Original Article

-Tocopherol supplementation of macrophages does not influence their ability to oxidize LDL

Correspondence to: Anna Baoutina.

We have investigated the effect of -tocopherol-loading of mouse peritoneal macrophages and human monocytes on their ability to oxidize human low density lipoprotein (LDL). Mouse peritoneal macrophages incorporated -tocopherol (-TOH) from culture medium supplemented with the vitamin in a time- and concentration-dependent manner. Subcellular fractionation by density gradient ultracentrifugation showed that the distribution of incorporated -TOH within the cell was similar to that of free cholesterol. Most (88%) of -TOH partitioned into the membrane fractions (plasma membrane 41%, mitochondria and lysosomes 26%, and endosomes plus endoplasmic reticulum 21%). Cellular -TOH was stable for at least 24 h in serum- or LDL-free media whether permissive (Ham's F-10) or non-permissive (Dulbecco's minimum essential medium, DMEM) for LDL oxidation. When incubated with LDL in DMEM, -TOH-preloaded cells transferred small amounts of -TOH (approximately 1 nmol/mg LDL protein after 9 h) to the lipoprotein. However, enrichment of the cells with -TOH did not change the kinetics of oxidation of either normal or TOH-depleted LDL in Ham's F-10 medium compared with non-loaded cells, as assessed by -TOH consumption, cholesteryl ester degradation, and cholesteryl ester hydroperoxide and 7-ketocholesterol accumulation. Nor did it alter superoxide release by the cells or their ability to reduce extracellular copper(II). Similar to mouse macrophages, enrichment of human monocytes with -TOH did not change the kinetics of cell-mediated LDL oxidation.

We conclude that elevated cellular levels of -TOH in mouse peritoneal macrophages and in human monocytes do not affect their ability to oxidize LDL lipids in vitro. This suggests that either cell-mediated oxidation of LDL under the conditions of this study is not dependent on cell-derived radical species or that cellular -TOH is unable to affect their formation.—Baoutina, A., R. T. Dean, and W. Jessup. -Tocopherol supplementation of macrophages does not influence their ability to oxidize LDL. J. Lipid Res. 1998. 39: 114–130.

Supplementary key words: atherosclerosis, LDL oxidation, cells, macrophages, monocytes, -tocopherol, antioxidants

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