Inhibition of phytohemagglutinin-induced lymphocyte mitogenesis by lipoxygenase metabolites of arachidonic acid: structure-activity relationships.

Phytohemagglutinin (PHA)-induced mitogenesis of mixed mouse spleen lymphocyte populations, measured by [3H]thymidine incorporation, was completely inhibited by micromolar concentrations of certain hydroxyeicosatetraenoic acids (HETE's). These are lipoxygenase metabolites of arachidonic acid which are synthesized in considerable concentrations by macrophages, lymphocytes, and other components of the immune system when appropriately stimulated. In the studies described here, the structural requirements for the maximum antimitogenic activities were examined. A series of monohydroxylated HETE's were prepared using a singlet oxygen photochemical procedure or by enzymatic synthesis from arachidonic acid substrate, and isolated by HPLC. Isomers containing different numbers of double bonds were synthesized using the appropriate unsaturated fatty acid as substrate, and the functional importance of the OH and carboxylic functions was tested using various acetoxy- and carbomethoxy derivatives. A serum-free mitogenesis assay system was used for testing, which minimized binding of the fatty acids by serum proteins and increased the inhibitory potency of the various HETE's several-fold. It was found that inhibition of cell proliferation was related to: hydroxyl proximity to the center of the eicosatetraenoic acid, decreasing in the order: 9 greater than 11 greater than 12 greater than 15 greater than 8 much greater than 5; the number of double bonds in the fatty acid chain, decreasing in the order: 15-OH, 20:4 greater than 15-OH 20:3 much greater than 15-OH, 20:2 much greater than 15-OH, 20:0; and the 15-position functional group as well as the 1-carboxylic group, decreasing in the order: 15-hydroxy, 1-carboxylic greater than 15-acetoxy, 1-carboxylic much greater than 15-hydroxy, 1-carbomethoxy greater than 15-acetoxy, 1-carbomethoxy.(ABSTRACT TRUNCATED AT 250 WORDS)