Human lipoprotein influence on the partition of 2,2′,4,4′,5,5′‐hexabromobiphenyl between 3t3l1 adipocytes and culture medium

Abstract

A previous study established that 2,2′,4,4′,5,5′‐hexabromobiphenyl (HBB) entered 3T3L1 adipocytes in culture by passive diffusion from the surrounding medium. The extent to which HBB accumulated within the cell was mediated by the level of triglyceride in the cell. The present study was concerned with the conditions that would facilitate HBB removal from adipocytes as part of a continuing effort to establish an effective and safe technology for reducing body burdens of lipophilic xenobiotics.

Addition of human lipoprotein to the culture medium increased HBB removal from preloaded adipocytes 18 to 80 times more than did the addition of other blood proteins. Lipoproteins also decreased equilibrium deposition of HBB in the cells. The order of effect was low‐density lipoprotein (LDL) > high‐density lipoproteins (HID) > very‐low‐density lipoproteins (VLDL). These results are consistent with the hypothesis that lipoproteins act as a depot by binding HBB to immobilize the xenobiotic in the medium.

The rate of removal of HBB was correlated with concentrations of lipoprotein cholesterol, cholesterol ester, and phospholipid in the culture medium (r > .95). Total lipoprotein fractions from individuals with high levels of serum cholesterol significantly increased HBB removal from preloaded adipocytes when compared with lipoproteins from normal human serum. Decreased removal was observed with lipoproteins from individuals with low serum cholesterol or triglyceride. These results suggest that cholesterol and/or cholesterol esters in the blood play an important role in both delivery and removal of HBB from the adipose tissue.

Evidence has been presented that supports the hypothesis that HBB moves freely across the adipocyte membrane and is sequestered in either the cell or pseudoblood according to its relative solubility in these compartments.