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)

Reye's syndrome and aspirin use: a possible immunological relationship.

Reye's syndrome is a serious childhood disease usually associated with an antecedent viral illness such as influenza or chicken pox. Recent reports indicate a relationship between moderate aspirin use during the viral infection and the development of Reye's disease. The blastogenic response of cultured lymphocytes to lectins mimics their in vivo response to viral antigens. We report here that physiological doses of the cyclooxygenase inhibitor aspirin, induce marked hyperactivity in this response. Mouse spleen lymphocyte cultures were treated with phytohemagglutinin (PHA) and mitogenesis was assayed after 72 hours by measuring incorporation of 3H thymidine. Addition of aspirin produced up to 3-fold increases in the PHA response. The effect was specific for T-lymphocytes and response to the B lymphocyte mitogen LPS was not significantly affected. The hyperproliferative effect was dose-dependent being maximum at aspirin levels of 300-400 microM and was reversed by addition of prostaglandin E2 (10-9M). Maximum effects were observed when aspirin was added to cells within 8-10 hours of exposure to antigen. The observations suggest that Reye's syndrome may result from an aspirin-induced aberration in the immune response to a viral infection.

Role of lipoxygenases in regulation of PHA and phorbol ester-induced mitogenesis.

The experiments described here confirm the critical involvement of products of arachidonic acid metabolism in immune cell function. The results suggest opposing activities of the cyclo-oxygenase versus the lipoxygenases products in these systems. However, in contrast to the situation with the prostaglandins, where addition of the pure compounds has reproduced the effects predicted from the inhibitor studies, identification of the specific lipoxygenase products involved and the induction of the predicted biological response by addition of these compounds remains to be accomplished.