Do peripheral melatonin agonists improve bone fracture healing? The effects of agomelatine and ramelteon on experimental bone fracture

The Therapeutic Potential of Melatonin and Its Novel Synthetic Analogs in Circadian Rhythm Sleep Disorders, Inflammation-Associated Pathologies, and Neurodegenerative Diseases

Melatonin, N-acetyl-5-methoxytryptamine, is a tryptophan-derived hormone mostly produced in the pineal gland, despite being synthesized locally at several tissues and organs. This production is rhythmically controlled by complex clock gene networks in the master pacemaker located in the suprachiasmatic nucleus of the hypothalamus. Melatonin is usually secreted only during the dark phase of the day and is essential to synchronize circadian rhythms and neuroendocrine physiological processes. Its main clinical use is associated with the treatment of jet lag and other circadian rhythm sleep disorders, with a growing number of other promising therapeutic applications due to the diverse physiological roles of melatonin. In this review, we explore melatonin and its receptors and provide an updated overview on research concerning the role of melatonin, either as an endogenous molecule or as a drug, in: sleep-wake cycle regulation; circadian rhythms; inflammatory processes that may compromise cardiovascular, respiratory, gastrointestinal, renal, and reproductive system functions; and neurodegenerative disorders such as Alzheimer's and Parkinson's disease. The most recent and promising research findings concerning melatonin synthetic analogs such as agomelatine and ramelteon are highlighted, pointing toward new compounds with promising pharmacological activity while emphasizing their structural differences and advantages when compared to melatonin.

Melatonin and bone-related diseases: an updated mechanistic overview of current evidence and future prospects

PURPOSE

Bone diseases account for an enormous cost burden on health systems. Bone disorders are considered as age-dependent diseases. The aging of world population has encouraged scientists to further explore the most effective preventive modalities and therapeutic strategies to overcome and reduce the high cost of bone disorders. Herein, we review the current evidence of melatonin's therapeutic effects on bone-related diseases.

METHODS

This review summarized evidences from in vitro, in vivo, and clinical studies regarding the effects of melatonin on bone-related diseases, with a focus on the molecular mechanisms. Electronically, Scopus and MEDLINE®/PubMed databases were searched for articles published on melatonin and bone-related diseases from inception to June 2023.

RESULTS

The findings demonstrated that melatonin has beneficial effect in bone- and cartilage-related disorders such as osteoporosis, bone fracture healing, osteoarthritis, and rheumatoid arthritis, in addition to the control of sleep and circadian rhythms.

CONCLUSION

A number of animal and clinical studies have indicated that various biological effects of melatonin may suggest this molecule as an effective therapeutic agent for controlling, diminishing, or suppressing bone-related disorders. Therefore, further clinical studies are required to clarify whether melatonin can be effective in patients with bone-related diseases.

The Putative Role of Neuroinflammation in the Interaction between Traumatic Brain Injuries, Sleep, Pain and Other Neuropsychiatric Outcomes: A State-of-the-Art Review

Sleep disturbances are widely prevalent following a traumatic brain injury (TBI) and have the potential to contribute to numerous post-traumatic physiological, psychological, and cognitive difficulties developing chronically, including chronic pain. An important pathophysiological mechanism involved in the recovery of TBI is neuroinflammation, which leads to many downstream consequences. While neuroinflammation is a process that can be both beneficial and detrimental to individuals' recovery after sustaining a TBI, recent evidence suggests that neuroinflammation may worsen outcomes in traumatically injured patients, as well as exacerbate the deleterious consequences of sleep disturbances. Additionally, a bidirectional relationship between neuroinflammation and sleep has been described, where neuroinflammation plays a role in sleep regulation and, in turn, poor sleep promotes neuroinflammation. Given the complexity of this interplay, this review aims to clarify the role of neuroinflammation in the relationship between sleep and TBI, with an emphasis on long-term outcomes such as pain, mood disorders, cognitive dysfunctions, and elevated risk of Alzheimer's disease and dementia. In addition, some management strategies and novel treatment targeting sleep and neuroinflammation will be discussed in order to establish an effective approach to mitigate long-term outcomes after TBI.

Melatonin promoted osteogenesis of human periodontal ligament cells by regulating mitochondrial functions through the translocase of the outer mitochondrial membrane 20

BACKGROUND AND OBJECTIVE

Melatonin plays an important role in various beneficial functions, including promoting differentiation. However, effects on osteogenic differentiation, especially in human periodontal cells (hPDLCs), still remain inconclusive. Mitochondria are highly dynamic organelles that play an important role in various biological processes in cells, including energy metabolism and oxidative stress reaction. Furthermore, the translocase of the outer mitochondrial membrane 20 (TOM20) is responsible for recognizing and transporting precursor proteins. Thus, the objective of this study was to evaluate the functionality of melatonin on osteogenesis in human periodontal cells and to explore the involved mechanism of mitochondria.

METHODS

The hPDLCs were extracted and identified by flow cytometry and multilineage differentiation. We divided hPDLCs into control group, osteogenic induction group, and osteogenesis with melatonin treatment group (100, 10, and 1 μM). Then we used a specific siRNA to achieve interference of TOM20. Alizarin red and Alkaline phosphatase staining and activity assays were performed to evaluate osteogenic differentiation. Osteogenesis-related genes and proteins were measured by qPCR and western blot. Mitochondrial functions were tested using ATP, NAD+/NADH, JC-1, and Seahorse Mito Stress Test kits. Finally, TOM20 and mitochondrial dynamics-related molecules expression were also assessed by qPCR and western blot.

RESULTS

Our results showed that melatonin-treated hPDLCs had higher calcification and ALP activity as well as upregulated OCN and Runx2 expression at mRNA and protein levels, which was the most obvious in 1 μM melatonin-treated group. Meanwhile, melatonin supplement elevated intracellular ATP production and mitochondrial membrane potential by increasing mitochondrial oxidative metabolism, hence causing a lower NAD⁺ /NADH ratio. In addition, we also found that melatonin treatment raised TOM20 level and osteogenesis and mitochondrial functions were both suppressed after knocking down TOM20.

CONCLUSION

We found that melatonin promoted osteogenesis of hPDLCs and 1 μM melatonin had the most remarkable effect. Melatonin treatment can reinforce mitochondrial functions by upregulating TOM20.

Homo sapiens May Incorporate Daily Acute Cycles of “Conditioning–Deconditioning” to Maintain Musculoskeletal Integrity: Need to Integrate with Biological Clocks and Circadian Rhythm Mediators

Human evolution required adaptation to the boundary conditions of Earth, including 1 g gravity. The bipedal mobility of Homo sapiens in that gravitational field causes ground reaction force (GRF) loading of their lower extremities, influencing the integrity of the tissues of those extremities. However, humans usually experience such loading during the day and then a period of relative unloading at night. Many studies have indicated that loading of tissues and cells of the musculoskeletal (MSK) system can inhibit their responses to biological mediators such as cytokines and growth factors. Such findings raise the possibility that humans use such cycles of acute conditioning and deconditioning of the cells and tissues of the MSK system to elaborate critical mediators and responsiveness in parallel with these cycles, particularly involving GRF loading. However, humans also experience circadian rhythms with the levels of a number of mediators influenced by day/night cycles, as well as various levels of biological clocks. Thus, if responsiveness to MSK-generated mediators also occurs during the unloaded part of the daily cycle, that response must be integrated with circadian variations as well. Furthermore, it is also possible that responsiveness to circadian rhythm mediators may be regulated by MSK tissue loading. This review will examine evidence for the above scenario and postulate how interactions could be both regulated and studied, and how extension of the acute cycles biased towards deconditioning could lead to loss of tissue integrity.

Relevance of Sleep Disturbances to Orthopaedic Surgery: A Current Concepts Narrative and Practical Review

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Sleep disturbances can increase the risk of falls and motor vehicle accidents and may reduce bone density.

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Poor sleep can lead to worse outcomes after fracture, such as chronic pain and delayed recovery.

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Orthopaedic surgeons can play an important role in the screening of sleep disorders among their patients.

Aprepitant: an antiemetic drug, contributes to the prevention of acute lung injury with its anti-inflammatory and antioxidant properties

OBJECTIVES

We investigated, the effects of aprepitant (APRE) on the lung tissues of rats with an experimental polymicrobial sepsis model (CLP: cecal ligation and puncture) biochemically, molecularly and histopathologically.

METHODS

A total of 40 rats were divided into 5 groups with 8 animals in each group. Group 1 (SHAM), control group; Group 2 (CLP), cecal ligation and puncture; Group 3 (CLP + APRE10), rats were administered CLP + 10 mg/kg aprepitant; Group 4 (CLP + APRE20), rats were administered CLP + 20 mg/kg aprepitant; and Group 5 (CLP + APRE40), rats were administered CLP + 40 mg/kg aprepitant. A polymicrobial sepsis model was induced with CLP. After 16 h, lung tissues were taken for examination. Tumour necrosis factor α (TNF-α) and nuclear factor-kappa b (NFK-b) messenger ribonucleic acid (mRNA) expressions were analysed by real-time PCR (RT-PCR), biochemically antioxidant parameters such as superoxide dismutase (SOD) and glutathione (GSH) and oxidant parameters such as malondialdehyde (MDA) and lung damage histopathologically.

KEY FINDINGS AND CONCLUSIONS

The GSH level and SOD activity increased while the MDA level and the expressions of TNF-α and NFK-b were reduced in the groups treated with APRE, especially in the CLP + APRE40 group. The histopathology results supported the molecular and biochemical results.

The Effects of Agomelatine Treatment on Lipopolysaccharide-Induced Septic Lung Injuries in Rats

Objective

We designed an experimental model of sepsis in rats to investigate the effects of agomelatine (AGO) on lung tissues using molecular and histopathological methods.

Materials and Methods

In our experimental model, the 32 rats were divided into 4 groups: group 1: control group (HEALTHY); group 2: lipopolysaccharide group (LPS); group 3: LPS plus 50 mg/kg AGO group (LPS + AGO50); and group 4: LPS plus 100 mg/kg AGO group (LPS + AGO100). An LPS-induced sepsis model was performed to replicate the pathology of sepsis. Rats from all 4 groups were killed after 12 hours, and their lungs were quickly collected. To investigate the therapeutic strategy, we evaluated tumor necrosis factor-alpha (TNF-α) and nuclear factor-kappa B (NF-κB) messenger RNA expressions by real-time polymerase chain reaction using molecular methods and lung tissue damage indicators using histopathological methods.

Results

The expressions of TNF-α and NF-κB were reduced in the groups treated with AGO. The histopathology results supported the molecular results.

Conclusion

In this experimental study, we demonstrated for the first time the positive effects of AGO on LPS-induced sepsis in lung tissue using molecular and histopathological methods, indicating that it contributes to the prevention of lung damage.

Agomelatine, A Potential Multi-Target Treatment Alternative for Insomnia, Depression, and Osteoporosis in Postmenopausal Women: A Hypothetical Model

Insomnia, which is associated with menopausal depression, is a common symptom of menopause. Both symptoms have a common etiology, and can affect each other significantly. Pharmacological interventions, including hypnotics and antidepressants, and non-pharmacological therapies are generally administered in clinical practice for insomnia treatment. As another menopausal disorder, osteoporosis is described as a disease of low bone mineral density (BMD), affecting nearly 200 million women worldwide. Postmenopausal osteoporosis is common among middle-aged women. Since postmenopausal osteoporosis mainly results from low estrogen levels, menopausal hormone therapy (HT) is considered the first-line option for the prevention of osteoporosis during the menopausal period. However, almost no study has evaluated novel treatments for the combined prevention of insomnia, depression, and osteoporosis. Hence, it is necessary to develop new multi-target strategies for the treatment of these disorders to improve the quality of life during this vulnerable period. Melatonin is the major regulator of sleep, and it has been suggested to be safe and effective for bone loss therapy by MT-2 receptor activity. As a result, we hypothesize that agomelatine, an MT-1 and MT-2 receptor agonist and 5-HT_2C receptor antagonist, holds promise in the combined treatment of insomnia, depression, and osteoporosis in middle-aged women during menopause.