Why is arachidonic acid described as a 'Dr. Jekyll and Mr. Hyde' fatty acid?

• A. Because it is only beneficial
• B. Because it is only harmful
• C. Because it can participate in both pro-inflammatory and potentially beneficial signaling
• D. Because it is not found in the brain

Answer: (C)

Arachidonic acid acts as a double-edged signaling molecule, because it serves as a substrate for enzymes that generate a range of signaling molecules with opposite effects. When released from membrane phospholipids, it can be converted by cyclooxygenases into prostaglandins and thromboxanes that promote inflammation, pain, and fever, and by lipoxygenases into leukotrienes that recruit immune cells. At the same time, other AA-derived mediators, including certain lipoxins and other pro-resolving molecules, help to dampen inflammation and promote healing. The outcome depends on the cellular context, enzyme activity, and the balance of pathways active at a given time. In the brain, arachidonic acid is part of normal neuronal signaling, and its metabolites can participate in both promoting and resolving inflammatory processes. So its role is not purely harmful or purely beneficial, which is why it’s described as a Dr. Jekyll and Mr. Hyde fatty acid.