Comparative neuroprotective and antioxidant roles of vitamin E isoforms: a review

Vitamin E comprises eight structurally related isoforms, including α-, β-, γ-, and δ-tocopherols and their corresponding tocotrienols. These isoforms differ in the degree of methylation of the chromanol ring and the saturation of the side chain, structural features that critically influence their bioavailability, antioxidant capacity, and neuroprotective functions. This mini review systematically summarizes recent advances in the antioxidant and neuroprotective roles of vitamin E isoforms, with particular emphasis on their distinct mechanisms of action in the nervous system. Evidence from cell-based studies, animal models, and human investigations indicates that the neuroprotective effects of vitamin E isoforms vary considerably. Tocotrienols, characterized by their unsaturated side chains, exhibit enhanced membrane mobility and broader biological activity, demonstrating superior neuroprotective properties through modulation of signaling pathways, maintenance of mitochondrial function, and inhibition of abnormal tau hyperphosphorylation. In addition, different tocopherol isoforms show complementary roles in scavenging reactive oxygen species and/or reactive nitrogen species. Despite substantial experimental evidence, clinical data remain limited, and challenges such as differences in bioavailability and incomplete understanding of isoform-specific mechanisms persist. Overall, vitamin E should be regarded not as a single molecule but as a family of functionally complementary isoforms, whose synergistic actions may play a crucial role in maintaining brain health and in the prevention and treatment of neurodegenerative diseases.