Reaction mechanism of melatonin oxidation by reactive oxygen species in vitro

Cadmium activates the innate immune system through the AIM2 inflammasome

Cadmium (Cd) is a widely used heavy metal and has recently been recognized as a possible source of human toxicity due to its ability to accumulate in organs. Accumulation of heavy metals has several adverse effects, including inducing inflammation, in multiple organs, such as the testis. However, how Cd ions are sensed by host cells and how tissue inflammation eventually occurs remains unclear. Here, we show that Cd activates the AIM2 inflammasome by mediating genomic DNA release into the cytoplasm after DNA damage via oxidative stress, to trigger IL-1β secretion and pyroptosis. Specifically, the toxicity effects induced by Cd in cells were prevented by melatonin, which served as an antagonist of oxidative stress. Accordingly, in a mouse model, Cd-induced inflammation in the testis and consequential male reproductive dysfunction were effectively reversed by melatonin. Thus, our results suggest a function of AIM2 in Cd-mediated testis inflammation and identify AIM2 as a major pattern recognition receptor in response to heavy metal Cd ions.

Current Aspects of Selected Factors to Modulate Brain Health and Sports Performance in Athletes

This review offers a comprehensive evaluation of current aspects related to nutritional strategies, brain modulation, and muscle recovery, focusing on their applications and the underlying mechanisms of physiological adaptation for promoting a healthy brain, not only in athletes but also for recreationally active and inactive individuals. We propose that applying the rule, among others, of good sleep, regular exercise, and a properly balanced diet, defined as "SPARKS", will have a beneficial effect on the function and regeneration processes of the gut-brain-muscle axis. However, adopting the formula, among others, of poor sleep, stress, overtraining, and dysbiosis, defined as "SMOULDER", will have a detrimental impact on the function of this axis and consequently on human health as well as on athletes. Understanding these dynamics is crucial for optimizing brain health and cognitive function. This review highlights the significance of these factors for overall well-being, suggesting that adopting the "SPARKS" approach may benefit not only athletes but also older adults and individuals with health conditions.

Combined Transcranial Doppler and Melatonin Levels to Predict Delayed Cerebral Ischemia After Subarachnoid Hemorrhage

OBJECTIVE

To investigate the early prediction value of transcranial Doppler ultrasound (TCD) combined with serum melatonin level for delayed cerebral ischemia (DCI) caused by subarachnoid hemorrhage (SAH).

METHODS

This paper is a prospective study. A total of 120 patients with SAH treated were included. The patients were divided into the DCI group (40 cases) and non-DCI group (80 cases) according to whether DCI occurred 14 days after SAH (DCI usually occurs 4 to 14 d after bleeding). Baseline data, serum melatonin level, and TCD test results within 24 hours after admission were compared between the 2 groups. Multivariate logistic analysis was used to analyze the factors affecting the occurrence of DCI after SAH. The value of serum melatonin level, middle cerebral artery mean blood flow velocity (MBFV) and their combination in predicting DCI in SAH patients was evaluated.

RESULTS

Univariate analysis showed that there were statistically significant differences in the proportion of Fisher grade, Hunt-Hess grade, serum melatonin level, middle cerebral artery systolic blood flow velocity (Vs), MBFV and pulse index (PI) between the 2 groups (P<0.05). Serum melatonin levels, middle cerebral artery Vs, MBFV, and PI in the DCI group were higher than those in non-DCI group. Logistic regression (LR) analysis showed that serum melatonin level (OR=1.796, 95% CI: 1.575-4.123) and middle cerebral artery MBFV (OR=3.279, 95% CI: 2.112-4.720] were the influencing factors for DCI in SAH patients (P<0.05).

CONCLUSION

Middle cerebral artery MBFV and serum melatonin levels were higher in patients with SAH complicated with DCI, and the combination of the 2 could provide a reference for early clinical prediction of DCI in patients with aneurysmal subarachnoid hemorrhage (aSAH).

Mitochondria-targeted melatonin photorelease supports the presence of melatonin MT1 receptors in mitochondria inhibiting respiration

The presence of signaling-competent G protein-coupled receptors in intracellular compartments is increasingly recognized. Recently, the presence of Gi/o protein-coupled melatonin MT1 receptors in mitochondria has been revealed, in addition to the plasma membrane. Melatonin is highly cell permeant, activating plasma membrane and mitochondrial receptors equally. Here, we present MCS-1145, a melatonin derivative bearing a triphenylphosphonium cation for specific mitochondrial targeting and a photocleavable o-nitrobenzyl group releasing melatonin upon illumination. MCS-1145 displayed low affinity for MT1 and MT2 but spontaneously accumulated in mitochondria, where it was resistant to washout. Uncaged MCS-1145 and exogenous melatonin recruited β-arrestin 2 to MT1 in mitochondria and inhibited oxygen consumption in mitochondria isolated from HEK293 cells only when expressing MT1 and from mouse cerebellum of WT mice but not from MT1-knockout mice. Overall, we developed the first mitochondria-targeted photoactivatable melatonin ligand and demonstrate that melatonin inhibits mitochondrial respiration through mitochondrial MT1 receptors.

Chronic obstructive pulmonary disease and emerging ER stress-related therapeutic targets

COPD pathogenesis is frequently associated with endoplasmic reticulum stress (ER stress) progression. Targeting the major unfolded protein response (UPR) branches in the ER stress pathway may provide pharmacotherapeutic selection strategies for treating COPD and enable relief from its symptoms. In this study, we aimed to systematically review the potential role of the ER stress inhibitors of major UPR branches (IRE1, PERK, and ATF6) in COPD-related studies and determine the current stage of knowledge in this field. The systematic review was carried out adhering to the PRISMA checklist based on published studies obtained from specific keyword searches of three databases, namely PubMed, ScienceDirect and Springer Database. The search was limited to the year 2000-2022 which includes all in vitro studies, in vivo studies and clinical trials related to the application of ER stress inhibitors toward COPD-induced models and disease. The risk of bias was evaluated using the QUIN, SYRCLE, revised Cochrane risk of bias tool for randomized trials (RoB 2.0) and NIH tool respectively. A total of 7828 articles were screened from three databases and a final total of 37 studies were included in the review. The ER stress and UPR pathways are potentially useful to prevent COPD progression and attenuate the exacerbation of COPD and related symptoms. Interestingly, the off-target effects from inhibition of the UPR pathway may be desirable or undesirable depending on context and therapeutic applications. Targeting the UPR pathway could have complex consequences as the production of ER molecules involved in folding may be impaired which could continuously provoke misfolding of proteins. Although several emerging compounds were noted to be potentially useful for targeted therapy against COPD, clinical studies have yet to be thoroughly explored.

Exogenous melatonin alleviates apple replant disease by regulating rhizosphere soil microbial community structure and nitrogen metabolism

Apple replant disease (ARD) is a common soil-borne disease afflicting apple plants. Melatonin is a broad-spectrum oxygen scavenger that plays a key role in alleviating stress-induced damage in plants. In this study, we aimed to determine whether adding melatonin to replant soil can promote plant growth by improving the rhizosphere soil environment and nitrogen metabolism. In replant soil, chlorophyll synthesis was blocked, reactive oxygen species (ROS) accumulated in large quantities, and membrane lipid peroxidation was aggravated; this eventually resulted in slow plant growth. However, the application of 200 μM exogenous melatonin enhanced the tolerance of plants to ARD by up-regulating the expression of antioxidant enzyme-related genes and increasing ROS scavenging enzyme activity. Exogenous melatonin also increased the absorption and utilization of ¹⁵N by increasing the expression of nitrogen absorption genes and the activity of nitrogen metabolism enzymes. Exogenous melatonin enhanced the soil microbial environment by promoting soil enzyme activity and bacterial richness and decreasing the abundance of several harmful fungi in rhizosphere soil. Mantel test results showed that soil properties (except for AP) and growth indexes were positively correlated with the rate of ¹⁵N absorption and utilization. Spearman correlation analysis showed that the above factors were closely related to the richness and diversity of bacteria and fungi, indicating that the composition of microbial communities might play a key role in mediating change in the soil environment and thus affect nutrient absorption and growth. These findings provide new insights into how melatonin enhances ARD tolerance.

Melatonin protects against cadmium-induced oxidative stress via mitochondrial STAT3 signaling in human prostate stromal cells

Melatonin protects against Cadmium (Cd)-induced toxicity, a ubiquitous environmental toxicant that causes adverse health effects by increasing reactive oxygen species (ROS) production and mitochondrial dysfunction. However, the underlying mechanism remains unclear. Here, we demonstrate that Cd exposure reduces the levels of mitochondrially-localized signal transducer and activator of transcription 3 (mitoSTAT3) using human prostate stromal cells and mouse embryonic fibroblasts. Melatonin enhances mitoSTAT3 abundance following Cd exposure, which is required to attenuate ROS damage, mitochondrial dysfunction, and cell death caused by Cd exposure. Moreover, melatonin increases mitochondrial levels of GRIM-19, an electron transport chain component that mediates STAT3 import into mitochondria, which are downregulated by Cd. In vivo, melatonin reverses the reduced size of mouse prostate tissue and levels of mitoSTAT3 and GRIM-19 induced by Cd exposure. Together, these data suggest that melatonin regulates mitoSTAT3 function to prevent Cd-induced cytotoxicity and could preserve mitochondrial function during Cd-induced stress.

Melatonin Can Modulate Neurodegenerative Diseases by Regulating Endoplasmic Reticulum Stress

As people age, their risks of developing degenerative diseases such as cancer, diabetes, Parkinson's Disease (PD), Alzheimer's Disease (AD), rheumatoid arthritis, and osteoporosis are generally increasing. Millions of people worldwide suffer from these diseases as they age. In most countries, neurodegenerative diseases are generally recognized as the number one cause afflicting the elderly. Endoplasmic reticulum (ER) stress has been suggested to be associated with some human neurological diseases, such as PD and AD. Melatonin, a neuroendocrine hormone mainly synthesized in the pineal gland, is involved in pleiotropically biological functions, including the control of the circadian rhythm, immune enhancement, and antioxidant, anti-aging, and anti-tumor effects. Although there are many papers on the prevention or suppression of diseases by melatonin, there are very few papers about the effects of melatonin on ER stress in neurons and neurodegenerative diseases. This paper aims to summarize and present the effects of melatonin reported so far, focusing on its effects on neurons and neurodegenerative diseases related to ER stress. Studies have shown that the primary target molecule of ER stress for melatonin is CHOP, and PERK and GRP78/BiP are the secondary target molecules. Therefore, melatonin is crucial in protecting neurons and treating neurodegeneration against ER stress.

Seasonal and temporal variation in the placenta during melatonin supplementation in a bovine compromised pregnancy model

Compromised pregnancies result in a poorly functioning placenta restricting the amount of oxygen and nutrient supply to the fetus resulting in intrauterine growth restriction (IUGR). Supplementing dietary melatonin during a compromised pregnancy increased uteroplacental blood flow and prevented IUGR in a seasonal-dependent manner. The objectives were to evaluate seasonal melatonin-mediated changes in temporal alterations of the bovine placental vascularity and transcript abundance of clock genes, angiogenic factors, and nutrient sensing genes in 54 underfed pregnant Brangus heifers (Fall, n = 29; Summer, n = 25). At day 160 of gestation, heifers were assigned to treatments consisting of adequately fed (ADQ-CON; 100% NRC; n = 13), nutrient restricted (RES-CON; 60% NRC; n = 13), and ADQ or RES supplemented with 20 mg/d of melatonin (ADQ-MEL, n = 13; RES-MEL, n = 15). The animals were fed daily at 0900 hours until day 240 where Cesarean sections were performed in the morning (0500 hours) or afternoon (1300 hours) for placentome collections. In both seasons, we observed a temporal alteration of the core clock genes in the cotyledonary tissue in a season-dependent manner. In the fall, ARNTL, CLOCK, NR1D1, and RORA transcript abundance were decreased (P ≤ 0.05) in the afternoon compared to the morning; whereas in the summer, ARNTL, PER2, and RORA expression were increased (P ≤ 0.05) in the afternoon. Interestingly, in both seasons, there was a concomitant temporal increase (P ≤ 0.05) of cotyledonary blood vessel perfusion and caruncular melatonin receptor 1A transcript abundance. Melatonin supplementation did not alter the melatonin receptor 1A transcript abundance (P > 0.05), however, in the summer, melatonin supplementation increased cotyledonary VEGFA, CRY1, and RORA (P ≤ 0.05) transcript abundance. In addition, during the summer the placentomes from underfed dams had increased average capillary size and HIF1α transcript abundance compared to those adequately fed (P ≤ 0.05). In conclusion, these data indicate increased cotyledonary blood vessel size and blood distribution after feeding to better facilitate nutrient transport. Interestingly, the maternal nutritional plane appears to play a crucial role in regulating the bovine placental circadian clock. Based on these findings, the regulation of angiogenic factors and clock genes in the bovine placenta appears to be an underlying mechanism of the therapeutic effect of dietary melatonin supplementation in the summer.

Design and Validation of the First Family of Photo-Activatable Ligands for Melatonin Receptors

Melatonin is a neurohormone released in a circadian manner with peak levels at night. Melatonin mediates its effects mainly through G protein-coupled MT₁ and MT₂ receptors. Drugs acting on melatonin receptors are indicated for circadian rhythm- and sleep-related disorders. Tools to study the activation of these receptors with high temporal resolution are lacking. Here, we synthesized a family of light-activatable caged compounds by attaching o-nitrobenzyl (o-NB) or coumarin photocleavable groups to melatonin indolic nitrogen. All caged compounds showed the expected decrease in binding affinity for MT₁ and MT₂. The o-NB derivative MCS-0382 showed the best uncaging and biological properties, with 250-fold increase in affinity and potency upon illumination. Generation of melatonin from MCS-0382 was further demonstrated by its ability to modulate the excitation of SCN neurons in rat brain slices. MCS-0382 is available to study melatonin effects in a temporally controlled manner in cellular and physiological settings.

Melatonin induces apoptotic cell death through Bim stabilization by Sp1-mediated OTUD1 upregulation

Melatonin, secreted by the pineal gland, regulates the circadian rhythms and also plays an oncostatic role in cancer cells. Previously, we showed that melatonin induces the expression of Bim, a pro-apoptotic Bcl-2 protein, at both the transcriptional and post-translational levels. In the present study, we investigated the molecular mechanisms underlying the melatonin-mediated Bim upregulation through post-translational regulation. We found that ovarian tumor domain-containing protein 1 (OTUD1), a deubiquitinase belonging to the OTU protein family, is upregulated by melatonin at the mRNA and protein levels. OTUD1 knockdown inhibited melatonin-induced Bim upregulation and apoptosis in cancer cells. OTUD1 directly interacted with Bim and inhibited its ubiquitination. Melatonin-induced OTUD1 upregulation caused deubiquitination at the lysine 3 residue of Bim, resulting in its stabilization. In addition, melatonin-induced activation of Sp1 was found to be involved in OTUD1 upregulation at the transcriptional level, and pharmacological inhibition and genetic ablation of Sp1 (siRNA) interrupted melatonin-induced OTUD1-mediated Bim upregulation. Furthermore, melatonin reduced tumor growth and induced upregulation of OTUD1 and Bim in a mouse xenograft model. Notably, Bim expression levels correlated with OTUD1 levels in patients with renal clear cell carcinoma. Thus, our results demonstrated that melatonin induces apoptosis by stabilizing Bim via Sp1-mediated OTUD1 upregulation.

Unravelling Melatonin's Varied Antioxidizing Protection of Membrane Lipids Determined by its Spatial Distribution

The antioxidizing capability of membrane antioxidants is strongly affected by the submolecular regions of the membrane that they locate. However, the concurrent determination of their location in the membranes and the consequent antioxidizing effect remains difficult. Using our field-induced droplet ionization mass spectrometry methodology, here we show the rapid determination of the antioxidation effect and the spatial distribution of melatonin in POPC membranes. Melatonin effectively protects the membrane lipids against hydroxyl radicals originating from the Fenton reactions in the water phase but cannot protect the lipids against singlet oxygen generated by a lipophilic photosensitizer in the lipid tail region (oil phase). These varied antioxidizing behaviors indicate that melatonin dwells at the headgroup subregion of the membranes. We anticipate that the methodology in this study can be widely utilized in the screening of antioxidants' spatial distribution and antioxidizing efficiency, and eventually in designing novel antioxidants that could deliver specific functions.

Melatonin salvages lead-induced neuro-cognitive shutdown, anxiety, and depressive-like symptoms via oxido-inflammatory and cholinergic mechanisms

INTRODUCTION

Lead is the most used nonphysiological neurotoxic heavy metal in the world that has been indicated to interfere with the cognitive and noncognitive processes via numerous mechanisms. The neuroprotective effect of melatonin is well known, but the effect of its interaction with lead in the brain remains inconclusive.

OBJECTIVE

To assess the therapeutic role of melatonin on cognitive deficit, anxiety and depressive-like symptoms in matured male Wistar rats exposed to a subchronic lead chloride (PbCl₂ ).

METHODS

Twenty male Wistar rats were blindly randomized into four groups (n = 5/group): group 1 to 4 underwent intragastric administration of physiological saline (10 ml/kg; vehicle), PbCl₂ (50 mg/kg), melatonin (10 mg/kg) and PbCl₂ + melatonin respectively for a period of 4 weeks during which neurobehavioral data were extracted, followed by neurochemical and histopathological evaluations.

RESULTS

Exposure to PbCl₂ reduced cognitive performance by increasing the escape latency and average proximity to the platform zone border, decreasing average path length in the platform zone, cognitive score, and time spent in probing. It raised the thigmotaxis percentage, time spent in rearing, number of pellet-like feces, and time spent in the dark compartment of a bright/dark box which are predictors of anxiety. It also induced depressive-like behavior as immobility time was enhanced. PbCl₂ deranged neurochemicals; malondialdehyde, interlukin-1β, and tumor necrotic factor-α were increased while superoxide dismutase and acetylcholinesterase were decreased without remarkable alteration in reduced glutathione and nitric oxide. Administration of PbCl₂ further disrupted neuronal settings of hippocampal proper and dentate gyrus. In contrast, the supplementation of melatonin reversed all the neurological consequences of PbCl₂ neurotoxicity by eliciting its properties against oxidative and nonoxidative action of PbCl₂ .

CONCLUSION

These findings suggest that melatonin down-regulates neurotoxicant interplays in the brain systems. Therefore, this study suggests the use of melatonin as an adjuvant therapy in neuropathological disorders/dysfunctions.

Melatonin regulates antioxidant strategy in response to continuous salt stress in rice seedlings

Melatonin mediates multiple physiological processes in plants and is involved in many reactions related to the protection of plants from abiotic stress. In this paper, the effect of melatonin on the antioxidant capacity of rice under salt stress was studied. Melatonin alleviated the inhibition of salt stress on the growth of rice seedlings, mainly by increasing the dry weight and fresh weight of shoots and roots. Melatonin alleviated the membrane damage caused by salt stress, which was mainly manifested by the decrease of TBARS content and the decrease of leaf and root damage. During the whole salt stress period, rice after melatonin pretreatment showed lower ROS (H₂O₂, O₂^•-,OH^-) accumulation. In the early stage (1-3 d) of stress, the rice after melatonin pretreatment showed a strong increase in antioxidant enzyme activity, while in the later stage (5,7 d), it showed a strong increase in antioxidant content. During the whole period of salt stress, melatonin had a weak regulatory effect on AsA-GSH cycle. Through the above regulation process, the decreasing effect of melatonin on ROS content of rice under salt stress did not decrease with prolonged stress time in a short time (1-7 d). In conclusion, melatonin improved the antioxidant capacity of rice under continuous salt stress, and rice showed variable antioxidant strategies after melatonin pretreatment.

Melatonin Attenuates Chromium (VI)-Induced Spermatogonial Stem Cell/Progenitor Mitophagy by Restoration of METTL3-Mediated RNA N6-Methyladenosine Modification

Spermatogonial stem cells (SSCs) are the basis of spermatogenesis, and any damage to SSCs may result in spermatogenic disorder and male infertility. Chromium (Cr) (VI) is a proven toxin, mutagen, and carcinogen, perpetually detrimental to environmental organisms due to its intricate and enduring detoxification process in vivo. Despite this, the deleterious effects of Cr (VI) on SSCs and the underlying mechanisms remain poorly understood. In this study, we identified that Cr (VI) impaired male reproductive system in mouse testes and induced mitochondrial dynamic imbalance and mitophagy in SSCs/progenitors. Cr (VI) also downregulated the RNA N⁶-methyladenosine (m⁶A) modification levels in mitochondrial dynamic balance and mitophagy genes in SSCs/progenitors. Inspiringly, the toxic effects of Cr (VI) could be relieved by melatonin pretreatment. Melatonin alleviated Cr (VI)-induced damage to male reproductive system and autophagy in mouse testes. Melatonin also attenuated Cr (VI)-induced cell viability loss and reactive oxygen species (ROS) generation, as well as mitochondrial dynamic disorders and mitophagy in SSCs/progenitors. The protective roles of melatonin against Cr (VI)-induced mitophagy were exerted by restoration of METTL3-mediated RNA m⁶A modification and activation of mitochondrial fusion proteins MFN2 and OPA1, as well as inhibition of the mitophagy BNIP3/NIX receptor pathway. Thus, our study provides novel insights into the molecular mechanisms for RNA m⁶A modification underlying the gene regulatory network responsible for mitochondrial dynamic balance, and also lays new experimental groundwork for treatment of Cr (VI)-induced damage to male fertility.

Utilization of redox modulating small molecules that selectively act as pro-oxidants in cancer cells to open a therapeutic window for improving cancer therapy

There is a rapidly growing body of literature supporting the notion that differential oxidative metabolism in cancer versus normal cells represents a metabolic frailty that can be exploited to open a therapeutic window into cancer therapy. These cancer cell-specific metabolic frailties may be amenable to manipulation with non-toxic small molecule redox active compounds traditionally thought to be antioxidants. In this review we describe the potential mechanisms and clinical applicability in cancer therapy of four small molecule redox active agents: melatonin, vitamin E, selenium, and vitamin C. Each has shown the potential to have pro-oxidant effects in cancer cells while retaining antioxidant activity in normal cells. This dichotomy can be exploited to improve responses to radiation and chemotherapy by opening a therapeutic window based on a testable biochemical rationale amenable to confirmation with biomarker studies during clinical trials. Thus, the unique pro-oxidant/antioxidant properties of melatonin, vitamin E, selenium, and vitamin C have the potential to act as effective adjuvants to traditional cancer therapies, thereby improving cancer patient outcomes.

Does lunar cycle affect biological parameters in young healthy men?

This study aimed to assess the effects of the lunar cycle on diurnal variation of biological, i.e, hormonal, biochemical, and hematological, profiles of diurnally active healthy men. Blood samples of 20 males were collected on four occasions [full moon (FM) and new moon (NM), in the morning (06:00-07:00 h) and evening (19:00-20:00 h)]. The results showed that melatonin and testosterone levels and neutrophils count were lower during the FM as compared to the NM in the morning (p < .001; d = 4.13, p < .001; d = 3.84, p < .01; d = 0.77, respectively) and evening (p < .001; d = 6.36, p < .001; d = 4.03, p < .05; d = 1.07, respectively) samples. However, cortisol level was higher during the FM compared to the NM, in the morning (p < .001; d = 0.74) and evening (p < .001; d = 3.54). Hemoglobinemia was higher only in the evening during the FM compared to the evening of the NM (p < .01; d = 1.22). In summary, this study confirmed that lunar cycle can affect human biological parameters independently of time of day.

Synthesis and characterization of novel protein nanodots as drug delivery carriers with an enhanced biological efficacy of melatonin in breast cancer cells

Melatonin is a potent antioxidant, chemotherapeutic and chemo preventive agent against breast cancer. However, its short half-life is one of the major limitations in its application as a therapeutic drug. To overcome this issue, the green-emitting protein nanodot (PND) was synthesized by a one-step hydrothermal method for loading melatonin. The synthesized pH-7 and pH-2 PND showed a quantum yield of 22.1% and 14.0%, respectively. The physicochemical characterization of both PNDs showed similar morphological and functional activities. Furthermore, the biological efficacy of melatonin-loaded PND (MPND) was evaluated in a breast cancer cell line (MDA-MB-231) for live-cell imaging and enhanced nano-drug delivery efficacy. Interestingly, the permeability of neutral pH PND in both cell cytoplasm and nucleus nullifies the limitations of real-time live-cell imaging, and ensures nuclear drug delivery efficacy. Neutral pH PND showed better cell viability and cytotoxicity as a fluorescence bioimaging probe compared to acidic PND. The bioavailability and cell cytotoxicity effect of MPND on MDA-MB-231 breast cancer cells were studied through confocal and migration assay. Results showed that MPND causes enhanced bioavailability, better cellular uptake, and inhibition of the migration of breast cancer cells as compared to the drug alone. Besides, the synthesized MPND showed no sign of fluorescence quenching even at a high concentration of melatonin, making it an ideal nanocarrier for bioimaging and drug delivery.

Associations between urinary 6-sulfatoxymelatonin excretion and diabetic vascular complications or arteriosclerosis in patients with type 2 diabetes

AIMS/INTRODUCTION

There are limited reports on the association between melatonin levels and vascular complications in patients with type 2 diabetes. The aim of this study was to determine the association between urinary 6-sulfatoxymelatonin, which is a urinary metabolite of melatonin, and diabetic vascular complications or arteriosclerosis in patients with type 2 diabetes.

MATERIALS AND METHODS

This retrospective study included patients (167 patients with type 2 diabetes and 27 patients without diabetes adjusted for age and sex) admitted to the hospital who underwent measurement of urinary 6-sulfatoxymelatonin. The urinary 6-sulfatoxymelatonin/creatinine ratio (6-SMT) was calculated.

RESULTS

The natural logarithmically scaled 6-SMT level (Ln 6-SMT) was significantly lower in type 2 diabetes patients (1.9 ± 1.1) compared with patients without diabetes (2.8 ± 1.0, P < 0.001). Multivariate linear regression analysis identified duration of diabetes, smoking status, urinary albumin-to-creatinine ratio, retinopathy and coronary heart disease as factors that could influence Ln 6-SMT levels in type 2 diabetes patients (R²  = 0.232, P < 0.001). Ln 6-SMT was associated with decreased odds of diabetic retinopathy, even after adjustment for various confounding factors (odds ratio 0.559, 95% confidence interval 0.369-0.846, P = 0.006). Similarly, Ln 6-SMT was associated with decreased odds of coronary heart disease (odds ratio 0.442, P = 0.030).

CONCLUSIONS

Our results showed the presence of low levels of Ln 6-SMT in type 2 diabetes patients relative to patients without diabetes. Furthermore, Ln 6-SMT is an independent risk factor of diabetic retinopathy and coronary heart diseases. These findings suggest that 6-SMT could be a useful biomarker for the prediction of micro- and macrovasculopathies in patients with type 2 diabetes.

Melatonin Regulatory Mechanisms and Phylogenetic Analyses of Melatonin Biosynthesis Related Genes Extracted from Peanut under Salinity Stress

Melatonin improves the tolerance of plants to various environmental stresses by protecting plant cells against oxidative stress damage. The objective of the current study was to determine whether exogenous melatonin (MT) treatments could help protecting peanut (Arachis hypogaea) seedlings against salinity stress. This was achieved by investigating enzymatic and non-enzymatic antioxidant systems and the expression of melatonin biosynthesis related genes in response to salinity stress with or without exogenous MT. The results showed a significant increase in the concentrations of reactive oxygen species (ROS) in peanut seedlings under salinity stress. The exogenous application of melatonin decreased the levels of ROS through the activation of antioxidant enzymes in peanut seedlings under salinity stress. Transcription levels of melatonin biosynthesis related genes such as N-acetylserotonin methyltransferase (ASMT1, ASMT2, ASMT3), tryptophan decarboxylase (TDC), and tryptamine 5-hydroxylase (T5H) were up-regulated with a 150 µM melatonin treatment under salinity stress. The results indicated that melatonin regulated the redox homeostasis by its ability to induce either enzymatic or non-enzymatic antioxidant systems. In addition, phylogenetic analysis of melatonin biosynthesis genes (ASMT1, ASMT2, ASMT3, TDC, T5H) were performed on a total of 56 sequences belonging to various plant species including five new sequences extracted from Arachis hypogaea (A. hypogaea). This was based on pairwise comparison among aligned nucleotides and predicted amino acids as well as on substitution rates, and phylogenetic inference. The analyzed sequences were heterogeneous and the A. hypogaea accessions were primarily closest to those of Manihot esculenta, but this needs further clarification.

Melatonin foliar sprays elicit salinity stress tolerance and enhance fruit yield and quality in strawberry (Fragaria × ananassa Duch.)

The increasing salinity in soils and irrigation water is a major concern for growers of strawberry, a salt-sensitive horticultural crop. The hormone melatonin (N-acetyl-5-methoxytryptamine) is involved in many biological processes and affects plant responses to environmental stresses. The effects of weekly 100 and 200 μM melatonin sprays on leaf composition parameters (photosynthetic pigment and macronutrient concentrations, oxidative stress markers, antioxidant defense systems and abscisic acid concentrations), fruit yield and quality parameters (soluble solids, total acidity, ascorbic acid, total antioxidants and phenolics and sugars), and leaf and fruit melatonin have been studied in strawberry grown under non-saline, moderate and intense salinity conditions (0, 40 and 80 mM NaCl, respectively). Salinity led to decreases in yield, fruit quality parameters and leaf photosynthetic pigments and macronutrient concentrations, as well as to increases in oxidative stress, with melatonin foliar application alleviating all these changes. On the other hand, salinity led to increases in the leaf levels of antioxidant enzymes, abscisic acid and melatonin, with foliar applications of melatonin boosting those increases. In the absence of salinity stress, melatonin led to smaller changes in all parameters in the same direction to that observed in the presence of salinity. Furthermore, melatonin resulted in increases in strawberry fruit yield and quality, especially in plants grown under salinity. Results indicate that the effects of melatonin application are associated with a boost in leaf antioxidant enzymes and abscisic acid, and support that the application of melatonin is a promising tool for mitigating salt stress in strawberry.

Anti-genotoxic and anti-mutagenic effects of melatonin supplementation in a mouse model of melanoma

Melanoma, an aggressive skin cancer originating from melanocytes, can metastasize to the lungs, liver, cortex, femur, and spinal cord, ultimately resulting in DNA mutagenic effects. Melatonin is an endogenous hormone and free radical scavenger that possesses the ability to protect the DNA and to exert anti-proliferative effects in melanoma cells. The aim of this study was to evaluate the effects of B16F10 melanoma cells and the effects of melatonin supplementation on genotoxic parameters in murine melanoma models. Thirty-two male C57Bl/6 mice were divided in the following four groups: PBS + vehicle (n = 6), melanoma + vehicle (n = 10), PBS + melatonin (n = 6), and melanoma + melatonin (n = 10). The melanoma groups received a B16F10 cell injection, and melatonin was administered during 60 days. After treatment, tumor sizes were evaluated. DNA damage within the peripheral blood, lungs, liver, cortex, and spinal cord was determined using comet assay, and the mutagenicity within the bone marrow was determined using the micronucleus test. B16F10 cells effectively induced DNA damage in all tissues, and melatonin supplementation decreased DNA damage in the blood, liver, cortex, and spinal cord. This hormone exerts anti-tumor activity via its anti-proliferative, antioxidative, and pro-apoptotic effects. As this result was not observed within the lungs, we hypothesized that melatonin can induce apoptosis in cancer cells, and this was not evaluated by comet assay. This study provides evidence that melatonin can reduce the genotoxicity and mutagenicity caused by B16F10 cells.

Integrative roles of nitric oxide and hydrogen sulfide in melatonin-induced tolerance of pepper (Capsicum annuum L.) plants to iron deficiency and salt stress alone or in combination

There seems to be no report in the literature on the effect of melatonin (MT) in relieving the detrimental effects of combined application of salt stress (SS) and iron deficiency (ID). Therefore, the effect of MT on the accumulation/synthesis of endogenous nitric oxide (NO) and hydrogen sulphide (H₂ S) and how far these molecules are involved in MT-improved tolerance to the combined application of ID and SS in pepper (Capsicum annuum L) were tested. Hence, two individual trials were set up. The treatments in the first experiment comprised: Control, ID (0.1 mM FeSO₄ ), SS (100 mM NaCl) and ID + SS. The detrimental effects of combined stresses were more prominent than those by either of the single stress, with respect to growth, oxidative stress and antioxidant defense attributes. Single stress or both in combination improved the endogenous H₂ S and NO, and foliar-applied MT (100 µM) led to a further increase in NO and H₂ S levels. In the second experiment, 0.1 mM scavenger of NO, 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide potassium salt (cPTIO) and that of H₂ S, hypotuarine (HT) were applied along with MT to get further evidence whether NO and H₂ S are involved in MT-induced tolerance to ID and SS. MT combined with cPTIO and HT under a single or combined stress showed that NO effect was reversed by the NO scavenger, cPTIO, alone but the H₂ S effect was inhibited by both scavengers. These findings suggested that tolerance to ID and SS induced by MT may be involved in downstream signal crosstalk between NO and H₂ S.

Characterization of the various functional pathways elicited by synthetic agonists or antagonists at the melatonin MT1 and MT2 receptors

Melatonin is a neurohormone that translates the circadian rhythm to the peripheral organs through a series of binding sites identified as G protein-coupled receptors MT1 and MT2. Due to minute amounts of receptor proteins in target organs, the main tool of studies of the melatoninergic system is recombinant expression of the receptors in cellular hosts. Although a number of studies exist on these receptors, studies of several signaling pathways using a large number of melatoninergic compounds are rather limited. We chose to fill this gap to better describe a panel of compounds that have been only partially characterized in terms of functionality. First, we characterized HEK cells expressing MT1 or MT2, and several signaling routes with melatonin itself to validate the approach: GTPγS, cAMP production, internalization, β-arrestin recruitment, and cell morphology changes (CellKey ® ). Second, we chose 21 compounds from our large melatoninergic chemical library and characterized them using this panel of signaling pathways. Notably, antagonists were infrequent, and their functionality depended largely on the pathway studied. This will permit redefining the availability of molecular tools that can be used to better understand the in situ activity and roles of these receptors.

Protective effects of pharmacological agents against aminoglycoside-induced nephrotoxicity: A systematic review

Introduction: Aminoglycosides have been long used for antibacterial treatment and are still commonly used in clinical practice. Despite their extensive application and positive effects, drug-related toxicity is considered as the main obstacle for aminoglycosides. Aminoglycosides induce nephrotoxicity through the endocytosis and accumulation of the antibiotics in the epithelial cells of proximal tubule. Most importantly, however, a number of pharmacological agents were demonstrated to have protective activities against nephrotoxicity in experimental animals.Areas covered: In the present systematic review, the authors provide and discuss the mechanisms and epidemiological features of aminoglycoside-induced nephrotoxicity, and focus mainly on recent discoveries and key features of pharmacological interventions. In total, 39 articles were included in this review.Expert opinion: The majority of studies investigated gentamicin-induced nephrotoxicity in animal models. Antioxidants, chemicals, synthetic drugs, hormones, vitamins, and minerals showed potential values to prevent gentamicin-induced nephrotoxicity. Indicators used to evaluate the effectiveness of nephroprotection included antioxidative indexes, inflammatory responses, and apoptotic markers. Among the nephroprotective agents studied, herbs and natural antioxidant agents showed excellent potential to provide a protective strategy against gentamicin-induced nephrotoxicity.

The Therapeutic Effect of Melatonin on GC by Inducing Cell Apoptosis and Autophagy Induced by Endoplasmic Reticulum Stress

Background

Gastric cancer (GC) is the main malignancy affecting a large population worldwide. Lack of effective enough treatment is one of the leading factors contributing to the high mortality rate. Melatonin, a naturally occurring compound, has been proven to exert cytotoxic and antiproliferative effects on human gastric cancers. Nevertheless, the mechanisms of anti-gastric cancer of melatonin remain elucidated. It is believed that endoplasmic reticulum (ER) stress and its resultant unfolded protein response (UPR) are connected to the survival, progression, and chemoresistance of various tumor cells via multiple cellular procedures, such as autophagy. In this study, the effects of melatonin on human gastric cancer cell lines AGS and SGC-7901 was assessed to reveal the interaction between melatonin, endoplasmic reticulum stress, and autophagy in gastric cancer.

Methods

CCK-8, the wound healing analysis, colony formation assay, immunofluorescence analysis, Western blotting, flow cytometry, and animal models were used in the current study.

Results

The data demonstrated that melatonin could inhibit GC growth, proliferation, and invasion both in vivo and in vitro. Apoptosis and autophagy induced in a concentration-dependent manner is response to melatonin-induced ER stress. Melatonin induced the expression of apoptotic and autophagy-related proteins, which was markedly attenuated by the ER stress inhibitor 4-PBA and autophagy inhibitor 3-MA. In addition, we used the specific IRE1 inhibitor STF 083010, finding that inhibiting IRE1 could considerably relieve ER stress-induced autophagy activity, as revealed by the reduction of LC3-II and Beclin-1.

Conclusion

This study confirmed that melatonin-induced inhibition of GC cell proliferation is mediated by the activation of the IRE/JNK/Beclin1 signaling.

Retracted Article: Melatonin protects spinal cord injury by up-regulating IGFBP3 through the improvement of microcirculation in a rat model

The present study was aimed at the investigation of the effects of melatonin on spinal cord injury (SCI) and the role of IGFBP3 in SCI both in vivo and in vitro. The rats received treatment with 100 mg kg-1 melatonin or both melatonin and pGenesil-1-si-IGFBP3 (50 µg per g bw) after SCI surgery. The motor function in rats was measured using the Basso-Beattie-Bresnahan (BBB) scale score; perfusion vessel area was determined by injecting FITC-conjugated lycopersicon esculentum agglutinin lectin (FITC-LEA), whereas the blood-spinal cord barrier permeability was measured using Evans blue. The pericytes were isolated, and the cells were cultured under hypoxia, treated with melatonin or transfected with si-IGFBP3. RT-qPCR and western blotting were conducted for the determination of IGFBP3, VEGF, MMP-2, ICAM-1 and Ang1. The expression of IGFBP3 was significantly down-regulated in the SCI rats, and melatonin significantly enhanced the IGFBP3 level. Melatonin improved the motor function, reduced the neuron injury, and improved the microcirculation in rats. However, the down-regulation of IGFBP3 significantly reversed these effects. Moreover, in both the SCI rat spinal cord tissues and the in vitro pericytes under hypoxia, the expressions of IGFBP3 and Ang1 were significantly down-regulated, whereas those of the proteins MMP-2, VEGF and ICAM-1 were significantly up-regulated, and melatonin dramatically inhibited these changes. Melatonin could protect the rats from SCI by improving the microcirculation through the up-regulation of IGFBP3.

Melatonin alleviates heat-induced damage of tomato seedlings by balancing redox homeostasis and modulating polyamine and nitric oxide biosynthesis

BACKGROUND

Melatonin is a pleiotropic signaling molecule that plays multifarious roles in plants stress tolerance. The polyamine (PAs) metabolic pathway has been suggested to eliminate the effects of environmental stresses. However, the underlying mechanism of how melatonin and PAs function together under heat stress largely remains unknown. In this study, we investigated the potential role of melatonin in regulating PAs and nitric oxide (NO) biosynthesis, and counterbalancing oxidative damage induced by heat stress in tomato seedlings.

RESULTS

Heat stress enhanced the overproduction of reactive oxygen species (ROS) and damaged inherent defense system, thus reduced plant growth. However, pretreatment with 100 μM melatonin (7 days) followed by exposure to heat stress (24 h) effectively reduced the oxidative stress by controlling the overaccumulation of superoxide (O₂^•-) and hydrogen peroxide (H₂O₂), lowering the lipid peroxidation content (as inferred based on malondialdehyde content) and less membrane injury index (MII). This was associated with increased the enzymatic and non-enzymatic antioxidants activities by regulating their related gene expression and modulating the ascorbate-glutathione cycle. The presence of melatonin induced respiratory burst oxidase (RBOH), heat shock transcription factors A2 (HsfA2), heat shock protein 90 (HSP90), and delta 1-pyrroline-5-carboxylate synthetase (P5CS) gene expression, which helped detoxify excess ROS via the hydrogen peroxide-mediated signaling pathway. In addition, heat stress boosted the endogenous levels of putrescine, spermidine and spermine, and increased the PAs contents, indicating higher metabolic gene expression. Moreover, melatonin-pretreated seedlings had further increased PAs levels and upregulated transcript abundance, which coincided with suppression of catabolic-related genes expression. Under heat stress, exogenous melatonin increased endogenous NO content along with nitrate reductase- and NO synthase-related activities, and expression of their related genes were also elevated.

CONCLUSIONS

Melatonin pretreatment positively increased the heat tolerance of tomato seedlings by improving their antioxidant defense mechanism, inducing ascorbate-glutathione cycle, and reprogramming the PAs metabolic and NO biosynthesis pathways. These attributes facilitated the scavenging of excess ROS and increased stability of the cellular membrane, which mitigated heat-induced oxidative stress.

Comparison of protective properties of resveratrol and melatonin in the radiation inactivation and destruction of glyceraldehyde-3-phosphate dehydrogenase and lactate dehydrogenase

Purpose: This work investigates the effect of resveratrol and melatonin on structural and functional changes of two enzymes, lactate dehydrogenase (LDH) and glyceraldehyde-3-phosphate dehydrogenase (GAPDH), exposed to radiation-induced reactive oxygen species.Materials and methods: Solutions of dehydrogenases with or without antioxidants (resveratrol or melatonin) were irradiated with X-rays under the atmosphere of air and at room temperature (21 ± 2 °C). In order to determine the protective effect of melatonin and resveratrol in radiation-induced damage to GAPDH and LDH spectroscopy and HPLC methods were used. Furthermore, plausible binding sites of melatonin or resveratrol to the GAPDH or LDH molecule were analysed.Results and conclusions: Resveratrol shows better protective properties in the inactivation of GAPDH when compared to melatonin. LDH does not contain ‒SH groups in its active site, and is not inactivated by water radiolysis products other than hydroxyl radicals or the secondary radicals of the studied low-molecular-weight compounds. Resveratrol and melatonin protected the structure of LDH to a greater extent than GAPDH. This difference can be attributed to the fact that LDH potentially binds more resveratrol or melatonin molecules (27 binding sites for resveratrol and 40 for melatonin) than GAPDH (10 binding sites for resveratrol and 18 for melatonin).

Melatonin-mediated nitric oxide improves tolerance to cadmium toxicity by reducing oxidative stress in wheat plants

Two independent trials were conducted to examine the involvement of nitric oxide (NO) in MT-mediated tolerance to Cd toxicity in wheat plants. Cadmium toxicity considerably led to a decrease in plant growth, total chlorophyll, PSII maximum efficiency (Fv/Fm), leaf water potential, potassium (K⁺) and calcium (Ca²⁺). Simultaneously, it caused an increase in levels of leaf malondialdehyde (MDA), hydrogen peroxide (H₂O₂), electron leakage (EL), cadmium (Cd) and nitric oxide (NO) compared to those in control plants. Both MT (50 or 100 μM) treatments increased plant growth attributes and leaf Ca²⁺ and K⁺ in the leaves, but reduced MDA, H₂O₂ as well as leaf Cd content compared to those in Cd-stressed plants. A further experiment was designed to understand whether or not NO played a role in alleviation of Cd stress in wheat seedlings by melotonin using a scavenger of NO, 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide potassium salt (cPTIO) combined with the MT treatments. Melatonin-enhanced tolerance to Cd stress was completely reversed by the supply of cPTIO, which in turn considerably reduced the levels of endogenous NO. The results evidently showed that MT enhanced tolerance of wheat seedlings to Cd toxicity by triggering the endogenous NO. This was reinforced by the rise in the levels of MDA and H₂O₂, and decrease in the activities of superoxide dismutase (SOD; EC 1.15.1.1), catalase (CAT; EC. 1.11.1.6) and peroxidase (POD; EC. 1.11.1.7). The cPTO supply along with that of MT caused growth inhibition and a considerable increase in leaf Cd. So, both MT and NO together enhanced Cd tolerance in wheat.

Protective stabilization of mitochondrial permeability transition and mitochondrial oxidation during mitochondrial Ca2+ stress by melatonin's cascade metabolites C3-OHM and AFMK in RBA1 astrocytes

Cyclic 3-hydroxymelatonin (C3-OHM) and N1-acetyl-N2-formyl-5-methoxykynuramine (AFMK) are two major cascade metabolites of melatonin. We previously showed melatonin provides multiple levels of mitochondria-targeted protection beyond as a mitochondrial antioxidant during ionomycin-induced mitochondrial Ca²⁺ (mCa²⁺ ) stress in RBA1 astrocytes. Using noninvasive laser scanning fluorescence coupled time-lapse digital imaging microscopy, this study investigated whether C3-OHM and AFMK also provide mitochondrial levels of protection during ionomycin-induced mCa²⁺ stress in RBA1 astrocytes. Interestingly, precise temporal and spatial dynamic live mitochondrial images revealed that C3-OHM and AFMK prevented specifically mCa²⁺ -mediated mitochondrial reactive oxygen species (mROS) formation and hence mROS-mediated depolarization of mitochondrial membrane potential (△Ψ_m ) and permanent lethal opening of the MPT (p-MPT). The antioxidative effects of AFMK, however, were less potent than that of C3-OHM. Whether C3-OHM and AFMK targeted directly the MPT was investigated under a condition of "oxidation free-Ca²⁺ stress" using a classic antioxidant vitamin E to remove mCa²⁺ -mediated mROS stress and the potential antioxidative effects of C3-OHM and AFMK. Intriguingly, two compounds still effectively postponed "oxidation free-Ca²⁺ stress"-mediated depolarization of △Ψ_m and p-MPT. Measurements using a MPT pore-specific indicator Calcein further identified that C3-OHM and AFMK, rather than inhibiting, stabilized the MPT in its transient protective opening mode (t-MPT), a critical mechanism to reduce overloaded mROS and mCa²⁺ . These multiple layers of mitochondrial protection provided by C3-OHM and AFMK thus crucially allow melatonin to extend its metabolic cascades of mitochondrial protection during mROS- and mCa²⁺ -mediated MPT-associated apoptotic stresses and may provide therapeutic benefits against astrocyte-mediated neurodegeneration in the CNS.

Melatonin attenuates detrimental effects of diabetes on the niche of mouse spermatogonial stem cells by maintaining Leydig cells

Diabetes mellitus affects a large number of men of reproductive age and it usually leads to serious reproductive disorders. However, the underlying mechanisms and specific therapies still remain largely unknown. We observed Leydig cell loss in the testes of diabetic mice. Continuous high glycemic status of testes stimulated expression of Caspase12, Grp78, and Chop, the three ERS response factors; this might induce cell cycle arrest and apoptosis of Leydig cells in response to ERS. In these diabetic mouse models, melatonin alleviated apoptosis of testicular stromal cell induced by ERS, and promoted SSCs self-renewal by recovering Leydig cells secretion of CSF1 after 8 weeks of treatment. To explore the relationship between CSF-1 and ERS in Leydig cells, we treated Leydig tumor cell line with an activator Tuniamycin and an inhibitor 4-Phenylbutyrate of ERS. Our data showed that the CSF-1 expression in mouse Leydig cell lines decreased six-fold while reversely increasing five-fold in the 4-Phenylbutyrate-treated group. Thus, melatonin likely alleviates the loss of Leydig cells in diabetic testes and provides a healthier niche for SSCs to self-renew and continually provide healthy sperm for male fertility.

Melatonin and its metabolites vs oxidative stress: From individual actions to collective protection

Oxidative stress (OS) represents a threat to the chemical integrity of biomolecules including lipids, proteins, and DNA. The associated molecular damage frequently results in serious health issues, which justifies our concern about this phenomenon. In addition to enzymatic defense mechanisms, there are compounds (usually referred to as antioxidants) that offer chemical protection against oxidative events. Among them, melatonin and its metabolites constitute a particularly efficient chemical family. They offer protection against OS as individual chemical entities through a wide variety of mechanisms including electron transfer, hydrogen transfer, radical adduct formation, and metal chelation, and by repairing biological targets. In fact, many of them including melatonin can be classified as multipurpose antioxidants. However, what seems to be unique to the melatonin's family is their collective effects. Because the members of this family are metabolically related, most of them are expected to be present in living organisms wherever melatonin is produced. Therefore, the protection exerted by melatonin against OS may be viewed as a result of the combined antioxidant effects of the parent molecule and its metabolites. Melatonin's family is rather exceptional in this regard, offering versatile and collective antioxidant protection against OS. It certainly seems that melatonin is one of the best nature's defenses against oxidative damage.

Modulation of Vascular Reactivity by Perivascular Adipose Tissue (PVAT)

PURPOSE OF REVIEW

In this review, we discuss the role of perivascular adipose tissue (PVAT) in the modulation of vascular contractility and arterial pressure, focusing on the role of the renin-angiotensin-aldosterone system and oxidative stress/inflammation.

RECENT FINDINGS

PVAT possesses a relevant endocrine-paracrine activity, which may be altered in several pathophysiological and clinical conditions. During the last two decades, it has been shown that PVAT may modulate vascular reactivity. It has also been previously demonstrated that inflammation in adipose tissue may be implicated in vascular dysfunction. In particular, adipocytes secrete a number of adipokines with various functions, as well as several vasoactive factors, together with components of the renin-angiotensin system which may act at local or at systemic level. It has been shown that the anti-contractile effect of PVAT is lost in obesity, probably as a consequence of the development of adipocyte hypertrophy, inflammation, and oxidative stress. Adipose tissue dysfunction is interrelated with inflammation and oxidative stress, thus contributing to endothelial dysfunction observed in several pathological and clinical conditions such as obesity and hypertension. Decreased local adiponectin level, macrophage recruitment and infiltration, and activation of renin-angiotensin-aldosterone system could play an important role in this regard.

Exogenous Melatonin Confers Cadmium Tolerance by Counterbalancing the Hydrogen Peroxide Homeostasis in Wheat Seedlings

Melatonin has emerged as a research highlight regarding its important role in regulating plant growth and the adaptation to the environmental stresses. In this study, we investigated how melatonin prevented the cadmium toxicity to wheat seedlings. The results demonstrated that cadmium induced the expression of melatonin biosynthesis-related genes and cause a significant increase of endogenous melatonin level. Melatonin treatment drastically alleviated the cadmium toxicity, resulting in increased plant height, biomass accumulation, and root growth. Cadmium and senescence treatment significantly increased the endogenous level of hydrogen peroxide, which was strictly counterbalanced by melatonin. Furthermore, melatonin treatment caused a significant increase of GSH (reduced glutathione) content and the GSH/GSSG (oxidized glutathione) ratio. The activities of two key antioxidant enzymes, ascorbate peroxidase (APX) and superoxide dismutase (SOD), but not catalase (CAT) and peroxidase (POD), were specifically improved by melatonin. Additionally, melatonin not only promoted the primary root growth, but also drastically enhanced the capacity of the seedling roots to degrade the exogenous hydrogen peroxide. These results suggested that melatonin played a key role in maintaining the hydrogen peroxide homeostasis, via regulation of the antioxidant systems. Conclusively, this study revealed a crucial protective role of melatonin in the regulation of cadmium resistance in wheat.

Melatonin Improves Heat Tolerance in Kiwifruit Seedlings through Promoting Antioxidant Enzymatic Activity and Glutathione S-Transferase Transcription

Evidence exists to suggest that melatonin (MT) is important to abiotic stress tolerance in plants. Here, we investigated whether exogenous MT reduces heat damage on biological parameters and gene expression in kiwifruit (Actinidia deliciosa) seedlings. Pretreatment with MT alleviates heat-induced oxidative harm through reducing H₂O₂ content and increasing proline content. Moreover, MT application raised ascorbic acid (AsA) levels and the activity of antioxidant enzymes, including superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD). We also observed elevation in the activity of enzymes related to the AsA-GSH cycle, such as ascorbate peroxidase (APX), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), and glutathione reductase (GR). Furthermore, MT application increased the expression of 28/31 glutathione S-transferase (GST) genes, reducing oxidative stress. These results clearly indicate that in kiwifruit, MT exerts a protective effect against heat-related damage through regulating antioxidant pathways.

Melatonin: A Versatile Protector against Oxidative DNA Damage

Oxidative damage to DNA has important implications for human health and has been identified as a key factor in the onset and development of numerous diseases. Thus, it is evident that preventing DNA from oxidative damage is crucial for humans and for any living organism. Melatonin is an astonishingly versatile molecule in this context. It can offer both direct and indirect protection against a wide variety of damaging agents and through multiple pathways, which may (or may not) take place simultaneously. They include direct antioxidative protection, which is mediated by melatonin's free radical scavenging activity, and also indirect ways of action. The latter include, at least: (i) inhibition of metal-induced DNA damage; (ii) protection against non-radical triggers of oxidative DNA damage; (iii) continuous protection after being metabolized; (iv) activation of antioxidative enzymes; (v) inhibition of pro-oxidative enzymes; and (vi) boosting of the DNA repair machinery. The rather unique capability of melatonin to exhibit multiple neutralizing actions against diverse threatening factors, together with its low toxicity and its ability to cross biological barriers, are all significant to its efficiency for preventing oxidative damage to DNA.

Melatonin improves the fertilization ability of post-ovulatory aged mouse oocytes by stabilizing ovastacin and Juno to promote sperm binding and fusion

STUDY QUESTION

What are the underlying mechanisms of the decline in the fertilization ability of post-ovulatory aged oocytes?

SUMMARY ANSWER

Melatonin improves the fertilization ability of post-ovulatory aged oocytes by reducing aging-induced reactive oxygen species (ROS) levels and inhibiting apoptosis and by maintaining the levels and localization of the fertilization proteins, ovastacin and Juno.

WHAT IS KNOWN ALREADY

Following ovulation, the quality of mammalian metaphase II oocytes irreversibly deteriorates over time with a concomitant loss of fertilization ability. Melatonin has been found to prevent post-ovulatory oocyte aging and extend the window for optimal fertilization in mice.

STUDY DESIGN, SIZE, DURATION

Mouse oocytes were randomly assigned to three groups and aged in vitro for 0, 6, 12 and 24 h, respectively. Increasing concentrations of melatonin (10-9 M, 10-7 M, 10-5 M and 10-3 M) were added to the 24 h aging group.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Sperm binding assays, in-vitro fertilization, immunofluorescent staining and western blotting were performed to investigate key regulators and events during fertilization of post-ovulatory aged mouse oocytes.

MAIN RESULTS AND THE ROLE OF CHANCE

We found that the actin cap which promotes a cortical granule (CG) free domain is disrupted with a re-distribution of CGs in the subcortex of aged oocytes. Ovastacin, a CG metalloendoprotease, is mis-located and prematurely exocytosed in aged oocytes with subsequent cleavage of the zona pellucida protein ZP2. This disrupts the sperm recognition domain and dramatically reduces the number of sperm binding to the zona pellucida. The abundance of Juno, the sperm receptor on the oocyte membrane, also is reduced in aged oocytes. Exposure of aged oocytes to melatonin significantly elevates in-vitro fertilization rates potentially by rescuing the above age-associated defects of fertilization, and reducing ROS and inhibiting apoptosis.

LARGE SCALE DATA

N/A.

LIMITATIONS, REASONS FOR CAUTION

We explored the mechanisms of the decline in fertilization ability decline in aged mouse oocytes, in vitro but not in vivo.

WIDER IMPLICATIONS OF THE FINDINGS

Our findings may contribute to the development a more efficient method, involving melatonin, for improving IVF success rates.

STUDY FUNDING/COMPETING INTEREST(S)

This study was supported by the National Natural Science Foundation (31571545) and the Natural Science Foundation of Jiangsu Province (BK20150677). The authors have no conflict of interest to disclose.

Vitamin C exerts novel protective effects against cadmium toxicity in mouse spermatozoa by inducing the dephosphorylation of dihydrolipoamide dehydrogenase

Cadmium (Cd) has been reported to inhibit mouse sperm motility by inducing the tyrosine phosphorylation of dihydrolipoamide dehydrogenase (DLD). This study aimed to assess the potential effects of vitamin C (Vc) on ameliorating Cd-induced tyrosine phosphorylation of DLD and the specific underlying mechanism. Vc induced the dephosphorylation of DLD or inhibited the tyrosine phosphorylation of DLD. Accordingly, DLD activity, nicotinamide adenine dinucleotide hydrogen (NADH) levels, ATP levels and motility parameters were all restored to normal levels by Vc. Moreover, the effects of Vc on ameliorating these indicators had striking similarities to the effects of ethylenediaminetetraacetic acid (EDTA). In addition, neither the antioxidant melatonin nor the universal oxidant H₂O₂ influenced the tyrosine phosphorylation of DLD. Hence, the protective effects of Vc on the tyrosine phosphorylation of DLD might be attributed to its binding to Cd ions outside or inside sperm, and were not due to its antioxidant properties.

Melatonin as an Anti-Inflammatory Agent Modulating Inflammasome Activation

Inflammation may be defined as the innate response to harmful stimuli such as pathogens, injury, and metabolic stress; its ultimate function is to restore the physiological homeostatic state. The exact aetiology leading to the development of inflammation is not known, but a combination of genetic, epigenetic, and environmental factors seems to play an important role in the pathogenesis of many inflammation-related clinical conditions. Recent studies suggest that the pathogenesis of different inflammatory diseases also involves the inflammasomes, intracellular multiprotein complexes that mediate activation of inflammatory caspases thereby inducing the secretion of proinflammatory cytokines. Melatonin, an endogenous indoleamine, is considered an important multitasking molecule with fundamental clinical applications. It is involved in mood modulation, sexual behavior, vasomotor control, and immunomodulation and influences energy metabolism; moreover, it acts as an oncostatic and antiaging molecule. Melatonin is an important antioxidant and also a widespread anti-inflammatory molecule, modulating both pro- and anti-inflammatory cytokines in different pathophysiological conditions. This review, first, gives an overview concerning the growing importance of melatonin in the inflammatory-mediated pathological conditions and, then, focuses on its roles and its protective effects against the activation of the inflammasomes and, in particular, of the NLRP3 inflammasome.

Exogenous Melatonin Confers Salt Stress Tolerance to Watermelon by Improving Photosynthesis and Redox Homeostasis

Melatonin, a pleiotropic signal molecule, has been shown to play important roles in the regulation of plant growth, development, and responses to environmental stresses. Since a few species have been investigated to unveil the effect of exogenous melatonin on salt stress, the underlying mechanism of melatonin-mediated salt stress tolerance in other plant species still remains largely unknown. In this study, the effects of melatonin on leaf photosynthesis and redox homeostasis in watermelon were examined under salt stress (300 mM NaCl) along with different doses of melatonin (50, 150, and 500 μM) pretreatment. NaCl stress inhibited photosynthesis and increased accumulation of reactive oxygen species and membrane damage in leaves of watermelon seedlings. However, pretreatment with melatonin on roots alleviated NaCl-induced decrease in photosynthetic rate and oxidative stress in a dose-dependent manner. The protection of photosynthesis by melatonin was closely associated with the inhibition of stomatal closure and improved light energy absorption and electron transport in photosystem II, while the reduction of oxidative stress by melatonin was attributed to the improved redox homeostasis coupled with the enhanced activities of antioxidant enzymes. This study unraveled crucial role of melatonin in salt stress mitigation and thus can be implicated in the management of salinity in watermelon cultivation.

Effect of long-term treatment with melatonin on vascular markers of oxidative stress/inflammation and on the anticontractile activity of perivascular fat in aging mice

Some reports have suggested that inflammation in perivascular adipose tissue (PVAT) may be implicated in vascular dysfunction by causing the disappearance of an anticontractile effect. The aim of this study was to investigate the effects of chronic melatonin treatment on the functional responses of the small mesenteric arteries and on the expression of markers of inflammation/oxidative stress in the aortas of senescence-accelerated prone mice (SAMP8), a model of age-related vascular dysfunction. We investigated seven SAMP8 and seven control senescence-accelerated resistant mice (SAMR1) treated for 10 months with melatonin, as well as equal numbers of age-matched untreated SAMP8 and SAMR1. The mesenteric small resistance arteries were dissected and mounted on a wire myograph, and the concentration-response to norepinephrine was evaluated in vessels with intact PVAT and after the removal of the PVAT. The expression of markers of oxidative stress, inflammation and aging in the aortas was evaluated by immunostaining. In addition, the adiponectin content and the expression of adiponectin receptor 1 were evaluated in the visceral adipose tissue. In untreated SAMP8 mice, we observed an overexpression of oxidative stress and inflammatory markers in the vasculature compared with the controls. No anticontractile effect of the PVAT was observed in untreated SAMP8 mice. Long-term treatment of SAMP8 mice with melatonin increased the expression of some markers of vasoprotection, decreased oxidative stress and inflammation and restored the anticontractile effect of the PVAT. Decreased expression of adiponectin and adiponectin receptor 1 was also observed in visceral fat of untreated SAMP8, whereas a significant increase was observed after melatonin treatment.