INTRODUCTION
Melatonin (N-acetyl-5-methoxytryptamine), the main
pineal hormone that relays light/ dark cycle information to
the circadian system, can also be produced in other tissues
[1]. Melatonin amphiphilic characteristics allow it to
reach any cell, compartment or body fluid [2]. Besides its
well-known functions in circadian and seasonal rhythms,
melatonin and its metabolites also decrease oxidative
stress by acting both as direct free radical scavenger and
by stimulating the activity and expression of antioxidant
enzymes [3–6]. Additionally, several other activities have
been attributed to melatonin: the regulation of the immune
system [7], the modulation of mitochondrial activity [8], as
well as regulation of cell death [9] and autophagy [10], and
an intrinsic antitumoral activity [11]. Due to the multitude
of its actions, a role in maintaining healthy aging has been
ascribed to melatonin [12].