Arachidonic Acid Transformation and Tumor Production

Publisher Summary This chapter deals with the transformation of Arachidonic acid that is the unsaturated fatty acid found in the highest concentration in cellular phospholipids. The endoperoxides (PGG2 and PGH2) are the immediate products of the cyclooxygenase and can undergo enzymatic and non-enzymatic transformations to form thromboxanes (TxA2 and TxB2), prostacyclins (PG12), and prostaglandins (PGE2, PGFza, and PGD2). These endoperoxide metabolites can exist in classes depending on the degree of unsaturation in their precursor fatty acids. Arachidonic acid is substrate for lipoxygenases, which also produce potent pharmacologically active compounds. Prostaglandins, prostacyclins, and thromboxanes are not stored to any considerable extent in mammalian tissues. Deacylation of phospholipids probably occurs by more than one enzymatic pathway. Carcinogenesis may be a multistep process. Increased prostaglandin production suppresses the host's immune response to tumor. Inhibition of prostaglandin production by anti-inflammatory drug permits the host's immune system to more effectively reject the tumor. Most cells also have the enzymatic capacity to transform the free arachidonic acid.