Melatonin: an ancient molecule that makes oxygen metabolically tolerable

Abstract

Melatonin is remarkably functionally diverse with actions as a free radical scavenger and antioxidant, circadian rhythm regulator, antiinflammatory and immunoregulating molecule, and as an oncostatic agent. We hypothesize that the initial and primary function of melatonin in photosynthetic cyanobacteria, which appeared on Earth 3.5-3.2 billion years ago, was as an antioxidant. The evolution of melatonin as an antioxidant by this organism was necessary as photosynthesis is associated with the generation of toxic-free radicals. The other secondary functions of melatonin came about much later in evolution. We also surmise that mitochondria and chloroplasts may be primary sites of melatonin synthesis in all eukaryotic cells that possess these organelles. This prediction is made on the basis that mitochondria and chloroplasts of eukaryotes developed from purple nonsulfur bacteria (which also produce melatonin) and cyanobacteria when they were engulfed by early eukaryotes. Thus, we speculate that the melatoninsynthesizing actions of the engulfed bacteria were retained when these organelles became mitochondria and chloroplasts, respectively. That mitochondria are likely sites of melatonin formation is supported by the observation that this organelle contains high levels of melatonin that are not impacted by blood melatonin concentrations. Melatonin has a remarkable array of means by which it thwarts oxidative damage. It, as well as its metabolites, is differentially effective in scavenging a variety of reactive oxygen and reactive nitrogen species. Moreover, melatonin and its metabolites modulate a large number of antioxidative and pro-oxidative enzymes, leading to a reduction in oxidative damage. The actions of melatonin on radical metabolizing/producing enzymes may be mediated by the Keap1-Nrf2-ARE pathway. Beyond its direct free radical scavenging and indirect antioxidant effects, melatonin has a variety of physiological and metabolic advantages that may enhance its ability to limit oxidative stress.

Effects of exogenous melatonin on antioxidant capacity in Actinidia seedlings under salt stress

“…Salt stress causes ion toxicity, osmotic stress and oxidative stress, leads to metabolic disorders, seriously affects the growth and development of fruit trees [1]. Melatonin (MT) is a neuroendocrine hormone secreted by pineal gland, which is N-acetyl-5-methoxytryptamine [2], exists in the vast majority of biological organisms [3]. A large number of studies have shown that MT can not only regulate the plant growth [4], but also improve the resistance of plants to drought, salt damage, heavy metals, UV radiation, high temperature, chilling injury and other stress [5,6].…”

Biological Impact of Melatonin on the Healing of Albino Rats’ Tongue Ulcer.

“…Perhaps, a potent anti-inflammatory property of melatonin is linked to its ability to act as a scavenger of exogenous and endogenous reactive oxygen species (ROS) and reactive nitrogen species (RNS) (31) During wound healing, fibroblasts differentiate into myofibroblasts, which generate large traction forces for wound closure and tissue remodeling. One of the best-characterized markers of myofibroblast phenotype is α-SMA (32) .…”

A tobozmirigy-csecsemőmirigy rendszer szerepe az autoimmunitás, öregedés és élettartam szabályozásában

“…A szerotoninból transzformálódott melatoninról később kiderült, hogy emlősökben, így emberben is a cirkadiális ritmus, az álom-ébrenlét fázisok fenntartásá-ért felelős, de számos egyéb, nem kevésbé fontos hatása is van. Így az ecto-ento dermalis eredetű endokrin mirigyek szabályozója [1], és jelentős az antioxidáns hatása, amellyel részben gátolja az oxidatív molekulák megjelenését, részben elősegíti azok lebontását, valamint részt vesz a szervezet homeosztázisának fenntartásában, az immunvédekezésben, befolyásolja a reproduktív szervek működését férfiban és nőben egyaránt [2,3].…”