Melatonin: A Promising Drug to Ameliorate Main Human Space Exploration Risks

Abstract

Melatonin is a small indole molecule synthesized by most cells in the mammalianbody. Circulating melatonin secreted by the pineal gland is a circadian signal thatregulates main rhythmic physiological processes, including sleep-wake cycle andbiological rhythms in cardiovascular function, metabolism, and immuneresponse. Both intracellular and extracellular melatonin have been shown to actas an effective protector for free radicals molecular and tissue injury. Duringhuman space exploration, crew members will be exposed to several risks, including exposure to radiation in the form of high-energy galactic cosmic rays andsolar particle events, bone loss and neurological disorders induced by microgravity, and sleep disruption. Due to its important chronobiotic and cytoprotectiveeffect, melatonin treatment could be a potential effective strategy to protectagainst most space radiation hazards. It has an anti-osteoclastogenic activityand a pro-osteoblastic activity that may reduce bone-loss induced by microgravity. Also, melatonin is potentially effective to prevent neurodegeneration that mayresult from long-term space exploration. Finally, its chronobiotic and hypnoticproperties may help to improve sleep and circadian synchronization, decreasingin turn, the risk of fatigue, performance decrements, and adverse health outcomes.Melatonin was presumably present from the very beginning of life on Earth, andevidence suggests that it could be a helpful partner for our first steps outside theplanet.