Antioxidant and antiinflammatory role of melatonin in Alzheimer's neurodegeneration

(1) By following the activities of melatonin, an ancient molecule that appeared 2.5–3.5 billion years ago, which is a well-known antioxidant and immunomodulatory indoleamine, this chapter focuses on the oxidative stress and inflammatory events as they occur in Alzheimer's disease (AD). (2) Melatonin synthesis and its mechanisms of action are explained to reveal why this pineal molecule may exert a therapeutic effect on AD. (3) A summarized description of free radical mechanism of production helps to understand the prominence of melatonin as a free radical scavenger and as an antioxidant. These mechanisms are particularly relevant in the brain, which consumes 20% of all oxygen in the organism. (4) To focus on the problem, an explanatory vision of where free radicals come from in AD is detailed and how melatonin scavenges free radicals in addition to its ability to stimulate the antioxidant systems. (5) Melatonin's role in breaking the deleterious neuroinflammation-oxidative stress cycle is explained. (6) With these precedents, we explain why the decreasing melatonin levels with age and Alzheimer's symptoms start to appear.