Vitamin E has been suggested to exert anti-inflammatory actions and has been shown to be effective in reducing inflammation in experimental asthma in mice and in asthmatics in studies in several countries in Europe (Finland and Italy). Disappointingly, vitamin E trials in the United States have failed to show benefit in asthma. We have recently discovered unrecognized properties of vitamin E isoforms (?-tocopherol and ?-tocopherol) that may explain these surprisingly disparate results in the clinical studies. ?-tocopherol and ?-tocopherol are the two major forms of vitamin E that are consumed by Americans. We have demonstrated that ??-tocopherol elevates inflammation. Moreover, ?-tocopherol, at as little as 10% the tissue concentration of ?- tocopherol, ablated the anti-inflammatory benefit of ?-tocopherol in experimental asthma in mice and in vitro in leukocyte migration. Furthermore, these tocopherols had direct effects on the endothelium during leukocyte migration. Since ?-tocopherol is found at high levels in the American diet, but not in most diets of Europeans, this tocopherol isoform antagonism could be of significant clinical relevance. Several reports indicate that plasma levels of ?-tocopherol in Americans are 2-5 times higher than Europeans. Furthermore, the studies that demonstrate a benefit of ?-tocopherol during inflammation in animal models are consistent with the very low levels of ?-tocopherol in animal diets. Before initiating human studies, it is very important to understand the molecular mechanisms for the opposing modulation of inflammation by these two major forms of vitamin E. The goal of the experiments described in this proposal is to test hypotheses regarding the mechanism of the anti-inflammatory effects of ?-tocopherol and the antagonism of these effects by ?-tocopherol. We will use purified natural ?- and ?-tocopherols and a combined in vitro and in vivo approach with well-developed model systems in mice and cultured cells. Information from our studies will have significant impact on the design of clinical studies and on vitamin E consumption by Americans. Hypothesis: Vitamin E, a complex mixture of tocopherols and tocotrienols, elicits anti-inflammatory effects that vary among the forms of tocopherols. Natural d-??-tocopherol inhibits signals for leukocyte trafficking by direct effects on endothelium via scavenging ROS and inhibiting PKC??. In contrast, natural d-??- tocopherol competes against the benefit of ?-tocopherol and exhibits non-antioxidant proinflammatory effects by elevating endothelial function during inflammation. Specific Aims: Aim 1. We shall determine whether the ?-tocopherol ablation of the benefit of ?- tocopherol is reversible in experimental asthma. AIM 2. We shall determine whether ?-tocopherol blocks and ?- tocopherol elevates leukocyte migration by modulating signals activated by the endothelial cell adhesion molecule VCAM-1. AIM 3. We shall determine whether ?-tocopherol blocks and ?-tocopherol elevates leukocyte migration by modulating signals activated by the endothelial cell adhesion molecule ICAM-1. PUBLIC HEALTH RELEVANCE: Our studies on forms of vitamin E reveal novel opposing effects of forms of vitamin E on asthma. Our data with vitamin E suggest that a source for the disparate results in vitamin E outcomes in studies with animals versus humans and in studies with Americans versus Europeans is that the ?-tocopherol form of vitamin E antagonizes the action of the ?-tocopherol form of vitamin E. Furthermore, the ?-tocopherol form is high in the American diet and is high in plasma in the United States as compared to European countries. This proposal addresses mechanisms for opposing effects of ?-tocopherol and ?-tocopherol on inflammation using in vivo and in vitro models. The mechanistic data from our studies will help define modified consumption of forms of vitamin E in future clinical studies.
NIH ExPorter
NIH ExPorter