alpha-Tocopherol, the most active form of vitamin E, causes a dose-dependent inhibition of serum-induced proliferation of smooth muscle cells (A7r5) in culture. Some tocopherol-related compounds exhibiting various degrees of antioxidant potency have also been tested on cellular proliferation. No direct correlation between the antioxidant activity of these compounds and their effect on smooth muscle cell growth could be observed. While most of the derivatives employed were not effective in inhibiting protein kinase C, in the case of alpha-tocopherol the antiproliferative effect was found to be parallel to the inhibition of protein kinase C activity, as measured in streptolysin-O permeabilized cells.
Certain aspects of tocopherol and tocotrienol absorption, plasma transport, and tissue distribution were examined in humans and hamsters. Plasma transport differed in that tocopherols were found primarily in low density lipoprotein and high density lipoprotein in association with plasma surface components, whereas tocotrienols disappeared from plasma with chylomicron clearance. In keeping with transport by triglyceride-rich lipoproteins, tocotrienols were deposited in conjunction with triglycerides in the adipose tissue of hamsters. In hamsters, tocopherols were the only tocol readily detected in all tissues, except adipose during tocotrienol supplementation. In fasting humans, the plasma tocotrienol concentration was not significantly increased after tocotrienol supplementation, whereas the platelet concentration of delta-tocotrienol doubled. Furthermore, tocotrienol intake did not appear to modulate the plasma cholesterol concentration in normolipemic hamsters. Thus, the transport, tissue concentration, and relative biologic function of tocopherol and tocotrienol appear somewhat disparate and possibly unrelated.