Long-chain metabolites of vitamin E: Interference with lipotoxicity via lipid droplet associated protein PLIN2.

The long-chain metabolites of vitamin E (LCM) emerge as a new class of regulatory metabolites and have been considered as the active compounds formed during vitamin E metabolism. The bioactivity of the LCM is comparable to the already established role of other fat-soluble vitamins. The biological modes of action of the LCM are far from being unraveled, but first insights pointed to distinct effects and suggested a specific receptor, which in turn lead to the aforementioned hypothesis. Here, a new facet on the interaction of LCM with foam cell formation of THP-1 macrophages is presented. We found reduced levels of mRNA and protein expression of lipid droplet associated protein PLIN2 by α-tocopherol (α-TOH), whereas the LCM and the saturated fatty acid, stearic acid, increased expression levels of PLIN2. In a lipotoxic setup (0-800 μM stearic acid and 0-100 μM α-TOH or 0-5 μM α-13'-COOH) differences in cellular viability were found. A reduced viability was observed for cells under co-treatment of α-TOH and stearic acid, whereas an increased viability for stearic acid incubation in combination with α-13'-COOH was observed. The striking similarity of PLIN2 expression levels and worsened or mitigated lipotoxicity, respectively, revealed a protective effect of PLIN2 on basal stearic acid-induced lipotoxic conditions in PLIN2 knockdown experiments. Based on our results, we conclude that α-13'-COOH protects cells from lipotoxicity, at least partially via PLIN2 regulation. Herewith another facet of LCM functionality was presented and their reputation as regulatory metabolites was further established.