Mechanisms ​of melatonin in anti-aging and its regulation effects in radiation-induced premature senescence

Radio-protective effects of melatonin therapy against testicular oxidative stress: a systematic review and meta-analysis of rodent models

Background

Radiation exposure is a concern in today's world, given the widespread use of electronic devices and medical procedures involving ionizing and non-ionizing radiation. Radiations may cause male infertility by inducing oxidative stress in testicular tissue. Melatonin has antioxidant properties.

Methods

The authors systematically reviewed the literature for the studies that have investigated the effects of melatonin therapy on radiation-induced oxidative stress in rodents' testicular tissue. PubMed, Scopus, and Web of Science were searched for relevant animal trials. Standardized mean difference and 95% CIs were used to pool the data. Subgroup and sensitivity analyses were done. The risk of bias was assessed using SYRCLE tool.

Results

Outcomes: histopathology and sperm analyses (testicular apoptotic cells, Johnsen's testicular biopsy score, seminiferous epithelial height, tubular diameter, sperm motility, viability, count, and morphology, concentration of spermatid, spermatocyte, and spermatogonia), body and testes weights (absolute and relative body and testicular weights), reproductive hormones (serum prolactin, FSH, and testosterone), and oxidative stress tissue markers (TBARS, CAT, GSH, GSH-Px, MDA, SOD, and XO, and total antioxidant capacity). Rats and mice were exposed to electromagnetic radiations (gamma, roentgen, microwave, radiofrequency, and high-power line energy) and particle waves (radioiodine and carbon-ion). Melatonin therapy was significantly associated with improved male reproduction.

Conclusion

Radiation exposure harms male fertility, but melatonin, as an antioxidant, is potentially associated with improved male reproductive function in rodents. Inconsistencies in research require further investigations.

FOXM1 affects oxidative stress, mitochondrial function, and the DNA damage response by regulating p21 in aging oocytes

Fertilization capacity and embryo survival rate are decreased in postovulatory aging oocytes, which results in a reduced reproductive rate in female animals. However, the key regulatory genes and related regulatory mechanisms involved in the process of postovulatory aging in oocytes remain unclear. In this study, RNA-Seq revealed that 3237 genes were differentially expressed in porcine oocytes between the MII and aging stages (MII + 24 h). The expression level of FOXM1 was increased at the aging stage, and FOXM1 was also observed to be enriched in many key biological processes, such as cell senescence, response to oxidative stress, and transcription, during porcine oocyte aging. Previous studies have shown that FOXM1 is involved in the regulation of various biological processes, such as oxidative stress, DNA damage repair, mitochondrial function, and cellular senescence, which suggests that FOXM1 may play a crucial role in the process of postovulatory aging. Therefore, in this study, we investigated the effects and mechanisms of FOXM1 on oxidative stress, mitochondrial function, DNA damage, and apoptosis during oocyte aging. Our study revealed that aging oocytes exhibited significantly increased ROS levels and significantly decreased GSH, SOD, T-AOC, and CAT levels than did oocytes at the MII stage and that FOXM1 inhibition exacerbated the changes in these levels in aging oocytes. In addition, FOXM1 inhibition increased the levels of DNA damage, apoptosis, and cell senescence in aging oocytes. A p21 inhibitor alleviated the effects of FOXM1 inhibition on oxidative stress, mitochondrial function, and DNA damage and thus alleviated the degree of senescence in aging oocytes. These results indicate that FOXM1 plays a crucial role in porcine oocyte aging. This study contributes to the understanding of the function and mechanism of FOXM1 during porcine oocyte aging and provides a theoretical basis for preventing oocyte aging and optimizing conditions for the in vitro culture of oocytes.

Mediterranean Diet and Melatonin: A Systematic Review

The Mediterranean diet (MD) has beneficial effects on human health, which is evidenced by the observation of lower incidence rates of chronic diseases in Mediterranean countries. The MD dietary pattern is rich in antioxidants, such as melatonin, which is a hormone produced mainly by the pineal gland and controls several circadian rhythms. Additionally, melatonin is found in foods, such as fruit and vegetables. The purpose of this systematic review was to assess the melatonin content in Mediterranean foods and to evaluate the influence of the MD on melatonin levels in both humans and model organisms. A comprehensive search was conducted in four databases (PubMed, Scopus, Cochrane Library and Web of Science) and data were extracted. A total of 31 records were chosen. MD-related foods, such as tomatoes, olive oil, red wine, beer, nuts, and vegetables, showed high melatonin contents. The consumption of specific MD foods increases melatonin levels and improves the antioxidant status in plasma.

The Safety and Efficacy of 1-Monoeicosapentaenoin Isolated from the Trebouxiophyceae Micractinium on Anti-Wrinkle: A Split-Face Randomized, Double-Blind Placebo-Controlled Clinical Study

The skin aging process is governed by intrinsic and extrinsic factors causing skin wrinkles, sagging, and loosening. The 1-monoeicosapentaenoin (1-MEST) is a component isolated from Micractinium, a genus of microalgae (Chlorophyta, Trebouxiophyceae). However, the anti-wrinkle effects of 1-MEST are not yet known. This study aimed to evaluate the anti-wrinkle effects of 1-MEST in vitro and in clinical trials. The cytotoxicity of 1-MEST was investigated in vitro using the MTS assay in human epidermal keratinocytes (HEKs). Expression of matrix metalloproteinase (MMP)-1 and MMP-9 was determined by ELISA in HEKs irradiated with UVB after treatment with 1-MEST. A split-face randomized, double-blind, placebo-controlled study was conducted to evaluate the safety and efficacy of 1-MEST. The study evaluated wrinkle parameters and visual assessment, self-efficacy and usability questionnaires, and adverse events. The study showed that the 1-MEST was not cytotoxic in HEKs, suppressed MMP-1 secretion and MMP-9 protein expression in HEKs irradiated with UVB. The wrinkle parameters and mean visual assessment score were significantly decreased in the test group after 12 weeks and differed from the control group. There were no significant differences in efficacy and usability. Adverse effects were also not observed. The 1-MEST showed anti-wrinkle properties to slow down or prevent skin aging.

Concentration-dependent stimulation of melanin production as well as melanocyte and keratinocyte proliferation by melatonin in human eyelid epidermis

It remains unclear how the multifunctional indoleamine neurohormone, melatonin, alters melanin production and melanocytes within intact human epidermis under physiologically relevant conditions. In the current pilot study, we aimed to clarify this in long-term organ-cultured, full-thickness human eyelid skin, selected for its clinically recognized sensitivity to pigmentation-modulatory hormones. Warthin-Starry histochemistry showed that 100 μM melatonin significantly increased epidermal melanin content and melanocyte dendricity after 6 days of organ culture, even though tyrosinase activity in situ was inhibited, as assessed by quantitative immunohistomorphometry. While the higher melatonin dose tested here (200 μM) did not change epidermal melanization, but again inhibited tyrosinase activity, it increased the number and proliferation of both gp100⁺ epidermal melanocytes and keratinocytes as well as protein expression of the premelanosomal marker, gp100, ex vivo. Contrary to most previous studies, these eyelid skin organ culture results suggest that long-term melatonin application exerts overall stimulatory, dose-dependent effects on the epidermal pigmentary unit within intact human skin, which appear surprisingly tyrosinase-independent. While these provocative preliminary findings require further work-up and independent confirmation, they encourage one to systematically explore whether prolonged melatonin therapy can (re-)stimulate melanogenesis and increase the pool/activity of epidermal melanocytes in hypopigmented skin lesions.

Melatonin as a Harmonizing Factor of Circadian Rhythms, Neuronal Cell Cycle and Neurogenesis: Additional Arguments for Its Therapeutic Use in Alzheimer's Disease

The synthesis and release of melatonin in the brain harmonize various physiological functions. The apparent decline in melatonin levels with advanced aging is an aperture to the neurodegenerative processes. It has been indicated that down regulation of melatonin leads to alterations of circadian rhythm components, which further causes a desynchronization of several genes and results in an increased susceptibility to develop neurodegenerative diseases. Additionally, as circadian rhythms and memory are intertwined, such rhythmic disturbances influence memory formation and recall. Besides, cell cycle events exhibit a remarkable oscillatory system, which is downstream of the circadian phenomena. The linkage between the molecular machinery of the cell cycle and complex fundamental regulatory proteins emphasizes the conjectural regulatory role of cell cycle components in neurodegenerative disorders such as Alzheimer's disease. Among the mechanisms intervening long before the signs of the disease appear, the disturbances of the circadian cycle, as well as the alteration of the machinery of the cell cycle and impaired neurogenesis, must hold our interest. Therefore, in the present review, we propose to discuss the underlying mechanisms of action of melatonin in regulating the circadian rhythm, cell cycle components and adult neurogenesis in the context of AD pathogenesis with the view that it might further assist to identify new therapeutic targets.

Utility of melatonin in mitigating ionizing radiation-induced testis injury through synergistic interdependence of its biological properties

Background

Ionizing radiations (IR) have widespread useful applications in our daily life; however, they have unfavorable effects on reproductive health. Maintaining testicular health following IR exposure is an important requirement for reproductive potential. The current study explored the role of melatonin (MLT) in mitigating IR-induced injury in young adult rat testis.

Methods

Rats were given daily MLT (25 mg/kg) for 3 and 14 days after receiving 4 Gy γ-radiation.

Results

Serum MLT levels and other antioxidants, including glutathione content, and the activity of glutathione peroxidase and glutathione reductase in the testis of the irradiated rats were remarkably maintained by MLT administration in irradiated rats. Hence, the hydrogen peroxide level declined with remarkably reduced formation of oxidative stress markers, 4-hydroxynonenal, and 8-Hydroxy-2′-deoxyguanosine in the testis of irradiated animals after MLT administration. The redox status improvement caused a remarkable regression of proapoptotic protein (p53, Cyto-c, and caspase-3) in the testis and improved inflammatory cytokines (CRP and IL-6), and anti-inflammatory cytokine (interleukin IL-10) in serum. This is associated with restoration of disturbed sex hormonal balance, androgen receptor upregulation, and testicular cell proliferation activity in irradiated rats, explaining the improvement of sperm parameters (count, motility, viability, and deformation). Consequently, spermatogenic cell depletion and decreased seminiferous tubule diameter and perimeter were attenuated by MLT treatment post irradiation. Moreover, the testis of irradiated-MLT-treated rats showed well-organized histological architecture and normal sperm morphology.

Conclusions

These results show that radiation-induced testicular injury is mitigated following IR exposure through synergistic interdependence between the antioxidant, anti-inflammatory, anti-apoptotic, and anti-DNA damage actions of MLT.

Tunneling nanotubes and mesenchymal stem cells: New insights into the role of melatonin in neuronal recovery

Efficient cell-to-cell communication is essential for tissue development, homeostasis, and the maintenance of cellular functions after injury. Tunneling nanotubes (TNTs) have emerged as a new important method of cell-to-cell communication. TNTs are primarily established between stressed and unstressed cells and can transport a variety of cellular components. Mitochondria are important trafficked entities through TNTs. Transcellular mitochondria transfer permits the incorporation of healthy mitochondria into the endogenous network of recipient cells, changing the bioenergetic profile and other functional properties of the recipient and may allow the recipient cells to recuperate from apoptotic processes and return to a normal operating state. Mesenchymal cells (MSCs) can form TNTs and transfer mitochondria and other constituents to target cells. This occurs under both physiological and pathological conditions, leading to changes in cellular energy metabolism and functions. This review summarizes the newly described capacity of melatonin to improve mitochondrial fusion/fission dynamics and promote TNT formation. This new evidence suggests that melatonin's protective effects could be attributed to its ability to prevent mitochondrial damage in injured cells, reduce senescence, and promote anastasis, a natural cell recovery phenomenon that rescues cells from the brink of death. The modulation of these new routes of intercellular communication by melatonin could play a key role in increasing the therapeutic potential of MSCs.

Melatonin finely tunes proliferation and senescence in hematopoietic stem cells

Human hematopoietic stem/progenitor cells (HSPCs) are pluripotent cells that gradually lose their self-renewal and regenerative potential, to give rise to mature cells of the hematopoietic system by differentiation. HSPC infusion is used to restore hematopoietic function in patients with a variety of onco-hematologic and immune-mediated disorders. The functionality of these cells is therefore of great importance to ensure the homeostasis of the hematopoietic system. Melatonin plays an important role as immunomodulatory and oncostatic hormone. In the present manuscript, we aimed at evaluating the activity of melatonin in modulating HSPC senescence, in the attempt to improve their hemopoietic regenerative potential. We exposed HSPCs to melatonin, in different conditions, and then analyzed the expression of genes regulating cell cycle and cell senescence. Moreover, we assessed cell senescence by β-galactosidase and telomerase activity. Our results showed the ability of melatonin to counteract HSPC senescence, thus paving the way for enhanced efficiency in their clinical application.

Revisiting the role of melatonin in human melanocyte physiology: A skin context perspective

The evolutionarily ancient methoxyindoleamine, melatonin, has long perplexed investigators by its versatility of functions and mechanisms of action, which include the regulation of vertebrate pigmentation. Although first discovered through its potent skin-lightening effects in amphibians, melatonin's role in human skin and hair follicle pigmentation and its impact on melanocyte physiology remain unclear. Synthesizing our limited current understanding of this role, we specifically examine its impact on melanogenesis, oxidative biology, mitochondrial function, melanocyte senescence, and pigmentation-related clock gene activity, with emphasis on human skin, yet without ignoring instructive pointers from nonhuman species. Given the strict dependence of melanocyte functions on the epithelial microenvironment, we underscore that melanocyte responses to melatonin are best interrogated in a physiological tissue context. Current evidence suggests that melatonin and some of its metabolites inhibit both, melanogenesis (via reducing tyrosinase activity) and melanocyte proliferation by stimulating melatonin membrane receptors (MT1, MT2). We discuss whether putative melanogenesis-inhibitory effects of melatonin may occur via activation of Nrf2-mediated PI3K/AKT signaling, estrogen receptor-mediated and/or melanocortin-1 receptor- and cAMP-dependent signaling, and/or via melatonin-regulated changes in peripheral clock genes that regulate human melanogenesis, namely Bmal1 and Per1. Melatonin and its metabolites also accumulate in melanocytes where they exert net cyto- and senescence-protective as well as antioxidative effects by operating as free radical scavengers, stimulating the synthesis and activity of ROS scavenging enzymes and other antioxidants, promoting DNA repair, and enhancing mitochondrial function. We argue that it is clinically and biologically important to definitively clarify whether melanocyte cell culture-based observations translate into melatonin-induced pigmentary changes in a physiological tissue context, that is, in human epidermis and hair follicles ex vivo, and are confirmed by clinical trial results. After defining major open questions in this field, we close by suggesting how to begin answering them in clinically relevant, currently available preclinical in situ research models.

Putative effect of melatonin on cardiomyocyte senescence in mice with type 1 diabetes mellitus

Background

To date, many investigators have tried to clarify the molecular mechanism of cardiovascular injuries after T1D. In present study, we evaluated the possible effects of melatonin on the levels of aging-related factors in the heart tissue of streptozotocin-induced diabetic mice.

Methods

40 male mice were enrolled in this study and randomly allocated into 4 groups (n = 10) as follows: Control group (C), Control group + melatonin (CM), Diabetic group (D), Diabetic + melatonin (DM) group. Single Streptozotocin (50 mg/kbW) was applied for the induction of T1D. 3 mg/kg melatonin was injected intraperitoneally twice a week for consequent four weeks. After the completion of this period, the animals were sacrificed and their heart tissue was obtained for histological examination (IHC analysis of vWF and α-SMA cells), aging and inflammation-related gene analysis.

Result

Hematoxylin and Eosin staining indicated cardiomyocyte toxicity in T1D mice. IHC analysis of vascular tissue showed the detachment of vWF and α-SMA cells and disintegration into the vascular lumen. Additionally, real-time PCR assay showed the up-regulation of β-galactosidase and suppression of SOX2, Klotho, and Telomerase genes in T1D mice compared to the control group (p < 0.05). We noted that melatonin administration can revert these condition and closed near-to-control levels. Along with these conditions, the levels of IL-1β were also decreased after melatonin treatment.

Conclusions

In general, one can hypothesize that modulation of different effectors associated with aging is beneficial to alleviate cardiac injuries under hypergylcemic condition. Melatonin can exert its therapeutic effects, in part, through anti-aging capacity.

Melatonin: Regulation of Biomolecular Condensates in Neurodegenerative Disorders

Biomolecular condensates are membraneless organelles (MLOs) that form dynamic, chemically distinct subcellular compartments organizing macromolecules such as proteins, RNA, and DNA in unicellular prokaryotic bacteria and complex eukaryotic cells. Separated from surrounding environments, MLOs in the nucleoplasm, cytoplasm, and mitochondria assemble by liquid-liquid phase separation (LLPS) into transient, non-static, liquid-like droplets that regulate essential molecular functions. LLPS is primarily controlled by post-translational modifications (PTMs) that fine-tune the balance between attractive and repulsive charge states and/or binding motifs of proteins. Aberrant phase separation due to dysregulated membrane lipid rafts and/or PTMs, as well as the absence of adequate hydrotropic small molecules such as ATP, or the presence of specific RNA proteins can cause pathological protein aggregation in neurodegenerative disorders. Melatonin may exert a dominant influence over phase separation in biomolecular condensates by optimizing membrane and MLO interdependent reactions through stabilizing lipid raft domains, reducing line tension, and maintaining negative membrane curvature and fluidity. As a potent antioxidant, melatonin protects cardiolipin and other membrane lipids from peroxidation cascades, supporting protein trafficking, signaling, ion channel activities, and ATPase functionality during condensate coacervation or dissolution. Melatonin may even control condensate LLPS through PTM and balance mRNA- and RNA-binding protein composition by regulating N6-methyladenosine (m6A) modifications. There is currently a lack of pharmaceuticals targeting neurodegenerative disorders via the regulation of phase separation. The potential of melatonin in the modulation of biomolecular condensate in the attenuation of aberrant condensate aggregation in neurodegenerative disorders is discussed in this review.