Cholesterol-induced Atherogenesis Research Articles

Effects of dietary flaxseed on vascular contractile function and atherosclerosis during prolonged hypercholesterolemia in rabbits

Dietary flaxseed has significant anti-atherogenic effects. However, the limits of this action and its effects on vascular contractile function are not known. We evaluated the effects of flaxseed supplementation on atherosclerosis and vascular function under prolonged hypercholesterolemic conditions in New Zealand White rabbits assigned to one of four groups for 6, 8, or 16 wk of feeding: regular diet (RG), 10% flaxseed-supplemented diet (FX), 0.5% cholesterol-supplemented diet (CH), and 0.5% cholesterol- and 10% flaxseed-supplemented diet (CF). Cholesterol feeding resulted in elevated plasma cholesterol levels and the development of atherosclerosis. The CF group had significantly less atherosclerotic lesions in the aorta and carotid arteries after 6 and 8 wk than the CH animals. However, the anti-atherogenic effect of flaxseed supplementation was completely attenuated by 16 wk. Maximal tension induced in aortic rings either by KCl or norepinephrine was not impaired by dietary cholesterol until 16 wk. This functional impairment was not prevented by including flaxseed in the high-cholesterol diet. Aortic rings from the cholesterol-fed rabbits exhibited an impaired relaxation response to acetylcholine at all time points examined. Including flaxseed in the high-cholesterol diet completely normalized the relaxation response at 6 and 8 wk and partially restored it at 16 wk. No significant changes in the relaxation response induced by sodium nitroprusside were observed in any of the groups. In summary, dietary flaxseed is a valuable strategy to limit cholesterol-induced atherogenesis as well as abnormalities in endothelial-dependent vasorelaxation. However, these beneficial effects were attenuated during prolonged hypercholesterolemic conditions.

Endogenous neutralizing antibodies against platelet-derived growth factor-aa inhibit atherogenesis in the cholesterol-fed rabbit.

Previous studies have shown that the B chain of platelet-derived growth factor (PDGF) has an important role in atherogenesis. In this study we have investigated the contribution of PDGF-A chain in cholesterol-induced atherogenesis in the New Zealand White rabbit. High titers of antibodies to PDGF-AA or to platelet cytosolic protein (PCP) were induced in these animals by immunization against recombinant human PDGF-AA or human PCP. Rabbits were then fed a 0.25% to 1% cholesterol-containing diet for 10 weeks to induce atherosclerotic lesions; the rabbits were then humanely killed and perfusion-fixed and their aortas were removed. The extent of atherosclerosis in the thoracic aortas was determined by quantitative morphometry after staining with oil red O. The intimal and medial areas in histological sections taken at the level of the first intercostal branch were quantified by image analysis. Immunization against PDGF-AA and PCP, but not against adjuvant alone, resulted in rising titers of antibodies within 2 weeks, the levels of which reached a plateau by 8 weeks. The antibodies to PDGF-AA were isoform-specific, recognized both human and rabbit PDGF-AA, and neutralized the biological activity of PDGF-AA in vitro. Integrated plasma cholesterol levels were similar in both groups. Compared with nonimmune rabbits (n=10), animals immunized against PDGF-AA (n=10) or PCP (n=10) had significantly smaller areas of the aorta covered by atherosclerotic lesions (24.6+/-5.1% and 18.7+/-4.2%, respectively, vs 34.4+/-4.3%; P<0.05). This was associated with a reduced aortic intimal-medial area ratio in PDGF-AA-immunized (0.009+/-0.006) and PCP-immunized (0.025+/-0.017) rabbits than in nonimmune animals (0.159+/-0.066; P<0.05). These data suggest that PDGF-AA is actively involved in cholesterol-induced atherosclerosis in the rabbit.

Reported anti atherosclerotic activity of silicon may reflect increased endothelial synthesis of heparan sulfate proteoglycans

Silicon plays a physiologically essential but mechanistically obscure role in promoting the synthesis of mucopolysaccharides and collagen. In light of reports that increased silicon ingestion impedes cholesterol-induced atherogenesis in rabbits and may be associated epidemiologically with reduced cardiovascular risk, it is reasonable to speculate that supplemental silicon may stimulate endothelial production of heparan sulfate proteoglycans that inhibit intimal hyperplasia.

Complementary vascular-protective actions of magnesium and taurine: A rationale for magnesium taurate

By a variety of mechanisms, magnesium functions both intracellularly and extracellularly to minimize the cytoplasmic free calcium level, [Ca 2+] i. This may be the chief reason why correction of magnesium deficiency, or induction of hypermagnesemia by parenteral infusion, exerts anti hypertensive, anti-atherosclerotic, anti-arrhythmic and antithrombotic effects. Although the amino acid taurine can increase systolic calcium transients in cardiac cells (and thus has positive inotropic activity), it has other actions which tend to reduce [Ca 2+] i. Indeed, in animal or clinical studies, taurine lowers elevated blood pressure, retards cholesterol-induced atherogenesis, prevents arrhythmias and stabilizes platelets — effects parallel to those of magnesium. The complex magnesium taurate may thus have considerable potential as a vascular-protective nutritional supplement, and might also be administered parenterally, as an alternative to magnesium sulfate, in the treatment of acute myocardial infarction as well as of pre-eclampsia. The effects of magnesium taurate in diabetes deserve particular attention, since both magnesium and taurine may improve insulin sensitivity, and also may lessen risk for the micro- and macrovascular complications of diabetes.

Nature of aortic smooth muscle cellular activity induced by cholesterol incorporation through an LDL-receptor-independent pathway: Preventive role of trifluoperazine on such activity

The present study was addressed to understand two specific issues: (a) whether atherogenic activity of smooth muscle cells could be initiated by incorporating cholesterol within their membranes through a LDL-receptor-independent pathway; and (b) whether trifluoperazine, which we had recently shown to prevent the cholesterol-induced atherogenesis in an experimental animal model system, could prevent such activity of these cells induced by cholesterol in vitro. The results of such a study revealed that trifluoperazine could prevent the cholesterol-induced stimulation of (a) DNA synthesis, (b) cholesterol synthesis, (c) intracellular cGMP levels, (d) intracellular free and esterified cholesterol accumulation, and (e) collagen secretion. Furthermore, the drug caused stimulation of cholesterol-induced suppression of LDL-receptor synthesis. On this basis, we suggest that acquisition of cholesterol by smooth muscle cells through the LDL-receptor-independent pathway may be the fundamental process responsible for atherogenic activity of these cells and that the drug trifluoperazine has the inherent capacity to prevent the membrane-cholesterol-modulated atherogenic activity of smooth muscle cells in vitro.

Effect of trifluoperazine on DNA and LDL-receptor synthesis in smooth muscle cells exposed to hypercholesterolemic medium in vitro

We recently demonstrated that calmodulin and/or protein kinase C may play a crucial role in cholesterol-induced atherogenesis in experimental animal model system. The present study, which was undertaken to elucidate the effect of trifluoperazine (known as a potent inhibitor of calmodulin and protein kinase C) on DNA and LDL-receptor synthesis of aortic smooth muscle cells exposed to hypercholesterolemic medium, revealed that (a) trifluoperazine at a concentration of 25 microM caused an approximately threefold increase in the [35S]methionine-incorporated LDL-receptor protein as compared with values found in control cells; (b) the drug at concentrations greater than or equal to 0.1 microM caused inhibition of DNA synthesis as compared with values found in control cells. These results demonstrate that the preventive effect of trifluoperazine on the atherogenic activity of smooth muscle cells may be due to its ability to increase LDL-receptors synthesis as well as concomitant inhibitory action on DNA synthesis of smooth muscle cells exposed to hypercholesterolemic medium.

Failure of diltiazem to suppress cholesterol-induced atherogenesis of endothelium-denudated arteries in pigs

To investigate the effect of diltiazem on the development of atherosclerosis, 15 pigs were fed a fat-poor basal diet to which 8% (w/w) lard fat and 2% (w/w) cholesterol were added for 8 months. To enhance the formation of atherosclerotic plaques endothelium of the aorta and the left anterior descending coronary artery was removed after 1 month and 0.5% (w/w) bile acids were added to the diet after 3 months. Seven animals served as control, while 8 animals also received diltiazem (the first 2 months 10 mg/kg twice daily and during the remainder of the dietary period 5 mg/kg twice daily). The diet-induced increases in plasma level of total cholesterol were not affected by diltiazem. Triglyceride levels did not change in the control group but decreased significantly in the diltiazem-treated animals. Collagen-induced (1 μg/ml) platelet aggregation was increased by diltiazem. The sum of free and esterified cholesterol was increased in the lesions of the aortic wall in the diltiazem-treated animals (9.8 ± 1.3 μg/g wet weight vs. 6.3 ± 1.0 μmol/g wet weight in the untreated animals), but coverage of the aorta with sudanophilic lesions was similar for both groups (40 ± 4% for the treated and 34 ± 9% for the control animals). Narrowing of the previously abraded coronary arteries was similar for the diltiazem-treated (median 7.1%, ranges 2.6–29.0%) and the control group (median 10.0%, ranges 2.3–24.1%). It is concluded that the dose range of diltiazem of 5–10 mg/kg twice daily, which is close to that used in the clinical setting, had no effect on the experimentally induced atherogenesis in pigs.

O-054 - Effect of S-2185 on dietary cholesterol-induced atherogenesis in rabbits.

O-054 - Effect of S-2185 on dietary cholesterol-induced atherogenesis in rabbits.

Evidence for increased aortic plasma membrane calcium transport caused by experimental atherosclerosis in rabbits.

Several lines of evidence, including the reported ability of calcium channel blockers to prevent atherogenesis in cholesterol-fed rabbits, suggest that calcium mediates one or more of the pathologic changes in atherosclerosis. Moreover, it has long been known that calcium accumulates in atherosclerotic blood vessels. To test the hypothesis that a substantial fraction of this accumulated calcium is intracellular and to identify possible causes of this accumulation, calcium fluxes and contents were determined in aortic segments from cholesterol-fed rabbits and age-matched controls. A new method, based on 45Ca efflux experiments and computer-assisted kinetic analysis, was used to measure intracellular and extracellular calcium contents (nmol calcium/g wet wt tissue) and fluxes. Total intracellular calcium increased from 269 +/- 11.6 to 1,300 +/- 352 nmol/g in cholesterol-fed animals compared with controls (p less than 0.01). This change was sufficient to account for the observed increase in total tissue calcium from 4,190 +/- 211 to 5,240 +/- 477 nmol/g (p less than 0.05). Thus, the fraction of tissue calcium that is intracellular increased significantly from 0.065 +/- 0.006 to 0.223 +/- 0.048 (p less than 0.01) in experimental atherosclerosis. In addition, the data were quantitatively consistent with the hypothesis that these changes are brought about by a 4.8-fold increase in the plasma membrane calcium permeability of aortic smooth muscle cells. These results provide evidence that increased intracellular calcium is a possible mediator of cholesterol-induced atherogenesis.

Collagen metabolism during the early stages of cholesterol-induced atherogenesis in rabbits.

The involvement of collagen in cholesterol-induced atherosclerosis in rabbits was investigated. Rabbits were fed a 2% cholesterol diet for 8, 16, 30, 60 and 90 days. Histological sections were taken and aortic free and esterified cholesterol were determined after separation on thin-layer chromatography. Prolyl hydroxylase activity was used as a measure of collagen synthetic rate and hydroxyproline levels as an estimate of collagen content. Cholesterol content was a significantly increased after 8 days, while at this time there were no gross aortic lesions. After 30 days there was some aortic disease and by 60 days most of the rabbits exhibited pronounced aortic lesions. Histologically, the lesions consisted mainly of intimal foam cells. There was no alteration in collagen synthetic rate or content at 8, 16, 30 or 60 days. These data indicate that 60 days of continuous cholesterol feeding results in a foam cell aortic lesion with no alteration in collagen metabolism. After 90 days of cholesterol feeding there was significant increase in collagen synthetic activity in the thoracic aorta. These data suggest that alteration of collagen synthetic activity is secondary response, resulting from injury induced by the aortic accumulation of large amounts of cholesterol.

Effects of ovariectomy on experimental atherosclerosis in rabbits.

The effect of previous ovariectomy on the development of cholesterol-induced atherogenesis in the rabbit was investigated. It was found that an ovariectomized group of animals had a significantly greater degree of hypercholesterolemia, but that the control group with intact ovaries developed slightly more aortic and coronary atheromatosis. The implications of these findings are discussed.