Crosstalk Between Aging,Circadian Rhythm,and Melatonin

Abstract

Circadian rhythms (CRs) are 24-hour periodic oscillations governed by an endogenous circadian pacemaker located in the suprachiasmatic nucleus (SCN), which organizes the physiology and behavior of organisms. Circadian rhythm disruption (CRD) is also indicative of the aging process. In mammals, melatonin is primarily synthesized in the pineal gland and participates in a variety of multifaceted intracellular signaling networks and has been shown to synchronize CRs. Endogenous melatonin synthesis and its release tend to decrease progressively with advancing age. Older individuals experience frequent CR disruption, which hastens the process of aging. A profound understanding of the relationship between CRs and aging has the potential to improve existing treatments and facilitate development of novel chronotherapies that target age-related disorders. This review article aims to examine the circadian regulatory mechanisms in which melatonin plays a key role in signaling. We describe the basic architecture of the molecular circadian clock and its functional decline with age in detail. Furthermore, we discuss the role of melatonin in regulation of the circadian pacemaker and redox homeostasis during aging. Moreover, we also discuss the protective effect of exogenous melatonin supplementation in age-dependent CR disruption, which sheds light on this pleiotropic molecule and how it can be used as an effective chronotherapeutic medicine.

Introduction

Circadian rhythms (CRs) are rhythmic patterns that occur approximately every 24 hours in various biological processes, including sleep/wake cycles, hormone regulation, attention, cognitive function, and emotional state.¹ These inherent rhythms play a vital role in the survival of organisms as they enable synchronization of internal biological functions with external cues from the environment, particularly the alternating light and dark cycles.

CRs are found in a wide range of living organisms, spanning from microorganisms to higher mammals.² Within mammals, the circadian pacemaker is located in the brain, specifically in a region called the suprachiasmatic nucleus (SCN).³ The SCN functions as the master biological clock, coordinating the peripheral circadian clocks to ensure optimal performance in response to external time cues (zeitgebers). This synchronization is crucial for maintaining a healthy and efficient timekeeping system.⁴

The SCN regulates rhythmic oscillations through a neuronal pathway that influences secretion of melatonin by the pineal gland.⁵ The decrease in melatonin production observed during the aging process is attributed to the circadian system's inability to accurately coordinate peripheral rhythms. This occurs because melatonin regulates the activity of the SCN through a feedback mechanism that inhibits its function.⁶

The rhythmic patterns of CRs undergo significant alterations as individual age, and these changes can potentially exacerbate the progression of the aging process.⁷ Aging is a natural and universal phenomenon characterized by the gradual accumulation of physical and molecular dysfunction, deterioration of tissues, and reduced organ function. These changes increase susceptibility to age-related diseases and, ultimately, result in death.⁸ Research conducted on molecular clocks in animal models demonstrates that as animals age, there is a decline in both the strength and consistency of rhythmic patterns.^9,10

Circadian rhythm disruption (CRD), which refers to a disturbance in biological timing, can manifest at various organizational levels within an organism. This disruption can affect diverse aspects, ranging from the molecular rhythms of individual cells to the misalignment of behavioral cycles with environmental fluctuations.¹¹ CRD can lead to various physiological irregularities, such as metabolic abnormalities,¹² neurodegeneration,¹³ disturbances in the sleep–wake cycle,¹⁴ oxidative damage,¹⁵ compromised DNA damage response,¹⁶ and reduced activity levels.¹⁷

Considering the current understanding of the aging mechanism, there is a proposal to investigate chronotherapeutic methods to downregulate the adverse effects of aging. This approach focuses on addressing disruptions in the CR to encourage a state of healthy aging.¹⁸ In this context, exogenous melatonin has been suggested as a versatile compound with the potential to slow down various age-related processes. These include disturbances in the CR, changes in metabolism, inflammation, oxidative stress (OS), and mitochondrial dysfunction.

Collectively, this review article examines the interplay between CRs and aging mechanisms. Additionally, it summarizes the latest discoveries regarding utilization of exogenous melatonin as a chronotherapeutic drug against deleterious effects of CRD during aging.

Ethical Approval No: IAEC/AU/2019(1)/08.

The Circadian System

Continuous rotation of the Earth around the Sun, along with rotation on its axis, gives rise to an intricate, yet remarkably predictable, series of rhythmic alterations in the physical environment. Synchronization of rhythms to exactly 24 hours is achieved through entrainment to environmental cues known as zeitgebers, such as the daily alternation of day and night or temperature variations.

Entrainment results in establishment of a distinct phase of expression, where a particular point in a rhythmic process (such as a peak or trough) becomes associated with a specific time of day. The circadian clock governs the regulation of numerous processes, making chronobiology crucial for comprehending how neuronal function is temporally regulated. The circadian pacemaker in mammals is situated within the SCN, which receives direct input from the retina and is responsible for synchronizing the internal rhythms with external light cues.¹⁹

The cells within the SCN operate as a closely interconnected network of neurons, and the neuropeptides, vasopressin and vasoactive intestinal peptide (VIP), play significant roles in facilitating communication between these cells.²⁰ The pacemaker located in the SCN also governs the synchronized phase observed in various other tissues throughout the body. Cells outside of the SCN possess an independent circadian rhythmicity.²¹

Our current understanding of how the SCN controls rhythmic activity in peripheral tissues is very limited and needs to be explored. However, experiments have indicated the significance of neuronal signals, humoral signals, and intermediary pathways that are influenced by factors such as food intake and body temperature.^22,23

Each cell possesses a molecular clock that constitutes an essential component of the circadian system (Fig. 1). The molecular clock comprises a transcriptional/translational feedback loop (TTFL) that undergoes cyclical activity lasting ∼24 hours even in the absence of external stimuli.²⁴ Light is recognized as the most influential zeitgeber, although the feeding cycle, temperature, and physical exercise can also serve as external stimuli for resetting the circadian clock.²⁵

FIG. 1.

Mammalian circadian clock. Ccgs, clock-controlled genes; BMAL1, brain and muscle Arnt-like protein 1; CLOCK, circadian locomotor output cycles kaput; CRY, cyrptochrome; PER, period homolog; ROR, retinoid-related orphan receptor.

The primary transcriptional activators encompass proteins known as circadian locomotor output cycles kaput (CLOCK), which bind to brain and muscle Arnt-like protein 1 (BMAL1). These proteins form a heterodimer that recognizes E-box motifs and governs the expression of numerous genes.²⁶ Among the clock-controlled genes, there are genes such as period (Per1, Per2, and Per3) and cryptochrome (Cry1 and Cry2), which function as repressors.²⁷ During the 24-hour cycle, PER and CRY proteins are phosphorylated and subsequently return to the nucleus to hinder the transcriptional activity of the CLOCK-BMAL1 complex. This inhibition leads to suppression of their expression, forming a negative feedback loop.

Furthermore, additional pivotal regulators of the circadian clock include the nuclear receptors, REV-ERBα and REV-ERBβ, along with the retinoic acid orphan receptors (RORs) (RORα, RORβ, and RORγ), which together form another feedback loop.²⁸ In particular, REV-ERBs function as transcriptional inhibitors of BMAL1 expression, whereas RORs play a positive role in regulating BMAL1 expression. RORs achieve this by binding to specific sites known as retinoic acid receptor-related orphan receptor elements (ROREs) located in the promoter region of the BMAL1 gene.

Collectively, these TTFLs operate in a cyclical manner and are fundamental for establishment of biological rhythms.²⁹

The Circadian Clock Network During Aging

To synchronize clocks in peripheral tissues, the master circadian clock, SCN, plays several roles that are altered throughout aging. For instance, the reduced ability of the lens to transmit light in older individuals leads to diminished sensitivity in detecting and responding to light as a signal for synchronization,³⁰ fewer retinal ganglion cells with intrinsic photoreceptors that transmit photic information to the SCN,³¹ and reduction in the functioning of the SCN itself.

A neurotransmitter VIP, an essential regulator of intercellular communication among individual SCN neurons, is expressed by fewer neurons in the old SCN in comparison with the young SCN.³² In addition, the SCN in older people exhibits a decrease in the number of synaptic terminals and an alteration in the intercellular connectivity between individual neurons.³³ As a result, the combined decline in (a) sensitivities to light input, (b) signal transmission efficiency, and (c) connectivity within neural networks leads to a diminished ability of the aging SCN to respond effectively to light stimuli.

Since there is a functional decline in the SCN with age, it significantly affects longevity. Transplanting the SCN from a young hamster into an old hamster extends life expectancy by ∼20%.³⁴ During aging, SCN neuronal cells have a lower circadian amplitude in intracellular signaling, and aging affects core clock gene expression in the SCN in a gene-specific manner.³⁵ These factors are likely implicated in the diminishing circadian clock outputs observed with age.

Bidirectional relationship between aging and CRs

With the continuous increase in the population of older individuals, it becomes imperative to enhance our understanding of the interdependent association between aging and CRs. Aging and age-related disorders are frequently a consequence of alterations in circadian clock functioning. Furthermore, some alterations may be indicators of/and triggers for age-related neurological diseases and cancer. Nevertheless, it remains uncertain whether circadian disruptions are indicative of the aging process itself or if these disturbances potentially contribute to accelerated aging and development of age-related disorders.

Disruptions in CR and sleep are common features of age-related disorders. For instance, people with neurodegenerative conditions such as Alzheimer's Disease frequently experience aggravated rhythmic disturbances.⁷ Furthermore, sleep deprivation can impact the immune system and contribute to cardiovascular disorders, with elderly individuals being particularly susceptible to more severe effects.³⁶

Modern lifestyle and a growing aged population simultaneously exposed to persistent disturbances in CRs, including shift work and irregular sleep patterns. Multiple studies indicate that CRD has the potential to hasten the aging process and contribute to the development of age-related disorders.³⁷ For example, numerous studies investigating chronic jet lag suggest that circadian disruptions raise the risk of cancer, and individuals engaged in shift work may have an increased susceptibility to developing cancer.³⁸

Consequently, circadian disturbances could result in age-related disorders. Avoiding light exposure at night and using bright light therapy are two ways people can perhaps enhance their CRs and sleeping habits. Understanding the connection between CRs and aging will not only help us with better treatment for elderly people but will also help to identify the cyclic disturbances that can cause age-related disorders.

Effect of Melatonin on SCN

The pineal gland releases melatonin during the dark period of the light–dark cycle and it suppresses the function of the master circadian clock through a feedback inhibitory mechanism.³⁹ It was commonly assumed that the impact of melatonin on the clock network in the SCN and other areas was attributable to the levels of circulating melatonin in blood.

This assumption was based on the well-established recognition of the blood melatonin rhythm for about 50 years, which has been extensively observed in numerous mammalian species.^40,41 The temporal pattern of melatonin in the bloodstream usually exhibits a gradual increase after the onset of darkness, reaching its highest point during the middle of the dark period, and subsequently decreasing during the latter half of the night.

On the other hand, the rhythmicity of melatonin in cerebrospinal fluid (CSF) rises promptly after the start of darkness, remains consistently elevated throughout the night, and experiences a sharp decline at the onset of light. Moreover, it is common for the amplitude of melatonin in the CSF to be higher compared with its levels in the bloodstream.⁴²

We proposed that instead of relying on blood melatonin levels, the CR of melatonin in the CSF plays a crucial role in synchronizing the master circadian clock as it detects the beginning and end of darkness more precisely. Subtle aspects of the melatonin rhythm in the CSF enable it to be more suitable for this role. Melatonin can readily reach SCN neurons that possess MT1 receptors by diffusing from the CSF in the supraoptic recess to adjacent responsive cells.

Alternatively, it can be transported from the CSF to the SCN through tanycytes.⁴³ If exogenous melatonin treatment leads to significantly higher levels of melatonin in the bloodstream compared with the CSF, these elevated blood levels likely override the signal provided by the concurrently reduced CSF melatonin levels. In such cases, melatonin acts as a chronobiotic for SCN.^44,45 This reveals how peripherally administered melatonin may serve as a pharmacological agent that affects the SCN rhythmic functions.

The SCN processes a variety of inputs and delivers neuronal and endocrine signals to peripheral oscillators in all cells to control physiological and behavioral responses, ensuring that they are temporally appropriate.⁴⁶ Even though in several species different brain areas have significantly different distributions of melatonin receptors in the central nervous system,⁴⁷ most mammals possess a significant quantity of high-affinity MT1 melatonin receptors that are coupled to G-proteins.⁴⁸ These receptors play a crucial role in mediating various functions of melatonin in the inherent circadian oscillations of the central endogenous clock.

However, there is another hypothesis that melatonin may directly interact with the SCN cells' proteasome, irrespective of any receptors, to alter temporal fluctuations in molecular clock genes.⁵ The predominant light–dark environment strongly affects the electrical circuitry and metabolic regulations of the SCN neurons. For example continuous exposure to artificial light particularly of short wavelengths causes phase shift in circadian amplitude.

Several investigations have documented the correlation between SCN and age-related neurodegenerative disorders.^13,49 For example, the functional decline of SCN plays a crucial part in the pathogenesis of AD and progression of sleep disturbances.⁵⁰ Wu and colleagues⁵¹ investigated the immunohistochemistry of the SCN in young and old participants and found that the number and density of MT1-expressing neurons decreased significantly in the older group.

Additionally, researchers observed that expression of MT1 receptors was exceedingly low in the advanced neuropathological stages of AD (Braak stages V–VI). As an individual ages, the presence of a consistent circadian melatonin pattern could potentially work in conjunction with SCN neurons to prevent neuronal degeneration and sustain CRs in the body. Maintaining persistent circadian rhythmicity is a beneficial characteristic that may contribute to delaying neurocognitive decline.^52,53

Melatonin and Regulation of Clock Genes

Since melatonin is mainly produced at night, it is often considered the “hormone of darkness.”⁵⁴ The length of the night is also reflected in the time that the nocturnal peak of melatonin secretion lasts.⁵⁵ Therefore, it is believed that the diurnal rhythms of melatonin are essential for healthy circadian function.⁵⁶ The existence of melatonin receptors explains the direct action of melatonin on various organs.

The relationship between melatonin production and the CR mechanism may be shown by the presence of melatonin receptors in the SCN and the regular synthesis of melatonin. The expression of circadian clock genes (CCGs) has been investigated in mice that possess normal levels of melatonin and in proficient mice (C3H), as well as mice that lack melatonin (C57BL).

Reduced levels of BMAL1, PER1, and CRY2 were found in the adrenal cortical region of C57BL mice when compared with C3H mice.⁵⁷ Pinealectomized mice did not exhibit diurnal cycles of Per1 mRNA and their protein levels in the striatum.⁵⁸ Melatonin lowered the expression of Per1 and Clock in primary neuronal cells generated from the murine striatum, while it enhanced the expression of NPAS2 and had no influence on the level of Bmal1. However, MT1 knockout animals did not exhibit these effects.⁵⁹

In a study examining the effects of melatonin on hypertensive TGR (mRen2)27 rats, it was observed that the expression of Per2 and Bmal1 in the heart was influenced by melatonin in a phase-dependent manner, particularly during the dark phase. These findings suggest that melatonin plays a role in regulating clock genes, although the exact mechanisms involved remain unclear.⁶⁰

In a study conducted by Mattam and Jagota,⁶¹ rats belonging to different age groups were administered melatonin (30 μg/kg) 1 hour before the onset of the dark phase [zeitgeber time (ZT)-11] for 11 days.⁶¹ Regardless of the light–dark phase or age group, administration of melatonin resulted in elevated levels of Bmal1, Per1, Per2, Cry1, and Cry2 mRNAs. These findings indicate that melatonin directly influences the transcription of these clock genes, although the gene expression patterns vary with the age of the animals.

Melatonin acts as a proteasome inhibitor, interfering with molecular loops to enhance BMAL1 and, subsequently, transcription of the Bmal1, Per, and Cry genes.⁶² Transcriptional modification in the nuclear orphan receptors (Rors and Rev-Erbα mRNAs) was used to assess the chronobiotic functions of melatonin. While melatonin did not affect Rorα, it effectively prevented Rorβ levels from dropping in the early hours.

In the first subjective night after melatonin administration, expression of Rev-Erbα was phase advanced; however, Bmal1 was merely phase shifted on the second night.⁶³ Therefore, the authors postulated that melatonin and the molecular clock machinery may be connected by the nuclear orphan receptor genes.

Circadian Clock, OS, and Aging

An imbalance that favors oxidants over antioxidants, which disrupts cellular redox homeostasis and control and/or causes molecular damage, is referred to as OS.⁶⁴ An important aspect of the aging process involves a rise in OS, which is considered to be among the molecular mechanisms believed to contribute to the onset and progression of various age-associated diseases. OS is triggered and regulated by a variety of factors.

Strong evidence suggests that OS is caused by mitochondrial dysfunction and contributes to age-related functional decline, in part, by oxidative damage.⁶⁵ Additionally, several signaling pathways control OS. In cells of higher living organisms, both Nrf2 and NFkB signaling mechanisms are regarded as the central switch that regulates OS.⁶⁶

Numerous studies demonstrate the link between disruption of the abovementioned mechanisms of OS and aging.^67,68 The disruption of sleep–wake patterns, resulting from an increase in OS, has been suggested to share similarities with the aging process. This phenomenon is believed to be partially attributed to the progressive accumulation of oxidative damage during aging.⁶⁹

Mice that have particular gene disruptions in the insulin/insulin-like growth factor (IGF) pathway, apoptosis, redox homeostasis, chromosome stability, controlling of the mutation rate, and telomere stability exhibit signs of accelerated aging.^70

–75 In the presence of neurological diseases, interruption in circadian clock function may make the brain more susceptible to oxidative damage and promote neurodegeneration.⁷⁶

Strong evidence suggests a relationship between the cellular balance of redox reactions and the functioning of the circadian clock.⁷⁷ The circadian system maintains reactive oxygen species (ROS) within normal physiological levels and protects living organisms against oxidative damage.⁷⁸ According to studies, BMAL1 is required for promotion of antioxidant defense to protect cells from OS or aging.⁷⁹

Additionally, BMAL1 activates the Nrf2 pathway and B cell lymphoma-2 (Bcl-2) response to maintain the antioxidant capacity within vascular smooth muscle cells.⁸⁰ These findings suggest that the role of BMAL1 is crucial in orchestrating the Nrf2-dependent antioxidant defense mechanism, which serves to counteract OS and mitigate the aging process.

OS and BMAL1/CLOCK genes

Increased OS caused by the global loss of BMAL1 accelerates aging phenotypes.⁸¹ Additionally, there is convincing evidence that BMAL1 controls ROS in a variety of distinct tissue types. Deletion of brain BMAL1 causes OS-mediated neurodegenerative processes and astrogliosis.⁷⁶ B cell failure triggered by OS and BMAL1 deletion in the pancreas results in the diabetes phenotype.⁸² However, the use of the glutathione precursor, N-acetyl-cysteine, can reverse the accelerated aging phenotype caused by BMAL1 knockout.⁸³

All the evidence points to the crucial role of OS in the aging phenotype caused by BMAL1 deficiency. Additionally, arrhythmic per01 flies have shown substantially higher amounts of protein carbonylation and increased lipid hydroperoxidation during aging.⁸⁴ Both in vitro and in vivo experimental settings suggest that reduced Bmal1 expression further worsens OS-induced neuronal death.⁷⁶

The most remarkable neurological abnormalities that Bmal1 ⁻-deficient mice exhibit are reduced brain functional communication, increased OS, synaptic deterioration, extensive astrogliosis,⁷⁶ impaired neurogenesis in the hippocampus,⁸⁵ and weakened memory and learning behavior.⁸⁶ Studies have demonstrated that BMAL1 plays a direct role in regulating the balance of ROS, indicating its potential involvement in the protective mechanisms employed by cells and tissues to counteract OS.⁸⁷

Additionally, CLOCK is involved in the regulation of various forms of senescence or the aging process in organs. According to Musiek et al.,⁷⁶ eliminating the clock genes (either BMAL1 or CLOCK) results in oxidative harm, significant activation of astrocytes, deterioration of axonal terminals, and disturbance in the functional connectivity observed during periods of rest. This discovery establishes a new connection between CCGs, oxidative injury in the brain, and the neurodegenerative process.

An earlier study revealed that CLOCK^Δ19 mutant mice exhibit a noticeable increase in peroxidation and endoplasmic reticulum stress (ERS), which ultimately leads to a striking representation of liver aging.⁸⁸

Melatonin as a Potential Antioxidant

Maintaining cellular redox balance is crucial for various physiological functions and is dependent on the proper control of ROS production and elimination. This equilibrium plays a significant role in regulating signaling pathways as well as facilitating the activation of redox-sensitive proteins and enzymes. Melatonin can counteract both ROS and reactive nitrogen species (RNS).⁸⁹

Due to its amphipathic nature, melatonin can effectively traverse cell membranes, enabling it to protect the subcellular compartments from damage caused by free radicals.⁹⁰ Melatonin achieves redox control through its ability to directly scavenge ROS using defense mechanisms of both enzymatic and nonenzymatic antioxidants.^91
–93 With its aromatic indole ring containing a plentiful supply of electrons, melatonin acts as a potent electron donor, effectively neutralizing free radicals and demonstrating its direct antioxidant characteristics.^90,94

Melatonin exhibits indirect antioxidant properties by stimulating the activation of antioxidant enzymes such as SOD, GSH-Px, and CAT⁹⁵ and by promoting the synthesis of glutathione.⁹⁶ These actions enhance the effectiveness of other antioxidants, leading to a combined synergistic effect.⁹⁷

Melatonin elicits cellular responses through both receptor-mediated and receptor-independent pathways.⁹⁸ Melatonin possesses the ability to directly traverse cell membranes without relying on receptors, enabling it to scavenge ROS within the cytosol and mitochondria of the cell. Melatonin is concentrated within the mitochondria, where it neutralizes both ROS and RNS.⁹⁹

Furthermore, melatonin provides a defense against the peroxidation of cardiolipin and protects respiratory chain complexes and mtDNA against oxidative damage induced by free radicals.¹⁰⁰ The antiapoptotic action of melatonin inhibits the function of Bax, resulting in a reduction in the opening of the mitochondrial permeability transition pore (mPTP) and ultimately decreasing the permeability of the membrane.^101,102

Melatonin and Nrf2

Nrf2 is acknowledged as the primary defense mechanism against OS, occupying a pivotal position in the transcriptional control of genes responsible for the synthesis of antioxidant enzymes, antiapoptotic transcription factors, detoxifying molecules, and drug transporters.¹⁰³ Research findings have indicated that melatonin enhances upregulation of genes and proteins linked to Nrf2 signaling and the functions of the peroxisome. By eliminating dysfunctional organelles such as mitochondria, autophagy mediated by Nrf2 enhances the effectiveness of adaptive mechanisms.¹⁰⁴

Melatonin shields Nrf2 from degradation and initiates the activation of the Keap1-ARE (Kelch-like ECH-associated protein 1–antioxidant response element) pathway.^105,106 The interaction between melatonin and Nrf2 enhances various beneficial effects, including cardioprotection, neuroprotection, antioxidant activity, anti-inflammatory effects, and antitumor effects, as well as improvements in bone microstructure and oocyte maturation.^107,108

Mitochondrial aging and melatonin

Aging contributes significantly to the decline in respiratory chain efficiency, amplification of electron leakage, and decrease in ATP synthesis, collectively resulting in mitochondrial dysfunction.¹⁰⁹ As a result, the impaired function of mitochondria initiates generation of ROS, subsequently promoting additional mitochondrial injury and cell death.¹¹⁰ The level of melatonin within mitochondria seems to be higher than the amount found in the bloodstream.¹¹¹ This is particularly advantageous since free radicals primarily originate from these cellular organelles.

Apart from efficiently counteracting ROS within these organelles, melatonin can decrease electron leakage from complexes within the mitochondrial respiratory chain, thereby enhancing ATP synthesis.¹¹² The action of reducing electron leakage also leads to a decrease in generation of free radicals, a phenomenon commonly referred to as radical avoidance.¹¹³ Melatonin demonstrates remarkable effectiveness in repairing damage, specifically targeting complexes I and IV.

Moreover, melatonin protects against the harmful effects induced by mitochondrial Ca²⁺ overload and depolarization of the mitochondrial membrane caused by H₂O₂, both of which are associated with caspase-mediated apoptosis.¹¹⁴ Based on the mechanism, melatonin-induced pro-oxidant activity can accelerate production of ROS by interacting with calmodulin. The interplay between melatonin and opening of mitochondrial transition pores or its complex III also stimulates generation of ROS.^89,115

Mitophagy and melatonin

Mitophagy plays a crucial role in preserving the redox stability of mitochondria by effectively reducing excessive production of ROS at the same time. Melatonin has exhibited promising potential in treating mitochondrial dysregulation through stimulation of mitophagy.¹¹⁶ Since mitochondrial oxidative damage is believed to be both the source and a potential target of ROS, reduced mitophagy is directly associated with decreased life span (Fig. 2).^117,118

FIG. 2.

Effect of melatonin on consequences associated with CRD. An excess of ROS results in oxidative injury, which contributes to onset of diseases and reduces the life span. Melatonin directly inhibits ROS and downregulates the expression of CCGs through feedback inhibitory mechanisms. The disturbance of circadian rhythms hinders the upkeep of physiological and cellular balance, leading to cellular senescence, mitochondrial dysfunction, and an accelerated aging process. Stimulation is indicated by arrows, while reduced responses are indicated by dashed arrows. ROS, reactive oxygen species; CCG, circadian clock gene; CRD, circadian rhythm disruption; MLT, melatonin.

Melatonin decreases the leakage of electrons from mitochondria, thereby reducing the production of ROS while preventing mPTP opening in unfavorable bioenergetic conditions, thereby preserving mitochondrial membrane potential (Δψ). Additionally, in normal circumstances, melatonin stimulates uncoupler proteins to gradually decrease Δψ.¹¹⁹

Emerging senotherapeutic approaches that focus on mitochondria and aim to activate melatonin-induced mitophagy have the potential to improve mitochondrial dysfunctions. Several feasible interventions, such as melatonin, have been examined for their potential to slow down aging in the senescence-accelerated mouse prone 8 (SAMP8) strain, although they have yielded conflicting results.^120
–122

Melatonin treatment can regulate molecular and morphological characteristics associated with senescence. Studies have shown that melatonin can enhance mitochondrial oxidative phosphorylation in both liver and brain tissues.^123,124 Mesenchymal stem cells (MSCs) undergoing replicative senescence often experience reduced mitophagy due to inhibition of mitofission, leading to increased mitochondrial dysfunction.

The treatment with melatonin inhibited replicative senescence by enhancing mitophagy and promoting mitochondrial activity through upregulation of the heat shock 70-kDa protein 1L (HSPA1L).¹²⁵ Although it is not possible to halt the natural aging process, mitigating the disruptive consequences of age-related changes in overall homeostasis in individuals is certainly achievable. The current utilization of melatonin as both a senotherapeutic and chemotherapeutic agent indicates that melatonin will continue to be extensively investigated in the future as one of the prominent molecules of interest.

Melatonin, aging, and CRD

It has been demonstrated that age-related alterations in melatonin synthesis are linked to CRD. Adults have a 200%–300% a rhythm-adjusted mean (MESOR) variation in the melatonin circadian pattern in their blood and saliva, but this amplitude is barely noticeable in people older than 80 years and decreases considerably after the sixth decade of life.¹²⁶ Although both MESOR and amplitude decrease, the synthesis of melatonin continues in longer lived humans.

Some authors contend that pineal production of melatonin declines with age and is not a necessary component of the aging process, while there have been several reports about the multiple beneficial impacts of melatonin on gerontological practice, and the effectiveness of melatonin in extending the life span has been shown in human beings as well as animals.^127,128 Importantly, changes in CRs of melatonin excretion are a major factor in peripheral mechanisms that interfere with a biosystem's natural temporal patterns during aging.¹²⁸

Prevention of the symptoms of age-related circadian disturbances is one of the possible mechanisms that allow the geroprotective action of melatonin.¹²⁹ Additionally, since melatonin deficit is linked to the advancement of macular degeneration, it suggests that inadequate endogenous production of melatonin escalates the signs of age-associated CRD, which have a connection to the afferent component of the circadian system.¹³⁰

Interestingly, chromaffin cells of the intestine were found to produce less endogenous melatonin during aging.¹³¹ These findings suggest that endogenous production of melatonin in the intestine as well as pharmaceuticals derived from melatonin may be crucial for preventing oxidative damage and tissue-specific CRD, which work in combination with melatonin synthesized by the pineal gland.

Melatonin's primary chronobiotic effect is its hypothermic action, which is linked to an increase in sleep quality and contributes to prevention of CRD, particularly that connected to aging.¹³² Interneuronal connectivity in the SCN deteriorates as a result of the SCN's impaired ability to compensate for temperature variations; therefore, the temperature factor plays a more substantial part in synchronization of CRs and contributes to resynchronization of neurons.¹³³

These CRDs are not only present in old mammals but can also be seen in middle-aged individuals.^9,134 A double-blind placebo-controlled investigation demonstrated that melatonin effectively restores age-related CRD by synchronizing the rhythmicity of body temperature, blood pressure, and heart rate.¹³⁵

Melatonin plays an important role in maintaining normal sleep patterns.¹³⁶ Currently, the disturbances in sleep observed among several aged individuals are believed to be mainly attributed to modulations in the CR.¹³⁷ The higher prevalence of insomnia during aging is attributed to dysregulation of the brain processes that maintain CRs and sleep–wake cycle patterns.¹³⁸

The circadian system is adversely affected by exposure to artificial light at night due to reduction in the release of the melatonin hormone,^94,139 which can lead to the emergence of CRD. Reduced melatonin levels accelerate aging, raise the probability of developing malignant tumors early in life and metabolic diseases, and ultimately shorten the life span.^128,130,140 Due to its ability to act as an antioxidant, prevent persistent inflammation,¹⁴¹ and exhibit contrasting impacts on cell apoptosis in both healthy and cancerous states, melatonin plays a vital role in prolonging the life span and delaying the initiation of the aging process.

Melatonin seems to be inadequate for treating sleep disorders in shift workers—rather, it may lengthen their sleep cycles¹⁴² with almost no side effects, as assessed in various clinical investigations and comparative trials throughout short periods (up to 3 months, at low doses).^143,144 Low doses of melatonin are generally safer and an improved substitute for sleeping pills that cannot be taken for an extended duration because they are not advised for long-term usage.¹⁴⁴

Melatonin-rich supplements could lengthen rest periods, delay disease onset, and reduce nighttime awakenings in individuals suffering from autism, particularly in children.^145,146 Recent research indicates that melatonin may be an effective and safe treatment for depression and sleeplessness in adults and children with attention-deficit/hyperactivity disorders, but longer and more comprehensive trials are required to determine the drug's long-term safety and ideal dosages.^147,148

Developing metabolic phenotype technologies can assist in identifying markers that accurately reflect how melatonin affects sleep, aging, and onset of diseases.^130,149

Conclusions

CRs are governed by an internal timekeeping machinery that regulates physiological and behavioral processes. The circadian clock is positively influenced by CLOCK and BMAL1, transcription factors that regulate the functioning of the circadian pacemaker. CRs contribute to the functioning of various physiological processes and individuals experience changes as a result of aging and associated diseases.

As organisms age, a decline in melatonin levels is commonly observed. This decrease in melatonin can result in various symptoms affecting the internal equilibrium of the organism. One of the frequently observed manifestations of this process is the deterioration of cellular clock regulation, leading to disruptions in proper functioning. Furthermore, the combination of diminished mitochondrial integrity and impaired functions, along with reduced melatonin levels, increases the vulnerability of older individuals to impaired regulation of redox processes and age-related disorders.

Age-related health abnormalities have a direct correlation with CRD. Increasing evidence from diverse organisms indicates that mutations in CCGs result in premature aging, shortened life span, and disturbances in sleep patterns. ROS are generated as by-products during mitochondrial energy metabolism, primarily within the electron transfer chain.

The circadian clock is intricately linked to the mitochondrial physiology and contributes to the regulation of ROS by coordinating generation of ROS within mitochondria and activation of antioxidant defense mechanisms. Melatonin is recognized as a “master hormonal regulator” that influences the CR, aging process, and cellular activity. Additionally, melatonin holds promise as a pharmacological agent due to its potent antioxidant properties.

The rhythmicity of melatonin in CSF also influences the molecular network within the SCN, thereby preserving optimal CRs. Furthermore, in the aging brain, mitochondria tend to generate excessive, harmful, partially reduced oxygen species. In this context, melatonin serves as a protective neuroendocrine molecule for this tissue by directly scavenging free radicals and stimulating antioxidative enzymes, thus preventing molecular damage.^99,150

The area of chronobiology research is progressively shifting toward developing innovative approaches for chronotherapy by focusing on either the molecular clock or administering medications based on specific times of the day. Enhancing biological clock functions and rectifying its disturbances through pharmacological intervention may offer a novel approach for effective management of aging and age-related diseases in a clinical setting.

To this end, different therapeutic doses of melatonin efficiently restore CRD in humans and distinct animal models of aging and its associated diseases. However, it is essential to conduct longitudinal studies in future, including repeated follow-up assessments, to determine the translational application of these findings in clinical practice.

Footnotes

Authors' Contributions

A.K.V. and S.I.R. contributed to the conceptualization and review and editing of the article. A.K.V. wrote the article. M.I.K. and F.A. contributed to writing—review.

Author Disclosure Statement

No competing financial interests exist.

Funding Information

No funding was received for this article.

References

Ruan

, Yuan

, Eltzschig

. Circadian rhythm as a therapeutic target. Nat Rev Drug Discov, 2021; 20(4):287–307; doi: 10.1038/s41573-020-00109-w

Gentry

, Ashbrook

, Fu

Y-H

, et al. Human circadian variations. J Clin Invest, 2021; 131(16):e148282; doi: 10.1172/JCI148282

Hastings

, Maywood

, Brancaccio

. Generation of circadian rhythms in the suprachiasmatic nucleus. Nat Rev Neurosci, 2018; 19(8):453–469; doi: 10.1038/s41583-018-0026-z

Patke

, Young

, Axelrod

. Molecular mechanisms and physiological importance of circadian rhythms. Nat Rev Mol Cell Biol, 2020; 21(2):67–84; doi: 10.1038/s41580-019-0179-2

Vriend

, Reiter

. Melatonin feedback on clock genes: A theory involving the proteasome. J Pineal Res, 2015; 58(1):1–11; doi: 10.1111/jpi.12189

Albrecht

. Timing to perfection: The biology of central and peripheral circadian clocks. Neuron, 2012; 74(2):246–260; doi: 10.1016/j.neuron.2012.04.006

Hood

, Amir

. The aging clock: Circadian rhythms and later life. J Clin Invest, 2017; 127(2):437–446; doi: 10.1172/JCI90328

Acosta-Rodríguez

, Rijo-Ferreira

, Green

, et al. Importance of circadian timing for aging and longevity. Nat Commun, 2021; 12:2862; doi: 10.1038/s41467-021-22922-6

Nakamura

, Nakamura

, Yamazaki

, et al. Age-related decline in circadian output. J Neurosci, 2011; 31(28):10201–10205; doi: 10.1523/JNEUROSCI.0451-11.2011

10.

Sato

, Solanas

, Peixoto

, et al. Circadian reprogramming in the liver identifies metabolic pathways of aging. Cell, 2017; 170(4):664–677.e11; doi: 10.1016/j.cell.2017.07.042

11.

Mathew

, Luo

, Bhatwadekar

. Circadian rhythm disruption results in visual dysfunction. FASEB Bioadv, 2022; 4(6):364–378; doi: 10.1096/fba.2021-00125

12.

Turek

, Joshu

, Kohsaka

, et al. Obesity and metabolic syndrome in circadian Clock mutant mice. Science, 2005; 308(5724):1043–1045; doi: 10.1126/science.1108750

13.

Verma

, Singh

, Rizvi

. Aging, circadian disruption and neurodegeneration: Interesting interplay. Exp Gerontol, 2023; 172:112076; doi: 10.1016/j.exger.2022.112076

14.

Ehlen

, Brager

, Baggs

, et al. Bmal1 function in skeletal muscle regulates sleep. Elife, 2017; 6:e26557; doi: 10.7554/eLife.26557

15.

Kumar Verma

, Singh

, Srivastava

, et al. Melatonin stabilizes age-dependent alterations in erythrocyte membrane induced by “Artificial Light at Night” in a chronodisrupted model of rat. Gen Comp Endocrinol, 2022; 316:113960; doi: 10.1016/j.ygcen.2021.113960

16.

Shafi

, McNair

, McCann

, et al. The circadian cryptochrome, CRY1, is a pro-tumorigenic factor that rhythmically modulates DNA repair. Nat Commun, 2021; 12(1):401; doi: 10.1038/s41467-020-20513-5

17.

Bunger

, Wilsbacher

, Moran

, et al. Mop3 is an essential component of the master circadian pacemaker in mammals. Cell, 2000; 103(7):1009–1017; doi: 10.1016/s0092-8674(00)00205-1

18.

Vaiserman

, Koliada

, Lushchak

, et al. Repurposing drugs to fight aging: The difficult path from bench to bedside. Med Res Rev, 2021; 41(3):1676–1700; doi: 10.1002/med.21773

19.

, Yt C

S H

, et al. Architecture of retinal projections to the central circadian pacemaker. Proc Natl Acad Sci USA, 2016; 113(21):6047–6052; doi: 10.1073/pnas.1523629113

20.

Ono

, Honma

K-I

, Honma

. Roles of neuropeptides, VIP and AVP, in the mammalian central circadian clock. Front Neurosci, 2021; 15:650154; doi: 10.3389/fnins.2021.650154

21.

Reppert

, Weaver

. Coordination of circadian timing in mammals. Nature, 2002; 418(6901):935–941; doi: 10.1038/nature00965

22.

Schibler

, Gotic

, Saini

, et al. Clock-Talk: Interactions between central and peripheral circadian oscillators in mammals. Cold Spring Harb Symp Quant Biol, 2015; 80:223–232; doi: 10.1101/sqb.2015.80.027490

23.

Silver

, LeSauter

, Tresco

, et al. A diffusible coupling signal from the transplanted suprachiasmatic nucleus controlling circadian locomotor rhythms. Nature, 1996; 382(6594):810–813; doi: 10.1038/382810a0

24.

, Takahashi

. Molecular components of the mammalian circadian clock. Hum Mol Genet, 2006; 15 Spec No 2:R271–R277; doi: 10.1093/hmg/ddl207

25.

Kramer

, Lange

, Spies

, et al. Foundations of circadian medicine. PLoS Biol, 2022; 20(3):e3001567; doi: 10.1371/journal.pbio.3001567

26.

Koike

, Yoo

S-H

, Huang

H-C

, et al. Transcriptional architecture and chromatin landscape of the core circadian clock in mammals. Science, 2012; 338(6105):349–354; doi: 10.1126/science.1226339

27.

Aryal

, Kwak

, Tamayo

, et al. Macromolecular assemblies of the mammalian circadian clock. Mol Cell, 2017; 67(5):770–782.e6; doi: 10.1016/j.molcel.2017.07.017

28.

Fagiani

, Di Marino

, Romagnoli

, et al. Molecular regulations of circadian rhythm and implications for physiology and diseases. Signal Transduct Target Ther, 2022; 7(1):41; doi: 10.1038/s41392-022-00899-y

29.

Partch

, Green

, Takahashi

. Molecular architecture of the mammalian circadian clock. Trends Cell Biol, 2014; 24(2):90–99; doi: 10.1016/j.tcb.2013.07.002

30.

Kessel

, Lundeman

, Herbst

, et al. Age-related changes in the transmission properties of the human lens and their relevance to circadian entrainment. J Cataract Refract Surg, 2010; 36(2):308–312; doi: 10.1016/j.jcrs.2009.08.035

31.

Lupi

, Semo

, Foster

. Impact of age and retinal degeneration on the light input to circadian brain structures. Neurobiol Aging, 2012; 33(2):383–392; doi: 10.1016/j.neurobiolaging.2010.03.006

32.

Krajnak

, Kashon

, Rosewell

, et al. Aging alters the rhythmic expression of vasoactive intestinal polypeptide mRNA but not arginine vasopressin mRNA in the suprachiasmatic nuclei of female rats. J Neurosci, 1998; 18(12):4767–4774.

33.

Nakamura

, Nakamura

, Tokuda

, et al. Age-related changes in the circadian system unmasked by constant conditions. eNeuro, 2015; 2(4):ENEURO.0064-15.2015; doi: 10.1523/ENEURO.0064-15.2015

34.

Hurd

, Ralph

. The significance of circadian organization for longevity in the golden hamster. J Biol Rhythms, 1998; 13(5):430–436; doi: 10.1177/074873098129000255

35.

Zhao

, Warman

, Cheeseman

. The functional changes of the circadian system organization in aging. Ageing Res Rev, 2019; 52:64–71; doi: 10.1016/j.arr.2019.04.006

36.

Balan

, Bilger

, Saparov

, et al. Sleep deprivation in middle age may increase dementia risk: A review. Cureus, 2023; 15(4):e37425; doi: 10.7759/cureus.37425

37.

Stowe

, McClung

. How does chronobiology contribute to the development of diseases in later life. Clin Interv Aging, 2023; 18:655–666; doi: 10.2147/CIA.S380436

38.

Koritala

BSC

, Porter

, Arshad

, et al. Night shift schedule causes circadian dysregulation of DNA repair genes and elevated DNA damage in humans. J Pineal Res, 2021; 70(3):e12726; doi: 10.1111/jpi.12726

39.

Pevet

, Challet

, Felder-Schmittbuhl

M-P

. Melatonin and the circadian system: Keys for health with a focus on sleep. Handb Clin Neurol, 2021; 179:331–343; doi: 10.1016/B978-0-12-819975-6.00021-2

40.

Rusak

, Yu

. Regulation of melatonin-sensitivity and firing-rate rhythms of hamster suprachiasmatic nucleus neurons: Pinealectomy effects. Brain Res, 1993; 602(2):200–204; doi: 10.1016/0006-8993(93)90683-e

41.

Torres-Farfan

, Mendez

, Abarzua-Catalan

, et al. A circadian clock entrained by melatonin is ticking in the rat fetal adrenal. Endocrinology, 2011; 152(5):1891–1900; doi: 10.1210/en.2010-1260

42.

Hedlund

, Lischko

, Rollag

, et al. Melatonin: Daily cycle in plasma and cerebrospinal fluid of calves. Science, 1977; 195(4279):686–687; doi: 10.1126/science.841305

43.

Rodríguez

, Guerra

, Peruzzo

, et al. Tanycytes: A rich morphological history to underpin future molecular and physiological investigations. J Neuroendocrinol, 2019; 31(3):e12690; doi: 10.1111/jne.12690

44.

Cardinali

, Brown

, Pandi-Perumal

. Chronotherapy. Handb Clin Neurol, 2021; 179:357–370; doi: 10.1016/B978-0-12-819975-6.00023-6

45.

Tricoire

, Malpaux

, Møller

. Cellular lining of the sheep pineal recess studied by light-, transmission-, and scanning electron microscopy: Morphologic indications for a direct secretion of melatonin from the pineal gland to the cerebrospinal fluid. J Comp Neurol, 2003; 456(1):39–47; doi: 10.1002/cne.10477

46.

Reiter

, Tan

, Korkmaz

, et al. Melatonin and stable circadian rhythms optimize maternal, placental and fetal physiology. Hum Reprod Update, 2014; 20(2):293–307; doi: 10.1093/humupd/dmt054

47.

Klosen

, Lapmanee

, Schuster

, et al. MT1 and MT2 melatonin receptors are expressed in nonoverlapping neuronal populations. J Pineal Res, 2019; 67(1):e12575; doi: 10.1111/jpi.12575

48.

Pévet

. Melatonin receptors as therapeutic targets in the suprachiasmatic nucleus. Expert Opin Ther Targets, 2016; 20(10):1209–1218; doi: 10.1080/14728222.2016.1179284

49.

Nassan

, Videnovic

. Circadian rhythms in neurodegenerative disorders. Nat Rev Neurol, 2022; 18(1):7–24; doi: 10.1038/s41582-021-00577-7

50.

Van Erum

, Van Dam

, De Deyn

. Sleep and Alzheimer's disease: A pivotal role for the suprachiasmatic nucleus. Sleep Med Rev, 2018; 40:17–27; doi: 10.1016/j.smrv.2017.07.005

51.

Reiter

, Ma

, Sharma

. Melatonin in mitochondria: Mitigating clear and present dangers. Physiology (Bethesda), 2020; 35(2):86–95; doi: 10.1152/physiol.00034.2019

52.

Reiter

, Sharma

, Cucielo

, et al. Brain washing and neural health: Role of age, sleep, and the cerebrospinal fluid melatonin rhythm. Cell Mol Life Sci, 2023; 80(4):88; doi: 10.1007/s00018-023-04736-5

53.

Suofu

, Li

, Jean-Alphonse

, et al. Dual role of mitochondria in producing melatonin and driving GPCR signaling to block cytochrome c release. Proc Natl Acad Sci USA, 2017; 114(38):E7997–E8006; doi: 10.1073/pnas.1705768114

54.

Jenwitheesuk

, Nopparat

, Mukda

, et al. Melatonin regulates aging and neurodegeneration through energy metabolism, epigenetics, autophagy and circadian rhythm pathways. Int J Mol Sci, 2014; 15(9):16848–16884; doi: 10.3390/ijms150916848

55.

Pevet

, Challet

. Melatonin: Both master clock output and internal time-giver in the circadian clocks network. J Physiol Paris, 2011; 105(4–6):170–182; doi: 10.1016/j.jphysparis.2011.07.001

56.

Schroeder

, Colwell

. How to fix a broken clock. Trends Pharmacol Sci, 2013; 34(11):605–619; doi: 10.1016/j.tips.2013.09.002

57.

Torres-Farfan

, Serón-Ferré

, Dinet

, et al. Immunocytochemical demonstration of day/night changes of clock gene protein levels in the murine adrenal gland: Differences between melatonin-proficient (C3H) and melatonin-deficient (C57BL) mice. J Pineal Res, 2006; 40(1):64–70; doi: 10.1111/j.1600-079X.2005.00279.x

58.

, Akhisaroglu

, Ahmed

, et al. The pineal gland is critical for circadian Period1 expression in the striatum and for circadian cocaine sensitization in mice. Neuropsychopharmacology, 2003; 28(12):2117–2123; doi: 10.1038/sj.npp.1300254

59.

Imbesi

, Arslan

, Yildiz

, et al. The melatonin receptor MT1 is required for the differential regulatory actions of melatonin on neuronal “clock” gene expression in striatal neurons in vitro. J Pineal Res, 2009; 46(1):87–94; doi: 10.1111/j.1600-079X.2008.00634.x

60.

Zeman

, Szántóová

, Stebelová

, et al. Effect of rhythmic melatonin administration on clock gene expression in the suprachiasmatic nucleus and the heart of hypertensive TGR(mRen2)27 rats. J Hypertens Suppl, 2009; 27(6):S21–S26; doi: 10.1097/01.hjh.0000358833.41181.f6

61.

Mattam

, Jagota

. Differential role of melatonin in restoration of age-induced alterations in daily rhythms of expression of various clock genes in suprachiasmatic nucleus of male Wistar rats. Biogerontology, 2014; 15(3):257–268; doi: 10.1007/s10522-014-9495-2

62.

Blancas-Velazquez

, Bering

, Bille

, et al. Role and neural regulation of clock genes in the rat pineal gland: Clock modulates amplitude of rhythmic expression of Aanat encoding the melatonin-producing enzyme. J Pineal Res, 2023; 75(2):e12893; doi: 10.1111/jpi.12893

63.

Agez

, Laurent

, Pévet

, et al. Melatonin affects nuclear orphan receptors mRNA in the rat suprachiasmatic nuclei. Neuroscience, 2007; 144(2):522–530; doi: 10.1016/j.neuroscience.2006.09.030

64.

Sies

. Oxidative Stress: Concept and some practical aspects. Antioxidants (Basel), 2020; 9(9):852; doi: 10.3390/antiox9090852

65.

Balaban

, Nemoto

, Finkel

. Mitochondria, oxidants, and aging. Cell, 2005; 120(4):483–495; doi: 10.1016/j.cell.2005.02.001

66.

Sies

. Oxidative stress: A concept in redox biology and medicine. Redox Biol, 2015; 4:180–183; doi: 10.1016/j.redox.2015.01.002

67.

Schmidlin

, Dodson

, Madhavan

, et al. Redox regulation by NRF2 in aging and disease. Free Radic Biol Med, 2019; 134:702–707; doi: 10.1016/j.freeradbiomed.2019.01.016

68.

Tilstra

, Clauson

, Niedernhofer

, et al. NF-κB in aging and disease. Aging Dis, 2011; 2(6):449–465.

69.

Koh

, Evans

, Hendricks

, et al. A Drosophila model for age-associated changes in sleep: Wake cycles. Proc Natl Acad Sci U S A, 2006; 103(37):13843–13847; doi: 10.1073/pnas.0605903103

70.

Chang

, Multani

, Cabrera

, et al. Essential role of limiting telomeres in the pathogenesis of Werner syndrome. Nat Genet, 2004; 36(8):877–882; doi: 10.1038/ng1389

71.

Kujoth

, Hiona

, Pugh

, et al. Mitochondrial DNA mutations, oxidative stress, and apoptosis in mammalian aging. Science, 2005; 309(5733):481–484; doi: 10.1126/science.1112125

72.

Kurosu

, Yamamoto

, Clark

, et al. Suppression of aging in mice by the hormone Klotho. Science, 2005; 309(5742):1829–1833; doi: 10.1126/science.1112766

73.

Mounkes

, Kozlov

, Hernandez

, et al. A progeroid syndrome in mice is caused by defects in A-type lamins. Nature, 2003; 423(6937):298–301; doi: 10.1038/nature01631

74.

Trifunovic

, Wredenberg

, Falkenberg

, et al. Premature ageing in mice expressing defective mitochondrial DNA polymerase. Nature, 2004; 429(6990):417–423; doi: 10.1038/nature02517

75.

Tyner

, Venkatachalam

, Choi

, et al. p53 mutant mice that display early ageing-associated phenotypes. Nature, 2002; 415(6867):45–53; doi: 10.1038/415045a

76.

Musiek

, Lim

, Yang

, et al. Circadian clock proteins regulate neuronal redox homeostasis and neurodegeneration. J Clin Invest, 2013; 123(12):5389–5400; doi: 10.1172/JCI70317

77.

Méndez

, Vázquez-Martínez

, Hernández-Muñoz

, et al. Redox regulation and pro-oxidant reactions in the physiology of circadian systems. Biochimie, 2016; 124:178–186; doi: 10.1016/j.biochi.2015.04.014

78.

Orozco-Solis

, Sassone-Corsi

. Circadian clock: Linking epigenetics to aging. Curr Opin Genet Dev, 2014; 26:66–72; doi: 10.1016/j.gde.2014.06.003

79.

Chhunchha

, Kubo

, Singh

. Clock protein Bmal1 and Nrf2 cooperatively control aging or oxidative response and redox homeostasis by regulating rhythmic expression of Prdx6. Cells, 2020; 9(8):1861; doi: 10.3390/cells9081861

80.

Lin

, Xu

, Tang

, et al. Clock gene Bmal1 disruption in vascular smooth muscle cells worsens carotid atherosclerotic lesions. Arterioscler Thromb Vasc Biol, 2022; 42(5):565–579; doi: 10.1161/ATVBAHA.121.316480

81.

Kondratov

, Vykhovanets

, Kondratova

, et al. Antioxidant N-acetyl-L-cysteine ameliorates symptoms of premature aging associated with the deficiency of the circadian protein BMAL1. Aging, 2009; 1(12):979–987; doi: 10.1863/2/aging.100113

82.

Lee

, Moulik

, Fang

, et al. Bmal1 and β-cell clock are required for adaptation to circadian disruption, and their loss of function leads to oxidative stress-induced β-cell failure in mice. Mol Cell Biol, 2013; 33(11):2327–2338; doi: 10.1128/MCB.01421-12

83.

Khapre

, Kondratova

, Susova

, et al. Circadian clock protein BMAL1 regulates cellular senescence in vivo. Cell Cycle, 2011; 10(23):4162–4169; doi: 10.4161/cc.10.23.18381

84.

Krishnan

, Kretzschmar

, Rakshit

, et al. The circadian clock gene period extends healthspan in aging Drosophila melanogaster. Aging (Albany NY), 2009; 1(11):937–948; doi: 10.1863/2/aging.100103

85.

Ali

AAH

, Schwarz-Herzke

, Stahr

, et al. Premature aging of the hippocampal neurogenic niche in adult Bmal1-deficient mice. Aging (Albany NY), 2015; 7(6):435–449; doi: 10.1863/2/aging.100764

86.

Wardlaw

, Phan

, Saraf

, et al. Genetic disruption of the core circadian clock impairs hippocampus-dependent memory. Learn Mem, 2014; 21(8):417–423; doi: 10.1101/lm.035451.114

87.

Kondratov

, Kondratova

, Gorbacheva

, et al. Early aging and age-related pathologies in mice deficient in BMAL1, the core componentof the circadian clock. Genes Dev, 2006; 20(14):1868–1873; doi: 10.1101/gad.1432206

88.

Yuan

, Hua

, Cai

, et al. Clock mediates liver senescence by controlling ER stress. Aging (Albany NY), 2017; 9(12):2647–2665; doi: 10.1863/2/aging.101353

89.

Wang

, Wang

, He

, et al. Antioxidant and pro-oxidant activities of melatonin in the presence of copper and polyphenols in vitro and in vivo. Cells, 2019; 8(8):E903; doi: 10.3390/cells8080903

90.

Mannino

, Pernici

, Serio

, et al. Melatonin and phytomelatonin: Chemistry, biosynthesis, metabolism, distribution and bioactivity in plants and animals-an overview. Int J Mol Sci, 2021; 22(18):9996; doi: 10.3390/ijms22189996

91.

Ding

, Wang

, Xu

, et al. Melatonin stimulates antioxidant enzymes and reduces oxidative stress in experimental traumatic brain injury: The Nrf2–ARE signaling pathway as a potential mechanism. Free Radic Biol Med, 2014; 73:1–11; doi: 10.1016/j.freeradbiomed.2014.04.031

92.

Verma

, Singh

, Garg

, et al. Melatonin exerts neuroprotection in a chronodisrupted rat model through reduction in oxidative stress and modulation of autophagy. Chronobiol Int, 2022; 39(1):45–56; doi: 10.1080/07420528.2021.1966025

93.

Verma

, Singh

, Rizvi

. Age-dependent effect of continuous “artificial light at night” on circadian rhythm in male rats: Neuroprotective role of melatonin. Biogerontology, 2021; 22(5):531–545; doi: 10.1007/s10522-021-09933-y

94.

Verma

, Garg

, Singh

, et al. Melatonin protects against membrane alterations affected by ‘Artificial Light at Night’ in a circadian-disrupted model of rat. Biol Rhythm Res, 2020; 2:317–328; doi: 10.1080/09291016.2020.1741265

95.

Liu

, Ng

. Effect of pineal indoles on activities of the antioxidant defense enzymes superoxide dismutase, catalase, and glutathione reductase, and levels of reduced and oxidized glutathione in rat tissues. Biochem Cell Biol, 2000; 78(4):447–453; doi: 10.1139/o00-018

96.

Limón-Pacheco

, Gonsebatt

. The glutathione system and its regulation by neurohormone melatonin in the central nervous system. Cent Nerv Syst Agents Med Chem, 2010; 10(4):287–297; doi: 10.2174/187152410793429683

97.

P M

A C

, Fj

, et al. Melatonin versus vitamin E as protective treatment against oxidative stress after extra-hepatic bile duct ligation in rats. J Pineal Res, 2001; 31(2):138–144; doi: 10.1034/j.1600-079x.2001.310207.x

98.

Verma

, Singh

, Rizvi

. Therapeutic potential of melatonin and its derivatives in aging and neurodegenerative diseases. Biogerontology, 2023; 24(2):183–206; doi: 10.1007/s10522-022-10006-x

99.

Reiter

, Mayo

, Tan

D-X

, et al. Melatonin as an antioxidant: Under promises but over delivers. J Pineal Res, 2016; 61(3):253–278; doi: 10.1111/jpi.12360

100.

Petrosillo

, Moro

, Ruggiero

, et al. Melatonin inhibits cardiolipin peroxidation in mitochondria and prevents the mitochondrial permeability transition and cytochrome c release. Free Radic Biol Med, 2009; 47(7):969–974; doi: 10.1016/j.freeradbiomed.2009.06.032

101.

Fang

, Zhao

, Xiang

, et al. Melatonin inhibits formation of mitochondrial permeability transition pores and improves oxidative phosphorylation of frozen-thawed ram sperm. Front Endocrinol (Lausanne), 2019; 10:896; doi: 10.3389/fendo.2019.00896

102.

Mehrzadi

, Pourhanifeh

, Mirzaei

, et al. An updated review of mechanistic potentials of melatonin against cancer: Pivotal roles in angiogenesis, apoptosis, autophagy, endoplasmic reticulum stress and oxidative stress. Cancer Cell Int, 2021; 21(1):188; doi: 10.1186/s12935-021-01892-1

103.

Rattan

SIS

. Physiological hormesis and hormetins in biogerontology. Curr Opin Toxicol, 2022; 29:19–24; doi: 10.1016/j.cotox.2022.01.001

104.

Calabrese

, Kozumbo

. The hormetic dose-response mechanism: Nrf2 activation. Pharmacol Res, 2021; 167:105526; doi: 10.1016/j.phrs.2021.105526

105.

Bona

, Fernandes

, Moreira

ACJ

, et al. Melatonin restores zinc levels, activates the Keap1/Nrf2 pathway, and modulates endoplasmic reticular stress and HSP in rats with chronic hepatotoxicity. WJGPT, 2022; 13(2):11–22; doi: 10.4292/wjgpt.v13.i2.11

106.

Vriend

, Reiter

. The Keap1-Nrf2-antioxidant response element pathway: A review of its regulation by melatonin and the proteasome. Mol Cell Endocrinol, 2015; 401:213–220; doi: 10.1016/j.mce.2014.12.013

107.

Gupta

, Behl

, Sehgal

, et al. Therapeutic potential of Nrf-2 pathway in the treatment of diabetic neuropathy and nephropathy. Mol Biol Rep, 2021; 48(3):2761–2774; doi: 10.1007/s11033-021-06257-5

108.

Kilic

, Kilic

, Tuzcu

, et al. Melatonin suppresses cisplatin-induced nephrotoxicity via activation of Nrf-2/HO-1 pathway. Nutr Metab (Lond), 2013; 10(1):7; doi: 10.1186/1743-7075-10-7

109.

Tjahjono

, Kirienko

. The emergent role of mitochondrial surveillance in cellular health. Aging Cell, 2022; 21(11):e13710; doi: 10.1111/acel.13710

110.

Lee

, Park

, Lee

, et al. Targeting mitochondrial metabolism as a strategy to treat senescence. Cells, 2021; 10(11):3003; doi: 10.3390/cells10113003

111.

Venegas

, García

, Escames

, et al. Extrapineal melatonin: Analysis of its subcellular distribution and daily fluctuations. J Pineal Res, 2012; 52(2):217–227; doi: 10.1111/j.1600-079X.2011.00931.x

112.

Hardeland

. Melatonin and the electron transport chain. Cell Mol Life Sci, 2017; 74(21):3883–3896; doi: 10.1007/s00018-017-2615-9

113.

Reiter

, Manchester

, Tan

D-X

. Neurotoxins: Free radical mechanisms and melatonin protection. Curr Neuropharmacol, 2010; 8(3):194–210; doi: 10.2174/157015910792246236

114.

Atayik

, Çakatay

. Mitochondria-targeted senotherapeutic interventions. Biogerontology, 2022; 23(4):401–423; doi: 10.1007/s10522-022-09973-y

115.

Zhang

H-M

, Zhang

. Melatonin: A well-documented antioxidant with conditional pro-oxidant actions. J Pineal Res, 2014; 57(2):131–146; doi: 10.1111/jpi.12162

116.

Süzen

, Atayik

, Sirinzade

, et al. Melatonin and redox homeostasis. Melatonin Res, 2022; 5(3):304–324; doi: 10.3279/4/mr112500134

117.

Chen

, Kroemer

, Kepp

. Mitophagy: An emerging role in aging and age-associated diseases. Front Cell Dev Biol, 2020; 8:200; doi: 10.3389/fcell.2020.00200

118.

Lin

, Chen

, Gu

, et al. New insights into mitophagy and stem cells. Stem Cell Res Ther, 2021; 12(1):452; doi: 10.1186/s13287-021-02520-5

119.

Atayik

, Çakatay

. Melatonin-related signaling pathways and their regulatory effects in aging organisms. Biogerontology, 2022; 23(5):529–539; doi: 10.1007/s10522-022-09981-y

120.

Caballero

, Vega-Naredo

, Sierra

, et al. Melatonin alters cell death processes in response to age-related oxidative stress in the brain of senescence-accelerated mice. J Pineal Res, 2009; 46(1):106–114; doi: 10.1111/j.1600-079X.2008.00637.x

121.

Cheng

, Ma

, Qu

, et al. Differential effects of melatonin on hippocampal neurodegeneration in different aged accelerated senescence prone mouse-8. Neuro Endocrinol Lett, 2008; 29(1):91–99.

122.

Okatani

, Wakatsuki

, Reiter

, et al. Melatonin reduces oxidative damage of neural lipids and proteins in senescence-accelerated mouse. Neurobiol Aging, 2002; 23(4):639–644; doi: 10.1016/s0197-4580(02)00005-2

123.

Manchester

, Coto-Montes

, Boga

, et al. Melatonin: An ancient molecule that makes oxygen metabolically tolerable. J Pineal Res, 2015; 59(4):403–419; doi: 10.1111/jpi.12267

124.

Reiter

, Rosales-Corral

, Tan

, et al. Melatonin as a mitochondria-targeted antioxidant: One of evolution's best ideas. Cell Mol Life Sci, 2017; 74(21):3863–3881; doi: 10.1007/s00018-017-2609-7

125.

Lee

, Yoon

, Song

, et al. Melatonin suppresses senescence-derived mitochondrial dysfunction in mesenchymal stem cells via the HSPA1L–mitophagy pathway. Aging Cell, 2020; 19(3):e13111; doi: 10.1111/acel.13111

126.

Zhao

Z-Y

, Xie

, Fu

Y-R

, et al. Aging and the circadian rhythm of melatonin: A cross-sectional study of Chinese subjects 30–110 yr of age. Chronobiol Int, 2002; 19(6):1171–1182; doi: 10.1081/cbi-120015958

127.

Golabchi

, Wu

, Li

, et al. Melatonin improves quality and longevity of chronic neural recording. Biomaterials, 2018; 180:225–239; doi: 10.1016/j.biomaterials.2018.07.026

128.

Hardeland

. Melatonin and the theories of aging: A critical appraisal of melatonin's role in antiaging mechanisms. J Pineal Res, 2013; 55(4):325–356; doi: 10.1111/jpi.12090

129.

Gubin

, Weinert

. [Temporal order deterioration and circadian disruption with age. 2. Systemic mechanisms and correction]. Adv Gerontol, 2016; 28(3):423–434.

130.

Hardeland

. Melatonin in aging and disease -multiple consequences of reduced secretion, options and limits of treatment. Aging Dis, 2012; 3(2):194–225.

131.

Diss

, Robinson

, Wu

, et al. Age-related changes in melatonin release in the murine distal colon. ACS Chem Neurosci, 2013; 4(5):879–887; doi: 10.1021/cn4000617

132.

Gubin

, Gubin

, Waterhouse

, et al. The circadian body temperature rhythm in the elderly: Effect of single daily melatonin dosing. Chronobiol Int, 2006; 23(3):639–658; doi: 10.1080/07420520600650612

133.

Buhr

, Yoo

S-H

, Takahashi

. Temperature as a universal resetting cue for mammalian circadian oscillators. Science, 2010; 330(6002):379–385; doi: 10.1126/science.1195262

134.

Farajnia

, Michel

, Deboer

, et al. Evidence for neuronal desynchrony in the aged suprachiasmatic nucleus clock. J Neurosci, 2012; 32(17):5891–5899; doi: 10.1523/JNEUROSCI.0469-12.2012

135.

Gubin

, Cornelissen

, Weinert

, et al. Circadian disruption and vascular variability disorders (VVD): Mechanisms linking aging, disease state and Arctic shift-work: Applications for chronotherapy. World Heart J, 2013; 5(4):285–306.

136.

Zisapel

. New perspectives on the role of melatonin in human sleep, circadian rhythms and their regulation: Melatonin in human sleep and circadian rhythms. Br J Pharmacol, 2018; 175(16):3190–3199; doi: 10.1111/bph.14116

137.

Crouse

, Carpenter

, Song

YJC

, et al. Circadian rhythm sleep-wake disturbances and depression in young people: Implications for prevention and early intervention. Lancet Psychiatry, 2021; 8(9):813–823; doi: 10.1016/S2215-0366(21)00034-1

138.

Wang

, Zhang

, Yu

, et al. Association between insomnia and subclinical atherosclerosis among Chinese steelworkers: A cross-sectional survey. Arch Public Health, 2022; 80(1):80; doi: 10.1186/s13690-022-00834-1

139.

Anisimov

, Vinogradova

, Panchenko

, et al. Light-at-night-induced circadian disruption, cancer and aging. Curr Aging Sci, 2012; 5(3):170–177; doi: 10.2174/1874609811205030002

140.

Obayashi

, Saeki

, Iwamoto

, et al. Exposure to light at night, nocturnal urinary melatonin excretion, and obesity/dyslipidemia in the elderly: A cross-sectional analysis of the HEIJO-KYO study. J Clin Endocrinol Metab, 2013; 98(1):337–344; doi: 10.1210/jc.2012-2874

141.

Hardeland

. Melatonin and inflammation-Story of a double-edged blade. J Pineal Res, 2018; 65(4):e12525; doi: 10.1111/jpi.12525

142.

Liira

, Verbeek

, Costa

, et al. Pharmacological interventions for sleepiness and sleep disturbances caused by shift work. Cochrane Database Syst Rev, 2014; 2014(8):CD009776; doi: 10.1002/14651858.CD009776.pub2

143.

Besag

FMC

, Vasey

, Lao

KSJ

, et al. Adverse events associated with melatonin for the treatment of primary or secondary sleep disorders: A systematic review. CNS Drugs, 2019; 33(12):1167–1186; doi: 10.1007/s40263-019-00680-w

144.

Buscemi

, Vandermeer

, Hooton

, et al. Efficacy and safety of exogenous melatonin for secondary sleep disorders and sleep disorders accompanying sleep restriction: Meta-analysis. BMJ, 2006; 332(7538):385–393; doi: 10.1136/bmj.38731.532766.F6

145.

Giannotti

, Cortesi

, Cerquiglini

, et al. An open-label study of controlled-release melatonin in treatment of sleep disorders in children with autism. J Autism Dev Disord, 2006; 36(6):741–752; doi: 10.1007/s10803-006-0116-z

146.

Jonsdottir

, Sjörs Dahlman

. Mechanisms in endocrinology: Endocrine and immunological aspects of burnout: A narrative review. Eur J Endocrinol, 2019; 180(3):R147–R158; doi: 10.1530/EJE-18-0741

147.

Bendz

, Scates

. Melatonin treatment for insomnia in pediatric patients with attention-deficit/hyperactivity disorder. Ann Pharmacother, 2010; 44(1):185–191; doi: 10.1345/aph.1M365

148.

Valdés-Tovar

, Estrada-Reyes

, Solís-Chagoyán

, et al. Circadian modulation of neuroplasticity by melatonin: A target in the treatment of depression. Br J Pharmacol, 2018; 175(16):3200–3208; doi: 10.1111/bph.14197

149.

Bonnefont-Rousselot

, Collin

. Melatonin: Action as antioxidant and potential applications in human disease and aging. Toxicology, 2010; 278(1):55–67; doi: 10.1016/j.tox.2010.04.008

150.

Hardeland

. Melatonin, its metabolites and their interference with reactive nitrogen compounds. Molecules, 2021; 26(13):4105; doi: 10.3390/molecules26134105