Cholesterol vehicle in experimental atherosclerosis. 23. Effects of specific synthetic triglycerides

Earlier work has shown that increasing concentration of palmitic acid at the sn-2 position of a fat enhances the atherogenic properties of that fat. This effect has been observed with lard, tallow, cottonseed oil, and palm oil. In the experiment reported here, we have studied the atherogenic effects of four synthetic fats fed to rabbits as 58% (w/w) of the total fat (15%) (w/w) of a semipurified diet containing 0.05% cholesterol. The fats being tested were: 1,3-stearoyl-2-oleoylglycerol (SOS); 1,2-stearoyl-3-oleoylglycerol (SSO); 1,3-palmitoyl-2-oleoylglycerol (POP); and 1,2-palmitoyl-3-oleoylglycerol (PPO). After 20 wk on diet there were no differences among the groups in weight gain, liver weight, serum, or liver lipids. These data are consistent with our previous findings. There were significant differences in atherosclerosis. The most severe atherosclerosis was observed in group PPO and the least in groups SSO and POP. Severity of atherosclerosis was graded visually on a 0-4 scale. The average atherosclerosis [(aortic arch and thoracic aorta) divided by 2] was: SOS--1.35; SSO--0.97; POP--0.83; and PPO--1.80. Fecal fat excretion (an indicator of fat absorption) was higher in the two groups fed the stearic acid-rich fats and lower in groups fed the palmitic acid-rich fats. There were no differences in low density lipoprotein particle size. The results confirm previous findings concerning the increased atherogenicity of fats bearing palmitic acid at the sn-2 position. The mechanism underlying these observations is moot but may, in part, reflect greater absorption of the atherogenic fat.