Abstract
Vitamin E is the most important lipid antioxidant which is widely used to prevent age-associated diseases. In the liver a-tocopherol (a-TOH), the most active isomer, is metabolized by side-chain truncation. Hydroxylation and oxidation steps in peroxisomes form the long-chain metabolite (LCM) a-13′-COOH, which has been recently reported by our group to occur in human serum. Only little is known about the modes of action of the LCM. We therefore investigate the influence of the physiologically relevant a-13′-COOH and the tocotrienol (T3)-related garcinoic acid (GA) on LPS-induced inflammatory response of murine macrophages (mMF). We report here that a-13′-COOH occurs in human serum and can be detected by LC/MS-QTOF which provides evidence for its systemic bioavailability. Translating these results into mechanistic studies we use semi-synthetically derived LCM starting with garcinoic acid, isolated from the bitternut Garcinia kola, because LCMs are not commercially available as pure compounds. We also report that a-13′-COOH and GA inhibit pro-inflammatory pathways in comparison to a-TOH in LPS-stimulated mMF. A screening of inflammation-related genes showed significant decreases of Il1ß by all compounds, while Il6 and Tnfa were only down-regulated by GA. However Cox2 and iNos were significantly reduced on mRNA and protein level by more than 70% and also the formation of signaling molecules, such as NO and PGE2, was significantly reduced by a-13′-COOH and GA. Key role in regulation of inflammatory response is regulated by activation of NF?B along with p65 subunit translocation. Neither expression nor translocation were regulated by a-13′-COOH and GA. The LCM and d-T3 show high activity in inhibiting pro-inflammatory pathways and associated signal transduction. We speculate that physiological a-LCM represent a new class of regulatory metabolites.