The uptake of tocopherols by RAW 264.7 macrophages

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

Tocopherols and the Etiology of Colon Cancer

Colorectal cancer is the second most common cause of cancer deaths in the United States for both sexes. Considerable evidence suggests that the risk of this cancer is increased by the mutagenic actions of free radicals, which are produced during oxidation reactions. Dietary factors, the intestinal flora (bacteria), and endogenously produced metabolites contribute to the production of free radicals in the colon. Dietary antioxidants, such as vitamin E, should reduce the levels of these harmful oxidation products. In the absence of vitamin E, polyunsaturated fats can be oxidized in the colon to produce mutagens, such as lipid hydroperoxides and malondialdehyde. Furthermore, fecal bacteria can generate a high flux of reactive oxygen species (e.g., the superoxide radical [O2*-]) at the surface of the intestinal lumen, and inflammatory cells in close proximity to the colon can produce reactive nitrogen species (e.g., nitrogen dioxide [NO2]). Increasing evidence suggests that the different chemical (e.g., α- and γ-tocopherol) and stereochemical (e.g., RRR- and all-racemic-α-toeopherol) forms of vitamin E have distinct biologic potencies, pharmacokinetics, and different abilities to prevent neoplastic transformation. This review considers and evaluates recent studies relating vitamin E and oxidative stress to colon cancer, emphasizing the distinct roles of α-and γ-tocopherols. In addition, recent findings on the anti-oxidant/pro-oxidant status of the digesta (ingested food) are discussed with respect to the use of antioxidants in chemoprevention trials for colon cancer

The Uptake of Tocopherols by RAW 264.7 Macrophages

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

The Influence of Dietary Iron and Tocopherols on Oxidative Stress and Ras-p21 Levels in the Colon

The purpose of this investigation was to determine how dietary levels of α-tocopherol, γ-tocopherol and iron influence oxidative stress and ras-p21 levels in the colon. Rats were fed diets deficient in tocopherols (-E) or supplemented with either 0.156 mmol of α-tocopherol (AE)/kg diet or 0.156 mmol of γ-tocopherol (GE)/kg of diet. Half the rats in each of these three groups received dietary iron at a level of 35 mg/kg diet and the other half at eight times this level (280 mg/kg diet). Rats fed the AE diets had higher levels of Vitamin E in feces, colonocytes, plasma and liver than did rats fed the GE diets. Dietary iron levels did not influence tocopherol levels in plasma, liver or feces. For colonocytes, high dietary iron decreased tocopherol levels. The ratio of γ-tocopherol (in the GE groups) to α-tocopherol (in the AE groups) was 0.13 for plasma, 0.11 for liver, 0.28 for colonocytes and 0.51 for feces. The plasma ratio is not, therefore, predictive of the ratio in colonocytes and feces. High levels of dietary iron increased levels of fecal lipid hydroperoxides. Moreover, rats fed the GE diets had lower levels of fecal lipid hydroperoxides than rats fed the AE diets. The levels of ras-p21 were significantly lower in rats fed the GE diets compared with rats fed the AE diets. The γ-tocopherol may, therefore, play a significant role in preventing colon cancer. High levels of dietary iron were found to promote oxidative stress in feces and colonocytes

Relative Bioavailability of RRR- and All-Rac-α-Tocopheryl Acetate in Humans: Studies Using Deuterated Compounds

Vitamin E in nutritional supplements in its most common form is α- tocopheryl acetate. Available stereoisomeric forms are RRR- (1 stereoisomer) and all-rac- (8 stereoisomers). We evaluated the relative bioavailability of RRR- and all-rac-α-tocopheryl acetate using the deuterium-labeled isotopes [5-CD3] 2R, 4\u27R and 8\u27R-α-tocopheryl acetate (d3), and [5,7-(CD3)2]-all- rac-α-tocopheryl acetate (d6). Six adults (three males, three females), aged 25-59 y, received 150 mg each of d3 and d6 for 11 consecutive days. Blood samples were collected on days -1, 0, 1-11, 13, 14, 20, 25, 30, 60, 74, 88, 102, 122, and 137. Plasma and red blood cell tocopherol were evaluated by using HPLC and gas chromatography/mass spectrometry to distinguish between d3 and d6 tocopherols. Cholesterol, triglycerides, and LDL and HDL cholesterol were measured. Relative bioavailability of d3 when compared with d6 was 2.0 ± 0.06 when area under the plasma time concentration curve (AUC d3/d6) by trapezoidal rule (P \u3c 0.05) was used. Correcting for lipid yielded the same finding. Unlabeled tocopherol (d0) decreased (P \u3c 0.05) with vitamin E administration. It was concluded that the ratio of bioavailability of RRR- all-rac-α-tocopheryl acetate is significantly greater than the currently accepted ratio of 1.36

LFA-1 expression in a series of colorectal adenocarcinomas

LFA-1 is an adhesion molecule which belongs to the β2-integrin family. Overexpression of LFA-1 in hepatic natural killer cells has been associated with increased apoptosis of neoplastic cells in colorectal cancer (CRC); moreover, studies in CRC have linked LFA-1 overexpression in neoplastic cells with vascular intrusion through adhesion to endothelial cells, thus implying a possible role in creation of metastases

Impacts of beekeeping on wild bee diversity and pollination networks in the Aegean Archipelago

Maintaining the diversity of wild bees is a priority for preserving ecosystem function and promoting stability and productivity of agroecosystems. However, wild bee communities face many threats and beekeeping could be one of them, because honey bees may have a strong potential to outcompete wild pollinators when placed at high densities. Yet, we still know little about how beekeeping intensity affects wild bee diversity and their pollinator interactions. Here, we explore how honey bee density relates to wild bee diversity and the structure of their pollination networks in 41 sites on 13 Cycladic Islands (Greece) with similar landscapes but differing in beekeeping intensity. Our large-scale study shows that increasing honey bee visitation rate had a negative effect on wild bee species richness and abundance, although the latter effect was relatively weak compared to the effect of other landscape variables. Competition for flowering resources (as indicated by a resource sharing index) increased with the abundance of honey bees, but the effect was more moderate for wild bees in family Apidae than for bees in other families, suggesting a stronger niche segregation in Apidae in response to honey bees. Honey bees also influenced the structure of wild bee pollination networks indirectly, through changes in wild bee richness. Low richness of wild bees in sites with high honey bee abundance resulted in wild bee networks with fewer links and lower linkage density. Our results warn against beekeeping intensification in these islands and similar hotspots of bee diversity, and shed light on how benefits to pollination services of introducing honey bees may be counterbalanced by detriments to wild bees and their ecosystem services.ISSN:0906-7590ISSN:1600-058