Modulation of Radiation-induced Base Excision Repair Pathway Gene Expression by Melatonin

A Systematic Review of the Chemo/Radioprotective Effects of Melatonin against Ototoxic Adverse Effects Induced by Chemotherapy and Radiotherapy

BACKGROUND

Although chemotherapy and radiotherapy are effective in cancer treatment, different adverse effects induced by these therapeutic modalities (such as ototoxicity) restrict their clinical use. Co-treatment of melatonin may alleviate the chemotherapy/radiotherapy-induced ototoxicity.

OBJECTIVE

In the present study, the otoprotective potentials of melatonin against the ototoxicity induced by chemotherapy and radiotherapy were reviewed.

METHODS

According to the PRISMA guideline, a systematic search was carried out to identify all relevant studies on "the role of melatonin against ototoxic damage associated with chemotherapy and radiotherapy" in the different electronic databases up to September 2022. Sixty-seven articles were screened based on a predefined set of inclusion and exclusion criteria. Seven eligible studies were finally included in this review.

RESULTS

The in vitro findings showed that cisplatin chemotherapy significantly decreased the auditory cell viability compared to the control group; in contrast, the melatonin co-administration increased the cell viability of cisplatin-treated cells. The results obtained from the distortion product otoacoustic emission (DPOAE) and auditory brainstem response (ABR) tests demonstrated a decreased amplitude of DPOAE and increased values of ABR I-IV interval and ABR threshold in mice/rats receiving radiotherapy and cisplatin; nevertheless, melatonin co-treatment indicated an opposite pattern on these evaluated parameters. It was also found that cisplatin and radiotherapy could significantly induce the histological and biochemical changes in the auditory cells/tissue. However, melatonin co-treatment resulted in alleviating the cisplatin/radiotherapy-induced biochemical and histological changes.

CONCLUSION

According to the findings, it was shown that melatonin co-treatment alleviates the ototoxic damage induced by chemotherapy and radiotherapy. Mechanically, melatonin may exert its otoprotective effects via its anti-oxidant, anti-apoptotic, and anti-inflammatory activities and other mechanisms.

New Insights into How Melatonin Ameliorates Bisphenol A-Induced Colon Damage: Inhibition of NADPH Oxidase

Bisphenol A (BPA) is an endocrine disruptor, widely employed, and detected in many consumer products and food items. Oral intake poses a great threat to intestinal health. Melatonin (MT) stands out as an endogenous, dietary, and therapeutic molecule with potent antioxidant capacity. To explore the protective effect of MT against BPA-induced colon damage and the role of NADPH oxidase (NOX) in this process, we established mice and colonic epithelial cell (NCM460) models of BPA exposure and treated with MT. In vitro and in vivo results showed that MT ameliorated BPA-induced oxidative stress, DNA damage, and the G2/M cell cycle arrest. MT also downregulated the expression of NOX family-related genes, reversed the inhibition of the base excision repair (BER) pathway, promoted the activation of non-homologous end-joining (NHEJ) pathway, and suppressed the mRNA and protein expression of ATM, Chk1/2, and p53. Diphenyleneiodonium chloride (DPI), a NOX-specific inhibitor, also attenuated the toxic effects of BPA on NCM460 cells. Furthermore, molecular docking revealed that MT could bind to NOX. Conclusively, our finding suggested that MT can ameliorate BPA-induced colonic DNA damage by scavenging NOX-derived ROS, which further attenuates G2/M cell cycle arrest dependent on the ATM-Chk1/2-p53 axis.

Endoplasmic reticulum as a target in cardiovascular diseases: Is there a role for flavonoids?

Flavonoids are found in natural health products and plant-based foods. The flavonoid molecules contain a 15-carbon skeleton with the particular structural construction of subclasses. The most flavonoid's critical subclasses with improved health properties are the catechins or flavonols (e.g., epigallocatechin 3-gallate from green tea), the flavones (e.g., apigenin from celery), the flavanones (e.g., naringenin from citrus), the flavanols (e.g., quercetin glycosides from berries, onion, and apples), the isoflavones (e.g., genistein from soya beans) and the anthocyanins (e.g., cyanidin-3-O-glucoside from berries). Scientific data conclusively demonstrates that frequent intake of efficient amounts of dietary flavonoids decreases chronic inflammation and the chance of oxidative stress expressing the pathogenesis of human diseases like cardiovascular diseases (CVDs). The endoplasmic reticulum (ER) is a critical organelle that plays a role in protein folding, post-transcriptional conversion, and transportation, which plays a critical part in maintaining cell homeostasis. Various stimuli can lead to the creation of unfolded or misfolded proteins in the endoplasmic reticulum and then arise in endoplasmic reticulum stress. Constant endoplasmic reticulum stress triggers unfolded protein response (UPR), which ultimately causes apoptosis. Research has shown that endoplasmic reticulum stress plays a critical part in the pathogenesis of several cardiovascular diseases, including diabetic cardiomyopathy, ischemic heart disease, heart failure, aortic aneurysm, and hypertension. Endoplasmic reticulum stress could be one of the crucial points in treating multiple cardiovascular diseases. In this review, we summarized findings on flavonoids' effects on the endoplasmic reticulum and their role in the prevention and treatment of cardiovascular diseases.

Melatonin Attenuates Inflammation, Oxidative Stress, and DNA Damage in Mice with Nonalcoholic Steatohepatitis Induced by a Methionine- and Choline-Deficient Diet

Nonalcoholic steatohepatitis (NASH) is a disease with a high incidence worldwide, but its diagnosis and treatment are poorly managed. In this study, NASH pathophysiology and DNA damage biomarkers were investigated in mice with NASH treated and untreated with melatonin (MLT). C57BL/6 mice were fed a methionine- and choline-deficient (MCD) diet for 4 weeks to develop NASH. Melatonin was administered at 20 mg/kg during the last 2 weeks. Aspartate aminotransferase (AST) and alanine aminotransferase (ALT) levels were measured, and hepatic tissue was dissected for histological analysis, evaluation of lipoperoxidation, superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx), as well as nuclear factor-erythroid 2 (Nrf2), tumor necrosis factor alpha (TNF-α), inducible nitric oxide synthase (iNOS), and transforming growth factor beta (TGF-β) expression by immunohistochemistry. DNA damage was evaluated using Comet assay, while a micronucleus test in bone marrow was performed to assess the genomic instability associated with the disease. Melatonin decreased AST and ALT, liver inflammatory processes, balloonization, and fibrosis in mice with NASH, decreasing TNF-α, iNOS, and TGF-β, as well as oxidative stress, shown by reducing lipoperoxidation and intensifying Nrf2 expression. The SOD and GPx activities were increased, while CAT was decreased by treatment with MLT. Although the micronucleus frequency was not increased in mice with NASH, a protective effect on DNA was observed with MLT treatment in blood and liver tissues using Comet assay. As conclusions, MLT slows down the progression of NASH, reducing hepatic oxidative stress and inflammatory processes, inhibiting DNA damage via anti-inflammatory and antioxidant actions.

Melatonin: A smart molecule in the DNA repair system

DNA repair is an important pathway for the protection of DNA molecules from destruction. DNA damage can be produced by oxidative reactive nitrogen or oxygen species, irritation, alkylating agents, depurination and depyrimidination; in this regard, DNA repair pathways can neutralize the negative effects of these factors. Melatonin is a hormone secreted from the pineal gland with an antioxidant effect by binding to oxidative factors. In addition, the effect of melatonin on DNA repair pathways has been proven by the literature. DNA repair is carried out by several mechanisms, of which homologous recombination repair (HRR) and non-homologous end-joining (NHEJ) are of great importance. Because of the importance of DNA repair in DNA integrity and the anticancer effect of this pathway, we presented the effect of melatonin on DNA repair factors regarding previous studies conducted in this area.

Melatonin as an Antioxidant and Immunomodulator in Atopic Dermatitis-A New Look on an Old Story: A Review

Atopic dermatitis (AD) is common inflammatory dermatosis, typically with chronic and recurrent course, which significantly reduces the quality of life. Sleep disturbances are considered to be remarkably burdensome ailments in patients with AD, and are routinely included during assessment of disease severity. Therefore, endogenous substances engaged in the control of circadian rhythms might be important in pathogenesis of AD and, possibly, be used as biomarkers of disease severity or even in development of novel therapies. Melatonin (MT), the indoleamine produced by pineal gland (but also by multiple other tissues, including skin), plays a pivotal role in maintaining the sleep/wake homeostasis. Additionally, it possesses strong antioxidant and anti-inflammatory properties, which might directly link chronic skin inflammation and sleep abnormalities characteristic of AD. The objective of this work is to systematically present and summarize the results of studies (both experimental and clinical) that investigated the role of MT in the AD, with a focus on the antioxidant and immunomodulatory effects of MT.

A "Failed" Assay Development for the Discovery of Rescuing Small Molecules from the Radiation Damage

With improving survival rates for cancer patients, the side effects of radiation therapy, especially for pediatric or more sensitive adult patients, have raised interest in preventive or rescue treatment to overcome the detrimental effects of efficient radiation therapies. For the discovery of rescuing small molecules for radiation damage to the endothelium, we have been developing a 96-well microplate-based in vitro assay for high-throughput compatible measurement of radiation-induced cell damage and its rescue by phenotypic high-content imaging. In contrast to traditional radiation assays with detached cells for clonogenic formation, we observed cells with live-cell imaging in two different kinds of endothelial cells, up to three different cell densities, two gamma-infrared radiation dose rates, more than four different radiation doses, and acute (within 24 h with one to two h intervals) and chronic (up to 7 days) responses by phenotypic changes (digital phase contrast) and functional assays (nuclear, live-cell, and dead-cell staining) at the end of the assay. Multiple potential small molecules, which have been reported for rescuing radiation damage, have been tested as assay controls with dose responses. At the end, we did not move ahead with the pilot screening. The lessons learned from this "failed" assay development are shared.

The role of melatonin on radiation-induced pneumonitis and lung fibrosis: A systematic review

PURPOSE

Pneumonitis and lung fibrosis, as the most common compliances of lung irradiation, can affect the quality of life. The use of radio-protective agents can ameliorate these injuries. This study aimed to review the potential protective role of melatonin in the treatment of radiation-induced Pneumonitis and lung fibrosis.

METHODS

The current systematic study was conducted based on PRISMA guidelines to identify relevant literature on " the effect of melatonin on radiation-induced pneumonitis and lung fibrosis" in the electronic databases of Web of Science, Embase, PubMed, and Scopus up to January 2021. Eighty-one articles were screened in accordance with the inclusion and exclusion criteria of the study. Finally, eight articles were included in this systematic review.

RESULTS

The finding showed that the lung irradiation-induced pneumonitis and lung fibrosis. The co-treatment with melatonin could alleviate these compliances through its anti-oxidant and anti-inflammatory actions. Melatonin through upregulation of some enzymes such as catalase, superoxide dismutase, glutathione, NADPH oxidases 2 and 4, dual oxidases 1 and 2, and also downregulation of malondialdehyde reduced oxidative stress following lung radiation. Moreover, melatonin through its anti-inflammatory effects, can attenuate the increased levels of nuclear factor kappa B, tumor necrosis factor alpha, transforming growth factor beta 1, SMAD2, interleukin (IL)-4, IL-4 receptor-a1 (IL4ra1), and IL-1 beta following lung radiation. The histological damages induced by ionizing radiation were also alleviated by co-treatment with melatonin.

CONCLUSION

According to the obtained results, it was found that melatonin can have anti-pneumonitis and anti-fibrotic following lung irradiation.

Metabolic Rewiring in Radiation Oncology Toward Improving the Therapeutic Ratio

To meet the anabolic demands of the proliferative potential of tumor cells, malignant cells tend to rewire their metabolic pathways. Although different types of malignant cells share this phenomenon, there is a large intracellular variability how these metabolic patterns are altered. Fortunately, differences in metabolic patterns between normal tissue and malignant cells can be exploited to increase the therapeutic ratio. Modulation of cellular metabolism to improve treatment outcome is an emerging field proposing a variety of promising strategies in primary tumor and metastatic lesion treatment. These strategies, capable of either sensitizing or protecting tissues, target either tumor or normal tissue and are often focused on modulating of tissue oxygenation, hypoxia-inducible factor (HIF) stabilization, glucose metabolism, mitochondrial function and the redox balance. Several compounds or therapies are still in under (pre-)clinical development, while others are already used in clinical practice. Here, we describe different strategies from bench to bedside to optimize the therapeutic ratio through modulation of the cellular metabolism. This review gives an overview of the current state on development and the mechanism of action of modulators affecting cellular metabolism with the aim to improve the radiotherapy response on tumors or to protect the normal tissue and therefore contribute to an improved therapeutic ratio.

Melatonin supplementation over different time periods until ageing modulates genotoxic parameters in mice

The ageing process is a multifactorial phenomenon, associated with decreased physiological and cellular functions and an increased propensity for various degenerative diseases. Studies on melatonin (N-acetyl-5-methoxytryptamine), a potent antioxidant, are gaining attention since melatonin production declines with advancing age. Hence, the aim of this study was to evaluate the effects of chronic melatonin consumption on genotoxic and mutagenic parameters of old Swiss mice. Herein, 3-month-old Swiss albino male mice (n = 240) were divided into eight groups and subdivided into two experiments: first (three groups): natural ageing experiment; second (five groups): animals that started water or melatonin supplementation at different ages (3, 6, 12 and 18 months) until 21 months. After 21 months, the animals from the second experiment were euthanized to perform the comet assay, micronucleus test and western blot analysis. The results demonstrated that melatonin prolonged the life span of the animals. Relative to genomic instability, melatonin was effective in reducing DNA damage caused by ageing, presenting antigenotoxic and antimutagenic activities, independently of initiation age. The group receiving melatonin for 18 months had high levels of APE1 and OGG1 repair enzymes. Conclusively, melatonin presents an efficient antioxidant mechanism aiding modulating genetic and physiological alterations due to ageing.

Photon versus proton neurotoxicity: Impact on mitochondrial function and 8-OHdG base-excision repair mechanism in human astrocytes

This study assesses and compares the neurotoxic effects of proton and photon radiation on mitochondrial function and DNA repair capabilities of human astrocytes. Human astrocytes received either proton (0.5 Gy and 3 Gy), photon (0.5 Gy and 3 Gy), or sham-radiation treatment. The mRNA expression level of the DNA repair protein OGG1 was determined via RT-qPCR. The levels of 8-OHdG in the cell media were measured via ELISA. Real-time kinetic analysis of extracellular oxygen consumption rates was performed to assess mitochondrial function. Radiation-induced changes in mitochondrial mass and oxidative activity were assessed using fluorescent imaging with MitoTracker™ Green FM and MitoTracker™ Orange CM-H₂TMRos dyes respectively. PCR was used to quantify the alteration in the mitochondrial DNA content, measured as the mitochondrial to nuclear DNA ratio. A significant increase in mitochondrial mass and levels of reactive oxygen species was observed after radiation treatment. Additionally, real-time PCR analysis indicated a significant depletion of mitochondrial DNA content in the irradiated cells when compared to the control. This was accompanied by a decreased gene expression of the DNA base-excision repair protein OGG1 and reduced clearance of 8-OHdG adducts from the genome. Photon radiation treatment was associated with a more detrimental cellular impact when compared to the same dose of proton radiation. These results are indicative of a radiation-induced dose-dependent decrease in mitochondrial function, an increase in senescence and astrogliosis, and impairment of the DNA repair capabilities in healthy glial cells. Photon irradiation was associated with a more significant disruption in mitochondrial function and base-excision repair mechanisms in vitro in comparison to proton treatment.

Mitigation of radiation-induced hematopoietic system injury by melatonin

BACKGROUND

Increased risks of exposure to accidental radiation events are a concern in today's world. Radiation terror, nuclear explosion, as well as accidental exposure to radioactive sources in some industries pose a threat to the life of exposed persons. Studies have been conducted using some low-toxic agents to mitigate radiation toxicity and increase survival probability for exposed people. In the current study, we aimed to show the mitigation of radiation-induced mortality and bone marrow toxicity using postirradiation treatment with melatonin.

METHOD

Mice whole bodies were exposed to 4 or 7 Gy radiation followed by treatment with melatonin after 24 hours. Survival of mice with or without melatonin, the levels of peripheral cells, transforming growth factor (TGF)-β and 8-hydroxy-2' -deoxyguanosine (8-OHdG) in the bone marrow, as well as the expression of NADPH oxidase (NOX)2 and NOX4 in bone marrow cells were evaluated.

RESULTS

Whole body irradiation led to mortality 30 days after irradiation. However, melatonin treatment reduced mortality. Irradiation also showed severe reduction of lymphocytes, platelets, and red blood cells. The expressions of NOX2 and NOX4, in addition to TGF-β level, were increased after exposure to radiation. Melatonin ameliorated the increased levels of these factors and improved the number of blood cells.

CONCLUSIONS

Melatonin showed ability to mitigate radiation-induced hematopoietic system toxicity and also increased survival rate. These results suggest that melatonin could be a potential mitigator for accidental radiation events.

Genome-Protecting Compounds as Potential Geroprotectors

Throughout life, organisms are exposed to various exogenous and endogenous factors that cause DNA damages and somatic mutations provoking genomic instability. At a young age, compensatory mechanisms of genome protection are activated to prevent phenotypic and functional changes. However, the increasing stress and age-related deterioration in the functioning of these mechanisms result in damage accumulation, overcoming the functional threshold. This leads to aging and the development of age-related diseases. There are several ways to counteract these changes: 1) prevention of DNA damage through stimulation of antioxidant and detoxification systems, as well as transition metal chelation; 2) regulation of DNA methylation, chromatin structure, non-coding RNA activity and prevention of nuclear architecture alterations; 3) improving DNA damage response and repair; 4) selective removal of damaged non-functional and senescent cells. In the article, we have reviewed data about the effects of various trace elements, vitamins, polyphenols, terpenes, and other phytochemicals, as well as a number of synthetic pharmacological substances in these ways. Most of the compounds demonstrate the geroprotective potential and increase the lifespan in model organisms. However, their genome-protecting effects are non-selective and often are conditioned by hormesis. Consequently, the development of selective drugs targeting genome protection is an advanced direction.

Neuroprotective effect of melatonin on radiation-induced oxidative stress and apoptosis in the brainstem of rats

This study aimed to determine the effects of melatonin on irradiation-induced apoptosis and oxidative stress in the brainstem region of Wistar rats. Therefore, the animals underwent whole-brain X-radiation with a single dose of 25 Gy in the presence or absence of melatonin pretreatment at a concentration of 100 mg/kg BW. The rats were allocated into four groups (10 rats in each group): namely, vehicle control (VC), 100 mg/kg of melatonin alone (MLT), irradiation-only (RAD), and irradiation plus 100 mg/kg of melatonin (RAM). An hour before irradiation, the animals received intraperitoneal (IP) melatonin and then were killed after 6 hr, followed by measurement of nitric oxide (NO), malondialdehyde (MDA), superoxide dismutase (SOD), glutathione peroxidase (GPx), catalase (CAT), and total antioxidant capacity (TAC) in the brainstem region. Furthermore, the western blot analysis technique was performed to assess the caspase-3 expression level. Results showed significantly higher MDA and NO levels in the brainstem tissues for the RAD group when compared with the VC group (p < .001). Moreover, the irradiated rats exhibited a significant decrease in the levels of CAT, SOD, GPx, and TAC (p < .01, p < .001, p < .001, and p < .001, respectively) in comparison to the VC group. The results of apoptosis assessment revealed that the expression level of caspase-3 significantly rose in the RAD group in comparison with the VC group (p < .001). Pretreatment with melatonin ameliorated the radiation-induced adverse effects by decreasing the MDA and NO levels (p < .001) and increasing the antioxidant enzyme activities (p < .001). Consequently, the caspase-3 protein expression level in the RAM group showed a significant reduction in comparison with the RAD group (p < .001). In conclusion, melatonin approximately showed a capacity for neuroprotective activity in managing irradiation-induced oxidative stress and apoptosis in the brainstem of rats; however, the use of melatonin as a neuroprotective agent in humans requires further study, particularly clinical trials.

Therapeutic effects of kaempferol affecting autophagy and endoplasmic reticulum stress

Regulated cell death (RCD) guarantees to preserve organismal homeostasis. Apoptosis and autophagy are two major arms of RCD, while endoplasmic reticulum (ER) as a crucial organelle involved in proteostasis, promotes cells toward autophagy and apoptosis. Alteration in ER stress and autophagy machinery is responsible for a great number of diseases. Therefore, targeting those pathways appears to be beneficial in the treatment of relevant diseases. Meantime, among the traditional herb medicine, kaempferol as a flavonoid seems to be promising to modulate ER stress and autophagy and exhibits protective effects on malfunctioning cells. There are some reports indicating the capability of kaempferol in affecting autophagy and ER stress. In brief, kaempferol modulates autophagy in noncancerous cells to protect cells against malfunction, while it induces cell mortality derived from autophagy through the elevation of p-AMP-activated protein kinase, light chain-3-II, autophagy-related geness, and Beclin-1 in cancer cells. Noteworthy, kaempferol enhances cell survival through C/EBP homologous protein (CHOP) suppression and GRP78 increment in noncancerous cells, while it enhances cell mortality through the induction of unfolding protein response and CHOP increment in cancer cells. In this review, we discuss how kaempferol modulates autophagy and ER stress in noncancer and cancer cells to expand our knowledge of new pharmacological compounds for the treatment of associated diseases.

Melatonin modulates IL-1β-induced extracellular matrix remodeling in human nucleus pulposus cells and attenuates rat intervertebral disc degeneration and inflammation

The inflammatory-associated factors interleukin-1β (IL-1β), interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) are widely reported to be associated with intervertebral disc (IVD) degeneration (IVDD). N-acetyl-5-methoxytryptamine (melatonin) is a natural hormone secreted by the pineal gland which has been shown to participate in several physiological and pathological progresses, such as aging, anti-inflammation, anti-apoptosis and autophagy regulation. However, the effects of melatonin on IVD remain unclear. In the present study, we treated human nucleus pulposus cells (NPCs) with melatonin and discovered that melatonin could modulate extracellular matrix (ECM) remodeling induced by IL-1β by enhancing collagen II and aggrecan expression levels and by downregulating matrix metalloproteinase-3 (MMP-3) levels. These findings were verified by western blot and immunofluorescence assays. Intraperitoneal injection of melatonin mitigated IVDD in the rat tail puncture model. X-ray and magnetic resonance imaging (MRI), as well as hematoxylin-eosin (H&E), Safranine O-Green, Alcian blue and Celium red staining methods were adopted to evaluate IVDD grades, the structural integrity of nucleus pulposus (NP) and annulus fibrosus (AF) and the damage and calcification of the cartilage endplate. Melatonin reduced inflammatory cell aggregation and the release of the inflammatory factors IL-1β, IL-6, TNF-α as determined by immunohistochemistry. In conclusion, the present study demonstrated that melatonin could modulate ECM remodeling by IL-1β in vitro and attenuate the IVDD and induction of inflammation in a rat tail puncture model in vivo. The data demonstrated that melatonin may contribute to the restoration processs of IVD following damage and may be used as a potential novel therapy for IVDD.

Mechanisms for Radioprotection by Melatonin; Can it be Used as a Radiation Countermeasure?

BACKGROUND

Melatonin is a natural body product that has shown potent antioxidant property against various toxic agents. For more than two decades, the abilities of melatonin as a potent radioprotector against toxic effects of ionizing radiation (IR) have been proved. However, in the recent years, several studies have been conducted to illustrate how melatonin protects normal cells against IR. Studies proposed that melatonin is able to directly neutralize free radicals produced by IR, leading to the production of some low toxic products.

DISCUSSION

Moreover, melatonin affects several signaling pathways, such as inflammatory responses, antioxidant defense, DNA repair response enzymes, pro-oxidant enzymes etc. Animal studies have confirmed that melatonin is able to alleviate radiation-induced cell death via inhibiting pro-apoptosis and upregulation of anti-apoptosis genes. These properties are very interesting for clinical radiotherapy applications, as well as mitigation of radiation injury in a possible radiation disaster. An interesting property of melatonin is mitochondrial ROS targeting that has been proposed as a strategy for mitigating effects in radiosensitive organs, such as bone marrow, gastrointestinal system and lungs. However, there is a need to prove the mitigatory effects of melatonin in experimental studies.

CONCLUSION

In this review, we aim to clarify the molecular mechanisms of radioprotective effects of melatonin, as well as possible applications as a radiation countermeasure in accidental exposure or nuclear/radiological disasters.

Activation of PTGS2/NF-κB signaling pathway enhances radiation resistance of glioma

Objective

We focused on the effects of PTGS2/NF‐κB signaling pathway on the radiation resistance of glioma in the study.

Methods

We downloaded the microarray data from the Gene Expression Omnibus (GEO) database. We verified transfection successfully through QRT‐PCR analysis. Immunofluorescence was used to detect γH2AX content under 2 Gy radiation. The survival rates of cells under 2 Gy irradiation were tested by clonogenic survival assay. Flow cytometry was used to detect cell cycle. Western blot was applied to detect the expression of NF‐κB pathway‐related proteins. We also used MTT assay to detect the proliferation of cells.

Results

In this research, we discovered that the expression of the PTGS2 was upregulated in radiation‐resistant glioma cells. The radio‐tolerance rate of U87 cells was obviously elevated after the overexpression of PTGS2. The radioresistance of U87R cells was significantly reduced after the knockdown of PTGS2. After radiotherapy, the number of cells arrested in G2/M phase decreased after PTGS2 overexpression in U87cells but increased in PTGS2 knockdown in U87R cells. The survival rate of U87 and U87R cells under radiation decreased significantly after the addition of NF‐κB inhibitor. The proliferation of U87 cells was suppressed by radiation and the addition of Bay 11. In addition, PTGS2 activated NF‐κB signaling pathway and prevented DNA damage after radiotherapy. Lastly, PTGS2 was proved to facilitate tumor cell proliferation and improve the radio‐tolerance.

Conclusion

PTGS2/NF‐κB signaling pathway was involved in radio‐tolerance of glioma cells, which provided a new insight into glioma therapy.

Biochemical and Histopathological Evaluation of the Radioprotective Effects of Melatonin Against Gamma Ray-Induced Skin Damage

BACKGROUND

Radiotherapy is one of the treatment methods for cancers using ionizing radiations. About 70% of cancer patients undergo radiotherapy. Radiation effect on the skin is one of the main complications of radiotherapy and dose limiting factor. To ameliorate this complication, we used melatonin as a radioprotective agent due to its antioxidant and anti-inflammatory effects, free radical scavenging, improving overall survival after irradiation as well as minimizing the degree of DNA damage and frequency of chromosomal abrasions.

METHODS

Sixty male Wistar rats were randomly assigned to 4 groups: control (C), melatonin (M), radiation (R) and melatonin + radiation (MR). A single dose of 30 Gy gamma radiation was exposed to the right hind legs of the rats while 40 mg/ml of melatonin was administered 30 minutes before irradiation and 2 mg/ml once daily in the afternoon for one month till the date of rat's sacrifice. Five rats from each group were sacrificed 4, 12 and 20 weeks after irradiation. Afterwards, their exposed skin tissues were examined histologically and biochemically.

RESULTS

In biochemical analysis, we found that malondialdehyde (MDA) levels significantly increased in R group and decreased significantly in M and MR groups after 4, 12, and 20 weeks, whereas catalase (CAT) and superoxide dismutase (SOD) activities decreased in the R group and increased in M and MR groups during the same time periods compared with the C group (p<0.05). Histopathological examination found there were statistically significant differences between R group compared with the C and M groups for the three different time periods (p<0.005, p<0.004 and p<0.004) respectively, while R group differed significantly with MR group (p<0.013). No significant differences were observed between C and M compared with MR group (p>0.05) at 4 and 20 weeks except for inflammation and hair follicle atrophy, while there were significant effects at 12 weeks (p<0.05).

CONCLUSION

Melatonin can be successfully used for the prevention and treatment of radiation-induced skin injury. We recommend the use of melatonin in optimal and safe doses. These doses should be administered over a long period of time for effective radioprotection and amelioration of skin damages as well as improving the therapeutic ratio of radiotherapy.

Melatonin and cancer: From the promotion of genomic stability to use in cancer treatment

Cancer remains among the most challenging human diseases. Several lines of evidence suggest that carcinogenesis is a complex process that is initiated by DNA damage. Exposure to clastogenic agents such as heavy metals, ionizing radiation (IR), and chemotherapy drugs may cause chronic mutations in the genomic material, leading to a phenomenon named genomic instability. Evidence suggests that genomic instability is responsible for cancer incidence after exposure to carcinogenic agents, and increases the risk of secondary cancers following treatment with radiotherapy or chemotherapy. Melatonin as the main product of the pineal gland is a promising hormone for preventing cancer and improving cancer treatment. Melatonin can directly neutralize toxic free radicals more efficiently compared with other classical antioxidants. In addition, melatonin is able to regulate the reduction/oxidation (redox) system in stress conditions. Through regulation of mitochondrial nction and inhibition of pro-oxidant enzymes, melatonin suppresses chronic oxidative stress. Moreover, melatonin potently stimulates DNA damage responses that increase the tolerance of normal tissues to toxic effect of IR and may reduce the risk of genomic instability in patients who undergo radiotherapy. Through these mechanisms, melatonin attenuates several side effects of radiotherapy and chemotherapy. Interestingly, melatonin has shown some synergistic properties with IR and chemotherapy, which is distinct from classical antioxidants that are mainly used for the alleviation of adverse events of radiotherapy and chemotherapy. In this review, we describe the anticarcinogenic effects of melatonin and also its possible application in clinical oncology.

The protective role of melatonin in chemotherapy-induced nephrotoxicity: a systematic review of non-clinical studies

BSTRACT Introduction: The aim of this study was to investigate the potential role of melatonin in the prevention of chemotherapy-induced nephrotoxicity at the preclinical level. Areas to be covered: To illuminate the possible role of melatonin in preventing chemotherapy-related nephrotoxicity, Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guideline was followed. A comprehensive search strategy was developed to include PubMed, Web of Science, Scopus, and Embase electronic databases from their inception to May 2018. Based on a set of prespecified inclusion and exclusion criteria, 21 non-clinical articles were ultimately included in the study. Expert opinion: Our findings clearly demonstrate that melatonin has a protective role in the prevention of chemotherapy-induced nephrotoxicity which may be caused by different chemotherapy agents such as cyclophosphamide, cisplatin, doxorubicin, methotrexate, oxaliplatin, etoposide, and daunorubicin. On the basis of current review of non-clinical studies, this protective effect of melatonin is attributed to different mechanisms such as reduction of oxidative stress, apoptosis, and inflammation. The findings presented in this review are based on non-clinical studies and thus conducting appropriate clinical trials to evaluate the real effectiveness of the concurrent use of chemotherapy agents with melatonin in the cancer patients is necessary.

Melatonin as an adjuvant in radiotherapy for radioprotection and radiosensitization

It is estimated that more than half of cancer patients undergo radiotherapy during the course of their treatment. Despite its beneficial therapeutic effects on tumor cells, exposure to high doses of ionizing radiation (IR) is associated with several side effects. Although improvements in radiotherapy techniques and instruments could reduce these side effects, there are still important concerns for cancer patients. For several years, scientists have been trying to modulate tumor and normal tissue responses to IR, leading to an increase in therapeutic ratio. So far, several types of radioprotectors and radiosensitizers have been investigated in experimental studies. However, high toxicity of chemical sensitizers or possible tumor protection by radioprotectors creates a doubt for their clinical applications. On the other hand, the protective effects of these radioprotectors or sensitizer effects of radiosensitizers may limit some type of cancers. Hence, the development of some radioprotectors without any protective effect on tumor cells or low toxic radiosensitizers can help improve therapeutic ratio with less side effects. Melatonin as a natural body hormone is a potent antioxidant and anti-inflammatory agent that shows some anti-cancer properties. It is able to neutralize different types of free radicals produced by IR or pro-oxidant enzymes which are activated following exposure to IR and plays a key role in the protection of normal tissues. In addition, melatonin has shown the ability to inhibit long-term changes in inflammatory responses at different levels, thereby ameliorating late side effects of radiotherapy. Fortunately, in contrast to classic antioxidants, some in vitro studies have revealed that melatonin has a potent anti-tumor activity when used alongside irradiation. However, the mechanisms of its radiosensitive effect remain to be elucidated. Studies suggested that the activation of pro-apoptosis gene, such as p53, changes in the metabolism of tumor cells, suppression of DNA repair responses as well as changes in biosynthesis of estrogen in breast cancer cells are involved in this process. In this review, we describe the molecular mechanisms for radioprotection and radiosensitizer effects of melatonin. Furthermore, some other proposed mechanisms that may be involved are presented.

Radiation-induced inflammation and autoimmune diseases

Currently, ionizing radiation (IR) plays a key role in the agricultural and medical industry, while accidental exposure resulting from leakage of radioactive sources or radiological terrorism is a serious concern. Exposure to IR has various detrimental effects on normal tissues. Although an increased risk of carcinogenesis is the best-known long-term consequence of IR, evidence has shown that other diseases, particularly diseases related to inflammation, are common disorders among irradiated people. Autoimmune disorders are among the various types of immune diseases that have been investigated among exposed people. Thyroid diseases and diabetes are two autoimmune diseases potentially induced by IR. However, the precise mechanisms of IR-induced thyroid diseases and diabetes remain to be elucidated, and several studies have shown that chronic increased levels of inflammatory cytokines after exposure play a pivotal role. Thus, cytokines, including interleukin-1(IL-1), tumor necrosis factor (TNF-α) and interferon gamma (IFN-γ), play a key role in chronic oxidative damage following exposure to IR. Additionally, these cytokines change the secretion of insulin and thyroid-stimulating hormone(TSH). It is likely that the management of inflammation and oxidative damage is one of the best strategies for the amelioration of these diseases after a radiological or nuclear disaster. In the present study, we reviewed the evidence of radiation-induced diabetes and thyroid diseases, as well as the potential roles of inflammatory responses. In addition, we proposed that the mitigation of inflammatory and oxidative damage markers after exposure to IR may reduce the incidence of these diseases among individuals exposed to radiation.

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 and Cancer Hallmarks

Melatonin is a natural indoleamine produced by the pineal gland that has many functions, including regulation of the circadian rhythm. Many studies have reported the anticancer effect of melatonin against a myriad of cancer types. Cancer hallmarks include sustained proliferation, evading growth suppressors, metastasis, replicative immortality, angiogenesis, resisting cell death, altered cellular energetics, and immune evasion. Melatonin anticancer activity is mediated by interfering with various cancer hallmarks. This review summarizes the anticancer role of melatonin in each cancer hallmark. The studies discussed in this review should serve as a solid foundation for researchers and physicians to support basic and clinical studies on melatonin as a promising anticancer agent.

Metformin: Prevention of genomic instability and cancer: A review

The diabetes drug metformin can mitigate the genotoxic effects of cytotoxic agents and has been proposed to prevent or even cure certain cancers. Metformin reduces DNA damage by mechanisms that are only incompletely understood. Metformin scavenges free radicals, including reactive oxygen species and nitric oxide, which are produced by genotoxicants such as ionizing or non-ionizing radiation, heavy metals, and chemotherapeutic agents. The drug may also increase the activities of antioxidant enzymes and inhibit NADPH oxidase, cyclooxygenase-2, and inducible nitric oxide synthase, thereby limiting macrophage recruitment and inflammatory responses. Metformin stimulates the DNA damage response (DDR) in the homologous end-joining, homologous recombination, and nucleotide excision repair pathways. This review focuses on the protective properties of metformin against genomic instability.