Inhibition of IgE-mediated histamine release from rat basophilic leukemia cells and rat mast cells by inhibitors of transmethylation.

This study evaluated the effect of inhibitors of transmethylation on histamine release from rat mast cells and rat basophilic leukemia cells. IgE-mediated histamine release from rat basophilic leukemia cells (RBL-2H3 cells) was inhibited by 3-deazaadenosine (DZA) in the presence of L-homocysteine thiolactone (Hcy) or the combination of adenosine, erythro-9-(2-hydroxy-3-nonyl) adenine (EHNA), and Hcy in a dose-dependent fashion. There were no significant changes in the cellular cAMP levels by these inhibitors. Histamine release induced by anti-IgE or dextran from normal rat mast cells was also blocked by DZA plus Hcy in a dose-dependent manner. DZA at 10(-3) M in the presence of 10(-4) M Hcy or the combination of 10(-3) M adenosine, 10(-4) M EHNA, and 10(-3) M Hcy inhibited lipid (perhaps phospholipid) methylation into RBL-2H3 cells without affecting choline incorporation. In the presence of 10(-3) M DZA plus 10(-4) M Hcy there was a 170-fold increase in 35SAdoHcy with the concomitant appearance of 3-deaza-AdoHcy when the cells were incubated with 35Smethionine, thus indicating that these drugs inhibited methylation reaction(s) through the intracellular accumulation of AdoHcy and 3-deaza-AdoHcy. In contrast, histamine release from rat mast cells induced by the calcium ionophore A23187, compound 48/80, polymyxin B, or ATP was not inhibited by these compounds. These results suggest that IgE- or dextran-mediated histamine release involves methylation reactions(s), whereas the other secretagogues bypass this early step.