Mitigative role of melatonin andα-tocopherol against mercury-induced genotoxicity

The protective role of melatonin in citalopram-induced reproductive toxicity via modulating nitro-oxidative stress and apoptosis in male mice

Citalopram is the most potent selective serotonin reuptake inhibitor, commonly prescribed as an antidepressant, which can cause sexual dysfunction. Melatonin is a natural, highly effective antioxidant playing a pivotal role in the male reproductive system. The present study aimed to explore the ameliorating potential of melatonin on citalopram-evoked testicular toxicity and injury in mice. In this regard, mice were randomly divided into six groups: control, citalopram, melatonin 10 mg/kg, melatonin 20 mg/kg, melatonin 10 mg/kg plus citalopram, and melatonin 20 mg/kg plus citalopram. Adult male mice were intraperitoneally (i.p.) injected with 10 mg/kg of citalopram for 35 days with or without melatonin. At the end of the study, sperm parameters, testosterone level, testicular levels of malondialdehyde (MDA), nitric oxide (NO), total antioxidant capacity (TAC), and apoptosis (Tunel essay) were evaluated. Our findings revealed that melatonin restored spermatogenesis by improving sperm count, motility, viability, morphology, and chromatin integrity. Testosterone levels and the histopathology of the testes were markedly improved in the melatonin-administrated groups. Furthermore, citalopram administration significantly increased oxidative stress; however, melatonin restored antioxidant status by enhancing TAC levels and decreasing NO and MAD levels. More notably, citalopram therapy induced a significant increase in the number of Tunel-positive cells, while melatonin administration significantly mitigated the apoptotic impacts of citalopram. Together, melatonin therapy provides protection against citalopram-induced testicular damage via modulating nitro-oxidative stress and apoptosis, which provides evidence for melatonin as a promising treatment against antidepressant drug-associated reproductive toxicity and male sub/infertility.

Genotoxicity of Mercury and Its Derivatives Demonstrated In Vitro and In Vivo in Human Populations Studies. Systematic Review

Beside partial coverage in three reviews so far (1994, 2009, 2019), there is no review on genotoxic studies dealing with mercury (Hg) and human exposure using the most usual genotoxic assays: sister chromatid exchanges (SCE), chromosomal aberrations (CA), cytochalasin B blocked micronucleus assay (CBMN), and single-cell gel electrophoresis (SCGE or alkaline comet assay). Fifty years from the first Hg genotoxicity study and with the Minamata Convention in force, the genotoxic potential of Hg and its derivatives is still controversial. Considering these antecedents, we present this first systematic literature overview of genotoxic studies dealing with Hg and human exposure that used the standard genotoxic assays. To date, there is not sufficient evidence for Hg human carcinogen classification, so the new data collections can be of great help. A review was made of the studies available (those published before the end of October 2021 on PubMed or Web of Science in English or Spanish language) in the scientific literature dealing with genotoxic assays and human sample exposure ex vivo, in vivo, and in vitro. Results from a total of 66 articles selected are presented. Organic (o)Hg compounds were more toxic than inorganic and/or elemental ones, without ruling out that all represent a risk. The most studied inorganic (i)Hg compounds in populations exposed accidentally, occupationally, or iatrogenically, and/or in human cells, were Hg chloride and Hg nitrate and of the organic compounds, were methylmercury, thimerosal, methylmercury chloride, phenylmercuric acetate, and methylmercury hydroxide.

Genotoxic risk in occupational exposure to petrol and its amelioration by vitamin C and vitamin E

Petrol contains mixture of mutagens and carcinogens which have potential health risk after prolonged occupational exposure. We have compared genotoxicity and its amelioration in blood samples from 70 petrol pump attendants, working in congested area of the Ahmedabad city, India and similar number (n = 70) of Control samples from office workers dwelling in less polluted areas of the city. The cytokinesis-block micronucleus assay showed highly significant frequencies of micronucleus in Exposed than in the Controls. The sister chromatid exchanges were also significantly increased while the cell cycle proliferative index was significantly decreased in the Exposed individuals than the Controls. Addition of standardized doses of vitamin C and vitamin E in the lymphocyte cultures (in vitro) significantly improved all the biomarkers. The long-term occupational petrol exposure causes genotoxic effects and use of vitamins C and E for protection should be further explored in randomized controlled studies.

In vitro genotoxicity assessment of functional ingredients: DHA, rutin and α-tocopherol

The in vitro genotoxicity of three compounds widely used as functional ingredients, docosahexaenoic acid (DHA), rutin and α-tocopherol, was assessed. A miniaturized version of the Ames test in Salmonella typhimurium TA97a, TA98, TA100, TA102, and TA1535 strains (following the principles of OECD 471), and the in vitro micronucleus test in TK6 cells (OECD 487) were performed. This strategy is recommended by the European Food Safety Authority for the in vitro genotoxicity assessment of food and feed. In addition, this approach was complemented with the in vitro standard and enzyme-modified comet assay (S9-/S9+) using hOGG1, EndoIII and hAAG in order to assess potential premutagenic lesions in TK6 cells. Rutin showed an equivocal response in the in vitro micronucleus test and also was a potent Salmonella typhimurium revertant inductor in the Ames test. DHA showed equivocal results in the in vitro micronucleus test. In this regard, DHA and rutin seemed to interact with the DNA at a chromosomal level, but rutin is also capable of producing frameshift mutations. No genotoxicity was observed in cells treated with α-tocopherol. This article complements the evidence already available about the genotoxicity of these compounds. However, more studies are needed in order to elucidate the consequences of their use as functional ingredients in human health.

Melatonin protects rats testes against bleomycin, etoposide, and cisplatin-induced toxicity via mitigating nitro-oxidative stress and apoptosis

There is growing concern that some cytotoxic regimens for cancer adversely affect spermatogenesis and male fertility. Increasing evidence demonstrated that melatonin has beneficial impacts on reproductive processes; however, whether melatonin can protect against bleomycin, etoposide, and cisplatin (BEP) chemotherapy regimen-induced testicular toxicity, remains obscure. The present study aimed to explore the effect of melatonin on BEP-evoked testicular injury in rats. Adult male Wistar rats (n = 10/group) were intraperitoneally (i.p.) injected with one cycle of 21 days of 0.33 therapeutically relevant dose levels of BEP (.5 mg/kg bleomycin, 5 mg/kg etoposide, and 1 mg/kg cisplatin) with or without melatonin. At the end of the study, sperm parameters, testosterone level, stereology of testes, testicular levels of malondialdehyde (MDA), nitric oxide (NO), and total antioxidant capacity (TAC), the expression of apoptosis-associated genes such as Bcl2, Bax, Caspase-3, p53, and TNF-α (Real-time PCR and Immunohistochemistry) were evaluated. Our findings showed that melatonin restored spermatogenesis by improving sperm count, motility, viability, and morphology. Testosterone level, histopathology, and stereology of testes were significantly improved in melatonin-administrated groups. Furthermore, melatonin recovered the oxidative status of the testes through elevating TAC and ameliorating MDA and NO levels. More importantly, melatonin therapy suppressed BEP-evoked apoptosis by modulating Bcl-2, Bax, Caspase-3, p53, and TNF-α expression in testes. In conclusion, melatonin protects the testes against BEP-induced testicular damage by attenuating nitro-oxidative stress, apoptosis, and inflammation, which provides evidence for melatonin as a possible clinical therapy against BEP-associated gonadotoxicity and male sub/infertility.

Melatonin and its metabolites as chemical agents capable of directly repairing oxidized DNA

Oxidative stress mediates chemical damage to DNA yielding a wide variety of products. In this work, the potential capability of melatonin and several of its metabolites to repair directly (chemically) oxidative lesions in DNA was explored. It was found that all the investigated molecules are capable of repairing guanine-centered radical cations by electron transfer at very high rates, that is, diffusion-limited. They are also capable of repairing C-centered radicals in the sugar moiety of 2'-deoxyguanosine (2dG) by hydrogen atom transfer. Although this was identified as a rather slow process, with rate constants ranging from 1.75 to 5.32 × 10²  M^-1 s^-1 , it is expected to be fast enough to prevent propagation of the DNA damage. Melatonin metabolites 6-hydroxymelatonin (6OHM) and 4-hydroxymelatonin (4OHM) are also predicted to repair OH adducts in the imidazole ring. In particular, the rate constants corresponding to the repair of 8-OH-G adducts were found to be in the order of 10⁴  M^-1 s^-1 and are assisted by a water molecule. The results presented here strongly suggest that the role of melatonin in preventing DNA damage might be mediated by its capability, combined with that of its metabolites, to directly repair oxidized sites in DNA through different chemical routes.

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.

The genotoxic effects of anti-cancer drug gossypol on human lymphocytes and its mitigation by melatonin

PURPOSE OF STUDY

To determine melatonin as a potential natural antioxidant to mitigate the genotoxic effects of promising anti-cancer drug gossypol in human lymphocytes.

INTRODUCTION

Gossypol, is a polyphenolic compound naturally occurring in cotton seed, was originally identified as a male contraceptive but it has several proposed clinical applications. Gossypol has anti-proliferative effects on cancer cell lines. However, its genotoxic effects on normal cells are not much studied. Hence, there is a paucity of data available. Hence, the study was conducted to investigate gossypol-induced genotoxic effects on lymphocytes.

METHODS

Peripheral blood lymphocyte cultures (PBLC) were done and exposed by two different doses of an anti-cancer drug, gossypol (0.274 mM, 1.645 mM) to check genotoxic effects. Melatonin (0.2 mM) is used as an antioxidant. Genotoxic indices such as sister chromatid exchanges (SCEs), cell cycle proliferative index (CCPI), average generation time (AGT), population doubling time (PDT) were assayed in the cultures.

RESULT

Gossypol-treated groups indicated significant increases in frequency of SCEs calculated for SCE/plate and SCE/chromosome. Furthermore, CCPI showed a remarkable reduction and increased AGT and PDT levels were found in exposed cultures. When the higher dose of gossypol cultures was treated along with melatonin, these indices were found to be declined and comparable to control.

CONCLUSION

Gossypol, an anti-cancer drug, induces genotoxicity on lymphocyte cells and co-supplementation of melatonin antioxidant ameliorates these toxic effects of gossypol.

In vitro and in vivo effects of melatonin on sister chromatid exchange in human blood lymphocytes exposed to hypoxia

OBJECTIVE

Many studies have shown that melatonin (MLT) has an anti-genotoxic effect in various tissues and cell lines. The aim of this study was to investigate the anti-genotoxic effect of MLT on normal human peripheral lymphocytes by assessing sister chromatid exchange (SCE) in vitro and in vivo.

MATERIALS AND METHODS

Cells were treated with 50 and 200 μM of MLT. The human volunteers (n = 20) for the in vivo study were administered a single dose of 3 mg MLT daily for 2 weeks. After sufficient time for its clearance, 1.5 mg of MLT daily was then administered to the same volunteers at same the period.

RESULTS

Our results demonstrated the anti-genotoxic effect of MLT in human blood lymphocyte in vitro and in vivo. In vitro, hypoxia increased the SCE frequency compared to the control and both doses of MLT significantly decreased the SCE frequency in the hypoxic cells (p < 0.001). In vivo, oral administration of 3 mg MLT significantly increased the frequency of SCE, yet a small increase of SCE by hypoxia was found. Oral administration of 1.5 mg MLT showed no DNA damage but it had an anti-genotoxic effect.

DISCUSSION AND CONCLUSION

MLT may prove useful for reducing the genotoxic effects of hypoxia in peripheral lymphocytes and suggest its possible role for ischemic diseases.

A review of metal-catalyzed molecular damage: protection by melatonin

Metal exposure is associated with several toxic effects; herein, we review the toxicity mechanisms of cadmium, mercury, arsenic, lead, aluminum, chromium, iron, copper, nickel, cobalt, vanadium, and molybdenum as these processes relate to free radical generation. Free radicals can be generated in cells due to a wide variety of exogenous and endogenous processes, causing modifications in DNA bases, enhancing lipid peroxidation, and altering calcium and sulfhydryl homeostasis. Melatonin, an ubiquitous and pleiotropic molecule, exerts efficient protection against oxidative stress and ameliorates oxidative/nitrosative damage by a variety of mechanisms. Also, melatonin has a chelating property which may contribute in reducing metal-induced toxicity as we postulate here. The aim of this review was to highlight the protective role of melatonin in counteracting metal-induced free radical generation. Understanding the physicochemical insights of melatonin related to the free radical scavenging activity and the stimulation of antioxidative enzymes is of critical importance for the development of novel therapeutic strategies against the toxic action of these metals.