New Cholesterol Study Reveals Patterns Of Protective Vitamin E Oxidant Activities
Research investigating the effects of tocopherols on cholesterol markers has suggested that the vitamin E molecules have different oxidation patterns depending on the compound they are attached to.
The study, published in The Journal of Nutritional Biochemistry, suggests that alpha- and gamma- tocopherols, both are forms of vitamin E, have contradictory oxidant activities, depending on the lipoprotein being oxidized.
Lipoproteins such as high density lipoprotein (HDL) and low density lipoprotein (LDL) are proteins that transport lipids such as cholesterol and triglycerides through the bloodstream. HDL is associated with being a marker of "good" cholesterol and LDL is associated with "bad" cholesterol.
Researchers from Queen's University Belfast, UK report that while the tocopherols both offered protection against oxidation with very low density lipoprotein (VLDL) and low density lipoprotein (LDL) both regarded as "bad" cholesterol, the tocopherols had a pro-oxidation effect when incorporated
into high density lipoprotein (HDL).
The researchers said that the pro-oxidant activity of both tocopherols toward HDL "may go some way to explain why supplementation studies with vitamin E have not been able to display cardio-protective effects."
The Vitamin E Tocopherols...
As a result, numerous experimental studies have strongly suggested a major role for oxygen-derived free radicals in the development of the disease, they added.
"It has been demonstrated that antioxidant vitamins can protect against oxidative injury and are therefore believed to provide protection against a myriad of diseases," said the authors.
There are 8 known forms of vitamin E: 4 forms of tocopherol, and 4 forms of tocotrienols, all of which are known to be antioxidants. Significantly more research attention has focused on the tocopherol forms, with many clinical trials investigating their role in preventing cardiovascular disease.
The Belfast-based scientists report that much of the research has focused on tocopherol's effects during LDL oxidation, with little attention being paid to VLDL and HDL. The team therefore questioned whether alpha- and gamma- tocopherols become incorporated into VLDL, LDL and HDL and influence their oxidation potential.
Vitamin E Study Details...
The tocopherols were found to protect VLDL and LDL against oxidation, and "surprisingly, the incorporation into HDL demonstrated pro-oxidant properties," reported the team.
In a similar study both tocopherols were again incorporated into all three lipoproteins, protecting VLDL and LDL against oxidation; but enhancing the oxidation of HDL.
They said their results may have physiological implications: "HDL is suggested to be responsible for the majority of reverse cholesterol transport in humans and is considered to be an atheroprotective molecule; however, when it becomes dysfunctional, for example, by oxidation, it loses these protective properties and may instead yield detrimental effects.
Most interestingly, these results have helped separate particular facts from a great deal of information about possible mechanisms whereby tocopherol is ineffective during large-scale supplementation studies in bringing about cardioprotective benefits," the researchers concluded.
Source: The Journal of Nutritional Biochemistry
(Published online)
"The two faces of α- and γ-tocopherols: an in vitro and ex vivo investigation into VLDL, LDL and HDL oxidation"
This article is for informational and educational purposes only, and is not intended to provide medical advice, diagnosis or treatment. Consult with your doctor or healthcare professional for medical and nutrition advice.
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