{"id":664,"date":"2017-10-26T15:37:30","date_gmt":"2017-10-26T15:37:30","guid":{"rendered":"https:\/\/courses.lumenlearning.com\/sunynutrition\/?post_type=chapter&p=664"},"modified":"2017-11-14T15:18:13","modified_gmt":"2017-11-14T15:18:13","slug":"9-22-vitamin-e-absorption-metabolism-excretion","status":"publish","type":"chapter","link":"https:\/\/courses.lumenlearning.com\/suny-herkimer-nutritionflex\/chapter\/9-22-vitamin-e-absorption-metabolism-excretion\/","title":{"raw":"9.22 Vitamin E Absorption, Metabolism, & Excretion","rendered":"9.22 Vitamin E Absorption, Metabolism, & Excretion"},"content":{"raw":"
\r\n\r\nYou might be saying to yourself, \u201cwho cares about natural versus synthetic alpha-tocopherol.\u201d But the small change in stereochemistry makes a big difference in how alpha-tocopherol is maintained in the body.\r\n\r\nAll forms of vitamin E (tocopherols, tocotrienols) are absorbed equally. Fat-soluble vitamins are handled like lipids and thus are incorporated into chylomicrons that have triglycerides removed by lipoprotein lipase. The chylomicron remnants containing the different forms of vitamin E are then taken up by the liver. The figure below shows the absorption, metabolism, and excretion of vitamin E.\r\n
\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"1023\"]\"\" Figure 9.221 The absorption, metabolism, and excretion of vitamin E[\/caption]\r\n\r\n<\/div>\r\nThe liver contains a protein called alpha-tocopherol transfer protein (alpha-TTP), which is responsible for maintaining higher levels of alpha-tocopherol in the body. Alpha-TTP preferentially binds to 2R alpha-tocopherol and helps facilitate its incorporation into VLDL. 2R means any form of alpha-tocopherol in which the 2 position is in the R conformation. The following table summarizes the forms of alpha-tocopherol that bind well to alpha-TTP, and those that don't bind well to alpha-TTP.\r\n\r\nTable 9.221 Alpha-tocopherol isomers and binding to alpha-TTP\r\n<\/colgroup>\r\n\r\n\r\n\r\n\r\n\r\n\r\n
Do not bind well to alpha-TTP<\/b><\/td>\r\nBind well to alpha-TTP<\/b><\/td>\r\n<\/tr>\r\n
SRR<\/td>\r\nRRR<\/td>\r\n<\/tr>\r\n
SSR<\/td>\r\nRRS<\/td>\r\n<\/tr>\r\n
SSS<\/td>\r\nRSS<\/td>\r\n<\/tr>\r\n
SRS<\/td>\r\nRSR<\/td>\r\n<\/tr>\r\n<\/tbody>\r\n<\/table>\r\nOther forms of vitamin E (gamma-tocopherol, tocotrienols) also don't bind well to alpha-TTP and thus, are found in lower levels than alpha-tocopherol in the body. The following graph shows plasma vitamin E levels from a study in which subjects were given 150 mg each of RRR-alpha-tocopherol, all-rac-alpha-tocopherol, or gamma-tocopherol1<\/sup>.\r\n
\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"890\"]\"\" Figure 9.222 Plasma vitamin E concentrations in response to a 150 mg dose of RRR-alpha-tocopherol, all-rac-alpha-tocopherol, or gamma-tocopherol. Adapted from reference 1[\/caption]\r\n\r\n<\/div>\r\nAs you can see in the figure, there was a greater rise in the plasma alpha-tocopherol levels after receiving RRR-alpha-tocopherol vs. all-rac-alpha-tocopherol. This is not a surprise because approximately 50% of all-rac-alpha-tocopherol is 2R alpha-tocopherol that binds well with alpha-TTP. You can also see that the plasma gamma-tocopherol concentration is much lower than either natural or synthetic alpha-tocopherol.\r\n\r\nFrom VLDL and subsequent lipoproteins, vitamin E reaches tissues, with most vitamin E in the body being found in the adipose tissue. There are two main routes of vitamin E excretion. The major route of excretion is through bile that is then excreted in feces. The second route is in the urine after vitamin E is chain-shortened in a process similar to beta-oxidation to make them more water-soluble.\r\n\r\nReference<\/b>\r\n\r\n1. Traber MG, Elsner A, Brigelius-Floh R. (1998) Synthetic as compared with natural vitamin E is preferentially excreted as alpha-CEHC in human urine: Studies using deuterated alpha-tocopheryl acetates. FEBS Lett 437(1-2): 145-148.\r\n\r\n<\/div>","rendered":"
\n

You might be saying to yourself, \u201cwho cares about natural versus synthetic alpha-tocopherol.\u201d But the small change in stereochemistry makes a big difference in how alpha-tocopherol is maintained in the body.<\/p>\n

All forms of vitamin E (tocopherols, tocotrienols) are absorbed equally. Fat-soluble vitamins are handled like lipids and thus are incorporated into chylomicrons that have triglycerides removed by lipoprotein lipase. The chylomicron remnants containing the different forms of vitamin E are then taken up by the liver. The figure below shows the absorption, metabolism, and excretion of vitamin E.<\/p>\n

\n
\"\"<\/p>\n

Figure 9.221 The absorption, metabolism, and excretion of vitamin E<\/p>\n<\/div>\n<\/div>\n

The liver contains a protein called alpha-tocopherol transfer protein (alpha-TTP), which is responsible for maintaining higher levels of alpha-tocopherol in the body. Alpha-TTP preferentially binds to 2R alpha-tocopherol and helps facilitate its incorporation into VLDL. 2R means any form of alpha-tocopherol in which the 2 position is in the R conformation. The following table summarizes the forms of alpha-tocopherol that bind well to alpha-TTP, and those that don’t bind well to alpha-TTP.<\/p>\n

Table 9.221 Alpha-tocopherol isomers and binding to alpha-TTP<\/p>\n\n\n\n<\/colgroup>\n\n\n\n\n\n\n
Do not bind well to alpha-TTP<\/b><\/td>\nBind well to alpha-TTP<\/b><\/td>\n<\/tr>\n
SRR<\/td>\nRRR<\/td>\n<\/tr>\n
SSR<\/td>\nRRS<\/td>\n<\/tr>\n
SSS<\/td>\nRSS<\/td>\n<\/tr>\n
SRS<\/td>\nRSR<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

Other forms of vitamin E (gamma-tocopherol, tocotrienols) also don’t bind well to alpha-TTP and thus, are found in lower levels than alpha-tocopherol in the body. The following graph shows plasma vitamin E levels from a study in which subjects were given 150 mg each of RRR-alpha-tocopherol, all-rac-alpha-tocopherol, or gamma-tocopherol1<\/sup>.<\/p>\n

\n
\"\"<\/p>\n

Figure 9.222 Plasma vitamin E concentrations in response to a 150 mg dose of RRR-alpha-tocopherol, all-rac-alpha-tocopherol, or gamma-tocopherol. Adapted from reference 1<\/p>\n<\/div>\n<\/div>\n

As you can see in the figure, there was a greater rise in the plasma alpha-tocopherol levels after receiving RRR-alpha-tocopherol vs. all-rac-alpha-tocopherol. This is not a surprise because approximately 50% of all-rac-alpha-tocopherol is 2R alpha-tocopherol that binds well with alpha-TTP. You can also see that the plasma gamma-tocopherol concentration is much lower than either natural or synthetic alpha-tocopherol.<\/p>\n

From VLDL and subsequent lipoproteins, vitamin E reaches tissues, with most vitamin E in the body being found in the adipose tissue. There are two main routes of vitamin E excretion. The major route of excretion is through bile that is then excreted in feces. The second route is in the urine after vitamin E is chain-shortened in a process similar to beta-oxidation to make them more water-soluble.<\/p>\n

Reference<\/b><\/p>\n

1. Traber MG, Elsner A, Brigelius-Floh R. (1998) Synthetic as compared with natural vitamin E is preferentially excreted as alpha-CEHC in human urine: Studies using deuterated alpha-tocopheryl acetates. FEBS Lett 437(1-2): 145-148.<\/p>\n<\/div>\n\n\t\t\t

\n\t\t\t

Candela Citations<\/h3>\n\t\t\t\t\t
\n\t\t\t\t\t\t
\n\t\t\t\t\t\t\t
CC licensed content, Shared previously<\/div>