 days. Some groups were fed diet and CLA. For effects on progression of atherosclerosis, rabbits with established atherosclerosis were fed a semipurified diet±CLA for 90 days. Results: At dietary levels as low as 0.1%, CLA inhibited atherogenesis. At dietary levels of 1%, CLA caused substantial (30%) regression of established atherosclerosis. This is the first example of substantial regression of atherosclerosis being caused by diet alone. Conclusion: Dietary CLA is an effective inhibitor of atherogenesis and also causes regression of established atherosclerosis.

Cholesterol vehicle in experimental atherosclerosis

Summary The atherogenic effects of diets containing cholesterol suspended in heated or unheated olive and corn oils were compared. The diet containing heated corn oil was more atherogenic than that containing unheated corn oil, confirming our previously published findings. The increased atherogenicity of the heated corn oil diet could be correlated with an increase in its free fatty acid content. The two olive oil diets were of comparable atherogenicity, and heating did not elevate the free fatty acid content of the olive oil. These findings further suggest that one of the factors affecting atherogenicity of heated fats is their free fatty acid content.

Conjugated linoleic acid isomer effects in atherosclerosis: Growth and regression of lesions

Conjugated linoleic acid (CLA), a mixture of positional and geometric isomers of octadecadienoic acid, has been shown to inhibit experimentally induced atherosclerosis in rabbits and also to cause significant regression of pre-established atheromatous lesions in rabbits. The two major CLA isomers (cis9,trans11 and trans10,cis12), now available at 90% purity, have been tested individually for their anti-atherogenic or lesion regression potency. The two major isomers and the mixture were fed for 90 d to rabbits fed 0.2% cholesterol. Atherosclerosis was inhibited significantly by all three preparations. The two CLA isomers and the isomer mix were also fed (1.0%) as part of a cholesterol-free diet for 90 d to rabbits bearing atheromatous lesions produced by feeding an atherogenic diet. A fourth group was maintained on a cholesterol-free diet. On the CLA-free diet atherosclerosis was exacerbated by 35%. Reduction of severity of atheromatous lesions was observed to the same extent in all three CLA-fed groups. The average reduction of severity in the three CLA-fed groups was 26±2% compared with the first control (atherogenic diet) and 46±1% compared with the regression diet. Insofar as individual effects on atherosclerosis were concerned, there was no difference between the CLA mix and the cis9,trans11 and trans10,cis12 isomers. They inhibit atherogenesis by 50% when fed as a component of a semipurified diet containing 0.2% cholesterol; and when fed as part of a cholesterol-free diet, they reduce established lesions by 26%. Reduction of atheromata to the observed extent by dietar means alone is noteworthy.

Cholesterol vehicle in experimental atherosclerosis Part 13. Randomized peanut oil

Abstract Peanut oil (PNO) is more atherogenic than is corn oil (CO) when fed to rabbits in a diet containing 2 % cholesterol and 6 % fat. To test the hypothesis that the arachidic and behenic acid content of PNO is responsible for this observation, four groups of rabbits were fed 2 % cholesterol plus 6 % PNO, CO or two fats, prepared by interesterification (randomization) of CO and a special fat, PGF, with a fat containing arachidic and behenic acids. The new fats, CO/R and PGF/R, contained levels of arachidic and behenic acids similar to those found in PNO. Average atheromata (arch plus thoracic/2) for a series of 3 experiments were: PNO — 1.59; PGF/R — 1.41; CO/R — 1.34; CO — 1.20 and PGF — 1.17. The data suggested an effect beyond fatty acid composition. We then compared PNO, CO and autorandomized peanut oil, PNO/A. The fatty acid composition of PNO/A is identical with that of PNO, but its triglyceride structure is markedly different. Average atheromata for 3 experiments were: PNO — 1.88; PNO/A — 1.18 and CO — 1.17. The data clearly indicate that triglyceride structure of a fat, as well as its fatty acid composition, is a determining factor in its atherogenic potency.

Experimental atherosclerosis in rabbits fed cholesterol-free diets. Part 7. Interaction of animal or vegetable protein with fiber.

Rabbits were maintained for 10 months on a semipurified, cholesterol-free atherogenic regimen. All diets contained sucrose (40%) and hydrogenated coconut oil (14%). The protein (25%) was either casein or soya protein and the fiber (15%) was either wheat straw, alfalfa, or cellulose. Within either protein group the order for induction of cholesteremia was cellulose=wheat straw greater than alfalfa. For atherogenesis, the effect was cellulose greater than wheat straw greater than alfalfa Soya-wheat straw or soya-cellulose diets were less cholesteremic and atherogenic than their casein counterparts. When alfalfa was the fiber, the two types of protein were almost equivalent. Our results show that casein may be more cholesteremic and atherogenic than soya protein under certain conditions (cellulose or wheat straw as fiber) but the addition of alfalfa to the diet renders the two proteins equivalent.

Experimental atherosclerosis in rabbits fed cholesterol-free diets: 5. Comparison of Peanut, Corn, Butter, and Coconut Oils

Abstract Four groups of Dutch belted rabbits were fed a semipurified diet containing 40% sucrose, 25% casein, and 14% fat for 10 months (without added cholesterol). The fats were peanut oil (PNO), corn oil (CO), butter oil (BO), and coconut oil (CNO). All diets were hyperlipidemic and hyperlipoproteinemic. The highest serum cholesterol and triglyceride levels were observed in the CNO groups, 330 and 286 mgm/dl, respectively. Serum cholesterol and triglyceride levels in the other groups (mgm/dl) were: PNO-205 and 51; CO-152 and 28; BO-292 and 48. The serum of α β lipoprotein cholesterol ratios were: PNO-0.28; CO-0.28; BO-0.19, and CNO-0.13. This ratio is about 0.35–0.40 in normal Dutch belted rabbits. Liver cholesterol levels were similar in all groups (1.35 ± 0.5 gm/100 gm). Liver triglyceride levels were (gm/100 gm): PNO-0.37; CO-0.55; BO-0.66; CNO-0.39. The most severe gross atherosclerosis was observed in the CNO group (25% of surface area) and the least in the CO group (2%). The involved surface area in the other two groups was: PNO-10% and BO-14%. Microscopic evaluation of the severity of the aortic lesions indicated that the rabbits fed CNO, BO, and PNO had the most frequent and severe lesions. In contrast, the animals fed CO consistently showed much less aortic disease. Gross aortic examination revealed distinct differences in the characteristics of atherosclerotic lesions induced by the four dietary fats. The most extensive lesions, observed in rabbits fed CNO, were characterized by intimal proliferation spread over the area of lipid deposition. BO tended to produce aortic lesions rich in lipid but a relatively small number of cells and little collagen deposition. The aortic lesions in rabbits fed PNO contained relatively little lipid and were characterized by thick fibrous plaques due to prominent intimal proliferation and a high proportion of collagen. The rabbits fed CO developed few aortic lesions, with minimal intimal proliferation and very little lipid. The relative atherogenicity of PNO was an unexpected finding.

Effects of casein and soy protein on hepatic and serum lipids and lipoprotein lipid distributions in the rat

Rats fed a semipurified diet containing casein developed higher levels of circulating triglycerides and cholesterol than animals fed a soy protein-containing diet. The increased serum lipid levels in non-fasted rats were associated largely with the d less than 1.006 g/ml lipoprotein particles (e.g. chylomicrons or very low density-like lipoproteins). In addition, casein-fed rats exhibited higher levels of circulating insulin and depressed hepatic 7 alpha-hydroxylase levels compared to soy-fed rats. Supplementation of the casein diet with arginine, to give an arginine/lysine ratio comparable to that in the soy diet, resulted in a reduction of d less than 1.006 g/ml lipids, a reduction in serum insulin levels and an elevation in hepatic 7 alpha-hydroxylase activity. Supplementation of the soy diet with lysine also resulted in modification of these parameters toward those observed with casein diets, albeit the effects were less dramatic. The results suggest that the hyperlipidemia associated with feeding casein-based diet is associated with decreased rates of clearance of chylomicron-like lipoproteins and their component triglycerides and cholesterol. Furthermore, this is largely prevented by addition of arginine to diets containing casein as the sole protein source.

Influence of graded levels of conjugated linoleic acid (CLA) on experimental atherosclerosis in rabbits

Abstract Dietary CLA inhibits experimental atherosclerosis when fed at a level of 0.1%. In this study rabbits were fed 0.2% cholesterol as part of a semi-purified diet which contained 0, 0.05, 0.075, 0.10 or 0.5% CLA. At levels as low as 0.05% of the diet CLA reduced severity of atherosclerosis in the aortic arch by 20% and in the thoracic aorta by 8%. As dietary concentrations of CLA rose severity of atherosclerosis fell. When the diet contained 0.10% CLA severity of atherosclerosis in the aortic arch and thoracic aorta fell by 40 (p

Experimental atherosclerosis in rabbits fed cholesterol-free diets. 2. Influence of various carbohydrates.

Summary It has been shown that the addition of saturated fat to a semi-synthetic, cholesterol-free ration is atherogenic for rabbits. Experiments were carried out in which the carbohydrate component, which comprised 40 % of the diet, was either glucose, sucrose, starch or hydrolyzed starch. This diet was fed for 33 weeks. Starch was the most hypercholesteremic and atherogenic of the carbohydrates used and glucose was the least. Hydrolyzed starch resulted in higher serum cholesterol levels than did sucrose, but in slightly lower atheromata. Serum β-lipoprotein cholesterol levels were elevated in all four dietary groups, least in the glucose-fed rabbits. The glucose group exhibited normal serum triglyceride and phospholipid levels. Serum phospholipid levels were only slightly elevated in the other dietary groups. Serum triglycerides were twice normal in the sucrose-fed rabbits and were elevated 3- and 5-fold in the starch and hydrolyzed starch groups, respectively. Liver cholesterol levels were elevated (4–6-fold) in all four carbohydrate-fed groups. Aortic cholesterol levels were elevated in all the experimental groups, and the aortic free/ester cholesterol ratio was much lower than that observed in the aortas of normal levels. The biliary bile acids were determined and showed deoxycholic acid to be the predominate component (over 90 %) in all groups. The data suggest that, in rabbits fed semi-synthetic diets, glucose is the least and starch the most atherogenic carbohydrate. In all rabbits fed the semi-synthetic diet, hypercholesteremia, elevations in serum β-lipoprotein cholesterol and atheromata were observed.

Age-related changes in the lipid metabolism of Fisher 344 rats

Lipid metabolism of male Fisher 344 rats aged 2–24 months was studied. Serum and liver cholesterol levels did not display the age-related gradual increase seen in other rat strains. An increase in the serum plus liver cholesterol pool from 2 to 6 months was followed by a plateau through 18 months and then another increase at 24 months of age. The triglyceride pool increased from 2 to 6 months and then remained unchanged through 24 months of age. Cholesterol synthesis from acetate decreased 50% between 2 and 9 months and fell only slightly through 24 months of age. Assay of 3-hydroxy-3-methyl glutaryl Coenzyme A (HMG-CoA) reductase showed a similar pattern but did not decrease further after 9 months of age. Cholesterol 7α hydroxylase activity was not significantly altered by age. These age- and strain-related differences present an opportunity for a comparative study of the aging process using the parameters of lipid metabolism as indicators.