Email updates

Keep up to date with the latest news and content from Nutrition Journal and BioMed Central.

Open Access Research

The uptake of tocopherols by RAW 264.7 macrophages

Rong Gao1, William L Stone2*, Thomas Huang1, Andreas M Papas3 and Min Qui2

Author Affiliations

1 Department of Chemistry, East Tennessee State University, Johnson City, Tennessee, 37614-0695, USA

2 Department of Pediatrics, East Tennessee State University, Johnson City, Tennessee, 37614-0578, USA

3 Health and Nutrition, Eastman Chemical Company, Kingsport, TN 37662, USA

For all author emails, please log on.

Nutrition Journal 2002, 1:2  doi:10.1186/1475-2891-1-2

Published: 15 October 2002

Abstract

Background

Alpha-Tocopherol and gamma-tocopherol are the two major forms of vitamin E in human plasma and the primary lipid soluble antioxidants. The dietary intake of gamma-tocopherol is generally higher than that of alpha-tocopherol. However, alpha-tocopherol plasma levels are about four fold higher than those of gamma-tocopherol. Among other factors, a preferential cellular uptake of gamma-tocopherol over alpha-tocopherol could contribute to the observed higher plasma alpha-tocopherol levels. In this investigation, we studied the uptake and depletion of both alpha-tocopherol and gamma-tocopherol (separately and together) in cultured RAW 264.7 macrophages. Similar studies were performed with alpha-tocopheryl quinone and gamma-tocopheryl quinone, which are oxidation products of tocopherols.

Results

RAW 264.7 macrophages showed a greater uptake of gamma-tocopherol compared to alpha-tocopherol (with uptake being defined as the net difference between tocopherol transported into the cells and loss due to catabolism and/or in vitro oxidation). Surprisingly, we also found that the presence of gamma-tocopherol promoted the cellular uptake of alpha-tocopherol. Mass balance considerations suggest that products other than quinone were formed during the incubation of tocopherols with macrophages.

Conclusion

Our data suggests that gamma-tocopherol could play a significant role in modulating intracellular antioxidant defence mechanisms. Moreover, we found the presence of gamma-tocopherol dramatically influenced the cellular accumulation of alpha-tocopherol, i.e., gamma-tocopherol promoted the accumulation of alpha-tocopherol. If these results could be extrapolated to in vivo conditions they suggest that gamma-tocopherol is selectively taken up by cells and removed from plasma more rapidly than alpha-tocopherol. This could, in part, contribute to the selective maintenance of alpha-tocopherol in plasma compared to gamma-tocopherol.