Melatonin Delays Brain Aging by Decreasing the Nitric Oxide Level

Therapeutic potential of melatonin and its derivatives in aging and neurodegenerative diseases

Aging is associated with increasing impairments in brain homeostasis and represents the main risk factor across most neurodegenerative disorders. Melatonin, a neuroendocrine hormone that regulates mammalian chronobiology and endocrine functions is well known for its antioxidant potential, exhibiting both cytoprotective and chronobiotic abilities. Age-related decline of melatonin disrupting mitochondrial homeostasis and cytosolic DNA-mediated inflammatory reactions in neurons is a major contributory factor in the emergence of neurological abnormalities. There is scattered literature on the possible use of melatonin against neurodegenerative mechanisms in the aging process and its associated diseases. We have searched PUBMED with many combinations of key words for available literature spanning two decades. Based on the vast number of experimental papers, we hereby review recent advancements concerning the potential impact of melatonin on cellular redox balance and mitochondrial dynamics in the context of neurodegeneration. Next, we discuss a broader explanation of the involvement of disrupted redox homeostasis in the pathophysiology of age-related diseases and its connection to circadian mechanisms. Our effort may result in the discovery of novel therapeutic approaches. Finally, we summarize the current knowledge on molecular and circadian regulatory mechanisms of melatonin to overcome neurodegenerative diseases (NDDs) such as Alzheimer's, Parkinson's, Huntington's disease, and amyotrophic lateral sclerosis, however, these findings need to be confirmed by larger, well-designed clinical trials. This review is also expected to uncover the associated molecular alterations in the aging brain and explain how melatonin-mediated circadian restoration of neuronal homeodynamics may increase healthy lifespan in age-related NDDs.

Effect of short-term oral supplementation of crocin on age-related oxidative stress, cholinergic, and mitochondrial dysfunction in rat cerebral cortex

BACKGROUND AND AIM

Aging is associated with oxidative stress and altered cholinergic and mitochondrial function. Crocin is a carotenoid antioxidant that quenches free radicals and protects cells and tissues from oxidation in biological systems. The aim of the present study is to investigate the effect of oral supplementation of Crocin on age-associated oxidative stress, cholinergic, and mitochondrial function in rat cerebral cortex.

MAIN METHODS

The middle-aged (15 months old) rats were segregated into three groups (n = 6): Control (ad-libitum fed +0.9% saline as vehicle), Cro 50 (ad-libitum fed + crocin 50 mg/kg/day), Cro 150 (ad-libitum fed + crocin 150 mg/kg/day). The experiment was scheduled for 45 days. The serum and brain parameters were estimated after euthanasia.

KEY FINDINGS

Crocin supplementation of Cro 50 and Cro 150 displayed a relative decline in body weight gain during the experimental period and significantly reduced age-associated serum triglyceride level over control. In rat cerebral cortex, age-associated macromolecular damage, decline in endogenous antioxidants and an increase in intracellular calcium concentration were significantly reversed due to oral supplementation of Crocin. Cro 150 significantly improved acetylcholine content as a consequence of acetylcholinesterase inhibition. Further, remarkable mitochondrial function was observed in Cro 150 over the control group as determined by citrate synthase and cytochrome C oxidase enzyme activities.

SIGNIFICANCE

Oral supplementation of Crocin significantly reversed age-associated oxidative stress and neuroinflammatory markers. Meanwhile, Cro 150 remarkably improved cholinergic and mitochondrial function over the control group and facilitated further delay in the aging process due to enhanced cognitive effect.

The role of melatonin, a multitasking molecule, in retarding the processes of ageing

Biological ageing is generally accompanied by a gradual loss of cellular functions and physiological integrity of organ systems, the consequential enhancement of vulnerability, senescence and finally death. Mechanisms which underlie ageing are primarily attributed to an array of diverse but related factors including free radical-induced damage, dysfunction of mitochondria, disruption of circadian rhythms, inflammaging, genomic instability, telomere attrition, loss of proteostasis, deregulated sensing of nutrients, epigenetic alterations, altered intercellular communication, and decreased capacity for tissue repair. Melatonin, a prime regulator of human chronobiological and endocrine physiology, is highly reputed as an antioxidant, immunomodulatory, antiproliferative, oncostatic, and endocrine-modulatory molecule. Interestingly, several recent reports support melatonin as an anti-ageing agent whose multifaceted functions may lessen the consequences of ageing. This review depicts four categories of melatonin's protective effects on ageing-induced molecular and structural alterations. We also summarize recent findings related to the function of melatonin during ageing in various tissues and organs.

Comparing the Behavioural Effects of Exogenous Growth Hormone and Melatonin in Young and Old Wistar Rats

Growth hormone (GH) and melatonin are two hormones with quite different physiological effects. Curiously, their secretion shows parallel and severe age-related reductions. This has promoted many reports for studying the therapeutic supplementation of both hormones in an attempt to avoid or delay the physical, physiological, and psychological decay observed in aged humans and in experimental animals. Interestingly, the effects of the external administration of low doses of GH and of melatonin were surprisingly similar, as both hormones caused significant improvements in the functional capabilities of aged subjects. The present report aims at discerning the eventual difference between cognitive and motor effects of the two hormones when administered to young and aged Wistar rats. The effects were tested in the radial maze, a test highly sensitive to the age-related impairments in working memory and also in the rotarod test, for evaluating the motor coordination. The results showed that both hormones caused clear improvements in both tasks. However, while GH improved the cognitive capacity and, most importantly, the physical stamina, the effects of melatonin should be attributed to its antioxidant, anxiolytic, and neuroprotective properties.

Serine racemase: a key player in apoptosis and necrosis

A fine balance between cell survival and cell death is required to sculpt the nervous system during development. However, an excess of cell death can occur following trauma, exposure to neurotoxins or alcohol, and some developmental and neurodegenerative diseases, such as Alzheimer's disease (AD). N-Methyl-D-aspartate receptors (NMDARs) support synaptic plasticity and survival of many neuronal populations whereas inappropriate activation may promote various forms of cell death, apoptosis, and necrosis representing the two extremes of a continuum of cell death processes both “in vitro” and “in vivo.” Hence, by identifying the switches controlling pro-survival vs. apoptosis and apoptosis vs. pro-excitotoxic outcome of NMDAR stimulation, NMDAR modulators could be developed that selectively block the cell death enhancing pro-survival signaling or synaptic plasticity mediated by NMDAR. Among these modulators, a role is emerging for the enzyme serine racemase (SR) that synthesizes D-serine, a key co-agonist with glutamate at NMDAR. This review summarizes the experimental evidence from “in vitro” neuronal cultures—with special emphasis on cerebellar granule neurons (CGNs)—and “in vivo” models of neurodegeneration, where the dual role of the SR/D-serine pathway as a master regulator of apoptosis and the apoptosis-necrosis shift will be discussed.