Dependence of plasma alpha-tocopherol flux on very low-density triglyceride clearance in humans

To evaluate the effect of dietary fat-induced alterations in triglyceride ( TG) metabolism on plasma and very low-density Lipoprotein (VLDL)-alpha -toc opherol, nine healthy males (mean +/- SEM, age: 36 +/- 3 years, BMI: 24.7 /- 1.1) consumed a 35%-fat diet (control) for one week followed by a 15% lo w-fat, high-carbohydrate diet for 5 weeks. After each dietary phase, the su bjects ingested an evening meal along with a 50 mg capsule of H-2(6)-RRR-al pha -tocopheryl acetate; blood samples were drawn over a 24 h period while the subjects remained fasted. Low-fat feeding increased fasting plasma TG c oncentrations by 53% (116 +/- 27 to 178 +/- 32, mg/dl, p < 0.0001) primaril y by reducing VLDL-TG clearance. Total plasma <alpha>-tocopherol concentrat ions (labeled + unlabeled) were unchanged (25.8 +/- 2.3 vs. 26.4 +/- 3.0 nm ol/ml plasma) and no differences between the diets were observed for plasma H-2(6)-alpha -tocopherol concentration (4.8 +/- 0.6 nmol/ml, for both diet s) or enrichments (18.1 +/-. 1.8% average for both diets). However, low-fat feeding significantly increased the amount of alpha -tocopherol in the VLD L fraction (43%, p = 0.04) in concert with elevations in VLDL-apoB and TG. The alpha -tocopherol and TG content of VLDL varied in parallel in individu al subjects and fractional replacement rates and clearance of alpha -tocoph erol and TG in VLDL were closely correlated. Kinetic parameters were decrea sed by 32-39% from high-fat to low-fat. These data suggest that vitamin E b ioavailability is similar between a 15 and 35% fat diet, with a redistribut ion of alpha -tocopherol in lipoproteins occurring during low-fat feeding ( increased in the VLDL fraction, reduced in the other lipoproteins), and tra nsfer of alpha -tocopherol from VLDL depends upon TG removal from the parti cle, consistent with previous observations in vitro and in animal studies. (C) 2000 Elsevier Science Inc.