MT1 and MT2 Melatonin Receptors: A Therapeutic Perspective

Peripheral mitochondrial DNA as a neuroinflammatory biomarker for major depressive disorder

In the pathogenesis of major depressive disorder, chronic stress-related neuroinflammation hinders favorable prognosis and antidepressant response. Mitochondrial DNA may be an inflammatory trigger, after its release from stress-induced dysfunctional central nervous system mitochondria into peripheral circulation. This evidence supports the potential use of peripheral mitochondrial DNA as a neuroinflammatory biomarker for the diagnosis and treatment of major depressive disorder. Herein, we critically review the neuroinflammation theory in major depressive disorder, providing compelling evidence that mitochondrial DNA release acts as a critical biological substrate, and that it constitutes the neuroinflammatory disease pathway. After its release, mitochondrial DNA can be carried in the exosomes and transported to extracellular spaces in the central nervous system and peripheral circulation. Detectable exosomes render encaged mitochondrial DNA relatively stable. This mitochondrial DNA in peripheral circulation can thus be directly detected in clinical practice. These characteristics illustrate the potential for mitochondrial DNA to serve as an innovative clinical biomarker and molecular treatment target for major depressive disorder. This review also highlights the future potential value of clinical applications combining mitochondrial DNA with a panel of other biomarkers, to improve diagnostic precision in major depressive disorder.

Enhancing prostate cancer cells' sensitivity to flutamide by resveratrol: An in-vitro study

BACKGROUND

As the most common cancer in men, and its progression poses a significant challenge. New and effective treatment strategies are needed to improve outcomes for patients with prostate cancer. This study examined if resveratrol, a natural substance, could improve prostate cancer cell lines' response to flutamide, a standard antiandrogenic treatment for untreated prostate cancer, while minimizing adverse effects.

METHOD

MTT assay was used to quantify resveratrol and flutamide IC50 values, Annexin-V/PI staining for apoptosis, PI staining for DNA cell cycle, and real-time PCR for BAX, BCL-2, VEGFC, HIF-1α, Snail1, E-Cadherin, and KLK3 mRNA levels Scratch-wound, colony-forming, and Hoechst staining analyzed cell migration, proliferation, and nucleus morphology. Spheroid creation in 3D was also considered. All tests used LNCaP, DU145, and PC3 prostate cancer cell lines at various stages.

RESULTS

Resveratrol, when combined with flutamide, can reduce malignant cell migration, colony formation, and proliferation and promote apoptosis in prostate cancer cell lines. Even in androgen-unresponsive cell lines (DU145 and PC3), it may benefit flutamide prostate cancer treatment. Apoptosis genes (BAX) were upregulated in LNCaP, DU145, and PC3 cancer cell lines when administered alone or with flutamide. Additionally, flutamide might significantly lower BCL-2 levels in PC3 cells. When combined with flutamide, resveratrol increased apoptosis and altered the expression of genes involved in angiogenesis (VEGFC), epithelial-mesenchymal transition (EMT, Snail1 and E-Cadherin), and prostate cancer biomarker (KLK3) in prostate cancer cell lines.

CONCLUSION

Resveratrol reduced the dose of flutamide in the treatment of prostate cancer cell lines (LNCaP, DU145, and PC3) and improved its side effects, as well as increasing the sensitivity of cells to flutamide treatment.

Melatonin and the nervous system: nanomedicine perspectives

The mechanism of action of melatonin on the nervous system, sleep, cognitive deficits, and aging is not fully understood. Neurodegenerative diseases (ND) are one of the leading causes of disability and mortality worldwide. Sleeping and cognitive impairments also represent common and serious public health problems, particularly deteriorating with the aging process. Melatonin, as a neuromodulatory hormone, regulates circadian rhythms and the sleep-wake cycle, with functions extending to antioxidant, anti-inflammatory, neuroprotective, and anti-aging properties. However, melatonin is a hydrophobic compound with relatively low water solubility and a short half-life. While melatonin can cross the blood-brain barrier, exogenous melatonin administered orally or intravenously has poor bioavailability, undergoes rapid metabolism in the circulation, and shows limited brain accumulation, ultimately compromising its therapeutic efficacy. In recent years, the convergence of melatonin research with nanomedicine ensures safe therapeutic uses, limited drug degradation, and perspectives for targeted drug delivery to the central nervous system. Here we outline the promising neurotherapeutic properties of nanomaterials as carriers loaded with melatonin drug alone or in combinations with other active molecules.

Unveiling the Protective Roles of Melatonin on Glial Cells in the Battle Against Alzheimer's Disease-Insights from In Vivo and In Vitro Studies

Alzheimer's disease (AD) is a chronic, progressive neurodegenerative disorder that predominantly affects the elderly. Characterized by amyloid-beta (Aβ) plaques and neurofibrillary tangles, AD leads to memory loss, cognitive decline, and severe behavioral changes. As the most common form of dementia, AD imposes a significant global health burden, highlighting the need for interventions that address underlying disease mechanisms rather than only symptomatic treatment. Glial cells, including microglia and astrocytes, play a crucial role in AD progression by mediating neuroinflammatory responses and modulating Aβ clearance and neuronal health. Dysfunction in these cells can exacerbate neuroinflammation and neuronal damage, making glial cells an important target for therapeutic intervention. This review synthesizes findings from in vivo and in vitro studies on melatonin's effects on glial cell dysfunction in AD, emphasizing the multi-mechanistic nature of its neuroprotective properties. Recent studies highlight melatonin's potential as a therapeutic agent that addresses AD-related mechanisms through its interactions with glial cells. Melatonin has demonstrated protective effects, including reducing oxidative stress, apoptosis, and inflammation, inhibiting Aβ fibrillogenesis, and modulating amyloid precursor proteins. Additionally, its influence on glial cell activity, through melatonin receptor pathways, suggests it can alleviate neuroinflammation, a key component of AD progression. The collective evidence points to melatonin's promise as a therapeutic tool with potential roles in both preventive and adjunctive treatments for AD. However, further research is necessary to establish its efficacy and safety in clinical settings.

Melatonin Interventions in Autism Spectrum Disorder: Sleep Regulation, Behavioral Outcomes, and Challenges Across the Lifespan

Autism spectrum disorder (ASD) poses complex challenges affecting social interaction, communication, and behavior, necessitating comprehensive and tailored interventions. Sleep disturbances, prevalent in up to 80% of individuals with ASD, significantly impact well-being. Central to circadian rhythms, melatonin emerges as a promising intervention, primarily recognized for its role in sleep regulation. This review explores melatonin's multifactor impact on ASD, covering sleep regulation, behavioral outcomes, neuroprotection, and potential synergies with other therapies. Melatonin exhibits promise in ameliorating sleep disturbances and enhancing overall well-being, with implications for social behaviors, communication, and repetitive behaviors. Its antioxidant and anti-inflammatory properties further suggest potential neuroprotective benefits. Future research directions focus on mechanistic insights, individualized medicine, and real-world effectiveness. As melatonin's versatile role unfolds, it stands as a valuable component in the personalized care of individuals navigating the complexities of ASD.

Fluorescent tools for imaging class A G-protein coupled receptors

G protein-coupled receptors (GPCRs) are pivotal in biological processes and represent a significant class of drug targets, with 516 approved drugs acting on 121 GPCRs. Many GPCRs, particularly orphan receptors, remain underexplored, emphasizing the need for innovative investigative tools. Fluorescent ligands provide a powerful means to characterize GPCRs including their functional mechanisms and spatial organization, bridging fundamental research and drug discovery. This review presents recent advances (2018-2024) in fluorescent probe development for Class A GPCRs, analyzing over 120 newly developed probes covering 60 GPCRs. We examine their distribution across receptor subclasses, comparing pre-2018 data with contemporary findings and identifying previously uncharted GPCRs that now have fluorescent ligands. Notably, novel probes have been developed for 12 new receptor subtypes and 6 orphan receptors such as GPR6, GPR52, GPR84, MAS1, MRGPRX2, and MRGPRX4. Advances in GPCR structural biology, driven by cryo-EM and AlphaFold technologies, have significantly enhanced probe development, facilitating the design of selective fluorescent ligands across aminergic, peptidergic, lipid, nucleotide, alicarboxylic, melatonin, protein, and orphan GPCRs. These innovations support a broad range of applications, from single-molecule imaging and in vivo bioimaging to diagnostics and fluorescence-guided surgery. By integrating fluorescence-based approaches with structural and pharmacological insights, this field continues to refine polypharmacology profiling, optimize drug-receptor interactions, and accelerate GPCR-targeted drug discovery.

Transcriptomic and proteomic analyses of sclera in lens-induced myopic guinea pigs

BACKGROUND

Myopia development is commonly assessed by an increase in axial length, which may lead to high myopia and visual impairment. This study aims to identify potential biomarkers and signaling pathways in the sclera during experimental axial elongation.

METHODS

A myopia guinea pig model was established using male guinea pigs aged 2-3 weeks, which underwent bilateral lens-induced myopization (LIM) (study group) or were left untreated (control group). An integrated analysis of transcriptomic and proteomic was performed to identify differentially expressed genes (DEGs) in the sclera. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses were conducted to explore the DEGs related signaling pathways. Promising candidate markers were further tested by Western blot analysis. Transmission electron microscopy was used to assess scleral fiber changes in myopic guinea pigs.

RESULTS

During the study period, axial elongation was significantly greater in the study group (0.59 ± 0.05 mm vs. 0.47 ± 0.02 mm; P < 0.001), accompanied by a reduction in the thickness of the retina (121.9 ± 2.50 μm vs. 134.6 ± 0.48 μm; P < 0.001), choroid (38 ± 1.0 μm vs. 50 ± 0.8 μm; P < 0.001), and sclera (100.8 ± 2.78 μm vs. 155.6 ± 4.78 μm; P < 0.001). Integrated transcriptomic and proteomic analyses identified 34 upregulated genes, with significant activation and enrichment of the circadian rhythm pathway. Among the top enriched pathways, key differentially expressed genes included retinoid-related orphan receptors RORα and RORβ, which are recognized as critical signals modulating the scleral hypoxia response. Western blot analysis confirmed upregulation of RORα, RORβ, melatonin receptor type 1 (MT1), and HIF-1α in the sclera, while melatonin receptor type 2 (MT2) expression remained unchanged between the groups. Transmission electron microscopy revealed a significantly higher proportion of thin collagen fibers compared to thick fibers in the LIM group (P < 0.05).

CONCLUSIONS

Axial elongation-related remodeling of scleral collagen is closely linked to circadian rhythm and hypoxia pathways, with RORα, RORβ, melatonin receptors, and HIF-1α identified as potential key regulators. Additionally, scleral fiber size decreases progressively with scleral remodeling in myopia development.

Alleviation of inflammation in paraventricular nucleus and sympathetic outflow by melatonin efficiently repairs endplate porosities and attenuates spinal hyperalgesia

Low back pain, largely attributed to intervertebral disc (IVD) degeneration, is correlated with increased sympathetic nerve activity. Toll-like receptor 4 (TLR4)-mediated inflammation in the paraventricular nucleus (PVN) triggers sympathetic nerve activation, which remains uncharted in IVD degeneration. We hypothesized that lumbar spine instability (LSI) surgery in mice elevated sympathetic outflow by activating TLR4/NF-κB axis in PVN, and exacerbated endplate porosities and spinal hyperalgesia following 4 or 8 weeks LSI surgery. Treatment of melatonin for 8 weeks notably alleviated the inflammation and sympathetic outflow in the PVN, and attenuated sympathetic nerve activity, oxidative stress, endplate porosities and spinal hyperalgesia in the peripheral. These effects were abolished by melatonin receptor antagonist luzindole. Immunofluorescent staining of melatonin receptor 1A (MT1) and 1B (MT2) confirmed that MT2 expression exceeded that of MT1 in PVN. Knockdown of MT2 in PVN blocked the inhibitory effect of melatonin on inflammation and sympathetic activation both in PVN and endplate, as well as spinal hyperalgesia, oxidative stress, and porosities of endplate. Additionally, norepinephrine induces inflammation and oxidative stress, disrupts metabolic homeostasis of endplate cells via α2-adrenergic receptor in vitro. This study suggests that melatonin, via activation of MT2, inhibits inflammation and sympathetic activities both in PVN and endplate, therefore, efficiently repairing endplate porosities and alleviating spinal hyperalgesia induced by LSI.

Modulation of autophagy by melatonin and its receptors: implications in brain disorders

Autophagy plays a crucial role in maintaining neuronal homeostasis and function, and its disruption is linked to various brain diseases. Melatonin, an endogenous hormone that primarily acts through MT1 and MT2 receptors, regulates autophagy via multiple pathways. Growing evidence indicates that melatonin's ability to modulate autophagy provides therapeutic and preventive benefits in brain disorders, including neurodegenerative and affective diseases. In this review, we summarize the key mechanisms by which melatonin affects autophagy and explore its therapeutic potential in the treatment of brain disorders.

Potential Benefits of Adding Alendronate, Celecoxib, Itraconazole, Ramelteon, and Simvastatin to Endometrial Cancer Treatment: The EC5 Regimen

Metastatic endometrial cancer continues to be a common cause of death as of 2024, even after maximal use of all currently available standard treatments. To address this problem of metastatic cancer generally in 2025, the drug repurposing movement within oncology identifies medicines in common general medical use that have clinical or preclinical experimental data indicating that they interfere with or inhibit a specific growth driving element identified in a given cancer. The drug repurposing movement within oncology also uses data from large scale in vitro screens of thousands of drugs, looking for simple empirical growth inhibition in a given cancer type. This paper outlines the data showing that five drugs from general medical practice meet these evidence criteria for inhibition of endometrial cancer growth, the EC5 regimen. The EC5 regimen uses the osteoporosis treatment drug, alendronate; the analgesic drug, celecoxib; the antifungal drug, itraconazole; the sleep aid, ramelteon; and the cholesterol lowering drug, simvastatin. Side effects seen with these drugs are usually minimal and easily tolerated by patients.

Malnutrition Risk in Older Adults: Evaluating the Diagnostic Relevance of Serum Biomarkers: SIRT-1, CCK-8, Melatonin, and Total Antioxidant Capacity (TAC)

Background/Objectives: Addressing the risk of malnutrition at an early stage is crucial to preventing its development, which can have a detrimental impact on physical and mental health status. This study investigates the potential role of biochemical biomarkers such as sirtuin 1 (SIRT-1), melatonin, cholecystokinin-8 (CCK-8), and total antioxidant capacity (TAC) in identifying the risk of malnutrition. Methods: This cross-sectional study assessed malnutrition risk in 153 community-dwelling older adults using the Mini Nutritional Assessment (MNA). Serum levels of SIRT-1, melatonin, and CCK-8 were analyzed with enzyme-linked immunosorbent assay (ELISA), and total antioxidant capacity (TAC) was measured using the ferric reducing ability of plasma (FRAP) method. Results: Serum levels of TAC and CCK-8 were significantly positively correlated with grip strength and visceral adipose tissue, with TAC levels also showing associations with appendicular skeletal muscle mass index (ASMI), total body water, total energy expenditure, fat-free mass index, and fat mass index (p < 0.001). CCK-8 emerged as a strong predictor of malnutrition risk (AUC = 0.58 in females, AUC = 0.64 in males), whereas SIRT-1 (AUC = 0.57 for both sexes), melatonin (AUC = 0.46 for females, AUC = 0.51 for males), and TAC (AUC = 0.42 for females, AUC = 0.54 for males) exhibited weaker predictive abilities. A multivariate model incorporating CCK-8 demonstrated excellent predictive accuracy (AUC = 0.84, 95% CI: 0.77-0.90) and indicated a potential association between elevated CCK-8 levels and a higher risk of malnutrition. Conclusions: In conclusion, this study highlights the effectiveness of a multi-parameter model incorporating CCK-8 as a reliable approach for assessing malnutrition risk in older adults, offering a comprehensive evaluation of the condition. However, further research is needed to confirm its applicability and accuracy in diverse elderly populations and clinical settings.

Assessment of adverse events of tasimelteon: a real-world pharmacovigilance study based on FAERS

BACKGROUND

Tasimelteon is a novel dual melatonin receptor agonist approved for the treatment of non-24-hour sleep-wake disorder (N24HSWD). The purpose of this study was to provide a comprehensive analysis of post-marketing adverse events (AEs) for tasimelteon by analyzing the U.S. FDA Adverse Event Reporting System (FAERS) database.

METHODS

Four algorithms are employed in this study to mine the significant signals: multi-item gamma poisson shrinker (MGPS), Bayesian confidence propagation neural network (BCPNN), reporting odds ratio (ROR), and proportional reporting ratio (PRR).

RESULTS

Tasimelteon was the primary suspected drug in 5,125 adverse event reports that were identified between the first quarter of 2014 and the first quarter of 2024. Significant system organ categories (SOC) included psychiatric disorders, general disorders and administration site conditions, and nervous system disorders. We not only confirmed the adverse reactions outlined in the prescribing information such as somnolence, nightmare or abnormal dreams, and inhibitory drug interaction, but also revealed new potential risks that were not documented, such as insomnia and sleep disorder.

CONCLUSIONS

This study revealed the characteristics of tasimelteon-associated adverse drug reactions, improved understanding of drug safety, and provided valuable signals for optimizing drug use regimens. Additional large-scale prospective studies remain necessary in the future.

Melatonin Alleviates Age-Related Lacrimal Gland Dysfunction Via SIRT-1/NLRP3 Pathway

Purpose

As a consequence of the natural aging process, the lacrimal glands may become dysfunctional. The present study aimed to investigate the potential role of melatonin (MLT) in the alleviation of age-related lacrimal gland dysfunction and to elucidate the underlying mechanism.

Methods

In this study, lacrimal glands of 2-month-old, 18-month-old, and MLT intraperitoneally injected 18-month-old mice were obtained for immunofluorescence, immunohistochemistry experiments, and Western blotting to detect inflammatory factors and AQP5 expression, and for electron microscopy to detect mitochondrial structure and dense granules. Lacrimal glands from 18-month-old mice were taken for cell culture, and PCR and Western blotting were performed to detect the signaling pathways in which MLT acts. In addition, the human lacrimal gland explant cultures were performed to validate the role of MLT and the SIRT-1/NLRP3 signaling pathways.

Results

In this study, we discovered that aging increased the inflammatory response, decreased secretory function, and led to mitochondrial dysregulation in lacrimal gland. Compared with 2-month-old mice, SIRT-1/3/6 gene transcript levels were significantly decreased in 18-month-old mice. MLT reduced inflammatory factors (IL-1β, IL-6, and TNF-α) and increased AQP5 expression via the SIRT-1/NLRP3 signaling pathway in aged lacrimal gland of human and mouse. Furthermore, MLT restored mitochondrial structure and increased dense granules in aged mouse lacrimal gland. In explants of human lacrimal gland, MLT relieved fibrosis.

Conclusions

The present study demonstrated that MLT alleviates age-related lacrimal dysfunction in mice and humans via the SIRT-1/NLRP3 pathway. MLT alleviated the inflammatory response and the decline in the secretory function of the aged lacrimal gland.

Melatonin induces white-to-beige adipocyte transdifferentiation through melatonin receptor 1-mediated direct browning and indirect M2 polarization

Previous studies have shown that melatonin induces adipocyte browning in vivo. However, the underlying mechanisms of melatonin action at the cellular level remain elusive. In this study, we investigated the mechanisms underlying melatonin-induced browning in 3T3-L1 adipocytes and RAW 264.7 macrophages. Melatonin caused the transdifferentiation of fully differentiated white adipocytes into beige adipocytes, which involves the activation of melatonin receptor 1, followed by increased phosphorylation of p38 MAPK and Akt. Both luzindole (LZ), a non-selective melatonin receptor antagonist, and selective melatonin receptor 1 knockdown attenuated the browning effects of melatonin. Melatonin also induced M2 polarization in RAW 264.7, involving the melatonin receptor 1-Src-STAT3/STAT6 phosphorylation signaling cascade. Melatonin-treated M2-conditioned medium (CM) contained increased levels of catecholamine (CA) and induced beige adipocytes when treated with differentiated 3T3-L1 white adipocytes. In vivo oral administration of melatonin to high-fat diet (HFD)-induced obese (DIO) mice reduced body weight, accompanied by increased expression of uncoupling protein-1 (UCP1) and peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α) in subcutaneous adipose tissues. Moreover, arginase-1 (Arg1) and mannose receptor C type-1 (MRC1) levels were markedly higher in the melatonin-treated groups, suggesting that melatonin induces adipose browning and M2 polarization in vivo. Collectively, melatonin-induced adipocyte browning appeared to be reflected by the sum of melatonin receptor 1-activated direct browning effects and indirect M2 polarization-mediated effects.

The impact of circadian rhythms on retinal immunity

The eye is an immune-protected organ, which is driven by factors such as cytokines, chemicals, light, and mechanical stimuli. The circadian clock is an intrinsic timing mechanism that influences the immune activities, such as immune cell count and activity, as well as inflammatory responses. Recent studies have demonstrated that the eye also possesses an intrinsic circadian rhythm, and this rhythmic regulation participates in ocular immune modulation. In this review, we discuss the immunoregulatory mechanisms of the circadian clock within the eye, and reveal new perspectives for the prevention and treatment of ocular diseases.

Insight into the cardioprotective effects of melatonin: shining a spotlight on intercellular Sirt signaling communication

Cardiovascular diseases (CVDs) are the leading causes of death and illness worldwide. While there have been advancements in the treatment of CVDs using medication and medical procedures, these conventional methods have limited effectiveness in halting the progression of heart diseases to complete heart failure. However, in recent years, the hormone melatonin has shown promise as a protective agent for the heart. Melatonin, which is secreted by the pineal gland and regulates our sleep-wake cycle, plays a role in various biological processes including oxidative stress, mitochondrial function, and cell death. The Sirtuin (Sirt) family of proteins has gained attention for their involvement in many cellular functions related to heart health. It has been well established that melatonin activates the Sirt signaling pathways, leading to several beneficial effects on the heart. These include preserving mitochondrial function, reducing oxidative stress, decreasing inflammation, preventing cell death, and regulating autophagy in cardiac cells. Therefore, melatonin could play crucial roles in ameliorating various cardiovascular pathologies, such as sepsis, drug toxicity-induced myocardial injury, myocardial ischemia-reperfusion injury, hypertension, heart failure, and diabetic cardiomyopathy. These effects may be partly attributed to the modulation of different Sirt family members by melatonin. This review summarizes the existing body of literature highlighting the cardioprotective effects of melatonin, specifically the ones including modulation of Sirt signaling pathways. Also, we discuss the potential use of melatonin-Sirt interactions as a forthcoming therapeutic target for managing and preventing CVDs.

Melatonin effects on animal behavior: circadian rhythm, stress response, and modulation of behavioral patterns

Melatonin plays a crucial role in various behavioral and physiological aspects of animals, including regulating their circadian rhythms. This review provides a comprehensive evaluation of the multifaceted effects of melatonin on animal behavior, such as temperament, stress, and aggression regulation. The focus is on the complex interactions between melatonin and the hormonal and neurotransmitter systems, highlighting how melatonin interacts with cortisol, serotonin, and dopamine to influence behavior. Additionally, it investigates the effects of melatonin on the hypothalamic-pituitary-gonada (HPG) axis and stress responses, emphasizing its potential to improve stress management and social interactions, thereby enhancing animal welfare. The review also examines the seasonal variations of melatonin and its impact on aggression and reproductive activities related to photoperiods, as well as its effects on learning and memory to suggest improvements in animal training methods and practices. Furthermore, it discusses the influence of melatonin on appetite and physical activity regulation, implying its involvement in metabolic processes. In conclusion, further research is needed to elucidate the complex mechanisms underlying the extensive influence of melatonin on animal behavior. Through this review, the aim is to integrate the overall knowledge about melatonin and animal behavioral temperament and to propose new research areas for animal management based on behavioral and hormonal regulation.

Melatonin alleviates oral epithelial cell inflammation via Keap1/Nrf2 signaling

BACKGROUND

Oral mucosal diseases manifest primarily as inflammatory conditions. These diseases affect approximately half a billion people worldwide.

OBJECTIVE

Novel and effective strategies for treating inflammatory diseases of the oral mucosa have great potential for improving patient outcomes, and warrant study.

METHODS

The impact of melatonin on inflammation was investigated using RAW264.7 macrophages and HOEC and HSC-3 oral epithelial cells.

RESULTS

Melatonin decreased macrophage-induced inflammation by acting through the melatonin receptor MTNR1A. Additionally, melatonin mitigated macrophage-induced inflammation in oral epithelial cells. Importantly, the results demonstrated that the effects of melatonin on oral epithelial inflammation were mediated through the KEAP1/Nrf2 signaling pathway.

CONCLUSION

These findings will contribute to the development of innovative therapies for inflammatory conditions affecting the oral epithelium.

Circadian Effects of Melatonin Receptor-Targeting Molecules In Vitro

Circadian rhythms are important for maintaining homeostasis, from regulating physiological activities (e.g., sleep-wake cycle and cognitive performance) to cellular processes (e.g., cell cycle and DNA damage repair). Melatonin is a key regulator of circadian rhythms and exerts control by binding to melatonin receptor 1 (MT1), decreasing neuronal firing in the suprachiasmatic nucleus (SCN). Previous work studying effects of melatonin on circadian rhythms utilized in vivo models. Since MT1 is also expressed outside of the brain, it is important to study impacts of melatonin on circadian gene oscillations in vitro. We evaluated the effects of melatonin and an MT1 inverse agonist, UCSF7447, in U2OS circadian reporter cell lines, which facilitate detailed assessments of oscillatory changes. We report that cellular circadian rhythms are responsive to treatment with MT1-targeting molecules; their activities are not dependent upon the SCN. Corroborating in vivo data, both melatonin and UCSF7447 lengthened the periods of BMAL1 and PER2, and while melatonin delayed circadian phases, UCSF7447 advanced them. Compounds were also dosed at two different times, however this did not yield changes. Our findings indicate the importance of utilizing in vitro models and that the direct effects of melatonin likely go beyond the SCN and should be explored further.

Validated UPLC-MS/MS method for quantification of melatonin receptor agonists and dual orexin receptor antagonists in human plasma and breast milk: Application to quantify suvorexant and lemborexant in clinical samples

Pharmaceutical care is important for mental health during the perinatal period, which is often characterized by insomnia. In recent years, prescriptions of melatonin receptor agonists (MRAs) and dual orexin receptor antagonists (DORAs) for insomnia have increased; however, their use during the perinatal period has scarcely been reported. In the present study, we developed a UPLC-MS/MS method for the quantification of ramelteon, its metabolite M-II, suvorexant, and lemborexant in human plasma and breast milk to accumulate information on the safety and transfer of MRAs and DORAs into breast milk. Samples of MRAs (ramelteon and M-II) in plasma and breast milk were prepared using liquid-liquid extraction (LLE) with ethyl acetate. For DORAs (suvorexant and lemborexant), LLE with ethyl acetate was applied to plasma samples. For breast milk samples, significant ion suppression was observed for LLE with ethyl acetate. Solid-phase extraction (SPE) cartridges capable of removing phospholipids improved the matrix effects. Finally, protein precipitation with methanol and an SPE cartridge, InertSep® Phospholipid Remover, were selected for breast milk sample preparation. An ACQUITY UPLC BEH C18 column was used for analyte separation. MRAs and DORAs were eluted using isocratic and gradient elution, respectively, and analyzed using electrospray ionization in the positive mode with multiple reaction monitoring. The range of calibration curve for MRAs and DORAs was 0.1-25 and 0.5-50 ng/ml, respectively. Both the plasma and breast milk samples exhibited good linearity over this range. The method was validated by evaluating its accuracy and precision, matrix effect, recovery, carry-over, stability, and dilution integrity. The validated method was successfully applied to clinical samples donated by breastfeeding women and the milk/plasma (M/P) ratio and relative infant dose (RID) of lemborexant (one case) and suvorexant (two cases) were estimated. The M/P ratio of lemborexant was <1, and the RID was 1.05 %. The M/P ratio of suvorexant was <0.1, and RID was 0.11-0.20 %. This method will be useful for future studies evaluating the safety of these drugs during breastfeeding.

The Melatonin Type 2 Receptor Agonist IIK7 Attenuates and Reverses Morphine Tolerance in Neuropathic Pain Rats Through the Suppression of Neuroinflammation in the Spinal Cord

BACKGROUND

Morphine analgesic tolerance (MAT) limits the clinical application of morphine in the management of chronic pain. IIK7 is a melatonin type 2 (MT2) receptor agonist known to have antioxidant properties. Oxidative stress is recognized as a critical factor in MAT. This study sought to assess the impact of IIK7 on the progression of MAT and its potential to reverse pre-existing MAT.

METHODS

Wistar rats underwent partial sciatic nerve transection (PSNT) surgery to induce neuropathic pain (NP). Seven days post nerve transection, we implanted an intrathecal (i.t.) catheter and linked it to an osmotic pump. Rats were randomly divided into the following groups: sham-operated/vehicle, PSNT/vehicle, PSNT/IIK7 50 ng/h, PSNT/MOR 15 g/h, and PSNT/MOR 15 g + IIK7 50 ng/h. We implanted two i.t. catheters for drug administration and the evaluation of the efficacy of IIK7 in reversing pre-established MAT. We linked one to an osmotic pump for MOR or saline continuous i.t. infusion. On the 7th day, the osmotic pump was disconnected, and 50 μg of IIK7 or the vehicle was administered through the second catheter. After 3 h, 15 μg of MOR or saline was administered, and the animal behavior tests were performed. We measured the levels of mRNA for Nrf2 and HO-1, pro-inflammatory cytokines (PICs), and the microglial and astrocyte activation in the spinal cord.

RESULTS

The co-administration of IIK7 with MOR delayed MAT development in PSNT rats by restoring Nrf2 and HO-1 while also inhibiting the microglial-cell and astrocyte activation, alongside the suppression of PICs. Additionally, a single injection of high-dose 50 μg IIK7 was efficient in restoring MOR's antinociception in MOR-tolerant rats.

CONCLUSIONS

Our results indicate that the co-infusion of ultra-low-dose IIK7 can delay MAT development and a high dose can reverse pre-existing MAT.

Chronobiotics: classifications of existing circadian clock modulators, future perspectives

The review summarizes recent achievements and future prospects in the use of chronobiotics for regulating circadian rhythms regulation. Special attention is paid to the mechanisms' action, their classification, and the impact of chemical interventions on the biological clock. Chronobiotics defined as a diverse group of compounds capable of restoring disrupted circadian functions, addressing challenges such as irregular work schedules, artificial light exposure or ageing. The review categorizes these compounds by their pharmacological effects, molecular targets, and chemical structures, underlining their ability to enhance or inhibit key circadian components like CLOCK, BMAL1, PER, and CRY. A particular focus is placed on the therapeutic applications of chronobiotics, including their potential for treating sleep disorders, metabolic issues, and age-related rhythm disturbances, underscoring their wide-ranging applicability in health care. Chronobiotic compounds have promising roles in maintaining physiological rhythms, supporting healthy aging, and enhancing personalised health care. Given their diverse therapeutic potential, chronobiotics are positioned as a significant avenue for further clinical application, marking them as a crucial area of ongoing research and innovation.

Melatonin and vitamin D as potential synergistic adjuvants for cancer therapy (Review)

Significant advancements have been made in cancer therapy; however, limitations remain with some conventional approaches. Adjuvants are agents used alongside primary treatments to enhance their efficacy and the treatment outcomes of patients. Modern lifestyles contribute to deficiencies in melatonin and vitamin D. Limited sun exposure affects vitamin D synthesis, and artificial light at night suppresses melatonin production. Both melatonin and vitamin D possess anti‑inflammatory, immune‑boosting and anticancer properties, rendering them potential adjuvants of interest. Studies suggest melatonin and vitamin D supplementation may address antioxidant imbalances in lip, oral and pharyngeal cancers. Moreover, promising results from breast, head and neck, brain, and osteosarcoma research indicate potential for tumor growth inhibition, improved survival, and a better quality of life of patients with cancer. The radioprotective properties of melatonin and vitamin D are another exciting area of exploration, potentially enhancing radiotherapy effectiveness while reducing side effects. For its part, the sleep‑promoting effects of melatonin may indirectly benefit patients with cancer by influencing the immune system. Thus, the prevalence of vitamin D and melatonin deficiencies highlights the importance of supplementation, as lower levels can worsen side‑effects from cancer treatments. The present review explores the potential of combining melatonin and vitamin D as synergistic adjuvants for cancer therapy. These agents have shown promise individually in cancer prevention and treatment, and their combined effects warrant investigation. Therefore, large‑scale controlled trials are crucial to definitively determine the optimal dosage, safety and efficacy of this combination in improving the lives of patients with cancer.

Circadian Regulation in Diurnal Mammals: Neural Mechanisms and Implications in Translational Research

Diurnal and nocturnal mammals have evolved unique behavioral and physiological adaptations to optimize survival for their day- or night-active lifestyle. The mechanisms underlying the opposite activity patterns are not fully understood but likely involve the interplay between the circadian time-keeping system and various arousal- or sleep-promoting factors, e.g., light or melatonin. Although the circadian systems between the two chronotypes share considerable similarities, the phase relationships between the principal and subordinate oscillators are chronotype-specific. While light promotes arousal and wakefulness in diurnal species like us, it induces sleep in nocturnal ones. Similarly, melatonin, the hormone of darkness, is commonly used as a hypnotic in humans but is secreted in the active phase of nocturnal animals. Thus, the difference between the two chronotypes is more complex than a simple reversal, as the physiological and neurological processes in diurnal mammals during the day are not equivalent to that of nocturnal ones at night. Such chronotype differences could present a significant translational gap when applying research findings obtained from nocturnal rodents to diurnal humans. The potential advantages of diurnal models are being discussed in a few sleep-related conditions including familial natural short sleep (FNSS), obstructive sleep apnea (OSA), and Smith-Magenis syndrome (SMS). Considering the difference in chronotype, a diurnal model will be more adequate for revealing the physiology and physiopathology pertaining to human health and disease, especially in conditions in which circadian rhythm disruption, altered photic response, or melatonin secretion is involved. We hope the recent advances in gene editing in diurnal rodents will promote greater utility of the diurnal models in basic and translational research.

Disruption of circadian rhythm as a potential pathogenesis of nocturia

Increasing evidence suggested the multifactorial nature of nocturia, but the true pathogenesis of this condition still remains to be elucidated. Contemporary clinical medications are mostly symptom based, aimed at either reducing nocturnal urine volume or targeting autonomic receptors within the bladder to facilitate urine storage. The day-night switch of the micturition pattern is controlled by circadian clocks located both in the central nervous system and in the peripheral organs. Arousal threshold and secretion of melatonin and vasopressin increase at night-time to achieve high-quality sleep and minimize nocturnal urine production. In response to the increased vasopressin, the kidney reduces the glomerular filtration rate and facilitates the reabsorption of water. Synchronously, in the bladder, circadian oscillation of crucial molecules occurs to reduce afferent sensory input and maintain sufficient bladder capacity during the night sleep period. Thus, nocturia might occur as a result of desynchronization in one or more of these circadian regulatory mechanisms. Disrupted rhythmicity of the central nervous system, kidney and bladder (known as the brain-kidney-bladder circadian axis) contributes to the pathogenesis of nocturia. Novel insights into the chronobiological nature of nocturia will be crucial to promote a revolutionary shift towards effective therapeutics targeting the realignment of the circadian rhythm.

The appropriate and inappropriate uses of saliva melatonin measurements

Melatonin is produced in the pineal gland under very tight control through the influences of light and the suprachiasmatic nucleus. As such, melatonin circulates in the blood at levels <3 pg/ml during the day and is only actively secreted at night reaching levels of approximately 100 pg/ml. As a consequence of binding to plasma proteins, free melatonin appears in saliva at approximately one third the plasma concentration. Measurement of melatonin is technically challenging because of these very low concentrations and while a number of commercial immunoassay kits are available and mass spectrometry assay methods have been published, not all are fit for purpose and can lead to unreliable conclusions. In this review I discuss the aspects of pineal melatonin production that saliva melatonin reflects, the factors influencing melatonin production or metabolism, saliva collection and analysis methods. Examples are provided of the appropriate use of saliva melatonin measurements; Dim Light Melatonin Onset (DLMO) assessment, impact of light on melatonin and the monitoring of rhythms prior to specific treatments. Examples of inappropriate use of saliva melatonin measurements are also provided including the use of poorly validated assays, morning saliva collections, attempts to stimulate melatonin, and linking specific illnesses to saliva melatonin levels.

Protective role of melatonin against radiation-induced disruptions in behavior rhythm of zebrafish (danio rerio)

Ionizing radiation, as an increasingly serious environmental pollutant, has aroused widespread public concern. Melatonin, as an indole heterocyclic compound, is known to have anti-inflammatory and antioxidant effects. However, few studies have considered the comprehensive impact of melatonin on radiation damage. In this study, we used zebrafish as experimental materials and employed methods such as acridine orange staining, enzyme-linked immunosorbent assay (ELISA), video tracking for automated behavior analysis, microscope imaging, and real-time fluorescence quantitative analysis. Zebrafish embryos at 2 h post-fertilization (hpf) were treated under four different experimental conditions to assess their growth, development, and metabolic consequences. Our findings indicate that 0.10 Gy gamma radiation significantly augments body length, eye area, spine width, and tail fin length in zebrafish, along with a marked increase in oxidative stress (P < 0.05). Moreover, it enhances cumulative swimming distance, time, and average speed, suggesting elevated activity levels. We observed circadian rhythm phase shifts, peak increases, and cycle shortening, accompanied by abnormal expression of genes pivotal to biological rhythms, exercise, melatonin synthesis, apoptosis/anti-apoptosis, and oxidation/antioxidant balance. The inclusion of melatonin (1 × 10-5 mol/L MLT) ameliorated these radiation-induced anomalies, while its independent effect on zebrafish was negligible. Melatonin can regulate oxidative stress responses, hinders apoptosis responses, and reprogramming the expression of rhythm-related genes in zebrafish embryos after reprogramming radiation stimulation. Overall, our research highlights melatonin's critical role in countering the biological damage inflicted by gamma radiation, proposing its potential as a therapeutic agent in radiation protection.

Melatonin mitigates matrix stiffness-induced intervertebral disk degeneration by inhibiting reactive oxygen species and melatonin receptors mediated PI3K/AKT/NF-κB pathway

Intervertebral disk degeneration (IVDD) may lead to an increase in extracellular matrix (ECM) stiffness, potentially contributing to the progression of the disease. Melatonin reportedly mitigates IVDD; however, its potential to attenuate elevated matrix stiffness-induced IVDD remains unexplored. Therefore, we aimed to investigate whether melatonin can alleviate the progression of IVDD triggered by increased matrix stiffness and elucidate its underlying mechanisms. Nucleus pulposus (NP) tissues were collected from patients, and ECM stiffness, reactive oxygen species (ROS) levels, apoptosis rates, and P65 expression in these tissues with varying Pfirrmann scores were determined. In vitro experiments were conducted to investigate the effects of melatonin on various pathophysiological mechanisms within the NP cells cultured on soft substrates with differing stiffness levels. Our findings revealed a positive correlation between ECM stiffness in human NP tissue and degree of IVDD. In addition, phosphorylation of P65 exhibited a strong association with matrix stiffness. Enhanced levels of ROS and cellular apoptosis were observed within degenerated intervertebral disks. In vitro experiments demonstrated that melatonin significantly inhibited catabolism and apoptosis induced by stiff matrices, along with elevated ROS levels. Furthermore, we observed that melatonin inhibited NP cell catabolism and apoptosis by reducing the melatonin receptors mediated activation of the PI3K/AKT and nuclear factor-kappa B (NF-κB) pathways. Also, we found that the reduction of ROS by melatonin can assist in inhibiting the activation of the NF-κB pathway. The outcomes of the in vivo experiments corroborated the results of the in vitro experiments, illustrating that melatonin treatment could alleviate the compression-induced upregulation of matrix stiffness in NP and IVDD. Collectively, melatonin can potentially alleviate high matrix stiffness-induced IVDD by reducing intracellular ROS levels and inhibiting the PI3K/AKT/NF-κB pathway.NEW & NOTEWORTHY Melatonin mitigates intervertebral disk degeneration (IVDD) induced by matrix stiffness through reactive oxygen species (ROS) reduction. Matrix stiffness is related to increased nucleus pulposus cell ROS, apoptosis, and degeneration. Melatonin inhibits PI3K/AKT/NF-κB pathways via melatonin receptors in a stiff matrix environment. In vivo, melatonin restores disk height and alleviates IVDD progression.

Impact of Modern Lifestyle on Circadian Health and Its Contribution to Adipogenesis and Cancer Risk

BACKGROUND

Recent research underscores a crucial connection between circadian rhythm disruption and cancer promotion, highlighting an urgent need for attention.

OBJECTIVES

Explore the molecular mechanisms by which modern lifestyle factors-such as artificial light exposure, shift work, and dietary patterns-affect cortisol/melatonin regulation and cancer risk.

METHODS

Employing a narrative review approach, we synthesized findings from Scopus, Google Scholar, and PubMed to analyze lifestyle impacts on circadian health, focusing on cortisol and melatonin chronobiology as molecular markers. We included studies that documented quantitative changes in these markers due to modern lifestyle habits, excluding those lacking quantitative data or presenting inconclusive results. Subsequent sections focused solely on articles that quantified the effects of circadian disruption on adipogenesis and tumor microenvironment modifications.

RESULTS

This review shows how modern habits lead to molecular changes in cortisol and melatonin, creating adipose microenvironments that support cancer development. These disruptions facilitate immune evasion, chemotherapy resistance, and tumor growth, highlighting the critical roles of cortisol dysregulation and melatonin imbalance.

CONCLUSIONS

Through the presented findings, we establish a causal link between circadian rhythm dysregulation and the promotion of certain cancer types. By elucidating this relationship, the study emphasizes the importance of addressing lifestyle factors that contribute to circadian misalignment, suggesting that targeted interventions could play a crucial role in mitigating cancer risk and improving overall health outcomes.

Melatonin attenuates liver ischemia-reperfusion injury via inhibiting the PGAM5-mPTP pathway

Phosphoglycerate mutase/protein phosphatase (PGAM5)-mediated cell death plays an important role in multiple liver diseases. However, few studies have confirmed the regulatory mechanism of melatonin acting on PGAM5-mediated cell death in the context of liver ischemia-reperfusion (I/R) injury. The liver I/R injury model and cell hypoxia-reoxygenation model were established after melatonin pretreatment. Liver injury, cell activity, cell apoptosis, oxidative stress index, and PGAM5 protein expression were detected. To investigate the role of PGAM5 in melatonin-mediated liver protection during I/R injury, PGAM5 silencing, and overexpression were performed before melatonin pretreatment. Our results indicated that PGAM5 was significantly elevated by I/R injury, and predominantly localized in the necrosis area. However, treatment with melatonin blocked PGAM5 activation and conferred a survival advantage of hepatocytes in liver I/R injury, similar to the results achieved by silencing PGAM5. In terms of mechanism, we illustrated that activated PGAM5 promoted mitochondrial permeability transition pore (mPTP) opening, and administration of melatonin inhibited mPTP opening and interrupted hepatocytes death via blocking PGAM5. Our data indicated that the PGAM5-mPTP axis is responsible for I/R-induced liver injury. In contrast, melatonin supplementation blocked the PGAM5-mPTP axis and thus decreased cell death, providing a protective advantage to hepatocytes in I/R. These results established a new paradigm in melatonin-mediated hepatocyte protection under the burden of I/R attack.

Exploring the association between melatonin and nicotine dependence (Review)

Due to the addictive qualities of tobacco products and the compulsive craving and dependence associated with their use, nicotine dependence continues to be a serious public health concern on a global scale. Despite awareness of the associated health risks, nicotine addiction contributes to numerous acute and chronic medical conditions, including cardiovascular disease, respiratory disorders and cancer. The nocturnal secretion of pineal melatonin, known as the 'hormone of darkness', influences circadian rhythms and is implicated in addiction‑related behaviors. Melatonin receptors are found throughout the brain, influencing dopaminergic neurotransmission and potentially attenuating nicotine‑seeking behavior. Additionally, the antioxidant properties of melatonin may mitigate oxidative stress from chronic nicotine exposure, reducing cellular damage and lowering the risk of nicotine‑related health issues. In addition to its effects on circadian rhythmicity, melatonin acting via specific neural receptors influences sleep and mood, and provides neuroprotection. Disruptions in melatonin signaling may contribute to sleep disturbances and mood disorders, highlighting the potential therapeutic role of melatonin in addiction and psychiatric conditions. Melatonin may influence neurotransmitter systems involved in addiction, such as the dopaminergic, glutamatergic, serotonergic and endogenous opioid systems. Preclinical studies suggest the potential of melatonin in modulating reward processing, attenuating drug‑induced hyperactivity and reducing opioid withdrawal symptoms. Chronotherapeutic approaches targeting circadian rhythms and melatonin signaling show promise in smoking cessation interventions. Melatonin supplementation during periods of heightened nicotine cravings may alleviate withdrawal symptoms and reduce the reinforcing effects of nicotine. Further research is required however, to examine the molecular mechanisms underlying the melatonin‑nicotine association and the optimization of therapeutic interventions. Challenges include variability in individual responses to melatonin, optimal dosing regimens and identifying biomarkers of treatment response. Understanding these complexities could lead to personalized treatment strategies and improve smoking cessation outcomes.

Efficacy of Melatonin as a Promising Intervention for Migraine Prevention: A Systematic Review of Randomized Control Trials

The availability and use of melatonin as an over-the-counter supplement have surged significantly in recent years due to the increased prevalence of sleep-wake disorders, notably in the post-COVID-19 era. While melatonin is known for managing insomnia, its applications extend beyond that. Its anti-inflammatory, antioxidant, and analgesic properties, along with increased usage, have garnered significant interest from researchers, particularly regarding its use in migraine prophylaxis and treatment. The aim of this systematic review is to evaluate the role of melatonin as prophylactic therapy for migraine, focusing on the efficacy and side effect profile of melatonin compared to standard therapy and placebo. Six databases were searched through June 2024, identifying 735 relevant articles. Only full-text randomized control trials involving humans, written or translated into English, were included in the study. Data were extracted, screened, sought for retrieval, and assessed for quality appraisal using the revised Cochrane risk-of-bias tool for randomized trials (RoB 2). A total of seven randomized control trials involving 1,283 participants who met the eligibility criteria and passed the quality appraisal have been included in the study. All seven trials included patients diagnosed with migraine who were treated with either melatonin or agomelatine and were compared to those treated with conventional prophylactic therapy or placebo. The findings of this review suggest that melatonin significantly reduces the frequency and severity of migraines, but its dose-dependent action and benefits remain debatable. Melatonin may also have a role in weight control, warranting additional research in this direction.

Homeostatic Shrinkage of Dendritic Spines Requires Melatonin Type 3 Receptor Activation During Sleep

High-frequency oscillatory activity in cognition-related neural circuits during wakefulness consistently induces the growth of dendritic spines and axonal terminals. Although these structural changes are essential for cognitive functions, it is hypothesized that if these newly expanded structures fail to establish functional connections, they may become superfluous. Sleep is believed to facilitate the reduction of such redundant structures to maintain neural homeostasis. However, the mechanisms underlying this pruning process during sleep remain poorly understood. In this study, that melatonin type 3 receptors (MT3Rs) are selectively expressed in the stellate neurons of the medial entorhinal cortex (MEC) is demonstrated, an area where high melatonin levels are detected during sleep. Activation of MT3Rs during sleep initiates the shrinkage of dendritic spines in stellate neurons by downregulating neural network activity and dephosphorylating synaptic proteins in the MEC. This process is disrupted when MT3R expression is knocked down or when MT3Rs are blocked during sleep. Notably, interference with MT3Rs in the MEC during sleep impairs the acquisition of spatial memory but does not affect object memory acquisition following sleep. These findings reveal novel molecular mechanisms involving melatonin and MT3Rs in the regulation of dendritic spine shrinkage during sleep, which is crucial for the acquisition and consolidation of spatial memory.

Melatonin inhibits voltage-gated potassium KV4.2 channels and negatively regulates melatonin secretion in rat pineal glands

Melatonin is synthesized in and secreted from the pineal glands and regulates circadian rhythms. Although melatonin has been reported to modulate the activity of ion channels in several tissues, its effects on pineal ion channels remain unclear. In the present study, the effects of melatonin on voltage-gated K+ (KV) channels, which play a role in regulating the resting membrane potential, were examined in rat pinealocytes. The application of melatonin reduced pineal KV currents in a concentration-dependent manner (IC50 = 309 µM). An expression analysis revealed that KV4.2 channels were highly expressed in rat pineal glands. Melatonin-sensitive currents were abolished by the small interfering RNA knockdown of KV4.2 channels in rat pinealocytes. In human embryonic kidney 293 (HEK293) cells expressing KV4.2 channels, melatonin decreased outward currents (IC50 = 479 µM). Inhibitory effects were mediated by a shift in the voltage dependence of steady-state inactivation in a hyperpolarizing direction. This inhibition was observed even in the presence of 100 nM luzindole, an antagonist of melatonin receptors. Melatonin also blocked the activity of KV4.3, KV1.1, and KV1.5 channels in reconstituted HEK293 cells. The application of 1 mM melatonin caused membrane depolarization in rat pinealocytes. Furthermore, KV4.2 channel inhibition by 5 mM 4-aminopyridine attenuated melatonin secretion induced by 1 µM noradrenaline in rat pineal glands. These results strongly suggest that melatonin directly inhibited KV4.2 channels and caused membrane depolarization in pinealocytes, resulting in a decrease in melatonin secretion through parasympathetic signaling pathway. This mechanism may function as a negative-feedback mechanism of melatonin secretion in pineal glands. NEW & NOTEWORTHY Melatonin is a hormone that is synthesized in and secreted from the pineal glands, which regulates circadian rhythms. However, the effects of melatonin on pineal ion channels remain unclear. The present study demonstrated that melatonin directly inhibited voltage-gated potassium KV4.2 channels, which are highly expressed in rat pinealocytes, and induced membrane depolarization, resulting in a decrease in melatonin secretion. This mechanism may function as a negative-feedback mechanism of melatonin secretion in pineal glands.

Mechanisms underlying delirium in patients with critical illness

Delirium is an acute, global cognitive disorder syndrome, also known as acute brain syndrome, characterized by disturbance of attention and awareness and fluctuation of symptoms. Its incidence is high among critically ill patients. Once patients develop delirium, it increases the risk of unplanned extubation, prolongs hospital stay, increases the risk of nosocomial infection, post-intensive care syndrome-cognitive impairment, and even death. Therefore, it is of great importance to understand how delirium occurs and to reduce the incidence of delirium in critically ill patients. This paper reviews the potential pathophysiological mechanisms of delirium in critically ill patients, with the aim of better understanding its pathophysiological processes, guiding the formulation of effective prevention and treatment strategies, providing a basis for clinical medication.

The role of nitric oxide and neuroendocrine system in pain generation

Previous studies have indicated a complex interplay between the nitric oxide (NO) pain signaling pathways and hormonal signaling pathways in the body. This article delineates the role of nitric oxide signaling in neuropathic and inflammatory pain generation and subsequently discusses how the neuroendocrine system is involved in pain generation. Hormonal systems including the hypothalamic-pituitary axis (HPA) generation of cortisol, the renin-angiotensin-aldosterone system, calcitonin, melatonin, and sex hormones could potentially contribute to the generation of nitric oxide involved in the sensation of pain. Further research is necessary to clarify this relationship and may reveal therapeutic targets involving NO signaling that alleviate neuropathic and inflammatory pain.

Melatonin in animal husbandry: functions and applications

Melatonin (N-acetyl-5-methoxytryptamine) is an essential small molecule with diverse biological functions. It plays several key roles, including regulating the secretion of reproductive hormones and the reproductive cycle, enhancing the functionality of reproductive organs, improving the quality of sperm and eggs, and mitigating oxidative stress in the reproductive system. Melatonin effectively inhibits and scavenges excess free radicals while activating the antioxidant enzyme system and reduces the production of inflammatory factors and alleviates tissue damage caused by inflammation by regulating inflammatory pathways. Additionally, melatonin contributes to repairing the intestinal barrier and regulating the gut microbiota, thereby reducing bacterial and toxin permeation. The use of melatonin as an endogenous hormone in animal husbandry has garnered considerable attention because of its positive effects on animal production performance, reproductive outcomes, stress adaptation, disease treatment, and environmental sustainability. This review explores the characteristics and biological functions of melatonin, along with its current applications in animal production. Our findings may serve as a reference for the use of melatonin in animal farming and future developmental directions.

Effect of melatonin as a therapeutic strategy against intrauterine growth restriction: a mini-review of current state

Intrauterine growth restriction (IUGR) or intrauterine growth retardation is a condition that the fetus does not grow as expected. And the biometric profile does not match with the age of fetus. This condition is associated with increased mortality and morbidity of the neonates along with increased risk of cardiovascular, lung, and central nervous system damage. Despite close monitoring of high-risk mothers and the development of new therapeutic approaches, the optimal outcome has not been achieved yet that it indicates the importance of investigations on new therapeutic approaches. Melatonin (MLT) is a neurohormone mainly produced by the pineal gland and has a wide range of effects on different organs due to the broad dispersion of its receptors. Moreover, melatonin is produced by the placenta and also its receptors have been found on the surface of this organ. Not only studies showed the importance of this neurohormone on growth and development of fetus but also they proved its highly anti-oxidant properties. As in IUGR the oxidative stress and inflammation increased melatonin could counteract these changes and improved organ's function. In this study, we found that use of MLT could be a good clinical approach for the treatment of IUGR as its high anti-oxidant activity and vasodilation could dampen the mechanisms lead to the IUGR development.

Melatonin Regulates Osteoblast Differentiation through the m6A Reader hnRNPA2B1 under Simulated Microgravity

Recent studies have confirmed that melatonin and N6-methyladenosine (m6A) modification can influence bone cell differentiation and bone formation. Melatonin can also regulate a variety of biological processes through m6A modification. Heterogeneous nuclear ribonucleoprotein A2/B1 (hnRNPA2B1) serves as a reader of m6A modification. In this study, we used the hindlimb unloading model as an animal model of bone loss induced by simulated microgravity and used 2D clinorotation to simulate a microgravity environment for cells on the ground. We found that hnRNPA2B1 was downregulated both in vitro and in vivo during simulated microgravity. Further investigations showed that hnRNPA2B1 could promote osteoblast differentiation and that overexpression of hnRNPA2B1 attenuated the suppression of osteoblast differentiation induced by simulated microgravity. We also discovered that melatonin could promote the expression of hnRNPA2B1 under simulated microgravity. Moreover, we found that promotion of osteoblast differentiation by melatonin was partially dependent on hnRNPA2B1. Therefore, this research revealed, for the first time, the role of the melatonin/hnRNPA2B1 axis in osteoblast differentiation under simulated microgravity. Targeting this axis may be a potential protective strategy against microgravity-induced bone loss and osteoporosis.

Participation of Ca2+-Calmodulin-Dependent Protein Kinase II in the Antidepressant-Like Effects of Melatonin

Melatonin (N-acetyl-5-methoxytryptamine) is an indoleamine secreted by the pineal gland during the dark phase of the photoperiod. Its main function is the synchronization of different body rhythms with the dark-light cycle. Research on melatonin has significantly advanced since its discovery and we now know that it has considerable significance in various physiological processes, including immunity, aging, and reproduction. Moreover, in recent years evidence of the pharmacological possibilities of melatonin has increased. Indoleamine, on the other hand, has antidepressant-like effects in rodents, which may be mediated by the activation of calcium-calmodulin-dependent kinase II (CaMKII) and are also related to the regulation of neuroplasticity processes, including neurogenesis, synaptic maintenance, and long-term potentiation. Remarkably, patients with major depression show decreased levels of circulating melatonin in plasma. This review presents evidence of the antidepressant-like effects of melatonin in preclinical models and the participation of CaMKII in these actions. CaMKII's role in cognition and memory processes, which are altered in depressive states, are part of the review, and the effects of melatonin in these processes are also reviewed. Furthermore, participation of CaMKII on structural and synaptic plasticity and the effects of melatonin are also described. Finally, the advantages of using melatonin in combination with other antidepressants such as ketamine for neuroplasticity are described. Evidence supports that CaMKII is activated by melatonin and downstream melatonin receptors and may be the common effector in the synergistic effects of melatonin with other antidepressants. SIGNIFICANCE STATEMENT: This review compiled evidence supporting that melatonin causes antidepressant-like effects in mice through calmodulin kinase II stimulation of downstream melatonin receptors as well as the participation of this enzyme in neuroplasticity, memory, and cognition. Finally, we describe evidence about the effectiveness of antidepressant-like effects of melatonin in combination with ketamine.

Ramelteon protects against social defeat stress-associated abnormal behaviors

Psychological stress affects the neuroendocrine regulation, which modulates mental status and behaviors. Melatonin, a hormone synthesized primarily by the pineal gland, regulates many brain functions, including circadian rhythms, pain, sleep, and mood. Selective pharmacological melatonin agonist ramelteon has been clinically used to treat mood and sleep disorders. Posttraumatic stress disorder (PTSD) is a psychiatric condition associated with severe trauma; it is generally triggered by traumatic events, which lead to severe anxiety and uncontrollable trauma recall. We recently reported that repeated social defeat stress (RSDS) may induce robust anxiety-like behaviors and social avoidance in mice. In the present study, we investigated whether melatonin receptor activation by melatonin and ramelteon regulates RSDS-induced behavioral changes. Melatonin treatment improved social avoidance and anxiety-like behaviors in RSDS mice. Moreover, treatment of the non-selective MT1/MT2 receptor agonist, ramelteon, markedly ameliorated RSDS-induced social avoidance and anxiety-like behaviors. Moreover, activating melatonin receptors also balanced the expression of monoamine oxidases, glucocorticoid receptors, and endogenous antioxidants in the hippocampus. Taken together, our findings indicate that the activation of both melatonin and ramelteon regulates RSDS-induced anxiety-like behaviors and PTSD symptoms. The current study also showed that the regulatory effects of neuroendocrine mechanisms and cognitive behaviors on melatonin receptor activation in repeated social defeat stress.

Bioactive Peptides in Dairy Milk: Highlighting the Role of Melatonin

Melatonin, an endogenous indolamine derived from tryptophan, is primarily synthesized by the pineal gland in mammals and regulated by a complex neural system. Its release follows a circadian rhythm, which is crucial for regulating physiological processes in response to light-dark cycles in both humans and animals. In this review, we report that the presence of this hormone in bovine milk, with significant differences in concentration between daytime and nighttime milking, has increased interest in milk as a natural source of bioactive molecules. Melatonin lowers cortisol levels at night, reduces body temperature and blood pressure, coinciding with decreased alertness and performance, acts as an antioxidant and anti-inflammatory agent, modulates the immune system, offers neuroprotective benefits, and supports gastrointestinal health by scavenging free radicals and reducing oxidative stress in dairy cows. Many factors influence the release of melatonin, such as the intensity of artificial lighting during nighttime milking, the frequency of milkings, milk yield, and genetic differences between animals. Nocturnal milking under low-intensity light boosts melatonin, potentially reducing oxidative damage and mastitis risk. Additionally, ultra-high temperature (UHT) treatment does not significantly affect the melatonin content in milk. However, further research on its stability during milk processing and storage is crucial for ensuring product efficacy. In some countries, nighttime milk with naturally elevated melatonin content is already commercialized as a natural aid for sleep. Thus, naturally melatonin-rich milk may be a promising alternative to synthetic supplements for promoting better sleep and overall well-being.

Significance of Melatonin in the Regulation of Circadian Rhythms and Disease Management

Melatonin, the 'hormone of darkness' is a neuronal hormone secreted by the pineal gland and other extra pineal sites. Responsible for the circadian rhythm and seasonal behaviour of vertebrates and mammals, melatonin is responsible for regulating various physiological conditions and the maintenance of sleep, body weight and the neuronal activities of the ocular sites. With its unique amphiphilic structure, melatonin can cross the cellular barriers and elucidate its activities in the subcellular components, including mitochondria. Melatonin is a potential scavenger of oxygen and nitrogen-reactive species and can directly obliterate the ROS and RNS by a receptor-independent mechanism. It can also regulate the pro- and anti-inflammatory cytokines in various pathological conditions and exhibit therapeutic activities against neurodegenerative, psychiatric disorders and cancer. Melatonin is also found to show its effects on major organs, particularly the brain, liver and heart, and also imparts a role in the modulation of the immune system. Thus, melatonin is a multifaceted candidate with immense therapeutic potential and is still considered an effective supplement on various therapies. This is primarily due to rectification of aberrant circadian rhythm by improvement of sleep quality associated with risk development of neurodegenerative, cognitive, cardiovascular and other metabolic disorders, thereby enhancing the quality of life.

Selective Enhancement of REM Sleep in Male Rats through Activation of Melatonin MT1 Receptors Located in the Locus Ceruleus Norepinephrine Neurons

Sleep disorders affect millions of people around the world and have a high comorbidity with psychiatric disorders. While current hypnotics mostly increase non-rapid eye movement sleep (NREMS), drugs acting selectively on enhancing rapid eye movement sleep (REMS) are lacking. This polysomnographic study in male rats showed that the first-in-class selective melatonin MT1 receptor partial agonist UCM871 increases the duration of REMS without affecting that of NREMS. The REMS-promoting effects of UCM871 occurred by inhibiting, in a dose-response manner, the firing activity of the locus ceruleus (LC) norepinephrine (NE) neurons, which express MT1 receptors. The increase of REMS duration and the inhibition of LC-NE neuronal activity by UCM871 were abolished by MT1 pharmacological antagonism and by an adeno-associated viral (AAV) vector, which selectively knocked down MT1 receptors in the LC-NE neurons. In conclusion, MT1 receptor agonism inhibits LC-NE neurons and triggers REMS, thus representing a novel mechanism and target for REMS disorders and/or psychiatric disorders associated with REMS impairments.

Melatonin via MTNR1B regulates METTL3 to protect ileum cell differentiation

Intestinal stem cells rapidly differentiate into various epithelial cells, playing a crucial role in maintaining intestinal homeostasis. Melatonin, a known endogenous molecule with anti-inflammatory and antioxidant properties, has its potential efficacy in ileum stem cells differentiation not fully understood to date. This study indicates that melatonin suppresses ileum inflammation and maintains normal differentiation of ileum stem cells through MTNR1B. Subsequent outcomes following treatment with MTNR1B inhibitors further substantiate these findings. Additionally, overexpression of METTL3 protein appears to be a potential instigator for promoting ileum inflammation and disruptions in cell differentiation. Treatment with the METTL3 inhibitor SAH significantly inhibits ileum inflammation and Wnt/β-catenin activity, thereby sustaining normal cellular differentiation functions. In summary, this study showed that melatonin may improve ileum inflammation and maintain cell differentiation functions by inhibiting abnormal METTL3 expression via MTNR1B.

Paraquat disrupts KIF5A-mediated axonal mitochondrial transport in midbrain neurons and its antagonism by melatonin

Paraquat (PQ) is a broad-spectrum herbicide used worldwide and is a hazardous chemical to human health. Cumulative evidence strengthens the association between PQ exposure and the development of Parkinson's disease (PD). However, the underlying mechanism and effective interventions against PQ-induced neurotoxicity remain unclear. In this study, C57BL/6 J mice were treated with PQ (i.p., 10 mg/kg, twice a week) and melatonin (i.g., 20 mg/kg, twice a week) for 8 weeks. Results showed that PQ-induced motor deficits and midbrain dopaminergic neuronal damage in C57BL/6 J mice were protected by melatonin pretreatment. In isolated primary midbrain neurons and SK-N-SH cells, reduction of cell viability, elevation of total ROS levels, axonal mitochondrial transport defects and mitochondrial dysfunction caused by PQ were attenuated by melatonin. After screening of expression of main motors driving axonal mitochondrial transport, data showed that PQ-decreased KIF5A expression in mice midbrain and in SK-N-SH cell was antagonized by melatonin. Using the in vitro KIF5A-overexpression model, it was found that KIF5A overexpression inhibited PQ-caused neurotoxicity and mitochondrial dysfunction in SK-N-SH cells. In addition, application of MTNR1B (MT2) receptor antagonist, 4-P-PDOT, significantly counteracted the protection of melatonin against PQ-induced neurotoxicity. Further, Kif5a-knockdown diminished melatonin-induced alleviation of motor deficits and neuronal damage against PQ in C57BL/6 J mice. The present study establishes a causal link between environmental neurotoxicants exposure and PD etiology and provides effective interventive targets in the pathogenesis of PD.

Melatonin regulates mitochondrial function to alleviate ferroptosis through the MT2/Akt signaling pathway in swine testicular cells

Increasing evidence has shown that many environmental and toxic factors can cause testicular damage, leading to testicular ferroptosis and subsequent male reproductive disorders. Melatonin is a major hormone and plays an vital role in regulating male reproduction. However, there is a lack of research on whether Mel can alleviate testicular cell ferroptosis and its specific mechanism. In this study, the results indicated that Mel could enhance the viability of swine testis cells undergoing ferroptosis, reduce LDH enzyme release, increase mitochondrial membrane potential, and affect the expression of ferroptosis biomarkers. Furthermore, we found that melatonin depended on melatonin receptor 1B to exert these functions. Detection of MMP and ferroptosis biomarker protein expression confirmed that MT2 acted through the downstream Akt signaling pathway. Moreover, inhibition of the Akt signaling pathway can eliminate the protective effect of melatonin on ferroptosis, inhibit AMPK phosphorylation, reduce the expression of mitochondrial gated channel (VDAC2/3), and affect mitochondrial DNA transcription and ATP content. These results suggest that melatonin exerts a beneficial effect on mitochondrial function to mitigate ferroptosis through the MT2/Akt signaling pathway in ST cells.

Sleep and Oxidative Stress: Current Perspectives on the Role of NRF2

Sleep is a fundamental conserved physiological state across evolution, suggesting vital biological functions that are yet to be fully clarified. However, our understanding of the neural and molecular basis of sleep regulation has increased rapidly in recent years. Among various processes implicated in controlling sleep homeostasis, a bidirectional relationship between sleep and oxidative stress has recently emerged. One proposed function of sleep may be the mitigation of oxidative stress in both brain and peripheral tissues, contributing to the clearance of reactive species that accumulate during wakefulness. Conversely, reactive species, such as reactive oxygen species (ROS) and reactive nitrogen species (RNS), at physiological levels, may act as signaling agents to regulate redox-sensitive transcriptional factors, enzymes, and other effectors involved in the regulation of sleep. As a primary sensor of intracellular oxidation, the transcription factor NRF2 is emerging as an indispensable component to maintain cellular redox homeostasis during sleep. Indeed, a number of studies have revealed an association between NRF2 dysfunction and the most common sleep conditions, including sleep loss, obstructive sleep apnea, and circadian sleep disturbances. This review examines the evidence of the intricate link between oxidative stress and NRF2 function in the context of sleep, and highlights the potential of NRF2 modulators to alleviate sleep disturbances.

Melatonin and Vascular Function

The indolamine hormone melatonin, also known as N-acetyl-5-methoxytrypamine, is frequently associated with circadian rhythm regulation. Light can suppress melatonin secretion, and photoperiod regulates melatonin levels by promoting its production and secretion at night in response to darkness. This hormone is becoming more and more understood for its functions as an immune-modulatory, anti-inflammatory, and antioxidant hormone. Melatonin may have a major effect on several diabetes-related disturbances, such as hormonal imbalances, oxidative stress, sleep disturbances, and mood disorders, according to recent research. This has raised interest in investigating the possible therapeutic advantages of melatonin in the treatment of diabetic complications. In addition, several studies have described that melatonin has been linked to the development of diabetes, cancer, Alzheimer's disease, immune system disorders, and heart diseases. In this review, we will highlight some of the functions of melatonin regarding vascular biology.

Melatonin as an add-on anti-seizure medication in children with epilepsy: An open-label randomized controlled trial

Objectives:

The primary objective of this study is to measure the effect of melatonin in decreasing seizure frequency in intervention group as compared to controls in children with drug-resistant epilepsy.

Materials and Methods:

An open-label randomized controlled trial was conducted from July 2020 to June 2022 in children between 2 and 14 years with drug-resistant epilepsy attending Pediatric and Neurology outpatient department and inpatient department. After noting down baseline seizure frequency, children were randomized into the melatonin group and control group. In the melatonin group, add-on melatonin was added to the existing ASM, and in the control group, ASMs were continued. The primary and secondary outcomes were measured after 3 months of follow-up.

Results:

The percentage change in the seizure frequency between both groups at the end of 3 months of follow-up was not statistically significant, but the percentage reduction of seizure frequency was more than 50% in the melatonin group. Melatonin was well tolerated in our children except for 4 (22%) who developed minor adverse effects.

Conclusion:

Add-on melatonin decreases seizure frequency to some extent which was not statistically significant with no major side effects. Further studies are needed to assess add-on melatonin’s long-term effectiveness and safety in children with drug-resistant epilepsy.