Eicosanoids in Insect Immune Signal Transduction

Abstract

Eicosanoid is a collective term for all biologically active, oxygenated metabolites of arachidonic acid and two other C20 polyunsaturated fatty acids. There are three major groups of eicosanoids. The prostaglandins (PGs), so named because they were first discovered in seminal fluids originating in the prostate gland, are products of the cyclooxygenase pathways. The cytochrome P₄₅₀ “epoxygenase pathways” yield the epoxyeicosatrienoic acids. Various lipoxygenase pathways are responsible for biosynthesizing a wide range of compounds, including leukotrienes and hydroxyeicosatetraenoic acids. The biosynthesis and structures of representatives of the major groups of eicosanoids are outlined in Figure 1, and described in detail elsewhere (Stanley, 1999). One or more members of the major eicosanoid groups have been detected in virtually all mammalian tissues and body fluids, where they serve as lipid mediators of cellular events. Among their important actions, eicosanoids modulate ion transport physiology, mediate contraction or relaxation of smooth muscles and exert tremendous influence in host defense mechanisms. It would be difficult to exaggerate the importance of eicosanoids in the vertebrate immune system. Sir John Vane shared in the 1982 Nobel Prize in Medicine or Physiology, which recognized his discovery that the analgesic effects of aspirin are due to inhibition of prostaglandin biosynthesis. This discovery launched a very large pharmaceutical research enterprise aimed at discovery of new non-steriodal anti-inflammatory drugs, all of which act through their inhibitory influence on prostaglandin biosynthesis.