Regulation of very low-density lipoprotein (VLDL) metabolism by dietary fat saturation and chain length

Abstract

Studies were carried out to determine effects of dietary fat saturation on very low density lipoprotein (VLDL) production in guinea pigs fed diets containing 15% (w/w) fat, either corn oil (CO, 58% linoleic), lard (LA, 42% oleic and 24% palmitic) or palm kernel oil (PK, 52% lauric and 18% myristic) for 4 weeks. In the first study, animals were injected with Triton WR1339 to block VLDL catabolism. VLDL-TAG secretion rates were significantly higher in animals fed LA (72.7 +/- 14.7 mg/kg-h) compared to PK groups (55.4 +/- 13.4 mg/kg-h) or CO (48.6 +/- 17.5 mg/kg-h). VLDL apo B secretion rates were highest in PK fed animals (3.1 +/- .8 mg/kg-h) compared to LA (1.5 +/- 0.8 mg/kg-h) or CO fed groups (1.1 +/- 0.6 mg/kg-h) diets (P < 0.005). Concurrent with VLDL analysis, ¹²⁵I-LDL turnover was measured and LDL-apo B specific radioactivity (cpm/μg) did not change over time, indicating that there was no direct hepatic LDL secretion. The data demonstrate that nascent VLDL particles from LA and CO diet groups have the same relative TAG content, whereas PK intake increases secretion of VLDL particles with less TAG content. The second study determined effects of dietary fat saturation on VLDL metabolic channeling, and conversion to LDL through delipidation cascade. VLDL particles were larger (P < 0.05) in LA (78 +/- 7 nm) and PK (69 +/- 10 nm) groups, compared to animals fed CO (49 +/- 5 nm). ¹²⁵I VLDL-apo B fractional catabolic rate (FCR) was highest in guinea pigs fed LA (1.5 +/- 0.14 pools/h) compared with PK (1.05 +/- 0.33 pools/h) or CO (0.65 +/- 0.08 pools/h) fed animals. VLDL-apo B flux was higher in LA (2.28 +/- 0.93 mg/kg-hr) compared to PK (0.88 +/- 0.4 mg/kg-hr) or CO (1.03 +/- 0.40 mg/kg-hr) fed animals. In addition, VLDL secreted by guinea pigs fed LA is preferentially removed by direct hepatic uptake (55%), while VLDL from PK fed animals is converted to LDL (92%) leading to increased LDL flux (1.53 +/- 0.23 mg/kg-hr) with PK intake compared to LA (0.85 +/- 0.03 mg/kg-hr) or CO (0.81 +/- 0.02 mg/kg-hr)diets. These results demonstrate that dietary fat chain length and saturation have specific effects on VLDL secretion, affecting particle number, size, composition and VLDL conversion to LDL which relates to LDL transport.