Characterization of dietary-induced hypercholesterolemia in the chicken

The effect of 2% dietary cholesterol on the distribution of cholesterol among the plasma lipoproteins was studied in 2-week old male chickens. Very-low-, intermediate-, low- and high-density lipoproteins (VLDL, IDL, LDL and HDL) were separated from plasma by density gradient ultracentrifugation in order to determine their concentration and chemical composition. VLDL were furthermore characterized as concerned their size, mobility and protein content. The lipoprotein profile was quantitatively and qualitatively normal in the control group (n = 6) fed the diet without cholesterol, HDL representing the major lipoprotein class (5.06 +/- 0.36 g/l) and the main carrier of cholesterol. Birds fed the cholesterol containing diets for 5 weeks (n = 6) exhibited a dramatic hypercholesterolemia (1.60 +/- 0.89 g/l free cholesterol and 6.70 +/- 3.22 g/l cholesteryl esters) and a shift in their lipoprotein pattern, with an accumulation of beta-VLDL (6.08 +/- 4.21 g/l) and a marked decrease in HDL level (3.53 +/- 0.91 g/l). The decrease or absence of LDL was balanced by a considerable amount of beta-VLDL remnants (namely IDL), so that the concentration of IDL + LDL considered as a whole was not modified significantly (2.10 +/- 0.95 g/l compared to 1.66 +/- 1.13 g/l in controls). Chicken beta-VLDL, smaller in size (31.0 nm) than control VLDL (33.5 nm), were typically enriched in cholesterol (67%) but they lacked apoE. About 60% of plasma cholesterol was associated with beta-VLDL which therefore represented the main atherogenic lipoprotein class and were probably responsible for the greater amount of cholesterol found in the aorta in these chickens (2.44 +/- 0.99 mg/g aorta vs. 1.32 +/- 0.57 in controls). Since LDL were very reduced or absent, the cholesterol-fed chicken provides a suitable model in which to study the role of beta-VLDL in atherogenesis.