Dietary fish oil enhances monocyte adhesion and fatty streak formation in the hypercholesterolemic rat

Using the rat model of atherosclerosis, the influence of dietary fish oil on early stages of atherosclerotic lesion formation was studied. Normocholesterolemic rats (serum cholesterol less than 100 mg/dl), moderately hypercholesterolemic rats fed cholesterol and cholic acid (serum cholesterol less than 400 mg/dl), and severely hypercholesterolemic rats fed cholesterol, cholic acid, and 2-thiouracil (serum cholesterol greater than 900 mg/dl) had their diets supplemented with 5% (w/w) "MaxEPA" fish oil for a period of 2 weeks. In each diet group safflower oil was used as a control for fish oil. Monocyte adhesion to the thoracic aorta and intimal foam cell formation were used to measure the extent of atherosclerotic lesion formation in each rat. Cholesterol and triglyceride levels were measured in both plasma and lipoprotein fractions. In normocholesterolemic rats, fish oil did not influence the morphology of the vessel wall. In moderately hypercholesterolemic rats, monocyte adhesion was the same irrespective of dietary oil, however, intimal foam cell formation was 2-fold higher in the fish oil-fed animals despite a reduction in serum cholesterol levels when compared to the safflower oil-fed animals. In severely hypercholesterolemic rats, monocyte adhesion to the vessel wall and intimal foam cell formation were both 4-fold higher in the fish oil compared with the safflower oil fed animals. These observations could not be attributed to differences in the plasma or lipoprotein profiles of safflower oil vs. fish oil fed rats. The results of this study suggest that dietary fish oil, when fed to hypercholesterolemic rats for a period of 2 weeks, enhances the rate of monocyte adhesion and fatty streak formation in the thoracic aorta.