Melatonin and viral infections

Melatonin's Impact on Wound Healing

Melatonin (5-methoxy-N-acetyltryptamine) is an indoleamine compound that plays a critical role in the regulation of circadian rhythms. While melatonin is primarily synthesized from the amino acid tryptophan in the pineal gland of the brain, it can also be produced locally in various tissues, such as the skin and intestines. Melatonin's effects in target tissues can be mediated through receptor-dependent mechanisms. Additionally, melatonin exerts various actions via receptor-independent pathways. In biological systems, melatonin and its endogenous metabolites often produce similar effects. While injuries are common in daily life, promoting optimal wound healing is essential for patient well-being and healthcare outcomes. Beyond regulating circadian rhythms as a neuroendocrine hormone, melatonin may enhance wound healing through (1) potent antioxidant properties, (2) anti-inflammatory actions, (3) infection control, (4) regulation of vascular reactivity and angiogenesis, (5) analgesic (pain-relieving) effects, and (6) anti-pruritic (anti-itch) effects. This review aims to provide a comprehensive overview of scientific studies that demonstrate melatonin's potential roles in supporting effective wound healing.

Progress towards understanding the effects of artificial light on the transmission of vector-borne diseases

Artificial light at night (ALAN) is a common form of light pollution worldwide, and the intensity, timing, duration, and wavelength of light exposure can affect biological rhythms, which can lead to metabolic, reproductive, and immune dysfunctions and consequently, host-pathogen interactions. Insect vector-borne diseases are a global problem that needs to be addressed, and ALAN plays an important role in disease transmission by affecting the habits and physiological functions of vector organisms. In this work, we describe the mechanisms by which ALAN affects host physiology and biochemistry, host-parasite interactions, and vector-borne viruses and propose preventive measures for related infectious diseases to minimize the effects of artificial light on vector-borne diseases.

Melatonin inhibits bovine viral diarrhea virus replication by ER stress-mediated NF-κB signal pathway and autophagy in MDBK cells

Bovine viral diarrhea-mucosal disease (BVD-MD) is a contagious disease in cattle, caused by the bovine viral diarrhea virus (BVDV). This virus continues to spread globally, exerting pressure on both public health and the economy. Despite its impact, there are currently no effective drugs for treating BVDV. This study utilized Madin-Darby bovine kidney (MDBK) cells as a model to investigate the antiviral effects of melatonin against Bovine Viral Diarrhea Virus (BVDV) and its connection with endoplasmic reticulum (ER) stress. Our results show that melatonin can suppress BVDV proliferation in MDBK cells by modulating the endoplasmic reticulum (ER) stress-mediated NF-κB pathway and autophagy. Specifically, melatonin alleviated ER stress, inhibited the activation of IκBα and p65, regulated autophagy, and reduced the expression levels of pro-inflammatory cytokines. Further, when we treated BVDV-infected cells with the ER stress inducer thapsigargin, it led to significant activation of the NF-κB pathway and autophagy. Conversely, treating the cells with the ER stress inhibitor 4-phenylbutyric acid reversed these effects. These findings suggest that melatonin exerts its antiviral effects primarily through the PERK-eIF2α-ATF4 of ER stress-mediated NF-κB pathway and autophagy. Overall, our study underscores the potential of melatonin as an effective protective and therapeutic option against BVDV, offering insights into its anti-infective mechanisms.

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

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

Exogenous Melatonin Regulates Plant-Disease Interaction by Inducing Maize Resistance and Decreasing the Pathogenicity of Fusarium graminearum

Plants cannot avoid environmental challenges and are constantly threatened by diverse biotic and abiotic stresses. However, plants have developed a unique immune system to defend themselves against the invasion of various pathogens. Melatonin, N-acetyl-5-methoxytryptamine has positive physiological effects in plants that are involved in disease resistance. The processes underlying melatonin-induced pathogen resistance in plants are still unknown. The current study explores how melatonin regulates the plant-disease interaction in maize. The results showed that 400 μM melatonin strongly reduced the disease lesion on maize stalks by 1.5 cm and corn by 4.0 cm caused by Fusarium graminearum PH-1. Furthermore, after treatment with melatonin, the plant defense enzymes like SOD significantly increased, while POD and APX significantly decreased compared to the control. In addition, melatonin can also improve maize's innate immunity, which is mediated by melatonin treatments through the salicylic acid signaling pathway, and up-regulate the defense-associated expression of PR1, LOX1, OXR, serPIN, and WIPI genes in maize. Melatonin not only inhibits the disease in the maize stalks and corn, but also down-regulates the deoxynivalenol (DON) production-related expression of genes Tri1, Tri4, Tri5, and Tri6 in maize. Overall, this study sheds new light on the mechanisms by which melatonin regulates antioxidant enzymes and defense-related genes involved in plant immunity to effectively suppress plant diseases.

Melatonin: A promising candidate for maintaining food security under the threat of phytopathogens

Plant immune response is tightly controlled by an interplay of various phytohormones and plant growth regulators. Among them, the role of salicylic acid, jasmonic acid, and ethylene is well established while some others such as nitric oxide, polyamines, and hydrogen sulfide have appeared to be key regulators of plant immunity. In addition, some other chemicals, such as melatonin (N-acetyl-5-methoxytryptamine), are apparently turning out to be the novel regulators of plant defense responses. Melatonin has shown promising results in enhancing resistance of plants to a variety of pathogens including fungi, bacteria, and viruses, however, the molecular mechanism of melatonin-mediated plant immune regulation is currently elusive. Evidence gathered so far indicates that melatonin regulates plant immunity by (1) facilitating the maintenance of ROS homeostasis, (2) interacting with other phytohormones and growth regulators, and (3) inducing the accumulation of defense molecules. Therefore, engineering crops with improved melatonin production could enhance crop productivity under stress conditions. This review extends our understanding of the multifaceted role of melatonin in the regulation of plant defense response and presents a putative pathway of melatonin functioning and its interaction with phytohormones during biotic stress.

Effects of Melatonin Alone or Associated with Acyclovir on the Suppressive Treatment of Recurrent Genital Herpes: A Prospective, Randomized, and Double-Blind Study

Suppressive therapy of recurrent genital herpes is a challenge, and melatonin may be an alternative. Objective: To evaluate the action of melatonin, acyclovir, or the association of melatonin with acyclovir as a suppressive treatment in women with recurrent genital herpes. Design: The study was prospective, double-blind, and randomized, including 56 patients as follows: (a) The melatonin group received 180 placebo capsules in the ‘day’ container and 180 melatonin 3 mg capsules in the ‘night’ container (n = 19); (b) The acyclovir group received 360 capsules of 400 mg acyclovir twice a day (one capsule during the day and another during the night) (n = 15); (c) the melatonin group received 180 placebo capsules in the ‘day’ container and 180 melatonin 3 mg capsules in the ‘night’ container (n = 22). The length of treatment was six months. The follow-up after treatment was six months. Patients were evaluated before, during, and after treatment through clinical visits, laboratory tests, and the application of four questionnaires (QSF-36, Beck, Epworth, VAS, and LANNS). Results: No statistically significant difference was observed for the depression and sleepiness questionnaires. However, in the Lanns scale for pain, all groups decreased the mean and median values in time (p = 0.001), without differentiation among the groups (p = 0.188). The recurrence rates of genital herpes within 60 days after treatment were 15.8%, 33.3%, and 36.4% in the melatonin, acyclovir, and association of melatonin with acyclovir groups, respectively. Conclusion: Our data suggest that melatonin may be an option for the suppressive treatment of recurrent genital herpes.

Melatonin Treatment in Kidney Diseases

Melatonin is a neurohormone that is mainly secreted by the pineal gland. It coordinates the work of the superior biological clock and consequently affects many processes in the human body. Disorders of the waking and sleeping period result in nervous system imbalance and generate metabolic and endocrine derangements. The purpose of this review is to provide information regarding the potential benefits of melatonin use, particularly in kidney diseases. The impact on the cardiovascular system, diabetes, and homeostasis causes melatonin to be indirectly connected to kidney function and quality of life in people with chronic kidney disease. Moreover, there are numerous reports showing that melatonin plays a role as an antioxidant, free radical scavenger, and cytoprotective agent. This means that the supplementation of melatonin can be helpful in almost every type of kidney injury because inflammation, apoptosis, and oxidative stress occur, regardless of the mechanism. The administration of melatonin has a renoprotective effect and inhibits the progression of complications connected to renal failure. It is very important that exogenous melatonin supplementation is well tolerated and that the number of side effects caused by this type of treatment is low.

Melatonin as a Possible Natural Anti-Viral Compound in Plant Biocontrol

Melatonin is a multifunctional and ubiquitous molecule. In animals, melatonin is a hormone that is involved in a wide range of physiological activities and is also an excellent antioxidant. In plants, it has been considered a master regulator of multiple physiological processes as well as of hormonal homeostasis. Likewise, it is known for its role as a protective biomolecule and activator of tolerance and resistance against biotic and abiotic stress in plants. Since infections by pathogens such as bacteria, fungi and viruses in crops result in large economic losses, interest has been aroused in determining whether melatonin plays a relevant role in plant defense systems against pathogens in general, and against viruses in particular. Currently, several strategies have been applied to combat infection by pathogens, one of them is the use of eco-friendly chemical compounds that induce systemic resistance. Few studies have addressed the use of melatonin as a biocontrol agent for plant diseases caused by viruses. Exogenous melatonin treatments have been used to reduce the incidence of several virus diseases, reducing symptoms, virus titer, and even eradicating the proliferation of viruses such as Tobacco Mosaic Virus, Apple Stem Grooving Virus, Rice Stripe Virus and Alfalfa Mosaic Virus in tomato, apple, rice and eggplant, respectively. The possibilities of using melatonin as a possible natural virus biocontrol agent are discussed.

Melatonin from Microorganisms, Algae, and Plants as Possible Alternatives to Synthetic Melatonin

Melatonin dietary supplements are widely consumed worldwide, with developed countries as the largest consumers, with an estimated annual growth rate of approximately 10% until 2027, mainly in developing countries. The wide use of melatonin against sleep disorders and particular problems, such as jet lag, has been added to other applications, such as anti-aging, anti-stress, immune system activation, anticancer, and others, which have triggered its use, normally without a prescription. The chemical industry currently covers 100% of the needs of the melatonin market. Motivated by sectors with more natural consumption habits, a few years ago, the possibility of obtaining melatonin from plants, called phytomelatonin, arose. More recently, the pharmaceutical industry has developed genetically modified microorganisms whose ability to produce biological melatonin in bioreactors has been enhanced. This paper reviews the aspects of the chemical and biological synthesis of melatonin for human consumption, mainly as dietary supplements. The pros and cons of obtaining melatonin from microorganisms and phytomelatonin from plants and algae are analyzed, as well as the advantages of natural melatonin, avoiding unwanted chemical by-products from the chemical synthesis of melatonin. Finally, the economic and quality aspects of these new products, some of which are already marketed, are analyzed.

Can melatonin reduce the severity of post-COVID-19 syndrome?

This short review aimed at (i) providing an update on the health benefits associated with melatonin supplementation, while (ii) considering future potential research directions concerning melatonin supplementation use relative to Coronavirus disease of 2019 (COVID-19). A narrative review of the literature was undertaken to ascertain the effect of exogenous melatonin administration on humans. Night-time melatonin administration has a positive impact on human physiology and mental health. Indeed, melatonin (i) modulates the circadian components of the sleep-wake cycle; (ii) improves sleep efficiency and mood status; (iii) improves insulin sensitivity; and (iv) reduces inflammatory markers and oxidative stress. Melatonin has also remarkable neuroprotective and cardioprotective effects and may therefore prevent deterioration caused by COVID-19. We suggest that melatonin could be used as a potential therapy in the post-COVID-19 syndrome, and therefore call for action the research community to investigate on the potential use of exogenous melatonin to enhance the quality of life in patients with post-COVID-19 syndrome. See also Figure 1(Fig. 1).

Efficacy and safety of oral melatonin in patients with severe COVID-19: a randomized controlled trial

Patients with COVID-19 have shown melatonin deficiency. We evaluated the efficacy and safety of administration oral melatonin in patients with COVID-19-induced pneumonia. Patients were randomly assigned in a 1:1 ratio to receive melatonin plus standard treatment or standard treatment alone. The primary outcomes were mortality rate and requirement of IMV. The clinical status of patients was recorded at baseline and every day over hospitalization based on seven-category ordinal scale from 1 (discharged) to 7 (death). A total of 226 patients (109 in the melatonin group and 117 in the control group) were enrolled (median age; in melatonin group: 54.60 ± 11.51, in control group: 54.69 ± 13.40). The mortality rate was 67% in the melatonin group and 94% in the control group (OR; 7.75, 95% CI, 3.27-18.35, P < 0.001). The rate of IMV requirement was 51.4% in the melatonin group and 70.9% in the control group, for an OR of 2.31 (95% CI, 1.34-4.00, P < 0.001). The median number of days to hospital discharge was 15 days (13-17) in the melatonin group and 21 days (14-24) in the control group (OR; 5.00, 95% CI, 0.15-9.84, P = 0.026). Time to clinical status improvement by ≥ 2 on the ordinal scale in was 12 days (9-13) in the melatonin group and 16 days (10-19) in the control group (OR; 3.92, 95% CI, 1.69-6.14, P = 0.038). Melatonin significantly improved clinical status with a safe profile in patients with severe COVID-19 pneumonia.

Potential Therapeutic Approach of Melatonin against Omicron and Some Other Variants of SARS-CoV-2

The Omicron variant (B.529) of COVID-19 caused disease outbreaks worldwide because of its contagious and diverse mutations. To reduce these outbreaks, therapeutic drugs and adjuvant vaccines have been applied for the treatment of the disease. However, these drugs have not shown high efficacy in reducing COVID-19 severity, and even antiviral drugs have not shown to be effective. Researchers thus continue to search for an effective adjuvant therapy with a combination of drugs or vaccines to treat COVID-19 disease. We were motivated to consider melatonin as a defensive agent against SARS-CoV-2 because of its various unique properties. Over 200 scientific publications have shown the significant effects of melatonin in treating diseases, with strong antioxidant, anti-inflammatory, and immunomodulatory effects. Melatonin has a high safety profile, but it needs further clinical trials and experiments for use as a therapeutic agent against the Omicron variant of COVID-19. It might immediately be able to prevent the development of severe symptoms caused by the coronavirus and can reduce the severity of the infection by improving immunity.

CD147-spike protein interaction in COVID-19: Get the ball rolling with a novel receptor and therapeutic target

The combat against the Corona virus disease of 2019 (COVID-19), has created a chaos among the healthcare institutions and researchers, in turn accelerating the dire need to curtail the infection spread. The already established entry mechanism, via ACE2 has not yet successfully aided in the development of a suitable and reliable therapy. Taking in account the constant progression and deterioration of the cases worldwide, a different perspective and mechanistic approach is required, which has thrown light onto the cluster of differentiation 147 (CD147) transmembrane protein, as a novel route for SARS-CoV-2 entry. Despite lesser affinity towards COVID-19 virus, as compared to ACE2, this receptor provides a suitable justification behind elevated blood glucose levels in infected patients, retarded COVID-19 risk in women, enhanced susceptibility in geriatrics, greater infection susceptibility of T cells, infection prevalence in non-susceptible human cardiac pericytes and so on. The manuscript invokes the title role and distribution of CD147 in COVID-19 as an entry receptor and mediator of endocytosis-promoted entry of the virus, along with the "catch and clump" hypothesis, thereby presenting its Fundamental significance as a therapeutic target for potential candidates, such as Azithromycin, melatonin, statins, beta adrenergic blockers, ivermectin, Meplazumab etc. Thus, the authors provide a comprehensive review of a different perspective in COVID-19 infection, aiming to aid the researchers and virologists in considering all aspects of viral entry, in order to develop a sustainable and potential cure for the 2019 COVID-19 disease.

5-Methoxyindole, a Chemical Homolog of Melatonin, Adversely Affects the Phytopathogenic Fungus Fusarium graminearum

Fusarium graminearum is a destructive fungal pathogen that threatens the production and quality of wheat, and controlling this pathogen is a significant challenge. As the cost-effective homolog of melatonin, 5-methoxyindole showed strong activity against F. graminearum. In the present study, our results showed the strong adverse activity of 5-methoxyindole against F. graminearum by inhibiting its growth, formation, and conidia germination. In addition, 5-methoxyindole could induce malformation, reactive oxygen species (ROS) accumulation, and cell death in F. graminearum hyphae and conidia. In response to 5-methoxyindole, F. graminearum genes involved in scavenging reactive oxygen species were significantly downregulated. Overall, these findings reveal the mechanism of antifungal action of melatonin-homolog 5-methoxyindole. To the best of our knowledge, this is the first report that a novel melatonin homolog confers strong antifungal activity against F. graminearum, and 5-methoxyindole is a potential compound for protecting wheat plants from F. graminearum infection.

The Coronavirus Disease 2019 (COVID-19): Key Emphasis on Melatonin Safety and Therapeutic Efficacy

Viral infections constitute a tectonic convulsion in the normophysiology of the hosts. The current coronavirus disease 2019 (COVID-19) pandemic is not an exception, and therefore the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, like any other invading microbe, enacts a generalized immune response once the virus contacts the body. Melatonin is a systemic dealer that does not overlook any homeostasis disturbance, which consequently brings into play its cooperative triad, antioxidant, anti-inflammatory, and immune-stimulant backbone, to stop the infective cycle of SARS-CoV-2 or any other endogenous or exogenous threat. In COVID-19, the corporal propagation of SARS-CoV-2 involves an exacerbated oxidative activity and therefore the overproduction of great amounts of reactive oxygen and nitrogen species (RONS). The endorsement of melatonin as a possible protective agent against the current pandemic is indirectly supported by its widely demonstrated beneficial role in preclinical and clinical studies of other respiratory diseases. In addition, focusing the therapeutic action on strengthening the host protection responses in critical phases of the infective cycle makes it likely that multi-tasking melatonin will provide multi-protection, maintaining its efficacy against the virus variants that are already emerging and will emerge as long as SARS-CoV-2 continues to circulate among us.

Molecular Characterization of the Alfalfa mosaic virus Infecting Solanum melongena in Egypt and the Control of Its Deleterious Effects with Melatonin and Salicylic Acid

During the spring of 2019, distinct virus-like symptoms were observed in the Kafr El-Sheikh Governorate in Egypt in naturally infected eggplants. Leaves of affected plants showed interveinal leaf chlorosis, net yellow, chlorotic sectors, mottling, blisters, vein enation, necrotic intervention, and narrowing symptoms. The Alfalfa mosaic virus (AMV) was suspected of to be involved in this disease. Forty plant samples from symptomatic eggplants and 10 leaf samples with no symptoms were collected. The samples were tested by double antibody sandwich ELISA (DAS-ELISA) using AMV-IgG. Six of the 40 symptomatic leaf samples tested positive for AMV, while, DAS-ELISA found no AMV in the 10 leaf samples without symptoms. The AMV Egyptian isolate (AMV-Eggplant-EG) was biologically isolated from the six positive samples tested by DAS-ELISA and from the similar local lesions induced on Chenopodium amaranticolor and then re-inoculated in healthy Solanum melongena as a source of AMV-Eggplant-EG and confirmed by DAS-ELISA. Reverse transcription polymerase chain reaction (RT-PCR) assay with a pair of primers specific for coat protein (CP) encoding RNA 3 of AMV yielded an amplicon of 666 bp from infected plants of Solanum melongena with AMV-Eggplant-EG. The amplified PCR product was cloned and sequenced. Analysis of the AMV-Eggplant-EG sequence revealed 666 nucleotides (nt) of the complete CP gene (translating 221 amino acid (aa) residues). Analysis of phylogeny for nt and deduced aa sequences of the CP gene using the maximum parsimony method clustered AMV-Eggplant-EG in the lineage of Egyptian isolates (shark-EG, mans-EG, CP2-EG, and FRE-EG) with a high bootstrap value of 88% and 92%, respectively. In addition to molecular studies, melatonin (MTL) and salicylic acid (SA) (100 μM) were used to increase the resistance of eggplant to AMV- infection. Foliar spray with MLT and SA caused a significant increase in the morphological criteria (shoot, root length, number of leaves, leaf area, and leaf biomass), chlorophyll and carotenoid content, antioxidant enzymes, and gene expression of some enzymes compared to the infected plants. On the other hand, treatment with MLT and SA reduced the oxidative damage caused by AMV through the reduction of hydrogen peroxide, superoxide anions, hydroxyl radicals, and malondialdehyde. In conclusion, MLT and SA are eco-friendly compounds and can be used as antiviral compounds.

Role of Melatonin on Virus-Induced Neuropathogenesis-A Concomitant Therapeutic Strategy to Understand SARS-CoV-2 Infection

Viral infections may cause neurological disorders by directly inducing oxidative stress and interrupting immune system function, both of which contribute to neuronal death. Several reports have described the neurological manifestations in Covid-19 patients where, in severe cases of the infection, brain inflammation and encephalitis are common. Recently, extensive research-based studies have revealed and acknowledged the clinical and preventive roles of melatonin in some viral diseases. Melatonin has been shown to have antiviral properties against several viral infections which are accompanied by neurological symptoms. The beneficial properties of melatonin relate to its properties as a potent antioxidant, anti-inflammatory, and immunoregulatory molecule and its neuroprotective effects. In this review, what is known about the therapeutic role of melatonin in virus-induced neuropathogenesis is summarized and discussed.

Melatonin and Its Homologs Induce Immune Responses via Receptors trP47363-trP13076 in Nicotiana benthamiana

Melatonin (N-acetyl-5-methoxytryptamine), a naturally occurring small molecule, can protect plants against abiotic stress after exogenous treatmenting with it. It is not known if melatonin homologs, such as 5-methoxytryptamine and 5-methoxyindole, that are easy and more cost-effective to synthesize can stimulate the plant immune system in the same manner as melatonin. In the present study, we assessed the biological activity of the melatonin homologs, 5-methoxytryptamin and 5-methoxyindole. The results showed that melatonin and its homologs all induced disease resistance against Phytophthora nicotianae in Nicotiana benthamiana plants. The application of all three compounds also induced stomatal closure and the production of reactive oxygen species. Gene expression analysis indicated that the expression of genes involved in hydrogen peroxide (H₂O₂), nitric oxide (NO) production, and salicylic acid (SA) biosynthesis was significantly upregulated by all three compounds. Four homologs of the melatonin receptors were identified by blasting search with the phytomelatonin receptor in Arabidopsis. Molecular docking studies were also used to identify four putative melatonin receptors in N. benthamiana. Further experimentation revealed that silencing of the melatonin receptors trP47363 and trP13076 in N. benthamiana compromised the induction of stomatal closure, PR-1a gene expression and SA accumulation by all three compounds. Collectively, our data indicate that the induction of defense responses in N. benthamiana by melatonin, 5-methoxytryptamine, and 5-methoxyindole involves the melatonin receptors trP47363 and trP13076.

Endogenous Antioxidant Cocktail Loaded Hydrogel for Topical Wound Healing of Burns

The main goal of this work is the study of the skin wound healing efficacy of an antioxidant cocktail consisting of vitamins A, D, E and the endogenous pineal hormone melatonin (MLT), with all of these loaded into a thermosensitive hydrogel delivery system. The resulting formulation was characterized by scanning electron microscopy. The antioxidant efficacy and microbiological activity against Gram positive and Gram negative strains were also assayed. The skin healing efficacy was tested using an in vivo model which included histological evaluation. Furthermore, atomic force microscopy was employed to evaluate the wound healing efficacy of rat skin burns through the determination of its elasticity at the nanoscale using force spectroscopy analysis. The resulting hydrogel exhibited sol state at low temperature and turned into a gel at 30 ± 0.2 °C. The hydrogel containing the antioxidant cocktail showed higher scavenging activity than the hydrogel containing vitamins or MLT, separately. The formulation showed optimal antimicrobial activity. It was comparable to a commercial reference. It was also evidenced that the hydrogel containing the antioxidant cocktail exhibited the strongest healing process in the skin burns of rats, similar to the assayed commercial reference containing silver sulfadiazine. Histological studies confirmed the observed results. Finally, atomic force microscopy demonstrated a similar distribution of Young's modulus values between burned skin treated with the commercial reference and burned skin treated with hydrogel containing the antioxidant cocktail, and all these with healthy skin. The use of an antioxidant cocktail of vitamins and MLT might be a promising treatment for skin wounds for future clinical studies.

Role of melatonin in the treatment of COVID-19; as an adjuvant through cluster differentiation 147 (CD147)

COVID-19 caused by the SARS-CoV-2 outbreak quickly has turned into a pandemic. However, no specific antiviral agent is yet available. In this communication, we aimed to evaluate the significance of CD147 protein and the potential protective effect of melatonin that is mediated by this protein in COVID-19. CD147 is a glycoprotein that is responsible for the cytokine storm in the lungs through the mediation of viral invasion. Melatonin use previously was shown to reduce cardiac damage by blocking the CD147 activity. Hence, melatonin, a safe drug, may prevent severe symptoms, reduce symptom severity and the adverse effects of the other antiviral drugs in COVID-19 patients. In conclusion, the use of melatonin, which is reduced in the elderly and immune-compromised patients, should be considered as an adjuvant through its CD147 suppressor and immunomodulatory effect.

The Role of Adaptogens in Prophylaxis and Treatment of Viral Respiratory Infections

The aim of our review is to demonstrate the potential of herbal preparations, specifically adaptogens for prevention and treatment of respiratory infections, as well as convalescence, specifically through supporting a challenged immune system, increasing resistance to viral infection, inhibiting severe inflammatory progression, and driving effective recovery. The evidence from pre-clinical and clinical studies with Andrographis paniculata, Eleutherococcus senticosus, Glycyrrhiza spp., Panax spp., Rhodiola rosea, Schisandra chinensis, Withania somnifera, their combination products and melatonin suggests that adaptogens can be useful in prophylaxis and treatment of viral infections at all stages of progression of inflammation as well as in aiding recovery of the organism by (i) modulating innate and adaptive immunity, (ii) anti-inflammatory activity, (iii) detoxification and repair of oxidative stress-induced damage in compromised cells, (iv) direct antiviral effects of inhibiting viral docking or replication, and (v) improving quality of life during convalescence.

Meditation and Yoga Practices as Potential Adjunctive Treatment of SARS-CoV-2 Infection and COVID-19: A Brief Overview of Key Subjects

Editor's Note: As an acute condition quickly associated with multiple chronic susceptibilities, COVID-19 has rekindled interest in, and controversy about, the potential role of the host in disease processes. While hundreds of millions of research dollars have been funneled into drug and vaccine solutions that target the external agent, integrative practitioners tuned to enhancing immunity faced a familiar mostly unfunded task. First, go to school on the virus. Then draw from the global array of natural therapies and practices with host-enhancing or anti-viral capabilities to suggest integrative treatment strategies. The near null-set of conventional treatment options propels this investigation. In this paper, researchers from the Massachusetts Institute of Technology, University of California-San Diego, Chopra Library for Integrative Studies, and Harvard University share one such exploration. Their conclusion, that "certain meditation, yoga asana (postures), and pranayama (breathing) practices may possibly be effective adjunctive means of treating and/or preventing SARS-CoV-2 infection" underscores the importance of this rekindling. At JACM, we are pleased to have the opportunity to publish this work. We hope that it might help diminish in medicine and health the polarization that, like so much in the broader culture, seems to be an obstacle to healing. -John Weeks, Editor-in-Chief, JACM.

Melatonin is responsible for rice resistance to rice stripe virus infection through a nitric oxide-dependent pathway

Rice stripe virus (RSV) causes one of the most important rice virus diseases of plants in East Asia. However, the molecular mechanisms controlling rice resistance to RSV infection are largely unknown. Recently, several studies presented a novel model that melatonin (MT) and nitric oxide (NO) participate in the plant-pathogen interaction in a synergetic manner. In this study, there was a difference in MT content between two rice varieties that correlated with one being susceptible and one being resistant to RSV, which suggested that MT is related to RSV resistance. In addition, a test with two NO biosynthesis inhibitors revealed that NO inhibitor were able to increase the disease incidence of RSV. A pharmacological experiment with exogenous MT and NO showed that increased MT and NO in the MT-pretreated plants led to lower disease incidences; however, only NO increased in a NO-releasing reagent [sodium nitroprusside (SNP)] pretreated plants. The expressions level of OsPR1b and OsWRKY 45 were significantly induced by MT and NO. These results suggest that rice resistance to RSV can be improved by increased MT through a NO-dependent pathway.

Dim light at night: physiological effects and ecological consequences for infectious disease

Light pollution has emerged as a pervasive component of land development over the past century. Several detrimental impacts of this anthropogenic influence have been identified in night shift workers, laboratory rodents, and a plethora of wildlife species. Circadian, or daily, patterns are interrupted by the presence of light at night and have the capacity to alter rhythmic physiological or behavioral characteristics. Indeed, biorhythm disruption can lead to metabolic, reproductive, and immunological dysfunction depending on the intensity, timing, duration, and wavelength of light exposure. Light pollution, in many forms and by many pathways, is thus apt to affect the nature of host-pathogen interactions. However, no research has yet investigated this possibility. The goal of this manuscript is to outline how dim light at night, a relevant and common form of light pollution, may affect disease dynamics by interrupting circadian rhythms and regulation of immune responses as well as opportunities for host-parasite interactions and subsequent transmission risk including spillover into humans. We close by proposing some promising interventions including alternative lighting methods or vector control efforts.

Intrafollicular melatonin concentration is elevated in patients with ovarian hyperstimulation syndrome (OHSS) and can serve as an important predictor of OHSS

PURPOSE

Melatonin is an important factor in regulating numerous processes in human female reproduction. The aim of the present study was to compare melatonin levels in the follicular fluid (FF) of ovarian hyperstimulation syndrome (OHSS) women with those of non-OHSS women undergoing in vitro fertilization (IVF)-embryo transfer and to evaluate the relationship between FF melatonin levels and IVF outcomes in these women.

METHODS

We determined FF melatonin levels in 20 OHSS women and 23 non-OHSS women on oocyte retrieval day.

RESULTS

OHSS patients had significantly higher melatonin levels as compared to the non-OHSS women (P < 0.001). In addition, melatonin levels of the patients were significantly positively correlated with antral follicle count (AFC), serum anti-Müllerian hormone (AMH) levels, serum estradiol (E₂) levels on human chorionic gonadotropin (HCG) administration day, number of retrieved oocytes, total fertilized oocytes, normally fertilized oocytes, cleaved zygotes, top quality embryos on day 3, blastocysts obtained and embryos suitable for transplantation (day 3 embryos + day 5/6 blastocysts) (P < 0.05). While, the intrafollicular melatonin levels were significantly negatively correlated with age, basal serum follicle-stimulating hormone (FSH) levels, serum FSH levels on HCG administration day (P < 0.01). Since younger women with more AFC, higher AMH levels, higher serum E₂ levels and larger number of retrieved oocytes are much easier to encounter OHSS, while FF melatonin levels are significantly correlated with these five indices in our study, we propose that intrafollicular melatonin concentration can also be an important predictor of OHSS.

CONCLUSIONS

This is the first demonstration that FF melatonin levels were significantly higher in OHSS patients than in non-OHSS group and FF melatonin levels may serve as an important predictor of OHSS.

Melatonin and its relationship to plant hormones

BACKGROUND

Plant melatonin appears to be a multi-regulatory molecule, similar to those observed in animals, with many specific functions in plant physiology. In recent years, the number of studies on melatonin in plants has increased significantly. One of the most studied actions of melatonin in plants is its effect on biotic and abiotic stress, such as that produced by drought, extreme temperatures, salinity, chemical pollution and UV radiation, among others.

SCOPE

This review looks at studies in which some aspects of the relationship between melatonin and the plant hormones auxin, cytokinin, gibberellins, abscisic acid, ethylene, jasmonic acid and salicylic acid are presented. The effects that some melatonin treatments have on endogenous plant hormone levels, their related genes (biosynthesis, catabolism, receptors and transcription factors) and the physiological actions induced by melatonin, mainly in stress conditions, are discussed.

CONCLUSIONS

Melatonin is an important modulator of gene expression related to plant hormones, e.g. in auxin carrier proteins, as well as in metabolism of indole-3-acetic acid (IAA), gibberellins, cytokinins, abscisic acid and ethylene. Most of the studies performed have dealt with the auxin-like activity of melatonin which, in a similar way to IAA, is able to induce growth in shoots and roots and stimulate root generation, giving rise to new lateral and adventitious roots. Melatonin is also able to delay senescence, protecting photosynthetic systems and related sub-cellular structures and processes. Also, its role in fruit ripening and post-harvest processes as a gene regulator of ethylene-related factors is relevant. Another decisive aspect is its role in the pathogen-plant interaction. Melatonin appears to act as a key molecule in the plant immune response, together with other well-known molecules such as nitric oxide and hormones, such as jasmonic acid and salicylic acid. In this sense, the discovery of elevated levels of melatonin in endophytic organisms associated with plants has thrown light on a possible novel form of communication between beneficial endophytes and host plants via melatonin.

Melatonin: A Review of Its Potential Functions and Effects on Dental Diseases

Melatonin is a hormone synthesised and secreted by the pineal gland and other organs. Its secretion, controlled by an endogenous circadian cycle, has been proven to exert immunological, anti-oxidant, and anti-inflammatory effects that can be beneficial in the treatment of certain dental diseases. This article is aimed at carrying out a review of the literature published about the use of melatonin in the dental field and summarising its potential effects. In this review article, an extensive search in different databases of scientific journals was performed with the objective of summarising all of the information published on melatonin use in dental diseases, focussing on periodontal diseases and dental implantology. Melatonin released in a natural way into the saliva, or added as an external treatment, may have important implications for dental disorders, such as periodontal disease, as well as in the osseointegration of dental implants, due to its anti-inflammatory and osseoconductive effects. Melatonin has demonstrated to have beneficial effects on dental pathologies, although further research is needed to understand the exact mechanisms of this molecule.

Melatonin, minocycline and ascorbic acid reduce oxidative stress and viral titers and increase survival rate in experimental Venezuelan equine encephalitis

Venezuelan equine encephalitis (VEE) virus causes an acute central nervous system infection in human and animals. Melatonin (MLT), minocycline (MIN) and ascorbic acid (AA) have been shown to have antiviral activities in experimental infections; however, the mechanisms involved are poorly studied. Therefore, the aim of this study was to determine the effects of those compounds on the viral titers, NO production and lipid peroxidation in the brain of mice and neuroblastoma cultures infected by VEE virus. Infected mouse (10 LD50) were treated with MLT (500 μg/kg bw), MIN (50mg/kg bw) or AA (50mg/kg bw). Infected neuroblastoma cultures (MOI: 1); MLT: 0.5, 1, 5mM, MIN: 0.1, 0.2, 2 μM or AA: 25, 50, 75 μM. Brains were obtained at days 1, 3 and 5. In addition, survival rate of infected treated mice was also analyzed. Viral replication was determined by the plaque formation technique. NO and lipid peroxidation were measured by Griess׳ reaction and thiobarbituric acid assay respectively. Increased viral replication, NO production and lipid peroxidation were observed in both, infected brain and neuroblastoma cell cultures compared with uninfected controls. Those effects were diminished by the studied treatments. In addition, increased survival rate (50%) in treated infected animals compared with untreated infected mice (0%) was found. MLT, MIN and AA have an antiviral effect involving their anti-oxidant properties, and suggesting a potential use of these compounds for human VEE virus infection.

Effects of melatonin on oxidative stress, and resistance to bacterial, parasitic, and viral infections: a review

Melatonin, a hormone secreted by the pineal gland, works directly and indirectly as a free radical scavenger. Its other physiological or pharmacological activities could be dependent or independent of receptors located in different cells, organs, and tissues. In addition to its role in promoting sleep and circadian rhythms regulation, it has important immunomodulatory, antioxidant, and neuroprotective effects suggesting that this indole must be considered as a therapeutic alternative against infections. The aim of this review is to describe the effects of melatonin on oxidative stress and the resistance to bacterial (Klebsiella pneumoniae, Helicobacter pylori, Mycobacterium tuberculosis, and Clostridium perfringens), viral (Venezuelan equine encephalomyelitis virus and respiratory syncytial virus), and parasitic (Plasmodium spp., Entamoeba histolytica, Trypanosoma cruzi, Toxoplasma gondii, and Opisthorchis viverrini) infections.

Is melatonin ready to be used in preterm infants as a neuroprotectant?

The prevention of neurological disabilities following preterm birth remains a major public health challenge and efforts are still needed to test the neuroprotective properties of candidate molecules. Melatonin serves as a neuroprotectant in adult models of cerebral ischemia through its potent antioxidant and anti-inflammatory effects. An increasing number of preclinical studies have consistently demonstrated that melatonin protects the damaged developing brain by preventing abnormal myelination and an inflammatory glial reaction, a major cause of white matter injury. The main questions asked in this review are whether preclinical data on the neuroprotective properties of melatonin are sufficient to translate this concept into the clinical setting, and whether melatonin can reduce white matter damage in preterm infants. This review provides support for our view that melatonin is now ready to be tested in human preterm neonates, and discusses ongoing and planned clinical trials.

Activity of melatonin against Leishmania infantum promastigotes by mitochondrial dependent pathway

Visceral leishmaniasis, a potentially fatal disease, remains a major international health problem. Only a limited number of effective antileishmanial agents are available for chemotherapy, and many of them are expensive with severe side effects or have a markedly reduced effectiveness due to the development of drug resistance. Hence, there is a genuine need to develop a novel effective and less toxic antileishmanial drug. Melatonin, a neurohormone found in animals, plants, and microbes, can participate in various biological and physiological functions. Several in vitro or in vivo studies have reported the inhibitory effect of melatonin against many parasites via various mechanisms, including modulation of intracellular concentrations of calcium in the parasite and/or any other suggested mechanism. Importantly, many of available antileishmanial drugs have been reported to exert their effects by disrupting calcium homeostasis in the parasite. The objective of the present study was to test the efficacy of exogenous melatonin against Leishmania infantum promastigotes in vitro. Interestingly, melatonin not only demonstrated a significant antileishmanial activity of against promastigote viability in tested cultures but was also accompanied by an alteration of the calcium homeostasis of parasite mitochondrion, represented by earlier mitochondrial permeability transition pore opening, and by changes in some mitochondrial parameters are critical to parasite survival. These pioneering findings suggest that melatonin may be a candidate for the development of novel effective antileishmanial agents either alone or in associations with other drugs.

Melatonin improves the quality of in vitro produced (IVP) bovine embryos: implications for blastocyst development, cryotolerance, and modifications of relevant gene expression

To evaluate the potential effects of melatonin on the kinetics of embryo development and quality of blastocyst during the process of in vitro bovine embryo culture. Bovine cumulus–oocyte complexes (COCs) were fertilized after in vitro maturation. The presumed zygotes were cultured in in vitro culture medium supplemented with or without 10⁻⁷ M melatonin. The cleavage rate, 8-cell rate and blastocyst rate were examined to identify the kinetics of embryo development. The hatched blastocyst rate, mortality rate after thawing and the relevant transcript abundance were measured to evaluate the quality of blastocyst. The results showed that melatonin significantly promoted the cleavage rate and 8-cell embryo yield of in vitro produced bovine embryo. In addition, significantly more blastocysts were observed by Day 7 of embryo culture at the presence of melatonin. These results indicated that melatonin accelerated the development of in vitro produced bovine embryos. Following vitrification at Day 7 of embryo culture, melatonin (10⁻⁷ M) significantly increased the hatched blastocyst rate from 24 h to 72 h and decreased the mortality rate from 48 h to 72 h after thawing. The presence of melatonin during the embryo culture resulted in a significant increase in the gene expressions of DNMT3A, OCC, CDH1 and decrease in that of AQP3 after thawing. In conclusion, melatonin not only promoted blastocyst yield and accelerated in vitro bovine embryo development, but also improved the quality of blastocysts which was indexed by an elevated cryotolerance and the up-regulated expressions of developmentally important genes.

The role of melatonin in the cells of the innate immunity: a review

Melatonin is the major secretory product synthesized and secreted by the pineal gland and shows both a wide distribution within phylogenetically distant organisms from bacteria to humans and a great functional versatility. In recent years, a considerable amount of experimental evidence has accumulated showing a relationship between the nervous, endocrine, and immune systems. The molecular basis of the communication between these systems is the use of a common chemical language. In this framework, currently melatonin is considered one of the members of the neuroendocrine-immunological network. A number of in vivo and in vitro studies have documented that melatonin plays a fundamental role in neuroimmunomodulation. Based on the information published, it is clear that the majority of the present data in the literature relate to lymphocytes; thus, they have been rather thoroughly investigated, and several reviews have been published related to the mechanisms of action and the effects of melatonin on lymphocytes. However, few studies concerning the effects of melatonin on cells belonging to the innate immunity have been reported. Innate immunity provides the early line of defense against microbes and consists of both cellular and biochemical mechanisms. In this review, we have focused on the role of melatonin in the innate immunity. More specifically, we summarize the effects and action mechanisms of melatonin in the different cells that belong to or participate in the innate immunity, such as monocytes-macrophages, dendritic cells, neutrophils, eosinophils, basophils, mast cells, and natural killer cells.

Melatonin signaling and its modulation of PfNF-YB transcription factor expression in Plasmodium falciparum

Malaria is one of the most severe tropical infectious diseases. More than 220 million people around the world have a clinical malaria infection and about one million die because of Plasmodium annually. This parasitic pathogen replicates efficiently in its human host making it difficult to eradicate. It is transmitted by mosquito vectors and so far mosquito control programs have not effectively eliminated this transmission. Because of malaria's enormous health and economic impact and the need to develop new control and eventual elimination strategies, a big research effort has been made to better understand the biology of this parasite and its interactions with its vertebrate host. Determination of the genome sequence and organization, the elucidation of the role of key proteins, and cell signaling studies have helped to develop an understanding of the molecular mechanisms that provide the parasite's versatility. The parasite can sense its environment and adapt to benefit its survival, indeed this is essential for it to complete its life cycle. For many years we have studied how the Plasmodium parasite is able to sense melatonin. In this review we discuss the melatonin signaling pathway and its role in the control of Plasmodium replication and development.

Respiratory syncytial virus infection: mechanisms of redox control and novel therapeutic opportunities

Respiratory syncytial virus (RSV) is one of the most important causes of upper and lower respiratory tract infections in infants and young children, for which no effective treatment is currently available. Although the mechanisms of RSV-induced airway disease remain incompletely defined, the lung inflammatory response is thought to play a central pathogenetic role. In the past few years, we and others have provided increasing evidence of a role of reactive oxygen species (ROS) as important regulators of RSV-induced cellular signaling leading to the expression of key proinflammatory mediators, such as cytokines and chemokines. In addition, RSV-induced oxidative stress, which results from an imbalance between ROS production and airway antioxidant defenses, due to a widespread inhibition of antioxidant enzyme expression, is likely to play a fundamental role in the pathogenesis of RSV-associated lung inflammatory disease, as demonstrated by a significant increase in markers of oxidative injury, which correlate with the severity of clinical illness, in children with RSV infection. Modulation of ROS production and oxidative stress therefore represents a potential novel pharmacological approach to ameliorate RSV-induced lung inflammation and its long-term consequences.

Melatonin and oral cavity

While initially the oral cavity was considered to be mainly a source of various bacteria, their toxins and antigens, recent studies showed that it may also be a location of oxidative stress and periodontal inflammation. Accordingly, this paper focuses on the involvement of melatonin in oxidative stress diseases of oral cavity as well as on potential therapeutic implications of melatonin in dental disorders. Melatonin has immunomodulatory and antioxidant activities, stimulates the proliferation of collagen and osseous tissue, and acts as a protector against cellular degeneration associated with aging and toxin exposure. Arising out of its antioxidant actions, melatonin protects against inflammatory processes and cellular damage caused by the toxic derivates of oxygen. As a result of these actions, melatonin may be useful as a coadjuvant in the treatment of certain conditions of the oral cavity. However, the most important effect of melatonin seems to result from its potent antioxidant, immunomodulatory, protective, and anticancer properties. Thus, melatonin could be used therapeutically for instance, locally, in the oral cavity damage of mechanical, bacterial, fungal, or viral origin, in postsurgical wounds caused by tooth extractions and other oral surgeries. Additionally, it can help bone formation in various autoimmunological disorders such as Sjorgen syndrome, in periodontal diseases, in toxic effects of dental materials, in dental implants, and in oral cancers.

Beneficial actions of melatonin in the management of viral infections: a new use for this "molecular handyman"?

Melatonin (N‐acetyl‐5‐methoxytryptamine) is a multifunctional signaling molecule that has a variety of important functions. Numerous clinical trials have examined the therapeutic usefulness of melatonin in different fields of medicine. Clinical trials have shown that melatonin is efficient in preventing cell damage under acute (sepsis, asphyxia in newborns) and chronic states (metabolic and neurodegenerative diseases, cancer, inflammation, aging). The beneficial effects of melatonin can be explained by its properties as a potent antioxidant and antioxidant enzyme inducer, a regulator of apoptosis and a stimulator of immune functions. These effects support the use of melatonin in viral infections, which are often associated with inflammatory injury and increases in oxidative stress. In fact, melatonin has been used recently to treat several viral infections, which are summarized in this review. The role of melatonin in infections is also discussed herein. Copyright © 2012 John Wiley & Sons, Ltd.

Melatonin improves the oocyte and the embryo in IVF patients with sleep disturbances, but does not improve the sleeping problems

PURPOSE

We aimed to analyse the in vitro fertilization-embryo transfer (IVF-ET) outcomes of the patients with sleep disturbances who were administered melatonin.

METHODS

A total of 60 patients with sleep disturbances were divided into two groups. The study group (group A, n=30) had underwent the IVF-ET with melatonin administration and the control group (group B, n=30) without melatonin. Sleeping status after melatonin administration and the IVF outcomes were compared between the two groups.

RESULTS

Sleeping status change was not significant (p>0.05). The mean number of the retrieved oocytes, the mean MII oocyte counts, the G1 embryo ratio were significantly higher in the melatonin administered group (group A) than that the non-administered group (group B); p=0.0001; p=0.0001; p<0.05 respectively.

CONCLUSION

IVF patients with sleep disorders may benefit from melatonin administration in improving the oocyte and the embryo quality, but the sleeping problem itself may not be fixed.

Suppression substractive hybridisation (SSH) and real time PCR reveal differential gene expression in the Pacific cupped oyster, Crassostrea gigas, challenged with Ostreid herpesvirus 1

Virus-induced genes were identified using suppression subtractive hybridisation (SSH) from Pacific cupped oyster, Crassostrea gigas, haemocytes challenged by OsHV-1. A total of 304 clones from SSH forward library were sequenced. Among these sequences, some homologues corresponded to (i) immune related genes (macrophage express protein, IK cytokine, interferon-induced protein 44 or multicopper oxidase), (ii) apoptosis related genes (Bcl-2) and (iii) cell signalling and virus receptor genes (glypican). Molecular characterization and phylogenic analysis of 3 immune-related genes (macrophage expressed protein, multicopper oxidase and immunoglobulin domain cell adhesion molecule) were performed. Finally, quantitative PCR revealed significant changes in the expression of immune related genes (multicopper oxidase, macrophage expressed protein, myeloid differentiation factor 88 and interferon-induced protein 44) in oysters experimentally challenged with OsHV-1. These findings provide a first basis for studying the role of innate immunity in response to viruses in bivalves and identified genes may serve as markers of interest in breeding programs in order to obtain selected oysters presenting OsHV-1 resistance.

Melatonin inhibits microglial activation, reduces pro-inflammatory cytokine levels, and rescues hippocampal neurons of adult rats with acute Klebsiella pneumoniae meningitis

Acute bacterial meningitis caused by Klebsiella pneumoniae (K. pneumoniae) is a major health threat with a high mortality rate and severe neuro-cognitive sequelae. The intense pro-inflammatory cytokine released from calcium-mediated microglial activation plays an important role in eliciting neuronal damage in the hippocampal region. Considering melatonin possesses anti-inflammatory and immuno-modulatory properties, the present study determined whether melatonin can effectively decrease inflammatory responses and prevent hippocampal damage in animals subjected to K. pneumoniae. Adult rats inoculated with K. pneumoniae received a melatonin injection immediately thereafter at doses of 5, 25, 50, or 100 mg/kg. Following 24 h of survival, all experimental animals were processed for time-of-flight secondary ion mass spectrometry (for detecting glial calcium intensity), isolectin-B4 histochemistry (reliable marker for microglial activation), pro-inflammatory cytokine measurement as well as cytochrome oxidase and in situ dUTP end-labeling (representing neuronal bio-energetic status and apoptotic changes, respectively). Results indicate that in K. pneumoniae-infected rats, numerous calcium-enriched microglia, enhanced pro-inflammatory cytokine, and various apoptotic neurons with low bio-energetic activity were detected in hippocampus. Following melatonin administration, however, all parameters including glial calcium intensity, microglial activation, pro-inflammatory cytokine levels, and number of apoptotic neurons were successfully decreased with maximal change observed at a melatonin dose of 100 mg/kg. Enzymatic data corresponded well with above findings in which all surviving neurons displayed high bio-energetic activity. As effectively reducing glia-mediated inflammatory response is neuro-protective to hippocampal neurons, the present study supports the clinical use of melatonin as a potential therapeutic agent to counteract K. pneumoniae meningitis-induced neuro-cognitive damage.

Update on the use of melatonin in pediatrics

Melatonin, an endogenously produced indoleamine, is a highly effective antioxidant, free radical scavenger, and a primary circadian regulator. Melatonin has important antioxidant properties owing to direct and indirect effects. It directly scavenges reactive oxygen and reactive nitrogen species, prevents molecular oxidation, improves mitochondrial physiology, and restores glutathione homeostasis. Its indirect antioxidant effects stem from its ability to stimulate the activities of the enzymes involved in the glutathione cycling and production. Melatonin, by reducing free radical damage, may be an effective protective agent for the fetus as it is in adults. Several clinical studies on melatonin have shown that it reduces oxidative stress in human newborns with sepsis, hypoxic distress, or other conditions, where there is excessive free radical generation. A role of melatonin in infant development has also been suggested. Pineal dysfunction may be associated with deleterious outcomes in infants and may contribute to an increased prevalence of sudden infant death syndrome. Delayed melatonin production is evident in infants who had experienced an apparent life-threatening event. Melatonin has been used as a pharmacologic treatment for insomnias associated with shift work, jet lag, and delayed sleep onset in adults for decades. In children as well, melatonin has value as a sleep-promoting agent. Evidence suggests that melatonin has utility as an analgesic agent presumably related to its ability to release β-endorphin. The data support the notion that melatonin, or one of its analogs, might find use as an anesthetic agent in children.

Inhibitory effect of melatonin on lung oxidative stress induced by respiratory syncytial virus infection in mice

Previous research has shown that antioxidant (butylated hydroxyanisole) treatment ameliorates respiratory syncytial virus (RSV)-induced disease and lung inflammation. Melatonin has been reported to exhibit a wide varieties of biological effects, including antioxidant and anti-inflammation, and has no evident toxicity and side effect. But it is not known whether melatonin would modify RSV-induced lung disease and oxidative stress. The present study was to establish the involvement of oxidative stress in the pathogenesis of RSV-induced lung inflammation, and to investigate the protective effect of administration of melatonin in mice with RSV-induced oxidative pulmonary injury for 4 days. Malondialdehyde (MDA), an end product of lipid peroxidation, and glutathione (GSH) and superoxide dismutase (SOD) and nitric oxide (NO) levels were evaluated in lung tissue homogenates by spectrophotometry. Hydroxyl radical (.-OH), one of the indicators of free radical formation, was also detected in lung homogenates by Fenton reaction. Tumor necrosis factor-a (TNF-a) concentrations in mouse serum were measured with ELISA assay. The results demonstrated that the mice intranasally inoculated with RSV resulted in oxidative stress changes by increasing NO, MDA and .-OH levels, and decreasing GSH and SOD activities, whereas administration of melatonin significantly reversed all these effects. Furthermore, melatonin inhibited production of proinflammatory cytokines such as TNF-a in serum of RSV-infected mice. These results suggest that melatonin ameliorates RSV-induced lung inflammatory injury in mice via inhibition of oxidative stress and proinflammatory cytokine production and may be as a novel therapeutic agent in virus-induced pulmonary infection.

Malaria: therapeutic implications of melatonin

Malaria, which infects more than 300 million people annually, is a serious disease. Epidemiological surveys indicate that of those who are affected, malaria will claim the lives of more than one million individuals, mostly children. There is evidence that the synchronous maturation of Plasmodium falciparum, the parasite that causes a severe form of malaria in humans and Plasmodium chabaudi, responsible for rodent malaria, could be linked to circadian changes in melatonin concentration. In vitro melatonin stimulates the growth and development of P. falciparum through the activation of specific melatonin receptors coupled to phospholipase-C activation and the concomitant increase of intracellular Ca2+. The Ca2+ signaling pathway is important to stimulate parasite transition from the trophozoite to the schizont stage, the final stage of intraerythrocytic cycle, thus promoting the rise of parasitemia. Either pinealectomy or the administration of the melatonin receptor blocking agent luzindole desynchronizes the parasitic cell cycle. Therefore, the use of melatonin antagonists could be a novel therapeutic approach for controlling the disease. On the other hand, the complexity of melatonin's action in malaria is underscored by the demonstration that treatment with high doses of melatonin is actually beneficial for inhibiting apoptosis and liver damage resulting from the oxidative stress in malaria. The possibility that the coordinated administration of melatonin antagonists (to impair the melatonin signal that synchronizes P. falciparum) and of melatonin in doses high enough to decrease oxidative damage could be a novel approach in malaria treatment is discussed.

The changing biological roles of melatonin during evolution: from an antioxidant to signals of darkness, sexual selection and fitness

Melatonin is a molecule present in a multitude of taxa and may be ubiquitous in organisms. It has been found in bacteria, unicellular eukaryotes, macroalgae, fungi, plants and animals. A primary biological function of melatonin in primitive unicellular organisms is in antioxidant defence to protect against toxic free radical damage. During evolution, melatonin has been adopted by multicellular organisms to perform many other biological functions. These functions likely include the chemical expression of darkness in vertebrates, environmental tolerance in fungi and plants, sexual signaling in birds and fish, seasonal reproductive regulation in photoperiodic mammals, and immunomodulation and anti-inflammatory activity in all vertebrates tested. Moreover, its waning production during aging may indicate senescence in terms of a bio-clock in many organisms. Conversely, high melatonin levels can serve as a signal of vitality and health. The multiple biological functions of melatonin can partially be attributed to its unconventional metabolism which is comprised of multi-enzymatic, pseudo-enzymatic and non-enzymatic pathways. As a result, several bioactive metabolites of melatonin are formed during its metabolism and some of the presumed biological functions of melatonin reported to date may, in fact, be mediated by these metabolites. The changing biological roles of melatonin seem to have evolved from its primary function as an antioxidant.

Melatonin and dehydroepiandrosterone combination: does this treatment exert a synergistic effect during experimental Trypanosoma cruzi infection?

Previous studies showed that melatonin or dehydroepiandrosterone (DHEA) enhances the immune response against parasitic pathogens. The present study investigated the in vitro activity of melatonin combined with DHEA in a period of 24 hr during the course of in vivo T. cruzi infection. The in vitro activity of melatonin or DHEA alone, as well as together, were tested for the trypomastigote forms (doses ranging from 0.5 to 128 microm). In vitro, neither melatonin nor DHEA alone had any activity against trypomastigote forms, although when the highest concentration of combined melatonin and DHEA was used, it was active against the trypomastigote forms of the parasite. However, for this concentration, a quite toxicity on peritoneal macrophages was observed. For in vivo evaluation, male Wistar rats were infected with the Y strain of T. cruzi. They were orally treated with 10 mg/kg body weight/day of melatonin and subcutaneously with 40 mg/kg body weight/day of DHEA. Treatment with melatonin, DHEA and the association showed a significant reduction in the number of blood trypomastigotes during the acute phase of infection as compared to untreated animals (P < 0.05). A significant increase in the number of macrophages and nitric oxide (NO) concentrations were observed during the peak of parasitaemia with melatonin alone or combined with DHEA. However, with DHEA alone the highest concentration of NO was observed (P < 0.05). Moreover, DHEA treatment increased TNF-alpha levels during the infection (P < 0.05). These results show that melatonin, DHEA or the combination of both reduces parasitemia during the acute phase of infection. The combined action of both molecules did not exert a synergic action on the host's ability to fight infection, and it seems that among all treatments DHEA induces a more efficient immune response.