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Abstract
Tocomonoenols are vitamin E derivatives present in foods with a single double bond at carbon 11’ in the sidechain. The α-tocopherol transfer protein (TTP) is required for the maintenance of normal α-tocopherol (αT) concentrations. Its role in the tissue distribution of α-11′-tocomonoenol (αT1) is unknown. We investigated the tissue distribution of αT1 and αT in wild-type (TTP+/+) and TTP knockout (TTP−/−) mice fed diets with either αT or αT1 for two weeks. αT1 was only found in blood, not tissues. αT concentrations in TTP+/+ mice were in the order of adipose tissue > brain > heart > spleen > lungs > kidneys > small intestine > liver. Loss of TTP function depleted αT in all tissues. αT1, contrary to αT, was still present in the blood of TTP−/− mice (16% of αT1 in TTP+/+). Autoclaving and storage at room temperature reduced αT and αT1 in experimental diets. In conclusion, αT1 is bioavailable, reaches the blood in mice, and may not entirely depend on TTP function for secretion into the systemic circulation. However, due to instability of the test compounds in the experimental diets, further in vivo experiments are required to clarify the role of TTP in αT1 secretion. Future research should consider compound stability during autoclaving of rodent feed.
Highlights
It has been suggested that the selective retention of αT is the result of an interaction of the catabolic pathway with the hepatic α-tocopherol transfer protein (TTP) [7]
We found no αT1 in tissues, which is in partial agreement with the previous publication, where it was not found in the lung and spleen [23]
Earlier investigations reported that the metabolism of tocotrienols involves enzymes, probably 2,4-dienoyl-coenzyme A-reductase, that catalyze the saturation of the sidechain, similar to those involved in the β-oxidation of unsaturated fatty acids [24]
Summary
The vitamin E family comprises eight structurally-related lipid-soluble compounds composed of a chromanol ring attached to a saturated (tocopherols (T)) or threefold unsaturated (tocotrienols). It has been suggested that the selective retention of αT is the result of an interaction of the catabolic pathway with the hepatic α-tocopherol transfer protein (TTP) [7]. This is a cytosolic protein that preferentially binds αT (100%) over the other congeners, β-tocopherol (38%), Molecules 2020, 25, 4803; doi:10.3390/molecules25204803 www.mdpi.com/journal/molecules. TTP is expressed primarily in the liver, but it has been detected in other tissues, such as the rat brain, spleen, lung, kidney [9], rat uterus [10], and eye retina [11], suggesting that its expression in other organs regulates distinct tissue-specific accumulations of the vitamin [12]. We investigated the tissue distribution of αT1 and αT in wild-type and TTP knockout mice (TTP−/− ) following ingestion of the diet for two weeks
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