Much early clinical research with “vitamin E” did not specify the chemical form used. ![]() Most commercial vitamin E supplements are all-racemic alpha-tocopheryl acetate which is also the form used in many clinical trials. Synthetic alpha-tocopherol is, therefore, only one-eighth RRR-alpha-tocopherol. Synthetic alpha-tocopherol has half R- and half S- at each of the three chiral carbons and is called all-racemic-alpha-tocopherol. Naturally occurring tocopherols all have chiral carbons with an R-stereochemical configuration, e.g., RRR-alpha-tocopherol. RRR-alpha-tocopherol is the primary form of vitamin E found in human plasma, but RRR-gamma-tocopherol is the primary form found in a Western diet. Naturally occurring forms of vitamin E have specific and functionally significant stereochemistry’s. Vitamin E is not a single organic molecule but refers to at least eight naturally occurring compounds, four tocopherols (alpha-, beta-, gamma- and -delta), and four tocotrienols (alpha-, beta-, gamma- and -delta) which are all lipid soluble and associated with lipid-protein complexes such as biomembranes and lipoproteins. Organic antioxidants can be either lipid soluble (vitamin E) or water soluble such as glutathione (GSH), ascorbate, and urate. A key goal is to understand how antioxidants modulate acts in signal transduction pathways.Īntioxidants can be small organic molecules such as ascorbate and urate, or enzymes such as superoxide dismutase. The physiochemical and physiological properties of individual antioxidants are complex, and not all molecules that function as antioxidants are necessarily beneficial to human health. This article will focus on physiologically significant antioxidants that have been studied either in humans, animal models, or relevant in vitro cellular models. Gamma-tocopherol which is the primary dietary form of vitamin E is both an antioxidant nutrient as well as a functional antioxidant. For example, “selenium” is considered an “antioxidant nutrient” but dietary selenium, in the form of selenite or selenate, is not a functional antioxidant: selenite and selenate must convert to L-selenocysteine which can then get incorporated into glutathione peroxidase (GPX) which is a key antioxidant selenoenzyme. An “antioxidant nutrient” can be either a precursor or cofactor for an antioxidant molecule or can be an antioxidant in its own right. Screening complex mixtures of organic molecules (e.g., a fruit juice) for their in vitro antioxidant capacities is popular, but the health-related significance of such measurements is questionable. In the most general sense, a natural or synthetic antioxidant directly or indirectly functions to minimize damage to biomolecules (mostly proteins, lipids, and DNA) caused by reactive oxygen species (ROS) and/or reactive nitrogen oxide species (RNOS). ![]() The term “antioxidant” is not always clearly defined in either popular or scientific literature.
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