Melatonin dietary supplement as an anti-aging therapy for age-related bone loss

Melatonin: a ferroptosis inhibitor with potential therapeutic efficacy for the post-COVID-19 trajectory of accelerated brain aging and neurodegeneration

The unprecedented pandemic of COVID-19 swept millions of lives in a short period, yet its menace continues among its survivors in the form of post-COVID syndrome. An exponentially growing number of COVID-19 survivors suffer from cognitive impairment, with compelling evidence of a trajectory of accelerated aging and neurodegeneration. The novel and enigmatic nature of this yet-to-unfold pathology demands extensive research seeking answers for both the molecular underpinnings and potential therapeutic targets. Ferroptosis, an iron-dependent cell death, is a strongly proposed underlying mechanism in post-COVID-19 aging and neurodegeneration discourse. COVID-19 incites neuroinflammation, iron dysregulation, reactive oxygen species (ROS) accumulation, antioxidant system repression, renin-angiotensin system (RAS) disruption, and clock gene alteration. These events pave the way for ferroptosis, which shows its signature in COVID-19, premature aging, and neurodegenerative disorders. In the search for a treatment, melatonin shines as a promising ferroptosis inhibitor with its repeatedly reported safety and tolerability. According to various studies, melatonin has proven efficacy in attenuating the severity of certain COVID-19 manifestations, validating its reputation as an anti-viral compound. Melatonin has well-documented anti-aging properties and combating neurodegenerative-related pathologies. Melatonin can block the leading events of ferroptosis since it is an efficient anti-inflammatory, iron chelator, antioxidant, angiotensin II antagonist, and clock gene regulator. Therefore, we propose ferroptosis as the culprit behind the post-COVID-19 trajectory of aging and neurodegeneration and melatonin, a well-fitting ferroptosis inhibitor, as a potential treatment.

Melatonin as a chronobiotic/cytoprotective agent in bone. Doses involved

Because the chronobiotic and cytoprotective molecule melatonin diminishes with age, its involvement in postmenopausal and senescence pathology has been considered since long. One relevant melatonin target site in aging individuals is bone where melatonin chronobiotic effects mediated by MT1 and MT2 receptors are demonstrable. Precursors of bone cells located in bone marrow are exposed to high quantities of melatonin and the possibility arises that melatonin acts a cytoprotective compound via an autacoid effect. Proteins that are incorporated into the bone matrix, like procollagen type I c-peptide, augment after melatonin exposure. Melatonin augments osteoprotegerin, an osteoblastic protein that inhibits the differentiation of osteoclasts. Osteoclasts are target cells for melatonin as they degrade bone partly by generating free radicals. Osteoclast activity and bone resorption are impaired via the free radical scavenger properties of melatonin. The administration of melatonin in chronobiotic doses (less than 10 mg daily) is commonly used in clinical studies on melatonin effect on bone. However, human equivalent doses allometrically derived from animal studies are in the 1-1.5 mg/kg/day range for a 75 kg human adult, a dose rarely used clinically. In view of the absence of toxicity of melatonin in phase 1 pharmacological studies with doses up to 100 mg in normal volunteers, further investigation is needed to determine whether high melatonin doses have higher therapeutic efficacy in preventing bone loss.

Absence of melatonin during development impairs craniofacial and dental onset in rats

OBJECTIVE

Herein, we evaluated pinealectomy-induced melatonin absence to determine its effects on craniofacial and dental development in the offspring.

DESIGN

Female Wistar rats in three groups, i.e., intact pregnant rats, pinealectomized pregnant rats (PINX), and pinealectomized pregnant rats subjected to oral melatonin replacement therapy, were crossed 30 days after surgery. The heads of 7-day-old pups were harvested for cephalometric and histological analyses, and maxillae and incisors were collected for mRNA expression analysis.

RESULTS

The PINX pups exhibited a reduction in neurocranial and facial parameters such as a decrease in alveolar bone area, incisor size and proliferation, and an increase in odontoblasts and the dentin layer. Based on incisor mRNA expression analysis, we found that Dmp1 expression was upregulated, whereas Col1a1 expression was downregulated. Maxillary mRNA expression revealed that Rankl expression was upregulated, whereas that of Opn and Osx was downregulated.

CONCLUSION

Our results demonstrated that the absence of maternal melatonin during early life could affect dental and maxillary development in offspring, as well as delay odontogenesis and osteogenesis in maxillary tissues.

CLINICAL RELEVANCE

Our findings suggest that disruptions or a lack of melatonin during pregnancy may cause changes in craniofacial and dental development, at least in animal experiments; however, in humans, these feedings are still poorly understood, and thus careful evaluations of melatonin levels in humans need to be investigated in craniofacial alterations.

Modulatory influence of melatonin on apical periodontitis in Wistar rats fed a high-fat diet

OBJECTIVE

This study aimed to evaluate the influence of high-fat diet (HFD) and melatonin (MEL) treatment on the progression of inflammation and alveolar bone resorption (ABR) in rats with AP.

DESIGN

Forty male Wistar rats were divided into four groups: apical periodontitis (AP), HFDAP, APMEL and HFDAPMEL. The animals were fed an HFD or standard diet for 107 days. On the 7th day, the rats were subjected to AP, and after 70 days, the rats in the MEL groups were treated with MEL for 30 days. Post treatment, the animals were euthanized, and their jaws were retrieved for evaluation of bone resorption, intensity of the inflammatory response, and immunohistochemical analysis including tartrate-resistant acid phosphatase (TRAP) and interleukin-1β (IL-1β) levels and tumor necrosis factor (TNF)-α expression.

RESULTS

The APMEL group showed reduction in the inflammatory infiltrate and IL-1β expression relation to HFDAP, while the TNF-α levels did not differ among the groups. The HFDAP group showed an increase in the ABR. MEL reduced the TRAP levels in the APMEL and HFDAPMEL groups.

CONCLUSIONS

while MEL could reduce TRAP levels in the APMEL and HFDAPMEL groups, the reduction in the HFDAPMEL group was smaller than that in the APMEL group, demonstrating that the interaction between AP and HFD decreased the anti-resorptive effects of MEL.

The role of MEK1/2 and MEK5 in melatonin-mediated actions on osteoblastogenesis, osteoclastogenesis, bone microarchitecture, biomechanics, and bone formation

Melatonin, the primary hormone involved in circadian entrainment, plays a significant role in bone physiology. This study aimed to assess the role of MEK1/2 and MEK5 in melatonin-mediated actions in mouse and human mesenchymal stem cells (MSCs) and on bone using small-molecule inhibitors and CRISPR/Cas9 knockout approaches. Consistent with in vitro studies performed in mMSCs and hMSCs, nightly (25 mg/kg, i.p., 45 days) injections with PD184352 (MEK1/2 inhibitor) or Bix02189 (MEK5 inhibitor) or SC-1-151 (MEK1/2/5 inhibitor) demonstrated that MEK1/2 and MEK5 were the primary drivers underlying melatonin's actions on bone density, microarchitecture (i.e., trabecular number, separation, and connectivity density), and bone mechanical properties (i.e., ultimate stress) through increases in osteogenic (RUNX2, BMP-2, FRA-1, OPG) expression and decreases in PPARγ. Furthermore, CRISPR/Cas9 knockout of MEK1 or MEK5 in mMSCs seeded on PLGA scaffolds and placed into critical-size calvarial defects in Balb(c) mice (male and female) revealed that treatment with melatonin (15 mg/L; p.o., nightly, 90 days) mediates sex-specific actions of MEK1 and MEK5 in new bone formation. This study is the first to demonstrate a role for MEK1/2 and MEK5 in modulating melatonin-mediated actions on bone formation in vivo and in a sex-specific manner.

Assessment of the Therapeutic Potential of Melatonin for the Treatment of Osteoporosis Through a Narrative Review of Its Signaling and Preclinical and Clinical Studies

Melatonin is a bioamine produced primarily in the pineal gland, although peripheral sites, including the gut, may also be its minor source. Melatonin regulates various functions, including circadian rhythm, reproduction, temperature regulation, immune system, cardiovascular system, energy metabolism, and bone metabolism. Studies on cultured bone cells, preclinical disease models of bone loss, and clinical trials suggest favorable modulation of bone metabolism by melatonin. This narrative review gives a comprehensive account of the current understanding of melatonin at the cell/molecular to the systems levels. Melatonin predominantly acts through its cognate receptors, of which melatonin receptor 2 (MT2R) is expressed in mesenchymal stem cells (MSCs), osteoblasts (bone-forming), and osteoclasts (bone-resorbing). Melatonin favors the osteoblastic fate of MSCs, stimulates osteoblast survival and differentiation, and inhibits osteoclastogenic differentiation of hematopoietic stem cells. Produced from osteoblastic cells, osteoprotegerin (OPG) and receptor activator of nuclear factor kappa B ligand (RANKL) critically regulate osteoclastogenesis and melatonin by suppressing the osteoclastogenic RANKL, and upregulating the anti-osteoclastogenic OPG exerts a strong anti-resorptive effect. Although the anti-inflammatory role of melatonin favors osteogenic function and antagonizes the osteoclastogenic function with the participation of SIRT signaling, various miRNAs also mediate the effects of the hormone on bone cells. In rodent models of osteoporosis, melatonin has been unequivocally shown to have an anti-osteoporotic effect. Several clinical trials indicate the bone mass conserving effect of melatonin in aging/postmenopausal osteoporosis. This review aims to determine the possibility of melatonin as a novel class of anti-osteoporosis therapy through the critical assessment of the available literature.

Targeting Sirt1, AMPK, Nrf2, CK2, and Soluble Guanylate Cyclase with Nutraceuticals: A Practical Strategy for Preserving Bone Mass

There is a vast pre-clinical literature suggesting that certain nutraceuticals have the potential to aid the preservation of bone mass in the context of estrogen withdrawal, glucocorticoid treatment, chronic inflammation, or aging. In an effort to bring some logical clarity to these findings, the signaling pathways regulating osteoblast, osteocyte, and osteoclast induction, activity, and survival are briefly reviewed in the present study. The focus is placed on the following factors: the mechanisms that induce and activate the RUNX2 transcription factor, a key driver of osteoblast differentiation and function; the promotion of autophagy and prevention of apoptosis in osteoblasts/osteoclasts; and the induction and activation of NFATc1, which promotes the expression of many proteins required for osteoclast-mediated osteolysis. This analysis suggests that the activation of sirtuin 1 (Sirt1), AMP-activated protein kinase (AMPK), the Nrf2 transcription factor, and soluble guanylate cyclase (sGC) can be expected to aid the maintenance of bone mass, whereas the inhibition of the serine kinase CK2 should also be protective in this regard. Fortuitously, nutraceuticals are available to address each of these targets. Sirt1 activation can be promoted with ferulic acid, N1-methylnicotinamide, melatonin, nicotinamide riboside, glucosamine, and thymoquinone. Berberine, such as the drug metformin, is a clinically useful activator of AMPK. Many agents, including lipoic acid, melatonin, thymoquinone, astaxanthin, and crucifera-derived sulforaphane, can promote Nrf2 activity. Pharmacological doses of biotin can directly stimulate sGC. Additionally, certain flavonols, notably quercetin, can inhibit CK2 in high nanomolar concentrations that may be clinically relevant. Many, though not all, of these agents have shown favorable effects on bone density and structure in rodent models of bone loss. Complex nutraceutical regimens providing a selection of these nutraceuticals in clinically meaningful doses may have an important potential for preserving bone health. Concurrent supplementation with taurine, N-acetylcysteine, vitamins D and K2, and minerals, including magnesium, zinc, and manganese, plus a diet naturally high in potassium, may also be helpful in this regard.

Melatonin increases bone mass in normal, perimenopausal, and postmenopausal osteoporotic rats via the promotion of osteogenesis

Background

Osteoporosis is a disease threatening the health of millions of individuals. Melatonin is found to be a potential anti-osteoporosis drug. However, whether melatonin plays a role against osteoporosis at different stages of the menopause and the underlying mechanisms are unknown.

Methods

Ovariectomy was utilized as a model of perimenopausal and postmenopausal osteoporosis. A total of 100 mg/kg melatonin, or solvent alone, was added to the drinking water of the rats over 8 weeks. Perimenopausal rats immediately received intervention following ovariectomy while postmenopausal rats received intervention 8 weeks after ovariectomy. All rats underwent overdose anesthesia following intervention after which blood samples and femurs were collected for further analysis. Rat femurs were scanned using micro-CT and examined histologically. The serum levels of melatonin and osteogenic biochemical markers were measured and the expression of osteogenesis-associated genes (Runx2, Sp7) were quantified by real-time quantitative PCR. Alkaline phosphatase (ALP) activity and the gene expression (Col1a1, Runx2, Alpl, and Bglap) were measured after bone marrow mesenchymal stem cells (BMSCs) were osteogenically induced, both with and without melatonin in vitro. ALP staining and Alizarin Red S staining were used to identify osteogenesis.

Results

Analysis by micro-CT and histological staining demonstrated that bone mass decreased and bone microarchitecture deteriorated over time after ovariectomy. Intervention with melatonin increased bone mass in normal, perimenopausal, and postmenopausal osteoporotic rats. Serum levels of ALP continuously increased after ovariectomy while osteocalcin levels initially rose, then decreased. Melatonin increased the serum levels of ALP and osteocalcin and mRNA expression levels of Runx2 and Sp7 in normal and postmenopausal rats, the opposite of the markers in perimenopausal rats. In vitro study demonstrated that 100 μmol/L melatonin increased the mRNA expression of Col1a1, Runx2, and Alpl three and/or seven days after intervention, and Alpl and Bglap 14 d after intervention. Melatonin increased ALP activity and the extent of ALP and matrix mineralization in the late stage of osteogenesis.

Conclusions

Bone mass continuously decreased after ovariectomy, while melatonin increased bone mass and ameliorated bone metabolism in normal, perimenopausal, and postmenopausal osteoporotic rats due to the induction of osteogenic differentiation in BMSCs.

Melatonin Improves the Resistance of Oxidative Stress-Induced Cellular Senescence in Osteoporotic Bone Marrow Mesenchymal Stem Cells

Accumulation of senescent bone marrow-derived mesenchymal stem cells (BMMSCs) has led to an age-related bone loss. However, the role of stem cell senescence in estrogen deficiency-induced osteoporosis remains elusive. Though melatonin plays a vital role in bone metabolism regulation, the underlying mechanisms of melatonin-mediated antiosteoporosis are partially elucidated. Therefore, this study purposed to explore (1) whether estrogen deficiency causes cellular senescence of BMMSCs, and if so, (2) the potential of melatonin in preventing bone loss via senescence signaling inhibition. BMMSCs derived from ovariectomized (OVX) rats (OVX BMMSCs) showed an impaired osteogenic capacity, albeit having comparable levels of senescence biomarkers than the sham cells. When exposed to low levels of hydrogen peroxide (H₂O₂), OVX BMMSCs rapidly exhibited senescence-associated phenotypes such as the increased activity of senescence-associated β-galactosidase (SA-β-gal) and upregulation of cell cycle inhibitors. Notably, the in vitro treatment with melatonin hindered H₂O₂-induced senescence in OVX BMMSCs and restored their osteogenic capacity. Treatment with either SIRT1 inhibitor (sirtinol) or melatonin receptor antagonists (luzindole and 4-P-PDOT) eliminated melatonin protective effects, thus indicating its potential in preventing stem cell senescence via SIRT1 activation through the melatonin membrane receptors. Following in vivo intravenous administration with melatonin, it successfully protected the bone microstructure and preserved the antisenescence property of BMMSCs in OVX rats. Collectively, our findings demonstrated that melatonin protected against estrogen deficiency-related bone loss by improving the resistance of BMMSCs to cellular senescence. Therefore, melatonin-mediated antisenescence effect on stem cells provides vital information to facilitate the development of a novel and effective strategy for treating postmenopausal OP.

Melatonin in neuroskeletal biology

Osteoporosis and neurodegenerative diseases are common diseases in the aging population. Studies demonstrate the complex communication among skeletal, muscular, and nervous systems and point to the emerging roles of neuromuscular systems in bone homeostasis. The discovery that the nervous system directly regulates bone remodeling implies that osteoporosis is a neuroskeletal disease. Melatonin, a hormone secreted from the pineal gland, is a melatonin receptor 1A (MT1) and 1B (MT2) agonist and influences the function of diverse systems. Melatonin is a pharmaceutical ingredient in numerous medicines, over-the-counter medicines, nutraceuticals, and dietary supplements, which benefit disease prevention and treatment, including osteoporosis and neurodegenerative diseases. This review aims to summarize the recent advances in preventing senile, postmenopausal, and neurodegenerative osteoporosis with melatonin and provide new insights into how neuromuscular systems influence bone homeostasis. More preclinical and clinical studies in neuroskeletal biology will eventually improve the lives of people fighting osteoporosis.

Combined Effects of Low-Frequency Pulsed Electromagnetic Field and Melatonin on Ovariectomy-Induced Bone Loss in Mice

Pulsed electromagnetic field (PEMF) therapy and melatonin (MEL) supplementation are expected to be important strategies for the treatment of osteoporosis. The aim of the current study was to investigate the efficacy of PEMF therapy, MEL supplementation, a combination of PEMF therapy, and MEL supplementation (PEMF + MEL) in mice with bilateral ovariectomy (OVX)-induced osteoporosis. Forty 12-week-old female C57/BL mice were randomly assigned to five groups (n = 8/group): OVX, PEMF, MEL, PEMF + MEL, and sham-operation (sham) groups. All mice in the first four groups were subjected to OVX. The mice in the PEMF and PEMF + MEL groups were exposed to PEMF (75 Hz, 1.6 mT, 1 h/day for 12 weeks), while those in the MEL and PEMF + MEL groups were administered MEL (50 mg/kg, i.p.). Body mass, micro-computed tomography, histology, immunohistochemistry, and real-time polymerase chain reaction were performed. PEMF + MEL treatment enhanced bone volume fraction (BV/TV) 2.2-fold over OVX control (P < 0.001) and increased expression levels of collagen type I (COL1) 1.9-fold and bone morphogenetic protein 2 (BMP2) 2.5-fold. PEMF + MEL also reduced the ratio of bone surface/bone volume (BS/BV) by 40% (P < 0.05) and appeared to reduce the number of osteoclasts in the metaphysis area. Preservation of bone value and bone microarchitecture in the combined therapy group were found to be superior to those in the single treatment groups. However, there were no apparent differences between the PEMF and MEL groups. The use of a combination of PEMF therapy and MEL supplementation may be an effective method to treat osteoporosis. © 2021 Bioelectromagnetics Society.

Melatonin effects on bone: Implications for use as a therapy for managing bone loss

Melatonin is the primary circadian output signal from the brain and is mainly synthesized in pinealocytes. The rhythm and secretion of melatonin are under the control of an endogenous oscillator located in the SCN or the master biological clock. Disruptions in circadian rhythms by shift work, aging, or light at night are associated with bone loss and increased fracture risk. Restoration of nocturnal melatonin peaks to normal levels or therapeutic levels through timed melatonin supplementation has been demonstrated to provide bone-protective actions in various models. Melatonin is a unique molecule with diverse molecular actions targeting melatonin receptors located on the plasma membrane or mitochondria or acting independently of receptors through its actions as an antioxidant or free radical scavenger to stimulate osteoblastogenesis, inhibit osteoclastogenesis, and improve bone density. Its additional actions on entraining circadian rhythms and improving quality of life in an aging population coupled with its safety profile make it an ideal therapeutic candidate for protecting against bone loss in susceptible populations. The intent of this review is to provide a focused discussion on bone loss and disorders of the bone as it relates to melatonin and conditions that modify melatonin levels with the hope that future therapies include those that include melatonin and correct those factors that modify melatonin levels like circadian disruption.

Melatonin Inhibits Osteoclastogenesis and Bone Loss in Ovariectomized Mice by Regulating PRMT1-Mediated Signaling

Melatonin, a pineal gland hormone, has been suggested to treat postmenopausal osteoporosis due to its inhibitory effect on osteoclast differentiation. We previously reported that protein arginine methyltransferase 1 (PRMT1) was an important mediator of receptor activator of nuclear factor-κB ligand (RANKL)-induced osteoclastogenesis. However, the relationship between melatonin and PRMT1 in osteoclast differentiation and estrogen deficiency-induced osteoporosis is unclear. In this study, we investigated the inhibitory mechanisms of melatonin in vitro and in vivo by focusing on PRMT1. Melatonin treatment effectively blocked RANKL-induced osteoclastogenesis by inhibiting PRMT1 and asymmetric dimethylarginine (ADMA) expression. RANKL-induced tumor necrosis factor receptor-associated factor 6 (TRAF6) and the phosphorylation of JNK were also suppressed by melatonin, and TRAF6 siRNA attenuated RANKL-induced p-JNK and PRMT1 production. Melatonin inhibited the transcriptional activity of NF-κB by interfering with the binding of PRMT1 and NF-κB subunit p65 in RANKL-treated bone marrow-derived macrophages. Our results also revealed that melatonin inhibits RANKL-induced PRMT1 expression through receptors-independent pathway. Thus, the anti-osteoclastogenic effect of melatonin was mediated by a cascade of inhibition of RANKL-induced TRAF6, JNK, PRMT1, and NF-κB signaling in melatonin receptors-independent pathway. In vivo, ovariectomy caused significant decreases in bone mineral density, but melatonin treatment alleviated the ovariectomized (OVX)-induced bone loss by inhibiting bone resorption. Furthermore, the expression PRMT1 and TRAP mRNA was upregulated in OVX-femurs, but effectively suppressed by melatonin injection. These findings suggest that melatonin inhibited osteoclast differentiation and estrogen deficiency-induced osteoporosis by suppressing RANKL-induced TRAF6, JNK, PRMT1, and NF-κB signaling cascades in melatonin receptors-independent pathway.

Insight into the roles of melatonin in bone tissue and bone‑related diseases (Review)

Bone‑related diseases comprise a large group of common diseases, including fractures, osteoporosis and osteoarthritis (OA), which affect a large number of individuals, particularly the elderly. The progressive destruction and loss of alveolar bone caused by periodontitis is a specific type of bone loss, which has a high incidence and markedly reduces the quality of life of patients. With the existing methods of prevention and treatment, the incidence and mortality of bone‑related diseases are still gradually increasing, creating a significant financial burden to societies worldwide. To prevent the occurrence of bone‑related diseases, delay their progression or reverse the injuries they cause, new alternative or complementary treatments need to be developed. Melatonin exerts numerous physiological effects, including inducing anti‑inflammatory and antioxidative functions, resetting circadian rhythms and promoting wound healing and tissue regeneration. Melatonin also participates in the health management of bone and cartilage. In the present review, the potential roles of melatonin in the pathogenesis and progression of bone injury, osteoporosis, OA and periodontitis are summarized. Furthermore, the high efficiency and diversity of the physiological regulatory effects of melatonin are highlighted and the potential benefits of the use of melatonin for the clinical prevention and treatment of bone‑related diseases are discussed.

Melatonin Attenuates AlCl3-Induced Apoptosis and Osteoblastic Differentiation Suppression by Inhibiting Oxidative Stress in MC3T3-E1 Cells

Aluminum (Al) inhibits osteoblast-mediated bone formation by oxidative stress, resulting in Al-induced bone disease. Melatonin (MT) has received extensive attention due to its antioxidant and maintenance of bone health effect. To evaluate the protective effect and mechanism of MT on AlCl₃-induced osteoblast dysfunction, MC3T3-E1 cells were treated with MT (100 μM) and/or AlCl₃ (8 μM). First, MT alleviated AlCl₃-induced osteoblast dysfunction, presenting as the reduced apoptosis rate as well as increased cell viability, alkaline phosphatase (ALP) activity, and type I collagen (COL-1) level. Then, MT significantly attenuated AlCl₃-induced oxidative stress, presenting as the reduced reactive oxygen species and 8-hydroxy-2'-deoxyguanosine levels as well as increased glutathione level and superoxide dismutase activity. Finally, MT protected MC3T3-E1 cells against p53-dependent apoptosis and differentiation suppression, as assessed by Caspase-3 activity, protein levels of p53, Bcl-2-associated X protein (Bax), B cell lymphoma gene 2 (Bcl-2), cytosolic Cytochrome c, Runt-related transcription factor 2 (Runx2), and Osterix, as well as the mRNA levels of Bax, Bcl-2, Runx2, Osterix, ALP, and COL-1. Overall, our findings demonstrate MT attenuates AlCl₃-induced apoptosis and osteoblastic differentiation suppression by inhibiting oxidative stress in MC3T3-E1 cells.

Ranitidine Impairs Bone Healing and Implant Osseointegration in Rats' Tibiae

PURPOSE

Ranitidine has been found to have an impact on bone metabolism by suppressing osteoclastogenesis. We hypothesized that the use of ranitidine would impair bone healing and implant osseointegration. This study investigated the effect of postoperative administration of ranitidine on bone healing and osseointegration in rats.

MATERIALS AND METHODS

Twenty-two Sprague-Dawley rats underwent surgery to create a unicortical bone defect in each tibia. A titanium implant was placed on the right tibial defect, whereas the contralateral defect was left unfilled. After surgery, the rats were randomly divided into 2 groups receiving a daily dose of ranitidine or saline solution for 14 days and then euthanized for assessment of bone healing and osseointegration using micro-computed tomography (CT) and histomorphometry.

RESULTS

Micro-CT analysis of the bone defect showed a larger bone defect volume in the ranitidine group (0.82 ± 0.13 μL vs 0.66 ± 0.16 μL, P = .034), thinner cortical thickness (0.54 ± 0.07 mm vs 0.63 ± 0.11 mm, P = .026), and less bone regeneration at the defect site (40% ± 12% vs 57% ± 11%, P = .003). Implant-site micro-CT analysis showed less osseointegration in the ranitidine group (34.1% ± 2.7% vs 43.5% ± 2.1%, P = .014), and implant-site histologic analysis showed less medullary (P = .021), cortical (P = .001), and total (P = .003) bone-implant contact and less peri-implant bone volume-tissue volume (P = .002) in the ranitidine group. Histologic analysis for osteoclastic activity showed a lower number of osteoclasts in the ranitidine group (4.8 ± 2.4 mm^-2 vs 9.1 ± 2.1 mm^-2, P = .026).

CONCLUSIONS

The postoperative use of ranitidine impaired bone healing and osseointegration.

Overexpression of MsASMT1 Promotes Plant Growth and Decreases Flavonoids Biosynthesis in Transgenic Alfalfa (Medicago sativa L.)

Melatonin (N-acetyl-5-methoxytryptamine) is a pleiotropic signaling molecule that plays important roles in plant growth, development and stress responses. Alfalfa (Medicago sativa L.) is an important and widely cultivated leguminous forage crop with high biomass yield and rich nutritional value. The effects of exogenous melatonin content regulation on alfalfa stress tolerance have been investigated in recent years. Here, we isolated and introduced the MsASMT1 (N-acetylserotonin methyltransferase) gene into alfalfa, which significantly improved the endogenous melatonin content. Compared with wild-type (WT) plants, MsASMT1 overexpression (OE-MsASMT1) plants exhibited a series of phenotypic changes, including vigorous growth, increased plant height, enlarged leaves and robust stems with increased cell sizes, cell numbers and vascular bundles, as well as more branches. We also found that the flavonoid content and lignin composition of syringyl to guaiacyl ratio (S/G) were decreased and the cellulose content was increased in OE-MsASMT1 transgenic alfalfa. Further transcriptomic and metabolomic exploration revealed that a large group of genes in phenylalanine pathway related to flavonoids and lignin biosynthesis were significantly altered, accompanied by significantly reduced concentrations of the glycosides of quercetin, kaempferol, formononetin and biochanin in OE-MsASMT1 transgenic alfalfa. Our study first uncovers the effects of endogenous melatonin on alfalfa growth and metabolism. This report provides insights into the regulation effects of melatonin on plant growth and phenylalanine metabolism, especially flavonoids and lignin biosynthesis.

SPRY4 is responsible for pathogenesis of adolescent idiopathic scoliosis by contributing to osteogenic differentiation and melatonin response of bone marrow-derived mesenchymal stem cells

Adolescent idiopathic scoliosis (AIS) is a complex, three-dimensional deformity of the spine that commonly occurs in pubescent girls. Decreased osteogenic differentiation and aberrant melatonin signalling have been demonstrated in mesenchymal stem cells (MSCs) from AIS patients and are implicated in the pathogenesis of AIS. However, the molecular mechanisms underlying these abnormal cellular features remain largely unknown. Our previous work comparing gene expression profiles between MSCs from AIS patients and healthy controls identified 1027 differentially expressed genes. In the present study, we focused on one of the most downregulated genes, SPRY4, in the MAPK signalling pathway and examined its role in osteogenic differentiation. We found that SPRY4 is markedly downregulated in AIS MSCs. Knockdown of SPRY4 impaired differentiation of healthy MSCs to osteoblasts, while SPRY4 overexpression in AIS MSCs enhanced osteogenic differentiation. Furthermore, melatonin treatment boosted osteogenic differentiation, whereas SPRY4 ablation ablated the promotional effects of melatonin. Moreover, SPRY4 was upregulated by melatonin exposure and contributed to osteogenic differentiation and melatonin response in a MEK-ERK1/2 dependent manner. Thus, loss of SPRY4 in bone marrow derived-MSCs results in reduced osteogenic differentiation, and these defects are further aggravated under the influence of melatonin. Our findings provide new insights for understanding the role of melatonin in AIS aetiology and highlight the importance of MSCs in AIS pathogenesis.

Melatonin: Another avenue for treating osteoporosis?

Melatonin is a signal molecule that modulates the biological circadian rhythms of vertebrates. Melatonin deficiency is thought to be associated with several disorders, including insomnia, cancer, and cardiovascular and neurodegenerative diseases. Accumulating evidence has also indicated that melatonin may be involved in the homeostasis of bone metabolism. Age-related reductions in melatonin are considered to be critical factors in bone loss and osteoporosis with aging. Thus, serum melatonin levels might serve as a biomarker for the early detection and prevention of osteoporosis. Compared to conventional antiosteoporosis medicines, which primarily inhibit bone loss, melatonin both suppresses bone loss and promotes new bone formation. Mechanistically, by activating melatonin receptor 2 (MT2), melatonin upregulates the gene expression of alkaline phosphatase (ALP), bone morphogenetic protein 2 (BMP2), BMP6, osteocalcin, and osteoprotegerin to promote osteogenesis while inhibiting the receptor activator of NF-kB ligand (RANKL) pathway to suppress osteolysis. In view of the distinct actions of melatonin on bone metabolism, we hypothesize that melatonin may be a novel remedy for the prevention and clinical treatment of osteoporosis.

Therapeutic effect of resveratrol on mice with depression

The effect and mechanism of resveratrol on depression-like behavior in mice with depression were investigated. A mouse model of depression was established by social isolation combined with chronic unpredictable stress. The mice were randomly divided into the control group, the model group, the low dose group, the medium dose group and the high dose group. The rats in the low, medium and high dose groups were intraperitoneally injected with resveratrol 10, 20 and 30 mg/kg, respectively. The control and model groups were intraperitoneally injected with an equal volume of normal saline. After 21 days of continuous treatment, the neurobehavioral changes of each group were analyzed by forced swimming test, tail suspension experiment and sucrose consumption experiment. Dopamine (DA) and serotoni (5-HT) and the level of brain-derived nerve growth factor (BDNF) in the prefrontal cortex of each group were analyzed by ELISA. The level of neuropeptide (NPY) expression was analyzed by western blot analysis. Compared with the model group, the immobility time of the tail suspension experiment and forced swimming experiment in the low, medium and high dose groups was significantly prolonged (P<0.05), while the 24 h sucrose consumption was significantly increased (P<0.05), showing a dose-dependent manner. Compared with the model group, the levels of DA and 5-HT in the prefrontal cortex of the low, medium and high dose groups were significantly increased, and showed a dose-dependent effect (P<0.05). Compared with the model group, the expression levels of NPY protein in the low, medium and high dose groups were significantly increased, and gradually increased with the increase of the dose, the difference was statistically significant (P<0.05). Resveratrol can significantly increase the levels of neurotransmitters DA and 5-HT in the prefrontal cortex and increase the expression of NPY in the brain, which can play an antagonistic role in depression.

The multiple protective roles and molecular mechanisms of melatonin and its precursor N-acetylserotonin in targeting brain injury and liver damage and in maintaining bone health

Melatonin is a neurohormone associated with sleep and wakefulness and is mainly produced by the pineal gland. Numerous physiological functions of melatonin have been demonstrated including anti-inflammation, suppressing neoplastic growth, circadian and endocrine rhythm regulation, and its potent antioxidant activity as well as its role in regeneration of various tissues including the nervous system, liver, bone, kidney, bladder, skin, and muscle, among others. In this review, we summarize the recent advances related to the multiple protective roles of melatonin receptor agonists, melatonin and N-acetylserotonin (NAS), in brain injury, liver damage, and bone health. Brain injury, including traumatic brain injury, ischemic stroke, intracerebral hemorrhage, subarachnoid hemorrhage, and newborn perinatal hypoxia-ischemia encephalopathy, is a major cause of mortality and disability. Liver disease causes serious public health problems and various factors including alcohol, chemical pollutants, and drugs induce hepatic damage. Osteoporosis is the most common bone disease in humans. Due in part to an aging population, both the cost of care of fracture patients and the annual fracture rate have increased steadily. Despite the discrepancy in the pathophysiological processes of these disorders, time frames and severity, they may share several common molecular mechanisms. Oxidative stress is considered to be a critical factor in these pathogeneses. We update the current state of knowledge related to the molecular processes, mainly including anti-oxidative stress, anti-apoptosis, autophagy dysfunction, and anti-inflammation as well as other properties of melatonin and NAS. Particularly, the abilities of melatonin and NAS to directly scavenge oxygen-centered radicals and toxic reactive oxygen species, and indirectly act through antioxidant enzymes are disscussed. In this review, we summarize the similarities and differences in the protection provided by melatonin and/or NAS in brain, liver and bone damage. We analyze the involvement of melatonin receptor 1A (MT1), melatonin receptor 1B (MT2), and melatonin receptor 1C (MT3) in the protection of melatonin and/or NAS. Additionally, we evaluate their potential clinical applications. The multiple mechanisms of action and multiple organ-targeted properties of melatonin and NAS may contribute to development of promising therapies for clinical trials.

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

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

Daily melatonin administration improves osseointegration in pinealectomized rats

The hypothesis of this study was that the peri-implant bone healing of the group of pinealectomized rats would differ from the control group. The samples were subjected to immunohistochemical, microtomographic (total porosity and connectivity density), and fluorochrome (mineralized surface) analyses.

Inhibition of iron overload-induced apoptosis and necrosis of bone marrow mesenchymal stem cells by melatonin

Iron overload induces severe damage to several vital organs such as the liver, heart and bone, and thus contributes to the dysfunction of these organs. The aim of this study is to investigate whether iron overload causes the apoptosis and necrosis of bone marrow mesenchymal stem cells (BMSCs) and melatonin may prevent its toxicity. Perls’ Prussion blue staining showed that exposure to increased concentrations of ferric ammonium citrate (FAC) induced a gradual increase of intracellular iron level in BMSCs. Trypan blue staining demonstrated that FAC decreased the viability of BMSCs in a concentration-dependent manner. Notably, melatonin protected BMSCs against apoptosis and necrosis induced by FAC and it was vertified by Live/Dead, TUNEL and PI/Hoechst stainings. Furthermore, melatonin pretreatment suppressed FAC-induced reactive oxygen species accumulation. Western blot showed that exposure to FAC resulted in the decrease of anti-apoptotic protein Bcl-2 and the increase of pro-apoptotic protein Bax and Cleaved Caspase-3, and necrosis-related proteins RIP1 and RIP3, which were significantly inhibited by melatonin treatment. At last, melatonin receptor blocker luzindole failed to block the protection of BMSCs apoptosis and necrosis by melatonin. Taken together, melatonin protected BMSCs from iron overload induced apoptosis and necrosis by regulating Bcl-2, Bax, Cleaved Caspase-3, RIP1 and RIP3 pathways.

Dietary Sources and Bioactivities of Melatonin

Insomnia is a serious worldwide health threat, affecting nearly one third of the general population. Melatonin has been reported to improve sleep efficiency and it was found that eating melatonin-rich foods could assist sleep. During the last decades, melatonin has been widely identified and qualified in various foods from fungi to animals and plants. Eggs and fish are higher melatonin-containing food groups in animal foods, whereas in plant foods, nuts are with the highest content of melatonin. Some kinds of mushrooms, cereals and germinated legumes or seeds are also good dietary sources of melatonin. It has been proved that the melatonin concentration in human serum could significantly increase after the consumption of melatonin containing food. Furthermore, studies show that melatonin exhibits many bioactivities, such as antioxidant activity, anti-inflammatory characteristics, boosting immunity, anticancer activity, cardiovascular protection, anti-diabetic, anti-obese, neuroprotective and anti-aging activity. This review summaries the dietary sources and bioactivities of melatonin, with special attention paid to the mechanisms of action.

Melatonin attenuates titanium particle-induced osteolysis via activation of Wnt/β-catenin signaling pathway

Wear debris-induced inhibition of bone regeneration and extensive bone resorption were common features in peri-prosthetic osteolysis (PPO). Here, we investigated the effect of melatonin on titanium particle-stimulated osteolysis in a murine calvariae model and mouse-mesenchymal-stem cells (mMSCs) culture system. Melatonin inhibited titanium particle-induced osteolysis and increased bone formation at osteolytic sites, confirmed by radiological and histomorphometric data. Furthermore, osteoclast numbers decreased dramatically in the low- and high-melatonin administration mice, as respectively, compared with the untreated animals. Melatonin alleviated titanium particle-induced depression of osteoblastic differentiation and mineralization in mMSCs. Mechanistically, melatonin was found to reduce the degradation of β-catenin, levels of which were decreased in presence of titanium particles both in vivo and in vitro. To further ensure whether the protective effect of melatonin was mediated by the Wnt/β-catenin signaling pathway, ICG-001, a selective β-catenin inhibitor, was added to the melatonin-treated groups and was found to attenuate the effect of melatonin on mMSC mineralization. We also demonstrated that melatonin modulated the balance between receptor activator of nuclear factor kappa-B ligand and osteoprotegerin via activation of Wnt/β-catenin signaling pathway. These findings strongly suggest that melatonin represents a promising candidate in the treatment of PPO.

STATEMENT OF SIGNIFICANCE

Peri-prosthetic osteolysis, initiated by wear debris-induced inhibition of bone regeneration and extensive bone resorption, is the leading cause for implant failure and reason for revision surgery. In the current study, we demonstrated for the first time that melatonin can induce bone regeneration and reduce bone resorption at osteolytic sites caused by titanium-particle stimulation. These effects might be mediated by activating Wnt/β-catenin signaling pathway and enhancing osteogenic differentiation. Meanwhile, the ability of melatonin to modulate the balance between receptor activator of nuclear factor kappa-B ligand and osteoprotegerin mediated by Wnt/β-catenin signaling pathway, thereby suppressing osteoclastogenesis, may be implicated in the protective effects of melatonin on titanium-particle-induced bone resorption. These results suggested that melatonin can be considered as a promising therapeutic agent for the prevention and treatment of peri-prosthetic osteolysis.

Melatonin as an antioxidant: under promises but over delivers

Melatonin is uncommonly effective in reducing oxidative stress under a remarkably large number of circumstances. It achieves this action via a variety of means: direct detoxification of reactive oxygen and reactive nitrogen species and indirectly by stimulating antioxidant enzymes while suppressing the activity of pro-oxidant enzymes. In addition to these well-described actions, melatonin also reportedly chelates transition metals, which are involved in the Fenton/Haber-Weiss reactions; in doing so, melatonin reduces the formation of the devastatingly toxic hydroxyl radical resulting in the reduction of oxidative stress. Melatonin's ubiquitous but unequal intracellular distribution, including its high concentrations in mitochondria, likely aid in its capacity to resist oxidative stress and cellular apoptosis. There is credible evidence to suggest that melatonin should be classified as a mitochondria-targeted antioxidant. Melatonin's capacity to prevent oxidative damage and the associated physiological debilitation is well documented in numerous experimental ischemia/reperfusion (hypoxia/reoxygenation) studies especially in the brain (stroke) and in the heart (heart attack). Melatonin, via its antiradical mechanisms, also reduces the toxicity of noxious prescription drugs and of methamphetamine, a drug of abuse. Experimental findings also indicate that melatonin renders treatment-resistant cancers sensitive to various therapeutic agents and may be useful, due to its multiple antioxidant actions, in especially delaying and perhaps treating a variety of age-related diseases and dehumanizing conditions. Melatonin has been effectively used to combat oxidative stress, inflammation and cellular apoptosis and to restore tissue function in a number of human trials; its efficacy supports its more extensive use in a wider variety of human studies. The uncommonly high-safety profile of melatonin also bolsters this conclusion. It is the current feeling of the authors that, in view of the widely diverse beneficial functions that have been reported for melatonin, these may be merely epiphenomena of the more fundamental, yet-to-be identified basic action(s) of this ancient molecule.

Defining 'nutraceuticals': neither nutritious nor pharmaceutical

There are widespread inconsistencies and contradictions in the many published definitions of 'nutraceuticals' and 'functional foods', demonstrating wholesale uncertainty about what they actually are. Furthermore, in a 2014 lecture, the inventor of the term 'nutraceutical', confessing that nutraceuticals do not work, said that 'the quest to demonstrate whether … long-term supplementation [with nutraceuticals] can prevent serious diseases … has come to an end'. Definitions of 'nutraceuticals' and related terms, still widely used, should therefore be explored systematically. There are no internationally agreed definitions of 'nutraceuticals' and 'functional foods', or of similar terms, such as 'health foods', or of terms related to herbal products, which are sometimes referred to as 'nutraceuticals', compounding the confusion. 'Nutraceuticals' and 'functional foods' are vague, nondiscriminatory, unhelpful terms; the evidence suggests that they should be abandoned in favour of more precise terms. The term 'dietary supplement' is widely used to designate formulations that are also called 'nutraceuticals' but it would be better restricted to individual compounds used to treat or prevent deficiencies. 'Fortified foods', sometimes called 'designer foods', are foods to which compounds of proven therapeutic or preventive efficacy (e.g. folic acid) have been added. Other terms, such as 'food', 'foodstuffs', 'eat', 'drink', and 'nutrition', are well defined, as are 'medicinal products' and 'pharmaceutical formulations'. Dietary regimens, such as Mediterranean or nitrate-rich diets or vegetarianism, can affect health. A dietary regimen of this kind can be defined as a programme of food, of a defined kind and/or quantity, prescribed or adopted for the restoration or preservation of health.

Reduced fat mass and increased lean mass in response to 1 year of melatonin treatment in postmenopausal women: A randomized placebo-controlled trial

OBJECTIVE

Apart from regulating the circadian rhythm, melatonin exerts a variety of actions in the living organism. Among these functions, melatonin is believed to have a positive effect on body weight and energy metabolism. So far, the evidence for this relies mainly on animal models. In this study, we aimed to determine the effects of melatonin on body composition, lipid and glucose metabolism in humans.

DESIGN/METHODS

In a double-blind, placebo-controlled study, we randomized 81 postmenopausal women to 1 year of treatment with melatonin (1 or 3 mg nightly) or placebo. Body composition was measured by DXA. Measures were obtained at baseline and after 1 year of treatment along with leptin, adiponectin and insulin. Markers of glucose homeostasis were measured at the end of the study.

RESULTS

In response to treatment, fat mass decreased in the melatonin group by 6·9% (95% CI: 1·4%; 12·4%, P = 0·02) compared to placebo. A borderline significant increase in lean mass of 5·2% was found in the melatonin group compared to placebo (3·3%, (IQR:-1·7; 6·2) vs -1·9%, (IQR: -5·7; 5·8), P = 0·08). After adjusting for BMI, lean mass increased by 2·6% (95% CI: 0·1; 5·0, P = 0·04) in the melatonin group. Changes in body weight and BMI did not differ between groups. Adiponectin increased borderline significantly by 21% in the melatonin group compared to placebo (P = 0·08). No significant changes were observed for leptin, insulin or markers of glucose homeostasis.

CONCLUSION

Our results suggest a possibly beneficial effect of melatonin on body composition and lipid metabolism as 1 year of treatment reduces fat mass, increases lean mass and is associated with a trend towards an increase in adiponectin.

Melatonin, bone regulation and the ubiquitin-proteasome connection: A review

Recently, investigators have shown that ubiquitin-proteasome-mediated protein degradation is critical in regulating the balance between bone formation and bone resorption. The major signal transduction pathways regulating bone formation are the RANK/NF-κB pathway and the Wnt/β-catenin pathway. These signal transduction pathways regulate the activity of mature osteoblasts and osteoclasts. In addition, the Wnt/β-catenin pathway is one of the major signaling pathways in the differentiation of osteoblasts. The ubiquitin ligases that are reported to be of major significance in regulating these pathways are the ubiquitin SCF(B-TrCP) ligase (which regulates activation of NF-κB via degradation of IkBα in osteoclasts, and regulates bone transcription factors via degradation of β-catenin), the Keap-Cul3-Rbx1 ligase (which regulates degradation of IkB kinase, Nrf2, and the antiapoptotic factor Bcl-2), and Smurf1. Also of significance in regulating osteoclastogenesis is the deubiquitinase, CYLD (cylindramatosis protein), which facilitates the separation of NF-κB from IkBα. The degradation of CYLD is also under the regulation of SCF(B-TrCP). Proteasome inhibitors influence the activity of mature osteoblasts and osteoclasts, but also modulate the differentiation of precursor cells into osteoblasts. Preclinical studies show that melatonin also influences bone metabolism by stimulating bone growth and inhibiting osteoclast activity. These actions of melatonin could be interpreted as being mediated by the ubiquitin ligases SCF(B-TrCP) and Keap-Cul3-Rbx, or as an inhibitory effect on proteasomes. Clinical trials of the use of melatonin in the treatment of bone disease, including multiple myeloma, using both continuous and intermittent modes of administration, are warranted.

Melatonin improves bone mineral density at the femoral neck in postmenopausal women with osteopenia: a randomized controlled trial

Melatonin is known for its regulation of circadian rhythm. Recently, studies have shown that melatonin may have a positive effect on the skeleton. By increasing age, the melatonin levels decrease, which may lead to a further imbalanced bone remodeling. We aimed to investigate whether treatment with melatonin could improve bone mass and integrity in humans. In a double-blind RCT, we randomized 81 postmenopausal osteopenic women to 1-yr nightly treatment with melatonin 1 mg (N = 20), 3 mg (N = 20), or placebo (N = 41). At baseline and after 1-yr treatment, we measured bone mineral density (BMD) by dual X-ray absorptiometry, quantitative computed tomography (QCT), and high-resolution peripheral QCT (HR-pQCT) and determined calciotropic hormones and bone markers. Mean age of the study subjects was 63 (range 56-73) yr. Compared to placebo, femoral neck BMD increased by 1.4% in response to melatonin (P < 0.05) in a dose-dependent manner (P < 0.01), as BMD increased by 0.5% in the 1 mg/day group (P = 0.55) and by 2.3% (P < 0.01) in the 3 mg/day group. In the melatonin group, trabecular thickness in tibia increased by 2.2% (P = 0.04), and volumetric bone mineral density (vBMD) in the spine, by 3.6% (P = 0.04) in the 3 mg/day. Treatment did not significantly affect BMD at other sites or levels of bone turnover markers; however, 24-hr urinary calcium was decreased in response to melatonin by 12.2% (P = 0.02). In conclusion, 1-yr treatment with melatonin increased BMD at femoral neck in a dose-dependent manner, while high-dose melatonin increased vBMD in the spine. Further studies are needed to assess the mechanisms of action and whether the positive effect of nighttime melatonin will protect against fractures.

Mitochondrial reactive oxygen species at the heart of the matter: new therapeutic approaches for cardiovascular diseases

Reactive oxygen species (ROS) have been implicated in a variety of age-related diseases, including multiple cardiovascular disorders. However, translation of ROS scavengers (antioxidants) into the clinic has not been successful. These antioxidants grossly reduce total levels of cellular ROS including ROS that participate in physiological signaling. In this review, we challenge the traditional antioxidant therapeutic approach that targets ROS directly with novel approaches that improve mitochondrial functions to more effectively treat cardiovascular diseases.

Melatonin Attenuates Oxidative Damage Induced by Acrylamide In Vitro and In Vivo

Acrylamide (ACR) has been classified as a neurotoxic agent in animals and humans. Melatonin (MT) has been shown to be potentially effective in preventing oxidative stress related neurodegenerative disorders. In this study, whether MT exerted a protective effect against ACR-induced oxidative damage was investigated. Results in cells showed that reactive oxygen species (ROS) and malondialdehyde (MDA) significantly increased after ACR treatment for 24 h. MT preconditioning or cotreatment with ACR reduced ROS and MDA products, whereas the inhibitory effect of MT on oxidant generation was attenuated by blocking the MT receptor. Increased DNA fragmentation caused by ACR was significantly decreased by MT coadministration. In vivo, rats at 40 mg/kg/day ACR by gavage for 12 days showed weight loss and gait abnormality, Purkinje cell nuclear condensation, and DNA damage in rat cerebellum. MT (i.p) cotreatment with ACR not only recovered weight and gait of rats, but also decreased nuclear condensation and DNA damage in rat cerebellum. Using MDA generation, glutathione (GSH) level, superoxide dismutase (SOD), and glutathione peroxidase (GSH-Px) activities in rat cerebellum as indicators, MT alleviated ACR-induced lipid peroxidation and depressed antioxidant capacity. Our results suggest that MT effectively prevents oxidative damage induced by ACR.