Tocopherol distribution and intracellular localization in human adipose tissue

Adipocytes, isolated from human adipose tissue, were disrupted and then centrifuged, resulting in three fractions: oil, interface between the oil and the hypotonic buffer (containing lipid droplets surrounded by unilamellar membranes), and pelleted portion (containing bilayer membranes, intracellular organelles, and debris). The ratios of tocopherol:cholesterol and tocopherol:triglyceride were similar for adipose tissue, adipocytes, oil, and interface. The bulk lipid (oil plus interface fractions) of the adipocytes contained 99% of the tocopherol, 98% of the triglyceride, and 91% of the cholesterol. The tocopherol:cholesterol ratio was nearly eightfold greater in the bulk lipid than in the bilayer membrane fraction. By use of radioactively labeled tocopherol and cholesterol, it was demonstrated that the isolation protocol did not alter the distribution of the intracellular lipids; furthermore, the tocopherol in the lipid droplet did not readily exchange. Thus, the majority of tocopherol in adipose tissue is located in the bulk-lipid stores.