Up-regulation of prostaglandin biosynthesis by leukotriene C4 in elicited mice peritoneal macrophages activated with lipopolysaccharide/interferon-{gamma}.

Leukotrienes (LT) and prostaglandins (PG) are proinflammatory mediators generated by the conversion of arachidonic acid via 5-lipoxygenase (5-LO) and cyclooxygenase (COX) pathways. It has long been proposed that the inhibition of the 5-LO could enhance the COX pathway leading to an increased PG generation. We have found that in in vitro models of inflammation, such as mice-elicited peritoneal macrophages activated with lipopolysaccharide (LPS)/interferon-gamma (IFN-gamma), the deletion of the gene encoding for 5-LO or the enzyme activity inhibition corresponded to a negative modulation of the COX pathway. Moreover, exogenously added LTC(4), but not LTD(4), LTE(4), and LTB(4), was able to increase PG production in stimulated cells from 5-LO wild-type and knockout mice. LTC(4) was not able to induce COX-2 expression by itself but rather potentiated the action of LPS/IFN-gamma through the extracellular signal-regulated kinase-1/2 activation, as demonstrated by the use of a specific mitogen-activated protein kinase (MAPK) kinase inhibitor. The LT-induced increase in PG generation, as well as MAPK activation, was dependent by a specific ligand-receptor interaction, as demonstrated by the use of a cys-LT1 receptor antagonist, although also a direct action of the antagonist used, on PG generation, cannot be excluded. Thus, the balance between COX and 5-LO metabolites could be of great importance in controlling macrophage functions and consequently, inflammation and tumor promotion.