Atherosclerosis. Chronic effects of fish oil and a therapeutic diet in nonhuman primates

Hepatic Vitamin A Concentrations in Vervets (Chlorocebus aethiops) Supplemented with Carotenoids Derived from Oil Palm

Commonly used in biomedical research, vervets (Chlorocebus aethiops) are omnivorous but primarily meet their vitamin A requirements from provitamin A carotenoids. Hypervitaminosis A has occurred in vervets that consume feed high in preformed vitamin A. We investigated the vitamin A status of vervets supplemented daily with various antioxidants derived from palm oil. Male vervets (n = 40) were placed for 23 wk on a high-fat diet (34.9% energy) containing 645 μ g retinol activity equivalents (RAE), with 515 μ g RAE from preformed vitamin A. Vervets were randomized to 5 treatments (duration, 20 mo): control; 100 mg d-α-tocopheryl acetate; 100 mg oil palm (Elaeis guineensis)-derived vitamin E; 50 mg oil palm-derived vitamin E + 50 mg carotenoid complex + unrestricted palm-derived water-soluble antioxidants; and 5) unrestricted water-soluble antioxidants. Livers (n = 38) were analyzed for vitamin A, α-retinol (α-vitamin A), and carotenoids. Median hepatic vitamin A and total carotenoid concentrations were 6.49 μ mol/g and 4.30 nmol/g, respectively. Compared with controls, vervets fed the carotenoid complex had higher hepatic vitamin A (11.9 ± 5.1 μ mol/g), α -vitamin A (1.3 ± 0.7 μ mol/g), α -carotene (11.5 ± 5.3 nmol/g), β-carotene (15.6 ± 8.6 nmol/g), and total carotenoids (28.1 ± 13.9 nmol/g) but lower lutein (0.66 ± 0.28 nmol/g) and zeaxanthin (0.24 ± 0.06 nmol). NHP may benefit from replacement of preformed vitamin A with carotenoids in feeds; however, bioconversion efficiency in these models should be investigated to determine optimal levels.

Habitual fish intake and clinically silent carotid atherosclerosis

BACKGROUND

Fish consumption is recommended as part of a healthy diet. However, there is a paucity of data concerning the relation between fish consumption and carotid atherosclerosis. We investigated the association between habitual fish consumption and asymptomatic carotid atherosclerosis, defined as the presence of plaques and/or increased intima-media thickness (≥ 0.90 mm), in non-diabetic participants.

METHODS

Nine hundred-sixty-one (range of age: 18-89 yrs; 37.1% males) adult participants without clinically known atherosclerotic disease were randomly recruited among the customers of a shopping mall in Palermo, Italy, and cross-sectionally investigated. Each participant answered a food frequency questionnaire and underwent high-resolution ultrasonographic evaluation of both carotid arteries. Routine laboratory blood measurements were obtained in a subsample of 507 participants.

RESULTS

Based on habitual fish consumption, participants were divided into three groups: non-consumers or consumers of less than 1 serving a week (24.0%), consumers of 1 serving a week (38.8%), and consumers of ≥ 2 servings a week (37.2%). Age-adjusted prevalence of carotid atherosclerosis (presence of plaques or intima media thickness ≥ 0.9 mm) was higher in the low fish consumption group (13.3%, 12.1% and 6.6%, respectively; P = 0.003). Multivariate analysis evidenced that carotid atherosclerosis was significantly associated with age (OR = 1.12; 95% CI = 1.09-1.14), hypertension on pharmacologic treatment (OR = 1.81; 95% CI = 1.16-2.82), and pulse pressure (OR = 1.03; 95% CI = 1.01-1.04), while consuming ≥2 servings of fish weekly was protective compared with the condition of consumption of <1 serving of fish weekly (OR = 0.46; 95% CI = 0.26-0.80).

CONCLUSIONS

High habitual fish consumption seems to be associated with less carotid atherosclerosis, though adequate interventional trials are necessary to confirm the role of fish consumption in prevention of cardiovascular disease.

Research priorities for intracranial atherosclerotic diseases

The current review summarizes the characteristics of existing experimental models for intracranial atherosclerosis in rabbits, pigs, and dogs with potential implications for research. New methodologies for understanding plaque morphology, and plaque quantitation and its prognostic implications are important for risk stratification in regards to ischemic events and lesion progression. A potential treatment strategy for intracranial atherosclerotic disease may be aimed at medical therapies that induce plaque regression. The treatment with statins to stabilize and/or promote plaque regression of intracranial atherosclerotic lesions is largely inferred from data in the coronary literature. In patients with multisegmented intracranial atherosclerotic diseases with no other therapeutic option, angiogenic growth factors may represent a new venue.

Intakes of long-chain n-3 polyunsaturated fatty acids and fish in relation to measurements of subclinical atherosclerosis

BACKGROUND

Data on the relations of different types of fish meals and long-chain n-3 polyunsaturated fatty acids (PUFAs) to measures of atherosclerosis are sparse.

OBJECTIVE

We examined intakes of long-chain n-3 PUFAs and fish in relation to clinical measures of subclinical atherosclerosis.

DESIGN

A cross-sectional study was conducted in a multiethnic group of 5,488 adults aged 45-84 y and free of clinical cardiovascular disease. Diet was assessed by using self-administered food-frequency questionnaires. Subclinical atherosclerosis was determined by measurements of common carotid intima-media thickness (cCIMT, >80th percentile), internal CIMT (iCIMT, >80th percentile), coronary artery calcium score (CAC score, >0), or ankle-brachial index (ABI, <0.90).

RESULTS

After adjustment for potential confounders, intakes of long-chain n-3 PUFAs and nonfried (broiled, steamed, baked, or raw) fish were inversely related to subclinical atherosclerosis determined by cCIMT but not by iCIMT, CAC score, or ABI. The multivariate odds ratio comparing the highest to the lowest quartile of dietary exposures in relation to subclinical atherosclerosis determined by cCIMT was 0.69 (95% CI: 0.55, 0.86; P for trend < 0.01) for n-3 PUFA intake; 0.80 (95% CI: 0.64, 1.01; P = 0.054) for nonfried fish consumption; and 0.90 (95% CI: 0.73, 1.11; P = 0.38) for fried fish consumption.

CONCLUSIONS

This study indicates that the dietary intake of long-chain n-3 PUFAs or nonfried fish is associated with a lower prevalence of subclinical atherosclerosis classified by cCIMT, although significant changes in iCIMT, CAC score, and ABI were not observed. Our findings also suggest that the association of fish and atherosclerosis may vary depending on the type of fish meal consumed and the measures of atherosclerosis.

Antiatherogenic effects of n-3 fatty acids - evidence and mechanisms

N-3 (omega-3) (polyunsaturated) fatty acids are thought to display a variety of beneficial effects for human health. Clues to the occurrence of cardiovascular protective effects have been, however, the spur for the first biomedical interest in these compounds, and are the best documented. Historically, the epidemiologic association between dietary consumption of n-3 fatty acids and cardiovascular protection was first suggested by Bang and Dyerberg, who identified the high consumption of fish, and therefore, of fish oil-derived n-3 fatty acids, as the likely explanation for the strikingly low rate of coronary heart disease events reported in the Inuit population. Since their initial reports, research has proceeded in parallel to provide further evidence for their cardioprotection and to understand underlying mechanisms. Decreased atherogenesis is currently thought to be a part of the cardiovascular protection by n-3 fatty acids. This article summarizes the evidence for such a claim and the mechanisms putatively involved.

The amount of dietary cholesterol changes the mode of effects of (n-3) polyunsaturated fatty acid on lipoprotein cholesterol in hamsters

This study was designed to investigate the effects of the interaction between dietary (n-3) polyunsaturated fatty acids (PUFA) and different dietary cholesterol content on plasma and liver cholesterol in hamsters. Male Syrian hamsters consumed diets containing an incremental increase in dietary cholesterol content (0, 0.025, 0.05, 0.1 and 0.2%, w/w) with either (n-3) PUFA (21 g/100 g fatty acids) or (n-6) PUFA (37.4 g/100 g fatty acids) fat for 6 weeks. In hamsters fed the nonatherogenic diet (0 or 0.025% dietary cholesterol), very low density lipoprotein (VLDL)-cholesterol levels in the (n-3) PUFA group were not significantly different from those in the (n-6) PUFA group, and low density lipoprotein (LDL)-cholesterol levels in the (n-3) PUFA group were significantly lower than those in the (n-6) PUFA group. In contrast, in hamsters fed the atherogenic diet (0.1 or 0.2% dietary cholesterol), VLDL- and LDL-cholesterol levels in the (n-3) PUFA group were significantly higher than those in the (n-6) PUFA group, in a dose-dependent manner. When the hamsters were fed with 0, 0.025, 0.05, 0.1 or 0.2% (w/w) dietary cholesterol, high density lipoprotein (HDL) cholesterol concentration was significantly lower in the (n-3) PUFA group than those in the (n-6) PUFA group. Hepatic cholesteryl esters were significantly lower, while hepatic microsomal acyl-coenzyme A:cholesterol acyltransferase activity and VLDL-cholesteryl esters were significantly higher in hamsters fed (n-3) PUFA with the atherogenic diet (0.1 or 0.2% dietary cholesterol) than in those fed (n-6) PUFA with the atherogenic diet. Our results demonstrate that the amount of dietary cholesterol is an important factor in determining the mode and extent of effects of dietary (n-3) PUFA, especially on VLDL- and LDL-cholesterol levels. When dietary cholesterol intake was above 0.1% (w/w), the plasma cholesterol-lowering effect of (n-3) PUFA disappeared, and instead, it showed a cholesterol-increasing effect. However, the effects of dietary (n-3) PUFA on HDL-cholesterol are independent of dietary cholesterol content.

Hyperlipidaemic effect of fish oil in Bio F1B hamsters

We investigated the dietary influence of low and high levels of fish oil, supplemented with or without dietary cholesterol, on the plasma lipoprotein profile in Bio F1B hamsters, a model susceptible to diet-induced hyperlipidaemia. The MIX diet, a diet supplemented with a mixture of lard and safflower-seed oil, was used as the control diet to maintain the saturated MUFA and PUFA levels similar to the fish-oil diet. The animals were fed the specific diets for 2 weeks and fasted for 14 h before killing. The plasma from the animals fed high levels of fish oil was milky and rich in chylomicron-like particles. The plasma total cholesterol, VLDL- and LDL-cholesterol and -triacylglycerol concentrations were significantly higher, whereas HDL-cholesterol was lower in hamsters fed fish oil compared with the MIX-diet-fed hamsters. Increasing the amount of fat in the diet increased plasma lipids in both the fish-oil- and the MIX-diet-fed hamsters; however, this hyperlipidaemic effect of dietary fat level was greater in the hamsters fed the fish-oil diet. The hepatic lipid concentrations were not dramatically different between the fish-oil-fed and the MIX-diet-fed hamsters. However, the hepatic LDL-receptor mRNA levels were significantly low in the fish-oil-fed hamsters compared with the MIX-diet-fed hamsters. Increasing the amount of fish oil in the diet further decreased the hepatic LDL-receptor mRNA expression. It is concluded that F1B hamsters are susceptible to fish-oil-induced hyperlipidaemia, especially at high fat levels, and this increase is partially explained by the inhibition of hepatic LDL-receptor mRNA expression.

Effect of palm olein oil in a moderate-fat diet on low-density lipoprotein composition in non-human primates

Plasma low-density lipoprotein cholesterol (LDL-C) concentrations in vervet monkeys (Cercopithecus aethiops) can be modulated by the type and amount of fat in the diet. There is, however, a paucity of information on the effect of different types and quantity of dietary fat on the plasma LDL composition in vervets. The objective of this study was to determine the effect of different sources of dietary fat on the concentrations and composition of circulating plasma LDL in vervets consuming moderate-fat diets containing either animal fat, sunflower oil or palm olein. Fifty adult male vervets, never exposed to a Western-type atherogenic diet, were randomly assigned to two groups. For 6 weeks 30 vervets were fed a moderate-fat (28%E) moderate-cholesterol (26 mg cholesterol/1000 kJ) diet (MFD) with a polyunsaturated to saturated fatty acid ratio (P/S) of 0.4; 20 vervets were fed a high-fat (34%E) high-cholesterol (98 mg cholesterol/1000 kJ) diet (HFD) with a P/S ratio of 0.6. Fasting blood samples were collected from all 50 vervets for plasma lipid measurements. The 30 vervets receiving the MFD were stratified into three comparable experimental groups of 10 each according to their LDL-C and high-density lipoprotein cholesterol (HDL-C) concentrations and bodyweight. One group continued with the MFD, in which 11%E was derived from lard (MFD-AF); in the other two groups the lard was substituted isocalorically with either sunflower oil (SO) (MFD-SO) or palm olein oil (PO) (MFD-PO). The three groups were fed the respective experimental diets for 24 months and LDL component concentrations and composition were assessed at 6-monthly intervals. In the long-term study the MFD-AF, MFD-SO and MFD-PO groups showed no significant time-specific group differences at 6, 12, 18 or 24 months with regard to the LDL component concentrations, composition, as well as the LDL molecular weight. As expected, after 6 weeks of dietary exposure the HFD group had significantly higher plasma and lipoprotein total cholesterol, LDL component and apolipoprotein AI concentrations, as well as a higher LDL-C : HDL-C ratio compared to the MFD group (P 0.0005). LDL particle size was not significantly different between the HFD and MFD groups, but the HFD group had significantly fewer triacylglycerol and significantly more unesterified cholesterol molecules per LDL particle compared to the MFD group (P 0.0018). PO in a MFD is no different from AF or SO in its effect on LDL component concentrations, composition or particle size. The increased LDL-C concentration seen with the HFD could be accounted for by a more than two-fold increase in the number of circulating LDL particles and not as a result of enrichment of particles with cholesterol.

Effect of palm olein oil in a moderate-fat diet on plasma lipoprotein profile and aortic atherosclerosis in non-human primates

Several studies have reported on the effect of palm olein oil (PO; palmitic acid content approximately 38%) incorporation into the diet on blood cholesterol concentration. Information on the effect of PO on atherosclerosis is, however, lacking. In vervet monkeys (Cercopithecus aethiops), low-density lipoprotein cholesterol (LDL-C) concen-trations can be modulated by the type and amount of fat in the diet. The vervet is a proven model for both the type and composition of human atherosclerotic lesions. The aim of this study was to determine the effect of PO in a moderate-fat moderate-cholesterol diet (MFD) on plasma lipoproteins and the progression of atherosclerosis in a non-human primate model after 25.5 months of dietary exposure. Thirty adult male vervets, never exposed to a Western-type atherogenic diet, were stabilised on a MFD (28%E fat; 26 mg cholesterol/1000 kJ) with a polyunsaturated to saturated fatty acid (P/S) ratio of 0.4 for six weeks. Baseline LDL-C, high-density lipoprotein (HDL)-C and bodyweight were used to stratify the vervets into three comparable groups of 10 each. One group continued with the MFD in which 11.0%E was derived from lard (AF). In the other two groups, the AF was substituted isocalorically with either sunflower oil (SO) or PO. Plasma lipids were measured at 6-monthly intervals and atherosclerosis was assessed in the aorta and in five peripheral arteries after 25.5 months of dietary exposure. The frequency of atherosclerosis in peripheral arteries and aortas was low. PO, relative to SO and AF, significantly reduced the risk for developing early lesions in peripheral arteries (P = 0.0277 and P = 0.0038, respectively) and, relative to AF, in aortas (P = 0.0335). The cholesterolaemic effect of MFD-PO was not significantly different from MFD-SO and MFD-AF. However, at 24 months the plasma total cholesterol concentration with MFD-AF was significantly higher than with MFD-SO (P = 0.0256). It is confirmed that a MFD with PO is no different from AF or SO in its cholesterolaemic effect. The anti-atherogenic efficacy of a MFD with PO, relative to SO and AF, was demonstrated in a non-human primate model of atherogenesis.

n-3 fatty acids: antiatherosclerotic effects

The low incidence of cardiovascular disease associated epidemiologically with high consumption of food rich in n-3 fatty acids suggests the possibility that part of the beneficial cardiovascular effects of these natural substances may be due to a reduction of atherosclerosis. This has been recently confirmed in autoptic data and in at least one prospective trial evaluating the progression of coronary atherosclerosis in humans. This paper reviews published literature on n-3 fatty acids and atherosclerosis in animal models and in humans and in vitro experimental data yielding suport to the hypothesis of antiatherosclerotic effects of these substances.

Diet can manipulate the metabolism of EPA and GLA in erythrocyte membrane and plasma

The effect of diet on the metabolism of eicosapentaenoic acid (EPA) and gammalinolenic acid (GLA) was investigated in two groups of African Green Vervet monkeys fed either a Western atherogenic diet (WAD; %E fat 43.5%; P:S 0.3; n=10) or a high carbohydrate diet (HCD; %E fat 20.5%; P:S 3.4; n=10). Vervets within each dietary treatment were supplemented with 300 mg/day with either an EPA concentrate (50% as free fatty acid, n=5) or a GLA concentrate (70% as free fatty acid, n=5) for 24 weeks, increasing the dose every 6 weeks to a maximum of 2400 mg/kg/day. Vervets in the WAD-Group consumed 433.7 mg/kg/day of EPA and those in the HCD-Group 318.2 mg/kg/day of EPA, whereas 421 mg/kg/day of GLA was consumed in the WAD Group and 340 mg/kg/day in the HCD Group during the last 6 weeks (week 18-24) of the supplementation period. The rate of disappearance of EPA and GLA from plasma and erythrocyte memebrane (EMB) phospholipids were estimated for the two diets after supplementation was stopped. The half-lives (t(1/2)) of EPA in EMB phosphatidylcholine (PC) were estimated to be 34.6 days (WAD) and 22.6 days (HCD), compared to 43.5 days (WAD) and 31.3 days (HCD) in EMB phosphatidylethanolamine (PE). In plasma cholesteryl ester (CE) t(1/2) was 23.5 days (WAD) compared to 14.1 days (HCD), and in plasma triacylglycerol (TAG) 17.4 days (WAD) compared to 9.4 days (HCD). Although accurate estimation of the GLA t(1/2) was difficult to assess due to the low tissue levels (probably due to rapid conversion to DGLA), the disappearance rates of GLA from EMB and plasma also suggested a faster metabolic rate in those animals consuming a HCD compared to a WAD. EPA also disappeared faster from EMB PC than from EMB PE. Disappearance of EPA from plasma TAG was also faster than from plasma CE, probably reflecting their relative turnover and metabolic rates. During supplementation, EPA substituted linoleic acid (C18:2 n-6), arachidonic acid (C20:4 n-6), and GLA (C18:3 n-6). This was reversed when supplementation was stopped. Plasma total cholesterol (TC) levels decreased by 17.06 +/- 17.67% in animals consuming the HCD with EPA as supplement, whereas in those consuming the WAD, plasma TC levels increased with 21.78 +/- 28.23% during the supplementation period. The delay of EPA and GLA disappearance from EMB and plasma in animals consuming a WAD, strongly suggests that metabolism of EPA and GLA is modulated by diet. Such a modulation could cause an accumulation of plasma TC levels that could explain the contradictory results reported by previous studies.

Atherosclerosis: aortic lipid changes induced by diets suggest diffuse disease with focal severity in primates that model human atheromas

Atherosclerosis in Vervet or African Green monkeys (Cercopithecus aethiops) models the morphology and cytology of the disease of humans, and it is well established that the rate of atherogenesis in Vervets is influenced by diet. Aortic intimal concentrations of lipids and phospholipids known to be major components of atheromas were determined in female Vervets fed for 4 years on either an atherogenic (AD) or a prudent Western diet (PD). Lipid concentrations detectable microscopically as cholesterol crystals and foam cells were confirmed biochemically. In addition, the AD was associated with diffuse, invisible accumulation of lipids throughout aortic tissue to the extent that tissue with no fatty streaks or plaque (AD) contained the same or more lipids than visible fatty streaks (PD). Correlations between lipid concentrations and atherosclerosis were highly positive, which supports known correlations between aortic, plasma, and dietary lipids during atherogenesis, and validates the aortic lipid analysis. These aortic lipid concentration results imply that atherosclerosis is not confined to focal pathologic anatomy, but in terms of lipid components of the disease, it develops throughout the arterial system of Old World omnivorous primates. If the results are applicable to people, they provide new insight and emphasize the need to minimize dietary sources of atherogenic lipids.

Controlled trial of fish oil for regression of human coronary atherosclerosis. HARP Research Group

OBJECTIVES

This randomized clinical trial tested whether fish oil supplements can improve human coronary atherosclerosis.

BACKGROUND

Epidemiologic studies of populations whose intake of oily fish is high, as well as laboratory studies of the effects of the polyunsaturated fatty acids in fish oil, support the hypothesis that fish oil is antiatherogenic.

METHODS

Patients with angiographically documented coronary heart disease and normal plasma lipid levels were randomized to receive either fish oil capsules (n = 31), containing 6 g of n-3 fatty acids, or olive oil capsules (n = 28) for an average duration of 28 months. Coronary atherosclerosis on angiography was quantified by computer-assisted image analysis.

RESULTS

Mean (+/- SD) baseline characteristics were age 62 +/- 7 years, plasma total cholesterol concentration 187 +/- 31 mg/dl (4.83 +/- 0.80 mmol/liter) and triglyceride levels 132 +/- 70 mg/dl (1.51 +/- 0.80 mmol/liter). Fish oil lowered triglyceride levels by 30% (p = 0.007) but had no significant effects on other plasma lipoprotein levels. At the end of the trial, eicosapentaenoic acid in adipose tissue samples was 0.91% in the fish oil group compared with 0.20% in the control group (p < 0.0001). At baseline, the minimal lumen diameter of coronary artery lesions (n = 305) was 1.64 +/- 0.76 mm, and percent narrowing was 48 +/- 14%. Mean minimal diameter of atherosclerotic coronary arteries decreased by 0.104 and 0.138 mm in the fish oil and control groups, respectively (p = 0.6 between groups), and percent stenosis increased by 2.4% and 2.6%, respectively (p = 0.8). Confidence intervals exclude improvement by fish oil treatment of > 0.17 mm, or > 2.6%.

CONCLUSIONS

Fish oil treatment for 2 years does not promote major favorable changes in the diameter of atherosclerotic coronary arteries.

Pleural Mesocestoides and cardiac shock in an obese vervet monkey (Cercopithecus aethiops)

Only one case of infection by tetrathyridia larvae of the tapeworm genus Mesocestoides was detected in 416 necropsies of captive vervet monkeys (Cercopithecus aethiops). Two hundred nine larvae were distributed between both pleural cavities. Mass and size ranges of larvae were determined. A plasma cell reaction indicated a humoral immune response to parasite antigens, which may have contributed to acute, lethal cardiac shock. Coagulative myocytolysis was confirmed. The history of this case and associated circumstantial evidence and reports in the literature suggest that infection of primates by tetrathyridia probably occurs after capture rather than before.

Fish oil, atherogenesis, and thrombogenesis

Marine fish consumption is known to reduce mortality from ischemic heart disease. The use of fish oil as a dietary supplement, however, is not universally recommended. In large doses, fish oil reduces plasma cholesterol and triacylglycerol but increases low density lipoprotein (LDL) levels and the potential for free radical generation and bleeding. Moderate marine fish consumption is known to reduce mortality without altering commonly measured variables, i.e., plasma cholesterol levels, in vitro platelet aggregation, and bleeding times. In swine, we observed that monocyte adhesions and platelet clumps over the lesion surface of proximal left anterior descending (LAD) coronary arteries are markedly reduced when an atherogenic diet was supplemented with cod-liver oil, even when the cholesterol levels were equalized with the untreated group. These findings suggest that fish oil is hypothrombogenic. We developed an in vitro assay to delineate the mechanism whereby fish oil reduced monocyte-endothelial cell interactions in vivo. The effects of supplementing the culture medium with different fatty acids on adhesions between lipopolysaccharide (LPS) stimulated swine aortic endothelial cells (SAEC) and the human monocyte-like cell line, U937, was investigated in a 10 minute adhesion assay at 37 degrees C. Exposure of SAEC for 6 hours to media containing 50-200 microMs eicosapentaenoic (EPA), stearic, oleic, linoleic, and arachidonic acid, respectively, revealed that only EPA reduced U937-SAEC adhesion. Exposure of U937 to EPA also reduced adhesions. EPA was not effective when added to the SAEC more than 2 hours after they were stimulated with LPS. Exposure of human umbilical vein endothelial cells (HUVEC) to EPA reduced the expression of VCAM-1, ELAM-1, and ICAM-1 after 5 hours of stimulation with LPS. These results suggest that EPA may functionally impair the induction/expression of adhesion molecules.

Fish oil and the prevention and regression of atherosclerosis

Epidemiological studies in the seventies have put forward that dietary rather than genetic factors are responsible for the lower incidence of ischemic heart disease in Greenland Inuit and have generated a large body of both in vitro and in vivo experimental studies, exploring the putative favorable effects of fish (oil) on atherogenesis and its risk factors. The first part of this report reviews the in vivo animal studies, concentrating on the hypercholesterolemic models and the arterialized vein graft model. In the hypercholesterolemic animal studies, the results are inconclusive as the studies reporting a protective effect are matched by the number of studies showing no effect or an adverse effect. The diversity in species, dose of fish oil, duration of study, type of vessel studied and type of fish oil preparation (content of n-3 fatty acids, unesterified n-3 fatty acids, ethylesters or triglycerides) could all contribute. Furthermore, the definitions and criteria used in the literature to evaluate atherogenesis are diverse and it appears that while one parameter is affected, another is not necessarily modified in the same direction, stressing the importance of extending the analysis of the effects on atherogenesis to more than one parameter. We also believe that it is time to reach a consensus as to which animal model mimics most closely a particular human situation. Only in appropriate models, investigating more than one atherosclerosis variable, can the effects of a putative anti-atherogenic drug or diet be verified. In the veno-arterial autograft model, mimicking the patient after coronary bypass grafting, dietary fish oil has been consistently effective in preventing accelerated graft intima proliferation. It could therefore be of interest to evaluate the effects of fish oil on graft patency in patients after coronary bypass surgery after a period of years. The results from studies on restenosis after percutaneous transluminal angioplasty are also reviewed and it is concluded that the two large scale trials, that are currently underway, might reliably answer the question whether fish oil is effective as a non-pharmacological adjuvants in the prevention of restenosis. Lastly, the studies on the effects of fish oil on the regression of experimental atherosclerosis are reviewed. In view of the small number of studies (i.e., four) investigating the effects of fish oil on the regression of atherosclerosis, it is premature to draw any conclusion, and therefore further experimental work is required.

The influence of fish oil supplementation on plasma lipoproteins and arterial lipids in vervet monkeys with established atherosclerosis

There is controversy about whether supplementing diets with marine fish oil can regress, promote or prevent atherosclerosis. Therefore the effects of an Atlantic pilchard oil (FO) supplement and dietary change were measured in a proven atherosclerosis model. Vervet or African Green monkeys were fed an atherogenic diet (AD) for long enough to ensure progression before treatments started. Matched groups were then treated for 20 months, either by adding FO to the AD (AD/FO), or by changing to a therapeutic diet with FO (TD/FO). Control treatments consisted of supplementing with sunflower oil (SO) instead of FO, so that treatments were AD/SO and TD/SO. The same total polyunsaturates were supplied by the FO and SO and the dose of FO was realistic (2.5% of total energy). A reference group (R) received the TD with no oil supplements. Supplementing with FO did not change the concentrations of total, low or high density lipoprotein cholesterol in plasma. After The AD/FO the intimas of aortas contained more total (p < or = 0.001), free (p < or = 0.05) and esterified (p < or = 0.05) cholesterol, total phospholipid (p < or = 0.01) and sphingomyelin (p < or = 0.05) than after the AD/SO. After FO supplementation eicosapentaenoic acid was significantly higher and arachidonic acid significantly lower in the plasma and aorta intima phosphatidylcholine. None of these changes was anti-atherogenic in terms of atherosclerosis measured in the same individuals (1). Nor did FO increase the efficacy of the TD.

Dietary fatty acids, lipoproteins, and cardiovascular disease

Dietary fat quality and quantity significantly affect the metabolism of all the plasma lipoproteins and probably constitute the most significant dietary determinants of plasma lipoprotein levels. Since the major role of the plasma lipoproteins is the transport of exogenous and endogenous fat, this would be expected of a highly regulated, metabolically homeostatic system. The data clearly show that dietary fat saturation affects all aspects of lipoprotein metabolism, from synthesis to intravascular remodeling and exchanges to receptor-mediated and nonspecific catabolism. The experimental data regarding dietary fatty acid effects on lipoprotein metabolism are complicated and at times contradictory due to the large degree of metabolic heterogeneity in the population, which, when coupled with the known abnormalities of lipoprotein metabolism associated with certain types of hyperlipoproteinemia, can present responses from A to Z. It is clear that the same dietary pattern has different effects in different individuals and that complicating factors of individuality raise some concerns regarding generalized dietary recommendations. As new knowledge of the role of dietary factors and CVD risk develops, and our abilities to characterize the individual patient's response to dietary interventions become more refined, it may be possible to specify dietary fat intervention from a patient-oriented concept rather than a single all-purpose diet approach. Thus it would be possible to design dietary interventions to match patient needs and gain both efficacy and compliance. With the spectrum of approaches possible--low fat, moderate fat with MUFA, n-3 PUFA, etc.--we should be able to approach dietary interventions to reduce CVD risk at both a population-based level and a patient-specific level. There remains much to learn regarding the effects of dietary fatty acids on the synthesis, intravascular modifications, and eventual catabolism of the plasma lipoproteins. The area of lipoprotein metabolism in health and disease, of its modifications by diets and drugs, and of the contributions of genetic heterogeneity to these processes is one of notable advances over the past two decades and continues to be an area of intense investigation.