Plasmalogens as endogenous antioxidants: somatic cell mutants reveal the importance of the vinyl ether

Exposure of plasmalogen-deficient variants of the murine cell line RAW 264. 7 to short-term (0-100 min) treatment with electron transport inhibitors an timycin A or cyanide (chemical hypoxia) resulted in a more rapid loss of vi ability than in the parent strain. Results suggested that plasmalogen-defic ient cells were more sensitive to reactive oxygen species (ROS) generated d uring chemical hypoxia; the mutants could be rescued from chemical hypoxia by using the antioxidant Trolox, an a-tocopherol analogue, and they were mo re sensitive to ROS generation by plumbagin or by rose bengal treatment cou pled with irradiation. In addition, the use of buffers containing (H2O)-H-2 greatly enhanced the cytotoxic effect of chemical hypoxia, suggesting the involvement of singlet oxygen. We used the unique enzymic deficiencies disp layed by the mutants to differentially restore either plasmenylethanolamine (the major plasma-logen species normally found in this cell line) or its b iosynthetic precursor, plasmanylethanolamine. Restoration of plasmenylethan olamine, which contains the vinyl ether, resulted in wildtype-like resistan ce to chemical hypoxia and ROS generators, whereas increasing levels of its precursor, which bears the saturated ether, had no effect on cell survival . These findings identify the vinyl ether double bond as a crucial element in cellular protection under these conditions and support the hypothesis th at plasmalogens, through the vinyl ether, act as antioxidants to protect ce lls against ROS. These phospholipids might protect cells from ROS-mediated damage during events such as chemical hypoxia.