Superoxide production by macrophages stimulated in vivo with synthetic ether lipids

The anticancer activity of synthetic ether lipids may depend in part upon their ability to activate cells of the monocyte/macrophage lineage. In the present study, we have sought to determine whether 1‐ O ‐octadecyl‐2‐ O ‐methyl‐ rac ‐glycero‐3‐phosphocholine (ET‐18‐OMe) and related ether lipids enhance superoxide production by mouse peritoneal macrophages. Ether lipids were administered intraperitoneally to C57BL/6 mice 4 d after injection with thioglycollate broth. Elicited peritoneal macrophages were harvested and purified one day later, and superoxide production was detected by measuring the superoxide dismutase inhibitable reduction of cytochrome c. Low levels of superoxide were secreted by macrophages in the absence of phorbol 12‐myristate 13‐acetate (PMA). When PMA was added in vitro to macrophages from ET‐18‐OMe‐treated mice, these cells secreted 194.2 nmol superoxide/mg protein in comparison to 53.5 nmol superoxide/mg protein for PMA‐treated control cells. The in vitro treatment of the macrophages with ET‐18‐OMe was not effective in stimulating superoxide secretion. Macrophages harvested from mice treated with a series of ether lipids (with and without phosphorus) were examined, and superoxide secretion was found to vary with structure. AM‐18‐OEt and CP‐7 were the most effective compounds, secreting 8.6 and 11.9 times more superoxide, respectively, than PMA‐stimulated control cells. Moreover, direct cytotoxicity of the compounds for HL60 human promyelocytic leukemic cells did not necessarily correlate with the ability of each drug to increase macrophage superoxide production.