Dietary lipid and arteriosclerosis

Mutagenic characterization of cholesterol epoxides in Chinese hamster V79 cells

The uptake, metabolism and alkylating properties of the diastereomeric cholesterol epoxides were studied using Chinese hamster lung fibroblasts (V79 cells). Specific emphasis is given to the comparative cyto- and geno-toxic effects of cholesterol 5 beta,6 beta-epoxide (beta CE) and cholesterol 5 alpha,6 alpha-epoxide (alpha CE) and data are provided for the first time indicating that beta CE can induce more 6-thioguanine-resistant cells than alpha CE. Cholesterol 5 beta,6 beta-epoxide induced colonies of cells resistant to 6-thioguanine at 2-3-fold the frequencies observed with the alpha-isomer, but neither compound produced ouabain-resistant colonies. The cytotoxicity (LD50) of alpha CE was estimated to be 45-50 microM whereas beta CE displayed an LD50 of 25-29 microM. Inhibition of DNA synthesis (IC50) was observed over the same dose ranges as the LD50 for each epoxide isomer. The epoxides were assimilated by cells to an equal extent, however, beta CE was metabolized to cholestane 3 beta,5 alpha-6 beta-triol twice as rapidly as the alpha-isomer. Both epoxides reacted with 4-(4'-nitrobenzyl)-pyridine to a similar extent, and with identical nucleophilic selectivity at pH 7.4, but their alkylating activity was estimated on this basis to be two orders of magnitude less than methyl methanesulfonate. Binding experiments with the DNA or cultured V79 cells or with calf-thymus DNA indicated that interactions were noncovalent and DNA binding did not correlate with the potency of the epoxides to induce the 6-thioguanine-resistant phenotype. Our results could be interpreted as indicating that both cholesterol epoxide isomers are weak mutagens or that they might induce some epigenetic event repressing the hypoxanthine guanine-phosphoribosyltransferase gene. The similarity of the epoxides' alkylating activity and their DNA-binding properties are inconsistent with their different potencies in inducing the 6-thioguanine-resistant phenotype, suggesting that the mechanism leading to this phenotype is not necessarily the result of DNA alkylation.

Biological autoxidation. II. Cholesterol esters as inert barrier antioxidants. Self-assembly of porous membrane sacs. An hypothesis

The antioxidation defenses recognized thus far appear too weak. Needed are inert barriers to encapsulate foci of activated oxygen (FAOs) and contain their spreading. These capsules must: 1. self-assemble nonenzymatically and spontaneously in face of adversity; 2. resist oxidation and dissolution in water; and 3. be moderately fluid and elastic enough to withstand flexing by tissues. Evidence shows activated oxygen: a. is produced by common cholesterolester (CE)-raising agents; b. boosts accumulation of CEs; and c. splits low-density lipoproteins (LDL), thus releasing CE-rich coalescence-prone lipid micelles. I am proposing that CEs, combined with polar lipids, are uniquely suited to form inert-lipid antioxidation barriers (ILABs). Porous ILAB capsules self-assemble from lipid micelles released by oxidatively degraded LDL. The capsules are thermodynamically unstable but elastic, durable and capable of self-repair through oxidation of ambient LDL. All capsules tend to contract into spheres. Enclosed needle-like "foreign bodies", such as asbestos, puncture the contracting capsules. Hence the odd bulbous architecture of asbestos bodies. ILABs protect from--and their failure initiates and promotes--carcinogenesis and atherosclerosis. ILABs may be mediators of membrane biogenesis. The loss of arterial flexibility in atherosclerosis protects ILAB capsules from breakage.

Cholesterol and repair processes in arteriosclerosis

The high cholesterol content of the atheroma and the correlation between elevation of the serum cholesterol and myocardial infractions gave rise to the lipid theory of arteriosclerosis, which assumes that cholesterol induces arteriosclerotic lesions and that its reduction counteracts their development. However, many facts contradict this theory. Therefore, a new hypothesis has been based on the high cholesterol content of old pathological lesions of granulomatous nature and the similarity of atheromata to granulomas. In the latter, a complicated tissue containing a high percentage of cholesterol is deposited in response to the injurious agent, which becomes walled off by this tissue. Thus, cholesterol forms part of a protective mechanism, a hypothesis compatible with the known facts about the relationship of cholesterol to arteriosclerosis.

[Etiology and pathogenesis of arteriosclerosis]

Cardiovascular diseases are the leading cause of death in Western countries, with an enormous increase in death rate and involvement of younger age groups during the last decades. This applies especially to coronary heart disease and is mainly caused by first-degree risk factors: hypertension, hyperlipoproteinemia, cigarette smoking, gout, obesity, polycythemia, lack of physical activity, and stress. These risk factors are discussed with special reference to overnutrition and increased cholesterol levels. Recent resuults of research concerning lipids and their relation to atherosclerosis are reviewed.

Neural factors contribute to atherogenesis

Electron microscopic evidence of early atherogenic changes in the aorta and coronary arteries was obtained in normal fed, conscious, unrestrained rats receiving electrical stimulation in the lateral hypothalamus for periods of up to 62 days. Hypertension and hypercholesterolemia were not etiologic factors. In view of recent observations concerning neuropsychological mechanisms in human ischemic heart disease, the findings raise the possibility that the human central nervous system has a role in the development of atherosclerotic lesions.